Impact of changing Arctic sea ice extent, sea ice age, and snow depth on sea salt aerosol from blowing snow and the open ocean for 1980-2017

Abstract

The Arctic is undergoing rapid change: temperature is rising at double the rate as the global average, sea ice extent is declining, the age of sea ice is becoming younger, and snow depth on sea ice is thinning. The effect of these changes on sea salt aerosol (SSA) produced by oceanic wave-breaking and the sublimation of wind-lofted salty blowing snow on sea ice is poorly understood. We use the GEOS-Chem chemical transport model to quantify how Arctic SSA concentrations have changed and assess the relative roles of changing extent of the open ocean, multi-year sea ice (MYI), first-year sea ice (FYI), and snow depths on SSA emissions for 1980-2017. We combine snow depths from the Lagrangian snow-evolution model (SnowModel-LG) together with an empirically-derived snow salinity function of snow depth to derive spatially and temporally varying surface snow salinity over Arctic FYI. We implement this surface snow salinity in the GEOS-Chem model, which simulates SSA emissions from blowing snow and from the open ocean. We contrast this simulation of SSA with a GEOS-Chem simulation assuming uniform snow salinity on FYI. Both simulations are consistent with multiyear (2005–2014) in situ observations of SSA mass concentrations at four sites in the Arctic. We find that surface snow salinity on Arctic sea ice is increasing at a rate of ~30% decade-1 and SSA emissions are increasing at a rate of 7-9% decade-1 during the cold season (November-April). These increases are due to the replacement of MYI with more saline FYI and thinning snow depth on sea ice. As a result, simulated SSA mass concentrations over the Arctic increase by 8-12% decade-1 in the cold season for the 1980-2017 period. This is consistent with the observed 10-12%/decade trend in SSA mass concentrations at Alert, Canada. During the warm season (May-Oct), our simulation predicts that SSA mass concentrations over the Arctic increase by 7-11% decade-1. This warm season increase is due to decreasing sea extent which results in increasing open ocean emissions of SSA. These large changes in SSA concentrations could potentially affect past and future bromine explosions as well as Arctic climate feedbacks.