Effect of Arctic Sea-Ice Melt on Inherent Optical Properties and Vertical Distribution of Solar Radiant Heating - Possible Feedbacks on Ice Melt

We investigated the effect of sea-ice melt waters on the inherent optical properties (IOP) and solar radiant heating in Arctic surface waters. IOP of Polar Waters (PW) exiting the Arctic Ocean in the East Greenland Current (EGC) on the east Greenland shelf, and of the inflowing Atlantic waters (AW) in the West Spitsbergen Current (WSC) near Spitsbergen were studied in late summer when surface freshening due to sea-ice melt was widespread. The absorption and attenuation coefficients in PW were significantly higher than previous observations from the western Arctic. High concentrations of colored dissolved organic matter (CDOM) results in 50-60% more heat deposition in the upper meters relative to clearest natural waters in PW. This demonstrates the influence of terrigenous CDOM inputs on the optical properties of waters in the Eurasian Basin. Sea-ice melt in CDOM-rich PW decreased CDOM absorption in surface layer, but an increase in scattering nearly compensated for lower absorption, and total attenuation was nearly identical in the sea-ice meltwater layer. This suggests a source of scattering material associated with sea-ice melt, and deserves further study. In the AW, melting sea-ice forms a fresher and well stratified surface layer with lower absorption and attenuation, than in well-mixed AW waters in late summer. It is likely that phytoplankton in the surface layer formed by sea-ice melt are nutrient limited. The presence of a more transparent surface layer shifts solar heat deposition to greater depths in late summer both in EGC and WSC waters. Thus this heat is not directly available for ice melt during periods of stratification but rather delays ice formation in fall.