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

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 on...

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Bibliographic Details
Main Authors: EVANS, D, SAGOO, N, RENEMA, W, COTTON, LJ, MULLER, W, TODD, JA, SARASWATI, PK, STASSEN, P, ZIEGLER, M, PEARSON, PN, VALDES, PJ, AFFEK, HP
Format: Article in Journal/Newspaper
Language:English
Published: NATL ACAD SCIENCES 2018
Subjects:
clumped isotope
Eocene
tropical sea-surface temperatures
polar amplification
seawater Mg/Ca
SEA-SURFACE TEMPERATURES
LARGE BENTHIC FORAMINIFERA
SOUTHWEST PACIFIC-OCEAN
THERMAL MAXIMUM
SEAWATER CHEMISTRY
CARBONATE
MODEL
WARM
RECORD
SIMULATIONS
Pacific
Planktonic foraminifera
Online Access:http://dspace.library.iitb.ac.in/xmlui/handle/100/22838
https://doi.org/10.1002/2014GL061189
Description
Summary: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.

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