Collaborative Proposal: Development and calibration of the oxygen isotope systematics of small terrestrial gastropods

陆地蜗牛是北美陆地地质记录中最常见的化石之一。它们的贝壳由碳酸钙组成，其贝壳的氧同位素组成记录了生长过程中的气候条件。因此，陆地蜗牛的氧同位素组成有可能在广阔的空间和时间尺度上重建过去的气候。然而，到目前为止，人们对可以从蜗牛中推断出的气候信息的种类知之甚少，因此，它们目前作为古气候档案的使用有限。这项提议将开发、测试和校准小型陆地蜗牛的氧同位素系统学，以作为北美陆地环境中的古气候指标。这一指标的现代校准将通过开发陆地古气候指标使社会受益，该指标能够在广泛的时空尺度上重建过去的气候，并将提高我们对陆地蜗牛的分类多样性和空间分布的理解，陆地蜗牛是一种在全球以令人震惊的速度减少的动物。该项目将教授和培训未来的科学家，从高中到博士生，整合来自多个领域(古生物学、生物学、第四纪地质学)的科学家，并扩大不同和代表性不足的群体的参与。结果的传播将包括不同的受众(专家和普通公众)，以英语和西班牙语到达美国和其他地方的西班牙裔社区。该项目将在代表性不足的群体和研究密集型大学的STEM学科之间建立联系。为了校准北美现代陆地蜗牛的氧同位素系统学，研究人员将分析大约1000个现代蜗牛壳样本的氧同位素组成，这些样本来自沿着两个选定的横跨北美从德克萨斯州南部到加拿大的横断面收集的现代蜗牛。他们将利用为陆生蜗牛开发的蒸发式稳态通量平衡-混合模型，通过量化Shellä18O与相关气候变量(温度、降水ä18O、降雨量、相对湿度)之间的关系，确定对Shellä18O值的主要气候控制。研究人员假设：(1)温带环境(北纬26至48度)的小型陆上钉螺的氧同位素组成主要反映降水中的氧同位素组成，因此可用于推断过去降水中氧同位素的变化；(2)生活在干旱至半干旱环境中的蜗牛的壳氧同位素值由于相对湿度较低，其值将高于预期。在对活体标本的氧同位素系统进行校准后，调查人员将进行两个案例研究，以确定小蜗牛的氧同位素值跟踪洞穴或其他替代记录的氧同位素记录的情况。这项拟议的工作将使人们能够更好地量化北美广大地区以及许多不同类型沉积物中过去的气候变化。

Land snails are one of the most common fossils in the terrestrial geologic record of North America. Their shells are composed of calcium carbonate and the oxygen isotopic composition of their shells record climatic conditions during growth. Therefore, the oxygen isotopic composition of land snails has the potential to reconstruct past climates on broad spatial and temporal scales. To date, however, there is a little understanding on the kinds of climatic information that can be inferred from the snails, and therefore, their current use as paleoclimatic archives is limited. This proposal will develop, test, and calibrate the oxygen isotope systematics of small land snails for use as a paleoclimatic proxy in terrestrial settings across North America. The modern calibration of this proxy will benefit society through the development of a terrestrial paleoclimatic proxy that is capable of reconstructing past climate over broad spatial and temporal scales and also will improve our understanding of the taxonomic diversity and spatial distribution of land snails, a fauna that is decreasing at an alarming rate globally. This project will teach and train future scientists, from high school to PhD candidates, integrate scientists from multiple fields (paleontology, biology, Quaternary geology), and broaden the participation of diverse and underrepresented groups. Dissemination of results will include a diverse audience (specialists and general public), in English and Spanish to reach the Hispanic community in USA and elsewhere. This project will establish linkages between underrepresented groups and STEM disciplines at research-intensive universities. To calibrate the oxygen isotope systematics of modern land snails in North America, investigators will analyze the oxygen isotope composition of approximately 1,000 shell samples from modern snails collected along two selected transects that cross North America from southern Texas to Canada. They will identify the primary climatic controls on shell ä18O values by quantifying the relation between shell ä18O and relevant climatic variables (temperature, ä18O of precipitation, precipitation amount, relative humidity) using an evaporative steady-state flux balance-mixing model developed for land snails. Researchers hypothesize that: (1) the oxygen isotope composition of small land snails in temperate environments (latitudes of 26 to 48 degrees N) primarily will reflect the oxygen isotope composition of precipitation, and therefore can be used to infer past changes in precipitation oxygen isotope values; and (2) shell oxygen isotope values of snails living in arid to semi-arid environments will yield higher values than predicted because of low relative humidity values. After calibration of the oxygen isotope systematics for living specimens, investigators will conduct two case studies to determine how well the oxygen isotope values of small snails track the oxygen isotope records of speleothems or other proxy records. The proposed work will allow better quantification of past climate change over broad areas of North America, and from many different types of deposits.