Sediment Transport and Distribution Over Continental Shelves: a Glimpse at Two Different River- Influenced Systems, the Cariaco Basin and the Amazon Shelf

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January 2012 Sediment transport and distribution over continental shelves: a glimpse at two different river- influenced systems, the Cariaco Basin and the Amazon Shelf. Laura Lorenzoni University of South Florida, [email protected]

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Sediment Transport and Distribution Over Continental Shelves: A Glimpse at Two

Different River-Influenced Systems, the Cariaco Basin and the Amazon Shelf

Laura Lorenzoni

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy College of Marine Science University of South Florida

Major Professor: Frank E. Muller-Karger, Ph.D. Claudia Benitez-Nelson, Ph.D. Don Chambers, Ph.D. David Hollander, Ph.D. Richard W. Murray, Ph.D.

Date of Approval: July 6, 2012

Keywords: Bottom Nepheloid Layers, Particulate Organic Carbon, Small Mountainous Rivers, River Plume, Sediment Transport

ACKNOWLEDGMENTS

I wish to acknowledge the CARIACO team for their help throughout this work, and for all of the years they have provided support to the program. In particular I am indebted to the personnel from Fundación La Salle de Ciencias Naturales, Estación de Investigaciones Marinas

Isla Margarita (FLASA/EDIMAR) for their continuous effort in maintaining the CARIACO

Time-series, especially Yrene Astor and Ramon Varela who make all of this a possibility. I am also grateful to Robert Thunell, Claudia Benitez-Nelson, Mary Scranton and Gordon Taylor for always being willing to help me in any way I needed. I am thankful to the crew of the R/V

Hermano. Ginés ; their patience and help during our cruises are noteworthy. A special thank you to German, the best cook I’ve ever encountered on a research vessel. I am very grateful to the

Instituto de Investigaciones Cientificas de Venezuela (IVIC), in particular Adriana Giuliante,

Rafael Rasse and Loreto Donoso, for letting me tag along in their river sampling, and for collecting samples for my work.

For the Amazon research, I would like to acknowledge the crew of the R/V Knorr, in particular Amy Simonneau, for her help and friendship throughout our work. I am also indebted to Paul Baker and David Hollander for the opportunity to participate on that cruise. I would like to give special thanks to Ethan Goddard, Eric Tappa and Claudia Benitez-Nelson for the analytical assistance provided; without them there would be no geochemical data on this manuscript.

The entire IMaRS family (past and present) have been wonderful, always providing me with continuous support, in and out of the lab. In particular I want to acknowledge my advisor,

Frank Muller-Karger, for his patience and guidance. I’ve said it many times, but I’ll say it again –

you are a great advisor and researcher. I want to particularly mention Inia Soto, Luchi Odriozola,

Damaris Torres, Enrique Montes and Digna Rueda for their friendship, as well as Chuanmin Hu for always being ready to help. I wish to acknowledge my committee members for their guidance and patience throughout this process, especially Claudia Benitez-Nelson. I would like to honor the memory of Dr. Ben Flower, whom embodied all an outstanding professor and researcher should be.

The gratitude I have towards my family is unmeasurable. Mamma, papá, Mauro – Thank you for believing in me and always being willing to provide advice and help, even if you had no clue what I was talking about. Gino, Gea, Leo – thank you for putting up with my crazy work schedules, months of travel and incessant questions (not to mention crazy science talk). I love you all more than words can say.

I was awarded the John B. Lake and Katherine Ann Fellowship in 2009 and the Knight

Fellowship in 2010, which allowed me to continue my pursuit of this degree; I am extremely grateful to the donors and the College of Marine Science for this financial support. Funding for this research was provided through NSF Chemical Oceanography grants OCE-0326268, 0326313 and 0963028. Support was also providedby the Fondo National de Investigaciones Científicas y

Tecnológicas (FONACIT, Venezuela, Award # 96280221).

Now, let the fun begin!

“Margarita está linda la mar, y el viento, lleva esencia sutil de azahar; yo siento en el alma una alondra cantar; tu acento: Margarita, te voy a contar un cuento:”Rubén Dario.

TABLE OF CONTENTS

List of Tables ...... iii

List of Figures ...... iv

Abstract ...... vi

Preface ...... 1

Chapter 1. Mechanisms of Lithogenic Sediment Distribution and Transport in the Cariaco Basin: Role of Nepheloid Layers and Episodic Events ...... 3 Introduction ...... 3 Regional setting and study area ...... 6 Methods ...... 11 Data collection ...... 11 Meteorological and river data ...... 14 Geochemical analyses ...... 16 Visualization of the data ...... 17 Results ...... 17 Meteorological conditions ...... 17 Riverine organic carbon and suspended sediments ...... 18 Hydrographic conditions ...... 21 Beam attenuation (c-beam coefficient or c p at 660 nm) ...... 24 SPM, POC, PN and their isotopic composition ...... 29 Discussion ...... 40 Organic matter and suspended sediment contribution by local rivers...... 40 Importance and distribution of nepheloid layers ...... 45 Nepheloid layer composition ...... 46 Physical dynamics of nepheloid layers ...... 49 Temporal variation and fate of horizontally transported particles ...... 51 Role of episodic events in the sequestration of continentally-derived POC ...... 56 Implication of episodic events on the sedimentary record of Cariaco ...... 62 Conclusions ...... 63

Chapter 2. Biogeochemistry of the Amazon Continental Shelf and Sediment Transport During February-March, 2010 ...... 67 Introduction ...... 67 Methods ...... 71 Data collection ...... 71 Geochemical analyses ...... 72 Meteorological and river discharge data ...... 74 Results ...... 75 Discussion ...... 88 Amazon Plume characteristics during 2010 ...... 88 Biogeochemistry of the Amazon Plume during 2010 ...... 90

Processes controlling the nature and transport of particles on the Amazon Shelf ...... 95 Summary and concluding remarks ...... 100

Epilogue ...... 103

References ...... 109

Appendices...... 126 Appendix 1: Supplementary figures...... 126 Appendix 2: Monthly concentration of dissolved and particulate organic matter (DOC and TOC) in the four main rivers draining into the Cariaco Basin ...... 131 Appendix 3: Hydrographic conditions of the Cariaco Basin for the study period...... 132

LIST OF TABLES

Table 1.1: Characteristics of the main rivers draining into the Cariaco Basin ...... 19

Table 1.2: Composition of surface (upper 5 cm) river bed sediments of the four main rivers draining into the Cariaco Basin...... 21

Table 1.3: Composition of near-surface and bottom (BNL) suspended sediments from selected locations sampled during September 2006 in the Cariaco Basin...... 34

Table 1.4: Composition of surface (~1m) and near-bottom (BNL) suspended sediments from selected locations sampled during September 2008 in the Cariaco Basin...... 35

Table 1.5: Composition of surface (~1m) and near-bottom (BNL) suspended sediments from selected locations sampled during March 2009 in the Cariaco Basin...... 36

Table 1.6: Geochemical composition of the canyon mouth turbidity plume (870 m)...... 40

Table 2.1: Surface (2-4 m) temperature, salinity, beam attenuation, chlorophyll fluorescence, oxygen, nutrients, dissolved organic carbon (DOC) ...... 79

Table 2.2: Geochemical results for selected sampled stations...... 83

Table 2.3: Carbon and nitrogen isotopic composition, and organic carbon and nitrogen content (in %) of particulate matter of Amazon shelf and slope surface sediments...... 86

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LIST OF FIGURES

Figure 1.1: Map of the Cariaco Basin...... 8

Figure 1.2: Sampling locations for the study period: (a) 2003 (diamonds) and 2006 (crosses). ... 13

Figure 1.3: (a) Average precipitation records between the four meteorological stations selected (see text for years averaged) ...... 20

Figure 1.4: Distribution of sea surface salinity during the study periods...... 25

Figure 1.5: Distribution of sea surface temperature during the study periods...... 26

Figure 1.6: Distribution of sea surface dissolved organic carbon (DOC) during the study periods ...... 27

Figure 1.7: Distribution of bottom nepheloid layers (BNL), measured as light beam -1 attenuation (c p(660), m )...... 30

Figure 1.8: Distribution of beam attenuation (cp (m-1)) and major isopycnals (salinity in kg m -3) for selected locations over (a) Region A and (b) Region B ...... 31

Figure 1.9: Transmissometer profiles collected at the CARIACO Time-Series site (segmented line) and at the canyon mouth (black line) during September 2008...... 32

Figure 1.10: Distribution of δ13 C (top 4 panels) and %POC (bottom 4 panels) in surface and BNL during September 2008 (FOSA1) and March 2009 (FOSA2)...... 37

Figure 1.11: Plot of the stable carbon isotopic composition of particulate organic carbon (δ13 POC) versus the atomic carbon:nitrogen ratio (C/N)...... 39

Figure 1.12: Monthly average of lithogenic and POC fluxes between 1995 and 2006 ...... 55

Figure 2.1 Amazon Basin and river network ...... 67

Figure 2.2: Major physical processes affecting the Amazon Shelf ...... 70

Figure 2.3: Location of the Amazon Shelf and sampling during 2010; expanded area details station numbers and location...... 73

Figure 2.4: Water discharge measured at Obidos between October2009- January 2011 (dotted line) and October 1989- January 1991 (broken line) ...... 75

Figure 2.5: Surface distribution of different variables along the OS and RM transects...... 78

-3 Figure 2.6 Chlorophyll fluorescence (mg m ) for the OS and RM transects...... 82

Figure 2.7: Vertical profiles of beam attenuation at 3 different stations on the OS transect...... 84

Figure 2.8: (left) Carbon isotopic composition of particulate organic carbon (POC) in surface sediments of the Amazon shelf; (right) POC content (in percent) of the Amazon shelf surface sediments...... 87

Figure 2.9: Precipitation anomalies ...... 89

Figure 3.1: (top) Time-series of TNA SST anomalies. (bottom) 10-year trend (centered) of the TNA SST climatology ...... 106

Supplementary Figure 1.1: Cartoon of the effects of El Niño around the world ...... 126

Supplementary Figure 1.2: Average precipitation rate for the four meteorological stations utilized...... 127

Supplementary Figure 1.3: Annual average precipitation vs. annual average discharge for the four meteorological stations utilized ...... 128

Supplementary Figure 1.4: Zonal wind ( u) for the years of study...... 129

Supplementary figure 2.1: Salinity profiles at stations over the OS Transect...... 130

ABSTRACT

The aim of this dissertation was to understand lithogenic suspended sediment transport mechanisms and distribution in two river-influenced margins: The Cariaco Basin, Venezuela, and the Amazon Shelf, Brazil. Lithogenic sediment input in the Cariaco Basin is controlled by small mountainous rivers (SMR), while in the Amazon Shelf it is dominated by the Amazon River, the largest river in the world in terms of freshwater discharge (~20% of global riverine discharge).

Optical transmissometer measurements were coupled with particulate organic matter (POM) observations to understand changes in the geochemical composition of suspended sediment and spatial/temporal distributions over the two regions of interest. In the Cariaco Basin sampling was conducted during the rainy seasons of September 2003, 2006 and 2008, and during the upwelling period (dry season) of 2009. Our results suggest that bottom nepheloid layers (BNL) originating at the mouth of the SMR discharging into the Cariaco Basin are a major delivery mechanism of terrigenous sediments to the basin’s interior year-round. Intermediate nepheloid layers (INL) were also observed near the shelf break (~100m) and appear to effectively carry terrigenous material laterally from the shelf to deep waters, thereby providing a plausible supply mechanism of the terrestrial material observed in sediment traps, deployed >70 km offshore as part of the

CARIACO Ocean Time-Series. These findings highlight the importance of small, local rivers in the Cariaco Basin as sources of terrestrial material. Indeed, the low isotopic composition of

13 particulate organic carbon ( δ Corg , ~-30 - -24‰) carried by the BNL suggests that this material

13 was continentally derived. BNL δ Corg also changed with season, indicating that the geochemical composition of BNL reflects particle source. These nepheloid layers contained relatively low

POM concentrations (average of 10%), agreeing well with published data, yet the fine sediment

of the BNL may serve as mineral ballast, enhancing the sinking velocities of POC and thus increasing the efficiency of the biological pump in Cariaco. We suggest that during the transition between the upwelling and rainy season BNL deliver sediment to the deep Cariaco Basin in pulses. During upwelling, BNL are retained on the inner shelf by onshore Ekman transport associated with upwelling. The nepheloid layers are later released as the upwelling subsides; this, coupled with high river discharge rates, may explain the seasonal pulse of sediment observed at the end of the upwelling period (May) in the sediment trap array.

The SMR in Cariaco also have the capacity to deliver large amounts of sediment to the

Cariaco Basin during episodic events, such as earthquakes and floods. During September 2008 a sediment density flow was observed in the eastern Cariaco Basin, likely triggered by a magnitude

5.2 earthquake that occurred on August 11, 2008 off the city of Cumaná. Elevated suspended sediments near the bottom were observed at the mouth of the Manzanares Canyon (> 90 g m -2, over a depth of 165 m) and decreased to ~11 g m -2 (over a depth of 40 m) 42 Km away from the canyon’s mouth at the CARIACO Ocean Time-Series site (10.5° N, 64.67° W). The sediment flux associated with this single event was ~ 10% of the total annual sediment flux that typically reaches the Cariaco Basin deep seafloor. Average carbon to nitrogen atomic ratios (C/N) as well as C and N isotopic composition confirm that most of the organic matter transferred by the sediment flow was of continental origin (C/N ratios of ~19.3, δ13 C of -27.04‰, and δ15 N of 6.83

‰). The Manzanares River mouth is located at the head of the canyon, and likely supplies most of the fine grained sediments and fresh organic carbon that accumulate in the upper part of the canyon. This suggests that the canyon is an active depositional center, and its proximity to the

Manzanares River and Cariaco Basin is critical for sediment supply offshore, which in turn can have a significant impact on the long-term sequestration of carbon into the deep basin.

The nutrient and sediment biogeochemistry of the outer Amazon Shelf was studied in

February-March 2010 to replicate observations made by the AmasSeds study in 1989-1991.

These transects roughly corresponded to the AmasSeds Open Shelf (OS) and River Mouth (RM)

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transects. Onshore winds (~6 m s -1) contained the Amazon plume within ~120 Km of the coast; the plume was visible only in the mid-shelf stations located closest to the coast in the OS transect.

Within the river plume, surface dissolved inorganic nutrient concentrations were near zero, except for silicates (4-6 µM). Coupled with oxygen supersaturation (AOU < 1), this suggested complete biological uptake of the major dissolved inorganic nutrients (N, P). Dissolved organic carbon

(DOC) was also highest within the plume (average of 116 µM), decreasing to ~73 µM in oceanic waters. Total suspended solids (TSS) in surface waters within the plume were ~1-1.5 mg l -1, decreasing to ~0.2-0.3 mg l -1 in all other sampled stations both over the shelf and in deeper waters. TSS were highest within BNL (22-33 mg l -1) observed over the inner shelf; BNL were not observed outside the area of the Amazon plume. Suspended particulate organic carbon (POC susp ) showed a depleted δ13 C isotopic signal (~-25‰ to -28‰) in surface and bottom waters, suggesting terrestrial provenance. Within the BNL, %POC was low (0.6-0.9%, as compared to 7-

18% in surface waters), showing extensive and rapid decomposition of organic matter over the shelf. Atomic C/N ratios in particulate organic matter both in surface waters and within BNL were relatively close to Redfield’s (8-14) and relatively stable over the area sampled. Particulate atomic organic carbon vs. particulate organic phosphorous (POC/POP) ratios were also low within the BNL (~110) and increased offshore (>500), suggesting a direct input of particulate P from the Amazon River or from reworked surface sediments. The fraction of POC in surface sediments was also low (0.73 ± 0.56%; N = 5) and relatively uniform across the region sampled.

We estimated instantaneous fluxes of 38.7 metric tons TSS s -1, 0.24 metric tons POC s -1 and 6.42 x 10 -3 metric tons POP s -1 northwestward over an area extending between ~50 Km and 120 Km offshore. Our TSS estimates are 30% lower than those calculated by Nittrouer et al. (1986) during peak discharge of the Amazon. We also calculated that some 1.50 Tg yr -1 of DOC were being flushed northwestward along the outer shelf annually, which represent ~6% of the total DOC transported by the Amazon.

viii

By analyzing these two geographical settings it was possible to compare and contrast transport mechanisms of continentally-derived material and establish the relative importance of each mechanism in their different environment. There is still much to be understood regarding

BNL in the Cariaco Basin, such as their role within the Manzanares Submarine Canyon with regards to sediment contribution and deposition. Additionally, during the last 30 years, anthropogenic influences on the small rivers around the Basin have significantly altered the drainage and sediment loads, yet reliable data to quantify the level of influence and change over time are not available. We need a better understanding of the natural variability of these small, tropical fluvial systems, trends and impact of episodic events, to better interpret the climate record stored at the bottom of the basin and predict future ecosystem changes in the region. In the

Amazon Shelf, more accurate estimates of DOC, POC and POP fluxes northwestward are warranted. The magnitude of the Amazon River discharge dampens changes that have occurred in the last 20 years within the Amazon Basin, suggesting that historic Amazon Shelf sediment and carbon estimates are still valid. The data presented here adds to the growing body of literature that highlights the significance of river-influenced continental margins as sites of organic carbon deposition, remineralization export and sequestration.

PREFACE

A significant portion of the organic carbon in the oceans is derived from terrigenous sources via rivers (Degens et al., 1991; Hedges and Keil, 1995; Goñi et al. 2008; Wheatcroft et al., 2010). Riverine sediment load and composition is a function of catchment basin drainage area, geology, topography, discharge rate, and human land use patterns (Milliman and Syvistski,

1992). Once the sediment is discharged onto the shelf, a variety of processes affect its distribution. In river-dominated continental margins, sediment distribution is controlled to a large degree by lateral dispersal and deposition, rather than direct vertical settling (Sahl et al., 1987;

Trowbridge et al., 1994). Other factors that affect the distribution and settling of sediments are wind, wave, tidal and other current patterns, as well as particle size and composition. In order to correctly interpret sediment records, accurately reconstruct past climate variations and predict future change, it is essential to understand the modern links between climate forcing and sediment sources and deposition.

This dissertation contributes to our understanding of sediment transport and distribution in two river-dominated margins: The Cariaco Basin, Venezuela, and the Amazon Shelf, Brazil.

These two systems have contrasting magnitudes of fluvial input. Small mountainous rivers drain the Cariaco Basin and such environments have the potential to transport large amounts of suspended sediments to the coastal ocean (Inman and Jerkins, 1999). Smaller watersheds are also prone to episodic flooding due to high precipitation events, during which large quantities of sediments can be delivered to the coastal ocean very quickly (Milliman and Syvitski, 1992). The

Amazon Shelf is dominated by the Amazon River, which discharges high amounts of water, solutes and particles. The Amazon is the largest river in the world in terms of freshwater discharge (~20%) and provides roughly 6% of the global riverine sediment discharge (Meade et

al., 1985). Due to its large scale, the Amazon is not susceptible to episodic events as smaller watersheds; rather, the quantity and fate of the material delivered by the river depends on the balance between transport and shelf circulation. The dissertation has been divided into two chapters, each addressing one region. The information contained in the first chapter has been partly published in two peer-reviewed manuscripts (Lorenzoni et al., 2009 and 2012a); a portion of the information within that chapter is included in a third manuscript submitted to Deep Sea

Research II (Lorenzoni et al., 2012b). A fourth manuscript which will include the inorganic geochemistry data presented here will be also submitted for publication. The second chapter, focusing on the Amazon Shelf, will be submitted for publication to a peer-reviewed journal.

By analyzing the two geographical settings it was possible to compare and contrast transport mechanisms of continentally-derived material and establish the relative importance of each mechanism in their different environments. Moreover, the data presented here adds to the growing body of literature that highlights the significance of river-dominated continental margins as sites of organic carbon deposition, remineralization and sequestration (e.g. Lyons et al., 2002;

Carey et al., 2005; Burdige, 2007; Goñi et al., 2008; Hilton et al., 2008; Goldsmith et al., 2008;

2010).

CHAPTER 1. MECHANISMS OF LITHOGENIC SEDIMENT DISTRIBUTION AND

TRANSPORT IN THE CARIACO BASIN: ROLE OF NEPHELOID LAYERS AND

EPISODIC EVENTS

Introduction

Understanding the transport of lithogenic material from land to sea is critical for understanding sedimentary sinks of a wide range of particle active elements, including carbon, nutrients, and trace elements (Brunskill, 2009). For example, it has been hypothesized that more than 80% of particulate organic carbon is buried on continental margins (e.g. Hedges and Keil,

1995) and recent evidence suggests that a significant portion of this organic carbon is continentally derived (Goñi et al. 2008). Rivers are the main conduit of sediment to the coastal ocean. Their sediment load is a function of basin geology, drainage area, discharge rate and human activity (Milliman and Syvistski, 1992). As sediment yield increases with decreasing basin size, small rivers draining steep coastal watersheds have the potential to transport large amounts of suspended sediments to the coastal ocean (Inman and Jerkins, 1999; Hicks et al., 2004).

Indeed, small mountainous rivers (SMRs), defined as those rivers that have headwaters at an elevation of more than 1000 m (Milliman and Syvitski, 1992), play a key role in the transport of terrestrially-derived sediment and organic carbon (OC) to the coastal ocean (Milliman and

Syvitski, 1992; Syvitski and Milliman, 2007). Yet the ultimate fate of this OC remains controversial, despite its role in oxygen accumulation and as a potential sink for atmospheric CO 2 over geologic time (Burdige, 2007). For example, several studies suggest that much of the river- transported terrestrial OC that is deposited on the continental margin is efficiently remineralized due to a combination of remobilization and oxidation (e.g. Burdige, 2005; Aller and Blair, 2006).

In contrast, regions dominated by high erosion, high sedimentation and/or limited sediment oxidation, such as the Bengal Fan, appear to store continentally derived OC much more effectively (Milliman and Syvitski, 1992; Masiello, 2007; Hilton et al., 2008). Smaller rivers also are more likely to experience episodic events such as floods, where the sediment and OC discharged to the sea within a narrow timeframe is considerable (Mulder and Syvitski, 1995;

Warrick and Milliman, 2003; Milliman et al., 2007; Alin et al., 2008). The magnitude of this sediment discharge, as well as OC delivery and burial efficiency, is not well known due to both insufficient monitoring and the highly episodic nature of discharge events (e.g. Milliman, 1995;

Warrick and Milliman, 2003; Hicks et al., 2004; Alin et al., 2008; Goldsmith et al., 2008; Hilton et al., 2008).

Once the sediment is discharged onto the shelf, a variety of processes affect its distribution (Sahl et al., 1987; Trowbridge et al., 1994). In river-dominated continental margins, sediment distribution is controlled to a large degree by lateral dispersal and deposition, rather than direct vertical settling. An important transport mechanism over continental shelves are subsurface nepheloid layers, which have the potential to carry significant quantities of sediment over long distances, from the coastal environment to the deep sea (McCave et al., 2001; Pak et al.,

1980; McPhee-Shaw et al., 2004; Inthorn et al., 2006). Bottom nepheloid layers (BNL) are found in the lower water column and are characterized by increased particle concentrations relative to surrounding waters. Intermediate nepheloid layers (INL) are similar, but occur at intermediate water depths; they are usually found near continental shelves and slopes and are associated with strong density gradients (McPhee-Shaw et al., 2004; Inthorn et al., 2006). Nepheloid layers vary spatially and temporally (they can be permanent or transitory) and their intensity and thickness depend on local conditions (McPhee-Shaw et al., 2004; Inthorn et al., 2006).

Many SMRs discharge onto narrow, active margins and/or directly into marine canyons, which help transport the sediment directly offshore (Paull et al., 2003; Puig et al., 2003;

Palanques et al., 2008; Xu et al., 2010). Along seismically active margins, earthquakes can cause

slope failure and turbidity currents, particularly in areas of unstable sediment accumulation such as alluvial deposits (Dadson et al., 2004; Syvitski and Milliman, 2007; Goldsmith et al., 2008), greatly increasing the supply of sediments to the ocean (Dadson et al., 2003; Eberhart-Phillips et al., 2003; Fine et al., 2005; Shirai et al., 2010).

In this chapter we examine both suspended and sinking particles collected over the southern margin of the Cariaco Basin as part of the CARIACO Ocean Time Series program. We also present observations of a turbidity flow in the Manzanares Canyon (Venezuela) during 2008.

The goal of this study is to better understand the influence of local rivers on the supply of terrestrial material to the basin and to assess the role of BNL and INL as mechanisms in the lateral transport and delivery of terrigenous sediment (and terrestrial derived organic matter) from the coast to the deep waters of the basin’s interior. We also explore the nature and implications of episodic events in terms of source material and mass transport to the interior of the basin, and their potential impact on the interpretation of paleoclimate records from the Cariaco Basin. The hypotheses we propose are the following:

1. Nepheloid layers are the main conduit of shelf-derived sediment to the deep

basin : BNL are a permanent feature in the Cariaco Basin and they play a

significant role in the transport of terrigenous material to deeper waters.

2. There are seasonal changes in the composition of nepheloid layer sediments :

The layers reflect the seasonal changes of particles; during the upwelling

season BNL are enriched in POC derived from marine primary production,

and during the rainy season the organic matter content in the BNL is lower and

of terrigenous origin.

3. Local rivers are responsible for most of the terrestrial material delivered to

the basin, and the fraction contributed by each particular river is identifiable:

the contribution of each river to the composition of sediments accumulating

within the central Cariaco Basin can be established since they drain

geologically-different watersheds.

4. Episodic events play an important role in the sequestration of terrigenous

material : Large quantities of continentally-derived carbon are sequestered into

the deep Cariaco Basin intermittently in response to episodic events of

different nature.

Regional setting and study area

The most seismically active region of Venezuela is the northeastern region of the country

(Audemard, 2007). The Cariaco Basin, located on the continental shelf off eastern Venezuela, likely owes its origins to tectonic activity. The basin is an east-west trending pull-apart basin which contains two sub-basins, eastern and western, each approximately 1400 m deep and divided by a saddle of about 900 m. (Figure 1.1; Schubert, 1982). The Cariaco Basin is connected to the Caribbean Sea through a sill of about 100 m deep, which is cut by the Centinela

Channel to the west and by the Tortuga Channel to the north, both of a depth of about 140 m. To the south, the basin borders the wide (~50 km), gently sloping (~0.2-0.3%), shallow (100 m depth) Unare Platform, which extends from Cabo Codera to close to the city of Cumaná. The platform is relatively wide to the west and center of the basin, and very narrow towards the east.

Most of the sediment that settles on the platform comes from small local rivers that drain into the basin. The main local rivers are the Manzanares, Neverí, Unare and Tuy (Table 1). The

Manzanares River enters the basin in the south-east. It discharges an approximate 18 m 3/s and its headwaters have their origin in the Turimiquire formation (part of the Cordillera de la Costa) at more than 2000 m of elevation. This formation is composed of igneous and metamorphic rocks.

The Manzanares discharges into the Cariaco Basin near the city of Cumaná (Martinez and Senior,

2001; Martinez et al.2010). Its waters are moderately contaminated, receiving discharge waters

from the local sugar cane industry and several heavily populated areas, including the city of

Cumaná (Senior, 1994; Martinez and Senior, 2001). Once it reaches the ocean, nearshore currents transport river sediments to the west of the river mouth, and most of this material is funneled into the Manzanares Canyon (Mora et al., 1968). Away from the canyon, the plume of the Manzanares

River remains close to the coast as it is pushed southwestward, due to the local currents and trade winds that affect the region (Marquez et al., 2002). The Manzanares Submarine Canyon lies west of the city of Cumaná and connects the Gulf of Cariaco to the eastern Cariaco Basin (Figure 1.1 and 2b); the canyon head opens at a depth of 50 m, about 2 to 3 km off the mouth of the

Manzanares River. Morelock et al. (1972) estimated that the Manzanares Canyon formed during the Pleistocene and linked its origin to the El Pilar Fault. The El Pilar fault system is a right- lateral strike-slip fault located in the northeast region of Venezuela that extends ~350 km in an approximately E-W direction (Audemard, 2007). More recent seismic surveys suggest that the canyon is not located on the active trace of the El Pilar fault (FUNVISIS, 1994). Rather, the canyon seems to have been carved by downslope sediment flows, with sediment failure in the head and walls linked to earthquake shocks (González et al., 2004; Audemard, 2006; 2007). The predominant sediments in the upper canyon are silt, clay, and coarse sand of continental origin

(Morelock et al., 1972; 1982). While most of the sediment found in the canyon comes from the

Manzanares River, the Gulf of Cariaco (Figure 1.1 and 1.2) also contributes sediment (Mora et al., 1968; Caraballo, 1982). These sediments are derived from the Cautaro and the Cariaco

Rivers, as well as from several smaller seasonal rivers ( arroyos ) (Gade, 1961; Caraballo, 1982;

Audemard et al., 2007). To the southeast of the Cariaco Basin is the Neverí River, which enters the basin near the city of Barcelona (Figure 1.1). This mountainous river also has its origins in the

Turimiquire formation. The Neverí River also receives wastewater from several cities, including the city of Barcelona. It discharges an estimated 37 m 3/s (Recursos Hídricos de Venezuela, 2006).

One of the most important rivers draining into the basin is the Unare River, which has one of the most extensive drainage basins in northern Venezuela (22.3 x 10 3 Km 2; Zink, 1977). It

Figure 1. 1: Map of the Cariaco Basin. Pentagon indicates location of the CARIACO Ocean Time-Series site (and location of the sediment trap array). The location of the meteorological stations used is also shown (except Caracas, which is west outside of the map domain). Red arrows indicate general direction of river plumes. Top insert illustra tes the seasonal position of the Inter Tropical Convergence Zone (ITCZ) relative to the location of the Cariaco Basin. (Map modified from Goñi et al., 2009). enters the basin directly to the south and discharges ~46 m 3/s (Recursos Hídricos de Venezuela,

2006). It runs through the Unare Depression and drains a variety of geological formations composed mainly of sedimentary rocks (Martinez et al., 2010). The plumes of the Unare and

Neverí rivers are influenced by the littoral currents, which vary according to season and basin circulation (Alvera-Azcárate et al., 2009). During the rainy season, the plume of the Unare River

has been observed to move northward, while that of the Neverí is transported northeastward

(Lorenzoni et al., 2009). Together, the Manzanares, Unare and Neverí rivers discharge an estimated 1.16 x 10 6 metric tons (1 metric ton = 1 x 10 3 Kg) of sediment per year (Milliman and

Syvitski, 1992; INIA-MARN, 2003). To the southwest, three rivers enter the basin (Figure 1.1 and 1.2): The Curiepe, Capaya and Tuy. Out of these three, the Tuy River is the largest, with a mean discharge of 65 m 3/s (Recursos Hídricos de Venezuela, 2006); the Cupira and Capaya have much smaller discharge (~5 m 3/s each; Recursos Hídricos de Venezuela, 2006). These three rivers drain the central portion of the Cordillera de la Costa, composed of metamorphic and igneous rocks. The Tuy River has a mean annual sediment load of ~ 12 x 10 6 metric tons/year (Milliman and Syvitski, 1992). Part of the Tuy watershed drains heavily populated areas, including the city of Caracas, and receives wastewater from active industrial and agricultural areas (Mogollon et al.,

1995; Jaffe et al., 1995). The Curiepe and Capaya watersheds drain moderately populated areas, and the littoral zone where they discharge is heavily influenced by tourism. The plumes of these rivers are generally transported northwestward along the coast by littoral currents, towards Cabo

Codera (Herrera and Bone, 2011), though at times the plume of the Tuy River has been observed to move northeastward towards the center of the western basin (Intecmar, 2000). For the purpose of this manuscript, we will refer to these rivers collectively as the Tuy river system, since it can be difficult to differentiate river plumes within the basin due to their proximity to one another.

Table 1 summarizes some of the main characteristics of each river.

The Cariaco Basin hydrology and hydrography are influenced by seasonal and climate- scale shifts in the position of the Intertropical Convergence Zone (ITCZ). During the first few months of the year (generally from December through April) the basin experiences the dry season, characterized by strong Trade Winds and little to no precipitation. Starting in May, the position of the ITCZ migrates northward and precipitation increases in northern Venezuela. The position of the ITCZ is regulated by surface temperature gradients (Biasutti et al., 2005, 2006;

Suzuki, 201). Rainfall in the Caribbean is also influenced by the El Niño Southern Oscillation

phenomenon (ENSO) and by variability in the pressure system of the North Atlantic (e.g. Enfield and Mayer, 1997; Giannini et al., 2000, 2001; Lee et al., 2008). However, this relationship is not straight forward. While a portion of the sea surface temperature variability (and hence rainfall) of the tropical North Atlantic (TNA) can be explained as a response to the ENSO (see Appendix 1, supplementary figure 1.1), this relationship depends on other factors such as the strength and duration of the ENSO in the tropical Pacific and the internal variability of the Atlantic (for example, the North Atlantic Oscillation) (Giannini et al., 2001; Lee et al., 2008). In the Cariaco

Basin this relationship is even more convoluted; several authors (e.g. Astor et al., submitted;

Taylor et al., submitted) have explored the connection between ENSO and SST/rainfall in the basin and have found that no more than ~30% of the variability in SST, precipitation and zonal winds can be explained by the ENSO. However, the effect of this climatic phenomenon has been noted in the basin; for example, Astor et al. (submitted) point out the connection between the strong ENSO of 1996-1997 and the warm temperatures and low productivity recorded at

CARIACO during 1998. ENSO effects in the TNA are visible roughly 6 months to a year after its onset in the tropical Pacific as drier than average conditions during July–October of the ENSO year and wetter (and warmer) than average conditions during January-June of the year following

ENSO (Enfield and Mayer, 1997; Poveda et al., 2001; 2006; Giannini et al., 2001). The warm and wet conditions of the TNA during the dry season are induced by weakened trade winds and increased convection over the region; it has also been ascribed to changes in the meridional position of the ITCZ (Chiang et al. 2000).

Over geologic time-scales the position of the ITCZ has also varied. During periods of cool northern-hemisphere temperatures (i.e. glacial periods, Younger Dryas and Little Ice Age) the ITCZ was located southward of its current position, generating more pronounced and prolonged ‘dry season’ conditions. During warm interstadials (i.e. Holocene Thermal Maximum), the ITCZ was instead more northwards, inducing high precipitation over northern South America

(an accentuated ‘rainy season’; Peterson et al., 2000; Peterson and Haug, 2006; Conroy et al.,

2008). River runoff peaks between August and September (Figure 1; Márquez et al., 2002;

Peterson and Haug, 2006). Regrettably, none of the rivers that drain into the Cariaco Basin are currently gaged; hence, in this study precipitation records have been used as a proxy of fluvial discharge. Water circulation within the basin is restricted, which, combined with the high annual primary productivity of the region (~500 gCm -2 yr -1), causes the basin to be permanently anoxic below ~250m (Muller-Karger et al., 2001; 2004). Its unique geography and laminated sediments provides an excellent record of tropical climate change that is particularly sensitive to shifts in the

ITCZ (Hughen et al., 1996; Peterson et al., 2000; Peterson and Haug, 2006, Black et al., 2007).

Methods

Data collection

The data presented in this chapter were collected during 4 oceanographic research cruises over 6 years. All cruises used the R/V Hermano Ginés of the Fundación la Salle de Ciencias

Naturales de Venezuela. The first set, COHRO 1 & CASEP 2, were conducted in September 2003 and 2006, respectively. Station locations were similar for both cruises (Figure 2a). Sampling during September, in the rainy season, sought to observe the influence of the rivers at high discharge (Astor et al., 1998). The second set, FOSA 1 & FOSA 2, were conducted in September

2008 and March 2009, respectively. Sampling during March was intended to observe the upwelling phenomenon. Station locations were also similar during these cruises (Figure 2b).

A rosette with 12 8-liter Niskin® bottles was used to collect water samples at each site. A Seabird

SBE25 CTD mounted on the rosette measured salinity and temperature profiles. Beam

-1 attenuation at 660 nm (c p(660), m ) profiles were obtained with a C-Star 25cm pathlength transmissometer (Wetlabs). During 2008 and 2009, samples for DOC were collected at the surface for all stations, and at the bottom of the water column for selected stations (Table 4 and

5). DOC samples were gravity filtered through 47mm precombusted (450°C, 5 hours) Whatman

GF/F filters (0.7 µm pore size) and the filtrate stored in acid-cleaned 60 ml HDPE polyethylene

bottles, washed three times with sample water prior to filling (Dickson et al., 2007). Samples were frozen until analysis. During 2006, 2008 and 2009 water samples for suspended particulate matter (SPM) analyses were collected at selected locations from the surface and bottom of the water column (6 stations during 2006, 8 stations during 2008 and 12 stations during 2009; Figure

2, Tables 3-5). The selection criteria depended on the presence/absence of nepheloid layers as detected with the transmissometer; transmissometer data provides a measure of water turbidity due to particles since attenuation by dissolved materials is negligible at 600 nm (Boss et al., 2001;

Behrenfeld and Boss, 2003). Between 1-5 liters of water (depending on the turbidity of the water) were drained into acid-cleaned tubs and filtered through acid-washed (10% HCl), precombusted

(450°C for 5 hours) GF/F filters (0.7 µm pore size) using an in-line polycarbonate filter holder and a submersible pump. Samples were gently stirred during filtration to avoid sedimentation on the bottom of the tub. Filters were refrigerated until they were transported to USF for further geochemical analyses ( see Section 3.3 ). Water samples (500 ml, unfiltered) for microbial abundances were collected from surface (1m) and near the bottom of the water column at the same locations and preserved in LDPE bottles with 2% borate-buffered formaldehyde (Taylor et al., 2001).

During FOSA 1 (September 2008), additional SPM samples were collected at the mouth of the Manzanares Canyon (10°30’ N; 64°22’ W; water depth of 1000 m, station 3 in Figure 2b).

The sampling was done roughly three weeks after a magnitude (M) 5.2 earthquake occurred near

Cumaná, Venezuela (10.51°N, 64.17°W) on August 11, 2008. SPM samples were collected within a layer of suspended sediments detected using the transmissometer at the canyon mouth, at

870 m depth. Sampling was done as described above.

Figure 1. 2: Sampling locations for the study period: (a) 2003 (diamonds) and 2006 (crosses). Station labels correspond to locations where suspended particulate matter was collected. Rectangles A and B indicate location of stations used for Figure 5. (b) 2008 and 2009; station labels correspond to locations where SPM was collected. Gray circle indicates location of CARIACO Ocean Time -Series site (10.5° N, 64.67° W). Station 3 corresponds to the Manzanares Canyon mouth. In sert illustrates a close -up of the area. Star shows the epicenter of the August 11, 2008,

Meteorological and river data

Figure 1.1 illustrates the location of the meteorological stations utilized. Wind for the period of study (2003, 2006, 2008-2009) was obtained from the meteorological station located at

Punta de Piedras, Margarita Island. This station is maintained by the Fundacion la Salle de

Ciencias Naturales (FLASA). Precipitation, which was used as a proxy for river discharge, was obtained from the meteorological station at Corcovada; this station is maintained by the

Venezuelan Department of the Environment (Ministerio del Poder Popular para el

Ambiente/MINAMB). River discharge will generally lag precipitation by up to several months

(e.g. Zeng, 1999). Corcovada is located relatively inland and should be representative of precipitation over the Unare, Neverí, and Manzanares watersheds. Unfortunately, the station only has records of precipitation from 1995-2000 (MINAMB). In order to complement the Corcovada record, precipitation for the study period was examined at the meteorological stations of

Barcelona and Cumaná. Barcelona is a location that may reflect variations in discharge of the

Unare/Neverí; however, it is located closer to the coast and may not mimic the relationship between river discharge and precipitation as well as the Corcovada station. Additional meteorological data are limited in this region. For the Manzanares River, precipitation measured in Cumaná should reflect the magnitude of river discharge (Márquez et al., 2002), with discharge rates usually lagging the peak in precipitation by one month (e.g., precipitation at Cumaná peaks during August, while river discharge peaks during September). For the Tuy River, the station of

Caracas was selected. Data were extracted from the Monthly Climatic Data for the World

Publications ( http://www7.ncdc.noaa.gov/IPS/mcdw/mcdw.html ) and from the MINAMB. Figure

1.3 compares the average precipitation at the four mentioned sites; average precipitation for

Barcelona was obtained between 1921-1991 (MINAMB) and between 1997 and 2011 (NCDC).

Average precipitation for Corcovada was calculated for the period 1968-2003 (MINAMB); precipitation for Caracas was averaged betwee 1955-1992 (MINAMB) and 2003-2009 (NCDC).

Average precipitation for Cumaná was calculated between 1967-1992 (MINAMB) and 2004-

2010 (NCDC).

Annual average discharge data from the Unare, Manzanares, Tuy and Neverí rivers were taken from the INIA-MARN publication “Recursos Hidricos de Venezuela” (2006) The values reported in the publication do not specify a time period; these numbers are lower than what was reported for the period 1958-1967 by Zink (1977), but we assume they are more recent, and hence more accurate, estimates for our current work. To evaluate the relationship between precipitation and river discharge, historical monthly river discharge data for the Tuy and Neverí rivers (1973-

1975) were obtained from the Research Data Archive (RDA; ( http://dss.ucar.edu ). Monthly discharge data for the Unare River (1964-1977) was extracted from the INIA-MARN (2003).

Monthly discharge data for the Manzanares was obtained from Marquez et al. (2002).

Dissolved and total organic carbon concentrations were sampled for the period

September 2008 - September 2009 in collaboration with the Instituto Venezolano de

Investigaciones Cientificas (IVIC). Monthly samples were collected in the Tuy, Unare, Neverí and Manzanares rivers, within 100 m of the river mouth. Water for dissolved organic carbon

(DOC) was collected using a submersible pump; the intake of the pump was placed approximately in the middle of the water column (between 1.5-3 m depth, depending on the river) and 2 – 3 liters of water collected and stored in HDPE amber bottles rinsed three times with sample water prior to collection. Samples were kept refrigerated and were transported to the laboratory at IVIC in Caracas within one day of collection. DOC was vacuum-filtered through

47mm precombusted (450°C, 5 hours) Whatman GF/F filters (0.7 µm pore size) and the filtrate was collected in acid-cleaned 60 ml HDPE polyethylene bottles rinsed three times with sample water prior to filling. (Dickson et al., 2007). Total organic carbon (TOC) samples were collected directly from the pump and stored in acid-cleaned 60 ml HDPE polyethylene bottles (or 30 ml

HDPE bottles for nutrients), rinsed three times with sample water prior to filling. All samples were frozen until analysis. During March 2009 samples for SPM were collected from each river;

between 300 and 800 ml of water were filtered through acid cleaned (10% HCl), pre-combusted

(450°C for 5 hours) GF/F filters (0.7 µm pore size). Filters were refrigerated until analysis. A Van

Veen grab was used to obtain sediment samples from each river bed. Sediments were first placed in aluminum foil, then in sealed plastic bags and refrigerated until processing and analysis.

Geochemical analyses

At the University of South Florida (USF), SPM filters were vacuum-rinsed with Milli-Q water to remove salts, and dried for 8 hours at 60°C before re-weighing. SPM (g m -3) was calculated as the difference between the initial and final weight divided by total volume of sample filtered (between 3 and 6 L per filter). Filters were then acid washed under vacuum with 10% HCl to remove carbonates and subsequently rinsed with DI water. Surface sediments from the river beds and coretop material were also acidified for carbonate removal with 10% HCl and rinsed several times with DI water prior to drying and processing.

Particulate organic carbon (POC), particulate nitrogen (PN), and stable isotopic composition ( δ13 C, δ15 N), for both filter pads and sediments were measured simultaneously using a Fison NA 1500 Elemental Analyzer using previously established methodology (Werne and

Hollander, 2004; Thunell et al., 2007). The standard used was Spinach Leaves (NIST 1570a). The

o 15 o operational precision for the isotopic compositions were ± 0.63 /oo for δ N and ± 0.74 /oo for

δ13 C. For POC and PN, the operational precision was ± 0.18 mg N and ± 0.28 mg C. Total particulate P (TPP) and particulate inorganic P (PIP) were measured following the methods described by Benitez-Nelson et al. (2007). Particulate organic phosphate (POP) was estimated by difference from TPP and PIP. TPP and PIP measurements have a standard error of 3%, while

POP has a standard error of 5%.

All DOC/TOC samples were analyzed within six months of collection at the Organic

Biogeochemistry Lab at the University of Miami (RSMAS) using high temperature catalytic oxidation (HTCO; Hansell et al., 2000). Accuracy of the analysis was about ± 1.0 µMC.

Visualization of the data

Surfer (Golden Software, Inc.), V.8.04, was used to generate the spatial distribution maps.

Minimum Curvature was chosen as the gridding method to produce the interpolated surfaces.

Sigmaplot V.10.0 (Systat Software, Inc) was used to generate the two-dimensional plots.

Results

Meteorological conditions

Rainfall at the four selected locations (Corcovada, Cumana, Barcelona and Caracas) exhibited the expected pattern of high precipitation during September-November, then low precipitation during December-May, and increasing precipitation after June (Figure 1.3).

Precipitation rate was highest in May for all locations, except Cumana (Appendix 1, supplementary figure 1.2). Precipitation records for the study period were within a standard deviation of historical averages. Higher than average precipitation was recorded in July 2003, likely associated with the passing of hurricane Claudette, which crossed the Caribbean in early

July ( http://www.nhc.noaa.gov/ ). With the appropriate lag, average precipitation at the selected sites was well correlated with river discharge (Appendix 1, supplementary figure 1.3); for the Tuy

River, the correlation with the precipitation measured in Caracas was R 2 = 0.91 and the lag was 4 months. This is a reasonable amount of time, considering that the meteorological station is located more than 100 Km from the river height stage. The correlation between Unare river discharge and precipitation in Barcelona was R 2 = 0.89 with a lag of 1 month (correlation with historical precipitation in Corcovada yielded a similar correlation and lag). For the Neverí river, the correlation was R 2 = 0.89 and the lag was of 2 months. The correlation between Manzanares

river discharge and precipitation at Cumaná was R 2 = 0.89 (lag = 1 month). It is possible that these lag times between precipitation and discharge are affected by the fact that we are utilizing monthly means, and hence averaging out a faster response. Unfortunately, we do not have higher resolution discharge or precipitation records to be able to resolve this at this time.

The zonal component of the wind speed (u) during 2003 was above average for the first 6 months of the year (~ 7.3 m/s during March 2003) then fell within the 15-year average wind speed recorded at the Punta de Piedras station (1996-2009; Appendix 1, supplementary figure

1.4). Zonal wind speeds are typically on the order of 6 m/s during March months. It is unclear whether the stronger wind speeds observed in 2003 were related with the 2002-2003 ENSO. For

2006, wind speeds were within the 15-year average record. Towards the end of 2008 and during

2009 u was weaker than the average records. Zonal wind speeds were 4.5 m/s. during March

2009. u increased after March 2009, reaching a maximum speed during April (5.4 m/s) and then decreased progressively to ~4 m/s, always remaining below average values. 2009 was the only year that exhibited significant ( p < 0.05) departure from average values.

Riverine organic carbon and suspended sediments

There was no significant correlation between monthly precipitation during 2008-2009 and monthly DOC concentration in any of the rivers. Most of the suspended organic carbon in the four sampled rivers was in the dissolved form (average of >90%, Appendix 2). The Unare River had the highest DOC concentration (annual average of 339.5 ± 212.3 µM), followed closely by the Tuy (annual average of 268.1 ± 74.7 µM), the Neverí (annual average of 167.8 ±25.5 µM) and lastly the Manzanares with the lowest concentration (annual average of 112.1 ± 42.0 µM).

The isotopic composition of suspended particles varied among rivers and relative to riverbed sediment (Tables 1 and 2).

Table 1.1: Characteristics of the main rivers draining into the Cariaco Basin. Suspended particulate organic matter concentration, isotopic composition and sediment and organic carbon fluxes are also shown. SPM: suspended particulate matter; δ13 C: stable isotopic ratio of organic carbon; δ15 N: stable isotopic ratio of organic nitrogen; POC: particulate organic carbon; PN: particulate nitrogen; POP: Particulate organic phosphorous; PIP: Particulate inorganic phosphorous; C/N: atomic organic carbon to nitrogen ratio; % POC: weight-percent POC content; % PN: Weight-percent PN content; % POP: Weight-percent POP content; % PIP: weight-percent PIP content; DOC: Dissolved organic carbon.

Tuy Neverí Unare Manzanares Drainage area (Km 2) 6,600 ᵃ 3,900 ᵃ 22,371 ᵇ 1,652 ᶜ

Flow rate (m 3/s) ᵈ 65 37 46 18

Flow rate (m 3/s) a 82 35 56 22

SPM (mg/l) 97 ± 1.15 5.25 ± 1.11 38.3 ± 2.31 7.18 ± 0.93

δ13 C (‰) -25.25 -24.60 -27.98 -24.89

δ15 N (‰) 4.45 2.33 12.46 3.69

POC (mgC/l) 2.00 0.63 0.69 0.30

PN (mgN/l) 0.32 0.12 0.17 0.06

mg POP/l (x10 -3) 38.76 8.03 25.61 7.47

mg PIP/l (x10 -3) 207.67 52.23 19.19 8.56

C/N 7.20 6.16 4.70 5.41

% POC 2.63 12.10 2.53 4.55

% POP 15.73 13.33 57.16 46.63

%PIP 84.27 86.67 42.84 53.37

SPM flux (Gg/year) 250.8 ± 2.98 5.79 ± 1.22 42.3 ± 2.5 7.92 ± 1.03

POC Flux (Gg/year) 5.17 0.69 1.29 0.21

DOC Flux x10 8 6.93 ± 1.93 1.85 ± 0.28 6.00 ± 2.14 0.77 ± 0.29 (mol/year) ᵃ From Zink et al., 1977 ᵇ From Rodríguez and Gonzalez, 2001 ᶜ From Marquez et al., 2002 ᵈ Recursos Hídricos de Venezuela, 2006

250 160 Barcelona 2006 Cumana Caracas a 140 2008 b 200 Corcovada 2009 Cumana 120 Average

150 100

100 60 Precipitation(mm) Precipitation (mm) 40 50 20

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

300 250 2003 Barcelona 2003 Caracas 2006 2006 250 2008 c 2008 d 2009 200 2009 Average Average 200 150

150

100 100 Precipitation (mm) Precipitation (mm)

50 50

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 1. 3: (a) Average precipitation records between the four meteorological stations selected (see text for years averaged). (b-d) Precipitation records for the years of study. Thick black line corresponds to the average precipitation at each station; error bars indicate one standard deviation from average. Location is indicated at the top of each plot.

Table 1.2: Composition of surface (upper 5 cm) river bed sediments of the four main rivers draining into the Cariaco Basin. Abbreviations are as in Table 1.

13 15 δ C ( ‰) δ N ( ‰ ) % POC % PN C/N

Tuy -25.55 3.23 1.33 0.15 10.08 Neverí -27.65 3.34 4.13 0.37 12.98 Unare -26.07 4.54 1.02 0.10 11.40 Manzanares -26.07 2.85 0.21 0.02 11.54

Riverbed sediment was relatively constant between rivers ( p > 0.05), in the range of -25 ‰ and -

27 ‰. %POC was higher in suspended sediments (2-12%), as compared to riverbed sediments

(0.2-4%), though not significantly ( p > 0.05). Average river discharge rate values were used to estimate fluxes of carbon and SPM to the ocean, which are summarized in Table 1.

Hydrographic conditions

Figures 1.4 and 1.5 show sea surface (1 m) salinity and temperature in the eastern

Cariaco Basin for September 2003 and 2006, and for the entire basin for 2008 and 2009. In

September 2003, average sea surface temperature (SST) over the cruise track was 27.91 °C, and salinity was 36.59. The Unare River plume showed lower salinity (35.38) and warmer (28.97°C) temperature than surrounding waters (see also Appendix 3). The Neverí and Manzanares river plumes were slightly cooler (27.57°C and 28.03°C, respectively), and average salinities near the mouths of these rivers were 36.01 and 36.75, respectively; the high salinity measured near the

Manzanares suggests that we did not capture the river plume at the time of sampling (refer to

Figure 1.1 for plume dynamics of the rivers). During September 2006, average SST in the eastern basin was 28.09 °C and average salinity was 36.47. Salinities (and temperatures) recorded near the mouths of the Unare, Neverí, and Manzanares rivers were 36.46 (28.20°C), 36.23 (27.87°C) and 36.53 (28.05°C), respectively. Salinity in the eastern basin during September 2008 was lower

than 2003 and 2006, while the average temperature was higher (29.05 °C). Salinity in the western basin was lower (36.11; SST = 28.99 °C). SST in September 2008 was the highest observed for the various periods studied (Figure 1.5). A trend of increasing temperature has been observed at the CARIACO Ocean Time-Series site. Annual surface temperature minima have increased ~1°C from 1995 to 2009 (Astor et al., submitted). In September 2008, the Unare river plume had an average temperature of 28.38°C (salinity of 36.24), the Tuy River of 28.53°C (salinity of 36.02), the Neverí river of 28.67 °C (salinity of 36.29) and the Manzanares of 29.18 °C (salinity of 36.35;

Appendix 3). In the eastern basin, between September 2003 and September 2008, there was an average salinity decrease of ~0.4. The salt budget within the basin is determined by local rainfall/river discharge, surface mixing with Caribbean waters and the contribution of the SUW.

Though this latter one is more important during the upwelling, SUW is always present inside the basin, the depth of its core dependent on the offshore Ekman transport (Rueda, 2012). Ekman offshore transport is upwelling favorable year-round in the Cariaco Basin (Rueda et al., 2012).

The higher salinity observed during 2003 could be attributed to a greater contribution of SUW to surface waters due to stronger mixing in the water column; the mixed layer depth (MLD) during

September 2003 for stations away from the coast (depth > 200m) was on average 22.5 m, and the overall SST of the basin was lower (28.01 °C; Figure 1.5) as compared to the other years, suggesting input from deeper, colder waters. The precipitation over Barcelona and Caracas was not abnormal, within one standard deviation from the mean (Figure 1.3). During 2006 the MLD decreased to 16.2 m, and the overall SST of the basin increased to 28.11 °C; once more, precipitation in the three meteorological stations did not exhibit any anomalous behavior. Though

Hurricane Ernesto was present in the Caribbean at the end of August, its influence was displaced northwestward from the Cariaco Basin (http://www.nhc.noaa.gov/ ). September 2008 was the freshest (average salinity of the eastern basin ~36.26) and warmest of the three years (average

SST of the eastern basin ~29.05°C). The MLD was 17.73 m, similar to that measured during

2006. Precipitation was relatively high in Cumana and Caracas, compared to the average (Figure

1.3) during August-September 2008, possibly contributing more freshwater to the basin. There was no hurricane activity in the Caribbean during 2008 ( http://www.nhc.noaa.gov/ ). It is also possible that the Caribbean may have had a stronger influence on surface salinity of the basin during 2008, though we currently have no data to substantiate this.

During March 2009 the average temperature of the Basin dropped to 24.83 °C, and salinity increased to 36.87; these values are similar to those measured by Lorenzoni (2005) in

2004 in the eastern basin. The upwelling plume was visible in the southeastern portion of the

Cariaco Basin; consistent with the location of the upwelling (see Herrera and Febres-Ortega,

1975; Herrera et al., 1980; Walsh et al., 1999; Lorenzoni, 2005; Rueda et al., 2012). The coldest temperature was recorded in the eastern basin near the Gulf of Cariaco (Station 5, 22.67 °C;

Figure 1.5). Upwelling was restricted to the southeastern portion of the basin. Although the overall temperature in the basin decreased, SST in the western basin remained >25 °C (Averages of 23.88 °C and 36.84 for the eastern basin; 25.52 °C and 36.73 for the western basin). The Unare

River plume was visible during March 2009 in the southern region of the basin as a warmer water mass (26.02 °C), compared to the surrounding waters, though not particularly fresher (salinity of

36.91). The Tuy River was slightly cooler (25.42 °C) and fresher (36.29) than the Unare. The plumes of the Manzanares and Neverí were not discernible with temperature or salinity.

Figure 1.6 illustrates the surface (1 m) distribution of DOC during September 2006. Higher TOC

(p < 0.01) was observed near the Unare River (average of 85.4 µM) and between Margarita Island and the Araya Peninsula (average of 79.1 µM), relative to the rest of the basin (average of 71.5

µM). Since there are no large rivers draining Margarita Island, the cause of the high DOC and

TOC observed between Margarita and the Araya Peninsula was likely the result of local upwelling. The surface (1 m) distribution of DOC during September 2008 and March 2009 is also shown in Figure 1.6. DOC concentrations during the rainy period (September 2008) were higher compared to the upwelling season of March 2009 ( p < 0.01). Overall, average concentrations of

DOC basin-wide decreased about 5 µM from September 2008 (~77.58 µM C) to March 2009

(~72.34 µM C). DOC concentrations during September 2008 were highest closer to the coast; the maximum DOC was measured near the Tuy River (84.01 µM C; Appendix 3).

Beam attenuation (c-beam coefficient or c p at 660 nm)

High coefficients of light attenuation (~1-5 m -1) were observed at the surface (1-2 m) near the mouths of most rivers (figure not shown) during all cruises. This high attenuation is caused by surface nepheloid layers (SNL) composed of particulate material being discharged into the basin by rivers. During September, attenuation was ~0.3-1 m -1 and the highest attenuation was measured near the Unare River (1.34 m -1) during September 2008. During March 2009, surface nepheloid layers near the mouth of the rivers were much less pronounced (attenuation of ~0.4-0.6 m-1), except near the Unare River and the Cúpira River (Figure 1.2b), where attenuation of 5.33 m-1 and 2.24 m -1 were measured, respectively. Higher surface attenuation was also recorded near

Gulf of Cariaco and the Gulf of Santa Fe (~0.3 – 0.4 m -1, respectively). The surface nepheloid layer (SNL) near the Manzanares River was intermittent; it was visible only during 2006. Surface cp(660) decreased within a short distance from the river mouths, suggesting that most riverine particles settle from surface waters rapidly.

The bottom beam attenuation coefficient (c p(660)) measured during September 2003, 2006, 2008 and March 2009 is shown in Figure 1.7. High attenuation was consistently observed 2-35 meters above bottom (m.a.b.) throughout the entire coastal area for the four years sampled, with highest values (~0.6 - 4.5 m -1) near the mouths of the rivers. This high beam attenuation observed near the seafloor was due to suspended sediment forming BNLs. During 2003 and 2006 c p values were similar, with the highest attenuation observed near the Unare River (1.2 – 2.2 m -1) and east of the

-1 Neverí River (average c p(660) of 0.5-0.6 m ). The BNL over the Unare Platform were well developed and extended northeastward. They varied in thickness, from about 5m thick near rivers

Figure 1. 4: Distribution of sea surface salinity during the study periods.

°C

29.8

29.5

29.2

28.9

28.6

28.3

27.7

27.4

27.1

26.8

26.5 °C

26.6

26.3

25.7

25.4

25.1

24.8

24.5

24.2

23.9

23.6

23.3

Figure 1. 5: Distribution of sea surface temperature during the study periods. Note the difference in color scales used: September months use the top scale; March 2009 uses the bottom scale.

90 88 86 84 82 80 78 76 74 72 70 68 66 64 62 60 58 56 54

Figure 1. 6: Distribution of sea surface dissolved organic carbon (DOC) during the study periods.

to ~15m thick near the shelf break. There were no BNL observed near the Manzanares River; rather, sediment layers over the narrow portion of the Unare Shelf (southwest of the Manzanares

River) were not well developed and were mostly detached from the bottom (~10 m.a.b; average

-1 cp(660) of 0.3-0.4 m ). Representative beam attenuation and density distributions for this region are shown in Figure 1.8a. Beam attenuation during 2008 was comparable to that of 2003 and

2006; highest values (~1.3-2.5 m -1) were measured near the mouths of the Tuy, Cúpira and Unare rivers in the western basin, and off the Unare River (1.39 m -1). In contrast to observations of 2003 and 2006, clearly defined BNL were measured southwest of the Manzanares River during 2008 and 2009. The attenuation of these layers (~0.2-0.3 m -1) was close to an order of magnitude less than that observed over the wide Unare Platform. The Neverí River did not exhibit a BNL during

September 2008. Rather, attenuation was high throughout the entire water column near the Neverí

River. During 2009 BNLs were more pronounced over the Unare Platform, as compared to those

-1 sampled in other years. Highest c p was measured near the mouths of the Neverí River (1.71 m ), the Unare River (4.53 m -1) and the Cúpira River (2.95 m -1). For the Tuy River, the attenuation measured during March 2009 was lower than that of September 2008 (1.05 m -1) (Figure 1.7).

A schematic representation of BNL over the Unare Platform is shown in Figure 1.8b. The thickness and location of the BNL was similar for all study periods. For September 2006, 2008 and March 2009 there was a good correlation between SPM and light attenuation (R2= 0.72;

N=12; p < 0.01 during September 2006; R2= 0.64; N=18; p < 0.01 during September 2008/March

2009). However, we did not find a clear relationship between POC and beam attenuation. In coastal environments this relationship is highly variable due to the different sources of particles present (Zaneveld, 1973).

We observed BNLs extending out to the 100m isobath, increasing in thickness (up to three-fold) towards the shelf break. Off the Unare Platform and over the deep Cariaco Basin, slightly increased c p(660) values indicated the presence of intermediate nepheloid layers (INLs).

INLs were observed at several locations, mainly in the area of the Gulf of Santa Fé, the Gulf of

Cariaco, and in the deeper basin. INL’s were generally associated with isopycnals, moving roughly over the same density surface ( σ = 26.1 Kg m -3 southwest of Cumaná; Figure 1.8a; σ =

25.5 – 25.9 Kg m -3 in the deeper basin, Figure 1.8b). The INLs varied in thickness (between 14 and 6 m), decreasing in thickness with increasing distance from the coast. Some INLs were observed over 60 Km from the coast.

-1 During September 2008, high beam attenuation (c p = ~0.15 m ) was observed in the

Manzanares Canyon mouth (hereafter referred to as the canyon mouth) between 850-870 m depth, within a suspended sediment layer that spanned from the seafloor at 1000 m to ~815 m depth (Figure1. 9). Outside this turbid layer, c p was almost an order of magnitude lower (~0.025 m-1) and comparable to values measured repeatedly in the basin as part of the CARIACO Ocean

Time-series program. At station 10, which corresponds to the CARIACO site, a layer of high beam attenuation between 1215-1255 m was also observed, which is ~150 m above the seafloor

-1 (Figure 1.9). The c p peak in this layer was 0.078 m , about half of the peak value measured in the sediment layer within the canyon mouth. This value was almost three times higher than the c p normally observed at similar depths in the Cariaco Basin (0.025 ± 0.007 m -1).

SPM, POC, PN and their isotopic composition

SPM, particulate organic carbon, nitrogen, and phosphorous, and the isotopic composition of these elements found in surface and BNL varied with season (tables 3 and 4 vs. table 5). In general, sediment concentration in both surface and BNL samples was higher during the rainy season (~1-7 mg l -1, as compared to 0.2-4.7 mg l -1 during March 2009), likely due to the greater input of particles from rivers at this time. This difference was only significant at the

- m

2.71

2.41

2.11

1.81

1.51

1.21

0.91

0.61

0.31

0.01

-1 m 4.5

4.1

3.7

3.3

2.9

2.5

2.1

1.7

1.3

0.9

0.5

0.1

-1 Figure 1. 7: Distribution o f bottom nepheloid layers (BNL) , measured as light beam attenuation (c p(660), m ). Note the difference in color scales used: September 2003 and 2006 use the top scale; September 2008 and March 2009 use the bottom scale.

-1 Figure 1. 8: Distribution of beam attenuation (c p (m )) and major isopycnals (salinity in kg m -3) for selected locations over (a) Region A and (b) Region B. (refer to Figure 2a for location). In (b) SNL indicates surface nepheloid layer; BNL and INL denote bottom and intermediate nepheloid layers, respectively. Note that for better visualization of INL’s, scales of offshore profiles have been resized.

surface ( p < 0.05). Samples collected during September 2008 and March 2009 were used to understand changes in POC sources to the water column. The difference in δ13 C values between surface and BNL was significant in both September 2008 and March 2009 (p < 0.05). In general, the δ13 C of BNL was always lower than that of surface POC. During September 2008, BNL isotopic composition was depleted (> -26 ‰; Figure 1.10), and it remained relatively low (~ -23

‰) during March 2009 (Tables 4 and 5). During March 2009, the isotopic composition of POC in surface waters was 3-5 ‰ higher than what was observed in September 2008 (p < 0.05),

Figure 1. 9: Transmissometer profiles collected at the CARIACO Time -Series site (segmented line) and at the canyon mouth (black line) during September 2008. Thick gray line indicates 2-year average (2006-2008) of beam attenuation data at the CARIACO Time- Series site; gray shadow indicates standard deviation. The ‘interface’ refers to the location of the oxic-anoxic water boundary where higher bacterial abundances lead to the attenuation peak.

especially in the southeastern part of the basin where the temperatures were colder. During

September 2006, δ13 C was higher as compared to September 2008 (p > 0.05; tables 3 and 4); values in September 2006 were higher or similar to what was measured during March 2009 ( p >

0.05; Table 5).

Figure 1.11 shows the δ13 C of all samples relative to their atomic C/N ratios, which can be used to infer the provenance of the organic matter. For reference, compositional ranges of marine and terrestrial end-members are shown in Figure 11. During the rainy season, suspended and BNL particles were closer to a terrestrial end-member. During September 2008, most samples fell on the mixing line between the two end-members, suggesting that the organic matter present near the coast during this period was a mixture of these sources. During both September 2006 and March

2009 samples also were near the mixing line, but closer towards the marine end-member, suggesting a higher marine contribution. Some samples were very near the marine end-member, and these corresponded to those stations located within the upwelling plume.

In general, surface samples contained higher %POC than BNL for all sampled periods

(Figure 1.10). DOC in BNL was not significantly different than DOC in surface waters ( P >

0.05). There was no significant increase in microbial abundance in BNL compared to surface waters. During September 2006 %POC was lower than that seen in 2008 ( P > 0.05; Tables 3 and

4). In 2006 the average % POC in surface waters for all sampled stations (Table 3) was 6.73 ± 0.9

%. During 2008 this percentage was ~10%, except in the southeastern part of the basin where it was 18.7% and 51.6% (Table 4). BNL POC was generally 1-6% lower ( P > 0.05) than what was measured in the surface (except near the Unare River, where BNL POC was 27.5%). During

March 2009 surface POC concentrations were not much different from September 2008 (Figure

1.10). In fact, some BNL exhibited a slight drop in POC content.

Table 1.3: Composition of near-surface and bottom (BNL) suspended sediments from selected locations sampled during September 2006 in the Cariaco Basin. Refer to Figure 1.1 for station location. Gray indicates BNL. D refers to the thickness of the BNL. C/TPP: atomic organic carbon to total particulate phosphorous ratio; C/POP: atomic organic carbon to particulate organic phosphorous ratio; C/PIP: atomic organic carbon to particulate inorganic phosphorous ratio. All other abbreviations are as in Table 1. Depth Station Lat SPM sampled Number Lon δ13 C δ15 N POC PN POP PIP D (mg/l) POC PN PIP C/N C/TPP C/PIP C/POP (m) -3 -3 (‰) (‰) (mg/l) (mg/l) (mg/l x10 ) (mg/l x10 ) (m) % % % 1 -24.04 6.15 0.11 0.01 1.23 0.30 1.72 6.48 0.59 0.20 12.7 188.0 959.0 233.9 10.18° 60 -65.08° 26 -24.47 6.23 0.13 0.01 1.40 1.05 4 2.74 4.69 0.49 0.43 11.1 135.5 316.1 237.1

13 -23.84 6.35 0.10 0.01 1.16 0.30 1.24 7.80 0.85 0.21 10.7 171.0 832.4 215.3 10.31° 37 -65.10° 55 -23.1 8.66 0.08 0.01 0.69 0.37 13 1.74 4.74 0.55 0.35 10.0 200.9 575.5 308.6

13 -23.89 6.65 0.09 0.01 0.96 0.45 1.46 6.48 0.68 0.32 11.1 173.3 542.9 254.5 10.36° 39 -64.83° 66 -23.14 7.85 0.09 0.01 0.55 0.70 2 1.84 5.16 0.53 0.56 11.3 196.1 350.2 445.7

10 -23.36 7.65 0.14 0.02 0.69 0.45 1.73 8.01 0.95 0.39 9.8 313.8 795.0 518.5 10.33° 27 -64.71° 48 -23.39 7.42 0.09 0.01 0.73 0.29 8 1.76 5.28 0.55 0.28 11.3 235.5 828.4 329.1

12 -23.85 7.19 0.08 0.01 0.35 0.54 1.44 5.39 0.59 0.61 10.7 225.1 371.0 572.5 10.28° 35 -64.80° 50 -23.34 6.74 0.08 0.01 0.82 0.77 7 1.47 5.67 0.56 0.48 11.8 135.5 279.8 262.7

11 -22.87 6.53 0.10 0.01 1.11 0.45 1.53 6.24 0.67 0.29 10.9 158.2 548.5 222.4 10.39° 38 -65.10° 66 -21.78 5.98 0.08 0.01 0.51 0.26 16 1.47 5.42 0.53 0.34 12.0 267.2 791.2 403.4

Table 1.4: Composition of surface (~1m) and near-bottom (BNL) suspended sediments from selected locations sampled during September 2008 in the Cariaco Basin. Refer to Figure 1.1 for station location. Gray indicates BNL. Abbreviations are as in Table 1 and 3.

Depth Station Lat δ13 C δ15 N POC PN POP PIP D SPM POC PN PIP sampled C/N C/TPP C/PIP C/POP number Lon (‰) (‰) (mg/l) (mg/l) (mg/l x10 -3) (mg/l x10 -3) (m) (mg/l) % % % (m) 1 -26.01 0.95 0.189 0.006 0.36 0.19 1.01 18.66 0.64 0.35 33.9 892.5 2571.9 1366.9 10.41° 5 -64.40° 190 -28.98 7.05 0.190 0.004 0.20 0.48 20 1.37 13.86 0.29 0.70 56.6 724.6 1032.2 2431.7

1 -26.01 n.a 0.531 0.006 0.75 0.12 1.03 51.56 0.62 0.14 96.7 1568.7 11400.4 1819.0 10.38° 6 -64.54° 109 -26.57 9.14 0.304 0.007 0.43 0.37 35 1.76 17.29 0.38 0.46 53.5 988.9 2133.3 1843.5 10.18° 20.7 15 27 -26.92 0.916 0.012 1.58 1.10 10 3.33 27.49 0.35 0.41 91.4 885.2 2155.2 1502.1 -65.08° 7 1 -25.12 6.10 0.292 0.016 1.16 0.83 2.85 10.26 0.57 0.42 21.1 379.9 914.8 649.8 10.16° 17 -65.32° 10 -29.55 5.79 0.128 0.010 1.17 0.58 2 2.11 6.06 0.50 0.33 14.3 188.6 571.2 281.5 10.9 1 -26.51 0.162 0.010 0.57 0.88 1.96 8.28 0.52 0.61 18.7 289.1 475.9 736.1 10.23° 0 24 -65.60° 10 -38.05 5.91 0.167 0.014 2.32 1.71 2 7.04 2.38 0.20 0.42 13.6 107.3 252.7 186.5

1 -26.90 3.75 0.302 0.005 0.62 0.15 2.75 10.98 0.19 0.19 68.4 1014.8 5273.6 1256.6 10.35° 25 -65.86° 20 -24.87 7.28 0.143 0.013 1.38 0.99 10 6.37 2.25 0.20 0.42 13.0 156.0 374.8 267.1 11.8 1 -21.73 0.118 0.018 1.85 3.01 2.44 4.85 0.72 0.62 7.9 63.0 101.6 165.7 10.49° 6 27 -66.00° 27 -22.96 7.62 0.146 0.015 1.68 1.59 10 3.35 4.37 0.46 0.49 11.2 115.7 237.5 225.4

1 -22.92 6.23 0.158 0.016 0.70 0.53 1.46 10.78 1.12 0.43 11.2 331.4 769.4 582.0 10.49° 28 -65.86° 55 -24.48 6.85 0.075 0.006 0.51 0.50 17 1.23 6.10 0.49 0.50 14.5 192.6 387.8 382.7

Table 1.5: Composition of surface (~1m) and near-bottom (BNL) suspended sediments from selected locations sampled during March 2009 in the Cariaco Basin. Refer to Figure 1.1 for station location. Gray indicates BNL. Abbreviations are as in Table 1 and 3.

depth Station Lat δ13 C δ15 N POC PN POP PIP D SPM POC PN PIP sampled C/N C/TPP C/PIP C/POP number Lon (‰) (‰) (mg/l) (mg/l) (mg/l x10 -3) (mg/l x10 -3) (m) (mg/l) % % % (m) 10.44º 1 -23.48 5.78 0.122 0.021 n.d. n.d. 0.45 27.10 4.66 n.d. 6.8 n.d. n.d. n.d. 4 -64.26º 190 -26.31 5.89 0.056 n.d. 0.433 0.172 24 0.28 20.10 n.d. 0.28 n.d 240.57 847.02 336.00

10.41º 1 -20.81 n.d. 0.227 0.122 n.d. n.d. 0.65 34.89 18.72 n.d. 2.2 n.d. n.d. n.d. 5 -64.40 190 -25.09 6.19 0.053 n.d. 0.642 0.341 20 0.67 7.95 n.d. 0.35 n.d 139.88 403.12 214.20

10.38º 1 -21.79 1.81 0.158 0.032 n.d. n.d. 0.54 29.17 5.92 n.d. 5.8 n.d. n.d. n.d. 6 -64.54º 105 -24.51 6.72 0.051 0.009 0.727 0.280 17 0.40 12.78 2.25 0.28 6.6 131.03 470.92 181.53

10.20º 1 -23.77 4.16 0.186 0.038 1.667 0.833 1.00 18.60 3.80 0.33 5.7 192.2 576.8 288.3 8 -64.73º 10 -23.17 5.83 0.143 0.027 2.910 0.460 4 1.05 13.61 2.54 0.14 6.3 109.23 799.86 126.50

10.30º 1 -23.37 5.25 0.114 0.022 n.d. n.d. 0.66 17.32 3.33 n.d. 6.1 n.d. n.d. n.d. 14 -64.99º 56 -23.91 5.59 0.089 0.013 n.d. n.d. 16 1.11 8.03 1.14 n.d. 8.2 n.d. n.d. n.d.

10.18º 1 -25.07 9.58 0.200 0.019 n.d. n.d. 0.85 23.57 2.24 n.d. 12.3 n.d. n.d. n.d. 15 -65.08º 22 -24.35 6.23 0.072 0.016 1.724 0.489 2 2.91 2.49 2.98 0.22 5.1 84.50 382.09 108.49 10.16º 17 8 -24.94 21.72 0.198 0.040 2.126 1.336 4 4.21 4.70 0.94 0.39 5.8 147.63 382.48 240.42 -65.32º 10.23º 1 -22.70 12.87 0.205 0.036 n.d. n.d. 2.90 7.07 1.25 n.d. 6.6 n.d. n.d. n.d. 24 -65.60º 15 -24.37 5.73 0.110 0.016 2.794 0.917 3 4.76 2.32 0.33 0.25 8.2 76.92 311.35 102.15 10.35º 25 1 -23.10 2.39 0.112 0.022 n.d. n.d. 0.68 16.42 3.21 n.d. 6.0 n.d. n.d. n.d. -65.86º 10.41º 1 -23.30 6.13 0.113 0.024 n.d. n.d. 1.83 6.16 1.30 n.d. 5.5 n.d. n.d. n.d. 26 -65.95º 10 -25.23 4.45 0.210 0.020 2.471 0.840 4 1.42 14.83 1.42 0.25 12.2 164.06 646.74 219.83 10.49ºN/- 27 1 -25.98 5.25 0.189 0.017 n.d. n.d. 0.60 31.48 2.81 n.d. 13.1 n.d. n.d. n.d. 66.00ºW 10.49ºN/- 1 -24.08 4.99 0.097 0.016 n.d. n.d. 1.26 7.73 1.28 n.d. 7.0 n.d. n.d. n.d. 28 65.86ºW 58 -23.98 4.17 0.079 0.013 0.925 0.421 12 0.87 9.12 1.55 0.31 6.9 151.89 485.98 220.94

‰

-21.8

-22.4

-23

-23.6

-24.2

-24.8

-25.4

-26

-26.6

-27.2

-27.8

-28.4

-29

Figure 1.10: Distribution of δ13 C (top 4 panels) and %POC (bottom 4 panels) in surface and BNL during September 2008 (FOSA1) and March 2009 (FOSA2).

PN concentrations near the coast increased two-to-five-fold during March 2009 relative to September 2006 and 2008 (Tables 3, 4 and 5), both at the surface ( P < 0.01) and within the

BNL ( P < 0.05). These changes in PN concentration were reflected in the C/N ratios of POM throughout the water column. C/N ratios decreased from >20 during September 2008 to ~6 during

March 2009; C/N during 2006 was 10-12. Changes in the isotopic composition of nitrogen between sampling periods were not significant. PIP and POP were generally higher within the nepheloid layers compared to the surface, sometimes by a factor of two. Their concentration in the BNL decreased with distance from the coast, and this was visible in the changes in C/P ratios.

The C/POP ratios showed a general increase in the offshore direction by ~60% in the BNL, while the C/PIP increased ~40%. This suggests an active removal of POP and PIP as the BNLs move offshore. In contrast, the C/PIP and C/POP ratios in surface waters did not change much with distance from shore, suggesting retention of P. The overall distribution of POP and PIP near the coast was affected by riverine dynamics, with higher values near the mouths of the rivers (Tables

3, 4 and 5). Though data was more limited during 2009, there seemed to be more POP in the BNL

(lower C/POP ratios). The higher C/PIP ratios observed in the eastern basin in 2008 reflect higher

POC in that area.

Carbon, nitrogen and their isotopic compositions were also examined within the suspended sediment layer observed at the Manzanares canyon mouth. Average POC and PN were

0.128 ± 0.01 g C m -3 (n = 3) and 0.008 ± 0.002 g N m -3 (n = 3), respectively. C/N ratios in the sediment plume at the canyon mouth averaged 19.3 ± 2.5 (Table 6). The δ13 C within the sediment layer averaged -27.04 ‰, whereas the δ15 N was ~6.83 ‰.

120 September 2008 BNL T September 2008 1m 100 March 2009 BNL March 2009 1m SPM rivers 2009 River sediment March 2009 80

60 C/N

20 River algae? M 0 -32 -30 -28 -26 -24 -22 -20 -18 -16 δ13 o C ( /oo )

Figure 1.11: Plot of the stable carbon isotopic composition of particulate organic carbon ( δ13 POC) versus the atomic carbon:nitrogen ratio (C/N) for suspended POC from surface waters and BNL for September 2006, 2008 and March 2009. Riverine suspended POC and river bed surface POC for March 2009 are also shown. The compositional ranges of different end members are included in the plot: T = Terrestrial; M = Marine.

Table 1.6: Geochemical composition of the canyon mouth turbidity plume (870 m). Average values ± standard deviations of variables collected at the CARIACO Ocean Time-Series site at 1310 m between 1996-2007 are also shown. SPM data for the CARIACO Time-Series site was estimated using the c p relationship described in the text.

CARIACO Time-Series Manzanares Canyon site turbidity plume SPM (g m -3) 0.10 ± 0.05 (N = 25) 1.00 ± 0.13 (N = 3) POC (g C m -3) 0.05 ± 0.01 (N = 113) 0.128 ± 0.01 (N = 3) -3 PN (g N m ) 0.007 ± 0.02 (N = 113) 0.008 ± 0.00 2 (N = 3) C/N 9.9 ± 5.4 (N = 113) 19.3 ± 2. 5 (N = 3) 13 o δ C ( /oo ) -20.7* -27.04 ± 1.45 (N = 3) 15 o ♦ δ N ( / ) 3.50 6.83 ± 0.31 (N = 3) oo *From Woodworth et al., 2004 ♦From Thunell et al., 2004

The relationship between beam attenuation and SPM described in the previous section was subsequently used to determine SPM integrated over the depth of the observed suspended sediment layers at both the canyon mouth and the CARIACO site. The mouth of the Manzanares

Canyon is located ~42 Km east of the CARIACO site. Depth-integrated SPM at the canyon mouth (over 165 m) was ~ 90 g m -2, while at the CARIACO site it was ~11 g m -2 (over 40 m).

Unfortunately, the suspended sediment layer was below the deepest sediment trap (1200 m) at the

CARIACO site (Thunell et al., 2007). Thus, no additional particulate matter from this event was captured by the sediment trap located at ~1200 m.

Discussion

Organic matter and suspended sediment contribution by local rivers

Runoff is generally well correlated with net precipitation over the river catchment

(Milliman and Farnsworth, 2011). The sediment transport capabilities of a river are primarily controlled by the basin size and topography, and by the climate of the region (Milliman and Mei- e, 1995; Fekete et al., 2003). From historical values there is an apparent reduction in discharge for rivers draining into the Cariaco Basin (Table 1). Unfortunately, the few data available preclude

anything conclusive; however, there is a global trend in river discharge and SPM load reduction attributed to both climatic changes and human activities (Syvitski et al., 2005; Milliman et al.,

2008; Walling, 2009). Natural changes in river discharge are caused mainly by a reduction in precipitation over the catchment, primarily in response to atmospheric signals (long and short term). Anthropogenic impacts on discharge include damming, irrigation and water extraction.

The annual flux of the suspended sediment load calculated in this study are ~15-50 times less than has been reported in the literature (refer to Table 1). For example, Milliman and Syvitski

(1992) reported values of ~12 x 10 6 metric tons of sediment per year for the Tuy River; Ramirez et al. (1992) reported almost three times as much for the same river system. Similar differences in suspended sediment fluxes are also observed for the other three rivers (e.g. Marquez et al., 2002 for the Manzanares; Milliman and Syvitski, 1992, for the Manzanares and Neverí; Rodríguez and

Gonzalez, 2001, and INIA-MARN, 2003 for the Unare). The SPM concentrations used for our flux calculations were measured during the peak of the dry season (March), when discharge is minimal, so these fluxes should be considered minimum estimates. Additionally, because suspended load depends on environmental conditions (e.g. floods and droughts) and on human activities, a large interannual variability in the rate of sediment transport is expected (Fenn, 1989;

Syvitski et al., 2000). The reported SPM fluxes will hence be dependent on the period of observation. It is also important to note that most of the previous flux estimates were made using pre-1970 river discharge estimates, which were higher than more recent values. The suspended sediment concentrations measured in the Tuy River during March 2009 were within the range of the concentrations measured by Ramirez and Andare (1993; 56-165 mg l -1 compared to 97 ± 1.15 mg l -1 measured in 2009). This suggests that at least part of the difference between our flux estimates and historical values could be attributed to the magnitude of river discharge. In the last

30-40 years the number of dams in the small rivers draining into the basin increased, as well as agriculture and other water-trapping activities within the river’s basins (Rodríguez and Gonzalez,

2001). Damming in particular affects the SPM load of the river by trapping sediment. For

example, INIA-MARN (2003) point out that currently > 41% of the Unare’s drainage basin is regulated.

In general, POC concentrations and percentages were comparable to observations made in similar small river systems (e.g. Masiello and Druffel, 2001; Carey et al., 2005; Goñi et al.,

2006; Hilton et al., 2008, 2010). In the Neverí River in particular %POC was relatively high compared to the other systems; we speculate the higher %POC can be attributed to riverine vegetation and/or primary production. This is in part supported by the more enriched isotopic composition of POC in Neverí waters (~ -24 ‰). Suspended particles from surface waters as a whole were more enriched in OM than river bed sediments (Tables 1 and 2), which suggests diminished OM content in the latter. This is in agreement with observations made in other riverine systems (Goñi et al., 2006; Hilton et al., 2008, 2010). In the case of river bed sediments, all samples displayed similarly depleted signatures independent of location ( δ13 C ~-25- -27‰), which is consistent with a terrestrial source of organic carbon. The C/N ratio (> 8) is low for an exclusively continental plant source (usually in the range >20; Leithold and Blair, 2001).

However, river bed material can be composed of a mixture of sources, with a substantial contribution from fossil POC derived from the bedrock within the watershed (Blair et al., 2004;

Goñi et al., 2006; Hilton et al., 2008). Unfortunately, information on the isotopic composition and organic matter content of the various geological formations that these rivers drain is limited and we can only speculate at this point that the composition of POC in river bed sediments contains old OC most likely eroded from upland regions. The water-column POC also contained a terrigenous isotopic signal, though more enriched than river bed samples. The C/N ratio was also lower, suggesting a higher nitrogen content of POM. These variations could be attributed to the presence of riverine/estuarine phytoplankton, which typically have isotopic compositions between

-19‰ and -21‰ and C/N ratios of 5-7 (Mook and Tan, 1991; Paolini, 1995; refer also to Figure

1.8). The contribution of aged POM cannot be ignored (Goñi et al., 2006).

The differences measured in suspended δ13 C between rivers could have been caused by the intrinsic differences between catchments (vegetation type, as well as lithology). In this sense, the differences in POP and PIP percentages also reflect differences in the river’s drainage basins, more specifically with regards to land-use. For example, the Tuy and Neverí rivers had relatively low concentration and percentage content of POP but high concentration and percentage content of PIP. In river waters, common sources for PIP include fertilizers, wastewater treatment plants, and agricultural byproducts. Both the Tuy and the Neverí drain extensive agricultural lands, which can contribute PIP. Additionally, the Tuy drains heavily populated areas, including the capital city of Caracas, and the wastewaters it receives undergo only minor treatment (MARNR,

1983; Mogollon et al., 1987). %PIP in the Unare River was about half of that of the Tuy and

Neverí, but the Unare’s %POP was the highest amongst the four rivers. The Unare drains a vast area (22,371 Km 2), mainly of the Venezuelan plains, known as the llanos (Rodriguez and

Gonzales, 2001). Some of the Unare’s tributaries drain the Serrania del Interior mountain range.

The soil is of relatively low fertility and agriculture is not highly developed. Cattle, mining and oil exploitation are the dominant economic activities in this region (Rodriguez and Gonzales,

2001). Manure is a known source of POP. With regards to the Manzanares, %PIP and %POP were relatively close; the Manzanares crosses populated and industrial areas, as well as agricultural lands (Senior et al. 2003), which can contribute to the river’s loading of P to various degrees.

Most of the organic carbon in the four sampled rivers was dissolved (DOC). It generally constituted between 80-100% of the total riverine organic carbon. This is consistent with observations of DOC in other tropical and subtropical rivers (Itterkot and Laane, 1988; Richey et al., 1990; Pollard and Ducklow, 2011). Though the observations were fewer during the rainy season, the amount of particulate material appeared to be higher during this season, decreasing the overall percentage contribution of DOC (Appendix 2). Similar observations have been made in other tropical locations, where a higher load of POC is observed during periods of high

precipitation (Richey et al., 1980; Depetris and Paolini, 1990; Battin, 1998; Carey et al., 2005).

Concentrations of DOC were similar to those measured in other Venezuelan whitewater rivers

(Castillo et al., 2004). The geology of the landscape, as well as the soil type and vegetation cover, directly influence the characteristics, quality and quantity of DOC in river waters. Sources of

DOC to rivers include terrestrial plants (allochthonous source) and in situ production by phytoplankton (autochthonous source) (Spitzy and Leenheer, 1990). Rivers that drain soils rich in organic carbon typically have high concentrations of DOC (Benner et al., 2004; Hansell et al.,

2004). Rivers that are extensively dammed have reduced sediment loads and increased autochthonous DOC (Spitzy and Leenheer, 1990). Unfortunately, we don’t have isotopic measurements on the riverine DOC, and can only infer that the variations in DOC concentration between river basins are mostly attributed to the geology of their drainage basin. For instance, the

Unare drains sedimentary rocks and soils composed of alfisols and ultisols, which have a moderate concentration of organic matter (Rivero et al., 1998; Rodriguez and Gonzalez, 2001), and therefore would reflect a high concentration of DOC.

Many rivers show a connection between discharge and DOC (Newbold et al., 1995;

Carey et al., 2005; Spencer et al., 2010). In our area, the lack of correlation may be due to water regulation within the river basins. Unfortunately we don’t have river discharge data for the period of sampling and can only speculate on the matter. Also, rainfall patterns and soil type can affect the amount of carbon mobilized (Martinez-Mena et al., 2011). At this point we are uncertain of what regulates DOC transport in the small rivers examined. It is also unclear whether the variations in DOC amongst rivers reflect landuse or soil types.

Due to its magnitude, the Tuy River had by far the largest POC and DOC fluxes into the basin, followed by the Unare River. Though DOC fluxes were similar to those reported in other analogous watersheds (McDowell and Asbury, 1994; Newbold et al., 1995; Carey et al., 2005;

Alkhatib et al, 2007; Lyons et al., 2008), POC fluxes were small compared to OC fluxes in other comparable tropical river systems (Ludwig et al., 1996; Giresse and Maley, 1999; Lyons et al.,

2002). This suggests that the input of organic matter to the Cariaco Basin by the local rivers is limited, and on a regular basis most likely affects only the littoral zone. Indeed, from the SST,

SSS and DOC distribution around the basin it is apparent that fluvial impact is restricted to an area of within ~20 Km from the point of discharge (see also discussion below).

Considering the relative narrow width of the Unare Platform (between ~8-40 Km), fluvial

SPM can be transported across the shelf directly to the deeper portions of the Basin via subsurface nepheloid layers (Section 5.2), thus reducing the exposure of the sediment to oxygenated waters. In order to further separate and identify the specific contribution of each river more refined studies would be required (e.g. trace metal analysis, terrestrial biomarkers, and time series of sediment trapping across the shelf).

Importance and distribution of nepheloid layers

Bottom nepheloid layers (BNL), particle-rich layers that typically occur near the ocean floor (Agrawal, 2004), are a ubiquitous feature of the Unare Platform in the southern margin of the Cariaco basin. The permanent presence of BNL suggests that they constitute a major cross- shelf transport mechanism of particles from the coast to the deep Cariaco Basin. Evidence for

BNL and INL as particle transport mechanisms has been documented elsewhere, including in the

East Indies (Milliman et al., 1999; Kineke et al., 2000), the Benguela upwelling system (Inthorn et al., 2006), off England (Dickson and McCave, 1986), the East China Sea (Hung et al., 2007), the Mediterranean and Iberian shelf (Puig and Palanques, 1998; Oliveira et al., 2002), the Baltic

Sea (Yurkovskis, 2005), and the western coast of the United States (Pak et al., 1980; Curran et al.,

2002; Puig et al., 2003; McPhee-Shaw et al., 2004).

Surface nepheloid layers (SNL) were also observed near the mouths of the main rivers draining into the basin. This three-layered distribution of particles in the water column (i.e., a layer of low particle concentration ‘sandwiched’ between two layers of high concentration in the surface and near the bottom) is often observed on continental shelves influenced by riverine

discharge and/or upwelling (Pak and Zaneveld, 1977; Gardner et al., 2001; Karp-Boss et al.,

2004; Inthorn et al., 2006). The intermittence in SNL presence near the Manzanares River was attributed to the dynamics of the river plume, which generally moves southwestward and can stay very close to the coast (Martínez et al., 2001).

Nepheloid layer composition

Changes in the carbon isotopic composition of POC reflect the source of the material.

Marine phytoplankton are enriched in δ13 C, with values reported between -18 to -22 ‰, while terrestrially-derived organic carbon is more depleted (-25 to -38 ‰, depending on the compound;

Eglinton and Eglinton, 2008). OC in the Cariaco Basin principally come from two different sources: rivers and in situ production. In situ production is most significant during the upwelling season. Unfortunately, there is limited information about the spatial distribution of POC in the basin, which can be variable in space and time (Gardner et al., 2001; Hales et al., 2006). During the rainy season, the overall lower carbon isotopic signature suggests that particles were continentally derived; this was particularly evident in 2008, where the more depleted δ13 C values were consistent with the scenario of a dominant terrestrial source of organic carbon throughout the coast. The predominance of lithogenic material in the Cariaco Basin during the rainy season has been confirmed by a number of other indirect studies. For example, Martinez et al. (2007) observed increases in the elemental ratios (Ti/Al, Fe/Al) of the sediment traps in the Cariaco

Basin during the rainy season, suggesting a shift towards more lithogenic material. This is consistent with the 50% increase in PIP observed during this period (Benitez-Nelson et al. 2007).

Elmore et al. (2008), studying the clay mineralogy of sediment samples collected in the basin, also concluded that high precipitation yielded more riverine derived sediment in the nearshore, with the Unare River being the main source of clay-sized lithogenic particles to the eastern basin.

Authochtonous POC production increased during the upwelling season. However, during

March 2009 POC concentrations were not much different from September 2008 because the upwelling of 2009 was weak compared to 16 years of data from the CARIACO Ocean Time-

Series. Near-surface (0-15 m) POC concentrations were nearly half of their typical values during this season. The small drop in BNL POC content observed during March 2009 could be attributed in part to rapid remineralization of the fresh POC on the shelf (De La Rocha and Passow, 2007).

The increase in marine POC production during upwelling was reflected in the shift of

δ13 C of POC in surface waters. POC was enriched by 3-5 ‰, especially in the southeastern part of the basin where the upwelling was most intense. The carbon isotopic value of BNL also responded to the seasonal shift in particle production, suggesting that the composition of BNL reflects particle source. The increase of δ13 C in BNL during the upwelling also shows dilution of terrestrial POC with freshly produced, isotopically-enriched marine POC. Freshly produced POC with high isotopic ratios can be transported into the BNL by sinking in the form of aggregates, fecal pellets or associated with minerals (Armstrong et al., 2009; Burd and Jackson, 2009; De La

Rocha and Passow, 2007). Similar variations in surface and BNL isotopic composition in response to regime changes have been observed in other river-dominated systems (e.g. Goñi et al., 2006). The low isotopic composition in the BNL of the Cariaco Basin during the upwelling season suggests a supply of terrigenous POC and/or slower degradation/transport of terrestrial

OM. Terrestrial organic matter is more resistant to mineralization than recently produced marine

POC and coastal sediments generally contain refractory land-derived organic matter (Hedges et al., 1994; Hedges and Keil, 1995)

Changes from a river-dominated to an upwelling-dominated shelf were also visible in the

C/N ratios. C/N ratios are widely used to discriminate between marine and terrestrial sources of organic matter; marine organic matter typically has low (4-7) C/N atomic ratios, while terrestrially-derived organic matter have higher ratios (Hedges et al., 1986). The decrease in C/N

ratios observed during the upwelling, as compared to the rainy season, was caused by the increase in particulate nitrogen (from ~0.006- 0.012 during the rainy season to 0.02 to 0.12 during upwelling) in response to the higher concentration of nutrients upwelled near the coast. This decrease in the C/N ratio occurred both near the surface and in the BNL, supporting the idea of a direct contribution of freshly produced POM to the BNL. The change in C/N was less apparent in the western basin, which is not as impacted by the upwelling as the eastern basin. C/N ratios measured during the upwelling were similar to ratios observed in other upwelling areas (e.g.

Karp-Boss et al., 2004; Jennerjahn et al., 2010).

Changes in δ15 N of PN can be used to track nutrient utilization in the water (Altabet and

Francois, 1994). δ15 N from continental sources is generally higher than marine δ15 N though it can be highly variable, since it reflects soil utilization (Peters et al., 1978). Highest δ15 N were consistently measured near the mouths of the Unare and Tuy rivers, likely reflecting the terrestrial source of nitrogen. δ15 N in coastal surface waters during March 2009 was about twice as high as the isotopic composition of sinking PN measured at the CARIACO Ocean Time-Series site ( δ15 N

≈ 3.5-4.0‰, Montes et al., 2012), probably reflecting the continental contribution of N to the PN pool.

The dynamics of the organic matter associated with nepheloid layers as it moved into deep water was less clear. Nepheloid layer POM concentrations were similar to or lower than that of the overlying water column and the isotopic ratios changed from a terrestrial to marine signature with increasing distance from the coast. This supports the suggestion that local rivers supply only limited amounts of terrestrially derived POC, PN and POP to the coastal environment and that their impact is restricted to the coastal area; most particles settled out of the water column soon after entering the ocean. Similar observations have been reported in the northwest

Mediterranean (Puig and Palanques, 1998) and the East China Sea (Hung et al., 2007). This supports the findings of Goñi et al. (1997), Thunell et al. (2000) and Woodworth et al. (2004),

who reported no significant contribution of terrestrial organic carbon in the CARIACO sediment traps.

Physical dynamics of nepheloid layers

The transport of the material from the near shore to deep waters may be related to the physical dynamics that affect the residence times of particles within the nepheloid layers. In the

Cariaco Basin, we found that the distribution of the nepheloid layers depended both on the hydrodynamics of the area, as well as the morphology. For better reference, we divided the Unare platform in two regions: A and B (Figure 1.2a). These regions correspond to two areas of the platform that have very different bathymetry and sediment distribution patterns. Region A comprises the Manzanares Submarine Canyon and the area southwest of the city of Cumaná. The platform in this part of the basin is narrow (on the order of 10 Km or less) and has a steep topography (~8%). This region is also characterized by stronger currents (Alvera-Azcárate et al.,

2009). Region B includes the rest of the platform, from near the city of Barcelona to Cape Codera in the western basin. In this area, the platform is relatively wide (>20 Km) and the slope is mild

(~0.2-0.4%). Currents are weaker over the platform (Alvera-Azcárate et al., 2009).

During September 2003 and 2006, detached BNLs dominated the narrow shelf in region

A. During September 2008, fully developed BNL were observed in this same area. These contrasting observations are likely attributed to changes in the current regime, with currents more favorable to the formation and maintenance of BNL over this area during 2008. Presumably, the

INLs measured offshore of region A were related to the advection of the detached BNLs and spread along constant density surfaces away from the coast. INLs develop most commonly over continental slopes and are associated with isopycnals and internal tides, with some sediments moving along-isopycnals after detaching from the shelf break (Pak et al., 1980; Azetsu-Scott et al., 1995; Oliveira et al., 2002; McPhee-Shaw et al., 2004; McPhee-Shaw, 2006). They are also found in and around submarine canyons. Based on our limited sampling, INLs in this area seemed

to dissipate within 30 km from their site of origin. Their dispersal could potentially be controlled by local currents, which advect the INL away from the shelf (Alvera-Azcárate et al., 2009), and/or by particle settling. INLs inside the Manzanares submarine Canyon were observed throughout the entire study period, transporting shelf material (both resuspended and fresh) into the canyon head. Hickey et al. (1986) determined that the dominant mode of sediment transport down Quinault Canyon (Washington coast) was by the episodic formation at intermediate depths of turbidity layers. Puig et al. (2003) also observed a persistent particle layer that contributed to off-shelf sediment transport in Eel Canyon (northern California). Puig and Palanques (1998) suggested that in continental margin canyons, such as the Foix Canyon (northwest Mediterranean

Sea), sediment transport is dominated by INL detachments and internal waves. Near the Sepik

River (Papua New Guinnea) down-canyon transport has also been observed, which disperses the sediment to more distal regions than would be possible by a simple surface plume (Kineke et al.,

2000). Similarly, the Manzanares submarine canyon directly funnels sediment discharged by the

Manzanares River to the deep basin, particularly during episodic storm or geologic events ( See section below ).

In Region B BNLs are more well-developed, similar to what happens along the Texas shelf (Sahl et al., 1987). The BNL measured in this area displayed a decrease in particle concentration and increase in thickness with increasing distance from the river mouths. Similar observations were made on the Barcelona continental margin off Spain (Puig and Palanques,

1998) and in the Celtic Sea (McCave et al., 2001). Two processes appear to maintain the nepheloid layers we observed in Region B: local river input and high energy coastal processes.

The maximum concentration of particles, recorded near river mouths (~2-7 mg L -1, Tables 3-5) was due to the contribution of material by the rivers. With increasing distance from the coast, resuspension due to bottom currents, tides, and near-inertial waves, probably plays an important role in the maintenance of the BNL. McCave et al. (2001) observed an increase in BNL thickness with depth over the Goban Spur area, consistent with increased current velocities. Lentz and

Trowbridge (1991) also found bottom mixed layer heights to be dependent on current velocity and direction, increasing with increasing currents. As the BNL reach the edge of the Unare

Platform, they are subject to increase in current velocities. Though highly variable, the Basin has a mean anticyclonic circulation at ~150 m depth with a peak subsurface current centered around

120m; this is believed to be part of a basin-wide gyre (Alvera-Azcárate et al., 2009; Virmani and

Weisberg, 2009). During September 2006 and 2008, and during March 2009 strong currents (>10 cm s -1) were recorded using a lowered acoustic Doppler current profiler (LADCP) at the edge of the Unare Platform which suggests a two-fold velocity increase from the coast to the platform edge. The INL’s observed in Region B were classified as ‘shelf-break INL’ (Puig and Palanques,

1998). These permanent INL’s extended almost twice as far as those INLs measured in Region A.

We currently don’t have an explanation for the formation of the deep INL (>150m) observed; they may be derived from intermittent erosion processes of the continental slope or resuspension by internal waves (Dickson and McCave, 1986; Oliveira et al., 2002; McPhee-Shaw et al., 2004).

Temporal variation and fate of horizontally transported particles

In order to assess temporal variations in particle transport and to understand the ultimate fate of particles originating on the continental shelf, we examined sediment trap particle flux data collected from the CARIACO Ocean Time Series program (Thunell et al. 2000, 2007. http://www.imars.marine.usf.edu/CAR/ ). The material captured by the sediment traps positioned at different depths in the center of the eastern Cariaco Basin provides a time-series of both vertical and lateral transport of sediments off the shelf (atmospheric sources of this material are negligible; Martinez et al., 2007). The mooring is equipped with five sediment traps (Z, A-D).

Traps A-D have been operational since November 1995 and are located at depths of 225, 410,

810 and 1200m, respectively. (Thunell et al., 2000). The fifth trap, Z, is located at 150 m, and was added in November 2003. Details regarding trap operation are found in Benitez-Nelson et al.

(2007) and Thunell et al. (2007). Often, the shallowest sediment trap (trap Z) collects less

lithogenic material than trap A. Though there are known issues with shallow traps (e.g. Gardner and Richardson, 1992; Gardner, 2000), we believe this supports the idea that most terrigenous material enters the Basin at mid-depth and is laterally supplied from shelf-break INLs, at depths in excess of 150m.

Sediment traps capture seasonal variations in terrigenous input in the Cariaco Basin

(Martinez et al., 2007). During the rainy season, terrigenous fluxes increased, especially in Trap

A, suggesting that this trap best reflects changes in the upper water column. Benitez-Nelson et al.

(2007) observed similar seasonal increases in PIP, and linked high PIP sediment trap fluxes to episodic riverine inputs; we did not observe higher PIP concentrations within nepheloid layers once they moved offshore, yet their particulate P concentration remained higher than that of surface waters. Sediment trap POC, PN and POP fluxes remain relatively low during the rainy season and only increase slightly with the onset of the upwelling season at the beginning of the year. This suggests that the terrestrial material that reaches the traps during the rainy season is not a significant source of organic matter (Woodworth et al., 2004; Thunell et al., 2007; Goñi et al., 2009). This agrees with the BNL POM data obtained in this study.

Though Trap A (~225 m) receives most of the lithogenic material, it is closely followed in certain instances by Trap B (~410 m) and Z (~150m). Trap D (~1200 m) usually records the lowest lithogenic flux (Figure 1.12), with the exceptions of July 1997, November 1999 and May

2004 where episodic events delivered exceptionally large concentrations of sediment to Trap D

(Section 5.4). Some of the highest average terrigenous and POC fluxes were consistently recorded in May each year (Figure 12). Spikes in PIP fluxes have also been observed repeatedly during

May (Benitez-Nelson et al. 2007). The synchronous increase in POC, PIP, and terrigenous material fluxes implies that some of the same processes may be governing the delivery of the material to the traps. May is a transition month, when the Trade Winds weaken and rainfall is beginning (Figure 1.12).

During winter and spring, favorable trade winds promote upwelling and productivity in the Cariaco Basin (Muller-Karger et al., 2001; 2004). The shoreward Ekman transport of dense subtropical underwater (SUW) along the bottom over the shelf would restrict the offshore extension of any bottom nepheloid layers. Thus, terrigenous material, including PIP, would effectively accumulate on the inner shelf. POC produced over the area is in part exported out to the open basin, but a portion of it settles on the shelf, as evidenced by the changes in isotopic composition of the BNL during March 2009. Indeed, Morales and Ottman (1961) found that the shelf sediments of the Cariaco Basin were rich in organic matter as a result of the primary production induced by upwelling.

We hypothesize that as the Trade Winds weaken, the dense upwelled water retreats and the sediments stored on the shelf, as well as the freshly-deposited autochtonous material, slump offshore together with the BNLs, generating a pulse of POC, PIP and other terrigenous material consistently observed in May. The highest precipitation rate is also observed in May, likely contributing to the mobilization of larger loads of sediment from the river catchments into the basin (Appendix 1, supplementary figure 1.2). Martinez et al. (2007) observed a spike in the chemical composition (Ti/Al, Fe/Al) of their May trap data, suggesting accumulation of both terrestrially derived material along with biogenic particles derived from upwelling-induced primary production. Similar mobilizations of BNLs have been identified along the Oregon coast

(Hales et al., 2006, Perlin et al., 2005), the Portuguese shelf (Oliveira et al., 2002), the Nabimian upwelling system (Inthorn et al., 2006) and the Cretan Sea (Chronis et al., 2000).

Isotopic data indicates that the pulse in POC export observed in May in all four traps is of marine origin, yet PIP, trace metal, and lithogenic fluxes clearly suggest that a significant component of the particles are terrestrially derived. This is consistent with our observations of

BNL compositional changes as they move offshore. We therefore suggest that nepheloid layers, which are enriched in fine-grained sediments, are acting as ballast for the effective transport of autochtonous POC to the deep basin. In essence, the “ballast hypothesis” suggests that mineral

ballast (mainly carbonate, opal and lithogenic material) enhances the transport of POC to depth, by increasing POC sinking rates (and hence reducing POC remineralization time), and by providing physical protection from degradation through the interaction between the organic matter and the mineral fraction (Ittekot, 1993; Armstrong et al., 2002; Francois et al., 2002; Klaas and Archer, 2002). In the open ocean, lithogenic material is low and ballast minerals are dominated by calcium carbonate (Francois et al., 2002; Klaas and Archer, 2002). However in coastal areas, the lithogenic fraction increases significantly and can constitute an important component of the mineral ballast (Ittekkot, 1993). Within the BNL, composed mostly of fine particles such as silts and clays, ballasting of marine-derived POC likely occurs as the sediment is retained on the shelf. Thunell et al. (2007) determined that mineral ballast is the single most important factor controlling POC fluxes in the Cariaco Basin. They found a uniform F OC /F M ratio, suggesting that most POC, including that observed in the shallowest sediment trap (225m) is associated with ballast material.

Consistent with the low upwelling intensity of 2009, POC fluxes into Trap Z (150 m) during the upwelling season of 2009 were below the 15-year average of the time-series (1995-

2010; there were no data available for Trap A. Figure 1.12). This supports in part the above hypothesis: the POC accumulated within the trap reflected the degree of POC enrichment of the

BNL.

Combined, these results underscore the importance of nepheloid layers as a source of terrestrially derived mineral ballast material in the Cariaco Basin. An analogous nepheloid layer/ballast mechanism for NW Africa was suggested by Fischer et al. (2007). Similar to the

Cariaco Basin (Thunell et al., 2007), both lithogenic and carbonate components were closely related to POC in NW Africa. Fischer et al. (2007) argued that particles transported offshore through subsurface nepheloid layers provided the necessary ballasting mineral for enhanced POC fluxes, highlighting the significant distances laterally transported particles can travel and the

Trap A (225 m) Trap B (410 m) Trap C (810 m) Trap D (150 m) 30 100 6.5 Trap Z (1200 m) Trap Z 2009 Precipitation rate 80 25 Wind 6.0 60

20 40 /month) 2 5.5 20 15 0 5.0 10 -20 Wind Speed (m/s)

-40 Lithogenic Flux (g/m

Precipitation rate (mm/month) 4.5 5 -60

0 -80 4.0 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Month

Trap A Trap B Trap C Trap D 4 100 6.5 Trap Z Trap Z 2009 Precipitation rate 80 Wind 6.0 60 3

/month) 5.5 2 20 2 0 5.0 -20 Wind Speed (m/s)

POC Flux (g/m 1 -40

Precipitation rate (mm/month) 4.5

-60

0 -80 4.0 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Month

Figure 1. 12 : Monthly average of lit hogenic and POC fluxes between 1995 and 2006. Mean wind speeds from Punta de Piedras and average precipitation from Corcovada are overlaid. Lithogenic and POC fluxes for Trap Z for 2009 (all data available) are also shown. Trap depths are indicated in the upper legend.

disconnect that may exist between sediment proxies and the overlying water column in certain ocean regions.

Role of episodic events in the sequestration of continentally-derived POC

Small rivers can have high sediment loads (Milliman et al., 1999), especially during episodic events such as floods and landslides. When small rivers respond to high rainfall and flooding, high quantities of sediment are introduced into the coastal ocean through hyperpycnal flows. Hyperpycnal flows, negatively buoyant subsurface freshwater plumes, contain high suspended sediment loads (usually in the order of tens of grams per L) that can often bypass the continental shelf and transport sediment directly to the deep ocean, if the density difference and velocity are sufficient (Mulder and Syvitski, 1995; Mulder et al., 2003). For example, Milliman and Kao (2005) and Goldsmith et al. (2008) observed high sediment delivery by Taiwanese rivers through hyperpycnal flows as a result of typhoons. Mulder et al. (1998) documented hyperpycnal flows as a result of severe storms in the Var River (France); similar storm-induced hyperpycnal flows were also observed in Californian rivers (USA; Ogston and Sternberg, 1999; Mullenbach and Nittrouer, 2000; Warrick and Milliman, 2003). Hyperpycnal flows have never been directly observed in the Cariaco Basin, largely because these events are generally short-lived and there is a lack of monitoring along the small rivers that surround the basin. Nonetheless, it is likely that such hyperpycnal flows have occurred, linked to anomalous precipitation events that have induced massive river flooding, such as in November-December, 1999. In this case, the mixture of “Nortes” (Lyon, 2003) and La Niña conditions in the Equatorial Pacific facilitated the setting for sustained, torrential rains along Cordillera de la Costa. The effects were most pronounced in the central part of Venezuela, where mudfloods and landslides claimed over 15,000 lives and over

US$1.8 billion in damage (Andressen and Pulwarty, 2001). In the Cariaco Basin, at the location of the CARIACO site, the delivery of sinking terrigenous flux increased four-fold during the

1999 flood, from an average for the month of November of 17.66 ± 17.02 g m -2 month -1 (1995-

2009; measured in the 225 m depth sediment trap) to 69.34 g m -2 month -1

(http://www.imars.marine.usf.edu/CAR/ ). Particulate organic carbon flux increased two-fold

(from the 14-year average of 1.95 ± 1.15 g m -2 month -1 measured in the 225 m trap to 3.54 g m -2 month -1). The same magnitude of sediment and organic carbon increase generated by the hyperpycnal flow of 1999 was observed in all traps. Thus, this single episodic event delivered to the deep basin more than 30% of the total average annual (1999) vertical terrigenous flux measured at 1200 m at the CARIACO site, and more than 20% of the annual POC flux for that same year within a time frame of two weeks (the time it takes for the cups in the traps to rotate position). A second flood-induced sediment flow was measured during May 2004; again, the event transported to the deep basin the equivalent of > 20% of the annual (2004) POC flux and >

35% of the total average annual vertical sinking flux measured at 1200 m at the CARIACO site for the same year. During November-December 2010, a similar event was observed, where precipitation along the Venezuelan coast increased threefold. Unfortunately, there is no corresponding measure of beam attenuation or sediment trap fluxes for that period. The fact that episodic floods can deliver a large amount of lithogenic material to the deep basin has important implications for the rapid transport and burial of sediments, including terrestrially-derived organic carbon (Goldsmith et al., 2008)

Aside from flood-induced turbidity flows, earthquakes can also trigger sediment displacement, particularly along active margins. In July 1997 a 400 m thick turbidity layer located immediately above the bottom at the CARIACO site was observed shortly after a M6.8 earthquake struck northeastern Venezuela (Thunell et al., 1999; Audemard et al., 2006). High lithogenic and POC fluxes were recorded in Trap D as a result of this event and high suspended particle loads of more than 1.0 mg L -1 persisted at the bottom of the CARIACO site for more than four months. This large increase in terrigenous material observed in 1997 was attributed to an earthquake-induced turbidity flow. The suspended sediment layers observed during September

2008 at the CARIACO site and at the mouth of the Manzanares Submarine Canyon bears a

similarity with the 1997 event (Thunell et al., 1999); when episodic sediment displacement occurs at the head of a submarine canyon, it often leads to high-energy sediment gravity flows or turbidity currents down the canyon (Heezen and Ewing, 1952; Arzola et al., 2008).

Submarine canyons are widely recognized as important conduits for the transport of terrestrially-derived material from continental shelves to the deep ocean. (Mullenbach and

Nittrouer, 2000; Johnson et al., 2001; Paull et al., 2003; Liu and Lin, 2004; Xu et al., 2010).

Events that enhance continentally-derived organic matter and sediment transport, such as storms

(Dadson et al., 2003; Palanques et al., 2008), dense shelf water cascading (Canals et al., 2006), or turbidity flows to the deep ocean are critical, since the organic matter injected into the deep sea is not remineralized but buried. Thus, this organic material ceases to be part of the present day global carbon cycle. Within submarine canyons, turbidity flows can be gravity-driven, resulting from energetic events such as earthquakes (Hilton et al., 2008), or flow-driven, induced by storms and floods, among other mechanisms (Canals et al., 2006; Palanques et al., 2008). The latter mechanism is particularly important if the river mouth is located near the canyon head, as the river plume can be advected directly into the canyon in the form of a hyperpycnal plume (Mulder and Syvitski, 1995; Johnson et al, 2001; Liu et al., 2008). Hyperpycnal flows can be deposited inside the canyon and later remobilized (e.g., Kineke et al., 2000; Mullenbach and Nittrouer,

2000) or can be funneled directly to the canyon mouth, if the density difference and velocity are sufficient (e.g., Johnson et al., 2001; Paull et al., 2003).

There are no significant currents in the deep portions of the Cariaco Basin that resuspend sediments (Alvera-Azcárate et al., 2009). Monthly transmissometer profiles collected as part of the CARIACO time series indicate that normally there are no nepheloid layers immediately above the sea-floor ( http://www.imars.marine.usf.edu/CAR/ ). As a result, the water below 400 m is typically very clear and homogenous (Virmani and Weisberg, 2009). Therefore, we suggest that the deep suspended sediment layers measured during this study were the result of an event-driven sediment density flow. In order to determine whether the sediment plume observed in September

2008 was caused by a hyperpycnal flow induced by anomalously large river discharge, the precipitation record measured at Cumaná for the month of August for the period 1967-1992 and

1998-2010 was analyzed (all available data, NCDC; MINAMB). The average August precipitation for this period was 88 ± 60 mm. During August 2008 precipitation recorded at

Cumaná was 147 mm (NCDC), within the standard deviation of the precipitation record. In

September 2008 there was no visible evidence of a hyperpycnal layer near the mouth of the

Manzanares River, which is not surprising, considering that hyperpycnal flows tend to be short- lived events (Milliman and Kao, 2005).

An alternative explanation for the observed suspended sediment event is that it was seismically triggered, either by the M5.2 earthquake that took place on August 11, 2008, at 10°

30.60’ N and 64° 10.20’ W (FUNVISIS, 2008) and/or by the aftershock of M3.0 that occurred in roughly the same location half an hour later. It is possible that post-seismic erosion rates near the

Gulf of Cariaco and Cumaná increased after the earthquake, due to seismically-induced landslides, but it is unlikely that this material contributed to the sediment plume observed near the canyon mouth. Sediment that is seismically weakened is generally flushed to the rivers and ultimately to the ocean by storm runoff (Dadson et al., 2003, 2004)., but as mentioned earlier, precipitation in Cumaná during the month of August was within historical values.

During July 1997, the turbidity flow was observed by Thunell et al. (1999) one week after the M6.8 earthquake. Data from the day before the earthquake (July 8 th ) showed no sediment near the sea-floor of the Cariaco Basin. This suggests that sediment remobilization occurred shortly after the earthquake. Whether part of the sediment in the turbidity flow observed in 1997 originated from co-seismic landslides is not known, but if this was the case, it is likely that it was mobilized by hyperpycnal plumes. Average precipitation for the entire month of July was 121 mm, above the historical (1967-1992; 1998-2010) average of 64 ± 45. During the July 16 sampling at the CARIACO site there was no indication of a hyperpycnal layer. The suspended sediment layer near the sea-floor was still visible in November 1997

(http://www.imars.marine.usf.edu/CAR/ ). Similar to 1997, the suspended sediment layer after the

2008 earthquake persisted through December 2008. ). Considering the observations of Thunell et al. (1999), this is the second time since the beginning of the CARIACO Ocean Time-Series

Program in November 1995 that turbidity layers have been observed near the bottom of the basin.

SPM concentrations estimated near the bottom at the canyon mouth (1.0 g m -3, Table 1) were similar to SPM measurements observed in the high turbidity layer after the 1997 earthquake at the CARIACO site (Thunell et al.; 1999). Unfortunately, for September 2008, we only have the observations at the canyon mouth and at the CARIACO site. We used these observations along with the beam attenuation data to calculate the amount of sediment within the turbid layer. At the canyon mouth, ~ 90 g m -2 was estimated to be within the sediment plume, while at the CARIACO site this decreased to ~11 g m -2. This latter estimate represents ~10% of the total average annual vertical sinking flux measured at 1200 m at CARIACO. Since our observations were made several weeks after the earthquake, these earthquake-related suspended sediment concentrations should be regarded as minimum estimates.

It is difficult to calculate the total amount of sediment delivered to the deep Cariaco

Basin by the August 2008 earthquake. However, if we use these observations and assume a linear decrease in concentration and sediment plume thickness, and integrate the SPM over the entire area of the eastern sub-basin below 1000 m (approximately 1200 Km 2), we can loosely estimate that ~ 50,000 metric tons of sediment and ~ 6,600 metric tons of POC delivered to the deep portion of the basin is a result of the sediment density flow. Sedimentation rates in the eastern

Cariaco Basin, estimated using sediment traps (Thunell et al., 2000), are on the order of 180,000 metric tons of sediment per year. Thus, approximately a third of the average vertical sinking flux of sediment and POC that normally reaches the Cariaco Basin seafloor annually was delivered during the 2008 turbidity flow. Thunell et al. (1999) found that approximately 145,000 tons of sediment were transported into the basin after the large (M6.8) earthquake of July 9, 1997; this is

80% of the typical annual vertical sinking flux measured at 1200 m. However, they assumed

sediment loads to be relatively low and uniformly distributed below the 1,100 m isobath. Our

2008 observations showed significantly higher sediment concentrations near the canyon mouth. If we assume that the 1997 event had a similar spatial distribution as that of 2008, then the amount of material delivered during the 1997 event may have been twice as large as that estimated previously.

Average POC concentrations within the suspended sediment layer at the canyon mouth were almost three times higher than the average (1995-2009) monthly suspended POC concentrations measured at 1310 m at the CARIACO site. Moreover, the POC measured at the canyon mouth was about 10% of the SPM within the turbidity plume, an order of magnitude higher that the POC estimated to be transported by regional rivers to the ocean (Ludwig et al.,

1996). PN concentrations within this sediment layer were similar to average PN values typically measured prior to the turbidity event. Therefore, the C/N ratios in the sediment plume at the canyon mouth were 16.4 ± 2.2, or about twice the average C/N value for sinking particles at 1200 m at the CARIACO site. This is significantly higher than the predicted Redfield C/N ratio for marine organic matter (around 6-7, Hedges et al., 2002), which suggests this material was of continental origin.

The carbon and nitrogen isotopic composition of particulate material within the suspended sediment layer at the canyon mouth is also indicative that the POC transported into the

15 o deep basin was primarily land derived. The δ N at the canyon (average of ~6.83 /oo ) was higher

o than that normally seen at similar depths at the CARIACO station (~3.50 /oo ; Thunell et al.,

15 o o 2004). A similar increase in δ N, from an average of 3.50 /oo to ~5.70 /oo , in the deepest

CARIACO sediment trap (1210 m) was also observed by Thunell et al. (2004) after the strong

13 o 1997 earthquake. The δ C (average of -27.04 /oo ) was depleted relative to values observed

o normally at the CARIACO site (-20.7 /oo ; Woodworth et al., 2004), with the latter being typical of marine organic carbon. Recent studies by Hilton et al. (2010, 2011) suggest that a significant

portion of terrestrial POC transported to the ocean by SMRs is fossil POC from exposed bedrock, and that this fraction has a δ13 C range that overlaps that of modern POC. Hilton et al. (2011) further hypothesized that the high erosion rates of coastal mountain ranges result in efficient transport of this fossil OC into marine sediments with minimal oxidation. The direct funneling of continental POC by submarine canyons can further enhance this transport. Though the carbon content of the Serranía del Interior is relatively high (1-6%; Alberdi and LaFargue, 1993; Tocco et al., 1994), there is no data available on the isotopic composition of this geologic formation or the relative fraction of modern versus fossil OC contained in the sediment flow. Thus Hilton’s hypotheses cannot be confirmed or ruled out in this region.

Over 60 seismic events of M4-M5 have been recorded in northeastern Venezuela since

1996 in the area of Cumaná and the Cariaco Basin. Such events may provide the necessary weakening of substrate material and the trigger for the rapid mobilization of continentally-derived materials temporarily deposited at the head of the Manzanares Canyon. Thus, the Manzanares

Canyon is likely to be an important source of sediments to the eastern Cariaco Basin and has the potential of funneling large quantities of terrestrially-derived organic matter down-canyon and effectively sequestering carbon on millennial time scales.

Implication of episodic events on the sedimentary record of Cariaco

Episodic events can deliver large amounts of lithogenic material, including organic carbon, to the deep ocean fast and efficiently; this not only has important implications for the rapid sequestration of continentally-derived organic carbon, but can also have an impact on the sedimentary paleoclimatic record. Earthquake-induced turbidites are a common feature of sedimentary cores in active margins; however, they are not always exploited for the information they could provide, considering the difficulties associated with the interpretation (Shiki, 1994;

Goldfinger, 2011). Yet turbidites can represent a valuable and complementary tool for the interpretation of past natural hazards such as floods and earthquakes (Inouchi et al., 1996;

Gorsline et al., 2000; Goldfinger et al., 2003; St-Onge et al., 2004; Goldfinger, 2009). There is significant evidence of turbidity flows over geologic time in the sediments of the Cariaco Basin.

Large turbidites, as well as microturbidites, have been identified in its sedimentary record and some linked to seismically-induced events (Thunell et al., 1999), with the largest turbidites corresponding to earthquakes in 1900 and 1929 (Hughen et al., 1996). This work provides additional constrains on the magnitude of the seismic event necessary to trigger a turbidity flow.

Additionally, the fact that episodic flooding can induce hyperpycnal turbidity currents has been highlighted, which can also lead to the deposition of microturbidites. Currently, there has been no clear identification of Cariaco microturbidites as deposits from hyperpycnal turbidity currents

(hyperpycnal turbidites), and though they can be difficult to recognize (Mulder et al., 2001) their frequency and magnitude could provide information on past continental climatic changes. Since turbidite deposition in the Cariaco Basin does not seem to erode the underlying sediment, they could serve as paleoseismic and paleoflood records for the region (Thunell et al., 1999; Carrillo et al., 2008; Goldfinger, 2011).

Conclusions

Nepheloid layers originating at the mouth of local rivers in the eastern Cariaco Basin are an important mechanism for delivery of terrigenous sediments to the deep basin year-round. This research also highlights the importance of small, local rivers in the Cariaco Basin as primary sources of terrestrial material. This is an example of the impact of small rivers on global continental margins. The small rivers examined here produced BNLs and INLs that transport material from the shelf into the deep basin. This flux explains the supply of terrigenous particles captured by the sediment trap array maintained as part of the CARIACO Ocean Time Series

Program. The lithogenic material transported by the BNLs and INLs during the rainy season is low in POM, agreeing well with published data. We suggest that the seasonal pulse of sediment to the interior of the Cariaco Basin observed each May is caused by the retention of nepheloid layers

on the inner shelf by onshore Ekman transport associated with upwelling. The nepheloid layers are later released as the upwelling subsides. The fine sediment of the nepheloid layers may further serve as mineral ballast, enhancing the sinking velocities of POC.

The SMRs draining into the Cariaco Basin have the capacity to deliver large amounts of sediment to the Cariaco Basin, as highlighted by measured episodic events. Event-driven downslope mobilization of sediment is an important means of continental OC sequestration and burial. Several episodic events have been indirectly observed in the basin in response to climatic

(i.e. floods) or tectonic events. Each of these events has transported to the deep basin >10% of the average annual sediment flux to the seafloor of the Cariaco Basin, making them an important local sedimentary sink. The rapid means that flood- or earthquake- triggered sediment flows reach the deeper portions of the basin (either via BNL/ hyperpycnal flows or by direct funneling to the deep via submarine canyon) has also important implications for the rapid transport and burial of sediments, including terrestrially-derived OC.

The sediment density flow that was observed within the Cariaco basin during September

2008 was the possible result of an earthquake that struck near the city of Cumaná, Venezuela, on

August 11 th , 2008. This single event transported an estimated 10% of the average annual sediment flux to the seafloor of the Cariaco Basin. Furthermore, the OC within the sediment plume appeared to be predominantly continentally-derived, reinforcing the hypothesis that turbidity flow events are significant sources of terrestrial carbon and sediment to the deep ocean. The

Manzanares River mouth is located at the head of the canyon, and likely supplies most of the fine grained sediments and fresh carbon that accumulate in the upper part of the canyon. This suggests that the canyon is an active depositional center, and its proximity to the Manzanares River and

Cariaco Basin is critical for sediment supply offshore.

The continental material estimated to have been delivered to the deep Cariaco Basin as a result of the sediment density flow is based only upon two measurements obtained almost a month after the seismic event. We can loosely estimate that approximately a third of the average

vertical sinking flux of sediment and POC that normally reaches the Cariaco Basin seafloor annually was delivered during this single event. However, it is very difficult to accurately assess the amount of sediment and carbon that reached the deep basin based solely on these observations. In order to correctly assess the transport of continentally derived material through the Manzanares Canyon, a more permanent observing system with simultaneous points of observation is required. This would enable episodic events to be captured when they occur and the ability to accurately measure the magnitude of material delivered to the deep basin. These observations emphasize the importance of submarine canyons as sediment conduits in our efforts to constrain off-shelf sediment and carbon. Earthquake- and flood- induced turbidites are uniquely preserved in the sediment record of the basin. Their study may provide insight into recurrence rates of episodic events in the Cariaco Basin, and help advance our understanding of carbon sequestration dynamics near margins that are affected by such events.

There is still much to be understood regarding subsurface nepheloid layers in the Cariaco

Basin, such as their role and interaction with the Manzanares Submarine Canyon with regards to sediment transport and deposition. More in-depth observations on the contribution and export of freshly produced marine organic matter within the BNL during the upwelling season are needed.

Nonetheless, these initial observations provide a preliminary understanding of the alternating influence of coastal upwelling and riverine inputs to particles settling at the bottom of the basin and highlight the importance of subsurface nepheloid layers in lateral particle transport and deposition.

Human alterations to river catchments can dramatically affect suspended sediment and

POC loads transported into the ocean. During the last 30 years, anthropogenic influences on the small rivers around the Basin have significantly altered the drainage and sediment load, yet reliable data to quantify the level of influence and change over time are not available.

Quantification of the sediment and terrestrially-produced organic carbon from rivers, especially small tropical watersheds, is important for a correct assessment of the global carbon cycle. We

need a better understanding of the natural variability of these fluvial systems, trends and impact of episodic events, to better predict future changes in the region. In a global context, a more recent re-assessment of historical fluxes is warranted to better estimate fluxes that have been estimated more than 20 years ago, in particular in tropical regions where population growth and anthropogenic alterations of watersheds are most dramatic.

CHAPTER 2. BIOGEOCHEMISTRY OF THE AMAZON CONTINENTAL SHELF

AND SEDIMENT TRANSPORT DURING FEBRUARY-MARCH, 2010

Introduction

River-influenced continental margins are dynamic regions that receive inputs of sediment and organic material derived from both terrestrial and marine sources (Bianchi et al., 2004;

Mckee et al., 2004). Most of the

sediments and terrestrially-derived

dissolved and particulate organic

matter that enters the ocean is

transported by wet tropical rivers,

such as the Amazon (Meybeck,

1993; Ludwig et al., 1996; Schlunz

and Schneider, 2000; Milliman and

Farnsworth, 2011). Oceanic

processes occurring on the shelves

adjacent to the river mouths control

the fate of the organic material, Figure 2. 1 Amazon Basin and river network. The southern basin comprises the region south of the Solimões-Amazon whether it is trapped and buried, mainstem, including the Madeira River. The northern basin comprises the region north of the mainstem (including the transformed or bypassed (Milliman Japurá, Branco, Negro and Trombetas rivers). See Tomasella et al., 201 0 for more information. The location of et al., 1975a; Nittrouer et al. 1995). the Obidos gaging station is indicated. Figure modified from HydroSTEMS/Lehner et al. 2008. For example, more than half of the

organic carbon transported by the Amazon is lost as it reaches the shelf by enhanced biological respiration and microbial decomposition (Berner, 1982; Aller et al., 1996; Aller and Blair, 2006).

However, the magnitude of some rivers is such that their influence can be traced several thousands kilometers from their mouths. The Amazon plume has been observed extending over

3500 km from its source, spreading over an area exceeding 500,000 km 2 (Muller ‐Karger et al.,

1988, 1995; Hellweger and Gordon, 2002; Hu et al., 2004; Del Vecchio and Subramaniam, 2004).

The Amazon basin (Figure 2.1) covers an area of 6.2x10 6 km 2 and is the source of approximately 20% of the world's riverine freshwater and roughly 6% of global riverine sediment discharge to the ocean (Meade et al., 1979; 1985). The river basin spans from about 7°N to 20°S

(Tomasella et al., 2010) and therefore collects rainwater year round. The Amazon flows roughly parallel to the equator, between ~ 5°S and the equator. As such, the temporal and spatial variability in Amazonian rainfall is high. Rainfall in the southern Amazon is higher during the austral summer (in the order of 8-10 mm day -1 between December-February; Marengo et al.,

1998; 2008; 2009; Marengo, 2006). The central basin, defined roughly by the river axis, experiences the highest precipitation approximately two months later. In northern Amazonia

(~2°N), rainfall varies with the position of the Intertropical Convergence Zone (ITCZ; Marengo et al., 2009), with peak precipitation approximately in June-August (Meade et al., 1991). The

Amazon’s discharge reaches a maximum between May and June and a minimum in October-

November (Nittrouer et al., 1991).

Modern sediment load in the Amazon River is derived from two distinct sources: The

Andes/western and the central/eastern Amazonia (Milliman et al., 1975a). The Andean region supplies an estimated 82% of the suspended sediment load to the Amazon River, even though it occupies only ~12% of the catchment area (Gibbs, 1967; Meade et al., 1985; McClain et al.,

1995). Most inorganic solutes (i.e. nutrients) in the Amazon are also derived from Andean sources (Gibbs, 1967; Devol et al., 1991). The central/eastern Amazon comprises the várzea

(floodplains) and the northern tributaries (such as the Trombetas, Negro and Branco River; Figure

2.1) which drain the Guyana Shield. Filizola and Guyot (2009) estimated ~7% sediment contribution from the rivers draining the shields (Guyana and Amazonian). Presumably, the rest of the sediment that is transported by the Amazon is remobilized from the floodplains. The várzea are completely inundated during peak discharge of the Amazon and act as both sources and sinks of sediments (Meade et al., 1985; Filizola and Guyot, 2009). Maximum sediment discharge to the ocean occurs during February, preceding the peak in water discharge of the Amazon River

(Richey et al., 1986; Figure 2.2). This differential source contribution is also reflected in the composition of organic matter that enters the Amazon mainstream, which undergoes minimal transformation as it travels through the river (Hedges et al., 1986; Richey et al., 1990). Several studies have focused on understanding the biogeochemical processes in the large Amazon estuary near the coast and offshore (Edmond et al., 1981; DeMaster et al., 1986; Berner and Rao, 1994;

Aller et al., 1996; DeMaster and Aller, 2001; Cooley and Yager, 2006; Santos et al., 2008;

Smoak, 2010). In particular, the Amazon shelf was the focus of intense research in the 1970’s –

1990’s (Milliman et al., 1975b; Richey et al., 1990; Nitrouer et al., 1991). Since then, major landscape and population changes have occurred in the region (Marengo et al., 2011a; Davidson et al., 2012).

The Amazon shelf is an area of active sediment deposition, with an estimated 600 x 10 6 metric tons of sediments accumulating on the Amazon shelf annually (Kuehl et al., 1986).

Fluctuations in this process are directly related to river discharge, which in turn is linked to precipitation patterns. The Shelf is also a site of complex oceanic circulation which ultimately controls the fate of the river-derived material discharged onto the shelf; Figure 2.2 summarizes some of the major physical forcings that affect the Amazon Shelf. The shelf is swept nearly continuously in a northwestward direction by the North Brazil Current (NBC), which advects the river plume parallel to the shoreline; Trade Winds blow cross-shelf at 7 – 8 m s -1 most intensely during January-February, and are lowest (cross-shelf wind of 1 – 3 m s -1) between June and July

(Geyer and Kineke, 1995; DeMaster and Pope, 1996), also influencing the extent of the plume.

J F M A M J J A S O N D

Figure 2. 2: Major physical processes affecting the Amazon Shelf (modified from Nittrouer and DeMaster, 1996). Vertical line indicates period of the AmasSeds II cruise and our 2010 cruise

The Amazon Shelf experiences a tidal range of the order of ~10 m at the mouth of the river with energetic tidal currents (Gibbs, 1982). However, the flow of the Amazon River is so large that the estuary effectively occurs over the inner shelf, in a band within 25 km off the river mouth. Mixing between marine and freshwater occurs on the shelf, where strong vertical and horizontal salinity and other property gradients exist in a turbulent environment (Geyer et al.,

1996).

In this chapter we describe some observations of biogeochemical variables made on the continental shelf off the mouth of the Amazon River which was re-visited in February-March

2010. Our objectives were to assess the offshore extent of the Amazon plume, to determine the presence and composition of bottom nepheloid layers (BNL), and to estimate the concentration of sediment and organic matter in the water column and in BNL. We compare our results with those from past research. We propose the following hypothesis: Bottom nepheloid layers on the

Amazon Shelf are a source of particulate organic carbon (POC) and phosphorus (POP) to the

Amazon shelf and to the continental shelf to the north and east of the Amazon delta. The Amazon plume transports a considerable amount of sediment to the adjacent shelf and northward along the outer part of the continental shelf of northern South America (Gibbs, 1973; Nittrouer et al.,

1986; Jewell et al., 1993). Yet the export of POC and particularly POP via BNL has not been estimated.

Methods

Data collection

Two transects were occupied over the Amazon shelf with the R/V Knorr , one near the river mouth and the other to the north on the open shelf, between February 24 and March 3, 2010

(Figure 2.3). The transects roughly coincided with those sampled by the AmasSeds (A

Multidisciplinary Amazon Shelf SEDiment Study) program conducted in the early 1990’s, and specifically, the AmasSeds cruise II, which also occurred during the early Spring (March 1990)

(Figure 2.3; Nittrouer et al., 1991). This period corresponds to a rising river discharge rate, and flow during the month of March should be similar in value to the long-term annual average flow rate of the river. Seven stations were occupied across the northern transect. For consistency with the AmasSeds program, we refer to this transect as the Open Shelf Transect (OS). Five additional stations were occupied across the southern transect, which we call the River Mouth Transect

(RM) as it corresponds to the location of the RM transect during AmasSeds.

The OS transect spanned approximately half of the shelf, from the 25 to 100m isobaths

(Figure 2.1). The RM transect only sampled about 25% of the outer shelf. Currents were measured from the ship along the cruise track with a hull-mounted ADCP (WorkHorse Mariner,

300 KHz; Teledyne-RDI). Salinity and temperature profiles were collected at each station with a

Seabird SBE911 CTD mounted on a rosette with 24 8-liter Niskin bottles. In vivo chlorophyll

-1 fluorescence and beam attenuation at 660 nm (c p(660), m ) profiles were obtained with an

ECO TM fluorometer and a C-Star TM 25cm pathlength transmissometer (both from WetLabs)

attached to the CTD. Dissolved and total organic carbon (DOC and TOC, respectively) were collected at the surface and at the bottom of stations 8 and 9 (within the BNL) and stored in acid- cleaned 60 ml HDPE bottles, rinsed three times with the sample prior to collection. DOC was gravity-filtered through precombusted (450°C for 5 hours) GF/F filters (0.7 µm pore size) using a polycarbonate in-line filter holder. Whole water samples (TOC) were taken directly from the

Niskin bottles. Both DOC and TOC samples were kept frozen at -20°C until analyzed (Dickson et al., 2007). Dissolved inorganic nutrients (nitrate, nitrite, ammonia, phosphorus and silica) were sampled at the surface in each station. Water for inorganic nutrients was vacuum-filtered through

0.8 µm pore size Nuclepore TM membrane filters into acid-cleaned 30 ml High Density

Polyethylene (HDPE) bottles washed three times with an aliquot of the filtrate, and frozen until analysis except for samples for silica which were kept refrigerated. Water samples for suspended sediment analyses were collected at selected stations (marked in red in Figure 2.3) from the surface and bottom of the water column. Water was drained into acid-cleaned containers, and filtered through precombusted (450°C for 5 hours) GF/F filters (0.7 m pore size) using pressurized N 2. Filters were refrigerated until processing. Between 2 and 17 liters were filtered at each location, depending on the concentration of suspended sediments in the water.

Box cores were collected at selected stations (Stations 4, 6, 8 and 9 on the OS transect and 13, 15 and 16 on the RM transect). The upper 1-2 cm of sediments from the box cores were sampled and stored frozen in glass jars until analysis.

Geochemical analyses

Tared filters with suspended material were rinsed with DI water for salt removal, dried for several hours at 60°C and re-weighed to determine total suspended solid (TSS) concentration (near- surface and bottom of the water column). Carbonate was removed from the filters by washing them several times with 10% HCl, followed by rinsing with DI water and re-drying. The

Figure 2. 3: Location of the Amazon Shelf and sampling during 2010; expanded area details station numbers and location. 100 m isobath is indicated. Transects from the AmasSeds program are shown(in gray). Northern transect corresponds to the Open Shelf transect (OS); southern transect corresponds to River Mouth transect (RM; for background on AmasSeds see Nittrouer and DeMaster, 1996).

same procedure was used to de-carbonate the surface sediments collected. Particulate organic carbon (POC) and nitrogen (PN) concentrations and their isotopic composition ( δ13 C and δ15 N) were simultaneously measured for both filters and surface sediments using a Fison NA 1500

Elemental Analyzer (Werne and Hollander, 2004; Thunell et al., 2007). The standard used was

Spinach Leaves (NIST 1570a). The operational precision for the isotopic compositions were ±

o 15 o 13 0.32 /oo for δ N and ± 0.24 /oo for δ C. For POC and PN, the operational precision was ± 0.02 mg C and ± 0.14 mg N. Total particulate P (TPP) and particulate inorganic P (PIP) were measured following Benitez-Nelson et al. (2007). Particulate organic phosphate (POP) was estimated by difference from TPP and PIP. TPP and PIP measurements have a standard error of

3%, while POP has a standard error of 5%. DOC and TOC were analyzed by the Organic

Biogeochemistry Lab at the University of Miami (RSMAS) using high temperature catalytic oxidation (HTCO). Their accuracy is ± 1.0 µM C. Total nitrogen (TN) and total dissolved nitrogen (TDN) was measured using the TOC and DOC water samples, respectively. In this regard, TDN includes both inorganic and organic dissolved nitrogen species.

Meteorological and river discharge data

To assess wind conditions over the region, we used satellite-derived wind data at 25 km spatial resolution collected with the Advanced Scatterometer (ASCAT; http://manati.orbit.nesdis.noaa.gov/products/ASCAT.php ). Images were examined starting one week prior to the sampling period and during the cruise. Precipitation anomaly maps for 2010 were obtained from the IRI/LDEO Climate Data Library ( http://iridl.ldeo.columbia.edu/); the

CPC CAMS-OPI v0208 monthly gridded precipitation data products were used

(http://www.cpc.ncep.noaa.gov/products/global_precip/html/wpage.cams_opi.html ). The anomalies were calculated using the 1979-2000 base period. Daily river discharge at the Obidos station (1° 35.55’ S; 55° 40.51’ W; Figure 2.4) was extracted from the HYBAM database

(www.ore-hybam.org ) for the years 2009-2011 (includes current sampling period) and 1989-1991

(includes AmasSeds study period).

Results

During the sampling conducted between February 24 and March 3, 2010, we did not observe the Amazon River plume seaward of the 50 m isobath (Station 8; ~120 Km from the coast); salinity was always > 35 for all other stations at all depths. River discharge for October

2009-January 2011 is shown in Figure 2.4. For comparison, river discharge for 1989-1991, which includes the AmasSeds sampling period, is also shown. River levels during the dry period of

November-December 1989 were higher than the climatological average by ~17% (roughly 20 x

10 3 m3 s-1, more than 1-standard deviation), while during November-December 2009; river discharge was lower than the average by some 13 x 10 3 m3 s-1 (more than 1-standard deviation), or 12% of total discharge. River discharge in February-March 2010 at Obidos was slightly lower

300

250 /s) 3 m

3 200

150 Discharge(10 Climatology 100 2009-2011 1989-1991

50 Oct Dec Feb Apr Jun Aug Oct Dec

Figure 2. 4: Water discharge measured at Obidos between October200 9- January 2011 (dotted line) and October 1989 - January 1991 (broken line). River discharge climatology (1968 -2010) is also shown (solid line). Gray line indicates 1 standard deviation. Arrow indicates sampling periods for both AmasSeds II and this study.

than that measured during the same months in 1990 (~10% lower), and within the standard deviation of climatology. Obidos is located ~750 Km from the Amazon River mouth, and a change in the discharge rate at Obidos arrives at the shelf roughly two weeks later (Salisbury et al., 2011).

Ship-based observations of sea surface temperature (SST), salinity (SSS), chlorophyll a

(Chl a), c p(660), oxygen, silica, TSS, DOC and TDN concentrations (all surface observations) are shown in Figure 2.5. The Amazon River plume was observed only in the stations closest to the shore in the northernmost transect (OS). No river signal (expressed as decrease in salinity < 30) was detected in the RM transect. Current velocities in the shelf region influenced by the river were uniform throughout the water column, and averages ~0.5 m s -1 in a general NW direction.

At station 8 the average water column current direction was 314° relative to true north, and the speed was 0.49 m s -1. At station 9, the station closest to land, the average water column current direction was 321° (relative to true north) with a velocity of 0.47 m s -1. Current velocity measurements in the transect between the two stations were similar (velocity of 0.51 m s -1, direction of 314° relative to true north). ASCAT winds showed a predominant NE direction

(cross-shelf), with an average wind speed of 6 m s -1 (data not shown).

Two regions were clearly identifiable in the OS transect: a region influenced by the river

(where surface TSS was > 1 mg l -1 and salinity was < 30), and a region with open-ocean characteristics (where TSS was < 1 mg l -1 and salinity was > 30). A vertical profile of salinity at stations 8 and 9 shows the surface plume of the river as a layer of salinity 24-27 in the upper ~12 m, and a well-mixed water column of salinity ~36 below the plume (Supp. Fig. 2.1). From station

7 offshore, the water column was well mixed (down to ~10 m at station 7 to ~100 m at station 3), with salinities > 36 (Supp. Fig. 1). In all the surface observations, Chl a, c p(660), oxygen concentration, TDN, DOC and silica were highest within the plume region (Table 1). Surface temperature also peaked in the plume region (28.57-28.65 ˚C, Table 1, Figure 2.5).

Most of the organic carbon and nitrogen measured at the surface was in dissolved form (>

90%). At Station 9, TDN decreased to ~80% of total N in surface waters; for simplicity, Table 1 only shows DOC and TDN values. The distribution of surface DOC concentration with salinity was linear (R 2 = 0.97; N = 10; P < 0.001). Surface nutrient concentrations increased offshore, with low or undetectable values for all nutrients, except silica, at stations 8 and 9. The highest inorganic nitrogen (NO 3, NO 2, but especially NH 4) concentrations were measured farthest offshore (Table 1). Silica exhibited an inverse pattern to the other nutrients, and was highest in the stations closer toward the coast in the OS transect and in the river plume. TDN was always higher than the sum of inorganic nitrogen species (NO 3 + NO 2 + NH 4), suggesting the presence of organic nitrogen. The concentration of TDN did not vary significantly with location ( P > 0.05;

Table 1). Surface chlorophyll fluorescence exhibited an inverse pattern to that of inorganic nitrogen, with highest values in the stations within the plume.

A simple budget of riverine DOC export from the Amazon shelf can be calculated based on the current velocities measured at stations 8 and 9. Assuming the surface DOC concentrations shown in Table 1 are representative of the upper meter of the water column, we estimate an instantaneous export of 5.78 Kg DOC s -1 northwestward across the distance between the two stations (~8 Km). Extrapolating this calculation to the width of the entire plume, from our station

8 up to ~50 Km from the coast (a shelf width of ~70 Km), we obtained an instantaneous northwestward transport of 47.74 Kg DOC s -1. We extended our extrapolation only to ~50 Km from the coast because the turbidity is high from this point landward (Nittrouer et al., 1986) and other processes may be controlling both the concentrations of DOC in surface waters and its transport (Bianchi et al,. 2004; Dagg et al., 2004). DOC export tracks the river’s discharge, increasing with raising water and decreasing with falling discharge (Richey et al., 1990).

Therefore, concentrations sampled during rising and falling discharge can be viewed as ‘average’

DOC concentrations. Using this assumption we extrapolated our flux estimates over a year and obtained a northwestward riverine transport of 1.50 Tg DOC yr -1.

-1 Beam attenuation (m ) Chlorophyll Fluorescence Salinity

Oxygen ( µM/Kg) SST (˚C) TDN ( µM)

TSS (mg/l) Silica ( µM) DOC ( µM)

Figure 2. 5: Surface distribution of different variables along the OS and RM transects. Sampled stations are indicated by the black dots. For reference, black line marks the approximate location of the 100m isobath.

Table 2.1: Surface (2-4 m) temperature, salinity, beam attenuation, chlorophyll fluorescence, oxygen, nutrients, dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) concentrations for the sampled stations (Figure 2.2). Temp: Temperature (in °C); cp: beam attenuation at 660 nm (in m -1); FChl a: Chlorophyll fluorescence (in mg m -3); Oxy.: Oxygen (in µM Kg -1); DOC: Dissolved organic carbon (in µM); TDN: total dissolved nitrogen (in µM); NO 3 + NO 2: nitrate plus nitrite (in µM); NO 2: nitrite (in µM); NH 4: ammonia (in µM); soluble reactive phosphorus (in µM); Sil: Silica (in µM). n.a.: not available; b.d. = below detection limit.

NO 3 + Station Latitude Longitude Temp. cp FChl a Salinity Oxy. AOU DOC TDN NO 2 NH 4 SRP Sil NO 2

Open Shelf Transect 1 04° 27.60 ' N 048° 36.83' W 27.78 0.273 0.02 35.80 190.90 4.6 74.22 4.57 0.12 0.04 1.26 3.19 0.85 2 04° 02.13' N 048° 20.45' W 27.73 0.260 0.02 35.85 191.15 n.a. 73.17 4.31 0.05 0.01 0.91 1.68 n.a. 3 03° 57.64' N 048° 32.49' W 27.82 0.254 0.05 35.93 190.91 4.3 75.87 5.42 0.04 0.01 0.74 0.01 1.51 4 03° 57.01' N 048° 36.42' W 27.79 0.393 0.04 36.04 190.09 5.1 73.11 5.22 b.d b.d 0.62 0.02 1.45 5 03° 48.05' N 048° 53.40' W 28.32 0.246 0.03 36.27 190.43 2.9 73.32 4.05 b.d. b.d. 0.58 0.04 1.38 6 03° 41.14' N 049° 3.78' W 28.34 0.261 0.01 36.28 189.18 4.1 73.21 4.16 b.d. b.d. 0.67 0.04 1.39 7 03° 27.67' N 049° 25.17' W 28.32 0.370 0.14 35.36 187.54 6.8 71.70 4.65 b.d. b.d. 0.55 0.03 2.90 8 03° 14.14' N 049° 47.51' W 28.57 0.937 0.73 27.72 201.04 0.8 105.70 5.80 b.d. b.d. 0.15 b.d. 4.77 9 03° 11.14' N 049° 51.85' W 28.65 1.002 1.10 24.01 211.86 -6.1 128.25 5.83 b.d. b.d. b.d. b.d. 6.56

River Mouth Transect 10 03° 46.67' N 048° 10.24' W 28.06 0.288 0.04 36.20 189.80 n.a. 73.93 4.34 b.d. b.d. 0.72 0.01 0.84 12 03° 04.42' N 047° 38.65' W 28.30 0.256 0.02 36.14 188.87 4.6 73.22 4.49 0.76 b.d. 0.82 0.09 1.40 13 02° 50.59' N 047° 44.37' W 28.43 0.236 0.02 36.30 189.96 3.0 76.58 4.98 0.28 0.02 0.78 0.07 1.49 14 02° 39.83' N 047° 49.16' W 28.39 0.213 0.05 36.28 189.60 3.5 73.85 4.31 b.d. b.d. 0.55 0.06 1.50 15 02° 34.45' N 047° 51.12' W 28.35 0.214 0.07 36.17 189.39 3.9 74.43 4.93 b.d. b.d. 0.56 0.06 1.56 16 02° 05.45' N 048° 03.16' W 28.31 0.270 0.19 36.29 183.56 9.8 67.05 4.55 0.20 b.d. 0.61 0.07 1.81 17 0° 21.41' N 044° 12.89' W 28.73 0.274 0.02 36.31 188.65 n.a. 74.42 4.52 0.36 0.03 0.78 0.08 1.09

Chlorophyll fluorescence and beam attenuation showed marked vertical structure over the shelf. In both the OS and RM transects a deep chlorophyll maximum (DCM) was observed between 40 – 100 m (Figure 2.6). A chlorophyll maximum was also observed in the upper 10 m of the water column in the OS transect (stations 8 and 9).

The vertical distribution of beam attenuation for stations 7, 8 and 9 in the OS transect is shown in Figure 2.7. Surface c p (660) increased in stations 8 and 9 relative to station 7 and other stations farther offshore. This peak in c p was identified as surface nepheloid layers (SNL). A peak in c p was also observed in the same stations near the bottom in a layer ~20-30m thick, which corresponded to the bottom nepheloid layer (BNL). Beam attenuation within the BNL was between 3 and 7 times higher than in the SNL. DOC inside the BNL was about half of that measured in the surface river plume (105.70 µM in surface waters of station 8 vs. 62.19 µM within the BNL at 42m water depth; 128.25 µM in surface waters of station 9 vs. 64.10 µM within the BNL at 30 m depth). DOC concentration within the BNL decreased with distance offshore.

The geochemistry of suspended particles sampled is presented in Table 2. Surface waters away from the influence of the Amazon plume had relatively low concentrations of TSS (< 1 mg l-1), POC (< 0.01 mg l -1) and PN (< 0.001 mg l -1). These concentrations increased about an order of magnitude within the river plume (Stations 8 and 9). In contrast, POP and PIP did not vary significantly ( P > 0.05) in surface waters, regardless of the location on the shelf. This was also reflected in the C/PIP and C/POP ratios, which did not change significantly with distance from shore ( P > 0.05).

TSS within the BNL at stations 8 and 9 was 15 to 25 times more concentrated than in the overlying surface waters (Table 2.2; Figure 2.7). However, concentrations of POC and PN within

BNL were similar to surface concentrations. %POC and %PN relative to TSS within the BNL at stations 8 and 9 were low (0.6-0.9 %POC; 0.08-0.11 %PN). This is significantly lower ( P < 0.01)

than %POC in surface waters at the same stations (7-18%), or near the bottom at locations not affected by the river plume (Table 2). There was a significant correlation between c p (660) and

TSS within the BNL (y = 4.79x - 0.18, R 2 = 0.95, N = 6, P < 0.01). A significant correlation

2 between c p (660) and POC was also observed within the BNL (y = 0.026x + 0.043, R = 0.75, N =

7, P < 0.05). The correlation between TSS and POC within the BNL was y = 0.005x + 0.048 (R 2

= 0.88, N = 6, P < 0.01).

The BNL at stations 8 and 9 was also enriched in both PIP and POP (Table 2). Outside of the river plume the concentration of these particulates within the BNL declined rapidly: within

~200 Km from the coast the concentration of P in particulate matter had dropped by over 90%.

This enrichment in P in areas under the plume influence was also visible in the atomic C/P ratios.

The atomic C/POP ratio within the BNL of station 9 was ~80% lower than in the BNL of station

6, from C/POP = 99.4 at station 9 to C/POP = 814.7 at station 6. The atomic C/PIP decreased

~70% between the same stations, from C/PIP = 87.6 at station 9 to C/PIP = 306.4 at station 6. We found a significant correlation between beam attenuation and POP (y = 0.76x + 0.25, R 2 = 0.87,

N = 7, P < 0.01), and between TSS and POP (y = 0.16x + 0.31, R 2 = 0.97, N = 6, P < 0.01) within the BNL.

Using the TSS, POC and POP data available, we estimated sediment fluxes from the

Amazon Shelf during our study period. Given our limited sampling of the biogeochemical parameters within the BNL, we used the relationship between beam attenuation and TSS, POC and POP described above for the BNL and derived a profile of TSS, POC and POP within the

BNL at stations 8 and 9. We then integrated, using a trapezoidal rule, the concentrations over the depth of the BNL and multiplied these values by the current velocity measured by the shipboard

ADCP to obtain instantaneous fluxes at these locations.

OS Transect

Station number

RM Transect

Station number

-3 Figure 2.6 Chlorophyll fluorescence (mg m ) for the OS and RM transects.

Table 2.2: Geochemical results for selected sampled stations. Gray lines indicate bottom samples. Stn.: Station number; D: Depth; δ13 C: stable isotopic ratio of organic carbon; δ15 N: stable isotopic ratio of organic nitrogen; POC: particulate organic carbon; PN: particulate nitrogen; POP: Particulate organic phosphorus; PIP: Particulate inorganic phosphorus; TSS: total suspended sediments; % POC: weight-percent POC content; % PN: Weight-percent PN content; % POP: Weight-percent POP content; C/N: atomic organic carbon to nitrogen ratio; C/P: atomic organic carbon to particulate phosphorus ratio; C/P: atomic organic carbon to particulate phosphorus ratio. Refer to Figure 2.2 for station location. n.a.: not available. POC PN POP PIP D δδδ13C δδδ15N TSS % % Stn. Latitude Longitude (mg (mg (mg l -1 (mg l -1 % PN C/N N/P C/POP C/PIP (m) (o/ ) (o/ ) (mg l -1) POC POP oo oo C l -1) N l -1) x10 -3) x10 -3)

Open Shelf Transect 4 03° 57.01' N 048° 36.42' W 1 -24.25 n.a 0.026 0.003 n.a n.a n.a. 0.61 0.08 n.a 9.2 n.a. n.a. n.a. 5 03° 48.05' N 048° 53.40' W 1 n.a n.a n.a n.a n.a n.a n.a n.a n.a n.a n.a n.a. n.a. n.a. 5 03° 48.05' N 048° 53.40' W 284 n.a n.a 0.017 n.a 0.114 0.116 0.21 8.33 n.a 49.73 n.a n.a. 392.4 n.a. 6 03° 41.14' N 049° 3.78' W 1 -25.94 4.48 0.020 0.002 n.a n.a n.a n.a n.a 1.05 10.9 n.a. n.a. n.a. 6 03° 41.14' N 049° 3.78' W 105 n.a n.a 0.022 n.a 0.069 0.183 0.30 7.25 n.a 27.33 n.a. n.a. 814.7 306.4 7 03° 27.67' N 049° 25.17' W 1 n.a n.a 0.082 0.007 1.20 0.76 0.44 18.57 0.04 61.11 14.3 7.5 175.8 276.2 7 03° 27.67' N 049° 25.17' W 82 n.a n.a 0.047 0.005 0.305 0.324 0.12 n.a. 4.50 48.48 10.4 18.5 396.6 373.2 8 03° 14.14' N 049° 47.51' W 1 -28.63 6.28 0.106 0.015 1.427 1.197 1.46 7.23 1.01 54.40 8.4 12.4 191.1 227.9 8 03° 14.14' N 049° 47.51' W 42 -24.64 6.41 0.218 0.029 4.650 8.215 22.28 0.98 0.13 36.15 8.8 4.9 120.9 68.4 9 03° 11.14' N 049° 51.85' W 1 -20.39 4.56 0.219 0.033 2.450 1.661 1.18 18.55 2.76 59.59 7.8 17.5 231.1 340.8 9 03° 11.14' N 049° 51.85' W 30 -25.27 4.13 0.205 0.024 5.324 6.043 33.71 0.61 0.07 15.79 10.1 4.6 99.4 87.6

River Mouth Transect

12 03° 04.42' N 047° 38.65' W 1 -25.85 4.19 0.018 0.003 n.a n.a n.a n.a n.a n.a 10.2 n.a. n.a. n.a. 13 02° 50.59' N 047° 44.37' W 1 -24.96 3.71 0.028 0.003 n.a n.a n.a n.a n.a n.a 8.3 n.a. n.a. n.a. 14 02° 39.83' N 047° 49.16' W 1 -23.96 6.70 0.022 0.003 n.a n.a n.a n.a n.a n.a 7.8 n.a. n.a. n.a. 15 02° 34.45' N 047° 51.12' W 1 -24.16 4.89 0.025 0.004 0.306 0.306 3.47 0.73 0.11 50.04 n.a 13.5 212.6 212.9 15 02° 34.45' N 047° 51.12' W 105 n.a. n.a. 0.048 n.a. 0.212 0.317 0.120 n.a. n.a. 40 7.6 n.a. 585.2 391.5 16 02° 05.45' N 048° 03.16' W 1 -27.48 3.17 0.037 0.006 0.759 0.416 n.a. n.a. n.a. 64.57 9.6 10.9 126.7 231.1 16 02° 05.45' N 048° 03.16' W 65 -23.94 1.92 0.071 0.009 0.563 0.497 0.63 11.31 1.38 53.13 9.2 18.0 324.6 368.1

The direction of the flux was northwestward, as defined by the direction of the current.

At station 8, the instantaneous fluxes of TSS, POC and POP within the BNL across a plane defined by our transect were 114.9 g s -1, 1.28 gC s -1, and 0.023 gP s -1, respectively. At station 9 these fluxes were 163.4 g s -1 for TSS, 1.28 gC s -1 for POC and 0.029 gP s -1 for POP. We additionally calculated flux at a point equidistant between the stations (the stations were ~8 km apart) using an average of the concentrations measured at the two stations, average BNL

% transmission

100 80 60 40 20 0 0 1 mg/l

20 33 mg/l

40 22 mg/l Depth(m)

60 35 m isobath 50 m isobath 75 m isobath 80 0.1 mg/l

Figure 2. 7: Vertical profiles of beam attenuation at 3 different stations on the OS transect. Total suspended sediment concentrations at the bottom of each station are shown for reference.

thickness (23.6 m) and the averaged current velocities measured between the two locations (0.5 m s-1). The fluxes of TSS, POC and POP within BNLs at this location were ~166 g s -1, ~1.5 gC s -1, and ~0.03 gP s -1, respectively.

To estimate the Amazon plume transport northwestward over the shelf, we used the relationship between TSS within the BNLs and distance offshore that Nittrouer et al. (1986) observed. This was done in a study prior to the AmasSeds program, which examined the Amazon

Shelf during May-July 1983. This relationship follows an exponential decay with the shape a*e -

0.046x where a and x are (respectively) the intercept (maximum sediment concentration at the shore) and the rate of decay (distance from the river mouth). We also estimated the thickness of the BNL utilizing the relationship between BNL thickness and distance from shore that was derived from the same study by Nittrouer et al. (1986). The relationship was again exponential, a*e 0.03x , where a corresponds to BNL thickness (which increases offshore) and x to the distance from shore.

Using this relationship we extrapolated our fluxes from ~50 Km from the coast offshore, covering a shelf width of ~70 Km from our station 8 (with the same transect heading). We limited our extrapolation to 50 Km from shore since closer to the coast estuarine processes dominate (e.g. flocculation, sorption; Gibbs, 1982; Geyer et al., 1996; Hedges and Keil, 1999). We assume these are different from BNL processes over the middle shelf. We used a constant current velocity of

0.45 m s -1, based on our observations and historical values (Geyer et al., 1996). Our calculations yielded an instantaneous, northwestward flux of 38.7 metric tons (mt) s -1 of TSS. Using the relationship between TSS and POC, and TSS and POP we can estimate an equivalent northwestward transport of 0.24 mt s -1 of POC and of 6.42 x 10 -3 mt s -1 of POP.

δ13 C values in surface waters of the OS transect ranged between - 28.63 ‰ at station 8 to

-20.39 ‰ at station 9 (Table 2). Station 9 also had the highest surface in vivo chlorophyll values, estimated at 1.10 mg m -3. In the RM transect the surface carbon isotopic composition did not vary significantly ( P >0.05; it remained between -23 ‰ to -25 ‰ for most stations). δ13 C of BNL for both transects was not significantly different than that of surface POC ( P > 0.05), and ranged

between -23.94‰ to -25.27‰. Atomic C/N ratios were similar between transects ( P > 0.05), and ranged between 7.5-14.3.

Stable isotope values and organic carbon and nitrogen content of surface sediments are shown in Table 3. Sediment δ13 C under the OS transect was ~-26 ‰, while in the RM transect sediments the δ13 C was lighter (between -20 ‰ and -23 ‰, P < 0.01; Figure 2.8). The δ15 N values did not show significant variations (between 5.25 ‰ and 6.72 ‰; P > 0.05). The POC content of surface sediments was relatively low, from 0.05% in station 16 (located mid-shelf in the southern transect) to >1.3% at stations 4 and 6 in the northeastern edge of the shelf (Figure

2.8). Atomic C/N ratios in the surface sediments were similar to those of suspended particles ( P >

0.05), except in station 4 where the ratio was >21.

Table 2.3: Carbon and nitrogen isotopic composition, and organic carbon and nitrogen content (in %) of particulate matter of Amazon shelf and slope surface sediments. Refer to Figure 2.1 for station location. Abbreviations are as in Table 2.2.

Station Latitude Longitude Depth (m) δδδ15 N δδδ13 C %POC % PN C/N Open Shelf Transect

4 03° 57.01' N 048° 36.42' W 643 4.72 -26.42 1.31 0.08 21.5 6 03° 41.14' N 049° 3.78' W 110 6.68 -20.13 1.56 0.29 6.4 8 03° 14.14' N 049° 47.51' W 55 5.55 -26.43 0.60 0.09 7.7 9 03° 11.14' N 049° 51.85' W 38 5.25 -26.02 0.65 0.10 7.9

River Mouth Transect 13 02° 50.59' N 047° 44.37' W 612 6.56 -23.45 0.82 0.12 7.9 15 02° 34.45' N 047° 51.12' W 115 6.72 -21.36 0.14 0.02 8.7 16 02° 05.45' N 048° 03.16' W 65 5.68 -20.90 0.05 0.01 9.1

%% ‰

Figure 2. 8: (left) Carbon isotopic composition of particulate organic carbon (POC) in surface sediments of the Amazon shelf; (right) POC content (in percent) of the Amazon shelf surface sediments. Station numbers are indicated in the right panel for reference

Discussion

Amazon Plume characteristics during 2010

Large river systems exert a significant influence on the associated continental margins, as they discharge substantial concentrations of terrestrially-derived dissolved and particulate materials (Dagg et al., 2004; Wysocki et al., 2006). Plume dynamics are highly complex and can vary on several time scales, depending on the different forcing mechanisms that control them. Yet the physical controls on the transport, mixing, and dispersal of these buoyant plumes are not fully understood (Dagg et al., 2004). Historical data show that the cross-shelf dimension of Amazon

River Plume can vary significantly over the shelf between 1°S and 5°N, with plume widths ranging from ~80 Km to more than 250 Km and covering most of the shelf (Neumann, 1969;

Gibbs, 1970; Lentz, 1995; Lentz and Limeburner, 1995). During the AmasSeds cruise II in March

1990, the Amazon plume along the RM and OS transects exceeded 200 Km in width (Lentz and

Limeburner, 1995). During our cruise, the plume extended ~120 Km and was detected only over the OS transect. The AmasSeds observations demonstrated that temporal variations of plume width can be short, in the order of weeks, and that the circulation over the shelf can lead to patchiness (Lentz and Limeburner, 1995; Geyer et al., 1996). The study showed that river discharge, the NBC, trade winds and semi-diurnal tides control the structure of the Amazon plume over the shelf. Long term observations over the shelf (e.g. Lentz, 1995; Geyer et al., 1996), satellite time-series observations (Morelli et al., 2010) and model simulation (e.g. Nikiema et al.,

2007) indicate that the structure of the northwestward extension of the Amazon plume over the north Brazil shelf is controlled by coastal currents, while short term variations in the structure of the plume are dictated by changes in the wind field. Geyer et al. (1996) proposed different plume structures under varying wind conditions. Under strong cross-shelf winds blowing from the northeast, such as the ones observed during February-March 2010 (~6 m s -1), the plume is kept bound to the inner shelf along the continent and does not extend far over the shelf. With added pressure from the NBC, the Amazon River water is forced to flow to the northwest on the shelf

(Lentz, 1995; Johns et al., 1998), as observed during our sampling. During AmasSeds in March

1990, winds were from a more northerly direction (Geyer et al., 1996; Lentz, 1995), which allowed relaxation of the plume to the east, leading in part to the difference in plume extent compared to that during our 2010 cruise.

Figure 2. 9: Precipitation anomalies for the months of January -March 2010 (left) and April -June 2010 (right). The approximate Amazon drainage basin area is outlined in black.

Changes in river discharge exert a relatively minor influence on offshore extension of the plume, even though river outflow is an important component of the Amazon shelf hydrography and biogeochemistry (Lentz and Limeburner, 1995; Nikiema et al., 2007; Morelli et al., 2010).

River discharge in early 2010 during the minimum in the hydrograph was below-average, while during early 1990 discharge was above average (Figure 2.4). River discharge is directly linked to precipitation over the Amazon Basin, which in turn is affected by climatic phenomena (Zeng,

1999; Marengo et al., 1998; Poveda et al., 2001; 2006; Marengo and Nobre, 2001; Nobre et al.,

2009). During the El Niño Southern Oscillation (ENSO), negative precipitation anomalies occur over northern and central Amazonia, while during La Niña wetter than normal conditions are observed. Figure 2.9 shows precipitation anomalies for January-March 2010 and April-June 2010.

January-March 2010 showed dry conditions over much of the Amazon basin. This should be the period of maximum rainfall for the southern part of the Amazon basin, while April-June typically marks the maximum rainfall for the central part of the basin and the beginning of high rainfall for the northern basin. ENSO conditions in the tropical Pacific during 2010 inhibited rainfall in central and western Amazonia (Tomasella et al., 2010; Marengo et al., 2011a). This led to the lower than average discharge during the low discharge season. During 1989 excess rainfall was recorded in the north and northeast region of the Amazon, linked to La Niña conditions (Marengo et al., 2012). This led to higher than average values during the low discharge period of early

1990. While not as large of a contributing factor to the river plume extension as the winds or currents, the difference in river discharge observed between 1990 and 2010 is consistent with our observations of a smaller Amazon plume over the shelf.

Biogeochemistry of the Amazon Plume during 2010

Large river systems also deliver substantial amounts of dissolved inorganic nutrients to coastal environments. These nutrients enhance biological production in regions impacted by the river plume. However, plume-associated biogeochemical processes can vary significantly, as they

are largely dependent on the magnitude of river discharge (DeMaster and Pope, 1996; Dagg et al.,

2004; McKee et al., 2004). To facilitate comparisons of our results with those from the

AmasSeds cruise II we divided the study area into two zones: an innermost shelf area influenced by the Amazon plume (comprising stations 8 and 9 of the OS transect) and areas not affected by the river (the rest of the sampled stations). This division matches zones II and III defined by

Smith and DeMaster (1996) during AmasSeds. Zone II included intermediate turbidity and salinity characteristics (sediment concentrations less than 10 mg l -1 and salinities less than 32) and zone III comprised the offshore area (salinities > 32). It is important to note, however, that while

‘zone II’ encompassed an area of > 200 Km over the shelf during March 1990, this river plume area was contained within 120 Km of the coast during February-March 2010. In March 2010, in vivo surface chlorophyll values were highest (0.7-1 mg m -3) in the uppermost 10 m of zone II

(river plume). These values were of the same order as chlorophyll a concentrations reported by

Smith and DeMaster (1996) for the same area/calendar month. Nitrate and phosphate concentrations in surface waters of zone II were below detection limits, while silica concentrations were higher in the plume (stations 8 and 9). Nutrient concentrations were also low

(< 1) relative to published values at comparable salinities in the plume (Edmond et al., 1981;

DeMaster et al., 1986; DeMaster and Pope, 1996). The undetectable concentrations of nitrate and phosphate suggest complete biological removal of nutrients in Zone II (Edmond et al., 1981;

DeMaster and Pope, 1996). The oxygen supersaturation in the river plume (negative AOU) is further evidence of high photosynthetic activity (DeMaster et al., 1996; DeMaster and Aller,

2001; García et al., 2006).

Surface chlorophyll in Zone III dropped to an average of 0.02 mg m -3 and a DCM was detected between ~80-100 m, immediately above the main thermocline. These observations agree with those reported by Santos et al. (2008), who examined the Amazon shelf and adjacent areas during the high discharge period of 1999. According to Santos et al. (2008), the base of the thermocline was within the 1% light penetration level. Similar observations have also been made

in other areas such as the Gulf of Cadiz (Navarro et al., 2006), the Levantine Basin in the

Mediterranean Sea (Ediger and Yilmaz, 1996), the BATS time-series station (Siegel et al., 2001), and the Eastern Agulhas Bank (Probyn et al., 1995). Nutrient concentrations in the oceanic Zone

III were comparable to those measured by AmasSeds and other authors (Edmond et al., 1981;

DeMaster and Pope, 1996). Phosphate and nitrogen concentrations (mainly ammonia) were highest off the shelf (stations 1 and 2). The reason for the higher nutrient concentrations offshore is currently unknown; temperature profiles show no evidence of upwelling of deeper water at the shelf edge. As evidenced from the TDN concentrations, dissolved organic nitrogen (DON) represented a substantial fraction of the total nitrogen within the Amazon plume and over the shelf. Large rivers deliver considerable amounts of nitrogen to the coastal ocean, including terrestrially-derived DON (Cotner and Gardner, 1993; Dagg et al., 2004). A fraction of this DON is likely refractory, which would explain the relatively unchanging TDN concentrations observed with increasing salinity (López-Veneroni and Cifuentes, 1994; Bronk, 2002).

To examine silica distribution across our 2010 OS transect, a two end member mixing model was used. The riverine end-member was fixed at 131 µM using published values (Edmond et al., 1981; DeMaster et al., 1986). Negative deviations from the mixing line suggest silica removal, while positive deviations indicate addition (DeMaster et al., 1986). A fundamental assumption is that only two types of water (riverine and open ocean) are mixed, which according to DeMaster et al. (1986) is not unreasonable for this system. Silica concentrations within the

Amazon plume were almost an order of magnitude lower than the predicted values based on the mixing line. Percent silica removal was calculated following DeMaster et al. (1986) as the predicted value minus the observed value, divided by the predicted value and multiplied by 100.

While DeMaster et al. (1986) reported a seasonally-dependent removal percentage between 20-

40%, DeMaster and Pope (1996) found this percentage could be as high as 90% in areas of low

(~1-5 mg l -1) suspended sediment concentrations. Our data indicates a biogenic removal of > 85% in suspended sediment concentrations < 2 mg l -1. The most diverse phytoplankton community

was observed within the area influenced by the river plume. Skeletonema costatum and

Pseudonitzschia sp. were the dominant species, with concentrations > 350,000 and > 85,000 cells l-1, respectively (Lorenzoni and Wolny, unpub. data). Diatoms were very low or absent in all other stations outside the plume.

Large rivers contribute significant concentrations of dissolved organic materials to the coastal ocean. Most of this organic matter is soil-derived and relatively resistant to microbial degradation (Meybeck, 1982; Ittekkot, 1988; Hedges et al., 1994; Benner et al., 1995). Indeed, over half of the DOC transported by the Amazon River is refractory (Richey et al., 1980, 1990;

Amon and Benner, 1996). The Amazon typically transports about 50% of its organic carbon load in dissolved form (Richey et al., 1990; Richey et al., 1991). However, our measurements in

March 2010 showed that DOC was over 80% of the organic carbon in surface water within the river plume. The correlation between DOC and salinity suggests that most of the DOC was associated with the river plume. DOC concentrations otherwise remained relatively constant across those stations not influenced by the Amazon. These concentrations were within the range reported for surface waters of the tropical Atlantic (Hansell et al., 2009).

The simple annual flux estimates that we calculated suggest a northwestward riverine transport of 1.50 Tg DOC. At Obidos, Richey et al. (1990) estimated an annual average discharge of DOC of 22.1 TgC yr -1. Thus, our estimates suggest that roughly 6% of the DOC discharged by the Amazon is advected along the coast in the river plume to be dispersed into the tropical

Atlantic, potentially contributing to the pool of DOC of the tropical North Atlantic (Bauer and

Druffel, 1998). It is important to stress, however, that this is a rough calculation. In it, we are not only assuming our DOC concentrations, as well as current velocities, to be representative of values for the entire river plume, but also unchanging throughout the year. Additionally, the DOC concentrations reported by Richey et al. (1990) against which we are comparing ours do not take into consideration DOC inputs via the Xingu River and from other smaller rivers that discharge into the Amazon mainstem after Obidos.

In most river systems, total organic carbon concentrations increase with suspended sediment concentrations (Meybeck, 1982; Hedges and Keil, 1999). The ratio of DOC/POC measured in 2010 within the plume (8-13) agreed with reported ratios for rivers with low (5-15 mg l -1) suspended sediment concentrations (Meybeck, 1982; Ittekkot and Laane, 1991). However, these ratios were high for published Amazon River waters (~1-5, Hedges et al., 1997; Ittekkot and

Laane, 1991). This difference was likely due to the low overall suspended sediment and POC concentrations in the plume during our sampling. Concentrations of TSS in surface waters influenced by the Amazon plume measured during 2010 (~1 mg l -1) were comparable to those reported by Milliman et al. (1975b) during February-March of 1973 for areas of similar salinity.

However, our values were low relative to those from the AmasSeds study; Smith and DeMaster

(1996) reported concentrations of suspended solids > 10 mg/l for March 1990 at similar salinities.

The concentration of suspended material carried by the river depends in part by the river discharge (Devol et al., 1995). The lower discharge rates seen during February-March 2010 may have contributed to these lower concentrations.

Processes controlling the nature and transport of particles on the Amazon Shelf

In addition to large quantities of dissolved organic and inorganic solutes, continental shelves impacted by large rivers also receive significant amounts of particulate materials. Surface and bottom nepheloid layers are important mechanisms for the lateral transport of riverborne particles from the shelf to the open ocean, in particular BNL. Several studies have documented that BNL contribute significantly to the advection of POM and sediment over long distances, effectively exporting material off the shelf (McPhee-Shaw et al., 2004; Inthorn et al., 2006;

Lorenzoni et al., 2009), while SNL are shorter-lived and have a more proximal impact. Overall, suspended POC concentration within the SNL measured during out study was comparable to that reported by Druffel et al. (2005), who collected samples during low discharge. Our suspended sediment δ13 C were similar to values reported by Showers and Angle (1986) and by Ruttenberg and Goñi (1997). The δ13 C of suspended particulate matter was representative of terrestrial material (-24‰ to -28‰). In surface waters, particularly within the SNL of the station most influenced by the river plume (station 9), %POC was high. This can be attributed to the high phytoplankton biomass present. Indeed, δ13 C was most enriched at this location (-20.39 ‰) indicating a direct marine source of carbon (Hedges et al., 1997). Atomic C/N ratios in surface waters also support this observation: values (8-14) were close to Redfield for oceanic phytoplankton (Hedges et al., 1997). Similar observations have been made by Edmond et al.

(1981) and Ruttenbert and Goñi (1997).

TSS within the BNL was 15 to 25 times more concentrated than in the SNL. The TSS concentrations we measured within the BNL were comparable to those measured by Nittrouer et al. (1986) in locations farther away from the river mouth. Within the BNL, %POC decreased with increasing sediment concentration; this is the result of dilution of organic matter by suspended minerals (Hedges and Keil, 1999). The atomic C/N ratio within the BNL (8-10) was similar to that of surface waters, and relatively low considering the direct influence of the river. Atomic

C/N ratios remained relatively constant with distance offshore. Ruttenberg and Goñi (1997) suggested processes on the shelf could enrich sediments in nitrogen and hence lower their ratios.

They also suggested that extensive reworking could explain the lack of systematic trend across the shelf.

Particulate phosphorus distributions over the shelf were different than that of POC. There was a significant enrichment in bottom TPP concentrations in areas influenced by the river, confirming an input of P from the Amazon to the adjacent shelf (Devol et al., 1991; Berner and

Rao, 1994). From inshore to offshore stations, atomic C/PIP ratios increased roughly 5 times, while C/POP ratios were ~3 times higher (Table 2). Similar ratios were observed by Ruttenberg and Goñi (1997) for surface sediments on the Amazon Shelf; the authors attributed their lower than expected ratios to bacterial biomass, which is characterized by low C/POP ratios. We suggest the low ratios observed in the suspended particles near the bottom on the shelf are the result of the direct input of particulate P from the Amazon River and/or reworking of bottom sediments, which may supply BNL with recently deposited P (Berner and Rao, 1994). This P also represents a source of phosphorous to the water column through solubilization, which can be rapidly taken up by phytoplankton fueling primary production (Edmond et al., 1981; Berner and

Rao, 1994). Unfortunately, our data are insufficient to determine which process dominates. In surface waters, atomic C/P ratios remained relatively constant with location on the shelf. The lack of variability in particulate P at the surface implies the available P is not being cycled. Away from the influence of the river atomic C/P ratios increased to > 300, and their distribution was relatively homogenous throughout the shelf.

Sediment fluxes from continental margins to the deep sea have an important effect on nutrient budgets (including POC) and the ocean biogeochemical cycle (Walsh, 1991; Devol et al.,

1991; Falkowski et al., 1994; Ludwig et al., 1996; Walling and Fang, 2003; McKee et al., 2004;

Muller-Karger et al., 2005). Understanding these fluxes allows for a better prediction of the

impact of human activities and the changing climate on such fluxes (Syvitski, 2003). Sediment flux estimates over the Amazon river/shelf are few. Models have been incorporated to assist with predicting the flux of sediments from rivers to the coastal ocean and offshore (e.g. Jewell et al.,

1993; Walling and Fang, 2003; Nikiema et al., 2007) to help fill the gap of information that exists and provide a means of predicting future changes in sediment (and to a certain extent) carbon discharge. However, these models still require calibration with observations. The instantaneous fluxes calculated in this study within the Amazon plume (Stations 8 and 9 and extrapolated landward) were 30% lower than those calculated by Nittrouter et al. (1986) for a period of peak discharge of the Amazon. Part of the difference observed between the two instantaneous flux measurements can be explained by the lower current velocities measured during February-March

2010, compared to currents reported by Nittrouer et al. (1986; our average of 0.50 m s -1 vs. their

1-2 m s -1). Nittrouer et al. (1986) point out the variations that exist when calculating fluxes over different time-scales. For example, their TSS fluxes, averaged over a period of one month, were significantly lower than their instantaneous fluxes (60 g s -1 vs. 300 g s -1). They attributed this to the likely underestimate of monthly-averaged velocities compared to instantaneous velocities:

0.12 m s -1 vs. 1-2 m s -1). The different (and variable) forcings to which the Amazon shelf is exposed to induce significant variability in the structure of the plume, which in turn leads to variations in the transport of riverborne sediments (Nittrouer et al., 1986; Geyer et al., 1991).

The extent of the impact of POM on coastal (and deeper ocean) nutrient budgets and biogeochemical cycles is subject to the rate of remineralization, which will depend on the quality

(fresh vs. refractory) and quantity (fluxes) of riverine POM discharged. Though Amazon River

POC contains a significantly portion of recalcitrant organic carbon (Hedges, 1992; Hedges and

Keil, 1999; Raymond and Bauer, 2001), the efficient remineralization that occurs on the Amazon shelf recycles up to ~70% of the terrestrial POC that enters the ocean (Aller et al., 1996;

DeMaster and Aller, 2001). The carbon excess that the Amazon provides, compared to N or P (as sees through the ratios of organic C to N and P, and by the magnitude of the fluxes), results in a

relative shortage of N and P, compared to C, for primary producers. DeMaster and Pope (1996) suggested that the Amazon shelf is not strongly phosphate limited, but rather that N is the limiting nutrient for phytoplankton growth. Indeed, a considerable amount of particulate P is transported by the river (seen in the BNL C/P and N/P ratios) and may be added to the water column through bacterial decomposition of riverborne POP (refer also to previous section; Berner and Rao, 1994).

While most river fluxes of carbon and nutrients do not have a significant impact on the global ocean, the magnitude of the Amazon River discharge not only alters the biogeochemical properties of the adjacent shelf, but the considerable northwestward fluxes of POC and POP through BNL can have an impact on the biogeochemistry of the Tropical North Atlantic

(Nittrouer et al., 1986; DeMaster and Aller, 2001; Dagg et al., 2004).

On wide shelves, most riverborne particulate material is trapped within the inner shelf and very little escapes to the deep ocean (Milliman and Syvitski, 1992; Brunskill, 2010). Organic matter deposited on such shelves and exposed to repeated resuspension/redeposition, as occurs on the Amazon shelf, is rapidly degraded (Burdige, 2007; Brunskill, 2010). Indeed, % POC in surface sediments across the Amazon Shelf was relatively low (0.05% - 0.82%; average of 0.73 ±

0.56 %; N = 5). These values are comparable to those reported by Showers and Angle (1986) and

Ruttenberg and Goñi (1997), who sampled the shelf area more extensively. Ruttenberg and Goñi

(1997) reported an overall mean of 0.64 ± 0.17 % (N = 6), with relatively low variations regardless of their sampling site. Showers and Angle (1986) also found a very uniform distribution of POC throughout the shelf, with an average of 0.66 ± 0.20 % (N = 22). Since the bottom sediments of the shelf are subject to constant resuspension, POC throughout the shelf should be uniform (Kuehl et al., 1986). Showers and Angle (1986) reported a single value higher than 1% over a carbonate shell hash to the northwest of the shelf and one value of 0.08% near the river mouth over sandy sediment. Our station 16 is roughly located at the same location where

Shower and Angle (1986) reported their lowest %POC value. %POC at station 16 was 0.05%;

this location is characterized by sub-arkosic sands that presumably were deposited during periods of lower sea level stand (Milliman et al., 1975a) and was identified by Kuehl et al. (1982) as one with lowest sediment accumulation rates. %POC for surface sediments was most elevated at station 4 (1.31%, closely following station 6 with 1.56%), and this location also had the highest

C/N ratio, suggesting a more C-rich sediment.

Overall, atomic C/N ratios of surface sediments were low for a river-dominated margin

(5.46-7.78, except at Station 4). Ruttenberg and Goñi (1997) suggested that the lower C/N ratios observed could be explained by moving away from the traditional two-end member model (i.e. marine and terrestrial) and including a third end-member enriched in nitrogen (for example bacteria) and/or a quicker remineralization rate of carbon as the sediments settle on the shelf.

The carbon isotopic composition of organic matter has been utilized to differentiate the origin of marine particulates (Hedges et al., 1997; Eglinton and Eglinton, 2008). For example, terrestrial organic matter derived from C3 plants has δ13 C values within the range of -26 ‰ and -

30 ‰, while marine phytoplankton has values between -19 ‰ and -22 ‰. C4 plants (e.g. tropical grasses) have a more enriched isotopic composition (around -12 ‰). Contrary to the patchy distribution of δ13 C observed in the BNL and SNL, a trend was visible in the δ13 C of surface sediments along the bottom on the shelf. While the RM transect exhibited a composition > -23

‰, the OS transect bore a distinct terrestrial signal of depleted organic carbon of < -26 ‰.

Shower and Angle (1986), Ruttenberg and Goñi (1997) and Druffel et al. (2005) reported lower isotopic values for surface sediments near the RM transect (between -26 ‰ and -24 ‰), while our δ13 C was ~2 ‰ higher ( P < 0.05). The observed isotopic composition for surficial sediments in the OS transect is typical of sediments dominated by a terrigenous source, while sediments in the RM transect suggest a mixed contribution from marine and terrestrial sources. This latter point is consistent with our observations of the Amazon Plume dynamic. The δ15 N values measured were higher than the ~3.4‰ reported by Medina et al. (2005) for areas close to the

Amazon River mouth, but comparable to δ15 N reported by the same authors for the Orinoco. Due to the high isotopic value of N (between 5.25‰ and 6.72‰) we cannot discard phytoplankton as an important source of 15 N for the shelf sediments (Medina et al., 2005).

These results paint a very coherent, and time-invariant, distribution of POC over the

Amazon shelf, although the extent of the Amazon plume may influence the source of the sedimentary organic matter on shorter time-scales than previously thought.

Summary and concluding remarks

Sampling conducted over the Amazon shelf during February-March 2010 at roughly the same locations sampled during the AmasSeds in 1990 study showed that the Amazon River plume was restricted to the inner shelf. This was likely due to the combined effect of onshore winds and lower seasonal river discharge (in part due to the presence of the ENSO). Though the overall annual discharge from the Amazon has not shown statistically significant changes since it was instrumented (Richey et al., 1989; Marengo et al., 2008), the record shows interannual variations induced by climatic phenomena with dryer periods, such as in 2010 coinciding with

ENSO and warm North Atlantic Ocean SST, and wetter years, such as 1989, with La Niña conditions (Marengo et al., 2010; 2012).

The impact of the Amazon plume on the shelf was lower than during the AmasSeds project, which took place 20 years ago during the same time of the year. The plume in both studies was located northwest of the river mouth. Oceanic waters over the mid-and outer shelf showed low nutrient, low chlorophyll, and uniform DOC concentrations (~73 µM). Within the plume, nutrient concentrations were near-zero which, coupled with the oxygen supersaturation, were indicative of biological activity. DOC concentrations within the plume (~116 µM) and current velocities (~0.5 m s -1) were used to calculate simplistic DOC export fluxes of 1.50 Tg y -1

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northwestward annually, which would represent ~6% of the total DOC transported by the

Amazon.

Suspended POC δ13 C found within the plume was dominated by a terrigenous source (-

24‰ – -28‰). Away from the influence of the river, suspended POC δ13 C showed a mixture of isotopic signals that indicated a patchy distribution between terrestrially-derived material and a material bearing a mixed contribution from marine and terrestrial sources. The predominant direction of transport of material, estimated through current measurements, was northwestward.

We estimated instantaneous transports of 38.73 metric tons s -1 of TSS, 0.24 metric tons s -1 of

POC, and 6.42 x 10 -3 metric tons s -1 of POP northwestward within BNL’s between 50 Km and

120 Km offshore (between the 10m and 50 isobaths). To our knowledge, these are the first horizontal POC and POP flux estimates for the Amazon shelf. The TSS estimates are 30% lower than those measured by Nittrouer et al. (1986) during high river discharge. Our results provide a contrast in sediment fluxes to earlier observations and show that fluxes depend on the magnitude of river discharge and shelf conditions.

POC Isotopic composition of surface sediments differed between the two transects, with more depleted δ13 C (~ -26‰) measured along the OS transect. The difference in δ13 C observed between transects may indicate a control on the provenance of the material by the river plume over short time-scales (i.e. weeks to months). %POC content of surface sediments on the shelf was strikingly uniform, consistent with the notion that bottom sediments of the shelf are subject to constant resuspension and reworking.

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102

EPILOGUE

Here we examined two tropical continental margins under different riverine influence: one dominated by small, mountainous rivers (the Cariaco Basin) and the second dominated by the largest river in the world in terms of freshwater discharge (the Amazon). In the Cariaco Basin we found that the small rivers lining the basin exerted a more pronounced effect during the rainy season than during the dry period. They discharged estimated annual fluxes of particulate organic carbon (POC) between 0.21-5.17 Gg y -1 and of dissolved organic carbon (DOC) between 0.93 –

8.32 Gg y -1 to the adjacent shelf. The influence of the rivers on the shelf was mainly controlled by the magnitude of the river discharge and was restricted to the coastal region. Permanent bottom nepheloid layers (BNL) extended from the mouth of most of the rivers offshore and served as the main conduit of sediment from the coast to the deeper basin year-round. In the Amazon shelf, the extent of the river plume on the shelf was mostly controlled by local wind and currents. During

February-March 2010, the influence of the plume was limited to within 120 Km from the coast; river discharge was ~10% lower than average, probably contributing to the narrow influence of the plume on the shelf. BNL on the Amazon Shelf was present only within the area under riverine influence. Within BNL, approximately 38.73 metric tons of suspended sediment per second and

0.24 metric tons of POC per second were estimated to be advected northwestward for the period of observation. Although the discharge of sediment and organic carbon to the ocean by the

Amazon River is several orders of magnitude higher than those of the small rivers emptying in the Cariaco Basin, the Amazon’s input of organic carbon to the deep ocean can be proportionally lower than that of the rivers in Cariaco. %POC in Cariaco’s BNL was always > 2%, while within the Amazon’s BNL it was < 1%.

The Amazon discharges on a passive continental margin and thus most of the sediment and organic carbon are deposited proximal to the river mouth and trapped on the shelf; only a relatively small portion of the suspended particulate matter escapes the shelf northwestward

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(Nittrouer et al., 1986; Milliman and Syvitski, 1992; Nittrouer et al., 1995). The small rivers draining into the Cariaco Basin, however, discharge on an active, narrow margin; sediments and organic carbon in this setting are more likely to escape the shelf and be transported to the deeper basin (Milliman and Syvitsky, 1992; Mulder and Syvitski, 1995, Goldsmith et al., 2008).

Episodic events, such as floods and earthquakes, also play an important role in the carbon and sediment sequestration in the Cariaco Basin, transporting up to a third (or more) of the average annual vertical sinking flux of sediment and POC that normally reaches the Cariaco Basin seafloor in single pulses (Thunell et al., 1999). Due to the magnitude of the Amazon, episodic flooding is muted and the annual sediment and carbon load are relatively constant and modulated by precipitation patterns (Hedges et al., 1986; Townsend-Small et al., 2005; Marengo et al., 2008;

Filizola and Guyot; 2009).

How will changes in climatic conditions affect the sediment and carbon fluxes in the Cariaco

Basin and Amazon shelf?

Climatic phenomena that control precipitation, and thus sediment and carbon fluxes, over the Amazon basin also affect climatic conditions in northern Venezuela. The El Niño Southern

Oscillation (ENSO) and high tropical North Atlantic (TNA) sea surface temperatures (SST) are the two mechanisms that have been more frequently invoked to explain interannual and long term variability observed in precipitation patterns over the Amazon and tropical South America

(Richey et al., 1989; Poveda et al., 2001; Nobre et al., 2009; Marengo et al., 2008; 2011; 2012 and references therein). Tropical South America exhibits negative anomalies in rainfall/river discharge during ENSO events; the opposite occurs during La Niña cold events (Poveda et al.,

2001). While over Amazonia the effects of the ENSO are observed shortly after its onset, the teleconnection over Venezuela manifests roughly 6 months after, during the boreal summer.

Trade Winds intensify which prevents deep convection and leads to drier conditions over northern South America. (Pulwarty et al., 1992; Giannini et al., 2001; Poveda et al., 2006).

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During the winter following ENSO, winds weaken and trigger TNA SST increases (Poveda et al.,

2006). The high TNA SST induce an anomalous northward displacement of the ITCZ and cause wetter conditions in the Caribbean and dry conditions in the south and western Amazon

(particularly severe during June-October) (Giannini et al., 2001; Poveda et al., 2006; Marengo et al., 2008; Zeng et al., 2008; Yoon and Zeng, 2010). The Caribbean coast of South America is also affected by the intermittent influence of the ‘Nortes’ (Lyon, 2003), extratropical cold fronts that move southward from North America into the tropics and have the potential to cause torrential rains.

2010 was the year with the highest SST anomaly in the TNA for the past 50 years (1.4

°C; April 2010; Figure 3.1, top). In the Amazon basin, 2010 was the worst drought to affect the region in the last decade, followed closely by the drought of 2005 (Marengo et al., 2011a; Xu et al., 2011). During 2010 the Cariaco Basin also exhibited weak upwelling during the dry season

(usually December-January through April); only one month had SST below 24°C (23.55 °C,

February) and production rates higher than 1 mg C m-2 d-1 (www.imars.marine.usf.edu/CAR/ ).

This reduced upwelling is consistent with the observations of a shift in the upwelling regime since 2004, which has induced progressive warming in surface waters (leading to water column stratification) and reduced overall primary production (Taylor et al., submitted). The warm temperatures in the TNA during 2010 induced a northward shift in the mean position of the ITCZ;

Marengo et al. (2011a) estimated that the mean position of the ITCZ was located ~5° northward between March-May 2010, driving precipitation away from central Amazonia and weakening

Trade Winds in the TNA. As a consequence of the 2009-2010 ENSO, precipitation remained higher than average in northern South America during November-December 2010 (beginning of the dry season) and induced flooding in northern Venezuela.

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Though the variation in TNA 2.0 SST appears to be part of decadal- 1.5 scale cycles and there is no apparent

C) 1.0 o trend in the warming (Figure 3.1, 0.5 bottom), it is possible that such 0.0 extremes become more frequent in -0.5 TNA SST Anomaly ( light of the changing climatological -1.0 conditions in tropical South America. -1.5

The IPCC report (2007) predicts more 1948 1952 1956 1960 1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008 2012 0.10 extreme events (including temperature 0.08 and precipitation) as a result of global 0.06

0.04 climate change. Changes in climate

C/year) 0.02 o conditions over tropical South 0.00

-0.02 America have already been noted by -0.04 10-year trend ( several authors. For example, Marengo -0.06 et al. (2011a) showed an increase in -0.08 -0.10 the length and intensity of the dry 1948 1952 1956 1960 1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008 2012 season in the Amazon Basin since 1950. Figure 3. 1: (top) Time -series of TNA SST anomalies. TNA Anomaly is calculated as the average of the monthly Taylor et al. (submitted) identified both SST from 5.5°N to 2 3.5°N and 15°W to 57.5°W minus the climatology. Climatology is 1951 -2000. a strengthening of the ITCZ and a http://www.esrl.noaa.gov/psd/data/climateindices/list/ northward migration, consistent with (bottom) 10 -year trend (centered) of the TNA SST climato logy. other studies that reported a shift in the position of the Atlantic ITCZ (Hastenrath and Greischar, 1993; Seidel and Randel, 2007).

How will changing climatological conditions affect the transport and delivery of sediments and organic carbon in the Cariaco Basin and the Amazon shelf? A weakening of the

Trade Winds is projected, with subsequent rainfall reductions in Amazonia and Northeast Brazil,

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as well as southern Venezuela. Rainfall increases are predicted for the northern coast of Peru,

Ecuador and in southern Brazil as a result of stronger convection (Marengo et al., 2009; 2010;

2011b). Precipitation is also expected to increase in northern South America/Southern Caribbean, along with an increase in SST, though there is a fair amount of discrepancy between models in this region (e.g. Angeles et al., 2007; Harris et al., 2008; Campbell et al., 2011). Drier climate in northern Amazon implies a lower contribution from tributaries located in the northern basin. The reduced discharge from northern tributaries may negatively impact the content of DOC in the

Amazon, as some of these rivers (e.g. Río Negro) carry high concentrations of DOC (Richey et al., 1980; 1990). An increase in precipitation in southern Brazil may lead to an increase in the load of particulate and dissolved matter derived from the Andes, which supply most of the solutes and sediments to the Amazon mainstem (Milliman et al., 1975a; Meade et al., 1985).

Weaker Trade Winds over northern South America will result in low upwelling conditions in the Cariaco Basin, and consequently low primary production (Astor et al., submitted; Taylor et al., submitted). This implies a reduction of marine-derived carbon flux from the surface to the deep basin, which also has an impact on the long-term sequestration of CO 2 from the atmosphere (Astor et al., 2005; Bates, 2007; LeQuere et al., 2009). Higher precipitation over northern South America does not imply more episodic flooding events, but it does suggest longer rainy seasons, which could increase the transport of sediment and terrestrially-derived organic matter into the basin. This would be analogous to very warm conditions observed in the paleoclimatic record (e.g. Holocene Thermal Maximum), where a more northerly position of the

ITCZ enhanced the transport of continental material into the basin (Peterson and Haug, 2006).

Continental margins play an important role in the global carbon cycle, accounting for more than 40% of the carbon sequestration in the ocean, and are sites of extensive organic matter burial (> 90% of total organic carbon; Hedges and Keil, 1995; Muller-Karger et al., 2005; Blair et al., 2004; Goñi et al., 2008). They also represent the connection between terrestrial and ocean environments. Changing climatic conditions may affect the delivery of continental organic carbon

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to the shelf, as well as the capacity of carbon burial/sequestration on temporal scales that are relevant in the context of climate change. In order to assess the impact of these changes it is critical to understand the connections between seasonal, interannual, and longer-term variability in the controls of sediment/carbon export and shelf biogeochemistry, especially in tropical regions. Regional and global biogeochemical models can provide a means to examine the linkages between sediment/carbon export in these areas and climate forcing, thus helping to predict how the global carbon cycle may be affected in the near future. It is important to note that the fluctuations observed in climatological conditions may be part of long-term climatic cycles.

For example, both the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation

(PDO) have been shown to have multi-decadal oscillations (Biondi et al., 2001; Gray et al., 2004; d'Orgeville and Peltier, 2007). Continuous sampling of riverine runoff and resulting fluxes to the ocean in these tropical regions are important to determine not only the impact of varying climatic conditions on the transport and delivery of riverine material to the ocean, but also whether the climatic drivers are part of such long-term cycles.

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REFERENCES

Agrawal, Y. 2004. Bottom nepheloid layer. Oceanography, 17 (2). Alberdi, M. and LaFargue, E. 1993. Vertical variations of organic matter content in Guayuta Group (upper Cretaceous), Interior Mountain Belt, Eastern Venezuela. Organic Geochemistry, 20 (4): 425–436. Alin, S. R., R. Aalto, M. A. Goni, J. E. Richey, and W. E. Dietrich. 2008. Biogeochemical characterization of carbon sources in the Strickland and Fly rivers, Papua New Guinea, Journal of Geophysical Research, 113, F01S05, doi:10.1029/2006JF000625 Alkhatib, M., T. C. Jennerjahn and J. Samiaji. 2007. Biogeochemistry of the Dumai River Estuary, Sumatra, Indonesia, a Tropical Black-Water River. Limnology and Oceanography 52 (6): 2410-2417. Aller, R.C., Blair, N.E., 2006. Carbon remineralization in the Amazon–Guianas tropical mobile mudbelt: a sedimentary incinerator. Continental Shelf Research 26 (17–18): 2241–2259. Aller, R.C., Blair, N.E., Xia, Q. and Rude, P.D. 1996. Remineralization rates, recycling, and storage of carbon in Amazon Shelf sediments. Continental Shelf Research 16,753–786. Altabet, M. A. and R. Francois. 1994. Sedimentary nitrogen isotopic ratio records surface ocean NO3 – utilization. Global Biogeochem. Cycles, 8: 103 - 116. Alvera-Azcárate, A., Barth, A., Weisberg, R., 2009. A nested model of the Cariaco Basin (Venezuela): description of the basin's interior hydrography and interactions with the open ocean. Ocean Dynamics, 59: 97-120. doi:10.1007/s10236-008-0169-y. Amon, R. M. and R. Benner, 1996. Bacterial utilization of different size classes of dissolved organic matter. Limnol. Oceanogr. 41: 41–51. Andressen, R. and R. Pulwarty. 2001. Análisis de las lluvias excepcionales causantes de la tragedia del Estado Vargas, Venezuela, en diciembre de 1999. IV Simposio Internacional de Desarrollo Sustentable en Los Andes. 25 noviembre – 2 diciembre, 2001. Mérida, Venezuela. Angeles, M. E., J. E. Gonzalez, D. J. Erickson III and J. L. Hernandez. 2007. Predictions of future climate change in the caribbean region using global general circulation models. Int. J. Climatol. 27: 555–569, Doi: 10.1002/joc.1416 Armstrong, R. A., C. Lee, J. I. Hedges, S. Honjo, and S. G. Wakeham. 2002. A new, mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of POC with ballast minerals, Deep-Sea Res., Part II, 49, 219– 236. Armstrong, R. A., M. L. Peterson, C. Lee and S. G. Wakeham. 2009. Settling velocity spectra and the ballast ratio hypothesis. Deep-Sea Research II, 56: 1470–1478. doi:10.1016/j.dsr2.2008.11.032 Arzola, RG; Wynn, RB; Lastras, G., D. G. Masson and P. P. E. Weaver. 2008. Sedimentary features and processes in the Nazare and Setubal submarine canyons, west Iberian margin. Marine Geology, 250 (1-2): 64-88. Astor, Y., J. Meri and F. Muller Karger. 1998. Variabilidad estacional hidrográfica en la Fosa de Cariaco. Mem. Soc. Cienc. Nat. La Salle, 63 (149): 61-72. Astor, Y.M., Lorenzoni, L., Thunell, R., Varela, R., Muller-Karger, F., Troccoli, L., Taylor, G.T., Scranton, M.I., Tappa, E., Rueda, D. Interannual variability in sea surface temperature and fCO 2 changes in the Cariaco Basin. Deep-Sea Research II, Submitted. Audemard, F. A., 2006. Surface rupture of the Cariaco July 09, 1997 Earthquake on the El Pilar fault, northeastern Venezuela. Tectonophysics 424, 19-39.

109

Audemard, F. A., 2007. Revised seismic history of El Pilar Fault, Northeastern Venezuela, after the Cariaco 1997 Earthquake and from recent preliminary paleoseismic results. Journal of Seismology 11, 311-326. Azetsu-Scott, K., B. D. Johnson and B. Petrie (1995). An intermittent, intermediate nepheloid layer in Emerald Basin, Scotian Shelf. Cont. Shelf Res. 15 (2–3) : 281–293. Bates, N.R. 2007. Interannual variability of the oceanic carbon dioxide sink in the subtropical gyre of the North Atlantic Ocean over the last two decades. Journal of Geophysical Research 112, C09013, http://dx.doi.org/10.1029/2006JC003759. Battin, T.J. 1998. Dissolved organic materials and its optical properties in a blackwater tributary of the upper Orinoco River, Venezuela. Org. Geochem. 28, 561– 569. Bauer, J.E., Druffel, E.R.M., 1998. Ocean margins as asignificant source of organic matter to the open ocean. Nature 392, 482–485 Behrenfeld M. J., Boss, E., 2003. The beam attenuation to chlorophyll ratio: an optical index of phytoplankton physiology in the surface ocean?. Deep Sea Research I 50, 1537–1549, doi:10.1016/j.dsr.2003.09.002 Benitez-Nelson, C., L. P. O'Neill, R. M. Styles, R. C. Thunell and Y. Astor. (2007) Inorganic and organic sinking particulate phosphorus fluxes across the oxic/anoxic water column of Cariaco Basin, Venezuela. Mar. Chem., 105: 90-100. Benner, R., B. Benitez-Nelson, K. Kaiser, and R. M. W. Amon. 2004. Export of young terrigenous dissolved organic carbon from rivers to the Arctic Ocean, Geophys. Res. Lett., 31, L05305, doi:10.1029/2003GL019251. Berner R. A., and Rao J.-L. 1994. Phosphorus in sediments of the Amazon River and estuary: Implications for the global flux of phosphorus to the sea. Geochimica et Cosmochimica Acta, 58 (10): 2333-2339. Berner, R. A. 1982. Burial of organic carbon and pyrite sulfur in the modern ocean: its geochemical and environmental significance. Amer. J. Sci., 282: 451–473. Bianchi, T.S., T. Filley, K. Dria, and P. Hatcher. 2004. Temporal variability in sources of dissolved organic carbon in the lower Mississippi River. Geochim. Cosmochim. Acta 68: 959-967. Biasutti, D. S., A. H. Sobel and Y. Kushnir. 2006. AGCM Precipitation Biases in the Tropical Atlantic. J. Climate, 19: 935-958. Biasutti, D. S., Battisti, and E. S. Sarachik, 2005. Terrestrial influence on the annual cycle of the Atlantic ITCZ. J. Climate, 18: 211–228. Biondi, F., A. Gershunov, and D. R. Cayan. 2001. North Pacific decadal variability since 1661, J. Clim., 14, 5–10. Black, D., M. A. Abahazi, R. C. Thunell, A. Kaplan, E. J. Tappa and L. C. Peterson. 2007. An 8- century tropical Atlantic SST record from the Cariaco Basin: Baseline variability, twentieth- century warming, and Atlantic hurricane frequency. Paleoceanography, 22, PA4204, doi: 10.1029/2007PA001427. Blair, N. E., E. L. Leitholda, R. C. Aller. 2004. From bedrock to burial: the evolution of particulate organic carbon across coupled watershed-continental margin systems. Marine Chemistry 92: 141– 156 doi:10.1016/j.marchem.2004.06.023 Boss, E., M.S. Twardowski and S. Herring. 2001. Shape of the particulate beam attenuation spectrum and its inversion to obtain the shape of the particulate size distribution. Appl. Optics, 40: 4885–4893. Bronk, D. A. 2002. Dynamics of dissolved organic nitrogen. In Biogeochemistry of Marine Dissolved Organic Matter. Hansell, D. A. and Carlson, C. A. Eds. Pp. 153-247. Brunskill, G. J. 2009. An Overview of Tropical Margins. In : K.-K. Liu et al. (eds.), Carbon and Nutrient Fluxes in Continental Margins, Global Change – The IGBP Series, 423. DOI 10.1007/978-3-540-92735-2 8

110

Burd, A. B. and G. A. Jackson. 2009. Particle Aggregation. Annual Review of Marine Science, Vol. 1: 65-90. DOI: 10.1146/annurev.marine.010908.163904 Burdige, D.J., 2005. Burial of terrestrial organic matter in marine sediments: A re-assessment. Global Biogeochemical Cycles, 19, GB4011, doi:10.1029/2004GB002368. Burdige, D.J., 2007. The preservation of organic matter in marine sediments: Controls, mechanisms and an imbalance in sediment organic carbon budgets? Chemical Reviews 107, 467-485. Campbell, J. D., M. A. Taylor, T. S. Stephenson, R. A. Watson and F. S. Whyte. 2011. Future climate of the Caribbean from a regional climate model. Int. J. Climatol. 31: 1866–1878; DOI: 10.1002/joc.2200 Canals, M., Puig, P., de Madron, X. D., Heussner, S., Palanques A., Fabres, J., 2006. Flushing submarine canyons. Nature, 444, doi:10.1038/nature05271 Caraballo, L. F., 1982. El Golfo de Cariaco, Parte I: Morfologia y batimetria sumbarina; estructuras y tectonismo reciente. Boletín del Instituto Oceanográfico de la Univerdisad de Oriente 21 (1-2), 13-35. Carey, A. E., C. B. Gardner, S. T. Goldsmith, W. B. Lyons and D. M. Hicks. 2005. Organic carbon yields from small, mountainous rivers, New Zealand Geophys. Res. Letters, 32, L15404, doi:10.1029/2005GL023159. Carrillo, E., Beck, C., Audemard, F. A., Moreno E., Ollarves, R., 2008. Disentangling Late Quaternary climatic and seismo-tectonic controls on Lake Mucubají sedimentation (Mérida Andes, Venezuela). Palaeogeography, Palaeoclimatology, Palaeoecology 259, 284-300. Castillo, M. M., J. D. Allan, R. L. Sinsabaugh and G. W. Kling. 2004. Seasonal and interannual variation of bacterial production in lowland rivers of the Orinoco basin. Freshwater Biology (2004) 49, 1400–1414 doi:10.1111/j.1365-2427.2004.01277.x Chronis, G., V. Lykousis, D. Georgopoulos, V. Zervakis, S. Stavrakakis and S. Poulos. (2000). Suspended particulate matter and nepheloid layers over the southern margin of the Cretan Sea (N.E. Mediterranean): seasonal distribution and dynamics. Progr. Oceanogr. 46 : 163–185 Cole J. J. and Caraco N. F. 2001. Carbon in catchments: Connecting terrestrial carbon losses with aquatic metabolism. Mar. Freshwater. Res. 52:101-110. Cooley, S.R. and P.L. Yager. 2006. Physical and biological contributions to the western tropical North Atlantic Ocean carbon sink formed by the Amazon River plume. Journal of Geophysical Research, 111, C08018, doi: 10.1029/2005JC002954. Curran, K.J., P.S. Hill and T.G. Milligan. 2002. Fine-grained suspended sediment dynamics in the Eel River flood plume. Cont. Shelf Res., 22, 2537–2550 Dadson, S. J., Hovius, N., Chen, H., Dade, W. B., Hsieh, M.-L., Willett, S. D. Hu, J.-C., Horng, M.-J., Chen, T.-C., Stark, C. P., Lague1, D., Lin, J.-C., 2003. Links between erosion, runoff variability and seismicity in the Taiwan orogen. Nature 426, 648-651. Dadson, S. J., Hovius, N., Chen, H., Dade, W. B., Lin, J.-C., Hsu, M.-L., Lin, C.-W., Horng, M.- J., Chen, T.-C., Milliman, J., Stark, C. P., 2004. Earthquake-triggered increase in sediment delivery from an active mountain belt. Geology 32 (8): 733-736; DOI: 10.1130/G20639.1 Dagg, M., R. Benner, S. E. Lohrenz, and D. Lawrence (2004), Transformation of dissolved and particulate materials on continental shelves influenced by large rivers: plume processes, Cont. Shelf Res., 24, 833–858. Davidson, E. A. de Araujo, A. C., Artaxo, P., Balch, J. K., Brown, I. F., Bustamante, M. M., Coe, M. T., DeFries, R. S., Keller, M., Longo, M., Munger, J. W., Schroeder, W., Soares-Filho, B. S., Souza, C. M. and Wofsy, S. C. 2012. The Amazon basin in transition. Nature, 481 (7381): 321-328. Doi: http://dx.doi.org/10.1038/nature10717. De La Rocha, C. and U. Passow. 2007. Factors influencing the sinking of POC and the efficiency of the biological carbon pump. Deep Sea Research II, 54: 639-658. doi:10.1016/j.dsr2.2007.01.004

111

Del Vecchio, R., and A. Subramaniam. 2004. Influence of the Amazon River on the surface optical properties of the Western Tropical North Atlantic Ocean, J. Geophys. Res., 109, C11001, doi:10.1029/2004JC002503. DeMaster, D.J., Aller, R.C., 2001. Biogeochemical processes on the Amazon shelf: changes to dissolved and particulate fluxes during river/ocean mixing. In : McClain, M.E., Richey, J.E. (Eds.), The Biogeochemistry of the Amazon Basin and its Role in a Changing World. Elsevier, Amsterdam, pp. 328–357. DeMaster, D.J., Pope, R. H., 1996. Nutrient dynamics in Amazon shelf waters: results from AMASSEDS. Cont. Shelf Res., 16: 263-289. DeMaster, D. J., S.A. Kuehl and C.A. Nittrouer. 1986. Effects of suspended sediments on geochemical processes near the mouth of the Amazon River: examination of biogenic silica uptake and the fate of particle-reactive elements. Cont. Shelf Res., 6. 107-125. DeMaster, D., Ragueneau, O. and Nittrouer, C. 1996. Preservation efficiencies and accumulation rates for biogenic silica and organic C, N, and P in high-latitude sediments: The Ross Sea. Journal of Geophysical Research 101(C8): doi: 10.1029/96JC01634. issn: 0148-0227 Depetris, P. and Paolini, J. (1990) Biogeochemical aspects of South American rivers: the Paraná and the Orinoco. In: Degens, E. T., Kempe, S. and Richey, J. (Eds) Biogeochemistry of Major World Rivers. SCOPE Report 42, John Wiley & Sons, pp.105-125. Devol, A. H., Forsberg, B. R., Richey, J. E. & Pimentel, T. P. (1995) Seasonal variation in chemical distributions in the Amazon (Solimões) River: a multiyear time series. Global Biogeochemical Cycles 9, 307–328. Devol, A. H., J. E. Richey, and B. F. Forsberg. 1991. Phosphorous in the Amazon River mainstem: Concentrations, forms and transport to the ocean. In: Phosphorous Cycles in Terrestrial and Aquatic Ecosystems, Regional Workshop 3: South and Central America. H. Tiessen, O. Lopez-Hernandez and I. H. Salcedo, Eds. pp. 9-23. SCOPE/Saskatchewan Inst. of Pedol., Saskatoon. Dickson, A.G., C. L. Sabine and J. R. Christian (Eds.) 2007. Guide to best practices for ocean CO 2 measurements. PICES Special Publication 3, 191 pp. Dickson, R.R., McCave, I.N. 1986. Nepheloid layers on the continental slope west of Porcupine Bank. Deep-Sea Res., 33: 791–818. d'Orgeville, M., and W. R. Peltier (2007), On the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation: Might they be related?, Geophys. Res. Lett., 34, L23705, doi:10.1029/2007GL031584. Druffel, E. R. M., J. E. Bauer, and S. Griffin. 2005. Input of particulate organic and dissolved inorganic carbon from the Amazon to the Atlantic Ocean, Geochem. Geophys. Geosyst., 6, Q03009, doi:10.1029/2004GC000842. Eberhart-Phillips, D., P. J. Haeussler, J. T. Freymueller, A. D. Frankel, C. M. Rubin, P. Craw, N. A. Ratchkovski, G. Anderson, G. A. Carver, A. J. Crone, T. E. Dawson, H. Fletcher, R. Hansen, E. L. Harp, R. A. Harris, D. P. Hill, S. Hreinsdo´ttir, R. W. Jibson, L. M. Jones, R. E. Kayen, D. K. Keefer, C. F. Larsen, S. C. Moran, S. F. Personius, G. Plafker, B. L. Sherrod, K. Sieh, N. Sitar, and W. K. Wallace. 2003. The 2002 Denali fault earthquake, Alaska: a large magnitude, slip partitioned event. Science, 300: 1113–1118. Ediger, D., Yilmaz, A. 1996. Characteristics of deep chlorophyll maximum in the North-eastern Mediterranean with respect to environmental conditions. Journal of Marine Systems, 9: 291-303. Edmond, J.M., E.A. Boyle, B. Grant and R.F. Stallard. 1981. The chemical mass balance in the Amazon plume: the nutrients. Deep-Sea Res., 28. 1339-1374. Eglinton, T. I. and G. Eglinton. 2008. Molecular proxies for paleoclimatology, Earth and Planetary Science Letters, 275 (1–2): 1-16. doi:10.1016/j.epsl.2008.07.012. Elmore, A. C., R. C. Thunell, R. Styles, D. Black, R. W. Murray, N. Martinez and Y. Astor. 2009. Quantifying the seasonal variations in fluvial and eolian sources of terrigenous material

112

to Cariaco Basin, Venezuela J. S. Am. Earth Sci., 27: 197–210. doi:10.1016/j.jsames.2008.11.002 Falkowski, P.G., Biscaye, P. E. and Sancetta, C. 1994. The lateral flux of biogenic particles from the eastern North American continental margin to the North Atlantic Ocean. Deep Sea Res. II, 41 (2–3): 583–601. Fekete, B., C. J. Vorosmarty, J. O. Roads and C. J. Willmott. 2003. Uncertainties in Precipitation and Their Impacts on Runoff Estimates. J. of Climate, 17: 294-104. Fenn, C. R. 1989. Quantifying the errors involved in transferring suspended sediment rating equations across ablation seasons. Ann. Glaciol., 13: 64-68. Fine, I.V., Rabinovich, A.B., Bornhold, B.D., Thomson, R.E. and Kulikov, E.A. 2005. The Grand Banks landslide-generated tsunami of November 18, 1929: preliminary analysis and numerical modeling. Marine Geology, 215 (1-2) 45-57. DOI: 10.1016/j.margeo.2004.11.007. Fischer, G., G. Karakas, M. Blaas, V. Ratmeyer, N. Nowald, R. Schlitzer, P. Helmke, R. Davenport, B. Donner, S. Neuer and G. Wefer. (2007). Mineral ballast and particle settling rates in the coastal upwelling system off NW Africa and the South Atlantic. Int. J. Earth Sci., DOI 10.1007/s00531-007-0234-7 Francois, R., S. Honjo, R. Krishfield, and S. Manganini. (2002). Factors controlling the flux of organic carbon to the bathypelagic zone of the ocean, Global Biogeochem. Cycles, 16(4), 1087, doi:10.1029/2001GB001722. FUNVISIS, 1994 Estudio Neotectónico y de Geología de Fallas Activas de la Región Nororiental de Venezuela. 3 Vols. Proyecto Intevep 92-175. Informe de FUNVISIS para Intevep S.A. FUNVISIS, 2008. http://www.funvisis.org.ve/ Gade, H. G., 1961. Informe sobre las condiciones hidrograficas en el Golfo de Cariaco, para el periodo que empieza en mayo y termina en noviembre de 1960. Boletín del Instituto Oceanográfico de la Univerdisad de Oriente 1 (1), 21-33. Garcia, H. E., R. A. Locarnini, T. P. Boyer, and J. I. Antonov. 2006. World Ocean Atlas 2005, Volume 3: Dissolved Oxygen, Apparent Oxygen Utilization, and Oxygen Saturation, Tech. rep., Ed. NOAA Atlas NESDIS 63, U.S. Government Printing Office, Silver Spring. Gardner, MD., W.D., Blakey, J.C., Walsh, I.D., Richardson, M.J., Pegau, S., Zaneveld, J.R.V., Roesler, C., Gregg, M.C., MacKinnon, J.A., Sosik, H.M. and Williams III, A.J. 2001. Optics, particles, stratification and storms on the New England continental shelf. Journal of Geophysical Research 106, 9473–9497. Gardner, W. D. 1989. Baltimore Canyon as a modern conduit of sediment to the deep sea. Deep- Sea Res., 36 (3): 323-358, 1989. Gardner, W. D., M.J. Richardson, K.R. Hinga and P.E. Biscaye. 1983. Resuspension measured with sediment traps in a high-energy environment. Earth Planet. Sci. Lett. 66: 262-278 Geyer W. R. and G. C. Kineke. 1995. Observations of currents and water properties in the Amazon frontal zone. Journal of Geophysical Research, 100,2321-2339. Geyer W. R., R. C. Beardsley, J. Candela, B. M. Castro, R. V. Legeckis, S. J. Lentz, R. Limeburner, L. B. Miranda and J. H. Trowbridge. 1991. The physical oceanography of the Amazon outflow. Oceanography. 4, 8-14. Geyer, W.R., Beardsley, R.C., Lentz, S.J., Candela, J., Limeburner, R., Johns, W.E., Castro, B.M., Soares, I.D., 1996. Physical oceanography of the Amazon shelf. Continental Shelf Research 16, 575–616. Giannini, A.; Chiang, J., Cane, M., Kushnir, Y. & Seager, R. (2001). The ENSO teleconnection to the tropical Atlantic Ocean: Contributions of the remote and local SSTs to rainfall variability in the tropical Americas. J. Climate, 14, 4530-4544.Gibbs, 1967 Gibbs R. J. 1970. Circulation in the Amazon River estuary and adjacent Atlantic Ocean. Journal of Marine Research, 28, 113-123. Gibbs R. J. 1982. Currents on the shelf of northeastern South America. Estuarine Coastal and Shelf Sciences, 14, 283-299

113

Gibbs R. J. 1972. Water chemistry of the Amazon River. Geochimica et Cosmochimica Acta, 36, 1061-1066. Goldfinger C. 2009. Subaqueous paleoseismology. In Paleoseismology, ed. JP McAlpin, vol. 95, pp. 119–70. Goldfinger, C. 2011. Submarine Paleoseismology Based on Turbidite Records. Annual Reviews of Marine Science, 3: 35–66 Goldfinger, C.; Nelson, C. H.; Johnson, J. E.; The Shipboard Scientific Party, 2003. Deep-water turbidites as Holocene earthquake proxies: the Cascadia subduction zone and Northern San Andreas Fault systems Ann. Geophys. 46(5): 1169-1194 Goldsmith, S. T., A. E. Carey, B. M. Johnson, S. A. Welch, W. B. Lyons, W. H. McDowell, and J. S. Pigott. 2010. Stream geochemistry, chemical weathering and CO2 consumption potential of andesitic terrains, Dominica. Geochimica et Cosmochimica Acta 74:85-103. Goldsmith, S., A. Carey, W. Berry Lyons, S-J Kao, T.-Y. Lee and J. Chen. 2008. Extreme storm events, landscape denudation, and carbon sequestration: Typhoon Mindulle, Choshui River, Taiwan. Geology, 36 (6): 483–486; doi: 10.1130/G24624A Goldsmith, S., Carey, A., Berry Lyons, W., Kao, S-J, Lee, T.-Y. and Chen, J. 2008. Extreme storm events, landscape denudation, and carbon sequestration: Typhoon Mindulle, Choshui River, Taiwan. Geology, 36 (6): 483–486; doi: 10.1130/G24624A Goñi, M. A., K. C. Ruttenberg and T. I. Eglinton (1997). Source and contribution of terrigenous organic carbon to surface sediments in the Gulf of Mexico . Nature, 389 (6648): 275–278. Goñi, M. A., N. Monacci, R. Gisewhite, J. Crockett, C. Nittrouer, A. Ogston, S.R. Alin and R. Aalto (2008). Terrigenous organic matter in sediments from the Fly River Delta (Papua New Guinea). J. Geophys. Res. 113: F01S10, doi:10.1029/2006JF00065. Goñi, M., N. Monacci, R. Gisewhite, A. Ogston, J. Crockett and C. Nittrouer (2006). Distribution and sources of particulate organic matter in the water column and sediments of the Fly River Delta, Gulf of Papua (Papua New Guinea). Estuarine, Coastal and Shelf Science (69): 225- 245 Goñi, M.A., H. Aceves, B. Benitez-Nelson, E. Tappa, R. Thunell, D. E. Black, F. Muller-Karger, Y. Astor and R. Varela (2009). Oceanographic and climatologic controls on the compositions and fluxes of biogenic materials in the water column and sediments of the Cariaco Basin over the Late Holocene. Deep-Sea Res. I, doi:10.1016/j.dsr.2008.11.010 González J, M. Schmitz, F. A. Audemard, R. Contreras, A. Mocquet, J. Delgado J and F. De Santis., 2004. Site effects of the 1997 Cariaco, Venezuela Earthquake. Engineering Geology 72 (1–2),143–177. Gorsline, D.S, T De Diego and E.H Nava-Sanchez. 2000. Seismically triggered turbidites in small margin basins: Alfonso Basin, Western Gulf of California and Santa Monica Basin, California Borderland. Sedimentary Geology, 135: 21-35. Gray, S. T., L. J. Graumlich, J. L. Betancourt, and G. T. Pederson (2004), A tree-ring based reconstruction of the Atlantic Multidecadal Oscillation since 1567 A.D., Geophys. Res. Lett., 31, L12205, doi:10.1029/ 2004GL019932. Hales, B., L. Karp-Boss, A. Perlin and P. A. Wheeler (2006) Oxygen production and carbon sequestration in an upwelling coastal margin. Global Biogeochem. Cycles, 20, GB3001, doi:10.1029/2005GB002517. Hansell, D., C. Carlson and Y. Suzuki. 2000. Dissolved organic carbon export with North Pacific Intermediate Water formation. Global Biogeochem. Cycles, 16 (1): 1007. Doi: 10.1029/2000GB00136. Hansell, D.A., Carlson, C.A., Repeta, D.J., Shlitzer, R., 2009. Dissolved organic matter in the ocean: new insights stimulated by a controversy. Oceanography 22(4): 202–211. http://dx.doi.org/10.5670/oceanog.2009.109 Hansell, D.A., D. Kadko and N. R. Bates. 2004. Degradation of Terrigenous Dissolved Organic Carbon in the Western Arctic Ocean. Science, 304: 858-861. DOI: 10.1126/science.1096175

114

Hastenrath S. and Greischar L. 1993. Circulation mechanisms related to northeast Brazil rainfall anomalies. J Geophys Res 98: 5093–5102 Hedges, J.I., Keil, R.G. and Benner, R. 1997. What happens to terrestrial organic matter in the ocean? Organic Geochemistry 27, 195–212. Hedges, J. I. and R. G. Keil, 1999. Organic geochemical perspectives on estuarine processes: sorption reactions and consequences. Mar. Chem., 65:55-65. Hedges, J.I., 1992. Global biogeochemical cycles: progress and problems. Mar. Chem. 39, 67–93. Hedges, J.I., Clark, W.A., Quay, P.D., Richey, J.E., Devol, A.H., Santos, U. de M. 1986. Compositions and fluxes of particulate organic material in the Amazon River. Limnol. Oceanogr. 31, 717– 738. Hedges, J.I., Cowie, G.L., Richey, J.E., Quay, P.D., 1994. Origins and processing of organic matter in the Amazon River as indicated by carbohydrates and amino acids. Limnol. Oceanogr. 39, 743–761. Hedges, J.I., Keil, R.G., 1995. Sedimentary organic matter preservation: an assessment and speculative synthesis. Mar. Chem. 49, 81– 115. Heezen, B.C., Ewing, M., 1952. Turbidity currents and submarine slumps, and the Grand Banks earthquake. Am. J. Sci. 250, 849–873 Hellweger, F. L., and A. L. Gordon. 2002. Tracing Amazon River water into the Caribbean Sea, J. Mar. Res., 60, 537–549, doi:10.1357/002224002762324202. Herrera, A. and D. Bone. 2011. Influence of riverine outputs on sandy beaches of Higuerote, central coast of Venezuela. Lat. Am. J. Aquat. Res., 39 (1): 56-70, DOI: 10.3856/vol39- issue1-fulltext-6 Herrera, L.E. and G. Febres-Ortega. 1975. Procesos de surgencia y de renovación de aguas en la Fosa de Cariaco, Mar Caribe. Bol. Inst. Oceanográfico Univ. de Oriente 14, 31–44. Herrera, L.E., G. Febres-Ortega and J. M. Andrés. 1980. Distribución de las masas de agua y sus vinculaciones dinámicas en el sector Centro-Occidental Venezolano, Mar Caribe. Bol. Inst. Oceanográfico Univ. de Oriente, 19, 93–118. Hickey, B.M., E. Baker and N.B. Kachel (1986). Suspended particle movement in and around Quinault Submarine Canyon. Mar. Geol. 71, 35–83. Hicks, D. M., Gomez, B. and Trustrum, N. A. 2004. Event suspended sediment characteristics and the generation of hyperpycnal plumes at river mouths: East coast continental margin, North Island, New Zealand, Journal of Geology, 112: 471– 485. Hilton, R. G.; Galy, A., Hovius, N., Horng, M-J., Chen, H., 2010. The isotopic composition of particulate organic carbon in mountain rivers of Taiwan. Geochimica et Cosmochimica Acta, 74: 3164-3181. Hilton, R. G.; Galy, A., Hovius, N., Horng, M-J., Chen, H., 2011. Effi cient transport of fossil organic carbon to the ocean by steep mountain rivers: An orogenic carbon sequestration mechanism. Geology, 39 (1); 71–74. doi: 10.1130/G31352.1. Hilton, R., Galy, A., Hovius, N., Chen, M-C., Horng, M-J., Chen, H., 2008. Tropical-cyclone- driven erosion of the terrestrial biosphere from mountains. Nature Geoscience 1, 759 – 762. doi:10.1038/ngeo333 Hu, C., E. T. Montgomery, R. W. Schmitt, and F. E. Muller-Karger. 2004. The dispersal of the Amazon and Orinoco River water in the tropical Atlantic and Caribbean Sea: Observation from space and S-PALACE floats, Deep Sea Res. Part II, 51, 1151–1171. Hughen, K. A., Overpeck, J. T., Peterson, L. C., Anderson R. F., 1996. The nature of varved sedimentation in the Cariaco Basin, Venezuela, and its paleoclimatic significance. In: Palaeoclimatology and palaeoceanography from Laminated Sediments. A. E. S. (ed.). Geological Society Special Publication No. 116. pp. 171-183. Hung, J.-J., C.-L. Chan and G.-C. Gong. (2007). Summer distribution and geochemical composition of suspended-particulate matter in the East China Sea. J. of Oceanography, 65: 189-202.

115

INIA-MARN. (2003) Establecimiento del equilibrio ecológico en las lagunas de Píritu y Unare: Comportamiento Hidráulico. Online document: http://es.mayeticvillage.com/QuickPlace/unare2/Main.nsf/h_Index/0A0DD2E94438EA90C12 56E650082FF99/?OpenDocument Inman, D.L. and S.A. Jenkins. (1999). Climatic change and the episodicity of sediment flux of small California rivers. J. of Geol. 107: 251-270. Intecmar, 2000. Línea de base ambiental del sistema Higuerote Carenero. Intecmar-USB. Inthorn, M., V. Mohrholz and M. Zabelc. 2006. Nepheloid layer distribution in the Benguela upwelling area offshore Namibia. Deep-Sea Res. I, 53: 1423–1438. IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp. Ittekkot, V. 2010. The Tropical Brazilian Continental Margin. In : Carbon and Nutrient Fluxes in Continental Margins: A Global Synthesis. JGOFS Continental Margins Task Team (CMTT). Editors: Kon-Kee Liu, Larry Atkinson, Renato Quinones, Liana Talaue-McManus. Springer- Verlag, Berlin/Heidelberg. Ittekkot.V. and Laane,R.W.P.M. 1991. Fate of riverine paniculate organic matter. In: Degens.E.T., Kempe.S. and RicheyJ.E. (eds)/ Biogeochemistry of Major World Rivers. John Wiley and Sons, Ltd. Chichester, pp. 233-243 Ittekot, V. 1993. The abiotically driven biological pump in the ocean and short term fluctuations in atmospheric CO 2 contents, Global Planet. Change, 8: 17– 25. Jaffe, R., I. Leal, J. Alvarado, P. Gardinali and J. Sericano. 1995. Pollution Effects of the Tuy River on the Central Venezuelan Coast: Anthropogenic Organic Compounds and Heavy Metals in Tivela mactroidea . Marine Pollution Bulletin, Vol. 30 (12): 820-825. Jennerjahn, T.C., B. Knoppers, W.F.L. de Souza, C.E.V. Carvalho, G. Mollenhauer, M. Hübner & V. Ittekkot. 2010. Factors controlling the production and accumulation of organic matter along the Brazilian continental margin between the equator and 22°S. In Carbon and Nutrient Fluxes in Continental Margins: A Global Synthesis. K.K. Liu, R. Quinones, L. Talaue- Mcmanus and L. Atkinson eds. CMTT/IGBP, Springer Publishing Company, New York, 427-442. Jewell P. W., R. F. Stallard and G. L. Mellor. 1993. Numerical studies of bottom shear stress and sediment distribution on the Amazon continental shelf. Journal of Sediment Petrology, 63,734-745. Johns, W.E., T.N Lee, R.C Beardsley, J Candela, R Limeburner and B Castro. 1998. Annual cycle and variability of the north brazil current. J. Phys. Oceanogr., 28: 103–128. Johnson, K. S., Paull, C. K., Barry, J. P. and Chavez, F. P. 2001. A decadal record of underflows from a coastal river into the deep sea. Geology, Vol. 29 (11): 1019–1022. Karp-Boss, L., P. A. Wheeler, B. Hales and P. Covert. 2004. Distributions and variability of particulate organic matter in a coastal upwelling system, J. Geophys. Res., 109, C09010, doi:10.1029/2003JC002184. Kineke, G.C., Woolfe, K.J., Kuehl, S.A., Milliman, J.D., Dellapenna, T.M. and Purdon, R.G. 2000. Sediment export from the Sepik River, Papua New Guinea: Evidence for a divergent sediment plume. Cont. Shelf Res. 20: 2239-2266. Klaas, C., and D. E. Archer (2002). Association of sinking organic matter with various types of mineral ballast in the deep sea: Implications for the rain ratio, Global Biogeochem. Cycles, 16 (4): 1116, doi:10.1029/2001GB001765. Kuehl, S.A., C.A. Nittrouer and D.J. DeMaster. 1982. Modern sediment accumulation and strata formation on the Amazon continental shelf. Marine Geology, 49: 279–300.

116

Kuehl, S.A., DeMaster, D.J., Nittrouer, C.A., 1986. Nature of sediment accumulation on the Amazon continental shelf. Continental Shelf Research 6, 209–225 Le Quere, C., Raupach, M. R., Canadell, J. G., Marland, G., Bopp, L. Ciais, P., Conway, T. J., Doney, S., Feely, R., Fester, P., Friedlingstein, P., Houghton, R. a., House, J., Huntingford, C., Levy, P., Lomas, M. R., Majkut, J., Metzl, N., Ometto, J., Peters, G. P., Prentice, I. C., Randerson, J. T., Rodenbeck, C., Running, S., Sarmiento, J., Schuster, U., Sitch, S., Takahashi, T., Vivoy, N., van der Werf, G. R., Woodward, F. I. 2009. Trends in the sources and sinks of carbon dioxide. Nature Geoscience 2: 831 – 836. Lehner B, Verdin K, and Jarvis A. 2008. New global hydrography derived from spaceborne elevation data. Eos Trans AGU 89: 93–94. Leithold , E.L., and Blair, N.E., 2001, Watershed control on the carbon loading of marine sedimentary particles: Geochimica et Cosmochimica Acta, v. 65, p.2231-2240. Lentz, S.J., Limeburner, R., 1995. The Amazon River plue during AmasSeds: spatial characteristics and salinity variables.Journal of Geophysical Research 100, 2355–2375. Lentz S. J. 1995. The Amazon River plume during AmasSeds: subtidal current variability and the importance of wind forcing. Journal of Geophysical Research, 100.2377-2390. Lentz, S.J. and J.H. Trowbridge. 1991. The bottom boundary layer over the northern California shelf. J. of Phys. Oceanogr., 21:1186–1201. Liu, J. P., Liu, C. S., Xu, K. H., Milliman, J. D., Chiu, J. K., Kao, J. K, Lin S. W. 2008. Flux and fate of small mountainous rivers derived sediments into the Taiwan Strait. Marine Geology 256: 65–76. doi:10.1016/j.margeo.2008.09.007 Liu, J. T. and Lin, H-L. 2004. Sediment dynamics in a submarine canyon: a case of river–sea interaction. Marine Geology, 207: 55–81, doi:10.1016/j.margeo.2004.03.015. Lopez-Veneroni, D. and L. A. Cifuentes. 1994. Transport of dissolved organic nitrogen in Mississippi River plume and Texas-Louisiana continental shelf near surface waters. Estuaries 17: 796–808. Lorenzoni, L., Muller-Karger, F., Varela, R., Montes, E., Taylor, G. T., Guzman, L. and Astor, Y. Evaluating the relevance of the CARIACO Ocean Time-Series station in measuring changing conditions in the Cariaco Basin and southeastern Caribbean Sea. Deep-Sea Research II, Submitted. Lorenzoni, L., C. Benitez-Nelson, R. C. Thunell, D. Hollander, R. Varela, Y. Astor and F. E. Muller-Karger. 2012a. Potential role of event-driven sediment transport on sediment accumulation in the Cariaco Basin, Venezuela, Mar. Geol. doi:10.1016/j.margeo.2011.12.009 Lorenzoni, L., Thunell, R. C., Benitez-Nelson, C., Hollander, D., Martinez, N., Tappa, E., Varela, R., Astor, Y., Muller-Karger F. E., 2009. The importance of subsurface nepheloid layers in transport and delivery of sediments to the Eastern Cariaco Basin, Venezuela. Deep-Sea Research I 56, 2249–2262. Ludwig, W., Probst, J.-L., and Kempe, S. 1996. Predicting the oceanic input of organic carbon by continental erosion: Global Biogeochemical Cycles, 10: 23–41. Lyon, B. 2003. Enhanced seasonal rainfall in Northern Venezuela and the extreme events of December 1999. J. of Climate, 16:2302-2306. Lyons, W. B., Goldsmith, S. T., Carey, A. E., McElwee, G. T. and Harmon, R. S. 2008. Dissovled organic carbon in small rivers, Panama. Ocean Sciences meeting, Orlando, Fl. March 2-7. Lyons, W.B., C.A. Nezat, A.E. Carey and D.M. Hicks. 2002. Organic carbon fluxes to the ocean from high-standing islands. Geology, 30 (5): 443-446. Marengo JA, Nobre CA, Tomasella J, Oyama M, Sampaio G, Camargo H, Alves LM. 2008. The drought of Amazonia in 2005. J Clim 21:495–516 Marengo JA, Tomasella J, Alves LM, SoaresWR, Rodriguez DA. 2011a. The drought of 2010 in the context of historical droughts in the Amazon region. Geophys Res Lett. doi:10.1029/2011GL047436

117

Marengo, J. A., C. A. Nobre, G. Sampaio, L. F. Salazar, and L. S. Borma. 2011b. Climate change in the Amazon Basin: Tipping points, changes in extremes, and impacts on natural and human systems. In : Tropical Rainforest Responses to Climatic Change, M. B. Bush, J. R. Flenley, and W. D. Gosling (Eds.), 2 nd . Edition, Springer-Verlag Berlin Heidelberg. Pp. 259- 283. Marengo, J. A. and Nobre, C. A. 2001. The hydroclimatological framework in Amazonia. In : J. Richey, M. McClaine, and R. Victoria (Eds.), Biogeochemistry of Amazonia, pp. 17–42. John Wiley & Sons, New York. Marengo J. A., Jones, R., Alves, L. M., and Valverde, M. 2009. Future change of temperature and precipitation extremes in South America as derived from the PRECIS regional climate modeling system. Int. J. Climatol., 30, 1–15. Marengo, J. A. 2006. On the hydrological cycle of the Amazon Basin: A historical review and current state of the art. Revista Brasileira de Meteorologia, 21, 1–19. Marengo, J. A., J. Tomasella, and C. Uvo, 1998: Trends in streamflow and rainfall in tropical South America: Amazonia, eastern Brazil, and northwestern Peru. J. Geophys. Res., 103, 1775–1784. Marengo, J. A., J. Tomasella, W. R. Soares, L. M. Alves and C. A. Nobre. 2012. Extreme climatic events in the Amazon basin: Climatological and hydrological context of recent floods. Theor Appl Climatol, 107:73–85. DOI 10.1007/s00704-011-0465-1 MARNR, 1983. Venezuela en Mapas. Departamento de Cartografia Temática, División de Mapas, Caracas, Venezuela. Márquez, A. Senior, W. Martínez, G. and Castañeda, J. 2002. Enviromental conditions of the waters of the Manzanares River, Cumaná-Sucre, Venezuela. Boletin Instituto Oceaografico de Venezuela. Universidad de Oriente. 41 (1 and 2): 15-24. Martinez, G. and W. Senior. 2001. Especiación de metales pesados (Cd, Zn, Cu y Cr) en el material en suspensión de la pluma del Rio Manzanares, Venezuela. Interciencia, 26 (2): 53- 61 Martínez et al., 2001 Martinez, N. C., R.W. Murray, R.C. Thunell, L.C. Peterson, F. Muller-Karger, L. Lorenzoni, Y. Astor and R. Varela. 2010. Local and regional geochemical signatures of surface sediments from the Cariaco Basin and Orinoco Delta, Venezuela. Geology, 38 (2): 159–162. doi: 10.1130/G30487.1. Martinez, N. C., R.W. Murray, R. C. Thunell, L. C. Peterson, F. Muller-Karger, Y. Astor and R. Varela. (2007) Modern climate forcing of terrigenous deposition in the tropics (Cariaco Basin, Venezuela). Earth and Planetary Science Letters, 264: 438-451. Martínez-Mena, M., J. López, M. Almagro, J. Albaladejo, V. Castillo, R. Ortiz and C. Boix- Fayos. 2011. Organic carbon enrichment in sediments: Effects of rainfall characteristics under different land uses in a Mediterranean area. CATENA, 94: 36-42. http://dx.doi.org/10.1016/j.catena.2011.02.005 , Masiello, C.A., and E. R. M. Druffel (2001), The isotope geochemistry of the Santa Clara River, Global Biogeochemical Cycles, 15, 407-416.Masiello, C., 2007. Quick burial at sea. Nature 450, 360-361. McCave, I.N. and I.R. Hall. (2002). Turbidity of waters over the Northwest Iberian continental margin. Progr. Oceanogr 52 (2–4) : 299–313. McCave, I.N., I.R. Hall, A.N Antia, L. Chou, F. Dehairs, R.S. Lampitt, L. Thomsen, T.C.E. van Weering and R. Wollast. (2001). Distribution, composition and flux of particulate material over the European margin at 47°50’N. Deep-Sea Res. II, 48: 3107–3139. McClain, M.E., Richey, J.E. and Victoria, R.L. 1995. Andean contributions to the biogeochemistry of the Amazon river system. Bulletin de l'Institut Francais d'Etudes Andines 24: 425-437 McDowell, W. H. and Asbury, C. E. 1994. Export of Carbon, Nitrogen, and Major Ions from three Tropical Montane Watersheds. Limnology and Oceanography, 39 (1): 111-125.

118

McKee, B.A., R.C. Aller, M.A. Allison, T.S. Bianchi, and G.C. Kineke. 2004. Transport and Transformation of Dissolved and Particulate Materials on Continental Margins Influenced by Major Rivers: Benthic Boundary Layer and Seabed Processes. Cont. Shelf Res. 24(7-8): 899- 926. McPhee-Shaw, E.E. 2006. Boundary–interior exchange: Reviewing the idea that internal-wave mixing enhances lateral dispersal near continental margins. Deep-Sea Res. II. 53: 42–59. McPhee-Shaw, E.E., R.W. Sternberg, B. Mullenbach and A.S. Ogston. (2004). Observations of intermediate nepheloid layers on the northern California continental margin. Cont. Shelf Res. 24 (6) : 693–720. Meade, R. H., C.F. Nordin, W.R. Curtiss, F.M. Rodriques, C.M. Dovale and J.M. Edmond. 1979. Sediment loads in the Amazon River. Nature, 278: 161–163. Meade, R. H., T. Dunne, J. E. Richey and U. De M. Santos. 1985. Storage and Remobilization of Suspended Sediment in the Lower Amazon River of Brazil. Science, Vol. 228 (4698): 488- 490. Meade, R.H., J.M. Rayol, S.C. Da Conceicao, J.R.G. Natividade, 1991. Backwater effects in the Amzon River basin of Brazil, Environmental and Geologic Water Sciences, (18):105–114. Medina E, Francisco M, Sternberg L, Anderson WT. 2005. Isotopic signatures of organic matter in sediments of the continental shelf facing the Orinoco Delta: possible contribution of organic carbon from savannas. Estuar. Coast Shelf Sci., 63:527–536 Meybeck, M. 1993. C, N, P, and S in rivers: From sourcesto global inputs. In : Interactions of C, N, P and S, Biogeochemical Cycles and Global Change. R. Wollast, F.T. Mackenzie, and L. Chou, Eds. 163-193, Springer-Verlag, New York. Meybeck, M. 1982. Carbon, nitrogen, and phosphorus transport by world rivers. Am. J. Sci., 282:401–450. Milliman, J. D. and K. M. Farnsworth. 2011. River Discharge to the Coastal Ocean: A Global Synthesis, Cambridge University Press, 392 p. Milliman, J. D., 1995. Sediment discharge to the ocean from small mountainous rivers: The new Guinea example. Geo-Marine Letters 15, 127-133. Milliman, J. D., and Kao, S. J. 2005. Hyperpycnal discharge of fluvial sediment to the ocean: impact of Super-Typhoon Herb (1996) on Taiwanese Rivers. Journal of Geology 113: 503– 516. Milliman, J. D., and Mei-e, R. 1995. River flux to the sea: Impact of human intervention on river systems and adjacent coastal areas. In D. Eisma, Climate change: Impact on coastal habitation (pp. 57-83). United States of America: Lewis Pub. Milliman, J. D.; Lin, S.; Kao, S. J.; Liu, J. P.; Liu, C. S.; Chiu, J. K.; and Lin, Y. C. 2007. Short- term changes in seafloor character due to flood-derived hyperpycnal discharge: Typhoon Mindulle, Taiwan, July 2004. Geology 35:779–782. Milliman, J., Summerhayes, C.P., Barretto, H.T., 1975b. Quaternary sedimentation on the Amazon continental margin; a model. Geological Society of America Bulletin 86 (5), 610– 614 Milliman, J.D., K.L. Farnsworth, P.D. Jones, K.H. Xu, L.C. Smith. 2008. Climatic and anthropogenic factors affecting river discharge to the global ocean, 1951–2000. Global and Planetary Change 62 (2008) 187–194. doi:10.1016/j.gloplacha.2008.03.001 Milliman, J.D., K.M. Farnsworth and C. Albertin. 1999. Flux and fate of fluvial sediments leaving large islands in the East Indies. J. Sea Res., 41, 97-107. Milliman, J.D., Summerhayes, C.P., Barretto, H.T., 1975a. Oceanography and suspended matter off the Amazon River, February–March 1973. Journal of Sedimentary Petrology 45 (1), 189– 206. Milliman, J.D., Syvitski, J.P.M., 1992. Geomorphic/tectonic control of sediment discharge to the ocean: The importance of small mountainous rivers. Journal of Geology 100, 525–544. Ministerio del Poder Popular para el Ambiente (MINAMB). http://www.minamb.gob.ve/

119

Mogollón, J.L., Ramirez, A.J. and Bifano, C., 1995. Influence of Sampling Strategy, Lithology, Vegetation and Rainfall on Metal Background Concentrations in Sediment of the Tropical Tuy River Basin, Venezuela. Chem. Geol., 121(1-4): 263-272. Mogollón, T., H. Freintzein and C. Bifano. 1987.Contaminación en sedimentos de la Cuenca del ríoTuy y controles geoquímicos que actúan en elsistema. Acta. Cient. Vzla. 38:47-58. Mook, W.G. and Tan, F.C., 1991. Stable carbon isotopes in rivers and estuaries. In : Biogeochemistry of Major World Rivers (E.T.Degens, S.Kemoe and J.E.Richey, eds.). SCOPE Volume, John Wiley & Sons, London, New York: 245-264. Mora, C., Lopez, M., Okuda, T., 1968. Algunas observaciones hidrograficas en la costa de Cumaná. Boletín del Instituto Oceanográfico de la Univerdisad de Oriente 6 (2), 303-327. Morales, P. R. and Ottmann, F. 1961. Primer estudio topográfico y geológico del Golfo de Cariaco. Bol. Inst. Oceanogr. Univ. Oriente, 1 (1):5-20. Morelli, G. S., E. M. L.deM. Novo and M. Kampel. 2010. Space-time variability of the Amazon River plume based on satellite ocean color. Cont. Shelf. Res., 30: 342–352. doi:10.1016/j.csr.2009.11.015 Morelock, J., 1982. Marine geology of the Gulf of Cariaco. Acta Científica Venezolana 33, 226- 234. Morelock, J., Maloney, N.J., Bryant, W. R., 1972. Manzanares submarine canyon. Acta Científica Venezolana 23, 143-147. Mulder, T. and Syvitski, J. P.M. (1995). Turbidity currents generated at river mouths during exceptional discharges to the world oceans. J. Geol. 103:285–299. Mulder, T., J. P.M. Syvitski, S. Migeon, J-C. Faugeres, B. Savoye. 2003. Marine hyperpycnal flows: initiation, behavior and related deposits. A review. Marine and Petroleum Geology 20 (2003) 861–882. doi:10.1016/j.marpetgeo.2003.01.003 Mulder, T., Migeon, S., Savoye, B., & Jouanneau, J.-M. (2001). Twentieth century floods recorded in the deep Mediterranean sediments. Geology, (11), 1011–1014. Mulder, T., Savoye, B., Piper, D. J. W., & Syvitski, J. P. M. (1998). The Var submarine sedimentary system: understanding Holocene sediment delivery processes and their importance to the geological record. In: M. S. Stocker, D. Evans, & A. Cramp (Eds.), Geological processes on continental margins: sedimentation, mass-wasting and stability (pp. 145–166). Geological Society of London, Special Publication 129. Mullenbach, B. L. and Nittrouer, C. A. 2000. Rapid deposition of fuvial sediment in the Eel Canyon, northern California. Continental Shelf Research 20: 2191-2212. Muller-Karger et al., 2005 Muller-Karger, F. E., C. R. McClain, and P. L. Richardson. 1988. The dispersal of the Amazon's water. Nature, 333: 56-59. Muller-Karger, F. E., P. L. Richardson, and D. McGillicuddy. 1995. On the offshore dispersal of the Amazon's Plume in the North Atlantic. Deep-Sea Research I, Vol. 42, No. 11/12, 2127- 2137. Muller-Karger, F. E., R. Varela, R. Thunell, M. Scranton, R. Bohrer, G. Taylor, J. Capelo, Y. Astor, E. Tappa, T. Y. Ho, and J. J. Walsh. 2001. Annual Cycle of Primary Production in the Cariaco Basin: Response to upwelling and implications for vertical export. J. of Geophys. Res. 106:C3. 4527-4542. Muller-Karger, F. E., R. Varela, R. Thunell, Y. Astor, H. Zhang, and C. Hu. (2004). Processes of Coastal Upwelling and Carbon Flux in the Cariaco Basin. Deep-Sea Research II. Special Issue: Views of Ocean Processes from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Mission: Volume 2 - Edited by D. A. Siegel, A. C. Thomas and J. Marra. Vol 51/10-11 pp 927-943. NCDC, http://www7.ncdc.noaa.gov/IPS/mcdw/mcdw.html

120

Neumann, G. 1969. Seasonal salinity variations in the upper strata of the western tropical Atlantic Ocean, I, Sea surface salinities, Deep Sea Res., 16(suppl.), 165-177. Newbold, J. D., B. W. Sweeney, J. K. Jackson, and L. A. Kaplan. 1995. Concentrations and export of solutes from 6 mountain streams in northwestern Costa Rica, J. N. Am. Benthol. Soc., 14: 21–37. Nikiema, O. J.-L. Devenon, M. Baklouti. 2007. Numerical modeling of the Amazon River plume. Continental Shelf Research, 27 (7): 873–899 Nittrouer, C.A. and DeMaster, D.J., 1996. The Amazon shelf setting: tropical, energetic, and influenced by a large river. Continental Shelf Research 16: 553–573. Nittrouer C. A., T. B. Curtin and D. J. DeMaster. 1986. Concentration and flux of suspended sediment on the Amazon continental shelf. Continental Shelf Research, 6: 161-174. Nittrouer C. A. and D. J. DeMaster. 1986. Sedimentary processes on the Amazon continental shelf: past, present and future research. Continental Shelf Research, 6: S-30. Nittrouer C. A. D. J. DeMaster, A. G. Figueiredo and J. M. Rinc (199l) AmasSeds: an interdisciplinary investigation of a complex coastal environment. Oceanography, 4: 3-7. Nittrouer, C.A., S.A. Kuehl, R.W. Sternberg, A.G. Figueiredo, and L.E.C. Faria. 1995. An introduction to the geological significance of sediment transport and accumulation on the Amazon continental shelf, Mar. Geol. 125, 177-192. Nobre, P., Malagutti, M., Urbano, D. F., de Almeida, R. A. F., and Giarolla, E.: Amazon Deforestation and Climate Change in a Coupled Model Simulation, J. Climate, 22, 5686– 5697, doi:10.1175/2009JCLI2757.1, 2009. Ogston, A.S., D.A Cacchione, R.W. Sternberg and G.C. Kineke. (2000). Observations of storm and river flood-driven sediment transport on the northern California continental shelf. Cont. Shelf Res., 20: 2141-2162. Oliveira, A., J. Vitorino, A. Rodrigues, J.M Jouanneau, J.A. Dias and O. Weber. (2002). Nepheloid layer dynamics in the northern Portuguese shelf. Progr. Oceanography, 52 (2–4): 195–213. Opsahl, S., Benner, R. 1997. Distribution and cycling of terrigenous dissolved organic matter in the ocean. Nature: 386, 480-482. Pak, H., J. R. V. Zaneveld, and J. Kitchen. 1980. Intermediate Nepheloid Layers Observed off Oregon and Washington. J. Geophys. Res ., 85(C11): 6697–6708. Palanques, A., Guillén, J., Puig, P., and Durrieu de Madron, X. 2008. Storm-driven shelf-to- canyon suspended sediment transport at the south- western end of the Gulf of Lions. Continental Shelf Research28: 1947–1956. Paolini, J. 1995. Organic Carbon and Nitrogen in the Orinoco River (Venezuela). Biogeochemistry, Vol. 29 (1): 59-70. Paull, C.K., Ussler, W., Greene, H.G., Keaten, R., Mitts, P., Barry, J., 2003. Caught in the act: the 20 December 2001 gravity flow event in Monterey Canyon. Geo-Marine Letters 22: 227– 232. Perlin, A., J. N. Moum, and J. M. Klymak (2005), Response of the bottom boundary layer over a sloping shelf to variations in alongshore wind, J. Geophys. Res., 110, C10S09, doi:10.1029/2004JC002500. Peters, K. E., R. E. Sweeney and I. R. Kaplan. 1978. Correlation of carbon and nitrogen stable isotope ratios in sedimentary organic matter. Limnol. Oceanogr., 23 (4): 598-604 Peterson, L. C., G.H. Haug. 2006. Variability in the mean latitude of the Atlantic Intertropical Convergence Zone as recorded by riverine input of sediments to the Cariaco Basin (Venezuela). Palaeogeography Palaeoclimatology Palaeoecology, 234(1):97-113. Peterson, L., G. Haug, K. Hughen and U. Rohl (2000). Rapid changes in the hydrologic cycle of the tropical Atlantic during the last glacial, Science 290, 1947-1951.

121

Pollard, P. C. and H. Ducklow. 2011. Ultrahigh bacterial production in a eutrophic subtropical Australian river: Does viral lysis short-circuit the microbial loop? Limnol. Oceanogr. 56(3): 1115–1129. doi:10.4319/lo.2011.56.3.1115 Poveda, G., A. Jaramillo, M. M. Gil, N. Quiceno, and R. Mantilla. 2001. Seasonality in ENSO related precipitation, river discharges, soil moisture, and vegetation index (NDVI) in Colombia. Water Resources Research 37:2169-2178. Poveda, G., Waylen, P.R, Pulwarty, R.S. 2006. Annual and interannual variability of the present climate in northern South America and southern Mesoamerica. Palaeogeography Palaeoclimatology, Palaeoecology 234:3–27 Probyn, T. A., Mitchell-Innes, B. A., Searson, S. 1995. Primary productivity and nitrogen uptake in the subsurface chlorophyll maximum on the Eastern Angulhas Bank. Continental Shelf Research, 13 (15): 1903-1920. Puig, P. and A. Palanques. 1998. Nepheloid structure and hydrographic control on the Barcelona continental margin, northwestern Mediterranean. Mar. Geol. 149 (1–4): 39–54. Puig, P., Ogston, A.S., Mullenbach, B.L., Nittrouer, C.A. and Sternberg. R.W. 2003. Shelf-to- canyon sediment-transport processes on the Eel continental margin (northern California). Marine Geology, 193 (1-2): 129-149. Pulwarty, R.S., Barry, R.G., Riehl, H., 1992. Annual and seasonal patterns of rainfall variability over Venezuela. Erdkunde 46, 273–289. Ramírez, A., J. Mogollón, C. Bifano and C. Yanes. 1992. Water, dissolved solids and suspended sediment discharge to Venezuelan coastline. Evolution des littoraux de Guyane et de la zone Caraïbe méridionale pendant le Quaternaire (Colloques et séminaires); Institut français de recherche scientifique pour le développement en cooperation, ORSTOM, Paris, pp. 437-456. Raymond, P. and J. Bauer, 200. 2001. Inputs of organic 14 C from rivers to the North Atlantic Ocean. Nature, 409: 497–500 Recursos Hídricos de Venezuela. 2006. 1st. Ed. FUNDAMBIENTE/MINAMB. Sky Vision Publicidad, Caracas, Venezuela. Pp. 167. Richey, J.E., Victoria, R.I., Salati, E. and Forsberg, B.R. 1991. The biogeochemistry of a major river system: the Amazon case study. In: Biogeochemistry of Major World Rivers. Degens, E.T., Kempe, S., Richey, J.E. (Eds.). Wiley, New York, pp. 57–74. Richey, J. E., Meade, R. H., Salati, E., Devol, A. H., Nordin, C. F. and dos Santos, U. 1986. Water discharge and suspended sediment concentrations in the Amazon River. Water Resour. Res. 22(5), 756–764. Richey, J. E., J. T. Brock, R. J. Naiman, R. C. Wissmar and R. F. Stallard. 1980. Organic carbon: Oxidation and transport in the Amazon River. Science, 207: 1348-1351. Richey, J.E., Hedges, J.I., Devol, A.H., Quay, P.D., Victoria, R., Martinelli, L., Forsberg, B., 1990. Biogeochemistry of carbon in the Amazon River. Limnol. Oceanogr. 35, 352– 371. Rivero, C., N. Senesi, J. Paolini and V. D’Orazio. 1998. Characteristics of humic acids of some Venezuelan soils. Geoderma, Vol. 81 (3–4): 227–239. Rochelle-Newall, EJ and TR Fisher. 2002. An investigation into phytoplankton as a source of chromophoric dissolved organic matter. Marine Chemistry, 77: 7-21 Rodriguez, J. L. and D. I. Gonzales, 2001. Estudio ambiental de la cuenca del Río Unare y las lagunas de Unare y Piritu. Cuadernos CENAMB no. 5. Universidad Central de Venezuela. Caracas, Venezuela. Pp. 114. Ruttenberg K. C. and Goñi M. A. 1997. Phosphorous distributions, C:N:P ratios, and d13Coc in arctic, temperate, and tropical coastal sediments: tools for characterizing bulk sedimentary organic matter. Marine Geology 139, 123-145. Seidel, D. J., and W. J. Randel. 2007. Recent widening of the tropical belt: Evidence from tropopause observations. J. Geophys. Res., 112, D20113, doi:10.1029/2007JD008861 Sahl, L.E., W.J. Merrell, D.W. McGrail and J.A. Webb. (1987). Transport of mud on continental shelves; Evidence from the Texas shelf. Mar. Geology, 76 (1/2):33-43.

122

Salisbury, J., D. Vandemark, J. Campbell, C. Hunt, D. Wisser, N. Reul and B. Chapron. 2011. Spatial and temporal coherence between Amazon River discharge, salinity, and light absorption by colored organic carbon in western tropical Atlantic surface waters. J. of Geophys. Res., 116, C00H02. doi:10.1029/2011JC006989 Santos, M. L., C. Medeiros, K. Muniz, F. A. N. Feitosa, R. Schwamborn and S. J. Macêdo. 2008. Influence of the Amazon and Pará Rivers on Water Composition and Phytoplankton Biomass on the Adjacent Shelf. Journal of Coastal Research, 243: 585-593. Schlunz, B. and R. R. Schneider. 2000. Transport of terrestrial organic carbon to the oceans by rivers: re-estimating flux- and burial rates. Int Journ Earth Sciences, 88: 599–606. Schubert, C., 1982. Origin of Cariaco Basin, southern Caribbean Sea. Marine Geology 47, 345- 360. Senior, W. 1994. Diagnóstico ambiental del Río Manzanares. Depart. Oceangr. Inst. Oceanogr. Univ. Oriente. Pp. 33. Shirai, M., Omura, A., Wakabayashi, T., Uchida J., Ogami, T., 2010. Depositional age and triggering event of turbidites in the western Kumano Trough, central Japan during the last ca. 100 years. Marine Geology 271, 225–235 Showers, W.J., Angle, D.G., 1986. Stable isotopic characterization of organic carbon accumulation on the Amazon continental shelf. Continental Shelf Research 6, 227–244. Siegel, D. A., Westberry, T.K., O'Brien, M. C., Nelson, N. B., Michaels, A.F., Morrison, J.R., Scott, A., Caporelli, E.A., Sorensen, J.C., Maritorena, S., Garver, S.A., Brody, E.A., Ubante, J., Hammer, M.A. 2001. Bio-optical modeling of primary production on regional scales: the Bermuda BioOptics project. Deep Sea Research II, 48: 1865-1896 Smith, W.O., DeMaster, D. J. 1996. Phytoplankton biomass and productivity in the Amazon River plume: Correlation with seasonal river discharge. Continental Shelf Research 16, 291– 319. Smoak, J.M. 2010. Carbon, Nitrogen, and Phosphorus Mass Balance for the Amazon Continental Shelf. In: Carbon and Nutrient Fluxes in Continental Margins: A Global Synthesis, eds. K- K. Liu, L. Atkinson, R. Quinones and L. Talaue-McManus, Springer-Verlag, Berlin. Pp. 443- 449. Spencer, R. G., P. J. Hernes, R. Ruf, A. Baker, R. Y. Dyda, A. Stubbins and J. Six. 2010. Temporal controls on dissolved organic matter and lignin biogeochemistry in a pristine tropical river, Democratic Republic of Congo. J. of Geophys. Res., 115, 12 p. G03013, doi:10.1029/2009JG001180 Spitzy, A. and Leenheer, J. 1990 Dissolved organic carbon in rivers. In : Biogeochemistry of Major World Rivers. Degens, E. T., Kempe, S. and Richey, J. (Eds) SCOPE Report 42, John Wiley & Sons, Chichester, pp. 213-232. St-Onge, G., Mulder, T., Piper, D.J.W., Hillaire-Marcel, C., and Stoner, J.S. 2004. Earthquake and flood-induced turbidites in the Saguenay Fjord (Québec): a Holocene paleoseismicity record: Quaternary Science Reviews, 23: 283-294. Suzuki, T. 2011. Seasonal variation of the ITCZ and its characteristics over central Africa. Theor Appl. Climatol, 103: 39–60. DOI 10.1007/s00704-010-0276-9 Syvitski, J., C. Vorosmarty, A. J. Kettner and P. Green. 2005. Impact of Humans on the Flux of Terrestrial Sediment to the Global coastal ocean. Science, 308: 376-980. DOI: 10.1126/science.1109454. Syvitski, J.P.M., Milliman, J.D., 2007. Geology, geography, and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean: Journal of Geology 115, 1–19. doi: 10.1086/509246. Syvitski, J.P.M., Morehead, M.D., Bahr, D., and Mulder, T., 2000. Estimating fluvial sediment transport: the Rating Parameters. Water Resource Research 36: 2747-2760.

123

Taylor, G. T., F. Muller-Karger, R. C. Thunell, M. I. Scranton, Y. Astor, R. Varela, L. Troccoli Ghinaglia, L. Lorenzoni, K. A. Fanning, S. Hameed and O. Doherty. Ecosystem Responses in the Southern Caribbean Sea to Global Climate Change. PNAS, Submitted. Taylor, G. T., Scranton, M. I., Iabichella, M., Ho, T.-Y., Thunell, R. C., Varela, R., Muller- Karger, F. E., 2001 Chemoautotrophy in the redox transition zone of the Cariaco Basin: A significant source of mid-water organic carbon production. Limnology and Oceanography 46 (1), 148-163. Thunell, R. C., Sigman, D. M., Muller-Karger, F., Astor, Y., Varela, R., 2004. Nitrogen isotope dynamics of the Cariaco Basin, Venezuela. Global Biogeochemical Cycles, 18, GB3001, doi:10.1029/2003GB002185. Thunell, R. E. Tappa., R. Varela, M. Llano, Y. Astor, F. Muller-Karger, and R. Bohrer. 1999. Increased marine sediment suspension and fluxes following an earthquake. Nature 398, 233- 236. Thunell, R., C. Benitez-Nelson, R. Varela, Y. Astor and F. Müller-Karger. 2007. Particulate Organic Carbon Fluxes Along Upwelling-Dominated Continental Margins: Rates and Mechanisms. Global Biogeochem. Cycles, 21, GB1022, doi:10.1029/2006GB002793. Thunell, R., R. Varela, M. Llano, J. Collister, F. Muller-Karger, and R. Bohrer. 2000. Organic carbon flux in an anoxic water column: sediment trap results from the Cariaco Basin. Limnol. Oceanogr.. 45: 300-308. Tocco, R., M. Alberdi, A. Ruggiero and N. Jordan. 1994. Organic geochemistry of the Carapita Formation and terrestrial crude oils in the Maturin Subbasin, Eastern Venezuelan Basin. Organic Geochemistry, 21 (10/11): 1107-111. Tomasella J, Borma LS, Marengo JA, Rodriguez DA, Cuartas LA, Nobre CA, Prado MCR. 2010. The droughts of 1996 1997 and 2004 2005 in Amazonia: hydrological response in the river mainstem. Hydrol Processes. doi:10.1002/hyp.7889 Townsend-Small, A., M. E. McClain and J. A. Brandes. 2005. Contributions of carbon and nitrogen from the Andes Mountains to the Amazon River: Evidence from an elevational gradient of soils, plants, and river material. Limnology and Oceanography, 50(2), 672-685. Trowbridge, J.H., B. Butman and R. Limeburner. (1994). Characteristics of the near-bottom suspended sediment field over the continental shelf off northern California based on optical attenuation measurements during STRESS and SMILE. Cont. Shelf Res., 14 (10-11): 1257- 1272, Virmani, J. and R. Weisberg. 2009. Fish Affects on Ocean Current Observations in the Cariaco Basin J. of Geophys. Res., 114, C03028, doi:10.1029/2008JC004889. Walsh, J. J. 1991. Importance of continental margins in the marine biogeochemical cycling of carbon and nitrogen. Nature, 350: 53 – 55. doi:10.1038/350053a0 Walsh, J.J., D.A. Dieterle, F.E. Muller-Karger, R. Bohrer, W.P. Bissett, , R. Aparicio, R.J. Varela H.T. Hochman, C. Schiller , R. Diaz, R. Thunell, G.T. Taylor, M.I. Scranton, K.A. Fanning, and E.T. Pelzer. 1999. Simulation of carbon/nitrogen cycling during spring upwelling in the Cariaco Basin. J. Geophys. Res., 104 (C4):7807-7825. Walsh, J.P. and C.A. Nittrouer. 1999. Observations of sediment flux on the Eel continental slope, northern California. Mar. Geol. 154, 55–68 Warrick, J. A. and Milliman, J. D. 2003 Hyperpycnal sediment discharge from semi-arid Southern California rivers: implications for coastal sediment budgets. Geology 31:781–784. Werne, J.P., Hollander D.J., 2004 Balancing supply and demand: Controls on carbon isotope fractionation in the Cariaco Basin (Venezuela) Younger Dryas to Present. Marine Chemistry 92 (1-4), 275-293. Woodworth, M., Goñi, M., Tappa, E., Tedesco, K., Thunell, R., Astor, Y., Varela, R., Díaz, J. R., Muller-Karger, F., 2004. Oceanographic controls on the carbon isotopic composition of sinking particles from the Cariaco Basin. Deep-Sea Research I, 51: 1955-1974.

124

Xu, L., A. Samanta, M. H. Costa, S. Ganguly, R. R. Nemani, and R. B. Myneni. 2011. Widespread decline in greenness of Amazonian vegetation due to the 2010 drought. Geophys. Res. Lett., 38, L07402, doi:10.1029/2011GL046824. Xu, J. P., Swarzenski, P. W., Noble, M. and Li, A-C. 2010. Event-driven sediment flux in Hueneme and Mugu submarine canyons, southern California. Marine Geology, 269: 74–88. doi:10.1016/j.margeo.2009.12.007. Yoon, J-H., and N. Zeng. 2010. An Atlantic influence on Amazon rainfall. Clim Dyn (2010) 34:249–264 DOI 10.1007/s00382-009-0551-6 Yurkovskis, A. 2005. Seasonal benthic nepheloid layer in the Gulf of Riga, Baltic Sea: Sources, structure and geochemical interactions. Cont. Shelf Res., 25: 2182–2195 Zaneveld, J. R. V. 1973. Variation of optical sea water parameters with depth, in Optics of the Sea Interface and In-Water Transmission and Imagery, AGARD Lect. Ser., 61, 2.3-1–2.3-22. Zeng N, Yoon, J-H, Marengo, JA, Subramaniam, A, Nobre CA, Mariotti, A. and Neelin, D. 2008. Causes and impacts of the 2005 Amazon drought. Environ Res Lett 3: doi:10.1088/1748- 9326/3/1/014002 Zeng, N. 1999. Seasonal cycle and interannual variability in the Amazon hydrologic cycle J. Geophys. Res. 104: 9097–106 Zinck, A. 1977. Ríos de Venezuela. Cuadernos Lagoven, Caracas, 63 p.

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APPENDICES

Appendix 1: Supplementary figures.

ENSO December -February

ENSO June -August

Supp lementary Figure 1.1 : Cartoon of the effects of El Niño around the world (modified from http://www.ncdc.noaa.gov/paleo/ctl/images/warm.gif ).

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120

100 Barcelona Caracas 80 Corcovada Manzanares 60

-20

Precipitation rate (mm/month) Precipitation rate -40

-60

-80 Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Supp lementary Figure 1. 2: Average precipitation rate for the four meteorological stations utilized. Rate was derived as the slope of the precipitation.

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250 220 100 50 Corcovada 200 Cumana

200 180 80 40 160 /s) /s) 3 3 140 150 60 30 120

100 100 40 20 80 Precipitation (mm) Precipitation Precipitation (mm) Precipitation River discharge (m discharge River 60 (m discharge River

50 40 20 10

0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

140 100 140 140 Barcelona Caracas 120 120 120 80

100 100 100 /s) /s) 3 3

60 80 80 80

60 60 60 40 Precipitation (mm) Precipitation Precipitation (mm) Precipitation

40 (m discharge River 40 40 (m discharge River

20 20 20 20

0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Supp lementary Figure 1. 3: Annual average precipitation vs. annual average discharge for the four meteorological stations utilized. Pink denotes river discharge while blue corresponds to precipitation. Refer to text for details on years utilized to calculate averages.

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-2

-3

-4

-5 (m/s) u

-6 Average u 2008 -7 2009 2003 2006

-8 July May April June March August January October Feburary December November September Supp lementary Figure 1. 4: Zonal wind ( u) for the years of study. Black line represents average; error bars represent one standard deviation.

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0 0 0

100 50 Station 3 Station 5 20 Station 6

200 100 40 300

150 400 60 Depth (m) Depth Depth (m) Depth Depth (m) Depth

500 200 80

600 250

100 700 300 34.0 34.5 35.0 35.5 36.0 36.5 34.8 35.0 35.2 35.4 35.6 35.8 36.0 36.2 36.4 35.4 35.6 35.8 36.0 36.2

Salinity Salinity Salinity

0 0 0

5 20 10

10 40 20

15 Depth (m) Depth (m) Depth 60 30 (m) Depth 20

80 Station 7 40 25 Station 8 Station 9

100 50 30 35.2 35.4 35.6 35.8 36.0 36.2 26 28 30 32 34 36 38 22 24 26 28 30 32 34 36 38

Salinity Salinity Salinity

Supplementary figure 2. 1: Salinity profiles at stations over the OS Transect. Note the change in depth and salinity scales for stations on the shelf and closer to the river mouth. The profile at Station 4 is very similar to that of Station 3 and hence is not shown.

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Appendix 2: Monthly concentration of dissolved and particulate organic matter (DOC and TOC) in the four main rivers draining into the Cariaco Basin for the period September 2008-2009. Months when basin-wide sampling was carried out are highlighted in bold. Percentage of DOC is also indicated. nd: not determined Tuy Date DOC ( µM) TOC ( µM) % DOC Sep-08 312.40 316.28 98.77 Oct-08 n.d. 412.92 n.d. Nov-08 379.43 383.13 99.03 Dec -08 333.54 334.20 99.80 Jan -09 241.32 244.10 98.86 Feb-09 174.43 182.91 95.37 Mar-09 163.67 219.25 74.65 Apr-09 264.37 285.11 92.73 Jun-09 n.d. 255.42 n.d. Jul-09 275.69 355.10 77.64 Aug-09 n.d. 226.29 n.d. Sep-09 n.d. 403.77 n.d. Neverí Sep-08 172.85 186.30 92.78 Oct-08 168.81 169.79 99.42 Nov-08 174.71 195.49 89.37 Dec-08 118.80 126.50 93.91 Jan-09 172.06 182.82 94.12 Feb-09 148.41 138.82 106.91 Mar-09 154.36 190.35 81.09 Apr-09 195.81 203.89 96.04 Jun -09 n.d. 179.58 n.d. Jul -09 n.d. n.d. n.d. Aug-09 n.d. 319.79 n.d. Sep-09 205.02 207.94 98.60 Unare Sep -08 316.19 n.d. n.d. Oct-08 569.49 564.78 100.83 Nov-08 220.38 220.24 100.06 Dec-08 437.41 462.10 94.66 Jan-09 310.70 337.62 92.03 Feb-09 395.06 388.09 101.79 Mar-09 353.91 417.40 84.79 Apr-09 400.54 420.49 95.26 Jun-09 140.52 157.65 89.14 Jul -09 n.d. 351.85 n.d. Aug -09 n.d. n.d. n.d. Sep-09 250.77 244.19 102.70 Manzanares Sep -08 139.38 140.98 98.87 Oct -08 89.69 87.92 102.00 Nov-08 214.39 219.56 97.65 Dec-08 98.10 99.89 98.20 Jan-09 99.69 100.97 98.73 Feb-09 n.d. 130.35 n.d. Mar-09 85.85 84.92 101.10 Apr-09 92.26 89.57 103.01 Jun-09 107.94 119.57 90.27 Jul-09 n.d. n.d. n.d. Aug-09 81.26 87.12 93.28 Sep -09 n.d. 102.19 n.d.

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Appendix 3: Hydrographic conditions of the Cariaco Basin for the study period. Lat: Latitude (decimal degrees); Lon: Longitude (decimal degrees); Stn.: Station number; SST: sea surface temperature; SSS: sea surface salinity; DOC: Dissolved organic carbon; nd: not determined

COHRO: September CASEP2: September 2003 2006 SST DOC SST DOC Lat Lon Stn. (°C) SSS (µµµM) Lat Lon Stn. (°C) SSS (µµµM) 10.83 -64.37 0 28.51 36.78 n.d. 10.90 -64.23 1 27.91 36.66 83.53 10.66 -64.37 1 28.26 36.75 n.d. 10.68 -64.23 5 26.48 36.61 79.62 10.50 -64.37 2 27.94 36.73 n.d. 10.83 -64.37 6 27.37 36.64 86.03 10.33 -64.55 3 27.90 36.52 n.d. 10.67 -64.37 7 27.08 36.53 85.53 10.50 -64.55 4 28.14 36.72 n.d. 10.50 -64.37 8 26.99 36.54 77.20 10.66 -64.55 5 28.34 36.75 n.d. 10.48 -64.22 9 28.05 36.54 80.62 10.83 -64.55 6 28.50 36.76 n.d. 10.45 -64.27 16 28.48 36.61 72.95 10.83 -64.71 7 28.21 36.71 n.d. 10.42 -64.41 17 28.18 36.58 73.20 10.67 -64.72 8 28.18 36.73 n.d. 10.42 -64.55 18 28.46 36.47 73.12 10.50 -64.67 9 28.38 36.56 n.d. 10.50 -64.55 19 27.98 36.47 87.70 10.33 -64.71 10 27.67 36.56 n.d. 10.66 -64.55 20 28.51 36.48 77.53 10.33 -64.89 11 27.93 36.50 n.d. 10.83 -64.55 21 27.98 36.51 68.17 10.23 -64.88 12 28.07 36.57 n.d. 10.92 -64.55 22 27.58 36.53 70.74 10.15 -64.03 13 28.00 36.61 n.d. 10.92 -64.72 23 28.65 36.43 69.52 10.20 -64.80 14 27.52 36.02 n.d. 10.83 -64.72 24 28.60 36.38 71.52 10.28 -64.80 15 27.61 36.55 n.d. 10.67 -64.72 25 28.63 36.37 70.77 10.50 -64.88 16 27.66 36.60 n.d. 10.50 -64.72 26 27.99 36.47 68.10 10.67 -64.88 17 27.66 36.60 n.d. 10.33 -64.72 27 27.76 36.46 68.00 10.83 -64.88 18 27.85 36.66 n.d. 10.18 -64.78 32 27.88 36.24 71.20 10.67 -65.05 19 27.69 36.64 n.d. 10.28 -64.80 35 27.82 36.35 67.82 10.50 -65.05 20 27.61 36.63 n.d. 10.31 -65.10 37 28.16 36.47 70.12 10.42 -65.05 21 27.41 36.66 n.d. 10.40 -65.10 38 28.24 36.46 69.82 10.33 -65.05 22 27.87 36.62 n.d. 10.37 -64.83 39 28.13 36.45 76.37 10.23 -65.05 23 27.47 36.52 n.d. 10.50 -64.88 40 27.94 36.45 66.57 10.23 -65.22 24 27.61 36.56 n.d. 10.50 -65.05 41 28.13 36.45 73.01 10.33 -65.22 25 27.41 36.62 n.d. 10.66 -64.89 42 28.52 36.47 72.08 10.42 -65.22 26 27.33 36.65 n.d. 10.67 -65.05 43 28.31 36.46 72.97 10.33 -65.38 27 27.64 36.61 n.d. 10.83 -64.88 44 28.81 36.39 73.10 10.42 -65.38 28 27.34 36.64 n.d. 10.83 -65.05 45 29.08 36.46 71.75 10.50 -65.22 29 27.42 36.66 n.d. 11.00 -65.13 47 28.66 36.43 75.40 10.83 -65.05 30 27.73 36.64 n.d. 11.10 -65.02 48 29.21 36.44 71.43 11.00 -65.05 31 27.63 36.68 n.d. 11.00 -64.88 50 29.01 36.37 71.60 11.00 -64.88 32 27.72 36.67 n.d. 11.10 -64.78 52 28.80 36.45 74.96 11.00 -64.72 33 27.96 36.69 n.d. 11.13 -64.58 54 27.85 36.54 68.59 11.00 -64.55 34 28.34 36.85 n.d. 11.17 -64.38 56 27.79 36.65 73.19 10.45 -64.27 48 28.04 36.73 n.d. 11.16 -64.24 58 27.11 36.62 76.72 10.15 -65.12 49 27.53 36.55 n.d. 10.18 -65.08 60 28.21 36.46 70.80 10.16 -65.22 50 27.52 36.50 n.d.

10.41 -64.41 51 27.90 36.60 n.d.

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Appendix 3: Cont.

FOSA 1 & FOSA 2 September 2008 March 2009 SST DOC SST DOC Lat Lon Stn. (°C) SSS (µµµM) (°C) SSS (µµµM) 10.83 -64.37 1 29.75 36.37 66.66 24.25 36.71 73.22 10.67 -64.37 2 29.49 36.06 78.67 23.73 36.81 n.d 10.50 -64.37 3 28.85 36.29 77.33 23.19 36.80 74.45 10.45 -64.27 4 29.18 36.35 77.83 23.19 36.70 76.98 10.42 -64.41 5 29.14 36.32 77.16 22.67 36.85 68.70 10.38 -64.55 6 29.27 36.31 78.17 23.35 36.86 71.08 10.33 -64.72 7 28.89 36.28 75.69 23.64 36.86 69.94 10.20 -64.73 8 28.69 36.29 78.67 23.22 36.88 64.86 10.21 -64.85 9 28.63 36.20 81.00 23.81 36.88 71.84 10.50 -64.72 10 29.23 36.22 80.67 23.92 36.86 70.71 10.67 -64.71 11 28.99 36.29 73.64 24.55 36.87 68.35 10.67 -65.00 12 28.91 36.28 72.42 24.07 36.87 69.83 10.50 -65.00 13 29.06 36.24 78.33 24.50 36.91 68.67 10.30 -65.00 14 28.72 36.27 78.42 24.62 36.90 n.d 10.18 -65.08 15 28.38 36.38 77.25 25.53 36.94 69.72 10.15 -65.19 16 28.40 36.12 81.00 26.52 36.88 74.75 10.17 -65.32 17 28.89 36.37 75.37 26.39 36.79 70.80 10.31 -65.31 18 29.17 36.32 76.90 25.76 36.95 67.09 10.50 -65.32 19 29.23 36.14 81.47 25.12 36.92 67.24 10.66 -65.32 20 29.30 36.18 77.01 24.86 36.90 66.74 10.67 -65.65 21 29.05 36.09 76.86 25.46 36.76 67.17 10.50 -65.65 22 29.45 36.11 79.42 25.46 36.88 68.07 10.36 -65.66 23 29.20 36.26 73.64 25.40 37.01 71.92 10.23 -65.60 24 28.66 36.32 76.63 26.56 36.28 79.35 10.35 -65.87 25 28.20 36.29 75.22 25.52 36.53 85.00 10.42 -65.95 26 28.83 36.12 78.58 25.55 35.60 72.91 10.50 -66.00 27 28.57 35.63 84.08 25.20 36.74 70.44 10.50 -65.87 28 29.13 36.05 80.58 25.05 36.78 67.52 10.67 -65.90 29 29.17 35.55 78.75 25.23 36.91 67.09 10.67 -66.10 30 29.81 35.57 79.08 25.43 36.84 73.53 10.90 -65.90 31 29.17 35.70 78.28 25.64 36.93 68.43 10.83 -65.65 32 29.39 36.10 78.08 25.45 36.92 70.52 10.83 -65.32 33 29.33 36.16 72.91 24.81 36.91 67.60 10.85 -65.00 34 29.03 36.24 69.41 24.71 36.89 72.76 10.93 -64.73 35 28.96 36.40 69.45 24.69 36.89 72.80 11.17 -64.78 36 28.96 36.13 69.17 24.33 36.73 66.77

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