PCMDI - IPCC

The Southern Ocean’s Subantarctic Mode Water and Antarctic Intermediate Water are two globally significant upper ocean water masses that circulate in all southern hemisphere subtropical gyres, and cross the equator to enter the North Pacific and North Atlantic Oceans. Simulations of Subantarctic Mode Water and Antarctic Intermediate water for the 20th century in eight climate models that provided their output in support of the Intergovermental Panel on Climate Change’s Fourth Assessment report (IPCC AR4) have been compared to the commonwealth Scientific and Industrial Research Organisation (CSIRO) Atlas of regional Seas. This study is the first step in a thorough analysis of climate model simulation of Southern Ocean water masses, involving both a comparison with observations and amongst the models. Significant model developments over recent years have resulted in a reasonable simulation of Subantarctic Mode Water and Antarctic Intermediate water in many models. Of particular interest is the generally better simulation of Subantarctic Mode Water and Antarctic Intermediate water in the southeast Pacific than in the Indian sector of the Southern Ocean. Combined model and observational studies will help unravel the relative importance of the many suggest processes involved in Subantarctic Mode water and Antarctic Intermediate water formation at and between these two formation regions. A greater understanding of present-day biases in climate model simulations of Subantarctic Mode water and Antarctic Intermediate water will provide important knowledge in the assessment of the impact of these
water masses on climate under IPCC future forcing scenarios.