1. Global Distribution of Karst
Karst ≈ Carbonate outcrops = ~25% of terrestrial earth surface
Karst aquifer provide ~25% of world’s of potable water
Global carbon cycling??? Climate??? Sea level???
Data from Falkowski et al., 2000, Science
CO2(g) + H2O + CaCO3 ↔ Ca2+ + 2HCO3-↕
H2S + 2O2 + CaCO3 → SO42- + Ca2+ + H2O + CO2(g)↑

2. Complete Aquifer System - Yucatan
What are the:
Sources of water?
Chemical compositions of sources?
Chemical transformations along flow path?
Possible water sources
Diffuse
Cenotes
Mangroves
Arnoldo’s talk ?
Océano ?
The kind of buoyant jet discharge I researched has this kind of schematic typical to the Yucatan Peninsula. Coastal aquifers are recharged through sinkholes known as cenotes which open to the groundwater. The water flows from the cenote through the aquifer and out at buoyant jet discharges in the coastal ocean. The jet discharge is modulated by the tides, during low tides the discharge is evident from the surface, with vertical flows of around 1 m/s. The head difference between the cenote and the ocean dictates the jet strength.
Acuífero ?

3. Some understanding from Bahamian blue holes (~Cenotes)
Thinner fresh water lens
Strongly tidally influenced
Exchange through conduit with ocean
Exchange between matrix rocks and conduit
Reactions at pycnocline - similar to Yucatan
Martin et al., 2012 J Hydro
Martin et al., 2013 Acta Carsologica

4. Madison Blue Spring, Florida
Some understanding from water intrusion into terrestrial conduits - Florida
Madison Blue Spring, Florida
Chemical reactions similar to Yucatan?
Brown et al., Chem. Geol., 2014

5. DOC reactions and calcite dissolution
Change through time net of mixing
DOC oxidized (remineralization)
Calcite dissolves
Nutrient production
DOC: N & P
Minerals: P
CH2O + O2 → CO2 + H2O
Brown et al., Chem. Geol., 2014
CO2 + H2O + CaCO3 → Ca2+ + 2HCO3-

6. ? Yucatan Questions Does water exchange between cenotes and aquifer?
What are chemical reactions in Yucatan cenotes and aquifer?
DOC remineralization – N & P sources?
Water-rock reactions – P and C sources?
What are chemical reactions along flow path: source to spring (ojos)?
Exchange into/out of ojos –
What are chemical reactions
and reaction products? ?

7. Yucatan – sampling transect
Cenotes
C7B
Chan Tuk Che
Mojarras
Kin Ha
Zapote
Mangroves
UNAM
Well
Beach pits
Ojos
Pargos
Gorgos
Laja
“Mini ojo”
Reef
“end member”
Two samplings
March 2014
September 2014 M
UNAM
CEN
CTC
C7B R G P
ZPT KH L

8. Three cenotes – Q. Roo, September 2014
Variable gradients at pycnocline
Highly variable pH
Sulfide oxidation = sulfuric acid
Drives mineral dissolution - precipitation reactions
Strong
pycnocline
Moderate
pycnocline
Limited pycnocline

9. Cenote 7 Bocas, March, 2014
Supersaturated
precipitate
Minerals near saturation except at pycnocline
Calcite/aragonite undersaturated
Increase in Mg/Ca ratio (seawater) increases dolomite saturation
Undersaturated
dissolve
Aragonite
Calcite
Dolomite

10. Cenote Siete Bocas; March 2014
Sulfide Layer
2CH2O +SO4-2→ 2HCO3- + HS- + H+
Top of Halocline
DOC-rich
Carbonate Reactions
H2S + 2O2 + Ca(P)CO3 → SO42- + Ca2+ + P + H2O + CO2(g)
H2S + 2O2 + CaMg(P)CO3 ← SO42- + Ca2+ + Mg2+ + P + H2O + CO2(g)

11. Example of matrix water composition
UNAM well, September 2014
Within aquifer matrix
Consider at discrete depths:
Salt
NO3
Sulfide
DOC concentrations
DOC characteristics
Type
Lability

12. UV specta – UNAM Well Absorbance “Quality” of OC
NO3 + Salt (Br, Cl)
Sulfide
Organic carbon
Absorbance
“Quality” of OC
SUNA – Submersible Ultraviolet Nitrate Analyzer
Wavelength

13. High DOC zone – degraded? UNAM well, September 2014 Moderate H2S
Halocline
Elevated H2S
September 2014

14. DOC mixing onshore-offshore March 2014
DOC source from salt zone inland?
Is there a change in character of OC?
C7B-20
Fore reef

15. Mixing of nutrients Mixing less clear Unique sources to each ojo?
Nitrogen
Consumption – transformation
NO3 mostly gone
Phosphorous
Sources carbonate & OC
Reactions with carbonate
C7B-20
Fore reef
Fore reef
C7B-20

16. Complete Aquifer System
Chemical fluxes critical:
- sulfide – toxic?
- nutrients – algal blooms?
Various source compositions
Océano
The kind of buoyant jet discharge I researched has this kind of schematic typical to the Yucatan Peninsula. Coastal aquifers are recharged through sinkholes known as cenotes which open to the groundwater. The water flows from the cenote through the aquifer and out at buoyant jet discharges in the coastal ocean. The jet discharge is modulated by the tides, during low tides the discharge is evident from the surface, with vertical flows of around 1 m/s. The head difference between the cenote and the ocean dictates the jet strength.
Reactions – water chemical alterations
Acuífero