Antarctic Bottom Water
Antarctic Bottom Water (AABW) is the coldest and densest water mass in the global ocean. It forms around Antarctica and spreads northward along the sea floor into the Atlantic, Indian and Pacific basins, filling much of the deep ocean.
Antarctic Bottom Water (AABW) is the coldest and densest water mass in the global ocean. It forms around Antarctica and spreads northward along the sea floor into the Atlantic, Indian and Pacific basins, filling much of the deep ocean.
Formation: How Does Antarctic Water Get So Dense?
On the Antarctic continental shelf, especially in the Weddell and Ross Seas, winds blow newly formed sea ice away from the coast, exposing open water that freezes again. Freezing rejects salt into the water below, so the water becomes both very cold, near −1 °C, and very salty. The dense water pours off the shelf and sinks down the continental slope.
Global Role: What Does It Do in the Ocean?
AABW forms the lower limb of the overturning circulation, described in thermohaline circulation. As it spreads, it carries oxygen and dissolved carbon to the abyss and takes up heat slowly from above. It lies beneath North Atlantic Deep Water, which sinks in the other polar region.
Change: Is Bottom Water Shrinking?
Repeated ocean surveys show that AABW has warmed and shrunk in volume in recent decades, a trend linked to freshening and changes in sea ice and ice-shelf melt from the cryosphere. Because the deep ocean stores so much heat, such changes affect the response of the climate system over centuries. See physical oceanography.
Antarctic Bottom Water at a Glance
| Property | Value |
|---|---|
| Typical temperature | Near or below 0 °C |
| Formation sites | Weddell and Ross Seas, other Antarctic shelves |
| Position | Deepest layer of the global ocean |