Abstract
ABSTRACTNumerous ice-sheet reconstructions of the last glacial cycle have been proposed, however due to limited geological evidence, reconstructing older Northern Hemisphere ice sheets remains a difficult exercise. Here we focus on the penultimate glacial maximum (PGM; ~140 ka BP) over the Northern Hemisphere. While some evidence of the PGM Eurasian ice-sheet extent were found, this is not the case for the corresponding Laurentide ice sheet. To improve the glaciological reconstructions of the PGM Northern Hemisphere ice sheets, we explore the parameter space of ice-sheet model uncertainties and carry out numerous univariate ice-sheet steady-state sensitivity simulations. We use two PGM climate simulations to force the ice-sheet model, differing in the prescribed Laurentide ice topography (small and large). The simulated Northern Hemisphere ice volume ranges from 124.7 to 152 m SLE when using the climate accounting for a small Laurentide ice sheet, which is compatible with global sea-level reconstructions of this period (−92 to −150 m). Conversely, using the climate simulation with a Laurentide ice sheet comparable in size to that of the last glacial maximum results in too large ice volumes. Changes in basal drag provide the upper bound ice volume of our experiments, whereas changes in the distribution of ice streams provide the lower bound.
Highlights
In the past, the Northern Hemisphere has been periodically affected by glaciations
In the third part we investigate the impact of each parameter category described in Section 2.3 on the simulated ice-sheet geometry (Table 1)
The overall aim of this study was to investigate the geometry of the Northern Hemisphere ice sheets during the penultimate glacial maximum (PGM) (∼140 ka BP)
Summary
The Northern Hemisphere has been periodically affected by glaciations. While numerous reconstructions of the last glacial cycle global ice-sheet topography exist, only limited geological evidence of the penultimate glacial cycle or older ice topography is available. We focus on the reconstruction of the Northern Hemisphere ice sheets during the Marine Isotope Stage 6 (MIS 6) glacial maximum (∼140 ka BP), denoted as the penultimate glacial maximum (PGM). For the PGM Eurasian ice sheet, an extent considerably larger than its Last Glacial Maximum (LGM; ∼21 ka BP) counterpart was provided by the QUEEN project (Svendsen and others, 2004). The advance of the eastern part of the Eurasian ice sheet could have occurred before the PGM, as two other advances during the MIS 6 glacial cycle, at ∼160 ka BP and ∼180 ka BP, have been identified (Astakhov, 2004; Svendsen and others, 2004). While geological evidence of the extent have been retrieved, there are only a few reconstructions of the PGM Eurasian ice-sheet volume. Based on the extent of the PGM Eurasian ice sheet from Svendsen and others (2004), Peyaud (2006) simulated an Eurasian ice volume of ∼70 m
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