This study highlights the potential of using a low frequency multibeam echosounder for detection ... more This study highlights the potential of using a low frequency multibeam echosounder for detection and visualization of shallow gas occurring several meters beneath the seafloor. The presence of shallow gas was verified in the Bornholm Basin, Baltic Sea, at 80 m water depth with standard geochemical core analysis and hydroacoustic subbottom profiling. Successively, this area was surveyed with a 95 kHz and a 12 kHz multibeam echosounder (MBES). The bathymetric measurements with 12 kHz provided depth values systematically deeper by several meters compared to 95 kHz data. This observation was attributed to enhanced penetration of the low frequency signal energy into soft sediments. Consequently, the subbottom geoacoustic properties contributed highly to the measured backscattered signals. Those appeared up to 17 dB higher inside the shallow gas area compared to reference measurements outside and could be clearly linked to the shallow gas front depth down to 5 m below seafloor. No elevated backscatter was visible in 95 kHz MBES data, which in turn highlights the superior potential of low frequency MBES to image shallow sub-seafloor features. Small gas pockets could be resolved even on the outer swath (up to 65). Strongly elevated backscattering from gassy areas occurred at large incidence angles and a high gas sensitivity of the MBES is further supported by an angular response analysis presented in this study. We conclude that the MBES together with subbottom profiling can be used as an efficient tool for spatial subbottom mapping in soft sediment environments.
Hydroacoustic detection of natural gas release from the seafloor has been conducted in the past b... more Hydroacoustic detection of natural gas release from the seafloor has been conducted in the past by using singlebeam echosounders. In contrast, modern multi-beam swath mapping systems allow much wider coverage, higher resolution, and offer 3-D spatial correlation. Up to the present, the extremely high data rate hampers water column backscatter investigations and more sophisticated visualiza-tion and processing techniques are needed. Here, we present water column backscatter data acquired with a 50 kHz prototype multibeam system over a period of 75 seconds. Display types are of swath-images as well as of a " resorted " sin-glebeam presentation. Thus, individual and/or groups of gas bubbles rising from the 24 m deep seafloor clearly emerge in the acoustic images, making it possible to estimate rise velocities. A sophisticated processing scheme is introduced to identify those rising gas bubbles in the hydroacoustic data. We apply a cross-correlation technique adapted from particle imaging velocimetry (PIV) to the acoustic backscatter images. Temporal and spatial drift patterns of the bubbles are assessed and are shown to match very well to measured and theoretical rise patterns. The application of this processing to our field data gives clear results with respect to unambiguous bubble detection and remote bubble rise velocimetry. The method can identify and exclude the main source of misinterpretations , i.e. fish-mediated echoes. Although image-based cross-correlation techniques are well known in the field of fluid mechanics for high resolution and non-inversive current flow field analysis, we present the first application of this technique as an acoustic bubble detector.
Natural seepage from the seafloor is a worldwide phenomenon but quantitative measurements of gas ... more Natural seepage from the seafloor is a worldwide phenomenon but quantitative measurements of gas release are rare, and the entire range of the dynamics of gas release in space, time, and strength remains unclear so far. To mitigate this, the hydroacoustic device GasQuant (180 kHz, multibeam) was developed to monitor the tempo-spatial variability of gas bubble releases from the seafloor. GasQuant was deployed in 2005 on the seafloor of the seep field Tommeliten (North Sea) for 36 h. This in situ approach provides much better spatial and temporal resolution of seeps than using conventional ship-born echo sounders. A total of 52 gas vents have been detected. Detailed time series analysis revealed a wide range of gas release patterns ranging from very short periodic up to 50 min long-lasting events. The bulk gas seepage in the studied area is active for more than 70% of observation time. The venting clearly exhibits tidal control showing a peak in the second quarter of the tidal pressure cycle, where pressure drops fastest. The hydroacoustic results are compared with video observations and bubble flux estimates from remotely operated vehicle dives described in the literature. An advanced approach for identifying and visualizing rising bubbles in the sea by hydroacoustics is presented in which water current data were considered. Realizing that bubbles are moved by currents helps to improve the detection of gas bubbles in the data, better discriminate bubbles against fish echoes, and to enhance the S/N ratio in the per se noisy acoustic data
[1] Multibeam sonar surveys have been conducted since their invention in the 1970s; however, main... more [1] Multibeam sonar surveys have been conducted since their invention in the 1970s; however, mainly reflections from the seafloor were considered so far. More recently, water column imaging with multibeam is becoming of increasing interest for fisheries, buoy, mooring, or gas detection in the water column. Using ELAC SEABEAM 1000 data, we propose a technique to detect gas bubbles (flares) although this system is originally not designed to record water column data. The described data processing represents a case study and can be easily adapted to other multibeam systems. Multibeam data sets from the Black Sea and the North Sea show reflections of gas bubbles that form flares in the water column. At least for reasonably intense gas escape the detection of bubbles is feasible. The multibeam technique yields exact determination of the source position and information about the dimension of the gas cloud in the water. Compared to conventional flare imaging by single-beam echo sounders, the wide swath angle of multibeam systems allows the mapping of large areas in much shorter time. Components: 4067 words, 5 figures, 1 table. Schneider von Deimling, J., J. Brockhoff, and J. Greinert (2007), Flare imaging with multibeam systems: Data processing for bubble detection at seeps,
[1] The distribution of dissolved methane in the water column of the Baltic Sea was extensively i... more [1] The distribution of dissolved methane in the water column of the Baltic Sea was extensively investigated. A strong correlation between the vertical density stratification, the distribution of oxygen, hydrogen sulfide, and methane has been identified. A widespread release of methane from the seafloor is indicated by increasing methane concentrations with water depth. The deep basins in the central Baltic Sea show the strongest methane enrichments in stagnant anoxic water bodies (max. 1086 nM and 504 nM, respectively), with a pronounced decrease towards the pelagic redoxcline and slightly elevated surface water concentrations (saturation values of 206% and 120%, respectively). In general the more limnic basins in the northern part of the Baltic are characterized by lower water column methane concentrations and surface water saturation values close to the atmospheric equilibrium (between 106% and 116%). In contrast, the shallow Western Baltic Sea is characterized by high saturation values up to 746%.
The importance of methanotrophic microorganisms in the sediment and water column for balancing ma... more The importance of methanotrophic microorganisms in the sediment and water column for balancing marine methane budgets is well accepted. However, whether methanotrophic populations are distinct for benthic and pelagic environments or are the result of exchange processes between the two remains an area of active research. We conducted a field pilot study at the Rostocker Seep site (Coal Oil Point seep field, offshore California, USA) to test the hypothesis that bubble-mediated transport of methane-oxidizing microorganisms from the sediment into the water column is quantifiable. Measurements included dissolved methane concentration showed a strong influence of methane seepage on the water-column methane distribution with strongly elevated sea surface concentrations with respect to atmospheric equilibrium (saturation ratio $ 17,000%). Using Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD FISH) analysis, aerobic methane oxidizing bacteria (MOB) were detected in the sediment and the water column, whereas anaerobic methanotrophs (ANME-2) were detected exclusively in the sediment. Critical data for testing the hypothesis were collected using a novel bubble catcher that trapped naturally emanating seep gas bubbles and any attached particles approximately 15 cm above the seafloor. Bubble catcher experiments were carried out directly above a natural bubble seep vent and at a nearby reference site, for which an " engineered " nitrogen bubble vent without sediment contact was created. Our experiments indicate the existence of a " Bubble Transport Mechanism " , which transports MOB from the sediment into the water column. In contrast, ANME-2 were not detected in the bubble catcher. The Bubble Transport Mechanism could have important implications for the connectivity between benthic and pelagic methanotrophic communities at methane seep sites.
[1] The Logatchev hydrothermal field at 14 45′N on the MAR is characterized by gas plumes that ar... more [1] The Logatchev hydrothermal field at 14 45′N on the MAR is characterized by gas plumes that are enriched in methane and helium compared to the oceanic background. We investigated CH 4 concentration and d 13 C together with d 3 He in the water column of that region. These data and turbidity measurements indicate that apart from the known vent fields, another vent site exists northeast of the vent field Logatchev 1. The distribution of methane and 3 He concentrations along two sections were used in combination with current measurements from lowered acoustic Doppler current profilers (LADCP) to calculate the horizontal plume fluxes of these gases. According to these examinations 0.02 mmol s À1 of 3 He and 0.21 mol s À1 of methane are transported in a plume that flows into a southward direction in the central part of the valley. Based on 3 He measurements of vent fluid (22 AE 6 pM), we estimate a total vent flux in this region of about 900 L s À1 and a total flux of CH 4 of 3.2 mol s À1 .
Based upon the molecular and isotopic composition of hydrocarbons it has been proposed that the s... more Based upon the molecular and isotopic composition of hydrocarbons it has been proposed that the source of CH 4 in Gulf of Cadiz mud volcanoes (MV) is a mixture of deep sourced thermo-genic CH 4 and shallow biogenic CH 4. We directly investigated this possibility by comparing porewater CH 4 concentrations and their δ 13 C values with the potential for Archaeal methanogenesis in Gulf of Cadiz mud volcano (MV) sediments (Captain Arutyunov, Bon-jardim, Ginsburg and Porto) using 14 Crate measurements. The CH 4 has a deep sourced thermogenic origin (δ 13 C ∼ −49‰) but becomes 13 C-depleted in and beneath the zone of anaerobic oxidation of methane (AOM) where the rates of hydrogenotrophic methanogenesis increase. Thus we infer that a portion of AOM-produced CO 2 is being recycled to CH 4 by methanogens yielding further 13 C-depleted CH 4 , which might be misinterpreted as indicative of a fully shallow biogenic origin for this gas. Production of H 2 is related to compositional changes in sedimentary organic matter, or to upward flux of substrate-enriched fluids. In contrast to other MVs in the Gulf of Cadiz, Ginsburg MV fluids are enriched in SO 2− 4 and contain very high concentrations of acetate (2478 µM below 150 cmbsf); however, the high levels of acetate did not stimulate methanogenesis but instead were oxidized to CO 2 coupled to sulphate reduction. Both anaerobic oxidation of thermogenic CH 4 linked to shallow methanogenesis and fluid geochemistry control the recycling of deep-sourced carbon at Gulf of Cadiz MVs, im-pacting near-surface δ 13 C-CH 4 values.
Extremely intense bubble plumes, like the North Sea 22/4b blowout megaplume (defined as more than... more Extremely intense bubble plumes, like the North Sea 22/4b blowout megaplume (defined as more than 10 6 L day −1), create very strong upwelling flows (>1 m s −1), which lead to detrainment of methane-enriched water, but leave direct bubble-mediated transport unaffected. Dissolved CH 4 depth profiles and atmospheric measurements during a fall 2011 survey of the 22/4b site suggest strong constraint of seabed CH 4 below the thermocline. Seabed bubbles were nearly pure CH 4. The effect of the upwelling flow on the fate of bubble plume CH 4 was investigated with a numerical bubble-propagation model. The model considered different representative bubble plume size distributions , φ, and a global (total) megaplume bubble size distribution, , synthesized from video survey data and φ from the literature. Simulations showed that none of the literature plumes or variations in the upwelling flow could constrain CH 4 sufficiently below the thermocline. Two new bubble megaplume processes were simulated, vortical bubble trapping (slow rise) and a hypothesized, enhanced bubble gas exchange, k BE , an enhancement factor applied to the normal bubble gas exchange rate, k B. The latter could arise from plume turbulence increasing bubble boundary-layer turbulence and thus its gas exchange. Observations could not be reproduced solely by slow rise, however, simulations with k BE ∼6 reproduced observational constraints, as could weaker k BE in conjunction with slow rise. Field validation of k BE is needed given its implications for the fate of megaplume CH 4 emissions (an-thropogenic or natural) for stratified and unstratified conditions. k BE suggests marine CH 4 geologic contributions to the atmosphere from all but shallow waters primarily arises from bubble plumes that are less than megaplume size.
Several acoustic and optical techniques have been used for characterizing natural and anthropogen... more Several acoustic and optical techniques have been used for characterizing natural and anthropogenic gas leaks (carbon dioxide, methane) from the ocean floor. Here, single-camera based methods for bubble stream observation have become an important tool, as they help estimating flux and bubble sizes under certain assumptions. However, they record only a projection of a bubble into the camera and therefore cannot capture the full 3D shape, which is particularly important for larger, non-spherical bubbles. The unknown distance of the bubble to the camera (making it appear larger or smaller than expected) as well as refraction at the camera interface introduce extra uncertainties. In this article, we introduce our wide baseline stereo-camera deep-sea sensor bubble box that overcomes these limitations, as it observes bubbles from two orthogonal directions using calibrated cameras. Besides the setup and the hardware of the system, we discuss appropriate calibration and the different automated processing steps deblurring, detection, tracking, and 3D fitting that are crucial to arrive at a 3D ellipsoidal shape and rise speed of each bubble. The obtained values for single bubbles can be aggregated into statistical bubble size distributions or fluxes for extrapolation based on diffusion and dissolution models and large scale acoustic surveys. We demonstrate and evaluate the wide baseline stereo measurement model using a controlled test setup with ground truth information.
Methane and carbon dioxide were measured with an autonomous and continuous running system on a fe... more Methane and carbon dioxide were measured with an autonomous and continuous running system on a ferry line crossing the Baltic Sea on a 2–3 day interval from the Mecklenburg Bight to the Gulf of Finland in 2010. Surface methane saturations show great seasonal differences in shallow regions like the Mecklenburg Bight (103–507 %) compared to deeper regions like the Gotland Basin (96–161 %). The influence of controlling parameters like temperature, wind, mixing depth and processes like upwelling, mixing of the water column and sedimentary methane emissions on methane oversaturation and emission to the atmosphere are investigated. Upwelling was found to influence methane surface concentrations in the area of Gotland significantly during the summer period. In February 2010, an event of elevated methane concentrations in the surface water and water column of the Arkona Basin was observed, which could be linked to a wind-derived water level change as a potential triggering mechanism. The Baltic Sea is a source of methane to the atmosphere throughout the year, with highest fluxes occurring during the winter season. Stratification was found to promote the formation of a methane reservoir in deeper regions like Gulf of Finland or Bornholm Basin, which leads to long lasting elevated methane concentrations and enhanced methane fluxes, when mixed to the surface during mixed layer deepening in autumn and winter. Methane concentrations and fluxes from shallow regions like the Mecklen-burg Bight are predominantly controlled by sedimentary production and consumption of methane, wind events and the change in temperature-dependent solubility of methane in the surface water. Methane fluxes vary significantly in shallow regions (e.g. Mecklenburg Bight) and regions with a temporal stratification (e.g. Bornholm Basin, Gulf of Finland). On the contrary, areas with a permanent stratification like the Gotland Basin show only small seasonal fluctuations in methane fluxes.
In the Arctic Seas, the West Spitsbergen continental margin represents a prominent methane seep a... more In the Arctic Seas, the West Spitsbergen continental margin represents a prominent methane seep area. In this area, free gas formation and gas ebullition as a consequence of hydrate dissociation due to global warming are currently under debate. Recent studies revealed shallow gas accumulation and ebullition of methane into the water column at more than 250 sites in an area of 665 km 2. We conducted a detailed study of a subregion of this area, which covers an active gas ebullition area of 175 km 2 characterized by 10 gas flares reaching from the seafloor at $ 245 m up to 50 m water depth to identify the fate of the released gas due to dissolution of methane from gas bubbles and subsequent mixing, transport and microbial oxidation. The oceanographic data indicated a salinity-controlled pycnocline situated $ 20 m above the seafloor. A high resolution sampling program at the pycnocline at the active gas ebullition flare area revealed that the methane concentration gradient is strongly controlled by the pycnocline. While high methane concentrations of up to 524 nmol L À 1 were measured below the pycnocline, low methane concentrations of less than 20 nmol L À 1 were observed in the water column above. Variations in the δ 13 C CH4 values point to a 13 C depleted methane source ($ À60‰ VPDB) being mainly mixed with a background values of the ambient water ($ À37.5‰ VPDB). A gas bubble dissolution model indicates that $ 80% of the methane released from gas bubbles into the ambient water takes place below the pycnocline. This dissolved methane will be laterally transported with the current northwards and most likely microbially oxidized in between 50 and 100 days, since microbial CH 4 oxidation rates of 0.78 nmol d À 1 were measured. Above the pycnocline, methane concentrations decrease to local background concentration of $ 10 nmol L À 1. Our results suggest that the methane dissolved from gas bubbles is efficiently trapped below the pycnocline and thus limits the methane concentration in surface water and the air–sea exchange during summer stratification. During winter the lateral stratification breaks down and fractions of the bottom water enriched in methane may be vertically mixed and thus be potentially an additional source for atmospheric methane.
Tommeliten is a prominent methane seep area in the Central North Sea. Previous surveys revealed s... more Tommeliten is a prominent methane seep area in the Central North Sea. Previous surveys revealed shallow gas-bearing sediments and methane gas ebullition into the water column. In this study, the in situ methane flux at Tommeliten is reassessed and the potential methane transport to the atmosphere is discussed, with regards to the hydrographic setting and gas bubble modeling. We have compiled previous data, acquired new video and acoustic evidence of gas bubble release, and have measured the methane concentration, and its C-isotopic composition in the water column. Parametric subbottom sonar data reveal the three-dimensional extent of shallow gas and morphologic features relevant for gas migration. Five methane ebullition areas are identified and the main seepage area appears to be 21 times larger than previously estimated. Our video, hydroacoustic, subbottom, and chemical data suggest that $ 1.5 Â 10 6 mol CH 4 /yr ($ 26 tons CH 4 /yr) of methane gas is being released from the seepage area of Tommeliten. Methane concentration profiles in the vicinity of the gas seeps show values of up to 268 nM ($ 100 times background) close to the seafloor. A decrease in d 13 C-CH 4 values at 40 m water depth indicates an unknown additional biogenic methane source within the well oxygenated thermocline between 30 and 40 m water depth. Numerical modeling of the methane bubbles due to their migration and dissolution was performed to estimate the bubble-derived vertical methane transport, the fate of this methane in the water column, and finally the flux to the atmosphere. Modeling indicates that less than $ 4% of the gas initially released at the seafloor is transported via bubbles into the mixed layer and, ultimately, to the atmosphere. However, because of the strong seasonality of mixing in the North Sea, this flux is expected to increase as mixing increases, and almost all of the methane released at the seafloor could be transferred into the atmosphere in the stormy fall and winter time.
Der Fachausschuss (FA) Akustik der Deutschen Gesellschaft für Wehrtechnik e. V. (DWT) hat vom 17.... more Der Fachausschuss (FA) Akustik der Deutschen Gesellschaft für Wehrtechnik e. V. (DWT) hat vom 17. bis 20. September 2012 am GEOMAR – Helmholtz-Zentrum für Ozeanforschung, Kiel eine wissenschaftliche Tagung mit dem Thema Schall und Schwingungen, Wellen und Turbulenz in sensibler Umgebung mit maritimem Schwerpunkt durchgeführt. Traditionell tagte der FA im Emsland an der Wehrtechnischen Dienststelle für Waffen und Munition (WTD 91) im jährlichen Wechsel mit dem FA Optik und Optronik von Prof. Rothe, Helmut-Schmidt-Universität (HSU). Diese zwei FA sind die zwei wissenschaftlichen Gremien der DWT. Vier Tage lang beschäftigten sich 160 Wissenschaftler aus Industrie, Universitäten, Forschungseinrichtungen und Amtsbereich mit einem breiten Themenspektrum in Form eines offenen zivil–militärischen Gedankenaustausches mittels wissenschaftlicher Fachvorträge, Postersession sowie Firmenausstellungen am GEOMAR. Damit stellte dies die bisher größte Veranstaltung dieser Tagungsreihe dar. Nach der Begrüßung der Tagungsteilnehmer durch den Leiter des FA begrüßte Herr Prof. Dr. Peter Herzig, Direktor des GEOMAR, als Gastgeber im Rahmen der Eröffnungsveranstaltung die Gäste. Für die Wehrtechnische Dienststelle für Schiffe und Marinewaffen, Maritime Technologie und Forschung (WTD 71) sprach Herr Dr. Kretschmer in Vertretung des Direktors Herrn Schlichting. Beide Institutionen, GEOMAR und WTD 71 mit ihrem Forschungsbereich, als auch die HSU waren Kooperationspartner der DWT und gestalteten die Tagung mit. Die zur klärende Frage des Tagungskonzeptes lautete: Welches sind im Über- aber insbesondere Unterwasserbereich vertretende Kernthemen auch benachbarter Institutionen, mit denen sich eine maritime Tagung mit zivilen und militärischen Nutzen gestalten lässt? Als Resultat kristallisierten sich sieben Themenbereiche mit insgesamt 44 Vorträgen heraus: - Geophysik/Turbulenz (Prof. Berndt/Dr. Fiekas) - Maritime Messtechnik (Dr. Schmidtke) - Unterwasserkommunikation (Dr. Nissen) - Akustische Überwachung mit Sensornetzwerken (Dr. Ehlers, Dr. Schulz) - Schiffbau (Dr. Stuntz) - Hydroakustik/Grenzschichtturbulenz (Dr. Abshagen) - Numerische Methoden (Dr. Schäfer, Ehrlich) Am ersten Tag lag der Schwerpunkt der Veranstaltung auf Geophysik/Turbulenz. Dieses Fachgebiet wird im benachbarten Forschungsbereich für Wasserschall und Geophysik (FWG) der WTD 71 von Dr. Heinz-Volker Fiekas geleitet, der zusammen mit Prof. Dr. Christian Berndt des GEOMAR den ersten Tag gestaltete. Hier zeigt sich die Verbundenheit beider Institute bezüglich dieses Themas. Im weiteren Verlauf der Tagung spielten neben Fragen der Ortung und Vermessung von Objekten am Meeresboden und in der Wassersäule mittels moderner Satellitentechnik auch die Beobachtung der Meeresoberfläche durch Synthetisches-Apertur-Radar (SAR) für Aufklärungszwecke eine bedeutende Rolle. Identifizierte, durch ein Schiff generierte Oberflächenwellen können die Position des Schiffes verraten. Dr. Susanne Lehner vom Deutschen Zentrum für Luft- und Raumfahrttechnik stellte modernste Möglichkeiten vor. Prof. Tuncay Akal aus der Türkei von SUASIS UNDERWATER SYSTEMS berichtete nicht nur von seiner langjährigen internationalen Erfahrung, sondern stellte ein gemeinsames Forschungsprojekt mit der Firma MICROFLOWN Avisa aus den Niederlanden zur experimentellen Bestimmung der akustischen Schnelle im Wasser vor. Ziel ist es, in die Lage versetzt zu werden, auch unter Wasser dominierende Schallquellen, sogenannte akustische „Hot Spots“, schnell und mobil zu identifizieren. Zivile und militärische Anwendungen haben bekanntlich oftmals dieselben Herausforderungen. Ob man sich zur Aufgabe gemacht hat ein Feldlager im Einsatzgebiet, eine Hafenanlage, ein Schiff auf Reede oder ein ozeanographisches Observatorium zur Erdsystembeobachtung zu schützen, zu sichern, zu überwachen oder zu betreiben, in jedem Fall ist hierzu die Beobachtung von systemrelevanten Daten notwendig. Die technischen oder wissenschaftlichen Herausforderungen sind hierbei in vielen Fällen ähnlich und koinzidieren auch. Es geht um kontinuierliche Datenerfassung und -fusion, moderne Sensornetzwerke, Zeit- und Kosteneffizienz, Satellitenverbindungen, Datenboten und -sammlern wie AUVs und Glider, hydrographische, akustische sowie seismische Messstationen und -verfahren. Bei all dem ist die Akustik gerade im Unterwasserbereich eine dominierende Technologieeinflußgröße. Zur Halbzeit der Tagung ging es nach Laboe, am Ehrenmal vorbei ins Restaurant Baltic Bay zum Konferenzdinner. In angenehmer, maritimer und stilvoller Atmosphäre direkt am Segelhafen wurden die fachlichen Gespräche fortgesetzt und persönliche Kontakte aufgenommen respektive intensiviert. Dr. Lüder Hogrefe, Geschäftsführer von Raytheon Anschütz GmbH, begrüßte vor Ort die Wissenschaftler und hielt die Dinner Speech. Dr. Hogrefe betonte den zivil-militärischen Ansatz der Tagung, welcher „noch vor 15 Jahren nicht möglich erschien“. Die Veranstaltung hat bewiesen, dass der eingeschlagene Weg diese duale Betrachtung zulässt. Der vorliegende Tagungsband möge dieses bestätigen. Er spiegelt den aktuellen maritimen Forschungsstand bezüglich der oben angegebenen Themenschwerpunkte wieder. Wir bedanken uns bei allen Autoren und Vortragenden für ihre eingestellten Beiträge. Besonderer Dank geht an Frau Angela Günther für die Leitung des Tagungsbüros sowie für die lange Zeit der intensiven Vor- und Nachbereitung. Dank geht ebenfalls an Herrn Michael Krüger für die großartige technische Unterstützung. Es kann nicht unerwähnt bleiben, dass so manche weitere Hilfe im Hintergrund durchaus wahrgenommen wurde, doch sei aus Platzgründen hierfür nur insgesamt, doch keineswegs weniger nachdrücklich, gedankt.
First direct evidence for ongoing gas seepage activity on the abandoned well site 22/4b (Northern... more First direct evidence for ongoing gas seepage activity on the abandoned well site 22/4b (Northern North Sea, 57°55 N, 01°38 E) and discovery of neighboring seepage activity is provided from observations since 2005. A manned submersible dive in 2006 discovered several extraordinary intense seepage sites within a 60 m wide and 20 m deep crater cut into the flat 96 m deep seafloor. Capture and (isotope) chemical analyses of the gas bubbles near the seafloor revealed in situ concentrations of methane between 88 and 90%Vol. with δ 13 C–CH 4 values around −74‰ VPDB, indicating a biogenic origin. Bulk methane concentrations throughout the water column were assessed by 120 Niskin water samples showing up to 400.000 nM CH 4 in the crater at depth. In contrast, concentrations above the thermocline were orders of magnitude lower, with a median value of 20 nM. A dye tracer injection into the gas seeps revealed upwelling bubble and water motion with gas plume rise velocities up to ∼1 ms −1 (determined near the seabed). However, the dissolved dye did not pass the thermocline, but returned down to the seabed. Measurements of direct bubble-mediated atmospheric flux revealed low values of 0.7 ± 0.3 kty −1 , much less than current state-of-the-art bubble dissolution models would predict for such a strong and upwelling in situ gas bubble flux at shallow water depths (i.e. ∼100 m). Acoustic multibeam water column imaging data indicate a pronounced 200 m lateral intrusion at the thermocline together with high methane concentration at this layer. A partly downward-orientated bubble plume motion is also visible in the acoustic data with potential short-circuiting in accordance to the dye experiment. This observation could partly explain the observed trapping of most of the released gas below the well-established thermocline in the North Sea. Moreover, 3D analyses of the multibeam water column data reveal that the upwelling plume transforms into a spiral expanding vortex while rising through the water column. Such a spiral vortex motion has never been reported before for marine gas seepage and might represent an important process with strong implication on plume dynamics, dissolution behavior, gas escape to the atmosphere, and is considered very important for respective modeling approaches.
This study highlights the potential of using a low frequency multibeam echosounder for detection ... more This study highlights the potential of using a low frequency multibeam echosounder for detection and visualization of shallow gas occurring several meters beneath the seafloor. The presence of shallow gas was verified in the Bornholm Basin, Baltic Sea, at 80 m water depth with standard geochemical core analysis and hydroacoustic subbottom profiling. Successively, this area was surveyed with a 95 kHz and a 12 kHz multibeam echosounder (MBES). The bathymetric measurements with 12 kHz provided depth values systematically deeper by several meters compared to 95 kHz data. This observation was attributed to enhanced penetration of the low frequency signal energy into soft sediments. Consequently, the subbottom geoacoustic properties contributed highly to the measured backscattered signals. Those appeared up to 17 dB higher inside the shallow gas area compared to reference measurements outside and could be clearly linked to the shallow gas front depth down to 5 m below seafloor. No elevated backscatter was visible in 95 kHz MBES data, which in turn highlights the superior potential of low frequency MBES to image shallow sub-seafloor features. Small gas pockets could be resolved even on the outer swath (up to 65). Strongly elevated backscattering from gassy areas occurred at large incidence angles and a high gas sensitivity of the MBES is further supported by an angular response analysis presented in this study. We conclude that the MBES together with subbottom profiling can be used as an efficient tool for spatial subbottom mapping in soft sediment environments.
Hydroacoustic detection of natural gas release from the seafloor has been conducted in the past b... more Hydroacoustic detection of natural gas release from the seafloor has been conducted in the past by using singlebeam echosounders. In contrast, modern multi-beam swath mapping systems allow much wider coverage, higher resolution, and offer 3-D spatial correlation. Up to the present, the extremely high data rate hampers water column backscatter investigations and more sophisticated visualiza-tion and processing techniques are needed. Here, we present water column backscatter data acquired with a 50 kHz prototype multibeam system over a period of 75 seconds. Display types are of swath-images as well as of a " resorted " sin-glebeam presentation. Thus, individual and/or groups of gas bubbles rising from the 24 m deep seafloor clearly emerge in the acoustic images, making it possible to estimate rise velocities. A sophisticated processing scheme is introduced to identify those rising gas bubbles in the hydroacoustic data. We apply a cross-correlation technique adapted from particle imaging velocimetry (PIV) to the acoustic backscatter images. Temporal and spatial drift patterns of the bubbles are assessed and are shown to match very well to measured and theoretical rise patterns. The application of this processing to our field data gives clear results with respect to unambiguous bubble detection and remote bubble rise velocimetry. The method can identify and exclude the main source of misinterpretations , i.e. fish-mediated echoes. Although image-based cross-correlation techniques are well known in the field of fluid mechanics for high resolution and non-inversive current flow field analysis, we present the first application of this technique as an acoustic bubble detector.
Natural seepage from the seafloor is a worldwide phenomenon but quantitative measurements of gas ... more Natural seepage from the seafloor is a worldwide phenomenon but quantitative measurements of gas release are rare, and the entire range of the dynamics of gas release in space, time, and strength remains unclear so far. To mitigate this, the hydroacoustic device GasQuant (180 kHz, multibeam) was developed to monitor the tempo-spatial variability of gas bubble releases from the seafloor. GasQuant was deployed in 2005 on the seafloor of the seep field Tommeliten (North Sea) for 36 h. This in situ approach provides much better spatial and temporal resolution of seeps than using conventional ship-born echo sounders. A total of 52 gas vents have been detected. Detailed time series analysis revealed a wide range of gas release patterns ranging from very short periodic up to 50 min long-lasting events. The bulk gas seepage in the studied area is active for more than 70% of observation time. The venting clearly exhibits tidal control showing a peak in the second quarter of the tidal pressure cycle, where pressure drops fastest. The hydroacoustic results are compared with video observations and bubble flux estimates from remotely operated vehicle dives described in the literature. An advanced approach for identifying and visualizing rising bubbles in the sea by hydroacoustics is presented in which water current data were considered. Realizing that bubbles are moved by currents helps to improve the detection of gas bubbles in the data, better discriminate bubbles against fish echoes, and to enhance the S/N ratio in the per se noisy acoustic data
[1] Multibeam sonar surveys have been conducted since their invention in the 1970s; however, main... more [1] Multibeam sonar surveys have been conducted since their invention in the 1970s; however, mainly reflections from the seafloor were considered so far. More recently, water column imaging with multibeam is becoming of increasing interest for fisheries, buoy, mooring, or gas detection in the water column. Using ELAC SEABEAM 1000 data, we propose a technique to detect gas bubbles (flares) although this system is originally not designed to record water column data. The described data processing represents a case study and can be easily adapted to other multibeam systems. Multibeam data sets from the Black Sea and the North Sea show reflections of gas bubbles that form flares in the water column. At least for reasonably intense gas escape the detection of bubbles is feasible. The multibeam technique yields exact determination of the source position and information about the dimension of the gas cloud in the water. Compared to conventional flare imaging by single-beam echo sounders, the wide swath angle of multibeam systems allows the mapping of large areas in much shorter time. Components: 4067 words, 5 figures, 1 table. Schneider von Deimling, J., J. Brockhoff, and J. Greinert (2007), Flare imaging with multibeam systems: Data processing for bubble detection at seeps,
[1] The distribution of dissolved methane in the water column of the Baltic Sea was extensively i... more [1] The distribution of dissolved methane in the water column of the Baltic Sea was extensively investigated. A strong correlation between the vertical density stratification, the distribution of oxygen, hydrogen sulfide, and methane has been identified. A widespread release of methane from the seafloor is indicated by increasing methane concentrations with water depth. The deep basins in the central Baltic Sea show the strongest methane enrichments in stagnant anoxic water bodies (max. 1086 nM and 504 nM, respectively), with a pronounced decrease towards the pelagic redoxcline and slightly elevated surface water concentrations (saturation values of 206% and 120%, respectively). In general the more limnic basins in the northern part of the Baltic are characterized by lower water column methane concentrations and surface water saturation values close to the atmospheric equilibrium (between 106% and 116%). In contrast, the shallow Western Baltic Sea is characterized by high saturation values up to 746%.
The importance of methanotrophic microorganisms in the sediment and water column for balancing ma... more The importance of methanotrophic microorganisms in the sediment and water column for balancing marine methane budgets is well accepted. However, whether methanotrophic populations are distinct for benthic and pelagic environments or are the result of exchange processes between the two remains an area of active research. We conducted a field pilot study at the Rostocker Seep site (Coal Oil Point seep field, offshore California, USA) to test the hypothesis that bubble-mediated transport of methane-oxidizing microorganisms from the sediment into the water column is quantifiable. Measurements included dissolved methane concentration showed a strong influence of methane seepage on the water-column methane distribution with strongly elevated sea surface concentrations with respect to atmospheric equilibrium (saturation ratio $ 17,000%). Using Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD FISH) analysis, aerobic methane oxidizing bacteria (MOB) were detected in the sediment and the water column, whereas anaerobic methanotrophs (ANME-2) were detected exclusively in the sediment. Critical data for testing the hypothesis were collected using a novel bubble catcher that trapped naturally emanating seep gas bubbles and any attached particles approximately 15 cm above the seafloor. Bubble catcher experiments were carried out directly above a natural bubble seep vent and at a nearby reference site, for which an " engineered " nitrogen bubble vent without sediment contact was created. Our experiments indicate the existence of a " Bubble Transport Mechanism " , which transports MOB from the sediment into the water column. In contrast, ANME-2 were not detected in the bubble catcher. The Bubble Transport Mechanism could have important implications for the connectivity between benthic and pelagic methanotrophic communities at methane seep sites.
[1] The Logatchev hydrothermal field at 14 45′N on the MAR is characterized by gas plumes that ar... more [1] The Logatchev hydrothermal field at 14 45′N on the MAR is characterized by gas plumes that are enriched in methane and helium compared to the oceanic background. We investigated CH 4 concentration and d 13 C together with d 3 He in the water column of that region. These data and turbidity measurements indicate that apart from the known vent fields, another vent site exists northeast of the vent field Logatchev 1. The distribution of methane and 3 He concentrations along two sections were used in combination with current measurements from lowered acoustic Doppler current profilers (LADCP) to calculate the horizontal plume fluxes of these gases. According to these examinations 0.02 mmol s À1 of 3 He and 0.21 mol s À1 of methane are transported in a plume that flows into a southward direction in the central part of the valley. Based on 3 He measurements of vent fluid (22 AE 6 pM), we estimate a total vent flux in this region of about 900 L s À1 and a total flux of CH 4 of 3.2 mol s À1 .
Based upon the molecular and isotopic composition of hydrocarbons it has been proposed that the s... more Based upon the molecular and isotopic composition of hydrocarbons it has been proposed that the source of CH 4 in Gulf of Cadiz mud volcanoes (MV) is a mixture of deep sourced thermo-genic CH 4 and shallow biogenic CH 4. We directly investigated this possibility by comparing porewater CH 4 concentrations and their δ 13 C values with the potential for Archaeal methanogenesis in Gulf of Cadiz mud volcano (MV) sediments (Captain Arutyunov, Bon-jardim, Ginsburg and Porto) using 14 Crate measurements. The CH 4 has a deep sourced thermogenic origin (δ 13 C ∼ −49‰) but becomes 13 C-depleted in and beneath the zone of anaerobic oxidation of methane (AOM) where the rates of hydrogenotrophic methanogenesis increase. Thus we infer that a portion of AOM-produced CO 2 is being recycled to CH 4 by methanogens yielding further 13 C-depleted CH 4 , which might be misinterpreted as indicative of a fully shallow biogenic origin for this gas. Production of H 2 is related to compositional changes in sedimentary organic matter, or to upward flux of substrate-enriched fluids. In contrast to other MVs in the Gulf of Cadiz, Ginsburg MV fluids are enriched in SO 2− 4 and contain very high concentrations of acetate (2478 µM below 150 cmbsf); however, the high levels of acetate did not stimulate methanogenesis but instead were oxidized to CO 2 coupled to sulphate reduction. Both anaerobic oxidation of thermogenic CH 4 linked to shallow methanogenesis and fluid geochemistry control the recycling of deep-sourced carbon at Gulf of Cadiz MVs, im-pacting near-surface δ 13 C-CH 4 values.
Extremely intense bubble plumes, like the North Sea 22/4b blowout megaplume (defined as more than... more Extremely intense bubble plumes, like the North Sea 22/4b blowout megaplume (defined as more than 10 6 L day −1), create very strong upwelling flows (>1 m s −1), which lead to detrainment of methane-enriched water, but leave direct bubble-mediated transport unaffected. Dissolved CH 4 depth profiles and atmospheric measurements during a fall 2011 survey of the 22/4b site suggest strong constraint of seabed CH 4 below the thermocline. Seabed bubbles were nearly pure CH 4. The effect of the upwelling flow on the fate of bubble plume CH 4 was investigated with a numerical bubble-propagation model. The model considered different representative bubble plume size distributions , φ, and a global (total) megaplume bubble size distribution, , synthesized from video survey data and φ from the literature. Simulations showed that none of the literature plumes or variations in the upwelling flow could constrain CH 4 sufficiently below the thermocline. Two new bubble megaplume processes were simulated, vortical bubble trapping (slow rise) and a hypothesized, enhanced bubble gas exchange, k BE , an enhancement factor applied to the normal bubble gas exchange rate, k B. The latter could arise from plume turbulence increasing bubble boundary-layer turbulence and thus its gas exchange. Observations could not be reproduced solely by slow rise, however, simulations with k BE ∼6 reproduced observational constraints, as could weaker k BE in conjunction with slow rise. Field validation of k BE is needed given its implications for the fate of megaplume CH 4 emissions (an-thropogenic or natural) for stratified and unstratified conditions. k BE suggests marine CH 4 geologic contributions to the atmosphere from all but shallow waters primarily arises from bubble plumes that are less than megaplume size.
Several acoustic and optical techniques have been used for characterizing natural and anthropogen... more Several acoustic and optical techniques have been used for characterizing natural and anthropogenic gas leaks (carbon dioxide, methane) from the ocean floor. Here, single-camera based methods for bubble stream observation have become an important tool, as they help estimating flux and bubble sizes under certain assumptions. However, they record only a projection of a bubble into the camera and therefore cannot capture the full 3D shape, which is particularly important for larger, non-spherical bubbles. The unknown distance of the bubble to the camera (making it appear larger or smaller than expected) as well as refraction at the camera interface introduce extra uncertainties. In this article, we introduce our wide baseline stereo-camera deep-sea sensor bubble box that overcomes these limitations, as it observes bubbles from two orthogonal directions using calibrated cameras. Besides the setup and the hardware of the system, we discuss appropriate calibration and the different automated processing steps deblurring, detection, tracking, and 3D fitting that are crucial to arrive at a 3D ellipsoidal shape and rise speed of each bubble. The obtained values for single bubbles can be aggregated into statistical bubble size distributions or fluxes for extrapolation based on diffusion and dissolution models and large scale acoustic surveys. We demonstrate and evaluate the wide baseline stereo measurement model using a controlled test setup with ground truth information.
Methane and carbon dioxide were measured with an autonomous and continuous running system on a fe... more Methane and carbon dioxide were measured with an autonomous and continuous running system on a ferry line crossing the Baltic Sea on a 2–3 day interval from the Mecklenburg Bight to the Gulf of Finland in 2010. Surface methane saturations show great seasonal differences in shallow regions like the Mecklenburg Bight (103–507 %) compared to deeper regions like the Gotland Basin (96–161 %). The influence of controlling parameters like temperature, wind, mixing depth and processes like upwelling, mixing of the water column and sedimentary methane emissions on methane oversaturation and emission to the atmosphere are investigated. Upwelling was found to influence methane surface concentrations in the area of Gotland significantly during the summer period. In February 2010, an event of elevated methane concentrations in the surface water and water column of the Arkona Basin was observed, which could be linked to a wind-derived water level change as a potential triggering mechanism. The Baltic Sea is a source of methane to the atmosphere throughout the year, with highest fluxes occurring during the winter season. Stratification was found to promote the formation of a methane reservoir in deeper regions like Gulf of Finland or Bornholm Basin, which leads to long lasting elevated methane concentrations and enhanced methane fluxes, when mixed to the surface during mixed layer deepening in autumn and winter. Methane concentrations and fluxes from shallow regions like the Mecklen-burg Bight are predominantly controlled by sedimentary production and consumption of methane, wind events and the change in temperature-dependent solubility of methane in the surface water. Methane fluxes vary significantly in shallow regions (e.g. Mecklenburg Bight) and regions with a temporal stratification (e.g. Bornholm Basin, Gulf of Finland). On the contrary, areas with a permanent stratification like the Gotland Basin show only small seasonal fluctuations in methane fluxes.
In the Arctic Seas, the West Spitsbergen continental margin represents a prominent methane seep a... more In the Arctic Seas, the West Spitsbergen continental margin represents a prominent methane seep area. In this area, free gas formation and gas ebullition as a consequence of hydrate dissociation due to global warming are currently under debate. Recent studies revealed shallow gas accumulation and ebullition of methane into the water column at more than 250 sites in an area of 665 km 2. We conducted a detailed study of a subregion of this area, which covers an active gas ebullition area of 175 km 2 characterized by 10 gas flares reaching from the seafloor at $ 245 m up to 50 m water depth to identify the fate of the released gas due to dissolution of methane from gas bubbles and subsequent mixing, transport and microbial oxidation. The oceanographic data indicated a salinity-controlled pycnocline situated $ 20 m above the seafloor. A high resolution sampling program at the pycnocline at the active gas ebullition flare area revealed that the methane concentration gradient is strongly controlled by the pycnocline. While high methane concentrations of up to 524 nmol L À 1 were measured below the pycnocline, low methane concentrations of less than 20 nmol L À 1 were observed in the water column above. Variations in the δ 13 C CH4 values point to a 13 C depleted methane source ($ À60‰ VPDB) being mainly mixed with a background values of the ambient water ($ À37.5‰ VPDB). A gas bubble dissolution model indicates that $ 80% of the methane released from gas bubbles into the ambient water takes place below the pycnocline. This dissolved methane will be laterally transported with the current northwards and most likely microbially oxidized in between 50 and 100 days, since microbial CH 4 oxidation rates of 0.78 nmol d À 1 were measured. Above the pycnocline, methane concentrations decrease to local background concentration of $ 10 nmol L À 1. Our results suggest that the methane dissolved from gas bubbles is efficiently trapped below the pycnocline and thus limits the methane concentration in surface water and the air–sea exchange during summer stratification. During winter the lateral stratification breaks down and fractions of the bottom water enriched in methane may be vertically mixed and thus be potentially an additional source for atmospheric methane.
Tommeliten is a prominent methane seep area in the Central North Sea. Previous surveys revealed s... more Tommeliten is a prominent methane seep area in the Central North Sea. Previous surveys revealed shallow gas-bearing sediments and methane gas ebullition into the water column. In this study, the in situ methane flux at Tommeliten is reassessed and the potential methane transport to the atmosphere is discussed, with regards to the hydrographic setting and gas bubble modeling. We have compiled previous data, acquired new video and acoustic evidence of gas bubble release, and have measured the methane concentration, and its C-isotopic composition in the water column. Parametric subbottom sonar data reveal the three-dimensional extent of shallow gas and morphologic features relevant for gas migration. Five methane ebullition areas are identified and the main seepage area appears to be 21 times larger than previously estimated. Our video, hydroacoustic, subbottom, and chemical data suggest that $ 1.5 Â 10 6 mol CH 4 /yr ($ 26 tons CH 4 /yr) of methane gas is being released from the seepage area of Tommeliten. Methane concentration profiles in the vicinity of the gas seeps show values of up to 268 nM ($ 100 times background) close to the seafloor. A decrease in d 13 C-CH 4 values at 40 m water depth indicates an unknown additional biogenic methane source within the well oxygenated thermocline between 30 and 40 m water depth. Numerical modeling of the methane bubbles due to their migration and dissolution was performed to estimate the bubble-derived vertical methane transport, the fate of this methane in the water column, and finally the flux to the atmosphere. Modeling indicates that less than $ 4% of the gas initially released at the seafloor is transported via bubbles into the mixed layer and, ultimately, to the atmosphere. However, because of the strong seasonality of mixing in the North Sea, this flux is expected to increase as mixing increases, and almost all of the methane released at the seafloor could be transferred into the atmosphere in the stormy fall and winter time.
Der Fachausschuss (FA) Akustik der Deutschen Gesellschaft für Wehrtechnik e. V. (DWT) hat vom 17.... more Der Fachausschuss (FA) Akustik der Deutschen Gesellschaft für Wehrtechnik e. V. (DWT) hat vom 17. bis 20. September 2012 am GEOMAR – Helmholtz-Zentrum für Ozeanforschung, Kiel eine wissenschaftliche Tagung mit dem Thema Schall und Schwingungen, Wellen und Turbulenz in sensibler Umgebung mit maritimem Schwerpunkt durchgeführt. Traditionell tagte der FA im Emsland an der Wehrtechnischen Dienststelle für Waffen und Munition (WTD 91) im jährlichen Wechsel mit dem FA Optik und Optronik von Prof. Rothe, Helmut-Schmidt-Universität (HSU). Diese zwei FA sind die zwei wissenschaftlichen Gremien der DWT. Vier Tage lang beschäftigten sich 160 Wissenschaftler aus Industrie, Universitäten, Forschungseinrichtungen und Amtsbereich mit einem breiten Themenspektrum in Form eines offenen zivil–militärischen Gedankenaustausches mittels wissenschaftlicher Fachvorträge, Postersession sowie Firmenausstellungen am GEOMAR. Damit stellte dies die bisher größte Veranstaltung dieser Tagungsreihe dar. Nach der Begrüßung der Tagungsteilnehmer durch den Leiter des FA begrüßte Herr Prof. Dr. Peter Herzig, Direktor des GEOMAR, als Gastgeber im Rahmen der Eröffnungsveranstaltung die Gäste. Für die Wehrtechnische Dienststelle für Schiffe und Marinewaffen, Maritime Technologie und Forschung (WTD 71) sprach Herr Dr. Kretschmer in Vertretung des Direktors Herrn Schlichting. Beide Institutionen, GEOMAR und WTD 71 mit ihrem Forschungsbereich, als auch die HSU waren Kooperationspartner der DWT und gestalteten die Tagung mit. Die zur klärende Frage des Tagungskonzeptes lautete: Welches sind im Über- aber insbesondere Unterwasserbereich vertretende Kernthemen auch benachbarter Institutionen, mit denen sich eine maritime Tagung mit zivilen und militärischen Nutzen gestalten lässt? Als Resultat kristallisierten sich sieben Themenbereiche mit insgesamt 44 Vorträgen heraus: - Geophysik/Turbulenz (Prof. Berndt/Dr. Fiekas) - Maritime Messtechnik (Dr. Schmidtke) - Unterwasserkommunikation (Dr. Nissen) - Akustische Überwachung mit Sensornetzwerken (Dr. Ehlers, Dr. Schulz) - Schiffbau (Dr. Stuntz) - Hydroakustik/Grenzschichtturbulenz (Dr. Abshagen) - Numerische Methoden (Dr. Schäfer, Ehrlich) Am ersten Tag lag der Schwerpunkt der Veranstaltung auf Geophysik/Turbulenz. Dieses Fachgebiet wird im benachbarten Forschungsbereich für Wasserschall und Geophysik (FWG) der WTD 71 von Dr. Heinz-Volker Fiekas geleitet, der zusammen mit Prof. Dr. Christian Berndt des GEOMAR den ersten Tag gestaltete. Hier zeigt sich die Verbundenheit beider Institute bezüglich dieses Themas. Im weiteren Verlauf der Tagung spielten neben Fragen der Ortung und Vermessung von Objekten am Meeresboden und in der Wassersäule mittels moderner Satellitentechnik auch die Beobachtung der Meeresoberfläche durch Synthetisches-Apertur-Radar (SAR) für Aufklärungszwecke eine bedeutende Rolle. Identifizierte, durch ein Schiff generierte Oberflächenwellen können die Position des Schiffes verraten. Dr. Susanne Lehner vom Deutschen Zentrum für Luft- und Raumfahrttechnik stellte modernste Möglichkeiten vor. Prof. Tuncay Akal aus der Türkei von SUASIS UNDERWATER SYSTEMS berichtete nicht nur von seiner langjährigen internationalen Erfahrung, sondern stellte ein gemeinsames Forschungsprojekt mit der Firma MICROFLOWN Avisa aus den Niederlanden zur experimentellen Bestimmung der akustischen Schnelle im Wasser vor. Ziel ist es, in die Lage versetzt zu werden, auch unter Wasser dominierende Schallquellen, sogenannte akustische „Hot Spots“, schnell und mobil zu identifizieren. Zivile und militärische Anwendungen haben bekanntlich oftmals dieselben Herausforderungen. Ob man sich zur Aufgabe gemacht hat ein Feldlager im Einsatzgebiet, eine Hafenanlage, ein Schiff auf Reede oder ein ozeanographisches Observatorium zur Erdsystembeobachtung zu schützen, zu sichern, zu überwachen oder zu betreiben, in jedem Fall ist hierzu die Beobachtung von systemrelevanten Daten notwendig. Die technischen oder wissenschaftlichen Herausforderungen sind hierbei in vielen Fällen ähnlich und koinzidieren auch. Es geht um kontinuierliche Datenerfassung und -fusion, moderne Sensornetzwerke, Zeit- und Kosteneffizienz, Satellitenverbindungen, Datenboten und -sammlern wie AUVs und Glider, hydrographische, akustische sowie seismische Messstationen und -verfahren. Bei all dem ist die Akustik gerade im Unterwasserbereich eine dominierende Technologieeinflußgröße. Zur Halbzeit der Tagung ging es nach Laboe, am Ehrenmal vorbei ins Restaurant Baltic Bay zum Konferenzdinner. In angenehmer, maritimer und stilvoller Atmosphäre direkt am Segelhafen wurden die fachlichen Gespräche fortgesetzt und persönliche Kontakte aufgenommen respektive intensiviert. Dr. Lüder Hogrefe, Geschäftsführer von Raytheon Anschütz GmbH, begrüßte vor Ort die Wissenschaftler und hielt die Dinner Speech. Dr. Hogrefe betonte den zivil-militärischen Ansatz der Tagung, welcher „noch vor 15 Jahren nicht möglich erschien“. Die Veranstaltung hat bewiesen, dass der eingeschlagene Weg diese duale Betrachtung zulässt. Der vorliegende Tagungsband möge dieses bestätigen. Er spiegelt den aktuellen maritimen Forschungsstand bezüglich der oben angegebenen Themenschwerpunkte wieder. Wir bedanken uns bei allen Autoren und Vortragenden für ihre eingestellten Beiträge. Besonderer Dank geht an Frau Angela Günther für die Leitung des Tagungsbüros sowie für die lange Zeit der intensiven Vor- und Nachbereitung. Dank geht ebenfalls an Herrn Michael Krüger für die großartige technische Unterstützung. Es kann nicht unerwähnt bleiben, dass so manche weitere Hilfe im Hintergrund durchaus wahrgenommen wurde, doch sei aus Platzgründen hierfür nur insgesamt, doch keineswegs weniger nachdrücklich, gedankt.
First direct evidence for ongoing gas seepage activity on the abandoned well site 22/4b (Northern... more First direct evidence for ongoing gas seepage activity on the abandoned well site 22/4b (Northern North Sea, 57°55 N, 01°38 E) and discovery of neighboring seepage activity is provided from observations since 2005. A manned submersible dive in 2006 discovered several extraordinary intense seepage sites within a 60 m wide and 20 m deep crater cut into the flat 96 m deep seafloor. Capture and (isotope) chemical analyses of the gas bubbles near the seafloor revealed in situ concentrations of methane between 88 and 90%Vol. with δ 13 C–CH 4 values around −74‰ VPDB, indicating a biogenic origin. Bulk methane concentrations throughout the water column were assessed by 120 Niskin water samples showing up to 400.000 nM CH 4 in the crater at depth. In contrast, concentrations above the thermocline were orders of magnitude lower, with a median value of 20 nM. A dye tracer injection into the gas seeps revealed upwelling bubble and water motion with gas plume rise velocities up to ∼1 ms −1 (determined near the seabed). However, the dissolved dye did not pass the thermocline, but returned down to the seabed. Measurements of direct bubble-mediated atmospheric flux revealed low values of 0.7 ± 0.3 kty −1 , much less than current state-of-the-art bubble dissolution models would predict for such a strong and upwelling in situ gas bubble flux at shallow water depths (i.e. ∼100 m). Acoustic multibeam water column imaging data indicate a pronounced 200 m lateral intrusion at the thermocline together with high methane concentration at this layer. A partly downward-orientated bubble plume motion is also visible in the acoustic data with potential short-circuiting in accordance to the dye experiment. This observation could partly explain the observed trapping of most of the released gas below the well-established thermocline in the North Sea. Moreover, 3D analyses of the multibeam water column data reveal that the upwelling plume transforms into a spiral expanding vortex while rising through the water column. Such a spiral vortex motion has never been reported before for marine gas seepage and might represent an important process with strong implication on plume dynamics, dissolution behavior, gas escape to the atmosphere, and is considered very important for respective modeling approaches.
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Papers by Jens Schneider von Deimling
are rare, and the entire range of the dynamics of gas release in space, time, and strength remains unclear so far.
To mitigate this, the hydroacoustic device GasQuant (180 kHz, multibeam) was developed to monitor the
tempo-spatial variability of gas bubble releases from the seafloor. GasQuant was deployed in 2005 on the
seafloor of the seep field Tommeliten (North Sea) for 36 h. This in situ approach provides much better spatial
and temporal resolution of seeps than using conventional ship-born echo sounders. A total of 52 gas vents have
been detected. Detailed time series analysis revealed a wide range of gas release patterns ranging from very short
periodic up to 50 min long-lasting events. The bulk gas seepage in the studied area is active for more than 70%
of observation time. The venting clearly exhibits tidal control showing a peak in the second quarter of the tidal
pressure cycle, where pressure drops fastest. The hydroacoustic results are compared with video observations
and bubble flux estimates from remotely operated vehicle dives described in the literature. An advanced
approach for identifying and visualizing rising bubbles in the sea by hydroacoustics is presented in which water
current data were considered. Realizing that bubbles are moved by currents helps to improve the detection of
gas bubbles in the data, better discriminate bubbles against fish echoes, and to enhance the S/N ratio in the per
se noisy acoustic data
- Geophysik/Turbulenz (Prof. Berndt/Dr. Fiekas)
- Maritime Messtechnik (Dr. Schmidtke)
- Unterwasserkommunikation (Dr. Nissen)
- Akustische Überwachung mit Sensornetzwerken (Dr. Ehlers, Dr. Schulz)
- Schiffbau (Dr. Stuntz)
- Hydroakustik/Grenzschichtturbulenz (Dr. Abshagen)
- Numerische Methoden (Dr. Schäfer, Ehrlich)
Am ersten Tag lag der Schwerpunkt der Veranstaltung auf Geophysik/Turbulenz. Dieses
Fachgebiet wird im benachbarten Forschungsbereich für Wasserschall und Geophysik (FWG) der WTD 71 von Dr. Heinz-Volker Fiekas geleitet, der zusammen mit Prof. Dr. Christian Berndt des GEOMAR den ersten Tag gestaltete. Hier zeigt sich die Verbundenheit beider Institute bezüglich dieses Themas. Im weiteren Verlauf der Tagung spielten neben Fragen der Ortung und Vermessung von Objekten am Meeresboden und in der Wassersäule mittels moderner Satellitentechnik auch die Beobachtung der Meeresoberfläche durch Synthetisches-Apertur-Radar (SAR) für Aufklärungszwecke eine bedeutende Rolle. Identifizierte, durch ein Schiff generierte Oberflächenwellen können die Position des Schiffes verraten. Dr. Susanne Lehner vom Deutschen Zentrum für Luft- und Raumfahrttechnik stellte modernste Möglichkeiten vor. Prof. Tuncay Akal aus der Türkei von SUASIS UNDERWATER SYSTEMS berichtete nicht nur von seiner langjährigen internationalen Erfahrung, sondern stellte ein gemeinsames Forschungsprojekt mit der Firma MICROFLOWN Avisa aus den Niederlanden zur experimentellen Bestimmung der akustischen Schnelle im Wasser vor. Ziel ist es, in die Lage versetzt zu werden, auch unter Wasser dominierende Schallquellen, sogenannte akustische „Hot Spots“, schnell und mobil zu identifizieren. Zivile und militärische Anwendungen haben bekanntlich oftmals dieselben Herausforderungen. Ob man sich zur Aufgabe gemacht hat ein Feldlager im Einsatzgebiet, eine Hafenanlage, ein Schiff auf Reede oder ein ozeanographisches Observatorium zur Erdsystembeobachtung zu schützen, zu sichern, zu überwachen oder zu betreiben, in jedem Fall ist hierzu die Beobachtung von systemrelevanten Daten notwendig. Die technischen oder wissenschaftlichen Herausforderungen sind hierbei in vielen Fällen ähnlich und koinzidieren auch. Es geht um kontinuierliche Datenerfassung und -fusion, moderne Sensornetzwerke, Zeit- und Kosteneffizienz, Satellitenverbindungen, Datenboten und -sammlern wie AUVs und Glider, hydrographische, akustische sowie seismische Messstationen und -verfahren. Bei all dem ist die Akustik gerade im Unterwasserbereich eine dominierende Technologieeinflußgröße. Zur Halbzeit der Tagung ging es nach Laboe, am Ehrenmal vorbei ins Restaurant Baltic Bay
zum Konferenzdinner. In angenehmer, maritimer und stilvoller Atmosphäre direkt am Segelhafen wurden die fachlichen Gespräche fortgesetzt und persönliche Kontakte aufgenommen respektive intensiviert. Dr. Lüder Hogrefe, Geschäftsführer von Raytheon Anschütz GmbH, begrüßte vor Ort die Wissenschaftler und hielt die Dinner Speech. Dr. Hogrefe betonte den zivil-militärischen Ansatz der Tagung, welcher „noch vor 15 Jahren nicht möglich erschien“. Die Veranstaltung hat bewiesen, dass der eingeschlagene Weg diese duale Betrachtung zulässt. Der vorliegende Tagungsband möge dieses bestätigen. Er spiegelt den aktuellen maritimen Forschungsstand bezüglich der oben angegebenen Themenschwerpunkte wieder. Wir bedanken uns bei allen Autoren und Vortragenden für ihre eingestellten Beiträge. Besonderer Dank geht an Frau Angela Günther für die Leitung des Tagungsbüros sowie für die lange Zeit der intensiven Vor- und Nachbereitung. Dank geht ebenfalls an Herrn Michael Krüger für die großartige technische Unterstützung. Es kann nicht unerwähnt bleiben, dass so manche weitere Hilfe im Hintergrund durchaus wahrgenommen wurde, doch sei aus Platzgründen hierfür nur insgesamt, doch keineswegs weniger nachdrücklich, gedankt.
are rare, and the entire range of the dynamics of gas release in space, time, and strength remains unclear so far.
To mitigate this, the hydroacoustic device GasQuant (180 kHz, multibeam) was developed to monitor the
tempo-spatial variability of gas bubble releases from the seafloor. GasQuant was deployed in 2005 on the
seafloor of the seep field Tommeliten (North Sea) for 36 h. This in situ approach provides much better spatial
and temporal resolution of seeps than using conventional ship-born echo sounders. A total of 52 gas vents have
been detected. Detailed time series analysis revealed a wide range of gas release patterns ranging from very short
periodic up to 50 min long-lasting events. The bulk gas seepage in the studied area is active for more than 70%
of observation time. The venting clearly exhibits tidal control showing a peak in the second quarter of the tidal
pressure cycle, where pressure drops fastest. The hydroacoustic results are compared with video observations
and bubble flux estimates from remotely operated vehicle dives described in the literature. An advanced
approach for identifying and visualizing rising bubbles in the sea by hydroacoustics is presented in which water
current data were considered. Realizing that bubbles are moved by currents helps to improve the detection of
gas bubbles in the data, better discriminate bubbles against fish echoes, and to enhance the S/N ratio in the per
se noisy acoustic data
- Geophysik/Turbulenz (Prof. Berndt/Dr. Fiekas)
- Maritime Messtechnik (Dr. Schmidtke)
- Unterwasserkommunikation (Dr. Nissen)
- Akustische Überwachung mit Sensornetzwerken (Dr. Ehlers, Dr. Schulz)
- Schiffbau (Dr. Stuntz)
- Hydroakustik/Grenzschichtturbulenz (Dr. Abshagen)
- Numerische Methoden (Dr. Schäfer, Ehrlich)
Am ersten Tag lag der Schwerpunkt der Veranstaltung auf Geophysik/Turbulenz. Dieses
Fachgebiet wird im benachbarten Forschungsbereich für Wasserschall und Geophysik (FWG) der WTD 71 von Dr. Heinz-Volker Fiekas geleitet, der zusammen mit Prof. Dr. Christian Berndt des GEOMAR den ersten Tag gestaltete. Hier zeigt sich die Verbundenheit beider Institute bezüglich dieses Themas. Im weiteren Verlauf der Tagung spielten neben Fragen der Ortung und Vermessung von Objekten am Meeresboden und in der Wassersäule mittels moderner Satellitentechnik auch die Beobachtung der Meeresoberfläche durch Synthetisches-Apertur-Radar (SAR) für Aufklärungszwecke eine bedeutende Rolle. Identifizierte, durch ein Schiff generierte Oberflächenwellen können die Position des Schiffes verraten. Dr. Susanne Lehner vom Deutschen Zentrum für Luft- und Raumfahrttechnik stellte modernste Möglichkeiten vor. Prof. Tuncay Akal aus der Türkei von SUASIS UNDERWATER SYSTEMS berichtete nicht nur von seiner langjährigen internationalen Erfahrung, sondern stellte ein gemeinsames Forschungsprojekt mit der Firma MICROFLOWN Avisa aus den Niederlanden zur experimentellen Bestimmung der akustischen Schnelle im Wasser vor. Ziel ist es, in die Lage versetzt zu werden, auch unter Wasser dominierende Schallquellen, sogenannte akustische „Hot Spots“, schnell und mobil zu identifizieren. Zivile und militärische Anwendungen haben bekanntlich oftmals dieselben Herausforderungen. Ob man sich zur Aufgabe gemacht hat ein Feldlager im Einsatzgebiet, eine Hafenanlage, ein Schiff auf Reede oder ein ozeanographisches Observatorium zur Erdsystembeobachtung zu schützen, zu sichern, zu überwachen oder zu betreiben, in jedem Fall ist hierzu die Beobachtung von systemrelevanten Daten notwendig. Die technischen oder wissenschaftlichen Herausforderungen sind hierbei in vielen Fällen ähnlich und koinzidieren auch. Es geht um kontinuierliche Datenerfassung und -fusion, moderne Sensornetzwerke, Zeit- und Kosteneffizienz, Satellitenverbindungen, Datenboten und -sammlern wie AUVs und Glider, hydrographische, akustische sowie seismische Messstationen und -verfahren. Bei all dem ist die Akustik gerade im Unterwasserbereich eine dominierende Technologieeinflußgröße. Zur Halbzeit der Tagung ging es nach Laboe, am Ehrenmal vorbei ins Restaurant Baltic Bay
zum Konferenzdinner. In angenehmer, maritimer und stilvoller Atmosphäre direkt am Segelhafen wurden die fachlichen Gespräche fortgesetzt und persönliche Kontakte aufgenommen respektive intensiviert. Dr. Lüder Hogrefe, Geschäftsführer von Raytheon Anschütz GmbH, begrüßte vor Ort die Wissenschaftler und hielt die Dinner Speech. Dr. Hogrefe betonte den zivil-militärischen Ansatz der Tagung, welcher „noch vor 15 Jahren nicht möglich erschien“. Die Veranstaltung hat bewiesen, dass der eingeschlagene Weg diese duale Betrachtung zulässt. Der vorliegende Tagungsband möge dieses bestätigen. Er spiegelt den aktuellen maritimen Forschungsstand bezüglich der oben angegebenen Themenschwerpunkte wieder. Wir bedanken uns bei allen Autoren und Vortragenden für ihre eingestellten Beiträge. Besonderer Dank geht an Frau Angela Günther für die Leitung des Tagungsbüros sowie für die lange Zeit der intensiven Vor- und Nachbereitung. Dank geht ebenfalls an Herrn Michael Krüger für die großartige technische Unterstützung. Es kann nicht unerwähnt bleiben, dass so manche weitere Hilfe im Hintergrund durchaus wahrgenommen wurde, doch sei aus Platzgründen hierfür nur insgesamt, doch keineswegs weniger nachdrücklich, gedankt.