On the extent and thickness of the Innuitian Ice Sheet: a postglacial-adjustment approach

1991 ◽  
Vol 28 (2) ◽  
pp. 231-239 ◽  
Author(s):  
A. M. Tushingham
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Tectonic Uplift ◽  
Ellesmere Island ◽  
Illustrative Case ◽  
Relative Sea Level ◽  
Sea Levels ◽  
Level Data ◽  
Illustrative Case Study ◽  
Raised Beaches

There is at present a controversy concerning the extent and thickness of the Innuitian Ice Sheet during the last glacial maximum (ca. 18 000 BP). Here, both a thick, extensive Innuitian Ice Sheet and a thin, limited ice sheet are isostatically modelled by employing disc-shaped elements and a radially symmetric Maxwellian Earth. The predicted relative sea-level curves for both models are compared with new data from Thores River, northernmost Ellesmere Island, and data from 29 other sites located in and around the Queen Elizabeth Islands. The data from Thores River are presented as an illustrative case study that particularly emphasizes the difficulty of relating sample elevations to ancient sea levels in this region. At all 30 sites, the relative sea-level data overwhelmingly favour the thick, extensive ice model. The hypothesis of tectonic uplift to explain the high raised beaches (> 100 m) found on Ellesmere Island and elsewhere in the region is rejected. The residual uplift of the thin, limited model is not spatially coherent, nor is it likely that tectonic uplift would exactly mimic the distinctive postglacial uplift. To reconcile geomorphological evidence (in the form of the preservation of preglacial maximum sediments and the general lack of glacial deposits) and the presence of high raised beaches, it is proposed that the Innuitian Ice Sheet was for part, possibly most, of its history a cold-based ice sheet (i.e., frozen to its bed).

Holocene delevelling of Devon Island, Arctic Canada: implications for ice sheet geometry and crustal response

1998 ◽  
Vol 35 (8) ◽  
pp. 885-904 ◽  
Author(s):  
Arthur S Dyke
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Bowhead Whale ◽  
Large Set ◽  
Relative Sea Level ◽  
Radiocarbon Dates ◽  
Level Curves ◽  
Devon Island ◽  
Ice Load ◽  
Raised Beaches

The raised beaches and deltas of Devon Island contain an abundance of dateable materials. A large set of radiocarbon dates (228), 154 of which are new, are used to construct relative sea level curves and isobase maps for the island. The best materials for this purpose are driftwood logs (61 dates) and bowhead whale bones (74 dates) from raised beaches and mollusc shells from marine-limit deltas (20 dates) or from altitudes close to marine limit (14 dates). During the last glacial maximum, the island is thought to have lain beneath the southeastern flank of the Innuitian Ice Sheet. The relative sea level history is congruent with that inferred ice configuration. The island spans half the ice sheet width. Relative sea level curves are of simple exponential form, except near the glacial limit where an early Holocene emergence proceeded to a middle Holocene lowstand below present sea level, which was followed by submergence attending the passage of the crustal forebulge. The response times of relative sea level curves and of crustal uplift decrease from the uplift centre toward the limit of loading, but the change appears strongest near the limit. The Innuitian uplift is separated from the Laurentide uplift to the south by a strong isobase embayment over Lancaster Sound. Hence, ice load irregularities with wavelengths of about 100 km were large enough to leave an isostatic thumbprint in this region of the continent. The apparent absence of a similar embayment over Jones Sound probably indicates a greater Late Wisconsinan ice load there, or a thicker crust than in Lancaster Sound.

scholarly journals Testing the mid-Holocene relative sea-level highstand hypothesis in North Wales, UK

The Holocene ◽  
2019 ◽  
Vol 29 (9) ◽  
pp. 1491-1502
Author(s):  
Greg T Rushby ◽  
Geoff T Richards ◽  
W Roland Gehrels ◽  
William P Anderson ◽  
Mark D Bateman ◽  
...  
Keyword(s):  
Sea Level ◽  
Late Holocene ◽  
Sea Level Changes ◽  
Relative Sea Level ◽  
Sea Levels ◽  
Isostatic Adjustment ◽  
North Wales ◽  
Level Data ◽  
Northwest Europe ◽  
Holocene Sea Level

Accurate Holocene relative sea-level curves are vital for modelling future sea-level changes, particularly in regions where relative sea-level changes are dominated by isostatically induced vertical land movements. In North Wales, various glacial isostatic adjustment (GIA) models predict a mid-Holocene relative sea-level highstand between 4 and 6 ka, which is unsubstantiated by any geological sea-level data but affects the ability of geophysical models to model accurately past and future sea levels. Here, we use a newly developed foraminifera-based sea-level transfer function to produce a 3300-year-long late-Holocene relative sea-level reconstruction from a salt marsh in the Malltraeth estuary on the south Anglesey coast in North Wales. This is the longest continuous late-Holocene relative sea-level reconstruction in Northwest Europe. We combine this record with two new late-Holocene sea-level index points (SLIPs) obtained from a freshwater marsh at Rhoscolyn, Anglesey, and with previously published regional SLIPs, to produce a relative sea-level record for North Wales that spans from ca. 13,000 BP to the present. This record leaves no room for a mid-Holocene relative sea-level highstand in the region. We conclude that GIA models that include a mid-Holocene sea-level highstand for North Wales need revision before they are used in the modelling of past and future relative sea-level changes around the British Isles.

Importance of Northern Hemisphere Vertical Land Motion for Geodesy and Coastal Sea Levels

2020 ◽  
Author(s):  
Carsten Ankjær Ludwigsen ◽  
Ole Baltazar Andersen ◽  
Shfaqat Abbas Khan ◽  
Ben Marzeion
Keyword(s):  
Mass Loss ◽  
Sea Level ◽  
Northern Hemisphere ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Coastal Regions ◽  
Relative Sea Level ◽  
Sea Levels ◽  
The North ◽  
Vertical Land Motion

<p>Vertical Land Motion (VLM) is a composite of several earth dynamics caused by changes of earth’s surface load or tectonics. In most of the Northern Hemisphere mainly two dynamics are causing large scale vertical land motion – Glacial Isostatic Adjustment (GIA), which is the rebound from the loading of the latest glacial cycle (10-30 kyr ago) and elastic rebound from contemporary land ice changes, that happens immediately when loading is removed from the surface.</p><p>With glacial mass balance data and observations of the Greenland Ice Sheet we have created an Northern Hemisphere ice history from 1996-2015 that is used to make a model for elastic VLM caused by ice mass loss that varies in time.</p><p>It shows that, in most cases, the elastic VLM model is able to close gaps between GIA induced VLM and GNSS-measured VLM, giving confidence that the combined GIA + elastic VLM-model is a better alternative to adjust relative sea level measurements from tide-gauges (where no (reliable) GNSS-data is available) to absolute sea level than 'just' a GIA-model. In particular for Arctic Sea Level, where elastic uplifts are prominent and large coastal regions have limited in-situ data available, the VLM-model is useful for correcting Tide Gauge measurements and thereby validate satellite altimetry observed sea levels, which is challenged by sea ice in the coastal Arctic.</p><p>Furthermore, our elastic VLM-model shows, that the uplift caused by the melt of the Greenland Ice Sheet (GIS) is far-reaching and even in the North Sea region or along the North American coast show uplift rates in the order of 0.4-0.7 mm/yr from 1996-2015. Interestingly, this is roughly equivalent to Greenland’s sea level contribution in the same period, thereby 'neutralizing' the melt of GIS. As GIS ice mass loss continues to accelerate, the elastic uplift will have increased importance for coastal regions and future relative sea level projections. Unfortunately, the opposite effect is true for the southern hemisphere or vice versa if Antarctic ice sheet mass loss would increase.</p>

Implications of the Radiocarbon Timescale for Ice-Sheet Chronology and Sea-Level Change

1993 ◽  
Vol 39 (1) ◽  
pp. 125-129 ◽  
Author(s):  
A. Mark Tushingham ◽  
W. Richard Peltier
Keyword(s):  
Sea Level ◽  
Last Glacial Maximum ◽  
Calibration Curve ◽  
Ice Sheet ◽  
Relative Sea Level ◽  
New Model ◽  
Last Glacial ◽  
Level Data ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractA new extended radiocarbon calibration curve has allowed a reexamination of relative sea-level data based on pre-Holocene dates. At sites located far from any Late Pleistocene ice sheet, the effect of employing this new calibration curve is that the calibrated data (with ages up to 17,100 14C yr B.P.) now agree with the corresponding relative sea-level curve predicted by the ICE-3G deglaciation model. An important implication of this new calibration curve is that the last glacial maximum (ca. 18,000 14C yr B.P.) is inferred to have occurred 22,000-21,000 cal yr B.P. This allows for additional ice to be incorporated in a revised deglaciation model than suggested by ICE-3G. The predicted relative sealevel curves of this new model match the relative sea-level data as well as those of ICE-3G. Further, the total sea-level rise of 124 m at Barbados since the last glacial maximum predicted by this new model agrees with the estimated value of 121 ± 5 m obtained from the depths of drowned reef-crest corals.

Evaluation of a numerical model of the British-Irish ice sheet using relative sea-level data: implications for the interpretation of trimline observations

2012 ◽  
Vol 27 (6) ◽  
pp. 597-605 ◽  
Author(s):  
Joseph Kuchar ◽  
Glenn Milne ◽  
Alun Hubbard ◽  
Henry Patton ◽  
Sarah Bradley ◽  
...  
Keyword(s):  
Numerical Model ◽  
Sea Level ◽  
Ice Sheet ◽  
Relative Sea Level ◽  
Level Data

scholarly journals Resolving discrepancies between field and modelled relative sea-level data: lessons from western Ireland

2017 ◽  
Vol 32 (7) ◽  
pp. 957-975 ◽  
Author(s):  
Robin Edwards ◽  
W. Roland Gehrels ◽  
Anthony Brooks ◽  
Ralph Fyfe ◽  
Katie Pullen ◽  
...  
Keyword(s):  
Sea Level ◽  
Relative Sea Level ◽  
Level Data ◽  
Western Ireland

Observations of postglacial uplift at Churchill, Manitoba

1992 ◽  
Vol 29 (11) ◽  
pp. 2418-2425 ◽  
Author(s):  
A. Mark Tushingham
Keyword(s):  
Sea Level ◽  
Tide Gauge ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial Isostatic Adjustment ◽  
Tide Gauge Record ◽  
Isostatic Adjustment ◽  
Absolute Gravimetry ◽  
The Earth ◽  
Level Data

Churchill, Manitoba, is located near the centre of postglacial uplift caused by the Earth's recovery from the melting of the Laurentide Ice Sheet. The value of present-day uplift at Churchill has important implications in the study of postglacial uplift in that it can aid in constraining the thickness of the ice sheet and the rheology of the Earth. The tide-gauge record at Churchill since 1940 is examined, along with nearby Holocene relative sea-level data, geodetic measurements, and recent absolute gravimetry measurements, and a present-day rate of uplift of 8–9 mm/a is estimated. Glacial isostatic adjustment models yield similar estimates for the rate of uplift at Churchill. The effects of the tide-gauge record of the diversion of the Churchill River during the mid-1970's are discussed.

scholarly journals Comparing a thermo-mechanical Weichselian ice sheet reconstruction to GIA driven reconstructions: aspects of earth response and ice configuration

2013 ◽  
Vol 5 (2) ◽  
pp. 2345-2388 ◽  
Author(s):  
P. Schmidt ◽  
B. Lund ◽  
J-O. Näslund
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Younger Dryas ◽  
Slow Phase ◽  
Glacial Isostatic Adjustment ◽  
Relative Sea Level ◽  
Isostatic Adjustment ◽  
Earth Models ◽  
Uplift Rates ◽  
Best Fit

Abstract. In this study we compare a recent reconstruction of the Weichselian ice-sheet as simulated by the University of Main ice-sheet model (UMISM) to two reconstructions commonly used in glacial isostatic adjustment (GIA) modeling: ICE-5G and ANU (also known as RSES). The UMISM reconstruction is carried out on a regional scale based on thermo-mechanical modelling whereas ANU and ICE-5G are global models based on the sea-level equation. The Weichselian ice-sheet in the three models are compared directly in terms of ice volume, extent and thickness, as well as in terms of predicted glacial isostatic adjustment in Fennoscandia. The three reconstructions display significant differences. UMISM and ANU includes phases of pronounced advance and retreat prior to the last glacial maximum (LGM), whereas the thickness and areal extent of the ICE-5G ice-sheet is more or less constant up until LGM. The final retreat of the ice-sheet initiates at earliest time in ICE-5G and latest in UMISM, while ice free conditions are reached earliest in UMISM and latest in ICE-5G. The post-LGM deglaciation style also differs notably between the ice models. While the UMISM simulation includes two temporary halts in the deglaciation, the later during the Younger Dryas, ANU only includes a decreased deglaciation rate during Younger Dryas and ICE-5G retreats at a relatively constant pace after an initial slow phase. Moreover, ANU and ICE-5G melt relatively uniformly over the entire ice-sheet in contrast to UMISM which melts preferentially from the edges. We find that all three reconstructions fit the present day uplift rates over Fennoscandia and the observed relative sea-level curve along the Ångerman river equally well, albeit with different optimal earth model parameters. Given identical earth models, ICE-5G predicts the fastest present day uplift rates and ANU the slowest, ANU also prefers the thinnest lithosphere. Moreover, only for ANU can a unique best fit model be determined. For UMISM and ICE-5G there is a range of earth models that can reproduce the present day uplift rates equally well. This is understood from the higher present day uplift rates predicted by ICE-5G and UMISM, which results in a bifurcation in the best fit mantle viscosity. Comparison of the uplift histories predicted by the ice-sheets indicate that inclusion of relative sea-level data in the data fit can reduce the observed ambiguity. We study the areal distributions of present day residual surface velocities in Fennoscandia and show that all three reconstructions generally over-predict velocities in southwestern Fennoscandia and that there are large differences in the fit to the observational data in Finland and northernmost Sweden and Norway. These difference may provide input to further enhancements of the ice-sheet reconstructions.

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