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Author Topic: No Tropical Thermostat during PETM  (Read 1709 times)

Cid_Yama

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No Tropical Thermostat during PETM
« on: March 15, 2017, 04:44:54 PM »
Extreme warmth and heat-stressed plankton in the tropics during the Paleocene-Eocene Thermal Maximum
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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.
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...we surmise that conditions became too hot for most dinoflagellate taxa during the body of the PETM, when SSTs rose to values >36°C. Such temperatures are considered uninhabitable for most marine eukaryotic organisms today (48) even for hardy dinoflagellates, which are among the most temperature-resilient eukaryote plankton groups (49). Apart from often displaying narrow temperature tolerance ranges (9), many modern thermophilic organisms show a sharp decline in productivity and, consequently, survival above optimum temperatures (50). A similar absence of mixed-layer planktonic foraminifera was observed in Tanzania (12), suggesting that heat stress may have been more widespread in tropical marginal marine settings during the PETM.
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Neven

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Re: No Tropical Thermostat during PETM
« Reply #1 on: March 15, 2017, 04:58:49 PM »
Another thread was opened for this study earlier today, here.
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