Everything brief Flashcards
Introduction
Brief history (500,000…10,000, scouring)
Anglian Glaciation- 450 ka
Late Devensian- 27ka
‘Mid-Pleistocene Transition’
Lambek, 1995
Model observes sea level change to permit paleobathymetry and paleo shorelines to be predicted for the British Isles region, including the North Sea.
Sea level has risen due to the isostatic rebound from the glacial unloading of northern Britain and the meltwater loading of the adjacent seas.
The parameters for the glacio-hydro-isostatic model are observations of sea level change for this period describing:
- The effective lithospheric thickness or rigidity
- The effective mantle viscosity
- Certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum.
Key findings:
- Maximum emergence of the North Sea occured after glaciation had started and lasted for an extended period from about 15000 to 12000 years.
- Shoreline retreat across the North sea became relatively rapid after about 10,000 years.
Improvements: Discrepancies between observations and predictions suggest that the Lateglacial ice volumes north of the Great Glen and possibly over Ireland need to be increased.
Boulton and Hagdorn, 2006
Use numerical ice sheet modelling and geological evidence to explore relationships between ice sheet form, ice streaming and marginal lobe formation.
Identifies major dispersal centres and ice flow pathways.
Inputs conditions and forcing functions in order to cause the modelled ice sheet to behave in ways that mimic the geologically deduced real ice sheet.
A strong conclusion is the importance of major ice streams in controlling the form and flow of the ice sheet, the pattern of dispersal of indicator erratics and the patterns and rates of erosion, transport and deposition in time and space.
Due to spatial resolution fails to reconcile the temporal and spatial complexities of the glacial geomorphological evidence that documents regional ice sheet build up and decay.
Does not focus on flow directional changes associated with multiple ice dispersal centres but rather give the impression that ice flowed from relatively static domes such as that over western Scotland.
Bradwell et al., 2009
Model uses bathymetric data/ sea-bed imagery.
This allows for a viable pattern of ice-sheet disintegration.
Findings include:
- tunnel valleys in the northern North Sea Basin
- large moraines on the West Shetland Shelf
- at its maximum extent a grounded ice sheet flowed from SE to NW across the northern North Sea Basin, terminating at the continental-shelf edge.
Final-stage deglaciation was marked by near-shore ice streaming and increasing topographic control on ice-flow direction.
Retreat of the British Ice Sheet continued until 16 ka when, following the North Atlantic iceberg-discharge event (Heinrich-1), ice was situated at the present-day coastline in NW Scotland.
Hubbard et al., 2009
Numerical modelling procedure to see the effect of ice streams, model looks at changes of air temperature and grounding lines.
Findings include:
- A series of binge/purge, cycles are identified which correspond to alternating periods of relatively cold-based ice and wet-based ice.
- Phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate, resulting in major iceberg/melt discharge events into the North Sea and Atlantic Ocean.
Timeline:
∼20 ka- maximum extent with fast-flowing ice across its western and northern sectors that extended to the continental shelf edge
∼19 ka- deglaciation is achieved in less than 2000 years, discharging the freshwater equivalent of ∼2 m global sea-level rise.
∼ 17 ka- a much reduced ice sheet centred on Scotland undergoes subsequent retrenchment and a series of advance/retreat cycles into the North Sea Basin
∼ 13 to 11.5 ka- sustained Younger Dryas event
∼ 10.5 ka- Modelled ice cover is persistent across the Western and Central Highlands until the last remnant glaciers disappear
Boulton et al., 2010
Looked at the dynamics of ice streams of the biis particularly vale of york and discovered that they had a high effective pressure and so moved in almost a bouyant state displaying a fast velocity.
He therefore applied these theories to suggest the BIIS was very unstable during the late devensian and this is one of the factors that led to fast ice sheet loss.
Findings:
- The ice sheet lobe advanced to its maximum extent driven by a very low gravitational shear stress of about 5–8 kPa.
- As such large ice fluxes could not be sustained over the whole terminal zone of the ice sheet, such a high velocity must have been restricted to features such as the Vale of York lobe, which must therefore have acted as an ice stream. There is currently no evidence, however, whether this stream was ephemeral, the result of a surge event or was sustained for a longer period.
- The effective pressure at the base of the ice stream in its terminal zone was very low. The ice stream was therefore very close to a buoyant state.
- The subglacial drainage system was a self-organised system largely adapted to the seasonally varying pattern of surface water recharge to the bed.
Clark et al., 2012
Reconstructed BIIS from mapping paleoecological data in the BRITICE database alongside cosmic (imminence) dating to determine age maps of retreat in the UK between 27 and 15 ka BP.
Cosmogenic nuclide dating uses interactions between cosmic rays and nuclides in glacially eroded bedrock to provide age estimates.
Timeline:
27 ka- maximum extent
23 ka- ice ice withdrawing along N boundaries and advanced along southern
19 ka- widespread marine based ice loss in both North and Irish Se
17 ka- ice no longer marine- all terrestrial- Final collapse of all marine sectors occurred by 17 ka BP and with most margins beginning to back-step onshore.
There is a lack of understanding when the ice bridge of the UK-Norway collapsed.
