Circumpolar Deep Water (CDW) is a designation given to the water mass in the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

and Indian oceans that is a mixing of other water masses in the region. It is characteristically warmer and saltier than the surrounding water masses, causing CDW to contribute to the melting of

ice shelves An ice shelf is a large platform of glacial ice floating on the ocean, fed by one or multiple tributary glaciers. Ice shelves form along coastlines where the ice thickness is insufficient to Displacement (fluid), displace the more dense surround ...

in the

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

region.

Physical properties

CDW, the greatest volume water mass in the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the world ocean, generally taken to be south of 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is the seco ...

, includes the

North Atlantic Deep Water North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the ...

(NADW), the Antarctic Bottom Water (AABW), Antarctic Intermediate Water (AAIW), as well as recirculated deep water from the Indian and Pacific Oceans. A distinguishing characteristic of the CDW is that the water is not formed at the surface, but rather by a blending of other water masses. CDW sits at a depth of around 500 meters, approximately at the depth of the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...

. There are two types of CDW: Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW). UCDW originates in the Indian and Pacific Oceans and has lower oxygen levels and higher nutrients than LCDW. LCDW comes from

and has a higher salinity. In the Indian Ocean, CDW has a temperature of . In the Pacific Ocean, it is slightly colder with a temperature of . The

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

of CDW is 34.62 to 34.73 ‰. Because CDW is a mix of other water masses, its temperature-salinity (TS) profile is the point where the TS lines of the other water masses converge. TS diagrams refer to temperature and salinity profiles, which are one of the major ways water masses are distinguished from each other. The convergence of the TS lines thus proves the mixing of the other water masses.

Influence on Antarctic ecosystems and ice shelves

CDW plays an important role in the Antarctic Circumpolar Current (ACC) because it contributes to the melting of the base of ice shelves.{{Cite journal , last1=Thompson , first1=Andrew F. , last2=Speer , first2=Kevin G. , last3=Schulze Chretien , first3=Lena M. , date=2020-08-28 , title=Genesis of the Antarctic Slope Current in West Antarctica , url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL087802 , journal=Geophysical Research Letters , language=en , volume=47 , issue=16 , doi=10.1029/2020GL087802 , bibcode=2020GeoRL..4787802T , issn=0094-8276 Glaciers ending in CDW have melted considerably while glaciers in the northwest, with no CDW, have not. The CDW is salty and slightly above freezing temperature, which is warm compared to ice shelves. When the CDW flows upward onto the continental shelf and travels through the deep canyons, it reaches the underside of the ice shelves. The warmer water makes contact with the shelves, contributing to the ice shelf melting. Gradients around Antarctica formed between shelf water and CDW are called the Antarctic Slope Front. The CDW also plays an important role in supporting Antarctic ecosystems.

Upwelling Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted sur ...

of the CDW onto the Antarctic continental shelves brings heat and nutrients that support ecosystems along the west

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martin in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctica. ...

References

Water masses