The Scientific Potential of Seafloor Observatories

The varied scientific presentations at the workshop demonstrated the significant potential of observatory science. Areas where time-series data collected from seafloor observatories would advance research include:

  • Studies of episodic processes—Episodic processes include eruptions at mid-ocean ridges, deep-ocean convection at high latitudes, earthquake swarms at subduction megathrusts, and biological, chemical, and physical impacts of episodic storm events. These processes can be anticipated only in a statistical sense; accurate prediction of the timing for an individual event is not possible. Lower-complexity mooring-based observatories are beneficial for the study of episodic processes, as they provide a lower-cost system for deployment in anticipation of or in the aftermath of an episodic event.

  • Process studies for periods of months to several years—The ability to deploy an observatory in remote locations to investigate oceanographic processes occurring on timescales of months to years is a critical need of the oceanographic community. These processes include hydrothermal activity and biomass variability in vent communities along portions of the mid-ocean ridge system, air-sea interactions in the Southern Ocean, and biological and chemical variability of the water column at both coastal and oceanic sites.

  • Observations of global and long-term processes—Moored observatories will be essential for the establishment of an observatory network to investigate global processes, such as the dynamics of oceanic lithosphere and thermohaline circulation. These moored systems would also



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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE The Scientific Potential of Seafloor Observatories The varied scientific presentations at the workshop demonstrated the significant potential of observatory science. Areas where time-series data collected from seafloor observatories would advance research include: Studies of episodic processes—Episodic processes include eruptions at mid-ocean ridges, deep-ocean convection at high latitudes, earthquake swarms at subduction megathrusts, and biological, chemical, and physical impacts of episodic storm events. These processes can be anticipated only in a statistical sense; accurate prediction of the timing for an individual event is not possible. Lower-complexity mooring-based observatories are beneficial for the study of episodic processes, as they provide a lower-cost system for deployment in anticipation of or in the aftermath of an episodic event. Process studies for periods of months to several years—The ability to deploy an observatory in remote locations to investigate oceanographic processes occurring on timescales of months to years is a critical need of the oceanographic community. These processes include hydrothermal activity and biomass variability in vent communities along portions of the mid-ocean ridge system, air-sea interactions in the Southern Ocean, and biological and chemical variability of the water column at both coastal and oceanic sites. Observations of global and long-term processes—Moored observatories will be essential for the establishment of an observatory network to investigate global processes, such as the dynamics of oceanic lithosphere and thermohaline circulation. These moored systems would also

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE provide long-term capabilities in remote regions where cabled observatories are unavailable or would be prohibitively expensive to install. The sections in this chapter summarize the discussions and scientific outcomes of breakout groups organized according to the six National Science Foundation (NSF) decadal report themes based on the “Futures ” workshops (Baker and McNutt, 1996; Jumars and Hay, 1999; Mayer and Druffel, 1999; Royer and Young, 1999). Each section addresses future directions and major scientific problems, the role of sustained time-series observations, and technical requirements for seafloor observatories. Boxes describing currently active observatory or time-series experiments have been included where they are appropriate to the science being discussed. In addition, tables (developed based on symposium discussions) have been added to each section, highlighting areas where observatories are “very useful” in investigating a scientific problem, and where they are “useful.” The term “very useful” is used to categorize scientific problems for which long-term, time-series datasets collected at seafloor observatories will result in substantial scientific progress that will either not be possible using a traditional expeditionary approach or can only be accomplished with limited success using more traditional means. “Useful” is used to categorize those scientific problems for which an observatory approach will provide a valuable complement to other more traditional research strategies. ROLE OF THE OCEAN IN CLIMATE Climate variations have widespread societal, economic, and environmental impacts. As a result, vigorous research efforts are currently aimed at improving understanding of the spectrum of climate system variations, discovering potentially predictable elements, and exploiting that potential. For example, El Niño/Southern Oscillation (ENSO) forecasts have demonstrated both the potential and the value of climate prediction. The ocean is an intrinsic component of Earth's climate system, playing an increasingly important role in determining the nature of climate variability as timescales increase. Researchers seek to improve our understanding of the role of ocean heat storage, transport, and release in the coupled ocean-atmosphere-land climate system, and of the interactions of oceanic biogeochemistry with the climate system (Boxes 2-1 and 2-2). FUTURE DIRECTIONS AND MAJOR SCIENTIFIC PROBLEMS Ultimately, we seek to predict climate variability and change. This requires accurately predicting the evolution of the ocean (especially near-surface temperatures) when changes in atmospheric forcing occur. Despite impressive

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE progress with forecasting seasonal-to-interannual evolution associated with ENSO events, there is considerable room in these and longer timescales for improvement in the observation, analysis, and assessment of predictability of the oceanic component of the coupled climate system. For example, it is now clear that Pacific decadal climate variability influences ENSO, and it is possibly strongly coupled to ENSO. Research has conclusively shown that the ocean exerts an important influence on decadal climate variability, but details of its role are unclear. Several hypotheses have been developed to explain the sparse oceanographic observations and climate model behavior. Another example involves the North Atlantic Oscillation influencing ocean physics on decadal time scales, such as Labrador Sea wintertime deep convection and the path of the Gulf Stream extension. Limited observations and models suggest that there is a feedback of the resultant ocean variability onto the atmosphere. An important problematic challenge before us is separating natural interannual-to-centennial climate variations from anthropogenically induced climate change. This understanding is critical for predicting future variations and magnitudes of climactic change. For both hypothesis testing and prediction purposes, we rely increasingly on models of the climate system. Even though the present generation of ocean general circulation models are much improved, representation of important ocean physics is still crude. A substantially improved observational basis for determining the needed model enhancements is required. Specific ocean science challenges include quantifying and understanding turbulent mixing; convection; water-mass formation and destruction; thermohaline circulation and its coupling to the wind-driven circulation; the generation, maintenance, and destruction of climatic anomalies; climatic oscillations and the extratropical coupling of the ocean and atmosphere on seasonal, decadal, and interdecadal timescales; and the physics of exchange processes between the ocean and the atmosphere (Royer and Young, 1999). The U.S. scientific community has played an important role in shaping and is actively participating in the World Climate Research Programme 's Climate Variability and Predictability (CLIVAR) program in order to address the challenges outlined above (NRC, 1994a; NRC, 1996a; NRC, 1998b; NRC, 1998c). CLIVAR scientists have worked with other ocean programs to develop plans for a global ocean-observing system that will meet the research requirements for major advances in understanding the role of ocean processes in the climate system and will provide a basis for predictability research (NRC, 1994b; NRC, 1997). THE ROLE OF SUSTAINED TIME-SERIES OBSERVATIONS Oceanographic variability has a significant influence on climate. Because of nonlinear scale interactions, it is essential for the study of climate to fully

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE BOX 2-1 THE HAWAII OCEAN TIME-SERIES Objectives: The Hawaii Ocean Time-series (HOT) objectives are to document seasonal and interannual variability of water masses in the North Pacific Ocean subtropical gyre; to relate water mass variations to gyre fluctuations; to develop a climatology of short-term variability; to document and understand seasonal and interannual variability in the rates of primary production, new production, and particle export from the surface ocean; to determine the mechanisms and rates of nutrient input and recycling, especially for nitrogen and phosphorus in the upper 200 m of the water column; to measure the time-varying concentrations of dissolved inorganic carbon in the upper water column; and to estimate the annual air-to-sea carbon dioxide flux. To achieve these objectives, biogeochemical and physical observations are collected monthly or near-monthly during three-day shipboard occupations of Station ALOHA. A subsurface sediment trap mooring is maintained at ALOHA, along with a surface mooring with meteorological, bio-optical, and physical sensors approximately 40 km away. A coastal station (Kahe Point) is also sampled during most cruises. Information is provided in Karl and Lukas (1996). Additional information on the HOT time-series can be found at http://hahana.soest.hawaii.edu/hot/hot.html (HOT, 2000). Location: Station ALOHA is located 100 km north of Oahu in 4,740 m of water. The Kahe Point station is about 10 km offshore in water depth of about 1,500 m (Figure 2-1). Established: HOT was established in late 1988 with National Science Foundation funding under the auspices of the Joint Global Ocean Flux Study (JGOFS) and World Ocean Circulation Experiment (WOCE) programs The surface mooring was first deployed in early 1997 resolve many scales of variability, and the consensus is that this will require nested, complementary observing systems (Table 2-1). In particular, the vision that is developing for an ocean-observing system for climate consists of a number of highly instrumented fixed sites around the world, a larger number of fixed sites of lesser capability, and a global array of Lagrangian samplers, all working in concert with global satellite remote sensing and global data assimi

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE FIGURE 2-1 Locations of HOT sampling stations with water depth indicated by the grayscale defined above (Lukas and Karl, 1998). lative modeling. Fixed site observatories would primarily consist of moorings, which are best suited for vertical and temporal sampling. Moorings also provide the means to sample scientifically critical regions, such as the upper few tens of meters of the ocean under ice cover in confined current systems and in abyssal layers (including bottom boundary layers; see “Turbulent Mixing and Biophysical Interaction” section in this chapter).

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE BOX 2-2 BERMUDA ATLANTIC TIME-SERIES STUDY Objective: The Bermuda Atlantic Time-series Study (BATS) commenced monthly sampling in the western North Atlantic subtropical gyre as part of the U.S. Joint Global Ocean Flux Study (JGOFS) program in 1988. The goals of U.S. JGOFS time-series research are to better understand basic processes controlling ocean biogeochemistry on seasonal to decadal timescales, to determine the role of the oceans in the global carbon budget, and ultimately to improve our ability to predict the effects of climate change on ecosystems. The BATS uses a monthly shipboard sampling scheme to resolve seasonal patterns and interannual variability. Core cruises last four to five days during which hydrography, nutrients, particle flux, pigments and primary production, bacterioplankton abundance and production, and complementary ancillary measurements are made. This study also incorporates data from nearby Hydrostation S, the Ocean Flux Project, and the Bermuda Testbed Mooring (BTM). Hydrostation S, established in 1954, is one of the longest-running oceanic and atmospheric time series. All of the data from the BATS program and many of the data from the Hydrostation S and BTM are available publicly at the Bermuda Biological Station for Research home page at http://www.bbsr.edu (and then following the links to the BATS data). Location: The BATS station lies 82 km southeast of the island of Bermuda (31 ° 40' N, 64° 10' W) in the Sargasso Sea, approximately 1,200 km from the east coast of the United States (Figure 2-2). Bottom depth at the BATS deployment area is ~4,680 m. Established: Monthly sampling commenced in October 1988. In addition, observatories, together with other elements of the nested observing system (such as Lagrangian samplers and satellites), provide the physical oceanographic context for interpreting biological and chemical distributions. Considerable planning for observatory-based science necessary for climate research has been conducted by the oceanographic community. The Ocean Observing System Development Panel (OOSDP) developed the scientific basis for global ocean observations for climate and prioritized the observations that would be made (Nowlin, 1999). The Ocean Observing Panel for Climate

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE FIGURE 2-2 Location of the BATS sampling station. SOURCE: Deborah K. Steinberg, Bermuda Biological Station for Research. (OOPC) is moving toward implementation of the OOSDP recommendations.OOPC and other groups representing climate research interests hosted a major international conference, OceanObs99, in St. Raphael, France, in October 1999 (OCEANOBS99, 1999); the conference gathered broad input from the ocean science and climate communities and helped further the scientific rationale for sustained observations. At present, we have very few sustained observing sites supporting research on the role of the ocean in climate. To further our understanding of the role of

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE TABLE 2-1 The Role of Ocean in Climate: Areas Where Observatories Are Very Useful to Investigate a Particular Scientific Problem and Where They Are Useful Observatory science is VERY USEFUL in accomplishing the following: Test and improve ocean circulation models; Observe and understand extratropical coupling of ocean and atmosphere on seasonal to interdecadal timescales; Understand the physics of the exchange processes between the ocean and atmosphere; Observe the generation, maintenance, and destruction of ocean climate anomalies; Predict climate variability and change; Monitor, understand, and predict the sequestration of carbon dioxide in the ocean; productivity and biomass variability, including identification of the factors that control them; the full temporal and vertical evolution of thermohaline structure; rapid episodic changes of the ocean (e.g., mixed-layer response to hurricanes, deep convection, meridional overturning circulation); changes in water mass transformation processes; air-sea exchanges of heat, moisture, momentum, and gases; thermohaline variability in the Arctic and Antarctic; vertical exchanges of heat, salt, nutrients, and carbon; the pathways of ocean transports, such as deep western boundary currents; and the role of eddies in transport and mixing. Provide reference sites for calibration or verification of air-sea fluxes from numerical weather prediction models, satellites, and other methods; absolute interior and Ekman layer velocities; remotely sensed variables (sea surface temperature, sea level, wind, color); and model statistics, physics, and parameterizations and how they change in evolving climate systems. Observatory science is USEFUL in investigating the following: Water mass formation and destruction; and The relationship of heat and freshwater fluxes to wind and buoyancy forcing.

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE the ocean in climate, seafloor observatories should be long-term (outliving individual investigator proposals), shared-use facilities that sustain climate community measurement goals while allowing technology to evolve. A fundamental change achieved by pursuing the observatory concept would be maintenance of existing sites and establishment of new sites. This may be the key to moving from our current focus on long-term science projects, such as CLIVAR (which may result in 5- to 10-year time series), to the implementation of a sustained global ocean-observing system. TECHNICAL REQUIREMENTS The technical requirements of the climate and turbulent mixing communities have an important overlap, and there are compatible needs for platforms. The strategy of nested, complementary elements of an observing system is shared, and it is agreed that fixed observatories are uniquely able to support the required observations. For the climate-science issues discussed above, the objectives do not, in general, require high power (present systems work at 5 W and less) or high data rates (tens to hundreds of numbers are now sent back per hour or per day). Long-range acoustic tomography requires more power (approximately 200 W) for driving acoustic sources. Acoustic tomography also produces large volumes of data that are not presently relayed using real-time telemetry. The availability of ocean observatory sites around the globe that could provide power and access to data telemetry and two-way communication would enable the climate and mixing communities to make greater progress toward their science goals. Furthermore, at the symposium, it was noted that the map of Global Eulerian Observatory (GEO) sites produced by the OceanObs99 climate conference had a number of sites close to sites proposed for the Ocean Seismic Network (OSN) (Plate II). This synergy emphasizes the need for a dialog between proponents of observatories for different science goals to maximize mutual benefits and to explore how observatory sites occupied for other reasons could enable further progress in climate and mixing research. Sites shown on Plate II fall into the category of global observatories, and would be key elements of the nested, complementary network required for global ocean observations for climate studies. These are viewed as relatively high-power, high-capability sites that would provide opportunities for instrument integration, data access, and a surface expression. Their design minimize radio frequency contamination of sensors, shadowing of sunlight, disturbance of flow in the atmosphere and ocean, and biological and chemical contamination of the ocean and atmosphere. The mooring design should also permit the storage and release on demand of garage floats, autonomous underwater vehicles (AUVs), weather balloons, and other autonomous instrument packages. These high-capacity sites would become focal points for multi

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE disciplinary oceanographic science and should contain a standard suite of instrumentation including bottom-pressure sensors; inverted echo sounders; electric-field sensors; temperature, salinity, velocity, surface meteorological, optical, and aerosol systems; and sensors to measure key chemical, optical, and biological parameters. Relocatable observatories consisting of one or more moored platforms would be highly valuable for climate-related process studies involving turbulent mixing, air-sea exchange, biochemistry, coupled upper-ocean optics, etc. Different types of relocatable observatories should be considered for investigating specific science questions. These could be repositioned for one or more years at different locations around the globe as needed, such as proposed for surveying turbulence parameter space in the “Technical Requirements” of the “Turbulent Mixing and Biophysical Interaction” section. Relocatable observatories should have power available along with data transmission capabilities. There was interest expressed at the symposium in taking relocatable observatories to extreme environments (for example, areas with high wind speeds) and data-sparse regions where significant impact on climate science would be anticipated. Further development of moored turbulence sensors is needed for use on relocatable observatories. Permanent cabled observatories are of interest as sites where multidisciplinary “laboratories” could be developed. Of particular interest would be efforts to fully image a three-dimensional (3-D) volume in the ocean, resolving the time and space variability of the physics, biology, chemistry, and geology on scales from centimeters to kilometers (the 3-D aspect is discussed in more detail in the “Turbulent Mixing and Biophysical Interaction” section). Such observatories should have the physical infrastructure to permit growth and easy addition of new users and instruments. FLUIDS AND LIFE IN THE OCEANIC CRUST The chemistry and biology of fluids within the oceanic crust is a cutting-edge research field for which seafloor observatories are thought to be a needed investigative approach (Table 2-2). One of the most exciting scientific problems that can be addressed using observatory science concerns the nature of the subsurface biosphere, thought to contain a population of dormant microbes that are periodically driven into a population explosion by input of heat and volatiles into the crust during magma emplacement events (Boxes 2-3 and 2-4; Delaney et al., 1998; Summit and Baross, 1998). In addition to the ridge crest and flanks, a population of microbes is also thought to exist in the extreme environment of subduction zones sustained by either continuous or episodic input of energy and nutrients (Cragg et al., 1995). Another exciting and closely related scientific problem concerns the general response of the hydrothermal system and associated biota to seafloor spreading events in which magma is

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE TABLE 2-2 Fluids and Life in the Oceanic Crust: Areas Where Observatories Are Very Useful to Investigate a Particular Scientific Problem and Where They Are Useful Observatory science is VERY USEFUL to investigate the following: The chemical and biological response to episodic volcanic and hydrothermal events; The formation of event plumes; Subsurface biosphere; Marine food webs on the seafloor; and The linkages between geological, biological, and chemical processes in ocean crust. Observatory science is USEFUL to investigate the following: Fluid flow on ridge flanks; and Simultaneous environmental variability in ridge crest, flanks, and convergent margins. To address the science where observatories are very useful, development or improvement of the following sensors is needed: Chemical, biological, and flow-rate sensors that can operate at high temperatures for long-term deployment without servicing; Fluid and biological samplers suitable for long-term deployment; AUVs, drifters, and other instruments for use in rapid-event response; Downhole sensors for use in boreholes; Instruments for acoustic event detection (such as the SOund SUrveillance System [SOSUS]); and Advanced capabilities for drilling into ocean crust. injected into the crust. This research would include the response of seafloor biological communities at convergent margin seepage sites to abrupt changes in fluid and chemical fluxes caused by seismic activity. Similarly, the dynamics of gas hydrate formation and dissociation, especially in response to perturbations produced by tectonic cycles or global warming, is a problem of current interest that could be addressed by observatory science. FUTURE DIRECTIONS AND MAJOR SCIENTIFIC PROBLEMS Four different oceanic environments are important for research on fluids and life in the ocean crust: ridge crests, ridge flanks, convergent margins, and coastal areas on passive margins. The ridge-crest environment can be further subdivided into sedimented versus non-sedimented ridges, magma-rich versus

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE TABLE 2-5 Turbulent Mixing and Biophysical Interaction: Areas Where Observatories Are Very Useful to Investigate a Particular Scientific Problem Observatory science is VERY USEFUL to accomplish the following: Observe and understand processes that modulate vertical turbulence statistics; Generalize turbulent flux parameterizations; Determine the relationships between temporal and spatial distribution of turbulence in the ocean (assuming AUV capabilities); Map subsurface distribution of mesoscale and sub-mesoscale horizontal turbulence (assuming AUV capabilities); and Determining the impacts of turbulent mixing on biochemical distributions. parameterization will be elusive. Because turbulence depends strongly on stratification, vertical resolution of turbulence parameters has the highest priority. Fine sampling in the horizontal will be more valuable than fine temporal sampling for resolving mixing issues. Repeated, high, vertical-resolution sampling with a coarse, horizontal array of moored conductivity, temperature, and depth (CTD) and velocity profilers is now possible, and such an array can be used to examine mixing issues independent of a seafloor observatory program. To add value to these arrays, the seafloor observatory concept must provide the needed horizontal resolution over much finer scales than presently possible. This increased resolution would provide fully four-dimensional sampling and could be obtained with AUVs. Near real-time telemetry and an active modeling and analysis component could be employed to optimize the sampling strategy. Other methods of obtaining high-resolution spatial information should also be explored, such as horizontal mooring lines and acoustic Doppler technology. The strategy outlined above could go far in terms of closing budgets or constraining numerical models. (Closure of heat, salt, momentum, and tracer budgets is important because it demonstrates sufficient observational accuracy and adequate resolution of advection and mixing.) A sequence of field programs in different dynamical regimes would provide us with a decadal leap in the understanding of mixing processes by covering the oceanic turbulence parameter space. A seafloor observatory program would be of great benefit to advancing our understanding and parameterization of mixing if it were to enable such a dedicated set of oceanic observations. Suggested dynamical regimes, which should not be considered exhaustive, are discussed in Box 2-9 below. A similar problem exists for observing and parameterizing the effects of horizontal turbulent motions, in particular for mesoscale eddies, although the technical challenge of observing those scales of turbulence is not nearly so high as for the very small scales of vertical mixing.

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE BOX 2-9 SURVEYING TURBULENCE REGIMES IN PURSUIT OF UNIVERSAL PARAMETERIZATION Some of the dynamic regimes that need to be observed to develop more universal turbulence parameterizations include the following: A smooth bottom dominated by steady geostrophic flows (e.g., the deep western boundary current below the Gulf Stream). Rough-bottom topography. Flow over bottom roughness that extends into the stratified water column can excite internal waves that propagate and break. Special cases are: Linear generation models. Nonlinear, finite amplitude bathymetry effects. Bottom boundary condition of downward propagating internal waves. Decay of low-mode tide above smooth bottom boundary, decoupled from internal tide generation problem. Marginal mixing. Roughness alters the secondary (turbulence-induced) circulations. This appears to be a generic response to mixing about topographically rough environments. Such flows have major implications for biological dispersal. Dense water formation. What limits the rate of dense water production and its final density? What role does mixing play in the two-layer outflow? What controls the downstream evolution of the turbulent boundary current on a sloping boundary? What controls vortex shedding and eddy formation, and are they important? Internal tidal solitons. Because of their large amplitude and high frequency of occurrence in climatically important regions, the role solitons play in mixing (especially in the near-surface layer) must be determined. Sill overflows. Mixing is an important process associated with constrained passages in the abyssal ocean. Extreme atmospheric forcing of the near-surface boundary layer. Double diffusive regime. Hydrothermal vent fields. Vents are a source of turbulence through buoyancy production. Plume dispersal is an important issue for biogeochemistry.

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE The continental shelf. How do alongshore flows effect cross-shelf transports? Vortex shedding. Flow over and along steep or rough topography can produce vortex shedding, which can efficiently advect and disperse water-mass properties, chemical compounds, and organisms. Baroclinic instability. The parameterization of fluxes resulting from this process is very important. Sediment gravity flows. There are important potential synergies that could be achieved by collocating biological and physical studies. These were not addressed by the workshop, but are alluded to in both the Report of the APROPOS Workshop (Royer and Young, 1999) and Report of the OEUVRE Workshop (Jumars and Hay, 1999). The idea of “imaging” a volume of the ocean to quantify circulation, mixing, biology, and chemistry within a high-resolution cabled observatory has been suggested. The connection of biomass “patchiness” to eddies is an important topic to be pursued. The turbulent mixing discussion at the workshop concluded that an observational and modeling strategy that uses the seafloor observatory infrastructure could significantly advance our understanding of turbulent mixing processes and our ability to parameterize them in ocean models. This, in turn, would have an important impact on biogeochemical models. The observatory concept is of limited value to the turbulent mixing community without the ability to implement the strategy of acquiring data in four dimensions while executing dedicated process studies. TECHNICAL REQUIREMENTS Platforms for turbulence measurements must be designed to minimize flow distortion and impacts on turbulence structures. Relocatable observatories will be needed to support process studies to survey turbulence parameter space, and to study the influences of turbulent motions on biological processes. To accomplish the required observations within a decade, three observatories must be dedicated to this task, with a deployment of 2 to 3 years in duration at

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE each location. This number of observatories allows for refurbishment and sequential deployments. Each observatory would consist of a coupled array of moorings and a number of AUVs. The moored array would consist of 3 to 5 (subsurface) moored profilers measuring velocity, pressure, temperature, salinity, fluorescence, light transmission, and irradiance; and a surface mooring measuring atmospheric forcing, near-surface currents, and other variables. The mooring could also employ a bottom tripod system, such as the Benthic Acoustic Stress Sensor. The AUVs should measure velocity, conductivity, temperature, depth, and turbulence parameters. Cabled observatories would be most appropriate for long-term intensive volumetric interdisciplinary studies with evolving capabilities, such as for investigating the interaction of biological processes with mesoscale eddies. There is a need for turbulence sensors that are compatible with long unattended deployment periods on moorings and AUVs. New sensors must be developed for nutrients (macro and micro) and other chemicals. Sensor development is also required for automated plankton, nekton, and benthic species identification and enumeration by , physiological state, and other traits of interest. The stability and calibration of all sensors requiring long-term deployment is an important consideration that needs to be addressed. Furthermore, the capability of tracking natural tracers (e.g., atmospheric inputs, seafloor vent effluent) and for releasing and tracking purposeful tracers (SF6; glass microballs for acoustic tracking) is important for quantifying the integral impacts of mixing. Technical requirements in common with the ocean climate objectives are given in the section titled “Role of the Ocean in Climate” earlier in this chapter. ECOSYSTEM DYNAMICS AND BIODIVERSITY Seafloor observatories are crucial for addressing many of the major scientific problems identified by the NSF Futures report on biological oceanography, Report of the OEUVRE Workshop (Jumars and Hay, 1999; Table 2-6). Specific questions benefiting most from the sustained time-series observations are those regarding time-dependent processes and episodically triggered events, and those requiring long-term datasets. These questions fall under broad integrative categories that range from oceanic biology and ecology to biogeochemistry. Other equally valid questions are not well served by the observatory approach, such as those concerned with details of specific biochemical, cellular, or physiological mechanisms occurring within organisms, or behaviors and environmental interactions occurring on the scale of individual organisms. It is also important to note that the observatory approach, while necessary for solving many problems in marine ecology and biological oceanography, is not sufficient alone, and must be used in concert with other approaches (e.g., controlled experimentation, modeling, analysis of the fossil record).

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE TABLE 2-6 Ecosystem Dynamics and Biodiversity: Areas Where Observatories Are Very Useful to Investigate a Particular Scientific Problem and Where They Are Useful. Observatory science is VERY USEFUL to accomplish the following: Detect and follow episodic ecological events (e.g., plankton blooms, faunal responses to volcanic eruptions or hydrothermal fluid events, faunal responses to detritus-deposition events in deep water, mass spawning events); Characterize and understand long-term (annual to decadal) ecological cycles (e.g., predator and prey population dynamics, spread of pathogens); Characterize and understand shorter-term (diel, tidal to seasonal ) biological cycles (e.g., biogeochemical implications of diel, ontogenetic, and seasonal migrations of populations); Detect and monitor ecosystem responses to anthropogenic perturbations (e.g., response of coastal systems to nutrient loading, impacts of large-scale enrichments, influences of climate change on nutrients, trace metals and trace gases, evaluating relationships between environmental forcing functions, and ecosystem state shifts over very long timescales); and Forecast population and community changes (e.g., forecasting changes in fisheries stocks and food-web dynamics). Observatory science is USEFUL to accomplish the following: Characterize changes in biodiversity and community structure; Determine the spatial scales of the connection between marine populations via dispersal of early life stages (e.g., local population isolation, barriers to dispersal, and linkages in the epidemiology of disease); Monitor dynamics of marine food webs (e.g., encounter rates of predators and prey, detection of processes generating large-scale patterns in ecosystems); and Characterize gamete mixing, fertilization success, and propagule dispersion. To address the science where observatories are very useful, development or improvement of the following sensors is needed: Long-range AUVs with biosensors and optics; Advanced ROVs for episodic sampling, experiment emplacement, and recovery; Active tracking sonars whose data can be coupled with satellite imagery; Chemical and biological sensors and optics (e.g., spectrophotometers, coulter counters, CHN (carbon, hydrogen, nitrogen) analyzers, video plankton recorders, gene chips); Time-sequencing settling plates and particle and organism traps suitable for long-term deployment; Both video and still cameras with either sensor or remote control of image collection; Active omnidirectional acoustic sonars; and In situ sample-processing and sample-collection and preservation capability.

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE Oceanic ecological observatories will extend into deep water the concept of the U.S. Long-Term Ecological Research Network (LTER), which now includes only a few ocean- and land-margin sites. The mission of the LTER is similar to that proposed for seafloor observatories in that it aims to understand ecological phenomena occurring over long temporal and broad spatial scales and to increase the understanding of major natural and anthropogenic environmental perturbations at selected sites. Just as restricting a seismometer network only to land limits the ability of geophysicists to understand the dynamics of the earth, restricting ecological observatories only to land limits the ability of ecologists to fully understand the dynamics of the biosphere (Box 2-10). For this discussion, a seafloor observatory is considered in the broadest sense as a system supporting measurements from the seafloor to the ocean surface, including a nested arrangement of instrumentation covering spatial scales of meters to hundreds of kilometers. An observatory might consist of a series of stationary observatory nodes to monitor the seafloor and water column and autonomous underwater vehicles dispatched to provide broader spatial and temporal coverage. This definition does not include Lagrangian drifters or floats per se, but their use will greatly complement an array of fixed observatory sites. In some cases, observatories will be most effective when used with more traditional approaches, such as drifters, ROVs, manned submersibles, and surface ships. The following are scientific questions well suited for study using seafloor observatories along with a description of the most compatible facility to address the particular scientific problem. How do environmental and biotic factors determine the distributions and activities of key species or communities important to biogeochemical cycles in both space and time? This question refers to a classical community ecology approach (explaining the distribution and abundance of species) to help understand a systems ecology problem (cycling of mass and energy). An associated question asks what the important interactions are among marine biota, global climate, and biogeochemistry. Important scientific problems related to this general question include responses of coastal margin systems to nutrient loading; biogeochemical implications of daily, seasonal, and life-cycle migrations of populations; food-web analysis; and influences of climate change on nutrients, trace metals, and trace gases. Research under this broad question might deal with the controls on harmful algal blooms, population dynamics of predators, deep-community responses to episodic nutrient pulses, or exploitation of fisheries and other resources.

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE BOX 2-10 LONG-TERM ECOSYSTEM UNDERWATER OBSERVATORY Objective: The Long-Term Ecosystem Underwater Observatory, 15 m below the surface (LEO-15), provides three subsea nodes for connection of instruments (Figure 2-9). The system provides both power and communications for these instruments via a cable between the subsea nodes at the LEO-15 situ and shore facilities at Rutgers University. Each of the identical nodes provides eight standard interfaces for guest instruments as well as a variety of specialized interfaces for other instruments. Continual measurements made at each node include water temperature, salinity, clarity, wave height, wave period, chlorophyll content, and current speed and direction. An electric/fiber-optic cable that connects to the two permanent subsea nodes at LEO-15 is designed to provide power and two-way, real-time, high-bandwidth communications (including video) to instruments, remote platforms, ROVs, and AUVs. The data received from LEO-15 instruments are used to model and predict currents and summertime upwelling and to aid biologists in the research of benthic communities and phytoplankton ecology. Location: Immediately offshore of Great Bay near Tuckerton, New Jersey; 15 m of water Established: August 1996 Long-term, cabled observatories are essential for examining important time-dependent aspects of the question above. This is especially true for those experiments needing instruments with large power requirements. Relocatable observatories will also be a useful approach when addressing ecological questions where shorter-term time series are sufficient (as with the study of hydrothermal vent communities). Global observatory coverage is not

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE FIGURE 2-9 Diagram of LEO-15 (Long-term Ecosystem Underwater Observatory, 15 meters below the surface). This picture shows the array of underwater instruments currently located and soon to be located at LEO. The fiber-optic cable and nodes were deployed in August 1996. These instruments measure water temperature, salinity, clarity, wave height, wave period, chlorophyll content, and current speeds and directions. The satellite data received in New Brunswick provides information about sea surface temperature, water quality, and phytoplankton content over a huge area (40 deg. latitude × 50 deg. longitude). SOURCE: Scott Glenn, Rutgers University (Rutgers University-COOL, 1999). necessary for these scientific questions, although a subset of the locations proposed for global climate and geodynamics studies may coincide with sites for these ecological studies. For certain applications, the sampling interval of data collection may be less than hourly, but data transfer would be required less frequently (e.g., daily or weekly). The main exception to this telemetry requirement would be

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE for applications that include detection and response to episodic events. For these projects, ‘smart' instruments should be installed with a capability for quick transmission of data at the onset of an event. As soon as an event or event-precursors are detected, sensors would begin sampling more frequently, two-way communications would be initiated, and associated sample collection or Lagrangian activities (drifters, surface ship) would be mobilized. Instruments required for this scientific question include stationary sensors recording a variety of physical, chemical, and biological parameters (the latter would include coulter counters, video plankton recorders, etc.); cameras (film, digital, or video); active tracking sonars and other acoustic instrumentation; and AUVs equipped with biosensors and optics. Cameras would most likely be operated in a time-lapse mode, with the exception of those coupled to public and education outreach projects. These would be operated continuously and require real-time data telemetry. Data collected from the sensors listed above should be correlated with satellite data providing optical information and radar imaging for current flow. It is anticipated that perturbation experiments, such as the controlled release of chemicals or tracers into the water column, or manipulations of seafloor communities using colonization surfaces, faunal clearances, faunal transplants, and predator inclusion and exclusions, will be conducted as part of the observatory activities, and that ecosystem responses will be recorded with sensors and by sampling. Although many studies will continue to require retrieval of water, microbes, plankton, and benthic organisms, this need will decrease as new in situ optical, acoustic, and genetic instruments for detecting and identifying organisms are developed. Samples that are collected could potentially be analyzed in situ using instruments adapted from those used in the laboratory (e.g., spectrophotometers, mass-spectrometers, coulter counters, CHN analyzers, gene chips3), or these samples could be preserved using chemical (injection of ethanol, formalin, etc.) or thermal (freezing) means. Alternatively, sampling could be conducted periodically by ROVs during scheduled observatory maintenance visits. What are the functional dynamics of populations and communities? Specific research topics related to this question deal with the spread of pathogens, the causes and consequences of synchronous spawning, and fertilization success. A longer-term aspect of the question above concerns quantifying the spatial scales over which marine populations are connected via dispersal 3   Gene chips - This technology promises to monitor the whole genome on a single chip so that researchers can have a better picture of the interactions among thousands of genes simultaneously.

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE of early life stages. Specifically, research in this area would investigate the influence of local population isolation and barriers to dispersal, and also linkages in the epidemiology of disease. Time-series observations are essential for addressing some aspects of these questions, but they are not sufficient to answer the questions comprehensively. Thus, observatory activities would need to be coordinated with more traditional ship- or submersible-based approaches. The research questions outlined above would require time-series measurements over a period of one to five years using a flexible (relocatable) observatory system located at strategic, problem-specific locations. Data would be collected at hourly or longer intervals, with the exception of periods following occurrences, such as spawning events, when frequencies of seconds to minutes would be useful to assess such issues as gamete mixing, fertilization success, and propagule dispersion. Data transmission requirements would be modest (on daily or longer frequencies) except during and immediately after events. For fertilization studies, only a few closely spaced nodes would be required, but for studies on the spread of pathogens numerous (on the order of 10) nodes spaced over 10s to 100s of km would be required. Necessary sensors and instruments would include physical, chemical, optical, and biological sensors, such as gene chips, time-sequencing settling plates, and traps. Perturbation experiments would be beneficial to these studies (e.g., induction of spawning through chemical or mechanical shock and controlled release of a non-reactive pathogen mimic), and sampling of organisms for in situ or laboratory analysis (as described above) may be necessary for some projects. What are the dynamics of marine food webs, and how will they respond to environmental perturbations? Specific scientific problems include encounter rates of predators and prey, long-term variations in population abundances, and detection of processes generating large-scale patterns in ecosystems. Both long-term and relocatable observatories are essential to address this question. Data recording and telemetry frequencies, locations and numbers of nodes and sensors, and methodologies are similar to those described for questions 1 and 2 above. How can population and community changes, such as fluctuations in fisheries stocks and food web dynamics, be accurately forecast? Furthermore, is it possible to evaluate the multiple-scale and pervasive human impacts on the sea, given the confounding effects of weather and climate change? To address these questions it is necessary to have long-term observations, particularly in relatively unimpacted environments where ecological baselines

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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE can be established. It is also important to collect time-series measurements that will illuminate the relationships between environmental forcing and changes in ecosystems over very long timescales. These scientific problems will benefit greatly from coordination within a multidisciplinary approach, including long time-series circulation and climate studies. Cabled observatories would be required for forecasting regional changes, while the coordinated use of data from many widely spaced cabled or moored buoy observatories would be needed to study large-scale physical-chemical-biological interactions. Long-term studies are likely to require a cabled network with a series of moorings with cameras, active omnidirectional acoustic sonars, and environmental sensors measuring physical, chemical, and biological properties. Because identification, genetic, and chemical analyses of organisms will be a component of the studies, procedures for in situ sample processing and sample collection will be needed. Perturbative and event-response approaches will be less important for these studies, but of possible use in specific projects.