One hundred seventeen year coastal temperature record reveals warming trends

08/24/04

After compiling what may be the longest coherent coastal sea surface temperature record in North America, oceanographers from the University of Rhode Island and the Woods Hole Oceanographic Institution have discovered some surprising and not-so-surprising trends.

The compilation and analysis of data by URI Graduate School of Oceanography (GSO) biological oceanographers Scott Nixon, Stephen Granger, and Betty Buckley and Woods Hole Oceanographic Institution (WHOI) staff Melissa Lamont and Brenda Rowell is described in a recent issue of Estuaries, a publication of the Estuarine Research Federation. Their work was supported in large part by the Rhode Island Sea Grant College Program.

Daily water temperature measurements were collected by the Branch of Fish Culture of the U.S. Commission of Fish and Fisheries at Great harbor, Woods Hole, Massachusetts, beginning in January 1886 and continuing for 33 years until 1919. After an eight-year gap, the U.S. Bureau of Fisheries resumed the sampling through December 1941 with a short lapse in 1930-1931. After a 26-month hiatus during World War II, the U.S. Coast and Geodetic Survey, through WHOI, assumed responsibility for collecting water temperature data in March 1944. WHOI measurements continued with relatively little change through 1997 and are ongoing with newer instrumentation.

"We believe that the total set of measurements collected over a 117-year period at Woods Hole represents the longest coherent record of coastal ocean water temperature in North America," said Nixon. "Our purpose in writing this article is to make the research community aware of this unique resource and to present some analyses of the data as they bear on the question of recent warming along the southern New England coast."

The record shows that a warming trend in the late 1940s was reversed by a cooling during the 1960s. However, since the 1960s a sustained warming has persisted. During the 32 years between 1970 and 2002, the temperature has increased an average of 0.04?C per year.

The scientists also found that while the mean annual water temperature only exceeded 11?C five times during the 50-year period between 1886 and 1948, it surpassed this temperature 26 times in the 30-year period between 1970 and 2000.

Water temperatures during the 1990s average 1.2?C warmer over the annual cycle than they did during the decades between 1890 and 1970, while the winters average 1.7?C warmer and the summers 1.0?C warmer. Spring and fall temperatures were increased by 1.2?C and 0.8?C, respectively.

"The cooling seen in the water at Woods Hole during the 1960s is also present in air temperatures for the coastal northeast and in water temperature at Boston Harbor and at Newport Harbor in Narragansett Bay," said Nixon. "There is also a strong overall correlation between the mean monthly water temperature at Woods Hole and Newport Harbor during 1955 to 1994, indicating that the Woods Hole record may provide a useful proxy for historical water temperature trends in neighboring waters south of Cape Cod."

The scientists suggest that the dramatic increases in water temperature of recent decades have stimulated further research and speculation, notably with regard to the relative abundance of fish species, the suppression of the winter-spring bloom of phytoplankton, the acceleration of the seasonal development of ctenophore populations, a northern extension of the range of the oyster disease Dermo, and the decline of eelgrass.

"If the relatively modest temperature increases documented so far have been responsible for some of the major ecological changes attributed to them, the consequences of further warming, should it occur, will certainly be profound," added Nixon.

Source: Eurekalert & others

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