Deglacial paleoceanographic history of the Bay of Plenty, New Zealand

Abstract

We present sea surface temperature (SST) records with centennial‐scale resolution from the Bay of Plenty, north of New Zealand. Foraminiferal assemblage‐based paleo‐SST estimates provide a deglacial record of SST since 16.5 14C ka. Average Holocene SSTs are 15.6°C for winter and 20.3°C for summer, whereas average glacial values were 14.2°C for winter and 19.5°C for summer. Compared to modern time, cooling of SSTs at the Last Glacial Maximum (LGM) was ∼0.9°C in winter and ∼1.5°C in summer. The shift from glacial to Holocene temperatures began at 14.25 14C ka, warming by ∼2°C until 12.85 14C ka when temperatures dipped back to glacial values at 11.65 14C ka. The timing of this return to glacial‐like SST correlates well with the Antarctic Cold Reversal (ACR) rather than the Younger Dryas and documents that the influence of the ACR extended into the subtropics of the Southern Hemisphere, at least in this region of the southwest Pacific. By 10.55 14C ka an SST maximum in summer SSTs of up to 3°C warmer than modern occurred (∼24°C), after which SST dropped, remaining at present‐day temperatures since 9.3 14C ka. This early Holocene climatic optimum has been widely noted in the Southern Ocean, and this record indicates that this phenomenon also extended into the subtropics to the north of New Zealand.