Azores Observatory – Atlantic Ocean The Azores and Mid-Atlantic Ridge area has special habitats associated with hydrothermal vents and sea floor morphology is distinct with recent crust spreading from the mid ocean ridge axis. Scientific context and relevance The MOMAR (“Monitoring the Mid-Atlantic Ridge”) project was initiated by the international InterRidge Programme, to study active mid-ocean ridge processes along a slow-spreading ridge segment (Lisbon, 1998). The goal is to promote and establish a coordinated and multidisciplinary long-term study of hydrothermal environments at the Mid-Atlantic Ridge (MAR) near the Azores (35°N to 40°N). Hydrothermal circulation at mid-ocean ridges is a fundamental process that impacts the transfer of energy and matter from the interior of the Earth to the crust, hydrosphere and biosphere. Seawater circulates through the permeable upper oceanic crust at mid-ocean ridges, exchanges chemicals with the surrounding rocks, and is heated up to temperatures of a few hundred degrees Celsius. This hot fluid flows up and is expelled at hydrothermal sites, in the form of black smokers, or diffuse vents. The unique faunal communities that develop near these vents are sustained by chemosynthetic microbes that use the chemicals in the hot fluids as a source of energy. Scientific objectives The objective of the MOMAR project is to study the temporal variability in active processes such as hydrothermalism, ecosystem dynamics, volcanism, seismicity and ground deformation, in order to constrain the dynamics of mid-ocean ridge hydrothermal ecosystems: • What are the feed-backs between volcanism, deformation, seismicity, and hydrothermalism? • How does the ecosystem couple with sub-surface processes? • What are the mass, energy and biological fluxes at hydrothermal vent fields? The implementation plan includes a multi-scale approach, ranging from the regional (>100 km) scale for seismicity, oceanography, and biological dispersion, to local (1 km) and very local (<1m) scales for the vent field and its ecosystem. The regional scale approach adresses fundamental issues such as: . the relation between intermediate depth hydrothermal fields, seamount ecosystems, and the evolution of fishing resources in the Azores area, . seismic and volcanic risks to populated areas in the Azores Islands, . and the movement of deep water masses and the consequences of changing thermohaline circulation in the North Atlantic on climate and on biodiversity. The planned regional seafloor system of geophysical observing sites will also be an important European contribution to the global network of seismic and magnetic observatories that is currently implemented to study the physics and chemistry of the Earth’s deep interior. The MAR near the Azores is ideally located for this marine multidisciplinary observatory project: it is near port (Horta on Faial Island; Figure 2), allowing for short transit times for the deployment and retrieval of tools, and making cable connection to shore an option for later stages of implementation of the project. 1/6 Azores Observatory – Atlantic Ocean The MAR near the Azores comprises 4 known hydrothermal vent fields, each with its own specific geological, chemical, hydrothermal, volcanic and biological characteristics (Lucky Strike, Rainbow, Menez Gwen, and Saldanha). It has been the focus of a great number of cruises in the past few years, as part of the FARA program (French-American Ridge Atlantic), the MARFLUX (MAST II EC program), AMORES and ASIMOV (MAST III EC program) and VENTOX (Framework V), EXOCET/D (Sarradin et al, 2005) and MoMARNET (Framework VI; Cannat et al., 2006) European projects. The geological-geophysical background of this region is well constrained, as are the general characteristics of the known hydrothermal vents, and the broad diversity of the associated ecosystems. The II and III MoMAR Workshops that took place in Horta, Azores (June 2002) (Santos et al, 2002), and in Lisbon (April 2005) provided an implementation plan for integrated studies and long-term observations in the MoMAR area. A list of critical experiments and an adequate order for implementation were established (all MOMAR workshop reports are available at www.momar.org). Following the II Workshop, the European scientific community coordinated several cruise proposals, and two EC proposals that have since been funded, one for development of observatory sensors (EXOCET/D; Sarradin et al., 2005), and the other a research and training EC network (MoMARnet; Cannat et al., 2006). A more recently funded FP6 project, NERIES, also includes MoMAR as one of its target sites for the long-term installation of a broad band Ocean Bottom Seismometer. The MoMAR ESONET node. Outline of the implementation plan Inside the MoMAR area, the Lucky Strike hydrothermal field (~37°37’N / 32°17’W) is the main target of the MoMAR ESONET node. Discovered in the nineties (Langmuir et al., 1997) this field has since been the object of many cruises, addressing its geological and geophysical characteristics (Detric et al., 1995; Cannat et al., 1999; Escartin et al., 2001; Miranda et al., 2005; Fouquet et al., 1995; Ondreas et al., 1997), as well as fluid chemistry and vent field biology (Desbruyères et al, 2001). Over 100 hydrothermal vents are distributed on the summit of a large axial volcano. Vent fluid temperatures range from the 330º C of black smokers, to low (200-212ºC), and very low (< 20ºC) temperature fluids (Von Damm et al., 1998; Cooper et al., 2000). Fluid temperatures at some vents appear to be very stable over a time scale of a few years (i.e., Tour Eiffel, 324±1°C), while others show variability of >10°C (Statue of Liberty, 202-185°C; Sintra, 176-215°C; Charlou et al., personal communication). A recent seismic exploration (SISMOMAR cruise; PI W Crawford) was able to identify the seismic signature of the axial magma chamber below the hydrothermal field, which is most likely the heat source for the Lucky Strike hydrothermal system. Long-term acoustic monitoring of the seismic activity (since 1999) of the Mid-Atlantic Ridge by networks of autonomous hydrophones moored in the SOFAR channel has demonstrated the usefulness of acoustic monitoring sensors deployed in the water column (e.g. Smith et al. 2002, Goslin et al. 2004). On average, due to the low attenuation of acoustic waves along their paths in the SOFAR channel, hydrophones are able detect 20 to 50 times more earthquakes than land-based networks (Figure 13) and provide better accuracy on their location (1-2 km error for events located within an hydrophone array). In July 2005, a network of 4 hydrophones has been specially deployed for a continuous monitoring of the low-magnitude seismic activity in the MoMAR sector at a regional scale (from 32°N to 39°N). This array will be turned-over in April 2006 for another year of monitoring (MARCHE cruises, PI J. Goslin). This hydroacoustic monitoring effort will provide the first long time-series of observation from the MoMAR observatory. Beyond 2007, real-time seismoacoustic monitoring will be a key issue for assessing the tectonic/magmatic/hydrothermal potential of future earthquake activity. 2/6 Azores Observatory – Atlantic Ocean The objective for the Lucky Strike MoMAR node is to set up a permanent seafloor observatory to record and relate seismicity, seafloor deformation, fluid flow, temperature and composition, with the dynamics of vent communities (including microbes). Implementation of the Lucky Strike MoMAR observatory has begun in 2005-2006 for seafloor deformation, near vents faunal communities monitoring, vent fluid temperature, and seismicity, with cruises funded primarily through the French system, with additional support from the EC FP6 EXOCET/D, and NERIES projects. In a first stage, sensors will be autonomous or linked acoustically to an ASSEM junction box equipped with messengers for periodic satellite data transmission to shore (Stage 1). Observatory experiments are presently planned for periods of 2 to 5 years, but decadal monitoring is aimed at, as it is the most adapted to the time scale of active processes in this ridge environment. Figure 1 : Earthquake epicenters identified along the Mid-Atlantic Ridge north and south of the Azores Plateau between June 1, 2002 and March 15, 2003. Black dots are the 1906 events recorded by the networks of autonomous hydrophones (deployment sites are the yellow stars and circles); white triangles are the 40 events recorded by land-based networks during the same period (NEIC catalog). As part of the MoMAR observatory, a network of 4 hydrophones was deployed around the MoMAR site (37N, 32W) in July 2005 for a period of two years (MARCHE cruises, PI J. Goslin). The longer term objective (>2008) is to implement an integrated monitoring infrastructure with real time data satellite transmission (stage 2), followed (>2012) by cable energy supply and data transmission (stage 3). It is envisioned that these later phases of the project should see an extension of real time monitoring to volcanic, hydrothermal and biological processes on the Azores Platform. This extension to nearer to shore active volcanic domains and biological hot spots will address the 3/6 Azores Observatory – Atlantic Ocean issues of volcanic and seismic hazard to the densely populated areas of the Azores Islands, and assist the Azores region for the durable management of its fishing resources. Existing national and international programs on the site Teams involved in the MOMAR project belong to 32 leading institutions corresponding to 9 European countries. Most have long experiences in seagoing operations, deep-sea experimentation and scientific and technological development. For many, the MoMAR project represents the exciting continuation of ongoing research efforts in the MAR - Azores Triple Junction region, with significant support through FP3, FP4 and FP5 programs, and from national funding agencies particularly in Germany, France, UK and Portugal. A few US colleagues are also involved in the planning, through the InterRidge Program. Although no US proposal has been funded so far, the involvement of these colleagues could lead to a formal EC-NSF agreement for the funding of the project in the years to come.