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

Abstract

Employing continuous in situ measurements of dissolved O 2 /Ar and O 2 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. O 2 /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 27% 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. O 2 /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.

Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

“…Eveleth et al . [] suggested using their equation (5) to calculate ΔAr to assess the physical oxygen changes. Comparison with the method used in equation of this paper, which assumes [Ar]/[Ar] sat = 1, shows the two methods agree within 0.17 ± 0.14% for the entire duration of the study and indicates the Ar concentration was close to saturation values.…”

“…While the MIMS technique provides an alternative estimate of NCP, the calculation of using this method is complicated in high latitude waters due to a number of processes including ice melt, temperature change, and the entrainment of oxygen undersaturated waters into the SML that can lead to underestimates of [e.g., Castro‐Morales et al ., ; Cassar et al ., ; Eveleth et al ., ]. Although these complications do provide challenges to interpretation of the O 2 /Ar signals in our study region, the method does provide an alternative estimate of NCP and addresses different time scales (days to weeks) compared to the seasonal estimates based on carbon and nitrate deficits.…”

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

“…For example, the GEMS could be used along with a second mass spectrometer measuring O 2 /Ar ratios (e.g., an equilibrator inlet mass spectrometer (Cassar et al, 2009), a membrane inlet mass spectrometer (Tortell, 2005;Virkki et al, 1995;Kana et al, 1994), or the GEMS system described above, with the getter chambers eliminated) and a well-calibrated sensor for O 2 concentration. The O 2 /Ar ratio and the O 2 concentration could be used to derive the Ar concentration (Eveleth et al, 2014;Hamme et al, 2012) and the other noble gas concentrations could be determined from the GEMS noble gas ratios and the Ar concentration. Another potential modification is changing the system to measure individual samples, instead of a continuous gas stream (Visser et al, 2013;Machler et al, 2012).…”

“…Simultaneous measurements of noble gases and bioactive gases would assist in separately quantifying the physical and biological fluxes for bioactive gases. It may be possible to determine concentrations of all four noble gases using the GEMS (in addition to their ratios) if the system is used alongside a second mass spectrometer measuring O 2 /Ar and a calibrated O 2 sensor (Kana et al, 1994;Cassar et al, 2009;Eveleth et al, 2014).…”

“…In water, measurements of dissolved noble gases in tandem with bioactive gases such as O 2 can be used to separate the effects of biological versus physical processes on the equilibrium state of gases, enabling accurate estimates of biological productivity (Stanley et al, 2010;Nicholson et al, 2010;Stanley et al, 2006). Dissolved noble gas measurements can also be used to quantify oceanic processes such as gas ventilation in deep-water formation regions, diapycnal mixing, and sea ice melting and formation (Loose and Jenkins, 2014;Eveleth et al, 2014;Nicholson et al, 2010;Hamme and Severinghaus, 2007). On land, measurements of noble gases in groundwater can be used to generate paleotemperature records and for studies of groundwater-aquifer and groundwater-ocean interactions (Aeschbach-Hertig and Solomon, 2013;Castro et al, 1998;Stute and Schlosser, 1993).…”