Carbon cycling in a shallow turbid estuary of southeast Texas: The use of plant pigment biomarkers and water quality parameters

Particulate organic carbon (POC), dissolved organic carbon (DOC), and plant pigments (chlorophylls and carotenoids) were measured approximately bimonthly from March 1992 to October 1993 in the Sabine-Neches estuary (Sabine Lake region), located on the Texas-Louisiana border. High freshwater inflow into this shallow turbid estuary results in the shortest hydraulic residence time (ca. 7 d) of all Texas estuaries (Baskaran et al. in press). Annual averages of chlorophyll-a (3.0 μg l^?1) and particulate organic carbon (1.1 mg l^?1) in the water column were extremely low in comparison to other shallow estuaries. The highest chlorophyll-a concentrations were observed in October 1993, in the mid and lower regions of the estuary, during the lowest river discharge. Zeaxanthin and fucoxanthin concentrations suggested that much of the chlorophyll-a during this low flow period was represented by cyanobacteria and diatoms that entered from the Gulf of Mexico. The range of DOC concentrations was generally high (4.4–20.9 mg l^?1) and were significantly correlated with POC, but not with chlorophyll-a concentrations. When total suspended particulate (TSP) concentrations were below 20 to 30 mg l^?1, there were significant increases in %POC and %PON of the TSP. The unusually high POC: chlorophyll-a ratios (highest value of 1423) suggested that much of the POC contained low concentrations of chlorophyll-a that had degraded during transport from wetlands in the Sabine and Neches rivers. Based on these data, this estuary can be characterized as a predominantly heterotrophic system, with low light penetrance, short particle-residence times, high DOC, and low inputs from autochthonous carbon sources.     

Negative δO values in Allan Hills 84001 carbonate: Possible evidence for water precipitation on mars

The Martian meteorite ALH84001 contains ∼1% by weight of carbonate formed by secondary processes on the Martian surface or in the shallow subsurface. The major form of this carbonate is chemically and isotopically zoned rosettes which have been well documented elsewhere. This study concentrates upon carbonate regions ∼200 μm across which possess previously unobserved magnesium rich inner cores, interpreted here as rosette fragments, surrounded by a later stage cement containing rare Ca-rich carbonates (up to Ca₈₁Mg₀₇Fe₀₄Mn₀₇) intimately associated with feldspar. High spatial resolution ion probe analyses of Ca-rich carbonate surrounding rosette fragments have δ¹⁸O_V-SMOW values as low as −10‰. These values are not compatible with deposition from a global Martian atmosphere invoked to explain ALH84001 rosettes. The range of δ¹⁸O values are also incompatible with a fluid that has equilibrated with the Martian crust at high temperature or from remobilisation of carbonate of rosette isotopic composition. At Martian atmospheric temperatures, the small CO₂(gas)-CO₂(ice) fractionation makes meteoric CO₂ an unlikely source for −10‰ carbonates. In contrast, closed system Rayleigh fractionation of H₂O can generate δ¹⁸O_H2O −30‰, as observed at high latitudes on Earth. We suggest that atmospheric transport and precipitation of H₂O in a similar fashion to that on Earth provides a source of suitably ¹⁸O depleted water for generation of carbonate with δ¹⁸O_V-SMOW = −10‰.     

Origin of flooding water through hydrogeochemical identification,the Buenos Aires plain,Argentina

Hydrogeochemical behaviour of samples of surface and groundwater collected on a cross-section from Mendoza to the Buenos Aires provinces was studied based on chemical trends, mass balance and water mixing. Hydrogeochemical modelling included major, minor elements as well as stable isotopes (deuterium and 18-O). The area investigated is located in the “Médanos Longitudinales” (longitudinal dunes) of the northwest of Buenos Aires province, Argentina. The study area is subject to alternating flooding and drought. Rainfall and surface water subsequently transferred by rivers, canals and lagoons have been usually considered responsible for local flooding. For this study, origins of excess water were investigated using physical and chemical characteristics of the water involved. The prevalence of groundwater inflow to rainfall events was proposed based on data interpretation. Groundwater influence of flows of local and intermediate nature were defined and the importance of recharge, transit and discharge zones was highlighted. Lagoon floodwater, as well as groundwater from observation wells and production boreholes, show components of intermediate origin. Regional recharge water was identified in Mendoza and San Luis provinces. Their discharge zone was inferred to be located beyond the Buenos Aires province.     

The IGS VTEC maps: a reliable source of ionospheric information since 1998

The International GNSS Service (IGS) Working Group on Ionosphere was created in 1998. Since then, the Scientific community behind IGS, in particular CODE, ESA, JPL and UPC, have been continuosly contributing to reliable IGS combined vertical total electron content (VTEC) maps in both rapid and final schedules. The details on how these products are being generated, performance numbers, proposed improvement as far as VTEC evolution trends during near one Solar Cycle, are summarized in this paper. The confirmation of (1) the good performance of the IGS combined VTEC maps, and (2) the characteristic VTEC variability periods, are two main results of this work.     

Non‐unique stratal geometries: implications for sequence stratigraphic interpretations

There is now strong evidence that stratal geometries on basin margins are most likely a consequence of multiple controls, not just variations in accommodation. Consequently, correct sequence stratigraphic interpretation of stratal geometries requires an understanding of how multiple different controls may generate similar geometries. Using a simple numerical stratigraphic forward model, we explore the impact of time variable sediment supply and different sediment transport rates on stratal geometries. We demonstrate how four common types of stratal geometry can form by more than one set of controlling parameter values and are thus likely to be non‐unique, meaning that there may be several sets of controlling factors that can plausibly explain their formation. For example, a maximum transgressive surface can occur in the model due to an increase in rate of relative sea‐level rise during constant sediment supply, and due to a reduction in rate of sediment supply during a constant rate of relative sea‐level rise. Sequence boundaries, topset aggradation and shoreline trajectories are also examples of non‐unique stratal geometries. If the model simulations in this work are sufficiently realistic, then the modelled stratal geometries are important examples of non‐uniqueness, suggesting the need for a shift towards sequence stratigraphic methods based on constructing and evaluating multiple hypotheses and scenarios.     

Low‐accommodation and backwater effects on sequence stratigraphic surfaces and depositional architecture of fluvio‐deltaic settings (Cretaceous Mesa Rica Sandstone,Dakota Group,USA)

The adequate documentation and interpretation of regional‐scale stratigraphic surfaces is paramount to establish correlations between continental and shallow marine strata. However, this is often challenged by the amalgamated nature of low‐accommodation settings and control of backwater hydraulics on fluvio‐deltaic stratigraphy. Exhumed examples of full‐transect depositional profiles across river‐to‐delta systems are key to improve our understanding about interacting controlling factors and resultant stratigraphy. This study utilizes the ~400 km transect of the Cenomanian Mesa Rica Sandstone (Dakota Group, USA), which allows mapping of down‐dip changes in facies, thickness distribution, fluvial architecture and spatial extent of stratigraphic surfaces. The two sandstone units of the Mesa Rica Sandstone represent contemporaneous fluvio‐deltaic deposition in the Tucumcari sub‐basin (Western Interior Basin) during two regressive phases. Multivalley deposits pass down‐dip into single‐story channel sandstones and eventually into contemporaneous distributary channels and delta‐front strata. Down‐dip changes reflect accommodation decrease towards the paleoshoreline at the Tucumcari basin rim, and subsequent expansion into the basin. Additionally, multi‐storey channel deposits bound by erosional composite scours incise into underlying deltaic deposits. These represent incised‐valley fill deposits, based on their regional occurrence, estimated channel tops below the surrounding topographic surface and coeval downstepping delta‐front geometries. This opposes criteria offered to differentiate incised valleys from flood‐induced backwater scours. As the incised valleys evidence relative sea‐level fall and flood‐induced backwater scours do not, the interpretation of incised valleys impacts sequence stratigraphic interpretations. The erosional composite surface below fluvial strata in the continental realm represents a sequence boundary/regional composite scour (RCS). The RCS’ diachronous nature demonstrates that its down‐dip equivalent disperses into several surfaces in the marine part of the depositional system, which challenges the idea of a single, correlatable surface. Formation of a regional composite scour in the fluvial realm throughout a relative sea‐level cycle highlights that erosion and deposition occur virtually contemporaneously at any point along the depositional profile. This contradicts stratigraphic models that interpret low‐accommodation settings to dominantly promote bypass, especially during forced regressions. Source‐to‐sink analyses should account for this in order to adequately resolve timing and volume of sediment storage in the system throughout a complete relative sea‐level cycle.     

The northern sea route as an element of the ICZM system in the Arctic: problems and perspectives

Characteristics of the current state of transportation problems along the Northern Sea Route are given. The required ice data necessary to guarantee the safety of navigation are discussed. A variety of developing transportation prospects along the Northern Sea Route, including international aspects, are disputed. Effective economic alternatives of the Northern Sea Route under the conditions of the current Russian economic crisis are analyzed.     

Role of the Radiation Factor in Global Climatic Events of the Late Holocene

Izvestiya, Atmospheric and Oceanic Physics - On the basis of calculations of insolation and insolation characteristics, taking into account changes in solar activity, the causes of global climatic...     

Fattening of wild short‐finned eels,Anguilla Australis schmidtii Phillipps

Short‐finned wild eels fed an artificial diet containing either a low (5%) or a high (20%) oil content were found to increase their mass by an average of more than 30% after a 34‐day feeding period; the lipid content of the eels’ muscle was also increased from about 10% to around 20%.     

On the use of ‘first spotless day’ as a predictor for sunspot minimum

Defining the first spotless day of a sunspot cycle as the first day without spots relative to sunspot maximum during the decline of the solar cycle, one finds that the timing of that occurrence can be used as a predictor for the occurrence of solar minimum of the following cycle. For cycle 22, the first spotless day occurred in April 1994, based on the International sunspot number index, although other indices (Boulder and American) indicated the first spotless day to have occurred earlier (September 1993). For cycles 9–14, sunspot minimum followed the first spotless day by about 72 months, having a range of 62–82 months; for cycles 15–21, sunspot minimum followed the first spotless day by about 35 months, having a range of 27–40 months. Similarly, the timing of first spotless day relative to sunspot minimum and maximum for the same cycle reveals that it followed minimum (maximum) by about 69 (18) months during cycles 9–14 and by about 90 (44) months during cycles 15–21. Accepting April 1994 as the month of first spotless day occurrence for cycle 22, one finds that it occurred 91 months into the cycle and 57 months following sunspot maximum. Such values indicate that its behavior more closely matches that found for cycles 15–21 rather than for cycles 9–14. Therefore, one infers that sunspot minimum for cycle 23 will occur in about 2–3 years, or about April 1996 to April 1997. Accepting the earlier date of first spotless day occurrence indicates that sunspot minimum for cycle 23 could come several months earlier, perhaps late 1995.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.