Relationships between wind speed and gas transfer, combined with knowledge of the partial pressure difference of CO2 across the air-sea interface are frequently used to determine the CO2 flux between the ocean and the atmosphere. Little attention has been paid to the influence of variability in wind speed on the calculated gas transfer velocities and the possibility of chemical enhancement of CO2 exchange at low wind speeds over the ocean. The effect of these parameters is illustrated using a quadratic dependence of gas exchange on wind speed which is fit through gas transfer velocities over the ocean determined by the natural-14C disequilibrium and the bomb-14C inventory methods. Some of the variability between different data sets can be accounted for by the suggested mechanisms, but much of the variation appears due to other causes. Possible causes for the large difference between two frequently used relationships between gas transfer and wind speed are discussed. To determine fluxes of gases other than CO2 across the air-water interface, the relevant expressions for gas transfer, and the temperature and salinity dependence of the Schmidt number and solubility of several gases of environmental interest are included in an appendix.

Relationship between wind speed and gas exchange over the ocean

Measurements of air-sea gas exchange rates are reported from two deliberate tracer experiments in the southern North Sea during February 1992 and 1993. A conservative tracer, spores of the bacterium Bacillus globigii var. Niger, was used for the first time in an in situ air-sea gas exchange experiment. This nonvolatile tracer is used to correct for dispersive dilution of the volatile tracers and allows three estimations of the transfer velocity for the same time period. The first estimation of the power dependence of gas transfer on molecular diffusivity in the marine environment is reported. This allows the impact of bubbles on estimates of the transfer velocity derived from changes in the helium/sulphur hexafluoride ratio to be assessed. Data from earlier dual tracer experiments are reinterpreted, and findings suggest that results from all dual tracer experiments are mutually consistent. The complete data set is used to test published parameterizations of gas transfer with wind speed. A gas ex- change relationship that shows a dependence on wind speed intermediate between those ofLiss and Merlivat [1986] and Wanninkhof [1992] is found to be optimal. The dual tracer data are shown to be reasonably consistent with global estimates of gas exchange based on the uptake of natural and bomb-derived radiocarbon. The degree of scatter in the data when plotted against wind speed suggests that parameters not scaling with wind speed are also influencing gas exchange rates.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999GB900091

In situ evaluation of air-sea gas exchange parameterizations using novel conservative and volatile tracers

This review is concerned with the isotopic relationships between organic compounds produced by a single organism, specifically their enrichments or depletions in 13C relative to total-biomass carbon. These relationships are biogeochemically significant because



1. An understanding of biosynthetically controlled, between-compound isotopic contrasts is required in order to judge whether plausibly related carbon skeletons found in a natural mixture might come from a single source or instead require multiple sources.

2. An understanding of compound-to-biomass differences must underlie the interpretation of isotopic differences between individual compounds and total organic matter in a natural mixture.



My approach is pedagogic. The coverage is meant to be thorough, but the emphases and presentation have been chosen for readers approaching this subject as students rather than as research specialists. In common with the geochemists in my classes, many readers of this paper may not be very familiar with biochemistry and microbiology. I have not tried to explain every concept from those subjects and I have not inserted references for points that appear in standard texts in biochemistry or microbiology. Among such books, I particularly recommend the biochemistry text by Garrett and Grisham (1999) and the microbiology text by Madigan et al. (2000). The biochemistry text edited by Zubay (1998) is also particularly elegant and detailed. White (1999) has written a superb but condensed text on the physiology and biochemistry of prokaryotes.

A schematic overview of the relevant processes is shown in Figure 1⇓. Plants and other autotrophs fix CO2. Animals and other heterotrophs utilize organic compounds. If the assimilated carbon is a small molecule (like CO2, CH4, or acetate), significant isotopic fractionation is likely to accompany the fixation or assimilation of C. Such fractionations establish the isotopic relationship between an organism and its carbon source. Those associated …

Fractionation of Carbon and Hydrogen Isotopes in Biosynthetic Processes

Electrolysis offers an attractive route to upgrade greenhouse gases such as carbon dioxide (CO2) to valuable fuels and feedstocks; however, productivity is often limited by gas diffusion through a liquid electrolyte to the surface of the catalyst. Here, we present a catalyst:ionomer bulk heterojunction (CIBH) architecture that decouples gas, ion, and electron transport. The CIBH comprises a metal and a superfine ionomer layer with hydrophobic and hydrophilic functionalities that extend gas and ion transport from tens of nanometers to the micrometer scale. By applying this design strategy, we achieved CO2 electroreduction on copper in 7 M potassium hydroxide electrolyte (pH ≈ 15) with an ethylene partial current density of 1.3 amperes per square centimeter at 45% cathodic energy efficiency.

CO2 electrolysis to multicarbon products at activities greater than 1 A cm−2

Publisher Summary This chapter discusses the effects of carbon and oxygen isotope effects in the exchange of carbon dioxide between terrestrial plants and atmosphere. Plants differ from the atmosphere in their average relative abundances of carbon isotopes. This variation arises because the kinetic parameters of chemical reactions can be affected by the atomic masses of the compounds involved. The chapter describes the processes affecting carbon isotope exchange between plants and the atmosphere. There is a significant difference between long-term isotope discrimination and short-term “on-line” measures of discrimination. The reasons for this remain to be determined, but fractionations postphotosynthesis may be involved. Oxygen isotopes are of interest to plant carbon and water relations. It is possible that the 18O /16O ratio of organic matter may be useful for determining whether differences between genotypes in δ13C and Cc/Ca are caused by differences in photosynthetic capacity or in stomatal conductance. The 18O/16O ratio in atmospheric CO2 provides an additional information about exchange between the atmosphere and water, some of which is via biological activity.

Carbon and Oxygen Isotope Effects in the Exchange of Carbon Dioxide between Terrestrial Plants and the Atmosphere

The diffusion coefficients D of important gas tracers dissolved in water and seawater were measured with a modified Barrer method. The measurements include the gases He, Ne, Kr, Xe, H2, CH4, and CO2 dissolved in distilled water in the temperature range from 5 to 35°C, and He and H2 dissolved in seawater in the same temperature range. The maximum systematic error is estimated to be well below 5%. The isotopic fractionation in the diffusion coefficient, ∈D, was determined to be (−0.87 ± 0.05)‰ for 13CO2/12CO2 and (15 ± 3)% for 3He/4He.

Wolfgang Dietrich

Papers

Measurement of the diffusion coefficients of sparingly soluble gases in water