Improved regional sea-level estimates from present day mass fluxes from Ice Sheets, Glaciers and land water using GRACE

Changes in ice sheets, glaciers and ice caps (GIC) and land water mass cause regional sea level variations that differ significantly from a uniform sea level, with a decrease in sea level near the sources of mass added to the ocean and an increase up to 30% larger than the global mean sea level in the far field. This effect called sea level fingerprints (SLF) are difficult to separate from the variation from ocean dynamics on short time and spatial scales. Most studies removed the uniform sea level to avoid this additional mass flux from atmosphere and land. However, as ice continues to melt, the SLF signal will become significantly different from uniform sea level. This makes removal of uniform mass flux to introduce additional error in the studies of ocean dynamic variation. Here, we employ observations of time variable gravity from GRACE over land, including the mass change of ice sheets, GIC, and land water storage to precisely calculate the SLF for the time period 2002-2015. We compare the results with sea level change from satellite radar altimetry (AVISO) corrected for the steric signal of the ocean from Argo measurements. We find an excellent agreement at the global scale in trend for the entire period between GRACE-derived SLF and AVISO minus Argo estimates. The agreement extends at the spatial scale of oceanic regions. Locally, the GRACE-derived SLF also agrees with in situ ocean bottom pressure recorder. The agreement demonstrates for the first time that SLF are reliable in terms of amplitude (intensity of mass loss), phase (spatial distribution of sources), and trends (increase in mass loss with time) using GRACE. During our observation period, we find that changes in land water mass dominate the seasonal variability of SLF. Greenland controls 42% of the total trend and 39% along the western and eastern US. Antarctica contributes 16% of the total trend and 21% in the western and eastern US. This work was performed at UC Irvine and at Caltech's Jet Propulsion Laboratory under a contract with NASA's Cryospheric Science Program.