Does Southern Ocean surface forcing shape the global ocean overturning circulation?

TitleDoes Southern Ocean surface forcing shape the global ocean overturning circulation?
Publication TypeJournal Article
Year of Publication2018
AuthorsSun S.T, Eisenman I, Stewart A.L
JournalGeophysical Research Letters
Date Published2018/03
Type of ArticleArticle
ISBN Number0094-8276
Accession NumberWOS:000428402400034
Keywordsantarctic 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.

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