The Caribbean Through-Flow is an important conduit between the North Atlantic Subtropical Gyre and the upper branch of the Atlantic Meridional Overturning circulation. Gradone et al. used observations collected during a series of consecutive 90-days glider transects during summer 2024. Their results show a significant decline in the magnitude of the zonal transport (by about 50%) which is attributed to a shift in dynamics from geostrophic balance to increased mesoscale activity. They provide an important insight into how ocean gliders in combination with other data streams help to further understand mesoscale circulation and quantify the contributions of eddies to transport in this understudied region of the Caribbean.

This is an interesting study using a large rotating tank in the laboratory to simulate the flow through the Strait of Gibraltar. Laboratory experiments in geophysical fluid dynamics are increasingly rare, yet are highly visual and stimulating. The results are of high impact for understanding the processes such as tides determining the exchange between the Mediterranean and the Atlantic.

The sea surface microlayer (SML) is the thin layer on top of the ocean that is in direct contact with the atmosphere which is crucial for air–sea interactions. A novel paper shows data profiles close to the water surface in a mesocosm experiment. Using microsensor profiles at high vertical resolution, it shows dissolved oxygen and temperature gradients from the air, through the sea surface microlayer and into the water below. Phytoplankton bloom dynamics and surfactant concentrations influence the oxygen concentration and the diffusive layer depth but not temperature gradients. This has implications for air-sea exchanges across the sea surface microlayer.

Oxygen is fundamental to ocean biogeochemical processes, with deoxygenation potentially reducing biodiversity, and disrupting biogeochemical cycles. This paper develops and implements a new inverse method to decompose oxygen change into its constituent parts by linking each process to concomitant changes in temperature and dissolved inorganic carbon (DIC). They apply this method to a GO-SHIP repeated section of the North Atlantic Ocean. They find that alterations in remineralisation, either local or upstream, are responsible for up to half of the total oxygen decrease seen in the upper 2000 m between 1992 and 2015. This method could be repeated on any dataset, observations or model, that includes temperature, DIC, and oxygen concentration data.

The paper contributes to our knowledge of the impact of marine heat waves on ecosystems, a subject that is topical and that we know little of. The impact on coccolithophores is important for carbon uptake. The impact of MHW more generally on algal blooms is also important for higher trophic levels, the wider ecosystem, and for commercial interests such as aquaculture. The study gives useful confirmation that the environmental ranges defined by O’Brien et al for coccolithophore blooms do seem to apply even in these anomalous MHW conditions and in two separate regions.