Variations in citations over time in papers focused on subterranean systems published in specialized journals. The average ± standard error number of Web of Science citations is based on a subset of articles published in Acta Carsologica, International Journal of Speleology, Journal of Cave and Karst Studies, and Subterranean biology (n= 969). Note that prior to 2005, no data was available for these journals in Web of Science.