Seasonal trends in calcite-raft precipitation from cenotes Rainbow, Feno and Monkey Dust, Quintana Roo, Mexico: Implications for paleoenvironmental studies

Calcite-raft precipitation was monitored in three Yucatan cenotes (Rainbow, Feno and Monkey Dust) over a 2-year period. Site-specific variables including water temperature, relative humidity, water level and salinity were recorded as well as rainfall (Cozumel). Calcite-raft surface area was monitored through trail cameras that collected photographs every 60 min. Accumulation rates were recorded using sediment traps that were collected in May and December of each year. Calcite-raft surface area was calculated using an image segmentation procedure that identified the boundary of objects (edge detection) that share certain pixel characteristics, removed non-points of interest and measured the sum of the area covered by the raft material. Results show that large rainfall events have a regional effect on the meteoric water mass (i.e. salinity), as well as the precipitation of calcite rafts. The large rainfalls and increased inflows cause dilution of the CaCO3 supersaturated meteoric water mass and cause increased flow hindering calcite-raft precipitation for days to weeks after the rainfall. Raft precipitation gradually returns with deceasing flow after the event, and stagnation allows the recurrence of CaCO3 supersaturation and accumulation of nucleation particles. Small rainfalls did not seem to have the same effect, as slower percolation of rainwater through the epikarst would be more saturated and micro-topographic relief may isolate the water pools from the lower flow. The sediment trap data shows that calcite rafts accumulate relatively constantly throughout the year in all three sites. Sedimentation rates from Feno and Monkey Dust responded to seasonal changes in surface-water disturbance associated with rainfall (wet and dry), although Rainbow didn't show any seasonality likely due to other site-specific factors affecting water disturbance (e.g. bats, wind).