Geocentric sea level trend using GPS and >100-year tide gauge record on a postglacial rebound nodal line

Abstract

For studies of global sea level change, 103 years of tide gauge data were analyzed from North Shields on the North Sea coast of Great Britain, near a predicted nodal line of postglacial rebound (PGR). Simultaneous estimation of statistically significant tidal components gives a relative sea level rate of 1.8 +/- 0.1 mm/yr with no significant acceleration. Analysis of a Global Positioning System (GPS) station, which we installed directly on the tide gauge structure, shows the tide gauge rising at 1.4 +/- 1.5 mm/yr relative to the international terrestrial reference frame (ITRF96), Leveling shows the tide gauge rising with statistical significance at 0.8 +/- 0.2 mm/yr relative to a nearby lighthouse (0.5 km away) situated on bedrock. Thus our geodetic estimate of geocentric crustal rise is 0.6 +/- 1.5 mm/yr, which is consistent with the PGR nodal hypothesis. Our estimate of geocentric sea level rise using local leveling and assuming the PGR nodal hypothesis (i.e., zero crustal rise with no model uncertainty) is therefore 2.6 +/- 0.2 mm/yr. Introducing an upper bound error based on observational evidence and PGR model differences modifies this to 2.6 +/- 1.0 mm/yr. This is to be compared with our model-independent GPS-based estimate of 3.2 +/- 1.5 mm/yr. We conclude that PGR and geodesy corroborate a geocentric sea level rise of 2.6 +/- 1.0 mm/yr (upper bound), which is larger than the tide gauge records alone (1.8 mm/yr) would indicate.