Optical complexity in Long Island Sound and implications for coastal ocean color remote sensing

Abstract

The optical properties of estuaries can vary considerably with the delivery of pigmented materials from surrounding watersheds and marine waters. In this study, optical properties sampled at 158 stations throughout the Long Island Sound (LIS) estuary between 2004 and 2007 show significant regional variability. Chlorophyll, total suspended matter, light absorption, and scattering are exceptionally high compared to other coastal data. Inherent optical properties and sea surface reflectances revealed at least two optical domains: a phytoplankton‐dominated regime in western LIS and New York Bight and a sediment‐dominated regime in central and eastern LIS. Multivariate ordination analysis identified clusters of stations conforming to these optical domains, as well as stations near the Hudson and Connecticut rivers representing optical end‐members in LIS characterized by high chromophoric dissolved material (CDM) and biomass (Hudson River) and high sediment loads (Connecticut River). However, winds, tides, and subtidal estuarine circulation redistribute optical constituents throughout the major basins of LIS and homogenize riverine influence. Ocean color parameters, used to define the spectral quality of optical constituents, such as the spectral slopes of particulate backscattering and CDM absorption, and the chlorophyll‐specific phytoplankton absorption did not cluster and are relatively constant throughout the region at all times of year. Therefore, variability in spectral reflectance in LIS is principally controlled by the relative magnitudes of the optical properties at each station rather than by significant differences in spectral quality of optically significant constituents. Consistency in these ocean color parameters minimizes the necessity for subregional or seasonal “tuning” of ocean color algorithms.