Marine PollulJOn Bulletin, Vo]. I0, pp. 203 -205 25-326X,"7~)/0701 4)203 $02,00/~ P Pergamon Press Ltd. 197~. Prlnled in Greal Britain The Fate of Stranded Pelagic Tar on a Bermuda Beach THOMAS M. ILIFFE and ANTHONY H. KNAP Bermuda Biological Station for Research, St. George's West, The major process involved in the removal of stranded petroleum residues or 'tar lumps' from sandy high energy beaches is the adsorption of sand and shell particles to the residues effecting a density change. This results in transport off the beach, sinking, and sometimes burial of the tar in sublittoral sediments. The occurrence of petroleum residues on the beaches of Bermuda has been well documented (Butler et al., 1973; Morris & Butler, 1973). The surface current patterns of the North Atlantic, which concentrate floating Sargassum weed into the central ocean gyre known as the Sargasso Sea, also accumulate and retain floating petroleum residues or 'tar lumps'. Since Bermuda is the only land mass in the Sargasso Sea, considerable quantities of the tar from this part of the North Atlantic may be eventually stranded on Bermuda's beaches. Although the fate of these petroleum residues at sea has been discussed (Butler, 1976), along with that of their weathering once on the beaches (Blumer et al., 1973; Zsolnay, 1978), there is little information available on the fate of beach deposited material, nor have there been any detailed experiments on the mechanical processes affecting beach tar distributions. Recently, the mechanics of the removal of stranded oil from a beach has been related to the energy conditions present (Owens, 1978). This present report discusses the physical processes occurring on a beach which receives considerable amounts of stranded pelagic tar. 1-15, Bermuda Observations The site chosen for this study was Whalebone Bay; a shallow bay on the northeastern coast of Bermuda. The semi-enclosed bay, rimmed with aeolian carbonate sand- stone, measures about 150 m by 200 m. It has a bare sandy substrate in the middle, with beds of the sea grasses Thalassia and Cymodocea fringing the edges. On the eastern side is a small sandy beach about 75 m long where much of the pelagic tar is stranded. During winter, the prevailing northerly winds blow directly into the bay. Under these con- ditions, Whalebone Bay receives the highest amounts of stranded pelagic tar found for any beach in Bermuda. The geometric mean of tar stranded at Whalebone Bay during January-June 1978 was 610 g m-l/6 days, while four other Bermuda beaches had geometric means ranging from 22-95 g m-V6 days. The large quantities of tar at Whalebone Bay make it an excellent site for the study of the distribution and fate of stranded tar. In order to examine factors influencing the distribution of tar on a beach, we utilized a I m wide transect extending from the upper edge of the storm tide line, across the beach, to 32 m past the low tide line (Fig. I a). The transect strip was located near the centre of the beach to minimize the influence of the adjacent rocky shore line. All tar that was visible was collected within sections of the transect at low tide. Tar lumps from each section were placed in a vessel containing seawater and the weights of tar that floated and sank deter- ~-Storm hde Level E ....... ' bevel ~ o- Sand E E i- o (o) & g -7- ~ -2- W r~ "6 20( I (b) Bedrock Mean water level Low water level Sand io(I ,I t _lll- I0 20 30 40 Distance seaward from storm high hoe level , m Fig. I Whalebone Bay I m wide beach transect. (a) Description and elevation of beach along transect. (b) Total weight of tar lumps per metre of transect; shaded bars represent total weigh[ of tar lumps that sink; unshaded bars represent weigh[ of" tar lumps that float_ 203