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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/gmd-2017-158
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Model experiment description paper
31 Jul 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).
A new approach for simulating the paleo evolution of the Northern Hemisphere ice sheets
Rubén Banderas1,2, Jorge Alvarez-Solas1,2, Alexander Robinson1,2, and Marisa Montoya1,2 1Universidad Complutense de Madrid (UCM)
2Instituto de Geociencias (UCM-CSIC)
Abstract. The aim of this study is to assess and improve the methods currently used to force ice sheet models offline. To this end, three different synthetic transient forcing climatologies are developed for the past 120 kyr following a perturbative approach and applied to an ice-sheet model. The results are used to evaluate their consequences for simulating the paleo evolution of the Northern Hemisphere ice sheets. The first method follows the usual approach in which temperature anomalies relative to present are calculated by combining a present-day climatology with a simulated glacial-interglacial climatic anomaly field interpolated through an index derived from ice-core data. In the second approach the representation of millennial-scale climate variability is improved by incorporating a simulated stadial-interstadial anomaly field. The third is a refinement of the second one in which the amplitudes of both orbital and millennial-scale variations are corrected to provide a perfect agreement with a recent absolute temperature reconstruction over Greenland. The comparison of the three climate forcing methods highlights the tendency of the usual approach to overestimate the temperature variability over North America and Eurasia at millennial timescales. This leads to a relatively high Northern Hemisphere (NH) ice-volume variability on these timescales. Through enhanced ablation, this results in too low an ice volume throughout the last glacial period (LGP), below or at the lower end of the uncertainty range of estimations. Improving the representation of millennial-scale variability alone yields an important increase of ice volume in all NH ice sheets, but especially in the Fennoscandian ice sheet (FIS). Optimizing the amplitude of the temperature anomalies to match the Greenland reconstruction results in a further increase of the simulated ice-sheet volume throughout the LGP. Our new method provides a more realistic representation of orbital and millennial scale climate variability and represents an improvement in the transient forcing of ice sheets during the last glacial period. Interestingly, our new approach underestimates ice-volume variations on millennial timescales as indicated by sea-level records. This suggests that either the origin of the latter is not the NH or that processes not represented in our study, notably variations in oceanic conditions, need to be invoked to account for an important role of millennial-scale climate variability on millennial-scale ice- volume fluctuations. We finally provide here both our derived climate evolution of the LGP using the three methods as well as the resulting ice-sheet configurations. These could be of interest for future studies dealing with the atmospheric or/and oceanic consequences of transient ice-sheet evolution throughout the LGP, and as a source of climate input to other ice sheet models.

Citation: Banderas, R., Alvarez-Solas, J., Robinson, A., and Montoya, M.: A new approach for simulating the paleo evolution of the Northern Hemisphere ice sheets, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2017-158, in review, 2017.
Rubén Banderas et al.
Rubén Banderas et al.
Rubén Banderas et al.

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Short summary
Here we present a new approach to force ice sheet models offline which accounts for a more realistic treatment of millennial-scale climate variability as compared to the existing methods. Our results reveal that an incorrect representation of the characteristic pattern of millennial-scale climate variability within the climate forcing not only affects NH ice-volume variations at millennial timescales, but has consequences for glacial-interglacial ice-volume changes too.
Here we present a new approach to force ice sheet models offline which accounts for a more...
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