Optical properties of CDOM across the Polar Front in the Barents Sea: Origin, distribution and significance

Colored Dissolved Organic Matter (CDOM) is an important optical constituent in seawater, which significantly attenuates the violet to blue portion of visible light. Thus, CDOM reduces the radiation energy available to phytoplankton and affects remote-sensing signals. We present data from two cruises transecting the Polar Front from Atlantic to Arctic waters in the Barents Sea, in 2007 and 2008. The latter took place during the spring bloom of phytoplankton in May (0.2<[Chl a]<13mgm−3) and the former during August (max. [Chl a]<2mgm−3). Absorption by CDOM at 443nm ranged from 0.004 to 0.080m−1 during May and from 0.006 to 0.162m−1 during August. Surprisingly, CDOM absorption differed little across the Polar Front, but was higher during August than during May (P<0.05). The slope coefficient of the absorption spectra (S) ranged from 0.008 to 0.036nm−1 (mean=0.015nm−1) including both cruises, and varied little across the Front (P>0.05). The CDOM remote sensing product from GlobColour correlated well with sampled data (R2=0.73) during May. However, during August the satellite product performed poorly (R2=0.02) due to extensive scattering caused by coccolithophorids in the Atlantic Water. The CDOM pool was of autochthonous (marine) origin as characterized from its S vs. absorption relationship. Modeling showed that CDOM, on average, contributed equally to the light absorption as did phytoplankton (at 1mg Chl a m−3), and thereby reduces the amount of light available for primary production.