Incorporation of nitrogen compounds into sea ice from atmospheric deposition

Temporal measurements of temperature, salinity, water–oxygen isotopic ratio and nutrient concentrations at Saroma-ko Lagoon, southern Sea of Okhotsk, were made in February–March 2008 to examine the processes by which nitrogen compounds from the atmosphere were incorporated via snowfall into sea ice. Granular ice made up more than half the ice thickness, and the mass fraction of snow in the snow-ice layer on top of the ice ranged from 0.8% to 46.9%. The high concentrations of NO₃⁻ + NO₂⁻ and NH₄⁺ observed in the snow and snowice throughout the study period were likely due to the proximity of the study site, in northern Japan, to the east coast of the Asian continent. Pollutants containing high NO₃⁻ and NH₄⁺ concentrations are transported from East Asia and deposited in snowfall over the sea ice in the southern part of the Sea of Okhotsk. Compared with NO₃⁻ + NO₂⁻ and NH₄⁺ concentrations, PO₄³⁻ concentrations in the snow and snow-ice were low. The strong correlation between the NO₃⁻ + NO₂⁻ and NH₄⁺ concentrations in the snow-ice and the mass fraction of snow indicates that the nitrogen compounds on top of the sea ice were controlled mainly by the snow contribution to the sea ice when snow-ice predominated. Our results indicate that chemical cycles in sea ice can be affected by polluted precipitation (snow) originating from a nonpolar sea.