Content uploaded by Kristian Kjellerup Kjeldsen
Author content
All content in this area was uploaded by Kristian Kjellerup Kjeldsen on Mar 11, 2016
Content may be subject to copyright.
1
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
www.nature.com/scientificreports
Holocene ice marginal uctuations
of the Qassimiut lobe in South
Greenland
Nicolaj K. Larsen1,2, Jesper Find1, Anders Kristensen1, Anders A. Bjørk2, Kristian K. Kjeldsen2,
Bent V. Odgaard1, Jesper Olsen3 & Kurt H. Kjær2
Knowledge about the Holocene evolution of the Greenland ice sheet (GrIS) is important to put the
recent observations of ice loss into a longer-term perspective. In this study, we use six new threshold
lake records supplemented with two existing lake records to reconstruct the Holocene ice marginal
uctuations of the Qassimiut lobe (QL) – one of the most dynamic parts of the GrIS in South Greenland.
Times when the ice margin was close to present extent are characterized by clastic input from the
glacier meltwater, whereas periods when the ice margin was behind its present day extent comprise
organic-rich sediments. We nd that the overall pattern suggests that the central part of the ice lobe in
low-lying areas experienced the most prolonged ice retreat from ~9–0.4 cal. ka BP, whereas the more
distal parts of the ice lobe at higher elevation re-advanced and remained close to the present extent
during the Neoglacial between ~4.4 and 1.8 cal. ka BP. These results demonstrate that the QL was
primarily driven by Holocene climate changes, but also emphasises the role of local topography on the
ice marginal uctuations.
In South Greenland the 100 km wide Qassimiut lobe (QL) is presently one of the most climate sensitive parts
of the Greenland ice sheet (GrIS)1 and it also experienced notably large changes during the Holocene2. e QL
consists of several relatively fast-owing marine terminating outlet glaciers intersected by more passive land-
based ice2 (Fig.1). e central proximal part of the ice lobe is situated below 500 m a.s.l. and the more distal parts
(anks) of the ice lobe lie between c. 900 m–1500 m a.s.l. Ice loss of the QL is dominated by melting but calving
ice production is appreciable at a number of the marine terminating glaciers3. During the Last Glacial Maximum
(LGM)4 the GrIS extended to the shelf break in South Greenland and it began to disintegrate around ~19–18 cal.
ka BP5–7. By ~14.1 cal. ka BP the southern tip of Greenland was ice-free and the outer part of Ikersuaq Fjord at
Julianehåb Bay was deglaciated slightly later at ~12 ka8–10. e ice margin reached the present extent by ~11.1–
10.5 ka11,12. Radiocarbon ages of reworked organic molluscs in Little Ice Age (LIA) moraines suggest that the ice
margin of the QL experienced large uctuations during the Holocene2 and sediment cores from the ice marginal
Qipisarqo lake reveal that the central part of the QL was retracted behind present day extent from ~9.1–0.4 cal.
ka BP13. In contrast, the ice margin to the east retreated behind its present extent ~6.9 cal. ka BP and readvanced
at ~3–2.8 cal. ka BP and ~0.4 cal. ka BP during the subsequent LIA11. Previous research has concluded that the
response of the QL was mainly governed by climatic changes and that the dierences of ice marginal response
were related to the local topographic setting between the two threshold lake sites11. However, it is not clear to what
extent local topography inuences the ice marginal behaviour and this warrants further investigation. Here, we
present new constraints on how the QL responded to Holocene climate forcing mechanisms.
Results–Core Description and Interpretation
In this study, we use proglacial threshold lakes to constrain the ice marginal uctuations of the QL. reshold
lakes are located adjacent to the ice margin and by analysing the sediment cores it is possible to determine when
the glaciers are present within the lake catchment (i.e. similar ice extent as today) and periods where the ice
margin was retracted and signicantly smaller than today14. ese changes are clearly seen in the sediment cores
as changes from clastic to organic-rich sediment (see methods). We cored and analysed six new threshold lakes
1Department of Geoscience, Aarhus University, Høegh Guldbergs Gade 2, 8000 Aarhus C, Denmark. 2Centre
for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350
Copenhagen K, Denmark. 3Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark.
Correspondence and requests for materials should be addressed to N.K.L. (email: nkl@geo.au.dk)
received: 23 November 2015
accepted: 12 February 2016
Published: 04 March 2016
OPEN
www.nature.com/scientificreports/
2
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
(Figs2–5); two are from the central part of the lobe (Sermilik, Kangerdluatsiaup tasia), three are from the mar-
gin of the ice lobe (Akuliarusseq, Storesø, Rundesø) and one is located 50 km northwest of the QL (Kingigtoq).
ese new results will, together with the existing data from South Greenland, give a more coherent picture of the
Holocene ice marginal uctuations of the QL.
Kingigtoq lake. Kingigtoq lake is located 550 m a.s.l. near the Ukassorssuaq glacier c. 30 km from the pres-
ent ice margin. It presently receives meltwater from outlet glaciers that terminate on land and it has to retreat an
unknown distance (km’s) before the meltwater inow ceases (Fig.1). e lake is 6 km long and 3.2 km wide and
consists of several sub-basins up to c. 60 m deep (Fig.2a). Two cores were retrieved from the southern part of one
of the sub-basins – one from the central part at 33 m water depth (Core 1219) and one close to the shore at 6 m
water depth (Core 1220). Cores 1219 and 1220 have been correlated and subdivided into ve sub-units – three
clay units 1, 3, 5 interlayered with clay-gyttja units 2, 4 (Fig.3a). e age models from the two cores (1219, 1220)
are based on six bulk ages and one macrofossil age (Fig.6). At 14 cm a paired terrestrial macrofossil and bulk age
suggest an oset of 650 ± 33 years and this oset has been used in the age models for both cores. In addition, a
number of links have been made between the two cores at the distinct clay units at 41 and 4 cm in core 1219 and
1220, respectively.
e clay units are interpreted as representing periods with glacial meltwater input to the lake whereas the
clay-gyttja units reect periods where the ice margin is retracted behind the present extent. e two age models
are considered reliable although the timing of the middle clay unit, unit 3, is somewhat uncertain. Based on the
age model, the lake was deglaciated before 9.5 cal. ka BP. Meltwater inow occurred until ~9 cal. ka BP and again
from ~4.5 to 3 cal. ka BP and was interrupted by a period of clay-gyttja deposition although the timing is uncer-
tain because of the poorly constrained age model at this interval (Fig.7). e most recent inow of meltwater
began ~0.3 cal. ka BP during the LIA. In between the periods with meltwater inow the ice margin was retracted
and clay-gyttja was deposited.
Sermilik lake. Sermilik lake is located 100 m a.s.l. in a small depression, 4 km from the present ice margin
at the central part of the QL (Fig.1). e lake currently receives meltwater and the ice margin has to retreat at
least several kilometres before the meltwater inow to Sermilik lake ceases (Fig.2b). e lake is 400 m wide and
200 m long and it consists of several smaller basins up to 6 m deep. Cores from three sites were retrieved from the
northern part of the lake: 1205 and 1207b (overlapping cores) at 4.4 m water depth and 1209, 1211, 1212 (1211
and 1212 are overlapping cores) at 4.2 m water depth. e cores have been correlated and subdivided into three
units: a lower unit composed of silty-clay (core 1212 has more sandy sediments); a middle unit composed of gyttja
with several distinct mm-to-cm thick layers of sand; and an upper unit composed of silty-clay (Fig.3b). In addi-
tion, there is a thin layer of gyttja below unit 1 in core 1209. e radiocarbon ages of the gyttja are younger than
the overlaying sediments and therefore the gyttja layer is believed to be a coring artifact caused when the corer
accidently was lowered back into the sediments when it was pulled-up. We hypothesise the same issues occurred
Figure 1. Overview map of the study area with the subdivision of the Greenland ice sheet, and local ice
caps42. Active areas of the Greenland ice sheet are marked in light blue and passive areas are marked as white
areas. New and existing threshold lakes are marked with red and black stars, respectively (Adobe Illustrator CS6
was used to create this map; https://www.adobe.com).
www.nature.com/scientificreports/
3
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
Figure 2. Detailed location and bathymetric maps of the threshold lakes analysed in this study showing the
relationship of the lake and the ice sheet. Red arrows mark inow and outow of the lakes Overview maps (le
hand) are derived from Landsat 8 satellite imagery (http://earthexplorer.usgs.gov/). Orthophotos (right hand)
are derived using aero-triangulated vertical stereo photogrammetric imagery recorded in 1985 (Ref. 1). (Maps
were created in ESRI’s ArcGIS ver. 10.3; http://www.esri.com). All images are orientated towards true north.
www.nature.com/scientificreports/
4
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
when retrieving core 1205, where three radiocarbon ages yield consistently younger ages than the succession
above. erefore we do not consider the results from these units of the cores in the following interpretation and
discussion. e age models are based on twenty-one macrofossil and three bulk radiocarbon ages. At two inter-
vals, paired bulk and macrofossil ages reveal an average oset of 516 ± 27 years and this has been used to correct
for the lowermost bulk age at 330 cm.
e clayey-silt units 1 and 3 are interpreted as representing periods with glacial meltwater input to the lake,
whereas gyttja unit 2 reects a period where the ice margin was retracted behind the present extent. e thin
sand layers in gyttja unit 2 (1205 and 1211) are interpreted as debris or grain ows formed close to the inlets of
the lake where deltas have formed and not as evidence of presence of glacier ice in the catchment. According to
the well-constrained age models (Fig.6), the lake was deglaciated before ~9.6 cal. ka BP and the meltwater inow
continued until ~9.4 cal. ka BP. Meltwater inow began again at ~0.5 cal. ka BP (Fig.7).
Kangerdluatsiaup tasia. Kangerdluatsiaup tasia (lake) is located in the foreland of the central part of the
QL adjacent to the Qaleragdlit Sermia (glacier) that terminates in a ord connected to Ikersuaq Fjord (Fig.1).
During the LIA the Qaleragdlit Sermia advanced more than 8 km from its present extent and dammed a valley
forming the Kangerdluatsiaup tasia 100 m a.s.l.15. Aer the glacier retreated, the lake remained dammed by the
sediments that were deposited during the LIA. Sediment outcrops reveal 15–20 m large delta foresets consisting
of sand and gravel below topset sediments (braided river) in the proximal part of the lake close to the ord. e
lake is 4.4 km long and 2.7 km wide and it consists of several sub-basins up to 50 m deep (Fig.2c). It was not
possible to record lake bathymetry in the southern part of the basin because of lake-ice. One core was retrieved
and analysed from a sub-basin in the northwestern part of the lake at 7.7 m water depth. e core consists of a
lower unit of sandy sediments with pebbles and small stones and an upper unit of laminated clay (Fig.4a). e
lamina consists of mm-to-cm thick alternating silty-clay and silty-sand layers, which are clearly expressed in
the magnetic susceptibility data. Little organic material is present in the core, particularly in the upper clay unit.
However, four macrofossil and bulk samples from the lower unit and one macrofossil sample from the upper unit
have been dated (Fig.4a).
e lower unit is interpreted as a soil covering the valley oor whereas the laminated clay was deposited when
the valley was dammed by the Qaleragdlit Sermia and meltwater owed into the valley and deposited foresets and
Figure 3. Sediment proxies (core images, stratigraphy, 14C ages, LOI and XRF K-counts) from: (a) Kingigtoq
subdivided into ve units. Note that the cores images appear darker due to the sediments oxidizing and (b)
Sermilik cores subdivided into three units. e green marks on the cores represent radiocarbon ages based
on terrestrial macrofossils, whereas red marks represent bulk radiocarbon ages. Note that the underlined
radiocarbon ages from the lowermost part of cores 1205 and 1209 show reversals and are therefore not used in
the age models (see main text).
www.nature.com/scientificreports/
5
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
topsets in the proximal part of the lake and bottomsets in the distal part. e bulk and macrofossil ages of the soil
are not in chronological order and range from ~2.1–6.7 cal. ka BP (Fig.4a). However, we consider the two macro-
fossil ages most reliable, which suggest an age of soil formation between ~5.2 and 6.7 cal. ka BP. We interpret the
clay deposition on the valley oor soil to represent a disconformity and therefore do not use those ages in the age
model. Instead, we use the youngest radiocarbon age of macrofossil within the clay as a minimum limiting age
and conclude that the meltwater inow began > 0.14 cal. ka BP during the LIA (Fig.7).
Akuliarusseq lake. Akuliarusseq lake is located adjacent to the outlet glacier that terminates in the Ikersuaq
ord in South Greenland (Fig.1). It receives meltwater when the ice margin is located close to the LIA limit, but
at present there is no inow of meltwater to the lake. Echo soundings reveal that the elongate lake consists of two
basins separated by the remnants of an end-moraine that acts a deep sill (Fig.2d). Two cores, 1202 and 1203, were
retrieved at 20.6 and 17.3 m water depth, respectively. e two cores have been correlated and subdivided into
four units (Fig.4b). e changes between the units of gyttja and clay are very distinct in the cores and the lower
boundary between the gyttja and clay is sharp, whereas the boundary between clay and gyttja is transitional. e
lower unit 1 only occurs in core 1203 and consists of gyttja with distinct 2–10 cm thick sand layers. Unit 2 has
been subdivided into three units and consists of clay interlayered with 2–15 cm gyttja. Unit 3 comprises laminated
gyttja followed by unit 4 consisting of massive to laminated clay. e age model of Akuliarusseq lake is based on
een radiocarbon samples of which three are bulk samples (Fig.6). e bulk samples appear in good agreement
with the terrestrial radiocarbon ages and hence no oset correction is applied. Clay bands based on lithology
and Potassium (K counts) in the two cores have been linked during age modelling at depths 211, 189, 141 and
89 in core 1203 with depth 145, 139, 127 and 41 cm in core 1202. e lower part of core 1202 has not been dated
Figure 4. Sediment proxies (core images, stratigraphy, 14C ages, LOI and XRF K-counts) from: (a)
Kangerdluatsiaup tasia subdivided into two units and (b) Akuliarusseq subdivided into four units. e green
marks on the cores represent radiocarbon ages based on terrestrial macrofossils whereas red marks represent
bulk radiocarbon ages. Note that underlined radiocarbon ages are not used in the age model.
www.nature.com/scientificreports/
6
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
because of absence of organic material in the clay. e two samples from the rst gyttja layer (unit 2B) are bulk
ages, and therefore we have more condence in the age model from core 1203. Accordingly, we base our conclu-
sion mainly on the age model from core 1203 in the lower part and use both age models in the upper part of the
cores where they agree very well.
e clayey-silt units are interpreted as representing periods of glacial meltwater input to the lake, whereas the
gyttja units reect periods where the ice margin was retracted behind the present extent. e distinct sand layers
in the gyttja in core 1203, which is located close to a small inlet in the most distal part of the lake, are interpreted
as sediment debris ow deposits and not as evidence of presence of glacier ice in the catchment. Based on visual
inspection and the sediment proxies, there is good correlation between the upper and the lower clayey-silt unit
in the two cores. Deglaciation of the lake basin is not recorded in the cores because the core bottoms out in gyttja
with a basal age of ~5.5 cal. ka BP (Fig.7). Meltwater inow was recorded during three events: ~3.4–3.0 cal. ka
BP, 2.5–1.9 cal. ka BP and again from ~0.4 cal. ka BP until the most recent ice retreat, which has le a thin layer of
gyttja at the top of core 1203.
Storesø og Rundesø. Storesø and Rundesø (lakes) are located 30 km north of Narsarsuaq and were over-
ridden when the Nordgletscher and Kiagtût sermiat (glaciers) merged and formed the Narsarsuaq moraines in
the east-west orientated valley draining into Nordbosø15. e lakes received meltwater during the Narsarsuaq
stage, but not during the LIA where the meltwater ponded in Hullet (proglacial lake) and was drained subglacially
below Kiagtût sermiat into the Narsarsuaq valley15. Storesø is a 1.7 km long and 0.6 km wide lake and consists of
several sub-basins. e core was retrieved at 14.5 m water depth (Fig.2e). Rundesø is a circular lake with a diame-
ter of 500 m and was cored at 9.9 m water depth (Fig.2e). One core from each lake was analysed and they showed
a similar lithology composed of two units (Fig.5). e lower unit, unit 1, consists of laminated clay and the upper
unit, unit 2, consists of gyttja. Four bulk and three macrofossil radiocarbon samples of the two cores have been
dated. However, due to the inconsistent results with inverted ages (outliers) no age models have been made from
the two lakes. Instead the few reliable ages are used to estimate the approximate timing of the change from clay
to gyttja in the two lakes.
e lower clay unit 1 is interpreted as representing a period of glacial meltwater input to the lake whereas the
gyttja reects a period where the ice margin was retracted behind the Narsarsuaq stage extent. In Storesø the
uppermost bulk age in the clay is ~0.6 cal. ka BP and in Rundesø the transition between clay and gyttja is xed
between ~0.7 and 0.4 cal. ka BP (Fig.5). Accordingly, meltwater owed into the lakes from > 0.9–0.6 cal. ka BP
aer which the ice margin retreated out of the catchment of the lakes (Fig.7).
Discussion
e initial deglaciation is recorded in two of the six new threshold lakes showing that the area was deglaciated by
~9.6 cal. ka BP. Furthermore, the records reveal that the QL ice margin retreated outside the lake catchment areas
between ~9.3–9.0 cal. ka BP (Fig.7). is agrees well with the Qipisarqo lake record, which shows gyttja deposi-
tion starting at ~9.1 cal. ka BP13. It is also consistent with the ages of reworked organic material in LIA moraines,
indicating that the ice margin of QL was retracted by ~9 cal. ka BP2. One exception is the Lower Nordbosø where
the glacier remained within the catchment until ~6.9 cal. ka BP, most likely as a result of local topography rather
than being governed by climate11. e timing of the initial ice retreat based on threshold lakes is ~1.3–1.9 ka;
younger than inferred from 10Be surface exposure ages proximal to the LIA moraines, suggesting that the ice
margin retreated within the late Holocene maximum extent by ~11.2–10.6 ka in South Greenland12. is dis-
crepancy may be attributed to two issues: First, the threshold lake records are minimum limiting ages from the
base of the sediment cores, which is oen clay-rich and lacking dateable organic material. Second, the 10Be ages
record when the ice retreated from the location proximal to the LIA moraines and thus it should be regarded as
a maximum age of when the ice margin could have retreated behind the present extent, assuming that the early
Figure 5. Sediment proxies (core images, stratigraphy, 14C ages, LOI, Magnetic susceptibility, and XRF K and
Ti-counts) from: (a) Storesø and (b) Rundesø which both are subdivided into two units. e green marks
on the cores represent radiocarbon ages based on terrestrial macrofossils whereas red marks represent bulk
radiocarbon ages. Note that underlined radiocarbon ages of bulk sediments are considered to be to old and are
not used in the analysis.
www.nature.com/scientificreports/
7
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
Holocene ice retreat occurred without any pauses. Accordingly, e QL ice margin reached the present extent by
~11.2–10.6 ka12 aer which it, in most places, retreated behind the present extent during the initial deglaciation
phase at minimum ~9.3–9.0 cal. ka BP (Fig.8a).
Following the initial deglaciation, the ice margin retreated behind its current margin until the Neoglacial
when the ice margin on the anks of the QL lobe (Akuliarusseq, Lower Nordbosø) and 50 km north of the QL
(Kingigtoq) reached its present extent between ~4.4 and 3.0 cal. ka BP. e ice remained at its present position
from ~3.0 to1.9 cal. ka BP with a short period of ice retreat (Figs7 and 8b). In contrast, the ice margin in the
central part of the QL (Qipisargo, Sermilik, Kangerdluatsiaup tasia) remained retracted until the LIA, although
it is likely that the central part of the lobe made a readvance similar to the marginal part of the lobe during the
Neoglacial (Fig.8b). A Neoglacial advance has also been recorded in threshold lakes in other areas of Greenland
and the timing of the meltwater inux appear in most lakes at ~3–2 cal. ka BP14,16–21. However, some lakes in West
and Southeast Greenland received meltwater as early as ~6.3 and ~5.0 cal. ka BP, respectively14,16. During this
time the ice sheet has been shown to be smaller than present. erefore, this seems to suggest that the ice mar-
ginal response in some places is strongly inuenced by local topographic conditions rather than being governed
by climate changes alone. is period of retracted ice margin coincides with the Holocene ermal Maximum
(HTM) ~8–5 cal. ka BP where the local air temperatures in South Greenland was as much as 2–4 °C warmer than
present22,23 and when there was increased inow of warm Atlantic water in East and West Greenland24–27. Recent
numerical modelling based on a large number relative sea level observations from Greenland suggest that the
GrIS reached a minimum Holocene ice extent ~4 ka ago and contributed with 16 cm to the global sea level28.
is modelled ice volume minimum occurs rather late compared to the temperature maximum in Greenland,
Figure 6. Age models for the sediment cores from Kingigtoq, Sermilik and Akuliarusseq lakes. No age
models were made for Rundesø, Storesø and Kangerdluatsiaup tasia because of an insucient number of
radiocarbon ages.
www.nature.com/scientificreports/
8
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
but it corresponds well with threshold lake records in southern Greenland and also suggests a signicant inertia
between local temperature forcing and ice sheet response16.
Aer the Neoglacial readvance that culminated between ~3 and 1.8 cal. ka BP the QL retreated in all sectors
and gyttja was deposited in the lakes until ~0.5–0.2 cal. ka BP. Subsequently, the ice margin re-advanced to its
LIA position (Figs7 and 8c). e period with retracted ice margin corresponds to the last part of the Roman
Warm Period (~2.25–1.6 cal. ka BP) the colder European Dark Ages (~1.6–1.25 cal. ka BP) and the Medieval
Warm Anomaly (~1.25–0.75 ka cal. ka BP). However it is still unresolved how these late Holocene climate events
aected local climate in Greenland. Some records show a reduced inow of warm Atlantic water in ords during
the Roman Warm Period and the Medieval Warm Anomaly29, while other records show a strengthening of the of
Atlantic water advection24–27,30 and increased atmospheric temperatures22,31 suggesting that the warmer climate
most likely triggered the retracted ice margin of QL during this period. One exception is the Kiagtût Sermiat
(glacier) near Narsarsuaq, which advanced outside the LIA position and formed the Narsarsuaq moraine. e
age of the moraine was originally dated to ~1.2 cal. ka BP using minimum limiting radiocarbon ages of lake sed-
iments32. However, a more recent study based on 10Be surface exposure ages suggests that Narsarsuaq moraine
was formed and abandoned by 1.5 ka and the ice margin has been within or at its LIA extent since 1.3 ka33. ese
data suggest that the Kiagtût Sermiat advanced at 1.5 ka and remained close to the LIA moraine until ~0.6 cal.
ka BP aer which it retreated behind the LIA extent. Our results from Storesø and Rundesø also show that the
Kiagtût Sermiat was retracted from c. 0.6 cal. ka BP. is behaviour is unlike the general pattern of the QL that
remained retracted until ~0.5–0.2 cal. ka BP where the ice margin reached its LIA position and therefore this sug-
gests that the Kiagtût Sermiat is not representative of the ice margin uctuations in southern Greenland. Instead
it may reect that Kiagtût Sermiat was inuenced by local topographic conditions or it may have experienced a
surge-type advance, although there is no historical evidence in support of this hypothesis.
In summary, using six new threshold lake records combined with two existing threshold lake records, radi-
ocarbon ages of reworked organic remains in LIA moraines, and published 10Be surface exposure ages we have
constrained the Holocene glacial history of the QL – the southernmost part of the GrIS. e locations of the
threshold lakes that have been analysed from various places around the QL, in conjunction to the published data,
provide a unique opportunity to assess both the spatial and temporal resolution of the ice marginal changes. At
the central part of the QL the ice margin was retracted from the initial deglaciation, ~9.3–9.0 cal. ka BP until the
LIA ~0.5–0.2 cal. ka BP. At the margins of the QL and adjacent to the ice lobe this long period of retracted ice mar-
gin position was interrupted by a Neoglacial readvance to the present ice extent between ~4.4 and 1.9 cal. ka BP.
In all sectors of the QL, the ice margin re-advanced during the LIA between ~0.5 and 0.2 cal. ka BP. ese results
clearly show that multiple threshold lakes may be needed to obtain a comprehensive history of ice marginal
uctuations of a larger ice lobe and that a single threshold lake record may not be sucient to infer ice marginal
uctuations for a large part of the ice sheet. However, in general, the results show that the southern margin of the
GrIS responded to the recorded Holocene climate forcings and also emphasises the role of local topography on
ice marginal changes.
Figure 7. Compilation of threshold lake data from South Greenland. e horizontal bars represent periods
with retracted ice margin – green: deglaciation, orange: Neoglacial, blue: LIA, yellow: Narsarsuaq stage
moraine33. Prolonged periods of ice retreat are recorded in the central part of the QL whereas less prolonged
periods of ice retreat is observed at the margin and adjacent to the QL.
www.nature.com/scientificreports/
9
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
Methods
We analysed sediment cores from six threshold lakes located adjacent to the present ice margin distal to the
QL in South Greenland to obtain a better understanding of its Holocene ice marginal uctuations. We chose
these threshold lakes because they only receive meltwater and clastic sediments (silt and clay) during periods of
close-to-present ice extent, whereas non-glacial organic rich sediments (gyttja) are deposited during intervals
with restricted ice extent in the catchment34. is approach has successfully been adapted to study ice marginal
uctuations of the GrIS and local ice caps in Greenland11,13,14,16,18,19,21.
e lakes were identied using satellite and aerial photographs. In the eld, an echo sounder with a built-in
GPS was used to measure the lake depth and create a bathymetric map. The lakes were cored using a cus-
tom built piston corer capable of obtaining 4 m of sediments at a lake depth up to 50 m. One exception is the
Kangerdluatsiaup tasia (lake) that was cored using the Uwitec coring equipment. Aer retrieval, the cores were
kept in an upright position and drained before being packed and shipped back to the laboratory where they were
stored at 2 °C. In the laboratory the cores were split in half, cleaned and a lithological description was made. An
ITRAX core scanner was used to take high-resolution pictures and measure micro-XRF and magnetic suscepti-
bility (MS) at every 2 mm and 0.5 mm, respectively. e XRF scans were made at Aarhus University core scanning
facility with a molybdenum tube set at 30 kV and 30 mA with a dwell time of 30 seconds. Prior to analysis the
sediment surfaces were carefully attened and subsequently covered with thin (4 m) ultralene lm. A step size
of 2 mm was selected to capture possible elemental variations in even small laminations. To illustrate the changes
Figure 8. Map showing when the threshold lakes adjacent to the QL received meltwater inux during the
Holocene: (a) Deglaciation, (b) Neoglacial and (c) LIA (Adobe Illustrator CS6 was used to create these maps;
https://www.adobe.com).
www.nature.com/scientificreports/
10
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
from gyttja to clastic sediments Ti, K or Si are oen used as a measure of clastic input11,35. In this study we have
used K normalized by incoherent and coherent to remove various instrumental scattering36. Loss-on-ignition
(LOI) was analysed for every 1 cm by combustion of 2 cm3 sample at 550 °C for 4 hours37.
Samples for radiocarbon dating were sub-sampled with the primary objective to date clastic layers (meltwater)
within the cores. We preferably sampled and identied terrestrial macrofossils in 1-cm intervals. When terrestrial
macrofossils were absent, we used moss or bulk samples (humic acid) for radiocarbon dating. Using bulk sample
to estimate the age of sediments can be problematic because bulk samples integrate carbon of both allochthonous
and autochthonous origins. Consequently eroded soil carbon may for example in some cases constitute a major
fraction of the bulk carbon. Hence bulk 14C ages therefore oen deviate substantially from the true age of sedi-
ments. Further, as the origin of bulk carbon will depend on hydrology, catchment processes and morphology the
bulk 14C age oset will most oen deviate between dierent lakes38,39. e 14C bulk age oset can be estimated
using paired bulk and terrestrial macrofossil samples in order to correct unpaired bulk 14C ages16. e samples
were dated at the AMS 14C Centre at Aarhus University (AAR), Lund University (LU) and Belfast University
(UBA). e age models are based on radiocarbon ages of 40 macrofossils and 18 bulk sediment samples that have
been converted into calendar years using Oxcal 4.2 and calibrated to calendar years using IntCal1340,41 and are
quoted as cal. yr BP or cal. kyr BP (Supplementary Data set 1). Depth-to-age models were constructed using the
depositional model method of Oxcal 4.2 except for lakes Kangerdluatsiaup tasia, Rundersø and Storesø where
there are too few radiocarbon ages to make a reliable age-depth model. In all age models the age of the top sedi-
ment is set to the year of coring.
References
1. jeldsen, . . et al. Spatial and temporal distribution of mass loss from the Greenland Ice Sheet since AD 1900. Nature 528,
396–400 (2015).
2. Weidic, A., elly, M. & Bennie, O. Late Quaternary development of the southern sector of the Greenland Ice Sheet, with particular
reference to the Qassimiut lobe. Boreas 33, 284–299 (2004).
3. Weidic, A., Bøggild, C. E. & nudsen, N. T. Glacier inventory and atlas of West Greenland. app Grønlands Geol Undersøgelse 158,
1–194 (1992).
4. Funder, S., jeldsen, . ., jær, . H. & Ó Cofaigh, C. e Greenland ice sheet during the last 300.000 years: a review. Dev
Quaternary Sci 15, 699–713 (2011).
5. nutz, P. C., Sicre, M. A., Ebbesen, H., Christiansen, S. & uijpers, A. Multiple-stage deglacial retreat of the southern Greenland Ice
Sheet lined with Irminger Current warm water transport. Paleoceanography 26, doi: 10.1029/2010pa002053 (2011).
6. Winsor, ., Carlson, A. E., Wele, B. & eilly, B. Early deglacial onset of southwestern Greenland ice-sheet retreat on the continental
shelf. Quaternary Sci ev (2015).
7. Carlson, A., Stoner, J. S., Donnelly, J. P. & Hillaire-Marcel, C. esponse of the southern Greenland Ice Sheet during the last two
deglaciations. Geology 36, 359–362 (2008).
8. Bennie, O. & Björc, S. Chronology of the last recession of the Greenland Ice Sheet. J Quaternary Sci 17, 211–219 (2002).
9. Winsor, ., Carlson, A. E., Caee, M. W. & ood, D. H. apid last-deglacial thinning and retreat of the marine-terminating
southwestern Greenland ice sheet. Earth Planet Sc Lett 426, 1–12 (2015).
10. Sparrenbom, C. et al. Holocene relative sea-level changes in the inner Bredeord area, southern Greenland. Quaternary Sci ev 69,
107–124 (2013).
11. Larsen, N. . et al. estricted impact of Holocene climate variations on the southern Greenland Ice Sheet. Quaternary Sci ev 30,
3171–3180 (2011).
12. Carlson, A. E. et al. Earliest Holocene south Greenland ice sheet retreat within its late Holocene extent. Geophys es Lett 41,
5514–5521 (2014).
13. aplan, M. ., Wolfe, A. P. & Miller, G. H. Holocene environmental variability in southern Greenland inferred from lae sediments.
Quaternary es 58, 149–159 (2002).
14. Briner, J. P., Stewart, H. A. M., Young, N. E., Philipps, W. & Losee, S. Using proglacial-threshold laes to constrain uctuations of the
Jaobshavn Isbrae ice margin, western Greenland, during the Holocene. Quaternary Sci ev 29 (2010).
15. Weidic, A. Ice margin features in the Julianehåb District. Medd Grønland 165, 1–133 (1963).
16. Larsen, N. . et al. e response of the southern Greenland ice sheet to the Holocene thermal maximum. Geology 43, 291–294
(2015).
17. Young, N. E. & Briner, J. P. Holocene evolution of the western Greenland Ice Sheet: Assessing geophysical ice-sheet models with
geological reconstructions of ice-margin change. Quaternary Sci ev 114, 1–17 (2015).
18. elley, S. E., Briner, J. P., Young, N. E., Babonis, G. S. & Csatho, B. Maximum late Holocene extent of the western Greenland Ice Sheet
during the late 20th century. Quaternary Sci ev 56, 89–98 (2012).
19. Young, N. E. et al. esponse of Jaobshavn Isbrae Greenland, to Holocene climate change. Geology 39, 131–134 (2011).
20. Håansson, L., Briner, J., Andresen, C. S., omas, E. . & Bennie, O. Slow retreat of a land based sector of the West Greenland Ice
Sheet during the Holocene ermal Maximum: evidence from threshold laes at Paaitsoq. Quaternary Sci ev 98, 74–83 (2014).
21. Levy, L. B. et al. Holocene uctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate along the Greenland Ice
Sheet margin. Quaternary Sci ev 92, 357–368 (2014).
22. Frechette, B. & de Vernal, A. elationship between Holocene climate variations over southern Greenland and eastern Ban Island
and synoptic circulation pattern. Clim Past 5, 347–359 (2009).
23. Wooller, M. J. et al. Quantitative paleotemperature estimates from delta O-18 of chironomid head capsules preserved in arctic lae
sediments. J Paleolimnol 31, 267–274 (2004).
24. Jennings, A., Andrews, J. & Wilson, L. Holocene environmental evolution of the SE Greenland Shelf North and South of the
Denmar Strait: Irminger and East Greenland current interactions. Quaternary Sci ev 30, 980–998 (2011).
25. Jennings, A. E. et al. Paleoenvironments during Younger Dryas-Early Holocene retreat of the Greenland Ice Sheet from outer Diso
Trough, central west Greenland. J Quaternary Sci 29, 27–40 (2014).
26. Lloyd, J. M., uijpers, A., Long, A., Moros, M. & Par, L. A. Foraminiferal reconstruction of mid- to late-Holocene ocean circulation
and climate variability in Diso Bugt, West Greenland. Holocene 17, 1079–1091 (2007).
27. Telesinsi, M. M., Spielhagen, . F. & Lind, E. M. A high-resolution Lateglacial and Holocene palaeoceanographic record from the
Greenland Sea. Boreas 43, 273–285 (2013).
28. Lecavalier, B. S. et al. A model of Greenland ice sheet deglaciation constrained by observations of relative sea level and ice extent.
Quaternary Sci ev 102, 54–84 (2014).
29. Seidenrantz, M. S. et al. Hydrography and climate of the last 4400 years in a SW Greenland ord: implications for Labrador Sea
palaeoceanography. Holocene 17, 387–401 (2007).
www.nature.com/scientificreports/
11
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
30. Miattinen, A., Divine, D. V., Husum, ., oc, N. & Jennings, A. Exceptional ocean surface conditions on the SE Greenland shelf
during the Medival Climate Anomaly. Paleoceanography 30, doi: 10.1002/2015PA002849 (2015).
31. aufman, D. S. et al. ecent Warming everses Long-Term Arctic Cooling. Science 325, 1236–1239 (2009).
32. Bennie, O. & Sparrenbom, C. J. Dating of the Narssarssuaq stade in southern Greenland. Holocene 17, 279–282 (2007).
33. Winsor, ., Carlson, A. E. & ood, D. H. Be-10 dating of the Narsarsuaq moraine in southernmost Greenland: evidence for a late-
Holocene ice advance exceeding the Little Ice Age maximum. Quaternary Sci ev 98, 135–143 (2014).
34. arlen, W. Lacustrine sediment studies - a technique to obtain a continous record of holocene glacier variations. Geogr Ann A 63,
273–281 (1981).
35. ylander, M. E., Ampel, L., Wohlfarth, B. & Veres, D. High-resolution XF core scanning analysis of Les Echets (France)
Sedimentary sequence: new insights from chemical proxies. J Quaternary Sci 26, 109–117 (2011).
36. ylander, M. E., laminder, J., Wohlfarth, B. & Löwemar, L. Geochemical responses to paleoclimatic changes in southern Sweden
since the late glacial: the Hässeldala Port lae sediment record. J Paleolimnol 50, 57–70 (2013).
37. Heiri, O., Lotter, A. F. & Lemce, G. Loss on ignition as a method for estimating organic and carbonate content in sediments:
reproducibility and comparability of results. J Paleolimnol 25, 101–110 (2001).
38. Abbott, M. B. & Staord, T. W. adiocarbon geochemistry of modern and ancient Arctic lae systems, Ban Island, Canada.
Quaternary es 45, 300–311 (1996).
39. Olsen, J., jær, . H., Funder, S., Larsen, N. . & Ludiova, A. High-Arctic climate conditions for the last 7000 years inferred from
multi-proxy analysis of the Bliss Lae record, North Greenland. J Quaternary Sci 27, 318–327 (2012).
40. amsey, C. B. Deposition models for chronological records. Quaternary Sci ev 27, 42–60 (2008).
41. eimer, P. J. et al. IntCal13 and Marine13 adiocarbon Age Calibration Curves 0–50,000 Years cal BP. adiocarbon 55, 1869–1887
(2013).
42. Weidic, A. Gletschere i Sydgrønland, historie, natur og omgivelser. Grønlands Geol Undersøgelse, 1–80 (1988).
Acknowledgements
is work is a part of the X_Centuries project funded by the Danish Council Research for Independent research
(FNU) (grant no. 0602-02526B), Villum Foundation, and the Centre for GeoGenetics. KKK acknowledges
support from the Danish Council Research for Independent research (grant no. DFF - 4090-00151). We thank
prof. Ian Snowball for lending us the Uwitec coring equipment.
Author Contributions
e work was conceived by N.K.L. and K.H.K. e eldwork was conducted by A.A.B., K.H.K., K.K.K. and
N.K.L. Sediment core analysis were performed by J.F., A.K., A.A.B., K.K.K. and N.K.L. Macrofossil identication,
radiocarbon dating and age modeling was done by B.V.O., J.O. and N.K.L. e paper was written by N.K.L. with
contributions from all co-authors.
Additional Information
Supplementary information accompanies this paper at http://www.nature.com/srep
Competing nancial interests: e authors declare no competing nancial interests.
How to cite this article: Larsen, N. K. et al. Holocene ice marginal uctuations of the Qassimiut lobe in South
Greenland. Sci. Rep. 6, 22362; doi: 10.1038/srep22362 (2016).
is work is licensed under a Creative Commons Attribution 4.0 International License. e images
or other third party material in this article are included in the article’s Creative Commons license,
unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license,
users will need to obtain permission from the license holder to reproduce the material. To view a copy of this
license, visit http://creativecommons.org/licenses/by/4.0/
