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

地球科学家对晚白垩世至古近纪中期(约1亿-4000万年前)的温室世界特别感兴趣，因为有良好的地质证据表明，此时热带/亚热带条件向南延伸至南极洲，向北延伸至北极。此时，南极冰盖要么要小得多，要么没有。许多现代动植物种群的进化根植于这个温室世界，它们的扩张可能直接与这段漫长的全球变暖时期有关。这个温室世界被白垩纪-古近纪界线(K-PG)65 Ma的大灭绝事件所打断。此外，这个温暖的世界被一系列突如其来的极端变暖事件或超热事件打断，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。与更短暂的高温相比，K-PG大灭绝事件对全球生态系统的影响可能要持久得多，但我们将通过调查极地地区的地质记录来检验这一观点，极地地区是地球上对环境和气候变化最敏感的地区。极地地区这段时间的大部分地质记录来自深海钻探地点，但最好的陆上暴露是在南极洲的西摩岛。我们最近对这一地区进行了详细的调查，现在有了从白垩纪末期、跨越K-PG界线到古近纪中期的高分辨率地质记录。对大量沉积物和植物和无脊椎动物化石的分析将为我们提供有关当时南极洲周围陆地气候和浅海温度的新信息。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。我们将绘制南极最新的白垩纪-中-古近纪时期的古温度曲线，并将评估到目前为止是否发生了过热事件。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，并调查生物多样性高的时期是否与气候变暖有关。例如，亚热带植物化石和不寻常的海洋化石组合是否代表了5500万年前全球变暖事件期间偏暖生物群的极地入侵，结果在更凉爽的条件回来后灭绝了？一些研究表明，K-PG物种的大规模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速度远远高于极地。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，该数据库涵盖了最新的白垩纪到古近纪中期。物种在两极通过这一区间的辐射真的较慢吗？如果是这样，为什么速率的变化发生在K-PG边界之后？我们对南极洲的古气候和生物多样性的记录与北极和低纬度地区的记录相比如何-高纬度社区对气候变化和环境干扰特别敏感，即使在温室世界？两极的森林是如何影响气候系统的？我们的化石记录与分子研究得出的现代海洋动物群的进化史相符吗？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、气候模拟)，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.