Light absorption properties of southeastern Bering Sea waters: Analysis, parameterization and implications for remote sensing

摘要

The absorption coefficients of phytoplankton (a_(PHY)(λ)), non-algal particles (NAP) (a_(NAP)(λ)) and colored dissolved organic matter (CDOM) (a_(CDOM)(λ)) were investigated and parameterized in the southeastern Bering Sea during July 2008. The absorption coefficients were well structured with respect to hydrographic and biogeochemical characteristics of the shelf. The highest values of a_(PHY)(443) were observed offshore and the lowest values of a_(PHY)(443) were found in the coastal domain, a low productivity region associated with limited macronutrients. Values of a_(DG)(λ) (a_(CDOM)(λ)+a_(NAP)(λ)) revealed an east-west gradient pattern with higher values in the coastal domain, and lower values in the outer domain. Lower chlorophyll specific a_(PHY)(λ) (a*_(PHY)(λ)) observed relative to middle and lower latitude waters indicated a change in pigment composition and/or package effect, which was consistent with phytoplankton community structure. a_(CDOM)(λ) was the dominant light absorbing coefficient at all wavelengths examined except at 676nm. Modeling of remote-sensing reflectance (R_(rs)(λ)) and the diffuse attenuation coefficient (K_d(λ)) from inherent optical properties revealed the strong influence of a_(CDOM)(λ) on R_(rs)(λ) and K_d(λ). Good optical closure was achieved between modeled and radiometer measured R_(rs)(λ) and K_d(λ) with average percent difference of less than 25% and 19% respectively, except at red wavelengths. The a_(CDOM)(λ) accounted for >50% of K_d(λ) which was vertically variable. Chlorophyll-a calculated by the NASA standard chlorophyll-a algorithm (OC4.v6) was overestimated due to higher a_(CDOM)(λ) and underestimated due to lower a*_(PHY)(λ) at low and high concentrations of chlorophyll-a, respectively.