Quaternary oscillations of the BIIS (British and Irish Ice Sheet)

More and more information is appearing in the literature regarding the events of the Wolstonian - now regarded in some quarters as a more significant episode than the preceding Anglian glaciation.  But it was not a single cold episode -- rather, it was a succession of cold phases separated by slightly warmer interludes.  Isotope stages MIS 10 - 6 are nowadays assigned to the Wolstonian:

MIS8 -- moderate glacial (starting 300 ka)

MIS7 -- Aveley interstadial / interglacial (starting 243 ka)

MIS6 -- strong glacial (starting 191 ka)

It may well be that some of the cemented glacial deposits of West Wales date from MIS6, around 200 ka.

The Quaternary evolution and estimates of the maximum extent of the BIIS have been the subject of several studies (Knutz et al. 2007; Scourse et al. 2009, 2021; Thierens et al. 2012; Peters et al. 2015, 2016; Clark et al. 2022).  Despite this, the history of the BIIS is not as well known prior to the last glacial cycle (Gibbard et al. 2022).  After the Middle Pleistocene, at least three stable ice-sheet phases during different glacial periods covered Britain and Ireland, the Anglian Ice Sheet (MIS 12) (Toucanne et al. 2009), Wolstonian Ice Sheet (MIS 10–6) and the Devensian Ice Sheet (MIS 5d–MIS 2) (Lee et al. 2011) (Fig. 2, Table 1).  The Wolstonian BIIS (Fig. 2) spanned multiple glacial cycles from MIS 10–6 (Gibbard et al. 2022), and during its maximum, it expanded eastwards in the North Sea and combined with Drenthe glaciation in the Netherlands (Gibbard et al. 2009, 2022; Moreauet al. 2012). The detailed history of the Wolstonian BIIS inception, demise and the history of its older phases are not well known, including records from MIS 7d, an anomalous stadial event (Toucanne et al. 2009; Hughes et al. 2020) within the interglacial MIS7. The  last BIIS phase, known as the Devensian (MIS 5d–MIS 2; Fig. 2), has been studied extensively (Eynaud et al. 2007; Clark et al. 2012; Peters et al. 2016; Bradwell et al. 2021; Scourse et al. 2021). Its evolution between 30 000–15 000 years ago is chronicled in detail by the BRITICE-CHRONO project (Clark et al. 2022), but its pre-LGM history is not as well known due to the sparseness of associated terrestrial glacial deposits (Gibbard et al. 2022). Thus, looking at proximal marine sedimentary records is necessary to fill in the gaps of the BIIS chronicle, particularly those older than the last glaciation cycle.                                                                                                                                                                                                                             


from:
Fabian, S.G., Gallagher, S. J.& De Vleeschouwer, D. 2023 (October): British–Irish Ice Sheet and polar front historyof the Goban Spur, offshore southwest Ireland over the last 250 000 years. Boreas,Vol. 52, pp. 476–497. 

https://doi.org/10.1111/bor.12631. 

ISSN 0300-9483.

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In this evolving scheme, the Ipswichian interglacial begins around 130 ka, culminates around 124 ka and ends around 119 ka.  That's only 11,000 years for the span of the last interglacial -- and I'm not sure that many glacial geomorphologists would agree with that.  The period between 124,000 ka and 71 ka is classed by some specialists as "Early Devensian", while others incorporate that period of cool or cooling and oscillating climate into the Ipswichian Interglacial.  The mid Devensian interstadial is classed as lasting from 71 ka to 29 ka -- the latter date marking the onset of the Late Devensian "strong glacial" episode.   Not everybody will accept this chronology, although I am intrigued by the sequence of events proposed for the Early and Middle Devensian:

moderate interglacial >> moderate glacial >> moderate interglacial >> moderate glacial >> moderate glacial >> intermediate

That is, six identifiable phases of cool or cold climate in which glacier ice will have been present in certain parts of the British Isles while periglacial conditions persisted elsewhere.

In my doctorate thesis dated 1965 I proposed, on the basis of the varied slope breccias between the Ipswichian raised beach and the base of the Irish Sea till layer, that there were multiple climatic oscillations over a long period of time during the Early and Middle Devensian.  Abermawr was one of my key sites:

I interpreted the four distinct layers of "main head" or slope breccia as having been accumulated during many thousands of years of cold / permafrost / periglacial climate -- and I'm happy to see that this now seems to match the interpretations of the sediments on the shelf edge by Fabian et al in 2023.

See also:

https://brian-mountainman.blogspot.com/2023/12/gradually-ice-front-approaches.html

See  also:

Cristiana Giglio, Sara Benetti, Ruth M.K. Plets, Paul Dunlop, Colm Ó Cofaigh, Fabio Sacchetti, Elaine Salomon, 2022.  Character of advance and retreat of the southwest sector of the British-Irish Ice Sheet during the last glaciation, Quaternary Science Reviews, Volume 291, 2022, 107655,

ISSN 0277-3791,

https://doi.org/10.1016/j.quascirev.2022.107655.

(https://www.sciencedirect.com/science/article/pii/S0277379122002864)

Abstract: 

Relict landforms and sediments across former glaciated settings provide information about ice-sheet dynamics and can contribute to the understanding of the behaviour of contemporary ice masses, for which observations are limited in spatial and temporal extent. In this study, we focus on the shelf offshore southwest Ireland, in the Celtic Sea, which was once occupied by the Irish Sea Ice Stream (ISIS), the largest ice stream draining the southern portion of the marine-terminating British-Irish Ice Sheet (BIIS). Newly acquired high-resolution multibeam echosounder, sub-bottom and core data enabled the investigation of the shelf geomorphology and of the sedimentology and chronology of glacial and glacimarine sediments. A suite of drumlins records ice sheet flow from the coastline towards the central part of the shelf in southwest Ireland. Pre-existing highs in the seafloor topography promoted the formation of arcuate and transverse landforms interpreted as a grounding-zone wedge and moraines and they document episodic retreat of the ISIS across this portion of the shelf. Observed lithofacies show consolidated subglacial till and laminated fine muds. The sediments provide evidence of ice grounded ca. 30 km off the south-west Irish coastline with subsequent deglaciation occurring under glacimarine conditions. These new data refine the current reconstructions of the dynamics of the southern BIIS. They reveal for the first time the interplay of marine- and land-based ice and the presence of grounded ice offshore SW Ireland. This study highlights the importance of high-resolution data in revealing palaeo-landscapes as valuable analogues to test possible scenarios of modern ice sheet changes.