TY - JOUR

T1 - Bed erosion during fast ice streaming regulated the retreat dynamics of the Irish Sea Ice Stream.

AU - Van Landeghem, Katrien

AU - Chiverrell, Richard

PY - 2020/10/1

Y1 - 2020/10/1

N2 - Marine-terminating ice stream behaviour often defines the stability of ice sheets and is driven by a complex interplay of climatic, oceanic, topographic and glaciological factors. Here, we use new integrated high resolution, extensive (2100 km2) and continuous geophysical, sedimentological and geotechnical data to reconstruct past glacial environments during the Last Glacial Maximum from a well-preserved palaeo-landscape. The data is from the axial centre of the Irish Sea Ice Stream (ISIS), which drained > 17% of the former British-Irish Ice Sheet. Recent geochronological data of the palaeo-ISIS show a build-up and advance of ice to marine-terminating maximum limits in the southern Celtic Sea 27‒25 ka BP, followed by rapid ice margin retreat into the northern Irish Sea Basin (ISB) by 20.8 ± 0.7 ka BP. However, the flow dynamics in the central and axial bed of the ISIS through this timeframe are not well understood. Here, we use our new glacial landscape reconstruction to identify the spatial and temporal patterns of flow re-organisation and re-activations for the marine-terminating ISIS. From this we infer how ice streaming was driven by a variety of factors through advance, deglaciation and towards a temporary lift-off of ice from its bed and an ultimate demise. Overprinted subglacial bedforms with differing ice flow directions indicate an on/off behaviour to the ice-streaming, an increasing topographical influence and substantial realignment of ice flows. Subsurface geophysical data reveal the erosive capability of the ice stream through time, with a first erosive component in the formation of mega-scale glacial lineations leaving bedrock exposed at the ice stream bed. The depositional component of MSGL crest building occurred in the same ice-flow phase. Whilst the ice stream was laterally constricted in two locations, likely contributing to changes in ice margin retreat rates, we also propose that changes in basal drag associated with exposed bedrock at the ice‒bed interface influenced the retreat dynamics, particularly when this exposure was near the grounding zone. The wider implications of this work are that episodic and highly erosive ice streaming during ice advance and early retreat can change ice‒bed conditions radically and in turn influence glacial dynamics during later retreat episode, thus constituting a feedback process to be considered in modelling the dynamics of marine-terminating ice streams.

AB - Marine-terminating ice stream behaviour often defines the stability of ice sheets and is driven by a complex interplay of climatic, oceanic, topographic and glaciological factors. Here, we use new integrated high resolution, extensive (2100 km2) and continuous geophysical, sedimentological and geotechnical data to reconstruct past glacial environments during the Last Glacial Maximum from a well-preserved palaeo-landscape. The data is from the axial centre of the Irish Sea Ice Stream (ISIS), which drained > 17% of the former British-Irish Ice Sheet. Recent geochronological data of the palaeo-ISIS show a build-up and advance of ice to marine-terminating maximum limits in the southern Celtic Sea 27‒25 ka BP, followed by rapid ice margin retreat into the northern Irish Sea Basin (ISB) by 20.8 ± 0.7 ka BP. However, the flow dynamics in the central and axial bed of the ISIS through this timeframe are not well understood. Here, we use our new glacial landscape reconstruction to identify the spatial and temporal patterns of flow re-organisation and re-activations for the marine-terminating ISIS. From this we infer how ice streaming was driven by a variety of factors through advance, deglaciation and towards a temporary lift-off of ice from its bed and an ultimate demise. Overprinted subglacial bedforms with differing ice flow directions indicate an on/off behaviour to the ice-streaming, an increasing topographical influence and substantial realignment of ice flows. Subsurface geophysical data reveal the erosive capability of the ice stream through time, with a first erosive component in the formation of mega-scale glacial lineations leaving bedrock exposed at the ice stream bed. The depositional component of MSGL crest building occurred in the same ice-flow phase. Whilst the ice stream was laterally constricted in two locations, likely contributing to changes in ice margin retreat rates, we also propose that changes in basal drag associated with exposed bedrock at the ice‒bed interface influenced the retreat dynamics, particularly when this exposure was near the grounding zone. The wider implications of this work are that episodic and highly erosive ice streaming during ice advance and early retreat can change ice‒bed conditions radically and in turn influence glacial dynamics during later retreat episode, thus constituting a feedback process to be considered in modelling the dynamics of marine-terminating ice streams.

KW - Quaternary

KW - Glaciology (incl. palaeo-ice sheets)

KW - Europe

KW - Geomorphology, glacial

KW - Geophysics

KW - Subglacial Bedforms

KW - British-Irish Ice Sheet

KW - Palaeo-ice streaming

KW - Deglaciation

U2 - 10.1016/j.quascirev.2020.106526

DO - 10.1016/j.quascirev.2020.106526

M3 - Article

VL - 245

JO - Quaternary Science Reviews

JF - Quaternary Science Reviews

SN - 0277-3791

M1 - 106526

ER -