Physical and biological controls on oxygen saturation variability in the upper Arctic Ocean

Abstract

Employing continuous in situ measurements of dissolved O2/Ar and O2 in the Arctic Ocean, we investigate the mechanisms controlling the physical (abiotic) and biological oxygen saturation state variability in the surface ocean beneath sea ice. O2/Ar measurements were made underway using Equilibrator Inlet Mass Spectrometry (EIMS) during an icebreaker survey transiting the upper Arctic Ocean across the North Pole in late summer 2011. Using concurrently collected measurements of total oxygen, we devolve biological oxygen saturation and physical oxygen (Ar) saturation signals at unprecedented horizontal resolution in the surface ocean. In the Nansen Basin, Ar is undersaturated up to -7% while biological oxygen supersaturation peaks at 18.4%. We attribute this to ice melt, Atlantic Water influence and/or cooling. In the Canadian Basin, Ar is supersaturated up to 3%, likely because of Ar injection from freezing processes and long residence times of gas under ice cover. The overall Canadian Basin to Eurasian Basin gradient of Ar supersaturation to undersaturation may reflect net freezing in the Canadian Basin and net melting in the Eurasian Basin over several seasons, either by Pacific to Atlantic sector ice transport or local changes over time. Ar saturation could thereby provide large-scale high-resolution estimates of current and future changes in these processes. O2/Ar supersaturation averages 4.9% with peaks up to 9.8% where first year ice and abundant melt ponds likely allow sufficient light for blooms in ice-covered regions.