scholarly journals Advection Impacts the Firn Structure of Greenland's Percolation Zone

2019 ◽  
Author(s):  
Rosemary Leone ◽  
Joel Harper ◽  
Toby Meierbachtol ◽  
Neil Humphrey
Keyword(s):  
Ice Core ◽  
Heat Content ◽  
Ice Flow ◽  
Surface Conditions ◽  
One Dimensional ◽  
Climate Gradients ◽  
Column Structure ◽  
Core Site ◽  
The Impact ◽  
Percolation Zone

Abstract. One dimensional simulations of firn evolution neglect horizontal transport during burial. Using a suite of model runs, we demonstrate the impacts of advection on the development of firn density, temperature, and the stratigraphy of melt features the 0Greenland ice sheet percolation zone. The simulations isolate processes in synthetic runs, and investigate four specific transects and an ice core site. The advection process tends to increase the pore close-off depth, reduce the heat content, and decrease the frequency of melt features with depth by emplacing firn sourced from higher locations under increasingly warm and melt-affected surface conditions. Horizontal ice flow interacts with topography, climate gradients, and meltwater infiltration to influence the evolution of the firn column structure; the interaction between these variables modulates the impact of advection on firn at locations around Greenland. Pore close-off and firn temperature are mainly impacted in the lowermost 20 km of the percolation zone, which may be relevant to migration of the lower percolation zone. Relatively high in the percolation zone, however, the stratigraphy of melt features can have an advection derived component that should not be conflated with changing climate.

scholarly journals Horizontal ice flow impacts the firn structure of Greenland's percolation zone

2020 ◽  
Vol 14 (5) ◽  
pp. 1703-1712 ◽  
Author(s):  
Rosemary Leone ◽  
Joel Harper ◽  
Toby Meierbachtol ◽  
Neil Humphrey
Keyword(s):  
Pore Space ◽  
Ice Core ◽  
Heat Content ◽  
Greenland Ice Sheet ◽  
Ice Flow ◽  
One Dimensional ◽  
Climate Gradients ◽  
Horizontal Advection ◽  
The Impact ◽  
Percolation Zone

Abstract. One-dimensional simulations of firn evolution neglect horizontal advection from ice flow, which transports the firn column across climate gradients as it is buried by accumulation. Using a suite of model runs, we demonstrate the impacts of horizontal advection on the development of firn density, temperature, and the stratigraphy of melt features through the Greenland ice sheet percolation zone. The simulations isolate processes in synthetic runs and investigate four specific transects and an ice core site. Relative to one-dimensional simulations, the horizontal advection process tends to increase the pore close-off depth, reduce the heat content, and decrease the frequency of melt features with depth by emplacing firn sourced from higher locations under increasingly warm and melt-affected surface conditions. Preservation of the advected pore space and cold content is strongly dependent upon the depth of meltwater infiltration. Horizontal ice flow interacts with topography, climate gradients, and meltwater infiltration to influence the evolution of the firn column structure; the interaction between these variables modulates the impact of horizontal advection on firn at locations around Greenland. Pore close-off and firn temperature are mainly impacted in the lowermost 20–30 km of the percolation zone, which may be relevant to migration of the lower percolation zone. Relatively high in the percolation zone, however, the stratigraphy of melt features can have an advection-derived component that should not be conflated with changing climate.

scholarly journals Reconstructing ice-sheet accumulation rates at ridge B, East Antarctica

2004 ◽  
Vol 39 ◽  
pp. 326-330 ◽  
Author(s):  
Gwendolyn J.-M. C. Leysinger Vieli ◽  
Martin J. Siegert ◽  
Antony J. Payne
Keyword(s):  
Numerical Models ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Ice Flow ◽  
One Dimensional ◽  
Ice Accumulation ◽  
Core Site ◽  
Past Climate Change

AbstractUnderstanding how ice sheets responded to past climate change is fundamental to forecasting how they will respond in the future. Numerical models calculating the evolution of ice sheets depend upon accumulation data, which are principally available from ice cores. Here, we calculate past rates of ice accumulation using internal layering. The englacial structure of the East Antarctic ice divide at ridge B is extracted from airborne ice-penetrating radar. The isochronous surfaces are dated at their intersection with the Vostok ice-core site, where the depth–age relationship is known. The dated isochrons are used as input to a one-dimensional ice-flow model to investigate the spatial accumulation distribution. The calculations show that ice-accumulation rates generally increase from Vostok lake towards ridge B. The western flank of the ice divide experiences markedly more accumulation than in the east. Further, ice accumulation increases northwards along the ice divide. The results also show the variability of accumulation in time and space around the ridge B ice divide over the last 124 000 years.

scholarly journals Bedrock features and ice flow near the EPICA Ice Core Site (Dome C, Antarctica)

2000 ◽  
Vol 27 (3) ◽  
pp. 405-408 ◽  
Author(s):  
Frédérique Rémy ◽  
Ignazio E. Tabacco
Keyword(s):  
Ice Core ◽  
Ice Flow ◽  
Core Site

scholarly journals Rapid and accurate polarimetric radar measurements of ice crystal fabric orientation at the Western Antarctic Ice Sheet (WAIS) Divide ice core site

2021 ◽  
Vol 15 (8) ◽  
pp. 4117-4133
Author(s):  
Tun Jan Young ◽  
Carlos Martín ◽  
Poul Christoffersen ◽  
Dustin M. Schroeder ◽  
Slawek M. Tulaczyk ◽  
...  
Keyword(s):  
Past History ◽  
Ice Core ◽  
Ice Sheet ◽  
Vertical Direction ◽  
Surface Strain ◽  
Polarimetric Radar ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Flow Models ◽  
Core Site

Abstract. The crystal orientation fabric (COF) of ice sheets records the past history of ice sheet deformation and influences present-day ice flow dynamics. Though not widely implemented, coherent ice-penetrating radar is able to detect bulk anisotropic fabric patterns by exploiting the birefringence of ice crystals at radar frequencies, with the assumption that one of the crystallographic axes is aligned in the vertical direction. In this study, we conduct a suite of quad-polarimetric measurements consisting of four orthogonal antenna orientation combinations near the Western Antarctic Ice Sheet (WAIS) Divide ice core site. From these measurements, we are able to quantify the azimuthal fabric asymmetry at this site to a depth of 1400 m at a bulk-averaged resolution of up to 15 m. Our estimates of fabric asymmetry closely match corresponding fabric estimates directly measured from the WAIS Divide ice core. While ice core studies are often unable to determine the absolute fabric orientation due to core rotation during extraction, we are able to identify and conclude that the fabric orientation is depth-invariant to at least 1400 m, equivalent to 6700 years BP (years before 1950) and aligns closely with the modern surface strain direction at WAIS Divide. Our results support the claim that the deformation regime at WAIS Divide has not changed substantially through the majority of the Holocene. Rapid polarimetric determination of bulk fabric asymmetry and orientation compares well with much more laborious sample-based COF measurements from thin ice sections. Because it is the bulk-averaged fabric that ultimately influences ice flow, polarimetric radar methods provide an opportunity for its accurate and widespread mapping and its incorporation into ice flow models.

scholarly journals Advection and non-climate impacts on the South Pole Ice Core

2020 ◽  
Vol 16 (3) ◽  
pp. 819-832 ◽  
Author(s):  
Tyler J. Fudge ◽  
David A. Lilien ◽  
Michelle Koutnik ◽  
Howard Conway ◽  
C. Max Stevens ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Climate Impacts ◽  
Lapse Rate ◽  
South Pole ◽  
Elevation Change ◽  
The South ◽  
The Core ◽  
Core Site ◽  
The Impact

Abstract. The South Pole Ice Core (SPICEcore), which spans the past 54 300 years, was drilled far from an ice divide such that ice recovered at depth originated upstream of the core site. If the climate is different upstream, the climate history recovered from the core will be a combination of the upstream conditions advected to the core site and temporal changes. Here, we evaluate the impact of ice advection on two fundamental records from SPICEcore: accumulation rate and water isotopes. We determined past locations of ice deposition based on GPS measurements of the modern velocity field spanning 100 km upstream, where ice of ∼20 ka age would likely have originated. Beyond 100 km, there are no velocity measurements, but ice likely originates from Titan Dome, an additional 90 km distant. Shallow radar measurements extending 100 km upstream from the core site reveal large (∼20 %) variations in accumulation but no significant trend. Water isotope ratios, measured at 12.5 km intervals for the first 100 km of the flowline, show a decrease with elevation of −0.008 ‰ m−1 for δ18O. Advection adds approximately 1 ‰ for δ18O to the Last Glacial Maximum (LGM)-to-modern change. We also use an existing ensemble of continental ice-sheet model runs to assess the ice-sheet elevation change through time. The magnitude of elevation change is likely small and the sign uncertain. Assuming a lapse rate of 10 ∘C km−1 of elevation, the inference of LGM-to-modern temperature change is ∼1.4 ∘C smaller than if the flow from upstream is not considered.

scholarly journals Holocene accumulation and ice flow near the West Antarctic Ice Sheet Divide ice core site

2016 ◽  
Vol 121 (5) ◽  
pp. 907-924 ◽  
Author(s):  
Michelle R. Koutnik ◽  
T. J. Fudge ◽  
Howard Conway ◽  
Edwin D. Waddington ◽  
Thomas A. Neumann ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
The West ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Core Site

scholarly journals Rapid and accurate polarimetric radar measurements of ice crystal fabric orientation at the Western Antarctic Ice Sheet (WAIS) Divide deep ice core site

2020 ◽  
Author(s):  
Tun Jan Young ◽  
Carlos Martín ◽  
Poul Christoffersen ◽  
Dustin M. Schroeder ◽  
Slawek M. Tulaczyk ◽  
...  
Keyword(s):  
Past History ◽  
Ice Core ◽  
Ice Sheet ◽  
Surface Strain ◽  
Polarimetric Radar ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Flow Models ◽  
Core Site ◽  
Core Rotation

Abstract. The Crystal Orientation Fabric (COF) of ice sheets records the past history of ice sheet deformation and influences present-day ice flow dynamics. Though not widely implemented, coherent ice-penetrating radar is able to detect anisotropic COF patterns by exploiting the birefringence of ice crystals at radar frequencies. Most previous radar studies quantify COF at a coarse azimuthal resolution limited by the number of observations made with a pair of antennas along an acquisition plane that rotates around an azimuth centre. In this study, we instead conduct a suite of quad-polarimetric measurements consisting of four orthogonal antenna orientation combinations at the Western Antarctic Ice Sheet (WAIS) Divide Deep Ice Core site. From these measurements, we are able to quantify COF at this site to a depth of 1500 m at azimuthal and depth resolutions of up to 1° and 15 m. Our estimates of fabric asymmetry closely match corresponding fabric estimates directly measured from the WAIS Divide Deep Ice Core. While ice core studies are often unable to determine the absolute fabric orientation due to core rotation during extraction, we are able to unambiguously identify and conclude that the fabric orientation is depth-invariant to at least 1500 m, equivalent to 7400 years BP (years before 1950), and coincides exactly with the modern surface strain direction at WAIS Divide. Our results support the claim that the deformation regime at WAIS Divide has not changed substantially through the majority of the Holocene. Rapid polarimetric determination of bulk COF compares well with much more laborious sample-based COF measurements from thin ice sections. Because it is the former that ultimately influences ice flow, these polarimetric radar methods provide an opportunity for accurate and widespread mapping of bulk COF and its incorporation into ice flow models.

scholarly journals A detailed radiostratigraphic data set for the central East Antarctic Plateau spanning from the Holocene to the mid-Pleistocene

2021 ◽  
Vol 13 (10) ◽  
pp. 4759-4777
Author(s):  
Marie G. P. Cavitte ◽  
Duncan A. Young ◽  
Robert Mulvaney ◽  
Catherine Ritz ◽  
Jamin S. Greenbaum ◽  
...  
Keyword(s):  
Ice Core ◽  
Radar Data ◽  
Glacial Cycles ◽  
Data Set ◽  
Ice Flow ◽  
The Holocene ◽  
Antarctic Plateau ◽  
The Us ◽  
Core Site ◽  
Program Data

Abstract. We present an ice-penetrating radar data set which consists of 26 internal reflecting horizons (IRHs) that cover the entire Dome C area of the East Antarctic plateau, the most extensive to date in the region. This data set uses radar surveys collected over the space of 10 years, starting with an airborne international collaboration in 2008 to explore the region, up to the detailed ground-based surveys in support of the Beyond EPICA – Oldest Ice (BE-OI) European Consortium. Through direct correlation with the EPICA-DC ice core, we date 19 IRHs that span the past four glacial cycles, from 10 ka, beginning of the Holocene, to over 350 ka, ranging from 10 % to 83 % of the ice thickness at the EPICA-DC ice core site. We indirectly date and provide stratigraphic information for seven older IRHs using a 1D ice flow inverse model, going back to an estimated 700 ka. Depth and age uncertainties are quantified for all IRHs and provided as part of the data set. The IRH data set presented in this study is available at the US Antarctic Program Data Center (USAP-DC) (https://doi.org/10.15784/601411, Cavitte et al., 2020) and represents a contribution to the SCAR AntArchitecture action group (AntArchitecture, 2017).

Three-dimensional ice sheet structure at Dome C, central East Antarctica: implications for the interpretation of the EPICA ice core

2001 ◽  
Vol 13 (2) ◽  
pp. 182-187 ◽  
Author(s):  
Martin J. Siegert ◽  
Richard D. Eyers ◽  
Ignazio E. Tabacco
Keyword(s):  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Local Variation ◽  
Radar Data ◽  
East Antarctica ◽  
Airborne Radar ◽  
Internal Layers ◽  
Ice Flow ◽  
Core Site

Airborne radar data acquired in 1995 by the Italian Antarctic Programme over Dome C in central East Antarctica were processed to develop maps of internal isochronous ice sheet layering around the EPICA ice core site. Three internal layers were traced continuously across the radar-survey area at ice depths of 1–2 km. The maps reveal that the ice core site is located where internal layers are near horizontal to depths of at least 2 km. The Italian radar data do not resolve internal layers below 2 km. However, radar data collected over this part of East Antarctica in the 1970s show the internal layers to depths of up to 4 km. These internal layers reveal the regional structure of ice to the west of Dome C. Layers from both surveys are dated through an existing chronostratigraphic link between the Vostok ice core site and Dome C. The pattern of internal layering at Dome C reflects relatively steady conditions of ice flow and accumulation for the last 100 000 years. However, for ice older than this we show that there is significant local variation in the thickness between internal layers and the ice-sheet base. Our maps provide an indication of the structure of the ice sheet from which the EPICA deep ice core will be taken.

scholarly journals Advection (non-climate) impact on the South Pole Ice Core

2019 ◽  
Author(s):  
Tyler J. Fudge ◽  
David A. Lilien ◽  
Michelle Koutnik ◽  
Howard Conway ◽  
C. Max Stevens ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Lapse Rate ◽  
South Pole ◽  
The South ◽  
Climate History ◽  
The Core ◽  
The Past ◽  
Core Site ◽  
The Impact

Abstract. The South Pole Ice Core (SPICEcore), which spans the past 54,300 years, was drilled far from an ice divide such that ice recovered at depth originated at a location upstream of the current core site. If the climate is different upstream, the climate history recovered from the core will be a combination of the upstream conditions advected to the core site and the temporal changes we seek to recover. Here, we evaluate the impact of ice advection on two fundamental records from SPICEcore: accumulation rate and water isotopes. We determined the past locations of ice deposition based on GPS measurements of the modern velocity field spanning 100 km upstream where ice of ~ 20 ka age would likely have originated. Beyond 100 km, there are no velocity measurements, but ice likely originates from Titan Dome, an additional 90 km distant. Shallow radar measurements extending 100 km upstream from the core site reveal large (~ 20 %) variations in accumulation but no significant trend. Water isotope ratios, measured at 12.5 km intervals for the first 100 km of the flowline, show a decrease with elevation (and distance upstream) of -0.008 ‰ m−1 for δ18O. Advection therefore adds approximately 1 ‰ for δ18O to the LGM-to-modern change. Assuming a lapse rate of 10 °C per km of elevation, the LGM-to-modern temperature change is ~ 1.5 °C greater than if the ice had been deposited at a fixed location.

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