Atmospheric CO₂ forcing on glacial thermohaline circulation and climate

Abstract

[1] A coupled climate model study indicates the paleoclimate record of glacial thermohaline circulation (THC) and reversed deep-sea temperature-salinity (T-S) distribution in the Atlantic can be explained largely by lower glacial atmospheric CO 2 alone. The reduced CO 2 leads to increased Southern Ocean wintertime sea-ice cover and salinity, increased production of dense Antarctic Bottom Water (AABW), enhanced cold and saline AABW penetration into the deep North Atlantic, increased oceanic vertical stability, and reduced North Atlantic Deep Water (NADW) circulation. The dominant role of CO 2 forcing during the glacial implies a positive feedback between the Southern Ocean regulated THC and the glacial global carbon cycle.

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

“…Consistent with the results discussed here, these changes have been attributed to enhanced sea-ice export around Antarctica (7) and ultimately reduced CO2 concentrations (8). However, whereas Shin et al (7) argue that enhanced sea-ice export is caused "ultimately by increased westerlies," (ref.…”

“…The results here are broadly consistent with some complex coupled climate model simulations (7,8), as well as with global ocean-only simulations under LGM boundary conditions (10).…”

“…Multiple studies have pointed toward the potential importance of sea ice and surface buoyancy fluxes around Antarctica in controlling changes in the deep ocean stratification and circulation between the present and Last Glacial Maximum (LGM) (7)(8)(9)(10)(11). Specifically, we recently showed that enhanced buoyancy loss around Antarctica is expected to lead to an increase in the abyssal stratification, an upward shift of NADW, and a clearer separation between NADW and southward-flowing AABW (11)-all in agreement with inferences made for differences in circulation and stratification between the present and LGM (3,6,12,13).…”

The impacts of deglacial meltwater forcing on the South Atlantic Ocean deep circulation since the Last Glacial Maximum

“…The mean global temperature was almost 6 • C lower than at pre-industrial times (Schneider von Deimling et al, 2006), which was further reinforced by lower atmospheric CO 2 concentrations (Monnin et al, 2001). These conditions led to increased sea ice formation (Liu et al, 2005) and extensive associated brine injection into the Southern Ocean (Shin et al, 2003). A salty (and therefore denser) version of the Antarctic Bottom Water (AABW) was present then (Adkins et al, 2002;Marchitto et al, 2002;Curry and Oppo, 2005), which acted as a subsurface salinity barrier, i.e., a strong vertical stratification that prevented other water masses from entering the AABW domain.…”

Influence of boundary conditions on the Southern Hemisphere atmospheric circulation during the last glacial maximum

“…It has been demonstrated that the presence of Laurentide and Fennoscandia ice sheets in the Northern Hemisphere has both a topographic and a thermal effect which occur simultaneously and lead to a greater stationary eddy forcing of the zonal mean flow ( Justino et al, 2005;Shin et al, 2003;Vettoretti et al, 2000). The glacial interhemispheric teleconnection has also been explored by (Liu et al, 2005) and (Shin et al, 2002). They argued that the weakening of the glacial North Atlantic Thermohaline Circulation (NADW) was partially caused by the enhanced equatorward sea-ice transport due to stronger extratropical westerlies in the Southern Ocean during the LGM.…”