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NSF Sponsored Workshop Workshop publications:
HTML version of workshop report: Ice-Based Observatories:
Woods Hole Oceanographic
Institution Compiled by November 12, 2004
2. The role of Ice Based Observatories (IBOs) in an Arctic 3. Requirements and Challenges for
IBOs 4. Summary and Recommendations Appendix 1: Plans for Arctic Observing
Systems An NSF-sponsored workshop entitled “Arctic Observing Based on Ice-Tethered Platforms” was held at the Woods Hole Oceanographic Institution in Woods Hole, MA from June 28-30, 2004. The assembly of 55 workshop participants from 8 countries that included Arctic scientists, engineers, industry representatives and program managers was tasked with identifying requirements for and components of the next generation of ice-based technologies for observing systems in the Arctic Ocean. Instrument development and project coordination were also discussed. The most important general conclusion of the Woods Hole workshop was that practical, cost-effective and proven Ice-Based Observatory (IBO) designs presently exist, can be readily extended to provide interdisciplinary observations, and should be implemented expeditiously as part of a coordinated effort to observe the coupled Arctic atmosphere-ice-ocean system. Specific recommendations were: - A relatively simple and robust IBO array, based on presently available technology, should be implemented immediately as part of a stepwise ramp-up to a multi-component, interdisciplinary Arctic observing system. An international body will be required to coordinate the various national programs (eliminate overlap, insure no data holes) and insure compatibility of data and their widespread distribution. - The 25 years of International Arctic Buoy Program (IABP) drift trajectories, existing data climatologies and available numerical simulations should be exploited to derive insight to optimal array design, deployment strategies, sampling intervals, and expected performance of an IBO array. - Since ice-based observations at a given site may consist of a distributed set of subsystems developed by multiple PIs, the logistical infrastructure for getting to the deployment sites is one of the most important shared assets of the observing system. A long-term, internationally coordinated logistics plan should be developed as an essential component in establishing an IBO array. - IBO designs should provide accommodation for novel sensors, acoustic receivers, and communication and navigation capabilities for mobile platforms. Emerging technologies for Arctic observation (including but not limited to: unattended biological and chemical sensors, electromechanical sensors, autonomous oceanographic vehicles and drifters, and unmanned aerial vehicles) should be developed within the framework of an integrated Arctic observing system. Ice-based instrument systems are a proven means of acquiring unattended
high quality atmosphere, ice, and ocean data from the central Arctic
during all seasons. Arctic Change is ongoing and measurements need
to begin now. An array of IBOs, deployed and maintained throughout
the central Arctic, is envisioned to observe the spatial structure
and annual to decadal variations of the polar atmosphere-ice-ocean
environment as one component of a coordinated Arctic Observing System The Arctic Ocean's role in global climate - while now widely appreciated - remains poorly understood. Lack of information about key processes and their interconnectivity within the oceanic, cryospheric, biological, atmospheric and geological disciplines will continue to impede physical understanding, model validation, and climate prediction until a practical observing system is designed and implemented. A review of recently observed changes in the physical and biological state of the Arctic and a justification for future Arctic observations are contained in the supporting document of the U.S. National Science Foundation’s “Study of Environmental Arctic Change” program (SEARCH; http://psc.apl.washington.edu/search/). Comparable Arctic study programs have been conceived as an international contribution to the proposed International Polar Year 2007/2008 (http://www.aosb.org/ipy.html). Future directions in instrument development for Arctic studies were also considered at a workshop at the Monterey Bay Aquarium Research Institute in autumn 2002 (http://www.mbari.org/rd/ArcticInstrumentationWorkshop). An important product of all of these discussions is a coherent vision for future Arctic research and observations. Three main components of this vision have been identified: (1) manned expeditions with enhanced capabilities; (2) basin-wide networks of autonomous ice-based instrument systems, bottom-anchored sensors and mobile platforms; and (3) cabled oceanographic observatories. Following up on the second of these themes, an international workshop entitled “Arctic Observing Based on Ice-Tethered Platforms” was held at the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts, USA from June 28 to 30, 2004. The assembly of 55 workshop participants from 8 countries that included Arctic scientists, engineers, industry representatives and program managers was tasked with identifying requirements for and components of the next generation of ice-based technologies for observing systems in the Arctic Ocean as part of a coordinated effort to observe the coupled Arctic atmosphere-ice-ocean system. The idea of ice-mounted instruments or drifting ice-anchored buoys is certainly not new. The first scientific drifting platform was Nansen’s Fram (1893-1896) which, over a three year period, drifted with the ice across the Arctic while making atmospheric and oceanic observations. A similarly remarkable scientific expedition that involved drifting on a sea-ice floe was accomplished by the USSR in 1937. That drift continued for 274 days, during which time the station traveled more than 2600 km. This began the "North Pole" station investigations that opened a new era in Arctic studies. From 1937 to the present, multinational drifting stations, ice camps and icebreaker programs have provided very important information from the Arctic. Autonomous instruments have become an increasingly important source of Arctic data. Since 1978, observations from the International Arctic Buoy Program (IABP) have contributed significantly to polar science by returning meteorological and sea-ice drift data for real-time operational requirements and research purposes (http://IABP.apl.washington.edu/Citations). Buoys with subsurface instrumentation have also been used with great success. Between 1985 and 1994, the Polar Science Center, University of Washington deployed 24 Polar Ocean Profiler (or SALARGOS) data buoys. And from 1992-1997, the Woods Hole Oceanographic Institution (WHOI) in collaboration with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) developed and deployed six Ice-Ocean Environmental buoys (IOEB; http://ioeb.whoi.edu/index.htm). Since 2000, JAMSTEC Compact Arctic Drifter (J-CAD) buoys (http://www.jamstec.go.jp/arctic/J-CAD_e/jcadindex_e) have been measuring the structure of upper-ocean currents and water properties under multi-year ice floes. Also beginning in spring 2000, an international research team supported by NSF has conducted annual expeditions each April to the North Pole to service and install an ensemble of autonomous scientific platforms, including a variety of sensors and instrument systems, collectively called the North Pole Environmental Observatory (NPEO, http://psc.apl.washington.edu/northpole/). Experience gained in these studies was discussed by workshop participants and used to develop the concept of an array of ice-based instrument systems or Ice-Based Observatories (IBOs) necessary to satisfy the needs of international multidisciplinary Arctic study programs. This workshop report is organized as follows: Section 2 discusses how an IBO array fits into an overall Arctic Observing System, Section 3 describes the requirements and challenges for development and implementation of IBOs, and Section 4 provides a summary of key points from the workshop and recommendations for IBO development and implementation. The first four appendices provide further details about international Arctic observing programs, the specifics of interdisciplinary observations from IBOs, and a possible scenario for interaction of autonomous and Lagrangian platforms with IBOs, respectively. The fifth appendix contains all submitted workshop abstracts and the sixth appendix contains a list of workshop participants. 2. The Role of Ice-Based
Observatories in an Arctic Observing System
There are many national and multinational initiatives for Arctic observations. Some are still in the planning stage, whereas others are already being implemented or are well established. Five prominent Arctic observing concepts were reviewed at the workshop: 1) the Study of Environmental Arctic Change (SEARCH) Observational System, including NOAA’s enhanced network of ice mass balance and upper ocean buoys; 2) the Arctic Ocean Observing System (AOOS) prepared for the International Polar Year in 2007-2008; 3) a Hybrid Arctic Float Observation System (HAFOS); 4) an acoustic-based observing network; and 5) an Arctic Ocean Monitoring System (AOMS) developed at the Instrumentation for Arctic Ocean Exploration workshop. Detailed descriptions of each of these concepts are included in Appendix 1, and a description of the ongoing IABP is given in Appendix 2. It was noted at the workshop that each of the Arctic observing concepts included ice-based observatories of some type as a central element. It is clear from the various observing system designs that numerous
tools can be applied to the study of the Arctic environment, including
satellite remote sensing, autonomous ice-based buoys and drifting
stations, ocean moorings, icebreaker-based field campaigns and hydrographic
transects, cabled observatories, mobile platforms (e.g., drifters,
profiling floats, gliders, Autonomous Underwater Vehicles (AUVs),
Unmanned Aerial Vehicles (UAVs)) and numerical models. For example,
satellite remote sensing provides the large-scale snapshots of such
basic parameters as ice distribution, melt zone, and cloud fraction
at intervals of half a day to a week. Buoys and moorings can contribute
high temporal resolution and can measure parameters currently unavailable
from space including ice thickness, internal ice temperature, and
ocean temperature and salinity. Field campaigns can be used to explore,
in detail, the processes that govern the ice cover. Numerical models
can be used to assess the character of the changes in the ice cover
and predict the impact of these changes on other elements of the
climate system. Thus, an IBO array was seen as a critical element
for observation of the atmosphere-ice-ocean system in the Arctic,
but it was recognized that such an array must be integrated with,
and complementary to, other observational and modeling components
to create a comprehensive Arctic observing system.
It was concluded that IBOs must be a key element of any comprehensive Arctic observing system, that IBOs are complementary to existing and planned observing system elements, and that IBO development should explicitly consider integration with other observing-system elements (e.g. satellites and other mobile and fixed platforms, see Sec. 3.4). An IBO network affords extraordinary opportunities for outreach activities, because of the public interest in both the Arctic and climate change. Data can be streamed to public web sites in near-real time, as can photographs and commentaries from field camps. The breadth of activities affords considerable opportunities to engage the next generation of researchers in such diverse fields as computer science, engineering, biology, chemistry and geophysics.
Workshop participants identified IBO’s as automated, drifting, ice-based sensor systems providing comprehensive data from the Arctic environment and incorporating the multidisciplinary needs of biological, chemical and physical oceanography, as well as different aspects of atmospheric and sea-ice studies. Moreover, in addition to supporting suites of sensors, these observatories may also serve in a network of acoustic receivers, as data transmission nodes and navigation beacons for autonomous vehicles operating between the stations. The basic requirements identified at the workshop for a future generation of ice-based unmanned platforms are: • Observation and real-time reporting, with high vertical resolution and high accuracy, of an interdisciplinary suite of parameters from the near-surface atmosphere, sea-ice, and upper ocean for multiple years (assuming deployment on robust ice floes) at temporal resolutions appropriate for each parameter; • Ease of deployment from landed aircraft and helicopters in addition to deployment by icebreaker; • Modest cost, allowing them to be deployed in large numbers (analogous to the present IABP) and, in some cases, to be considered expendable; • Accommodation, through standard interface and communication protocols, of future surface and/or subsurface instrumentation, including acoustic communication (for data transfer, and navigation) with other mobile and fixed platforms. A more detailed description of IBO requirements, and associated challenges, are in the following sections. 3.1. Spatial and temporal
coverage of an IBO array
Recent observations and modeling results indicate that the Arctic system is particularly sensitive to and of considerable importance in the dynamics of global change. Our understanding of the Arctic's sensitivity and dynamic linkages is hampered by poorly known oceanic variability. Since the Arctic Ocean is an important climatic component of both the Arctic and the global system, knowledge of the Arctic Ocean changes based on sustained observations is essential to correctly interpret processes of atmosphere-ice-ocean interactions and their relation to the climate change problem. The Arctic Ocean area can be subdivided into several sub-regions according to objective parameters that characterize their climate and its variability. For example, regions which are covered by sea-ice year round and regions where sea-ice coverage changes seasonally need different instruments and supporting platforms. Similarly, its area can be sub-divided according to bathymetric features and natural boundaries of the Arctic Ocean, using straits, marginal seas, and deep basin boundaries. Likewise, the Arctic Ocean can be described according to natural layers or water masses, which in general, include surface water, Pacific Water, Atlantic Water and deep water masses. In these contexts, the observation strategy, tactics and instrumentation requirements vary substantially. In theory, it is necessary to include all possible regions, water mass and layers and processes of the Arctic Ocean, but in practice it is important to formulate priorities and determine major scientific problems that can be most readily addressed. As initially conceived, a typical IBO was considered to be deployed in the multi-year pack ice of the central Arctic basin and include a long "tether", or vertical instrument string, that would penetrate several hundred meters into the water column. Figure 3.1.1 schematically shows different elements of the Arctic Ocean and identifies spatial and temporal boundaries for this region. In the permanent ice zone, one sees that IBOs with tethers as long as 800 m are able to sample at least 40% of the Arctic Ocean area (excluding the Bering and Greenland Seas, and bays within the Canadian Archipelago). Due to its permanent ice cover and remoteness, this region remains the most inaccessible part of the world, which also makes it particularly attractive for sustained autonomous observations.
Based on these considerations, the workshop primarily concentrated on the means for sustained observations in central Arctic Ocean (water depths > 800m). The participants mainly considered long-tethered IBOs that would operate in deep waters up to the continental margins of the Arctic Ocean, but not encompass the shelf seas. Arctic shelf seas were not considered a target location for long-tethered IBOs because, in addition to being shallow, they tend to have few multi year ice floes that can support the systems year round. It is noted however that a significant number of IABP trajectories have transited areas shallower than 800 m (e.g. on the Chukchi and Beaufort Shelves), suggesting IBOs with reduced-length tethers may in fact be able to survive for long times in some of these regions. Arctic shelves represent half of the Arctic Ocean surface area and have major physical, biological, and chemical influences on the deep basins. For example, the advection of fresh water from river run-off, the formation of new ice and brine-enriched shelf waters play a significant role in the formation of the cold halocline. It was thus recognized that there are compelling incentives to consider options for IBO deployment on shallow shelves, in seasonal ice zones, and in regions of highly deforming ice (e.g. simple, inexpensive IBOs with real-time data reporting capability designed to be "sacrificial" after a finite lifetime). It was proposed that, in combination with cable observatories, floats, AUVs, etc., simultaneous technological development of IBOs suited by cost and configuration to deployment and operation in this extremely dynamic sea-ice environment is needed to address the challenge of Arctic shelf monitoring.
In similar spirit, a different mix of instrumentation will be required to observe narrow, topographically-constrained boundary currents, the deep exchange flows between the Arctic sub-basins and the inflows and outflows between the Arctic and subpolar oceans. Here, bottom anchored arrays would seem most appropriate. The present workshop focused on IBO's. From the 25 years of archived IABP drift trajectories, with concomitant fields of physical ocean variables, has come some understanding of cycles on seasonal and longer time scales. Individual IBOs will continue to sample these fields and cycles in an irregular pattern over space and time. An array of IBOs will sample these fields sporadically in space, at rather low spatial resolution from an oceanographic viewpoint and perhaps not in the best places. What will one learn about the ocean from an array of IBOs? Could one have detected the Atlantic/Pacific frontal shift of the early 1990s with data from a typical array? Could one detect events of halocline ventilation? The archived IABP buoy data set from 1978-2000 could be used to simulate the sampling of historical data fields, in order to explore which circulation and hydrographic features would have been revealed by such an array of IBOs. One could also learn something about optimal array design and density (e.g. what would be the useful life, statistically, of an 800-m tether before grounding). Simulations of IBO system performance for ocean chemistry and biology might also be possible (e.g. could biological sensors be shut down for much of the year, to conserve power?). Figure 3.1.3 shows a very coarse time/space diagram for key physical processes and water mass distributions in the Arctic Ocean, and a rough indication of those processes and features that could be observed and quantified using Ice-Based Observatory technology. Here, a distinction is made between processes that could be observed directly (e.g. the location of water mass fronts) and those which indirect or statistical properties could be collected. Some features and processes (e.g. buoyancy-boundary currents, bottom water) are beyond the range of ITP and IBO technology. 3.2. Principal elements
of an Ice-Based Observatory
Workshop participants agreed that the capability to produce practical, cost-effective and proven IBO designs presently exists, can be readily extended to provide interdisciplinary observations, and should be implemented expeditiously as part of a coordinated Arctic observing system. A relatively simple and robust IBO array, based on presently available technology, should be implemented immediately as part of an incrementally developed, multi-component, interdisciplinary Arctic observing system. A large and diverse number of parameters and sensors are required to detect and quantify changing Arctic conditions. It is unlikely that a single platform will be able to accommodate all sensors and instruments, and still meet reasonable size, weight, and power requirements, so an observing system with multiple platforms at a single node is necessary. Furthermore, since a full, high resolution spatial survey for all relevant parameters is neither technically nor financially feasible, a hierarchy of the observed fields is needed. On the basis of this hierarchy, data from relatively cheap sensors, such as temperature and salinity, need to be available at comparable spatial and temporal resolution to the global Argo array. More complicated sensors, such as oxygen, nutrients or biological parameters, are to be added at the next level, the data from which can be evaluated in the context of the hydrographic fields. Simple sensors of relatively low cost and energy consumption can be mounted on basic, long duration IBOs, while more expensive and power hungry sensors may need to be employed on specialized, shorter duration IBOs.
The workshop participants recommended that an interdisciplinary suite of physical, chemical, biological, and geochemical parameters of the atmosphere, sea-ice, and ocean be obtained by IBOs. Descriptions of the scientific motivations and specific parameters identified during the workshop are presented briefly here (see Table 2) and in greater detail in Appendix 3. Atmospheric studies emphasized the need to determine the Arctic heat, humidity and momentum fluxes, and variability of radiative and turbulent properties, in addition to obtaining standard meteorological parameters (air temperature, barometric pressure, wind direction and velocity, etc). Sea-ice studies focused on measurements of the thermodynamics (growth, decay, and mass balance, including consideration of the snow cover and radiative properties) and the dynamics (deformation, ridging, and failure). Physical oceanographic studies primarily seek pressure, temperature, salinity and current measurements to understand the ocean circulation, freshwater and heat contents, vertical structures, water masses and other physical parameters. An improved understanding of surface fluxes, finescale to mesoscale ocean variability, and mixing processes were also considered important to better predict changes in the ice-ocean system. Biological and chemical studies stressed the need to understand processes occurring under the ice during winter, and to evaluate the seasonal and interannual variability of numerous biological and chemical parameters (nutrients, dissolved oxygen and other gases, PAR, fluorescence, optical, etc.) in the atmosphere, sea-ice and ocean on the same temporal and spatial scales as the physical variables. Geochemical tracer studies provide information about freshwater, ocean circulation and mixing processes that cannot be derived from physical measurements alone. While historically these tracer data have primarily been obtained by shipboard collection of water sample and subsequent analysis, it is important to pursue next-generation sensors (such as new sensors based on inline reaction chemistry, optical measurements and microfluidic systems) for integrating geochemical and biogeochemical measurements into autonomous IBOs.
The capability to transmit near-real time data back to the laboratory is an essential ingredient of an IBO. At high latitudes, only a few options currently exist. The Argos data collection service has been a low bandwidth option for many years. Relatively recently, the Iridium Satellite System has made higher bandwidth mobile voice and data cellular telephone communications available for all latitudes, at reasonable cost and power requirements. Another important element of an IBO that is necessary to ensure longevity of the system, are mechanisms that deter interference by animals. Polar bears and foxes are the principal offenders that may destroy or render inoperable an ice-based platform. Buoy packages and any instruments or sensors which protrude from them (such as antennae and meteorological masts) may be pushed over, removed, or destroyed by bears. Bears are also particularly fascinated by moving things like anemometers. Cables are especially susceptible to digging and chewing by foxes, as well as handling by bears. The design of IBOs should certainly recognize these risks and should tap into existing expertise on animal deterrence to create the best defenses.
3.3. New Technologies
and Sensors for Ice-Based Observatories
Despite the excitement over ideas for new technology that were presented at the meeting, the consensus of scientists (as distinct from technology proponents) appeared to favor a relatively simple platform (at least for now) to keep IBO implementation costs relatively low. On the other hand, new sensor technology is required for sampling in all regions, not only the Arctic. From this view point, new sensors, and lower power versions of existing proven devices, should be endorsed within an initiative for new technologies for all oceanographic disciplines worldwide. At the same time, it must be recognized that there are additional challenges for developing instrumentation for polar regions, so that all new technology may not be applicable to the Arctic environment. For example, new micro- and nano-fabrication capabilities have revolutionized sensory systems. Micro and Nano ElectroMechanical Systems (MEMS and NEMS) have many advantages over their macro-scale counterparts. Low cost, small volume and weight, and low power consumptions are among the many attractive features of MEMS and NEMS sensors. MEMS/NEMS sensors can play a major role in the next generation of atmosphere-ice-ocean measurement systems. In order to reliably operate in harsh oceanic conditions (including polar regions), special MEMS/NEMS sensors must be designed. However, such developments have been limited due to the lack of immediate commercial interest. It is anticipated that the Arctic research community will benefit significantly from the development of MEMS/NEMS sensors for scientific applications, including polar regions. Unmanned aerial vehicles (UAVs), and in particular micro aerial platforms, are expected to introduce extraordinary capabilities for measurement and imaging in the polar region. Such vehicles are able to operate from land bases close to the area of interest or even from ice-based platforms. For more details and a summary refer to the presentation abstract by K. Monseni in Appendix 5. 3.4. Integration of
fixed and mobile assets
Because the Arctic region is data-poor and so hard to access, the Arctic Ocean is a good candidate location for concerted multi-platform, multi-sensor studies that rely on automated and autonomous systems that include fixed and mobile assets. Fixed assets or platforms include cabled observatories, mooring networks, beacons and acoustic transmitters while mobile assets or platforms include drifters, profiling floats, gliders, Autonomous Underwater Vehicles (AUVs), and Unmanned Aerial Vehicles (UAVs). Three levels of integration are envisioned at this time in order to develop IBOs and promote the IBO concept within a more comprehensive and multi-faceted Arctic observing system. The first level is integration of multiple sensors and platforms within an IBO “node”. Second, it is necessary to determine how the IBOs fit into an integrated system for Arctic observations. Third, because different elements of an Arctic Observing System have been proposed by different institutions, countries, and scientific groups (see Appendix 1), and it is likely that they would be funded independently, an integration and coordination effort is needed to ensure that the deployed systems can communicate with each other to some agreed upon extent (i.e. providing core data to a central telemetry system in a compatible format) without over-complicating the system to the point of lowering its flexibility, usefulness or reliability. Integration among elements of an IBO node: Various sensor packages are available as autonomous instruments and could be integrated to form an IBO node with a common energy supply and data telemetry system. Integrating these systems, however, is time consuming and susceptible to error. It may therefore be more effective to deploy a suite of independent instruments in close proximity, enjoying the benefit of joint logistics (transport for deployment, maintenance and potential recovery), but being operationally independent once deployed. This system is simpler, and is likely to benefit from shorter development time, lower deployment cost and smaller risk of failure than more complex systems. If one component fails, the other instruments will keep on working. For example, an effective scheme might be to deploy an ice tethered profiler and an acoustic ranging and communication station next to each other instead of installing sound sources and receivers on the profiling cable. Despite the appeal of independent subsystems, it may still be cost effective and logistically convenient to share data among the subsystems and/or utilize a common telemetery system for data transmission via satellite to ground stations. A dedicated study may be needed to optimize the design of IBO nodes, including identifying the demanding needs of multi-disciplinary sensors and instruments. Integration of fixed and mobile assets with an IBO node: IBOs ability to interact with fixed and mobile platforms can be exploited to benefit an overall Arctic observing system. For example, data uplink from subsurface moorings by means of an AUV or glider serving as a data shuttle. This could reduce costs whereby some moorings would then not require recovery for data return. Another example would be IBOs serving as navigation beacons for long-range AUVs running Arctic transects. Thus, accommodation should be made, through adoption of standard interface and communication protocols, for future surface and/or subsurface instrumentation. This would include acoustic communication (for data transfer, and navigation) with mobile platforms. The most important recommendation would be to ensure first that in addition to standard protocols for data transfer via satellite uplink, the IBOs have also the ability to exchange data with mobile platforms (undersea vehicles, gliders and either floating or other ice-surface vehicles), vessels (both surface and submarine), and aircraft, using both acoustic and radio frequency, such that the data collected will be retrievable by multiple pathways. This capability needs to be managed to minimize power drain (e.g., through scheduling or when data volume reaches a specified level), while remaining reliable, and robust, i.e., such that the failure of a single antenna or transmitter doesn't result in data loss. At a minimum, the IBO should be able to accept data from known floats and gliders, and transmit its data through Service Argos or Iridium satellite constellations. All mobile observing systems to be used under the ice need acoustic navigation. It is therefore of high priority to develop standards for navigation beacons. The highest priority is to determine the sound frequency and to ensure that deployed sound sources are compatible with all potential systems that are now under development. These problems are planned to be resolved under activities of the US-NSF PLUTO concept (Polar Links to Undersea Telecommunications and Observatories) which is a particularly versatile concept that would link acoustic tomography, cabled observatories, moorings, gliders and AUVs to provide coordinated synoptic Arctic data sets. Low frequency transmissions at 40 Hz would permit basin-wide acoustic tomography. However, the sound sources would be large and difficult to deploy and the accuracy of this band for navigation has yet to be determined. Transmitters at the medium frequency range of 260 Hz are small enough to be used on moorings and IBOs, but the effective range for this frequency is an open research question and is still under debate. Transmissions at 260 Hz seem to be promising from experience in the Weddell Sea where ranges of more than 600 km were obtained, but the use of the same frequency in the Arctic has resulted in significantly smaller range (~100 km in winter). If deployed on drifting IBOs the acoustic devices must be able to transmit their position, and therefore a code for transmission of position must be developed for common use. A possible scenario for interaction of autonomous and Lagrangian platforms with IBOs is presented in Appendix 4, which could be used as a starting point for IBO design and implementation. 3.5. Coordination and
oversight
No single institution can claim sufficient expertise to fully support
an Arctic observing system, therefore coordination of the efforts
of several institutions from different countries will be essential
for the successful development and implementation of a comprehensive
system. Multilevel international, interagency, and inter-institutional
coordination is needed for design, fabrication and implementation
of an IBO array in the Arctic. Several levels of coordination may
be needed at different stages of system development, implementation
and management. These stages include: IBO system design, fabrication,
and deployment, and the receipt, archiving, processing, and distribution
of data from the array. Accordingly, it is necessary to coordinate
sensor characteristics, inter-calibration procedures, deployment
and recovery operations, logistics plans, data extraction, processing
and distribution, reporting procedures, and, finally system improvements
in order to satisfy changing scientific goals and objectives which
will accompany this project as the results are processed and digested.
• Science Oversight Committee A Science Oversight Committee would play a key role in formulating, consolidating and coordinating scientific problems to be solved by an IBO array, and its integration into an Arctic Observing system. This committee would also consider the strategy and priorities of IBO array development and implementation, and respectively determine necessary steps in system improvements and changes in the future. There are several examples of managing operational observational oceanic projects such as Argo and IABP. This experience should be evaluated and modified accordingly, in order to take into account specific characteristics and limitations of the IBO project (multidisciplinary needs of biological, atmospheric, cryospheric and oceanic science; vast amount of information because of high vertical resolution and multi-sensor arrays; real time reporting, including communication with mobile and moving assets). An international body (International Coordination Committee) will be required to coordinate the various national programs (eliminate overlap, insure no data holes), create and maintain an efficient logistical structure to ensure the initial deployment and re-seeding of the array, and insure compatibility of data, their widespread distribution, and their storage in a robust and accessible archive. Arctic Change is ongoing and it is important to develop the IBO system quickly to monitor these changes. A stepwise ramping up of the multi-component system is needed, with accommodation for further components that can be added according to progress in sensor development, knowledge of Arctic change, and funding possibilities. The first step should be to bring into operation IBOs as a measurement system using existing sensors because few navigation, communication and power supply problems are expected with these. Later, additional components can be added as they become available, and/or are deemed necessary. Simultaneously, technological development of autonomous platforms (e.g., drifters, profiling floats, gliders, AUVs, and UAVs) should be promoted such that these technical hurdles can be cleared for these platforms, as well. An operational center with an executive office is needed to get the real work of logistics coordination, field deployment, and data collection/archiving done. The workshop recommends a call for proposals to run such a center. 3.6. IBO Deployment
and logistics
The types of proposed IBOs discussed at the workshop would generally require a moderate field operation for deployment, as well as for maintenance or recovery of certain specialized systems. For instance, deployment of an ice-tethered platform with subsurface instrumentation typically requires occupation of an ice floe, drilling a hole through the floe, installing the subsurface tether and instruments (usually with a mechanical tripod), and attaching the surface package and sensors. While some simple air beacons may be easily deployed by dropping from airplanes, masts with more complex meteorological sensors and Ice Mass Balance (IMB) buoys also require occupation of an ice floe and drilling holes for installation. Since an IBO would consist of a combination of these platforms, logistics associated with some type of field operation on the ice represents a shared asset. Accordingly, a long-term logistics plan would be an essential complement to scientific and technical plans to deploy an array of IBOs in the Arctic. The ARCUS produced, NSF sponsored report “Arctic Research Support and Logistics: Strategies and Recommendations for System-scale Studies in a Changing Environment” (available at http://www.arcus.org/Logistics/logistics03) should be considered in this regard. IBOs would be particularly well suited to sustain observations in the deepest, most inaccessible regions of the central Arctic basins (see section 3.1). Logistically, the challenge in the perennial ice is remoteness and difficulty of access by ships (high cost of heavy icebreakers) and aircraft (range limitations and landing sites). IBO deployments would not necessarily need their own (costly) single purpose cruise, but could inexpensively be deployed during other expeditions on an opportunity basis. Ship use would allow comprehensive surveys of the IBO site to be made at the time of the deployment, which would be useful in interpreting IBO data. The more remote parts of the IABP array have always been maintained via air drops from long-range patrol aircraft, but air dropping of the types of IBOs discussed at the workshop would probably not be practical. In the past, USN submarines have made some contribution to IABP deployments and could possibly be used to deploy IBOs. Another possibility is the identification of 'seeding' sites, convenient locations from which IBOs might distribute themselves over the Arctic Basin through ice drift over time. The histories of IABP trajectories, in conjunction with existing numerical simulations, provide the most useful existing information for the exploration of this concept. However, the basins only represent less than half of the area of the Arctic Ocean, and specialized IBOs should also be deployed over the shallow continental shelves, which are typically characterized by seasonal ice cover. In the seasonal ice zone, the challenge is associated less with difficulty of access than with required timing of access. Seeding may be required at intervals of few months. Seasonal cycles of other societal activity (e.g. marine re-supply) and darkness may be limiting if aircraft landings or the presence of a ship is required. 3.7. IBO Data reporting
and distribution
The workshop concluded that in order for the IBO array implementation to be valuable to the greater scientific community, usable products must be generated, such as the IABP datasets distributed by the Polar Science Center at the University of Washington, Seattle. It was noted that quality controlled, gridded fields combining the results from a critical mass of IABP buoys (tens or hundreds) over many years have served as the basis for many previous and ongoing climatologic studies and have reportedly been of greater interest to the community than raw time series from individual buoys. This was probably true for the range of Arctic research activities in the past; however, under the present conditions of Arctic change, for the purpose of developing comprehensive models of Arctic processes, and for the requirements of Arctic Ocean reanalysis problems formulated by SEARCH, it is extremely important to have at least two IBO products: • Information for scientific and operational needs (data assimilation for Arctic reanalysis, submarine navigation, process studies, remote sensing and modeling data validation). For these purposes, the data, once retrieved, should be vetted through a relatively simple preliminary processing and quality control, and made publicly available in near-real time with the accuracy and time resolution that it was collected at and stored in a publicly accessible format in an internet-accessible database, so a broad range of scientists could immediately obtain and analyze the operational data. Data standards exist for profile data through Argo and JCOMM, and are being coordinated through CliC and WCRP. Therefore it is recommended that IBO data formats should be coordinated with existing standards of data distribution and exchange. • A second level of data reporting and distribution, similar to the IABP datasets. These products should include high quality time series of all parameters, gridded fields, and derived characteristics (such as freshwater and heat content, water mass composition, etc.) and provide higher levels of data analysis useful for a broader range of Arctic community interests. These products should be consolidated monthly and/or annually, depending on community needs and recommendations. The workshop general consensus is that IBO data needs to be available in real time via the internet if possible, otherwise as soon as possible thereafter. It is recommended that the operational needs and the secondary level of data reprocessing and distribution be provided by the IBO executive office and its personnel under control of the coordination and oversight science committees. 4. Summary and Recommendations
Experience gained in previous studies was used by workshop participants to develop the concept of an array of ice-based instrument systems, or Ice-Based Observatories (IBOs) that would satisfy the needs of international Arctic science programs. Workshop participants identified IBOs as automated, drifting, ice-based sensor systems providing comprehensive data from the Arctic environment and incorporating the multidisciplinary needs of biological, chemical and physical oceanography, as well as different aspects of atmospheric and sea-ice studies. Moreover, in addition to supporting suites of sensors, these observatories may also act as a network of acoustic receivers, data transmission nodes for a mooring network and various autonomous platforms, and navigation beacons for autonomous vehicles operating near or between stations. 4.1. Requirements and
Challenges
The basic requirements identified at the workshop for a future generation of ice-based unmanned platforms are: • Observation and real-time reporting, with high vertical resolution and high accuracy, of an interdisciplinary suite of parameters from the near-surface atmosphere, sea-ice, and upper ocean for multiple years (assuming deployment on robust ice floes) at temporal resolutions appropriate for each parameter; • Ease of deployment from landed aircraft and helicopters in addition to deployment by icebreaker; • Modest cost, allowing them to be deployed in large numbers (analogous to the present IABP) and, in some cases, to be considered expendable; • Accommodation, through standard interface and communication protocols, of future surface and/or subsurface instrumentation, including acoustic communication (for data transfer, and navigation) with mobile platforms. Although much of the necessary IBO technology already exists and routine observations are presently underway using the IBO concept, there are a variety of challenges that must be addressed en route to the development of a comprehensive multi-disciplinary IBO array. Workshop participants agreed that platform instrumentation should be improved by continued development of profiling systems for atmosphere, ice and ocean with the goal of sampling biological and chemical variables on the same spatial and temporal scales as physical variables in order to separate biological and /or chemical transformations from changes due to physical mechanisms. Profiling systems for many physical variables are presently available or easily adapted for routine use in the Arctic, whereas apart from oxygen and nitrate sensors, bio-chemical profiling systems will require additional development effort. Relating to the platforms themselves, it was noted that IBOs would be best suited to deployment in perennial pack ice. However, the seasonal sea-ice zone accounts for a majority of the northern marine cryosphere, and most of this is in shallow water (<500 m). Specialized IBO designs will likely be needed for the seasonal ice zone, platform lifetimes will be short, and frequent re-deployments will be required. Alternate technology (e.g. profiling floats) may also be required. Finally, the integration of mobile assets with IBOs needs to be addressed in design studies. There are specific technological issues (e.g. navigation, communication and energy transfer) relating to interactions among IBOs, floats, gliders and AUVs that should be addressed concurrently with an IBO array implementation. 4.2. Distinguishing
features of the IBO concept
The following features distinguish the IBO concept from previously designed, developed, and implemented Arctic drifting observing platforms: • The IBO represents and satisfies the multidisciplinary needs of Arctic oceanic climate system covering each of the biological, atmospheric, cryospheric and oceanic regimes; • The IBO provides simultaneous, high vertical resolution data over sea-ice (near surface atmospheric boundary layer), under sea-ice (upper 800m ocean layer), and within sea-ice; • An array of IBOs is envisioned and, similar to IABP array, will allow coverage of more than 40% of the Arctic Basin area; • The IBO reports in near-real time, and data from IBO are openly available via the internet; • The IBO provides communication and data exchange capabilities among different observing systems including but not limiting to AUVs, moorings, gliders, floats, cable observatories, and acoustic tomographic systems. The combination of features listed above makes the IBO concept unique, and is the major accomplishment of the workshop. 4.3. Proof of concept:
IBO prototypes in the field
At least four prototypes versions of oceanic observing systems are already operating in the Arctic, providing real time information, including: • IABP buoy array accompanied by IMB buoys (see http://iabp.apl.washington.edu/, Appendix A1.1, and abstracts by Hanna et al. and Perovich et al. in Appendix 5) • JAMSTEC J-CAD buoy in combination with IMB buoys (see http://www.jamstec.go.jp/arctic/J-CAD_e/jcadindex_eand Kikuchi et al. abstract in Appendix 5) • WHOI’s Ice-Tethered Profiler (ITP) in combination with IMB buoy (see http://www.whoi.edu/itp/data, Appendix A1.5, and Krishfield and Toole abstract in Appendix 5). • North Pole Environmental Observatory (NPEO; which includes Arctic Ocean Flux Buoys (AOFB), J-CADs and IMB buoys (see http://psc.apl.washington.edu/northpole, http://www.oc.nps.navy.mil/~stanton/fluxbuoy, and abstracts by Stanton, Kikuchi et al., and Perovich et al. in Appendix 5), More information on each of these systems is also available in the workshop presentations at: http://www.whoi.edu/science/PO/arcticgroup/projects/ipworkshop_presentations.html. Therefore, practical, cost-effective and proven IBO designs presently exist, can be readily extended to provide interdisciplinary observations, and should be implemented expeditiously as part of a coordinated Arctic observing system. Arctic change is ongoing and measurements need to begin now to identify the causes of these changes. An array of IBOs maintained throughout the Arctic Ocean interior is envisioned to observe the spatial structure and annual to decadal variations of the polar atmosphere-ice-ocean environment. Practical, cost-effective and proven IBO designs presently exist, can be readily extended to include interdisciplinary observations, and should be implemented expeditiously as part of a coordinated Arctic observing system. Specific recommendations were: • A relatively simple and robust IBO array, based on presently available technology, should be implemented immediately as part of a stepwise development of a multi-component, interdisciplinary Arctic observing system. An international body will be required to coordinate the various national programs (eliminate overlap, insure no data holes) and insure compatibility of data and their widespread distribution. • The 25 years of IABP drift trajectories, existing data climatologies and available numerical simulations should be exploited to derive insight to optimal array design, deployment strategies, sampling intervals, and expected performance of an IBO array. • Since ice-based observations at a given site may consist of a distributed set of subsystems developed by multiple PIs, the logistics infrastructure for getting to the deployment sites is one of the most important shared assets of the observing system. A long-term, internationally coordinated logistics plan should be implemented as an essential complement to scientific and technical plans for an IBO array. • IBO designs should provide accommodation for novel sensors, acoustic receivers, and communication and navigation capabilities for mobile platforms. Emerging technologies for Arctic observation (including but not limited to: unattended biological and chemical sensors, electromechanical sensors, autonomous oceanographic vehicles and drifters, and unmanned aerial vehicles) should be developed within the framework of an integrated Arctic observing system. We gratefully acknowledge contributions from all workshop participants, and in particular the keynote speakers listed, along with a summary of their presentations and the workshop agenda, at http://www.whoi.edu/science/PO/arcticgroup/. Thomas Pyle of the National Science Foundation (NSF) provided the impetus for the workshop. Financial support was provided by NSF through Grant No. OPP-0349416 from the Office of Polar Programs.
Workshop participants acknowledged several designs
for Arctic Observing Systems, some of which are discussed below
(see also abstracts of presentations in Appendix 5
of this document and workshop Power Point presentations at the workshop
web site: A1.1. Study of Environmental
Arctic Change (SEARCH)
A review of recently observed changes in the physical and biological state of the Arctic and a justification for future Arctic observations are contained in the supporting document of the U.S. National Science Foundation’s SEARCH program (http://psc.apl.washington.edu/search/).
In general, NOAA’s plan for oceanic observatories (Figure A1.1.2) is in agreement with the SEARCH observational plan. In this context, the existing IABP program, as well as the NPEO, is being enhanced with deployment of IMBs. One aspect of the NOAA’s SEARCH initiative is to autonomously monitor changes in the thickness of the Arctic sea-ice cover (Overland et al., 2002).
A1.2. Arctic Ocean Observing
System (AOOS)
A design for an AOOS (http://www.aosb.org, Figure A1.2) was prepared for the International Polar Year in 2007-2008 and beyond on behalf of the Arctic Ocean Sciences Board. According to this plan AOOS mainly will address fundamental questions and issues concerning the Arctic ice-pack and its seasonal and interannual variability, taking into consideration internal and external factors (thermodynamics and dynamics) influencing the growth and decay of sea-ice. The AOOS should operate all year long and for several years in a quasi autonomous mode. The AOOS would be articulated around four main components: (1) a space component based on remote sensing, satellite data transmission and precise geolocations, (2) a surface component based on ice-tethered platforms equipped with meteorological and oceanographic sensors (including sea-ice), and (3) an underwater component based on autonomous underwater ballast controlled floats equipped with ice profiling upward looking sonars (ULS) and self regulated gliders equipped with CTD. An integrator component, (4), will be dedicated to data analysis and data integration in conjunction with numerical models to bridge gaps and develop interactions and synergies between observations and models.
A1.3. Hybrid Arctic Float Observation
System (HAFOS)
HAFOS is a vision for extension of the Argo system of vertically profiling floats (http://www.argo.ucsd.edu/, Figure A1.3) into the Arctic Ocean, where the presence of ice limits use of existing designs. Since location and data transmission under the ice is presently only possible by acoustic means, an observation system of water mass properties and currents in the deep Arctic or Antarctic Ocean requires the combination of different technologies. It comprises ice resistant profiling subsurface floats, surface drifters on the ice and moored stations. The envisioned system consist of RAFOS (ranging and fixing of sound) type subsurface profiling floats which obtain their position by ranging of sound sources on moored stations. The float measures vertical profiles of temperature and conductivity/salinity, but it does not reach the surface if it floats under the ice. Therefore it has to store the data until it reaches an ice free area. In this first version no real time data can be obtained and the data are lost, if the float does not reach open water again. Therefore a second step is planned to install a sound source on the float (SOFAR). During the period when the float profiles under the ice it transmits a reduced data set acoustically, since the energy consumption for sound transmission is the limiting factor of the system. The full data set is stored until the floats can reach the surface in open water. Receivers are mounted on the moorings with the sound sources for ranging which can be under a seasonally varying or even permanent sea-ice cover and on surface stations deployed as buoys drifting on the sea-ice. From the sea-ice buoys data can be transmitted to satellites to be available in real time. The development of HAFOS is planned to take 10 years. The first steps were successful to deploy floats which will not return to the surface under ice cover and to determine the acoustic range in ice covered areas by use of RAFOS floats.
A1.4. Arctic Acoustic
Thermometry and Tomography
Acoustic remote sensing, namely acoustic thermometry, was first demonstrated in the Arctic Ocean in 1994 revealing the basin scale warming of the Atlantic Water layer. Acoustic thermometry and tomography (Figure A1.4) provides an integrated measurement of temperature and currents that can be applied to a variety of observational scales. For basin scales acoustic thermometry integrates over mesoscale and higher wave number phenomena to provide large scale averages of temperature and heat content that are needed for climate oriented studies and are difficult, if not impossible, to obtain with an ensemble of point measurements, especially in the Arctic Ocean. Measurement of transport, thermocline depth, even salinity and sea-ice properties are also possible and are in various stages of development.
Acoustic remote sensing requires an acoustic source and hydrophones. These can be installed on “conventional” oceanographic moorings and can therefore extend the point measurements obtained at the moorings with integrated measurements between the moorings. If the acoustic capability is designed into the moorings at the planning stages the marginal cost is comparable to other sensor packages. Connecting such Arctic Ocean moorings back to shore is envisioned exploiting an existing sea-shore link in the Lincoln Sea and a planned link into the Beaufort Sea from Barrow, Alaska providing the real-time synoptic capability
An NSF-sponsored workshop entitled, “Instrumentation for Arctic Ocean Exploration: Technology for accessing the water column and seafloor” was held at the Monterey Bay Aquarium Research Institute in Moss Landing, CA from October 16-18, 2002. The workshop was convened in response to the fact that: (1) the Arctic Ocean is a high-priority target for a diverse set of scientific investigations including key topics such as global climate change, life in extreme environments, and the origin of life on Earth, (2) virtually all Arctic oceanography, regardless of discipline, is limited by a small set of common technological barriers, (3) a number of recent technological developments present opportunities to overcome these barriers and truly revolutionize the conduct of Arctic oceanography, and (4) the aggregate national funding for Arctic operations, research, and instrumentation is at alarmingly low levels after being in steady decline for nearly a decade. There are five over-arching technical challenges that presently
limit most types of Arctic research: An important outcome of the workshop was the development of a coherent vision for the future of Arctic research that would fundamentally change the way observations are made in the Arctic by exploiting the potential of new technologies to solve these technical challenges and create a new paradigm for Arctic oceanography. The three components of this vision are; (1) expeditions with enhanced capabilities, (2) a basin-wide network of ice-mounted buoys and mobile platforms (i.e. gliders, drifters, autonomous underwater vehicles), and (3) cabled oceanographic observatories with real-time data and power connections to shore. In this vision (Figure A1.5), ice-tethered platforms are the key
element responsible for ocean sampling will be augmented with AUV
transects to provide synoptic observation of the Arctic basin at
regional scales. The drifting ice buoys will serve as acoustic navigation
beacons for AUV operations, and will utilize long, short, and ultra-short
baseline acoustic technologies to establish waypoints for AUV navigation
and for acoustic homing. AUVs will be developed with complementary
hardware and software to allow for operation within the buoy and
cabled network, and will utilize docking technology to allow for
data and power transfer from the fixed resources to the AUVs at
key nodes.
Appendix 2: The International Arctic Buoy Program  The International Arctic Buoy Programme (IABP, http://iabp.apl.washington.edu/index.html) maintains a network of drifting buoys in the Arctic Ocean to provide meteorological, oceanographic and sea-ice data for real-time operational requirements and research purposes including support to the World Climate Research Programme (WCRP) and the World Weather Watch (WWW) Programme of the World Meteorological Organization (WMO). The IABP consists of 23 Participants from 9 nations, and is organized as an action group of the WMO Data Buoy Coordination Panel. Participation in the IABP is open and voluntary. The IABP functions according to a set of Operating Principles and Terms of Reference for the IABP Coordinator. The IABP operates under the guidance of an Executive Committee (Excomm) that is elected by the Participants. The directives of the Excomm and the daily operations of IABP are carried out by the Coordinator, acting as the focal point for the Programme, and performing the following functions in collaboration with the Participants: • Monitor data in near Real-Time The IABP began in 1978 and is ongoing, with a 25-plus year track record of producing real-time and research-quality data characterizing the Arctic Ocean environment. IABP's gridded datasets have emphasized surface air pressure, surface (2 meter) air temperature, and large scale sea-ice velocity. In addition, IABP has acquired and made available datasets on upper ocean temperature and salinity structure, and sea-ice mass balance. Over 450 scientific and technical publications have benefited from observations of the IABP (http://IABP.apl.washington.edu/Citations). For example, IABP data were fundamental to studies: (1) showing the drop in Arctic sea level pressure and increase in cyclonic surface winds during the late 1980's-early 1990's; (2) showing the patterns of multidecadal trends in surface temperature over the Arctic Ocean; (3) showing the changing patterns and decrease in areal extent of old (> 10 year) sea-ice in the Arctic Ocean from 1979-2004. Enhancements of the IABP have been recommended
as a key component of the SEARCH Arctic Ocean Observing System,
including Ice Mass Balance Buoys (IMB) and ocean Temperature-Salinity
(T-S) buoys. The IABP plan for 2005 includes 13 IMB's and 6 T-S
buoys (http://iabp.apl.washington.edu/AOOS/).
The combination of automated systems to measure meteorological,
sea-ice (including mass balance) and upper ocean variables has been
dubbed "Automatic Drifting Stations" in the SEARCH implementation
plan Appendix 3: Elements of an Ice-Based Observatory
Science questions: The atmosphere is an important element of the Arctic climate system but there is a substantial lack of observations over the Arctic Ocean. Currently the biggest uncertainty in Arctic climate simulations are connected with limitations to the accuracy of measurements of albedo, surface fluxes and cloud cover. The International Arctic Buoy Program (IABP) provides information about surface atmospheric pressure and 2 meters air temperature with the remaining information on atmospheric conditions coming from operative numerical models and data reanalysis projects. These models are not perfect and the most probably causes for the large disagreements in Polar Regions between model results and observations are related to unrealistic parameterizations of a variety of feedbacks. Our understanding of the interactions and feedbacks among the components of the Arctic climate system can be significantly advanced by integrating new observations of Arctic climate variables with global and regional coupled atmosphere-ice-ocean models. The relationships and feedbacks between climate variables are not fixed over time and space and the ratio of thermal and dynamical drivers could change (buoyancy/convection and vertical wind shear). This establishes the need to compare the temporal evolution and spatial pattern of model relationships with the corresponding covariability in observed and measured climate variables on decadal time scales. The proposed measurements can identify physically based causes for disagreement and focus on physical processes (e.g. surface fluxes in the stable and unstable planetary boundary layer, albedo-radiation-low cloud feedbacks, the importance of synoptic-scale atmospheric dynamical processes for the regional variability of sea ice cover, the influence of Arctic aerosols, etc.). The use of different measurements, e.g. from field campaigns, like the Surface Heat Budget of the Arctic ocean (SHEBA) program or satellites, can be used to improve the accuracy of the models by evaluating the realism of their output, analyzing feedback mechanisms and relationships among climate variables but in parallel a network of drifting platforms providing sustained measurements of atmospheric surface parameters over the Arctic ice and ocean is needed. These measurements together with theoretical approaches will allow us to answer some key scientific questions, namely: • What are the physical processes within the coupled atmosphere-ocean-sea-ice system that determine the Arctic surface heat, humidity and momentum fluxes? Measurements of surface energy fluxes on time scales relevant for climate time scales and climate modeling are needed in order to resolve decadal and interdecadal variability. • What is the variability of radiative and turbulent properties of the atmosphere on climatically relevant time and space scales? Model results show that there is a reasonable representation of the annual cycle and selected climate variables with major shortcomings in the planetary boundary layer and the near surface. Therefore, atmospheric measurements from automated IBO should include basic parameters characterizing processes and fluxes at interfaces atmosphere-sea-ice and atmosphere-ocean. Correct representation of these parameters is extremely important for calculations and simulations of sea-ice and ocean dynamics and thermodynamics which respectively influence atmospheric conditions. Summarizing, the following physical characteristics of the near surface atmosphere layer is necessary to determine the surface energy budget and to answer a suite of very practical questions, such as: What are the radiative fluxes? How much radiation is incident, reflected, absorbed, and transmitted? What is the cloud cover (amount and properties)? What is the stratification and thickness of boundary layer over the ice and ocean? What are the turbulent fluxes in this layer? Recommended atmospheric parameters: • Air pressure (Paroscientific sensor); Spatial coverage over the Arctic could be similar to IABP array (with perhaps 1-2 buoys per 500 km), although a 5 to 10 times higher resolution would be desirable in some areas for comparisons with regional climate model simulations. Analysis using IABP experience and modeling capabilities should be used to determine the spatial resolution parameters and respective number of IBOs in the array. Thermodynamics (growth, decay, mass balance): General circulation models indicate that Arctic sea-ice may be a sensitive indicator of climate change. Accordingly, efforts are underway to improve and expand observing systems designed to monitor changes in the Arctic sea-ice cover. The mass balance of the ice cover is an important component of such observing systems, since it is an integrator of both the surface heat budget and the ocean heat flux. Satellites provide information on ice extent, as well as the onset of melt and freeze-up and submarine surveys furnish large-scale information on changes in ice thickness. However, neither method delineates potential sources of observed changes: e.g. differences in surface heat budget, variations in ocean heat flux, or modifications due to ice deformation. Ice mass balance data provide this critical insight. Autonomous buoys provide a means of routinely monitoring the ice mass balance at many locations. Ice mass balance buoys consist of, but are not limited to, a combination of a data logger, an Argos transmitter, a barometer, a GPS, acoustic sensors monitoring the positions of the ice surface and bottom, and a vertical string of thermistors extending from the snow surface to the ocean surface. The buoys provide time series information on vertical temperature profiles, ice growth and decay, snow accumulation and ablation, and ocean heat flux. In the past few years, nearly a dozen of these buoys have been deployed as part of the Study of Environmental Arctic Change (SEARCH) program. The ice buoys have been collocated with other instruments including ice thickness profilers and ocean and meteorological buoys. Data from these integrated sensor systems will be assimilated and synthesized with other direct observations, remote sensing data, and sea-ice models, to study the large-scale evolution of ice mass balance. Recommended parameters and sensors for sea-ice thermodynamics: • Position (GPS); Dynamics (deformations, ridging, failure): At scales of 10-300 km sea-ice consists of a collection of plates with differential motion along discontinuities. It is equivalent to the oceanographic mesoscale (10-100 km) which is rich in high energy dissipation processes (e.g., eddies). At this scale, differential sea-ice motion plays an analogous dissipative role through the development of leads, slip lines, cracks, and pressure ridges. Within the sea-ice community there is no formal definition of this scale, with nomenclature such as “linear features”, “piece-wise rigid motion”, and “aggregate scale” beginning to emerge. Researchers are only recently able to explore this scale thanks to availability of high-spatial resolution, all-weather, Synthetic Aperture Radar (SAR) images. A fundamental caveat with SAR imagery on polar orbiting satellites is limited temporal resolution (typically 3 days and rarely less than one day in cross-overs). Under the influence of fast moving storms, significant non-linear changes in discontinuities occur at temporal scales much less than 3 days with sea-ice deforming rapidly, resulting in large changes in orientation, distribution, and size of continuous and discontinuous regions. Complimentary to polar SAR imagery, ice-mounted GPS-equipped buoys have high-temporal resolution (hourly) but are spatially sparse in the field (low-spatial resolution) with episodic deployments. Our approach is the development of a high-temporal, high-spatial synthesis using buoys, SAR imagery, and a Lagrangian discrete element ice models. Such a synthesis provides valuable regional information for improving our understanding of sea-ice processes, short-term (up to one week) forecasting, and model validation. Efforts toward this goal are underway with interim results already showing great merit in both Arctic and Antarctic regions. Relevant science, logistic, and technological issues include: • With the revisit time of satellites limited to one day or longer, the temporal resolution of Lagrangian buoys (typically 1 hour) still far exceeds any space borne platforms. The addition of low-cost (< $2K) GPS buoys scattered around a base ice-tethered system provides critical information in determining local ice dynamics in a way that can not be capture by remote sensing (not now and not for a very long time to come). Their high temporal resolution (typically 1 hour) captures fundamental high energy processes like storms, tides, inertial oscillations, and sub-surface oceanic eddies manifested in the ice. Even weekly atmospheric synoptic events like storms are poorly resolved in high spatial resolution space-borne SAR imagery. • A simple scaling experiment clarifies the practical advantages of utilizing sea-ice to understand geophysical scale dynamic processes. Velocity is computed from a point measurement and associated changes of that moving point with time. Deformation is computed from spatial changes at multiple points with time. As such, deformation of any material captures both spatial and temporal characteristics while velocity captures only the temporal variability. Hence observations of sea-ice divergence and shear are far more encompassing in describing processes related to the surface fluxes and navigation while velocity is an intermediate point measurement toward that result. Relatively high spatial and temporal correlation length scales of ice (of order 100 km and months, respectively) make it possible to estimate mesoscale/regional/local deformation based on a relatively small cluster (of order 10) of point measurements. This is in contrast to the need for several hundred surface drifters to cover similar scales in the atmosphere and ocean. Hence regional sea-ice dynamics and variability measured through sea-ice deformation arrays is both easier and more cost effective than for either mesoscale atmospheric or oceanic systems; a benefit of sea-ice utilized since the time of Fridtjof Nansen over 100 years ago. • The number of GPS stations around an ice-tethered platform is more critical than the scale they are deployed. A minimum of 6 buoys is required for a statistical characterization and 10-12 are preferable in dynamic regions. In combination with high spatial resolution SAR images one can get away with 6 or so stations if used primarily as temporal tie-points to connect non-linear events between images. Spatial scales should be determined based on critical regional mesoscale processes and be deployed in clusters accordingly (5-200km). Helicopter range from a main buoy has traditionally defined the outer bound (around 200km). • The following is a recommendation (in order of cost) of practical add-ons to remote mesoscale units in terms of cost optimization and relevant data retrieval (to add on as budgets permit but not at the expense of enough cluster buoys). o Temperature sensor at the snow-ice interface; Science questions: Recent measurements in the Arctic Ocean show that "the Arctic is in the midst of change extending from the stratosphere to below 1000 m in the ocean" (Morison, J.H., K. Aagaard, and M. Steele, Arctic, 53: 359-371, 2000). Such changes resonate with global climate modelling studies that consistently show the Arctic to be one of the most sensitive regions to climate change. In turn, processes occurring in the Arctic Ocean appear able to influence the subpolar North Atlantic and possibly the global ocean circulation. There are numerous science questions related to the Arctic Ocean circulation, freshwater and heat contents, vertical structures, water masses and other physical parameters and their variability. It is also important to understand the role of small to mesoscale processes such as turbulent mixing near the air-ice-ocean interface, double diffusion (pervasive in the Atlantic Water core), internal wave mixing, and mesoscale eddies. Among these problems the following questions are likely to be resolved with data from the implementation of IBOs: • What is the current state of the Arctic Ocean hydrography? A coordinated effort of sample collection and data synthesis is
needed to solve these questions. The data collection effort proposed
here will fill crucial gaps in the modern and historical data sets
available in the Arctic Ocean. It is important to: • Quantify the vertical and temporal scales of variability in the temperature and salinity fields, especially in the Pacific and Atlantic halocline layers where many dramatic changes have occurred during the past decade. • Assess the impact of regional effects on large-scale changes in the circulation and properties of the Arctic Ocean. Parameters and sensors and real time profiling technology: There are four measurable parameters traditionally used by physical oceanographers for their studies (water temperature, salinity, pressure, and ocean currents) and there are proven means for their sampling. Progress in documenting and understanding climate variability of the Arctic Ocean requires a sustained ocean observing system that is cost effective and practical. The need for broad-scale, frequent ocean sampling is being addressed outside the polar latitudes by the multinational Jason/Argo programs that are providing satellite altimeter measurements of sea level anomalies and drifting profiling floats measurements of the upper ocean temperature and salinity fields, all feeding a global data assimilation effort (GODAE). Although sea-ice precludes the use of these techniques for observing the Arctic Ocean and quantifying its circulation, it does provide a natural support platform for the deployment of ocean sampling systems. Ice-tethered drifters discussed in the introduction with discrete subsurface instrumentation such as the SALARGOS, IOEB and J-CAD buoys, have been successfully deployed in the Arctic in recent years, demonstrating that automated buoys are a viable means of acquiring long-term, in situ data from beneath the ice pack. Development of automated profiling instruments is required to overcome the limitations of discrete depth systems (for examples see abstracts in Appendix 5 by Krishfield and Toole and Kikuchi, et al.). For climate variability studies, arrays of platforms are needed to better resolve the spatial and temporal variability of the data from individual drifters. Year round observations with daily or more frequent temporal resolution and better than 1 meter vertical resolution of the upper 500-800 meters would allow polar oceanographers not only to successfully detect the heat and freshwater content of the Arctic Ocean but also to investigate and better parameterize numerous polar ocean processes including vertical mixing within thermohaline diffusive staircases and lateral stirring by thermohaline intrusions and eddies. Additionally, an IBO array could establish a telecommunications link through the surface ice pack to serve as a future framework for two-way transmissions of data and/or navigation information among buoys, AUVs, and subsurface moorings measuring physical properties in the Arctic Ocean. Recommended parameters for physical oceanographic studies (all profiling from the surface to at least 500 m with 1 m resolution): • Pressure; The identification of a small subset of key variables for biology and chemistry is relatively difficult because of the diverse and broad range of critical variables relevant to various aspects of Arctic ecology, chemistry, and biochemical transformations. The important variables, naturally, depend on the biological and chemical question to be addressed. Therefore, it is important to recognize that multiple combinations of biological and chemical sensors may be considered to be critical. Important Questions: Two overarching, critical questions that remain unanswered given the spatial and temporal paucity of data were identified, namely: • How do biological and chemical parameters vary seasonally and inter-annually? • What is going on, biologically and chemically, during winter? Encompassed within both of these questions are more specific processes or feature oriented questions that remain critical to our understanding of the ecosystem and of material fluxes. The following serve as examples of important questions but are not perceived as all inclusive. • What are the budgets of key biological and chemical parameters under the ice? • What is the extent and heterogeneity of ice cover and open water and how does this heterogeneity impact light transmission, light quality, and under ice production? • What is the vertical distribution of key bio-chemi |
