Hydroclimate Evolution Along Chile Over the Last 20,000 Years: Insights from Leaf-Wax Hydrogen Isotope Records

Abstract. The climate of the western coast of South America is controlled by large climate systems known as the Intertropical Convergence Zone (ITCZ), the Subtropical Pacific High (SPH) and the Southern Hemisphere Westerly wind (SWW) belt. While the large-scale evolution of the SWW belt and the location of the ITCZ are well constrained, the interaction between these two climate features is not well understood as a high resolution spatial and temporal reconstruction of the SWW belt is still lacking. Here, we use the hydrogen isotope ratios of leaf-wax n-alkanes in marine sediments between 33° S and 36° S offshore Chile to reconstruct past hydrological regimes and the evolution of the SWW belt since the Last Glacial Maximum (LGM, ca. 20,000 cal yr BP). Our results suggest overall wet conditions during the LGM, followed by increasing aridity during the deglaciation period. This shift toward drier conditions was briefly interrupted during the Antarctic Cold Reversal. The early Holocene was then marked by dry conditions until ca. 7,500 cal yr BP, after which a return to wetter conditions marked latitudes south of 36° S. During the last 5,500 years, wetter conditions progressively characterized latitudes as far north as 30° S. These results reflect past changes in the latitudes of the SWW belt and imply a northward position of the SWW belt during the LGM, followed by a southward migration of the SWW belt during the deglaciation period. This shift southward was briefly interrupted during the Antarctic Cold Reversal. The SWW belt reached its southernmost latitudes during the early Holocene. At ca. 7,500 cal yr BP, a displacement northward of the SWW belt was detected at latitudes south of 36° S and during the last 5,500 years, the SWW belt progressively migrated northward. Our reconstruction, compared with past latitude of the ITCZ, shows that the climate was predominantly, but not exclusively, controlled by the El-Niño Southern Oscillation and insolation during the Holocene, while atmospheric pathways associated with large interhemispheric temperature gradient and changes in the Hadley cell circulation prevailed from 17,000 to 11,500 cal yr BP.