Search results for "oceanic"

Sediment characteristics and macrofauna distribution along a human-modified inlet in the Gulf of Oristano (Sardinia, Italy)

2007

We studied the spatial variability and within-year temporal changes in hydrological features, grain size composition and chemical characteristics of sediments, as well as macrofaunal assemblages, along a heavily modified inlet in the Gulf of Oristano (western Sardinia, Italy). The inlet connects the Cabras lagoon to the gulf through a series of convoluted creeks and man-made structures, including a dam and fish barriers built in the last three decades. Sediments were muddy and mainly composed of the "non-sortable" fraction (i.e., < 8 mu m particle size) in all four areas investigated: Lagoon, Creeks, Channel and Seaward. Along the inlet, however, the ratio between the < 8 mu mn and the 8-64…

Crust–mantle transition and Moho model for Iceland and surroundings from seismic, topography, and gravity data

2005

An increasing data set exists on the nature and thickness of the Iceland crust. This paper relates topography, i.e., elevation and bathymetry (TOP), Bouguer gravity anomalies (BA) and Moho depths to each other to assess the consequences of the “thick crust model” for Iceland in the context of the North Atlantic. Results of regression of TOP and BA vs. Moho depth are converted into “Airy densities” Δρ* (mantle crust density contrasts in the case of ideal Airy isostasy). For Iceland, Δρ* is very low (105±10 kg/m3); for the adjacent continental margins and relicts, it is high and intermediate for the Jan Mayen Ridge. The values are affected by lithosphere cooling and systematic variations of i…

Temporal evolution of the Fogo Volcano magma storage system (Cape Verde Archipelago): a fluid inclusions perspective

2023

The architecture of the magma storage system underneath Fogo Volcano (Cape Verde Archipelago) is characterised using novel fluid inclusion results from fifteen basanites, spanning the last 120 thousand years of volcanic activity, and encompassing a major flank collapse event at -73 ka. Fluid inclusions, hosted in olivine and clinopyroxene, are made of pure CO2, and based on their textural characteristics, are distinguished in early (Type I) and late (Type II) stage. Inclusions homogenize to a liquid phase in the 2.8 to 30.8 degrees C temperature range. Densities values, recalculated assuming an original 10% H2O content at the time of trapping, range from 543 to 952 kg center dot m(-3), and …

Eastern Pontides and Black Sea: gravity inversion, crustal structure, isostasy and geodynamics

2002

Abstract Lacking detailed seismic data on the crustal structure of Anatolia and the transition to the Black Sea, it is attempted to invert gravity for crust-mantle structure with constraints from the limited a priori information available, as average continental and oceanic crust, local topography, an isostatic model, published marine seismic data and a tentative “fix point” from recent seismological receiver functions near the Black Sea coast. An initial 2D-model for a north–south profile along about 40°E longitude is constructed and adjusted to fit the Bouguer anomaly taken from a published Turkish map and results from satellite radar altimetry. Isostasy, seismic data and gravity inversio…

Partial Melting and Counterclockwise P T Path of Subducted Oceanic Crust (Sierra del Convento Melange, Cuba)

2007

Interannual to decadal variability of summer sea surface temperature in the Sea of Okhotsk recorded in the shell growth history of Stimpson's hard cl…

2017

Abstract Sclerochronological and shell stable oxygen isotopic analyses were conducted on live-caught specimens of Stimpson's hard clams, Mercenaria stimpsoni , from the southern Sea of Okhotsk, off northern Hokkaido, Japan. In this region, the main growing season of this species during early ontogeny (below the age of 12 years) lasts from mid-spring to mid-fall at sea surface temperatures (SST) between approximately 10 and 22 °C. Growth cessation begins between late fall and early spring at SST, below approximately 6 °C; however, shell growth was largely limited to the summer season later in life. Counting of annual increments indicated that this species had a relatively long life span of u…

Geochronology of the mid-German crystalline rise west of the River Rhine

1996

The mid-German crystalline rise has its westernmost exposures at the western margin of the Rhine graben in the southern Pfalz and the northern Alsace. The outcrops are made up of granitoid rocks and minor volcano-sedimentary sequences. Radiometric ages obtained by U/Pb, Pb/Pb, Sm/Nd and Rb/Sr analyses of the igneous rocks from this area range from ∼433 to ∼325 Ma thus covering a time span from the Silurian to the end of the lower Carboniferous. Because the investigated rocks are — according to their chemical composition — largely related to subduction zone environments, the following three geodynamical scenarios are postulated, always taking subduction of oceanic crust beneath the mid-Germa…

Modeling Volcanic Eruption Parameters by Near-Source Internal Gravity Waves

2016

AbstractVolcanic explosions release large amounts of hot gas and ash into the atmosphere to form plumes rising several kilometers above eruptive vents, which can pose serious risk on human health and aviation also at several thousands of kilometers from the volcanic source. However the most sophisticate atmospheric models and eruptive plume dynamics require input parameters such as duration of the ejection phase and total mass erupted to constrain the quantity of ash dispersed in the atmosphere and to efficiently evaluate the related hazard. The sudden ejection of this large quantity of ash can perturb the equilibrium of the whole atmosphere triggering oscillations well below the frequencie…

Detecting the chaotic nature of advection in complex river flows

2012

In order to detect signatures of chaotic advection in river surface motion, surface buoys equipped with GPS were deployed in a field experiment in River Danube, Hungary. The buoys were released in the vicinity of groynes where complex mixing processes occur. A detailed analysis of the trajectories was carried out, focusing on the time evolution of the distance between buoy pairs. The analysis included the determination and comparison of local Lyapunov exponents and prediction times of finite-time hyperbolic behaviour, which is related to strong mixing. Despite of the small number of applied buoys we found evidence on Lagrangian chaos in the wake of a groyne field. In order to supplement the…

Adhesive root hairs facilitate Posidonia oceanica seedling settlement on rocky substrates

2015

Posidonia oceanica, the dominant Mediterranean seagrass, has been historically described as a species typically growing on mobile substrates whose development requires precursor communities. During more than 10 years of direct observations, we noticed that P. oceanica seedlings were often firmly anchored to rocky reefs, even at exposed sites. Thus, we analysed the ultrastructural features of seedling root systems to identify specific traits that may represent adaptations for early seedling anchorage on rocky bottoms. Subapical sections of adventitious roots were obtained from 2-3 months old specimens collected in the field and were observed at SEM revealing an extensive coverage of adhesive…