Tropical Atlantic SST during the mid-Pleistocene transition (MPT) of ODP Hole 175-1077B

We compare a new mid-Pleistocene sea surface temperature (SST) record from the eastern tropical Atlantic to changes in continental ice volume, orbital insolation, Atlantic deepwater ventilation, and Southern Ocean front positions to resolve forcing mechanisms of tropical Atlantic SST during the mid-Pleistocene transition (MPT). At the onset of the MPT, a strong tropical cooling occurred. The change from a obliquity- to a eccentricity-dominated cyclicity in the tropical SST took place at about 650 kyr BP. In orbital cycles, tropical SST changes significantly preceded continental ice-volume changes but were in phase with movements of Southern Ocean fronts. After the onset of large-amplitude 100-kyr variations, additional late glacial warming in the eastern tropical Atlantic was caused by enhanced return flow of warm waters from the western Atlantic driven by strong trade winds. Pronounced 80-kyr variations in tropical SST occurred during the MPT, in phase with and likely directly forced by transitional continental ice-volume variations. During the MPT, a prominent anomalous long-term tropical warming occurred, likely generated by extremely northward displaced Southern Ocean fronts. While the overall pattern of global climate variability during the MPT was determined by changes in mean state and frequency of continental ice volume variations, tropical Atlantic SST variations were primarily driven by early changes in Subantarctic sea-ice extent and coupled Southern Ocean frontal positions.我们将东热带大西洋海域新获取的中更新世海表温度（sea surface temperature, SST）记录，与大陆冰量变化、轨道日照（orbital insolation）、大西洋深层水通风（Atlantic deepwater ventilation）以及南大洋锋面（Southern Ocean fronts）的变化进行对比，以解析中更新世过渡期（mid-Pleistocene transition, MPT）内热带大西洋海表温度的驱动机制。在中更新世过渡期启动之初，发生了显著的热带降温事件。热带海表温度的旋回规律从以斜度周期为主转变为以偏心率周期为主，这一转变发生在约650 kyr BP。在轨道尺度旋回中，热带海表温度的变化显著超前于大陆冰量变化，但与南大洋锋面的位移相位一致。在大振幅100千年尺度旋回启动后，东热带大西洋海域额外的冰消期变暖事件，是由强信风驱动的西大西洋暖水回流增强所引发的。中更新世过渡期内，热带海表温度存在显著的80千年尺度旋回变化，其相位与过渡期大陆冰量变化一致，且很可能直接受其驱动。中更新世过渡期内还出现了一次显著的异常长期热带增温事件，其成因很可能是南大洋锋面向北发生了极端大幅的位移。尽管中更新世过渡期内全球气候变率的整体格局由大陆冰量变化的平均状态和频率变化所决定，但热带大西洋海表温度的变化主要受亚南极海冰范围（Subantarctic sea-ice extent）的早期变化以及耦合的南大洋锋面位置变化所驱动。