NSFGEO-NERC: C-Streams: The Gulf Stream control of the North Atlantic carbon sink

海洋吸收了人类每年排放的大约四分之一的二氧化碳，减缓了气候变化。北大西洋对人为碳吸收尤为重要。北大西洋还拥有强大的由生物和物理过程驱动的“自然”碳循环。来自美国和英国的一组科学家将通过关注控制北大西洋碳汇的机制——特别是海洋环流的影响——来解决海洋碳汇在未来将如何演变的基本知识缺口。这是一个由美国国家科学基金会地球科学理事会（NSF/GEO）和英国国家环境研究委员会（NERC）通过NSF/GEO-NERC牵头机构协议共同资助的项目。该协议允许美国/英国提交一份联合提案，并由其调查员拥有最大比例预算的机构进行同行评审。在成功地共同确定一个奖项推荐后，每个机构资助预算的比例，以支持各自国家机构的科学家。除了美英合作外，该项目还包括与巴哈马群岛学校的合作，大量的公共宣传，以及对早期职业博士后研究员的支持。关于北大西洋在碳吸收方面的作用的普遍观点是，它受地表通量控制，因此加强分层将减少未来的吸收。该项目团队假设，墨西哥湾流输送的营养物质和低碳水也将影响北大西洋未来的碳吸收。墨西哥湾流向北大西洋注入了富含营养物质和人为碳含量低的旧水，推动了海洋中一些最高的二氧化碳吸收率，并形成了大部分亚极地和亚热带环流的二氧化碳吸收率模式。该项目的目标是：(1)量化和了解佛罗里达海峡湾流的源水；(2)测量并模拟墨西哥湾流进入北大西洋时所携带的营养物质和碳的变化过程；(3)了解墨西哥湾流如何影响北大西洋现在和未来的碳吸收；(4)将这一新的认识传播给那些指导未来海洋二氧化碳吸收测量和管理我们对气候变化反应的人。该项目的具体成果将包括：(1)为期两年的佛罗里达海峡每日物理、生物地球化学和速度场的时间序列，表征墨西哥湾流特性的源点变化；(2)墨西哥湾流及其南半球的动力和生物地球化学输送的2年时间序列和再循环成分。这些输送变化的特征及其与全盆地环流的关系；(3)将新观测资料与长期原位和卫星观测资料以及有针对性的模式实验相结合，以了解墨西哥湾流营养物和低碳运输如何随近场和远场海洋和风条件而变化，并推断它们如何在几十年的时间尺度上变化。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。

The ocean takes up about one-quarter of the carbon dioxide (CO2) emitted by humans each year, slowing climate change. The North Atlantic Ocean is disproportionately important for anthropogenic carbon uptake. The North Atlantic also hosts a strong “natural” carbon cycle driven by both biological and physical processes. A team of scientists from the US and UK will address a fundamental knowledge gap as to how the oceanic carbon sink will evolve in the future, by focusing on the mechanisms controlling the North Atlantic carbon sink – particularly the effect of ocean circulation. This is a project jointly funded by the National Science Foundation’s Directorate for Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award recommendation, each Agency funds the proportion of the budget that supports scientists at institutions in their respective countries. In addition to the US/UK collaboration, the project includes a partnership with The Island School in the Bahamas, substantial public outreach, and support for an early career postdoctoral researcher.The prevailing view of the North Atlantic’s role in carbon uptake is that it is controlled by surface fluxes, such that strengthening stratification will reduce future uptake. The project team hypothesize that the transport of nutrients and low-carbon waters by the Gulf Stream will also influence future carbon uptake over the North Atlantic. The Gulf Stream injects old nutrient rich and anthropogenic carbon-poor waters into the North Atlantic, driving some of the highest rates of CO2 uptake seen anywhere in the ocean and shaping patterns of CO2 uptake across much of the subpolar and subtropical gyres. The project objectives are to: (1) Quantify and understand the source waters that feed the Gulf Stream at Florida Straits;(2) Measure and model the processes that modify the nutrients and carbon carried by the Gulf Stream as it enters the North Atlantic; (3) Understand how the Gulf Stream affects North Atlantic carbon uptake now and into the future; (4) Disseminate this new understanding to those steering future measurements of oceanic CO2 uptake and managing our response to climate change. Specific outcomes from the project will include: (1) A two-year time series of daily physical, biogeochemical, and velocity fields across the Florida Straits, characterizing the source-point variability of Gulf Stream properties; (2) A two-year time series of dynamical and biogeochemical transports of the Gulf Stream and their southern hemisphere and recirculating components. Characterisation of the variability of these transports and how they relate to the basin-wide circulation; (3) Synthesis of the new observations with long-term in situ and satellite observations and with targeted model experiments to build an understanding of how Gulf Stream nutrient and low-carbon transports vary in relation to near-field and far-field oceanic and wind conditions and to infer how they may be changing over multi-decadal time scales.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.