W&M ScholarWorks
Dissertations, Theses, and Masters Projects Theses, Dissertations, & Master Projects
2008
Controls on continental shelf stratigraphy: Waiapu River, New Zealand
Heidi M. Wadman College of William and Mary - Virginia Institute of Marine Science
Follow this and additional works at: https://scholarworks.wm.edu/etd
Part of the Geology Commons
Recommended Citation Wadman, Heidi M., "Controls on continental shelf stratigraphy: Waiapu River, New Zealand" (2008). Dissertations, Theses, and Masters Projects. Paper 1539616896. https://dx.doi.org/doi:10.25773/v5-c2b8-r329
This Dissertation is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. Controls on Continental Shelf Stratigraphy: Waiapu River, New Zealand
A Dissertation
Presented to
The Faculty of the School ofMarine Science
The College of William and Mary in Virginia
In Partial Fulfillment
of the Requirements for the Degree of
Doctor of Philosophy
by
Heidi M. Wadman
2008 APPROVAL SHEET
This dissertation is submitted in partial fulfillment of
the requirements for the degree of
Doctor of Philosophy
Approved by the Committee, August 2008
~ , ven 'A. Kue ·· .D. CL-r~ Carl T. Friedrichs, Ph.D. B on, h.D. University o Pennsylvania Philadelphia, Pennsylvania Wadman: Controls on Continental Shelf Stratigraphy TABLE OF CONTENTS Page ACKNOWLEDGMENTS ...... 5 ABSTRACT ...... 6 INTRODUCTION ...... 8 CHAPTER 1: Stratigraphic spatial variation on the inner shelf of a high-yield river, Waiapu River, New Zealand: Implications for fine-sediment dispersal and preservation Abstract ...... 15 Introduction ...... 16 Background ...... 18 Methods ...... 24 Results ...... 26 Discussion ...... 31 Conclusions ...... 42 Acknowledgements ...... 43 References ...... 44 List of Figures ...... 61 Figures ...... 66 CHAPTER 2: Black carbon chronostratigraphic evidence of deforestation preserved on the inner shelf of the Waiapu River, New Zealand Abstract ...... 81 Introduction ...... 83 Background ...... 87 Methods ...... 94 Results ...... 101 Discussion ...... 106 Conclusions ...... 116 Acknowledgements ...... 117 References ...... 118 List ofTables ...... 134 List ofFigures ...... 134 Tables ...... 138 Figures ...... 141 CHAPTER 3: Structural controls on preservation of Holocene shelf stratigraphy: Waiapu River, New Zealand Abstract ...... 152 Introduction ...... 154 Methods ...... 158 Results ...... 15 9 Discussion ...... 163 Conclusions ...... 171 3 Wadman: Controls on Continental Shelf Stratigraphy Acknowledgements ...... 172 References ...... 173 List ofFigures ...... 180 Figures ...... 181 CONCLUSIONS ...... 192 APPENDIX ...... 199 4 ACKNOWLEDGMENTS After nearly eight years as a student at VIMS, four as a Ph.D. student, attempting to list everyone who has helped me in completing my degree is a daunting task at best. To all of the faculty who have guided me- both in advising and teaching roles- I can only thallk them for constantly challenging me as a scientist, teaching me to look beyond the obvious, and to learn to support my ideas with confidence and sound science. Carl Friedrichs and Steve Kuehl advised me during my master's, and continued to offer advice and challenges during my PhD quest. Jim Bauer and Ben Horton taught me about the rigors of the carbon world, and the dangers inherent in the powerful 14C dating techniques. Liz Canuel donated time, effort, lab space, supplies, and a wealth of kind encouragement as I followed a tenuous lead into the ultimately amazing world ofblack carbon. Linda Shaffner, Courtney Harris, Iris Anderson, Mark Patterson, Mark Brush, Ken Moore and Jerome Maa all challenged me in the academic setting, ultimately helping to make me a bett~r scientist. Finally, to my Ph.D. advisor, Jesse McNinch. Jesse was a constant source of encouragement, well-meaning criticism, and advice, both personally and professionally. He taught me to always be well-prepared to defend any new idea, and to recognize not just "cool" science, but science that would advance the knowledge of the community as a whole. Finally, with his, as well as Steve and Carl's, caring, support, and patience during one of the most trying times of my life, I found I do have the inner strength to take on any challenge I may ever have to face. Jesse, when I most wanted to quit, you simply told me no (and I foolishly believed you had a say), and I am deeply grateful not just for your guidance but for your friendship. In tackling this work, I have made some amazing friends on the other side of the world, in particular Bernard Cranswick, Tui Warmenhoven, Dave Peacock, Nicola Litchfield, Hannah Brackley, Lisa Northcote, Alan Orpin, Lionel Carter and too many others to name. In the day-to-day challenge ofbeing a student, Cindy Hornsby, Cynthia Harris, Fonda Powell, Louise Lawson and Paulette Lewis all managed to keep me paid and up-to-date on the essential, often bewildering paperwork. A special thanks is extended to Sue Presson, who was constantly either fixing my registration, or registering for me, as well as hunting down all of the forms I constantly mislaid. Sue, VIMS won't know what it is losing when you retire until it is too late. I am eternally grateful I was able to finish with you. I have been blessed by having not orily many wonderful acquaintances at VIMS, but also several wonderful friends. Bob Gammisch and Wayne Reisner have been two of the most outstanding and constant friends and colleagues I could have ever hoped to work with. To "the boys": here's hoping a lifetime more of friendship. Beth Waterson Lerberg, Linda Meneghini and Dave Perkey were beyond patient and kind in the lab, as well as a great deal of fun out of it. While I have too many VIMS friends to list them all, I do want to extend a special thanks to Kelly Johnson, Lisa Addington, Lila Gerald, Grace Browder, Jennifer Miselis, Jim Gartland, Kate Brodie, Katie Farnsworth, Tara Kniskern, Jim Goins, Phil Sadler and the late, wonderful Curtis Lee. Finally, to my family. I know that I'm the odd one out, the black sheep, but without their constant love and support (tempered with a little bemusement and consternation from time to time with regard to all of my travels and antics), I would not be here today. It looks like the eternal student is going to finish after all! Aroha nui! 5 ABSTRACT A quantitative understanding of the processes controlling sediment transport and deposition across the land/sea interface is crucial to linking terrestrial and marine environments and understanding the formation of marine stratigraphy. The nature and distribution of terrestrial-derived sediment preserved in shelf stratigraphy in turn provides insight into the complex linkages inherent in source-to-sink sediment dynamics. The distribution of marine sediments and associated formation of shelf stratigraphy is complicated because it is a function of not only sediment yield, water depth, and wave current interactions, but is also influenced by local and regional tectonics. Located inboard of an actively subducting plate boundary and characterized by one ofthe highest sediment yields in the world, the Waiapu River in New Zealand presents an excellent location to improve our understanding of the factors controlling the formation of continental shelf stratigraphy and associated sediment transport. Though regressive settings with high sediment discharge have occurred during sea level fluctuations in the past, modern analogs are rare. The small, mountainous, high yield Waiapu River offers an opportunity to study sediment discharge and strata formation in a tectonically-active, open-shelf regressive setting. Over 850km ofhigh-resolution seismic and swath bathymetry data ground-truthed by cores show significant stratigraphic spatial variation is preserved on the Waiapu continental shelf. On the inner shelf, this spatial variation is likely controlled by regionally-specific sediment deposition and resuspension processes as well as antecedent geology. Chronostratigraphic control obtained from black carbon analyses reveal that deforestation of the Waiapu catchment (source) is preserved as a distinct event in the adjacent inner shelf stratigraphy (sink), and further indicates that the inner shelf is currently capturing -17% of the total Waiapu sediment budget. C/N ratios and inner shelf chronology suggest that this is due to deforestation-enhanced sediment yield overwhelming the system's ability to segregate and bypass fine-grained sediment, not changes in riverine or oceanic processes. Preserved shelf-wide stratigraphy shows that the thickest deposits of Holocene stratigraphy are found in tectonically-created accommodation spaces, highlighting the role of neotectonics in strata formation in this location. Morphological evidence from a stratigraphic paleosurface coupled with preserved paleochannel drainage patterns and infilling indicates the importance of structural controls on strata formation. During Holocene low-stands, a tectonically controlled fluvial drainage pattern is presumed to have steered sediment into the structurally-low Waiapu Shelf Basin, while during high-stands it is speculated that sediments continued to be steered south, preferentially filling in the morphological lows overlying the flooded paleochannel. Finally, despite being mostly infilled, the tectonically-controlled paleodrainage likely still influences modern-day sediment transport via the effects of small-scale, modem bathymetric lows. These lows overlie a paleochannel and steer gravity-dependent sediment flows at the river mouth. The primary control on strata formation on the Waiapu continental shelf is presumed to be tectonically-steered, local sediment supply. 6 Controls on Continental Shelf Stratigraphy: Waiapu River, New Zealand INTRODUCTION A quantitative understanding of sediment exchange at the land-sea interface is critical for elucidating the complex linkages between continent-to-coastal ocean sediment dynamics. The inner shelves of continental margins play an important role as the interface between terrestrial environments and the deeper continental shelf. The majority of open-coast studies directed towards understanding fine-sediment dynamics on energetic shelves, however, have previously focused on the mid to outer shelf. It has been long thought that the high slopes and energetic physical regime characteristic of inner shelves result in only short-term, if any, deposition of fine-grained ( <63 J..Lm) sediment. This assumption, however, may be in part due to the fact that quantitative studies of sediment transport and deposition on energetic inner shelves are few in number, given the difficulties inherent in working in these shallow locations. Recent research on the inner shelf of the Eel River, northern California (Crockett and Nittrouer, 2004) suggests that under high-yield conditions, sequestration of fine-grained sediment within inner shelf strata occurs, possibly due to inefficient sediment segregation. High-yield, episodic sedimentation from small, mountainous rivers via oceanic floods has the ability to advect and deposit material quickly across narrow continental shelves (e.g., Wheatcroft, 2000; Wheatcroft and Drake, 2003), dominating strata formation in these environments. The nature of fine-sediment transport and deposition during flood events depends in large part on the concentration of suspended sediment within the flood layer. When the sediment-controlled density of the flood layer is lower then the density of the surrounding ocean water, the flood layer is transported by ambient waves and currents and deposited as a dominantly fine-grained layer (e.g., Wheatcroft 8 and Borgeld, 2003). When the density of the flood layer exceeds that ofthe surrounding -1 -1 ocean water (-30g 1 to 40g 1 ) and the shelf slope is sufficiently steep (>0. 7°), the flood layer becomes autosuspending (e.g. Wright et al., 1990). This density-driven (hyperpycnal) layer may then move downslope under the influence of local bathymetry and independent of the wave and current regime. These hyperpycnal floods have recently been identified as important mechanisms in the formation of preserved continental margin stratigraphy, but their behavior and preservation is poorly understood at best. In tectonically active areas, the distribution of marine sediments is a function not only of water depth and wave/current interactions, but is also influenced by regional and local tectonics. Assumptions of shelf-wide sediment transport that focus on sea level and hydrodynamics as the primary influences on sediment delivery to continental shelves risk neglecting the potentially significant role of tectonics on stratigraphy formation, particularly in the creation of accommodation space and in the steering of terrestrial material (see review by Sommerfield et al., in press). Most of our short-term sediment transport models rely on integrating observed hydrodynamics with gross-scaled (>1OOm) modem bathymetry. These models, however, find it difficult or near-impossible to account for the influence of framework geology on long-term stratigraphy formation. Modem bathymetry cannot simply be scaled back in time to simulate earlier sediment transport without knowing the shape and slope of earlier paleosurfaces. The influence of tectonics ultimately makes it difficult to bridge the gap between observable shelf sediment dynamics and preserved shelf stratigraphy, complicating attempts to understand linkages between the land and sea. 9 The Waiapu River catchment, located on the North Island ofNew Zealand, was extensively deforested around the tum of the century by European settlers to create pastureland, exposing a suite ofhighly crushed and sheared, sedimentary and metamorphic rocks. The combination of frequent erosion generating storms and the exposure of these highly erodable rocks has resulted in numerous scars of massive debris flows up to 3000 km2 in volume (Collot et al., 2001). Subsequent abundant erosion has resulted in channel aggradation ofthe Waiapu River as well as its two main tributaries. Channels are widening via inundation and bank erosion, and the rapid rate of aggradation is a major threat to the floodplain, roads and bridges (e.g. Page et al., 2000). In addition, progradation of the shoreline near the Waiapu mouth due to the increased sediment load has resulted in an apparent local regression off of the East Cape of the North Island (e.g. Gibb, 1981). Sediment yields from the Waiapu River have increased 4-5-fold since post colonial deforestation, and the system has shifted from a rivulet-dominated to a gully dominated erosion system, greatly increasing the amount of fine sediment discharged to the sea (Page et al., 2000; HieRs et al., 2003). The Waiapu River currently discharges approximately 36 x 106 tonnes of sediment a year ranking it among the highest sediment yielding rivers in the world. Previous research indicates that suspended sediment concentrations regularly exceed the threshold for density-dependent (hyperpycnal) flood events over the course of a year (e.g. Hicks et al., 2004). Sediments discharged onto the inner shelf are subsequently influenced not only by a very active hydrodynamic regime (average wave height ~3m, exceeding lOrn in storms), but also by the poorly understood role of active tectonics influencing the formation, and destruction, of accommodation 10 space, as well as the possible steering of fluvial transport. The above factors all combine to make the inner shelf off of the Waiapu River an ideal location for refining our understanding of the complex interactions between processes controlling sediment transport and stratigraphy formation on continental shelves. In this study, we seek to better understand the controls on modem, fine-grained sediment transport, deposition, and subsequent stratigraphy formation on the energetic inner shelf of the Waiapu River, North Island, New Zealand. Over 850km of high resolution, interferometric swath bathymetry data and chirp sub-bottom data was collected to image the fine-scale (<1OOm grid size) bathymetry and stratigraphy of the continental shelf. Seismic data was groundtruthed on the inner shelf via nine vibracores, thirty-one box cores and one kasten core. Subsequent sediment analysis included grainsize percentages (sand, silt, and clay), radioisotope e10Pb) analyses, total organic carbon (TOC) and total nitrogen (TN) percentages, carbon-to-nitrogen ratios (C/N), as well as coarse-fine black carbon (BC) analyses. In Chapter 1, evidence of significant spatial variation in the stratigraphy preserved on the Waiapu inner shelf is presented, showing flood deposits being preserved along a given isobath primarily south of the river mouth. High-resolution bathymetry indicates that this may be due to structurally-controlled bathymetry preferentially steering gravity dependent flood material southwards, along the axis of a preserved paleochannel. Approximately 46% of the sediment comprising the upper 150cm of the inner shelf is fine-grained, suggesting that this energetic region potentially sequesters a significant portion of the Waiapu sediment budget. 11 Chapter 2 establishs chronological control via both well-established (e.g. 14C dating) methodologies coupled with more novel approaches. Specifically, increases across the black carbon spectrum preserved within the inner shelf sediments are identified as representing the chronostratigraphic signature of European deforestation. Given the lack of a single identifying marker for deforestation in marine sediments, the black carbon results not only highlight an excellent example of source-to-sink linkages, but provide a potentially valuable chronological tool for use in non-steady state, herterogenous sedimentary environments. Results further indicate that the energetic inner shelf is currently sequestering ~16-34% of the modem Waiapu sediment budget, roughly equal to or greater then that accounted for on the more quiescent mid-outer shelf, and casting doubt on previous assumptions that this narrow continental shelf is a region of sediment bypassing. Analyses of organic material preserved within the shelf sediments suggests that terrestrial flood material is being captured south of the river mouth, supporting our previous interpretation of the influence of fine-scale bathymetry on sediment transport. Chapter 3 examines the structure of the entire Waiapu continental shelf to examine the influence of neotectonics on the formation of both past and more recent continental margin stratigraphy. Regional subduction tectonics are complicated by the impact of multiple, well-documented subductions of a series of seamounts, most recently that of the Ruatoria seamount ~2Ma, with subsequent slope failure and avalanching approximately 170±40kya (Collot et al., 2001; Lewis et al., 2004). These neotectonics are at least partly responsible for high rates of uplift on land and downdrop on the adjacent continental shelf. The influence of structural control on sediment deposition and strata 12 formation is seen both in the location of major sediment depocenters on the Waiapu shelf, as well as in structural control of fluvial drainage as manifested by the rectilinear nature of the Waiapu paleochannel. The southward-steering of sediment as illustrated by TOC, TN and the spatial extent of flood layers, as well as the fine-scale bathymetry near the river mouth, are all shown to be controlled at least to some extent by the underlying geology. These data highlight the role of neotectonics and related shelf structure in stratigraphy formation on this narrow continental shelf. Each chapter is presented in standard manuscript form. At the time of this defense, chapter 1 has been published in Continental Shelf Research (doi:10.1016/j.csr.2008.01.013) and the full citation can be found on the associated chapter title page. 13 Controls on Continental Shelf Stratigraphy: Waiapu River, New Zealand Chapter 1 Stratigraphic spatial variation on the inner shelf of a high-yield river, Waiapu River, New Zealand: Implications for fine-sediment dispersal and preservation Manuscript Citation: Wadman, H.M. and McNinch, J.E., 2008. Stratigraphic spatial variation on the inner shelf of a high-yield river, Waiapu River, New Zealand: Implications for fine-sediment dispersal and preservation, Continental ShelfResearch 28, 865-886. Abstract The inner shelves of active, energetic continental margins are frequently defined as regions of sediment segregation and fine-sediment bypassing. The Waiapu River, North Island, New Zealand, presents an opportunity to study fine-sediment segregation and strata formation in a spatially constrained, highly energetic, aggradational setting, with one of the highest sediment yields on earth. We present evidence that the inner shelf of the Waiapu River plays a significant role in both the fate of fine-grained (<63J.!m) riverine sediments and the formation of continental margin stratigraphy. Results obtained from high-resolution interferometric bathymetry and high- frequency seismic mapping ground-truthed by cores show significant stratigraphic spatial variation preserved on the Waiapu inner shelf. This spatial variation is likely controlled by spatially-distinct sediment deposition and resuspension processes as well as antecedent geology. Two distinct depositional regions are interpreted as: 1) surface plume-dominated with partial resuspension, characterized by acoustically transparent seismic reflection profiles and muddy sands; and 2) event-layer dominated, characterized by thickly laminated sediments. A modem- day bathymetric low overlying an observed paleochannel may influence the fate ofhyperpycnal flows transiting the shelf via bathymetric steering. Fining-upward sequences found over the entire shelf are interpreted to represent deforestation-induced sedimentation that has overwhelmed the ability of the energetic system to resuspend and segregate fine sediments. We conclude that the primary control on strata formation on the inner shelf of the Waiapu River is local sediment supply. Key Words: New Zealand, fine-grained sediment segregation, hyperpycnal, hypopycnal, interferometric, inner shelf, Waiapu River 15 1.0 Introduction The inner shelf of continental margins, as defined by stratigraphic sequences and physical processes, plays an important role as the interface between terrestrial environments and the deeper continental shelf. Riverine sediments discharged to coastal seas must navigate the energetic inner shelf on their journey from source to sink. Unfortunately, the majority of open-coast studies directed towards understanding fine sediment dynamics on energetic shelves have focused on the mid to outer shelf (e.g., Smith and Hopkins, 1972; Cacchione et al., 1987; Drago et al., 1998; Nittrouer, 1999; Wiberg et al., 2002). It is widely believed that the high slopes and physical regime characteristic of inner shelves result in the accommodation of only short-term deposition of fine-grained sediment. Any significant fine-grained sediment transported to these regions is usually considered to be segregated and resuspended, if deposited at all, and carried offshore (e.g., McCave, 1972; Drake et al., 1985; Nittrouer and Wright, 1994; Cacchione et al., 1999; Zhang et al, 1999; Wright et al., 2001; Vitorino et al., 2002; Kniskern et al., 2006a, b). Recent research on the inner shelf of the Eel River, northern California (Crockett and Nittrouer, 2004), however, suggests that under high-yield conditions sequestration of fine-grained sediments occurs, possibly due to inefficient sediment segregation. Much of our understanding of shoreline dynamics and sediment deposition has largely been directed by investigations on passive margins where sea level is rising and little or no new sediment is delivered to the beach (e.g., Wright and Nittrouer, 1995; Kuehl and Milliman, 1996; Kineke et al., 2000). While it is understood that regressive settings with high sediment discharge have occurred during sea level fluctuations in the 16 past, modem analogues are rare. Other studies have shown the importance of episodic, high-load river sediment deposition to the continental shelf, particularly in the formation of continental margin strata (e.g., Drake and Cacchione, 1985; Milliman and Syvitski, 1992; Nittrouer and Wright, 1994; Wright and Nittrouer, 1995; Wheatcroft et al., 1997; Wheatcroft, 2000; Imnan and Syvitski, 2000). Since episodic sedimentation has the ability to advect and deposit material quickly across narrow continental shelves (Wheatcroft and Drake, 2003), the controls on stratigraphy formation on modem-day regressive and/or active continental margins could deviate from processes which have been previously described on passive margins (Kindiger, 1988; Field and Trincardi, 1991; Kuehl and Milliman, 1996; Kineke et al., 2000; Wheatcroft and Drake, 2003; Poresbski and Steel,· 2006). Analysis of strata formation and related fine-sediment segregation and dispersal across active, regressive inner shelves is essential for improving our understanding of stratigraphy formation and preservation on continental margins. We present evidence that the energetic inner shelf of the Waiapu River, located on the North Island of New Zealand, plays a significant role in affecting both the fate of fine-grained ( <63 flm) riverine sediments and the formation of continental margin stratigraphy. Results obtained from seismic profiles ground-truthed by cores collected on the inner shelfwere used to address the following objectives: 1) map the spatial variation of the stratigraphy and the antecedent geology; 2) measure the amount of fine-grained sediment captured in the shallow stratigraphy; and 3) evaluate the efficiency of sediment segregation and/or sequestration under the influences of a deforestation-enhanced sediment yield. These data will enable us to better understand the apparent variability of deposition and resuspension processes affecting the entire shelf. We think these findings 17 contribute to the community's understanding of fine-sediment dynamics and strata formation in similar environments, and may be useful in refining existing stratigraphic models. 2.0 Background 2.1 Study Area Located on the East Cape of the North Island ofNew Zealand (Figure 1), the Waiapu River has an annual yield of approximately 36 x 106 Mt of sediment per year 2 1 (20,520 t km- y{ ), among the highest in the world (Walling and Webb, 1996; Hicks et al., 2000; Hicks et al., 2004). This extraordinary yield is the result ofhighly erodable rocks in the Waiapu catchment, high annual rainfall rates, and extensive gully erosion caused by widespread deforestation since the mid-twentieth century (O'Byrne, 1965; Eden and Page, 1998; Page et al., 2001; Glade, 2003; Ewers et al., 2006). Previous research based on an irregular suspended sediment sampling regime (Peacock, 2004b) and rating curves (Hicks et al., 2000; Hicks et al., 2004) indicates that the greatest discharge through multiple flooding events occurs from June through September and that the most intense wave energy is from April through July. During floods, suspended sediment concentrations are predicted to regularly exceed the threshold for hyperpycnal flow (e.g., Hicks et al., 2000; Hicks et al., 2003; Hicks et al., 2004), over the course of a year (Ma et al., in press; Hicks et al., 2004; Peacock, 2004b ). For the purposes ofthis study, the inner shelf is defined by both physical and stratigraphic parameters. The inner·shelfis commonly described as the region seaward of the suff zone where the depths are shallow enough to allow frequent agitation by waves 18 on the seabed (e.g., Wright, 1995; Harris and Wiberg, 2001; Harris and Wiberg, 2002). Previous studies for other energetic systems have defined maximum water depths based on wave and climate regimes and/or the spatial distribution of easily erodable sediments. Examples range from:S35m (e.g., Dias and Nittrouer, 1984; Drake et al. 1985; Drago et al., 1999; Wright et al., 2002), to depths of up to 50m (e.g., Kineke et al., 1996; Kuehl et al., 1996; Cacchione et al., 1999; Crockett and Nittrouer, 2004; Roberts and Boyd, 2004). In the context of this study, the energetic physical regime characterizing the Waiapu continental shelf indicates a likely deep inner shelf. A northern extension of the Wairarapa Coastal Current flows along the Waiapu continental shelf (Chiswell, 2000; Chi swell, 2005) and unpublished current meter records taken offshore of the Ruakumara Peninsula mouth indicate the mid-water column currents attain speeds of up to 0.5m/s and tend to be directed northward (Stanton, 1998; Wright et al., 2006; Ma et al., in press). Wright et al. (2006) and Ma et al. (in press) noted that recent storm data from a typical winter storm produced near-bed current speeds of ~0.6m/s, and a moderate period swell with>5m waves. From the existing hydrodynamic data, it is clear that the seabed is regularly agitated by waves at water depths of 60m, providing one estimate for maximum water depth of the inner shelf (e.g., Ma et al., in press, Kniskern et al.2006a). In the context of stratigraphic parameters, shallow-water stratigraphic sequences can be followed in seismic profiles from~ 18-m water depth to depths of 56-72m. From these data, the Waiapu inner shelf is conservatively estimated to extend to 50m of water depth, and has previously presumed to be a region of fine-sediment bypassing (Friedrichs and Wright, 2004; Wright et al., 2006; Kniskern et al., 2006a, b) 19 2.2 Wave-Dominated Deltas Deltas form where the rate of sediment supply to a basin exceeds the combined power of wave and tidal currents to transport the sediment away from a river mouth. Subaqueous morphology depends on the balance between the following primary controlling factors: fluvial discharge, tidal currents and wind-induced waves (e.g., Coleman and Wright, 1973; Galloway, 1975; Pigott, 1995; McManus 2002), and changes in relative sea level and sediment supply (e.g.,; Coleman et al., 1983; Posamentier et al., 1992; Postma, 1995; Posamentier and Allen, 1999; Kolla et al., 2000; Porebski and Steel, 2006). Our results indicate that a classic wave-dominated delta appears on the inner shelf ofthe Waiapu River, a feature that frequently occurs off of rivers with an intense wave climate and large sediment discharge. In these systems, the inner shelf is characterized by the formation of a small, gently sloping delta composed of coarse sediments, generally in the form of a series of prograding clinoforms. Any fine-grained sediments temporarily deposited on the delta front are assumed to be quickly resuspended and transported offshore (e.g., Coleman and Wright, 1973; Wright and Coleman, 1973; Galloway 1975; McManus, 2002; Kapsimalis et al., 2005). Across-shelf variations in the morphology of deltas are classically described as a function of variations in ocean wave and river discharge regimes (e.g., Wright and Coleman, 1973; McManus, 2002); however, the processes and forces that operate along the main delta region are generally assumed to be uniform. 20 2.3 Fine-Sediment Dynamics Studies undertaken in settings characterized by small, steep rivers indicate that the primary mode of fine-sediment delivery from these systems is via episodic, density dependent, hyperpycnal plumes, which might initially deposit fine-sediment layers on the inner shelf (e.g., Mulder and Syvitski, 1995; Wright and Nittrouer, 1995; Mulder et al., 1998; Wright et al., 2001; Mulder et al., 2003; Geyer et al, 2004; Wright and Friedrichs, 2006). In addition, buoyant river plumes have been observed to deposit both fine and coarse sediments close to the shore and on the inner shelf (e.g., Geyer et al., 2000; Traykovski et al., 2000; Geyer et al., 2004). It is generally assumed, however, that the movement of recently deposited sediment in the wave boundary layer exposes fine grained sediment to resuspension when shear stresses become sufficiently high. These resuspended sediments are then transported offshore by waves and currents, resulting in only a fraction of the original fine-grained sediment deposit preserved in the inner shelf region (e.g., Nittrouer and Wright, 1994; Geyer et al., 2000; Ogston et al., 2000; Traykovski et al., 2000; Wright et al., 2001; Harris and Wiberg, 2002; Scully et al., 2003; Kniskern et al., 2006b ). In regions where the slope of the inner shelf is gentle enough to trap fine-grained sediment, it is considered only a matter of time before the slope of the inner shelf is quickly built up, ultimately resulting in fine-sediments bypassing the inner shelf region (Sommerfield and Nittrouer, 1999; Wright et al., 2001; Harris and Wiberg, 2002; Scully et al., 2002). In wave-dominated delta systems, such as that off of the Waiapu River, the tendency for wave action along the delta front to resuspend and transport any fine-grained sediments temporarily deposited in shallower waters only 21 serves to decrease the probability of fine-grained sediments being sequestered on the inner shelf (Kapsimalis et al., 2005). The role of an active inner shelf environment in controlling fine-sediment dynamics has been studied extensively off of the Eel River in northern California. Initial observations ofbed slope values for the inner shelf indicated that the region was in an equilibrium state, and that fine-grained sediments discharged in major deposition events from the Eel bypassed the inner shelf, settling farther offshore (e.g., Sommerfield and Nittrouer, 1999; Zhang et al., 1999; Traykovski et al., 2000). Despite this equilibrium profile and the. significant wave energy available for resuspension along the Eel shelf, further studies conducted by Crockett and Nittrouer (2004) determined that ~6-13% of the total preserved stratigraphic sequence on the inner shelf was composed of silts and clays, a significant finding considering that only ~20% of the fine-grained sediments discharged from the Eel were accounted for in the previously recognized mid-shelf mud deposit (Sommerfield and Nittrouer, 1999). In addition to background levels of 5-15% mud within the inner shelf sands, layers of up to 70% mud were preserved on the inner shelf. These distinct layers on the Eel shelf and in other environments have been interpreted as storm or event deposits that are thick enough to resist complete resuspension and therefore are preserved in the stratigraphic sequence (Wheatcroft and Borgeld, 2000; Sommerfield et al., 2002; Scully et al., 2003; Wheatcroft and Drake, 2003; Crockett and Nittrouer, 2004). These findings suggest that the role of energetic inner shelves in sequestering and preserving fine-grained sediments may have been previously overlooked and warrant additional work. 22 2.4 Stratigraphic History The continental shelf offshore of the Waiapu River presents an opportunity to study a system that has switched to progradational processes due to anthropogenic forcing (Gibb, 1981; Gibb, 1994; Hannah, 2004; Peacock, 2004a). Increased coastal sedimentation as a result ofwidespread deforestation (e.g., Eden and Page, 1998; Page et al., 2001; Glade, 2003) has outpaced eustatic sea level rise ( Gibb, 1981; Willard, 1987; Gibb, 1994; Glade 2003; Litchfield, 2005). Estimated rates of shoreline progradation measured between 1915 and 1979 range from 85-140m south ofthe river mouth to 108- 380m north ofthe river mouth (Gibb, 1981), and correspond well with anecdotal reports of recent coastal plain change. Additionally, the East Cape ofNew Zealand is located inboard of an active plate boundary, and high rates of uplift on land(~ 4mm/yr; Brown, 1995) coupled with subsidence of the outer continental shelfhave resulted in regional tilting, possibly creating substantial accommodation space on the outer continental shelf (Lewis et al., 2004 ). As a result, an ~1OOm thick deposit of sediment interpreted to be post-LGM (Orpin et al., 2002) has been recognized on the Waiapu outer shelf. Increased inputs of fluvial sediment to inner shelves have been described in regressive locations as a series of prograding clinoforms (e.g., Posamentier and Vail, 1988; Posamentier et al., 1988; Posamentier et al., 1992; Hanebuth et al., 2003), and in deforestation affected regions in New Zealand as a thick Holocene sand layer (Goff, 1997; Sorrell and Partridge, 1999; Anderson et al., 2004 ). The inner shelf of the Waiapu River is thus an excellent natural laboratory in which the formation of progradational strata in a modem regressive setting can be observed. 23 3.0 Methods 3.1 Seafloor and sub-bottom mapping More than 450km of high-resolution swath bathymetry was collected over the ~60km2 inner shelf (Figure 1) durir~g three cruises in order to produce a detailed map of seafloor bathymetry. An interferometric swath system (Sea SwathPlus, 234kHz) was used in August 2003 and in October/November of 2004 to collect shallow-water bathymetry (~5-50m) on board the FV Osprey. Deeper water bathymetry (>50m) was collected with a multibeam swath bathymetry system (EM-I 002) in May/June 2004 on board the RV Kilo Moana. Line spacing ranged from 50-180m depending on water depth, and the position of each data point was related to WGS84 using differential GPS. Vessel heave, pitch and roll were corrected in real-time using an IXSEA Octans motion sensor. Seafloor depths were tide-corrected to Mean Lower-Low Water (MLLW) using observed tides from Poverty Bay adjusted for the East Cape region as published by Land Information, New Zealand. Each data set was initially gridded using line averaging at a 2-m resolution and was despiked, filtered and smoothed. For purposes of shelf-wide bathymetric mapping, the data were later gridded using a weighted moving average at resolutions ranging from 5m to 75m. Over 750km ofhigh-resolution seismic reflection data (Figure 1) were collected over four cruises and used to image the sub-bottom structure of the region. Seismic profiles were collected simultaneously with the interferometric bathymetry on the FV Osprey in August 2003 and October/November 2004 using an EdgeTech Chirp 216s (average resolution of 15-20cm). In addition, seismic profiles were collected with an EdgeTech Chirp 512i (average resolution of20-30cm) in August 2003 on board the RV Tangaroa, 24 and in May/June 2004 on board the RV Kilo Moana. Seismic reflection data were processed using SonarWeb Pro, and continuous and non-continuous reflectors were identified and digitized, as was the seafloor reflection surface. Heave is apparent in the seismic profiles because no swell filter was applied during acquisition or post-processing. Digitization of the reflectors was visually estimated through the heave for both the seafloor and subbottom reflection surfaces by one person in order to limit the subjective differences that may arise when others participate in digitizing. Sediment thicknesses were calculated by subtracting the digitized subbottom reflector depths from the seafloor depths at each digitized point. The isopach map of antecedent geology obtained from the differences between the reflector and the seafloor depths was gridded at 25-m spacing. These data allowed a multidimensional approach in mapping not only the alongshore and cross-shore variability of the seafloor and the surface sediment, but also the vertical variability of the underlying strata. 3.2 Cores Nine vibracores (averaging 5 .25m in length with a maximum of 6. 77m) and one kasten core (0.84m in length) were collected in May/June 2004 on board the RV Kilo Moana in water depths ranging from 19-42m (Figure 1). A vibracoring unit was used because traditional gravity coring methods were unable to penetrate the poorly sorted, inner-shelf sediments. The single exception to this was a kasten core used to collect the soft mud located in the northern portion of the inner shelf (see Section 4.1.1, below). Due to the short amount of ship time available for shallow-water vibracoring, as well as the difficulty of working along the energetic Waiapu inner shelf, all core locations were 25 carefully chosen based on analysis of the previously collected sub-bottom profile data. Specific sample locations were selected to maximize the interpretation of the seismic record with a minimum number of cores. The vibracores were split on board and sub sampled in 2cm sections at 1Ocm intervals. Cores were also sub-sampled where lithologic changes were observed. Regions of possible washdown were described but sediment was not sampled unless it was clearly in place. The kasten core was also sub sampleq on board, in 2cm thick sections, with the first 1Ocm of the core being collected in full. Subsequently, 2cm thick samples were collected every 3cm down to 55cm from the top of the core, at which point samples were collected every Scm for the remainder of the core. Samples were bagged and immediately frozen to preserve them for future 14C dating. Finally, 31 box cores (averaging 13cm in length with a maximum of 35cm) were collected in October 2004 on the FV Anoura Bay (Figure 1) in order to better delineate the nature of short-term sedimentation. Each box core was sub-sampled with a 15cm diameter PVC tube, and then immediately extruded and sampled at 1cm intervals. Sand/silt/clay ratios were generated for every sample collected from all three core types using standard wet sieve and pipette analysis (Gee and Bauder, 1986). 4.0 Results 4.1 Spatial Variation Seismic and core data show two different modes of sediment deposition preserved on the Waiapu inner shelf. Each region is characterized by distinctive seismic profiles and lithology: Region 1 -poorly sorted muddy sands with little distinctive layering in 26 either the seismic profiles or the cores; and Region 2 - poorly sorted muddy sands laminated with layers of clayey silt or silty clay. The term "fine-grained sediment" is used to distinguish grain sizes of less than 63 J.Lm (i.e., mud). 4.1.1 Region 1 Region 1 is characterized as a typical open shelf setting that comprises ~54% of the total study area and is located primarily north of the river mouth (see delineated boundaries, Figure 2A). The generalized bathymetry used for clarity in Figure 2A also highlights the inability of gross-scaled bathymetry (1 :300,000; Jaques, 2002) to discern subtle but important morphological features. High-resolution bathymetry data reveal three noteworthy features: 1) A gently sloping, asymmetric river delta with an average along-shelf extent of 4.5km and an average across-shelf slope of 0.409 (Figure 2B). The along-shelf slope is steeper along the southern edge of the delta (0.153), and more gradual on the northern edge (0.044; Figure 3A). 2) A 2B). 3) Outcropping rocky substrates forming enclosures dominate the northern third of Region 1 (Figur~s 2C, 3B-C). Seismic profiles in the shallower portion of Region 1 are acoustically transparent except for a single reflection surface at an average depth of 3m below the seafloor that deepens offshore (Figure 4A). This reflection surface caps a paleo-river channel which trends to the south, under the bathymetric low (Figure 5). Seisrriic profiles from the deeper portion of Region 1 are acoustically transparent throughout (Figure 4B). A notable exception is found in the rocky enclosures located in the northern portion of 27 Region 1 (Figure 6). Here, all seismic profiles show a ~90cm-deep reflection surface, with multiple reflection surfaces beneath it (Figures 6A-B). In order to characterize the nature of Region 1 sediments, 18 box cores, 6 vibracores and 1 kasten core were collected. Overall, box cores indicate that the upper 1Ocm of sediment in Region 1 is primarily composed of sand, with total fine-grained sediment comprising 18% to 51% of the sample (Figure 4C) and increasing seaward. Within the rocky enclosures, box core samples contained less than 9% sand, the least amount of sand found anywhere on the inner shelf (Figure 6C). Significant 7Be activities determined from surface sediment samples collected within this region indicate recent deposition (Kniskern et al, 2006a). Vibracores showed similar near-surface grain size as adjacent box cores. Overall, the upper 50cm of sediment is comprised of clayey sand, which transitions with depth to sand (Figure 4D). In addition, the distinctive 3m-depth reflection surface seen in the shallow portions of Region 1 was penetrated in three vibracores. Core data show that this surface corresponds to a layer of~25cm of poorly sorted, rounded gravels and angular mudstone, interbedded with sands, silts and clay. The minimum thickness of25cm is within the resolution error for the Edgetech 216s used to collect these specific seismic lines. Immediately overlying this gravel layer is up to 20cm of a recent shell hash (based on unpublished 14C dates of three samples ofless than 900yrs), including larger whole shells and some articulated material, capped with a thin layer of clay. Within the rocky enclosures, vibracore and kasten core data indicate that the upper 85cm of sediment contains less than 5% sand (Figure 6D). The kasten core did not penetrate farther, but vibracore data show sediments deeper than 85cm alternate between sandy silts and silty 28 clays, correlating well with seismics from this portion ofRegion 1 (Figure 5). All of Region 1 exhibits a fining-upward sequence (Figures 4D, 6D), with an increase from less than10% to 39% fine-sediment in the upper 150cm. An exception to this is within the rocky enclosures where the upper 150cm is comprised of an average of 85% fine sediments. 4.1.2 Region 2 The rest of the inner shelf, defined here as Region 2, is located largely south of the river delta (see delineated boundaries Figure 7A). Noteworthy bathymetric features seen in the high-resolution bathymetry (Figure 7B) include: 1) a seaward extension of the bathymetric low which continues to the south (Figure 8A); 2) a general concave-upwards shelf profile with no rocky outcrops; and 3) a steep slope to the north at depths greater than 40m (Figure 8B). In contrast to the acoustically transparent seismic profiles seen in Region 1, all seismic profiles from this region show multiple reflection surfaces. The number of seismic reflection surfaces increase to the south. For example, along the -30m isobath, a seismic profile collected ~2km south of the river mouth shows at least six different reflection surfaces, ranging from 20-60cm in thickness, over a vertical span of 7m (Figure 9A). Along this same isobath directly offshore of the river mouth, the same seismic profile shows only two reflection surfaces, both within the upper ~ 130cm of the profile (Figure 1OA). The vertical profile then becomes acoustically transparent below 130cm. North ofthe river mouth, the 30-m isobath falls within Region 1 and consists of the previously described acoustically transparent profiles. All of the laminations 29 draping Region 2 on the inner shelf begin to change in character around ~50m water depth, thinning and cropping out with increasing depth offshore, and are no longer present in seismic records collected in water depths exceeding 72m. A total of 13 box cores and 2 vibracores show an average of 69% fine sediment in the upper 1Ocm and 56% in the upper 150cm. These averages represent a composite of laminated substrates with a much greater percentage of fines in the muddy layer and less in the sand layers, whereas Region 1 sediments were simply muddy sands (Figures 9B, 1OB). Significant 7Be activities determined on surface sediment samples collected within this region indicate recent deposition (Kniskern et al, 2006a), similar to that seen in Region 1, The vibracore located farthest to the south shows that the reflections seen in the proximal seismic profiles correspond to alternating layers of muddy sand and fine sediments. Sediments from the upper 50cm are characterized by a fining-upward sequence (from 27% to 82%) of muddy sands interlaminated with layers of fine sediment (Figure 9A, C). Below 50cm, muddy sands (average 33% fines) are interlaminated with fine-sediment layers (average 60%; Figure 9C). In the northern portion of Region 2, near the river mouth, fewer laminations are present in the cores (Figure 10). Two layers of alternating muddy sands (~46% fines) and fine-sediment layers (~66% fines) correspond to reflection surfaces seen in the adjacent seismic profile (~50 and 75cm depth; Figure lOA, C). 30 5.0 Discussion Several types of fine-sediment transport processes have been recognized on continental shelves, including: 1) advection by positively buoyant river plumes (e.g., Wright, 1985; Wright and Nittrouer, 1995; Geyer et al., 2000; Geyer et al. 2004); 2) resuspension and advection of dilute suspensions (e.g., Harris and Wiberg, 2001); 3) transportation by negatively buoyant plumes discharged directly from extremely turbid rivers (e.g., Mulder and Syvitski, 1995; Mulder et al., 1998a; Imnan and Syvitski, 2000); and 4) fine-sediment settling from buoyant plumes mixed by ambient waves and currents and moved along- and/or down-slope under the influence of currents and gravity (e.g., Wright and Nittrouer, 1995; Wright et al., 1999; Wright et al., 2001). Along-shelf variations in strata formation resulting from combinations of these forcings in wave dominated delta systems and open-coastal inner shelves have been previously documented by other researchers (e.g., Kineke et al., 2000; McManus, 2002; Kapsimalis et al., 2005; Palinkas et al., 2006). To the best of our knowledge, however, the extent of along-shelf variation in inner shelf stratigraphy that was observed in this study over a small spatial scale (e.g., 31 Results from the Waiapu show a spectrum of oceanographic/fluvial conditions, ranging from quiescent to storm, creating very different depositional environments on the inner shelf. 5.1 Spatial Variation The substantial differences in seismic and lithologic stratigraphy documented in Regions 1 and 2 are difficult to explain given simplified assumptions of depth-dependent sediment segregation/resuspension and gross-scaled bathymetry. Over an along-shelf distance of -2km on a representative isobath, acoustically transparent muddy sands in Region 1 grade to muddy sands highly laminated with silty clays in Region 2 (Figure 11 ). At water depths greater than 40m, event layers are preserved along the entire inner shelf; however, there are always more layers preserved on the southern portion of any given isobath. These data suggest that event deposits are being at least initially steered to the south and Region 2, or that event layers are being preferentially resuspended in Region 1. As detailed in the following sections, we propose that the spatially-varying stratigraphy recently preserved on the Waiapu inner shelf has likely been dominated by advection from positively and negatively buoyant plumes and has been further controlled by the geologic structure of the shelf. 5.1.1 Quiescent Conditions - Controls on Deposition Point measurements of suspended sediment concentrations coupled with published ratings curves indicate that the average suspended sediment concentration of the Waiapu River exceeds lOg m-3 (e.g., Hicks et al., 2004; Peacock, 2004b; Ma et al, in 32 press), and generates a persistent surface sediment plume (exemplified by Figure 11). Initial deposition is controlled by the extent and trajectory of the plume, which is in turn controlled by river discharge, the local wind and wave climate (e.g., Wright and Nittrouer, 1995; Geyer et al2000; Geyer et al. 2004), and by the rate of settling (e.g., Hill et al., 2000; Geyer et al., 2004 and references within). As the Waiapu River enters the sea, suspended sediment likely undergoes intense flocculation and settling within the inner shelf, similar to the behavior exhibited by the Eel River under conditions of high discharge (e.g., Hill et al., 2000; Geyer et al., 2000; Ogston et al., 2000). Depending on the prevailing winds, the Waiapu River plume has been observed in the field (Figure 12) to hug the coast and flow either to the north around East Cape, or to the south. The nature of the poorly sorted muddy sands that dominate the sedimentary fabric of Region 1 and the coarser layers of Region 2 are what would be expected from settling out of a buoyant plume, with at least some resuspension after deposition. For example, Kineke et al. (2000) interpreted similar poorly sorted muddy.sand and sandy mud surface sediments on the Sepik River shelf as being incompletely winnowed sediment deposits from the buoyant plume. The comparable deposits on the Waiapu River inner shelf are similarly interpreted to be partially winnowed deposits. The rocky enclosures found in the northern portion of Region 1 may, in particular, serve to shelter sediments from significant wave or current resuspension. The rock ridges also effectively isolate sediments from density-driven deposition generated from the Waiapu River (see Section 5 .1.3, below). An additional source of sediment to this region might be from advection of recently resuspended sediment temporarily deposited elsewhere on the inner shelf. 33 5.1.2 Storm Events- Flood-derived Stratigraphy Episodic sedimentation from small, mountainous rivers via oceanic floods has the ability to advect and deposit material quickly across narrow continental shelves (e.g., Wheatcroft, 2000; Wheatcroft and Drake, 2003), dominating strata formation in these environments. The nature of fine-sediment transport and deposition during flood events depends in large part on the concentration of suspended sediment within the flood layer. When the sediment-controlled density of the flood layer is lower then the density of the surrounding ocean water, the flood layer is transported by ambient waves and currents and deposited as a dominantly fine-grained layer (e.g., Wheatcroft and Borgeld, 2003 ). These event layers are frequently thick enough to resist complete resuspension and are preserved in stratigraphic sequences as fine-grained sedimentary deposits with distinctive internal structures (Wheatcroft and Borgeld, 2000; Sommerfield et al., 2002; Scully et al., 2003; Wheatcroft and Drake, 2003; Crockett and Nittrouer, 2004). When the density of the flood layer exceeds that of the surrounding ocean water 1 1 (~30g r to 40g r ; Wright et al., 1990; Mulder and Syvitski, 1995) and the shelf slope is sufficiently steep (>0.7°; Wright et al., 2001), the flood layer becomes autosuspending. This density-driven (hyperpycnal) layer moves downslope under the influence of local bathymetry and independent of the wave and current regime. Sedimentary layers associated with hyperpycnal flows have been recognized in several coastal environments and are characterized by a fine-scale internal structure different from that associated with flood deposits (e.g., Mulder et al., 2001 a; Mulder et al., 2001 b). Wave-induced, gravity driven transport of dense flood layers has also been recognized as a significant transport mechanism on continental shelves with slopes gentler than that required for 34 autosuspension (see review by Wright and Friedrichs, 2006). In these cases, the downslope transport of a hyperpycnallayer is complicated by the fact that high-density, turbid layers can move along-slope or even up-slope under the influence of ambient current stresses and pressure gradients (Wright et al., 1997; Wright et al., 2001). In the absence of any apparent bathymetric controls (i.e., such as on gently sloping continental shelves), processes that allow steering by waves and/or currents may ultimately be as important to the location of hyperpycnal deposition as gravitational steering (Wright et al., 2001). The Waiapu River undergoes flooding events several times a year and concentrations are predicted to regularly exceed the threshold for hyperpycnal flow (e.g., Hicks et al., 2000; Hicks et al., 2003; Hicks et al., 2004). In fact, hyperpycnal conditions may be met annually (Hicks et al., 2004), if not more commonly (Peacock, 2004b). Recent analysis of tripod data at 40-m and 60-m depths, including acoustic Doppler velocimeters (ADV), pulse-coherent acoustic Doppler profilers (PC-ADP) and a YSI multi-purpose sensor, indicates that the Waiapu underwent hyperpycnal conditions during the time of study (October 2004- October 2005; Wright et al., 2006; Ma et al., in press). Multiple reflection surfaces correlated to distinctive (greater than 65% <63!J.m) fine-grained layers are easily identifiable in Region 2 (Figures 9, 10). These layers are very similar to flood strata described off of the Eel River margin (e.g., Wheatcroft and Drake, 2003; Crockett and Nittrouer, 2004), and are interpreted to be event layers deposited during either low-density oceanic floods or high-density, hyperpycnal events. The sampling strategy used to describe the Waiapu vibracores does not permit us to specifically distinguish between hyperpycnal or flood-deposited layers. Results from 35 hydrodynamic observations and models discussed below, however, suggest that at least some of these layers may in fact be hyperpycnal deposits. 5.1. 3 Storm Events -Influence ofHydrodynamics on Density-dependent Deposition The slope ofthe Waiapu inner shelf is likely too gentle (<0.7°) for bathymetry alone to support high-density sediment transport (Figure 13A; Wright et al., 2001; Ma et al., in press) and net direction of movement is theoretically driven by the ambient waves and currents. Analysis of the hydrodynamics during a specific high-density flood event suggests that the dominant transport direction of the resulting density-dependent plume was to the north (Ma et al., in press). These observations correspond well with the primary observed northward direction of the mean coastal currents (Chiswell, 2000; Wright et al., 2006). Moreover, when local wind forcing is taken into consideration, model predictions based on gross-scale bathymetry indicate that transport and deposition of a given high-density flood deposit is equally likely along the entire inner shelf (Kniskern et al., 2006b). A noteworthy point is that observations and models of waves and currents do not show substantial southward-directed sediment transport, which is markedly different from what we see preserved in the shallow stratigraphy (Figure 11 ). 5.1.4 Storm Events- Influence ofSmall-Scale Bathymetry and Antecedent Geology on Density-dependent Deposition We suspect that the discrepancy between hydrodynamic observations and models with preserved stratigraphy may be explained by the influence of small-scale, subtle gradients in bathymetry. Even on gently sloping shelves, small-scale bathymetric lows 36 near the river mouth may have a great influence on the steering of a density-dependent plume until it becomes well-mixed with the overlying water column. High-resolution, interferometric data reveal a bathymetric low trending towards the southern edge of the continental shelf when viewed in the context of the offshore transport of sediment (Figure 13). This low persists until ~40-m water depth where the bathymetry changes to a gentle slope towards the north (profile H, Figure 13B). While we cannot rule out event-layer deposition by a variety of processes, the preferential preservation of event layers documented in Region 2 may result from high-density plumes being partially constrained and steered towards the south when first entering the sea. The effect of relict geology, particularly that of paleo-river channels, influencing modem-day coastal sediment dynamics has been well documented (e.g., Bjerkeus et al., 1994; Roberts and Snyder, 2001; Boss et al., 2002; Browder and McNinch, 2006). Region 1 of the inner shelf is characterized in part by the presence of a strong, continuous reflection surface capping a paleochannel (Figures 5, 14). When this reflection surface is contoured across the shelf, a paleo-bathymetric low (~2m, average relief) extends offshore and south of the river mouth, following the underlying paleochannel (Figure 14D). The modern-day bathymetric low also overlies this paleochannel (Figures 5, 13, 14). The ability ofhyperpycnal flows to be erosive at high velocities may serve to minimize deposition and preserve channel characteristics on the moden seafloor (Mulder et al., 1998). Work done by Addington et al., (2007) indicate that the outer shelf of the Waiapu records similar along-shelf stratigraphic spatial variation within a series of sediment trapping basins. In their study of three transects along one hi-lobed and one single-lobed 37 basin (160-180m water depth), Addington et al., (2007) concluded that the primary direction of hyperpycnal deposition to the outer shelf was towards the south. They also showed that deposition was not consistent within outer shelf basins, as might be expected from preliminary model results which show an equal shelf-wide dispersal of density dependent plumes (Kniskern et al., 2006b ). Although Addington et al., (2007) did not identify a specific mechanism that would account for their observed spatial variation, it is consistent with the idea that density-dependent plumes follow the southward-trending bathymetric low across the inner shelf and may continue that course to the outer shelf. 5.1. 5 Controls on resuspension and preservation Sediment resuspension rates are typically high where buoyant plumes enter energetic, well-mixed coastal zones (e.g., Geyer et al2004). Under storm conditions, elevated shear stress greatly increases resuspension of recently deposited, fine-grained sediments (e.g., Nittrouer and Wright, 1994; Sommerfield and Nittrouer, 1999; Zhang et al., 1999; Harris and Wiberg, 2001 ). Subsequent transport off of the inner shelf can occur as a fluid mud layer (e.g., Traykovski et al., 2000; Geyer et al2004), a dilute suspension (e.g. Harris and Wiberg, 2001 ), an isopycnal flow (e.g., Kineke et al., 2000), or as a wave and/or current supported, high-density gravity flow (e.g., Wright et al., 2001; Wright and Friedrichs, 2006). On the Waiapu inner shelf, bottom stresses in both quiescent and storm conditions have been estimated to be high enough to allow complete resuspension of all fine-grained sediment (Wright et al., 2006; Kniskern et al., 2006b ), leading to assumptions that the inner shelf is a region of fine-sediment bypassing, and should not preserve any record of flood events. Model simulations further indicate that 38 there is no significant along-isobath difference in bottom shear stresses responsible for sediment resuspension, and thus resuspension potential should be equal along the entire inner shelf. These simulations, however, do not take into account the effects of bed armoring (e.g., Wiberg et al., 1994), or bed cohesion and consolidation (e.g., Wheatcroft and Drake, 2003; Van Ledden et al., 2004). Sediments in a sand-dominated matrix with as little as 5-10% clay have been shown to have weakly cohesive properties (Van Ledden et al., 2004 ). Both of the stratigraphic regions identified on the Waiapu shelf are characterized by sediments with greater than 5-10% clay (<3.9J.Lm) and, when averaged over the upper 150cm, 46% of the inner shelf sediments are fine-grained. In Region 1, surface sediments contain a minimum of 7% clay, with up to 52% clay in the rocky enclosures. Region 2 surface sediments contain a minimum of 15% clay, and the amount of clay increases both towards the south and with increasing water depth. The sediments that characterize the Waiapu inner shelf are at least weakly cohesive, and resuspension estimates which do not take this into account may be in error. The fine-grained sediment preservation documented in the numerous cores and seismic profiles across the region may be explained by bed armoring and cohesion properties minimizing complete resuspension. The poorly sorted muddy sands seen in Regions 1 and 2 are interpreted to be partially winnowed plume deposits. The presence of these deposits suggests that resuspension potential is relatively equal along the shelf, though not completely efficient as would be expected from hydrodynamic observations and modeling results. Event layers are likely preserved, despite widespread conditions favorable for resuspension, because of their rapid deposition and high clay content. The presence of event-layers in 39 the shallow stratigraphy of Region 2 (and lack thereof in Region 1) cannot be explained by differing resuspension potential along a given isobath and may simply reflect preferential steering of density-dependent plumes. 5.2 Fine-Grained Sediments and Deforestation Significant increases in sedimentation following widespread deforestation have been documented by changing grain-size regimes in estuarine (e.g., Sorrell and Partridge, 1999; Temmerman et al., 2003, Anderson et al. 2004), deltaic (e.g., Coleman et al., 1998; McManus, 2002) and shallow marine environments (e.g., Bruckner, 1986; Goff, 1999; Gomez et al., 2004; Kazanci et al., 2004; Owen and Lee, 2004). Deforestation-induced changes in New Zealand nearshore stratigraphy have been linked to the introduction of coarser, terrigenous layers in the Kongahu Swamp (Sorrell and Partridge, 1999), the Okura Estuary (Anderson et al., 2004) and Wellington Harbor (Goff, 1997). In the Waiapu River catchment, erosion has increased 4 to 5-fold since deforestation, which began with Maori settlements around 800-500 14C yr BP (Page et al., 2000; Page et al., 2001). Deforestation accelerated through the mid-eighteenth century with the arrival of Europeans. Present rates of erosion are 5 times greater than pre-European rates and the system has shifted from a catchment to a gully-dominated system, greatly increasing the amount of fine-grained sediment discharged to the shelf (Eden and Page, 1998; Page et al., 2000; Hicks et al., 2000; Collot et al., 2001 ). On the Waiapu inner shelf, sediments deposited within the last 900 years (as constrained by unpublished 14C data) show a fining upward sequence along the entire shelf (Figures 4D, 6D, 9D, lOD). Mechanisms responsible for forming this sequence may 40 include a rise in local sea level, a weakening of the local wave climate, or an overwhelming increase in local sediment supply. Holocene history is characterized_ by a slow rise in eustatic sea level over the past 7000 years (Schioler et al., 2002; Hannah, 2004). This would be preserved in inner shelf stratigraphy as a gradually fining upward sequence if the shoreline and distance. from the sediment source .increased with the transgression. The shoreline near the Waiapu River, however, is experiencing a rapid regression (see Section 2.4; Gibb, 1981). While variations in the mean currents do occur off ofthe East Cape of New Zealand, the mean direction and velocities are assumed to have been relatively constant over at least the last 500 years (Chiswell, 2000; McCave et al., 2004; Chiswell, 2005) and local wave intensities have not likely_.decreased (Allan and Komar, 2002). Thus, neither arelative rise in sea level nor a weakening oflocal current/wave magnitudes is likely controlling the formation of the fining-upward sequence preserved in the Waiapu inner shelf strata. Gomez et al. (2004) recognized a fining upward sequence preserved in one of three drill cores collected within three main depocenters on the East Coast Continental Margin (~180km south of the Waiapu River). In the shelf core, they documented a fining upward sequence and tentatively attributed the observed stratigraphic change to an increase in sedimentation which they related to an increase in gully-dominated erosion due to deforestation. We suspect.that dramatic increases in sediment discharge of the Waiapu River is overwhelming sorting and segregation of fine-grained sediment, ultimately resulting both in a fining-upward sequence as well as an increase in the amount of fine-grained sediments sequestered on the inner shelf(Figures 4D, 6D, 9D, lOD). The deforestation-linked increase in sedimentation also increases the likelihood 41 that sediment discharge of a given flood event will be high enough that the density of the flooding layer will exceed that of the ambient ocean water, thus being more likely to be steered by local bathymetry. 6.0 Conclusions Stratigraphic observations from the Waiapu inner shelf show: 1) spatial variability in strata formation and preservation along given isobaths and over very small distances; 2) the direction of density-dependent plume transport may be sensitive to small-scale bathymetric features near the river mouth; 3) high sediment discharge may overwhelm resuspension efficiency in energetic environments; and 4) increased sediment supply due to.land use changes influences the formation of continental margin stratigraphy. These findings have important implications relevant to modeling continental shelf stratigraphy in similar high-sediment yield and high-energy environments. Fining upward sequences identified in other locations may not always result from relative sea level rise. While there is little doubt that the present increase in sediment supply to the Waiapu shelf is anthropogenic, several natural causes of increased local sediment supplies might be similarly preserved in the stratigraphic record on the shelf in other localities (e.g., Whilmshurst et al., 1997; Vajda et al., 2001). Furthermore, a minimum of 46% ofthe sediments preserved in the upper 150cm ofthe inner shelf are fine-grained and likely reflect inefficient sediment segregation. Assumptions that inner shelves are regions of fine-sediment bypassing need to be explored further. 42 Acknowledgements Support for this research was provided by the National Science Foundation (OCE0326831 and OCE0504690). Thanks for field and logistical support provided by R.A. Gammisch, W. Reisner, L. Carter, L. Northcote, B. Lee, and the crews of the RIV Tangaroa and RIV Kilo Moana. Thanks for logistical support and historical data is also given to Tui Warmenhoven, Project Manager of the Taonga Tuku Iho Research Project. Special thanks for permission and vessel blessings are given to members of the Ngati Porou iwi. Comments from A. Orpin, J. Crockett and an anonymous reviewer greatly improved this manuscript. 43 References Addington, L., Kuehl, S.A. and McNinch, J.E., 2007. Contrasting modes of shelf sediment dispersal off a high-yield river: Waiapu River, New Zealand. Marine Geology, doi:10.1016/j.margeo.2007.04.018. Allan, J.C. and Komar, P.D., 2002. Extreme storms on the Pacific Northwest coast during the 1997-98 El Nino and 1998-99 La Nina. Journal of Coastal Research 18 ( 1), 175-193. Anderson, M.J., Ford, R.B., Feary, D.A. and Honeywill, C., 2004. Quantitative measures of sedimentation in an estuarine system and its relationship with intertidal soft sediment infauna. Marine Ecology Progress Series 272, 33-48. Bjerkus, M., Gelumbauskaite, Z., Sturkell, E., Floden, T. and Grigelis, A., 1994. Paleochannels in the East Central part ofthe Baltic proper. Baltica 8, 15-26. Boss, S.K., Hoffman, C.W. and Cooper, B., 2002. Influence of fluvial processes on the Quaternary geologic framework of the continental shelf, North Carolina, USA. Marine Geology 183, 45-65. Browder, A.G. and McNinch, J.E., 2006. Linking framework geology and nearshore morphology: Correlation of paleo-channels with shore-oblique sandbars and gravel outcrops. Marine Geology 231(1-4), 141-162. Brown, L.J., 1995. Holocene shoreline depositional processes at Poverty Bay, a tectonically active area, northeastern North Island, New Zealand. Quaternary International26, 21-33. Bruckner, H., 1986. Man's impact on the evolution of the physical environment in the Mediterranean region in historical times. GeoJournal, 13(1) 7-17. 44 Cacchione, D.A., Grant, W.D., Drake, D.E. and Glenn, S.M., 1987. Storm-dominated bottom boundary layer dynamics on the northern California continental shelf: measurements and predictions. Journal of Geophysical Research, 92(C2) 1817- 1827. Cacchione, D.A., Irish, J., Traykovski, P., Wiberg, P.L. and Lynch, J., 1999. Estimates of suspended-sediment flux and bedform activity on the inner portion of the Eel continental shelf. Marine Geology, 154(1-4) 83-97. Chiswell, S.M., 2000. The Wairarapa Coastal Current. New Zealand Journal ofMarine and Freshwater Research, 34(2) 303-315. Chiswell, S.M., 2005. Mean and variability in the Wairarapa and Hikurangi Eddies, New Zealand. New Zealand Journal ofMarine & Freshwater Research, 39 121-134. Coleman, J.M. and Wright, L.D., 1973. Modem river deltas: variability of process and sand bodies. In: M.L. Broussard (Editor), Deltas, Models for Exploration. Houston Geological Society, Houston, pp. 99- 149. Coleman, J.M., Prior, D.B. and Lindsay, J.F., 1983. Deltaic influences on shelf edge instability processes. In: D.J. Stanley and G.T. Moore (Editors), The shelfbreak: critical interface on continental margins. SEPM Special Publication, 33, pp. 121- 137. Coleman, J.M., Roberts, H.H. and Stone, G.W., 1998. Mississippi River delta: An overview. Journal ofCoastal Research 14(3), 698-716. 45 Collot, J.Y., Lewis, K., Lamarche, G. and Lallemand, S., 2001. The giant Ruatoria debris avalanche on the Northern Hikurangi margin, New Zealand: Result of oblique seamount subduction. Journal of Geophysical Research B: Solid Earth 106(9), 19271-19297. Crockett, J.S. and Nittrouer, C.A., 2004. The sandy inner shelf as a repository for muddy sediment: An example from Northern California. Continental ShelfResearch 24(1), 55-73. Dias, J.M.A. and Nittrouer, C.A., 1984. Continental shelf sediments of northern Portugal. Continental ShelfResearch 3(2), 147-165. Drago, T., Oliveria, A., Magalhaes, F., Cascalho, J., Jouanneau, J.-M., and Vitorino, J. Oliveira 1998. Some evidences of northward fine sediment transport in the northern Portuguese continental shelf. Oceanologica Acta 21 (2), 223-231. Drago, T., Jouanneau, J.M., Araujo, F., Valerio, P. and Weber, 0., 1999. Geomorphological control of fine sedimentation on the northern Portuguese shelf. Boletin - Instituto Espana! de Oceanografia 15( 1-4), 111-122. Drake, D.E., Cacchione, D.A. and Karl, H.A., 1985. Bottom currents and sediment transport on San Pedro shelf, California. Journal ofSedimentary Petrology 55(1 ), 15-28. Eden, D.N. and Page, M.J., 1998. Palaeoclimatic implications of a storm erosion record from late Holocene lake sediments, North Island, New Zealand. Palaeogeography, Palaeoclimatology, Palaeoecology 139(1-2), 37-58. 46 Ewers, R.M., Rutledge, D., Harding, J. S., Didham, R. K., Kliskey, A. D. and Walker, S., 2006. Past and future trajectories of forest loss in New Zealand. Biological Conservation 13 3 (3 ), 312-3 25. Field, M.E. and Trincardi, F., 1991. Regressive coastal deposits on Quaternary continental shelves: preservation and legacy. In: R.H. Osborne (Editor), From shoreline to abyss: contributions in marine geology in honor of Francis Parker Shepard. SEPM, Tulsa, Special Publication, 46, pp. 107-122. Friedrichs, C.T. and Wright, L.D., 2004. Gravity-driven sediment transport on the continental shelf: implications for equilibrium profiles near river mouths. Coastal Engineering 51, 795- 811. Friedrichs, C.T., Kim, S.C., Wright, L.D. and Hepworth, D.A., 2000. Bottom-boundary layer processes associated with fine sediment accumulation in coastal seas and bays. Continental ShelfResearch 20(7), 807-841. Galloway, W.E., 1975. Process framework for describing the morphologic and stratigraphic evolution of deltaic depositional systems. In: M.L. Broussard (Editor), Deltas, Models for Exploration. Houston Geological Society, Houston, pp. 87-98. Gee, G.W. and Bauder, J.W., 1986. Particle-size analysis. In: A. Klute (Editor), Methods of Soil Analysis: Part 1. Physical and Mineralogical Methods. Agronomy. Soil Science Society of America, Madison, USA, pp. 383-411. Geyer, W.R., Traykovski, P., Hill, P. and Milligan, T., 2000. The structure of the Eel river plume during floods. Continental Shelf Research 20(16), 2067-2093. 47 Geyer, W.R.~ Hill, P.S. and Kineke, G.C., 2004. The transport, transformation and dispersal of sediment by buoyant coastal flows. Continental ShelfResearch 24(7- 8), 927-949. Gibb, J.G., 1981. Coastal hazard mapping as a planning technique for Waiapu County, East Cape, North Island, New Zealand. Water and Soil Technical Publication 21, 63. Gibb, J.G., 1994. Initial Assessment of Areas Sensitive to Coastal Hazards for Selected Parts of the Gisbome District Council, Bay ofPlenty. Glade, T., 2003. Landslide occurrence as a response to land use change: A review of evidence from New Zealand. Catena 51(3-4), 297-314. Goff, J.R., 1997. A chronology of natural and anthropogenic influences on coastal sedimentation, New Zealand. Marine Geology 138(1-2), 105-117. Goff, J.R. and Chague-Goff, C., 1999. A late Holocene record of environmental changes from coastal wetlands: Abel Tasman National Park, New Zealand. Quaternary International 56, 39-51. Gomez, B., Roberts, A.P., Carter, L., Trustrum, N.A. and Palmer, A.S., 2004. El Nino Southern Oscillation signal associated with middle Holocene climate change in intercorrelated terrestrial and marine sediment cores, North Island, New Zealand. Geology 32(8),653-656. Hanebuth, T.J.J., Uidmann, T., Wong, H.K., Stattegger, K. and Schimanski, A., 2003 . . Late Pleistocene forced-regressive deposits on the Sunda Shelf (Southeast Asia). Marine Geology 199(1-2),139-157. 48 Hannah, J., 2004. An updated analysis of long-term sea level change in New Zealand. Geophysical Research Letters 31(3),L03307 1-4. Harris, C.K. and Wiberg, P.L, 2001. A two-dimensional, time-dependent model of suspended sediment transport and bed reworking for continental shelves. Computers and Geosciences 27(6),675-690. Harris, C.K. and Wiberg, P., 2002. Across-shelf sediment transport: Interactions between suspended sediment and bed sediment. Journal of Geophysical Research C: Oceans 107(1),8-1 - 8-12. Hicks, D.M., Gomez, B. and Trustrum, N.A., 2000. Erosion thresholds and suspended sediment yields, Waipaoa River basin, New Zealand. Water Resources Research 36, 1129-1142. Hicks, M., Shankar, U. and McKerchar, A., 2003. Sediment Yield Estimates: a GIS tool. Water and Atmosphere 11(4),26-27. Hicks, D.M., Gomez, B. and Trustrum, N., 2004. Event suspended sediment characteristics and the generation of hyperpycnal plumes at river mouths: East Coast Continental Margin, North Island, New Zealand. The Journal of Geology 112,471-485. Hill, P.S., Milligan, T.G. and Geyer, W.R., 2000. Controls on effective settling velocity of suspended sediment in the Eel River flood plume. Continental Shelf Research 20(16), 2095-2111. Inman, J. and Syvitski, J.P.M., 2000. Impact of extreme river events on the coastal ocean. Oceanography 13, 85-92. 49 Jaques, W.F., Commander, 2002. Curvier Island to East Cape. In: N.Z. Land Information (Editor), North Island- East Coast. Office of Royal New Zealand Navy, Auckland, NZ, pp. 1:300,000. Kapsimalis, V., Collins, M., Poulos, S.E., Karageorgis, A.P. and Pavlakis, P., 2005. Recent evolution of a Mediterranean deltaic coastal zone: Human impacts on the Inner Thermaikos Gulf, New Aegean Sea. Journal ofthe Geological Society 162(6), 897-908. Kazanci, N., Emre, 6., Kibar, M., 6ncel, S., Leroy, S. and Ileri, 6., 2004. Late Holocene erosion in NW Anatolia from sediments of Lake Manyas, Lake Ulubat and the so1:1thern shelf of the Marmara Sea, Turkey. Catena 57(3), 277-308. Kindinger, J.L., 1988. Seismic stratigraphy ofthe Mississippi-Alabama shelf and upper continental slope. Marine Geology 83(1-4), 79-94. Kineke, G.C., Sternberg, R. W., Trowbridge, J.H. and Geyer, W.R., 1996. Fluid-mud processes on the Amazon continental shelf. Continental Shelf Research 16(5-6), 667-696. Kineke, G.C., Milliman, J.D., Dellapenna, T. M., Purdon, R. G., Woo1fe, K. J. and Kuehl, S. A., 2000. Sediment export from the Sepik River, Papua New Guinea: Evidence for a divergent sediment plume. Continental ShelfResearch 20(16), 2239-2266. Kniskern, T.A., Harris, C.K. and Kuehl, S.A., 2006a. Sediment Deposition on the Waiapu River Shelf, N.Z., Implications for Sediment Transport Mechanisms and Event Preservation. EOS, Transactions (AGU) 87(36), OS11L-04. 50 Kniskern, T.A., Harris, C.K. and Kuehl, S.A., 2006b. Flood Sediment Dispersal and Deposition on the Waiapu River Shelf, East Cape, New Zealand. EOS, Transactions (AGU) 87(52), OS12A-02. Kolla, V., Biondi, P., Long, B. and Fillon, R., 2000. Sequence stratigraphy and architecture of the Late Pleistocene Lagniappe delta complex, northeast Gulf of Mexico. Geological Society London Special Publication (172), 291-327. Kuehl, S.A. and Milliman, J.D., 1996. Siliciclastic margins record terrestrial and oceanographic conditions. EOS, Transactions (AGU) 77, 356. Lentz, S., Herbers, T.H.C., Guza, R.T., Elgar, S. and Feddersen, F., 1999. Momentum balances on the North Carolina inner shelf. Journal of Geophysical Research C: Oceans 104(8), 18,205-18,226. Lewis, K.B., Lallemand, S.E. and Carter, L., 2004. Collapse in a Quaternary shelf basin off East Cape, New Zealand: evidence for passage of a subducted seamount inboard of the Ruatoria giant avalanche. New Zealand Journal of Geology & Geophysics 47, 415-429. Litchfield, N.J. and Berryman, K.R., 2005. Correlation of fluvial terraces within the Hikurangi Margin, New Zealand: Implications for climate and baselevel controls. Geomorphology 68(3-4), 291-313. Ma, Y., Wright, L.D. and Friedrichs, C.T., in press. Observations of sediment transport on the continental shelf off the mouth of the Waiapu River, New Zealand: Evidence for current-supported gravity flows. Continental ShelfResearch in press. .51 Madsen, O.S., Wright, L.D., Boon, J.D. and Chisholm, T.A., 1993. Wind stress, bed roughness and sediment suspension on the inner shelf during an extreme storm event. Continental ShelfResearch 13(11 ), 1303-1324. McCave, LN., 1972. Transport and escape of fine-grained sediment in shelf areas. In: D.J.P. Swift, D.B. Drake and O.H. Pilkey (Editors), Shelf Sediment Transport: Process and Pattern. Dowden, Hutchinson & Ross, Inc., Stroudsburg, P A, pp. 225-248. McCave, LN., Hayward, B.W., Carter, L. and Carter, R.M., 2004. Cenozoic oceanographic evolution of the SW Pacific gateway: Introduction. Marine Geology 205(1-4), 1-7. McManus, J., 2002. Deltaic responses to changes in river regimes. Marine Chemistry 79(3-4), 155-170. Milliman, J.D. and Syvitski, J.P.M., 1992. Geomorphic/tectonic control of sediment discharge to the ocean: the importance of small mountainous rivers. Journal of Geology 100(5), 525-544. Mulder, T. and Syvitski, J.P.M., 1995. Turbidity currents generated at river mouths during exceptional discharges to the world oceans. Journal of Geology 103(3), 285-299. Mulder, T., Savoye, B., Piper, D.J.W. and Syvitski, J.P.M., 1998. The Var submarine sedimentary system: understanding Holocene sediment delivery processes and their importance to the geological record. Geological Society Special Publication 129, 145-166. 52 Mulder, T., Syvitski, J.P.M. and Skene, K.I., 1998. Modeling of erosion and deposition by turbidity currents generated at river mouths. Journal ofSedimentary Research A: Sedimentary Petrology and Processes 68(1), 124-137. Mulder, T., Migeon, S., Savoye, B. and Faugeres, J.C., 2001a. Inversely graded turbidite sequences in the deep Mediterranean: A record of deposits from flood-generated turbidity currents? Ceo-Marine Letters 21(2), 86-93. Mulder, T., Migeon, S., Savoye, B. and Jouanneau, J.-M., 2001b. Twentieth century floods recorded in the deep Mediterranean sediments. Geology 29(11 ), 1011- 1014. Mulder, T., Savoye, B., Syvitski, J.P.M., Migeon, S. and Faugeres, J.C., 2003. Marine hyperpycnal flows: Initiation, behavior and related deposits. A review. Marine and Petroleum Geology 20(6-8), 861-882. Nittrouer, C.A. and Wright, L.D., 1994. Transport of particles across continental shelves. Reviews ofGeophysics 32(1), 85-113. Nittrouer, C.A., 1999. STRATAFORM: overview of its design and synthesis of its results. Marine Geology 154(1 ), 3-12. O'Byrne, 1965. A correlation of rock types with soils, topography and erosion in the Gisborne-East Cape region. New Zealand Journal ofGeology & Geophysics 10, 217-231. Ogston, A.S., Kineke, G.C., Cacchione, D.A. and Sternberg, R.W., 2000. Observations of storm and river flood-driven sediment transport on the northern California continental shelf. Continental ShelfResearch 20(16), 2141-2162. 53 Orpin, A.R. et al., 2002. Deposition from very high sediment yield New Zealand river is captured in upper margin basins. Margins Newsletter 9, 1-4. Owen, R.B. and Lee, R., 2004. Human impacts on organic matter sedimentation in a proximal shelf setting, Hong Kong. Continental ShelfResearch 24(4-5), 583-602. Page, M., Trustrum, N. and Gomez, B., 2000. Implications of a century of anthropogenic erosion for future land use in the Gisbome-East coast region ofNew Zealand. New Zealand Geographer 56(2), 13-24. Page, M., Harmsworth, G., Trustrum, N., Kasai, M. and Marutani, T., 2001. Waiapu River. Source-to-Sink Sedimentary Cascades in Pacific Rim Geo-Systems 184. Palinkas, C.M., Nittrouer, C.A. and Walsh, J.P., 2006. Inner shelf sedimentation in the Gulf of Papua, New Guinea: A mud-rich shallow shelf setting. Journal of Coastal Research 22(4), 760-772. Peacock, D.H., 2004. Bed level changes in the Raparapaririki, Mangapoi and Mangawhairiki streams, Ruatoria, Gisbome District Council, Gisbome. Peacock, D.H., 2004b. Unpublished Waiapu River discharge and suspended sediment data. Pigott, J.D., 1995. A seismic classification scheme for clastic shelf wedges (deltas). In: M.N. Oti and G. Postma (Editors), Geology of deltas. Balkema, pp. 17-29. Porebski, S.J. and Steel, R.J., 2006. Deltas and sea-level change. Journal ofSedimentary Research 76(3-4), 390-403. 54 Posamentier, H.W. and Vail, P.R., 1988. Eustatic controls on clastic deposition 11<>9d\sequence and systems tract models. In: C.K. Wilgus et al. (Editors), Sea level changes: an integrated approach. SEPM, Tulsa, Special Publication 42, pp. 125-154. Posamentier, H.W., Allen, G.P. and James, D.P., 1992. High resolution sequence stratigraphy - the East Coulee Delta, Alberta. Journal ofSedimentary Petrology 62(2), 310-317. Posamentier, H.W. and Allen, G.P., 1999. Siliciclastic Sequence Stratigraphy: Concepts and Applications. SEPM, Concepts in Sedimentology and Paleontology 9, 210. Postma, G., 1995. Causes of architectural variation in deltas. In: M.N. Oti and G. Postma (Editors), Geology of deltas. Balkema, pp. 3-16. Rennie, S., Largier, J.L. and Lentz, S.J., 1999. Observations of a pulsed buoyancy current downstream of Chesapeake Bay. Journal of Geophysical Research C: Oceans 104(8), 18,227-18,240. Roberts, C.S. and Snyder, S.W., 2001. Relationships between shoreline retreat rates, bottom facies, and subbottom stratigraphy, northern Outer Banks, NC. Abstracts with Programs- Geological Society ofAmerica 33(2), 72. Roberts, J.J. and Boyd, R., 2004. Late Quaternary core stratigraphy of the northern New South Wales continental shelf. Australian Journal ofEarth Sciences 51(1), 141- 156. 55 Schioler, P., Crampton, J.S. and Laird, M.G., 2002. Palynofacies and sea-level changes in the Middle Coniacian- Late Campanian (Late Cretaceous) of the East Coast Basin, New Zealand. Palaeogeography, Palaeoclimatology, Palaeoecology 188, 101-125. Scully, M.E., Friedrichs, C.T. and Wright, L.D., 2002. Application of an analytical model of critically stratified gravity-driven sediment transport and deposition to observations from the Eel River continental shelf, Northern California. Continental ShelfResearch 22(14), 1951-1974. Scully, M.E., Friedrichs, C.T. and Wright, L.D., 2003. Numerical modeling of gravity driven sediment transport and deposition on an energetic continental shelf: Eel River, northern California. Journal of Geophysical Research C: Oceans 108( 4 ), 17-1 - 17-14. Smith, J.D. and Hopkins, T.S., 1972. Sediment transport on the continental shelf off of Washington and Oregon in light of recent current measurements. In: D .J.P. Swift, D.B. Drake and O.H. Pilkey (Editors), Shelf Sediment Transport: Process and Pattern. Dowden, Hutchinson & Ross, Inc., Stroudsburg, PA, pp. 143-180. Sommerfield, C.K. and Nittrouer, C.A., 1999. Modem accumulation rates and a sediment budget for the Eel shelf: A flood-dominated depositional environment. Marine Geology 154(1-4), 227-241. Sommerfield, C.K., Drake, D.E. and Wheatcroft, R.A., 2002. Shelfrecord of climatic changes in flood magnitude and frequency, north-coastal California. Geology 30(5), 395-398. 56 Sorrell, B. and Partridge, T., 1999. Conservation values and management of the Kongahu Swamp, Buller District. Science for Conservation (124), 1-50. Stanton, B.R., 1998. Ocean surface winds off the west coast ofNew Zealand: a comparison of ocean buoy, ECMWF model, and land-based data. Journa1 of Atmospheric and Oceanic Technology 15, 1164-1170. Temmerman, S., Wartel, S., Govers, G. and Meire, P., 2003. Modeling long-term tidal marsh growth under changing tidal conditions and suspended sediment concentrations, Scheidt estuary, Belgium. Marine Geology 193(1-2), 151-169. Traykovski, P., Lynch, J.F., Geyer, W.R. and Irish, J.D., 2000. The role of wave-induced density-driven fluid mud flows for cross-shelf transport on the Eel River continental shelf. Continental Shelf Research 20(16), 2113-2140. Trowbridge, J.H. and Kineke, G.C., 1994. Structure and dynamics of fluid muds on the Amazon continental shelf. Journal of Geophysical Research 99(C1), 865-874. Vajda, V., Raine, J.I. and Hollis, C.J., 2001. Indication of global deforestation at the Cretaceous-Tertiary boundary by New Zealand fern spike. Science 294(5547), 1700-1702. Van Ledden, M., Van Kesteren, W.G.M. and Winterwerp, J.C., 2004. A conceptual framework for the erosion behavior of sand-mud mixtures. Continental Shelf Research 24(1 ), 1-11. Vitorino, J., Drago, T., Oliveira, A. and Jouanneau, J.M., 2002. Winter dynamics on the northern Portuguese shelf. Part 2: Bottom boundary layers and sediment dispersal. Progress in Oceanography 52(2-4), 155-170. 57 Walling, D.E. and Webb, B.W., 1996. Erosion and sediment yield: global and regional perspectives. Proceedings of an international symposium, Exeter, July 1996. In: D.E. Walling and B.W. Webb (Editors), Erosion and sediment yield: global and regional perspectives. Proceedings of an international symposium, Exeter, July 1996. International Association of Hydrological Sciences, Publication, 236, pp. 586. Wheatcroft, R.A., Nittrouer, C.A., Sommerfield, C.K., Drake, D.E. and Borgeld, J.C., 1997. Rapid and widespread dispersal of flood sediment on the northern California margin. Geology 25(2), 163-166. Wheatcroft, R.A., 2000. Oceanic flood sedimentation: A new perspective. Continental ShelfResearch 20(16), 2059-2066. Wheatcroft, R.A. and Borgeld, J.C., 2000. Oceanic flood deposits on the northern California shelf: Large-scale distribution and small-scale physical properties. Continental ShelfResearch 20(16), 2163-2190. Wheatcroft, R.A. and Drake, D.E., 2003. Post-depositional alteration and preservation of sedimentary event layers on continental margins, I. The role of episodic sedimentation. Marine Geology 199(1-2), 123-137. Wiberg, P., Drake, D.E. and Cacchione, D.A., 1994. Sediment resuspension and bed armoring during high bottom stress events on the northern California inner continental shelf: measurements and predictions. Continental Shelf Research 14{10111), 1191-1219. 58 Wiberg, P.L., Noble, M., Drake, D.E. and Harris, C.K., 2002. Sediment transport on the Palos Verdes shelf over seasonal to decadal time scales. Continental Shelf Research 22(6-7), 987-1004. Willard, G., 1987. Coastal Resources: East Cape Region Coastal Erosion I Accretion Map. East Cape Catchment Board, Gisbome, NZ. Wilmshurst, J.M., McGlone, M.S. and Partridge, T.R., 1997. A late Holocene history of natural disturbance in lowland podocarp/hardwood forest, Hawke's Bay, New Zealand. New Zealand Journal ofBotany 35(1), 79-96. Wright, L.D. and Coleman, J.M., 1973. Variations in morphology of major river deltas as functions of ocean wave and river discharge regimes. American Association of • Petroleum Geology 57(2), 370-398. Wright, L.D., 1985. River Deltas. In: D.E. Drake (Editor), Coastal Sedimentary Environments. Springer, New York, pp. 1-76. Wright, L.D., Wiseman, W.J., Yang, Z-S., Bornhold, B.D., Keller, G.H., Prior, D.B. and Suhayda, J.N., 1990. Processes of marine diserpsal and deposition of suspended silts off the modem mouth of the Huanghe (Yellow River). Continental Shelf Research 10, 1-40. Wright, L.D. and Nittrouer, C.A., 1995. Dispersal of river sediments in coastal seas: six contrasting cases. Estuaries 18(3), 494-508. Wright, L.D., 1995. Morphodynamics oflnner Continental Shelves. CRC Press, Boca Raton, 241 pp. 59 Wright, L.D., Sherwood, C.R. and Sternberg, R.W., 1997. Field measurements of fair weather bottom boundary layer processes and sediment suspension on the Louisiana inner continental shelf. Marine Geology 140(3-4), 329-345. Wright, L.D., Kim, S.C. and Friedrichs, C.T., 1999. Across-shelfvariations in bed roughness, bed stress and sediment suspension on the northern California shelf. Marine Geology 154(1-4), 99-115. Wright, L.D., Scully, M.E., Friedrichs, C.T. and Kim, S.C., 2001. Effects of ambient currents and waves on gravity-driven sediment transport on continental shelves. Marine Geology 175(1-4), 25-45. Wright, L.D., Friedrichs, C.T. and Scully, M.E., 2002. Pulsational gravity-driven sediment transport on two energetic shelves. Continental ShelfResearch 22(17), 2443-2460. Wright, L.D., Ma, Y., Scully, M.E. and Friedrichs, C.T., 2006. Observations of Across Shelf Sediment Transport During High Energy Flood Events offthe Mouth of the Waiapu River, New Zealand. EOS, Transactions (AGU) 87(36), OSllL-03. Wright, L.D. and Friedrichs, C.T., 2006. Gravity-driven sediment transport on continental shelves: A status report. Continental ShelfResearch 26(17-18), 2092-2107. Zhang, Y., Niedoroda, A.W., Reed, C.W., Swift, D.J.P. and Fan, S., 1999. Two dimensional numerical modeling of storm deposition on the northern California shelf. Marine Geology 154(1-4), 155-167. 60 Figure Captions Figure 1: Study area. Survey lines for both the interferometric bathymetry and the seismic reflection are shown as thick grey lines. Box core locations are plotted as filled circles and vibracore locations are plotted as open circles. The single kasten core was collected at the same location as the northernmost vibracore. Map projection is UTM, Zone 60S. Figure 2: Bathymetry of Region 1. All map projections are UTM, Zone 60S. All white cross-section location lines are shown to scale. A: Generalized bathymetry, region boundaries, and core locations for data presented in Figures 4, 5. Depth intervals are in meters above MLL W, contours are in 5m intervals. Generalized bathymetry, similar to that available prior to our high-resolution study, is used in Figure 2A both for clarity and to show limitations in detail available with this type ofbathymetry. B: Detailed bathymetry ofRegion 1. Depth intervals are in meters above MLLW, contours are in 4m intervals, vertical exaggeration is 6x. White box indicates extent of rocky enclosures (inset shown in C). Black arrow shows direction of bathymetric low relative to offshore sediment transport. Location of bathymetric sections (Figure 3) are noted by solid white lines A-A'. Location of seismic sections (Figure 4) are noted by solid white lines d-d' and e-e'. C: Detailed bathymetry ofthe rocky enclosure area within Region 1. Depth intervals are in meters above MLLW, contours are in 4m intervals. Note change in horizontal scale; all other scaling remains constant. B-B' and C-C' lines indicate bathymetric cross-sections shown in Figure 3. 61 Figure 3: Bathymetric cross-sections. A, Band C show bathymetric cross-sections A-A', B-B' and C'C' (Figure 2), respectively. Vertical exaggeration is 6x. Location of seismic cross-sections (Figure 5) are indicated by white f-f and g-g' lines, respectively. Figure 4: Seismic profiles from Region 1, with associated sediment data. A: Seismic profile d-d' showing the 3m reflection surface (see Fig. 2 for locations). B: Acoustically transparent seismic profile e-e' (see Fig. 2 for locations). Representative box core and vibracore grain-size data are plotted inC and D, respectively. Dashed line on D indicates beginning of fining-upward sequence. D includes a core log of sediment type based on the field description of the vibracore sediments (vertical scale consistent with presented vibracore data). Figure 5: Location of the observed Waiapu paleochannel in reference to the bathymetric low. A: Black line shows location of A-A' bathymetric section; dashed-white portion indicates relative length of seismic section b-b'. Depth intervals are in meters above MLL W. B: Bathymetric section A-A' with location of seismic section b-b'. C: Seismic section b-b'. Figure 6: Seismic profiles from the rocky enclosures. in Region 1, with associated sediment data. A shows profile f-f; B shows profile g-g' (see Fig. 3 for locations). Representative box core and vibracore grain-size data are plotted inC and D, respectively. Dashed line on D indicates beginning of fining-upward sequence. D includes a core log of sediment type based on the field description of the vibracore 62 sediments (vertical scale consistent with presented vibracore data). Figure 7: Bathymetry of Region 2. All map projections are UTM, Zone 60S. All white cross-section location lines are shown to scale. Vertical exaggeration is 6x. A: Generalized bathymetry, region boundaries, and core locations for data presented in Figures 9, 10. B: Detailed bathymetry for Region 2. Depth intervals are in meters above MLL W, contours are in 4m intervals. Black arrow shows direction of bathymetric low relative to offshore sediment transport. Location of bathymetric sections (Figure 8) are noted by solid white lines A-A' and B-B'. Location of seismic sections (Figures 9, 10) are noted by solid white lines c-c' and d-d'. Figure 8: Bathymetric cross-sections. A and B show bathymetric cross-sections A-A' and B-B' (Figure 7), respectively. Vertical exaggeration is 6x. Figure 9: Seismic profiles from the southern portion of Region 2, with associated sediment data. A: Representative seismic profile a-a' (see Fig. 7 for location). Representative box core and vibracore grain-size data are plotted in B and C, respectively. Dashed line on C indicates beginning of fining-upward sequence. C includes a core log of sediment type based on the field description of the vibracore sediments (vertical scale consistent with presented vibracore data). Figure 10: Seismic profiles from the northern portion of Region 2, with associated sediment data. A: Representative seismic profile b-b' (see Fig. 7 for location). 63 Representative box core and vibracore grain-size data are plotted in B and C, respectively. Dashed line on C indicates beginning of fining-upward sequence. C includes a core log of sediment type based on the field description of the vibracore sediments (vertical scale consistent with presented vibracore data). Figure 11: Seismic profile taken along a representative (30m) inner shelf isobath. Map projection is UTM, Zone 60S. A: Location of seismic line, shown to scale. Black arrow shows direction of bathymetric low relative to offshore sediment transport. B, C, D: Example of seismic profiles along the same bathymetric contour. Figure 12: Photograph of the Waiapu River surface plume. View is to the north, towards East Cape. Photo courtesy of J. McNinch. Figure 13: Bathymetric sections showing the location of the southern-trending bathymetric low. Map projection is UTM, Zone 60S, view is looking offshore. Vertical exaggeration is 6x. A: Map view showing the relative location of the river mouth and location of cross sections (white lines) profiled in 88 . Red lines indicate where the across-shelf slopes between 5 and 50 meters water depth were calculated. Yell ow arrow shows the direction the bathymetric low trends across the shelf when the offshore transport of sediment discharged from the Waiapu River is considered. B: Along-shelf bathymetric sections, from north to south, deepening offshore. Colors of cross-sections represent depth in meters above MLL W, and correspond to colors on A. Relative river location is denoted by red arrows, and paleochannel cross-section (as defined in Figure 64 7), is noted by red bracket. Yellow arrow delineates offshore-trend of bathymetric low in the context of offshore transport of sediment from the Waiapu River. Figure 14: Location of paleochannel and reconstructed paleosurface. All map projections are UTM, Zone 60S A: Location map with dashed box representing approximate zoomed-in region in panels Band D. Depth intervals are in meters above MLLW, contours are in 5m intervals. B: Modem bathymetric surface. Depth intervals are in meters above MLL W, contours are in 5m intervals. Black lines represent digitized paleochannel from the seismic profiles. Red hashed and solid lines indicate probable and observed extent of paleochannel in the seismic record, respectively. Orange J-J' line indicates location of cross-section shown in C. C: Representative seismic line showing the paleochannel, and the overlying, continuous reflection surface. D: Contoured continuous reflection surface, as derived from digitized seismic profiles. Contours are in lm intervals, and represent depth below modem seafloor. Red lines indicate the location of the modem bathymetric low (from Figure 12) relative to a similar low in the underlying strata. 65 Legend 8 Boxcore · · '-~'."'' 0 Vibracore ...... V'l 0 \0 Q) c 148 0 N ~ I- ::> 122 -0\ c ..!::. +-' lo.... 0 z 620000 630000 640000 650000 Easting (UTM Zone 605) Figure 1-1 620000 East Cape, New Zealand X X 0 X ~0 Cll 0 X 0 0 Figure 1-2 ~ ....J ~ ~ A 0 (I) .a -E ..c::-...... a. (I) "'0 B "'- ...... (I) ca ~ c South distance (m) along transect North Figure 1-3 SOOfneters A e e' ------500 meters 6 meters B -<>-VC % Sand1 -<>-BC% Sand Region 1 Region 1 :-+-VC% Fine~ Vibracore -+-BC%Fines' Box Core Weight Percent Weight Percent 0 50 100 0 50 100 c 300 l.------1 D Figure 1,-4 Easting (UTM Zone 60S) 620000 640000 East Cape, New Zealand X X 0 X X _.._0 (/)0 X X cO (0 ~ Q) It) t: ~ X ::2 1- X 2. Cl X :ct: t:: z0 South North Figure 1-5 f' A ----=-~------Rocky Area ~VC%Sand Rocky Area Box Core ~VC% Fines Vibracore Weight Percent Weight Percent 0 50 100 0 50 100 0 O· 0 .!::: "iii >. 2 50 ~ ttl 3 u "0 4 0 1: E" E"1oo · 0 ttl .e. .e. VI... -5 5 -5 0 Cl. Cl. 1: CD CD .E c 6 0150 .!: 7 "§- 0 8 200 0 "iii N - >. (II 9 >. uttl 10 c D Figure 1-6 Easting (UTM Zone 60S) 620000 640000 East Cape, New Zealand X X X X X Figure 1-7 A --E -..c_. a. Q) "'C L- _.Q) ca B 3: South distance (m) along transect North Figure 1-8 south north a a' -<>- BC % Sand [ Region 2 South Region 2 Sout ....._.BC%Fines[ Box Core ' ...... vc%Fines Vibracore Weight Percent Weight Percent 0 50 100 0 50 100 Clayey sand w/ laminae of clayey silt. 10 100 e Percent ~ I 150 ;; 15 clay in the ..,c. t c .! 200 clayey sand 20 increases 250 up-core. 0 300 0 M 350 c Figure 1-9 south north b b' northernmost in region 2 500 meters ~eafloor multi ple----.,.J ~BC%Sand Region 2 North ~~VC%Sand Region 2 Nort Box Core -+-BC% Fines : -+-VC % Fines Vibracore Weight Percent Weight Percent 0 50 100 0 50 100 50 e ~--- f150~------<~ a. 2: 200 "'0 c 1'0 Vl 300 l.....------1 c Figure 1-10 Figure1-11 Figure 1-12 North South North relative location paleochanneiSouth I I) ' --- A . - --, - ___ A' lOll 0 1000 "0 J illOO 4000 B' iOIJll c 4000 A D 1!1iJO I, - - G ~-=~= ~~~i~:-~~~~~~~~:_-- -~~~:= c1 -- -='5-~-=~~~=~~~;:~a--~,=---=--~2~-=---=oa=_~~-2-'::_~~~~~~~ , --~=-~~~~~=c~-'~~~=~~~~s--.0~:::~ ~ -=:=-~~-~,~~~~,~," )S J H ' H' 4} () - --~ ~ -~ --~ ------(J I()()() ')(I ](1()0 400() B distance (m) along transect Figure 1-13 Easting (UTM Zone 60S) 620000 630000 0 0 0 Easting (UTM Zone 60S) 0 N Ui 00 620000 640000 0 1.() (0 Q) East Cape, New Zealand c: 0 rno X X N gg X ::2 1- 0 Q)O 0 eN 2. 0 O A B Easting (UTM Zone 60S) 630000 0 0 0 0 N ~ 00 ~ 1.() 10 (0 Q) c ~ 15 ::2 1- 2. c:Cl :c t zg0 0 1.()...... 00 c 1.() D Figure 1-14 Controls on Continental Shelf Stratigraphy: Waiapu River, New Zealand Chapter 2 Black carbon chronostratigraphic evidence of deforestation preserved on the inner shelf of the Waiapu River, New Zealand Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Abstract The nature and distribution of terrestrial-derived sediments preserved in the marine stratigraphic record provides insight into the complex linkages inherent in source to-sink sediment dynamics. New Zealand provides an ideal locale for refining our understanding of these linkages due to widespread deforestation, the majority of which occurred at turn of the last century with the rapid expansion of European settlements. Recent studies have identified several changes in sedimentation patterns in New Zealand estuaries and coastal environments which appear to be related to extensive catchment clearing, though the actual effects may be system-specific. As of yet, no single, definitive indicator of the onset of deforestation in New Zealand catchments has been identified in the adjacent marine sinks. The catchment of the Waiapu River was heavily deforested from ~ 1920-1940 by European slash-and-bum practices, and the resulting increase in gully erosion elevated the sediment discharge nearly 5-fold. This widespread burning likely resulted in a significant increase in black carbon (BC) discharged to the continental shelf. In this study, we: 1) document the presence ofBC as an indicator of deforestation; and 2) . establish the recent geochronology of the marine stratigraphic record as characterized by non-steady-state deposition and heterogeneous sediment distributions, using total organic carbon (TOC), total nitrogen (TN), carbon/nitrogen ratios (C/N), and the black carbon (BC) spectrum preserved in sediment cores from the Waiapu River inner shelf. Using the presence of BC as a unique and presumably unambiguous chronostratigraphic marker, we calculate that the inner shelf currently sequesters ~ 16-34% of the total Waiapu fine sediment budget. These data also suggest that sediment capture on the inner shelf results 81 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 from the system's ability to segregate fine sediment being overwhelmed by increased sediment discharge, and not necessarily from a change in oceanic or riverine dispersal mechanisms. 82 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 1.0 Introduction 1.1 Deforestation and source-to-sink dynamics A quantitative understanding of sediment exchanges at the land-sea interface is critical for elucidating the complex linkages between continent-to-coastal ocean sediment dynamics. A key component of the Margins Source-to-Sink initiative focuses on the relationships between: 1) erosion and sediment transfer in catchments (source); and 2) associated deposition and stratigraphy formation on continental shelves (sink). In New Zealand, previous studies have attempted to relate changes in continental shelf . sedimentation and associated marine stratigraphy formation to the onset of deforestation induced sedimentation (e.g. Goff, 1997; Sorrell and Partridge, 1999; Anderson et al., 2004; Gomez et al., 2004). These approaches and others are needed for refining our understanding of the influence of catchment processes on nearby continental shelf sediment dynamics. Previous research in severely deforestation-affected coastal environments has . sought to: 1) identify changes in sediment deposition preserved in coastal and shelf stratigraphy; and 2) relate these changes to the onset ofdeforestation-enhanced sedimentation. Increased inputs of terrigneous matter to coastal bays, estuaries and continental shelves have been identified in sediments using several approaches including, but not limited to, changing grain-size regimes (e.g. Goffet al., 1997; Anderson et al., 2004), mineralogical shifts (e.g. Gomez et al., 2004), increases in carbon/nitrogen (C/N) ratios (e.g. Gomez et al., 2003; Forrest et al., 2007) and shifts in pollen types, as indicative of changing land plant distributions and abundances (e.g. Wilmshurst, 1997; Wilmshurst et al., 1997). These tools and the resultant observations have been critical for 83 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 refining our understanding of the influence of catchment processes on nearby coastal sediment dynamics. Changes in the above indicators, however, are not always the result of deforestation-influenced processes alone. Therefore, identifying a parameter which can be definitively linked to deforestation is essential for defining the specific response of a coastal sink to a specific change in its associated catchment source. To the best of our knowledge, no study has yet identified a specific and unambiguous, chronostratigraphic horizon within continental shelf sediments that is the actual footprint or signature of deforestation itself. This is important because the specific response of coastal and continental shelf sediment dynamics to deforestation may be system-specific. For instance, deforestation-induced sedimentation has been suggested as a key factor causing an increase in coarse sediment in Wellington Harbor and the Okura estuary (Goff, 1997; Anderson et al., 2004) and, conversely, an increase in fine sediment offshore ofthe Waipaoa and Waiapu rivers (Gomez et al., 2004; Wadman and McNinch, 2008). These seemingly contradictory observations may be explained by differences in transport mechanisms as well as by both increases in coarse sediment load (via more direct input, such as landsliding) and/or corresponding decreases in particle segregation efficiency. These observations suggest that recognizing shifts in grainsize regimes, or · other individually measured parameters, may not be sufficient to definitively attribute an observed stratigraphic shift solely to deforestation at a given location. Techniques used to identify changing sedimentation patterns in specific environments (e.g. shifts in coarse-grained mineralogy) are not always applicable to other systems (e.g. muddy mid outer shelves). Compounding the problem, chronological control using traditional radioisotopes is not applicable in all deforestation-affected environments (e.g. Smith, 84 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 2001; Gehrels et al., 2008). If the signature of deforestation itself can be identified in coastal and marine sediments using a widely-applicable technique, then the influence of various deforestation-induced changes in sedimentation may be more clearly id~ntified. 1.2 Potential role ofblack carbon Black carbon (BC) is the ubiquitous stable product of the incomplete combustion of biomass and fossil fuel and is found nearly everywhere due to widespread aeolian transport (e.g. Masiello, 2004 ). BC particles range in size from macroscopic charred plant biomass and charcoal (coarse BC) to microscopic soot and graphite (fme BC) sourced from sedimentary rocks as well as the incomplete combustion of fossil fuels. BC particles are relatively inert, and have been recognized as a significant potential sink for atmospheric,C02 (e.g. Hedges and Keil, 1995; Jones and Chaloner, 1991; Dickens et al., 2004; Druffel, 2004; Masiello, 2004; Brodowski et al., 2005; Bond et al., 2007; Hammes et al., 2007). Data from shallow coastal shelves indicate that BC usually accounts for less than 50% ofthe total marine sedimentary organic carbon (Hedges and Keil, 1995; Masiello, 2004). While soils are one of the largest initial sinks of BC particles, the inert nature makes them readily transportable, and the deep ocean is considered to be a significant, if poorly understood, BC sink (e.g. Masiello, 2004). A region that has been extensively _ burned during wide-scale deforestation, such as the Waiapu River catchment, would be expected to have relatively high levels of BC present in its soils (e.g. Hedges and Keil, 1995; Clark and Royall, 1996; Masiello, 2004 ). If wide-scale deforestation is coupled 85 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 with extensive erosion, the eroded sediments might be expected to have high levels of BC (Masiello, 2004). Coarse BC (plant char and charcoal) provides an immediate paleotracer over a range of transport distances of meters to kilometers, with increases of coarse BC in lacustrine and soil profiles being strongly linked to local biomass burning (Clark and Royall, 1996; Clark, 1997; Clark et al., 1998; Ohlson and Tryterud, 2000; Carcaillet et al., 2001; Lynch et al., 2003; Masiello, 2004; Asselin and Payette, 2005). In contrast, due to the widespread nature of aeolian transport of fine-grained material, soot and graphitic BC provides a potentially much longer paleotracer range of up to 10 3km (Hedges et al., 2000; Masiello, 2004). This complicates the use of fine BC as a small-scale (e.g. watershed) paleotracer, as unlike coarse BC, increases in fine BC may have a more eustatic, rather than just local, source. Increases in fine BC in near-surface marine sediments have been linked not just to regional biomass burning but also to the heightened combustion of fossil fuels in the latter half of the 20th century (e.g. Gustafsson et al., 1997; 2001; Bucheli et al., 2004; Masiello, 2004; Wakeham et al., 2004; Bond et al., 2007; Elmquist et al., 2007). In heavily burned regions, increases in both coarse and fine BC from combustion preserved within adjacent coastal sediment cores indicate significant local or regional burning, as well as preserving a record of the onset of increase modem fossil fuel combustion, providing powerful chronological tools. Thus, elevated levels of BC within a sedimentary deposit can potentially be used as a chronological and stratigraphic indicator of the onset ofwidespread burning and deforestation (Masiello, 2004 ). 86 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 This study examines the distribution of BC preserved in sediment cores from the inner continental shelf off the Waiapu River to: 1) document BCpresence as an indicator of deforestation; and 2) establish recent geochronology in marine stratigraphy characterized by non-steady-state deposition and heterogeneous sediment. We use BC distribution as a chronological baseline from which to estimate the percentage of modern fine-sediment budget preserved onthe Waiapu inner shelf. Sediment grainsize, total organic carbon (TOC), total nitrogen (TN) and carbon/nitrogen (C/N) ratios above and below this BC marker are quantified to support the use of BC as an indicator of the deforestation event itself, and elucidate changes, if any, in riverine and oceanic processes due to deforestation. 2.0 Background 2.1 Study area Located on the East Cape of the North Island ofNew Zealand (Figure 1), the Waiapu River discharges approximately 36 x 106 tonnes of sediment a year and is ranked among-the highest sediment yielding rivers in the world (Walling and Webb, 1996; Hicks et al., 2000; Hicks et al., 2004). Rocks in the Waiapu catchment are composed primarily of crushed and sheared portions of the sedimentary East Coast Allocthon as well as poorly consolidated Miocene-Pliocene mudstones and sandstones (Moore and Mazengarb, 1992). The East Cape region is tectonically active and has experienced more than six earthquake events of magnitude >6 between 1964 and 1994. Abundant precipitation in the region averages 2400 mm/yr ( ~ 1600mm/yr at coast, >4000mm/yr in 87 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 mountains; Page et al., 2000). These conditions contribute to the susceptibility of the rocks to gully and deep-seated earthflow erosion. In their study of the shallow stratigraphy of the inner shelf, Wadman and McNinch (2008) delineated large-scale differences in the character of the sediment being preserved on the Waiapu inner shelf(Figure 1). Located mostly north ofthe river mouth, Region 1 was characterized as being primarily plume-dominated, with poorly-sorted and fining-upward muddy sands overlying a transgressive lag. South of the river mouth, Region 2 was characterized by muddy sands interlaminated with muds, and interpreted to represent a shelf dominated by bathymetrically-controlled flood deposition and preservation. For the purposes of this study, we interpret Region 1 as being dominated by settling from hypopycnal plumes and Region 2 as being dominated by deposition from repeated flood events. Wadman and McNinch (2008) tentatively linked the fining upward sequence preserved in most of the cores to inefficient segregation of deforestation-enhanced sediment yields, but lacked any definitive chronological control to support these interpretations. On the mid-outer shelf, Kniskern et al (in review) related high rates of modem deposition of muddy sediments, based in part on non-steady-state 210Pb accumulation profiles, to deforestation-enhanced sediment yields, but were unable to recognize the exact onset of deforestation in any of their cores. Finally, Addington et al. (2007) and Ma et al. (2008) observed southward-directed steering ofbathymetrically controlled flood deposits across the shelf and ultimately preserved within outer-shelf basins, similar to that observed on the inner shelf by Wadman and McNinch (2008). 88 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 2.2 Deforestation and catchment response Colonization ofNew Zealand by Polynesian (Maori) settlers commenced approximately 900-800 14C yr B.P. (Wilmshurst, 1997; Eden and Page, 1998; McGlone and Wilmshurst, 1999). Within a few hundred years, up to 40% of New Zealand native forest and bush had been cleared for agricultural purposes by a combination of logging and burning (McGlone et al., 1994; Eden and Page, 1998; McGlone and Wilmshurst, 1999; Page et al., 2001). Very little Maori-related burning, however, was documented specifically in the Waiapu catchment (e.g. McGlone and Wilmsurst, 1999). European settlement-related deforestation of much of the remaining indigenous forest in New Zealand accelerated between 1860 and 1940. Burning reached a peak in the previously unaltered Waiapu catchment around 1920 (Page et al., 2000). By 1940, European settlers had cleared most of the Waiapu hinterland and all but a few percent of the land was converted to pasture, initiating a phase of greatly increased erosion and sediment transfer (Page et al., 2001). Currently, the Waiapu catchment contains 37% pasture, 26% exotic forest, 21% indigenous forest and 12% scrub (Page et al., 2001 ). In the Waiapu River catchment, erosion has accelerated 4-5-fold since post colonial deforestation, and the system has shifted from a rivulet-dominated to a gully dominated erosion system, greatly increasing the amount of fine sediment discharged to the sea (Page et al., 2000; Hicks et al., 2003). The combination of frequent erosion generating storms and the exposure via deforestation of highly erodable rocks has resulted in numerous scars of massive debris flows up to 3000 km2 in volume (Collot et . al., 2001). This abundant erosion has resulted in channel aggradation of the Waiapu River as well as its two main tributaries, the Tapuaeroa and Mangaoporo Rivers. 89 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Channels are widening via inundation and bank erosion, and the rapid rate of aggradation is a major threat to the floodplain, roads and bridges (Page et al., 2000). In addition, progradation of the shoreline near the Waiapu mouth due to the increased sediment load has resulted in an apparent local regression off of the East Cape ofthe North Island (Gibb, 1981, 1994). High aggradation rates along the beaches (from 85-140 meters south ofthe mouth, to 108-380 meters north ofthe river from 1915-1979; Gibb, 1981), reflect the migration of the shoreline seaward. 2.3 Sources and characteristics ofcoastal organic matter ·The composition of buried organic matter (OM) in continental shelf sediments is a reflection of both watershed and oceanic processes (e.g. Blair et al., 2004; Leithold et al., 2005; Leithold et al., 2006), and it is estimated that as much as 90% of total oceanic organic carbon burial is sequestered in continental shelf and slope sediments (Hedges and Keil, 1995). Although riverine OM consists largely of highly degraded, nitrogen-poor remains of terrestrial organisms, this dissolved and particulate organic carbon still represents a potentially significant pool of labile OM which may subsequently be remineralized in the oceans, primarily in continental margins, waters and sediments (e.g. Hedges et al., 1997; Aller, 1998; Aller and Blair, 2006). Ultimately, the composition and amount of OM associated with a shelf sediment deposit is a function of several factors including oxygen concentration, local sediment composition and rate of deposition, the magnitude of river and estuarine inputs, hydrodynamic sorting of sediments during deposition and the total productivity of overlying waters (e.g., Hedges and Keil, 1995; Bergamaschi et al1997; Leithold et al., 2005; Leithold et al., 2006). 90 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 The total organic carbon (TOC) to total nitrogen (TN) ratio (C/N ratio) of OM is strongly influenced by its origin and degradation, with land-derived OM having a higher CIN ratio than marine OM (e.g. Bordovskiy, 1965; Prahl et al., 1980; Meyers, 1997; Maksymowska et al., 2001 ). Marine plankton generally have a C/N ratio of ~6- 7, while terrestrial C/N ratios from vascular plants range from 15 to 20 or greater (Redfield et al., 1963; Meyers, 1994, 1997; Jaffe et al., 2001; Maksymowska et al., 2001; Forrest et al., 2007). C/N ratios for OM associated with marine sediments may thus be used as an indicator of terrestrial and riverine influences (e.g. Stepanauskas et al., 2002; Forrest et al., 2007). A potential complication arising from the common elemental analysis of TOC and TN in a sample lies in the assumption that after removal of inorganic carbon, all of the nitrogen left in the sample is organic. In most marine sediments, the inorganic nitrogen concentration is small relative to the organic nitrogen, and thus not likely to affect C/N ratios derived from a sample after removal of carbonate carbon (Meyers, 1997, 2003). In sediments having low OM concentrations (Corg<0.03%), however, inorganic nitrogen may represent a significant portion of the TN (e.g. Meyers, 1997; Jia and Peng, 2002). 2.3 Influence ofcatchment and sediment burial dynamics on OM and C/N distributions Recent work on the Eel River margin has shown that the faster terrestrial OM is transported through a watershed and buried below the actively resuspended layer, the more likely it is to preserve its terrestrial signature (Blair et al.,2004; Leithold et al., 2005). Specifically, OM derived from the catchments of small, mountainous rivers with high sediment yields and dominated by gully erosion will undergo little change in 91 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 composition before delivery, as significant exchange processes for OM during its transport from source to sink have not been identified. Organic material is ultimately delivered unaltered to the adjacent continental shelf, resulting in the preservation of significant amounts of old (kerogen) carbon (Massielo and Druffel, 2001; Blair et al., 2004; Gofii et al., 2005; Ogrinc et al., 2005; Leithold et al., 2006). Where the adjacent shelf experiences high rates of sediment accumulation and associated OM matter burial due at least in part to frequent flood events and high sediment yields, such as on the Eel and Waiapu mid-outer shelves, terrestrial OM is not always completely remineralized before removal from the actively resuspended layer. As such, OM in these environments has been shown to be a mixture of marine, terrestrial and bedrock-derived (kerogen) material (Blair et al., 2004, Leithold et al., 2005; Leithold et al., 2006). The effect ofthe Waiapu River catchment changing from landslide-dominated to gully-dominated erosion on OM composition and burial in marine sediments is still unknown. Previous work indicates that OM from Waiapu River samples is bimodal in age, indicating OM is comprised not just of recent plant material but also a significant amount of ancient, bedrock-derived carbon (Lyons et al., 2002; Carey et al., 2005; Leithold et al., 2006). Wadman and McNinch (2008) found that a substantial amount of fine-grained sediment, and thus any associated OM, was preserved on the energetic inner shelf. They also showed that small-scale, antecedent bathymetry near the river mouth was pivotal in steering the direction, and ultimate deposition and preservation, of flood derived sediment. The organic C/N ratios in a sediment profile spanning the pre- to post deforestation period is hypothesized to reflect an increase in the preservation of terrestrial OM, making the inner shelf an excellent part of the system for examining the influence of 92 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 major shifts in catchment dynamics on marine sediments. By further comparing the C/N ratios preserved both along the shelf and within a given sediment profile, the influence of small-scale antecedent bathymetry on shelf-wide sediment transport should be more fully delineated. Another factor complicating the above-mentioned influence of catchment and burial dynamics on OM composition is grainsize effects. Organic carbon (OC) content is strongly correlated with surface area (Hedges and Keil, 1995; Meyers, 1997) and OM associated with sand-sized grains is distinctly different from that associated with finer material, representing material of distinct origins or diagenetic history (e.g. Prahl et al., 1994; Hedges and Keil, 1995; Bergamaschi et al., 1997; Meyers, 1997; Blair et al., 2004). For example, OM associated with sand-sized material has been shown to have a greater terrestrial contribution while OM associated with finer material may in some environments be associated with fossil (kerogen) bedrock carbon (e.g. Bergamaschi et al., 1997; Blair et al., 2004; Leithold et al., 2006). As a result, factors that control grainsize distributions frequently play a significant role in determining the type and amount of organic matter preserved in heterogeneous sediment (Bergamaschi et al., 1997; Blair et al., 2004; Leithold et al., 2006). 2.4 Chronological control ofsediment accumulation in heterogeneous environments Natural and anthropogenic radioisotopes are the mostwidely used method for identifying the onset of Holocene to modem (~ 1OOya) sediment accumulation in estuarine and coastal environments. Common and well-understood tracers of sediment accumulation and biological mixing for modem accumulation include 234Th (24.1 days), 93 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 7Be (53.3 days), 210Pb (22.3 yr), 137Cs (30.1 yr), bomb-spike increased 14C (5730 yr) and 239 40 4 • Pu (2.4x10 , 6563yr; see review by Sommerfield et al., in press)._ Each of these methodologies, however, has inherent limitations that must be considered when attempting to apply them to estuarine and coastal environments. For example, sediment accumulation rates based on 210Pb decay profiles can be strongly influenced by non steady state 210Pb atmospheric fluxes (e.g. Kuehl et al., 1986), non-steady state sediment deposition (e.g. Smith, 2001), bioadvection (e.g. Carpenter et al., 1982; DeMaster et al., 1985) and sediment grain-size and porosity effects (e.g. He and Walling, 1996). The use of an independent chronological marker such as 137Cs can help elucidate the above complications, but given the low fallout rates of bomb spikes in the southern hemisphere, its application in New Zealand is limited at best (e.g. Smith, 2001; Gehrels et al., 2008). Therefore, in regions ofNew Zealand characterized by non-steady state sediment deposition and heterogeneous grainsize, traditional radioisotope dating methods may not always be able to confidently identify the onset of modern sediment accumulation (e.g. Gehrels et al., 2008). In this study, we will attempt to apply traditional 210Pb dating methodology to the Waiapu inner shelf sediments, providing a first-order comparison of traditional vs. more novel dating techniques in heterogeneous sedimentary environments. 3.0 Methods 3.1 Core selection and lithologic analysis Wadman and McNinch (2008) identified two regions on the inner shelf, based on seismic profile characteristics and grainsize profiles derived from box cores and vibracores, where: 1) sediment deposition was dominated by hypopycnal plume settling; 94 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 and 2) sediment deposition was dominated by flood events. For the purposes of this study, we selected two representative cores from each region(Figure 1). Cores A and B represent the protected rocky areas and exposed shelf areas of the plume-dominated region, respectively. Cores C and D represent areas of varying flood layer preservation from the flood-dominated region. Core E (plume-dominated region) was not chosen for detailed analysis as it is very similar in lithology to Core B. However, due to the excellent preservation of a likely transgressive lag layer and its potential for constraining regional chronostratigraphy, several samples were selected from CoreE for 14C dating (Figure 1). A series of nine vibracores was collected on the inner shelf in May and June of 2004 on the RN Kilo Moana in order to groundtruth previously collected seismic data. After recovery, vibracores were immediately cut into 1.5-meter lengths and frozen on board to preserve them for OM-related analyses. Additional description of the sampling strategy for the vibracores is presented in Wadman and McNinch (2008). In order to facilitate sub-sampling, the individual 1.5-meter sections were briefly thawed prior to splitting and the outside of the barrels cleaned to minimize potential contamination. Core sections were split on-deck and immediately carried into a clean laboratory, placed on a workbench covered with clean aluminum foil, and sliced open using piano wire cleaned with DI water. Core sections were photographed and the sediment described at the centimeter level prior to sampling. One half of the core was designated for various OM analyses and sub-samples were immediately re-frozen in whirlybags. Care was taken to not include sediment that was in obvious contact with the sides of the vibracore barrel in order to minimize potential contamination. The other core 95 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 half was sampled at the same interval for lithology (grain-size) analysis. All cores were sampled at 1Ocm intervals, in addition to where lithologic changes were noted. Core logs are based on field descriptions and photographs. Sand/silt/clay ratios were generated for all samples using standard wet sieve and pipette analysis (Gee and Bauder, 1986). For the purposes of this study, the term "fine-grained" refers to sediments :S63 J.tm. 3.2 TOC and TN analyses Sediment from frozen core subsamples was used for organic C and N analysis. Subsamples were thawed, homogenized, and split into two fractions for both bulk and fine analysis. Given the heterogeneous nature ofWaiapu inner shelf sediments, OM composition was determined for both bulk and fine ( <63 J.tm) sediment fractions in order to account for potential grainsize influences. The bulk sub-sample was dried at 60°C and pulverized using a COORS ceramic-glazed mortar and pestle. Approximately 25-50mg of sample was weighed into pre-tared tin capsules using a Fisons Instruments Sartorious M2P electronic microbalance, with triplicates being weighed for all samples. Samples were then acidified using 1M HCl to remove carbonates and the composition of the prepared samples was determined using a CE Elantech FlashEA 1112 Series NC Soils elemental analyzer at standard operating parameters. Several acetanilide standards and blanks were included with each sample run. Standard deviations between replicates were determined using ThermoElectron software. If the standard deviation (95%CI) of a sample (as determined from the replicates) was greater than 0.15, additional replicates were analyzed as needed to ensure a relative standard deviation of all replicates to be less than 0.15. 96 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 For TOC and TN analysis of the fine (<63J..UU) fraction, approximately lOg of sediment was placed into pre-weighed and muffled beakers and ~ 1Oml of sodium 1 1 metaphosphate (51gL- ) and sodium bicarbonate (0.3gL- ) dispersant mixed with high purity DI water was gently stirred into the sample. Samples were sieved using muffled glassware and acetone-cleaned sieves. Once sieved, the coarse fraction was retained for coarse BC analysis. Approximately 500-7 50ml of fines were pipetted from each sieved sample and allowed to dry, loosely covered by muffled aluminum foil, at 60°C. Samples were recovered using muffled spatulas and stored until use in pre-muffled scintillation vials. Elemental analysis followed the procedure outlined above for bulk sediments, with duplicates or triplicates analyzed for all fine-sediment samples. Unfortunately, insufficient frozen sample was available for sieving the fine-grained fraction of Core B samples for TOC and TN analysis. Therefore, bulk TOC and TN results are only reported for this core. 3.3 Black carbon analyses Much of the current research concerning BC is focused on improving quantification methods over various parts of the combustion continuum in an aim to better quantify this poorly understood, yet potentially significant, carbon sink (see reviews in Masiello, 2004 and Hammes et al., 2007). Currently, no single, ideal method exists that can easily and quantitatively measure the total BC spectrum in a given sample (Hammes et al., 2007). By combining multiple methods, however; a measure of relative changes in total BC in marine sediments can be obtained. Specifically, coarse BC (char and charcoal) can be quantified via sieved microscopic, thin section or pollen slide counts 97 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 (e.g. Clark et al., 1998; Carcaillet et al., 2001; Asselin and Payette, 2005) while fine BC can be quantified using a variety of chemical techniqes. While several methods are currently being developed that can quantify fine BC (soot and graphitic), chemo-thermal oxidation (CT0-375) as developed by Gustafsson et al. ( 1997; 2001) has repeatedly been shown to be a relatively simple and yet rigorous methodology for use in marine sediments (e.g. Middleburg et al., 1997; Hammes et al., 2007). A key advantage to the Gustafsson et al., (1997) method is that it has been specifically developed for determination of low quantities of BC in complex sedimentary matrices with refractory OM and carbonate minerals (e.g. Middleburg et al., 1997; Masiello, 2004; Hammes et al., 2007). A disadvantage to CT0-375 is that it may create BC due to incomplete combustion (charring) related to oxygen-starvation (Gustafsson et al., 2001; Hammes et al., 2007). This potential artifact may be minimized by loose packing of samples, careful loading of the muffle furnace, and by introducing excess oxygen during the combustion-phase (e.g. Gustafsson et al., 2001). In a comparison study involving CT0-375 methodologies where the primary difference was the presence or absence of controlled amounts of excess oxygen (muffle furnace vs. tube furnace with external oxygen supply), Gustafsson et al. (200 1) determined that with thinly spread and finely homogenized samples accompanied by low muffle furnace loadings, there was ample oxygen supply and insignificant charring. They further suggested that when TOC profiles are decoupled from BC profiles that little significant overestimation ofBC via charring had likely occurred. 98 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 3.3.1 Coarse sedimentary black carbon analysis The coarse (>63J.Lm) sediment fraction recovered from sieving for fine-grained TOC and TN analysis was analyzed for coarse BC in cores A, C and D, following the methodology outlined in Clark et al. (1998) and Carcaillet et al. (200 1). Briefly, 1cm 3 sub-samples were separated for each sample, and spread onto gridded Petri dishes. Charred particles were identified as described by Clark et al. (1998) using a dissecting microscope. Coarse BC samples for core B were recovered by sampling and sieving non frozen sediment samples. Standard deviations were calculated using Excel software based on the background coarse BC counts per sample (cps) for each core. 3.3.2 Fine sedimentary black carbon analysis The sample remaining from fine-grained TOC and TN analysis for cores A, C and D was used for fine BC analysis. The protocol follows that described in Gustafsson et al. (1997). Briefly, after drying, samples were pulverized and ~50mg of sample was thinly spread over pre-tared and pre-muffled porcelain crucibles, covered loosely with muffled aluminum foil, and combusted at 375°C for 24 hours. Care was taken to loosely spread the samples on the crucibles and to use low muffle furnace loadings, as excess oxygen was not introduced into the furnace. After combustion, ~ 20mg (depending on residue availability) was weighed into pre-tared tin capsules, with duplicates being prepared for all samples. Samples were then acidified following the Gustafsson et al. (1997) protocol to ensure complete removal of carbonate carbon, and then run on a CE Elantech FlashEA 1112 Series NC Soils elemental analyzer at standard operating parameters. All measured carbon was assumed to be black carbon. Several standards (acetanilide) and blanks were 99 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 also run. In addition, several carbon-free samples were prepared using the Gustafsson et al. (1997) protocol to assess potential charring during preparation. Fine BC samples for core B were recovered by pipetting and drying the fine-fraction obtained by sieving non frozen sediment samples for coarse BC analysis. Standard deviations were determined in the same manner as those for TN and TOC. 3.4 14C analysis Several wood, shell and bulk sediment samples from cores B, C, D and E were selected for 14C analysis. First, two wood samples (plus one replicate) presumably from a flood layer preserved in both cores C and D, and identifiable in all ofthe seismic profiles from Region 2, were analyzed for 14C. Second, three radiocarbon analyses were performed on articulated shell material found above the gravel surface (presumed transgressive lag), two shells from coreE and one from core B. Finally, three bulk 14C analyses were performed on OM removed from both the gravel-sized (2 samples, 2 depths) and fine-grained (<63Jlm) fraction of the poorly-sorted gravel layer characterizing Region 1. All samples were sent to the National Ocean Sciences AMS (NOSAMS) facility at Woods Hole Oceanographic Institute for analysis. 14C wood dates . were calibrated using CALIBOMB or CALIB (Stuiver and Reimer, 1993), with a 2std dev error (95%CI) reported. For shell material, dates were calibrated using an average of corrections reported in the proximity ofthe New Zealand East Cape region as noted in the CHRONO Marine Reservoir Database and calibrated using CALIB (Stuiver and Reimer, 1993). Due to the fact that the southern hemisphere extends back only~ 11 kya (McCormac et al., 2004), bulk sediment 14C dates could not be calibrated. 100 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 4.0 Results 4.1 Core logs and grainsize results Core A was comprised of less than 10% sand in the upper 80cm, coarsening downward to primarily clayey silt with minor sand (Figure 2A). The upper 300cm of Core B was comprised of silty-fine sand with a fining-upward sequence (Figure 2B). No storm laminations were preserved in this core~ At a core depth of ~300cm, a layer of pure clay overlaid shell hash and some articulated material. These sediments capped a layer of poorly sorted gravel with some angular material. Below the gravel layer, sediments were comprised primarily of clayey silt with minor sand and abundant coarse volcanic material. Two layers of pure clay(~ 370 and 580cm) and one fine to medium grained layer of volcanic material ( ~608-635) were also observed. Core C sediments were characterized as clean, fine-medium sand with a fining upward sequence. Two distinctive fine layers preserved at 46 and 71cmwere also reflected in the inner shelf seismic profiles (Figure 2C; Wadman and McNinch, 2008). Core D preserved a record of dominantly clayey silt with minor sand interlaminated with silty clay layers over the entire 6-meter core length. These fine-grained layers, - previously identified as flood deposits (Wadman and McNinch, 2008) became more frequent and contained a higher percentage of clay up-core (Figure 2D). 101 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 4.2 Organic matter results 4.2.1 Total Organic Carbon Total organic carbon (TOC) for all samples is presented in Figure 3. Average % TOC measured in the bulk fraction was lower than that measured in the fine fraction in Cores A and B (0.154±0.023 vs. 0.160±0.018, respectively; Figure 3A, B). Cores C and D showed higher average %TOC in the bulk fraction vs. the fine fraction (0.125±0.011 vs. 0.093±0.006, respectively; Figure 3C, D). Values were consistent with depth and between cores with minor exceptions in Cores A, B and C. Core B showed slightly lower %TOC above 300cm compared to below, preserved the highest TOC content at 373cm, with the reported value (0.386±0.175) representing the average of 5 replicate samples. Cores A and C showed an increase in %TOC between 40 and 80cm in depth (Figure 3A, C). 4.2.2 Total Nitrogen Total nitrogen (TN) for all samples is presented in Figure 4. Overall, very little TN is preserved in the inner shelf sediments. Average %TN measured in the bulk fraction was lower than that measured in the fine fraction in Cores A and B (0.016±0.002 vs. 0.017±0.002, respectively; Figure 4A, B). Cores C and D showed higher average %TN in the bulk fraction vs. the fine fraction (0.014±0.002 vs. 0.012±0.002, respectively; Figure 4C, D). Values were consistent with depth and between cores with minor exceptions in Cores A, Band C. Core B showed slightly lower %TN above 300cm compared to below and Cores A and C showed an increase in %TN between 40 to 80cm in depth (Figure 4A, C). 102 Wadman: Controls on Continental Sh~lf Stratigraphy, Chapter 2 4.2.3 C/N Ratios Sediment C/N distributions for all samples are presented in Figure 5. Average C/N ratios calculated in the bulk fraction were lower than those calculated in the fine fraction in Cores A and B (9.547±0.828 vs. 10.861±0.942, respectively; Figure 5A, B). Cores C and D showed higher average % TOC in the bulk fraction vs. the fine fraction (10.539±0.439 vs. 9.572±0.499, respectively; Figure 5C, D). C/N ratios were consistent with depth in cores A and C. The upper 40cm of Core B had an average C/N ratio of 9.286±0.901, contrasting with the upwards decreasingC/N ratios of9.773±1.067 to 5.440±0.008, from depths of ~200 to 140cm, respectively (Figure 5B). C/N ratios in CoreD varied greatly in the upper 150cm, and ranged from 8.821±0.239 to 16.269±1.777 (Figure 5D). 4.3 Coarse-grained black carbon Two distinct types of coarse BC were identified in the Waiapu inner shelf sediments. Coarse BC in the plume-dominated region was comprised primarily of low density, charred, fibrous material (Figure 6A). Coarse BC in the flood-dominated region lacked any fibrous material and was instead comprised of denser, char and charcoal-type fragments (Figure 6B). The upper portion of core B contained a few pieces of this charcoal, but the lower portion coarse BC was dominated by fibrous material. Total coarse BC abundance is reported as number per sample for all samples presented in Figure 7. Spikes in coarse BC were determined by averaging all of the total 103 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 coarse BC and identifying samples with total coarse BC of at least two standard deviations above the core average. Core A had the highest average coarse BC of all the cores, with an average coarse BC count of72±24. The highest total coarse BC abundances in Core A are found between 65 and 135cm depths, with a maximum of 628 at lOlcm. Other elevated abundances were measured at depths of 173, 193 and 485cm (434, 240 and 326, respectively). Core B had an average coarse BC count of 50±69. The highest coarse BC in Core C was found at 594cm depth (269 total counts). Other elevated abundances were measured at depths of 484 and 534 (206 and 119 total counts, respectively). Core C had an average coarse BC count of 3 8±46. The highest coarse BC abundance in Core C was found between 161 and lOlcm depths, with a maximum of 151cps at 131cm. Other elevated counts were measured at depths between 51 and lOlcm, though the actual abundances fall within the high end of the standard deviation of the background averages (between 51-77cps). Core D had an average coarse BC count of 66±99. The highest coarse BC abundances in CoreD were found between 50 and lOOcm depths, with a maximum of 628 counts at lOlcm. No other significant elevated abundances were observed within the core. 4.4 Fine-grained black carbon Total% fine BC for all samples is presented in Figure 7. All cores averaged 0.028±0.010% fine BC over the entire core. This average is significantly (95% C.I.) higher than the average % fine BC measured in the carbon-free standards ( avg. 0.016±0.005). The highest relative increases in% fine BC in cores A and D occur at depths of ~160 to 65cm (with maximum% fine BC 0.072±0.007 and 0.043±0.004 at 104 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 95cm in Core A and 149cm in CoreD; respectively). The highest relative increases in% fine BC in Core B begin at ~150cm depth (maximum% fine BC 0.043±0.002 at 133cm), but due to sediment washdown, the upper-depth at which the values return to background levels cannot be determined. The upper-depth of the highest relative increases in % fine BC in Core C begins at a depth of ~80cm (maximum% fine BC 0.061±0.007 at 191cm). Unfortunately, there was not sufficient fine sample to continue the analysis deeper than 191cm (coarsening-downward grainsize shifted to sand) and the deeper-end ofthe highest relative increases in Core C cannot be determined. All cores show slight increases from background% fine BC values in the upper ~30cm of the cores. Relative trends of total coarse BC and % fine BC are independent of one another with the exception of ~80-150cm down-core where increases in % fine BC are mirrored by increases in coarse BC abundance (Figure 7). Relative increases and decreases in fine BC are independent of any trends in TOC (r2< 0.2; Figure 8), and appear to be independent oftrends in TN, CIN and grainsize (Figures 2-7). 4.5 14C ages ofcore materials Several different types of sample materials were selected for 14C analysis, and the results are presented in Table 1. Two wood fragments and one replicate were collected from a distinctive flood event ( ~68-79cm depth) traceable via seismic profiles across much of flood-dominated Region 2 and identified in both cores C and D. In core D, the wood (and replicate) at 74cm depth yield a calibrated age range of ~3300-3600yrs. Wood from the same flood layer in core C (71cm depth) yields a modem age (post bomb spike), ~1960-1980. The gravel layer preserved in cores B, C and E (and limiting the 105 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 depth of core C) found at depths below the seafloor ranging from ~ 3 to ~6m, is capped by a layer of shell hash and articulated material, which in turn is overlain by a layer of clay. Radiocarbon ages from two shells from CoreE and one shell from Cores B (at depths of 389, 373cm and 519cm, respectively) yielded calibrated radiocarbon ages of740±35, 515±35 and 900±35 yrBP. Finally, radiocarbon analysis was performed on bulk OM from within the gravel layer itself. Bulk OM from the gravel near the base of the ~20cm thick layer in Core E yielded an age of 241 00± 170, compared to an age of 18200±95 from near the surface. Bulk OM from the clay mixed in with the gravel in Core B yielded an age of 18900±120. 5.0 Discussion 5.1 Identification ofthe black carbon deforestation signal in marine sediments. European deforestation has not been the only source of major forest fires, and thus coarse BC material, to the Waiapu River catchment. Biomass burning sparked by volcanic events, lightening strikes and other natural factors have also been documented in New Zealand history (e.g. McGlone and Wilmshurst, 1999; Ewers et al., 2006). Natural, local fires have been shown to result in an increase in coarse BC in adjacent (within several meters to less than a kilometer) soils and sediments (e.g. Clark et al., 1998; Carcaillet et al., 2001 ). The onset of Maori deforestation approximately 500 yr BP (Eden and Page, 1998; McGlone and Wilmshurst, 1999) could also have resulted in a local increase in coarse BC. A summary of percent fines, C/N ratios, coarse BC, fine BC, and 14C chronology for cores from the plume-dominated Region 1 and flood-dominated Region 2 are presented in Figures 9 and 10, respectively. Relative small increases in 106 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 coarse BC observed in cores A, B and D, but which do not span multiple sampling intervals, are likely the record of several such small-scale events (Figures 7, 9-1 0). Despite the potential complication of multiple local fire events being preserved in shelf stratigraphy, the peak of European slash-and-bum practices, which resulted in the extensive clearing of the catchment hinterland, was arguably the largest sustained catchment burning in modem East Cape history (McGlone et al., 1994; Eden and Page, 1998; Page et al., 2000). We speculate that not only was burning widespread and sustained long enough to generate a very large coarse BC signal in the local soils and adjacent continental shelf, but the associated increase in erosion and sediment transfer served to transport the locally deposited coarse BC fraction to the adjacent shelf, concentrating the record preserved in the marine sediment. This is supported by the increase in both coarse and fine BC in all of the sediment cores at roughly the same depth ( ~ 150cm). Cores A, C and D show the highest increases of coarse BC between ~ 150 and 50cm, while core B shows a similar slight increase in coarse BC at~ 150cm of depth before the sample is lost due to washdown (Figure 7). The fact that the increase is spread over nearly a meter of sedimentation argues that the burning was prolonged in nature, as opposed to a relatively quick natural burn, consistent with the decades-long European deforestation. These data also suggests that surficial coarse BC deposits from the watershed were quickly transported from the eroding catchment and preserved in the adjacent continental shelf sediments. The largest increases in fine BC in the cores also reflect this pattern. Below ~ 150cm, fine BC is relatively constant, and does not appear to be related to local increases in coarse BC in a given core (Figure 7). Since local fires tend to be limited in 107 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 scope and time, any fine BC produced by these small events will likely be transported by aeolian processes well away from the local watershed affected, resulting in no significant fine BC increases preserved in the local soil or sedimentary record (e.g. Clark et al., 1998; Carcaillet et al., 2001; Asselin and Payette, 2005). In contrast, the decades-long, regional burning of the north island by European deforestation likely resulted in a significantly larger release of fine BC than a short-term natural forest fire, a portion of which could easily be trapped within soils and marine sediments. We speculate that the nearly exponential increase in fine BC preserved at the same depths as the largest coarse BC increase reflects the signature of not just local but regional burning practiced by European deforestation (Figures 8-9). The decrease in fine BC deposition and preservation follows the cessation of slash-and-bum practices and the subsequent decrease in coarse BC being formed and transported to the continental shelf. Finally, we suspect the small increase in fine BC near the top (~30cm) of all of the cores (Figures 9- 10) is related to anthropogenic increases in fossil fuel combustimi, similar to what has been previously reported from other coastal environments (e.g. Gustafsson et al., 1997; 2001; Bucheli et al., 2004; Masiello, 2004; Wakeham et al., 2004; Bond et al., 2007; Elmquist et al., 2007) and explore this further in Section 5.2. 5.2 Inner shelfchronology and accumulation rates We interpret the maximum increases in both coarse BC and fine BC at the same depths as representing an unambiguous chronostratigraphic indicator of deforestation from which modern (past 100-150 years) sedimentary accumulation rates can be estimated. By using the onset of correlated increases in coarse BC and fine BC at 108 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 ~150cm in all ofthe cores (Figures 9-10) as a "first-appearance" baseline for deforestation and subsequent modem sedimentation since the turn of the century, a modem "accumulation rate" of~ 1.5cm per year can be calculated for the inner shelf. This high accumulation rate is consistent with colloquial reports of rapid and widespread burial of shellfish beds by sediment in the last century (Warmenhoven, 2004, personal communication). This rate is similar to accumulation rates calculated using 210Pb for the mid-outer shelf by Kniskern et al., (in review). If this estimate is accurate, the first appearance ofbomb-related isotopes should be present at~ 75cm depths in the cores. Unfortunately, due to the mixed grainsize nature of the inner-shelf sediments, the low deposition of bomb-related isotopic fallout and potentially low 210Pb deposition rates in New Zealand (e.g. Gehrels et al., 2008), 210Pb and 137 Cs analysis of 169 samples of inner shelf sediments yielded very low activities that were unreliable for chronological estimates even with corrections applied for percent clay (Appendix 1). 14C dates of wood, however, within the ~ 70cm flood layer yielded modem (post-bomb spike) ages, supporting our accumulation rate interpretations (Table 1; Figure 10). In addition, 14C dates ranging from ~1420-1980 years BP from shell material collected at depths of~ 3 70cm or greater indicate that the deforestation signal should be preserved in the upper portion of the cores, and increases in coarse BC or fine BC below this depth are not modem (Table 1; Figures 9-1 0). The modem chronology of all four cores is outlined using these data in Figures 9 and 10. Given that our methodology is based on a deforestation-linked signature preserved in the sediment records, additional deforestation-related markers could be assessed to test our BC-based chronology. An increase in weed and grass pollen 109 Wadman: Controls on Continental Shelf Str~tigraphy, Chapter 2 coinciding with the deforestation-induced decrease in tree pollen could be used as an independent marker of this same chronostratigraphic horizon (e.g. Eilliot et al., 1995; Whilmshurst et al., 1997; Elliot et al., 1998; Wilmshurst et al., 1999; Nichol et al., 2000; Horrocks et al., 2001; Byrami et al., 2002; Horrocks et al., 2002; Wilmshurst et al., 2007). Given the widespread distribution of atmospherically-distributed pollen, however,, distinguishing European vs. Maori deforestation using shifts in pollen species abundance without radiocarbon dating of the individual pollen grains might be problematic. Other possible techniques that might supplement the BC chronology and organic C/N ratios include profiles of stable isotopes and various organic biomarkers, such as lipids, fatty alcohols and lignin (e.g. Forrest et al., 2007; Canuel, 2001; Deshmukh et al., 2001; Shi et al., 2001; Gofii et al., 2003; Gordon and Gofii, 2003; Cook et al., 2004; Routh et al., 2004) in the sediment cores. While several workers have documented an increase in sedimentary BC in the latter half of the 20th century related in part to increases in coal burning and fossil fuel combustion, others suggest that the advent of cleaner technology has all but negated these effects (e.g. Novakov et al., 2003; Ito and Penner, 2005; Bond et al., 2007). Despite these uncertainties, studies have related an increase in near-surface (upper 10-40cm) sediment BC associated with the presence of hydrocarbons and P AHs, and subsequently related these BC increases to the increased burning of fossil fuels in combustion engines (e.g. Gustafsson et al., 1997; 2001; Bucheli et al., 2004; Masiello, 2004; Wakeham et al., 2004; Bond et al., 2007; Elmquist et al., 2007). All ofthe cores show a secondary, less dramaticincrease in fine BC in the upper ~30cm ofthe profiles (Figure 7, 8, 9). We speculate that this secondary increase in fine BC is related to similar increases in fossil 110 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 fuel combustion, and the depth of this increase correlates well with our proposed accumulation rates. The values for fine BC we report in this increase are similar to those previously reported for combustion-related BC increases in marine sediments (e.g. Gustafsson et al., I 997; Figure 7). 5.3 Inner-shelf modern sediment budget While it is widely recognized that fine-grained sediments can be transported to inner shelves, these sediments are usually considered to be efficiently segregated and resuspended, if deposited at all, and carried offshore (e.g., McCave, 1972; Drake et al., 1985; Nittrouer and Wright, 1994; Cacchione et al., 1999; Zhang et al, 1999; Wright et al., 2001; Vitorino et al., 2002; Kniskern et al., 2006a, b). Earlier attempts to characterize Waiapu continental shelf sediment dynamics assumed that the inner shelfwas a region of efficient fine-grained sediment bypassing (Friedrichs and Wright, 2004; Wright et al., 2006; Kniskern et al., 2006a, b). Our data, however, indicate that the Waiapu inner shelf plays a significant role in fine-sediment preservation. Using the same depth increases in both coarse and fine BC as a deforestation related chronostratigraphic baseline, we estimated the total percentage of the modern (<100ya) Waiapu fine-budget being preserved on the inner shelf. We calculated our budget based on the average first appearance of deforestation-induced black carbon on the inner shelf at 150-cm depth. We included in our estimate the aggradation of the shoreline between 1915 and 1979 as previously reported by Gibb (1981 ). Seismic coverage previously reported for the inner shelf (Wadman and McNinch, 2008) was used to delineate the total area for the plume- and flood-dominated regions via krigging using 111 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Surfer software, and the volume extrapolated using a chronostratigraphic baseline of 150 16 centimeters (Table 2). Percent fines for each region were based on box core and vibracore averages (Wadman and McNinch, 2008) and corrected for an average porosity of 60% (Table 2). From these data, we estimate that a minimum of 17% ±8% of the modem (< 1OOya) Waiapu sediment budget can be accounted for in inner shelf sediments (Table 2), a significant amount given that Kniskern et al (in review) accounted for only ~24% of the budget on the mid-outer shelf. Several sources of error might potentially affect our budget estimates. The 8% error reported above is based on the error associated with the precision of the equipment used to generate the inner shelf volumes (specifically, ~ 1Ocm vertical error associated with swath bathymetry and ~20cm vertical error associated with chirp sub-bottom reflector depths). Previous research on the Waiapu inner shelf suggests that significant small-scale spatial variation in the distribution of fine-grained sediment exists, but we are unable to quantify this potential source of error given our core distribution (Wadman and McNinch, 2008). Volume estimates are based on the extent of seismic mapping, underestimating the entire inner-shelf littoral zone. Other potential sources of error include using a uniform baseline and porosity for the entire inner shelf. Due to the fact that percent sands and/or percent bedload data is not available for t}le measured Waiapu River discharge, in calculating our sediment budgets we assumed the entire reported discharge (Hicks et al., 2000; Hicks et al., 2004) was fine-grained. Finally, we did not _account for the reported 4-5 fold increase in sediment load over the last 100 years. These assumptions likely overestimate the volume of fine-grained material discharged to the 112 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 shelf, subsequently underestimating the percentage of fines sequestered on the inner shelf. To estimate a first-order error range for our reported sediment budget, we first re calculated the budget to account for the greater inner shelf area (and volume) of the entire littoral cell, not just the mapped region. We attempted to account for the coarse-grained fraction by assuming approximately 5% of the sediment yield was suspended and bedload-transported, coarse-grained material (sand and gravel), similar to that reported for the nearby Waipaoa River (e.g., Page et al., 2000; Hicks et al., 2004). Finally, while paleodischarge data is not available for the Waiapu River, Kettner et al. (2007) modeled the last 3000 years of discharge for the nearby Waipaoa River. While the Waiapu produces a significantly higher modem sediment yield than the Waipaoa (36 x 106 tonnes vs. ~15 x 106 tonnes; Walling and Webb, 1996; Hicks et al., 2000; Hicks et al., 2004), both rivers have experienced exponential increases in sediment yields in the last century due to deforestation-enhanced erosion. Using HydroTrend, Kettner et al. (2007) suggest that European deforestation-linked increases in sediment yield for the Waipaoa are nearly linear, and ultimately stabilized ~20 years ago. We assumed a similar linear increase and recent stabilization in sediment yield for the Waiapu River. When the above factors are taken into consideration, the energetic inner shelf potentially sequesters ~16-34% (±8%) ofthe total modem fine-sediment budget (Table 3), roughly equal to or greater than amount reported for the more quiescent mid-outer shelf ( ~24%; Kniskern et al., in review). Kinskem et aL(in review) do not provide sediment budget estimates that account for the coarse-fraction of the reported suspended yield, the total potential area ofthe shelf-wide littoral zone, or the increase in 113 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 deforestation-enhanced sediment yield over the last 100 years, nor did they account for the percentage of fine-grained sediment likely sequestered on the inner shelf. It stands to reason that their initial budget is likely a gross underestimate of the total fine-grained sediment preserved on the mid-outer shelf. At the very least, the narrow, energetic Waiapu continental shelf is sequestering up to ~50% of the modem sediment yield, and very likely is capturing much more, providing a very different view of a system originally assumed to be mostly bypassing. 5. 4 Implications for persistence ofdepositional processes Regional variations in sediment C/N ratios help elucidate patterns of shelf-wide sediment transport. Calculated percentages of TN and TOC from the bulk and fine sediments were similar in magnitude and scale over the length of all of the cores. As might be expected in a heterogeneous environment, however, percentages of TN and TOC were different in the bulk sediment vs. the fine sediment. In plume-dominated Region 1, the bulk fraction consistently underestimated the percentages of TN and TOC compared to the fine fraction (Figure SA, B). The opposite trend was observed in the cores from flood-dominated Region 2, where the bulk fraction consistently overestimated the percentages of TN and TOC compared to the fine fraction, indicating the importance of coarse-grained OM in this flood-dominated region (Figure 5C, D). This is consistent with previous observations which suggest that during flooding events, significant OM is associated with the coarse fraction of deposited sediment during flood conditions (e.g. Bergamaschi et al., 1997). 114 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Region 1 C/N ratios were consistently a mixture of terrestrial and marine, but a slightly more terrestrial signal was preserved in Core A relative to core B (10.851±0.471 vs. 8.035±0.914, respectively; Figures 5, 8), with a C/N of ~6-7 considered marine and ~15-20 considered terrestrial (e.g. Redfield et al., 1963; Meyers, 1994, 1997; Jaffe et al., 2001; Maksymowska et al., 2001; Forrest et al., 2007). These observations are consistent with interpretations of Region 1 being dominated by plume-derived sedimentation, with more terrestrial matter preserved in the northern isolated and protected rocky enclosures (Figure 1). The preservation of the lighter, fibrous and potentially easily resuspendable coarse BC material in core A but not in core B also supports the interpretation that the rocky enclosures prevent significant resuspension of recently deposited sediment (Figures 6, 7). Flood-dominated Region 2 is characterized by a slightly stronger terrestrial signal in the modern sediments which increases with distance south of the river mouth (average 9.547±0.828 vs. 11.581±0.546, respectively; Figures 5, 9). Higher C/N values are generally associated with fine-grained flood layers (Figure 10). Overall, these observations suggest that modern terrigenous material is being preferentially steered towards the southern inner shelf, consistent with early observations based on lithology, stratigraphy and fine-scale bathymetry (Wadman and McNinch, 2008). Despite a well-documented increase in terrigenous organic carbon discharged from the Waiapu river, no significant shifts are seen in the C/N ratios within Cores A, C and D. Slight near-surface increases in the TOC or TN of individual cores likely reflect diagenetic changes. A significant shift in the C/N ratios of Core B, however, is seen on either side of the 3-meter reflection surface. Sediment above ~300cm have more marine CIN values than sediment below ~300cm (8.574±1.789 vs. 12.367±1.046. respectively; 115 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Figures 5, 9). Chronology data, however, indicate that there is a significant depositional/erosional hiatus at this surface and differences in C/N ratios above and below it do not reflect recent modem influences (Table 1, Figure 9). CIN values are thus not changing to reflect the increase in terrestrial material delivered to the inner shelf, possibly due to efficient biological consumption and/or remineralization of the increased OM. Due to the fact that the C/N ratios stay relatively constant in a given core over time, these data suggest that riverine and oceanic processes controlling the steering and deposition of terrigenous material on the inner shelfhave not changed; rather, the amount preserved has increased due to inefficient sorting of increased sediment loads (Wadman and McNinch, 2008). 6.0 Conclusions • The sediments of the inner shelf preserve a chronostratigraphic footprint of deforestation across a continuum of BC sizes, which can be used to estimate modem sediment accumulation rates and budgets. BC is an excellent indicator of local and regional burning, is relatively simple and inexpensive to quantify, and, due to its presence across different grainsizes, can be quantified in locales regardless of local grainsize. • The inner shelf is currently sequestering a minimum of ~16% ofthe Waiapu fine sediment budget over the past 100 years, with an error range of ~16-34%. The error inherent in these calculations suggests the energetic inner shelf sequesters comparable amounts of fine-grained sediment as the more quiescent mid-outer shelf. 116 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 • CIN ratios from Region 1 are primarily consistent with what would be expected from plume settling, and are best preserved in the rocky, protected enclosures. In contrast, C/N ratios from Region 2 are consistent with increased terrigenous deposition related to flood deposits. These data support previous interpretations that flood-derived sediment is being steered towards the southern inner shelf. • Regional variations in C/N ratios indicate the importance of coarse-grained, organic material in the flood-dominated region. • Despite a well-documented increase in terrigenous OM to the inner shelf in the last 100 years, C/N ratios do not reflect this increase in a given core. These data suggest that modem-day, southern-steering of flood deposits is reflective of similar transport pathways under lower-yield conditions. Acknowledgements Thanks for field, logistical and laboratory support provided by R.A. Gammisch, W. Reisner, L. Carter, L. Northcote, B. Lee, E. Lerberg, J. Miselis, G. Gray, M. Scully and the crews of the RIV Tangaroa and RIV Kilo Moana. Thanks for logistical support and historical data is also given to Tui Warmenhoven, Project Manager of the Taonga Tuku lho Research Project and Dave Peacock, Gisbome District Council. Special thanks for permission and vessel blessings are given to members ofthe Ngati Porou iwi. Valuable advice regarding black carbon was graciously provided by Carrie Masiello, Yves Gelinas and Sidhhartha Mitra. Support for this research was provided by the National Science Foundation (OCE0326831 and OCE0504690). 117 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 References Addington, L., Kuehl, S.A. and McNinch, J.E., 2007. Contrasting modes of shelf sediment dispersal off a high-yield river: Waiapu River, New Zealand. Marine Geology, 243: 18-30. Aller, R.C., 1998. Mobile deltaic and continental shelf muds as suboxic, fluidized bed reactors. Marine Chemistry, 61(3-4): 143-155. Aller, R.C. and Blair, N.E., 2006. Carbon remineralization in the Amazon-Guianas tropical mobile mudbelt: A sedimentary incinerator. Continental ShelfResearch, 26(17-18): 2241-2259. Anderson, M.J., Ford, R.B., Feary, D.A. and Honeywill, C., 2004. Quantitative measures of sedimentation in an estuarine system and its relationship with intertidal soft sediment infauna. Marine Ecology Progress Series, 272: 33-48. Asselin, H. and Payette, P., 2005. Detecting local-scale fire episodes on pollen slides. Review of Palaeobotany and Palynology, 137: 31- 40. Bergamaschi, B.A. et al., 1997. The effect of grain size and surface area on organic matter, lignin and carbohydrate concentration, and molecular compositions in Peru Margin sediments. Geochimica et Cosmochimica Acta, 61(6): 1247-1260. Bianchi, T.S., Filley, T., Dria, K. and Hatcher, P.G., 2004. Temporal variability in sources of dissolved organic carbon in the lower Mississippi River. Geochimica et Cosmochimica Acta, 68: 959-967. Blair, N.E., Leithold, E.L. and Aller, R.C., 2004. From bedrock to burial: The evolution of particulate organic carbon across coupled watershed-continental margin systems. Marine Chemistry, 92(1-4, Spec. Iss.): 141-156. 118 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Bond, T.C. et al., 2007. Historical emissions of black and organic carbon aerosol from energy-related combustion, 1850-2000. Global Biogeochemical Cycles, 21(GB2018): 16. Bordovskiy, O.K., 1965. Accumulation and transformation of organic substances in marine sediment. Marine Geology, 3: 3-114. Brodowski, S., Glaser, B., Amelung, W., Rodionov, A. and Haumaier, L., 2005. Revised black carbon assessment using benzene polycarboxylic acids. Organic Geochemistry, 36(9): 1299-1310. Bucheli, T.D., Blum, F., Desaules, A. and Gustafsson, 0., 2004. Polycyclic aromatic hydrocarbons, black carbon, and molecular markers in soils of Switzerland. Chemosphere, 56: 1061-1076. Byrami, M. et al., 2002. A palynological study of Polynesian and European effects on vegetation in Coromandel, New Zealand, showing the variability between four records from a single swamp. Journal ofthe Royal Society ofNew Zealand, 32(3): 507-531. Cacchione, D.A., Irish, J., Traykovski, P., Wiberg, P.L. and Lynch, J., 1999. Estimates of suspended-sediment flux and bedform activity on the inner portion of the Eel continental shelf. Marine Geology, 154(1-4): 83-97. Canuel, E.A., 2001. Relations between river flow, primary production and fatty acid composition of particulate organic matter in San Francisco and Chesapeake Bays: a multivariate approach. Organic Geochemistry, 32: 563-583. 119 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Carcaillet, C., Bouvier, M., Frechette, B., Larouche, A.C. and Richard, P.J.H., 2001. Comparison of pollen-slide and sieving methods in lacustrine charcoal analyses for local and regional fire history. The Holocene, 11(4): 467--476. Carey, A.E., Hicks, D.M., Gardner, C.B., Goldsmith, S.T. and Lyons, W.B., 2005. Organic carbon yields from small, mountainous rivers, New Zealand. Geophysical Research Letters, 32(15): 1-5. Carpenter, R., Peterson, M.L. and Bennett, J.T., 1982. Pb-210 derived sediment accumulation and mixing rates for the Washington continentalslope. Marine Geology, 48: 135-164. Clark, J.S. and Royall, P.D., 1996. Local and regional sediment charcoal evidence for fire regimes in presettlement north-eastern North America. Journal ofEcology, 84(3): 365-382. Clark, J.S., 1997. Facing short-term extrapolation with long-term evidence: Holocene fire in the north-eastern US forests. Journal ofEcology, 85: 377-380. Clark, J.S., Lynch, J., Stocks, B.J. and Goldammer, J.G., 1998. Relationships between charcoal particles in air and sediments in west-central Siberia. Holocene, 8(1): 19- 29. Collot, J.Y., Lewis, K., Lamarche, G. and Lallemand, S., 2001. The giant Ruatoria debris avalanche oil the Northern Hikurangi margin, New Zealand: Result of oblique seamount subduction. Journal ofGeophysical Research B: Solid Earth, 106(9): 19271-19297. 120 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Cook, P.L.M., Revill, A.T., Clementson, L.A. and Volkman, J.K., 2004. Carbon and nitrogen cycling on intertidal mudflats of a temperate Australian estuary. III. Sources of organic matter. Marine Ecology Progress Series, 280: 55-72. DeMaster, D.J., McKee, B.A., Nittrouer, C.A., Qian, J.C. and Chen, G.D., 1985. Rates of sediment accumulation and particle reworking based on radiochemical measurements from continental shelf deposits in the East China Sea. Continental Shelf Research, 4: 143-158. Deshmukh, A.P., Chefetz, B. and Hatcher, P.G., 2001. Characterization of organic matter in pristine and contaminated coastal marine sediments using solid-state 13C NMR, pyrolytic and thermochemolytic methods: A case study in the San Diego harbor area. Chemosphere, 45(6-7): 1007-1022. Dickens, A.F., Gelinas, Y., Masiello, C.A., Wakeham, S.G. and Hedges, J.I., 2004. Reburial of fossil organic carbon in marine sediments. Nature, 427: 336-339. Drake, D.E., Cacchione, D.A. and Karl, H.A., 1985. Bottom currents and sediment transport on San Pedro shelf, California. Journal ofSedimentary Petrology, 55(1): 15-28. Druffel, E.R.M., 2004. Comments on the importance of black carbon in the global carbon cycle. Marine Chemistry, 92: 192-200. Eden, D.N. and Page, M.J., 1998. Palaeoclimatic implications of a storm erosion record from late holocene lake sediments, North Island, New Zealand. Palaeogeography, Palaeoclimatology, Palaeoecology, 139(1-2): 37-58. 121 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Elliot, M.B., Striewski, B., Flenley, J.R. and Sutton, D.G., 1995. Palynological and sedimentological evidence for a radiocarbon chronology of environmental change and Polynesian deforestation from Lakes Taumatawhana, Northland, New Zealand. Radiocarbon, 37(3): 899-916. Elliot, M.B., Flenley, J.R. and Sutton, D.G., 1998. A late Holocene pollen record of deforestation and environmental change from the Lake Tauanui catchment, Northland, New Zealand. Journal ofPaleolimnology, 19(1): 23-32. Elmquist, M., Zencak, Z. and Gustafsson, 0., 2007. A 700 year sediment record of black carbon and polycyclic aromatic hydrocarbons near the EMEP air monitoring station in Asprevten, Sweeden. Environmental Science and Technology, 41: 6926- 6932. Ewers, R.M. et al., 2006. Past and future trajectories of forest loss in New Zealand. Biological Conservation, 133(3): 312-325. Forrest, B.M., Gillespie, P.A., Comelisen, C.D. and Rogers, K.M., 2007. Multiple indicators reveal river plume influence on sediments and benthos in a New Zealand coastal embayment. New Zealand Journal ofMarine and Freshwater Research, 41: 13-24. Friedrichs, C.T. and Wright, L.D., 2004. Gravity-driven sediment transport on the continental shelf: implications for equilibrium profiles near river mouths. Coastal Engineering, 51: 795-811. Gee, G.W. and Bauder, J.W., 1986. Particle-size analysis. In: A. Klute (Editor), Methods of Soil Analysis: Part 1. Physical and Mineralogical Methods. Agronomy. Soil Science Society of America, Madison, USA, pp. 383-411. 122 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Gehrels, W.R., Hayward, B.W. and Southall, K.E., 2008. A 20th century acceleration of sea-level rise in New Zealand. Geophysical Research Letters, 35(L02717, doi: 10.1 029/2007GL032632,2008). Gibb, J.G., 1981. Coastal hazard mapping as a planning technique for Waiapu County, East Cape, North Island, New Zealand. Water and Soil Technical Publication, 21: 63. Gibb, J.G., 1994. Initial Assessment of Areas Sensitive to Coastal Hazards for Selected Parts of the Gisbome District Council, Bay of Plenty. Goff, J.R., 1997. A chronology of natural and anthropogenic influences on coastal sedimentation, New Zealand. Marine Geology, 138(1-2): 105-117. Gomez, B. et al., 2003. Production, storage, and output of particulate organic carbon: Waipaoa River basin, New Zealand. Water Resources Research, 39(6): ESG21- ESG28. Gomez, B., Roberts, A.P., Carter, L., Trustrum, N.A. and Palmer, A.S., 2004. El Nino Southern Oscillation signal associated with middle Holocene climate change in intercorrelated terrestrial and marine sediment cores, North Island, New Zealand. Geology, 32(8): 653-656. Gofii, M.A., Teixeira, M.J. and Perkeya, D.W., 2003. Sources and distribution of organic matter in a river-dominated estuary (Winyah Bay, SC, USA). Estuarine, Coastal and ShelfScience, 57(5-6): 1023-1048. Gofii, M.A., Eglinton, T.I., Yunker, M.B. and Macdonald, R.W., 2005. The supply and preservation of ancient and modem components of organic carbon in the Canadian Beaufort Shelfofthe Arctic Ocean. Marine Chemistry, 93(1): 53-73. 123 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Gordon, E.S. and Goni, M.A., 2003. Sources and distribution of terrigenous organic matter delivered by the Atchafalaya River to sediments in the northern Gulf of Mexico. Geochimica et Cosmochimica Acta, 67(13): 2359-2375. Gustafsson, 0., Haghseta, F., Chan, C., MacFarlane, J. and Gschwend, P.M., 1997. Quantification of the dilute sedimentary soot phase: implications for P AH speciation and bioavailability. Environmental Science and Technology, 31 ( 1): 203-209. Gustafsson, 0. et al., 2001. Evaluation of a protocol for the quantification of black carbon in sediments. Global Biogeochemical Cycles, 15(4): 881-890. Hammes, K. et al., 2007. Comparison of quantification methods to determin fire-derived (black/elemental) carbon in soils and sediments using reference materials from soil, water, sediment and the atmosphere. Global Biogeochemical Cycles, 21: GB30 16, doi: 10.1 029/2006GB002914,2007. He, Q. and Walling, D.E., 1996. Interpreting particle size effects in the adsorption of 137Cs and unsupported 210Pb by mineral soils and sediments. Journal of Environmental Activity, 30(2): 117-137. Hedges, J.I. and Keil, R.G., 1995. Sedimentary organic matter preservation: an assessment and speculative synthesis. Marine Chemistry, 49: 81-115. Hedges, J.I., Keil, R.G. and Benner, R., 1997. What happens to terrestrial organic matter in the ocean? Organic Geochemistry, 27(5/6): 195-212. Hedges, J.I., et al., 2000. The molecularly-uncharacterized component of nonliving organic matter in natural environments. Organic Geochemistry, 31: 945- 958. 124 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Hicks, D.M., Gomez, B. and Trustrum, N.A., 2000. Erosion thresholds and suspended sediment yields, Waipaoa River basin, New Zealand. Water Resources Research, 36: 1129-1142. Hicks, M., Shankar, U. and McKerchar, A., 2003. Sediment Yield Estimates: a GIS tool. Water and Atmosphere, 11(4): 26-27. Hicks, D.M., Gomez, B. and Trustrum, N., 2004. Event suspended sediment characteristics and the generation ofhyperpycna1 plumes at river mouths: East Coast Continental Margin, North Island, New Zealand. The Journal of Geology, 112: 471-485. Horrocks, M., Augustinus, P.C., Nichol, S.L., Gregory, M.R. and Creese, R., 2001. A holocene pollen and sediment record ofWhangape Harbour, far Northern New Zealand. Journal ofthe Royal Society ofNew Zealand, 31(2): 411-424. Horrocks, M., Nichol, S.L. and Shane, P .A., 2002. A 6000-year palaeoenvironmental record from Harataonga, Great Barrier Island, New Zealand. New Zealand Journal ofBotany, 40(1): 123-135. Hughen, K.A. et al., 2004. Marine04 marine radiocarbon age calibration, 0-26 cal kyr BP. Radiocarbon, 46(3): 1059-1086. Ito, A. and Penner, J.E., 2005. Historical emissions of carbonaceous aerosols from biomass and fossil fuel burning for the period 1870- 2000. Global Biogeochemical Cycles, 19: GB2028, doi:10.1029/2004GB002374. Jaffe, R., Mead, R., Hernandez, M.E., Peralba, M.C. and DiGuida, O.A.,2001. Origin and transport of sedimentary organic matter in two subtropical estuaries: a comparative, biomarker-based study. Organic Geochemistry, 32: 507-526. 125 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Jia, G.-D. and Peng, P.-A., 2003. Temporal and spatial variations in signatures of sedimented organic matter in Lingding Bay (Pearl estuary), southern China. Marine Geology, 82(1-2): 47-54. Jones, T.P. and Chaloner, W.G., 1991. Fossil charcoal, its recognition and palaeoatmospheric significance. Palaeogography,.Palaeoclimatology, Palaeoecology (Global & Planetary Change Section), 97(1-2): 39-50. Kettner, A.J., Gomez, B. and Syvitski, J.P.M., 2007. Modeling suspended sediment discharge from the Waipaoa River system, New Zealand: The last 3000 years. Water Resources Research, 43: W07411, doi:10.1029/2006WR005570. Kniskern, T.A., Harris, C.K. and Kuehl, S.A., 2006a. Sediment Deposition on the Waiapu River Shelf, N.Z., Implications for Sediment Transport Mechanisms and Event Preservation. EOS; Transactions (AGU), 87(36): OS11L-04. Kniskern, T.A., Harris, C.K. and Kuehl, S.A., 2006b. Flood Sediment Dispersal and Deposition on the Waiapu River Shelf, East Cape, New Zealand. EOS, Transactions (AGU), 87(52). Kniskern, T.A., Kuehl, S.A., Harris, C.K. and Carter, L., in review. Sediment accumulation patterns and fine-strata formation on the Waiapu River shelf, New Zealand. Marine Geology. Kuehl, S.A., Demaster, D.J. and Nittrouer, C.A., 1986. Nature of sediment accumulation on the Amazon continental shelf. Continental ShelfResearch, 6(1-2): 209-225. Leithold, E.L., Perkey, D.W., Blair, N.E. and Creamer, T.N., 2005. Sedimentation and carbon burial on the northern California continental shelf: The signatures of land use change. Continental ShelfResearch, 25(3): 349-371. 126 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Leithold, E.L., Blair, N.E. and Perkey, D.W., 2006. Geomorphologic controls on the age of particulate organic carbon from small mountainous and upland rivers. Global Biogeochemical Cycles, 20(GB3022, doi: 10.1 029/2005GB002677, 2006). Litchfield, N.J. and Berryman, K.R., 2005. Correlation of fluvial terraces within the Hikurangi Margin, New Zealand: Implications for climate and baselevel controls. Geomorphology, 68(3-4): 291-313. Lynch, J.A., Finney, B.P.B.P., Clark, J.S., Bigelow, N.H. and Edwards, M.E., 2003. Geographic and temporal variations in fire history in boreal ecosystems of Alaska. Journal of Geophysical Research D: Atmospheres, 108(1 ): FFR 8-1 FFR 8-17. Lyons, W.B., Nezat, C.A., Carey, A.E. and Hicks, D.M., 2002. Organic carbon fluxes to the ocean from high-standing islands. Geology, 30(5): 443-446. Maksymowska, D., Richard, P., Piekarek-Jankowska, H. and Riera, P., 2000. Chemical and Isotopic Composition of the Organic Matter Sources in the Gulf of Gdansk (Southern Baltic Sea). Estuarine, Coastal and Shelf Science, 51: 585-598. Masiello, C.A. and Druffel, E.R.M., 2001. Carbon Isotope Geochemistry of the Santa Clara River. Global Biogeochemical Cycles, 15(2): 407--416. Masiello, C.A., 2004. New directions in black carbon organic geochemistry. Marine Chemistry, 92(1-4, Spec. Iss.): 201-213. McCave, I.N ., 1972. Transport and escape of fine-grained sediment in shelf areas. In: D.J.P. Swift, D.B. Drake and O.H. Pilkey (Editors), Shelf Sediment Transport: Process and Pattern. Dowden, Hutchinson & Ross, Inc., Stroudsburg, P A, pp. 225-248. 127 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 McCormac, F.G. et al., 2004. SHCal04 Southern Hemisphere Calibration 0- 1000 cal BP. Radiocarbon, 46: 1087-1092. McGlone, M.S., Anderson, A.J. and Holdaway, R.N., 1994. An ecological approach to the Polynesian settlement ofNew Zealand. In: V. Diaz (Editor), El Nino: Historical and Paleoclimatic Aspects of the Southern Oscillation. Cambridge University Press, Cambridge, pp. 151-173. McGlone, M.S. and Wilmshurst, J.M., 1999. Dating initial Maori environmental impact in New Zealand. Quaternary International, 59: 5-16. Meyers, P.A., 1994. Preservation of elemental and isotopic source identification of sedimentary organic matter. Chemical Geology, 144: 389-302. Meyers, P .A., 1997. Organic geochemical proxies of paleoceanographic, paleolimnologic, and paleoclimatic processes. Organic Geochemistry, 27(5/6): 213-250. Meyers, P.A., 2003. Applications of organic geochemistry to paleolimnological reconstructions: a summary of examples from the Laurentian Great Lakes. Organic Geochemistry, 34(2): 261-289. Middelburg, J.J., Nieuwenhuize, J. and van Breugel, P., 1999. Black carbon in marine sediments. Marine Chemistry, 65: 245-252. Moore, P.R. and Mazengarb, C., 1992. Geology and Landforms ofthe Raukumara Peninsula. In: J.M. Soons and M.J. Selby (Editors), Landforms of New Zealand, Second Edition, pp. 334-343. 128 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Nichol, S.L., Horrocks, M., Augustinus, P.C., Gregory, M.R. and Creese, R., 2000. Geomorphic and sedimentary evidence of human impact on the New Zealand coastal landscape. Physical Geography, 21(2): 109-132. Nittrouer, C.A. and Wright, L.D., 1994. Transport of particles across continental shelves. Reviews ofGeophysics, 32(1): 85-113. Novakov, T. et al., 2003. Large historical changes of fossil-fuel black carbon aerosols. Geophysical Research Letters, 30(6): 1324, doi: 10.1029/2002GL016345. Ogrinc, N., Covelli, S., Fontolan, G. and Faganeli, J., 2005. Carbon and nitrogen isotope compositions of organic matter in coastal marine sediments (the Gulf of Trieste, N Adriatic Sea): Indicators of sources and preservation. Marine Chemistry, 95(3- 4): 163-181. Oguchi, T ., Saito, K., Kadomura, H. and Grossman, M., 2001. Fluvial geomorphology and paleohydrology in Japan. Geomorphology, 39: 3-19. Ohlson, M. and Tryterud, E., 2000. Interpretation ofthe charcoal record in forest soils: forest fires and their production and deposition of macroscopic charcoal. The Holocene, 10(4): 519-525. Page, M., Trustrum, N. and Gomez, B., 2000. Implications of a century of anthropogenic erosion for future land use in the Gisbome-East coast region of New Zealand. New Zealand Geographer, 56(2): 13-24. Page, M. et al., 2000. Waipaoa River. Source-to-Sink Sedimentary Cascades in Pacific Rim Geo-Systems (184): 86-100. 129 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Page, M., Harmsworth, G., Trustrum, N., Kasai, M. and Marutani, T., 2001. Waiapu River. Source-to-Sink Sedimentary Cascades in Pacific Rim Geo-Systems (184): 102-111. Prahl, F .G., Bennet, J. T. and Carpenter, R., 1980. The early diagenesis of aliphatic hydrocarbons and organic matter in sedimentary particles from Dabob Bay, Washington. Geochimica et Cosmochimica Acta, 44: 1967-1976. Prahl, F.G., Ertel, J.R., Goni, M.A., Sparrow, M.A. and Eversmeyer, B., 1994. Terrestrial organic carbon contributions to sediments on the Washington margin. Geochimica et Cosmochimica Acta, 4(63-67). Redfield, A. C., Ketchum, B.H. and Richard, F .A., 1963. The influence of organisms on the composition ofthe sea water. In: M.N. Hill (Editor), The Sea. Wiley, New York, pp. 26-49. Routh, J. et al., 2004. Sedimentary geochemical record of human-induced environmental changes in the Lake Brunnsviken watershed, Sweden. Limnology and Oceanography, 49(5): 1560-1569. Shi, W., Sun, M.-Y., Molina, M. and Hodson, R., 2001. Variability in the distribution of lipid biomarkers and their molecular isotopic composition in Altamaha estuarine sediments: implications for the relative contribution of organic matter from various sources. Organic Geochemistry, 32: 453-467. Smith, J.N., 2001. Why should we believe 210Pb sediment geochronologies? Journal of Environmental Radioactivity, 55: 121-123. 130 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Sommerfield, C.K. et al., in press. Oceanic dispersal and accumulation of river sediment. In: C. Nittrouer et al. (Editors), Continental-Margin Sedimentation: Transport to Sequence. Blackwell Publishing, pp. 157-212. Sorrell, B. and Partridge, T., 1999. Conservation values and management of the Kongahu Swamp, Buller District. Science for Conservation (124): 1-50. Stepanauskas, R. et al., 2002. Summer inputs of riverine nutrients to the Baltic Sea: Bioavailability and eutrophication relevance. Ecological Monographs, 72(4): 579- 597. Stuiver, M. and Reimer, P.J., 1993. Extended 14C database and revised CALIB radiocarbon calibration program. Radiocarbon, 35: 215-230. Vitorino, J., Drago, T., Oliveira, A. and Jouanneau, J.M., 2002. Winter dynamics on the northern Portuguese shelf. Part 2: Bottom boundary layers and sediment dispersal. Progress in Oceanography, 52(2-4 ): 155-170. Wadman, H.M. and McNinch, J.E., 2008. Stratigraphic spatial variation on the inner shelf of a high-yield river, Waiapu River, New Zealand: Implications for fine-sediment dispersal and preservation. Continental ShelfResearch, 28(7): 865-886. Wakeham, S.G. et al., 2004. Hydrocarbons in Lake Washington Sediments. A 25-Year Retrospective in an Urban Lake. Environmental Science and Technology, 38(2): 431-439. 131 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Walling, D.E. and Webb, B.W., 1996. Erosion and sediment yield: global and regional perspectives. Proceedings of an international symposium, Exeter, July 1996. In: D.E. Walling and B.W. Webb (Editors), Erosion and sediment yield: global and regional perspectives. Proceedings of an international symposium, Exeter, July 1996, International Association ofHydrological Sciences, Publication, 236, pp. 586. Warmenhoven, T., 2004. Project Manager, Taonga Tuku Iho Research Project, HOMNUTI Trust, Turanga, New Zealand. Wilmshurst, J.M., 1997. The impact ofhuman settlement on vegetation and soil stability in Hawke's Bay, New Zealand. New Zealand Journal ofBotany, 35: 97-111. Wilmshurst, J.M., McGlone, M.S. and Partridge, T.R., 1997. A late Holocene history of natural disturbance in lowland podocarp/hardwood forest, Hawke's Bay, New Zealand. New Zealand Journal ofBotany, 35(1): 79-96. Wilmshurst, J.M., Eden, D.N. and Froggatt, P.C., 1999. Late Holocene forest disturbance in Gisborne, New Zealand: A comparison of terrestrial and marine pollen records. New Zealand Journal ofBotany, 37(3): 523-540. Wilmshurst, J.M., McGlone, M.S., Leathwick, J.R. and Newnham, R.M., 2007. A pre deforestation pollen-climate calibration model for New Zealand and quatitative temperature reconstructions for the past 18 000 years BP. Journal of Quaternary Science, 22(5): 535-547. Wright, L.D., Scully, M.E., Friedrichs, C.T. and Kim, S.C., 2001. Effects of ambient currents and waves on gravity-driven sediment transport on continental shelves. Marine Geology, 175(1-4): 25-45. 132 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Wright, L.D. and Friedrichs, C.T., 2006. Gravity-driven sediment transport on continental shelves: A status report. Continental ShelfResearch, 26(17-18): 2092-2107. Zhang, Y., Niedoroda, A.W., Reed, C.W., Swift, D.J.P. and Fan, S., 1999. Two dimensional numerical modeling of storm deposition on the northern California shelf. Marine Geology, 154(1-4): 155-167. 133 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Table Captions Table 1: 14C ages (in calendar years BP or 14C age BP) for wood, shell and bulk sediment samples from cores B, C, D, and E. Errors and calibration information included where applicable. 3 Table 2: Calculated sediment volume (m ), total sediment (metric tonnes), average percent fines, calculated total fine sediment (metric tonnes), and porosity corrections for each region of the Waiapu inner shelf. Values do not include 8% precision error. Table 4: Influence of error on sediment budgets. A) Total modem (~ 100 years) percent fines captured, accounting for variations in volume (area and baseline) as well as bedload. B) Total modem (~100 years) percent fines captured, accounting for the above factors as well as the 4-5 fold increase in sediment discharge. Values do not include 8% precisiOn error. Figure Captions Figure 1: Study regions and core locations. Modified from Wadman and McNinch (2008). Figure 2: Core logs and grains-ize (percent fines) distributions in study areas. A-B) Cores A and B from the plume-dominated region (region 1); C-D) Cores C·and D from the flood-dominated region (region 2). Core logs are based on em-scale field descriptions. 134 .. Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Figure 3: Total Organic Carbon (TOC) distributions in study cores. A) Cores A and B from the plume-dominated region (region 1); B) Cores C and D from the flood dominated region (region 2). Bulk sediment TOC values are plotted as open circles, fine sediment TOC values are plotted as filled circles. Standard deviations at the 95% confidence interval are shown. Figure 4: Total Nitrogen (TN) distributions in study cores. A) Cores A and B from the plume-dominated region (region 1); B) Cores C and D from the flood-dominated region (region 2). Bulk sediment TN values are plotted as open squares, fine sediment TN values are plotted as filled squares. Standard deviations at the 95% confidence interval are shown. Figure 5: Calculated C/N distributions for study cores. A) Cores A and B from the plume-dominated region (region 1); B) Cores C and D from the flood-dominated region (region 2) are shown in Panel B. Bulk sediment C/N ratios are plotted as open triangles, fine sediment C/N ratios are plotted as filled triangles. Standard deviations at the 95% confidence interval are shown. Figure 6: Examples of char and charcoal observed in the Waiapu shelf sediments. A) Fibrous material from plume-dominated Region 1; B) Dense material from flood dominated Region 2. All images acquired using an HP Precision Scan digital scanner, set at 1200dpi, and adjusted for maximum sharpness and resolution. 135 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 Figure 7: Black carbon distributions in study cores. A) Cores A&B from the plume- dominated region (region 1); B) Cores C&D from the flood-dominated region (region 2). Coarse BC (CCBC) total counts are plotted as closed gray diamonds on the upper x-axis and% fine BC (SGBC) values are plotted as open white diamonds on the lower x-axis. Standard deviations at the 95% confidence interval are shown for % fine BC values. Figure 8: Fine BC (SGC) vs TOC in study cores. In all plots,% fine BC vs fine or bulk TOC is plotted as closed blue diamonds and open red squares, respectively. Regression ~I equations for % fine BC vs fine or bulk TOC are plotted in blue and red font, respectively. A) Fine BC (SGC) plotted vs. both bulk and fine TOC from all four study cores. B) Fine BC (SGC) plotted vs. both bulk and fine TOC from Core A (plume region). C) Fine BC (SGC) plotted vs. bulk TOC from Core B (plume region). D) Fine BC (SGC) plotted vs. both bulk and fine TOC from Core C (flood region). E) Fine BC (SGC) plotted vs. both bulk and fine TOC from Core D (flood region). Figure 9: Plume-dominated Region 1 chronostratigraphic results. Core A (protected region) results are plotted in Panels A and B. Core B (open shelf region) results are plotted in Panels C and D. Panels A and C show bulk C/N ratios (open white triangles) on the upper x-axis and percent fines (closed gray triangles) on the, lower x-axis. Panels Band D show coarse BC (CCBC) abundances (filled diamonds) on the upper x-axis and fine BC (SGBC; wt. %; open diamonds) on the lower x-axis. Gray box identifies the deforestation signal, indicating the onset of slash-and-bum, and the dashed line on the 136 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 2 left-hand side shows the beginning of the fining-upward sequence. 14C dates plotted where applicable. Figure 10: Flood-dominated Region 2 chronostratigraphic results. Core C results are plotted in Panels A and B. Core D results are plotted in Panels C and D. Panels A and C show bulk C/N ratios (open triangles) on the upper x-axis and percent fines (filled triangles) on the, lower x-axis. Panels Band D show coarse BC (CCBC) abundances (filled diamonds) on the upper x-axis and fine BC (SGBC; wt. %; open diamonds) on the lower x-axis. Gray box identifies the deforestation signal, indicating the onset of slash and-bum, and the dashed line on the left-hand side shows the beginning of the fining upward sequence. 14C dates plotted where applicable. 137 depth below 95.4% (20') relative area 14 Sam ole Core seafloor (em) C aae vr BP cal age ranges under distribution calibration data wood* c 71 Modern cal BP 1963-1981 1 ManninQ and Melhuish, 1994 ' Hua and Barbetti 2004 wood D 74 4770±40 cal BP 3634-3553 0.32 McCormac et al., 2004 ' ' cal BP 3541-3488 0.222 ' ' ' cal BP 3472-3372 0.458 ' shell1 E 389 740±35 cal BP 1526-1681 1 Hughen et al. 2004 shell2 E 373 515±35 cal BP 1724-1743 0.028 Hughen et al. 2004 ' ' cal BP 1752-1790 0.064 ' ' ' cal BP 1801-1950** 0.907 ' shell3 B 519 900±35 cal BP 1420-1528 1 Hughen et al. 2004 bulk orq qrav1 B 529 24100±170 ------bulk ora clav B 534 18200±95 ------bulk orq qrav2 E 391 18900±120 ------All ages calibrated using CALIB, Stuiver and Reimer, 1993 (version 5.0), with the exception of*. *Calibrated using CALIBOMB, Stuiver and Reimer, 1993. **Modern age. Table 2-1 15Q~m bil::i~lio~ Recico :1 basios Recico :1 Recico 2 Coastal ~laio 3 Volume (m ) 2.E+07 5.E+08 4.E+08 1.13E+08 metric tonnes 3.57E+07 9.31E+08 8.53E+08 2.25E+08 oercent fines 85.3 50.7 45.9 19.8 total fine sediment (metric tonnes) 3.04E+07 4.72E+08 3.92E+08 4.45E+07 corrected for oorositv 1.83E+07 2.83E+08 2.35E+08 2.67E+07 total fine sediment* 5.63E+08 *equal to -17% of the 1DO-year fine-sediment budget Table 2-2 100-year discharge: baselines constant 150cm 1QQcm n. - ;~; measured area 0.16 0.17 0.17 est. littoral cell 0.23 0.24 0.23 measured area olus 5% 0.17 0.18 0.18 est. littoral cell olus 40% olus 5% 0.24 0.26 0.25 100-year discharge: baselines increasinq linearlv 15Q c.m 1QQ c.m C"'l. - ;~; measured area 0.23 0.25 0.24 est. littoral cell 0.32 0.34 0.33 measured area plus 5% 0.23 0.25 0.24 est. littoral cell plus 40% plus 5% 0.32 0.34 0.33 Table 2-3 Easting (UTM Zone 60S) 620000 640000 East Cape, New Zealand X X 0 X X -..o C/) 0 X X 0 0 Waiapu River <0 coN Q) LO Vibracore Sites r::: Mouth -- V I• I 0 N X I' ~ I- X ::> --C> r::: 0 X .r::: 0 Region 1 t 0 0 0 (plume-dominated) z ~ co LO I I Region 2 \ (flood-dominated) \ 168 170 172 174 176 178 Figure 2-1 A B LEGEND Plume Region. Core A Plume Region. Core B Owashdown Percent Fines Percent Fines 0 20 40 60 0 20 40 60 80 j''d·.,"j clean sand 07-----~--~----~----~--~ 07--~--::--:ool>-----"----'----. clayey silt 100 100 - muddy ~.- 200 '"""- sand ~ ::: I~------~~~--~--~ ~ 3oo l --~~o;.;.. 1C;:;;;;;;;;;;;~o~::::==~~ gravel layer with overlying t.. t I clay and shell c 400 1------····- - ~ ~ 40011------~~~ I] volcanic-rich material 500 +-- ················-··---··- -~ 500 1------~----o. 600 + 600 Immm m~ • m•••• ~mm ?:- c D Flood Region, Core C Flood Region, Core D Percent Fines Percent Fines 0 20 40 60 80 0 20 40 60 80 100 0 i ·-~ 01 ~02 .... "· 100 100 1-- mmmc m "'"""'~ 200~ I 200 e ~- ~ 300 :S Q. ~ 400 1- - 1::: r-~ -:;;--~ 500 soo 1 o.ex ~ 600 I·····························-··· l 6oo I " ~ :!! lO .....c: f't) N I N A B Plume Region. Core A Plume Region. Core B Total Organic Carbon (% wt mg) Total Organic Carbon (% wt mg; bulk) 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 100 200 200 . ? ~300+-----~~~------~ 300 .c i c. cCll g 400 +-----·~~.,.-,.c ______---1 Legend Legend 600 ··1--- ·---- ...... 0 BulkTOC ~_...... _ .... _.... ___..... __, 0 BulkTOC '------1 e Fine TOC D Flood Region, Core C Total Organic Carbon(% wt mg) Total Organic Carbon(% wt mg) 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0 100 100 200 200 ? ? ~ 300 ~ 300 sQ, i g 400 g 400 500 500 Le~end 600 600 0 BulkTOC 0 BulkTOC e FineTOC e FineTOC Figure 2-3 A B Plume Region. Core A Plume Region. Core B Total Nitrogen(% wt mg) Total Nitrogen(% wt mg; bulk) 0 0.01 0.02 0.03 0 0.01 0.02 0.03 o+----...... o[]oo,,------i 100 200 'E 'E .e. 300 .. .e. 300 .c .c ii ii ~ 400 ~ 400 500 600 ...... ··- ...... 600 [] BulkTN '------1 IIIII Fine TN c ,...... -····················································· Q Flood Region, Core C Flood Region, Core D Total Nitrogen(% wt mg) Total Nitrogen (% wt mg) 0 0.01 0.02 0.03 0 0.01 0.02 0.03 0 0 100 100 200 200 'E 'E .e. 300 .e. 300 .c .c ii ii ~ 400 ~ 400 500 500 Legend Legend 600 [] BulkTN 600 [] Bulk TN '------1 IIIII! Fine TN '------1 IIIII Fine TN Figure 2-4 Plume Region. Core A Plume Region. Core B C/N C/N (bulk) 0 5 10 15 20 25 0 5 10 15 20 25 200 'E .e. 300 .::: Q. ~ 400 +···································· 500 Legend 600 A BulkC/N '------1 .t. Fine C/N Flood Region, Core C Flood Region, Core D C/N C/N 0 5 10 15 20 0 5 10 15 20 25 200 'E .e. 300 .::: Q. ~ 400 500. -- Legend Legend 6oo+---- A BulkC/N 600 A BulkC/N '------1 &. Rne C/N Figure 2-5 Figure 2-6 A CCBC abundance (number per em) B CCBC abundance (number per em) 0 200 400 600 0 200 400 600 0~~-r~~~~-rl oi. lfr'... . ' ...... _ 200 E ~ .J:: ...... c...... ~ ~ 0. • 0 400. Q) • Legend 0 400 • Legend <>Coarse BC <>Coarse BC (CCBC) (CCBC) Fine BC Fine BC t> (SGBC) "'(SGBC) 600 Pluflle Regi!on. Co e A 600 Plume Regi\)n. Core B I 0.02 0.04 0.06 0.08 0.02 0.04 0.06 0.08 o/o SGBC o/o SGBC c CCBC abundance (number per em) D CCBC abundance (number per em) 0 wo ~0 ~0 0 200 400 600 0 0 r-~~*T--~~~--~--Tj E' 200 ~ .J::...... c...... 0.. 0. Q) Q) 0 400 Legend 0 400 Legend <>Coarse BC <>Coarse BC (CCBC) (CCBC) Fine BC + (SGBC) . r~~~~~ 600 600 Floo c Flood Regio~, Core p 0.02 0.04 0.06 0.08 0.02 0.04 0.06 0.08 o/o SGBC o/o SGBC Figure 2-7 SGCfTOC correlations (all cores) 0.08 ------y = -0.0231x + 0.0346 0.07 n • R2 = 0.005 0.06 1---~·~~.~~~------~.~-----.. rn 0 y = -0.0044x + 0.0313 (.) 0.05 D + D 0 D- 2 (!) 0.04 ·~ R = 0.0003 en -+----_L.L~_____.o~ • •: ~------1 ------, 0.03 ---- + with TOC fines 0.02 1------.-~ D D with TOC bulk 0.01 ------··------Linear (with TOC fines) 0 --Linear (with TOC bulk) 0 0.05 0.1 0.15 0.2 0.25 0.3 TOC A ,------~-- y = -0.2717x + 0.0787 Correlation Plume Region, Core A Correlation Plume Region, Core B y = -0.0322x + 0 0319 R2 = 0.157 R7 = 0.1871 = + 0.08 yo------·------, y 0.047x 0.0276 0.05 ,..------~ O.D7 -- _____o ___ .___ ·------R7 = 0.0166 0.04 ______[]______------0.06 ------·------,..------,a- -.-~;,.;:roc~ u 0.05 ~---· -"*~[[]"------1 c ~0.04 -~ D with TOC bulk g 0.03 j----00u:z~~bi1F.o~~~!i:"!;~A:::Eo -Linear (with TOC fines) 0 O.D3 . .ffi"- .. ~ 0.02 0.02 - ----~cr,.~'Q------Linear (with TOC bulk) 0.01 --· -·-- __i'l ______0.01 ------ 0.05 0.1 0.15 0.2 0.25 0.3 0.05 0.1 0.15 0.2 0.25 i____ ,_ TOC B TOC c ---- y = -0.2011x + 0.0494 Correlation Flood Region, Core D Correlation Flood Region, Core C y = -0.06. 0.0. 7 4~~-·+ 3531 R =0 1181 R2 = 0.0486 0.07 ,------, y = -0.0939x + 0.0423 0.05 .,------~ y = -0 017x + 0 031 R2 -= 0.0365 c 0.06 ---~+t----.o+Hc--£1------j------~ ...... R'=_o_:-'l09"_..., I 0.04 ~ 0.05 1-----.---.,------·------• with TOC fines • with TOC fines !· 0 0 U 0 with TOC bulk 0.03 --- --~...r·~e~,_Dr;D:zD~~--.~;;;;;;--1 D with TOC bulk CJ ~ •[J'11ttJ e ~c au g o.04 j____ ...... __:...... ,'!!L'!=-::::::;~------...-----==·-:;-- -Linear (with TOC fines) i -unear (with TOC fines) en 0.02 ------·• c+D • o------.- -Linear (with TOC bulk) !! 0 ~:~~ 1---,---.-••t df-~~- -:...- -Linear (with TOC bulk) 0.01 0.05 0.1 0.15 0.2 0.05 0.1 TOC D TOC E Figure 2-8 A Plume-dominated Region 1I Core A CCBC abundance (number per em) 5 20 0 200 600 200 -E ~ ..r:. ..r:...... a. a. ClJ ClJ 0400 0 400 • Legend Legend 0 Fine BC 600 0 %Fines 600 * Coarse BC I> C/N ratio Plume Region. Core A Plume Region. Core A 0 20 40 60 80 100 0.02 0.04 0.06 0.08 %Fines o/oSGBC B Plume-dominated Region 1I Core B C/N ratio CCBC abundance (number per em) 0 5 10 15 20 25 0 200 600 ot---~·~·~j~~~--~--- 0 r---~~--~--~~~--~~ Plume Region. Core B ..r:...... a. ..r:...... ClJ a. 0 ClJ bulk organics range 400 0400 -18-24kya Legend volcanic layer o Fine BC * Coarse BC 600 600 lo= ~ Plume Region. Core B t>t 0 20 40 60 80 100 0.02 0.04 0.06 0.08 %Fines o/oSGBC Figure 2-9 c Flood-dominated Region 2, Core C CCBC abundance (number per em) 0 0 200 400 600 200 ...... E ~ ..c ..c shell range .j.J ...... a. a. 476-861 +/-500 QJ QJ 0400 0400 Legend Legend 0 Fine BC t %Fines • Coarse BC 600 600 I> C/N ratio Flood Region, Core C Flood Region, Core C 0 20 40 60 80 100 0.02 0.04 0.06 0.08 % Fines % SGBC D Flood-dominated Region 2, CoreD C/N ratio CCBC abundance (number per em) 0 5 10 15 20 25 0 200 400 600 200 ...... E ~ ..c .j.J ..c a. .j.J QJ a. QJ 0400 0400 Legend 0 Fine BC t %Fines 600 • Coarse BC I> C/N ratio 600 Flood Region, Core D Flood Region, Core D 0 20 40 60 80 100 0.02 0.04 0.06 0.08 %Fines %SGBC Figure 2-10 Controls on Continental Shelf Stratigraphy: Waiapu River, New Zealand Chapter 3 Structural controls on preservation of Holocene shelf stratigraphy: Waiapu River, New Zealand Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Abstract High-energy continental shelves such as that off of the Waiapu River, New Zealand present an opportunity to study the influence of active tectonics on the distribution of marine sediments and associated continental shelf stratigraphy. Well documented evidence for the subduction of a large seamount ~2Ma, coupled with subsequent slope failure and avalanching ~ 170±40kya, indicates that this event strongly affected the morphology of the northeast New Zealand continental shelf, possibly influencing shelf sediment transport and preservation. Over 850km of high-resolution seismic reflection data collected on the Waiapu shelf provide evidence that the thickest deposits of preserved Holocene stratigraphy are found in tectonically-created accommodation space, highlighting the role of neotectonics in strata formation. A single reflection surface, interpreted as Miocene-age sedimentary rock, spans the entire continental shelf and serves as an acoustic basement on which Holocene-age sediment is deposited. The subduction of the seamount and the associated deformation of the shelf created two basins which have acted as sediment depocenters: 1) a shore-oblique depocenter located on the southern Waiapu shelf; and 2) a shore-parallel depocenter located near the edge of the Waiapu shelf above a folded and faulted zone. The hinge zone between the uplifting East Cape and the adjacent down-dropping continental shelf is possibly revealed in the rectilinear drainage pattern of the W aiapu paleochannel. During Holocene low-stands, this tectonically-controlled fluvial drainage pattern is presumed to have steered sediment into the structurally-low Waiapu Shelf Basin, while during high stands it is speculated that sediments continued to be steered south, preferentially filling in the morphological lows overlying the flooded paleochannel. Despite being mostly 152 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 infilled, the tectonically-controlled paleodrainage likely still influences modem-day sediment transport via the effects of small-scale, modem bathymetric lows overlying this paleochannel which steer gravity-dependent sediment flows at the river mouth. Morphological evidence from the paleosurface of the acoustic basement, coupled with preserved paleochannel drainage patterns and infilling, indicates the importance of structural controls on strata formation through the Holocene as well as in modem-day shelf sediment transport. 153 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 1.0 Introduction The distribution of marine sediments in tectonically active areas is a function not only of water depth and wave/current interactions, but is also influenced by regional and local tectonics. Assumptions of shelf-wide sediment transport that focus on sea level and hydrodynamics as the primary influences on sediment delivery to continental shelves risk neglecting the potentially significant role of tectonics on marine sedimentation and stratigraphy formation, particularly in the creation of accommodation space and in the steering of terrestrial material (see reviews by Sommerfield et al., in press; Leeder, 2007). Therefore, better understanding of the role of tectonics relative to sea level fluctuations and other processes regulating the transfer of marine sediment and the formation of continental margin strata is a key component of source-to-sink studies. Evidence for the subduction of a large seamount under the East Cape of the North Island ofNew Zealand near the mouth of the Waiapu River ~2Ma has been found preserved in shelf and slope stratigraphy (Collot et al., 2001; Lewis et al., 2004). This tectonic event, coupled with regional subduction tectonics, has resulted in uplift on the East Cape and downdrop on the adjacent continental shelf(e.g. Brown 1995; Lewis et al., 2004). The influence of these active tectonics on Holocene and modem·strata formation, however, remains poorly understood. Most short-term shelf sediment transport models rely on integrating observed hydrodynamics with gross-scaled modem bathymetry (e.g. Zhang, 1999; Harris and Wiberg, 2001, 2002; Wiberg and Harris, 2002; Kniskern et al., 2006). Modem bathymetry, however, cannot be scaled back in time to simulate earlier sediment dynamics without knowing the shape and slope of earlier paleosurfaces, complicating 154 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 attempts to bridge the gap between observable shelf sediment dynamics and preserved shelf stratigraphy. The continental shelf of adjacent to the Waiapu River exemplifies these complications, as current attempts to model modem shelf sediment dynamics cannot account for the influence of active tectonics (Kniskern et al., 2006), limiting their ability to provide insight on long-term shelf strata formation. Observed patterns of modem Waiapu shelf transport including: 1) the distribution of inner shelf flood layers; 2) the observed influence of small-scale bathymetry near the river mouth; 3) inner shelf and shelf-edge basin C/N ratios; and 4) the distribution of steady-state vs. non-steady state 210Pb accumulation profiles in shelf-edge basins all suggest a southward steering of modem terrestrial sediment (Addington et al., 2007, Wadman and McNinch, (2008), Wadman et al., in prep). This interpretation is at odds with hydrodynamic observations and modeling efforts that show either an equal shelf-wide distribution or northward steering of modem sediment (Kniskern et al., 2006; Ma et al., 2008), suggesting active tectonics and small-scale bathymetry might be influencing modem sediment transport and long-term strata formation. 1.1 Influence ofactive tectonics on continental shelfstrata formation The influence of tectonics on continental shelf sediment dynamics and strata formation has been observed in several ways. First, active tectonics frequently result in the creation (or destruction) of shelf accommodation space, with sediment being steered towards new depocenters (e.g. Foster and Carter, 1997; Maldonado and Nelson, 1999; Bezerra et al., 2001; Chamyal et al., 2003; Goodbred et al., 2003; Lewis et al., 2004; Gutierrez-Mas et al., 2004; Orpin et al., 2006; Normark et al., 2006; Anastasakis et al., 155 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 2007; Leeder, 2007). Second, the influence of active tectonics frequently results in a continental shelf with fault-controlled morphology and associated fluvial discharge. Together, these have been observed to direct shelf sediment transport both by influencing modem current dynamics as well as by controlling fluvial discharge during low-stands (Maldona and Nelson, 1999; McCulloh et al., 2000; Bezerra et al., 2001; Gutierrez-Mas et al., 2004; Anastasakis et al., 2007). Finally, tectonically-controlled subaerial drainage can influence marine continental shelf sediment transport by the preferential filling of fluvial channel-related lows during high-stands (Maldona and Nelson, 1999; Gutierrez Mas et al., 2004). 1. 2 Study area The Waiapu River continental shelflies inboard of an actively subducting plate boundary, and high rates of uplift on land (-4mrnlyr; Brown, 1995) are coupled with similar rates of subsidence on the outer continental shelf (Figure 1; Lewis et al., 2004 ). Regional subduction tectonics are complicated by the impact of well-documented subductions of a series of seamounts, most recently that of the Ruatoria seamount ~ 2Ma, with subsequent slope failure and avalanching approximately 170±40kya (Collot et al., 2001; Lewis et al., 2004). The immediate event resulted in a debris avalanche which left an ~ 31 00km3 deposit on the continental slope. The seamount itself is postulated to currently lie ~ 1Okm inshore, under East Cape (Figure 1; Collot et al., 2001; Lewis et al., 2004). This event is considered to be in part responsible for the high rates of uplift on land and downdrop on the adjacent continental shelf. Lewis et al. (2004) speculated that a significant amount of Quaternary sediment was preserved on the continental shelf, 156 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 especially within a southern, shore-oblique basin (the Waiapu Shelf Basin, Figure 1). The low-frequency seismic pulse generated by their GI Airgun (411105 mode) did not, however, provide detailed resolution of near-surface stratigraphy, and cores were not available to ground-truth their Quaternary interpretations. In the present study, we identify major depocenters for marine sedimentation on the Waiapu continental shelf and examine the influence of Quaternary (neo)tectonics on sediment dynamics and the evolution of stratigraphy. We present data showing an acoustic basement, on which Holocene and later sediment is deposited, sloping southward towards the structurally-deeper, southern basin defined by Lewis et al. (2004). Isopach maps of sediment preserved above this basement, coupled with extraction of the basement paleosurface, reveal two main depocenters on the narrow Waiapu continental shelf. Finally, along-isobath stratigraphic variation and rectilinear paleochannel drainage patterns suggest a channel-controlled, southward-steering of terrestrial sediment during low-stands, preferential filling of these channel lows during high-stands, and the continued influence of this channel on modem sediment dynamics via its expression in the modem bathymetry near the river mouth. These data highlight the role of neotectonics and related shelf structure in stratigraphy formation on this narrow continental shelf. The difference in resolution and scale of the techniques employed in this study allow a much more rigorous examination of the shallow stratigraphy on the Waiapu continental shelf, providing insight into the multiple processes controlling more recent stratigraphic evolution of the northern East Cape margin. 157 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 2.0 Methods 2.1 Seismic data collection Over 850km of high-resolution seismic reflection data (Figure 2) were collected over four cruises during 2003-2004 and used to image the sub-bottom of the Waiapu continental shelf. The study was executed using two seismic acquisition systems: an EdgeTech Chirp 216s (average resolution of 15-20cm) and an EdgeTech Chirp 512i (average resolution of 30-50cm; Figure 3). These systems are designed for shallow coastal research and their high-frequency and multi-pulse abilities allow for high resolution of shallow ( < 75m) reflection surfaces. Further details regarding data collection are provided in Wadman and McNinch (2008). Seismic reflection data were processed using SonarWeb Pro, and continuous and non-continuous reflectors were identified and digitized, as was the seafloor reflection surface. Heave is apparent in the seismic profiles because no swell filter was applied during acquisition or post-processing. Digitization of the reflectors was visually estimated through the heave for both the seafloor and sub bottom reflection surfaces by one person in order to limit the subjective differences that may arise when others participate in digitizing. A speed of sound of 1650m/s was used to transform acoustic reflection time to reflector depth (thickness). Sediment thickness was calculated by subtracting digitized sub-bottom reflector depths from the seafloor depths at each digitized point. The paleosurface map for the acoustic basement was obtained from the differences between the seismic reflector and the Mean Lower-Low Water (MLLW)-defined seafloor depths, and was gridded with Fledermaus. Pro using a weighted moving average algorithm at 75m spacing. These data provide a 3- dimensional surface which highlights subtle morphology variations of underlying strata. 158 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 2.2 Bathymetric data collection High-resolution interferometric swath (Sea SwathPlus, 234kHz) and multibeam swath (EM-1 002) bathymetry data were collected simultaneously with the seismic data. Further details regarding the collection of bathymetry data are provided in Wadman and McNinch (2008). Line spacing ranged from 50-180m depending on water depth, and the position of each data point was related to WGS84 using differential GPS. Vessel heave, pitch and roll were corrected in real-time using an IXSEA Octans motion sensor. Seafloor depths were tide-corrected to MLLW using observed tides from Poverty Bay adjusted for the East Cape region as published by Land Information, New Zealand. Data was initially gridded using line averaging at 2-meter resolution and was despiked, filtered and smoothed. Cleaned data was subsequently gridded at a variety of resolutions. For the purposes of this study, bathymetry from depths of 5 meters to approximately 500 meters was gridded using a weighted moving average algorithm at a resolution of75 meters (25 weight spacing) with Fledermaus Pro software. 3.0 Results 3.1 Seismic reflection surfaces Portions of the sub-bottom data, particularly in the northern portion of the study area, show some degree of pulse interference associated with the presence of gas in the sediments (Figure 4). Originating from the decay of organic matter, free gas has a pronounced effect on sediment acoustic properties, including reducing sediment strength and low-frequency sound speed, ultimately reflecting and scattering acoustic energy (e.g. 159 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Anderson and Hampton, 1980a,b; Floodgate and Judd, 1992; Judd and Hovland, 1992; Briggs and Richardson, 1996; Wever et al., 1998; Wilkens and Richardson, 1998). Presence of gas in the seismic data is manifested as a dark smear on the sub-bottom record, blanking out the reflection surfaces (Figure 4; e.g. Davis, 1992; Yuan et al., 1992; Lafferty et al., 2006). Seafloor reflection amplitude data, representing variations in the strength of seismic waves reflected from the seafloor, was used to distinguish gas from sediments in the seismic record (e.g. MacDonald et al., 2003; Sager et al., 2003). Derived from the acoustic reflection coefficient, reflection amplitudes are dependent on the changes in density, or hardness, of the seafloor and the underlying sediment. Positive amplitudes indicate increasing sound speed, related to increases in sediment hardness or density (such as in the presence of sand or rock). Negative amplitudes indicate decreasing sound speed, related to decreases in sediment hardness or density (such as in the presence of fine-grained sediment or free gas; e.g. Sager et al., 2003). Pockets of gas were identified where negative amplitudes coincided with blanking or smearing of the sub-bottom record, and care was taken not to include these regions in our analysis of the reflection surfaces. Resolvable seismic data from the entire shelf reveal a single, dominant reflection . surface, referred to in this study as R03, exemplified in three representative shore perpendicular lines (Figures 2, 5). This surface is exposed in the shallow, northern portion ofthe inner-mid shelf(water depths from 5-60m), and1ust south ofthe river mouth on the inner shelf (water depths <50m). On the northern portion ofthe inner shelf, R03 is identified from outcrops as a rocky substrate that forms a series of protective, 160 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 mud-filled enclosures (Wadman and McNinch, 2008). On the inner shelf south of the river mouth, exposures ofR03 were observed to be a similar rocky substrate. From ~50m water depth and deeper, R03 is present as a strong, continuous reflection surface. Near the outer continental shelf, R03 is folded and faulted before cropping out offshore (water depths ~140-180m) and along the entire outer shelf-edge (water depths over ~180m; Figure 5). Spatial variation in the number and extent of reflection surfaces above R03 is apparent in shore-parallel, along-isobath lines, as shown iri Figure 6. Representative seismic profiles collected along the ~80m isobath north of the river mouth are acoustically transparent (Figure 6, A-A') above R03. Seismic profiles collected south of the river mouth on the same isobath, however,show multiple reflection surfaces preserved above R03 (Figure 6, B-B'), as well as a preserved paleochannel, explored in more detail in section 3.2, below. 3.2 Paleochannels Seismic profiles reveal a well-preserved paleochannel on the Waiapu shelf (Figure 7). On the inner shelf the channel is ~600m wide and is capped by a reflection surface distinct from R03 (Figure 6; Wadman and McNinch, (2008); Wadman et al., in prep). On the mid-outer shelf, the channel widens to up to ~ 1400m (Figure 7). Spatially, the channel follows a nearly rectilinear pattern, exemplified in Figure 7. On the inner shelf, the narrow channel trends ~E/W across the shelf, turning N/S at ~25m water depth. The channel widens as it trends nearly straight N/S along the shoreline in water depths ranging from ~25-60m water depth, along the southern continental shelf. Approximately 161 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 17km south of the present river mouth, the channel turns nearly 90° towards the east and trends offshore, across the continental shelf. Preservation is poor in the deeper seismic lines, but the channel can be confidently observed until ~80m water depth (Figure 7). 3.3 Sediment thickness Sediment thickness between the seafloor and R03, as revealed by isopach maps based on seismic data from across the entire shelf, averages ::;18m thick over much of the continental shelf (Figure 8). Two linear-shaped regions characterized by greater thickness include: 1) a narrow ( ~Skm wide), shore-parallel region near the offshore edge (~140-180m water depth) ofR03 with an average thickness of ~30m, thickening towards the south; and 2) a wider ( ~8km wide), shore-oblique region on the southern continental shelf (~30-95m water depth) with an average thickness of ~30m that thickens towards the outer shelf (Figure 8). Profiles across these regions reveal a maximum thickness of 42m in the southern edge of the shelf where the two regions meet (Figure 8). 3.4 Paleosuiface The contoured paleosurface ofR03 is presented in Figure 9. Overall, R03 slopes offshore (average slope ~0.441 %) and towards the south (average slope ~0.146%) on the inner shelf. The surfaces becomes flatter and tilts towards the north (average slope ~0.051) on the outer she1f(>-90m depths). Along-she1fprofiles which allow for examination of subtle variations in this surface reveal small depressions in the- surface of R03 which underlie the paleochannel described in Section 3.3. It should be noted that 162 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 terrace-like patterns in the surfaces of profiles C-C', D-D' and E-E' in Figure 9 are gridding artifacts. 4.0 Discussion 4.1 Identification ofthe acoustic basement The nature of the dominant reflection surface extending over the entire Waiapu continental shelf, referred to in this study as R03, is speculative at best. Where it is exposed on the inner shelf, R03 is identified in this study as a friable mudstone and/or siltstone, similar to the Miocene-age sedimentary rocks that form the shoreline cliffs along East Cape and comprise the primary substrate of East Island (Moore and Mazengarb, 1992). The same reflection surface dominates the near-surface stratigraphy over the rest of the continental shelf (Figure 5). The folded and faulted nature of R03 where it is exposed offshore is likely due to shelf-wide buckling and faulting caused by the seamount subduction (Collot et al., 2001; Lewis et al., 2004). A similar Miocene-age rock unit spanning the Waiapu continental shelf was previously identified by Lewis et al. (2004) in their near-surface stratigraphy, albeit not at the exact same depths below the seafloor on the mid-outer shelf. This possible vertical discrepancy could be due to the comparatively coarse resolution of their lower frequency airgun utilized by Lewis et al. (2004). Orpin et al. (2002) presented a similar sub-bottom surface in their large-scale study of the shallow stratigraphy off of the East Cape region. Their surface is visually very similar to our R03 surface and is found at roughly the same depths below the seafloor (Figure 10). Orpin et al. (2002) were unable to core their surface; however, they tentatively identified it as representing the last post-glacial 163 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 transgression erosive surface, or perhaps even younger (Holocene), in age. Despite problems with gas masking part of their records, they.used this similar reflection surface as the baseline for their estimates of post-glacial sediment volumes. Although we were unable to core R03 on the mid-outer shelf, given the continuous nature of the reflection surface and the identification made possible by our more extensive data from the inner shelf, we tentatively interpret the entire surface as representing the same Miocene-age, sedimentary formation exposed along the northern East Cape coastline. Given the influence of free gas on portions of the seismic record, however, we cannot rule out the interpretation of Orpin et al. (2002); namely, that R03 represents a transgressive lag. Despite some uncertainty as to the exact nature ofR03, we agree with Orpin et al.' s (2002) interpretation that this surface represents the acoustic basement upon which Holocene sediment is deposited (Figure 10). 4.2 Tectonically-controlled accommodation space The creation of accommodation space by active tectonics has been seen to influence sediment transport and preservation in several coastal environments (e.g. Maldonado and Nelson, 1999; Bezerra et al., 2001; Gutierrez-Mas et al., 2004; Anastasak:is et al., 2007; Leeder, 2007). To determine if the morphology ofR03 includes tectonically-controlled accommodation space, the paleosurface ofR03 was generated for the entire shelf to examine it for evidence of morphological lows (Figure 9). Along-shelf profiles reveal that the R03 paleosurface slopes to the south over much of the continental shelf, forming a depression overlying the Waiapu Shelf Basin as defined by Lewis et al. (2004). From these data, we speculate that the formation of the Waiapu Shelf Basin 164 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 resulted in the creation of accommodation space on the southern continental shelf, subsequently resulting in the southern slope ofR03. Across-shelf profiles reveal that the R03 paleosurface on the outer shelf is dominated by a central depression, deepest on the south-central edge of the shelf, with extensive folding and faulting preserved in the overlying seismic profiles, and forming a second, shore-parallel low (Figures 5, 9). These data suggest that the subduction of the Ruatoria seamount, likely coupled with regional subduction tectonics, created significant accommodation space in these two locations on the continental shelf via faulting and folding. 4.3 Complete burial ofstructural basins The isopach map of stratigraphy preserved above R03 (Figure 8) reveals two areas of significant (>20m thick) sediment preservation, or depocenters, on the Waiapu continental shelf. The first depocenter is shore-oblique and located south of the river mouth, directly overlying the actively subsiding Waiapu Shelf Basin as described by Lewis et al. (2004; Figure 8). This depocenter preserves the thickest stratigraphy deposits as well as several reflection surfaces, and thus potentially several sequences of deposition and erosion (Figures 5, 8). The second depocenter is shore-parallel, trending near the edge of the shelf in water depths ranging from ~90-150m and overlying the main offshore fold and fracture zone observed in R03. These data indicate that sediment here has filled structural lows caused by the buckling and folding ofR03 (Figures 5B, 5C, 8). A faint, offshore sloping reflection surface is apparent near the surface of this region, suggesting at least one sequence of deposition and erosion preserved in this depocenter (Figure 5). 165 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 These data suggest that tectonically-controlled morphological lows in the R03 paleosurface as described in Section 4.1 functioned as increased accommodation space for shelf sediment transport and strata preservation, thus influencing the formation and preservation of shelf stratigraphy within these regions. If so, the depocenters of maximum sediment thickness should overly the increased accommodation space, manifested as morphological lows in the R03 paleosurface. To test this, we first outlined the boundaries of the depocenters using the 20-m sediment thickness contour line (Figure 11a). We then overlaid these boundaries on maps of the R03 paleosurface as well as the modem bathymetry (Figures 11b, 11c, respectively): When plotted on the R03 paleosurface, both depocenter boundaries clearly overlie both the southern shore-oblique and the along-shore R03 paleosurface morphological lows (Figures 9, lib). When plotted on the modem bathymetry, however, the southern shore-oblique depocenter overlies a modem bathymetric high (Figure 11 c). In addition, the shore-parallel depocenter does not directly overlie the steepest part of the modem along-shelf bathymetry. These data collectively suggest the tectonically-controlled R03 paleosurface greatly influenced Holocene sediment transport and subsequent strata preservation on the Waiapu tontinental shelf. Furthermore, the high sediment-yield Waiapu has apparently provided sufficient sediment to infill the R03 paleosurface lows, such that they are not apparent in the modem-day bathymetry. 4.4 Influence ofpaleochannels Paleochannels preserved in shelf stratigraphy can influence sedimentation by: 1) transporting sediment to tectonically-created accommodation space during low-stands; 2) 166 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 transporting sediment along faults or other tectonic features during low-stands; and 3) preferentially filling-in of paleochannel morphological lows during high-stands (e.g. Maldonado and Nelson, 1999; McCulloh et al., 2000; Bezerra et al., 2001; Gutierrez-Mas et al., 2004; Anastasakis et al., 2007). The paleochannel preserved on the Waiapu continental shelf can be followed from the current river mouth south along the shelf and offshore, into the shore-oblique depocenter and associated R03 paleosurface low (Figure 7). Lewis et al. (2004) observed paleochannels of similar cross-channe~ size trending into the deeper, underlying structure ofthe Waiapu Shelf Basin. These data strongly suggest that during low-stands, sediment was transported south via fluvial processes towards this structural and paleosurface low. During high-stands, it is possible that sediment continued to be transported south towards the shore-oblique low, preferentially filling the bathymetric lows left by the flooded paleochannel. Ultimately, the combination of these processes resulted in the infilling of this accommodation space, as manifested by the modem bathymetric high in this shore-oblique region (Figure 11 c). Similar depocenters related to the infilling of paleochannels have been recognized in the tectonically-active Iberian Gulf of Cadiz margin (Maldonado and Nelson, 1999; Gutierrez-Mas et al., 2004). If shelf-sediment transport was being preferentially steered towards the southern, shore-oblique R03 paleosurface low via a combination of fluvial and marine processes, we would expect to see both increased sediment thicknesses preserved in this region as well as multiple reflection surfaces indicating the preservation of repeated cycles of deposition and erosion (Figures 6, 8). Along-isobath stratigraphic variation previously observed on the inner shelf (Wadman and McNinch, 2008) and now observed over the entire shelf (Figure 6) shows the greatest number of reflection surfaces preserved in 167 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 stratigraphy south of the river mouth, overlying the southern, shore-oblique depocenter. These data further support the argument that sediment transport during high and low stands was steered south towards the shore-oblique Waiapu Shelf Basin and the southern end of the shore-parallel faulted zone, resulting in the sediment thickness patterns observed in the shelf stratigraphy. 4. 5 Implications for modern sediment transport The influence of tectonics on modern sediment transport is in part a function of the continuing influence of the buried paleochannel. Modern bathymetry slopes along shelf towards a low in the north, indicating that the southern accommodation space created by the formation of the Waiapu Shelf Basin has been filled (Figure llc). From bathymetry alone it would be expected that modern sediment would be transported either to the north or directly offshore, the shortest route to the steeper continental slope. Observation and modeling data characterizing modern sediment dynamics do not show substantial southward-directed sediment transport (Kniskern et al., 2006; Ma et al., 2008). Kniskern et al (in review), thus suggesting that the distribution of flood layers, as defined by high 210Pb accumulation rates and non-steady state 210Pb profiles, indicates preferential deposition of fine-grained flood layers northwards. Substantial evidence from the Waiapu shelf, however, including the spatial distribution of inner shelf flood sediment deposits and organic matter C/N ratios (Wadman and McNinch, 2008; Wadman et al., in prep), evidence from outer-shelfbasins, including C/N ratios and non-steady-state 210Pb profiles (Addington et al., 2007); and the southern location of the highest accumulation of mud on the mid- to outer-shelf, as 168 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 mapped by Kniskern et al (in review), indicates that terrestrial; gravity-dependent (hyperpycnal) flood deposits are being steered towards the southern continental shelf. Wadman and McNinch (2008) speculated that this was due to subtle but significant effects of the paleochannel, preserved in the modem, inner shelfbathymetry as a small scale, southern-directed bathymetric low, initially steering, via in the influence of gravity, gravity-dependent flood layers discharged from the Waiapu River towards the south. Our data indicate that the paleochannel preserved on the inner shelf ultimately trends towards the south and the Waiapu shelf basin (Figure 7), thus providing evidence of continued tectonic-influence on modem, shelf-wide sediment transport. 4. 6 Hinge Zone The fluvial drainage pattern in many tectonically active areas is controlled by underlying tectonics, with the result that fluvial discharge in these regions is frequently radial or rectilinear in nature. On the W aiapu continental shelf, the paleochannel is observed to tum sharply (nearly 90°) on the inner shelf towards the south, following a shore-parallel (N/S) path for~ 17km before turning sharply (nearly 90°) again, E/W and into the Waiapu Shelf Basin (Figure 7). This rectilinear drainage is likely fault controlled. While Lewis et al. (2004) were unable to definitively identify the location of the hinge zone between the uplifted land and the subsiding continental shelf resulting from the Ruatoria seamount subduction, they did speculate that it was in water depths of less than lOOm. The course ofthe paleochannel, oriented N/S along the ~60m isobath, may follow a major tectonic fault and quite possibly the as-yet unidentified hinge zone. 169 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 This interpretation implies that the inner shelf is being uplifted relative to the down dropping mid-outer shelf. Chronological data from the inner shelf supports this interpretation. Assuming uplift rates of~ 4rnrnlyr (Brown, 1995; Lewis et al., 2004) have been relatively constant since the Ruatoria collapse and seamount subduction, this would translate into a minimum uplift of~ 80m since the last glacial maximum (LGM) and substantial erosion and/or non-deposition on the uplifting inner shelf (e.g. Ridente and Trincardi, 2002). Wadman and McNinch (2008) observed a gravel surface in ~20m water depth on the inner shelf, interpreted to be a transgressive lag. Chronological constraints from black carbon analysis supported by three separate bulk organic 14C dates from the same surface collected in two different cores, have dated this surface as LGM (~ 18-24kya; Wadman et al., in prep). The LGM transgressive lag has been mapped in water depths of~ 18-25m, at depths of~ 3-6m below the seafloor. When adjusted to an estimated inner shelf uplift of ~80m since LGM, this reflection surface corresponds to non-uplifted depths of~ 104- lllm, well within the depth tentatively identified for deeper water LGM sediments by Lewis et al. (2004) and close to the commonly accepted eustatic LGM depth range of ~120m (e.g. Hanebuth et al., 2000; Peltier, 2002; Peltier and Fairbanks, 2006). Given the lack of accommodation space on the narrow, uplifting inner shelf, we would expect that this region of the shelf is not conducive to sediment storage. Wadman and McNinch (2008), however, observed that the inner shelf was capturing fine-grained . sediment both in a small subaqueous delta as well as in plume-dominated and flood dominated sedimentary deposits. Further chronological work indicates that most of this sediment capture has occurred in the last ~100 years and equates to at least ~16-34% of 170 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 the modem Waiapu fine-grained sediment budget (Wadman et al., in prep). We speculate that modem sediment deposition and preservation on the inner shelf is due to the effects of local deforestation-enhanced sediment supply (e.g. Page et al., 2000; Page et al., 2001; Hicks et al., 2003) overwhelming the lack of accommodation space. The presence of a small delta on the inner shelf (Wadman and McNinch, (2008) further supports our interpretation that local sediment supply is overwhelming available accommodation space (e.g. Boyd et al., 1992; Goodbred et al., 2003; Sommerfield et al., (2008)). Given the rapid accumulation of modem sediment on the uplifting inner shelf (~ 1.5crnlyr; Wadman et al., in prep) we expect the inner shelf will ultimately reach a threshold for deposition after which the system will shift from accumulation to bypassing. 5.0 Conclusions • Seismic data reveal a Miocene-aged acoustic basement on which Holocene and later sediment is deposited, sloping southward towards the Waiapu Shelf Basin. • Two main depocenters are observed on the narrow Waiapu continental shelf: 1) a shore-parallel structural low on the outer shelf(water depths ~90-150m) formed by the buckling of the underlying basement in response to well-documented and massive faulting related to the Ruatoria seamount subduction; and 2) a shore oblique structural low overlying the Waiapu shelfbasin as defined by Lewis et al. (2004) along the southern shelf, with associated paleochannel drainage and the thickest preserved sedimentary deposits. • Along-isobath stratigraphic variation previously observed on the inner shelf (Wadman and McNinch, (2008)) is found over the entire shelf, suggesting that 171 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 sediment deposition during high and low-stands has been steered towards the south and the Waiapu Shelf Basin. • Rectilinear paleochannel drainage patterns preserved in the stratigraphy of the continental shelf suggest a southerly-steering of terrestrial sediment during low stands and preferential filling of these lows during high-stands. The paleochannel may be influencing modem sediment dynamics via its expression in the modem bathymetry near the river mouth. • The rectilinear paleochannel indicates structural control on fluvial drainage and may be useful in fine-tuning the location of the hinge zone between the uplifting East Cape and downdropping adjacent shelf. Acknowledgements Support for this research was provided by the National Science Foundation (OCE0326831 and OCE0504690). Thanks for field and logistical support provided by R.A. Gammisch, W. Reisner, L. Carter, L. Northcote, B. Lee, and the crews of the R/V Tangaroa and R/V Kilo Moana. Special thanks for help with seismic and bathymetry data collection extended to J. Miselis, G. Gray, R.A. Gammisch, and M. Scully. Thanks for logistical support and historical data is also given to Tui Warmenhoven, Project Manager of the Taonga Tuku Iho Research Project. Special thanks for permission and vessel blessings are given to members of the Ngati Porou iwi. This work was enhanced by valuable discussions with N. Litchfield, L. Rose, T. Kniskern, L. Addington and K. Brodie. 172 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 References Addington, L., Kuehl, S.A. and McNinch, J.E., 2007. Contrasting modes of shelf sediment dispersal off a high-yield river: Waiapu River, New Zealand. Marine Geology, 243: 18-30. Anastasakis, G., Piper, D.J.W. and Tziavos, C., 2007. Sedimentological response to neotectonics and sea-level change in a delta-fed, complex graben: Gulf of Amvrakikos, western Greece. Marine Geology, 236(1-2): 27-44. Anderson, A.L. and Hampton, L.D., 1980. Acoustics of gas-bearing sediments. I. Background. Journal, Acoustical Society ofAmerica, 67(6): 1865-1889. Anderson, A.L. and Hampton, L.D., 1980. Acoustics of gas-bearing sediments. II. Measurements and models. Journal, Acoustical Society ofAmerica, 67(6): 1890- 1903. Bezerra, F.H.R., Saadi, A., Amaro, V.E. and Vita-Finzi, C., 2001. Pliocene-Quaternary fault control of sedimentation and coastal plain morphology in NE Brazil. Journal ofSouth American Earth Sciences, 14( 1): 61-7 5. Brown, L.J., 1995. Holocene shoreline depositional processes at Poverty Bay, a tectonically active area, northeastern North Island, New Zealand. Quaternary International, 26: 21-33. Boyd, R., Dalrymple, R. and Zaitlin, B.A., 1992. Classification of clastic coastal depositional environments. Sedimentary Geology, 80: 139-150. Chamyal, L.S., Maurya, D.M. and Raj, R., 2003. Fluvial systems of the drylands of western India: A synthesis of Late Quaternary environmental and tectonic changes. Quaternary International, 104: 69-86. 173 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Collot, J.Y., Lewis, K., Lamarche, G. and Lallemand, S., 2001. The giant Ruatoria debris avalanche on the Northern Hikurangi margin, New Zealand: Result of oblique seamount subduction. Journal of Geophysical Research B: Solid Earth, 106(9): 19271-19297. Davis, A.M., 1992. Shallow gas: an overview. Continental Shelf Research, 12(10): 1077- 1079. Floodgate, G.D. and Judd, A.G., 1992. The origins of shallow gas. Continental Shelf Research, 12(10): 1145-1156. Foster, G. and Carter, L., 1997. Mud sedimentation on the continental shelf at an accretionary margin- Poverty Bay, New Zealand. New Zealand Journal of Geology and Geophysics, 40(2): 157-173. Goodbred, S.L. Jr., Sarker, M.H., Kuehl, S.A. and Steckler, M.S., 2003. Controls on facies distribution and stratigraphic preservation in the Ganges-Brahmaputra delta sequence. Sedimentary Geology, 155(3-4): 301-316. Gutierrez-Mas, J.M., Achab, M. and Gracia, F.J., 2004. Structural and physiological control on Holocene marine sedimentation in the bay of Cadiz (SW Spain). Geodinamica Acta, 17(2): 153-161. Hanebuth, T., Statteger, K. and Grootes, P.M., 2000. Rapid flooding ofthe Sunda shelf: a late glacial sea level record. Science, 288: 1033-1035. Harris, C.K. and Wiberg, P.L., 2001. A two-dimensional, time-dependent model of suspended sediment transport and bed reworking for continental shelves. Computers and Geosciences, 27(6): 675-690. 174 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Harris, C.K. and Wiberg, P., 2002. Across-shelf sediment transport: Interactions between suspended sediment and bed sediment. Journal of Geophysical Research C: Oceans, 107(1): 8-1-8-12. Hicks, M., Shankar, U. and McKerchar, A., 2003. Sediment Yield Estimates: a GIS tool. Water and Atmosphere, 11 ( 4): 26-2 7. Judd, A. G. and Hovland, M., 1992. The evidence of shallow gas in marine sediments. Continental ShelfResearch, 12(10): 1081-1095. Kniskern, T.A., Harris, C.K. and Kuehl, S.A., 2006. Flood Sediment Dispersal and Deposition on the Waiapu River Shelf, East Cape, New Zealand. EOS, Transactions (AGU), 87(52). Lafferty, B., Quinn, R. and Breen, C., 2006. A side-scan sonar and high-resolution Chirp sub bottom profile study of the natural and anthropogenic sedimentary record of . Lower Lough Erne, northwestern Ireland. Journal ofArchaeological Science, 33: 756-766. Leeder, M., 2007. Cybertectonic Earth and Gaia's weak hand: Sedimentary geology, sediment cycling and the Earth system. Journal ofthe Geological Society, 164(2): 277-296. Lewis, K.B., Lallemand, S.E. and Carter, L., 2004. Collapse in a Quaternary shelf basin off East Cape, New Zealand: evidence for passage of a subducted seamount inboard of the Ruatoria giant avalanche. New Zealand Journal of Geology & Geophysics, 47:415-429. 175 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Ma, Y., Wright, L.D. and Friedrichs, C.T., (2008). Observations of sediment transport on the continental shelf off the mouth of the Waiapu River, New Zealand: Evidence for current-supported gravity flows. Continental ShelfResearch, in press. MacDonald, I.R., Sager, W.W. and Peccini, M.B., 2003. Gas hydrate and chemosynthetic biota in mounded bathymetry at mid-slope hydrocarbon seeps: Northern Gulf of Mexico. Marine Geology, 198(133-158). Maldonado, A. and Nelson, C.H., 1999. Interaction oftectonic and depositional processes that control the evolution of the Iberian Gulf of Cadiz margin. Marine Geology, 155(1-2): 217-242. McCulloh, T.H., Beyer, L.A. and Enrico, R.J., 2000. Paleogene strata of the Eastern Los Angeles basin, California: Paleogeography and constraints on neogene structural evolution. Bulletin ofthe Geological Society ofAmerica, 112(8): 1155-1178. Moore, P.R. and Mazengarb, C., 1992. Geology and Landforms of the Raukumara Peninsula. In: J.M. Soons and M.J. Selby (Editors), Landforms ofNew Zealand, Second Edition, pp. 334-343. Normark, W.R., Piper, D.J.W. and Sliter, R., 2006. Sea-level and tectonic control of middle to late Pleistocene turbidite systems in Santa Monica Basin, offshore California. Sedimentology, 53(4): 867-897. Orpin, A.R., Carter, L., Kuehl, S.A., Trustrum, N.A., Lewis, K.B., Alexander, C.R. and Gomez, B., 2002. Deposition from very high sediment yield New Zealand river is captured in upper margin basins. Margins Newsletter, 9: 1-4. 176 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Orpin, A.R., Kuehl, S., Walsh, J.P., Alexander, C. and Carter, L., 2006. Temporal and spatial complexity in post-glacial sedimentation on the tectonically active, Poverty Bay continental margin of New Zealand. Continental Shelf Research, 26(17-18): 2205-2224. Page, M., Trustrum, N. and Gomez, B., 2000. Implications of a century of anthropogenic erosion for future land use in the Gisborne-East coast region ofNew Zealand. New Zealand Geographer, 56(2): 13-24. Page, M., Harmsworth, G., Trustrum, N., Kasai, M. and Marutani, T., 2001. Waiapu River. Source-to-Sink Sedimentary Cascades in Pacific Rim Geo-Systems: 184. Peltier, W.R., 2002. On eustatic sea level history: Last Glacial Maximum to Holocene. Quaternary Science Reviews, 21(1-3): 377-396. Peltier, W.R. and Fairbanks, R.G., 2006. Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record. Quaternary Science Reviews Critical Quaternary Stratigraphy, 25(23-24): 3322-3337. Ridente, D. and Trincardi, F., 2002. Eustatic and tectonic control on deposition and lateral variability of Quaternary regressive sequences in the Adriatic basin (Italy). Marine Geology, 184: 273-293. Sager, W.W., MacDonald, I.R. and Hou, R., 2003. Geophysical signatures of mud mounds at hydrocarbon seeps on the Louisiana continental slope, northern Gulf of Mexico. Marine Geology, 198: 97-132. Sommerfield, C.K. et al., in press. Oceanic dispersal and accumulation of river sediment. In: C. Nittrouer et al. (Editors), Continental-Margin Sedimentation: Transport to Sequence. Blackwell Publishing, pp. 157-212. 177 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Wadman, H.M., Canuel, E.A., McNinch, J.E., Bauer, J.E., and Perkey, D.W., in prep. Black carbon chronostratigraphic evidence of deforestation preserved on the inner shelf of the Waiapu River, New Zealand. in preparation for submission to Marine Geology. Wadman, H.M. and McNinch, J.E., (2008). Stratigraphic spatial variation on the inner shelf of a high-yield river, Waiapu River, New Zealand: Implications for fine sediment dispersal and preservation. Continental Shelf Research. In press. Wever, T.F., Abegg, F., Fiedler, H.M., Fechner, G. and Stender, I.H., 1998. Shallow gas in the muddy sediments of Eckemf6rde Bay, Germany. Continental Shelf Research, 18: 1715-1739. Wiberg, P.L., Noble, M., Drake, D.E. and Harris, C.K., 2002. Sediment transport on the Palos Verdes shelf over seasonal to decadal time scales. Continental Shelf Research, 22(6-7): 987-1004. Wilkens, R.H. and Richardson, M.D., 1998. The influence of gas bubbles on sediment acoustic properties: in situ, laboratory, and theoretical results from Eckemf6rde Bay, Baltic sea. Continental Shelf Research, 18(14-15): 1859-1892. Wright, L.D., Ma, Y., Scully, M.E. and Friedrichs, C.T., 2006. Observations of Across Shelf Sediment Transport During High Energy Flood Events off the Mouth of the Waiapu River, New Zealand. EOS, Transactions (AGU), 87(36): OS11L-03. Yuan, F., Bennell, J.D. and Davis, A.M., 1992. Acoustic and physical characteristics of gassy sediments in the western Irish Sea. Continental Shelf Research, 12(10): 1121-1134. 178 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Zhang, Y., Niedoroda, A.W., Reed, C.W., Swift, D.J.P. and Fan, S., 1999. Two dimensional numerical modeling of storm deposition on the northern California shelf. Marine Geology, 154(1-4): 155-167. 179 , Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Figure Captions Figure 1: Location and general tectonics map. All map projections are UTM, Zone 60S. Depth intervals are in meters above MLL W, contours are in 1OOm intervals. Note the change in bathymetric contour interval between 500m and 1OOOm. RS (circled) indicates the postulated location of the subducted Ruatoria seamount. Modified after Lewis et al., 2004. Figure 2: Seismic tracklines location map. All map projections are UTM, Zone 60S. Depth intervals are in meters above MLL W. Yell ow highlight indicates seismic lines presented in the text. Figure 3: EdgeTech Sub-bottom sampling equipment. A: Retrieval of the Edgetech 512i on board the RIV Kilo Moana. B: EdgeTech 216s. C: Surveying with the EdgeTech 216s on the FN Osprey. Photos taken by H.M. Wadman and J.E. McNinch. Figure 4: Example of gas in a shore perpendicular seismic line. Reflection surface depths are based on a speed of sound of 1600 cm/s. Figure 5: Shore perpendicular seismic lines. Line locations are noted on Figure 2. Interpretations for each profile are shown below the actual data. Note the change in horizontal and vertical scale between profiles. Reflection surface depths are based on a speed of sound of 1600 cm/s. A: northmost profile line. B: central profile line. C: enlarged inset of folded and fracture zone. D: southernmost profile line. 180 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 Figure 6: Stratigraphic spatial variation. Map projection is UTM, Zone 60S. Depth intervals are in meters above MLL W, contours are in 1Om intervals. The exact location of the seismic line was indicated in Figure 2. The upper panel shows modem bathymetry and the specific location of seismic profiles A~A' and B~B'. Interpretations for each profile are shown below the actual data. Figure 7: Paleochannel. Map projection is UTM, Zone 60S. Depth intervals are in meters above MLLW, contours are in 15m intervals. Left panel shows georeferenced paleochannel boundaries and trending pattern. Dashed line indicates extent of channel preserved in seismic profiles. Right panels show examples of seismic profiles from the inner (top panel) and lower (bottom panel) shelf, respectively. Interpretations for each profile are shown below the actual data. Location ofWaiapu Shelf Basin, depicted as a dashed line with arrows, is interpreted from Lewis et al. (2004). Figure 8: Isopach map of sediment preserved above R03. Map projections is UTM, Zone 60S. Left~hand map shows sediment thickness above R03 relative to MLL W. Isopach contours are in 1Om intervals. Black dashed lines indicate locations of profiles A~A', B B' and C'C'. Gray dashed ovals show the location of the shore-oblique and shore perpendicular depocenters. Figure 9: Paleosurface ofR03. Map projections is UTM, Zone 60S. Left-hand map shows the paleosurface ofR03 relative to MLLW. Contours are in lOrn intervals. Dashed 181 Wadman: Controls on Continental Shelf Stratigraphy, Chapter 3 lines show locations of profiles A-A', B-B'. C-C, D-D' and E-E'. The general dimensions of the folded and faulted zone described in Figure 5 are outlined with a dashed, white box. Terraced pattern apparent in profiles C-C', D-D' and E-E' is a gridding artifact. Figure 10: Shore perpendicular seismic line showing the acoustic basement as defined both in this study (Panels A and B), as well as by Orpin et al (2002; Panel C). Reflection surface depths for A and B are based on a speed of sound of 1600 cm/s. Figure 11: Preserved depocenters relative to paleosurface and modern bathymetry. All map projections are UTM, Zone 60S. A: Isopach map of sediment thickness preserved above R03. The 20-meter contour is outlined in white. B: Paleosurface ofR03 with the isopach 20-meter contour outlined in white. C: Modern bathymetry with the isopach 20- meter contour outlined in black. 182 AUSTRALIAN PLATE -365 -385 -405 -425 1 174E 176E 1 178E 180 178W I I I Easting (UTM Zone 605) Vi' 0 \0 QJ 0 t: 0 0 0 N 0 I"() :E co ~ U") 2. 0'1 t: ..c: ...... z0 0 0 0 0 0co U") Figure 3-1 Figure 3-2 Figure 3-3 Figure 3-4 ~.,A~ R03 fold/fracture zone ""= :::.: '""~ ! .. ~ '<~ seafloor I fold/fracture zone reflection R03 -, surfaces ~. ------~ ' seafloor fold/fracture zone paleochannel reflection R03 surface reflection surfaces Figure 3-5 seafloor Ro3/ reflectors Ro3/ Figure 3-6 A A' 0 0 0 -o(/)('1) Oco <.OLO Q) t: 0 No seafloor :28 1-o ::>o...... co ,=~ O>LO - t: ·- paleochannelR~ -~ Fill .t: to 00 Zo 0 1'- 1' LO 600000 620000 640000 660000 Easting (UTM Zone 60S) seafloor Figure 3-7 co I C"') ! :::1 C) u:: 0\ I rt"' ....Q) :l u::O'l seafloor seafloor acoustic basement B (R03) NW SE shoreward seafloor seaward Southern Waiapu shelf acoustic basement C (Orpin et al., 2002) Figure 3-10 ,.... ,.... I I'V'l .....Q) :::1 u:Ol CONCLUSIONS Although the Waiapu River dispersal system has been characterized by significant and recent anthropogenically-driven change, most notably in its sediment yield, the results presented here indicate that the principle forcings on sediment transport and stratigraphy formation have remained consistent. What has changed is the efficiency of the system with regards to steering and segregation of fine-grained sediment. The results highlight: 1) the limitations inherent in assumptions of fine-sediment bypassing of energetic inner shelves; 2) the potential variability of stratigraphy, even on small spatial scales; and 3) the importance of framework geology, as manifested by fine-scale, near shore bathymetry, on shelf-wide sediment transport. Identifying anthropogenic influences in the stratigraphic record is part of the overarching goals of the Margins source to sink program. While the influence of deforestation has been identified in other locations via parameters such as changing grainsize regimes, shifts in mineralogy, changes in pollen species and abundances, and changes in sediment C/N ratios, these are all simply system responses to anthropogenic forcings, with potentially natural causes. The identification of the black carbon signal in the Waiapu inner shelf sediments (Chapter 2, Figures 7-9) provides an unambiguous chronostatigraphic benchmark for the onset of slash-and-bum processes, the end result of which was increased erosion and corresponding sediment yields. Application of this relatively simple and inexpensive technique in other regions could provide a valuable chronologie tool in environments characterized by heterogeneous sediments that do not lend themselves well to traditional chronological tools. 192 While much has been made of the exponential increase in river sediment yields post-European deforestation, these data show that the processes involved in sediment transport along and across the Waiapu continental shelfhave remained relatively constant for at least the last -1 OOOya. Vibracores showed little variation in C/N ratios downcore, in contrast to the variation along the shelf (plume-dominated north vs. flood/terrigenous dominated south), suggesting that the preferential steering ofterrestrial material to the south has persisted over time (Chapter 2, Figure 5). The large erosional/depositional hiatus preserved in the inner shelf stratigraphy ( Modem accumulation rates on the inner shelf, as defined by black carbon chronological control, are similar to those previously reported by Kniskern et al. (in review) for the mid-outer shelf. The results further indicate that the inner shelf is trapping -16-34% of the Waiapu fine-grained sediment budget, roughly equal to or larger to the amount previously accounted for on the mid-outer shelf. Coupled with Kniskern et al's (in review) estimate of -24% capture on the mid-outer shelf, these data show that -40-58% of the 100-year sediment budget is retained on the narrow Waiapu continental shelf. For reasons outlined in Chapter 2, Kniskern et al's (in review) fine-grained sediment budget estimate (-24%) likely underestimates the amount of sediment trapped 193 on the mid-outer continental shelf within the last 100 years, resulting in probable overestimation of shelf-sediment bypassing. Given the unfavorable sediment environment for 210Pb chronologies, black carbon analysis on the mid-outer shelf might enable the calculation of more refined shelf-wide sediment budgets. The role of antecedent geology is manifested both in the tectonic control of the Waiapu's paleochannel and in the shape and slope of earlier paleosurfaces, both of which influenced the past steering of terrestrial (and flood) material towards the south (Chapter 3, Figures 7, 9). Antecedent geology still exerts a subtle influence on sediment transport today, likely influencing the initial steering of gravity-driven plumes towards the south, along a geologically-controlled, fine-scale bathymetric low (Chapter 1, Figure 13; Chapter 3, Figure 7). Given the difficulties inherent in incorporating structural controls on stratigraphy formation using short-term sediment transport models, the results of this study may be of particular importance to the modeling community. In particular, the incorporation of paleosurfaces into short-term sediment transport models might enable a better connection between theoretical models and observed stratigraphy. 194 Appendix: 210Pb data Total Activity at Corrected Weight Absolute Percent Sample 10 Midpoint {g) Time of Plating Error Clay Activity VC3 0 9.51 1.510 0.143 40.890 5.299 VC3 2 9.38 0.833 0.084 39.949 6.046 VC3 7 9.60 0.981 0.099 38.832 5.163 VC3 9 9.71 0.984 0.090 34.106 4.953 VC3 11 9.53 1.690 0.157 46.311 2.654 VC3 15 9.49 1.229 0.117 47.794 2.293 VC3 19 9.22 1.096 0.100 33.711 3.513 VC3 23 9.48 1.184 0.108 39.098 3.466 VC3 29 8.38 1.355 0.125 38.774 2.824 VC3 35 9.02 1.095 0.102 56.542 2.184 VC3 41 8.78 1.235 0.116 56.602 2.182 VC3 47 8.80 1.258 0.115 49.603 2.537 VC3 53 9.00 1.047 0.099 46.062 2.272 VC3 59 9.65 1.054 0.108 39.941 2.639 VC3 65 9.05 1.032 0.118 41.967 2.460 VC3 79 9.24 1.024 0.207 43.828 1.024 VC3 88 9.19 0.893 0.090 21.349 0.893 VC7 1 8.79 0.800 0.087 20.442 3.914 VC7 11 8.88 0.786 0.106 27.729 2.833 VC7 21 8.93 0.842 0.085 19.903 0.423 VC7 25 8.76 0.523 0.056 12.282 4.256 VC7 29 8.89 0.693 0.075 5.271 13.159 VC7 41 8.64 0.604 0.063 7.067 8.543 VC7 51 8.49 0.940 0.092 15.177 6.196 VC7 61 8.76 0.774 0.085 16.243 4.765 VC7 71 8.58 0.361 0.039 19.104 1.891 VC7 75 8.49 0.808 0.082 17.453 4.630 VC7 81 8.40 0.857 0.086 20.942 4.095 VC7 91 8.77 0.641 0.076 11.008 5.822 VC7 101 8.84 0.926 0.094 20.015 4.624 VC7 111 9.45 0.899 0.091 15.366 5.847 VC7 121 8.59 0.909 0.108 23.334 3.896 VC7 141 8.96 0.997 0.122 23.241 4.291 VC7 149 8.69 0.939 0.111 22.033 4.264 VC7 redo 1 14.27 0.760 0.077 20.442 3.719 VC7 redo 11 8.73 0.854 0.082 27.729 3.078 VC7 redo 21 14.14 0.729 0.067 19.903 0.366 VC7 redo 25.5 7.23 0.708 0.072 12.282 5.764 VC7 redo 29 9.45 0.706 0.082 5.271 13.398 VC7 redo 41 10.14 0.597 0.069 7.067 8.449 VC7 redo 51 12.85 0.855 0.078 15.177 5.635 VC7 redo 61 13.75 0.721 0.068 16.243 4.440 195 VC7 redo 71 13.89 0.256 0.027 19.104 1.339 VC7 redo 75 13.41 0.718 0.066 17.453 4.117 VC7 redo 81 12.24 0.758 0.075 20.942 3.618 VC7 redo 91 13.10 0.656 0.063 11.008 5.962 VC7 redo 101 13.50 0.855 0.079 20.015 4.269 VC7 redo 111 14.24 0.761 0.081 15.366 4.948 vc8 1 13.97 0.497 0.052 2.400 20.728 vc8 11 14.27 0.549 0.053 3.494 15.731 vc8 21 13.99 0.559 0.054 0.000 7.574 vc8 31 13.90 0.617 0.076 5.608 10.993 vc8 41 13.88 0.572 0.056 6.863 8.331 vc8 46 12.42 0.853 0.083 25.026 3.407 vc8 51 13.05 0.998 0.116 24.068 4.147 VC8 61 14.50 0.634 0.058 6.157 10.296 vc8 71 14.62 0.824 0.116 18.970 4.341 vc8 81 14.87 0.536 0.065 6.101 8.788 vc8 91 14.61 0.494 0.045 4.731 10.438 KC21 1 9.76 2.554 0.236 39.179 6.519 KC21 3 9.51 1.882 0.174 20.392 9.232 KC21 5 9.55 1.618 0.151 45.571 3.551 KC21 7 9.84 1.484 0.139 46.343 3.201 KC21 9 8.78 1.884 0.175 34.243 5.501 KC21 14 9.14 1.654 0.150 28.561 5.793 KC21 19 8.89 1.324 0.123 50.719 2.611 KC21 24 8.50 1.303 0.121 52.258 2.494 KC21 29 9.32 1.035 0.099 22.688 4.560 KC21 34 8.79 1.382 0.139 56.419 2.450 KC21 39 9.81 1.245 0.119 40.836 3.049 KC21 44 8.73 1.264 0.120 48.374 2.613 KC21 49 9.33 0.941 0.094 21.625 4.350 KC21 56 9.35 1.115 0.103 22.514 4.954 KC21 63 9.35 1.136 0.107 47.316 2.401 KC21 70 9.31 1.444 0.134 38.770 3.725 KC21 77 8.77 1.250 0.114 57.225 2.184 KC21 84 8.76 1.112 0.106 52.535 2.116 HBC8 0.5 13.08 2.347 0.241 16.269 14.428 HBC8 1.5 13.16 1.455 0.154 21.190 6.866 HBC8 2.5 13.81 0.958 0.093 18.540 5.168 HBC8 3.5 13.69 1.638 0.164 19.422 8.435 HBC8 4.5 13.06 1.475 0.137 15.180 9.719 HBC8 5.5 12.99 1.357 0.128 16.353 8.297 HBC8 6.5 14.33 1.185 0.133 10.175 11.643 HBC8 7.5 14.23 0.856 0.081 10.402 8.232 HBC8 8.5 14.31 0.975 0.091 16.129 6.047 HBC8 9.5 14.12 0.913 0.082 14.017 6.511 HBC8 10.5 14.52 1.039 0.091 18.686 5.562 HBC8 11.5 13.57 0.924 0.081 25.188 3.670 HBC8 18 14.22 1.130 0.101 16.093 7.024 196 HBC8 25 13.46 1.007 0.088 22.735 4.429 HBC9 0.5 13.03 1.704 0.148 27.667 6.159 HBC9 1.5 13.76 1.739 0.153 31.833 5.464 HBC9 2.5 13.03 1.430 0.131 38.199 3.743 HBC9 3.5 13.41 1.438 0.135 45.003 3.195 HBC9 4.5 13.33 1.257 0.111 46.070 2.727 HBC9 5.5 13.03 1.123 0.150 49.375 2.274 HBC9 6.5 13.16 1.152 0.163 49.732 2.317 HBC9 7.5 13.14 1.206 0.110 55.471 2.174 HBC9 8.5 13.04 1.138 0.131 53.029 2.147 HBC9 9.5 13.39 1.371 0.139 40.605 3.376 HBC10 0.5 14.51 0.970 0.108 8.803 11.022 HBC10 1.5 14.99 0.993 0.091 7.269 13.659 HBC10 2.5 12.61 1.064 0.094 9.590 11.092 HBC10 3.5 14.66 1.114 0.113 12.327 9.035 HBC10 4.5 14.65 1.210 0.108 13.432 9.012 HBC10 5.5 14.11 1.355 0.139 16.426 8.249 HBC10 6.5 13.90 1.314 0.122 14.027 9.369 HBC10 7.5 14.42 1.256 0.112 12.441 10.099 HBC10 8.5 13.85 1.510 0.135 11.163 13.527 HBC10 9.5 13.86 1.552 0.139 12.238 12.682 HBC 11 0.5 13.72 1.437 0.122 16.983 8.463 HBC 11 1.5 13.28 1.362 0.172 13.620 10.000 HBC 11 2.5 13.37 1.322 0.132 12.143 10.890 HBC 11 3.5 13.24 1.265 0.110 13.013 9.718 HBC 11 4.5 13.36 1.326 0.136 13.087 10.135 HBC 11 5.5 13.15 1.753 0.169 28.065 6.245 HBC 11 6.5 13.46 1.611 0.144 11.342 14.207 HBC 11 7.5 13.94 1.364 0.147 11.335 12.030 HBC 11 8.5 13.07 1.170 0.106 9.054 12.927 HBC 11 9.5 13.23 1.224 0.110 18.219 6.721 HBC18 0.5 12.32 3.509 0.298 30.240 11.605 HBC18 1.5 12.50 3.199 0.279 30.267 10.568 HBC18 2.5 12.02 3.133 0.288 27.803 11.270 HBC18 3.5 12.11 2.919 0.261 32.260 9.048 HBC18 4.5 12.06 3.111 0.266 29.891 10.406 HBC25 0.5 13.30 1.195 0.118 11.572 10.325 HBC25 1.5 13.46 1.373 0.168 11.298 12.157 HBC25 2.5 13.52 1.278 0.110 9.073 14.087 HBC25 3.5 13.63 1.166 0.122 9.877 11.800 HBC25 4.5 13.98 1.014 0.134 10.203 9.935 HBC25 5.5 13.26 0.880 0.076 7.783 11.310 HBC25 6.5 13.69 1.087 0.152 8.837 12.297 HBC30 0.5 12.78 1.273 0.187 24.700 5.152 HBC30 1.5 12.61 0.839 0.136 20.569 4.079 HBC30 2.5 13.26 1.489 0.149 23.561 6.321 HBC 30 3.5 14.19 0.960 0.131 27.361 3.510 HBC30 4.5 14.07 1.382 0.238 27.284 5.067 197 HBC30 5.5 13.44 1.425 0.269 31.730 4.491 HBC30 6.5 13.79 1.481 0.230 41.051 3.609 HBC30 7.5 13.35 1.446 0.130 33.376 4.332 HBC30 8.5 13.41 1.428 0.154 26.823 5.323 HBC30 9.5 13.59 2.389 0.236 24.600 9.711 HBC30 15 14.35 0.915 0.092 6.565 13.932 HBC32 0.5 13.02 1.248 0.105 15.130 8.246 HBC32 1.5 13.35 1.305 0.111 19.427 6.719 HBC32 2.5 13.58 1.851 0.169 24.581 7.529 HBC3i 3.5 14.70 1.352 0.120 25.051 5.396 HBC32 4.5 13.55 1.649 0.151 21.672 7.607 HBC32 5.5 13.94 1.038 0.097 14.280 7.272 HBC32 6.5 13.91 0.863 0.084 12.397 6.960 HBC32 7.5 13.48 0.829 0.083 7.903 10.491 HBC32 8.5 13.54 0.778 0.076 7.454 10.440 HBC32 9.5 13.62 0.932 0.089 8.627 10.801 HBC32 10.5 13.54 1.007 0.097 14.123 7.131 HBC32 11.5 13.56 1.234 0.114 23.777 5.191 HBC32 12.5 13.66 0.956 0.103 24.409 3.917 HBC32 13.5 13.81 1.224 0.119 13.830 8.852 HBC32 14.5 14.18 0.895 0.086 4.884 18.331 HBC32 15.5 14.56 0.667 0.077 5.496 12.138 HBC32 17.5 14.58 0.741 0.073 4.455 16.640 HBC32 18.5 14.76 0.804 0.077 4.097 19.623 HBC32 21 13.85 0.638 0.060 4.885 13.060 HBC32 25 13.52 1.007 0.087 12.636 7.968 HBC33 0.5 14.76 0.792 0.090 4.709 16.820 HBC33 1.5 14.50 2.331 0.233 5.286 44.102 HBC33 2.5 14.78 5.634 0.735 7.637 73.772 HBC33 3.5 14.73 0.554 0.055 4.762 11.636 HBC33 4.5 14.58 0.513 0.050 4.419 11.615 198 VITA Heidi M. Wadman Born in Roseburg, Oregon, 27 October, 1975. Graduated from West Linn High School in 1993. Earned B.S. in Geological Sciences from The College of William and Mary in 1998. Received M.S. in Marine Sciences from the College of William and Mary, School of Marine Science in 2004. Entered doctoral program in College of William and Mary, School of Marine Science in 2004. 199