Material Detail

Due to its close linkage to changes in ocean heat content and melting land ice, global mean sea level (GMSL) is one of the key climate change indicators. While

the modern observing system of altimetric satellites,ARGO floats (providing temperature and salinitymeasurements for the top 2000 m), and the Gravity Recovery and Climate Experiment (GRACE) (providing mass changes in the ocean and over the continents) provides global coverage of the spatially and temporally highly variable mean sea level (MSL) and its components, before 1992 the estimation of GMSL changes relies on a sparse set of tide gauges situated along the coast of the continental margins. Reconstructing GMSL from these tide gauges is a challenging task for a number ofdifferent reasons:

1. Tide gauges measure sea level relative to the land on which they are grounded and are, therefore, highlysensitive to the effects of vertical land motion (VLM)(Wöppelmann and Marcos 2016), which can be either induced by glacial isostatic adjustment (GIA, Peltieret al. 2004) and/or local effects such as groundwaterdepletion, earthquakes, etc.

2. There is no global reference system to which tide gauges measure sea level and the national datums vary widely.

 3. As pointwise measurements, tide gauges track localsea levels, which reflect the geographical patternsinduced by ocean dynamics and geoid changes in response to mass load redistribution (Kopp et al.2015).