Quantifying air-sea gas exchange using noble gases in a coastal upwelling zone

Abstract

The diffusive and bubble-mediated components of air-sea gas exchange can be quantified separately using time-series measurements of a suite of dissolved inert gases. We have evaluated the performance of four published air-sea gas exchange parameterizations using a five-day time-series of dissolved He, Ne, Ar, Kr, and Xe concentration in Monterey Bay, CA. We constructed a vertical model including surface air-sea gas exchange and vertical diffusion. Diffusivity was measured throughout the cruise from profiles of turbulent microstructure. We corrected the mixed layer gas concentrations for an upwelling event that occurred partway through the cruise. All tested parameterizations gave similar results for Ar, Kr, and Xe; their air-sea fluxes were dominated by diffusive gas exchange during our study. For He and Ne, which are less soluble, and therefore more sensitive to differences in the treatment of bubble-mediated exchange, the parameterizations gave widely different results with respect to the net gas exchange flux and the bubble flux. This study demonstrates the value of using a suite of inert gases, especially the lower solubility ones, to parameterize air-sea gas exchange.

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

“…The transition between the two phases coincided with the highest total wind speeds and highest southward (upwelling-favorable) wind speeds observed during the cruise (Manning et al, 2016c). Our data suggest that during Phase 2, we sampled multiple water masses including a colder water mass with lower O 2 and higher nutrients, consistent with recently upwelled water (Pennington and Chavez, 2000;Ryan et al, 2009;Johnson, 2010), a warmer water mass that had biogeochemical characteristics more similar to Phase 1, and also mixtures of these two water masses.…”

“…In Chapter 3 (Manning et al, 2016c), I use a six-day time-series of the five stable noble gases collected in Monterey Bay, California along with a one dimensional geochemical model to evaluate the performance of four different gas exchange parameterizations. The tested parameterizations include three that explicitly quantify the flux from partially and completely dissolving bubbles (Stanley et al, 2009b;Nicholson et al, 2011;Liang et al, 2013) and one that does not explicitly include bubble fluxes (Sweeney et al, 2007).…”

“…Rates of turbulent kinetic energy dissipation were calculated using the profiler's shear probes and fast temperature sensor, and diapycnal dissipation and diffusivity ( ) were estimated following Wolk et al (2002). These diffusivity measurements are used to quantify the impact of vertical mixing on the mass balance of the gas tracers (Manning et al, 2016c).…”

“…In this paper we only use the [Ar] results, which had an estimated error (combined precision and accuracy) of 0.24 %RSD (relative standard deviation). See Manning et al (2016c) for the complete noble gas data.…”

“…the fraction of autrophic production available for export from the mixed layer. The time-series approach allowed us to quantify non-steady state O 2 fluxes, which can be a significant portion of the total O 2 flux in many regions (Hamme et al, 2012;Tortell et al, 2014;Manning et al, 2016b). We quantify GOP with discrete measurements of the triple oxygen isotopic composition of O 2 and NOP with near-continuous measurements of the O 2 /Ar saturation anomaly (Cassar et al, 2009).…”