THERMOCLINE

Dear Mr. Lane:

 I received your request for information about the causes of our
summer upwelling, and I would be pleased to share with you what I can in
that regard.  I have conducted several upwelling studies since coming to
Harbor Branch in 1977,   I never got very far north of Cape Canaveral.
However  I believe the situation we have down here is similar to what
you have on your section of  the continental shelf.

 A  summary is that the primary push is given by the Florida Current
(which merges with the Antilles Current to form the   Gulf Stream in
your area), but that seasonally shifting winds also play an  important
role.

 In summer months,  northward volume transport in the Florida  Current
reaches its annual maximum, and Frank Chew (at the Atlantic
Oceanographic and Meteorological Laboratories in Miami) has shown that
the  axis of the current shifts westward at the same time.  There
apparently is a  cause-and-effect relationship, but I can't say that I
understand it.

 Anyway, when the Florida Current comes in contact with the outer
continental shelf off our east coast, friction slows the current and
deflects near-bottom water landward.  That is our upwelling.
Apparently,   this is a relatively common occurrence (and not
necessarily restricted to   summer months), but when winds are out of
the southeast quadrant the seaward  transport in near-surface layers
reinforces the landward transport in
near-bottom layers.  The result is a major upwelling event that usually
makes it all the way to the coast. Upwelling affects relatively short
lengths of coastline at any  one time.  Thus, we are not all in this
together--at least not at the same  time.

Ned P. Smith,

jlane-dab@ieee.org