Hydrographic changes across the Atlantic Ocean on interannual to decadal time scales – an EN4 profile data analysis

The Atlantic Ocean is influenced by large-scale physical variability like changes in the Subpolar Gyre (SPG), the Atlantic Multidecadal Variability (AMV), the Atlantic Meridional Mode (AMM) or changes in the South Atlantic Anticyclone (SAA). Associated changes in temperature and salinity may severely impact open-ocean and deep-sea ecosystems. We study the variability of potential temperature and salinity profiles associated with large-scale physical variations focusing on 12 marine regions across both the North and South Atlantic Ocean (subpolar Mid-Atlantic Ridge off Iceland; Rockall Trough to Porcupine Abyssal Plain; central Mid-Atlantic Ridge; northwest Atlantic; Sargasso Sea; eastern tropical North Atlantic; central equatorial Atlantic; ecosystems from Angola to the Congo Lobe; the Benguela Current region; ecosystems off Brazil; the Vitória-Trindade Seamount Chain off Brazil; Malvinas Upwelling Current off Argentina). These regions were selected within the framework of the EU Horizon 2020 iAtlantic project. They are in proximity to major ocean circulation pathways as well as ocean monitoring arrays and are important for international conservation, Blue Growth and Blue Economy attempts.

Our methodology builds on recent work (Johnson et al., accepted, Frontiers in Marine Science) that shows that climate indices are associated with statistically-significant and spatially-coherent changes in bottom conditions across the northern North Atlantic. We use the same composite approach to investigate the relationship between indices of physical variability and potential temperature and salinity but extend the analysis to include additional indices (e.g. AMM, SAA) and to cover the entire Atlantic basin. Additionally, we use profile data instead of a gridded data product and investigate the full water column by density class, rather than focusing on bottom conditions. This enables physical mechanisms of any observed signals across the Atlantic Ocean as a whole to be explored.