Increase of marine litter at two stations of the Arctic deep-sea observatory Hausgarten
Supervisor: Melanie Bergmann (Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven)
Since the 1960s an increased global production of plastics has been mirrored by an accumulation of plastic litter in marine environments worldwide. In 2013, the global plastic production reached 299 million t. Land-based inputs (≤12.7 million t) exceed litter data from field studies by 1-3 magnitudes raising again the question ‘Where is all the plastic?’

Litter on the deep seafloor has not been taken into account in such global estimates and was recently put forward as a possible sink of marine litter. However, little information is available about temporal trends in general and trends of litter on the deep seafloor. One of the few time-series studies in the deep sea assessed images from the LTER observatory HAUSGARTEN (79° N) taken at the same location in the Arctic in 2002, 2004, 2007, 2008 and 2011 at 2500 m depth and indicated increasing litter densities between 2002 and 2011. Here, I continued this time series by analyzing new footage from the same location taken in 2012 and 2014. In addition, images taken at a HAUSGARTEN station located further to the north at the same depth (2500m) in 2004, 2007, 2011, 2012, 2013 and 2014 was analyzed to assess spatial variability in litter. The northern station is located within the marginal ice zone, which may act as a barrier to litter inputs whereas the central station is subject to lower ice coverage.

Total results indicated litter densities between 873 – 6,566 items km-2 with a six-fold increase between 2007 and 2011-2012; and a range of 4,731 – 6,566 items km-2 after 2011-2012 at total HAUSGARTEN. Although no significant differences in litter density were found between the two stations, there were significant differences between years along with litter types, sizes and megafaunal encounters. Plastic, glass, metal, rope, fabric were the main litter type categories identified, and Cladorhiza gelida, Caulophacus arcticus and Bathycrinus carpenterii were the main species of megafaunal encounters with litter items. Differences in litter type and size between the two stations may suggest different pathways of anthropogenic litter reaching the deep Arctic seafloor caused by different environmental conditions. For example, the northern station experienced significantly longer periods of sea ice cover than the central HAUSGARTEN station which may explain the densities of small-sized plastics, which may be released from sea ice upon thawing events. The changes in litter could be an indirect consequence of the receding sea ice, which increasingly opens the Arctic Ocean to the impacts of man’s activities including pollution.