Late Wisconsin Ice-Surface Profile Calculated from Esker Paths and Types, Katahdin Esker System, Maine

1985 ◽  
Vol 23 (1) ◽  
pp. 27-37 ◽  
Author(s):  
Ronald L. Shreve
Keyword(s):  
Flow Line ◽  
Ice Sheets ◽  
Surface Profile ◽  
Independent Evidence ◽  
Geological Evidence ◽  
Sea Levels ◽  
Isostatic Rebound ◽  
The Past ◽  
Ice Surface ◽  
The Difference

Values of the gradient of the former ice surface can be inferred at points along a flow line from deviations of esker paths or transitions in esker type and numerically integrated to give the profile. A profile calculated in this way shows that during formation of the Katahdin esker system about 12,700 yr ago the ice thickness at distances of 10, 20, 50, 100, and 140 km from the terminus, which is about two thirds of the distance to the ice divide, was approximately 200, 300, 600, 750, and 900 m. The terminal reach was computed by assuming an unknown uniform basal drag and matching the profile to its known elevation at the terminus and known gradient 10 km upglacier. Correction for isostatic rebound based on the elevations of contemporaneous deltas and of the marine limit proved unnecessary, because the tilt due to the difference in uplift at the two ends of the profile is only 0.1 m km−1. With other plausible assumptions as to sea levels in the past, elevations of the marine limit, or exact location of the terminus the profile could be as much as roughly 100 m higher. It hits Mount Katahdin about 500 m below its summit, which is at 1600 m, in agreement with the geological evidence farther west. The steepening of the upper part of the profile suggests that the mountain dammed and diverted the ice. Basal drag computed from the profile varies from about 20 kPa (0.2 bar) near the terminus to 30 kPa (0.3 bar) at 100 km to 70 kPa (0.7 bar) at 140 km. The relatively low values away from the influence of Mount Katahdin agree with independent evidence from deep-sea cores of substantial late Wisconsin ice-sheet thinning without comparable areal reduction. The method has potential for application over wide areas that were occupied by the Laurentide and Scandinavian ice sheets.

Glacier Melting, Disaster and Awareness Programme

2016 ◽  
Vol 8 (02) ◽  
pp. 131-138
Author(s):  
Bharat Raj Singh ◽  
Amar Bahadur Singh
Keyword(s):  
Agricultural Soils ◽  
Ice Sheets ◽  
Storm Surges ◽  
Past Century ◽  
Sea Levels ◽  
Ice Caps ◽  
Ice Melt ◽  
The Past ◽  
Glacier Melting ◽  
Awareness Programme

Large ice formations, like glaciers and the polar ice caps, naturally melt back a bit each summer. But, in the winter, snows, made primarily from evaporated seawater, are generally sufficient to balance out the melting. Recently, though, persistently higher temperatures caused by global warming have led to greaterthan- average summer melting as well as diminished snowfall due to later winters and earlier springs. This imbalance results in a significant net gain in runoff versus evaporation for the ocean, causing sea levels to rise. Satellite measurements tell us that over the past century, the Global Mean Sea Level (GMSL) has risen by 4 to 8 inches (10 to 20 centimeters). However, the annual rate of rise over the past 20 years has been 0.13 inches (3.2 millimeters) a year, roughly twice the average speed of the preceding 80 years. As with glaciers and the ice caps, increased heat is causing the massive ice sheets, that cover Greenland and Antarctica to melt at an accelerated pace. Scientists also believe ice-melt water from above and seawater from below is seeping beneath Greenland's and West Antarctica's ice sheets, effectively lubricating ice streams and causing them to move more quickly into the sea. Moreover, higher sea temperatures are causing the massive ice shelves that extend out from Antarctica to melt from below, weaken, and break off. When sea levels rise rapidly, as they have been doing, even a small increase can have devastating effect on coastal habitats. As seawater reaches farther inland, it can cause destructive erosion, flooding of wetlands, contamination of aquifers and agricultural soils, and lost habitat for fish, birds, and plants. When large storms hit land, higher sea levels mean bigger, more powerful storm surges that can strip away everything in their path. In addition, hundreds of millions of people live in areas that will become increasingly vulnerable to flooding. Higher sea levels would force them to abandon their homes and relocate. Low-lying islands could be submerged completely. Thus, it needs launching of serious awareness programme through print media, electronic media to curb the glacier melting by reducing heavy consumption of hydrocarbon and focus on zero pollution researches to develop energy production alternatives.

scholarly journals Ice-Age Climate and Continental Ice Sheets: Some Experiments with A General Circulation Model

1984 ◽  
Vol 5 ◽  
pp. 100-105 ◽  
Author(s):  
S. Manabe ◽  
A. J. Broccoli
Keyword(s):  
North America ◽  
General Circulation Model ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Circulation Model ◽  
Geological Evidence ◽  
The Difference ◽  
Continental Ice Sheets

The climatic influence of the land ice which existed 18 ka BP is investigated using a climate model developed at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration. The model consists of an atmospheric general circulation model coupled with a static mixed layer ocean model. Simulated climates are obtained from each of two versions of the model: one with the land-ice distribution of the present and the other with that of 18 ka BP.In the northern hemisphere, the difference in the distribution of sea surface temperature (SST) between the two experiments resembles the difference between the SST at 18 ka BP and at present as estimated by CLIMAP Project Members (1981). In the northern hemisphere a substantial lowering of air temperature also occurs in winter, with a less pronounced cooling during summer. The mid-tropospheric flow field is influenced by the Laurentide ice sheet and features a split jet stream straddling the ice sheet and a long wave trough along the east coast of North America. In the southern hemisphere of 18 ka BP, the ice sheet has little influence on temperature. An examination of hemispheric heat balances indicates that this is because only a small change in interhemispheric heat transport exists, as the In situ radiative compensation in the northern hemisphere counterbalances the effective reflection of solar radiation by continental ice sheets.Hydrologic changes in the model climate are also found, with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in North America and Eurasia. These findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum.

scholarly journals Surface outburst of a subglacial flood from the Greenland Ice Sheet

2021 ◽  
Author(s):  
Jade Bowling ◽  
Amber Leeson ◽  
Malcolm McMillan ◽  
Stephen Livingstone ◽  
Andrew Sole ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Theoretical Models ◽  
Arctic Climate ◽  
Ice Melting ◽  
Subglacial Lake ◽  
The Past ◽  
Ice Surface ◽  
Earth’S Climate

Abstract As Earth’s climate warms, surface melting of the Greenland Ice Sheet is projected to intensify, contributing to rising sea levels1–4. Observations5–7 and theory8–10 indicate that meltwater generated at the surface of an ice sheet can drain to its bed via crevasses and moulins, where it flows relatively unhindered to the coast. This understanding of the movement of water within, and beneath, ice sheets, underpins theoretical models which are used to make projections of ice sheet change11. In this study, we show the first evidence of a disruptive drainage pathway in Greenland, whereby a subglacial flood – triggered by a draining subglacial lake – breaks through the ice sheet surface. This unprecedented outburst of water causes fracturing of the ice sheet, and the formation of 25-metre-high ice blocks. These observations reveal a complex, bidirectional coupling between the surface and basal hydrological systems of an ice sheet, which was previously unknown in Greenland. Analysis of over 30 years of satellite imagery confirms that the subglacial lake has drained at least once previously. However, on that occasion the floodwater failed to breach the ice surface. The two contrasting drainage regimes, coupled with the increased rates of ice melting and thinning that have occurred over the past three decades years, suggest that Arctic climate warming may have facilitated a new, disruptive mode of hydrological drainage on the ice sheet. As such, our observations reveal an emerging and poorly understood phenomenon, which is not currently captured in physical ice sheet models.

scholarly journals Ice-Sheet Surface Topography From Seas at Radar Altimetry (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 351
Author(s):  
H.J. Zwally ◽  
R. Bindschadler ◽  
R.H. Thomas ◽  
Tom Martin
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Surface Profile ◽  
Greenland Ice Sheet ◽  
Altimeter Data ◽  
Radar Altimeter ◽  
Antarctic Ice Sheet ◽  
Sheet Surface ◽  
Servo Tracking ◽  
The Difference

Greenland and Antarctic ice-sheet surface elevations have been obtained from Seasat radar altimeter data after computer retracking of the return waveforms. The height of the altimeter above the surface is determined from the measured time between transmission of radar pulses and their return. The altimeter servo-tracking circuit attempted to maintain the midpoint of the ramp of the return waveform in the center of 60 time gates, each equivalent to 0.47 m in range. Waveforms representing an average of 100 pulse returns were recorded each 0.1 s, corresponding to a distance interval of 662 m on the surface. Deviations of the midpoint of the waveform ramp from the central-gate position were caused by changes in range larger than the design limits of the servo-circuit, thereby producing errors in the height indicated by the altimeter. If the deviation was greater than about 25 gates (13 m range), the waveform ramp moved outside the time gates and the servo-tracking was temporarily interrupted. These larger deviations resulted in a loss of about 30% of the data over the ice sheets. Both surface undulations and the steeper slopes near the ice-sheet edge produced range velocities sufficient to cause interruption of altimeter tracking. Waveforms that remained within the 60 gates have been corrected by a computer curve-fitting procedure applied to each waveform. Preliminary contour maps of surface elevation at 100 m contour intervals have been created for much of the East Antarctic ice sheet north of 72°S and the Greenland ice sheet south of 72°N. The standard deviation of the difference in elevation at 1 032 crossover points in the retracked Greenland elevation profiles is 1.9 m, which is largely due to radial errors in determination of the satellite position. Adjustment of the radial components of the orbits to minimize the crossover differences in select regions reduces the difference to 0.25 m, which is indicative of the optimum obtainable precision over the ice sheets. This precision is comparable to the value of 0.05 to 0.10 m obtained over the oceans where waveform averages of 1 s are used. The data are sufficiently dense to permit contouring at smaller intervals (2 to 10 m) only in the regions near the maximum latitudes of ±72°. Contouring at the smaller intervals illustrates the three dimensional characteristics of some of the observed undulations. Several methods were tested for correcting slope-induced displacements, which are typical of reflection-range measurements using a wide-angle beam. The slope-induced displacement hα2/2 is about 40 m for a satellite altitude h of 800 km and a surface slope a of 10−2. In a simulation experiment, an apparent surface profile was created by computer simulation of the altimeter measurement of an actual ice-surface profile and was then corrected for slope-induced displacement. The results show that the residual error between reconstructed and actual surfaces is about 15% of the displacement. Along the sub-satellite track the data are sufficiently dense to permit such correction for along-track slope-induced displacements caused by both undulations and regional slopes, but in the other dimension the data are generally only sufficient to permit across-track correction for regional slopes.

scholarly journals Ice-Age Climate and Continental Ice Sheets: Some Experiments with A General Circulation Model

1984 ◽  
Vol 5 ◽  
pp. 100-105 ◽  
Author(s):  
S. Manabe ◽  
A. J. Broccoli
Keyword(s):  
North America ◽  
General Circulation Model ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Circulation Model ◽  
Geological Evidence ◽  
The Difference ◽  
Continental Ice Sheets

The climatic influence of the land ice which existed 18 ka BP is investigated using a climate model developed at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration. The model consists of an atmospheric general circulation model coupled with a static mixed layer ocean model. Simulated climates are obtained from each of two versions of the model: one with the land-ice distribution of the present and the other with that of 18 ka BP.In the northern hemisphere, the difference in the distribution of sea surface temperature (SST) between the two experiments resembles the difference between the SST at 18 ka BP and at present as estimated by CLIMAP Project Members (1981). In the northern hemisphere a substantial lowering of air temperature also occurs in winter, with a less pronounced cooling during summer. The mid-tropospheric flow field is influenced by the Laurentide ice sheet and features a split jet stream straddling the ice sheet and a long wave trough along the east coast of North America. In the southern hemisphere of 18 ka BP, the ice sheet has little influence on temperature. An examination of hemispheric heat balances indicates that this is because only a small change in interhemispheric heat transport exists, as the In situ radiative compensation in the northern hemisphere counterbalances the effective reflection of solar radiation by continental ice sheets.Hydrologic changes in the model climate are also found, with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in North America and Eurasia. These findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum.

scholarly journals Ice-Sheet Surface Topography From Seas at Radar Altimetry (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 351-351
Author(s):  
H.J. Zwally ◽  
R. Bindschadler ◽  
R.H. Thomas ◽  
Tom Martin
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Surface Profile ◽  
Greenland Ice Sheet ◽  
Altimeter Data ◽  
Radar Altimeter ◽  
Antarctic Ice Sheet ◽  
Sheet Surface ◽  
Servo Tracking ◽  
The Difference

Greenland and Antarctic ice-sheet surface elevations have been obtained from Seasat radar altimeter data after computer retracking of the return waveforms. The height of the altimeter above the surface is determined from the measured time between transmission of radar pulses and their return. The altimeter servo-tracking circuit attempted to maintain the midpoint of the ramp of the return waveform in the center of 60 time gates, each equivalent to 0.47 m in range. Waveforms representing an average of 100 pulse returns were recorded each 0.1 s, corresponding to a distance interval of 662 m on the surface. Deviations of the midpoint of the waveform ramp from the central-gate position were caused by changes in range larger than the design limits of the servo-circuit, thereby producing errors in the height indicated by the altimeter. If the deviation was greater than about 25 gates (13 m range), the waveform ramp moved outside the time gates and the servo-tracking was temporarily interrupted. These larger deviations resulted in a loss of about 30% of the data over the ice sheets. Both surface undulations and the steeper slopes near the ice-sheet edge produced range velocities sufficient to cause interruption of altimeter tracking. Waveforms that remained within the 60 gates have been corrected by a computer curve-fitting procedure applied to each waveform.Preliminary contour maps of surface elevation at 100 m contour intervals have been created for much of the East Antarctic ice sheet north of 72°S and the Greenland ice sheet south of 72°N. The standard deviation of the difference in elevation at 1 032 crossover points in the retracked Greenland elevation profiles is 1.9 m, which is largely due to radial errors in determination of the satellite position. Adjustment of the radial components of the orbits to minimize the crossover differences in select regions reduces the difference to 0.25 m, which is indicative of the optimum obtainable precision over the ice sheets. This precision is comparable to the value of 0.05 to 0.10 m obtained over the oceans where waveform averages of 1 s are used. The data are sufficiently dense to permit contouring at smaller intervals (2 to 10 m) only in the regions near the maximum latitudes of ±72°. Contouring at the smaller intervals illustrates the three dimensional characteristics of some of the observed undulations.Several methods were tested for correcting slope-induced displacements, which are typical of reflection-range measurements using a wide-angle beam. The slope-induced displacement hα2/2 is about 40 m for a satellite altitude h of 800 km and a surface slope a of 10−2. In a simulation experiment, an apparent surface profile was created by computer simulation of the altimeter measurement of an actual ice-surface profile and was then corrected for slope-induced displacement. The results show that the residual error between reconstructed and actual surfaces is about 15% of the displacement. Along the sub-satellite track the data are sufficiently dense to permit such correction for along-track slope-induced displacements caused by both undulations and regional slopes, but in the other dimension the data are generally only sufficient to permit across-track correction for regional slopes.

scholarly journals Predicting subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

2013 ◽  
Vol 7 (2) ◽  
pp. 1177-1213 ◽  
Author(s):  
S. J. Livingstone ◽  
C. D. Clark ◽  
J. Woodward
Keyword(s):  
Interpolation Method ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Surface ◽  
Ice Stream ◽  
The Difference ◽  
Subglacial Lakes ◽  
The Antarctic ◽  
Modelling Approach

Abstract. In this paper we use the Shreve hydraulic potential equation to predict subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. For the Antarctic Ice Sheet we are able to predict known subglacial lakes with a >70% success rate, which demonstrates the validity of this method. Despite the success in predicting known subglacial lakes the calculations produce two-orders of magnitude more lakes than are presently identified, covering 4% of the ice-sheet bed. The difference is thought to result from our poor knowledge of the bed (which has resulted in artefacts associated with the interpolation method), intrinsic errors associated with the simplified modelling approach and because thousands of subglacial lakes, particularly smaller ones, remain to be found. Applying the same modelling approach to the Greenland Ice Sheet predicts only 90 lakes under the present-day ice-sheet configuration, covering 0.2% of the bed. The paucity of subglacial lakes in Greenland is thought to be a function of steeper overall ice-surface gradients. As no lakes have currently been located under Greenland, model predictions will make suitable targets for radar surveys of Greenland to identify subglacial lakes. During deglaciation from the Last Glacial Maximum both ice sheets had more subglacial lakes at their beds, though many of these lakes have persisted to present conditions. These lakes, inherited from past ice-sheet configurations would not form under current surface conditions, suggesting a retreating ice-sheet will have many more subglacial lakes than an advancing ice sheet. This hysteresis effect has implications for ice-stream formation and flow, bed lubrication and meltwater drainage. The lake model also allows modelling of the drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Significantly, key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are shown to have been susceptible to drainage switches and capture by neighbouring networks during deglaciation thus far.

scholarly journals Climate evolution across the Mid-Brunhes Transition

2018 ◽  
Vol 14 (12) ◽  
pp. 2071-2087 ◽  
Author(s):  
Aaron M. Barth ◽  
Peter U. Clark ◽  
Nicholas S. Bill ◽  
Feng He ◽  
Nicklas G. Pisias
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
High Amplitude ◽  
Climate System ◽  
Atmospheric Co2 ◽  
Sea Levels ◽  
The Past ◽  
Climate Evolution ◽  
Monsoon Strength ◽  
Climate Variance

Abstract. The Mid-Brunhes Transition (MBT) began ∼ 430 ka with an increase in the amplitude of the 100 kyr climate cycles of the past 800 000 years. The MBT has been identified in ice-core records, which indicate interglaciations became warmer with higher atmospheric CO2 levels after the MBT, and benthic oxygen isotope (δ18O) records, which suggest that post-MBT interglaciations had higher sea levels and warmer temperatures than pre-MBT interglaciations. It remains unclear, however, whether the MBT was a globally synchronous phenomenon that included other components of the climate system. Here, we further characterize changes in the climate system across the MBT through statistical analyses of ice-core and δ18O records as well as sea-surface temperature, benthic carbon isotope, and dust accumulation records. Our results demonstrate that the MBT was a global event with a significant increase in climate variance in most components of the climate system assessed here. However, our results indicate that the onset of high-amplitude variability in temperature, atmospheric CO2, and sea level at ∼430 ka was preceded by changes in the carbon cycle, ice sheets, and monsoon strength during Marine Isotope Stage (MIS) 14 and MIS 13.

scholarly journals Climate evolution across the Mid-Brunhes Transition

2018 ◽  
Author(s):  
Aaron M. Barth ◽  
Peter U. Clark ◽  
Nicholas S. Bill ◽  
Feng He ◽  
Nicklas G. Pisias
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
High Amplitude ◽  
Climate System ◽  
Atmospheric Co2 ◽  
Sea Levels ◽  
The Past ◽  
Climate Evolution ◽  
Monsoon Strength ◽  
Climate Variance

Abstract. The Mid-Brunhes Transition (MBT) began ∼ 430 ka with an increase in the amplitude of the 100-kyr climate cycles of the past 800,000 years. The MBT has been identified in ice-core records, which indicate interglaciations became warmer with higher atmospheric CO2 levels after the MBT, and benthic oxygen isotope (δ18O) records, which suggest that post-MBT interglaciations had higher sea levels than pre-MBT interglaciations. It remains unclear, however, whether the MBT was a globally synchronous phenomenon that included other components of the climate system. Here we further characterize changes in the climate system across the MBT through statistical analyses of ice-core and δ18O records as well as sea-surface temperature, benthic carbon isotope, and dust accumulation records. Our results demonstrate that the MBT was a global event with a significant increase in climate variance in most components of the climate system assessed here. However, our results indicate that the onset of high-amplitude variability in temperature, atmospheric CO2, and sea level at ∼ 430 ka was preceded by changes in the carbon cycle, ice sheets, and monsoon strength during MIS 14 and 13.

Smart Estimation Ver-H.1.0

2018 ◽  
Author(s):  
Sigit Haryadi
Keyword(s):  
Sample Size ◽  
Confidence Level ◽  
Time Span ◽  
Regression Equation ◽  
Weight Factor ◽  
The Past ◽  
Level Of Confidence ◽  
The Future ◽  
Future Value ◽  
The Difference

We cannot be sure exactly what will happen, we can only estimate by using a particular method, where each method must have the formula to create a regression equation and a formula to calculate the confidence level of the estimated value. This paper conveys a method of estimating the future values, in which the formula for creating a regression equation is based on the assumption that the future value will depend on the difference of the past values divided by a weight factor which corresponding to the time span to the present, and the formula for calculating the level of confidence is to use "the Haryadi Index". The advantage of this method is to remain accurate regardless of the sample size and may ignore the past value that is considered irrelevant.

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