Spatial heterogeneity and seasonal evolution of surface properties and radiative fluxes of Arctic sea ice

Abstract

In recent years, the Arctic sea ice has experienced a significant decline, characterised by the smaller extent, longer melt season, and a shift from thick multi-year ice to thinner first-year ice. As a result, more solar radiative energy is deposited into the Arctic sea ice and the ocean underneath, further enhancing sea ice melt and ocean heat. When the Arctic is transitioning from melt onset to freeze onset, the sea ice surface spatial variability becomes stronger, altering the spatial distribution of radiative energy deposition. Understanding the seasonal evolution and spatial variability of solar radiative fluxes is a key step to broadening our knowledge of the changing Arctic sea ice. In this thesis, I investigate the year-round changes in solar radiative fluxes within the Arctic sea ice, both temporally and spatially. I examine the changes in optical properties during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition (MOSAiC) in 2020. This thesis utilises a wide range of sensors and platforms, ranging from long-term continuous point measurement, to weekly under-ice mapping of light field, and to ice-floe size parameterization. This thesis highlights the spatial variability of the solar radiative fluxes of Arctic sea ice: under the same atmospheric condition and located on the same ice floe, different locations show highly variable evolution. The largest variability is in the middle of the melt season, due to the changing melt pond coverage and status. The sea ice types and surface conditions are crucial for the sea ice energy budget, thus further controlling the melting process. This thesis provides a comprehensive 3-dimensional view of the sea ice radiative fluxes and improves the parameterization of sea ice optical properties. Also, by investigating the effects of spatial surface variability, which is a function of time and area, this thesis guides future observations of the new Arctic sea ice regime. This study bridges in-situ observation to floe-size parameterisation, advances our understanding of the upscaling of solar radiative energy fluxes both onto and through the Arctic sea ice, and deepens our understanding of the impact of sea ice heterogeneity on the large-scale energy budget of the melting Arctic sea ice.