A shutdown of ocean convection in the subpolar North Atlantic, triggered by enhanced melting over Greenland, is regarded as a potential transition point into a fundamentally different climate regime^1,2,3. Noting that a key uncertainty for future convection resides in the relative importance of melting in summer and atmospheric forcing in winter, we investigate the extent to which summer conditions constrain convection with a comprehensive dataset, including hydrographic records that are over a decade in length from the convection regions. We find that warm and fresh summers, characterized by increased sea surface temperatures, freshwater concentrations and melting, are accompanied by reduced heat and buoyancy losses in winter, which entail a longer persistence of the freshwater near the surface and contribute to delaying convection. By shortening the time span for the convective freshwater export, the identified seasonal dynamics introduce a potentially critical threshold that is crossed when substantial amounts of freshwater from one summer are carried over into the next and accumulate. Warm and fresh summers in the Irminger Sea are followed by particularly short convection periods. We estimate that in the winter 2010–2011, after the warmest and freshest Irminger Sea summer on our record, ~40% of the surface freshwater was retained.

格陵兰岛融化加剧引发北大西洋次极海对流停止，被认为是向根本不同的气候体制^1,2,3的潜在过渡点。。注意到未来对流的一个主要不确定因素在于夏季融化和冬季大气强迫的相对重要性，我们使用综合数据集（包括距离水文记录长达十年的水文记录）调查了夏季条件在多大程度上限制了对流。对流区域。我们发现，温暖而清新的夏季，其特征是海面温度升高，淡水浓度和融化，伴随着冬季热量和浮力的降低，这导致淡水在地表附近的持续时间更长，并导致对流延迟。通过缩短对流淡水出口的时间跨度，确定的季节动态会引入潜在的临界阈值，当一个夏天的大量淡水结转至下一个夏天并积累时，就会越过该阈值。在艾明格海温暖而清新的夏季之后，是特别短的对流期。我们估计，在2010-2011年冬季，在有记录以来最温暖和最新鲜的艾明格海夏天之后，约40％的地表淡水得以保留。