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Glacier Expansion in Southern Patagonia Throughout the Antarctic Cold Reversal

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Glacier Expansion in Southern Patagonia Throughout the Antarctic Cold Reversal Glacier expansion in southern Patagonia throughout the Antarctic cold reversal Juan L. García1*, Michael R. Kaplan2, Brenda L. Hall3, Joerg M. Schaefer2, Rodrigo M. Vega4, Roseanne Schwartz2, and Robert Finkel5 1Instituto de Geografía, Facultad de Historia, Geografía y Ciencia Política, Pontifi cia Universidad Católica de Chile, Campus San Joaquín, Avenida Vicuña Mackenna 4860, comuna Macul, Santiago 782-0436, Chile 2Geochemistry, Lamont-Doherty Earth Observatory, Palisades, New York 10964, USA 3Earth Sciences Department and Climate Change Institute, University of Maine, Orono, Maine 04469, USA 4Instituto de Ciencias de la Tierra y Evolución, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile 5Earth and Planetary Science Department, University of California–Berkeley, Berkeley, California 94720, USA ABSTRACT essential for understanding its cause, as well Resolving debated climate changes in the southern middle latitudes and potential telecon- as the cryosphere-atmosphere-ocean links that nections between southern temperate and polar latitudes during the last glacial-interglacial operated during the late glacial to Holocene transition is required to help understand the cause of the termination of ice ages. Outlet gla- transition (Ackert et al., 2008). ciers of the Patagonian Ice Fields are primarily sensitive to atmospheric temperature and also We use 10Be and 14C techniques to establish precipitation, thus former ice margins record the extent and timing of past climate changes. a detailed reconstruction of ice fl uctuations 38 10Be exposure ages from moraines show that outlet glaciers in Torres del Paine (51°S, south during the entire ACR in the Torres del Paine Patagonia, Chile) advanced during the time of the Antarctic cold reversal (ACR; ca. 14.6– National Park (51°S, 73°W; Fig. 1), southern 12.8 ka), reaching a maximum extent by ~14,200 ± 560 yr ago. The evidence here indicates Chile. Torres del Paine has one of the prime late that the South Patagonian Ice Field was responding to late glacial climate change distinctly glacial moraine records in the southern middle earlier than the onset of the European Younger Dryas stadial (ca. 12.9 ka). Major glacier latitudes. The excellent preservation and conti- recession and deglaciation in the Torres del Paine region occurred by 12.5 ka and thus early in nuity of moraines, as well as their geographical the Younger Dryas. We provide direct evidence for extensive ice in Patagonia at the very start location, make them ideal to test hypotheses of the ACR that agrees with atmospheric and marine records from the Southern Ocean and of late glacial climate change at the middle Antarctica. Atmospheric conditions responsible for the early late glacial expansion at Torres latitudes, ~51°S (Figs. 1 and 2). In Torres del del Paine resulted from a climate reorganization that prompted a northern migration of the Paine, previous work (Marden and Clapper- south westerly wind belt to the latitude of Torres del Paine at the onset of the ACR chronozone. ton, 1995) defi ned four distinct moraines belts INTRODUCTION Figure 1. Location of Tor- Understanding millennial-scale climate vari- ODP1233 200 km res del Paine (white box CLD LGM STF N ability that interrupted the last deglaciation in main image) in south- AC (18.0–11.5 ka) affords insight into the nature ern South America. Solid and cause of the termination of ice ages. One arrows depict inferred prominent event, the Antarctic cold reversal approximate location of Lago General Carrera/Buenos Aires south westerly wind belt HPN (ACR, ca. 14.6–12.8 ka; Lemieux-Dudon et at present (Miller, 1976) 46°40'S al., 2010) in the high southern polar latitudes, HPS and different key peri- PB moraines was contemporaneous with the Bølling-Allerød ods during last glacial- ACR TDP warm period in the north and ended at the onset interglacial transition as PRESENT inferred from sedimento- SM of the Younger Dryas stadial (ca. 12.9–11.7 ka; SAF logical and paleoecologi- TF Blunier and Brook, 2001), but its cause remains BC cal records of Lamy et al. HS1 - YD CDD obscure. Recent studies (Strelin et al., 2011; (2004), Heusser (2003), Putnam et al., 2010a; Kaplan et al., 2010) Moreno et al. (1999), and show evidence for a late glacial ice expansion Anderson et al. (2009). PF White dashed lines indi- 58°20'S in southern middle latitudes near the end of the cate approximate present ACR ca. 13.0 ka, followed by substantial gla- positions of Polar Front cier recession in the subsequent millennium. (PF), Sub-Antarctic Front However, marine and ice-core evidence indi- (SAF), and Subtropical Southern Ocean Front (STF). TDP—Torres cates environmental changes associated with del Paine; CLD—Chil- the onset of the ACR much earlier than 13.0 ka ean Lake District; AC— (EPICA Community Members, 2004 [EPICA— Archi piélago de Chiloé; European Project for Ice Coring in Antarctica]; HPN—Hielo Patagónico Norte; HPS—Hielo Pa- Blunier and Brook, 2001; Barker et al., 2009], 70°00'S tagónico Sur; PB—Puerto and the nature of climate dynamics through- Bandera; SM—Strait of out the ACR around Patagonia remains unclear Magellan; TF—Tierra (Kaplan et al., 2008; Sugden et al., 2005). Thus, del Fuego; BC—Beagle resolving the timing and structure of climate Channel; CD—Cordillera 81°40'W 70°00'W 58°20'W Darwin ice cap; LGM— changes throughout this time period on land is Last Glacial Maximum; ACR—Antarctic cold reversal; HS1—Heinrich stadial event; YD— Younger Dryas; ODP—Ocean Drilling Program. Base map modifi ed from University of Maine *E-mail: [email protected]. Environmental Change Model (http://ecm.um.maine.edu). GEOLOGY, September 2012; v. 40; no. 9; p. 859–862; Data Repository item 2012241 | doi:10.1130/G33164.1 | Published online 23 July 2012 GEOLOGY© 2012 Geological | September Society 2012of America. | www.gsapubs.org For permission to copy, contact Copyright Permissions, GSA, or [email protected]. 859 E E E faces (Schaefer et al., 2009) allowing precision Laguna Geomorphology σ 13.8 ± 0.3 LA0704 River scarp River bed in our ages that averages 3.9% (1 ; Fig. DR3 11.2 ± 0.5 LA0512 Azul TDP IV 14.6 ± 0.4 LA0703 Alluvial fan Talweg in the Data Repository). Our exposure ages are 15.0 ± 1.3 LA0522 LA0707 N 14.5 ± 0.3 Talus slope Mire 13.8 ± 0.5 LA0728 10 14.0 ± 0.3 LA0901 Lake terrace Bedrock calculated using a Be production rate based on 14.6 ± 0.6 LA0727 12.312.3 ± 0.10.1 * Lake shoreline a New Zealand site (Putnam et al., 2010b; see Glacial geomorphology 10 12.512.5 ± 0.070.07 N the Data Repository). This Be production rate TDP I main outwash plain Vega Baguales TDP I moraine recently has been confi rmed in the Lago Argen- TDP I moraine ridge tino area (Kaplan et al., 2011), <100 km north TDP I ACR main outwash plain 13.8 ± 0.4 RP0701 TDP III TDP II ACR outwash plain of Torres del Paine. We detected and rejected 14.4 ± 0.4 RP0705 9.3 ± 0.7 LA0714 ACR moraine 13.9 ± 0.5 RP0703 13.9 ± 0.5 LA0715 the outliers by applying the Grubbs (1969) test ACR moraine ridge 16.9 ± 0.6 LA0716 and a 2σ criteria (see the Data Repository). Post-ACR outwash plain 13.8 ± 0.6 LA0720 21.3 ± 0.8 LA0732 Meltwater channel Scoured bedrock RESULTS Physiography * For each respective moraine belt, the 10Be N 12.512.5 ± 0.040.04 100 m interval topographic countour Lake boulder ages show a normal distribution and 12.512.5 ± 00.1.1* River Road exhibit high internal consistency after exclud- 10Be sample 14C sample 14.6 ± 0.5 RP0815 N ing outliers (Fig. DR5; see the Data Reposi- 15.0 ± 0.5 RP0817 14.1 ± 0.5 VN0525 1 0.5 0 km 1 tory). Boulders from the TDP II moraines 13.9 ± 0.4 VN0526 13.4 ± 0.5 RP0820 yielded ages ranging from 13.4 to 15.0 ka, with 13.9 ± 0.4 RP0903 an arithmetic mean of 14.2 ± 0.5 ka (n = 14) 14.1 ± 0.4 RP0906 13.7 ± 0.6 RP0905 (Fig. DR5A). The TDP III moraine boulders 14.0 ± 0.6 RP0904 range from 13.7 to 15.0 ka, with a mean of 14.1 ± 0.5 ka (n = 10) (Fig. DR5B), and those of the TDP IV moraines (including 2 ages recalcu- N Laguna lated from Moreno et al., 2009) yielded ages of Amarga Rio de las Chinas io 13.8–15.3 ka, with a mean of 14.1 ± 0.7 ka (n = Rio Paine 13.7 ± 0.4 SAR0705 6) (Fig. DR5C). The resulting 10Be mean ages 12.6 ± 0.7 SAR0719 N 14.3 ± 0.4 SAR0907 13.9 ± 0.5 SAR0718 indicate that deposition of all three moraine 13.9 ± 0.4 SAR0725 14.0 ± 0.6 SAR0908 systems occurred, within error, during the 15.3 ± 0.6 SAR0721 same time interval, and thus rapidly. The num- 18.7 ± 1.0 SAR0724 8.7 ± 0.3 SAR0701 13.8 ± 0.9 SAR0723 13.0 ± 0.4 SAR0702 ber, size, and continuity of the moraine ridges 16.4 ± 0.9 SAR0722 7.4 ± 0.5 SAR0906 suggest that the ice was active and capable of 14.3 ± 0.4 SAR0703 14.3 ± 0.4 SAR0713 eroding, transporting, and depositing a large Lago Sarmiento de Gamboa volume of sediment during their formation. In E EEthe Lago Sarmiento, the TDP II moraine cross- Figure 2. Glacial geomorphic map of Laguna Azul–Lago Sarmiento area in Torres del Paine cuts the older TDP I moraine, suggesting that at National Park (inset with red box delineating extent of main map).
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