Quaternary Science Reviews xxx (2013) 1e12
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Quaternary Science Reviews
journal homepage: www.elsevier.com/locate/quascirev
Holocene fluctuations of Bregne ice cap, Scoresby Sund, east
Greenland: a proxy for climate along the Greenland Ice Sheet margin
Laura B. Levy a, *, Meredith A. Kelly a, Thomas V. Lowell b, Brenda L. Hall c, Laura A. Hempel a,
William M. Honsaker b, Amanda R. Lusas c, Jennifer A. Howley a, Yarrow L. Axford d
a
Department of Earth Sciences, Dartmouth College, Hanover, NH, USA
Department of Geology, University of Cincinnati, Cincinnati, OH, USA
School of Earth and Climate Sciences and Climate Change Institute, University of Maine, Orono, ME, USA
d
Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL, USA
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 February 2013
Received in revised form
13 June 2013
Accepted 20 June 2013
Available online xxx
The Greenland Ice Sheet is a major component of the Arctic cryosphere and the magnitude of its response
to future climate changes remains uncertain. Longer-term records of climate near the ice sheet margin
provide information about natural climate variability and can be used to understand the causes of past
changes in the Greenland Ice Sheet. As a proxy for Holocene climate near the ice sheet margin, we
reconstruct the fluctuations of Bregne ice cap in the Scoresby Sund region of central east Greenland.
Bregne is a small ice cap (2.5 km2 in area) and responds sensitively to summer temperatures. We employ
a multi-proxy approach to reconstruct the ice cap fluctuations using geomorphic mapping, 10Be ages of
boulders and bedrock and lake sediment records.
Past extents of Bregne ice cap are marked by moraines and registered by sediments in downvalley
lakes. 10Be ages of bedrock and boulders outboard of the moraines indicate that Bregne ice cap was
within w250 m of its present-day limit by at least 10.7 ka. Multi-proxy data from sediments in Two Move
lake, located downvalley from Bregne ice cap, indicate that the ice cap likely completely disappeared
during early and middle Holocene time. Increasing magnetic susceptibility and percent clastic material
from w6.5 to w1.9 cal ka BP in Two Move lake sediments suggest progressively colder conditions and
increased snow accumulation on the highlands west of the lake. Laminated silt deposited at
w2.6 cal ka BP and w1.9 cal ka BP to present registers the onset and persistence of Bregne ice cap during
the late Holocene. 10Be ages of boulders on an unweathered, unvegetated moraine in the Bregne ice cap
forefield range from 0.74 to 9.60 ka. The youngest 10Be age (0.74 ka) likely represents the age of the
moraine whereas older ages may be due to 10Be inherited from prior periods of exposure. This late
Holocene moraine marks the second largest advance of the ice cap since deglaciation of the region at the
end of the last ice age. The oldest moraine in the forefield dates to 2.6 cal ka BP. The fluctuations of
Bregne ice cap were likely influenced by Northern Hemisphere summer insolation throughout the Holocene and abrupt late Holocene cold events.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Greenland Ice Sheet
Holocene
Scoresby Sund
Greenland
10
Be dating
Lake sediment cores
1. Introduction
Although the potential contribution to future sea-level rise by
the Greenland Ice Sheet is large, the sensitivity of the ice sheet to
climate changes is not fully understood (e.g. IPCC, 2007; Rignot
et al., 2011; AMAP, 2012; Yoshimori and Abe-Ouchi, 2012). In
response to recent warming, the ice sheet is experiencing increased
ice-flow velocities, dynamic thinning of its outlet glaciers and
* Corresponding author.
E-mail address: [email protected] (L.B. Levy).
extensive surface melting (Gregory et al., 2004; Pritchard et al.,
2009; Nghiem et al., 2012; Sasgen et al., 2012). Determining how
the sensitive ice sheet margins have responded to past climate
changes may offer insight into how they will respond to future
climate changes. Historical records of ice sheet extents exist for
limited areas and only extend as far as the 18th century
(e.g. Weidick, 1968). Geologic records of both ice margin fluctuations and regional climate conditions provide a means to examine
how the ice sheet responded to both warmer and colder climate
conditions over longer time periods.
In an effort to further the understanding of longer-term climate
conditions near the ice sheet margins, we present a geologic record
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http://dx.doi.org/10.1016/j.quascirev.2013.06.024
Please cite this article in press as: Levy, L.B., et al., Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate
along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
2
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
of Holocene climate changes in the Scoresby Sund region of central
east Greenland. We focus on a small ice cap known as Bregne ice
cap (informal name), located only w90 km east of the ice sheet
margin. Small glaciers and ice caps respond sensitively to summer
temperatures (Lowell, 2000; Oerlemans, 2001, 2005) and we use
the Holocene fluctuations of Bregne ice cap to examine hypothesized forcings of Holocene climate change such as Northern
Hemisphere summer insolation (Berger and Loutre, 1991) and more
abrupt climate events (Bond et al., 1997, 2001; Mayewski et al.,
2004; Wanner et al., 2011). We suggest that the climate conditions which influenced Bregne ice cap also influenced the nearby
ice sheet margin.
2. Study area
2.1. Geographic setting and Holocene history of Scoresby Sund
The largest embayment in east Greenland is a wide, shallow
fjord known as Scoresby Sund (Fig. 1). West of Scoresby Sund, an
extensive system of deep fjords (as much as 1600 m below sea level
in Nordvest fjord) extends as far as 300 km inland, with the fjords
hosting outlets of the Greenland Ice Sheet (Funder et al., 1998). The
upland regions between the fjords reach as high as 2500 m asl.
Small glaciers and ice caps occur on these uplands and are independent from the Greenland Ice Sheet. Annual precipitation in the
Scoresby Sund region is low (15e50 mm water equivalent per year)
and monthly mean temperatures range from 14 C to 5 C (at
Ittoqqortoormiit; Carstensen and Jørgensen, 2009). The low saline,
cold East Greenland Current flows southward along the east
Greenland coast, and strongly influences the climate of the Scoresby Sund region (Aagaard and Coachman, 1968). As a result of the
East Greenland Current, surface air temperatures by the coast are
colder than those inland, near the ice sheet (Funder, 1978). Vegetation in the Scoresby Sund region is in the High Arctic zone. Upland regions host fell fields (Funder, 1989) with minor vegetation
consisting of Salix arctica, Cassiope tetragona, Dryas octopetala, and
Vaccinium uliginosum.
Much of what is known about Holocene climate and environmental conditions in east Greenland has been determined using
lake sediment records. Numerous records indicate rapid warming
during the early Holocene (e.g. Funder, 1978; Funder and Hansen,
1996; Wagner et al., 2000; Cremer et al., 2001; Wagner and
Melles, 2002; Funder et al., 2011) and sustained widespread
warm climate conditions during the middle Holocene (i.e. the
Holocene Thermal Maximum; Kaufman et al., 2004; Vinther et al.,
2009). Palynological and lake sediment records register the
warmest conditions of the Holocene between 9.0 and 6.7 cal ka BP
(Funder, 1978; Wagner et al., 2000), slightly earlier than the period
of greatest warmth (8e5 ka) measured in boreholes at the summit
of the Greenland Ice Sheet (Dahl-Jensen et al., 1998).
The onset of cooler climate conditions as early as 5.6 cal ka BP is
inferred from palynological studies in the Scoresby Sund region,
with an abrupt decrease in temperature at w2.8 cal ka BP (Funder,
1978). Farther afield, 250 km north of Scoresby Sund, lacustrine
proxies register cool and dry conditions from 3.0 to 1.0 cal ka BP on
Geographical Society Ø (Wagner et al., 2000). A diatom record from
Raffles Ø, 25 km north of Scoresby Sund, indicates the onset of
perennial lake ice and “the greatest environmental change of the
n
rde
sfjo
gh
Nio
GRIP
Greenland Sea
erd
fj
alv
Geographical
Society Ø
East Greenland
Current
Schuchert Dal
Stauning Alper
N
Istorvet ice cap
r
No
stfjord
dv e
Jameson Land
Liverpool
Land
Raffles Ø
ice core
site
Renland
Bregne ice cap
Kap Brewster
Milne Land
Scoresby Sund
N
Fig. 1. Map of Greenland (inset) and the Scoresby Sund region with the locations of Bregne ice cap in northeastern Milne Land and other studies discussed in the text. Gray shaded
areas indicate present-day ice cover. Bregne ice cap is located w90 km east of the Greenland Ice Sheet margin and 60 km southeast of the Renland ice core site.
Please cite this article in press as: Levy, L.B., et al., Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate
along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
Holocene” at 1.8 cal ka BP (Cremer et al., 2001). Palynological evidence from Geographical Society Ø and d18O values from the Renland ice core register a slight warming from 1.0 to 0.8 cal ka BP,
interpreted as a weak Medieval Warm Period (Johnsen et al., 1992;
Wagner et al., 2000) and the coldest Holocene climate conditions
from 800 to 100 cal yr BP, coinciding with the Little Ice Age (Wagner
et al., 2000).
Recent research by Lowell et al. (2013) and the results reported
here provide multi-proxy records of Holocene fluctuations of small
ice caps in the Scoresby Sund region. Istorvet ice cap, located near
the coast on Liverpool Land (Fig. 1), was near its present-day margin
by w11.7 ka (Lowell et al., 2013). During the middle and late Holocene, Istorvet ice cap was likely small and there is strong evidence
for it being smaller than at present from AD 200 to 1025 (Lowell
et al., 2013). Istorvet ice cap reached its maximum Holocene
extent by AD 1150 and since has retreated from this limit. Similarly,
mountain glaciers in the Stauning Alper reached their maximum
Holocene extents during late Holocene time (Kelly et al., 2008; Hall
et al., 2008a). The climate conditions during late Holocene time
influenced some glaciers to reach near their Lateglacial extents
(Kelly et al., 2008).
2.2. Bregne ice cap
Bregne ice cap (70.912 N, 25.630 W) is located in northeastern
Milne Land at the western end of Scoresby Sund (Fig. 1). The ice cap
is small (2.5 km2 in area), thin (<200 m depth) and ranges in
elevation from w720 to 945 m asl. The ice cap surface topography
likely reflects the underlying bedrock topography (Fig. 2). The main
ice divide occurs in the western part of the ice cap and a majority of
ice flows to the east. A cross-section of the topography, from the ice
cap summit to Two Move lake (informal name), shows that Bregne
ice cap is relatively flat-topped and dips to the east (Fig. 2).
Although we cannot preclude that the bedrock topography and
drainage differs from those of the ice cap, we suspect that a significant amount of subglacial meltwater also drains from west to
the east. The bedrock adjacent to Bregne ice cap is granitic, with
areas of sillimanite- and garnet-bearing mica schists and quartzites
to the south and west. A thin band of marble, less than 500 m wide,
exists south of the schists and quartzites (Bengaard and Henriksen,
1982).
Our research focuses on the eastern margin of Bregne ice cap
which extends into a basin containing a series of lakes (Fig. 2). At
present, meltwater from Bregne ice cap flows into a small morainedammed pond, through a channel incised into the moraines and
into Two Move lake (Fig. 2). Two Move lake is a small (0.15 km2),
glacially fed lake located 0.4 km southeast of the Bregne ice cap
margin and 0.2 km distal to the moraines of Bregne ice cap (Fig. 2).
Last Move lake is a small, glacially fed lake (0.02 km2) downstream
of Two Move lake (Fig. 2). Last Move lake receives meltwater
indirectly from Bregne ice cap via Two Move lake. Therefore, we use
sediment records from Two Move as the primary means to reconstruct fluctuations of Bregne ice cap. Last Chance lake is a small
(0.007 km2) lake that has not received glacial meltwater since
deglaciation at the end of the last ice age (Fig. 2). We use sediments
from Last Chance lake to develop a record of sedimentation and
paleoenvironmental conditions not influenced by glacial
meltwater.
3. Methods
Using field data and samples collected during two seasons
(August 2006, 2010), we developed a multi-proxy record of the
Holocene extents of Bregne ice cap. We present results and interpretations from geomorphic mapping, lake sediment cores from
both glacially fed and non-glacially fed lakes and
boulders and bedrock.
3
10
Be dating of
3.1. Geomorphic mapping
We used a combination of black and white aerial photography
(1:150,000 resolution) from 2004 and WorldView1 (0.5 m resolution) panchromatic satellite imagery from 2009 to conduct
geomorphic mapping of the study area prior to conducting fieldwork. In the field, we checked our mapping with detailed examinations of landform morphology, weathering features and
sedimentology. We used an ASTER digital elevation model (15 m
resolution) overlain on the WorldView imagery to determine the
elevation of the August 2009 snowline, which we employed to estimate the snowline altitude of Bregne ice cap (e.g. Oerlemans, 2001).
3.2. Lake sediment cores
Prior to extracting lake sediment cores, we conducted detailed
mapping of the lake-floor bathymetry using a HumminbirdÒ 798 SI
combo fish finder mounted on an inflatable raft with an electric
motor and Dr. DepthÓ software. We selected coring sites on flat
areas of the lake floors, away from steep walls where down-wasting
of sediments may occur. Using a Universal Corer from Aquatic
Research Instruments, which employs a check valve and no piston,
we obtained cores of the sedimentewater interface. We extracted
deeper sediments by making repeated, overlapping drives with a
modified square-rod piston (Bolivian) corer. We cored until we hit
gravel or till with the bottom of the core barrel. All cores were
shipped directly from Greenland to the Limnological Research
Center (LRC) at the University of Minnesota.
At the LRC, prior to splitting the cores, we measured gamma
density and whole core magnetic susceptibility at 0.5 cm resolution
using a Geotek Multi-Sensor Core Logger standard model. On split
cores, we made detailed core descriptions and obtained highresolution images. We measured high-resolution magnetic susceptibility on split cores at 0.5 cm intervals. We archived one half of
each core at the LRC and shipped the working core halves to
Dartmouth College. At Dartmouth College, we measured loss on
ignition at 2 cm intervals, burning samples at 550 C and 1000 C to
determine percent organic matter and percent total inorganic carbon, respectively. We sampled for grain size at 2 cm intervals and
prepared these samples using protocols of the Sedimentary Records
of Environmental Change (SREC) laboratory at Northern Arizona
University (NAU). We measured grain size on a LS Coulter 230
particle-size analyzer. We sent samples from the Last Chance lake
cores for biogenic silica measurements to the SREC laboratory at
NAU.
In order to investigate the finely laminated sediments in the
Two Move lake cores, we made both smear slides and thin-sections.
Using LRC protocols, we made smear slides of core TML10-1C-1N-1
at 5 cm intervals from 30 to 55 cm. The upper 50 cm of sediments in
core TML10-1B-1L-1 were cured in epoxy at the LRC and made into
thin sections by National Petrographics. We obtained highresolution images of the thin-sections using a flatbed scanner and
then spliced the images together using Adobe PhotoshopÒ. We
counted and measured the laminations using Adobe IllustratorÒ.
We applied radiocarbon dating of macrofossils and bulk sediments to develop a chronology for the sediment cores. Terrestrial
macrofossils in all lake cores were rare. This was not surprising,
since there is little-to-no vegetation on the modern landscape
(Fig. 2), likely due to the coarse substrate. Where available, we used
aquatic macrofossils (plant or insect remains) to determine radiocarbon ages. In places, we sampled both macrofossils and bulk
sediments in the same horizon to test whether bulk samples
Please cite this article in press as: Levy, L.B., et al., Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate
along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
4
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
Fig. 2. a) Worldview satellite image of the field area at Bregne ice cap taken on August 23rd, 2009 showing the locations of the moraines and drift, Two Move lake (glacially fed
lake), Last Move lake (glacially fed lake) and Last Chance lake (non-glacially fed lake). Sediment records from Last Move lake are discussed in the Supplementary material. Contour
interval is 25 m. Arrows show hypothetical flow of ice cap based on ice cap surface topography. A cross-section of transect AeA0 is shown in panel b; b) Cross-section of AeA0 . The
upper surface of Bregne ice cap is relatively flat and dips to the east. Note the vertical exaggeration is 5:1. c) Photograph of Two Move lake, view to the east. The coring platform is in
the center-left of the lake. A delta of glaciogenic fine-grain sediment (i.e., silt and fine sand) being built in the lake is apparent in the center of the photo. d) Photograph of Last
Chance lake, view to the southeast. The coring boat is in the center of the lake.
yielded robust ages, or whether they may have been influenced by a
“hard water” effect due to the presence of nearby carbonates (e.g.
Child and Werner, 1999). All samples were measured at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS)
facility at Woods Hole Oceanographic Institution and ages were
calibrated using the online program Calib 6.0 based on the IntCal09
calibration curve (Reimer et al., 2009; Stuiver et al., 2010).
Throughout the paper, we present calibrated radiocarbon ages as
the midpoint of the 2s calibrated age range and 2s error, in years
before present (cal yr BP) (Table 2).
3.3.
10
Be dating
We applied the surface-exposure dating method using the
cosmogenic nuclide 10Be (hereafter referred to as 10Be dating) to
determine the exposure ages of boulders and bedrock. In the field,
we opted for large (>1 m3) boulders that appeared stable on the
landscape with abundant (>30%) quartz. We selected boulders or
bedrock that were free of debris cover that would decrease the
production of 10Be in the underlying rock surface and yield
anomalously young ages. We measured sample locations using a
handheld GPS and rock-surface orientations and surrounding topographies using a clinometer and compass. We obtained samples
using either a hammer and chisel or the drill-and-blast method of
Kelly (2003).
We isolated quartz from whole rock samples and extracted
beryllium following the methods described in Schaefer et al.
(2009). All 10Be/9Be ratios were measured at the Center for Accelerator Mass Spectrometry (CAMS) at Lawrence Livermore National
Laboratory (LLNL). We calculated 10Be ages using the CRONUS Earth
online calculator (Balco et al., 2008) and the Northeastern North
American production rate (Balco et al., 2009) which has been
recently confirmed for west Greenland (Briner et al., 2012). We
scaled the production rate to our sample locations using the
methods of Desilets and Zreda (2003) and Desilets et al. (2006).
Since the annual precipitation in the Scoresby Sund region is low,
we did not correct 10Be ages for cover by snow. Boulders on moraines and drift had smoothed surfaces and in some cases preserved glacial polish. For these samples, we assumed that no
boulder erosion occurred. The surfaces of boulders and bedrock
outboard of the moraines were lichen covered and showed evidence of erosion (i.e., pitting and raised surfaces). For samples from
Please cite this article in press as: Levy, L.B., et al., Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate
along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
5
Table 1
10
Be ages and associated metadata. All ages are calculated using the CRONUS-Earth online calculator (Balco et al., 2008) with the Northeastern North American production rate
(Balco et al., 2009) scaled to the sample locations using Desilets and Zreda (2003) and Desilets et al. (2006). 10Be ages calculated using other scaling schemes (i.e., Lal, 1991 and
Stone, 2000 with geomagnetic correction of Nishiizumi et al., 1989; Dunai, 2001; Lifton et al., 2005) show age differences of <6% (see Supplementary material). Samples MKG161, 161a, and 162 were all processed at the cosmogenic lab at Lamont Doherty Earth Observatory with “Lamont carrier 4”. All others were processed at the cosmogenic lab at
Dartmouth College with “4G carrier”.
Sample
ID
Latitude
( N)
Longitude
( W)
Elevation
(m asl)
Boulders and bedrock outside of the morainesc
MKG-161
70.910
25.595
784
MKG-161a
70.910
25.595
744
MKG-162
70.910
25.594
735
Boulders from Datum moraine and drift
MKG-159
70.910
25.595
740
MKG-160
70.910
25.596
746
MKG-165
70.908
25.599
733
MKG-166
70.906
25.604
752
LL1029
70.909
25.598
724
LL1030
70.909
25.598
714
LL1031
70.909
25.596
733
LL1035
70.905
25.606
765
LL1036
70.905
25.606
754
Shielding
correction
Thickness
(cm)
10
Be conc.
(atoms/g)a
Uncertainty
(atoms/g)b
Age uncertainty
(ka)b
Age uncertainty (ka)
(uplift corrected)b
0.993
0.993
0.994
3.4
2.7
1.6
8.97 104
9.69 104
9.18 104
1.72 103
2.11 103
1.60 103
10.44 0.20
11.63 0.25
11.02 0.19
10.70 0.21
12.00 0.26
11.33 0.20
0.996
0.999
1
0.996
0.999
0.999
0.999
0.998
0.999
2.8
5.8
5.7
2.4
2.3
2.5
2.1
2.2
1.9
3.82
8.09
6.08
5.54
1.15
2.68
7.19
2.29
1.11
104
104
103
104
104
104
104
104
104
1.13
1.53
2.26
1.06
3.11
5.32
1.37
4.63
3.75
103
103
102
103
102
102
103
102
102
4.51
9.60
0.74
6.45
1.37
3.22
8.48
2.62
1.28
0.13
0.18
0.03
0.12
0.04
0.06
0.16
0.05
0.04
e
e
e
e
e
e
e
e
e
a
All samples were measured using the beryllium standard 07KNSTD (Nishiizumi et al., 2007).
Uncertainty is reported as internal AMS uncertainty.
c 10
Be ages outside of the moraines are calculated assuming an erosion rate of 0.0002 cm yr1. We accounted for isostatic uplift following Hall et al. (2008b) with a MatlabÒ
program created by Goehring et al. (2011).
b
these surfaces, we assumed an erosion rate of 0.0002 cm yr1 based
on the height of raised quartz veins and prior work (Kelly et al.,
2008). Since these samples yielded early Holocene ages, we corrected the elevations of these samples for glacial isostatic uplift
following Hall et al. (2008b) using a MatlabÒ program designed by
Goehring et al. (2011).
4. Results
4.1. Geomorphic mapping
A series of six moraines exist within w250 m of the present-day
Bregne ice cap margin (Figs. 2 and 3). The moraines are 1e6 m high,
1e3 m wide, have minimal soil development and less than 5%
vegetation cover, predominantly of Salix spp. Whereas the moraines are generally unweathered and unvegetated, boulders and
bedrock outboard of the moraines show surface erosion and
extensive lichen cover. The innermost four moraines trend
northeast-southwest, parallel to the present-day ice cap margin
(Fig. 3). The outermost two moraines, informally named the
Wishbone moraines, trend more east-northeast than the inner
moraines (Fig. 3). The Wishbone moraines are cross-cut by the
distal-most inner moraine, informally named the Datum moraine,
and are therefore older than the Datum moraine (Fig. 3). The glacial
limit marked by the Datum moraine is continuous to the south and
transitions from a moraine to a thin drift of boulders on bedrock.
Boulders on the Datum moraine and drift are composed of granite
and schist.
Table 2
Radiocarbon sample information and ages from lake sediment cores. Radiocarbon ages are calibrated with Calib 6.0 and IntCal09 (Reimer et al., 2009; Stuiver et al., 2010).
Core
Sample
depth
(cm)
Two Move Lake (TML)
TML10-1A-2L-1
28
TML10-1A-2L-1
33.5
TML10-1A-2L-1
34
TML10-1A-2L-1
35
TML10-1C-1N-1 35
TML10-1C-1N-1 38.25
TML10-1C-1N-1 54
TML10-1C-1N-1 54
Last Chance Lake (LCL)
LCL10-1A-1N-1
16.5
LCL10-1A-1N-1
33
LCL10-1A-1N-1
38
LCL10-1A-1N-1
50.5
LCL10-1A-1N-1
65.75
LCL10-1C-1L-1
21
LCL10-1C-1L-1
48.5
LCL10-1D-1L-1
10
LCL10-1D-1L-1
19.25
LCL10-1D-1L-1
30.5
LCL10-1D-1L-1
45
LCL10-1D-1L-1
47.5
a
b
c
Absolute
sample
depth (cm)a
Sample
materialb
Accession
#
Radiocarbon
age (yr BP)
36
39
39.25
40
35
38.25
54
54
AP
Bulk
AP
AP
AP
Bulk
Bulk
Bulk
OS-98646
OS-86683
OS-86684
OS-98647
OS-98651
OS-98750
OS-86554
OS-90188
1540
2850
2710
2600
1660
2660
8020
8270
25
30
30
30
35
35
35
35
0.8256
0.7008
0.7135
0.7231
0.8137
0.7178
0.3685
0.3572
16.5
33
38
50.5
65.75
35.5
49.25
47
56.25
67.5
82
84.5
IM
AP
AP
IM
IM
AP
AP
AP
IM
IM
AP
AP
OS-94704
OS-94705
OS-94701
OS-95134
OS-94700
OS-86687
OS-86710
OS-94698
OS-94703
OS-95133
OS-90460
OS-95132
1940
4140
4440
6540
8900
4100
5930
5490
5650
8830
4690
2770
60
65
55
100
85
35
40
45
70
300
100
120
0.7855
0.5969
0.5756
0.4432
0.3300
0.5998
0.4778
0.5046
0.4951
0.3332
0.5576
0.7084
Radiocarbon age
uncertainty (yr)
d13C
(&)c
Cal age
range (2s)
(cal yr BP)
Cal age
midpoint 2s
error (cal yr BP)
0.0027
0.0027
0.0028
0.0028
0.0035
0.0033
0.0017
0.0017
35.52
33.52
33.18
NM
36.26
34.13
28.77
29.79
1370e1519
2880e3060
2760e2860
2620e2771
1418e1692
2742e2844
8770e9010
9130e9400
1445
2960
2810
2695
1555
2790
8890
9270
75
100
50
75
135
50
120
140
0.0061
0.0049
0.0039
0.0058
0.0036
0.0025
0.0025
0.0029
0.0045
0.0125
0.0071
0.0104
28.57
25.88
25.45
26.73
23.76
26.43
26.19
25.69
24.98
NM
26.64
27.55
1721e2035
4450e4838
4872e5286
7265e7590
9705e10,224
4450e4820
6670e6880
6207e6397
6300e6628
9137e10,690
5050e5610
2543e3262
1880
4640
5080
7750
9960
4635
6775
6300
6460
9910
5330
2900
160
190
210
160
260
185
105
100
160
780
280
360
Fraction
modern
The total sample depths of core TML10-1A-2L-1 are based on estimated stratigraphic correlation to core TML10-1C-1N-1.
Bulk ¼ Bulk Sediment, AP ¼ Aquatic Plant, IM ¼ Insect Material.
NM ¼ Not measured.
Please cite this article in press as: Levy, L.B., et al., Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate
along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
6
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
Fig. 3. Worldview satellite image showing the forefield of Bregne ice cap and moraines. The Wishbone moraines are the oldest moraines and are cross-cut by the Datum moraine
and drift. Unnamed moraines inboard of the Datum moraine are also mapped. 10Be sample numbers, ages and uncertainties are shown.
Using the WorldView satellite imagery and digital elevation
model, we determined an elevation (820e875 m asl) for the August
2009 snowline on Bregne ice cap. This snowline increases from the
north to the south (Fig. 2), similar to the elevation of the ice cap.
Based on the August 2009 snowline altitude, an increase in the
snowline altitude of 40e70 m would render the entire ice cap an
ablation zone. Applying an environmental lapse rate of 0.65 C
100 m1 (e.g. Dahl and Nesje, 1992), we estimate that sustained
summer temperatures 0.26e0.46 C higher than at present would
cause significant ice loss.
4.2. Lake sediment cores: Two Move lake
We retrieved three sediment cores from the deepest part of Two
Move lake (Fig. 4). Cores range from 0.55 to 0.74 m in length and
were retrieved from 21.5 to 22.5 m water depth (see Supplementary
material). We correlated the three cores based on the visual stratigraphy. Only core TML10-1C-1N-1 contains the complete stratigraphic sequence including the sedimentewater interface (Fig. 4;
see Supplementary material) and therefore we focused the proxy
analyses on this core.
Core TML10-1C-1N-1 is 60 cm in length and has three distinct
sedimentological units; basal diamicton (60e55 cm), laminated
dark-brown gyttja (55e36 cm), and finely laminated, minerogenic
silt (36e0 cm) (Fig. 4). The basal diamicton contains clasts as large
as 2 cm in diameter and generally has low percent organic matter,
total inorganic carbon, and magnetic susceptibility values. The
transition to overlying laminated, dark-brown gyttja is a sharp
contact. The percent organic matter peaks mid-way through the
gyttja and then decreases steadily to the top of the unit. Total
inorganic carbon in the gyttja unit is low (0e3%), but variable.
Magnetic susceptibility values are near zero over the basal 5 cm of
the gyttja and then increase sharply and peak near the top of the
unit. Fine (<1e5 mm thick) laminations of light tan, minerogenic
silt increasingly occur in the upper 12 cm of the gyttja unit with a
prominent 5 mm layer of silt at 38 cm. Smear slides of the gyttja
show a mix of organic material and diatoms with increasing clastic
material in the uppermost 12 cm of the unit. The uppermost unit in
core TML10-1C-1N-1 consists of finely laminated, minerogenic,
light tan, medium silt (Fig. 4). The percent organic matter, total
inorganic carbon and magnetic susceptibility values of the silt are
relatively constant. Several very thin (<1 mm), layers of darkbrown gyttja occur at the base and at the top of this unit. Smear
slides of the silt unit show relatively uniform size clastic grains that
are smaller than clasts within the gyttja unit.
The thin sections of the silt unit in core TML10-1B-1L-1 (adjacent to the core TML10-1C-1N-1) reveal a sequence of couplets
(0.1e5 mm thick) composed of an underlying clay layer and overlying silt layer. The base of each couplet is defined by a sharp
contact. Silt layers contain multiple, graded laminations of silt and
fine sand. We conducted two independent counts of the couplets in
the silt unit (28e0 cm depth in core TML10-1B-1L-1) using high-
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along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
7
Fig. 4. Two Move lake core records. Shown are the age-depth model, core image and interpreted stratigraphic column with locations and ages of radiocarbon samples of aquatic
macrofossils (macro) and bulk sediments (bulk sed.). The ageedepth model is based on calibrated radiocarbon ages. Brackets show 2s error. Black circles represent included ages,
white circles represent ages not included in the age-depth model. Also shown are magnetic susceptibility (MS), percent organic matter (OM) and percent total inorganic carbon (TIC)
values as well as grain size distribution.
resolution digital imagery. Both counts yielded 230 5 couplets.
Core TML10-1B-1L-1 does not contain the sediment water interface, but we estimate no more than a few centimeters of sediment
are missing based on the correlation with core TML10-1C-1N-1
(Fig. S2). Pellets or aggregates (0.5e1 mm diameter) of fine sand
size sediment grains (Fig. 5) occur within some couplets. These
pellets are subangular to subrounded and more than one pellet
commonly occurs within a couplet. Sediment below the pellets
appears warped or displaced and sediment above appears to drape
over the pellets.
4.2.1. Two Move lake: core chronology
We constructed a chronology using five radiocarbon ages from
core TML10-1C-1N-1 (Fig. 4, Table 2, Fig. S3). Macrofossils and bulk
sediment samples from the same horizon yielded similar ages, with
bulk sediment ages <150 14C years older than macrofossil ages.
Therefore where macrofossils were not present, we used bulk
sediment for radiocarbon dating (see Supplementary material).
Two radiocarbon ages of bulk sediment from the same depth
(54 cm) are 8890 120 and 9270 140 cal yr BP (Table 2). We used
the older of the two radiocarbon ages from this horizon as we
believe this gives a better constraint on the earliest timing of
deglaciation of the basin. Three radiocarbon ages from within the
gyttja unit yield ages of 5145 155, 3605 95, 2790 50 cal yr BP
(Table 2). One radiocarbon age from 1 cm above the base of the silt
unit is 1555 135 cal yr BP.
Using these radiocarbon ages, we constructed a model of sediment age vs. depth (Fig. S3). We used a linear sedimentation rate
between the lowest two ages, a 2nd order polynomial for the
middle four ages (R2 ¼ 0.99) and a linear sedimentation rate between the uppermost radiocarbon age and the sedimentewater
interface, which we assume to be modern (Figs. 4 and S3). Our agee
depth model shows that the contact between the basal diamicton
and the gyttja unit is w10 cal ka BP, the base of the 5 mm silt layer is
w2.6 cal ka BP and the contact between the gyttja unit and the
overlying silt unit is w1.9 cal ka BP. We acknowledge that there are
uncertainties associated with this ageedepth model, with less
uncertainty in areas near radiocarbon ages. The sedimentation rate
in the gyttja unit ranges from 0.0015 to 0.0037 cm yr1 and in the
silt unit is 0.0225 cm yr1. We also obtained four radiocarbon ages
from core TML10-1A-2L-1 to confirm the ages of the contacts between the stratigraphic units (Table 2, Supplementary material).
Please cite this article in press as: Levy, L.B., et al., Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate
along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
8
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
Fig. 5. Thin section from the laminated silt unit in core TML10-1B-1L-1 (14e15 cm
depth) showing couplets. Black lines mark silt layers and white lines mark the overlying clay layers. One blackewhite line represents one couplet. The arrow points to
pellets within a couplet. The scale bar on the left shows 1 mm increments.
We use only the radiocarbon ages from core TML10-1C-1N-1 for the
ageedepth model, but the ages from core TML10-1A-2L-1 support
this model.
4.3. Lake sediment cores: Last Chance lake
We retrieved four sediment cores from Last Chance lake (see
Supplementary material). Cores are 0.23e0.94 m in length and
were retrieved from the center of the basin at 8.5 m water depth.
Core LCL10-1A-1N-1 contains the sedimentewater interface and
core LCL10-1D-1L-1 contains the basal diamicton. Core LCL10-1C1L-1 does not contain the sedimentewater interface or the basal
diamicton, but its stratigraphy overlaps with cores LCL10-1A-1N-1
and LCL10-1D-1L-1. Correlating these cores yields a complete
stratigraphy with a total sediment thickness of 83.5 cm. Percent
biogenic silica values are very similar between cores and therefore
we used these values to correlate the three cores and generate a
continuous record (Fig. 6).
The complete, composite sediment record in Last Chance lake
has two distinct units; basal diamicton (83.5e75.5 cm) and finely
laminated gyttja with layers of aquatic plant macrofossils (75.5e
0 cm) (Fig. 6). The basal diamicton has clasts as large as 1 cm in
diameter and near zero magnetic susceptibility, percent organic
matter and biogenic silica values (Fig. 6). The gyttja unit is
composed of finely laminated organic material with layers of
aquatic plants and other macrofossils. Laminations (2e3 mm thick)
of dark-brown gyttja occur in the upper 20 cm of the unit. Magnetic
susceptibility values are near zero in the gyttja unit with a small
peak at 5e0 cm. Percent organic matter and biogenic silica show
similar trends with near zero values from the base of the unit, peak
values at w40 cm, decreasing values from 40 to 10 cm, and a small
peak at 10e0 cm.
4.3.1. Last Chance lake: core chronology
We constructed a chronology using nine radiocarbon ages from
cores LCL10-1A-1N-1, LCL10-1D-1L-1 and LCL10-1C-1L-1 (Table 2,
Supplementary material). Macrofossils from these cores are aquatic
plants and insect parts including chitinous material and daphnia
Fig. 6. Last Chance lake core records. Shown are the age-depth model, core images and interpreted stratigraphic column with locations and ages of radiocarbon samples of aquatic
macrofossils (macro). The ageedepth model is based on calibrated radiocarbon ages. Brackets show 2s error. Black circles represent included ages, white circles represent ages not
included in the age-depth model. Also shown are magnetic susceptibility (MS), percent organic matter (OM), and percent biogenic silica (BSi) values.
Please cite this article in press as: Levy, L.B., et al., Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate
along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
ephippia. We omitted three radiocarbon ages from the chronology
because they are not in stratigraphic order. These anomalous ages
may be due to plant material being dragged to depth during coring.
We fitted a 2nd order polynomial to the radiocarbon ages
(R2 ¼ 0.989) and a linear sedimentation rate between the uppermost radiocarbon age and sedimentewater interface, which we
assume to be modern. The sedimentation rate changes slightly
through the gyttja because we used both a 2nd order polynomial
and a linear regression to construct the chronology. Sedimentation
rates range from w0.006 to 0.008 cm yr1 (Fig. S3).
4.4.
10
Be ages
We obtained twelve 10Be ages of boulders and bedrock near
Bregne ice cap (Fig. 3, Table 1). Three 10Be ages are from boulders
and bedrock outboard of the moraines. Two of these samples are
from boulder surfaces (MKG-161, 10.70 0.21 ka; MKG-162
11.33 0.20 ka) and one (MKG-161a 12.00 0.26 ka) is from a
bedrock surface adjacent to sample MKG-161. As these sample sites
were influenced by early Holocene isostatic uplift, we corrected the
10
Be ages for the difference in sample elevations between the time
of deglaciation and the present. This correction yields 10Be ages
approximately three percent older than those uncorrected (Table 1).
Nine 10Be ages are from boulders on the Datum moraine and drift
(Fig. 3). These ages range from 0.74 0.03 to 9.60 0.18 ka.
5. Interpretations e Holocene extents of Bregne ice cap
We interpret the timing of deglaciation at the end of the last ice
age near Bregne ice cap using 10Be dating of the landscape and lake
sediment records. The 10Be ages of boulders and bedrock <80 m
outboard of the moraines indicate that Bregne ice cap was within
the limit of the moraines by at least 10.7 ka (Fig. 3). The onset of
organic sedimentation in Two Move lake at w10 cal ka BP provides
additional support for deglaciation by this time. We interpret the
basal diamictons in Two Move and Last Chance lakes as till
deposited during the last ice age.
Evidence for a reduced extent of Bregne ice cap and relatively
warm climate conditions during early and middle Holocene time
comes from the lake sediment records. In Two Move lake, the slow
accumulation of gyttja and little-to-no clastic sediment deposited
between w10 and w2.6 cal ka BP indicates a lake environment
dominated by biological production and no glaciogenic input
(Fig. 4). In Last Chance lake, increasing percent organic matter and
biogenic silica values from w9 to 5.5 cal ka BP suggest warm conditions that were favorable for biological activity in the lake (Fig. 6).
Our snowline altitude calculations indicate that sustained summer
temperatures w0.5 C higher that at present would render the
entire ice cap an ablation zone and, thus, lead to significant ice loss.
GRIP borehole measurements register temperatures w2.5 C
warmer than at present during the Holocene Thermal Maximum
(8e5 ka) (Dahl-Jensen et al., 1998). Based on the lake sediment
records and snowline estimate, we suggest that Bregne ice cap was
smaller than at present, and may have disappeared completely,
during the early and middle Holocene.
Within the gyttja unit in the Two Move lake cores, from w6.5 to
1.9 cal yr BP, magnetic susceptibility values increase (Fig. 4). Examination of smear slides of the gyttja unit documents a coeval
increase in clastic sediments, which may be the source of the
magnetic susceptibility values. Although increased magnetic susceptibility values and clastic sediment deposition in lake cores
commonly indicate input of glaciogenic sediments, increased
runoff from the surrounding landscape, or perhaps storm activity
(e.g., Snowball and Sandgren, 1996; Noren et al., 2002), there are no
similar increases in the Last Chance lake cores (Fig. 6). We suggest
9
that the magnetic grains (influencing the magnetic susceptibility
values) and clastic sediment input into Two Move lake were derived
locally, likely from the highlands west the lake. Last Chance lake is
isolated from these highlands by a bedrock ridge (Fig. 2) and
therefore would not receive the same clastically derived material.
Since we observe the present-day transport of silt from the Bregne
ice cap margin to Two Move lake (Fig. 2), the magnetic susceptibility values (w20 SI 105 units) and grain size of the upper silt
unit are likely characteristic of glacially eroded material transported to the lake. In contrast, the magnetic susceptibility values of
the gyttja unit increase from 0 to 70 SI 105 units. In addition, the
clastic sediment in the silt unit (likely reflecting glacially eroded
material) is finer-grained than that in the gyttja unit. Therefore, we
suggest that the clastic sediment in the gyttja unit has a different
source from the silt unit and is not glacially derived. The clastic
sediment in the gyttja unit may result from progressively colder
temperatures and increased snow accumulation on the highlands
west of Two Move lake causing coarser sediment input into the
lake. Alternatively, the magnetic susceptibility values and clastic
sediment in the gyttja unit may result from sediment transported
from a different bedrock source area, perhaps available due to a
smaller extent of Bregne ice cap during the middle Holocene.
The first evidence of glacially derived sediment in the Two Move
lake core is a thin (0.5 cm) lamination of minerogenic, light-tan silt,
the basal contact of which dates to w2.6 cal ka BP (Fig. 4). We
suggest that this was the first time since deglaciation at the end of
the last ice age that summer temperatures were cool enough for
Bregne ice cap to form. Above the silt lamination, another 1.5 cm of
laminated gyttja appears to represent a brief time when glacially
eroded sediment was not deposited in Two Move lake, perhaps due
to a reduced Bregne ice cap extent. Although we cannot preclude
the possibility that meltwater from the ice cap drained elsewhere
during this time, our interpretations of the subglacial bedrock
topography suggest that any ice on the highlands west of Two Move
lake would drain meltwater into the lake. The silt unit in the Two
Move lake cores, from w1.9 cal ka BP to present, is evidence for a
continuous influx of glacially eroded sediment into the lake and,
thus, the presence of Bregne ice cap.
Although the base of the silt unit in the Two Move lake cores
dates to w1.9 cal ka BP, the top of the unit is modern and there are
no obvious unconformities, we counted only 230 couplets in the
silt. If these couplets represent annual layers (e.g. varves), we would
expect w1900 couplets. Therefore we suggest that these couplets
do not represent annual sedimentation in the lake (i.e. the couplets
represent cycles of more or less than one year). For example, during
cold summers Bregne ice cap may not have experienced melt and
Two Move lake may have been perennially frozen, resulting in
little-to-no sediment deposition in Two Move lake. If the couplets
were annual layers, then w1700 years are missing from the record.
Using the sedimentation rate in the silt unit (230 years in 28 cm, or
w8 yr cm1), we estimate that 1700 years of deposition would
result in w2 m of sediment. We find it unlikely that 2 m of sediment
are missing from the Two Move lake cores.
The Lateglacial and early Holocene 10Be ages on boulders and
bedrock outboard of the Wishbone and Datum moraines indicate
that these moraines represent the largest Holocene ice cap advances. The unweathered, unvegetated surfaces of boulders on the
moraines compared with the weathered, lichen-covered Lateglacial
and early Holocene boulder and bedrock surfaces also suggest that
the moraines are relatively young and were likely deposited during
late Holocene time. Although the 10Be ages of the Datum moraine
and drift have a wide age distribution (0.74e9.60 ka; Table 1; Fig. 3)
and do not appear to reflect moraine age directly, we use them to
derive information about Holocene Bregne ice cap extents and also
basal ice conditions. Whereas the three 10Be ages from surfaces
Please cite this article in press as: Levy, L.B., et al., Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate
along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
10
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
outboard of the moraines yield Lateglacial and early Holocene ages,
all 10Be ages from the Datum moraine and drift yield Holocene ages.
We suggest that glacial erosion during the last ice age effectively
removed 10Be that was produced during prior periods of exposure
(i.e. inherited 10Be, cf. Kelly et al., 2008). Therefore the scatter of 10Be
ages on the Datum moraine and drift results from 10Be produced
during the Holocene. As Bregne ice cap is only a thin drape on the
landscape (<200 m thick), it may not have effectively eroded the
underlying bedrock or 10Be produced during its Holocene advances.
We suggest that the youngest 10Be age from the Datum moraine
(0.74 ka) best represents the age of the moraine; however it too may
contain inherited 10Be. The oldest 10Be age from the Datum moraine
(9.60 ka) provides an estimate on the maximum inventory of 10Be
produced in rock surfaces during the Holocene. Therefore, this age
affords a minimum amount of time that rock surfaces near or under
Bregne ice cap were ice free during the Holocene.
The most conservative approach to dating the moraines is provided by the Two Move lake sediment records. As noted above, we
observe the present-day transport of silt from the Bregne ice cap
margin to Two Move lake (Fig. 2). Since the moraines mark an ice
extent more advanced than at present, meltwater from the ice cap
must have entered Two Move lake when the moraines were
deposited. Therefore, based on the Two Move lake sediment record,
a conservative estimate on the maximum age of the most distal
moraines, the Wishbone moraines, is either w2.6 cal ka BP, when a
thin, clastic sediment layer was deposited, or w1.9 cal ka BP to
present, when clastic sedimentation dominated the Two Move lake
record. The Datum moraine and drift and other moraines more
proximal to the ice cap, therefore, must represent subsequent advances or stillstands of Bregne ice cap during late Holocene time.
6. Discussion
Our interpretations of the Holocene fluctuations of Bregne ice
cap offer insight into climate conditions near the Greenland Ice
Sheet margin and the mechanisms that influenced Holocene climate
changes. Many records from the Scoresby Sund region demonstrate
rapid deglaciation at the end of the last ice age, warm conditions
during early and middle Holocene time, and colder conditions
during the late Holocene. The Renland ice core (Fig. 1), located 60 km
northwest of Bregne ice cap, registers warmer temperatures from
11.6 to w9.5 ka (Fig. 7; Johnsen et al., 1992). By w10.0 cal ka BP many
regions of Scoresby Sund were deglaciated, from Raffles Ø to lakes in
western Jameson Land, 60 km east of Bregne ice cap (Fig. 1; Funder,
1978; Björck et al., 1994; Cremer et al., 2001). Local glaciers were
near their late Holocene extents by w10.0 cal ka BP in Schuchert Dal
(Hall et al., 2008a) and by w11.7 ka in Liverpool Land (Fig. 1, Lowell
et al., 2013). Similar to these records, Bregne ice cap was within its
late Holocene extent by at least 10.7 ka. Although Bregne ice cap is at
a higher elevation and further inland than these other records, the
similar timing of deglaciation indicates that early Holocene warming occurred rapidly throughout the Scoresby Sund region. Since
Bregne ice cap is located w90 km east of the Greenland Ice Sheet
margin, we suggest that these warm climate conditions likely
influenced recession of the ice sheet margin.
The multi-proxy records presented here indicate that Bregne
ice cap was small or nonexistent from w10.0 to w2.6 cal ka BP.
Similarly, other records in the region indicate warm conditions
and reduced ice extents during early and middle Holocene time
(e.g. Funder, 1978; Wagner et al., 2000; Cremer et al., 2001; Kelly
et al., 2008; Hall et al., 2008a; Lowell et al., 2013). Although this
early Holocene warmth likely influenced the Greenland Ice Sheet
margin, few studies have documented ice marginal fluctuations
during this time in central east Greenland. One exception is kame
terraces dated at 7.5e8.6 cal ka BP that were formed as ice sheet
outlet glaciers retreated and marine water invaded the fjords
(Funder, 1971). However, further north, numerous studies report
reduced ice at this time (Kelly and Lowell, 2009 and references
therein). In Nioghalvfjerdsfjorden in northeastern Greenland
(Fig. 1), radiocarbon ages of marine mammal bones and driftwood
range from 3.87 to 8.14 cal ka BP and show that the fjord was free
of ice in the middle Holocene (Bennike and Weidick, 2001). The
early and middle Holocene warming in Greenland is generally
attributed to high Northern Hemisphere summer insolation
(Berger and Loutre, 1991; Kaufman et al., 2004). However, the
timing of peak Holocene warmth along the coast of east Greenland
may also have been influenced by changes in the position of the
East Greenland Current (Koç et al., 1993; Jennings et al., 2011).
Diatom assemblages in sediment cores from the Greenland Sea
indicate that the sea ice margin had significantly retreated to a
northerly position by w7.0 cal ka BP. During this time, cooler
Arctic conditions occurred only along a narrow region on the East
Greenland coast, perhaps due to a restricted East Greenland Current (Koç et al., 1993).
Although the late Holocene expansion of Bregne ice cap was
likely due to decreasing Northern Hemisphere summer insolation
(Fig. 7), evidence for a brief ice expansion at w2.6 cal ka BP and
sustained ice expansion at w1.9 cal ka BP suggest that the ice cap
may have also responded to more abrupt climate changes. Recurring, widespread, abrupt cold events across the North Atlantic
Ocean during the Holocene have been documented by several
proxies, such as diatom assemblages and the recurrence of icerafted debris in ocean sediment cores (e.g., Bond et al., 1997,
2001; Wanner et al., 2011). The times of expansion of Bregne ice
cap generally correlate with widespread cold conditions in the
North Atlantic Ocean at 3.3e2.5 cal ka BP and 1.75e1.35 cal ka BP
(Fig. 7; Wanner et al., 2011). We suggest that low Northern Hemisphere summer insolation during late Holocene time enabled the
growth of Bregne ice cap fluctuations and that the ice cap
responded to regional cold events. Higher Northern Hemisphere
summer insolation during early and middle Holocene time likely
precluded significant ice cap expansions.
The recent advance of Bregne ice cap (at w0.74 ka) is similar to
the timing of small glacier and ice cap advances in other locations in
the Scoresby Sund region. Similar to Bregne ice cap, unweathered,
unvegetated moraines marking the largest advance of the Holocene
occur in the Stauning Alper and Liverpool Land (Kelly et al., 2008;
Hall et al., 2008a; Lowell et al., 2013). Late Holocene moraines in
the Stauning Alper are 0.78e0.31 ka (Kelly et al., 2008) and Istorvet
ice cap reached its maximum Holocene extent at 0.8e0.3 ka (Lowell
et al., 2013). Together, these records indicate cold climate conditions in central east Greenland at w0.8e0.3 ka, likely associated
with the Little Ice Age (e.g., Grove, 2004). Although the Greenland
Ice Sheet likely responded to the cold climate conditions of the late
Holocene, ice sheet fluctuations during this time are not well
documented.
7. Conclusions
We use a multi-proxy approach including geomorphic mapping,
Be ages of boulders and bedrock and lake sediment records to
develop a continuous record of the Holocene fluctuations of Bregne
ice cap. These records document significant changes in the ice cap
extent that reflect Holocene climate conditions. Bregne ice cap
retreated to within its late Holocene extent by at least 10.7 ka, was
likely smaller than at present or nonexistent from w10.0 to
1.9 cal ka BP and reached a late Holocene maximum by w0.74 ka.
The Holocene fluctuations of Bregne ice cap were likely in response
to decreasing Northern Hemisphere summer insolation. Ice cap
expansions at w2.6 and w1.9 cal ka BP may have been also
10
Please cite this article in press as: Levy, L.B., et al., Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate
along the Greenland Ice Sheet margin, Quaternary Science Reviews (2013), http://dx.doi.org/10.1016/j.quascirev.2013.06.024
L.B. Levy et al. / Quaternary Science Reviews xxx (2013) 1e12
11
Fig. 7. Two Move lake magnetic susceptibility (MS), percent organic matter (OM), and Last Chance lake percent biogenic silica (BSi) plotted with summer insolation at 65 north
latitude (Berger and Loutre, 1991), the Renland d18O record (Johnsen et al., 1992) and GRIP borehole temperatures (Dahl-Jensen et al., 1998). Light blue horizontal panels show the
timing of widespread abrupt cold periods in the North Atlantic region at 8.6e8.0, 6.5e5.9, 4.8e4.5, 3.3e2.5, 1.75e1.35, and 0.7e0.15 cal ka BP (Wanner et al., 2011). Dark blue lines
show timing of Bond events at 1.4, 2.8, 4.2, 5.9, 8.1, 9.4 cal ka BP (Bond et al., 1997, 2001). The timing of the Holocene Thermal Maximum (HTM), the Medieval Warm Period (MWP)
and the Little Ice Age (LIA) are shown on the GRIP borehole temperature record (Dahl-Jensen et al., 1998) by vertical bars (red ¼ warmer than at present conditions, dark
blue ¼ colder than at present conditions). Bregne ice cap advances at w2.6 and w1.9 cal ka BP are marked by dashed lines. The advances of Bregne ice cap are similar in timing to
abrupt cold events in the North Atlantic region only during late Holocene time, when Northern Hemisphere summer insolation was low.
influenced by late Holocene abrupt cold events. Although other
records exist from Scoresby Sund region, Bregne ice cap is the
closest to the eastern margin of the Greenland Ice Sheet and
therefore provides a robust record of Holocene climate conditions
that influenced the ice sheet margin.
Acknowledgments
We thank C. Smith and B. Goehring for assisting with fieldwork
and S. Hammer for conducting lake sediment analyses. J. Chipman
provided Geographic Information System expertise, O. Bennike
helped identify macrofossils for radiocarbon dating and A. Giese
offered helpful comments on the manuscript. S. Funder and an
anonymous reviewer gave valuable comments that improved the
manuscript. POLOG and CHM2Hill Polar Field Services and Air
Greenland provided field logistics. The Greenland Bureau of Mines
and Petroleum offered permits to conduct this research. D. Kaufman and K. Sides measured biogenic silica. We thank NOSAMS for
radiocarbon measurements and R. Finkel and D. Rood at LLNL CAMS
for beryllium measurements. The LRC staff assisted with sediment
core shipping and processing. This project was funded by National
Science Foundation (NSF) grants ARC-0909270 (Kelly), ARC0909285 (Lowell), ARC-0908081 (Hall). L. Hempel was funded by a
Stiffler Family Undergraduate Grant at Dartmouth College. The
2006 field season was supported by the Comer Science and Education Foundation and an NSF grant (ANT-0527946 to Kelly).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.quascirev.2013.06.024.
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