Recent environmental changes in Laguna Mar Chiquita (central Argentina): a sedimentary model for a highly variable saline lake

Abstract

Laguna Mar Chiquita, a highly variable closed saline lake located in the Pampean plains of central Argentina, is presently the largest saline lake in South America ( 6000 km 2 ). Recent variations in its hydrological budget have produced dry and wet intervals that resulted in distinctive lake level fluctuations. Results of a multiproxy study of a set of sedimentary cores indicate that the system has clearly recorded these hydrological variations from the end of the Little Ice Age ( ad 1770) to the present. Sedimentological and geochemical data combined with a robust chronology based on 210 Pb profiles and historical data provide the framework for a sedimentary model of a lacustrine basin with highly variable water depth and salinity. Lake level drops and concurrent increases in salinity promoted the development of gypsum-calcite-halite layers and a marked decrease in primary productivity. The deposits of these dry stages are evaporite-bearing sediments with a low organic matter content. Conversely, highstands are recorded as diatomaceous organic matter-rich muds. Average bulk sediment accumulation rose from 0AE22 g cm )2 year )1 in lowstands to 0AE32 g cm )2 year )1 during highstands. These results show that Laguna Mar Chiquita is a good sensor of high-and low-frequency changes in the recent hydrological budget and, therefore, document climatic changes at middle latitudes in south-eastern South America. Dry conditions were mostly dominant until the last quarter of the twentieth century, when a humid interval without precedent during the last 240 years of the lake's recorded history started. Thus, it is an ideal system to model sedimentary and geochemical response to environmental changes in a saline lacustrine basin.

Comparison of 20th century and pre-industrial climate over South America in regional model simulations

“…Instead, the model shows a dipole pattern with reduced precipitation in the northern and increased precipitation in the southern parts. This pattern also contradicts to the results of Boninsegna (1995) and Piovano et al (2002), reporting drier conditions in central Chile for the 17th and 18th century around 30 • S. For south-eastern Patagonia the wetter conditions suggested by Mayr et al (2005) and Haberzettl et al (2005) are also only partly reflected in the regional simulations for austral winter. For the annual situation, no clear-cut changes are evident over this region.…”

“…Regions showing qualitative agreements are related to southern Patagonia during summer (Neukom et al, 2010b) and the decrease in precipitation over central Chile in the course of the 20th century (Christie et al, 2010). However, other records (Piovano et al, 2002;Boninsegna, 1995), show a different situation with drier conditions during the 17th and 18th century over the more equatorward regions. It should, however, be noted that the comparison between the model results and proxy data is hampered by the fact that simulations are carried out as quasi-equilibrium simulations without any varying external forcing factors.…”

“…Wetter and cooler conditions are also supported by analysis based on glacial advances Masikoas et al, 2009). In contrast, for the more northern regions around 30 • S drier conditions have been reconstructed for the 17th and 18th century based on lake level fluctuations (Piovano et al, 2002) and tree-ring data (Boninsegna, 1995).…”

A millennial multi-proxy reconstruction of summer PDSI for Southern South America

“…As a further validation for our reconstructions, we used a published sedimentological record of Mar Chiquita's lake levels fluctuations (Piovano et al, 2002). Mar Chiquita is a large Sub-Tropical lake (about 6000 km 2 in size) that drains a vast area (about 127 000 km 2 ).…”

“…As an independent validation for our work, we checked the correspondence between our reconstruction and the 1767-2002 reconstruction of Laguna Mar Chiquita water-levels fluctuation (Piovano et al, 2002). We used the average PDSI within the lake's watershed for a comparison (60-65 • W; 20-25 • S).…”