Arctic Oceanography: Marginal Ice Zones and Continental Shelves

288 Pages·1995·0.48 MB·English

by  Walker O. Smith Jr.

Coastal and Estuarine Studies
Series Editors'
Malcolm J. Bowman Christopher N.K.
Coastal
and Estuarine Studies
49
Walker O. Smith, Jr. and
Jacqueline M. Grebmeier (Eds.)
Arctic Oceanography:
Marginal Ice Zones and
Continental Shelves
American Geophysical
Washington, DC
Series Editors
Malcolm J. Bowman
Marine Sciences Research Center, State University of New York
Stony Brook, N.Y. 11794, USA
Christopher N.K. Mooers
Division of Applied Marine Physics
RSMAS/Universityo f Miami
4600 RickenbackerC swy.
Miami, FL 33149-1098, USA
Editors
Walker O. Smith, Jr.
Graduate Program in Ecology
University of Tennessee
Knoxville, TN 37996
Jacqueline M. Grebmeier
Graduate Program in Ecology
University of Tennessee
Knoxville, TN 37996
Library of CongressC ataloging-in-Publication Data
Arctic oceanography : marginal ice zones and continental shelves / Walker
O. Smith and Jacqueline M. Grebmeier (eds.).
p. cm.- (Coastal and estuarian studies; 49)
Includes bibliographical references.
ISBN 0-87590-263-4
1. Oceanography--Arctic Ocean. I. Smith, Walker O.
II. Grebmeier, Jacqueline M., 1955- III. Series.
GC401.A755 1995
551.46'8(cid:127)c20 95-9541
CIP
ISSN 0733-9569
ISBN 0-87590-263-4
Copyright1 995 by the AmericanG eophysicalU nion,2 000 FloridaA venue, NW, Washington,
DC 20009, U.S.A.
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Printed in the United States of
CONTENTS
PREFACE ............................................................................................ vii
Satellite Remote Sensingo f the Arctic Ocean and Adjacent Seas
Jose(cid:127)no C. Comiso .................................................................... 1
Atmosphere-Ocean Interactions in the Marginal Ice Zones
of the Nordic Seas
Peter S. Guest, Kenneth L. Davidson, James E. Overland,
and Paul A. Frederickson .......................................................... 51
Small-Scale Physical Processesin the Arctic Ocean
Laurie Padman ........................................................................ 97
New Insights on Large-Scale Oceanography in Fram Strait:
The West Spitsbergen Current
ß. ... (cid:127)"(cid:127) Gascard, Claude Richez, and Catherine Rouault .... 131
Chemical Oceanography of the Arctic and its Shelf Seas
Leif G. Anderson .................................................................... 183
DOC Storage in Arctic Seas: The Role of Continental Shelves
John J. Walsh ....................................................................... 203
Biological Processeso n Arctic Continental Shelves:
Ice-Ocean-Biotic Interactions
Jacqueline M. Grebmeier, Walker O. Smith, Jr., and
Robert J. Conover .................................................................. 231
Resolved: The Arctic Controls Global Climate Change
Richard B. Alley .................................................................... 263
EPILOGUE ........................................................................................ 285
LIST OF CONTRIBUTORS ..................................................................
PREFACE
The Arctic Ocean is the least understood ocean on Earth, and yet its importance
to the world's oceans and climate is immense. For example, it has been suggested
that the Arctic is the region most likely to be affected by increased atmospheric
temperatures which might occur as a result of anthropogenic releases of green-
house gases. It also plays a critical role in global oceanic circulation, in that it
modulates the formation of deep water in the North Atlantic via ice export.
Despite its pivotal role in global processes,t he Arctic remains poorly understood.
This volume is an attempt to highlight and synthesize some of the recent advances
in our knowledge of Arctic oceanography and includes topics that will interest
physical, biological, chemical, and geological oceanographersa s well as atmo-
spheric scientists.
That the Arctic is so poorly known relative to other oceans is not surprising. It is
largely ice-covered throughout the year, with only some of its continental shelves
becoming ice-free in summer. Its ice is mostly multi-year and very thick, making
penetration into the deeper portions impossible except by the most powerful
ice-breakers. However, in recent years new technologiesh ave been applied to the
Arctic, and our understandingo f the physical, chemical, biological and geological
processesw hich occur within it is rapidly increasing. Satellite sensorso bserve the
Arctic continually, allowing us to follow ice circulation, storms, and openings in
the pack ice that had never been observed previously. Moorings, ships and buoys
now can withstand many of the rigors of the Arctic, and observations of the water
column and seabed are becoming more common. Finally, because of its impor-
tance to global processes, studies of the Arctic are attracting scientists not only
from Arctic nations but from nations around the world. Arctic oceanographyt ruly
has become an international effort.
Approximately 30% of the surface area of the Arctic Ocean is occupied by its
continental shelves, and hence the impact of the shelf area on the deeper regions
of the basin can be expected to be greater than in other oceans. Shelves also are
thought to play a major role in the production of the Arctic's shallow permanent
halocline, one of its unique features. They are also heavily impacted by seasonal
riverine discharges, and hence potentially can be influenced by fiver-borne
sediments, nutrients and pollutants to a greater extent than in other ocean basins.
Furthermore, the shelf region is covered and uncovered seasonally by ice, and
hence the rates of biogeochemical cycling are greatest there. Shelves also are
frequently the sites of marginal ice zones, which have been the focus of a
substantiala mount of research in the Arctic in the past decade. Marginal ice zones
also occur in deep regions, such as the Greenland Sea. Regardlesso f their depth,
marginal ice zones have been shown to be highly dynamic regions with regard to
their physics and biology. For example, they can generate fronts, jets, and eddies,
have unusual vortex pairs, and be the sites of intense biological activity (due to
upwelling and downwelling) and material transfer. Their roles in the ice dynamics
and biogeochemical cycles of polar systems are still being re-evaluated.
The purpose of this volume is to present both new results from recent studies in
the Arctic, in particular the marginal ice zone and the Arctic' s continental shelves,
as well as to synthesize a variety of multidisciplinary studies which have been
recently conducted. It is not intended by any means to be all inclusive, and
readers can consult other volumes for treatment of the various sub-disciplineso f
Arctic oceanography which have not been treated in detail. We hope that the
papers included in this volume prove to be stimulating to Arctic researchersa nd
non-polar oceanographers alike, and that they point the way towards potentially
significant research directions in the coming decades.
The editors would like to thank our colleagues( who are too numerous to mention
by name) who reviewed these papers under short deadlines and whose excellent
jobs insured the quality of the contributions. Partial support during the prepara-
tion of this volume was provided by the Office of Polar Programs, National
Science Foundation to both of the editors.
Walker O. Smith, Jr.
JacquelineM . Grebmeier
Universityo f
1
SatelliteR emote SensingO f The Arctic
OceanA nd Adjacent Seas
Josefino C. Comiso
Abstract
Many of the large-scales urfacep hysicala nd biologicalc haracteristicosf the Arctic Ocean
and adjacents easc an bestb e studiedw ith satelliter emotes ensingb ecauseo f the vastness
of, adversew eatherc onditionsa, nd long periodso f darknessin the region.S cientifica ppli-
cationss pecifict o the polar regionsa re discussedin termso f the informationa ffordedb y
variouss ystemsp, assiveo r active,a ndb y the microwavei,n frared,a nd visiblep ortionso f
the electromagnetics pectrumI.n the sea-icer egion,t he key parameterso f interesta re ice
concentrationi,c e type, surfacea nd ice temperaturei,c e velocity,i ce extenta nd area, snow
cover,a nd melt coverageI.n the openw ater region,t he correspondinpga rametersa re phy-
toplanktonp igmentc oncentrations, urfacet emperaturew, ind velocity,d ynamict opogra-
phy, internal waves, eddies, and wave propagationc haracteristicsS. ome atmospheric
parameterss ucha s water vapor, liquid water, precipitation,a nd cloud cover are also of
interest.T he strengthsa nd weaknesseso f the variouss ystemsa re considereda nd sources
of errorsa nd ambiguitiesa re pointedo ut. Synergistict echniquesu, sings everals ensorsin
concert,a re alsod iscussedb ecauseth eyp rovidea meanst o obtaina more accurateo r com-
plete characterizationo f the Arctic Ocean and adjacents eas.W hile existing systemsa re
alreadyp rovinge ffectivenessn, ew systemsp lannedf or the next decadew ill evenb e more
versatilea nd shouldu shera new era of a comprehensivaen dc onsistenct overageo f Earth's
systemsi,n cludingt he Arctic system.
Introduction
The moste ffective( andp erhapso nly) way to studyl arge-scales urfacep hysicala ndb iolog-
ical characteristicosf the Arctic Oceana nd its adjacents easi s throught he useo f satellite
Arctic Oceanography: Marginal Ice Zones and Continental Shelves
Coastal and Estuarine Studies, Volume 49, Pages 1-50
This paper is not subject to U.S. copyright.
Published in 1995 by the American Geophysical
2 SatelliteR emote Sensingo f the Arctic Ocean
remotes ensingt echniques[O nstotta nd Shuchman,1 990; Comiso, 1991; Thomas,1 990;
Carsey,1 992]. The power of remotes ensinga s appliedt o the polar regionsh asb eend is-
cusseda ndd emonstrateidn severapl ublications[Z wally et al., 1983;P arkinsone t al., 1987;
Gloersene t al., 1992]. Mounted on satellitep latforms,s ensorsp rovidet he synoptica nd
temporal distributionst hat are neededi n many environmentalp rocesss tudies,a nd the
spatiala nd temporalo bservationc onsistencayn d detail requiredf or climate-changes tud-
ies. Sensorsa lsop rovidet he meansf or extrapolatingo bservationfsr om shipsa nd surface
stationsa nd for evaluatingth e global( aso pposedto local) impacto f mesoscalep rocesses.
A dominanta specto f theA rctic Oceana ndi ts adjacents easi s their sea-icec over.A lthough
it is just a thin sheet( a few meterst hicko n the average)c omparedt o the deptho f the ocean,
thei ce covero ccupiesa vasta reaa ndi s knownt o havea profoundin fluenceo n thep hysical,
chemical,a nd biological characteristicso f the ocean. In particular,t he ice cover alters
surface ocean salinity through brine rejection where ice is formed and through the
introductiono f low-salinity water in the melt regions.I t is also an effectivei nsulating
interfaceb etween the ocean and the atmosphered uring winter, and a good reflectoro f
radiationd uringt he summer.S ea ice modifiest he oceand ynamicallyd ue to friction at the
ocean/iceb oundaryl ayer. Furthermore,s ea ice suppressesth e penetrationo f sunlight
neededb y marine life during photosynthetipc rocessesa nd impedest he mixing effect of
wind. Also, in the middle of the ice pack are surfacef eaturesl ike leadsa nd polynyas,t he
occurrenceo f which alter the heat, humidity, and salinity fluxes and the ventilationa nd
circulationc haracteristicos f the underlyingo cean.W hile processesin the ice covered
portiona re uniquea nd important,p rocessetsh at continuallyo ccura t or adjacentt o the ice
edge shouldn ot be overlooked.T he marginali ce zone, a very activer egion that includes
the ice edge,i s the site where interactionsb etweent he ocean,i ce, and the atmospheraer e
mosti ntenseA. lso, abouth alf of the winteri ce coverd isappearsd uringt he summerm, ainly
in the continentals helfr egion,w herep lanktona nd otherm arine life go throughm assive
seasonavl ariations.W ithout the aid of remote sensing,m any of these and other Arctic
processecsa ng o undetectede, speciallyin winter,w heni ce is moste xtensivea ndt her egion
is in near-total darkness.
The various geophysicalp arametersi n ice-coveredr egions that can be derived from
satelliter emote-sensingd ata are sea-icec oncentrationi,c e type, ice velocity, physical
surface temperature,s now cover, surface roughness,c loud cover, and surfacem elt
conditions [Gloersen and Salomonson, 1975; Thomas, 1990; Massom, 1991; Comiso,
1991]. In the adjoiningi ce-free areas,t he correspondingp arametersa re phytoplankton
pigmentc oncentrationc,l oud cover,s eas urfacet emperatureW, indv elocity,t opography,
precipitationa, ndw avep ropagationc haracteristic[sW ilheit andC hang,1 980;W entze t al.,
1986; Baker and Wilson, 1987; Apel, 1987; McClain et al., 1993]. No singles ensorc an
provided ata for all theseg eophysicapl arametersa, nd the accuraciesin the determination
of someo f them may be marginal.N ew sensorsw ith improvedc apabilitiesh ave been
launchedr ecently and even more versatileo nes are expectedi n the near future. The
accumulationo f long-termd ata setso f parametersi,n cludingi ce concentrations, urface
temperaturec, loud cover,a nd phytoplanktonc oncentrationw ould providea n invaluable
resourcefo r Arctic- andE arth-sciences tudiesT. his chapterp resentsa review andu pdateo f
presenta nd future
Comiso 3
The Arctic EnvironmentsPhysicala nd Radiative
Characteristics
Remotes ensingd ataa re mostu sefuli f observablecsa n be consistentlya nd reliably inter-
pretedi n termso f geophysicapl arametersT. his requiresa goodu nderstandinogf what a
sensomr easuresa ndw hatp hysicalp ropertyo f the surfaceo f interestis beingo bservedF. or
example,i t is importantt o recognizet hat over seai ce, visibles ensorso bserves urface( i.e.,
skin) propertieso nly while microwaves ensorss ees ubsurfacec haracteristicsO. n the other
hand, over ice-free ocean, the reverse is true. In the case of sea ice, microwave radiances
may comef rom the snowc over,t he snow-icei nterfaceo r within the ice itselfd ependingo n
the wavelengtho f the radiation,t he type of ice, and statea nd deptho f the snow cover.I n
the openo cean,a lthought he surfacei s opticallyt hick for long wavelengthsi,t s radiative
andb ackscattecr haracteristicms ay be considerablya lteredb y thep resenceo f foam andb ig
waves.T o completelyu nderstandth e physicsb ehindt he observationsa, combinationo f
field measurementasn d radiativet ransferm odelingi s needed.T he physicala nd electrical
characteristicso f the different surfaces relative to the sensor should be measured, and the
propagationc haracteristicosf radiationa t differentw avelengthsa ndp olarizationw ithin the
media should be understood.
Efforts in this directionh aveb eenc onductedin the last severaly earsi n the Arctic region
(e.g., Marginal Ice Zone Experiment,S easonalI ce Zone Experiment,a nd Lead Experi-
ment).T he stateo f the art in measurementosf remotes ensingp arametersa t high latitudes
is summarizedb y Hallikainen and Winebrenner[ 1992] in the microwaver egion, and by
Steffene t al. [ 1993] in thev isiblea ndi nfraredr egionsA. lso, modelings tudiesin the micro-
wave,i nfrared,a ndv isibler egionsh aveb eenp erformeda t differentl evelso f sophistication
[Funga nd Chen, 1981;T sanga nd Kong, 1981; Ulaby et al., 1981-86; Grenfell, 1983; Per-
ovick, 1989], while studieso f the fundamentapl hysicala nde lectricalp ropertieso f seai ce
haveb eenu ndertaken[A ddison,1 969;V ant et al., 1978;W eeksa ndA ckley, 1982; Stogryn,
1985;T uckere t al., 1992]. In somec asest,h e surfacea nds ubsurfacper opertiesa re soc om-
plex that correcti nterpretationo f data may be difficult even with models.I n this section,
key observableisn theA rctic andt he environmentacl onditionsth atd irectlyr elatet o remote
sensingd ataa nd theiro bservationaal ccuraciesw ill be discussed.
The Sea-Ice Cover
The Arctic sea-icec overc onsistso f two main componentst:h e perenniali ce covera nd the
seasonailc e cover.T he perenniailc e cover,w hichc onsistso f predominantlmy ultiyeari ce
floes,o ccupiesa largef ractiono f theA rctic Ocean'sd eepr egionsd uringt he summerT. he
seasonailc e coveri s thatw hichc omesa ndg oesw ith seasona ndi s normallyl ocatedi n shal-
low and shelfw aters.I t is alsoc onvenientto divide the winter ice packi nto outera nd inner
zones.T heset wo zonesh aved istinctc haracteristicse,a chh avinga uniquer ole in the phys-
ical andb iologicalp rocesseisn the region.A erial photographssh owingt he outera ndi nner
zonesa re showni n Figures 1a and lb, respectivelyA. s shown,t he outer zone is a very
dynamicr egion where ice floes are distinctlys eparateda nd fragmentedb ecauseo f the
influenceo f wavesa nd atmosphericfo rcing,w hile the inner zonei s an almostc ontinuous
ice sheet,e xceptf or the occasionapl resenceo f leadsa nd
4 SatelliteR emoteS ensingo f the Arctic Ocean
' "a) OuteZr one
MIZ
b) Inner Zone
Figure1 .P hotographosf Arctics eai ce in (a) theo uterz onea nd( b) thei nnerz onei n theF ramS trait
on May 20,