Reconstruction of the hydrologic history of a shallow Patagonian steppe lake during the past 700 yr, using chemical, geologic, and biological proxies

Abstract

The limnological conditions during the past 700 yr were reconstructed based on multiproxy analysis of a short sedimentary sequence from El Toro Lake (~40°S, 70°W). Mineralogical and geochemical features, as well as ostracods and chironomids, record hydrologic changes in the El Toro Lake basin. The ostracod Limnocythere rionegroensis var. 1, a reliable indicator of high salinity, and Eucypris fontana, a euryhaline species with preferences for moderate-salinity waters, are studied as paleolimnological proxies. The chironomid fauna indicates less saline conditions in the mid-twentieth century. These salinity changes are interpreted in terms of negative–positive hydrologic balance. High lake level and low salinity between AD 1500 and 1700 match with the wetter and colder climate during the second pulse of the Little Ice Age in northern Patagonia. High-salinity conditions occurred during the late nineteenth century, corresponding to the driest period during the past 400 yr in northeastern Patagonia. An increase in the precipitation around the middle of the twentieth century, in contrast to the records from the Chilean side of the mountains, correlates with a positive phase of the Southern Annular Mode. This is associated, in turn, with a strengthening, poleward shift of the midlatitude westerlies, possibly enhancing easterly moist air flows into central-north Patagonia.

Environmental effects of ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2017

“…For example, changes in fauna (ostracods and chironomids) from lake sediments in El Toro Lake (40°S, 70°W) indicate that the lake has become fresher (less saline) as a result of increased precipitation since the middle of the 20 th century, associated with the positive phase of SAM. 169 Ozone depletion and the positive phase of SAM are also associated with more extreme precipitation events in south-eastern South America (a very important area for food production 11 ), and SW Madagascar. 170 The rainfall of the southern Amazon basin has been reconstructed from Centrolobium microchaete tree rings 171 and suggests that the extreme wet seasons (from droughts to extremely wet) since 1950 may be unmatched since 1799.…”

Geochemical and mineralogical characterization of sediments from Lake Futalaufquen (42.8°S, Andean Patagonia) to evaluate their potential as paleoclimatic proxies

“…Note the short time of agreement between both reconstructions. References with indication of chronology quality (dpm: 14 C dates per millennium, model applied when corresponds; other methods; Blaauw et al, 2018): 1 Fletcher and Moreno, 2012 (4, Oxcal; 210 Pb); 2 Coviaga et al, 2017 (2, Oxcal; 137 Cs); 3 Fagel et al, 2008 (varve/ 137 Cs/ 210 Pb); 4 Bertrand et al, 2005 (varve/ 137 Cs/ 210 Pb/ Tephra); 5 Ariztegui et al, 2007 (4; varve/ 137 Cs); 6 Serra et al, 2016 ( 210 Pb/Tephra); 7 Lamy et al, 2001 (1, linear interpolation); 8 Villalba, 1994 (dendrochronology); 9 Lara and Villalba, 1993 (dendrochronology); 10 Williams et al, 2016 ( 137 Cs/ 210 Pb/Tephra); 11 Williams et al, 2019 ( 137 Cs/ 210 Pb/Tephra); 12 Masiokas et al, 2010 (dendrogeomorphic); 13 # This study (1.3, Oxcal; 137 Cs/Tephra); 14 Bertrand et al, 2014 (5, Clam); 15 Stine, 1993 (dead trees); 16 Ohlendorf et al, 2014 (2, mixed regression); 17 Fey et al, 2009 (4, linear interpolation); 18 Moreno et al, 2009 (2, cubic spline); 19 Moy et al, 2008 (3, 3 rd -order polynomial); 20 Haberzettl et al, 2005 (2, polynomial); 21 Mayr et al, 2005 (3, linear interpolation); 22 Schimpf et al, 2011 (Th/U ages); 23 van Bellen et al, 2016 (7–9, Bacon); 25 Waldmann et al, 2010 (0.2; Tephra); 25 Mauquoy et al, 2004 (9.3); 26 Ponce et al, 2011 (0.5, 2 rd -order polynomial).…”

Changes in ostracod assemblages and morphologies during lake‐level variations of Lago Cardiel (49°S), Patagonia, Argentina, over the last 15.6 ka

“…In modern environments, L. rionegroensis MII is also associated with parthenogenetic lineages in and around Lago Cardiel whereas MI and MIII morphotypes of this species were recently found living in mesohaline to polyhaline environments from northern Patagonia (CG and El Toro lakes) with a sexual as well as parthenogenetic reproductive strategies (Coviaga et al . ; Ramos et al . ).…”

“…In general, parthenogens are often dominant in habitats with no significant environmental fluctuations, short-lived or predictably unstable environments, whereas sexuality seems to be the more successful reproduction strategy to persist in unpredictably unstable habitats (Martens 1998). In modern environments, L. rionegroensis MII is also associated with parthenogenetic lineages in and around Lago Cardiel whereas MI and MIII morphotypes of this species were recently found living in mesohaline to polyhaline environments from northern Patagonia (CG and El Toro lakes) with a sexual as well as parthenogenetic reproductive strategies (Coviaga et al 2017;Ramos et al 2017). Reproduction modes, environmental instability and dissolved solute concentration may be linked with the L. rionegroensis ornamentation type; however, further investigations of populations from Patagonian lakes are in progress to better evaluate this hypothesis.…”