Tuesday, July 1, 2014

Oceanic plastic mystery: where's it all going?

It certainly isn’t news that the oceans are full of plastics; The news is perhaps how little we know about it.

(Image: plastics collected on the Malaspina Expedition. Credit: CSIC.)

“Our awareness of the significance of plastic pollution in the ocean is relatively recent, and basic questions remain unresolved. Indeed, the quantity of plastic floating in the ocean and its final destination are still unknown,” write scientists who participated in a recent Spanish science expedition.

They found plastics throughout the oceans, and a scientific paper on the results concluded that they’re getting into the marine food chain. 

The researchers emphasized how little is known about the impacts of the plastics—and even where some of the plastic goes. A lot of it is unaccounted for: “Resolving the fate of the missing plastic debris is of fundamental importance to determine the nature and significance of the impacts of plastic pollution in the ocean.”

The Malaspina Expedition of 2010, sent out by the Spanish National Research Council (CSIC), was named after an early Spanish scientific circumnavigation from 1789 to 1794, headed by Alessandro Malaspina and José de Bustamante y Guerra.

They collected plastics in all the world’s oceans. And they found plastic in both the North Pacific and Atlantic, where it was known to occur in large amounts, but they also found large amounts in the southern oceans: the South Pacific, South Atlantic and the Indian Ocean.

"Ocean currents carry plastic objects which split into smaller and smaller fragments due to solar radiation. Those little pieces of plastic, known as microplastics, can last hundreds of years and were detected in 88% of the ocean surface sampled during the Malaspina Expedition 2010,” said Andrés Cózar, of the University of Cadiz.

"These microplastics have an influence on the behavior and the food chain of marine organisms.

“On one hand, the tiny plastic fragments often accumulate contaminants that, if swallowed, can be passed to organisms during digestion; without forgetting the gastrointestinal obstructions, which are another of the most common problems with this type of waste.

“On the other hand, the abundance of floating plastic fragments allows many small organisms to sail on them and colonize places they could not access to previously. But probably, most of the impacts taking place due to plastic pollution in the oceans are not yet known,” Cózar said.

The amounts of plastic estimated to be in the oceans is stunning. The Malaspina 2010 paper middle estimates are that there are 4.8 thousand tons in the North Pacific, 2.7 in the North Atlantic, 2.2 in the Indian Ocean, 2.6 in the South Atlantic and 2.1 in the South Pacific.

Some of the plastic is at the surface but even if it is buoyant, some is carried down through the water column via the added weight of biofouling, or being contained in the feces of marine life forms that eat the plastic.

And there may be other methods for sinking the plastics.

“Our observations also show that large loads of plastic fragments with sizes from microns to some millimeters are unaccounted for in the surface loads. The pathway and ultimate fate of the missing plastic are as yet unknown. We cannot rule out either of the proposed sink processes or the operation of sink processes yet to be identified,” the paper says.

It could be that the plastic is being broken down into such small pieces that they’re not getting caught in the sampling nets of marine scientists: “Missing micro- plastic may derive from  nano-fragmentation processes, rendering the very small pieces undetectable to convectional sampling nets, and/or may be transferred to the ocean interior.”

The University of Hawai`i’s Dave Karl edited the paper, Plastic debris in the open ocean, which was published in the Proceedings of the National Academy of Sciences. The authors are
Andrés Cózar,  Fidel Echevarría, Ignacio González-Gordillo, Xabier Irigoien, Bárbara Úbeda, Santiago Hernández-León, Álvaro T. Palma, Sandra Navarro, Juan García-de-Lomas, Andrea Ruiz, María L. Fernández-de-Puelles, and Carlos M. Duarte.

If you’re conversant in Spanish, the Malaspina 2010 website is here. 

© Jan TenBruggencate 2014

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