100 m of coastline. Assuming this flow accumu- 

 lates within a zone extending 300 km offshore, 

 this represents for the 1-mo period a lens of ex- 

 cess surface water about 24 m thick. If the flow 

 away from the coast which must balance this ac- 

 cumulation occurs below the pycnocline the re- 

 sult is a downward shift of the upper density 

 structure an average of 24 m over the shoreward 

 300 km. Such a shift implies an extreme increase 

 in baroclinicity in this already highly baroclinic 

 area, tending to accelerate the westward geo- 

 strophic flow along the northern boundary of the 

 Gulf of Alaska. 



The striking negative anomalies for the same 

 month in charts of the index at lat. 60 °N, long. 

 146 °W and at lat. 57 °N, long. 137 °W indicate 

 that this feature existed over the major portion 

 of the northern Gulf of Alaska coastline. This 

 wide geographical extent justifies such a two- 

 dimensional treatment as presented in the pre- 

 vious paragraph. It also indicates a possibly far- 

 reaching effect on the marine environment of this 

 region. 



Several similar short-term intense negative 

 values of the index appear in the charts at other 

 times. In each case the major pulse is confined 

 to only one monthly value but has spatial coher- 

 ence in the Northern Gulf. Most impressive along 

 with February 1950 just discussed are the months 

 of January during the years 1959, 1966, and 1971. 

 January 1971 differs from the others in that the 

 absence of a strong anomaly at lat. 57°N, long. 

 135°W indicates a lesser eastward extent of 

 the feature. 



Periods of Intense Winter Convergence 

 off Washington and Oregon 



The monthly charts of the index at lat. 45°N, 

 long. 125 °W indicate the periods of December 

 1957 through February 1958 and January through 

 March 1961 as having been intervals of extreme 

 convergence of wind-drifted surface waters at 

 the coast. Winter of 1958, in particular, exhibits 

 a striking anomaly in the charts for locations 

 extending from lat. 51 °N to lat. 39 °N. These 

 periods differ from the intense convergences 

 previously described for the more northerly re- 

 gion in containing several successive months of 

 anomalously large negative values of the index 

 rather than a single extreme month and are 



highly evident in the charts of quarterly sum- 

 maries presented in the appendix. The effect of 

 this apparent downwelling at the coast upon the 

 density structure would be to accelerate north- 

 ward flow or to decelerate southward flow. Either 

 situation would favor an anomalous warm ad- 

 vection. 



Long-Term Groupings of 

 Mean Yearly Values 



In examining these data for long-term or re- 

 gional trends it is sometimes helpful to filter out 

 some of the shorter term variability by means 

 of annual averages. For example the charts of 

 mean yearly values indicate anomalously high 

 mean annual upwelling throughout the most 

 recent 8-yr period, 1964 through 1971, from Cape 

 Blanco to San Diego (lat. 42 °N to lat. 33 °N). In 

 contrast, along Baja California (lat. 30 °N to lat. 

 24 °N) strikingly low anomalies are indicated for 

 the 4 successive years, 1965 through 1968. 



The period 1955 through 1959 has anomalously 

 high values from the Los Angeles Bight to the 

 southernmost point covered by the grid (lat. 

 33°N to lat. 21°N). In fact, the anomalously high 

 values during this period extend all the way north 

 to the Straits of Juan de Fuca (lat. 48°N) if the 

 year 1958 which is anomalously low in the more 

 northern area is left out. The low yearly mean 

 values for 1958 are largely due to the extremely 

 low first quarter value previously discussed. 



Low annual absolute values of the indices are 

 found for the first 4 yr of the series (1946-49) at 

 nearly all locations. As previously mentioned this 

 may be due, at least in part, to relatively sparse 

 data coverage in the early years leading to some 

 smoothing of the gradients used in the computa- 

 tions. 



Conclusion 



Anomalies of the type discussed may have im- 

 portant marine biological consequences. Vertical 

 displacements of the thermocline due to intense 

 convergences or divergences such as that indi- 

 cated for February 1950 may affect the depth 

 on the continental shelf where groundfish are 

 located. Anomalous upwellings and downwellings 

 undoubtably affect productivity and the concen- 

 trations of primary producers and zooplankton. 



11 



