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Welcome to Commencement Bay!
Welcome to Commencement Bay!
View of Commencement Bay from main water way.
The Commencement Bay area is a deep-sea harbor that’s located between Point Defiance and Browns Point, in the southern end of the Main Basin (Cannon and Grigsby 1982). With the bay being originally formed by a intrusion of a glacial ice sheet, the bays deposited with glacial till all along the shorelines (Orlob et al. 1950). The bay has a depth of 42 meters to 185 meters connecting to the Main Basin, stretching 4.7 km along the southwest shore of Point Defiance, by 4.3 km across the inner bay, and 4.7 km along the northern shore (Cannon and Grigsby 1982). Along with the Puyallup river running off into the mouth of the bay, sediments in Commencement Bay could be drastically different among the sampling stations (Figure 1). Commencement Bay plays host to the port city of Tacoma, including the ports eight waterways: Blair, Hylebos, Middle, Milwaukee, Osgood, Sitcum, St. Paul, Thea Foss, and Wheeler. The channelization of the Puyallup River Delta, which started in the 1800's, helped formulate the many waterways. The main source of fresh water into the Bay comes mainly from the Puyallup River. Smaller creeks, such as the Hylebos, Mason, and Puget, also contribute freshwater to the Bay.
Wooden debris floating in bay.
Wooden debris floating in bay.
Burnt boat near mouth of Hylebos creek in Commencement Bay.
Burnt boat near mouth of Hylebos creek in Commencement Bay.
Sampling Stations
Sampling Stations
Figure 1: Sampling stations. Data taken 14 April, 2023.
Table 1: Station identification and information.
Meteorological Conditions During Sampling Period
Meteorological Conditions During Sampling Period
Partly cloudy conditions during morning sampling cleared the way for mostly sunny skies during afternoon sampling. No rain and mild winds allowed for stable water conditions.
April 13, 2023
April 14, 2023
Figure 2: Weather report for 13 April, 2023 (top), and 14 April, 2023 (bottom). (Sourced from Weather Underground -- measurements taken from Seattle-Tacoma Intl Airport).
Figure 3: Hourly weather forecast for 14 April, 2023. (Sourced from FORECA, Tacoma Narrows Airport)
Pressure is measured in inches of Mercury (inHg)
Tidal Patterns During Sampling Period
Tidal Patterns During Sampling Period
Figure 4: Tidal patterns for 14 April, 2023 (Sourced from NOAA).
CTD Water Property Sections
CTD Water Property Sections
Commencement Bay Outer Latitudinal Transect
(Stations: 1, 2, 3).
Temperature (C)
Salinity (PSU)
Density (kg/m^3)
Temperature, salinity, and density are compared here due to their close connection with one another. The top layer of the salinity graph indicates a fresh water layer, likely from the Puyallup River. We can see the deep water is fairly well-mixed, and this can be due to the proximity of the stations to the channel where the tidal currents are stronger. The connection between these three measurements are apparent. The deeper, cooler water is also host to higher salt concentrations. Subsequently, this coincides with the denser water readings.
Dissolved Oxygen (ml/L)
Fluorescence (mg/m3 )
Transmissivity (%)
There is little to zero fluorescence indicated in the graph, indicating not much phytoplankton. What were seeing in the transmissivity graph is likely sediment and nutrients carried into the bay from the Puyallup river. Additionally, the dissolved oxygen graph is relatively consistent, and also shows a similar pooling near the same depth as the transmissivity graph. It is also indicating a lot of mixing as it is relatively thinned out.
Commencement Bay Longitudinal Transect
(Stations: 2, 4, 6).
Temperature (C)
Salinity (PSU)
Salinity (PSU)
Density (kg/m^3)
Density (kg/m^3)
This transect is interesting in that it has input from the channel (station two - outer), but also input from the harbor (which has extreme influence from the Puyallup river). We can see the black layer at the top of the graphs indicating a large influence from the Puyallup river on the right, and thins slightly as you head left towards the channel. The same trends continue regarding relationships between temperature, salinity, and density.
Dissolved Oxygen (ml/L)
Dissolved Oxygen (ml/L)
Fluorescence (mg/m3 )
Fluorescence (mg/m3 )
Transmissivity (%)
Transmissivity (%)
Fluorescence is absent due to low concentrations of phytoplankton at the time of sampling. The transmissivity graph shows clear water towards the channel, but a huge influx of sediment (and potentially nutrients) from the Puyallup river, as indicated on the right. Dissolved oxygen concentrations are relatively consistent throughout the water column, with slightly lower concentrations at lower depths.
Commencement Bay Inner Latitudinal
Transect (Stations: 5,6,7,8).
Temperature (C)
Salinity (PSU)
Salinity (PSU)
Density (kg/m3 )
Density (kg/m3 )
As alluded previously; salinity, density, and temperature are closely related. From our graphs, we can see that there is a thin layer of fresh water at the surface. Stations 5,6,7, and 8 are in close proximity to the mouth of the Puyallup river; therefore, this fresh water layer is likely coming from the Puyallup River. The temperature graph indicates a consistent, low temperature starting at ~5 meters. Salinity also tracks density in the stratified layers, showing high salinity and density towards the sea floor.
Dissolved Oxygen (ml/L)
Dissolved Oxygen (ml/L)
Fluorescence (mg/m3 )
Fluorescence (mg/m3 )
Transmissivity (%)
Transmissivity (%)
From our graphs, we can see that there is a very low presence of phytoplankton near the harbor. Looking at the transmissivity graph, we see a higher reading near the surface, which is likely due to sediments being carried out from the Puyallup River. The transmissivity layer on the top matches the fresh layer from our salinity graph. The higher reading of dissolved oxygen near the surface could be due to tidal mixing and influx of fresh water.
Comparison of CTD Data with Discrete Water Sample Data
Comparison of CTD Data with Discrete Water Sample Data
Figure 5: Correlation between Chlorophyl and Discreet.
Figure 6: Correlation between Dissolved Oxygen and Discreet.
(Left) - There is very little correlation between the Discrete and CTD chlorophyll reading, as shown by the R2 value (0.2011). The unit equivalence of (mg/m3 ) is (ug/L). This was our first attempt at compiling this data; therefore, the correlation factor appears to be low as we learned how to run these samples.
(Right) - There is a strong correlation between the discrete and CTD dissolved oxygen reading, as shown by the R2 value of (0.7118).
Secchi Disk
Secchi Disk
Figure 7: Inital secchi reading depth in meters.
Figure 8: Light Penetrative Depths via Percent Incident Irradiance conversion.
(Top) - The secchi depths were taken in meters. This measurement gave us the ability to see how clear the water is at the surface, and to estimate how far light is penetrating. This is important for phytoplankton growth.
(Bottom) - This graph takes the initial measurement in meters and applies a percent incident irradiance factor, which allows us to calculate much more accurately how deep light is penetrating. This gives us a more precise measurement regarding the light layer with which phytoplankton has to grow. The depths portrayed in figure 8 represent the depth to which at least 1% light penetrates.
Our Secchi readings indicate station 1 had the highest reading at 21 meters, followed by station 3 at 18 meters. All other stations falls around the 15 meter mark, with the exception of station 6 (7.5 meters) and 8 (12 meters).
Phytoplankton
Phytoplankton
Table 2: Nets phytoplankton abundance table. Credit: Clint Howell
Figure 9: Surface phytoplankton abundance graph. Credit: Clint Howell
Credit: Clint Howell
Chaetoceros Decipiens
Chaetoceros Decipiens
The phytoplankton abundance table indicates there aren't any significant concentrations of phytoplankton. Phytoplankton presence was in fact quite rare, contrary to the previous week which saw a bloom. From the concentration graph we can see that stations 3, 7, and 8 had higher levels of concentrations of Chaetoceros decipiens.
Nutrient Data
Nutrient Data
Figure 10: Si(OH)4 concentrations (left), and dissolved inorganic nitrogen concentrations (right).
Table 3: Nutrient levels for both surface and deep water measurements in Commencement Bay.
(Left) - Si(OH)4 concentrations were much more prevalent in the deep water samples compared to the surface water. This could be due to greater concentrations of silicates towards the sea floor where the samples were taken and influx from the Puyallup River.
(Right) - There are not obvious differences between surface/deep water samples regarding dissolved inorganic nitrogen (DIN). Overall, DIN concentrations were higher closer to the harbor and thinned out slightly towards the outer stations.
(Bottom) - This table illustrates the various nutrients in the water column.
Sediment Data
Sediment Data
Credit: Mateo Schuler
Graph: Higher particle size and concentration values correlate with higher TOC %.
Discussion of Observations
Discussion of Observations
Samples taken in Commencement Bay on 14 April, 2023 provided the team with a vast array of data points. CTD data showed very little stratification below ~5 meters, which indicates that the deep bay was well-mixed at the time of sampling. This is usually the case in the strong tidal currents have a large impact on mixing.
The outer latitudinal transect (stations 1,2, and 3) -- showed temperature, salinity, and density readings displaying very similar trends. This is an expected result as cold water is dense and sinks, salinity adds to the density, and that is reflected in the contour sections. Additionally, due to the fresh water layer from the Puyallup river, the contour sections indicate a highly stratified surface layer above the well-mixed bottom. This incoming layer of fresh water provides nutrients and sediments into the bay, which is reflected in the transmissivity readings. The right to left, the influx of river erosion is apparent as it heads towards the channel. Contrary to the prior week of sampling, fluorescence was not detected in the bay on the 14th of April. This could be due to a strong fresh water influence from the Puyallup river and tidal fluctuations that help push out phytoplankton from the bay.
The longitudinal transect (stations 2,4, and 6) -- This transect has input from both the channel (station two - outer), as well as the harbor (station 6). The channel station has a faster current and is much more mixed than the harbor location of the bay. The temperature provided a cold, consistent reading. This is another indication of thorough mixing, which is expected near the channel. The harbor has a thick black layer at the top of the contour sections indicating a large influence from the Puyallup river on the right, and thins slightly as we head left towards the channel. This river debris affects the transmissivity, as well as the dissolved oxygen. As with the previously discussed transects, this transect also indicated a very low number of phytoplankton. The fluorescence contour section shows zero green. This doesn't mean that there are no phytoplankton there, but rather that the trace amount that are there are not meeting the minimum threshold.
The inner latitudinal transect (stations 5,6,7, and 8) -- As alluded previously; salinity, density, and temperature are closely related. From our graphs, we can see that there is a thin layer of fresh water at the surface. Due to all four stations being in close proximity to the mouth of the Puyallup river, there is little doubt that the Puyallup river is the source. The temperature graph indicates a consistent, low temperature starting at ~5 meters. Salinity also tracks density in the stratified layers, showing high salinity and density towards the sea floor. A major difference between this transect and the rest are how stratified the layers are. The harbor is super stratified compared to the well-mixed stations out on the channel. Commencement Bay's CTD data was fairly consistent from station to station, with again, the biggest difference in fresh water input and stratification.
From our phytoplankton abundance table, we can see that there is very little phytoplankton presence in Commencement Bay. We suspect that this could be due to the large inflow of fresh water from the Puyallup River combined with the tidal flushing. Phytoplankton counts plummeted compared to the previous week of sampling. However, the salinity was also significantly more stratified compared to the previous week.
Nutrients indicated that Si(OH)4 (silicic acid) was higher in the deeper portions of the bay. Typically, silicate is spread throughout the water column; however, due to phytoplankton being near the surface -- silicate levels are lower as the phytoplankton utilize it to help build their shells. Dissolved inorganic nitrogen (DIN) was unusually even during our sampling. While the differences between surface/deep within a station were minute, the differences become clearer from station to station. The abundance of DIN is heavier towards the harbor, and thins out towards the channel.
Looking at the composition of the sediments of Commencement Bay. We see that majority of the structure being sand and silt. With sediments being carried out from the Puyallup river from glacial melt, we believe this is the result. Looking at the transmissivity graphs, we can see how cloudy the water is flowing out from the Puyallup. We can also see how the sediments mix between layers and ultimately sink towards the bottom.
Data Repository
Data Repository
Page developed by Arthur Weisberg and Tim Wahlstrom
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