the significance of marine boreal molluscs in the early pleistocene faunas of the mediterranean area abstract repeated migration of boreal guests into the mediterranean during the early pleistocene has been considered a weak paleoclimatic oceanographic tool this attitude is partly held because the plio pleistocene boundary as defined in the mediterranean does not seem to coincide with isotopic events more important than those of the piacenzian an analysis of their present biogeographical distributions suggests that the successful migration of the boreal elements into the early pleistocene mediterranean was caused by the establishment of a climatic phase of high seasonality with winter temperatures lower than 9 10 c and summer temperatures not lower than 20 c such a situation would also have been suitable for the taxa of warm affinity that characterize the present mediterranean moroccan bioprovince this hypothesis applies mainly to the first phase of migration santernian substage which is the best known from a malacological point of view the available paleoclimatic and isotopic record seems in agreement with the hypothesis

late quaternary marine mollusca as palaeoenvironmental proxies a compilation and assessment of basic numerical data for ne atlantic species found in shallow water abstract temperature salinity and depth limits are given for selected molluscs from boreal and arctic regions of the ne atlantic and adjacent shelf seas the significance of the data for palaeoenviromental analysis is briefly discussed

late quaternary relative sea level changes and the role of glaciation upon continental shelves sea levels of the past 20 kyr are largely determined by the response of the earth to the last ice age consequently sea level indicators are an important source of information about the interaction between cryosphere and hydrosphere and the solid earth based on the material presented at a recent european science foundation conference the present paper pin points some of the topics currently under discussion with respect to sea level evidence found on continental shelves these topics include possible effects of erosion and changes in palaeotidal ranges on indicators of former relative sea levels as well as the problems involved in the determination of palaeo water depth in addition to former sea levels more evidence is being gathered for substantial small scale patterns in the sea level changes at or nearby to the former ice margins these patterns are not reproduced by the available geophysical models which reconcile on first order level only the large scale pattern

results of global atmospheric circulation experiments on an earth with a meridional pole to pole continent four general circulation models forced by mean annual insolation and having an energy balance ocean have been run for pole to pole continents 1 low relief 750 m average elevation 2 high plateau 1500 m average elevation 3 mostly low 750 m but with 3 km mountains on the west and 4 mostly low 750 m but with 3 km mountains on the east the high plateau continent emphasizes the contrast between high and low pressure systems marginal mountains on either coast enhance moisture transport from the west to the continental interior but mountains on the east eliminate the tropical wet belt and produce the most arid scenario in none of the experiments do zonal climate boundaries trend steeply equatorward from east to west all of the models produce more arid continental conditions than exist today

late devensian to early holocene palaeoenvironmental changes in the viking bank area northern north sea abstract lithological and macrofaunal analysis of vibrocores collected from northwest of the viking bank enables the devensian to holocene strata to be subdivided into eight informal units three of which occur widely in the northern north sea for the viking bank area it is suggested that sea level was more than 100 110 m below that at present between 15 500 and 13 600 bp a time when some parts of the area were dry land and others covered by a shallow high arctic sea sea level may have been even lower more than 140 m below its present level prior to 15 500 bp during the windermere interstadial 13 000 11 000 bp polar water was replaced by atlantic water and the environment was low arctic with a regime of strong tidal currents sea level at approximately 12 000 bp had risen to some 80 100 m below present the loch lomond stadial and early holocene generally were characterised by high arctic followed by boreo arctic to boreal faunas relatively low energy conditions and probably rapidly rising sea level

the contribution of malacology in dating the pleistocene submarine levels of the english channel abstract the submerged pleistocene beach conglomerate is an underwater shelly and cobble rich formation that has been found only on the southern flanks of the english channel it resulted from the cementation of beach deposits that were overlain by loessic silts at a time of lower sea level study of the fauna within this conglomerate allows the separation of three shelly belts located between 24 and 54 m around the channel islands of the normano breton gulf 40 and 65 m off tregor and 52 and 80 m off leon these belts are correlated with three regressive pleistocene episodes a comparison with one of shackleton9s published sea level curves has produced age estimates that date the three beach deposits at around 105 110 73 80 and 30 57 ka respectively these beaches were sealed by three phases of loess deposition around 103 67 and 18 ka we assume that there are at least three different pleistocene beach conglomerates in the english channel some of them show differences in their fossil fauna that could be partly a factor of contemporaneous water temperature a fourth beach conglomerate without fossil fauna may exist at 93 m

holocene palaeoecology and floodplain evolution of the muge tributary lower tagus basin portugal abstract the lower muge valley a tributary of the lower tagus river portugal features an important archaeological record of mesolithic shell midden sites archaeological research has long assumed that tidally influenced valley floor environments in the immediate locality of the sites provided a rich food resource attracting mesolithic settlement to date there has been little attempt to use palaeoenvironmental records to reconstruct holocene floodplain evolution in the lower tagus valley the cultivated freshwater lower muge floodplain is locally underlain by 11 m of homogeneous fine grained sediments and peat comprising buried floodplain environments contemporary with mesolithic occupation 6200 4800 cal bc pollen and foraminifera analyses demonstrate that fine grained deposition forced by sea level rise commenced 6200 cal bc in an estuarine setting the lower muge floodplain experienced maximum tidal influence 5800 5500 cal bc subsequently sediment supply rates overtook the decreasing rate of sea level rise and fluvial environments expanded the pollen record may suggest regional desiccation from 5000 cal bc estuarine environments disappeared suddenly 3800 cal bc when freshwater wetlands were established although the initiation of mesolithic settlement is shown to coincide with the beginning of tidal influence site abandonment does not match with any major environmental change sea level still stand 2600 cal bc has been linked to valley floor stabilisation and soil formation alder floodplain woodland developed prior to 230 cal bc and was cleared probably during roman times for agriculture renewed deposition after 230 cal bc may relate to internal mechanisms or to human impact upon the catchment vegetation

an initial study of the sensitivity of modeled cretaceous climate to cyclical insolation forcing some cretaceous rhythmic sedimentation such as the colorado greenhorn formation deposited in the western interior seaway u s may have been produced by cyclic precipitation intensity change responding to orbitally produced insolation forcing to test this hypothesis a general circulation model was forced with the seasonal maximum and minimum insolation calculated from assumed cretaceous orbital parameters geographic comparisons for july and january of surface temperature surface pressure and precipitation were prepared for january maximum land sea contrast produced an increase of more than 6 mm day precipitation over the interior seaway however the july maximum simulation did not produce precipitation increase despite an anticipated monsoonlike circulation over the region north america appears to be very arid during cretaceous northern hemisphere summer

numerical climate modeling a frontier in petroleum source rock prediction results based on cretaceous simulations organic productivity and preservation are primary controls of the distribution of petroleum source beds both organic productivity and preservation are in part a function of geographic setting and climate therefore the prediction of paleoclimates is a major frontier in petroleum source rock prediction a climate model based on the fundamental laws thought to govern atmospheric circulation is applied here to the prediction of upwelling regions associated with very high productivity and bottom conditions that may become anoxic despite a high oxygen supply the potential and limitations of climate modeling in the prediction of upwelling regions are examined by 1 demonstrating the ability of the model to predict present day winds and upwelling regions 2 demonstrating t at the model and the location of upwelling regions is sensitive to geography continental positions sea level and topography and 3 investigating whether the model sensitivity to past geographies is realistic i e if predicted upwelling regions for the cretaceous period correspond to source rock localities the model predictions of ocean and coastal upwelling compare very favorably with present day observations and with estimates of primary productivity the location of middle latitude and high latitude upwelling locations are sensitive to model specified geography the location of low latitude upwelling is less sensitive to changes in global geography if coastlines are oriented appropriately despite some limitations a comparison of source rock localities with model predictions is promising the results of these studies suggest that numerical climate modeling is a potential tool in petroleum source rock prediction

modeling tides in monterey bay california abstract in the process of developing a tide permitting coastal ocean forecasting system tidal signals are added to an oceanic general circulation model for monterey bay california the model which is configured from the regional ocean modeling system roms has three one way nested domains with the finest resolution of 1 6 km in the horizontal direction and 32 levels in the vertical direction in present research the tidal simulation of the system is validated against tide gauges adcp current observations high frequency radar surface current observations and compared with the output from two barotropic tidal models the results indicate that the barotropic tides from the model compare well with observations in terms of sea surface height with discrepancies in amplitude of less than 10 of the amplitude of the most energetic m 2 constituent however the discrepancy for the barotropic tidal currents can reach 30 among models with similar accuracy in sea surface height the generation and propagation of baroclinic tides associated with the monterey submarine canyon are qualitatively reproduced by the model with weaker strength the surface tidal current simulation is improved especially in terms of magnitude when the model has a more realistic stratification through changes in both barotropic and baroclinic tidal currents

cretaceous climate a comparison of atmospheric simulations with the geologic record abstract atmospheric simulations using realistic cretaceous geography 100 million years ago suggest that paleography is an important factor governing the nature of the circulation the simulated cretaceous atmospheric circulations are markedly different both from the present day atmospheric circulation and from the classical hypotheses of a weaker circulation and poleward displacement of circulation features e g the subtropical high therefore they pose specific questions which can be tested against the geologic record aspects of the cretaceous simulations are verified in comparisons with the geologic record the simulations serve to guide areas of future paleoclimatic research and to formulate better the nature of the problem of warm equable climates

continental drift runoff and weathering feedbacks implications from climate model experiments changes in atmospheric carbon dioxide have been proposed as a major regulator of climate during the last 570 million years continental weathering and its variation over time are hypothesized to be important for controlling atmospheric carbon dioxide continental weathering is altered by changes in total runoff as well as changes in the size and elevation of the land masses to be weathered when paleogeographic information for the phanerozoic 570 m y ago to present is used in a global climate model the model exhibits substantial variations in precipitation evaporation and runoff even with dramatically different land ocean distributions an increase in global surface temperature leads to an increase in global precipitation but not always an increase in global runoff during the early phanerozoic 514 342 ma when the continents are relatively small and widely distributed runoff depends on continental evaporation and temperature as the continents migrate into subtropical latitudes global runoff decreases as global land temperatures and evaporation increase as the continents shift to higher latitudes global runoff increases as global land temperatures and evaporation decrease during the middle to late phanerozoic 306 ma present when large continental land masses predominate runoff depends on continental precipitation experiments with increased atmospheric co 2 for the middle ordovician 458 ma when the paleocontinent of gondwana was centered at subtropical latitudes and the early silurian 425 ma when gondwana had shifted to middle and high latitudes also point to a correlation between land mass location and runoff global runoff increases 15 with increased co 2 at 425 ma but remains unchanged for 458 ma even though global mean temperature and precipitation increase comparable amounts for the two time periods these results imply that weathering feedback between temperature and runoff may be dependent on land ocean configuration

the cause of the late cenozoic northern hemisphere glaciations a climate change enigma the ultimate cause of the onset of glaciations remains elusive but in the case of northem hemisphere glaciation it is probable that several factors acted in combination general global cooling resulted from reduction of atmospheric c02 by weathering of silicate rocks exposed by erosion of late cenozoic uplifts uplifts in south asia southwestern north america and scandinavia occurred at distances appropriate for the generation of quasi permanent rossby waves in the atmosphere the resulting winds given suitable moisture sources were favourable for causing large scale precipitation at mid latitudes on the northern continents moisture sources were provided by the closure of the central american isthmus gulf stream flow increased carrying warm subtropical waters to high latitudes the denmark strait deepened permitting greater outflow of deep water from the norwegian greenland sea the relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity studies

climate change on tectonic time scales abstract observational and modeling studies relevant to climate change on tectonic time scales are reviewed probably the most significant climate result from this time scale involves inferences about nearly ice free conditions for some intervals of earth history some additional results suggest relatively rapid transitions between climate states modeling studies indicate that although tectonic changes significantly modify the atmosphere and ocean circulation in most cases such modifications do not appear to be sufficient to explain ice free climates increased atmospheric co2 levels 5 10 presentvalues may be needed to completely reconcile models and data although the co2 paradigm has received widespread attention in the last few years the results summarized herein indicate that co2 is only one of several important factors influencing climate i believe the time is appropriate for contemplating climate change on tectonic time scales in terms of a post co2 synthesis in which direct tectonic factors are approximately equal in importance to co2 fluctuations in the last few years modeling studies have progressed from a state of virtually no work on the topic to one where the models are in some respect ahead of the observations in the sense that data have not been compiled to test even some of the most basic model predictions in particular information is needed on past atmospheric co2 levels tropical sea surface temperatures seasonality of continental interiors and locations and production rates of deep waters initial steps are being taken to integrate observational and modeling activities on tectonic time scales and some of these shortcomings may be rectified over the next few years

shell bioerosion in high latitude low energy environments firths of clyde and lorne scotland abstract the agents of bioerosion in the firths of clyde and lorne include endolithic algae cliona phoronids acmaea virginea lepidopleurus asellus and regular echinoids which directly and indirectly cause shell disintegration and the production of calcareous sediments algae and acmaea are very effective in shell erosion but are confined to the photic zone where over 90 of the shells have suffered from their attack other bioerosion agents are not depth restricted but individually affect a lesser number of shells the photic limit approx 30 m is estimated from the disappearance of the deepest growing algae conchocelis and ostreobium the density of algal boring is high due to the low energy at the bottom it is shown that algal borings and acmaea grazing are also important as palaeobathymetric tools

ice proximal glaciomarine sedimentation and sea level change in the inverness area scotland a review of the deglaciation of a major ice stream of the british late devensian ice sheet abstract evidence of both rising and falling relative sea levels and glacitectonic movements is preserved in two formations of raised glaciomarine deposits that were laid down in front of an oscillating grounded tidewater glacier in the inverness firth these changes occurred during the latter stages of the disintegration of the moray firth ice stream one of the major ice streams that drained the british main late devensian ice sheet most of the glaciomarine deposits antedate a sequence of glacio isostatically tilted late devensian marine shorelines and associated littoral and estuarine deposits the shorelines began forming at about 13 000 bp and record a progressive fall in relative sea level a new model for the deglaciation of the moray firth region is proposed after a critical appraisal of published accounts of both onshore and offshore quaternary sequences the disintegration of the moray firth ice stream involved several rapid phases of retreat to pinning points caused by iceberg calving and triggered by rising global sea level each retreat was followed by minor readvances or stillstands possibly caused by short lived accelerated periods of glacio isostatic rebound and concomitant temporary falls in relative sea level two such events occurred in the inverness firth the ardersier oscillation and the alturlie stillstand substantial differences lower relative sea levels later deglaciation are apparent between the pattern of ice retreat in the moray firth region and published accounts of the deglaciation of the irish sea basin these differences require a reassessment of some current hypotheses concerning the disintegration of major ice streams associated with high relative sea levels furthermore geological and geomorphological evidence suggesting both rising and falling sea levels in the inverness area prior to ca 13 500 bp is not fully compatible with recently published computer simulations of the dissolution of the british main late devensian ice sheet

late devensian and holocene relative sea level changes on the isle of skye scotland uk detailed litho and biostratigraphical analyses from three coastal sites in contrasting coastal settings on the isle of skye scotland uk reveal evidence for several changes in relative sea level during the late devensian and holocene at the start of the record relative sea level in the area was high at ca 12 500 14c ca 14 800 cal yr bp but then fell reaching a low point during the younger dryas at ca 11 000 10 000 14c ca 13 000 11 600 cal yr bp when a rock platform correlated with the main rock platform was formed in the early middle holocene relative sea level was rising by ca 8000 14c ca 8800 cal yr bp and in northeast skye a lagoonal surface correlated with the main postglacial shoreline was formed at ca 6600 14c ca 7500 cal yr bp by the late holocene relative sea level was again falling but a rise registered at at least two sites began probably before ca 4000 14c ca 4500 cal yr bp and a second lagoonal surface in northeast skye correlated with the blairdrummond shoreline was formed although by ca 3000 14c ca 3200 cal yr bp relative sea level in the area had resumed its downward trend the pattern of relative sea level changes disclosed is compared with evidence elsewhere in scotland

interglacial and glacial climate oscillations in a marine shelf sequence from northern denmark a multidisciplinary study abstract a 22 5 m long marine shelf sequence in northern denmark covers the climatic shifts from glacial environments through interglacial and into early glacial conditions the interglacial was interrupted by two cool intervals also the early glacial succession experienced oscillations of the climate and a period with ameliorated temperature conditions has been separated as an interstadial these results are based on a multidisciplinary high resolution study of lithology foraminifera ostracods macrofauna diatoms and stable isotopes in a silty clay sequence from a borehole at norre lyngby 70 5 48 0 m depth the lithostratigraphy and the variations in depositional environment in the area is supported by a reflection seismic profile across the core site the chronostratigraphy is discussed on the basis of biostratigraphical correlation and seismostratigraphy as well as optically stimulated luminescence osl dating and amino acid measurements the biostratigraphy and the osl dates suggest an eemian age for the interglacial while amino acid results point to an older age if the interglacial is confirmed as eemian we believe that the succeeding interstadial period is likely to be correlated with the brorup interstadial the climatic changes in this eastern part of the north sea region are closely linked with changes in the north atlantic circulation pattern and the environmental fluctuations at norre lyngby are therefore believed to reflect fluctuations in the past regional climatic and oceanic system

simple energy balance model resolving the seasons and the continents application to the astronomical theory of the ice ages a one level seasonal energy balance climate model which has explicit two dimensional land sea geography is introduced and its properties analyzed the model distinguishes land from sea surface strictly by the local thermal inertia employed the transport is governed by a smooth latitude dependent diffusion mechanism the model s seasonal cycle is solved for with and without ice feedback in each case good agreement with real data is accomplished with minimal tuning of the adjustable parameters the model sensitivity for small solar constant changes is in agreement with that of other accepted models however when the solar constant is lower a few percent the ice cap grows discontinuously from covering greenland and vicinity to a size three times larger and mostly into northern canada a similar discontinuous growth occurs when the orbital elements are changed to favor cool summers in the northern hemisphere this discontinuous sensitivity is discussed in the context of the milankovitch theory of the ice ages and the associated branch structure is shown to be analogous to the so called small ice cap instability known from simpler models although the discontinuity in sensitivity is somewhat conjectural both linear and nonlinear models have their largest sensitivity to orbital parameter changes in the northern portions of the large continents in the western hemisphere this also corresponds to the ice sheet boundary suggesting that the land sea configuration is crucial to large glacier growth irrespective of moisture budgets other experiments and implications are also discussed the remarkable paper by hays et al 1976 hereafter his presented compelling empirical evidence that continental ice sheet volume changes and sea surface temperature variations in the last 700 000 years are correlated with the changes in the earth s orbital elements theoretical arguments for such a connection date back to the last century but the most detailed and convincing arguments are due to milankovitch 1941 and the theory usually is associated with his name if the hypothesis is correct the theory and observations provide the cleanest experiment to determine the sensitivity of the earth s climate to truly external influences such a measure of climate sensitivity is of obvious importance considering the recent interest in estimating the change in climate due to other forcings such as the enhanced greenhouse effect due to increased levels of co2 in the atmosphere e g ramanathan 1981 hansen et al 1981 manabe and stouffer 1980 in effect climate models might be tested or calibrated by this natural experiment climate modeling has progressed dramatically in the last decade with the construction and testing of several general circulation models gcm s although some interesting ice age experiments have been done with these models gates 1976 manabe and hahn 1977 they still include only crude parameterizations of the slower components such as the oceans these numerical models are the ultimate tool that can be brought to bear upon the climate problem however they are almost as complicated as the climate itself hence experiments must be carefully designed and the interpretation is often difficult due to the expense of obtaining definitively long runs in parallel with gcm construction has been the development of x permanently at applied research corporation landover maryland 20785

late weichselian early holocene stratigraphy and environmental conditions in southwestern varmland sweden reflected by benthic foraminifera and molluscs abstract the biostratigraphy at two sites lake uppsalstjarnet and lake osten southwestern varmland southwestern sweden has been investigated the main interest is put on glaciomarine and marine sediments deposited shortly after deglaciation foraminifera and molluscs were present at the deglaciation and some hundred years after arctic faunas dominate in the lowermost layers deposited close to the ice front a transition to faunas affected by increased meltwater influence and higher temperature is recorded higher up in the sequences ams datings of bivalves and foraminifera have yielded ages between ca 10 100 and 9750 bp which infers that southwestern varmland was deglaciated during the latest part of the younger dryas to early preboreal the marine sediments are overlain by varved and sulphide stained clay units deposited when a connection with the sea still was open but the ingression of saline water had ceased

seasonal pteropod sedimentation in the norwegian sea pteropods of the species limacina helicina dalli polar species and limacina retroversa fleming subpolar species were collected in three sediment traps deployed in the norwegian greenland sea the three traps were stationed in the lofoten basin 69 n near bear island 76 n and in the fram strait 79 n in the lofoten basin the relatively warm and saline atlantic water provides optimal living conditions for the subpolar pteropod species limacina retroversa pteropod sedimentation in the lofoten basin was limited to the time period between august and november changes in the abundance distributions of shell sizes indicate that reproduction was taking place at a high rate during this time at this station pteropod shells contributed 11 to the total carbonate collected during the study period the pattern of pteropod sedimentation in the fram strait and in the vicinity of bear island differed from that observed in the lofoten basin colder and less saline water produced by mixing of the east greenland current with the norwegian current is found in the area of these stations in contrast to observations in the lofoten basin the pteropod population in these two regions was comprised of the two species limacina helicina and limacina retroversa the sedimentation of pteropods at the two northern traps did not begin until september bear island october fram strait and continued until february bear island march fram strait reproduction at significant rates was not observed at these locations it is likely that currents transported pteropods northwards to these areas from regions such as the lofoten basin an area of vigorous reproduction of subpolar species and the east greenland shelf which provides favourable living conditions for polar species the flux of pteropod carbonate in the lofoten basin is 52 and 57 times higher than that of bear island and the fram strait respectively the contribution of pteropod carbonate to the total carbonate over the course of the study was less than 1 in the vicinity of bear island and 1 7 in the fram strait scanning electron microscope photographs of limacina retroversa from the lofoten basin displayed dissolution structures however it was not possible to quantify the carbonate loss due to dissolution

the use of ostracods from marginal marine brackish waters as bioindicators of modern and quaternary environmental change abstract ostracoda microscopic aquatic crustacea from brackish waters have a great potential for ecological monitoring and palaeoenvironmental analyses in highly variable environments this has been proven in many articles during recent decades but their potential has yet to be fully developed or utilised the analysis of ostracod assemblage composition species distributions eco phenotypic variability and the analysis of stable isotopes and trace elements in ostracod shells provide valuable information on present and past water salinity temperature and chemistry hydrodynamic conditions substrate characteristics climate sea level variations oxygen and nutrient availability this article provides an overview on the application of ostracods from brackish waters for palaeoenvironmental reconstruction in the quaternary and for environmental studies in present day environments

relative sea level change and evidence for the holocene storegga slide tsunami from a high energy coastal environment cocklemill burn fife scotland uk a site in the cocklemill burn valley on the north shore of the firth of forth scotland provides evidence of relative sea level changes during the holocene from ca 7970 to ca 5090 radiocarbon years bp and of the holocene storegga slide tsunami dated here as having taken place after ca 7215 radiocarbon years bp marine sediments associated with two shorelines widely present in mainland scotland the main postglacial shoreline and the blairdrummond shoreline are recorded the holocene storegga slide tsunami deposits are unique here in the record of such sediments in eastern scotland in that they occur within marine sands of which the upper horizons are intertidal sandflat deposits the tsunami deposits probably accumulated shortly after a period of accelerated relative sea level rise the pattern and timing of which could have played a role in triggering the holocene storegga slide

the palaeogeography of mesolithic settlement subsistence and shell midden formation in the muge valley lower tagus basin portugal this paper reports the first detailed palaeogeographical analysis of the environmental context of late mesolithic shell midden sites in the lower tagus area and focuses on the lower muge valley which contains an internationally significant mesolithic record the lower muge valley fill comprises buried estuarine and fluvial environments contemporary with mesolithic settlement holocene environmental and palaeogeographic changes influenced mesolithic settlement subsistence and midden accumulation the sudden appearance of large late mesolithic shell middens throughout portugal represents a process of increased visibility and preferential preservation of the archaeological record prior to 6100 cal bc aggrading valley floor environments did not occupy the entire width of the present lower tagus floodplain and any sites located in the early holocene valley are currently deeply buried shell midden occupation on terrace levels followed the establishment of aggrading estuarine environments containing produ

global atmospheric circulation experiments on an earth with polar and tropical continents two general circulation models forced by mean annual insolation and having an energy balance ocean have been run on an earth with polar continents and a tropical continent polar continents produce strong meridional temperature gradients and a maximum hydrological cycle a tropical continent produces the warmest planet and a minimal hydrological cycle both models produce more arid continents than exist today

atmospheric circulation during warm geologic periods is the equator to pole surface temperature gradient the controlling factor paleoclimatologists have hypothesized that the equator to pole surface temperature gradient is a dominant control on the paleocirculation of the oceans and the atmosphere atmospheric simulations using realistic cretaceous 100 m y ago geography are used to examine quantitatively the relationships between paleogeography surface temperature gradients and the nature of the atmospheric circulation these results raise questions concerning the classical theories and interpretations of warm paleoclimates and suggest that paleogeography is an important factor governing the nature of the circulation