Preliminary Paleoclimatic Variations through Magnetic Proxies on Sediments from Laguna Potrok Aike (51º57’S, 70º24’W, Argentina)

IRURZUN, M.A.; GOGORZA, C.S.G.; SINITO, A.M.; OLHENDORF,C.; ZOLITSCHKA, B

Foz do Iguazu

Congreso; American Geophysical Union (AGU) - Meeting of the Americas; 2010

American Geophysical Union (AGU)

Lake sediments are excellent sources for many different paleoenvironmental and paleoclimatic information as they provide continuous and high-resolution records. They are also first class recorders of magnetic parameters widely used around the world as proxies for paleoenvironmental variations, because every change in the catchment area (rainfall and drought periods, temperature changes, differences in sedimentation rates) is likewise reflected in variations of the magnetic parameters. This study was carried out on piston cores collected from Laguna Potrok Aike (51º57’S 70º24’W), a maar lake of about 100 m depth that probably never dried out completely. The following measurements were performed on 309 samples from the present to about 7800 cal. BP: magnetic susceptibility at low frequency (specific X, and volumetric, k) and high frequency; isothermal remanent magnetisation reaching the saturation (SIRM); back-field, in growing steps until cancelling the magnetic remanence; anhysteretic remanent magnetisation (ARM95mT), with a direct field of 0.1mT and a peak alternating field of 95mT. Associated parameters also were calculated: S (IRM-300mT/SIRM), %soft IRM ((SIRM-IRM-40mT)/SIRM), coercivity remanent (HCR), frequency-dependence magnetic susceptibility (F-factor) and anhysteretic susceptibility (kanh). Relationships between magnetic parameters, total organic carbon, total inorganic carbon, different elements, gastropods (Haberzettl et al., 2007), pollen (Wille et al., 2001) and diatom frustules (Mayr et al., 2009) were analysed to infer lake level changes and to suggest related hydrological and climate fluctuations. The results from these previous studies suggest periods of drier conditions between 7640 and 5880 cal BP, followed by an increase of available moisture. A lower lake level event was recognized around 7000 cal BP and periodic changes among low and high lake levels were identified for the last 1500 cal BP with a particular high lake level between 500 and 150 cal BP which is attributed to the “Little Ice Age”.