Postglacial relative sea-level changes and the deglaciation of northwest Iceland

Abstract

Iceland provides an important opportunity to investigate relative sea-level (RSL) changes and Last Glacial Maximum (LGM) glaciation in a sensitive area of the North Atlantic. This project employs new and existing RSL data, coupled with glacio-isostatic adjustment (GIA) modelling, to resolve the current debates surrounding the extent of the LGM Icelandic ice sheet (IIS). Robust understanding of the LGM IIS is important, because there are two markedly different maximum and minimum ice loading scenarios, with very different implications for global thermohaline circulation. Previous studies of glacial geomorphology and sedimentology have failed to differentiate between these scenarios. Reconstructing RSL changes in northwest Iceland can address this issue because the two LGM glaciation scenarios yield significantly contrasting RSL histories. Northwest Iceland is also an important location in which to determine Earth models for Iceland. In this study, a series of new sea-level index points (SLIPs) have been generated for northwest Iceland from isolation basin and coastal lowland sediment samples along two perpendicular transects. Diatom, tephrochronological and radiocarbon analyses have allowed the generation of new RSL curves for the region, showing higher marine limit elevations close to loading centres and differing influences of Younger Dryas ice re-advance. Mapping of the marine limit has shown differences in the pattern of deglaciation due to fjord width and morphology. The contrasting LGM glaciation scenarios have been tested using the GIA modelling, with the new and existing RSL dataset as a constraint. Both field data and GIA model outputs support the maximum glaciation hypothesis.