[Coral-List] Orinoco River Plume in the Caribbean
Estrella.Malca at noaa.gov
Wed Apr 29 12:37:07 EDT 2009
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
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