The Gulf Stream control of the North Atlantic carbon sink

湾流对北大西洋碳汇的控制

• 批准号: NE/W009579/1
• 负责人: Daniel Jones
• 金额: $ 50.74万
• 依托单位: British Antarctic Survey
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FW009579%2F1
• 关键词: Gulf; Stream; control; North; Atlantic

We are all aware that atmospheric CO2 has risen over our lifetimes leading to global warming. The ocean has played an important role in moderating that atmospheric rise by taking up and storing 25% of the emitted carbon. However, the extent to which the ocean will continue to act in this manner as the ocean warms and becomes more acidic is unclear, as is the response in the future as we reduce carbon emissions to net zero in the next 20-30 years. A key region in addressing this question is the North Atlantic, which is disproportionately important for ocean carbon uptake. This carbon sink involves both the uptake of natural carbon (due to surface cooling and biological uptake) and of anthropogenic carbon (due to the rise in atmospheric CO2). A prevailing view is that this carbon sink will weaken in the future as surface warming decreases solubility and increases stratification, which inhibits the supply of nutrients and carbon to the surface ocean. However, this viewpoint takes a local perspective and does not account for the effect of the circulation in redistributing nutrients and carbon over the global ocean.We wish to propose and test the alternative viewpoint that the circulation plays a central role in determining the carbon sink, by setting the supply of nutrients and carbon to the surface waters of the North Atlantic. In particular, there is a phenomenon - the western boundary current or Gulf Stream - that is crucial for this problem. We know that the Gulf Stream is important for supplying heat to higher latitudes, leading to a warmer European climate. However, its role in driving carbon uptake remains little explored. Surface observations show that there are elevated rates of carbon uptake downstream of the Gulf Stream. This uptake occurs as older waters carried below the surface by the Gulf Stream are transferred downstream to the surface. These older waters are rich in nutrients and depleted in anthropogenic carbon. When these waters outcrop to the surface, they determine the surface nutrient and carbon concentrations, and so control the carbon uptake from the atmosphere. How much carbon uptake is driven by this nutrient and carbon 'stream' in the North Atlantic depends on multiple climate-sensitive processes, including the density range of the stream, the Gulf Stream transport, and a suite of physical and biogeochemical processes occurring along its path. We will use observations and models to comprehensively understand this pivotal phenomenon, distinguishing between several different mechanisms that transform the fluxes of properties at the beginning of the Gulf Stream to those entering the North Atlantic. We will make new measurements of how the Gulf Stream supply of nutrients and carbon varies all the way from Florida Straits to a carbon uptake hotspot downstream, a distance of over 2000 miles. We will employ moorings in Florida Straits to determine the nutrient and carbon properties at the start of the Gulf Stream. We will deploy a fleet of BioArgo floats and gliders to reveal how nutrients and carbon are conveyed from low to high latitudes, documenting their downstream evolution through the effects of physical transport, mixing and biological cycling. Our work programme sits between two ongoing observing arrays of the Atlantic meridional overturning circulation, RAPID at 26N and OSNAP between Labrador and Scotland, and these arrays place our observations in a wider context. We will test our ideas using experiments in circulation models, including assessing the sensitivity of the North Atlantic carbon sink to physical processes. Finally, we will evaluate how the carbon sink varies in climate model projections and establish whether the models' responses occur for the right reasons. Unravelling these controls of the ocean carbon sink is crucial if we are to understand and credibly predict the future evolution of the carbon sink, especially given the uncertain ocean response to net zero emissions.

我们都知道，大气二氧化碳在我们的一生中已经上升，从而导致全球变暖。海洋通过占用和存储25％的发射碳来调节大气上升，发挥了重要作用。但是，随着海洋变暖并变得更加酸性，海洋将继续以这种方式行事，而将来的反应也是如此，因为我们在未来20 - 30年内将碳排放量减少到净零。解决这个问题的一个关键区域是北大西洋，这对于海洋碳吸收非常重要。该碳水槽既涉及自然碳的摄取（由于表面冷却和生物学摄取）和人为碳（由于大气CO2的升高）。一个普遍的观点是，随着表面变暖降低溶解度并增加了分层，该碳汇将来会减弱，从而抑制养分和碳向地表海洋的供应。但是，该观点具有本地视角，并不解释循环在全球海洋上重新分配养分和碳的影响。我们希望提出和测试循环的替代观点，即通过将营养素和碳的供应设置为北部大西洋地区的地表水的供应，在确定碳汇中起着核心作用。特别是，存在一种现象 - 西部边界电流或海湾流 - 对于此问题至关重要。我们知道，海湾流对于向更高纬度的热量供应很重要，从而导致欧洲气候温暖。但是，它在驱动碳吸收中的作用仍然很少探索。表面观察表明，海湾流下游的碳吸收率升高。这种吸收发生时，由于墨西哥湾流在表面下方携带的较旧水被下游转移到表面。这些较旧的水富含营养，并在人为碳中耗尽。当这些水露头到表面时，它们会确定表面养分和碳浓度，从而控制大气中的碳吸收。北大西洋的这种营养和碳“流”驱动了多少碳吸收，这取决于多种气候敏感的过程，包括河流的密度范围，墨西哥湾流的传输以及一套沿其路径发生的物理和生物地球化学过程。我们将使用观察值和模型全面理解这种关键现象，从而区分了几种不同的机制，这些机制将墨西哥湾流的开头转化为进入北大西洋的人的特性通量。我们将对从佛罗里达海峡到下游的碳吸收热点（超过2000英里）的养分和碳的供应方式进行新的测量。我们将在佛罗里达海峡使用系泊设备来确定海湾流开始时的养分和碳特性。我们将部署一组生物argo浮子和滑翔机的机队，以揭示营养和碳从低纬度传达到高纬度的方式，从而通过物理运输，混合和生物循环的影响来记录其下游的进化。我们的工作计划位于两个正在进行的观察到大西洋子午翻转循环的阵列之间，在拉布拉多和苏格兰之间的26N和OSNAP之间，这些阵列将我们的观察结果置于更广泛的环境中。我们将使用循环模型中的实验测试我们的想法，包括评估北大西洋碳汇对物理过程的敏感性。最后，我们将评估气候模型预测的碳汇如何变化，并确定由于正确原因而出现模型的响应。如果我们要理解并可靠地预测碳汇的未来演变，尤其是考虑到海洋对净零排放的不确定反应，揭开对海洋碳汇的这些控制至关重要。