title: Sea-ice transport driving Southern Ocean salinity and its recent trends.
abstract: Recent salinity changes in the Southern Ocean are among the most prominent signals of climate change in the global ocean, yet their underlying causes have not been firmly established. Here we propose that trends in the northward transport of Antarctic sea ice are a major contributor to these changes. Using satellite observations supplemented by sea-ice reconstructions, we estimate that wind-driven northward freshwater transport by sea ice increased by 20 ± 10 per cent between 1982 and 2008. The strongest and most robust increase occurred in the Pacific sector, coinciding with the largest observed salinity changes. We estimate that the additional freshwater for the entire northern sea-ice edge entails a freshening rate of -0.02 ± 0.01 grams per kilogram per decade in the surface and intermediate waters of the open ocean, similar to the observed freshening. The enhanced rejection of salt near the coast of Antarctica associated with stronger sea-ice export counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater. Although the data sources underlying our results have substantial uncertainties, regional analyses and independent data from an atmospheric reanalysis support our conclusions. Our finding that northward sea-ice freshwater transport is also a key determinant of the mean salinity distribution in the Southern Ocean further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the ocean, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep ocean and surface waters.
authors: Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland.|Center for Climate Systems Modeling, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland.
authors: F Alexander
authors: FA
authors: Haumann
authors: Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland.|Center for Climate Systems Modeling, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland.
authors: Nicolas
authors: N
authors: Gruber
authors: Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland.
authors: Matthias
authors: M
authors: Münnich
authors: Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland.|Biogeochemical Modelling, GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors: Ivy
authors: I
authors: Frenger
authors: Integrated Climate Data Center (ICDC), Center for Earth System Research and Sustainability, University of Hamburg, Hamburg, Germany.
authors: Stefan
authors: S
authors: Kern
mesh_terms: D000864:Antarctic Regions; D001272:Atmosphere / Q000737:chemistry; D057231:Climate Change / Q000706:statistics & numerical data; D005615:Freezing; D005618:Fresh Water / Q000032:analysis*; D049673:History, 20th Century; D049674:History, 21st Century; D046448:Ice Cover / Q000737:chemistry*; D009792:Oceans and Seas; D054712:Salinity; D012623:Seawater / Q000032:analysis* / Q000737:chemistry*; D013696:Temperature; D035501:Uncertainty; D014872:Water Movements; D014919:Wind