Testing algal-based pCO2 proxies at a modern CO2 seep (Vulcano, Italy)
Caitlyn Witkowski, Marcel T. J. van der Meer, Nadine T. Smit, Jaap S. Sinninghe Damsté, Stefan Schouten
Abstract
Abstract Understanding long-term trends in atmospheric concentrations of carbon dioxide ( p CO 2 ) has become increasingly relevant as modern concentrations surpass recent historic trends. One method for estimating past p CO 2 , the stable carbon isotopic fractionation associated with photosynthesis (Ɛ p ) has shown promise over the past several decades, in particular using species-specific biomarker lipids such as alkenones. Recently, the Ɛ p of more general biomarker lipids, organic compounds derived from a multitude of species, have been applied to generate longer-spanning, more ubiquitous records than those of alkenones but the sensitivity of this proxy to changes in p CO 2 has not been constrained in modern settings. Here, we test Ɛ p using a variety of general biomarkers along a transect taken from a naturally occurring marine CO 2 seep in Levante Bay of the Aeolian island of Vulcano in Italy. The studied general biomarkers, loliolide, cholesterol, and phytol, all show increasing depletion in 13 C over the transect from the control site towards the seep, suggesting that CO 2 exerts a strong control on isotopic fractionation in natural phytoplankton communities. The strongest shift in fractionation was seen in phytol, and p CO 2 estimates derived from phytol confirm the utility of this biomarker as a proxy for p CO 2 reconstruction.