 |
|||||||||||||
 |
|||||||||||||
|
|||||||||||||
|
Contents:
Overview
|
|||||||||||||
|
A FIBER OPTIC "TELESCOPE" TO INNER SPACE EXECUTIVE SUMMARY Ocean and planetary scientists are on the threshold of a major revolution in terms of the issues they are beginning to face and the technologies becoming available to address those issues. Rapidly evolving advancements in submarine communications, robotics, and sensor design are providing new opportunities to comprehensively address intellectually compelling and societally relevant issues such as the search for life beyond earth and the anticipation of crippling natural hazards. To fully realize these opportunities, scientists and society must face significant new challenges that will require long-term commitments to facilities and research programs focused on integrated, in situ scientific experimentation within remote or hostile environments on earth and on other planets. One such opportunity arises from recent evidence that submarine volcanic activity supports a substantial, unexplored high-temperature microbial biosphere sustained by volatile fluxes from the earth’s interior. This insight implies that seafloor hydrothermal vent sites may be "the tips of icebergs" in terms of total biomass supported by modern submarine hydrothermal systems. In short, a significant microbial biosphere apparently thrives within the brittle outer shell of the volcanically active submarine portions of Earth. Because similar submarine volcanic systems may exist on other solar bodies, such as Europa, this new field of microbial volcanic ecology emerges as doubly powerful. By designing innovative strategies to explore linkages between volcanoes and the life they support here on Earth, we gain essential knowledge about newly discovered processes and life forms on our own planet. We also obtain critical new insights about how we might explore other solar bodies for signs of life. A system like NEPTUNE will allow intimate real-time access to the vigorous geophysical and geochemical processes that sustain this sub-seafloor volcanic biosphere.
The goal of NEPTUNE is to establish a coherent system of high speed, submarine communication-control links using fiber-optic cables to connect remote, interactive experimental sites with land-based research laboratories and classrooms. The system will provide real-time flow of data to shore, interactive control over robotic vehicles on site, and power to the instruments and the vehicles. This facility will enable a broad range of long-term, real-time, four-dimensional experiments focused on dynamic earth processes. Because many globally significant processes operate at or below the scale of tectonic plates, the NEPTUNE cable system will be constructed at the scale of a lithospheric plate. NEPTUNE will allow scientists and educators to analyze and utilize data bearing on the linkages and feedback mechanisms within and between key oceanographic and plate tectonic processes. More complete understanding and effective modeling of complex natural systems requires a continuous interactive presence within these active portions of our planet. A comprehensive, long-term investigation of one such system can provide new and detailed insights into the dynamic behavior of similar systems that operate throughout our planet. The site selected for NEPTUNE is the Juan de Fuca Plate located within several hundred miles of the US-Canadian West Coast. This site has several advantages. It is the only locale this close to North America where a full suite of plate tectonic activities is operative, producing a broad spectrum of interactive physical, chemical, and biological processes within a few hundred kilometers of land. It is the locus of active continental shelf sedimentation and a variety of oceanographic processes tied to North American weather and climate and to a major fishing industry. Using remote intervention capabilities, coupled with real-time data flow from thousands of instruments, many of these basic oceanographic and geophysical systems will be explored with entirely new investigative strategies. Extended characterization of complex, co-varying processes will provide a powerful complement to the traditional focus on spatial characterization achieved by mapping and sampling, which has dominated the ocean sciences for fifty years. Long-term commitment to well-designed experimental inquiries will reveal much about the dynamic behavior of our planet.
The scientific and educational returns from access to a network of cabled observational sites will be extensive and multifaceted. A series of cabled seafloor instrumented sites would provide a national and international focal point for innovative ocean and planetary science investigations, engaging the imaginations of researchers and the public alike. The project will drive improvements in deep submergence technology and could provide unparalleled test beds for robotic exploration of extreme habitats involving submarine volcanism, plate tectonics, or oceanographic processes. Ideally, many of the instrument arrays and robotic systems would be accessible on the Internet, allowing novel forms of involvement by scientists, students of all ages, and the general public. The public could have an intimate, over-the-shoulder view as scientists interact with some of the most basic and dynamic of planetary processes.
The following paragraphs outline a set of scientific issues for which NEPTUNE could enable major breakthroughs by using new technology and innovative experimental approaches. The examples are illustrative rather than inclusive. The opportunities outlined here are oriented to the tectonic environment first, then the oceanographic environment. A number of additional scientific thrusts will undoubtedly emerge, as the scientific community becomes more familiar with the opportunities provided by NEPTUNE. Spreading Centers -- Seafloor spreading is an intermittent, shifting balance among strain accumulation, normal faulting, and volcanic accretion. The relative importance of tectonism and plutonism varies in both time and space and reflects the interplay between magma supply from the mantle and heat loss to the ocean, which is dominated by vigorous hydrothermal circulation. Along mid-ocean ridges, hydrothermal fluids transport dissolved materials, and the chemical potential energy produced as they rise and mix with seawater sustains diverse communities of chemosynthetic lifeforms both on the seafloor and in subsurface pore spaces. Periodic diking-eruptive events flush existing hydrothermal fluids from the crust and constitute natural perturbation experiments. They may cause short-lived bursts of very vigorous hydrothermal venting and lead to spectacular microbial blooms. Fault motions and cracking events induced by thermal contraction may open new pathways for circulating fluids to enter hot rock, thus temporarily increasing hydrothermal fluxes and changing the chemistry. It is extremely difficult to assemble the full array of equipment necessary to monitor all aspects of these interrelated systems at the same time. Stand-alone experiments are limited by practical considerations to periods that are significantly shorter than the time scales of the volcanic and tectonic cycles responsible for seafloor spreading. A cable-supported natural laboratory would provide the infrastructure necessary to concentrate multidisciplinary observations at a few key sites on appropriate time scales. It would allow scientists to observe events in their entirety, adapting their experiments in real time to respond to changes in the system. Plate Interiors -- Oceanic plates occupy two thirds of Earth's surface. Consequently intraplate processes are globally important. For example, much of Earth's heat is lost through cooling over entire lithospheric plates. Stresses within them provide critical clues about the various forces that drive and resist plate motion. Hydrothermal circulation on mid-ocean ridge flanks is responsible for the exchange of large amounts of heat and chemical constituents between the oceans and the oceanic crust, and may fuel thermophilic microbes that take advantage of the chemical potentials in this dynamic regime. Many of the questions that remain unanswered about intraplate processes and structure can be addressed well, and in some cases only, through observatory studies. A transect of sites that crosses the full breadth of the plate from central Washington to the Endeavour segment of the Juan de Fuca Ridge and uses existing drill holes for long-term hydrologic, seismic, and related studies will allow many of these questions to be addressed. A cable link to shore is a central infrastructural requirement for such experiments. Subduction Processes -- Subduction zones host a wide variety of fundamental and important geological processes: for example, intraplate slip along subduction thrusts is the cause of the worlds largest tsunami generating earthquakes. The three-dimensional architecture of subduction zones and their accretionary prisms have been well characterized in some locations around the world. Yet, our understanding of the time dependence of the processes affecting them is poor for the simple technological reason that comprehensive time series observations at long time scales are difficult to obtain at sea, and many of the most significant processes are only active well offshore. Further progress will require decadal time-series observations made at deep ocean sites. The case for using a submarine cable to establish this style of multidisciplinary program of observations is compelling for a variety of reasons. First, many of the instruments (especially, broadband seismometers) have power requirements that preclude the use of autonomous (i.e., battery powered) instruments except on the very short term (i.e., a few months at most). Second, a major focus at subduction zones is the covariation of seismic, deformation, hydrologic, and biological processes, and hence contemporaneous measurements of disparate variables over long time scales are essential to their characterization and understanding. Third, the relevant processes are clearly episodic, and there is considerable scientific value in the capability to modify sampling and measurement protocols in response to changes. Fourth, there is clearly societal value in having real-time data from offshore to aid in modeling and predicting patterns of subduction zone processes. Finally, a cabled system offers a level of reliability that cannot be matched by surface moorings. Sediment Transport -- The primary source for most dissolved and particulate material in the ocean is terrestrial environments, and the mechanisms that move this material across continental margins to the deep ocean are poorly understood. The burial of the particles not only creates important natural resources, but also creates a record of past environmental processes experienced on the Earth's surface. The seaward transport of particles, integrated over time, leads to the growth of continents in a range of diverse architectural styles that reflect climatic conditions, sea-level fluctuations, and rates and mechanisms of sediment transport. The latter have been poorly constrained, because observational techniques have been limited in both space and time. Most of the transport occurs during episodic events. Thus, long-term cabled observatories are needed to make substantial advances in our knowledge of the rates and mechanisms of mass flux to the deep ocean. Upwelling and Productivity -- Coastal upwelling occurs on the west coasts of most continents, all of which are areas of enhanced biological productivity. An improved understanding of the upwelling ecosystem in the Pacific Northwest will provide valuable insights into many other locales. Some aspects of coastal upwelling are dependent on the local combination of dynamic, physical, and biological processes, all of which are characterized by dramatic temporal and spatial variability and are not well constrained by satellite, shipboard, or self-contained mooring observations. A cabled observatory system would complement these other approaches and facilitate a dramatic leap toward overcoming our limited knowledge of these systems. Most importantly, cabled observatories have the capability to examine the multiple linkages between the disparate, but successional processes that influence the timing and strength of coastal upwelling and the subsequent influence on marine ecosystem structure and function. These studies would clearly be linked to primary and secondary productivity as related to predation and recruitment in the fisheries industry in the Pacific Northwest. Biological Diversity -- NEPTUNE can serve as a locus for interdisciplinary studies of patterns and controls on biological diversity at the plate scale, with traditional sampling conducted within the context of cable-facilitated measurements of dynamic and spatially varying environmental parameters. A new view of the deep sea was recently highlighted by the suggestion that it may contain as many as 10 million species, a level of diversity that rivals that in tropical rainforests and coral reefs. Maintenance of a species-rich deep sea in what was originally thought to be a monotonous, homogeneous environment begs attention. Explanations for this contrast tend to focus on disequilibrium processes related to spatial and temporal heterogeneity on scales relevant to individual organisms and addressable by long-term monitoring of the underlying physiochemical processes controlling such rich diversity. Organic Carbon Fluxes -- Over the past two decades, oceanographers have gained an appreciation for temporal variability in the flux of organic material to the seafloor and for seasonality in processes such as growth, reproduction, and recruitment in benthic invertebrates, but compelling evidence for the link between productivity and these processes has been elusive. Cable-facilitated measurements of organic flux and other environmental parameters can be combined with traditional methods of sampling organisms to resolve the dynamics of supply and response under a variety of seafloor settings at the plate scale. Any seafloor observatory must support real-time data telemetry, real-time instrument and vehicle control, and a constant supply of power for observatory equipment and instruments. Only a direct connection to land using a submarine cable can reliably provide continuous power at the level of thousands of watts. Real-time, two-way communications at multi-gigabit per second rates are required to support large numbers of seafloor instruments and to anticipate changes in oceanographic technology over the 20+ year lifetime of an observatory system. Submarine cables inherently distribute power and communications over a wide area rather than limiting it to a restricted number of point sites. A scientific fiber-optic cable system consists of two core components: a trunk system and a series of scientific interfaces, or "junction boxes," which connect to the trunk system. The trunk will utilize industry-standard fiber-optic telephone equipment and constitutes the core technology needed to implement NEPTUNE. This approach takes advantage of commercially available hardware (thereby minimizing development costs) that is designed for high reliability, low failure rate operation. State-of-the-art systems have a data capacity of 100 Gbit/s, and this number is expected to approach 1 Tbit/s within a few years. These data rates seem high for present day oceanography, but that situation is likely to change over the coming decades as the research and educational communities learn to take advantage of such bandwidth.
The scientific interfaces will have to be developed. They will consist of a series of junction box nodes connected to the main or secondary fiber-optic cables to which experiments or multiplexers may be connected. These nodes will supply power from the cable system to users, and will contain the controlling software and hardware necessary to coordinate the function of multiple nodes on a single cable. The junction boxes will have to incorporate both sensor communication and user power interfaces, as well as standard electro-optical connectors and a variety of mechanical interfaces. To accommodate large numbers of variable data rate sensors, it will be necessary to use a multiplexer hierarchy. The highest data rate sensors or high-level multiplexers plug into a junction box and are connected directly to the trunk system. This system will also include a series of secondary junction boxes operating at reduced data rates extending down in a tree structure to interface with lower data rate sensors. Individual sensors plugged into NEPTUNE will be discipline- and investigator-specific, and typically will either be adaptations of existing types or new sensors developed to answer specific scientific questions or to take advantage of the new capabilities that NEPTUNE offers. NEPTUNE should catalyze instrument development. Indeed, the ability to interact with seafloor instruments in real time will change the way we think about instrument design in oceanography. In addition, there are other instrument systems that are more generic and hence either will be needed in more than one discipline or are necessary work tools to make NEPTUNE function. Two prominent examples are remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs). The installation of hundreds of sensor packages will require advances in ROV numbers and capability, as many of the required operations are at the limits of present ROV capability. It is also certain that AUVs based at seafloor docking stations, where power can be uploaded and data can be downloaded, will play a major role in NEPTUNE science. |
|||||||||||||
