Charles Stump

O2, Ar, N2, and 222Rn in surface waters of the subarctic Ocean: Net biological O2 production

Distributions of oxygen, argon, nitrogen, and radon in the upper ocean of the subarctic Pacific distinguish the fluxes controlling the oxygen mass balance during the summers of 1987 and 1988. The difference between the net O2 flux (in mmol m−2 d−1) to the atmosphere via gas exchange (32) and the integrated decrease with time (−14) is balanced by biological production (13-17), air injection by bubble entrainment (5), and O2 flux to the thermocline −(0-4). Nitrogen/argon and oxygen/argon ratios reveal that ˜15% of the oxygen supersaturation in summer is produced by air injection and ˜40% by biological production, with the rest induced by surface water warming. Our estimate of biologically induced oxygen production when translated stoichiometrically to nitrogen uptake agrees to within error estimates with both the particulate and dissolved nitrogen mass balances for the upper ocean determined in the SUPER program during the same time period. The oxygen mass balance requires a net carbon production in the euphotic zone of ˜140 mg C m−2 d−1 (PQ=1.5), which is 20–30% of the level of 14C primary production determined by SUPER investigators.

Accurate measurement of O2, N2, and Ar gases in water and the solubility of N2

The degree of atmospheric saturation for O2, Ar, and N2 gases in water can be determined to accuracies of ±0.1–0.3% using mass spectrometry to determine the gas ratios and Winkler titrations for oxygen analysis. We describe methods used to obtain this level of accuracy and precision. Oxygen accuracy of ±0.1% can be obtained by careful attention to standardization using KIO3 standards that have been corrected for impurities. Accurate O2/Ar and O2/N2 gas ratios (±0.1–0.2%) are obtainable by measuring the mass ratios against the atmosphere if the effect of different gas concentrations on the performance of the mass spectrometer are taken into account. Oxygen and argon saturation values have been determined previously to accuracies of less than or equal to ±0.1%, but published estimates of the saturation value for nitrogen differ by more than 1%. We have redetermined the N2 saturation value at 19°C and zero salinity to be 0.92% greater than the results reported in the work of Weiss (1970).

Subsurface ocean argon disequilibrium reveals the equatorial Pacific shadow zone

[1] Surface water in the ocean invades the subsurface vertically, against the density gradient, and along constantdensity surfaces from surface outcrops in high latitudes. We present dissolved argon data that distinguishes a diapycnally ventilated upper thermocline in the equatorial Pacific versus an isopycnally ventilated subtropical location near Hawaii. The lower thermocline is shown to be isopycnally ventilated at both locations, in contrast with theoretical and model predictions. Citation: Gehrie, E., D. Archer, S. Emerson, C. Stump, and C. Henning (2006), Subsurface ocean argon disequilibrium reveals the equatorial Pacific shadow zone, Geophys. Res. Lett., 33, L18608, doi:10.1029/2006GL026935. [2] The chemistry of seawater is altered at the sea surface by exchange of naturally occurring atmospheric gases such as O2 ,C O2, and Ar. The atmospheric imprint on seawater is carried into the ocean interior by fluid flow from the Ekman layer and by mixing, processes known collectively as ‘‘ventilation’’. Pathways and mechanisms of ocean ventilation determine the circulation of the thermocline and affect the ocean response to climate change, uptake of anthropogenic CO2, and the distribution of oxygen and nutrients in subsurface waters. [3] Some parts of the subsurface ocean (e.g. the subtropics) are ventilated by fluid flow. Luyten et al. [1983] postulated that after a fluid parcel is isolated from the atmosphere, its trajectory is governed by conservation of potential vorticity. In oceanic ‘‘shadow zones’’ like the equatorial Pacific, vorticity-conserving fluid flow trajectories intersect the boundaries of the ocean or close in upon themselves, rather than outcropping at the sea surface. Ventilation of shadow zones takes place via eddy or turbulent diffusion, either in the vertical (diapycnal) direction or along isopycnal surfaces.