The FIGO team
Jürgen Kusche¹,Roelof Rietbroek¹, Jens Schröter², Sandra-Esther Brunnabend², Ralph Timmermann²
¹Astronomische, Physikalische und Mathematische Geodäsie, Institut für Geodäsie und Geoinformation, Bonn, Germany
²Alfred-Wegener-Institut (AWI), Bremerhaven, Germany
The aim of the FIGO project is quantifying the different contributions to the present day sea level rise. Currently, we know that virtually all of the Earth's ice sheets are melting, but we are much less certain on the actual melting rates and have problems quantifying the physics behind it.
Due to the gravitational attraction of masses, a changing ice sheet will cause, besides a direct sea level change, a change in gravity, which is stronger in the vicinity of the melting source. The change in sea level, which responds to those gravitational perturbations, will therefore exhibit a specific spatial pattern, depending on the ice sheets location and mass.
Within the FIGO project we will investigate whether those specific sea level 'fingerprints' can be detected in GRACE (satellite gravimetry), Altimetry (sea surface height ) and tide gauge data. More importantly, by combining the data we will have the opportunity to quantify and separate the different sources of ice loss.
Figure left: Contribution from the Antarctic Peninsula Ice sheet to the relative sea level rate (in mm/yr) based on GRACE data only (simplified inversion). Figure right: the same but for Greenland.
Ice sheets, Glacial isostatic adjustment and Sea level change
By solving the sea level equation for the ice sheets separately ( figure 3) we can construct a fingerprint for each ice sheet. The observed sea level changes can then be considered as the summation of the individual ice sheet contributions + the contribution of glacial isostatic adjustment. Additionally when using altimetry we also observe a mass conserving expansion of the sea due to thermal and salinity changes.
Figure 3: The physical effects contributing to the sea level equation.
- Calculation of 'fingerprints' for several sources (ice sheets, land glaciers, hydrological sources (see project REGHYDRO), GIA, ..)
- Retrieval of melting rates, surface loading, steric by (joint) inversion of data from GRACE, altimetry and tide gauges. ( see also JIGOG project)
- Investigate the long term ocean response to melting scenarios by means of ocean modelling
- Quantification of melting rates of the most important ice sheets
- Separation of steric/eustatic sea level changes
- Effect of the melting sources on ocean modelling
- Provide geographic dependencies of the sea level rise (in particular for the European coast)
- Provide constraints for GIA models (in collaboration with VILMA)
Selection of relevant publications
Chen, J. L., Wilson, C. R., & Tapley, B. D., 2006. Satellite gravity measurements confirm accelerated melting of Greenland ice sheet, Science, 313(5795).
Clarke P.U., Mitrovica J.X., Milne G.A., Tamisea M.E. (2002) Sea-Level fingerprinting as a direct test for the source of a global melt water pulse IA, Science, 295, 2438
Mitrovica J.X., Tamisea M., Davis J.L., Milne G. (2001), Recent mass balance of polar ice sheets inferred from patterns of global sea level change, Nature, 409, 1026-1029
Plag H.-P. and Jüttner H.-U. (2001). Inversion of global tide gauge data for present-day ice load changes, Mem. Nat. Inst. Polar Res., 54:301-317
Velicogna I. and J. Wahr (2006) Measurements of Time-Variable Gravity Show Mass Loss in Antarctica, Science Vol. 311. no. 5768, pp. 1754 – 1756, DOI: 10.1126/science.1123785
Lombard A., D. Garcia, G. Ramillien, A. Cazenave, R. Biancale, J.-M. Lemoine, F. Flechtner, R.Schmidt and M. Ishii, 2007, Estimation of steric sea level variations from combined GRACE and Jason-1 data, EPSL, 254, 194-202
Milne, G.A. and J.X. Mitrovica (1998), Postglacial sea-level change on a rotating Earth, Geophys. J. Int., 133, 1-19
Peltier W. R., 2004, Global glacial isostasy and the surface of the ice-age Earth: the ICE-5G (VM2) model and GRACE, Annual Rev. of Earth Planet. Sci., 32, 111-149