Melting processes of the marginal ice zone inferred from floe size distributions measured with a drone in the southern Sea of Okhotsk

Abstract

In the marginal ice zone, sea ice melts by absorbing heat from the surrounding seawater. Given that for the same sea ice area, total perimeter is longer for smaller ice floes, the information on floe size distribution is essential to predict the melting rate of sea ice. Our study was conducted in the southern Sea of Okhotsk under relatively calm and warm conditions in mid-February 2020. For the first time we used a drone to measure ice floes at a scale of less than a few meters and deduce the melting processes. Our results revealed that the cumulative floe size distribution is represented well by the power law with an exponent of 1.51 for floes larger than 0.9 m, and that each floe geometry has self-similar properties with an aspect ratio of 1.73. For floes below 0.9 m, it was shown that the floe size distribution deviates somewhat from the power law, associated with thermodynamic breakup which is caused by the increase in sea ice porosity. The surface heat budget analysis using the meteorological reanalysis datasets suggests that the efficient heat absorption from the open water and internal melting contributed to this process.