A new large-scale gravitational complex discovered in the Gulf of Squillace (central Mediterranean): tectonic implications.

Seismic reflection (2D/3D), borehole and bathymetric data are used to recognize a new gravitational complex in the Gulf of Squillace, Southern Italy, named the Squillace Complex. The complex has a NE-striking headwall connected to a basal detachment formed between Messinian evaporites and Tortonian shales. Its sense of movement changes to a W-E direction in the toe region. In plan view, the Squillace Complex is marked by the presence of sinuous and continuous seafloor scarps, just a few kilometers offshore, over an elongated morphological high. Seismic-well ties reveal that the complex was initiated in the Zanclean (~ 4 Ma) and continued its movement into the Gelasian (~ 2.1 Ma) at an average rate of 1.9 mm/year. Movement slowed down in the Calabrian (middle Pleistocene) and continued until the present day at a lower rate of 0.1 mm/year. Gravitational collapse of the Squillace Complex correlates with discrete contractional/transpressional events affecting the Calabrian region, which caused basin shortening and the temporary arrest of Calabrian Arc migration. These episodes resulted in tectonic uplift in the study area after 0.45 Ma (Late Pleistocene). Conversely, the complex's slower movement recorded since the Calabrian (middle Pleistocene) is associated with slab rollback of the Ionian plate under the Calabrian Arc.

Combined oil spill modelling and shoreline sensitivity analysis for contingency planning in the Irish Sea.

Offshore oil spills often result in severe environmental and socio-economic consequences. This work focuses on a busy, yet poorly studied part of NW Europe, the Irish Sea, to assess the impact of future oil spills on the nearby coast. By integrating numerical models and shoreline sensitivity analyses for two confined areas, Liverpool Bay and Milford Haven, this work acknowledges wind direction and speed as principal controls on the movement of oil under winter/storm conditions and in shallow waters. Ocean currents play a secondary role, but are significant in deeper waters and in low-wind summer conditions. The temporal elements used in the modelling thus stress that when the spill occurs is just as important as where. As a corollary, the fate of spilled oil is determined in this work for distinct scenarios and types. Response strategies are recommended to minimise the impact of future spills on coastal populations.

Submarine canyon systems focusing sub-surface fluid in the Canterbury Basin, South Island, New Zealand.

This work uses a high-quality 3D seismic volume from offshore Canterbury Basin, New Zealand, to investigate how submarine canyon systems can focus sub-surface fluid. The seismic volume was structurally conditioned to improve the contrast in seismic reflections, preserving their lateral continuity. It reveals multiple pockmarks, eroded gullies and intra-slope lobe complexes occurring in association with the Waitaki Submarine Canyon. Pockmarks are densely clustered on the northern bank of the canyon and occur at a water depth of 500-900 m. In parallel, near-seafloor strata contain channel-fill deposits, channel lobes, meandering channel belts and overbank sediments deposited downslope of the submarine canyon. We propose that subsurface fluid migrates from relatively deep Cretaceous strata through shallow channel-fill deposits and lobes to latter seep out through the canyon and associated gullies. The new, reprocessed Fluid Cube meta-attribute confirms that fluids have seeped out through the eroded walls of the Waitaki Canyon, with such a seepage generating seafloor depressions in its northern bank. Our findings stress the importance of shallow reservoirs (channel-fill deposits and lobes) as potential repositories for fluid, hydrocarbons, or geothermal energy on continental margins across the world.

Scientific, societal and pedagogical approaches to tackle the impact of climate change on marine pollution.

Marine pollution impacts coastal nations around the world, and more so: (a) in confined maritime areas with significant marine traffic, (b) where exploitation of natural and mineral resources is taking place, or (c) in regions witnessing pressure from tourism, local population growth, and industry. In this work, Digital Elevation Models, hydrographic, and climatic data are used together with computer simulations to understand the control of climate change on marine pollution. The results show that different climate change signals can potentially alter the flow and concentration of pollution in the European Seas, when compared to the present day. Ultimately, this work identifies the main sources of marine pollution as: (1) rivers and streams near cities and industrialised areas, (2) coastal areas experiencing sudden demographic pressures, (3) offshore shipping lanes in which oil and other marine debris are released, and (4) areas of rugged seafloor where industrial fishing takes place. This paper finishes by describing new educational material prepared to teach school children around the world. It explains why how a new training curriculum and e-game developed by Sea4All can be crucial in future Environmental Education and Education for a Sustainable Development.

Inter-core crosstalk in weakly coupled MCFs with arbitrary core layout and the effect of bending and twisting on the coupling coefficient.

We investigate the bending and twisting-induced longitudinal variation of the inter-core coupling coefficient (ICCC) and its effect on inter-core crosstalk (ICXT) in weakly coupled multi-core fibers (MCFs) with an arbitrary core layout. An analytical discrete changes model (DCM) for ICXT field propagation under those conditions is proposed for the first time, providing very fast and rather accurate mean ICXT power estimates. The analytical mean ICXT power estimates are validated through numerical simulation. It is predicted that the mean ICXT power between adjacent cores of the outer ring of the 19-core MCF can be more than 10 dB higher than the one between adjacent cores of the inner ring. It is also predicted that the difference between the mean ICXT power of cores in the inner and outer rings can be much smaller by decreasing the core pitch and increasing the bending radius. This behavior is attributed to the ICXT dependence on the bending and twisting-induced longitudinal variation of the ICCCs. In particular, larger bending and twisting-induced fluctuations of the ICCCs along the longitudinal coordinate are observed in the cores of the outer ring, but the fluctuations become smaller for smaller core pitches and larger bending radii. Furthermore, it is shown that, if the ICCCs' longitudinal variation is neglected, the mean ICXT power estimates between two adjacent cores are very similar despite the location of those cores. This means that neglecting the longitudinal variation of the ICCCs can lead to misleading estimates of the mean ICXT power, with an error exceeding 15 dB.

Characterization of the stochastic time evolution of short-term average intercore crosstalk in multicore fibers with multiple interfering cores.

A theoretical model for the stochastic time evolution of the intercore crosstalk (ICXT) in homogeneous weakly-coupled multicore fibers (MCF) with multiple interfering cores is proposed and validated experimentally. The model relies on the introduction of non-stationary time varying random phase shifts at every center point between the phase matching points of the MCF where the difference of the effective refractive indexes of the core of the originating signal and the core suffering from ICXT is zero. Closed form-expressions for the autocovariance of the short-term average ICXT (STAXT) with stationary and non-stationary phase shift models in MCFs with multiple excited cores are derived and validated by comparison with experimental results. These expressions enable estimating the decorrelation time of the STAXT generated by multiple interfering cores from the decorrelation times of the STAXT generated by each pair of cores. The proposed model and the ICXT measurements taken continuously over more than 150 hours show that the decorrelation time of the STAXT generated by multiple interfering cores exceeds the one obtained for the pair of cores with shorter decorrelation time. The proposed model is increasingly important to simulate and design MCF-based systems where the ICXT dynamics must be properly accounted for to develop efficient ICXT-tolerant techniques.

Performance of adaptive DD-OFDM multicore fiber links and its relation with intercore crosstalk.

Adaptive direct-detection (DD) orthogonal frequency-division multiplexing (OFDM) is proposed to guarantee signal quality over time in weakly-coupled homogenous multicore fiber (MCFs) links impaired by stochastic intercore crosstalk (ICXT). For the first time, the received electrical power of the ICXT and the performance of the adaptive DD-OFDM MCF link are experimentally monitored quasi-simultaneously over a 210 hour period. Experimental results show that the time evolution of the error vector magnitude due to the ICXT can be suitably estimated from the normalized power of the detected crosstalk. The detected crosstalk results from the beating between the carrier in the test core and ICXT originating from the carrier and modulated signal from interfering core. The results show that the operation of DD-OFDM systems employing fixed modulation can be severely impaired by the presence of ICXT that may unpredictable vary in both power and frequency. The system may suffer from deleterious impact of moderate ICXT levels over a time duration of several hours or from peak ICXT levels occurring over a number of minutes. Such power fluctuations can lead to large variations in bit error ratio (BER) for static modulation schemes. Here, we show that BER fluctuations may be minimized by the use of adaptive modulation techniques and that in particular, the adaptive OFDM is a viable solution to guarantee link quality in MCF-based systems. An experimental model of an adaptive DD-OFDM MCF link shows an average throughput of 12 Gb/s that represents a reduction of only 9% compared to the maximum throughput measured without ICXT and an improvement of 23% relative to throughput obtained with static modulation.

Multidisciplinary oil spill modeling to protect coastal communities and the environment of the Eastern Mediterranean Sea.

We present new mathematical and geological models to assist civil protection authorities in the mitigation of potential oil spill accidents in the Eastern Mediterranean Sea. Oil spill simulations for 19 existing offshore wells were carried out based on novel and high resolution bathymetric, meteorological, oceanographic, and geomorphological data. The simulations show a trend for east and northeast movement of oil spills into the Levantine Basin, affecting the coastal areas of Israel, Lebanon and Syria. Oil slicks will reach the coast in 1 to 20 days, driven by the action of the winds, currents and waves. By applying a qualitative analysis, seabed morphology is for the first time related to the direction of the oil slick expansion, as it is able to alter the movement of sea currents. Specifically, the direction of the major axis of the oil spills, in most of the cases examined, is oriented according to the prevailing azimuth of bathymetric features. This work suggests that oil spills in the Eastern Mediterranean Sea should be mitigated in the very few hours after their onset, and before wind and currents disperse them. We explain that protocols should be prioritized between neighboring countries to mitigate any oil spills.

Modelling of oil spills in confined maritime basins: The case for early response in the Eastern Mediterranean Sea.

Oil spill models are combined with bathymetric, meteorological, oceanographic, and geomorphological data to model a series of oil spill accidents in the Eastern Mediterranean Sea. A total of 104 oil spill simulations, computed for 11 different locations in the Levantine Basin, show that oil slicks will reach the coast of Cyprus in four (4) to seven (7) days in summer conditions. Oil slick trajectories are controlled by prevailing winds and current eddies. Based on these results, we support the use of chemical dispersants in the very few hours after large accidental oil spills. As a corollary, we show shoreline susceptibility to vary depending on: a) differences in coastline morphology and exposure to wave action, b) the existence of uplifted wave-cut platforms, coastal lagoons and pools, and c) the presence of tourist and protected environmental areas. Mitigation work should take into account the relatively high susceptibility of parts of the Eastern Mediterranean.

A three-step model to assess shoreline and offshore susceptibility to oil spills: the South Aegean (Crete) as an analogue for confined marine basins.

This study combines bathymetric, geomorphological, geological data and oil spill predictions to model the impact of oil spills in two accident scenarios from offshore Crete, Eastern Mediterranean. The aim is to present a new three-step method of use by emergency teams and local authorities in the assessment of shoreline and offshore susceptibility to oil spills. The three-step method comprises: (1) real-time analyses of bathymetric, geomorphological, geological and oceanographic data; (2) oil dispersion simulations under known wind and sea current conditions; and (3) the compilation of final hazard maps based on information from (1) and (2) and on shoreline susceptibility data. The results in this paper show that zones of high to very-high susceptibility around the island of Crete are related to: (a) offshore bathymetric features, including the presence of offshore scarps and seamounts; (b) shoreline geology, and (c) the presence near the shore of sedimentary basins filled with unconsolidated deposits of high permeability. Oil spills, under particular weather and oceanographic conditions, may quickly spread and reach the shoreline 5-96 h after the initial accident. As a corollary of this work, we present the South Aegean region around Crete as a valid case-study for confined marine basins, narrow seaways, or interior seas around island groups.

Analytical characterization of four wave mixing effect in direct-detection double-sideband OFDM optical transmission systems.

A closed-form expression for the variance of the four-wave mixing (FWM) induced in each subcarrier of a double sideband orthogonal frequency division multiplexing (OFDM) system employing direct detection is proposed and validated. Particularly, using a small signal analysis, equivalent transfer functions that characterize the frequency response of the FWM effect are derived taking into account the walkoff effect between the modulated pump waves and the FWM wave. The accuracy of the variance estimates provided by the closed-form expression is assessed for different sets of system parameters. The closed-form expression provides good variance estimates of the FWM-induced degradation caused by degenerate and nonsymmetric nondegenerate FWM components. For symmetric non-degenerate FWM components, the proposed expression provides reliable but pessimistic variance estimates, not exceeding the actual FWM variance in 1.5 dB for modulation indexes of interest.

Transmission of OFDM wired-wireless quintuple-play services along WDM LR-PONs using centralized broadband impairment compensation.

The simultaneous transmission of four orthogonal frequency-division multiplexing (OFDM)-based signals used to provide quintuple-play services along wavelength division multiplexing (WDM) long-reach passive optical networks (LR-PONs) is demonstrated experimentally. Particularly, the transmission performance of custom signal bearing Gigabit Ethernet data, Worldwide Interoperability for Microwave Access, Long Term Evolution and Ultra Wideband (sub-bands 2 and 3) signals is evaluated for different LR-PONs reaches, considering single-wavelength and WDM transmission, and using a centralized impairment compensation technique at the central office that is transparent to the services provided.It is shown that error vector magnitude-compliant levels are obtained for all the OFDM-based signals in WDM LR-PONs reaching 100 km and that negligible inter-channel crosstalk is obtained for a channel spacing of 100 GHz regardless the OFDM-based signal considered. The successful multi-format OFDM transmission along the 100 km-long WDM LR-PON is achieved in the absence of optical dispersion compensation or single sideband modulation, and it is enabled by the performance improvement provided by the centralized impairment compensation realized.

SNR approach for performance evaluation of time-stretching photonic analogue to digital converter system.

A semi-analytical simulation method (SASM) is proposed to evaluate the signal-to-noise ratio (SNR) of time stretched signals at the output of photonic analogue-to-digital converter (Ph-ADC) system. Analytical expressions of the signal at Ph-ADC output considering generic electrical signals applied to the electro-optic modulators of the Ph-ADC are derived. The contribution to the total variance of the received signal from the noise introduced by the electrical transmitter and receiver, and by the optical amplifier are derived analytically taking into account the pulsed nature of the optical signal. The proposed SASM shows excellent agreement of SNR estimates with the estimates provided by Monte Carlo simulation. This result is confirmed for variance dominantly imposed by the noise introduced by the electrical transmitter, by the optical amplifier and by the electrical receiver. A simplified approach is also proposed and compared with previous work. It is shown that mean power estimates obtained from this simplified approach are valid while the modulator is operating in the linear region and the signal is not affected by the frequency response of the electrical receiver filter. Additionally, it is concluded that the estimates of the noise variance due to the electrical transmitter are acceptable when a small signal analysis of noise along the Ph-ADC is valid.

Semi-analytical approach for performance evaluation of direct-detection OFDM optical communication systems.

A semi-analytical method to evaluate the bit error ratio (BER) in direct-detection (DD) optical fibre transmission systems employing orthogonal frequency division multiplexing (OFDM) and optically pre-amplified receivers is proposed. The method considers a Gaussian approach for the signal at the equalizer output and allows evaluating accurately the BER of each OFDM subcarrier for the receiver structure considered and for practical optical and electrical filters shapes, being a powerful tool to perform the optimization of these systems. The results obtained by the proposed method have shown excellent agreement with Monte Carlo estimates for DD-OFDM ultra-wideband radio signals and for two different DD-OFDM signals proposed for long-haul systems.