Characterization of air-sea gas exchange processes and dissolved gas/ice interactions using noble gasses

Abstract

In order to constrain the processes controlling the cycles of biogeochemically important gases such as 02 and CO 2 , and thereby infer rates of biological activity in the upper ocean or the uptake of radiatively important "greenhouse" gases, the noble gases are used to characterize and quantify the physical processes affecting the dissolved gases in aquatic environments. The processes of vertical mixing, gas exchange, air injection, and radiative heating are investigated using a 2 year time-series of the noble gases, temperature, and meteorological data from Station S near Bermuda, coupled with a 1-dimensional upper ocean mixing model to simulate the physical processes in the upper ocean. The rate of vertical mixing that best simulates the thermal cycle is 1.1 ±0.1 x10 4 m s1. The gas exchange rate required to simulate the data is consistent with the formulation of Wanninkhof (1992) to ± 40%, while the formulation of Liss and Merlivat (1986) must be increased by a factor of 1.7± 0.6. The air injection rate is consistent with the formulation of Monahan and Torgersen (1991) using an air entrainment velocity of 3±1 cm s1. Gas flux from bubbles is dominated on yearly time-scales by larger bubbles that do not dissolve completely, while the bubble flux is dominated by complete dissolution of bubbles in the winter at Bermuda. In order to obtain a high-frequency time-series of the noble gases to better parameterize the gas flux from bubbles, a moorable, sequential noble gas sampler was developed. Preliminary results indicate that the sampler is capable of obtaining the necessary data. Dissolved gas concentrations can be significantly modified by ice formation and melting, and due to the solubility of He and Ne in ice, the noble gases are shown to be unique tracers of these interactions. A three-phase equilibrium partitioning model was constructed to quantify these interactions in perennially ice-covered Lake Fryxell, and this work was extended to oceanic environments. Preliminary surveys indicate that the noble gases may provide useful and unique information about interactions between water and ice.

Ocean/ice shelf interaction in the southern Weddell Sea: results of a regional numerical helium/neon simulation

“…It is still debatable whether a reduction of the saturation due to sea-ice formation has an impact on the neon concentration in freshly ventilated water masses of the deep ocean. Hood (1997) suggests that sea ice formation erodes the neon supersaturation originating from ocean/ice shelf interaction, though Well and Roether (2003) argue that such strong neon reduction is not consistent with tracer observations in the Southern Ocean. Therefore, we further have to speculate about the processes which cause the observed slight supersaturation of neon in the abyssal ocean.…”

A determination of air-sea gas exchange and upper ocean biological production from five noble gases and tritiugenic helium-3

“…The former is mitigated by noble gas signatures integrating over a few weeks so samples only need be collected within a few weeks of the storm event. In addition samples can be collected with a moored noble gas sampler that can collect samples in any conditions (Hood, 1998).…”

Measurement of dissolved neon by isotope dilution using a quadrupole mass spectrometer

“…Carbon export can be determined from an oxygen mass balance, but only if the effect of bubbles on oxygen supersaturations can be accurately estimated from measurement of gases like Ne (Craig and Hayward, 1987;Spitzer and Jenkins, 1989;Emerson et al, 1995;Hamme, 2003 Kulongoski and Hilton (2002) getter & 77K charcoal trap isotope dilution 0.7 Lott (2001) getter & 9K stainless trap air aliquots 0.3 Hood (1998) getter & 8K charcoal trap air aliquots 0.3 Roether et al (1998) 25K charcoal trap air aliquots 0.4 Ludin et al (1998) 24K and 10K charcoal traps air aliquots 0.2-0.5 Poole et al (1997) getter & 77K charcoal trap isotope dilution 0.3 Top et al (1988) 77K charcoal trap isotope dilution < 1 Sano et al (1982) combustion & 77K charcoal trap air aliquots 10-20 Bieri et al (1968) getter & 77K charcoal trap isotope dilution 0.6-1.5 Craig et al (1967) getter & 77K charcoal trap isotope dilution 1.4…”

“…When properly used, copper tubes provide excellent sample preservation . For analysis, copper tubes are attached to a vacuum line where the dissolved gases are fully extracted from the water (Hood, 1998;Ludin et al, 1998). The most common method of quantifying Ne samples is quadrupole mass spectrometry in static mode, but methods used to separate Ne from interfering gases and to standardize the measurement differ (Table 1).…”