RAPID POST-GLACIAL EMERGENCE RATES MEASURED WITH 10BE MATCH GPS-DETERMINED CONTEMPORARY UPLIFT RATES IN SOUTHEAST GREENLAND

Isostatic rebound is occurring across coastal Greenland as a result of rapid deglaciation driven by recent climate warming. However, modelling and quantifying glacio-isostatic rebound is uncertain, especially over long timescales, due to spatially varying mantle viscosities, crustal morphologies, and glacial masses. Recent, high-precision GPS data from Kulusuk, SE Greenland, show extremely rapid contemporary uplift rates of 7.7 ± 0.1 m/ky from 1996-2016 (Khan et al., 2016, Sci Adv.). This rapid, mostly elastic response is thought by Rysgaard et al. (2018, Scientific Reports) to reflect low viscosity rock at depth created by hotspot passage ~40 Mya and the current East Greenland hotspot. By quantifying post-glacial, millennial-scale emergence using ¹⁰Be and comparing them to contemporary, decadal-scale uplift rates determined by GPS, we provide insight into future isostatic rebound rates in Kulusuk (and other areas of low mantle viscosity) caused by continued glacial retreat, with implications for associated relative sea-level change.

Here, we date late Pleistocene deglaciation and subsequent isostatic rebound near Kulusuk using in-situ ¹⁰Be analysis of a vertical transect of 11 samples from surface rocks. We use these data to generate a post-glacial emergence curve and calculate minimum paleo-uplift rates over the past ~12 kya. Inferred ¹⁰Be exposure ages are 6.7-14.7 ka (with one older sample likely containing nuclides from previous exposure). Based on the curve produced by these data, deglaciation occurred at 12.8±0.5 ky (n = 3) and was followed by rapid relative sea level fall, which persisted for ~4 ky following deglaciation. Total post-glacial relative sea level fall in Kulusuk is ~36 m, calculated from the averages of the middle and lower elevation data points. The rate of uplift is therefore 7.8 m/ka, assuming constant uplift over time and that uplift began when the three highest-elevation sample locations were deglaciated.

The uplift rate we infer with ¹⁰Be is similar to contemporary GPS uplift data from Kulusuk. The similarity between decadal and millennial uplift rates suggests that modern isostatic rebound in Kulusuk may result in uplift rates like those that characterized the late Pleistocene deglaciation, accelerating to an extremely rapid ~10 m/ky due to low-viscosity asthenosphere.