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Sensitivity experiments to sea surface temperatures,
sea-ice extent and ice-sheet reconstruction, for the Last
Glacial Maximum
Gilles Ramstein, Sylvie Joussaume
To cite this version:
Gilles Ramstein, Sylvie Joussaume. Sensitivity experiments to sea surface temperatures, sea-ice extent
and ice-sheet reconstruction, for the Last Glacial Maximum. Annals of Glaciology, International
Glaciological Society, 1995, 21, pp.343-347. �10.3189/S0260305500016049�. �hal-03011873�
.-ll1l1all oJ (;Iaciolog), 21 1995
C International Glaciological Societ\'
Sensitivity experiIllents to sea surface teIllperatures,
sea-ice extent and ice-sheet reconstruction, for the
Last Glacial MaxiDluDl
G.
R,\\ISTEL\Laboraloire de .Iiodel/salioll d" Chl1wl el de l'EIIl'irollllelllenl CE \. Sad(~)'. Bal. 709. GiFl'1Ir-Jioelle 91191, Frallce
S
.
JOUSSAUi\IELa/Joraloire de .l/odel/salioll dl! Cl/owl 1'1 de l'EIIl'irollllclI7enl alld LOD1(;, C\RSjClliz'ersile P. & ill. CllriejORSTO.I/, Parij, Prallce
ABSTRACT.
For the Last Glacial .\laximum, (LG:'l: 21 000 BP). simulationsusing atmospheric general-circulation models \AGC\ls arc I'ery sensilil'C to the
prescribed boundary conditions. \lost of the recent numerical experimenls halT used rhe CLI\IAP (1981) data set for ice-sheet topography. sea-ice extenl and sea surface
temperatures (SSTs). To demonstrate the impact of ice-sheet reconstruction on the LG\l climate, \\'e performed tl\'O simulations: onc using CLI\IAP (1981) ice-sheet topography, the other using the nel\' reconstruction pro"ided by Peltier. " 'e shol\' thal, although the geographical structure of the annually a\'C'J'aged temperature is not modified, there are important seasonal and regional impacts on the temperature
distribution. In a second step. to analyze the efl(~cts of cooler SSTs and sea-ice extent, \\'e performed Cl simulation using CLr~IAP (1981) for the ice-sheet topography. but I\'ith present SSTs. We find that the cooling due to ice sheets for the LGi\1 climate is one-third of the global annually a\Traged cooling, and that the south\\'ard shift of the
~orth Atlantic 101\' in \I'inter is not due to sea-ice extent, but is an orographic eflect due to the Laurelllide ice sheet. This set of sensitil'ity experiments allo\\'s us also to
discriminate bet\l'een thermal and QI'ographic forcings and to sho\,' the impact of the ice-sheet topography and cooler SSTs on the pattern of planetary \I'al'es during the
LGi\I climate,
1.
INTRODUCTION
Atmospheric general-circulation models (AGC:'I[si are important lOols [or recollstructing past atmospheric circulations and studying the physieal mechanisms of climate change. To illl'Cstigate the role of the difTerent
components (or boundary conditions of'the Last Glacial \Iaximum (LG\I) climate, we performed a set of (QUI'
numerical experiments, using the Laboratoire de i\Ietc
or-ologie Dynamique (L~ID) AGCi\1. i\Iany simulations
hal'C been done \\'ith difTerent !\GCi\Is to quantify the cflect of' boundary conditions on the global temperature
decrease during the LG?lI. For example, Broccoli and ~lanabe \ 1987). using an AGC:--I coupled \\'ith a slab ocean model, emphasized the role of lo\\' CO2 partial
pressure, especially for the Southern Hemisphere. \I'hile Rind (1987) sho\\'ed the impact ofsno\l' feed-back and of the topography of the ice sheets,
2, lee-sheet reconstructions (ISRs) for which (\\'0 data
sets are ClI'ailable, CLl\IAP (1981) and a rel'ised one
prm'ided bl' Peltier (199+),
Our approach focuses on the role of t\l'O major boundary conditions:
I, Sea surf~lce temperatures (SSTs) as gil'en by CLI-~I:\P. (\lclntyre and Cline, 1981; hereafter called CLl ~lAP (1981)) in \lin ter and summer for the LG "'I and modern climates,
Some sellsiti\'ity experiments \I'ith SST and ISR halT already been performed, Rind (1987) studied the impact
orCLI\IAP (1981) LG\] SSTs under present climatic conditions, and Rind and Peteet (1985) made a sensitil'ity experiment uniformll' lowering the CLIMAP (1981) LGi\l SST by 2cC to impro'T the consistency of' 1011' -latitude temperatures deduced from data and from models; bu t there is still no st ud y of presen t-c1ima te
SST impact on LG\! dynamics,
On the other hand. Shinn and Barron 1989 i hal'e
studied the sensitil'ity of the LG\I climate to extreme continental in>-sheel size and configuration, In their experimenl, the difTerences bet\\'een maximum and minimulll ice sheets are huge in comparison \I'jth our simulation; yet some interesting comparisons. especially
about the splitting of the polar jet due to the Laurentide ice sheet, can be made, ~Iol'Co\'er. the fact that all the
modellers il1\'oh'Cd in the Paleoclimate \[odeling Inter-comparison Project (personal communication from S, Joussaume and K. Taylor, 1994) will use the ne\\' ice
Ralllsleill al/d ]ollSSallll7e: SfIIsilil'if)' njJerilllelllsJor Ihe Lasl Glacial .I/rl\imulI1
intelTst in \\'hether changing the ISR has an important
impact on the LC\( climate,
2. MODEL AND SIMULATION DESCRIPTION
All the simulations were performed with the Li-.1D \'ersion
+
J\CCi\L (Le Treut and Li, J991) which is a grid-pointmodel. \\'e used the low-resolution \'ersion, corresponding
to 48 points regularly spaced in longitude and 36 points
regularly spaced in sine or latitude, At the equaror. the grid spacing is 830 km of'longitude
x
270 km of'latitude.and at 45 of latitude it corresponds to 590 km longitude
x
530 km latirude. The model has II !c\'e!s in normalizedpressure coordinate (a), The mode! soh-cs the dynamic
and thermodynamic equations, and the continuity
equation for mass and water \'apour (Sadourny ane!
La\'al, 1984), The predicted clouds arc considered for the
radiati\'e-transfer calculations (Le Treut and La\'al,
1984). Each experiment includes the [ull seasonal cycle
and lasts 6 years; a\'erages arc made o\'er the last 5 years.
(Laurentide), The ,hape and sizc or these ice sheets ha\'e
an important impact on the atmospheric dynamics O\'Cr
the Northern Hemisphere during the LC.\!. Delllon and H ughes (1981) pro\'ided for CUJ\ [i\ P (\\'0 reconstructions
referenced as J\IIi\' and J\IAX, corresponding to a eLlstatic
sea-b'c1 rise or 127 and 163 m, respecti\'e!y. Peltier (1994)
sholl's tha t e\'Cn the 1\ 11 N reconst runion was excessi \'e, and
proposes a new reconstruction bascd on a gra \'i ta tionall y self~consistellt theory or relati\'e sea-Ie\'C1 changes \\'hich
corresponds to a eusLatic sea-le\'c1 rise of 105 m. and to a
55'10 reduction of the ice \'olumc in comparison lI'ith the
CL TJ\IAP J\IAX reconstruction. Figure I a and b sholl' the
change in ele\'ation betll'een the LCJ\1 and the present
climate [or the CLIJ\[AP and Pcltier reconstructions. The
extent oj'ice sheets is not \'Cry difTcrent, but the ele\'ation is
1500111 higher O\'er Lau rentidc and about 1000 m higher
over Fennoscandia in the CLI J\IAP reconstruction. The
The first of the four simulations (E~PI) is the control
run lI'hich simulates the present climate. The second
(EXP2) is a simulation of the LC:'I using the CLli\[AP
~
(1981) data set [or SST and lSR. The third (EXP3) is a j
scnsiti\it)' experiment with the ice-sheet tOpography in
which 11( ' replaced the CUl\lAP (1981) reconstruction by
the nell' reconstruction prO\'ided by Peltier (1994): all rhe
other boundary conditions are identical to EXP2, The
fourth simulation (EXP4) is a sensiti\'it)' experiment with
SST in II'hich the CLl \IAP (1981) reconstructed SST [or
the Last Glacial :-'Iaximum has been replaced by the present climate SSI' of the cOlltrol run, lI'ith all the other boundan'
conditions remaining identical to EXP2 (Table I),
Comparing EXP3 and E~P2 lI'ill gi\'e us the
sensitivity of the LCJ\I climate to thc differences in ice
-sheet reconstruction, Comparing EXP4 and EXPI which
both have the same prescribed SST will gi\'e us the impact
of' thc ice-sheet topograph)'. Finally, comparing EXP+
and EXP2, \\'hich both ha\'(' the same CLIl\IAP (1981)
[SR, will gi\'e us the SST impact on t1w LC\l climate,
3. CHANGES IN BOUNDARY CONDITIONS 3.1 Ice-sheet reconstruction
A major difTerence between present and LGJ\I climate is
the huge ice sheets co\'Cring northwestern Europe
(Fennoscandia) and the northern part of' North America
·Ieo ·120 ~ 0 60 120 180
a LONGITUDE
b ·'80 ·120 ~ 0 60
LONGITUDE
120 180
F
ig.
I, DiJfereJlcesin
elel'alion (111111) belu.'een /he presenl( EXP l) alld Ihe Le:, I J, using (a) CLLILIP (1981) Jar
U;.I/ ice-sheellojJograJ)/~)' (EXP2), (b) Pellier (199-1) Ior I,G,I! ice-sllfl'l lojJogmjJII)' ('~·.\'P3), Dark gr~)'
(orresj)ollds 10 elevalioll differences qf 1I10re Ihall 2000 Ill,
l/IediuIII grl!)' 10 elel'alioll differences oJ more /hall 1000 Ill, fighl grq 10 Ihe emerged lallds al Ihe Le:,\[, /sol/lies Jar 1500 alld 500 m are also drm('II,
Table 1, Jlain jJarameler differences Jar Ihe SI'/ oJ 1/l/llIerica/ el/Jerill1enls
34+
co
:?
ppm EXPl control run 320 EXP2-LG:-.[ CLL\lAP (1981) 200 EXP3-LG:-'I Peltier (1994) 200 EXP4-LCl\l (SST present) 200 [molalioll 1950 21 ka BP 21 ka BP 21 ka BPSST dala sel [SR dala .1'1'/
Present Present
CLIJ\IAP (1981) CLIi\IAP (1981)
CLTMAP (1981) Peltier (1994)
Present
e
Ll .\
[A P (I 98 I )Ralllsleill alld ]Ollssallllle: Smsilil'il), el'periJl1f17lsfor Ihe Lasl Glacial JIrlli1ll1l17l
10\l'er sea-level rise in Peltier's reconstruction. compared Il'ith CLE1AP, leads to a reduction of the emerged lands.
\\·C take this into account and use difTerent sea/land masks
ror the lll'O simulations,
3.2 Sea surface te:rnperatures
l\Iost or the recent simulations of' the LGl\I climate.
perlormecl \I'ith AGCl\Is and prescribed SSTs. hal'c used
the reconstruction 0(' the sea-ice e"tent and or the sea
surface temperatures, for summer and winter seasons. prO\'ided by CUl\lAP (1981), These data are still
contrO\'ersial, e.g, in the tropical area (\\'ebster and Streten. 1978; Rind and Peteet. 1985), bu t no global -180 a -120 ·80 0 80 120 180 LONGITUDE re\'ision or LG'\I SST is I'el al'ailable. ancl \I'e use
§
CLIl\LAP (1981) to rcconstruct daily cI'olution 01' SST
I::
and sea-ice e"ten t. j
The SST differences between the LG 1\1 and the
present climate are about 4° to 6"C for Southern and Northern Hemisphere mid-latitudes. and reach ahout
10-C for the Nonh Atlantic, during \I'inte!'. The cooling ol'er tropical areas is reduced to 10
or 2"C. with large
areas of the Pacific Ocean where temperatures el'en
increase slightly
(
+
1
°
to 2cC),
Because of the Bering Strait, the difference in sea-Ice
e"tent between the LGl\r and the present climate is small in high latitudes [or the North PaciIie. but there is a huge equato[,lI'ard shirt or the sea-ice extent rrom 70 lO 50
latitude for the North Atlantic and SOllthern Hemisphere.
The seasonality of the sea ice is \Veakened during the
LG1\l, and the sea-ice extent is only slightly reduced
during the summer season,
4. DISCUSSION
4.1 Orographical i:rnpact of the ice sheet for the LGM cli:rnate
As with most or the ACCl\(s' simulations of' the LG'\l (Rind, 1987; Joussaume, 1993), the main features are
reprocluced in EXP2 and EXP3: shin oC the storm tracks southward ol'the ice sheet, deepening of'the North Pacific
10\1' and southll'<lrd shirt or the Nonh Atlantic 10\1'. and
splilting or the jet around the Laurentide ice sheel. Comparison or EXP4 and EXPI, which both hale the same present SSTs and sea-ice extent. displays the impact
o
f'
the ol'ographical forcing of the ice sheets, In EXP+,there is no enhancement of the Aleutian low (not shown). thus prm'ing that this enhancement. during the LGl\l, is
mostlv due to changes in SS']'s. In contrast. the
southll'ard shift or the Atlantic loll' is obsen'ecl in EXP2, EXP3 and EXP4; it is clearly related to the
presence of' the Lauren tide ice sheet.
In Figure 2a (EXP4 minus EXP]), we illustrate the efTect of orogra phical forcing on the geopoten tial heigh tat
500 hPa, for the lI'inter season. The impact of' the orographical f()JTing is rather local, leading to anticy
-clonic circulation westward or the ice caps, in agreement \lith Held (1983) and Cook and Held (1988), These
major changes in atmospheric circulation are also dependent on the size and configuration of' the ice sheel. as illustrated in neXl paragraph, -180 -120 ~o ~ 120 100 b LONGITUDE -110 -120 ~ 0 &0 120 180 c LONGITUDE
Fig, 2, (;eojJolflllial heighl (ill 11/) al 500hPa dijprmre5
Jor December. j allllalJ alld Febmal), (a) belu'eeJl EXP.f.
alld EXPI. (b) belu'CClI E.\P2 alld EXP3, al/d (e)
bell('el'll r;;XP2 alld t:_\.P.f., ill (a) {(lid (b) dark gr~]' is
liSI'd Ior dijJi'rence" /Iighl'/ tltall 200111, light gr~]' Jor
difji'/"('II!'e.l higltn I//{{II 100 Ill; i_Iolilles {(re drawlI Ior
differellm eqllal la 50 alld ljO 1/1 .. ill (() dark gr~l' is IIsed
Jor differellces lower Ihall -200 111. lighl gre),Jor dijJerfllces
lower lIiall lOO 171; i,wlille,l (Ire drau'IIJor dijjereJlccs eqllal
lo50alld-150m,
4.2 Sensitivity to different ice-sheet
reconstructions for the LGM cli:rnate
The comparison bct\lTcn EXP2 and EXP3 re\Tals the
changes in LCl\( atmospheric circulation due to the
difTerenccs in ice-sheet reconstructions, Although the globall\' anci annually a\Tragecl cooling is identical for the t\l'O LG;\1 simulations (l},T = -3.3"C) and the geographical structure or the annllal mean cooling is also l'erY similar. there arc important differences in the
seasonal c)Tles. In Figure 3a, \l'e depict the temperature
diflerences bet\l'een EXP2 and EXPl for the SUlllmer
season, A \I'armer region appears clearly in EXP2 and
extends southward or Fennoscanclia, from the north
-eastern .\leclitcrranean coast to central Russia, This
\I'arming is se\'erely damped in EXP3. as sl1o\l'n in
Ralllsteill alld ]oussallllle: Sensitil'i~)' nperimentsJor the Lasl Glacial .IJarimum Jol
§
""
j:: -<...
Jol c:. P""
j:: j IX> eo 30 ·30 .eo .go ·1B() ·120 -60 0 eo 120 a LONGITUDE IX> eo 30 ·30 .eo -iIO ·1B() b ·120 -60 LONGITUDE 0 eo 120 C ·1B() ·120 -60 0 eo LONGITUDE 120Fig. 3 . . -1ir temperature differences ( C) Jar June, Ju£l'
alld AllgllS/ (aJ be/ween E.\P2 and EXPt, (b) be/wee/{
E. \P3 alld E. tP J. (c
J
be/wem EXP4 a/{d E. \P J. Darkgrr:)' is llsed Jar temjJerature difJerences Izigl/er than
3"(;,
Light gr~JI Jar tem/malllre difJerences higher thall
re.
IsoLilles are drawn Jar
T
=2
°
and4
°
C.
180
sensiti\'C to the Fennoseandian rec0l1StruClion. This broad
warmer region still exists in EXP4, as shown in Figure 3c, which pro\'es that it is not induced by the CLDIAP
SSTs. The warming obtained using the CLI?dAP lSR corresponds to an increase in temperature or
+
30to SaC, contradicting the data synthesis providcd by Peterson and
others (1979) and more recently by 'vVebb and others (1993). These data are in better agreement with the
results obtained with the Peltier (1994) reconstruction. [n
the winter season, the same phenomenon is obsen'ed OWl' Alaska westward or the Laurentide (not shown). In both
cases, the differences in temperature patterns demonstrate the impact or the ice-sheet reconstructions on the
mid-latitude atmospheric dynamics. We now illustrate this reature with the winter circulation.
Figure 2b shows the difference or geopotential height at 500 hPa, in winter, between EXP2 and EXP3.
Isocontours indicate changes in the mean Oow. The
warming O\'Cf Alaska cannot be a direct orographical effect: there is no difference in ice-sheet ele\'ation O\'er Alaska between the two reconstructions. The higher 346
e\cnltion or the Laurentide in EXP2 intensifies the planetary \\'a\'es and heat transport, leading to an
increase in temperature and geopotential height. As
mentioned in the previous paragraph, the higher
elevation of the CLlr-lAP [SR induces an enhancement of the anticyclonic circulation westward of' the ice sheet. The wind at 850 hPa during winter (not sho\yn) confirms
the enhanced deepening of the Aleutian low, leading to greater transport of warmer air rrom the North Pacific to
Alaska rol' CLIl\1AP ISR (EXP2), which explains the
development or a warmer region oyer Alaska in winter.
Another \\'ay to illustrate the impact of ice-sheet ele\'ation on \\'inter atmospheric circulation for the LG;\[ is the splitting or the jet. As Kutzbach and \ \'righ t (1985)
noted, this splitting is a fllllction of ice-cap size and distribution. In this sensitivity experiment, the ice-cap configuration modifies the structure of the sp[i tting, \V e
find, for the simulation using CLIMAP ice-sheet reconstruction (EXP2), the same results deseri bed by
COH]\lAP (Anderson and others, 1988): a splitting orthe
jet with a northern branch at the edge orthe ice cap and a southern branch on the southern part or l\orth America (Fig. 4a), With Peltier reconstruction (EXP3), I\T find
the same intensity but a more zonal circulation for the
..,
'"
~
j Jol § t:..
j 00 ·00 -60 ·00 -180 ·120 -<10 0..,
120 100 a LONGITUDE ·100 ·120 .eo 0 .., 120 180 b LONGITUDE C IX> eo 30 ·00 ~ -iIO ·180 ·120 -eo 0 eo 120 180 LONGITUDEFig, -I. a. Wind speed a/ 200 ItPaJor EXP2 ill December,
Jal111al), and Febn(([I)" b, Tile same JOT EXP3. (.
DifJerences ill wind sjJeed between a and b,
Ramsleill alld Joussaume: Sellsililli!), e:rjJerimel1ls /or Ihe Lasl Glacial ,Ha,lill/uIII northern branch oC the jet (Fig, 4b), Because o[ the lower
ele\'ation of the Laurentide. the westerlies are streng th-ened O\'er the ice cap. as shown in Figure 4c,
corresponding to the wind-speed differences between EXP2 and EXP3, The impact of the ice-sheet topogra -phy is, in our case, weaker than in Shinn and Barron's
(1989) extreme-sensiti\'ity experiment, [or which they found a more defined structure of the splitting using their maximum reconstruction.
4.3 Change in SST for the LGM
Comparing EXP2 and EXP4, lI'e can analyze the effect of the change of SSTs on the LG\I climate. The global annuall>' a\'t'l'aged cooling reaches only 1.1 cC in EXP4. implying that the ice sheet is responsible [or 33% o[ the global cooling during the LG;\l. The diITerence of geopotential height at 500 hPa between E:\:P2 and EXP4 [or the \I'inter season. shown in Figure 2c, demonstrates the extensi\'e thermal forcing due to the SST \'ariations, A st rong trough de\'elops o\'Cr the cold l'\ orth Atlan tic, co\'ered bv sea ice, as a rcsult of' the decrease of the surface heat Ouxes, Howe\'er, the major difference in winter sea-ice extent between the LGM and the present climate is not responsible for the southward shift of the Atlantic low II'hich is \'ery similar in both simulations.
5. CONCLUSIONS
The approach de\'eloped 111 this paper aIlO\<\·s a better understanding 0(' the orographical and thermal fOl-cings. These sensi ti\·i ty experi men to sho\\' the im pact oC ice-sheet orography and SSTs with emphasis on the eITect o[ diffcrent ice-sheet reconstructions on the LGf-1 climate. \ \' e fi nd that the tempera tures si m ula ted for Pel tier reconstruction do not show the important warmer regions for the LGi\I that many other models found using CLI1\IAP (1981) reconstruction (Rind, 1987), and \I'hich contradicted to data. \Vc also sho\\' that thc deepening of the Aleutian low is due to the LG"'I SSTs but that the southward shift of the Atlantic low is due to the circulation induced bl' the Laurentide. Finalh', we illustrate the diITerent contributions of SSI' and ISR on thc pattern of planetary wa\'cs o\'Cr thc :\forthern Hemisphere during the LG1\1.
ACKNOWLEDGEMENTS
\ ,. e gra tefull y acknowledge the Laboratoire de ~li:teor
ologie D),namique (CNRS, Paris, France) [or pro\'iding
us with the \'Crsion 4 of their GCM, Dr Peltier [or providing the new ice-sheet reconstruction, ~1. Dou tria ux (L1\1D) for participating in the simulations and
J
.
Y. Peterschmitt (LMCE) for the graphic outputs.REFERENCES
,\nderson. P,~1. alld 32 olhers, Climatic changes or the la,t 13.000 'Tars:
obsers'ations and model simulations, Srinlle. 241 (·fH69 , 10+3-1052.
Broccoli. A,,J. ane! S, :'slanabc. 1987, The innuencc or continclllal ice,
atmospheric CO2, and land albedo 011 the climl1H' of the last glacial
maximum, Clilll(/Ie D)'II.. 1(2), 87 99.
Cook, K, H, and l. id, Held. 1988. Stationars' IVal'e, or the ice age
climate,
J.
Clilllale .. 1(8), 807-819,Delllon, G, H, and 1'.,J, Hughes. el!,. 1981. The IIHI greal ifl' shedS. Ne,,'
York. etc.. ,John \I'i1c, and Sons,
Held. I :'sI. 1983, Stationars' and quasi stationar\' eddies in the extratropical troposphere: theory. [1/ I-Ioskins. D . .1 and R. P. Pearcc. er!'. LIII;ge swle dl'lIallliwl jJrOCl'SJel ill Ihe allllo,phaf, London.
Academic Press, 127- 159,
Joussaulllc, S. 1993, Paleoclimiltic tracers: an illl'estigalion ming
atmospheric general circulation model under ir(' agc conditions
I. Dcsert dust.
J.
Geo/Jh)',. Re,l .. 98(02), 2767 2805.hutLbach, J, E, and 1-1, E, \I'right. 1985. Simulation or the climate of
18,OOO,'Cars BP: results ror tlw North American/North Atlanticl
Europl"(ln sector and comparison ,,"ith the gCQiog"lc record
o
r
~onhAmerica, Qpal, Sci. Ret .. 4(3),1+7-187,
Le Treul. H, and K, Lm·al. 198+. The importance of cloud radiation tnteractlon [or the simulation of climate. [11 Berger, .\. and C.
Nicolis. edJ. ,\elt' /}frJj)('rlivec, ill dim ate model/ing .. \nlsterdalll. 1~~I"i('\'if"rl
199-221.
Le 'Trcllt. H. and L •. Li. 1991. Scnsitjyity of an atlllosphcric general
circulation model to prescribed SST changes: ICed back cfl('Ct
associatecJ with the simulation of cloud optical properties. Clima/e
D1'I1 .. 5,171-185.
:'slcl nLyre. A. ane! R, Cline, pds, 1981. Seasollal recom/ruclioll of Ihl' Earth',
'lIIj{/ce at Ihe la,1 glacial mIll illlUIII , Boulder, CO, Geological Society or
,\merica. \:'sl ap and Chart Series 1\1 C-36,).
Pelticr. R, \\', 1994. Ice age paleotopography. Seima. 265 5169),
195 201,
Pctcrson, G. :'sI.. T. \I'ebb, I I I, J, E. E-;.utLbach, T. ,'an der I-Iatllmen,
'J'. :\, \I'ijmstra and F, A, Street. 1979. The continental record of en\'ironmentai concJitions at 18,000)'1' BP: an initialcI'<t1uarion, 01111,
Re", 12( I). +7 82,
Rind, O. 1987, Components or the ice age circulation. ]. (;eophn. RI".,
92(0+, -12+1 +281,
Rind. D. and D. Petrel. 1985. Terrestrial conditiolls at tllC' last glacial
maximulll (lnci CLL\lAP sea surface temperature cstinlalcs: arc they
consistent' 01(11, ReI" 2411 i. I 22,
Sadoul'!l\', R, and K, Lal·al. 198-kJanuary andJuly performance of the
L:'sID general circulation model. III Bcrger, .-\. and C. Nicolis. er/."
. I 'elL' jJers/,et'lil'eJ ill ciilllllit' 1II(j(Mlillg. Amstcrdam. Else,·i"r. 173 198. Shinn, R. A, ancl E . .1. Barron, 1989, Climate sensiti,'ity to continental
ice sheet size ancl configuration.
J.
.1111 .. l/eleorol. SO( .. 2 12 . Ijl7 1537.\\'cbb, \1'" III alld 7 IIlhO's, 1993. Climate change during the past 18.000
vears: regional syntheses. mechanisms, and causcs. [1/ \I'right. H.E.,
Jr. ed. Global clillla/es sillce the last giaciaimarillllllll, ?dinneapolis. Id~,
Uni'Trsitl or :'slinnesota Press. 51+-536.
\I'cbstcr. P . .1, ancl:\f. ,\. Strclen. 1978, Latc Quaternary icc agc climates
oC lropical .\uqralasia: intcrpretations and rccon~tructions. QJlal.
