scholarly journals Assessment of historical changes (1959-2012) and the causes of recent break-ups of the Petersen ice shelf, Nunavut, Canada

2015 ◽  
Vol 56 (69) ◽  
pp. 65-76 ◽  
Author(s):  
Adrienne White ◽  
Luke Copland ◽  
Derek Mueller ◽  
Wesley Van Wychen
Keyword(s):  
Loss Rate ◽  
Open Water ◽  
Shelf Area ◽  
Ice Shelf ◽  
Pack Ice ◽  
The Mean ◽  
Landfast Sea Ice ◽  
Ice Pressure ◽  
Ground Penetrating ◽  
Thickness Measurements

AbstractAerial photography and satellite imagery of the Petersen ice shelf, Nunavut, Canada, from 1959 to 2012 show that it was stable until June 2005, after which a series of major calving events in the summers of 2005, 2008, 2011 and 2012 resulted in the loss of ∼61% of the June 2005 ice-shelf area. This recent series of calving events was initiated by the loss of extensive regions of ˃50-year-old multi-year landfast sea ice from the front of the ice shelf in summer 2005. Each subsequent calving event has been preceded by open-water conditions and resulting loss of pack-ice pressure across the front of the ice shelf, and most occurred during record warm summers. Ground-penetrating radar (GPR) ice thickness measurements and RADARSAT-2 derived observations of surface motion indicate that tributary glaciers provided total ice input of 1.19-5.65 Mta–1 to the ice shelf from 2011 to 2012, far below the mean surface loss rate of 28.45 Mta–1. With recent losses due to calving and little evidence for current basal freeze-on, this suggests that the Petersen ice shelf will no longer exist by the 2040s, or sooner if further major calving events occur.

scholarly journals Albedo of the ice covered Weddell and Bellingshausen Seas

2012 ◽  
Vol 6 (2) ◽  
pp. 479-491 ◽  
Author(s):  
A. I. Weiss ◽  
J. C. King ◽  
T. A. Lachlan-Cope ◽  
R. S. Ladkin
Keyword(s):  
Sea Ice ◽  
Surface Albedo ◽  
Austral Summer ◽  
Open Water ◽  
Weddell Sea ◽  
First Year ◽  
Pack Ice ◽  
Bellingshausen Sea ◽  
The Mean ◽  
The Antarctic

Abstract. This study investigates the surface albedo of the sea ice areas adjacent to the Antarctic Peninsula during the austral summer. Aircraft measurements of the surface albedo, which were conducted in the sea ice areas of the Weddell and Bellingshausen Seas show significant differences between these two regions. The averaged surface albedo varied between 0.13 and 0.81. The ice cover of the Bellingshausen Sea consisted mainly of first year ice and the sea surface showed an averaged sea ice albedo of αi = 0.64 ± 0.2 (± standard deviation). The mean sea ice albedo of the pack ice area in the western Weddell Sea was αi = 0.75 ± 0.05. In the southern Weddell Sea, where new, young sea ice prevailed, a mean albedo value of αi = 0.38 ± 0.08 was observed. Relatively warm open water and thin, newly formed ice had the lowest albedo values, whereas relatively cold and snow covered pack ice had the highest albedo values. All sea ice areas consisted of a mixture of a large range of different sea ice types. An investigation of commonly used parameterizations of albedo as a function of surface temperature in the Weddell and Bellingshausen Sea ice areas showed that the albedo parameterizations do not work well for areas with new, young ice.

Low phytoplankton biomass and ice algal blooms in the Weddell Sea during the ice-filled summer of 1997

2002 ◽  
Vol 14 (3) ◽  
pp. 231-243 ◽  
Author(s):  
ELSE N. HEGSETH ◽  
CECILIE H. VON QUILLFELDT
Keyword(s):  
Algal Blooms ◽  
Phytoplankton Bloom ◽  
Open Water ◽  
Weddell Sea ◽  
Ice Algae ◽  
Ice Shelf ◽  
Growth Season ◽  
Pack Ice ◽  
Phaeocystis Antarctica ◽  
Upper Mixed Layer

The summer of 1997 was characterized by unusually large amounts of pack ice in the southeastern Weddell Sea, and less than 10% of the area that is commonly ice-free in summer was open. A modest phytoplankton bloom developed in the upper mixed layer in the northernmost area (72°S). The bloom peaked in mid-February with max chlorophyll concentrations of 1.5 μg l−1, and integrated stocks of 55–60 mg m−2. Autotrophic flagellates dominated the biomass (80–90% of the chlorophyll) at first, while diatoms increased relative to flagellates during the bloom. Nutrient deficits, however, indicated that a much larger biomass was produced than was observed. Freezing starting after mid-February probably terminated the bloom, resulting in a pelagic growth season limited in time (less than two months) and space. The sea ice had a distinct brown layer of algae, usually at 1–2 m depth, with average chlorophyll biomass of 10.3 mg m−2. The ice cover exhibited a substantial amount of ridges, with ice algae growing in cavities and other structures, but with lower biomass than in the bands. Ice algae were also found growing on the lower 2 m of the ice shelf (visible at low tide). The overall growth season in the ice lasted several months, and ice algal production may have exceeded pelagic production in the Weddell Sea during the growth season of 1997. Pennate diatoms, like Fragilariopsis curta and F. cylindrus, dominated both in ice and in open water above the pycnocline, while Phaeocystis antarctica dominated in deeper layers and in crack pools. Euphausiids, particularly young stages, were frequently observed grazing on ice algae in ridges and on all sides of the floes, (confirmed by the gut content). Ice algae would thus have served as an ample food supply for the krill in the summer of 1997.

scholarly journals Debris characteristics and ice-shelf dynamics in the ablation region of the McMurdo Ice Shelf, Antarctica

2006 ◽  
Vol 52 (177) ◽  
pp. 223-234 ◽  
Author(s):  
Neil Glasser ◽  
Becky Goodsell ◽  
Luke Copland ◽  
Wendy Lawson
Keyword(s):  
Ross Sea ◽  
Ice Shelf ◽  
Low Velocity ◽  
Flow Forming ◽  
Ice Shelves ◽  
Surface Ablation ◽  
Debris Transport ◽  
Shelf Dynamics ◽  
Ground Penetrating ◽  
Thickness Measurements

AbstractThis paper presents observations and measurements of debris characteristics and ice-shelf dynamics in the ablation region of the McMurdo Ice Shelf in the Ross Sea sector of Antarctica. Ice-shelf surface processes and dynamics are inferred from a combination of sedimentological descriptions, ground-penetrating radar investigations and through ablation, velocity and ice-thickness measurements. Field data show that in the study area the ice shelf moves relatively slowly (1.5–18.3ma–1), has high ablation rates (43–441 mm during 2003/04 summer) and is thin (6–22 m). The majority of debris on the ice shelf was originally transported into the area by a large and dynamic ice-sheet/ice-shelf system at the Last Glacial Maximum. This debris is concentrated on the ice-shelf surface and is continually redistributed by surface ablation (creating an ice-cored landscape of large debris-rich mounds), ice-shelf flow (forming medial moraines) and meltwater streams (locally reworking material and redistributing it across the ice-shelf surface). A conceptual model for supraglacial debris transport by contemporary Antarctic ice shelves is presented, which emphasizes these links between debris supply, surface ablation and ice-shelf motion. Low-velocity ice shelves such as the McMurdo Ice Shelf can maintain and sequester a debris load for thousands of years, providing a mechanism by which ice shelves can accumulate sufficient debris to contribute to sediment deposition in the oceans.

scholarly journals Calculation of glacier volume from sparse ice-thickness data, applied to Schaufelferner, Austria

2009 ◽  
Vol 55 (191) ◽  
pp. 453-460 ◽  
Author(s):  
Andrea Fischer
Keyword(s):  
Ice Thickness ◽  
Volume Loss ◽  
Glacier Inventory ◽  
Ice Volume ◽  
Digital Elevation ◽  
The Mean ◽  
Ground Penetrating ◽  
Thickness Measurements ◽  
Scaling Algorithms

AbstractIn order to develop and evaluate a method for the determination of glacier volume from ice-thickness data, the volume of Schaufelferner, Austria, is calculated (1) by manual interpolation of ground-penetrating radar (GPR) data based on measurements at 36 locations in 1995, (2) by manual interpolation of 144 GPR measurements acquired for a higher-resolution estimate in 2003 and 2006, (3) by multiplying the mean of the measured ice-thickness data by the glacier area, (4) by automatic kriging of the 1995 GPR data and (5) by application of area/volume scaling algorithms to the Austrian glacier inventory data of 1969, 1997 and 2006. The so determined glacier volumes are compared with the ice-volume changes calculated from digital elevation models (DEMs) of the Austrian glacier inventories. The manually interpolated volumes based on the 1995 and 2003/06 GPR data yielded a volume loss only slightly different from volume loss calculated from the glacier inventories of 1997 and 2007. Other methods were not able to reproduce the volume losses of the glacier inventory DEMs. To assess the accuracy of deriving ice-thickness changes with GPR, repeated ice-thickness measurements at the same locations were carried out between 2005 and 2008.

Evidence for an Antarctic winter coastal polynya

1993 ◽  
Vol 5 (2) ◽  
pp. 221-226 ◽  
Author(s):  
P. S. Anderson
Keyword(s):  
Meteorological Data ◽  
Open Water ◽  
Supporting Evidence ◽  
Austral Winter ◽  
Ice Shelf ◽  
The North ◽  
Pack Ice ◽  
Coastal Polynya ◽  
Infra Red ◽  
Meteorological Observations

Satellite infra-red imagery and meteorological data suggest the presence of winter open water (polynya) in the coastal pack ice to the north and west of the Brunt Ice Shelf. Satellite imagery, although only available for a limited number of occasions, provides evidence for the polynya during the austral winter of 1991. Indirect meteorological observations from the British Antarctic Survey's Halley station (75° 36′S, 26° 42′W) provide very strong supporting evidence of open water to the west of the ice shelf in previous years.

Observations on the Quaternary geology around Nioghalvfjerdsfjorden, eastern North Greenland

1999 ◽  
pp. 56-60
Author(s):  
Ole Bennike ◽  
Anker Weidick
Keyword(s):  
Late Summer ◽  
Open Water ◽  
Quaternary Geology ◽  
Mean Annual Precipitation ◽  
Outlet Glacier ◽  
Ice Caps ◽  
North East ◽  
Pack Ice ◽  
Lake Deposits ◽  
North Greenland

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Bennike, O., & Weidick, A. (1999). Observations on the Quaternary geology around Nioghalvfjerdsfjorden, eastern North Greenland. Geology of Greenland Survey Bulletin, 183, 56-60. https://doi.org/10.34194/ggub.v183.5205 _______________ In North and North-East Greenland, several of the outlet glaciers from the Inland Ice have long, floating tongues (Higgins 1991). Nioghalvfjerdsfjorden (Fig. 1) is today occupied by a floating outlet glacier that is about 60 km long, and the fjord is surrounded by dissected plateaux with broad valleys (Thomsen et al. 1997). The offshore shelf to the east of Nioghalvfjerdsfjorden is unusually broad, up to 300 km wide (Cherkis & Vogt 1994), and recently small low islands were discovered on the western part of this shelf (G. Budeus and T.I.H. Andersson, personal communications 1998). Quaternary deposits are widespread around Nioghalvfjerdsfjorden and include glacial, glaciofluvial, marine, deltaic and ice lake deposits. Ice margin features such as kame deposits and moraines are also common (Davies 1972). The glaciation limit increases from 200 m a.s.l. over the eastern coastal islands to 1000 m in the inland areas; local ice caps and valley glaciers are common in the region, although the mean annual precipitation is only about 200 mm per year. Most of the sea in the area is covered by permanent sea ice, with pack ice further east, but open water is present in late summer in some fjords north of Nioghalvfjerdsfjorden, and in the Nordøstvandet polynia.

scholarly journals Sensitivity of Pine Island Glacier, West Antarctica, to changes in ice-shelf and basal conditions: a model study

2002 ◽  
Vol 48 (163) ◽  
pp. 552-558 ◽  
Author(s):  
Marjorie Schmeltz ◽  
Eric Rignot ◽  
Todd K. Dupont ◽  
Douglas R. MacAyeal
Keyword(s):  
Shear Stress ◽  
Element Model ◽  
Shelf Area ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Stream ◽  
Model Study ◽  
Grounding Line ◽  
Glacier Velocity ◽  
Basal Shear

AbstractWe use a finite-element model of coupled ice-stream/ice-shelf flow to study the sensitivity of Pine Island Glacier, West Antarctica, to changes in ice-shelf and basal conditions. By tuning a softening coefficient of the ice along the glacier margins, and a basal friction coefficient controlling the distribution of basal shear stress underneath the ice stream, we are able to match model velocity to that observed with interferometric synthetic aperture radar (InSAR). We use the model to investigate the effect of small perturbations on ice flow. We find that a 5.5–13% reduction in our initial ice-shelf area increases the glacier velocity by 3.5–10% at the grounding line. The removal of the entire ice shelf increases the grounding-line velocity by > 70%. The changes in velocity associated with ice-shelf reduction are felt several tens of km inland. Alternatively, a 5% reduction in basal shear stress increases the glacier velocity by 13% at the grounding line. By contrast, softening of the glacier side margins would have to be increased a lot more to produce a comparable change in ice velocity. Hence, both the ice-shelf buttressing and the basal shear stress contribute significant resistance to the flow of Pine Island Glacier.

Ground-penetrating radar profiles of the McMurdo Shear Zone, Antarctica, acquired with an unmanned rover: Interpretation of crevasses, fractures, and folds within firn and marine ice

Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. WA21-WA34 ◽  
Author(s):  
Steven A. Arcone ◽  
James H. Lever ◽  
Laura E. Ray ◽  
Benjamin S. Walker ◽  
Gordon Hamilton ◽  
...  
Keyword(s):  
Shear Zone ◽  
Ground Penetrating Radar ◽  
Ice Accretion ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ross Ice Shelf ◽  
Robotic Vehicle ◽  
Ground Penetrating ◽  
Depth Ranges ◽  
Radar Antennas

The crevassed firn of the McMurdo shear zone (SZ) within the Ross Ice Shelf may also contain crevasses deep within its meteoric and marine ice, but the surface crevassing prevents ordinary vehicle access to investigate its structure geophysically. We used a lightweight robotic vehicle to tow 200- and 400-MHz ground-penetrating radar antennas simultaneously along 100 parallel transects over a [Formula: see text] grid spanning the SZ width. Transects were generally orthogonal to the ice flow. Total firn and meteoric ice thickness was approximately 160 m. Firn crevasses profiled at 400 MHz were up to 16 m wide, under snow bridges up to 10 m thick, and with strikes near 35°–40° to the transect direction. From the top down, 200-MHz profiles revealed firn diffractions originating to a depth of approximately 40 m, no discernible structure within the meteoric ice, a discontinuous transitional horizon, and at least 20 m of stratified marine ice; 28–31 m of freeboard found more marine ice exists. Based on 10 consecutive transects covering approximately [Formula: see text], we preliminarily interpreted the transitional horizon to be a thin saline layer, and marine ice hyperbolic diffractions and reflections to be responses to localized fractures, and crevasses filled with unstratified marine ice, all at strikes from 27° to 50°. We preliminarily interpreted off-nadir, marine ice horizons to be responses to linear and folded faults, similar to some in firn. The coinciding and synchronously folded areas of fractured firn and marine ice suggested that the visibly unstructured meteoric ice beneath our grid was also fractured, but either never crevassed, crevassed and sutured without marine ice inclusions, or that any ice containing crevasses might have eroded before marine ice accretion. We will test these interpretations with analysis of all transects and by extending our grid and increasing our depth ranges.

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