Descent toward the Icehouse: Eocene sea surface cooling inferred from GDGT distributions
Descent toward the Icehouse: Eocene sea surface cooling inferred from GDGT distributions
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DOI：
10.1002/2014pa002723
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发表时间：
2015-07-01
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通讯作者：
Pancost, Richard D.
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作者：
Inglis, Gordon N.;Farnsworth, Alexander;Pancost, Richard D.
TEX86 代理基于海洋异戊二烯甘油二烷基甘油四醚脂质 (GDGT) 的分布，越来越多地用于重建始新世 (56.0-33.9 Ma) 期间的海面温度 (SST)。在这里，我们汇编了已发表的 TEX86 记录，根据 TEX86 古测温学的新理解对它们进行批判性的重新评估，并用新数据对其进行补充，以评估始新世的长期温度趋势。我们使用支链类异戊二烯四醚指数 (BIT)、GDGT-0 相对于 crenarchaeol 的丰度 (%GDGT-0) 和甲烷指数 (MI) 研究了海洋奇古菌以外的古菌对 TEX86 值的影响。我们还引入了一个新的比率，％GDGTRS，这可能有助于识别地质记录中的红海型 GDGT 分布。使用 TEX86H 和 TEX86L (Delta H-L) 之间的偏移以及 GDGT-2 和 GDGT-3 之间的比率 ([2]/[3])，我们评估了不同的 TEX86 校准，并提出了始新世（55 至 34 Ma）的第一个综合海表温度编译。尽管可用数据仍然很少，但现在可以解决一些地理趋势。在高纬度地区（>55度），始新世期间出现了大幅降温（大约6摄氏度）。我们编制的记录还表明，同一时间段内热带气温下降了约 2.5 摄氏度。使用跨越始新世的气候模型模拟集合，我们的结果表明，重建的温度变化中只有一小部分（大约 10%）可以归因于海洋门户重组或古地理变化。总的来说，这表明大气中的二氧化碳 (pCO(2)) 可能是下降到冰室期间地表水冷却的驱动因素。
The TEX86 proxy, based on the distribution of marine isoprenoidal glycerol dialkyl glycerol tetraether lipids (GDGTs), is increasingly used to reconstruct sea surface temperature (SST) during the Eocene epoch (56.0-33.9 Ma). Here we compile published TEX86 records, critically reevaluate them in light of new understandings in TEX86 palaeothermometry, and supplement them with new data in order to evaluate long-term temperature trends in the Eocene. We investigate the effect of archaea other than marine Thaumarchaeota upon TEX86 values using the branched-to-isoprenoid tetraether index (BIT), the abundance of GDGT-0 relative to crenarchaeol (%GDGT-0), and the Methane Index (MI). We also introduce a new ratio, % GDGTRS, which may help identify Red Sea-type GDGT distributions in the geological record. Using the offset between TEX86H and TEX86L (Delta H-L) and the ratio between GDGT-2 and GDGT-3 ([2]/[3]), we evaluate different TEX86 calibrations and present the first integrated SST compilation for the Eocene (55 to 34 Ma). Although the available data are still sparse some geographic trends can now be resolved. In the high latitudes (>55 degrees), there was substantial cooling during the Eocene (similar to 6 degrees C). Our compiled record also indicates tropical cooling of similar to 2.5 degrees C during the same interval. Using an ensemble of climate model simulations that span the Eocene, our results indicate that only a small percentage (similar to 10%) of the reconstructed temperature change can be ascribed to ocean gateway reorganization or paleogeographic change. Collectively, this indicates that atmospheric carbon dioxide (pCO(2)) was the likely driver of surface water cooling during the descent toward the icehouse.