/library/oar/handle/123456789/13767 2025-12-15T18:17:05Z /library/oar/handle/123456789/141939 Title: Long short-term memory neural networks for forecasting sea level and seiche occurrences in the Maltese Islands Authors: Borg, Nicole; Sammut, Fiona; Suda, David; Gauci, Adam; Deidun, Alan Abstract: The ability to predict seiches can help prevent the damage and mitigate the risks associated with these natural phenomena. This paper presents a novel approach for seiche prediction in Marsaxlokk, Malta, using Long Short-Term Memory (LSTM) neural network models. The LSTM models are implemented on time series data obtained from two tide gauge stations installed in Marsaxlokk and Portomaso, Malta. Two recurrent neural networks, the Vanilla recurrent neural network (RNN) models and gated recurrent unit (GRU) models, along with time-lagged multiple linear regression models are also fitted as baseline models. Due to the presence of missing data, this paper also explores the use of gap filling methods to obtain complete datasets for the recurrent neural network model training and testing. Two variants of each recurrent neural network model are presented. These are trained on the Portomaso dataset and tested on the Marsaxlokk dataset with the second version of each model involving calibration. The significantly superior calibrated LSTM model was able to identify with good precision the seiches that occurred on November 28, 2021 and June 30, 2022 and to also model the long-term dependencies that are important for predicting sea levels with enough lead time. 2025-01-01T00:00:00Z /library/oar/handle/123456789/141936 Title: Wind and seasonal variabilities of concentrations of oxides of nitrogen, measured at Giordan Lighthouse Geosciences Observatory, Gozo (Maltese Archipelago) Authors: Saliba, Martin; Micallef, Alfred Abstract: Concentrations of oxides of nitrogen (NOx), as the sum total of nitric oxide (NO) and nitrogen dioxide (NO2), the individual parts, i.e., NO and NO2, (NOx = NO + NO2), and wind speed and direction measurements were gathered over a thirteen-year period (2011–2023) at the Giordan Lighthouse Geosciences Observatory, located on the Island of Gozo, forming part of the Maltese Archipelago (Central Mediterranean). The atmospheric concentration measurements were recorded with a Thermo Scientific Model 42i NOx analyser, which employs the chemiluminescence technique to detect atmospheric traces of NOx concentrations. In this case study, an investigation was conducted to understand the wind and seasonal variabilities of the measured concentrations. The highest NOx concentrations occurred when the prevailing wind originated from the SE, while a broad minimum was observed when the wind blew from the S–W sector. The maxima were primarily associated with land-based sources, predominantly vehicular emissions on the main island, i.e., Malta. The amplitudes for NO, NO2, and NOx in relation to wind direction were 63%, 125%, and 121%, respectively. Significant variabilities were observed during the autumn season. Regarding wind speed, the NOx concentrations reached their peak during high-wind-speed events, which are associated with transboundary pollution. A secondary broad maximum was observed for wind forces between 2 and 4, while the lowest concentrations were recorded at wind force 9. The NOx concentrations exhibited a seasonal maximum in spring and a minimum in winter, which contrasts with the findings from the Monte Cimone station in Italy. The seasonal amplitudes for NO, NO2, and NOx were 46%, 15%, and 17%, respectively. It is evident that NO concentrations exhibited a greater seasonal variability, whereas NO2 concentrations demonstrated significant variability in relation to wind direction. 2025-01-01T00:00:00Z /library/oar/handle/123456789/139799 Title: Modelling the influence of erosive fluidization on the morphology of fluid flow and escape structures Authors: Gupta, Shubhangi; Micallef, Aaron Abstract: Focused fluid flow through sub-seafloor pipes and chimneys, and their seafloor manifestations as pockmarks, are ubiquitous. However, the dynamics of flow localization and evolution of fluid escape structures remain poorly understood. Models based on geomechanical mechanisms like hydro-fracturing and porosity wave propagation offer some useful insights into fluid flow and escape dynamics, but face limitations in capturing features like mobilized granular matter, especially in the upper sediment layers where the link between fracture and pockmark is not always clear. Here, we propose a mathematical model based on the multiphase theory of porous media, where changes in subsurface and seafloor morphology are resolved through seepage-induced erosion, fluidization, transport, and re-deposition of granular material. Through simulation of an idealized scenario of gas escape from overpressured shallow gas reservoir, we demonstrate that our model can capture flow localization and formation of pipes, chimneys, and pockmarks. Our simulations show (1) formation of conical focused-flow conduits with a brecciated core and annular gas channels; (2) pockmarks of W and ring shapes; and (3) pulsed release of gas. Sediment erodibility and flow anisotropy control the morphology of focused fluid flow and escape structures,while permeability shows negligible impact. While the geological setting for this study is theoretical, we show that our results have real-world analogs. 2023-01-01T00:00:00Z /library/oar/handle/123456789/139241 Title: The first record of the non-indigenous 𝘈𝘤𝘢𝘯𝘵𝘩𝘶𝘳𝘶𝘴 𝘹𝘢𝘯𝘵𝘩𝘰𝘱𝘵𝘦𝘳𝘶𝘴 Valenciennes, 1835 (Actinopterygii: Acanthuridae) in Sicilian waters suggests a rapid westward dispersal in the Mediterranean Authors: Insacco, Gianni; Corsini-Foka, Maria; Zava, Bruno; Crobe, Valentina; Tinti, Fausto; Deidun, Alan Abstract: A sub-adult individual of Acanthurus xanthopterus Valenciennes, 1835 was caught from the shallow waters off the southeastern coast of Sicily, Italy, in autumn 2024. The subsequent taxonomic species identification was carried out through integrated morphological and molecular analyses. The species is recorded for the first time from Italian waters. This record, that comes just three years after its first collection from Egyptian Mediterranean waters, seems to indicate a rapid westward expansion of this tropical Indo-Pacific acanthurid from the east to the central Mediterranean Sea, although additional (and independent) introduction events could be contemplated, due to the current scarcity of distribution data for the species. 2025-01-01T00:00:00Z