Vertical land motion in the Iberian Atlantic coast and its implications for sea level change evaluation

Abstract

<jats:title>Abstract</jats:title><jats:p>In this study, we estimate vertical land motion for 35 stations primarily located along the coastline of Portugal and Spain, using GPS time series with at least eight years of observations. Based on this set of GPS stations, our results show that vertical land motion along the Iberian coastline is characterized, in general, by a low to moderate subsidence, ranging from −2.2 mm yr<jats:sup>−1</jats:sup> to 0.4 mm yr<jats:sup>−1</jats:sup>, partially explained by the glacial isostatic adjustment geophysical signal. The estimates of vertical land motion are subsequently applied in the analysis of tide gauge records and compared with geocentric estimates of sea level change. Geocentric sea level for the Iberian Atlantic coast determined from satellite altimetry for the last three decades has a mean of 2.5 ± 0.6 mm yr<jats:sup>−1</jats:sup>, with a significant range, as seen for a subset of grid points located in the vicinity of tide gauge stations, which present trends varying from 1.5 mm yr<jats:sup>−1</jats:sup> to 3.2 mm yr<jats:sup>−1</jats:sup>. Relative sea level determined from tide gauges for this region shows a high degree of spatial variability, that can be partially explained not only by the difference in length and quality of the time series, but also for possible undocumented datum shifts, turning some trends unreliable. In general, tide gauges corrected for vertical land motion produce smaller trends than satellite altimetry. Tide gauge trends for the last three decades not corrected for vertical land motion range from 0.3 mm yr<jats:sup>−1</jats:sup> to 5.0 mm yr<jats:sup>−1</jats:sup> with a mean of 2.6 ± 1.4 mm yr<jats:sup>−1</jats:sup>, similar to that obtained from satellite altimetry. When corrected for vertical land motion, we observe a reduction of the mean to ∼1.9 ± 1.4 mm yr<jats:sup>−1</jats:sup>. Actions to improve our knowledge of vertical land motion using space geodesy, such as establishing stations in co-location with tide gauges, will contribute to better evaluate sea level change and its impacts on coastal regions.</jats:p>

Vertical land motion component is underestimated in sea-level projections from northern Spain

“…Ref. 17 showed low to moderate subsidence with a mean rate of ~ 0.6 mm/yr along the Iberian Atlantic coast, but with signi cant spatial variations and up to 2.2 mm/yr subsidence along the northern Spain coast that re ects more localised effects 59 . More importantly, the Oka estuary is located in the Basque-Cantabrian Basin that formed with the opening of the North Atlantic Ocean and the Bay of Biscay 60 .…”

“…Rising global mean sea level (GMSL) is primarily driven by thermal expansion of ocean water 7 and ice mass loss from glaciers, ice caps and the Greenland and Antarctica Ice Sheets 8-10 . However, local RSL rise can deviate from GMSL 3,11,12 because of processes such as vertical land motion (VLM) [13][14][15][16][17] .…”

Simplified Marsh Response Model (SMRM): A Methodological Approach to Quantify the Evolution of Salt Marshes in a Sea-Level Rise Context

“…He inferred vertical uplift rates from 0.08 to 0.28 mm/year. Different results have been obtained by [56]. These authors computed vertical land motions along the Iberian Atlantic coast using GPS time series with more than 8 years of observations.…”

“…Vertical land movements shown in this study for Cascais and Setúbal-Tróia tide gauges indicate low subsidence at both stations, at rates of −0.766 ± 0.238 and −0.766 ± 0.320 mm/year, respectively. As correctly pointed out by [56,57], the above estimates should be taken with caution, given that different studies use different methodological approaches, contrasting lengths of the data series, heterogeneity in the spatial distribution of GPS source stations, and possible undocumented problems affecting both GPS and tide-gauge stations, and differences in data analysis and correction.…”