Palaeogeography, Palaeoclimatology, Palaeoecology, 95 (1992): 229-252 229 Elsevier Science Publishers B.V., Amsterdam

Paleoclimate of the Kimmeridgian/Tithonian (Late Jurassic) world: II. Sensitivity tests comparing three different paleotopographic settings

George T. Moore a, Lisa Cirbus Sloan b, Darryl N. Hayashida a and Natasha P. Umrigar a aChevron Oil Field Research Company, La Habra, CA, USA bUniversity of Michigan, Ann Arbor, MI, USA (Received December 3, 1991; revised and accepted March 14, 1992)

ABSTRACT

Moore, G.T., Sloan, L.C., Hayashida, D.N. and Umrigar, N.P., 1992. Paleoclimate of the Kimmeridgian/Tithonian (Late Jurassic) world: II. Sensitivity tests comparing three different paleotopographic settings. Palaeogeogr,, Palaeoclimatol., Palaeoecol., 95: 229-252.

Topography and location of continents largely determine present-day climate. We conclude that in the geologic past paleoto- pographic expression was equally important. However, in the geologic record paleotopography is difficult to assess and compile because it is largely a self-destructive environment without record and is rarely addressed in the literature. An objective of this study is to test the sensitivity of paleoclimate to paleotopography by comparing three different Late Jurassic scenarios. Paleotopography influences many paleoclimate parameters to varying degrees. To test the sensitivity of paleoclimate to modeled paleotopography for simulations incorporating a Late Jurassic reconstruction, we ran three simulations using the same boundary conditions of paleogeography (land and ocean) and atmospheric CO2 concentration, 4x the pre-lndustrial level (1120 ppm). One simulation contained mountain ranges of variable height to 3 kin. In another, all the mountain ranges were reduced to 1 km highlands. The third simulation used a constant 500 m height for all land grid cells. The sensitivity tests indicate that paleotopography is an important boundary condition. Without realistic paleotopography, flat or idealized continents surrounded by bodies of water do not produce realistic pateoclimate results. We conclude that in paleogeographic reconstructions the location and extent of mountain ranges and highlands should be recognized and given suitable elevations consistent with their plate tectonic origins, settings, and geologic ages.

Introduction Tithonian, two connections were established between the Tethys Sea and the Panthalassa Ocean The Late Jurassic, particularly the Kimmerid- (Ross et al., 1992). Second, the Triassic Jurassic gian and Tithonian (154.7-145.6 Ma) (Harland high sea level stand occurs within this interval. et al., 1990), were significant stages of the Mesozoic Third, Upper Jurassic rocks contain immense, Era for several reasons. First, the time represented economically important deposits including petro- the important interval of Pangea's tectonic disin- leum source rocks, reserves of oil and gas, coal, tegration by the formation of new and the re- and evaporites. Finally, paleoclimate modeling of establishment of ancient seaway connections this epoch has not been attempted previously with (Fig. 1). North America completed its separation a general circulation model (GCM). from Gondwana, and Gondwana was split into a Modeling of this interval and correlation with northern and southern continent by the rift system paleoclimatically-sensitive sedimentary rocks con- opening the proto-Indian Ocean. By the late firms that the Late Jurassic was a time of high CO2 (Budyko et al., 1985; Berner, 1990) and an elevated Correspondence to: G.T. Moore, Chevron Oil Field Research greenhouse effect (Hallam, 1985; Moore et al., Company, La Habra, California. 1992). In this study, we used ll20ppm CO2, 4×

0031-0182/92/$05.00 © 1992 -- Elsevier Science Publishers B.V. All rights reserved. 230 G.T. MOORE ET AL.

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N

60N "L ."*- "._ C"c'L,"/',,~AC'C-~Y",~., • ~ --._A,-

• 30N

0 - "a~aL ...... 0

30S- Ocean 30S

60S 60S

Austra/ ~.~Y-'~~ ~ ~ ~aSea 90~ i ~ ] i ~ I i i I ~ i I ~ i I i 1 J i i I i ~ I t r I i r I i i r i i ~S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

Fig. 1. Late Jurassic (Kimmeridgian/Tithonian; 154.7-145.6 Ma) paleogeography showing modern shorelines. Reconstruction based on Rowley (1992). the pre-Industrial level of 280 ppm CO2 (Pearman influence various model-generated paleoclimate et al., 1986; Barnola et al., 1987; Kuo et al., 1990). parameters. The first scenario we term "variable", Paleotopography is an important boundary con- with mountain ranges extending to elevations of dition for GCMs. There have been several climate 3 km. The heights are based on the plate tectonic modeling studies, which address the sensitivity of settings of the mountain ranges and the range of climate to topographic variations, and all agree on present-day elevations in similar settings. In the the importance of incorporating mountains into second simulation we set all the mountain ranges model boundary conditions (e.g. Kasahara and at a 1 km height. We term this case "1 km high- Washington, 1971; Manabe and Terpstra, 1974; lands". In the third simulation, all the continents Barron and Washington, 1984; Kutzbach et al., and islands are at 500 m with no topographic 1989; Ruddiman and Kutzbach, 1989; Sloan and variation. We refer to this case as "500 m Barron, 1992a). These investigations indicate that plateaus". orographic influence changes with latitude, season, continental distribution, and topographic Model description expression. Most prior paleotopographic studies considered The GCM used in this study is the National present day or late Cenozoic changes in mountain Center for Atmospheric Research's (NCAR) Com- elevations. Because of the nature of current geogra- munity Climate Model (CCM) Version 0. It runs phy and topographic expression, these cases dealt on a Cray X-MP at Chevron Oil Field Research primarily with climatic sensitivity to topographic Company, La Habra, California. The CCM uses changes in the Northern Hemisphere. The study thermodynamic and hydrodynamic laws applied presented here is different from those listed above to the atmosphere. The vertical dimension consists in two major ways. First, we explore paleoclimate of nine atmospheric levels and extends through sensitivity to paleotopography in the Late Jurassic. the troposphere into the middle stratosphere. The Second, the range of topographic changes consid- horizontal dimension consists of 40 latitude by 48 ered here includes substantial variations in the longitude grid points with each grid cell having an paleotopography of both hemispheres. approximate resolution of 4.5 ° latitude by 7.5 ° The purpose of this study is to evaluate three longitude. different paleotopographic scenarios and how they Moore et al. (1992) examine the simulated paleo- PALEOCkIMATE OF KIMMERIDGIAN/TITHONIAN WORLD: II. COMPARING PALEOTOPOGRAPHIC SETTINGS 231 climate of the Late Jurassic world with variable or quantitative elevation information is available, paleotopography. They describe the evolution of so we used a deductive approach to reconstruct the model and give pertinent characteristics of the the paleotopography. The distribution of "moun- CCM. Hereafter, Moore et al., (1992) will be tains" existing in the latest Jurassic was taken from referred to as "Part I". In this study we use a Ziegler et al. (1983) and modified with respect to solar constant value of 1370 W m -2 and a global the Late Jurassic plate tectonic framework (Row- CO2 concentration of l l20ppm. The bases for ley, 1992; Scotese, 1992). We assigned values in choosing these values are detailed in Part I. one kilometer intervals (up to 3 kin) to elevated These simulations employ a seasonal model in land grid points using present topographic ana- which solar insolation varies throughout the year. logues occurring in equivalent plate tectonic set- The atmosphere is coupled thermally but not tings as a model (the "variable" case). Non- dynamically to a mixed layer ocean, 50 m deep, mountain land cells are 500 m high. For the case with 5° x 5° surface resolution (Washington and of the "1 km highlands" we reduced all the moun- Meehl, 1984). Sea surface temperature (SST) and tains to a one km height. For the "500 m plateaus" sea ice extent are computed as a function of the case, all land grid cells are assigned that elevation. surface energy balance. Sea ice forms when the The distribution and elevation of the mountain SST falls below -1.8°C. The deeper ocean is ranges used in the simulations are shown in Fig. 2. external to the model. The lack of dynamic cou- The northern hemisphere mountain ranges consist pling has obvious model-induced limitations on of the meridionally oriented Sierra Nevada and oceanic heat transport and related atmospheric the NE-trending, rejuvenated Appalachians bor- feedbacks. dering the western and eastern margins of North America, respectively. We interpret the Sierra Nevada to have elevations ranging up to 3 kin. Kimmeridgian/Tithonian physical world and CCM Elevations in the Appalachians are limited to a boundary conditions 2 km maximum. The extensive eastern Asian range represents a continuous, meridionally oriented Paleogeography mountain system with the higher elevations exceed- ing 3 km. Three major rift systems produced oceanic sea- The southern hemisphere contains three regions ways that separated Pangea into major continental of elevated topography. Western and northwestern segments: North America, Eur-Asia, and Gond- Gondwana are rimmed by a mountain system wana (Fig. 1). The compound Gondwana conti- related to doming associated with the opening of nent was subdivided further into north and south. The paleogeography used for these simulations northwestern Tethys (proto-Gulf of Mexico) and shows the ocean-continent relationships at the subduction along the western margin of South beginning of the Kimmeridgian (middle Late Jur- America. We assign values up to 3 km for this assic). This reconstruction was used as the ocean- mountain system and term it the proto-Andes. We land input boundary conditions for the paleocli- interpret doming and formation of highlands mate simulations (Fig. 2). For further details approximately 1 km in elevation to occur along regarding the paleogeographic setting and ration- the southwest Tethys rift, forming the proto-Indian ale the reader is referred to Part I. This paleogeog- Ocean. The third region is of variable height along raphy is the same for all three cases of the current the margin of Antarctica poleward of 80°S and is study. associated with possible plate readjustment. CCM results are plotted in the form of a rectilin- Paleotopography ear grid and all the paleoclimate maps in this study are in such a format. An overlay of the continents The CCM requires elevation to be specified for is made to aid the reader in locating specific grid points designated as land. Little qualitative geographic areas (Fig. 2). 232 G.T. MOORE ET AL.

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N

60N

30N

30S

60S

90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E Fig: 2. Late Jurassic paleogeography at 154.7 Ma with geologically interpreted ("variable") paleotopography (contours in km). Reconstruction based on Rowley(1992) with islands in the Panthalassa Ocean derived from Ross and Ross (1983). Continents and islands in model grid format are outlined and shaded.

Paleotopography sensitivity tests each case, addition of topography (vs. plateau- type continents) resulted in a general average sur- Introduction face temperature decrease of 1.1°C. Barron and Washington (1984) noted a "clear association" Topography, the location of continents, and the between areas of greatest temperature and of great- chemical state of the atmosphere with respect to est topographic difference. Further, they noted the radiative trace gases largely determine present-day occurrence of direct and indirect effects of topo- climate. Bolin (1950) was one of the first to observe graphic variation upon climate. that the generation and location of jet streams are Kutzbach et al. (1989) and Ruddiman and Kutz- influenced by continental distributions and moun- bach (1989) examined late Cenozoic uplifts in tain range locations. Bolin (1950) also observed western North America and in southern Asia that planetary waves are anchored by mountains through a sensitivity study which incorporated such that wave ridges are generally located over three different descriptions of continental eleva- mountain crests and wave troughs are located in tions. This study reiterated the general atmospheric mountain lees. These relationships between atmo- circulation results of Manabe and Terpstra (1974) spheric circulation and topography have also been and the thermal response seen by Barron and simulated in several GCM studies. Manabe and Washington (1984), but also provided insight into Terpstra (1974) examined a present day world with possible mechanisms of late Cenozoic climatic and without mountains. They found that flow of change relating to tectonic uplift. Kutzbach et al. the atmosphere is anchored by mountains, with (1989) and Ruddiman and Kutzbach (1989) stationary troughs occurring in mountain lees. demonstrated that the expression of paleotopogra- Their results show that atmospheric flow is less phy was a critical factor in accurate simulations zonal when mountains are included in model of late Cenozoic paleoclimates. boundary conditions and that precipitation distri- Sloan and Barron (1992a) examined the effects butions vary substantially between topographic of two different specified elevations of the Rocky cases. Barron and Washington (1984) examined Mountains upon Eocene paleoclimate. Except for the effect of topographic definition upon both limited temperature and precipitation changes, present day and Cretaceous simulated climates. In they found little response of paleoclimate to eleva- PALEOCLIMATE OF KIMMERIDGIAN/TITHONIAN WORLD: I1. COMPARING PALEOTOPOGRAPHIC SETTINGS 233 tion changes for cases incorporating mountain becomes more zonal, a result that is most notice- heights of 500 m and 1 kin. Sloan and Barron able in the winter hemispheres. This response is (1992a) suggested that a critical mountain height most enhanced for the "500 m plateaus" case. The for perturbation of atmospheric flow was not summer patterns are more complicated by the reached by this range of specified elevation. In a summer jet being weaker and responding to inter- 1988 study, Rind found that climate simulated by ference by thermal contrasts between the oceans the Goddard Institute for Space Studies' GCM and continents. The equatorial counter flow like- was greatly influenced by the spatial resolution of wise is weaker in the "1 km highlands" and "500 specified paleotopography. In this case the implica- m plateaus" paleotopographic simulations than in tion is that, not only is inclusion of paleotopogra- the fully "variable" paleotopographic case. phy important to simulated paleoclimate, but how The simplification of jet stream pathways toward that topography is described also may be critical. more linearity from the "variable" to the "500 m plateaus" case affects the position of the winter Results mid-latitude storm tracks. This is shown by the two extreme cases (Figs. 5 and 6). Surprisingly, We completed three seasonal paleoclimate simu- intensity of the storm tracks does not change lations with the same Kimmeridgian/Tithonian substantially between the "variable" and "500 m paleogeography and differing paleotopography. In plateaus" cases for either season. For DJF, inclu- all these cases, the CCM was initialized with sion of the fully "variable" topography produces isothermal conditions and run for sixteen model a winter storm track which circumvents the Sierra years. The results compared here are 90-day sea- Nevada. The mountains of the eastern Asian range sonal averages taken from model year 15.5 (June/ at maximum height effectively disrupt continuity July/Aug; JJA) and model year 16.0 (Dec/Jan/Feb; of the storm track. In contrast, the storm track of DJF). Paleotopography is the only boundary con- the "500 m plateaus" case is quite zonal and more dition that was changed between the simulations. uniform in intensity. In JJA of the southern hemi- We analyze the results of the three simulations sphere, due to the zonal orientation of the southern with varying paleotopography for overall plane- Tethyan shoreline (India and Australia) at about tary tropospheric and lower stratospheric circula- 50°S and its relatively low coastal relief, the storm tion as well as for the global paleoclimatic effects track is in the same position and about as strong at the Earth's surface. We use surface temperature, in both simulations. sea level pressure together with surface winds, precipitation, and latent heat to evaluate the global Surface temperature surface effects of modified paleotopography. Surface tempera~ture results vary in response to Jet stream patterns and storm tracks changing paleotopography. The "variable" case produces more complex thermal patterns for both As in previous GCM investigations of topogra- seasons over land in the northern hemisphere phy (e.g., Manabe and Terpstra, 1974), we find (N.H.) than the other two cases (Figs. 7 and 8). that increasing topographic expression produced However, such a response is not as obvious in the increasingly azonal wind patterns. Beyond this land surface temperatures for the southern hemi- result, responses to paleotopographic variations sphere (S.H.). The absence of this association in from case to case are less systematic. the S.H. may result from less paleotopographic The orographic effects of particularly meridio- variation than in the N.H. but also may be related nally-oriented mountain ranges in the "variable" to less sea ice in the S.H. to influence nearby case are manifested in the deflection of flow from continental temperatures (Part I). The sea surface a more zonal to an oblique orientation (Figs. 3 temperature (SST) likewise becomes strongly zonal and 4). When all the mountain ranges are reduced in the "1 km highlands" and "500 m plateaus" to "1 km highlands" the atmospheric circulation cases (Figs. 7 and 8). 234 G.T. MOORE ET AL.

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N r ¢ I i i I i = I i / I = I = i I = i I i ¢ I , , I , , 90N

30N • ----:

: : :u .,- c,.: >:~:..-:~-~'~, ;; z c "Variable"

,:.,~._.__.~ ~_.__..,_~ , ...... ~ ~-j-~.E ~~ ~--~ ~ -

I-2 km

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N l, i I I i i I I i I i I I I i [ i i I i i I i i I i i I i i I i i I = i 90N 2, ¢,#J. :-':'~_--~w>~,~y ,x ,x ~ ~ ...... :..-...... --'-,:_4--~-~ ...... ~. 1, r

30N 30N "1 km

-~d~~3AK~--~I- Highlands" o o

30S 30S

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

I ! / / / ///~.~j~= ~,.~ \ \\,~ 90N ..... : 7 .-" ~ -- ~.

60N 60N

3ON ~~-~:~4~-.- 3ON "500 m

- • ~ < : 2 - _ ~ _ _ ~_~_._~. Plateaus" o ~~~_;. o

~ ~ ~ ~'--"~ ~ ~'~ ~ ~ ['-7

30S i~ : Y" ~ " ~''q " ~ J''": j" 30S

~os ~~=~'~:/~ ~os

90S ...... " " ~" ~ ...... 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

Scaling vector ~ = 5ms-1

Fig. 3. Dec/Jan/Feb wind vectors at 500 mb for three Late Jurassic, 1120 ppm CO~ simulations with differing paleotopography. For identification of each simulation, refer to right hand margin. Continents and islands in model grid format are outlined. In maps where appropriate, H and L refer to high and low values, respectively within closed contours. Dashed contours represent negative values. PALEOCLIMAFE OF KIMMERIDGIAN,I-ITHONIAN WORLD: II. COMPARING PALEOTOPOGRAPHIC SETTINGS 235

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N I J I L I L [ ~ L I = ~ 90N

o0N- - , ~%1 # "4 >-- ...... " ~?" :-'i "Variable"

.... I > .... : ~ 2-3 km 3os. ! sos ~ 1-2 km

60S 60S

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

ION180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120f 150E 180E90 N

60N 60N

30N 1~ f 30N "1 km ,, Highlands

30 S 0S

60 60S

90S - ~">'~'~ ~ ~" ~'f ~-~ ...... 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N ~ J~ "~

60N 60N

o~~~;~ o Plateaus"m

90S I ~ ~ I ~ ' I ' ~ I ~ ~ I ~ I ~ ' 1 ~ ~ I ~ ' I ' 1 ~ ~ I ' ~ I ~ ~ 908 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

Scaling vector ~ = 5ms-1

Fig. 4. June/July/Aug wind vectors at 500 mb for three Late Jurassic 1120ppm CO 2 simulations with differing paleotopography. See Fig. 3 for explanation. 236 G.T. MOORE ET AL.

180W 150W 120W 90W 60W 30W 0 30E 60E WE 120E 150E 180E 90N ~N

60N 60N

30N 30N

o "Variable"

30S 3os ~ > 3 km 2-3 km

60S 6os ~ 1-2 km

90S 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N I I L i ~ I i = 1 t I t J i l ~ i I L = t L i I = i I t i I L ~ I = = 90N

-- 16 16. " (]ON

30N 30N

---?-~- ~_~.- ~~-L~_-- .... ~-=-~ ...... 0 "500 m Plateaus"

30S ~-. 6 [~ 16.

60S 60S

5.,~ 6.11 90S J i I , J I , i I J ' I i , I I r I r r i 1 1 I 1 i I I r I J , I r I 908 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E Fig. 5. Dec/Jan/Feb storm tracks from the time-filtered (2.5-6 days) standard deviation of the geopotential height field (m) at 500 mb in the "variable" (top) and "500 m plateaus" (bottom) cases. CI = 8 m. See Fig. 3 for explanation.

Seasonal DJF and JJA temperature difference cooling of regions with increasing elevation, especi- plots are shown to highlight the regions of signifi- ally in the "variable" minus "500 m plateaus" cant change or the lack thereof (Figs. 9 and 10). comparison. The mountain ranges of the Sierra Both the "1 km highlands" and "500 m plateaus" Nevada, eastern Asia, and the north end of the cases are individually compared to and subtracted proto-Andes are cooler in the "variable" case in from the "variable" one, grid cell by grid cell. both seasons. However, the "variable" minus the Positive values (solid lines) indicate that temper- "500 m plateaus" comparisons show a consistently ature values in the "variable" simulation are higher stronger lapse rate-related cooling in the summer than in the subtracted case. For negative values season of both hemispheres. Further, the difference (dashed lines) the reverse is true, the temperature maps indicate that areas some distance from the values are lower in the "variable" simulation than reduced paleotopographic contrasts experience in the subtracted case. temperature changes apparently due to certain Maps of surface temperature differences (Figs. indirect effects of the modified conditions. 9 and 10) emphasize the direct effect of paleotopog- The most significant global changes in the DJF raphy upon temperature through lapse rates, a temperature difference plots occur in the N.H. PALEOCLIMATE OF K MMER1DGIAN/TITHONIAN WORLD: II. COMPARING PALEOTOPOGRAPHIC SETTINGS 237

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N 90N

60N 60N

30N 30N

"Variable" • >3km 30S 30S 2-3 km

60S 60S [] 1-2 km

90S 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90NI LLILIJll[lllll]lLjIJILILlllJl[llk~l 90N

"500 m Plateaus"

rT[r i I ill 180W 150W 12W ~W 60W 30W 0 30E 60E 90E 120E 15 E 180E Fig. 6. June/July/Aug storm tracks from the time-filtered (2.5-6 days) standard deviation of the geopotential height field (m) at 500 mb between the "variable" (top) and "500 m plateaus" (bottom) cases. CI = 8 m. See Fig. 3 for explanation. north of 50 ° latitude (Fig. 9). The northern Pantha- plots show the northern Panthalassa Ocean tem- lassa Ocean is warmed (~ 30°C) in both the "1 km perature changes in the "l km highlands" and highlands" and "500 m plateaus" cases. The Boreal "500 m plateaus" cases are about one-third that Sea in the same respective cases cools near north- of the DJF range (Fig. 10), the most significant western North America. In all probability, this large scale change in the simulations. The remain- reflects a change in hemispheric circulation caused der of the world ocean exhibits little change for by lowered elevations in the eastern Asia range. the most part. Temperatures decrease over the Otherwise the oceans show little change. Southern eastern Asian range in the "l km highlands" and Asia shows strong warming (western) and cooling "500 m plateaus" cases when compared with the (eastern) trends along the margin of the Tethys "variable" case. Sea in the two restricted paleotopographic cases. Generally, interior Gondwana temperatures are Sea level pressure and surface winds higher in the "1 km highlands" and "500 m pla- teaus" cases (Fig. 9). DJF and JJA sea level pressure maps for the By comparison, the JJA temperature difference three paleotopographic sensitivity cases are paired (].T. MOORE ET AL. 238

30E 60E 90E 120E 150E 180E 180W 150W 120W 90W 60W 30W 0 90N

9°N1-, \ -" 60N 60N

30N - 30N "Variable" o ~~~ =. ,~==~.~ ~~ ...... --_-7 o I > 3 km

60S

~--~- ~ ~-~-~ 7- 9oS

180W 150W 120W 90W 60W 30W 0 30E E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W O' 30E 60E 90E 120E 150E 180E & • I I I I I ~- I ~ i I i J I l I J~l I i I I I L ~ 90N e ...... <

3o. ~o. :; 3oN "1 km ~o.~---- Highlands"

o ...... -- ...... -~ .... o

°os 60S ~~ -- ~

~S I , i i , i i i , , ] , i ' ~) ', , , T-'--~'~ ..... 180W 1510W 120W 90W 60W 30W 3DE 60E E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

IL_l 90N .._ -- , ...... :/:::::::-f ...... ,

BON , "'-==~.s:=~ -:-_££SjS;.z_:j__;~-- ~ ~-= :- 60N

3o. 3ON "500 m Plateaus" o~--~ ...... ~ I--I

60S

~s ~o.~ L ~ ~s

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E lS0E 180E Fig. 7. Dec/Jan/Feb surface temperature (°C) for three Late Jurassic 1120 ppm CO~ simulations with differing paleotopograpby. CI = 5°C. See Fig. 3 for explanation. PALEOCLIMATE OF KIMMERIDGIAN TITHONIAN WORLD: 11. COMPARING PALEOTOPOGRAPHIC SETTINGS 239

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E ~N • J I I I L l I I I I I J I I J I [ I I L I I l I 1 I 1 I I [ l I . J I L J 90N

j ~ ~.~~~~ ) "Variable"

-~----- ~°~------~ 1-2 km

90S I L , "r I ' ' I ~ ' I ~ ' I ~ ' I ' ' I r " ," I ' ' I m--~ I ' ' I , ' 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

!SOw 150w 120W gOW 60W 30w 0 30~ 60£ 9OE ~2OE 15OE 18OE 9©N

60N

"1 km Highlands"

50S

60S

180W 150W 120W 90W 60W 50W 9 ~0E 60E 9OE 120E 150£ 180£

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N ~ i 1 k i J ~ l I L I ~ L L 1 L t [ I ~ I L ~ [ I ~ 1 ~ ~ h ~ I i L I 90N

60N - 60N

30N 30N "500 m Plateaus"

60S ...... - - - 80S

90S , i I ~ f I ' r I ~ r I I , I i i I- i ul I T ~ I ~ q I J ~ I ' ' I f i ~- 90S 180W 150W 120W 90W 60W 30W O 30E 60E 90E 120E 150E 180E

Fig. 8. June/July/Aug surface temperature (C) for three Late Jurassic 1120 ppm CO 2 simulations with differing paleotopography, CI = 5°C. See Fig. 3 for explanation. 240 G.T. MOORE ET AL.

180W 1 ~OW 120W 90W 6Ow 30W Q 30E 60E 90E 12QE 150E 18OE 90N i I I i i I i i 1 I I I I J I I I ] I I i I ~ I I I I 4 ~ I a I I + I 90N

...... : ..... , ,-., },,,£.q:;~

o ff____._~,_v~_~~ ~r-'L .... ~ ...... o "Variable" - t ~ o o../~-~ ~-v~. ~ I -~/----'-'% <0 • "1 km Highlands"

90 S~ I , ~ I , , 1@ • r~g;t~£) , r = , I , , r , , p , , I , , ~ , , I , , [ , , r~r~T-- 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

1SOW 150W 120W gOW 60W 30W 0 30E 60E 90E 120C 150E 180E 90N t , , I , I I J I I I I I I I ~ I ~ I + J I I ~ J h ~ I L P I I I I J J 90N

60 .... . , , 60N

:_o "Variable" - ...... %--~ ...... Plateaus"

9oc , ,,,,,,,, , ,~ ~ r ..... ~,,,, i , ..... , , -7-.~;~ 180W 150W 120W 90W 60W 30W 0 JOE 60E 90E T 20 E 150E 180E

Fig. 9. Dec/Jan/Feb difference plots for surface temperature (°C) between the "variable" minus "1 km highlands" and "variable" minus "500 m plateaus". CI = 5°C. See Fig. 3 for explanation. with their comparable surface wind vector maps warm the continents sufficiently to develop and (Figs. 11 and 12, 13, 14, respectively). Sea level maintain continental low pressure systems versus pressure in the "variable" simulation shows a oceanic high pressure systems in the mid-latitudes marked difference from the other two cases. This (Figs. 7 and 8; 11 and 13). Thus, the summer result is mimicked by surface wind patterns. Gen- circulation patterns in both hemispheres, while erally, surface wind vector plots illustrate increased simplified, remain dominated by paleogeography, flow diversion with increasing paleotopographic irrespective of paleotopography. expression and more zonal flow with flatter conti- Regionally, the intense DJF low in the central nents. A trend exists toward very simplified zonal part of the Boreal Sea forms a zonally-oriented circulation in each of the winter hemispheres from low centered in the eastern ocean in the "1 km the "variable" to the "500 m plateaus" simulations. highlands" and "500 m plateaus" simulations This occurs despite the dissimilar paleogeographies (Fig. 11). This can be directly attributed to the in the hemispheres. The winter equator-to-pole northward deflection of the subtropical high over temperature gradients appear stronger than any the Sierra Nevada range in western North America, land-sea differentials (Figs. 7 and 8). In contrast, which constrains the low pressure system over the the respective hemisphere summer temperatures ocean in the "variable" case (Fig. 11). PALEOCLIMATE OF KIMMERIDGIAN/TITHONIANWORLD: 11. COMPARING PALEOTOPOGRAPHICSETTINGS 241

18QW 15QW "2QW 90W 6QW 30'W 0 !OE 60E 90E '20E 150~ 18QE

0 L~ '~91 i

0 0 "Variable" - "1 km Highlands"

• , 1')9 3os

180W 150W 120W 90W 60W ,30W 30E 60E 90E --~80E

180W ;50W 120w 90W 60W 30W 0 3OE 60E 90E 120E 150£ 180E

I / E~ "" - .....

3O "1 ' ' /'" '''~ ~ 30N "Variable" - o - ...... ~ .... -t- ~:.'S:a- v.~ ~- ...... ~ 0 "500 rn Plateaus"

30 30S

80W 150W ! 20W 90W 60W 30W 0 ~OE 60E 90E 120E T5~E " 'J ~80E

Fig. 10. June/July/Aug difference plots for surface temperature (°C) between the "variable" minus "1 km highlands" and "variable" minus "500 m plateaus". CI = 5°C. See Fig. 3 for explanation.

The JJA pressure differential between the sub- among the three paleotopographic cases, overall tropical high over the eastern Panthalassa Ocean the intensities of the centers and the regional and the low over North America decreases in the pattern of the rainbelts are not significantly "1 km highlands" and "500 m plateaus" simula- different (Figs. 15 and 16). The DJF precipitation tions (Fig. 13). This causes a weakening of the center over northeastern Gondwana results largely northeast trade winds. The JJA deep monsoonal from the onshore flow of marine air brought by low and associated wind circulation over south- the easterlies (Fig. 12). The wind pattern is similar eastern Asia progressively weakens (Figs. 13 and for all three cases. The regionally complex center 14) in the "1 km highlands" and "500 m plateaus" transforms to a more linear pattern where the paleotopographic cases. interior highlands paralleling the proto-Indian Ocean are not present to orographically force Precipitation precipitation in the "500 m plateaus" case (Fig. 17). Moderate rainfall associated with the The location of landmasses strongly influences Sierra Nevada is not affected significantly by the the distribution of precipitation belts and centers. range of elevations specified for these mountains. While the main centers of tropical rainfall change Precipitation patterns reflect monsoon circula- 242 G.T. MOORE ET AL.

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N

60N ~ ~ ~ -- 60N

30N "Variable"

...... 0 • >3km • 2-3 km 3os ~ -- ~~ 30S O 1-2 km

60S

j tll,[,jilfl~11 90S 0 30E 60E 90E 120E 15 E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N 90N

60N 60N

3~,N 30N "1 km Highlands"

30S 30S

60S 60S

, , , 90S 90S , , I i , I , , r ' ' I i , ~ i r I ' I , , i , I r , I , ] 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W - 0 30E 60E 90E 120E 150E 180E 90N 90N

60N " 60N

30N - 30N "500 m Plateaus" 0- ...... r

30S - 30S

60S- 60S

90S , i ''I''L''I 'L~L i I l , I ' ~ r T L l i 90S 180W 150W 120W g0w 60W 30W 30E 60E 9 E 120E 1 E 180E

Fig. 11. Dec/Jan/Feb sea level pressure (mb) for three Late Jurassic 1120 ppm CO 2 simulations with differing paleotopography. CI = 2 mb. See Fig. 3 for explanation. PALEOCLIMATE OF KIMMERIDGIAN TITHONIAN WORLD: II. COMPARING PALEOTOPOGRAPHIC SETTINGS 243

180W 150W 120W 90W 60W 30W 0 3OE 60E 90E 120E 150E 180E i L i I I i i I i i I i , I , , I_ t I I , , i j.. I ~ ~ ] 90N 90N i ...... '~ ~ ~ < < < < < <,,',,',,'-(~" t ~ . ~ \

60N 6ON

30N 30N "Variable" 7 o I >3km 0 I 2-3 km

30S a0s ~ 1-2 km J]. ff 77

60S 60S

1/7tl ~ ~[~l///lll i~1#1~1 i I I f f i= 90S 90S , r" l ' ' ! ~ i 1 i i I i , I 180W 150W 120W 90W 60W 30W 0 30E 6OE 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E qriN I I I I i i I = i I i I I $ i I i L I i i I I I I J I I [ i I 90N

-, ,,L, ~{ 771 ivlil, .... \ k \\ ~ ~ ~ \ t ~ , .

36.-l-;-?jq-.r~::[/ 7" 7] ~ /'/IA~*.-'~'/ .... .Ib' ...... - ,~~?',', ,.i'Z=~..'-~,~i--~bJ-~ ,IXm~ // ;/ ;] ;. (7"4.~ ~--~'/';-~-'~-/".'~-'tJ .... :y3 6N "1 km ~~//~_.~~~.j~1./ ~ /+ 11 - i. - ~_,~ ~- ~ ~ Highlands"

30S 30S

9os I ~'" ; ~'"" ', ""i I 186W 150W 120W 90W 66W 30W 0 30E 66E 90E 120E 150E 180E

80W 50W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N i , I i i I ~ , l -. I l i I ', I i i I i i I i I I i i I l i I i t I I l J 90N

6ON~~IA- ' 'i --.'b~ , • - x:.- .~ ".7~" ,. ::, 60

~o~ ¢~:.: ?? ,,.. , .< ...... ~o~ "500m if'. ~ ~¢i liillii . :/- .. Plateaus" o o ["-]

60S -~ -~ -" ' •

,os, ..... , , ...... 7777777 oo. 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

Scaling vector - = 5ms-1

Fig. 12. Deci'Jan.IPeb surface wind vectors for three Late Jurassic 1 ]20 ppm CO~ simulations with differing paleotopography. See

Fig. 3 for explanation. 244 G.T. MOOREET AL,

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

90N _ / I ~ 90N

60N ~~ 60N

30N 30N + _ "Variable"

i 2-3 km 3os aos D 1-2 km

6os. ~ ,~'~==~--=~S '~ (<~\h.._q<<,~_ +os

90S '"~'~~"~ i i l r i I ] i I i i [ i i I i i [ i i i i ; I , r I i i I i t I ~ t i 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

60N 60N

~~~~~C...... HighlandsD

30S 30S

60S 60S

90S 90S + i I ' ' / i i I , i ] i i I i I r i f i I , I 180W 150W 120 W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N

60N

30N- 30N "500 m Plateaus" 0 0 30S 30S

60S

90S 180W 150W 120W 90W 60W 30W 0 30 E 60E 90E 120E 150E 180E

Fig. 13. June/July/Aug sea level pressure (mb) for three Late Jurassic 1120 ppm CO2 simulations with differing paleotopography. CI = 2 mb. See Fig. 3 for explanation. PALEOCLIMATE OF KIMMERIDGIAN,'TITHONIAN WORLD: 11. COMPARING PALEOTOPOGRAPHIC SETTINGS 245

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

60N

"Variable"

0- 0 |-> 3km | 2-3 km 1-2 km

90S .~ ~ 180W ~50W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N-~ ~ ~ ~ ,L(~ ' ,

60N , >~.5/7~,>~; 2~ - -: x

-~~ ~ ~,~S,~ ~' ,' I- "1 km Highlands" O- 0 O

3os_ 3os _ ~~.-j~.- - .~

_

90S i ~ I 1 i I i i I i , l I I I' I i 1 I I , I ' i I ? P l ' i l i p I 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E ...... / ~ - 90N

.... ' *~ l,J q 'r-1-,~',.-/~./17t ~1"~ ", < ~. t .~ t [~Jd ' ~.:,= ~'N~ ~'..'_~- "~ "500 m Plateaus" 0 D

3os .'.-1" =~.~"-. "~'.-\ x~,, • ' -1-~ .... \', LL~L...... ~%~,,,, ,i-

90S ...... ' ' ~ ' ...... ]-90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

Scaling vector ~ = 5m s-1

Fig. 14. June/July/Aug surface wind vectors for three Late Jurassic, 1120 ppm CO 2 simulations with differing paleotopography. See Fig. 3 for explanation. 246 G.T. MOORE ET AL.

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E i80E 90N ~L '; ' I , , I I , i ~ I I , , I , , I , , I ' L' i , , i~ , ~ , , I , L 90N

60N

30N 30N "Variable" 0 ' o i >3km i 2-3 km 3O5 aos [] 1-2 km

~S 60S

905 90S 180W 150W t20W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N 90N

60N 60N

30N 30N "1 km Highlands"

30S 30S

60S 60S

90S 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N t , = I t ~ 1 J ~ I t t I t i I i , [ I I I I I I I I I I I J I I [ I x 90N

60N

30N 6. ? 30N "500 m Plateaus" 0 ff]

30S

60S

~S r ~ I ' i I ' ' I ' ' I ' ' I ' ' 1 i r ' 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

Fig. 15. Dec/Jan/Feb precipitation (mm d-l) for three Late Jurassic, 1120 ppm CO 2 simulations with differing paleotopography. CI = 2 mm d- 1. See Fig. 3 for explanation. PALEOCLIMATE OF KIMMERIDGIAN,'TITHONIAN WORLD: 11. COMPARING PALEOTOPOGRAPHIC SETTINGS 247

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N ~ J I L h [ t L I t t I J i I i i I i i I J = I i L I i ~ I i ~ I iI iI J 90N

60N

30N "Variable"

0 • >3km L 2-3 km 30S D 1-2 km

60S

I 905 i i I i t t i ] I r i t/I • i I I I I i i t i i l t ] "t ] I t, ,' I ,I F''I 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N 90N

60N 60N

30N 30N "1 km Highlands" Q

30S • 30S

60S 60S

90S - 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 9OW 60W 30W 0 30E 60E 90E 120E 150E 180E 90N 90N

"500 m Plateaus" K]

30S 30S

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

Fig. 16. June/July/Aug precipitation (mm d-1) for three Late Jurassic, 1120 ppm CO 2 simulations with differing paleotopography. CI = 2 mm d- 1. See Fig. 3 for explanation. 248 G.T. MOORE ET AL.

180W 150W 120W gOW 60W 30W 0 JOE 60E 90E 12QE 150E 180E 90N- ~ I I I J I I I I I I I I t I I J I I I I I I I I I I I I I I I 90N

604- <' o.~H;, ' °"~~\'-~1 (3 I;;2 0 ,..<2r-~. j" "~ ,--~ con

oo • " ,",:" ""'/ ....'" ,-':::-:',,-::'" O . . 4 9 b . .... %" "

0 0 "Variable" - "1 km Highlands"

30 " ~- -,O " o 30S l .90

ol .1 52 < " o t 90~ I a , I , ,, " I, , , I i i 905 180W 150W 120W 90W 60W 30W " ,30£ 60E 90E 120E 150E 180E

180W 150W 12QW 90W 60W 30W 0 30E 6QE 90E 120E 150E 180E 90H LL_ I I I I I I ] I I ~- [ ~ I J I I I I i t t ~ L i J t i I I h I i i 90N

60N

"Variable" - "500 rn Plateaus"

305 , . ".' , . . . 305

60S

90S 180W 150W 120W g0W 60W 30W 0 30E 60E 90E 120E !50E 180E

Fig. 17. Dec/Jan/Feb difference plots for precipitation (mm d-1) between the "variable" minus "1 km highlands" and "variable" minus "500 m plateaus". CI = 2 mm d- 1. Dashed contours represent negative values. See Fig. 3 for explanation. tion in the low latitudes, with paleotopography monsoonal and easterly circulation (Figs. 16 and contributing typical orographic effects (e.g., rain 18). This is seen also in the northwestern North shadows) relating to the location and quantity of American JJA precipitation center forced by the rainfall. Rain shadows are best developed in the Sierra Nevada. In contrast, areas for which precipi- winter h~mispheres of the "variable" case (e.g. tation is not sensitive to altered paleotopography westerri side of the Asian range). Changes in include Australia and the margins of India and precipitation associated with the orographically Antarctica. enhanced monsoon in southeastern Asia dramati- cally show the effects of paleotopography (Figs. Latent heat 16 and 18). This example shows the importance of the orientation of mountain ranges and how The latent heat difference plots compare the paleotopography strongly influences the Volume "variable" with the other two cases (Fig. 19). In and extent of associated rainfall (Figs. 15-18). these plots, some high values coincide with regions Similar, though weaker correlations, occur in the where precipitation has decreased in the "1 km JJA precipitation related to the North American highlands" and "500 m plateaus" cases relative to PALEOCLIMATE OF KIMMERIDGIAN/TITHONIAN WORLD: II. COMPARING PALEOTOPOGRAPHIC SETTINGS 249

1809k' '50w 120w 90w 6Cw 30w 0 ~C,F 60£ 90E 12CE 150E 'BOE

J : 4L1

o ~ "Variable" - "1 km Highlands"

'L,'-' '..ow' °;

180W 15QW 120w 90W 60W 30w O 30E 60E 90E 120E 150E 18QE 90 ' 90N

6O 60N

"Variable" - "500 rn Plateaus"

90~ -~-~ i ~ [ i . ~ ii i - ] ] ] ] i i ] ] ~ i i , ] , i ] i @ gOS ' 80w ! 50w T 2@w 9CW 60W 30W 0 30E 60E ' ' 90£ ~ 20 E ! 50E i 50£

Fig. 18. June/July/Aug difference plots for precipitation (mm d-1) between the "variable" minus "1 km highlands" and "variable" minus "500 m plateaus". CI = 2 mm d- a. Dashed contours represent negative values. See Fig. 3 for explanation. the "variable" case (Fig. 10). Three prominent high "1 km highlands" and "500 m plateaus" cases, the centers coincide with diminished precipitation rates surface will be at, a lower position on the lapse related to changed orography in the Sierra Nevada, rate curve (5-10°C increase per 1 km of descent). Appalachian, and eastern Asian ranges (Fig. 19). Lowering elevations will warm the land surface These mountain regions also possess cooler surface simply by this effect. Second, the orographically- temperatures due to lapse rate in the "variable" related precipitation increase in the "variable" case case as shown by the JJA temperature maps results in more moisture available for evaporation. (Fig. 8) and difference plots (Fig. 10). This suggests Therefore, the "variable" case is more susceptible a causal relationship between the regional heating to evaporative cooling. Thus, land surface temper- in the "1 km highlands" or "500 m plateaus" cases atures (LST), a well-utilized parameter by paleocli- (Fig. 8); less or no paleotopographically forced mate modelers, are intimately tied to the precipitation (Fig. 16) with attendant loss of radia- paleotopography on regional scales. That relation- tive evaporation; and a positive latent heat flux ship alone in this sensitivity study results in'a difference (Fig. 19). maximum JJA LST warming of ~17°C and The change in latent heat flux is caused by two ~24°C in the "1 km highlands" and "500 m factors. First, because of lowered elevations in the plateaus"-cases respectively where orographically 250 G.T. MOORE ET AL.

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N 90N

60N 60N

"Variable" -- "1 km Highlands" - f

90S. ~ " " 90S 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E

180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180E 90N I I I I a 1 I I I I I I I I I I i I * t I J i I t ~ I I I I I I I I I

60N ~N

30N "/ ' -- '" 30N

_ a£'22. _.azz~- ..... 0 "Variable" --

I~ o ". ", ,2 "500 m Plateaus" ~~:, ,' " " ---: "£ - - : :.,, ~ "4. "'~;- 30S.

60S.

90S ' f I ' ' I , , I , , I r l I i i ' I , ; i ~ , i , , i J' f "I ", , I , f 90$ 180W 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E I~E

Fig. 19. June/July/Aug difference l)lots for latent heat flux (W m -2) between the "variable" minus "1 km highlands" and the "variable" minus "500 m plateaus". CI= 20 W m -2. See Fig. 3 for explanation. forced precipitation in the eastern Asia range is plex thermal patterns over land than the other an important process (Fig. 10). In contrast, where two. As paleotopographic contrasts are reduced, the process is not an important factor, such as the summer temperature isotherms over the conti- with the high latitude mountains of southern Gon- nents develop a concentric pattern, whereas the dwana, little LST change occurs in either season winter patterns are zonal, indicating a greater (Figs. 9 and 10). influence of continentality. The oceans exhibit zonal SST patterns in both Summary and discussion seasons. As paleotopographic contrasts decrease from the "variable" to the "500 m plateaus" cases, Comparison of three Late Jurassic simulations, the temperature patterns become more zonal. SST each with the same paleogeography and CO2 of the high latitude oceans warm with decreasing factor, but with differing paleotopography ("vari- relief. The warmer SST's restrict sea ice extent and able", "1 km highlands", and "500 m plateaus") thickness (Part I). The continents are generally yields the following observations. warmer overall, but the extremes are similar among The "variable" simulation possesses more corn- cases. PALEOCLIMATE OF KIMMERIDGIAN'TITHONIAN WORLD: I1. COMPARING PALEOTOPOGRAPHIC SETTINGS 251

Seasonally, temperature trends in the DJF sea- tion. However, in terms of influencing results, the son for the three cases show: a largely zonal pattern effects of paleotopography upon model-produced for the isotherms across the N.H.; temperatures climate are not always predictable. along the periphery of the S.H. continents reflect Comparison of the "variable" case to the "1 km marine influence and warm toward the interior; highlands" and "500 m plateaus" cases shows that the more simplified the paleotopography is in the simplified paleotopography produces simplified S.H., the more concentric is the isotherm pattern global circulation. but with a steeper gradient along the continental Orographically forced circulation patterns, pre- margins; and the oceans warm as the paleotopogra- cipitation, and other climate-driven processes are phy becomes more simplified with the significant modified when paleotopography is simplistic or changes occurring poleward of 50 ° (Figs. 7 and 9). ignored. The effects of paleotopography upon the Temperature trends in the JJA season for the three paleoclimate are neither cumulative nor necessarily cases show: the equatorial ocean is virtually with- proportional to changing elevations. The results out change; the 0 ° SST isotherm progressively shown here demonstrate an interplay between migrates poleward in the S.H. with simpler paleo- orography, effects of continent size, and land-sea topography; the low (1 km) topography of Gond- thermal differences. Thus, paleotopographic varia- wana does not force interior temperatures as the tion must be considered important in its influence isotherms show little variation between the "500 upon the paleoclimate of any geologic time interval m plateaus" case and the other two (Figs. 8 and and must be incorporated into simulations. 10). The location and height of mountain ranges Sea level pressure and surface wind patterns in influence each investigated parameter. Further, the winter hemispheres trend toward more simpli- paleotopography is linked as a driving force to fied zonal circulation as paleotopographic con- atmospheric circulation, surface temperature, and trasts decrease with the simplest pattern occurring the hydrologic cycle. Hence, to evaluate a simula- in the "500 m plateaus" simulation. This is com- tion properly in terms of the preserved geologic mon to both hemispheres despite dissimilar paleo- record, we believe that paleotopography is on a geographies. In contrast, the summer circulation par with the accuracy of the paleogeography patterns in both hemispheres, while simplified, employed. remain dominated by paleogeography, irrespective Land and sea surface temperatures (LST, SST) of paleotopography. generated in GCM simulations are employed by The locations of land masses influence precipita- both modelers and other scientists of varying disci- tion. The rate and areal extent of orographically plines for various reasons. One of the more com- forced precipitation are influenced strongly by mon usages is calibration of the model results with paleotopography. Our results further support the the preserved geologic record of floras, faunas, contention that precipitation response is strongly and/or environmentally sensitive sedimentary influenced by other paleoclimate feedbacks. rocks (Sloan and Barton, (1992b). This study The jet stream pathways in both hemispheres, shows that because of lapse rate effects, the LST and resulting mid-latitude storm tracks, become is intimately tied to the paleotopography on a simplified and linear without the effects of paleoto- regional scale. Thus, before using LSTs from a pography. simulation with confidence, due consideration should be given to the authors' selection of both Conclusions paleogeographic (which is obvious) and paleotopo- graphic (which is far more subtle) boundary con- In conclusion, sensitivity tests comparing three ditions. simulations with the same paleogeography and As an additional observation, if only two end paleoatmospheric concentration of CO z member paleotopographic specifications are (ll20ppm), but differing land elevations, show employed, a logical extension might be that all paleotopography is an important boundary condi- paleotopographic specifications within those 252 G.T. MOORE ET AL. bounds would influence climate in a similar, inter- Kutzbach, J.E., Guetter, P.J., Ruddiman, W. and Prell, W.L., 1989. Sensitivityof climate to late Cenozoic uplift in southern mediate fashion. In the Late Jurassic cases shown Asia and the American west: Numerical experiments. here we have found that such an assumption would J. Geophys. Res., 94: 18,393-18,407. be incorrect, except for a few basic responses such Manabe, S. and Terpstra, T.B., 1974. The effects of mountains as the development of rain shadows. This suggests on the general circulation of the atmosphere as identified by numerical experiments. J. Atmos. Sci., 31: 3-42. that all paleotopographic cases must be considered Moore, G.T., Hayashida, D.N., Ross, C.A. and Jacobson, independently of one another and not simply inter- S.R., 1992. The paleoclimate of the Kimmeridgian/Tithonian polated between two simulations. (Late Jurassic) world: I Results using a general circulation model. Palaeogeogr., Palaeoclimatol., Palaeoecol., 93: 113-150. Acknowledgements Pearman, G.I., Etheridge, D., De Silva, F. and Fraser, P.J., 1986. Evidence of changing concentrations of atmospheric CO2, N20, and CH~ from air bubbles in Antarctic ice. We thank S.R. Jacobson, C.A. Meyer, and two Nature, 320: 248-250. anonymous reviewers for providing many con- Rind, D., 1988. Dependence of warm and cold climate depiction structive suggestions that materially improved the on climate model resolution. J. Climate, 1: 965-997. manuscript. J.D. Koishor and J.L. Bube prepared Ross, C.A. and Ross, J.R.P., 1983. Late Paleozoic accreted terranes of western North America. In: C.H. Stevens (Editor), the figures and B.A. Villegas typed the manuscript. Pre-Jurassic Rocks in Western North American Suspect We appreciate their help and attention to detail. Terranes. Pac. Sect. SEPM, Los Angeles, CA, pp. 7-22. The authors thank Chevron Oil Field Research Ross, C,A., Moore, G.T. and Hayashida, D.N., 1992. Late Company for permission to publish this paper. Jurassic paleoclimate simulation--Paleoecological implica- tions for ammonoid provinciality. Palaios, in press. Rowley, D.B., 1992. Preliminary Jurassic reconstructions of References the Circum-Pacific region. In: G.E.G. Westermann (Editor), The Jurassic of the Circum-Pacific, IGCT Project 171. Cam- Barnola, J.M., Raynaud, D., Korotkevich, Y.S. and Lorius, bridge Univ. Press, pp. 15-27. C., 1987. Vostok ice core provides 160,000-year record of Ruddiman, W.F. and Kutzbach, J.E., 1989. Forcing of late atmospheric CO2. Nature, 329: 408-414. Cenozoic northern hemisphere climate by plateau uplift in Barron, E.J. and Washington, W.M., 1984. The role of geo- southern Asia and the American west. J. Geophys. Res., 94: graphic variables in explain!ng paleoclimates: Results from 18,409-18,427. Cretaceous climate model sensitivity studies. J. Geophys. Scotese, C.R., 1992. Atlas of Phanerozoic Plate Tectonic Recon- Res., 84: 1267-1279. structions. Am. Geophys. Union, Washington, DC, in prep. Berner, R.A., 1990. Atmospheric carbon dioxide levels over Sloan, L.C. and Barron, E.J., 1992a. Paleogene climatic evolu- Phanerozoic time. Science, 249: 1382-1386. tion: A climate model investigation of the influence of Bolin, B., 1950. On the influence of the Earth's orography on continental elevation and sea surface temperature upon conti- the general character of the westerlies. Tellus, 2: 184-195. nental climate. In: D. Prothero (Editor), Eocene-Oligocene Budyko, M.I., Ronov, A.B. and Yanshin, A.L., 1985. Changes Climatic and Biotic Evolution. Princeton Univ. Press, in the chemical composition of the atmosphere during the Princeton, NJ, in press. Phanerozoic. Int. Geol., 27: 423-433. Sloan, L.C. and Barron, E.J., 1992b. A comparison of Eocene Hallam, A., 1985. A review of Mesozoic climates. J. Geol. Soc. climate model results to quantified paleoclimatic inter- London, 142: 433-445. pretations. Palaeogeogr., Palaeoclimatol., Palaeoecol., in Harland, W.B., Armstrong, R.L., Cox, A.V., Craig, L.E., press. Smith, A.G. and Smith, D,G., 1990. Geologic Time Scale Washington, W.M. and Meehl, G.A., 1984. Seasonal cycle 1989. Cambridge Univ. Press. experiment on the climate sensitivity due to a doubling of Kasahara, A. and Washington, W.M., 1971. General circulation CO2 with an atmospheric general circulation model coupled experiments with a six-layer NCAR model, including orogra- to a simple mixed-layer ocean. J. Geophys. Res., 89: 9475- phy, cloudiness, and surface temperature calculations. 9503. J. Atmos. Sci., 28: 657-701. Ziegler, A.M., Scotese, C.R. and Barrett, S.F., 1983. Mesozoic Kuo, C., Lindberg, C. and Thompson, D.J., 1990. Coherence and Cenozoic paleogeographic maps. In: P. Brosche and established between atmospheric carbon dioxide and global J. S/indermann (Editors), Tidal Friction and the Earth's temperature. Nature, 343: 709-714. Rotation II. Springer, Berlin, pp. 240-252.