NOAA/WDS Paleoclimatology - Late Quaternary SW Pacific Foraminifer Data

A series of cores from east of New Zealand have been examined to determine the paleoceanographic history of the late Quaternary in the SW Pacific using planktonic foraminiferal data. Distinct shifts of species can be seen between glacial and interglacial times especially south of Chatham Rise east of South Island. Foraminiferal fragmentation ratios and benthic/planktonic foraminiferal ratios both show increased dissolution during glacials, especially isotope stage 2 to the south of Chatham Rise. The present-day Subtropical Convergence appears to be tied to the Chatham Rise at 44°S, but during glacial times this rise separated cold water to the south from much warmer water to the north, with an associated strong thermal gradient across the rise. We estimate that this gradient could have presented as much as an 8°C temperature change across 4° of latitude during the maximum of the last ice age. There is only weak evidence of the Younger Dryas cool event, but there is a clear climatic optimum between 8 and 6.4 ka with temperatures 1°–2°C higher than the present day. The marine changes compare well with vegetational changes on both South and North Island.

本研究利用浮游有孔虫（planktonic foraminifera）数据，对新西兰东部的一系列岩芯开展分析，以重建西南太平洋晚第四纪的古海洋演化历史。冰期与间冰期的物种组成存在显著更替，这一特征在南岛东部查塔姆海隆（Chatham Rise）南侧区域尤为明显。冰期时，有孔虫破碎率以及底栖/浮游有孔虫比值均显示溶解作用增强，该现象在查塔姆海隆南侧的同位素2期（isotope stage 2）中尤为突出。现今的亚热带辐合带（Subtropical Convergence）大致位于南纬44°，与查塔姆海隆重合；但在冰期，该海隆将南侧冷水与北侧暖水完全分隔，海隆两侧形成了极强的温度梯度。经估算，在末次冰盛期巅峰阶段，该温度梯度在4个纬度范围内可产生高达8℃的温差。新仙女木（Younger Dryas）冷事件的相关证据较为薄弱，但在8~6.4 ka期间存在清晰的气候适宜期，当时的温度较现今高出1~2℃。该海域的环境变化与南岛、北岛的植被演化记录具有良好的一致性。