Abstract
Abstract. Observations from permanent Global Navigation Satellite System (GNSS) stations are commonly used to correct tide-gauge observations for vertical land motion (VLM). We combine GRACE (Gravity Recovery and Climate Experiment) observations and an ensemble of glacial isostatic adjustment (GIA) predictions to assess and evaluate the impact of solid-Earth deformation (SED) due to contemporary mass redistribution and GIA on VLM trends derived from GNSS stations. This mass redistribution causes relative sea-level (RSL) and SED patterns that not only vary in space but also exhibit large interannual variability signals. We find that for many stations, including stations in coastal locations, this deformation causes VLM trends on the order of 1 mm yr−1 or higher. In multiple regions, including the Amazon Basin and large parts of Australia, the SED trend flips sign between the first half and second half of the 15-year GRACE record. GNSS records often only span a few years, and due to these interannual variations SED causes substantial biases when the linear trends in these short records are extrapolated back in time. We propose a new method to avoid this potential bias in the VLM-corrected tide-gauge record: instead of correcting tide-gauge records for the observed VLM trend, we first remove the effects from GIA and contemporary mass redistributions from the VLM observations before computing the VLM trend. This procedure reduces the extrapolation bias induced by SED, and it also avoids the bias due to sea-floor deformation: SED includes net sea-floor deformation, which is ignored in global-mean sea-level reconstructions based on VLM-corrected tide-gauge data. We apply this method to 8166 GNSS stations. With this separation, we are able to explain a large fraction of the discrepancy between observed sea-level trends at multiple long tide-gauge records and the global-mean sea-level trend from recent reconstructions.
Highlights
Recent global and local studies have shown that local vertical land motion (VLM) explains a significant part of spatial variations in tide-gauge trends, which, if ignored, biases estimates of global and local sea-level changes (e.g., King et al, 2012; Wöppelmann et al, 2014; Hamlington et al, 2016)
glacial isostatic adjustment (GIA) causes changes in the gravitational potential observed by Gravity Recovery and Climate Experiment (GRACE) satellites, causes solid-Earth deformation (SED) which affects VLM observed by Global Navigation Satellite System (GNSS) stations, and causes local relative sealevel (RSL) changes, which are observed by tide gauges (Tamisiea, 2011)
The global-mean land mass changes due to contemporary mass redistribution are shown in Fig. 6 and Table 1, which show that all cryospheric processes cause a net land mass loss while terrestrial water storage (TWS) does not show a significant positive or negative linear trend
Summary
Recent global and local studies have shown that local vertical land motion (VLM) explains a significant part of spatial variations in tide-gauge trends, which, if ignored, biases estimates of global and local sea-level changes (e.g., King et al, 2012; Wöppelmann et al, 2014; Hamlington et al, 2016). Mass loss from glaciers and ice sheets and changes in terrestrial water storage (TWS) have resulted in an increase in ocean mass and a rise in global-mean sea level over the past decades (WCRP Global Sea Level Budget Group, 2018), but they have caused substantial local SED patterns (Riva et al, 2017; Spada, 2017) This process explains a nonnegligible part of VLM signals observed by permanent GNSS stations (Santamaría-Gómez and Mémin, 2015; Pfeffer et al, 2017; Schumacher et al, 2018). We apply the residual VLM trends to the long tide-gauge records to see whether land motion explains a part of this discrepancy
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