Did Deep Waters Form at High Latitudes During the Late Cretaceous Greenhouse?

这个为期三年的项目将调查极端总体温暖和高大气温室气体浓度的气候间隔期间的海洋热传输。这种“温室”气候状态的特点是赤道到两极的温度梯度明显低于现代。较平坦的纬向温度梯度意味着通过海洋或大气环流增强的向极地的热量输送。研究小组将确定南大洋中层和深层沃茨的组成，以检验深层沃茨在温室气候期间形成于高纬度地区的假设。确定深海沃茨形成的位置和它们是如何循环的，对于评估深海在向极地的热量输送和维持全球温暖气候所特有的低赤道到极地的热梯度方面的作用是必要的。研究小组选择南大洋的大西洋/印度洋部分作为全球重建白垩纪中期至晚期中层和深水组成的起点，以解决深层沃茨是在低纬度（温暖、含盐的深层沃茨）还是在极端温暖时期的高纬度形成的问题。目前可用的稳定同位素记录不允许确定深水的物源或循环模式，然而，最近的模型模拟表明，大规模的对流发生在南大洋和北太平洋的深水沃茨在晚白垩世。该小组将通过记录目标区域深海钻探项目（DSDP）和ODP站点的化石鱼碎片的新石器时代同位素组成，确定Cenomanian晚期至Campanian晚期（95 - 75 Ma）的中层和深水质量的组成。此外，Nd同位素分析保存完好的南极有孔虫将提供深入了解深水源区和风化输入南大洋的变化。锶同位素数据从鱼的牙齿将提供年龄控制在两个网站缺乏生物地层年龄control.Intellectual优点：这项研究提供了一种手段，评估性质的深海环流在一个间隔的温室气候和增加了解的更大的作用，在温室气候间隔的全球热量重新分配的赤道翻转环流。项目结果有助于过去气候的数值模型，提供通过地质时期的气候变化的速率和幅度的估计。更广泛的影响：本科生和研究生是不可或缺的研究活动。学生参与样品制备，数据采集和解释，并可能在同行评审的科学期刊上发表结果，并参加专业会议。在德克萨斯农工大学多元化项目的帮助下，来自传统上在地球科学领域代表性不足的群体的学生成为参与的目标。&该项目将促进一名年轻女性地球科学家的职业生涯，并有助于延续深海钻探项目和大洋钻探计划的遗产。研究成果已纳入教育和外联活动。对社会的间接惠益包括有助于了解温室气候条件期间的气候变化。

This three-year project will investigate oceanic heat transport during climate intervals of extreme overall warmth and high atmospheric greenhouse gas concentrations. Such 'greenhouse' climate states are characterized by equator to pole thermal gradients significantly lower than the modern. Flatter meridional temperature gradients imply enhanced poleward heat transport either via oceanic or atmospheric circulation. The research team will establish the composition of intermediate and deep waters in the Southern Ocean to test the hypothesis that deep waters formed in high latitude regions during greenhouse climates. Determining where deep waters formed and how they circulated is necessary for evaluating the role of the deep oceans in poleward heat transport and maintenance of low equator to pole thermal gradients characteristic of globally warm climates. The team selected the Atlantic/Indian sector of the Southern Ocean as a starting point for global reconstruction of middle to Late Cretaceous intermediate- and deep-water composition to address the issue of whether deep waters formed at low latitudes (warm, saline deep waters) or high latitudes during periods of extreme warmth. Presently available stable isotope records do not permit determination of deep-water provenance or circulation patterns, however, recent model simulations suggest that large-scale convection of deep waters occurred in the Southern Ocean and North Pacific during the Late Cretaceous. The team will determine the composition of intermediate- and deep-water masses during late Cenomanian to late Campanian (95-75 Ma) by generating records of the Neodymium isotopic composition of fossil fish debris from Deep Sea Drilling Project (DSDP) and ODP Sites in the targeted region. In addition, Nd isotope analyses of well-preserved planktic foraminifera will provide insight into deep-water provenance and changes in weathering inputs to the Southern Ocean. Strontium isotope data from fish teeth will provide age-control in the two sites lacking biostratigraphic age control.Intellectual Merit: The research provides a means of assessing the nature of deep-sea circulation during one interval of greenhouse climate and of increasing understanding of the larger role of meridional overturning circulation in global heat redistribution during greenhouse climate intervals. Project results contribute to numerical models of past climates that provide estimates of rates and magnitudes of climate change through geologic time.Broader Impacts: Undergraduate and graduate students are integral to the research activities. Students are involved in sample preparation, data acquisition and interpretation, and may publish results in peer-reviewed, scientific journals and participate in professional meetings. Students from groups traditionally under-represented in the geosciences are targeted for participation with assistance from diversity programs at Texas A&M University. The project will enhance the career of a young female geoscientist, as well as help to perpetuate the legacy of the Deep-Sea Drilling Project and Ocean Drilling Program. The research results are integrated into education and outreach activities. Indirect benefits to society include contributions made to understanding climate variations during periods of greenhouse climate conditions.