Abstract
Abstract. We here reconstruct the paleotopography of Northern Hemisphere ice sheets during the glacial maxima of marine isotope stages (MIS) 5b and 4.We employ a combined approach, blending geologically based reconstruction and numerical modeling, to arrive at probable ice sheet extents and topographies for each of these two time slices. For a physically based 3-D calculation based on geologically derived 2-D constraints, we use the University of Maine Ice Sheet Model (UMISM) to calculate ice sheet thickness and topography. The approach and ice sheet modeling strategy is designed to provide robust data sets of sufficient resolution for atmospheric circulation experiments for these previously elusive time periods. Two tunable parameters, a temperature scaling function applied to a spliced Vostok–GRIP record, and spatial adjustment of the climatic pole position, were employed iteratively to achieve a good fit to geological constraints where such were available. The model credibly reproduces the first-order pattern of size and location of geologically indicated ice sheets during marine isotope stages (MIS) 5b (86.2 kyr model age) and 4 (64 kyr model age). From the interglacial state of two north–south obstacles to atmospheric circulation (Rocky Mountains and Greenland), by MIS 5b the emergence of combined Quebec–central Arctic and Scandinavian–Barents-Kara ice sheets had increased the number of such highland obstacles to four. The number of major ice sheets remained constant through MIS 4, but the merging of the Cordilleran and the proto-Laurentide Ice Sheet produced a single continent-wide North American ice sheet at the LGM.
Highlights
We here address a fundamental information gap in climate science, Northern Hemisphere paleotopography during the last interglacial-to-glacial transition
A good understanding of Northern Hemisphere paleotopography exists for the last glacial maximum (LGM) and the deglacial phase of the last glacial cycle (Peltier, 2004)
Idealized coupled atmosphere–ice-sheet models have demonstrated that the interaction between ice sheet topography and atmospheric circulation can strongly influence the spatial distribution of continental-scale ice sheets (Roe and Lindzén, 2001; Liakka et al, 2011)
Summary
Considerable progress has been made in understanding ice sheet dynamics in this elusive time interval (Stokes et al, 2012), but the scarcity of geological and geomorphological data (Kleman et al, 2010) that can constrain numerical models is still an impediment to our understanding of the time periods of most rapid ice sheet build-up This situation hampers research regarding ice sheet topographical feedbacks on atmospheric circulation (Cook and Held, 1988; Roe and Lindzén, 2001; Langen and Vinther, 2009; Liakka and Nilsson, 2010), and is an obstacle to our understanding of Northern Hemisphere atmospheric circulation during periods which were very different from both interglacial and full-glacial conditions in terms of number, location and size of ice sheets.
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