Ocean circulation and terrestrial runoff dynamics in the Mesoamerican region from spectral optimization of SeaWiFS data and a high resolution simulation

The evolution in time and space of terrestrial runoff in waters of the Mesoamerican region was examined using remote sensing techniques combined with river discharge and numerical ocean circulation models. Ocean color SeaWiFS images were processed using a new Spectral Optimization Algorithm for atmospheric correction and ocean property retrieval in Case-2 waters. A total of 157 SeaWiFS images were collected between 1997 and 2006 and processed to produce Colored Detrital Material images of the Mesoamerican waters. Monthly terrestrial runoff load and river discharge computed with a land-elevation model were used as input to a numerical model, which simulated the transport of buoyant matter from terrestrial runoff. Based on land cover for years 2003-2004, modeling results showed that the river discharge seasonality was correlated with the image averaged CDM, and the simulated plume reproduces the spatial patterns and temporal evolution of the observed CDM plume. River discharge peaked in August and CDM peaked from September to January. The buoyant matter concentration was high from October to January, and was at its lowest from March to April. Between October and December the plume was transported out of the Mesoamerican waters by a cyclonic gyre located north of Honduras. Part of the runoff from Honduras was transported towards Chinchorro Banks and the Yucatan Channel, part re-circulated into the Gulf of Honduras, and part taken toward the outside of the Mesoamerican Barrier Reef System. This study shows that all the reefs of the MBRS, including the most offshore atolls of the region, are under the influence of terrestrial runoff on a seasonal basis, with maximum effect during October to January, and minimum from March to April. Furthermore, what is seen as a giant plume in satellite images is in fact composed of runoffs of different ages.