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Quaternary International xxx (xxxx) xxx
Please cite this article as: Aage Paus, Quaternary International, https://doi.org/10.1016/j.quaint.2020.09.008
Available online 8 September 2020
1040-6182/© 2020 Elsevier Ltd and INQUA. All rights reserved.
Lake Heimtjønna at Dovre, Mid-Norway, reveals remarkable late-glacial
and Holocene sedimentary environments and the early establishment of
spruce (Picea abies), alder (Alnus cf. incana), and alpine plants with present
centric distributions
Aage Paus
Department of Biological Science, University of Bergen, Post Box 7803, Thormøhlens gate 53A, N-5020, Bergen, Norway
ARTICLE INFO
Keywords:
Alpine mid-Norway
Deglaciation
Late-glacial
Holocene
Sediment environment
Biogeography
Dating errors
Hiati
ABSTRACT
Two and a half meters of sediments from Lake Heimtjønna in the Scandes Mountains reveal changes in the
vegetation, climate, and sediment environment since deglaciation. The lake was deglaciated in the Late-Glacial
(LG), perhaps as early as 16-18 ka cal BP. After deglaciation, the sediment environment at the Heimtjønna coring
point was extraordinary and challenging to interpret. The genesis of the 1.7 m basal unsorted sediments
including large stones is discussed concluding that the layer was rafted by lake-ice after the LG deglaciation. The
Younger Dryas (YD) established a semi-perennial lake-ice that stopped the deposition of the ice-rafted stone-rich
sediments. In the early Holocene, the unstratied and well-sorted clayey silt shows uvial origin. In late Ho-
locene, strong ood activity including the major ood disaster ‘Stor-Ofsen’ in AD 1789, caused a sediment hiatus
at the coring point from ca 9.5 ka cal BP to ca 250 a cal BP. The LG interstadial warming initiated the succession
from pioneer plants on mineral soils towards local dwarf-shrub heath. July temperatures reached at least 7–8
O
C.
In the LG and early Holocene, Papaver radicatum, Artemisia norvegica, and Campanula cf. uniora today occurring
at Dovre and with centric Scandinavian distributions, locally established. All have previously been connected to
Weichselian survival on nunatak refugia. Continuous pollen curves of spruce (Picea abies) support the much-
debated LG and early Holocene presence of spruce in the Scandes mountains. For the rst time, it is shown
that both grey alder (Alnus incana) and Armeria occurred in the Scandes in the LG and early Holocene. Due to
dating errors, LG ages is exclusively based on stratigraphical correlations and considerations. The LG chronology
must be thoroughly tested by future studies providing reliable AMS
14
C-dates of terrestrial fossils.
1. Introduction
In Scandinavia, the thickness of the Weichselian ice, the time of the
deglaciation, and the migration and development of life during and after
deglaciation, have long been debated. The dominant view that one
massive central ice-dome totally covered Scandinavia during the Last
Glacial Maximum, and that the Scandes Mountains became ice-free in
the early Holocene (e.g. Andersen, 1981; Hughes et al., 2016; Stroeven
et al., 2016), is challenged by the view of a uctuating and thin
multi-domed ice-sheet and mountains becoming ice-free during the
Late-Glacial (Dahl et al., 1997; Lambeck et al., 1998, 2010; Kullman,
2008; Lane et al., 2020). Nunataks that remained ice-free throughout the
glacial have also been postulated (Nesje et al., 1988; Nesje, 1989) in line
with the theory of nunatak survival of plants during glacial periods (e.g.
Gjærevoll, 1963; Westergaard et al., 2019). In central Norway, Bøe et al.
(2007), Goehring et al. (2008), Marr et al. (2018), and Lane et al. (2020)
suggest that areas were ice-free from ca. 19–15 ka cal BP. However,
these ages are based on modelling and imprecise terrestrial cosmogenic
nuclide (TCN), optically stimulated luminescence (OSL) dates, and
Schmidt-hammer exposure-age dating. Radiocarbon dates of tree meg-
afossils in J¨
amtland (Kullman, 2008) support a Late Glacial (LG)
deglaciation of the Swedish Scandes from about 17 ka cal BP.
In order to test models on Weichselian ice thickness in central
Scandinavia, the time of deglaciation, and the immigration of ora and
fauna to newly deglaciated areas, the project WHENSED (Weichselian
and early Holocene environment and species establishment in the Dovre
mountains, mid-Norway) was initiated in 2004. The project included
multiproxy analyses of lake sediments at high elevations (1100–1300 m
E-mail address: aage.paus@uib.no.
Contents lists available at ScienceDirect
Quaternary International
journal homepage: www.elsevier.com/locate/quaint
https://doi.org/10.1016/j.quaint.2020.09.008
Received 26 June 2020; Received in revised form 2 September 2020; Accepted 4 September 2020
Quaternary International xxx (xxxx) xxx
2
a.s.l.). These lakes have the potential to signal an early deglaciation of
nunataks that formed during the down melting of the Weichselian ice.
Four adjacent lakes at Dovre were chosen for detailed multiproxy studies
(Paus et al., 2006, 2011; 2015, 2019; Paus, 2010). Although reliable
AMS-dates of terrestrial macrofossils could not be obtained, the bio- and
lithostratigraphy pointed to a LG emergence of nunataks and rapid
species immigration. This is reasonable as the study sites lie ca 20–30 km
proximal to the reconstructed and fragmented Younger Dryas (YD) end
moraines (Olsen et al., 2013), and that a YD glacier regrowth should be
expected as recorded elsewhere along the Scandinavian ice margin. In
line with this, distinct hiati in the sediments of two Dovre lakes indicated
that YD glaciers/ice caps of restricted sizes reformed and covered the
lakes preventing sedimentation though without removing the underly-
ing interstadial sediments (Paus et al., 2015).
In the present study, palaeoecological results are presented from the
sediments of Lake Heimtjønna (1200 m a.s.l.). The lake is adjacent to Mt.
Knutshø (Fig. 1) which is renowned for its well-developed and species-
rich ora that includes plants of so-called centric distributions in Scan-
dinavia. Based on these phytogeographical features, the “in situ glacial
survival” theory was formulated (Blytt, 1882; Sernander, 1896). The
Heimtjønna studies were initiated in 2008 but abandoned due to inter-
pretative problems regarding sedimentation, chronology, and pollen
stratigraphy. However, later analyses from other WHENSED lakes (Paus,
2010; Paus et al., 2011, 2015) increased the experience and
Fig. 1. Maps of the study area with characteristic site names. The small map in the middle shows the Dovre area with Heimtjønna (black square) and the Flåfattjønna
site (black circle) studied by Paus et al. (2006). The map to the left shows the position of Heimtjønna and the mountain ridge where Ristjønna, Finnsjøen, and
Topptjønna are located (Paus et al., 2011, 2015). The map to the right shows elevations in m a.s.l. (white numbers). The black ring marks the coring site. The outlet
and main inlet of Lake Heimtjønna are shown.
Table 1
The Heimtjønna lake sediment lithology.
Depth (cm) Description (Troels-Smith, 1955) Colour Comments
1332–1333 Ld
3
3, Ag1, Ga+Brown, nig.3 Minerogenic gyttja, sharply delimited below
1333–1333.2 Ga2, Ag1, As1, Ld
0
+Brown, nig.2 Sand with clay/silt
1333.2–1334 Ld
0
1, As1, Ag1, Ga1 Light-brown,
nig.1+
Sandy clay/silt-gyttja
1334-1338 As1, Ag1, Ga2, Ld
0
+Brown, nig.2 Brown sand shining from minerogenic particles, three narrow clay bands (nig.1) at 1334.5, 1336.5,
and 1337.5 cm depth.
1338-1350 As2, Ag2, Ld
0
+Yellow-brown,
nig.1+
Clay/silt with ca 20 brown and narrow sand lamina <0.5 cm; two 0.5 cm thick sand lenses at 1340
and 1344 cm depth
1350–1410 As1, Ag3, Ga+Grey, nig.2 Clayey silt. Clasts of sand found in the upper part in one of the two parallel cores
1410–1581 Gg (maj.) 2, Gg (min.) 1, Gs1, Ga+,
Ag+, As+
Grey, nig.2+Unsorted clay, silt, sand, stones (<11 cm)
A. Paus
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understanding of the deglacial environments at Dovre. For that reason,
the Heimtjønna studies was resumed. Though the position of the
Heimtjønna coring point appears not to be optimal, and the presented
data involve hiati/incomplete sedimentation and lack of dating preci-
sion, the results reveal after all new knowledge of the late-glacial/early
Holocene sedimentation and the local establishment of the earliest
pioneer plants. Furthermore, I have experienced among scientists many
similar problematic results that are put into the drawer and never
published, even if the data contain items of interest. By publishing and
sharing the experience of problematic data, this can represent warnings
and learning of how to avoid the problems but also provide new insights
of and possible solutions to the problems.
2. Regional setting
Lake Heimtjønna (1100 ×630 m, 0.44 km
2
) is situated in a depres-
sion at 1200 m a.s.l. between the Knutshø mountains (1690 m a.s.l.) and
Mount Heimtjønnshøa (1555 m a.s.l.) in Trøndelag County (Fig. 1). The
surrounding mountains delimit a catchment of 10.1 km
2
. The main inlet
is located in the northern end of the lake, whereas other smaller inlets
are situated on the western bank (one inlet) and in the southern end of
the lake (three inlets).
The area surrounding Heimtjønna is situated within the upper low-
alpine zone with lichen-dominated dwarf-shrub tundra including
Empetrum, Vaccinium spp., and Betula nana. The calciphilous Dryas
octopetala, Potentilla crantzii, Pulsatilla vernalis, Saxifraga oppositifolia,
and Salix polaris occur, and Juniperus and Salix shrubs are found in
protected sites.
The regional climate is continental with July and January mean
temperatures of ca. 7.5–8 ◦C and −11 ◦C, respectively and an annual
precipitation of 450 mm. The temperatures are estimated using data
from the nearest climate stations at Kongsvold and Fokstugu (DNMI,
2020), assuming a lapse rate of 0.6 ◦C/100 m (Laaksonen, 1976). The
regional forest-line of Betula pubescens is situated at about 1050–1100 m
a.s.l. In continental areas, the forest-line roughly follows the 10 ◦C July T
isotherm (Odland, 1996).
The bedrock consists of the metamorphic greenschist, greenstone,
garben schist, and amphibolite (NGU, 2020). Presence of
lime-demanding plants (see above) shows that carbonates occur in
bedrock and/or local tills. Adjacent areas are assumed to have been
deglaciated around 18–15 ka cal BP (Paus et al., 2006, 2015; Bøe et al.,
2007; Goehring et al., 2008; Lane et al., 2020), though YD ice caps
re-established in areas of favourable conditions for snow/ice accumu-
lation (Paus et al., 2015). On the other hand, glacial lineations have been
interpreted to reect northeastern and northwestern ows of regional
ice in the early YD and late YD, respectively (Follestad, 2005; Follestad
and Fredin, 2007). Furthermore, glacial deposits within the Heimtjønna
catchment have been mapped (NGU, 2020).
3. Material and methods
3.1. Sampling and lithostratigraphy
Lake sediments were retrieved using a 110 mm piston corer (Nesje,
1992) at maximum water depth (13.3 m) by coring from the 0.9 m thick
winter-ice. The coring point (UTM 32V 0538 258 6 910 458) is situated
halfway between the shore and the lake centre and ca. 200 m SE of the
main inlet (Fig. 1). Two parallel cores were sampled of which one core
included the topmost sediments. Sediments were described (Troels--
Smith, 1955, Table 1), and the organic content was estimated at 0.5–1
cm intervals by measuring percentage loss-on-ignition (LOI) at 550 ◦C.
3.2. Pollen
Samples were treated with HF and acetolysed according to Fægri and
Iversen (1989). Lycopodium tablets were added to the samples (1 cm
3
)
Table 2
Results of the eight
14
C-dates from Heimtjønna. Calibrated ages (Stuiver et al., 2020) show probabilities within two sigma. Median value in brackets.
Sediment type Lab. ref. Depth cm Date Uncal. Cal. Age BP 2 SD δ
13
C ‰ Dating material
mg C dated type and weight
Minerogenic gyttja Ua-44734 1332–1333 237 ±30 147-422 (282) −27.5 Leaves and/or seeds of Betula nana, Cerastium, Dryas, Salix polaris (68 mg)
Laminated sand ETH-46616 1334-1338 983 ±38 767-930 (880) −29.6 0.81 Very fragmented remains of leaves, stems, twigs (2.8 mg)
Silt/clay ETH-74321 1370-1375 9636 ±28 10,860-11175 (10,959) −26 0.33 Salix polaris leaves (0.9 mg)
Coarsely minerogenic with large stones ≤11 cm ETH-75471 1400–1410 5769 ±61 6432-6717 (6569) −27.4 Fragmented stems and leaves (0.5 mg)
ETH-75470 1420–1430 9199 ±89 10,215-10581 (10,380 −22.4 Unidentied fragments of leaves and stem (0.9 mg)
ETH-74320 1440–1460 18,274 ±49 21,919-22338 (22,146) −22 0.28 Unidentied fragments of leaves and stem, including wood (0.9 mg)
ETH-73065 1450–1460 40,462 ±402 43,245-44789 (44,023) −35.8 0.45 Wood fragments (1.8 mg)
ETH-73066 1560–1580 8325 ±86 9088-9496 (9324) −34 0.07 gas Saxifraga oppositifolia leaf fragments, unidentied mosses (0.7 mg)
A. Paus
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for estimates of concentration and inux (Stockmarr, 1971). Identi-
cations 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 material. Betula nana pollen was distinguished using pollen
morphological criteria (Terasm¨
ae, 1951). The pollen diagram was
drawn by the computer program CORE 2.0 (Kaland and Natvig, 1993)
and divided into seven local pollen assemblage zones (PAZ H1 – PAZ H7)
by visual inspection.
Principle Component Analysis (PCA) in the computer program
CANOCO 4.5 (ter Braak and Smilauer, 1997–2002) was used for
detecting and graphing ordination patterns in the terrestrial vegetation
development within the Heimtjønna area. In addition, to simplify the
correlation of the Heimtjønna pollen data with those of four other Dovre
lakes (Paus et al., 2006, 2011, 2015), the merged pollen data from all
ve lakes were ordinated by PCA. Palynological terrestrial richness (PR)
estimates E(T
118
) with the basic sum 118, were achieved by rarefaction
analyses (program RAREPOLL; Birks and Line, 1992). PR is a proxy for
the total oristic richness including all terrestrial seed plants and spore
plants within the pollen source area.
3.3. Dating
Eight samples of terrestrial plant remains were dated from
Heimtjønna (Table 2). Sediments between the dating samples contained
no datable material. The hand-picked macrofossils were stored in water
for less than one day to prevent fungi development (Wohlfarth et al.,
1998). All dates are given in calibrated years BP (cal BP; present 1950
AD) based on the InCal13 calibration curve and CALIB 8.2 (Stuiver et al.,
2020).
4. Results
4.1. Lithostratigraphy
The sediment sequence (Table 1) mainly consists of loosely
consolidated minerogenic deposits (1350-1581 cm; Fig. 2) where LOI is
less than 1%. The upper 19 cm (1332-1350 cm, Fig. 3) are slightly more
organic (LOI between 1% and 10%). Except for the brown and distinctly
stratied upper silt above the hiatus at 1338 cm depth (Fig. 3), all layers
are homogenous and uniform.
4.2. AMS
14
C-dates and sources of error
The upper sample (Ua-44734) including many well-preserved mac-
rofossils (Table 2; Fig. 3) is assumed to give a reliable date. Likewise, the
date of a few well-preserved Salix polaris leaves (ETH-74321) indicating
in situ position in level 1370–1375 cm depth, is assumed reliable.
The dating sample ETH-46616 at 1334–1338 cm depth (Fig. 3) is
apparently of late Holocene age. Both this sample and the three dating
samples from the stony layer and younger than the in situ Salix polaris
leaves above (Table 2), contain minor organic fragments. Some of these
were probably caught in the upper organic layer by the sediment catcher
(metal iris shutter at the base of the coring tube) and released into the
sediments further down (see discussion in Paus et al., 2011). To avoid
the inclusion of ex situ fragments into dating samples, the outer 2–3 cm
of the core were tried removed. However, the stony layer made this
difcult, so dates might be contaminated by young material.
Two other dates from the stony layer gave surprisingly old results. In
level 1450–1460 cm, three rounded wood fragments with a polished
surface were picked for dating. Their clean surfaces with no discernible
contamination attached, indicate that the dating result 44 ka cal BP
would be reliable. Obviously, the wood fragments are reworked. Dates
of similar ages from the Dovre-Jotunheimen area (Thoresen and Ber-
gersen, 1983; Lie and Sandvold, 1997; Paus et al., 2011; Hufthammer
et al., 2019) show ice-free conditions during MIS 3 (see discussion in
Hufthammer et al., 2019). The dates fall within the period 35–45 ka BP
when Fennoscandia experienced reduced ice volume/ice-free conditions
(Olsen et al., 2013), and when the western coast of Norway showed two
ice-free periods; the Austnes and Ålesund interstadials (Mangerud et al.,
2010).
Fig. 2. The sediment core of LG and early
Holocene layers with minimal organic con-
tent (LOI ≤1%). The horizontal depth scale
is shown with the deepest part (15.8 m
depth) to the left and the topmost part (13.4
m depth) to the right. Material >0.5 mm (in
boxes) and stones are placed outside the core
at their original depths. Dated fragments are
from levels shown by bold horizontal bars.
Their dating results are shown in ka cal BP.
The position of the pollen diagram (starting
at 1464 cm depth) with interpreted periods
indicated. Here, LGI represent PAZ H1–H2,
YD-PBO represents PAZ H3–H4, and Holo-
cene covers PAZ H5 and PAZ H6.
Fig. 3. The sediment core of the upper 30 cm of sedi-
ments with LOI between 1% and 10%. The horizontal
depth scale is shown with the deepest part (1353 cm
depth) to the left and the topmost part (1332 cm depth)
to the right. The occurrence of several hiati in the late
Holocene spanning ca 9000 years (ca 9500-250 cal yrs
PB) starts at 1338 cm depth with brown and distinct
sand layers above. Levels shown by with lines include
dated fragments in years cal BP. (For interpretation of
the references to colour in this gure legend, the reader
is referred to the Web version of this article.)
A. Paus
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Fig. 4. Lake Heimtjønna pollen diagram. It also includes LOI-estimates, palynological richness (PR) estimates E(T
118
), PCA sample scores, total pollen concentration,
and tentative total pollen inux. Shaded curves represent 10x exaggeration of the scale. Lithostratigraphical details can be found in Table l and Figs. 2 and 3. The
hiatus at the PAZ H6/H7 transition and spanning the period from ca 9500-250 cal yrs BP, is indicated.
A. Paus
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The other old sample (1440–1460 cm depth) includes several types
of minor fragments giving a date of 22.1 ka cal BP (Table 2). The date
probably reects in situ material being contaminated by reworked old
material (and by young material dragged down by the coring equip-
ment, also?). Altogether, the ve dates from the stony layer (LOI <1%)
show how old or young contaminants heavily inuence dating results of
samples with low carbon content.
4.3. Pollen results and statistical analysis
One hundred terrestrial taxa were identied in 55 levels at 1–4 cm
intervals (Fig. 4). The pollen sum ΣP varied between 102 (in PAZ H3)
Fig. 4. (continued).
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and around 760–780 (in PAZ H2 and H7) with the mean ΣP of 362 grains
per level. In the pollen diagram (Fig. 4), the percentage calculation basis
(ΣP) comprises the total sum of terrestrial pollen taxa. For a taxon X
within aquatic plants (AQP) and spores, the calculation basis is ΣP +X.
Below the lowermost analysed level of the diagram (1464 cm), the
coarsely minerogenic sediments down to the basal 1581 cm level
contain too small amounts of pollen to be included in a percentage di-
agram (Table 3). Here, the basal 20 cm show slightly increased pollen
content. Pollen grains are generally well-preserved through the whole
core which reects primary origin. Though unidentied triporate grains
of less than 10% representation (Fig. 4), could be reworked. The old
AMS
14
C-dated fragments advocate that reworking processes are
involved (see 4.2.).
The pollen diagram represents the time elapsed from the local
deglaciation to present. However, the pollen curves (Fig. 4) do not
display features typical for LG and Holocene pollen results elsewhere
from Dovre. It is possible that the sediment catcher thought to drag
fragments downwards during coring (see 4.2.), also could have brought
pollen grains from above. However, the sudden appearance of countable
amounts of pollen at the lower PAZ H-1 zone border and the seven
distinctly dened pollen assemblage zones show that the primary pollen
deposited in situ is not neutralized by material brought downwards by
the coring equipment. The pollen assemblage zones with their main
characteristics are described in Table 4.
The Heimtjønna sediments contains unusually low amounts of pol-
len. The total pollen concentration in Fig. 4 varies between ca 200 and
6000 pollen grains cm
3
, where the latter represents the present pollen
concentration deposited in the upper surface layer. Using a tentative
chronology for the Heimtjønna sediments (Fig. 4), the tentative total
pollen inux of 1–45 pollen grains cm
−2
a
−1
appears throughout the
diagram. This is extremely low and comparable to modern values from
the Arctic (Fredskild, 1973; Gajewski, 2015) and from Weichselian
deglaciation periods at Andøya (Alm, 1993) and Dovre (Paus et al.,
2011).
The Principle Component Analysis (PCA) of the Heimtjønna pollen
data (Figs. 4 and 5) concentrates the pioneers on shallow disturbed soils
(e.g. Beckwithia, Papaver, Saxifraga spp.) to the lower right (Fig. 5),
whereas plants on fertile humus-soils (e.g. Filipendula, Polypodiaceae,
Urtica) are found in the upper left. By this, successional stages in the
local vegetation development can be identied.
PCA of the merged pollen data (Figs. 6 and 7) compares pollen data
from ve adjacent Dovre sites: Flåfattjønna (Paus, 2010; Paus et al.,
2006), Topptjønna and Ristjønna (Paus et al., 2011), and Finnsjøen
(Paus et al., 2015) in addition to Heimtjønna. By this, regional features
in vegetation development should be displayed. Quite extraordinary,
PCA axis 1 captures as much as 72% of the total data variation along a
gradient of presence/dominance of pollen taxa showing rare taxa to the
left and dominant/frequently occurring taxa to the right (Fig. 6). No
apparent ecological gradients linked to e.g. soil features, vegetation
closure, or temperature can be inferred from axis 1. This is shown by that
the 55 unspecied rare taxa in Fig. 6, includes taxa of quite different
ecological demands (e.g. pioneer species on dry soils: Astragalus alpinus,
Armeria, snowbed plants: Koenigia, Saxifraga cernua, Sibbaldia, tall herbs:
Geum, Valeriana, Urtica, trees: Sorbus, Populus). In a test, the 55 rare taxa
occurring in less than 10% of the samples, were removed from the
merged data set before a new PCA was carried out (not gured). Then
axis 1 captured 67% of the total data variation still displaying a gradient
of presence/dominance of pollen taxa. PCA of the data set excluding the
Heimtjønna data (Paus et al., 2015) shows that axis 1 captures 30% of
the total data and displays taxa along a main gradient of soil thickness.
Hence, it is the inclusion of the Heimtjønna data that causes the unusual
PCA ordination which shows how strongly the Heimtjønna pollen data
deviates from the pollen data of the other Dovre sites.
In contrast to PCA axis 1, axis 2 can be interpreted in ecological
terms. Along axis 2 (Fig. 6), positive values with e.g. Empetrum, Vacci-
nium, Dryas, Corylus, Ulmus, Alnus, Pediastrum and Botryococccus,
correlate with (1) humus-soil formation indicated by local pollen taxa,
(2) fertile thick soils indicated by long-distance transported pollen, and
(3) ourishing algae. Hence, positive values show favourable terrestrial
and limnic growth conditions, and can therefore reect summer tem-
peratures. However, algal growth can also depend on light transperancy
and nutrient concentrations in the water masses (Weckstr¨
om et al.,
Table 3
The number of microfossils from below the lowermost pollen spectrum (1464 cm depth) of the pollen diagram (Fig. 4). No pollen was found in the samples 1490 cm,
1510 cm, and 1540 cm depth below water surface.
Depth cm → 1470 1480 1500 1520 1530 1550 1560 1570 1580
Pinus 2 2 4 4 1
Betula 1 2 1 2 2 1
Betula nana 1
Alnus 1 2
Vaccinium-type 1
Poaceae 1 1 1 2 2
Cyperaceae 1 2 1
Arenaria-type 1
Artemisia 4 1
A.norvegica 2 1
Beckwithia glac. 1
Chenopodiaceae 1
Oxyria-type 1 3
Papaver radicatum-type 1
Saxifraga. opp. 1
Silene dioica 1
Thalictrum 1 1
Lyc. annotinum 1
Lyc. clavatum 1
Polypodiaceae 1 1
Selaginella 2 1
Sum terrestrial microfossils 1 2 3 6 3 8 11 26 5
Sum terr. taxa 1 2 2 4 3 6 6 14 5
Pediastrum 1
Botryococcus 1
Concentration: Terrestrial microfossils per cm
3
9 18 7 19 19 14 40 55 18
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2010).
5. Discussion
5.1. The deposition of the stony layer
The 171-cm thick minerogenic basal layer (1410–1581 cm depth) is
homogenous, unstratied, and unsorted (see particle sizes in Table 1,
Fig. 2.) and may apparently be a till. However, the layer is unconsoli-
dated, easily penetrated by the hand-driven coring equipment, and the
pebbles are angular (Fig. 2). Hence, the layer cannot be classied as a
subglacial till (e.g. Bennett and Glasser, 2009). Flow till/sediment ow
diamicts of supraglacial origin normally contain angular erratics (Evans,
2018), but would most likely deviate from the Heimtjønna deposit by
being more consolidated and stratied by ow packages (Bennett and
Glasser, 2009). If glacier margins, oating or land-based, were close to
Heimtjønna, glaciolacustrine outwash ows may have resulted in
stratied and sorted subaqueous deposits (Bennet and Glasser, 2009),
sometimes annually laminated (Earle, 2019). This deviates from the
unsorted Heimtjønna sediments. Also, if the unsorted Heimtjønna de-
posits indicate the absence of an adjacent ice margin, then iceberg rafted
mud with drop stones cannot have contributed to the Heimtjønna stony
layer either.
Snow avalanches can bring mud and stones to the surface of winter-
ice and may potentially have contributed to the deposition of the stony
layer (Luckman, 1975; Hartshorn and Lewkowicz, 2000). However, the
catchment topography of Lake Heimtjønna is gentle (Fig. 8), which in-
dicates that a major stone and pebble contribution from snow ava-
lanches, is unlikely. Alternatively, stones/pebbles from eroded bedrock
and/or slush material in-washed by ow activity during melting periods,
would be frozen to anchor lake ice (Evans, 2018) that formed along the
shores and in shallow parts of Heimtjønna during winter. The later
release of the adfrozen material after lifting and drift of the lake ice
during spring melt (e.g. Heron and Woo, 1994; Smith, 2000; Evans et al.,
2006), could have contributed to the deposition of the Heimtjønna basal
stone layer. This is a parallel to how lake deposition of erratics have been
explained elsewhere (e.g. Gilbert, 1990; Johansson, 1995; Bennett et al.,
1996; Hartshorn and Lewkowicz, 2000; Paus et al., 2006). By this, the
stony layer in Heimtjønna would represent a minerogenic parallel to the
present Arctic ‘mud-lakes’ with more organic sediments (Nichols, 1967).
In contrast to the lithology of the stone layer, its microfossil content
can be divided into distinct layers. The basal 21 cm (1560–1581 cm)
contains small amount of pollen, whereas in the 96 cm above
(1464–1560 cm), pollen is almost absent (Table 3). From 1464 cm depth
to the top (1410 cm), the abruptly appearing and countable amounts of
pollen can be divided into the pollen assemblage zones H1 and H2
(Fig. 4). Pollen is well preserved as shown by the presence of complete
and large Picea grains in PAZ H2 (Fig. 9) which suggests primary pro-
duction and proximal deposition. The pollen assemblages show a
gradual vegetation development. Hence, the layer, at least the upper
third, was not deposited in one event. In line with this, distinct repre-
sentation of the algae Pediastrum and Botryococcus shows low turbidity
and high light transparency and hence low-energic and slow deposition
of the upper stony layer (PAZ H2, Fig. 4). So, the biostratigraphy ex-
cludes a glacier-induced and vigorous deposition of the entire stony
layer.
The same is inferred from stone layers of similar lithostratigraphy to
Heimtjønna, though much thinner, described from three other alpine
lakes in the Dovre Mountains (Paus et al., 2006, 2011). If their
biostratigraphy reects in situ (non-disturbed) sedimentation, a bio-
stratigraphical correlation between the closely situated Topptjønna,
Ristjønna and Heimtjønna (Fig. 1) shows that the stone layers were
Table 4
Names, assumed dates, and biostratigraphical features of the local pollen assemblage zones.
PAZ Name Tentative Age
(cal. ka BP)
Pollen assemblage zone characteristics Diagnostic taxa not included in Fig. 4
H7 Betula-Pinus 0–0.3 Betula, Pinus, Selaginella, and algae distinctly increase to diagram
maximum values. Betula nana, Artemisia, and Poaceae decrease to
minimum diagram values. Loss-on-ignition (LOI), total pollen
conc. (TPC) and tentative total pollen inux (TTPI) distinctly
increase.
Calluna vulgaris, Campanula cf. uniora, Geranium, Melampyrum,
Parnassia palustris, Pteridium aquilinum; Ulmus
H6 Betula nana-
Artemisia
ca 9.5-10.2 Artemisia and Betula nana shows maximum values. Pinus shows a
maximum in early H6. Juniperus and Oxyria increase, Dryas
appears for the rst time since H2. In late H6, LOI rises. TPC
increases, thereafter showing variating values. TTPI decreases to
ca 10 grains cm
−2
a
−1
.
Ephedra distachya-type, Ephedra fragilis-type, Plantago maritima,
Polypodium vulgare, Rhinanthus, Rubus chamaemorus, Ulmus
H5 Betula 10.2–11.2 Betula and Botryococcus show distinct maxima. Filipendula
displays continuous representation. In mid H5, Artemisia rises. PR
slightly decrease. TPC slightly increase, whereas TTPI distinctly
decrease to 20 grains cm
−2
a
−1
.
H4 Salix-Artemisia-
Poaceae
11.2–11.7 Betula, shrubs, and Selaginella increase. Poaceae shows dominant
percentages. TPC slightly rise, whereas TTPI reach maximum
diagram values of 45 grains cm
−2
a
−1
. Towards the H4/H5
boundary, features of H3 appear, such as low Betula values and
high Poaceae and PC1 axis values.
Circium-type, Onagraceae, Plantago lanceolata, Silene dioica-type,
Toeldia pusilla, Ulmus
H3 Poaceae-
Arenaria-
Saxifraga
11.7–12.8 Poaceae, Artemisia norvegica, and Arenaria increase. Betula, Alnus,
shrubs, Selaginella, TPC and TTPI show distinct minima. Values of
PCA axis1increase and shows improved representation of pioneer
species on disturbed soils (Fig. 5).
Campanula cf. uniora
H2 Alnus-Pinus-
Pediastrum
12.8–13.8 Alnus and algae show maxima throughout the zone. Poaceae,
Rumex, Thalictrum and Selaginella show distinct percentages.
Cyperaceae declines, whereas Pinus, Betula nana, and Artemisia
increase. Palynological richness (PR) shows diagram maximum
values. TPC and TTPI reach 1200 grains cm
−3
and 40 grains cm
−2
a
−1
, resp.
Arctous alpina, Campanula cf. uniora, Circium-type Ephedra
fragilis-type, Helianthemum, Melampyrum, Onagraceae, Pedicularis,
Potamogeton sect. Eupotamogeton, Rhinanthus-type, Rubus
chamaemorus, Silene dioica-type, Ulmus
H1 Salix-
Cyperaceae
13.8–14.5 Salix and Cyperaceae reach their diagram percentage maxima.
Betula, Poaceae, Astragalus alpinus, Beckwithia glacialis, and
Saxifraga oppositifolia show distinct representation. PR shows
diagram minimum values. Total pollen conc. (TPC) and tentative
total pollen inux (TTPI) reach 800 grains cm
−3
and 25 grains
cm
−2
a
−1
, resp.
Polygonum aviculare-type, cf. Rhododendron lapponicum,
Trifolium-type
A. Paus
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asynchronously deposited (Fig. 7). As the deglaciation would have
occurred more-or-less simultaneously at these adjacent sites, the asyn-
chronous stone layers were not deposited by glacial processes. As dis-
cussed above in this sub-section, it is more probable that drop stones and
mud from lake ice are the origin of the stony/pebbly basal layers in the
high-mountain lakes at Dovre. Also, pollen deposition indicates local
vegetation in ice-free catchments and hence, an additional supply of
material by erosion of running water into the lakes.
The abrupt cessation of the stone-dominated layer at 1410 cm depth
(at the PAZ H2/H3 transition; Fig. 4) must signal a similarly abrupt
event. According to the inferred stone layer genesis, no adjacent glaciers
seem to have been present, so the depositional change may not be
glacially induced. Most probably, a severe cooling established a peren-
nial lake-ice that prevented ice rafting and deposition of stones and
pebbles in the lake (Paus et al., 2006, 2011). A perennial lake ice could
have caused a hiatus. It cannot be excluded that sedimentation through
the ice (Squyres et al., 1991) and/or the presence of ice-free narrow
moats along the lake shores allowed delimited deposition during sum-
mers as seen by the strongly reduced though distinct pollen concentra-
tions in the lowermost well-sorted sediments (Fig. 4).
Also, during the period of permanent lake ice, material could have
been brought to the ice surface by avalanches and/or debris ows. When
climate ameliorated, this material would then have been released upon
melting as the nal deposition of stones and pebbles. After this, the
transport of stones into the lake disappeared most probably due to
thinning of lake ice, depletion of sources along the lake margins, and
cessation of debris ows derived from melting snow and ice.
5.2. Sedimentation of the younger layers
The deposition above 1410 cm depth of homogeneous clayey silt
shows sorting of sediments by owing water. No distinct end-moraines
appear in LIDAR or are reported within the lake catchment (Fig. 8), so
the water input in the early Holocene should mainly reect the yearly
melting of snow. The large catchment of 10.1 km
2
indicates a production
of considerable amounts of meltwater. Today, the main inlet is a
brooklet except during snow melt when it grows to size of a river.
The change from grey to brown deposits at 1350 cm depth (Fig. 3)
shows slightly increasing LOI most probably due to increased organic
production within the catchment as the local vegetation developed. The
dated layer of Salix polaris leaves (Table 2) and occasional sand lenses in
the upper part of the clayey silt (Table 1) reect periodically variations
of current strength. However, the brown sand layers above 1338 cm
depth (Fig. 3) show that melt water started to erode other minerogenic
deposits within the catchment. Each of these coarse sand layers sepa-
rated by ner minerogenic material most probably reect big ood-
driven turbidity ows causing graded beds ning upwards (Bøe et al.,
2006). In south Norway, strong ood events increased their frequency
from 2.5 ka cal BP (Støren et al., 2010) culminating with the major ood
disaster ‘Stor-Ofsen’ in July AD 1789 (Bøe et al., 2006; Støren et al.,
2010). Above the sand layers, one cm of organic sediments occurs
reecting the sediment surface and dated to ca 250 a BP (Table 2).
The rapid sediment shifts and the abrupt pollen assemblage changes
at the PAZ H6/H7 transition indicate that the Late Holocene oods
removed sediments and caused at least one hiatus. The lack of distinct
Holocene pollen features shows that the hiatus spanned the period ca
9.5–0.25 ka cal BP (see 5.4.). These oods were so strong, that even if
the coring site is positioned halfway towards the lake center from the
shore and as far as 200 m from the main inlet (Fig. 1), they were able to
remove sediments from the site. During eld work, a course bathymetry
was obtained (Fig. 8), and the coring site for sediment and pollen
analysis (Figs. 1 and 4) was placed at the site with maximum water
depth. Such sites usually show to have sediments best suited for palae-
ecological studies. The Heimtjønna studies denitely challenge this
view. From the bathymetry, it seems that the coring site may have hit a
channel running through the lake oor from the inlet and outwards.
The upper one cm of rather organic sediments (LOI 10%; Fig. 4,
Table 1) from the last 250 years has not been removed. The reason could
be that no oods of similar strength have occurred since “Stor-Ofsen”
(Støren et al., 2010). Also, one can speculate whether the upper layer
contains more minerogenic matter and is heavier than the sediments
removed by the oods. The local introduction of summer farming ca
250–300 years ago (Streitlien, 1980) and the impact of grazing, caused
break up of vegetation and increasing erosion of minerogenic deposits.
Furthermore, during summers in the last 100 years, herds of horses at
Bekklegret (Fig. 1) have been grazing in the area around Heimtjønna and
would have increased the erosion.
Fig. 5. PCA of species included in the Heimtjønna data set, as displayed for
samples in Fig. 4. A DCA gradient length of 1.5 standard deviation units of
turnover suggests linear response curves. Hence, PCA was chosen as ordination
technique. Eigenvalues: axis 1: 0.220, axis 2: 0.160, axis 3: 0.072, axis 4: 0.048.
Fig. 6. PCA of species included in the total Dovre data set (Heimtjønna, Top-
ptjønna, Ristjønna, Finnsjøen, Flåfattjønna), as displayed for samples in Fig. 7. A
DCA gradient length of 1.2 standard deviation units of turnover suggests linear
response curves. Hence, PCA was chosen as ordination technique. Eigenvalues:
axis 1: 0.721, axis 2: 0.095, axis 3: 0.046, axis 4: 0.024. The total data set in-
cludes 120 identied taxa in 245 samples. Fifty-ve rare taxa, occurring in less
than 10% of the samples and displayed to the left are not specied in the gure.
A. Paus
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5.3. Chronology
Due to sources of error such as reworking processes and contami-
nation, a reliable
14
C-chronology for the Heimtjønna sediments is pre-
vented. Instead, three lines of evidence dene a tentative chronology:
(1) the date of Salix polaris leaves from the homogenous silt, (2) The
abrupt cessation of the stone layer deposition, and (3) the microfossil
content of the stone layer. Similar studies in adjacent lakes at Dovre
(Paus et al., 2006, 2011; 2015, 2019; Paus, 2010) support the dened
Heimtjønna chronology.
(1) The date of well-preserved in situ leaves of Salix polaris of 11 ka
cal BP (Table 2) is assumed reliable. The leaves postdate the onset
of the warming after the Pre-Boreal Oscillation (see 5.4.)
signalled by similar biostratigraphy within the Dovre region
(Fig. 7 and Paus et al., 2011, 2015; Paus, 2010).
(2) Most probably, the stone deposition ceased when a perennial lake
ice established due to a severe cooling (see 5.1.). Only the onset of
the strong YD cooling could have been the responsible factor. No
perennial lake-ice established in adjacent lakes at higher altitudes
during Holocene coolings such as the Pre-Boreal oscillation, the
Erdalen event, or the 8.2 event (Paus et al., 2011, 2015, 2019).
That YD stopped the deposition of stones was also indicated for a
similar sediment change in Flåfattjønna, ca 30 km E of
Heimtjønna (Paus et al., 2006; Paus, 2010).
(3) The microfossils in the stone layer (PAZ H2) reect a mild period.
The cool MIS 3 interstadials from Dovre (Thoresen and Bergersen,
1983; Paus et al., 2011) deviates from PAZ H2 by the absence of
Alnus and Corylus (Fig. 4). In addition, deposits from the Eemian
interglacial and warm MIS 5 interstadials show distinctly higher
LOI and more obvious traces of forests (e.g. Helle et al., 1981;
Mangerud et al., 1981; Helmens, 2014) than the Heimtjønna
stony layer. PCA ordination shows that PAZ H2 correlates to
(parts of) LG interstadial (Bølling-Allerød) pollen assemblages, at
four other Dovre sites (Fig. 7). PAZ H1 signals rapidly increasing
local pollen production/vegetation closure as a (delayed?) local
response to the global Bølling warming 14.6 ka cal BP (K¨
ohler
et al., 2011, 2014; Brendryen et al., 2020).
There is little evidence to suggest any reliable age for the base the
stony layer 116 cm below the lowest part of PAZ H1 (Fig. 4). However,
the layer is homogenous and unconsolidated and without any traces of
hiati (section 5.1.) and must be expected to have been deposited during/
after the nal deglaciation. Assuming similar sedimentation rates below
the pollen diagram (sediments of 116 cm thickness) and the 54 cm thick
sediments covering the LG interstadial (PAZ H1/H2), the core bottom
can roughly be dated to ca 16–18 ka cal BP. This estimate also depends
on to what degree the local vegetation response lagged the global Bølling
warming. However, using other estimate methods at Dovre, Paus et al.
(2006, 2011) and Lane et al. (2020) suggested similar deglaciation ages
(16–18 ka BP). Dating results (15–19 ka BP) from the Scandes Mountains
(Bøe et al., 2007; Goehring et al., 2008; Kullman, 2008; Marr et al.,
2018) are in line with this. It must be underlined that the deglaciation of
Dovre and the Scandes have never been reliably dated by in situ terres-
trial plant material, which is widely accepted as the denite evidence for
dating deglaciations. Apparently, during the rst period after deglacia-
tion, the local development of pioneer vegetation was too sparse to give
datable organic signals in sediments to reveal the time of deglaciation.
5.4. Vegetation and environmental history
In the LG interstadial, i.e. Bølling-Allerød (PAZ H1/H2 at 1410-1464
cm depth), the herb-/graminid-dominated pollen assemblages infer a
local vegetation mosaic formed by the variations in topography and
exposure. The mosaic included pioneer species on moist mineral soils (e.
g. Beckwithia, Oxyria, Saxifraga spp.) and well-drained minerals soils (e.
g. Armeria, Artemisia norvegica, Astragalus alpinus, Papaver). In open
grasslands, light-demanding species such as Botrychium, Selaginella,
Pedicularis, and Rhinanthus occurred. Dwarf-shrubs such as Dryas,
Empetrum, Vaccinium together with Juniperus and Rubus chamaemorus
show developing humus-soils. In PAZ H2, the increasing representation
of dwarf-shrubs, the improved long-distance signal of Populus and Cor-
ylus, and the algae bloom indicates warmer climate both on local and
regional scale. Local representation of Juniperus, Betula nana, and
Selaginella indicates July mean temperatures of at least 7-8 ◦C (Kolstrup,
1979) which is similar to the present.
PAZ H3 (1404–1410 cm depth) shows increasing Poaceae and
minima in trees and the Pediastrum algae. A few pioneer taxa (Arenaria-
type, Artemisia norvegica-type, Saxifraga spp.) increased their represen-
tation. PCA axis1 values show the return to early PAZ H1 vegetation
(Fig. 4). This vegetation regression indicates a cooling. Simultaneously,
the cessation of stone deposition indicates the formation of perennial
Fig. 7. PCA of samples for the total Dovre data set
(this study and Paus et al., 2006, 2011, 2015). As no
reliable 14C-dates exist from Dovre, the y-axis reects
a depth scale. The three correlated periods include
period 1 (pre-YD), period 2 (from YD to end of the
PreBoreal Oscillation, PBO), and period 3 (the early
Holocene after PBO). The white horizontal lines show
the onset of the Holocene. Note that period 2 is absent
in the Flåfattjønna sediments. The oldest early Holo-
cene AMS
14
C-dates of terrestrial macrofossils at each
site (stippled white arrows) are shown in ka cal BP.
The vertical extension of unsorted stone-rich deposits
is visualized by S’es in the curve of PCA axis 2 values.
A. Paus
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Fig. 8. Features of the Heimtjønna catchment. (A) LIDAR map (Kartverket, 2020). An altitudinal prole is shown from Nordre Knutshøa (1684 m a.s.l.) to the left, via
the Heimtjønna coring point (blue circle), to Heimtjønnshøa (1555 m a.s.l.). (B): map showing the distribution of supercial sediments (NGU, 2020) and a course lake
bathymetry. The bathymetric contour lines (10m and 5 m, respectively) are ovals around the coring point. The deposits are described as thin morainic material
(TnM), thick morainic material (TcM), weathering material (WM), glaciuvial deposits (G), and peat (P). BR reects bare rock. (For interpretation of the references to
colour in this gure legend, the reader is referred to the Web version of this article.)
A. Paus
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lake ice as a response to the YD cooling (see 5.1.). YD is represented by 6
cm of sediments, only. In line with this, perennial lake ice “hermetically”
sealing lakes, is described from the Arctic for the recent past, today
showing a July mean and January mean of about 3 and -32 ◦C, respec-
tively (Doubleday et al., 1995).
PAZ H4 (1377–1404 cm depth) indicates the Holocene warming by a
regrowth of shrubs and dwarf-shrubs, whereas herbs and grasses
decreased. Apparently, vegetation and temperatures were at least 7–8 ◦C
as also indicated for PAZ H2. In contrast to the local signals, the long-
distance representation of Corylus and Populus, show a delay to the
ameliorating conditions. This also accounts for Pediastrum inuenced by
turbid sediment environments.
At the close of PAZ H4, a small-scale parallel to the cooling in PAZ H3
occurred by showing increasing herbs, reduced tree representation, and
similar PCA patterns (Fig. 4). This short-lasting cooling is dated to
shortly before 11 ka cal BP and probably reects the Pre-Boreal Oscil-
lation (PBO) that is recorded in lake sediments elsewhere at Dovre (Paus
et al., 2011, 2015).
At the onset of PAZ H5 (1363–1377 cm depth) around 11.2 ka cal BP,
birch and the alga Botryococcus rapidly rose and reached a distinct
maximum. The same patterns signal the post PBO warming elsewhere at
Dovre (Paus et al., 2011, 2015). Here, the birch expansion reects forest
establishment in the lowlands (Paus et al., 2015, 2019). Though less
pronounced, the pine rise in early PAZ H6 (1338–1363 cm depth) could
reect the increasing pine around 10.2 ka cal BP as frequently recorded
at Dovre (Paus, 2010; Paus et al., 2011, 2015, 2019). After this pine rise,
no pollen stratigraphic features can be linked to the further Holocene
vegetation development as recorded elsewhere in the Scandes, such as
the local birch-forest period, the Alnus rise around 9.3 ka cal BP, signals
of the 8.2 event, the maximum in the warmth-demanding deciduous
forests reected by long-distance transport, the local deforestation, and
the subsequent juniper dominance (e.g. Høeg, 1994; Segerstr¨
om and von
Stedingk, 2003; Giesecke, 2005; Velle et al., 2005; Paus, 2010; Paus
et al., 2015, 2019). This shows that the sediments are lacking from the ca
9.5–0.25 ka cal BP which is explained by late Holocene oods removing
material at the coring site (see 5.2.). After ca 250 cal a BP, the PAZ H7
shows the long-distance dominance of Betula and Pinus and the local
herb-rich dwarf-shrub tundra.
5.5. Plant geography
5.5.1. Centric plants
Lake Heimtjønna is located close to the Knutshøa Mountains (Fig. 1)
well known for its species-rich alpine ora including so-called centric
species conned to southern and/or northern areas within the Scandes
Mountains. Both the southern centric Artemisia norvegica and the
bicentric Campanula uniora connected to the theory of “in situ glacial
survival” (Blytt, 1882; Sernander, 1896) are common within the
Heimtjønna area today. Hence, the distinctly spiny pollen grains of A.cf.
norvegica and C. cf. uniora in the pollen assemblages could reect their
local appearance in early LG interstadial (Fig. 4) or earlier (Table 3).
5.5.2. Armeria
In seven core levels from PAZ H1 to H6, fragments of the large,
distinctly reticulate and spiny Armeria grains have been found (Fig. 9C).
Armeria is insect pollinated and a sparse pollen-producer, so single-grain
occurrences indicate local presence. Armeria is regularly recorded in the
lowlands during the LG together with other seashore-plants (e.g.
Iversen, 1954; Paus, 1988, 1989), whereas the Heimtjønna nds from
PAZ H1 in early LG interstadial to the Holocene PAZ H6 are the rst
alpine pollen records of Armeria. The only occurring Armeria species in S
Norway today is the common seashore-plant A. maritima. This species is
also growing at a few inland sites (Artsdatabanken, 2020) including sites
at Hardangervidda 1200 m a.s.l. (personal observation). Hence, these
inland sites could represent relicts from an early and wider pioneer
Armeria distribution also including alpine areas.
5.5.3. Alnus
Well-preserved Alnus grains, apparently of primary origin, occur
from early LG interstadial (PAZ H1) to late Holocene (PAZ H7). In PAZ
H2, maximum Alnus values correlate to the assumed LG interstadial
maxima at Dovre (Fig. 7 and Paus et al., 2006, 2011, 2015). In YD and
pre-interstadial periods, Alnus decreased and almost disappeared. LG
interstadial Alnus has also been reported from W Norway (Mangerud,
1977). The inverse LG pattern has been found in other studies (e.g.
David, 1993; Bigelow and Edwards, 2001; Demske et al., 2005; Lacourse
et al., 2005; De Klerk, 2008; Kaufman et al., 2012) showing
well-represented Alnus in the pre-interstadial and/or YD. This suggests
that the LG Alnus-pollen maxima at Dovre do not reect long-distance
transport but reect local/extra-local origin. A clump of ca 30 Alnus
Fig. 9. Light microscope photographs. Length of scale
bars is given in
μ
m.
(A) A clump of Alnus pollen grains from Finnsjøen
(PAZ F-1, Paus et al., 2015). PAZ F-1 is correlated to
Heimtjønna PAZ H2 (Fig. 4) and the period 1 (Fig. 7)
with distinct Alnus representation in all the studied
Dovre sites.
(B) p
ollen grain of Picea abies (PAZ H2, 1412 cm depth
below water surface) (
C) pollen grain fragment of Armeria maritima type A
(PAZ H4, 1390 cm depth below water surface).
A. Paus
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pollen grains found in LG interstadial sediments of Finnsjøen (Fig. 9A)
accords with this. All the LG interstadial Alnus grains at Dovre have 4–5
distinctly protruding pores and well-developed arci. These features ex-
cludes the representation of the subgenus Alnobetula including e.g.
A. virides and A.crispa (Leopold et al., 2012).
The indicated July mean of at least 7–8 ◦C in PAZ H2 could indicate
local/extra local growth of the cold tolerant Alnus incana. Today, A.
incana is growing at 1200 m a.s.l. at the birch tree line in Central Norway
(Artsdatabanken, 2020). In addition, A. incana with N-xing root nod-
ules is thriving on minerogenic soils of ooded riverbanks and active
sandurs (e.g. Fåbergstøsgrandane) in central Norway today. Similar
minerogenic substrates must have been common at Dovre after degla-
ciation (Fig. 8). During the Last Glacial Maximum, Alnus incana survived
in northern refugia and rapidly migrated northwards during LG (Douda
et al., 2014; Mandak et al., 2016; Dering et al., 2017). Macrofossils of A.
incana and Alnus sp. are found at the southern coast of the Baltic Sea
from 13.5 ka cal BP (Douda et al., 2014; Mandak et al., 2016). Studies
including the present, show that alpine areas in Central Norway was
ice-free in the LG interstadial (Paus et al., 2006, 2011; 2015; Bøe et al.,
2007; Goehring et al., 2008; Marr et al., 2018). Hence, long distance
dispersal of Alnus seeds might have reached Central Norway and
developed local populations in climatic favourable sites during the LG
interstadial.
After PAZ H3, Alnus frequently occurs (Fig. 4). This contrasts the
more fragmented early Holocene Alnus representation elsewhere at
Dovre before the distinct rise around 9.3 ka cal BP (Paus, 2010; Paus
et al., 2011, 2019), synchronous to Alnus rises in the Scandes mountains
from Setesdalen in the south to inner Troms in the north (e.g. Høeg,
1994; Segerstr¨
om and von Stedingk, 2003; Bergman et al., 2005; Bjune,
2005; Eide et al., 2006; Jensen and Vorren, 2008). This could indicate
that A. incana occurred sparsely in the mountains almost undetected due
to low temperatures reducing pollen production (cf. Moe, 1998; Hicks,
2006), until its main expansion around 9.3 ka cal BP. In line with this,
Giesecke and Brewer (2018) postulate Alnus establishment of N Euro-
pean outposts in the earliest Holocene. The Alnus records in Heimtjønna
and other Dovre sites could accord this view assuming a rapid early
Holocene re-establishment of A. incana outposts after being forced
southwards by the YD cooling.
5.5.4. Picea abies
Picea abies pollen grains are found in every spectrum except two
(Figs. 4 and 9B). The well-preserved and often complete Picea grains
constituting up to 1–2% ΣP, indicate their primary origin. In forests,
such values should indicate local presence (Giesecke and Bennett, 2004;
Latałowa and van der Knaap, 2006). However, as the Heimtjønna dia-
gram reects low pollen-producing pioneer vegetation/dwarf-shrub
tundra, the Picea values could reect long-distance transport from
expanding spruce south-southeast of the Baltic Sea both during the LG
and during the early Holocene (Latałowa and van der Knaap, 2006;
Heikkil¨
a et al., 2009; Gałka and Tobolski, 2013; Amon et al., 2014;
Stanˇ
cikait˙
e et al., 2015). On the other hand, Picea pollen grains are large
and heavy and have reduced ability to travel such long distances ac-
cording to e.g. Segerstr¨
om and von Stedingk (2003) who postulated
early Holocene establishment of sparse Picea populations in the
mid-Scandes based on even single-grain occurrences. The early Holo-
cene presence of Picea in the mid-Scandes has later been evidenced by
sedaDNA (Parducci et al., 2012) and megafossils (e.g. ¨
Oberg and Kull-
man, 2011). Therefore, the representation in PAZ H4 – H7 in the
Heimtjønna diagram would most probably reect the early Holocene
establishment of Picea abies populations in low abundance at Dovre.
Today, spruce individuals occur at 1000–1200 m a.s.l. 5–7 km from
Heimtjønna (Artsdatabanken, 2020).
The Picea percentages in the LG interstadial (PAZ H1 and H2, Fig. 4)
are similar to those of the early Holocene. This could indicate that spruce
also established within the Dovre area during the LG. Climate may not
have been restrictive for its growth as Picea abies can survive and
occasionally produce viable seeds at mean July–August temperatures
down to 5 ◦C (Kullman, 2002). In LG, July mean temperatures reached at
least 7–8 ◦C locally (see 5.4.). Finds of Picea megafossils (Kullman, 2008)
and stomata (Paus et al., 2011) advocate its LG presence at Dovre.
6. Conclusions
•Heimtjønna was deglaciated earlier than 11 ka cal BP according to
AMS dated terrestrial plant macrofossils. Bio- and lithostrati-
graphical considerations and correlations suggest a nal deglaciation
before the onset of Bølling, perhaps as early as 16-18 ka cal BP.
•Two dates older than 20 ka cal. BP suggest that vegetation estab-
lished at Dovre during one or more ice-free Weichselian interstadials.
The presence of the old material reects reworking processes and a
pulsating ice cap during the last glacial.
•The basal 1.7 m of the Heimtjønna deposits consists of unconsoli-
dated and unsorted clay, silt, sand, pebbles, and larger stones (≤11
cm) interpreted to reect material rafted by lake-ice during melting
in spring/early summer in the LG interstadial (Bølling-Allerød).
•YD established a semi-perennial lake-ice preventing deposition of
ice-rafted material.
•Late Holocene oods including “Stor-Ofsen” AD 1789 removed
sediments spanning the period of ca 9.5–0.25 ka cal BP, from the
coring site.
•The minerogenic Heimtjønna sediments contained extremely low
amounts of datable material, so sources of error such as reworked
material and young material brought from above by the coring
equipment, heavily impacted dating results. Dates of fewer and
larger remains are assumed reliable.
•The local response to the LG interstadial warming initiated the suc-
cession from pioneers on mineral soils towards local dwarf-shrub
heath. July temperatures reached at least 7–8 ◦C.
•In the LG, the seashore plant Armeria maritima and arctic/alpine
pioneers of centric distribution today (Papaver, Artemisia norvegica,
Campanula cf. uniora) occurred. Individuals of Picea and Alnus cf.
incana were present in favourable sites at Dovre.
•The biostratigraphy of the thin YD sediment sequence signals vege-
tation regression towards pioneer conditions.
•In the early Holocene, local dwarf-shrub heath re-established locally.
Picea abies and Alnus cf. incana re-established within the Dovre area.
•As no reliable radiocarbon dates on in situ macrofossils exist, the LG
chronology is exclusively based on stratigraphical correlations and
considerations. It must be thoroughly tested by future studies
providing reliable AMS
14
C-dates of terrestrial fossils.
•The problematic Heimtjønna sediments from a dynamic area have
thrown new light upon LG and Holocene environmental conditions
and change. This shows that scientic contributions from an atypical
site can be of value.
Declaration of competing interest
The author declares that they have no known competing nancial
interests or personal relationships that could have appeared to inuence
the work reported in this paper.
Acknowledgements
Espen Paus, Erling Straalberg, and Ståle Samuelshaug helped during
coring. Jan Berge, Linn Cecilie Krüger, and Arild Breistøl prepared the
Heimtjønna pollen samples. Thanks also to David J.A. Evans, Atle Nesje,
and John-Inge Svendsen for comments regarding the deposition of the
basal stony layer. I also want to thank Irka Hajdas, ETH Zürich, for
discussions regarding dating problems, and Atle Nesje and the Depart-
ment of Earth Science for loan of coring equipment. Thanks also to
Antony Brown and one anonymous reviewer for their valuable com-
ments signicantly improving the mansucript. This work was nancially
A. Paus
Quaternary International xxx (xxxx) xxx
14
supported by the Olaf Grolle-Olsen and Meltzer University Foundations,
University of Bergen, Norway.
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