Mid-shelf Area Research Articles

Оценка точности общедоступных цифровых моделей рельефа дна океанов на примере участков покрытия многолучевой съемкой Норвежского и Баренцева морей

The accuracy of publicly available bathymetry grids such as GEBCO_08, SRTM30_Plus, and Predicted Topography is evaluated at six studied polygons of GIN RAS multibeam (MB) coverage. High-resolution and accuracy, independent GIN RAS MB grids are used as the ground truth. Comparison of GIN RAS MB grids with USCGC “Healy” and RV “Oden” gridded MB data revealed no systematic errors in the GIN RAS data. In order to assess the accuracy an algorithm was developed to calculate depth difference between grids built in different map projections with grid cells that do not match. The assessment revealed that GEBCO_08 is more accurate than S&S over three of the six polygons, which include mid oceanic ridge, shelf and continental slope areas (polygons 1, 5 and 6). The observed differences in the accuracy between GEBCO_08 and S&S are due to the source data accuracy at polygon 1, better source data coverage in GEBCO_08 for polygons 5 and 6 (MB data), and poor performance of the interpolation in the shelf areas for S&S at polygons 4, 5 and 6. These results show that morphology of the seafloor, source data accuracy and coverage as well, as interpolation method affect the accuracy of the final output bathymetry surface.

Origins of terrestrial organic matter in surface sediments of the East China Sea shelf

Terrestrial organic matter (TOM) is an important component of marine sedimentary OM, and revealing the origins and transport mechanisms of TOM to the East China Sea (ECS) is important for understanding regional carbon cycle. A novel approach combining molecular proxies and compound-specific carbon isotopes is used to quantitatively constrain the origins and transport mechanisms of TOM in surface sediments from the ECS shelf. The content of terrestrial biomarkers of (C27+C29+C31) n-alkanes (52 to 580 ng g−1) revealed a seaward decreasing trend, the δ13CTOC values (−20.6‰ to −22.7‰) were more negative near the coast, and the TMBR (terrestrial and marine biomarker ratio) values (0.06 to 0.40) also revealed a seaward decreasing trend. These proxies all indicated more TOM (up to 48%) deposition in the coastal areas. The Alkane Index, the ratio of C29/(C29+C31) n-alkanes indicated a higher proportion of grass vegetation in the coastal area; While the δ13C values of C29 n-alkane (−29.3‰ to −33.8‰) indicated that terrestrial plant in the sediments of the ECS shelf were mainly derived from C3 plants. Cluster analysis afforded detailed estimates of different-sourced TOM contributions and transport mechanisms. TOM in the Zhejiang-Fujian coastal area was mostly delivered by the Changjiang River, and characterized by higher %TOM (up to 48%), higher %C3 plant OM (68%–85%) and higher grass plant OM (56%–61%); TOM in the mid-shelf area was mostly transported by aerosols, and characterized by low %TOM (less than 17%), slightly lower C3 plant OM (56%–72%) and lower grass plant OM (49%–55%).

Size-dependent photoacclimation of the phytoplankton community in temperate shelf waters (southern Bay of Biscay)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 543:73-87 (2016) - DOI: https://doi.org/10.3354/meps11580 Size-dependent photoacclimation of the phytoplankton community in temperate shelf waters (southern Bay of Biscay) Eva Álvarez1,*, Xosé Anxelu G. Morán1,2, Ángel López-Urrutia1, Enrique Nogueira1 1Instituto Español de Oceanografía, Centro Oceanográfico de Gijón/Xixón, Asturias, Spain 2Present address: Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia *Corresponding author: eva.alvarez.suarez@gmail.com ABSTRACT: Shelf waters of the Cantabrian Sea (southern Bay of Biscay) are productive ecosystems with a marked seasonality. We present the results from 1 yr of monthly monitoring of the phytoplankton community together with an intensive sampling carried out in 2 contrasting scenarios during the summer and autumn in a mid-shelf area. Stratification was apparent on the shelf in summer, while the water column was comparatively well mixed in autumn. The size structure of the photoautotrophic community, from pico- to micro-phytoplankton, was tightly coupled with the meteo-climatic and hydrographical conditions. Over the short term, variations in the size structure and chlorophyll content of phytoplankton cells were related to changes in the physico-chemical environment, through changes in the availability of nutrients and light. Uncoupling between the dynamics of carbon biomass and chlorophyll resulted in chlorophyll to carbon ratios dependent on body size. The slope of the size dependence of chlorophyll content increased with increasing irradiance, reflecting different photoacclimation plasticity from pico- to micro-phytoplankton. The results have important implications for the productivity and the fate of biogenic carbon in this region, since the size dependence of photosynthetic rates is directly related to the size scaling of chlorophyll content. KEY WORDS: Phytoplankton · Hydrography · Chlorophyll:carbon ratio · Size spectra · Size scaling · Continental shelf · Cantabrian Sea Full text in pdf format PreviousNextCite this article as: Álvarez E, Morán XAG, López-Urrutia Á, Nogueira E (2016) Size-dependent photoacclimation of the phytoplankton community in temperate shelf waters (southern Bay of Biscay). Mar Ecol Prog Ser 543:73-87. https://doi.org/10.3354/meps11580 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 543. Online publication date: February 03, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Spatial and temporal variability in sediment deposition and seabed character on the Waipaoa River margin, New Zealand

The stratigraphic record is the manifestation of a wide range of processes, interactions and responses to environmental drivers. Understanding the functioning of river sediment dispersal systems is necessary to determine the fate of sediment and associated material in the marine environment and differentiate key influences in the development of the stratigraphic record. To that end, this study uses sediment cores collected on four successive cruises (January, May and September 2010 and February 2011) on the Waipaoa River margin, New Zealand, to provide insight into spatial and temporal variability in sediment deposition and seabed character.The Waipaoa River discharges a large sediment load into an energetic coast that has a complex margin morphology. Several flood and wave events occurred during the study, and sedimentation varied spatially and temporally. X-radiographs and short-lived radioisotopes indicate emplacement of new event layers prior to all cruises. Notable variation in surficial seabed character (grain-size composition, loss-on-ignition percentage) was apparent on the inner shelf (water depths <40m), but mid-shelf areas and seaward had more homogeneous sediment properties. 7Be inventories indicate variable patterns of deposition related to fluvial and oceanographic conditions prior to cruises. Ephemeral sediment storage occurs on the inner-shelf of Poverty Bay, into which the Waipaoa River discharges directly, and subsequent export and dispersal patterns are linked to the relative timing and size of flood and wave events. Surficial deposits with characteristics of fluid muds and wave-enhanced sediment gravity flows were noted at some (<25 sites total) mid-shelf and shallower sites from all cruises. During the last cruise considerable inter- and intra-site seabed variability occurred in the interbedded river-proximal inner-shelf deposits over spatial scales of less than a few kilometers. Evidence from earlier sidescan data infer that this could be related to variation in bedform development or influence. Contrasts in the observed event layering recorded over the experiment with the longer pattern of accumulation suggests stochastic dispersal behavior and reworking over time must shape the seabed to produce the time-averaged pattern of shelf sediment accumulation. This research highlights our improved ability to comprehend strata development and sheds light on the challenge of interpreting historical and ancient strata across spatial and temporal scales.

Distinct bacterial-production–DOC–primary-production relationships and implications for biogenic C cycling in the South China Sea shelf

Abstract. Based on two summer spatio-temporal data sets obtained from the northern South China Sea shelf and basin, this study reveals contrasting relationships among bacterial production (BP), dissolved organic (DOC) and primary production (PP) in the transition zone from the neritic to the oceanic regions. Inside the mid-shelf (bottom depth &lt;100 m), where inorganic nutrient supplies from river discharge and internal waves were potentially abundant, BP, DOC and PP were positively intercorrelated, whereas these three measurements became uncorrelated in the oligotrophic outer shelf and slope. We suggest that the availability of limiting minerals could affect the couplings/decouplings between the source (i.e. phytoplankton) and sink (i.e. bacteria) of organic carbon, and thus DOC dynamics. DOC turnover times were homogeneously low (37–60 days) inside the mid-shelf area and then increased significantly to values &gt;100 days in the outer shelf, indicating that riverine (Pearl River) DOC might be more labile. The actual mechanism for this is unknown, but might relate to higher inorganic nutrient supply from river/terrestrial sources. The positive correlation of the BP / PP ratios vs. phosphate (and nitrate) concentrations in the inner shelf implies that if anthropogenic mineral loading keeps increasing in the foreseeable future, the near-shore zone may become more heterotrophic, rendering the system a stronger source of CO2.

Microphytobenthos along the Louisiana continental shelf during mid-summer hypoxia

Microphytobenthos may influence benthic processes, such as the oxygen dynamics in the bottom-water of the hypoxic area of the northern Gulf of Mexico. We collected sediment along the Louisiana continental shelf ∼14–20m isobath from the Mississippi River to Lake Calcasieu, LA, during periods of extensive bottom-water hypoxia in July 2006–2008 to estimate microphytobenthos biomass (chlorophyll a) and community composition. Typical sediment chlorophyll a concentrations were <1.0μggdrysed−1, with the highest mean concentration at a sandier mid-shelf area, and the lowest mean concentration at a station near the Mississippi River. Microphytobenthos abundances in the size fraction >3μm ranged from 0.7×101 to 1×105cellsgdrysed−1. Benthic cells represented on average 67% of total cell abundance, varying from 1 to 99%, while pelagic and tychopelagic phytoplankton cells contributed to the remainder. Microphytobenthos were composed of diatoms (Nitzschia, Gyrosigma, Pleurosigma and Bacillaria) and cyanobacteria (filamentous and colonial). Our results indicate that environmental variables, mainly seafloor PAR and bottom-water nutrient concentrations correlated the most with the spatial distribution of microphytobenthos biomass and composition. Microphytobenthos along the Louisiana continental shelf, in turn, could influence benthic processes, such as secondary production, nutrient fluxes and oxygen dynamics.

Early Silurian (Aeronian) East Point Coral Patch Reefs of Anticosti Island, Eastern Canada: First Reef Recovery from the Ordovician/Silurian Mass Extinction in Eastern Laurentia

An extensive late Aeronian patch reef swarm outcrops for 60–70 km on Anticosti Island, eastern Canada, located in the inner to mid-shelf area of a prominent tropical carbonate platform of southeastern Laurentia, at 20°–25° S paleolatitude of the southern typhoon belt. This complex, described here for the first time, includes more than 100 patch reefs, up to 60–80 m in diameter and 10 m high. Reefs are exposed three-dimensionally on present-day tidal flats, as well as inland along roads and rivers. Down the gentle 1°–2° paleoslope, the reefs grade into coral-sponge biostromes, and westerly they grade into inter-reef or deeper ‘crinoidal meadow’ facies. The reef builders were dominantly tabulate and rugose corals, with lesser stromatoporoids. Other components include crinoids, brachiopods, green algae (especially paleoporellids), and encrusting cyanobacteria: reefs display some of the earliest known symbiotic intergrowths of corals and stromatoporoids. Reefs were variably built on a base of crinoidal grainstones, meadows of baffling tabulate corals, brachiopod shells, or chlorophytes. These reefs mark an early phase of reef recovery after a prominent reef gap of 5–6 million years following the Ordovician/Silurian mass extinction events. The reefs feature a maximal diversity of calcifying cyanobacteria, corals and stromatoporoids, but low diversity of brachiopods, nautiloids and crinoids. Following the North American Stratigraphic Code, we define herein the Menier Formation, encompassing the lower two members of the existing Jupiter Formation.

Ice sheet retreat dynamics inferred from glacial morphology of the central Pine Island Bay Trough, West Antarctica

Pine Island Glacier drains portions of the West Antarctic Ice Sheet into the Amundsen Sea. During the Last Glacial Maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf. Unusually restricted sea-ice cover during the austral summer of 2010 allowed for a systematic multibeam swath-bathymetric and chirp sonar survey of the mid-shelf section of Pine Island Trough. The mapped glacial landforms reveal new information about the paleo-Pine Island Ice Stream's dynamic retreat from the mid-shelf area and confirm previous suggestion of a retreat in distinct steps. The periods of grounding line stability during the overall retreat phase are marked by sediment accumulations, i.e. grounding zone wedges. These wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment. Considering a range of sediment flux rates from the paleo-Pine Island Ice Stream we estimate that the largest and most clearly defined grounding zone wedge, located at about 73°S in the surveyed area, took between 600 and 2000 years to form. The ice stream retreated landward of this wedge before 12.3 cal ka BP. The swath-bathymetric imagery of landforms in Pine Island Trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break-up. The depths of grounding line wedges decrease in a landward direction, from 740 to 670 m, and record elevation of the grounding line as it stepped landward. In all, the grounding line elevation varied by only ∼80 m over a distance of just over 100 km, implying a low ice sheet profile during retreat. Finally, we revisited seismic reflection profile NB9902, acquired along Pine Island Trough in 1999, in combination with the newly acquired swath-bathymetric imagery from 2010. Together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area in central Pine Island Trough where a high in dipping bedrock strata exists and the glacial trough is narrow, forming a bathymetric “bottle neck”.

Acoustic evidence for a gas migration and release system in Arctic glaciated continental margins offshore NW-Svalbard

High-resolution 3D and 2D seismic data offshore NW-Svalbard, west of Prins Karls Forland, provide geophysical evidence for geologically controlled fluid migration pathways, gas hydrate occurrence, and an active seabed gas expulsion system. The investigated seabed area covers ∼1600 km2 and lies between Kongsfjorden cross-shelf trough in the north and Isfjorden cross-shelf trough in the south ranging in water depths from ∼200 m on the shelf to 800 m on the upper continental slope. Acoustic evidence for present day methane release from the seabed to the water column comes from more than 220 gas flares at the outer shelf while past methane release activity at the mid-shelf area is evident from pockmarks without flares. The fluid migration pathways towards the seabed can be drawn from sub-seabed acoustic anomalies. Fluid migration towards the upper slope occurs mostly along strata in upslope direction and largely prevails over vertical focused migration. Fluids accumulate in the uppermost part of the slope just westward of the shelf break, where they are trapped beneath the prograding glacigenic sequence, which is not permeable enough for fluids to migrate through. Fluids are expelled on the shelf where the base of the glacigenic sequence outcrops. Some gas-charged fluids may originate from deep-seated hydrocarbon reservoirs and can be temporally stored in gas hydrates in the shallow subsurface. Though evidence for hydrates on the uppermost slope is missing the seismic data from the lower slope clearly suggest the occurrence of gas hydrate.

Nitrogen uptake and primary productivity rates in the Mid-Atlantic Bight (MAB)

Nutrient concentrations, primary productivity, and nitrogen uptake rates were measured in coastal waters of the Mid-Atlantic Bight over a two-year period that included measurements from all four seasons. In order to assess carbon productivity and nitrogen demand within the context of the physical environment, the region was divided into three distinct hydrographic regimes: the Chesapeake and Delaware Bay outflow plumes (PL), the southern Mid-Atlantic shelf influenced by the Gulf Stream (SS), and the mid-shelf area to the north of the Chesapeake Bay mouth (MS). Annual areal rates of total nitrogen (N) uptake were similar across all regions (10.9 ± 2.1 mol N m −2 y −1). However, annual areal rates of net primary productivity were higher in the outflow plume region (43 mol C m −2 y −1), than along the Mid-Atlantic shelf and in areas influenced by the Gulf Stream (41 and 34 mol C m −2 y −1, respectively). Rates of net primary productivity were not well correlated with Chl a concentrations and were uncoupled with net N uptake rates. Seasonally averaged annual areal rates of net primary productivity for the Mid-Atlantic Bight measured in this study were higher than those calculated in previous decades and provide important validation information for biogeochemical models and satellite remote sensing algorithms developed for the region.

Vertical distribution of benthic invertebrate larvae during an upwelling event along a transect off the tropical Brazilian continental margin

Abundance and composition of marine benthic communities have been relatively well studied in the SE Brazilian coast, but little is known on patterns controlling the distribution of their planktonic larval stages. A survey of larval abundance in the continental margin, using a Multi-Plankton Sampler, was conducted in a cross-shelf transect off Cabo Frio (23°S and 42°W) during a costal upwelling event. Hydrographic conditions were monitored through discrete CDT casts. Chlorophyll- a in the top 100 m of the water column was determined and changes in surface chlorophyll- a was estimated using SeaWiFS images. Based on the larval abundances and the meso-scale hydrodynamics scenario, our results suggest two different processes affecting larval distributions. High larval densities were found nearshore due to the upwelling event associated with high chlorophyll a and strong along shore current. On the continental slope, high larval abundance was associated with a clockwise rotating meander, which may have entrapped larvae from a region located further north (Cabo de São Tomé, 22°S and 41°W). In mid-shelf areas, our data suggests that vertical migration may likely occur as a response to avoid offshore transport by upwelling plumes and/or cyclonic meanders. The hydrodynamic scenario observed in the study area has two distinct yet extremely important consequences: larval retention on food-rich upwelling areas and the broadening of the tropical domain to southernmost subtropical areas.

Bottom temperature and in situ development of chokka squid eggs (Loligo vulgaris reynaudii) on mid-shelf spawning grounds, South Africa

Abstract Oosthuizen, A., and Roberts, M. J. 2009. Bottom temperature and in situ development of chokka squid eggs (Loligo vulgaris reynaudii) on mid-shelf spawning grounds, South Africa. – ICES Journal of Marine Science, 66: 1967–1971. The aim of the study was to test the development success of squid eggs on the mid-shelf (60–150 m deep) spawning grounds in relation to previous laboratory results, and to describe the mid-shelf temperature environment and how it could affect egg development. A series of in situ egg incubation experiments was conducted on the mid-shelf (∼119 m deep) spawning grounds using cages, temperature sensors, and acoustic releases for retrieval. Newly spawned eggs were collected by scuba, and continuous temperature data were collected at two points between the known inshore spawning grounds and the mid-shelf areas. Temperature variations followed a seasonal warming and cooling cycle, with superimposed peaks and troughs. Egg development data indicated that warm temperature peaks (10–13°C) are sufficient for normal development of eggs on the mid-shelf. Egg development time on the mid-shelf was 2–3 times longer (50–60 vs. 20–30 d) than inshore. The scarcity of abnormalities (0.45%) disputes previous laboratory results that suggested that ∼50% of eggs would suffer abnormalities in the colder mid-shelf temperature environment.

Surface structure and stability of the Larsen C ice shelf, Antarctic Peninsula

AbstractA structural glaciological description and analysis of surface morphological features of the Larsen C ice shelf, Antarctic Peninsula, is derived from satellite images spanning the period 1963–2007. The data are evaluated in two time ranges: a comparison of a 1963 satellite image photomosaic with a modern digital mosaic compiled using 2003/04 austral summer data; and an image series since 2003 showing recent evolution of the shelf. We map the ice-shelf edge, rift swarms, crevasses and crevasse traces, and linear longitudinal structures (called ‘flow stripes’ or ‘streak lines’). The latter are observed to be continuous over distances of up to 200 km from the grounding line to the ice-shelf edge, with little evidence of changes in pattern over that distance. Integrated velocity measurements along a flowline indicate that the shelf has been stable for ∼560 years in the mid-shelf area. Linear longitudinal features may be grouped into 12 units, each related to one or a small group of outlet feeder glaciers to the shelf. We observe that the boundaries between these flow units often mark rift terminations. The boundary zones originate upstream at capes, islands or other suture areas between outlet glaciers. In agreement with previous work, our findings imply that rift terminations within such suture zones indicate that they contain anomalously soft ice. We thus suggest that suture zones within the Larsen C ice shelf, and perhaps within ice shelves more generally, may act to stabilize them by reducing regional stress intensities and thus rates of rift lengthening.

Dynamics of a subtropical seagrass landscape: links between disturbance and mobile seed banks

Disturbance is a well known modifier of landscapes. In marine systems hurricanes may not only remove or bury subtidal seagrasses but they may also impact the seed banks of these taxa. We ask whether seagrass landscape pattern and seed dispersal are influenced by physical disturbance in a subtropical deep water setting. We examined the spatial dynamics of an offshore landscape composed of the seagrass, Halophila decipiens in summer 1999 and again in 2000 after the passage of a hurricane. A towed video camera was used to collect data within a 1 km2 area and construct benthic maps of seagrass, macroalgae, hard bottom outcrops, and sediments from over 20,000 video frames. The appearance of sand and seagrass at a portion of the site in summer 2000 that was previously hard substrate verified sediment and seed movement. Although seeds released by this seagrass are deposited into sediments near parent plants, movement en masse of the seagrass seed reservoir appears to be an important component of dispersal. The generation of new landscape patches when disturbance is large and intense suggests that large-scale disturbance, resulting in the local redistribution of sediment and the seed bank, appears to mold the spatial signature of the resulting seagrass landscape in a MidShelf area. This impact of physical disturbance differs from that previously reported for factors influencing spatial arrangements of seagrass in shallow waters but has some features similar to those of large infrequent disturbances studied in terrestrial settings.

Nature and rates of fine-sedimentation on a mid-shelf: “La Grande Vasière” (Bay of Biscay, France)

The study area, “La Grande Vasière” (LGV), stretches out on the French Atlantic continental shelf (at ca. 100 m water depth), along 250 km from the Glénan Islands at the north to the southwest of Rochebonne at the south. Box-cores were sampled in this mid-shelf area during four cruises in June 1995, and in April, June and September 2002. They were investigated using sedimentological approaches (X-radiographs and grain-size analyses) and radionuclide studies ( 210Pb geochronology and excess 234Th). The main results are: (1) the surficial sediments are generally organized into a decimetre-scale fining up sequence which can be the result of extreme storms; (2) an upper mixing layer of 7–20 cm reflects an important biological benthic activity and/or the impact of fishing (i.e. trawlers); (3) a thin (i.e. a few mm) surficial mud-rich layer is the result of the present-day sedimentation; (4) an apparent annual sedimentation rate of 1–3 mm is recorded in several loci of the study area. Some seasonal variations appear, corresponding to the deposition of fine material from April to September, and to the reworking and the re-suspension during the winter. This fine material is the result of the decantation of estuarine plumes, mainly the Loire and the Vilaine rivers, over the study area. LGV lies (1) under the influence of a winter-to-spring thermo-haline wedge that acts as a filter for the transfer of fine river-borne material to the slope and the open sea, and (2) below water depths where the mean swell action permits sedimentation, mainly in summer. From the point of view of the nature of its sediments, LGV is not a mud-belt, but a heterolithic and patchy sandy area that is submitted to increasing silting with environmental changes, on a seasonal-time scale.

Late Quaternary climate and sea-level changes recorded in sediment composition off the Büyük Menderes River delta (eastern Aegean Sea, Turkey)

Influences of Holocene climatic and sea level changes on sedimentation on the continental shelf off the Büyük Menderes River delta, SW Turkey were investigated using grain size and X-ray clay mineralogical data on surficial and 14C-dated core sediments collected at 19–81m water depths. Modern, fine-grained, siliciclastic sediments cover most of the seafloor of inner to mid-shelf areas. A narrow, relict belt extends from northwest to south (at 66–81m water depths), where sediments are characterized by abundant sand and gravel (27–52%) and biogenic carbonate (16–44%) contents, and microscopic examination suggests an older origin. The radiocarbon ages of mid and lower sections in cores (3670–10,380yrBP) reflect sedimentation under depositional conditions from early to late Holocene in the study area. Additionally, downcore changes of grain size toward coarser-grained sediments most probably record global climatic effects with sea level changes, specifically the transition from lowstand in early Holocene to highstand at mid–late Holocene. The presence of this relict belt in offshore waters can be attributed largely to active uplift tectonics. The coarser-grained relict belt, compared with available seismic profiles, corresponds to an lowstand unconformity of bottomset beds of the prograding Büyük Menderes Delta.Reconstruction from nautical charts clearly showed the presence of an E–W-trending submarine canyon (“Paleo-Büyük Menderes River valley”) in the course of Büyük Menderes Graben. This is interpreted as product of combination of sea-level lowstands and subsidence tectonics throughout the late Quaternary.Smectite (35–62%), illite (28–51%) and kaolinite (12–19%) constitute the dominant clay minerals in the <2μm fraction of the surface sediments. The patterns of clay mineral distribution suggest sediment transport from the Büyük Menderes River and dispersal from the river to the outer continental shelf by the prevailing current regime. Downcore changes in the clay mineral assemblages (downward-decreasing smectite/illite ratios) reflect changes in weathering conditions of the terrigenous source, from a colder climate during early Holocene to relatively warmer periods toward the present. Widely occurring partly metamorphosed volcanic rocks characterize the major geological sources of clay minerals on the adjacent hinterland.

Copepod egg production during highly productive late spring conditions: importance of freshly ingested food and lipid storage

The reproductive activity of 2 calanoid copepods, Calanus helgolandicus and Calanoides carinatus, under post-bloom conditions was investigated during a cruise in the central Cantabrian Sea (SW Bay of Biscay) in May 2000. Several mesoscale structures, such as an upwelling of rich waters associated with the topography of one submarine canyon, were observed on the continental shelf. Consequently, a high biomass of large phytoplankton was found in coastal and mid-shelf areas. These unexpected productive conditions after the spring bloom supplied copepods with favourable food resources. Accordingly, females showed mature gonads, high percentages of spawning and high egg production rates (EPRs). A surface saline current was detected flowing parallel to the coast along the slope. A microbial food web prevailed there and, unlike the coast and mid-shelf areas, low chlorophyll concentrations and a high proportion of small phytoplankton were found. The microbial food web did not seem to be suitable to support copepod production; thus, only a few females had mature gonads and fecundity was low. The number of eggs produced increased as herbivorous feed- ing increased, but feeding on phytoplankton did not cover the carbon requirements at all stations, and a mixed diet was suggested. The relationship between EPR and diatom concentration showed a saturation response for both species, but interestingly the saturation concentration was low and fecundity values were sub-maximal. Females had low lipid levels and low C:N ratios, indicating that egg production could be entirely fuelled by freshly ingested food. The low lipid reserves of females could also help to explain the sub-maximal EPR of C. helgolandicus. Nevertheless, low lipid storage was not a constraint for C. carinatus because it is well known that this species uses only freshly ingested food to support egg production. The implications of this extra productive time at the end of spring on the annual recruitment of C. helgolandicus and C. carinatus are discussed.

Validation of soft bottom benthic habitats identified by single-beam acoustics

Acoustic diversity charts were produced for a Portuguese soft bottom mid-shelf area, depth from 30 to 90 m, using a single-beam echo sounder coupled to the acoustic systems QTC VIEW™ Series IV and V. A similar acoustic pattern was identified by both systems, which, after ground-truth interpretation based in available sediment and biological data, established a preliminary spatial distribution model of the benthic habitats in this coastal area. However, some of the acoustic areas were interpreted using one or very few sediment and benthic samples. A specific validation survey was conducted a posteriori, in which the positioning of the sediment and benthic community sampling sites was based on the acoustic diversity previously identified. The results clearly confirm the benthic habitats distribution model suggested by the acoustic method, indicating a high potential for the use of such approach in the identification and mapping of large-scale soft bottom coastal shelf habitat diversity.

Climbing ripple structure and associated storm-lamination from a Proterozoic carbonate platform succession: Their environmental and petrogenetic significance

The Mesoproterozoic Pandikunta Limestone, a shallow water carbonate platform succession in the Pranhita-Godavari Valley, south India, displays well developed climbing ripple lamination and storm deposited structures, such as HCS, wave ripple-lamination, combined-flow ripple-lamination and low angle trough cross-stratification. Different types of stratification developed in calcisiltite with minor amounts of very fine quartz sand and silt. The climbing ripple structures exhibit a complex pattern of superposition of different types (type A, B and S) within cosets pointing to a fluctuating rate of suspension depositionversus bedform migration, and an unsteady character of the flow. Close association of climbing ripple structures, HCS with anisotropic geometry, wavy lamination and combined-flow ripple-lamination suggest that the structures were formed by storm generated combined-flow in a mid-shelf area above the storm wave base. The combined-flow that deposited the climbing ripple structures had a strong unidirectional flow component of variable magnitude. The climbing ripple structure occurs as a constituent of graded stratified beds with an ordered vertical sequence of different types of lamination, reflecting flow deceleration and increased rate of suspension deposition. It is inferred that the beds were deposited from high-density waning flows in the relatively deeper part of the ancient shelf. The structures indicate that the Pandikunta platform was subjected to open marine circulation and intense storm activities.The storm deposited beds, intercalated with beds of lime-mudstone, consist primarily of fine sand and silt size carbonate particles that were hydrodynamically similar to quartz silt. Detrital carbonate particles are structureless and are of variable roundness. The particles were generated as primary carbonate clasts in coastal areas by mechanical disintegration of rapidly lithified beds, stromatolites or laminites, and the finest grade was transported to the offshore areas by storm-generated currents.

The biogeochemical cycling of phosphorus in the upper ocean of the East China Sea

Natural activities of 32P ( t 1/2=14.3 days ) and 33P ( t 1/2=25.3 days ) in total dissolved P (TDP), suspended particulate matter, net-plankton and rainwater during the spring of 2001 were measured by an ultra-low level liquid scintillation counter. A continuous steady-state model was used to estimate residence times of various phosphorus pools and uptake rates of the biological food chain within the upper ocean of the East China Sea. 32P/ 33P ratios increased from the dissolved pools to the suspended matter and to net-plankton, reflecting that the age of P increased as one moved up through the food chain. The residence times of P in the dissolved pools of coastal water and mid-shelf area were very short (3–4 days), which suggests that low phosphorus concentrations could support relatively high levels of primary production. A phytoplankton assimilating flux of 189–814 mg C m −2 day −1 and a zooplankton grazing flux of 10–161 mg C m −2 day −1 were also estimated and show that grazing rates of carbon corresponded to 3–20% of primary production. In addition, the particulate organic carbon fluxes from the upper ocean were calculated by directly comparing the measured seawater inventory of 32P and 33P to that measured in rain, and were found to range between 8.5 and 81.0 mmol m −2 day −1. These results show that the naturally produced 32P and 33P can provide much needed information regarding the biogeochemical cycling of P in marine systems and can be of use in the development of ecosystem models that seek to address mechanisms that affect primary production in the ocean.