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 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 reveal distinct dry and wet phases caused by the past latitudinal migration of the SWW belt – with wetter intervals associated with a northerly SWW belt and drier intervals associated with a southerly SWW belt. Our findings 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 (ca. 14 700 to 13 000 cal yr BP). The SWW belt reached its southernmost latitudes during the early Holocene. At ca. 7500 yr BP, a displacement northward of the SWW belt was detected at latitudes south of 36° S and, during the last 5500 years, the SWW belt progressively migrated northward. From 17 000 to 11 500 cal yr BP, these migrations appear to be tied to atmospheric circulation regimes resulting from large changes in the interhemispheric temperature gradient and subsequent changes in the Hadley cell circulation, while the migrations in the Holocene (11 500 cal yr BP to present) appear to be predominantly controlled by insolation and atmospheric circulation regimes resembling those of El Niño-Southern Oscillation events.