Using Noble Gas Measurements to Derive Air‐Sea Process Information and Predict Physical Gas Saturations

Abstract

Dissolved gas distributions are important because they influence oceanic habitats and Earth's climate, yet competing controls by biology and physics make gas distributions challenging to predict. Bubble‐mediated gas exchange, temperature change, and varying atmospheric pressure all push gases away from equilibrium. Here we use new noble gas measurements from the Labrador Sea to demonstrate a technique to quantify physical processes. Our analysis shows that water‐mass formation can be represented by a quasi steady state in which bubble fluxes and cooling push gases away from equilibrium balanced by diffusive gas exchange forcing gases toward equilibrium. We quantify the rates of these physical processes from our measurements, allowing direct comparison to gas exchange parameterizations, and predict the physically driven saturation of other gases. This technique produces predictions that reasonably match N2/Ar observations and demonstrates that physical processes should force SF6 to be ∼6% more supersaturated than CFC‐11 and CFC‐12, impacting ventilation age calculations.

Oxygen Saturation Surrounding Deep Water Formation Events in the Labrador Sea From Argo‐O2 Data

“…Oxygen and argon have very similar solubilities, temperature dependencies, and diffusion rates, such that argon saturation anomalies quantify the impact of physical processes (cooling, atmospheric pressure, and bubbles) on oxygen. Hamme et al () report argon saturation anomalies in Labrador Sea Water of −1.26 ± 0.15%. The difference between the oxygen and argon saturation anomalies of approximately −5% to −6.2% represents the deep biological deficit not erased by gas exchange.…”

Air‐Sea Gas Transfer: Determining Bubble Fluxes With In Situ N2 Observations

“…The departure of the two lines above U 10 = 8–10 m/s is due to the gas exchange process in large bubbles. This process is difficult to separate from that at the air‐sea surface, since they both depend on molecular diffusion across an interface (i.e., Hamme et al, ). One cannot determine the entire mechanism for large bubble exchange from the data in the figure because the purposeful tracer releases give no information about the value of the pressure inside large bubbles, ∆ P , which is very important for transfer of insoluble atmospheric gases (N 2 , O 2 , Ar, and noble gases) to the ocean by large bubbles.…”

“…The behavior of small bubbles in the surface ocean is not well understood because of the difficulty of measuring them, and studies of the volume scattering function indicate that some of bubbles this size may be stabilized by organic coatings (Zhang et al, ). Nonetheless, the saturation anomalies of noble gases and N 2 in the ocean require a formulation like that in equation to explain the results (Hamme et al, ).…”

Using Noble Gases to Compare Parameterizations of Air‐Water Gas Exchange and to Constrain Oxygen Losses by Ebullition in a Shallow Aquatic Environment

“…Processes and environmental changes that may affect gas concentrations and saturation states in a shallow, tidally isolated aquatic setting are plotted in Figure a, and the resulting potential effects on Ne and Kr in this study are plotted as changes in saturation state (Figure b) relative to solubility equilibrium concentrations, that is, ΔNe = ([Ne]/[Ne] sat − 1) * 100%. These processes and parameters include diffusive gas exchange, changes in temperature, salinity, and atmospheric pressure, as well as bubble processes in the water column (Bieri, ; Hamme et al, ; Stanley & Jenkins, ). Additionally, noble gases partition between porewater and bubbles in sediment (e.g.…”