Holocene rainfall variability in southern Chile: a marine record of latitudinal shifts of the Southern Westerlies

Abstract

Geochemical and clay mineral parameters of a high accumulation marine sediment core from the Chilean continental slope (41³S) provide a 7700 yr record of rainfall variability in southern Chile related to the position of the Southern Westerlies. We especially use the iron content, measured with a time-resolution of ca. 10 yr on average, of 14 Caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron-poor Coastal Range and iron-rich Andean source rocks. Variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position. Based on these interpretations, we find a pronounced rainfall variability on multicentennial to millennial time-scales, superimposed on generally more arid conditions during the middle Holocene (7700 to 4000 cal yr B.P.) compared to the late Holocene (4000 to present). This variability and thus changes in the position of the Southern Westerlies are first compared to regional terrestrial paleoclimate data-sets from central and southern Chile. In order to derive possible wider implications and forcing mechanisms of the Holocene latitudinal shifts of the Southern Westerlies, we then compare our data to ice-core records from both tropical South America and coastal Antarctica. These records show similar bands of variability centered at ca. 900 and 1500 yr. Comparisons of band pass filters suggest a close connection of shifts of the Southern Westerlies to changes within the tropical climate system. The correlation to climate conditions in coastal Antarctica shows a more complicated picture with a phase shift at the beginning of the late Holocene coinciding with the onset of the modern state of El Nin ¬ o-Southern Oscillation system. The presented data provide further evidence that the well known millennial-scale climate variability during the last glacial continued throughout the Holocene. ß

Fire responses to postglacial climate change and human impact in northern Patagonia (41–43°S)

“…During the Last Glacial Maximum, annual insolation was at the minimum value of the last 23,000 y. Temperatures in Antarctica, inferred from oxygen isotopes ratios from the Taylor Dome ice core (28), were low, leading to a strengthening and/or shift of the Southern Westerlies northward of their present-day position (29). As a result, cold dry conditions prevailed throughout Patagonia (34)(35)(36).…”

“…The long-term trend from Early Holocene aridity to Late Holocene cool wet and variable climate conditions favored gradual tree population establishment and expansion. Comparison of Holocene regional trends in tree abundance, fire activity, temperature (28), and precipitation (29) suggests that biomass burning was relatively low during warm/dry steppe-dominated landscapes in the late glacial/Early Holocene transition, and increased as more-humid-than-before conditions allowed forest development and higher vegetation cover during the Middle and Late Holocene. The close link between fuel load (forest taxa pollen) and biomass burning (CHAR) suggests that conditions in the late glacial and Early Holocene were conducive for fires, but discontinuous fuel cover limited their occurrence along the ecotone (39).…”

“…9. Glacier advances (25)(26)(27), oxygen isotope ratios from Taylor Dome (28), precipitation off shore in Chile at 41°S (29), and ENSO (30). These independent paleoclimate records are compared with regional trends in forest taxa percentages and CHAR, which have been estimated with GAMs and converted to the appropriate units (i.e., pollen percentages and charcoal particles cm 2 ·y −1 ; this study).…”

Transient simulations, empirical reconstructions and forcing mechanisms for the Mid-holocene hydrological climate in southern Patagonia

“…Markgraf 1993;Schäbitz 1999;Lamy et al 2001;Jenny et al 2003;Markgraf et al 2003;Mancini et al 2005;Gilli et al 2005a,b). These hypotheses were usually derived in a two step process.…”

“…Different hypotheses on the latitudinal position and strength of the SHWs over southern South America during the midHolocene have been formulated in several studies. Lamy et al (2001) analysed iron contents from a marine sediment core from the Chilean continental slope (approx. 41°S; 74°W) and reconstructed less humid conditions between 7.7 ka and 4 cal ka BP than in the late Holocene.…”