The Occurrence and Effect of Sulfate Reduction and Sulfide Oxidation on Coastal Limestone Dissolution in Yucatan Cenotes

Abstract

Dissolution of carbonate minerals in the coastal halocline is taking place in the karst terrain along the northeastern coast of the Yucatan Peninsula. The dissolution is being accelerated in cenotes (sinkholes) where sulfate reduction and oxidation of the produced sulfide is occurring. Hydrogen‐sulfide concentrations ranged from 0.06 to 4 mmolal within the halocline in two sinkholes. Relative to concentrations expected by conservative mixing, fluids with high hydrogen‐sulfide concentrations were correlated with low sulfate concentrations, high alkalinities, low pH values, and heavy sulfur isotope values for sulfate. Hydrogen‐sulfide concentrations were less than those predicted from sulfate reduction, calculated from deficiencies in measured sulfate concentrations, indicating mobility and loss of aqueous sulfide. Fluids with low hydrogen‐sulfide concentrations were correlated with very high calcium concentrations, high strontium and sulfate concentrations, slightly elevated alkalinities, low pH values, and sea‐water sulfur isotope values for sulfate. Gypsum dissolution is supported by the sulfur isotopes as the major process producing high sulfate concentrations. However, oxidation of aqueous sulfide to sulfuric acid, resulting in carbonate‐mineral dissolution is needed to explain the calcium concentrations, low pH values, and only slightly elevated alkalinities. The halocline may trap hydrogen sulfide that has been stripped from the underlying anoxic salt water. The halocline can act as a stable, physical boundary, holding some of the hydrogen sulfide until it is oxidized back to sulfuric acid through interaction with the overlying, oxygenated fresh water or through the activity of sulfide‐oxidizing bacteria.

Comparison of an inactive submarine spring with an active nearshore anchialine spring in Florida

“…They also identified bacterially mediated sulfide oxidation at the chemocline, which reduces pH and may enhance dissolution of the carbonate rock. Similar processes were also documented in cenotés of the Yucatan Peninsula (Stoessell et al, 1993;Schmitter-Soto et al, 2002).…”

The biogeochemistry of anchialine caves: progress and possibilities

“…The groundwater hydrology and factors that control mixing between meteoric freshwater and marine waters have been the subject of several investigations (Back et al, 1986;Stoessell et al, 1993;Beddows, 2004). Biogeochemical investigations, however, are limited to a stable carbon and nitrogen isotope based study that delineated the organic matter sources and food web trophic structure within the 18 km ?…”

“…Studies in anchialine sinkholes, collapse features and pits, which are often connected to vast cave networks, have contributed to the basic understanding of what biogeochemical processes are possible within isolated anchialine caves (Stoessell et al, 1993;Humphreys, 1999;Socki et al, 2002;Seymour et al, 2007;Gonzalez et al, 2011). However, the biogeochemistry of anchialine caves is generally distinct from anchialine sinkholes, where atmospheric gas exchange, aquatic primary production, and detrital inputs from vascular plants are prevalent.…”

The key role of the chemolimnion in meromictic cenotes of the Yucatan Peninsula, Mexico

“…Within the chemolimnion of Nohoch Hol, the pH range is consistent with other meromictic cenotes in the Carribean coast (Wilson & Morris, 1994;Stoessell et al, 1993). Xcolac, an inland meromictic Yucatan cenote (Fig.…”

“…Most of the cenotes found throughout the peninsula typically present characteristics intermediate between the lentic-lotic endmembers proposed by Schmitter-Soto et al (2002). The well studied cenotes of Angelita, and the three cenotes located in the Calica Quarry are all lentic pit cenotes in this scheme (Moore et al, 1992Stoessell et al, 1993Stoessell et al, , 2002Soteres, 2000).…”