Some high-latitude glaciers are found to remain sensitive to 41 000 years obliquity variations despite a global climate paced at roughly 100 000 years.

Nature communications by Mackay and Marchant.

The last 8 glacial cycles, as retrieved from paleoclimate archives such as Antarctica’s ice cores, are characterised by glacial-interglacial cycles with an ‘irregular periodicity’ of ~100,000 years. However, this was not always the case. Paleoclimate records prior to the mid-Pleistocene transition (prior to 700 ka–1,250 ka ago) show glacial-interglacial cycles paced at around ~41,000 years related primarily to the variations in solar forcing due to cyclical changes in the Earth’s obliquity. In this study, Mackay and Marchant describe a new archive of climate change recorded in debris-covered glaciers. Specifically, they evaluate whether some high latitude glaciers in Antarctica maintain a sensitivity to obliquity forcing despite a global climatic system reacting at a slower tempo. To do so, they gathered observations of massive inclined englacial debris layers, interpreted as indicators of periods of net ablation, from two glaciers in the southern Transantarctic Mountains: the Mullins and Friedman glaciers. They found similar patterns in the two separate glaciers, indicating regional climate change driving their respective mass balance.

By integrating variations in past climatic conditions inferred from the Taylor Dome ice core and reconstructed high-latitude insolation into an energy balance model, they were able to explain non-linear mass balance and geomorphic changes in the two glaciers. The modelled mass balances were then coupled to a model for the development of the inclined englacial debris layers, and they were able to match the model results to the observed englacial debris patterns and corresponding surface topography (Fig. 1).

Fig 1: Correlations between the surface morphology, modelled mass balance, debris layer growth, and climatic forcing over the last 250 000 years at Mullins glacier: a) hillshade relief map of the Mullins glacier showing surface discontinuities associated with englacial inclined debris layers; b) modelled output for the formation of supraglacial debris in the upper accumulation zone; c) modelled mass balance in the critical zone; d) integrated summer energy; e) and f) temperature variations and accumulation, respectively, from the Taylor Dome ice core; and, g) temperature variation from the Vostok ice core.

The results show that, over at least the past ~220 ka, the Mullins and Friedman glaciers have remained sensitive to obliquity variations at ~41,000 years, despite the dominant global climatic response at ~100,000 years during the same time period. In addition to providing a new and independent archive of past climate change, this article highlights the importance of insolation in influencing the dynamics of glaciers systems at high latitudes, shows the complexity of climate-driven geomorphic response between different glacial systems, and points the way for interpreting past climate changes from the analysis of surface patterns on debris-covered glaciers on both Earth and Mars.

 

Mackay, S.L. and Marchant, D.R. (2017) Obliquity-paced climate change recorded in Antarctic debris-covered glaciers. Nature Communications 8, 14194.

MC

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