Glacial isostatic adjustment and the anomalous tide gauge record of eastern North America

SEA-LEVEL variations, as recorded by the global network of tide gauges, represent a rich data set for studying a wide range of natural and anthropogenic phenomena, such as the sea-level rise induced by possible global warming. For this purpose, long-term sea-level trends must be corrected for the \textquoterightcontaminating\textquoteright effects of continuing glacial isostatic adjustment1-5 (GIA). The numerical correction procedure has, for sites on the east coast of North America, yielded a set of highly anomalous sea-level rates characterized by systematic geographical trends2,4,5. We demonstrate that these trends are a consequence of inadequacies in the previous \textquoterightstandard\textquoteright numerical prediction for GIA. In particular, we find that the well-known trends in the GIA-corrected tide gauge rates are eliminated if the lower-mantle viscosity of the Earth model used in the GIA prediction is increased. This result obviates the need to explain the anomalous trend as a manifestation of Gulf Stream ocean circulation4 or neotectonic processes2.