Coccolithophore assemblage and palaeoproductivity proxies at sediment cores PS75/076-2 and PS75/079-2

Proxy-based reconstructions of past changes in the marine biological carbon pumps are limited, especially in the Southern Ocean. This work provides new insights into the productivity variations in the Pacific sector of the Southern Ocean. We present new data derived from three sediment cores that show glacial/interglacial coccolithophore variability across Marine Isotope Stage 11 (MIS 11). The cores were retrieved during R/V Polarstern cruise PS75 from the Subantarctic and Polar Front Zones at the western flank of the East Pacific Rise and in the vicinity of the Antarctic-Pacific Ridge. Coccolithophore assemblages were overwhelmingly dominated by the species Gephyrocapsa caribbeanica and small Gephyrocapsa. Total numbers of coccoliths, coccolith accumulation rates, coccolith fraction (CF; <20 µm-fraction) Sr/Ca data and temperature-corrected CF Sr/Ca records consistently showed an increase in coccolithophore productivity during Termination V (MIS 12-11 boundary), highest productivity throughout MIS 11 (424-374 kyr), and a decrease during late MIS 11 in all the cores. We end with a discussion of back-calculated coccolith calcification rate in the surface ocean and its potential contribution to changes in the concentration of atmospheric CO2.基于替代指标重建过去海洋生物碳泵（marine biological carbon pump）的历史变化，目前仍存在诸多局限，在南大洋（Southern Ocean）区域这一问题尤为突出。本研究为南大洋太平洋扇区的生产力变化提供了全新的认知视角。我们通过3根沉积物岩芯获取了全新数据，这些数据揭示了海洋同位素阶段11（Marine Isotope Stage 11，MIS 11）期间冰期/间冰期尺度的颗石藻（coccolithophore）变化特征。这些岩芯由极星号（R/V Polarstern）PS75航次在东太平洋海隆西翼的亚南极带与极锋带，以及南极-太平洋海岭附近海域采集获得。颗石藻群落以加勒比桥石藻（Gephyrocapsa caribbeanica）和小型桥石藻（Gephyrocapsa）占绝对优势。颗石总数、颗石堆积速率、颗石组分（CF；<20 µm组分）的锶钙（Sr/Ca）数据，以及经温度校正的CF Sr/Ca记录均一致显示：在终止事件V（MIS 12-11界线）期间，颗石藻生产力有所提升；在海洋同位素阶段11（42.4~37.4万年）期间，生产力维持最高水平；而在MIS 11晚期，所有岩芯的颗石藻生产力均出现下降。本研究最后探讨了表层海水经反演计算得到的颗石藻钙化速率，及其对大气二氧化碳（CO₂）浓度变化的潜在影响。