Western Shelf Water Research Articles

Assessment of an ocean-ecosystem model in simulating the Indian coastal marine ecosystem dynamics

ABSTRACT This study describes an assessment of an ocean-ecosystem model in simulating marine ecosystem dynamics in the Indian coastal waters. Long-term sustained in-situ observations of temperature, salinity, chlorophyll-a and dissolved oxygen (DO) collected in the coastal waters of India, and ship-based observations are used for this assessment. The model captures observed trend of temperature, salinity and chlorophyll-a with high correlation in both eastern and western shelf waters except for salinity and DO along west and DO along east coast. The model performs very well in simulating the Indian coastal shelf ecosystem dynamics. The seasonal occurrence of prominent phytoplankton bloom in the central-east coast during pre-monsoon, south-west coast during monsoon and north-west coast during post-monsoon is realistically reproduced by the model. The model also reproduces the seasonal presence of significantly low DO content in the upwelled water at a shallow depth leading to coastal hypoxia in the south-west and central-east coast of India during summer monsoon. A fine-tuned model is useful in understanding better Indian coastal shelf ecosystem and predicting future changes in time and space, like the occurrence of coastal hypoxia or anticipating phytoplankton blooms. Such information is useful for predicting potential fishing grounds in coastal waters and fisheries management.

Microzooplankton in the coastal Gulf of Alaska: Regional, seasonal and interannual variations

Microzooplankton communities in the coastal Gulf of Alaska (CGOA) were studied during two contrasting years: 2011, with a greatly reduced spring phytoplankton bloom, and 2013, with a robust spring bloom. Other sampling contrasts were season (spring, summer, fall) and region (eastern versus western shelf waters). Ciliates and dinoflagellates comprised nearly all microzooplankton in the ≥ 15 µm size class. Many of the strongest contrasts in the biomass and taxonomic composition of the microzooplankton community were regional. The east had generally lower microzooplankton biomass levels and a greater proportion of ciliates than the west, even in the face of basin-wide seasonal and interannual contrasts. This difference is likely a consequence of the narrower shelf in the east, which leads to a lower productivity environment. Interannual differences in spring bloom intensity were reflected in microzooplankton biomass (higher in spring 2013, especially in the east), while interannual differences in taxonomic composition persisted throughout the year, with a greater representation of ciliates in 2011. Ciliate dominance could reflect adaptations to lower productivity conditions, with many of the largest taxa likely retaining chloroplasts as a strategy (mixotrophy) for survival during times of prey scarcity. Microzooplankton: phytoplankton biomass ratios varied widely over time and space. These ratios indicate that lower productivity regions (east) and seasons (summer) also tend to be locations and times of reduced trophic transfer efficiency from phytoplankton to ciliates and dinoflagellates. Ciliates and dinoflagellates can be preferred prey of mesozooplankton, including dominant CGOA copepod species. Thus multiple mechanisms conspire to reduce the flow of matter and energy to higher trophic levels in low productivity locations and time periods in the CGOA.

The seasonal evolution of shelf water masses around Bouvetøya, a sub-Antarctic island in the mid-Atlantic sector of the Southern Ocean, determined from an instrumented southern elephant seal

Our study makes use of a fortuitous oceanographic data set collected around the remote sub-Antarctic island of Bouvetoya by a conductivity–temperature–depth recorder (CTD) integrated with a satellite-relayed data logger deployed on an adult female southern elephant seal ( Mirounga leonina ) to describe the seasonal evolution of the western shelf waters. The instrumented seal remained in waters over the shelf for 259 days, collecting an average of 2.6 (±0.06) CTD profiles per day, providing hydrographic data encompassing the late austral summer and the entire winter. These data document the thermal stratification of the upper water layer due to summer surface heating of the previous year’s Antarctic Surface Water, giving way to a cold subsurface layer at about 100 m as the austral winter progressed, with a concomitant increase in salinity of the upper layer. Upper Circumpolar Deep Water was detected at a depth of approximately 200 m along the western shelf of Bouvetoya throughout the year. These oceanographic data represent the only seasonal time series for this region and the second such animal–instrument oceanographic time series in the sub-Antarctic domain of the Southern Ocean. Keywords: Biotelemetry; diving; elephant seal; oceanography; marine predators; CTD-SRDL. (Published: 27 October 2016) To access the supplementary material for this article, please see supplementary files in the column to the right (under Article Tools). Citation: Polar Research 2016, 35 , 28278, http://dx.doi.org/10.3402/polar.v35.28278

Internal tides and baroclinicity in the southern Weddell Sea: 1. Model description

Near the continental shelf break in the southern Weddell Sea, Warm Deep Water and Western Shelf Water meet. Mixing mechanisms, such as internal tides, have the potential to mix these water masses and form Antarctic Bottom Water. A modified version of the Princeton Ocean Model was utilized to investigate the internal tidal fields generated by the interaction of the M2 barotropic tide with topography for transects across the continental shelf and slope in the southern Weddell Sea. Internal tides were generated over the upper continental slope as predicted by linear internal wave theory. Although the essentially two‐dimensional domain resulted in differences between the model elevations and the observations exceeding the observational uncertainties, the cross‐slope velocities agreed well with differences less than the uncertainties for 78% of the existing observations.

Isotope data from Ice Station Weddell: Implications for deep water formation in the Weddell Sea

Helium isotope data (3He/4He ratios and 4He concentrations) and H218O/H216O ratios obtained from stations occupied during the drift of Ice Station Weddell (February to June 1992) are used, together with hydrographic data, to study formation of deep and bottom water in the western Weddell Sea. The data indicate deep and bottom water formation along the entire track of the ice station (71.4 to 65.8°S, ≈53°W). Ice Shelf Water (ISW) seems to contribute significantly to the formation of Weddell Sea Deep Water (WSDW) and Weddell Sea Bottom Water (WSBW) in the southern part of the drift track. Toward the north, the fraction of ISW contained in WSDW/WSBW decreases. This trend is overlaid by high ISW fractions in the deep and bottom waters found in the vicinity of the Larsen Ice Shelf. The fraction of Western Shelf Water (WSW) in WSBW shows the opposite trend, increasing from south to north. The combined fraction of ISW and WSW in waters with potential temperatures below 0°C is about 20%, corresponding to a roughly 200 m thick layer. Overall, WSW seems to contribute approximately 2 to 3 times more water than ISW to the water column below the 0°C isotherm. Using the estimated flow of ISW over the sill north of the Filchner Depression of 1 Sv [Foldvik et al., 1985a] together with the ratio of WSW plus Winter Water (WW) to ISW, we calculate a value of about 5 Sv for the formation rate of WSBW with a potential temperature of −0.7°C. About one third of this flux represents near‐surface waters (WSW/WW) which have recently been equilibrated with the atmosphere, whereas pure ISW contributes about 10%.

Temperature variability beneath Ronne Ice Shelf, Antarctica, from thermistor cables

Thermistor cables have been deployed at two sites beneath Ronne Ice Shelf, Antarctica. One site is to the east of a submarine ridge that delineates the eastern boundary of the Ronne Depression, and the other is 100 km to the north, above the eastern slope of the depression. Long records from the cables (up to 22 months) indicate a large difference in the temperature variability at the two sites, being an order of magnitude greater in the Ronne Depression (site 2). Although the records appear otherwise similar, there is no significant correlation between them. The high variability in the site 2 record has allowed the construction of a simple descriptive model of the local oceanographic regime. Winter freezing in the open water north of the ice front generates Western Shelf Water (WSW), a type of High Salinity Shelf Water, which travels southwest beneath the ice shelf, appearing at site 2 as a slope‐trapped current at the bottom of the water column. Baroclinic instability in the flow manifests itself in the site 2 temperature record as oscillations on time scales of 5 to 15 days. The disturbances cause a periodic east‐west advection of water masses across the Ronne Depression. Site 2 is on the eastern slope of the depression, where the wave‐induced eastward motion forces Ice Shelf Water to rise, resulting in periodic ice‐platelet formation in the water column, as surmised from conductivity‐temperature‐depth measurements at the site. The depth of the WSW layer decreases by 40 to 60 m during a 100‐day period, starting some 4 months after the beginning of the summer. Assuming an absence of significant WSW production during the summer, the 4‐month delay implies a minimum average speed of WSW flow of about 0.02 m s−1. The WSW flux into the Ronne Depression is estimated at 3 × 105 m3s−1.

A model of ice shelf‐ocean interaction with application to the Filcher‐Ronne and Ross Ice Shelves

A simple analytical model has been developed to study the formation of Ice Shelf Water (ISW). ISW is assumed to flow as a buoyancy‐driven layer underneath the ice shelf. A relation between potential temperature and salinity in the ISW layer is calculated from the mass and energy balance. This temperature‐salinity relation is shown to depend only on the temperature and the salinity of the source water mass and to be practically independent of entrainment and melt rates. The model results are obtained without making any assumptions about entrainment and melt rates. The model is in good agreement with observations under the Ronne Ice Shelf, and it indicates that ISW in the Filchner Depression is formed from Western Shelf Water (WSW) with salinity higher than 34.75 practical salinity units. Such high‐salinity water is only observed in the Ronne Depression in the western part of the continental shelf. This implies a circulation of WSW, under the Filchner‐Ronne Ice Shelf, from the Ronne Depression into the Filchner Depression. Similarly, the model shows that the ISW observed under J9 at the Ross Ice Shelf has been formed from Low Salinity Shelf Water (LSSW) from the eastern parts of the Ross Sea continental shelf. LSSW must therefore circulate under the eastern parts of the Ross Ice Shelf.

The oceanic environment beneath the northwest Ronne Ice Shelf, Antarctica

Oceanographic data have been obtained from beneath the Ronne Ice Shelf at a site on the southeastern side of a sea-floor trough, the Ronne Depression. The data consist of 5 d of conductivity temperature depth (CTD) profiling and a long-term temperature record from a thermistor cable. The water column was found to be composed of two layers: a cold buoyant layer of lce Shelf Water (ISW) overlying a layer of unmodified Western Shelf Water (WSW).A change in the water column was observed on the last day of profiling, the WSW layer thinning, a cold intrusion appearing directly above the WSW and the ISW becoming colder. In addition, on three profiles the ISW cooled further and increased in salinity, becoming apparently statically unstable. The temperature record from the thermistor cable confirms that the ISW layer occasionally becomes colder. with greater variation in temperature than seen on the CTD profiles. These low temperatures and high salinities arc interpreted as indicating that water containing ice crystals in suspension has been advected beneath the site.

The oceanic environment beneath the northwest Ronne Ice Shelf, Antarctica

Oceanographic data have been obtained from beneath the Ronne Ice Shelf at a site on the southeastern side of a sea-floor trough, the Ronne Depression. The data consist of 5 d of conductivity temperature depth (CTD) profiling and a long-term temperature record from a thermistor cable. The water column was found to be composed of two layers: a cold buoyant layer of lce Shelf Water (ISW) overlying a layer of unmodified Western Shelf Water (WSW). A change in the water column was observed on the last day of profiling, the WSW layer thinning, a cold intrusion appearing directly above the WSW and the ISW becoming colder. In addition, on three profiles the ISW cooled further and increased in salinity, becoming apparently statically unstable. The temperature record from the thermistor cable confirms that the ISW layer occasionally becomes colder. with greater variation in temperature than seen on the CTD profiles. These low temperatures and high salinities arc interpreted as indicating that water containing ice crystals in suspension has been advected beneath the site.

The oceanic environment beneath the northwest Ronne Ice Shelf, Antarctica

Oceanographic data have been obtained from beneath the Ronne Ice Shelf at a site on the southeastern side of a sea-floor trough, the Ronne Depression. The data consist of 5 d of conductivity temperature depth (CTD) profiling and a long-term temperature record from a thermistor cable. The water column was found to be composed of two layers: a cold buoyant layer of lce Shelf Water (ISW) overlying a layer of unmodified Western Shelf Water (WSW). A change in the water column was observed on the last day of profiling, the WSW layer thinning, a cold intrusion appearing directly above the WSW and the ISW becoming colder. In addition, on three profiles the ISW cooled further and increased in salinity, becoming apparently statically unstable. The temperature record from the thermistor cable confirms that the ISW layer occasionally becomes colder. with greater variation in temperature than seen on the CTD profiles. These low temperatures and high salinities arc interpreted as indicating that water containing ice crystals in suspension has been advected beneath the site.

Temperature and salinity beneath Ronne Ice Shelf, Antarctica

Salinity and temperature measurements have been made beneath Ronne Ice Shelf, Antarctica. Access to the seawater was gained by hot‐water drilling through 562 m of ice at a site 300 km from the ice front. The ice column is composed of 516 m of meteoric‐origin ice, underlain by 31 m of consolidated saline ice, with a further 15 m of unconsolidated slush at the base. The 360‐m‐deep water column beneath the ice shelf consists broadly of a 210‐m layer of Ice Shelf Water (ISW) at a potential temperature of −2.30°C and salinity 34.53, overlying a 100‐m‐thick layer of modified Western Shelf Water (−2.03°C, 34.64). The layers are separated by a weak 50‐m‐thick pycnocline. Isotopic analyses of water samples support this interpretation of the water types. Comparison of the data with published oceanographic observations from the shore lead indicate that the source of the water is either the western Berkner shelf or north of the ice front in the Ronne Depression. The measurements from the drill site broadly match predictions from a simple plume model of the sub‐ice‐shelf water circulation. In that model the basal slope of the ice shelf plays a central role in determining the properties of the ISW plume. With the exception of the upper few tens of meters the temperature and salinity of the entire water column vary by about 0.04°C and 0.03 on tidal timescales, and there is evidence for a longer‐term drift, presumably connected with shifts in the larger‐scale circulation. There is also much variability from internal wave activity. The salinity and deuterium budgets indicate that the meltwater fraction in the ISW observed at the drill site was between 5.3 and 6.5‰, in reasonable agreement with values previously found for ISW in the open ocean.

Chlorofluorocarbon evidence for rapid ventilation of the Ross Sea

Chlorofluorocarbon (CFC)-12 and -11 (CF 2Cl 2 and CFCl 3) measurements were made in seawater on the Ross Sea continental shelf and adjacent slope region in 1984. Concentrations of CFC-12 and CFC-11 in Ross Sea continental shelf water averaged nearly half that of saturated surface water. Circumpolar Deep Water within 50 km of the Ross Sea continental shelf also contained measureable CFC-12 and CFC-11, but an order of magnitude less than shelf waters. CFC-12 and CFC-11 concentrations in the deep water overlying the continental slope increased with depth, indicating recent ventilation and bottom water formation near the continental shelf. Several water masses on the continental shelf that are commonly distinguished on the basis of temperature and salinity characteristics also varied in CFC content, and thus in their modes and rates of ventilation and renewal. A time-dependent model reproducing the 1984 sub-surface shelf water CFC concentrations demonstrates the relative importance of mixed layer entrainment, gas exchange through leads in the winter sea ice field, and mixing with source waters derived from the Circumpolar Deep Water. Model results show that mixed layer entrainment at the beginning of winter is the dominant process ventilating sub-surface shelf water in the eastern Ross Sea, while western shelf waters also require significant gas exchange during winter. Shelf water residence time can only be constrained by the model and available data to 10 years, but most probable values are ∼2.5 years in the eastern Ross Sea and ∼4 years in the western Ross Sea. CFC concentrations in water which has circulated beneath and has been modified by the Ross Ice Shelf indicate that the transformation time from High Salinity Shelf Water to Ice Shelf Water can be as short as 3.5 years. With reasonable oxygen consumption and nutrient regeneration rates, the balance of ventilation and mixing processes that reproduced observed shelf water CFC-12 concentrations also can account for observed oxygen and nitrate levels, if the western surface waters are undersaturated by ∼10% at entrainment.

Variability Of Thermohaline Circulation Under An Ice Shelf

The production of Antarctic Bottom Water is mainly influenced by Ice Shelf Water, which is formed through the modification of shelf water masses under huge ice shelves. To simulate this modification a two-dimensional thermohaline circulation model has been developed for a section perpendicular to the ice-shelf edge. Hydrographic data from the Filchner Depression enter into the model as boundary conditions. In the outflow region they also serve as a verification of model results. The standard solution reveals two circulation cells. The dominant one transports shelf water near the bottom toward the grounding line, where it begins to ascend along the inclined ice shelf. The contact with the ice shelf causes melting with a maximum rate of 1.5 m a−1 at the grounding line. Freezing and therefore the accumulation of “sea ice” at the bottom of the ice shelf occurs at the end of the melting zone at a rate on the order of 0.1 ma−1. Both rates are comparable with values estimated or predicted by models concerning ice-shelf dynamics. As one example of model sensitivity to changing boundary conditions, a higher sea-ice production in the southern Weddell Sea, as might be expected for a general climatic cooling event, is assumed. The resultant decrease/ increase in temperature/salinity of the inflow (Western Shelf Water) reduces the circulation under the ice shelf and therefore the outflow of Ice Shelf Water by 40%. The maximum melting and freezing rate decreases by 0.1 ma−1 and 0.01 m a−1, respectively. and the freezing zone shifts toward the grounding line by 100 km. In general the intensity of the circulation cells, the characteristics of Ice Shelf Water, the distribution of melting and freezing zones and the melting and freezing rates differ from the standard results with changing boundary conditions. These are the temperature and salinity of the inflow, the surface temperature at the top, and the extension and morphology of the ice shelf.

Variability Of Thermohaline Circulation Under An Ice Shelf

The production of Antarctic Bottom Water is mainly influenced by Ice Shelf Water, which is formed through the modification of shelf water masses under huge ice shelves. To simulate this modification a two-dimensional thermohaline circulation model has been developed for a section perpendicular to the ice-shelf edge. Hydrographic data from the Filchner Depression enter into the model as boundary conditions. In the outflow region they also serve as a verification of model results.The standard solution reveals two circulation cells. The dominant one transports shelf water near the bottom toward the grounding line, where it begins to ascend along the inclined ice shelf. The contact with the ice shelf causes melting with a maximum rate of 1.5 m a−1 at the grounding line. Freezing and therefore the accumulation of “sea ice” at the bottom of the ice shelf occurs at the end of the melting zone at a rate on the order of 0.1 ma−1. Both rates are comparable with values estimated or predicted by models concerning ice-shelf dynamics.As one example of model sensitivity to changing boundary conditions, a higher sea-ice production in the southern Weddell Sea, as might be expected for a general climatic cooling event, is assumed. The resultant decrease/ increase in temperature/salinity of the inflow (Western Shelf Water) reduces the circulation under the ice shelf and therefore the outflow of Ice Shelf Water by 40%. The maximum melting and freezing rate decreases by 0.1 ma−1 and 0.01 m a−1, respectively. and the freezing zone shifts toward the grounding line by 100 km.In general the intensity of the circulation cells, the characteristics of Ice Shelf Water, the distribution of melting and freezing zones and the melting and freezing rates differ from the standard results with changing boundary conditions. These are the temperature and salinity of the inflow, the surface temperature at the top, and the extension and morphology of the ice shelf.

Helium: a new tracer in Antarctic oceanography

The abyssal characteristics of the world oceans are strongly influenced by the northward propagation of Antarctic Bottom Water (AABW). An important source of AABW is Weddell Sea Bottom Water (WSBW), which is formed, in part, on the continental slope of the southern Weddell Sea1–3. The formation of WSBW on the continental slope is related to the floating ice shelves of the southern Weddell Sea (Filchner/Ronne Ice Shelves). Western Shelf Water (WSW) is modified under the ice shelves by cooling and admixture of melt water to form Ice Shelf Water (ISW), and a substantial part of the ISW flows over the sill that separates the Filchner Depression from the Weddell Sea and participates in the formation of WSBW4,5. The data reported here demonstrate that the water/ice interaction leads to a strong 4He-supersaturation of the ISW due to dissolution of air entrapped in the ice-shelf melt water. The 4He-supersaturation of the ISW can be used as a tracer of this water mass and also influences the 4He balance of the WSBW.

Physical oceanography studies in the Weddell Sea during the Norwegian Antarctic Research Expedition 1978/79

Hydrographic and current measurements obtained during the Norwegian Antarctic Research Expedition 1978/79 to the southern Weddell Sea are presented. Cold, dense Ice Shelf Water circulating under the floating ice shelves is observed to leave the shelf as a concentrated bottom flow. From moored current metres this discharge is estimated at 0.7. lo6 m3/s at -2.oC (one year average) and with no appreciable seasonal variation. This contribution to the Weddell Sea Bottom Water is clearly identified through extreme temperature gradients at our deepest stations (below 2500 m). The core of Weddell Deep Water shows a considerable (T ~ 0.5C) warming up since 1977, presumably due to the lack of polynya activity in the intervening period. Measurements in the coastal current at the ice shelf (70%. 2W) show step structures which are probably due to cooling and melting at the vertical ice barrier. Slight supercooling due to circulation under the ice shelf is also seen. The net effect of the ice shelf boundary seems to be a deep reaching cooling and freshening of the coastal current providing the low salinity. freezing point Eastern Shelf Water. This process is considered a preconditioning which enhances production of the saline Western Shelf Water which in turn is transformed to Ice Shelf Water.

Oceanographic conditions on the Weddell Sea Shelf during the German Antarctic Expedition 1979/80

Hydrographic (CTD), current and water level measurements obtained in the vicinity of the floating Ronne and Filchner Ice Shelves are presented. The distribution of Western Shelf Water (S > 34.7) and Ice Shelf Water (T<-1.9"C) are discussed. The general circulation in the area seems to consist of two large cyclonic gyres, one in the Filchner Depression and one north of the Ronne Ice Shelf. Each gyre shows a warm' (T ~ -1°C) southgoing flow of Modified Weddell Deep Water and a cold northward flow of Ice Shelf Water. The mean surface current was found to be 8cm/s towards the north-west along the barrier. The mean flow below the ice shelf shows significant components normal to the bamer, and mixing seems to be very efficient here. Well mixed layers down to more than 150 m were observed. North of Berkner Island the water level shows a typical mixed tide with tidal range -3 m. In the tidal currents the semidiurnal constituents dominate (-30 cm/s) and with the largest current components normal to the barrier.

Geochemical studies of the Weddell sea

The origin of Antarctic Bottom Water is discussed in terms of the distributions of a number of geochemical tracers in the major water masses of the Weddell Sea. Oxygen, phosphate, nitrate and total inorgabic carbon are shown to be negligibly altered by consumption or production during sub-surface circulation and mixing. All the conservative properties of Weddell Sea Bottom Water and Antarctic Bottom Water are explained as simple mixtures of Winter Water, Warm Deep Water, and Western Shelf Water. Silica is markedly non-conservative, showing enrichments up to ≈35 μM kg −1 which are due mainly to interactions with the bottom. The deuterium and oxygen-18 stable isotope data show that the high salinity of Western Shelf Water is principally the result of freezing rather than evaporation. The isotopic composition of Western Shelf Water also requires a significant admixture of melt-water from the base of the Filchner Ice Shelf, and mass-balance calculations linking the rate of shelf ice melting to the formation of bottom water give a production rate of about 5 × 10 6 m 3 s −1 for Weddell Sea Bottom Water with potentiatial −0.9°C, or about 8 × 10 6 m 3 s −1 in terms of classical Antarctic Bottom Water with a potential temperature of −0.4°C. Concentrations of the radioisotopes carbon-14 and tritium are exceptionally low in the Weddell Sea despite the fact that the CO 2 atmospheric exchange rate is comparable to the global average. The low values are seen to be the result of a short surface residence time, a large sub-surface mixing component, and exchange inhibition by sea ice especially during the winter. Unlike the average world ocean, where molecular exchange is about three times more important than precipitation in transporting atmospheric tritium to surface waters, about four times more tritium is added to the Weddell Sea by precipitation than by molecular exchange. The flux of new Weddell Sea Bottom Water based on the tritium data is estimated very roughly at about 3 × 10 6 m 3 s −1, or about 4.5 × 10 6 m 3 s −1 expressed in terms of classical Antarctic Bottom Water.

Mass-Balance Aspects of Weddell Sea Pack Ice

AbstractThe Weddell Sea pack ice undergoes several unique advance–retreat characteristics related to the clockwise transport in the Weddell Gyre, the physical setting for the pack ice, and the free boundary with the oceans to the north. From satellite-derived ice charts, the annual cycle of the pack ice advance and retreat is depicted. The Weddell pack advance is characterized by a strong east-moving component as well as the north advance seen in other regions such as East Antarctica.Physical characteristics of the pack ice at the summer minimum ice edge are presented. Indications are that deformation is a significant component of the ice accumulation, deformed ice accounting for c. 15 to 20% of the area covered in the year-round pack. Ablation characteristics are inferred from observations made during field work and from satellite imagery. These observations indicate that surface-melt ablation typically seen on Arctic pack is not seen on the Weddell pack inside the summer edge.Using the physical-property data and transport inferred from ship and iceberg drifts, a new annual ice accumulation η < 3 m is inferred over the continental shelf in the South compared to η < 2 m previously estimated (Gill, 1973). The implication is that salt flux into the ocean over the shelf may be significantly larger, thereby increasing the production of Western Shelf Water, a component of Antarctic Bottom Water.

Mass-Balance Aspects of Weddell Sea Pack Ice

AbstractThe Weddell Sea pack ice undergoes several unique advance–retreat characteristics related to the clockwise transport in the Weddell Gyre, the physical setting for the pack ice, and the free boundary with the oceans to the north. From satellite-derived ice charts, the annual cycle of the pack ice advance and retreat is depicted. The Weddell pack advance is characterized by a strong east-moving component as well as the north advance seen in other regions such as East Antarctica.Physical characteristics of the pack ice at the summer minimum ice edge are presented. Indications are that deformation is a significant component of the ice accumulation, deformed ice accounting forc. 15 to 20% of the area covered in the year-round pack. Ablation characteristics are inferred from observations made during field work and from satellite imagery. These observations indicate that surface-melt ablation typically seen on Arctic pack is not seen on the Weddell pack inside the summer edge.Using the physical-property data and transport inferred from ship and iceberg drifts, a new annual ice accumulationη< 3 m is inferred over the continental shelf in the South compared toη< 2 m previously estimated (Gill, 1973). The implication is that salt flux into the ocean over the shelf may be significantly larger, thereby increasing the production of Western Shelf Water, a component of Antarctic Bottom Water.