Pathways and Upstream Origins of Warming Dense Waters Supplying the Faroe Bank Channel Overflow

Dense, cold water passes through the Faroe Bank Channel (FBC) which contributes to the lower branch of the Atlantic Meridional Overturning Circulation (AMOC). Observations have shown that the bottom water warmed at an average rate of 0.1°C per decade since around 2000. Using GLORYS12 reanalysis (1/12°), we find that it captures the observed variability including warming and a lagged salinification trend since 2004. To investigate the sources and pathways of warming dense bottom waters, we seed Lagrangian particles in the Faroe Shetland Channel (FSC) from 2000–2020, and backtrack them for 10 years. We find two upstream flow pathways, one via the East Greenland and on through the Jan Mayen Channel. These two source flows converge, both via cyclonic circulation around the Iceland Sea into the East Icelandic Current (EIC), and where the EIC and southward flow along the Jan Mayen Ridge merge. The total western-sourced overflows subsequently follow the north slope of the Iceland-Faroe ridge and the Faroe plateau prior to entering the FSC. Particles either directly enter the FSC or overshoot the channel and recirculate southwards along the Norwegian shelf slope. An additional eastern pathway emerges from a previously overlooked source along the Norwegian shelf slope originating from the Lofoten Basin. The Greenland Sea deep gyre warms faster than other regions in the Nordic Seas with weak connectivity in the basin center. However, recirculation and lateral exchanges distribute warmer interior waters from the Greenland Sea into surrounding basins.