ENSO–cave drip water hydrochemical relationship: a 7-year dataset from south-eastern Australia
Speleothems (cave deposits), used for palaeoenvironmental reconstructions, are deposited from cave drip water. Differentiating climate and karst processes within a drip-water signal is fundamental for the correct identification of palaeoenvironmental proxies and ultimately their interpretation wi...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-11-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://www.hydrol-earth-syst-sci.net/20/4625/2016/hess-20-4625-2016.pdf |
| Summary: | Speleothems (cave deposits), used for palaeoenvironmental reconstructions, are
deposited from cave drip water. Differentiating climate and karst processes
within a drip-water signal is fundamental for the correct identification of
palaeoenvironmental proxies and ultimately their interpretation within
speleothem records. We investigate the potential use of trace element and
stable oxygen-isotope (<i>δ</i><sup>18</sup>O) variations in cave drip water as
palaeorainfall proxies in an Australian alpine karst site. This paper presents
the first extensive hydrochemical and <i>δ</i><sup>18</sup>O dataset from Harrie Wood
Cave, in the Snowy Mountains, south-eastern (SE) Australia. Using a 7-year long
rainfall <i>δ</i><sup>18</sup>O and drip-water Ca, Cl, Mg / Ca, Sr / Ca and
<i>δ</i><sup>18</sup>O datasets from three drip sites, we determined that the
processes of mixing, dilution, flow path change, carbonate mineral
dissolution and prior calcite precipitation (PCP) accounted for the observed
variations in the drip-water geochemical composition. We identify that the
three monitored drip sites are fed by fracture flow from a well-mixed
epikarst storage reservoir, supplied by variable concentrations of dissolved
ions from soil and bedrock dissolution. We constrained the influence of
multiple processes and controls on drip-water composition in a region
dominated by El Niño–Southern Oscillation (ENSO). During the El Niño and dry periods, enhanced PCP, a
flow path change and dissolution due to increased soil CO<sub>2</sub> production
occurred in response to warmer than average temperatures in contrast to
the La Niña phase, where dilution dominated
and reduced PCP were observed.
We present a conceptual model, illustrating the key processes impacting the
drip-water chemistry. We identified a robust relationship between ENSO and
drip-water trace element concentrations and propose that variations in speleothem Mg / Ca and Sr / Ca ratios may be interpreted to reflect
palaeorainfall conditions. These findings inform palaeorainfall reconstruction
from speleothems regionally and provide a basis for palaeoclimate studies
globally, in regions where there is intermittent recharge variability. |
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| ISSN: | 1027-5606 1607-7938 |