Beschreibung: Investigations of biogeochemical dynamics in the ocean depend first and foremost on the measurement capabilities in an adequate time and space domain. One limited approach for obtaining high (spatio-temporal) resolution in situ data is aimed at the ARGO observatory. With the intention to extend this platform for biogeochemical observations around the Cape Verde Ocean Observatory (CVOO) we modified and operated a NEMO profiling float successfully, equipped with CO2 partial pressure (pCO2) and O2 sensors for the first time. In cooperation with our local partner in Cape Verde (INDP) two campaigns were conducted at CVOO (Nov. 2010 – Feb. 2011) during which the instrument recorded 60 profiles in the upper 200 m of the water column. Each profile contains high resolution data for pCO2, oxygen, salinity, temperature, and pressure. First, we present instrument design and conducted campaigns. Second, we give a brief overview of data processing and quality of obtained measurements. Third, air-sea flux estimations derived from float- and land-based (CVAO) measurements will be shown.

Beschreibung: Carbon dioxide (CO2) and methane (CH4) concentrations in the oceans are key parameters for addressing many scientific questions as well as industrial applications. Extensive greenhouse gas datasets are important for reliable climate modeling. “Point measurements” help to understand the underlying processes or form the basis for countermeasures. Ocean acidification, natural gas seepage, carbon capture and storage (CCS) as well as pipeline monitoring are only some examples for fields of applications. The need for extended in situ measurements of dissolved CO2 or CH4 can only be met by having the right instrumentation combined with and efficiently integrated into modern platforms. Therefore the sensors need to be small, reliable and intelligent. The demands on sensors and platforms recently follow the same trend of becoming more and more autonomous. Thus it is very important to emphasize the point of sensor integration into platforms at an early stage in order to achieve an intelligent combination of the measuring device and its carrier. The concrete orientation of sensor improvements and developments to the platform manufacturer’s as well as scientific and industrial end-user’s needs leads to an effective, applied and hence successful integration. Sensors of the HydroC family for dissolved CO2 and CH4 determine gas concentrations in a membrane equilibrated headspace using non-dispersive IR-spectrometry. The small size and fast response time of the sensors lead to the deployment on different well-established as well as modern platforms such as buoys, remotely operated and autonomous underwater vehicles (ROVs, AUVs). From November 2010 until today a profiling float being equipped with a HydroC/CO2 as part of its sensor suite (CTD, dissolved oxygen) records an unique dataset. The sensors are continuously improved to e.g. further reduce their power requirements and size. By that even more challenging platforms such as gliders should be accessed.

Beschreibung: Dissolved greenhouse gas measurements (GHG) are of increasing importance for science, monitoring agencies and industry. Sensors for dissolved carbon dioxide (CO2) and methane (CH4) are applied in a growing number of applications. At the same time the number of mobile platforms deployed in the field is growing. Modern mobile platforms can sample on spatial and temporal scales that previously were not easily accessible thereby providing cost efficient data. Furthermore a trend towards the interconnection of mixed platforms and sensors is recognizable. The connection between these trends is discussed on the basis of sensor integrations into platforms. An approach between sensor and platform manufacturers becomes necessary to achieve an intelligent combination of contemporary measuring devices and their carriers as well as to make the adaptations on both sides efficient. Instruments of the HydroC™ family were successfully deployed on versatile stationary and mobile platforms, such as AUVs and floats. Platform and application demands for the deployment of dissolved gas sensors on diverse platforms are discussed. Fields of improvement for the instruments are identified to make them more versatile and access further platforms in the future.

Beschreibung: Carbon dioxide sequestration in sub-seafloor aims to store CO2 inside geological trapping structures below the seafloor. However there are concerns related to the possibility of leakage from the storage sites and potential consequences on the marine environment. In order to develop safe and reliable methods for CO2 monitoring, field studies were conducted in a natural analogue–an area where there is a natural release of CO2 from the seafloor. Due to the very high volume of gas emitted, this natural analogue could be considered as the worst-case scenario for a possible leakage from a sub-seabed storage site. Sampling procedures for free and dissolved gas and measuring techniques of the main physical and chemical parameters were developed for use both from the surface and directly underwater by scientific scuba divers. The first results of the research indicate that high levels of CO2 released in the marine realm strongly affect the local environmental conditions with a generalized acidification of the seawater. The experience gained in this study allows further development of a more accurate and suitable monitoring suite that will integrate sensors for measuring pH, dissolved CO2, and eventually, acoustic systems for the detection, monitoring and quantification of gas bubbles. The monitoring system could be deployed on the seafloor for long-term monitoring or could be carried onboard movable platforms such as ROV’s (Remote Operated Vehicles) or AUV’s (Autonomous Underwater Vehicles) for systematic surveys of the sub-seabed storage areas.

Beschreibung: Woolsey Mound, a 1km-diameter carbonate-gas hydrate complex in the northern Gulf of Mexico, is the site of the Gulf’s only seafloor monitoring station-observatory in its only research reserve, Mississippi Canyon 118. Active venting, outcropping hydrate, and a thriving chemosynthetic community recommend the site for study. Since 2005, the Gulf of Mexico Hydrates Research Consortium has been conducting multidisciplinary studies to 1. Characterize the site, 2. Establish a facility for real-time monitoring-observing of gas hydrates in a natural setting, 3. Study the effects of gas hydrates on seafloor stability, 4. Establish fluid migration routes and estimates of fluid-flux at the site, 5. Establish the interrelationships between the organisms at the vent site and the association-dissociation of hydrates. A variety of novel geological, geophysical, geochemical and biological studies has been designed and conducted, some in survey mode, others in monitoring mode. Geophysical studies involving merging multiple seismic data acquisition systems accompanied by the application of custom processing techniques verify communication of surface features with deep structures. Supporting geological data derive from innovative recovery techniques. Geochemical sensors, used experimentally in survey mode, including aboard an AUV, double as monitoring devices. A suite of pore-fluid sampling devices has returned data that capture change at the site in daily increments; using only noise as an energy source, hydrophones have returned daily fluctuations in physical properties. Ever-expanding capabilities of a custom-ROV have been determined by research needs. Processing of new as well as conventional data via unconventional means has resulted in the discovery of new features…..vents, faults, benthic fauna…..and modification of others including pockmarks, hydrate outcrops, vent activity, and water-column chemical plumes. Though real-time monitoring awaits communications and power link to land, periodic data-collection reveals a carbonate-hydrate mound, part of an immensely complex hydrocarbon system.