Chemical variability in coastal and mixed layer waters

Andrea Magnuson, University of Rhode Island


An understanding of the chemical variability in the surface waters of the ocean requires measurements made at time and space scales that are similar to or of higher resolution than the processes controlling the variations. Continuous underway measurements of temperature, salinity, dissolved oxygen, pH and chlorophyll fluorescence were obtained in the continental shelf waters off of the east coast of the United States out to the Gulf Stream. Carbon dioxide system variables were calculated from the in situ measurements and discrete alkalinity samples. Dissolved oxygen, carbon dioxide and chlorophyll fluorescence were tightly coupled to transitions between large scale hydrographic features, although these parameters exhibited a higher frequency variability than temperature and salinity. Variability in oxygen and carbon dioxide exhibited strong inverse relationships in the slope waters adjacent to a Gulf Stream meander, warm core ring waters, and shelf waters. Slope waters adjacent to a Gulf Stream meander and waters within the warm core ring were regions of net photosynthesis, while a transition from a region of net photosynthesis to net respiration occurred across the continental shelf.^ The alkalinity-salinity relationship in Narragansett Bay was characterized from greater than 100 samples obtained over an annual cycle using a purge titration method. The purge method is introduced as modification to the traditional Gran titration, and is found to have improved linearity and require less extrapolation to the endpoint. The relationship between alkalinity and salinity was linear throughout the Bay, with the exception of samples from Mt. Hope Bay, a semi-enclosed portion of the Bay fed by a single river. A positive intercept at zero salinity represented the residual alkalinity, and was similar in magnitude to independent measurements of the riverine endmembers. A close examination of specific alkalinity in the West Passage revealed short-lived dilution effects associated with precipitation events.^ An uninterrupted, year-long time series of in situ (temperature, salinity, dissolved oxygen, pH and pressure) and meteorological variables (wind speed/direction, barometric pressure, air temperature, and solar radiation) was obtained in the West Passage of Narragansett Bay. Carbon dioxide system variables were calculated for the time series using the empirically defined alkalinity-salinity relationship for the West Passage. A calibration protocol was developed that specifically addressed the difficulties associated with long term time series measurements, primarily the effects of temperature on the performance of pH electrodes and their drift over time. The progressive growth and decay of seasonal and event scale blooms are captured. Over long time scales the West Passage is revealed as a significant source of carbon dioxide to the atmosphere. (Abstract shortened by UMI.) ^

Subject Area

Biology, Oceanography

Recommended Citation

Andrea Magnuson, "Chemical variability in coastal and mixed layer waters" (1997). Dissertations and Master's Theses (Campus Access). Paper AAI9831114.