109 research outputs found
Population dynamics advected by chaotic flows: a discrete-time map approach
A discrete-time model of reacting evolving fields, transported by a
bidimensional chaotic fluid flow, is studied. Our approach is based on the use
of a Lagrangian scheme where {\it fluid particles} are advected by a
symplectic map possibly yielding Lagrangian chaos. Each {\it fluid particle}
carries concentrations of active substances which evolve according to its own
reaction dynamics. This evolution is also modeled in terms of maps. Motivated
by the question, of relevance in marine ecology, of how a localized
distribution of nutrients or preys affects the spatial structure of predators
transported by a fluid flow, we study a specific model in which the population
dynamics is given by a logistic map with space-dependent coefficient, and
advection is given by the standard map. Fractal and random patterns in the
Eulerian spatial concentration of predators are obtained under different
conditions. Exploiting the analogies of this coupled-map (advection plus
reaction) system with a random map, some features of these patterns are
discussed.Comment: 22 pages, 5 figure
Contrasting surface warming of a marginal basin due to large-scale climatic patterns and local forcing
The Mediterranean Sea is one of the first regions where sea surface temperature (SST) increase
was linked to greenhouse effects and global warming. Due to its sensitivity to climate variability
and its high impact on local and remote climate conditions, much effort has been made to assess
the SST variability in the Mediterranean as a whole. However, the Mediterranean is composed of
several basins, each of which plays a different role in its conveyor belt’s function. This study focuses
on the basin of the Tyrrhenian Sea which represents one of the crucial areas for deep mixing of the
Mediterranean main water masses. Thirty-seven years (1982–2018) of satellite-derived data were
used to investigate the SST variability in relation to large-scale and local forcing mechanisms. A
significant warming trend of 0.034 ± 0.004 °C/year was found, which led to an average warming of
1.288 ± 0.129 °C over the considered period. The observed warming presents time-dependent spatial
patterns as well as changes in the seasonal cycle. Our results highlight that the Tyrrhenian’s individual
long-term surface variability has different characteristics than the Mediterranean as a whole and
provide insight into the relative influence of large-scale teleconnection patterns and local air-sea
interaction on this variability
Near-surface eddy dynamics in the Southern Ocean
The Antarctic Circumpolar Current (ACC) is a crucial component of the global ocean conveyor belt, acting as a zonal link among the major ocean basins but, to some extent, limiting meridional exchange and tending to isolate the ocean south of it from momentum and heat income. In this work we investigate one of the most important mechanisms contributing to the poleward transfer of properties in the Southern Ocean, that is the eddy component of the dynamics. For this particular purpose, observations obtained from near-surface drifters have been used: they represent a very useful data set to analyse the eddy field because of their ability to catch a large number of scales of motion while providing a quasi-synoptic coverage of the investigated area. Estimates of the eddy heat and momentum fluxes are carried out using data taken from the Global Drifter Program databank; they refer to Surface Velocity Program drifter trajectories collected in the area south of 358S between 1995 and 2006. Eddy kinetic energies, variance ellipses, momentum and heat fluxes have been calculated using the pseudo-Eulerian method, showing patterns in good agreement with those present in the literature based on observational and model data, although there are some quantitative differences. The eddy fluxes have been separated into their rotational and divergent portions, the latter being responsible for the meridional transports. The associated zonal and depth-exponentially integrated meridional heat transport exhibits values spanning over a range between -0.4 PW and -1.1 PW in the ACC region, consistent with previous estimates. Keywords: Antarctic Circumpolar Current; eddy fluxes; Global Drifter Program data; Lagrangian oceanography; Helmholtz decomposition (Published: 30 December 2011) Citation: Polar Research 2011, 30 , 11203, DOI: 10.3402/polar.v30i0.1120
"Pseudodiaptomus Marinus" Sato, 1913, a New Invasive Copepod in Lake Faro (Sicily): Observations on the Swimming Behaviour and the Sex-Dependent Responses to Food
Background: The calanoid copepod Pseudodiaptomus marinus Sato, 1913 is an estuarine-coastal species, living in shallow eutrophic inshore waters. It is native of the Indo-Pacific region, but in the last 50 years, it has successfully colonized new areas worldwide. P. marinus, first recorded in Lake Faro (Messina, Italy) in October 2008, is now a stable component of the zooplankton assemblage of the lake. By means of video recordings, for the first time, the swimming behaviour of males and non-ovigerous and ovigerous females of P. marinus has been studied. The individuals were filmed in the presence and absence of food to evaluate how the presence of prey might affect the swimming behaviour. Results: The swimming motion showed marked sex-dependent features and responses to the presence of food. Mechanisms through which behaviour might influence the outcome of a new colonization were analysed. The behaviour of P. marinus was then compared with that of the congeneric Pseudodiaptomus annandalei showing the typical behaviour displayed by the representatives of the genus Pseudodiaptomus of living in proximity of the bottom. Conclusions: Environmental and hydrological conditions in Lake Faro have likely provided the newly introduced P. marinus a suitable environment for settling, although normally the presence of an anoxic deep layer would be detrimental for a demersal species. In this case, the plasticity in the behaviour of P. marinus enhanced its capacity for colonising new environments. Switching from demersal to pelagic habitat or being fully planktonic allowed it to express its large individual variability in motion strategies and thus to successfully colonize the lake
Measurement of Sea Waves
Sea waves constitute a natural phenomenon with a great impact on human activities, and their monitoring is essential for meteorology, coastal safety, navigation, and renewable energy from the sea. Therefore, the main measurement techniques for their monitoring are here reviewed, including buoys, satellite observation, coastal radars, shipboard observation, and microseism analysis. For each technique, the measurement principle is briefly recalled, the degree of development is outlined, and trends are prospected. The complementarity of such techniques is also highlighted, and the need for further integration in local and global networks is stressed
Sea Storm Analysis: Evaluation of Multiannual Wave Parameters Retrieved from HF Radar and Wave Model
Intense atmospheric disturbances, which impact directly on the sea surface causing a significant increase in wave height and sometimes strong storm surges, have become increasingly frequent in recent years in the Mediterranean Sea, producing extreme concern in highly populated coastal areas, such as the Gulf of Naples (Western Mediterranean Sea, Central Tyrrhenian Sea). In this work, fifty-six months of wave parameters retrieved by an HF radar network are integrated with numerical outputs to analyze the seasonality of extreme events in the study area and to investigate the performance of HF radars while increasing their distances from the coast. The model employed is the MWM (Mediterranean Wind-Wave Model), providing a wind-wave dataset based on numerical models (the hindcast approach) and implemented in the study area with a 0.03° spatial resolution. The integration and comparison with the MWM dataset, carried out using wave parameters and spectral information, allowed us to analyze the availability and accuracy of HF sampling during the investigated period. The statistical comparisons highlight agreement between the model and the HF radars during episodes of sea storms. The results confirm the potential of HF radar systems as long-term monitoring observation platforms, and allow us to give further indications on the seasonality of sea storms under different meteorological conditions and on their energy content in semi-enclosed coastal areas, such as the Gulf of Naples
Energetic plumes over the western Ross Sea continental slope
Rapid descent of dense Drygalski Trough (western Ross Sea, Antarctica) shelf water over the continental slope, within 100 to 250 m thick benthic plumes, is described. Speeds of up to 1.0 m/s are recorded flowing at an average angle of 35° to the isobaths, entraining ambient Lower Circumpolar Deep Water en route. This process is predominant in determining the concentration and placement of the shelf water injected into the deep sea as a precursor Antarctic Bottom Water. Nonetheless, a 4-hour duration pulse of undiluted shelf water was observed at depth (1407 m) directly north of the Drygalski Trough, moving at around 90 degrees to isobaths, and at a speed of 1.4 m/s. Thus the export of Ross Sea shelf water to the deep sea is accomplished within plumes descending at moderate angle to isobaths, punctuated by rapid downhill cascades
A New Orbiting Deployable System for Small Satellite Observations for Ecology and Earth Observation
In this paper, we present several study cases focused on marine, oceanographic, and
atmospheric environments, which would greatly benefit from the use of a deployable system for
small satellite observations. As opposed to the large standard ones, small satellites have become an
effective and affordable alternative access to space, owing to their lower costs, innovative design
and technology, and higher revisiting times, when launched in a constellation configuration. One
of the biggest challenges is created by the small satellite instrumentation working in the visible
(VIS), infrared (IR), and microwave (MW) spectral ranges, for which the resolution of the acquired
data depends on the physical dimension of the telescope and the antenna collecting the signal. In
this respect, a deployable payload, fitting the limited size and mass imposed by the small satellite
architecture, once unfolded in space, can reach performances similar to those of larger satellites.
In this study, we show how ecology and Earth Observations can benefit from data acquired by
small satellites, and how they can be further improved thanks to deployable payloads. We focus on
DORA—Deployable Optics for Remote sensing Applications—in the VIS to TIR spectral range, and
on a planned application in the MW spectral range, and we carry out a radiometric analysis to verify
its performances for Earth Observation studies
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