COLLABORATIVE RESEARCH: Constraining Tertiary Temperatures, Salinities, and Ocean Chemistry: An Isotopic and Trace-metal Study of Serially-sampled Mollusks

限制第三纪温度、盐度和海洋化学：连续取样软体动物se的同位素和痕量金属研究。第三纪（5500万~ 200万年前）是我们研究从无冰的“温室世界”到今天的“冰窖世界”转变的最佳机会，也是我们了解当前和未来气候对高大气二氧化碳水平的反应的最佳机会。该提案将利用美国墨西哥湾沿岸的极好的化石记录和古代海洋温度的两个独立测量，氧同位素（18O/16O）和化石壳中的锶/钙比值，来描述全球气候的巨大变化。这些结果将解决早第三纪气候的长期争议，即“凉爽的热带悖论”。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时期，热带海洋表面温度较低。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都必须比今天高得多。对这种差异的一种常见解释是，浮游有孔虫的古温度数据受到沉积后化学蚀变（成岩作用）的修正。通过对原始软体动物壳的分析，本研究将消除以往研究的这一局限性。第二个目标是提高我们对始新世-渐新世边界附近气候转变的性质和原因的理解，该转变与南极快速冰川作用和动物群翻转有关。最近对美国墨西哥湾沿岸平原沉积物中鱼类耳石的氧同位素比率的研究表明，动物群的翻转与季节性增加有关，特别是该地区的冬季更冷。然而，对这些数据的解释受到全球冰量和当地盐度变化估计的限制。这项研究将使用软体动物Sr/Ca和18O/16O的配对测量来检查低纬度海面温度的变化和季节性。最后，将收集来自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数据的现代软体动物样本。这些样品将分析稳定同位素和痕量金属（特别是Sr/Ca），以校准痕量金属与温度的关系。

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.