Late Holocene covariability of the southern westerlies and sea surface temperature in northern Chilean Patagonia

Abstract

18The climate of Chilean Patagonia is strongly influenced by the southern westerlies, which 19 control the amount and latitudinal distribution of precipitation in the southern Andes. In 20 austral summer, the Southern Westerly Wind Belt (SWWB) is restricted to the high latitudes. 21It expands northward in winter, which results in a strong precipitation seasonality between 22 ~35 and 45°S. Here, we present a new precipitation seasonality proxy record from Quitralco 23 fjord (46°S), where relatively small latitudinal shifts in the SWWB result in large changes in 24 precipitation seasonality. Our 1400 yr record is based on sedimentological and geochemical 25 data obtained on a sediment core collected in front of a small river that drains the 26 2 Patagonian Andes, which makes this site particularly sensitive to changes in river discharge. 27Our results indicate Fe/Al and Ti/Al values that are low between 600 and 1200 CE, increasing 28 at 1200-1500 CE, and high between 1500 and 1950 CE. Increasing Fe/Al and Ti/Al values 29 reflect a decrease in mean sediment grain-size from 30 to 20 µm, which is interpreted as a 30 decrease in seasonal floods resulting from an equatorward shift of the SWWB. Our results 31 suggest that, compared to present-day conditions, the SWWB was located in a more 32 poleward position before 1200 CE. It gradually shifted towards the equator in 1200-1500 CE, 33where it remained in a sustained position until 1950 CE. This pattern is consistent with most 34 precipitation records from central and southern Chile. The comparison of our record with 35 published regional sea surface temperature (SST) reconstructions for the late Holocene 36shows that equatorward shifts in the SWWB are systematically coeval with decreasing SSTs 37 and vice versa, which resembles fluctuations over glacial-interglacial timescales. We argue 38 that the synchronicity between SST and SWWB changes during the last 1400 years 39 represents the response of the SWWB to temperature changes in the Southern Hemisphere. 40 41 Keywords 42Southern westerlies, inorganic geochemistry, paleohydrology, paleohydroclimatology, fjord 43 sediments, southern South America, Chilean Patagonia 44 45 Introduction 46The southern westerlies are the prevailing winds at the mid latitudes of the Southern 47Hemisphere, blowing between the subtropical anticyclone and the cyclonic subpolar air 48 masses. The Southern Westerly Wind Belt (SWWB) extends roughly between 30 and 60ºS, 49and it exhibits latitudinal variations at seasonal to glacial-interglacial timescales. Due to the 50 3 absence of continental barriers in the Southern Ocean, the SWWB directly controls the 51 strength of the Antarctic Circumpolar Current (ACC), which in turn affects the release of CO 2 52 from the deep ocean up to the atmosphere, particularly on glacial-interglacial timescales 53 (Anderson et al., 2009). In addition to modulating the strength of the ACC, the SWWB also 54 controls the amount of precipitation on the windward side of the mountain ranges located 55 along its ...

Limited Influence of Sediment Grain Size on Elemental XRF Core Scanner Measurements

“…One of the reasons is that the XRF radiation for these elements is heavily absorbed by the variable water film that forms between the sediment surface and the covering plastic foil (Kido et al 2006;Tjallingii et al 2007). Since fjord sediments are deposited in environments of highly variable salinity, using chlorine to correct the XRF peak areas for absorption by the interstitial water layer, as proposed by Tjallingii et al Bertrand et al 2012aBertrand et al , 2014 (2007), does not improve the correlations for Al and Si. For the XRF data obtained on pressed pellets, the correlation coefficients between XRF peak areas and ICP-AES elemental concentrations are better for all elements except Sr (Table 19.2 in Appendix; Fig.…”

Elevated dust deposition in Tierra del Fuego (Chile) resulting from Neoglacial Darwin Cordillera glacier fluctuations

“…Southern westerlies contract and expand seasonally at the present day (Garreaud et al ., ) and have migrated and/or contracted and expanded in the past (e.g. Lamy et al ., ; Fletcher and Moreno, ; Kohfeld et al ., 2013; Bertrand et al ., ). However, during the mid‐ and late‐Holocene, the intensity of the southern westerlies was relatively stable in the study region at 54°S (e.g.…”

Late Holocene precipitation variability recorded in the sediments of Reloncaví Fjord (41°S, 72°W), Chile

“…dga.cl); iii) Puelo River discharge reconstructed from tree rings (CE 1600, Lara et al, 2008; iv) Fe/Al record from Quitralco Fjord (Bertrand et al, 2014a); v) the Southern Annular Mode (SAM) (from http://www.nerc-bas.ac.uk/icd/gjma/sam.html, CE 1957-2010) and the SAM-NCEP reconstructed for the CE 1409-2006 period (Villalba et al, 2012 from ftp://ftp.ncdc.noaa.gov/pub/data/paleo/treering/ reconstructions/villalba2012sam.txt); and vi) alkenone-derived sea surface temperature (SST) anomaly for 41-51°S, which was obtained using four SST records: GeoB3313 (41°S; Lamy et al, 2002), GeoB7186 (44°S; Mohtadi et al, 2007), PC33 (44°S; Sepúlveda et al, 2009), and MD07-3124 (51°S; Caniupán et al, 2014). These four records were interpolated at 1-yr intervals using the Interp component of Arand software (http://www.ncdc.noaa.gov/paleo/softlib/arand/arand.html), and SST anomalies were calculated independently for each record, using the CE 1300-2000 period as a reference (Bertrand et al, 2014a). The resulting SST anomalies (deviation from the mean, in°C) were then averaged over the four cores.…”

“…CE 1957CE -2010, and reconstructed Puelo River discharge from Lara et al (2008), gray line (CE 1600(CE -2000. c) Fe/Al (g/g) in Quitralco fjord at 46°S (red circles; Bertrand et al, 2014a). d) Periods of high precipitation in Lago Puyehue at 41°S (dark-yellow rectangle; Bertrand et al, 2005), in the Jacaf Fjord at 44°S (green rectangles; Sepúlveda et al, 2009), and Lago Plomo 47°S (winter precipitation only; yellow rectangles; Elbert et al, 2011).…”

“…In Northern Patagonia, numerous terrestrial pollen records from peat bogs, lake and fjord sediments have been used to reconstruct past vegetation and climate changes during the Holocene (e.g., Jara and Moreno, 2012;Montade et al, 2012). A recent study by Bertrand et al (2014a) suggested that changes in wind-driven precipitation co-varied with sea surface temperature in northern Chilean Patagonia over the last 1400 yr, with a northward migration of the wind belt during cold phases and vice versa. However, few works have used a multi-proxy approach (e.g., Rebolledo et al, 2008;Sepúlveda et al, 2009;Fletcher and Moreno, 2012), and little information exists on the variability of precipitation, runoff and terrigenous organic carbon contents preserved in sedimentary cores of Northern Patagonia during the last 2000 yr.…”