Chinese scientists will start to drill a deep ice core at Kunlun station near Dome A in the near future with the expectation of finding very old ice. Uncertainties are introduced by a complicated bedrock topography underneath the in parts more than three kilometre thick ice masses, imposed by the deep valleys of the Gamburtsev mountains. This, and the fact that we resolve ice flow around a dome, makes the deployment of a full Stokes model necessary. Further impact on the basal distribution of the age of the ice is given by the certainly existing ice fabric and the consequently anisotropic viscosity of the ice. Based on findings from other drill sites, we impose different type of prescribed fabrics and use an ortho-normal model for non-linear anisotropic ice flow. The second highly influential parameter determining the basal age of the ice is the geothermal heatflux at the bottom and – with somewhat lower impact - the averaged surface temperature. By variations of those three parameters (fabric distribution, geothermal heat flux and mean surface temperature) on a fixed domain (which excluded the study of changing accumulation and surface elevation), the authors found that large uncertainties of about 500ka for the age at 95% depth underneath Kunlun station based on best fits to existing measured dates in the upper
first third of the ice core exists. In other words, the model is able to fit the existing age/depth horizon with a non-unique set of parameter combinations. A second finding is, that basal conditions are very sensitive to those parameters and gradients of spatial distribution of the age close to the bottom are extraordinary high. Despite the challenges this imposes for this drill site, this can turn out to be an asset, as high resolution ice cores (at places with significant basal melt) as well as very old basal ice could be accessible at the very same spot, just a few hundred metres apart.
The picture shows the distribution of the vertical velocity (left column) and the age of the ice (right column) over depth underneath Kunlun station for several combination of the above discussed model parameters. Measured dates are marked with black dots.
Sun, B., Moore, J. C., Zwinger, T., Zhao, L., Steinhage, D., Tang, X., Zhang, D., Cui, X., and Martín, C., 2014: How old is the ice beneath Dome A, Antarctica?, The Cryosphere, 8, 1121-1128, doi:10.5194/tc-8-1121-2014 [link to paper]
Elmer/Ice Talks and Posters at International Symposium on Glaciers and Ice Sheets Contribution to Sea-Level Change (Observations, Modelling and Prediction), to be held in Chamonix-Mont-Blanc, France, 26-30 May 2014. In total, 5 orals and 10 posters presenting some Elmer/Ice related results over the 220 presentations of the symposium. The whole program of the symposium can be obtained here.
- Monday, 26 May, 16h54: Jean KRUG, Investigating the impact of melange on glacier dynamics
- Monday, 26 May, 17h12: Fabien GILLET-CHAULET, Could the non-linear creep behaviour observed at low stresses be associated with the yield stress of ice?
- Wednesday, 28 May, 10h48: Marianne HASELOFF, Modelling the dynamics of ice stream shear margins
- Thursday, 29 May, 14h00: Josefin AHLKRONA, The Fast Full Stokes Method (FFS) applied to the Greenland Ice Sheet
- Friday 30 May, 11h42: Martina SCHÄFER, Effect of elevation feedback in coupling a climatic mass-balance model to an ice-flow model: Vestfonna ice cap, Nordaustlandet/Svalbard
Poster Session A, Tuesday 15:30:
- Dorothée VALLOT, Seasonal evolution of basal friction coefficients in Kronebreen, Svalbard, using Elmer/Ice.
- Yongmei GONG, Sensitivity of Austfonna ice cap transient behavior to model physics and basal boundary conditions
- Ilona VÄLISUO, Simulations of the effect of mass-balance forcing on Midtre Lovénbreen, Svalbard, with a full-Stokes glacier model
- Thomas ZWINGER, Continuum and discrete models for calving and fracturing in glaciers
Poster Session B, Thursday 15:30:
- Jaime OTERO, Analysis of front position changes of a tidewater glacier and its control mechanisms
- Joe TODD, Flow and seasonal calving dynamics in a 2D model of Store Glacier, West Greenland
- Anne SOLGAARD, Inferring basal conditions at Engabreen from surface measurements
- Gwendolyn LEYSINGER VIELI, Investigating conditions for freeze-on at the ice sheet base and its effect on the ice sheet
- Sue COOK, The role of subaqueous melt in grounded ice: does it really enhance calving?
- Marion REVEILLET, Three-dimensional simulations of Glaciar Zongo (Bolivia, 16°S) over the next century, based on different IPCC scenarios
Cook and co-authors present a flow-line model of Helheim glacier that has been tuned using observations (velocity, temperature distribution) including Benn's calving criterion. The model was forced with different melting scenarios at its face, different surface melt distributions and - in a simplistic way – also ice mélange in front of the terminus. According to the findings with this model, it is rather the changing surface mass balance than the expected increase in ocean induced melting or the disappearing ice mélange that have the highest impact on accelerating the downwasting of a Greenlandic tide-water glacier such as Helheim.
The picture shows the difference in stress distributions and obtained crevasse depths with respect to the undisturbed ice front for different values of applied back-stress (representing the effect of ice mélange).
Cook, S., I.C. Rutt, T. Murray, A. Luckman, T. Zwinger, N. Selmes, A. Goldsack, and T.D. James, 2014: Modelling environmental influences on calving at Helheim Glacier in eastern Greenland, The Cryosphere, 8, 827-841, doi:10.5194/tc-8-827-2014 [link to paper]