TEX86H proxy and BIT index of sediment core GeoB9528-3 and reconstructed temperature data from NW Africa surface sediments

Changes in the strength of Atlantic meridional overturning circulation (AMOC) are known to have profound impacts on global climate. Coupled modelling studies have suggested that, on annual to multi-decadal time scales, a slowdown of AMOC causes a deepening of the thermocline in the tropical Atlantic. However, this process has been poorly constrained by sedimentary geochemical records. Here, we reconstruct surface (UK'37 Index) and thermocline (TEX86H) water temperatures from the Guinea Plateau Margin (Eastern tropical Atlantic) over the last two glacial-interglacial cycles (~ 192 kyr). These paleotemperature records show that periods of reduced AMOC, as indicated by the d13 C benthic foraminiferal record from the same core, coincide with a reduction in the near-surface vertical temperature gradient, demonstrating for the first time that AMOC-induced tropical Atlantic thermocline adjustment exists on longer, millennial time scales. Modelling results support the interpretation of the geochemical records and show that thermocline adjustment is particularly pronounced in the eastern tropical Atlantic. Thus, variations in AMOC strength appear to be an important driver of the thermocline structure in the tropical Atlantic from annual to multi-millennial time scales.

大西洋经向翻转环流（Atlantic Meridional Overturning Circulation, AMOC）强度的变化，已被证实对全球气候具有深远影响。耦合模式研究表明，在年际至数十年的时间尺度上，AMOC的减缓会导致热带大西洋温跃层加深。然而，这一过程尚未得到沉积地球化学记录的充分约束。本研究基于东热带大西洋几内亚高原边缘的岩芯，重建了过去两个冰期-间冰期旋回（约192 kyr）的表层（UK'37 Index）与温跃层（TEX86H）海水温度记录。这些古温度记录显示，由同一岩芯的底栖有孔虫碳同位素（δ¹³C）记录所指示的AMOC减弱时段，与近表层垂直温度梯度降低相吻合，首次证实了AMOC驱动的热带大西洋温跃层调整可在千年尺度的更长时间周期上存在。模式模拟结果佐证了地球化学记录的解释结论，并表明温跃层调整在东热带大西洋区域尤为显著。综上，无论在年际还是多千年尺度上，AMOC强度的变化均是调控热带大西洋温跃层结构的重要驱动因素。