Speleothems as archives for terrestrial dissolved organic carbon export – a radiocarbon perspective

Terrestrial ecosystems are one of the Earth's largest active carbon reservoirs and hold three times more carbon than the atmosphere. However, their sensitivity and response to global climate change remain debated and may be dependent on multiple processes acting on different spatial and temporal scales. Speleothems, secondary cave carbonate deposits, offer a unique, but under-exploited opportunity to reconstruct the export of dissolved carbon species at the local to regional scale. In this context, radiocarbon is the proxy of choice to unveil the dynamics of the carbon cycle, as it can give information on reservoir turnover times and mixing ratios between different carbon sources. We use an approach consisting in the extraction and isotopic analysis (14C and δ13C) of non-purgeable organic carbon extracts from speleothems, which gives us insight into dissolved organic carbon (DOC) export from the surface. Such observations, especially over periods of rapid climate change exceeding present-day variability, could be invaluable to better constrain the sensitivity of carbon export fluxes to environmental and climatic changes. In this contribution, we will review the progress our group has made over the past years in methodological advances that allow us to develop reproducible and precise DOC reconstructions based on trace amounts of organic matter incorporated in speleothems. We show that, while strongly driven by local conditions, speleothems do retain information on the dynamics and export of DOC from the terrestrial biosphere, and discuss best steps and practices to achieve reliable results.