Eddy-driven subduction exports particulate organic carbon from the spring bloom

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Science  10 Apr 2015:
Vol. 348, Issue 6231, pp. 222-225
DOI: 10.1126/science.1260062
  • Fig. 1 (A) Eddy-driven subduction transports POC- and oxygen-rich surface water along tilted isopycnals.

    (B) Examples of Seaglider profiles of POC (gray, range 71 mg m−3), dissolved oxygen (DO) (red, range 25 mmol m−3), and spice (π, blue, range 0.17 kg m−3) from yearday 121 show features with elevated concentrations below the mixed layer (depth defined by Δσt = 0.03, dashed black line). (C) Thirty-day time series of 71 (of 772) POC profiles with distinct subsurface features versus depth. Black segments indicate the σt span (0.005) of each feature. (D) POC profiles from (C) versus σt, with 33 of the features falling within the same water mass (defined by σt = 27.48 ± 0.005 kg m−3) indicated by purple shading. (E) Locations of the subsurface features (colored symbols) from (C) and (D) overlaid on the tracks of the Seagliders (gray lines) and mixed-layer float (open circles, locations shown every 3 hours). The approximate location and yearday of the mixed-layer float is indicated by arrows. Most features were observed in the vicinity of anticyclonic regions (the dynamic height is shown in colors, with anticyclonic streamlines indicated by blue colors and an overall range of 8 cm), based on objective mapping of the depth-averaged currents (DAC) from gliders.

  • Fig. 2 AOU versus POC averaged within the subducted features (solid circles) and over the mixed layer (open circles), colored by yearday.

    The AOU increases as the POC decreases on the subducted features over time, indicative of respiration and diverging from simultaneously measured surface values. The best fit to the filled circles (dashed black line) has a slope of 1.5, consistent with a respiratory quotient arising from bacterial metabolization. AOU is defined as the difference between the saturation oxygen (at measured temperature, salinity, and surface pressure) and the measured oxygen.

  • Fig. 3 A subdomain of modeled (A) relative vorticity (ζ) normalized by planetary vorticity (f) and (B) POC from 200 to 600 m depth on yearday 125.

    The x-y locations of subsurface features identified with the model are indicated by black points in the z = 200 m plane. Black lines indicate the potential density (σt) contours. The domain is selected to intersect a region at the periphery of an anticyclone, containing high POC and deep negative vorticity consistent with frontogenetic subduction. (C) Examples of 96 model POC (mgC m−3) profiles at y = 0 show that roughly 10% contain subsurface features of elevated POC similar to the observations with Seagliders. The depth range shown in (A) and (B) is indicated by blue shading.

  • Fig. 4 Model-based estimate of eddy-driven subduction of POC.

    (A) The model-derived flux of POC F100 = 〈wPOC′〉 at 100-m depth is compared with a model-based scaling estimate Embedded Image. The two are correlated with r2 = 0.88. (B) A global estimate of eddy-driven subduction of POC. (C) The contribution of eddy-driven subduction [shown in (B)] as a percentage of the total export of POC. The total POC export is defined as the sinking export (33) plus the eddy-driven export (fig. S18).

Supplementary Materials

  • Eddy-driven subduction exports particulate organic carbon from the spring bloom

    Melissa M. Omand, Eric A. D'Asaro, Craig M. Lee, Mary Jane Perry, Nathan Briggs, Ivona Cetinić, Amala Mahadevan

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

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    • Materials and Methods
    • Figs. S1 to S18
    • Table S1
    • References

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