First Global Analysis of Cave Drip Waters
(12 July 2019)
For a better understanding of how human activities are impacting climate across the globe, long-term reconstructions of past climate (before the Industrial Revolution) are essential. Stalagmites found in caves are widely acknowledged to be excellent recorders of past climate over hundreds of thousands of years. Researchers at Durham University, UK have previously used stalagmite oxygen isotope records to reconstruct North Atlantic hurricane activity (Baldini et al., 2016) and tropical rainfall belt position (Ridley et al., 2015) over several centuries, revealing the extent that human activities have and are continuing to impact the global water cycle.
The oxygen isotope composition of stalagmites is widely used recorder past rainfall. This is because cave drip water that deposits stalagmites originated from rainfall, providing a direct link to climate at the surface. Understanding the extent that the oxygen isotopic composition of drip water is related to rainfall is a fundamental research question that will unlock the full palaeoclimate potential of cave deposits.
Dr Lisa Baldini joined an international team of researchers led by Andy Baker at UNSW Sydney to complete the first ever global analysis of cave drip waters. The research team compared the oxygen isotope composition of the drip water to that of contemporaneous rainfall and modelled groundwater recharge, revealing, for the first time, climate thresholds on cave drip water composition.
In cool climate regions (such as the UK and northern Europe), the oxygen isotope composition of cave dripwater and surface rainfall are strongly linked, meaning stalagmite oxygen isotopes can be used to reconstruct long-term changes in past rainfall.
In warmer and drier climate regions (such as southern Europe, western North America, and Australia), cave drip water oxygen isotope composition is more similar to that of modelled groundwater recharge (water that actually reaches the groundwater and is not stored in the soil, used by vegetation or returned to the atmosphere by evaporation). In these regions, stalagmite oxygen isotopes can be used to reconstruct past ground water recharge (and drought).
According to Baldini, "This study is a culmination of years of cave dripwater and rainwater monitoring efforts by the global speleothem community. By combining individual datasets across 163 drip sites, 39 caves, and five continents, we've been able to develop a key for interpreting stalagmite records across the globe, even at hard to access cave sites where long-term monitoring studies are prohibitive".
Andy Baker1*, Andreas Hartmann2,3,1, Wuhui Duan4,5,1, Stuart Hankin6, Laia Comas-Bru7,8, Mark O. Cuthbert9,1, Pauline C. Treble6,1, Jay Banner10, Dominique Genty11, Lisa M. Baldini12, Miguel Bartolomé13,14, Ana Moreno13, Carlos Pérez-Mejías13 and Martin Werner15
1 Connected Waters Initiative Research Centre, UNSW Sydney, Sydney 2052, Australia.
2 Faculty of the Environment and Natural Resources, University of Freiburg, Friedrichstrasse 39, 79098 Freiburg, Germany.
3 Department of Civil Engineering, University of Bristol, UK.
4 Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China.
5 CAS Center for Excellence in Life and Paleoenvironment, Beijing, 100044, China.
6 ANSTO, Lucas Heights 2234, Australia.
7 School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
8 School of Archaeology, Geography & Environmental Sciences, University of Reading, Whiteknights, Reading, RG6 6AH, UK.
9 School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK.
10 Jackson School of Geosciences and Environmental Science Institute, The University of Texas at Austin, 2305 Speedway, Austin TX 78712, USA.
11 Environnements et Paléoclimats Océaniques et Continentaux, Université de Bordeaux, Allée Geoffroy Saint Hilaire, 33615 Pessac, France.
12 Department of Geography, Durham University, South Road, Durham, DH1 3LE, UK.
13 Dpto. de Procesos Geoambientales y Cambio Global, Instituto Pirenaico de Ecología-CSIC, Avda. Montañana 1005, 50059 Zaragoza, Spain.
14 Departamento de Geología, Museo Nacional de Ciencias Naturales (CSIC), C/ José Gutiérrez Abascal, 2, 28006 Madrid, Spain.
15 Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bussestraße 24, 27570 Bremerhaven, Germany.