|Title||Does Southern Ocean surface forcing shape the global ocean overturning circulation?|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Sun S.T, Eisenman I, Stewart A.L|
|Journal||Geophysical Research Letters|
|Type of Article||Article|
|Keywords||antarctic circumpolar current; atmospheric co2; climate model; climate-change; deep-ocean; Geology; global ocean overturning circulation; last glacial maximum; model; north-atlantic; sea-ice; Southern Ocean; stratification; tracer release|
Paleoclimate proxy data suggest that the Atlantic Meridional Overturning Circulation (AMOC) was shallower at the Last Glacial Maximum (LGM) than its preindustrial (PI) depth. Previous studies have suggested that this shoaling necessarily accompanies Antarctic sea ice expansion at the LGM. Here the influence of Southern Ocean surface forcing on the AMOC depth is investigated using ocean-only simulations from a state-of-the-art climate model with surface forcing specified from the output of previous coupled PI and LGM simulations. In contrast to previous expectations, we find that applying LGM surface forcing in the Southern Ocean and PI surface forcing elsewhere causes the AMOC to shoal only about half as much as when LGM surface forcing is applied globally. We show that this occurs because diapycnal mixing renders the Southern Ocean overturning circulation more diabatic than previously assumed, which diminishes the influence of Southern Ocean surface buoyancy forcing on the depth of the AMOC.
In summary, this study used CESM ocean‐only simulations to investigate the influence of Southern Ocean surface forcing on the AMOC depth, which is believed to play an important role in glacial‐interglacial changes in atmospheric CO2. The results suggest that the AMOC depth is sensitive to both Southern Ocean and North Atlantic surface buoyancy forcing due to diapcynal mixing in the Southern Ocean.