Circumpolar deep water

Circumpolar Deep Water (CDW) is a designation given to the water mass in the Pacific and Indian oceans that essentially characterizes a mixing of other water masses in the region. A distinguishing characteristic is the water is not formed at the surface, but rather by a blending of other water masses, including the North Atlantic Deep Water (NADW), the Antarctic Bottom Water (AABW), and the Pacific Intermediate Water masses.

CDW, the greatest volume water mass in the Southern Ocean, is a mixture of NADW, AABW, and Antarctic Intermediate Water (AAIW), as well as recirculated deep water from the Indian and Pacific Oceans.

Because the CDW is a mix of other water masses, its temperature-salinity (TS) profile is simply 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. Circumpolar deep water is between 1–2 °C (34–36 °F) and has a salinity between 34.62 and 34.73 practical salinity units (PSU).[1][2]

In recent decades, hundreds of glaciers draining the Antarctic Peninsula (63° to 70°S) have undergone systematic and progressive change. These changes are widely attributed to rapid increases in regional surface air temperature, but it is now clear that this cannot be the sole driver. A strong correspondence has been discovered between mid-depth ocean temperatures and glacier-front changes along the approximately 1000-kilometer western coastline.[3]

In the south, glaciers that terminate in warm CDW have undergone considerable retreat, whereas those in the far northwest, which terminate in cooler waters, have not. Furthermore, a mid-ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat. The conclusion is that changes in ocean-induced melting are the primary cause of retreat for glaciers in this region.[3]