Thursday, June 24, 2010
In earlier years we have collected large numbers of late stage larval bluefish at a depth of about 10 meters inshore of an upwelling front in the New Jersey seascape.
Winds from the north and east reinforce corelis forcing and cause downwelling conditions along the NJ coast that can drive the Hudson Raritan estuarine plume down along the New Jersey coast as far as Atlantic City.
The coastline of Long Island near our seascape lies at an angle of about 84 degrees true or nearly due east. Strong eastward and alongshore winds can cause similar upwelling along Long Island. What interesting is what happens off Long Island when these easterly winds relax. The water tends to snap back toward the west along the coast and therefor has a very long residence time. This is described in the following papers:
Weifeng G. Zhang, John L. Wilkin, and Oscar M. Schofield - Simulation of Water Age and Residence Time in New York Bight - Journal of Physical Oceanography - vol. 40
Donglai Gong, Josh T. Kohut,1 and Scott. M. Glenn - Seasonal climatology of wind‐driven circulation on the New Jersey Shelf - JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, C04006, doi:10.1029/2009JC005520, 2010
Water residence time in the New Jersey Seascape appears to be much shorter. Larval fish should be retained near the spawning areas of adults off Long Island for longer periods than those spawned off New Jersey. These differences in circulation and dispersal might produce differences in the ratio of "residents" to "immigrants" and thus community dynamics in the two seascapes.
Below is a nice sea surface temperature and HF radar image showing the effects of strong northward winds on currents and sea surface temperatures. Below that is the most recent and clear Chlorophyll-A image of the New Jersey Coast from the 18th of June. In the first image water leaving the estuary on the ebb tide is forced to the northeast by the wind and cold upwelled water sits right in our New Jersey Seascape. The second image indicates there is relatively high primary production inshore along the entire coastline. Today it is blowing pretty hard out of the west southwest (18-20knots) in advance of the weak front cold front I mentioned yesterday. "The pump is primed" for strong upwelling conditions during the first few days of our research cruise.