Higher than present global mean sea level recorded by an Early Pliocene intertidal unit in Patagonia (Argentina)

Abstract

Reconstructions of global mean sea level from earlier warm periods in Earth?s history can helpconstrain future projections of sea level rise. Here we report on the sedimentology and age ofa geological unit in central Patagonia, Argentina, that we dated to the Early Pliocene(4.69?5.23 Ma, 2σ) with strontium isotope stratigraphy. The unit was interpreted as representativeof an intertidal environment, and its elevation was measured with differential GPS atca. 36m above present-day sea level. Considering modern tidal ranges, it was possible toconstrain paleo relative sea level within ±2.7m (1σ). We use glacial isostatic adjustmentmodels and estimates of vertical land movement to calculate that, when the Camaronesintertidal sequence was deposited, global mean sea level was 28.4 ± 11.7m (1σ) above present.This estimate matches those derived from analogous Early Pliocene sea level proxies inthe Mediterranean Sea and South Africa. Evidence from these three locations indicates thatEarly Pliocene sea level may have exceeded 20m above its present level. Such high globalmean sea level values imply an ice-free Greenland, a significant melting of West Antarctica,and a contribution of marine-based sectors of East Antarctica to global mean sea level.