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)↑

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 ?

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

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

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-

? 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? ?

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

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

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

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)

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

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

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

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

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

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