Stable isotopes of subfossil bat guano as a long-term environmental archive: insights from a Grand Canyon cave deposit

Abstract

We investigated the utility of subfossil bat guano as a paleoenvironmental archive by comparing elemental ratios and δ13C, δ15N, and δD values of various simple extracts from bulk material. Solvent-extracted guano yielded consistent C:N and N:H ratios, and δ13C values of solvent-extracted guano exhibited strong covariation with δD values, as well as with the δ13C values of other simple extracts (bulk guano, bulk lipid). The results suggest that reliable records are easily recovered for δ13C, and also indicate that δ15N values may have utility as a paleoenvironmental archive. Despite coeval δ13C values of bulk guano and solvent-extracted guano, 14C ages of the different fractions did not always yield similar ages, indicating that future refinement of a suitable extraction protocol is required. Applying these protocols to an ancient bat guano deposit allowed us to infer that climate at the Grand Canyon during the late Pleistocene was more variable and generally cooler and wetter, relative to Holocene climate. We conclude that guano deposits are an underutilized, yet powerful continental paleoenvironmental archive of climate change for semi-arid and tropical regions.