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Concept
Antarctic bottom water
Summary
The Antarctic bottom water (AABW) is a type of water mass in the Southern Ocean surrounding Antarctica with temperatures ranging from −0.8 to 2 °C (35 °F) and absolute salinities from 34.6 to 35.0 g/kg. As the densest water mass of the oceans, AABW is found to occupy the depth range below 4000 m of all ocean basins that have a connection to the Southern Ocean at that level.
The major significance of Antarctic bottom water is that it is the coldest bottom water, giving it a significant influence on large-scale movement in the world's oceans through thermohaline circulation.
Initially, AABW has a high oxygen content relative to the rest of the oceans' deep waters but this depletes over time. This early oxygen abundance comes from the precursor water mass of the AABW, which is cold, relatively salty and oxygen-rich dense shelf water (DSW) formed above Antarctica’s continental shelf by wintertime cooling and brine rejection. This water sinks at four distinct regions around the margins of the continent and forms the AABW; this process leads to ventilation of the deep ocean, or abyssal ventilation.
Antarctic bottom water is created in part due to the major overturning of ocean water.
Antarctic bottom water is formed in the Weddell and Ross Seas, off the Adélie Coast and by Cape Darnley from surface water cooling in polynyas and below the ice shelf. A unique feature of Antarctic bottom water is the cold surface wind blowing off the Antarctic continent. The surface wind creates the polynyas which opens up the water surface to more wind. This Antarctic wind is stronger during the winter months and thus the Antarctic bottom water formation is more pronounced during the Antarctic winter season. Surface water is enriched in salt from sea ice formation. Due to its increased density, it flows down the Antarctic continental margin and continues north along the bottom. It is the densest water in the free ocean, and underlies other bottom and intermediate waters throughout most of the southern hemisphere.
Official source
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