Science Results : Daily Update

Daily Update | Current SEA Research

July 10, 2010

By Giora Proskurowski

This expedition is dedicated to looking at marine debris in the North Atlantic. While 99 percent of this debris is plastic, we also see other types. The main other type we observe out here is tar. As we were leaving Bermuda the words "tar ball" were being discussed in the media, driven by the interest in the fate of the oil from the Deepwater Horizon spill.

While we have caught exactly 100 pieces of tar in our nets this expedition, I want to be absolutely clear that there is no evidence that any of these tar balls are from Deepwater Horizon. Given the time horizon, it is unlikely that any oil from the Gulf spill made it far enough into the Atlantic to be sampled on this expedition. You never know, however, so we are taking special care of tar we do collect for geochemical fingerprinting analysis back on shore.

The tar we have collected so far is usually small pieces, about the size of a typical plastic fragment – half the size of a pencil eraser, dark brown to black, with a consistency ranging from crumbly to goopy. Sometimes it is difficult to tell black plastic from tar, but what usually gives it away is that when grasped with a pair of tweezers, tar will give in to squeezing, while plastic holds its shape. So far, 44 of 107 surface net stations have had tar in them, with the highest number of tar balls coinciding with the highest concentration of plastic.

For each tar ball we see in our buckets we photograph it on a petri dish with a label and a ruler, place it in a clean aluminum foil pouch (to avoid any additional organic material contamination), and store it in the freezer. These tar samples will go back to Robert Nelson's lab at Woods Hole Oceanographic Institution (WHOI) for geochemical fingerprint analysis. We hope his results will help us learn how these tar samples change and degrade as they persist at sea.

SEA has been recording and collecting tar for 35 years, longer than we have been keeping statistics on plastic. This data set offers a crucial baseline comparison for any studies that may get ramped up to assess the open-ocean impact of the Deepwater Horizon spill.