Options
Geraga, Maria
Loading...
Preferred name
Geraga, Maria
ORCID
4 results
Now showing 1 - 4 of 4
- PublicationOpen AccessGas Seepage-Induced Features in the Hypoxic/Anoxic, Shallow, Marine Environment of Amfilochia Bay, Amvrakikos Gulf (Western Greece)(2021-01-05)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Amfilochia Bay (Eastern Amvrakikos Gulf, Western Greece), a complex marine area affected by tectonism, was investigated for seabed seepage manifestations and for possible inter-relationships between shallow gas accumulations and hypoxia. For this purpose, an integrated research methodology that combined geophysical, geochemical, and hydrographic surveys was applied. Marine geophysical and bathymetric surveys led to the discovery of a gas-induced pockmark group in the study area. Oceanographic surveying confirmed that the bay is hypoxic/anoxic below a depth of 15 m (dissolved oxygen from ~4 to 60 μM). Very weak CH4 seepage was detected in correspondence to the pockmark group that seemed to slightly enhance the hypoxic environment locally and close to the seabed, with no effect in shallower waters and the oxycline. Methane isotopic analysis showed variable carbon isotopic composition (from −41‰ to −86‰) which could be either related to differential CH4 oxidation or mixing between microbial and thermogenic gas. However, the pathway of degassing is clearly related to the fault-controlled pockmark group. A protrusion mound, which has erroneously been reported as a submarine “volcano” since 1876, could be the result of mud volcanism based on the geophysical data of this study.174 46 - PublicationOpen AccessInvestigating hypoxia in aquatic environments: diverse approaches to addressing a complex phenomenon(2014)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Friedrich, J. ;Janssen, F. ;Aleynik, D. ;Bange, H. W. ;Boltacheva, N. ;Çagatay, M. N. ;Dale, A. W. ;Etiope, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Erdem, Z. ;Geraga, M. ;Gilli, A. ;Gomoiu, M. T. ;Hall, P. O. J. ;Hansson, D. ;He, Y. ;Holtappels, M. ;Kirf, M. K. ;Kononets, M. ;Konovalov, S. ;Lichtschlag, A. ;Livingstone, D. M. ;Marinaro, G. ;Mazlumyan, S. ;Naeher, S. ;North, R. P. ;Papatheodorou, G. ;Pfannkuche, O. ;Prien, R. ;Rehder, G. ;Schubert, C. J. ;Soltwedel, T. ;Sommer, S. ;Stahl, H. ;Stanev, E. V. ;Teaca, A. ;Tengberg, A. ;Waldmann, C. ;Wehrli, B. ;Wenzhöfer, F. ; ; ; ; ; ; ;; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;In this paper we provide an overview of new knowledge on oxygen depletion (hypoxia) and related phenomena in aquatic systems resulting from the EU-FP7 project HYPOX (“In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and landlocked water bodies”, www.hypox.net). In view of the anticipated oxygen loss in aquatic systems due to eutrophication and climate change, HYPOX was set up to improve capacities to monitor hypoxia as well as to understand its causes and consequences. Temporal dynamics and spatial patterns of hypoxia were analyzed in field studies in various aquatic environments, including the Baltic Sea, the Black Sea, Scottish and Scandinavian fjords, Ionian Sea lagoons and embayments, and Swiss lakes. Examples of episodic and rapid (hours) occurrences of hypoxia, as well as seasonal changes in bottom-water oxygenation in stratified systems, are discussed. Geologically driven hypoxia caused by gas seepage is demonstrated. Using novel technologies, temporal and spatial patterns of watercolumn oxygenation, from basin-scale seasonal patterns to meter-scale sub-micromolar oxygen distributions, were resolved. Existing multidecadal monitoring data were used to demonstrate the imprint of climate change and eutrophication on long-term oxygen distributions. Organic and inorganic proxies were used to extend investigations on past oxygen conditions to centennial and even longer timescales that cannot be resolved by monitoring. The effects of hypoxia on faunal communities and biogeochemical processes were also addressed in the project. An investigation of benthic fauna is presented as an example of hypoxia-devastated benthic communities that slowly recover upon a reduction in eutrophication in a system where naturally occurring hypoxia overlaps with anthropogenic hypoxia. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on the microbially mediated redox cycling of elements. Observations and modeling studies of the sediments demonstrate the effect of seasonally changing oxygen conditions on benthic mineralization pathways and fluxes. Data quality and access are crucial in hypoxia research. Technical issues are therefore also addressed, including the availability of suitable sensor technology to resolve the gradual changes in bottom-water oxygen in marine systems that can be expected as a result of climate change. Using cabled observatories as examples, we show how the benefit of continuous oxygen monitoring can be maximized by adopting proper quality control. Finally, we discuss strategies for state-of-the-art data archiving and dissemination in compliance with global standards, and how ocean observations can contribute to global earth observation attempts.470 247 - PublicationRestrictedThe geological links of the ancient Delphic Oracle (Greece): A reappraisal of natural gas occurrence and origin(2006)
; ; ; ; ; ;Etiope, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Papatheodorou, G.; Department of Geology, University of Patras, Rio, 26500 Patras, Greece ;Christodoulou, D.; Department of Geology, University of Patras, Rio, 26500 Patras, Greece ;Geraga, M.; Department of Geology, University of Patras, Rio, 26500 Patras, Greece ;Favali, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; ; Recent studies have speculated that the prophetic powers of Pythia, the woman of the Delphic Oracle, at the Temple of Apollo in Greece, were induced by hydrocarbon vapors, specifically ethylene, rising from bedrock fissures at the intersection of the E-W Delphi fault with the NNW-SSE Kerna fault, and producing neurotoxic effects, including trance and delirium. New surveys including gas flux from soil, gas in groundwater, and isotopic analyses of spring scales, provide the experimental confirmation of the gas release in the Delphi area. Presently, methane, ethane, and carbon dioxide are being released from a thermogenic (catagenetic) hydrocarbon-prone environment. This environment is not prone to biogenic production of ethylene in amounts inducing neurotoxic effects (hundreds or thousands of ppmv). A WNW-ESE–trending subsidiary fault within the Delphi fault zone, extending for 2 km, passes under the Temple of Apollo and shrine of Athena. The Temple of Apollo, located above this fault, may have been the site of enhanced degassing in the past. If gas-linked neurotoxic effects upon Pythia need to be invoked, they should be sought in the possibility of oxygen depletion due to CO2-CH4 exhalation in the indoor temple. Alternatively, a plausible geological explanation behind the natural presence of sweet scents could be the occurrence of aromatic hydrocarbons, such as benzene, dissolved in the groundwater spring.205 58 - PublicationOpen AccessGeophysical and Geochemical Exploration of the Pockmark Field in the Gulf of Patras: New Insights on Formation, Growth and Activity(2023)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ;The Patras Gulf Pockmark field is located in shallow waters offshore Patras City (Greece) and is considered one of the most spectacular and best-documented fluid seepage activities in the Ionian Sea. The field has been under investigation since 1996, though surveying was partially sparse and fragmentary. This paper provides a complete mapping of the field and generates new knowledge regarding the fluid escape structures, the fluid pathways, their origin and the link with seismic activity. For this, data sets were acquired utilising high-resolution marine remote sensing techniques, including multibeam echosounders, side-scan sonars, sub-bottom profilers and remotely operated vehicles, and laboratory techniques focusing on the chemical composition of the escaping fluids. The examined morphometric parameters and spatial distribution patterns of the pockmarks are directly linked to tectonic structures. Acoustic anomalies related to the presence of gas in sediments and in the water column document the activity of the field at present and in the past. Methane is the main component of the fluids and is of microbial origin. Regional and local tectonism, together with the Holocene sedimentary deposits, appear to be the main contributors to the growth of the field. The field preserves evidence that earthquake activity prompts the activation of the field.49 11