Temporal trends in marine litter at three stations of the Hausgarten observatory in the Arctic deep sea (2002-2017).

Supervisor: Melanie Bergmann (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research).
Litter has been recorded in all compartments of the marine environment, from the sea surface to the seafloor all over the world. Even though the final fate of marine debris remains unclear, it has been suggested that the deep seafloor represents a major sink for plastic debris even in regions as secluded as the Arctic Ocean. Since the discovery of increasing litter quantities on the seafloor of the HAUSGARTEN observatory located at ca 79° N in the Arctic, a time series for litter was built for the northern (N3) and central station (HG-IV). Here, seafloor images from the southernmost station S3 and from three more years of the other two stations were analyzed to assess temporal and spatial variability of marine litter over a latitudinal gradient and to increase the temporal and spatial scale. Images from a towed camera system were analyzed to determine litter abundance, composition, size and interactions with epibenthic fauna. Indicators of local maritime traffic and summer sea ice extent were examined as potential sources. A total of 16,157 images taken between 2002 to 2017 were included (5,768 analyzed in this thesis). Over the whole observatory, litter density ranged between 816 and 6,717 items/km2 with a peak in 2011 (six-fold) and a second peak in 2014 (one-fold). Litter density clearly increased over time. Although N3 displayed the clearest temporal increase, litter densities at the other two more southern stations remained at an elevated level after the 2011 peak. Overall, the majority of litter was plastics (45%) except at the northern station where glass was dominant (41%). Small-sized items accounted for 63% of the total litter, but at the central station HG-IV medium-sized items were dominant (56%). Litter-fauna interactions were frequent (44%) in terms of entanglement with sponges, colonization by anemones or in contact with small crustaceans. Litter densities were positively correlated with tourism vessels and yet stronger correlated with other-type-of-activities vessels e.g. cargo, research, and fishing vessels. No correlation between litter density and summer sea ice extent was found. However, the litter density temporal trend at N3 and the summer sea ice coverage from 2015 to 2017 were reversed. This could mean that sea ice can act as both sink and barrier. The sources for litter at HAUSGARTEN are likely (1) ocean currents that transport litter from the Atlantic Ocean, (2) local inputs from maritime traffic and (3) sea ice that may transport litter from the Central Arctic to the Fram Strait via the Transpolar Drift. Regardless of the exact source, the litter densities found in this study make clear that the current waste management systems are insufficient such that fragile already stressed Arctic ecosystems are subject to increasing plastic pollution in addition to global climate change.