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Deep Ocean Circulation and Carbon Cycle Links During the Quaternary

第四纪深海环流与碳循环的联系

基本信息

批准号：
NE/K005235/1
负责人：
Alex Piotrowski
金额：
$ 57.34万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2013
资助国家：
英国
起止时间：
2013 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FK005235%2F1
关键词：
Deep Ocean Circulation Carbon Cycle

项目摘要

The overall focus of this proposal is to reconstruct global deep-ocean circulation and the carbon cycle changes during glacial/interglacial cycles over the last 1.5 million years. During that time period northern hemisphere glaciation increased in intensity and the periodicity of ice ages shifted from a 40 kyr to a 100 kyr cycle. The causes for these changes are unknown, but were likely triggered by processes internal to the climate system. The research we propose will develop a better understanding of the mechanisms of past ocean circulation and its link to storage of carbon in the deep ocean. We focus on the Pacific, the largest deep ocean by volume, and the flow of lower nutrient Atlantic-sourced waters into it. The large volume of the deep Pacific means that changes in its circulation and carbon contents affect atmospheric carbon dioxide levels. We have chosen cores that allow comparison between multiple proxies of ocean circulation and climate variation. Their distribution along a major deep-water flowpath into the deep Pacific Ocean, and different depths in the water column, will allow us to reconstruct how much Atlantic-sourced nutrient and carbon poor water entered the Pacific.We will measure neodymium (Nd) isotopes as a tracer of water mass on cores which already have multiple palaeoceanographic proxy records (bottom-water temperature, ice volume, benthic carbon isotopes, sortable silt, and others). This is the first time that all of these geochemical tools will be applied on the same cores and the samples of the same age, so we will be able to directly compare the results of these different tracers, both temporally and spatially. One core, ODP Site 1123, records ocean conditions going back 1.5 million years, with a well-developed chronology, while the Chatham Rise cores are a depth transect of cores from intermediate to abyssal depths. These cores will allow us to understand past changes from both temporal and vertical perspectives. Comparing Nd isotope records from the south-western Pacific to records from the Atlantic and Indian Oceans, can provide new information about changes in global-scale thermohaline circulation.The combined use of Nd isotopes and benthic foraminiferal carbon isotope proxies can be used to deconvolve the role of ocean circulation, which affects both proxies, from global carbon cycling changes, which affect only carbon isotopes. The preliminary data we show in this proposal illustrate that the Nd isotopic composition of foraminiferal coatings is a robust archive of deep-water chemistry during the past few million years. We can now observe that many cores in the ocean have Nd isotope and benthic foraminiferal carbon isotopes which are compatible with changes in deep-water circulation on long pathlengths, though decoupling from this behaviour exists at some sites and time periods, including in the south-western Pacific. Having complete comparable records for both proxies will greatly advance our understanding of how water masses propagate through the deep ocean with implications for modelling how ocean circulation may react to anthropogenic climate change. Deep-water source and flow will also be constrained by an ocean model, which can use the distribution of multiple chemical proxies to deduce flowpaths and quantify the contributions of deep-water formation areas, as well as inputs at boundaries. The model can be used to fit all the palaeo-data, rather than simply doing scenario simulations, and global distributions of Nd isotopes can be produced and tested for different time periods. The model is high resolution for a palaeoceanographic study, but it is still computationally efficient enough to be run for many thousands of years. This data/model collaboration with a multi-proxy approach will transform our understanding of deep-ocean water-mass sourcing and structure and carbon storage at a key location in the global thermohaline circulation.

该提案的总体重点是重建全球深海环流和过去150万年来冰期/间冰期循环期间的碳循环变化。在这段时间里，北方半球冰川作用的强度增加，冰河时代的周期从40 kyr转变为100 kyr。这些变化的原因尚不清楚，但可能是由气候系统内部的过程引发的。我们提出的研究将更好地了解过去海洋环流的机制及其与深海碳储存的联系。我们重点关注太平洋，这是体积最大的深海，以及营养含量较低的南极沃茨流入太平洋。太平洋深海的体积很大，这意味着其环流和碳含量的变化会影响大气中的二氧化碳水平。我们选择的岩心可以比较海洋环流和气候变化的多个代理。它们的分布沿着一条主要的深海水流通道进入太平洋，并且在水柱的不同深度，将使我们能够重建有多少来自南极的营养物质和贫碳水进入太平洋。我们将测量钕（Nd）同位素作为已经有多个古海洋代用记录的岩心上的水团示踪剂（底层水温、冰量、底栖碳同位素、可分选的淤泥等）。这是第一次将所有这些地球化学工具应用于相同的岩心和相同年龄的样品，因此我们将能够在时间和空间上直接比较这些不同示踪剂的结果。大洋钻探计划1123号站点的岩芯记录了150万年前的海洋状况，并有一套完善的年表，而查塔姆海隆岩芯则是从中层到深海深度的岩芯深度剖面。这些核心将使我们能够从时间和垂直角度理解过去的变化。比较西南太平洋和大西洋、印度洋的Nd同位素记录，可以提供全球尺度温盐环流变化的新信息，Nd同位素和底栖有孔虫碳同位素代用指标的联合使用可以从仅影响碳同位素的全球碳循环变化中反卷积出影响这两个代用指标的海洋环流的作用。我们在这个建议中显示的初步数据表明，有孔虫涂层的Nd同位素组成是一个强大的档案深水化学在过去的几百万年。我们现在可以观察到，海洋中的许多岩心具有Nd同位素和底栖有孔虫碳同位素，这些同位素与长路径上深水环流的变化相一致，尽管在某些地点和时间段，包括在西南太平洋，与这种行为脱钩。拥有两个代理人的完整可比记录将大大推进我们对水团如何通过深海传播的理解，并对海洋环流如何对人为气候变化做出反应的建模产生影响。深海水源和水流也将受到海洋模型的制约，该模型可以利用多种化学代用指标的分布来推断水流路径，并量化深水形成区的贡献以及边界处的输入。该模型可用于拟合所有的古数据，而不是简单地进行情景模拟，并且可以产生和测试不同时间段的Nd同位素的全球分布。该模型对于古海洋学研究来说分辨率很高，但计算效率仍然足够高，可以运行数千年。这种数据/模型与多代理方法的合作将改变我们对深海水团来源和结构以及全球温盐环流关键位置碳储存的理解。