Sea level at Saint Paul Island, southern Indian Ocean, from 1874 to the present

A data archeology exercise was carried out on sea level observations recorded during the transit of Venus across the Sun observed in 1874 from Saint Paul Island (38 degrees 41'S, 77 degrees 31 E) in the southern Indian Ocean. Historical (1874) and recent (1994-2009) sea level observations were assembled into a consistent time series. A thorough check of the data and its precise geodetic connection to the same datum was only possible thanks to the recent installation of new technologies (GPS buoy and radar water level sensor) and leveling campaigns. The estimated rate of relative sea level change, spanning the last 135 years at Saint Paul Island, was not significantly different from zero (-0.1 +/- 0.3mm yr(-1)), a value which could be reconciled with estimates of global average sea level rise for the 20th century assuming the DORIS vertical velocity estimate at Amsterdam Island (100 km distant) could be applied to correct for the land motion at the tide gauge. Considering the scarcity of long-term sea level data in the Southern Hemisphere, the exercise provides an invaluable additional observational constraint for further investigations of the spatial variability of sea level change, once vertical land rates can be determined.