Annual resolution rainfall proxy for central-eastern Brazil from high resolution speleothem magnetism

Recent advances in magnetic imaging technology now allow investigation of speleothem magnetism on the annual to decadal timescale. Here we use the quantum diamond microscope to obtain a potential annual to decadal resolution precipitation signal from a speleothem collected in the Onça cave (Peruaçu National Park, central-eastern Brazil). Peruaçu National Park is an important locality for high-resolution paleoclimate reconstruction due to the marked local temperature increase over the past century. Saturation isothermal remanent magnetization (SIRM) intensity provides information about local cave infiltration, presenting new opportunities for quantifying local rainfall. Using an Onça cave speleothem spanning the year 1913 to today with U/Th age precision of +/- 4 years, we demonstrate a statistically robust correlation between the SIRM intensity in speleothem laminae and rain gauge measured rainfall. Our magnetization-derived record of precipitation complements and extends existing paleoclimate records at a resolution previously unachievable. In particular, speleothem magnetization can provide an independent constraint on local precipitation to help disentangle the multiple factors that result in d ¹⁸O variations. The response of South American precipitation to climate warming remains unclear, but high-resolution paleoclimate proxies like SIRM intensity present new opportunities to characterize sub-decadal monsoon precipitation in distinct paleoclimate states. Our approach helps bridge the gap between the long-term mean climate conditions commonly inferred from paleoclimate proxies and the sub-decadal variability that will impact human livelihood in a warmer world.