Research ArticleGEOPHYSICS

High geothermal heat flux measured below the West Antarctic Ice Sheet

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Science Advances  10 Jul 2015:
Vol. 1, no. 6, e1500093
DOI: 10.1126/sciadv.1500093
  • Fig. 1 Site maps.

    Maps showing the location of West Antarctica and SLW, where the data and samples described in this study were collected. (A) Antarctic map showing geographic regions and location of field area below the confluence of the Whillans and Mercer Ice Streams. Grounded ice is shown in gray, and ice shelves are shown in tan. (B) Overview of the Whillans Ice Plain showing the surface morphology and position of the WAIS grounding line (39), the lateral limits of ice streams (yellow lines) (30), and the outlines of subglacial lakes (16, 40), identified as follows: SLC, Subglacial Lake Conway; SLM, Subglacial Lake Mercer; SLW, Subglacial Lake Whillans; SLE, Subglacial Lake Engelhardt; L7, Lake 7; L8, Lake 8; L10, Lake 10; and L12, Lake 12.

  • Fig. 2 Thermal data and interpreted values.

    Processing details and complete field records are included in Materials and Methods and the Supplementary Materials, respectively. (A) Temperature-time record after probe penetration during the first tool deployment below SLW, as modeled to derive equilibrium temperature. Every fourth data point is shown for clarity. The solid curve shows the fit of data from sensor TS1 (open circles) to an analytical model for tool equilibration in sediments after penetration. The large circles show the range of TS1 data fit with the model. The horizontal dotted line shows the equilibrium temperature for TS1. Record from the bottom water probe, TBW (x symbols), was averaged over the interval shown (between large squares) to calculate bottom water temperature. (B) Temperature-time record after probe penetration during the second tool deployment below SLW, as modeled to derive equilibrium temperature. Symbols are the same as in (A). (C) Compilation of thermal conductivity values determined on sediment core recovered using the gravity multicorer.

  • Fig. 3 DTS data.

    SLW and geothermal temperature data and interpretations are also shown, with temperature values plotted relative to top of ice. (A) DTS records from 2013 [immediately after deployment, conditions strongly perturbed by drilling (dashed blue line)] and 2014 [after a year of freezing and conductive equilibration (solid blue line)]. Base of ice is at 802 m bis, as is the temperature measured in SLW with the bottom water sensor in the GT (BW, open square). Result shown for a one-dimensional advection-conduction model (Pe ~ 4.6, ice accumulation rate of ~0.19 m/year), fitted to DTS data from 200 to 700 m bis (dotted pink line). (B) Detail of the deepest 200 m of 2014 DTS record (solid blue), with extrapolation of fit from one-dimensional advection-conduction model (pink dotted line) and linear fit of depth interval from 600 to 730 m bis (dashed purple line). The thermal gradient range shown for the base of the ice incorporates the values determined from the advection-conduction model (0.049°C/m) and the linear fit (0.052°C/m). The positive thermal anomaly at ~760 m bis is coincident with a zone of excessive melting during borehole operations, which had not reached thermal equilibrium when data were collected in 2014. The inverted triangle indicates the in situ sediment temperature determined with the GT.

  • Fig. 4 Comparison of measured and modeled geothermal heat flux.

    (A) Map of geothermal heat flux from a model based on space-borne geomagnetic data (12). (B) Map of geothermal heat flux from a model based on global seismic model data (11). (C) Compilation of regional geothermal heat flux values and estimates, superimposed on the map of the same area shown in (A) and (B), using the same color scale. Labeled symbols/areas are for this study (SLW), WAIS divide [WAIS-D (14)], ANDRILL sites 1 and 2 [AND-1 and AND-2 (10, 41)], Siple Dome [SIP (42)], Hut Point Peninsula [HP (43)], and Thwaites Glacier [THW (15)]. Additional values were tabulated by Morin et al. (10). Also shown are the grounding line (thick black line), areas with elevation lower than 500 m below mean sea level (gray), subglacial lakes (dark blue dots and outlines), and ice streams (surface velocity >50 m/year, pale blue areas). (D) Cross plot of observed/calculated versus modeled geothermal heat flux values, with labels corresponding to same values shown in (C). Horizontal bars show the results of geophysical calculations (11, 12) for equivalent locations (lower and higher values, respectively). Vertical bars show the uncertainties associated with each measurement or modeled estimate. Inset plot shows the global compilation of continental heat flux values (22), excluding 25 values <0 (inverted gradients) and 160 values >400 mW/m2.

  • Table 1 Summary of results from two deployments of the WISSARD GT at SLW.

    Values reported in this table are discussed in Materials and Methods. TBW, temperature of bottom water in SLW; TS1, equilibrium temperature of the deepest sensor on the lance of the GT; zS1, depth below the bottom of SLW.

    GT-1GT-2Uncertainty
    Date, time
    (local)
    31 Jan 2013,
    1035
    31 Jan 2013,
    1600
    TBW (°C)−0.555−0.556±0.01
    TS1 (°C)0.387−0.390±0.01
    zS1 (m)0.810.78±0.08
    ΔTz (°C/m)0.2070.213+0.04, −0.07
    λ (W/m K)1.361.36±0.12
    q (mW/m2)28029080

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/6/e1500093/DC1

    Fig. S1. WISSARD GT deployed below SLW.

    Fig. S2. Example calibration results from two autonomous probes used with the WISSARD GT deployed below SLW.

    Fig. S3. Complete records from GT deployments below SLW.

    Fig. S4. Example records from needle-probe thermal conductivity determinations made on a core sample recovered from the bottom of SLW.

    Fig. S5. Calculations of the thermal disturbance that could occur as a function of time owing to an abrupt change in bottom water temperature or an adjacent tool insertion.

    Table S1. Physical parameters used to fit the 2014 DTS data to a one-dimensional, steady-state conduction-advection model.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. WISSARD GT deployed below SLW.
    • Fig. S2. Example calibration results from two autonomous probes used with the WISSARD GT deployed below SLW.
    • Fig. S3. Complete records from GT deployments below SLW.
    • Fig. S4. Example records from needle-probe thermal conductivity determinations made on a core sample recovered from the bottom of SLW.
    • Fig. S5. Calculations of the thermal disturbance that could occur as a function of time owing to an abrupt change in bottom water temperature or an adjacent tool insertion.
    • Table S1. Physical parameters used to fit the 2014 DTS data to a onedimensional, steady-state conduction-advection model.

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