Research ArticleOCEANOGRAPHY

Reframing the carbon cycle of the subpolar Southern Ocean

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Science Advances  28 Aug 2019:
Vol. 5, no. 8, eaav6410
DOI: 10.1126/sciadv.aav6410
  • Fig. 1 Two-dimensional framework for the subpolar Southern Ocean carbon cycle.

    Schematic illustration of the conventional, two-dimensional, overturning-centric framework for the subpolar Southern Ocean carbon cycle. Dotted lines delineate surface water (SW), CDW, and upper and lower layers of AABW.

  • Fig. 2 Circulation and carbon in the Weddell Gyre.

    (A) Location of the Weddell Gyre and hydrographic sections. On the right panel, contours of mean dynamic topography (MDT) are plotted, revealing the cyclonic gyre circulation (contours every 0.1 m). These data are the June-July-August mean in 2005, taken from the Southern Ocean State Estimate (41). The 2008 annual mean chlorophyll-a concentration, derived from satellite measurements of ocean color, is also plotted (green shading) (47). (B) Cumulative horizontal circulation around the boundary of the Weddell Gyre, derived from the inversion (11). Volume transports for each station pair are integrated from left to right. Note the reversed direction of the y axis such that export is upward. (C) Overturning circulation in the Weddell Gyre, derived from the inversion, in neutral density layers. Bars correspond to the volume transport in each layer ([v]i). The center location and thickness of each bar correspond to the mean depth and thickness of that layer. Horizontal dotted lines denote the interfaces between major water masses. (D) Area-weighted mean carbon concentration in each layer (CT¯i). (E) Carbon concentration, CT, around the Weddell Gyre. As for (C) and (D), dotted lines denote the interfaces between the major water masses. Pink contours correspond to the concentrations (80, 90, and 100 μmol kg−1) of the remineralized organic matter component (Csoft) of the carbon partitioning formulation (see Materials and Methods), with thicker contours denoting greater concentration.

  • Fig. 3 Total, overturning, and horizontal carbon transports in the Weddell Gyre.

    (A) Total transport of carbon in the Gyre (TC; blue) and the transport due to the overturning component of the circulation (TCo; green), for each layer (upper panel) and summed over the full depth (lower panel). Full-depth transports include export of carbon in sea ice, assuming a sea-ice carbon concentration of 600 μmol kg−1 (17). (B) Transport of carbon due to the horizontal component of the circulation (TCh), for each layer (upper panel) and summed over the full depth (lower panel). (C) Horizontal transport of carbon [gray bars; same as in (B)] separated into contributions from each constituent of the carbon partitioning (see Materials and Methods), for each layer (upper panel) and summed over the full depth (lower panel). Note that for all panels, the x axis has a different scale between the layer-wise (upper panel) and the full-depth (lower panel) transports. All of the full-depth transports (bottom panels) have the same scale.

  • Fig. 4 A three-dimensional perspective of the subpolar Southern Ocean carbon cycle.

    Schematic illustration of the subpolar Southern Ocean carbon cycle, with the nearside exactly as in Fig. 1 and extended outward to recognize the crucial role of the horizontal circulation of mid-depth waters and their enrichment in carbon by biological production and remineralization in the central gyre region. Dotted lines delineate surface water (SW), CDW, and upper and lower layers of AABW.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/8/eaav6410/DC1

    Fig. S1. Transports of the layer-wise carbon anomaly in CDW.

    Fig. S2. Carbon partitioning in the Weddell Gyre.

    Fig. S3. CFC-11 in the Weddell Gyre.

    Fig. S4. Carbon and carbon partitioning in the Ross Sea.

    Fig. S5. Salinity-alkalinity relationship in the Weddell Gyre surface ocean.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Transports of the layer-wise carbon anomaly in CDW.
    • Fig. S2. Carbon partitioning in the Weddell Gyre.
    • Fig. S3. CFC-11 in the Weddell Gyre.
    • Fig. S4. Carbon and carbon partitioning in the Ross Sea.
    • Fig. S5. Salinity-alkalinity relationship in the Weddell Gyre surface ocean.

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