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Highlights

  • In tropical, wet guano, maximum acidity, temperature, and k values occur at depths of ~10-30 cm
  • Guano moisture level is the most significant control on k
  • Guano k values can have an enormous range – from 0.01 in wet tropical caves, down to 3 x 10-6 in extremely dry caves
  • SEM studies demonstrate that 3 kyr old guano in extremely dry conditions is essentially unaltered
  • Chitin survival under favorable conditions can thus be extrapolated to timescales of 105 years

Abstract

Cave guano deposits are increasingly being recognized as valuable repositories of paleo-climatic and paleo-environmental information. However, that value is constrained by rates of guano decomposition, and these rates have not been previously well-studied. Here we show that field and laboratory studies of deep insectivorous bat guano sequences in the caves of Borneo demonstrate the extreme dependence of decomposition rate on guano water content. Under tropical conditions, moist guanos exhibit decomposition coefficients (k) values of ~ 0.01, implying the loss of most of the organic content on decadal timescales. Under similar temperatures but drier conditions, k values drop to ~3 x 10-6, permitting significant organic (chitin) content to persist for tens of thousands of years. One of the implications of these findings for paleo-environmental records older than the limit of carbon dating is that a value for k can be calculated based on a single carbon date, which then allows an estimate of likely age at base of deposit.

DOI

https://doi.org/10.5038/1827-806X.53.1.2494

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