Machine learning

Ecology

Proxy (statistics)

Mediterranean climate

Sea surface temperature

Pleistocene

Plankton

Geology

Climate change

Bacteria

Biology

Mediterranean sea

Thaumarchaeota

Sapropel

Computer science

Early Pleistocene

Environmental science

Phylum

Oceanography

Paleontology

Paleoclimatology

Paleoceanography and Paleoclimatology

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 ‐derived SSTs before, during, and after each sapropel event. ‐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.

Impacts of Paleoecology on the TEX <sub>86</sub> Sea Surface Temperature Proxy in the Pliocene‐Pleistocene Mediterranean Sea

Impacts of Paleoecology on the TEX 86 Sea Surface Temperature Proxy in the Pliocene‐Pleistocene Mediterranean Sea

Impacts of Paleoecology on the TEX ₈₆ Sea Surface Temperature Proxy in the Pliocene‐Pleistocene Mediterranean Sea