Nora I. Maidana

New insights into paleoenvironmental changes in Laguna Potrok Aike, southern Patagonia, since the Late Pleistocene: The PASADO multiproxy record

A series of long sediment cores was retrieved from Laguna Potrok Aike, Southern Patagonia, within the framework of PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Project), an ICDP (International Continental Scientific Drilling Program) lake drilling project. This maar lake, located at 52°S, 70°W in the Province of Santa Cruz (Argentina), in the southernmost continental area of the world, is one of the few permanent lakes in the region, providing a unique continuous paleoclimatic and paleoecological lacustrine record for the last glacial cycle. Previous multiproxy studies of this site have characterized the environmental history of these dry lands in the Patagonian Steppe for the last 16 cal. ka BP. This new series of sediment cores provides a much longer record of climate variability in Southern Patagonia since 51.3 cal. ka BP. Using a multiproxy strategy, a set of samples (mostly from core catcher material) was analyzed for physical properties, rock magnetism, geochemistry, CNS elemental analysis, stable isotopes, pollen and diatoms. This preliminary multiproxy limnogeological interpretation sheds new light on the regional Pleistocene and Holocene environmental history, revealing lake-level variations through time and identifying time windows of interest where higher resolution analyses will be carried out.

Post-Wisconsinian paleoenvironments at Salinas del Bebedero basin, San Luis, Argentina

We present a climatic reconstruction of Holocene lacustrine episodes in the Salinas del Bebedero basin (Argentina), based on geological and diatom information.Morphological, sedimentological and diatom evidence between 11600 ± 140 yr BP and 325 ± 95 yr BP, allowed us to interpret the paleoenvironments of the basin. Episodes of high energy (sandy levels) are linked to large inflow of meltwater through the Desaguadero River, related to development of glaciers on the Andes. This inflow is characterized by peaks of relative abundance of the brackish water diatom Cyclotella choctawatcheeana Prasad. The values of C. choctawatcheeana decrease in deposits of low energy (clay levels), where it co-dominates with oligohalobous Fragilaria and Epithemia spp.To the last two peaks of large inflow of meltwater, radiocarbon dates corrected to sidereal ages, are AD 1280/1420 and AD 1443/1656. These ages agree with two cold episodes clearly recorded in dendrological studies from the Patagonian Andes and were correlated to the Little Ice Age. Thus, older Holocene episodes of large inflow of water to the basin were correlated with the Neoglacial Advances defined by Mercer (1976) for the Andes.

THALASSIOSIRA PATAGONICA SP. NOV. (THALASSIOSIRACEAE, BACILLARIOPHYCEAE), A NEW LACUSTRINE CENTRIC DIATOM FROM SANTA CRUZ, ARGENTINA

A new recent and fossil diatom species, Thalassiosira patagonica, found in lake and quaternary lacustrine sediment samples from Southern Argentina (Santa Cruz province), is described. Its main morphological features are the prominent central undulation of the valve, the lack of striae in the raised portion of the central area and the marginal fultoportulae with external peg-like or wing-like projections. On the basis of the ecological preferences of the associated diatom species, it is believed that this new diatom also prefers slightly brackish, nutrient rich and alkaline waters. Its relationship with other members of Thalassiosiraceae is discussed.

Patagonian ostracods as indicators of climate-related hydrological variables: implications for paleoenvironmental reconstructions in Southern South America

Different precipitation regimes across Patagonia generate an environmental gradient that is expected to reflect upon the solute composition and concentration of lake water through the ensuing differences in water balance. In turn, this hydrochemical gradient could influence the occurrence and distribution of ostracods in the area. A cluster analysis on hydrochemical data of 36 Southern Patagonian waterbodies shows that low salinity, bicarbonate-dominated waters characterize Andean and ecotonal lakes, located in the wetter part of the precipitation gradient, while their steppe counterparts, which receive a much lower precipitation input, are more saline, enriched in all major anions and sodium-dominated. Kruskal–Wallis tests followed by Mann–Whitney pairwise comparisons show statistically significant differences in the ostracod species each water type hosts, with L. patagonica, E. cecryphalium, P. smaragdina and P. incae being found in the more dilute waters characteristic of Andean and ecotonal lakes and Limnocythere rionegroensis in the mesohaline, evaporatively evolved waters typical of steppe lakes. Other species studied do not appear to have such distinct distributions, having been found throughout the range of conditions studied. These findings promote the use of the aforementioned ostracods as semi-quantitative paleohydrological indicators, which could improve paleoclimatic reconstructions in Patagonia.

CORBELLIA CONTORTA GEN. & SP. NOV. (BACILLARIOPHYCEAE). A NEW DIATOM GENUS FROM SANTA CRUZ PROVINCE (ARGENTINA)

A new raphid diatom genus and species is described. It has extremely thin frustules and is unusual in the twisting of the valve surface around the apical axis. In addition, there is a slight asymmetry to the valves.

AMPHORA TUCUMANA SP. NOV., A NEW SPECIES FROM CUMBRES CALCHAQUÍES, TUCUMÁN, ARGENTINA

Amphora tucumana sp. nov. is described from bottom sediments of the Laguna Nostra (Cumbres Calchaquis, 4300 m altitude, Tucuman province, Argentina). Its valvar structure is described, using LM and SEM. The principal characteristics of the species are its transapical costa-like internal thickenings, the raphe-ledge covered by small and irregular depressions, and its areolae of irregular length. Its relationships are discussed.

THE GENUS NAVICULA SENSU STRICTO IN THE UPPER LERMA BASIN, MEXICO I

In order to characterize and analyze the distribution of species of the genus Navicula sensu stricto in the Lerma River and its tributaries, biannual samplings (wet and dry seasons) for the period 2003 to 2005 were made at eleven locations in the Upper Lerma basin, central-western Mexico. Twenty-one species of Navicula Bory, were identified, of which fourteen represent new records for Mexico and five were new to the study area. Most of the species of Navicula s. str. observed in the study area are tolerant to high contents of organic matter, which is incorporated into the aquatic ecosystems as a product of agricultural and industrial activities and from deficiently treated municipal discharges of cities and towns present in the study area at the sites most affected by these activities. Cosmopolitan species with broad tolerances to organic pollution and eutrophic conditions, such as Navicula antonii, N. germainii, N. perminuta, N. rostellata and N. erifuga were present throughout the year. N. tripunctata and N. veneta, widely reported as tolerant to pollution from industrial activities in other regions of the world, were present at the sites most affected by these activities.

MORPHOLOGY AND TAXONOMY OF AMPHORA ATACAMAE FRENGUELLI (BACILLARIOPHYCEAE)

Materials containing Amphora atacamae Frenguelli from the type locality in Chile and two localities in Argentina have been examined with LM and SEM. This diatom has narrowly lanceolate to elliptic-lanceolate frustules, semi-lanceolate to slightly triangular valves with a convex dorsal margin and concave ventral margin. The raphe is filiform and slightly curved; dorsal and ventral striae are uniseriate, composed of conspicuous, transapically elongated areolae. The girdle is composed of numerous copulae. Type material of Amphora boliviano Patrick was also studied with LM and SEM, and we conclude this species should be considered a synonym of A. atacamae. The diagnosis of A. atacamae has been emended based on our observations, and a lectotype has been selected as Frenguelli did not designate a holotype slide from his collection.

Changes in motility and induction of enzymatic activity by nitrogen and phosphate deficiency in benthic Halamphora luciae (Bacillariophyceae) from Argentina

Abstract: Cells of Halamphora luciae were isolated from the mudflat of the Bahía Blanca estuary. Unialgal axenic cultures were grown in f/2 with limiting concentrations of N or P and in f/2 medium deprived of one or both macronutrients. On the one hand, limited macronutrient supply did not affect growth rate, but final cell yield was lower than in the complete medium. On the other hand, N or P deprivation reduced growth rates as well as final cell yield in the stationary phase. P deficiency enhanced the secretion of soluble extracellular polymeric substances (EPS), the percentage and speed of gliding cells, as well as the activity of alkaline phosphatase, especially after a previous prolonged P starvation. Regarding the morphology of the frustules, P deprivation reduced areola size but did not alter cell biovolume. N deficiency had a deleterious effect on the motility of the cells, and reduced the secretion of soluble EPS and cell biovolume. After incubation in N-deprived media for 10 days, cells exhibited enhanced protease activity.

Paleohydrological Changes in Highland Desert Rivers and Human Occupation, 7000‐3000 Cal. Yr B.P., South‐Central Andes, Argentina

This article focuses on local paleohydrological changes experienced by the Las Pitas and Miriguaca Rivers in the south‐central Andes of Argentina and their impacts on hunter‐gatherers as they transitioned to food‐producing communities 7000–3000 cal. yr B.P. Paleoenvironmental reconstruction based on geomorphology, alluvial sedimentology, and diatom evidence indicates a dry phase of reduced streamflow between ca. 6700 and 4800 cal. yr B.P. for the Las Pitas River, and 6600 and 3000 cal. yr B.P. for the Miriguaca River. A phase of more humid environmental conditions commenced after ca. 4900 cal. yr B.P. along the Las Pitas River, and after 3000 cal. yr B.P. along the Miriguaca River. Differences in the chronology and magnitude of hydrological changes along both rivers are related to topographic and hydrological characteristics of their respective watersheds. Higher catchment elevation and enhanced orographic precipitation favored greater sensitivity for the Las Pitas River to short humid events during the middle‐to‐late Holocene. The archaeological evidence suggests that the paleohydrological changes within these catchments played a significant role in human occupational dynamics such that the Las Pitas River offered better environmental conditions for human occupation relative to the Miriguaca River as foragers increasingly relied on plant and animal domestication.