Global variability of phytoplankton functional types from space: assessment via the particle size distribution

[摘要] A new method of retrieving the parameters of a power-law particle sizedistribution (PSD) from ocean color remote sensing data was used to assessthe global distribution and dynamics of phytoplankton functional types(PFT's). The method retrieves the power-law slope, ξ, and theabundance at a reference diameter, N₀, based upon the shape andmagnitude of the particulate backscattering coefficient spectrum. Relatingthe PSD to PFT's on global scales assumes that the open ocean particulateassemblage is biogenic. The retrieved PSD's can be integrated to definethree size-based PFT's by the percent volume concentration contribution ofthree phytoplankton size classes – picoplankton (0.5–2 μm inequivalent spherical diameter), nanoplankton (2–20 μm) andmicroplankton (20–50 μm). Validation with in-situ HPLC diagnosticpigments resulted in better match-ups for the pico- and micro-phytoplanktonsize classes as compared to nanoplankton. Global decadal averages derivedfrom SeaWiFS monthly data reveal PFT and particle abundance spatial patternsthat are consistent with current understanding. Oligotrophic gyres arecharacterized by lower particle abundance and higher contribution bypicoplankton-sized particles than transitional or eutrophic regions.Seasonal succession patterns for size-based PFT's reveal good correspondencebetween increasing chlorophyll concentration and percent contribution by microplankton, as well asincreasing particle abundance. Long-term trends in particle abundances aregenerally well correlated with the MEI index indicating increasedoligotrophy (i.e. lower particle abundance and increased contribution ofpicoplankton-sized particles) during the warm phase of an El Niño event.This work demonstrates the utility and future potential of assessingphytoplankton functional types using remote characterization of the particlesize distribution.

[学科分类] 地球化学与岩石