Research ArticleWATER POLLUTION

The Arctic Ocean as a dead end for floating plastics in the North Atlantic branch of the Thermohaline Circulation

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Science Advances  19 Apr 2017:
Vol. 3, no. 4, e1600582
DOI: 10.1126/sciadv.1600582
  • Fig. 1 Environmental conditions and concentrations of floating plastic debris in the Arctic Ocean.

    (A) At-sea vessel density. (B) Human population and Arctic sea ice extent. Annual minimum and maximum ice extents correspond to the monthly mean of September and March, respectively. Historic data account for the 1981 to 2010 median. (C) Remote-sensed sea surface salinity for August 2013 at the mid-sampling period. The seasonal cycle is shown in fig. S1. psu, practical salinity units. (D) Locations and plastic concentrations of the sites sampled. The summer extension of the polar ice cap in August 2013 is shown in white area, and the classical schematic drawing of the North Atlantic SOG and the THC poleward branch is indicated by green curves (8). The northern passage from Barents Sea to Kara Sea is zoomed in, with contour lines describing salinity measured at a depth of 5 m. (E) Plastic concentrations as total weight (upper graph) and abundances per plastic type (lower graph) along the circumpolar track, from the Greenland Sea to the Labrador Sea, as indicated in the left map by the black line connecting the sampling sites. Salinity at depths of 5 and 20 m is also shown in the upper graph, and two dashed lines are used as reference for 34.5 salinity and the median of plastic concentrations measured in the inner accumulation zones of SOGs [175 g·km−2 (2)]. The correlation between plastic and salinity is shown in fig. S2. Note that the plastic fibers, presented in the lower graph as a dotted line, were excluded from all our analyses, including total plastic concentrations and load estimates in both weight and number. The Arctic Polar Circle (66.34°N) is marked in all maps.

  • Fig. 2 Typology and size distribution of the floating plastic debris collected in the Arctic Ocean compared to the plastic accumulation zones in the SOGs and the Mediterranean Sea.

    In the pie charts, the percentages of plastic types are shown in relation to weight (charts showing the number of items and surface area are presented in fig. S3). The size distributions are presented in the lower graph. Horizontal axes indicate both log-transformed and nontransformed size limits of the bins. Plastics in the interval from 0.32 to 0.50 mm are graphed using open circles because these abundances are possibly underestimated for the Arctic due to the sampling net with combined 0.5- and 0.33-mm meshes for the body and cod end, respectively. Sample collections for the SOGs (4173 items) and the Mediterranean (3854 items) are described in previous reports (2, 7). The total number of items used for the analyses in the Arctic was 796; absolute abundances for each size bin are provided in table S1. The number of large items (>12.6 mm) in relation to the total was 2.1% (17 items), 3.2% (134 items), and 4.4% (170 items) for the Arctic Ocean, the SOGs, and the Mediterranean Sea, respectively.

  • Fig. 3 Oceanic pathway of the plastic accumulations in the Greenland Sea (upper maps) and the Barents Sea (lower maps) obtained by simulations backward in time.

    Tracers were released at the locations of maximal plastic concentrations in Greenland and Barents seas (red circles), and their surface transport was modeled for the previous years (1 to 3 years). Units are expressed as percentage of tracers in each pixel. The background image for the ocean shows the vessel density in gray scale. Note the close agreement between the modeled plastic pathway and the THC route described in the literature (Fig. 1). Likewise, the tracers released in the Northeastern Barents Sea were placed 1 year before into a zone where high plastic concentrations were also measured.

  • Table 1 Range of floating plastic concentrations in the Arctic compared to accumulation and nonaccumulation zones in tropical and temperate oceans.

    The minimum, median, and maximum concentrations in number and weight are shown separately for the Greenland and Barents seas (the Arctic sector from 35°W to 74°E longitude) and the rest of the Arctic Ocean. Plastic concentrations in the inner accumulation zone of the SOGs and tropical/temperate nonaccumualation zones were obtained from a previous global report (2). The total number of samples for each zone (n) is also shown.

    ×103 items·km−2g·km−2n
    MinMedianMaxMinMedianMax
    Greenland and Barents seas06.3 × 1013.2 × 10206.5 × 1014.6 × 10217
    Rest of the Arctic Ocean002.7 × 101005.1 × 10121
    Subtropical accumulation zones04.4 × 1011.3 × 10301.8 × 1026.8 × 103275
    Tropical/temperate nonaccumulation zones01.9 × 1001.9 × 10203.6 × 1003.4 × 102629
  • Table 2 Ratios of surface plastic load to local pollution sources in the Arctic and other ocean basins.

    Land-based pollution sources (L) were estimated from a population in a 50-km coastal strip, and sea-based pollution sources (S) were estimated from at-sea vessel density. Surface plastic loads (P) were obtained from the present work and previous reports (2, 7). L and S are expressed in persons or vessels per square kilometer of ice-free waters, respectively. S:L ratios are expressed in vessels per person, P:L ratios are expressed in grams of plastic per person, and P:S ratios are expressed in grams of plastic per vessel. Global estimates do not include the Southern Ocean because of the lack of plastic pollution data for that basin.

    LSS:LP:LP:S
    Arctic1.5 × 10−11.7 × 10−21.1 × 10−13.4 × 1023.1 × 103
    Mediterranean7.6 × 1013.1 × 10−14.1 × 10−35.5 × 1001.3 × 103
    North Atlantic8.8 × 1006.7 × 10−27.6 × 10−36.9 × 1009.1 × 102
    North Pacific9.6 × 1004.7 × 10−24.9 × 10−36.6 × 1001.3 × 103
    Indian7.6 × 1003.2 × 10−24.2 × 10−34.0 × 1009.5 × 102
    South Atlantic2.4 × 1001.8 × 10−27.4 × 10−32.6 × 1013.5 × 103
    South Pacific9.4 × 10−17.1 × 10−37.5 × 10−32.7 × 1013.6 × 103
    Global6.2 × 1003.4 × 10−25.5 × 10−37.8 × 1001.4 × 103

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1600582/DC1

    Supplementary Text

    fig. S1. Seasonal cycle of ocean surface salinities for 2013 provided by the Aquarius Mission (NASA and Space Agency of Argentina; http://aquarius.umaine.edu).

    fig. S2. Relationship between salinity (depths, 5 and 20 m) and surface plastic debris measured in the present study.

    fig. S3. Pie charts in number of items (upper) and surface area (lower) of the plastic types found in the Mediterranean Sea (left), SOGs (center), and Arctic Ocean (right).

    fig. S4. Images of different categories of microplastics found in the Arctic Ocean.

    fig. S5. Relationship between the estimates of total surface plastic load [(2, 7); this work], coastal population, and presence of vessels per great basins: Arctic, Mediterranean (Med), North Atlantic (N Atl), South Atlantic (S Atl), North Pacific (N Pac), South Pacific (S Pac), and Indian Ocean.

    table S1. Size distribution of floating plastic debris collected for the present study.

    table S2. Number of items per tow (fibers, nonfibers, and total items) and concentrations in abundance and weight per square kilometer (excluding fibers).

    References (28, 29)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. Seasonal cycle of ocean surface salinities for 2013 provided by the Aquarius Mission (NASA and Space Agency of Argentina; http://aquarius.umaine.edu).
    • fig. S2. Relationship between salinity (depths, 5 and 20 m) and surface plastic debris measured in the present study.
    • fig. S3. Pie charts in number of items (upper) and surface area (lower) of the plastic types found in the Mediterranean Sea (left), SOGs (center), and Arctic Ocean (right).
    • fig. S4. Images of different categories of microplastics found in the Arctic Ocean.
    • fig. S5. Relationship between the estimates of total surface plastic load (2, 7); this work, coastal population, and presence of vessels per great basins: Arctic, Mediterranean (Med), North Atlantic (N Atl), South Atlantic (S Atl), North Pacific (N Pac), South Pacific (S Pac), and Indian Ocean.
    • table S1. Size distribution of floating plastic debris collected for the present study.
    • table S2. Number of items per tow (fibers, nonfibers, and total items) and concentrations in abundance and weight per square kilometer (excluding fibers).
    • References (28, 29)

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