Tidal effects on ecosystem variability in the Chesapeake Bay from MODIS-Aqua

Abstract

Eight-year ocean color observations between 2002 and 2009 from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the satellite Aqua are used to quantitatively assess the tidal effects on variability of ocean's optical, biological, and biogeochemical properties in the Chesapeake Bay. We demonstrate that tidal variation in the lower Chesapeake Bay is one of the important ocean processes that drive significant changes of the ocean's optical and biogeochemical properties. Normalized water-leaving radiance spectra (nLw(λ)), water diffuse attenuation coefficient at the wavelength of 490nm (Kd(490)), and total suspended sediment (TSS) concentration show significant tidal variations in the lower Chesapeake Bay. Indeed, in the lower Bay region, Kd(490) increases from 0.9m−1 under low tidal current conditions at 0.10–0.15m/s to 1.35m−1 under high tidal current conditions at 0.45–0.50m/s, while chlorophyll-a concentration in the lower Bay region decreases slightly with an increase of the tidal current. Tide-driven variability in Kd(490) and TSS in the lower Bay is similar to and slightly larger than the seasonal variability in the region. On the other hand, different from the variability in the lower Bay, the tidal effects on the ecosystem are small and negligible in the middle and a large part of upper Chesapeake Bay regions.