11

Arctic Sea Ice and Ocean Observations

This article was preparedby Ignatius G. Rigor, of

the Applied Physics Labo-ratory (APL), University

of Washington, Seattle;Jackie Richter-Menge, of

the U.S. Army ColdRegions Research and

Engineering Laboratory;and Craig Lee, of APL.

The Arctic and sea ice play several importantroles in the global climate system, includingeffects on the surface heat budget and the globalthermohaline circulation. Excess latent and sensi-ble heat from the sun absorbed at lower latitudesis transported poleward by the atmosphere andocean, where it is radiated back out to space.Sea ice over the Arctic Ocean insulates the atmo-sphere from the ocean, thus reducing the amountof heat lost to space. Sea ice also has a higheralbedo (reflectivity) than the darker ocean, reduc-ing the amount of sunlight absorbed by the sea-ice-covered ocean. A decrease in sea ice wouldincrease the exposed area of the darker ocean,increasing the amount of sunlight absorbed, thuswarming the ocean, melting more sea ice, andamplifying the initial perturbations (this is calledice–albedo positive feedback). However, the mois-ture fluxes into the atmosphere are also higherover open water than over sea ice, which mayincrease the areal coverage of fog and low clouds,increasing the albedo near the surface and damp-ing the initial perturbations (this is called cloud–

radiation negative feedback). These opposingfeedbacks underscore the complexity of the Arcticand global climate systems.

Understanding the changes in Arctic climateand sea ice is important, since these changes havesignificant impacts on wildlife and people. Manyspecies and cultures depend on the sea ice forhabitat and subsistence. For example, Inupiat huntfor bowhead whales, and polar bears hunt andraise their young on the sea ice. The lack of sea icein an area along the coast may expose the coast-line to ocean waves, which may threaten low-lyingcoastal towns and accelerate the rate of erosion.From an economic viewpoint, the extent of Arcticsea ice affects navigation from the Atlantic to thePacific through the Arctic along the Northern SeaRoute and Northwest Passage, which are as muchas 60% shorter than the conventional routes fromEurope to the west coast of the U.S. or Japan.

NOAA plays an important role in monitoringthe Arctic and supporting research to understandand predict these changes. This article describessome of the many programs that NOAA supportsto monitor Arctic sea ice and the ocean, such asthe International Arctic Buoy Programme (IABP)and the Study of Environmental Arctic Change(SEARCH).

International ArcticBuoy Programme

In 1974 the U.S. National Academy of Sciencesrecommended the establishment of a network ofautomatic data buoys to monitor synoptic-scalefields of sea level pressure, surface air tempera-ture, and ice motion throughout the Arctic Ocean.As a result, the Arctic Ocean Buoy Program wasestablished by the Polar Science Center, AppliedPhysics Laboratory (APL), University of Wash-ington, in 1978 to support the Global WeatherExperiment. Operations began in early 1979, and

Arctic connections toglobal climate. Excess

heat (temperature, T, andhumidity, q) absorbed atlower latitudes is trans-ported poleward by theatmosphere and ocean,

where it is radiated backout to space (longwave

radiation, L). Sea ice overthe Arctic Ocean insulates

the atmosphere from theocean, thus reducing the

amount of heat lost tospace, but it also has ahigher albedo than the

ocean, which reduces theamount of heat absorbedby the ice-covered ocean(shortwave radiation, S).Most of the heat from the

ocean escapes into theatmosphere through the

cracks in the sea ice(heat flux, F).

This document has been archived.

12

Current locations of International Arctic Buoy Programme (IABP) buoys and the IABP deployment plans for 2005. The current locations offundamental meteorological buoys (gray dots), ice mass balance (IMB) buoys (red dots), and automated drifting stations (ADS) (red stars) areshown. The planned deployments of buoys are shown in blue. More details can be obtained from http://iabpl.apl.washington.edu/Deploy2005/.

13

the program continued through 1990 under fund-ing from various agencies. In 1991 the IABP suc-ceeded the Arctic Ocean Buoy Program, but thebasic objective remains: to maintain a network ofdrifting buoys on the Arctic Ocean to providemeteorological and oceanographic data for real-time operational requirements and research pur-poses, including support to the World ClimateResearch Programme and the World WeatherWatch Programme.

The IABP currently has 33 buoys deployed onthe Arctic Ocean. Most of the buoys measure sealevel pressure and surface air temperature, butmany buoys are enhanced to measure other geo-physical variables, such as sea ice thickness,ocean temperature, and salinity. This observational

Observations from anIABP ice mass balance

(IMB) buoy and a JapanAgency for Marine-Earth

Science and Technology(JAMSTEC) compactArctic drifter (JCAD),which were deployed

together on the driftingArctic sea ice. These

buoys measure sea levelpressure, surface air

temperature, ice thick-ness and temperatures,snow depth, and ocean

temperatures and salinity.

array is maintained by the twenty participantsfrom ten countries, who support the programthrough contributions of buoys, deploymentlogistics, and other services. The U.S. contribu-tions to the IABP are coordinated by the U.S.Interagency Arctic Buoy Program (USIABP),which is managed by the NOAA/Navy NationalIce Center. Of the 33 IABP buoys currently report-ing, 13 buoys were purchased by the USIABP, and18 buoys were deployed using logistics coordi-nated by the USIABP. The USIABP also funds thecoordination and data management of the IABPby the Polar Science Center, at the University ofWashington. The observations from the IABP areposted on the Global Telecommunications Systemfor operational use, are archived at the World DataCenter for Glaciology at the National Snow andIce Data Center (http://nsidc.org), and can beobtained from the IABP web server for research(http://iabp.apl.washington.edu).

The observations from the IABP have beenessential for:

• Monitoring Arctic and global climate change;• Forecasting weather and sea ice conditions;• Forcing, assimilating, and validating global

weather and climate models; and• Validating satellite data.

As of 2005, over 500 papers have been writtenusing the observations collected by the IABP. Theobservations from IABP have been one of thecornerstones for environmental forecasting andstudies of climate and climate change. Many ofthe changes in Arctic climate were first observedor explained using data from the IABP.

USIABP CONTRIBUTORS

U.S. Coast Guard

International Arctic Research Center, University ofAlaska Fairbanks

National Aeronautics and Space Administration

National Oceanic and Atmospheric Administration(NOAA), Arctic Research Office

NOAA, National Environmental Satellite, Data andInformation Service

NOAA, Office of Global Programs

Naval Oceanographic Office

Naval Research Laboratory

National Science Foundation

Office of Naval Research

14

Study of EnvironmentalArctic Change

SEARCH is a coordinated U.S. interagencyprogram established in recognition of the impor-tant role of the Arctic region in global climate.SEARCH’s focus is to understanding the fullscope of changes taking place in the Arctic andto determine if the changes indicate the start ofa major climate shift in this region. NOAA hasinitiated its contribution to the SEARCH programwith seed activities that address high-priorityissues relating to the atmosphere and the cryo-sphere. One element of the NOAA SEARCHprogram is an Arctic Ocean Observing System(AOOS).

The SEARCH AOOS is envisioned to includesix categories of in situ observations: ocean path-way moorings, cross-shelf exchange moorings,basin moorings, gateway moorings, repeatedhydrographic sections, automated drifting sta-tions, and drifting buoys. Enhancement of theIABP and deployment of automated drifting sta-tions (ADSs), like the one at the North Pole Envi-ronmental Observatory (NPEO: http://psc.apl.washington.edu/northpole/), have been identifiedas two of the key components of the SEARCHAOOS. These enhancements and the deploymentof drifting buoys have been the initial focus ofNOAA’s efforts. More specifically, the focus hasbeen on establishing a network of instrumentationto monitor and understand changes in the thick-ness of the ice cover.

The “Vision” for theSEARCH Arctic Ocean

Observing System(AOOS), which includes

six categories of in situobservations: ocean

pathway moorings, crossshelf exchange moorings,basin moorings, gateway

moorings, repeatedhydrographic sections,

automated driftingstations, and

drifting buoys.

15

Data CollectionCentral to the progress that has been made in

establishing a network to monitor changes in thethickness of the ice cover has been the develop-ment and employment of autonomous ice massbalance (IMB) buoys. An IMB buoy is equippedwith thermistor strings that extend through thethickness of the ice cover, acoustic sensors thatmonitor the position of the top and bottom surfacesof the ice, a barometer, a GPS, and a satellite trans-mitter. These buoys provide a time series of sealevel pressure, surface air temperature, snow accu-mulation and ablation, ice mass balance, internal

Components of the ArcticOcean Observing System

(AOOS).

ice temperature fields, and temporally averagedestimates of ocean heat flux. Together, these datanot only provide a record of changes in the icethickness, but equally important they provide theinformation necessary to understand the sourceof these changes. This is critical to extending theresults from these individual sites to other regionsof the Arctic. The buoys are installed in the icecover and, hence, drift with the ice cover. Monitor-ing the drift of the buoys also provides informa-tion on the circular automated drifting stations(ADSs). These sites will be established throughcollaboration with the Alfred Wegner Institute inGermany, the NPEO, the Japan Agency for Marine-

16

Earth Science and Technology, and Woods HoleOceanographic Institution’s Arctic Group. Thesestations provide critical atmospheric, ice, andupper ocean hydrographic measurements thatcannot be obtained by other means.

Since the drifting buoys move with the ice andsurface currents and thus cannot reliably samplethe main subsurface currents of the Arctic, theseobservations must also be complemented bymoorings and hydrographic sections across theArctic Ocean. In August 2003 a new mooring sitewas established in the northern Chukchi Sea. Themooring is equipped with an ice profiling sonar(IPS) to measure the ice draft and velocity as theice drifts overhead, providing a measure of the icethickness distribution. This site was located usingthe results from a coupled ice–ocean sea icedynamics model. The model was used to estimatethe basin-wide mean annual thickness using a 52-year window: 1948–1999. Using these estimates, acorrelation analysis was applied to investigate theeffectiveness of establishing a second seafloor-moored IPS to monitor changes in the annual meanthickness of the Arctic sea ice cover. The analysisrecognized and was dependent on the existenceof the IPS at the NPEO. The results of the analysisindicated that a moored IPS located in the north-ern Chukchi Sea, coupled with the results from theestablished NPEO site, could explain 86% of thevariance of the basin-wide annual mean ice thick-ness. The location of a second mooring signifi-cantly improves the data collected from a singlemoored IPS at the North Pole, where the explainedvariance is estimated to be 65%. Data from themooring sites are only available after the mooringis recovered. The first recovery of the mooring inthe Chukchi Sea is scheduled for September 2004.

A potential AOOS design requires a range ofcomplementary platforms with combined capabili-ties that address SEARCH requirements. TheAOOS includes drifting buoys, moorings, autono-mous platforms (floats, gliders, and propeller-driven autonomous underwater vehicles), andhydrographic sections occupied by ships andaircraft landings. Drifting buoys and moorings,already employed for Arctic observing, would pro-vide sites for acoustic navigation and communica-tions beacons and serve as data repositories andlinks across the ice interface for satellite communi-cations. New autonomous platforms, especiallyfloats and gliders, will provide unprecedentedaccess to Arctic and subarctic regions. Theseplatforms have seen significant successes in mid-latitude oceans and are currently being adapted

for use in ice-covered environments as part of theNSF-supported Freshwater Initiative (see http://iop.apl.washington.edu for additional informa-tion). The first missions beneath the ice will inves-tigate freshwater exchange through Davis Strait.Broader high-latitude application of autonomousplatforms will require the development of long-range acoustic navigation and communicationssystems. An ideal system would supply long-range acoustic navigation to all platforms (Arcticunderwater GPSs), allow mobile platforms to hometo targets (drifting ocean buoys and moorings),and provide short-range, high-bandwidth commu-nications for rapid data exchange. In this vision,moored platforms provide time series, datastorage, and a relay through the ice to satellites;autonomous platforms provide broad spatialcoverage, data shuttling, and satellite links (whenin ice-free waters); and ship- and aircraft-basedhydrography provide critical tracer measurementsthat cannot be obtained by autonomous sensors.This combination of platforms offers comprehen-sive coverage and creates a “store-and-forward”network to improve the timeliness and reliabilityof data return.

ConclusionsRecent progress has been made in establishing

components of an AOOS. The initial focus is on anetwork of instruments to monitor and understandchanges in the thickness of the ice cover and innear-surface ocean characteristics. Central to thesuccess of this network is the coordination ofthese efforts with other national and internationalprograms. The use of sea ice dynamics models hasalso been important, helping to optimize the loca-tion of instrumentation and the allocation of limitedresources.

Data are only just beginning to be receivedfrom the recently deployed sites, but regional andinterannual variability in the changes in the thick-ness of the ice cover and upper ocean is alreadyapparent. This observation is consistent with otherhistorical observations.These data will be madegenerally available to the scientific community foruse in validating satellite-derived products; forforcing, calibration, and assimilation into numeri-cal models; and for forecasting weather and iceconditions. Maintaining and further developingthis network will provide a more consistent recordof change, necessary for improving understandingof this complex and important component of theglobal climate system.

The establishment ofthe components of the

AOOS discussed in thisarticle would not have

been possible without thecommitted collaboration

among many internationalinstitutions and

programs, such as theparticipants of the

International Arctic BuoyProgramme. The authorsexpress their appreciation

to the scientific partici-pants and crew members

onboard the Canadianicebreakers Louis St.

Laurent and Sir WilfredLaurier, the German ice-

breaker Polarstern, theRussian icebreaker

Kapitan Dranitsin, theSwedish icebreaker Oden,

and the U.S.icebreaker Healy.

17

ReferencesArctic Climate Impacts Assessment (2004) Impacts

of a Warming Arctic: Arctic Climate ImpactsAssessment. Cambridge University Press, 139 p.

Lynch, A.H., E.N. Cassano, J.J. Cassano, and L.R.Lestak (2003) Case studies of high wind eventsin Barrow, Alaska: Climatological context anddevelopment processes. Monthly WeatherReview, Vol. 131, No. 4, p. 719–732.

Melling, H., and D.A. Riedel (1996) Developmentof seasonal pack ice in the Beaufort Sea duringthe winter of 1991-1992: A view from below.Journal of Geophysical Research, Vol. 101, No.C5, p. 11,975–11,991.

Perovich, D.K., B.C. Elder, and J.A. Richter-Menge(1997) Observations of the annual cycle of sea

ice temperature and mass balance. GeophysicalResearch Letters, Vol. 24, No. 5, p. 555–558.

Perovich, D.K., T.C. Grenfell, J.A. Richter-Menge,B. Light, W.B. Tucker, and H. Eicken (2003)Thin and thinner: Sea ice mass balance mea-surements during SHEBA. Journal of Geophys-ical Research (Oceans), Vol. 108, No. C3.

SEARCH Science Steering Committee (2001)SEARCH: Study of Environmental ArcticChange, Science Plan. Polar Science Center,Applied Physics Laboratory, University ofWashington, Seattle, 91p.

Zhang, J., D. Thomas, D.A. Rothrock, R.W. Lind-say, Y. Yu, and R. Kwok (2003) Assimilation ofice motion observations and comparisons withsubmarine ice thickness data. Journal of Geo-physical Research, Vol. 108, No. C6, p. 3170.