Ocean Science 

Summer 2022 was memorable and record-breaking in much of Europe - for example heatwaves in France. This paper discusses marine heatwaves in the Mediterranean and northeastern Atlantic Ocean and their importance for European climate. It investigates the causes of increased sea surface temperature during summer 2022 for the seas around France through assessing the different atmospheric fluxes determining the upper ocean heat budget. It highlights the need for continuous monitoring of the ocean surface in order to assess the impact of these marine heatwave events.

Increasing Greenland Ice Sheet--melting is anticipated to impact water mass transformation in the subpolar North Atlantic and ultimately the meridional overturning circulation. Greenland meltwater redistribution pathways in and impact on the subpolar North Atlantic and overturning circulation is currently among the most debated topics. The manuscript provides new insights to both physical oceanographic processes and climate modelling. Based on a systematic setup of model configurations the importance of atmospheric feedbacks and mesoscale dynamics for specific regions of the subpolar North Atlantic are emphasized. This reaches beyond aspects of model techniques and also addresses the need for continued and improved observations in critical locations of the subpolar North Atlantic gyre circulation.

Closing the sea level budget (between observed rise and the sum of its causes) has been a challenge, is an ongoing effort and has primarily concerned the global mean. Here, the authors use machine learning to identify sub-areas with similar trends to close the sea level budget on a regional level, with much reduced errors compared with 1-degree grid points.

Internal tides are an important agent of ocean mixing which affects water mass character and circulation. This paper highlights the sensitivity of internal tide generation, propagation and dissipation (related to their mixing impact) to their context (stratification and circulation).

In this paper, a new hypothesis is put forward to explain the remarkable freshening of the Subpolar North Atlantic that peaked in 2016. The hypothesis emphasizes the increased surface circulation in the Labrador Sea region, following a reduction in heat loss to the atmosphere during the period 2000-2013. This new hypothesis, supported by the analysis of a very high resolution ocean model, contrasts with other studies that concluded to an overwhelming role of the reduced Atlantic Meridional Overturning Circulation in the freshening. In the present study, the AMOC decline is shown to account for not more than 27% of the freshening. Overall, this paper points out that surface properties of the Subpolar North Atlantic Ocean, which are important for European climate, cannot be understood in terms of AMOC variability only, but rather depend on the horizontal circulation at the ocean surface and on regional air-sea exchanges.