In a recent issue of the Journal of Geophysical Research, Chris Kincaid and Robert Pockalny from URI's Graduate School of Oceanography (GSO), and Linda Huzzey, from the U.S. Coast Guard Academy presented results of a study designed to enhance further understanding of RIS and the relationship between RIS and the Bay.
This work represents one component of a 3-year multi-disciplinary observational study that was funded by Rhode Island Sea Grant. While Kincaid's group was focused on physical processes governing the exchange of water between the two systems, other groups from GSO and URI Biological Sciences worked to characterize chemical and biological exchange through the mouth the Bay.
This information is critically important for the development of better, more accurate computer models that are used in predicting how the Bay will respond to environmental or manmade changes.
The scientists used instruments called Acoustic Doppler Current Profilers (ADCPs) to map out circulation patterns. These instruments provide detailed images of flow throughout the water column. The paper by Kincaid, Pockalny, and Huzzey reported on results from 15 separate surveys conducted on a survey grid that spanned the entrance to the Bay and extended approximately 3 miles out into RIS. The ADCP is strapped to the side of research vessel and continuously driven around the survey grid. A typical survey would begin at 10 pm and continue through to 2pm the next day when the daily sea breeze produced unfavorable sampling conditions. The time period was chosen so that the sloshing effects of the tides could be filtered out, revealing the longer term circulation that is most efficient at transporting material.
This data set provides the most detailed spatial images of circulation ever collected within the Bay. The results show that water predominantly enters the Bay through the deeper portion of the East Passage along the eastern side of the channel and that this pattern is remarkably similar in winter and summer. The dominant outflow from the Bay occurs in the surface waters, along the western side of the East Passage. Results show a striking difference in flow within RIS between summer and winter.
During summer a strong flow runs from east to west just outside the mouth of the Bay that sweeps the Bay's outflow to the west-southwest. New water is supplied to the Bay from the southeast, or the direction of Brenton Reef. During winter this longshore flow is absent from RIS, and new water is supplied to the mouth region of the Bay by a deep flow from the southwest, or the direction of Pt. Judith.
While these surveys provide detailed pictures of circulation patterns for discrete time periods, other ADCPs were placed in bottom moorings to provide better information on time variability in flow patterns. Moorings were deployed for more than a year with information being collected every 6 minutes. The locations were 3 miles south of Beavertail Lighthouse, under the Newport Bridge and off the GSO pier in the West Passage. The data reveal how winds (including hurricane Floyd) and seasonal changes influenced exchange between the Bay and RIS and results are reported in a manuscript submitted to the journal, Continental Shelf Research.
"Such a detailed observational study, involving the deployment of scientific gear within coastal waters, presents a myriad of challenges," said Kincaid. "It would not have been possible without the support provided by a number of people and organizations."
The project funded thesis work for two Rhode Island graduate students at URI who have continued on to work with local environmental companies, William Deleo, Environmental Science Services, East Providence, and Kurt Rosenberger, SAIC, Newport. URI's Equipment Development Laboratory designed and built the mooring systems used in this study. URI research vessels Cap'n Bert, captained by Tom Puckett, and CT1, captained by Dick Wing, were instrumental in this study. The moorings were serviced by Tom Brady's Newport Dive Services, who provided extraordinary support, including finding gear when it went missing. The best data set was obtained beneath the Newport Bridge, made possible by the generous contributions of the Newport Bridge Authority.