Research ArticleCLIMATOLOGY

Extreme warmth and heat-stressed plankton in the tropics during the Paleocene-Eocene Thermal Maximum

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Science Advances  03 Mar 2017:
Vol. 3, no. 3, e1600891
DOI: 10.1126/sciadv.1600891

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Abstract

Global ocean temperatures rapidly warmed by ~5°C during the Paleocene-Eocene Thermal Maximum (PETM; ~56 million years ago). Extratropical sea surface temperatures (SSTs) met or exceeded modern subtropical values. With these warm extratropical temperatures, climate models predict tropical SSTs >35°C—near upper physiological temperature limits for many organisms. However, few data are available to test these projected extreme tropical temperatures or their potential lethality. We identify the PETM in a shallow marine sedimentary section deposited in Nigeria. On the basis of planktonic foraminiferal Mg/Ca and oxygen isotope ratios and the molecular proxy Embedded Image, latest Paleocene equatorial SSTs were ~33°C, and Embedded Image indicates that SSTs rose to >36°C during the PETM. This confirms model predictions on the magnitude of polar amplification and refutes the tropical thermostat theory. We attribute a massive drop in dinoflagellate abundance and diversity at peak warmth to thermal stress, showing that the base of tropical food webs is vulnerable to rapid warming.

Keywords
  • heat
  • temperature proxy
  • paleocence - eocene
  • Plankton
  • heat stress
  • dinoflagellate
  • PETM
  • SST
  • polar amplification
  • Tropics

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