Gabriela Cusminsky

Assemblage diversity and isotopic signals of modern ostracodes and host waters from Patagonia, Argentina

Abstract Ostracode species assemblages and stable oxygen and carbon isotope ratios of living and recent ostracodes, together with δ 18 O and δ 13 C DIC (DIC: dissolved inorganic carbon) values of host water samples, provide a first data set that characterizes a wide range of modern aquatic environments in the Laguna Cari-Laufquen (41°S, 68–69°W) and the Lago Cardiel area (48–49°S, 70–71°W) in Patagonia, Argentina. This data set will ultimately be used to interpret and calibrate data acquired from lake sediment cores with the goal of reconstructing past climate. Species assemblages and isotope values can be assigned to three groups: (1) springs, seeps and streams, (2) permanent ponds and lakes, and (3) ephemeral ponds and lakes. Springs, seeps and streams are characterized by Darwinula sp., Heterocypris incongruens , Eucypris fontana , Amphicypris nobilis and Ilyocypris ramirezi . Ostracode and water isotope values range between −13 and −5‰ for oxygen, and between −15 and −3‰ for carbon. They are the most negative of the entire sample set, reflecting ground water input with little or no evaporative enrichment. Limnocythere patagonica , Eucypris labyrinthica , Limnocythere sp. and Eucypris aff. fontana are typical species of permanent ponds and lakes. Isotope values indicate high degree of evaporation of lake waters relative to feeder springs and streams and range between −7 and +5‰ for oxygen, and −5 and +4‰ for carbon. Limnocythere rionegroensis is the dominant species in ephemeral ponds and lakes. These systems display the most enriched isotope values in both ostracodes and host waters, extending from −5 to +7‰ for oxygen, and from −5 to +6‰ for carbon. Living ostracodes show a positive offset from equilibrium values of up to 2‰ for oxygen. Carbon isotope values are up to 6‰ more negative than equilibrium values in highly productive pools. Comparison of ostracode and host water isotope signals permits assessment of the life span of the aquatic environments. Valves from dead ostracodes collected from ephemeral ponds and lakes show a wide scatter with each sample providing a snapshot of the seasonal history of the host water. The presence of the stream species I. ramirezi and a wide range of ostracode isotope values suggest that ephemeral ponds and lakes are fed by streams during spring run-off and seasonally dry. A temporary character of waters is also indicated by H. incongruens , a drought-resistant species that occupies most springs and seeps. In addition, L. rionegroensis has adjusted its reproduction strategies to its environment. Whereas only females were collected in fresh host waters, males were found in ephemeral ponds and lakes with higher solute content. Sexual reproduction seems to be the more successful reproduction strategy in waters with high and variable salinities and affected by seasonal droughts. The temporary character of the aquatic environments shows that the availability of meteoric water controls the life span of host waters and underlines the sensitivity of the area to changes in precipitation.

Holocene benthic foraminifera from Bahía Blanca estuary: a review and update of systematic and palaeoenvironmental aspects

Assemblages of benthic foraminifera in a Holocene core from the outer area of Bahía Blanca estuary in Argentina were studied. The systematic of the group was updated, and provided 28 genera distributed among 59 species, six species with nomenclature aperta. The main species recorded were Buccella peruviana f. campsi (Boltovskoy), Ammonia beccarii (Linné), Elphidium gunteri Cole, Elphidium galvestonense Kornfeld, Elphidium articulatum d’Orbigny and Elphidium discoidale (d’Orbigny). These species allowed an estuarine environment to be determined. Qualitative and quantitative studies conducted on the faunistic content in the core allowed identification of three subenvironments closely linked to sea-level fluctuations during the mid Holocene: a lower zone (6350 yr BP) corresponding to a high intertidal environment, an intermediate zone (2460 yr BP) representing a low intertidal environment related to a system of channels and variations in environmental energy, and an upper zone characterized by the development of a high-energy littoral environment affected by the action of waves, tides and tidal currents, which underwent progressive change until it attained present-day conditions.

Calcareous Microfossils (Foraminifera and Ostracoda) of the Late Cenozoic from Patagonia and Tierra del Fuego: A Review

Publisher Summary The abundance of microfossils in certain rocks is of great value in biostratigraphical and evolutionary research. Among important groups of microfossils are the Ostracoda, Foraminifera, Radiolaria and Conodonta, all animals and such plant groups as diatoms, carophytes, calcareous nannoplankton, spores and pollen. This chapter comprises a bibliographical synopsis of the most significant works on the Order Foraminiferida and the Class Ostracoda from the Late Miocene to present-day in Patagonia and Tierra del Fuego. The chapter focuses on the continental sequences, which includes all the lacustrine records systems studied followed by the marine sequences referred to outcrops and core analysis of marine sediments in the analyzed area. These studies demonstrate that the distribution of both, ostracods and foraminifers, would response to different paleogeographic and paleoclimatic events occurring in that area from the Late Miocene to the present day confirming the usefulness of microfossils in the contribution of the overall scientific knowledge of the area.

Morphotypes of the lacustrine ostracod Limnocythere rionegroensis Cusminsky & Whatley from Patagonia, Argentina, shaped by aquatic environments

This study describes and quantifies morphological valve traits of the ostracod Limnocythere rionegroensis from Patagonian steppe lakes and explores their association with lake water characteristics. Surface ornamentation was examined by scanning electron and transmitted light microscopy, and valve size and shape were analyzed using morphometric techniques. Limnocythere rionegroensis shows remarkable variations in surface ornamentation, based on which three morphotypes (MI, MII, and MIII) were identified. Valves of morphotypes MI and MIII are larger, show slight to moderate external reticulation, and a higher shape variability, whereas MII is characterized by a very conspicuous reticulation, lower shape variability, and smaller valves. Outline analysis yielded a great shape disparity related to the dorsal margin slope. MI was found in sexual populations from euhaline to mesohaline ephemeral lake; MII occurs in parthenogenetic populations from mesohaline to oligohaline permanent or ephemeral lakes; and MIII, from both sexual and asexual populations, inhabits a broad range of environmental conditions in terms of salinity and stability. Limnocythere rionegroensis intraspecific variations may be caused by environmental parameters and genetic factors associated to reproductive strategies. These results contribute to the knowledge of extant L. rionegroensis morphological variability and provide additional clues to improve the environmental interpretation of fossil assemblages.

Study of the distribution of Elphidium aff. poeyanum (D’ORBIGNY) and Buccella peruviana (D’ORBIGNY) from the Colorado basin (South America): Holocene paleoenvironmental inferences

Benthic foraminiferal assemblages recovered from T1 core samples of the Colorado basin, in the continental margin of southeastern Argentina, were analyzed to understand their distribution patterns and ecological preferences. The foraminiferal assemblages showed two well-represented species: Elphidium aff. poeyanum (d’Orbigny) and Buccella peruviana (d’Orbigny), among others of very low proportion. Statistical analyses allowed identifying positive correlations between the abundance of E. aff. poeyanum and silt content and between B. peruviana and the sand content, reflecting better conditions for the development of both species. From a paleoenvironmental point of view, the assemblages recorded are characteristic of an inner shelf, showing a passage from typical shallow waters to normal marine conditions; such a passage represents a rise in the sea level during the post-last glacial maximum transgression. The results obtained contribute to the knowledge of South American foraminifers and paleoenvironments during the Holocene.

Dynamics of ostracod populations from shallow lakes of Patagonia: life history insights

Wetlands are one of the most valuable natural resources, providing a number of ecosystem services and socio-economic values. Small ponds sustain a rich aquatic biodiversity and because of their short hydrological regimen and small size are excellent environments for population studies of microcrustaceans such as ostracods. This study describes the population dynamics of the Ostracoda fauna in three temporary shallow lakes during one hydroperiod in Argentine Patagonia. Three cosmopolitan species were determined: Cypris pubera, Tonnacypris lutaria and Eucypris virens. Among them, T. lutaria is here reported for the first time from the Neotropical region. Multivariate ordination techniques were used to examine the relationships among environmental variables and ostracod density on each sampling site. High values of conductivity, absorption at 320 nm (as a measure of dissolved organic matter), dissolved oxygen concentration, temperature and chlorophyll a concentration correlated positively with ostracod density. All the populations studied reproduced parthenogenetically, and the life cycles of E.virens and C. pubera were followed in detail by weekly sampling of their populations. The former displayed continuous reproduction, whereas the latter showed a multivoltine strategy. The life history of C. pubera was affected by the seasonality of the habitat. The development rate correlated positively with water temperature; conductivity and temperature had a positive effect on adult size in C. pubera, while conductivity had a negative effect on adult size in E. virens. In this study, we present the first data set on the development and life history of ostracods in Patagonian freshwater environments. However, several questions remain and encourage us to further investigate the relative importance of ostracods in food webs, as well as the importance of inter-specific interactions between ostracods and other taxa.

Ecology of freshwater ostracods from Northern Patagonia and their potential application in paleo-environmental reconstructions

In order to generate a database of the auto-ecology and distribution of Argentinian North Patagonian ostracods (Argentina), a survey in 40 aquatic systems has been carried out. For this purpose, we report the ostracod diversity and assess the relationships between ostracod occurrence and abundance considering abiotic environmental variables. Twenty-two ostracod species have been found, three of which first record for Neotropical region and one for Argentina. Conductivity, temperature, and energy level have significantly explained ostracod distribution and abundance. Based on host waters features, three ostracod assemblages have been recognized: (1) temperate waters with moderate to high conductivity have presented in Sarscypridopsis aculeata, Potamocypris unicaudata, Heterocypris hyalinus, and Cypridopsis vidua as typical fauna; (2) environments with flowing waters were dominated by Ilyocypris ramirezi and Heterocypris incongruens, whereas (3) in cold and low conductivity environments, Tonnacypris lutaria, Eucypris virens, and Bradleystrandesia fuscata were the characteristic taxa. Our data indicate that Patagonian ostracods are largely influenced by host waters features, mainly conductivity and temperature. Likewise, due to the fact that eight of the twenty-two identified taxa in this survey were recovered in Holocene sequences from Patagonia, this study provides valuable information for future paleo-environmental reconstructions in North Patagonia.

Late Quaternary lacustrine ostracods (Ostracoda, Crustacea) and charophytes (Charophyta, Charales) from the Puna Plateau, Argentina

Relatively little is known about the recent palaeontological records of the high-altitude closed basin lakes of the Central Andes, but a great need exists to remedy this knowledge gap if microfossils are to be used to infer climatic and ecological transitions from lake sediment cores. Here, eight species of non-marine ostracods and two calcareous algae are recorded from modern sediments and late Quaternary strata from Laguna de los Pozuelos, Jujuy Province, northwestern Argentina. Four species, Limnocythere alexanderi, Limnocythere foresteri, Limnocythere lysandrosi and Limnocythere ruipunctifinalis, are described as new species. Limnocythere titicaca Lerner-Seggev, 1973 has only been recorded in Lake Titicaca prior to this study and this is the first time the species is recognized outside of Bolivia. The cypridoideans Ilyocypris ramirezi Cusminsky & Whatley, 1996, Eucypris virgata Cusminsky & Whatley, 1996 and Chlamydotheca pseudobrasiliensis Martens & Behen 1994 are known species that are rare in the stratigraphic sequence in core LP06-6A. Also, the gyrogonites of two well-known species of Charophyta, Chara filiformis Hertzsch and Chara vulgaris Linnaeus, are occasionally present in the sediment from Laguna de los Pozuelos. The results provide a new vehicle for clarifying the Quaternary palaeohydrological history of the Pozuelos Basin, which is a RAMSAR wetland that is likely to be sensitive to global environmental change.

Organomineralization processes in freshwater stromatolites: a living example from eastern Patagonia

Living stromatolites have been mostly described within shallow marine and (hyper)saline lacustrine environments. Southernmost South America lacks detailed investigations of these (organo)sedimentary buildups, particularly in regions experiencing extreme and variable environmental conditions. Here, we report and describe living freshwater stromatolites in the Maquinchao region, north‐western Patagonia, Argentina. Fossil stromatolites characterized by globular and cauliflower shapes are also present in a continuous palaeoshoreline of a former lake at an altitude of 830 m, whereas their living counterparts only occur in the calm waters of sheltered or meandering sections of the Maquinchao River. The living stromatolites and their host waters have been sampled and studied using various chemical and microscopic techniques to better constrain the environmental versus biological factors controlling their development. Our results indicate that today stromatolites only proliferate in freshwater when Ca2+ levels are high. A microscopic inspection of the living stromatolite mat indicates stronger photosynthetic activity in the upper green layer associated with crypto/microcrystalline calcite (nanoglobules) compared to the lower beige‐white biofilm. This biofilm contains more low‐Mg calcite (rhombohedra) precipitates, which can form millimetre‐sized aggregates in the underlying anoxic layer. Although sulphate‐reducing bacteria are living in the entire mat, they appear more abundant and widely distributed in the lower beige‐white layer and are always associated with Mg calcite. Low salinity and low‐turbidity water along with microbial (photosynthetic and heterotrophic) activity are the most important factors promoting low‐Mg calcite precipitation in the Maquinchao Basin. These conditions are very different from those proposed for recently described lacustrine stromatolites at high altitude in the subtropical and tropical Andes as well as in Chilean Patagonia. Hence, all these observations in modern freshwater stromatolites show the importance of geomicrobiological studies in identifying proxies of the hydrological conditions prevailing during their formation.

Semicytherura Wagner: its inner lamella and its close allies

The genus Semicytherura Wagner differs from all other members of the Cytherurinae in the nature and course of its inner margin/line of concrescence. The inner lamella is very wide anteriorly, while posteriorly the inner margin extends anteriorly almost to the position of the closing muscles. However, two species examined by the authors, Semicytherura clavata (Brady, 1880) and Semicytherura contraria Zhao & Whatley, 1989, from the SW Atlantic and SE Asia respectively are shown to exhibit this characteristic feature only in the male. In the female of both these species, while the anterior inner lamella is identical to that of the male, posteriorly their inner margins parallel the posterior margin. Similar sex-linkage was show in the genus Angulicytherura which is probably closer to Cytherura than Semicytherura, with a narrow and vestibulate inner lamella.