drip composition and stalagmite growth...

Drip composition and stalagmite growth rates

James U.L. Baldini Department of Earth Sciences, Durham University, UK.

photo by J.Frost

photo by Steve Partridge

Mitchell Caverns, CA

Mohave National Preserve, CA

But water is clearly important

for growth!

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.”

Allison V. C. (1926) The antiquity of the deposit in Jacob’s Cavern. Amer. Mus. Nat. Hist. Anthropol. Pap.

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.”

• 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):

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

Modern perspectives

Dreybrodt, 1980:

Dreybrodt 1980, Chemical Geology

Thin

film

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

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

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

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

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

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

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

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

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

Genty et al. 2001, Chemical Geology

Modern perspectives

Genty et al also used monitoring data to predict seasonality in speleothem growth

Stalagmite growth depends on:

Water: enough water must exist to transfer Ca2+ to stalagmite

Stalagmite growth depends on:

Water: enough water must exist to transfer Ca2+ to stalagmite

Soil bioproductivity: Recharge water must equilibrate with high PCO2 atmosphere

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

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

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

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

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

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

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

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

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

Baker and Fairchild, 2012 Nature Education Knowledge

Fracture flow

Diffuse flow

Karst is inherently dynamic!

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

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

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:

T =10 ºC

DR = 1 drip/min

T =10 ºC

DR = 1 drip/min

T =10 ºC

DR = 1 drip/min

T =10 ºC

DR = 1 drip/min

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’

Modelled versus actual growth rates: a case study from Crag Cave

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

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

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

Large-scale permanent PCO2 shifts: Yok Balum, Belize

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)

summer

winter

Ridley et al. 2015 JCKS (in press)

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)

Ridley et al. 2015 JCKS (in press)

Yok Balum

• Back entrance formed by roof collapse

• Pre-collapse cave only had one entrance

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?

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?

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

• 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

Baker et al 2014, EPSL