Differences in diversity, structure, and variability between intertidal and subtidal meiofaunal assemblages

[EN] Meiofaunal assemblages from intertidal and shallow subtidal seabeds were studied at two sites (one dominated by volcanic sands and the other by organogenic sands) at Tenerife (Canary Islands, NE Atlantic Ocean) throughout an entire year (May 2000?April 2001). Specifically, we aimed (i) to test for differences in diversity, structure, and stability between intertidal and subtidal meiofaunal assemblages, and (ii) to determine if differences in the meiofaunal assemblage structure may be explained by environmental factors (granulometric composition, availability of organic matter, and carbonate content in sediments). A total of 103,763 meiofaunal individuals were collected, including 203 species from 19 taxonomic groups (Acari, Amphipoda, Cnidaria, Copepoda, Echinodermata, Gastrotricha, Isopoda, Insecta, Kinorrhyncha, Misidacea, Nematoda, Nemertini, Oligochaeta, Ostracoda, Polychaeta, Priapulida, Sipuncula, Tanaidacea, and Turbellaria). Nematodes were the most abundant taxonomic group. Species diversity was higher in the subtidal than in the intertidal zone at both sites, as a result of the larger dominance of a few species in the intertidal zone. The meiofaunal assemblage structure was different between tidal levels at both sites, the intertidal presenting greater temporal variability (multivariate dispersion) in the meiofaunal assemblage structure than the subtidal. Sediment grain size, here quantified by the different granulometric fractions, explained the variability in meiofaunal assemblage structure to a greater extent than the percentage of carbonates, a variable linked to sediment origin. This study revealed differences in diversity, assemblage structure, and variability between intertidal and subtidal meiofauna.

Laboratory verification of predicted permanent deformation in asphalt materials following climate change.

In the past a change in temperature of 5°C most often occurred over intervals of thousands of years. According to estimates by the IPCC, in the XXI century is expected an increase in average temperatures in Europe between 1.8 and 4.0°C in the best case caused by emissions of carbon dioxide and other GHG from human activities. As well as on the environment and economic context, global warming will have effects even on road safety. Several studies have already shown how increasing temperature may cause a worsening of some types of road surface damages, especially rutting, a permanent deformation of the road structures consisting in the formation of a longitudinal depression in the wheelpath, mostly due to the rheological behavior of bitumen. This deformation evolves during the hot season because of the heating capacity of the asphalt layers, in fact, the road surface temperature is up to 24°C higher than air. In this thesis, through the use of Wheeltrack test, it was studied the behavior of some types of asphalt concrete mixtures subjected to fatigue testing at different temperatures. The objectives of this study are: to determine the strain variation of different bituminous mixture subjected to fatigue testing at different temperature conditions; to investigate the effect of aggregates, bitumen and mixtures’ characteristics on rutting. Samples were made in the laboratory mostly using an already prepared mixtures, the others preparing the asphalt concrete from the grading curve and bitumen content. The same procedure was performed for each specimen: preparation, compaction using the roller compactor, cooling and heating before the test. The tests were carried out at 40 - 50 - 60°C in order to obtain the evolution of deformation with temperature variation, except some mixtures for which the tests were carried out only at 50°C. In the elaboration of the results were considered testing parameters, component properties and the characteristics of the mixture. Among the testing parameters, temperature was varied for each sample. The mixtures responded to this variation with a different behavior (linear logarithmic and exponential) not directly correlated with the asphalt characteristics; the others parameters as load, passage frequency and test condition were kept constant. According to the results obtained, the main contribution to deformation is due to the type of binder used, it was found that the modified bitumen have a better response than the same mixtures containing traditional bitumen; to the porosity which affects negatively the behavior of the samples and to the homogeneity ceteris paribus. The granulometric composition did not seem to have interfered with the results. Overall has emerged at working temperature, a decisive importance of bitumen composition, than the other characteristics of the mixture, that tends to disappear with heating in favor of increased dependence of rutting resistance from the granulometric composition of the sample considered. In particular it is essential, rather than the mechanical characteristics of the binder, its chemical properties given by the polymeric modification. To confirm some considered results, the maximum bulk density and the air voids content were determined. Tests have been conducted in the laboratories of the Civil Engineering Department at NTNU in Trondheim according to European Standards.

Grain size composition of sediments from ODP Leg 164 sites

This research was designed to check the assumption of the grain-size control on a gas hydrate presence in the Blake Ridge sediments; the assumption had originated from the data gained at Deep Sea Drilling Project (DSDP) Site 533. Granulometric analysis (the combined pipette-sieve method) of the 345 sediment samples obtained after pore-water squeezing from Ocean Drilling Program (ODP) Sites 994, 995, and 997 has provided support for this assumption. The zone of negative anomalies of pore-water chlorinity, which is generally recognized to be gas hydrate bearing, is confined, as a whole, to the interval of comparatively coarse-grained sediments in each of the three site columns because content of the fine fractions <0.05, <0.01, <0.005, and <0.001 mm is lower there (although the character of this control changes from site to site). The individual chlorinity anomalies also coincide, for the most part, with relatively coarse-grained sediments.

Mud, sand, heavy and light minerals composition in lower Cretaceous at DSDP Hole 93-603B

During the drilling of Hole 603B on Deep Sea Drilling Project Leg 93, an unexpected series of sand-, silt-, and claystone turbidites was encountered from Cores 603B-45 through -76 (1224-1512 m sub-bottom depth). Complete and truncated Bouma sequences were observed, some indicating deposition by debris flows. Sand emplacement culminated with the deposition of a 30-m-thick, unconsolidated sand unit (Cores 603B-48 through -45). The purpose of this preliminary study is to determine the nature of the heavy mineral suites of this sediment in order to make tentative correlations with onshore equivalents. The heavy mineralogy of Lower Cretaceous North American mid-Atlantic coastal plain sediment has been extensively studied. This sediment is classified as the Potomac Group, which has a varied heavy mineral suite in its lower part (Patuxent Formation), and a limited suite in its upper part (Patapsco Formation). The results of this study reveal a similar trend in the heavy mineral suites of sediment in Hole 603B. Hauterivian through lower Barremian sediment has a heavy mineral suite that is dominated by zircon, apatite, and garnet, with minor amounts of staurolite and kyanite. Beginning in the mid-Barremian, a new source of sediment becomes dominant, one which supplies an epidote-rich heavy mineral suite. The results of the textural analyses show that average grain size of the light mineral fraction increases upsection, whereas sorting decreases. The epidote-rich source may have delivered sediment with a slightly coarser mean grain size. This sediment may represent a more direct continental input at times of maximum turbidite activity (mid-Barremian) and during deposition of the upper, unconsolidated sand unit.