Biogeosciences Discuss., 10, 5619-5670, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG.
Light absorption and partitioning in Arctic Ocean surface waters: impact of multi year ice melting
S. Bélanger1, S. A. Cizmeli1,2, J. Ehn3, A. Matsuoka4, D. Doxaran5, S. Hooker6, and M. Babin4
1Université du Québec à Rimouski, Département de Biologie, Chimie et Géographie and BORÉAS, 300 allée des Ursulines, Rimouski, Québec G5L 3A1 Canada
2Arctus inc., 300 allée des Ursulines, Rimouski, Québec G5L 3A1 Canada
3University of Manitoba, Center for Earth Observation Science, 337 Wallace Building, Winnipeg, MB, R3T 2N2, Canada
4Takuvik Joint International Laboratory (CNRS & ULaval), Département de Biologie, Québec-Océan and Arcticnet, Université Laval, Pavillon Alexandre-Vachon, 1045, av. de la Médecine, Québec (Québec), G1V 0A6 Canada
5CNRS, Université Pierre et Marie Curie-Paris 6, UMR 7093, Laboratoire dOcéanographie de Villefranche/Mer, 06230 Villefranche-sur-Mer, France
6NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Greenbelt, Maryland 20771, USA

Abstract. Ice melting in the Arctic Ocean exposes the surface water to more radiative energy with poorly understood effects on photo-biogeochemical processes and heat deposition in the upper ocean. In August 2009, we documented the vertical variability of light absorbing components at 37 stations located in the southeastern Beaufort Sea including both Mackenzie river-influenced waters and polar mixed layer waters. We found that melting multi-year ice released significant amount of non-algal particulates (NAP) near the sea surface relative to sub-surface waters. NAP absorption coefficients at 440 nm (aNAP(440)) immediately below the sea surface (0-) were on average 3-fold (up to 10-fold) higher compared to sub-surface values measured at 2–3 m depth. The impact of this unusual feature on the light transmission and remote sensing reflectance (Rrs) was further examined using a radiative transfer model. A 10-fold particle enrichment homogeneously distributed in the first meter of the water column slightly reduced photosynthetically available and usable radiation (PAR and PUR) by ~6% and ~8%, respectively, relative to a fully homogenous water column with low particles concentration. In terms of Rrs, the particle enrichment significantly flattered the spectrum by reducing the Rrs by up to 20% in the blue-green spectral region (400–550 nm). These results highlight the impact of melt water on the concentration of particles at sea surface, and the need for considering nonuniform vertical distribution of particles in such systems when interpreting remotely sensed ocean color. Spectral slope of aNAP spectra calculated in the UV domain decreased with depth suggesting that this parameter is sensitive to detritus composition and/or diagenesis state (e.g., POM photobleaching).

Citation: Bélanger, S., Cizmeli, S. A., Ehn, J., Matsuoka, A., Doxaran, D., Hooker, S., and Babin, M.: Light absorption and partitioning in Arctic Ocean surface waters: impact of multi year ice melting, Biogeosciences Discuss., 10, 5619-5670, doi:10.5194/bgd-10-5619-2013, 2013.
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