Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf

Journal name:
Nature Geoscience
Volume:
4,
Pages:
519–523
Year published:
DOI:
doi:10.1038/ngeo1188
Received
Accepted
Published online
Corrected online

In 1994, ocean measurements near Antarctica’s Pine Island Glacier showed that the ice shelf buttressing the glacier was melting rapidly1. This melting was attributed to the presence of relatively warm, deep water on the Amundsen Sea continental shelf. Heat, salt and ice budgets along with ocean modelling provided steady-state calving and melting rates2, 3. Subsequent satellite observations and modelling have indicated large system imbalances, including ice-shelf thinning and more intense melting, glacier acceleration and drainage basin drawdown4, 5, 6, 7, 8, 9, 10. Here we combine our earlier data with measurements taken in 2009 to show that the temperature and volume of deep water in Pine Island Bay have increased. Ocean transport and tracer calculations near the ice shelf reveal a rise in meltwater production by about 50% since 1994. The faster melting seems to result mainly from stronger sub-ice-shelf circulation, as thinning ice has increased the gap above an underlying submarine bank on which the glacier was formerly grounded11. We conclude that the basal melting has exceeded the increase in ice inflow, leading to the formation and enlargement of an inner cavity under the ice shelf within which sea water nearly 4°C above freezing can now more readily access the grounding zone.

At a glance

Figures

  1. Ocean stations in the eastern Amundsen Sea and greater PIB (>[sim]74[deg][thinsp]S).
    Figure 1: Ocean stations in the eastern Amundsen Sea and greater PIB (>~74°S).

    Bathymetry and coastline24 are zoomed out on the insets. Black dots are the 2009 CTD profiles in Fig. 2a; red triangles the 2009 CTDs 16-23 in Figs 2b, 3b and 4. White squares are paired CTDs from 1994, 2000, 2007 and 2009 (Fig. 3). Water column profiling included dissolved oxygen, and LADCP measurements after 1994.

  2. Vertical temperature and salinity sections.
    Figure 2: Vertical temperature and salinity sections.

    a,b, Vertical temperature and salinity sections (a) from the CTDs shown in the Fig. 1 inset and extended beneath the PIG and (b) along the PIG calving front, looking toward the ice shelf. Both panels show temperature in colour relative to the in situ freezing point, salinity by black contours and the surface-referenced 27.75 isopycnal and potential temperature maximum by thick and thin white lines. Open circles in b show ice draft above the ridge crest (black dots) beneath the PIG, from airborne radar and Autosub measurements11.

  3. Temperature and salinity in PIB.
    Figure 3: Temperature and salinity in PIB.

    a, Cruise average, 50-dbar (~50m) mean temperature above freezing (TTf) and salinity profiles from January–March 1994, 2000, 2007 and 2009 CTDs within 25km (mean <10km) of prior measurements (Fig. 1), with 1 σ (standard deviation) at 200, 500 and 800dbar in 2009. Inset: the same data in Tθ (potential temperature)/Salinity space. b, Tθ (top scale, coloured in TTf) and salinity profiles at CTD 16, and Tθ (right scale)/salinity at CTDs 16 (black) and 17–23 (light grey) from Fig. 2b. Red and black boxes are 1994 and 2009 CDW and Winter Water properties (see Methods).

  4. Meltwater fractions and geostrophic current velocities near the PIG ice front.
    Figure 4: Meltwater fractions and geostrophic current velocities near the PIG ice front.

    a, Meltwater profiles from ocean tracers22 in 2009 (black) and 1994 (red), with means (solid lines) and range (1 σ, shaded, darker where σ is enlarged by surface effects at CTDs near the ice front (Fig. 1)). b, Adjusted geostrophic velocity profiles perpendicular to the ice front between gates defined by the indicated 1994 (red) and 2009 (black) profiles. c,d, Adjusted geostrophic velocities in 2009 and 1994 perpendicular to the ice front (positive denotes outflow). Dashed black and white lines show the excluded surface layer (shaded darker in a) and initial reference levels before adjustment (dashed lines in a).

Change history

Corrected online 29 June 2011
In the version of this Letter originally published online, Fig. 4b–d were incorrectly described in the caption. This error has now been corrected in all versions of the Letter.

References

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Affiliations

  1. Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA

    • Stanley S. Jacobs &
    • Claudia F. Giulivi
  2. British Antarctic Survey, Natural Environment Research Council, Cambridge, CB3 0ET, UK

    • Adrian Jenkins &
    • Pierre Dutrieux

Contributions

S.S.J. and A.J. proposed the research, analysed the results and wrote the text. C.F.G. and P.D. processed the data. C.F.G., P.D. and A.J. prepared the figures. All authors read and commented on the paper.

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The authors declare no competing financial interests.

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