Six millennia of atmospheric dust deposition in southern South America (Isla Navarino, Chile)

Abstract

To characterize dust deposition in southern South America for the Holocene, a 542 cm long core from a peat bog in southern Chile (Oreste bog, Isla Navarino) was studied. Peat formation started ~11 160 14C yr before present (BP). The titanium (Ti) concentration in bulk peat, combined with dry bulk density, and peat accumulation rate, were used to calculate the mineral accumulation rate (MAR) in the Oreste bog. The distribution of calcium (Ca), manganese (Mn) and titanium (Ti) showed that mineral accumulation for the last c. 6000 yr was predominantly atmospheric with a record of effectively constant deposition (0.43 ± 0.12 g/m2 per yr). Similarly, Ti and zirconium (Zr) concentrations in the acid insoluble ash (AIA) were also effectively constant and agreed well with the MAR for the last six millennia, except at c. 4200 cal. yr BP, where Zr was enriched relative to Ti. Here, Scanning Electron Microscope (SEM) micrographs showed that the AIA was dominated by volcanic particles (>20—40 μm), with the Mt Burney eruption identified as the most likely source. In contrast with this anomalous zone, SEM studies showed that the mineral particles found in the majority of the sample were predominantly fine grained (<20 μm) and rounded. Derived from surficial sediment and supplied by long-range atmospheric transport, they reflect the climate stability for the past 6000 yr.