Paleoenvironment and environmental degradation of a tropical island: Evidence from cave calcites (Puerto Rico)

Isotopic (oxygen and carbon) and petrographic (crystal length and roundness) analyses were performed on two speleothem from the tropical island of Mona, Puerto Rico, which grew over the last 1.5 kyrs of the Late Holocene in order to determine if they contain a recognizable paleoenvironmental signal and signs of the historically documented human-induced environmental degradation of the island through extensive guano mining. These records were compared to the nearest well-documented high-resolution proxy, the Quelccaya Ice Core.; Carbon and oxygen isotopes are shown to respond mainly to paleotemperature changes in the pre-1510 timeframe of relative climate stability and for most of the Little Ice Age. For both isotopes, the higher the temperature, the greater the depletion (caused by the cave temperature effect for delta 18O and the biological effect for delta13C). Paleoprecipitation becomes a dominant control only in droughts. Crystal morphology is shown to indicate extreme environmental events such as droughts (hot or cold) and hot-wet events. Both of the isotopes and crystallographic records clearly indicate anthropogenically-induced environmental change.