Deglacial Sea-Surface Temperatures off New Zealand

Glacial geologic and geochronologic data from New Zealand indicate a re-advance of mountain glaciers synchronous with the Younger Dryas (YD) Chron. Yet pollen studies do not support any appreciable cooling at this time, suggesting that the glacial advances may have resulted from enhanced precipitation rather than decreased temperature. A paucity of detailed marine climate records from the region leave an uncertain picture of deglacial climate change in the vicinity of New Zealand. The question remains open whether abrupt deglacial climate changes so prominent in the North Atlantic region involved the southwest Pacific Ocean. Here we present a detailed record of deglacial and Holocene sea-surface temperatures (SSTs) off the north island of New Zealand using the alkenone paleotemperature technique and show evidence for cooling synchronous with the Younger Dryas Chron. Core MD97-2121 was recovered in 2314 m of water at 40°S, 178°E, southeast of Hawke Bay, New Zealand. The 35-m core contains a continuous record of sedimentation spanning the last 136 kyr. Age control for the deglacial period and the Holocene is provided by 26 radiocarbon dates on planktonic foraminifera and tephra layers. Exceptional rates of sedimentation averaging 36 cm/kyr during the last 25 kyr are maintained by large fluxes of terrigenous detritus from New Zealand resulting from pronounced seismicity, volcanism and continental weathering. Presently the site is under the influence of the southward-flowing East Cape Current, which transports 10-25 Sv of warm, salty, subtropical water. The northward flowing Wairarapa Coastal Current flows just west of the core site and transports 1.6 Sv of cool, low-salinity water derived from Australasian Subantarctic Water via the Southland Current. Although a relatively minor influence today, this cool, fresh current system may have influenced SSTs over the core site at times in the past. Late Holocene alkenone-derived SSTs of 17 deg C are consistent with atlas mean annual SSTs. Temperatures during the LGM were 13 deg C. Deglacial warming was 5 deg C, with maximum temperatures of 18-18.5 deg C attained 9-10 cal kyr ago. This deglacial SST change is consistent with other estimates from marine records in the vicinity. Cooling of 1.5 deg C occurred in the mid-Holocene, between 4-8 kyr ago. A cool episode occurred 12.3-11.6 cal kyr ago, during the Younger Dryas Chron. As evidenced by oxygen isotopic ratios in multiple species of planktonic foraminifera, the cool phase occurred at the end of an interval of enhanced stratification of surface waters (< 400 m) that commenced during the Antarctic Cold Reversal and lasted from 14-12 cal kyr ago. The deglacial climate record east of New Zealand thus displays common features with those in both the North Atlantic region and in Antarctica.