A Lagrangian view of fluorescent chromophoric dissolved organic matter distributions in the Mississippi River plume

In April 2001, three instrumented surface drifters were deployed in the Mississippi River plume near the mouth of Southwest Pass. The plume was characterized by strong surface gradients of salinity, temperature, and chromophoric dissolved organic matter fluorescence (FCDOM). The drifters initially headed west and attained peak speeds of 1 m s−1 within 5 h after release. Thereafter, velocity decreased as the triad headed north in the Louisiana Bight. Linear relationships between FCDOM and salinity identified two subsurface sources of high salinity water (salinity >35) underlying the surface plume. The platforms stalled in a surface front about 40 h after deployment, and then slowly drifted south along the eastern perimeter of the plume. Shoreward of the plume front there were patches of low-salinity, high FCDOM ‘patches’ of surface waters that likely originated in the marshes, bayous, and other smaller distributaries of the delta.