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

Fram Strait, located between Svalbard and Greenland, serves as a crucial gateway connecting the Arctic Ocean and the North Atlantic, facilitating the exchange of heat and freshwater between these regions. Warm and saline Atlantic Water (AW) is carried northwards by the West Spitsbergen Current (WSC), and constitutes the main source of oceanic heat and salt entering the Arctic Ocean. Variations in the AW inflow strongly influence both Arctic ocean and sea ice conditions. An array of moorings has been monitoring the year-round inflow of AW in the WSC, providing hydrographic and current data from 1997 – 2024. A robust, long-term AW warming trend of 0.20°C/decade is identified, leading to a total increase of 0.54°C over the 27-year record. Distinct multi-annual warm and cold anomalies are identified, lasting ~2 years, with two warm periods (2005–2007 and 2015–2017) and two cold periods (1997–1999 and 2019–2024), linked to distinct shifts in the AW temperature regime. Notably, the most recent cold anomaly persisted for over five years—more than twice the duration of previous events. The interannual variability in AW temperatures results from a combination of advection from upstream in the Nordic Seas and local atmospheric forcing. Temperature anomalies propagate northward into the Arctic Ocean along the AW inflow pathway to the north of Svalbard, with a 2-month lag relative to Fram Strait, thus the expected continued rise in AW temperatures and associated heat transport will have profound and lasting impacts on the future state of the Arctic Ocean.