Relative sea-level fall since the last interglacial stage: Are coasts uplifting worldwide?

The growing interest in quantification of vertical ground motion stems from the need to understand in detail how the Earthʹs crust behaves, for both scientific and social reasons. However, only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies. Although there are many local studies of Quaternary vertical motions of coastlines, we know of no comprehensive worldwide synthesis. Here we provide a compilation of 890 records of paleoshoreline sequences, with particular emphasis on the last interglacial stage (Marine Isotopic Stage [MIS] 5e, ~ 122 ka). The quality of dating MIS 5e makes it a reliable marker to evaluate vertical ground motion rates during the late Quaternary on a global scale. The results show that most coastal segments have risen relative to sea-level with a mean uplift rate higher than 0.2 mm/yr, i.e. more than four times faster than the estimated eustatic drop in sea level. The results also reveal that the uplift rate is faster on average for active margins than for passive margins. Neither dynamic topography nor glacio-hydro-isostasy may explain sustained uplift of all continental margins, as revealed by the wide distribution of uplifted sequences of paleoshorelines. Instead, we suggest that only plate-tectonic processes reconcile all observations of Quaternary coastal uplift. We propose that long-term continental accretion has led to compression of continental plates and uplift of their margins. Therefore this study concludes that plate-tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic. These results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record.