Southwest Pacific modulation of abrupt climate change during the Antarctic Cold Reversal–Younger Dryas

The giant piston core, MD97-2121 (2314-m water depth), collected north of the Subtropical Front, New Zealand, provides a well-dated, stable isotopic record of subtropical and sub-Antarctic influences on the surface and deep ocean over the last deglaciation, especially during the Antarctic Cold Reversal (ACR; ~ 14.1–12.4 ka) and Younger Dryas (YD; 13.0–11.5 ka). After the Last Glacial Maximum, benthic foraminiferal δ18Ob changed in phase with Antarctica — the ACR being represented by a pause in the δ18Ob deglacial trend. In contrast, surface waters, as represented by the stable isotopes of 3 planktic foraminifers from 3 different depth zones, and alkenone-based sea surface temperatures, showed no immediate response to the ACR. It was not until the Reversal was at its coldest, starting ~ 13.5 ka that the surface ocean responded. It became less warm, its fertility reduced sharply, and its surface structure changed as shown by the merger of the δ18Opl planktic profiles. Onshore, these changes were accompanied by an expansion of cool climate vegetation, an advancement of alpine glaciers and a likely pause in the post-glacial transgression. These onshore and offshore changes, which continued well into YD time, probably resulted from modification of polar conditions by subtropical influences. The ACR caused cooler temperatures, weakened seasonality and stronger winds. However, its onset and impact were ameliorated by a strengthened inflow of subtropical water, although ACR-driven atmospheric conditions prevailed. By comparison, south of the Subtropical Front, where subtropical influences are weak and water masses have direct links with Antarctica, the surface waters cooled in phase with the ACR.