Optical Measurements and Analysis of Sea Ice in the Chukchi Sea during the Onset of 2014 Melt

Abstract:

Partitioning of solar radiation by the sea ice-ocean system controls sea ice melt and light availability for primary production in the upper ocean. Morphological changes occurring as the Chukchi Sea transitions to a first year ice cover with a higher melt pond fraction are likely altering the surface radiation budget and thereby impacting physical and biological systems. Field observations were conducted from the onset of snowmelt to the formation of melt ponds at several locations in the Chukchi Sea from May 18 to June 17, 2014. The state and variability of incident, reflected, and transmitted spectral irradiance as well as vector and scalar photosynthetically active radiation (PAR) were measured coincident with snow depth and ice thickness. These in situ observations were combined with coincident satellite imagery to describe the radiation budget and solar partitioning at an aggregate scale. Results show decreasing albedo and increasing transmission as melt progressed with trends interrupted by a late season snowfall. Albedo declined steadily from a high of 85% to a low of 53%, while transmitted light available for primary production remained well below 1% prior to snow melt and when highly absorbing algae was present at the bottom of the ice. Comparison of our solar partitioning observations with similar observations in multiyear ice highlights the profound impact changing ice morphology has on solar partitioning of the Chukchi Sea.