Impact of global disturbances on the evolution of life in the polar regions during the early Cenozoic PALEOPOLAR

地球科学家对白垩纪晚期至古近纪中期（约1亿至4000万年前）的温室世界特别感兴趣，因为有良好的地质证据表明，当时热带/亚热带条件延伸到南部的南极洲和北部的北极。在这个时候，南极冰盖要么小得多，要么不存在。许多现代植物和动物的进化根源都在这个温室世界，它们的扩张可能与这一长期的全球变暖直接相关。这个温室世界在白垩纪-古近纪边界（K-Pg）的65 Ma发生了大规模灭绝事件。此外，这个温暖的世界被一系列突然的极端变暖事件或超温现象所打断，这可能是由于大量二氧化碳突然释放到大气和海洋中造成的。K-Pg大灭绝事件对全球生态系统的影响可能比更短暂的高温更持久，但我们将通过调查极地地区的地质记录来测试这一想法，地球上对环境和气候变化最敏感的地区。这段时间内极地地区的大部分地质记录来自深海钻探基地，但最好的陆上暴露是在南极洲的西摩岛。我们最近详细调查了这个地方，现在有一个高分辨率的地质记录，从白垩纪末，跨越K-Pg边界，进入中期古近纪。对大量沉积物、植物和无脊椎动物化石的分析将为我们提供有关当时陆地气候和南极洲周围浅海温度的新信息。这些化石还使我们能够重建生活在极地地区的动物群和植物群的组成，并确定它们的多样性如何随着时间的推移而变化。我们将制作一条新的南极白垩纪-古近纪中期的古温度曲线，并将评估是否有超高温事件发生在如此之南。通过将化石多样性与气候记录相匹配，我们将评估植物和动物从K-Pg大灭绝中恢复所需的时间，并调查高生物多样性的时间是否与变暖事件有关。例如，亚热带植物化石和一个不寻常的海洋化石组合是否代表了在5500万年前的全球变暖事件中，爱好温暖的生物向极地入侵，只是在凉爽的条件下灭绝？一些研究表明，K-Pg大灭绝永远重置了全球进化时钟，新物种随后在热带地区的出现率远远高于两极。我们将通过将我们新的南极化石数据添加到全球数据库中来测试这一重要理论，该数据库涵盖了白垩纪末到古近纪中期。在两极，物种在这段时间内的辐射真的较慢吗？如果是这样，为什么在K-Pg边界之后立即发生了速率的变化？我们南极洲的古气候和生物多样性记录与北极和低纬度地区的记录相比如何--即使在温室世界中，高纬度社区是否对气候变化和环境干扰特别敏感？极地森林如何影响气候系统？我们的化石记录是否与通过分子研究从现代海洋动物群得出的进化历史相匹配？通过使用一系列古环境指标和分析技术（同位素地球化学，沉积相分析，古植物学，古生物学，气候建模），我们将重建过去的温室世界，并评估戏剧性的全球事件对生命进化的影响，特别是在极地地区。

The greenhouse world of the Late Cretaceous to mid-Paleogene (~100 - 40 million years ago) is of particular interest to earth scientists because there is good geological evidence to show that at this time tropical/subtropical conditions extended into Antarctica in the south and into the Arctic in the north. At this time the south polar ice cap was either much smaller or absent. Many modern groups of plants and animals have their evolutionary roots in this greenhouse world and it is possible that their expansion related directly to this prolonged period of global warmth. This greenhouse world was punctuated by a mass extinction event at 65Ma at the Cretaceous - Paleogene boundary (K-Pg). In addition, this warm world was interrupted by a series of abrupt extreme warming events, or hyperthermals, probably caused by the sudden release of massive amounts of CO2 into the atmosphere and oceans. The K-Pg mass extinction event probably had a much longer-lasting effect on global ecosystems than the more transient hyperthermals but we will test this idea by investigating the geological record from the polar regions, the regions on Earth most sensitive to environmental and climate change. Much of the geological record for this time interval for the polar regions comes from deep sea drill sites but the best onshore exposure is found on Seymour Island, Antarctica. We have recently investigated this locality in detail and now have a high resolution geological record from the end of the Cretaceous period, across the K-Pg boundary and into the mid-Paleogene period. Analysis of large collections of sediments and plant and invertebrate fossils will provide us with new information about climates on land and temperatures in shallow seas around Antarctica at that time. The fossils also allow us to reconstruct the composition of faunas and floras that lived in the polar regions and to determine how their diversity changed over time. We will produce a new palaeotemperature curve for the latest Cretaceous - mid-Paleogene interval in Antarctica, and will assess whether the hyperthermal events occurred so far south. By matching fossil diversity with the climate record we will assess the time taken for plants and animals to recover from the K-Pg mass extinction and investigate whether times of high biodiversity were linked to episodes of warming. For example, do sub-tropical plant fossils and an unusual marine fossil assemblage represent poleward incursions of warmth-loving biotas during a global warming event 55 million years ago, only to go extinct when cooler conditions returned? Some studies indicate that the K-Pg mass extinction reset the global evolutionary clock forever, with new species subsequently appearing at a much higher rate in the tropics than at the poles. We will test this important theory by adding our new Antarctic fossil data to a global database for the latest Cretaceous to the mid-Paleogene. Was the radiation of species through this interval really slower at the poles, and if so, why did the change in rates occur immediately after the K-Pg boundary? How does our record of palaeoclimate and biodiversity from Antarctica compare to that from the Arctic and from low latitude sites - were high latitude communities particularly sensitive to climate change and environmental disturbance, even in a greenhouse world? How did forests at the poles affect the climate system? Does our fossil record match the evolutionary history derived from modern marine faunas by molecular studies? By using a range of palaeoenvironmental indicators and analytical techniques (isotope geochemistry, sedimentary facies analysis, palaeobotany, palaeobiology, climate modelling) we will reconstruct the greenhouse world of the past and assess the impact of dramatic global events on the evolution of life, particularly in the polar regions.