Tracking Atlantic Water heat content anomalies from the sub-polar Atlantic to the Arctic

Yueng Djern Lenn, Bangor University, School of Ocean Sciences, Menai Bridge, United Kingdom, Camille Lique, Laboratoire de Physique des Océans, Ifremer, Brest, France, N. Penny Holliday, National Oceanography Centre, Southampton, United Kingdom and Benjamin Iolo Barton, University of Western Brittany, Laboratoire d'Océanographie Physique et Spatiale (LOPS), Plouzané, France
Satellite observations show that the sea ice extent in the Eurasian Arctic has receded so far north that the much of the northern Barents Sea is ice-free even in winter. Recent work by Barton et al., 2018 demonstrates that this has coincided with 'atlantification', i.e, warming and increasing salinity, of the Barents Sea itself originating in the Atlantic Water (AW) inflow. Indeed, atlantification is also apparent in the Eurasian Arctic Ocean north of Fram Strait (Polyakov, 2017). Thus, medium-term forecasting of the Arctic stratification and sea ice may be improved by better monitoring of anomalies propagating along the AW pathways into the Arctic Ocean and Barents Seas as well as upstream through the sub-polar seas.

Within the Barents Sea, deep ventilation that modifies inflowing AW into Barents Sea Water (BSW) makes sea surface temperature (SST) a reliable indicator of heat content and thermostatic height. A comparison between thermosteric height inferred from \it{in situ} data and combined satellite altimetry and eustatic height shows considerable promise for monitoring BSW heat content variability from space, and highlights changes in seasonality observed in the last decade and a half. In the Greenland, Irminger and Norwegian (GIN) seas, we show that upper ocean heat content can accurately pinpoint the core of Arctic-bound AW, more so than SST observations alone. This implies that satellite altimetry may also be as useful for tracking AW heat content anomaly propagation through the GIN seas, upstream of the Barents Sea and Arctic Ocean. Observed AW heat content anomalies reaching the Barents Sea Opening track more coherently northwards from \sim 62 ^\circ N, downstream of where the main Greenland/Irminger Sea AW recirculation branch bifurcates from the Arctic-bound branch. This bifurcation point may be the natural southward limit for the monitoring of AW heat content anomalies useful for Arctic sea ice and stratification forecasts.