INTRODUCTION 



Tarballs are lumps of weathered petroleum pro- 

 ducts which are found floating on the sea surface. 

 The origin of tarballs have been attributed to both 

 man-made oil spills and natural crude seepage. 

 General reviews of the subject include those by 

 Butler, Morris and Sass (1973), Butler (1975), and 

 National Academy of Sciences (1975). For several 

 years the U.S. Coast Guard has been involved with 

 collecting samples of this oil residue. The goal of 

 this program was to learn something about the 

 distribution of tarballs and obtain baseline data on 

 their concentration in the ocean so that long term 

 trends could be observed. This monitoring of long 

 term changes would provide an evaluation of the 

 effectiveness of control measures in oil trans- 

 portation (by water) and offshore drilling. 



EQUIPMENT AND PROCEDURES 



Data for the tarball program were collected by 

 tarball tows conducted from Coast Guard cutters. 

 The program was started in December 1971, and 

 over 1000 tows have been made. The tows were 

 made daily when a ship occupied an Ocean Station 

 or when on fisheries patrol, on a not-to-interfere 

 with primary mission basis. In addition, tows were 

 taken on special cruises as directed by Area Com- 

 manders. The equipment utilized consisted of a 

 Neuston net (Fig. 1) attached to a towing frame 

 developed at the Coast Guard Research and 

 Development Center, Groton, Connecticut. The 

 net and frame were attached to a boom aboard the 

 ship by a wire harness. A propeller- type, digital 

 flow meter was hung in the mouth of the net to 

 measure the horizontal distance of the tow. 



Tows were generally made at 3 knots or less for 

 a duration of between 45 to 60 minutes. Tarballs 

 were separated by hand from any other material 

 collected during the tow. Then they were sent to 

 the Coast Guard Oceanographic Unit where they 

 are presently in storage. Additional measurements 

 made while conducting the tow were sea surface 

 and air tempertures, wave /swell height and direc- 

 tion, and wind speed and direction. The tarballs 

 were weighed at the Oceanographic Unit, and the 

 concentration of tarballs on the sea surface (in 



mg/m^) was calculated. These measurements were 

 entered in a data log along with the ship's name 

 and cruise designation, the location and time of the 

 tow, and other environmental information and 

 were submitted to the National Oceanographic 

 Data Center (NODC). 



The data have been separated into four 

 geographic locations: 1) The North Pacific Ocean 

 and adjacent areas, 2) The Gulf of Mexico, 3) The 

 North Atlantic Ocean and adjacent areas, and 4) 

 Ocean Weather Station Hotel. The data for the 

 North Atlantic and Pacific Oceans was further' 

 broken down by location. A 5° x 5° grid was utilized 

 as the division of each locale. For the Gulf of Mex- 

 ico a 2° X 5° grid was used due to the much smaller 

 area of the Gulf. The concentration of tarballs 

 (mg/m^) was found in each grid giving some indica- 

 tion of the quantity of petroleum residue present. 



Due to the large number of tows made at OWS 

 Hotel and their continuity, it provided an ideal 

 location to observe variations in tarball concentra- 

 tion. Both seasonal change and those due to differ- 

 ing water masses and sea currents were examined. 

 The data were grouped into four three-month 

 seasons. Winter spanned December through 

 February; Spring, March through May; Summer, 

 June to August; and Fall, September through 

 November. Again the concentrations in each 

 season were averaged. 



NORTH PACIFIC OCEAN AND ADJACENT 

 AREAS 



Several observations can be made and others 

 deduced from the data thus far collected by the 

 Coast Guard in the tarball program. 



It was found that the concentration of tarballs in 

 the Gulf of Alaska was very low. With nearly two 

 hundred tows made in the Gulf of Alaska, the tar- 

 ball concentration averaged less than 0.03 mg/m^ 

 of sea surface area (Fig. 2). There are numerous 

 natural seeps along the coast of Alaska which may 

 account for a substantial amount of these tarballs. 

 With the opening of the Alaska Pipeline, and the 

 resultant increase in tanker traffic through these 



