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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, C03026, doi:10.1029/2003JC001977, 2004

Analysis of apparent optical properties and ocean color models using measurements of seawater constituents in New England continental shelf surface waters

Rebecca E. Green

Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA


Heidi M. Sosik

Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA


Abstract

We used budgets of absorption (a), scattering (b), and backscattering (b b ) for particles and chromophoric dissolved organic matter (CDOM) to investigate sources of seasonal variations in apparent optical properties (AOPs) of New England continental shelf surface waters. Spectral a, b, and b b budgets for particles were estimated from flow cytometric measurements of eukaryotic pico/nanophytoplankton, Synechococcus, heterotrophic prokaryotes, detritus, and minerals; AOPs were modeled with Hydrolight radiative transfer software. For late summer and spring, our modeled values of the diffuse attenuation coefficient (K d ) and remote sensing reflectance (R rs) were on average within 15% and 9%, respectively, of independent measurements. This close agreement allowed us to examine how different seawater constituents contributed to AOP variability. Higher values of K d in the spring, compared to summer, were due to higher absorption by eukaryotic phytoplankton (a euk) and CDOM (a CDOM), which coincided with higher nutrient levels and less stratified conditions than in the summer. Differences in the spectral shape of R rs between the seasons were caused by a combination of differences in a euk, a CDOM, and b b from non-phytoplankton particles (minerals and detritus combined). For non-phytoplankton b b the major seasonal difference was a higher inverse wavelength dependence in the summer due to the effects of small organic detritus. We applied two semianalytical ocean color models to our data, in order to evaluate whether the assumptions and parameterizations inherent in these models are applicable for New England shelf waters. We show how differences between observed and modeled chlorophyll a specific phytoplankton absorption, a CDOM, and non-phytoplankton b b cause errors in chlorophyll a concentration and IOPs retrieved from reflectance inversion models.

Received 22 May 2003; accepted 14 January 2004; published 17 March 2004.

Index Terms: 4847 Oceanography: Biological and Chemical: Optics; 4219 Oceanography: General: Continental shelf processes; 4275 Oceanography: General: Remote sensing and electromagnetic processes (0689); 4227 Oceanography: General: Diurnal, seasonal, and annual cycles.

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Citation: Green, R. E., and H. M. Sosik (2004), Analysis of apparent optical properties and ocean color models using measurements of seawater constituents in New England continental shelf surface waters, J. Geophys. Res., 109, C03026, doi:10.1029/2003JC001977.