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

高纬度地区的深水是在白垩纪晚期温室形成的吗？

• 批准号: 0617330
• 负责人: Deborah Thomas
• 金额: $ 15.56万
• 依托单位: Texas A&M Research Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-09-15 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0617330&HistoricalAwards=false
• 关键词: Did; Deep; Waters; Form; Latitudes

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.

这个为期三年的项目将调查极端总体温暖和大气温室气体浓度较高的气候时段的海洋热量传输。这种“温室”气候状态的特点是赤道到极地的温度梯度明显低于现代气候。平坦的经向温度梯度意味着通过海洋或大气环流向极地的热量输送增强。研究小组将确定南大洋中深水的组成，以检验深水在温室气候期间形成于高纬度地区的假设。为了评估深海在向极地热量输送和维持低赤道至极地温度梯度方面的作用，有必要确定深水在哪里形成和如何循环，这是全球温暖气候的特点。该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晚期中深水组成的起点，以解决在极端温暖时期深水是在低纬度(温暖的咸水深水)还是在高纬度形成的问题。现有的稳定同位素记录不能确定深水来源或环流模式，然而，最近的模式模拟表明，在晚白垩世期间，南大洋和北太平洋发生了大规模的深水对流。该小组将通过产生深海钻探项目和目标区内ODP点的鱼类化石残留物的钕同位素组成的记录，来确定塞诺曼晚期至坎帕尼亚晚期(95-75 Ma)的中深水团的组成。此外，对保存完好的浮游有孔虫进行的Nd同位素分析将有助于深入了解深海来源和南大洋风化输入的变化。来自鱼牙的锶同位素数据将在缺乏生物地层年龄控制的两个地点提供年龄控制。智力上的好处：该研究提供了一种方法来评估一个温室气候间隔期间的深海环流的性质，并增加对温室气候间隔期间经向翻转环流在全球热量重新分配中的更大作用的理解。项目成果对过去气候的数值模型做出了贡献，这些模型提供了对地质时期气候变化速度和程度的估计。广泛的影响：本科生和研究生是研究活动的组成部分。学生参与样本准备、数据获取和解释，并可以在同行评议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样性项目的帮助下，来自地球科学界传统上代表性不足的群体的学生将成为参与目标。该项目将促进一名年轻女性地球科学家的事业，并有助于使深海钻探项目和大洋钻探计划的遗产永垂不朽。研究成果被纳入教育和外展活动。对社会的间接惠益包括为了解温室气候条件时期的气候变化作出的贡献。