Introduction

CHALLENGES AND OPPORTUNITIES

The ocean exerts a pervasive influence on Earth's environment; thus, it is important that we learn the intricacies of how this system operates (NRC, 1992; 1998b; 1999). For example, the ocean is an important regulator of climate change through its surface temperature and its control on atmospheric composition (IPCC, 1995). Understanding the link between natural and anthropogenic climate change and ocean circulation is essential if we are to predict the magnitude and impact of future changes in Earth's climate. Understanding our ocean and the complex physical, biological, chemical, and geological systems operating within it should be an important goal for the coming decades of the 21st century. This increased understanding will capture the public's imagination, and it will also, by necessity, bring about advancements in fields as diverse as engineering and biomedical technology. Another important motivating force to increase our understanding of ocean systems is that the global economy is highly dependent on the ocean for tourism, transportation, fisheries, hydrocarbons, and mineral resources (Summerhayes, 1996, and references therein). Thus, with continued population growth, it is inevitable that ocean resources will be increasingly relied on and will need to be used more effectively.

Recent oceanographic research has demonstrated that to understand the complex interaction of the various ocean systems, long-term time-series measurements of critical oceanographic parameters are needed to supplement traditional seagoing investigations (NRC, 1999). The more traditional method of investigating components of the ocean environment in isolation must be incorporated into a more holistic approach. The establishment of a global



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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE Introduction CHALLENGES AND OPPORTUNITIES The ocean exerts a pervasive influence on Earth's environment; thus, it is important that we learn the intricacies of how this system operates (NRC, 1992; 1998b; 1999). For example, the ocean is an important regulator of climate change through its surface temperature and its control on atmospheric composition (IPCC, 1995). Understanding the link between natural and anthropogenic climate change and ocean circulation is essential if we are to predict the magnitude and impact of future changes in Earth's climate. Understanding our ocean and the complex physical, biological, chemical, and geological systems operating within it should be an important goal for the coming decades of the 21st century. This increased understanding will capture the public's imagination, and it will also, by necessity, bring about advancements in fields as diverse as engineering and biomedical technology. Another important motivating force to increase our understanding of ocean systems is that the global economy is highly dependent on the ocean for tourism, transportation, fisheries, hydrocarbons, and mineral resources (Summerhayes, 1996, and references therein). Thus, with continued population growth, it is inevitable that ocean resources will be increasingly relied on and will need to be used more effectively. Recent oceanographic research has demonstrated that to understand the complex interaction of the various ocean systems, long-term time-series measurements of critical oceanographic parameters are needed to supplement traditional seagoing investigations (NRC, 1999). The more traditional method of investigating components of the ocean environment in isolation must be incorporated into a more holistic approach. The establishment of a global

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE network of seafloor observatories will help provide the means to accomplish this goal. In this report, seafloor observatories are defined as unmanned, fixed systems of instruments, sensors, and command modules connected either acoustically or via a seafloor junction box to a surface buoy or a fiber optic cable to land. These observatories will have power and communication capabilities and will provide support for spatially distributed sensing systems and mobile platforms. Sensors and instruments that are used at seafloor observatories will potentially collect data from above the air-sea interface to below the seafloor and will provide support for in situ manipulative experiments. Seafloor observatories will also be a powerful complement to satellite measurement systems by providing the ability to collect vertical measurements within the water column for use with the spatial measurements acquired by satellites while also providing the capability to calibrate remotely sensed satellite measurements. Ocean observatory science has already had major successes. For example, the Tropical Atmosphere-Ocean (TAO) array has enabled improved detection, understanding, and prediction of El Niño events and is an example of the achievements that can be accomplished with simple systems. TAO consists of approximately 70 moored ocean buoys in the tropical Pacific Ocean that telemeter oceanographic and meteorological data to shore in real-time via the ARGOS satellite system. TAO Autonomous Temperature Line Acquisition System (ATLAS) buoys (Figures 1-1 and 1-2) measure surface winds, air temperature and relative humidity, and ocean temperatures in the upper 500 m of the ocean, whereas TAO Equatorial Current Meter buoys include additional instruments to measure ocean currents and variables, such as shortwave radiation and rainfall. Another success is the SOund SUrveillance System (SOSUS), which is a fixed component of the U.S. Navy's Integrated Undersea Surveillance Systems network used for deep-ocean surveillance during the Cold War. SOSUS consists of bottom-mounted hydrophone arrays connected by undersea communication cables to facilities on . The combination of location within the oceanic sound channel and the sensitivity of large-aperture hydrophone arrays allows the system to detect radiated acoustic power of less than a watt at ranges of several hundred kilometers. SOSUS is an important tool for both continuous monitoring of low-level seismicity around the northeast Pacific Ocean and real-time detection of volcanic activity along the northeast Pacific spreading centers, and has provided a useful means to track whale migrations (Plate I). Although traditional seagoing investigations will continue to be prominent in oceanographic research, the question posed to this Committee was whether there is scientific justification for the establishment of a major coordinated seafloor observatory effort and whether such an effort is technically

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE FIGURE 1-1 Schematic drawing of a standard ATLAS mooring (PMEL, 1999).

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE FIGURE 1-2 Recovering an ATLAS mooring. The ATLAS buoy consists of a toroidally shaped fiberglass casing over foam with an aluminum tower and a stainless steel bridle. The toroid is 2.3 m in diameter. When completely rigged, the system has an air weight of approximately 225 kg, a net buoyancy of nearly 1800 kg, and an overall height of 4.9 m. The electronics tube is approximately 1.5 m long, 0.18 m in diameter, and weighs 27 kg. The buoy can be seen on radar for 4 to 8 miles depending on sea conditions (PMEL, 1999).

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE BOX 1-1 STATEMENT OF TASK This study will examine the scientific merit of, technical requirements for, and overall feasibility of establishing the infrastructure needed to implement a system of seafloor observatories. Recently, many seafloor observatory programs have been discussed or proposed. This study will assess the extent to which seafloor observatories will address future requirements for conducting multidisciplinary ocean research, and attempt to gauge the level of support for such programs within ocean science and the broader scientific community. feasible in the near future. To this end, the National Science Foundation (NSF) requested a study from the National Research Council's (NRC) Ocean Studies Board (OSB) to investigate the scientific merit and technical feasibility of establishing a series of seafloor observatories. A steering committee of eight members representing major areas of oceanographic science and ocean engineering was appointed to addresses the Statement of Task (Box 1-1) and write this externally reviewed consensus report. Although the statement of task for this study states that the committee will “gauge the level of support for such programs within ocean science and the broader scientific community,” no statistical measures were used. Instead, the very positive response to the symposium over a broad range of scientific disciplines and the enthusiastic nature of the discussions that occurred were used as evidence for broad community support for this initiative. WHY ESTABLISH SEAFLOOR OBSERVATORIES? In recent decades ocean, earth, and planetary sciences have been shifting from an intermittent, expeditionary mode of exploration and problem definition toward a mode of sustained in situ observation and experimentation. The motivation for this change is intellectually grounded and stimulated by new scientific discoveries and the unanticipated effects of earth and ocean processes on mankind. Examples of these include: the detection of formerly unknown, chemosynthetically based ecosystems hosted on and beneath the seafloor;

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE the widespread destruction wrought by the Northridge, California, and Kobe, Japan, earthquakes; the intense influence on global weather of the El Niño events of 1982-1983 and 1997-1998; and the clear realization that humans have affected marine ecosystems worldwide, both directly and indirectly through release of organic and inorganic pollutants, harvesting of fish and shellfish, and introduction of exotic species, and indirectly through climate alteration. This change in the mode of investigation stems from the realization that Earth and its oceans are not static, but are dynamic on many time and space scales, not just the relatively short timescales involved in the catastrophic examples above. Thus, understanding Earth and its oceans requires investigating processes as they occur, which cannot be satisfactorily accomplished with occasional mapping and sampling. A scientifically powerful component of the observatory concept is the collection of multiple oceanographic variables at a single location. These multidisciplinary datasets will enable the enhancement of more traditional oceanographic methods and allow for the development of new and creative ways of doing ocean science. While spatial mapping and exploration remains essential in setting the stage for process-oriented studies, a sustained time-series approach will be required to truly comprehend earth and ocean processes, and to develop predictive capabilities. Such an approach is implicit in recommendations of the recent NSF long-range planning “Futures ” reports (Baker and McNutt, 1996; Jumars and Hay, 1999; Mayer and Druffel, 1999; Royer and Young, 1999). For example, the APROPOS1 Report states that “long time-series observations … provide essential data on oceanographic processes, particularly those related to climate change” and recommends “a national effort to support sustained high-quality global observations over decades” (Royer and Young, 1999). In essence, this approach requires a sustained observational presence on the seafloor. In some subdisciplines, the seafloor observatory initiative is taking the form of adaptive “observatory” science based on long-term deployment of a wide variety of seafloor instrumentation, occasionally with real-time data transmission and instrument control. A strong case has been made that such capabilities will offer earth and ocean scientists unique potential to (a) study multiple interrelated processes over a range of timescales, in some cases conducting in situ perturbation experiments involving artificial modification of the natural environment to observe the effects of this modification; (b) conduct comparative studies of regional processes and spatial variability; 1   APROPOS - Advances and Primary Research Opportunities in Physical Oceanography Studies

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE and (c) map whole-earth and global ocean structures tomographically 2 using artificial and natural source signals. Fulfilling the scientific and societal potential of the seafloor observatory approach will entail significant philosophical and intellectual re-orientation within the oceanographic community, building on and complementing the more traditional focus in some disciplines on short-term spatial mapping and sampling. The reorientation for other disciplines with longer histories of collecting sustained time-series datasets will be more technological, particularly in terms of automating recording and also using two-way real-time communication. TYPES OF SEAFLOOR OBSERVATORIES DISCUSSED IN THIS REPORT In this report a “seafloor observatory” is defined as an unmanned system at a fixed site in the ocean providing power, command and control, and communications to sensors located on or below the seafloor, in the overlying water column, or at the air-sea interface. Sensors may be acoustically, electrically, or fiber-optically linked to the observatory node. The node may also support long-endurance mobile vehicles (e.g., Autonomous Underwater Vehicles [AUVs] and Remotely Operated Vehicles [ROVs]) that are capable of repeat surveys of a broader area around each node. We do not include various Lagrangian3 drifters or floats in this definition, but recognize that these systems would complement an array of fixed observatory sites as part of an integrated ocean observing system. In this report, we consider two classes of seafloor observatories: cable-based observatory networks and moored-buoy observatories. Cabled-based observatories will use undersea telecommunications cables to supply power, communications, and command and control capabilities to scientific monitoring equipment at nodes along the cabled system. Each node can support a range of devices that may include equipment such as an AUV docking station. Cabled systems will be the preferred approach when power and data telemetry requirements of an observatory node are high. The high cost of fiber optic cable and the need for a given location to support a nearby cable landing will limit the spatial coverage of these observatories. Moored-buoy observatories consist of a surface buoy acting as a central instrument node with a satellite or direct radio link to shore. The surface buoy is connected to the seafloor node acoustically or via an electrical or fiber optic 2   Tomographically - the use of changes in sound velocity to map variations in ocean structure or water mass circulation. 3   Lagrangian - following the path taken by a parcel of water as it moves relative to the earth.

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE riser, or both. Instruments and communicate via an acoustic communication link. Power generation for moored-buoy observatories can be achieved by a variety of means depending on the required wattage. These include solar and wind for low-power requirements and diesel generators for high-power requirements. Mooring-based observatories would be well suited to meet the needs of several major areas of science activities, including (1) studies of episodic events, (2) process studies for periods of months to several years, and (3) long-term observation in remote areas where cabled observatories are unavailable or prohibitively expensive to install. The spatial coverage of moored buoys will be dependent on their complexity and thus their unit cost. In general, moored buoys are lower in cost than for the equivalent capability in a cabled observatory. As such, buoys can be deployed in greater number and act as a network of nodes that have the potential to provide significant areal coverage. MAJOR PROPOSED AND ACTIVE OBSERVATORY PROGRAMS The scientific benefits of establishing a seafloor observatory network for oceanographic, climatic, and meteorological investigations have been recognized for many years. As such, numerous independent national and international observatory efforts have been proposed or are underway. Although a description of all of these observatory efforts is beyond the scope of this report, some are summarized here and in the chapters that follow. During the 1990s several workshops were held outlining long-term scientific strategies for the use of observatories in geophysics research. In 1996, a subset of the convenors for these workshops met to discuss the establishment of a national seafloor observatory initiative, concentrating on geophysics, that would combine but not subsume existing individual observatory efforts. In 1997, the initiative was named Deep Earth Observatories on the Seafloor (DEOS) and its membership and charter were formalized. Initially, the focus of DEOS was on deep-water geo-observatories, but this subsequently was expanded to include nearshore observatories and water-column studies. To reflect this effort to engage the wider oceanographic community, the acronym definition was changed to Dynamics of Earth and Ocean Systems in 1999. DEOS steering committee members represented the major national geoscience observatory programs (BOREHOLE,4 CABLE,RIDGE,5 MARGINS, and OSN6) with additional membership from the microbiological community (University of Miami, 1999). 4   BOREHOLE - BOREHole Observatories, Laboratories, and Experiments. 5   RIDGE - Ridge InterDisciplinary Global Experiments. 6   OSN - Ocean Seismic Network.

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE One major component of the DEOS planning effort is North East Pacific Time-series Undersea Networked Experiments (NEPTUNE), a proposal to establish a plate-scale observatory network on the Juan de Fuca Plate off the coasts of Oregon and Washington linked to land-based research laboratories and classrooms using high-speed, fiber-optic submarine telecommunication cables (NEPTUNE, 2000). This system has been designed to provide real-time data transmission to shore, interactive control over robotic vehicles on site, and power to instruments and vehicles. As many globally significant earth processes operate at or below the scale of tectonic plates, the proposed rationale behind NEPTUNE is that the seafloor observatory network should be constructed at the scale of a lithospheric plate. The site selected is the Juan de Fuca Plate located within a few hundred kilometers of the U.S.-Canadian west coast. It is proposed that NEPTUNE will allow scientists and educators to analyze and use data bearing on the linkages between key oceanographic and plate tectonic processes (NEPTUNE, 2000). Another major component of DEOS is the establishment of a permanent OSN consisting of ~20 sites throughout the world's oceans for improved geophysical imaging of the internal structure of Earth. These planetary-scale, fixed ocean observatories may also serve as long-term measurement sites for other types of oceanographic and climate studies, such as those envisioned by the Global Eulerian Observations (GEO) system of moorings (Plate II). The goal of GEO is to establish oceanographic observatories at select sites around the world's oceans for the collection of time-series measurements of surface meteorology; air-sea exchanges of heat, freshwater, and momentum; and full-depth profiles of water properties, including temperature and salinity, and ocean velocity. It is proposed that recent and future advances in mooring and instrumentation technology will enable the maintenance of the GEO observatories at a fraction of the cost of previous ocean weather stations. If successful, the sites will be an important element in an integrated observational system by providing the data necessary to develop a description of the ocean's role in climate. These observatories will also provide key observations of water mass formation and transformation. In addition, the data collected could be used to quantify the transports of the major ocean current systems, to assess vertical variability in ocean structure, and to document the role of eddy processes in the transport of heat and other properties. Time-series measurements from the GEO observatories will be an essential element of the strategy developed to construct accurate fields of air-sea fluxes. These observation stations have been proposed as an important component of the Global Ocean Observing System (GOOS). GOOS is an observatory framework formally initiated by the Intergovernmental Oceanographic Commission Executive Council in 1992 in cooperation with the World Meteorological Organization, United Nations Environment Programme, and the International Council of Scientific Unions (GOOS Project

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE Office, 1999; NRC, 1997). GOOS was conceived as an international system for gathering, coordinating, quality controlling, and distributing oceanographic data and derived data products as defined by the requirements of user groups. Support for planning and implementation is apportioned among GOOS sponsoring organizations and is supplemented through these organizations by financial and in-kind contributions from participating nations. The implementation is largely dependent on the commitment of supporting nations to their national observing systems. This commitment not only includes the infrastructure of the observatories themselves, but also the scientific and technical research that is needed to support data centers. The purpose of GOOS is to provide a framework to ensure long-term, systematic observations of the global ocean and to provide the mechanisms and infrastructure to make these data available to various nations for the solution of problems related to environmental change. GOOS is organized to resemble the global meteorological observation and prediction network presently supported by individual nations and implemented through the contributions of national agencies, organizations, and industries. Thus, observatories established under the auspices of GOOS will be primarily operational in nature. GOOS will include existing observing systems in addition to new systems, such as the proposed GEO observatories discussed above, that may become part of the GOOS network. Furthermore, it is likely that much of the data collected from a network of research-driven observatories, such as that proposed here, would be merged into the datasets that will be collected as part of GOOS. Much of the impetus for the GOOS plan has come from the need for operational oceanographic data to improve nowcasts and forecasts of ocean conditions and weather and climate. With the numerous multipurpose ocean observatory efforts in place or proposed, some of which are discussed in boxes later in this report, a great opportunity exists for synergy among these groups. This interaction was an important point of discussion at the symposium, and numerous common areas of interest were noted. For example, there is significant overlap in the locations needed to complete the OSN and those sites necessary for the GEO observatories (Plate II). If a major network of seafloor observatories were planned in the future, to conserve resources and share common technology it will be important to develop channels for interaction between established and proposed observatory efforts. It was not part of the Committee's charge to assess the strengths and weaknesses of existing observatory programs. A thorough review of these programs will be an important task during the drafting of an implementation plan for establishing a seafloor observatory program. When writing this implementation plan, the design strengths and weaknesses of existing programs be considered in detail.