Relative abundances of sea ice-related diatoms in sediment core MD03-2601

Diatom data from a marine sediment core give insight on Holocene changes in sea-surface conditions and climate at high southern latitudes off Adélie Land, East Antarctica. The early to mid-Holocene was warmer than the late Holocene with a transition at ~4000 calendar years B. P. Sea ice was less present and spring-summer growing season was greater during the warm period relative to the cold one, thus limiting sea ice diatom production and favoring more open ocean diatom to develop. The long-term Holocene climatic evolution in East Antarctica is explained by a combination of a delayed response to local seasonal insolation changes coupled to the long memory of the Southern Ocean. Abrupt variations of the diatom relative abundances, indicating rapid climate changes, are superimposed to the Holocene long-term trends. Spectral analyses calculate robust frequencies at ~1600 a (where “a” is years), ~1250 a, ~1050 a, ~570 a, ~310 a, ~230 a, ~150–125 a, ~110 a, ~90 a, and ~66 a. Such periods are very close to solar activity cyclicities, except for the periods at ~310 a and ~1250 a, which are close to internal climate variability cyclicities. Wavelet analyses estimate the same periods but indicate nonstationary cyclicities. Rapid climate changes at high southern latitudes may therefore be explained by a combination of external (solar) and internal (thermohaline circulation) forcings.

采自东南极洲阿德利兰（Adélie Land）外南极高纬度海域的海洋沉积岩芯中的硅藻数据，为全新世（Holocene）以来该区域的海表环境与气候演化提供了重要研究视角。全新世早中期气候整体暖于全新世晚期，二者的气候转型节点约在距今4000个日历年前（B.P.）。相较于寒冷的全新世晚期，温暖的早中期海冰覆盖范围更小，春夏生长期更长，这抑制了海冰硅藻的繁殖，并更利于开阔海洋硅藻的生长发育。东南极洲全新世长期气候演化，可通过当地季节日照变化的滞后响应与南大洋的长记忆效应的共同作用得到合理解释。硅藻相对丰度的突变（指示气候快速变化）叠加于全新世长期气候演化趋势之上。频谱分析结果显示存在多个统计稳健的显著周期：约1600年（文中"a"代表年）、1250年、1050年、570年、310年、230年、150–125年、110年、90年及66年。除约310年和1250年这两个周期外，其余周期均与太阳活动周期高度吻合；而310年与1250年周期则接近南大洋内部气候变率的周期特征。小波分析同样检测到了上述周期，但结果显示这些周期具有非平稳性特征。因此，南极高纬度地区的气候快速变化，可通过外部强迫（太阳活动）与内部强迫（温盐环流（thermohaline circulation））的共同作用得到合理解释。