Role of the Overturning Circulation in Carbon Accumulation (ROCCA)

翻转循环在碳积累中的作用（ROCCA）

• 批准号: NE/Y005252/1
• 负责人: Richard Williams
• 金额: $ 1.27万
• 依托单位: University of Liverpool
• 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%2FY005252%2F1
• 关键词: Role; Overturning; Circulation; Carbon; Accumulation

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.

人类活动导致大气中二氧化碳含量急剧增加，但海洋吸收了大约四分之一的人为碳（Canth），从而减缓了其增长速度。在全球范围内，由于当地从大气中吸收二氧化碳，以及大规模的洋流，尤其是大西洋经向翻转环流（AMOC），北大西洋储存了最多数量的Canth，将Canth的高水位输送到北部地区，在那里它们冷却，变得更稠密并下沉到远离大气的更深处。模型预测，尽管大气中的二氧化碳持续增加，但由于地表变暖增加了分层，降低了二氧化碳的溶解度，并且在未来几十年内，碳汇的规模仍将减少。 AMOC 减弱会减慢稠水向深处的输送。然而，关于通量峰值和下降时间的模型存在很大差异。相同的模型显示了海洋碳传输的大范围，通常与 AMOC 表示有关。因此，海气通量和北大西洋角积累的海洋运输之间的平衡在现在和未来都没有得到很好的限制，并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角积累的贡献，以便协助模型验证和确认。然而，目前还不可能直接测量人为的气海二氧化碳通量——它们在化学上与“正常”、非人类来源的二氧化碳相同。虽然它们可以通过跨洋盆地十年重复巡航来间接计算，但这种方法存在很大的不确定性。因此不可能限制为什么通量（或碳传输）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，并频繁地估计海洋中碳浓度增加的速度。该项目将致力于做到这一点。首先，我们将根据 RAPID（10 天）和 OSNAP（每月）系泊阵列的输出，对穿越北大西洋副热带和副极地边界的 Canth 输运进行新的高分辨率估计。在 RAPID，我们将把我们在 2021 年发布的 2004-2013 年时间序列延长到 2024 年，该序列确定了一个稳定的、向北的 Canth 输运，该输运在所有时间尺度（每周、每月、季节性、每年、年际）上变化很大，并且高度变化。与 AMOC 相关。我们将在西部边界的佛罗里达海峡收集新的次季节水样。流经海峡的水域代表了翻转环流的上部向北流动的绝大多数部分，但我们目前在运输计算中没有考虑到水团特征（化学或其他）的任何变化，因此尚未完全表征 AMOC：碳耦合。我们将在 OSNAP 生成 2014-2022 年新的 Canth 传输时间序列，确定它如何与 AMOC 和 RAPID 碳传输共同变化。我们将使用基于船舶和自主平台数据的新颖的公开数据集来跟踪不断变化的内部（人为）碳信号。结合起来，我们将形成一个北大西洋预算，其中包括南部和北部边界的运输，以及不断发展的内陆地区的集中度。残差将代表Canth通过地表进入（或离开）的——海气通量。海气通量和海洋环流对区域碳积累的贡献将被确定，更好地了解它们如何与AMOC共同储存碳。在将观测结果与模拟输出进行比较之前，计算方案、其组成部分以及运输/海气通量/AMOC 关系将在地球系统模型中进行测试。我们的发现将有助于提高气候模型的准确性，这对于预测气候变化的影响至关重要。