Importance of Boundary Processes for Heat Uptake in the Subpolar North Atlantic
Importance of Boundary Processes for Heat Uptake in the Subpolar North Atlantic
复制标题
DOI：
10.1029/2020jc016366
复制
发表时间：
2020-07
期刊：
影响因子：
--
通讯作者：
D. Desbruyères;B. Sinha;E. McDonagh;S. Josey;N. P. Holliday;D. Smeed;A. New;A. Megann;B. Moat-B.-M
中科院分区：
文献类型：
--
作者：
D. Desbruyères;B. Sinha;E. McDonagh;S. Josey;N. P. Holliday;D. Smeed;A. New;A. Megann;B. Moat-B.-M
北大西洋次极环流（700 ~ 2000 m）的年代际至多年代际温度变化显著地反映了全球海洋热吸收格局。在这里，通过海洋分析产品（EN4）、海洋状态估计（ecco4）和理想化的建模方法，研究了这种变异性的起源和主要途径。SPG中温的持续增减与上层海洋的长期冷暖状态有关，最大的垂直异常热交换发生在大陆边界和强洋流附近。特别是，沿拉布拉多、伊明格和纽芬兰盆地边界的垂直扩散过程是1996 - 2014年观测到的近期中深度变暖趋势的重要驱动因素。这些过程的总体影响通过具有适当的类边界参数化的一维扩散模型来捕捉，并通过在三维数值模拟中被动示踪剂的边界聚焦向下传播来证明。我们的研究结果表明，SPG中中等温盐性的缓慢和准周期性通风以及相关的热吸收并不是严格由公海的对流重新激活事件驱动的，而是受到边界下沉和混合的关键贡献。因此，北大西洋中深度海洋特性建模和预测技术的提高，将需要对环绕格陵兰岛和纽芬兰岛的边界洋流内的表层-深层动力联系进行适当的表示。北大西洋亚北极盆地在调节气候系统中起着重要作用。这在海洋表面（以及大气）和深海层之间的直接联系中尤为明显，这使得物理和生物地球化学异常（例如热量和碳）的长期封存和随后的传播成为可能。在这里，我们采用多工具方法来研究异常热量在该区域向下渗透的机制。1950 - 2016年收集的历史观测资料，结合理想化的模拟策略表明，中间层的年代际温度趋势与上层海洋的长期冷暖状态密切相关，这表明具有一级可预测性的潜力。利用数值模型中的实际海洋再分析和示踪剂传播实验，我们将重点集中在观测良好的年代（1992 - 2016），表明相关的温度异常向下渗透受到拉布拉多海、伊尔明格海和纽芬兰盆地高能边界流的混合和平流的重要贡献。
The decadal to multidecadal temperature variability of the intermediate (700 – 2,000 m) North Atlantic Subpolar Gyre (SPG) signi fi cantly imprints the global pattern of ocean heat uptake. Here, the origins and dominant pathways of this variability are investigated with an ocean analysis product (EN4), an ocean state estimate (ECCOv4), and idealized modeling approaches. Sustained increases and decreases of intermediate temperature in the SPG correlate with long ‐ lasting warm and cold states of the upper ocean with the largest anomalous vertical heat exchanges con fi ned to the vicinity of continental boundaries and strong ocean currents. In particular, vertical diffusive processes along the boundaries of the Labrador, Irminger, and Newfoundland basins are important drivers of the recent intermediate depth warming trend observed during 1996 – 2014. The overall effect of those processes is captured by a one ‐ dimensional diffusive model with appropriate boundary ‐ like parametrization and demonstrated through the boundary ‐ focused downward propagation of a passive tracer in a 3 ‐ D numerical simulation. Our results imply that the slow and quasi ‐ periodic ventilation of intermediate thermohaline properties and associated heat uptake in the SPG are not strictly driven by convection ‐ restrati fi cation events in the open seas but also receives a key contribution from boundary sinking and mixing. Increased skill for modeling and predicting intermediate ‐ depth ocean properties in the North Atlantic will hence require the appropriate representation of surface ‐ deep dynamical connections within the boundary currents encircling Greenland and Newfoundland. Summary The subarctic basins of the North Atlantic Ocean play a fundamental role in regulating the climate system. This occurs notably throughout direct connections between the ocean surface (and hence the atmosphere) and deep oceanic layers, which enable the long ‐ term sequestration and subsequent propagation of physical and biogeochemical anomalies (e.g., heat and carbon). Here, we employ a multitool approach to investigate the mechanisms by which anomalous heat can penetrate downward in this region. Historical observations gathered during 1950 – 2016 and combined with idealized modeling strategy suggest that decadal temperature trends in the intermediate layer strongly correlate with long ‐ lasting warm and cold states of the upper ocean, suggesting potential for fi rst ‐ order predictability. Focusing on the well ‐ observed era (1992 – 2016) using a realistic ocean reanalysis and tracer propagation experiments in a numerical model, we show that the associated downward penetration of temperature anomalies receives an important contribution from mixing and advection within the energetic boundary currents of the Labrador Sea, Irminger Sea, and Newfoundland basin.