Speleothems Speleothems (a.k.a. (a.k.a. the tropical ice cores)the tropical ice cores)

Cave depositsCave deposits Laminated structure of CaCOLaminated structure of CaCO33

Evaporation-depositionEvaporation-deposition Slow COSlow CO22 degassing == degassing ==

minimal disequilibrium with minimal disequilibrium with drip watersdrip waters

Rapid CORapid CO22 degassing == degassing == disequilibrium precipitationdisequilibrium precipitation

Possibility for water-soil or Possibility for water-soil or water-rock chemical water-rock chemical equilibration == equilibration == undermines reliability of undermines reliability of speleothems as speleothems as paleothermometers paleothermometers

Schwartz (2007)

Geochemistry of Geochemistry of speleothemsspeleothems T (°C) = 16.5 - 4.3 (T (°C) = 16.5 - 4.3 (1818OOctct - - 1818OOww) + 0.14 () + 0.14 (1818OOctct - - 1818OOww))2 2 (Epstein (Epstein

et al. 1953)et al. 1953) 1818OOctct would also reflect precipitation patterns would also reflect precipitation patterns

Caveat: the “amount” effect in Caveat: the “amount” effect in 1818OOw w (increase in (increase in 1818O during O during heavy rain events)heavy rain events)

Age control:Age control: 14C - have to correct for nonradioactive C introduced into DIC 14C - have to correct for nonradioactive C introduced into DIC

from dissolution of calcite in the soil zonefrom dissolution of calcite in the soil zone U/Th - have to account for detrital 230Th in ‘dirty’ calciteU/Th - have to account for detrital 230Th in ‘dirty’ calcite

Geochemistry of Geochemistry of speleothemsspeleothems

Have to estimate Have to estimate 1818O of drip water:O of drip water: Close to annual average of Close to annual average of 1818OOpptppt

But local alteration due to surface evaporation, But local alteration due to surface evaporation, transpiration, selective recharge of seasonal transpiration, selective recharge of seasonal precipitation (snow meltwater)precipitation (snow meltwater)

Some assumptions and ways to estimate Some assumptions and ways to estimate w:w: Secular variation in Secular variation in 1818OOpptppt = annual (seasonal) variation = annual (seasonal) variation

(assumes a particular rate of change with time)(assumes a particular rate of change with time) Analysis of fluid inclusions in the speleothems (Analysis of fluid inclusions in the speleothems (D of the D of the

water should be unchanged)water should be unchanged) DDpptppt = 8 = 8 1818OOpptppt + + 00 ( (00 is deuterium excess, 10permil) is deuterium excess, 10permil)

Using models for variation in Using models for variation in 1818OOpptppt (derivation of water (derivation of water vapor from seawater with known variability in vapor from seawater with known variability in 1818O)O)

Paleoclimate studiesPaleoclimate studies Matching Matching

changes in North changes in North Atlantic climate Atlantic climate and South Chinaand South China Greenland - Greenland -

cooling; cooling; coincidentally, coincidentally, enhanced enhanced summer summer monsoon rains monsoon rains in South in South China, China, reflected in reflected in the isotopesthe isotopes

Wang et al. 2001

But what about the But what about the carbon?carbon? Fractionation between DIC and calcite is very small; so, Fractionation between DIC and calcite is very small; so,

1313C reflecting isotopic composition of drip waterC reflecting isotopic composition of drip water 1313C in calcite affected by:C in calcite affected by:

C3/C4 plants balance; C4 - higher C3/C4 plants balance; C4 - higher 1313CC Plant vegetation density above cave -- dissolution by Plant vegetation density above cave -- dissolution by

reaction w/ atm = higher reaction w/ atm = higher 1313CC

13C increases with decreasing rainfall due to decrease in the contribution of HCO3

- to the drip water (Frumkin et al. 1999,2000)