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Dangosydd eitem ddigidol (DOI)

  • Sarah Louise Callard
    Durham University
  • C. Ó Cofaigh
    Department of Geography, Durham University, Lower Mountjoy, South Road, Durham, DH1 3LE, UK
  • Sara Benetti
    School of Geography and Environmental Sciences, Ulster University, Coleraine, Londonderry, BT52 1SA, UK
  • R.C. Chiverrell
    Department of Geography and Planning, University of Liverpool, Liverpool, L69 3BX, UK
  • Katrien Van Landeghem
  • Margot Saher
  • Jenny Gales
    University of Plymouth, School of Biological and Marine Sciences, Drake Circus, Plymouth, PL4 8AA, UK
  • David Small
    Department of Geography, Durham University, Lower Mountjoy, South Road, Durham, DH1 3LE, UK
  • Chris Clark
    Department of Geography, Sheffield University, Sheffield, S10 2TN, UK
  • S.J. Livingstone
    Department of Geography, Sheffield University, Sheffield, S10 2TN, UK
  • Derek Fabel
    Scottish Universities Environmental Research Centre
  • Steven Moreton
    Natural Environment Research Council, Radiocarbon Facility, East Kilbride, Scotland, G75 OQF, UK
During the Last Glacial Maximum (LGM) the marine-terminating Barra Fan Ice Stream (BFIS), a major conduit of the British Irish Ice Sheet (BIIS), drained much of western Scotland and northwest Ireland with ice streaming onto the continental shelf of the Malin Sea. The extent and retreat history of this ice stream across the shelf, until now, is not well known. In particular, geochronological constraints on the history of this ice stream have thus far been restricted to deep-sea cores or terrestrial cosmogenic nuclide dating onshore, with ages across the shelf absent. To understand the possible external forcing factors acting on this marine terminating ice stream during retreat, improved geochronological constraint on its deglaciation is necessary. Here, we present new geophysical data, marine sediment cores and over forty radiocarbon dates to provide important constraints on maximum extent of the BFIS, as well as the timing and pattern of retreat back across the Malin Shelf. Dated moraines and grounding-zone wedges (GZW) seen in seafloor sub-bottom profiles provide evidence that the BFIS reached the Malin Shelf edge during the LGM and was at its maximum extent around 26.7 ka BP. The presence of two sets of GZWs suggests that the style of retreat was episodic. The new radiocarbon chronology shows that retreat from the shelf edge was underway by 25.9 ka BP, with the majority of the continental shelf ice free by 23.2 ka BP, and that glacimarine conditions were present in the Sea of Hebrides by 20.2 ka BP at the latest. Collectively, these results indicate that the majority of the Malin Shelf was free of grounded ice by ∼21.5–20 ka BP, which is up to 4000 years earlier than previously reconstructed. We attribute this early deglaciation to high relative sea level caused by glacial isostatic depression when the BIIS reached its maximum extent promoting ice shelf and grounding line instability. Two deep troughs, forming reverse bed slopes, aided the continued retreat of the BFIS. This suggests that local ice loading and bed morphology can be significant controls on the destabilisation of a marine-terminating ice stream and can override the influence of ocean and atmospheric temperatures.

Allweddeiriau

Iaith wreiddiolSaesneg
Tudalennau (o-i)280-302
CyfnodolynQuaternary Science Reviews
Dyddiad ar-lein cynnar26 Hyd 2018
Dynodwyr Gwrthrych Digidol (DOIs)
StatwsCyhoeddwyd - 1 Rhag 2018

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