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

Abstract

The five noble gases (helium, neon, argon, krypton, and xenon) are biologically and chemically inert, making them ideal oceanographic tracers. Additionally, the noble gases have a wide range of solubilities and molecular diffusivities, and thus respond differently to physical forcing. Tritium, an isotope of hydrogen, is useful in tandem with its daughter helium-3 as a tracer for water mass ages. In this thesis, a fourteen month time-series of the five noble gases, helium-3 and tritium was measured at the Bermuda Atlantic Time-series Study (BATS) site. The time-series of five noble gases was used to develop a parameterization of air-sea gas exchange for oligotrophic waters and wind speeds between 0 and 13 m s −1 that explicitly includes bubble processes and that constrains diffusive gas exchange to ± 6% and complete and partial air injection processes to ± 15%. Additionally, the parameterization is based on weeks to seasonal time scales, matching the time scales of many relevant biogeochemical cycles. The time-series of helium isotopes, tritium, argon, and oxygen was used to constrain upper ocean biological production. Specifically, the helium flux gauge technique was used to estimate new production, apparent oxygen utilization rates were used to quantify export production, and euphotic zone seasonal cycles of oxygen and argon were used to determine net community production. The concurrent use of these three methods allows examination of the relationship between the types of production and begins to address a number of apparent inconsistencies in the elemental budgets of carbon, oxygen, and nitrogen.

Dissolved gases in the deep North Atlantic track ocean ventilation processes

“…These uncertainties account both for BATS sample measurement uncertainties and uncertainties in the solubility equilibrium ratios. We find remarkably close agreement between our deep BATS Δ(Xe/Ar) and Δ(Kr/Ar) measurements and previous measurements from the early 2000s ( 24 , 25 ), adding confidence to these data ( SI Appendix , Fig. S1 and Fig.…”

Net biological oxygen production in the ocean: Remote in situ measurements of O2 and N2 in surface waters

“…By measuring oxygen and an inert gas simultaneously it is possible to isolate the physical processes causing O 2 change in the upper ocean. It has long been realized that the noble gas argon is ideal for this purpose because it has a similar solubility to oxygen [ Benson , 1964] and the O 2 –Ar pair have been used over the years [e.g., Craig and Hayward , 1987; Spitzer and Jenkins , 1989; Emerson et al , 1995; Kaiser et al , 2005; Hamme and Emerson , 2006; Reuer et al , 2007; Juranek , 2007; Stanley , 2007]. Our goal is to demonstrate the utility of simultaneous measurements of oxygen and nitrogen gases to separate the physical and biological processes causing oxygen change because it is presently possible to measure these two in situ and remotely, which is not yet the case for argon.…”

“…Thus it is important to be able to determine the relative importance of the two mechanisms. Gas exchange studies using a suite of inert gases at the Hawaii and Bermuda time series sites [ Hamme and Emerson , 2006; Stanley , 2007] indicate that these two mechanisms are of similar importance with total collapse being responsible for more than half of bubble processes. Since we are dealing with only one inert gas, N 2 , we have to guess about the relative importance of these mechanisms, and that introduces an element of uncertainty in calculation of the effect bubble fluxes on O 2 concentration.…”

Evaluating triple oxygen isotope estimates of gross primary production at the Hawaii Ocean Time‐series and Bermuda Atlantic Time‐series Study sites

“…NCP in the model was set using an idealized productivity curve from surface to compensation depth, with respiration below set in proportion to oxygen utilization rate (OUR) such that depth‐integrated NCP was zero following Stanley et al [2009]. The magnitude of euphotic zone NCP of O 2 was seasonally modulated following a sine curve peaking in June with an annual magnitude of 2.5 mol m −2 y −1 typical of subtropical rates of NCP [ Gruber et al , 1998; Stanley , 2007]. While the NCP parameterization influenced the net oxygen evolution in the model, it had only as small impact on 17 Δ dis because 17 Δ dis is not directly affected by respiration and is only weakly sensitive to changes in NCP.…”