Coastal lake records add constraints to the age and magnitude of the Younger Dryas ice‐front oscillation along the Skagerrak coastline in southern Norway

Abstract

Basal records from nine lake basins, located within a small area inside the Younger Dryas Ra moraine in southern Norway, were analysed and radiocarbon dated. Six reworked shell fragments from the lowermost facies in five different basins date to the Bølling–Allerød chronozone and are interpreted to represent an ice‐free coastline before a Younger Dryas ice sheet readvance of at least 8 km. The widespread shell fragments within the Younger Dryas ice margin but pre‐dating the Younger Dryas are demonstrated using a systematic survey of the lowermost strata in a collection of lake basins. A further 13 dated samples, mostly in situ articulated bivalves found in clayey silt overlying the basal facies, yielded overlapping ages close to the Younger Dryas–Holocene boundary. The 13 shell dates, along with two additional similar ages obtained on terrestrial plant macrofossils from basal strata in two basins near the marine limit, provide a minimum‐limiting age of 11.6k cal a BP for ice sheet retreat from the Ra moraine. This suggests that the ice sheet in south‐east Norway retreated from its Younger Dryas maximum position nearly a thousand years later than previously assumed. Similar systematic approaches may lead to improved ice sheet reconstructions from other formerly glaciated coastlines.

Palaeolake sediment records reveal a mid‐ to late Younger Dryas ice‐sheet maximum in Mid‐Norway

“…Also, a recent study from southern Norway (Romundset et al . 2019) yielded new age constraints on the YD ice‐sheet extent that are compatible with the above‐mentioned studies from western Norway. An equivalent late YD glacial event in Mid‐Norway – termed the Hoklingen event (Fig.…”

“…11.6 ka (Romundset et al . 2019) respectively, the latter contrasting with a purported early YD age for the YD ‘Ra Moraines’ in the outer Oslofjord region (Andersen et al . 1995b; Fig.…”

On the timing of retreat of the Loch Lomond (‘Younger Dryas’) Readvance icefield in the SW Scottish Highlands and its wider significance

“…A late GS-1 readvance of ice is not only suggested for Scotland, for some glaciers in parts of western and south-western Norway also readvanced at this time (Bondevik and Mangerud, 2012;Mangerud et al, 2016) while rapid retreat of the ice sheet in western Norway and from the Ra Moraine in the Skagerrak area did not commence until ~11.6 ka (Mangerud et al, 2019;Romundset et al, 2019). Ice growth also continued after the onset of the Holocene in some parts of Svalbard (Farnsworth et al, 2018).…”

Timing the Emergence and Development of Arable Farming in Southeastern Norway by Using Summed Probability Distribution of Radiocarbon Dates and a Bayesian Age Model

“…There has been a continuous postglacial land upheaval around the Oslo fjord, and during the mid-and late Holocene, increasingly more land was exposed. The situation is different for the southernmost part where a mid-Holocene transgression occurred between 8500 and 7000 cal BP (Romundset et al 2015).…”

“…The Scandinavian Ice Shield covered most of the region until ca. 11,500 cal BP and the marine limit varies between 220 m and 5 m above present sea level (Bergstrøm 1999;Romundset et al 2019). There has been a continuous postglacial land upheaval around the Oslo fjord, and during the mid-and late Holocene, increasingly more land was exposed.…”