Seafloor evidence for palaeo‐ice streaming and calving of the grounded Irish Sea Ice Stream: Implications for the interpretation of its final deglaciation phase

Abstract

High resolution swath bathymetry data reveal a previously glaciated submarine terrain 20 km offshore Anglesey, north Wales, UK. The detailed documentation of remarkably well‐preserved subglacial and ice‐marginal bedforms provides evidence for a grounded part of the Irish Sea Ice Stream in a phase of deglaciation. The observed ribbed moraines, drumlins, flutes and eskers indicate a converging ice flow to the west, which then turns south into the deeper central Irish Sea Basin. Using the relative position of the bedforms, their spatial distribution and the morphological resemblance with bedforms described in the literature, this subglacial terrain is interpreted as representing a transition zone of frozen to thawed bed conditions during deglaciation, with an eastwards migrating thawing front that partly altered the edge of the surveyed ribbed moraine field by drumlinization. The abundant De Geer moraines and iceberg scour marks superimposed on drumlins and flutes reveal that the final retreat of the grounded ice margin in the surveyed area terminated into a water‐mass with extensive iceberg calving. As the glacial terrain is well preserved, no significant burial has taken place, either by glacially or terrestrially derived sediment. The strong tidal currents at present keep the submarine terrain swept clean of contemporary sediment cover.

Glacial sediment and landform record offshore NW Scotland: a fjord–shelf–slope transect through a Late Quaternary mid-latitude ice-stream system

“…The depth and width of ploughmarks are consistent with those seen at other mid-latitude palaeo-ice sheet margins (e.g. van Landeghem et al 2009). Their narrow water-depth distribution (70-90 m) and absence below 150 m indicates relatively large but uniform icebergs, whilst their state of preservation (not glacially modified) implies a relatively late (MIS-2) formation date.…”

Periglacial disruption and subsequent glacitectonic deformation of bedrock: an example from Anglesey, North Wales, UK

“…Geomorphological mapping of part of the offshore area to the north of Anglesey (Van Landeghem et al, 2009) has shown that a comparable suite of glacigenic landforms occur beneath this part of the Irish Sea. Phillips et al (2010) demonstrated that changes in the morphology, orientation and distribution of the subglacial landforms on Anglesey closely matches the underlying bedrock, concluding that bedrock geology potentially played an important role in controlling the relative velocity of the overriding Irish Sea Ice.…”

Bedrock controls on subglacial landform distribution and geomorphological processes: Evidence from the Late Devensian Irish Sea Ice Stream

“…The polyphase deformation histories recorded by these often complex sedimentary successions have been equated with repeated phases of readvance during retreat of a highly dynamic ice sheet margin (Thomas and Chiverrell, 2007). Recently, swath bathymetry data has revealed that subglacial and ice-marginal landform systems associated with the Irish Sea Ice Stream are locally well-preserved offshore of Anglesey, providing evidence for the grounding of the ice sheet during deglaciation (van Landeghem et al, 2008(van Landeghem et al, , 2009.…”