Multiple pathways of deep waters in the Nordic Seas elucidate the warming and salinification of eastern overflow waters

The Faroe Bank Channel (FBC) transports dense, cold overflow water that contributes to the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). By comparing the Copernicus GLORYS12 reanalysis data (1/12°) with 27 years of CTD and ADCP data in the FBC (Larsen et al., 2024), we find that GLORYS12 well-represents an observed warming and a lagged salinification trend since the mid-1990s. To investigate the sources and pathways of warming dense bottom waters upstream of the FBC, we re-release Lagrangian particles every 5 days, randomly distributed between 650 and 1100 m, and backtrack them in time for 27 years using the ocean reanalysis data. Our analysis reveals a basin-wide warming trend of approximately 0.1°C per decade in the Greenland and Iceland Seas. However, the primary flow pathways of FBC overflows appear to originate from the Arctic via an extension of the East Greenland Current and from a previously ignored source in the Lofoten Basin, with strong mixing and recirculation between these deep current pathways. Fewer particles traced back to the Greenland Sea gyre deep water. We explore the upstream effects and locations of the warming sources and their impact on variability in the overflows within the FBC, which may improve our understanding of AMOC dynamics.