Crag Cave StudyA look into the past

Dillon DolezalUndergrad Geology Major

NDSU Geol 428 Geochemistry2010

Summary

• Background Information• Importance of Caves• Previous Work– My Modeling

• Previous Work– My Modeling

• Conclusions

BackgroundCrag Cave, CastleIsland, County Kerry, Ireland

Image from Google maps

Background

• 1859– Caves in area

• 1981– Efforts to explore

• 1983– Sump Explored A cave diver returned after diving

describing the other side as “caverns measureless to man”

Example of a sumpImage from wiki

www.cragcave.comCrag Cave Sump

Flickr.com

Background• 1981

– ≈1km surveyed

• 1983 - 1984– ≈ 3 additional km

• Late 1980’s – Open to tourists– New bigger entrance

• Lord of the Rings– Halls of Gondor– Hall of Moria– Minus Tirith– White Tree– Forest of Fangorn

“The whole cave was explored“ Gunn 1982

www.cragcave.com

Importance of Caves

• Paleoclimate Reconstruction (Baldini et al)

– Not fully understood– Speleothems could show high resolution

• Stalagmites– C, O, Fulvic acid, U• Ground Cover, Temperature, Precipitation, Age Dating

– Future climate change • Contamination Concerns– High mobility

• Can move far distances

yunus.hacettepe.edu.tr/~harun/karst.htm

Previous Work• Baldini et al (2008)

– Stalagmite growth and its preservation of oxygen isotope-based paleoclimate• They determined fast growth rates were bias to heavy Oxygen• High frequency in growth rates

My Plan: Show influences that can alter growth rates: WEB-PHREEQ

Influences on Growth

Decreasing CO2 Pressure

This graph shows SI increasing as C02 pressure decreases. Lower C02

pressures allows for H2C03 to degass and the equation to move to the right.

• PCO2– The soil has a higher CO2 pressure

than the cave.

– -1.5 = Soil– -2.2 = cave– -3.5 = outside

Influences on Growth• Little change in SI• Caves typically have little

change in temp– Crag cave = 10.5 C year

round (Tooth and Fairchild)

Ca= 110 mg/LMg = 11mg/LLog Pco2 = -2.5

This model shows that Dolomite SI has a much higher slope than Calcite

When looking at my models, changes in C02 Pressure seems to be the most influential to stalagmite growth

So where do changes in CO2 pressure come from?

Tooth and Fairchild• Stalagmites with high Mg/Ca ratio could characterize dry periods.

– Slow trickling water provides time for Calcite (CaCO3) to precipitate which removes Ca

Tooth and Fairchild (2003)

Mg/Ca Ratio vs Drip rates; Evidence for Calcite Precipitation

Previous Work

My Plan: Look into why this is and any variables

My Modeling

– Log PCO2 of soil = -1.4 to -1.8• Tooth and Fairchild

– Slow water movement during dry weather

– Calcite can precipitate in the soil which in return raises the Mg/Ca ratio

• Issues– Soil Pco2 comes from

decaying material• Biological influences?

Decreasing CO2 Pressure

This graph shows SI increasing as C02 pressure decreases. Lower C02 pressures allows for H2C03 to degas and the equation to move to the right.

10.5 C110mg/L Ca11mg/L Mg

Conclusions

• Ventilation was a major influencer on results– It messed up the traditional O isotope proxy– The new entrance could have altered the ventilation– Crag cave is deep and has a sump that can minimize

ventilation• Is Pco2 as variable?• If Pco2 is a lot higher, would speleothems grow slower?

• Mg/Ca ratios maybe a way to determine precipitation• Interpreting climate from caves involves many

variables and each cave is unique, so they must be understood individually to construct climate.

References• Baldini, J. et al. (2008). Very high-frequency and seasonal cave atmosphere PCO2

variability: Implications for stalagmite growth and oxygen isotope-based paleoclimate records. Earth and Planetary Science Letters. 272, 118–

129• Gunn, John. (April 1982). The Irish Naturalists' Journal Vol. 20, No. 10 (Apr., 1982),

pp. 445-449. Irish Naturalists' Journal Ltd. http://www.jstor.org/stable/2553860

• Mattey, Dan; et al (2010) Seasonal microclimate control of calcite fabrics, stable isotopes and trace elements in modern speleothem from St Michaels

Cave, Gibraltar (in Tufas and speleothems; unravelling the microbial and physical controls) Geological Society Special Publications, 336 323-34

• Tooth and Fairchild. (2003). Soil and karst aquifer hydrological controls on the geochemical evolution of speleothem-forming drip waters, Crag

Cave,southwest Ireland. Journal of Hydrology. 273, 51–68