Glacial geomorphology of terrestrial- terminating fast flow lobes/ice stream margins in the southwest Laurentide Ice Sheet

Glacial geomorphological mapping of southern Alberta, Canada, reveals landform assemblages that are diagnostic of terrestrial-terminating ice streams/fast flowing outlet glaciers with lobate snouts. Spatial variability in features that comprise the landform assemblages reflects changes in (a) palaeo-ice stream activity (switch on/off); and (b) snout basal thermal regimes associated with climate sensitive, steady state flow. Palaeo-ice stream tracks reveal distinct inset sequences of fan-shaped flowsets indicative of receding lobate ice stream margins. Former ice lobe margins are demarcated by (a) major, often glacially overridden transverse moraine ridges, commonly comprising glacitectonically thrust bedrock; and (b) minor, closely spaced recessional push moraines and hummocky moraine arcs. Details of these landform types are well exhibited around the former southern margins of the Central Alberta Ice Stream, where larger scale, more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges (MTR types 1–3), hummocky terrain (HT types 1–3), flutings, and meltwater channels/spillways. The MTR type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined. The MTR type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts. The MTR type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain. The close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin, where the HT type 3 hummocks represent former ice-walled lake plains. The ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern Alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream/fast flow lobes of the southern Laurentide Ice Sheet, where alternate cold, polythermal, and temperate marginal conditions associated with climate sensitive, steady state flow sequentially gave way to more dynamic streaming and surging activity

Flow and retreat of the Late Quaternary Pine Island-Thwaites palaeo-ice stream, West Antarctica

Multibeam swath bathymetry and sub-bottom profiler data are used to establish constraints on the flow and retreat history of a major palaeo-ice stream that carried the combined discharge from the parts of the West Antarctic Ice Sheet now occupied by the Pine Island and Thwaites glacier basins. Sets of highly elongated bedforms show that, at the last glacial maximum, the route of the Pine Island-Thwaites palaeo-ice stream arced north-northeast following a prominent cross-shelf trough. In this area, the grounding line advanced to within similar to 68 km of, and probably reached, the shelf edge. Minimum ice thickness is estimated at 715 m on the outer shelf, and we estimate a minimum ice discharge of similar to 108 km(3) yr(-1) assuming velocities similar to today's Pine Island glacier (similar to 2.5 km yr(-1)). Additional bed forms observed in a trough northwest of Pine Island Bay likely formed via diachronous ice flows across the outer shelf and demonstrate switching ice stream behavior. The "style" of ice retreat is also evident in five grounding zone wedges, which suggest episodic deglaciation characterized by halts in grounding line migration up-trough. Stillstands occurred in association with changes in ice bed gradient, and phases of inferred rapid retreat correlate to higher bed slopes, supporting theoretical studies that show bed geometry as a control on ice margin recession. However, estimates that individual wedges could have formed within several centuries still imply a relatively rapid overall retreat. Our findings show that the ice stream channeled a substantial fraction of West Antarctica's discharge in the past, just as the Pine Island and Thwaites glaciers do today

The sedimentary legacy of a palaeo-ice stream on the shelf of the southern Bellingshausen Sea: Clues to West Antarctic glacial history during the Late Quaternary

A major trough ("Belgica Trough") eroded by a palaeo-ice stream crosses the continental shelf of the southern Bellingshausen Sea (West Antarctica) and is associated with a trough mouth fan ("Belgica TMF") on the adjacent continental slope. Previous marine geophysical and geological studies investigated the bathymetry and geomorphology of Belgica Trough and Belgica TMF, erosional and depositional processes associated with bedform formation, and the temporal and spatial changes in clay mineral provenance of subglacial and glaciomarine sediments. Here, we present multi-proxy data from sediment cores recovered from the shelf and uppermost slope in the southern Bellingshausen Sea and reconstruct the ice-sheet history since the last glacial maximum (LGM) in this poorly studied area of West Antarctica. We combined new data (physical properties, sedimentary structures, geochemical and grain-size data) with published data (shear strength, clay mineral assemblages) to refine a previous facies classification for the sediments. The multi-proxy approach allowed us to distinguish four main facies types and to assign them to the following depositional settings: 1) subglacial, 2) proximal grounding-line, 3) distal sub-ice shelf/sub-sea ice, and 4) seasonal open-marine. In the seasonal open-marine fades we found evidence for episodic current-induced winnowing of near-seabed sediments on the middle to outer shelf and at the uppermost slope during the late Holocene. In addition, we obtained data on excess Pb-210 activity at three core sites and 44 AMS C-14 dates from the acid-insoluble fraction of organic matter (AIO) and calcareous (micro-) fossils, respectively, at 12 sites. These chronological data enabled us to reconstruct, for the first time, the timing of the last advance and retreat of the West Antarctic Ice Sheet (WAIS) and the Antarctic Peninsula Ice Sheet (APIS) in the southern Bellingshausen Sea. We used the down-core variability in sediment provenance inferred from clay mineral changes to identify the most reliable AIO C-14 ages for ice-sheet retreat. The palaeo-ice stream advanced through Belgica Trough after similar to 36.0 corrected C-14 ka before present (B.P.). It retreated from the outer shelf at similar to 25.5 ka B.P, the middle shelf at similar to 19.8 ka B.P., the inner shelf in Eltanin Bay at similar to 12.3 ka B.P., and the inner shelf in Ronne Entrance at similar to 6.3 ka B.P. The retreat of the WAIS and APIS occurred slowly and stepwise, and may still be in progress. This dynamical ice-sheet behaviour has to be taken into account for the interpretation of recent and the prediction of future mass-balance changes in the study area. The glacial history of the southern Bellingshausen Sea is unique when compared to other regions in West Antarctica, but some open questions regarding its chronology need to be addressed by future work. (C) 2010 Elsevier Ltd. All rights reserved

Submarine glacial-landform distribution along an Antarctic Peninsula palaeo-ice stream: A shelf-slope transect through the Marguerite Trough system (66-70° S)

The Antarctic Peninsula comprises a thin spine of mountains and islands presently covered by an ice sheet up to 500 m thick that drains eastwards and westwards via outlet glaciers (Davies et al. 2012). Recently, the Peninsula has undergone rapid warming, resulting in the collapse of fringing ice shelves and the retreat, thinning and acceleration of marine-terminating outlet glaciers (e.g. Pritchard & Vaughan 2007). At the Last Glacial Maximum (LGM), the ice sheet expanded to the continental-shelf break around the Peninsula, and was organised into a series of ice streams that drained along cross-shelf bathymetric troughs (Ó Cofaigh et al. 2014). Marguerite Bay is located on the west side of the Antarctic Peninsula, at about 66° to 70° S (Fig. 1). A 12–80 km wide and 370 km long trough extends across the bay from the northern terminus of George VI Ice Shelf to the continental shelf edge. Extensive marine-geophysical surveys of the trough reveal a suite of glacial landforms which record past flow of an ice stream, which extended to the shelf edge at, or shortly after, the LGM. Subsequent retreat of the ice stream was underway by ~14 kyr ago and proceeded rapidly to the mid-shelf, where it slowed before accelerating once again to the inner shelf at ~9 kyr (Kilfeather et al. 2011).This is the author accepted manuscript. The final version is available from the Geological Society of London via https://doi.org/10.1144/M46.18

Micheál Ó Conghaile: Scribhneoir Cumasach Dásachtach

ls scríbhneoir conspóideach dásachtach é Micheál Ó Conghaile. Is follas go bhfuil cuspóir faoi leith aige ina chuid scríbhneoireachta nuair a dhéantar scagadh ar na saothair dhifriúla a scríobh sé idir dhrámaí, úrscéalta, agus ghearrscéalta. Is é sin tuiscint agus aird an léilheora a dhíriú ar chruachás mionlach sa tsochaí. Feicfear coimhlint go minie idir cruachás carachtair amháin sna scéalta agus an tsochaí ina maireann na carachtair sin. I gcuid mhaith de na scéalta is aonaráin iad na príomhcharachtair agus nil cuid mhór den tsochaí ina maireann siad in ann iad a thuiscint. Cothaítear conspóid sna scéalta mar thoradh ar an íogaireacht agus ar an macántacht a thaispeánann roinnt de na carachtair. Feicfear gur tréith stile ag an gConghaileach é na sonraí is pearsanta de chuid na gcarachtar a nochtadh ar mhodh luairisciúil don léitheoir. Léiríonn an Conghaileach cumas agus máistreacht a cheirde sa chaoi a bhfuil sé in ann bá an léitheora a mhúscailt agus a chothú le cruachás na gcarachtar úd agus is minie a spreagtar fíorspéis an léitheora, dar üom. I gCaibidil a hAon ba mhaith liom díriú isteach ar fhéiniúlacht na gcarachtar i gcomhthéacs na bhfadhbanna inmheánacha a bhíonn acu. Féachfar ar an mbealach atá acu chun déileáil lena gcás féin, agus ar na bealaí atá acu chun déileáil leis an tsochaí mórthimpeall orthu. An cuspóir a chuir mé romham i gCaibidil a Dó ná féachaint ar an tslí a bhíuil an Conghaileach conspóideach agus dúshlánach, fiú, ina chuid scríbhneoireachta. Tabharfar faoi deara go bhíuil sé conspóideach sa chaoi a gcuireann sé smaointe na gcarachtar ó thaobh na hEaglaise Caitlicí i láthair chomh maith leis an gcaoi a gcuirtear a gcuid mianta collai i láthair. I gCaibidil a Tri beifear ag féachaint ar an éigiall sa dá chnuasach gearrscéalta is deireanaí uaidh. Is iad sin An Fear A Phléasc (1997) agus An Fear Nach nDéanann 5 Gáire (2003). Feicfear an claonadh scéalaíochta céanna maidir leis an gcoimhlint idir carachtar amháin agus an tsochai ina maireann sé/si ann agus thairis sin, feicfear bua na cumadóireachta, an tsamhlaiocht chruthaitheach agus an greann ag teacht chun cinn go mór sna scéalta taitneamliacha úd. Feicfear an Conghaileach ag éirí nios muinini ina chuid scribhneoireachta sna slite éagsúla ina mbaineann sé leas as an éigiall sna scéalta. Tá féidearthachtaí aimsithe aige nach raibh aige cheana féin agus ar ndóigh, scríbhneoir níos críochnúla agus níos bisiúla is ea é dà bharr. Is i an chonclúid a bhainimse as mo chuid anailise ar shaolhar an mhórscríbhneora seo ná gur scríbhneoir comhaimsearlha, cumasach, dásachtach é Micheál Ó Conghaile sa chaoi a bhfuil sé in ann na tuairimí agus na gníomhaíochtaí is príobháidí agus is íogaire dá chuid carachtar a nochtadh go neamhbhalbh don léitheoir agus san am céanna tuiscint an léitheora a dhíriú agus a chothú ar chás na gcarachtar úd. Is cuma cén seanrá ina scríobhann sé feictear an tslí éifeachtach ala ag an scríbhneoir seo chun déileáil leis na fadhbarma conspóideacha atá ag roinnt mhaith dá chuid carachtar. Tabharfar faoi deara go n-éiríonn an Conghaileach níos turgnamhaí le himeacht na mblianta ionas go bhfeictear meascán iontach den éigiall agus den réalachas sna scéalta ina bhfuil a shamhlaíocht chruthaitheach ag teacht chun cinn go mór

Micheál Ó Conghaile: Scribhneoir Cumasach Dásachtach

ls scríbhneoir conspóideach dásachtach é Micheál Ó Conghaile. Is follas go bhfuil cuspóir faoi leith aige ina chuid scríbhneoireachta nuair a dhéantar scagadh ar na saothair dhifriúla a scríobh sé idir dhrámaí, úrscéalta, agus ghearrscéalta. Is é sin tuiscint agus aird an léilheora a dhíriú ar chruachás mionlach sa tsochaí. Feicfear coimhlint go minie idir cruachás carachtair amháin sna scéalta agus an tsochaí ina maireann na carachtair sin. I gcuid mhaith de na scéalta is aonaráin iad na príomhcharachtair agus nil cuid mhór den tsochaí ina maireann siad in ann iad a thuiscint. Cothaítear conspóid sna scéalta mar thoradh ar an íogaireacht agus ar an macántacht a thaispeánann roinnt de na carachtair. Feicfear gur tréith stile ag an gConghaileach é na sonraí is pearsanta de chuid na gcarachtar a nochtadh ar mhodh luairisciúil don léitheoir. Léiríonn an Conghaileach cumas agus máistreacht a cheirde sa chaoi a bhfuil sé in ann bá an léitheora a mhúscailt agus a chothú le cruachás na gcarachtar úd agus is minie a spreagtar fíorspéis an léitheora, dar üom. I gCaibidil a hAon ba mhaith liom díriú isteach ar fhéiniúlacht na gcarachtar i gcomhthéacs na bhfadhbanna inmheánacha a bhíonn acu. Féachfar ar an mbealach atá acu chun déileáil lena gcás féin, agus ar na bealaí atá acu chun déileáil leis an tsochaí mórthimpeall orthu. An cuspóir a chuir mé romham i gCaibidil a Dó ná féachaint ar an tslí a bhíuil an Conghaileach conspóideach agus dúshlánach, fiú, ina chuid scríbhneoireachta. Tabharfar faoi deara go bhíuil sé conspóideach sa chaoi a gcuireann sé smaointe na gcarachtar ó thaobh na hEaglaise Caitlicí i láthair chomh maith leis an gcaoi a gcuirtear a gcuid mianta collai i láthair. I gCaibidil a Tri beifear ag féachaint ar an éigiall sa dá chnuasach gearrscéalta is deireanaí uaidh. Is iad sin An Fear A Phléasc (1997) agus An Fear Nach nDéanann 5 Gáire (2003). Feicfear an claonadh scéalaíochta céanna maidir leis an gcoimhlint idir carachtar amháin agus an tsochai ina maireann sé/si ann agus thairis sin, feicfear bua na cumadóireachta, an tsamhlaiocht chruthaitheach agus an greann ag teacht chun cinn go mór sna scéalta taitneamliacha úd. Feicfear an Conghaileach ag éirí nios muinini ina chuid scribhneoireachta sna slite éagsúla ina mbaineann sé leas as an éigiall sna scéalta. Tá féidearthachtaí aimsithe aige nach raibh aige cheana féin agus ar ndóigh, scríbhneoir níos críochnúla agus níos bisiúla is ea é dà bharr. Is i an chonclúid a bhainimse as mo chuid anailise ar shaolhar an mhórscríbhneora seo ná gur scríbhneoir comhaimsearlha, cumasach, dásachtach é Micheál Ó Conghaile sa chaoi a bhfuil sé in ann na tuairimí agus na gníomhaíochtaí is príobháidí agus is íogaire dá chuid carachtar a nochtadh go neamhbhalbh don léitheoir agus san am céanna tuiscint an léitheora a dhíriú agus a chothú ar chás na gcarachtar úd. Is cuma cén seanrá ina scríobhann sé feictear an tslí éifeachtach ala ag an scríbhneoir seo chun déileáil leis na fadhbarma conspóideacha atá ag roinnt mhaith dá chuid carachtar. Tabharfar faoi deara go n-éiríonn an Conghaileach níos turgnamhaí le himeacht na mblianta ionas go bhfeictear meascán iontach den éigiall agus den réalachas sna scéalta ina bhfuil a shamhlaíocht chruthaitheach ag teacht chun cinn go mór

Continental slope records indicate a grounded ice sheet margin during past glacials, South Shetland Trench, Antarctica

The South Shetland Trench (SST) is located around 100 km northwest, and parallel to, the South Shetland Islands, located between the Antarctic Peninsula and South America. Although a number of studies examining glacial history have been undertaken in the Bransfield Strait located between the South Shetland Islands and the Antarctic Peninsula to the south, the authors believe this is the first study of the seafloor glacial geomorphology, and recent glacial history of the SST. This paper presents the results from a Eurofleets2 expedition to the SST that took place in December 2015. There is evidence from other sub-Antarctic islands such as the South Orkney Islands and Elephant Island for glaciations that extended well onto their continental shelves although a lack of age constraint from marine cores means it cannot be tied to a specific glaciation. Multibeam echosounder data reveal the study area on the southern flank of the South Shetland Trench to host a system of linear downslope gullies and glacigenic debris flows. Downslope gullies have been observed on other glaciated margins such as the Scotian slope offshore Canada, Ross Sea Antarctica, north-western Barents Sea and West Shetland Margin offshore north-western UK. The gullies are inferred as being eroded by turbidity currents comprising cold, dense, sediment-rich meltwater released from an ice front located at or near the continental shelf break. Glacigenic debris flows are found to extend from the continental shelf break to the lower continental slope. Sub-bottom profiler data penetrated up to 150ms below seafloor in places and reveal a stacked sequence of debris flows suggestive of a fluctuating ice front that was grounded to, and retreated from, the shelf break on several occasions. The trench floor appears to be devoid of major geomorphological features as revealed by the multibeam echosounder data and comprise a relatively well layered sequence imaged by the sub-bottom profiler. In addition 3 gravity cores up to 2.79 m in length and one core catcher sample were recovered from the study area. The cores will be analysed on their return to the UK and combined with the acoustic data to produce a shallow geological model specifically looking at the fluctuating ice margin located north of the South Shetland Islands