Monday, December 16, 2013

Student research on Port Angeles Harbor

Students from my Introduction to Oceanography class deploy an oceanographic mooring off of the Port Angeles pier

My Peninsula College Introduction to Oceanography class just wrapped up for the quarter. This year, I tried a new thing (getting my students out on the water for a mini research cruise on the Olympic Coast National Marine Sanctuary's R/V Tatoosh), but also re-hashed an activity that was very successful last year: Building and deploying oceanographic moorings off of the Port Angeles pier. This year, though, I put more of an emphasis on analyzing the temperature and light data series that we collected between October and November.

The ingredients of a mooring

This is a tall order for students at the introductory level - I am asking them to create a hypothesis, plot these data and analyze them critically in order to try to ferret out patterns. But in the end I hope it is a valuable exercise and provides some insight into the process of science. Anyhow, I wanted to share one of this year's top papers, by Miranda Elsberry, who looked at the potential role that tides play in controlling the water temperature in the harbor. She does a nice job showing that in our data, there seems to be some relationship between the neap tide cycle and elevated water temperature in the harbo. Makes sense, right? We might assume that the residence time of water in the harbor goes up during the neap tide cycle, mixing is reduced, and temperature is thereby increased.

Introduction to Oceanography students building moorings

Anyhow,Here it is, in its entirety. Enjoy!

Tidal Water Levels and Bottom Water Temperature

For this final assignment I wanted to ask a question that I did not already know the answer to, I already knew the likely outcomes of questions like “Does Temperature vary with depth?” or “Does air temperature affect water temperature?” and so on. So I decided to explore the idea of tides. The question I had going into this assignment was: Does tidal water level affect the water temperature at the bottom of Station B? I chose to look at Station B because I thought that if the answer to my question was yes then it would be clearer at the medium depth of about 16 feet, rather than the deeper Station C or shallow station A. I did not choose to study Station A because of the possibility of the nearby creek changing the water temperature data.

Here are the stations referred to in her paper, for context

To see if there was a relation between water temperature and water level, I plotted the water temperature data collected by the Station B HOBO and the water level data that was provided in Canvas on the same chart. After plotting the data I looked for areas where the temperature and water level changed together.

Overall, I found that temperature did not clearly change with water level. However, even though the temperature line was clearly falling over time, there seemed to be a very slight change in the temperature plot where water level shows there was a neap tide cycle around the 16th and 28th of October. In my first plot (fig.1) I have circled the slight upwards bulges of the temperature line that occurred during the neap tide cycles.

Figure 1: Water Temperature at Bottom of Station B and Tidal Water Level Plot

I wondered if those slight changes were due to changes in air temperature instead of the tides. So I took the air temperature data that was provided in Canvas and plotted it on a chart with the bottom water temperature from Station B (fig. 2)

Figure 2: Air Temperature and Station B Bottom Water Temperature Plot

Other than the 5°F dip in air temperature and slight dip in bottom water temperature at the same time from around the 18th to the 23rd of October, the plot does not seem to show a very clear relationship between change in air and bottom water temperatures. So air temperature must not have caused the slight bulges in my first plot.

With plotting this data and examining it, I have found that there seems to be a connection between the water temperature at the bottom of Station B and the twice a month neap tide cycles. I do not know why neap tides would affect the temperature of water 16 feet below the surface, but there were very slight (by one degree) rise in temperature of the water when neap tides occurred. The change was very small, but it was visible on my chart, so it should be relevant. There are many other weather factors that I could explore that might have caused the temperature change, but air temperature did not seem to have caused it.

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