Glacier response to North Atlantic climate variability during the Holocene

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DOI: 10.5194/cp-11-1587-2015
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Abstract
Small glaciers and ice caps respond rapidly to climate variations, and records of their past extent provide information on the natural envelope of past climate variability. Millennial-scale trends in Holocene glacier size are well documented and correspond with changes in Northern Hemisphere summer insolation. However, there is only sparse and fragmentary evidence for higher-frequency variations in glacier size because in many Northern Hemisphere regions glacier advances of the past few hundred years were the most extensive and destroyed the geomorphic evidence of ice growth and retreat during the past several thousand years. Thus, most glacier records have been of limited use for investigating centennial-scale climate forcing and feedback mechanisms. Here we report a continuous record of glacier activity for the last 9.5 ka from southeast Greenland derived from high-resolution measurements on a proglacial lake sediment sequence. Physical and geochemical parameters show that the glaciers responded to previously documented Northern Hemisphere climatic excursions, including the "8.2 ka" cooling event, the Holocene Thermal Maximum, Neoglacial cooling, and 20th century warming. In addition, the sediments indicate centennial-scale oscillations in glacier size during the late Holocene. Beginning at 4.1 ka, a series of abrupt glacier advances occurred, each lasting ~100 years and followed by a period of retreat, that were superimposed on a gradual trend toward larger glacier size. Thus, while declining summer insolation caused long-term cooling and glacier expansion during the late Holocene, climate system dynamics resulted in repeated episodes of glacier expansion and retreat on multi-decadal to centennial timescales. These episodes coincided with ice rafting events in the North Atlantic Ocean and periods of regional ice cap expansion, which confirms their regional significance and indicates that considerable glacier activity on these timescales is a normal feature of the cryosphere. The data provide a longer-term perspective on the rate of 20th century glacier retreat and indicate that recent anthropogenic-driven warming has already impacted the regional cryosphere in a manner outside the natural range of Holocene variability.
Clim. Past, 11, 1587–1598, 2015
www.clim-past.net/11/1587/2015/
doi:10.5194/cp-11-1587-2015
© Author(s) 2015. CC Attribution 3.0 License.
Glacier response to North Atlantic climate variability
during the Holocene
N. L. Balascio1,2, W. J. D’Andrea1, and R. S. Bradley3
1Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA
2Department of Geology, College of William & Mary, Williamsburg, VA 23187, USA
3Department of Geosciences, University of Massachusetts, Amherst, MA 01003, USA
Correspondence to: N. L. Balascio (nbalascio@wm.edu)
Received: 16 April 2015 – Published in Clim. Past Discuss.: 27 May 2015
Revised: 23 October 2015 – Accepted: 27 October 2015 – Published: 4 December 2015
Abstract. Small glaciers and ice caps respond rapidly to
climate variations, and records of their past extent provide
information on the natural envelope of past climate vari-
ability. Millennial-scale trends in Holocene glacier size are
well documented and correspond with changes in North-
ern Hemisphere summer insolation. However, there is only
sparse and fragmentary evidence for higher-frequency varia-
tions in glacier size because in many Northern Hemisphere
regions glacier advances of the past few hundred years were
the most extensive and destroyed the geomorphic evidence
of ice growth and retreat during the past several thousand
years. Thus, most glacier records have been of limited use
for investigating centennial-scale climate forcing and feed-
back mechanisms. Here we report a continuous record of
glacier activity for the last 9.5ka from southeast Greenland
derived from high-resolution measurements on a proglacial
lake sediment sequence. Physical and geochemical param-
eters show that the glaciers responded to previously docu-
mented Northern Hemisphere climatic excursions, including
the “8.2 ka” cooling event, the Holocene Thermal Maximum,
Neoglacial cooling, and 20th century warming. In addition,
the sediments indicate centennial-scale oscillations in glacier
size during the late Holocene. Beginning at 4.1 ka, a series of
abrupt glacier advances occurred, each lasting 100years
and followed by a period of retreat, that were superimposed
on a gradual trend toward larger glacier size. Thus, while
declining summer insolation caused long-term cooling and
glacier expansion during the late Holocene, climate system
dynamics resulted in repeated episodes of glacier expan-
sion and retreat on multi-decadal to centennial timescales.
These episodes coincided with ice rafting events in the North
Atlantic Ocean and periods of regional ice cap expansion,
which confirms their regional significance and indicates that
considerable glacier activity on these timescales is a normal
feature of the cryosphere. The data provide a longer-term per-
spective on the rate of 20th century glacier retreat and indi-
cate that recent anthropogenic-driven warming has already
impacted the regional cryosphere in a manner outside the nat-
ural range of Holocene variability.
1 Introduction
Glaciers and ice caps represent a small but important portion
of the cryosphere (785000 km2; Dyurgerov and Meier,
2005). Their mass wasting during the 20–21st century is
responsible for 60% of the sea-level rise unattributable to
ocean warming (Meier, 2007) and they continue to retreat
at an exceptional rate (Zemp et al., 2012). Moreover, be-
cause small glaciers and ice caps respond rapidly to climate
changes and there is a strong relationship between glacier
mass balance and summer temperature (Oerlemans, 2005),
past glacier extent can inform us about past climate variabil-
ity.
Holocene glacier activity in the Arctic is reasonably
well documented at millennial timescales (Miller et al.,
2010). Northern Hemisphere glaciers receded in the early
Holocene and were smaller than present during the mid-
Holocene. Centennial-scale variations, however, are not well
constrained because there are few high-resolution and con-
tinuous records, and because in many regions the most ex-
tensive glacier advances since the early Holocene took place
Published by Copernicus Publications on behalf of the European Geosciences Union.
1588 N. L. Balascio et al.: Glacier response to North Atlantic climate variability
within the past few hundred years, destroying geomorphic
evidence of intervening glacier positions. This is the case in
Greenland, where historical (AD 1200–1940) advances of lo-
cal glaciers were generally the most extensive since at least
the early Holocene (Kelly and Lowell, 2009).
Evidence from the Greenland Ice Sheet (Kobashi et al,
2011), marine sediments (Bond et al., 1997; Thornalley et
al., 2009; Moffa-Sánchez et al., 2014; Jiang et al., 2015),
and terrestrial archives (D’Andrea et al., 2011; Larsen et
al., 2012; Olsen et al., 2012) indicate that abrupt changes
in atmospheric circulation and ocean dynamics, including
abrupt cooling events, have punctuated the Holocene. These
episodes have alternately been attributed to solar variabil-
ity, freshwater forcing, volcanic activity, and/or changes in
Atlantic Meridional Overturning Circulation (Wanner et al.,
2011). How sensitive were glaciers to these abrupt episodes,
and did glaciers throughout the North Atlantic respond uni-
formly? During the period from AD 1250–1900, often re-
ferred to as the “Little Ice Age”, well-resolved records from
the North Atlantic region suggest coherence in ice cap activ-
ity that was potentially driven by volcanic activity coupled
with sea-ice/ocean feedbacks (Miller et al., 2012). However,
prior to the last 1000 years there are sparse data for use in in-
vestigating the synchrony of glacier response to climate vari-
ability in the North Atlantic region.
Lakes that receive meltwater from temperate glaciers can
be used to develop continuous records of glacier activity.
Bedrock erosion at the base of glaciers provides sediment
supply for meltwater transport to proglacial lakes. In catch-
ments where other sources of sediment are limited (such
as from mass wasting, paraglacial effects, or the release of
stored sediment) there is a strong relationship between sed-
iment properties and glacier size (Nesje et al., 2000; Dahl
et al., 2003; Jansson et al., 2005), which also follows from
the assumption that large glaciers produce more minerogenic
material and meltwater than small glaciers. Measurements
of physical and geochemical properties of proglacial lake
sediments can therefore be used to reconstruct records of
past glacier size. Here we report a continuous 9.5ka record
of glacier activity on Kulusuk Island, southeast Greenland
developed using sediment cores recovered from Kulusuk
Lake (65.56N, 37.11W; 202m) (Fig. 1). We character-
ize changes in sedimentation using measurements of phys-
ical sediment properties, including the following: bulk den-
sity, organic matter content, magnetic susceptibility, and ac-
cumulation rates. We also measured the relative elemental
compositions of the sediment using scanning X-ray fluores-
cence (XRF) to characterize minerogenic changes at higher
resolution and with greater sensitivity. These data provide de-
tailed information on sedimentation in Kulusuk Lake related
to glacier input.
Figure 1. Location and catchment setting of Kulusuk Lake. The
white dashed line marks the watershed boundary and the red dashed
line defines the crest of moraines in front of both glaciers mapped
in the field. Cores were collected in the deepest basin (red circle).
Image: Google, NASA.
2 Study site
Kulusuk Lake (0.8 km2, 69m maximum depth) is located be-
low a cirque with two small glaciers and is within a low arctic
maritime region (MAT 1C, MAP 900 mm). Characteris-
tic erosional features indicate that local glaciers have tem-
perate thermal structures (Humlum and Christiansen, 2008).
Distinct moraines defined by sharp crests are located in front
of both glaciers, and the recently glaciated area accounts for
50% of the catchment, which is composed of Archaen
gneisses (Bridgwater, 1976) (Fig. 1). Kulusuk Lake is ideally
situated to capture and preserve a clear sedimentary record of
glacier activity because (i) it only receives runoff from a very
small catchment (catchment :lake area ratio of 2:1), mini-
mizing the potential for long-term storage of sediments prior
to deposition and limiting sediment input from non-glacial
processes, (ii) the proximity of the glaciers to the lake results
in minimal sediment transport distance, and (iii) the small
size of the glaciers makes them sensitive to minor climate
variations (Fig. 1). Therefore, bedrock erosion by the glaciers
provides the primary source of minerogenic sediment to the
lake and changes in glacier size should clearly be reflected in
sediment properties.
3 Methods
3.1 Sediment core collection and analysis
Sediment cores were recovered from Kulusuk Lake in
April 2010 when the lake was ice covered. Bathymetric mea-
surements were made manually through holes drilled in the
ice, and sediment cores were collected using Uwitec grav-
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N. L. Balascio et al.: Glacier response to North Atlantic climate variability 1589
ity and percussion coring devices from the deepest location,
which has a water depth of 69m. A composite 3.5 m record
was compiled by matching the physical stratigraphy and
scanning XRF profiles from a 26cm gravity core (Kul-10D-
B) and multiple overlapping percussion cores (Kul-10G-A1,
-B1, -A2).
The magnetic susceptibility of the cores was measured ev-
ery 0.5cm using a Bartington MS2E sensor. The organic-
matter content of the cores was measured by loss-on-ignition
(LOI) on contiguous 1-cm3samples taken at 1cm intervals.
Organic-matter content was calculated as the difference be-
tween the weight of dried 1-cm3samples and their weight af-
ter heating for 4 h at 550C (Dean, 1974). Bulk density mea-
surements (gcm3) and the calculated sedimentation rates
(cmyear1) were used to determine mass accumulation rates
(MAR; g cm2year1). Grain size measurements were made
at 10cm increments. Samples were pre-treated with a 30 %
hydrogen peroxide solution to digest organic material and
analyzed using a Beckman Coulter LS200 particle-size an-
alyzer.
3.2 Chronology
An age–depth model was established based on 210Pb anal-
ysis of the upper sediments and AMS radiocarbon dates on
macrofossils. The 210Pb activity of samples taken every 1cm
from the upper 10cm of the record was measured by Flett
Research Ltd. (Winnipeg, Canada), and ages were modeled
from these data using a constant rate of supply model. AMS
radiocarbon measurements were made on plant/wood frag-
ments and Daphnia ephippia that were wet sieved from core
samples. All radiocarbon ages were calibrated to calendar
years using CALIB v. 6.0 (Stuiver and Reimer, 1993) with
the IntCal09 calibration data set (Reimer et al., 2009). Ages
are presented in calendar years prior to AD 1950 (BP) unless
otherwise indicated.
3.3 Scanning X-ray fluorescence
To characterize minerogenic changes at higher resolution and
with greater sensitivity, an ItraxXRF core scanner was
used to produce profiles of relative elemental compositions
(Croudace et al., 2006). The Itraxcontinuously scans the
surface of sediment cores at sub-mm resolution with a micro
X-ray beam (20mm ×100 µm), and the relative concentra-
tions of a range of elements are determined based on the de-
tection of dispersive energy spectra. Dispersive energy spec-
tra are acquired across each measured interval, and peak area
integrals are calculated for each element. Peak area integrals
are related to elemental concentrations within the sediment,
but can also be influenced by characteristics of the sedimen-
tary matrix and therefore only indicate relative changes in
elemental composition (Croudace et al., 2006; Rothwell et
al., 2006). Our analysis focused on the elements K, Ca, Ti,
Mn, Fe, Zn, Rb, Sr, which have detection limits that range
from 150 to 5ppm (Croudace et al., 2006). All of the cores
were scanned at 200µm intervals with an exposure time of
10s, voltage of 30kV, and current of 55 nA.
4 Results
4.1 Sediment stratigraphy and chronology
The 3.5m composite sediment record from Kulusuk Lake
contains distinct lithologic changes, defined by visual stratig-
raphy, magnetic susceptibility, organic matter content, and
elemental data acquired by scanning XRF. The record can be
divided into four lithologic units (Fig. 2). Unit I, 3.0–3.5 m, is
a gravelly sand. Unit II, from 3.0 to 1.8m, is a massive gray
clayey silt. There is an abrupt transition to Unit III, a brown,
organic-rich sediment that extends from 1.8–1.2m. Unit IV,
1.2–0 m, is a laminated sequence with frequent sandy layers.
Laminations consist of fining-upward sequences and impart
strong variability in all data sets.
Chronologic data show that there are significant changes in
sedimentation rate that correspond to lithostratigraphic units
(Fig. 2). An age–depth model was generated assuming that
changes in sedimentation rate occurred at the boundaries of
these units. In Unit IV, a third-order polynomial was applied
to the radiocarbon ages, the core top date that represents
when the cores were collected in AD 2010 (60cal yr BP),
and the date of the base of the 210Pb profile at 10 cm
(111cal yr BP) (Table 1). This relationship was extrapolated
to the base of Unit IV. Linear interpolation between the re-
maining radiocarbon ages was used to generate the age–
depth relationship for Units III and II. There is no chrono-
logic control below 215cm so we did not interpret sedimen-
tation prior to 9.5cal ka BP.
Magnetic susceptibility, organic matter, and mass accu-
mulation rate (MAR) profiles further define these lithologic
changes with higher magnetic susceptibility values across in-
tervals with coarser sediment and with lower organic con-
tent (Fig. 3). Moderate organic matter, 5%, and magnetic
susceptibility, 400 SI 105, values characterize the inter-
val from 2.5–1.8m. From 1.8–1.6m, magnetic susceptibility
values decrease to zero and organic matter values increase
to 19% (with the exception of two brief intervals of de-
creased values at 176 and 171cm) and remain elevated to
1.4m. From 1.4–1.2 m, organic content declines and mag-
netic susceptibility values increase and then display more mi-
nor fluctuations across the upper 1.2m. These intervals are
clearly defined by MARs, which incorporate sediment den-
sity measurements that range from 0.8–1.8g cm3, but are
primarily controlled by the large sedimentation rate changes
(Fig. 2).
4.2 Scanning XRF data analysis
Elemental scans acquired by scanning XRF show a response
similar to magnetic susceptibility with higher values across
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1590 N. L. Balascio et al.: Glacier response to North Atlantic climate variability
Figure 2. Magnetic susceptibility profile, percent sand, and mass accumulation rate (MAR) shown next to the age–depth model for the
composite Kulusuk Lake record. The four lithostratigraphic units and the corresponding sedimentation rates are shown. A dash line marks
the period below the last radiocarbon age (9.5 calka BP) where rates of sedimentation are extrapolated.
Table 1. Geochronologic data for the Kulusuk Lake record.
Composite Description Laboratory 14C age Calibrated age range Median age
depth
(cm) IDa(yr BP) (1σ) (2σ) (calyrBP)
0 Core Top 60
1210Pb – – – – 53
2210Pb – – – – 46
3210Pb – – – – 36
4210Pb – – – – 25
5210Pb – – – – 7
6210Pb – – – – 24
7210Pb – – – – 44
8210Pb – – – – 57
9210Pb – – – – 83
10 210Pb – – – – 111
34 Daphnia ephippia OS-96479 335±40 316–459 306–486 393
59.5 Plant/wood UCI-89386 940±20 798–914 795–919 852
95 Daphnia ephippia OS-96454 1290±25 1183–1276 1178–1283 1237
132 Plant/wood UCI-87240 3410±60 3574–3814 3484–3832 3664
138.5 Plant/wood UCI-87241 3820±60 4095-4378 4008-4415 4224
170.5 Daphnia ephippia OS-96461 7620±50 8377–8452 8359–8539 8418
214.5 Daphnia ephippia OS-96746 8510±130 9312–9659 9135–9887 9501
aUCI – University of California Irvine Keck-CCAMS Facility; OS – National Ocean Sciences AMS Facility
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N. L. Balascio et al.: Glacier response to North Atlantic climate variability 1591
Table 2. XRF PC1 factor loadings and correlation matrix for scanning XRF elemental data.
PC1 K Ca Ti Mn Fe Zn Rb Sr
loadings
K 0.950 1
Ca 0.868 0.891 1
Ti 0.969 0.938 0.797 1
Mn 0.815 0.672 0.594 0.783 1
Fe 0.945 0.876 0.748 0.946 0.814 1
Zn 0.861 0.759 0.609 0.842 0.727 0.836 1
Rb 0.831 0.743 0.601 0.791 0.637 0.790 0.727 1
Sr 0.686 0.689 0.803 0.583 0.412 0.488 0.436 0.455 1
coarser, clastic intervals. However, the XRF data have a
greater sensitivity to minerogenic changes and were mea-
sured at higher resolution (0.2mm) (Fig. 3). We focused
our analysis on the following elements: K, Ca, Ti, Mn, Fe,
Zn, Rb, and Sr, which are common in siliciclastic sedi-
ments. Changes in the concentrations of these elements re-
flect changes in the contribution of minerogenic material
eroded from catchment bedrock and delivered to the lake.
Statistical analysis of the scanning XRF data indicates that
all of the elements are highly correlated and that there is
a strong primary trend in the data. Correlation coefficients
show the strong significant relationships among the majority
of the elements (Table 2). Rather than relying on a single ele-
ment (e.g., Ti), we used principal component analysis (PCA)
to define the leading mode of variability (PC1) among the
elemental data. PCA allows for a multidimensional exami-
nation of the data set in order to identify the primary sig-
nal(s). PCA results indicate that there is one strong primary
trend in the elemental data with the first eigenvector (PC1)
accounting for 76% of the total variance. The factor load-
ings reveal the high correlations between individual element
profiles and PC1 (Table 2). The trends in PC1 are similar to
those in the lower-resolution magnetic susceptibility and or-
ganic matter content records, justifying use of PC1 data to
infer past minerogenic changes (Fig. 3). The choice to use
PC1 rather than a single representative element (e.g., Ti) to
represent changes in sedimentary minerogenic content has no
impact on any of our conclusions.
5 Discussion
5.1 Sedimentation in proglacial lakes
Sedimentation in proglacial lakes can be the result of a
complex set of physical processes associated with the ero-
sion, storage, and transport of sediment within glacial and
proglacial systems (Dahl et al., 2003; Jansson et al., 2005).
It is important to consider these complicating factors when
selecting sites for glacier reconstructions and when interpret-
ing sedimentary records. Glaciers fundamentally impact the
amount and character of minerogenic sediment in proglacial
lakes. Glacier size, erosive ability, and meltwater produc-
tion directly influence the amount of minerogenic sediment
delivered to a proglacial lake. However, sedimentation in
a proglacial lake can also be impacted by mass wasting
processes in paraglacial environments (particularly in land-
scapes with steep unstable slopes), and by the delayed re-
lease of sediment stored along the transport pathway between
the glacier and the lake (for example, sediment stored in ex-
tensive meltwater stream channels). Relative to minerogenic
material, organic sedimentation is typically a minor com-
ponent in proglacial lakes and is related to the input of or-
ganic matter from autochthonous and allochthonous primary
productivity, and the preservation thereof. In proglacial en-
vironments in the Arctic, low temperatures restrict vegeta-
tion and soil cover, and minerogenic sediment input to lakes
from glacial meltwater results in turbidity that impedes au-
tochthonous productivity.
Techniques for analyzing sediment from proglacial lakes
therefore focus on investigating changes in the character of
minerogenic sediment. The minerogenic content of lake sed-
iments, used as a proxy for glacier size, is commonly eval-
uated by measuring the magnetic susceptibility and organic
matter content of the sediments. The abundances of the ma-
jor elements from bedrock material (measured by XRF) sim-
ilarly serve as a proxy for the relative contribution of minero-
genic material, versus organic matter, to the lake. Mag-
netic susceptibility reflects the amount of magnetic minerals
eroded and input to a lake, the abundance of major elements
from bedrock (measured by XRF) also reflects the relative
contribution of minerogenic material input to the lake, and
organic matter content is a function of dilution by minero-
genic input, changes in primary productivity, and preserva-
tion.
At Kulusuk Lake, processes that can complicate the mech-
anistic link between minerogenic input and glacier size are
fundamentally limited. Input of sediment from non-glacial
processes is restricted due to the small catchment and small
catchment to lake-area ratio (2:1), and the proximity of
the glaciers to the lake. These factors also limit the potential
for sediment storage between the glaciers and the lake. Fur-
thermore, the landscape surrounding the lake is composed
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1592 N. L. Balascio et al.: Glacier response to North Atlantic climate variability
Figure 3. Kulusuk Lake record. (Top) First principal component of the scanning XRF data (PC1). (Middle) Magnetic susceptibility presented
on a log scale. A dotted line defines the interval from 165–140 cm where some zero values were measured. (Bottom) Organic-matter content.
Black bars indicate the location and age of chronologic control points (Table 1). The yellow shaded region on the PC1 plot shows where we
have interpreted little to no glacier ice in the catchment during the Holocene Thermal Maximum (HTM). Blue shading defines the Neoglacial
period when ice was reformed during the late Holocene (4.1ka–present).
of shallow, low-elevation slopes that minimize the likelihood
of mass wasting events. Therefore, at Kulusuk Lake, it is
reasonable to interpret changes in minerogenic content as a
function of glacier size.
Variations in magnetic susceptibility, organic matter con-
tent, and scanning XRF data (PC1) represent changes in the
relative amount and grain size of minerogenic sediment de-
livered to Kulusuk over the last 9.5 ka (Fig. 3). Magnetic sus-
ceptibility and PC1 are directly related to, and organic con-
tent is inversely proportional to, minerogenic content. The
highest magnetic susceptibility and PC1 values correspond
to intervals with coarser grain size. We therefore interpret the
sedimentological system in Kulusuk Lake as follows: during
periods of increased glacier size, more coarse minerogenic
sediment was eroded from the bedrock and delivered to the
lake by meltwater; during periods of smaller glacier size, less
minerogenic sediment was deposited and a greater relative
proportion of organic matter content accumulated.
5.2 Holocene glacier fluctuations in southeast
Greenland
Dramatic changes in minerogenic input to Kulusuk Lake over
the last 9.5 ka reveal that the size of the Kulusuk glaciers has
varied significantly throughout the Holocene (Fig. 3). Begin-
ning ca. 8.7ka, increasing organic matter content and de-
creasing minerogenic content, inferred from magnetic sus-
ceptibility and XRF data, document significant retreat of
the Kulusuk glaciers, corresponding closely in time with the
deglaciation of a nearby inland catchment ca. 8.4ka (Balas-
cio et al., 2013), following deglaciation of local coastal ar-
eas ca. 11.1–9.5ka (Long et al., 2008; Roberts et al., 2008).
A brief interval of increased minerogenic input shows that
this early Holocene retreat was interrupted by an episode
of advance at 8.5ka, coeval with reductions in sea surface
temperatures and bottom water circulation in the subpolar
North Atlantic, as seen in high-resolution marine records (El-
lison et al., 2006; Kissel et al., 2013). Another abrupt episode
of minerogenic input ca. 8.2ka signifies another glacier ad-
vance. This advance occurred contemporaneously with the
largest abrupt Holocene climate cooling event inferred from
Greenland ice core records (Thomas et al., 2007), which is
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N. L. Balascio et al.: Glacier response to North Atlantic climate variability 1593
also marked by the advance of Jakobshavn Isbræ, an out-
let glacier of the Greenland Ice Sheet in western Greenland
(Young et al., 2011, 2013). The temporal resolution and age
control of this section of our record cannot provide new con-
straints on the exact timing of these events, however it clearly
demonstrates the sensitivity of the Kulusuk glaciers to rapid,
regional climate events.
Between 7.8–4.1ka, the Kulusuk glaciers were at their
minimum Holocene extent, inferred from low minerogenic
content, low MAR, and high organic matter content in the
lake sediments (Fig. 3). We interpret this as an interval with
little to no glacier ice in the catchment, primarily based on
the XRF and magnetic susceptibility data, which are lowest
and show reduced variability at this time, relative to the last
4.1 ka. This interval is also marked by extremely high organic
matter content that is greater than 12% (with a maximum of
19 %), suggesting that this period was accompanied by an in-
crease in primary productivity due to a lack of input of glacial
flour. If the catchment was completely deglaciated, this indi-
cates that the regional equilibrium-line altitude would have
been greater than 676m, which is the elevation of the
mountain peak above the lake. Magnetic susceptibility re-
mains close to zero throughout the mid-Holocene section
of the core and appears insensitive to the minor minero-
genic changes inferred from the XRF data, which could be
attributed to paraglacial processes or seasonal runoff con-
tributing very minor amounts of clastic sediment. There are
two excursions in the PC1 record during this interval (ca.
7.2 and 6.2ka), which we interpret as sediment influxes
from paraglacial activity rather than as glacier advances be-
cause they are short-lived and do not match the amplitude
of variation observed elsewhere. Thus, this record provides
well-dated constraints on the Holocene Thermal Maximum
(HTM) in this area, which refine previous estimates extrapo-
lated for this region (Kaufman et al., 2004) and is similar to
the interval when the Greenland Ice Sheet margin was behind
its present limit, broadly constrained to ca. 7–4ka (Larsen et
al., 2015).
At 4.1ka, a sharp increase in XRF- and MS-inferred
minerogenic content and decrease in organic matter content
indicate the glaciers once again grew large enough to con-
tribute minerogenic material to the lake. The regrowth of
the Kulusuk glaciers represents the lowering of the regional
snowline, and the precise timing could be considered unique
to this catchment. However, the timing is contemporaneous
with hydrologic changes at nearby Flower Valley Lake, likely
related to an increase in the duration of lake ice cover (Bal-
ascio et al., 2013). We propose that this represents significant
cooling and the onset of the regional Neoglacial period. The
oscillatory and stepwise increase in minerogenic input (de-
crease in organic matter content) after 4.1ka suggests that
rather than advancing steadily toward their historical extent,
the Kulusuk glaciers episodically advanced and retreated at
centennial timescales until ca. 1.3ka. After advancing at ca.
1.3ka, they stabilized after 0.7ka until their rapid 20th cen-
tury retreat (Fig. 3). Importantly, the major sedimentologi-
cal transitions in the record are all located near radiocarbon
dates, thereby maximizing the certainty of their timing and
the calculations of sediment accumulation rates. The timing
of glacier size variations between radiocarbon-dated inter-
vals since 4.1ka are interpolated, and we estimate the ac-
curacy to be better than ±100 years, the average 2-σuncer-
tainty of the ages.
5.3 Evidence for synchronous regional glacier response
during the late Holocene
The Kulusuk glacier reconstruction documents centennial-
scale episodes of glacier advance during the Neoglacial (4.1
to 1.3ka) coeval with other records of glacier growth in the
North Atlantic region. After 4.1 ka, six major advances of the
Kulusuk glaciers occurred (4.1, 3.9, 3.2, 2.8, 2.1, and 1.3ka)
and each successive advance resulted in greater glacier extent
(Fig. 4). The progressive increase in glacier size is consis-
tent with declining NH summer insolation, which is likely
the mechanism driving millennial-scale changes in glacier
size. However, each episode of glacier advance was followed
by a period of retreat (or at least stabilization), suggesting
that the glaciers repeatedly grew out of equilibrium with
external insolation forcing and then retreated back toward
an equilibrium state, indicating centennial-scale variability
likely driven by internal climate dynamics. The episodic ad-
vances of the Kulusuk glaciers during the past 4.1 ka are
similar in timing to the cooling episodes in the North At-
lantic Ocean inferred from ice-rafted debris (IRD) identified
in marine sediment cores (Bond et al., 1997, 2001) (Fig. 4).
Cooling events at these times have also been documented on
the East Greenland and Icelandic shelves and attributed to in-
creased strength of the East Greenland Current (Giraudeau et
al., 2000; Jennings et al., 2002; Ran et al., 2008). Moreover,
the Langjökull ice cap in Iceland advanced along with the
Kulusuk glaciers and the North Atlantic IRD events (Larsen
et al., 2012) (Fig. 4), and advances of the Bregne ice cap
in east Greenland at ca. 2.6 and 1.9ka (Levy et al., 2014),
within chronological uncertainty of the Kulusuk glacier ad-
vances ca. 2.8 and 2.1ka, have also been documented. We
propose that continuous records of glacier activity around the
North Atlantic during the Neoglacial are beginning to show
evidence for synchronous glacier response to abrupt episodes
of climate change.
It is also worth noting that Winsor et al. (2014) found ev-
idence for an advance of an outlet glacier of the Greenland
Ice Sheet in southern Greenland ending at ca. 1.5 ka, the tim-
ing of which is supported by minimum-limiting radiocarbon
ages from the same region dating to ca. 1.2ka (Bennike and
Sparrenbom, 2007). We acknowledge that this is the only lo-
cation on the ice sheet margin where such a late Holocene
advance has been documented, but nonetheless it highlights
that changes in the ice margin position are beginning to be
constrained more accurately.
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1594 N. L. Balascio et al.: Glacier response to North Atlantic climate variability
Figure 4. Regional response of glaciers to Holocene climate changes. (a) Kulusuk glaciers interpreted from PC1 data with July insolation
anomalies at 65N (Berger and Loutre, 1991). (b) Hematite-stained grains (HSG) identified in core MC52-VM29-191 interpreted to indicate
ice-rafting events (Bond et al., 1997). (c) Ratio of total organic carbon to total nitrogen (C/N) and (d) changes in sedimentation rate from
Hvítárvatn, interpreted to reflect changes in the size of the Langjökull ice cap, Iceland, and catchment instability in response to climate
cooling (Larsen et al., 2012). Yellow shading marks the timing of the Holocene Thermal Maximum (HTM), as interpreted at Kulusuk, and
the dashed line on the PC1 plot shows where we have interpreted the absence of ice from the catchment during the HTM. Blue bars highlight
intervals of glacier advance and increased ice rafting that define Neoglacial cooling events comparable among the records.
The amplitude of variability in the proxy measurements
during the past 1.3ka is lower than earlier in the Holocene,
due to the greater size and stability of the Kulusuk glaciers;
however, it is worthwhile to examine the changes in the sed-
iment properties where advances are interpreted as sustained
above average PC1 values. The very high sediment accu-
mulation rates during this interval (0.8mmyr1) allow sub-
annual XRF measurements and, if interpreted in the same
manner as periods with smaller glacier size, can afford a de-
tailed examination of changes in glacier size using the XRF
PC1 data (Fig. 5). The overall trend reveals a small and very
gradual glacier expansion after 0.7ka followed by 20th cen-
tury retreat, which resembles the overall trend in Arctic tem-
peratures over the last 2ka (Kaufman et al., 2009).
Multi-decadal variations in inferred glacier size during the
past 1.3 ka also appear to be synchronous with those of other
glaciers in the region after ca. AD 1250 (Fig. 5). Kulusuk
glaciers increased in size ca. AD 1250–1300 and again ca.
AD 1450, similar to when ice caps on Baffin Island (Miller
et al., 2012) and Iceland (Larsen et al., 2011) were expand-
ing (Fig. 4). After AD 1450 Kulusuk glaciers continued to
expand, as did Langjökull on Iceland, while evidence from
the Baffin ice caps indicates continuous ice cover (Miller et
al., 2012).
Both Kulusuk and Langjökull glaciers appear to have ad-
vanced in at least two phases, at ca. AD 1450–1630 and
ca. AD 1700–1930. Magnetic susceptibility trends, linked to
glacier size changes, from another high-resolution proglacial
lake record on Baffin Island (Big Round Lake) reveal two
Clim. Past, 11, 1587–1598, 2015 www.clim-past.net/11/1587/2015/
N. L. Balascio et al.: Glacier response to North Atlantic climate variability 1595
Figure 5. Change in the size of the Kulusuk glaciers since AD 700 compared with other high-resolution glacier and ice caps records from
the region. (a) The Kulusuk PC1 record. Black horizontal line shows average value over this period. (b) Big Round Lake, Baffin Island, varve
thickness and magnetic susceptibility (Thomas and Briner, 2009; Thomas et al., 2010). (c) Baffin Island ice cap activity reconstructed using
vegetation kill dates with text showing original interpretations (Miller et al., 2012). (d) Langjökull ice cap, Iceland-based on varve thickness
from Lake Hvítárvatn (Larsen et al., 2011). Blue shading marks periods of increased glacier size (sustained above average PC1 values).
similar distinct glacier advances at these times (Fig. 5) as
well as an earlier advance ca. AD 1250–1300, which is also
observed in the Kulusuk record (Thomas et al., 2010). How-
ever, varve thickness data from Big Round Lake, which has
previously been interpreted to represent summer tempera-
ture, resemble trends in magnetic susceptibility (Thomas and
Briner, 2009). This discrepancy can possibly be attributed to
how the two proxies track different sedimentary processes
operating over different timescales (annual vs. centennial),
but without further analysis of those records we cannot ac-
count for this apparent contradiction. We argue that the mag-
netic susceptibility data from Big Round Lake are consistent
with other data from around Greenland, indicating that the
most extensive glacier advances since the early Holocene oc-
curred between AD 1250 and 1900, and provide evidence
for regionally coherent cooling phases during the Little Ice
Age (Grove, 2001). We note that this timing contrasts with
evidence from east Greenland that suggests the Istorvet Ice
Cap advanced approximately 100 years earlier (ca. AD 1150;
Lowell et al., 2013), unless the data are reinterpreted as sug-
gested by Miller et al. (2013).
Therefore, there seems to have been regional coherence in
glacier activity not only during the past 1.3ka, as previously
suggested (Miller et al., 2012), but also during the past 4.1 ka,
and glacier growth in response to episodic climate change has
been a common feature in the North Atlantic region through-
out, at least, the last 4.1ka.
Cold events are an important feature of centennial-scale
climate of the Holocene (Wanner et al., 2011). Cooling
events in the North Atlantic region are possibly associated
with changes in Atlantic Meridional Overturning Circulation
(AMOC) (Denton and Broecker, 2008). IRD records suggest
that periodic circulation changes of the North Atlantic Ocean
resulted in an advection of cold, fresh surface water south
and east during ice-rafting events throughout the Holocene
(Bond et al., 1997). Ocean circulation and sea-surface tem-
perature changes associated with IRD events have been at-
tributed to solar forcing (Bond et al., 2001; Moffa-Sánchez et
al., 2014; Jiang et al., 2015), and some modeling studies have
www.clim-past.net/11/1587/2015/ Clim. Past, 11, 1587–1598, 2015
1596 N. L. Balascio et al.: Glacier response to North Atlantic climate variability
Figure 6. Relative rates of change in the size of the Kulusuk glaciers interpreted from scanning XRF PC1 data. Red bars show 105-year
intervals when the average rate was positive indicating glacier retreat, and blue bars show intervals when the average rate was negative
indicating glacier advance. Values not calculated during the mid-Holocene when we interpret glaciers to be absent.
confirmed that AMOC can switch between distinct modes in
response to a small external forcing, such as solar variabil-
ity (Jongma et al., 2007). However, modeling results are in-
consistent and it is also possible that cooling events might
have simply resulted from internal ocean dynamics (Schulz
and Paul, 2002). Regardless of the mechanism, our results
demonstrate that glaciers responded quite actively to natural
climate variations of the Holocene.
5.4 Rates of glacier change during the Holocene
This well-dated, high-resolution record of changes in the size
of the Kulusuk glaciers also allows comparison among the
rates of past glacier size variations. We present relative rates
of change inferred from the first derivative of the XRF PC1
data in 105-year binned averages, an interval chosen using
the interval with the lowest resolution (Fig. 6). We acknowl-
edge the caveat that they are based on the assumption that
the relationship between minerogenic input and glacier size
has remained constant. The analysis indicates that the rate of
20th century retreat of the Kulusuk glaciers was greater than
during any other century of the past 1.3ka, including during
the Medieval Climate Anomaly. Furthermore, the 20th cen-
tury retreat rate was 2–3times the rate of any other period of
retreat during the past 4.1 ka, and almost twice as rapid as the
early Holocene retreat that marked the transition into the re-
gional HTM (Fig. 6). This comparison helps to place the rate
of 20th century glacier loss in the context of natural episodes
of past glacier activity.
6 Conclusions
The Kulusuk Lake sediment record was used to generate a
high-resolution record of changes in the size of the Kulusuk
glaciers over the last 9.5ka. Characteristics of the lake and
catchment limit the potential for sedimentation from non-
glacial processes making it ideally situated to clearly cap-
ture changes related to glacier activity. The record shows
that the glaciers were sensitive to a number of previously
documented regional climate fluctuations and improves our
understanding of Holocene climate dynamics in this sector
of the Arctic. In particular, the record clearly constrains the
Holocene Thermal Maximum at this site to between 7.8 and
4.1 ka, when the glaciers likely completely melted away.
The regrowth of the Kulusuk glaciers at 4.1ka corresponds
with regional hydrologic changes and reflects the onset of
the Neoglacial period. The last 4.1ka is marked by a series
of abrupt glacier advances as the size of the Kulusuk glaciers
increased. These episodes of glacier growth correspond with
ice rafting events in the North Atlantic Ocean, as well as re-
gional ice cap expansion, and demonstrate that glaciers in
this sector of the Arctic were very active during the late
Holocene in response to abrupt cooling events that punctu-
ated millennial-scale insolation-driven cooling. The recon-
struction of Kulusuk glacier activity provides a new and re-
fined perspective on late Holocene cold events, which are im-
portant features of centennial-scale climate variability.
Acknowledgements. This research was supported by a LDEO
Postdoctoral Fellowship to NLB, NSF grant ARC-0851642 to
WJD, NOAA grant NA09OAR4600215 and NSF grant ARC-
0909354 to RSB. We thank Lucien von Gunten, Sam Davin, and
Greg de Wet for assistance with field work, as well as Jason Briner,
Anders Carlson, and three anonymous reviewers for comments on
earlier drafts.
Edited by: V. Rath
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2005–2010, Vol. X: World Glacier Monitoring Service, Zurich,
Switzerland, 336 pp., 2010.
Clim. Past, 11, 1587–1598, 2015 www.clim-past.net/11/1587/2015/
Glacier response to North Atlantic climate variability during the Holocene.pdf
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  • Article
    Understanding Arctic glacier sensitivity is key to predicting future response to air temperature rise. Previous studies have used proglacial lake sediment records to reconstruct Holocene glacier advance–retreat patterns in South and West Greenland, but high‐resolution glacier records from High Arctic Greenland are scarce, despite the sensitivity of this region to future climate change. Detailed geochemical analysis of proglacial lake sediments close to Zackenberg, northeast Greenland, provides the first high‐resolution record of Late Holocene High Arctic glacier behaviour. Three phases of glacier advance have occurred in the last 2000 years. The first two phases (c. 1320–800 cal. a BP) occurred prior to the Little Ice Age (LIA), and correspond to the Dark Ages Cold Period and the Medieval Climate Anomaly. The third phase (c. 700 cal. a BP), representing a smaller scale glacier oscillation, is associated with the onset of the LIA. Our results are consistent with recent evidence of pre‐LIA glacier advance in other parts of the Arctic, including South and West Greenland, Svalbard, and Canada. The sub‐millennial glacier fluctuations identified in the Madsen Lake succession are not preserved in the moraine record. Importantly, coupled XRF and XRD analysis has effectively identified a phase of ice advance that is not visible by sedimentology alone. This highlights the value of high‐resolution geochemical analysis of lake sediments to establish rapid glacier advance–retreat patterns in regions where chronological and morphostratigraphical control is limited.
  • Article
    Mountain glaciers and ice caps (GIC) independent of the Greenland Ice Sheet respond rapidly to climate variations and records of their past extent provide information on the natural envelope of climate variability. Here, we use a multi-proxy approach that combines proglacial lake sediment analysis, cosmogenic nuclide surface-exposure dating (in situ ¹⁰Be and ¹⁴C), and radiocarbon dating of recently ice-entombed moss to generate a centennial-scale record of Holocene GIC fluctuations in southwestern Greenland. Following local deglaciation ∼10-9 ka, sediments from proglacial Crash Lake record a glacier advance at ∼9 ka that is indistinguishable from nearby ice sheet moraines, implying a synchronous response of GIC and the Greenland Ice Sheet to a centennial-scale climate event. Following this local glacier advance, GIC experienced net recession until ∼4.6 ka. Radiocarbon ages of in situ moss (n = 29) and Crash Lake sediments reveal intervals of glacier expansion at ∼1.8, 1.2 and 0.7 ka that are superimposed on an overall trend of net glacier expansion throughout the late Holocene. In situ ¹⁴C concentrations from bedrock adjacent to radiocarbon-dated moss samples further constrain the duration of ice cover through the Holocene in this region. We find that our glacier-size proxy records during the past ∼4 ka are broadly consistent with relatively lower temperatures recorded in GISP2 and occur during, or following, intervals of volcanic perturbations. Thus, we speculate that volcanic activity, although less frequent and intense than in the early Holocene and during the Little Ice Age, may have led to centennial-scale variability imprinted on net glacier expansion due to decreasing summer insolation through the late Holocene.
  • Article
    The Arctic warms faster than any other region of our planet. Besides melting glaciers, thawing permafrost and decreasing sea-ice, this amplified response affects earth surface processes. This geomorphological expression of climate change may alter landscapes and increase the frequency and magnitude of geohazards like floods or mass-movements. Beyond the short span of sparse monitoring time series, geological archives provide a valuable long-term context for future risk assessment. Lake sediment sequences are particularly promising in this respect as continuous recorders of surface process change. Over the past decade, the emergence of new techniques that characterize depositional signatures in more detail has enhanced this potential. Here, we present a well-dated Holocene-length lake sediment sequence from Ammassalik Island on southeast Greenland. This area is particularly sensitive to regional shifts in the Arctic climate system due to its location near the sea-ice limit, the Greenland Ice Sheet and the convergence of polar and Atlantic waters. The expression of Holocene change is fingerprinted using physical (grain size, organic content, density), visual (3-D Computed Tomography) and geochemical (X-Ray Fluorescence, X-Ray Diffraction) evidence. We show that three sharp transitions characterize the Holocene evolution of Ymer Lake. Between 10 and 9.5 cal. ka BP, rapid local glacier loss from the lake catchment culminated in an outburst flood. Following a quiescent Holocene climatic optimum, Neoglacial cooling, lengthening lake ice cover and shifting wind patterns prompted in-lake avalanching of sediments from 4.2 cal. ka BP onwards. Finally, glaciers reformed in the catchment around 1.2 cal. ka BP. The timing of these shifts is consistent with the regional expression of deglaciation, Neoglacial cooling and Little Ice Age-type glacier growth, respectively. The novel multi-proxy approach applied in this study rigorously links depositional sediment signatures to surface processes and thereby provides a key step towards a process-based understanding of climate responses.
  • Article
    Local glaciers and ice caps (GICs) comprise only ~5.4% of the total ice volume, but account for ~14–20% of the current ice loss in Greenland. The glacial history of GICs is not well constrained, however, and little is known about how they reacted to Holocene climate changes. Specifically, in North Greenland, there is limited knowledge about past GIC fluctuations and whether they survived the Holocene Thermal Maximum (HTM, ~8 to 5 ka). In this study, we use proglacial lake records to constrain the ice‐marginal fluctuations of three local ice caps in North Greenland including Flade Isblink, the largest ice cap in Greenland. Additionally, we have radiocarbon dated reworked marine molluscs in Little Ice Age (LIA) moraines adjacent to the Flade Isblink, which reveal when the ice cap was smaller than present. We found that outlet glaciers from Flade Isblink retreated inland of their present extent from ~9.4 to 0.2 cal. ka BP. The proglacial lake records, however, demonstrate that the lakes continued to receive glacial meltwater throughout the entire Holocene. This implies that GICs in Finderup Land survived the HTM. Our results are consistent with other observations from North Greenland but differ from locations in southern Greenland where all records show that the local ice caps at low and intermediate elevations disappeared completely during the HTM. We explain the north–south gradient in glacier response as a result of sensitivity to increased temperature and precipitation. While the increased temperatures during the HTM led to a complete melting of GICs in southern Greenland, GICs remained in North Greenland probably because the melting was counterbalanced by increased precipitation due to a reduction in Arctic sea‐ice extent and/or increased poleward moisture transport.
  • Article
    Helheim Glacier ranks among the fastest flowing and most ice discharging outlets of the Greenland Ice Sheet (GrIS). After undergoing rapid speed-up in the early 2000s, understanding its long-term mass balance and dynamic has become increasingly important. Here, we present the first record of direct Holocene ice-marginal changes of the Helheim Glacier following the initial deglaciation. By analysing cores from lakes adjacent to the present ice margin, we pinpoint periods of advance and retreat. We target threshold lakes, which receive glacial meltwater only when the margin is at an advanced position, similar to the present. We show that, during the period from 10.5 to 9.6 cal ka BP, the extent of Helheim Glacier was similar to that of todays, after which it remained retracted for most of the Holocene until a re-advance caused it to reach its present extent at c. 0.3 cal ka BP, during the Little Ice Age (LIA). Thus, Helheim Glacier's present extent is the largest since the last deglaciation, and its Holocene history shows that it is capable of recovering after several millennia of warming and retreat. Furthermore, the absence of advances beyond the present-day position during for example the 9.3 and 8.2 ka cold events as well as the early-Neoglacial suggest a substantial retreat during most of the Holocene.
  • Article
    The middle to late Holocene (8,200 years ago to present) in the Arctic is characterized by cooling temperatures and the regrowth and advance of glaciers. Whether this Neoglaciation was a threshold response to linear cooling, or was driven by a regional or Arctic-wide acceleration of cooling, is unknown. Here we examine the largest-yet-compiled multiproxy database of Arctic Holocene temperature change, along with model simulations, to investigate regional and Arctic-wide increases in cooling rate, the synchronicity of Neoglacial onset, and the observed and simulated rates of temperature change. We find little support for an Arctic-wide onset of Neoglacial cooling but do find intervals when regions experienced rapid increases in long-term cooling rate, both in the observations and in climate model simulations. In the model experiments, Neoglacial cooling is associated with indirectly forced millennial-scale variability in meridional heat transport superposed on the long-term decline of summer insolation.
  • Article
    Full-text available
    Records of Neoglacial glacier activity in the Arctic constructed from moraines are often incomplete due to a preservation bias toward the most extensive advance, often the Little Ice Age. Recent warming in the Arctic has caused extensive retreat of glaciers over the past several decades, exposing preserved landscapes complete with in situ tundra plants previously entombed by ice. The radiocarbon ages of these plants define the timing of snowline depression and glacier advance across the site, in response to local summer cooling. Erosion rapidly removes most dead plants that have been recently exposed by ice retreat, but where erosive processes are unusually weak, dead plants may remain preserved on the landscape for decades. In such settings, a transect of plant radiocarbon ages can be used to construct a nearcontinuous chronology of past ice margin advance. Here we present radiocarbon dates from the first such transect on Baffin Island, which directly dates the advance of a small ice cap over the past two millennia. The nature of ice expansion between 20 BCE and 1000 CE is still uncertain, but episodic advances at ∼1000 CE, ∼1200, and ∼1500 led to the maximum Neoglacial dimensions ∼1900 CE.We employ a two-dimensional numerical glacier model calibrated using the plant radiocarbon ages ice margin chronology to assess the sensitivity of the ice cap to temperature change. Model experiments show that at least ∼0.44 C of cooling over the past 2 kyr is required for the ice cap to reach its 1900 CE margin, and that the period from ∼1000 to 1900 CE must have been at least 0.25 C cooler than the previous millennium, results that agree with regional temperature reconstructions and climate model simulations. However, significant warming since 1900 CE is required to explain retreat to its present position, and, at the same rate of warming, the ice cap will disappear before 2100 CE.
  • Article
    The Holocene, which currently spans ~11 700 years, is the shortest series/epoch within the geological time scale (GTS), yet it contains a rich archive of evidence in stratigraphical contexts that are frequently continuous and often preserved at high levels of resolution. On 14 June 2018, the Executive Committee of the International Union of Geological Sciences formally ratified a proposal to subdivide the Holocene into three stages/ages, along with their equivalent subseries/subepochs, each anchored by a Global boundary Stratotype Section and Point (GSSP). The new stages are the Greenlandian (Lower/Early Holocene Subseries/Subepoch) with its GSSP in the Greenland NGRIP2 ice core and dated at 11 700 a b2k (before 2000 CE); the Northgrippian (Middle Holocene Subseries/Subepoch) with its GSSP in the Greenland NGRIP1 ice core and dated at 8236 a b2k; and the Meghalayan (Upper/Late Holocene Subseries/Subepoch) with its GSSP in a speleothem from Mawmluh Cave, north‐eastern India, with a date of 4250 a b2k. We explain the nomenclature of the new divisions, describe the procedures involved in the ratification process, designate auxiliary stratotypes to support the GSSPs and consider the implications of the subdivision for defining the Anthropocene as a new unit within the GTS.
  • Article
    Full-text available
    Strong similarities in Holocene climate reconstructions derived from multiple proxies (BSi, TOC – total organic carbon, δ¹³C, C∕N, MS – magnetic susceptibility, δ¹⁵N) preserved in sediments from both glacial and non-glacial lakes across Iceland indicate a relatively warm early to mid Holocene from 10 to 6ka, overprinted with cold excursions presumably related to meltwater impact on North Atlantic circulation until 7.9ka. Sediment in lakes from glacial catchments indicates their catchments were ice-free during this interval. Statistical treatment of the high-resolution multi-proxy paleoclimate lake records shows that despite great variability in catchment characteristics, the sediment records document more or less synchronous abrupt, cold departures as opposed to the smoothly decreasing trend in Northern Hemisphere summer insolation. Although all lake records document a decline in summer temperature through the Holocene consistent with the regular decline in summer insolation, the onset of significant summer cooling occurs ∼5ka at high-elevation interior sites but is variably later at sites closer to the coast, suggesting that proximity to the sea may modulate the impact from decreasing summer insolation. The timing of glacier inception during the mid Holocene is determined by the descent of the equilibrium line altitude (ELA), which is dominated by the evolution of summer temperature as summer insolation declined as well as changes in sea surface temperature for coastal glacial systems. The glacial response to the ELA decline is also highly dependent on the local topography. The initial ∼5ka nucleation of Langjökull in the highlands of Iceland defines the onset of neoglaciation in Iceland. Subsequently, a stepwise expansion of both Langjökull and northeast Vatnajökull occurred between 4.5 and 4.0ka, with a second abrupt expansion ∼3ka. Due to its coastal setting and lower topographic threshold, the initial appearance of Drangajökull in the NW of Iceland was delayed until ∼2.3ka. All lake records reflect abrupt summer temperature and catchment disturbance at ∼4.5ka, statistically indistinguishable from the global 4.2ka event, and a second widespread abrupt disturbance at 3.0ka, similar to the stepwise expansion of Langjökull and northeast Vatnajökull. Both are intervals characterized by large explosive volcanism and tephra distribution in Iceland resulting in intensified local soil erosion. The most widespread increase in glacier advance, landscape instability, and soil erosion occurred shortly after 2ka, likely due to a complex combination of increased impact from volcanic tephra deposition, cooling climate, and increased sea ice off the coast of Iceland. All lake records indicate a strong decline in temperature ∼1.5ka, which culminated during the Little Ice Age (1250–1850 CE) when the glaciers reached their maximum Holocene dimensions.
  • Article
    Full-text available
    The Arctic region is very sensitive to climate change and important in the Earth’s climate system. However, proxy datasets for Arctic climate are unevenly distributed and especially scarce for Svalbard because glaciers during the Little Ice Age, the most extensive in the Holocene, destroyed large quantities of sediment records in Svalbard. Fortunately, palaeo-notch sediments could withstand glaciers and be well-preserved after deposition. In this study, we reconstructed a mid-to-late Holocene record of climate changes in a palaeo-notch sediment sequence from London Island. Multiple weathering indices were determined, they all showed consistent weathering conditions in the study area, and they were closely linked to climate changes. Total organic carbon (TOC) and total nitrogen (TN) were also determined, and their variation profiles were similar to those of weathering indices. The climate change record in our sediment sequence is consistent with ice rafting record from North Atlantic and glacier activity from Greenland, Iceland and Svalbard, and four cold periods are clearly present. Our study provides a relatively long-term climate change record for climate conditions from mid-to-late Holocene in Svalbard.
  • Article
    Ammassalik Island is located on the elevated, passive continental margin of SE Greenland. The island itself is dominated by high ground, presumably representing part of an upwarped zone along the continental margin, separated from an adjacent narrow coastal plain. Most of the present relief must have formed during the Palaeocene and Eocene, or later during the Neogene. During the Quaternary the area was covered by the Greenland Ice Sheet, with the exception of a few nunataqs located at the junction of the elevated bedrock plateau and the escarpment. The geomorphological evolution during the Holocene has been characterised by both glacial and periglacial processes, intensifying during the late Holocene. Especially the Little Ice Age period (c. 1200-1900 AD) appears to have been a period of enhanced geomorphological activity, mainly controlled by growing glaciers and increasing activity of periglacial processes and aggrading permafrost. Following the end of the Little Ice Age, the 20th century have seen a net development towards warmer climate with retreating glaciers and presumably also in the intensity degrading of periglacial processes and of permafrost.
  • Article
    Full-text available
    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.
  • Article
    Full-text available
    Mounting evidence from proxy records suggests that variations in solar activity have played a significant role in triggering past climate changes. However, the mechanisms for sun-climate links remain a topic of debate. Here we present a high-resolution summer sea-surface temperature (SST) record covering the past 9300 yr from a site located at the present-day boundary between polar and Atlantic surface-water masses. The record is age constrained via the identification of 15 independently dated tephra markers from terrestrial archives, circumventing marine reservoir age variability problems. Our results indicate a close link between solar activity and SSTs in the northern North Atlantic during the past 4000 yr; they suggest that the climate system in this area is more susceptible to the influence of solar variations during cool periods with less vigorous ocean circulation. Furthermore, the high-resolution SST record indicates that climate in the North Atlantic regions follows solar activity variations on multidecadal to centennial time scales.
  • Article
    In southernmost Greenland near Narsarsuaq, the terminal Narsarsuaq moraine was deposited well outside of a historical Little Ice Age (LIA) moraine adjacent to the modern ice margin. Using 10Be surface exposure dating, we determine Narsarsuaq moraine abandonment at 1.51 ± 0.11 ka. A second set of 10Be ages from a more ice-proximal position shows that ice has been within or at its historical (i.e., LIA) extent since 1.34 ± 0.15 ka. Notably, Narsarsuaq moraine abandonment was coincident with climate amelioration in southern Greenland. Southern Greenland warming at ∼1.5 ka was also concurrent with the end of the Roman Warm Period as climate along the northern North Atlantic sector of Europe cooled into the Dark Ages. The warming of southern Greenland and retreat of ice from the Narsarsuaq moraine is consistent with studies suggesting possible anti-phase centennial-scale climate variability between northwestern Europe and southern Greenland. Other southernmost Greenland ice-margin records do not preclude a pre-LIA ice-margin maximum, potentially concurrent with a Narsarsuaq advance prior to ∼1.51 ka, but also lack sufficient ice-margin control to confirm such a correlation. We conclude that there is a clear need to further determine whether a late-Holocene pre-LIA maximum was a local phenomenon or a regional southern Greenland ice maximum, and if this advance and retreat reflects a regional fluctuation in climate.
  • Article
    Full-text available
    here were several centennial-scale fluctuations in the climate and oceanography of the North Atlantic region over the past 1,000 years, including a period of relative cooling from about AD 1450 to 1850 known as the Little Ice Age1. These variations may be linked to changes in solar irradiance, amplified through feedbacks including the Atlantic meridional overturning circulation2. Changes in the return limb of the Atlantic meridional overturning circulation are reflected in water properties at the base of the mixed layer south of Iceland. Here we reconstruct thermocline temperature and salinity in this region from AD 818 to 1780 using paired δ18O and Mg/Ca ratio measurements of foraminifer shells from a subdecadally resolved marine sediment core. The reconstructed centennial-scale variations in hydrography correlate with variability in total solar irradiance. We find a similar correlation in a simulation of climate over the past 1,000 years. We infer that the hydrographic changes probably reflect variability in the strength of the subpolar gyre associated with changes in atmospheric circulation. Specifically, in the simulation, low solar irradiance promotes the development of frequent and persistent atmospheric blocking events, in which a quasi-stationary high-pressure system in the eastern North Atlantic modifies the flow of the westerly winds. We conclude that this process could have contributed to the consecutive cold winters documented in Europe during the Little Ice Age.
  • Article
    Full-text available
    Climate in the Arctic region and northwestern Europe is strongly affected by the North Atlantic Oscillation (NAO), the dominant mode of atmospheric variability at mid-latitudes in the North Atlantic region. The NAO index is an indicator of atmospheric circulation and weather patterns: when the index is positive, Europe and the eastern US are mild and wet, whereas Greenland and northern Canada are cold and dry. A negative index is associated with the reverse pattern. Reconstructions of the NAO have so far been limited to the past 900 years. Here we analyse a 5,200-year-long, high-resolution lake sediment record from southwestern Greenland to reconstruct lake hypolimnic anoxia, and link the results to an existing reconstruction of the NAO index from tree rings and speleothems. Using the relationship between the two records, we find that around 4,500 and 650 years ago--around the end of the Holocene Thermal Maximum and the beginning of the Little Ice Age, respectively--the NAO changed from generally positive to variable, intermittently negative conditions. We suggest that variability in the dominant state of the NAO tend to coincide with large-scale changes in Northern Hemisphere climate. However, the onset of the Medieval Climate Anomaly was not associated with any notable changes in the NAO.