Fossil dripwater in stalagmites reveals Holocene temperature and rainfall variation in Amazonia

Most proxy records used for reconstruction of Holocene climate of Amazonia are unable to quantitatively distinguish between the effect of temperature and rainfall amounts. We present a new isotope technique applied to a ∼ 13,500 yr stalagmite archive from Peruvian Amazonia. By analysing the coupled isotope composition of fossil dripwater trapped in stalagmite fluid inclusions, and that of the calcite hosting the fluid inclusions, we were able to calculate independent paleotemperatures and rainfall amounts. This stalagmite record shows that Holocene climate variation was controlled by orbitally-forced Southward migration of the Inter Tropical Convergence Zone. While temperature remained constant, isotope variation of rainwater, reflected in fluid inclusion water δ 18O composition, suggests a ∼ 15–30% increase in convective rainfall through the Holocene. A comparison of the low-land Peruvian fluid inclusion record with the high Andean Huascaran ice core record shows a constant ∼ 12‰ offset of δ 18O curves for the Holocene, suggesting that Andean vertical temperature gradients (lapse rates) did not vary much over the last 9000 years. During the Younger Dryas interval, however, the offset of δ 18O values was much higher than in the Holocene. This may be attributed to a relative drop in air temperatures in the highlands (higher lapse rate), caused by long distance teleconnections to climate perturbations in the North Atlantic. In a wider perspective, fluid inclusion isotope analysis drastically improves paleotemperature reconstructions based on speleothem calcite δ 18O data, because it provides the δ 18O value of drip water through time, which is usually the most important unknown in paleotemperature equations.