Research ArticleGEOCHEMISTRY

Increased fluxes of shelf-derived materials to the central Arctic Ocean

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Science Advances  03 Jan 2018:
Vol. 4, no. 1, eaao1302
DOI: 10.1126/sciadv.aao1302
  • Fig. 1 Radium-228 activities in surface waters (2 m) of the Arctic Ocean.

    Ice back-trajectories determined for each of the sampling stations are shown in black. The red, green, and magenta symbols indicate the position of the ice 6, 12, and 18 months before each sample was collected, respectively. The 200-m isobath is highlighted in bold.

  • Fig. 2 Radium-228 activities in surface waters (<50 m) above 85°N as a function of percent meteoric water.

    Open symbols represent samples collected in 2015 on the GN01 transect, and closed symbols represent samples collected in 2007 on the GIPY11 transect (16). Error bars for the data collected in 2007 are smaller than the symbols.

  • Fig. 3 Activities of 228Ra and 226Ra measured in surface waters in 2015 (circles), shown with historical measurements of shelf and river endmembers.

    Error bars for the 2015 data are smaller than the symbols. ††This study; +Rutgers van der Loeff et al. (19); *Smith et al. (15).

  • Fig. 4 The coastal flux of 228Ra to each ocean basin.

    The flux is shown (A) in atoms year−1 and (B) normalized to the area of each basin in atoms km−2 year−1. The fluxes from basins other than the Arctic are from Kwon et al. (12), and areas are from the ETOPO1 surface relief model (56). The area of the Arctic basin is from Jakobsson (1).

  • Table 1 Radium-228 sources and sinks (all in 1022 atoms year−1) in the Arctic surface ocean.

    The shelf flux was determined by difference, assuming that, at steady state, the sources of 228Ra to the surface layer must be balanced by sinks. The best estimate for each term was used in the mass balance calculation; see Materials and Methods for details on how the minimum and maximum flux estimates were determined.

    SinksBest-estimate flux (1022 atoms year−1)Minimum flux (1022 atoms year−1)Maximum flux (1022 atoms year−1)% of total sinks
    Decay8.26.69.955
    Advection6.85.41645
    SourcesBest-estimate flux (1022 atoms year−1)Minimum flux (1022 atoms year−1)Maximum flux (1022 atoms year−1)% of total sources
    Ice-rafted sediment0.0890.0120.40<1
    Advection2.21.43.115
    Rivers0.550.200.994
    Shelf127.52581

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/1/eaao1302/DC1

    fig. S1. Activities of 228Ra in the upper 500 m of the water column with contours indicating the fraction of meteoric water.

    fig. S2. Surface water (<15 m) activities of 228Ra from GN01 (circles) shown with activities of 228Ra measured on historical expeditions in the Arctic.

    fig. S3. Profiles of 228Ra on the GN01 cruise (2015) compared to the surface samples collected on the GIPY11 cruise (2007) (16).

    fig. S4. Radium-228 activities in the Transpolar Drift in 1994, 2007, and 2015.

    fig. S5. Radium-228 activities in surface waters (2 m) sampled on the GN01 transect in 2015.

    fig. S6. Radium-228 activities in surface waters (7 m) on the GIPY11 transect in 2007, measured by Rutgers van der Loeff et al. (16).

    fig. S7. Model of 228Ra and 228Th activities.

    fig. S8. Inventory of 228Ra in the top 500 m at each of the stations where water column samples were collected and the bottom depth was ≥1000 m.

    fig. S9. Dissolved 228Ra activities measured in the Mackenzie River.

    fig. S10. Dissolved 228Ra activities in the Mackenzie River estuary (East Channel).

    fig. S11. Satellite-derived record of open water days.

    fig. S12. Dissolved 226Ra activities in surface water (<50 m) above 85°N as a function of the fraction of meteoric water in each sample.

    fig. S13. Surface water (<15 m) activities of 226Ra from GN01 (circles) shown along with activities of 226Ra measured on historical expeditions in the Arctic.

    table S1. Locations of stations used to determine the surface water 228Ra inventory.

    table S2. Activities of 228Ra and 226Ra measured in ice-rafted sediments and melted ice.

    References (57, 58)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Activities of 228Ra in the upper 500 m of the water column with contours indicating the fraction of meteoric water.
    • fig. S2. Surface water (<15 m) activities of 228Ra from GN01 (circles) shown with activities of 228Ra measured on historical expeditions in the Arctic.
    • fig. S3. Profiles of 228Ra on the GN01 cruise (2015) compared to the surface samples collected on the GIPY11 cruise (2007) (16).
    • fig. S4. Radium-228 activities in the Transpolar Drift in 1994, 2007, and 2015.
    • fig. S5. Radium-228 activities in surface waters (2 m) sampled on the GN01 transect in 2015.
    • fig. S6. Radium-228 activities in surface waters (7 m) on the GIPY11 transect in 2007, measured by Rutgers van der Loeff et al. (16).
    • fig. S7. Model of 228Ra and 228Th activities.
    • fig. S8. Inventory of 228Ra in the top 500 m at each of the stations where water column samples were collected and the bottom depth was ≥1000 m.
    • fig. S9. Dissolved 228Ra activities measured in the Mackenzie River.
    • fig. S10. Dissolved 228Ra activities in the Mackenzie River estuary (East Channel).
    • fig. S11. Satellite-derived record of open water days.
    • fig. S12. Dissolved 226Ra activities in surface water (<50 m) above 85°N as a function of the fraction of meteoric water in each sample.
    • fig. S13. Surface water (<15 m) activities of 226Ra from GN01 (circles) shown along with activities of 226Ra measured on historical expeditions in the Arctic.
    • table S1. Locations of stations used to determine the surface water 228Ra inventory.
    • table S2. Activities of 228Ra and 226Ra measured in ice-rafted sediments and melted ice.
    • References (57, 58)

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    Correction (28 February 2018): A version of the Supplementary Materials which included incorrect in-text reference mentions was published in error. Mentions of reference 59 were corrected to 57 in fig. S2, mentions of reference 60 were corrected to 58 in fig. S13, and mentions of references 20, 29, and 37 were corrected to 19, 28, and 36 respectively, in both figures.

    The original version is accessible here.

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