In the marginal sea ice zone (MIZ), where relatively small ice floes are dominant, the floe size distribution is an important parameter affecting melt processes given the larger cumulative perimeter of multiple small floes compared with a single ice floe of the same area. Smaller ice floes are therefore subject to increased lateral melt. However, the available data have been very limited so far. Analysis of sea ice in the Sea of Okhotsk revealed that while floe size distribution is basically scale invariant, a regime shift occurs at a size of about 40 m. In order to extend this preliminary result to the Antarctic MIZ and further examine the controlling factors, the first concurrent ice floe size and ice thickness measurements were conducted in the northwestern Weddell Sea and off Wilkes Land (around 64°S, 117ºE) with a heli-borne digital video camera in the late winter of 2006 and 2007, respectively. The floe sizes ranged from 2 to 100 m. Our analysis shows: 1) the scale invariance and regime shift are confirmed in both regions; 2) the floe size at which regime shift occurs slightly increases from 20 to 40 m, with ice thickness, consistent with the theory of the flexural failure of sea ice; and 3) the aspect ratio is 1.6-1.9 on average, close to the previous results. Based on these results, the processes affecting the floe size distribution and the subsequent implications on melt processes are discussed.By applying a renormalization group method to interpret the scale invariance in floe size distribution, the fractal dimension is related to the fragility of sea ice. These results indicate the importance of wave-ice interaction in determining the floe size distribution.
[1] The size distribution of sea ice floes was observed by coordinated Landsat imagery and video monitoring conducted from an icebreaker and a helicopter for an area 38 km  26 km in seasonal sea ice in the southern Sea of Okhotsk in February 2003. The combination of imagery on several scales allowed measurements of ice floes over three orders of magnitude, from 1 m to 1.5 km. Two different regimes were observed: floes larger than about 40 m have a power-law number density with an exponent of À1.87, in the lower range of earlier results. Below 40 m, the power law exponent is À1.15. The cause of these two different regimes is hypothesized to lie in the effects of swell on floes of different sizes and thicknesses. The importance of the floe size distribution for lateral melting is elucidated.Citation: Toyota, T., S. Takatsuji, and M. Nakayama (2006), Characteristics of sea ice floe size distribution in the seasonal ice zone, Geophys. Res. Lett., 33, L02616,
A B S T R A C TIn order to clarify the CO 2 exchange between the seawater and the overlying air during the sea-ice formation, we have carried out tank experiments in a low-temperature room. CO 2 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 CO 2 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 CO 2 solubility and dissociation constants of carbonic acid. The CO 2 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 CO 2 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 CO 2 between brine and air as compared to that of competitive change in the brine volume. Present results suggest the necessity to examine the CO 2 exchange between the seawater and air in seasonal sea-ice areas.
ABSTRACT. The air-sea-ice CO 2 flux was measured in the ice-covered Saroma-ko, a lagoon on the northeastern coast of Hokkaido, Japan, using a chamber technique. The air-sea-ice CO 2 flux ranged from -1.8 to +0.5 mg C m -2 h -1 (where negative values indicate a sink for atmospheric CO 2 ). The partial pressure of CO 2 (pCO 2 ) in the brine of sea ice was substantially lower than that of the atmosphere, primarily because of the influence of the under-ice plume from the Saromabetsu river located in the southeastern part of the lagoon. This suggests that the brine had the ability to take up atmospheric CO 2 into the sea ice. However, the snow deposited over the sea ice and the superimposed ice that formed from snowmelting and refreezing partially blocked CO 2 diffusion, acting as an impermeable medium for CO 2 transfer. Our results suggest that the air-sea-ice CO 2 flux was dependent not only on the difference in pCO 2 between the brine and the overlying air, but also on the status of the ice surface. These results provide the necessary evidence for evaluation of the gas exchange processes in ice-covered seas.
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