Discussion

Salinity, density and temperature were within normal range for Puget Sound at this time of year (Ebbesmeyer et al. 2001). At the outer shelf the summer salinity minimum coincides with a temperature maximum, producing a density minimum in June. The temperature minimum occurs about the same time as the salinity maximum, and the temperature maximum as the salinity minimum, with a resulting density minimum in winter. (Huyer, 1977) Our results compare to the results from a study off the Oregon coast, by Adriana Huyer (1977) showing a maximum salinity of approximately 34 ppt and a minimun of approximately 30 ppt. Salinity and density had similar results along the longitudinal sampling course at all depths (Figures 1 and 2).

Figure 1. Salinity contours from CTD data along a longitudinal course from offshore into Puget Sound in depths up to 200 meters (UWT 2002).

Figure 2. Density contours from CTD data along a longitudinal course from offshore into Puget Sound in depths up to 200 meters (UWT 2002).

The highest values were obtained offshore and at greater depths. Salinity and density decreased sharply at all depths beginning at station 12, Atop Admiralty Inlet until inside Main Basin at the Triple Junction and then remained lower through the longitudinal course to station 15, Nisqually. Station 6, Shelf Break 2 had lower salinity and density values near the surface compared to other samples outside of Admiralty Inlet. Station 18, North of Brown's Point also had lower salinity and density values than the surrounding sample sites.

The salinity and nutrient content of the deep Juan de Fuca inflow have a strong seasonal cycle that varies in phase with seasonal upwelling on the outer coast. This is particularly clear from a June-December 1973 monthly time series of nutrient profiles across mid-Juan de Fuca Strait. (Harrison, et al, 1994)

During June and July 1984 CTD readings were taken in the Strait of Juan de Fuca. Surface salinity during the July pulse suggests a poleward-tending low salinity plume with a slight offshore bulge. Minimum salinity (29.5ppt) is observed at the mouth of the strait and is roughly the same as that observed in the eastern basin (Hickey, et al, 1991). Except at the mouth of the strait, the freshest water occurs slightly offshore.

Temperature followed a general pattern of warmest at the surface and cooling upon descending in depth. Ranges averaging 8.7°C at the surface down to 2.2°C at around 2300 meters deep off the shelf in the Pacific Ocean (Table 1). Station 6, Shelf Break 2, had slightly higher temperature between 11-30 meters deep (Figure 3 and 4) than at the surface.

Depth	Temperature °C	Salinity PSU	Density kg/l
<10	8.732	30.088	23.309
11-30	8.636	30.941	23.997
31-65	8.272	30.748	23.851
66-115	7.794	32.05	24.99
116-210	7.523	32.251	25.134
211-360	6.3	33.977	26.709
750-805	3.995	34.292	27.232
1450-2300	2.192	34.573	27.634

Table 1. Averages taken per depth for 20 sampled stations on a longitudinal course from offshore into Puget Sound.


Figure 3. Temperature contours from CTD data along a longitudinal course from offshore into Puget Sound in depths up to 200 meters (UWT 2002).

Temperature increased slightly from station 11 to station 13 through Admiralty Inlet. The decrease most likely resulted from the sill at the top of Admiralty Inlet, which caused a barrier incoming ocean water flow and mixture (Ebbesmeyer et al. 2001). The tail end of a strong NW wind could have augmented the surface out flowing water and a less intense bottom water intrusion. Temperatures at station #6, Shelf Break 2, increased at the same areas as salinity and density decreased indicating fresher water.

There was a slight rise in measured DO in less than 30 meters of water at station 6, Shelf Break 2, which corresponded with a rise in surface temperature, lower salinity and density, rise in fluorescence and a higher phytoplankton count. This was particularly noted in the 11-30 meter depth. DO decreased sharply from station 11 to station 13 through Admiralty Inlet (Figure 4 & 5).

Figure 4. Averaged percent saturation of oxygen in depths of less that 30 meters along a longitudinal course from offshore into Puget Sound.


Figure 5. Oxygen contours from CTD data along a longitudinal course from offshore into Puget Sound in depths up to 200 meters (UWT 2002).

Higher DO from Admiralty Inlet south to Nisqually in the deeper waters and in the surface water indicated an oxygen rich environment. Sources for oxygen for these samples could be from fresh water inflow, the recent strong wind stirring up the surface, mixing of the waters and oxygen produced from phytoplankton. The areas of high DO, fluorescence and chlorophyll represent the areas of high plankton.

The highest measured fluorescence and chlorophyll were within the first 50 meters of the water at stations 1, 6, 13, 14, 15, 16, 18, 19, and 20 (Figure 5). These stations were located from inside Admiralty Inlet down to Nisqually. Within this group of higher fluorescence, station #17 named Dalco Passage had relatively low numbers and Station 6, Shelf Break 2, was the only station with higher fluorescence outside of the straits.

Figure 5. Fluorescence contours from CTD data along a longitudinal course from offshore into Puget Sound in depths up to 200 meters (UWT 2002).

Sediment size decreased from stations #6-2, which is probably from the glacier deposits many years ago and also from the drainage of the rivers into the Puget Sound.

Nitrogen levels were highest offshore at station #2, Abyssal Plain, which reflect that the largest store of nitrogen is found in the atmosphere where it exists as a gas. The atmospheric store is about one million times larger than the total nitrogen contained in living organisms and other major stores of nitrogen include matter in soil and oceans (The Nitrogen Cycle 2002)

The phosphate cycle is not as abundant as the nitrate and is not as mobile as nitrogen. Phosphorus does not get airborne as nitrogen does. It weathers off rocks and is taken up by plants. The plants are eaten by herbivores and then the herbivores are consumed by carnivores or omnivores. Phosphorus is then entered into land as waste. The waste washes away to the ocean. From continental rise, the nutrients are returned to land (Phosphorus Cycle, 2002). Additional nutrients can be a result of pollutants such as chemicals and fertilizers being washed out in runoff.

Oceans are major stores for nitrogen, but phosphorus is limited. In Juan de Fuca Strait, surface nitrate range about 8-25 uM. In deep water (>100 m), nitrates average about 30 uM (Harrison, et al, 1994). The average of our sample of site#7, which is near the mouth of the Strait of Juan de Fuca. Harrison noted the same location of higher level of nitrate, but his measured levels were slightly lower than this study.