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| Weddell Sea Bottom Water | |
|---|---|
| Name | Weddell Sea Bottom Water |
| Type | Antarctic bottom water mass |
| Location | Weddell Sea, Southern Ocean |
| Depth | abyssal |
| Temperature | near-freezing |
| Salinity | high |
| Formation | dense shelf water cascading, polynyas |
| Key features | cold, saline, oxygen-rich, nutrient-bearing |
Weddell Sea Bottom Water is a dense, abyssal water mass formed in the Weddell Sea sector of the Southern Ocean that contributes to the cold bottom limb of the global ocean circulation. It is a major source of Antarctic Bottom Water that ventilates the deep Atlantic Ocean, Indian Ocean, and Pacific Ocean basins and interacts with Antarctic continental margins such as Antarctic Peninsula and Coats Land. Studies of its formation, properties, and variability involve expeditions like International Weddell Sea Project, institutions such as the Alfred Wegener Institute and British Antarctic Survey, and programs including the World Ocean Circulation Experiment and Southern Ocean Observing System.
Weddell Sea Bottom Water occupies the deepest layers of the Weddell Sea basin and adjacent abyssal plains, characterized by near-freezing temperatures and elevated salinities relative to overlying water masses like Weddell Sea Deep Water and Circumpolar Deep Water. Observations from cruises by RV Polarstern, RRS James Clark Ross, and ARA Bahía Paraíso show it is oxygen-rich owing to recent surface contact and mixing, while tracer studies using chlorofluorocarbons and radiocarbon tie it to convective events and dense shelf processes. The water mass influences bathymetric features such as the Filchner Trough and interacts with ice shelves like Filchner-Ronne Ice Shelf and Larsen Ice Shelf.
Formation occurs when cold, saline shelf waters overflow continental margins during polynya events (e.g., the Weddell Polynya) and cascade into the deep basin, a process documented by observational programs including ANTARES and modelling efforts by groups at Scripps Institution of Oceanography and Lamont–Doherty Earth Observatory. Dense water production links to katabatic winds descending from East Antarctica, interactions with sea-ice formation near the Maud Rise, and brine rejection under fast ice associated with pack-ice dynamics observed by NSF Antarctic Program. The newly formed bottom water spreads along abyssal contours, following pathways constrained by bathymetry near features like South Orkney Islands and exchanging with deep water masses transported by the Antarctic Circumpolar Current.
Typical temperatures approach the freezing point of seawater measured in studies by Sverdrup, with salinities elevated by brine rejection quantified in field campaigns by teams from Commonwealth Scientific and Industrial Research Organisation and University of Tasmania. Dissolved oxygen concentrations are high relative to aged deep waters, while nutrient and carbon inventories reflect recent contact with surface waters influenced by phytoplankton blooms and winter convection observed by research from Monash University and University of Cape Town. Chemical tracers such as stable isotopes of oxygen and boron, and transient tracers like sulfur hexafluoride, are used by laboratories at Woods Hole Oceanographic Institution and National Oceanography Centre to fingerprint source waters and mixing.
Weddell Sea Bottom Water feeds the lower limb of the global thermohaline circulation, contributing to the formation of Antarctic Bottom Water that ventilates the deep Atlantic Meridional Overturning Circulation and influences heat and carbon storage in distant basins studied by the Global Carbon Project. Its export pathways connect to major ocean basins recognized in mapping efforts by NOAA and UNESCO's Intergovernmental Oceanographic Commission, and its variability can alter abyssal stratification affecting climate teleconnections examined in IPCC assessments and coupled climate models developed at Hadley Centre and Max Planck Institute for Meteorology.
The production and modification of Weddell Sea Bottom Water are tightly coupled to sea-ice formation, polynyas, and ice-shelf basal melting under features such as the Ronne Ice Shelf and Ekström Ice Shelf. Processes like brine rejection during sea-ice growth and sub-ice-shelf freshwater inputs from glacier discharge influence density and circulation, documented by satellite missions including ICESat and CryoSat as well as airborne campaigns by NASA Operation IceBridge. Interactions affect grounding line dynamics of outlet glaciers like Pine Island Glacier analogues and are central to projections from Paleoclimate reconstructions and contemporary observations by the International Thwaites Glacier Collaboratory.
By ventilating abyssal habitats, Weddell Sea Bottom Water supplies oxygen and nutrients that sustain benthic communities observed by submersible surveys from National Geographic Society and benthic ecology programs at Smithsonian Institution. Its role in transporting dissolved inorganic carbon and influencing alkalinity affects carbon sequestration quantified by the Global Ocean Data Analysis Project and biogeochemical models at MIT. Exchanges between bottom water and continental margins drive bentho-pelagic coupling studied by marine biologists at University of British Columbia and influence distributions of deep-sea fauna such as echinoderms and sponges documented in biodiversity inventories by organizations like SCAR.
Long-term observation relies on hydrographic surveys, moorings, autonomous platforms (e.g., Argo floats adapted for polar use), and remote sensing used by programs like Southern Ocean Time Series. High-resolution numerical models implemented by NOAA Geophysical Fluid Dynamics Laboratory and the European Centre for Medium-Range Weather Forecasts simulate cascading, mixing, and export pathways, while data assimilation projects leverage datasets curated by PANGAEA and EMODnet. Ongoing interdisciplinary efforts combine field campaigns by USAP, technological advances from WHOI, and international collaborations through SCAR to resolve trends in formation rate, variability, and responses to anthropogenic climate forcing.