Anthropogenic footprints: litter and microplastic pollution in the Fram Strait

The global change induced decline of sea ice has led to increasing anthropogenic presence in the Arctic Ocean. The Fram Strait is likely to become an important shipping lane as indicated by increasing numbers of fishing vessels and cruise liners in this area. One footprint of anthropogenic activities in the oceans is litter pollution, especially long-lived plastic, which is recognised as a global problem of growing concern given annual global production rates of 299 million t. Litter affects >580 marine species primarily by entanglement and ingestion, through which it can also enter food webs. Although recent reports indicate that anthropogenic waste has made it to the remotest parts of our oceans, there is still only limited information about temporal trends and its distribution, especially in polar and deep seas. Still less information is available about the contamination with microplastics, a degradation product of larger fragmented litter items. Mean litter densities from the water surface recorded during ship- and helicopter-based surveys in the Fram Strait (2012) were 0.0062 items km-1, which is comparable with observations from Antarctica. Despite the notion that plastic floats at the water surface, 50% of municipal waste exceeds the density of seawater and sinks. Repeated camera transects from the seafloor of two stations of the HAUSGARTEN observatory (2500 m depth) showed that litter densities increased from 3,523 in 2002 to 6,566 items km-2 in 2014, comparable to densely populated European seas. There was also an increase in smaller-sized items, indicating fragmentation. Differences in litter type and size between the two stations may suggest different pathways of litter to the deep seafloor. For example, the northern station experienced longer periods of sea ice cover, which may explain the higher densities of small-sized plastics, released from sea ice upon melting. Microplastic concentrations in two sea ice cores from the FRAM Strait were analysed by FT-IR Imaging technology and exceeded those from previous reports in the Arctic by four orders of magnitude. The upper sections of the core contained far more microplastics compared to those in direct contact with the underlying seawater corroborating the assumption that sea ice is a source for microplastic in the Fram Strait. Considering the ever increasing production rates of plastic (ca.4% p.a.) and the failure of solid waste management practice, our footprints are likely to become larger unless serious mitigating actions are taken to reduce the amounts of litter entering the oceans.