(Table S1) Stable carbon and oxygen isotopes and Mg/Ca ratios of planktonic foraminifera from ODP Hole 198-1209B

The Paleocene-Eocene Thermal Maximum (PETM) has been attributed to a rapid rise in greenhouse gas levels. If so, warming should have occurred at all latitudes, although amplified toward the poles. Existing records reveal an increase in high-latitude sea surface temperatures (SSTs) (8° to 10°C) and in bottom water temperatures (4° to 5°C). To date, however, the character of the tropical SST response during this event remains unconstrained. Here we address this deficiency by using paired oxygen isotope and minor element (magnesium/calcium) ratios of planktonic foraminifera from a tropical Pacific core to estimate changes in SST. Using mixed-layer foraminifera, we found that the combined proxies imply a 4° to 5°C rise in Pacific SST during the PETM. These results would necessitate a rise in atmospheric pCO2 to levels three to four times as high as those estimated for the late Paleocene.

古新世-始新世极热事件（Paleocene-Eocene Thermal Maximum, PETM）通常被归因于温室气体浓度的快速升高。若该假说成立，则全球所有纬度均应出现升温现象，且极地地区的升温幅度会更为显著。现有记录显示，高纬度海表温度（sea surface temperatures, SST）升高了8℃至10℃，底层水温升高了4℃至5℃。但截至目前，该事件期间热带海表温度响应的特征仍未得到明确约束。本研究利用采自热带太平洋岩芯的浮游有孔虫的成对氧同位素与微量元素（镁钙比）比值，估算海表温度的变化以填补这一研究空白。通过分析混合层浮游有孔虫，我们发现这两种代用指标共同指示：古新世-始新世极热事件期间太平洋海表温度升高了4℃至5℃。该结果意味着大气二氧化碳分压需升至古新世晚期估算值的3至4倍。