Space geodesy constrains ice age terminal deglaciation: The global ICE‐6G_C (VM5a) model

Abstract

A new model of the last deglaciation event of the Late Quaternary ice age is here described and denoted as ICE-6G_C (VM5a). It differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available Global Positioning System (GPS) measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal. Additional space geodetic constraints have also been applied to specify the reference frame within which the GPS data are described. The focus of the paper is upon the three main regions of Last Glacial Maximum ice cover, namely, North America, Northwestern Europe/Eurasia, and Antarctica, although Greenland and the British Isles will also be included, if peripherally, in the discussion. In each of the three major regions, the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the Gravity Recovery and Climate Experiment satellites as an independent means of verifying the improvement of the model achieved by applying the GPS constraints. Several aspects of the global characteristics of this new model are also discussed, including the nature of relative sea level history predictions at far-field locations, in particular the Caribbean island of Barbados, from which especially high-quality records of postglacial sea level change are available but which records were not employed in the development of the model. Although ICE-6G_C (VM5a) is a significant improvement insofar as the most recently available GPS observations are concerned, comparison of model predictions with such far-field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration.

Differences between the last two glacial maxima and implications for ice-sheet, δ18O, and sea-level reconstructions

“…A data-gap exists in the Red Sea LGM record due to an indurated 16.6 n/r 78.6 n/r n/r 22.3 n/r 121.5 n/r ICE-4G (Peltier, 1994(Peltier, , 1996 (LGM at 21 ka) i 24.86 j n/r 64.24 n/r 6.38 k n/r 18.09 n/r 114.12 n/r ICE-5G v.1.2 (Peltier, 2004) (LGM at 26 ka) i 22.73 j n/r 83.71 n/r 2.45 k n/r 18.04 n/r 127.48 n/r ICE-6G v.2 (Argus et al, 2014;Peltier et al, 2015) (LGM at 26 ka) i 22.23 j n/r 88.14 n/r 2.34 k n/r 13.23 n/r 126.81 n/r Siegert et al, 2001 (LGM at~20 ka) 14 n/r n/r n/r n/r n/r n/r n/r n/r n/r van den LGM at~25 ka)~22 n/r n/r n/r n/r n/r n/r n/r n/r n/r Patton et al, 2016 (LGM at~22 ka) 17 n/r n/r n/r n/r n/r n/r n/r n/r n/r…”

Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

“…The most direct measurements of LIS remnants, from ice on the Barnes Ice Cap, yield d 18 O values of À21 to À40‰ (Hooke and Clausen, 1982) at a high-latitude site (70 N) on Baffin Island proximal to a marine isotopic source (Andrews et al, 2002). Given the d 18 O values of LGM ice on Greenland, and LIS model estimates with maximum thickness of 3e4 km (Argus et al, 2014;Gregoire et al, 2012;Peltier et al, 2015), it is not unreasonable to expect more negative isotopic values as well as greater heterogeneity in meltwater derived from the central LIS. Regional temperatures in the interior of North America up to 25 C colder than modern values (Annan and Hargreaves, 2013) would also have contributed to extremely In our record, core intervals prior to MWP-1a (15.5e14.6 ka; time slices H b , H c , and B a in Fig.…”

“…Numerical models provide insight into the spatial and temporal patterns of the history of continental ice sheets such as the Laurentide Ice Sheet (LIS) during the last glacial cycle. However, ice-sheet thickness remains one of the greatest sources of uncertainty in constraining ice-sheet dynamics (Ullman et al, 2014), and modeled thicknesses for the LIS vary depending on model selection (Argus et al, 2014;Clark et al, 1994;Gregoire et al, 2012;Kleman et al, 2002;Lambeck et al, 2002;Marshall et al, 2000;Peltier et al, 2015;Rutt et al, 2009;Tarasov and Peltier, 2004). Oxygen isotope variations within an ice sheet are controlled by temperature, latitude, and altitude (Bowen and Wilkinson, 2002;Oerlemans, 1982), so the geochemical heterogeneity of the ice within an ice sheet preserves a record of physical parameters that affect Rayleigh fractionation, including ice-sheet elevation.…”

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…Likewise, the recent expansion of coverage of measurements of present-day vertical velocities from continuous or repeat GPS (e.g. Kierulf et al, 2014) has significantly improved constraint data for GIA-based ice sheet reconstructions (Argus et al, 2014;Peltier et al, 2015).…”