Stalagmite Survival: 500kyr of Cyclical Growth and Natural Attrition of Stalagmites in Sulawesi

Wednesday, 17 December 2014
Nick Scroxton1, Michael K Gagan1, Gavin B Dunbar2, Linda K Ayliffe1, Wayhoe S Hantoro3, Chuan-Chou Shen4, John Hellstrom5, Jian-Xin Zhao6, Hai Cheng7,8, R. Lawrence Edwards7, Hailong Sun4,9 and Hamdi Rifai10, (1)Australian National University, Canberra, Australia, (2)Victoria University of Wellington, Antarctic Research Centre, Wellington, New Zealand, (3)Indonesian Institute of Sciences, Research Center for Geotechnology, Bandung, Indonesia, (4)NTU National Taiwan University, Taipei, Taiwan, (5)University of Melbourne, Parkville, Australia, (6)University of Queensland, St Lucia, Australia, (7)University of Minnesota Twin Cities, Dept. of Earth Sciences, Minneapolis, MN, United States, (8)Xi'an Jiaotong University, Xian, China, (9)Chinese Academy of Sciences, The State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Guiyang, China, (10)State University of Padang, Department of Physics, Padang, Indonesia
Numerous speleothem studies have analysed the age distribution of stalagmites harvested from multiple caves and inferred important changes in paleoclimates to explain stalagmite growth phases. However, stalagmites take tens to hundreds of thousands of years to grow, and thus the twin desires to preserve the cave condition for future generations and advance palaeoclimate science are often in conflict. In this study we use U/Th ages from low impact mini-cores extracted in situ from the bases of stalagmites, thus keeping the intrinsic value of the cave intact.

Our case study is based on 77 individual stalagmites drilled in situ in thirteen caves located in and around Bantimurung-Bulusaraung National Park, South Sulawesi, Indonesia. The stalagmites grew during discrete time intervals within the last ~530,000 years, and analysis of their age distribution shows an exponential decrease in the number of older stalagmites surviving to the present day. The age distribution indicates that the rate of natural attrition of stalagmites is approximately constant through time, probably in response to a number of natural processes, including downward erosion of the karst terrain, cave collapse, in-cave erosional processes and in-cave sedimentation covering stalagmites. Natural attrition of stalagmites is likely to be a general cave phenomenon, and has important implications for cave conservation because it highlights that random removal of stalagmites without prior knowledge of their ages will result in unnecessary replication and a failure to sample the full length of the available paleoclimate record.

Departure from this “normal” exponential profile can be used to infer palaeoclimate information: significant deviations are produced by periods of more frequent stalagmite growth, inferred here to reflect increases in monsoon rainfall over Sulawesi (345–340, 75–70 and 10–5 kyr BP). By adjusting the record to account for stalagmite attrition, more statistically robust paleoclimate information can be inferred.

Crucially, these insights on past climates have been obtained entirely from reconnaissance-style basal mini-core ages. This novel technique is therefore suitable for caves where the removal of stalagmites would cause irreparable damage, or jeopardize local cultural and tourism potential.