Table 1. — Data and hydrographic equipment used on the FRS Oregon II groundfish cruises. 



Cruise 

 no. 



Hydrographic equipment 



Salinity 



Temperature 



Date XBT STD Niskin bottles Refractometer Surface Bottom Surface Bottom 



X 

 X 

 X 

 X 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 

 X 

 X 

 X 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 

 X 

 X 

 X 

 X 

 X 

 X 



perature were recorded using a Plessey Environmental 

 System Model No. 9060 Graphic, self-recorded, STD 

 unit. The degree of variation between the STD and the 

 refractometer was 0.5 ppt. Because the XBT failed on 

 cruise 44 and the STD on cruise 55, the environmental 

 data are incomplete east of the Delta. Weather data were 

 taken from the FRS Oregon 11 weather log for cruises 48 

 to 64. The September and October wind roses for SA2 

 and SA3 are incomplete because of inadequate weather 

 data for that time. 



Figures 2 to 43 show mean bimonthly differences 

 between surface and bottom temperature and salinity, 

 mean bimonthly air temperature, and surface and bot- 

 tom isotherms and isohalines for each cruise. Isotherm 

 contours were not drawn for cruise 40 (Fig. 9) because of 

 the narrow range between data points. Isotherms and 

 isohaline contours were not drawn around the mouth of 

 the Mississippi River (Figs. 9 to 37, 39, 42) because of the 

 wide range in values due to the influence of the 

 Mississippi River. 



DISCUSSION 



Meteorological conditions and the discharge from the 

 Mississippi River within this survey area have a sig- 

 nificant effect on seasonal variations (Drennan 1968). 

 Within the primary area, salinity and temperature data 

 have been separated by depth and survey area to detect 

 seasonal changes. Calculated bimonthly mean surface 

 and bottom temperatures are shown in Table 2. Mean 

 differences between surface and bottom temperatures 

 have been computed bimonthly to demonstrate an an- 

 nual seasonal cycle for each survey area (Figs. 2-4). Data 

 indicated that both a summer and winter season are well 

 defined within the primary area. The change in seasons 

 is recognized when surface and bottom temperatures are 

 similar. The summer season begins in March and April 

 at all depths. This change is correlated with changing 

 meteorological conditions as the wind shifts from a 

 northerly to a southerly direction (Figs. 2-4). This shift in 

 direction is accompanied by a decrease in intensity of 

 wind speed and an increase in air temperature (Fig. 5). 

 Water and air temperatures reach a peak in July and 

 August accompanied by frequent calm winds (Figs. 2-4). 

 Little wind-mixing during the period, coupled with solar 



Table 2. — Mean bimonthly surface and bottom temperatures CO 

 for each survey area. The top figure represents surface temperature 

 and the bottom figure represents the bottom temperature. 



heating, results in a large difference between surface and 

 bottom temperatures. The summer season begins to dis- 

 appear in September and October with a drop in air tem- 

 perature and a wind shift. By November and December 

 the winter season has begun with southeasterly winds 

 shifting to a more northerly direction (Figs. 2-4). This 

 change in wind direction and intensity produces 

 northers, causing the mean air temperature to drop ap- 

 proximately 9°C from the July and August high (Leip- 

 per 1954). The wind generally remains out of the north to 

 northwest in January and February bringing colder tem- 

 peratures within the survey area. This is the coldest 

 period of the year. By March and April the winter season 

 ends with a general warming of air temperature and a 

 wind shift to the southeast, thus completing the annual 

 cycle. 



