Salinity Shelf Water Research Articles

Potential vorticity estimates of absolute velocities on the Ross Sea shelf

We analyze absolute velocities on the continental shelf off Cape Adare, in the western sector of the Ross Sea (Antarctica). Such a velocity field is here inferred by using a novel inverse method of absolute velocity determination, namely the tracer PV method, related to potential vorticities of temperature and salinity. This theoretical choice allows us to directly use in situ temperature and salinity data. Moreover, it avoids high-order derivatives, which can give large uncertainties that affect estimates made using previous approaches. The tracer PV method also allows us to separately estimate the steady and non-diffusive component and the unsteady and diffusive components of the flow. The western sector of the Ross Sea is characterized by a surface layer of Antarctic Surface Water over layers of Low Salinity Shelf Water and High Salinity Shelf Water, flowing northward with average velocities ∼6–7 cm/s. At ∼200 m depth an intrusion of warmer and saltier Circumpolar Deep Water is also evident in our data. The steady absolute velocities are in good agreement with those obtained from the classical Margules equation, in particular regarding the northward flux of the High Salinity Shelf Water. Furthermore, velocities due to diffusive processes and mesoscale activity are discussed. Finally, a steady “thermal” approximation is discussed; it allows for a qualitative check of the results by means of temperature horizontal sections only.

Early summer thermohaline characteristics and mixing in the western Weddell Sea

Abstract The Ice Station POLarstern (ISPOL) cruise revisited the western Weddell Sea in late 2004 and obtained a comprehensive set of conductivity–temperature–depth (CTD) data. This study describes the thermohaline structure and diapycnal mixing environment observed in 2004 and compares them with conditions observed more than a decade earlier. Hydrographic conditions on the central western Weddell Sea continental slope, off Larsen C Ice Shelf, in late winter/early spring of 2004/2005 can be described as a well-stratified environment with upper layers evidencing relict structures from intense winter near-surface vertical fluxes, an intermediate depth temperature maximum, and a cold near-bottom layer marked by patchy property distributions. A well-developed surface mixed layer, isolated from the underlying Warm Deep Water (WDW) by a pronounced pycnocline and characterized by lack of warming and by minimal sea-ice basal melting, supports the assumption that upper ocean winter conditions persisted during most of the ISPOL experiment. Much of the western Weddell Sea water column has remained essentially unchanged since 1992; however, significant differences were observed in two of the regional water masses. The first, Modified Weddell Deep Water (MWDW), comprises the permanent pycnocline and was less saline than a decade earlier, whereas Weddell Sea Bottom Water (WSBW) was horizontally patchier and colder. Near-bottom temperatures observed in 2004 were the coldest on record for the western Weddell Sea over the continental slope. Minimum temperatures were ∼0.4 and ∼0.3 °C colder than during 1992–1993, respectively. The 2004 near-bottom temperature/salinity characteristics revealed the presence of two different WSBW types, whereby a warm, fresh layer overlays a colder, saltier layer (both formed in the western Weddell Sea). The deeper layer may have formed locally as high salinity shelf water (HSSW) that flowed intermittently down the continental slope, which is consistent with the observed horizontal patchiness. The latter can be associated with the near-bottom variability found in Powell Basin with consequences for the deep water outflow from the Weddell Sea.

Natural and anthropogenic hydrocarbons in the water column of the Ross Sea (Antarctica)

In the framework of the Italian Research Programme in Antarctica (PNRA) an oceanographic cruise was carried out between December 2000 and February 2001 in the Western Ross Sea. n-Alkanes and PAHs concentrations were analysed in sea-water samples collected at different depths at four sites (D, B, CA2, and CA). Vertical profiles of pressure, temperature, salinity and fluorescence were also performed in order to distinguish the water masses present in the sampling areas. n-Alkanes concentrations were consistent with those found in the same area during previous expeditions and showed higher values in the particulate due to the low temperatures. n-Alkanes profiles exhibited different features in the dissolved and particulate phases. The dissolved phase was characterised by a bimodal distribution with two maxima at C16 and C24 and prevalent compounds in the range C15–C32 whereas particulate was strongly dominated by long chain n-alkanes C23–C34 with C24 (Site B, CA and CA2) or C32 (Site B) as Cmax. CPI values and Pr/Ph ratios suggested a prevalent biogenic origin for aliphatic hydrocarbons. n-Alkanes vertical distributions were affected by the dynamic of the pack-ice melting and phytoplankton activity as well by the chemical–physical properties of water masses. Higher n-alkanes values were found in the High Salinity Shelf Waters (HSSW), lower n-alkanes values were found in the Antarctic Surface Waters (AASW) and Modified Circumpolar Deep Water (MCDW). The low PAHs concentration levels confirmed the still pristine character of the Antarctic environment. Neither particular trend in total PAHs concentrations along the water column and nor correlations with the most characteristic water masses of the investigated area of the Ross Sea were observed, except that total PAH higher concentrations were generally observed in correspondence of HSSW.

Anthropogenic carbon distribution in the Ross Sea, Antarctica

AbstractThe Ross Sea is an area of dense water formation within the Southern Ocean, hence it potentially plays an important role for anthropogenic CO2 sequestration. In order to estimate the penetration of anthropogenic carbon in the Ross Sea from total inorganic carbon (TCO2) measurements carried out in 2002–03 Antarctic Italian Expedition, we applied two independent models. Anthropogenic carbon was present throughout the water column. The highest concentrations were associated with the recently ventilated shelf waters, namely High Salinity Shelf Water (HSSW) and Ice Shelf Water (ISW), due to their recent contact with the atmosphere. The lowest concentrations were observed for Circumpolar Deep Water (CDW), due to its relatively older ventilation age. This water mass intrudes onto the shelf in some parts of the Ross Sea and hence is observed in the sampled section, where it is recognizable for its low O2 and high TCO2 concentrations. The overflow of the dense High Salinity Shelf Water out of the continental slope was observed in the area off Cape Adare. Since this recently formed shelf water contributes to the formation of the Antarctic Bottom Water (AABW), this process represents a pathway for anthropogenic carbon export down to the deep ocean.

Effect of the mesoscale hydrographic features on larval fish distribution across the shelf break of East China Sea

Surveys of fish larvae and oceanographic conditions were conducted along transects across the shelf break region in the East China Sea (ECS) in May 2001. The objective of this study was to investigate the distribution and assemblages of fish larvae across the shelf break region and their relationships to mesoscale hydrographic features. There was a warm surface streamer from the Kuroshio which extended toward the shelf region of the ECS; concurrently, we observed the intrusion of the less saline shelf water into the subsurface layer towards the offshore. In all 66 taxa (65 families and 1 order) of larvae were collected by oblique net tows using a bongo net, the larval fish density and number of families sampled were lower in the low-temperature area. Based on cluster analysis and environmental factor, two larval fish assemblages were identified: off-shelf/Kuroshio and shelf break. In shelf break assemblage, Auxis spp. and Diaphus spp. were abundant in the warm surface streamer. In contrast, Maurolicus japonicus, Synagrops spp., Bregmaceros sp. and Champsodon spp. were found in the off-shelf region where the offshore intrusion of less-saline water occurred. This different pattern of the horizontal distribution would reflect vertical distribution of the larvae in the water column. Moreover, copepod nauplii density was higher in the upper layer of the shelf region. Thus, dynamic interactions between the Kuroshio and shelf waters at the frontal boundary are concluded to potentially affect larval fish transport and prey availability.

The areas and ice production of the western and central Ross Sea polynyas, 1992–2002, and their relation to the B-15 and C-19 iceberg events of 2000 and 2002

For 1992–2002, the paper investigates the heat loss and area of three polynyas in the western and central Ross Sea. These are the Ross Sea Polynya (RSP) and the much smaller Terra Nova Bay and McMurdo Sound polynyas. The importance of these polynyas is that their associated salt rejection contributes to the formation of the High Salinity Shelf Water (HSSW) that is crucial to the Antarctic Bottom Water formation. The study divides into two parts, 1992–1999, when there was negligible iceberg activity, and 2000–2002, when major icebergs calved and interacted with the polynyas. To retrieve the ice thicknesses and heat fluxes within the polynyas, the paper uses an algorithm based on the ratio of the vertically and horizontally polarized Special Sensor Microwave/Imager (SSM/I) 25-km resolution 37-GHz channels, combined with meteorological data. Because of sidelobe contamination, the ice shelf and icebergs are masked. Our results show that for the polynyas, and consistent with other observations, their mean winter area is about 30,000 km 2 and their combined ice production is about 500 km 3y − 1 . We also find that the polynya ice production approximately equals the ice export. This is in contrast to the Weddell Sea, where the polynya ice production equals about 6% of the ice export. For the years 2000 and 2002, the calving of large icebergs directly affect the ice production by inhibiting the ice production off the shelf due to piling up of first year ice upwind of the bergs and by generating new polynyas downwind of the bergs. The period 1992–2001 exhibits an upward trend in polynya productivity. The decadal increase in the ice production suggests that the observed HSSW salinity decrease in the western Ross Sea is not due to the polynyas, but is rather due to a change in the properties of the water flowing into the Ross.

Possible source of the antarctic bottom water in the Prydz Bay Region

It has been inferred that the Prydz Bay region is one of the source regions of Antarctic Bottom Water (AABW) based on rather indirect evidence. In order to examine this inference, we investigate the hydrographic condition of the bay based mainly on XCTD data obtained during the Japanese Whale Research Program in the Antarctic (JARPA). The JARPA hydrographic data reveal Circumpolar Deep Water (CDW), which is a salty, warm water mass approaching the shelf break, and capture Modified CDW (MCDW) intruding into the shelf water. AABW production requires mixing of CDW and cold shelf water saltier than 34.6 psu, which is a saltier type of Low Salinity Shelf Water (LSSW). Saltier LSSW is observed near the bottom over the shelf, being mixed with MCDW. We further identify saltier LSSW near the shelf break. This saltier LSSW appears close enough to unmodified CDW to be mixed with it over the continental slope, indicating a possible source of AABW in Prydz Bay.

The evolution of density currents and nepheloid bottom layers in the Ross Sea (Antarctica)

In this study we have analyzed the thermohaline, light transmission and particulate matter data, obtained in the western sector of the Ross Sea during the X Italian Expedition, for the purpose of investigating the evolution of the High Salinity Shelf Water in this area. In particular CTD data were used to estimate the baroclinic velocity field. Light transmission and total particulate matter data (from Niskin bottles mounted on a Carousel water sampler) were used to analyze the nepheloid layers and the evolution of the suspended sediments. This basin is characterized by a northward flow of very dense High Salinity Shelf Water ( 1.95°C, S 34.90), much colder than the incoming Circumpolar Deep Water ( 1.20°C, S 34.70). We obtained a scenario in which the High Salinity Shelf Water interacts with the Circumpolar Deep Water along the Antarctic Slope Front, and deviates from its geostrophic equilibrium. Interestingly, this cold dense water mixes with Circumpolar Deep Water at the shelf break and flows downward until it seems to disappear. Below this cold flow, a thin turbulent current has been observed, again moving northward with a high velocity 0.2–1.0 m s . This thin flow also contains high concentration of suspended matter produced by the interaction of the dense water and the bottom sediments. The various elementary mechanisms ruling the dynamics of such down-flows, namely the effects of topographic irregularities, bottom friction, Ekman benthic boundary layers or the effect of the variability of the Antarctic Circumpolar Current, which can push offshore the dense water, are discussed in this paper.

Chlorophyll‐a variability off Patagonia based on SeaWiFS data

Seasonal to interannual variability of satellite derived chlorophyll‐a over the Patagonia shelf and shelf break in the western South Atlantic are studied based on 7 years of ocean‐color data (1998–2004) from the Sea‐Viewing Wide Field‐of‐View Sensor (SeaWiFS). Strong chlorophyll‐a seasonal variability (>4 mg m−3) is observed compared to the open ocean (<1.5 mg m−3). North of 45°S, chlorophyll‐a blooms initiate in early austral spring (September and October), while south of 45°S blooms begin in late spring to early summer (November through January). The spring maximum (>3.5 mg m−3) extends from the midshelf to the shelf break between 37°S and 44°S and southward to 51°S along a narrow shelf break band. In summer the shelf break maximum persists from 37°S to 51°S, and two inner‐shelf blooms develop off Valdés Peninsula and along a near‐coastal band between 46°S and 52°S (>3 mg m−3). Chlorophyll‐a concentrations in the northern midshelf sharply decay in late spring, reaching lowest concentrations in summer (February and March) and a secondary maximum in early winter (June). Though all regions present substantial interannual variations, the bloom locations are stable. The shelf break maximum is located inshore of the front between the low salinity shelf waters and the cold, salty, and nutrient‐rich Malvinas Current waters. The inner shelf maxima are offshore of fronts separating well‐mixed coastal waters from the stratified midshelf. North of 41°S the midshelf bloom is also associated to a bottom trapped thermal front. Thus, all the high chlorophyll‐a regions are associated to well‐defined fronts.

Pacific ventilation of the Arctic Ocean's lower halocline by upwelling and diapycnal mixing over the continental margin

Pacific winter waters, a major source of nutrients and buoyancy to the Arctic Ocean, are thought to ventilate the Arctic's lower halocline either by injection (isopycnal or penetrative) of cold saline shelf waters, or by cooling and freshening Atlantic waters upwelled onto the shelf. Although ventilation at salinity (S) > 34 psu has previously been attributed to hypersaline polynya waters, temperature, salinity, nutrient and tracer data suggest instead that much of the western Arctic's lower halocline is in fact influenced by a diapycnal mixing of Pacific winter waters (with S ∼ 33.1 psu) and denser eastern Arctic halocline (Atlantic) waters, the mixing taking place possibly over the northern Chukchi shelf/slope. Estimates from observational data confirm that sufficient quantities of Atlantic water may be upwelled to mix with the inflowing Pacific waters, with volumes implying the halocline over the Chukchi Borderland region may be renewed on timescales of order a year.

Variability of dense water formation in the Ross Sea

This paper presents results from a model study of the interannual variability of high salinity shelf water (HSSW) properties in the Ross Sea. Salinity and potential temperature of HSSW formed in the western Ross Sea show oscillatory behaviour at periods of 5–6 and 9 years superimposed on long-term fluctuations. While the shorter oscillations are induced by wind variability, variability on the scale of decades appears to be related to air temperature fluctuations. At least part of the strong decrease of HSSW salinities deduced from observations for the period 1963–2000 is shown to be an aliasing artefact due to an undersampling of the periodic signal. While sea ice formation is responsible for the yearly salinity increase that triggers the formation of HSSW, interannual variability of net freezing rates hardly affects changes in the properties of the resulting water mass. Instead, results from model experiments indicate that the interannual variability of dense water characteristics is predominantly controlled by variations in the shelf inflow through a sub-surface salinity and a deep temperature signal. The origin of the variability of inflow characteristics to the Ross Sea continental shelf can be traced into the Amundsen and Bellingshausen Seas. The temperature anomalies are induced at the continental shelf break in the western Bellingshausen Sea by fluctuations of the meridional transport of circumpolar deep water with the eastern cell of the Ross Gyre. In the Amundsen Sea, upwelling due to a persistently cyclonic wind field carries the signal into the surface mixed layer, leading to fluctuations of the vertical heat flux, anomalies of brine release near the sea ice edge, and consequently to a sub-surface salinity anomaly. With the westward flowing coastal current, both the sub-surface salinity and deep temperature signals are advected onto the Ross Sea continental shelf. Convection carries the signal of salinity variability into the deep ocean, where it interacts with modified circumpolar deep water upwelled onto the continental shelf as the second source water mass of HSSW. Sea ice formation on the Ross Sea continental shelf thus drives the vertical propagation of the signal rather than determining the signal itself.

Columbia River plume fronts. I. Hydrography, zooplankton distribution, and community composition

Well-defined fronts develop at the leading edge of the Columbia River (USA) plume. Convergent flow at these frontal boundaries may concentrate zooplanktonic organisms, which may in turn increase local prey availability to planktivorous fishes. In May 2001 and 2002, we compared the density, biomass and community structure of planktonic and neustonic zooplankton among plume fronts, low-salinity plume waters, and within the more saline, coastal marine waters. Fronts were characterized by distinct color discontinuities and high wave energy and were usually accom- panied by foam and flotsam. The surface manifestation of the fronts was narrow and formed a thin lens of warm, low-salinity water overlying colder and more saline shelf waters. Overall, neither zoo- plankton nor neuston densities were higher in frontal regions. However, some zooplankton taxa were more abundant at fronts, and plankton biomass was 4 to 47 times higher in the frontal regions than in the neighboring plume and more oceanic shelf waters. The zooplankton community in the front habi- tat was distinct, particularly in the near-surface neuston, and was comprised of more surface-oriented organisms compared to the adjacent ocean and plume waters. We conclude that convergence zones at frontal regions at the leading edge of the Columbia River plume concentrate organisms that, either through active swimming or positive buoyancy, are maintained near the surface. Time scales of these fronts are much shorter than generation times in these organisms and therefore we believe that the observed changes in biomass and community composition in the front habitat are due to physical concentrating mechanisms and not to in situ growth. Increased zooplankton biomass at plume fronts may provide a unique and valuable food resource for planktivorous fishes, including juvenile salmonids as they transition from freshwater to the ocean environment.

Distribution of dissolved organic matter in the eastern Bering Sea, Chukchi Sea (Barrow Canyon) and Beaufort Sea

The distribution of dissolved organic carbon (DOC) in the western Arctic Ocean is greatly influenced by conservative riverine DOC flux into the northern Bering Sea, Bering Strait and Beaufort Sea, as indicated by an inverse correlation with salinity. Based on the relations between DOC, salinity and seawater temperature, several water masses could be identified. These included riverine water, ice‐melt water, surface mixed water, cold and saline shelf water, and Atlantic Ocean water. High concentrations of chlorophyll a and DOC were found in some parcels of dense shelf water in Barrow Canyon. In addition, labile DOC compounds, such as polyunsaturated fatty acids (PUFA), were found in the dense shelf water, suggesting the dense shelf water contains a product (marine organic matter) of the biological CO2 pump.

Atlantic sources of the Arctic Ocean surface and halocline waters

Data obtained during the last 20 years from selected hydrographic stations throughout the Arctic Ocean basins and at the continental slopes and northern parts of the surrounding shelf seas are examined to estimate the contribution of Atlantic water to the upper part of the Arctic Ocean water column, and to follow the circulation of the Atlantic derived halocline waters around the Arctic Ocean basins. A substantial fraction of the Atlantic water entering the Arctic Ocean in the two inflow branches, the Fram Strait branch and the Barents Sea branch, is transformed into less dense waters. The inflow through Fram Strait encounters and melts sea ice. Its upper part becomes less saline, and in winter, ice formation homogenizes this low salinity upper part into a winter mixed layer, which follows the boundary flow eastward. The inflow over the Barents Sea mainly becomes colder, less saline and denser due to cooling and net precipitation, but melting of sea ice also here creates a less dense upper layer, which is subsequently homogenized by haline convection. Both these components enter the Nansen Basin via the St. Anna Trough and flow eastward along the Siberian continental slope. A third component of the Barents Sea inflow, mainly comprising Norwegian Coastal Current water, remains on the shelf, where it absorbs the runoff from the large Siberian rivers and evolves into low salinity shelf water. This part continues as far east as the Laptev Sea before a major inflow to the deep Arctic Ocean basins occurs. Winter convection, which in most of the Nansen Basin extends to the Atlantic layer, then becomes limited to the injected low salinity shelf water, and the more saline upper layers of the Fram Strait and the Barents Sea branches are transformed into halocline waters. The Fram Strait branch supplies the halocline water of the Amundsen, Makarov and part of the Canada basins, while the upper part of the Barents Sea branch, initially confined to the Siberian continental slope, becomes the main source of the lower halocline below the Pacific water in the Canada Basin beyond the Chukchi Cap. Less dense Pacific water close to the North American continent prevents the Atlantic derived upper layers from fl owing through the Canadian Arctic Archipelago and their main exit is Fram Strait. Only some of the Barents Sea branch halocline water passes through Nares Strait and may occasionally renew the deep and bottom waters of Baffin Bay.

Atlantic sources of the Arctic Ocean surface and halocline waters

Data obtained during the last 20 years from selected hydrographic stations throughout the Arctic Ocean basins and at the continental slopes and northern parts of the surrounding shelf seas are examined to estimate the contribution of Atlantic water to the upper part of the Arctic Ocean water column, and to follow the circulation of the Atlantic derived halocline waters around the Arctic Ocean basins. A substantial fraction of the Atlantic water entering the Arctic Ocean in the two inflow branches, the Fram Strait branch and the Barents Sea branch, is transformed into less dense waters. The inflow through Fram Strait encounters and melts sea ice. Its upper part becomes less saline, and in winter, ice formation homogenizes this low salinity upper part into a winter mixed layer, which follows the boundary flow eastward. The inflow over the Barents Sea mainly becomes colder, less saline and denser due to cooling and net precipitation, but melting of sea ice also here creates a less dense upper layer, which is subsequently homogenized by haline convection. Both these components enter the Nansen Basin via the St. Anna Trough and flow eastward along the Siberian continental slope. A third component of the Barents Sea inflow, mainly comprising Norwegian Coastal Current water, remains on the shelf, where it absorbs the runoff from the large Siberian rivers and evolves into low salinity shelf water. This part continues as far east as the Laptev Sea before a major inflow to the deep Arctic Ocean basins occurs. Winter convection, which in most of the Nansen Basin extends to the Atlantic layer, then becomes limited to the injected low salinity shelf water, and the more saline upper layers of the Fram Strait and the Barents Sea branches are transformed into halocline waters. The Fram Strait branch supplies the halocline water of the Amundsen, Makarov and part of the Canada basins, while the upper part of the Barents Sea branch, initially confined to the Siberian continental slope, becomes the main source of the lower halocline below the Pacific water in the Canada Basin beyond the Chukchi Cap. Less dense Pacific water close to the North American continent prevents the Atlantic derived upper layers from fl owing through the Canadian Arctic Archipelago and their main exit is Fram Strait. Only some of the Barents Sea branch halocline water passes through Nares Strait and may occasionally renew the deep and bottom waters of Baffin Bay.

Intrusion of less saline shelf water into the Kuroshio subsurface layer in the East China Sea

Intrusion of less saline shelf water into the Kuroshio subsurface layer in the East China Sea

Intrusion of Less Saline Shelf Water into the Kuroshio Subsurface Layer in the East China Sea

The possible origin and cause of the less saline shelf water detected in the Kuroshio subsurface layer around the shelf edge of the East China Sea are investigated using observational results obtained in May 1998–2001 in conjunction with a dataset archived by Japan Oceanographic Data Center and a numerical model. The observations show that subsurface intrusions of less saline water are always detected in May in layers above 24.5σθ isopycnal surface, and that salinity inversions (i.e., areas in which the less saline water lies beneath the saline water) are detected around the trough of the Kuroshio frontal eddy (or wave). Analyses of the archived dataset reveal that the isopycnal surface of 24.5σθ is the deepest layer of the Kuroshio pycnocline outcropping to the sea surface on the shallow shelf in early spring. Outcropping isopycnals above 24.5σθ encounter a less saline water plume originating from the Changjiang, especially in the western East China Sea. Thereafter, the less saline water moves along isopycnal layers and reaches the Kuroshio front around the shelf edge. Numerical models demonstrate that, when the frontal wave captures the less saline water, the shelf water takes the form of a salinity inversion in the trough because isohalines in the frontal wave have a phase lag between the upper and lower layers in consequence of the baroclinic instability.

A model of the plume front of the Pearl River Estuary, China and adjacent coastal waters in the winter dry season

The Princeton Ocean Model was employed for a detailed examination of the plume front dynamics of the Pearl River Estuary (PRE), China, and the small scale circulation associated with the plume front in the dry season during the winter. In general, the plume front in the PRE is formed by the salinity gradient between the riverine water and the higher salinity shelf waters. Although the basic features in the deeper waters of the plume front of the PRE are similar with respect to tidal variations and, wind and river discharge, both the tide and river discharge affect the subsurface front, while these dynamic factors modify the surface features of the plume front.A two-layer circulation in the vertical occurs within the plume front, while at the same time a horizontal circulation converges in the plume frontal zone. The density-driven current that is associated with the frontal dynamics plays a dominant role in modifying the dynamic behavior (both the strength and the scale) of the circulation. Basically, the small scale circulation associated with the plume front dynamics dominates the estuarine dynamics as well as the dynamic behavior of the western coastal part of the plume front. Moreover, most of the diluted water is transported along the plume front from the estuary to the western coastal region due to the fact that most of the water converges on two sides of the plume front. The sub-tidal current plays an important role in transporting suspended substances along the plume front during a spring tide due to the non-linear effect of the tide on the heterogeneous density field and on the topography.

Downslope flow observations near Cape Adare shelf-break

The analysis of two high resolution hydrological datasets acquired during the 1997 and 2001 summers across the Antarctic continental shelf-break near Cape Adare (Ross Sea) is presented. The main focus of these cruises was the investigation of the overflow of the High Salinity Shelf Water (HSSW). This dense and salty water mass forms along Victoria Land and flows northward, descending the slope near Cape Adare. Water types characterizing the study area are detected through vertical salinity profiles and by the horizontal distributions of the temperature and salinity. Temperature and salinity hydrological sections obtained by means of objective analysis method well describe the water masses interactions at the shelf/slope edge. The 1997 dataset shows evidence of a strong HSSW signature on the slope, but it is difficult to quantify the spatial scales involved in the spreading mechanism, because the overflow takes place at the edge of the investigation area. The 2001 data, collected at the same position with improved spatial and temporal resolution, clearly indicates the absence of a “true” HSSW downslope process. Even though no estimation of the amount of downslope flow can be given at present due to the resolution of the available dataset, it is possible to get a better phenomenological picture of the process by comparing the two years.

Summertime water masses off the northern Larsen C Ice Shelf, Antarctica

We report on oceanographic observations made at the northern end of Larsen C Ice Shelf in the western Weddell Sea. It appears that the Larsen C continental shelf is flushed not by High Salinity Shelf Water from the southern continental shelf, but by Modified Weddell Deep Water (MWDW) flowing across the shelf break. MWDW is observed at the ice front, having tracked west along the northward facing slopes of depressions that reach to the shelf break. Ice Shelf Water observed near the ice front is not, however, derived from MWDW directly, but from MWDW pre‐conditioned by winter cooling and by salinification from sea ice production. If the ice shelf base generally is being melted only by pre‐conditioned MWDW, then, contrary to recent suggestions, changes in the temperature of the deep Weddell Sea are unlikely to have a major impact on melt rates at the base of Larsen C Ice Shelf.