Sources of spatial variability in light absorbing components along an equatorial transect from 165°E to 150°W

Abstract

Spatial variability of major light-absorbing components in seawater was analyzed at the equator from 165°E to 150°W during the Zonal Flux Cruise aboard the R/V Thompson from 20 April to 10 May 1996. Spectral absorption coefficients were separated into phytoplankton, nonphytoplankton chromophoric particulate material (CPM) and chromophoric dissolved organic material (CDOM). CPM and phytoplankton absorption account for about 20% and 80% of the total particulate absorption, respectively, above 100 m. The <0.2 μm CDOM absorption accounts for nearly 80% of the total absorption below 100 m. A significant portion of spatial variability in particulate absorption was due to conservative processes in the upper 100 m. Non-conservative spatial variability of phytoplankton absorption was zonally determined by the biomass changes of a spectrally invariant taxonomic community and vertically by photoacclimation. Distributions of size-fractionated CDOM absorption are suggestive of the presence of new (0.2 to 0.7 μm) and old (<0.2 μm) DOM pools. Photochemical reactions and microbial activity are nonconservative processes that act upon these pools, respectively. New DOM was found primarily in the upper water column, while an analysis of variance showed that <0.2 μm CDOM originating from deep water composes the background CDOM in the Equatorial Pacific.