Presentation on theme: "Crag Cave Study A look into the past Dillon Dolezal Undergrad Geology Major NDSU Geol 428 Geochemistry 2010."— Presentation transcript:
Crag Cave Study A look into the past Dillon Dolezal Undergrad Geology Major NDSU Geol 428 Geochemistry 2010
Summary Background Information Importance of Caves Previous Work – My Modeling Previous Work – My Modeling Conclusions
Background Crag 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 sump Image from wiki Crag Cave Sump Flickr.com
Background 1981 – ≈1km surveyed – ≈ 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
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 CO 2 Pressure This graph shows SI increasing as C0 2 pressure decreases. Lower C0 2 pressures allows for H 2 C0 3 to degass and the equation to move to the right. P CO2 – 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/L Mg = 11mg/L Log 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 P CO2 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 CO 2 Pressure This graph shows SI increasing as C0 2 pressure decreases. Lower C0 2 pressures allows for H 2 C0 3 to degas and the equation to move to the right C 110mg/L Ca 11mg/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 Irish Naturalists' Journal Ltd. Irish Naturalists' JournalIrish Naturalists' Journal Ltd 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, 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