Eos,Vol. 83, No. 33,13 August 2002

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1 of continuing to increase the ratio of poster to oral presentations. Should the Fall Meeting stay in San Francisco? Repeated surveys of the membership have indicated very strong support for maintaining the meeting in San Francisco. Key Questions Key questions are, will and should the growth of the meeting continue? The membership and activities of the AGU, including the Fall Meeting, have grown dramatically over the last few decades owing to many factors. In addition to the simple increase in population, AGU has grown because of the increased relevance of geophysical sciences to society and the expansion of the number of disciplines and topical areas included under the AGU umbrella. Obviously, government support for science is an important variable in the equation over the long term. How will this support vary in the years ahead? Despite short-term fluctuations and shifts in emphasis, it is difficult to anticipate a dramatic reduction, although the details are unknowable. Over the last several years, the Fall Meeting has grown about 8% from a year in which there was an Ocean Sciences Meeting, to one in which it was not; and about 2% from a year in which there was not a separate Ocean Sciences Meeting to one in which it was. Attendance was down slightly from 2000 to 2001 by about 2%, versus the projected growth of 2%, perhaps owing at least in part to a reluctance to travel after the September 11 terrorist attacks.within all these uncertainties, we are planning for continued modest growth in attendance. If the meeting continues to grow Eos,Vol. 83, No. 33,13 August 2002 at its current rate, attendance will exceed 10,000 in the year 2004, and without adding additional meeting rooms, the percentage of poster presentations will increase to about 83%. Is continued growth of the Fall Meeting in the best interests of the membership? Perhaps we need to ask what we are and are not trying to achieve with the Fall Meeting. As mentioned above, the Fall Meeting provides an unparalleled opportunity to drink from a fire hose of the latest in geophysics, and to network with colleagues. Historically the Fall Meeting has been a relatively open meeting with almost no rejection rate for abstracts.this provides for a free market in ideas, which many find very attractive.lt would, of course, be possible to develop a system that would reject more abstracts and limit growth in this way although to date there has not been much support for this approach. We have not heard from the members or attendees that such an action is necessary or desirable. One of the special aspects of both Spring and Fall Meetings is that they present the opportunity to view your discipline and specific area of interest in the context of the broad spectrum of geophysical sciences.this is one of the strengths of the Fall Meeting, and it would be a mistake to change this aspect of the meeting. What would be gained and what would be lost from dividing the Fall Meeting into sub-meetings; for example, as has been done with the AGU journal JGR? For the most part, other meetings serve the individual disciplines, but no other meetings provide the multi-disciplinary interaction and synergistic energy Obviously intimacy and reflection are not strong points of the current format. Is there interest in more personal interactions through more section or topical activities within the context of the meeting? Can we take advantage of the demographics of the meeting to provide for more personal interactions; e.g., activities aimed at retirees and seniors, or undergraduates? Certainly through the Publications Program and Chapman Conferences, AGU provides for more reflective and intimate scientific exchanges outside the Fall and Spring Meetings. Your Views The bottom line is that the AGU meetings staff, the Program Committee, and the Meetings Committee will do all we can to respond to what we perceive as the desires and needs of the membership to keep the Fall Meeting exciting and productive. If it grows organically in response to member interest, then it grows and we will work to accommodate that growth. What are your views? How would you like to see the Fall Meeting evolve? What do you find most rewarding about the Fall Meeting? What drives you nuts? The Program Committee, the Meetings Committee, and the AGU Meetings staff all want to know Please share your thoughts with us by ing fmviews@agu.org. Authors Tim Grove, MIT, Cambridge, Mass., USA, and Chair, Meetings Committee; and Rob Wesson, U.S. Geological Survey Denver, Colo, USA, and Chair, Fall Meeting Program Committee^ North Pole Environmental Observatory Delivers Early Results PAGES 357, Scientists have argued for a number of years that the Arctic may be a sensitive indicator of global change, but prior to the 1990s, conditions there were believed to be largely static.this has changed in the last 10 years. Decadal-scale changes have occurred in the atmosphere, in the ocean, and on land [Serreze et ai, 2000]. Surface atmospheric pressure has shown a declining trend over the Arctic, resulting in a clockwise spin-up of the atmospheric polar vortex. In the 1990s, the Arctic Ocean circulation took on a more cyclonic character, and the temperature of Atlantic water in the Arctic Ocean was found to be the highest in 50 years of observation [Morison et ai, 2000]. Sea-ice thickness over much of the Arctic decreased 43% in and [Rothrock etai, 1999]. Many of the programs that monitored the Arctic environment, and particularly the Arctic Ocean, from the 1940s to the 1980s ended just as these changes began to occur.two examples are the Soviet North Pole long-term drifting stations and the Sever airborne hydrographic surveys, sponsored by the Soviet Union. The North Pole Environmental Observatory (NPEO) was recently established to provide the types of long-term, multi-faceted research observations that are needed to understand how the Arctic is changing. Early results from the NPEO are helping to track the ongoing changes in the Arctic environment until more widespread observational efforts are instituted to replace the long-term observation programs that have been lost in recent years.the operational lessons learned in the first NPEO deployments will aid development of future long-term observation strategies. Further information on NPEO, near-real-time North Pole data, and past data can be found at washington.edu/northpole/index.html. NPEO demonstrates how to provide the long-term measurements needed to track the changing Arctic environment. Some of the measurements needed are time series beneath the surface at fixed locations. Others are needed at the surface in a reference frame drifting with the sea ice, and still others such as ocean temperature and salinity are needed as repeated sections over hundreds of kilometers.thus, the North Pole Environmental Observatory is more than a single installation (Figure 1). It includes a deep-sea instrument mooring, an automated drifting station consisting of cluster buoys fixed to the drifting sea ice, and airborne hydrographic surveys conducted each year during deployment of the mooring and drifting station.the instrumented mooring is installed close to the Pole and stretches from the ocean floor at a depth of over 4000 m to within 50 m of the surface.the drifting buoys measuring atmosphere, ice, and upper ocean properties are installed near the Pole, and during a year's time, they drift out of the Arctic Ocean. Ocean hydrographic sections run from the Pole into several key basins of the Arctic Ocean. The North Pole is an excellent location for such activities. Near the flank of the Lomonosov Ridge, it has proven to be a sensitive site for changes in upper ocean frontal structure and in the Atlantic water flowing along the ridge [Serreze et ai, 2000; Morison et ai, 2000].A history of expeditions to the North Pole provides a benchmark of ocean observations

2 Eos, Vol. 83, No. 33,13 August 2002 stations, and the mooring location in 2001 are shown in Figure 2. Operating from the Canadian Forces Station Alert in Nunavut, Canada, in 2000, a six-member science team deployed the first NPEO drifting station and conducted the first hydrographic survey The station consisted of five buoys measuring ocean, ice, and atmos pheric variables (Figure 1, inset).the first hydrographic survey included seven hydrographic stations between Alert,the North Fble,and beyond (Figure 2; detailed hydrographic station posi tions are available at the NPEO Web site). In 2001, a slightly larger group deployed a similar automated drifting station, performed a 300-km hydrographic section from the Pole toward Alaska (Figure 2),and installed the first longterm oceanographic mooring at the North Pole. Information is still being collected from the 2001 instruments. Initial results from NPEO 2000 and 2001 are generally consistent with the changes observed in the 1990s. Fig. 1. This schematic of the North Pole Environmental Observatory shows that it consists of an automated drifting station that drifts with the ice from an installation point near the North Pole, a mooring that remains anchored to the bottom near the North Pole, and a yearly airborne hydrographic survey that is performed as part of the deployment effort. there. Drifting station deployment at the North Pole fills a gap in drifting buoy coverage that has plagued the International Arctic Buoy Pro gram's measurements of ice drift, atmospheric temperature, and pressure.time series obser vations of ice thickness there provide a unique measure in the transpolar drift of sea ice. Airborne hydrographic surveys radiating from the Pole provide repeated sections of ocean properties in critical areas that are difficult to reach by other means. Deployments of the NPEO were carried out in the spring of 2000 and The program will continue through The location of the hydrographic stations, the deployment position and tracks of the automated drifting Hydrographic Surveys During NPEO 2000, hydrographic stations were made with conductivity-temperaturedepth (CTD) instruments and two lightweight, battery-operated winches capable of profiling to 500 m and 1000 m.the winch equipped for shallower depth provided for taking single water samples with a small-diameter, 1.5-liter Niskin sampling bottle. It was used at most stations to sample at 5 m and 125 m. Samples were drawn for salinity barium, 0, and nutrients. The survey in 2001 utilized a larger winch that was operated directly from the survey aircraft, with provisions for making CTD casts with sampling bottles at four depths and for drawing the water samples in a heated space. 18 Temperature and salinity measured at the North Pole in 2000 and 2001 have been com pared with profiles from the US.-Russian winter atlas [EWG, 1997], the 1991 cruise of the Swedish icebreaker Oaen, and the NSF- and ONR-sponsored SCICEX U.S. Navy submarine cruises of 1993, 1995,1997,1998,and 1999.The NPEO 2000 and 2001 results are similar to the SCICEX data of the 1990s, in that salinity in the salt-stratified halocline is elevated about 1 above the climatological values of the 1950s through the 1980s. In 2001, the North Pole surface salinity, above 25 m,was somewhat less than in 2000 and the late 1990s, and it was about equal to the maximum found in the 1950s through the 1980s.The 2000 and 2001 temperature data reflect the increased Atlantic water temperature char acteristic of the 1990s.The depth of the tem perature maximum was 300 m in 2000 and 2001.This is about 25 m deeper than was found during SCICEX, but not nearly as deep as the 400-m characteristic of the 1950s through the 1980s. The temperature below 600 m is greatest Fig. 2. This perspective view shows NPEO 2000 and NPEO 2001 automated drifting station drift in the 2000 data; due to equipment failure, tracks (magenta line for 2000, blue line for 2001), hydrographic stations (open circles, magenta there were no CTD data below 500 m in for 2000 and blue for 2001), and color contours of hydrographic station salinity anomalies In general, ocean conditions at the Pole in 2000 relative to EWG [1997]. The 2000 station drift began April 2000 and reached the point shown in and 2001 appear to have relaxed somewhat the figure by the end of December It subsequently drifted south in the Greenland Sea and stopped operating in the ice edge region near 70 N, 14 Wat the end of March The 2001 sta toward climatology near the surface, remained nearly steady at mid-1990s values in the Atlantic tion began operating in April 2001 and had reached the position shown by the end of the year. The 2001 mooring was deployed near the site of the 2001 hydrographic station 1. Original color water core ( m),and departed slightly image appears at the back of this volume. farther from climatology at depth.this variation

3 Eos, Vol. 83, No. 33,13 August 2002 (a) Salinity (psu) on Depth (m) = N 82 N 84 N 86 N 88 N Temperature ( C) Salinity (psu) Fig. 3. (a) Horizontal distribution of salinity at 20-m depth is shown. Note that the data along the trajectory are measured by J-CAD1, and the background describes the EWG [1997] winter climatology.vertical profiles of (b) temperature and (c) salinity are shown in the vicinity of the North Pole at Nand W (red) for J-CAD1 and at N, W for EWG (1997) climatology (blue). Original color image appears at the back of this volume. in trends with depth may be related to the ocean response time at different depths to changes in atmospheric forcing. In 2001, the Arctic Oscillation (AO) index, for which positive trends correspond to decreasing Arctic atmospheric pressure, showed a significantly negative winter average for the first time in over 10 years. Many suspect that the decadal change in upper ocean conditions is caused by the decadal increase in the AO. In our experience, it is reasonable to assume that the ice and mixed layer could respond to changes in AO on seasonal-toannual time scales and produce the decreased 2001 mixed-layer salinity The deeper Atlantic water near the Pole probably responds on time scales comparable to the transit time from the Fram Strait to the Pole; that is, several years.the water below the Atlantic water probably responds to changes in atmospheric circulation on time scales of a decade or more. The NPEO 2000 and 2001 CTD survey sections capture the counter-clockwise shift of the front between Atlantic-derived and Pacific-derived upper ocean waters that characterized the 1990s: increased salinity Atlantic-derived water appears at the Fble and decreased salinity Pacificderived water appears off Ellesmere Island. Figure 2 shows the deviation of NPEO 2000 and 2001 measured salinities from the cli matology [EWG, 1997]; contours of deviation from climatology appear in perspective view below the hydrographic station tracks.the salinity deviation in the upper ocean near the Fble (NPEO 2000 station l,npeo 2001 station 1) and in the Amundsen Basin (NPEO 2000 sta tion 3) is 1.5 to 2, a condition characteristic of the change in the 1990s.The 2001 section shows that the salinity increase in the upper halocline extends across the Makarov Basin and the southernmost portion shows a +1 salinity anomaly between 50 m and 100 m.these anomalies are similar to those measured near the same locations during SCICEX cruises in 1995, 1998, and Except for salinity at NPEO 2001 station 3, where the 200-m salinity anom aly was slightly greater in 1995, the NPEO 2001 anomalies at stations 3,4, and 5 are greater than the SCICEX anomalies near the same loca tions. In contrast, the southern end of the NPEO 2000 section shows a minus 1.5 salinity devia tion. Conditions there are similar to those found by Newton and Sotirin [1997] in 1994 and represent movement of Pacific-derived upper ocean waters eastward along the Canadian margin. NPEO 2000 ocean temperature anomalies (not shown) indicate a 1 C warming relative to climatology in the Atlantic water layer near the Pole and in the Amundsen Basin.The southern portion of the 2001 section suggests a positive temperature anomaly at 200 m cen tered at station 4.These are consistent with the pattern in the 1990s. The position of the temperature and salinity anomalies over the north slope of the Alpha Ridge and the timing of the most recent increases in salinity suggest that we are seeing a progression of the 1990s' Atlantic water and upper halocline changes counter-clockwise around the Makarov Basin and toward Canada along the Alpha Ridge. All the surface water tracers measured in 2000 showed a gradation toward more Pacific like character extending from the Pole south toward Ellesmere Island, with a marked transi tion between stations 2 and 4. In 2001, surface waters showed increasing Pacific-like character from the Fble toward Alaska, with a pronounced transition between stations 4 and 5. Barium concentrations in surface waters were generally higher approaching Ellesmere Island and Alaska, consistent with more barium-enriched riverine, inputs in the Pacific sector. Relatively high barium concentrations were observed in the surface water at the 2001 station 3 over the Makarov Basin.This correlates to a riverine oxygen iso tope signal imbedded in a mostly Atlantic seawater contribution.variable riverine contributions in the transpolar drift are the likely cause of this. Higher phosphate concentrations trended toward the south in both years, presumably due to the enriched phosphate contents of the Bering Sea input. Nitrate-to-phosphate rela tionships suggest that the surface waters in the southern part of the NPEO 2000 section and at station 5 in the 2001 section are almost com pletely Pacific-derived.Together, the 2000 and 2001 tracer data suggest that the 50% AtlanticPacific boundary has shifted toward Ellesmere Island and toward Alaska relative to its position reported by Jones et al. [1998]. Measurements of Si, indicative of Pacific influence, in the upper halocline were limited in 2000, although an upper halocline Si maxi mum was observed at stations 5 and 6. No pronounced Si maximum was found in the halocline at any 2001 stations. The upper halo cline layer of Pacific origin has yet to re-occupy the Makarov Basin as it did before the 1990s. Automated Drifting Stations The buoys of the automated drifting stations are tracked with Global Positioning System

4 Eos,Vol. 83, No. 33,13 August 2002 NP20276 Apr20 May20 Juo2OJul20 Aug2Q Sap20 Oct20 Nov20 Dec20 Jsn20 Feb 20 Fig. 4. Results from the ice mass balance buoy are shown; top panel shows air temperature. Middle panel shows temperature contours in the ice, bottom position inferred from temperature, and upper surface and snow thickness as measured by an acoustic sounder. The measured water temperature and the calculated ocean heat flux are given in the bottom panel. Original color image appears at the back of this volume. receivers and ARGOS. Data are gathered con tinuously and telemetered through the ARGOS and ORBCOM (JCAD) satellite systems (see the NPEO Web site for details).the NPEO 2000 drifting station suffered an early loss of the meteorological and radiometer buoys of the National Oceanic and Atmospheric Adminis trations Pacific Marine Environmental Laboratory (PMEL) (Figure 1) due to iceridging.the Japan Marine Science and Technology Center (JAMSTEC) Compact Arctic Drifter # \ (JCAD-1) and ice mass balance buoys provided ocean, ice, and atmospheric data through the year long drift. Starting with deployment in April 2000, the NPEO 2000 drifting station traversed diagonally across the Greenland end of the Amundsen Basin (Figure 2), exited Fram Strait at the end of 2000, and drifted south through the western part of the Greenland Sea, where it expired at the ice edge in late March The JCAD-1 buoy at the station provides a picture of ocean change through the Amundsen Basin. Figure 3a illustrates the measured 20-m salinity, representative of upper ocean conditions.the JCAD-1 20-m salinity is 1 greater than the climatology [EWG, 1997]; along the same track, the measured temperature at 250 m is C warmer than climatology The 1990s' advance of higher salinityatlantic-derived surface water toward the Alaskan end of the Arctic Basin is apparent. The profiles of temperature and salinity from JCAD-1 in Figure 3b and 3c illustrate the effect on the cold halocline. They are compared with the climatological salinity and temperature profiles near the middle of the Amundsen Basin.The JCAD-1 profiles reveal that in spite of return of the cold halocline to the Russian end of the Amundsen Basin [Boyd et ai, 2002], the salinity in the upper ocean along the drifting station track was still elevated so as to greatly weaken or eliminate the cold halocline. The ice mass balance buoy of the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) provides a thermodyna mic history of the NPEO 2000 drifting station ice floe. Ice temperature contours from CRREL buoy 1, as well as air temperature, water temper ature, snow thickness, and the calculated ocean heat flux are shown in Figure 4.The ice temperature profiles allow an estimation of heat conducted through the ice. The depth below which the temperature becomes con stant at the freezing point is taken as the icewater interface.tracking this depth reveals bottom melt and growth rates. The ocean heat flux to the ice shown in Figure 4 is computed as a residual between conduction and the heat lost for growth. Snow thickness is measured by the CRREL buoy using an acoustic sounder. In April, the upper part of the ice was quite cold, but by 25 June, it warmed to near the freezing pointthe snow disappeared about the same time. Once this occurred, top and bottom ablation was substantial, even though the air temperature (top panel) was not above 0 C. Without the high albedo of the snow, radiative heating readily melts the ice.the radiation is able to produce bottom melt as well as top surface melt because some radiation penetrates the ice cover and heats the water.this, in turn, causes ocean heat flux to melt back the ice-water interface. In late August the snow returned, and surface melt stopped, though gradual bottom melt continued. Starting in November, near the time the station reached Fram Strait, the ice cooled rapidly and began to grow at the lower surface.this continued until the buoy came near the ice edge in late January and ocean heat flux from below melted the floe rapidly. The buoys comprising the NPEO 2001 drifting station were similar to those deployed in Unfortunately, many of them were damaged or destroyed by major ice deformation in the early part of the drift. The meteorological sen sors on the JCAD buoy and the radiometer buoy continued to operate. The station was visited on 15 September 2001, by an air crew from the U.S. Coast Guard cutter Heafy. They installed an additional atmospheric temperature and pressure buoy from the Alfred Wegner Institute (AWI).The station drifted in a circuitous pattern in the Amundsen Basin for an extended time and had not reached Fram Strait as of the end of 2001 (Figure 2; see the NPEO Web site for updated positions).the NPEO 2001 PMEL/ CRREL Radiometer Buoy has provided the first successful automated measurement of radiation through the spring heat balance transition.the observed shortwave solar radiation and atmos pheric longwave radiation are characterized, especially in the early part of the record, by a diurnal cycle in solar radiation on clear days with low infrared; see the NPEO Web site for an illustration of these data. On cloudy days, the longwave radiation is enhanced and sunlight is reduced. The last record from the radiometer buoy was on 14 August The NPEO Mooring The first recovery of the NPEO mooring is planned for April 2002.The mooring (Figure 1)

5 incorporates an upward-looking sonar at 50 m to measure ice draft; temperature/conductivity recorders at 55 m, 110 m,210 m,260 m, 1000 m, 1701 m,and 2500 m; an acoustic Doppler current profiler to measure water and ice velocity in the upper 80 m; and recording current meters to measure water velocity, temperature, and conductivity at 84 m, 235 m, 600 m, and 1700 m.the mooring was established at the North Pole to fulfill the following objectives: Determine the statistics and low-frequency including annual to inter-annual variability of both the ice drift and water velocity in the mixed layer and halocline. Quantify the vertical and temporal scales of variability in temperature and salinity, especially in the halocline and the Atlantic layer, where many of the dramatic changes of the past decade have occurred. Assess the impact in this region of large-scale changes in the circulation and properties of the Arctic Ocean. Provide a long-term comparison base for earlier measurements in the region. By measuring time series of sea ice draft, estimate the temporal variations of the sea ice thickness distribution in the transpolar drift and compare these with concurrent variations in the local environment, and with variations in the AO, North Atlantic Oscillation, and other indices of change. Provide a platform for community-wide Eulerian measurements in the interior Arctic Ocean. Eos,Vol. 83, No. 33,13 August Deployment The 2002 NPEO deployment was completed as this article was going to press. The 2001 mooring was recovered successfully and a new mooring deployed at the same location. The drifting station was also deployed and includes a new ocean flux buoy from the US. Naval Postgraduate School and a Web camera that provides near-real-time images of the station. The hydrographic survey consisted of a closely spaced CTD section across the Lomonosov Ridge and 2 full hydrographic stations in the Makarov Basin.The data from these efforts are beginning to be retrieved and analyzed. For the most recent results, data, and up-to-date images of the 2002 drifting station, visit the NPEO Web site at index.html. Acknowledgments This work is supported by the U.S. National Science Foundation's Office of Polar Programs grant OPP , and the Japan Marine Science and Technology Center. We also thank coinvestigators Andy Heiberg, Miles McPhee, and Jackie Richter-Menge for their substantial efforts. We also thank the participants of the USCGC Healy-F.S.Fblarstern cruise for inspecting the 2001 drifting station and installing the AWI buoy Authors J. H. Morison, K. Aagaard, K. K. Falkner, K. Hatakeyama, R. Moritz, J. E. Overland, D. Perovich, K. Shimada, M. Steele, T.Takizawa,and R. Woodgate For additional information, contact James Morison at the Polar Science Center, Applied Physics Laboratory College of Ocean and Fisheries Sciences, University of Washington, Seattle, USA; morison@apl.washington.edu References Boyd.T. J., M. Steele, R. D. Muench, and J.T Gunn, Partial recovery of the Arctic Ocean halocline, Geophys. Res. Lett., in press, Environmental Working Group (EWG), Joint U.S.- Russian Atlas of the Arctic Ocean, prepared by the Environmental Working Group of the Gore-Chernomyrdin Commission, CD-ROM available from the National Snow and Ice Data Center (NSIDC), Boulder, Colo., 1997 ( Jones, E. P, L. G.Anderson, and J. H. Swift, Distribution of Atlantic and Pacific waters in the upper Arctic Ocean: Implications for circulation, Geophys. Res. tor., 25, ,1998. Morison, J. H., K. Aagaard, and M. Steele, Recent environmental changes in the Arctic: A review, Arctic, 55,4,2000. Newton,J.L.,and B. J.Sotirin, Boundary undercurrent and water mass changes in the Lincoln Sea,./ Geophys. Res., 102,3393B3403,1997. Rothrock,D.A.,YYu,and G. A. Maykut:Thinning of the Arctic sea-ice cover, Geophys. Res. Lett, 26, 3469B3472,1999. Serreze, M.C.,et al., Observational evidence of recent change in the northern high latitude environment, Clim. Change, 46, ,2000. Test Ban Treaty Provides High Level of Verification, Explosion Detection Capabilities, Report Notes PAGE 358 The international nuclear test monitoring system of the Comprehensive Nuclear Test Ban Treaty or CTBT, provides a high level of confidence to verify treaty compliance and detect nuclear explosions, according to a new report. This is with or without additional U.S. national technical means of verification, the report notes.the high level of confidence assumes the full capability of the international monitoring system, which is currently under construction and will eventually include a global network of 337 sensors and laboratories to detect seismic, infrasound, hydroacoustic, and radionuclide signals. The 31 July report, issued by the National Academy of Sciences (NAS), attempts to put to rest several major technical concerns that were raised about the CTBT during the U.S. Senate's 1999 debate that resulted in failure to ratify the treaty The CTBT, which could be brought up for ratification by the U.S. Senate at a future date, will enter into force when all 44 nuclear capable states listed in the treaty ratify it. Currently, 31 have done so. The NAS report/technical Issues Related to the Comprehensive Nuclear Test Ban Treaty?' also concludes that the United States has the technical capability to maintain its existing nuclear weapon stockpile under the CTBT. Any potential cheating on the treaty by triggering explosion yields below detection levels would be technically difficult and provide limited insights, adds the report. "In the absence of special efforts at evasion, nuclear explosions with a yield of 1 kiloton (kt) or more can be detected and identified with high confidence in all environments," assuming the treaty operates at full capability, the report states. In some locations, underground explosions can be reliably detected down to a yield of 0.1 kt or even to 0.01 kt, while underwater explosions in the ocean can be detected down to yields of kt or lower, according to the report. Scenarios for small evasive testing, such as by masking the seismic signals of a nuclear explosion with a simultaneous chemical explosion are technically difficult to conduct without detection. However, attribution of a test conducted by a party outside of its own territory could be a problem in some instances, the report notes. "We hope that this [report] will lead to recognition that the concerns raised in the October 1999 [Senate] debate have satisfactory answers," said NAS committee chair John Holdren. Holdren is director of the program in science, technology and public policy at Harvard University's John F Kennedy School of Government in Cambridge, Massachusetts. He added,"with respect to the potential impact on U.S. security interests and concerns of the low-yield nuclear tests that could plausibly occur without detection under a CTBT, one needs to compare the risks associated with this to the risks that would occur if there were no CTBT at all." The NAS report confirms the conclusions of AGU and the Seismological Society of America, that it is technically feasible to meet the verification goals of the CTBT. These conclusions are set forth in a 1999 position statement available at test_ban.html. Monitoring Capability "Not Perfect" Committee member Raul Richards of Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York, said that although the report answers many technical concerns raised about the CTBT, it may not end all criticism about the treaty including the potential problem of attribution of explosions. "Have we put to rest all concerns of detection capability and monitoring capability? In general,

6 Eos, Vol. 83, No. 33,13 August 2002 Fig. 2. This perspective view shows NPEO 2000 and NPEO 2001 automated drifting station drift tracks (magenta line for 2000, blue line for 2001), hydrographic stations (open circles, magenta for 2000 and blue for 2001), and color contours of hydrographic station salinity anomalies relative to EWG [1997]. The 2000 station drift began April 2000 and reached the point shown in the figure by the end of December It subsequently drifted south in the Greenland Sea and stopped operating in the ice edge region near 70 N, 14 Wat the end of March The 2001 station began operating in April 2001 and had reached the position shown by the end of the year.the 2001 mooring was deployed near the site of the 2001 hydrographic station 1. Page 357

7 Eos,Vol. 83, No. 33,13 August 2002 NP20276 Apr20 May20 Jun20 Jul20 Aug20 Sep20 Oct20 Nov20 Dec20 Jan20 Feb20 Fig. 4. Results from the ice mass balance buoy are shown; top panel shows air temperature. Middle panel shows temperature contours in the ice, bottom position inferred from temperature, and upper surface and snow thickness as measured by an acoustic sounder. The measured water temperature and the calculated ocean heat flux are given in the bottom panel.

8 (a) 80 N 82 N 84 N 86 N 88 N 90 Wi Eos, Vol. 83, No. 33,13 August 2002 Salinity (psu) on Depth (m) = Q Page Temperature ( C) Salinity (psu) 35 Fig. 3. (a) Horizontal distribution of salinity at 20-m depth is shown. Note that the data along the trajectory are measured by J-CAD1, and the background describes the EWG [1997] winter climatology. Vertical profiles of (b) temperature and (cj salinity are shown in the vicinity of the North Pole at N and W (red) for J-CAD1 and at N,45.000W for EWG (1997) climatology (blue).