Palaeotemperatures and carbon cycling in the southern Tethys during the Late Cretaceous

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For much of Earth history atmospheric CO2 levels and average global temperatures are thought to have been much higher than at present. These periods of time are known as 'greenhouse' climates. The Cretaceous (145 to 65 million years ago) was an extreme end-member of a greenhouse climate. Then the climate was much warmer than it is today; there was little or no polar ice and sea-levels were high. In polar areas, like Alaska and Antarctica, which are cold today, dinosaurs, crocodiles and tropical plants flourished. However, what the actual temperature of the ocean was during the Cretaceous is still much debated. The Cretaceous ocean was also sensitive to changes in oxygen concentration, and, at times, became completely devoid of oxygen over widespread areas (so-called 'oceanic anoxic events' or OAEs). The relationship between climate change and these events is of great interest as they may well have been a response to brief periods of additional warming and so may have lessons for how the planet responds to future climate change over 1000s of years.Modern techniques allow us to use the chemical remains of single-celled microorganisms organisms (bacteria and archaea) found in ancient sediments to estimate what sea-surface temperatures were like in the past. To date, much of the work using this technique has focused on the Atlantic Ocean, which was relatively narrow during the Cretcaeous. Hence, it is not clear if the temperatures generated from the Atlantic are representative of the entire globe. Particularly puzzling are data from near the Falkland Islands in the South Atlantic that suggest extremely high temperatures at ~60 degrees S, which climate models have struggled to reproduce. Are these results biased or representative of conditions at 60 degrees S in the Cretaceous? Drilling during Expedition 369 will provide new cores from offshore Australia, also at ~60 degrees S, that will permit this question to be addressed. These new cores will also recover evidence for local oceanographic conditions during one of the Cretaceous OAEs and, thus, also the opportunity to reconstruct the relationship between climate and low-oxygen conditions in the southern hemisphere for the first time.