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

特提斯南部晚白垩世古气温和碳循环

• 批准号: NE/R012369/1
• 负责人: Stuart Robinson
• 金额: $ 6.44万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FR012369%2F1
• 关键词: Palaeotemperatures; carbon; cycling; southern; Tethys

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.

在地球历史上的大部分时间里，大气中的二氧化碳水平和全球平均温度被认为比现在高得多。这段时间被称为“温室”气候。白垩纪(1.45亿至6500万年前)是温室气候的极端末端。当时的气候比现在温暖得多，极地冰层很少，甚至没有，海平面很高。在今天寒冷的阿拉斯加和南极洲等极地地区，恐龙、鳄鱼和热带植物繁衍生息。然而，白垩纪海洋的实际温度仍然存在很大争议。白垩纪海洋对氧气浓度的变化也很敏感，有时在大片区域变得完全缺乏氧气(所谓的海洋缺氧事件或OAE)。气候变化和这些事件之间的关系非常令人感兴趣，因为它们很可能是对短暂的额外变暖的反应，因此可能为地球在未来数千年内如何应对气候变化提供经验教训。现代技术使我们能够利用在古代沉积物中发现的单细胞微生物(细菌和古生菌)的化学遗骸来估计过去的海表面温度。到目前为止，使用这项技术的大部分工作都集中在大西洋上，在白垩纪时期，大西洋相对狭窄。因此，目前还不清楚大西洋产生的温度是否代表整个地球。尤其令人费解的是来自南大西洋福克兰群岛附近的数据，这些数据表明S的气温达到了约60华氏度，而气候模型很难再现这种温度。这些结果对白垩纪S 60度的条件是否有偏颇或代表性？369探险期间的钻探将提供来自澳大利亚近海的新岩心，也是在S摄氏60度左右，这将使这个问题得以解决。这些新的岩心还将恢复白垩纪OAEs期间当地海洋条件的证据，从而也有机会首次重建南半球气候和低氧条件之间的关系。