GPS Imaging of Global Vertical Land Motion for Studies of Sea Level Rise

Abstract

We estimate the rates and patterns of vertical land motion (VLM) on all locations on Earth's land surface using GPS Imaging. The solution is based on a large database of uniformly processed GPS data from solutions that are aligned to the International Terrestrial Reference Frame. We provide global maps and estimates of VLM at all tide gauges of the Permanent Service for Mean Sea Level to better constrain the difference between geocentric and relative sea level rise. To enable critical assessment of the VLM estimate, the temporal and spatial contributions to rate uncertainty and variability are generated and included for every gauge. Seasonality and trends of uplift are assessed and found to be strongly correlated with observations from gravity data suggesting that loading from the terrestrial hydrosphere is a dominant driver of non-glacial isostatic adjustment (non-GIA) VLM. Although stations are dominantly concentrated at subsiding parts of continents, GPS Imaging geographically balances VLM signals, correcting for bias associated with network distribution. This allows us to make a global assessment of the budget of uplift and subsidence attributable to GIA and non-GIA sources. We show that the surface motion of the continents is on average upward, implying that the unobserved areas (composed of the ocean basins and ice-covered areas) move on average downward with respect to Earth center. However, after correcting for the GIA the reverse is true, and observed areas subside on average implying that the unobserved areas undergo net non-GIA-related uplift.