Collaborative Research: Gases in the Overturning and Horizontal circulation of the Subpolar North Atlantic Program (GOHSNAP)

每年冬天，从北美大陆向东吹来的冷风使位于加拿大和格陵兰岛之间的拉布拉多海的表层海水变冷。随着海洋变冷，大气中的氧气和二氧化碳混合成一层厚厚的水层，最终向南扩散，填满北大西洋和更远的地方。这种水团的存在使北大西洋的任何地方都不会完全缺氧。拉布拉多海的垂直混合也将二氧化碳重新分配到深海中，在那里它可以停留数百年，防止它对温室效应做出贡献。然而，控制海洋吸收气体的过程还没有得到很好的理解或量化。有鉴于此，在过去的一个世纪里，海洋的氧气逐渐耗尽，同时也吸收了大量的人为二氧化碳，观察气体交换过程对于理解和预测海洋和气候系统的演变至关重要。自2014年以来，人们一直在监测拉布拉多海的环流，从海底一直延伸到海洋表面的一系列仪器电缆。该项目将气体传感器添加到该阵列中，以研究控制气体交换的速率和过程。通过该项目，学生和博士后将在丰富的国际合作者网络中接受跨学科海洋学的培训。为了响应提高公众海洋素养的需求，项目科学家将与罗德岛大学内部空间中心合作，向合作高中的教育工作者直播互动科学课程，并将在三所参与学校进行现场科学培训。考虑到拉布拉多海在为氧气（O2）和二氧化碳（CO2）进入海洋的中间深度提供通道方面的独特作用，对盆地中气体吸收和运输的量化和机制理解是一个主要的科学优先事项。拉布拉多海水的氧化作用阻止了大西洋任何地方大规模缺氧的发生，该盆地的人为二氧化碳储存量是全球海洋中最高的。在大西洋，O2和CO2的吸收及其变率与热损失的动力学和翻转环流有关的假设在文献中广泛存在，但从未在直接观测的基础上进行过评估。因此，GOHSNAP（北大西洋次极地翻转和水平环流中的气体项目）解决了这一空白，并迫切需要更好地了解气体吸收、输送和翻转环流之间的相互作用。具体来说，该项目将利用美国主导的国际亚极地北大西洋倾覆项目（OSNAP）的系泊基础设施，提供连续2年的跨盆地、跨拉布拉多海南部边界O2全水柱运输记录。在该阵列上增加不同深度的氧气传感器，辅以自主平台收集的观测数据，将允许对Labrador海的氧气输出进行量化。这些数据将进一步用于碳浓度的经验模型和估计碳出口。拟议的仪器还将测量两个冬季的混合层O2和二氧化碳分压，由此计算海气交换，并与拉布拉多海对流内部的类似观测结果进行比较。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Every winter, frigid winds blowing eastward from the North American continent cool the surface waters of the Labrador Sea, which is situated between Canada and Greenland. As the ocean cools, oxygen and carbon dioxide are mixed from the atmosphere into a thick layer of water that ultimately spreads southward to fill a large volume of the North Atlantic and beyond. The presence of this water mass prevents the North Atlantic anywhere from becoming completely devoid of oxygen. Vertical mixing in the Labrador Sea also redistributes carbon dioxide into the deep ocean, where it can remain for hundreds of years, preventing it from contributing to the greenhouse effect. Yet, the processes governing the uptake of gases by the ocean are not well understood or quantified. Given that, over the last century, the ocean has become steadily more depleted in oxygen while also absorbing a large fraction of anthropogenic carbon dioxide, observing gas exchange processes is essential for understanding and predicting the evolution of the ocean and climate system. The circulation of the Labrador Sea has been monitored since 2014 with an array of instrumented cables extending from the seafloor to nearly the ocean surface. This project adds gas sensors to this array to investigate the rates and processes governing gas exchange. Through this project, a student and postdoc will be trained in interdisciplinary oceanography with a rich network of international collaborators. Responding to the need to increase public ocean literacy, the project scientists will work with University of Rhode Island’s Inner Space Center to broadcast live, interactive science sessions to educators at partner high schools and will follow-up with in-person science cafés at three participating schools.Given the unique role of the Labrador Sea in providing a pathway for oxygen (O2) and carbon dioxide (CO2) to enter the intermediate depths of the ocean, a quantification and mechanistic understanding of the gas uptake and transport in the basin is a leading scientific priority. Oxygenation of Labrador Sea water prevents large-scale hypoxia from developing anywhere in the Atlantic Ocean and anthropogenic CO2 storage in the basin is the highest in the global ocean. The assumption that, in the Atlantic Ocean, O2 and CO2 uptake and their variability are tied to the dynamics of heat loss and the overturning circulation pervades the literature but has never been evaluated on the basis of direct observations. Thus, GOHSNAP (Gases in the Overturning and Horizontal circulation of the Subpolar North Atlantic Program) addresses this gap and the urgent need to better understand interactions between gas uptake, transport, and the overturning circulation. Specifically, this program will provide a continuous 2-year record of the trans-basin, full water column transport of O2 across the southern boundary of the Labrador Sea, leveraging the mooring infrastructure of the US-lead, international Overturning in the Subpolar North Atlantic Program (OSNAP). The addition of O2 sensors at various depths on this array, supplemented by observations collected by autonomous platforms will allow for the quantification of O2 export from the Labrador Sea. The data will further be used to empirically model carbon concentrations and estimate carbon export. Proposed instruments will also measure the mixed layer O2 and pCO2 for two winters, from which air-sea gas exchange will be calculated and compared against analogous observations in the convective interior of the Labrador Sea.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.