Climate, sea-level and anthropogenic processes controlling the environmental evolution of shallow lakes in the southeastern Pampa plain (South East South America) during the last 12 ka

DE FRANCESO, CLAUDIO G.; STUTZ, SILVINA; HASSAN, GABRIELA S; TONELLO, MARCELA; SANCHEZ VUICHARD, GUILLERMINA; BONAVITA, MAURO; GARCIA RODRIGUEZ, FELIPE; FONTANA, SONIA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2022 vol. 116

0895-9811

The evolution of both Lake Hinojales-San Leoncio (37°23?S; 57°23?W) and Tobares(37°30?S; 57°28?W) was reconstructed using pollen, non-pollen palynomorphs, plantmacrofossil remains and associated fauna, diatoms and mollusks. This is the firstpaleolimnological reconstruction covering the hydroclimatic variability over the last 12ka for the southeastern Pampa plain. At the onset of the Holocene (12-11 ka), shallowclear brackish-to-hypersaline water bodies subject to episodic expansion/retractioncycles developed in the area under wet climatic conditions. During the Early Holocene,unstable environments were inferred due to intercalated episodes of total desiccation,associated with a drop in rainfall that promoted drier conditions than those previouslyinferred. The Middle Holocene (only represented in Lake Hinojales-San Leoncio) wascharacterized by the development of a brackish-saline lake with a deeper watercolumn, under drier climatic conditions than those recorded previously. The temporalpersistence of this saline paleolake might have been influenced by the marinetransgressive-regressive cycle dated between 6000 and ca. 2000 yr BP in the coastalarea close to the lake. From nearly 2500 to ca. 600 cal yr BP there was a gradualchange from brackish to freshwater-brackish water conditions, as a consequence of aregional increase in rainfall together with the decrease in sea level that promoted theestablishment of modern humid to sub-humid climatic conditions prevailing today in thePampa plain. The last 35 cal yr BP represented the onset of modern eutrophicconditions within the lake, which are concomitant with the agriculture intensification inthe region. The regional changes in the different biological proxies analyzed here,support the hypothesis of a predominance of external climatic triggers over intrinsiclimnological processes as main causes of paleoenvironmental changes modulating theevolution of lakes. The main environmental forces affecting these lakes seem to beindirectly related to precipitation during the Early Holocene, sea level changes duringthe Middle Holocene and the recent (Anthropocene) human impacts related to theintensification of farming activities.