Modeling the Acid–Base Surface Properties of Aquatic Sediments

We propose a model that explains the acid–base surface properties of clastic sediments from two Argentinean reservoir lakes. The model uses potentiometric titration data sets and fixed parameters such as the apparent stability constants and reaction stoichiometries of acid–base equilibriums involving known mineral phases. The model considers that sediments act as a set of independent sorption surfaces, such as organic matter, clay silicate, and iron (hydr)oxides, thus the acid–base equilibrium and the correspondent protolytic constants are represented by a humic acid, a Na-illite, and a poor crystalline Fe-hydr(oxide). In agreement with experimental data, the model predicts that all sediment samples show a similar charging behavior, increasing the negative charge as the pH increases. The net charge of sediments is controlled by the presence of negatively charged minerals and/or organic matter coatings. This reveals the great influence of clays and organic matter functional groups on the acid–base surface properties of sediments, and consequently on the surface reactivity toward contaminant transport.     

Iron,manganese and trace metal concentrations in seaweeds from the central west coast of the Gulf of California

Concentrations of Co, Cu, Fe, Mn, Ni, Pb and Zn in four macroalgae species (Ulva lactuca, Chondracanthus squarrulosus, Sargassum sinicola and Gracilariopsis lemaneiformis) were obtained for the first time from the central part of the west coast of the Gulf of California. Generally, no differences in metal concentrations were found among the different seaweed species, although spatial differences were apparent. Iron, Mn and Cu exhibited higher concentrations at the stations located in front of Angel de la Guarda Island, probably because of high vertical mixing processes present in the zone. The results were compared with dissolved metal concentrations reported for the Gulf of California (Cd, Mn and Fe) and the North Pacific Ocean. The resulting linear regression of the results vs. North Pacific Ocean concentrations indicated that the levels of Cu, Ni and Zn measured in this study were within its 95% confidence level. Furthermore, this comparison was capable of detecting dissolved Fe and Mn enrichments in Gulf of California waters relative to the North Pacific Ocean concentrations. Calculations of total masses of metals associated with algal biomass on the west coast of the Gulf of California indicated that the lowest masses were represented by Cu (108 ± 25 kg) and Ni (184 ± 52 kg), whereas Pb (1.1 ± 0.6 ton) and Fe (10.9 ± 8.5 ton) were the elements with the highest associated masses.     

Oceanic transport and storage of carbon emissions

Using a global carbon cycle model (GLOCO) that considers seven terrestrial biomes, surface and deep ocean layers based on the HILDA model and a single mixed atmosphere, we analyzed the response of atmospheric CO₂ concentration and oceanic DIC and DOC depth profiles to additions of carbon to the atmosphere and ocean. The rate of transport of carbon to the deepest oceanic layers is rather insensitive to the atmosphereic-ocean surface gas exchange coefficient over a wide range, hence discrepancies between researchers on the precise global average value of this coefficient do not significantly affect predictions of atmospheric response to anthropogenic inputs. Upwelling velocity, on the other hand, amplifies oceanic response by increasing primary production in the upper ocean layers, resulting in a larger flux into DOC and sediments and increased carbon storage; experiments to reduce the uncertainty in this parameter would be valuable.The location of the carbon addition, whether it is released in the atmosphere or in the middle of the oceanic thermocline, has a significant impact on the maximum atmospheric CO₂ concentration (pCO₂) subsequently reached, suggesting that oceanic burial of a significant fraction of carbon emissions (e.g. via clathrate hydrides) may be an important management option for limiting pCO₂ buildup. Our analysis indicates that the effectiveness of ocean burial decreases asymptotically below about 1000 m depth. With a constant emissions scenario (at 1990 levels), pCO₂ at year 2100 is reduced from 501 ppmv considering all emissions go to the atmosphere, to 422 ppmv with ocean burial at a depth of 1000 m of 50% of the fossil fuel emissions. An alternative scenario looks at stabilizing pCO₂ at 450 ppmv; with no ocean burial of fossil fuel emissions, the rate of emissions has to be cut drastically after the year 2010, whereas oceanic burial of 2 GtC/yr allows for a smoother transition to alternative energy sources.     

Comparative dating of a Bison-bearing late-Pleistocene deposit,Térapa,Sonora, Mexico

A recently discovered Bison-bearing fossil locality at Térapa, Sonora, Mexico, had previously been dated to 440 ± 130 ka using whole rock ⁴⁰Ar/³⁹Ar on a basalt flow that impounds the deposit. This age is considerably older than the accepted age of about 240–160 ka for the migration of Bison into greater North America. The Térapa deposit also contains a mixture of fossils from extralimital or extinct tropical animals and temperate animals. Constraining the age of the deposit is critical to interpret the paleontologic and paleoclimatologic implications of this unique Sonoran fossil locality. Three additional geochronological methods have been applied to this deposit (infrared stimulated luminescence (IRSL), amino acid racemization (AAR), and radiocarbon) and the data from the original ⁴⁰Ar/³⁹Ar age were revisited. The IRSL data suggest that the impounding basalt flow and the sediments that abut it were emplaced 43 ka ago and that the oldest sediments were deposited shortly after. Two radiocarbon ages suggest the fossiliferous sediments were emplaced by 42 ka. Effective diagenetic temperatures inferred from the AAR results, combined with AAR data from a similar-age deposit in southern Arizona, are in accordance with the 40–43 ka age estimates. For the AAR results to corroborate the ⁴⁰Ar/³⁹Ar age, the effective diagenetic temperature for the area would need to be approximately 3 °C, which is unrealistically low for northern Mexico. The new geochronological results suggest the Térapa deposit and fossils are 40–43 ka old. The anomalously old ⁴⁰Ar/³⁹Ar age for the impounding basalt is probably the result of low ⁴⁰Ar* concentrations and inherited ⁴⁰Ar.     

Multivariate analyses of water chemistry: surface and ground water interactions

Multivariate statistical methods (MSMs) applied to ground water chemistry provide valuable insight into the main hydrochemical species, hydrochemical processes, and water flowpaths important to ground water evolution. The MSMs of principal component factor analysis (FA) and k-means cluster analysis (CA) were sequentially applied to major ion chemistry from 211 different ground water-sampling locations in the Amargosa Desert. The FA reduces the number of variables describing the system and finds relationships between major ions. The CA of the reduced system produced objective hydrochemical facies, which are independent of, but in good agreement with, lithological data. The derived factors and hydrochemical facies are innovatively presented on biplots, revealing composition of hydrochemical processes and facies, and overlaid on a digital elevation model, displaying flowpaths and interactions with geologic and topographic features in the region. In particular, a distinct ground water chemical signature is observed beneath and surrounding the extended flowpath of Fortymile Wash, presenting some contradiction to contemporary water levels along with potential interaction with a fault line. The signature surrounding the ephemeral Fortymile Wash is believed to represent the relic of water that infiltrated during past pluvial periods when the amount of runoff in the wash was significantly larger than during the current drier period. This hypothesis and aforementioned analyses are supported by the examination of available chloride, oxygen-18, hydrogen-2, and carbon-14 data from the region.     

Air temperature and wind changes in Costa Rica during the total solar eclipse of July 11, 1991

Air temperature and wind measurements on the surface and in the free atmosphere taken during the total solar eclipse of July 11, 1991, are analyzed. Surface air temperature decreased significantly, 2 to 5 °C in general, with the lowest values occurring 10 to 30 minutes after totality. In some places, surface wind speed decreased gradually during the eclipse, as a result of the decrease of air temperature and temperature gradients. In other places, it increased due to local atmospheric conditions. A radiosonde launched at 13:26 LT (local time) appeared to have been affected by the moon's shadow at about 13 km height. At this altitude temperature was relatively lower than usual and the balloon carrying the radiosonde experienced an upward acceleration. Also at this altitude wind direction changed and wind speed decreased