Water-level change recorded in Lake Pac Chen Quintana Roo, Mexico infers connection with the aquifer and response to Holocene sea-level rise and Classic Maya droughts

Pac Chen Lake is located on the Yucatan Peninsula, Mexico and is ~ 42 km from the coast and ~ 22 km NE of Coba. It has an area of ~ 36,735 m2 and maximum depth of 25 m. Four sediment cores along a depth transect provide a 4-ka record of the evolution of the eastern deep basin (core PC1 at 25 m depth) and the shallow margin (cores PC2–4 at 0.25–5 m depth). PC1 shows the effect of water-level rise and flooding of the shallow margin (2.8–1.8 ka) through a lithological (organic to carbonate) and geochemical (μXRF; decreased Ti, Fe, K and Ca) change along with a reduction in sediment accumulation (~ 0.2927 to 0.0343 cm year−1). This change in sedimentation matches basal ages of PC2 and PC4 at 2.5 and 1.8 ka respectively, indicating water-level rise and flooding of the shallowly sloped margin which is within estimates of Holocene sea-level rise thus indicating connection with the aquifer. Corroborating evidence for connection with the aquifer comes from water-level monitoring (30 min intervals; 6 months December 12, 2018 to June 6, 2019) which shows a semi-diurnal tidal fluctuation (1–1.5 cm). Droughts have been thoroughly discussed as a proponent of the decline of the Classic Maya, with lakes being inferred to be isolated from the aquifer and experiencing water level drawdown. However, during the Classic Maya droughts lake drawdown in Pac Chen would be minimal, and there is no evidence of a water level drop in our lake margin stratigraphy (PC2–4). Water mass characteristics measured in March 2016 (temperature, conductivity) indicate some hydrological isolation from the aquifer. This isolation would have allowed for recording of environmental changes, but also likely changed through time as flooding of the lake progressed. The shallow margin core PC4, however, recorded several rapid drops in K and Fe from ~ 1100 to 975, and 925–875 yr BP, which we interpret as periods of reduced inputs of terrigenous weathering during times of reduced rainfall and runoff. These periods are consistent with other regional paleoclimate records (lake and speleothem) of the Classic Maya droughts (1200–850 yr BP).