25 research outputs found
Uncertainty in mass-balance trends derived from altimetry: a case study along the EGIG line, central Greenland
This is the author accepted manuscript. The final version is available from The International Glaciological Society via http://dx.doi.org/10.3189/2015JoG14J123AbstractRepeated measurements of density profiles and surface elevation along a 515 km traverse of the Greenland ice sheet are used to determine elevation change rates and the error in determining mass-balance trends from these rates which arises from short-term fluctuations in mass input, compaction and surface density. Mean values of this error, averaged over 100 km sections of the traverse, decrease with time from the start of observations in 2004, with a half-time of ∼4 years. After 7 years the mean error is less than the ice equivalent mass imbalance.This
project
is
a
contribution
to
the
calibration
and
validation
of
the
European
Space
Agency
(ESA)
CryoSat
satellite
altimeter
and
is
supported
by
ESA
and
by
the
UK
Natural
Environment
Research
Council
(NERC)
Consortium
grant
NER/O/S/2003/00620.
We
are
grateful
to
the
NERC
Geo-
physical
Equipment
Facility
and
the
University
of
Edinburgh
for
the
loan
of
Leica
GPS
systems.
Logistic
support
for
the
traverses
was
provided
by
CH2M
HILL
Polar
Services,
G.
Somers,
J.
Pailthorpe,
H.
Chamberlain,
M.
Hignell
and
J.
Sweeny
gave
invaluable
assistance
in
the
field
and
T.
Benham
provided
Figure
1.
Finally,
we
thank
R.
Arthern
for
useful
discussions
and
our
Scientific
Editor,
H.
Fricker,
and
two
anonymous
reviewers
for
helpful
comments
Techniques for measuring high-resolution firn density profiles: case study from Kongsvegen, Svalbard
Arctic sea surface height variability and change from satellite radar altimetry and GRACE, 2003-2014
Arctic sea surface height (SSH) is poorly observed by radar altimeters due to the poor coverage of the polar oceans provided by conventional altimeter missions and because large areas are perpetually covered by sea ice, requiring specialized data processing. We utilize SSH estimates from both the ice-covered and ice-free ocean to present monthly estimates of Arctic Dynamic Ocean Topography (DOT) from radar altimetry south of 81.5°N and combine this with GRACE ocean mass to estimate steric height. Our SSH and steric height estimates show good agreement with tide gauge records and geopotential height derived from Ice-Tethered Profilers. The large seasonal cycle of Arctic SSH (amplitude ∼5 cm) is dominated by seasonal steric height variation associated with seasonal freshwater fluxes, and peaks in October–November. Overall, the annual mean steric height increased by 2.2 ± 1.4 cm between 2003 and 2012 before falling to circa 2003 levels between 2012 and 2014 due to large reductions on the Siberian shelf seas. The total secular change in SSH between 2003 and 2014 is then dominated by a 2.1 ± 0.7 cm increase in ocean mass. We estimate that by 2010, the Beaufort Gyre had accumulated 4600 km3 of freshwater relative to the 2003–2006 mean. Doming of Arctic DOT in the Beaufort Sea is revealed by Empirical Orthogonal Function analysis to be concurrent with regional reductions in the Siberian Arctic. We estimate that the Siberian shelf seas lost ∼180 km3 of freshwater between 2003 and 2014, associated with an increase in annual mean salinity of 0.15 psu yr−1. Finally, ocean storage flux estimates from altimetry agree well with high-resolution model results, demonstrating the potential for altimetry to elucidate the Arctic hydrological cycle
Inland Thinning of Pine Island Glacier, West Antarctica
The Pine Island Glacier (PIG) transports 69 cubic kilometers of ice each year from ∼10% of the West Antarctic Ice Sheet (WAIS). It is possible that a retreat of the PIG may accelerate ice discharge from the WAIS interior. Satellite altimetry and interferometry show that the grounded PIG thinned by up to 1.6 meters per year between 1992 and 1999, affecting 150 kilometers of the inland glacier. The thinning cannot be explained by short-term variability in accumulation and must result from glacier dynamics
Subglacial melt channels and fracture in the floating part of Pine Island Glacier, Antarctica
A dense grid of ice-penetrating radar sections acquired over Pine Island Glacier, West Antarctica has revealed a network of sinuous subglacial channels, typically 500 m to 3 km wide, and up to 200 m high, in the ice-shelf base. These subglacial channels develop while the ice is floating and result from melting at the base of the ice shelf. Above the apex of most channels, the radar shows isolated reflections from within the ice shelf. Comparison of the radar data with acoustic data obtained using an autonomous submersible, confirms that these echoes arise from open basal crevasses 50–100 m wide aligned with the subglacial channels and penetrating up to 1/3 of the ice thickness. Analogous sets of surface crevasses appear on the ridges between the basal channels. We suggest that both sets of crevasses were formed during the melting of the subglacial channels as a response to vertical flexing of the ice shelf toward the hydrostatic condition. Finite element modeling of stresses produced after the formation of idealized basal channels indicates that the stresses generated have the correct pattern and, if the channels were formed sufficiently rapidly, would have sufficient magnitude to explain the formation of the observed basal and surface crevasse sets. We conclude that ice-shelf basal melting plays a role in determining patterns of surface and basal crevassing. Increased delivery of warm ocean water into the sub-ice shelf cavity may therefore cause not only thinning but also structural weakening of the ice shelf, perhaps, as a prelude to eventual collapse