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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 11
Clim. Past, 11, 1575–1586, 2015
https://doi.org/10.5194/cp-11-1575-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Clim. Past, 11, 1575–1586, 2015
https://doi.org/10.5194/cp-11-1575-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 26 Nov 2015

Research article | 26 Nov 2015

Modelled glacier equilibrium line altitudes during the mid-Holocene in the southern mid-latitudes

C. Bravo1,2,3,a, M. Rojas1,2,3, B. M. Anderson4, A. N. Mackintosh4, E. Sagredo3,5, and P. I. Moreno2,3,6 C. Bravo et al.
  • 1Department of Geophysics, Universidad de Chile, Santiago, Chile
  • 2Center for Climate and Resilience Research (CR2), Universidad de Chile, Santiago, Chile
  • 3Millennium Nucleus Paleoclimate of the Southern Hemisphere, Santiago, Chile
  • 4Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand
  • 5Institute of Geography, Pontificia Universidad Católica de Chile, Santiago, Chile
  • 6Department of Ecological Sciences and Institute of Ecology and Biodiversity, Universidad de Chile, Santiago, Chile
  • anow at: Glaciology Laboratory, Centro de Estudios Científicos, Valdivia, Chile

Abstract. Glacier behaviour during the mid-Holocene (MH, 6000 years BP) in the Southern Hemisphere provides observational data to constrain our understanding of the origin and propagation of palaeoclimate signals. In this study we examine the climatic forcing of glacier response in the MH by evaluating modelled glacier equilibrium line altitudes (ELAs) and climatic conditions during the MH compared with pre-industrial time (PI, year 1750). We focus on the middle latitudes of the Southern Hemisphere, specifically Patagonia and the South Island of New Zealand. Climate conditions for the MH were obtained from PMIP2 model simulations, which in turn were used to force a simple glacier mass balance model to simulate changes in ELA. In Patagonia, the models simulate colder conditions during the MH in austral summer (−0.2 °C), autumn (−0.5 °C), and winter (−0.4), and warmer temperatures (0.2 °C) during spring. In the Southern Alps the models show colder MH conditions in autumn (−0.7 °C) and winter (−0.4 °C), warmer conditions in spring (0.3 °C), and no significant change in summer temperature.

Precipitation does not show significant changes but exhibits a seasonal shift, with less precipitation from April to September and more precipitation from October to April during the MH in both regions. The mass balance model simulates a climatic ELA that is 15–33 m lower during the MH compared with PI conditions. We suggest that the main causes of this difference are driven mainly by colder temperatures associated with the MH simulation. Differences in temperature have a dual effect on glacier mass balance: (i) less energy is available for ablation during summer and early autumn and (ii) lower temperatures cause more precipitation to fall as snow rather than rain in late autumn and winter, resulting in more accumulation and higher surface albedo. For these reasons, we postulate that the modelled ELA changes, although small, may help to explain larger glacier extents observed by 6000 years BP in South America and New Zealand.

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We examine the climatic forcing of glacier expansion in the mid-Holocene (MH) by evaluating modelled glacier equilibrium line altitude (ELA) and climate conditions during the MH compared with pre-industrial (PI) time in the mid-latitudes of the Southern Hemisphere. Glaciers in both analysed regions have an ELA that is 15-33m lower than the PI during the MH. We postulate that the modelled ELA changes may help to explain larger glacier extents observed in the mid-Holocene in both regions.
We examine the climatic forcing of glacier expansion in the mid-Holocene (MH) by evaluating...
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