Fig. 3.

Schematic representation of ocean surface circulation and intermediate/deep water mass formation responses to Late Pliocene Antarctic cooling. Dotted lines represent reduced water mass formation or current strength. (Upper) The warm Pliocene was characterized by a reduced WAIS volume and sea ice extent and duration during interglacials. Such conditions during Pleistocene glacial-interglacial transitions are associated with southward migration of Southern Ocean fronts (60, 61), allowing for greater connectivity of the Pacific, Indian, and Atlantic subtropical gyres, and may have promoted enhanced AMOC (61, 62). (Lower) Antarctic Ice Sheet expansion and sea ice growth in the Late Pliocene, and associated northward migration of the Southern Ocean frontal systems restricts water exchange between ocean basins, and reduces the AMOC (61). Increased sea ice extent during these steps resulted in increased AABW formation (55) (blue arrows) and the intensified frontal systems likely promoted AAIW and SAMW formation (66).