1,720,982 research outputs found
MESOSCALE AND SUB-MESOSCALE VARIABILITY ALONG THE COASTS OF THE EASTERN SOUTHERN EASTERN TYRRHENIAN SEA
No full textHYDROGRAPHIC CHARACTERISTICS OF WATER MASSES AND CIRCULATION IN THE NORTHERN IONIAN SEA
No full textThe hydrography of intermediate and deep water masses in the Northern Ionian Sea (Apulian Plateau) was studied through four quasi-synoptic multidisciplinary surveys carried out in 2004-2006 as an ancillary oceanographic activity in the frame of the APLABES project. This area plays a crucial role for the entire Mediterranean Basin, being influenced by the water outflow of Adriatic origin, which, under severe winter conditions, is a primary source of dense water for the Eastern Mediterranean. At the end of the 1980s such outflow showed a different behavior, and only in the recent years has a gradual re-establishing of the former condition been detected. As such, the Adriatic Sea has regained its role as a main source of the East Mediterranean Deep Water, which was temporarily inhibited during the well known Eastern Mediterranean Transient which progressively modified the intermediate and deep layers of the Mediterranean Sea.
The general structure of water masses was similar through the investigated period, but interesting differences within the bottom layer have been detected. The interaction of the different water types present in the basin is reviewed by means of property-property plots, vertical sections, isopycnal analyses and using an Optimum Multiparameter Analysis (OMP), which is an objective method to measure the mixing of water masses. Due to the lack of any direct information about the dynamics of the water column in the area of the Apulian Plateau during the whole analyzed period, the classical method to infer the baroclinic velocity from the mass field has been applied to hydrographic data. The well-known indeterminacy of this method due to the barotropic component of the velocity field has been resolved using a short time series of current velocities acquired synoptically by a mooring located in the northern part of the studied area. The wavelet transform was adopted for localizing and quantifying the variability of currents simultaneously in both frequency and time domains.
The presence of the Adriatic Deep Water close to the bottom was detected on all four surveys, with different signature as underlined by the objectively analysis (with the Optimum Multiparameter Analysis) of the thermohaline field. A core of cold, less-saline and oxygenated water of Adriatic origin coming from the Otranto Channel was identified. This water mass moved in geostrophic balance along the isobaths at 600-1000 m depth at the isopycnal surface of 29.18 kg m-3, not being dense enough to reach the deeper layers of the Ionian Basin, carrying 0.27-0.36 Sv
New Insights into Tyrrhenian Sea Warming and Heat Penetration through Long-Term Expendable Bathythermograph Data
Full text linkThe warming trend of the Mediterranean region is already well known, but there is still a lack of information on its seasonal/annual to multidecadal time scales and its distribution in all water masses, including deep water. New temporal and spatial evidence of this thermal variability has been presented in the Tyrrhenian Sea, thanks to twenty-year continuous monitoring by eXpendable BathyThermographs (XBTs) along a fixed route from Genoa to Palermo. The Tyrrhenian Sea is one of the deepest Mediterranean sub-basins (with a maximum depth of about 4000 m), but its interaction with neighbouring basins is controlled by topographical factors, such as the Sardinian Channel to the south and the Corsican Channel to the north. The way in which the warm signal, originating from the Levantine sub-basin, and entering from the south, affects the entire Tyrrhenian Basin spreading rapidly northwards is studied, considering its peculiarities, such as topography, surface circulation, and strong stratification, as well as its climate variability. The warming trend observed for the Tyrrhenian Sea is consistent with the trend for the Mediterranean Sea as a whole. However, the Tyrrhenian Sea shows some peculiar features: around 2014, a shift to a new equilibrium (warmer) state was detected, with mean values along the monitored route that were significantly higher than the previous period (from 1999 to 2013), especially for the subsurface level, from 100 to 450 m depth
Anomalies of oxygen measurements performed with Aanderaa optodes
No full textFour sets of measurements performed between 2005 and 2010 in the deep central
Atlantic, the deep north-western Mediterranean Sea, and in the Arctic Ocean revealed
strange anomalies in the performance of the Aanderaa optode 3830 sensors mounted
on RCM11 current meters in low current regimes (current speeds >10 cm s–1). All
oxygen datasets collected during these deployments showed significant drops of oxygen
(50–100 ìmol) affecting the data stability of the optode sensors in low hydrodynamic
conditions.
High correlations between all acquired parameters (temperature, turbidity, speed and
direction of currents) verified that no unusual event occurred in the mooring areas
during the periods of acquisition, although natural events responsible for such abrupt,
short and intense oxygen variations cannot be easily identified. Despite the well-known
performance of the Aanderaa optodes, these experiments demonstrate that the data
acquired by those installed on RCM11s cannot be always reliable, especially in low
energy systems (typical for the deep ocean), and that current speeds should always be
considered in order to verify the reliability of the data recorded.Published29-391.8. Osservazioni di geofisica ambientaleJCR Journalreserve
Oceanographic signals at the Benthic Boundary Layer in the Mediterranean Sea
No full textThe Benthic Boundary Layer (BBL) is considered a quite homogeneous environment
where a wide variety of processes (chemical, physical, geological and biological) occur
often producing front structures or inducing turbulence phenomena. The typical
stratification of these zones can be interrupted by episodic events which effects can
diffuse to the ocean interior exploiting by local current and mixing processes.
According to hydrodynamic definition, the BBL thickness may vary from few millimetres
up to 100 metres depending on the friction intensity with the sea bed and the
stability of water column above it. Generally in deep-sea condition, the BBL thickness
is defined by the ratio between the friction velocity and the Coriolis parameter
according to the Ekman scale.
In the latest years several experiments have been carried out in the deep water of
Mediterranean Sea, focusing on the survey and study of benthic processes following
a multidisciplinary approach.
Benthic observatories, such as SN-1 and GEOSTAR, allow to record long time-series
of geochemical, seismological, geomagnetic, geodetic and oceanographic data and
allow to understand the dynamics and evolution of the processes though comparison
and interpolation of different types of signals.
From a oceanographic point of view, the technology of these benthic observatories
brings the possibility to observe and measure directly the hydrological properties at
the seafloor collecting data for long-time series and with high sampling rate.
The observatories deployed in Mediterranean Sea, have provided good information
about variations and oscillations of hydrological parameters in deep water where the monitoring is almost lacking.
In some cases it has been possible to link these deep-sea datasets with upper data
collected by ship-handled system during the same period or during different cruises.
This allows to have a more complete idea of the linkage between surface, intermediate
and bottom sea.
Hence the multidisciplinary approach represents a very important aspect for this kind
of study, because it allows not only a cross check of functionality among all the instruments
but also an important tool to recognise and better understand possible nonphysical-
oceanographic phenomena.PublishedVienna, Austriaope
Oceanographic signals at the Benthic Boundary Layer in the Mediterranean Sea
No full textThe Benthic Boundary Layer (BBL) is considered a quite homogeneous environment
where a wide variety of processes (chemical, physical, geological and biological) occur
often producing front structures or inducing turbulence phenomena. The typical
stratification of these zones can be interrupted by episodic events which effects can
diffuse to the ocean interior exploiting by local current and mixing processes.
According to hydrodynamic definition, the BBL thickness may vary from few millimetres
up to 100 metres depending on the friction intensity with the sea bed and the
stability of water column above it. Generally in deep-sea condition, the BBL thickness
is defined by the ratio between the friction velocity and the Coriolis parameter
according to the Ekman scale.
In the latest years several experiments have been carried out in the deep water of
Mediterranean Sea, focusing on the survey and study of benthic processes following
a multidisciplinary approach.
Benthic observatories, such as SN-1 and GEOSTAR, allow to record long time-series
of geochemical, seismological, geomagnetic, geodetic and oceanographic data and
allow to understand the dynamics and evolution of the processes though comparison
and interpolation of different types of signals.
From a oceanographic point of view, the technology of these benthic observatories
brings the possibility to observe and measure directly the hydrological properties at
the seafloor collecting data for long-time series and with high sampling rate.
The observatories deployed in Mediterranean Sea, have provided good information
about variations and oscillations of hydrological parameters in deep water where the monitoring is almost lacking.
In some cases it has been possible to link these deep-sea datasets with upper data
collected by ship-handled system during the same period or during different cruises.
This allows to have a more complete idea of the linkage between surface, intermediate
and bottom sea.
Hence the multidisciplinary approach represents a very important aspect for this kind
of study, because it allows not only a cross check of functionality among all the instruments
but also an important tool to recognise and better understand possible nonphysical-
oceanographic phenomena.PublishedVienna, Austriaope
Investigation of Benthic Boundary Layer processes through seafloor observatories
No full textThe investigation of the Benthic Boundary Layer (BBL) involves the study of a wide
spectrum of different, but connected, processes. In order to study the evolution of
physical, geochemical, geological and biological phenomena, and to comprehend their
possible relationships, a long-term monitoring with the seafloor observatory support
is necessary.
Unlike mooring approach, the sea bottom observatories represent a more stable platform
wherein a wide variety of instrument can be mounted, giving several advantages
on power autonomy and higher sampling rate. In addition, the shortest distance to the
bottom of observatory instruments, permits to appreciate even phenomena that can
happen close to the sea bottom.
The stable localisation of all the instruments at the same bottom depth and their accurate
unit time reference allow a relatively easier and efficient comparison of different
kind of signals recorded in situ, offering a new and interesting possibility to better
understand and describe possible benthic processes.
Although to collect long-time series often can give some instrumental drifting problems
(especially for the electrode sensors or, in shallow environment, due to bigger
befouling activity), an efficient instrumental pre and post-calibration, as well as the
possibility to collect water samples during the long period of measurements, guarantee
to restore the signals recorded during the data processing phases.
The versatility of these observatories then offers a good opportunity to investigate, in
the same time, different natural fields and with different instrumental approaches. In
addition, it permit to discover that the BBL is not at all a stable environment but, as all the interface layers, it is dominated by strong dynamics processes.PublishedVienna, AUSTRIAope
Investigation of Benthic Boundary Layer processes through seafloor observatories
No full textThe investigation of the Benthic Boundary Layer (BBL) involves the study of a wide
spectrum of different, but connected, processes. In order to study the evolution of
physical, geochemical, geological and biological phenomena, and to comprehend their
possible relationships, a long-term monitoring with the seafloor observatory support
is necessary.
Unlike mooring approach, the sea bottom observatories represent a more stable platform
wherein a wide variety of instrument can be mounted, giving several advantages
on power autonomy and higher sampling rate. In addition, the shortest distance to the
bottom of observatory instruments, permits to appreciate even phenomena that can
happen close to the sea bottom.
The stable localisation of all the instruments at the same bottom depth and their accurate
unit time reference allow a relatively easier and efficient comparison of different
kind of signals recorded in situ, offering a new and interesting possibility to better
understand and describe possible benthic processes.
Although to collect long-time series often can give some instrumental drifting problems
(especially for the electrode sensors or, in shallow environment, due to bigger
befouling activity), an efficient instrumental pre and post-calibration, as well as the
possibility to collect water samples during the long period of measurements, guarantee
to restore the signals recorded during the data processing phases.
The versatility of these observatories then offers a good opportunity to investigate, in
the same time, different natural fields and with different instrumental approaches. In
addition, it permit to discover that the BBL is not at all a stable environment but, as all the interface layers, it is dominated by strong dynamics processes.PublishedVienna, AUSTRIAope
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