scholarly journals Pliocene-Pleistocene Orbital Cyclostratigraphy and Glacial Evolution of the East Antarctic Ice Sheet from Continental Rise IODP Site U1361, Wilkes Land Margin, East Antarctica

2021 ◽  
Author(s):  
◽  
Georgia Rose Grant
Keyword(s):  
Spectral Analysis ◽  
Late Pleistocene ◽  
Gamma Ray ◽  
Physical Property ◽  
East Antarctica ◽  
Antarctic Ice Sheet ◽  
Continental Rise ◽  
Depositional Processes ◽  
Core Site ◽  
Wilkes Land

<p>Stability of the East Antarctic Ice Sheet (EAIS), in response to the orbitally-paced cooling climate of the Late Neogene, is largely unknown. The Wilkes Land margin of East Antarctica, largely grounded below sea level, has previously been proposed to respond dynamically during the warmer climate of the Pliocene, similarly to other marine based sectors of Antarctica (i.e. West Antarctica). Sediment deposition on the Wilkes Land continental rise, recovered in Integrated Ocean Drilling Program U1361A drillcore provides a distal but continuous record of EAIS fluctuations. Changes in sedimentary depositional environments at U1361A core site, were determined through analysis of lithofacies and physical property logs: natural gamma-ray (NGR), gamma-ray attenuation bulk density (GRA), magnetic susceptibility (MS) and L* colour reflectance. NGR primarily reflected biogenic content and a synchronous relationship between NGR, GRA and MS was used to identify interglacial and glacial phases, whereby decreased NGR, GRA and MS values indicated an increase in biogenic material. L* colour reflectance was more variable through time, displayed higher frequency fluctuations and a changing relationship with the other physical property logs down core. Two depositional models, based on facies interpretations and the defined physical property relationships, were produced for the Middle Late Pleistocene (last ~550 kyr; model A) and mid-Pliocene (~4.2-3.6 Ma; model B), which represent end members. Depositional processes common to both models occurred in the intervening core, spanning the Late Pliocene-Early Pleistocene (3-1 Ma). Model A, applied to the Middle Late Pleistocene, shows that alternating diatom-rich clays to silty clays in the upper 9 m of core U1361A, reflect the large amplitude ~100 kyr paced glacial-interglacial cycles, which is confirmed by spectral analysis of the physical properties for this interval. Model B, applied to the Early Pliocene, suggest that the depositional processes recorded by facies may have been less sensitive to EAIS fluctuations, probably due to the fact that the ice margin was generally more distal to the core site during glacial-interglacial cycles of advance and retreat. Nevertheless, these more subtle changes in lithology were characterised by variations in the physical property logs, and spectral analysis of these time series implied orbital pacing was still influential on depositional processes at this time (displaying power in precession and obliquity frequencies). Spectral analysis of the physical property logs and visual correlations to the benthic δ18O stack, confirmed the 4.2-1 Ma interval was paced by ~40 kyr and implies obliquity-paced oscillations of the margin of the EAIS. Precession periodicities, significant in spectra throughout the 4.2 Myr record, are proposed to be the response of phytoplankton productivity in response to seasonal insolation controlling sea-ice extent.</p>

scholarly journals Pliocene-Pleistocene Orbital Cyclostratigraphy and Glacial Evolution of the East Antarctic Ice Sheet from Continental Rise IODP Site U1361, Wilkes Land Margin, East Antarctica

2021 ◽  
Author(s):  
◽  
Georgia Rose Grant
Keyword(s):  
Spectral Analysis ◽  
Late Pleistocene ◽  
Gamma Ray ◽  
Physical Property ◽  
East Antarctica ◽  
Antarctic Ice Sheet ◽  
Continental Rise ◽  
Depositional Processes ◽  
Core Site ◽  
Wilkes Land

<p>Stability of the East Antarctic Ice Sheet (EAIS), in response to the orbitally-paced cooling climate of the Late Neogene, is largely unknown. The Wilkes Land margin of East Antarctica, largely grounded below sea level, has previously been proposed to respond dynamically during the warmer climate of the Pliocene, similarly to other marine based sectors of Antarctica (i.e. West Antarctica). Sediment deposition on the Wilkes Land continental rise, recovered in Integrated Ocean Drilling Program U1361A drillcore provides a distal but continuous record of EAIS fluctuations. Changes in sedimentary depositional environments at U1361A core site, were determined through analysis of lithofacies and physical property logs: natural gamma-ray (NGR), gamma-ray attenuation bulk density (GRA), magnetic susceptibility (MS) and L* colour reflectance. NGR primarily reflected biogenic content and a synchronous relationship between NGR, GRA and MS was used to identify interglacial and glacial phases, whereby decreased NGR, GRA and MS values indicated an increase in biogenic material. L* colour reflectance was more variable through time, displayed higher frequency fluctuations and a changing relationship with the other physical property logs down core. Two depositional models, based on facies interpretations and the defined physical property relationships, were produced for the Middle Late Pleistocene (last ~550 kyr; model A) and mid-Pliocene (~4.2-3.6 Ma; model B), which represent end members. Depositional processes common to both models occurred in the intervening core, spanning the Late Pliocene-Early Pleistocene (3-1 Ma). Model A, applied to the Middle Late Pleistocene, shows that alternating diatom-rich clays to silty clays in the upper 9 m of core U1361A, reflect the large amplitude ~100 kyr paced glacial-interglacial cycles, which is confirmed by spectral analysis of the physical properties for this interval. Model B, applied to the Early Pliocene, suggest that the depositional processes recorded by facies may have been less sensitive to EAIS fluctuations, probably due to the fact that the ice margin was generally more distal to the core site during glacial-interglacial cycles of advance and retreat. Nevertheless, these more subtle changes in lithology were characterised by variations in the physical property logs, and spectral analysis of these time series implied orbital pacing was still influential on depositional processes at this time (displaying power in precession and obliquity frequencies). Spectral analysis of the physical property logs and visual correlations to the benthic δ18O stack, confirmed the 4.2-1 Ma interval was paced by ~40 kyr and implies obliquity-paced oscillations of the margin of the EAIS. Precession periodicities, significant in spectra throughout the 4.2 Myr record, are proposed to be the response of phytoplankton productivity in response to seasonal insolation controlling sea-ice extent.</p>

scholarly journals Ice dynamics and ocean productivity during the Late Miocene, offshore Wilkes Land, East Antarctica

2021 ◽  
Author(s):  
◽  
Rebecca Pretty
Keyword(s):  
Grain Size ◽  
Late Miocene ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ocean Current ◽  
Significant Advance ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Depositional Processes ◽  
Wilkes Land

<p>The middle Miocene Climatic Transition (~14 Ma) is commonly interpreted to represent the significant advance of the East Antarctic Ice Sheet (EAIS), and the transition to a hyper-arid climate and a stable polar-styled ice sheet. However, an increasing number of studies provide evidence for continued instability and abundant meltwater processes influencing the low-lying margins of the EAIS during the Late Miocene (~11.6-5.3 Ma). The history of the EAIS during this period remains ambiguous due to the sparse number of records, and those that do exist have poor age resolution. This thesis investigates Integrated Ocean Drilling Program Site U1361 (64°24.5°S 143°53.1°E), located on the lowermost continental rise of the Wilkes Land margin. It aims to assess the variability of the EAIS and associated changes in palaeoceanography offshore one of the largest marine-based sectors of East Antarctica, the Wilkes Subglacial Basin, and to establish if the EAIS was responding to orbital forcings during the Late Miocene.  The study period (~11.7 to 10.8 Ma) contains six intervals of nannofossil-rich mudstones, interbedded with laminated mudstones and diatom-rich mudstones. Nannofossils are absent elsewhere in core U1361A, which covers the past ~14 Ma. To identify the sedimentary and depositional processes which influenced this anomalous interval of calcareous biological productivity, a high-resolution record (using ~450 samples) of Iceberg Rafted Debris (IBRD), grain size analysis and bulk geochemistry XRF analysis have been developed.   A lithofacies scheme has been established and used to provide an interpretation of the shifting sedimentary processes through time. Repeating cycles of faintly laminated mudstones were interpreted to represent the influence of bottom current activity on overbank turbidites, that spill onto a channel leeve, during glacial periods. The contouritic nature of the facies is likely associated with the low-relief channel-levee system at this time. Interglacial sedimentation is characterised by an increase in biogenic content, IBRD and bioturbation, with deposition occurring during biologically productive open marine conditions. Two types of biogenic productivity are present over the interval (silica and/or carbonate). The intervals of diatom-rich mud were interpreted to be associated with enhanced upwelling of Circumpolar Deep Water (CDW). While, the nannofossil-rich mudstones suggest a significantly warmer climate, with coccolithophore production proposed to represent the influence of meltwater and shifting Southern Ocean frontal systems, acting to restrict nutrient upwelling and increase water temperatures.  Nannofossil-rich muds are only present for a short interval (700 kyr), suggesting that the anomalous depositional environment between ~11.7 to 11.0 Ma was potentially related to the significant retreat and surface meltwater processes at the EAIS margin. Interglacial sedimentation at Site U1361 is also accompanied by an increase in grain size (i.e. silt), interpreted to represent oceanic current intensification which acts to restrict the deposition of finer material, relative to glacial intervals. This intensification of ocean current strength may have resulted in increased heat delivery to the EAIS margin triggering a terrestrial based ice sheet, and the delivery of nutrients stimulating marine productivity.  Spectral analysis of the mean grain size (MGS) and IBRD Mass Accumulation Rate (MAR) records revealed that during the Late Miocene (~11.7 to 10.8 Ma), the ice sheet was paced by ~100 kyr eccentricity cycles, and a low frequency ~20 kyr processional component. This is consistent with two Late Miocene 𝛿¹⁸O records that are also paced by eccentricity, suggesting that the Antarctic Ice Sheet was contributing a significant signal to the global 𝛿¹⁸O record during this interval of the Late Miocene. However, the presence of nannofossil suggests a warmer world, rather than the colder climate state that are often inferred to lead to eccentricity/precession variability. A recent hypothesis proposed by Levy et al., (2019) invokes that a warmer climate may lead to surface melt processes which at high latitudes are dominated by eccentricity/precession. Although this style of climate is commonly thought to have occurred prior to ~14 Ma in East Antarctica, the evidence presented in this study suggests such a state existed at the Wilkes Land margin until at least ~11.0 Ma.</p>

scholarly journals Ice dynamics and ocean productivity during the Late Miocene, offshore Wilkes Land, East Antarctica

2021 ◽  
Author(s):  
◽  
Rebecca Pretty
Keyword(s):  
Grain Size ◽  
Late Miocene ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ocean Current ◽  
Significant Advance ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Depositional Processes ◽  
Wilkes Land

<p>The middle Miocene Climatic Transition (~14 Ma) is commonly interpreted to represent the significant advance of the East Antarctic Ice Sheet (EAIS), and the transition to a hyper-arid climate and a stable polar-styled ice sheet. However, an increasing number of studies provide evidence for continued instability and abundant meltwater processes influencing the low-lying margins of the EAIS during the Late Miocene (~11.6-5.3 Ma). The history of the EAIS during this period remains ambiguous due to the sparse number of records, and those that do exist have poor age resolution. This thesis investigates Integrated Ocean Drilling Program Site U1361 (64°24.5°S 143°53.1°E), located on the lowermost continental rise of the Wilkes Land margin. It aims to assess the variability of the EAIS and associated changes in palaeoceanography offshore one of the largest marine-based sectors of East Antarctica, the Wilkes Subglacial Basin, and to establish if the EAIS was responding to orbital forcings during the Late Miocene.  The study period (~11.7 to 10.8 Ma) contains six intervals of nannofossil-rich mudstones, interbedded with laminated mudstones and diatom-rich mudstones. Nannofossils are absent elsewhere in core U1361A, which covers the past ~14 Ma. To identify the sedimentary and depositional processes which influenced this anomalous interval of calcareous biological productivity, a high-resolution record (using ~450 samples) of Iceberg Rafted Debris (IBRD), grain size analysis and bulk geochemistry XRF analysis have been developed.   A lithofacies scheme has been established and used to provide an interpretation of the shifting sedimentary processes through time. Repeating cycles of faintly laminated mudstones were interpreted to represent the influence of bottom current activity on overbank turbidites, that spill onto a channel leeve, during glacial periods. The contouritic nature of the facies is likely associated with the low-relief channel-levee system at this time. Interglacial sedimentation is characterised by an increase in biogenic content, IBRD and bioturbation, with deposition occurring during biologically productive open marine conditions. Two types of biogenic productivity are present over the interval (silica and/or carbonate). The intervals of diatom-rich mud were interpreted to be associated with enhanced upwelling of Circumpolar Deep Water (CDW). While, the nannofossil-rich mudstones suggest a significantly warmer climate, with coccolithophore production proposed to represent the influence of meltwater and shifting Southern Ocean frontal systems, acting to restrict nutrient upwelling and increase water temperatures.  Nannofossil-rich muds are only present for a short interval (700 kyr), suggesting that the anomalous depositional environment between ~11.7 to 11.0 Ma was potentially related to the significant retreat and surface meltwater processes at the EAIS margin. Interglacial sedimentation at Site U1361 is also accompanied by an increase in grain size (i.e. silt), interpreted to represent oceanic current intensification which acts to restrict the deposition of finer material, relative to glacial intervals. This intensification of ocean current strength may have resulted in increased heat delivery to the EAIS margin triggering a terrestrial based ice sheet, and the delivery of nutrients stimulating marine productivity.  Spectral analysis of the mean grain size (MGS) and IBRD Mass Accumulation Rate (MAR) records revealed that during the Late Miocene (~11.7 to 10.8 Ma), the ice sheet was paced by ~100 kyr eccentricity cycles, and a low frequency ~20 kyr processional component. This is consistent with two Late Miocene 𝛿¹⁸O records that are also paced by eccentricity, suggesting that the Antarctic Ice Sheet was contributing a significant signal to the global 𝛿¹⁸O record during this interval of the Late Miocene. However, the presence of nannofossil suggests a warmer world, rather than the colder climate state that are often inferred to lead to eccentricity/precession variability. A recent hypothesis proposed by Levy et al., (2019) invokes that a warmer climate may lead to surface melt processes which at high latitudes are dominated by eccentricity/precession. Although this style of climate is commonly thought to have occurred prior to ~14 Ma in East Antarctica, the evidence presented in this study suggests such a state existed at the Wilkes Land margin until at least ~11.0 Ma.</p>

Late Pleistocene oceanographic and depositional variations along the Wilkes Land margin (East Antarctica) reconstructed with geochemical proxies in deep-sea sediments

2020 ◽  
Vol 184 ◽  
pp. 103045 ◽  
Author(s):  
Francisco J. Jimenez-Espejo ◽  
Massimo Presti ◽  
Gerhard Kuhn ◽  
Robert Mckay ◽  
Xavier Crosta ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Deep Sea ◽  
East Antarctica ◽  
Geochemical Proxies ◽  
Deep Sea Sediments ◽  
Wilkes Land

scholarly journals Short Note: New marine core record of Late Pleistocene glaciation history, Rauer Group, East Antarctica

2009 ◽  
Vol 21 (3) ◽  
pp. 299-300 ◽  
Author(s):  
Sonja Berg ◽  
Bernd Wagner ◽  
Duanne A. White ◽  
Holger Cremer ◽  
Ole Bennike ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Late Quaternary ◽  
Short Note ◽  
Ice Sheet ◽  
East Antarctica ◽  
Prydz Bay ◽  
Pleistocene Glaciation ◽  
Antarctic Ice Sheet ◽  
Significant Variability ◽  
East Antarctic Ice Sheet

The evolution of the East Antarctic Ice Sheet (EAIS) during the Late Quaternary is poorly known, partly because some regions, such as the Prydz Bay vicinity, indicate significant variability in the glaciation patterns (e.g. Domack et al. 1998, Zwartz et al. 1998, Hodgson et al. 2005).

Late Neogene sediment properties in the Wilkes Land continental rise (IODP Exp. 318 Hole U1359A), East Antarctica

2017 ◽  
Vol 21 (1) ◽  
pp. 21-32
Author(s):  
Boo-Keun Khim ◽  
Buhan Song ◽  
Hyen Goo Cho ◽  
Trevor Williams ◽  
Carlota Escutia
Keyword(s):  
East Antarctica ◽  
Sediment Properties ◽  
Continental Rise ◽  
Late Neogene ◽  
Wilkes Land ◽  
Neogene Sediment

scholarly journals Gamma-Ray Attenuation to Evaluate Soil Porosity: An Analysis of Methods

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Luiz F. Pires ◽  
André B. Pereira
Keyword(s):  
Gamma Ray ◽  
Particle Density ◽  
Pore Space ◽  
Physical Property ◽  
Soil Bulk Density ◽  
Soil Porosity ◽  
Porous System ◽  
Soil Pore Space ◽  
Gamma Ray Attenuation ◽  
Dry Soil

Soil porosity (ϕ) is of a great deal for environmental studies due to the fact that water infiltrates and suffers redistribution in the soil pore space. Many physical and biochemical processes related to environmental quality occur in the soil porous system. Representative determinations ofϕare necessary due to the importance of this physical property in several fields of natural sciences. In the current work, two methods to evaluateϕwere analyzed by means of gamma-ray attenuation technique. The first method uses the soil attenuation approach through dry soil and saturated samples, whereas the second one utilizes the same approach but taking into account dry soil samples to assess soil bulk density and soil particle density to determineϕ. The results obtained point out a good correlation between both methods. However, whenϕis obtained through soil water content at saturation and a 4 mm collimator is used to collimate the gamma-ray beam the first method also shows good correlations with the traditional one.

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