TEX86H proxy and BIT index of sediment core GeoB9528-3

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 (TEXH86) 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.

学界普遍认为，大西洋经向翻转环流（Atlantic meridional overturning circulation, AMOC）的强度变化会对全球气候产生深远影响。耦合模式研究表明，在年际至数十年的时间尺度上，大西洋经向翻转环流的放缓会导致热带大西洋温跃层加深。然而，这一过程鲜有沉积地球化学记录能够对其进行有效限定。本研究基于热带东大西洋几内亚高原陆缘的沉积物岩芯，重建了过去两个冰期-间冰期旋回（约192千年）的表层海水（UK'37指数，UK'37 Index）与温跃层海水（TEXH86指标，TEXH86）温度。这些古温度记录显示，由同一岩芯底栖有孔虫碳同位素（δ¹³C）记录所指示的大西洋经向翻转环流减弱时段，与近表层垂直温度梯度降低的时期相吻合——这首次证实了，由大西洋经向翻转环流驱动的热带大西洋温跃层调整，可在更长的千年时间尺度上存在。模式结果支持了对上述地球化学记录的解释，并表明温跃层调整在热带东大西洋区域尤为显著。因此，从年际至千年以上的时间尺度来看，大西洋经向翻转环流的强度变化，似乎是调控热带大西洋温跃层结构的重要驱动因素。