Effects of sea-ice light attenuation and CDOM absorption in the water below the Eurasian sector of central Arctic Ocean ( > 88°N)

This is a study of the optical, physical and biological parameters of sea ice and the water below it at stations (n = 25) in the central (> 88 degrees N) Eurasian sector of the Arctic Ocean during the summer 2012 record low sea-ice minimum extent. Results show that photosynthetically active radiation (PAR) transmittance of the ice was low (0.09) and apparently related to a high degree of backscattering by air-filled brine channels left by brine draining. The under-ice PAR was also low (8.4 +/- 4.5 SD mu mol photons m(-2) s(-1)) and partly related to the low transmittance. There were no significant differences in multi-year and first-year PAR transmittances. In spite of this low under-ice PAR, only 3% of the transmitted PAR through the ice was absorbed by phytoplankton in the water. On average, chlorophyll-a concentrations were low (0.34 +/- 0.69 SD mg chl-a m(-3)) in the water compared to the high (a(375) = 0.52 m(-1)) coloured dissolved organic matter (CDOM) absorption coefficient with a strong terrestrial optical signature. Two distinct clusters of stations with waters of Pacific and North Atlantic origin were identified based on significant differences in temperature, salinity and CDOM absorption coefficient between water masses. The under-ice light field for bare ice was parameterized as follows: I-z = I-o(1 -0.55)*(0.09)* exp ((-0.17*z)).