Greenland ice sheet mass loss time series fill-in by CryoSat, IceBridge and GNET

The time gap between GRACE and GRACE-FO is a problem for the provision of a consistent, long-term mass change time series of the Greenland ice sheet, a key essential climate variable of global significance due to the impact on sea level rise. Other space-based methods for monitoring the Greenland ice sheet changes have significant errors in estimating mass losses: for CryoSat radar altimetry errors due to ice sheet margin sampling and radar penetration can be large; flux-gate input-output mass change methods based on space velocity ice flow mapping need models of accumulation and bed thickness; and mass changes inferred from GPS land uplift are restricted to marginal zones and affected by GIA errors.

In the presentation we use CryoSat elevation change data, supplemented with auxillary firn model and IceBridge data, along with GNET and some ice velocity data, to develop a composite GRACE-consistent monthly mass change parameter in the GRACE/CryoSat overlap period 2010-16. We subsequently use this time series to estimate the Greenland ice sheet changes beyond the termination of reliable GRACE data. The short-term events of Greenland ice sheet mass changes have shown large fluctuations in the last decade, due to large changes in regional ice dynamics as well as large interannual melt season changes; these events are picked up clearly in the composite time series as well, and validated by independent model-based estimates of Greenland mass balance from meteorological data.