Planktonic foraminifera Mg/Ca-based temperatures and planktonic foraminiferal cenus counts of core GeoB10065-7 (Lombok Basin, Indonesia)

Modern variability in upwelling off southern Indonesia is strongly controlled by the Australian-Indonesian monsoon and the El Niño-Southern Oscillation, but multi-decadal to centennial-scale variations are less clear. We present high-resolution records of upper water column temperature, thermal gradient and relative abundances of mixed layer- and thermocline-dwelling planktonic foraminiferal species off southern Indonesia for the past two millennia that we use as proxies for upwelling variability. We find that upwelling was generally strong during the Little Ice Age (LIA) and weak during the Medieval Warm Period (MWP) and the Roman Warm Period (RWP). Upwelling is significantly anti-correlated to East Asian summer monsoonal rainfall and the zonal equatorial Pacific temperature gradient. We suggest that changes in the background state of the tropical Pacific may have substantially contributed to the centennial-scale upwelling trends observed in our records. Our results implicate the prevalence of an El Niño-like mean state during the LIA and a La Niña-like mean state during the MWP and the RWP.

印度尼西亚南部海域上升流的现代变率主要受澳印尼季风（Australian-Indonesian Monsoon）与厄尔尼诺-南方涛动（El Niño-Southern Oscillation）的强烈调控，但数十年至百年尺度的变化仍尚不明确。本研究获取了过去两千年来印度尼西亚南部海域上层水柱温度、热梯度，以及混合层与温跃层栖息浮游有孔虫（planktonic foraminifera）物种相对丰度的高分辨率记录，并将其作为上升流变化的代用指标。研究发现，上升流在小冰期（Little Ice Age, LIA）整体较强，而在中世纪暖期（Medieval Warm Period, MWP）与罗马暖期（Roman Warm Period, RWP）则相对较弱。上升流与东亚夏季风降水及赤道太平洋纬向温度梯度呈显著负相关。本研究认为，热带太平洋背景态的变化可能对本记录中观测到的百年尺度上升流趋势起到了重要驱动作用。本研究结果表明，小冰期时期整体处于类似厄尔尼诺的平均状态，而中世纪暖期与罗马暖期则整体呈现类似拉尼娜的平均状态。