NOAA/WDS Paleoclimatology - Paleocene-Eocene Boundary Equatorial Pacific and Subtropical Atlantic Planktonic Mg/Ca and d18O Data

The Paleocene-Eocene Boundary (PEB) was marked by an extraordinary climatic event, hypothesized to originate from a large perturbation to the carbon cycle which fueled global warming, the rapid dissociation of oceanic methane hydrates. The pattern of surface warming interpreted from existing sea surface temperature records is not consistent with a greenhouse origin for this event, which would have fueled sea surface warming globally. Although oxygen isotope (d18O)-based reconstructions indicate polar warming, results for the tropics and subtropics are ambiguous because of uncertainties associated with interpreting planktonic foraminiferal d18O. To remedy this, we have constructed high-resolution temperature records based on Mg/Ca of multiple species of both surface and thermocline-dwelling planktonic foraminifera across the PEB in the equatorial Pacific and subtropical Atlantic. During the carbon isotope excursion (CIE), surface temperatures increased by 3.5°ŋ4°C and thermocline temperatures warmed by 3°C. Estimates of surface water and thermocline salinity based on paired Mg/Ca and d18O data indicate a pattern of hydrographic changes in the equatorial and subtropical oceans that is different from previously proposed, with a more vigorous hydrologic cycle during warming. The pattern of warming and salinity changes are consistent with this being a greenhouse-induced global warming event, and the timing of hydrographic changes relative to the CIE supports the hypothesis that gradual warming of intermediate/deep waters triggered methane hydrate dissociation.

古新世-始新世界线（Paleocene-Eocene Boundary, PEB）以一场极端气候事件为标志性特征，该事件被假设施加于碳循环的大规模扰动所引发，该扰动驱动了全球变暖，其中海洋甲烷水合物的快速解离是关键诱因。现有海表温度（sea surface temperature）记录反演得到的海表变暖模式，与该事件的温室成因假说并不一致——温室成因本应驱动全球范围内的海表升温。尽管基于氧同位素（oxygen isotope, d18O）的重建结果显示极地存在变暖现象，但热带与亚热带地区的相关结果却存在歧义，这是因为浮游有孔虫（planktonic foraminifera）的d18O数值解译存在诸多不确定性。为弥补这一研究局限，本研究基于赤道太平洋与亚热带大西洋跨越PEB层位的多门类表层栖居与温跃层栖居浮游有孔虫的镁钙比（Mg/Ca），构建了高分辨率温度记录序列。在碳同位素漂移事件（carbon isotope excursion, CIE）期间，海表温度上升了3.5至4摄氏度，温跃层温度上升了3摄氏度。基于配对镁钙比与氧同位素数据估算得到的表层水与温跃层盐度结果显示，赤道与亚热带大洋的水文变化模式与此前提出的假说存在显著差异，变暖期间的水文循环更为活跃。此次变暖与盐度变化的模式，与该事件为温室效应引发的全球变暖事件这一结论完全相符；而水文变化相对于碳同位素漂移事件的时间节点，也支持了"中层/深层海水的逐步变暖触发了甲烷水合物解离"这一科学假说。