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的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（Canth）。在全球范围内，北大西洋储存了最多的坎斯，这是由于当地从大气中吸收了二氧化碳，以及大规模的洋流，特别是大西洋经向翻转环流（AMOC）将坎斯的沃茨输送到北方，在那里它们冷却，密度越来越大，下沉到远离大气层的深度。模型预测，这种碳汇的大小将在未来减少尽管大气CO2持续增加，但由于地表变暖增加了分层，降低了CO2溶解度，并且AMOC减弱减缓了密集沃茨向深度的输送，因此，然而，在通量峰值和下降时间方面存在大量模型差异。同样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，气-海通量和海洋运输之间的平衡，以北大西洋坎斯积累没有很好地约束现在和未来，并受到很大的不确定性，以前的观测研究试图量化这些过程的贡献坎斯积累，以协助模型的验证和确认。然而，目前还不可能直接测量人为的海气CO2通量--它们在化学上与“正常”、非人为来源的CO2通量相同。虽然它们可以通过跨洋盆地十年重复巡航间接计算，但这种方法存在很大的不确定性。因此，不可能限制通量（或碳运输）在较短时间尺度上变化的原因，或者它们如何与AMOC相互作用。为此，我们需要经常对海洋运输进行估计，并经常估计海洋中碳浓度增加的速度。首先，我们将根据RAPID（10天）和OSNAP（每月）系泊阵列的输出，对北大西洋亚热带和亚极地边界的Canth输送进行新的高分辨率估计。在RAPID，我们将延长到2024年的2004-2013年的时间序列，我们在2021年发表，并确定了一个稳定的，向北的Canth传输，是高度可变的所有时间尺度（每周，每月，季节性，每年，年际），并高度相关的AMOC。我们将收集新的亚季节水样在佛罗里达海峡，在西部边界。流经海峡的沃茨代表了绝大多数的上部，向北流动的翻转环流的一部分，但我们目前没有考虑任何变化的水团特征（化学或其他）在运输计算，所以没有充分表征AMOC：碳耦合。我们将产生一个新的Canth运输时间序列2014-2022在OSNAP，确定它如何与AMOC，快速碳运输共变。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与运输在南部和北方边界，并在内陆不断发展的浓度。剩余部分将代表坎斯通过表面进入（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一起工作来储存碳。将在地球系统模型中测试计算方案、其组成部分和输送/海气通量/AMOC关系，然后将观测结果与模拟结果进行比较。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。