Abstract
We propose a revisited approach to estimating sea level change trends based on the integration of two measuring systems: satellite altimetry and tide gauge (TG) time series of absolute and relative sea level height. Quantitative information on vertical crustal motion trends at six TG stations of the Adriatic Sea are derived by solving a constrained linear inverse problem. The results are verified against Global Positioning System (GPS) estimates at some locations. Constraints on the linear problem are represented by estimates of relative vertical land motion between TG couples. The solution of the linear inverse problem is valid as long as the same rates of absolute sea level rise are observed at the TG stations used to constrain the system. This requirement limits the applicability of the method with variable absolute sea level trends. The novelty of this study is that we tried to overcome such limitations, subtracting the absolute sea level change estimates observed by the altimeter from all relevant time series, but retaining the original short-term variability and associated errors. The vertical land motion (VLM) solution is compared to GPS estimates at three of the six TGs. The results show that there is reasonable agreement between the VLM rates derived from altimetry and TGs, and from GPS, considering the different periods used for the processing of VLM estimates from GPS. The solution found for the VLM rates is optimal in the least square sense, and no longer depends on the altimetric absolute sea level trend at the TGs. Values for the six TGs’ location in the Adriatic Sea during the period 1993–2018 vary from −1.41 ± 0.47 mm y−1 (National Research Council offshore oceanographic tower in Venice) to 0.93 ± 0.37 mm y−1 (Rovinj), while GPS solutions range from −1.59 ± 0.65 (Venice) to 0.10 ± 0.64 (Split) mm y−1. The absolute sea level rise, calculated as the sum of relative sea level change rate at the TGs and the VLM values estimated in this study, has a mean of 2.43 mm y−1 in the period 1974–2018 across the six TGs, a mean standard error of 0.80 mm y−1, and a sample dispersion of 0.18 mm y−1.
Highlights
Sea level is a crucial index of climate change [1]
The two altimetric datasets span different periods of time, as Sea Level Climate Change Initiative (SLCCI) data is confined to the period 1993–2015, while C3S is continuously updated, and the period covered in this study extends from 1993 to 2018
We estimated relative and absolute sea level trends as well as vertical land motion rates, with their errors, at six locations in the Adriatic Sea; we used data produced by three measuring systems, integrating the information from those systems in order to maximize the knowledge, both qualitatively and quantitatively
Summary
Sea level is a crucial index of climate change [1]. Its variation reflects critical processes involving our environment of both natural and anthropogenic origin. Other phenomena (e.g., oceanic circulation changes due to modified atmospheric circulation at synoptic scale and other coastal processes such as storm surges) that have a high impact on coastal settlements may contribute to worsen the rising sea level scenario in the mid to long term [2,3]. The traditional technique for measuring sea level is to use a tide gauge (TG), which observes sea level height changes relative to the solid land surface where it is grounded. It accounts for both sea level change and land vertical displacement. Global Navigation Satellite System (GNSS) devices such as Global Positioning System (GPS) supply measurement of the land surface absolute geocentric height above the Earth’s center of mass. The relative and absolute sea-level change rates measured by TGs and satellite altimetry, respectively, and u.
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