Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry
Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry
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DOI：
10.1073/pnas.1714744115
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发表时间：
2018-02-06
影响因子：
11.1
通讯作者：
Affek, Hagit P.
中科院分区：
文献类型：
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作者：
Evans, David;Sagoo, Navjit;Affek, Hagit P.
过去的温室效应时期，大气CO2浓度升高，其特点是全球海表温度（SST）升高。然而，高纬度地区比热带地区变暖的程度（极地放大）仍然受到很大的限制，特别是因为只有少数热带地区的温度重建。因此，CO2增加、热带变暖程度和由此产生的纬度SST梯度之间的关系并不为人所知。在这里，我们提出了耦合成团同位素（δ（47））-镁/钙测量有孔虫从一组全球分布的网站在热带和中纬度地区。Delta（47）对海水化学不敏感，因此对热带SST提供了一个强有力的约束。至关重要的是，耦合这些数据与镁/钙测量允许精确重建的镁/钙-SW在整个始新世，使重新解释的所有南极有孔虫镁/钙数据。综合数据集将始新世热带SST的范围限制在30-36摄氏度（来自所有盆地的站点）。我们将这些精确的热带SST与深海温度进行比较，作为对高纬度SST的最小约束。这导致了对始新世早期纬度梯度的稳健保守重建，与现在相比至少减少了32 +/- 10%，表明极地放大比大多数气候模型捕获的更大。
Past greenhouse periods with elevated atmospheric CO2 were characterized by globally warmer sea-surface temperatures (SST). However, the extent to which the high latitudes warmed to a greater degree than the tropics (polar amplification) remains poorly constrained, in particular because there are only a few temperature reconstructions from the tropics. Consequently, the relationship between increased CO2, the degree of tropical warming, and the resulting latitudinal SST gradient is not well known. Here, we present coupled clumped isotope (Delta(47))-Mg/Ca measurements of foraminifera from a set of globally distributed sites in the tropics and midlatitudes. Delta(47) is insensitive to seawater chemistry and therefore provides a robust constraint on tropical SST. Crucially, coupling these data with Mg/Ca measurements allows the precise reconstruction of Mg/Ca-sw throughout the Eocene, enabling the reinterpretation of all planktonic foraminifera Mg/Ca data. The combined dataset constrains the range in Eocene tropical SST to 30-36 degrees C (from sites in all basins). We compare these accurate tropical SST to deep-ocean temperatures, serving as a minimum constraint on high-latitude SST. This results in a robust conservative reconstruction of the early Eocene latitudinal gradient, which was reduced by at least 32 +/- 10% compared with present day, demonstrating greater polar amplification than captured by most climate models.