Research ArticleArctic Oceanography

Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean

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Science  21 Apr 2017:
Vol. 356, Issue 6335, pp. 285-291
DOI: 10.1126/science.aai8204
  • Fig. 1 Sea-ice fraction and thickness in the eastern Eurasian Basin (EB) since 2003.

    Sampling of the sea-ice state within the region [of 0.41 × 106 km2, defined in (A)] shows a positive trend in annual open-water coverage [in months, integrated over a seasonal cycle, (B)]; this is accompanied by decreases in mean March ice thickness and monthly mean sea-ice coverage in (C) (measured as fraction of the total area). For the past five summers (2011 through 2015), the mean September ice coverage has been less than 10% ice coverage and seems to be approaching a seasonally ice-free state. Dashed box (in blue) shows the geographic coverage of the map in Fig. 2A, within the Arctic Basin. Red dashed line in (A) identifying the Lomonosov Ridge that separates the Amerasian and Eurasian basins.

  • Fig. 2 Mooring locations and time series and their wavelet transforms from the mooring site M14, eastern EB of the Arctic Ocean.

    (A) Map showing locations of oceanographic moorings. The Gakkel Ridge (GR) divides the EB into the Nansen Basin (NB) and the Amundsen Basin (AB). The Lomonosov Ridge (LR), Novosibirskiye Islands (NI), Severnaya Zemlya (SZ), Franz Joseph Land (FJL), and Makarov Basin (MB) are indicated. Dotted lines show latitudes and longitudes; gray solid lines show depth in meters. (B) Vertical profiles show increasing water temperature (°C) and salinity and decreasing stability expressed as the logarithm of squared Brunt-Väisälä frequency (N2, s−2, a measure of water-column stability) within the cold halocline layer (CHL) and upper pycnocline (~40 to 150 m) in the 2000s and early 2010s. (C) Composite time series of water temperature (dotted lines for daily means, solid lines for monthly means). White segments indicate missing data. (D) Original (light blue) and detrended (dark blue) time series of the upper Atlantic water (AW) boundary (defined by 0°C isotherm, left) and wavelet transforms of detrended time series (right). In panels with wavelet transforms, 95% statistical significance and cones of influence are shown by gray lines.

  • Fig. 3 Seasonal evolution of the upper ocean layers in the Eurasian Basin of the Arctic Ocean.

    (Top) Potential temperature (°C), (middle) salinity, and (bottom) logarithm of N2 (s−2) from (A) mooring and (B to D) along the Ice-Tethered Profiler drifts. White segments indicate missing data. White solid lines show the depth of the surface mixed layer (SML) and black solid lines show the depth of the underlying cold halocline layer (CHL) base; disappearance of the black line signifies disappearance of CHL and ventilation of the upper ocean.

  • Fig. 4 Winter ventilation of the upper ocean in the eastern Eurasian Basin.

    (Left) Depth (m)–time distributions of temperature, T, and (right) time series of heat content, Q, (dotted blue lines, daily means; solid blue lines, monthly means; green dashed line, standard errors) for the 65- to 130-m layer (see mooring locations in Fig. 2). Maxima and minima of wavelet transforms were used to define the boundary of winter seasons (fig. S4). These boundaries were used to calculate trends in Q shown by red (winter 2013–2014) and orange (winter 2014–2015) lines. Slope of trends defines the rate of change of Q in time, which is equivalent to the divergent heat flux Fh (shown in red and orange).

  • Fig. 5 Conceptual model of “atlantification” of the eastern EB continental margin in recent years.

    The broad arrow extending from the right side shows the encroachment of a suite of processes associated with “atlantification”; these are (i) increased penetration of surface signature of AW (increased flow, heat content, or both) into the eastern EB, (ii) reduction in ice cover resulting in (iii) greater surface heat and moisture flux and (iv) increased depth of winter penetrative convection, bringing additional heat and nutrients from AW into the Arctic surface water and transformation of the permanent cold halocline layer (CHL) to a seasonal halocline. SML and UPP indicate the surface mixed layer and upper permanent pycnocline. WC shows winter convection; red arrows indicate upward heat fluxes. Horizontal red arrows show inflows.

  • Table 1 Estimates of upward heat fluxes Fh (W/m2).

    RegionTopographyDepth levelFhMethodSource
    Previous estimates, Eurasian Basin
    Yermak PlateauSteepHalocline25Microstructure profiles(46)
    Yermak PlateauSteepIce-ocean interface22Turbulent flux buoy(47)
    North of SvalbardSteepIce-ocean interface
    Halocline
    O(100)
    O(100)
    Eddy covariance, Microstructure profiles(48)
    North of SvalbardSlopeHalocline2-4Microstructure profiles(49)
    Laptev SeaSlopeAbove AW core (>250 m)3Microstructure profiles(29)
    Amundsen BasinInteriorUpper CHL
    SML
    0.05
    0.2
    Microstructure profiles(50)
    Amundsen BasinInteriorBetween SML and AW core3-4ITP, heat content difference(14)
    Estimates from this study, eastern Eurasian Basin
    Eastern EB, off Severnaya ZemlyaSteep slopeBetween SML and AW core5.0-10.3Heat content differenceM6b mooring
    Eastern EB, central Laptev Sea, 125°ESlopeBetween SML and AW core8.4-24.1Heat content differenceM13 mooring
    Eastern EB, 125°EInteriorBetween SML and AW core6.9-11.2Heat content differenceM16 mooring
    Eastern EB, off Novosibirskiye IslandsSlopeBetween SML and AW core3.3-9.5Heat content differenceM3e mooring

Supplementary Materials

  • Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean

    Igor V. Polyakov, Andrey V. Pnyushkov, Matthew B. Alkire, Igor M. Ashik, Till M. Baumann, Eddy C. Carmack, Ilona Goszczko, John Guthrie, Vladimir V. Ivanov, Torsten Kanzow, Richard Krishfield, Ronald Kwok, Arild Sundfjord, James Morison, Robert Rember, Alexander Yulin

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

    Download Supplement
    • Materials and Methods
    • Supplementary Text
    • Figs. S1 to S6
    • Table S1
    • References

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