Note-1 Deglaciation - climate instability
There is no detailed data regarding the paleoclimate of the Heart of Avalonia region during the years between the last glacial maximum and the commencement of the Holocene. However, there is good evidence that the climate records inferred from analysis of deep Greenland ice cores reflect climate conditions extending far beyond Greenland. In particular, it is accepted that Greenland climate records are well correlated with northern hemisphere climate fluctuations and even more strongly correlated with climate fluctuations over the North Atlantic.
There is a large difference between present-day average temperatures in south-eastern Newfoundland and present-day temperatures over the ice cap in central Greenland. Using a seasonal average temperature of 5 deg. C for the Avalon Peninsula and a seasonal average of -32 deg. C for the GISP2 (Greenland Ice Sheet Project 2) core extraction location in central Greenland, a 37 deg.C average temperature difference between the two locations is observed. The Avalon Peninsula is about 3000 km south of GISP2 and about 3 km lower in elevation.
The chart shown above presents a hypothetical temperature vs. time curve for the Avalon Peninsula during the deglaciation years extending from 15000 years ago to 11000 years ago. The curve comprises the GISP2 inferred temperature data augmented by a constant 37 deg. C. The deglaciation years were characterized by a degree of climate instability greatly exceeding any climate fluctuations seen during the Holocene. It is not clear why the deglaciation paleoclimate fluctuated so severely, although feedbacks associated with the deglaciation process itself may have played a role. Specifically the Younger Dryas cold interval (-12.9 kA to -11.7 kA) could have been caused by a cessation in the Atlantic meridional overturning circulation, this cessation resulting from rapid glacial runoff.
Intervals of abrupt climate change occurred during the deglaciation period. Ice core data from Greenland shows changes in mean annual temperature of the order of 10 deg. C occurring over decade-scale time frames.
The impact of climate instability on the erosion of glaciated bedrock is twofold. Firstly, rapid increases in temperature would accelerate melting of glaciers, potentially steepening ice slopes and increasing ice flow rates. Glaciers not already warm-based would become warm-based and would then move largely by basal slip, smoothing and streamlining bedrock landforms. During a rapid warming interval, bedrock would experience large decreases in glacial ice load and correspondingly significant elastic rebound as hydrostatic stress diminished (Note 4). Secondly, during a rapid cooling of the ambient climate, warm-based glaciers would convert to polythermal glaciers with the thinned edge regions frozen hard to the bedrock. Such freezing around the edges of steep-sloping glaciers could trap groundwater beneath cold ice, leading to conditions favorable to disruption of bedrock by hydraulic action and ice segregation. Trapped groundwater originating under thick ice at high elevation could cause hydraulic bedrock frost heave (Note 5) at locations of lower elevation sharing a common aquifer. Hydraulic bedrock frost heave features can develop under substantial glacial ice (Note 10).
Abundant bedrock frost heave of apparent hydraulic origin is observed on the Avalon Peninsula. The period of interest for generating this hydraulic bedrock frost heave is indicated in blue on the above chart. This time interval corresponds to the time during which cold deglaciation of parts of the Avalon Peninsula might have taken place. During the cold climate of the Younger Dryas interval, a concurrent lack of precipitation could account for downwasting of cold-based glaciers and the consequent unloading of frozen bedrock hosting pressurized groundwater. Alternatively, a sudden onset of severe climate warming with resultant rapid glacier surface melting could thin a cold-based glacier without substantially warming the base. In either case, migration of pressurized groundwater to a hard-frozen ice-bedrock interface would potentially cause development of the observed widespread bedrock frost heave and other ice-disrupted bedrock features. These features, caused mainly by ice segregation occurring in a subglacial environment, provide evidence of an unusual deglaciation process (cold deglaciation) having occurred on parts of the Avalon just prior to the Holocene. The features could also imply special permeability and porosity characteristics in the regionally metamorphosed rocks found on the Avalon Peninsula.
There is a large difference between present-day average temperatures in south-eastern Newfoundland and present-day temperatures over the ice cap in central Greenland. Using a seasonal average temperature of 5 deg. C for the Avalon Peninsula and a seasonal average of -32 deg. C for the GISP2 (Greenland Ice Sheet Project 2) core extraction location in central Greenland, a 37 deg.C average temperature difference between the two locations is observed. The Avalon Peninsula is about 3000 km south of GISP2 and about 3 km lower in elevation.
The chart shown above presents a hypothetical temperature vs. time curve for the Avalon Peninsula during the deglaciation years extending from 15000 years ago to 11000 years ago. The curve comprises the GISP2 inferred temperature data augmented by a constant 37 deg. C. The deglaciation years were characterized by a degree of climate instability greatly exceeding any climate fluctuations seen during the Holocene. It is not clear why the deglaciation paleoclimate fluctuated so severely, although feedbacks associated with the deglaciation process itself may have played a role. Specifically the Younger Dryas cold interval (-12.9 kA to -11.7 kA) could have been caused by a cessation in the Atlantic meridional overturning circulation, this cessation resulting from rapid glacial runoff.
Intervals of abrupt climate change occurred during the deglaciation period. Ice core data from Greenland shows changes in mean annual temperature of the order of 10 deg. C occurring over decade-scale time frames.
The impact of climate instability on the erosion of glaciated bedrock is twofold. Firstly, rapid increases in temperature would accelerate melting of glaciers, potentially steepening ice slopes and increasing ice flow rates. Glaciers not already warm-based would become warm-based and would then move largely by basal slip, smoothing and streamlining bedrock landforms. During a rapid warming interval, bedrock would experience large decreases in glacial ice load and correspondingly significant elastic rebound as hydrostatic stress diminished (Note 4). Secondly, during a rapid cooling of the ambient climate, warm-based glaciers would convert to polythermal glaciers with the thinned edge regions frozen hard to the bedrock. Such freezing around the edges of steep-sloping glaciers could trap groundwater beneath cold ice, leading to conditions favorable to disruption of bedrock by hydraulic action and ice segregation. Trapped groundwater originating under thick ice at high elevation could cause hydraulic bedrock frost heave (Note 5) at locations of lower elevation sharing a common aquifer. Hydraulic bedrock frost heave features can develop under substantial glacial ice (Note 10).
Abundant bedrock frost heave of apparent hydraulic origin is observed on the Avalon Peninsula. The period of interest for generating this hydraulic bedrock frost heave is indicated in blue on the above chart. This time interval corresponds to the time during which cold deglaciation of parts of the Avalon Peninsula might have taken place. During the cold climate of the Younger Dryas interval, a concurrent lack of precipitation could account for downwasting of cold-based glaciers and the consequent unloading of frozen bedrock hosting pressurized groundwater. Alternatively, a sudden onset of severe climate warming with resultant rapid glacier surface melting could thin a cold-based glacier without substantially warming the base. In either case, migration of pressurized groundwater to a hard-frozen ice-bedrock interface would potentially cause development of the observed widespread bedrock frost heave and other ice-disrupted bedrock features. These features, caused mainly by ice segregation occurring in a subglacial environment, provide evidence of an unusual deglaciation process (cold deglaciation) having occurred on parts of the Avalon just prior to the Holocene. The features could also imply special permeability and porosity characteristics in the regionally metamorphosed rocks found on the Avalon Peninsula.