The effect of sea-ice growth on air–sea CO2 flux in a tank experiment

Daiki Nomura,Hisayuki Yoshikawa-Inoue

doi:10.1111/j.1600-0889.2006.00204.x

Daiki Nomura, Hisayuki Yoshikawa-Inoue

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https://doi.org/10.1111/j.1600-0889.2006.00204.x

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Abstract

In order to clarify the CO2 exchange between the seawater and the overlying air during the sea-ice formation, we have carried out tank experiments in a low-temperature room. CO2 concentration above the sea-ice began to increase since the beginning of the sea-ice formation, and increased at larger rates with time and the decrease in air temperature. This increase of CO2 concentration in air was mainly caused by the increase in dissolved inorganic carbon concentration in the brine of the upper part of sea-ice, changes in CO2 solubility and dissociation constants of carbonic acid. The CO2 flux increased logarithmically with time, and reached a level of 2 × 10-4 to 5 × 10-4 g-C m-2 hr-1 at 50 mm ice thickness. We found that the CO2 flux was correlated well with the salinity and negatively with the volume of the brine in the upper part of the sea-ice. These suggested the larger role of the difference in partial pressure of CO2 between brine and air as compared to that of competitive change in the brine volume. Present results suggest the necessity to examine the CO2 exchange between the seawater and air in seasonal sea-ice areas.

Highlights

In high latitudes, oceans are covered with sea-ice whose extent of surface area varies seasonally within a range of 3–6% of the earth’s surface (Comiso, 2003), and the impacts of sea-ice cover on the global environment are significant
Before sea-ice formation, air temperature in the low-temperature room was kept constant at −1.3 ◦ C, and CO 2 concentration in dry air equilibrated with seawater was adjusted to be in the range from 216 to 292 ppm by adding small amounts of H 3 PO 4 or NaOH solution
In order to clarify the CO 2 exchange between the seawater and overlying air during sea-ice formation and the factors controlling it, we have carried out tank experiments in a low-temperature room, installing an ice formation tank made of acryl

Summary

Introduction

Oceans are covered with sea-ice whose extent of surface area varies seasonally within a range of 3–6% of the earth’s surface (Comiso, 2003), and the impacts of sea-ice cover on the global environment are significant. Sea-ice increases albedo, which implies an increase of short-wave solar radiation that has been reflected back to space from the surface. Discharge of brine from sea-ice to seawater leads to dense water formation, which plays an important role in determining ocean circulation and transferring carbon from the surface to the abyssal depths of the ocean (Wakatsuchi, 1983; Wakatsuchi and Ono, 1983; Anderson et al, 2004; Hoppema, 2004). From the viewpoint of geochemical cycles, sea-ice has been considered to impede the gas exchange between the ocean and atmosphere (Tison et al, 2002 and references cited therein). No carbon cycle models have included CO 2 exchange between the two through sea-ice. there have been a few studies that report the possibility of gas exchange through the sea-ice. For example, Gosink et al (1976) noted that, unlike

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