Observations of floating anthropogenic litter in the Barents Sea and Fram Strait, Arctic

Although recent reports indicate that anthropogenic waste has made it to the remotest parts of our oceans, there is still only limited information about its spread, especially in polar seas. Here, we present litter densities recorded during ship- and helicopter-based observer surveys in the Barents Sea and Fram Strait (Arctic). Thirty-one items were recorded in total, 23 from helicopter and eight from research vessel transects. Litter quantities ranged between 0 and 0.216 items km−1 with a mean of 0.001 (±SEM 0.005) items km−1. All of the floating objects observed were plastic items. Litter densities were slightly higher in the Fram Strait (0.006 items km−1) compared with the Barents Sea (0.004 items km−1). More litter was recorded during helicopter-based surveys than during ship-based surveys (0.006 and 0.004 items km−1, respectively). When comparing with the few available data with the same unit (items km−1 transect), the densities found herein are slightly higher than those from Antarctica but substantially lower than those from temperate waters. However, since anthropogenic activities in the Fram Strait are expanding because of sea ice shrinkage, and since currents from the North Atlantic carry a continuous supply of litter to the north, this problem is likely to worsen in years to come unless serious mitigating actions are taken to reduce the amounts of litter entering the oceans.


Introduction
Objects floating at the sea surface have been reported from locations all over the world (e.g. Eriksen et al. 2014;Galgani et al. 2015). Such objects can be of both natural and anthropogenic origin. Natural floatsam comprises seaweeds, wood, other plant debris, animal carcasses and volcanic pumice (Kiessling et al. 2015). Floating anthropogenic litter was first brought to our attention in the early 1960s when recovered from the alimentary tract of seabirds (Ryan 2015). Such objects comprise timber, tar lumps and to a great extent plastic (Kiessling et al. 2015).
Although the disposal of solid waste at sea was already prohibited under the MARPOL Convention (Annex V) in 1988, increasing numbers of reports indicate that the problem continues to be widespread (Galgani et al. 2015) highlighting the importance of land-based litter entering the oceans. Even the remotest environments such as polar regions and the deep ocean floor are no longer free of litter (Barnes 2002;Galgani et al. 2015). Plastic accounts for the great majority of marine litter (Cózar et al. 2014), which is not surprising given an annual global production of 299 million tons (status 2013(status , PlasticsEurope 2015. Recently, it has been estimated that 275 million tons of plastic waste were generated in 192 coastal countries in 2010, of which up to 12.7 million t entered the ocean (Jambeck et al. 2015). However, Eriksen et al. (2014) reported 'only' 250,000 t of litter floating in the oceans worldwide. This discrepancy of several orders of magnitude indicates the presence of hitherto unidentified sinks of marine litter.
Floating litter interacts with marine life in various ways. Most obviously, it causes entanglement and suffocation and interferes with food uptake and digestion of 580 marine species . Plastics are long lasting and non-biodegradable (Andrady 2015) and carry added and/or adsorbed pollutants (Engler 2012). If ingested, these may accumulate through the food web . Entanglement in or attachment to floating litter opens new routes of biota transportation, which could enable alien invasion (Kiessling et al. 2015). Long-distance transport may be enhanced by storms/strong winds (Kukulka et al. 2012). The risk of alien invasion may pose a particular threat to polar regions (Barnes 2002) such as the Arctic, which is currently one of the fastest warming areas of our planet. The resulting decrease in sea ice, which previously might have acted as a barrier to marine litter inputs and which has already led to increased shipping traffic in the area (Bergmann and Klages 2012), may result in greater litter inputs to the Arctic Ocean. Van Sebille et al. (2012) projected the presence/formation of a sixth garbage patch in the Barents Sea region, which may leak into the Fram Strait. Despite these implications, only limited information is currently available on the distribution of floating litter in polar regions (Barnes 2002;Prokhorova 2014). To address this issue, we report sightings of litter floating at the sea surface of the Barents Sea and Fram Strait recorded from a helicopter and a research vessel.

Study area
In 1999, the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, established the HAUS-GARTEN observatory (Bergmann and Klages 2012) in the eastern Fram Strait (Arctic), which was the focus of the current expedition. The Fram Strait is the only deep-water connection for exchange of deep and intermediate water masses between the North Atlantic and the Arctic Ocean. The hydrography is characterised by the inflow of warm Atlantic water from the Nordic Seas into the central Arctic Ocean. At 78°-80°N, part of the northward flowing Atlantic water (West Spitsbergen Current) is re-circulated within the Return Atlantic Current (Beszczynska-Möller et al. 2012) (Fig. 1). Here, the remaining Atlantic water divides into the Svalbard Branch, following the perimeter of the Svalbard Islands, and the Yermak Branch, flowing along the western and northern flanks of the Yermak Plateau. Cooler less saline polar waters from the central Arctic Ocean flow along the western Fram Strait (East Greenland Current). The eastern and western currents are separated by the East Greenland Polar Front. As a result, the sea ice cover is variable, with permanently ice-covered areas in western parts, permanently ice-free areas in southeastern parts and seasonally varying ice conditions in the central and northeast Fram Strait.

Counts of floating litter
Litter items floating at the sea surface were recorded as part of a long-term study on the distribution of seabirds and marine mammals in polar seas (Joiris 2000) during RV Polarstern expedition ARK XXVII/2 in July 2012. They were recorded during 30-min transect counts from the bridge while sailing at a mean speed ranging from 4.7 to 12.7 knots. Observations were done up to a 90°angle on either starboard or portside of the bridge (18 m above sea level) depending on the light conditions and visibility without width limitation [see Joiris (2000) for more details]. Objects were detected by eye and suspicions confirmed with high-quality binoculars (Swarovski and Kite, 10 9 42 and 10 9 50) or telescopes (Swarovski or Zeiss, 25-50x-80). The position of floating litter was taken from the ship's data acquisition system. The minimum size of detected floating objects was 20 cm.
In addition, helicopter flights were undertaken to increase the geographic range and to allow comparison between data obtained from the two different observation platforms. Helicopters of the model MBB BO-105 CBS (HeliService International GmbH, Germany) were used at a mean flight altitude between 53 and 249 m (Table 1) and a mean speed ranging from 109 to 182 km h -1 . Litter was recorded by the pilot and two observers using a hand-held Garmin GPS for navigational data acquisition.
Unfortunately, no calibration had been done to estimate the transect widths prior to helicopter flights and ship surveys as this had not been a part of the mammal/bird survey protocol used. Therefore, we were unable to calculate litter densities per area and rather converted counts to linear density (items per km distance). To this end, the survey distances were calculated from the ship's and helicopter's position acquisition systems, which enabled conversion of litter counts to linear density (item km -1 ).
Data analysis was done using the software Minitab 14.

Results
A total of 44 surveys of different lengths were conducted (109 h). Thirteen helicopter flights (=20 h) were undertaken. A total distance of 5568.5 km was surveyed by ship and helicopter flights. Thirty-one items of floating litter were observed during 12 of these surveys (27 %) (Table 1; Fig. 1). All litter items were classified as plastic, three of which were plastic bags and one piece was rope, presumably originating from fisheries. The majority could not be classified further due to advanced stages of weathering and distance to objects. One piece of wood was observed but classified as natural wood rather than timber.
A total distance of 2031.0 km was covered in 31 shipbased surveys (Table 1). Eight floating plastic litter items were seen in total during six of these (19 %), and quantities ranged from 0 to 0.21570 items km -1 . Although the majority of floating litter was observed on the westernmost flanks of the area surveyed (eastern Fram Strait, west of Svalbard), three items were also recorded from the Barents Sea during RV Polarstern's transit to Tromsø (Fig. 1). Less litter was observed closer to the coast of Svalbard. Ice was only seen during the four northernmost transects, where no flotsam was recorded. Litter density was significantly correlated with ship speed (Pearson correlation, r = -0.45, p = 0.012).  A total distance of 3537 km was surveyed by helicopter and litter observed during six of the 13 flights undertaken (46 %) (Table 1). Mean litter quantities ranged from 0 to 0.01850 items km -1 . Twenty-three items of floating plastic were recorded during these flights. The quantity of floating litter recorded was not significantly correlated with flight altitude (r = 0.44, p = 0.133) or speed (r = -0.12, p = 0.709).
Although the majority of floating litter was observed in the eastern Fram Strait west of Svalbard, six items were also recorded from the western Barents Sea (Fig. 1). Unlike the results from ship-based surveys, litter recorded during helicopter flights was not restricted to the westernmost flanks of the surveyed area.
More floating litter was recorded during helicopterbased surveys than during ship-based surveys (0.0065 and 0.0039 items km -1 , respectively). If all surveys were divided into Fram Strait and Barents Sea (south of Svalbard) transects, litter densities were slightly higher in the Fram Strait (0.0062 items km -1 ) than in the Barents Sea (0.0044 items km -1 ). However, while the densities obtained from helicopter-based surveys were similar in both regions (0.0066 and 0.0063 items km -1 in the Barents Sea and Fram Strait, respectively), the ship-based surveys yielded almost twice as much litter in the northern (0.0053 items km -1 ) compared with the southern survey area (0.0028 items km -1 ). We did not run statistical tests as 39 transects were done in the Fram Strait compared with only five in the Barents Sea.

Discussion
Our results highlight the presence of floating plastic litter items in the Barents Sea and in the Arctic. However, since the distance between the objects and the ship was not estimated and as no calibration was undertaken prior to helicopter flights, we can only provide linear densities (km -1 ) rather than litter densities per area (km -2 ). Therefore, our data are not comparable with those from many other studies (e.g. Ryan 1988;Lecke-Mitchell and Mullin 1997;Barnes and Milner 2005;Pichel et al. 2007Pichel et al. , 2012. Still, conversion of figures given in Ryan (2013Ryan ( , 2014, Ryan et al. (2014) and Miranda-Urbina et al. (2015) to items km -1 enables a comparison with our ship-based data. This suggests that floating debris in the Barents Sea/Fram Strait area (0.0039 items km -1 ) is slightly higher than that in the Antarctic (0.0013 items km -1 ) and sub-Antarctic Southern Ocean (0.0015 items km -1 ), but much lower than that at lower latitudes such as the temperate Southern Ocean (0.0217 items km -1 ), South Atlantic (0.1030 items km -1 ), South Pacific (0.0768 items km -1 ), Bay of Bengal (0.2484 items km -1 ) or even the Straits of Malacca (15.9389 items km -1 ).
It could be concluded that sea ice still hinders the spread of floating litter to polar regions to some extent and/or that the distance to more populated areas currently still limits the spread of litter to polar regions.
In annual Barents Sea fisheries surveys, plastic also dominates floating litter and tends to drift along the main currents (Prokhorova 2014), with most counts located between 69°and 74°N and 25°and 45°E-an area influenced by the North Cape and Murman Currents. However, the area surveyed is located further to the east than ours, north of Murmansk, and cannot be compared as no reference to distance or area covered is provided. Their highest litter counts coincide with areas of intensive fishery and shipping. Indeed, Sswat et al. (2015) reported evidence of trawling activities at all stations [300 m depth on the seabed northwest of Svalbard.
Our linear litter densities can also be compared with those from the seafloor of the HAUSGARTEN observatory, which is located below the parts of the present study area: analysis of images taken by a towed camera system yielded 2.24-18.47 items km -1 at 2500 m water depth (data from Bergmann and Klages (2012), converted to linear transect length for comparison). Surface litter quantities recorded in the HAUSGARTEN area (this study) were between 0 and 0.22 items km -1 and were thus 1-2 orders of magnitude lower compared with benthic litter. From this, it could be inferred that the seafloor may act as a sink of litter, as proposed by Woodall et al. (2014). Contrary to a common notion that most plastics are characterised by a low density and will only sink after fouling organisms and sediments have added weight, it has been estimated that 50 % of the plastics from municipal waste exceed the density of sea water such that it readily sinks to the seafloor (Engler 2012), which is enhanced by strong winds and storms (Kukulka et al. 2012). However, litter quantities on the seafloor were probably also higher because the camera was towed at lower altitude (1.5 m) compared with the distance between helicopter-or shipbased observers and the sea surface, resulting in higher counts of (smaller-sized) litter on the seafloor.
Despite the advantage of the large geographic ranges covered, few studies rely on aircraft for the assessment of floating litter. Ryan (1988) reported mean densities of large plastic items on aerial transects 10 and 50 km off Cape Columbine and Cape Point of 1.64 and 19.64 items km -2 , respectively, at a flight altitude of 130 m. Lecke-Mitchell and Mullin (1997) reported densities of 1 litter item km -2 from the Gulf of Mexico (229 m altitude). Although Pichel et al. (2007) flew at lower speed (100 m s -1 ) but at a higher altitude (300 m), their surveys in the North Pacific yielded seemingly higher litter counts (279-875 litter items). However, strictly speaking no comparison can be made as no area estimate was provided. Pichel et al. (2012) reported 102 items of anthropogenic or terrestrial origin in the Gulf of Alaska, but no transect lengths were given. Sighting data from aerial surveys conducted for a variety of purposes (e.g. fishery patrols, coast guard) could be used in an 'aircraft-of-opportunity' approach to increase our knowledge on the global distribution of litter, especially in poorly known remote areas. However, standard operational protocols are needed to ensure the comparability of data. To aid comparability, future surveys should provide both linear and area density estimates or at least survey distances as 'ship/aircraft-of-opportunity' type of surveys may not always be able to do the calibrations required to derive area density estimates, whereas platform positions are often recorded by default. From this, survey distance and linear density can be calculated, which would increase our knowledge base, especially for poorly sampled regions.
Since the global plastic production grows *4 % per year and demand reached 299 million t in 2013 (Plas-ticsEurope 2015), the contamination of the ocean with litter is likely to rise (Jambeck et al. 2015). Our report highlights once again that even remote and thus presumably pristine environments such as the Arctic are not exempt from plastic pollution. Indeed, litter pollution in the Arctic is likely to increase as anthropogenic pressure will grow due to easier access to this region caused by the decreased sea ice cover. In addition, the long-term mean net volume transport in the West Spitsbergen Current, which is derived from the North Atlantic, was estimated at 6.6 Sverdrup (Beszczynska-Möller et al. 2012). This implies that there will be a constant supply of litter transported to the north with water masses of Atlantic origin. This notion is corroborated by models projecting the formation of a sixth garbage patch in the Barents Sea region (van Sebille et al. 2012), which is probably due to highly populated coasts of the North Atlantic and may leak to the north. Assuming that significant litter inputs began in the 1970s and that the formation of this garbage patch is projected for 50 years, it seems reasonable to assume that there are already significant quantities in this region to be detected. Unfortunately, we cannot compare our data with these projections due to low spatial model resolution and because no true litter density units are provided.
One of the threats posed by floating litter is the risk of alien invasion through long-distance transport and ingestion. Indeed, plastic debris from Svalbard harboured xenobiota such as the barnacle Semibalanus balanoides and the bryozoan Membranipora membranacea (Barnes and Milner 2005). The risk of alien invasion in the Arctic may be ever higher when sea ice shrinkage reduces an effective barrier to both litter and exotics (Barnes 2002). In terms of the risk of ingestion, 8 % of Greenland sharks (Somniosus microcephalus) caught off South Greenland and 3 % of conspecifics from Kongsfjord, close to our study area, ingested litter as did 88 % northern fulmars (Fulmarus glacialis) from the nearby Isfjord (Leclerc et al. 2012;Nielsen et al. 2014;Trevail et al. 2015).
The global increase in marine litter, even at remote locations such as the poles, highlights the fact that the implementation of the current legislation does not suffice to tackle the problem of poor practices of solid waste management. Unless effective action is taken, it will only continue to worsen in years to come (Jambeck et al. 2015).