Post‐1850 changes in glacier benito, north patagonian icefield, chile

Abstract

Glacier Benito is a temperate outlet glacier on the west side of the North Patagonian Icefield. Rates of thinning and ablation were obtained using data collected by the ritish Joint Services Expedition in 1972/73 and subsequent data collected in 2007 and 2011. Ice‐front recession rates were based on dendrochronological dating for the terminal moraines and aerial and satellite imagery of the ice front in 1944, 1998 and 2002. Between the first Benito survey in 1973 and 2007, the lower glacier thinned by nearly 150 m at an average rate of 4.3 m yr⁻¹ with the rate increasing to 6.1 m yr⁻¹ between 2007 and 2011, a 28.7% increase during the latter period. Increases in ice movement and ablation were negligible: ice movement for 1973 and 2007 averaged 0.45 m day⁻¹ and ablation averaged 0.05 m day⁻¹. Ice front recession along the glacier's centre line from 1886 to 2002 was approximately 1860 m. Retreat rates between 1886 and 1944 averaged 8.9 m yr⁻¹. Thereafter glacier asymmetry makes measurement along the glacier centre line unrepresentative of areal change until 1998 when symmetry was restored; retreat between 1944 and 1998 was 15.4 m yr⁻¹. From 1998 to 2002 the rate increased dramatically to 127.2 m yr⁻¹. Recession from the southern end of Benito's terminal moraine in the 1850s supports an early date for initial retreat of the Icefield's glaciers.

Key words:

• glacier thinning
• ice movement
• ablation
• recession
• retreat rates
• dendrochronology

Acknowledgements

We thank CONAF (Corporación Nacional Forestal, Chile) for permission to carry out this research. The expedition was initiated, organized and led by Martin Sessions. In Chile, Graham Hornsey supplied vital logistics and radio contact. Participants other than the authors during phase one of the expedition were Stuart Harron (also a member of the British Joint Services Expedition), Aase Richter and Susie Russell. During the second phase team members were Garth Coghlan, Stephanie Goodrick and Michael John; all are warmly thanked for their valiant support. Funding for V. Winchester was received from The Percy Sladen Memorial Fund administered by the Linnean Society, and John Fell Fund, University of Oxford. Funding for equipment hire and transportation in Chile, including sea transport between Tortel and Abra Kelly, was provided by legacies from Patrick and Barney Sessions. Our anonymous referees are warmly thanked for their helpful comments.

Additional information

Notes on contributors

Vanessa Winchester

Vanessa Winchester, School of Geography and the Environment, OUCE, University of Oxford, Oxford, OX1 3QY, UK

E‐mail: [email protected]

Martin Sessions

Martin Sessions, 9 Eliza St, Amaroo, ACT 2914, Australia

E‐mail: [email protected]

Jammie Valdivia Cerda

Jammie Valdivia, Universidad Tecnologica Metropolitana (UTEM) Santiago, Chile

E‐mail: [email protected]

Olaf Wündrich

Olaf Wüendrich, Colibri Ventura, Casilla 113, Coyhaique, XI Region de Aysén, Chile

E‐mail: [email protected]

Samuel Clemmens

Samuel Clemmens and Neil Glasser, Institute of Geography & Earth Sciences, Aberystwyth University, Llandinam Building, UK

E‐mail: [email protected]; [email protected]

Megan Nash

Megan Nash, Australian National University, ACT, Australia.

E‐mail: [email protected]