Abstract

Relative sea level data, such as those gained from salt marshes provide important insights into sea level change over centennial and multi decadal time periods, spanning the Medieval Warm Period and Little Ice Age. This presentation explores the regional changes in sea-level experienced across the North Atlantic, specifically Greenland, and attempts to interpret and constrain the contributions in terms of local and regional ice sheet mass balance and thermo- and halosteric changes in sea-level.

During the period spanning the MWP and the LIA , reconstructions of century-scale relative sea-level (RSL) extracted from salt marsh deposits in Greenland reveal that the century-scale RSL trends differ significantly to millennial-scale trends inferred from isolation basin data in their respective areas. At sites in west Greenland RSL rise slows from _{3 mm/yr to} 0 mm/yr at _{1600AD. Further south, at Nanortalik, the sea level continues to rise until} 200 years before present after which the sea-level slows by ~ 3mm/yr. At Pakitsoq, salt marsh records show a slowdown in sea-level rise during the mid 19th century, coinciding with retreat of nearby Jakobshavn Isbrae, a major ice stream draining 7% of the Greenland Ice Sheet.

Large contributions to sea-level change from steric changes and cryospheric sources outside of Greenland are ruled out as major drivers of this deceleration in sea-level fall. Very little is known about the detailed regional climate and mass balance of the Greenland Ice Sheet during the Medieval Warm Period (MWP) and the Little Ice Age (LIA) but model sensitivity tests indicate that regional changes in ice thick- ness 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. However, it is plausible that some of the RSL fall may be due to reduced accumulation 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.