Deep-Sea Research II 49 (2002) 3599–3629
Fluxes of micro-organisms along a productivity gradient in the Canary Islands region (291N): implications for paleoreconstructions
F. Abrantesa,*, H. Meggersb, S. Navea, J. Bollmanc, S. Palmad, C. Sprengelb, J. Henderiksc, A. Spiesb, E. Salgueiroa, T. Moitad, S. Neuerb a Departamento de Geologia Marinha, Instituto Geologico! e Mineiro, Aptdo 7586, Estrada da Portela, 2720 Alfragide, Portugal b Department of Geosciences, University of Bremen, Postbox 330440, D-28334 Bremen, Germany c Geological Institute ETH Z, Sonnggstrasse 5, CH-8092 Zurich, Switzerland d Instituto das Pescas e do Mar (IPIMAR), 1200 Lisboa, Portugal
Received 18 May 2000; received in revised form 16 February 2001; accepted 23 May 2001
Abstract
To understand the processes controlling the formation of the sediment record, seasonal variations of living communities, fluxes through the water column, and sediment accumulation rates of diatoms, coccolithophores (phytoplankton), and planktic foraminifera (zooplankton) were studied through seasonal water-column sampling, sediment traps, and box- and multi-core sediment sampling in the Canary Islands region (291N), from the productive NW African coastal area to offshore oligotrophic waters. A close relationship between the phytoplankton composition and hydrographic conditions was observed. Coccolithophores dominate the phytoplankton community throughout the year. The seasonal flux variability of the various groups as measured in the upper-trap samples (E500–900 m water depth) reflects the seasonal changes of their vertically integrated standing stocks in the overlying water column. Distinct high-standing stocks of all three groups can be related to the influence of upwelling filaments at the near-shore site (EBC). At the offshore sites (ESTOC and LaPalma) all groups display a late winter/early spring maxima related to local increased production. In addition, the increase in flux of all the organisms observed in the deeper traps at both offshore sites can be explained by lateral advection of living material by surface filaments. In addition, the occurrence in the traps of diatom and foraminifera species characteristic of high-productivity coastal areas indicates that the material must come from a highly productive coastal region, rather than production in the overlying oligotrophic surface water. Investigation of the phytoplankton assemblages in the water column, sediment traps, and surface sediments reveals: (i) sediment assemblages have been somewhat modified both by differential dissolution in the water column and the sediments and possibly also by reworking and (ii) the original composition is fundamentally preserved. Diatoms, in spite of being the most affected by differential dissolution both during settling and within the sediments, show a clear relation to the upwelling process. Planktic foraminifera (zooplankton) appear to be less altered by dissolution. For both groups, however, the dominant taxa during the upwelling episodic events (Chaetoceros and Globigerina bulloides) dominate the assemblages found in the sediments underlying Cape Ghir, the most productive area of the Canary Islands region. r 2002 Elsevier Science Ltd. All rights reserved.
*Corresponding author. Tel.: +351-21-4718922; fax: +351-21-4719018. E-mail address: [email protected] (F. Abrantes).
0967-0645/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0967-0645(02)00100-5 3600 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629
1. Introduction Eastern Boundary Current System was investi- gated. The chosen organisms were: diatoms— The planktic organisms that thrive in the near- silica-bearing algae that dominate the phytoplank- surface layers of the oceans are the ones most ton community in upwelling regions (Margalef, influenced by and most tightly coupled with 1978) and have very similar assemblages for most climatic changes. It is usually assumed that coastal upwelling areas (Estrada and Blasco, their sedimentary record represents an adequate 1985); coccolithophores—unicellular gold-brown proxy of variations in the epipelagic realm, and, algae covered with small calcium carbonate hence, in global or regional climate. However, plates—coccoliths, which are important bloom paleoreconstructions suffer several limitations: formers in low productivity warm waters, but are (1) most paleoceanographic reconstructions are also an important component of the phytoplank- generally based on the paleoecological meaning ton communities found on the N Atlantic coasts of a single group; (2) the proportion of the (Wefer and Fisher, 1993; Abrantes and Moita, water-column production represented in the sedi- 1999); and planktic foraminifera—carbonate-bear- ments at any given location and time is unknown; ing heterotrophic zooplankters, known to mirror and (3) differences between the water-column surface-water temperatures, water masses, cur- assemblages and the sediment assemblages are rents, and upwelling conditions (Kennett, 1982; unquantified. Thunell and Reynolds, 1984; Thunell and Sautter, Sediment trapping technology has certainly 1992). made a difference. Since the early works by Honjo Seasonal distribution of the different groups and (1978), sediment-trap surveys have allowed the species composition and their coupling to ecologi- quantification of the exported flux of particles cal factors and water masses characteristics is from the euphotic zone, as well as seasonal investigated through sampling of the water column variations and composition. There also have been at different seasons. The influence of coastal many trap studies that investigate the relation of upwelling productivity to the flux of plankton planktic organisms to the hydrographic conditions organisms to the seafloor was approached by the of the considered areas (foraminifera—e.g., Rey- study of a 9-month time-series of sediment-trap nolds and Thunell, 1985; Thunell and Honjo, data collected at three trap sites deployed along 1987; Thunell and Sautter, 1992; diatoms—e.g., the 291N temperature and productivity gradient Takahashi, 1986; Sancetta, 1989; Takahashi et al., transect: from the northwest African coast influ- 1989; Sancetta, 1992; Sancetta, 1995; Romero, enced by the Eastern Boundary Canary (EBC) 1998; coccolithophores—e.g., Ziveri et al., 1995; current to the oligotrophic open-ocean waters of Andruleit, 1997; Sprengel et al., 2000). Given the differences in ecological affinity and fossilization potential of the various plankton groups that occur as constituents of the same Table 1 Locations of moorings and multi-core stations community, any study of several groups will give a more complex but more faithful picture of the Site Latitude Longitude Distance Water processes that control the formation of the (N) (W) from depth shore (m) sediment record. However, very few studies (km) comprise quantitative analyses of different groups of shell-bearing plankton groups (Sautter and EBC 28142.5 13109.3 996 GeoB4234 28153.4 13113.6 180 1360 Sancetta, 1992; Samtleben et al., 1995). As part of the Canary Islands Azores Gibraltar Observa- ESTOC 29111.0 15127.0 3610 tions project—CANIGO—the influence of the GeoB4301 29110.0 15127.2 387 3610 environmental variability on the planktic organ- isms and resulting fluxes along an East–West LaPalma 29145.7 17157.3 4327 GeoB4242 29140.9 17153.4 630 4292 transect positioned at 291N in the North Atlantic F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3601
33 MADEIRA ISLAND
February 1999 32
1000 m 31 4000 m Cape 3500 m 3000 m 4500 m Ghir ° N ) E ( 30 LP 500 m ESTOC 1500 m L A T I T U D 29 EBC
28 Cape Juby MOROCCO C A NA R Y I S L A N D S
27 19 18 17 16 15 14 13 12 11 10 9 L O N G I T U D E (° W )
Fig. 1. Location of mooring sites (closed circles) and surface sediment samples (open circles) and plankton-sampling stations of the February 1999 cruise (triangles).
LaPalma (LP) via the European Station for coastal jet that generally separates the cool and Time-series in the Ocean (ESTOC) (Table 1, nutrient-rich upwelled waters from the warmer, Fig. 1). Changes in species occurrence is addressed nutrient-depleted offshore waters is not a simple by comparing the uppermost and Holocene sedi- unbroken alongshore feature, but rather punctu- ments to the trap assemblages and the living ated by mesoscale structures (filaments). Filaments community. Quantification of the changes in- of upwelling water spreading from the NW curred within the water column is attempted by African upwelling zone into the Canary Island comparing the accumulation rates determined for region (Hill et al., 1998) are clearly visible in the sediments to the estimated mean fluxes Advanced Very High Resolution Radiometer measured in the traps. (AVHRR), Coastal Zone Color Scanner (CZCS) and the SEAWIFs images. The most persistent filaments, which seem to occur irrespective of the 2. Oceanographic setting and production conditions season, extend from Capes Ghir and Yubi (Fig. 1) and spread westwards and south to the Canary This study was undertaken at 291N, on the Islands, up to 500 km (Erimesco, 1966—in Hagen eastern Canary Basin, immediately to the north of et al., 1996; Nykjaer, 1988; Barton et al., 1998; the Canary Islands, between a major upwelling Knoll et al., 1999; Parrilla et al., 1999). region, the northwest African coast, and the Due to the resupply of nutrients by coastal oligotrophic open ocean. Along the African coast, upwelling, high biological productivity occurs north of about 251N, upwelling occurs during along the African coast, with maximum phyto- summer and early fall (Wooster et al., 1976). The plankton biomass concentrated on the shelf. Data upwelling zone itself is restricted to a coastal band obtained during the course of the CANIGO of 50–70 km (Mittelstaedt, 1989). However, as in project (Parrilla et al., 1999) indicate chlorophyll many margins where coastal upwelling occurs, the a concentrations of 2–4 mg m 3 and primary 3602 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 production (PP) up to 5 g C m 2 d 1 in the following the dynamics of the upwelling filament eutrophic area, near the African coast. In the off Cape Ghir. Concentrated samples were taken oligotrophic offshore area, chlorophyll a concen- within the upper 100 m of the water column trations and PP values are very low (0.05 mg m 3 (integrated sampling) with a 20-mmmeshsize and 100 mg C m 2 d 1, respectively). At 301N the plankton net. The net was rinsed with seawater seasonality of PP near the coast is reflected by and the material was transferred into a plastic bottle 309 mg C m 2 d 1 in June, 373–545 in April, and and stained with Glutardialdehyde. Planktic for- 451 in October (Parrilla et al., 1999). In terms of aminifera were recovered during the spring and phytoplankton community, in the upwelling cen- summer cruises, but samples relative to winter and ter, and despite the relatively low ratio of dissolved fall although at approximately the same locations silica to nitrate (about 2:5), the flux gave rise to were collected at different cruises Victor Hensen 96/ large populations of diatoms as well as large 2 (winter—January 24–29, 1996) and Poseidon 212/ phytoflagellates, as earlier found by Margalef 1 (fall—September 22–26, 1995). Samples were (1978, 1981, 1985). collected at five depth intervals (0–25, 25–50, 50– Substantial evidence indicates that filaments 150, 150–300, and 300–500 m) using a multiple also constitute important sites of aggregation of opening–closing net (MCN), equipped with five nets biological activity (Hill et al., 1998). During the of 63-mm mesh size and a mouth area of 0.25 m2. time that these nutrient-rich filament waters spend in the deep ocean, vertical velocities of the same 3.2. Sediment traps order as in usual upwelling areas are observed (Hagen et al., 1996) and chlorophyll-like pigment All sediment-trap samples were collected using concentration detected from satellites are higher cone-shaped particle traps of the Kiel-type (Aqua- than ambient levels of PP (Barton et al., 1998; tec) with 20 cups and a collection area of 0.5 m2. Davenport et al., 1999). As so, in the CANIGO Sediment traps were located at three sites along region between the oligotrophic water in the 291N off the NW African coast between 800 m subtropical area and the high productive area in (EBC) and 4200 m (LP) water depths (Table 1, the EBC current, there is a transition zone, Fig. 1). At the deeper sites (ESTOC and LP) three influenced by offshore transport of nutrients and traps were located at around 700, 900, and 3700 m organisms through filaments. water depth (Table 2). The sampling interval was mostly 2 weeks. Initial sample processing was carried out at Bremen University following Wefer 3. Sample collection and Fisher (1993). Each sample was further wet split by means of an electric rotary sample divider 3.1. Water column (Fritsch, Laborette 27) using trap water as the split medium. Aliquots ranged between 1/25 and 1/125 To determine the seasonal distribution of total depending on the particle content of the source phytoplankton, diatoms, and coccolithophores in material. Trap failures during the experiment led to the water-column, seawater samples were taken the deficit of data from the LP upper trap (700 m). with 10-l rosette bottles coupled to a Neil Brown CTD probe, at the surface, 10, 25, 50, 75, 100, 125, 3.3. Sediments 150, 200, 250, and 300 m at three locations near the trap mooring stations during five cruises: winter The sediment samples were collected under each 1997 (Meteor M37/2b—December 28–January mooring using a multi-coring device at EBC and 22), spring 1998 (Poseidon P237/leg3-4—April 4– ESTOC, and a box-corer at LP (Table 1). Multi- 8), summer 1998 (Meteor M42/1b—June 28–July core sediment samples were sliced into 1-cm depth 5), and fall 1997 (Poseidon P233—September 1– intervals immediately after recovery onboard. 21). An extra cruise was carried out in February Samples used in this study correspond to the 1999 (February 15–26), with the objective of uppermost sediment slice (0–1 cm), and samples F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3603
Table 2 Table 2 (continued) Trap depth, sampling periods, and intervals analyzed for the different micro-organisms (d-diatoms; c-coccolithophores; Site Sample Sampling interval Micro-organisms f-planktic foraminifera) analyzed (sediment From To trap depth m) Site Sample Sampling interval Micro-organisms analyzed (sediment 2 1/20/97 2/3/97 d, c, f d, c From To trap depth m) 3 2/3/97 2/17/97 d, c, f d, c 4 2/17/97 3/3/97 d, c, f d, c EBC 5 3/3/97 3/17/97 d, c, f d, c 700 6 3/17/97 3/31/97 d, c, f d, c 1 1/2/97 1/6/97 d, f 7 3/31/97 4/14/97 d, c, f d, c 2 1/6/97 1/20/97 d, c, f 8 4/14/97 4/28/97 d, c, f d, c 3 1/20/97 2/3/97 d, c, f 9 4/28/97 5/12/97 d, c, f d, c 4 2/3/97 2/17/97 d, c, f 10 5/12/97 5/26/97 d, c, f d, c 5 2/17/97 3/3/97 d, c, f 11 5/26/97 6/9/97 d, c, f d, c 6 3/3/97 3/17/97 d, c, f 12 6/9/97 6/23/97 d, c, f d, c 7 3/17/97 3/31/97 d, c, f 13 6/23/97 7/7/97 d, c, f d, c 8 3/31/97 4/14/97 d, c, f 14 7/7/97 7/21/97 d, c, f d, c 9 4/14/97 4/28/97 d, c, f 15 7/21/97 8/4/97 d, c, f d, c 10 4/28/97 5/12/97 d, c, f 16 8/4/97 8/18/97 d, c, f d, c 11 5/12/97 5/26/97 d, c, f 17 8/18/97 9/1/97 d, c, f d, c 12 5/26/97 6/9/97 d, c, f 18 9/1/97 9/15/97 d, c, f d, c 13 6/9/97 6/23/97 d, c, f 19 9/15/97 9/29/97 d, c, f d, c 14 6/23/97 7/7/97 d, c, f 20 9/29/97 10/13/97 — d 15 7/7/97 7/21/97 d, c, f 16 7/21/97 8/4/97 d, c, f 17 8/4/97 8/18/97 d, c, f from the depth interval based on the age models 18 8/18/97 9/1/97 d, c, f presented by Henderiks et al. (2002) correspond to 19 9/1/97 9/15/97 d, c, f the Holocene. The accumulation rates (AR) of 20 9/15/97 9/29/97 d, c, f various micro-organisms (diatoms, coccolithophores, ESTOC and planktic foraminifera) were determined as 500 750 3000 2 1 1 12/23/ 1/5/97 d, f — d Accumulation rate ð#valves=cellscm kyr Þ 96 ¼ micro-org: abundance ð#valves=cellsg 1Þ 2 1/6/97 1/19/97 d, f d, c d, c 3 1 3 1/20/97 2/2/97 d, f d, c d, c DBD ðgcm ÞLSR ðcmkyr Þ; 4 2/3/97 2/16/97 d, f d, c d, c 5 2/17/97 3/2/97 d, f d, c d, c whereDBDisthedrybulkdensity determined for 6 3/3/97 3/16/97 d, f d, c d, c each level, and LSR is the linear sedimentation rate 7 3/17/97 3/30/97 d, f d, c d, c determined for the gravity cores collected at the same 8 3/31/97 4/13/97 d, f d, c d, c sites. For detailed descriptions see Henderiks et al. 9 4/14/97 4/27/97 d, f d, c d, c 10 4/28/97 5/11/97 d, f d, c d, c (2002). 11 5/12/97 5/25/97 d, f d, c d, c 12 5/26/97 6/8/97 d, f d, c d, c 13 6/9/97 6/22/97 d, f d, c d, c 4. Methods of analysis 14 6/23/97 7/6/97 d, f d, c d, c 15 7/7/97 7/20/97 d, f d, c d, c 16 7/21/97 8/3/97 d, f d, c d, c 4.1. Living phytoplankton and diatoms 17 8/4/97 8/17/97 d, f d, c d, c 18 8/18/97 8/31/97 d, f d, c d, c 4.1.1. Water column 19 9/1/97 9/14/97 d, f d, c d, c The major phytoplankters, diatoms, coccolitho- LP phores, and dinoflagellates were counted and 900 3700 identified from 250-ml seawater subsamples. On- 1 1/6/97 1/20/97 d, c, f d, c board, seawater was poured into dark plastic 3604 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629
flasks containing 30 ml of a 20% solution of general, for each sample about 300 specimens were hexamethylenetetramine buffered formalin to ob- identified to the genus or species level and raw tain a final concentration of 2.4% (Thondsen, counts were then converted to percent abundance. 1978). Subsamples of 100 ml, a volume chosen due In samples containing low diatom abundances the to the low concentration of diatoms in oceanic number of specimens identified was between 100 waters (Hasle, 1978a), were introduced in settling and 200. chambers and phytoplankton was allowed to settle for 72 h (Margalef, 1969). Major phytoplankton 4.1.3. Sediments constituents were counted and diatoms identified All sediment samples (uppermost and Holocene) by the Utermohl. method using a Zeiss IM35 were treated and slides prepared as described in inverted microscope equipped with phase contrast Abrantes (1988). Counting and identification and bright-field illumination (Hasle, 1978b). A procedures were the same as for sediment-trap total of 578 samples were studied. Taxonomic samples. problems were solved through the observation of the concentrated samples with a scanning electron 4.2. Coccolithophores microscope (SEM—JEOL JSM-5200) usually at 10 kV accelerating voltage. For SEM observation, 4.2.1. Water column diatom frustules were cleaned using the Simon- Seawater was filtered onboard through Nucleo- sen’s method (Tomas, 1996) and coated with gold. pore filters (0.8 mm porosity, 47 mm diameter) using a low vacuum filtration device. Filtration 4.1.2. Sediment traps was concluded if the filter became clogged. The Diatoms were analyzed in a total of 116 trap amount of remaining water in clogged samples was samples (Table 2). Sample splits were rinsed of measured and recorded. After filtration the filter preservative by repeated settling in distilled water membranes were rinsed with 50 ml buffered and cleaned of organic matter by H2O2. Slides of distilled water (NH4OH, pH 8.5) to eliminate all the entire aliquot were prepared using the eva- traces of sea salt. Rinsed filters were immediately poration-tray method of Battarbee (1973), dried in an oven at 401C for at least 12 h. mounted with Permount medium, and examined Coccolithophore cell density (#/l) and taxo- under a Nikon Labophot 2 microscope equipped nomic composition were determined using a with Differential Interference Contrast (DIC), HITACHI S2300 and a Philips XL30 SEM at a 10 eyepieces and 100 objectives. Diatoms magnification of 3000 . For these analyses a were counted in 100 randomly selected fields of piece of filter was mounted on an aluminium stub view per slide and in three of the four slides using carbon tape and coated with 15 nm of gold. prepared from each sample (Abrantes et al., 1994). Both SEMs were equipped with a computer Diatom flux was calculated as controlled stage used to count all samples (for details see Bollmann et al., 1999a, b; Cortes, 1998). F ¼ððNÞðA=aÞðVÞðSÞðXÞÞ=D; A fixed area in each filter was analyzed along a where the flux F is expressed as number of valves transect from the center to the edge. Thirty to m 2 d 1, N is the number of valves counted in 100 forty equidistant tracks of observation were randomly selected fields of view (a) which repre- analyzed along this transect. Each track of sent a fraction of the total tray area (A), V is the observation consists of 64 single screens each dilution volume, S is the split fraction, X is the 900 mm2 observed at a magnification of 3000 . conversion factor from the collecting area to 1 m2, The number of coccolithophores in 1 l of water and D is the sampling interval in days for each was calculated as CD=ðANÞ=ðavÞ; where CD is sample. the cell density (cells per liter of seawater), A the Relative abundance of diatom taxa was deter- filtration area,N the total number of individuals, a mined for each sample following the counting the observed area, and v the volume of filtered procedures of Schrader and Schuette (1968). In water. F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3605
4.2.2. Sediment traps aluminium sample holder and sputtered with gold A total of 93 trap samples from the three prior to SEM analysis. Weighing of microbeads deployments were analyzed for coccolithophore and sediments for nannofossil analyses was done abundance and assemblage composition (Table 2). with a Mettler AE260 with a precision of 10 6 g. Each sample aliquot was filtered and dried All coccolith analyses were conducted on a according to the methods described in Sprengel Hitachi S2300 SEM. Counts were done at a et al. (2002). Coccolith analysis was carried out on magnification of 4000 and 6000 . All coccoliths a randomly chosen small section of filter fixed on and added microbeads in a given field of view were an aluminium stub and sputtered with gold/ counted. From the ratio between counted and palladium using a Zeiss DMS 940A SEM, usually added microbeads the number of coccoliths per at 10 kV accelerating voltage. Coccolith and weight dry sediment were calculated. Identification coccosphere abundances were determined on the followed the taxonomy of Jordan and Kleijne basis of the number counted along measured (1994) and Perch-Nielsen (1985). Repeated pre- transects at a magnification of 3000–5000 paration and counting of the same sample (30 depending on particle density on the filter. times) revealed a standard deviation of 710.5% Identification generally followed the taxonomy (Bollmann et al., 1999a, b). proposed by Jordan and Kleijne (1994). Taxo- nomic counts were converted into daily fluxes of 4.3. Planktic foraminifera coccoliths m 2 using the following equation: Coccolith flux ð#coccoliths m 2d 1Þ 4.3.1. Water column ¼ðFCSÞ=ðADOÞ; The opening–closing net (MCN) samples col- lected were preserved on board with a saturated 2 where F is the filter area (mm ), C the number of solution of HgCl2, stained with Bengal Rose coccoliths counted, S the split factor, A the methanol solution in order to distinguish living investigated filter area (mm 2), D the sampling (stained plasma) from dead (unstained, empty interval, and O the area of the trap aperture (m 2). shells) organisms and stored at 41C in glass bottles sealed with Parafin. In the laboratory, all planktic foraminifera were removed from the wet sample 4.2.3. Sediments using a pipette, followed by separating into plasma Dried and weighed sediment samples were wet- bearing and empty tests. Samples were next treated sieved over 63- and 38-mm meshed sieves, respec- with a sodium tetraborate buffered hyperchloride tively, collecting the 38-mm fraction as a o solution for a period of 24 h to remove tissues. suspension that was subsequently poured over a Tests were rinsed in tap water, dried and measured Millipore filtering system. All size fractions ( 38, o with an ocular micrometer under a binocular 38–63, >63 mm) were dried in an oven at 501C for microscope. All individuals larger than 125 mm 20–25 h and weighed after cooling. From the bulk were identified to species level and counted. The dry sediment weight and the weight of the two taxonomy follows Be! (1977) and Hemleben et al. larger fractions, the wt% of the 38 mm (fine o (1989). Raw specimen counts were converted to fraction) was calculated. All sediment weighing specimens per 1000 m3 by dividing the total procedures were done with a Mettler H10T number of tests per sample by the filtered water balance with a precision of 70.1 mg. volume. For absolute nannofossil abundance analysis, a subsample of the o38 mm fraction was weighed and mixed with a known amount of polystyrene 4.3.2. Sediment traps microbeads (as a tracer), put in suspension with Planktic foraminifera were counted and identi- denaturated alcohol and sprayed on a coverglass fied in the o1 mm size-fraction of the collected (SMS Method, Bollmann et al., 1999a, b). After material as described for the MCN samples but drying, the coverglass was mounted on an without using Bengal Rose. 3606 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629
4.3.3. Sediments productivity gradient at all periods but the Sediment samples for planktic foraminifera summer, when higher cell densities are found at analyses were freeze-dried, weighed, and washed the ESTOC site (Fig. 3A). through a 63-mm mesh-size sieve. After splitting In the traps, except for the ESTOC upper trap into smaller subfractions, the >125 mm fraction (500 m), where no diatoms were found, the highest was split into aliquots of at least 300–500 planktic diatom fluxes co-occur with flux maxima of total foraminifera. Quantification and species identifica- particles for all traps (Neuer et al., 1999). At the tion was done using a binocular microscope. EBC site, diatoms show a bimodal distribution occurring in mid-winter (106 valves m 2 d 1) and again in late spring/early summer (105 2 1 5. Results valves m d ). At ESTOC and LP, the medium traps (E750 and 900 m) show the mid-winter 5.1. Living phytoplankton and diatoms maximum even though fluxes are one order of magnitude lower than registered in the EBC trap. E The composition and distribution of the living As for the deeper traps ( 3000 and 3700 m), both phytoplankton community along the 291N trans- at ESTOC and LP diatoms show a bimodal ect reveal a numerical dominance of coccolitho- occurrence, in mid-winter and again in late phores at all seasons, with diatoms varying spring/early summer (Fig. 3B). between a minimum of 2% of the total phyto- Daily mean fluxes found at the medium traps (700, 750, and 900 m) of all sites reveal values one plankton in January 1997 and a maximum of 28% 5 in April 1998 (Fig. 2). Diatom abundances in the order of magnitude higher at EBC (10 valves m 2 d 1) than at ESTOC and LP (104 plankton and the sediment trap were compared for 2 1 the four seasons (Fig. 3). Higher diatom standing valves m d ). However, the deeper traps at both stocks are observed in spring and fall at the EBC. offshore sites (ESTOC and LP) show, respectively, Abundance decreases towards offshore, along the 2 and 5 times increased fluxes relative to the medium-depth traps (Table 3, Fig. 4). When AR the uppermost sediment are deter- Mean Phytoplankton Community mined, values are on the order of 105 valves m 2 d 1, decreasing from EBC to ESTOC, Diatoms Coccolithophores Dinoflagellates along the expected decrease in productivity. A new 7000 increase occurs towards LP where diatom AR is of (54)
6000 the same order as at EBC (Fig. 4). (93)
(44) In terms of assemblages, a total of 130 taxa (37 5000 at the genera level and 93 species) have been 4000 identified, 57 in the plankton samples, 84 in the
(67) traps, and 53 in the sediments (Table 4); 37 taxa
Cells/l 3000 (80) were only present in the water column, 29 taxa 2000 were only identified in the traps, and 5 could only (28) (64) 1000 be found in the sediments. Of all the identified (20) (10) (10) (16) (5)
(4) taxa, only 12 were found in all three data sets, nine (2) (2) 0 at the genus level, and three at the species level. The fact that common taxa are found mostly at the Sep.97 Jan. 97 July 98 Febr. 99 Febr.
April 98 genus level arises from difficulties associated with o Cape Ghir Filament 29 N Transect water-column sample preparation (which did not include cleaning of the organic matter), lack of Fig. 2. Phytoplankton community along the 291N transect during the sampling periods (depth-integrated 0–200 m). routine SEM observations (which in many cases Numbers in parenthesis represent percent abundance. February led to the non-identification of many species of 99 data correspond to the Cape Ghir Filamento 99 cruise. genera such as Pseudo-nitschia, Nitzschia, and F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3607
DIATOMS (A) Seasonal Plankton Sampling
5 2 5 2 Diatoms (cellx10 /m ) Chaetoceros spp. (cellx10 /m )
168 196 268 Winter 20 0 20
Spring 0 0 196 260 3614 1070
34 674 186 Summer 0 108 0
106 260 1206 Fall 0 50 76
LP ESTOC EBC LP ESTOC EBC
(B) Time series (Sediment trap)
LP ESTOC EBC
4.5 1.4 1.4 900 m 750 m 4.0 700 m 1.2 1.2 3.5 ) 1 _ 1.0 1.0 3.0 day 2 _
m 2.5 6 0.8 0.8 2.0 0.6 0.6 Diatom Flux 1.5
(valves 10 (valves 0.4 0.4 1.0
0.2 0.2 0.5
0.0 0.0 0.0 JFMAMJJAS O JFMAMJJAS JFMAMJJAS
Winter Spring Summer Fall 1.4 3700 m 1.4 3000 m 1.2 1.2 ) 1 _ 1.0 1.0 day 2 _
m 0.8 0.8 6 Diatom Flux 0.6 0.6 Chaetoceros spores Flux Diatom Flux 0.4
(valves 10 (valves 0.4
0.2 0.2
0.0 0.0 JFMAMJJAS O JFMAMJJAS
Winter Spring Summer Fall Winter Spring Summer Fall Fig. 3. Total diatom and Chaetoceros abundances along the 291N. (A) Standing stock in Plankton and (B) flux in the sediment traps. Note different scale for the EBC 700 m trap. 3608
Table 3 Standing stock, trap measured flux, sediment accumulation rate, and preservation efficiency estimated for diatoms, coccolithophores and planktic foraminifera, as well as indicator species of each group
Marine diatoms Coccolithophores (cells and coccoliths) Planktic foraminifera
Standing Trap and Upper Preservation Standing stock Trap and Upper Preservation Standing Trap and Upper Preservation stock diatoms sediment flux preservation efficiency coccolithophores sediment flux preservation efficiency (PE) stock (# sediment preservation efficiency (PE) (# valves m 2 ) (# valves m 2 d 1 ) Efficiency (PE) (# cells m 2 ) (# coccoliths m 2 d 1 ) efficiency shells m 2 ) flux (# shells efficiency (UPE) (UPE) m 2 d 1 ) (UPE) .Arne ta./De-e eerhI 9(02 3599–3629 (2002) 49 II Research Deep-Sea / al. et Abrantes F. EBC Water column 2.74E+08 1.19E+10 78452 Trap (700) 2.75E+05 1.38E+09 277 Sediment 3.75E+05 1.37 1.37 9.02E+08 0.66 0.66 428 1.55 1.55 (uppermost) Sediment (Holocene) 1.63E+04 0.06 0.06 1.39E+09 1.01 1.01 457 1.65 1.65
ESTOC Water Column 6.95E+07 8.04E+09 51191 Trap (500 m) 0.00E+00 5.73E+08 166 Trap (750 m) 2.37E+04 — — Trap (3000 m) 4.06E+04 1.03E+09 — Sediment 8.01E+04 3.38 1.97 1.05E+09 1.84 1.02 253 1.53 — (uppermost) Sediment (Holocene) 1.13E+04 0.48 0.28 1.13E+09 1.98 1.10 315 1.90 —
LaPalma Water Column 4.11E+07 7.42E+09 19850 Trap (900 m) 5.31E+04 6.75E+08 121 Trap (3700 m) 2.54E+05 1.86E+09 — Sediment 2.44E+05 4.59 0.96 7.68E+08 1.14 0.41 147 1.21 — (uppermost) Sediment (Holocene) 5.99E+04 1.13 0.24 9.41E+08 1.39 0.51 302 2.50 —
Chaetoceros spp. G. ericsonii G. bulloides EBC Water Column 5.83E+07 4.41E+09 6384 Trap (700) 9.39E+04 1.97E+08 69 Sediment 5.65E+04 0.60 0.60 5.72E+07 0.29 0.29 160 2.32 2.32 (uppermost) Sediment (Holocene) — 6.50E+07 0.33 0.33 246 3.57 3.57
ESTOC Water Column 7.90E+06 2.30E+09 323 Trap (500 m) — 8.25E+07 2 Trap (750 m) 2.24E+03 — — Trap (3000 m) 1.90E+03 1.01E+08 — Sediment 1.74E+04 7.77 9.15 2.40E+07 0.29 0.24 22 11.00 — (uppermost) Sediment (Holocene) — 6.08E+07 0.74 0.60 14 7.00 — LaPalma Water Column 1.00E+06 8.53E+08 62 Trap (900 m) 1.16E+04 9.60E+07 0 Trap (3700 m) 4.88E+04 1.33E+08 — Sediment 8.50E+04 7.35 1.74 2.96E+07 0.31 0.22 10 ind. — (uppermost) Sediment (Holocene) — 2.19E+07 0.23 0.16 17 ind. —
Thalassionema nitzschioides E. huxleyi G. ruber (white) EBC Water Column 2.06E+07 2.44E+09 3667 Trap (700) 2.41E+04 5.61E+08 39 Sediment 8.39E+04 3.49 3.49 3.56E+08 0.64 0.64 39 1.00 1.00 (uppermost) Sediment (Holocene) — 5.75E+08 1.03 1.03 57 1.46 1.46 .Arne ta./De-e eerhI 9(02 3599–3629 (2002) 49 II Research Deep-Sea / al. et Abrantes F.
ESTOC Water Column 3.13E+06 1.51E+09 3239 Trap (500 m) — 2.10E+08 14 Trap (750 m) 1.84E+03 — — Trap (3000 m) 1.54E+03 3.23E+08 — Sediment 5.98E+03 3.25 3.88 2.81E+08 1.34 0.87 58 4.06 — (uppermost) Sediment (Holocene) — 3.60E+08 1.71 1.11 64 4.48 —
LaPalma Water Column 0.00E+00 1.69E+09 1331 Trap (900 m) 6.93E+03 3.36E+08 5 Trap (3700 m) 1.28E+04 6.77E+08 — Sediment 2.11E+04 3.04 1.65 2.75E+08 0.82 0.41 34 6.21 — (uppermost) Sediment (Holocene) — 4.10E+08 1.22 0.61 60 10.96 —
Nitzschia spp. F. profunda EBC Water Column 3.10E+06 6.83E+08 Trap (700) 4.38E+04 2.60E+08 Sediment 3.58E+04 0.82 0.82 1.50E+08 0.58 0.58 (uppermost) Sediment (Holocene) — 2.26E+08 0.87 0.87
ESTOC Water Column 8.25E+05 1.24E+09 Trap (500 m) — 1.05E+08 Trap (750 m) 4.47E+03 — Trap (3000 m) 5.80E+03 2.38E+08 Sediment 1.81E+04 4.06 3.13 2.57E+08 2.44 1.08 (uppermost) Sediment (Holocene) — 2.25E+08 2.13 0.95
LaPalma Water Column 2.00E+05 1.03E+09 Trap (900 m) 7.41E+03 9.63E+07 Trap (3700 m) 4.34E+04 4.38E+08 Sediment 2.19E+04 2.95 0.50 1.72E+08 1.78 0.39 (uppermost) 3609 Sediment (Holocene) — 2.13E+08 2.21 0.49 3610 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629
Fig. 4. Diatoms, coccolithophores, and planktic foraminifera mean annual standing stocks, integrated over sampled depth; mean daily fluxes at the traps for each deployment (EBC, ESTOC, LP); AR estimated for the uppermost sediment, and the average AR of all Holocene samples. F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3611
Table 4 List of diatom taxa found in the plankton, traps, and sediments (EBC—Eastern Boundary Current, ESTOC station, LP—LaPalma trap mooring)
Plankton Traps Sediments
Actinocyclus normanii (Gregory) Hustedt EBC, ESTOC, LP Actinocyclus octonarius Ehrenberg EBC, ESTOC, LP ESTOC, LP Actinocyclus spp. EBC, ESTOC, LP EBC, ESTOC, LP Actinoptychus senarius (Ehrenberg) Ehrenberg EBC EBC, ESTOC Actinoptychus spp. EBC, ESTOC, LP EBC Alveus marinus (Grunow) Kaczmarska et G. Fryxell EBC, ESTOC, LP EBC, ESTOC, LP Amphiprora spp. LP Amphora spp. EBC, ESTOC LP Asteromphalus spp. EBC, ESTOC, LP EBC, ESTOC, LP Azpeitia africana (Janisch ex Schmidt) Fryxell et EBC, ESTOC, LP LP Watkins Azpeitia neocrenulata (Grunow) Fryxell et Watkins EBC, ESTOC, LP ESTOC Azpeitia nodulifera (Schmidt) Fryxell et Simonsen EBC, ESTOC, LP ESTOC, LP Azpeitia spp. EBC, ESTOC, LP EBC, ESTOC, LP Aulacoseira granulata (Ehrenberg) Twaites EBC, ESTOC, LP EBC, ESTOC, LP Aulacoseira spp. EBC, ESTOC, LP ESTOC, LP Bacteriastrum delicatulum Cleve ESTOC Bacteriastrum hyalinum Lauder EBC, ESTOC Bacteriastrum spp. ESTOC, LP EBC, ESTOC Biddulphia spp. EBC Cerataulina pelagica (Cleve) Hendey EBC, ESTOC Chaetoceros affinis Lauder ESTOC Chaetoceros atlanticus Cleve EBC Chaetoceros concavicornis Mangini ESTOC, LP Chaetoceros curvisetus Cleve ESTOC Chaetoceros danicus Cleve ESTOC Chaetoceros pendulus Cleve ESTOC Chaetoceros radicans Schutt. EBC, ESTOC, LP LP LP Chaetoceros spp. (veg. cells) EBC, ESTOC, LP LP LP Chaetoceros spp. (spores) EBC, ESTOC, LP EBC, ESTOC, LP Cocconeis scutellum Ehrenberg ESTOC Cocconeis surirella LP Cocconeis spp. EBC, ESTOC, LP EBC, ESTOC, LP Corethron criophilum Castracane EBC, ESTOC Coscinodiscus radiatus Schmidt EBC, LP EBC, LP Coscinodiscus spp. EBC, ESTOC, LP LP LP Cyclotella meneghiniana Kutzing. LP Cyclotella ocellata Pantocsek ESTOC, LP EBC, ESTOC Cyclotella striata (Kutzing). Grunow LP Cyclotella (triangular type) Servant-Vildary ESTOC Cyclotella spp. EBC, LP LP Cylindrotheca closterium (Ehrenberg ) Reiman et EBC, ESTOC, LP Lewin Delphineis surirella (Ehrenberg) Grunow ex Van EBC Heurck Detonula pumila (Castracane) Gran EBC, ESTOC Dactyliosolen fragilissimus (Bergon) Hasle EBC, ESTOC Dimmerogramma spp. LP
Diploneis sp1 EBC, ESTOC, LP EBC, ESTOC, LP Diploneis spp. EBC, LP EBC, ESTOC, LP EBC, ESTOC, LP Epithemia spp. LP Eucampia zoodiacus Ehrenberg EBC 3612 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629
Table 4 (continued)
Plankton Traps Sediments
Eucampia spp. ESTOC Eunotia spp. LP Fragilaria construens (Ehrenberg) Grunow LP EBC, LP Fragilaria lapponica Grunow LP Fragilaria spp. EBC EBC, ESTOC, LP EBC, LP Fragilariopsis doliolus (Wallich) Medlin et Sims LP Fragilariopsis kerguelensis (O’Meara) Hustedt LP Fragilariopsis spp. ESTOC Grammatophora undulata Ehrenberg LP Grammatophora spp. EBC, ESTOC, LP EBC, ESTOC Guinardia cylindrus (Cleve) Hasle ESTOC Guinardia delicatula (Cleve) Hasle EBC Guinardia flaccida (Castracane) Peragallo ESTOC Guinardia striata (Stolterfoth) Hasle EBC, ESTOC Hantzschia amphioxys (Ehrenberg) Grunow LP ESTOC Hemiaulus hauckii Grunow in Van Heurck EBC, ESTOC, LP Hemiaulus membranaceus Cleve ESTOC Hemiaulus sinensis Greville EBC, LP Hemidiscus cuneiformis Wallich ESTOC ESTOC Hemidiscus spp. ESTOC EBC, ESTOC, LP Lauderia annulata Cleve ESTOC, LP Leptocylindrus danicus Cleve EBC, ESTOC, LP Leptocylindrus mediterraneus (Peragallo) Hasle EBC, ESTOC Leptocylindrus minimus Gran ESTOC, LP Lioloma pacificum (Cupp) Hasle EBC, LP Mastogloia rostrata (Wallich) Husted comb. nov EBC, ESTOC, LP Meuniera membranacea (Cleve) P. C. Silva ESTOC Navicula palpebralis Breb.! LP Navicula spp. EBC, ESTOC, LP EBC, ESTOC, LP EBC, LP Nitzschia bicapitata Cleve EBC, ESTOC, LP ESTOC, LP ESTOC Nitzschia bifurcata Kaczmarska et Licea LP Nitzschia inflatula var. capitata Simonsen EBC, ESTOC, LP ESTOC Nitzschia interruptestriata Simonsen EBC, ESTOC, LP EBC, ESTOC, LP Nitzschia longissima (de Brebisson! in Kutzing). Ralfs in EBC, ESTOC Pritchard Nitzschia sicula (Castracane) Hustedt EBC, ESTOC, LP Nitzschia sicula (Castracane) Hustedt var. sicula LP Nitzschia spp. EBC, ESTOC, LP EBC, ESTOC, LP EBC, ESTOC, LP Odontella cf. mobiliensis EBC Paralia sulcata (Ehrenberg) Cleve EBC, ESTOC, LP EBC, ESTOC, LP Planktoniella sol EBC, ESTOC Pleurosigma spp. LP EBC, ESTOC, LP Podosira stelliger (Bailey) Mann ESTOC EBC Probosciaa alata (Brightwell) Sundstrom. EBC, ESTOC, LP EBC, ESTOC Psammodictyon cf. panduriformis Gregory EBC Psammodictyon panduriformis Gregory LP Psammodictyon panduriformis var. minor Grunow EBC, ESTOC Psammodiscus nitidus (Gregory) Round & Mann ESTOC ESTOC, LP Pseudo-nitzschia subpacifica (Hasle) Hasle LP Pseudo-nitzschia spp. EBC, ESTOC, LP Raphoneis spp. EBC, ESTOC, LP EBC, LP Rhizosolenia bergonii Peragallo EBC, ESTOC EBC, ESTOC, LP EBC, ESTOC, LP Rhizosolenia hebetata (Bailey) Gran EBC, ESTOC LP Rhizosolenia hebetata f. semispina (Hensen) ESTOC F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3613
Table 4 (continued)
Plankton Traps Sediments
Rhizosolenia setigera Brightwell ESTOC Rhizosolenia imbricata Brightwell EBC Rhizosolenia styliformis Brightwell EBC, ESTOC, LP Rhizosolenia spp. EBC, ESTOC, LP EBC, ESTOC, LP EBC, ESTOC, LP Rhopalodia spp. LP Roperia tesselata (Roper) Grunow ex Pelletan EBC, ESTOC, LP EBC, ESTOC, LP Skeletonema costatum (Greville) Cleve EBC, ESTOC Spatangidium arachne (Brebisson)! Ralfs in Pritchard EBC, ESTOC, LP Stephanodiscus astrea (Ehrenberg) Grunow LP Stephanodiscus astrea var. minutula (Kutzing). Grunow ESTOC Stephanodiscus spp. EBC, ESTOC, LP EBC, ESTOC, LP Surirella fastuosa Ehrenberg ESTOC Surirella spp. EBC Synedra spp. EBC Thalassionema bacillare (Heiden) Kolbe LP Thalassionema nitzschioides (Grunow) Grunow ex EBC, ESTOC EBC, ESTOC, LP EBC, ESTOC, LP Hustedt Thalassionema nitzschioides Grunow var. parva Heiden EBC, ESTOC, LP EBC, ESTOC, LP et Kolbe Thalassiosira eccentrica (Ehrenberg) Cleve EBC, ESTOC, LP EBC, ESTOC, LP Thalassiosira gracilis (Karsten) Hustedt var. gracilis LP Thalassiosira intranula Herzing & Fryxell LP Thalassiosira lineata Jouse! EBC, ESTOC, LP EBC, ESTOC Thalassiosira oestrupii (Ostenfeld) Hasle LP ESTOC, LP Thalassiosira sackettii f. sackettii G. Fryxell LP ESTOC Thalassiosira symmetrica Fryxell & Hasle LP Thalassiosira spp. EBC, ESTOC, LP EBC, ESTOC, LP EBC, ESTOC, LP Thalassiotrix spp. EBC, ESTOC, LP EBC, ESTOC, LP EBC, ESTOC, LP Trachyneis spp. EBC, LP Triceratium spp. EBC, ESTOC
Thalassiosira), and the need to pool Chaetoceros 5.2. Coccolithophores resting spores into one category. The plankton assemblage is dominated by The plankton coccolithophore cell densities Pseudo-nitzschia spp. in winter, while Chaetoceros found at the mooring stations show that maximum spp. and Leptocylindrus danicus dominate the cell densities occur at the EBC site in winter and spring and summer assemblages. In the traps the summer, with a strong gradient between the near- mid-winter diatom maximum found at all sites is shore (EBC) and the open-ocean sites (LP) dominated by resting spores of the genus Chaeto- (Fig. 5A). In spring (April), the cell density ceros, but an increased contribution of oceanic gradient reverses, with low cell densities at the species of the genus Nitzschia is noticeable at both near-shore location. the medium and deeper traps at the ESTOC site At the medium traps maximum coccolith flux (Nave et al., 1998a). In the sediments, spores of was reached simultaneously at all three sites in Chaetoceros dominate the diatom assemblage mid-winter (Fig. 5B), with comparable total coc- closer to the coast and mainly off Cape Ghir. colith fluxes at the oceanic sites LP and ESTOC, Seaward there is an increase in the abundance of but significantly increased fluxes at EBC. A second oceanic species of the genus Nitzschia (Nave et al., maximum in flux values is observed in the EBC 1998b; Nave et al., 2001; Meggers et al., 2002). trap in late spring/early summer. 3614 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629
COCCOLITHOPHORES
(A) Seasonal Plankton Sampling Coccolithophores (cellx109/m2) Gephyrocapsa ericsonii (cellx109/m2)
Winter 6 4 15 3 2 8
8 9 3 Spring 1 3 1
Summer 4 7 15 1 2 4
1 21 Fall 1 0.1 0
LP ESTOC EBC LP ESTOC EBC
(B) Time series (Sediment trap)
LP ESTOC EBC
90 80 80 80 ) 70
-1 70 70 900 m 60 750 m 700 m
day 60 2
- 60
m 50 50 8 50 40 40 40 30 30 30
Coccolith Flux 20 20 20 10
(coccoliths 10 10 10 0 0 0 JFMAMJJAS JFMAMJJAS O JFMAMJJAS
80 80 Winter Spring Summer Fall 70 3700 m 70 3000 m 60 60 )
-1 50 50
day 40 2 40 - Coccolithophores Flux m 8 30 30 20 20 G. ericsonii Flux 10 10 Coccolith Flux 0 0 JFMAMJJAS O (coccoliths 10 JFMAMJJAS
Winter Spring Summer Fall Winter Spring Summer Fall Fig. 5. (A) Seasonal variation of total coccolithophore and G. ericsonii standing stocks in the plankton (depth-integrated 0–200 m) and (B) coccolith fluxes in sediment traps (January–September 1997) at different water depths.
The mean daily coccolith fluxes measured in the ments, coccolith AR are quite similar at all sites upper traps are very similar at ESTOC and LP but decrease slightly from EBC and ESTOC to LP (E0.57–0.67 109 coccoliths m 2 d 1) but twice as (0.9—1–0.7 109 coccoliths m 2 d 1). high at EBC (1.38 109 coccoliths m 2 d 1) (Table In terms of assemblages, 109 taxa were identi- 3, Fig. 4). As found for diatoms, fluxes increase 2– fied, 51 of which only could be found in the water 3 times towards the deeper traps at the open-ocean column (Table 5). Of the 58 taxa reaching the traps sites (ESTOC and LP). In the uppermost sedi- (53%), only 20 taxa (18%) are preserved in the F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3615
Table 5 List of coccolithophores taxa found in the plankton, traps, and sediments (EBC—Eastern Boundary Current, ESTOC station, LP— LaPalma trap mooring)
Plankton Traps Sediments
Acanthoica acanthifera Lohmann, 1912 ex Lohman, 1913 LP, EBC Acanthoica quattrospina Lohmann, 1903 LP, ESTOC, EBC LP, ESTOC, EBC Acanthoica sp. LP, ESTOC, EBC LP, ESTOC, EBC Algirosphaera oryza Schlauder, 1945 LP, ESTOC, EBC LP, ESTOC, EBC Algirosphaera robusta (Lohmann, 1902) Norris, 1984 LP, ESTOC, EBC LP, ESTOC, EBC Algirosphaera sp. LP, ESTOC, EBC Alisphaera spatula Steinmetz, 1991 LP, ESTOC, EBC Alisphaera unicornis Okada and McIntyre, 1977 LP, ESTOC, EBC LP, ESTOC, EBC Alveosphaera bimurata (Okada and McIntyre, 1977) Jordan LP, ESTOC, EBC and Young, 1990 Anacanthoica acanthos (Schiller, 1925) Deflandre, 1952 EBC Anacanthoica cidaris (Schlauder, 1945) Kleijne, 1992 LP Anacantoica sp. LP, ESTOC, EBC Anoplosolenia brasiliensis (Lohmann 1919) Deflandre, 1952 LP, ESTOC, EBC LP, ESTOC, EBC Braarudosphaera bigelowi (Gran and Braarud, 1935) Deflandre, ESTOC, EBC 1947 Calcidiscus leptoporus (Murray et Blackman, 1898) Loeblich et LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Tappan, 1978 Calciopappus rigidus Heimdal in Heimdal and Gaarder, 1981 EBC Calciopappus sp. LP, ESTOC, EBC Calciosolenia murrayi Gran, 1912 LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Canistrolithus valliformis Jordan and Chamberlain, 1993 ESTOC, EBC Ceratolithus cristatus Kamptner, 1950 var. cristatus LP, ESTOC, EBC Ceratolithus cristatus Kamptner, 1950 var. telesmus (Norris, LP, ESTOC, EBC 1965), Jordan and Young, 19909 Coccolithus pelagicus (Wallich, 1877) Schiller, 1930 f. pelagicus LP, ESTOC, EBC LP, ESTOC, EBC Coronosphaera binodata (Kamptner, 1927) Gaarder, in EBC LP, ESTOC, EBC Gaarder and Heimdal, 1977 Coronosphaera mediterranea (Lohmann, 1902) Gaarder, in LP, ESTOC, EBC LP, ESTOC, EBC Gaarder and Heimdal, 1977 Cyrtosphaera aculeata (Kamptner, 1941) Kleijne, 1992 EBC LP, ESTOC, EBC Discosphaera tubifera (Murray and Blackman, 1898) Ostenfeld, LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC 1900 Emiliania huxley (Lohman, 1902) Hay and Mohler, in Hay LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC et al., 1967 Florisphaera profunda Okada and Honjo, 1973 LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Gaarderia corolla (Lecal, 1966) Kleijne 1993 LP, ESTOC, EBC LP, ESTOC, EBC Gephyrocapsa protohuxleyi McIntyre 1970 LP, ESTOC, EBC Gephyrocapsa ericsonii McIntyre and Be, 1967 LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Gephyrocapsa muellerae Breheret, 1978 LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Gephyrocapsa oceanica Kamptner, 1943 LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Gephyrocapsa omata Heimdal, 1973 LP, ESTOC, EBC LP, ESTOC, EBC Gladiolithus flabellatus (Halldal and Markali, 1955) Jordan and LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Chamberlain, 1993 Hayaster perplexus (Bramlette et Riedel, 1954) Bukry, 1973 LP, EBC LP, ESTOC, EBC Helicosphaera carteri (Wallich, 1877) Kamptner, 1954 LP, EBC LP, ESTOC, EBC LP, ESTOC, EBC Helicosphaera pavimentum Okada and McIntyre, 1977 LP, ESTOC, EBC Helicosphaera wallichi Wallich, 1877 LP, EBC Michaelsarsia adriaticus (Schiller, 1914) Manton etal., 1984 LP, ESTOC, EBC Michaelsarsia elegans Gran, 1912, emend. Manton et al., 1984 LP, ESTOC, EBC LP, ESTOC, EBC Neosphaera coccolithomorpha Lecal-Schlauder, 1950 LP, ESTOC, EBC LP, ESTOC, EBC Oolithotus fragilis (Lohmann, 1912) Martini et Muller, 1972 LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC 3616 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629
Table 5 (continued)
Plankton Traps Sediments var. fragilis Oolithotus fragilis var. cavum (Okada & McIntyre 1977) Jordan LP, ESTOC, EBC & Young 1990 Ophiaster hydroideus (Lohmann, 1903) Lohmann, 1913, LP, ESTOC, EBC LP, ESTOC, EBC emend. Manton and Oates, 1983 Ophiaster reductus Manton and Oates, 1983 ESTOC, EBC Ophiaster sp. LP, ESTOC, EBC Palusphaera vandelii Lecal, 1965 emend. Norris, 1984 LP, ESTOC, EBC Papposphaera lepida Tangen, 1972 ESTOC, EBC LP, ESTOC, EBC Papposphaera sagittifera Manaton, Sutherland &mcCully 1976 ESTOC Papposphaera sp. LP, ESTOC, EBC Polycrater galapagensis Manton and Oates, 1980 LP, ESTOC, EBC Pontosphaera multipora (Kamptner, 1948) Roth, 1970 LP, ESTOC Pontosphaera spp. LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Reticulofenestra parvula (Okada and McIntyre, 1977 Biekart, LP, ESTOC, EBC ESTOC 1989 var. parvula Reticulofenestra punctata (Okada & McIntyre 1977) Jordan & LP, ESTOC, EBC Young 1990 Reticulofenestra sessilis (Lohmann, 1912) Jordan and Young, LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC 1990 Rhabdosphaera clavigera Murray and Blackmann, 1898 var. LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC clavigera Rhabdosphaera clavigera var. stylifera (Lohmann, 1902) Kleijne LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC and Jordan, 1990 Rhabdosphaera xiphos (Deflandre and Fert, 1954) Norris, 1984 LP, ESTOC, EBC LP, ESTOC, EBC Scyphosphaera apsteinii Lohmann, 1902 LP, ESTOC, EBC LP, ESTOC Syracosphaera anthos (Lohmann, 1912) Janin, 1987 LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera borealis Okada and McIntyre, 1977 LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera corrugis Okada and McIntyre, 1977 LP, ESTOC, EBC Syracosphaera epigrosa Okada and McIntyre, 1977 LP, ESTOC, EBC ESTOC Syracosphaera exigua Okada and McIntyre, 1977 LP, ESTOC, EBC Syracosphaera halldalii Gaarder, in Gaardeer and Hasle, 1971 EBC LP, ESTOC, EBC ex Jordan and Green, 1994 Syracosphaera histrica Kamptner, 1941 LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera lamina Lecal-Schlauder, 1951 EBC LP, ESTOC, EBC Syracosphaera marginoporata ESTOC, EBC LP Syracosphaera molischii Schiller, 1925 LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera nana (Kamptner, 1941) Okada and McIntyre, LP, ESTOC, EBC 1977 Syracosphaera nodosa Kamptner, 1941 LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera noroitica Knappertsbusch, 1993 ESTOC Syracosphaera orbiculus Okada and McIntyre, 1977 LP, ESTOC, EBC Syracosphaera ossa (Lecal, 1966) Loeblich and Tappan, 1968 LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera pirus Halldal and Markali, 1955 LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera prolongata Gran, 1912, ex Lohmann, 1913 LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera pulchra Lohmann, 1902 LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera rotula Okada and McIntyre, 1977 LP, ESTOC, EBC LP, ESTOC, EBC Syracosphaera type ‘‘I’’ LP Syracosphaera type ‘‘J’’ LP Syracosphaera type ‘‘K’’ LP, ESTOC, EBC Syracosphaera spp. (small) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Tetralithoides quadrilaminata (Okada and McIntyre, 1977) LP, ESTOC, EBC Jordan et al., 1993 Umbellosphaera irregularis Paasche, in Markali and Paasche, LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3617
Table 5 (continued)
Plankton Traps Sediments
1955 Umbellosphaera tenuis (Kamptner, 1937) Paasche, in Markali LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC and Paasche, 1955 Umbilicosphaera hulburtiana Gaarder, 1970 LP, ESTOC, EBC LP, ESTOC, EBC Umbilicosphaera sibogae var. foliosa (Kamptner, 1963) Okada LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC and McIntyre, 1977 Umbilicosphaera sibogae (Weber-van Bosse, 1901) Gaarder, LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC 1970 var. sibogae Umbilicosphaera scituloma Steinmetz 1991 LP, ESTOC, EBC Vexillarius cancellifer Jordan & Chamberlain 1993 LP, ESTOC Heterococcolithophores spp. LP, ESTOC, EBC Anthosphaera sp. LP, ESTOC, EBC Calyptrolithophora papillifera (Halldal 1953) Heimdal, in LP, ESTOC, EBC Heimdal and Gaarder, 1980 Calyptrosphaera oblonga Lohmann, 1902 LP, ESTOC, EBC Calyptrosphaera sp. EBC C. lepoporus f. rigidus ESTOC Corisphaera gracilis LP, ESTOC, EBC Flosculosphaera sp. ESTOC Helladosphaera cornifera (Schiller 1913) Kamptner, 1937 LP, ESTOC, EBC Homozygosphaera sp. LP, ESTOC, EBC Periphyllophora mirabilis (Schiller 1913) Kamptner, 1937 ESTOC, EBC Poricalyptra sp. LP, ESTOC, EBC Syracolithus dalmaticus (Kamptner 1927) Loeblich and ESTOC Tappan, 1966 Syracolithus quadriperforatus (Kamptner, 1937) Gaarder, 1962 LP, ESTOC, EBC Syracolithus sp. LP, ESTOC, EBC Zygosphaera sp LP, ESTOC, EBC Holococcolithophores spp. LP, ESTOC, EBC LP, ESTOC, EBC
sediments. On the other hand, only three taxa, et al., 2002). At EBC E. huxleyi and F. profunda Coccolithus pelagicus f. pelagicus, Helicosphaera shift in abundance, with E. huxleyi dominating pavimentum, and Tetralithoides quadrilaminata during times of maximum coccolithophore flux were not found in the plankton. while F. profunda peaks during periods of stronger Four coccolithophore species dominate most upwelling (Sprengel et al., 2002). plankton assemblages: Gephyrocapsa ericsonii, the In the sediments, the dominant contributors are most abundant species living in the upper photic the same three species observed for the trap zone (0–100 m), followed by Emiliania huxleyi and samples, which maintain also their relative abun- Umbellosphaera tenuis. Florisphaera profunda is the dances, but higher relative abundance of dissolu- most abundant species in the deeper sampled levels tion-resistant coccolithophores taxa such as (Bollman et al., 1999a, b). Calcidiscus leptoporus, Gephyrocapsa mullerae,and In the trap samples from the three mooring sites, Gephyrocapsa oceanica is noticed in the sediments taxonomic composition was quite similar with of the offshore sites (Sprengel et al., 2002). most species exhibiting comparable seasonal pat- terns. The dominant species at all sites are 5.3. Planktic foraminifera Emiliana huxleyi and F. profunda (relative abun- dance ranging from 60 to >80%) with G. ericsonii A comparison of the planktic foraminifera being the third most abundant species (Sprengel analyzed for the four seasons in multi-net samples 3618 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629
FORAMINIFERA (A) Seasonal Plankton Sampling
Forams (cellx102/m2) Globigerina bulloides (cell/m2)
Winter 663 1892 2658 53 847 1439
42 40 9 Spring 40 40 87
36 54 150 Summer 114 390 5104
53 61 321 Fall 42 16 18906
LP ESTOC EBC LP ESTOC EBC
(B) Time series (Sediment trap)
LP ESTOC EBC
1200
1000 500 m ) -1
day 800 2 - 600
400 (forams m 200 Planktic Foraminifera Flux Planktic Foraminifera
0 JFMAMJJAS 1200 1200 1000 900 m Winter Spring Summer Fall
) 1000 700 m -1
800 ) -1
day 800 2 -
600 day 2 - 600 400 400
(forams m 200 (forams m
Planktic Foraminifera Flux Planktic Foraminifera 200
0 Flux Planktic Foraminifera O JFMAMJJAS 0 JFMAMJJAS Winter Spring Summer Fall Winter Spring Summer Fall Planktic Foraminifera Flux G. bulloides Flux Fig. 6. Total planktic foraminifera and Globigerina bulloides (>125 mm) north of the Canary Islands (291N-transect). (A) Results from seasonal plankton sampling with a multi-net (down to 500 m water-depth) and (B) Planktic foraminifera flux in the 700 m water-depth sediment traps (900 m at LaPalma). and the EBC trap, the upper ESTOC trap and the a bimodal distribution, with maxima in winter and medium LP trap is presented in Fig. 6. This group in the upwelling summer/fall season, while at undergoes substantial changes throughout the oligotrophic sites (ESTOC and LP) the distribu- year. At EBC planktic foraminifera density shows tion is unimodal, with a single winter maximum. F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3619
Table 6 List of planktic foraminifera taxa found in the plankton, traps, and sediments (EBC—Eastern Boundary Current, ESTOC station, LP—LaPalma trap mooring)
Plankton Traps Sediments
Globigerina bulloides d’Orbigny LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globigerina falconensis Blow LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Turborotalita quinqueloba (Natland) LP, ESTOC, EBC ESTOC, EBC LP, ESTOC Turborotalia humilis (Brady) LP, ESTOC, EBC LP,ESTOC, EBC LP, ESTOC, EBC Globoturborotalita rubescens Hofker LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globigerinella calida (Parker) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globigerinella siphonifera (d’Orbigny) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globigerinella digitata (Brady) EBC ESTOC Hastigerina digitata (Rhumbler) EBC LP, EBC Hastigerina pelagica (d’Orbigny) LP, ESTOC, EBC LP, ESTOC Globigerinoides ruber ‘‘pink’’ (d’Orbigny) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globigerinoides ruber ‘‘white’’ (d’Orbigny) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globigerinoides sacculifer (Brady) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globigerinoides conglobatus (Brady) ESTOC, LP LP, ESTOC, EBC Globigerinoides tenellus (Parker) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Orbulina universa d’Orbigny LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Neogloboquadrina dutertrei (d’Orbigny) LP, ESTOC, EBC LP, EBC Neogloboquadrina pachyderma (Ehrenberg) LP, ESTOC, EBC EBC LP Neogloboquadrina incompta (Ehrenberg) Cifelli LP, ESTOC, EBC LP,ESTOC, EBC LP, ESTOC, EBC Neogloboquadrina p-d integrade LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Pulleniatina obliquiloculata (Parker & Jones) LP, ESTOC, EBC LP, ESTOC, EBC ESTOC, EBC Globigerinata glutinata (Egger) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globigerinita uvula (Ehrenberg) ESTOC ESTOC Globorotalia menardii d’Orbigny EBC ESTOC Globorotalia ungulata Bermudez EBC Globorotalia hirsuta (d’Orbigny) LP, ESTOC, EBC LP, ESTOC, EBC ESTOC, LP Globorotalia theyeri Fleisher EBC LP, EBC Globorotalia crassaformis (Galloway & Wissler) LP LP, ESTOC, EBC Globorotalia inflata (d’Orbigny) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globorotalia truncatulinoides (d’Orbigny) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globorotalia scitula (Brady) LP, ESTOC, EBC LP, ESTOC, EBC LP, ESTOC, EBC Globorotalia anfracta (Parker) ESTOC ESTOC
This pattern is clearly reflected in the traps except In terms of assemblages, out of the 32 taxa for the EBC, where the water column fall identified (Table 6), the only species not found in maximum is not observed and there is a late the sediments is Hastigerina pelagica, a species spring/early summer maximum instead, a discre- very prone to dissolution and which occurs in pancy that can easily be attributed to the short fall samples in low numbers. Taxa only present in the period covered by the trap sampling. sediments, although in very low abundance The planktic foraminifera daily mean flux in the (o2%) are three species of the genus Globorotalia, upper traps (the only ones analyzed) shows a G. ungulata, G. thyeri and G. crassaformis. pattern similar to that observed for the cocco- The upwelling maximum in late spring/early lithophores: similar fluxes (120–160 shells m 2 d 1) summer is associated with the highest abundances at ESTOC and LP, and about twice as high at of Globigerina bulloides (Fig. 6A). In the sediments EBC (277 shells m 2 d 1). This trend is maintained G. bulloides and G. ruber are the dominant taxa, by the planktic foraminifera AR in the sediments with distribution patterns almost mutually exclu- (Table 3, Fig. 4). sive, G. bulloides being dominant near the coast 3620 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 and off Cape Ghir while G. ruber dominates the In the EBC trap (700 m), and within the offshore region (Meggers et al., 2002). resolution of the trap data, both diatoms and coccolithophores shift simultaneously at mid- winter while planktic foraminifera highest fluxes 6. Discussion occur with one sample delay (14 days). A second maximum occurs in mid-spring for both cocco- 6.1. What proportion of the plankton production is lithophores and planktic foraminifera, and in late represented in the sediments? spring/early summer for diatoms (Fig. 7). G. bulloides is a planktic foraminifera with In order to use the micro-organisms preserved in preference for productive environments, and on sediments to interpret past oceanographic and association with the phytoplankton bloom succes- climatic conditions it is necessary to understand sion (Be! and Tolderlund, 1971; Thiede, 1983; the nature of the record. Such investigation is Hemleben et al., 1989), and is considered a good seriously obstructed by the different sampling indicator of upwelling conditions (Thunell and techniques and the disparity between the time Sautter, 1992). The highest fluxes of G. bulloides scales. However, an estimation of the proportion occur during the second maximum, contrary to the of the total production represented at any given diatom genus Chaetoceros whose major peak location and time is necessary. In this work, occurs in winter. Chaetoceros species possess long seasonal variability is assessed by comparison of setae, and are certainly not easily ingested nor the plankton standing stock of the considered easily handled by the spinose G. bulloides. As so, groups determined for each cruise (cell densities despite the omnivorous feeding habits of forami- integrated over the entire photic zone—Table 3, nifera (Hemleben et al., 1989), this discrepancy Fig. 6), as representative for each season, to the also can be a reflection of G. bulloides preference trap flux measured for the same months/season. for less spinose diatoms and possibly the cocco- Major changes in diatom abundances through lithophore G. ericsonii (Figs. 3, 5 and 6). time and space appear to be mainly induced by At ESTOC and LP high standing stocks of all seasonal changes in the hydrographic/productivity three groups (diatoms, coccolithophores, and conditions at the Canary Islands region. Although planktic foraminifera) are reported for mid/late the EBC site is located outside the primary winter, at the time of the local winter bloom, as upwelling zone, it is influenced by the Cape Jubi inferred from the SEAWIFs images (Parrilla et al., filament as revealed by SEAWIFs data (Parrilla 1999). The fact that the 500 m ESTOC trap is et al., 1999). Major changes in plankton diatom barren of diatoms points to very low production or abundances through time at EBC are concomitant total dissolution of opaline micro-organisms in the with the higher PP values measured at 301Nnear water column at this site, while the loss of the LP the coast, 545 mg C m 2 d 1 in spring, and 451 mg upper trap makes it impossible to access export Cm 2 d 1 in fall (Fig. 3; Knoll et al., 1999; Parrilla production at LP. However, the simultaneous et al., 1999). At times of increased diatom increase in all groups’ fluxes between February abundance the dominant coccolithophores are and March associated to the presence of Chaeto- pushed out of the near-shore areas, the dominant ceros vegetative cells, at the LP medium trap species shift from E. huxleyi to F. profunda, and G. (900 m), allows an inference of locally enhanced ericsonii increases in abundance (Fig. 5; Sprengel productivity possibly due to localized upwelling of et al., 2002). Planktic foraminifera standing stocks nutrients generated by island circulation only can be compared to the phytoplankton (Zeitzschel, 1978 and references therein). groups for spring and summer (the winter and fall In spite of the different sampling techniques, a data are from different years), and both total good agreement was found for the seasonal planktic foraminifera and the high productivity cyclicity of each group between the vertically related taxa G. bulloides show a response similar to integrated standing stocks in the water column Coccolithophores and G. ericsonii (Figs. 5 and 6). and the fluxes in the traps. Taxa dominating the F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3621
1200 9 3.0x106 ) 8x10 ) 1 -1 EBC -
9 d (700m) 7x10 -2 1000 2.5x106 .day ) -2 -1 6x109
.day 800 2.0x106 -2 5x109
600 4x109 1.5x106 (shell .m 3x109 400 1.0x106 Planktic Foraminifera Flux Planktic Foraminifera
9 Diatom Flux (valves.m
2x10 Coccolith flux (coccoliths m 200 5.0x105 1x109
0 0x100 0.0x100
1200 8x109 3.0x106 ) ) -1
ESTOC 1 - 9 d 7x10 -2 (750m) 6 ) 1000 2.5x10 .day -1 -2 6x109 .day 6 -2 800 2.0x10 5x109
600 4x109 1.5x106 (shell .m
3x109 6 Planktic Foraminifera Flux Planktic Foraminifera 400 1.0x10 9 Coccolith flux (coccoliths m
2x10 Diatom Flux (valves.m 200 5.0x105 1x109
0 0x100 0.0x100
1200 9 3.0x106 8x10 ) ) -1 LP 1 - 9 d (900m) 7x10 -2 6 1000 2.5x10 .day -2 ) 9 -1 6x10 800 2.0x106 .day 9
-2 5x10
600 4x109 1.5x106 (shell .m 3x109 400 1.0x106
Planktic Foraminifera Flux Planktic Foraminifera 9 Diatom Flux (valves.m 2x10 Coccolith flux (coccoliths m 200 5.0x105 1x109
0 0x100 0.0x100 Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. O
winter spring summer fall Days (1997) Fig. 7. Seasonal pattern of diatom, coccolithophore, and planktic foraminifera mean flux is in the upper traps of all three sites (700 m for EBC; 750 m for ESTOC; 900 m for LP). 3622 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 diatom and planktic foraminifera trap assem- 2002; Nave et al., 1998a). With the objective of blages at times of maximum fluxes (Chaetoceros checking this assumption an extra cruise was resting spores and G. bulloides, respectively) are carried out in February 1999 (Fig. 1). Total also the ones that dominate the sediment assem- phytoplankton determined for samples collected blages (see also Meggers et al., 2002). These data between Cape Ghir and ESTOC indicate that point to strong bias of the diatom and planktic diatoms are the dominant group (>6000 cells l 1) foraminifera sediment record. Plankton taxa representing 54% of the counted phytoplankton produced during blooms are preserved with great- (Fig. 2). Off Cape Ghir, the high number of er efficiency than those produced during non- diatoms was expected given the upwelling condi- bloom periods such as inferred by Nelson et al. tions; however, abundances of both total phyto- (1995), revealed by data in Abrantes and Moita plankton and diatoms were maintained at the (1999), and quantitatively demonstrated by Ortiz ESTOC station. In addition, the assemblage is also and Mix (1997). dominated by the same taxa: Asterionellopsis In terms of annual production, the loss of the glacialis, Pseudo-nitzschia spp. and Chaetoceros 700 m trap at LP does not allow a clear compar- spp. Nevertheless, significantly higher fluxes are ison for the same water depth. However, a clear observed in the deep LP trap for both diatoms and decrease between EBC and ESTOC is noticed for coccolithophores. Furthermore, the appearance all three groups, especially for diatoms, which were only in the LP deeper trap of 10 diatom species not found at the ESTOC upper trap (Table 3, (Table 4), mainly of the genus Thalassiosira, Fig. 4). If the ESTOC and LP medium traps generally present at the outskirts of upwelling loci (E750 and 900 m, respectively) are used for (Margalef, 1978; Estrada and Blasco, 1985), makes comparison with the 700 m EBC trap, mean it necessary to consider other sources of laterally annual fluxes decrease to the oceanic sites by one advected particles to the LP site. Advection of order of magnitude for diatoms and to about 12 particles from higher productive shelf waters to the for coccolithophores and planktic foraminifera. deeper LP trap also is supported by the presence of This pattern appears to reflect chlorophyll con- a high number of juvenile planktic foraminifera, centrations as determined from the satellite images which are often abundant in surface waters of over the entire sampling period with the high shallow nutrient-rich areas (Hemleben et al., values at the EBC site and a significant offshore 1989). decrease (Parrilla et al., 1999). Another set of problems arises if a quantitative A comparison of the medium and deeper trap assessment of the proportion of the plankton fluxes (Table 3, Fig. 4) indicates a flux increase of production represented in the sediments is at- both phytoplankton groups towards the deepest tempted. Even though there is no accurate way to trap at both offshore sites (ESTOC and LP). The approach it, over annual timescales new produc- increased sedimentation with depth found at the tion should be balanced by particle export (Eppley ESTOC site has been attributed to lateral advec- and Peterson, 1979), but no data exist for tion of material from higher productive coastal individual organism groups. Besides, we cannot regions by Neuer et al. (1997) and Davenport et al. assume that each group of organisms the flux that (1999). According to these authors, the Cape Ghir reaches the deepest traps proportional to its filament, given its annual pattern (Nykjaer, 1988; production in the overlying water, analogous to Nykjaer and Van Camp, 1994) and geographical new and export production (Eppley and Peterson, location with respect to ESTOC, may play an 1979), since lateral advection plays an important important role in the advection of material, role. It might be assumed that the export flux is similarly to the Cape Blanco filament in the best represented by the upper-trap flux, but, California margin (Ortiz et al., 1995). This difficulties arise with the coccolithophores since hypothesis is supported by the similarity of comparing standing stock with flux requires assemblages found in the two traps for both knowing the number of coccoliths per cocco- diatoms and coccolithophores (Sprengel et al., sphere, which is only known for a few species F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3623
(Haidar et al., 2002). The only clear estimate of the nitzschioides it increases significantly (about three proportion of the diatoms, coccolithophores and times) at all three sites. planktic foraminifera represented in the sediments These data point to much better diatom is the relative mean annual flux measured at the preservation than expected. It investigations sedi- deepest traps. Using the example of ‘‘preservation ment-traps based on only 9 months data, however, efficiency—PE’’ (burial:total production) used for could be misleading because: (i) they sampled only the major chemical components, we have deter- three seasons, and (ii) they may not reflect a typical mined the ratio sediment AR:annual mean deeper year. In addition, the uppermost sediment sample trap flux, as well as an ‘‘upper preservation may representing just the ‘‘fluff’’ recently arrived efficiency—UPE’’ the ratio between the sediment to the bottom and not yet modified by the AR and the annual mean flux found in the upper dissolution and/or benthic organisms reworking trap (Table 3). This estimation was attempted for that it is likely to suffer during its progressive the three groups of micro-organisms and a few burial in the sediments. Studies on the pore waters species and genera that, from their importance in Si content indicate that dissolution within the the sediments assemblages and presence in all three sediments will be most intense in the top 10–30 cm data sets, appear paleoceanographically important (Van Cappellen, 1996 and references within). To (Tables 4–6; Abrantes and Moita, 1999; Meggers assess dissolution within sediments, but avoid et al., 2002). possible differences due to climatic change, a High preservation of diatoms (on the order of mean of the Holocene samples AR (40 cm at 5%) occurs in the northeastern Pacific (Takahashi, EBC, 15 cm at ESTOC, and 8 cm at LP— 1994), while in the northeastern Atlantic upwelling Henderiks et al., 2002) was used to calculate a areas values are around 1% (Abrantes, 2000). At Holocene PE (Table 3). A close observation of the our oceanic sites (ESTOC and LP), dissolution obtained values reveals an important loss of rates for biogenic opal at the sediment/water diatoms as a whole at all sites but preservation interface are expected to be relatively high, but efficiencies at ESTOC and LP two times higher this is not the case. Diatom AR estimated for the than at EBC. The fact that Chaetoceros UPE is sediments is either equal or slightly higher than the higher than PE at LP and lower at ESTOC, as well mean annual flux found in the deeper traps. as the higher difference observed for the two Besides, when bulk diatom AR in the sediments indices at LP for Nitzschia and T. nitzschioides, are compared to the exported production as indicates that LP receives material by lateral measured from the upper trap for the offshore advection in a more consistently, or from more sites (Table 3), the percentage being incorporated productive sources. into the sediment is as much as three times higher Coccolithophores PE indicates total preserva- at ESTOC and four times higher at LP, reflecting tion at ESTOC (E1), but a loss of about 40–50% the importance of lateral advection. at EBC and LP, respectively. The amount of the If the individual taxa are considered, PE for upper-trap bulk export flux preserved in the Chaetoceros resting spores is specially high at sediments shows increased ARs relatively to the ESTOC (9.15), >1 at LP, but o1 at EBC, a trend trap fluxes for ESTOC and LP. When single also followed by the lightly silicified oceanic forms species are considered, E. huxleyi and F. profunda of Nitzschia. As for T. nitzschioides, a diatom PE and UPE mimic the total coccolithophore common in and around upwelling centers (Hasle pattern, but with an higher increase in F. profunda and Mendiola, 1967; Margalef, 1978) and known for the LP deeper trap. G. ericsonii, on the after to be dissolution-resistant, sediment AR is 2–4 hand, shows increased preservation at ESTOC. If times higher than the mean annual deep-trap Holocene PE is determined, no major changes are fluxes. UPEs for the same taxa indicate that revealed either for the group or for the three sediments contain seven times more Chaetoceros different taxa analyzed. These data indicate that and three times more Nitzschia than the upper coccolithophore dissolution occurs mainly at the traps at both ESTOC and LP, while for T. sediment/water interface and is relatively more 3624 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 important at EBC and LP. At EBC it may be the genera Pseudo-nitzschia, Bacteriastrum, Guinardia, result of the higher organic carbon export to the Hemiaulus, Leptocylindrus, and Skeletonema, all of sediments and resulting CO2 production (Emerson them lightly silicified, very prone to dissolution, and Bender, 1981). At the LP site (4292 m water and rarely preserved in sediments (Sancetta, 1989; depth), sediments may already be affected by more Sancetta, 1995; Lange et al., 1994; Abrantes and carbonate-corrosive waters, even though the cal- Moita, 1999). Another important genus in the cite lysocline is thought to lie at 4500 m in the water column (spring and summer) is Chaetoceros. Canary Basin (Crowley, 1983). This suggests a The species of this genus are, like the ones listed more persistent lateral advection from more above, fragile forms rarely found in the traps and productive areas at LP, as also indicated by sediments at this latitude. However, when nutri- diatoms. ents are nearly exhausted in the euphotic zone, this For the planktic foraminifera, PE could only be genus form resting spores (Margalef, 1978; Blasco calculated in relation to the upper trap. Planktic et al., 1980, 1981), which are very resistant to foraminifera show values that vary between 1.21 dissolution and become a major component of and 1.55 (Table 3), revealing an increase in both the trap and sediment assemblages. In foraminifera AR in relation to the traps. G. contrast, taxa such as Actinocyclus, Actinoptychus, bulloides and G. ruber PE, increase 5–6 times from Azpeitia, Cyclotella, and Paralia, fairly rare in the EBC to LP. Holocene PEs are higher than those plankton in general (Blasco et al., 1981; Moita, found for the uppermost sediments for all but G. 1993) and not found in our water-column samples, bulloides at ESTOC. The relatively higher PE are contributors to the sediment assemblages, as values found for the planktic foraminifera and the also reported elsewhere (Schuette, 1980; Abrantes two species examined indicate an important and Sancetta, 1985; Sancetta, 1989). This may be increase of this group and specially of G. bulloides explained by its higher degree of silicification and G. ruber in the offshore sediments. Besides the associated with the loss of many of the more indication of no carbonate dissolution within the fragile taxa abundant in the water column, sediments, these increased AR found in the together with some lateral advection and/or sediments may reflect conditions more favorable resuspension of bottom sediments. to planktic foraminifera production in the recent Diatom evidence from other regions of the past than the 9-month trap record, but reworking world ocean supports the contention that a and bottom-current transport and/or sediment significant amount of sinking biogenic opal is focusing also has to be considered. dissolved at the seafloor (Takahashi and Honjo, 1981; Wefer and Fisher, 1991). In the Canary 6.2. How different are the plankton assemblages Islands area, important differential dissolution in from the sediment assemblages? the upper 500–900 m of the water column is apparent from the comparison between the taxa Several papers have dealt with composition present in the water column and the upper/ changes at the different trap sites and depths medium traps. Quantitative diatom loss due to (Sprengel et al., 2002; Nave et al., 2001). In this post-depositional processes is also important, as paper, the differences between the water column, discussed in 6.1, although the similar assemblages trap and sediment assemblages are accessed by an found in the deeper traps and sediments analysis of the taxa found at each depth level for (R ¼ 0:98—Nave et al., 1998a) indicate no differ- the studied organisms (Tables 4–6). ential dissolution at the sediment/water interface. We find taxa only present in the water column When Holocene assemblages are inspected, no but not in the sediments, and taxa from present in major differences in the dominant taxa are the sediments but not in the plankton samples. noticed. However, increased contributions of Major discrepancies are found for the diatoms. resistant marine and freshwater forms at EBC 62% of the total plankton taxa are lost during and ESTOC confirm selective dissolution within settling to the upper trap, mainly species of the the top centimeters (40 cm at EBC and 15 cm at F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 3625
ESTOC). At LP, the presence of the fragile forms by bottom-current activity also may con- vegetative forms of Chaetoceros in all sediment tribute to the occurrence of certain taxa of all three samples clearly supports better preservation at the groups. However, sediments represent average islands surroundings, probably due to an excess of records over considerable time periods, and we silica entering the ocean as the result of chemical therefore may be comparing the present-day erosion of volcanic formations (Lisitzin, 1972). patterns to a recent past with different oceano- The mean Holocene coccolithophores and graphic conditions. planktic foraminifera AR is slightly greater than found for the uppermost samples at all sites, with maximum increase (1.5 times) at EBC. Most 7. Conclusions species and their contributions are maintained, but there is a shift towards higher relative Coccolithophores dominate the phytoplankton abundances of dissolution-resistant coccolitho- community at all seasons, with higher diatom phores taxa in the sediments of the offshore sites contributions coinciding with stronger upwelling/ (Sprengel et al., 2002). Dissolution also is indicated productivity conditions along the NW African by the loss of dissolution prone taxa at all sites, coast. The occurrence of coastal upwelling off NW but total AR points to either input of coccolitho- Africa determines the seasonality observed for phores and planktic foraminifera by reworking, diatoms, coccolithophores, and planktic foramini- bottom-current focusing, or higher production of fera standing stocks at the EBC mooring site, as carbonate-producing plankton in the earlier Ho- well as of the mean annual fluxes at the three sites, locene relative to modern conditions. both of which are clearly reflected by the trap From PE estimates and assemblage comparison, record. At ESTOC and LP the mid-winter bloom it appears that within the sediments both cocco- is related to local increased production. lithophores and diatoms suffer some dissolution The organism fluxes measured at both ESTOC but greater dissolution occurs for diatoms. Com- and LP sites reflect both the downward vertical parable loss of both diatoms and coccolitho- component and an important advective compo- phores, by differential dissolution among the less nent, which accounts for at least 42–44% of the dissolution-resistant taxa, occurs in the upper 500– deeper trap flux at ESTOC and 60–70% at LP. 900 m. The relatively large degree of diatom The low variability of species composition at all dissolution can be explained for two primary trap depths, both for diatoms and coccolitho- reasons: (A) production is limited to a relatively phores, may be indicative of a common source. narrow area of strong turbulence and high nutrient The dominance of the diatom assemblage by availability and occurs over relatively brief periods resting spores of a coastal-upwelling genus, (Margalef, 1978; Parrilla et al., 1999); (B) the Chaetoceros, and the water column results of the strong chemical dissolution of opal in the North Filamento 99 cruise support the hypothesis of Atlantic, both in the water column and at the lateral advection from the Cape Ghir (Neuer et al., sediment/water interface, contrasts to carbonate, 1997). However, given the higher input observed at which has good preservation (Broecker and Peng, the LP deeper trap as well as the specific 1982). occurrence of diatom species of the genus Tha- In addition to selective dissolution during lassiossira and juvenile forms of planktic forami- settling, which is clearly higher for the opaline nifera, an additional source, more productive and/ organisms, differences in species makeup and or more local, for LP cannot be excluded. proportion in the plankton and the traps also Based on the comparison of standing stocks, can arise as a consequence of plankton patchiness fluxes, and sediments better diatom preservation (Siegel and Deuser, 1997) or infrequent blooms appears to occur at the offshore sites. Given that not sampled by our plankton samples. Lateral sediments comprise average records of consider- advection from productive coastal environments, able time periods (400–500 years), such a fact may resuspension and sedimentation of reworked be due to changes in environmental conditions or 3626 F. Abrantes et al. / Deep-Sea Research II 49 (2002) 3599–3629 result from the input of Si from the erosion of in the Glacial Oceans. NATO ASI. Springer, Berlin, volcanic rocks. pp. 425–439. The bulk of the phytoplankton production Andruleit, H., 1997. Coccolithophore fluxes in the Norwegian– Greenland Sea: seasonality and assemblage alterations. (mainly diatoms) is dissolved in the upper 500– Marine Micropaleontology 31, 45–64. 900 m of the water column. Further diatom Barton, E., Aristegui, J., Tett, P., Canton, M., Garcia-Braun, dissolution occurs within the sediment, leaving J., Hernandez-Leon, S., Nykjaer, L., Almeida, C., Almunia, only a minor portion of the original production. 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