Question 3 Dissolved oxygen dynamics.

A marine biologist colleague of yours has measured temperature and dissolved oxygen (O2) concentrations in a shallow bay. He has given you the data as mean daily values of Temp (oC) and dissolved oxygen (DO in mg/kg) see attached Table. He is interested in the dynamics of oxygen in this system and is asking your opinion on how to interpret the dissolved O2 time series. He did not measure salinity but thinks it should be about 30.

3.1) Determine the expected DO concentrations if the surface waters were at equilibrium with the atmosphere for each day assuming given salinity, measured temperature and 1 atmosphere of air pressure (assume air is saturated with water vapor). These are DOsaturation concentrations (hint: there are different ways to arrive at this answer, so make sure to clearly explain the source of your data)

3.2) Plot the concentrations of DOmeasured and DOsaturation as a function of days in September. Explain how these two variables change in relationship to the water temperature trends.

3.3) Calculate the difference from saturation as a percent (DO (%)= [(DOmeas-DOsat)/DOsat]x100. Plot DO as a function of days in September. What processes explain the observed variability? Be specific when explaining deviations from saturation.

3.4) After giving your report to your colleague; he mentions that salinity was unlikely to have remained constant after all. He tells you that while salinity was ~30 on the first 10 days of the study, it slowly increased as the month progressed, so that by day 21 salinity in the bay was 33 and by the end of the month (day 29) it was up to full ocean value of 35. Use this information to revise your estimates of DOsaturation and %DO for the those days. Do your explanations regarding the processes controlling DO in this system change, if so how?

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