24 
Figure 15. Spring 
bloom in the North 
Atlantic. (Courtesy of 
G. Feldman and W. 
Esaias) 
Western Boundary Currents 
and Eddies 
Eddies and other physical processes asso- 
ciated with the large horizontal shears in the Gulf 
Stream and other major ocean currents give rise 
to significant lateral mixing and cross-frontal en- 
trainment. The resulting exchange of physical, 
chemical, and biological properties often results 
in a large modification of the local environment 
causing noticeable changes in the distribution of 
animals and plants at or near the frontal inter- 
face. Fishermen routinely make use of such con- 
ditions to locate commercially exploitable quanti- 
ties of fish that tend to congregate along oceanic 
fronts in search of prey. 
The variety of ocean eddies and the different 
environments in which they are found are the 
basis for a great diversity in physical and biologi- 
cal effects. For instance, eddy systems observed 
off the U.S. West Coast draw plumes of cold, 
pigment-rich coastal waters offshore. This pro- 
~ PHYTOPLANKTON PIGMENT mg m3 
05.1.2 .3.4.5.6.7.8 .9 1 31030 
cess is an important mechanism for enriching off- 
shore waters with plankton and nutrients. Gulf 
Stream eddies off the U.S. East Coast north of 
Cape Hatteras, NC, constitute an important mech- 
anism for exchanging chemical and biological 
properties between coastal and offshore waters. 
CZCS imagery, such as shown in Figure 16, and 
AVHRR observations provided the first synoptic 
view of Gulf Stream eddies and showed how ed- 
dies are formed, how long they last, and where 
they go during their lifetime. 
It is clear the processes associated with mix- 
ing along the edge of eddies, coastal currents, 
western boundary currents, etc., are not only 
quite complex, but also that they vary greatly from 
one region and oceanographic feature to the 
next. Given their importance in the mixing of 
oceanographic parameters (salinity, temperature, 
biological populations, etc.), a better understand- 
ing of this variability is critical to gaining a better 
understanding of the distribution of oceano- 
graphic parameters in general. 
