Assessing the effect of dissolution on key Pliocene Mg/Ca-based tropical temperature records

评估溶解对上新世主要基于镁/钙的热带温度记录的影响

基本信息

批准号：
1658553
负责人：
Ana Ravelo
金额：
$ 11.26万
依托单位：
University of California-Santa Cruz
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-04-01 至 2020-03-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1658553&HistoricalAwards=false
关键词：
Assessing effect dissolution key Pliocene

项目摘要

The tropical Pacific harbors the largest mass of very warm water of the world's ocean and is a primary source of heat and moisture to the atmosphere. Changes in the temperature gradients across the tropical Pacific drive major changes in tropical circulation and global climate. Studies of the tropical Pacific during the Pliocene Epoch (three to five million years before present) can provide important insight into how the Earth's climate behaved at a time in the geologic past when atmospheric carbon dioxide concentrations were similar to today (~100 ppm higher than preindustrial values). Reconstructions of Pliocene tropical Pacific temperatures using geochemical techniques agree with some Pliocene climate model simulations, but not others. This unresolved issue is the focus of this research project. The aim of this project is to re-evaluate the Pliocene temperature estimates that are based on the magnesium to calcium ratio (Mg/Ca) of fossil shells by quantifying whether changes in the preservation of the shells resulted in biased temperature estimates. The results of this work willl provide important validation of climate models used to simulate warm climate states. This project involves the professional training of a graduate student, training of undergraduate students from underrepresented groups in STEM fields, and outreach to undergraduates in the San Francisco and Monterey Bay Areas. Many of the existing sea surface temperature records from the tropical Pacific are derived from the Mg/Ca composition of planktonic foraminifera, which is susceptible to dissolution on the seafloor and in the sediments; enhanced dissolution results in a cold temperature bias. It is standard practice to correct for the effect of dissolution using carbonate ion concentrations at the location and water depth of the sediment core. However, dissolution can change with time and the effects of changing dissolution on Mg/Ca-based temperature estimates is the most likely source of proxy bias in the tropical Pacific. This project will measure the boron to calcium (B/Ca) ratio of benthic foraminifera in the same samples that were used to produce published Mg/Ca-temperature estimates in the tropical Pacific over the last 5 Myrs. B/Ca is a proxy for carbonate ion concentration, and thus can be used to properly adjust the Mg/Ca-temperature estimates to account for dissolution. The new B/Ca analyses will be applied to evaluating potential dissolution biases at Ocean Drilling Project (ODP) Hole 806 in the West Pacific warm pool, but will also, using a more limited set of analyses, evaluate ODP 847 in the East Pacific cold tongue. Both the absolute temperatures and the West-East temperature difference will be quantified once the effect of dissolution is taken into account, and compared to climate model simulations of the Pliocene warm period.

热带太平洋拥有世界海洋中最温水的最大质量，是大气中的热和水分的主要来源。热带太平洋地区温度梯度的变化驱动了热带循环和全球气候的重大变化。在上新世时期对热带太平洋的研究（在现场前三到五百万年）可以提供重要的见解，以了解地质二氧化碳浓度与今天相似的地质碳浓度在地质学过去的一次表现（比工业前值高约100 ppm）。使用地球化学技术的上新世热带太平洋温度的重建与某些上新世气候模型模拟一致，但与众不同。这个未解决的问题是该研究项目的重点。该项目的目的是通过量化壳体保存的变化是否导致温度估计值，重新评估基于化石壳的镁与钙比（mg/ca）的上新世温度估计。这项工作的结果将对用于模拟温暖气候状态的气候模型进行重要验证。该项目涉及对研究生的专业培训，对STEM领域中代表性不足小组的本科生的培训，以及向旧金山和蒙特雷湾地区的本科生宣讲。来自热带太平洋的许多现有海面温度记录源自浮游有孔虫的mg/ca组成，浮游物有孔虫易于在海底和沉积物中溶解。增强的溶解导致冷温偏置。在沉积物芯的位置和水深下，使用碳酸盐离子浓度纠正溶解的效果是标准实践。但是，溶解可能会随着时间而变化，而改变溶解对基于Mg/Ca的温度估计的影响是热带太平洋的最可能的代理偏差来源。该项目将在过去5个MYR中在热带太平洋中用来在热带太平洋中产生公开的Mg/Ca-temperature估计的相同样品中底栖有孔虫的硼与钙（B/CA）比率。 B/CA是碳酸盐离子浓度的代理，因此可以用于正确调整Mg/Ca-temperature估计值以解释溶解。新的B/CA分析将用于评估西太平洋暖池的海洋钻井项目（ODP）806的潜在溶出偏置，但还将使用更有限的分析来评估东太平洋冷舌的ODP 847。一旦考虑到溶解的效果，将量化绝对温度和西方温度差，并将其与上新世热时期的气候模型模拟进行比较。