Recent hiatus caused by varying heat sink and the salinity anomalies in the North Atlantic

Abstract

The global surface warming started to slow down at the beginning of the 21st century which is recognized as a “hiatus”. Observation-based and model-based analyses have proposed different perspectives to explain where the heat goes and the underlying mechanisms, such as a reduction in radiative forcing or a heat sequestration in deep oceans. This study using the ocean hindcast simulations shows that the increased heat was mostly stored in upper 700 m in global oceans. The Atlantic and the Pacific have the largest contributions in heat rearrangement. In Pacific, it occurred mainly in the upper 700 m layer, dominated by a La Niña pattern in the tropical Pacific during the hiatus; while in the Atlantic, the increased heat has penetrated to 2500 m and was most prominent in the tropical area and the subpolar area. In the subpolar North Atlantic, the salinity anomaly corresponded well with the ocean heat content (OHC) anomaly. The positive salinity/OHC anomaly indicated a weaker Atlantic Meridional Overturning Circulation (AMOC) during the hiatus, and the formation/melting of sea ice also corresponded well with salinity variations.