Abundance and Taxonomic Diversity of Bacteria Inhabiting the Sediment-Water Interface in a Marine Harbor Channel

Ocean Science Journal - The abundance of bacteria inhabiting the sediment-water interface and their taxonomic composition were determined with the fluorescence in situ hybridization (FISH) method...     

Late Miocene to Quaternary slip history across the Qiulitag anticline in the southern Tianshan piedmont

In this study, we reconstruct the Miocene to Quaternary shortening history across the Qiulitag anticline, a complex fault‐bend fold located in southern Tianshan. We studied the Yaha and Kuche sections, where we combined surface structural measurements and seismic imaging to model the stratigraphic horizons. The history of folding was reconstructed based on magnetostratigraphic analyses and eight cosmogenic burial ages in Kuche. Pleistocene deformation rates were also quantified in Yaha based on a deformed fluvial terrace that we dated to ~67 ka using a cosmogenic depth profile. Our results suggest that the fold grew at a mean slip rate of 0.9–1.3 mm/a in both sections but accelerated to ~2.5 mm/a during the Pleistocene in Kuche. These results support a migration of the deformation towards the basin during the Pleistocene and suggest that most of the present deformation in the Tianshan is accommodated across the external structures of the range.     

Using NWP to Assess the Influence of the Arctic Atmosphere on Midlatitude Weather and Climate

The influence of the Arctic atmosphere on Northern Hemisphere midlatitude tropospheric weather and climate is explored by comparing the skill of two sets of 14-day weather forecast experiments using the ECMWF model with and without relaxation of the Arctic atmosphere towards ERA-Interim reanalysis data during the integration. Two pathways are identified along which the Arctic influences midlatitude weather: a pronounced one over Asia and Eastern Europe, and a secondary one over North America. In general, linkages are found to be strongest(weakest) during boreal winter(summer) when the amplitude of stationary planetary waves over the Northern Hemisphere is strongest(weakest). No discernible Arctic impact is found over the North Atlantic and North Pacific region, which is consistent with predominantly southwesterly flow. An analysis of the flow-dependence of the linkages shows that anomalous northerly flow conditions increase the Arctic influence on midlatitude weather over the continents. Specifically, an anomalous northerly flow from the Kara Sea towards West Asia leads to cold surface temperature anomalies not only over West Asia but also over Eastern and Central Europe. Finally, the results of this study are discussed in the light of potential midlatitude benefits of improved Arctic prediction capabilities.     

The evaluation of “social risk” due to volcanic eruptions of Vesuvius

A re-evaluation of the demographic risk per number of inhabitants due to volcanic eruptions in the Vesuvius area was made on the basis of the Census data of 2001. We introduced other variables (population density and number of houses) which permit to upgrade the existing models. Using the Geographical Information Systems (GIS) and particularly ArcGIS 9.0 software we have elaborated a land use map, an urbanization map and a series of new risk maps which lead us to obtain a map of what we call “social risk” due to volcanic eruptions, derived from the combination of the data used and the overlay of the maps. We have proposed an integrated model which can be easily updated to follow the evolution of the volcanic risk in the overpopulated Vesuvius area, with the aim of supporting the planning of Civil Protection and Local Authorities, for an evacuation scenarios and the possibility of taking into account the potential infrastructural damages. This methodology can be tested in other volcanic regions.     

Kaolin deposits in the lower cretaceous Baqueró formation (Santa Cruz Province, Patagonia, Argentina)

Sedimentary kaolin deposits in the Lote 18 area (Santa Cruz Province, Patagonia, Argentina) have been mined since 1951. They constitute 30% of the country's production and are mainly used in the ceramic whiteware industry. The deposits belong to the Baqueró Formation (Lower Cretaceous) and unconfomably overlie either the ash-flow tuffs of the Chon-Aike Formation (Middle Jurassic), which are altered to kaolinite and minor illite, or the ash-fall tuffs of Bajo Grande Formation (Upper Jurassic-Lower Cretaceous), which are altered mainly to smectites. The presence of illite or smectite, as well as the kaolinite crystallinity, depends on the stratigraphic position of the kaolin horizons within the Lower Member of the Baqueró Formation and on the lithology of the underlying rocks. Kaolin beds composed of well-crystallized kaolinite at the base of the sequence overlaying Chon-Aike rocks are the purest. Kaolinite becomes less well cystallized with transport. Edge-to-face and swirl SEM textural patterns indicate the compaction of flocculated clays and clay movement during drainage and compaction. Mineralogical, petrological, and physico-structural evidence (i.e., form, extent, thickness) indicates that the kaolin deposits are sedimentary, formed by the transportation and deposition of previously formed kaolinite. Kaolin beds are ovoidal in plan and lenticular in profile, with thickness ranging from centimeters to 11 meters, and the culmination of fining-upward clastic sequences. Sedimentary facies analysis indicates that the kaolin deposits were formed in a fluvial environment from currents with a high suspended-load/bed-load ratio, as would result from deposition in ox-bow lakes.     

Pyroclastic deposits of the November 13, 1985 eruption of Nevado del Ruiz volcano, Colombia

The November 13, 1985 eruption of Nevado del Ruiz produced a series of pyroclastic flows and surges that eroded channels on the surface of the summit glacier and generated lahars which descended down most of the rivers that drain the volcano. The stratigraphy of the proximal pyroclastic deposits indicates that there were at least four episodes to the eruption. Episode I, deposited an unusual surge consisting of small pieces of ice mixed with ash and exhibiting planar stratification. Ballistically emplaced fragments are also intercalated with this unit. During Episode II, at least two pyroclastic flows were erupted. Their deposits contain the most evolved pumice of the entire eruption; SiO₂ content of matrix glass ranges between 74.5 and 74.9%. Episode III is marked by the emplacement of a welded tuff with an average SiO₂ content of about 66% in the matrix glass. The final Episode IV was characterized by the development of a high-altitude eruption column and the emplacement of several nonwelded pyroclastic flows. Banded pumice are common in the pyroclastic flow as well as in the pumice fall deposits. Co-existing dark and light pumice bands differ in SiO₂ content by 3.5% and in general are similar to the composition of the welded pumice from Episode III.The compositional zonation of the pyroclastic deposits from Episode I to IV suggests that a nearsurface compositionally-stratified portion of the magma body was tapped during Episode II. During Episodes III and IV the main body of magma was involved although the coexistence of the compositionally distinct pumice clasts at similar stratigraphic levels argues for mixing of magma from different levels in the chamber during the eruptive process.     

Growth Dynamics, Production, and Nutrient Status of the Seagrass Cymodocea nodosa in a Mediterranean Semi-Estuarine Environment

Abstract. Cymodocea nodosa is a relatively small seagrass species which is common in the Mediterranean. An intensive survey on its growth and production was carried out in a dense, monospecific stand located in a semi-estuarine embayment. Data on leaf appearance and growth, shoot recruitment and death, rhizome growth, above- and belowground biomass, and nutrient content in the different parts of the plant were obtained over 2 years. All these variables showed a clear seasonality. In general, maximum growth and production occurred in early summer (July), and maximum biomass was reached between July and September. Biomass, shoot density, growth and production showed clear minima in winter.     

Isotopic signatures of organic matter in sediments of the continental shelf facing the Orinoco Delta: Possible contribution of organic carbon from savannas

The ⁸⁷Sr, ¹³C, and ¹⁵N isotopic signatures of organic matter in sediments from the continental shelf facing the Orinoco Delta were measured to determine the contribution of sediments transported from the Amazon River by the coastal Guayana current and the sediments transported by the Orinoco River. Box core samples between 60 and 300 m water depth collected along 4 transects located eastwards to the Orinoco Delta were analyzed. Carbon and nitrogen concentrations decreased with depth under water on the shelf, and were strongly correlated indicating homogeneity of organic matter composition. Phosphorus content was also associated to organic matter in most samples, but some of them revealed deposition of P-enriched sediments. The ⁸⁷Sr/⁸⁶Sr ratios showed a strong continental signature averaging 0.7117, therefore, limiting the possible carbon and nitrogen sources associated with these sediments to C3 trees, C4 grasses, or freshwater phytoplankton. The δ¹³C values were relatively high averaging −21‰, above values reported for sediments on the Amapá shelf and the Amazon River in Brazil. Average δ¹³C values did not differ significantly among transects. High δ¹³C values point to the influence of organic matter transported from the C4-plants dominated savannas in the northern fringe of the Orinoco River. δ¹⁵N values were positive and averaged 5‰, being within the range of values measured in the Marajo island (Amazon River) and the estuary of the Pará River. The δ¹⁵N values differed significantly among transects (4.9–5.2‰), lowest values corresponding to the northernmost transect near the coast of Trinidad, and the highest values corresponding to the transect located at the southernmost position.