Common Era sea-level change in the North Atlantic

Abstract

Relative sea-level (RSL) varies in time and space in response to a suite of different controlling mechanisms. The reliable reconstruction of RSL using foraminifera buried in high-saltmarsh sediments enable the development of near continuous records of RSL change and provides a context for better understanding the temporal and spatial processes driving RSL. However, due to the spatial bias of recent RSL reconstructions, there remains considerable uncertainty regarding the contribution from regional and local scale processes to spatial and temporal RSL variability. This study establishes four new RSL records from the North Atlantic, two from Ireland and two from Prince Edward Island, Canada (PEI). New regional training sets of contemporary saltmarsh foraminifera are presented to quantify the relationship between elevation and foraminiferal assemblage and produce transfer functions to predict palaeomarsh surface elevation (PME) from where the height of former RSL can be established. Composite chronologies are established from 210Pb and radiocarbon (14C) dating of saltmarsh plant macrofossils coupled with chronohorizons inferred from down-core profiles of radionuclides (e.g., 137Cs) and elemental concentrations of known age. The new records demonstrate that RSL rose by ~0.5 m since 1880 CE in Cromane (Ireland), ~0.2 m since 1813 CE in Dungarvan (Ireland), ~2.1 m since 530 CE in Augustine (PEI) and ~1.1 m since 1465 CE in Haldimand River (PEI). These records are integrated into an updated global RSL database of instrumental and proxy sea level and analysed by a spatiotemporal empirical hierarchical model that quantifies the contribution to RSL from global, regional, and local-scale processes along both coasts of the North Atlantic. The analysis of the patterns and timing of RSL change suggests the that the influence of barystatic and sterodynamic processes controlled the regional variability of RSL across the North Atlantic during the Common Era. This study produces an updated global mean sea level (GMSL) curve for the Common Era consistent with estimates of global mean surface temperature (GMST) and confirms the unprecedented acceleration of RSL during the 20th century. Examination of the inflexion in the rate of sea-level rise in the North Atlantic suggests a later acceleration in NW Europe and Atlantic Canada that likely reflects the regional contribution of Greenland Ice Sheet melt to the RSL records from these regions.