The Iceland-Faroe warm-water flow towards the Arctic estimated from satellite altimetry and in situ observations

• Main Authors: Hansen, Bogi, Larsen, Karin Margretha Húsgarð, Hátún, Hjálmar, Olsen, Steffen Malskær, Gierisch, Andrea Martina Ulrike, Østerhus, Svein, Ólafsdóttir, Sólveig Rósa
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; Arctic Ocean; Faroes; Global warming; Iceland; Nordic Seas
• Online Access: https://doi.org/10.5194/egusphere-2023-828; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-828/

The inflow of warm and saline Atlantic water to the Arctic Mediterranean (Nordic Seas and Arctic Ocean) between Iceland and the Faroes (IF inflow) is the strongest Atlantic inflow branch in terms of volume transport and is associated with a large transport of heat towards the Arctic. The IF inflow is monitored in a section east of the Iceland–Faroe Ridge (IFR) by use of sea level anomaly (SLA) data from satellite altimetry, a method that has been calibrated by in situ observations gathered over 2 decades. Monthly averaged surface velocity anomalies calculated from SLA data were strongly correlated with anomalies measured by moored acoustic Doppler current profilers (ADCPs) with consistently higher correlations when using the reprocessed SLA data released in December 2021 rather than the earlier version. In contrast to the earlier version, the reprocessed data also had the correct conversion factor between sea level slope and surface velocity required by geostrophy. Our results show that the IF inflow crosses the IFR in two separate branches. The Icelandic branch is a jet over the Icelandic slope with average surface speed exceeding 20 cm s −1 , but it is narrow and shallow with an average volume transport of less than 1 Sv (10 6 m 3 s −1 ). Most of the Atlantic water crosses the IFR close to its southernmost end in the Faroese branch. Between these two branches, water from the Icelandic branch turns back onto the ridge in a retroflection with a recirculation over the northernmost bank on the IFR. Combining multi-sensor in situ observations with satellite SLA data, monthly mean volume transport of the IF inflow has been determined from January 1993 to December 2021. The IF inflow is part of the Atlantic Meridional Overturning Circulation (AMOC), which is expected to weaken under continued global warming. Our results show no weakening of the IF inflow. Annually averaged volume transport of Atlantic water through the monitoring section had a statistically significant (95 % confidence level) increasing trend of ( ...