Century-scale relative sea-level changes in West Greenland — A plausibility study to assess contributions from the cryosphere and the ocean

Abstract

This paper interprets high resolution relative sea-level (RSL) reconstructions obtained from recently deposited salt-marsh sediments in Greenland. The primary aim of this study is to determine the relative contribution to the RSL observations from local to regional ice mass changes as well as density-related (steric) variations in the adjacent ocean. At sites in west Greenland, RSL rise slows from ~ 3 mm/yr to ~ 0 mm/yr at 400 years BP and is stable thereafter. In south Greenland, a similar RSL slowdown is also observed but this occurs approximately 200 yrs later. Substantial contributions from oceanographic changes are ruled out as dominant drivers of the RSL slowdown in western Greenland but could be more important at Nanortalik. Model sensitivity tests indicate that the RSL data are not compatible with a dominant dynamic ice loss via the Jakobshavn Isbrae outlet glacier as the region of ice loss and the resulting sea-level trends are too localised. Regional changes in ice thickness related to surface mass balance changes can explain the observed RSL signals but only if there is dominant mass loss during the period 400 years BP to present. This conclusion is unaffected even when uncertainties in Earth viscosity structure are taken into account. However, it is plausible that some of the RSL fall may be due to reduced ice growth at the onset of the Little Ice Age. A high resolution mass balance history of the Greenland Ice Sheet over the past few millennia and the influence of lateral Earth structure on predictions of RSL change are identified as priority areas of study in order to confidently separate local, ‘transient’ (e.g. elastic and gravitational) RSL changes from the long-term viscous contribution associated primarily with deglacial changes.