Vertical Deformation and Residual Altimeter Systematic Errors around Continental Australia Inferred from a Kalman-Based Approach

We further developed a space-time Kalman approach to estimate time-variable signals in residual altimeter systematic errors and vertical land motion (VLM) around the Australian coast since the 1990s, through combining multi-mission absolute sea-level (ASL), relative sea-level (RSL) from tide gauges (TGs) and GPS heights records. Our results confirmed continent-wide subsidence and TG-specific VLMs yielding a ~40% reduction in RMSE of geographical ASL variability, compared with rates determined using spatially interpolated GPS velocities that fail to capture localized trends by up to ~1.5 mm/yr. Stacked time series of non-linear deformation at TGs and nearby GPS showed some correlation, suggesting the technique was partially successful in reflecting the surface loading. Site-by-site inspection revealed spurious non-linearity likely caused by residual oceanographic signals present between the TG and altimeter measurement locations. Our average mission-specific error estimates are small but significant, typically within ~±0.5-1.0 mm/yr, with negligible effect implied on the overall rate of ASL. Analysis of the time variability of altimeter errors confirmed stability for most missions except for Jason-2 with an anomaly reaching ~2.8 mm/yr in the first ~3.5 years of operation which is supported by analysis from the Bass Strait altimeter validation facility. Weak correlation with the dominant climate mode suggests potential deficiencies in the resolution of the time-variable gravity field used for orbit determination as a possible cause, yet other drivers cannot be discounted. Our approach advances the ability to estimate TG-specific VLMs and regional altimeter systematic errors, and highlights that residual oceanographic signals remain a fundamental limitation to such techniques.

Ocean mass, sterodynamic effects, and vertical land motion largely explain US coast relative sea level rise

Regional sea-level changes are caused by several physical processes that vary both in space and time. As a result of these processes, large regional departures from the long-term rate of global mean sea-level rise can occur. Identifying and understanding these processes at particular locations is the first step toward generating reliable projections and assisting in improved decision making. Here we quantify to what degree contemporary ocean mass change, sterodynamic effects, and vertical land motion influence sea-level rise observed by tide-gauge locations around the contiguous U.S. from 1993 to 2018. We are able to explain tide gauge-observed relative sea-level trends at 47 of 55 sampled locations. Locations where we cannot explain observed trends are potentially indicative of shortcomings in our coastal sea-level observational network or estimates of uncertainty.

Measuring Sea Level Rise Along the Coast

Scientists created a global map of vertical land motion to show how the solid ground is moving relative to the planet’s rising seas.

Sinking land intensifies sea-level rise: a global InSAR analysis of coastal cities

Coastal land is being lost worldwide at an alarming rate due to relative sea-level rise (RSLR) resulting from vertical land motion (VLM). This problem is understudied at a global scale, due to high spatial variability and difficulties reconciling VLM between regions. Here we provide self-consistent, high spatial resolution VLM observations derived from Interferometric Synthetic Aperture Radar for the 51 largest coastal cities, representing 22% of the global urban population. We show that peak subsidence rates are faster than current global mean sea-level rise rates and VLM contributions to RSLR are greater than IPCC projections in 90% and 53% of the cities respectively. Localized VLM worsens RSLR impacts on land and population in 73-75% of the cities, with Chittagong (Bangladesh), Yangon (Myanmar) and Jakarta (Indonesia) at greatest risk. With this dataset, accurate projections and comparisons of RSLR effects accounting for VLM are now possible for urban areas at a global scale.

Studying the Sensitivity of Satellite Altimetry, Tide Gauge and GNSS Observations to Changes in Vertical Displacements

Tide gauge observations provide sea level relative to the Earth’s crust, while satellite altimetry measures sea level variations relative to the centre of the Earth’s mass. Local vertical land motion can be a significant contribution to the measured sea level change.Satellite altimetry was traditionally used to study the open ocean, but this technology is now being used over inland seas too.The difference of both observations can be used to estimate vertical crustal movement velocities along the sea coast. In this paper, vertical crustal movement velocities were investigated at tide gauge sites along the Adriatic Sea coast by analyzing differences between Tide Gauge (TG) and Satellite Altimetry (SA) observations. Furthermore, the estimated vertical motion rates were compared with those from nearby GNSS measurements.The study determines the practical relationships between these vertical crustal movements and those determined from unrelated data acquired from the neighbouring GNSS stations. The results show general consistence with the present geodynamics in the Adriatic Sea coastal zone.

North SEAL: a new dataset of sea level changes in the North Sea from satellite altimetry

Information on sea level and its temporal and spatial variability is of great importance for various scientific, societal, and economic issues. This article reports about a new sea level dataset for the North Sea (named North SEAL) of monthly sea level anomalies (SLAs), absolute sea level trends, and amplitudes of the mean annual sea level cycle over the period 1995–2019. Uncertainties and quality flags are provided together with the data. The dataset has been created from multi-mission cross-calibrated altimetry data preprocessed with coastal dedicated approaches and gridded with an innovative least-squares procedure including an advanced outlier detection to a 6–8 km wide triangular mesh. The comparison of SLAs and tide gauge time series shows good consistency, with average correlations of 0.85 and maximum correlations of 0.93. The improvement with respect to existing global gridded altimetry solutions amounts to 8 %–10 %, and it is most pronounced in complicated coastal environments such as river mouths or regions sheltered by islands. The differences in trends at tide gauge locations depend on the vertical land motion model used to correct relative sea level trends. The best consistency with a median difference of 0.04±1.15 mm yr−1 is reached by applying a recent glacial isostatic adjustment (GIA) model. With the presented sea level dataset, for the first time, a regionally optimized product for the entire North Sea is made available. It will enable further investigations of ocean processes, sea level projections, and studies on coastal adaptation measures. The North SEAL data are available at https://doi.org/10.17882/79673 (Müller et al., 2021).

Strain Transformation Adjacent to the West Qinling Orogen: Implications for the Growth of the Northeastern Tibetan Plateau

The West Qinling orogen has played an important role in accommodating the deformation in the northeastern Tibetan Plateau induced by the India-Eurasia convergence. Here we construct a vertical land motion (VLM) model based on the latest leveling observations adjacent to the West Qinling orogen. Combined with the horizontal deformation field, the crustal deformation pattern in this area is investigated. Additionally, slip rate and coupling coefficients of the West Qinling fault, the longest fault separating the West Qinling orogen from the Lanzhou (Longxi) block, are inverted and constrained with GPS and VLM observations. Results show that the West Qinling fault slips slowly at a rate of 1–2 mm/yr and is strongly coupled with a moment magnitude deficit of Mw7.4. The crustal uplift rates adjacent to the West Qinling orogen are 0–3 mm/yr; which combined with 0–12.5 × 10−9/yr contraction rates, suggests that strain transformation plays a key role in controlling the tectonic uplift in the West Qinling orogen, and furthers our understanding of the contemporary geomorphic and topographic features. We identify a significant deformation transition belt at longitudes of 105°–106°E, which indicates that crustal deformation, induced from the northeastern expansion of the Tibetan Plateau, is mainly constrained to the plateau, rather than accommodated by crustal materials escaping eastward along the Qinling Mountains.