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 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 Impact of Cyclonic Ocean Eddies on Upper Ocean Thermodynamic Response to Typhoon Soudelor

2019 ◽  
Vol 11 (8) ◽  
pp. 938 ◽  
Author(s):  
Jue Ning ◽  
Qing Xu ◽  
Han Zhang ◽  
Tao Wang ◽  
Kaiguo Fan
Keyword(s):  
Vertical Mixing ◽  
Heat Content ◽  
Mesoscale Eddies ◽  
Upper Ocean ◽  
Surface Cooling ◽  
Ocean Eddies ◽  
Horizontal Advection ◽  
Content Change ◽  
Order Of Magnitude ◽  
The Impact

By using multiplatform satellite datasets, Argo observations and numerical model data, the upper ocean thermodynamic responses to Super Typhoon Soudelor are investigated with a focus on the impact of an ocean cyclonic eddy (CE). In addition to the significant surface cooling inside the CE region, an abnormally large rising in subsurface temperature is observed. The maximum warming and heat content change (HCC) reach up to 4.37 °C and 1.73 GJ/m2, respectively. Moreover, the HCC is an order of magnitude larger than that calculated from statistical analysis of Argo profile data in the previous study which only considered the effects caused by typhoons. Meanwhile, the subsurface warming outside the CE is merely 1.74 °C with HCC of 0.39 GJ/m2. Previous studies suggested that typhoon-induced vertical mixing is the primary factor causing subsurface warming but these studies ignored an important mechanism related to the horizontal advection caused by the rotation and movement of mesoscale eddies. This study documents that the eddy-induced horizontal advection has a great impact on the upper ocean responses to typhoons. Therefore, the influence of eddies should be considered when studying the responses of upper ocean to typhoons with pre-existing mesoscale eddies.

scholarly journals Ice flow between the Greenland Ice Core Project and Greenland Ice Sheet Project 2 boreholes in central Greenland

1997 ◽  
Vol 102 (C12) ◽  
pp. 26851-26859 ◽  
Author(s):  
C. Schøtt Hvidberg ◽  
D. Dahl-Jensen ◽  
E. D. Waddington
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Flow ◽  
Core Project

scholarly journals Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling

2018 ◽  
Author(s):  
Achim Heilig ◽  
Olaf Eisen ◽  
Michael MacFerrin ◽  
Marco Tedesco ◽  
Xavier Fettweis
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Pore Space ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Liquid Water Content ◽  
Water Infiltration ◽  
Near Surface ◽  
Percolation Zone

Abstract. Increasing melt over the Greenland ice sheet (GrIS) recorded over the past years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness are observable in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779° N/46.2856° W) at 2120 m a.s.l. The radar is capable to monitor quasi-continuously changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well, for both, timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg/m2 into firn beneath the summer surface of 2015. We find that continuous observations of liquid water content, percolation depths and rates for the seasonal mass fluxes are sufficiently accurate to provide valuable information for validation of model approaches and help to develop a better understanding of liquid water retention and percolation in perennial firn.

scholarly journals Shallow firn cores 1989–2019 in southwest Greenland's percolation zone reveal decreasing density and ice layer thickness after 2012

2021 ◽  
pp. 1-12
Author(s):  
Åsa K. Rennermalm ◽  
Regine Hock ◽  
Federico Covi ◽  
Jing Xiao ◽  
Giovanni Corti ◽  
...  
Keyword(s):  
Layer Thickness ◽  
Pore Space ◽  
Greenland Ice Sheet ◽  
Infiltration Capacity ◽  
In Situ Observations ◽  
Percolation Zone ◽  
Over Time ◽  
Southwest Greenland

Abstract Refreezing of meltwater in firn is a major component of Greenland ice-sheet's mass budget, but in situ observations are rare. Here, we compare the firn density and total ice layer thickness in the upper 15 m of 19 new and 27 previously published firn cores drilled at 15 locations in southwest Greenland (1850–2360 m a.s.l.) between 1989 and 2019. At all sites, ice layer thickness covaries with density over time and space. At the two sites with the earliest observations (1989 and 1998), bulk density increased by 15–18%, in the top 15 m over 28 and 21 years, respectively. However, following the extreme melt in 2012, elevation-detrended density using 30 cores from all sites decreased by 15 kg m−3 a−1 in the top 3.75 m between 2013 and 2019. In contrast, the lowest elevation site's density shows no trend. Thus, temporary build-up in firn pore space and meltwater infiltration capacity is possible despite the long-term increase in Greenland ice-sheet melting.

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 The physical basis for gas transport through polar firn: a case study at Summit, Greenland

2013 ◽  
Vol 7 (3) ◽  
pp. 2455-2487 ◽  
Author(s):  
A. C. Adolph ◽  
M. R. Albert
Keyword(s):  
Gas Transport ◽  
Pore Space ◽  
Ice Core ◽  
Physical Nature ◽  
Atmospheric Composition ◽  
Transport Parameters ◽  
Microstructural Parameters ◽  
Gas Diffusivity ◽  
Direct Measurements ◽  
The Impact

Abstract. Compared to other natural porous materials, relatively little is known about the physical nature of polar firn. This intricate network of ice and pore space that comprises the top 60–100 m of the polar ice sheets is the framework that forms the natural archive of past climate information. Despite the many implications for ice core interpretation, direct measurements of physical properties throughout the firn column are limited. Models of gas transport through firn are used to interpret in-situ chemical data which is retrieved to analyze past atmospheric composition. These traditional models treat the firn as a "black box," with gas transport parameters tuned to match gas concentrations with depth to known atmospheric histories. Though this method has been largely successful and provided very useful insights, there are still many questions and uncertainties to be addressed. This work seeks to understand the impact of firn structure on gas transport in firn from a first principles standpoint through direct measurements of permeability, gas diffusivity and microstructure. The relationships between gas transport properties and microstructure will be characterized and compared to existing relationships for general porous media. Direct measurements of gas diffusivity are compared to diffusivities deduced from models based on firn air chemical sampling. Our comparison illuminates the primary importance of including microstructural parameters, beyond just porosity or density, in mass transport modeling, and it provides insights about the nature of gas transport throughout the firn column. Guidance is provided for development of next-generation firn air transport models.

scholarly journals Brief communication: Improved simulation of the present-day Greenland firn layer (1960–2016)

2018 ◽  
Author(s):  
Stefan R. M. Ligtenberg ◽  
Peter Kuipers Munneke ◽  
Brice P. Y. Noël ◽  
Michiel R. van den Broeke
Keyword(s):  
Regional Climate Model ◽  
Mass Balance ◽  
Climate Model ◽  
Pore Space ◽  
Regional Climate ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Percolation Zone ◽  
Full Simulation

Abstract. By providing pore space for storage or refreezing of meltwater, the Greenland ice sheet firn layer strongly modulates runoff. Correctly representing the firn layer is therefore crucial for Greenland (surface) mass balance studies. Here, we present an improved simulation of the Greenland firn layer with the firn model IMAU-FDM forced by the latest output of the regional climate model RACMO2, version 2.3p2. In the percolation zone, much improved agreement with firn density and temperature observations is found. A full simulation of Greenland firn at high temporal (10 days) and spatial (11 km) resolution is available for the period 1960–2016.

Late Holocene thermohaline perturbation of the N-Atlantic Subpolar Gyre linked to exceptional Greenland Ice Sheet melting between 4.4 and 4.0 ka BP

2020 ◽  
Author(s):  
Antoon Kuijpers ◽  
Marit-Solveig Seidenkrantz ◽  
Ralph Schneider ◽  
Camilla S. Andresen ◽  
Signe Hygom Jacobsen ◽  
...  
Keyword(s):  
Late Holocene ◽  
Deep Convection ◽  
Water Discharge ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Subpolar Gyre ◽  
The Holocene ◽  
Master Thesis ◽  
The Impact

<p>Knowledge of the impact of past climate warming on Greenland Ice Sheet stability is an important issue for assessing  thresholds that are critical for a potential ice sheet collapse. For the late Holocene, evidence has recently been found of a so-called 4.2 ka BP event(1) including a prominent warming spike in several ice core records from Greenland and Canada (Agassiz).  Also lake records from both Northwest(2) and South Greenland(3) support pronounced summer warming during that time. After c. 4.0 ka BP NW Greenland July air temperature dropped by about 3<sup>o</sup> C. Coeval with this exceptional atmospheric warming anomaly over northern Canada and parts of Greenland, abrupt cooling and freshening affected  the N-Atlantic subpolar gyre where Labrador Sea deep convection ceased(4). Northern N-Atlantic climate generally deteriorated. With our contribution we present Holocene sub-bottom profiling  and sedimentary shelf and  fjord records from Southwest Greenland and Disko Bay that indicate exceptional Greenland Ice Sheet melting 4.4-4.0 ka BP at a rate and magnitude not recorded since early Holocene deglaciation. Extremely strong melt water discharge resulted in erosion of fjord sediments(5) and local deposition of up to several meters thick meltwater sediment on the shelf(6-8).  Timing of this melting event corresponds to a significant anomaly in hydrographic parameters of the Labrador Current off Newfoundland(9,10), which is concluded to have resulted in thermohaline perturbation of the N-Atlantic Subpolar gyre.   </p><ul><li>(1) Weiss, H. 2019. Clim Past doi:10.5194/cp-2018-162-RC2</li> <li>(2) McFarlin, J.M. et al. 2018. PNAS doi:10.1073/pnas.1720420115</li> <li>(3) Andresen, C.S. et al. 2004. J Quat Sci 19(8) doi:10.1002/jqs.886</li> <li>(4) Klus, A. et al. 2018. Clim Past doi:10.5194/cp-14-1165-2018</li> <li>(5) Ren, J. et al. 2009. Mar Micropal doi:10.1016/j.marmicro.2008.12.003</li> <li>(6) Hygom Jacobsen, S. 2019. Master Thesis Aarhus Univ, Dept. of Geoscience, pp105</li> <li>(7) Schneider, R. 2015. Cruise Rep epic.awi.de/id/eprint/37062/131/msm-44-46-expeditionsheft.pdf</li> <li>(8) Kuijpers, A. et al. 2001. Geol. Greenland Surv Bull 189, 41-47</li> <li>(9) Solignac, S. et al. 2011. The Holocene, doi: 10.1177/0959683610385720</li> <li>(10) Orme, L. et al 2019. The Holocene (submitted)</li> </ul>

scholarly journals Upstream flow effects revealed in the EastGRIP ice-core using a Monte Carlo inversion of a 2D ice-flow model

2021 ◽  
Author(s):  
Tamara Annina Gerber ◽  
Christine Hvidberg ◽  
Aslak Grinsted ◽  
Daniela Jansen ◽  
Steven Franke ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Source Area ◽  
Model Parameters ◽  
Ice Flow ◽  
East Greenland ◽  
Ice Stream ◽  
Flow Effects ◽  
Upstream Flow

<p>The North East Greenland ice-stream (NEGIS) is the largest active ice-stream on the Greenland ice-sheet and is a crucial contributor to the ice-sheet mass balance. To investigate the ice-stream dynamics and to gain information about the past climate, a deep ice-core is drilled in the upstream part of the NEGIS, termed the East Greenland ice-core project (EastGRIP). Upstream flow effects introduce non-climatic bias in ice-cores and are particularly strong at EastGRIP due to high ice-flow velocities and the location in an ice-stream on the eastern flank of the Greenland ice-sheet. Understanding and ultimately correcting for such effects requires information on the source area and the local atmospheric conditions at the time of ice deposition. We use a two-dimensional Dansgaard-Johnsen model to simulate ice-flow along three approximated flow-lines between the summit of the ice-sheet and EastGRIP. Model parameters are determined using a Monte Carlo inversion by minimizing the misfit between modeled isochrones and isochrones observed in radio-echo-sounding images. We calculate backward-in-time particle trajectories to determine the source area of ice found in the EastGRIP core today and present estimates of surface elevation and past accumulation-rates at the deposition site. The thinning function and accumulated strain obtained from the modeled velocity field provide useful information on the deformation history in the EastGRIP ice. Our results indicate that increased accumulation in the upstream area is predominantly responsible for the constant annual layer thickness observed in the upper part of the ice column at EastGRIP. Inverted model parameters suggest that the imprint of basal melting and sliding is present in large parts along the flow profiles and that most internal ice deformation happens close to the bedrock. The results of this study can act as a basis for applying upstream corrections to a variety of ice-core measurements, and the model parameters can be useful constraints for more sophisticated modeling approaches in the future. </p>

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