Experimental investigation of the partitioning of radiation in the melt pond-ice-ocean system

To study the partitioning of solar radiation over the melting Arctic sea ice and address the lack of systematic measurements of the optical properties of melt ponds and the underlying ice, four experiments in non-Arctic regions were designed to explore the distribution of solar irradiance on pond surface, pond bottom, and underlying ice. These experiments also investigated the influence of different pond depths (Hp), underlying ice thicknesses (Hi), and melt pond sidewall conditions (i.e., the black sidewalls, ice sidewalls, and pond horizon size) on the apparent optical properties (AOPs) of melt ponds. The black sidewalls with a small pond radius (barrel experiment) showed the greatest influence on the AOPs, significantly lowering the albedo and transmittance, and increasing the energy absorbed by the pond (psi p) and underlying ice (psi i). Different sidewall types, such as the black and ice sidewalls, did not affect the AOPs' trend, but affected their values. The AOPs were also influenced by pond size. The albedo linearly decreased and psi p linearly increased with the increase of pond radius. The albedo and psi p were almost independent of pond radius as pond radius larger than 0.58 m and 1.25, respectively. The black sidewalls experiment, in which the pond radius was 2.5 m, and the pond size experiment showed that solar energy was mainly absorbed by the melt pond. psi p increased from 19% to 62%, which corresponded to Hp increasing from 5 cm to 35 cm in the pond size experiment. The results of the four experiments were consistent with the values obtained from numerical simulations and in situ measurements in the Arctic. The experiments conducted in this study were shown to be effective tools to complement and verify the optical measurements of Arctic melt ponds. They allow us to obtain the key information in Arctic pond measurements, which is difficult to achieve due to the severe weather conditions and marine environment.