Title: Investigating Two Regimes of Arctic System Variability

OPP 9806926 $501,081 15 April 98 – 14 April 01

This award has provided support to extend the results of work (Proshutinsky and Johnson, 1997) that first established the existence of two Arctic climate regimes. The research focuses on understanding the relationship between atmospheric driving of ice and upper ocean circulation and the ocean's temperature and salinity structure, ice thickness and extent, permafrost temperatures across Alaska and Russia, precipitation across the circumpolar (ocean and land) regions, and the influx of warm Atlantic water into the central Arctic Basin. The relationship between these phenomena is spelled out for the first time in the publications listed below, and a conceptual model of the behavior of the Arctic climate is under development. In addition to a number of presentations at national and international meetings (not listed), the following two papers have been produced:

Title: Arctic Research from Submarines

OPP 9619180 $65,000 15 May 97 – 30 April 98

This award provided support for pre-cruise planning for the hydrographic portion of the SCICEX-97 cruise. Assistance was provided in the design of the Submarine Launched Expendable Temperature Depth (SSXCDT) probe sampling scheme and selecting a Transarctic submarine track aimed at optimizing the interests and goals of all SCICEX-97 participants. The performance of the re-designed SSXCTD probe was evaluated before the SCICEX-97 cruise and a revised fall rate algorithm was devised. The eddy data collected during SCICEX-96 was analyzed and a detailed eddy-sampling scheme was recommended for SCICEX-97. A matched drop calibration scheme was provided for SCICEX-97 that successfully confirmed SSXCTD probe performance during the SCICEX-97 cruise.

The SSXCTD data collected during SCICEX-97 was processed and evaluated. Temperature (T) and salinity (S) measurements were merged with historical data to create full water column sound speed profiles. An environmental assessment was performed along the SCICEX-97 submarine track to determine the spatial and temporal variability of the region. T/S data were compared to previous SCICEX cruise data and to historical databases. Oceanographic and acoustic results of the analysis of the SSXCTD data collected during SCICEX-97 have been presented at national and international scientific conferences.

Title: Bioacoustic Research Software Instrumentation

BIR-8915149 $115,990 February 90 – March 93

Title: Software and Hardware Instrument Development and Computer Hardware for Bioacoustic Research

BIR-9211761 $172,344 April 93 – May 95

These two awards supported the development of Canary, a sound analysis program that runs on Macintosh computers, for advanced development of the software, for development and publication of the user's manual, and for development of specialized signal acquisition and digital signal processing hardware to enhance the capabilities of the software. Three versions of Canary have been released since the software was first made available to the public in 1992. Since that time, Canary has been extremely successful, becoming one of the most widely used tools in the research community for the analysis of animal sounds.

Canary allows the user to digitize audio data using the Macintosh's built-in sound input port, and can display waveform, spectrogram, and spectrum views of a signal. A full spectrum of editing tools (cut, copy, paste, amplify, filter) is included. Canary provides explicit control of all parameters of short-time Fourier transform (STFS) spectrum analysis. To facilitate measurements based on absolute signal amplitude, Canary lets the user calibrate signals and copy calibration parameters between signals recorded under the same conditions. The measurement panel can be configured to display any combination of over 70 individual signal measurements. Measurements can be transferred to a data log and be saved in a variety of formats for export to other programs. Canary can read and write sound files in six different formats, which facilitates data exchange with other programs.

Numerous scientific publications have used Canary for acoustic measurements or display. Over 60 articles have been explicitly identified.

Title: Point Franklin Archaeology Project

OPP 9321112 $392,000 April 1994 – April 1999

The project investigated a prehistoric coastal whaling village and a subsequent historic occupation of the same location on Point Franklin between Barrow and Wainwright (Shehan, 1995). A supplement allowed for the scientific documentation of "the little frozen girl of Ukkuqsi," an 800 year old burial recovered in Barrow. The child, a c.6 year-old girl, was the most perfectly preserved prehistoric body recovered in Alaska. She suffered from a genetic disease, alpha-one antitripsin deficiency. Previously unsuspected cultural occupations, insights into prehistoric construction techniques, and health and cultural issues were documented (Sheehan, 1997; Zimmerman, Sheehan and Jensen in press). Numerous North Slope residents and students participated in the field and laboratory work. Project investigators have given over 40 community and school presentations in Wainwright and Barrow, and have presented numerous professional papers.

Title: Cooperative Agreement: Facilitation of Arctic Research in the Barrow Environmental Observatory

OPP 9706494 $583,000 1 September 1997 – 31 August 2000

This program provides for activities in support for and assistance to Barrow-region NSF-funded research projects, for the management and maintenance of the BEO, and for public outreach to bring scientists and the community together. Current activities include construction in conjunction with the Ilisagvik College Vocational Education Department to improve the access road to NOAA/CMDL that also services ARM and the BEO; editing and producing the proceedings of the NARL 50^th Anniversary meetings; production of GIS-based maps for the BEO and vicinity; provision of equipment, supplies, technicians, guides and bear watch personnel to research parties; rental of laboratory, shop and storage space to research projects; sponsorship of public speaking programs by researchers; and participation in formal and informal efforts to upgrade support facilities for researchers. The Cooperative Agreement provides support for an Executive Director and a Logistics Coordinator.

Title: Broadband and Seismic Measurements on the Deep Sea Floor: A Pilot Experiment

OCE 9522114 $635,000 5 December 1995 – 30 November 1998

The primary goal of the Ocean Seismic Network (OSN) Pilot Experiment was to learn how to make high-quality broadband (0.003–5 Hz) seismic measurements on the seafloor. The experiment was carried out at the OSN-1 drill site (ODP Hole 843B) 225 km southwest of Oahu. On the deployment cruise in Jan. and Feb. 1998, three broadband seismic instruments were deployed: a borehole seismometer, a sensor buried in the surface sediments, and a sensor resting on the seafloor. The borehole seismometer was a Teledyne KS54000 similar to the sensors used in the global IRIS/IDA and GSN networks. It was placed in the borehole using the MPL/JOI Wireline Reentry System. The seafloor and shallow buried sensors were Guralp CMG-3T seismometers, referred to as BBOBS (Broadband Ocean Bottom Seismograph). In addition to the broadband seismometers three conventional OBS with 1 Hz geophone sensors, differential pressure gauges, a conventional hydrophone and a current meter were deployed. All three of the broadband instruments recorded data continuously and autonomously on the seafloor from early February until late May or early June (at least 115 days). Over fifty teleseismic earthquakes were observed on the broadband systems ranging from a 4.5 Mb event at 44° epicentral distance to the 8.1 Mw Balleny islands earthquake at 91°epicentral distance. Signal-to noise-ratios varied depending on frequency band, ambient noise conditions, and sensor design. Preliminary analysis indicates that the borehole system provided comparable quality data to similar continental and island stations over the 0.001–5 Hz band. The shallow-buried broadband system compared favorably with the borehole system for signals in the frequency band from 0.001 to 0.07 Hz.

Publications:

The Barrow Arctic Ocean Observatory (BAO) will open the first permanent year-round continuous observation research "window" into the interior of the Arctic Ocean. In the "Report of the Barrow Area Research Support Workshop" (BARS Report) to be issued by the Arctic Research Consortium of the United States, the Recommendations Summary includes under high priority near term needs (<2 years), the requirement to "install fiber-optic cable across the shore-ocean boundary." The BAO will consist of two undersea oceanographic/acoustic/seismic moorings in the Beaufort Sea for Arctic climate, oceanographic, acoustic, seismic and marine mammal studies. There will be a 1,700 m vertical line array, the Beaufort Sea Array (BSA), which will include acoustic and oceanographic sensors, and a bottom mounted four element seismic array (each element consisting of a 3-component Ocean Bottomed Seismometer (OBS) and Ocean Bottomed Hydrophone (OBH). The second mooring will be a horizontal bottomed array consisting of three groups of 5 hydrophones each for the Marine Mammal Listening and Tracking Array (MLTA). The BSA will be moored 150 km off Barrow, and the MLTA will be moored 9.5 kms off Barrow. These moorings will be connected via deep-sea powered fiber-optic cable to a shore facility in Barrow. These moorings and the shore facility will provide continuous, real-time, long-term observations of (1) basin scale Arctic Ocean temperature, (2) sea ice thickness changes (a capability under research), and (3) thermocline depth (also under research), using acoustic thermometry and acoustic remote sensing, and point measurements of (4) currents, (5) salinity, (6) temperature, (7) tides, (8) seismicity, and (9) marine mammal acoustic vocalizations. The BAO will provide marine coastal zone, and through the acoustic remote sensing, Arctic Ocean basin scale data. The BAO data and research combined with the significant on-going terrestrial research at the Barrow Environmental Observatory (BEO), and atmospheric research at the Climate Monitoring and Diagnostic Laboratory (CMDL) and the Radiation Measurement sites "will allow for integrative studies of the causes and effects of global change, strengthening our understanding of significant relationships at the local level", quoting again from the BARS Report (adding the important role of ocean processes). The close monitoring of the marine mammals and particularly the Bowhead whale migration and census will be correlated with the physical oceanography measurements. Finally, the ocean bottom seismometer array (four OBS/OBH's) that will be part of the BAO will provide for the first time, real-time, year-round observations of Arctic seismicity for seismic events in the Arctic Ocean and surrounding margins from sensors within the Arctic Ocean itself.

The BAO project will realize considerable leverage of both the scientific expertise and experience from the ACOUS project and the research team that has been working together since the early 1990's. Research on acoustic thermometry in the Arctic was begun in 1990 by SAIC as an outgrowth of the Acoustic Thermometry of Ocean Climate (ATOC) Program [Mikhalevsky, et al., 1991]. MIT and WHOI were early and on-going partners. The project was formalized under the name ACOUS as a collaborative program with Russia in 1994 under the auspices of the Gore-Chernomyrdin Commission (now Gore-Stepashin Commission) and a Memorandum of Understanding was signed by the U.S. Secretary of Defense, the Russian Deputy Minister of Defense, and the Russian Minister of Science. UAF, BASC, and the Department of Wildlife Management, North Slope Borough joined the ACOUS effort in 1996. The Russian participation has and will continue to be important to the success of ACOUS. Their participation has permitted the ACOUS program access to Russian Arctic territory for experiments, to Russian research institutes and researchers and the vast store of Russian data, experience and technical expertise in the Arctic, previously unavailable to western researchers. The Institute of Applied Physics (IAP) in Nizhny Novgorod has been responsible for the Arctic acoustic source design. They successfully designed, built and deployed the 20 Hz source used during the TAP experiment in April, 1994. This experience went into the design of the autonomous source that is currently operating in the Arctic. Data acquired at an ice camp established in April 1999 have shown that the source is operating exactly according to specifications. The U.S. Navy has independently confirmed the source operation. The Shirshov Institute of Oceanology, and the Andreev Acoustics Institute in Moscow have been key performers on the program and the lead Russian Principal Investigator, Dr. Alexander Gavrilov, is from Shirshov. Important analyses and access to Arctic Ocean data bases has been provided by the Arctic Antarctic Research Institute (AARI) in St. Petersburg and they also provided ice breaker services of the Akademik Fedorov this past October.

ACOUS source being installed from the Russian icebreaker, Akademik Fedorov, in the Franz Victoria Strait, Oct. 9, 1998.

The ACOUS project has also been working with the European Commission funded program called Acoustic Monitoring of the Ocean Climate in the Arctic. This project was started in 1997, spurred by the success of the TAP experiment, and is currently in a research phase with a primary focus on the use of acoustic remote sensing to determine ice thickness and correlate the acoustic data with satellite remote sensing data. The project leader is Prof. Ola M. Johannessen, Director, Nansen Environmental and Remote Sensing Center (NERSC) and includes the University of Cambridge, Scott Polar Research Institute (UCAM-SPRI), the Max Planck Institute for Meteorology (MPI), and the Nansen International Environmental and Remote Sensing Center (NIERSC), Russia. Researchers from UCAM-SPRI will be aboard the Polar Star this June/July 1999 and will be recording signals from the ACOUS source. Synergy is expected with this project when it enters its field program phase in the coming years.

(1) Arctic Ocean temperature measurements using acoustic thermometry
Performers: SAIC, MIT, Shirshov, UAF

Acoustic transmissions from the source in the Franz Victoria Strait will be received at the BAO. The acoustic signal processing will include beamforming, modal detection, and pulse compression processing and phase detection to determine the arrival times of the pulses as a function of acoustic mode. These steps are straightforward and have already been successfully demonstrated in the Arctic during the Transarctic Acoustic Propagation (TAP) experiment in April 1994 [Mikhalevsky, et al., 1995a; Gavrilov and Mikhalevsky, 1996, and Mikhalevsky, et al., 1999], and from data just recently collected at the APLIS Ice Camp in April 1999 in the Chukchi Sea. The travel time data (one 20.7 min sample every four days) will be converted to temperature and heat content change and compared to model runs (see (4) below) and SCICEX CTD transects. Under the proposed effort recordings will begin in the summer of 2002 with the installation of the BAO (a 2001 installation is discussed below, but this would require an acceleration of funding in the first two years of the project). A minimum 5 year+ time series is planned, based upon the expected life of the undersea systems (see below for more details). These data combined with the SCICEX transects, the TAP measurement, and the current data being taken in the Lincoln Sea will provide a total time series of over a decade. The theory that the Arctic is cycling or oscillating between two regimes based upon model runs [Proshutinsky and Johnson, 1997, and Johnson et al., 1999] and historical data analysis [Grotenfendt, et al., 1998] suggest a 5–7 year cycle, and there is evidence that the cyclonic regime of the early 1990's is or has already shifted to it's anticyclonic state, however, it is not clear whether this has manifested itself in changes in the cooling of the Atlantic Layer of the Arctic Ocean. In fact, recent data from the acoustic section taken at the APLIS Ice Camp in April 1999, indicate that temperatures have remained the same or may have even increased slightly since 1998, but more careful analysis is needed to confirm this. The BAO will provide the observations needed to understand the phasing of atmospheric and ocean changes in the Arctic and test the Arctic Oscillation theories as well as detect any longer term secular trends that might be occurring.

The oceanographic structure of the Arctic Ocean makes it especially suitable for acoustic monitoring. The half-channel acoustic duct with the upward refracting sound speed profile creates a propagation condition in which the acoustic modes extend from the surface deeper into the water column as mode number increases. At the operating frequency of 20 Hz mode 1 is trapped above the thermocline and propagates in the upper mixed layer above the Atlantic Intermediate Layer. Mode 2 extends into and propagates almost entirely within the Atlantic Intermediate Layer, while modes 3 and higher sample the deeper depths in the Arctic Ocean. This has been shown with modeling [Gavrilov and Mikhalevsky, 1995] and from analysis of the TAP data [Mikhalevsky et al., 1995a; and Mikhalevsky et al., 1999].

This unique aspect of acoustic propagation in the Arctic also causes temporal dispersion of the modes. Mode 1 travels in the slowest sound speeds associated with the upper mixed layer and successive modes extending deeper are propagating at faster group velocities due to the increasing sound speed with depth. Over the 2,600 km propagation path from Turpan, the TAP source camp north of Svalbard, to SIMI, the receive array camp in the Beaufort Sea (Fig. 1), this resulted in a temporal separation of approximately 15 secs between mode 1 and mode 2 and approximately 2 secs between mode 2 and mode 3. This permits tracking of the travel time changes for each mode, and thus observations of the temperature changes, that can be associated with the important vertical stratifications within the Arctic Ocean. Indeed, it was the measurement of a 2 sec faster travel time of mode 2 from the TAP experiment when compared to a modeled result using historical climatology, that calculated to an average increase in temperature of the Atlantic Intermediate Layer along the TAP propagation path of .4° C. Subsequent direct measurements from Arctic sections taken by the icebreaker CCGS Louis S. St-Laurent, and the transect taken by the USS Cavalla (SSN-684) confirmed this result [Mikhalevsky, Keenan, and Baggeroer, 1996]. The largest temperature change, up to 1º C, was observed in the core of the Atlantic water, over the Lomonosov Ridge, which may be due to change in the water inflow from the North Atlantic. A considerable decrease of the heat loss in the Norwegian Sea is assumed to be one of the causes of that phenomenon [Carmack et al., 1995b]. The TAP measurement was made in April, 1994. As discussed above another measurement was made in April 1999 from the APLIS Ice Camp with the ACOUS source installed in Oct. 1998 and this travel time corrected for the range difference between the two experiments showed a decrease in travel time of an additional 2.6 secs since the April 1994 measurement or an increase of the average temperature in the core of the Atlantic Layer of another .5° C for a total of .9° C since April 1994. This result is consistent with the SCICEX 1998 section shown in Fig. 1, and actually indicates that there may be an additional .1° –.2° C increase since 1998. These data are being analyzed now, so results are preliminary, and will be compared to the SCICEX 1999 CTD section (SAIC will receive the data in July, 1999) which was taken along the acoustic propagation path along the same track as SCICEX 1998 (see Fig. 2).

Data from the propagation path from Turpan to the Lincoln Sea during the TAP experiment has also been extensively analyzed. Due to the shoaling of the path into the Lincoln Sea to depths substantially less than the turning depths of modes 2–5, modal coupling occurs. This can result in acoustic energy traveling at different group velocities associated with the amount of time the energy "spends" in each mode. Travel time changes associated with this phenomenon must be accounted for. Recent analysis has shown that using the modal phase to measure the travel time changes [Gavrilov and Mikhalevsky, 1999] reduces the sensitivity to changes due to modal coupling [Gavrilov and Mikhalevsky, 1999]. Travel time errors for the Lincoln Sea path due to these effects should not exceed an equivalent temperature measurement error of 5 m° C [Gavrilov and Mikhalevsky, 1999]. While the Beaufort Sea array will be placed in deep water to avoid any mode coupling problems, future source and receive sites could well be located on some of the shallower shelf regions in the Arctic. The techniques developed here can be used to assess various sites to insure that mode coupling effects can be properly accounted for.

Another unique aspect of the acoustic channel in the Arctic is its remarkable phase stability. This was first observed in 1981 over a 330km path in the Eastern Arctic [Mikhalevsky, 1981]. This was again observed in 1994 during the TAP experiment over the 2,600 km path from Turpan to SIMI [Mikhalevsky et al., 1995a, and Mikhalevsky, et al., 1999] and to the Lincoln Sea [Pawlowicz et al., 1996; Gavrilov and Mikhalevsky, 1999]. This stability is a consequence of the order of magnitude less energy in the Arctic internal wave, and mesoscale fields compared to the temperate oceans. Over the 2,600 km propagation path in TAP these perturbations were less than .5msec rms, or equivalently .1m° C. Thus travel time measurements using the phase of standard tomographic Maximal Length Sequences at 20 Hz which were transmitted during the TAP experiment and which are currently being used in ACOUS have accuracy's less than 1 msec in travel time (~.1m° C) for the open ocean paths, and 5–10 msecs (~5m° C) over shoaling paths like the path to the Lincoln Sea. The temperature differences shown in Figure 3 and the resulting trends are easily detected (see a complete analysis in Mikhalevsky, et al., 1999) and would have been detected had an acoustic thermometry grid been in place in the early 1990's when these changes began. Modeling runs for the travel time differences along the long transarctic path associated with the Arctic Ocean circulation regime shifts proposed by Proshutinsky [Proshutinsky and Johnson, 1997] are approx. 1 sec., and seasonal variations are estimated to be approx. .1 secs. All of these signals are well above the measured travel-time noise level of approximately 5–10 msec and will be easily detected and tracked by the acoustic measure.

(2) Arctic Ocean sea ice thickness and roughness measurements
Performers: SAIC, MIT, Shirshov, UAF

The goal of this research is to develop a reliable measure of average ice thickness along acoustic paths in the Arctic Ocean to provide a measure of sea ice volume, a critical input for global climate models for which no affordable technique exists today.

The first objective is to quantify the acoustic attenuation as a function of the important ice parameters, including, roughness, thickness, and correlation lengths. This will involve using principally three ice loss models as discussed in the background below to solve this forward problem. The goal is to quantify the achievable resolution of thickness and roughness changes that can be derived from the measured changes in attenuation. The use of submarine ice profile data and satellite remote sensing data to provide ground truth with the measured ACOUS 20 Hz data will be important for this research.

The second objective is to examine the use of broadband or multi-frequency approaches and other systems concepts that might use drifting transceiver buoys for example with separations of hundreds, vice thousands of km's to permit the use of higher frequencies that will be more sensitive to the ice parameters. At 20 Hz the ice cover has no effect on the phase or travel time of the acoustic signals, only on the attenuation. At higher frequencies, greater than 100 Hz, not only is the attenuation much greater over the same range, but changes in travel time could be another observable.

Although the intensity of an acoustic signal is diminished by the interaction with the ice surface, the detailed physics of the interaction is still an open research question. To use the ACOUS signal to monitor the average ice roughness and ice thickness we consider 3 ice loss models. The simplest ice loss model is the U.S. Navy standard ice loss model [Keenan, 1989] that is empirical in nature and is only sensitive to the standard deviation roughness of the under-ice draft averaged in 1 nm segments. The Russian [Gavrilov, Mikhalevsky, and Andreyev, 1995] and LePage-Schmidt [Lepage and Schmidt, 1994] ice loss models are both physics based models but each makes different assumptions about the properties of the ice surface and each require a different set of ice statistics. Some coincident acoustic measurements with measured ice draft data are available. When the parameters required for each of the models are computed from the measured ice draft data, the models show very good agreement among themselves and with data. The physics based ice loss models relate the ice loss, hence acoustic intensity degradation, to both the ice roughness and ice thickness that we wish to monitor acoustically. The Russian ice loss model incorporates a two-scale model of the ice structure associated with the ridges and flat ice that characterize real sea ice morphology, and may provide the best approach for attenuation modeling, given good ground truth data. Indeed, the significant limitation in making more progress on relating the physical parameters of the ice to modeled results has been the lack of a suitable data base of coincident acoustic propagation and ice draft, and ice type measurements. Given periodic baseline measurements along the ACOUS propagation tracks of under-ice draft in order to calculate the actual ice statistics using the upward looking Digital Ice Profiling Sonar (DIPS) during the April, 1999 submarine SCICEX cruise and the acoustic transmissions recorded at the APLIS Ice Camp will provide such coincident data. The use of satellite remote sensing data including RADARSAT will be employed to assist in providing some ground truth for ice type and extent as well.

(3) Arctic Ocean mixed layer depth measurement using acoustic techniques
Performers: SAIC, MIT, WHOI, Shirshov

This research involves analyzing the capability of using a multiple frequency acoustic remote sensing technique to reliably determine the depth of the Arctic thermocline. The analysis will also determine the resolution that can be obtained using the 20 Hz ACOUS signal through observation of changes in the group velocity of mode 1. Because much of the interannual variability in the Arctic Ocean temperature is confined to the upper layers it will be important to quantify effects associated with thermocline changes, and other variability.

The accurate mode arrival time measurements that will be made by the ACOUS experiment vertical line array can potentially be used determine the depth of the main thermocline in the Arctic Ocean. The thermocline, a small region characterized by steep temperature gradients, separates the warm Atlantic Intermediate Water and the cold Arctic Subsurface water and mixed layer. There have been some indications from data taken during the 1995 and 1996 SCICEX cruises in the Arctic that the upper mixed layer and the associated thermocline may be weakening [Steele and Boyd, 1998]. The thickness of the upper mixed layer is important because the surface waters act as a thermal buffer between the warmer Atlantic Intermediate Water and the Arctic ice cover. Changes in this upper layer could portend major shifts in the Arctic Ocean, including an ice-free state.

The following method will be explored to measure the average depth of the thermocline. For low frequency (20 Hz) sound, the acoustic normal mode 1 is trapped in the surface duct. Spending it's time in the cold and slow surface waters, and interacting with the ice canopy will cause it to arrive significantly later and more attenuated then the other modes, which are not trapped. As the frequency of the acoustic signal goes up, mode 2 and then mode 3 are eventually trapped. By measuring the frequency at which modes 1, 2 and/or 3 are trapped in the surface duct, the depth of the thermocline can be determined at any given time. Modes trapped in the surface layer have group speeds on the order of 1435 m/s, compared with 1460 m/s for modes that are not trapped. For a propagation range of 1,000 km this corresponds to a 12 second delay in arrival time. Clearly, any observations of such large changes an the arrival time of mode 1, 2, or 3 could be the result of capture or release from the surface duct and also provide an estimate of the thermocline depth. The relationship of these travel time changes with other changes needs to be quantified.

(4) Arctic Ocean coupled atmosphere-ice-ocean modeling and data assimilation
Performers: UAF, Shirshov

The fundamental objective of this proposal's modeling component is to develop appropriate methodology for determining the ocean's present climate, and for predicting probable future climate, using acoustic data acquired from the BAO. Acoustic transmission data will provide a history of snapshot measurements of the state of the ocean along the slice between the source and the receiver. The first goal will be to determine the present state of the ocean by comparing the real acoustic data with simulated acoustic data from runs with our 3-D coupled ice-ocean model as described below. The second objective is to gain the necessary expertise to begin numerical experiments in acoustic data assimilation. Because acquisition of acoustic data is a relatively recent accomplishment, assimilation of acoustic data into numerical models is in the early developmental stage. Our 3-D coupled ice-ocean model closely simulates the real ocean, based on comparisons with hydrographic data, satellite observations, and buoy drift data [Polyakov, et al., 1999]. It is now appropriate to begin training in the techniques and problems of incorporating acoustic data into an existing, validated, ice-ocean model.

Currently available atlases, manuals, and reference books [Gorshkov, 1980; Levitus, 1982; Treshnikov, 1985; EWG, 1997] include information about multiyear mean atmospheric, oceanic, and ice characteristics, or at best, information about the multiyear mean seasonal cycle. These sources of information do not account for the arctic seasonal evolution related to different arctic climatic states that have been demonstrated in recent studies by [Mysak et al., 1990; Proshutinsky and Johnson, 1997; Mysak and Venegas, 1998; Thompson and Wallace, 1998]. For example, Proshutinsky and Johnson [1997] documented two wind-driven circulation regimes, or two climate states, of the arctic atmosphere and ocean, showing that wind-driven ice motion and upper ocean circulation alternate between anticyclonic and cyclonic states. Shifts between regimes occur at 5- to 7-year intervals, resulting in a 10- to 15-year period. The anticyclonic circulation regime (ACCR) has been observed in the model results for 1946–1952, 1958–1962, 1972–1979, and 1984–1988. The cyclonic circulation regime (CCR) prevailed during 1953–1957, 1963–1971, 1980–1983, and 1989–1997. The river runoff, permafrost temperature, ice extent, index of the North Atlantic Oscillation, water temperature in the Iceland Sea, sea ice anomalies in Davis Strait, and other parameters have a similar variability and correlate well with the circulation regimes (see Figure 18 in Proshutinsky and Johnson, 1997). Based on our results to date, we expect substantial differences among the seasonal cycles of ice, oceanic, and atmospheric parameters associated with different arctic climatic states. One goal of this proposed research is to be able to measure and predict shifts between these states.

The seasonal variability of the atmosphere, ocean, and ice in high latitudes depends on coupled dynamics and thermodynamics in ways not yet fully understood. Changes of amplitude or timing of the arctic seasonal cycle can be modulated by interannual variability, implying an important coupling between the seasonal and interannual time scales. The true climatic impact of the seasonal signal on arctic interannual variability remains unknown. Unresolved issues concerning the evolution of the arctic seasonal cycle require further investigation in order to advance our understanding of climate variability in the region.

Although some modeling studies have reproduced the arctic ice and ocean seasonal behavior, their real focus was mean arctic climatic conditions [Hibler and Bryan, 1987; Oberhuber, 1993; Piacsek et al., 1991]. Semtner's [Semtner, 1987] modeling experiments give a realistic representation of the Arctic's ice-ocean seasonal variability. He concludes that the oceanic heat flux not only governs the wintertime ice extent in the Greenland and Barents seas, but also regulates the summertime ice extent in the Arctic's marginal seas. According to Semtner, the latter process is related to the dynamics of the intermediate Atlantic water layer. Observations confirm this conclusion [Nikiforov and Shpaikher, 1980]. A special investigation of the Arctic Ocean's seasonal climatology has been carried out by [Hakkinen and Mellor, 1992] using a coupled sea ice-ocean model. These authors reproduced the seasonal change of the ice mass, oceanic heat flux to the lower ice surface, and other ice and oceanic parameters quite well.

This research is designed to improve understanding of the mechanisms affecting the seasonal cycle, and the relationship between seasonal and interannual variability, processes that have not been previously stressed in observational studies. Based on Proshutinsky and Johnson [1997] results, we recognize differences among seasonal cycles of sea ice, oceanic, and atmospheric parameters associated with the ACCR and CCR. The acoustic results will be used to establish the differences between the ACCR and CCR seasonal signals and to evaluate a contribution of seasonal changes to arctic ocean interannual variability.

(5) Marine mammal research
Performers: Cornell, DWM/NSB, and SAIC

The ACOUS BSA and the MLTA, located off Pt. Barrow, will provide a significant opportunity to study marine mammals. The BSA will have a frequency coverage of 10-960 Hz, with 10 of the 45 hydrophones having coverage up to 12 kHz. The MLTA will have coverage from 10 Hz to 5 kHz.

These frequency ranges will permit listening and recording of bowhead, gray, and beluga whales and bearded seals. Much of the bioacoustic research will be focused on the bowhead whale. This research will provide both practical benefits and heretofore unavailable basic research opportunities. As an endangered species, the protection and recovery of the BCB bowhead population is vital importance. The migration of the Bering-Chukchi-Beaufort Seas (BCB) stock of the bowhead whale occurs each year during the spring and autumn. Off Pt. Barrow, the spring migration occurs from as early as mid-April to as late as mid-June, during which period the offshore pack ice restricts the eastward migration into a 10-30 km funnel, and there are typically massive ridges of grounded shorefast ice. This combination of funneling and shorefast ice have proven crucial for the success of the spring bowhead census efforts. The shorefast ice ridges provide a safe location from which to conduct a whale census, while the funneling effect of the offshore pack ice means that most of the migration must pass within close proximity to the census effort. These census studies integrate both visual and acoustic methods and have led to improved population estimates indicating that the population is slowly recovering (Raftery and Zeh 1998). In contrast, during the fall migration, which occurs from late August to late October, the lead is open so the migration is broadly distributed and there are no platforms from which to conduct a census. As a result, aerial surveys have been the only mechanism for studying the fall migration. The installation of the BSA and MLTA in conjunction with advanced data recording and signal processing systems will, for the first time, provide the opportunity to conduct research during both the spring and fall bowhead migrations. The MLTA will exploit currently used methods based upon the Time Difference Of Arrival (TDOA) of vocalizations to provide bearings and ranges to vocalizing bowheads (Clark et al. 1996). The BSA vertical line array can be used to localize in depth and range by utilizing Matched Field Processing (MFP) [Baggeroer, Kuperman and Mikhalevsky, 1993]. Because it's a vertical array, bearing localization will only be possible if the array is tilted (due to currents) or if the whale is in the shallower depths near the Barrow canyon where the anisotropic bathymetry can be used to break the azimuthal symmetry. Preliminary simulations have been performed in which a Bowhead whale call was digitized and used as the source spectrum. In this simulation, the vocalizing whale was located 105 km from the array in shallow water (30m depth) near the Barrow canyon at a depth of 10 m and at a bearing of 254°. Realistic phase errors were added to each array element to simulate typical errors. By exploiting the anisotropic bathymetry, the whale was easily localized in range to within 100m, depth to within 5m, and bearing to within a few degrees. These preliminary results are extremely encouraging.

The quality acoustic data recorded by the BAO BSA and MLTA arrays, acoustic modeling and signal processing will provide the opportunity to make the following advancements in bowhead whale census efforts:

(1) During the spring migration, the MLTA will be used to detect, locate and track vocalizing bowheads, and these results will be compared to those of the traditional acoustic methods. This will help to both validate the MLTA and provide evidence of whether or not a portion of the bowhead population is migrating beyond the range of the visual-acoustic census effort. It is strongly suspected that the combination of the offshore MLTA and the traditional nearshore acoustic methods will greatly improve our present understanding of the bowhead whale's offshore distribution.

(2) Other than acoustics, during the fall migration there are no viable techniques available today to determine if there are bowheads migrating beyond 20-30 km from shore. With real time, 24 hour, acoustic monitoring, the presence of bowheads offshore can be determined. The MLTA will be used to detect, locate and track vocalizing bowheads to determine the far offshore distribution of animals. If there is a portion of the Bowhead population migrating farther offshore than present methods allow, this could impact the present estimate of the Bowhead population as well as out understanding of how to utilize the arctic habitat at different times of the year. Furthermore, these data will provide important baseline information on ambient noise conditions that can be used to evaluate the responses of bowheads, belugas and bearded seals to changes in ambient conditions, both natural and man-made.

(3) Perform near real-time localization. With real-time access to the data and current computing power, the locations of vocalizing whales will be determined within a few seconds after the data are acquired. These data will be used to produce tracks and estimate basic parameters of the migrating hear (e.g., swimming speed, direction of travel, number of animals, call rates/animal) that are critical to model for estimating poulation size (Raftery and Zeh 1998).

(4) These data will be integrated with large-scale information on ice conditions, and will permit biologists to look at whale behavior and migrating patterns relative to oceanographic variables.

(5) With whale localization, and the vertical array data of the acoustic vocalization, it may be possible in some cases to backpropagate the signal to look at the sound the whale is putting in the water. This information can be used to see if different whales generate different sounds and to begin to study the physiology of Bowhead whale vocalizations.

(6) Accurately determine the depth at which bowheads vocalize. With the depth of the whales vocalizing, some information about their diving habits can be obtained.

(6) Arctic seismicity research
Performers: MIT and WHOI

Today there are just two land based seismic stations adjacent to the Arctic Ocean, one near Banks Island in northern Canada and a second in Spitzbergen (Fig. 4). The Arctic Ocean can be divided into two regions separated by the Lomonosov Ridge. To the east the Eurasian Basin with the Mid Arctic Ridge which is an extension of the Mid Atlantic Ridge, while to the west Amerasian Basin with the Alpha-Mendeleev ridges leading to the Canada Basin under the Beaufort Sea [Johnson, Pogrebitsky, and Macnab, 1994]. While the tectonic structure of the eastern Arctic is well understood, there have been a number of hypotheses for the tectonics of the western Arctic [Lawver and Scotese, 1990]. Most of the seismicity in the Arctic is the result of shallow earthquakes at the Mid Arctic Ridge; however, events have been recorded on the continental margins in Canada and Alaska (Fig. 5).

Fig. 4 Existing seismic monitoring stations in the Arctic regions.

Fig 5. Compilation of Arctic Ocean seismic events.

The proposed Beaufort Sea Array (BSA) system takes advantage of the availability of the wideband data link to connect four ocean bottom seismometers. A bottom-mounted 4-element seismic array will be cabled to the Offshore Junction Box of the BSA. The seismic array will consist of 4, 3 component Ocean Bottom Seismometers and an Ocean Bottom Hydrophone (OBS/OBH) (16 channels, 24 bit digitizer) deployed in the form of an `X', with the length of the `X' being 300 meters. When combined with the hydrophones on the BSA, this system represents a prototype ocean observation system capable of long term, continuous monitoring. The objective of the system is to monitor the seismicity of the Arctic and its adjacent margins with an array that has significant gain and contribute to a better understanding of the Arctic Ocean tectonics. The array would be a station in the Global Seismic Network in a region where there presently are no observations; moreover, there are relatively few systems worldwide which can provide continuous, real time directional seismicity. In addition, local crustal structure near the array can be measured using seismic refraction techniques. While local, there is a paucity of such data in the Arctic.

Though the 300 meter aperture is limited by deployment constraints, there is enough aperture to resolve the direction and phase speed of events within the band of the instruments with appropriate array signal processing, especially when combined with data from the BSA. The seismometers are specified to work in the 1–100 Hz band that is rich in teleseismic events, and the wide dynamic range permits extending the lower cutoff significantly into the infrasonic region.

The Vertical Line Beaufort Sea Array (BSA) will be deployed at 72-35 N 156-00W, a distance of 142 kilometers from Barrow, Alaska. The array location is in 1,762 meters of water on the east flank of the Barrow Trench. The BSA will be 1730 meters in length and constructed of South Bay SB42338 fiber optic cable, 1.25 inches in diameter, with 75 twisted pairs of fiber and a 5,000 pound Kevlar strength member. The BSA will have 45 High Tech HTI 1-90-U low noise omnidirectional Hydrophones spaced at 25 meters above 600 meters depth and 50 meters below 600 meters depth. There will be 3 InterOcean S4RT Current Meters, located at the top, middle and bottom of the array. There will be 25 Sea-Bird Micro- Cat SBE-37-SI combination temperature and salinity sensors, with 21 co-located with the top 21 hydrophones and 4 distributed among the bottom 24 hydrophones. A Paroscientific 8B2000-1 Tide Gauge will be located on the array anchor assembly. Four Dukane Transponder Beacons will be located equidistant around the base of the array to be used for determining array element location. An Offshore Junction Box will be mounted at the base of the array. Fig. 6 shows a sketch of the BSA. A bottom-mounted 4-element seismic array will be cabled to the Offshore Junction Box. The seismic elements will be 3 component Ocean Bottom Seismometers and an Ocean Bottom Hydrophone (OBS/OBH) sensors deployed in the form of an `X', with the length of each leg of the `X' being 300 meters. The BSA trunk cable will be 145 kilometers of Alcatel URC-1 lightweight fiber optic underwater cable with one fiber optic amplifier installed mid-way. Telemetry for the data from the BSA will be provided by a SONET/ATM OC-3 fiber optic backbone.

Fig. 6 Beaufort Sea Array (BSA).

A Near-shore Junction Box will be located 9.5 kilometers from the shore in 200 meters of water. The bottom mounted horizontal Marine Mammal Listening and Tracking Array (MLTA) will be connected at the junction box. The MLTA will be 4 kilometers in length containing 15 low noise omnidirectional hydrophones in 3 groups of 5 hydrophones each with 7.5 meter spacing between each hydrophone. The location of the MLTA is shown in Fig. 7.

The Connector Cable from the Near-shore Junction Box will be 10.5 kilometers of Alcatel lightweight fiber optic cable. 4.5 kilometers of the Connector Cable from the 20-fathom curve to the 10-fathom curve will be double armored for resistance to damage from shore-fast ice. The Connector Cable will be installed in heavy-walled conduit pipe from the 10-fathom curve through the surf zone and across the beach for ice and surf zone protection. The conduit pipe will be buried to 2 meter depth to the inboard side of the Barrow Beach Road. The Connector Cable will then be laid overhead on poles to the UIC-NARL Building 360 where the Shore Facility will be located.

The Shore Facility system will consist of Windows NT Pentium workstations with PCI DSP embedded processors. There will be hard disk storage for data quality and analytical processing, as well as tape recorder playback facilities. GPS/IRIG clock cards will provide accurate timing and modems will route the data southward.

Fig. 7 Location of Marine Mammal and Listening Tracking Array.

Since the off-shore location of the BSA is normally ice-covered year around, an ice-reinforced vessel will be used to install the BSA and lay the trunk cable back to the Near-shore Junction Box. The vessel proposed for this work is the U.S. Coast Guard vessel POLAR STAR. A support vessel, smaller and more maneuverable than the Polar Star will conduct the near-shore cable laying. The HENRY A. McGAW out of Ventura, CA, is proposed as the near-shore support vessel. The near-shore and surf zone burial of the conduit pipe to a depth of 2 meters will be accomplished with a high-pressure water jet method. The land burial of the conduit pipe will be done by Ditch-Witch to minimize the amount of excavation. Local contractors and labor will be employed wherever possible to maximize the favorable impact the installation will have on the North Slope Borough.

The design, construction and installation of the BSA and the MLTA will be led by the SAIC/ Maripro Operation located in Goleta, CA. SAIC/Maripro brings over 35 years of experience in the design, building and deploying of underwater systems. SAIC/.Maripro designed, built and deployed the undersea cables systems to support the U.S. Navy's RDT&E and Fleet Tactical Underwater Ranges, including the ranges at AUTEC in 1963, and BARSTUR/BSURE in Hawaii, the SOAR range at San Clemente and the AURA range in Perth, Australia, as well as numerous other noise measurement arrays and fixed surveillance systems for the U.S. Navy and foreign governments. These systems have proven extremely reliable; in fact, all of the original hydrophones in the AUTEC and BARSTUR systems are still operational after more than 25 years of continuous operation. SAIC/Maripro built and deployed the vertical line arrays used in the Acoustic Thermometry of Ocean Climate (ATOC) Project. These arrays were operational for over 5 years and were re-deployed in 1998 as part of the North Pacific Acoustic Laboratory (NPAL). As an ISO 9001 registered company, with proven quality assurance, configuration management, and development engineering plans and procedures, SAIC/Maripro has successfully designed, manufactured, and installed over 300 cabled systems comprised of more than 3,000 kilometers of cable and various underwater electronic housing.

The BSA, the MLTA, and the trunk cable system are designed to withstand the rigors of being installed and operated in the harsh Arctic environment. The design life of the major components of the system including the trunk cable is 20 years. The design life of the arrays and fiber optic telemetry electronics is a minimum of 5 years. The only component of the system that will require replacement about every 3 years will be the autonomous battery-operated Dukane Transponder Beacons.

An autonomous acoustic source complex transmitting at 20 Hz for 20 minutes every fourth day is currently installed in the Franz Victoria Trough northwest of Franz Josef Land. This source is the potential signal for the Beaufort Sea Array, however, the batteries of the source complex will be exhausted in September–October 2001, after operating for their design life of 3 years. Since the BSA will not be installed until July 2002, a replacement acoustic source complex has been proposed under this effort. A design study for a replacement acoustic source will be conducted during the first year of this effort and will incorporate improvements including increased battery capacity and source reliability. A replacement autonomous source will be built during year 2 and installed coincident with the BSA. The design and construction of the replacement acoustic source will be accomplished by the Institute of Applied Physics, Nizhny Novgorod, Russia, where the present acoustic source was constructed and the TAP source was designed and built. The deployment of the replacement source will be conducted by a Russian icebreaker under the auspices of the joint US-Russian MOU on the ACOUS Project.

It is important to note that a significant percentage of the funding requested under Years 1, 2, and 3 of this proposal is for the infrastructure required to enable the research, namely, construction and installation of the Beaufort Sea Array (including the seismic array), the Marine Mammal Listening and Tracking Array, and the replacement of the Arctic Acoustic Source. Table 1 shows the percentage of the funding requested that will be used for this infrastructure. The remainder of the money supports the research. This proposal provides for a 3-year schedule to complete the construction, testing and installation of the BSA and MLTA. This schedule could be completed in two years if sufficient early funding were made available (total funding for the 5 years remains the same). Table 2 shows a funding profile that would allow the BSA and MLTA to be built and installed in two years, such that data collection and analysis could begin in 2001 instead of 2002. (Note under the 2-year install program, years 4 and 5 remain the same.)

Table 1

Table 2

The infrastructure costs are a significant part of the overall budget. The cost of the OBS/OBH seismic array, design, construction and deployment is $728K and the MLTA is $374K when conducted as part of the BAO installation and using the trunk cable and sea-shore interface. Such installations by themselves would cost an additional $2M each, clearly not realistic. The sea-shore interface alone costs approximately $600K. With the BAO installed researchers can use the sea-shore conduit to run additional cables to moorings at sea and tap into the junction boxes of the trunk cable for additional moorings and expansion of the system. An endorsement letter for the BAO is attached to the end of the Project Description section from OAII Chair Prof. J. Grebmeier, University of Texas, describing potential benefits of the BAO to enable a benthic observatory for benthic sediment and biological processes and carbon flux event monitoring, as well as providing a capability to obtain water samples for water column chemical and biological measurements. We are sure that this is only a sample of the kinds of additional research that will be enabled, over which the infrastructure costs of the BAO need to be amortized.

A future notional Arctic system network building on the BAO concept with 6 receive array/ocean observatory cabled moorings and 3 autonomous acoustic source moorings is shown in Fig. 8. While this network is for illustrative purposes only, it shows that an 18 acoustic path system will sample every major Arctic Ocean basin and intersect every major Arctic Ocean current and frontal structure. The acoustic signal takes 30 mins to propagate along the longest path from Franz Josef Land to the Beaufort Sea array. The ACOUS source currently operating in the Arctic sends a 20.7 min signal every four days. Thus the notional grid shown could provide a snapshot of the entire Arctic Ocean in less than one hour every four days, and could operate unattended for years with all of the data being provided to researchers in real-time. This qualifies as "very high resolution" in time. As discussed under BAO Research Area (1) above the data would yield direct information as a function of depth, through inversion of the mode arrivals, yielding the temperature changes in the upper layers, the Atlantic layer and the deep Arctic Water. Clearly, a tomographic inversion of the notional grid would yield a horizontal resolution that would vary from 100 kms to many 100's kms depending upon the density of the crossing paths at any given location. Assimilating the acoustic data and the point measurements continuously into a couple atmosphere-ice-ocean model as described in BAO Research Area (4) above is a key element of the proposed research. Ultimately then, resolutions to model scales could be achievable. The current 3D model described in BAO Research Area (4) above is being run on a 55.56 km resolution and 17 km is the next step.

The goal for the next generation of the BSA will be to design the Acoustic Thermometry and Autonomous Moorings (ATAM) and the network to be as cost effective as possible. As discussed in research area (1) above the Arctic Ocean acoustic waveguide is highly dispersive. This means that each mode travels at a different group speed. The longer the acoustic path the more time spread there is between modal arrivals. Separating the modes in time in principal requires only one hydrophone and not an array, and that could realize significant cost savings with very simple receive systems. There is a tradeoff between source bandwidth and path length that will be done to develop the required source bandwidth such that temporal filtering of the modes can be realized. Preliminary calculations indicate that a bandwidth of 5 Hz would be sufficient for the shorter paths (the currently operating ACOUS source has a bandwidth of 2 Hz, 5 Hz is easily achievable). The network ATAM moorings will be designed to accommodate thermisters, salinometers, current meters, chemical and biological sensor packages, and seismometers. Analyses will be done to see if upward looking sonar and ADCP's can be included depending upon power budgets and trunk cable power capabilities. Data and power reserve will be built in to accommodate emerging technologies such as AUV support.

The autonomous source moorings will build upon the successful design of the ACOUS source deployed in the Franz Victoria Strait in October 1998 (Fig. 3). The entire source complex is shown in Fig. 3, except for the mooring cable and anchor. The source is self-contained with all of the electronics and four of the six battery packs installed inside the radiating complex (two of the battery packs are installed in pressure-proof containers on the outside, one is visible in Fig. 3). This source is controlled by a Rubidium time standard and has a design life of 3 years. Additional efficiencies in the existing design have already been identified and future sources will be designed to include greater frequency capability and longer life.

The notional network shown in Fig. 8 represents approximately 24,000 kms of acoustic path length. In order to obtain an average temperature on these 18 acoustic paths that would be equivalent to the acoustic thermometry, by direct measurement of temperature, it would require sampling along each path at the mesoscale correlation length of approximately 25–50 kms (for the SCICEX cruises the CTD sample spacing has been an average of 40 kms). This would therefore require installing and maintaining a continuous presence of 600–1,000 buoys equipped with at least a 1 km long thermister chains that must be mounted through the ice in locations that span the entire Arctic, which given the realities of Arctic logistics is operationally as well as economically infeasible. The International Arctic Buoy Program (IABP) maintains 20–30 buoys at any given time on the ice that measure atmospheric variables and are tracked for ice drift. Their goal is to maintain a spacing not less than 500 km. This is two orders of magnitude less than required and the buoys that would measure ocean temperature or acoustic data would be much more difficult to transport and deploy with their long arrays. However, the Arctic buoys are the right technology for sampling the atmospheric properties and ice drift and will be a critical part of an integrated Arctic observing system when coupled with the Arctic Ocean observing system built on the BAO. Much smaller numbers of oceanographic and acoustic buoys would be feasible for ice and thermocline acoustic measurements as discussed in BAO Research Area (2) above.

Fig. 8 A future notional monitoring grid in the Arctic Ocean building on the proposed BAO and utilizing the existing seashore termination from Alert, CA into the Lincoln Sea to realize a cabled network of Acoustic Thermometry and Autonomous Moorings (ATAM) for real-time, year-round observation in the Arctic Ocean.

A preliminary cost analysis of the notional system depicted in Fig. 8 has been performed. The network shown in Fig. 8 includes two sea-shore interfaces, one in Barrow, Alaska, and one in Alert, Canada. The sea-shore termination is where the cable crosses shore and must be protected from shore-fast and rafted ice. The sea-shore termination already exists in Alert, Canada and is a slant drilled conduit that goes from the shore to a point at sea well beyond any potential coastal ice-scour zones. The sea-shore interface at Barrow is included in this proposal and involves jetting in reinforced drill pipe to a depth of 2–3 meters. Slant drilling would be even more robust, but would add approximately $500K to the cost for a total of approximately $1M for the sea-shore interface. The latter cost is used in the preliminary cost estimate below.

The total cost is $26M (if this system were built on the BAO then only 5 ATAM's would be needed since the BSA would already be installed), and for a 5-year program of observations amortized costs are $5.1M/year, for a 10-year program (replacing sources and ATAM arrays once) amortized costs are $3.2M/year. An additional $1M/year is likely needed to support the research and operations costs. For a 10-year program this yields a total of $42M or $4.2M/year. For comparison the SHEBA program cost to date is approximately $22M with an estimated $3M/year for three years to support the research and data analysis, for a total of $31M. The SCICEX submarine program has been running at approximately $2–3M/year (exclusive of the acquisition and operating costs of a nuclear submarine!) for a total cost of approximately $20M if a SCICEX 2000 is executed. The largest cost of the ATAM/ACOUS network is the acquisition of the undersea trunk cable. Termination to Russian coasts could cut this cost in half, substantially reducing the cost of the network. Additional cost reductions in the ATAM arrays are possible with much simplified acoustic receivers exploiting the modal time dispersion discussed above. There is no other technology that can provide a decade of synoptic, real-time, year-round, distributed sampling of the Arctic Ocean with costs that are comparable to contemporary Arctic initiatives.

• document variations in the Arctic Ocean's climate, and identify major factors maintaining interannual variability.
• improve our understanding of the Arctic Ocean's role in arctic and global climate variability.
• quantify the processes associated with the two regimes of circulation that impact ocean and ice circulation and heat exchange among the ocean, ice and atmosphere.
• determine the extent to which the Arctic acts as a self-contained, self-regulated system by acoustically measuring the amount of oceanic heat input by incoming Atlantic Water.
• determine how variations in the integrated heat content of the Arctic Ocean (from the ACOUS measurments) affect precipitation (rainfall, snowfall, river discharge), ice cover and thickness, and other climate parameters (wind speed, direction, cloudiness) in the circum-arctic region.
• match measured ACOUS data with model data to test and validate ice-ocean models and determine where present position falls in conceptual cycle of Arctic Ocean climate variations.
• determine how inputs of oceanic heat translate into processes of global climate dynamics.
• quantify the sensitivity of acoustic remote sensing to measuring average ice thickness and roughness and the depth of the Arctic Ocean thermocline.
• improve our understanding of bowhead whale population, distribution, diving habits, and physiology of bowhead whale vocalizations.
• improve our understanding of the impact ice, oceanographic conditions, and ambient noise (both natural and man-made) on marine mammal behavior and migration patterns.
• improve our understanding of Arctic Ocean tectonics through monitoring of in-situ Arctic Ocean seismicity using array processing of teleseismic events.
• using seismic refraction runs for estimating local crustal structure near the arrays in the Beaufort Sea.

The proposed program of oceanographic, acoustic remote sensing, climate, marine mammal, and seismic research represents a unique set of interdisciplinary studies capitalizing on in-situ data collection coincident in time and space in a part of the world that has traditionally lacked such a focus. The Barrow Arctic Ocean Observatory with it's sea-shore interface, deep sea powered fiber optic cables, offshore junction boxes, arrays and shore facilities will enable a broad range of interdisciplinary research well into the future.