England Matthew H, Li Zhi, Huguenin Maurice F, Kiss Andrew E, Sen Gupta Alex, Holmes Ryan M, Rahmstorf Stefan
Centre for Marine Science and Innovation (CMSI) and ARC Australian Centre for Excellence in Antarctic Science, University of New South Wales, Sydney, New South Wales, Australia.
Research School of Earth Sciences and ARC Centre of Excellence for Climate Extremes, Australian National University, Canberra, Australian Capital Territory, Australia.
Nature. 2025 Jun;642(8068):636-643. doi: 10.1038/s41586-025-08903-5. Epub 2025 Jun 4.
North Atlantic Ocean circulation and temperature patterns profoundly influence global and regional climate across all timescales, from synoptic to seasonal, decadal, multidecadal and beyond. During 2023, an extreme and near-basin-scale marine heatwave developed during Northern Hemisphere summer, peaking in July. The warming spread across virtually all regions of the North Atlantic, including the subpolar ocean, where a cooling trend over the past 50-100 years has been linked to a slowdown in the meridional overturning circulation. Yet the mechanisms that led to this exceptional surface ocean warming remain unclear. Here we use observationally constrained atmospheric reanalyses alongside ocean observations and model simulations to show that air-sea heat fluxes acting on an extremely shallow surface mixed layer, rather than anomalous ocean heat transport, were responsible for this extreme ocean warming event. The dominant driver is shown to be anomalously weak winds leading to strongly shoaling (shallowing) mixed layers, resulting in a rapid temperature increase in a shallow surface layer of the North Atlantic. Furthermore, solar radiation anomalies made regional-scale warming contributions in locations that approximately correspond to some of the region's main shipping lanes, suggesting that reduced sulfate emissions could also have played a localized role. With a trend towards shallower mixed layers observed over recent decades, and projections that this will continue into the future, the severity of North Atlantic marine heatwaves is set to worsen.
北大西洋环流和温度模式在所有时间尺度上，从天气尺度到季节、年代际、多年代际及更长时间尺度，都对全球和区域气候产生深远影响。在2023年，北半球夏季出现了一次极端且近乎全洋盆规模的海洋热浪，于7月达到峰值。变暖几乎蔓延至北大西洋的所有区域，包括亚极地海洋，在过去50 - 10年里该区域的降温趋势与经向翻转环流的减缓有关。然而，导致这种异常的海洋表面变暖的机制仍不清楚。在此，我们结合海洋观测数据和模型模拟，利用受观测约束的大气再分析资料，表明作用于极浅表面混合层的海气热通量，而非异常的海洋热输送，是造成这次极端海洋变暖事件的原因。主要驱动因素是异常微弱的风，导致混合层强烈变浅，使得北大西洋浅表层温度迅速上升。此外，太阳辐射异常在大致对应该区域一些主要航道的位置上对区域尺度的变暖有贡献，这表明硫酸盐排放减少也可能起到了局部作用。鉴于近几十年来观测到混合层有变浅的趋势，并且预计这种趋势未来还将持续，北大西洋海洋热浪的严重程度将加剧。
