SON 



45N 



J FMAMJJASONDJJ 



AMJJASONDJ 



40N 



3 5N 



30N 



OFFSHORE EKMAN TRANSPORT (M^'/sec/M) SEA SURFACE TEMPERATURE (°C) 



I25W I20W 



VANCOUVER I. ' 



II5W 

 SON 



45N 



40N 



35 N 



30 N 



Figure 1. — Time series isograms of long-term composite monthly offshore Ekman transports (m% per meter of coastline) and sea 

 surface temperature (degrees Celsius) for the 20-yr (1948-67) period within the indicated 1° coastal squares. 



September. The weakness of the transport is 

 reflected by the presence of substantial seasonal 

 warming. The region defined by temperatures 

 greater than 15°C, located off Washington- 

 Oregon during late summer, probably reflects the 

 warming of the low-salinity Columbia River 

 plume water which spreads over a large area of 

 ocean surface. Some of the apparent warming 

 may be due also to the concavity of the coastline 

 in this area which could cause a greater proportion 

 of the observations to be taken farther offshore, 

 both because the 1° squares extend farther off the 

 coast and because the coastwide shipping tracks 

 may be displaced offshore. 



South of Cape Blanco an abrupt increase of 

 summer offshore Ekman transport is indicated, 

 particularly during June and July. This is 

 associated with a suppression of seasonal warm- 

 ing during early summer. Consequently, the 

 period of maximum sea surface temperature is 

 delayed until September when offshore transport 

 has relaxed considerably. 



South of Cape Mendocino Ekman transport is 

 directed offshore for virtually the entire year and 

 reaches its greatest value for the whole coast at 

 about lat. 39°N during May through August. This 

 maximum corresponds to an extreme suppression 

 of seasonal warming indicated by nearly hori- 

 zontal isotherms in the figure. 



South of Point Conception, the offshore Ekman 

 transport, although remaining generally positive 

 throughout the year, is small and an abrupt 



southward increase in temperature, particularly 

 during the summer, is apparent. Due to the 

 tendency for a cyclonic eddy to form in the 

 Southern California Bight (Reid, Roden, and 

 Wyllie, 1958), warm advection not directly related 

 to upwelling may be an important factor in this 

 increase. 



Literature Cited 



Ekman, V. W. 



1905. On the influence of the Earths rotation on ocean 

 currents. Ark. Mat. Astron. Fys. 2(ll):l-55. 

 Lynn, R. L. 



1967. Seasonal variation of temperature and salinity at 

 10 meters in the California Current. Calif. Coop. 

 Oceanic Fish. Invest., Rep. 11:157-186. 

 Reid, J. L., Jr., G. I. Roden, and J. G. Wyllie. 



1958. Studies of the California Current system. Calif. 

 Coop. Oceanic Fish. Invest., Prog. Rep., 1 July 1956 to 1 

 Jan. 1958, p. 27-57. 

 SVERDRUP, H. U. 



1938. On the process of upwelling. J. Mar. Res. 

 1:155-164. 

 Wooster, W. S., and J. L. Reid, Jr. 



1963. Eastern boundary currents. In M. N. Hill (editor). 

 The sea, ideas and observations on progress in the study 

 of the seas. Vol. 2, p. 253-280. Interscience Publ., N.Y. 



Andrew Bakun 



Douglas R. McLain 



Frank V. Mayo 



Pacific Environmental Group 



National Marine Fisheries Service 



NOAA 



Monterey, CA 93940 



844 



