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

该奖项由极地方案办公室南极地质和地球物理方案提供，为调查南极洲西摩岛始新世古环境条件的研究提供资金。从始新世早期最温暖的时期开始，到渐新世早期南极洲永久冰盖的增长达到顶峰的冷却趋势标志着第三纪气候变化最重要的时期，这既是因为其幅度，也是因为其对大陆架动物群的组成、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，气候和环境变化之间的相互作用可以直接关系到大型无脊椎动物的同时进化。由于西摩岛位于南纬度较高的位置，它的古近纪沉积序列可能会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区更精确。此外，由于演替是高度的生物多样性，无脊椎动物群落的多样性和生态的变化模式，可以直接在环境变化的背景下进行评估。这些高纬度大陆架动物群在古近纪的演化特别重要，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（多芬岛海洋实验室）和丹尼尔·布莱克（伊利诺伊大学）提出，始新世的冷却对高纬度浅海动物群的生态产生了深远的影响。他们假设，冷却消除了大量存在于温暖沃茨中的破坏贝壳的捕食者，从而提高了对剩余软体动物群的捕食压力。 作为回应，他们预测钻壳腹足动物的捕食压力将随着时间的推移而增加，而防御破壳者的特征外壳结构将出现下降。他们目前正在西摩岛上对始新世拉梅塞塔组进行古生物学调查，以验证这一假设。然而，为了评估他们的假设，即冷却是生态变化的直接原因，至关重要的是，温度的历史被独立评估，并直接与他们记录的捕食模式。 该项目将与Aronson和Blake合作，为西摩岛的始新世剖面生成高分辨率的温度曲线。 这一记录将来自壳碳酸盐的d18O值从几个双壳类，腹足类，腕足类类群采样从相同的层位用于他们的古生态学研究。将通过对贝壳层内的多个分类群进行密集采样，对共同发生的分类群之间可能的抵消（生命效应）进行量化，以确保能够收集有意义的复合长期记录。 将从每个取样层收集每个现有分类群的重复样品，以便在评估整个始新世观察到的变化幅度时，能够适应时间范围内的变化。 同位素分析的样品将在该项目下收集，同时作为阿伦森和布莱克的实地小组的成员工作。这将确保温度和动物群变化的记录有明确的联系。这种综合办法将使人们更全面地了解变冷对南极生态系统的演变和生态影响，并使人们深入了解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.