A significant change in sea ice diffuse attenuation coefficient with temperature and its implications for the Arctic Ocean

Sea ice transparency is essential to the ecology of the ice-covered sea. Research suggests that the diffuse attenuation coefficient of downwelling irradiance (K-d) varies with ice temperature (T-ice); however, the characteristics of its response are not well understood yet, particularly from a quantitative perspective. In an attempt to fill this gap, three independent laboratory experiments were performed between 2016 and 2022 to investigate the variations of K-d with changing T-ice. Validation experiments were further performed in Liaodong Bay in 2018 and 2022. To explore the dominant factors controlling this phenomenon, corresponding changes in scattering properties were estimated through a two-stream radiative transfer model. To examine its implications for local ice algal primary production and radiation transport, K-d of Arctic sea ice was parameterized as a function of T-ice. Our results from the laboratory and field experiments showed that K-d decreases (increases) with ice warming (cooling), and a 1 degrees C change in Tice results in a 0.29 m(-1) average change in K-d. The response of K-d to Tice between-9 degrees C and-2 degrees C is more notable than that observed between-24 degrees C and-9 degrees C. This is associated with the different variations in the scattering properties of sea ice. It reveals a significant effect on ice algal primary production under severe light-limited conditions but a weaker effect on radiation transport. Knowledge of this K-d-temperature dependence would further improve our understanding of the optical properties of sea ice and the parameterization of ice transparency in large-scale climate models.