Role of the Overturning Circulation in Carbon Accumulation (ROCCA)

人类活动导致大气二氧化碳水平急剧增加，但海洋吸收了大约四分之一的人为碳(CATH)，减缓了大气CO2水平的增长。在全球范围内，北大西洋储存着数量最多的坎特海，这是由于当地从大气中吸收二氧化碳，以及大规模洋流，特别是大西洋子午线翻转环流(AMOC)，将坎特海中的高密度水域输送到北部地区，在那里它们变冷，密度变大，并下沉到远离大气接触的深处。模型预测，尽管大气中的二氧化碳继续增加，但在未来几十年，这种碳汇的大小将会减小，因为表面变暖增加了层化，二氧化碳的溶解度降低，而AMOC的减弱减缓了稠密水向深处的输送。然而，关于流量峰值和下降时机，存在大量的模型价差。同样的模型显示了海洋碳传输的很大范围，通常与AMOC表示有关。因此，海气通量和海洋输送对北大西洋CATH累积的平衡在现在和未来都没有得到很好的约束，而且存在很大的不确定性。以前的观测研究试图量化这些过程对CATH累积的贡献，以帮助模型验证和验证。然而，目前还不可能直接测量人为的大气-海洋二氧化碳通量--它们在化学上与那些“正常”的、非人类来源的二氧化碳的通量相同。虽然可以通过跨大洋盆地十年一遇的重复航次间接计算，但这种方法存在很大的不确定性。因此，不可能限制通量(或碳传输)为什么在较短的时间尺度上变化，或者它们如何与AMOC相互作用。为此，我们需要频繁地估计海洋运输量，并经常估计海洋中碳浓度增加的速度。这个项目将寻求做到这一点。首先，我们将根据快速(10天)和OSNAP(每月)系泊阵列的输出，生成跨越北大西洋副热带和亚极地边界的CATH传输的新的高分辨率估计。在RAPID上，我们将把我们在2021年发布的2004-2013年时间序列延长到2024年，该序列确定了稳定的向北Canth输送，在所有时间尺度上(每周、每月、季节性、每年、每年)都是高度可变的，并与AMOC高度相关。我们将在西部边界的佛罗里达海峡收集新的亚季节性水样。流经海峡的水代表了倾覆环流中向北流动的上层部分的绝大多数，但我们目前在那里的输送计算中没有考虑到水团特征(化学或其他)的任何变化，因此没有完全描述AMOC：碳耦合。我们将在OSNAP生成一个新的2014-2022年Canth输送时间序列，确定它如何与AMOC和快速碳输送共同变化。我们将使用基于船舶和自主平台数据的新颖的、公开可用的数据集来跟踪不断变化的内部(人为)碳信号。联合起来，我们将形成一个北大西洋预算，在南部和北部边界进行运输，并在内陆不断发展集中。残留物将代表石灰岩通过表面--海-气通量进入(或离开)。将确定海-气通量和海洋环流对区域碳积累的贡献，从而更好地理解在AMOC的作用下，它们如何共同储存碳。在将观测结果与模拟结果进行比较之前，将在地球系统模型中测试计算方案、其组成部分以及传输/海-气通量/AMOC关系。我们的发现将有助于提高气候模型的准确性，这对预测气候变化的影响至关重要。

Human activities have caused atmospheric CO2 levels to increase dramatically, but their growth has been slowed by the oceans absorbing approximately one quarter of this anthropogenic carbon (Canth). Globally, the North Atlantic Ocean stores the highest quantities of Canth, due to local CO2 uptake from the atmosphere, and large-scale ocean currents, particularly the Atlantic Meridional Overturning Circulation (AMOC) delivering waters high in Canth to northern locations where they cool, get denser and sink to great depths away from contact with the atmosphere.Models project that the size of this carbon sink will reduce in the coming decades despite continued atmospheric CO2 increases, as surface warming increases stratification, decreases CO2 solubility, and AMOC weakening slows the transport of dense waters to depth. However there is substantial model spread regarding flux peak, and decline timing. The same models show a large range in ocean carbon transports, often related to AMOC representation. The balance between air- sea fluxes and ocean transports to North Atlantic Canth accumulation is thus not well constrained both now and into the future, and subject to large uncertainties.Previous observational studies have attempted to quantify the contributions of these processes to Canth accumulation in order to assist with model verification and validation. However, it is not currently possible to directly measure anthropogenic air-sea CO2 fluxes - they are chemically identical to those with 'normal', non-human-derived CO2. And while they can be calculated indirectly from trans-ocean basin decadal repeat cruises, this approach is subject to large uncertainties. It is thus impossible to constrain why fluxes (or carbon transports) vary on shorter timescales, or how they interact with the AMOC. For this we require frequent estimates of ocean transports combined with frequent estimates of how quickly carbon concentrations are increasing in the ocean.This project will look to do precisely that. Firstly, we will generate new high-resolution estimates of Canth transports across the subtropical and subpolar boundaries of the North Atlantic, relying on the outputs from the RAPID (10day) and OSNAP (monthly) mooring arrays. At RAPID, we will extend to 2024 the 2004-2013 time-series we published in 2021 and that identified a stable, northward Canth transport that was highly variable over all time scales (weekly, monthly, seasonally, annually, interannually), and highly correlated to the AMOC.We will collect new sub-seasonal water samples in Florida Straits, at the western boundary. The waters that flow through the Straits represent the vast majority of the upper, northward-flowing part of the overturning circulation but we don't currently account for any variability in water mass characteristics (chemical or otherwise) in the transport calculation there, so are not fully characterising the AMOC:carbon coupling.We'll generate a novel Canth transports time-series for 2014-2022 at the OSNAP, identifying how it co-varies with AMOC, and RAPID carbon transports. We'll track the changing interior (anthropogenic) carbon signal using novel, publicly-available datasets based on ship and autonomous platform data. Combined, we'll form a North Atlantic budget with transports at the southern and northern boundaries, and evolving concentrations in the interior. The residual will represent Canth entering (or leaving) through the surface - the air-sea flux.The contributions of air-sea fluxes and ocean circulation to regional carbon accumulation will be determined, better understanding how, with AMOC, they work together to store carbon. The calculation scheme, its components and transport/air-sea flux/AMOC relationships will be tested in earth system models, before observations are compared to simulation outputs. Our findings will help improve the accuracy of climate models, which is crucial for predicting the effects of climate change.