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Updated: Jul 5, 2026

Resurrection of Dormant Daphnia magna: Protocol and Applications
Published on: January 19, 2018
A transient rise in tropical sea surface temperature during the Paleocene-Eocene thermal maximum
James C Zachos1, Michael W Wara, Steven Bohaty
1Earth and Ocean Sciences Departments, University of California, Santa Cruz, CA 95064, USA. jzachos@es.ucsc.edu
Abstract:
The Paleocene-Eocene Thermal Maximum (PETM) has been attributed to a rapid rise in greenhouse gas levels. If so, warming should have occurred at all latitudes, although amplified toward the poles. Existing records reveal an increase in high-latitude sea surface temperatures (SSTs) (8 degrees to 10 degrees C) and in bottom water temperatures (4 degrees to 5 degrees C). To date, however, the character of the tropical SST response during this event remains unconstrained. Here we address this deficiency by using paired oxygen isotope and minor element (magnesium/calcium) ratios of planktonic foraminifera from a tropical Pacific core to estimate changes in SST. Using mixed-layer foraminifera, we found that the combined proxies imply a 4 degrees to 5 degrees C rise in Pacific SST during the PETM. These results would necessitate a rise in atmospheric pCO2 to levels three to four times as high as those estimated for the late Paleocene.
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