Western Shelf Research Articles

Sea Ice and Current Response to the Wind: A Vector Regressional Analysis Approach

The authors describe a two-dimensional (vector) regressional model for examining the anisotropic response of ice drift and ocean current velocity (“drift velocity”) to surface wind forcing. Illustration of the method is limited to sea ice response. The principal mathematical and physical properties of the model are outlined, together with estimates of the “response matrices” and the corresponding “response ellipses” (drift velocity response to a unity wind velocity forcing). For each direction, φ, of the wind vector the method describes a corresponding “wind factor” α(φ) (relative drift speed) and “turning angle” θ(φ) (the angle between the drift velocity and wind vector). The major ellipse axis corresponds to the direction of the “effective wind” (φ = φmax) and the minor axis to the direction of the “noneffective” wind. The eigenvectors of the response matrix define wind directions that are the same as the wind-induced drift velocity directions. Depending on the water depth and offshore distance, six analytical cases are possible, ranging from rectilinear response ellipses near the coast to purely circular response ellipses in the open ocean. The model is used to examine ice drift along the western shelf of Sakhalin Island (Sea of Okhotsk). Responses derived from the vector regression (four parameter) method are less constrained and therefore more representative of wind-induced surface motions than those derived using the traditional complex transfer function (two parameter) approach.

Formation, transport and decay of an intense phytoplankton bloom within the High-Nutrient Low-Chlorophyll belt of the Southern Ocean

The blooms associated with South Georgia coincide with the largest predicted carbon sink in the Southern Ocean. A major injection of iron and silica is required to sustain them over a long growth season that exceeds 4 months. The mechanisms for this are still poorly known but a cruise in January 2005 provided an opportunity to sample waters both upstream and downstream of the North Scotia Ridge to examine the processes involved. SeaWiFS imagery gave a misleading impression of bloom progression due to pronounced but highly regionalised subsurface chlorophyll- a (chl- a) maxima. Our combined measurements of oceanography, macronutrients, chl- a and floral composition showed that a single bloom that had seeded over the western shelf of South Georgia two months before the cruise developed into two distinct entities. Water retention and turbulent mixing south of the island led to severe nutrient depletion, low chl- a concentrations in surface waters (and in SeaWiFS images) yet pronounced subsurface maxima. By contrast the bloom over the northern shelf persisted in a shallow mixed layer, was florally different and appeared to be advected downstream into oceanic waters to the north. We found evidence for upwelling of nutrients on the upstream shelf edge of the island where the flow diverges to pass around each side of its shelf. This would provide one mechanism for the injection of iron and silica to sustain these massive South Georgia blooms and seed waters downstream for an extended growing season.

The Gulf of Cádiz pelagic ecosystem: A review

The Gulf of Cádiz, strategically situated between the North Atlantic Ocean and the Mediterranean Sea, has been the focus of attention of a few oceanographic studies dealing with the deep circulation in order to understand the dynamics of the dense plume of Mediterranean water. Much less attention has been paid to the surface pelagic layer which holds important living resources of commercial and ecological interest. This overview summarizes the recent advances that have been made concerning the regional oceanography of the northern half of this important basin from an interdisciplinary point of view. Probably the most relevant oceanographic feature of the basin is its strong seasonality, which is linked to the meteorologically-induced seasonality of the eastern boundary current system of the North Atlantic. The prominent cape Santa Maria divides the continental shelf off the southern Iberian Peninsula in two shelves of different shape that hold different oceanographic processes, which in turn determine the characteristics of the pelagic ecosystem. Mass and energy inputs from land as well as tidally-driven processes makes the wider eastern shelf be more productive while the narrower western shelf, cut by a sharp submarine canyon, is under the influence of the almost-permanent upwelling spot off cape San Vicente. Under easterlies, the west-going, warm coastal countercurrent that is observed in the eastern shelf may invade the western shelf thus connecting biologically both shelves in an east-to-west direction. Westerlies induce generalised upwelling off the southern Iberia Peninsula, which adds to the almost-permanent one off cape San Vicente and generates an upwelling jet that moves eastwards. Cape Santa Maria may deflect this flow by generating a cold filament that extends southward and diverts water from the western shelf to the open ocean. This pattern of circulation hampers the biological connection between shelves in the west-to-east direction, which is therefore less effective. The eastern shelf is prone to hold a cyclonic circulation cell during summer. This cell seems to be part of the reproductive strategy of fish species like anchovy with significant commercial interest in the region. The coupling between spawning and circulation is particularly beneficial under westerlies, when productivity in the eastern shelf is enhanced and the plankton is confined within the cyclonic cell. Easterlies favour oligotrophy and the westward export of plankton, which has an adverse effect on the recruitment and correlates low anchovy catches with periods of noticeable easterly intensity.

Seismic expression of gas and gas hydrates across the western Black Sea

This study is a synthesis of gas-related features in recent sediments across the western Black Sea basin. The investigation is based on an extensive seismic dataset, and integrates published information from previous local studies. Our data reveal widespread occurrences of seismic facies indicating free gas in sediments and gas escape in the water column. The presence of gas hydrates is inferred from bottom-simulating reflections (BSRs). The distribution of the gas facies shows (1) major gas accumulations close to the seafloor in the coastal area and along the shelfbreak, (2) ubiquitous gas migration from the deeper subsurface on the shelf and (3) gas hydrate occurrences on the lower slope (below 750 m water depth). The coastal and shelfbreak shallow gas areas correspond to the highstand and lowstand depocentres, respectively. Gas in these areas most likely results from in situ degradation of biogenic methane, probably with a contribution of deep gas in the shelfbreak accumulation. On the western shelf, vertical gas migration appears to originate from a source of Eocene age or older and, in some cases, it is clearly related to known deep oil and gas fields. Gas release at the seafloor is abundant at water depths shallower than 725 m, which corresponds to the minimum theoretical depth for methane hydrate stability, but occurs only exceptionally at water depths where hydrates can form. As such, gas entering the hydrate stability field appears to form hydrates, acting as a buffer for gas migration towards the seafloor and subsequent escape.

High-frequency time-series of the dynamic sedimentation processes on the western shelf of the Mississippi River Delta

Multiple box cores were collected on the continental shelf in the Mississippi Deltaic Region adjacent to Southwest Pass and analyzed for particle reactive radionuclides 234Th and 7Be to examine seasonal sediment dynamics associated with variations of river discharge and hydrodynamics. Three stations located along a line west of Southwest Pass were cored and reoccupied in October, November, and December of 2003 and March, April, and May of 2004. High-frequency sampling (∼monthly) comparable to the short half-life of the radiotracers ( 234Th t 1/2=24.1 d; 7Be t 1/2=53.3) enabled us to isolate the relative influence that various forcing agents (river discharge, waves, currents) had on sediment inventories of 7Be and 234Th. In addition, the primary source of 7Be (fluvial) differs from 234Th (marine), providing further insight into processes affecting sediment transport and supply. Monthly 7Be inventories showed a significant positive relationship to river discharge ( P=0.03) proximal to Southwest Pass. Sites further from Southwest Pass exhibited little to no relationship between 7Be inventories and river flow. At these sites, monthly 7Be inventories demonstrated a significant positive relationship with average wave orbital velocity ( P<0.01). During our sampling period, the transport of 7Be-rich sediments to sites located on the middle to outer shelf were dependent on sea conditions not river discharge. Relatively high wave orbital velocities potentially allow particles to remain in suspension longer and travel further distances before initial deposition. In addition, 234Th inventories showed evidence of sediment focusing during periods of high wave orbital velocities.

Quaternary sedimentation, margin architecture and ocean circulation variability around the Faroe Islands, North Atlantic

The Quaternary development offshore the Faroe Islands has been studied using high-resolution seismic and core data from the R/V DANA 2000 cruise and previous cruises. Several glacial-related features and deposits are observed, all bearing witness to former extensive glaciations of the Faroe area. On the shelves, overlaying a mid-Pleistocene glacial erosional surface, glacial and glacimarine deposits form a sheet geometry interrupted by ridges of sediment that are likely to represent ice-front deposits. An iceberg turbate north of the Faroe Islands provides evidence of large-scale drift of ultra-deep draft (>600 m) icebergs in the Nordic Seas at pre-Weichselian glacial stage(s). Marginal and transverse troughs found on the eastern and western shelf are suggested to have formed during the same glacial period(s) as the iceberg turbate. Iceberg plough-marks and abundant ice rafted material of non-Faroese origin, together with the relict moraine ridges encircling the Faroe Islands at around the 100 and 200 m water depth contours, indicate that the outer shelf was probably ice free during the Weichselian ice age. On the slopes and basinal parts, the formation of fine-grained contourites was favoured during (Weichselian) glacial stages when bottom currents were reduced. Sediment overloading during these glacial stages resulted in repeated slope instability, causing mass failures of the contourite deposits.

Sediment transport and resuspension due to combined motion of wave and current in the northern Adriatic Sea during a Bora event in January 2001: A numerical modelling study

The Adriatic Sea general circulation model coupled to a third generation wave model SWAN and a sediment transport model was implemented in the Adriatic Sea to study the dynamics of the sediment transport and resuspension in the northern Adriatic Sea (NAS) during the Bora event in January 2001. The bottom boundary layer (BBL) was resolved by the coupled model with high vertical resolution, and the mechanism of the wave–current interaction in the BBL was also represented in the model. The study found that, during the Bora event of 13–17 January 2001, large waves with significant wave height 2 m and period of 5 s were generated by strong winds in the northwestern shelf of the Adriatic where the direction of wave propagation was orthogonal to the current. The combined motion of the wave and current in the BBL increased the bottom stress over the western Adriatic shelf, resulting in stronger sediment resuspension there. Combining stronger bottom resuspension and strong upward vertical flux of resuspended sediments due to turbulent mixing, the model predicted that sediment concentration near the Po River was much higher than that predicted by the model run without wave forcing. The study also shows that wave–current interaction in the BBL reduced the western Adriatic Coastal Currents (WACCs) in the shallower north. It is concluded that wave forcing significantly changed the sediment distributions and increased the total horizontal fluxes over the western shelf. These results signified wave effect on sediment flux and distribution in the NAS, and suggested that waves cannot be neglected in the study of dynamics of sediment transport and resuspension in the shallow coastal seas. By including the tidal forcing in the coupled model, we also examined the effect of tides on the sediment transport dynamics in the NAS.

Variability of the distribution of the transparency and suspended matter: Concentration in the surface layer of the northwestern part of the Black Sea in the summer period

Particular features of the distribution of the transparency and particulate matter content, their variability, and their interdependence in the surface water layer (0–5 m) over the northwestern shelf and in the adjacent abyssal part of the Black Sea in the summer were considered on the basis of long-term simultaneous optical, biological, and hydrological observations (1979–1993). In the shelf regions with different river discharges and in the waters of the open part of the sea, the distributions of the transparency, the total particulate matter, and its organic components (organic carbon, nitrogen, and chlorophyll a), as well as the relative content of particulate organic carbon in the total amount of the particulate matter and the content of chlorophyll a in the particulate organic carbon, were considered. The distributions of the transparency and particulate matter and their dependence on the water dynamics are in good agreement. It was demonstrated that extreme anthropogenic eutrophication influences the western and northern coastal shelf areas. The water transparency and particulate organic matter distributions in the central shelf area subjected to the influence of transformed river water and the water properties of the southern part of the shelf, which is influenced by the waters of the open sea, were determined according to the particular structure of the phytoplankton, its abundance, and the processes of its production and destruction.

The sea-floor morphology of a Mediterranean shelf fed by small rivers, northern Alboran Sea margin

Depositional geometries and distribution patterns of shelf sediment wedges mainly derived from small rivers located in the northern margin of the Alboran Sea, Western Mediterranean Basin, are reported in this study, in order to understand: (1) their generation under particular physiographic and climatic conditions of river basins; (2) the interaction of shallow-water wedges with submarine valleys. A high amount of data has been used in this study, including river discharge and wave climate data, multibeam bathymetry, high-resolution seismic profiles and surficial sediment samples. The eastern shelf of the study area comprises the prodeltaic wedge off the Guadalfeo River and its eastward continuation, interrupted by the deeply indented Carchuna Canyon head. In contrast, the western shelf receives the contributions of a smaller river, the Verde River, whose associated prodeltaic wedge is limited to the inner shelf. Morphological features of both prodeltas are similar and differ from other Mediterranean prodeltaic bodies, resembling fan deltas. Those similarities include very steep foresets and bottomsets, very shallow and close to the coast offlap break, coarse sediment composition, lobate shape and common occurrence of crenulated sea floor. All these features point out to an origin linked to the activity of high-density sediment flows, rapid sedimentation and limited lateral redistribution. Those processes are favoured by the existence of an abrupt onshore physiography, a regional climate with a marked seasonality that conditioned torrential fluvial regimes and high availability of loose sand and gravel. Shelf sediment by-pass is a likely process during the Holocene in the eastern shelf, as suggested by the identification of two types of submarine valleys: (1) numerous gullies occur from the distal toe of the Guadalfeo River prodelta to the slope; (2) submarine canyon heads affect to the Holocene sedimentary wedge in the eastern sector of the study area. In the western shelf, however, the influence of shelf sedimentation processes on deeper domains is minimal, due to shelf widening, prevalence of relict features and absence of submarine valleys.

Nature of decadal-scale sediment accumulation on the western shelf of the Mississippi River delta

Sediment delivered to coastal systems by rivers (15×10 9 tons) plays a key role in the global carbon and nutrient cycles, as deltas and continental shelves are considered to be the main repositories of organic matter in marine sediments. The Mississippi River, delivering more than 60% of the total dissolved and suspended materials from the conterminous US, dominates coastal and margin processes in the northern Gulf of Mexico. Draining approximately 41% of the conterminous US, the Mississippi and Atchafalaya river system deliver approximately 2×10 8 tons of suspended matter to the northern Gulf shelf each year. Unlike previous work, this study provides a comprehensive evaluation of sediment accumulation covering majority of the shelf (<150 m water depth) west of the Mississippi Delta from 92 cores collected throughout the last 15 years. This provides a unique and invaluable data set of the spatial and modern temporal variations of the sediment accumulation in this dynamic coastal environment. Three types of 210Pb profiles were observed from short cores (15–45 cm) collected on the shelf. Proximal to Southwest Pass in 30–100 m water depths, non-steady-state profiles were observed indicating rapid accumulation. Sediment accumulation rates in this area are typically >2.5 cm yr −1 (>1.8 g cm −2 yr −1). Kasten cores (∼200 cm in length) collected near Southwest Pass also indicate rapid deposition (>4 cm yr −1; >3 g cm −2 yr −1) on a longer timescale than that captured in the box cores. Near shore (<20 m), profiles are dominated by sediments reworked by waves and currents with no accumulation (the exception is an area just south of Barataria Bay where accumulation occurs). The remainder of the shelf (distal of Southwest Pass) is dominated by steady-state accumulation beneath a ∼10-cm thick mixed layer. Sediment accumulation rates for the distal shelf are typically <0.7 cm yr −1 (<0.5 g cm −2 yr −1). A preliminary sediment budget based on the distribution of 210Pb accumulation rates indicates that 40–50% of the sediment delivered by the river is transported out of the study region. Sediment is moved to distal regions of the shelf/slope through two different mechanisms. Along-isobath sediment movement occurs by normal resuspension processes west of the delta, whereas delivery of sediments south and southwest of the delta may be also be influenced by mass movement events on varying timescales.

Principal features of the tectonic evolution of sedimentary basins in the Western Chukchi shelf and their petroleum resource potential

The history of the formation of sedimentary basins located predominantly in the western shelf of the Chukchi Sea is considered along with the data on the geology of adjacent areas of the American part of the sea and northern Alaska reported in the available publications on this region. The main lithotectonic complexes that correspond to particular stages of evolution of the region are identified. The tectonic rearrangement of the structural grain in response to the formation of the Canada Basin resulted in the development of the North Chukchi Trough. Intense subsidence of this trough and accumulation of thick sedimentary sequence favored, in turn, the balanced inversion uplift of the Wrangel-Herald Zone spatially related to depocenters of older sediments. Vigorous uplift and folding ceased in the Albian. In the geologic record, these processes are marked by unconformity and overstep of the older structural features. The inversion uplifts continued to rise later. Analysis of the data available provides new insights into the structure and evolution of the region. The sedimentary basins with a great thickness of their fill were favorable for generation and accumulation of hydrocarbons. The large uplifted blocks, extensive wedge-out zones, and stratigraphic unconformities at the walls of troughs and uplift slopes are especially favorable for hydrocarbon accumulation. Permissive beds are correlated with the Neocomian-Aptian sequence in Alaska that hosts oil and gas fields. The Upper Paleozoic and Lower Mesozoic strata, which are the main petroliferous sedimentary rocks in Alaska, may occur at a shallow depth in the Wrangel-Herald Inversion Zone. The conclusions drawn in this paper should be taken into account during reappraisal of the petroleum resources throughout the entire Chukchi shelf. At present, several oil and gas prospects are outlined in the Russian part of the Chukchi Sea.

Spatial analysis of the wind field on the western coast of Galicia (NW Spain) from in situ measurements

We used wind data measured at six meteorological stations to study their spatial representativity on atmosphere–ocean interactions along the western shelf of Galicia and inside the Ría of Vigo. The correlation as a function of distance and complex empirical orthogonal functions of the wind field were computed, allowing us to divide the region into three sub-domains: the open ocean, the shelf and the Ría of Vigo. Afterwards, wind gradients among stations were computed to determine specific spatial wind features: results showed an expected wind channelling effect inside the Ría of Vigo, but also a zonal onshore negative frictional gradient on the shelf that generates Ekman pumping during upwelling favourable winds. Finally, the Ekman transport estimated from meteorological stations was compared with measured transport from two moorings located inside the Ría of Vigo and on the shelf, and we determined that the meteorological station most representative of the wind field in the shelf is the one installed in a moored buoy on the shelf.

Seismic stratigraphy of Late Quaternary sediments of western Mersin Bay shelf, (NE Mediterranean Sea)

High-resolution shallow seismic-reflection profiles obtained from the western Mersin Bay have revealed the existence of the two distinct depositional sequences (C and B) lying on a narrow and relatively steeply-sloping continental shelf which mainly receives its sediments from the ephemeral rivers. The upper Holocene sedimentary sequence (C) is characterized by stratified (simple to complex) to chaotic reflection configurations produced by the development of a prograding wedge of terrigenous sediment. Particular occurrences of slope- and front-fill facies and the lack of a sharp boundary, which has, however, been observed on the western shelf of this bay, between the Early Holocene and latest Pleistocene deposits are related to possible movement of underlying deposits due to local gravity mass movements or synsedimentary tectonics due to adjustment of the underlying evaporites in adjacent basin. The maximum thickness of the topmost sequence C is associated with the Tarsus–Seyhan delta, which lies to the northeast of the area and is prograding along the shelf. Other variations in thickness (5–40 m) of this topmost sequence are related to the variable sediment discharge along the coast, and the distance from the coast. It is at a maximum (40 m) in the nearshore area just west of the Lamas river mouth and at a minimum (5–15 m) in the offshore area. The lower depositional pre-Holocene sequence (B) is characterized by continuous to wavy reflection configurations and how some cyclicity, suggesting coarse, heterogeneous sediments deposited under high energy conditions (fan-deltas) of Plio-Pleistocene age. The combined interpretation of seismic reflection profiles with the available bore-hole data reveals the existence of a widespread Miocene acoustic basement (A) off the Susanoğlu–Tırtar coasts and Karapınar–Gilindirez rivers mouths. Unusual features in some profiles suggest the escape of coastal freshwater into the accumulating sediment.

Features of the nonlinear internal wave spectrum in the coastal zone

This paper studies two examples of internal wave band temperature fluctuation spectra from moored instruments on the central Mexican Pacific Shelf and the western shelf of the Japan/East Sea. It is observed that for band f ≪ ω ≪ N, where N is the buoyancy frequency and f is the inertial frequency, the spectral falloff rate with frequency ω tends to ω−3. These features of spectra are simulated by the model spectrum of nonlinear internal waves in the shallow sea. It is shown that nonlinear internal waves with frequencies f ≪ ω ≪ N are governed by the modified simple wave equation. This equation underlie of the model spectrum of nonlinear internal waves on the shelf. The model spectrum shows ω−3 falloff rate with frequency in contrast with model spectrum proposed with Garrett and Munk, which shows ω−2 falloff rate.

Erosional processes and paleo-environmental changes in the Western Gulf of Lions (SW France) during the Messinian Salinity Crisis

Current interpretation of the Messinian Salinity Crisis (MSC) involves partial “desiccation” of the Mediterranean Sea coupled with the deposition of thick evaporites in the deep basins. New sets of seismic reflection profiles in the western part of the Gulf of Lions confirm the basinward extension of the Messinian erosion and enable the mapping of distinctive seismic markers indicating the Messinian Erosional Surface (or Messinian unconformity), the basin-margin detrital deposits, and the deep evaporite sequence. The geometrical relationship between these three elements and their relationship to the paleogeography of the margin during the MSC provide new information about the evolution of the study area during the Messinian. The Messinian Erosional Surface (MES), commonly correlated with the “desiccation” phase and the deposition of deep evaporites during the apogee of the event, is generally interpreted as a subaerial feature. In the Gulf of Lions, it is a complex diachronic polygenic erosional surface observed at the base of the prograding Plio-Quaternary sequence beneath the shelf and slope; it extends downslope beneath the deep basin Upper Evaporites and the Salt, and possibly correlates conformably with the base of the so-called deep Lower Evaporites. The whole morphology of the MES reflects a buried drainage pattern, supporting the interpretation of fluvial erosion driven by a substantial drop in sea level. Our results also suggest that large submarine gravity flows occurred prior to any significant accumulation of Salt in the basin and prior to the Upper Evaporites. Consequently, interbedded clastic deposits may partly account for the parallel reflectors of the Lower Evaporites. Since river erosion persisted throughout the MSC, the Salt and Upper Evaporite units may also contain a large amount of detrital sediments. The good quality of the new seismic data clearly reveals fan-shaped Messinian deposits in the downstream part of the main Messinian valleys (i.e., the Nile, Var, and Spanish rivers). The depositional scenarios generally involve a substantial sea-level fall coupled with deltaic/prodeltaic accumulations. A chaotic seismic unit (Unit D) filling Messinian lows and extending beneath the Salt within the study area is interpreted as a Messinian clastic unit. We propose a polyphase scenario of detrital fan deposition involving pre-, syn-, and post-Salt deposition in subaqueous/subaerial environments. In the Gulf of Lions, a late Miocene tectonic phase that affected the western shelf also played an important role in controlling (a) the pattern of the Messinian fluvial network, (b) the location of maximum erosion on the shelf, and (c) the location of the detrital fan depocentre downslope.

Intrusion of the Bay of Bengal water into the Arabian Sea during winter monsoon and associated chemical and biological response

Situated in similar latitudes and subjected to similar atmospheric forcing, the tropical basins of the Arabian Sea looses fresh water due to excess evaporation over precipitation while Bay of Bengal receives freshwater via excess rain and river run off. The hydrological imbalance thus created on an annual scale will have to be balanced by the inter‐basin exchange. In winter this happens through the intrusion of Bay of Bengal waters into the Arabian Sea, when the southward flowing East India Coastal Current carrying low salinity waters from the northern Bay feeds into the West India Coastal Current flowing north along the shelf in the Arabian Sea. Advection of nutrients by this intrusion triggers enhanced levels of chlorophyll near the southern part of the western shelf of India and may play a role in altering the biogeochemistry of this intense hypoxic region.

MODERN FORAMINIFERAL FAUNAS OF THE SOUTHWESTERN TO NORTHERN ICELAND SHELF: OCEANOGRAPHIC AND ENVIRONMENTAL CONTROLS

Surface sediment samples for analysis of modern foraminiferal assemblages were collected from 32 sites on the western and northern Iceland shelf during cruise B997 of the Icelandic ship Bjarni Saemundsson. The purpose of the study is to provide a basis for interpreting the variations in foraminiferal content in late glacial through Holocene sediments from cores at the same sites. Cluster analysis and principal components analysis of the benthic foraminiferal data and associated modern environmental parameters including hydrography, water depth, and sediment characteristics show that large progressive changes in the foraminiferal assemblages coincide with changes in the dominant oceanic surface currents and water masses around Iceland. The western areas of the shelf are overlain by relatively warm and saline Atlantic Water of the Irminger Current. The western shelf fauna is dominated by Cassidulina laevigata and other boreal species, whereas the planktic fauna is dominated by dextrally coiling Neogloboquadrina pachyderma. In Djupall, off the Northwest Peninsula, and in the shallow nearshore sites on the northern shelf, the boreal elements of the fauna diminish and arctic species become more important. However, the dominant species in these areas are Cibicides lobatulus and Astrononion gallowayi, attesting to winnowing of the shallow shelf areas by currents. In Isafjardardjup, the large fjord indenting the Northwest Peninsula, Cassidulina reniforme and Elphidium excavatum dominate the fauna as a result of cooler waters and more variable salinity conditions. A very large faunal shift is registered in the deep basins of the northern shelf. This faunal shift coincides with large changes in salinity and temperature stratification of the water column, reflecting the presence of the East Iceland Current. The fauna in the deep basins on the northern shelf are dominated by C. neoteretis, an indicator of modified Atlantic Water, and infaunal species that reflect organic fluxes to the seabed: Nonionellina labradorica and Melonis barleeanus, and the arctic species Islandiella norcrossi and I. helenae.

Does the Taiwan warm current exist in winter?

It has been argued for many years whether the Taiwan Warm Current (TWC) exists in winter, though there is no question about its existence in summer. A regional CTD survey and anchored ADCP measurements were conducted off the mouth of the Changjiang on the western shelf of the East China Sea from 24 February to 10 March 2001. Both hydrographic and current data showed an evidence of the TWC, which flowed northeastward along the 50‐m isobath and intruded into the submerged river valley off the Changjiang. This current is sub‐surface intensified, with a maximum velocity of 30 cm/s occurring at a depth of 30 m below the surface. This finding was consistent with the satellite‐derived SST image received on 26–30 January 1986 and MODIS SST image received on 18 February 2001. It suggests that the TWC is at least an episodic feature in the East China Sea and its occurrence and duration might vary due to meandering of the Kuroshio around the Taiwan Strait.

Contrasting primary production regimes around South Georgia, Southern Ocean: large blooms versus high nutrient, low chlorophyll waters

During the austral summer of 2002, a large and persistent phytoplankton bloom was detected with SeaWiFS imagery in the Georgia Basin to the north–west of South Georgia, while waters to the east of the island were relatively unproductive. A British Antarctic Survey research cruise in January 2002 confirmed this west/east difference with production values of up to 2.5 g C m −2 d −1 and chlorophyll a (chl a) values up to 15 mg m −3 at stations to the northwest of the island and 0.17 g C m −2 d −1 and 1.3 mg chl a m −3 to the northeast. These differences were not attributable to light limitation as mixed layer depth never exceeded critical depth. Instead, substantial nutrient depletions to the northwest of the island compared with the northeast suggested a difference in nutrient use between the two regions. The exceedingly high nutrient depletions (to <6.0 and 0.3 mmol m −3 for NO 3-N and PO 4-P, respectively) measured to the northwest were associated with an anticyclonic eddy situated over the Northwest Georgia Rise. Furthermore, differences in NO 3-N:PO 4-P depletion ratios suggested a greater ability in the northwest phytoplankton to utilise NO 3-N, and a greater dependence on NH 4-N at the northeast stations. Three distinct station groups were identified around the island based on watermass and size-fractionated chlorophyll. To the east, waters were characterised by a high proportion of microplankton and low NO 3-N:PO 4-P depletion ratios, to the west, by either a high proportion of microplankton and high NO 3-N:PO 4-P depletion ratios, or a high proportion of nanoplankton and moderate NO 3-N:PO 4-P depletion ratios. We consider this to be indicative of greater Fe availability, promoting NO 3-N use, to the northwest of South Georgia. However, an absence of microplankton over the western shelf regions may be due to size selective grazing by krill. Our field data, in conjunction with SeaWiFS imagery, indicated that the Georgia Basin phytoplankton most likely originated upstream of South Georgia. Subsequent interactions with the Northwest Georgia Rise and South Georgia's south-western shelf promoted increased growth that converged to the west of the island to form a large bloom in the Georgia Basin.

Late Cenozoic phosphogenesis on the western shelf of South Africa in the vicinity of the Cape Canyon

The strontium isotope ( 87Sr/ 86Sr) composition of phosphorite (carbonate fluorapatite) cemented grains (PCG), phosphate-cemented limestone (PCL), skeletal phosphorite grains (SPG) and biogenic calcite (mollusc shell, benthic foraminifera and echinoid spines) from sediment on the outer continental shelf in the vicinity of the Cape Canyon ranges from 0.707981 to 0.709167 and corresponds to an age range of late early Oligocene to late Pleistocene. Most biogenic carbonate Sr ages agree with biostratigraphic ages, but some samples contain significantly older and reworked robust (>250 μm) benthic foraminifera. Although the Sr ages of biogenic and phosphorite grains indicate that sedimentation was fairly continuous, most sediment is reworked with only lower Miocene, upper Pliocene and upper Pleistocene successions generally preserved in the study area. The initial phosphogenic episode from the latest Oligocene to early early Miocene (21–26 Ma) was the largest, with additional phosphogenic episodes in the late early Miocene (16–19 Ma) and middle Miocene (10–15 Ma). Most phosphorite occurs as PCG that formed during marine transgressions and highstands from the late Oligocene warming event until the mid-Miocene climatic optimum, a period of episodic Antarctic glaciation and several positive marine δ 13C excursions. Upper Oligocene to lower Miocene PCG have been extensively reworked and are associated with major erosional unconformities. PCG vary from peloidal sands to gravel mollusc moulds and contain variable amounts of quartz, glauconite and pyrite inclusions. PCL formed from 9 to 17 Ma by cementation and replacement of older calcareous sediment during the middle to late Miocene marine regression. Phosphorite, as well as associated glauconite and pyrite, indicate that periods of rapid accumulation of organic-rich, terrigenous muds derived from the focusing of the suspended load of rivers and organic matter produced in areas of coastal upwelling have occurred episodically on the margin since the late Oligocene. The relative paucity of phosphorite younger than the middle Miocene may result from frequent erosional events as documented by pronounced unconformities on the shelf that reflect lowered eustatic sea level, tectonic uplift and high-frequency, high-amplitude Quaternary sea-level fluctuations.