Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry

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Publisher: National Academy of Sciences
Document Type: Report
Length: 6,830 words
Lexile Measure: 1570L

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Abstract :

Past greenhouse periods with elevated atmospheric C[O.sub.2] 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 C[O.sub.2], the degree of tropical warming, and the resulting latitudinal SST gradient is not well known. Here, we present coupled clumped isotope ([[DELTA].sub.47])-Mg/Ca measurements of foraminifera from a set of globally distributed sites in the tropics and midlatitudes. [[DELTA].sub.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.sub.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 [+ or -] 10% compared with present day, demonstrating greater polar amplification than captured by most climate models. clumped isotope | Eocene | tropical sea-surface temperatures | polar amplification | seawater Mg/Ca

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Source Citation   

Gale Document Number: GALE|A534663917