 |
| Titel |
Palaeo-ice streams in the Amundsen Sea sector of the West Antarctic Ice Sheet during the last glacial period: flow dynamics, retreat histories, and geological controls |
| VerfasserIn |
Alastair Graham, James Smith, Robert Larter, Karsten Gohl, Claus-Dieter Hillenbrand, Gerhard Kuhn |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250054940
|
|
|
|
|
|
| Zusammenfassung |
| The potentially unstable parts of the West Antarctic Ice Sheet contain enough water to raise
global sea levels by ~3.3 metres were it to be discharged rapidly into the oceans. Of this,
approximately one third is frozen into the ice within the Amundsen Sea sector, which is
considered one of the most vulnerable drainage systems in the ice sheet today. Recent
dynamic thinning and grounding-line recession in the Amundsen Sea’s glaciers have
suggested the sector may be on the verge of a rapid phase of ice retreat, but it is
unclear whether current changes are unprecedented or simply reflect a short-term
deviation from the ice sheet’s long-term retreat trajectory. To test this hypothesis it is
necessary to establish the maximum extent of ice during the last glaciation, the
timing and pattern of its subsequent retreat, and the controls on the dynamics of past
flow.
Here, multibeam swath bathymetry, sub-bottom profiler, and sediment core data are used
to establish constraints on the flow and retreat history of major palaeo-ice streams that carried
the combined discharge from two parts of the Amundsen Sea sector: (1) the area now
occupied by the Pine Island and Thwaites glacier basins, in the east; and (2) the region of the
Dotson-Getz ice shelves, in the west.
Sets of highly-elongated bedforms show that, at the Last Glacial Maximum, major
palaeo-ice streams flowed along several prominent cross-shelf troughs. In the east the
grounding line advanced to within ~68 km of, and probably reached the shelf edge, while
in the west ice covered the entire middle shelf, and we assume reached the shelf
break also. For the Pine Island-Thwaites Ice Stream, minimum ice-thickness is
estimated at 715 m on the outer shelf, and we estimate a minimum ice discharge of
~108 km3 yr-1 assuming velocities similar to today’s Pine Island Glacier (~2.5 km
yr-1). Additional bedforms observed in a trough northwest of Pine Island Bay are
interpreted to have formed via diachronous ice-flows across the outer shelf, and
demonstrate switching ice-stream behaviour. In the west, mapping of bedforms shows
an equally dynamic ice sheet with a shelf geomorphology imprinted by multiple
phases of ice flow indicating a complex former ice-basal regime. In addition, the
pattern and geometry of bedforms imply strong geological controls upon both the
relict bed signature, and the processes facilitating fast-flow within the ancient ice
sheet.
The style of ice-retreat in the Pine Island-Thwaites system is evident in five mapped
grounding zone wedges, which suggest episodic deglaciation characterised by halts in
grounding-line migration up-trough. Stillstands occurred in association with changes in
ice-bed gradient, and phases of inferred rapid retreat correlate to higher bed-slopes,
supporting theoretical studies that show bed geometry as a control on ice-margin recession. A
new, detailed radiocarbon chronological dataset for the Dotson-Getz system generally
supports a stepped deglaciation of the Amundsen Sea Embayment, highlighting variable rates
of ice retreat through the Late Quaternary-to-Holocene with increased rates of retreat across
deep inner shelf basins. However, maximum rates of retreat from the Holocene to the present
day are found to be orders of magnitude lower than late 20th Century grounding-line
recession of Pine Island Glacier, suggesting that present rapid deglaciation of the sector is
driven by recent effects rather than being a continued response to past changes. |
|
|
|
|
|
|