Remote sensing of size structure of phytoplankton communities using optical properties of the Chukchi and Bering Sea shelf region

摘要

Recent ocean warming and subsequent sea ice decline resulting from climatechange could affect the northward shift of the ecosystem structure in theChukchi Sea and Bering Sea shelf region (Grebmeier et al., 2006b). The sizestructure of phytoplankton communities provides an index of trophic levelsthat is crucial to understanding the mechanisms underlying such ecosystemchanges and their implications for the future. This study proposes a newocean color algorithm for deriving this characteristic by using the region'soptical properties. The size derivation model (SDM) estimates thephytoplankton size index F_L on the basis of size-fractionatedchlorophyll-a (chl-a) using the light absorption coefficient of phytoplankton,a_ph(λ), and the backscattering coefficient of suspended particlesincluding algae, b_bp(λ). F_L was defined as the ratio of algal biomassattributed to cells larger than 5 μm to the total. It was expressed bya multiple regression model using the a_ph(λ) ratio,a_ph(488)/a_ph(555), which varies with phytoplankton pigmentcomposition, and the spectral slope of b_bp(λ), γ, which is an index of themean suspended particle size. A validation study demonstrated that 69% ofunknown data are correctly derived within F_L range of ±20%. Thespatial distributions of F_L for the cold August of 2006 and the warmAugust of 2007 were compared to examine application of the SDM to satelliteremote sensing. The results suggested that phytoplankton size was responsiveto changes in sea surface temperature. Further analysis of satellite-derivedF_L values and other environmental factors can advance our understandingof ecosystem structure changes in the shelf region of the Chukchi and BeringSeas.