The influence of Totten Glacier on the Late Cenozoic sedimentary record

2020 ◽  
Vol 32 (4) ◽  
pp. 288-300 ◽  
Author(s):  
Federica Donda ◽  
German Leitchenkov ◽  
Giuliano Brancolini ◽  
Roberto Romeo ◽  
Laura De Santis ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Coastal Region ◽  
Late Cenozoic ◽  
Seismic Profiles ◽  
Continental Rise ◽  
Evolutionary Step ◽  
Progressive Growth ◽  
International Ocean Discovery Program ◽  
Channel Levees

AbstractAnalysis of multichannel seismic profiles collected on the continental rise off the Sabrina Coast, East Antarctica, has allowed the determination of the acoustic features that are indicative of major evolution steps of the East Antarctic Ice Sheet (EAIS) and highlights the role of meltwater that originated from Totten Glacier in shaping the margin architecture. The arrival of marine-terminating glaciers into the coastal region was recorded by an enhanced sediment input on the continental rise and the nucleation of channel-levees. Downslope sedimentary processes were dominant throughout the Late Cenozoic, testifying to the progressive growth of a highly dynamic, temperate ice sheet on the continent. The last evolutionary step marks the transition to when a full polar glacial regime occurred. The development of a prograding wedge with steeply dipping foresets on the continental shelf and slope exemplifies sedimentation at this time. Other sub-sea-floor observations indicate that downslope fluxes, triggered by glacial meltwater, were still able to deeply erode and deliver sediments to the rise area. This study's findings have led to the identification of expanded and well-preserved sedimentary successions, which we suggest should be considered as priority targets for future International Ocean Discovery Program deep drilling due to the sensitivity of the ice sheet in this area.

scholarly journals The Determination of Snow Albedo from Satellite Measurements Using Fast Atmospheric Correction Technique

2020 ◽  
Vol 12 (2) ◽  
pp. 234 ◽  
Author(s):  
Alexander Kokhanovsky ◽  
Jason E. Box ◽  
Baptiste Vandecrux ◽  
Kenneth D. Mankoff ◽  
Maxim Lamare ◽  
...  
Keyword(s):  
Atmospheric Correction ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Correction Algorithm ◽  
Satellite Measurements ◽  
Snow Albedo ◽  
Single View ◽  
French Alps ◽  
Correction Technique

We present a simplified atmospheric correction algorithm for snow/ice albedo retrievals using single view satellite measurements. The validation of the technique is performed using Ocean and Land Colour Instrument (OLCI) on board Copernicus Sentinel-3 satellite and ground spectral or broadband albedo measurements from locations on the Greenland ice sheet and in the French Alps. Through comparison with independent ground observations, the technique is shown to perform accurately in a range of conditions from a 2100 m elevation mid-latitude location in the French Alps to a network of 15 locations across a 2390 m elevation range in seven regions across the Greenland ice sheet. Retrieved broadband albedo is accurate within 5% over a wide (0.5) broadband albedo range of the (N = 4155) Greenland observations and with no apparent bias.

XXV.—The Determination of Temperature Gradients over the Greenland Ice Sheet by Optical Methods

1957 ◽  
Vol 64 (4) ◽  
pp. 381-397
Author(s):  
R. A. Hamilton
Keyword(s):  
Temperature Gradient ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temperature Gradients ◽  
Lower Atmosphere ◽  
Optical Methods ◽  
Snow Surface ◽  
Vertical Angle ◽  
Gradient Measurements

SynopsisThe temperature gradient in the lower atmosphere can be directly determined by measuring the optical refractive index of the air. This method is suitable for use on the Greenland ice sheet where errors introduced by water vapour are small, and where the strong solar radiation reflected by the snow surface makes it difficult to measure temperature differences over height differences of about I metre.The refraction was measured by observing the apparent vertical angle of each of a set of targets at distances up to 4 km. from a theodolite. The refraction was found to vary linearly with the distance of the target. The true vertical angle to the targets was determined when a second theodolite was available and reciprocal sights could be taken with it from the site of target to the fixed theodolite. The true vertical angle varied with time due to slow descent of the theodolite as the firn slumped; a correction for this was made. The standard error of the temperature gradient measurements was about 1.5 × 10−2 C.° per metre. It is considered that the method could be developed and improved so that over a range of only 100 metres temperature gradients could be measured to an accuracy of about 0·1° C. per metre.

scholarly journals The relative roles of CO<sub>2</sub> and palaeogeography in determining Late Miocene climate: results from a terrestrial model-data comparison

2012 ◽  
Vol 8 (2) ◽  
pp. 715-786 ◽  
Author(s):  
C. D. Bradshaw ◽  
D. J. Lunt ◽  
R. Flecker ◽  
U. Salzmann ◽  
M. J. Pound ◽  
...  
Keyword(s):  
Late Miocene ◽  
Ice Sheet ◽  
Co2 Concentration ◽  
Model Data ◽  
Data Comparison ◽  
Fully Coupled

Abstract. The Late Miocene (∼11.6–5.3 Ma) palaeorecord provides evidence for a warmer and wetter climate than that of today and there is uncertainty in the palaeo-CO2 record of at least 150 ppmv. We present results from fully coupled atmosphere-ocean-vegetation simulations for the Late Miocene that examine the relative roles of palaeogeography (topography and ice sheet geometry) and CO2 concentration in the determination of Late Miocene climate through comprehensive terrestrial model-data comparisons. Assuming that the data accurately reflects the Late Miocene climate, and that the Late Miocene palaeogeographic reconstruction used in the model is robust, then results indicate that the proxy-derived precipitation differences between the Late Miocene and modern can be largely accounted for by the palaeogeographic changes alone. However, the proxy-derived temperatures differences between the Late Miocene and modern can only begin to be accounted for if we assume a palaeo-CO2 concentration towards the higher end of the range of estimates.

scholarly journals Impact of sea-level fluctuations on the sedimentation patterns of the SE African margin: implications for slope instability

2019 ◽  
Vol 500 (1) ◽  
pp. 267-276 ◽  
Author(s):  
Aaron Micallef ◽  
Aggeliki Georgiopoulou ◽  
Andrew Green ◽  
Vittorio Maselli
Keyword(s):  
South Africa ◽  
Sea Level ◽  
Coastal Region ◽  
Passive Margin ◽  
Slope Instability ◽  
Bottom Current ◽  
The South ◽  
Sea Level Fluctuations ◽  
International Ocean Discovery Program ◽  
Seismic Reflection Profiles

AbstractThe sheared-passive margin offshore Durban (South Africa) is characterized by a narrow continental shelf and steep slope hosting numerous submarine canyons. Supply of sediment to the margin is predominantly terrigenous, dominated by discharge from several short but fast-flowing rivers. International Ocean Discovery Program Expedition 361 provides a unique opportunity to investigate the role of sea-level fluctuations on the sedimentation patterns and slope instability along the South African margin. We analysed >300 sediment samples and downcore variations in P-wave, magnetic susceptibility, bioturbation intensity and bulk density from site U1474, as well as regional seismic reflection profiles to: (1) document an increase in sand input since the Mid-Pliocene; (2) associate this change to a drop in sea-level and extension of subaerial drainage systems towards the shelf-edge; (3) demonstrate that slope instability has played a key role in the evolution of the South Africa margin facing the Natal Valley. Furthermore, we highlight how the widespread occurrence of failure events reflects the tectonic control on the morphology of the shelf and slope, as well as bottom-current scour and instability of fan complexes. This information is important to improve hazard assessment in a populated coastal region with growing offshore hydrocarbon activities.

scholarly journals Internal ice-sheet radar layer profiles and their relation to reflection mechanisms between Dome C and the Transantarctic Mountains

2001 ◽  
Vol 47 (157) ◽  
pp. 205-212 ◽  
Author(s):  
Martin J. Siegert ◽  
Shuji Fujita
Keyword(s):  
Accurate Determination ◽  
Ice Sheet ◽  
Radar Data ◽  
Internal Reflection ◽  
Frequency Data ◽  
Dual Frequency ◽  
Simple Method ◽  
Antarctic Research ◽  
Transantarctic Mountains

AbstractCauses of ice-sheet layering at ice depths greater than about 900 mina transect between Dome C and the Transantarctic Mountains are examined using 60 MHz radar data, collected in the 1970s by the U.K.–U.S.–Danish collaboration. Normally, a dual-frequency technique is required for accurate determination of internal reflection mechanisms. However, by extracting the depth-related features of 60 MHz radar profiles and comparing them with the dual-frequency data collected by the Japanese Antarctic Research Expedition, we have identified a simple method to estimate internal reflection mechanisms. Two zones can be distinguished: (1) the CA zone, where change in electrical conductivity due to variation in acidity is the major cause of internal reflection, and (2) the PCOF zone, where change in dielectric permittivity due to crystal-orientation fabrics is the major cause of internal reflections. Our analysis shows that the radar data reveal the development of PCOF zones in regions where large amounts of ice shearing are expected. This analysis shows how a similar interpretation of the full radar-data archive may reveal information on internal reflection mechanisms across a large part of the East Antarctic ice sheet.

scholarly journals Accumulation in Antarctica and Greenland derived from passive-microwave data: a comparison with contoured compilations

1995 ◽  
Vol 21 ◽  
pp. 123-130 ◽  
Author(s):  
H. Jay Zwally ◽  
MARIO B. Giovinetto
Keyword(s):  
Field Data ◽  
Grid Point ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Hyperbolic Function ◽  
West Antarctica ◽  
The Mean ◽  
The Antarctic ◽  
Mass Accumulation

The annual rate of net mass accumulation at the surface in the Antarctic and Greenland ice sheets is determined from firn emissivity based on Nimbus-5 ESMR and Nimbus-7 THIR data. In this study the determinations are limited to the areas of dry-snow facies and are based on a hyperbolic function of emissivity. Two coefficients of the function are selected for particular regions of each ice sheet after a comparison with field data selected for their reliability (82 stations in East Antarctica, 69 stations in West Antarctica and 89 stations in Greenland). Derived accumulation values are produced for grid-point locations 100 km apart which cover 56–94% of the dry-snow areas and 32–58% of the accumulation areas of each ice sheet. These values are compared with interpolated values obtained from the latest contoured compilations of field data. The means of derived values for East and West Antarctica are 12% and 39% larger, respectively, than the mean obtained from interpolated values, suggesting that the isopleth patterns as drawn in the compilation of field data lead to underestimates. The mean of derived values for Greenland is 5% smaller than the mean obtained from interpolated values, suggesting that the compilation of field data may lead to small overestimates that are within the error of determination and the variability of accumulation. Improving facies zonation and the determination of coefficients for the areas of upper percolation facies should improve these preliminary assessments.

scholarly journals Experimental Determination of the Buckling Loads of Floating Ice Sheets

1983 ◽  
Vol 4 ◽  
pp. 260-265 ◽  
Author(s):  
D. S. Sodhi ◽  
F. D. Haynes ◽  
K. Kato ◽  
K. Hirayama
Keyword(s):  
Experimental Data ◽  
Boundary Conditions ◽  
Experimental Determination ◽  
Characteristic Length ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Experimental Results ◽  
Buckling Loads ◽  
Data Points

Experiments were performed to determine the forces required to buckle a floating ice sheet pushing against structures of different widths. The characteristic length of each ice sheet was determined to enable a comparison to be made between the theoretical and experimental results.Most of the experimental data points are within the range of the theoretical values of normalized buckling loads for frictionless and hinged boundary conditions, which represent the extreme situations for ice-structure contact. Thus, the agreement between the theoretical and experimental buckling loads is considered to be good. Photographs of the buckled ice sheets show a resemblance to the theoretical mode of buckling.

scholarly journals Experimental Determination of the Buckling Loads of Floating Ice Sheets

1983 ◽  
Vol 4 ◽  
pp. 260-265 ◽  
Author(s):  
D. S. Sodhi ◽  
F. D. Haynes ◽  
K. Kato ◽  
K. Hirayama
Keyword(s):  
Experimental Data ◽  
Boundary Conditions ◽  
Experimental Determination ◽  
Characteristic Length ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Experimental Results ◽  
Buckling Loads ◽  
Data Points

Experiments were performed to determine the forces required to buckle a floating ice sheet pushing against structures of different widths. The characteristic length of each ice sheet was determined to enable a comparison to be made between the theoretical and experimental results. Most of the experimental data points are within the range of the theoretical values of normalized buckling loads for frictionless and hinged boundary conditions, which represent the extreme situations for ice-structure contact. Thus, the agreement between the theoretical and experimental buckling loads is considered to be good. Photographs of the buckled ice sheets show a resemblance to the theoretical mode of buckling.

scholarly journals Evaluation of sperm quality of Erythrolamprus poecilogyrus sublineatus (Cope, 1860) (Serpentes, Dipsadidae)

2017 ◽  
Vol 77 (3) ◽  
pp. 553-557
Author(s):  
A. C. Silva ◽  
A. S. Varela Junior ◽  
T. F. Cardoso ◽  
E. F. Silva ◽  
D. Loebmann ◽  
...  
Keyword(s):  
Sperm Quality ◽  
Membrane Integrity ◽  
Coastal Region ◽  
Rio Grande ◽  
Rio Grande Do Sul ◽  
Sperm Analysis ◽  
Pampa Region

Abstract Erythrolamprus poecilogyrus sublineatus (Cope, 1860), is a species widely distributed in the Pampa Domain, occurring in Rio Grande do Sul, Argentina and Uruguay, mainlyin the pampa region. In the coastal region of southern Brazil this is serpent is considered one of the most abundant. The purpose of the present study is to describe the techniques of sperm evaluation in vitro for E. poecilogyrus sublineatus in the coastal plain of Rio Grande do Sul, Brazil. After laparatomy the efferent vases were collected and the semen was diluted in 1ml Beltsville Thawing Solution. The characteristics of motility, membrane integrity, mitochondria, acrosome, DNA, cell viability and cellular functionality were evaluated. Fluorescent probes were used for the evaluation of sperm structure in epifluorescence microscope. With the techniques described, it was possible to identify intact and injured cells, enabling the determination of cell characteristics for the spring season (October and November). It was observed in the analyses that 80% of sperm cells were mobile and that 84.1 ± 8.0% of sperm membranes were intact. The standards found were of 48 ± 13.8% of intact acrosome, 73.6 ± 6.0 of perfect DNA and of 91.8 ± 4.0 of functional mitochondria. Thus, these values from the sperm analysis can be used as standards for the species Erythrolamprus poecilogyrus sublineatus.

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