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Ice mass loss in the polar regions of the Earth and mantle viscosity from GRACE data

Valentina Roberta Barletta(1), Roberto Sabadini(1) and Andrea Bordoni(1)

(1) University of Milan, Via Mangiagalli, 34, Milan, Italy

Abstract

Updated analyses of GRACE data show that estimates of mass imbalance in the polar regions of the Earth are sensitive to the level-2 monthly gravity field estimate products released by the various analysis centres and to the various corrections, such as ocean pole tide. After careful analysis, we have chosen to make use of the reliable and most recent GFZ-03 level-2 products. We have thus verified that previous analyses of mass imbalance in the polar regions of the Earth based on CSR-01 level 2 products may be affected by errors.

To estimate mass variations in the polar regions of the Earth, it is necessary to take into account the Post Glacial Rebound (PGR) contribution, which alter the mass trend much more than hydrologic contribution and ocean leakage corrections. GRACE data are affected by spatial and temporal errors which require appropriate filtering, while PGR predictions do not suffer from these problems, but only from uncertainties on the mantle viscosity profile and on the deglaciation model. For this reason, in order to constrain the Antarctic and Greenland ice mass changes, we have decided to estimate the mass imbalance from GRACE data and PGR separately, and only at the end to compare the two contributions.

We found that ice mass variation in Antarctica and Greenland is sensitive to mantle viscosity profile. For a weak mantle (lower mantle of 1021 Pa s), Antarctica is predicted to slightly accumulate ice mass at the rate of about 15 Gt/yr; to the other extreme for a stiff mantle (lower mantle of 1022 Pa s), when Antarctica is predicted to lose ice mass at the rate of about 210 Gt/yr. Other mantle viscosity profiles produce ice mass variation in between the aforementioned end members. The stiff lower mantle estimate of -210 Gt/yr is 25% lower than previous estimates of -280 Gt/yr obtained from Satellite Laser Ranging (SLR) analyses, over 20 yr of long wavelength gravity data. This difference can be due to the difference in the time interval covered by gravity data; the shorter time interval spanned by GRACE data makes the mass trend more sensitive to short scale time variation.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry