Geodetic measurements of postglacial adjustments in Greenland

Abstract

[1] We analyze data from seven continuous Global Positioning System (GPS) receivers and one tide gauge, all located along the edge of the Greenland ice sheet, to determine vertical uplift rates. We compare our results with predictions based on the ICE-5G deglaciation model of Peltier (2004). Results from the GPS receiver at Kellyville (À1.2 ± 1.1 mm/a) and from the tide gauge at Nuuk (À2.2 ± 1.3 mm/a), indicate that ICE-5G overestimates the subsidence rates at those locations by 2.1 and 1.1 mm/a, respectively. Kellyville and Nuuk are located along the southwestern margin of the Greenland ice sheet, and the observed negative uplift rates are consistent with independent evidence that the ice margin along the southwestern edge readvanced during the last $8 ka to its current position. The ICE-5G glaciation-deglaciation history includes a readvance between the latitudes of 62°N and 72°N. The GPS measurements suggest the ICE-5G readvance may be too large or mistimed. Our GPS results at Qaqortoq, located at the southern tip of Greenland, suggest a secular subsidence rate of À0.3 ± 1.1 mm/a, while ICE-5G predicts an uplift rate of 1.0 mm/a. ICE-5G assumes no ice sheet readvance in south Greenland, including no readvance of the Qassimiut lobe. The difference of 1.3 ± 1.1 mm/a can tentatively be explained as due to a $33 km readvance of the Qassimiut lobe during the last $3 ka. For the other GPS sites, the observed/predicted uplift rates are 3.6 ± 1.1/À0.1 mm/a at Thule, 0.0 ± 1.1/2.0 mm/a at Scoresbysund, and À0.4 ± 1.1/À1.7 mm/a at Kulusuk. For Thule, Kulusuk, and Scoresbysund the differences between the observed and predicted rates are on the order of 1.3-3.7 mm/a, though with opposite signs, and indicate that ICE-5G does not exactly reproduce the correct rebound signal at those locations.

Using relative sea-level data to constrain the deglacial and Holocene history of southern Greenland

“…In contrast to the high elevation areas, Letreguilly et al (1991) suggest that the lower lying Qassimiut Lobe would be more sensitive to climate change, with a modelled retreat of 40 to 50 km behind its present margin under 3 degrees of warming. Khan et al (2008) demonstrate that the inclusion of a neoglacial readvance of the Lobe of about 33 km is required to satisfy present day GPS observations of vertical motion with model predictions by ICE-5G, which did not previously contain a readvance of this Lobe.…”

“…Fleming and Lambeck (2004) showed previously how the inclusion of a neoglacial ice sheet readvance causes RSL predictions in Disko Bugt to fall below present in the late Holocene and fit RSL observations (Long et al, 1999), but neither their tuned model, nor that of Tarasov and Peltier (2002) include a neoglacial readvance of the Qassimiut Lobe. A more recent modelling study using ICE-5G suggests that a 33 km readvance of the Qassimiut Lobe during the last 3 k yr is needed to explain present-day GPS measurements of land uplift (Khan et al, 2008). In contrast, although the Huy2 model of Simpson et al (2009) includes a 20 km neoglacial readvance in the south, this is too small i12 (Simpson et al, 2011) to generate the timing and magnitude of the RSL lowstand which, at Nanortalik and Qaqortoq, is the largest seen in all of Greenland (up to -10 m at c. 6 cal.…”

Improved Constraints on Models of Glacial Isostatic Adjustment: A Review of the Contribution of Ground-Based Geodetic Observations

“…Moreover, the latest estimate of Kellyville subsidence, 1.2 ± 1.1 mm/year, by Khan et al (2008) using a dataset that expands that of Wahr et al (2001) by including seven more years of data at Kellyville and Kulusuk and adding the three continuous GPS sites at Thule, Scoresbysund, and Qaqortoq, also differs from the previous two, by up to 4.6 mm/year. These differences, which are attributed to reference frame realization and from applying different models and/or different model options, highlights the need for an improved GPS observational paradigm in Greenland.…”

Secular changes in Earth’s shape and surface mass loading derived from combinations of reprocessed global GPS networks

“…Signals appear seasonally and inter-seasonally (van Dam and Francis 1998;van Dam et al 2001;Cretaux et al 2002;Bennett 2008;Bos et al 2008) and over transient (Arriagada et al 2011;Chen et al 2011;Reddy et al 2011) and secular (Larson et al 1997;Mitrovica et al 1994;Wahr et al 2001;Khan et al 2008) time scales. The focus of this study is on the secular trends, in particular the estimation of present-day surface mass loading (SML).…”