Author(s): Uusikivi Jari; V. Vahatalo Anssi; A. Granskog Mats; Gali Tapias Marti

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Abstract: In March 2007, spectral irradiance measurements were conducted above and beneath the landfast sea ice in Santala Bay near the entrance to the Gulf of Finland, Baltic Sea. The measurements included the spectral albedo, extinction coefficient of the sea ice, and also extinction coefficients separately to granular and columnar ice layers. Ice included particle matter (PM) and colored dissolved organic matter (CDOM) absorption coefficients were measured from melted ice samples to quantify their contribution to light attenuation in ice. PM and CDOM absorption dominate absorption spectrum in the shorter wavelengths (320- 550nm), and are most important reason for high extinction coefficients at ultraviolet in the Baltic Sea ice. CDOM was found to be most significant absorber in the UVR (<380nm) with the exception of the surface ice layer for which the CDOM absorption spectrum was clearly different from the ice layers below. Photochemical reactions induced by high ultraviolet radiation could have altered the composition of CDOM at the ice surface layer. We found that CDOM absorption in the ice cover contributed 42 %, 37%, 33% and 20 % of light attenuation at 305 nm, 322 nm, 360 nm and 550 nm, respectively.

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Year: 2008