Elsevier

Earth and Planetary Science Letters

Volume 411, 1 February 2015, Pages 72-86
Earth and Planetary Science Letters

Rock-magnetic proxies of wind intensity and dust since 51,200 cal BP from lacustrine sediments of Laguna Potrok Aike, southeastern Patagonia

https://doi.org/10.1016/j.epsl.2014.11.007Get rights and content

Highlights

  • Aeolian activity derived from lake sediment since the last glacial in SE Patagonia.

  • Bulk magnetic susceptibility indicates dust concentration at the millennial time scale.

  • MDFIRM reflects grain size variability of windblown magnetite-bearing silts.

  • MDFIRM is a wind intensity proxy up to the centennial time scale.

Abstract

The sedimentary archive from Laguna Potrok Aike is the only continuous record reaching back to the last Glacial period in continental southeastern Patagonia. Located in the path of the Southern Hemisphere westerly winds and in the source region of dust deposited in Antarctica during Glacial periods, southern Patagonia is a vantage point to reconstruct past changes in aeolian activity. Here we use high-resolution rock-magnetic and physical grain size data from site 2 of the International Continental scientific Drilling Program (ICDP) Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO) in order to develop magnetic proxies of dust and wind intensity at 52°S since 51,200 cal BP. Rock-magnetic analysis indicates the magnetic mineral assemblage is dominated by detrital magnetite. Based on the estimated flux of magnetite to the lake and comparison with distal dust records from the Southern Ocean and Antarctica, kLF is interpreted as a dust indicator in the dust source of southern Patagonia at the millennial time scale, when ferrimagnetic grain size and coercivity influence are minimal. Comparison to physical grain-size data indicates that the median destructive field of isothermal remanent magnetization (MDFIRM) mostly reflects medium to coarse magnetite bearing silts typically transported by winds for short-term suspension. Comparison with wind-intensity proxies from the Southern Hemisphere during the last Glacial period and with regional records from Patagonia since the last deglaciation including marine, lacustrine and peat bog sediments as well as speleothems reveals similar variability with MDFIRM up to the centennial time scale. MDFIRM is interpreted as a wind-intensity proxy independent of moisture changes for southeastern Patagonia, with stronger winds capable of transporting coarser magnetite bearing silts to the lake.

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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