The Warming of Narragansett Bay
By Scott W. Nixon, Steve Granger, and Betty Buckley
The beach at Narragansett has long been a popular spot for photographers in summer, and it is common to find sepia images of our ancestors looking a little silly in their very modest antique bathing costumes decorating local restaurants, hotels, and history books. The beach in winter is another matter, however, and it must have taken something quite unusual to attract the photographer who recorded the grim picture shown inset at left of Narragansett Beach thick with ice in the winter of 1917–18. It is possible for us to have some idea how cold and unusual that winter was because the crew of the Brenton Reef lightship measured the temperature of the water off the mouth of Narragansett Bay almost every day for 64 years, from July 1878 through January 1942. In their long record of over 22,000 measurements, the coldest winter was that of 1917–18, when the average water temperature from December through February was only 0.7 C (33.2 F). The average for these months over the whole period of their record is much warmer at 3.9 C (39.1 F).
The Brenton Reef lightship measurements were among the earliest and longest running coastal water temperature measurements on the Atlantic coast, but they suffered the same fate as virtually all other early monitoring efforts. They were discontinued or disrupted as different government agencies stopped and started measurement programs or switched the location where measurements were made. After January 1942 there appears to have been no regular program of daily water temperature measurements in Narragansett Bay until August 1954, when daily measurements began in Newport Harbor that continued until the mid-1990s. While the shift from Brenton Reef to Newport Harbor is not far, there is no period during which measurements were made at both locations. Without some overlap, we can not adjust the data from the two stations to assemble a "continuous" record of water temperature for the Bay.
Frustrated by the lack of a long-term coherent record for such an important and interesting feature of Narragansett Bay, we looked to nearby Woods Hole, Mass., where the tradition of coastal marine research goes back to the founding of the first National Marine Fisheries Service Laboratory by Spencer Baird in 1871. It seemed a good bet that if a long-term continuous record of New England coastal water temperature existed, it would come from Woods Hole. In 1957 Dean Bumpus, a well-known oceanographer at the Woods Hole Oceanographic Institution (WHOI), had summarized approximately daily water temperature measurements at Woods Hole into monthly means for the period from January 1880 through December 1956, but we learned that daily readings had continued virtually unchanged until November 1997. At that time an electronic sensor replaced the human observer, but measurements continued at the same location and are ongoing. In collaboration with Melissa Lamont and Brenda Rowell at WHOI, we digitized all of these data, documented the history of the collection, and posted the entire data base on the Internet at: http://dunkle.whoi.edu/dlaweb/data/h2o/frameset.html
We also examined the Woods Hole data for long-term trends and found that there was no statistically significant trend from the mid-1880s to the 1950s. There was a cooling during the 1960s that preceded a 30-year warming trend that continued until the end of our analysis in December 2002. During the 1990s, mean annual water temperatures averaged approximately 1.1 C (almost 2 F) warmer than they had been between 1890 and 1970; winter (December through February) temperatures were 1.5 C (2.7 F) warmer, and summer (June through August) temperatures were 0.8 C (1.4 F) warmer. This warming of the coastal water is considerably larger than the 0.3 C (0.5 F) increase in the temperature of the surface 300 meters of the world ocean recently documented by Levitus et al. (2000). It seems increasingly clear that this warming is due to the emission of anthropogenic (human-induced) greenhouse gases (Levitus et al., 2001; Barnett et al., 2001). A manuscript describing the Woods Hole data and our analysis will appear in a forthcoming issue of the journal Estuaries. Copies are also available on request.
While these changes may seem small compared with the day-to-day, seasonal, and interannual variation we all experience in air temperatures, they may be having profound effects of the ecology of the Bay by changing the physiological rates and, perhaps more importantly, the behavior of various species. For example, warming may be at least partly responsible for recent declines in the winter-spring bloom of diatoms (Keller et al., 1999; Oviatt et al., 2002), the loss of eelgrass (Bintz et al., in press) increases in the predation pressure exerted by the comb jelly Mnemiopsis leidyi on zooplankton (Sullivan et al., 2001), and the replacement of winter flounder by other fish and invertebrates (Jeffries and Terceiro, 1985; Jeffries, 2002). If the modest warming of the water seen thus far really is the culprit behind such changes, further warming predicted for the future may have us longing for the cold old days of the winter of 1917–18 or even the winter of 1740, when Rhode Island Gov. William Green of Warwick noted that "...the Narragansett Bay was soon frozen over, and the people passed and repassed from Providence to Newport on the ice, and from Newport to Bristol" (Updike, 1907). Writing of that winter to a friend in Ireland, Reverend James McSparran, owner of McSparran Hill in South Kingstown, site of the present day observational tower at the intersection of U.S. Route 1 and R.I. Route 138, noted that, "As from my lands I can see the Atlantic Ocean, I have seen it froze as far as the human eye could reach."
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—Scott W. Nixon is URI Professor of Oceanography; Steve Granger and Betty Buckley are Marine Researchers at the URI Graduate School of Oceanography.