U.S.
REVIEWS OF GEOPHYSICS, VOL. 25, NO. 2, PAGES 227-233,
MARCH 1987
NATIONAL REPORT TO INTERNATIONAL UNION OF GEODESY AND GEOPHYSICS 1983-1986
POLAR
OCEANS
Arnold L. Gordon
Lamont-Doherty
GeologicalObservatory
of ColumbiaUniversity
W. Brechner Owens
WoodsHole Oceanographic
Institution
We surveyprogressin studiesof ocean
observingperiod. Furthermore,eddy statisticsare resolved
circulation, water mass formation, and ocean-ice interaction
to sufficientdetail to allow meaningfulestimatesof eddy
fluxes of heat and momentumas well as partitioningof
energywithin a broadspectralband(figure 1).
The ISOS current meter and pressure transducer
1979-1980 time seriesin the Drake Passageindicate a
transportabove2500 metersof 125 Sv (Sverdrup(Sv) = 1 x
Abstract.
in boththe SouthernOceanandthe Arctic regionduringthe
period 1983-86. This review placesemphasison U.S.
publications,
butothersignificantworkis included.It is not
meantto be a completesynthesis
of polaroceanography
of
the last four years, but rather to provide an overview of
progress.Thereare articlesincludedin thereferencelist not
106m3/sec)
witha standard
deviation
of 10Sv(Whitworth,
1983; Whitworth and Peterson,1985). The baroclinicmode
cited in the text.
accounts
for 70% of thetransport,with thebarotropicmode
accounting
for theremaindermainlyat the higherendof the
frequencyrange. The pressuretransducerdata set (from
sensorsplaced at 500 meters depth on both sidesof the
Drake Passage),which extendto March 1982 (Whitworth
andPeterson,1985) agreeswith the currentmeterresultsto
Southern Ocean
The polar oceanographiccommunity lost a valued
member when Sir George E. R. Deacon died on 16
November1984 (Chamock,1985). Sir Georgeestablished
the basisof understanding
for the SouthernOcean,upon
whichmuchof thepresentresearch.
is built.
within 24 Sv.
SignificantvariabilityoccurswithintheACC at a variety
of spatial and temporal scales.It extendsthroughoutthe
There were three main streams of research in Southern
Oceanoceanography
duringthe 1983-1986period. These
water column (Klinck and Hofmann, 1986). However, time
are: advances in our understan•ng of the Antarctic
CircumpolarCurrent(ACC) dyna.,mics
stemmingfrom the
productive observational program of the 1970's, the
InternationalSouthernOcean Studies (ISOS); water mass
lags of one to three days are observedin the deeplevels
relativeto the 500 metervariability,whichis attributedto the
effectsof local bottomtopographyratherthanadvectionof
disturbancesthrough the Drake Passage (Klinck and
Hofmann, 1986). Energeticand deep-reachingmesoscale
tings, generatedprimarily by baroclinicinstabilityalongthe
structureand modification,primarilywithin the Weddell
Gyre; andthe oceanography
of the continentalmarginsof
Antarctica.
various frontal zones associated with the ACC,
Data derived from satellitesare increasinglylinked to
progresswithin these areas. They provide a large scale
synopticview of the SouthernOcean,unattainableby any
are
commonly observedmoving through the Drake Passage
(TableI, from Nowlin andKlinck, 1986). They are strongly
influencedby topography(Pillsbury and Bottero, 1984;
Holmann and Whitworth, 1985); they, in turn would effect
the transport through the deep passages(Klinck and
Hofmann, 1986).
other method. The 3 month Seasat•fimeter data setreveals
low frequency,large scalevariability of the ACC, with a
generalacceleration
towardstheeast(Fu andChelton, 1984,
1985). Seaice trendsduringthe mid:1970'swere recorded
by passivemicrowaveradiometers(Zwally et al, 1983).
This coveragealong with visible and infra-red imagery, is
establishing
a mostusefulfully circumpolar
time seriesof ice
cover. StumaanandAnderson(1985) cornparetheestimates
The eddyfield associated
with the ACC continuesto
attractinterest,sinceit appears
to be significant
to theoverall
heat,freshwater and perhaps,momentumbalanceof the
region. The sourceof thesefluctuationsappearsto be
barotropic
andthefirst modebaroclinicinstability(Inoue,
1985). The fastestgrowingwavesare at 183 km wave
of seaice cover basedon satellitedata since1980, carriedout
by a numberof authors;theyconcludethatthe estimatesare
techniquedependent,e.g. meanmonthlyseaice areafrom
the variousestimatesvaries by approximately2 million
squarekilometers.
Duringthe 1979-19821UGGperiodtherewere a series
of review articles and atlases pertaining to polar
oceanography(see the IUGG polar oceans review of
lengthin thenorthern
DrakePassage
(subantarctic
zone)and
91 km in the southcontinentalmargin zone, with growth
ratesof 3 to 5 daysin thefrontsand15to 40 daysbetween
fronts. Measurementof velocityfluctuationssoutheast
of
New Zealand,near49ø 30' S, 170øW overa two yearperiod
(BrydenandHeath, 1985)revealsenergeticeddieswith
characteristic
amplitudesof 20 cm/secat 1000 metersand
temporalscaleof 20 days. Thesefeaturesare vertically
coherentto 5000 meters,with onl'f a slighttendencyfor the
deeperflow to lead the shallowerexpressionof the
fluctuations. The eddy kinetic energy decreaseswith
Gordon,1983). Thistrendcontinues
intothepresent
period
with a reviewof ACC research
by Nowlin andKlinck (1986)
and a study of the ACC characteristicsby Sarukhanyan
(1985). JoeReid (1986) produceda comprehensive
study
on the South Pacific circulation,which includesa large
segmentof the SouthernOcean. Foster(1984) providesa
generalreview of the SouthernOcean.
increasing
depth
from169cm2/sec
2at1000meters
to58and
38 cm2/sec2
at 2000and4000metersrespectively.
These
values are similar to those found in the northern Drake
AntarcticCircum_tx)lar
Corr•nt
Passage
andrelativelyenergetic
in comparison
to theGulf
We now havereliablevaluesfor the ACC transportand
A compilation
fromnumerous
sources
indicates
thatthe
totaloceanicheatlosssouthof 60ø S is approximately
5.4 x
Stream or Kuroshio.
variabilitythroughthe Drake Pa,ssageduringthe ISOS
10!4Watts,with 3.1 x 10!4Wattsof oceanic
heatlossfor
theregionsouthof the ACC (approximately
53øS for the
circumpolar
average;
figure2). Largeoceanicheatlossto the
atmosphere
southof 60ø S is supported
by 1986 austral
Copyright1987by theAmericanGeophysical
Union.
winter measurements obtained from the POLARsTERN
Paper number 7R0070.
8755-1209/87/007R-0070515.00
alongtheGreenwich
meridian,particularly
in thevicinityof
227
228
Gordon and Owens: Polar Oceans
across
theentireDrakePassage
of 3.7 kW/m2. However,
15.1kW/m2,isaccomplished
inthenorthern
DrakePassage,
witha valuecloser
to40kW/m2fortheupper1000meters.
Thisis closetothevalue(30kW/m2)reported
forthe1000
64Z
46•
S42
50dll••_l
TM
I 31Z
I 2d>T>2
hr I
271•
38z
33•,
I
I
I,ne•ml
Osclllattons
J
49•
I Indturnal
plus
semiI
I
dturnll
ttdM
b•nds
I 56•
1oz
I
lnte•
characteristic
of thenorthernsideof thePassage,
whichis
most appropriatefor comparisonto the oceanic heat loss
south
of theACC,wouldp.roduce
fourtimestherequired
445
heat flux. However, in v•ew of the large uncertaintyin
estimatingoceanic heat loss south of the ACC and the
I Coherent! I Hotc(•erent I
wtth ttdal I
I wtth I Idal
meter level alongthe northernedgeof the ACC southeastof
New Zealand (Bryden and Heath, 1985).
While
extrapolationof the averageDrake Passagevaluefor the full
depthcircumpolarbelt yieldsnetpolewardheatflux roughly
equivalentto the oceanheatlosssouthof the ACC, the value
I
questionable
reliability
of extrapolating
DrakePassage
values
Fig. 1. Partitioningof kineticenergyof horizontalmotionsat
Drake Passage.Fractionsshownaboveboxesare averages
for entirepassage;thosebelow the boxesare averagesfrom
the central passagelocations. From Nowlin, Bottero and
Pillsbury, 1986.
Maud Rise.
Northward mass flux within the surface Ekman
layercarriesapproximately30 Sv acrossthe ACC. Sincethis
water is warmer than the averagetemperatureof the water
southof the ACC, the Ekman transporteffectivelyexports
heat from the ocean south of the ACC.
When this amount is
included in the net heat loss to the south, the total
requirementfor polewardheatflux acrossthe ACC increases
to 4.6 x 10TMWatts(deSzoeke
andLevine,1981;Nowlin
and Klinck, 1986).
There are a number of mechanisms which could account
for this flux: mean flow, eddy field and deep boundary
currents.The meanflow is ruled out as being significantin
regard to meridional heat flux by deSzoeke and Levine
to the full circumpolarbelt, the agreement,at least,indicates
that eddy flux is the best candidate for maintenanceof
thermal balance of the SOuthern Ocean.
Analysisof FGGE drifter data set hasproduceduseful
results. Peterson (1985) compares drifter tracks to the
extensive1979 ISOS currentmeterarray. The deepflow as
measuredby the current meters was well reflected in the
driftertracks.Deviationscorrespondto thewindactionon
thedriftersandon the surfacelayerof theocean.The drifters
generallymovedat 3.4% of thewind speedat an angleof 25ø
to the left of the wind. Hofmann (1985) and Patterson
(1985)discuss
largescalecirculationpatternsrevealedby the
drifters. Pattersonprovidesmapsof the mean and eddy
kineticenergydistributions.Thesecomparefavorablywith
mapsproducedfrom hydrographicdata and from Seasat
altimeter (Cheney, Marsh and Beckley, 1983). A clear
relationship between ACC characteristics and bottom
topographyis observed. Hofmann (1985) finds that the
driftertracksrespondto thebasicmulti-filamentnatureof the
ACC.
(1981). The near bottom currentsof cold Antarctic Bottom
Water (AABW) balancing southward flowing warmer
Water Masses(Weddell Gyre)
CircumpolarDeep Water (CDW), might accountfor 25%,
but direct measurement of these features are needed to assess
this means of heat transfer.
Estimatesof the eddy heat flux indicatethat at scales
fromthe4 to 90 daysin theDrakePassage
(Nowlin,Worley
andWhitworth,1985)andfrom20 to 50 dayssoutheast
of
New Zealand(Brydenand Heath, 1985), eddy activity
provides
for significant
poleward
heatflux. Nowlin,Worley
andWhitworth(1985)determine
anaverage
eddyheatflux
The southern extreme of the South Atlantic sector of the
SouthernOceanis occupiedby a largesluggish
flowingbut
deepreachingcyclonicgyre,theWeddellGyre. The water
masscharacteristics
within the gyre suggestthat it is the
source of much of the bottom water for the world ocean.
Interestin the watermassformationanddeepventilationin
thisareagrewafterobservation
of anisolatedwinterperiod
Table 1. Estimatesof PropertyAnomaliesfor Select SouthernOceanCurrentRings
From Nowlin and Klinck, 1986
Petersonet al. [ 1982]•'
Pillsbur),and Bottero
[1985]:]:
Joyceet al. Relativeto PFZ Relativeto SAZ
[1981]* Characteristics
Characteristics
Anticyclonic
Cyclonic
Available
potential
energy,
J 5.1X 1014
......
Kineticenergy,
J
3.4x 10t4
......
HeatanomalY,
J
1.2x 10t9 0.8x 10t9
3 x 10t9
Saltanomaly,
kg
8 x l0 tt
2.5x l0tl
2.0x l0 tl
0.9X 1014 3.9X 1014
0.5x 10t4 1.5x 10"4
1.0x 10t" -1.9 x 10t"
".....
*Anomalies,relative to Polar Front Zone characteristics,
were integratedbetweena, = 27.0 and 27.7
(approximately
seasurface
to !500m in PFZ)based
ona section
through
a 1975cyclonic
ringin the
PolarFrontalZone.Kineticenergyis basedon gcostrophic
speeds
relativeto 2800dbar.
•Anomalies
integrated
froma, = 27.0to 27.8(approximately
seasurface
to 2500m in thePFZ) based
on a verticalsectionthrougha 1979cyclonicringin the Polar FrontalZone.
•:Valuesof velocities
and tcm•raturesobtainedfroma symmetricringmodelwith parameters
deter-
minedby timeseries
observations
of theseparameters.
Valuesshownon theleftarefor an anticyclonic
ring of Polar Frontal Zone waterand thoseon the right are the averagefor five cyclonicringsof
continentalwater,all observedin the AntarcticZone. Anomaliesrelativeto AntarcticZone character-
isticswereintegrated
downto 35.00m asa nominalbottomdepth.
Gordon and Owens:
30-
Polar Oceans
229
passive microwave (SMMR) data, in order to establish
improvedunderstanding
of the satellitesignal. Different
sensitivities
z
• •20-20 •
"' •0-
•
-•0
o
IO1972
• OCEAN
HAT
SOUTHOF
60øS
(Gordon
1981)
/man
13xLOSS
1013col/see
/ Bunker
P.C.
\
I
i/
s0os
53øS
.54.x 101:5
watts
\1
60øS
SMMR
channels to ice
as the Weddell-Scotia Confluence, between the Weddell
ß ß 70øS'•
which increases downstream from the initial contact of the
9
Gord•on\/
Huber
1984
1972
P.C.
1972
•
• Gordon
1981
-30-
OCEAN
two circulation regimes. The sea ice along this front is
investigatedwith the shuttleimagingradar-B (SIR-B) by
Carseyet al (1986). ComisoandSullivan(1986)compare
passivemicrowavedatafrom satellitewith field observations
alongthe ice edgeof theregion.
\Fletcher
1969
!•dSHELF
zm•eon\
'3'5
/
Zillmon
Bunker
Sieversand Nowlin (1984) discussthe water massand
frontal zone structureof the water enteringthe ScotiaSea
from the Drake Passage.The frontalzone,oftenreferredto
Gyre and the Scotia Sea is discussedby Foster and
• eee IE•---'•S
ICH
ELFMiddleton
(1984). This regionhasintenseeddyactivity,
/
-
ATMOSPHERE
HEAT
ß ß ß ß
of the various
characteristics
are found:the 18 GHz providesthe best
description
of thespringice edge.
OCEAN
HEAT
FLUX
GLACIAL
FLUX
ICE
Fig. 2. Ocean-atmosphere
heatexchangefor thecircumpolar
area south of 47 ø S. The values are drawn from numerous
sources,as indicated.
ContinentalMatins
The continentalmarginsare the focusof a collectionof
articlesin a AntarcticResearchSeriesvolumeeditedby S.
Jacobs(1985). The followingpresents
anoverviewof some
of these articles.
The WeddellSearegionis discussed
by Foldviket al
(1985a,b)usinghydrographicandyear-longcurrentmeter
data. They providea full hydrographic
sectionalongthe
barriers of the Filchner and Ronne Ice Shelves. Ice shelf
ice free region, now referredto as the Weddell Polynya
(Carsey,1980). Parkinson(1983) providesthe mostrecent
modellingattemptof thepolynya.ComisoandGordon(in
press)presentpassivemicrowavedata which indicates
recurring
polynyasin thevinicityof MaudRiseandnear65ø
S and 45ø E (CosmonautPolynya). These polynyasare
smalleranddo not persistfor the entirewinter,but eachis
associated
with shallowingof the pycnocline,consideredto
be aneffectivepreconditioner
for convection.
TheGreenwich
meridian
regionwasinvestigated
during
Octoberand November1981 duringthe US-USSR Weddell
Polynya Expedition, aboard the Soviet ship MIKHAIL
SOMOV. The SOMOV, which attaineda southernpoint of
62.5 ø S, about 550 km southof the ice edge, provided a
significantdata setpertinentto the studyof seaice, sea-air
exchange,
physicalandchemicaloceanography
andbiology
(thecollectedreprintsof theprojectareavailable,Ackleyand
Murphy,1986). In the australwinterand springof 1986
moreextensivework was cardedout from the Germanship
POLARSTERNover a six monthperiod, reachingthe
continental margin and covering the region from the
Greenwich
meridian
to the eastern side of the Filchner
Depression
in theWeddellSea.
Using the SOMOV dataGordonand Huber (1984) and
Gordon, Chen and Metcalf (1984) report that the mixed
layer below the sea ice is slighdy above freezing (average
+0.035ø C) and is undersaturated
(86% of full saturation)in
oxygen.This conditionis attributedto entrainmentof deep
water into the surface mixed layer, brought about by
buoyancy flux at the sea surface and perhaps more
importantly, mechanical stirring due to relative ice
movements.The incorporationof deepwater heat and salt
appearsto be a significantfactorin the heat and freshwater
balance,and to have an importantimpact on the sea ice
wateris observed
leavingtheFilchnerDepression
forminga
slopeplumewith a transport
of 1 Sv producinga totalof 2
Sv of newAntarcticBottomWater. Thecurrentmeterarray
at the shelfbreakdisplaysstrongtidal currents,dominated
by the solardiurnalcomponent,
thoughthis component
weakensduringthe winter,perhapsin response
to reduced
thermohaline stratification.
Currentsand temperaturealong the RossIce Shelf
Barter arepresented
by PillsburyandJacobs(1985). These
measurements
were obtainedJanuaryto August 1978 and
fromFebruary1983through
January
1984aspartof a study
of the exchangeof waterbetweenthe openoceanand the
water below the Ross Ice Shelf. These data show that the
warmwaterfeatureapparentin summerhydrographic
data
between 170ø and 175 ø W flows into the ocean volume below
thefloatingice shelf. Typicalvelocitiesare5 to 9 cm/sec.A
mooring within the colder water to the west reveals flow
away from the ice shelf, in a pattern consistentwith
circulation schemes inferred from water mass considerations.
Higherkineticenergylevelsareevidentduringthewinter,as
are generallylower averagetemperatures;
thoughwarm
eventsarecommonduringthe winter.
The overall water mass structureand budgetsare
discussed
by Jacobset al (1985), usinghydrographyand
stableisotopes
of oxygenandhydrogen.Warmslopewater
spreads
ontotheshelfwhereit is modifiedby theatmosphere
and interactionwith the glacial ice, to form variousshelf
water masses.The slopewater providesthe primary heat
sourcefor meltingof glacialice. A bestestimatefor shelf
water residencetime is 6 years with a total circumpolar
bottomwaterproductionrate of 13 Sv, accompanying
0.4
meters/year
of basalice shelfmeltingandseaiceproduction
of 1.9 meters/year.
Oceanography
relatedto theglacialice is thesubjectof 4
otherpapersin thevolume. MacAyeal(1985a,b)reportson
budget. The SOMOV datarevealeda seriesof warmdeep
the results of a numerical model of tidal flow below the Ross
water cells, accompaniedby shallowingof the pycnocline
(Gordon and Huber, 1984). Their spin down dynamicsis
investigatedby Ou and Gordon (1986), who find that the
cells survive for long periods and may be effective
preconditioners
for deepconvection.
Comiso, Ackley and Gordon (1984) relate the sea ice
observationsfrqm SOMOV to the NIMBUS 7 satellite
Ice Shelf. Rectificationof theperiodictidalcurrentsinduces
a largescalemeancirculation
patternthatmaybe a factorin
theheatandmassexchange
betweentheiceshelfregionand
theopenocean.The rectification
associated
with Roosevelt
Islandmay initiatethe flow of warm shelfwaterinto the
sub-ice ocean volume near 170ø-175 ø W. However, tidal
rectification
is notsufficient
by itselfto ventilate
theentire
230
Gordon and Owens: Polar Oceans
water volume below the ice shelfat the rate suggestedby the
stableisotopedata; thermohalinecirculationis required.
However,tidal rectificationmay alsocontributeby triggering
thermohaline
plumesof meltwater,at depthsgreaterthan550
m. The Coriolis force attenuatesthis process,unlessthe
plumesare channelled,as is the caseunder the GeorgeVI
ice shelf.
Potter and Paren (1985) report ocean glacial ice
interactionat theGeorgeVI ice shelf,whichis locatedwithin
a narrow channel between the west coast of the Antarctic
Peninsula
andAlexander
Island.Strongmeltingis induced
by relativelyWarmwater(about! oC) whichflowsfromthe
circumpolardeepwatermassto belowthe glacialice by way
of thenorthernbarrier(Marguerite
Bay). Thiscirculation
patternmeltsbetween1.1 to 3.6 meters/year
of glacialice,
whichmay accountfor one-sixthof the totalglacialice loss
(assumingequilibrium).
Injection of glacial ice melt water into the ocean is
discussed by Schlosser (1986) and Jacobs (1986).
Schlosserfinds a supersaturated
helium layer which he
attributesto glacialmelt water,derivedfrom the air bubbles
trapped in the ice and freed upon ice melting. Jacobs
discusses
thepossiblerole of glacialmelt waterin formation
of bottom water, at least as a tracer.
Passive microwave
radiometer
measurements
from
NIMBUS satelliteshaverevealednumerouscoastalpolynyas
with widths of a few hundred kilometers
at various sites
aroundAntarctica(Zwally et al, 1985). Coastalpolynyasare
primarilylatentheatfeatures,in thatthelargeheatflux to .the
atmosphere
is maintained
by releaseof latentheatof fusion
asice formsandis thentransported
awayby thewind. This
processmay be an importantfactorin increasingthe shelf
water salinity,enoughto allow deep-reaching
continental
marginconvection
(Zwally et al 1985;CavalieriandMartin,
1985). The amountof ice formedwithin thesepolynyasmay
be aslargeastensof metersperwinter,elevatingshelfwater
salinityby approximately
0.3 ppt. A recurringpolynyain
TerraNovaBay,justnorthof theDrygalskiIce Tongue,also
appearsto be a latentheatpolynya(KurtzandBromwich,
1985). It may play a role in supplyingsalt to the high
salinityshelfwaterof theRossSea.
Arctic Circulation
Since the last review, there have been significant
developments
in thedescription
of theflow withinboththe
halocline
anddeeplayersof theArctic"Mediterreanean"
Sea,
thatis theArcticOceanandits surrounding
seasthatlie north
of the Greenland-Scotland
ridge. This work supportsthe
earlierwork of Aagaardand co-workers(Aagaard,1981;
Swift and Aagaard, 1981; Aagaard, Coachman, and
Carmack, 1981).
Circulation
and water masses
Within the central Arctic, water massformation along
continentalmarginsof the Arctic, rather than inflow of
GreenlandSeadeepwater,appears
to bethesourcefor water
lyingbelowthesalinitymaximum.Therecentworkis based
on new high quality hydrographicand geochemicaldata,
particularlyfrom the Iceland,Greenland,and Norwegian
Seasandfrom theArcticOceanin thevicinityof FramStrait.
ThisdatawascollectedduringtheTransientTracersin the
usedto calculatepotentialdensitythereis no possiblepath
for deep water formed in the Greenland Sea or in the
EurasianBasinto enterthe CanadianBasin. Similarly, they
showthatthe'only
deepwaterthatenters
theEurasian
Basin
throughFram Strait(NorwegianSeaDeepWater overlying
fresherGreenlandSeaDeepWater)cannotproduceEurasian
Basin Deep Water without additionalair-seaheat or mass
exchangewithin the Arctic basin(Swift, Takahashi,and
Livingston,1983). Concentrations
of radionuclidessuggest
that a significantfraction of this water is formed on the
BarentsSea shelf by atmosphericcooling. However, this
neednotincludebrineproductionduringice formation,asis
thecasein theCanadian
basin,butonlyatmospheric
cooling.
The inflow of DeepGreenlandSeawaterthroughthe Fram
Straitmixeswith the waterproducedon the shelfto givethe
freshetEurasian
BasinDeepwatercompared
to thatin the
Canadian basin. The shallow sills to the south exclude these
deepwatersfromentering
theIcelandseaand,in turn,the
North Atlantic. As a result the deep circulationmust be
internallyrecirculatingwith diabaficmixing balancingthe
shelfandmid-gyredeepwaterproduction.
It nowappears
thatthemid-gyrebottomwaterformation
withinthe GreenlandSeais alsoa morecomplicated
process
than previouslydepicted. As it nears Fram Strait, the
intowing Atlantic Water bifurcates, with some water
circulatingwestwardas in the northernpart of a Greenland
Sea gyre (Aagaard,Swift and Carmack, 1985) and some
enteringthe Arctic Ocean. Within the Arctic this water is
continuously
mixedwith colder,freshetwaterformedon the
continentalmargins(Aagaard, Coachman,and Carmack,
1981). It thenexits in a narrowcurrenton the westernsideof
FramStraitandappearsin thewesternGreenlandSeawith
localpotential
density
equalto Greenland
SeaDeepWater.
Aagaard,Swift and Carmack(1985) arguethat the vertical
and horizontal confinement of this water is caused by
compressibility
androtational
effects,
respectively.
Mixing
by doublediffusionbetweenthesewatersand the Ariantic
watermay be partialsourcesfor GreenlandSeaDeepwater
(McDougall,1983).
Smethie,Ostlund,andLoosli(1986) haveuseda simple
box model to estimate residence times of the Greenland Sea
and Norwegian Sea deep water and the transportsbetween
the surfaceanddeeplayersof the GreenlandSeaaswell as
between the deep waters of the Greenland Sea, the
NorwegianSea and the Arctic Eurasianbasin. They found
shortresidencetimes,approximately10 yearssouthof Fram
Strait, and interbasintransportsconsistentwith the above
circulation
scheme.
Other
recent
measurements
and
analysesof radionuclidessuggestthat the residencetimes
withintheupperlayersof theArcticMediterranean
arequite
short,with renewal occurringon time scalesof 2-10 years
(Aagaard,Swift and Carmack,1985). Using only isotope
and salinity data, Ostlund (1982) and Ostlund and Hut
(1984)estimate
thattheaverage
residence
timein both'the
surface and pycnocline waters of the Arctic Ocean is
approximately10 years.
Eddy Variabiliw
The decreased residence times within these layers
compared
to thosebasedon meancirculationadvection
may,
to a largedegree,be dueto strongmixingby a veryvigorous
eddyfield. Manley andHunkins(1985) haveshownthatthe
Ocean(TTO) cruiseaswell asmorerecenthydrographic Arctic Oceancontainsmany small scale,intenseeddiesat
surveys
of theregionby Clarke,Swift, andKoltermann
depthsbetween
50 and300 metersdepth. Withinthe
(Aagaard, Swift, and Carmack, 1985; Koltermann and
CanadianBasin,theseeddiesmayoccupyup to onefounJ•of
the area. Water property anomalieswithin the eddies
Swift, in preparation;
Smethie,Ostlund,andLoosli,1986).
Similar quality data has also been gatherednear the
Lomonosov
Ridge(Moore,Lowings,andTan, 1983).
In a excellentsynthesisAagaard,Swift and Carmack
(1985) showthatwhenan appropriate
deepreference
levelis
suggests
that they originatenear the ChukchiSea and
Alaskan Shelf.
DuringtherecentArcticInternal
WaveExperiment
in the
BeaufortSea, D'Asaro(in preparation)was able to survey
Gordon and Owens: Polar Oceans
severalof these eddies describingtheir dynamic structure
fromvelocityanddensitydata. Theseeddiesoftenappearin
pairs,althoughthey appearedto separate
quickly,possibly
due to mean vertical shear. Their dynamicsignatureswere
quite strong, with potential vorticities approachingthe
magnitudeof thelocalCoriolisparameter.
Very strongeddyactivityhasalsobeenobservedin the
marginalice zonesin boththe BeringSea(Muench,1983)
and in the Greenland Sea (Smith, Morrison, Johannessen,
and Untersteiner, 1984; Wadhams and Squire, 1983).
Further descriptionsof these eddies and their role in
determiningthe structureof themarginalice zoneshouldbe
published
soonasthedataobtained
duringthe 1984Marginal
Ice ZoneExperiment(Johannesen,
et. al. 1983)areanalyzed.
Sea Ice - Ocean Interactions
The
interaction
of the sea ice with
rejectionand mid-gyre convection,both of which occuron
smallscales.Hibler andWalsh (1982) alsohaveinvestigated
the seasonal
andinterannualvariabilityof Arctic seaice.
OngoingandFutureWork
Within
the Southern Ocean there is a need to extend the
resultsof the Drake Passageresearchto the full circumpolar
belt. While the ACC does have many featureswhich are
invariant with longitude, there is significant spatial
variability. Thesechangesappearto be relatedto the nature
of thebottomtopography.
The ACC is a well definedjet-like
flow over high relief featuresbut more diffuse over broad
abyssalbasins. The intensity of temporalvariability also
varies spatially in a pattern suggesting response to
topographic
features.The exactnatureof thiscouplingneeds
to be defined.
the ocean
has
continuedto be an active area of research. McPhee (1983)
hasinvestigatedthe transferof momentumandheatthrough
theoceanicboundarylayer.Interactions
betweentheinternal
wave field and the ice edgehave been studiedby Muench
(1983) in the Bering Sea. Muench, Hendricks,and Stegen
(1985) have estimatedthe heat budgetin the vicinity of the
ice edgein theBeringSea. Furtherwork canbe expectedas
the MIZEX-84 data is analyzed. Hakkinen (1986a, b)
investigatesthe ocean-icecouplingwithin the marginalice
zone. Wind generationof vertical circulationand eddies
(inducedfrom instabilityof an ice edge current)at the ice
margin influences the nature of the ice edge and may
preconditionthe oceanfor convection.
Shelf Processes
The Drake PassageISOS results must be reliably
extended to the full circumpolar region. To do this
measurementof mean flow and eddy variability like those
alreadyobtainedin the Drake PassageduringISOS, should
be extendedto the full circumpolarregion. With suchdata
thezonallyintegratedbalances
of heatandmomentumfluxes
can be investigated. Simple extrapolationof the Drake
Passageresultsis risky beforethe representativeness
of the
Drake Passagefor the full circumpolarbelt is determined.
There is still the major questionas to how the wind energy
introducedinto the ACC is dissipated.The eddyfield seems
inadequateas doesthe bottomstress;form dragis a likely
candidate.
Polewardof the ACC thereis majorlossof oceanicheat
to theatmosphere
througha seasonal
andoftenpartialseaice
cover.
Associated with this exchange is water mass
modification
As was described above, it is now clear that shelf
processes
are importantbothfor their economicsignificance
and for their role in producing,or modifying, water masses
throughout
the watercolumnin theArctic Ocean. As partof
their synthesisAagaard, Swift and Carmack (1985) also
show some new data from the Alaskan shelf and slope
indicating significantsalinity increaseby brine rejection
induced by ice formation. Melling and Lewis (1982)
describe plume drainagedown the continentalslopein the
CanadianBeaufortandpresenta gravitydrivenmodelof the
flow. The effectsof a polynya on the productionof cold
water over the Bering shelf are discussedby Schumacher,
Aagaard,Pease,andTripp (1983). Usingcurrentmeterdata
Aagaard, Roach, and Schumacher(1985) have studied
variationsin the flow from the shallowBering Sea into the
ArcticoceanthroughtheBeringStrait.
Modeling
Semptner
hascarriedoutthreeseparate
modeling
efforts
focused on seasonal to climatic time scales in the Arctic
Ocean. He studiestheresponse
to Sovietriver diversions,
usinga primitiveequation
modelintegrated
to steadystate
with a crudeice boundarycondition. Two caseswere run,
onewithclimatological
runoffandonewithdecreased
river
outflow.It appears
thatthereis increased
icebuildupdueto
decreased
inflow of warmAtlanticwater(Semptner,1984a).
A simpleone dimensional
ice-modelhasbeenusedby
Semptner
(1984b)to investigate
theeffectsof changes
in
atmospheric
carbon
dioxide.Semptner
(submitted)
hasalso
developed
a newnumerical
model,
usinga simplified
version
of Hibler's (1979) ice modelappropriateto seasonaltime
scales.Simulations
of theseasonal
cycleappearquiterobust
in termsof iceextent,butfail topredicttheobserved
ratesof
deepwaterformation.
Thisdeficiency
isprobably
duetothe
coarse resolution of the model and lack of a new
parameterization
of suchsmallscale
processes
asshelfbrine
which leads to ventilation of much of the world
ocean. Exchangeof waterandgasessuchas CO2 is also
consideredto be large. While progresshas been made
recently in gaining a quantitativeunderstandingof these
fluxes, much more remains to be done if the Southern Ocean
is to be well represented
in the globalscaleclimatemodels.
Included in this requirementis better understandingof the
interactionof theoceanwith the glacialice.
The extensive Southern Ocean data set obtained from the
POLARSTERN during the austral winter of 1986 in the
Weddell gyre region, will be analyizedduringthe coming
years. This shoulddo muchto expandour understanding
of
winterand springoceanatmosphere
ice interaction.
Becauseof the difficulties of working in ice covered
regionsthereare few directmeasurements
of the currentsin
the polar regions. Increaseduseof instrumentedmooredor
drifting monitoring arrays; acousticalmethods, such as
SOFAR/RAFOS floats, tomographicmethodsand doppler
profilers,woulddramaticallyextendour knowledgeof polar
oceandynamics.Thesestudiesshouldbe closelycoupledto
observations from satellites. CTD hydrographic work
coupledwith tracergeochemistry,would be mosteffective
in the investigationof watermass formationandof specific
features within both the Arctic Seas and Southern Ocean are
needed. Theseobservationaltechniquesshouldbe planned
andconsidered
in conjunction
with modellingefforts.
Sincethe Fram Straitis suchan importantchokepointin
the circulation of the Arctic Mediterranean, a monitoring
programof currentmetersacrossthe widthof the straitwas
begunin 1984by Aagaard.This workhascontinued
under
the direction of Meincke and Aagaard and will provide
estimatesof the flow throughthis passagefor at leastthree
years.We canexpectimportantresultsfromthesemoorings
to appearin thenearfuture.A majorinternational
experiment
aimedat the circulationanddeepwaterproductionprocesses
in the GreenlandSeais in the final planningstagesandis to
beginin 1988.
As was mentioned above in the section on eddy
232
Gordon and Owens: Polar Oceans
variability, in May 1985 an experimentto examinethe
internalwave activityin the BeaufortSeawas carriedout.
Preliminaryindications
arethattheinternalwavefieldunder
the ice is 1-2 ordersof magnitudelessenergeticthanin the
open ocean(D'Asaro, in preparation;C. Morrison and
Paulson,personalcommunication).
This resultclearlyhas
importantimplicationsfor the role of varioussourcesand
Acknowled•ment_s.
The oolar research of ALG is
supported
by theDivisionof PolarPrograms
of NSF, Grant
DPP8502386.Thepolarresearch
of WBOis supported
by
the Office of Naval Research,GrantN00014-86-C-0050 and
NSF, Grant DPP 85 18747.
sinks for internal waves.
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