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Eos, Vol. 84, No. 30,29 July 2003

VOLUME 84

NUMBER 30

29 JULY 2003 PAGES 281-288

EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION

A Long-term Circulation and Water Mass Monitoring Program for the Arctic Ocean PAGES 281,284-285

Substantial changes have occurred in the Arctic over the last few decades.These changes are linked with the variability of external climate system in ways not yet fully understood. Unresolved issues concerning the driving processes and mechanisms behind these changes in the Arctic environment require further investigation. A major constraint on our ability to under­ stand linkages between the Arctic Ocean and the global climate system is the scarcity of observational data. We have thus initiated efforts to establish a long-term, mooring-based observational system in the Eurasian and Canadian basins of the Arctic Ocean. A num­ ber of regional monitoring programs have elu­ cidated local details of the circulation, but none has provided the large-scale coverage proposed here (Figure l).The widely spaced array of moorings discussed here will empha­ size the largest-scale modes of variability over relevant time scales. The overall purpose of the project is to pro­ vide a quantitative, observation-based assess­ ment of circulation, water mass transformations, and key mechanisms of variability in the Arctic Ocean on a broad range of time scales (from hours to years). The program encompasses both the Eurasian Basin (NABOS: Nansen and Amundsen Basins Observational System), and the Canadian Basin (CABOS: CAnadian Basins Observational System). NABOS is currently conducted jointly by the International Arctic Research Center (IARC),the Institute of Marine Science (IMS), and the Arctic and Antarctic Research Institute (AARI), Russia.CABOS,an observa­ tional program complementary to NABOS, is jointly initiated by IARC and the Institute of Ocean Sciences (IOS), Canada.These two pro­ grams are jointly funded by the U.S. National

BY I. POLYAKOV, D.WALSH, I. DMITRENKO, R. COLONY, J. HUTCHINGS, L.TIMOKHOV, M . JOHNSON, AND E. CARMACK

Science Foundation and Frontier (FRSGC; Japan).The vision is for NABOS/CABOS to evolve into a long-term observational program which, together with other observa­ tional programs like the NSF-led Study of Environmental ARctic CHange (SEARCH) program, the Japan/Canada JWACS (Joint Western Arctic Climate Studies) program, the European Union observational program in the Fram Strait, and the international ASOF (Arctic/Subarctic Ocean Fluxes) program, will provide crucial information for detection of major climatic changes in the Arctic Ocean.

The growing list of interconnected Arctic Ocean field programs demonstrates an impor­ tant value-added property, with each comple­ menting the other in a synergistic manner.

Rationale for

NABOS/CABOS

The Arctic Ocean consists of two major basins: the Eurasian and Canadian (Figure 1). Some changes in the Arctic Ocean are advected from upstream locations in the Eurasian Basin, where warm Atlantic waters enter via the Fram Strait and the Barents Sea. As an example, the effects of an influx of anomalously warm Atlantic water, which entered the Nansen Basin in 1989 [Carmack etal., 1995] have been followed around the Arctic Basin, with the signal having recently arrived in the Beau­ fort Sea [McLaughlin et al, 2002] .Atlantic waters flow in narrow topographically trapped cur­ rents, and are known to be strongly modified

m

I I deployed and recovered in 2001 © deployed in 2002 and to be deployed in future O to be deployed in 2003 and in future

to be deployed in future Atlantic water pathways

Fig. 1. Locations of planned and previously deployed oceanographic moorings. The icebreakers Kapitan Dranitsyn and Sir Wilfrid Laurier were used to deploy NABOS/CABOS moorings in summer 2002. A mooring schematic is shown in the upper left corner. Original color image appears at back of volume.

Eos, Vol. 84, No. 30,29 July 2003 MMP Temperature (°C)

Nov

Dec Salinity ( P S U )

diffused upward, potentially to thin the ice; and this may have a dramatic effect on the ice cover and fresh water balance in the Arctic Ocean under scenarios of global warming. The Canadian Basin, the largest of the Arctic basins, has the capacity to store vast quantities of heat and especially fresh water, and the eventual fate of this may have important con­ sequences for Arctic climate. A major gap in current studies is lack of appreciation for storage within the halocline "reservoirs" [see Carmack, 2000]. Current knowledge of the circulation within the Canada Basin is at best sketchy. Narrow boundary currents carry warm water of Atlantic origin around the basin in a counter­ clockwise sense; but the near-surface circula­ tion, exposed to direct effects of wind forcing, is clockwise. Some fraction of the low-salinity upper waters leaving the Canada Basin exit through the Canadian Archipelago to major global, deep-water formation sites, believed to be critical to the world ocean thermohaline circulation [e.g.,Aagaard and Carmack, 1994]. If true, the flow through the archipelago could be of global climatic significance and its mon­ itoring is a key scientific challenge.

Program

Methods

The primary monitoring tool of the NABOS/ CABOS program will be a series of moorings placed at carefully chosen locations around the Arctic Ocean.Time series obtained from these moorings will allow separation of synopticscale (but interesting) noise (e.g., eddies,shelf waves) from longer-term climatic signal. Located along the major pathways of water, heat, and salt transport, such moorings should capture climatically important changes in oceanic conditions.The NABOS/CABOS moorings will operate for 1 year at a time, with replacement every year. A gradual increase in the number of moorings is planned, from two deployed in summer 2002, to the full-scale monitoring system (Figure 1) after several years.

33

S (PSU) Fig. 2. Time series of the water temperature (top,°C) and salinity (middle, psu) measured by the MMP profiler.Vertical axis is pressure in decibars (which corresponds roughly to depth in meters); the horizontal axis is time in days. The bottom panel shows TS data measured by the MMP profiler (red), by the seacat CTD at approximately 453 m, and by the microcat SBE37 CTD at approximately 60 m. Original color image appears at back of volume. by mixing processes as they make their way around the basin. To understand the integrated effect of climatically induced fluctuations in Atlantic water inflow, it is necessary to monitor not only the point of entry of anomalous water masses, but also to observe how they are modified en route. Atlantic water loses large

amounts of heat along the slope in the Nansen Basin between Franz Josef Land and Novosibirskiye Islands [Blinov and Popkov, 1986] (i.e., where there are plans to deploy our NABOS moorings; Figure 1),suggesting that this area may be particularly important to Arctic climate and its variability. A portion of this Atlantic water heat is advected and/or

Twelve moorings grouped into four crosssections crossing the continental margins of the European Basin (NABOS), and five or six moorings dispersed through the Canadian Basin (CABOS) form the mooring scheme (Figure l).The locations of moorings within each cross-section are designed to capture the major near-slope transports within surface, intermediate, and bottom layers; resolve important shelf-basin interaction processes; and document the complex interactions of the Fram Strait and Barents Sea branches of the inflowing Atlantic water. The NABOS moorings will also provide detailed informa­ tion pertaining to small-scale processes at the mooring locations, particularly heat losses from the warm Atlantic layer, lateral exchange processes, double-diffusive convection, and thermohaline interleaving. Understanding the splitting of sub-surface Atlantic waters between the two branches—one following the Lomonosov Ridge, and another, the continental slope of the Makarov Basin—will also be among the major targets of the program.

Eos, Vol. 84, No. 30,29 July 2003 for the NABOS program. An essential part of the program is analysis of new data, in combi­ nation with historical data. Following this prin­ ciple, the first paper (with joint U.S.-Russian co-authorship) on Arctic Ocean variability based was submitted on analysis of historical data [Polyakov et al., 2003]. 2001-2002 Experiment in the Canada Basin

Fig. 3. Vertical profiles of the water temperature measured in summer 2002 during the NABOS cruise onboard the icebreaker Kapitan Dranitsyn, and during the summer 1995 cruise of the research vessel Polarstern. Note the significantly higher (up to 0.8°C) water temperature in 1995 compared with 2002. Original color image appears at back of volume.

After several years of observation, the number of moorings within certain cross-sections may be reduced, based on what is found, with the remaining of key moorings to be maintained indefinitely Some moorings may be relocated, broadening observational domain, depending on information obtained during the initial program. In the Canadian Basin, three moorings are planned along the Alpha-Mendeleyev Ridge, and two moorings are placed more toward the head of the basin (Figure l).The mooring locations will be changed to best complement existing Canadian, Japanese, and U.S. moorings, so that international coordination is essential.This large-scale array of moorings will allow measurement of internal variability, including basin-scale shifts in temperature, salinity, and density surfaces—critical to our understanding of the Canadian Basin's role as a reservoir for storage of heat and fresh water. The CABOS moorings will provide detailed information on small-scale processes at the mooring locations, but the primary goal is to resolve large-scale modes of variability. The widely spaced array will therefore sacrifice some of the finer horizontal resolution provided by for example, the NABOS cross-sections, emphasizing instead the largest-scale modes of variability. Most NABOS/CABOS moorings will be equipped with the "McLane Moored Profiler" (MMP).The same tool was used on the pre-

NABOS/CABOS mooring deployed in the Beaufort Sea in summer 2001 (Figure l).This instrument is capable of profiling vertically along the mooring line, covering up to 10 m during its deployment. The MMP is typically equipped with a CTD sensor and a three-com­ ponent acoustic velocimeter.The up-anddown motion of the profiler is programmable, making it possible to focus on specific depth ranges and time periods, giving a high degree of flexibility in designing a sampling scheme. 6

Getting Started: Pilot Project

2001-2002

The first step in initiating the observational program was a pilot project, consisting of a highly simplified version of the full planned program.The pilot project tested international connections and operational capabilities, and provided necessary experience for the fullscale field program. During the project, the core NABOS/CABOS team of scientists and techni­ cians was assembled. One of the most impor­ tant missions was to establish channels for obtaining Russian permits, and making customs arrangements for oceanographic work within the Russian Exclusive Economical Zone (EEZ). Subsequent to meetings of representatives of IARC,AARI,and various Russian institutions and agencies, permission was obtained for a CTD survey in the northern part of the Laptev Sea as a part of the summer 2002 field program. Work continues to secure future permissions

On 23 September 2001, scientists from I ARC and IOS deployed a mooring in 460 m of water at the mouth of Mackenzie Canyon from the CCGS Sir Wilfrid Laurier (139°7.79'W 70° 16.36'N; Figure 1). Mackenzie Canyon, located in the southern Beaufort Sea, just north of the Yukon Territory, is a region charac­ terized by intense up- and down-welling events and internal Kelvin wave generation [Carmack andKulikov, 1998].The mooring contained an upward-looking sonar to meas­ ure ice draft (contributed by R. Moritz, Univer­ sity of Washington), in addition to two Seabird CTDs and a MMP Profiler.The MMP was pro­ grammed to profile between 65 m and 450 m every 4 hours throughout the deployment, thus giving a high-resolution view of the spa­ tio-temporal evolution of the water column during the observation period. Figure 2 shows contour maps of temperature (T, top) and salinity (S, center) for the period from late September through early February; and Figure 2 (bottom) shows a T-S plot from the MMP data, including data from the Seabird CTD instruments located at the top and bottom of the mooring. The data show a cold, fresh surface layer, approximately 0.3°C above freezing, with T and S increasing down­ ward toward the Atlantic water layer, reaching a maximum of 0.57°C near the bottom.The contour plots clearly show a low-period undu­ lation of the water column, with an amplitude of perhaps 70-80 m,with numerous higher-fre­ quency (5 to 7 per day) asymmetric events superimposed. Preliminary analysis suggests the low-frequency variability is closely related to surface wind forcing, while the cause of the higher frequency variability is still under investigation.The additional scatter apparent in the SBE37 data follows from the fact that it sam­ pled near-surface waters every 15', while the MMP made corresponding shallow measure­ ments only (approximately) every 4 to 5 hours. On 16 September 2002, the Mackenzie Canyon mooring was recovered, and a second mooring was deployed in 1117 m of water in the southern Beaufort Sea, at 134°04'W; 71° 23'N.This mooring was deployed specifically to monitor the warm Atlantic water boundary current flowing around the perimeter of the Canada Basin. Its design was similar to that of the Mackenzie Canyon mooring, with the addition of two RCM7/8 current meters along the main mooring line, a SAMI C0 sensor (courtesy of M. DeGrandpre, University of Montana), and an additional microcat CTD placed above the main flotation, at a depth of about 35 m.The hope is that the mooring will provide valuable information about Atlantic and halocline water transport, variability, and water-mass transformation mechanisms. 2

Eos, Vol. 84, No. 30, 29 July 2003 Summer 2002: Experiment Basin

in Eurasian

On 26 August 2002, the Russian icebreaker Kapitan Dranitsyn left Kirkenes, Norway, on a 22-day voyage to the northern Laptev Sea. Ten Russian scientists from AARI and one repre­ sentative of the Russian Navy, together with four researchers from the University of AlaskaFairbanks and one from the Canadian Ice Ser­ vice, were aboard the icebreaker to deploy the first NABOS MMP-equipped mooring in the Eurasian Basin (Figure l ) , a n d to conduct attendant oceanographic, meteorological, and ice observations on the Laptev Sea slope. Twenty-two CTD profiles were taken during the cruise. Observations from the 1990s showed that the Atlantic water here was nearly 1 °C warmer compared with climatological data [e.g., SCICEX Data Sets]. This Atlantic water temperature anomaly entered the Arctic via the Fram Strait in the late 1980s-early 1990s, and found its way to the Arctic Ocean interior along the continental margins. However, Boyd et al. [2003] and Morison et al. [2002] reported that by the end of the 1990s, the temperature anomaly had dis­ appeared from the Barents and Laptev seas slope, presumably having been advected far­ ther downstream.The new CTD data (Figure 3a) show that the Atlantic water temperature is now close to the climatic mean temperature [EWG, 1997]. One of the CTD profiles shows relatively homogeneous water between 2501500-m depth, indicative of strong vertical mixing (Figure 3b). Such mixing eroded the 250-700-m portion of the Atlantic layer, but at the same time, increased the heat content within the 700-1500-m layer. We speculate that an eddy located below the halocline could have produced this feature. Long-term mooring observations north of the Novosibirskiye Islands support this possibility [Woodgate et al., 2001]. Shipboard estimates are integral to the proj­ ect. On the 2002 cruise, we found the mean ice thickness to be a meter within the multiyear pack ice, and the ice extent was anom­ alously low. An upward-looking sonar is planned for next year's deployment, which will provide ice draft measurements through­ out the year.This data, combined with shipboard estimates and satellite observations, should provide insight about the variability of ice in the Eurasian Basin and how this is linked to Atlantic water variability

What Is Next? On 1 September 2003, a second NABOS cruise to the northern Laptev Sea is planned, again using the Russian icebreaker Kapitan Dranitsyn. Retrieval of the MMP mooring deployed in summer 2002 and replacement with another,similar MMP mooring is expected, initiating the planned multi-year record at this location in the Eurasian Basin.Two to three additional moorings will be added, forming the basis of the two NABOS cross-sections (Figure l ) . O n e of these moorings is planned for deployment within the Russian EEZ. Atten­ dant CTD, ice, meteorological, biological, and chemical (including isotope and C 0 ) obser­ vations in the same area of the Laptev Sea slope will also be made.The plan for the CABOS program includes recovery of the mooring from the Canada Basin and deploy­ ment of one or two additional moorings, depending on ship availability (Figure 1). 2

The plan is to continue analysis of available historical data, and to finalize the next joint U.S.-Russian publication on halocline during the next year. Future plans on fieldwork antici­ pate a gradual increase in the number of moorings, depending on funding.The plans for 2003 and beyond are indeed significantly more complex than those of the 2002 pilot project, but the lessons learned from the first year of cooperation provide a solid founda­ tion for future work. The Search for Scientific Partners The planned program to document Arctic Ocean variability over a wide range of temporal/ spatial scales is beyond the capability of any single research institution or country, and thus international cooperation is essential.We con­ sider participation of international scientific partners at every stage of the project to be cru­ cial to its success.We will continue our efforts to develop a new agreement between the governments of the United States and the Russian Federation on cooperation in oceano­ graphic research, in which NABOS appears as a specific project. We hope to establish strong ties with scientists from other U.S. and interna­ tional institutions, and invite inquiries from any and all interested colleagues.

A recent U.S. Senate committee hearing about the re-authorization of the Marine Mammal Protection Act of 1972 focused on one word; harassment. Concern about whether anthropogenically produced underwater noise actually harasses or even may be involved in the deaths of

Author

Information

Igor Polyakov, David Walsh, Igor Dmitrenko, Roger Colony, Jennifer Hutchings, International Arctic Research Center, University of Alaska-Fairbanks; Leonid Timokhov, Arctic and Antarctic Research

References Aagaard, K. and E. C. Carmack, The Arctic Ocean and climate: a perspective, in The Polar Oceans and Their Role in Shaping the Global Environment: The

Ocean Acoustics Research Figures in Debate About Protecting Marine Mammals PAGE 282

Nansen Centennial Volume, Geophys. Monogr. Ser., vol. 85, edited by O. M. Johannessen, R. D. Muench, and J. E. Overland, pp. 5-20, AGU,Washington, D.C., 1994. Blinov, N. I., and S. N. Popkov, On the heat exchange of the Atlantic water in the Arctic Basin, Arctic and Antarctic Research Institute, Leningrad, Gydrometeoizdat, Transactions, 408,90-98,1986. Boyd,T.I, M. Steele, R. D. Muench, and J.T. Gunn, Partial recovery of the Arctic Ocean halocline, Geophys. Res. Lett., in press. Carmack, E. C.,The Arctic Ocean's freshwater budget: Sources, storage and export, in The Freshwater Budget of the Arctic Ocean, edited by E. L. Lewis et al., pp. 91-126, Kluwer,The Netherlands, 2000. Carmack, E. C , and E. A. Kulikov, Wind-forced upwelling and internal Kelvin wave generation in Mackenzie Canyon, Beaufort S e a , i Geophys. Res., 705,18,447-18,458,1998. Carmack, E. C , R. Macdonald, R. Perkin, F McLaughlin, and R. Pearson, Evidence for warming of Atlantic water in the southern Canadian Basin of the Arctic Ocean: Evidence from the Larsen-93 Expedition, Geophys. Res. Lett., 22,1061-1065, 1995. Environmental Working Group ( E W G ) , Joint U.S.­ Russian Atlas of the Arctic Ocean [CD-ROM], National Snow and Ice Data Center, Boulder, Colorado, 1997. McLaughlin, F, E. Carmack, R. Macdonald, A. J. Weaver, and J.Smith.The Canada Basin, 1989-1995: Upstream events and far-field effects of the Bar­ ents Sea, J. Geophys. Res., W7(C7), 3082,2002. Morison,J. H.et al., North Pole environmental obser­ vatory delivers early results,Eos, Trans., AGU, 83, 241,244-245,249,2002. Polyakov, I., D.Walsh, I. Dmitrenko, R. Colony and L. Timokhov, Arctic Ocean variability derived from historical observations, Geophys. Res. Lett., 30(6), 1298, doi: 10.1029/2002GL016441,2003. SCICEX Data Sets,ARCSS Data Coordination Center, National Snow and Ice Data Center, Boulder, Colorado (http://arcss.colorado.edu/data/arcss. html). Woodgate, R.A.et al.,The Arctic Ocean boundary current along the Eurasian slope and the adjacent Lomonosov Ridge: Water mass properties, trans­ ports and transformations from moored instruments, Deep-Sea Research, Part 1,48, 1757-1792,2001.

some marine mammals has become a heated issue which has led to recent lawsuits and court rulings to halt or restrict some scientific research and U.S. naval operations. (See Eos, 29 April 2003). At a 16 July hearing, Sen. Olympia Snowe (R-Maine), chair of the Senate Commerce Sub­ committee on Oceans, Fisheries, and Coast Guard, said a balance needs to be found

Institute, St. Petersburg, Russia; Mark Johnson, Insti­ tute of Marine Science, University of AlaskaFairbanks; and Eddy Carmack, Institute of Ocean Sciences, Sydney, B.C., Canada

between research needs and military readiness on one hand, and protection of marine mammals on the other hand. The Act currently defines harassment as any act of pursuit, torment, or annoyance which has the potential to injure a marine mammal or stock in the wild; or has the potential to disturb the animal or stock by causing disrup­ tion of behavioral patterns such as breeding, feeding, or migrating. Legislation supported by the Bush adminis­ tration, but not yet introduced in Congress,would modify the definition of harassment to include "any act that injures or has the significant

Eos, Vol. 84, No. 30, 29 July 2003

& deployed and recovered in 2001 • to be deployed in future © deployed in 2002 and to be deployed in future Atlantic water pathways O to be deployed in 2003 and in future Fig. 1. Locations of planned and previously deployed oceanographic moorings. The icebreakers Kapitan Dranitsyn and Sir Wilfrid Laurier were used to deploy NABOS/CABOS moorings in summer 2002. A mooring schematic is shown in the upper left corner.

Eos, Vol. 84, No. 30, 29 July 2003 MMP Temperature (°C)

Oct

Nov

Dec

Jan

Feb

Jan

Feb

Salinity ( P S U )

Q_

Oct

"

2

31

Nov

32

Dec

33

34

35

S (PSU) Fig. 2. Time series of the water temperature (top,°C) and salinity (middle, psu) measured by the MMP profiler.Vertical axis is pressure in decibars (which corresponds roughly to depth in meters); the horizontal axis is time in days. The bottom panel shows T-S data measured by the MMP profiler (red), by the seacat CTD at approximately 453 m, and by the microcat SBE37 CTD at approximately 60 m.

Page 284

Eos, Vol. 84, No. 30,29 July 2003

(a) -

2 I

(b)

Temperature, °C - 1 0 1 i

L_

_J

i

Temperature, °C -1 0 1

L_

O

o

LO

o o o

I § (D

in

o o o CM

O O LO CM

f Blue - IB Kapitan Dranitsin September 3,2002 79.263N, 125.937E Blue - RV Polarstem August 18,1995 79.988N, 134.913E Red - IB Kapitan Dranitsin September 4,2002 79.806N, 133.449E

o CM

Black - IB Kapitan Dranitsin September 10,2002 79.274N, 125.901 E Red - IB Kapitan Dranitsin September 9, 2002 78.943N. 126.Q57E

Fig. 3. Vertical profiles of the water temperature measured in summer 2002 during the NABOS cruise onboard the icebreaker Kapitan Dranitsyn, and during the summer 1995 cruise of the research vessel Polarstem. Note the significantly higher (up to 0.8°C) water temperature in 1995 compared with 2002.