Science Results : Daily Update

Daily Update | Current SEA Research

June 29, 2010

By Giora Proskurowski

It has been a week since our gigantic plastic haul, perhaps the largest concentration of plastic debris ever observed in the open ocean. In the past week we've seen a much smaller, but consistent, amount of plastic. Whereas we got 23,000 fragments of plastic in our net last Monday, we've been averaging about 100 or so pieces per tow since. While there is a big difference between those two numbers, in my mind it is a bigger difference to go from 0 to 100 pieces of plastic in a tow. The ocean should not have any plastic debris in it, and, in fact, the majority of the ocean doesn't have any plastic pollution – it is largely confined to the subtropical gyres.

SEA Semester programs sail in the Pacific, from the Tahiti to Hawaii, and then from Hawaii to San Francisco. On the voyage across the equator from Tahiti to Hawaii, if we find one piece of plastic in our nets it is a big deal – as all other nets will have no plastic. On the voyage through the North Pacific Subtropical Gyre, from Hawaii to San Francisco, if we find only one piece of plastic in our nets it is a big deal – as all other nets will have hundreds of pieces.

By starting and ending in Bermuda, this cruise track was designed to sample within the gyre, and to find plastics. I feel like this crew has become somewhat desensitized to seeing plastic in our nets, that they've forgotten that most of the ocean is a pristine wilderness. Since our big haul I've heard quite a few comments like "when are we going to see more plastic?" or "I hope we get flat calm conditions so we can see big plastic numbers."

For me, seeing the huge amount of plastic in our nets was obvious and shocking, but the importance of this trip lies in getting the best data set, not in getting a record on an obscure list. The numbers we now see, of plastic concentrations ranging from 20,000 to 200,000 pieces per square kilometer, are in line with what we've observed west of here for the past 25 years. Every neuston tow and Tucker trawl adds valuable information – whether the result is a huge outlier like last Monday, or an unexpectedly small number like yesterday's dawn tow. Ultimately, we have to be able to define what "high plastic concentration" is before we can answer the question, "How big is this region of high plastic concentration?"

By systematically sampling this region for plastics, mapping the results, and analyzing them within the context of sound oceanographic science, we can begin to make some sense of the role of plastic debris in this exceedingly complex and dynamic region of the Earth.