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Holocene evolution of Hans Tausen Iskappe (Greenland) and implications for the palaeoclimatic evolution of the high Arctic
Abstract
In this study the Holocene evolution of Hans Tausen Iskappe (Peary Land, North Greenland) is investigated. Constraints on the ice cap evolution are combined with climatic records in a numerical ice flow e surface mass balance (SMB) model to better understand the palaeoenvironmental and climatic evolution of this region. Our simulations suggest that after disconnecting from the Greenland Ice Sheet (GrIS) the ice cap had roughly its present-day size and geometry around 9e8.5 ka BP. During the Holocene Thermal Maximum (HTM) the southern part of the ice cap is modelled to collapse, while the northern part of the ice cap survived this warmer period. The late Holocene regrowth of the ice cap to its maximum Neo-glacial extent at the end of the Little Ice Age (LIA) can be reproduced from the temperature reconstruction. The simulations suggest that over the last millennia the local precipitation may have been up to 70e80% higher than at present. By coupling the pre-industrial temperature forcing to a post-LIA warming trend, it is suggested that the warming between the end of the LIA and the period 1961 e1990 was between 1 and 2 C. In all experiments the ice flow model complexity and horizontal resolution have only a minor effect on the long-term evolution of the ice cap. We further conclude that the glacial isostatic adjustment has a significant effect on the modelled Holocene ice cap evolution. This suggests that modelling studies of millennial-scale ice cap evolution should focus on SMB and boundary conditions, rather than on complex ice dynamics.
... It is less certain if the older age from 11-GC on the outer sill (11.6-12.6 cal ka BP) (Fig. 8, (Fig. 2). The strong meltwater signal captured in the LU5 coincides with the rapid Early Holocene reduction in the height of the Greenland ice sheet (Lecavalier et al., 2017) (Fig. 9). ...
... cal ka BP. This timing for glacier advance is consistent with cooling seen in lake based temperature reconstructions around 4 cal ka BP (Lasher et al., 2017) and the oldest estimated age (3.5 to 4.0 cal ka BP) for 515 ice at the base of the southern dome of Hans Tausen ice cap, which had disappeared during the Middle Holocene (Madsen and Thorsteinsson, 2001;Landvik et al., 2001;Zekollari et al., 2017). ...
... Greenland towards the end of the middle Holocene. This is reflected in the development of more prolonged winter ice cover 520 in Bliss Lake after 5.9 cal ka BP (Olsen et al., 2012) and a period of low melt rates for the north Greenland ice sheet inferred from elevation changes at Camp Century (Lecavalier et al., 2017) (Fig. 9). Therefore the prolonged slow deposition of coarse IRD during LU3 is likely a combined effect of limited but persistent iceberg calving, the slow melt-out of englacial material from the disintegrated ice tongue, as well as continued input of sea-ice rafted material entrained during periods of shore-fast sea ice growth and decay. ...
The northern sector of the Greenland ice sheet is considered to be particularly susceptible to ice mass loss arising from increased glacier discharge in the coming decades. However, the past extent and dynamics of outlet glaciers in this region, and hence their vulnerability to climate change, are poorly documented. In the summer of 2019, the Swedish icebreaker Oden entered the previously unchartered waters of Sherard Osborn Fjord, where Ryder Glacier drains approximately 2 % of Greenland's ice sheet into the Lincoln Sea. Here we reconstruct the Holocene dynamics of Ryder Glacier and its ice tongue by combining radiocarbon dating with sedimentary facies analyses along a 45 km transect of marine sediment cores collected between the modern ice tongue margin and the mouth of the fjord. The results illustrate that Ryder Glacier retreated from a grounded position at the fjord mouth during the Early Holocene (>10.7 ± 0.4 cal ka BP) and receded more than 120 km to the end of Sherard Osborn Fjord by the Middle Holocene (6.3 ± 0.3 cal ka BP), likely becoming completely land-based. A re-advance of Ryder Glacier occurred in the Late Holocene, becoming marine-based around 3.9 ± 0.4 cal ka BP. An ice tongue, similar in extent to its current position was established in the Late Holocene (between 3.6 ± 0.4 and 2.9 ± 0.4 cal ka BP) and extended to its maximum historical position near the fjord mouth around 0.9 ± 0.3 cal ka BP. Laminated, clast-poor sediments were deposited during the entire retreat and regrowth phases, suggesting the persistence of an ice tongue that only collapsed when the glacier retreated behind a prominent topographic high at the landward end of the fjord. Sherard Osborn Fjord narrows inland, is constrained by steep-sided cliffs, contains a number of bathymetric pinning points that also shield the modern ice tongue and grounding zone from warm Atlantic waters, and has a shallowing inland sub-ice topography. These features are conducive to glacier stability and can explain the persistence of Ryder’s ice tongue while the glacier remained marine-based. However, the physiography of the fjord did not halt the dramatic retreat of Ryder Glacier under the relatively mild changes in climate forcing during the Holocene. Presently, Ryder Glacier is grounded more than 40 km seaward of its inferred position during the Middle Holocene, highlighting the potential for substantial retreat in response to ongoing climate change.
... The climatology used to force ice sheet models through time remains a primary source of uncertainty, and great strides have been made to improve our understanding of past climate history in Greenland through improved reconstructions of temperature (e.g., Kobashi et al., 2017;Lecavalier et al., 2017) and methods involving data assimilation of paleoclimate proxies with climate model output (Hakim et al., 2016;Buizert et al., 2018). Although recent experiments have investigated sensitivities to model formulation (Zekollari et al., 2017) and horizontal resolution over past climates (Zekollari et al., 2017;Seguinot et al., 2016;Golledge et al., 2012), testing the sensitivity of simulated ice retreat to the ice flow dynamics model (i.e., the level of complexity in its numerical approximations) and to model resolution, both in time and space, still remains an important area of research. ...
... The climatology used to force ice sheet models through time remains a primary source of uncertainty, and great strides have been made to improve our understanding of past climate history in Greenland through improved reconstructions of temperature (e.g., Kobashi et al., 2017;Lecavalier et al., 2017) and methods involving data assimilation of paleoclimate proxies with climate model output (Hakim et al., 2016;Buizert et al., 2018). Although recent experiments have investigated sensitivities to model formulation (Zekollari et al., 2017) and horizontal resolution over past climates (Zekollari et al., 2017;Seguinot et al., 2016;Golledge et al., 2012), testing the sensitivity of simulated ice retreat to the ice flow dynamics model (i.e., the level of complexity in its numerical approximations) and to model resolution, both in time and space, still remains an important area of research. ...
... We choose the higher-order approximation of Blatter (1995) and Pattyn (2003), hereafter referred to as BP, to solve the momentum balance equations. Although recent work has used the higher-order approximation in simulations over past time periods (Zekollari et al., 2017), this ice flow approximation is still rarely used when simulating over pale- oclimate timescales. We use this approximation, however, as our choice is based upon representing the past dynamics of the ice sheet history as best as possible even though computational time is increased over conventional paleoclimate ice sheet models using the more common shallow ice approximation (SIA; Hutter, 1983). ...
Geologic archives constraining the variability of the Greenland ice sheet (GrIS) during the Holocene provide targets for ice sheet models to test sensitivities to variations in past climate and model formulation. Even as data–model comparisons are becoming more common, many models simulating the behavior of the GrIS during the past rely on meshes with coarse horizontal resolutions (≥10 km). In this study, we explore the impact of model resolution on the simulated nature of retreat across southwestern Greenland during the Holocene. Four simulations are performed using the Ice Sheet System Model (ISSM): three that use a uniform mesh and horizontal mesh resolutions of 20, 10, and 5 km, and one that uses a nonuniform mesh with a resolution ranging from 2 to 15 km. We find that the simulated retreat can vary significantly between models with different horizontal resolutions based on how well the bed topography is resolved. In areas of low topographic relief, the horizontal resolution plays a negligible role in simulated differences in retreat, with each model instead responding similarly to retreat driven by surface mass balance (SMB). Conversely, in areas where the bed topography is complex and high in relief, such as fjords, the lower-resolution models (10 and 20 km) simulate unrealistic retreat that occurs as ice surface lowering intersects bumps in the bed topography that would otherwise be resolved as troughs using the higher-resolution grids. Our results highlight the important role that high-resolution grids play in simulating retreat in areas of complex bed topography, but also suggest that models using nonuniform grids can save computational resources through coarsening the mesh in areas of noncomplex bed topography where the SMB predominantly drives retreat. Additionally, these results emphasize that care must be taken with ice sheet models when tuning model parameters to match reconstructed margins, particularly for lower-resolution models in regions where complex bed topography is poorly resolved.
... Crystal size analyses from an ice-core drilled to the bed of the ice cap indicated that the ice is~3.5 to 4.0 ka old, suggesting that the ice cap disappeared during the Holocene Thermal Maximum (HTM; Madsen & Thorsteinsson 2001). During the Tausen Iskappe suggest that while the southern part of the ice cap disappeared completely, the northern part of the ice cap survived the HTM (Zekollari et al. 2017). On the north coast of Peary Land, a small ice cap (Sifs glacier) probably survived the HTM and expanded between~9.6 ...
... The status of the Hans Tausen Iskappe in central north Greenland is more complex. An ice-core record has been interpreted to reflect complete melting during HTM and regrowth between~4 and 3.5 ka (Madsen & Thorsteinsson 2001) while ice modelling suggests that the ice cap survived the HTM (Zekollari et al. 2017). ...
... Several studies have suggested that the temperature-driven sea-ice reduction in the Arctic Ocean during the HTM led to increased precipitation, which prevented ice retreat in North Greenland at the same pace as seen in southern Greenland (Hjort 1997;M€ oller et al. 2010;Funder et al. 2011a;Larsen et al. 2016b). Recent ice modelling furthermore demonstrates that increased precipitation most likely resulted in the survival of Hans Tausen Iskappe, despite a significantly warmer climate during the HTM (Zekollari et al. 2017). A similar pattern can be observed at Flade Isblink today where increased precipitation counterbalances the increased surface melt allowing the ice cap to persist (Rinne et al. 2011;Bolch et al. 2013). ...
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.
... Ice Cap of NE Greenland today, which partially retreated in the early Holocene and re-grew during later Holocene time, (Zekollari et al., 2017). Distal icecaps such as Hans Tausen do not impact RSL in the Petermann region (model results not shown here), suggesting a need for relatively local ice constraints and much higher resolution ice modeling to simulate the impact of ice-margin thickness changes and peripheral ice caps on local RSL changes. ...
... 11G). Regional glaciers today have a low temperature sensitivity but relatively high precipitation sensitivity (Braithwaite, 2005;Funder et al., 2011;Larsen et al., 2016Larsen et al., , 2019M€ oller et al., 2010;Rinne et al., 2011;Zekollari et al., 2017). Following the findings of a mid-Holocene increase in winter snowfall in western Greenland ( Fig. 11H; Thomas et al., 2016Thomas et al., , 2020 we speculate that increased moisture availability contributed to mid-Holocene ice cap growth near Petermann Glacier. ...
Relative Sea Levels (RSLs) derived primarily from marine bivalves near Petermann Glacier, NW Greenland, constrain past regional ice-mass changes through glacial isostatic adjustment (GIA) modeling. Oxygen isotopes measured on bivalves corrected for shell-depth habitat and document changing meltwater input. Rapid RSL fall of up to 62 m/kyr indicates ice loss at or prior to ∼9 ka. Transition to an RSL stillstand starting at ∼6 ka reflects renewed ice-mass loading followed by further mass loss over the past few millennia. GIA simulations of rapid early RSL fall suggest a low regional upper-mantle viscosity. Early loss of grounded ice tracks atmospheric warming and pre-dates the eventual collapse of Petermann Glacier's floating ice tongue near ∼7 ka, suggesting grounding zone stabilization during early phases of deglaciation. We hypothesize mid-Holocene regrowth of regional ice caps in response to cooling and increased precipitation, following loss of the floating shelf ice. Remnants of these ice caps remain present but are now melting.
... Whereas surrounding regions have previously been the focus of palaeoclimatic and palaeoglaciological analyses (e.g. Evans et al., 2009;Landvik et al., 2001;Larsen et al., 2016;Zekollari et al., 2017), KCL itself has received relatively little attention -perhaps due to logistical difficulties in reaching its interior. It is thought that the GrIS coalesced with local ice caps and extended across Peary Land at the LGM (Landvik et al., 2001), where there is clear evidence of a 5-10km ice-cap outlet glacier advance and subsequent retreat during the Younger Dryas cooling, which is thought to have been more prominent than farther south in Greenland due to the distance from the climate-modulating influence of the Atlantic Meridional Overturning Circulation (Larsen et al., 2016). ...
... Given the proximity of the cold East Greenland current, which flows southwards from the Arctic Ocean through Fram Strait, it seems likely that the Younger Dryas glacial advance will be similarly prominent in KCL. Radio-carbon dating (Landvik et al., 2001) and modelling (Zekollari et al., 2017) suggest that the Hans Tausen Iskappe (the largest and highest elevation ice cap in Peary Land) partly deglaciated by the end of the mid-Holocene (approximately 6.5-7.5 ka). This agrees broadly with the reconstructed evolution of Flade Isblink (Hjort, 1997), situated c.375km to the northeast, and therefore suggests that many of the smaller, lower elevation, ice caps in northeast Greenland, including those in KCL, probably disappeared completely during this period, but re-formed later in the Holocene. ...
Over the last few decades atmospheric warming across the Arctic has been far more rapid than elsewhere in the world, contributing to an increase in the sea-level contribution from the Greenland Ice Sheet. Given predictions of continuing atmospheric warming during the 21st century and beyond, it is crucial to understand how the ice sheet has responded to past variations in climate. Kronprins Christian Land lies in a climatically sensitive, yet sparsely studied part of northeast Greenland, in an inter-ice-stream region just north of Nioghalvfjerdsbrae. This paper presents the results of preliminary geomorphological mapping from a 2m spatial-resolution digital elevation model of a 5500km2; region around Centrumsø, as well as a report of sampling for cosmogenic exposure dating, and field observations concerning the extent and nature of palaeo-ice coverage and dynamics. Twenty-one 2kg samples were collected from carefully selected glacial erratics of various lithologies using a hammer and chisel as well as a small angle-grinder. In general, moraine ridges in the study area are relatively small (2–5m in height) and lack a prominent peak, reflecting limited sediment availability, and suggesting some post-glacial re-mobilization of sediment or deflation caused by melting of the moraines' ice cores. Striated cobbles and boulder-sized clasts were observed at up to 540m a.s.l., sub-rounded erratics (some of which were sampled) at up to 800m a.s.l. and streamlined bedrock at up to 360m a.s.l., all of which indicate sliding between the ice and the bedrock and temperate basal conditions. In addition, several proglacial spillways were noted, along with numerous terraces, commonly situated between lateral moraines and valley sides, which are probably kame terraces formed by glaciofluvial transport and deposition. The prevalence of these landforms indicates significant glaciofluvial action requiring large volumes of meltwater, suggesting this region experienced high-volume melt in short intensive summers during past ice-recession events.
... Analyses of biomarkers in sediment cores from the Lincoln Sea suggest that the period between about 11.3 and 9.7 ka BP may while simulations of Hans Tausen Iskapp showed that precipitation rates higher than modern-day values were crucial in buffering higher temperatures during the HTM and the survival of the ice cap (Zekollari et al., 2017). Greater than modern-day laminated facies that lacks evidence of bioturbation, suggests that Ryder maintained its floating tongue for a substantial period of time as the grounding line retreated away from the inner sill (O'Regan et al., 2021). ...
The Greenland Ice Sheet's negative mass balance is driven by a sensitivity to both a warming atmosphere and ocean. The fidelity of ice-sheet models in accounting for ice-ocean interaction is inherently uncertain and often constrained against recent fluctuations in the ice-sheet margin from the previous decades. The geological record can be utilised to contextualise ice-sheet mass loss and understand the drivers of changes at the marine margin across climatic shifts and previous extended warm periods, aiding our understanding of future ice-sheet behaviour. Here, we use the Ice-sheet and Sea-level System Model (ISSM) to explore the Holocene evolution of Ryder Glacier draining into Sherard Osborn Fjord, Northern Greenland. Our modelling results are constrained with terrestrial reconstructions of the paleo-ice sheet margin and an extensive marine sediment record from Sherard Osborn Fjord that details ice dynamics over the past 12.5 ka years. By employing a consistent mesh resolution of <1 km at the ice-ocean boundary, we assess the importance of atmospheric and oceanic changes to Ryder Glacier's Holocene behaviour. Our simulations show that the initial retreat of the ice margin after the Younger Dryas cold period was driven by a warming climate and the resulting fluctuations in Surface Mass Balance. Changing atmospheric conditions remain the first order control in the timing of ice retreat during the Holocene. We find ice-ocean interactions become increasingly fundamental to Ryder's retreat in the mid-Holocene; with higher than contemporary melt rates required to force grounding line retreat and capture the collapse of the ice tongue during the Holocene Thermal Maximum. Regrowth of the tongue during the neo-glacial cooling of the late Holocene is necessary to advance both the terrestrial and marine margins of the glacier. Our results stress the importance of accurately resolving the ice-ocean interface in modelling efforts over centennial and millennial time scales, in particular the role of floating ice tongues and submarine melt, and provide vital analogous for the future evolution of Ryder in a warming climate.
... The inferred re-advance into Sherard Osborn Fjord, marked by increased sediment delivery at the onset of LU2, occurred around 3.9 ± 0.4 ka cal BP. This timing for glacier advance is consistent with cooling seen in lake-based temperature reconstructions around 4 ka cal BP (Lasher et al., 2017) and the oldest estimated age (3.5 to 4.0 ka cal BP) for ice at the base of the southern dome of Hans Tausen ice cap, which had disappeared during the Middle Holocene -although northern parts of the ice cap survived (Madsen and Thorsteinsson, 2001;Landvik et al., 2001;Zekollari et al., 2017). However, it should be emphasized that the onset of deposition of LU2 at 3.9±0.4 ...
The northern sector of the Greenland Ice Sheet is considered to be particularly susceptible to ice mass loss arising from increased glacier discharge in the coming decades. However, the past extent and dynamics of outlet glaciers in this region, and hence their vulnerability to climate change, are poorly documented. In the summer of 2019, the Swedish icebreaker Oden entered the previously unchartered waters of Sherard Osborn Fjord, where Ryder Glacier drains approximately 2 % of Greenland's ice sheet into the Lincoln Sea. Here we reconstruct the Holocene dynamics of Ryder Glacier and its ice tongue by combining radiocarbon dating with sedimentary facies analyses along a 45 km transect of marine sediment cores collected between the modern ice tongue margin and the mouth of the fjord. The results illustrate that Ryder Glacier retreated from a grounded position at the fjord mouth during the Early Holocene (> 10.7±0.4 ka cal BP) and receded more than 120 km to the end of Sherard Osborn Fjord by the Middle Holocene (6.3±0.3 ka cal BP), likely becoming completely land-based. A re-advance of Ryder Glacier occurred in the Late Holocene, becoming marine-based around 3.9±0.4 ka cal BP. An ice tongue, similar in extent to its current position was established in the Late Holocene (between 3.6±0.4 and 2.9±0.4 ka cal BP) and extended to its maximum historical position near the fjord mouth around 0.9±0.3 ka cal BP. Laminated, clast-poor sediments were deposited during the entire retreat and regrowth phases, suggesting the persistence of an ice tongue that only collapsed when the glacier retreated behind a prominent topographic high at the landward end of the fjord. Sherard Osborn Fjord narrows inland, is constrained by steep-sided cliffs, contains a number of bathymetric pinning points that also shield the modern ice tongue and grounding zone from warm Atlantic waters, and has a shallowing inland sub-ice topography. These features are conducive to glacier stability and can explain the persistence of Ryder's ice tongue while the glacier remained marine-based. However, the physiography of the fjord did not halt the dramatic retreat of Ryder Glacier under the relatively mild changes in climate forcing during the Holocene. Presently, Ryder Glacier is grounded more than 40 km seaward of its inferred position during the Middle Holocene, highlighting the potential for substantial retreat in response to ongoing climate change.
... Soil erosion is a process affected by precipitation, vegetation, soil characteristics, topography, and human activities and is widely recognized as a response to climate variability and human activities (Dotterweich, 2013;Nearing et al., 2017). Environmental factors, such as climate and vegetation, and human activities, have had different regimes during the Holocene in climatically and topographically diverse regions of the world (Jenny et al., 2019;Zekollari et al., 2017). Multi-proxy (sedimentological, palynological, and geochemical) analyses have been widely employed in previous research to decode soil erosion processes response to past environmental changes (Bajard et al., 2017a;Barreiro-Lostres et al., 2017;Francke et al., 2019;Giguet-Covex et al., 2011). ...
Quantifying the relative influences of anthropogenic activities and climate change on soil erosion and deposition during the Holocene, when both forces have been interacting is a complex problem. Analysis of long-term patterns in soil erosion and lake deposition in a basin can provide the basis for untangling the complexities of climate and anthropogenic forcings. In this paper, sedimentary sequences from Xingyun Lake are compared with simulated soil erosion rates in the basin to explore the relationship between river basin soil erosion and lake deposition during the Holocene in Yunnan, China. Modern soil erosion rates are calculated using RUSLE, while Holocene soil erosion rates are estimated using modern rates with reconstructed precipitation and vegetation cover sequences. Through this investigation, we found the following results. First, Holocene vegetation in the lake basin was mainly affected by climate change, and the vegetation experienced the same pattern of changes as the climate. Soil erosion and lake deposition rates, along with changes to vegetation cover, were synchronous with precipitation trends during the Holocene. Second, soil erosion and lake deposition have been exacerbated by human activities, such as deforestation and land reclamation in the Xingyun Lake basin. Finally, this study provides new insights into the effects by anthropogenic impacts and climate forcing on the processes of soil erosion and lake deposition on the millennium scale.
... Presently the ice margin is close to its LIA maximum . Information about local glaciers and ice caps is very sparse but it has been determined that the two largest ice caps in the area -Flade Isblink and Hans Tausen Iskappewere smaller than at present, but did not completely melt away during the Holocene Thermal Maximum (HTM; Zekollari et al. 2017;Larsen et al. 2019). During the LIA, local glaciers and ice caps generally re-advanced to their Late Holocene maximum position (Weidick 2001;Larsen et al. 2019). ...
Knowledge about the deglaciation history of the Greenland Ice Sheet (GrIS) is important to put the recent observations of ice loss into a longer‐term perspective. In southern Greenland, the deglaciation history is generally well constrained. In this study, we use 43 new ¹⁰Be surface exposure ages combined with existing minimum‐limiting ¹⁴C ages to constrain the deglaciation history of eastern North Greenland, including the three major fjord systems – Independence Fjord, Hagen Fjord and Danmark Fjord. The ¹⁰Be ages are generally scattered and many of the samples are significantly older than expected, with pre‐LGM ages being a result of inheritance from previous exposures. By using a Bayesian statistical approach to combine the new ¹⁰Be ages and existing ¹⁴C ages, we are able to constrain the deglaciation history. We find that the outer coast and deep fjords were rapidly deglaciated between ̃11 and 10 ka. Subsequently, the deglaciation progressed far inland up the fjords, probably as a result of increased summer surface temperatures and subsurface ocean temperatures during the Holocene Thermal Maximum. The rapid retreat of the Middle Holocene slowed when the ice sheet became land‐based in the central and southern part of the study area where the ice margin first reached its present extent by ̃6.7 ka. As the onset of Neoglacial ice advance had already commenced at ̃5 ka this limits the period when the ice margin could retreat farther inland and it probably remained within max. 30–40 km of its present extent. The contrasting behaviour between the fjords and inter‐fjord areas shows a clear topographic effect on the stability of the GrIS. These results inform how the GrIS may respond to a warmer climate in various topographic settings and may provide useful constraints for future ice‐sheet models.
... Inferences from melt layers at Agassiz ice cap indicate that summer temperatures during the~11-10 ka peak of the HTM were 2e2.5 C warmer than modern and a (loosely constraining) minimum of 3.5e4 C warmer than the coldest millennium of the late Holocene. Zekollari et al. (2017) argued that geologic data and ice cap modeling from Hans Tausen Ice Cap in Peary Land (~850 km northeast of Deltasø) support extrapolating that large amplitude of warming over a broader region of northern Greenland. Paleotemperature reconstructions from three northwest Greenland lakes (Deltasø, Secret Lake and Wax Lips Lake) now further support Lecavalier et al.'s (2017) reinterpretation of data from Agassiz ice cap. ...
Arctic temperature shifts drive changes in carbon cycling, sea ice extent and Greenland Ice Sheet mass balance, all of which have global ramifications. Paleoclimate data from past warm periods provide a unique means for assessing the sensitivity of these systems to warming climate, but the magnitude and timing of past temperature changes in many parts of the Arctic are poorly known. Here we assess orbital-scale Holocene temperature change in northwest Greenland near the margin of the ice sheet using subfossil insect assemblages from lake Deltasø. Based upon sedimentation history in this currently proglacial lake, we also place constraints on Holocene extents of the adjacent North Ice Cap, a large independent ice cap. Reconstructed summer temperatures were warmer than present at the onset of lacustrine sedimentation following regional deglaciation by the Greenland Ice Sheet, sometime between 10.8 and 10.1 ka BP. Deltasø experienced the warmest summer temperatures of the Holocene between ∼10 and 6.2 ka BP, followed by progressive cooling that continued through the late Holocene as summer insolation declined, culminating in the lowest temperatures during the pre-industrial last millennium. Deltasø chironomids indicate peak early Holocene summer temperatures at least 2.5–3 °C warmer than modern and at least 3.5–4 °C warmer than the pre-industrial last millennium. We infer based upon lake sediment organic and biogenic content that in response to declining temperatures, North Ice Cap reached its present-day size ∼1850 AD, having been smaller than present through most of the preceding Holocene. Our synthesis of paleoclimate evidence from northwest Greenland, Ellesmere Island and northern Baffin Bay supports the timing of temperature trends inferred at Deltasø, and suggests that quantitative temperature reconstructions from Deltasø may represent a minimum bound on regional early Holocene warming. Collectively, records from the region indicate >4 °C summer cooling through the Holocene. Intense early Holocene warmth around northwest Greenland argues against delayed onset of warmer-than-present conditions due to the influence of the nearby waning Laurentide Ice Sheet, and has implications for understanding the Greenland Ice Sheet's sensitivity to climate change.
... Today, 3-D ice flow models constitute the most comprehensive method to determine the flow of an ice body (e.g. Huybrechts et al., 2007;Goelzer et al., 2012;Pattyn et al., 2017;Zekollari et al., 2017b). However, the use of a 3-D ice flow model is not justified here, as various boundary conditions have large uncertainties. ...
... Today, 3-D ice flow models constitute the most comprehensive method to determine the flow of an ice body (e.g. Huybrechts et al., 2007;Goelzer et al., 2012;Pattyn et al., 2017;Zekollari et al., 2017b). However, the use of a 3-D ice flow model is not justified here, as various boundary conditions have large uncertainties. ...
Antarctic blue ice zones, the most productive locations for meteorite recovery on Earth, contain old ice that is easily accessible and available in large quantities. However, the mechanisms behind these meteorite traps remain a topic of ongoing debate. Here, we propose an interdisciplinary approach to improve our understanding of a meteorite trap in Dronning Maud Land (East Antarctica) on the Nansen blue ice field meteorite trap (2600–3100 m above sea level), where more than half of the Asuka meteorites have been collected. Based on 185 surface blue ice samples, one of the largest observed spatial patterns in oxygen isotopic variation to date is found. Relying on meteorites for which the terrestrial ages are determined using ¹⁴C and ³⁶Cl, this surface ice is interpreted to date from the Last Interglacial up to the present-day. By combining state-of-the-art satellite derived surface velocities, surface mass balance modelling and ice flow modelling, we estimate that about 75–85% of the meteorites found on the ice field were supplied by ice flow after entering the ice sheet in an accumulation area of a few hundred square kilometres located south (upstream) of the ice field. Less than 0.4 new meteorites per year are supplied to the ice field through ice flow, suggesting that the hundreds of meteorites found 25 years after the first visit to this ice field mostly represent meteorites that were previously not found, rather than newly supplied meteorites. By combining these findings, the infall rate of meteorites from space is estimated, which is in line with values from the literature, but situated at the higher end of the range. A comparison of the oxygen isotopic variation of the surface blue ice to that of the European Project for Ice Coring in Antarctica (EPICA), Dronning Maud Land (EDML) ice core (located 750 km to the west, at the same elevation), suggests that the regional changes in topography have been relatively limited since the Last Interglacial, supporting theories of an overall stable East Antarctic Ice Sheet (EAIS) over this time period.
... TopoZeko is based on MATLAB scripts that have been used to visualize the Morteratsch glacier (Switzerland) and the Hans Tausen ice cap (Greenland) in earlier modeling studies [12][13][14][15]. These scripts were extended, generalized and transformed into a single MATLAB function in order to be applicable for different settings and purposes. ...
TopoZeko is a MATLAB function for plotting a variety of natural environments with a pronounced
topography, such as glaciers, volcanoes and lakes in mountainous regions. This function extends existing
MATLAB plotting routines and allows for high-quality 3-D landscape visualization, with a single color
defining a featured surface type or with a color scale defining the magnitude of a variable. As an input,
only the elevation of the subsurface (typically the bedrock) and the surface are needed, which can be
complemented by various input parameters. Several visualization examples are provided alongside with
animations, which can directly be generated in the code. Additionally a simple function to calculate the
position of the sun is introduced, which can be used to visualize the daily insolation/shadow cycle over a
landscape.
Glaciers in the Tien Shan are vital for freshwater supply, emphasising the importance of modelling their future evolution. While detailed 3D models are suitable for well-studied glaciers, regional and global assessments rely on simplified approaches. However, their accuracy remains understudied. Here, we compare the evolution of six glaciers in the Tien Shan using (i) a 3D higher-order ice flow model and (ii) a global glacier model (GloGEMflow). Additionally, we explore the impact of using in-situ measurements of mass balance and ice thickness, as opposed to relying on globally available data. Our findings reveal that the choice of mass balance model complexity and calibration has a minimal impact on aggregated volume projections, with less than 3 % variation by 2050 and less than 1 % thereafter. The use of a detailed versus a simplified ice flow model results in some noticeable discrepancies in the first half of the century, with an 8 % variation in aggregated volume change by 2050. These disparities primarily stem from calibration, while the glacier evolution pattern remains consistent, showing good agreement between the detailed and simplified model. In general, our results demonstrate that the initial ice thickness estimation has the largest effect on the future remaining ice volume, potentially resulting in 2 to 3, and even up to 4 times, more ice mass remaining. Our findings thus suggest that when modelling small to medium-sized glaciers the emphasis should be on having a reliable reconstruction of the glacier geometry rather than focusing on a detailed representation of ice flow and mass balance processes.
Glaciers play a crucial role in the Earth System: they are important water suppliers to lower‐lying areas during hot and dry periods, and they are major contributors to the observed present‐day sea‐level rise. Glaciers can also act as a source of natural hazards and have a major touristic value. Given their societal importance, there is large scientific interest in better understanding and accurately simulating the temporal evolution of glaciers, both in the past and in the future. Here, we give an overview of the state of the art of simulating the evolution of individual glaciers over decadal to centennial time scales with ice‐dynamical models. We hereby highlight recent advances in the field and emphasize how these go hand‐in‐hand with an increasing availability of on‐site and remotely sensed observations. We also focus on the gap between simplified studies that use parameterizations, typically used for regional and global projections, and detailed assessments for individual glaciers, and explain how recent advances now allow including ice dynamics when modeling glaciers at larger spatial scales. Finally, we provide concrete recommendations concerning the steps and factors to be considered when modeling the evolution of glaciers. We suggest paying particular attention to the model initialization, analyzing how related uncertainties in model input influence the modeled glacier evolution and strongly recommend evaluating the simulated glacier evolution against independent data.
Geophysical Research Abstracts Vol. 18, EGU2016-3062, 2016
In this study the dynamics and sensitivity of Hans Tausen Iskappe (western Peary Land, Greenland) to climatic forcing is investigated with a coupled ice flow–mass balance model. The surface mass balance (SMB) is calculated from a precipitation field obtained from the Regional Atmospheric Climate Model (RACMO2.3), while runoff is calculated from a positive-degree-day runoff–retention model. For the ice flow a 3-D higher-order thermomechanical model is used, which is run at a 250 m resolution. A higher-order solution is needed to accurately represent the ice flow in the outlet glaciers. Under 1961–1990 climatic conditions a steady-state ice cap is obtained that is overall similar in geometry to the present-day ice cap. Ice thickness, temperature and flow velocity in the interior agree well with observations. For the outlet glaciers a reasonable agreement with temperature and ice thickness measurements can be obtained with an additional heat source related to infiltrating meltwater. The simulations indicate that the SMB–elevation feedback has a major effect on the ice cap response time and stability. This causes the southern part of the ice cap to be extremely sensitive to a change in climatic conditions and leads to thresholds in the ice cap evolution. Under constant 2005–2014 climatic conditions the entire southern part of the ice cap cannot be sustained, and the ice cap loses about 80 % of its present-day volume. The projected loss of surrounding permanent sea ice and resultant precipitation increase may attenuate the future mass loss but will be insufficient to preserve the present-day ice cap for most scenarios. In a warmer and wetter climate the ice margin will retreat, while the interior is projected to thicken, leading to a steeper ice cap, in line with the present-day observed trends. For intermediate- (+4 ∘C) and high- warming scenarios (+8 ∘C) the ice cap is projected to disappear around AD 2400 and 2200 respectively, almost independent of the projected precipitation regime and the simulated present-day geometry.
In this study the dynamics and sensitivity to climatic forcing of Hans Tausen Iskappe (western Peary Land, Greenland) are investigated with a coupled ice flow – mass balance model. The surface mass balance is calculated from a Positive Degree-Day runoff/retention model, for which the input parameters are derived from field observations. The precipitation field is obtained from the Regional Climate Model RACMO2.3. For the ice flow a 3-D higher-order thermo-mechanical model is used, which is run at a 250 m resolution. A higher-order solution is needed to accurately represent the ice flow in the outlet glaciers. Compared to the Shallow-Ice Approximation this modifies the steady state ice cap volume by 6-8% and the area by 2-4%. Under 1961-1990 climatic conditions a steady state ice cap is obtained that is overall similar in geometry to the present-day ice cap. Ice thickness, temperature and flow velocity in the interior agree well with observations. For the outlet glaciers a reasonable agreement with temperature and ice thickness measurements can be obtained with an additional heat source related to infiltrating meltwater. The simulations indicate that the SMB-elevation feedback has a major effect on the ice cap response time and stability. This causes the southern part of the ice cap to be extremely sensitive to a change in climatic conditions and leads to thresholds in the ice cap evolution. Under constant 2005-2014 climatic conditions the entire southern part of the ice cap cannot be sustained and the ice cap loses about 80% of its present-day volume. The projected loss of surrounding permanent sea-ice and corresponding precipitation increase may attenuate the future mass loss, but will be insufficient to preserve the present-day ice cap for most scenarios. In a warmer and wetter climate the ice margin will retreat while the interior is projected to grow, leading to a steeper ice cap, in line with the present-day observed trends. For intermediate (+4°C) and high warming scenarios (+8°C) the ice cap is projected to disappear respectively around 2400 and 2200 A.D., almost irrespective of the projected precipitation regime and the simulated present-day geometry.
As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ∼ 130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate–ice sheet interactions are modelled in a consistent framework.
Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet–climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.
This study presents a data set of daily, 1 km resolution
Greenland ice sheet (GrIS) surface mass balance (SMB) covering the period
1958–2015. Applying corrections for elevation, bare ice albedo and
accumulation bias, the high-resolution product is statistically downscaled
from the native daily output of the polar regional climate model RACMO2.3 at
11 km. The data set includes all individual SMB components projected
to a down-sampled version of the Greenland Ice Mapping Project (GIMP) digital
elevation model and ice mask. The 1 km mask better resolves narrow ablation
zones, valley glaciers, fjords and disconnected ice caps. Relative to the
11 km product, the more detailed representation of isolated glaciated areas
leads to increased precipitation over the southeastern GrIS. In addition, the
downscaled product shows a significant increase in runoff owing to better
resolved low-lying marginal glaciated regions. The combined corrections for
elevation and bare ice albedo markedly improve model agreement with a newly
compiled data set of ablation measurements.
The surface temperature of the Greenland ice sheet is among the most important climate variables for assessing how climate change may impact human societies due to its association with sea level rise. However, the causes of multidecadal-to-centennial temperature changes in Greenland temperatures are not well understood, largely owing to short observational records. To examine these, we calculated the Greenland temperature anomalies (GTA[G-NH]) over the past 800 yr by subtracting the standardized northern hemispheric (NH) temperature from the standardized Greenland temperature. This decomposes the Greenland temperature variation into background climate (NH); polar amplification; and regional variability (GTA[G-NH]). The central Greenland polar amplification factor as expressed by the variance ratio Greenland/NH is 2.6 over the past 161 yr, and 3.3–4.2 over the past 800 yr. The GTA[G-NH] explains 31–35% of the variation of Greenland temperature in the multidecadal-to-centennial time scale over the past 800 yr. We found that the GTA[G-NH] has been influenced by solar-induced changes in atmospheric circulation patterns such as those produced by the North Atlantic Oscillation/Arctic Oscillation (NAO/AO). Climate modeling and proxy temperature records indicate that the anomaly is also likely linked to solar-paced changes in the Atlantic meridional overturning circulation (AMOC) and associated changes in northward oceanic heat transport.
We present a finite difference implementation of a three-dimensional higher-order ice sheet model. In comparison to a conventional centred difference discretisation it enhances both numerical stability and convergence. In order to achieve these benefits the discretisation of the governing force balance equation makes extensive use of information on staggered grid points. Using the same iterative solver, a centred difference discretisation that operates exclusively on the regular grid serves as a reference. The reprise of the ISMIP-HOM experiments indicates that both discretisations are capable of reproducing the higher-order model inter-comparison results. This setup allows a direct comparison of the two numerical implementations also with respect to their convergence behaviour. First and foremost, the new finite difference scheme facilitates convergence by a factor of up to 7 and 2.6 in average. In addition to this decrease in computational costs, the accuracy for the resultant velocity field can be chosen higher in the novel finite difference implementation. Changing the discretisation also prevents build-up of local field irregularites that occasionally cause divergence of the solution for the reference discretisation.
The improved behaviour makes the new discretisation more reliable for extensive application to real ice geometries. Higher accuracy and robust numerics are crucial in time dependent applications since numerical oscillations in the velocity field of subsequent time steps are attenuated and divergence of the solution is prevented.
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.
This review provides updated estimates of the glacial isostatic adjustment (GIA) component of present-day uplift at a suite of Global Navigation Satellite System (GNSS) sites in Greenland using the most recently published global ice sheet deglaciation histories. For some areas of Greenland (e.g. the north-west and north-east), the use of GNSS to estimate elastic uplift rates resulting from contemporary mass balance changes is more affected by the choice of GIA correction applied compared to other regions (e.g. central-west). The contribution of GIA to GRACE estimates of mass imbalance is becoming increasingly insignificant for large areas of Greenland as it enters a period of extreme warmth, and in total represents <5 % contribution (−6 to +10 Gt/year) to the observed Greenland-wide mass trends over the last decade. However, differences between deglacial histories and uncertainties in their assumed viscoelastic Earth structure combine to result in significantly different region-by-region estimates of GIA.
As the most recent warm period in Earth’s history with a sea-level stand higher than present, the Last Interglacial period (~130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully-coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere and the Greenland and Antarctic ice sheets. In this set-up, sea-level evolution and climate-ice sheet interactions are modelled in a consistent framework.
Surface mass balance changes are the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet-climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea-level and reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show multi millennial time scale variations as indicated by some reconstructions.
This paper summarizes current knowledge about the postglacial history of the vegetation of the Canadian Arctic Archipelago (CAA) and Greenland. Available pollen data were used to understand the initial migration of taxa across the Arctic, how the plant biodiversity responded to Holocene climate variability, and how past climate variability affected primary production of the vegetation. Current evidence suggests that most of the flora arrived in the area during the Holocene from Europe or refugia south or west of the region immediately after local deglaciation, indicating rapid dispersal of propagules to the region from distant sources. There is some evidence of shrub species arriving later in Greenland, but it is not clear if this is dispersal limited or a response to past climates. Subsequent climate variability had little effect on biodiversity across the CAA, with some evidence of local extinctions in areas of Greenland in the late Holocene. The most significant impact of climate changes is on vegetation density and/or plant production.
The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis
of decadally resolved proxy temperature records from poleward of 60°N covering the past 2000 years, which indicates that a
pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient
climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation
as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven
reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades
of our 2000-year-long reconstruction occurring between 1950 and 2000.
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 expansions 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.
A two-dimensional surface mass-balance model is coupled to a three-dimensional higher-order ice flow model to assess the imbalance between climate and glacier geometry for the Morteratsch (Engadine, Switzerland) glacier complex. The climate–geometry imbalance has never been larger than at present, indicating that the temperature increase is faster than the geometry is able to adapt to. We derive response times from transient and steady-state geometries and find that the volume response time is correlated to the magnitude of the mass-balance forcing. It varies between 22 and 43 years, while the length response time is between 47 and 55 years. Subsequently, the modelled response times are compared with different analytical methods from the literature. The effect of a climatic perturbation on the response time, which produces a spatially distributed mass-balance forcing, is also examined. We investigate the effect of glacier size on the response time and project that the response time will decrease in the future due to a surface steepening. Finally, volume–area scaling methods with different parameters are tested and an alternative method is proposed that takes into account the surface slope. The effect of a transient state on the method is also evaluated.
We use a 3-D higher-order glacier flow model for Vadret da Morteratsch, Engadin, Switzerland, to simulate its strong retreat since the end of the Little Ice Age (LIA) and to project its future disintegration under a warming climate. The flow model, coupled to a 2-D energy-balance model,
is initialized with the known maximum glacier extent during the LIA and subsequently forced with mean monthly precipitation and temperature records. To correctly reproduce the observed retreat of the glacier front for the period 1864–2010, additional mass-balance perturbations are required
to account for uncertainties in the initial state, the mass-balance model and climate variations not captured by the ambient meteorological records. Changes in glacier volume and area are in good agreement with additional information from historical topographic maps. Under constant 2001–10
climate conditions, a strong retreat and mass loss continue and Vadret da Morteratsch disconnects from its main tributary, Vadret Pers, before 2020. The future glacier evolution is analysed in detail to understand the timing and rate of retreat, and to assess the role of ice dynamics. Assuming
a linearly increasing warming of >3°C by 2100, only isolated and largely stagnant ice patches remain at high elevation.
The areal extent, concentration and thickness of sea ice in the Arctic Ocean and
adjacent seas have strongly decreased during the recent decades, but cold, snow-rich
winters have been common over mid-latitude land areas since 2005. A review is presented
on studies addressing the local and remote effects of the sea ice decline on weather and
climate. It is evident that the reduction in sea ice cover has increased the heat flux from the
ocean to atmosphere in autumn and early winter. This has locally increased air temperature,
moisture, and cloud cover and reduced the static stability in the lower troposphere.
Several studies based on observations, atmospheric reanalyses, and model experiments
suggest that the sea ice decline, together with increased snow cover in Eurasia, favours
circulation patterns resembling the negative phase of the North Atlantic Oscillation and
Arctic Oscillation. The suggested large-scale pressure patterns include a high over Eurasia,
which favours cold winters in Europe and northeastern Eurasia. A high over the western
and a low over the eastern North America have also been suggested, favouring advection of
Arctic air masses to North America. Mid-latitude winter weather is, however, affected by
several other factors, which generate a large inter-annual variability and often mask the
effects of sea ice decline. In addition, the small sample of years with a large sea ice loss
makes it difficult to distinguish the effects directly attributable to sea ice conditions.
Several studies suggest that, with advancing global warming, cold winters in mid-latitude
continents will no longer be common during the second half of the twenty-first century.
Recent studies have also suggested causal links between the sea ice decline and summer
precipitation in Europe, the Mediterranean, and East Asia.
Although recent ecological changes are widespread in Arctic lakes, it remains unclear whether they are more strongly associated with climate warming or the deposition of reactive nitrogen (Nr) from anthropogenic sources. We developed a 3500-yr paleolimnological record from the world's northernmost lake to explore this question. Microfossils indicate that siliceous diatoms and chrysophytes were abundant initially, but disappeared 2400 yr ago in concert with Neoglacial cooling. Microfossils reappear in 20th-century sediments and reach unprecedented concentrations in sediments deposited after ca. A.D. 1980, tracking increasing summer temperatures in the absence of evidence for atmospheric nutrient subsidies. These results indicate that current warming in northern Greenland is unprecedented in the context of the past 2400 yr, and that climate change alone is responsible for the marked biological changes observed.
We use a three-dimensional thermo-mechanically coupled model of the
Greenland ice sheet to assess the effects of marginal perturbations on
volume changes on centennial timescales. The model is designed to allow
for five ice dynamic formulations using different approximations to the
force balance. The standard model is based on the shallow ice
approximation for both ice deformation and basal sliding. A second model
version relies on a higher-order Blatter/Pattyn type of core that
resolves effects from gradients in longitudinal stresses and transverse
horizontal shearing, i.e. membrane-like stresses. Together with three
intermediate model versions, these five versions allow for gradually
more dynamic feedbacks from membrane stresses. Idealised experiments are
conducted on various resolutions to compare the time-dependent response
to imposed accelerations at the marine ice front. If such marginal
accelerations are to have an appreciable effect on total mass loss on a
century timescale, a fast mechanism to transmit such perturbations
inland is required. While the forcing is independent of the model
version, inclusion of direct horizontal coupling allows the initial
speed-up to reach several tens of kilometres inland. Within one century,
effects from gradients in membrane stress alter the inland signal
propagation and transmit additional dynamic thinning to the ice sheet
interior. But the centennial overall volume loss differs only by some
percents from the standard model, as the dominant response is a
diffusive inland propagation of geometric changes. For the experiments
considered, this volume response is even attenuated by direct horizontal
coupling. The reason is a faster adjustment of the sliding regime by
instant stress transmission in models that account for the effect of
membrane stresses. Ultimately, horizontal coupling decreases the
reaction time to perturbations at the ice sheet margin. These findings
suggest that for modelling the mass evolution of a large-scale ice
sheet, effects from diffusive geometric adjustments dominate effects
from successively more complete dynamic approaches.
In the field seasons from 1993 to 1995 several data set describing glacier surface and thickness have been collected at the Hans Tausen Ice Cap in Peary Land, North Greenland. This is the description of how this geophysical data have been used in order to produce digital elevation models for both the surface and the bedrock topography of the area. The two models are consequently used to construct a digital ice thickness model of the Hans Tausen Ice Cap. Based on this model, calculated estimates for both the surface area and the total glacier volume are computed.
The paper presents studies of various chemical and isotopical parameters from ice cores drilled in the northernmost located ice cap, Hans Tausen Iskappe, Pearyland, Greenland (HT). The 346 m main ice core (MC95) was drilled to bedrock in 1995 as well as a 35 m shallow core (SC95). A 60 m shallow core (SC75) and a 51 m shallow core (SC76) was drilled at two different positions in1975 and 1976, respectively. A 60 m shallow core (SC94) was drilled in 1994. Continuous stable isotope records exist for all of these cores, total β-activity only from SC75 and SC76. Continuous ECM inferred acidity records exist along the 1995 cores (MC95 and SC95) and finally detailed records of dust and water soluble ion concentrations exist on selected parts of MC95. To determine a time scale for the ice core is an important prerequisite for the interpretation of other records. The age scale is based on acid layers, caused by known volcanic eruptions, and by comparison of the chemical composition of these layers to that found in ice cores from other arctic locations. The total β-activity data from SC75 and SC76 provide fixed points to the time scale because a pronounced increase in total β-activity is related to the thermo-nuclear tests in the atmosphere in the early 1960'ies. Many of the investigated parameters exhibit seasonal variations e.g. δ18O, acidity, Cl– and dust, therefore the study of the accumulation history of the ice cap improves our knowledge of the question if the mass balance of the Hans Tausen Iskappe is in equilibrium or not. In the upper half part of the ice core the MC95 ECM record reveals several events of high acidity which can be connected to volcanic events known from other Greenland ice core records. Among the identified volcanic events are AD 1912 (Katmai, Alaska), AD 1815 (Tambora, Indonesia), AD 1783 (Laki, Iceland), AD 934 (Eldgjà, Iceland) and e.g. the signals of AD 1259 and 49 BC. The two latter signals originate from major volcanic eruptions of unknown eruption sites with a probable location close to the Equator in the case of the AD 1259 event. Some of the volcanic events are selected for an analysis of dust and water soluble chemical components, including F–, CH3SO2–, Cl–, NO3–, SO42–, Na+,NH4+, K+, Mg2+ and Ca2+. Coulter counter technique was used for the dust measurements and the chemical analysis were carried out by ion chromatography.
The 345 m long ice core retrieved from the Hans Tausen Ice Cap in 1995 (82,5°N, 38°W) in Western Peary Land was sampled in situ for later paleoclimatic δ18Omeasurements in Copenhagen. The upper 125 m covers a little more than 1000 years and indicates strong persistent warming from the late 1920-ties, a maximum warming in the early 1960-ties and a variable climate with no particular trend since the 1960-ties. The δ record over the past 100 years shows similarities with the temperature records from the Greenland west coast stations, Iceland, and the Faroe Islands. The 20th century is the warmest in the entire record, while the periode 1700-1900 A.D. is the coldest during the past 2000 years. A maximum of warm climate seems to be reached around 900-1100 A.D. which then declines to the colder conditions around 1700 A.D. The climatic interpretation of the deepest 105 m of the δ record is more complicated due to the non-steady state of the ice cap: The implication for the paleoclimatic interpretation will be discussed. No glacial ice is present in the bottom ice.
A mass balance model based on a positive degree-day approach is used to model the mass balance-elevation relationship for Hans Tausen Iskappe (82.5°N, 37.5°W). Model parameters are estimated by means of field data from a glacier basin in the north-east corner of the ice cap. The mass balance model is run for the total Hans Tausen Iskappe by using additional information on the snow fall distribution based on accumulation data from three local ice cores. The model indicates that, in the period 1975-1995, the total balance of Hans Tausen Iskappe was negative (–0.14 m/y of ice equivalent averaged over the icecap, corresponding to –104% of the annual average accumulation in the period). During the same period, the central part of the ice cap was very likely thickening. The sensitivity of the total mass balance to changing summer temperature is –0.17 m ice/y/K. With a 5% increase of snow fall per degree increase of summer temperature, the sensitivity is changed to –0.14 m ice/y/K. Model studies with larger deviations of the summer temperature from the present value indicate that a 5 K warmer temperature would result in ablation over the entire ice cap, which would then melt away completely in a few hundred years. Even a three-fold, simultaneous increase of the accumulation rate would not in general restore the mass balance, but might secure survival of small isolated icecaps in the northern mountainous landscape. The firn warming (the increase of the temperature at 10 m depth above the mean annual air temperature) of the central area of the ice cap is also studied. Extreme changes of climate conditions as those mentioned above, are needed in order to change the thermal regime of the central region of Hans Tausen Iskappe from cold to temperate. This indicates that Hans Tausen Iskappe was a cold glacier during most of its existence.
Prior to the last deglaciation, probably in the Late Weichselian, glaciers draining the Inland Ice were present in Independence Fjord and Jørgen Brønlund Fjord. and a glacier draining an ice cap in the north was present in the Børglum Elv valley. It is proposed that glacier fronts were situated at the mouth of Jørgen Brønlund Fjord during a halt in the deglaciation 8000-9000 years BP, and that this halt led to a low initial rate of emergence. Jørgen Brønlund Fjord was deglaciated 8000-7600 years BP. The early Holocene marine limit is c. 65 m above sea-level in the fjord, and c. 80 m east of the fjord. The slow initial rate of emergence was soon followed by rapid emergence. Emergence of the land continued until about 1000 years BP. Part of the marine invertebrate fauna was established just after deglaciation. The same probably applies to the terrestrial flora and fauna. By 6000 years BP entry of driftwood and southern marine mammals began, and it continues today. Around 4000 years BP the Independence I people made their appearance, later the Independence II people and the Thule eskimos inhabited the area. The geomorphological features show a resemblance to those from valleys in Antarctica.
The main goals of the project were to investigate the present and past climate and glacier dynamics of North Greenland by means of ice-core records, ice margin studies, mass balance and climate studies and glacial geological studies on and around Hans Tausen Iskappe.
Significance
Reconstructions of past environmental changes are important for placing recent climate change in context and testing climate models. Periods of past climates warmer than today provide insight on how components of the climate system might respond in the future. Here, we report on an Arctic climate record from the Agassiz ice cap. Our results show that early Holocene air temperatures exceed present values by a few degrees Celsius, and that industrial era rates of temperature change are unprecedented over the Holocene period (∼12,000 y). We also demonstrate that the enhanced warming leads to a large response of the Greenland ice sheet; providing information on the ice sheet's sensitivity to elevated temperatures and thus helping to better estimate its future evolution.
Climate models project a strong increase in Arctic precipitation over the coming century, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow. However, little is known about future changes in the distributions of rainfall and snowfall in the Arctic. Here we use 37 state-of-the-art climate models in standardized twenty-first-century (2006-2100) simulations to show a decrease in average annual Arctic snowfall (70°-90° N), despite the strong precipitation increase. Rain is projected to become the dominant form of precipitation in the Arctic region (2091-2100), as atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rainfall and snowfall will heavily impact Arctic hydrology (for example, river discharge, permafrost melt), climatology (for example, snow, sea-ice albedo and melt) and ecology (for example, water and food availability).
All present glacier units in central Peary Land, North Greenland, have been systematically indexed in order to register existing documentation on glacier changes. The basis for this inventory work Is the series of wide angle vertical aerial photographs flown in 1978 for Kort- og Matrikelstyrelsen. Determination of the glaciation limit on this base indicates a rise from 200 m a.s.l. at the outer coast of the Arctic Ocean to between 900 and >1000 m a.s.l. in the central areas of Peary Land. This trend is related to relatively higher precipitation and lower summer temperature at the outer coast compared to further inland. The present glacier activity of individual glacier units has been investigated by study of all available aerial photographs from the years of 1950, 1960-63 and 1978. Locally photographic documentation can be extended back to 1938. In general, the glacier changes in this century have been very small, and significant changes are restricted to outlets of the Inland Ice, and to a minor degree outlets of local glaciers with mainly western and northern aspect. Semi-permanent ice cover in the fjords leads to formation and retention of extensive floating lobes of glacier fronts. The climate of the 20th century appears to have been characterised by borderline conditions between periods of ice-free fjords and those of semi-permanent ice cover. Neoglacial maximum is generally referred to A.D. 1900, with major thinning (downwasting) and recession in the first half of the 20th century, followed by slower recession, stand-still or even readvances during the last half of the century.
Recent observations indicate that ice-ocean interaction drives much of the recent increase in mass loss from the Greenland Ice Sheet; however, the role of ocean forcing in driving past glacier change is poorly understood. To extend the observational record and our understanding of the ocean-cryosphere link, we used a multi-proxy approach that combines new data from proglacial lake sediments, C-14-dated in situ moss that recently emerged from beneath cold-based ice caps, and Be-10 ages to reconstruct centennial-scale records of mountain glacier activity for the past similar to 10 k. y. in West Greenland. Proglacial lake sediment records and C-14 dating of moss indicate the onset of Neoglaciation in West Greenland at ca. 5 ka with substantial snowline lowering and glacier expansion at ca. 3.7 ka followed by additional ice expansion phases at ca. 2.9, ca. 1.7, and ca. 1.4 ka and during the Little Ice Age. We find that widespread glacier growth at ca. 3.7 ka in West Greenland coincides with marked cooling and reduced strength of the West Greenland Current in Disko Bugt. The transition to cooler ocean conditions at ca. 3.7 ka identified in Disko Bugt is registered by marine proxy data farther afield in East Greenland and on the northwestern Icelandic shelf, implying large-scale paleoceanographic changes across the North Atlantic during this interval. The similarity between glacier change on West Greenland and multiple marine and terrestrial records across the North Atlantic suggests that glaciers are strongly influenced by changes in ocean circulation and consequently implies that the ocean-cryosphere teleconnection is a persistent feature of the Arctic system.
We develop a posteriori ‘mechanical’ error estimators that are able to evaluate the solution discrepancy between two ice flow models. We first reformulate the classical shallow ice flow models by applying simplifications to the weak formulation of the Glen–Stokes model. This approach leads to a unified hierarchical formulation which relates the Glen–Stokes model, the Blatter model, the shallow ice approximation and the shallow shelf approximation. Based on this formulation and on residual techniques commonly used to estimate numerical errors, we derive three a posteriori estimators, each of which compares a pair of models using measures of the velocity field from the simpler (shallower) model. Numerical experiments confirm that these estimators can be used to assess the validity of the shallow ice models that are commonly used in glacier and ice sheet modelling.
Barnes Ice Cap is a remnant of the Laurentide Ice Sheet, which covered much of northern North America during the Last Glacial Maximum. Barnes reached a quasi-equilibrium state ~2000 years ago and has remained similar in size since, with a small increase during the Little Ice Age. In this study, we combine historical observations (1960-1980) with more recent satellite and airborne data (1995-2010) to drive a mass-balance model coupled to a transient thermo-mechanical model with an adaptive mesh geometry. The model is used to characterize the current state of the ice cap and to investigate its stability as a function of climate and its own internal dynamics. On millennial time scales we show that ice flow is influenced by adjustment of an unsteady shape, by gently sloping bedrock, and by contrasting viscosities between the Pleistocene and Holocene ice. On shorter time scales, Barnes is affected by surge activity. Sensitivity tests reveal that Barnes experienced climate conditions which enabled its stability 2000 to 3000 years ago, but will disappear under current climate conditions in the next millennium.
Full Stokes ice sheet models provide the most accurate description of ice sheet flow, and can therefore be used to reduce existing uncertainties in predicting the contribution of ice sheets to future sea level rise on centennial time-scales. The level of accuracy at which millennial time-scale palaeo-ice sheet simulations resolve ice sheet flow lags the standards set by Full Stokes models, especially, when Shallow Ice Approximation (SIA) models are used. Most models used in paleo-ice sheet modeling were developed at a time when computer power was very limited, and rely on several assumptions. At the time there was no means of verifying the assumptions by other than mathematical arguments. However, with the computer power and refined Full Stokes models available today, it is possible to test these assumptions numerically. In this paper, we review (Ahlkrona et al., 2013a) where such tests were performed and inaccuracies in commonly used arguments were found. We also summarize (Ahlkrona et al., 2013b) where the implications of the inaccurate assumptions are analyzed for two paleo-models – the SIA and the SOSIA. We review these works without resorting to mathematical detail, in order to make them accessible to a wider audience with a general interest in palaeo-ice sheet modelling. Specifically, we discuss two implications of relevance for palaeo-ice sheet modelling. First, classical SIA models are less accurate than assumed in their original derivation. Secondly, and contrary to previous recommendations, the SOSIA model is ruled out as a practicable tool for palaeo-ice sheet simulations. We conclude with an outlook concerning the new Ice Sheet Coupled Approximation Level (ISCAL) method presented in Ahlkrona et al. (2016), that has the potential to match the accuracy standards of full Stokes model on palaeo-timescales of tens of thousands of years, and to become an alternative to hybrid models currently used in palaeo-ice sheet modelling. The method is applied to an ice sheet covering Svalbard.
A thin section study of crystal structure has been carried out on a 345 m long ice core drilled to bedrock on Hans Tausen Iskappe, 1995. In addition a meltlayer stratigraphy was set up, showing how the fraction of meltlayer-ice in the core increases with depth. Main characteristics of crystal structure are increasing mean crystal size from top to bottom in the core and development of a weak single maximum c-axis fabric. The rate of ice crystal growth in the well dated upper half of the core is much lower than expected from studies of the normal grain growth regime in other polar ice cores. Probably the grain boundary movements are impeded by impurities, which are present in relatively high concentrations in the Hans Tausen ice. Asuming the applicability of the calculated growth rate throughout the core, a late Holocene origin of the oldest ice is suggested by the size of the crystals close to bedrock. Presented data furthermore implies that bottom ice temperatures were never near the melting point and it is concluded that there was no ice cap on the Hans Tausen plateau earlier in Holocene.
This chapter discusses that identifying the glacial ice sheet margins in Greenland from ground evidence poses a special problem because, except for the youngest period of glaciation, the entire ice margin has stood on the shelf. Therefore, its position has to be often judged from indirect and circumstantial evidence on land, such as the presence or absence of glacial landforms and weathering and their altitudes, and isostatic uplift. It provides the pattern for the interpretation of areas that lack such evidence. Some control on the position and timing of the LGM ice margin is offered by modern glaciological modeling. The chapter also reviews that for the ice-marginal lines three categories of decreasing certainty have been distinguished, which are the presence of (1) both age-evidence and morphological expression, (2) only age or morphological expression, and (3) conceptual, that is, deduced from topography, general shelf bathymetry and comparison with other areas. The expansion of the ice sheet was to a large extent dependant on the drainage capacity of the shelf– its width and size and frequency of cross-shelf troughs. The basic outline of these features are shown on the map, based on the new detailed bathymetric map provided by integrating the International Bathymetric Chart of the Arctic Ocean (IBCAO) with the previous Earth-Topography-Five-Minute Gridded Elevation Data Set, and ETOPO5.
The Younger Dryas (YD) is a well-constrained cold event from 12,900 to 11,700 years ago but it remains unclear how the cooling and subsequent abrupt warming recorded in ice cores was translated into ice margin fluctuations in Greenland. Here we present 10Be surface exposure ages from three moraines in front of local glaciers on a 50 km stretch along the north coast of Greenland, facing the Arctic Ocean. Ten ages range from 11.6 ± 0.5 to 27.2 ± 0.9 ka with a mean age of 12.5 ± 0.7 ka after exclusion of two outliers. We consider this to be a minimum age for the abandonment of the moraines. The ages of the moraines are furthermore constrained using Optically Stimulated Luminescence (OSL) dating of epishelf sediments, which were deposited prior to the ice advance that formed the moraines, yielding a maximum age of 12.4 ± 0.6 ka, and bracketing the formation and subsequent abandonment of the moraines to within the interval 11.8-13.0 ka ago. This is the first time a synchronous YD glacier advance and subsequent retreat has been recorded for several independent glaciers in Greenland. In most other areas, there is no evidence for re-advance and glaciers were retreating during YD. We explain the different behaviour of the glaciers in northernmost Greenland as a function of their remoteness from the Atlantic Meridional Overturning Circulation (AMOC), which in other areas has been held responsible for modifying the YD drop in temperatures.
Polycrystalline blocks of ice have been tested under compressive stresses in the range from 1 to 10 bars at temperatures from -13 degrees C to the melting-point. Under these conditions ice creeps in a manner similar to that shown by metals at high temperatures; there is a transient creep component and also a continuing or quasi-viscous component. The relation between the minimum observed flow rate , the applied stress and the absolute temperature T is = B exp (-Q/RT) , where R is the gas constant, and B, n and Q are constants; the value of n is about 32, that of Q is 32 kcal/mole, and that of B is 7 10 if the stress is measured in bars and the strain rate in years. At the higher stresses a third, accelerating stage of creep was observed; on the basis of the appearance and behaviour of sections cut from the specimens, this acceleration was attributed to recrystallization. The effect of changing the load during a test has also been studied; for large reductions creep recovery was observed. The results of these tests are discussed in connexion with previous work on metals and ice, and also with measurements of glacier flow.
Climate-model simulations are used to examine the impact of a collapse of the West Antarctic Ice Sheet (WAIS) on the surface climate of Antarctica. The lowered topography following WAIS collapse produces anomalous cyclonic circulation with increased flow of warm, maritime air towards the South Pole, and cold-air advection from the East Antarctic plateau towards the Ross Sea and Marie Byrd Land, West Antarctica. Relative to the background climate, areas in East Antarctica adjacent to the WAIS warm, while substantial cooling (several degrees C) occurs over parts of West Antarctica. Anomalously low isotope-paleotemperature values at Mt. Moulton, West Antarctica, compared with ice core records in East Antarctica, are consistent with collapse of the WAIS during the last interglacial period, Marine Isotope Stage (MIS) 5e. More definitive evidence might be recoverable from an ice core record at Hercules Dome, East Antarctica, which would experience significant warming and positive oxygen-isotope anomalies if the WAIS collapsed.
Meteorological station records, ice cores, and regional climate model output are combined to develop a continuous 171-yr (1840–2010) reconstruction of Greenland ice sheet climatic surface mass balance (Bclim) and its subcomponents including near-surface air temperature (SAT) since the end of the Little Ice Age. Independent observations are used to assess and compensate errors. Melt water production is computed using separate degree-day factors for snow and bare ice surfaces. A simple meltwater retention scheme yields the time variation of internal accumulation, runoff, and bare ice area.
At decadal time scales over the 1840–2010 time span, summer (June–August) SAT increased by 1.6°C, driving a 59% surface meltwater production increase. Winter warming was +2.0°C. Substantial interdecadal variability linked with episodic volcanism and atmospheric circulation anomalies is also evident. Increasing accumulation and melt rates, bare ice area, and meltwater retention are driven by increasing SAT. As a consequence of increasing accumulation and melt rates, calculated meltwater retention by firn increased 51% over the period, nearly compensating a 63% runoff increase. Calculated ice sheet end of melt season bare ice area increased more than 5%.
Multiple regression of interannual SAT and precipitation anomalies suggests a dominance of melting on Bclim and a positive SAT precipitation sensitivity (+32 Gt yr−1 K−1 or 6.8% K−1).
The Bclim component magnitudes from this study are compared with results from Hanna et al. Periods of shared interannual variability are evident. However, the long-term trend in accumulation differs in sign.
Precipitation changes projected for the end of the twenty-first century show an increase of more than 50 per cent in the Arctic regions. This marked increase, which is among the highest globally, has previously been attributed primarily to enhanced poleward moisture transport from lower latitudes. Here we use state-of-the-art global climate models to show that the projected increases in Arctic precipitation over the twenty-first century, which peak in late autumn and winter, are instead due mainly to strongly intensified local surface evaporation (maximum in winter), and only to a lesser degree due to enhanced moisture inflow from lower latitudes (maximum in late summer and autumn). Moreover, we show that the enhanced surface evaporation results mainly from retreating winter sea ice, signalling an amplified Arctic hydrological cycle. This demonstrates that increases in Arctic precipitation are firmly linked to Arctic warming and sea-ice decline. As a result, the Arctic mean precipitation sensitivity (4.5 per cent increase per degree of temperature warming) is much larger than the global value (1.6 to 1.9 per cent per kelvin). The associated seasonally varying increase in Arctic precipitation is likely to increase river discharge and snowfall over ice sheets (thereby affecting global sea level), and could even affect global climate through freshening of the Arctic Ocean and subsequent modulations of the Atlantic meridional overturning circulation.
observed rapid loss of thick multiyear sea ice over the last 7 years and
the September 2012 Arctic sea ice extent reduction of 49% relative to
the 1979-2000 climatology are inconsistent with projections of a nearly
sea ice-free summer Arctic from model estimates of 2070 and beyond made
just a few years ago. Three recent approaches to predictions in the
scientific literature are as follows: (1) extrapolation of sea ice
volume data, (2) assuming several more rapid loss events such as 2007
and 2012, and (3) climate model projections. Time horizons for a nearly
sea ice-free summer for these three approaches are roughly 2020 or
earlier, 2030 ± 10 years, and 2040 or later. Loss estimates from
models are based on a subset of the most rapid ensemble members. It is
not possible to clearly choose one approach over another as this depends
on the relative weights given to data versus models. Observations and
citations support the conclusion that most global climate model results
in the CMIP5 archive are too conservative in their sea ice projections.
Recent data and expert opinion should be considered in addition to model
results to advance the very likely timing for future sea ice loss to the
first half of the 21st century, with a possibility of major loss within
a decade or two.