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Biomass effects on stalagmite growth and isotope ratios: A 20th century analogue from Wiltshire, England |
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| Authors: | JUL Baldini F McDermott LM Baldini L Bruce Railsback |
| Institution: | a UCD School of Geological Sciences, University College Dublin, Belfield, D4, Ireland b School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK c Geology Department, Royal Holloway College, University of London, Egham, Surrey, TW20 OEX, UK d Department of Geology, University of Georgia, Athens, GA 30602, USA |
| Abstract: | Increases in calcite deposition rates combined with decreases in δ13C and δ18O in three modern stalagmites from Brown's Folly Mine, Wiltshire, England, are correlative with a well-documented re-vegetation above the mine. Increased soil PCO2 resulted in greater amounts of dissolved CaCO3 in the drip waters, which consequently increased annual calcite deposition rates. The absence of deposition prior to 1916 (28 years after the mine was closed) indicates that vegetation had not yet sufficiently developed to allow higher PCO2 values to form in the soil. Lower δ13C values through time may reflect the increased input of isotopically light biogenic carbon to the total dissolved inorganic carbon (DIC). δ18O decreased synchronously with δ13C, reflecting the increased importance of isotopically light winter recharge due to greater biomass-induced summer evapotranspiration. This is the first empirical demonstration that vegetation density can control stalagmite growth rates, δ13C, and δ18O, contributing critical insights into the interpretation of these climate proxies in ancient stalagmites. |
| Keywords: | stalagmite carbon isotopes oxygen isotopes fractionation vegetation growth rate |
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