Constraining the mass balance of the Greenland Ice Sheet
Constraining the mass balance of the Greenland Ice Sheet Professor Jonathan Bamber (Bristol Glaciology Centre, University of Bristol) Dr Mark Tamisiea (Proudman Oceanographic Laboratory, Liverpool) CASE studentship This studentship is a CASE award (providing additional funding) with the Proudman Oceanographic Laboratory, Liverpool. Sea level rise is considered to be the most significant and dangerous consequence of global warming. Clearly, a major potential contribution to sea level rise are the ice sheets of Antarctica and Greenland, with the latter predicted to be particularly vulnerable to climate change over the next century [Gregory et al., 2004; Gregory and Huybrechts, 2006]. Complete removal of the ice sheet would result in a mean global sea level rise of around 6 m [Bamber et al., 2007]. Recent observations suggest that the mass loss from Greenland has increased dramatically over the last ~decade, possibly as a consequence of regional increases in ocean and atmospheric temperature [Rignot and Kanagaratnam, 2006]. Satellite remote sensing data offer our best chance of quantifying and monitoring the mass trends of the Greenland Ice Sheet (GrIS) but, unfortunately, the various approaches available suffer from errors and issues that render no one approach adequate [Cazenave, 2006; Thomas et al., 2006] (see Fig 1). The three main satellite methods comprise measuring elevation changes through time (dh/dt) [Zwally et al., 2005], changes in the gravity field from the GRACE satellites [Luthcke et al., 2006], and mass budget
Fig 1. Various satellite estimates of the mass balance of the Greenland ice sheet [Cazenave, 2006]. The thickness of the boxes indicates the error for the estimate. Note that, in some cases, the boxes do not overlap, which means that they do not agree within their combined errors, even though several of the estimates use a similar approach.
calculations using satellite observations of velocity with estimates of the surface mass balance [Rignot and Kanagaratnam, 2006].The aim of this project is to combine all three approaches to allow us to solve for the different errors that afflict each method and, as a consequence, solve for the mass balance and post glacial rebound signals. Measuring the
latter can provide valuable information about ice volume changes on longer timescales [Tamisiea et al., 2007]. Aims: The overarching goal of this project is to produce a consistent, time-evolving mass balance estimate for the Greenland ice sheet by combining gravity, dh/dt and mass budget data to reduce the uncertainties in each dataset/method. Approach: To achieve this goal, we will use a 4-D (space and time) data assimilation technique to solve for the changes in ice mass in space and time by assimilating measured elevations from airborne and satellite altimetry, gravity anomalies from the GRACE, outgoing mass fluxes from satellite velocity data and surface mass balance trends from a regional climate model [Fettweis, 2007]. Candidate Profile The student will get experience at the cutting-edge of glaciological and climate change research. The project would be most suited to a student with a quantitative training and experience with the use of computers for the analysis of spatial data sets and numerical modelling would be desirable but full training will be given in all aspects of the project. We are thus seeking applications from people with a background in a quantitative science (e.g. physics, geophysics, physical geography, remote sensing, electrical engineering, computer science) with an interest in applying their expertise to geophysical research. The post offers the opportunity for working in an important and exciting area of glaciology and solid earth geophysics and the opportunity to collaborate with scientists at POL/BGC (substitute as appropriate). For further information please contact Professor Jonathan Bamber email: [email protected] tel: +44 (0) 117 928 8102 Dr Mark Tamisiea email: [email protected] tel: +44 (0) 115 795 8421 References : 1. Bamber, J. L., et al. (2007), Rapid response of modern day ice sheets to external forcing, Earth Plan. Sci. Lett., 257, 1-13. 2. Cazenave, A. (2006), How fast are the ice sheets melting?, Science, 314(5803), 12501252. 3. Fettweis, X. (2007), Reconstruction of the 1979-2006 Greenland ice sheet surface mass balance using the regional climate model MAR, The Cryosphere, 1(1), 21-40. 4. Gregory, J. M., et al. (2004), Threatened loss of the Greenland ice-sheet, Nature, 428(6983), 616-616. 5. Gregory, J. M., and P. Huybrechts (2006), Ice-sheet contributions to future sea-level change, Phil Trans Roy Soc, A, 364(1844), 1709-1731. 6. Luthcke, S. B., et al. (2006), Recent Greenland ice mass loss by drainage system from satellite gravity observations, Science, 314(5803), 1286-1289. 7. Rignot, E., and P. Kanagaratnam (2006), Changes in the Velocity Structure of the Greenland Ice Sheet, Science, 311(5763), 986-990. 8. Tamisiea, M. E., et al. (2007), GRACE gravity data constrain ancient ice geometries and continental dynamics over Laurentia, Science, 316(5826), 881-883. 9. Thomas, R., et al. (2006), Progressive increase in ice loss from Greenland, Geophysical Research Letters, 33(10), L10503. 10. Zwally, H. J., et al. (2005), Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992–2002, J. Glaciol., 51(175), 509-527.
Fig 1. Various satellite estimates of the mass balance of the Greenland ice sheet [Cazenave, 2006]. The thickness of the boxes indicates the error for the estimate. Note that, in some cases, the boxes do not overlap, which means that they do not agree within their combined errors, even though several of the estimates use a similar approach.
calculations using satellite observations of velocity with estimates of the surface mass balance [Rignot and Kanagaratnam, 2006].The aim of this project is to combine all three approaches to allow us to solve for the different errors that afflict each method and, as a consequence, solve for the mass balance and post glacial rebound signals. Measuring the
latter can provide valuable information about ice volume changes on longer timescales [Tamisiea et al., 2007]. Aims: The overarching goal of this project is to produce a consistent, time-evolving mass balance estimate for the Greenland ice sheet by combining gravity, dh/dt and mass budget data to reduce the uncertainties in each dataset/method. Approach: To achieve this goal, we will use a 4-D (space and time) data assimilation technique to solve for the changes in ice mass in space and time by assimilating measured elevations from airborne and satellite altimetry, gravity anomalies from the GRACE, outgoing mass fluxes from satellite velocity data and surface mass balance trends from a regional climate model [Fettweis, 2007]. Candidate Profile The student will get experience at the cutting-edge of glaciological and climate change research. The project would be most suited to a student with a quantitative training and experience with the use of computers for the analysis of spatial data sets and numerical modelling would be desirable but full training will be given in all aspects of the project. We are thus seeking applications from people with a background in a quantitative science (e.g. physics, geophysics, physical geography, remote sensing, electrical engineering, computer science) with an interest in applying their expertise to geophysical research. The post offers the opportunity for working in an important and exciting area of glaciology and solid earth geophysics and the opportunity to collaborate with scientists at POL/BGC (substitute as appropriate). For further information please contact Professor Jonathan Bamber email: [email protected] tel: +44 (0) 117 928 8102 Dr Mark Tamisiea email: [email protected] tel: +44 (0) 115 795 8421 References : 1. Bamber, J. L., et al. (2007), Rapid response of modern day ice sheets to external forcing, Earth Plan. Sci. Lett., 257, 1-13. 2. Cazenave, A. (2006), How fast are the ice sheets melting?, Science, 314(5803), 12501252. 3. Fettweis, X. (2007), Reconstruction of the 1979-2006 Greenland ice sheet surface mass balance using the regional climate model MAR, The Cryosphere, 1(1), 21-40. 4. Gregory, J. M., et al. (2004), Threatened loss of the Greenland ice-sheet, Nature, 428(6983), 616-616. 5. Gregory, J. M., and P. Huybrechts (2006), Ice-sheet contributions to future sea-level change, Phil Trans Roy Soc, A, 364(1844), 1709-1731. 6. Luthcke, S. B., et al. (2006), Recent Greenland ice mass loss by drainage system from satellite gravity observations, Science, 314(5803), 1286-1289. 7. Rignot, E., and P. Kanagaratnam (2006), Changes in the Velocity Structure of the Greenland Ice Sheet, Science, 311(5763), 986-990. 8. Tamisiea, M. E., et al. (2007), GRACE gravity data constrain ancient ice geometries and continental dynamics over Laurentia, Science, 316(5826), 881-883. 9. Thomas, R., et al. (2006), Progressive increase in ice loss from Greenland, Geophysical Research Letters, 33(10), L10503. 10. Zwally, H. J., et al. (2005), Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992–2002, J. Glaciol., 51(175), 509-527.
