Descripción: The thermohaline structure across the tidal fronts of the continental shelf off Patagonia is analyzed using historical and recent summer hydrographic sections. The near-summer tidal front location is determined on the basis of the magnitude of vertical stratification of the water column as measured by the Simpson parameter. Sea surface and air CO2 partial pressures based on data from eleven transects collected in summer and fall from 2000 to 2004 are used to estimate CO2 fluxes over the shelf. The near-shore waters are a source of CO2 to the atmosphere while the midshelf region is a CO2 sink. The transition between source and sink regions closely follows the location of tidal fronts, suggesting a link between vertical stratification of the water column and the regional CO2 balance. The highest surface values of Chl a are associated with the strongest CO2 sinks. The colocation of lowest CO2 partial pressure (pCO2) and highest Chl a suggests that phytoplankton blooms on the stratified side of the fronts draw the ocean's CO2 to very low levels. The mean shelf sea-air difference in pCO2 (ΔpCO2) is -24 μatm and rises to -29 μatm if the shelf break front is included. Peaks in ΔpCO2 of -110 μatm, among the highest observed in the global ocean, are observed. The estimated summer mean CO2 flux over the shelf is -4.4 mmol m-2 d-1 and rises to -5.7 mmol m-2 d-1 when the shelf break area is taken into account. Thus, during the warm season the shelf off Patagonia is a significant atmospheric CO2 sink. Copyright 2005 by the American Geophysical Union.

Descripción: Most insects' assemblages differ with forest type and show vertical stratification. We tested for differences in richness, abundance and composition of hymenopteran families and mymarid genera between sugar maple (Acer saccharum) and white pine (Pinus strobus) stands and between canopy and understory in northeastern temperate forests in Canada. We used flight interception traps (modified malaise traps) suspended in the canopy and the understory in a split-split block design, with forest type as the main factor, forest stratum as the first split factor, and collection bottle location as the second split factor. Hymenopteran families and mymarid genera differed in their diversity depending on forest type and stratum. Both family and genera richness were higher in maple than in pine forests, whereas family richness was higher in the canopy and top bottles and generic richness was higher in the understory and bottom bottles. Multivariate analysis separated samples by forest type, vegetation stratum, and bottle location. Family composition showed 77% similarity between forest types and 73% between the canopy and understory. At the lower taxa level, mymarid genera showed only 47% similarity between forest types and 40% between forest strata, indicating vertical stratification and relatively high β-diversity. Our study suggests that hymenopteran diversity and composition is strongly dependent on forest type and structure, making flying members of this order particularly vulnerable to forest management practices. It also shows that insect assemblage composition (especially at low-taxon levels), rather than relative abundance and richness, is the community attribute most sensitive to forest type and vertical stratification. © 2007 Entomological Society of America.

Descripción: Both the biomass of autotrophic dinoflagellates and its contribution to total chlorophyll were found to increase significantly with seawater temperature and the level of stratification in southern Patagonian waters during spring and winter. The highest peak of biomass corresponded to a single species, Prorocentrum minimum (Pavillard) Schiller, and was detected in middle shelf waters, coinciding with the primary productivity and CO 2 uptake maxima reported for the area under spring conditions. © The Author 2011. Published by Oxford University Press. All rights reserved.

Descripción: Fil:Simionato, C.G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: For the first time a taxonomic and ecological study of species belonging to Helicostomella was performed over a mesoscale spatial distribution by examining ca. 3000 loricae collected in Argentine shelf waters during the austral autumn. Microscopic and statistical analysis revealed that the general shape and the oral diameter remained practically constant in the whole area surveyed, despite a continuous length fluctuation of ca. 300 μm, which includes the entire range present in eight previously reported species. Consequently, we consider that the genus may be represented only by H. subulata, whose strong fluctuations in length (mostly attributed to an increase in the collar length), density and biomass seem to respond to temperature, food availability and front-related processes. In Buenos Aires coastal waters associated with a quasi permanent estuarine front (40-40.5°S), mixed conditions would favour moderate abundances of long loricae, whereas in northern (42.5-45.5°S) and southern (46-54.5°S) Patagonian waters, high (103 ind. L-1) and low (<5 ind. L-1) densities of short loricae seem to be a consequence of stratification and encystment, respectively. The non-occurrence of the species at 41-42°S, together with a three-fold reduction in length-related parameters between specimens from Buenos Aires and Patagonian waters, suggests a disjunct distribution.

Descripción: Microbial oncoids have been found in the Oxfordian limestones of the La Manga Formation in the La Vaina section at Potimalal River, Mendoza province. The oncoids ocurr either in packstone or floatstone-rudstone or are scattered in the wackestones. They are mostly elliptical, ameboidal and subordinately spherical in shape. Different types of oncoids were recognized, according to their features of envelopes: (1) micritic laminations, (2) grumose laminations, and (3) organism-bearing laminations. Molluscs and echinoid fragments, peloids, and intraclasts acted as oncoid nuclei. Laminae follow the shape of nuclei, especially in the inner zone of the cortices. However, in the outer zones the laminae contain encrusting organisms dominated by nubeculariids and serpulids. Some oncoids, especially the ameboidal or elliptical forms, are characterized by multiple nuclei, represented by small oncoids. The oncoids are associated with bivalves, echinoderms, forams, and serpulids. The fauna is indicative of calm, shallow conditions and the excellent preservation of echinoderms suggests minimal transport prior to burial. Growth histories are in evidence. The oncoids grew in a shallow, low energy, slightly to moderate agitated subtidal normal sea water environment. The limited rolling growth oncoids was probably accompanished by intermittent currents that reoriented the oncoids parallel to stratification. The discontinuous organisms-bearing laminations reflect periods of non-agitation and litification, which facilitated the growth of encrusting organisms on static oncoid particles during a period of low sedimentation rate. Deposition of the oncoid-bearing limestones took place during shallowing of the carbonate interval and associated with emersion, subaerial exposition and paleokarst as consequence of sea level fluctuations.