Henry’s law constant for CO2 in aqueous sodium chloride solutions at 1 atm and sub-zero (Celsius) temperatures

Highlights

• Henry’s Law constant for CO2 was determined in NaCl solutions at temperatures from −1 to −10 °C.
• CO2 solubility in cold seawater and sea ice-brines is higher than previously estimated.
• Air-sea exchange of CO2 and climate modeling need to revisit the solubility of CO2 at sub-zero temperatures.

Abstract

The solubility of CO2 in seawater is known to increase at colder temperatures, but few studies have examined the CO2 solubility in seawater and in sea-ice brines at sub-zero (Celsius) temperatures. The thermodynamic Henry’s Law constant (KH) for CO2 in concentrated NaCl solutions was determined for the first time at sub-zero temperatures and salinities resembling those of the cryospheric seawater and sea-ice brine environments in polar and sub-polar oceans. The temperature (T, in Kelvin) dependence of the KH within the temperature and salinity ranges of this study (263 ≤ T ≤ 272 K and 35 ≤ S ≤ 152) is described by the following best-fit equation: ln KH = −2.484 + 2.775 × 10−2(274 − T) − 9.854 × 10−2/(274 − T) − 1.009 × 10−1 ln (274–T). The results show that the general practice, in geochemical and coupled climate‑carbon cycling models, of extrapolating KH values from above-zero to sub-zero temperatures underestimates the solubility of CO2 by up to 19%.

Bailey N., Papakyriakou T. N., Bartels C. & Wang F., in press. Henry’s law constant for CO2 in aqueous sodium chloride solutions at 1 atm and sub-zero (Celsius) temperatures. Marine Chemistry. Article.

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