Search

Within the general trend of post-Eocene cooling, the largest and oldest outlet of the East Antarctic Ice Sheet underwent a change from ice-cliff to ice-stream and/or ice-shelf dynamics, with an associated switch from line-source to fan sedimentation. Available geological data reveal little about the causes of these changes in ice dynamics during the Miocene Epoch, or the subsequent effects on Pliocene-Pleistocene ice-sheet history. Icesheet numerical modeling reveals that bed morphology was probably responsible for driving changes in both ice-sheet extent and dynamics in the Lambert-Amery system at Prydz Bay. The modeling shows how the topography and bathymetry of the Lambert graben and Prydz Bay control ice-sheet extent and flow. The changes in bathymetric volume required for shelf-edge glaciation correlate well with the Prydz Channel fan sedimentation history. This suggests a negative feedback between erosion and glaciation, whereby the current graben is overdeepened to such an extent that shelf-edge glaciation is now not possible, even if a Last Glacial Maximum environment recurs. We conclude that the erosional history of the Lambert graben and Prydz Bay in combination with the uplift histories of the surrounding mountains are responsible for the evolution of this section of the East Antarctic Ice Sheet, once the necessary initial climatic conditions for glaciation were achieved at the start of the Oligocene Epoch. [ABSTRACT FROM AUTHOR]

Results from a numerical ice-sheet model were matched with geological evidence detailing the extent and timing of the Late Weichselian ice sheet in the Eurasian Arctic, through simple adjustments in the model’s environmental inputs. The numerical model predicts the spatial and temporal variation in (1) subglacial sediment transport and deposition, (2) rates of iceberg calving and (3) rates of supraglacial melting over the past 30 000 yr. The ice sheet is characterised by a series of ice streams occupying bathymetric troughs in the Barents Sea and west of Norway, which act as sources for glacial sediment build-up and iceberg production. Our model indicates that significant volumes of sediment are deposited over the Bear Island fan (3000 km3 in 12 000 yr), Franz Victoria Trough fan (500 km3 in 8000 yr) and a series of smaller fans west of Norway (which combine to yield 4000 km3 in 12 000 yr). The Norwegian Channel ice stream operated for only 4000 yr, during which time 400 km3 of sediments were deposited on the adjacent fan. The ice sheet experienced two major periods of iceberg production where the rate of calving increased by ∼50% at about 15 000 and 12 500 yr ago. However, the time-dependent response of iceberg calving to sea-level rise for individual ice streams is shown to be more complicated than the generalised ice-sheet response. The marine portions of the ice sheet decayed after 15 000 yr ago, resulting in several embayments at the mouths of bathymetric troughs. A second pulse of enhanced iceberg calving at 12 500 yr ago caused further decay of the marine ice sheet and the ice margin retreated back to the shorelines of island archipelagos in the northern Barents Sea. Ice loss through surface melting was restricted mostly to the southern margin of the ice sheet. [Copyright &y& Elsevier]

Abstract: Airborne radio-echo sounding (RES) data display layering within the Antarctic ice sheet. At ice depths below 1000 m these layers are caused by horizons of ice with relatively high acidity which were originally deposited on the ice surface after large volcanic events. Layering which is less than 1000 m from the ice surface can also be due to variation in ice density. Theoretically, therefore, internal RES layering below 1000 m should represent isochronous planes. This theory is upheld under examination of existing RES data where internal layers have been observed to follow the rules of superposition. For example, RES layers are deposited as discrete bands, fold and fault in a manner analogous to geological features, never cross over each other and, in an undisturbed deposit, have a depth?age relationship which means that the oldest layers are located at the lowest level. Moreover, the location of internal layering is independent of radiowave receiver altitude, the frequency of the radiowave does not affect layer depth, and the pulse width of the e/m wave does not affect identification of layers. Thus, RES reflects actual dielectric layering within the ice sheet. Glaciologists use RES layering for a number of reasons, including: (1) correlating ice cores; (2) as boundary conditions for numerical models to help determine the direction of ice flow; and (3) as a means of identifying the three-dimensional ice-sheet geometry and architecture. [ABSTRACT FROM AUTHOR]

Quaternary continental margin sedimentation in the Norwegian–Greenland Sea has been a response to a combination of tectonic, oceanographic, and glacial activity. Using geophysical survey data (6.5 kHz side-scan sonar and 3.5 kHz penetration echo sounding), in association with bathymetric datasets, the magnitude and frequency of the main forms of margin sedimentation into the Lofoten and Norwegian Basins of the Norwegian Sea during the Late Weichselian and Holocene are estimated. By comparing these geophysically determined estimates of sediment fluxes with numerically modelled ice-sheet sediment delivery, the role of ice-sheets in shaping the processes acting on this margin is assessed. Sediment flux at the shelf edge during the Late Quaternary is dominated by ice-sheet delivery of sediments, focused at the mouths of fast-flowing ice streams formed in bathymetric troughs. Interglacials are, by contrast, characterised by comparatively little sediment accumulation. Submarine fans, at the margins of cross-shelf troughs, are major depocentres on this glacier-influenced margin. However, occasional large-scale failures of the continental slope account for approximately 75% of the basin sediment accumulation during the past 30 000 yr, by eroding substantial quantities of pre-Quaternary deposits. Trough mouth fan and a combination of hemipelagic and glacimarine processes are responsible for the accumulation of the remaining 15% and 7% of basin sediments, respectively. [Copyright &y& Elsevier]

Abstract: We present a detailed analysis of bed roughness beneath Institute and Möller Ice Streams, west Antarctica, using radio-echo sounding data (RES) acquired in the austral summer of 2010/11. We assess roughness using a two-parameter approach and also assess the directionality of roughness relative to present-day ice flow. Our work highlights the wealth of additional information that resides in analyses of bed roughness. Employing these multiple approaches we show that spatially variable roughness patterns are partly a consequence of the ability of flowing ice not only to smooth the bed but also to redistribute and remove sediments, and to do this along-flow. Accordingly, we identify some fast-flow tributaries underlain by topography that has been streamlined and other tributaries that are underlain by sediments. We also identify locations that are currently protected from erosion, but where more ancient erosion may once have occurred. We conclude that detailed roughness analysis is a useful tool for landscape interpretation; and we suggest that the roughness of an ice-sheet's bed should be viewed not only as the consequence of ancient marine sedimentation, but also as a product of more contemporary erosion and redistribution of sediments, as well as bedrock-smoothing that is ongoing because of continuing dynamic activity. In this way, basal roughness has the potential to evolve continually with ice sheet form and flow, and should not be viewed simply as a snapshot of either present-day or palaeo-basal conditions. [Copyright &y& Elsevier]

The pattern of postglacial emergence in the Barents Sea is pivotal to constraining the timing of deglaciation and extent and thickness of the last ice sheet in northern Eurasia. This review unites records of Holocene relative sea level from Svalbard, Franz Josef Land, and Novaya Zemlya to better understand the geometries of past ice sheet loads. Emergence data from northern Eurasia confine the maximum area of glacier loading to the northwestern Barents Sea, where >100 m of emergence is measured on Kongsøya. Deglacial unloading commenced on western and northern Spitsbergen c. 13–12 14C ka ago, and by c. 10.5 14C ka on eastern Svalbard and more distal sites on Franz Josef Land and Novaya Zemlya. The marine limit phase (c. 13–12 14C ka) on western and northern Spitsbergen is characterized by the construction of spits indicating a dominance of long-shore drift over storm-generated fetch, reflecting extensive sea-ice coverage of coastal areas. At sites in proximity to the ice sheet margin on western and northern Spitsbergen there is evidence for a transgressive–regressive cycle c. 6–4 14C ka, possibly reflecting back migration of displaced mantle material. A modern transgression is inferred from the marine erosion of 17th century cultural features and 14C ages of whalebone and terrestrial peat buried by modern storm gravels that place sea level at its present position by c. 2 to 1 ka ago. The greatest observed emergence on Franz Josef Land occurs on Bell Island, with a marine limit at 49 m aht, formed c. >10 14C ka. Available emergence data since 9 ka show rising strandlines toward the southwest at ∼0.3 m/km. The northern limit of emergence on Franz Josef Land is poorly constrained because relative sea-level data is sparse north of 80°30′N. In contrast to Svalbard and Franz Josef Land, the marine limit on northern Novaya Zemlya is only 10–15 m above high tide and formed between 6.5 and 5.0 14C ka when global sea level was stabilizing. All sites show little apparent emergence during the past 2 ka, with the youngest raised landforms at identical heights to storm beaches. This minimal glacio-isostatic signature on Novaya Zemlya and on Vaygach Island, where deglaciation commenced >10 ka ago, indicates ice sheet thicknesses of <1.5 km. The spatial variation in emergence for the Barents Sea indicates that western and northern Spitsbergen and Novaya Zemlya were near the reactive margin of the ice sheet and these areas sustained the briefest ice coverage (2–6 ka) and were probably not in isostatic equilibrium. In contrast, central and eastern Svalbard and southern Franz Josef Land were beneath a substantial ice load and probably sustained this load for c. 10 14C ka and achieved isostatic equilibrium. Isostasy residual from an ice sheet model portrays well the general pattern of uplift and load response at the centre of ice sheets, but deviates substantial at the ice sheet margin or areas covered by thin ice, like Novaya Zemlya. [Copyright &y& Elsevier]