Geochemical data to characterize chemical water column properties of flooded caves (Ox Bel Ha and Cenote Crustacea) within the coastal aquifer of the Yucatan Peninsula, Quintana Roo, from December 2013 to January 2015

Discrete water samples were collected from Ox bel Ha cave (Cenote Jailhouse, Cenote Odyssey, and Cenote Naach Wennen Ha) and another cave (Cenote Crustacea) during three sampling events: December 2013, August 2014, and January 2015. Cenote and cave samples were collected by scuba divers following protocols established by the American Academy of Underwater Sciences and the National Speleological Society Cave Diving Section. Water samples for geochemical analysis of dissolved materials were collected near sonde profile locations in plastic 60 ml syringes fitted with 3-way stopcocks. The syringes were rinsed with distilled water and dried prior to the dive, and flushed with sample water prior to closing the stopcock. Samples were kept cool during transport to the field lab and preserved within eight hours of collection. More details related to the processing of the samples after collection are provided in the Methods section of Brankovits and others, 2017.

Analysis of the samples was performed at the Woods Hole Oceanographic Institution (WHOI) and U.S. Geological Survey (USGS) in Woods Hole MA, USA. Sulfate and chloride concentrations were determined using a Metrohm 881 Compact Plus ion chromatograph (IC) equipped with a Metrosep A Supp 5-250 anion column. Chloride concentrations milliMolar (mM) were converted to milligrams per liter (mg l-1) and multiplied by 0.0018066 to determine salinity (psu). The analytical error for chloride and sulfate was +/-3.5 percent (%) of the IAPSO standard sulfate and chloride values.
Dissolved inorganic carbon (DIC) concentrations were determined with a Model 5011 UIC coulometer and quantified relative to a seawater certified reference material (CRM) with a relative standard deviation (RSD) of 4 percent (%) relative to the CRM value (2.2 millimolar, mM). The stable carbon isotopic content of the DIC was measured with a Thermo-Finnigan DELTAplus XP IRMS with an analytical error (1-sigma) of 1.1 per mil.
Headspace methane concentrations were determined using a Shimadzu 14-B gas chromatograph (GC) equipped with a flame ionization detector (FID). Headspace concentrations were converted to dissolved concentrations using the method of Magen and others, 2014 and are reported with a relative standard deviation of 2 percent (%).
The stable carbon isotope composition of methane from the headspace of the serum vials was determined using a Thermo-Finnigan DELTAPlus XL isotope ratio mass spectrometer (IRMS) coupled to an Agilent 6890 Gas Chromatograph (GC) via a Finnigan GCCIII combustion interface with 1-sigma deviation of 1.6 per mil.
DOC concentration and d13C were analyzed by high-temperature combustion-isotope ratio mass spectrometry (HTC-IRMS) at the USGS-WHOI Dissolved Carbon Isotope Lab (DCIL). The DCIL HTC-IRMS system consists of an OI 1030C total carbon analyzer and a Graden molecular sieve trap interfaced to a Thermo-Finnigan DELTA-PLUS XL IRMS. DOC concentrations are reported with an RSD of less than 5 percent (%) of the measured value. Stable carbon isotope ratios for DIC, methane and DOC are reported in the standard delta-notation relative to VPDB (Vienna Pee Dee Belemnite) with a 1-sigma deviation of less than 0.5 per mil.
All sample analyses were performed by David Brankovits under the supervision of John Pohlman. More details about the laboratory analyses are described in the Geochemical Analysis portion of the Methods section of Brankovits and others, 2017). Sample processing occurred between 2014 and 2015.