Environmental changes of a highly variable saline lake (Laguna Mar Chiquita, Argentina) since Last Glacial Maximum

FELIPE GARCÍA- RODRÍGUEZ; FLORENCE SYLVESTRE; EDUARDO PIOVANO; CAROLINA CUÑA RODRÍGUEZ

Berlin

Simposio; 25th International Diatom Symposium; 2018

Freie Universitat - Botanical Garten Berlin

Laguna Mar Chiquita (30°54′ S ? 62°51′ W) is an extensive saline lake located in central Argentina. It is a sensitive system to past and present hydroclimatic changes located in the middle latitudes of South America. Prolonged intervals with either negative or positive hydrological balances have severely modified lake water levels, salinity and primary productivity which is reflected on diatoms assemblages, sedimentary features and geochemical proxies. A high resolution multiproxy analysis along 4 m sedimentary record allowed to reconstruct the environmental variability occurred in Laguna Mar Chiquita over the last 23.6 cal ka BP. Here we report the fossil diatom analysis which evidenced throughout the record three main stages. The first stage (12.3 ? 23.6 cal ka BP), comprising the LGM, HS1 and ACR, was characterized by an ephemeral hypersaline lake with high abundances of benthic species (i.e., Tryblionella punctata, Amphora coffeaeformis and Amphora sp.). The second stage (3.5 ? 12.3 cal ka BP) should be consider as a transitional system, since shallower conditions with the predominance of benthic species (i.e, Tryblionella punctata, Diploneis ovalis, Tabularia fasciculata and Rhopalodia gibberula) moved toward a system with higher water level where the planktonic species Cyclotella striata were dominant and then a hypersaline ephemeral system with high percentages of tychoplanktonic species (i.e., Paralia sulcata) were established. The core chronology allowed us to ascribe this stage to the Mid-Holocene, a period characterized by abrupt hydrological changes alternating between drought and flood episodes in the region. The third stage (2002 AD ? 3.5 cal ka BP) is characterized by a perennial productive system with high frequency variability, which was subdivided into three sub-stages. The first sub-stage (1.0 ? 3.5 cal ka BP) is characterized by high lake level where the planktonic species Cyclotella striata was predominant. Considering the chronology of this sub-stage, it is contemporaneous of the MCA, a warm and wet period in the Argentinean pampean plain. The second sub-stage (1970 AD ? 1.0 cal ka BP) corresponds to a low water level period with the predominance of aerophilic benthic species (i.e., Amphora coffeaeformis, Amphora sp.1, Nitzschia pusilla), this sub-stage being ascribed to the LIA, a cold and arid period. The third sub-stage (2002 ? 1970 AD) marked the return to high lake levels associated with high percentages of Cyclotella striata. These diatom-based results, allowed to reconstruct the magnitude and the expression of the hydroclimatic variability at a regional scale as well as the response of the lake system to different environmental and climatic conditions.