Snapshots of the Greenland ice sheet configuration in the Pliocene to early Pleistocene

AbstractThe geometry of the ice sheets during the Pliocene to early Pleistocene is not well constrained. Here we apply an ice-flow model in the study of the Greenland ice sheet (GIS) during three extreme intervals of this period constrained by geological observations and climate reconstructions. We study the extent of the GIS during the Mid-Pliocene Warmth (3.3–3.0 Ma), its advance across the continental shelf during the late Pliocene to early Pleistocene glaciations (3.0–2.4 Ma) as implied by offshore geological studies, and the transition from glacial to interglacial conditions around 2.4 Ma as deduced from the deposits of the Kap København Formation, North Greenland. Our experiments show that no coherent ice sheet is likely to have existed in Greenland during the Mid-Pliocene Warmth and that only local ice caps may have been present in the coastal mountains of East Greenland. Our results illustrate the variability of the GIS during the Pliocene to early Pleistocene and underline the importance of including independent estimates of the GIS in studies of climate during this period. We conclude that the GIS did not exist throughout the Pliocene to early Pleistocene, and that it melted during interglacials even during the late Pliocene climate deterioration.

Download Full-text

Sensitivity of Greenland Ice Sheet Projections to Model Formulations

Journal of Glaciology ◽

10.3189/2013jog12j182 ◽

2013 ◽

Vol 59 (216) ◽

pp. 733-749 ◽

Cited By ~ 87

Author(s):

H. Goelzer ◽

P. Huybrechts ◽

J.J. Fürst ◽

F.M. Nick ◽

M.L. Andersen ◽

...

Keyword(s):

Regional Climate Model ◽

Sea Level ◽

Flow Model ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Flow ◽

Outlet Glacier ◽

Glacier Dynamics

AbstractPhysically based projections of the Greenland ice sheet contribution to future sea-level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself. Here a higher-order, three-dimensional thermomechanical ice flow model is used, initialized to the present-day geometry. The forcing comes from a high-resolution regional climate model and from a flowline model applied to four individual marine-terminated glaciers, and results are subsequently extended to the entire ice sheet. The experiments span the next 200 years and consider climate scenario SRES A1B. The surface mass-balance (SMB) scheme is taken either from a regional climate model or from a positive-degree-day (PDD) model using temperature and precipitation anomalies from the underlying climate models. Our model results show that outlet glacier dynamics only account for 6–18% of the sea-level contribution after 200 years, confirming earlier findings that stress the dominant effect of SMB changes. Furthermore, interaction between SMB and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing. Forcing from the regional climate model produces a 14–31 % higher sea-level contribution compared to a PDD model run with the same parameters as for IPCC AR4.

Download Full-text

Permafrost at the Ice Base of Recent Pleistocene Glaciations–Inferences from Borehole Temperature Profiles

Bulletin of Geography Physical Geography Series ◽

10.2478/v10250-012-0001-x ◽

2012 ◽

Vol 5 (1) ◽

pp. 7-28 ◽

Cited By ~ 3

Author(s):

Jacek Majorowicz

Keyword(s):

Low Temperature ◽

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Temperature Reconstruction ◽

Temperature Profiles ◽

Pleistocene Glaciations ◽

Large Variability ◽

Glacial Ice ◽

Borehole Temperature

Abstract Paleo-temperature reconstruction from precise depth (>2.0 km) well temperature logs can offer information on whether the bed of an ice sheet was frozen. Inversion or upward extrapolation of the >2-km-deep geothermal profile is the only method by which temperature evolution at the base of long-disappeared ice sheets such as the Laurentide and Fennoscandian in the northern part of the Northern Hemisphere in North America and Europe can be inferred. It is obvious from the results from well temperature profiles that there were spatial variations in temperature at the base of the ice sheets during glaciations. This comes as no surprise, since modern-day measurements of temperature profiles through the ice of existing glaciers show a similarly large variability. Present bedrock temperatures measured beneath the central part of the Yukon Rusty glacier are near 0°C to -2°C while Greenland ice sheet base temperatures are -8 and -13°C. In case of very low paleo-temperatures derived from the interpretation of temperature profiles in the areas presently outside the current extent of glacial ice it can be shown that low temperature conditions under glacial ice could facilitate the existence of moderate (some 100-200 m) to thick (0.5 km-1 km) permafrost conditions. It is speculated here that, in many cases, paleo-glacial cold base ice could have existed right on top of paleo-permafrost in sediments just below. Such ice-bonded permafrost may have been frozen to glacial ice above, forming pillars which fixed glacial ice to permafrost below, thus limiting ice movement in such places and resulting in the -extended persistence of permafrost.

Download Full-text

Supplementary material to "Application of GRACE to the evaluation of an ice flow model of the Greenland Ice Sheet"

10.5194/tc-2015-224-supplement ◽

2016 ◽

Author(s):

N.-J. Schlegel ◽

D. N. Wiese ◽

E. Y. Larour ◽

M. M. Watkins ◽

J. E. Box ◽

...

Keyword(s):

Flow Model ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Flow ◽

Supplementary Material

Download Full-text

Greenland Ice Sheet sensitivity and sea level contribution in the mid-Pliocene warm period – Pliocene Ice Sheet Model Intercomparison Project PLISMIP

Climate of the Past Discussions ◽

10.5194/cpd-10-2821-2014 ◽

2014 ◽

Vol 10 (4) ◽

pp. 2821-2856 ◽

Cited By ~ 4

Author(s):

S. J. Koenig ◽

A. M. Dolan ◽

B. de Boer ◽

E. J. Stone ◽

D. J. Hill ◽

...

Keyword(s):

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Warm Period ◽

Future Climate Change ◽

Potential Range ◽

Ice Caps ◽

Statistical Measures ◽

Intercomparison Project

Abstract. The understanding of the nature and behavior of ice sheets in past warm periods is important to constrain the potential impacts of future climate change. The mid-Pliocene Warm Period (2.97 to 3.29 Ma) has global temperatures similar to those projected for future climates, nevertheless Pliocene ice locations and extents are still poorly constrained. We present results from the efforts to simulate mid-Pliocene Greenland ice sheets by means of the international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP). We compare the performance of existing numerical ice sheet models in simulating modern control and mid-Pliocene ice sheets by a suite of sensitivity experiments guided by available proxy records. We quantify equilibrated ice sheet volume on Greenland, identifying a potential range in sea level contributions from warm Pliocene scenarios. A series of statistical measures are performed to quantify the confidence of simulations with focus on inter-model and inter-scenario differences. We find that Pliocene Greenland ice sheets are less sensitive to differences in ice sheet model configurations and internal physical quantities, than to changes in imposed climate forcing. We conclude that Pliocene ice was most likely to be limited to highest elevations in East and South as simulated with the highest confidence and by synthesizing available regional proxies, although extents of those ice caps need to be further constrained by using a range of GCM climate forcings.

Download Full-text

The timing of fjord formation and early glaciations in North and Northeast Greenland

10.5194/egusphere-egu2020-10880 ◽

2020 ◽

Author(s):

Vivi Kathrine Pedersen ◽

Nicolaj Krog Larsen ◽

David Lundbek Egholm

Keyword(s):

Late Miocene ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Early History ◽

Early Pleistocene ◽

Late Pliocene ◽

Isostatic Uplift ◽

History Of ◽

Erosional Unloading ◽

North Greenland

The timing and extent of early glaciations in Greenland, and their co-evolution with the underlying landscape remain elusive. In this study, we explore the timing of fjord erosion in Northeast and North Greenland between Scoresby Sund (70&#176;N) and Independence Fjord (82&#176;N). By determining the timing of fjord formation, we can improve our understanding of the early history of the Greenland Ice Sheet in these regions.We use the concept of geophysical relief to estimate fjord erosion and calculate the subsequent flexural isostatic response to erosional unloading. The timing of erosion and isostatic uplift is constrained by marine sediments of late Pliocene-early Pleistocene age that are now exposed on land between ~24 and 230 m a.s.l.We find that the northern Independence Fjord system must have formed by glacial erosion at average rates of ~0.5-1 mm/yr since ~2.5 Ma, in order to explain the current elevation of the marine Kap K&#248;benhavn Formation by erosion-induced isostatic uplift. In contrast, fjord formation in the outer parts of southward Scoresby Sund commenced before the Pleistocene, most likely in late Miocene, and continued throughout the Pleistocene by fjord formation progressing inland. Our results suggest that the inception of the Greenland Ice Sheet began in the central parts of Northeast Greenland before the Pleistocene and spread to North Greenland only at the onset of the Pleistocene. &#160;

Download Full-text

Steady-State Temperatures at the Bottom of Ice Sheets and Computation of the Bottom Ice Flow Law from the Surface Profile

Journal of Glaciology ◽

10.3189/s002214300002058x ◽

1968 ◽

Vol 7 (51) ◽

pp. 363-376 ◽

Cited By ~ 1

Author(s):

L. Lliboutry

Keyword(s):

Steady State ◽

Ice Sheets ◽

Ice Sheet ◽

Surface Profile ◽

Greenland Ice Sheet ◽

Bottom Temperature ◽

Ice Flow ◽

Actual Surface ◽

Flow Law ◽

Strain Heating

AbstractA solution for the steady flow of a cold ice sheet is recalled, which takes account of the heat released by deformation. As this strain heating increases the strain velocity, the bottom temperature may be unstable. A set of five equations with five unknowns is written, which allows the surface profile and the bottom temperature to be computed step by step by an iterative process. This has been done by computer for three very different models of ice sheets. and in each case with three distinct values of the constant B in Glen’s ice flow law. It was found in every case that steady-state temperature profiles could not be computed beyond a moderate distance from the ice divide. The correct value of B for bottom ice may be deduced from the actual surface profile. At the bottom of Greenland ice sheet, B ≈ 2.18 bar −3 year−1. This is about thirteen times bigger than for the bulk of the alpine glaciers.

Download Full-text

Postglacial Isobases from Northern Ellesmere Island and Greenland: New Data

Géographie physique et Quaternaire ◽

10.7202/032650ar ◽

2007 ◽

Vol 40 (3) ◽

pp. 299-305 ◽

Cited By ~ 5

Author(s):

John England ◽

Jan Bednarski

Keyword(s):

Response Times ◽

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ellesmere Island ◽

Radiocarbon Dates ◽

Sea Levels ◽

Ice Caps ◽

History Of ◽

Considerable Range

ABSTRACT Over seventy new 14C dates on former relative sea levels from Hall Land, northwest Greenland, and Clements Markham Inlet, northern Ellesmere Island, are combined with previous data to revise the regional isobases for this area. These isobases show : 1) a centre of maximum postglacial emergence over northwest Greenland extending to; 2) an intervening cell of lower emergence over northeast Ellesmere Island which was isostatically-dominated by the Greenland Ice Sheet; in turn, extending to 3) a higher centre of emergence over the Grant Land Mountains, northernmost Ellesmere Island, associated with the independent history of local ice caps there. Radiocarbon dates from raised marine shorelines show a 2000 year lag between glacial unloading on northwest Greenland and northernmost Ellesmere Island. This lag in glacioisostatic adjustments suggests a considerable range in the glacier response times and/or glacioclimatic regimes in this area. Throughout the area the last ice limit was ca. 5-60 km beyond present ice margins. Maximum emergence at these ice limits is marked by shorelines built into a full glacial sea which range from 124 m asl in Clements Markham Inlet to 150 m asl in Hall Land. This indicates that similar emergence (120-150 m) in other areas does not necessarily require the removal of entire ice sheets although this has been commonly assumed in the literature. The geophysical implications of this warrant consideration.

Download Full-text

Evidence for early glaciation of southeastern Beringia

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2019-0048 ◽

2020 ◽

Vol 57 (2) ◽

pp. 199-226

Author(s):

Rodney Arthur Savidge

Keyword(s):

North America ◽

Ice Sheet ◽

Extended Period ◽

Pleistocene Glaciations ◽

Late Pliocene ◽

Ice Caps ◽

Northwestern North America ◽

Working Hypotheses ◽

Minimal Research ◽

Red Bed

Between the Klondike Plateau and Yukon–Tanana highlands of Yukon and Alaska, respectively, current maps explain glaciated alpine locales and periglacial areas in terms of localized Pliocene–Pleistocene montane ice caps, alpine glaciers, and periglacial changes. However, this region’s plateau topography is populated with long undulating ridges having wide flattened tops; it contrasts with relief of other regions of northwestern North America also affected by ice caps, cryoplanation, and erosion over similar duration during the same epochs. This region has received minimal research and appears to present a new opportunity for resolving outstanding glaciological and stratigraphy issues. The glaciological history is reviewed, placing particular emphasis upon the low-elevation ridges within the “unglaciated” region, suggesting that those ridges are relict arête/cirque remnants. Sites of subalpine glacial grooving and mountaintop planing are also identified, and a conglomeratic red bed containing erratic clasts is described. All indications point to the “unglaciated” region having been glaciated before late Pliocene. Two working hypotheses are proposed: (1) The landscape once supported a range of young mountains that became glaciated then overridden and pared to a plateau by an ice sheet. (2) Following deglaciation, an extended period of paraglacial activity removed most of the former drift and excised new valleys to give the region an unglaciated appearance, which thereafter became modified into its present state by local montane/alpine glaciations, interglacial cryoplanation, periglacial gelifraction, and erosion. In addition to Pliocene–Pleistocene glaciations, a northeastward advancing Miocene ice sheet seems plausible and, on the basis of paleographic considerations and lithology, a Cretaceous glaciation evidently is also not out of the question.

Download Full-text

Simulations of large climate transition occurring at high and low latitudes during the late Pliocene (3.3 Ma) and the Plio/Pleistocene (3-2.5 Ma) boundary

10.5194/egusphere-egu2020-20914 ◽

2020 ◽

Author(s):

Ning Tan ◽

Emma Yule ◽

Gilles Ramstein ◽

Doris Barboni ◽

Rani Raj ◽

...

Keyword(s):

Northern Hemisphere ◽

Energy Transport ◽

Hydrological Cycle ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Large Change ◽

Early Pleistocene ◽

Oceanic Circulation ◽

Late Pliocene ◽

Opening And Closing

The late Pliocene corresponds to a large cooling over Northern Hemisphere associated with sporadic occurrences of glaciations. The most important event occurred during the marine isotope stage M2 (MIS M2, 3.312&#8211;3.264 Ma) when a large glaciation took place with a sea level drop from 20 to 60 m, but its duration is short and the summer insolation forcing change at 65&#176;N is weak. De Schepper et al (2013) invoked to explain the onset and termination of this glaciation with the opening and closing of the Central American Seaway (shallow CAS). Based on their hypothesis, we have intensively studied the onset mechanism of&#160; MIS M2 through a series of sensitivity experiments using the IPSL AOGCM and the asynchronous coupling with an Ice sheet model (GRISLI). Our results demonstrate that the shallow CAS helps to precondition the low-latitude oceanic circulation and affects the related northward energy transport, but cannot alone explain the onset of the M2 glaciation, the most important contribution on MIS M2 are from the large change of pCO2 as well as the internal feedbacks of vegetation and ice sheet. Moreover, we have also investigated the period from the late Pliocene to the early Pleistocene (3-2.5 Ma) through a transient-like simulation using the same AOGCM and ISM. This enables to simulate the Greenland Ice Sheet (GRIS) onset and development using the pCO2 reconstructions from different proxies. All these simulations were analyzed with emphasis on cryosphere and focused on the Northern Hemisphere (mid-to-high latitudes). Here we used the same modeling simulations but with a focus over the tropical Africa. We first depict the large changes of temperatures and hydrological cycle produced over this area during these two periods and compare our data to reconstructions. Moreover, by prescribing our climate results as inputs for the vegetation model (Biome4), we compare more directly the simulated plant functional types (PFTs) with that constructed by the pollen data. In addition, we further quantify the respective impact of various driving factors on these PFTs variations.

Download Full-text

Ice-dynamic projections of the Greenland ice sheet in response to atmospheric and oceanic warming

The Cryosphere Discussions ◽

10.5194/tcd-8-3851-2014 ◽

2014 ◽

Vol 8 (4) ◽

pp. 3851-3905 ◽

Cited By ~ 2

Author(s):

J. J. Fürst ◽

H. Goelzer ◽

P. Huybrechts

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Flow Model ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Melting ◽

Strong Impact ◽

Ice Dynamics ◽

Ice Flow ◽

Over Time

Abstract. Continuing global warming will have a strong impact on the Greenland ice sheet in the coming centuries. During the last decade, both increased surface melting and enhanced ice discharge from calving glaciers have contributed 0.6 ± 0.1 mm yr−1 to global sea-level rise, roughly in shares of respectively 60 and 40 per cent. Here we use a higher-order ice flow model, initialised to the present state, to simulate future ice volume changes driven by both atmospheric and oceanic temperature changes. For these projections, the ice flow model accounts for runoff-induced basal lubrication and ocean warming-induced discharge increase at the marine margins. For a suite of ten Atmosphere and Ocean General Circulation Models and four Representative Concentration Pathway scenarios, the projected sea-level rise lies in the range of +1.4 to +16.6 cm by the year 2100. For two low emission scenarios, the projections are conducted up to 2300. Ice loss rates are found to either abate when the warming already peaks in this century, allowing to preserve the ice sheet in a geometry close to the present-day state, or to remain at a constant level over three hundred years under moderate warming. The volume loss is predominantly caused by increased surface melting as the contribution from enhanced ice discharge decreases over time and is self-limited by thinning and retreat of the marine margin reducing the ice–ocean contact area. The effect of enhanced basal lubrication on the volume evolution is found to be negligible on centennial time scales. The presented projections show that the observed rates of volume change over the last decades cannot simply be extrapolated over the 21st century on account of a different balance of processes causing ice loss over time. The results also indicate that the largest source of uncertainty arises from the surface mass balance and the underlying climate change projections, and not from ice dynamics.

Download Full-text