Light absorption and partitioning in Arctic Ocean surface waters: impact of multiyear ice melting
- 1Université du Québec à Rimouski, Département de Biologie, Chimie et Géographie and BOR\'EAS, 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 multiyear ice released significant amount of non-algal particulates (NAP) near the sea surface relative to subsurface waters. NAP absorption coefficients at 440 nm (aNAP(440)) immediately below the sea surface were on average 3-fold (up to 10-fold) higher compared to subsurface 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 particle 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 meltwater on the concentration of particles at sea surface, and the need for considering non-uniform vertical distribution of particles in such systems when interpreting remotely sensed ocean color. Spectral slope of aNAP spectra calculated in the UV (ultraviolet) domain decreased with depth suggesting that this parameter is sensitive to detritus composition and/or diagenesis state (e.g., POM (particulate organic matter) photobleaching).