COLLABORATIVE RESEARCH: Constraining Tertiary Temperatures, Salinities, and Ocean Chemistry: An isotopic and Trace-Metal Study of Serially-Sampled Mollusks

控制第三纪温度、盐度和海洋化学：对连续采样的软体动物的同位素和微量金属研究格罗斯曼、Y·罗森塔尔和C.李尔在第三纪(距今5500万年到200万年前)为我们提供了最好的机会来研究从无冰的“温室世界”到今天的“冰室世界”的转变，并了解现在和未来气候对大气中高二氧化碳水平的反应。这项提议将利用美国墨西哥湾沿岸出色的化石记录和两个独立的古代海洋温度测量指标--氧同位素(18O/16O)和化石贝壳中的锶/钙比--来描述全球气候的这种戏剧性变化。这些结果将解决关于早第三纪气候的一个长期争议，即“凉爽热带悖论”。浮游有孔虫的氧同位素测量表明，在高纬度地区经历异常温暖的一段时间里，热带海面温度较低。这与温室世界气候的模型模拟相矛盾，该模型预测，极地和热带的温度肯定比今天高出很多。对这种差异的一种常见解释是，浮游有孔虫的古温度数据被沉积后的化学变化(成岩作用)所修改。通过对原始软体动物贝壳的分析，本研究将消除以往研究的这一局限性。第二个目标是增进我们对始新世-渐新世边界附近与南极快速冰川作用和动物群翻转有关的气候过渡的性质和原因的理解。最近利用美国墨西哥湾沿岸平原沉积物中的鱼类耳石中的氧同位素比率进行的研究表明，动物群的颠覆与季节性的增加有关，特别是该地区较冷的冬季。然而，由于对全球冰量和局部盐度变化的估计很差，对这些数据的解释受到限制。这项研究将使用软体动物锶/钙和18O/16O的配对测量来研究这次事件中低纬海面温度和季节性的变化。最后，将利用墨西哥湾和以色列埃拉特不同地点的温度、盐度和海水18O/16O数据收集现代软体动物样本。将对这些样品进行稳定同位素和痕量金属(特别是锶/钙)的分析，以校准痕量金属-温度关系。

ABSTRACTConstraining Tertiary Temperatures, Salinities, and Ocean Chemistry: An Isotopic and Trace-metal Study of Serially-sampled MollusksE. Grossman, Y. Rosenthal, and C. Lear The Tertiary Period (55 to ~2 million years ago) presents our best opportunity to study the transition from an ice-free "greenhouse world" to today's "icehouse world" and to understand the response of present and future climates to high atmospheric carbon dioxide levels. This proposal will take advantage of the superb fossil record of the US Gulf Coast and two independent measures of ancient ocean temperatures, oxygen isotope (18O/16O) and strontium/calcium ratios in fossil shells, to characterize this dramatic change in global climate. These results will address a longstanding controversy of early Tertiary climate, the "cool tropics paradox". Oxygen isotope measurements of planktonic foraminifera indicate cool tropical sea-surface temperatures for a time when high latitudes experienced unusual warmth. This contradicts model simulations of greenhouse world climates that predict that both polar and tropical temperatures must have been significantly warmer than today. A common explanation for the discrepancy is that paleotemperature data from planktonic foraminifera have been modified by post-depositional chemical alteration (diagenesis). By analyzing pristine mollusk shells, this study will obviate this limitation of previous studies. A second objective is to improve our understanding of the nature and causes of the climatic transition near the Eocene-Oligocene boundary associated with rapid Antarctic glaciation and faunal overturn. Recent work using oxygen isotope ratios in fish otoliths from US Gulf Coastal Plain sediments has linked faunal overturn to increased seasonality, in particular colder winters in this region. However, interpretation of such data is limited by poorly constrained estimates of global ice volume and local salinity variations. This study will use paired measurements of mollusk Sr/Ca and 18O/16O to examine changes in low-latitude sea-surface temperatures and seasonality across this event. Lastly, modern mollusk samples will be collected with temperature, salinity, and seawater 18O/16O data from various sites in the Gulf of Mexico and Eilat, Israel. These samples will be analyzed for stable isotopes and trace metals (especially Sr/Ca) to calibrate trace metal-temperature relations.