[Coral-List] Orinoco River Plume in the Caribbean

[Estrella Malca]

The NOAA RV Nancy Foster conducted an oceanographic and ichthyoplankton 
survey in the US and BVI, and leeward Islands from April 7-21st, 2009.. 
During that time frame we encountered the Orinoco River plume water. 
Below is a short description and an attached image showing the extent of 
the plume in mid April . We will have a more extensive report with 
mapped surface features available at the end of the week. Please contact 
Dr. Trika Gerard (trika.gerard at noaa.gov) and/or Dr. Libby Johns 
(Libby.Johns at noaa.gov) for additional information./
/
April 19, 2009
Hello from the Caribbean Sea. Just wanted to share with you an unusual 
event in the area around US Virgin Islands and Puerto Rico we are 
experiencing on the current USVI cruise. The first week of the cruise 
oceanographic conditions were normal for the region, typical 
oligotrophic waters with low chlorophyll values throughout the region.. 
However, in the second week, the Orinoco river plume had pushed up into 
the region and now extends north of the Virgin Islands. This river plume 
water has decreased salinity with a very strong chlorophyll and colored 
dissolved organic matter (CDOM) signature. The low salinity, high 
chlorophyll layer is present at the surface and extends approximately 20 
meters in depth. Plankton volumes are at least 4 times higher in the 
plume, compared to samples collected outside the plume.
I have attached a MODIS color image showing the extent of the Orinoco 
river plume. Sampling stations are plotted in white. The Chl a and CDOM 
are scaled with red showing the highest and blue the lowest. Although 
this is a yearly event, the Orinoco outflow rarely reaches this far north.

When we first started tracking the plume, it appeared to move north and 
then be advected west to Saint Croix and Puerto Rico by a cyclonic eddy. 
The high chlorophyll water subsequently wrapped around the western end 
of Saint Croix, and then north to Saint Thomas. At the same time another 
branch moved north along the Leeward Islands, and currently extends 
north through the Anegada Passage.
We are presently mapping the extent of the plume around Saint Croix. The 
maximum chlorophyll is at 20 meters depth instead of at the surface and 
appears to extend well inshore onto the reefs. We have reports from 
fishermen of ‘green water’ from St. Thomas and Puerto Rico as well. The 
impact of this event on the ecosystem is as yet unknown.

Trika Gerard, Estrella Malca, Barbara Muhling, Akihiro Shiroza, 
Francisco Fuenmayor, John Lamkin - Southeast Fisheries Science Center
Libby Johns, Ryan Smith, Nelson Melo, Grant Rawson- Atlantic 
oceanographic and Meteorology Laboratory