Accurate dating of stalagmites from low seasonal contrast tropical Pacific climate using Sr 2D maps, fabrics and annual hydrological cycles

Tropical Pacific stalagmites are commonly affected by dating uncertainties because of their low U concentration and/or elevated initial Th-230 content. This poses problems in establishing reliable trends and periodicities for droughts and pluvial episodes in a region vulnerable to climate change. Here we constrain the chronology of a Cook Islands stalagmite using synchrotron mu XRF two-dimensional mapping of Sr concentrations coupled with growth laminae optical imaging constrained by in situ monitoring. Unidimensional LA-ICP-MS-generated Mg, Sr, Ba and Na variability series were anchored to the 2D Sr and optical maps. The annual hydrological significance of Mg, Sr, Ba and Na was tested by principal component analysis, which revealed that Mg and Na are related to dryseason, wind-transported marine aerosols, similar to the host-rock derived Sr and Ba signatures. Trace element annual banding was then used to generate a calendar-year master chronology with a dating uncertainty maximum of +/- 15 years over 336 years. Our approach demonstrates that accurate chronologies and coupled hydroclimate proxies can be obtained from speleothems formed in tropical settings where low seasonality and problematic U-Th dating would discourage the use of high-resolution climate proxies datasets.

Automated summary

This study successfully constrained the chronology of a Cook Islands stalagmite using synchrotron mu XRF and optical imaging techniques, revealing the relationship between trace elements like Mg, Sr, Ba and Na with hydroclimate environment through principal component analysis. A calendar-year master chronology was generated based on trace element annual banding, with a dating uncertainty maximum of +/- 15 years over 336 years of history.