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Holocene ice marginal fluctuations of the Qassimiut lobe in South Greenland


Abstract and Figures

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 fluctuations 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 find 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 fluctuations.
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Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
Holocene ice marginal uctuations
of the Qassimiut lobe in South
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 dierences 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 inuences 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 signicantly 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:
received: 23 November 2015
accepted: 12 February 2016
Published: 04 March 2016
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
(Figs2–5); 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 (kms) before the meltwater inow 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 oset of 650 ± 33 years and this oset 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 reect 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 inow 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 inow of meltwater
began ~0.3 cal. ka BP during the LIA. In between the periods with meltwater inow 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 inow 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;
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 inow and outow of the lakes Overview maps (le
hand) are derived from Landsat 8 satellite imagery ( 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; All images are orientated towards true north.
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 oset 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 reects 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 inow
continued until ~9.4 cal. ka BP. Meltwater inow 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. Aer 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).
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 inow 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 inow 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 oset 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.
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 condence 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 reect 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 inow 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 reects 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
aer which the ice margin retreated out of the catchment of the lakes (Fig.7).
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 oen 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.
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 aer 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 (Figs7 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 inux 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 inuenced 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 inow 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 insucient number of
radiocarbon ages.
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
but it corresponds well with threshold lake records in southern Greenland and also suggests a signicant inertia
between local temperature forcing and ice sheet response16.
Aer 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 (Figs7 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
aected local climate in Greenland. Some records show a reduced inow 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 aer 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 reect that Kiagtût Sermiat was inuenced 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 sucient 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.
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
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 identied 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. Aer 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 inux during the
Holocene: (a) Deglaciation, (b) Neoglacial and (c) LIA (Adobe Illustrator CS6 was used to create these maps;
Scientific RepoRts | 6:22362 | DOI: 10.1038/srep22362
from gyttja to clastic sediments Ti, K or Si are oen 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 identied 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 oen 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 oset will most oen deviate between dierent lakes38,39. e 14C bulk age oset 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.
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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 identication,
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
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).
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... As expected, we found that generally younger ages were modelled by as much as 400 years (e.g., Kaplan et al., 2002;Larsen et al., 2011Larsen et al., , 2015Larsen et al., , 2016Larsen et al., , 2017Levy et al., 2017). Using age estimates from context-specific and reliable models built consistently across the dataset would likely improve the accuracy of these estimates. ...
... The remaining lakes (n=9) record an older Neoglacial advance with no distinct LIA signal within the minerogenic layer. Only two lakes (Storesø and Rundesø) in Southwest Greenland capture older or potentially older, organic sequences that may indicate a larger Neoglacial compared to the LIA threshold scenario (Larsen et al., 2016). However, poor age constraints at these sites preclude establishing the timing of an older Neoglacial onset. ...
... However, poor age constraints at these sites preclude establishing the timing of an older Neoglacial onset. Furthermore, these lakes receive meltwater input during glacier fluctuations that were related to local climate and/or topography independent of regional ice sheet fluctuations (Larsen et al., 2016). ...
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... Kiagtût Sermiat was influenced by local topographic conditions or internal dynamics and is not representative of regional glacier fluctuations in southern Greenland (22). ...
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Accelerated melting of the Greenland Ice Sheet has increased freshwater delivery to the Arctic Ocean and amplified the need to understand the impact of Greenland Ice Sheet meltwater on Arctic greenhouse gas budgets. We evaluate subglacial discharge from the Greenland Ice Sheet for carbon dioxide (CO2) and methane (CH4) concentrations and δ13C values and use geochemical models to evaluate subglacial CH4 and CO2 sources and sinks. We compare discharge from southwest (a sub-catchment of the Isunnguata Glacier, sub-Isunnguata, and the Russell Glacier) and southern Greenland (Kiattut Sermiat). Meltwater CH4 concentrations vary by orders of magnitude between sites and are saturated with respect to atmospheric concentrations at Kiattut Sermiat. In contrast, meltwaters from southwest sites are supersaturated, even though oxidation reduces CH4 concentrations by up to 50 % during periods of low discharge. CO2 concentrations range from supersaturated at sub-Isunnguata to undersaturated at Kiattut Sermiat. CO2 is consumed by mineral weathering throughout the melt season at all sites; however, differences in the magnitude of subglacial CO2 sources result in meltwaters that are either sources or sinks of atmospheric CO2. At the sub-Isunnguata site, the predominant source of CO2 is organic matter (OM) remineralization. However, multiple or heterogeneous subglacial CO2 sources maintain atmospheric CO2 concentrations at Russell but not at Kiattut Sermiat, where CO2 is undersaturated. These results highlight a previously unrecognized degree of heterogeneity in greenhouse gas dynamics under the Greenland Ice Sheet. Future work should constrain the extent and controls of heterogeneity to improve our understanding of the impact of Greenland Ice Sheet melt on Arctic greenhouse gas budgets, as well as the role of continental ice sheets in greenhouse gas variations over glacial–interglacial timescales.
Understanding the long-term difference in the response times of ice sheets, peripheral ice caps and glaciers may provide information about their respective sensitivities to climate change. However, there are only a few places where the history of local glaciers, ice caps (GICs) and the Greenland Ice Sheet (GrIS) have been recorded in the same area. In this study, we use proglacial threshold lake records from four sites around Sermilik Fjord, in southeast Greenland to determine the Holocene ice marginal variations. Combined with other published records from the area, we find that the GrIS margin receded to within its present extent in the Early Holocene ∼9.6 cal ka BP, probably reaching its minimum extent by ∼7.3 to 6.3 cal ka BP before readvancing to its maximum Late Holocene position between ∼2.6 and 0.3 cal ka BP. The GICs began to retreat ∼9.5 cal ka BP and completely melted away for an extended period between ∼8 and 4 ka during the Middle Holocene. Regrowth of the GICs began during the early- and late Neoglacial and they reached their maximum extent between ∼1.2 and 0.7 cal ka BP. In general, we find a coherent pattern of ice marginal variations between the GrIS and GICs, which coincides with the major Holocene climate changes. However, our results also demonstrate that there are differences in the synchronicity between individual records, which largely are dictated by the local topography that determines when ice marginal changes were recorded in proglacial lakes. Accordingly, this study illustrates both the advantages and limitations of the method and highlight the need for multiple proglacial lake records to constrain past glacier variations in a region.
Cosmogenic exposure dating is one of the most widely used methods to constrain the deglaciation history of former glaciated areas. In Greenland, more than 1000 cosmogenic ¹⁰Be exposure ages (¹⁰Be ages) have been published within the last two decades. However, a recurring problem is that many of these studies have reported variable amounts of nuclide inheritance making the ¹⁰Be ages too old and difficult to assess without large datasets or independent age control. In this study, we test the accuracy of ¹⁰Be dating of Holocene moraines using independent age constraints from threshold lake records. In Kangerlussuaq, West Greenland, the ¹⁰Be ages of the Ørkendalen moraine system are highly clustered with a mean age of 6.8 ± 0.3 ka (no outliers). In contrast, the nearby LIA moraine yields scattered ¹⁰Be ages ranging from 2.5 to 0.1 ka but with a mean of 0.18 ± 0.06 ka after excluding outliers which coincides with independent age constraints from threshold lakes and boulder kill dates. At Gletscherlukket, Southeast Greenland, the ¹⁰Be ages of the LIA moraine range from 10.2 to 1.6 ka with a mean of 1.9 ± 0.2 ka after excluding outliers. This is ∼1.7 ka older than recorded in the proglacial threshold lakes and suggests that all samples from this site contain a significant amount of nuclide inheritance. Our results are consistent with other reports of skewed ¹⁰Be age distributions in LIA re-advance moraines and it probably reflects nuclide inheritance from exposure during the Holocene Thermal Maximum when the glaciers in Greenland were inside the LIA extent. In contrast, there is no evidence of nuclide inheritance in the Ørkendalen moraines, most likely because the glacial erosion was more intense prior to the formation of the moraines i.e. sometime between the advance phase during Last Glacial Maximum position and the subsequent lateglacial and Holocene deglaciation. Our results highlight a potential pitfall related to dating re-advance moraines using cosmogenic exposure dating and we recommend using a multi-method dating approach.
Knowledge about the deglaciation history of the Greenland Ice Sheet (GrIS) is important to put the recent observations of ice loss into a longer‐term perspective. In southern Greenland, the deglaciation history is generally well constrained. In this study, we use 43 new ¹⁰Be surface exposure ages combined with existing minimum‐limiting ¹⁴C ages to constrain the deglaciation history of eastern North Greenland, including the three major fjord systems – Independence Fjord, Hagen Fjord and Danmark Fjord. The ¹⁰Be ages are generally scattered and many of the samples are significantly older than expected, with pre‐LGM ages being a result of inheritance from previous exposures. By using a Bayesian statistical approach to combine the new ¹⁰Be ages and existing ¹⁴C ages, we are able to constrain the deglaciation history. We find that the outer coast and deep fjords were rapidly deglaciated between ̃11 and 10 ka. Subsequently, the deglaciation progressed far inland up the fjords, probably as a result of increased summer surface temperatures and subsurface ocean temperatures during the Holocene Thermal Maximum. The rapid retreat of the Middle Holocene slowed when the ice sheet became land‐based in the central and southern part of the study area where the ice margin first reached its present extent by ̃6.7 ka. As the onset of Neoglacial ice advance had already commenced at ̃5 ka this limits the period when the ice margin could retreat farther inland and it probably remained within max. 30–40 km of its present extent. The contrasting behaviour between the fjords and inter‐fjord areas shows a clear topographic effect on the stability of the GrIS. These results inform how the GrIS may respond to a warmer climate in various topographic settings and may provide useful constraints for future ice‐sheet models.
To put recent Greenland Ice Sheet (GrIS) ice loss into a longer-term context, we must understand its behavior during late-glacial and Early Holocene warming. Previous results seem to suggest that there is a large contrast in the timing of deglaciation between South and Southeast Greenland. However, because of lack of available data, in particular in Southeast Greenland, it is difficult to assess how the ice sheet responded to major late-glacial and Early Holocene climate changes. In this study, we use 41 new ¹⁰Be ages to constrain the deglaciation chronology in 12 new locations from the coast to the present ice margin in South and Southeast Greenland. We find that South Greenland (south of 61.5°N) deglaciated between ∼14.8 and 11.9 ka, whereas Southeast Greenland (61.5°N to 68.2°N) deglaciated between ∼11.4 and 11.3 ka. The deglaciation of the coastal, low-intermediate topography in South Greenland coincides with increased air surface temperatures during the Bølling-Allerød with fjords continuing to deglaciate into the Early Holocene. In contrast, the ice sheet persisted at the coast until the late-glacial and Early Holocene in Southeast Greenland, likely because of increased precipitation in the high alpine topography and fjord geometry and bathymetry (e.g. width of fjords and presence of sills). This multi-phased deglaciation demonstrates a contrasting response of the southern GrIS to changes in climate and variations in topographic setting, and that the spatial deglaciation of the GrIS was complex and likely did not respond to a single external climate forcing.
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Diatom inferred 2900-year-long records of August sea surface temperature (aSST) and April sea-ice concentration (aSIC) are generated from a marine sediment core from the SE Greenland shelf with a special focus on the interval ca. 870–1910 Common Era (CE) reconstructed in subdecadal temporal resolution. The Medieval Climate Anomaly (MCA) between 1000 and 1200 CE represents the warmest ocean surface conditions of the SE Greenland shelf over the late Holocene (880 BCE–1910 CE). It was characterized by abrupt, decadal to multidecadal changes, such as an abrupt warming of ~2.4 °C in 55 years around 1000 CE. Temperature changes of these magnitudes are rare on the North Atlantic proxy data. Compared to regional air temperature reconstructions, our results indicate a lag of about 50 years in ocean surface warming either due to increased freshwater discharge from the Greenland ice sheet or intensified sea-ice export from the Arctic as a response to atmospheric warming at the beginning of the MCA. A cool phase, from 1200–1890 CE, associated with the Little Ice Age (LIA), ends with the rapid warming of aSST and diminished aSIC in the early 20th century. The results show that the periods of warm aSST and aSIC minima are coupled with the solar minima suggesting that solar forcing possibly amplified by atmospheric forcing have been behind the variability of surface conditions on the SE Greenland over the last millennium. The results indicate that the SE Greenland shelf is a climatologically sensitive area where extremely rapid changes are possible and highlights the importance of the area under the present warming conditions.
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The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis of decadally resolved proxy temperature records from poleward of 60°N covering the past 2000 years, which indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.
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Marine-terminating outlet glaciers are a major source of modern ice loss from the Greenland Ice Sheet (GrIS), but their role in GrIS retreat during the last deglaciation is not well constrained. Here, we develop deglacial outlet glacier retreat chronologies for four regions in southwest and south Greenland to improve understanding of spatial variations in centennial- to millennial-scale ice loss under a warming climate. We calculate 10Be surface exposure ages of boulders located in fjords near the towns of Qaqortoq, Paamiut, Nuuk, and Sisimiut. Our northernmost study site, Sisimiut, deglaciated earliest at ∼18 ka to ∼15 ka with an average thinning rate of 0.1–0.3 m yr−1. Inland retreat from Sisimiut to the modern ice margin took ∼7 ka at an average retreat rate of 15–20 m yr−1. A 10Be-dated moraine ∼25 km from the modern GrIS margin deposited at ∼8 ka suggests a possible ice-margin still-stand, but this does not change overall retreat rates. After retreat from the small coastal Sisimiut fjords, the GrIS margin was mainly land-terminating in this region. In contrast, earliest exposure occurred at ∼12 ka near Qaqortoq, and 11–10 ka near Nuuk and Paamiut, with ice thinning at rates of 0.2–0.3 m yr−1 to instantaneous within measurement uncertainty. Ice retreat inland through the extensive Nuuk, Paamiut, and Qaqortoq fjord systems to near modern ice margins occurred in <1 ka, resulting in minimum retreat rates of 25–65 m yr−1 and maximum retreat rates of ∼95 m yr−1 to instantaneous within the uncertainty of our measurements. This rapid thinning and retreat of marine-terminating southwest GrIS margins is contemporaneous with an incursion of relatively warm ocean waters into the Labrador Sea and toward the southwest Greenland coast, suggesting that a warming ocean may have contributed to the more rapid retreat of marine GrIS termini in the Nuuk, Paamiut, and Qaqortoq fjord systems relative to the slower ice retreat inland from Sisimiut. Our results highlight past outlet glacier–ocean interaction as a potentially important driver in rapid GrIS retreat.
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To determine the long-term sensitivity of the Greenland ice sheet to a warmer climate, we explored how it responded to the Holocene thermal maximum (8-5 cal. kyr B.P.; calibrated to calendar years before present, i.e., A.D. 1950), when lake records show that local atmospheric temperatures in Greenland were 2-4 °C warmer than the present. Records from five new threshold lakes complemented with existing geological data from south of 70°N show that the ice margin was retracted behind its present-day extent in all sectors for a limited period between ca. 7 and 4 cal. kyr B.P. and in most sectors from ca. 1.5 to 1 cal. kyr B.P., in response to higher atmospheric and ocean temperatures. Ice sheet simulations constrained by observations show good correlation with the timing of minimum ice volume indicated by the threshold lake observations; the simulated volume reduction suggests a minimum contribution of 0.16 m sea-level equivalent from the entire Greenland ice sheet, with a centennial ice loss rate of as much as 100 Gt/yr for several millennia during the Holocene thermal maximum. Our results provide an estimate of the long-term rates of volume loss that can be expected in the future as regional air and ocean temperatures approach those reconstructed for the Holocene thermal maximum.
The present report deals with the extension of the ice margin deposits in the Julianehåb district, South Greenland. An attempt is made to establish a Holocene chronology for the ice margin deposits within the region on the basis of their association with raised marine shorelines, combined with a determination of fluctuations of the glaciation limits of the individual stages in Holocene times. As the Narssarssuaq region in the north-eastern part of the district contains numerous extensive ice deposits, this region is treated in more detail than the other localities within the district. On the basis outlined above, it is attempted to establish a relative chronology for the ice margin deposits in the Narssarssuaq region. The remaining deposits within the district are then tentatively incorporated in the chronological scheme for the Narssarssuaq region. After the deglaciation of the district during the last phases of the Wisconsin, four periods of stagnation or readvance of the glacier lobes and the ice caps (four "stages") seem to have given rise to the formation of ice deposits. The earliest of these stages is the Niaqornakasik stage (older Dryas??), succeeded by the Tunugdliarfik stage (probably younger Dryas), the Narssarssuaq stage (probably Roman time), and the maximum extension of the ice in historie times (ca. 1750-1900 A.D.). The variation in the volume of the ice coverings (the inland ice and the Julianehåb ice cap) during the period from the Tunugdliarfik stage to the present day is studied. The superficial conditions of the ice covering above an altitude of ca. 1,700 m do not seem to have altered much since the Tunugdliarfik stage. Finally, deposits from former ice-dammed lakes in the Narssarssuaq region are treated. All the deposits from such lakes found here seem to show that all the lakes at the glacier front had a maximum height of the water level of 120-150 m. This is in accordance with J.W. Glen's theory of subglacial outbursts of ice-dammed lakes.
A continuous record of Holocene glacier fluctuations cannot be obtained with the techniques currently in use, which are mostly based on the dating of moraines. The likelihood of obtaining a continuous record by studying sediment cores taken from lakes receiving glacial meltwater is discussed. Sediments from four lakes receiving glacial meltwater are discussed, and then compared with sediments from a lake not receiving glacial meltwater. Characteristic differences were observed in the inorganic content of the sediments: sediments from non-glacial lakes were much more homogenous.
The glacier inventory and atlas provides the localisation and description of over 5000 glacier units in western Greenland between 59° 30´ and 71° 00´N. Registration is based on natural hydrological basins, in accordance with the recommendations of the International Commission on Snow and Ice (ICSI) but modified and simplified to meet Greenland conditions. The work is divided into three parts: a description of the procedure used in compilation of the glacier inventory and the glaciological conditions, a tabulated presentation of the information and description of the individual glacier units, and a 1:300 000 map presentation showing the position and delineation of the individual glacier units.
The response of the Greenland Ice Sheet (GIS) to changes in temperature during the twentieth century remains contentious, largely owing to difficulties in estimating the spatial and temporal distribution of ice mass changes before 1992, when Greenland-wide observations first became available. The only previous estimates of change during the twentieth century are based on empirical modelling and energy balance modelling. Consequently, no observation-based estimates of the contribution from the GIS to the global-mean sea level budget before 1990 are included in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age at the end of the nineteenth century. We estimate the total ice mass loss and its spatial distribution for three periods: 1900-1983 (75.1±29.4 gigatonnes per year), 1983-2003 (73.8±40.5 gigatonnes per year), and 2003-2010 (186.4±18.9 gigatonnes per year). Furthermore, using two surface mass balance models we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term. We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years. Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0±9.4millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget, which remains crucial for evaluating the reliability of models used to predict global sea level rise.