Hells Bells project - results of sampling campaign in February 2020

This data set compiles the results of water chemical analyses as well as bulk chemical analyses of the particles suspended in the water columns of cenotes (sinkholes) obtained during a sampling campaign in Mexico in February 2020. Three stratified cenotes from North-Eastern Yucatan Peninsula were investigated: El Zapote and Siete Bocas with Hells Bells underwater speleothems and cenote Angelita without these structures. The goal of the sampling and analyses was to obtain a high depth resolution of water data around the pelagic redoxclines of the cenotes for a better understanding of the biogeochemical processes and particle formation in these particular water layers, especially with regard to the biologically promoted precipitation of calcite (Ritter et al., 2019). This process is apparently involved in the formation of underwater speleothems termed as Hells Bells. The comparison of cenotes with Hells Bells (El Zapote and Siete Bocas) with a similar cenote without Hells Bells (Angelita) allows to identify the prerequisites for biologically promoted calcite precipitation and thus, Hells Bells formation. Furthermore, cenote Xcolac from the northern-central Yucatan Peninsula was investigated. Prior studies indicated that Hells Bells-like underwater speleothems might occur in cenote Xkolac (Ritter S.M., 2020). In order to verify, the cenote was explored and investigated in February 2020 by a team of divers and scientists. Below ~52 m water depth, the limestone walls actually revealed brownish calcitic coatings forming pine-cone like structures at overhangs (see video: Ritter et al., 2021). These novel underwater speleothems were termed as "Pinas de Yucatan". The hydrogeochemistry around the pelagic redoxcline indicates biologically-promoted calcite precipitation in the water depth level at which sulfide is re-oxidized to elemental sulfur. Based on this discovery, Hells Bells and Pinas de Yucatan might represent a novel sub-type of underwater speleothems, the redoxithems. This special kind of speleothems are formed by a common formation mechanism, which is the microbially promoted calcite precipitation in pelagic redoxclines of very stagnant aquatic systems.