Collaborative Research - Eocene Climate Record of Seymour Island: The Environmental Context for Ecological and Evolutionary Change

该奖项由极地计划办公室南极地质和地球物理计划提供，为一项研究提供资金，以调查南极西摩岛始新世的古环境条件。始新世早期开始的降温趋势，到渐新世早期南极永久冰盖的增长达到顶峰，标志着第三纪气候变化最显著的时期，这既是因为它的规模，也是因为它对陆架动物群的组成、多样性和生态的影响。南极半岛上的西摩岛提供了一个独特的环境，在这个环境中，气候和环境变化之间的相互作用可以直接与无脊椎动物大型动物的同时进化有关。由于西摩岛的南纬位置较高，西摩岛的古近纪沉积序列可以记录冷却开始的时间以及随时间变化的幅度，比敏感性较低的低纬度地点更准确。此外，由于演替是高度僵化的，在这种环境变化的背景下，可以直接评估无脊椎动物群落多样性和生态的变化模式。这些高纬度陆架动物群在古近纪的演化尤为重要，因为它们可能是许多南半球暖水动物群多样化的来源。理查德·阿伦森(Dauphin Island Sea Lab)和丹尼尔·布莱克(Daniel Blake)(伊利诺伊大学)表示，始新世的冷却对高纬度浅海动物的生态产生了深远的影响。他们假设，冷却消除了温暖水域中大量存在的粉碎贝壳的捕食者，从而解除了对剩余软体动物的捕食压力。作为回应，他们预测，贝壳钻探腹足类动物的捕食压力将随着时间的推移而增加，而抵御贝壳破碎者的特有贝壳结构将显示出下降。他们目前正在通过对西摩岛始新世La Meseta组的古生物调查来验证这一假设。然而，为了评估他们的假设，即冷却是生态变化的直接原因，关键是要独立评估温度历史，并直接与它们记录的捕食模式联系在一起。该项目将与阿伦森和布莱克合作，为西摩岛上的始新世剖面生成高分辨率的温度曲线。这一记录将来自几个双壳类、腹足类和腕足类贝壳碳酸盐的d18O值，这些分类群来自于用于古生态研究的相同层位。将通过对贝壳床内的多个分类群进行密集采样来量化共生分类群之间可能的偏移量(重要影响)，以确保可以汇编有意义的综合长期记录。将从每个采样层收集每个可用分类单元的重复样本，以便在评估在整个始新世观察到的变化幅度时，能够适应时间层内的变异性。作为Aronson和Blake野外团队的一员，将在该项目下收集用于同位素分析的样本。这将确保温度和动物群变化的记录明确联系在一起。这种综合办法将使我们更全面地了解气候变冷对南极生态系统的进化和生态影响，并洞察动物群对全球气候变化的反应。

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for a study to investigate paleoenvironmental conditions during the Eocene on Seymour Island, Antarctica. The cooling trend that began with early Eocene peak warmth and culminated in the growth of permanent ice sheets on Antarctica in the early Oligocene marks the most significant interval of climate change in the Tertiary, both because of its magnitude and the effects it had on the composition, diversity and ecology shelf faunas. Seymour Island on the Antarctic Peninsula provides a unique setting within which the interplay between changes in climate and environment can be directly related to the concurrent evolution of invertebrate macrofaunas. Because of its high southern latitude location, the Paleogene sedimentary sequence at Seymour Island may record the timing of the onset of cooling, and the magnitude of that change through time, more precisely than less sensitive lower latitude sites. In addition, because the succession is highly fossiliferous, patterns of change in the diversity and ecology of invertebrate communities can be directly evaluated within this context of environmental change. The evolution of these high latitude shelf faunas during the Paleogene is especially important as they may represent the source of diversification for many southern hemisphere warm water faunas. Richard Aronson (Dauphin Island Sea Lab) and Daniel Blake (University of Illinois) have suggested that cooling during the Eocene had a profound affect on the ecology of shallow marine faunas at high latitudes. They hypothesize that cooling eliminated the shell-crushing predators that abound in warmer waters, thus lifting the predation pressure on the remaining molluscan fauna. In response, they predict that predation pressure by the shell drilling gastropods will show an increase through time, and that characteristic shell architectures that defend against shell crushers will show a decline. They are currently testing this hypothesis through a paleontological investigation of the Eocene La Meseta Formation on Seymour Island. However, to evaluate their hypothesis that cooling is the direct cause of ecological change, it is critical that a temperature history be assessed independently and tied directly to their documented patterns of predation. This project will work collaboratively with Aronson and Blake to generate a high-resolution temperature curve for the Eocene section on Seymour Island. This record will be derived from the d18O values of shell carbonate from several bivalve, gastropod, and brachiopod taxa sampled from the identical horizons used for their paleoecologic study. Possible offsets among co-occurring taxa (vital effects) will be quantified through intensive sampling of multiple taxa within shell beds to ensure that a meaningful composite, long-term record can be assembled. Replicate samples for each available taxon will be collected from each sampling horizon, so that variability within time horizons can be accommodated when assessing the magnitudes of change observed throughout the Eocene. Samples for isotope analysis will be collected under this project while working as a member of Aronson and Blake's field team. This will ensure that the records of temperature and faunal change are explicitly linked. Such an integrated approach will provide a more complete understanding of the evolutionary and ecological effects of cooling on the Antarctic ecosystem, and offer insight into the response of faunas to global climate change.