Rock-magnetic proxies of wind intensity and dust since 51,200 cal BP from lacustrine sediments of Laguna Potrok Aike, southeastern Patagonia
Graphical abstract
Introduction
The Southern Hemisphere westerly winds (SWW) play an important role in ocean circulation and the global climate system (e.g., Anderson et al., 2009, Sijp and England, 2008, Toggweiler et al., 2006). Yet the latitudinal position and intensity of the SWW in the past remain an open question (Kohfeld et al., 2013). Patagonia is one of the five major dust producing regions of the globe (Roberts et al., 2011) and is of particular interest because it is the main source area for dust deposited in Antarctica during glacial cycles (Basile et al., 1997; Delmonte et al., 2010, Delmonte et al., 2004; Gaiero, 2007, Petit et al., 1999, Sugden et al., 2009). Dust emission is believed to be related to changes in environmental conditions and possibly wind intensity (e.g., Muhs, 2013, Basile et al., 1997, Sugden et al., 2009). Sugden et al. (2009) argued that Patagonian glacier discharge into outwash plains or proglacial lakes acted like an on/off switch for dust deposition in Antarctica, hence providing evidence for environmental control on dust emission during the last glaciation. In contrast, there is to date no record of paleo-wind intensities extending beyond the Late Glacial in southern Patagonia, where the available records mainly reach back to the Holocene and deglacial periods (e.g., Villa-Martinez and Moreno, 2007, Björck et al., 2012, Lamy et al., 2010; Mayr et al., 2007a, Mayr et al., 2013; Moreno et al., 2012, Moreno et al., 2009; Waldmann et al., 2010). In order to fully address dust emission in southern Patagonia during the last Glacial and better constrain past changes in the SWW, paleo-wind intensity records from the source region of dust deposited in Antarctica are needed.
Paleo-wind indicators in southern Patagonia are commonly moisture proxies (e.g., pollen, paleo-fire history, lake level, and mineralogical data) assuming a major control of wind intensity on rainfall (Kilian and Lamy, 2012, Kohfeld et al., 2013). However on the eastern side of the Andes, precipitation is only weakly correlated to westerly wind strength because the very low precipitation mostly comes from the east and south–west (Garreaud et al., 2013) and evaporation strongly influences available moisture (Lamy et al., 2010, Moy et al., 2008, Ohlendorf et al., 2013). As a result, numerous moisture-related wind intensity proxies are difficult to interpret (Fletcher and Moreno, 2012, Moreno et al., 2009) and there is a need for different types of proxies.
The long sedimentary archive from Laguna Potrok Aike is the only continuous paleoenvironmental archive from this region reaching back to the last Glacial period (Kilian and Lamy, 2012, Zolitschka et al., 2013). Haberzettl et al. (2009) revealed that the millenial-scale variability of magnetic susceptibility measured on an independently dated short sediment core collected from low water depth corresponds to the non-sea-salt calcium (a dust proxy) from the Antarctic ice core EDC (Röthlisberger, 2002). Such comparison of magnetic susceptibility signal to dust record were also reported in sediments from the Southern Ocean and used to constrain chronologies (Pugh et al., 2009, Weber et al., 2012). Magnetic susceptibility documents how “magnetisable” the sediment is and while it often primarily reflects changes in the concentration of ferrimagnetic minerals, it can also be significantly influenced by dia-, antiferro-, para-, and superparamagnetic material when the concentration of ferrimagnetic mineral is low, as well as by changes in magnetic grain size (e.g., Dearing, 1999, Liu et al., 2012). Interpreting magnetic susceptibility records is therefore not straightforward and detailed rock-magnetic studies from Laguna Potrok Aike are necessary to investigate its environmental significance (Haberzettl et al., 2009; Maher, 2011). Here we use high-resolution rock-magnetic data from the sediment deposited in the deepest part of Laguna Potrok Aike in order to investigate what controls the magnetic susceptibility signal and develop a new proxy of wind intensity in southeastern Patagonia since 51,200 cal BP.
Section snippets
Geological setting
Laguna Potrok Aike (51°58′S, 70°23′W; 113 m a.s.l.) is a maar lake in the Pali Aike volcanic field of southern Argentina (Fig. 1A) containing a series of mass movement deposits associated with hydrological changes, major volcanic eruptions and possibly earthquakes (Anselmetti et al., 2009, Kliem et al., 2013a, Kliem et al., 2013b). The maximum water depth is 100 m and the maximum diameter is 3.5 km (Haberzettl et al., 2005, Zolitschka et al., 2006). The lake is located in the mid-latitudes of
Coring and sampling
The international science team of the Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO) cored the sediments of Laguna Potrok Aike in the framework of the International Continental scientific Drilling Program (ICDP) during austral spring 2008. The sedimentary infill of the maar was sampled up to a depth of ca. 100 m at two sites in the central basin using a hydraulic piston corer on the GLAD800 platform operated by DOSECC Inc.
Site 2 (Fig. 1A) was selected as the principal record
Magnetic mineralogy
The first rock-magnetic and paleomagnetic-dedicated studies from Laguna Potrok Aike were published as part of the South Argentinean Lake Sediment Archives (SALSA) project (past 16,000 cal BP; Gogorza et al., 2011, Gogorza et al., 2012; Irurzun et al., 2014) and the ICDP–PASADO project (past 51,200 cal BP; Recasens et al., 2012; Lisé-Pronovost et al., 2013, Lisé-Pronovost et al., 2014). Altogether these studies clearly identified magnetite as the dominant magnetic carrier as indicated by
Interpretation of magnetic susceptibility
Higher amount of magnetite grains brought to the lake during the Last Glacial can possibly be attributed to the activation of a source richer in detrital magnetite and/or a larger surface of erodible land such as outwash plains (Sugden et al., 2009), increased runoff due to permafrost (Kliem et al., 2013b), and/or enhanced gustiness of winds (McGee et al., 2010) capable of transporting more detrital magnetite to the lake. However, interpretation of the magnetic susceptibility signal is
Conclusions
High-resolution rock-magnetic studies of the sediment deposited in the maar lake Laguna Potrok Aike since 51,200 cal BP revealed a lacustro-aeolian record in the dust source-region of southern Patagonia. The magnetic susceptibility signal (kLF) displays a very clear LGM signal (from 31,500 to 17,300 cal BP), not provided by most other proxies from Laguna Potrok Aike. There is an inverse correlation of kLF with ferrimagnetic coercivity and grain-size indicators (e.g., MDFIRM, kARM/IRM) at the
Acknowledgments
We acknowledge J. Labrie, F. Barletta, M.-P. St-Onge and D. Veres for their help in the laboratory at ISMER. We are grateful to two anonymous reviewers for constructive comments on the manuscript as well as A. Chauvin and J. Stoner for reading an earlier draft. Thanks to A. Mazaud and Q. Simon for fruitful discussions and to S. Björck, A. Hahn, P. Kliem, F. Lambert, L. Pichevin, D. Schimpf, M. Tonello, M. Weber and T. Whittaker for sharing their data. This research was supported by the
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