Variations of the Absorption of Chromophoric Dissolved Organic Matter in the Pearl River Estuary

Abstract

Analysis of in-situ measurements during a spring cruise survey in the Pearl River Estuary (PRE) reveals that, controlled by the two-layer gravitational circulation, chromophoric dissolved organic matter (CDOM) absorption shows a clear horizontal distribution pattern at both water surface and bottom, with higher CDOM absorption and lower spectral slope in the northwestern estuary, and a reversed pattern in the southeastern estuary and near the Hong Kong waters. The surface CDOM has higher absorption and lower spectral slope than the bottom. Horizontal transport is suggested to be the dominant hydrodynamic mechanism affecting CDOM distribution pattern in the PRE. With a regional algorithm tailored for the PRE CDOM absorption retrieval, a time series of CDOM absorption and spectral slope in the PRE and the Hong Kong waters in spring from 2012 to 2018 is produced based on satellite images obtained by four sensors with different spatial and spectral resolutions: the Visible Infrared Imaging Radiometer Suite (VIIRS), the Ocean and Land Colour Instrument (OLCI), the Hyperspectral Imager for the Coastal Ocean (HICO), and the Operational Land Imager (OLI). A correlation is revealed between the multi-temporal CDOM absorption and the monthly averaged river discharge, indicating the capability of CDOM ocean color products in identifying hydrodynamic processes in estuaries and coastal waters.