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

[摘要] Ice melting in the Arctic Ocean exposes the surface water to moreradiative energy with poorly understood effects onphoto-biogeochemical processes and heat deposition in the upperocean. In August 2009, we documented the vertical variability oflight absorbing components at 37 stations located in thesoutheastern Beaufort Sea including both Mackenzie River-influencedwaters and polar mixed layer waters. We found that meltingmultiyear ice released significant amount of non-algal particulates(NAP) near the sea surface relative to subsurface waters. NAPabsorption coefficients at 440 nm (a_NAP(440))immediately below the sea surface were on average 3-fold (up to10-fold) higher compared to subsurface values measured at2–3 m depth. The impact of this unusual feature on thelight transmission and remote sensing reflectance (R_rs)was further examined using a radiative transfer model. A 10-foldparticle enrichment homogeneously distributed in the first meter ofthe water column slightly reduced photosynthetically available andusable radiation (PAR and PUR) by ∼6and∼8%, respectively, relative to a fully homogenous watercolumn with low particleconcentration.In terms of R_rs,the particle enrichment significantly flattered the spectrum byreducing the R_rs by up to 20% in the blue-greenspectral region (400–550 nm). These results highlight theimpact of meltwater on the concentration of particles at seasurface, and the need for considering non-uniform verticaldistribution of particles in such systems when interpreting remotelysensed ocean color. Spectral slope of a_NAP spectracalculated in the UV (ultraviolet) domain decreased with depth suggesting thatthis parameter is sensitive to detritus composition and/ordiagenesis state (e.g., POM (particulate organic matter) photobleaching).

[学科分类] 地球化学与岩石