Characterization of global ocean turbidity from moderate resolution imaging spectroradiometer ocean color observations

Abstract

Seasonal global ocean turbidity is studied and quantified using the diffuse attenuation coefficient at the wavelength of 490 nm, Kd(490), derived from measurements of the Moderate Resolution Imaging Spectroradiometer onboard the Aqua satellite. The shortwave infrared-based atmospheric correction algorithm and a newly developed Kd(490) algorithm have been used to derive Kd(490) data for both the global open ocean and coastal turbid waters. The spatial pattern of global open ocean turbidity shows significant seasonal Kd(490) variations with highs in the boreal (or austral) spring and summer and lows in the winter for the Northern Hemisphere (or Southern Hemisphere). The clear water with Kd(490) 0.1 m-1 covers an average of ∼95.67% of the global ocean. The modestly turbid waters with Kd(490) values ranging from ∼0.1 to 0.3 m -1 has about 5.12% and 3.07% of the global ocean region in the summer and winter, respectively, with average coverage of ∼3.59%. Turbid waters with Kd(490) over 0.3 m-1 are all located in the coastal regions, river estuaries, and inland lakes with an average global coverage of ∼0.74%, accounting for ∼8% to 12% of the total global continental shelf area. The world's major turbid water regions are identified and evaluated in this study. Amazon River Estuary ranks as the world's most turbid region with the mean Kd(490) value of ∼5 m-1. In addition, different mechanisms for the water turbidity in the open oceans and coastal turbid waters are investigated. In the open ocean, variability in the seasonal turbidity is related to the seasonal variation of chlorophyll a concentration, i.e., the seasonal phytoplankton bloom dominates the global geographic perspective of the water turbidity (for waters with Kd(490) ≤ 0.3 m-1). In the coastal region, on the other hand, high turbidity (Kd(490) > 0.3 m-1) is attributed to the high loading of sediment concentration due to various physical processes, such as sediment resuspension, river runoff, etc. © 2010 by the American Geophysical Union.