Sea ice influence on the neon balance of the surface waters in the Arctic Ocean

Neon (Ne) and Helium (He) isotope data sets collected in the ‘Switchyard’ region of the Arctic Ocean between 2005 and 2013 show a distinct excess in Ne concentrations in the upper waters, mostly in the surface mixed layer of ice-covered waters. The average ΔNe values have an excess in the ice-covered surface layer of about 7.5 %. These observed Ne concentrations fall above those expected from solubility equilibrium with the atmosphere and typical excess air concentrations due to partial and/or full bubble dissolution. Meanwhile, the average Δ 4 He values which are close to 3.5 %, are constant with depth in the Switchyard Region. In contrast, data sets from several Greenland and Norwegian seas (GSNS) cruises where samples were collected in waters without sea ice cover show that both ΔNe and Δ 4 He values are nearly constant with depth. The Greenland and Norwegian Seas serve as a control region, representing a similar open-ocean field environment but lacking sea-ice formation in the regions where our samples were taken. This contrast allows us to isolate the neon saturation anomalies that arise specifically due to sea-ice formation processes in the Arctic Ocean. We attribute the near surface ΔNe anomaly in the Switchyard area of the Arctic Ocean to the rejection of Ne during sea-ice formation. Using sea-ice formation estimates from the oxygen isotope (δ 18 O) method as a base line, we derive a central Arctic Ocean, field-based Ne sea-ice/seawater partition coefficient of 0.38 ± 0.05. This estimate indicates stronger rejection of Ne during ice formation into surface waters than has been previously reported. This analysis contributes to our understanding of the Ne budget in the sea-ice covered Arctic Ocean and can serve as a framework for studying other ice-covered surface ocean regions. • Surface waters beneath Arctic sea ice contain a clear excess of neon, revealing a distinct gas imbalance. • Sea-ice formation drives the neon anomaly by rejecting neon into surface ocean waters. • A new field-based central Arctic Ocean estimate of the Ne sea-ice/seawater partition coefficient of 0.38 ± 0.05, calculated using δ 18 O-derived ice formation rates, indicates that neon is excluded more strongly during sea-ice formation than previously reported.