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Impacts of Paleoecology on the TEX 86 Sea Surface Temperature Proxy in the Pliocene‐Pleistocene Mediterranean Sea
Author(s) -
Polik Catherine A.,
Elling Felix J.,
Pearson Ann
Publication year - 2018
Publication title -
paleoceanography and paleoclimatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.927
H-Index - 127
eISSN - 2572-4525
pISSN - 2572-4517
DOI - 10.1029/2018pa003494
Subject(s) - sapropel , sea surface temperature , pleistocene , mediterranean sea , mediterranean climate , thaumarchaeota , early pleistocene , proxy (statistics) , oceanography , geology , plankton , paleoclimatology , glacial period , climate change , climatology , ecology , paleontology , biology , phylum , machine learning , bacteria , computer science
The TEX 86 proxy, based on the distribution of isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) from planktonic Thaumarchaeota, is widely used to reconstruct sea surface temperature (SST). Recent observations of species‐specific and regionally dependent TEX 86 ‐SST relationships in cultures and the modern ocean raise the question of whether nonthermal factors may have impacted TEX 86 paleorecords. Here we evaluate the effects of ecological changes on TEX 86 using one Pliocene and two Pleistocene sapropels from the Mediterranean Sea. We find that TEX 86 ‐derived SSTs deviate from U 37 K ’ ‐derived SSTs before, during, and after each sapropel event. U 37 K ’ ‐derived SSTs vary by less than 6 °C, while TEX 86 ‐derived SSTs vary by up to 15 °C within a single record. Compound‐specific carbon isotope compositions indicate minimal confounding influence on TEX 86 from exogenous sources. Some of the variation can be accounted for by changes in nitrogen cycling intensity affecting thaumarchaeal iGDGT biosynthesis, as demonstrated by an inverse relationship between TEX 86 and δ 15 N TN . TEX 86 ‐derived SSTs also consistently show warm anomalies in the Pleistocene, while the Pliocene samples exhibit both warmer and cooler relative offsets. These anomalies result from systematic differences between Plio‐Pleistocene iGDGT distributions and both modern Mediterranean and modern, globally distributed core top samples. Through characteristic GDGT distributions, we suggest the existence of three distinct endemic populations of Thaumarchaeota in the Pliocene, Pleistocene, and modern Mediterranean Sea, respectively. Importantly, these communities prevailed during both sapropel and oligotrophic conditions. Our results demonstrate that ecological and community‐specific effects must be considered when applying the TEX 86 proxy to paleorecords.