Sunlight and seasonal sea ice during melt

The sea ice cover of the Beaufort and Chukchi seas has undergone a significant decline in recent decades. The melt season is starting earlier, ice is thinner, and first year ice dominates. We apply a discrete ordinates method radiative transfer model to explore the interplay of the changing physical properties of the sea ice cover with the reflection, absorption, and transmission of sunlight. We use inherent optical properties for sea ice derived from previous field studies and modeling work. Field observations provide data on the evolution of snow depth, ice thickness, and melt pond properties. Special attention is paid to the impact of the variegated summer surface conditions on light transmission into the ice and upper ocean. Solar heat absorption in the ice and upper ocean is calculated and the euphotic zone depths are estimated. The potential impacts of algae in the ice and phytoplankton in the upper ocean are explored. Model results show that as the snow melts, transmitted light increases by an order of magnitude in just a few days. As ponds form and develop, transmitted light levels increase greatly as does the contrast between light levels under bare and ponded ice.