Light absorption and partitioning in Arctic Ocean surface waters: impact of multiyear ice melting

• Published in: Biogeosciences
• Main Authors: Bélanger, S., Cizmeli, S.A., Ehn, J., Matsuoka, A., Doxaran, D., Hooker, S., Babin, M.
• Other Authors: Departement de Biologie, Chimie et Géographie, Université du Québec à Rimouski (UQAR), Groupe de recherche sur les environnements nordiques BORÉAS, Arctus Inc. (ARCTUS), University of Manitoba Winnipeg, Takuvik Joint International Laboratory ULAVAL-CNRS, Université Laval Québec (ULaval)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'océanographie de Villefranche (LOV), Observatoire océanologique de Villefranche-sur-mer (OOVM), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), NASA Goddard Space Flight Center (GSFC)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2013
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; Arctic; Arctic Ocean; Mackenzie River; Beaufort Sea; Mackenzie river
• Online Access: https://hal.sorbonne-universite.fr/hal-01537660; https://hal.sorbonne-universite.fr/hal-01537660/document; https://hal.sorbonne-universite.fr/hal-01537660/file/bg-10-6433-2013.pdf; https://doi.org/10.5194/bg-10-6433-2013

International audience Ice melting in the Arctic Ocean exposes the surface water to more radiative energy with poorly understood effects on photo-biogeochemical processes and heat deposi-tion 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 (a NAP (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 (R rs) was further examined using a ra-diative 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 R rs , the particle enrichment significantly flattered the spectrum by reducing the R rs 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 a NAP 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).