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Drip composition and stalagmite growth rates
James U.L. Baldini Department of Earth Sciences, Durham University, UK.
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photo by J.Frost
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photo by Steve Partridge
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Mitchell Caverns, CA
Mohave National Preserve, CA
But water is clearly important
for growth!
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Allison, 1923, Journal of Geology
Allison, 1923: • Identifies five key
factors • Attempted to classify
stalagmites (32 classes) • Attempted to date
samples using morphology
Controls on stalagmite growth – early work
“Approximately equal rates of vertical growth are noted for drips varying from 3 to 368 seconds, although the diameter increases with the rate of drip.”
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Allison V. C. (1926) The antiquity of the deposit in Jacob’s Cavern. Amer. Mus. Nat. Hist. Anthropol. Pap.
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Allison V. C. (1926) The antiquity of the deposit in Jacob’s Cavern. Amer. Mus. Nat. Hist. Anthropol. Pap.
Review of Allison 1926 by Nelson, 1928: “The scientifically minded are supposed to court accuracy, and I personally would welcome nothing so much as an absolute chronology for prehistoric times, but this is too much.”
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• First attempt at directly measuring stalagmite growth
• Confirmed Allison’s earlier growth controls
• Recognised that stalactites growing under concrete structures have anomalous growth rates
Johnson, 1930 (Science):
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Modern perspectives
Dreybrodt, 1980:
• Builds on earlier work on carbonate geochemistry
• Theory for stalagmite growth
• Recognises importance of the thickness of the thin film
• Highlights degassing of carbon dioxide as a critical control
Dreybrodt 1980, Chemical Geology
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Modern perspectives
Dreybrodt, 1980:
Dreybrodt 1980, Chemical Geology
Thin
film
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Modelling stalagmite growth
Where:
Ro = growth rate (mm yr-1)
Ca = drip water [Ca2+] (mmol L-1)
Caapp = drip water [Ca2+] at equilibrium (mmol L-1)
d = thin film of water thickness (mm)
DT = time between drips (sec)
a = ‘kinetic constant’ dependent on
d and temperature
CC-Bil
Baldini et al., EPSL 2008. Adapted from: Buhmann and Dreybrodt, 1985; Baker et al., 1998; Dreybrodt, 1999
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Where:
Ro = growth rate (mm yr-1)
Ca = drip water [Ca2+] (mmol L-1)
Caapp = drip water [Ca2+] at equilibrium (mmol L-1)
d = thin film of water thickness (mm)
DT = time between drips (sec)
a = ‘kinetic constant’ dependent on
d and temperature
Baldini et al., EPSL 2008. Adapted from: Buhmann and Dreybrodt, 1985; Baker et al., 1998; Dreybrodt, 1999
CC-Bil
Modelling stalagmite growth
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Where:
Ro = growth rate (mm yr-1)
Ca = drip water [Ca2+] (mmol L-1)
Caapp = drip water [Ca2+] at equilibrium (mmol L-1)
d = thin film of water thickness (mm)
DT = time between drips (sec)
a = ‘kinetic constant’ dependent on
d and temperature
CC-Bil
Baldini et al., EPSL 2008. Adapted from: Buhmann and Dreybrodt, 1985; Baker et al., 1998; Dreybrodt, 1999
Modelling stalagmite growth
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Where:
Ro = growth rate (mm yr-1)
Ca = drip water [Ca2+] (mmol L-1)
Caapp = drip water [Ca2+] at equilibrium (mmol L-1)
d = thin film of water thickness (mm)
DT = time between drips (sec)
a = ‘kinetic constant’ dependent on
d and temperature
CC-Bil
Baldini et al., EPSL 2008. Adapted from: Buhmann and Dreybrodt, 1985; Baker et al., 1998; Dreybrodt, 1999
Modelling stalagmite growth
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Where:
Ro = growth rate (mm yr-1)
Ca = drip water [Ca2+] (mmol L-1)
Caapp = drip water [Ca2+] at equilibrium (mmol L-1)
d = thin film of water thickness (mm)
DT = time between drips (sec)
a = ‘kinetic constant’ dependent on
d and temperature
CC-Bil
Baldini et al., EPSL 2008. Adapted from: Buhmann and Dreybrodt, 1985; Baker et al., 1998; Dreybrodt, 1999
Modelling stalagmite growth
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Baker et al., 2014, EPSL
Baker et al., 2014:
• Used lab experiments to determine controls on thin film thickness
• Curvature of surface affects d
• Surface microtopography affects d
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Where:
Ro = growth rate (mm yr-1)
Ca = drip water [Ca2+] (mmol L-1)
Caapp = drip water [Ca2+] at equilibrium (mmol L-1)
d = thin film of water thickness (mm)
DT = time between drips (sec)
a = ‘kinetic constant’ dependent on
d and temperature
CC-Bil
Baldini et al., EPSL 2008. Adapted from: Buhmann and Dreybrodt, 1985; Baker et al., 1998; Dreybrodt, 1999
Modelling stalagmite growth
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Where:
Ro = growth rate (mm yr-1)
Ca = drip water [Ca2+] (mmol L-1)
Caapp = drip water [Ca2+] at equilibrium (mmol L-1)
d = thin film of water thickness (mm)
DT = time between drips (sec)
a = ‘kinetic constant’ dependent on
d and temperature
CC-Bil
Baldini et al., EPSL 2008. Adapted from: Buhmann and Dreybrodt, 1985; Baker et al., 1998; Dreybrodt, 1999
Modelling stalagmite growth
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Modern perspectives
Genty et al., 2001: • Found that drip water Ca2+
and Temp strongly determine growth rate
• Temperature helps control Ca2+ by controlling bioproductivity – so indirect control
Genty et al. 2001, Chemical Geology
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Genty et al. 2001, Chemical Geology
Modern perspectives
Genty et al also used monitoring data to predict seasonality in speleothem growth
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Stalagmite growth depends on:
Water: enough water must exist to transfer Ca2+ to stalagmite
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Stalagmite growth depends on:
Water: enough water must exist to transfer Ca2+ to stalagmite
Soil bioproductivity: Recharge water must equilibrate with high PCO2 atmosphere
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Stalagmite growth depends on:
Water: enough water must exist to transfer Ca2+ to stalagmite
Soil bioproductivity: Recharge water must equilibrate with high PCO2 atmosphere
---------- Case study from Brown’s Folly Mine
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1886: All entrances to the mine were closed.
1904: All mining in area ceases. Area converted to nature reserve
1970s: Cavers re-open entrances
Brown’s Folly Mine, Bath, SW England
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Vegetation increased steadily since the early 1900s…but climate remained essentially static.
JUNE 1945: Most of Bathford Hill is still deforested
Brown’s Folly Mine, Bath, SW England
Baldini et al., 2005, EPSL
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Vegetation increased steadily since the early 1900s…but climate remained essentially static.
JUNE 1945: Vegetation covered less than half of Bathford Hill
JUNE 1968: Vegetation has reclaimed a substantial amount of land
Brown’s Folly Mine, Bath, SW England
Baldini et al., 2005, EPSL
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Vegetation increased steadily since the early 1900s…but climate remained essentially static.
JUNE 1945: Vegetation covered less than half of Bathford Hill
JUNE 1968: Vegetation has reclaimed a substantial amount of land
JUNE 1989: The majority of the hill is covered by deciduous forest
Brown’s Folly Mine, Bath, SW England
Baldini et al., 2005, EPSL
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Vegetation increased steadily since the early 1900s…but climate remained essentially static.
JUNE 1945: Vegetation covered less than half of Bathford Hill
JUNE 1968: Vegetation has reclaimed a substantial amount of land
JUNE 1989: The majority of the hill is covered by deciduous forest
Brown’s Folly Mine, Bath, SW England
1907 1998
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BFM: A perfect natural laboratory!
• Three stalagmites (BFM9, Boss, F2) sampled and sectioned
• All three annually laminated
• Chronology and growth rates determined
Typical ‘juvenile’ stalagmite from BFM
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Lamina count
• Stalagmite nucleation does not occur prior to 1920.
• Growth rates increase through time
• No long-term change in climate apparent
More bioproductivity = higher growth rate
Baldini et al., 2005, EPSL
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Stalagmite growth depends on:
Water: enough water must exist to transfer Ca2+ to stalagmite
Soil bioproductivity: Recharge water must equilibrate with high PCO2 atmosphere
Residence time: Water must reside in karst long enough to dissolve bedrock
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Baker and Fairchild, 2012 Nature Education Knowledge
Fracture flow
Diffuse flow
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Karst is inherently dynamic!
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Stalagmite growth depends on:
Water: enough water must exist to transfer Ca2+ to stalagmite
Soil bioproductivity: Recharge water must equilibrate with high PCO2 atmosphere
Residence time: Water must reside in karst long enough to dissolve bedrock
Cave air PCO2: must be lower than dissolved PCO2 for degassing to occur
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Modelling stalagmite growth
Where:
Ro = growth rate (mm yr-1)
Ca = drip water [Ca2+] (mmol L-1)
Caapp = drip water [Ca2+] at equilibrium (mmol L-1)
d = thin film of water thickness (mm)
DT = time between drips (sec)
a = ‘kinetic constant’ dependent on
d and temperature
CC-Bil Baldini et al. 2008 EPSL
Baldini et al., EPSL 2008. Adapted from: Buhmann and Dreybrodt, 1985; Baker et al., 1998; Dreybrodt, 1999
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Modelling stalagmite growth
CC-Bil
Caapp (equilibrium drip water [Ca2+] ) is controlled by ambient PCO2 and temperature according to:
Baldini et al., 2008 EPSL. Derived from data presented in: Dreybrodt, 1996; Kaufmann, 2003
at all PCO2 values:
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T =10 ºC
DR = 1 drip/min
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T =10 ºC
DR = 1 drip/min
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T =10 ºC
DR = 1 drip/min
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T =10 ºC
DR = 1 drip/min
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Implications for high-resolution climate research:
• Caves ventilate at different times and during different seasons
• Seasonal bias in deposition caused by variable cave air PCO2
• Oxygen isotope records from stalagmites could be biased towards a particular season
• Seasonal ‘micro-hiatuses’
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Modelled versus actual growth rates: a case study from Crag Cave
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13-month monitoring scheme • All growth determining
variables monitored
• Drip water electrical conductivity (proxy for Ca2+)
• Iceland spar calcite placed under drip
Sherwin and Baldini 2011, GCA
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CO2 controls on Ca2+
• Recharge (dilution) principal control on Ca2+
• Variable PCP driven by PCO2 shifts exerts clear secondary control
• 1 ppm Ca2+ shift by PCP requires a 333 and 667 ppm PCO2 shift
Sherwin and Baldini 2011, GCA
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Modelled GR matches actual GR
• Iceland spar and overgrowth sectioned and overgrowth measured
• Secondary growth on Iceland spar matches predicted growth
• Growth models appear valid
Sherwin and Baldini 2011, GCA
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Large-scale permanent PCO2 shifts: Yok Balum, Belize
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Yok Balum
• Well monitored site
• Substantial stalagmite deposition from modern to ~50 ka BP…
• …but none found older than ~50 ka BP.
Ridley et al. 2015 JCKS (in press) Ridley et al. 2015 JCKS (in press)
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summer
winter
Ridley et al. 2015 JCKS (in press)
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Ridley et al. 2015 JCKS (in press)
Yok Balum
• Ventilates on daily timescales
• Ventilates on seasonal timescales
• Low PCO2, particularly in winter
Ridley et al. 2015 JCKS (in press)
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Ridley et al. 2015 JCKS (in press)
Yok Balum
• Back entrance formed by roof collapse
• Pre-collapse cave only had one entrance
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Yok Balum
• Back entrance formed by roof collapse
• Pre-collapse cave only had one entrance
• Stalagmites on entrance breakdown started growing ~50 ka BP
• Stalagmite growth initiated by ventilation?
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Ridley et al. 2015 JCKS (in press) Ridley et al. 2015 JCKS (in press)
Yok Balum
• Yok Balum with only one entrance would have unusual geometry
• Slopes up into cave
• No density-driven ventilation prior to ~50 ka BP?
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Summary
• Current theoretical models predict stalagmite growth very well
• Seasonal growth may complicate palaeoclimate interpretations
• Cave air CO2 variability is important for modulating growth
• Ventilation shifts can suddenly promote/discourage stalagmite growth
• Understanding how stalagmites grow is fundamental for interpreting climate proxy records
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• How do different impurities in drip water affect stalagmite growth?
• How do differences in calcite porosity affect stalagmite growth?
• Instantaneous growth rates versus vertical extension rates
• Are interpretations based on modern monitoring applicable for older climate records?
Some remaining questions
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Baker et al 2014, EPSL