Pattern, style and timing of British-Irish Ice Sheet retreat: Shetland and northern North Sea sector

Bradwell, Tom, Small, David, Fabel, Derek, Clark, Chris D, Chiverrell, Richard C ORCID: 0000-0002-7307-2756, Saher, Margot H, Dove, Dayton, Callard, S Louise, Burke, Matthew J, Moreton, Steven G
et al (show 7 more authors) (2021) Pattern, style and timing of British-Irish Ice Sheet retreat: Shetland and northern North Sea sector. JOURNAL OF QUATERNARY SCIENCE, 36 (5). pp. 681-722.

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<jats:title>ABSTRACT</jats:title><jats:p>The offshore sector around Shetland remains one of the least well‐studied parts of the former British–Irish Ice Sheet with several long‐standing scientific issues unresolved. These key issues include (i) the dominance of a locally sourced ‘Shetland ice cap’ <jats:italic>vs</jats:italic> an invasive Fennoscandian Ice Sheet; (ii) the flow configuration and style of glaciation at the Last Glacial Maximum (i.e. terrestrial <jats:italic>vs</jats:italic> marine glaciation); (iii) the nature of confluence between the British–Irish and Fennoscandian Ice Sheets; (iv) the cause, style and rate of ice sheet separation; and (v) the wider implications of ice sheet uncoupling on the tempo of subsequent deglaciation. As part of the Britice‐Chrono project, we present new geological (seabed cores), geomorphological, marine geophysical and geochronological data from the northernmost sector of the last British–Irish Ice Sheet (north of 59.5°N) to address these questions. The study area covers ca. 95 000 km<jats:sup>2</jats:sup>, an area approximately the size of Ireland, and includes the islands of Shetland and the surrounding continental shelf, some of the continental slope, and the western margin of the Norwegian Channel. We collect and analyse data from onshore in Shetland and along key transects offshore, to establish the most coherent picture, so far, of former ice‐sheet deglaciation in this important sector. Alongside new seabed mapping and Quaternary sediment analysis, we use a multi‐proxy suite of new isotopic age assessments, including 32 cosmogenic‐nuclide exposure ages from glacially transported boulders and 35 radiocarbon dates from deglacial marine sediments, to develop a synoptic sector‐wide reconstruction combining strong onshore and offshore geological evidence with Bayesian chronosequence modelling. The results show widespread and significant spatial fluctuations in size, shape and flow configuration of an ice sheet/ice cap centred on, or to the east of, the Orkney–Shetland Platform, between ~30 and ~15 ka <jats:sc>BP.</jats:sc> At its maximum extent ca. 26–25 ka <jats:sc>BP</jats:sc>, this ice sheet was coalescent with the Fennoscandian Ice Sheet to the east. Between ~25 and 23 ka <jats:sc>BP</jats:sc> the ice sheet in this sector underwent a significant size reduction from ca. 85 000 to &lt;50 000 km<jats:sup>2</jats:sup>, accompanied by several ice‐margin oscillations. Soon after, connection was lost with the Fennoscandian Ice Sheet and a marine corridor opened to the east of Shetland. This triggered initial (and unstable) re‐growth of a glaciologically independent Shetland Ice Cap ca. 21–20 ka <jats:sc>BP</jats:sc> with a strong east–west asymmetry with respect to topography. Ice mass growth was followed by rapid collapse, from an area of ca. 45 000 km<jats:sup>2</jats:sup> to ca. 15 000 km<jats:sup>2</jats:sup> between 19 and 18 ka <jats:sc>BP</jats:sc>, stabilizing at ca. 2000 km<jats:sup>2</jats:sup> by ~17 ka <jats:sc>BP.</jats:sc> Final deglaciation of Shetland occurred ca. 17–15 ka <jats:sc>BP</jats:sc>, and may have involved one or more subsidiary ice centres on now‐submerged parts of the continental shelf. We suggest that the unusually dynamic behaviour of the northernmost sector of the British–Irish Ice Sheet between 21 and 18 ka <jats:sc>BP</jats:sc> – characterized by numerous extensive ice sheet/ice mass readvances, rapid loss and flow redistributions – was driven by significant changes in ice mass geometry, ice divide location and calving flux as the glaciologically independent ice cap adjusted to new boundary conditions. We propose that this dynamism was forced to a large degree by internal (glaciological) factors specific to the strongly marine‐influenced Shetland Ice Cap.</jats:p>

Item Type: Article
Uncontrolled Keywords: continental shelf, deglaciation, geochronology, ice sheet, Pleistocene
Depositing User: Symplectic Admin
Date Deposited: 12 Dec 2019 16:30
Last Modified: 04 Sep 2023 09:03
DOI: 10.1002/jqs.3163
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