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

合作提案：小型陆生腹足动物氧同位素系统的开发和校准

• 批准号: 1528733
• 负责人: Jason Rech
• 金额: $ 6.06万
• 依托单位: Miami University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1528733&HistoricalAwards=false
• 关键词: Collaborative; Proposal; Development; calibration; oxygen

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.

陆地蜗牛是北美陆地地质记录中最常见的化石之一。它们的壳是由碳酸钙组成的，它们壳的氧同位素组成记录了生长期间的气候条件。因此，陆地蜗牛的氧同位素组成有可能在广阔的时空尺度上重建过去的气候。然而，迄今为止，人们对从蜗牛中推断出的气候信息种类知之甚少，因此，它们作为古气候档案的当前用途是有限的。该提案将开发、测试和校准小型陆地蜗牛的氧同位素系统，用于北美陆地环境中的古气候代理。这一代用物的现代校准将通过陆地古气候代用物的发展造福社会，该代用物能够在广泛的空间和时间尺度上重建过去的气候，也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范围内以惊人的速度减少的动物群。该项目将教授和培养未来的科学家，从高中到博士候选人，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群体的参与。结果的传播将包括不同的受众（专家和一般公众），以英语和西班牙语传播到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，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，这些样本是在从德克萨斯州南部到加拿大的两条横贯北美的横断面上收集的。他们将利用为陆地蜗牛开发的蒸发稳态通量平衡混合模型，通过量化壳ä18O与相关气候变量（温度、降水ä18O、降水量、相对湿度）之间的关系，确定壳ä18O值的主要气候控制因素。研究人员认为：(1)温带环境（纬度26 ~ 48°N）小型陆生螺的氧同位素组成主要反映降水的氧同位素组成，因此可以用来推断过去降水氧同位素值的变化；(2)由于相对湿度较低，生活在干旱~半干旱环境的蜗牛壳氧同位素值高于预测值。在对活标本的氧同位素系统进行校正后，研究人员将进行两个案例研究，以确定小蜗牛的氧同位素值与洞穴动物或其他代理记录的氧同位素记录的追踪程度。这项提议的工作将使我们能够更好地量化北美广大地区和许多不同类型的沉积物过去的气候变化。