Support for a More Extensive Greenland Ice Sheet in Southwestern Greenland During the LGM

Abstract:

The configuration of the Greenland Ice Sheet (GrIS) in Southwestern Greenland during the Last Glacial Maximum (LGM) is debated. Published reconstructions in the Sisimiut region range from a nearshore inner-shelf position to a maximum extent at the shelf break. We use two approaches to resolve LGM ice extent in the Sisimiut region. First, we develop a 2D crustal rebound model to simulate relative sea level curves for contrasting ice sheet sizes and compare these simulated curves with existing relative sea level data. Our simulated relative sea level curve only matches field observations when using a GrIS configuration that extends to the shelf break during the LGM. Second, we constrain the LGM ice sheet thickness using cosmogenic ¹⁰Be, ²⁶Al and ¹⁴C exposure dating from two summit areas. Collectively, 24 exposure ages, combined with model derived ice sheet profiles, reveal that both summits were ice covered during the LGM and deglaciated ~11.6 ka; these summits were not nunataks through the last glacial cycle. In-situ ¹⁴C measurements in samples with inherited ¹⁰Be reveal the true deglaciation age and agree with inheritance-free ¹⁰Be ages on erratics. At one site, inherited in-situ ¹⁴C concentrations in bedrock, paired with the likely timing of site deglaciation, results in a modeled age for the LGM advance over the summit of 17.1±2.5 ka. Collectively, these multiple approaches support a maximum GrIS configuration that reached the shelf break during the LGM.