Ocean circulation causes the largest freshening event for 120 years in eastern subpolar North Atlantic

N. Penny Holliday (1) , Manfred Bersch (2) , Barbara Berx (3) , Léon Chafik (4, 5) , Stuart Cunningham (6) , Cristian Florindo-López (1) , Hjálmar Hátún (7) , William Johns (8) , Simon Josey (1) , Karin Margretha H. Larsen (7) , Sandrine Mulet (9) , Marilena Oltmanns (10) , Gilles Reverdin (11) , Tom Rossby (12) , Virginie Thierry (13) , Hedinn Valdimarsson (14) , Igor Yashayaev (15)

1 NOC - National Oceanography Centre [Southampton]
2 Institute of Oceanography [Hamburg]
3 MSS - Marine Scotland Science
4 MISU - Department of Meteorology [Stockholm]
5 Bolin Centre for Climate Research
6 SAMS - Scottish Association for Marine Science
7 Faroe Marine Research Institute
8 RSMAS - Rosenstiel School of Marine and Atmospheric Science
9 CLS - Collecte Localisation Satellites [Toulouse]
10 GEOMAR - Helmholtz Centre for Ocean Research [Kiel]
11 PROTEO - Processus et interactions de fine échelle océanique
12 Graduate School of Oceanography [Narragansett]
13 LOPS - Laboratoire d'Océanographie Physique et Spatiale
14 MFRI - Marine and Freshwater Research Institute
15 Bedford Institute of Oceanography

The Atlantic Ocean overturning circulation is important to the climate system because it carries heat and carbon northward, and from the surface to the deep ocean. The high salinity of the subpolar North Atlantic is a prerequisite for overturning circulation, and strong freshening could herald a slowdown. We show that the eastern subpolar North Atlantic underwent extreme freshening during 2012 to 2016, with a magnitude never seen before in 120 years of measurements. The cause was unusual winter wind patterns driving major changes in ocean circulation, including slowing of the North Atlantic Current and diversion of Arctic freshwater from the western boundary into the eastern basins. We find that winddriven routing of Arctic-origin freshwater intimately links conditions on the North West Atlantic shelf and slope region with the eastern subpolar basins. This reveals the importance of atmospheric forcing of intra-basin circulation in determining the salinity of the subpolar North Atlantic.

Domaines: Géophysique [physics.geo-ph]

N. Penny Holliday, Manfred Bersch, Barbara Berx, Léon Chafik, Stuart Cunningham, et al.. Ocean circulation causes the largest freshening event for 120 years in eastern subpolar North Atlantic. Nature Communications, 2020, 11 (1), pp.585. ⟨10.1038/s41467-020-14474-y⟩. ⟨hal-03147373⟩