Ocean bottom deformation due to present-day mass redistribution and its impact on sea level observations

Present-day mass redistribution increases the total ocean mass and, on average, causes the ocean bottom to subside elastically. Therefore, barystatic sea-level rise is larger than the resulting global-mean geocentric sea-level rise,observed by satellite altimetry and GPS-corrected tide gauges. We use realistic estimates of mass redistribution from ice-mass loss and land-water storage to quantify the resulting ocean-bottom deformation and its effect on global and regional ocean-volume change estimates. Over 1993-2014, the resulting globally-averaged geocentric sea-level change is 8 percent smaller than the barystatic contribution. Over the altimetry domain, the difference is about 5 percent, and due to this effect, barystatic sea-level rise will be underestimated by more than 0.1 mm/y over 1993 -2014. Regional differences are of-ten larger: up to 1 mm/y over the Arctic Ocean and 0.4 mm/y in the South Pacific. Ocean bottom deformation should be considered when regional sea-level changes are observed in a geocentric reference frame.