scholarly journals On the Joint Interpretation of Total Gas Contents and Stable Isotope Ratios in Ice Cores

1982 ◽  
Vol 3 ◽  
pp. 152-155 ◽  
Author(s):  
D. Jenssen ◽  
U. Radok
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Temperature History ◽  
Recent Analysis ◽  
Algebraic Expression ◽  
Linear Relationships ◽  
Ice Sheet Modeling ◽  
History Of ◽  
Joint Interpretation ◽  
Climatic History

Total gas contents of ice cores together with temperature estimates derived from 180/160 and 2D/1H values have been used to separate topographic and climatic changes in the deposition temperature history of the ice (Raynaud 1977, Jenssen 1978). The most recent analysis (Jenssen in press) made use of two linear relationships (one purely empirical, the other established empirically but subsequently justified theoretically) to derive an algebraic expression for the change of surface temperature with ice-sheet elevation. A physical line of reasoning is presented which instead infers the climatic history from changes in the surface topography of the ice sheet. This suggests that a complete interpretation of core data must go hand in hand with ice-sheet modeling.

scholarly journals On the Joint Interpretation of Total Gas Contents and Stable Isotope Ratios in Ice Cores

1982 ◽  
Vol 3 ◽  
pp. 152-155 ◽  
Author(s):  
D. Jenssen ◽  
U. Radok
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Temperature History ◽  
Recent Analysis ◽  
Algebraic Expression ◽  
Linear Relationships ◽  
Ice Sheet Modeling ◽  
History Of ◽  
Joint Interpretation ◽  
Climatic History

Total gas contents of ice cores together with temperature estimates derived from 180/160 and 2D/1H values have been used to separate topographic and climatic changes in the deposition temperature history of the ice (Raynaud 1977, Jenssen 1978). The most recent analysis (Jenssen in press) made use of two linear relationships (one purely empirical, the other established empirically but subsequently justified theoretically) to derive an algebraic expression for the change of surface temperature with ice-sheet elevation. A physical line of reasoning is presented which instead infers the climatic history from changes in the surface topography of the ice sheet. This suggests that a complete interpretation of core data must go hand in hand with ice-sheet modeling.

Greenland Ice Sheet History Since the Last Glaciation

1974 ◽  
Vol 4 (4) ◽  
pp. 429-440 ◽  
Author(s):  
Norman W. Ten Brink ◽  
Anker Weidick
Keyword(s):  
Average Rate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Large Area ◽  
West Greenland ◽  
Last Glaciation ◽  
History Of ◽  
Inland Ice

The position of the Inland Ice margin during the late Wisconsin-Würm glaciation (ca. 15,000 yr BP) is probably marked by offshore banks (submarine moraines?) in the Davis Strait. The history of the Inland Ice since the late Wisconsin-Würm can be divided into four principal phases: (1) Relatively slow retreat from the offshore banks occurred at an average rate of approximately 1 km/100 yr until ca. 10,000 yr BP (Younger Dryas?) when the Taserqat moraine system was formed by a readvance. (2) At ca. 9500 yr BP, the rate of retreat increased markedly to about 3 km/100 yr, and although nearly 100 km of retreat occurred by ca. 6500 yr BP, it was punctuated by frequent regional reexpansions of the Inland Ice that formed extensive moraine systems at ca. 8800-8700 yr BP (Avatdleq-Sarfartôq moraines), 8400-8100 yr BP (Angujârtorfik-Fjord moraines), 7300 yr BP (Umîvît moraines), and 7200-6500 yr BP (Keglen-Mt, Keglen moraines). (3) Between 6500 and 700 yr BP, discontinous ice-margin deposits and ice-disintegration features were formed during retreat, which may have continued until the ice margin was near or behind its present position by ca. 6000 yr BP. Most of the discontinuous ice-margin deposits occur within 5–10 km of the present ice margin, and may have been formed by two main phases of readvance at ca. 4800-4000 yr BP and 2500-2000 yr BP. (4) Since a readvance at ca. 700 yr BP, the Inland Ice margin has undergone several minor retreats and readvances resulting in deposition of numerous closely spaced moraines within about 3 km of the present ice margin. The young moraines are difficult to correlate regionally, but several individual moraines have the following approximate ages: A.D. 1650, 1750, and 1880–1920.Inland Ice fluctuations in West Greenland were very closely paralleled by Holocene glacial events in East Greenland and the eastern Canadian Arctic. Such similarity of glacier behavior over a large area strongly suggests that widespread climatic change was the direct cause of Holocene glacial fluctuations. Moreover, historical advances of the Inland Ice margin followed slight temperature decreases by no more than a few decades, and 18O data from Greenland ice cores show that slight temperature decreases occurred frequently throughout the Holocene. Therefore, we conclude that construction of the major Holocene moraine systems in West Greenland was caused by slight temperature decreases, which decreased rates of ablation and thereby produced practically immediate advances of the ice sheet margin, but did not necessarily affect the long-term equilibrium of the ice sheet.

Antarctic ice volume for the last 740 ka calculated with a simple ice sheet model

2005 ◽  
Vol 17 (2) ◽  
pp. 281-287 ◽  
Author(s):  
J. OERLEMANS
Keyword(s):  
Sea Level ◽  
Deep Sea ◽  
Relative Phase ◽  
Ice Sheet ◽  
Ice Cores ◽  
Temperature History ◽  
Glacial Cycle ◽  
Ice Volume ◽  
The Antarctic ◽  
And Sea Level

Fluctuations in the volume of the Antarctic ice sheet for the last 740 ka are calculated by forcing a simple ice sheet model with a sea-level history (from a composite deep sea δ18O record) and a temperature history (from the Dome C deuterium record). Antarctic ice volume reaches maximum values of about 30 × 1015 m3, 3 to 8 ka after glacial maxima [defined as maximum values of the deep sea δ18O record]. Minimum values of ice volume reached in the course of interglacial periods are about 26 × 1015 m3. Most of the time the temperature forcing (larger accumulation) and sea-level forcing (grounding-line retreat) tend to have competing effects. However, towards the end of a glacial cycle, when temperature rises and sea-level is still relatively low, the ice volume reaches a peak. The peak value is very sensitive to the relative phase of the sea-level forcing with respect to the temperature forcing. This is further studied by looking at the response of the model to purely periodic forcings with different relative phase. The large sensitivity of ice sheet size to the phase of the forcings may have some implications for dating of deep ice cores. Care has to be taken by using anchor points from the deep sea record.

scholarly journals Large-scale ice-sheet modelling as a means of dating deep ice cores in Greenland

1997 ◽  
Vol 43 (144) ◽  
pp. 307-310 ◽  
Author(s):  
Ralf Greve
Keyword(s):  
Surface Temperature ◽  
Large Scale ◽  
Piecewise Linear ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Temperature History ◽  
Geothermal Heat ◽  
Annual Layer

Abstract The three-dimensional ice-sheet model SICOPOLIS is used to simulate the dynamic/thermody namic behaviour of the entire Greenland ice sheet from 250 000 a BP until today. External forcing consists of a surface-temperature history constructed from δ18O data of the GRIP core, a snowfall history coupled linearly to that of the surface temperature, a piecewise linear sea-level scenario and a constant geothermal heat flux. The simulated Greenland ice sheet is investigated in the vicinity of Summit, the position where the maximum elevation is taken, and where the two drill sites GRIP and GISP2 are situated 28km apart from each other. In this region, the agreement between modelled and observed topography and ice temperature turns out to be very good. Computed age-depth profiles for GRIP and GISP2 are presented, which can he used to complete the dating of these cores in the deeper regions where annual-layer counting is not possible. However, artificial diffusion influences the computed ages in a near-basal boundary layer of approximately 15% of the ice thickness, so that the age at the bottom of the cores cannot be predicted yet.

scholarly journals Variability of black carbon deposition to the East Antarctic Plateau, AD 1800–2000

2011 ◽  
Vol 11 (11) ◽  
pp. 31091-31114 ◽  
Author(s):  
M. M. Bisiaux ◽  
R. Edwards ◽  
J. R. McConnell ◽  
M. R. Albert ◽  
H. Anschütz ◽  
...  
Keyword(s):  
Black Carbon ◽  
Geometric Mean ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Antarctic Ice Sheet ◽  
Decadal Scale ◽  
History Of ◽  
Aerosol Emissions

Abstract. Refractory black carbon aerosols (rBC) from biomass burning and fossil fuel combustion are deposited to the Antarctic ice sheet and preserve a history of emissions and long-range transport from low latitudes. Antarctic ice core rBC records may thus provide information with respect to past combustion aerosol emissions and atmospheric circulation. Here, we present six East Antarctic ice core records of rBC concentrations and fluxes covering the last two centuries with approximately annual resolution (cal. yr. 1800 to 2000). The ice cores were drilled in disparate regions of the high East Antarctic ice sheet, at different elevations and net snow accumulation rates. Annual rBC concentrations were log-normally distributed and geometric means of annual concentrations ranged from 0.10 to 0.18 μg kg−1. Average rBC fluxes were determined over the time periods 1800 to 2000 and 1963 to 2000 and ranged from 3.4 to 15.5 μg kg−1 m−2 a−1 and 3.6 to 21.8 μg kg−1 m−2 a−1 respectively. Geometric-mean concentrations spanning 1800 to 2000 increased linearly with elevation at a rate of 0.025 μg kg−1/500 m. Spectral analysis of the records revealed significant decadal scale variability, which at several sites was comparable to decadal ENSO variability.

scholarly journals Spatial and temporal oxygen isotope variability in northern Greenland – implications for a new climate record over the past millennium

2015 ◽  
Vol 11 (3) ◽  
pp. 2341-2388
Author(s):  
S. Weißbach ◽  
A. Wegner ◽  
T. Opel ◽  
H. Oerter ◽  
B. M. Vinther ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Signal To Noise Ratio ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Ice Age ◽  
Temperature History ◽  
Mean Values ◽  
The North ◽  
North Greenland

Abstract. We present for the first time all 12 δ18O records obtained from ice cores drilled in the framework of the North Greenland Traverse (NGT) between 1993 and 1995 in northern Greenland between 74 to 80° N, 36 to 49° W and 2000 to 3200 m a.s.l. The cores cover an area of 680 km × 317 km, ~200 000 km2 or 10 % of the area of Greenland. Depending on core length (100–175 m) and accumulation rate (90–200 kg m−2 a−1) the records reflect an isotope-temperature history over the last 500–1100 years. The δ18O signal in northern Greenland is influenced by temperature, accumulation and the topography of the North Greenland ice sheet between 72 and 80° N. About 12 % of the variability can be attributed to the position of the single drill sites in relation to the ice sheet topography. Lowest δ18O mean values occur north of summit and east of the main divide. In general, ice cores drilled on the main ice divide show different results than those drilled east of the main ice divide that might be influenced by secondary regional moisture sources. A stack of all 12 NGT records and the NGRIP record is presented with improved signal-to-noise ratio. This stack represents the mean δ18O signal for northern Greenland that is interpreted as proxy for temperature. Our northern Greenland δ18O stack indicates isotopically enriched periods compared to their average during medieval times, about 1420 ± 20 AD and from 1870 AD onwards. The period between 1420 AD and 1850 AD was isotopically depleted compared to the average for the entire millennium and represents the Little Ice Age. The 20th century has isotopic values higher than the 1000 years mean and is comparable to the medieval period but lower than about 1420 AD.

scholarly journals A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century

2021 ◽  
Vol 118 (13) ◽  
pp. e2021442118
Author(s):  
Andrew J. Christ ◽  
Paul R. Bierman ◽  
Joerg M. Schaefer ◽  
Dorthe Dahl-Jensen ◽  
Jørgen P. Steffensen ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Plant Macrofossils ◽  
Early Pleistocene ◽  
Last Interglacial ◽  
Stratigraphic Record ◽  
History Of ◽  
And Behavior

Understanding the history of the Greenland Ice Sheet (GrIS) is critical for determining its sensitivity to warming and contribution to sea level; however, that history is poorly known before the last interglacial. Most knowledge comes from interpretation of marine sediment, an indirect record of past ice-sheet extent and behavior. Subglacial sediment and rock, retrieved at the base of ice cores, provide terrestrial evidence for GrIS behavior during the Pleistocene. Here, we use multiple methods to determine GrIS history from subglacial sediment at the base of the Camp Century ice core collected in 1966. This material contains a stratigraphic record of glaciation and vegetation in northwestern Greenland spanning the Pleistocene. Enriched stable isotopes of pore-ice suggest precipitation at lower elevations implying ice-sheet absence. Plant macrofossils and biomarkers in the sediment indicate that paleo-ecosystems from previous interglacial periods are preserved beneath the GrIS. Cosmogenic 26Al/10Be and luminescence data bracket the burial of the lower-most sediment between <3.2 ± 0.4 Ma and >0.7 to 1.4 Ma. In the upper-most sediment, cosmogenic 26Al/10Be data require exposure within the last 1.0 ± 0.1 My. The unique subglacial sedimentary record from Camp Century documents at least two episodes of ice-free, vegetated conditions, each followed by glaciation. The lower sediment derives from an Early Pleistocene GrIS advance. 26Al/10Be ratios in the upper-most sediment match those in subglacial bedrock from central Greenland, suggesting similar ice-cover histories across the GrIS. We conclude that the GrIS persisted through much of the Pleistocene but melted and reformed at least once since 1.1 Ma.

scholarly journals Large-scale ice-sheet modelling as a means of dating deep ice cores in Greenland

1997 ◽  
Vol 43 (144) ◽  
pp. 307-310
Author(s):  
Ralf Greve
Keyword(s):  
Surface Temperature ◽  
Large Scale ◽  
Piecewise Linear ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Temperature History ◽  
Geothermal Heat ◽  
Annual Layer

AbstractThe three-dimensional ice-sheet model SICOPOLIS is used to simulate the dynamic/thermody namic behaviour of the entire Greenland ice sheet from 250 000 a BP until today. External forcing consists of a surface-temperature history constructed from δ18O data of the GRIP core, a snowfall history coupled linearly to that of the surface temperature, a piecewise linear sea-level scenario and a constant geothermal heat flux. The simulated Greenland ice sheet is investigated in the vicinity of Summit, the position where the maximum elevation is taken, and where the two drill sites GRIP and GISP2 are situated 28km apart from each other. In this region, the agreement between modelled and observed topography and ice temperature turns out to be very good. Computed age-depth profiles for GRIP and GISP2 are presented, which can he used to complete the dating of these cores in the deeper regions where annual-layer counting is not possible. However, artificial diffusion influences the computed ages in a near-basal boundary layer of approximately 15% of the ice thickness, so that the age at the bottom of the cores cannot be predicted yet.

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