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Ice mass loss from Greenland and Antarctic ice sheets contribute approximately half of the current global sea level rise and in recent years the Greenland Ice sheet is observed to increase its mass loss rapidly. The quasi-simultaneous acceleration, thinning and retreat of the largest outlet glaciers (Jakobshavn, Helheim and Kangerdluqssuag) in the early 2000s suggested a common climate forcing and increasing air and ocean temperatures were indicated as potential triggers. We present a new record of calving activity of Helheim Glacier, East Greenland, extending back to c. 1890 AD. This record was obtained by analysing sedimentary deposits from Sermilik Fjord, where Helheim Glacier terminates, and uses the annual deposition of sand grains as a proxy for iceberg discharge. The 120 year long record reveals large fluctuations in calving rates, but that the present high rate was reproduced only in the 1930s. A comparison with climate indices indicates that high calving activity coincides with increased Atlantic Water and decreased Polar Water influence on the shelf, warm summers and a negative phase of the North Atlantic Oscillation. Our analysis provides evidence that Helheim Glacier responds to short-term (3-10 years) large-scale oceanic and atmospheric fluctuations.
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LETTERS
PUBLISHED ONLINE: 11 DECEMBER 2011 | DOI: 10.1038/NGEO1349
Rapid response of Helheim Glacier in Greenland to
climate variability over the past century
Camilla S. Andresen1*, Fiammetta Straneo2, Mads Hvid Ribergaard3, Anders A. Bjørk4,
Thorbjørn J. Andersen5, Antoon Kuijpers1, Niels Nørgaard-Pedersen1, Kurt H. Kjær4, Frands Schjøth6,
Kaarina Weckström1and Andreas P. Ahlstrøm1
During the early 2000s the Greenland Ice Sheet experienced
the largest ice-mass loss of the instrumental record1, largely
as a result of the acceleration, thinning and retreat of
large outlet glaciers in West and southeast Greenland2–5.
The quasi-simultaneous change in the glaciers suggests
a common climate forcing. Increasing air6and ocean7,8
temperatures have been indicated as potential triggers. Here,
we present a record of calving activity of Helheim Glacier,
East Greenland, that extends back to about AD 1890, based
on an analysis of sedimentary deposits from Sermilik Fjord,
where Helheim Glacier terminates. Specifically, we use the
annual deposition of sand grains as a proxy for iceberg
discharge. Our record reveals large fluctuations in calving
rates, but the present high rate was reproduced only in the
1930s. A comparison with climate indices indicates that high
calving activity coincides with a relatively strong influence of
Atlantic water and a lower influence of polar water on the
shelf off Greenland, as well as with warm summers and the
negative phase of the North Atlantic Oscillation. Our analysis
provides evidence that Helheim Glacier responds to short-term
fluctuations of large-scale oceanic and atmospheric conditions,
on timescales of 3–10 years.
The forcings behind the rapid increase in mass loss from the
Greenland Ice Sheet in the early 2000s (ref. 1) are still debated. It
is unclear whether the mass loss will continue in the near future
and, if so, at what rate. These uncertainties are a consequence of our
limited understanding of mechanisms regulating ice-sheet variabil-
ity and the response of fast-flowing outlet glaciers to climate vari-
ability. In southeast Greenland, Helheim Glacier, one of the regions
largest glaciers, thinned, accelerated and retreated during the period
2003–2005 (ref. 4) and although it has since slowed down and re-
advanced9, it has still not returned to its pre-acceleration flow rates.
It has been suggested that warming8,10 and/or inflow
variability11,12 of the nearby subsurface ocean currents triggered
the acceleration, but to establish a causal relationship between
glacier and climate variability, long-term records are needed. Here
we present three high-resolution (1–3 years per sample) sedi-
mentary records from Sermilik Fjord (Fig. 1 and Supplementary
Information) that capture the 2001–2005 episode of mass loss,
and use them to reconstruct the calving variability of Helheim
Glacier over the past 120 years. Next, this record is compared with
records of climate indices.
1Geological Survey of Denmark and Greenland, Department of Marine Geology and Glaciology, Øster Voldgade 10, 1350 Copenhagen K, Denmark,
2Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA, 3Danish Meterological
Institute, Centre for Ocean and Ice, Lyngbyvej 100, 2100 Copenhagen Ø, Denmark, 4Centre for GeoGenetics, Natural History Museum, Øster Voldgade 5-7,
1350 Copenhagen K, Denmark, 5Institute for Geology and Geography, Øster Voldgade 10, Univ. of Copenhagen, 1350 Copenhagen K, Denmark,
6Geological Survey of Denmark and Greenland, Geological Data Centre, Øster Voldgade 10, 1350 Copenhagen K, Denmark. *e-mail:csa@geus.dk.
Helheim Glacier discharges in the deep (600–900 m) Sermilik
Fjord, which is connected with two deep troughs (500–700 m) that
transect the shallow shelf (100–200 m) allowing exchange with shelf
waters. The fjord is characterized by an upper 100–150-m-thick
layer of polar water from the East Greenland Current and a deeper
layer (500 m thick) of warm (3.5–4 C) and saline Atlantic water
from the North Atlantic Current11, with the latter primarily driving
submarine melting12. At the northern end, the fjord branches into
three smaller fjords, each containing calving glaciers. Of these,
Helheim Glacier is one of the most prolific iceberg exporters
in Greenland1, whereas the two northern glaciers, Midgaard and
Fenris glaciers, are smaller and far less discharging13. The fjord is
mostly sea-ice covered from January to June and a large ice mélange
extends year-round in front of Helheim Glacier.
Three sediment cores were collected (Fig. 1) and age models
for the past 120 years were established on the basis of 210Pb
geochronology (Supplementary Fig. S2). The massive diamicton
facies in the cores is produced by delivery of heterogeneous debris
from drifting icebergs, commonly referred to as ice-rafted debris
(IRD; clay, silt, sand and pebbles), and the down-fjord diminishing
input of fine mud (clay and silt) suspended in the turbid meltwater
plume extending from the base of Helheim Glacier. This lithofacies
interpretation is in accordance with the findings from other East
Greenland fjords with marine-terminating glaciers14,15.
To reconstruct a record of calving activity of Helheim Glacier, it
is assumed that changes in IRD deposition rate are directly related to
changes in calving activity through iceberg rafting. This is supported
by a study from the nearby Kangerdlugssuaq Fjord showing that
the mean annual calving rate dominates the IRD deposition rates,
whereas the influence of temperature on melting of icebergs is far
less important16. The sand fraction is used as a proxy for IRD
because sand grains are too large (63–1,000 µm) to be carried in
suspension by the meltwater plume and thus allow differentiation
between the plume and icebergs. Accordingly, we propose that
increased sand deposition reflects increased iceberg calving from
Helheim Glacier and to a far lesser extent also from the Midgaard
and Fenris glaciers (Supplementary Information).
Iceberg residence time in the mélange is less than a year
(K. Scharrer, personal communication, 2011), implying that
variations in IRD entrainment over time do not significantly
affect the variability in sand deposition rates down-fjord over the
investigated time span (Supplementary Information).
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LETTERS NATURE GEOSCIENCE DOI: 10.1038/NGEO1349
66° 30' N
66° 00' N
65° 30' N
Helheim
Fenris
Tasiilaq
Midgaard
Bathymetry
38° 00' W 37° 00' W
ER13
ER07
ER11
¬100 m
¬200 m
¬300 m
¬400 m
¬500 m
¬600 m
¬700 m
¬800 m
¬900 m
Latitude
Longitude
Longitude
38° 00' W 37° 00' W
Figure 1 |Sermilik Fjord and Helheim Glacier with position of cores. The length of the fjord is about 90km and the width is 5–12 km. Cores ER13, ER07 and
ER11 are retrieved from 660m, 525 m and 600 m water depth, respectively. The bathymetry is a compilation of data obtained during cruises conducted in
recent years by the Geological Survey of Denmark and Greenland, Woods Hole Oceanographic Institution, Swansea University and Nansen Environmental
Remote Sensing Center (Supplementary Information). The background image is an oblique Landsat scene (L5231014_01419860911) draped over a digital
elevation model.
Sand deposition rates in the three cores vary both in magnitude
and variability (Fig. 2a–c). The mean rate decreases down-fjord,
consistent with the notion that icebergs become progressively
IRD depleted as they transit down-fjord15,17. Generally, the multi-
decadal variability is similar, but ER13, the closest to Helheim,
shows higher-frequency variability than ER07 and ER11. This
is attributed to the initial high particle fluxes in the meltwater
plume from Helheim Glacier decaying abruptly south of ER13
(ref. 12). This favours deposition of larger amounts of suspended
mud at ER13, thus diluting the IRD sand fraction and allowing
a higher time resolution when compared with ER07 and ER11
(Supplementary Fig. S4). Differences in the timing of the high-
frequency variability are attributed to factors such as wind,
fjord circulation and sea-ice cover, which affect iceberg routing16
and hence the local iceberg rafting. Thus, to obtain a mean
sand-deposition-rate time series for Sermilik Fjord, we created a
composite record by averaging the sand deposition rates of the three
cores (Fig. 2d) under the assumption that the average of the three
cores is indicative of the mean deposition rate within most of the
fjord. The validity of the composite sand deposition record as a
proxy for the calving history of Helheim Glacier is supported by its
agreement with changes in its front position according to satellite
data and historical aerial photographs (Fig. 2d).
The reconstructed 120-year-long calving record from Helheim
Glacier shows calving maxima and minima lasting 2–5 years and
often bundled into longer episodes of 5–10 years. Two pronounced
calving maxima are observed: one during the past 10 years, the
other in the late 1930s/early 1940s. The long-term calving increase
is probably due to a shift from the Little Ice Age conditions,
which were characterized by low air temperatures and strong
polar-water influence in the Denmark Strait region and ended after
ad 1900 here18.
Most of the climate-related mechanisms proposed to explain
glacier acceleration and increased calving invoke increased lo-
cal air and/or ocean temperatures. Warming summer air tem-
peratures will increase surface melt which, in turn, can affect
the glacier by increasing sliding19 (although this process is small
for Helheim Glacier20), by destabilizing the glacier’s tongue by
feeding its crevasses21, or enhance submarine melting if re-
leased at depth in the fjord22. Increased ocean temperatures will
also enhance submarine melt rates and, by changing the char-
acteristics at the terminus, influence glacier stability7,23. Both
ocean and air warming can reduce the level of sea-ice forma-
tion in the fjord and within the ice mélange in front of the
glacier, potentially increasing the calving rate by destabilizing
the glacier tongue17.
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NATURE GEOSCIENCE DOI: 10.1038/NGEO1349 LETTERS
Sand deposition rate
(g m¬2 yr¬1)
Sand deposition rate
(g m¬2 yr¬1)
Sand deposition rate
(g m¬2 yr¬1)
Glacier calving
increased
Glacier margin
retreated
Glacier margin position
(km)
Composite of ER13, ER07 and ER11
ER13
ER11
1880 1900 1920 1940 1960 1980 2000
Date
1880 1900 1920 1940 1960 1980 2000
Date
1880 1900 1920 1940 1960 1980 2000
Date
600
400
200
0
1,000
800
600
400
200
0
1,000
800
600
400
200
0
8
6
4
2
0
d
c
Sand deposition rate
(g m¬2 yr¬1)
ER07
1880 1900 1920 1940 1960 1980 2000
Date
1,000
800
600
400
200
0
b
a
Figure 2 |Sand deposition rates in the cores. a, ER11. b, ER07. c, ER13.
d, Reconstructed calving record of Helheim Glacier calculated as the
average sand (63–1,000µm) deposition rate (g m2yr1) of the three
cores (Supplementary Information). Error bars are a function of 1 sigma
error of mass accumulation rates and sand content. The chronology of ER13
in the composite record is adjusted towards a timescale two years older
(within 1 sigma error bar) during the interval 1980–2000 to improve the fit
with glacier images (Supplementary Fig. S3). The glacier margin positions
(red) are relative to the 1993 position according to aerial and satellite
images (Supplementary Fig. S5 and Supplementary Information).
Helheim Glacier’s calving record is compared with local
oceanic and atmospheric variability to determine whether a
statistically significant correlation exists between them (Fig. 3).
Ocean variability is influenced by both the surface polar water
and the subsurface Atlantic water. As there are no long-term
ocean measurements from Sermilik Fjord or the nearby shelf,
we rely on the upstream/near-source variability of the two
watermasses (Supplementary Information) and the finding that
they are continuously renewed through exchange with the shelf11.
For Atlantic water we use direct measurements of sea surface
temperature (SST) from a region south of Iceland where Atlantic
water extends to the surface (Fig. 3b). For polar-water variability,
we use changes in the northernmost multi-year sea-ice extent off
southwest Greenland (storis index24) assuming that it is correlated
with polar-water variability (Fig. 3c). Hydrographic variability
on the shelf mostly reflects changes in the relative volume of
Atlantic water and polar water; thus, the Atlantic-water and polar-
water indices were combined into a shelf index (Fig. 3d and
Supplementary Fig. S6)—a positive shelf index indicates a thicker
and warmer Atlantic water (at the expense of polar water) and vice
versa. The shelf index is validated through independent data sources
in the Supplementary Information. Air temperature variability is
taken from the observed summer temperatures near Tasiilaq25
(Fig. 3f). Finally, we examine the correlation between calving
activity and the winter time North Atlantic Oscillation (NAO)
index26, representative of the dominant mode of atmospheric
climatic variability in the North Atlantic region (Fig. 3e).
Although non-climatic factors intrinsic to Helheim Glacier (for
example, glacier bed topography and internal glacier dynamics)
are expected to influence calving activity27, our analysis indicates
that a significant fraction of the calving variability of Helheim
Glacier since ad 1890 is consistent with increased Atlantic water
(temperature and/or volume), decreased polar water, a positive
shelf index, increased summer air temperatures and a negative NAO
index as implied by significant correlations on the bulk data sets
(Table 1 and Supplementary Information).
To investigate the timescales involved, we first consider the
correlation between the 25-year low-pass filtered calving and
climate records (Supplementary Fig. S7). This shows that on
multi-decadal timescales, calving is mostly linked with synchronous
changes in the source Atlantic water and the local summer air
temperature, which, in turn, track the Atlantic Multi-decadal
Oscillation28. Given the regional oceanic and atmospheric co-
variance on these timescales, it is not possible to separate their
relative contribution to glacier variability.
On shorter-term timescales (3–10 years), we find that the
correlation of the residual calving variability and the residual
climate variability is significant only for the NAO index and
the shelf index (Table 1). The high correlation with the NAO
index is expected because local winds and air temperatures as
well as variability in both the polar-water and Atlantic-water
source regions often co-vary with the NAO (ref. 29) on these
timescales. A negative NAO phase, in particular, is associated
with a warm subpolar gyre and increased penetration of Atlantic
water on the shelf8. However, this analysis also indicates that
episodes of increased polar-water inflow, for example the Great
Salinity Anomalies between 1965 and 1972 and during the early
1980s and early 1990s (ref. 30; Fig. 3c), were associated with
diminished calving activity, probably due to stabilization of the
glacier terminus and mélange and/or reduced Atlantic-water
penetration on the shelf.
The climate characteristics found for a composite of the ten
highest short-term calving episodes (HC1–HC10 in Fig. 3a and
Supplementary Table S1) support the conclusion that the shelf
index and the phase of the NAO are significant players in
modulating short-term calving variability.
Our analysis indicates that the recent increase in calving activity
observed at Helheim Glacier is not unique but that a similarly
large event occurred in the late 1930s/early 1940s (HC6 Fig. 3a).
These two episodes occurred at times when the temperature of
the Atlantic-water source was high (positive/warm Atlantic Multi-
decadal Oscillation phase) and the polar-water export was at a
record low (even if fluctuating). The NAO index was also frequently
negative, but not markedly more than during many of the other
calving episodes. Interestingly, both episodes are characterized by
record high summer temperatures since 1895 (1939, 1941 and
2003). These conditions probably resulted in increased surface and
submarine melt that may have contributed to the marked mass loss
from Helheim Glacier.
Our study provides evidence that Helheim Glacier responds to
changes in atmosphere–ocean variability on timescales as short
as a few years. Therefore, the prediction of future ice-sheet
mass-balance changes associated with dynamic adjustments from
outlet glaciers needs to incorporate atmosphere–ocean climate
models that are capable of reproducing the regional variability on
these same timescales.
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LETTERS NATURE GEOSCIENCE DOI: 10.1038/NGEO1349
Warming of
summer air
Negative index
Increase in
Atlantic water on shelf
Decrease in
Polar water
Increase in
Atlantic water
Helheim Glacier
calving
Reconstructed calving
record
Date
10 9 8 7 6 5 4 3 2 1
5
4
3
2
1
10
9.5
9.0
8.5
8.0
7.5
GSA
GSA
GSA
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
¬2
0
2
4
4
2
0
¬2
–4
¬2
¬1
0
1
f
e
d
c
b
a
Tair Tasiilaq (°C)
Apr.¬Sep.
NAO indexShelf indexStoris index
Annual SST (°C)
south of Iceland
Figure 3 |Comparison between calving record and climate indices. a, Reconstructed calving record of Helheim Glacier. The grey line is unfiltered data.
Increased calving events (HC1–HC10) are highlighted in red (intensity of calving indicated by different shading) and correspond to the residual variability.
b, Annual mean SST for an area south of Iceland (20–30W, 60–63N; Supplementary Information). c, Storis index25. GSA, Great Salinity Anomaly.
d, Shelf index (normalized Atlantic water temperature and storis index weighted 1:1). e, NAO winter time index27.f,Tair summer (April–September) in
Tasiilaq26. For bf, black lines are 3-year running mean data and the grey line is unfiltered data.
Table 1 |Pearson correlation coefficients between calving and climate indices.
rvalue with calving Tair summer NAO index Storis index Atlantic water Tannual Shelf index
Bulk data (r0.29) 0.45 0.45 0.36 0.38 0.41
Multi-decadal variability (r0.74) 0.73 0.53 0.61 0.72 0.69
Intra-decadal variability (r0.29) 0.24 0.42 0.18 0.27 0.29
Climate data were applied with a 3-yr running mean and all data werelinearly detrended before computing rvalues (bulk data). Multi-decadal variability was highlighted by 25-yr low-pass Fourierfiltering
and intra-decadal variability was obtained as a residual after subtracting the low-pass-filtered time series from the bulk data. For bulk data and residuals rvalues 0.29 are statistically significant and for
the low pass-filtered data rvalues 0.74 are statistically significant at the 95% level. See also Supplementary Information.
Methods
Core chronologies were established by measuring the 210Pb and 137 Cs activity and
mass accumulation rates were estimated. Grain size distribution was analysed by a
Malvern Mastersizer 2000 laser particle sizer. The cumulative volume percentage
was determined for the clay and silt fraction (<63 µm) and the sand fraction
(63–1,000 µm). X-ray radiography (Supplementary Fig. S1) and grain size analysis
(Supplementary Fig. S3) of the cores reveals diamicton facies in all three cores
with a mean content of sand of 9%, 22% and 18%, in cores ER13, ER07 and
ER11, respectively, reflecting a more condensed stratigraphy of the two last cores.
Sand deposition rates (iceberg rafting) were estimated as the flux of sand grains
(g m2yr1) and the composite was produced as an average of the three cores. For
documentation of past glacier margin positions, images from satellite and aerial
photographs were geo-referenced using ortho-rectified aerial photographs from
1981 with a 2-m spatial resolution. Time series of annual mean SST for an area south
of Iceland (20–30W, 60–63N) were constructed using mainly the ICES database
(www.ices.dk) and are used as a proxy for Atlantic-water temperatures. A time series
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NATURE GEOSCIENCE DOI: 10.1038/NGEO1349 LETTERS
of maximal multi-year sea-ice extent along southwest Greenland in May, June and
July was used as a proxy for the volume of polar water. The shelf index was produced
by normalizing these proxy records and further subtracting the resultant polar-
water index from the Atlantic-water index. The Pearson correlation coefficients
between the calving record and climate indices were calculated by filtering the
data with a 3-yr running mean (except the calving record). All data were linearly
detrended and a 25-year low-pass Fourier filter was applied to differentiate between
longer- and shorter-term variability. The residuals were estimated by subtracting
the low-pass-filtered data from the 3-year filtered and linearly detrended data set. A
detailed description of the methods is given in the Supplementary Information.
Received 21 June 2011; accepted 14 November 2011;
published online 11 December 2011
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Acknowledgements
This study has been supported by Geocenter Denmark in financial support to the
SEDIMICE project. C.S.A. was supported by the Danish Council for Independent
Research |Nature and Universe (Grant no. 09-064954/FNU). F. Straneo was supported
by NSF ARC 0909373 and by WHOI’s Ocean and Climate Change Institute and M.H.R.
was supported by the Danish Agency for Science, Technology and Innovation. We thank
Y. O. Kwon for insightful discussions on the climate data analysis and K. K. Kjeldsen for
help with the digital elevation model image.
Author contributions
A.P.A., C.S.A. and A.K. conceived the study and C.S.A. and N.N-P. conducted fieldwork.
C.S.A. is mainly responsible for data interpretation and sediment core data analysis
and led the writing of the paper. F. Straneo contributed expertise on oceanography,
statistical analysis and data interpretation and M.H.R. provided the oceanographic data
compilation south of Iceland and updated the storis index from 2000 to 2008. A.A.B. and
K.H.K. are responsible for glacier image analysis. T.J.A. measured the 210Pb and 137 Cs
activities. F. Schjøth compiled bathymetry data into the map. All authors contributed to
data interpretation and writing of the manuscript.
Additional information
The authors declare no competing financial interests. Supplementary information
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... However, instrumental records from Greenland only cover the last few decades in detail, and the last century at much coarser temporal resolution. Marine sediment cores from around Greenland can be used to reconstruct long-term records of ocean conditions and outlet glacier stability beyond the instrumental time period (Andresen et al., 2012(Andresen et al., , 2013bWangner et al., 2020;Vermassen et al., 2019aVermassen et al., , 2019b and can cover thousands of years (Andresen et al., 2011(Andresen et al., , 2013bJennings et al., 2002;Ruddiman, 1977;Sheldon et al., 2016;Wangner et al., 2018). In such studies, benthic foraminifera are among the most valuable proxies for determining past ocean conditions at and near the seabed due to these organisms' high sensitivity to bottom-water temperature, salinity, food availability and turbidity (Murray, 1991). ...
... Glaciological changes can be reconstructed using the variability in iceberg-rafted debris (IRD) as a measure of iceberg production or glaciological setting (calving glacier vs ice tongue or extensive melange) based on grain size analyses in marine sediment records (Andresen et al., 2011(Andresen et al., , 2012. However, the relationship between IRD and glacier activity is complex, and an increase in IRD can potentially be caused by either a glacier advance or by a retreat event (Ekblom Johansson et al., 2020;Funder et al., 1998;McManus et al., 1999). ...
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Sediment core ER11-16 from Køge Bugt in Southeast Greenland is used to assess early Holocene palaeoceanographic changes and sediment rafting from icebergs calved from the large outlet glaciers in the area. Diatom analysis reconstructs variability in surface water temperature, salinity and sea-ice concentrations, and benthic foraminiferal assemblages is used to reconstruct subsurface ocean conditions. We report Holocene Thermal Maximum in Southeast Greenland during the early Holocene (at least since onset of the record 9100 cal yr BP) until around 4500 cal yr BP, which contrasts with a delay until the mid-Holocene of the Holocene Thermal Maximum in South and Southwest Greenland. The early Holocene warming in Southeast Greenland was caused by a combination of high solar insolation and a weakened subpolar gyre, both of which served to warm the Irminger Current waters subducting onto the shelf. At the same time, the surface temperature was relatively high and sea-ice cover in the polar surface waters of the East Greenland Current was relatively low. High levels of iceberg rafting occurred in Køge Bugt during the early Holocene, synchronously with these warm oceanic temperatures. This is attributed to an increase in iceberg production from the extensive, but retreating, Greenland Ice Sheet. The warm surface conditions were interrupted by a marked and short-lived increase in sea ice around 8200 years ago, providing the first evidence of this global cold episode in Southeast Greenland. After 4500 cal. yr BP, sea-ice cover increased with an expansion of the East Greenland Current, suppressing the inflow of warmer subsurface Irminger Current water to the Southeast Greenland shelf. We relate this oceanic shift to the decreased Northern Hemisphere summer solar insolation. Multi-centennial variability is observed in the grain size spectrum of iceberg rafted debris; a finding we interpret in the context of palaeoceanographic changes.
... Its dynamics through the early 21st century showed pronounced variability, including episodes of multi-annual retreat and readvance 3,15,20 and net mass gain while most Greenland outlet glaciers were losing mass 21 . Sediment records from the past century suggest that Helheim responds to atmospheric and oceanic variability on time scales of a few years 22 , highlighting the importance of understanding its dynamics on seasonal to multi-annual time scales. The high ice flux through Helheim Glacier 23,24 , its recent variability 15,20,25 , and its sensitivity to short-term variation in climate forcings 22,26 motivate a quantitative comparison of hypothesized controls on velocity variability. ...
... Sediment records from the past century suggest that Helheim responds to atmospheric and oceanic variability on time scales of a few years 22 , highlighting the importance of understanding its dynamics on seasonal to multi-annual time scales. The high ice flux through Helheim Glacier 23,24 , its recent variability 15,20,25 , and its sensitivity to short-term variation in climate forcings 22,26 motivate a quantitative comparison of hypothesized controls on velocity variability. ...
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The Greenland Ice Sheet discharges ice to the ocean through hundreds of outlet glaciers. Recent acceleration of Greenland outlet glaciers has been linked to both oceanic and atmospheric drivers. Here, we leverage temporally dense observations, regional climate model output, and newly developed time series analysis tools to assess the most important forcings causing ice flow variability at one of the largest Greenland outlet glaciers, Helheim Glacier, from 2009 to 2017. We find that ice speed correlates most strongly with catchment-integrated runoff at seasonal to interannual scales, while multi-annual flow variability correlates most strongly with multi-annual terminus variability. The disparate time scales and the influence of subglacial topography on Helheim Glacier’s dynamics highlight different regimes that can inform modeling and forecasting of its future. Notably, our results suggest that the recent terminus history observed at Helheim is a response to, rather than the cause of, upstream changes.
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Two major oceanographic changes have recently propagated through several trophic levels in coastal areas of Southeast Greenland (SEG). Firstly, the amount of drift-ice exported from the Fram Strait and transported with the East Greenland Current (EGC) has decreased significantly over the past two decades, and a main tipping element (summer sea ice) has virtually disappeared since 2003 leading to a regime shift in oceanographic and ecological conditions in the region. The following 20-year period with low or no coastal sea ice is unique in the 200-year history of ice observations in the region, and the regime shift is also obvious in the volume of ice export through the Fram Strait after 2013. In the same period, the temperature of the EGC south of 73.5 N has increased significantly (>2°C) since 1980. Secondly, the warm Irminger Current, which advects warm, saline Atlantic Water into the region, has become warmer since 1990. The lack of pack ice in summer together with a warming ocean generated cascading effects on the ecosystem in SEG that are manifested in a changed fish fauna with an influx of boreal species in the south and the subarctic capelin further north. At higher trophic levels there has been an increase in the abundance of several boreal cetaceans (humpback, fin, killer, and pilot whales and dolphins) that are either new to this area or occur in historically large numbers. It is estimated that the new cetacean species in SEG are responsible for an annual predation level of 700,000 tons of fish. In addition, predation on krill species is estimated at >1,500,000 tons mainly consumed by fin whales. Simultaneously, there has been a reduction in the abundance and catches of narwhals and walruses in SEG and it is suggested that these species have been impacted by the habitat changes.
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We characterize the joint Bayesian posterior distribution over spatially-varying basal traction and ice rheology of an ice sheet model from observations of surface speed using stochastic variational inference, the first application of such methods to large-scale fluid simulations subject to real-world observations. Assuming a low-rank Gaussian process posterior, we use natural gradient descent to minimize the Kullback-Leibler divergence between this assumed distribution and the true posterior. By also placing a Gaussian process prior over traction and rheology, and by casting the problem in terms of eigenfunctions of a kernel, we gain substantial control over prior assumptions on parameter smoothness and length scale, while also rendering the inference tractable. In a synthetic example, we find that this method recovers known parameters and accounts for situations of parameter indeterminacy. We also apply the method to Helheim Glacier in Southeast Greenland and show that the proposed method is computationally scalable to catchment-sized problems. We find that observations of fast flow provide substantial information gain relative to a prior distribution, however even precise observations offer little information in slow-flowing regions. The approach described here is a road-map towards robust and scalable Bayesian inference in a wide array of physics-informed problems.
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We reconstructed Holocene paleoceanography of the Sherard Osborn Fjord (SOF), N Greenland, and Lincoln Sea in the eastern Arctic Ocean using sediment properties and micropaleontology from cores obtained during the Ryder 2019 Expedition. Our aims were to better understand faunal indicators of water mass influence on Ryder Glacier and the Lincoln Sea at water depths >500 m. Benthic microfaunal reflect glacio-marine interval during late deglaciation ~10.5 to 8.5 ka (kiloannum) during the Holocene Thermal Maximum (HTM) with dominant benthic foraminiferal species Cassidulina neoteretis, Cassidulina reniforme, and the ostracode Rabilimis mirabilis. Casssidulina neoteretis is considered an indicator of Atlantic Water (AW) throughout the Arctic Ocean and Nordic Seas; C. reniforme reflects glacio-marine conditions from the retreating Ryder Glacier. Deglaciation was followed by a period of elevated productivity and diverse ostracode faunal assemblages that suggest AW influence from 8.5 to 6 ka in the Lincoln Sea and inside SOF. The Holocene occurrence of the ostracode species Acetabulastoma arcticum, that appears in low numbers in the Lincoln Sea and briefly (~ 4–3 ka) in SOF, reflects the presence of variable sea ice in this region. Based on the similarities of the Lincoln Sea and fjord ostracodes to modern and glacial-deglacial faunas from the central Arctic Ocean, the AW influence likely originates from recirculation of AW water from the central Arctic Basin. In general, our results suggest a strong but temporally varying influence of AW during the entire 10.5 kyr record of the Lincoln Sea and SOF.
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Based on sediment cores and geophysical data collected from Petermann Fjord and northern Nares Strait, NW Greenland, an Arctic ice shelf sediment facies is presented that distinguishes sub and pro ice shelf environments. Sediment cores were collected from sites beneath the present day Petermann Ice Tongue (PIT) and in deglacial sediments of northern Nares Strait with a focus on understanding the glacial and oceanographic history over the last 11,000 cal yr BP. The modern sub ice shelf sediment facies in Petermann Fjord is laminated and devoid of coarse clasts (IRD) due to strong basal melting that releases debris (debris filtering) from the basal ice at the grounding zone driven by buoyant subglacial meltwater and entrained Atlantic Water. Laminated sediments in the deep basin proximal to the gounding zone comprise layers of fine mud formed by suspension settling from turbid meltwater plumes (plumites) interrupted by normally graded very fine sand to medium silt layers with sharp basal contacts and rip-up clasts of mud, interpreted as turbidites. An inner fjord sill limits distribution of sediment gravity flows from the grounding zone to the deep inner fjord basin, such that sites on the inner sill and beyond the ice tongue largely only comprise plumites. Bioturbation and foraminiferal abundances increase with distance from the grounding zone. The benthic foraminiferal species, Elphidium clavatum is absent beneath the ice tongue, but dominant in the turbid meltwater influenced environment beyond the ice tongue. The very sparse IRD in sediments beneath the PIT and in the fjord beyond the PIT derives mainly from englacial debris in the ice tongue, side valley glaciers, rock falls from the steep fjord walls and sea ice. We use the modern ice shelf sediment facies characteristics to infer the past presence of ice shelves in northern Nares Strait using analyses of sediment cores from several cruises (OD1507, HLY03, 2001LSSL, RYDER19). On bathymetric highs, bioturbated mud with dispersed IRD overlies a 10–15 m thick, distinctly laminated silt and clay unit with rare coarse clasts and sparse foraminifera which forms a sediment drape of nearly uniform thickness. We interpret these laminated sediments to represent glaciomarine deposition by meltwater plumes emanating from ice streams that terminated in floating ice shelves. IRD layers, shifts in sediment composition (qXRD, MS and XRF) and faunal assemblage changes in the laminated unit document periods of ice-shelf instability sometimes, but not always, coupled with grounding zone retreat. Our deglacial reconstruction, including ice shelves, begins ∼10.7 cal ka BP, with confluent ice streams grounded in Hall Basin fronted by the Robeson Channel ice shelf. Ice shelf breakup and grounding zone retreat to relatively stable grounding zones at Kennedy Channel and the mouth of Petermann Fjord was accomplished by 9.4 cal ka BP when the Hall Basin ice shelf was established. This ice shelf broke up and reformed once prior to the final break up at 8.5 to 8.4 cal ka BP marking ice stream collapse, separation of Greenland and Innuitian ice sheets, and the opening of Nares Strait for Arctic-Atlantic throughflow. The Petermann ice shelf remained in Hall Basin until the Petermann Glacier retreated from the fjord mouth ∼7.1 cal ka BP. The resilience of these northern ice streams to strong early Holocene insolation and subsurface Atlantic Water advection is attributed to their northern aspect, buttressing by narrow passages, and high ice flux from the Greenland Ice Sheet (GIS).
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