Decades of Change: Warming Trends and Hydrographic Variability of Atlantic Water as observed in the West Spitsbergen Current (1997–2024)

Fram Strait is the main gateway between the Arctic Ocean and the North Atlantic, where warm, saline Atlantic Water (AW) flows northward via the West Spitsbergen Current (WSC) - the main source of oceanic heat and salt entering the Arctic Ocean. An array of moorings has continuously monitored the year-round inflow of AW in the WSC from 1997 to 2024, providing a 27-year record of hydrographic and current measurements. A robust, long-term AW warming trend of 0.20°C per decade was identified, amounting to a total increase of 0.54°C over the observational period. Distinct multi-annual warm and cold anomalies were identified, typically lasting ∼2 years. Two warm periods (2005–2007 and 2015–2017) and two cold periods (1997–1999 and 2019–2024) are linked to distinct shifts in the AW temperature regime. These anomalies were generally accompanied by salinity changes, with warm periods associated with more saline conditions and cold periods with fresher waters. The most recent cold anomaly is notable for persisting for over five years - more than twice as long as previous events. Interannual variability in AW temperatures reflects a combination of upstream advection of anomalies from the Nordic Seas and modulation by local atmospheric forcing. These temperature anomalies are advected into the Eurasian Basin and influence downstream conditions. The expected continued AW warming and associated increase in ocean heat transport will have profound and lasting implications for the physical and ecological future state of the Arctic Ocean.