For anyone who lived in Bermuda during the 1960s and 1970s, seeing tar balls and oil on local beaches was a frequent, if not regular, occurrence. Floating tar balls are the result of petroleum in the marine environment, either from onshore and offshore oil production, processing and handling, shipping operations, or natural oil seeps. Because some tar balls float, they can be carried over large distances by ocean currents before they are deposited on the shoreline.
In the article, “A Review of Observations of Floating Tar in the Sargasso Sea,” published recently in a special issue of Oceanography, Dr. Andrew Peters (Associate Scientist at BIOS) and Dr. Amy Siuda (Associate Professor, Sea Education Association) reviewed decades of scientific papers and data to construct a comprehensive history of tar balls in the Sargasso Sea. The review touches on some of the early research on tar balls in the North Atlantic, which was initiated and led by past president and former BIOS Life Trustee Dr. James Butler. Dr. Butler pioneered methods to monitor and investigate the impacts of pelagic tar on the ecology of the Sargasso Sea. His work on pelagic tar during the 1970s earned him international recognition in the field, and the techniques he used to document tar balls and analyze oil samples were integral in persuading oil companies to reduce the pollution.
According to the study authors, the prevalence of tar balls during the 1960s and 1970s was due, primarily, to “the result of tank and ballast water flushing at sea, a prevailing practice in oil tanker operations at the time.” This was confirmed by early chemical analyses of tar balls that revealed they had a composition indicative of “crude-oil sludge, distinct from whole crude oil, suggesting a source from oil tanker operations.”
However, by the early 1980s new international shipping conventions were enacted aimed at reducing the discharge of petroleum products from ships (i.e., via the release of water used to clean oil tanker cargo holds). As a result, fewer tar balls were showing up on Bermuda’s beaches. The study authors report that neuston net tows (used to sample zooplankton in the ocean but also good at collecting tar balls) conducted in from the mid-1980s to mid-1990s showed that tar balls had “decreased substantially over the whole area” of the Western North Atlantic Ocean, “although significant amounts were still present in the Sargasso Sea.”
While international conventions reducing oil inputs to the marine environment have decreased the overall incidence of tar balls in the ocean, tanker accidents and oil spills (e.g., the 2010 BP Deepwater Horizon spill in the Gulf of Mexico) still represent ongoing sources of petroleum and tar balls. These sources are important to remember as many marine organisms, including zooplankton and juvenile sea turtles, can ingest the tar balls and pellets that float in the ocean’s surface water.
To read or download the full article, please visit http://www.tos.org/oceanography/archive/27-1_peters.html