scholarly journals Investigating the potential to determine the upstream accumulation rate, using mass-flux calculations along a cross-section on a small tributary glacier in Heimefrontfjella, Dronning Maud Land, Antarctica

2004 ◽  
Vol 39 ◽  
pp. 175-180 ◽  
Author(s):  
Veijo Allan Pohjola ◽  
Jim Hedfors ◽  
Per Holmlund
Keyword(s):  
Cross Section ◽  
Catchment Area ◽  
Accumulation Rate ◽  
Surface Velocity ◽  
Velocity Data ◽  
High Accumulation ◽  
Glacier Surface ◽  
Mass Fluxes ◽  
Orographic Enhancement ◽  
Dronning Maud Land

AbstractHow well can we estimate the incoming ice flux by calculating the ice flux through a well-defined cross-section? We test this by comparing calculated ice flux out from the small glacier Bonnevie-Svendsenbreen with the measured accumulation rate integrated over the well-defined catchment area in the Sivorgfjella plateau, Dronning Maud Land, Antarctica (74˚45’ S, 11˚10’ W). The ice flux is calculated using ice-dynamical properties from an ice temperature model and the distribution of forces calculated using a force-budget model. The input we use includes velocity data of the glacier surface, combined with ice-thickness measurements. The result is an accumulation rate on the Sivorgfjella plateau of 0.50 ± 0.05 mw.e. a–1. We find that this is similar to the accumulation rate recorded by ground-penetrating radar work in the area. We therefore find the balance-flow method, in combination with the force-budget technique and ice temperature modeling, to be a useful tool for studies of mass fluxes in a catchment area. The most important source of uncertainty in these calculations is the quality and the spatial distribution of the ice surface velocity data. The high accumulation rate shows the effect of orographic enhancement on accumulation in montane areas in Antarctica.

scholarly journals Correlation dispersion as a measure to better estimate uncertainty of remotely sensed glacier displacements

2021 ◽  
Author(s):  
Bas Altena ◽  
Andreas Kääb ◽  
Bert Wouters
Keyword(s):  
Large Data ◽  
Surface Velocity ◽  
Dominant Factor ◽  
Fast Method ◽  
Imaging Data ◽  
Velocity Data ◽  
Correlation Peak ◽  
Glacier Surface ◽  
Fast Processing ◽  
Single Number

Abstract. In recent years a vast amount of glacier surface velocity data from satellite imagery has emerged based on correlation between repeat images. Thereby, much emphasis has been put on fast processing of large data volumes. The metadata of such measurements are often highly simplified when the measurement precision is lumped into a single number for the whole dataset, although the error budget of image matching is in reality not isotropic and constant over the whole velocity field. The spread of the correlation peak of individual image offset measurements is dependent on the image content and the non-uniform flow of the ice. Precise dispersion estimates for each individual velocity measurement can be important for inversion of, for instance, rheology, ice thickness and/or bedrock friction. Errors in the velocity data can propagate into derived results in a complex and exaggerating way, making the outcomes very sensitive to velocity noise and errors. Here, we present a computationally fast method to estimate the matching precision of individual displacement measurements from repeat imaging data, focussing on satellite data. The approach is based upon Gaussian fitting directly on the correlation peak and is formulated as a linear least squares estimation, making its implementation into current pipelines straightforward. The methodology is demonstrated for Sermeq Kujalleq, Greenland, a glacier with regions of strong shear flow and with clearly oriented crevasses, and Malaspina Glacier, Alaska. Directionality within an image seems to be dominant factor influencing the correlation dispersion. In our cases these are crevasses and moraine bands, while a relation to differential flow, such as shear, is less pronounced.

scholarly journals Modeling the density variation in the shallow firn layer

2004 ◽  
Vol 38 ◽  
pp. 309-313 ◽  
Author(s):  
Jun Li ◽  
H. Jay Zwally
Keyword(s):  
Temperature Gradient ◽  
Accumulation Rate ◽  
Greenland Ice Sheet ◽  
Densification Rate ◽  
High Accumulation ◽  
Overburden Pressure ◽  
Annual Variations ◽  
Transfer Processes ◽  
Temperature Conditions ◽  
Vapor Transfer

AbstractVapor-transfer theory is incorporated into a previous firn-densification model to investigate the effect of vapor-transfer processes on densification in firn within 10 m of the surface. The densification rate in the model is governed by the change of overburden pressure (determined by the accumulation rate), the firn temperature, and the temperature gradient. The time of exposure to temperature gradients at shallow depths is a critical factor determining the importance of vapor-transfer processes. In high-accumulation and high-temperature conditions such as for the Greenland ice sheet, the temperature gradient and vapor transfer are less important due to the shorter exposure times. The high summer temperatures dominate the rate of densification and annual variations in density. In low-accumulation and low-temperature conditions, such as for inland Antarctica, the vapor transfer driven by the temperature gradient has a stronger effect on the densification rate, and temperature-driven processes are less important. These factors determine both the rate of density increase with depth and the amplitudes of annual variations in density with depth.

scholarly journals Small-scale spatio-temporal characteristics of accumulation rates in western Dronning Maud Land, Antarctica

2008 ◽  
Vol 54 (185) ◽  
pp. 315-323 ◽  
Author(s):  
Helgard Anschütz ◽  
Daniel Steinhage ◽  
Olaf Eisen ◽  
Hans Oerter ◽  
Martin Horwath ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Temporal Variations ◽  
Spatial Variations ◽  
Small Scale ◽  
Accumulation Rates ◽  
Order Of Magnitude ◽  
Dronning Maud Land ◽  
Spatio Temporal ◽  
Ground Penetrating ◽  
Firn Core

AbstractSpatio-temporal variations of the recently determined accumulation rate are investigated using ground-penetrating radar (GPR) measurements and firn-core studies. The study area is located on Ritscherflya in western Dronning Maud Land, Antarctica, at an elevation range 1400–1560 m. Accumulation rates are derived from internal reflection horizons (IRHs), tracked with GPR, which are connected to a dated firn core. GPR-derived internal layer depths show small relief along a 22 km profile on an ice flowline. Average accumulation rates are about 190 kg m−2 a−1 (1980–2005) with spatial variability (1σ) of 5% along the GPR profile. The interannual variability obtained from four dated firn cores is one order of magnitude higher, showing 1σ standard deviations around 30%. Mean temporal variations of GPRderived accumulation rates are of the same magnitude or even higher than spatial variations. Temporal differences between 1980–90 and 1990–2005, obtained from two dated IRHs along the GPR profile, indicate temporally non-stationary processes, linked to spatial variations. Comparison with similarly obtained accumulation data from another coastal area in central Dronning Maud Land confirms this observation. Our results contribute to understanding spatio-temporal variations of the accumulation processes, necessary for the validation of satellite data (e.g. altimetry studies and gravity missions such as Gravity Recovery and Climate Experiment (GRACE)).

High-resolution radiocarbon dating to reconstruct last century environmental changes in the pacific island of Espiritu Santo

2021 ◽  
Author(s):  
Giorgia Camperio ◽  
Caroline Welte ◽  
S. Nemiah Ladd ◽  
Matthew Prebble ◽  
Nathalie Dubois
Keyword(s):  
High Resolution ◽  
Radiocarbon Dating ◽  
Environmental Changes ◽  
Accumulation Rate ◽  
Sediment Cores ◽  
Volcanic Eruptions ◽  
High Accumulation ◽  
Sedimentary Records ◽  
The Pacific ◽  
Rapid Accumulation

<p>Espiritu Santo is one of the 82 islands of the archipelago of Vanuatu and is the largest, highest, and most biodiverse of the insular country. Climatic changes linked to El Niño and extreme events such as cyclones and volcanic eruptions are a daily challenge in this remote area. These events can be recorded in sedimentary archives. Here we present a multi-proxy investigation of sediment cores retrieved from two small lakes located on the West coast of Espiritu Santo. Although the records span the last millennium, high-resolution radiocarbon dating of macrofossils reveals a rapid accumulation of sediment in the past 100 years. The high accumulation rate coupled with the high-resolution dating of freshwater sediments allows us to compare the <sup>14</sup>C bomb curve with the biogeochemical proxies of the sedimentary records. The results can then be validated against written and oral historical records linked with the societal perception of recent environmental changes in this vulnerable ecosystem.</p><div> <div title="Translate selected text"></div> <div title="Play"></div> <div title="Copy text to Clipboard"></div> </div>

scholarly journals Variations in the surface velocity of an alpine cirque glacier

2018 ◽  
Vol 64 (248) ◽  
pp. 969-976 ◽  
Author(s):  
J. W. SANDERS ◽  
K. M. CUFFEY ◽  
K. R. MACGREGOR ◽  
J. L. KAVANAUGH ◽  
C. F. DOW
Keyword(s):  
Water System ◽  
Heavy Rain ◽  
Temporal Variations ◽  
Surface Velocity ◽  
Channel Network ◽  
Glacier Surface ◽  
Ice Dynamics ◽  
Speed Up ◽  
Water Volumes ◽  
One Year

ABSTRACTFollowing pioneering work in Norway, cirque glaciers have widely been viewed as rigidly rotating bodies. This model is incorrect for basin-filling cirque glaciers, as we have demonstrated at West Washmawapta Glacier, a small glacier in the Canadian Rocky Mountains. Here we report observations at the same glacier that assess whether complex temporal variations of flow also occur. For parts of three summers, we measured daily displacements of the glacier surface. In one year, four short-duration speed-up events were recorded. Three of the events occurred during the intervals of warmest weather, when melt was most rapid; the fourth event occurred immediately following heavy rain. We interpret the speed-up events as manifestations of enhanced water inputs to the glacier bed and associated slip lubrication by increased water volumes and pressures. No further speed-ups occurred in the final month of the melt season, despite warm temperatures and several rainstorms; the dominant subglacial water system likely transformed from one of poorly connected cavities to one with an efficient channel network. The seasonal evolution of hydrology and flow resembles behaviors documented at other, larger temperate glaciers and indicates that analyses of cirque erosion cannot rely on simple assumptions about ice dynamics.

scholarly journals Combined measurements of Subglacial Water Pressure and Surface Velocity of Findelengletscher, Switzerland: Conclusions about Drainage System and Sliding Mechanism

1986 ◽  
Vol 32 (110) ◽  
pp. 101-119 ◽  
Author(s):  
Almut Iken ◽  
Robert A. Bindschadler
Keyword(s):  
Functional Relationship ◽  
Water Pressure ◽  
Drainage System ◽  
High Water ◽  
Water Levels ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Measured Velocity ◽  
Sliding Mechanism ◽  
Velocity Variations

AbstractDuring the snow-melt season of 1982, basal water pressure was recorded in 11 bore holes communicating with the subglacial drainage system. In most of these holes the water levels were at approximately the same depth (around 70 m below surface). The large variations of water pressure, such as diurnal variations, were usually similar at different locations and in phase. In two instances of exceptionally high water pressure, however, systematic phase shifts were observed; a wave of high pressure travelled down-glacier with a velocity of approximately 100 m/h.The glacier-surface velocity was measured at four lines of stakes several times daily. The velocity variations correlated with variations in subglacial water pressure. The functional relationship of water pressure and velocity suggests that fluctuating bed separation was responsible for the velocity variations. The empirical functional relationship is compared to that of sliding over a perfectly lubricated sinusoidal bed. On the basis of the measured velocity-pressure relationship, this model predicts a reasonable value of bed roughness but too high a sliding velocity and unstable sliding at too low a water pressure. The main reason for this disagreement is probably the neglect of friction from debris in the sliding model.The measured water pressure was considerably higher than that predicted by the theory of steady flow through straight cylindrical channels near the glacier bed. Possible reasons are considered. The very large disagreement between measured and predicted pressure suggests that no straight cylindrical channels may have existed.

scholarly journals Glacial–interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ<sup>15</sup>N measurements

2013 ◽  
Vol 9 (3) ◽  
pp. 983-999 ◽  
Author(s):  
E. Capron ◽  
A. Landais ◽  
D. Buiron ◽  
A. Cauquoin ◽  
J. Chappellaz ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Detailed Comparison ◽  
Last Deglaciation ◽  
Depth Study ◽  
Dronning Maud Land ◽  
The Last Deglaciation ◽  
Correct Estimation ◽  
Lock In

Abstract. Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial–interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML – a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas–ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model–δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

scholarly journals Carbon dynamics in boreal peatlands of the Yenisey region, western Siberia

2015 ◽  
Vol 12 (23) ◽  
pp. 7057-7070 ◽  
Author(s):  
E. D. Schulze ◽  
E. Lapshina ◽  
I. Filippov ◽  
I. Kuhlmann ◽  
D. Mollicone
Keyword(s):  
Organic Carbon ◽  
Vegetation History ◽  
Accumulation Rate ◽  
West Siberian Plain ◽  
High Accumulation ◽  
Boreal Peatlands ◽  
Constant Rate ◽  
Northern Peatlands ◽  
River Valleys ◽  
Local Hydrology

Abstract. Here we investigate the vegetation history and peat accumulation at the eastern boarder of the West Siberian Plain, near the Yenisey River, south of permafrost. In this region, peat started to accumulate 15 000 years ago as gyttja of shallow lakes in ancient river valleys. This peat is older than previously reported, mainly due to separating particulate organic carbon (POC) from dissolved organic carbon (DOC), which was 1900–6500 years younger than POC. The probability of finding peat layers older than 12 000 years is about 2 %. Peat accumulated as fen peat at a constant rate of 0.2 mm yr−1 and 0.01 kg C m−2 yr−1. The accumulation was higher in ancient river valley environments. Over the last 2000 years these bogs changed into Sphagnum mires which have accumulated up to about 0.1 kg C m−2 yr−1 until present. The long-lasting fen stage, which makes the Yenisey bogs distinct from the western Siberian bogs, is discussed as a consequence of the local hydrology. The high accumulation rate of peat in unfrozen mires is taken as an indication that thawing of permafrost peat may also change northern peatlands into long-lasting carbon sinks.

scholarly journals State of Balance of the Ice Sheet in the Antarctic Peninsula

1982 ◽  
Vol 3 ◽  
pp. 77-82 ◽  
Author(s):  
Christopher S. M. Doake
Keyword(s):  
Antarctic Peninsula ◽  
East Coast ◽  
Accumulation Rate ◽  
Level Line ◽  
Ice Shelf ◽  
High Accumulation ◽  
Glacier Recession ◽  
Valley Glacier ◽  
The Antarctic ◽  
Small Valley

Data from ice rises on the east coast of the Antarctic Peninsula can be interpreted as showing that the ice is thinning at rates of up 0.5 m a−1. However, a level line between two nunataks in Palmer Land showed no change in surface elevation over a period of 5 a. Melt rates on George VI Ice Shelf vary with position and may indicate that parts of the ice shelf are thickening at the rate of several m a−1, presumably in response to a higher accumulation rate over the peninsula a few hundred years ago. A small valley glacier, Spartan Glacier, is wasting away at about 0.27 m a−1. Ice fronts on both east and west coasts of the peninsula have been retreating for the last 30 a. It seems that there is general glacier recession in response to a wanner climate and decreased snowfall for at least the last 30 a, while parts of the peninsula are still thickening in response to a high accumulation rate several hundred years ago.

scholarly journals The Flow of a Glacier in a Channel of Rectangular, Elliptic or Parabolic Cross-Section

1965 ◽  
Vol 5 (41) ◽  
pp. 661-690 ◽  
Author(s):  
J. F. Nye
Keyword(s):  
Cross Section ◽  
Numerical Solutions ◽  
Maximum Shear Stress ◽  
Surface Velocity ◽  
Channel Section ◽  
Ice Surface ◽  
Centre Line ◽  
Symmetry Principles ◽  
Wide Range ◽  
Flow Law

AbstractNumerical solutions are found for the steady rectilinear flow of ice, obeying Glen’s non-linear flow law, down uniform cylindrical channels of rectangular, semi-elliptic and parabolic cross-section. The results are also directly applicable to the pumping of a non-Newtonian fluid down a pipe. There is assumed to be no slip of the ice on the channel surface. Certain results on the centre-line velocity in symmetrical channels may be derived purely from dimensional and symmetry principles. An analytical solution due to Dr. W. Chester is given for a semi-elliptic channel section which departs only slightly from a semi-circle. Contrary to a view sometimes held, the maximum shear stress at the ice surface in a parabolic channel and in some elliptical channels does not always occur at the edge. With the flow law, strain-rate proportional to (stress)3, the velocity averaged across the ice surface, which is easily measured with a line of stakes, is close to the average velocity over the whole section for a wide range of parabolic sections; the hydrological importance of this result is that the discharge may be inferred without the need to measure the velocity at depth. Arguments are given to show that the result still holds when there is slipping on the bed and when the power in the flow law differs somewhat from 3, Depending on the amount of bed slip and the shape of the channel section, the kinematic wave velocity for a range of parabolic channels is between 2.0 and 2.3 times the centre-line velocity of the ice, and between 2.0 and 3.5 times the mean surface velocity of the ice.

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