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

该奖项由极地项目办公室的南极地质和地球物理项目提供，为一项研究提供资金，以调查南极洲西摩岛始新世的古环境条件。从始新世早期的温度峰值开始，到渐新世早期南极洲永久冰盖的形成，这一降温趋势标志着第三纪气候变化最显著的时期，无论是从其规模还是对陆架动物的组成、多样性和生态的影响来看都是如此。南极半岛上的西摩岛提供了一个独特的环境，在这里，气候和环境变化之间的相互作用可以直接关系到无脊椎大型动物的同步进化。由于西摩岛位于南纬高纬度地区，古近系的沉积序列可能比不太敏感的低纬度地区更准确地记录了冷却开始的时间，以及随时间变化的幅度。此外，由于演替是高度化石化的，因此可以在这种环境变化的背景下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，因为它们可能代表了许多南半球暖水动物群多样化的来源。理查德·阿伦森（海豚岛海洋实验室）和丹尼尔·布莱克（伊利诺伊大学）认为始新世的降温对高纬度地区浅海动物的生态产生了深远的影响。他们假设，温度的降低消除了大量存在于温暖水域的碎壳捕食者，从而减轻了对剩余软体动物的捕食压力。作为回应，他们预测钻壳腹足类动物的捕食压力将随着时间的推移而增加，而防御壳粉碎机的特征壳结构将会下降。他们目前正通过对西摩岛始新世拉梅塞塔地层的古生物学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，对温度历史进行独立评估并直接与他们记录的捕食模式联系起来是至关重要的。该项目将与Aronson和Blake合作，为西摩岛始新世剖面生成高分辨率温度曲线。这一记录将从若干双壳类动物、腹足类动物和腕足类动物的壳碳酸盐d18O值中得到，这些壳碳酸盐样品取自用于古生态学研究的同一层位。通过对壳床内的多个分类群进行密集采样，量化共同发生的分类群之间可能的抵消（重要效应），以确保能够形成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，以便在评估整个始新世观测到的变化幅度时，可以适应时间范围内的变异性。作为Aronson和Blake现场团队的一员，将在该项目下收集同位素分析样本。这将确保温度和动物变化的记录明确地联系在一起。这种综合方法将使我们更全面地了解变冷对南极生态系统的进化和生态影响，并深入了解动物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.