CHEMICAL TRACERS OF BIOLOGICAL PROCESSES
The main metabolites involved in photosynthesis and respiration are oxygen, carbon, nitrogen, phosphorus and silicate. These two processes are the major driving forces for changes in the chemistry of sea water. Oceanographers use the distribution of dissolved O2, C, N, P, and Si in seawater as tracers of the rate of these biological processes.
In Ocean surface waters, where there is plenty of light, concentrations of nutrients are depleted and oxygen is enriched because of net biological production. Specifically, the concentration of oxygen is greater than the value you would expect to have if the water were in equilibrium with the atmospheric pressure, pO2, at the observed temperature and salinity. This oxygen supersaturation is a result of both physical and biological processes. A first-order approximation for near shore waters like Puget Sound is that the flux of O2 to the atmosphere from the water is equal to the net biological oxygen production in the euphotic zone. This oxygen flux averaged over a long-enough time period and scaled to Redfield ratios is proportional to the export of carbon from the euphotic zone to deeper waters.
Organic matter that finds its way to the deeper waters away from light is respired. The process of respiration releases nutrients to the water and consumes oxygen in ratios (Redfield ratios) that have been characterized using many years of measurements in all areas of the ocean. The extent of oxygen depletion in the deeper waters is determined by the rate of respiration and the time since the water was in contact with the surface. These processes can cause the waters of the more isolated basins in the Sound to become depleted of oxygen (hypoxic) to an extent that might cause fish kills.
The Chemical Oceanography part of Ocean 220 will explore the stoichiometries and rates of change of O2, N, P and Si measured in a series of profiles in Whidbey Basin of Puget Sound. Specific potential projects are:
1. The flux of O2 from the ocean surface waters to the atmosphere as a measure of net community biological production.
2. Redfield ratios among N, P and O2 during respiration in Whidbey Basin.
3. The role of diatoms in controlling concentrations of NO3 and H4SiO4 in Puget Sound waters.
4. Estimating carbon respiration rates using AOU and residence times in Hood Canal.
5. Variations in the forms of N (e.g. nitrate, nitrite, and ammonium) throughout Whidbey Basin.