Bjerkreim Late-glacial

Published: 29 November 2022| Version 1 | DOI: 10.17632/vxs9xswjgz.1
Aage Paus


The following shows our findings and conclusions of the work Bjerkreim was deglaciated around 16 ka BP. Estimated July mean temperatures 12-13℃ in Bølling, 9℃ in Older Dyas, between 9.5 and 11℃ in Allerød, between 6.5 and 9℃ in Younger Dryas, and 11.5 – 12.5℃ in the early Holocene. The chronology is based on the Vedde Ash and Saksunarvatn ash beds, chronohorizons of well-defined climatic boundaries, and AMS 14C-dated remains of terrestrial plants, chironomids, and Cladocera. Dominant vegetation was open pioneer vegetation in pre-Bølling, dwarf shrubs and snow-beds in Bølling, shrubs and open birch-forests in Allerød, snow beds in Younger Dryas, and Betula/Populus/Corylus-forests in the early Holocene. Elm and oak were probably present regionally around 11 ka BP. Through macrofossil finds, we present the first evidence of the LG presence of tree-birch in Norway. Its sparse presence in Bølling with temperatures well above the requirements for birch-forest development shows that factors such as shallow soils and drought restricted tree-birch growth. The Empetrum expansions in Rogaland with a lag towards the east (mid-Bølling vs early Allerød), reflect the development of acid humus-soils controlled by an erosion/outwash gradient decreasing towards the east. Compared to other LG studies in N Europe, the coastal position of Rogaland with surplus access of moisture/water, facilitated the early formation of dwarf-shrub heath. The three interstadial cooling events (Older Dryas/GI-1d, G1-1c2, GI-1b/Gerzensee) are distinctly signaled in the pollen and lithostratigraphical records as small-scale parallels to YD, showing the ecotonal position of Bjerkreim with low resilience to these changes. A tentative effort to distinguish local pollen from long-distance pollen from the continental N-Europe include comparison of plants present temperature demands vs estimated palaeotemperatures, and pollen records in SW Norway vs those in continental N-Europe. We also assess the high ecological variation of LG habitats at Bjerkreim, and plant features such as ecology, pollen production and dispersal capacities. Based on these considerations, we assume that Populus tremula, Fagopyrum, Hippohaë rhamnoides, Jasione montana, Alisma plantago-aquatica, Hedysarum hedysaroides, Sanguisorba officinalis, and S. minor belonged to the LG vegetation of Norway. This must be confirmed by macrofossils and/or DNA. The presence of the North Sea Continent/Doggerland was crucial for the rapid immigration of species into SW Norway.


Steps to reproduce

The Sumpamyra sediments were retrieved using a 110 mm Livingstone piston corer. The sediment profile was described (Troels-Smith, 1955) and percentage loss-on-ignition (LOI) at 550 ℃ was measured at 1-2 cm intervals. Colour image of the core sections is documented using the digital line-scan camera on the Cox ITRAX core scanner. Pollen samples were treated with HF and acetolysed according to Fægri and Iversen (1989) and Lycopodium tablets added to the samples (1 cm3) for estimates of concentration and influx (Stockmarr, 1971). Identifications were based on Fægri and Iversen (1989), Moore et al. (1991), and Punt et al. (1976-1996), in combination with a reference collection of modern pollen. Betula nana pollen was distinguished in selected levels using pollen morphological criteria (Terasmäe, 1951). Chironomid samples were prepared following Brooks et al. (2007). Chironomid larval head capsules were identified with reference to Brooks et al. (2007) and Wiederholm (1983) and the chironomid reference collection at the Natural History Museum, London, UK. Mean July air temperature estimates were derived from the square-root transformed fossil chironomid percentage abundance data using a modern Norwegian chironomid-based temperature calibration dataset expanded from Brooks and Birks (2001). Eight samples consisting of terrestrial plant remains, chironomids and Cladocera, were dated using the AMS 14C method


Universitetet i Bergen


Vegetation Succession, Paleomagnetism, Paleoclimate, Chironomids, Pollen, Paleoecology