Relative sea-level changes and evidence for a Holocene low stand in southern Greenland

We present new relative sea-level (RSL) data from southern Greenland, an area critical for understanding the Greenland Ice Sheet's (GrIS) sensitivity to climate change. Our RSL reconstruction from the inner Isortoq Fjord spans the last ~10,000 years and is based on stratigraphic analyses, magnetic susceptibility, X-ray fluorescence core scanning, loss-on-ignition, macrofossil identification, and AMS radiocarbon dating of 10 sediment cores. Isolation and transgression sequences identified in lake and submerged basin sediments reveal a rapid RSL fall during the Early Holocene driven by crustal unloading in response to the retreat of the GrIS. During the Early Holocene, RSL dropped from the regional marine limit at ~36 m above mean sea-level (MSL) to near present-day MSL by ~9 cal. ka BP. A Middle Holocene low stand above 20 m below today's MSL at ~6 cal. ka BP is followed by a gradual Late Holocene transgression, with sea level returning to present-day MSL sometime during the last millennium. Similar to records from Paamiut to the north and Qaqortoq and Nanortalik to the southeast, early isolation of low-lying basins in the Isortoq region reflects rapid isostatic rebound. In contrast, the Late Holocene transgression is more gradual and less well defined, likely reflecting a combination of local glacier and ice sheet advances and perhaps a broader isostatic signal from the retreat of the North American Ice Sheet Complex. Comparison with Huy3 model predictions shows that observed RSL changes in this region were of greater magnitude than simulated, highlighting the need for refined GIA modelling.