Characterization of a high chlorophyll plume in the northeastern Gulf of Mexico

In the northern Gulf of Mexico (NGMx), plumes of high chlorophyll shelf waters have been observed to extend across the shelf-break to the central basin. Prior research has shown an association between this cross-shelf flow of water and materials and the adjacent rotation of cyclonic and anticyclonic eddies. Satellite remote sensing data were used here to identify such an eddy-driven plume and to detect and characterize both the mechanisms driving the plume and its biogeochemical impacts. Satellite imagery included chlorophyll (CHL), fluorescence line height (FLH) and chromophoric dissolved organic matter (CDOM) measurements from SeaWiFS and MODIS-Aqua, sea surface temperatures from MODIS-Terra, QuikSCAT wind fields and a merged multi-platform sea surface height product (SSHa). In early June 2007 images, a prominent high-CHL plume (HCP) was seen extending from the continental shelf of the NGMx. A comparison of the CHL and SSHa fields revealed that the HCP was coincident with a cyclone-anticyclone pair, thus linked to an apparent cross-shelf transport. Nearest to the shelf, the CHL values associated with the transport fell within the usual CHL temporal and magnitude range for the summer CHL maximum. Further offshore, the HCP-associated CHL increase was temporally offset, occurring several weeks earlier than expected seasonal CHL peaks. Within the HCP, the relationship of CHL:CDOM:FLH notably diverged from the climatological status, supporting the hypothesis that the HCP composition includes modified shelf waters. Estimates of primary productivity across the study region revealed significant increases in productivity within the HCP's boundaries. (C) 2014 Elsevier Inc. All rights reserved.