The plastic rubbish we see washed up on the beaches and coast lines is only a small amount of the total marine plastic rubbish. We estimate it is approximately 15%. About the same amount is thought to be floating on the seas and to be under water in the sea. However by far the largest amount has sunk and is to be found on the sea beds. This percentage seems to be growing. Here are some figures on the oceanic contamination by rubbish:
The volume of rubbish entering the oceans yearly is now at some 10 million tons; in 1997 it was „only“ 6.4 million tons.
One reckons that some 100-142 million tons are already distributed throughout the oceans of the world.
These estimations mean on average 13.000 particles of plastic rubbish per square kilometre of ocean surface.
In the southern North Sea 236 pieces of rubbish were found per 100m of coastline and on the sea bed there were approximately on average 11kg of rubbish.
In the Baltic Sea it has been estimated that 5.500 to 10.000 fishing nets have been lost and are now so called „phantom nets“.
An up-to-date report details the results from 24 expeditions (2007 through 2013) about all five subtropical gyres on the Australian coast, the Bay of Bengal and the Mediterranean, whereby the data were collated by net count and also visual counting.
A model calculation calibrated the measured data collected. The result is estimated as a minimum of 5250 billion particles with a combined weight of 268.940 tons. (1). This weight is far lower than earlier projections which was quite surprising. However only a very small amount of microplastic (< 5mm) was found, which has been explained as that these particles have probably sunk by settlement and are now on the sea bed. This suggestion has already been partly proved by sediment examinations. (2)
(1)Eriksen M, Lebreton LCM, Carson HS, Thiel M, Moore CJ, et al. (2014) Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea. PLoS ONE 9(12): e111913. doi:10.1371/journal.pone.0111913
(2)Where does our plastic rubbish go? http://www.spektrum.de/news/wohin-verschwindet-unser-plastikmuell/1315749