Niels Reeh

University of Southern Denmark

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Hans Oerter

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

H.H Thomsen

Geological Survey of Denmark and Greenland

Carl Egede Bøggild

Technical University of Denmark

OΒ

Ole Β. Olesen

Geological Survey of Denmark and Greenland

N. Gundestrup

University of Copenhagen

Anne Letréguilly

Laboratoire de Glaciologie et Géophysique de l’Environnement

S. J. Johnsen

University of Copenhagen

W. Dansgaard

University of Copenhagen

C. U. Hammer

University of Copenhagen

Johan Jacob Mohr

Technical University of Denmark

Cooperative Institutions

University of Alaska Fairbanks

University of Copenhagen

University of Colorado Boulder

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Geological Survey of Denmark and Greenland

Technical University of Denmark

Université du Québec à Montréal

Centre National de la Recherche Scientifique

Durham University

Earth System Science Interdisciplinary Center

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Discussions of Arctic climate feedback mechanisms

Eos (2004)

Sebastian Gerland Birgit Njåstad Elisabeth Isaksson Vladimir Pavlov Jens Hesselbjerg Christensen

The Arctic Climate Impact Assessment process (ACIA; see http://www.acia.uaf.edu/) is an international project of the Arctic Council and the International Arctic Science Committee (IASC) to evaluate and synthesize knowledge on climate variability climate change, increased ultraviolet radiation, and their consequences. As a part of the Norwegian work within ACIA (see http://acia.npolar.no/), an international workshop on Arctic climate feedback mechanisms was held in November 2003 at the Norwegian Polar Institute. Invited talks were presented in five sessions focused on climate programs, terrestrial systems, oceans, sea ice, and atmosphere. Poster presentations and working groups were organized for four sessions in the various scientific fields, identifying the state of knowledge and challenges, and making recommendations.

Norwegian

10.1029/2004eo150006

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Glacier surface velocity measurements from radar interferometry and the principle of mass conservation

Johan Jacob Mohr Niels Reeh

Presents a relation between the three glacier surface velocity components, the surface flux-divergence, glacier thickness and bottom melt and displacement. The relation can be used as an extension to the surface parallel flow assumption often used with interferometric synthetic aperture measurements of glacier velocities. The assumptions for the derivation are described and important limitations high-lighted.

Divergence (linguistics)

10.1109/igarss.2002.1025773

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Citations (2)

Ice stratigraphy at the Pâkitsoq ice margin, West Greenland, derived from gas records

Journal of Glaciology (2009)

Hinrich Schaefer V. V. Petrenko Edward J. Brook Jeffrey P. Severinghaus Niels Reeh

Abstract Horizontal ice-core sites, where ancient ice is exposed at the glacier surface, offer unique opportunities for paleo-studies of trace components requiring large sample volumes. Following previous work at the Pâkitsoq ice margin in West Greenland, we use a combination of geochemical parameters measured in the ice matrix (δ 18 O ice ) and air occlusions (δ 18 O atm , δ 15 N of N 2 and methane concentration) to date ice layers from specific climatic intervals. The data presented here expand our understanding of the stratigraphy and three-dimensional structure of ice layers outcropping at Pâkitsoq. Sections containing ice from every distinct climatic interval during Termination I, including Last Glacial Maximum, Bølling/Allerød, Younger Dryas and the early Holocene, are identified. In the early Holocene, we find evidence for climatic fluctuations similar to signals found in deep ice cores from Greenland. A second glacial–interglacial transition exposed at the extreme margin of the ice is identified as another outcrop of Termination I (rather than the onset of the Eemian interglacial as postulated in earlier work). Consequently, the main structural feature at Pâkitsoq is a large-scale anticline with accordion-type folding in both exposed sequences of the glacial–Holocene transition, leading to multiple layer duplications and age reversals.

Ice core

Eemian

10.3189/002214309788816704

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Citations (20)

ICE CORE RECORDS | Ice Margin Sites

Elsevier eBooks (2007)

Niels Reeh

Ice core

Ice divide

Ice-sheet model

Margin (machine learning)

Fast ice

10.1016/b0-44-452747-8/00347-1

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Microclimate, spectral reflectance and energy-balance on the Storstrømmen glacier

Carl Egede Bøggild Hans Oerter Niels Reeh Frederik Jung‐Rothenhäusler

Microclimate

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Mass balance and ice dynamics of the North-East Greenland ice sheet margin

Niels Reeh Hans Oerter Carl Egede Bøggild

Greenland ice sheet

Ice-sheet model

Margin (machine learning)

Glacier mass balance

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Citations (1)

A Plasticity Theory Approach to the Steady-State Shape of a Three-Dimensional Ice Sheet

Journal of Glaciology (1982)

Niels Reeh

Abstract The differential equation determining the elevations of a perfectly plastic three-dimensional steady-state ice sheet is set up. Analytical solutions of the equation are obtained in two simple case, (1) an ice sheet on a horizontal base with an arbitrary edge curve, and (2) an ice sheet on a plane sloping base with a rectilinear ice margin. The solutions are discussed, particularly with reference to the development of ice divides and ice streams. For arbitrary base and ice-margin geometries, solutions are obtained by means of the method of characteristics, which reduces the problem to solving simultaneously three ordinary first-order differential equations. The integration, which is performed by numerical methods, is generally commenced at the ice margin, where the necessary boundary conditions are known. The method has been applied to model the elevation contours and the flow pattern of the central Greenland ice sheet, using the bottom topography revealed by radio echo soundings and the present ice margin geometry. The result is in surprisingly good agreement with our knowledge of the ice-sheet topography and flow pattern, all significant ice divides and ice streams being reproduced. This suggests, that the method can be applied to model the shape and flow pattern of ice sheets under glacial conditions, using information about former ice-margin positions.

Ice divide

Pressure ridge

Ice-sheet model

Fast ice

Margin (machine learning)

10.1017/s0022143000005049

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Citations (53)

A Flow-line Model for Calculating the Surface Profile and the Velocity, Strain-rate, and Stress Fields in an Ice Sheet

Journal of Glaciology (1988)

Niels Reeh

Abstract A flow-line model is presented for calculating the surface profile and the velocity, strain-rate, and stress fields in an ice sheet with given base-elevation profile, ice thickness at the dome (divide), flow-law parameters, mass-balance distribution, and convergence/divergence conditions along the flow line. The model, which is based on a “quasi-similarity” hypothesis as regards the horizontal velocity-depth profiles, accounts for changes along the flow line in the depth distributions of temperature, normal stress deviators, and possible enhanced flow of deep ice of Wisconsin origin. A curvilinear coordinate system is applied with horizontal axes along flow lines and surface-elevation contours, respectively. The flow equations are reduced to two differential equations, one for the surface-elevation profile, and the other for a profile function that determines the depth distributions of velocities and strain-rates. The two equations are coupled through a profile parameter that communicates the influence of velocity-profile changes to the surface-profile equation. It is shown that the variation along the flow line of this parameter should also be considered when deriving flow-law parameters from ice-sheet flow-line data. For a symmetric dome, explicit expressions are derived for the depth distributions of the vertical velocity, strain-rates, and stresses. The strain-rate profiles display an inflection about half-way down the ice sheet, and, in the case of isothermal ice, have surface values 2.2 times their depth-averaged values. The depth distribution of the vertical velocity indicates that a relatively thick layer of almost stagnant ice is present at the ice-sheet base below a dome.

Inflection point

Flow line

10.3189/s0022143000009059

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Citations (20)

Past and present energy-balance studies of Northeast Greenland

Carl Egede Bøggild Niels Reeh Hans Oerter

Greenland ice sheet

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The subglacial cavity and implied dynamics under Nioghalvfjerdsfjorden Glacier, NE‐Greenland

Geophysical Research Letters (2000)

Christoph Mayer Niels Reeh Frederik Jung‐Rothenhäusler Philippe Huybrechts Hans Oerter

Seismic depth soundings on Nioghalvfjerdsfjorden Glacier (NFG), NE Greenland, reveal an overdeepened trough under the floating glacier. The maximum depth of the trough reaches more than 900 m below sea level. Mass balance calculations indicate considerable ice loss due to strong subglacial melting with a mean melt rate of 8 m a −1 . The geometry of the cavity and water mass characteristics from CTD measurements suggest the existence of a well defined regional circulation system. Warm, saline and rather dense water follows the inward inclining basal slope through the deep valley of Dijmphna Sund towards the grounding line. Shallow ridges at the eastern glacier front prevent this water mass entering from that direction. The comparatively cold, fresh and less dense melt water follows the subglacial ice topography leaving the cavity through the gaps towards the east. The abundance of subglacial melt water east of NFG is most probably one of the main reasons for the semi permanent sea ice cover in this region. Cold water masses upwelling in the Northeast Water Polynia and detected by satellite remote sensing are very likely influenced and modified by the subglacial melt water production.

Trough (economics)

Glacier ice accumulation

Glacier morphology

Circumpolar deep water

10.1029/2000gl011514

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Citations (89)