Distribution of colloidal trace metals in the San Francisco Bay estuary

The size distribution of trace metals (Al, Ag, Cd, Cu, Fe, Mn, Ni, Sr, and Zn) was examined in surface waters of the San Francisco Bay estuary. Water samples were collected in January 1994 across the whole salinity gradient and fractionated into total dissolved (<0.2 μm colloidal (10 KDa–0.2 μm) and < 10 kDa molecular weight phases. In the low salinity region of the estuary, concentrations of colloidal A1, Ag, and Fe accounted for ≥84% of the total dissolved fraction, and colloidal Cu and Mn accounted for 16–20% of the total. At high salinities, while colloidal Fe was still relatively high (40% of the dissolved), very little colloidal Al, Mn, and Cu (<10%) and no colloidal Ag was detectable. Colloidal Zn accounted for <3% of the total dissolved along the estuary, and colloidal Ni was only detectable (<2%) at the river endmember. All of the total dissolved Cd and Sr throughout the estuary consisted of relatively low molecular weight (<10 kDa) species. The relative affinity of metals for humic substances and their reactivity with particle surfaces appear to determine the amounts of metal associated with colloids. The mixing behavior of metals along the estuary appears to be determined by the relative contribution of the colloidal phase to the total dissolved pool. Metals with a small or undetectable colloidal fraction showed a nonconservative excess (Cd, Cu, Ni, and Mn) or conservative mixing (Sr) in the total dissolved fraction, relative to ideal dilution of river water and seawater along the estuary.

The salt-induced coagulation of colloidal A1, Fe, and Cu is indicated by their highly nonconservative removal along the salinity gradient. However, colloidal metals with low affinity for humic substances (Mn and Zn) showed conservative mixing behavior, indicating that some riverine colloids are not effectively aggregated during their transport to the sea. While colloidal metal concentrations correlated with dissolved organic carbon, they also covaried with colloidal Al, suggesting that colloids are a mixture of organic and inorganic components. Furthermore, the similarity between the colloidal metal:A1 ratios with the crustal ratios indicated that colloids could be the product of weathering processes or particle resuspension. Distribution coefficients for colloidal particles (K_c) and for large, filter-retained particles (K_d) were of the same magnitude, suggesting similar binding strength for the two types of particles. Also, the dependence of the distribution coefficients on the amount of suspended particulate matter (the so-called particle concentration effect) was still evident for the colloids-corrected distribution coefficient (K_p+c) and for metals (e.g., Ni) without affinity for colloidal particles.     

Holocene sea-level fluctuation in the southern hemisphere

If rising sea levels dominate in the northern hemisphere (NH), falling or fluctuating sea levels predominate in the southern hemisphere (SH). Endogenic processes (tectonics, isostasy or geoidal changes) could explain local or regional mean sea level (MSL) fluctuations but not an hemispherical one.Evidence from South America, Africa, Antarctica, Australia and the Pacific and Indian Oceans suggest that the Holocene transgression rose above the present MSL, in higher latitudes before the tropics. By plotting latitude against the age of MSL arrival at present coasts, good correlation is observed.Oceanic salinity mixing has been already proposed to explain this mid-Holocene sea-level fluctuation. Climate could be the only factor responsible for this hemisphere-wide behavior of MSL. It has been suggested previously that the climate of the SH precedes that of the NH by 3000 years. The climatic optimum, or maximum warmth, occurred predominantly about 6000 BP in the NH, but about 10–9000 BP in the SH.Short-term climatic effects on the sea level (monsoons, southern oscillation/El Niño phenomena) should have significant occurrences during the past in the windiest oceanic hemisphere.This latitudinal trend in former MSL should be considered when using shorelines as reference points for measuring vertical crustal movements.     

Critical tissue copper residues for marine bivalve (Mytilus galloprovincialis) and echinoderm (Strongylocentrotus purpuratus) embryonic development: conceptual, regulatory and environmental implications

Critical tissue copper (Cu) residues associated with adverse effects on embryo-larval development were determined for the Mediterranean mussel (Mytilus galloprovincialis) and purple sea urchin (Strongylocentrotus purpuratus) following laboratory exposure to Cu-spiked seawater collected from San Diego Bay, California, USA. Whole body no-observed-effect-residues (NOER) were similar, with means of 21 and 23mugg(-1)dw, for M. galloprovincialis and S. purpuratus, respectively. Mean whole body median effect residues (ER50) were 49 and 142mugg(-1)dw for M. galloprovincialis and S. purpuratus, respectively. The difference in ER50s between species was reduced to a factor of <2 when expressed as soft tissue residues. Coefficients of variation among whole body-ER50s were 3-fold lower than median waterborne effect concentrations (EC50) for both species exposed to samples varying in water quality characteristics. This suggests that tissue concentrations were a better predictor of toxicity than water concentrations. The CBRs described herein do not differentiate between the internal Cu concentrations that are metabolically available and those that are accumulated and then detoxified. They do appear, however, to be well enough related to the level of accumulation at the site of action of toxicity that they serve as useful surrogates for the copper concentration that affects embryonic development of the species tested. Results presented have potentially important implications for a variety of monitoring and assessment strategies. These include regulatory approaches for deriving saltwater ambient water quality criteria for Cu, contributions towards the development of a saltwater biotic ligand model, the conceptual approach of using CBRs, and ecological risk assessment.     

On the resurfacing of Ganymede by liquid-water volcanism

A long-popular model for producing Ganymede's bright terrain involves flooding of low-lying graben with liquid water, slush, or warm, soft ice. The model suffers from major problems, however, including the absence of obvious near-surface heat sources, the negative buoyancy of liquid water, and the lack of a mechanism for confining the flows to graben floors. We present new models for cryovolcanic resurfacing to overcome these difficulties. Tidal heating within an ancient Laplace-like orbital resonance (Showman and Malhotra 1997, Icarus 127, 93; Showman et al., 1997, Icarus 129, 367) provides a plausible heat source and could allow partial melting to occur as shallow as 5-10 km depth. Our favored mechanism for delivering this water to the surface invokes the fact that topography—such as a global set of graben—causes subsurface pressure gradients that can pump water or slush upward onto the floors of topographic lows (graben) despite the negative buoyancy of the liquid. These eruptions can occur only within the topographic lows; furthermore, as the low areas become full, the pressure gradients disappear and the resurfacing ceases. This provides an explanation for the observed straight dark-bright terrain boundaries: water cannot overflow the graben, so resurfacing rarely embays craters or other rough topography. Pure liquid water can be pumped to the surface from only 5-10 km depth, but macroscopic bodies of slush ascending within fractures can reach the surface from much greater depths due to the smaller negative buoyancy of slush. A challenge for these models is the short predicted gravitational relaxation timescale of topographic features at high heat flows; the resurfacing must occur before the graben topography disappears. We also evaluate alternate resurfacing mechanisms, such as pumping of liquid water to the surface by thermal expansion stresses and buoyant rise of water through a silicate-contaminated crust that is denser than liquid water, and conclude that they are unlikely to explain Ganymede's bright terrain.     

Compilation of radiogenic isotope data in Mexico and their petrogenetic implications

Seven hundred and twenty-five Sr, two hundred and forty-three Nd and one hundred and fifty-one Pb isotopic ratios from seven different Mexican magmatic provinces were compiled in an extensive geochemical database. Data were arranged according to the Mexican geological provinces, indicating for each province total number of analyses, range and mean of values and two times standard deviation (2σ). Data from seven provinces were included in the database: Mexican Volcanic Belt (MVB), Sierra Madre Occidental (SMO), Baja California (BC), Pacific Ocean (PacOc), Altiplano (AP), Sierra Madre del Sur (SMS), and Sierra Madre Oriental (SMOr). Isotopic values from upper mantle and lower crustal xenoliths, basement outcrops and sediments from the Cocos Plate were also compiled. In the MVB the isotopic ratios range as follows:⁸⁷Sr/⁸⁶Sr 0.703003-0.70841;¹⁴³Nd/¹⁴⁴Nd 0.512496-0.513098;²⁰⁶Pb/²⁰⁴Pb 18.567-19.580;²⁰⁷Pb/²⁰⁴Pb 15.466-15.647;²⁰⁸Pb/²⁰⁴Pb 38.065-38.632. The SMO shows a large variation in⁸⁷Sr/⁸⁶Sr ranging from ∼0.7033 to 0.71387.¹⁴³Nd/¹⁴⁴Nd ratios are relatively less variable with values from 0.51191 to 0.51286. Pb isotope ratios in the SMO are as follows:²⁰⁶Pb/²⁰⁴Pb 18.060-18.860;²⁰⁷Pb/²⁰⁴Pb 15.558-15.636;²⁰⁸Pb/²⁰⁴Pb 37.945-38.625. PacOc rocks show the most depleted Sr and Nd isotopic ratios (0.70232-0.70567 for Sr and 0.512631-0.513261 for Nd). Pb isotopes for PacOc show the following range:²⁰⁶Pb/²⁰⁴Pb 18.049-19.910;²⁰⁷Pb/²⁰⁴⁷Pb 15.425-15.734;²⁰⁸Pb/²⁰⁴Pb 37.449-39.404. The isotopic ratios of the AP rocks seem to be within the range of those from the PacOc. Most samples with reported Sr and Nd isotopic data are spread within and around the “mantle array”. The SMO seems to have been formed by a mixing process between mantle derived magmas and continental crust. The MVB appears to have a larger mantle component, with AFC as the dominant petrogenetic process for the evolved rocks. There is still a need for Pb isotopic data in all Mexican magmatic provinces and of Nd isotopes in BC, AP, SMS, and SMOr.     

Late Holocene marine terraces of the Cartagena region,southern Caribbean: The product of neotectonism or a former high stand in sea-level?

The detailed stratigraphic survey and paleontological study (mollusks, corals, foraminifera and ostracods) of four low-level, ～3 m, marine terrace sections: Punta Canoas, Manzanillo del Mar, Playa de Oro, and Tierra Bomba Island, from the Cartagena region, southern Caribbean, supplemented with 22 radiocarbon dates, reveals that the northern terraces were deposited as parasequences in a clastic depositional system compared to the Tierra Bomba Island succession that was deposited in a carbonate depositional system between ～3600 and ～1700 cal yrs BP. Drier conditions and the southern location of the ITCZ at about 3 ka triggered stronger easterly Trades and more dynamic southwestward sediment drift fed by the Magdalena River mouth, thus promoting the formation of sand spits that ultimately isolated the Cienaga de Tesca coastal lagoon from the Caribbean Sea. Our estimates support the hypothesis that the present position of the terraces is the product of neotectonism rather than a higher 3 ka, sea-level. Upheaval of the terraces varies between ～3.8 mmyr^?1 at Punta Canoas and ～2.2 mmyr^?1 at Tierra Bomba to ～1.5 mmyr^?1 at Manzanillo del Mar and Playa de Oro terraces. Our study corroborates previous contentions on the role of mud diapirism and the dynamics of the Dique Fault as late Holocene upheaval mechanisms.     

Deriving snow‐cover depletion curves for different spatial scales from remote sensing and snow telemetry data

During the melting of a snowpack, snow water equivalent (SWE) can be correlated to snow‐covered area (SCA) once snow‐free areas appear, which is when SCA begins to decrease below 100%. This amount of SWE is called the threshold SWE. Daily SWE data from snow telemetry stations were related to SCA derived from moderate‐resolution imaging spectroradiometer images to produce snow‐cover depletion curves. The snow depletion curves were created for an 80 000 km² domain across southern Wyoming and northern Colorado encompassing 54 snow telemetry stations. Eight yearly snow depletion curves were compared, and it is shown that the slope of each is a function of the amount of snow received. Snow‐cover depletion curves were also derived for all the individual stations, for which the threshold SWE could be estimated from peak SWE and the topography around each station. A station's peak SWE was much more important than the main topographic variables that included location, elevation, slope, and modelled clear sky solar radiation. The threshold SWE mostly illustrated inter‐annual consistency. Copyright © 2015 John Wiley & Sons, Ltd.     

Climate controls on rainfall isotopes and their effects on cave drip water and speleothem growth: the case of Molinos cave (Teruel,NE Spain)

The interpretation of stable isotopes in speleothems in terms of past temperature variability or precipitation rates requires a comprehensive understanding of the climatic factors and processes that influence the δ¹⁸O signal in the way through the atmosphere to the cave, where carbonate precipitates acquiring its final isotopic composition. This study presents for the first time in the Iberia Peninsula an integrated analysis of the isotopic composition of rainfall (δ¹⁸O_p) during 2010–2012 years and, through a detailed monitoring survey, the transference of the primary isotopic signal throughout the soil and epikarst into the Molinos cave (Teruel, NE Spain). Both air temperature and amount of precipitation have an important effect on δ¹⁸O_p values, clearly imprinting a seasonal variability modulated by an amount effect when rainfall events are more frequent or intense. Air mass history and atmospheric circulation influences are considered through the study of weather types, synoptic-scale climate patterns and large-scale atmospheric circulation indexes (North Atlantic Oscillation and Western Mediterranean Oscillation) revealing a dominant source effect on δ¹⁸O_p values in this region where tropical North Atlantic and Western Mediterranean are the two moisture source regions. A delay of 2–3 months occurs between the dripwater oxygen isotopic composition (δ¹⁸O_d) respect to δ¹⁸O_p values as a consequence of large residence time in the epikarst. Limited calcite precipitates are found from winter to spring when δ¹⁸O_d values are less negative and dripwater rates are constant. This study suggests that NE Iberian δ¹⁸O_calcite proxy records are best interpreted as reflecting a combination of parameters, not just paleotemperature or paleorainfall and, if extending present-day situation towards the recent past, a biased signal towards winter values should be expected in Molinos speleothem records.     

Evaluating the performance of CMIP3 and CMIP5 global climate models over the north-east Atlantic region

One of the main sources of uncertainty in estimating climate projections affected by global warming is the choice of the global climate model (GCM). The aim of this study is to evaluate the skill of GCMs from CMIP3 and CMIP5 databases in the north-east Atlantic Ocean region. It is well known that the seasonal and interannual variability of surface inland variables (e.g. precipitation and snow) and ocean variables (e.g. wave height and storm surge) are linked to the atmospheric circulation patterns. Thus, an automatic synoptic classification, based on weather types, has been used to assess whether GCMs are able to reproduce spatial patterns and climate variability. Three important factors have been analyzed: the skill of GCMs to reproduce the synoptic situations, the skill of GCMs to reproduce the historical inter-annual variability and the consistency of GCMs experiments during twenty-first century projections. The results of this analysis indicate that the most skilled GCMs in the study region are UKMO-HadGEM2, ECHAM5/MPI-OM and MIROC3.2(hires) for CMIP3 scenarios and ACCESS1.0, EC-EARTH, HadGEM2-CC, HadGEM2-ES and CMCC-CM for CMIP5 scenarios. These models are therefore recommended for the estimation of future regional multi-model projections of surface variables driven by the atmospheric circulation in the north-east Atlantic Ocean region.