Changes in the intermediate water mass formation rates in the global ocean for the Last Glacial Maximum, mid‐Holocene and pre‐industrial climates

Abstract

The paleoclimate version of the National Center for Atmospheric Research Community Climate System Model version 3 (NCAR‐CCSM3) is used to analyze changes in the water formation rates in the Atlantic, Pacific, and Indian Oceans for the Last Glacial Maximum (LGM), mid‐Holocene (MH) and pre‐industrial (PI) control climate. During the MH, CCSM3 exhibits a north‐south asymmetric response of intermediate water subduction changes in the Atlantic Ocean, with a reduction of 2 Sv in the North Atlantic and an increase of 2 Sv in the South Atlantic relative to PI. During the LGM, there is increased formation of intermediate water and a more stagnant deep ocean in the North Pacific. The production of North Atlantic Deep Water (NADW) is significantly weakened. The NADW is replaced in large extent by enhanced Antarctic Intermediate Water (AAIW), Glacial North Atlantic Intermediate Water (GNAIW), and also by an intensified of Antarctic Bottom Water (AABW), with the latter being a response to the enhanced salinity and ice formation around Antarctica. Most of the LGM intermediate/mode water is formed at 27.4 <σθ < 29.0 kg/m3, while for the MH and PI most of the subduction transport occurs at 26.5 < σθ < 27.4 kg/m3. The simulated LGM Southern Hemisphere winds are more intense by 0.2–0.4 dyne/cm2. Consequently, increased Ekman transport drives the production of intermediate water (low salinity) at a larger rate and at higher densities when compared to the other climatic periods.