Dating Antarctic blue ice areas using a novel ice flow model

Grinsted, Aslak; Moore, John C.; Spikes, V. B.; Sinisalo, Anna

doi:10.1029/2003gl017957

Cited by 25 publications

(80 citation statements)

References 13 publications

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“…The flow line defined the sampling location of the horizontal ice core. Note that this flow line is different from our previously suggested flow line (Grinsted et al, 2003), when we believed that flow originated mainly outside the valley for the inner blue ice region. Now we think that the main source of ice for the northwest part of the inner BIA is the snow accumulation region between the two BIAs -east of stake 4 north of stake 22 (see Fig.…”

Section: Study Area: Heimefrontfjella Scharffenbergbotnencontrasting

confidence: 44%

“…9b), where all stream lines are shifted to originate from areas close to the bedrock from within the outer part of the valley, more resembling the flow line inferred from observations of banding in the valley and the flow line marked in Fig. 1 used for the previous studies (Grinsted et al, 2003). Another clear distinction between the two configurations is the integration time, i.e., the travel time of a particle as a result from the Runge-Kutta method to advect a particle from the surface along the stream line back to that particular position.…”

Section: Simulations Using Prescribed Fabrics In 3-dmentioning

confidence: 94%

“…In addition to the complete three-dimensional setup, we also investigated the dynamics using a flow-line model, as there have been earlier attempts to compute the age distribution with such models (Grinsted et al, 2003). Initially chosen to reduce the complexity and the size of the problem, the twodimensional (2-D) flow-line model illustrates the necessity of using a full three-dimensional flow simulation.…”

Section: Comparison Of 3-d Results With 2-d Flow-line Modelmentioning

confidence: 99%

“…Several attempts have been made using simplified flow models constrained by limited data (Naruse and Hashimoto, 1982;Azuma et al, 1985;Van Roijen, 1996;Grinsted et al, 2003;Sinisalo et al, 2004Sinisalo et al, , 2007Moore et al, 2006). However the complex geometry, usually including large ice thickness variations along the blue ice field, suggests that a three-dimensional, higher order or full-Stokes model is needed to produce realistic ice flow simulations.…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

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Influence of anisotropy on velocity and age distribution at Scharffenbergbotnen blue ice area

et al. 2014

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Abstract. We use a full-Stokes thermo-mechanically coupled ice-flow model to study the dynamics of the glacier inside Scharffenbergbotnen valley, Dronning Maud Land, Antarctica. The domain encompasses a high accumulation rate region and, downstream, a sublimation-dominated bare ice ablation area. The ablation ice area is notable for having old ice at its surface since the vertical velocity is upwards, and horizontal velocities are almost stagnant there. We compare the model simulation with field observations of velocities and the age distribution of the surface ice. No satisfactory match using an isotropic flow law could be found because of too high vertical velocities and much too high horizontal ones in simulations despite varying enhancement factor, geothermal heat flux and surface temperatures over large ranges. However, the existence of a pronounced ice fabric may explain the observed present-day surface velocity and mass balance distribution in the inner Scharffenbergbotnen blue ice area. Near absence of data on the temporal evolution of Scharffenbergbotnen since the Late Glacial Maximum necessitates exploration of the impact of anisotropy using prescribed ice fabrics: isotropic, single maximum, and linear variation with depth, in both two-dimensional and threedimensional flow models. The realistic velocity field simulated with a noncollinear orthotropic flow law, however, produced surface ages in significant disagreement with the few reliable age measurements and suggests that the age field is not in a steady state and that the present distribution is a result of a flow reorganization at about 15 000 yr BP. In order to fully understand the surface age distribution, a transient simulation starting from the Late Glacial Maximum including the correct initial conditions for geometry, age, fabric and temperature distribution would be needed. This is the first time that the importance of anisotropy has been demonstrated in the ice dynamics of a blue ice area and demonstrates the need to understand ice flow in order to better interpret archives of ancient ice for paleoclimate research.

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Section: Study Area: Heimefrontfjella Scharffenbergbotnencontrasting

confidence: 44%

Section: Simulations Using Prescribed Fabrics In 3-dmentioning

confidence: 94%

Section: Comparison Of 3-d Results With 2-d Flow-line Modelmentioning

confidence: 99%

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

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Influence of anisotropy on velocity and age distribution at Scharffenbergbotnen blue ice area

et al. 2014

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“…Dating of ice parcels is the principal problem when using ablation sites for climatic reconstruction [ Sinisalo and Moore , 2010, and references therein]. Several methods have been used, including radiometric dating of tephra layers [e.g., Dunbar et al , 2008], flow line modeling [ Azuma et al , 1985; Grinsted et al , 2003; Moore et al , 2006], stratigraphical matching of gas and water isotope measurements to well‐dated ice core records [e.g., Reeh et al , 2002; Petrenko et al , 2006; Aciego et al , 2007; Schaefer et al , 2009], and radiocarbon dating of micro‐particles [ Jenk et al , 2007]. Early on it was realized that radiocarbon dating of the CO 2 present in the air bubbles trapped in polar ice can potentially be used as an absolute dating method for ice cores and BIA samples [ Fireman and Norris , 1982; Andree et al , 1984].…”

Section: Introductionmentioning

confidence: 99%

In situ cosmogenic radiocarbon production and 2‐D ice flow line modeling for an Antarctic blue ice area

et al. 2012

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Radiocarbon measurements at ice margin sites and blue ice areas can potentially be used for ice dating, ablation rate estimates and paleoclimatic reconstructions. Part of the measured signal comes from in situ cosmogenic 14C production in ice, and this component must be well understood before useful information can be extracted from 14C data. We combine cosmic ray scaling and production estimates with a two‐dimensional ice flow line model to study cosmogenic 14C production at Taylor Glacier, Antarctica. We find (1) that 14C production through thermal neutron capture by nitrogen in air bubbles is negligible; (2) that including ice flow patterns caused by basal topography can lead to a surface 14C activity that differs by up to 25% from the activity calculated using an ablation‐only approximation, which is used in all prior work; and (3) that at high ablation margin sites, solar modulation of the cosmic ray flux may change the strength of the dominant spallogenic production by up to 10%. As part of this effort we model two‐dimensional ice flow along the central flow line of Taylor Glacier. We present two methods for parameterizing vertical strain rates, and assess which method is more reliable for Taylor Glacier. Finally, we present a sensitivity study from which we conclude that uncertainties in published cosmogenic production rates are the largest source of potential error. The results presented here can inform ongoing and future 14C and ice flow studies at ice margin sites, including important paleoclimatic applications such as the reconstruction of paleoatmospheric 14C content of methane.

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Understanding the dynamics of black carbon and associated contaminants in glacial systems

Hodson

2014

WIREs Water

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More than one billion people depend upon glaciers for water, yet this exploitation is seldom underpinned by science-led water management practice. Previous work has detected that glaciers store and then subsequently release contaminants to downstream ecosystems, revealing a potentially harmful legacy that needs to be managed in conjunction with contemporary atmospheric pollution and climate change. Remarkably, while several classes of harmful organic pollutants have been considered in this context, almost no attention has been given to black carbon, a dark aerosol that is host to several adsorbed contaminants and that greatly increases glacier melt by enhancing the absorption of solar radiation. The future impact of black carbon upon glacier melt and contaminant release cannot be managed until we know how much historical black carbon is stored in Earth's glaciers. Further, as the residence time of ice within many mountain glaciers is between 100 and 1000 years, major changes in these impacts can be anticipated in the near future. A case is therefore made for using glacier dynamic models to understand the distribution of postindustrial, contaminated ice within glaciers, so that their impacts upon melt water quantity and quality can be forecast. A research framework is proposed that ranges from high flux, dynamic glaciers which are replete with postindustrial ice, to low flux, polar glaciers which are unlikely to become replete before they disappear. Research into the processing of contaminants following their melt-out is also required, because microbial processes will lead to their bioflocculation and biodegradation on glacier surfaces. © 2014 Wiley Periodicals, Inc. How to cite this article:WIREs Water 2014Water , 1:141-149. doi: 10.1002Water /wat2.1016 INTRODUCTION P eople's dependence upon water supply from glacier ice is far greater than is immediately apparent. It ranges from the consumption of groundwaters replenished by Pleistocene ice sheets in urban communities such as Chicago, through the hydroelectric power production of Norway, Switzerland, and New Zealand, to the collection of surface runoff from glaciers for irrigation and * Correspondence to: a.j.hodson@sheffield.ac.uk 1 Department of Geography, University of Sheffield, Sheffield, UK 2 Arctic Geology, University Centre in Svalbard, Longyearbyen, Norway Conflict of interest: The author has declared no conflicts of interest for this article. domestic use in rural parts of the Himalayas and Andes. Historically, the use of glacial melt waters for irrigation in Asia has involved farmers sprinkling ash over glaciers to enhance melting. The effect of the ash is to reduce the surface reflectance of the ice and thus increase the absorption of solar radiation. As a consequence of industrialization during the so-called Anthropocene, the atmospheric deposition of carbonaceous particles (hereafter black carbon or 'BC') is having precisely the same effect (see Box 1). Several potentially harmful classes of persistent organic pollutants (POPs) are also known to ...

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Dating Antarctic blue ice areas using a novel ice flow model

Cited by 25 publications

References 13 publications

Influence of anisotropy on velocity and age distribution at Scharffenbergbotnen blue ice area

Influence of anisotropy on velocity and age distribution at Scharffenbergbotnen blue ice area

In situ cosmogenic radiocarbon production and 2‐D ice flow line modeling for an Antarctic blue ice area

Understanding the dynamics of black carbon and associated contaminants in glacial systems

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