Deep North Atlantic Salinity, Density and Pre-formed Nitrate during the Last Glacial Maximum

大气中二氧化碳的增加被认为是世界上最紧迫的环境挑战之一。这一挑战的许多细节需要进一步的科学理解，包括海洋环流、大气二氧化碳和气候之间的反馈。人们普遍认为，在过去的80万年里，二氧化碳在海洋和大气之间的转移推动了二氧化碳与气候的协同变化。然而，对于是什么推动了这些转移，目前还没有达成共识，主要是因为缺乏数据来测试拟议的机制。拟议的项目直接旨在了解海洋环流与气候之间的关系，特别是在最后一次冰川盛期(LGM，约18,000年前)期间大气二氧化碳的关系。更好地了解海洋环流和气候之间的关系具有重要的社会意义，因为未来环流的变化可能会产生重大影响，如欧洲西北部气候的变化、热带辐合带(ITCZ)的位置以及人为二氧化碳进入海洋的吸收。对海洋应对气候变化的控制的科学理解将为社会对人为二氧化碳的反应提供信息。此外，该项目将支持一名女性博士生在科学领域的全面参与和领导力发展。更具体地说，这项工作的重点是对最近在北大西洋进行的一次研究考察期间收集的沉积孔隙流体进行实验室分析，并对数据进行解释。这项分析和解释工作旨在解决以下假设：-在最后一次冰川盛期(LGM)期间，北大西洋深海密度分层主要由盐度变化而不是温度变化主导。-在末次盛会期间，北大西洋深水是源自北大西洋的水和源自南大洋的水的混合物。-D18O与水密度之间的当前关系存在于末次冰期，从而能够利用海底碳酸盐D18O来推断密度。-主要硝酸盐(NO3-)去除过程的相对平衡与今天类似，深水中NO3-的平均浓度也是如此。-北大西洋LGM的深水主要是低营养的预制水。分析工作包括通过滴定高精度测定氯离子浓度，开发一种新的基于密度的古盐度测定方法以及硝酸盐的同位素分析(O和N同位素)。这些数据将被用来约束反扩散模型，以推断北大西洋西部LGM的底水性质。

Increasing atmospheric CO2 is recognized as one of the world's most pressing environmental challenges. Many details of this challenge require further scientific understanding, including the feedbacks between ocean circulation, atmospheric CO2 and climate. It is generally accepted that CO2 transfer between the ocean and atmosphere has driven the co-variation of CO2 and climate over the past 800,000 years. However, there is no consensus on what drives these transfers principally because there is a lack of data to test proposed mechanisms. The proposed project is directly aimed at understanding the relationship between ocean circulation and climate, particularly atmospheric CO2, during the Last Glacial Maximum (LGM, ~18,000 years ago). The improved understanding of the relationship between ocean circulation and climate is societally important because future changes in the circulation are likely to have large effects, such as changes in the climate of northwest Europe, the position of the Intertropical Convergence Zone (ITCZ) and the uptake of anthropogenic CO2 into the ocean. Scientific understanding of the controls of ocean response to climate change will inform the societal response to anthropogenic CO2. Additionally, this project will support full participation and leadership development of a female Ph.D. student in science. More specifically, the work focuses on laboratory analysis of sedimentary pore fluids collected during a recent research expedition in the North Atlantic, and interpretation of the data. This analytical and interpretative work is aimed at addressing the following hypotheses: - During the Last Glacial Maximum (LGM), deep-ocean density stratification in the North Atlantic was dominated by salinity variation rather than temperature variation. - During the LGM, North Atlantic deep water was a mixture of water originating in the North Atlantic and water originating in the Southern Ocean. - The present relationship between d18O and water density existed during the LGM, enabling use of benthic carbonate d18O to infer density. - The relative balance of the key nitrate (NO3-) removal processes was similar to that of today, as was the average NO3- concentration in deep water. - Deep water in the LGM North Atlantic was dominated by low preformed nutrient water. - A significant fraction of atmospheric pCO2 reduction during the LGM was due to the low pre- formed nutrients in the Atlantic.The analytical work includes, high precision determination of chloride concentrations by titration, the development of a new density based method of paleo-salinity determination and the isotopic analysis (O and N isotopes) of nitrate. This data will be used to constrain inverse diffusion models to infer bottom water properties of the LGM western North Atlantic.