Almorth, Elin

Andersson, Sara

Apler, Anna

Hall, Per

Nilsson, Madeleine

Tengberg, Anders

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INSTRUMENTATION VIEWPOINTSessions303. ConclusionsWe have successfully created the fi rst ocean bottom geomagnetic observatory. One of the most important and diffi  cult tasks (orienta-tion of measurements) is done using a gyroscope. The system is de-signed to deliver geomagnetic and geoelectric data in real-time.4. References[1] B.A. Buff et, Earth’s core and the geodynamo, Science, 288, 2007-2012, 2000.[2] National Research Council, “The National Geomagnetic Initiative”, Washing-ton D.C.: National Academy Press, 246 pp., 1993.[3] J.C. Larsen, Transport and heat fl ux of the Florida Current at 27 N derived from cross-stream voltages and profi ling data: Theory and observations, Phil. Trans. R. Soc. Lond. A338, 169-236, 1992.[4] A.H. Flosadottir, J.C. Larsen & J.T. Smith, Motional induction in North Atlan-tic circulation models, J. Geophys. Res., 102, 10353-10372, 1997.[5] A.D. Chave, F.K. Duennebier, R. Butler, R.A. Petitt, Jr., F.B. Wooding, D. Harris, J.W. Bailey, E. Hobart, J. Jolly, A.D. Bowen, and D.R. Yoerger, H2O: The Hawaii-2 Observatory,in L. Beranzoli, P. Favali, and G. Smriglio (eds.), Science-Technology Synergy for Research in the Marine Environment: Challenges for the XXI Century, Develop-ments in Marine Technology Series 12, Amsterdam: Elsevier, pp. 83-92, 2002.[6] J.H. Filloux, “Instrumentation and experimental methods for oceanic stud-ies”, in J.A. Jacobs (ed.), Geomagnetism, Vol. 1, New York: Academic Press, 143-248, 1987.[7] INTERMAGNET, “INTERMAGNET Technical Reference Manual”, 73 pp., 1994.OBSERVATORIES AND LANDERS TO STUDY OXYGEN DYNAM-ICS IN THE MARINE ENVIRONMENTAnders Tengberg, Elin Almroth, Sara Andersson, Anna Apler, Per Hall and Madeleine NilssonDept. of Chemistry, Göteborg University, SwedenIntroduction:Most chemical and biological processes result in changes in disolved oxygen concentrations. Oxygen is therefore a prime parameter to measure in marine environmental studies. Because of technological limitations of existing sampling methods and sensors long term mon-itoring of oxygen was not possible until the introduction of accurate and stable optical oxygen sensors. This technology has revolution-ized the possibilities to measure oxygen and has also open the door to obtain two dimensional pictures of the oxygen distribution at the sediment-water interface. In this presentation we will demonstrate new insights in the dynamics of oxygen in the marine environment by giving numerous examples ranging from shallow coastal areas to the deep Arctic Ocean. The presented investigations have been done combining a wide range of instrumentation mounted on both fi xed bottom platforms and autonomous landers. The rationale of using oxygen in environmental investigations will be described as well as the techniques. We will demonstrate that such combined measure-ments will make it possible not only to know more about the oxygen dynamics per se but also to use oxygen as a proxy for the ongoing biological, chemical and physical processes in the water column and at the bottom.Rationale of using oxygen to monitor the overall water quality: In near shore waters1. Biological production/consumption: During primary produc-tion in oceans and lakes CO2 and nutrients are incorporated by phytoplankton to create organic material (chemically written as (CH2O)106(NH3)16H3PO4). As a result of this process oxygen is pro-duced. Chemically the reaction can be expressed as: 106 CO2 + 122 H2 + 16 NHO3 + H3PO4   (CH2O)106(NH3)16H3PO4 + 138 O2. As written in the equation the approximate atomic ratios between oxy-gen, carbon, phosphorus and nitrogen are O138C106:N16:P1 which is known as the Redfi eld/Richards ratio. The phytoplankton can then be decomposed or consumed by zooplankton or fi sh which will in turn generate organic matter in the form of fecal pellets and dead organisms. The particulate organic matter sinks towards the bottom and on the way it can be further decomposed (by e.g. bacteria) and dissolved before it reaches the seafl oor. At the bottom organic matter is subjected to decomposition (mineralization), dissolution, and buri-al. Through mineralization oxygen is consumed and nutrients can be recycled to the water. This process can approximately be expressed as the reverse of the reaction described above.2. Water mixing: Oxygen conditions in the aquatic environment are aff ected by water circulation. Horizontal currents can bring in water which has been more exposed to bottoms with high oxygen demand or to discharge of industrial or urban waste water with chemical (COD) or biological oxygen demand (BOD).3. Air-water exchange: The dissolution of oxygen in surface water is aff ected by variations in air pressure according to the common gas law. The role of atmospheric air pressure changes on the total stock of dissolved oxygen is normally minor compared to oxygen varia-tions induced by biological production/consumption. Nevertheless it should be taken into account especially during the less productive parts of the year.4. Pollution induced oxygen consumption: Pollution from industry (mainly COD) and urban population (BOD) can play a signifi cant role in boosting the oxygen demand. This might lead to serious biological damages and will also signifi cantly infl uence on chemical equilibra-tions.Since oxygen concentrations are coupled to the four above listed fac-tors measuring oxygen in diff erent levels will mirror the sum of these changes. To be able to separate the reasons for oxygen concentration changes from each other it is crucial to measure water circulation, salinity and temperature in parallel. Useful information is also gained by adding sensors for chlorophyll, particles and light (if the water is shallow).Technology to study oxygen dynamics: In combination with other measurements, briefl y described above, we have used three diff erent techniques to study the oxygen dy-namics.1. Incubations: We have measured oxygen consumption as well as the total carbonate (TCO2) and nutrient production in-situ by mak-ing parallel chamber incubations of the sediment and the overlying water. This work has been done with autonomous landers which sink freely to the sea fl oor. There chambers are gently pushed into the sediment leaving about 20 cm of overlying water. Incubations start when lids are closed and stirrers start to mix the chamber water. Dur-ing incubations, which generally lasts for 36-48 h the oxygen concen-tration is continuously monitored in the enclosed waterusing oxygen optodes and samples (ten from each chamber) are au-tomatically collected into syringes. The water samples are analysed on-board once the lander has been recovered. The evolution in sol-ute concentrations with time gives information about the degrada-tion and burial of organic matter.M2INSTRUMENTATION VIEWPOINTSessions312. Planar Optode: A so called planar optode has been used to obtain the oxygenconcentration in two dimensions in the sediment and at the sediment-water interface. A planar optode is like an “inverted periscope” which is gently inserted into the sediment. Through a spe-cial optical technique, called luminescence quenching, it ispossible to obtain high resolution oxygen images. From the oxygen images oxygen concentration gradients (profi les) can be extracted. About 600 oxygen profi les can be extracted from each image and from the profi les the sediment oxygen consumption can be calculat-ed, which gives an independent estimate of carbon turnover rates.3. Oxygen gradients in the water: Oxygen optodes have been mount-ed at diff erent levelsin the water column. These sensors reveal the dynamism of the aquatic environmentand it is possible to extract gradients with lower concentrations for example closer tothe bottom and higher close to layers with active primary produc-tion. Together with information about the currents we have devel-oped methods that can be used calculate the oxygen consumption/production in diff erent layers.CUMASCABLED UNDERWATER MODULE FOR ACQUISITION OF SEISMOLOGICAL DARA FOR GEO-HAZARD MONITORING IN SHALLOW WATERG. Iannaccone (1), S. Guardato (1), M. Vassallo (2), L. Beranzoli (1)(1) Istituto Nazionale di Geofisica e Vulcanologia,Via Diocleziano 328, 80124 Naples, ITALY+39-081-6108305, iannaccone@ov.ingv.it(2)  Dipartimento di Scienze Fisiche, Università degli Studi di Napoli “Federico II” 1. IntroductionCUMAS is an underwater module developed for the acquisition of geophysical signals in shallow seafl oor for geohazard monitoring in volcanic areas. It was conceived for a specifi c application in the Campi Flegrei Caldera (Southern Italy) where the main features of the present volcanic activity consists of slow soil movements (brady-seism) accompanied by intense and shallow seismic activity. The latest strong episode occurred in the period 1982-84 with a ground uplift of more than 170 cm followed by a slow and continuous sub-sidence still ongoing with of small amplitude uplift episodes (few centimeters). It is worth noting that the seismic activity only appears during the uplift phase.CUMAS is the fi rst step toward the extension of the present operating land-based monitoring networks of the Campi Flegrei in the marine sector of the Caldera, roughly covering more than one third of the volcanic area. 2. CUMAS features and functionalities CUMAS has the aim to    -continuously acquire on the seafl oor geophysical and oceano        graphic data according to a single time reference;    -transmit acquired data in real time to a acquisition centre on land;    -receive commands from the land centre and accordingly modify its acquisition confi guration.CUMAS is powered through a cable connecting the module to a sur-face infrastructure; this ensure a long lasting deployment on the sea-fl oor.All these features make CUMAS fully integrated in centralised moni-toring system of the Neapolitan volcanic areas (Vesuvio, Campi Fle-grei and Ischia Island) managed by Osservatorio Vesuviano-INGV.CUMAS consists of a frame of steel with a shape of truncated pyramid of about 1 m high and a square base of 1 m per side. The total weight including the equipment is about 430 kg in air.In the CUMAS frame the following sensor packages are installed:1. seismological sensors aimed at recording local earthquakes related to volcanic activity and artifi cial explosions often caused by fi sher-men; the sensors include   -a three component broad band seismometer (0.025 s - 40 s) Guralp CMG-40T OBS with auto-levelling platform    - a broad band hydrophone (1 Hz – 65kHz) Sensor Technology SQ03 model2. physical oceanographic sensors are aimed at the long-term moni-toring of the water current regime also useful for seafl oor seismic microtremor studies; a further task consists in testing the feasibil-ity of the use of water pressure measurements at seafl oor to detect changes in water column pressure potentially related to bradiseismic activity. The oceanographic sensors include   -a single point three component acoustic current meter 3D-ACM Falmouth   -a pressure gauge Series 8000 Paroscientifi c.Data acquisition in performed by a Quanterra Q330 digitiser equipped with external hard disk as local mass storage. The digitiser is installed inside a cylindrical aluminium vessel and it is used to acquire the seis-mological sensors, both sampled at 125 sps. The data acquistion analog sensors and data acquisition embedded computer for sensors with digital output. The physical-oceanograph-ic sensors with digital output are acquired by an  embedded compu-ter with Linux o.s.Further sensors installed in the vessel are acquired by the Linux PC, namely tilt and heading sensors, for the measure of the real module attitude on the seafl oor, and status sensors for the monitoring of the internal status of the vessel (e.g., internal temperature, power absorp-tion, water intrusion).Both acquisition systems are linked via Ethernet cable to a router con-nected to an electro-mechanical cable for the real time data trans-mission to the sea surface. A Wi-Fi communication system ensures the seafl oor data transfer to the land acquisition centre in the city of Naples.M2

Observatories and landers to study oxygen dynamics in the marine environment

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