Last Glacial Maximum to present day precipitation changes from speleothem growth rates and in climate simulations

To reliably predict future changes, it is crucial to understand the response of the climate system to past changes in radiative forcing, which are investigated using climate models as well as information extracted from paleoclimate archives such as speleothems. Hydrological changes in past, present, and future are, however, far less understood and more uncertain than changes in temperature.

Speleothems are terrestrial archives in the low to mid latitudes. Their growth rate changes are hypothesized to reflect local changes in precipitation amount, albeit the response may be non-linear and subject to karst specific processes. Full coverage of glacial-interglacial cycles and high precision dating through U/Th measurements makes them a suitable archive to assess and constrain state-dependent precipitation changes. However, speleothem inherent features, such as growth hiatuses or large and abrupt changes in growth rates, are a challenge for current age-depth modelling methods.

Here, we compare modelled precipitation amount from the Paleoclimate Modeling Intercomparison Project (PMIP), in particular time slices of the Last Glacial Maximum (around 21.000 years before present) and the Mid-Holocene (around 6.000 years before present) to growth rate changes of speleothems from the global speleothem database SISALv2. We perform case studies on a large ensemble of synthetic speleothems to systematically assess the resolution of age measurements necessary to reliably detect and model growth rate changes. These synthetic speleothems cover a large range of characteristic speleothem features observed in the SISALv2 database and are analyzed by six different age-depth modeling methods (linear regression, linear interpolation, copRa, StalAge, Bacon, and Bchron). Comparing the simulated changes with speleothems selected from SISALv2 according to these criteria can thus help to constrain past precipitation changes and subsequently confine uncertainty of future changes.