prepared by Anderson, Barnes, Budinger, Love, 

 and McManus (1961). An atlas of July oceano- 

 graphic conditions was prepared as a supplement 

 to the present work by Owen (1967b). 



RECURRENT FEATURES OF DISTRIBUTIONS OF 

 VARIABLES 



Both in the surface and deep layers, patterns 

 of distribution of physical variables recur from 

 summer to summer over the region off Oregon- 

 Washington. This recurrent nature permits dis- 

 cussion of physical mechanisms that operate in 

 the region. 

 Upper Zone 



Above the main halocline (fig. 2) the area is 

 divisible in summer into three meridionally 

 bounded regions on the basis of physical processes 

 believed to produce the distributions of variables 

 characteristic of each. These regions may be 

 termed nearshore province, plume province, and 

 offshore province (fig. 1). 



Nearshore Province. — The first subdivision, near- 

 shore province, lies along the coast in summer as a 

 band of cold, saline water about 50 nautical miles 

 (90 km.) wide, interrupted only by fresher water 

 from coastal soiu-ces. It is dominated by the effects 

 of coastal upwelling. Intense horizontal gradients 

 of temperature, salinity, density, and oxygen 

 concentration are encountered from the sea sur- 

 face to depths exceeding 250 m. (figs. 3, 4, 5, and 6). 

 These gradients result from transformation of 

 offshore vertical gi'adients, recognized there as 

 the thermocline, halocline, pycnocline, and 

 oxycline, into nearshore horizontal gradients by 

 upwelling. 



The offshore summer thermocline (fig. 7) does 

 not coincide with the permanent halocline, but 

 lies above it. Consequently, the corresponding 

 horizontal temperature gradient of the nearshore 

 regime lies farther from the coast than does the 

 horizontal gradient associated with the permanent 

 halocline (compare figs. 7 and 8). Once transported 

 to the near-surface layer by upweUing, water of 

 subsurface origin is warmed by local heat exchange 

 across the sea surface. Because of this local heat 

 gain neither temperature nor temperature gi'adient 

 permits close assessment of intensity of upwelling, 

 although both serve to indicate the offshore extent 

 of upwelling influence. 



The nearshore distribution of salinity is rela- 

 tively uninfluenced by processes other than diffu- 

 sion and upwelling in the nearshore province, 



except where dilution occurs near coastal sources 

 of fresh water. The water of the offshore halocline 

 is displaced upward within upweUing areas and 

 usually reaches the surface layers. The inshore 

 occurrence near the sea surface of water of the 

 same salinity (33.8°/oo) as that at the bottom of the 

 offshore halocline (fig. 8) indicates upward trans- 

 port of water from depths below the permanent 

 halocline. Diffusion and transport across surfaces 

 of constant salinity near shore apparently are 

 important; the near-surface horizontal gradient of 

 salinity in this province is about three orders of 

 magnitude less than the corresponding vertical 

 gradient in the halocline offshore. 



Distribution of mass in the nearshore province 

 follows the pattern characteristic of coastal up- 

 weUing in general: large horizontal gradients of 

 density are normal to the coastline in the upper 

 layer (fig. 5), and vertical gradients of density are 

 weak. Mass transport probably takes place across 

 surfaces of constant density within the near- 

 surface layers, however, because density is de- 

 creased locaUy there by net heat gain from 

 insolation. 



Oxygen concentration may exhibit significant 

 local increase in upweUed water due to photosyn- 

 thetic processes and to rapid exchange with 

 atmospheric oxygen (fig. 6). These local changes 

 are not sufficiently rapid, however, to obscure the 

 effect of upweUing on oxygen concentration; low 

 oxygen values that denote deep offshore origin are 

 consistently present in surface layers of the near- 

 shore province. 



Water in the siu-face layers of the nearshore 

 province is of deep offshore origin. Water of (t,>26, 

 corresponding in density to water near the bottom 

 of the offshore halocline (fig. 9), is common in the 

 nearshore surface layers (fig. 5). The density of 

 some of this water must have been decreased, 

 however, by mixing in transit and by local heating; 

 therefore, it must have come from depths in excess 

 of that of the offshore halocline. 



Plume Province. — The second subdivision, plume 

 province, is characterized by near-surface water 

 of low salinity, the result of dUution by coastal 

 fresh water. The Oregon-Washington coast rep- 

 resents a variable line source of fresh water. The 

 Columbia River, however, with a mean annual 

 discharge of 7.3 x lO'm.' sec."' and a maximum 

 discharge (in June) of about 16.0 x lO^m.' sec."', 

 contributes more than 73 percent of the average 



OCEAA'OGRAPHIO CONDITIONS IN NORTHEAST PACIFIC OCEAN 



505 



