Sammendrag
Data from Dovre, central Norway, add new arguments to the discussion of when Scandinavia was deglaciated. From 650 cm organic sediments in Lake Finnsjøen (1260 m a.s.l.), 21 AMS-dates of plant macrofossils show a continuous record from 11300 cal. yrs BP up to present. XRF-analyses indicate annual varves, whereas plant sedimentary ancient DNA (sedaDNA), macrofossil- and pollen-analyses visualize the development from pioneer vegetation via forests to the present tundra.
Below the organic sediments, a 110 cm minerogenic layer contains a 3 cm basal clay/silt gyttja, followed by a 7 cm sand layer, a 70cm clay/silt layer with more than 200 laminae, and an uppermost homogenous 30 cm clay/silt layer.
The laminated clay/silt contains sparse amounts of well-preserved pollen (3-400 per cm3) of pioneers such as Papaver, Salix, and Artemisia cf. norvegica. sedaDNA shows the presence of Salicaceae and Asteraceae. In the uppermost clay/silt, pollen concentration doubles, birch and pine pollen distinctly rise, and Artemisia and grasses decline. These changes indicate, though 14C-dates are lacking, the onset of the Holocene. Hence, the laminated sequence below reflects at least 200 years of the closing of YD, if the laminations are annually deposited.
Well-preserved pollen from the basal gyttja shows abrupt changes from high total pollen concentrations (9 x 103 per cm3) with dominant pine, alder, and juniper to low conc. (500 per cm3) with dominant Artemisia and grasses. Most probably, this shows a hiatus formed when an early YD local cirque glacier established and prevented sediment deposition. The sand layer above may reflect rapid outwash when ice melted in late YD.
Dominant pollen of pine, alder, and juniper in the basal gyttja is identical to the LG interstadial (LGI) assemblages in the adjacent Lake Topptjønna and Lake Ristjønna (Paus et al. 2011). Ristjønna shows uninterrupted records from LGI to early Holocene, whereas the Topptjønna records extend back to pre LGI. Including the Finnsjøen data, a continuous record from pre LGI up to present can now be constructed at Dovre. So, Dovre was deglaciated earlier than LGI and stayed unglaciated thereafter, though local YD glaciers formed.
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