Absorption properties in shoal dominated regions of the Atchafalaya shelf, Louisiana,USA

The shoal dominated region of the Atchafalaya shelf in the northern Gulf of Mexico is an important resource for sand mining in Louisiana, USA. Algal blooms are seen each year in the study area like most of the northern Gulf of Mexico. Absorption measurements carried out in this region are presented and analyzed. The freshwater input from the Atchafalaya River and the surrounding coastal wetlands and submerged shoals make this area optically complex. Case 1 Ocean Color Algorithms (OCA) do not perform well in these complex case 2 waters. This is because these algorithms do not account for strong blue wavelength absorption by CDOM (colored dissolved organic matter) and NAP (non-algal particulate matter) as observed in our study area. Also the specific phytoplankton absorption a*_PHY(lambda) was found to be variable which indicated the pigment packaging effect would influence retrieval of chlorophyll concentration from standard OCA. OCA´s that can separate contributions of CDOM and NAP and based on the red region of the spectrum where interference of CDOM and NAP is less will work better towards remote monitoring of blooms.