paleoclimatic significance of the stratigraphic occurrence of photosynthetic biomarker pigments in the nordic seas sedimentary chlorins and porphyrins are diagenetic products of chlorophyll molecules and are considered to be chemical fossils or biomarkers of phototrophic organisms the stratigraphic occurrence of such components was investigated in four cores from the nordic seas that span the last deglacial period the presence of chlorins in all the samples deposited during the younger dryas and at the end of the last glacial period indicated that photosynthetic activity occurred during these cold episodes and hence that ice free conditions existed at least seasonally in the nordic seas vanadyl porphyrins were found in sediments deposited during termination ia in only two of the cores close to the barents shelf we argue that they derive from erosion and advection of organic rich deposits as ice rafted debris during melting of the barents ice sheet thus we suggest that the sedimentary occurrence of vanadyl porphyrins in nordic sea cores can be used as a marker of ice rafted debris from the barents ice sheet the absence of such components during termination ib indicates that the complete destruction of the barents ice sheet took place during the first stage of the deglaciation

effect of wind changes during the last glacial maximum on the circulation in the southern ocean present day surface wind stress climatology is manipulated to simulate wind conditions during the last glacial maximum these estimated wind fields force a one layer wind driven numerical model of the southern ocean to determine if a change in the strength of the surface wind stress can shift the location of the antarctic polar front which is part of the antarctic circumpolar current a change in the forcing by a factor of 0 5 2 0 results in a change in the speed of the flow by an identical factor with no change in position however if the present day wind climatology is shifted meridionally there is a change in both strength of the circulation and spatial pattern a shift of the wind stress of more than 5 of latitude is required to produce a shift in the location of the polar front

tropical cooling at the last glacial maximum and extratropical ocean ventilation1 1 the ncar csm is used to simulate the climate at last glacial maximum the csm simulates a tropical sst cooling of 2 1 c it is shown that about half of this tropical cooling is associated with the upper ocean circulation especially the ventilation of thermocline and intermediate waters from the mid high latitude south pacific

signatures of natural catastrophic events and anthropogenic impact in an estuarine environment new zealand the sedimentary record of known natural catastrophic events and anthropogenic activity in an estuarine environment is assessed using sedimentological chemical and geochronological techniques shallow cores collected from intertidal and salt marsh sediments in ahuriri estuary hawke s bay reveal a variety of signatures of natural and human disturbance evidence for the 1931 hawke s bay earthquake which resulted in an uplift of one to two metres in the napier area is given by a change from silt to sand dominated sediment in the lower estuary which is consistent with a shift toward higher energy depositional conditions following uplift however based on physical properties of sediments the 1931 uplift event does not appear to have caused major changes in depositional conditions in the upper estuary similarly no changes were recorded at one site in the lower estuary which seems to represent an area of low energy depositional environment although the 1960 chilean tsunami resulted in structural damage in napier it did not produce any recognisable sedimentological and geochemical signature in the sedimentary record suggesting that the study sites were possibly beyond the limit of sedimentation of the tsunami post european settlement impact is mainly restricted to the lower estuary where increased concentrations of zn cr pb and cu are attributed to industrial discharges evidence of agricultural runoff is shown by an increase in cu concentrations within a fine grained depositional environment that is distal from industrial sources in the town of napier chemical data cl and s suggest a change in the depositional environment in the upper estuary due to increased freshwater influx and or decrease in seawater influence dating by 210pb suggests that this occurred around the middle part of the 19th century and might be attributed to river flooding in the region at that time

estimates of sea surface temperature in the coral sea at the last glacial maximum the climap 1981 reconstruction of the coral sea found relatively little cooling 2 c in the low latitudes 10 s but a warming off australia at about 25 s the small low latitude changes are of interest because terrestrial pollen and snowline data from the new guinea highlands imply that surface temperatures may have been 6 to 9 c colder at the last glacial maximum lgm the purpose of this paper is to evaluate these conclusions on the basis of additional core sites new oxygen isotope stratigraphy and new sea surface temperature sst estimates using the modern analog technique mat in the northern coral sea planktonic foraminifer assemblages consist of tropical subtropical species that show little change over the past 20 kyr quantitative estimates of sst using the modern analog technique mat confirm the climap 1981 conclusion that little or no temperature change occurred in this tropical region at the lgm thus reinforcing the conflict with terrestrial evidence in the southern region 25 s two cores indicate that foraminifer faunas became more subtropical at the lgm the mat estimates for the lgm are 3 to 4 c colder than modern producing a steeper thermal gradient in the southern coral sea these data remove the warm sst anomaly along the eastern coast of australia and indicate that during the lgm cool high latitude waters were displaced northward along the coast of australia into the southern coral sea

tropical climates at the last glacial maximum a new synthesis of terrestrial palaeoclimate data i vegetation lake levels and geochemistry palaeodata in synthesis form are needed as benchmarks for the palaeoclimate modelling intercomparison project pmip advances since the last synthesis of terrestrial palaeodata from the last glacial maximum lgm call for a new evaluation especially of data from the tropics here pollen plant macrofossil lake level noble gas from groundwater and delta 18 o from speleothems data are compiled for 18 2 ka c 14 32 degrees n 33 degrees s the reliability of the data was evaluated using explicit criteria and some types of data were re analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month mtco mean annual temperature mat plant available moisture pam and runoff p e cold month temperature mat anomalies from plant data range from 1 to 2 k near sea level in indonesia and the s pacific through 6 to 8 k at many high elevation sites to 8 to 15k in s china and the se usa mat anomalies from groundwater or speleothems seem more uniform 4 to 6 k but the data are as yet sparse a clear divergence between mat and cold month estimates from the same region is seen only in the se usa where cold air advection is expected to have enhanced cooling in winter regression of all cold month anomalies against site elevation yielded an estimated average cooling of 2 5 to 3 k at modern sea level increasing to approximate to 6 k by 3000m how ever neotropical sites showed larger than the average sea level cooling 5 to 6 k and a non significant elevation effect whereas w and s pacific sites showed much less sea level cooling 1 k and a stronger elevation effect these findings support the inference that tropical sea surface temperatures ssts were lower than the climap estimates but they limit the plausible average tropical sea surface cooling and they support the existence of climap like geographic patterns in sst anomalies trends of pam and lake levels indicate wet lgm conditions in the w usa and at the highest elevations with generally dry conditions elsewhere these results suggest a colder than present ocean surface producing a weaker hydrological cycle more arid continents and arguably steeper than present terrestrial lapse rates such linkages are supported by recent observations on freezing level height and tropical ssts moreover simulations of greenhouse and lgm climates point to several possible feedback processes by which low level temperature anomalies might be amplified aloft

effect of vegetation on an ice age climate model simulation a growing number of studies suggest that vegetation changes can significantly influence regional climate variations herein we utilize a climate model genesis with a land surface vegetation package to evaluate the potential role of the very large vegetation changes that occurred during the last glacial maximum lgm in particular we focus on the potential response to a significant reduction in the area of tropical rainforest simulations employed a global vegetation reconstruction for the lgm and climate long range investigation mapping and prediction climap sea surface temperature sst estimates results indicate that expansion of dryland vegetation causes a 15 30 additional lgm cooling for australia 0 4 c and africa 0 9 c respectively turnover from conifer to tundra also causes cooling of 2 4 c or more in western europe and siberia however for the largest rainforest area amazon basin inclusion of realistic vegetation increased modeled temperatures 2 4 c and decreased precipitation by 10 35 these latter results are similar to those obtained with sensitivity experiments of the effects of future amazon deforestation initial assessment of the potential effect of decreased stomatal resistance due to lower ice age co2 levels indicates little significant response to this effect comparison of model predicted low elevation lgm temperature changes with estimates from proxy data indicate that inclusion of realistic vegetation estimates for the lgm results in slightly more than 50 agreement between models and data for low elevation sites in low mid latitudes data at variance with model predictions would appear to be explainable by considering additional changes in vegetation ice age dust or a 1 2 c cooling below climap values this conclusion is at variance with a 3 4 c tropical cooling suggested by some studies for explaining estimated land temperature changes during the lgm in some western european sites model temperatures are colder than proxy data by 2 8 c this model data discrepancy may be explained by less sea ice in the subpolar north atlantic than stipulated by climap a conclusion consistent with new marine data from that region

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

oxygen isotopes versus climap 18 ka temperatures a comparison from the tropical atlantic glacial interglacial differences in 18 o values of globigerinoides sacculifer have been mapped in the western and central tropical atlantic using data from surface and core sediments glacial interglacial differences in the western tropical atlantic if attributed to temperature changes only are at odds with temperature reconstructions performed by climap in the ceara rise region delta 18 o values exceeding 2 are recorded they can only be partly attributed to changes in the precipitation evaporation regime i e higher salinities and 18 o enriched precipitation an additional cooling of 1 2 c as compared to climap9s results is required to balance the 18 o record thus temperature changes from glacial to modern times amount to 2 3 c in the tropical atlantic off the northern coast of brazil

the oceanic salt pump does it contribute to the glacial interglacial difference in atmospheric co2 content sea ice formation drives salt from the surface to the deep sea in so doing it lowers the salinity of polar surface waters we show here that this reduction in turn lowers the co2 partial pressure of polar surface waters and hence also of the atmosphere we propose that during glacial time when more sea ice existed this pumping action may have been stronger if so part of the glacial to interglacial atmospheric co2 content change observed in ice cores may have been driven by the ocean s salt pump

glacial and interglacial wind regimes over the eastern subtropical atlantic and north west africa analysis of aeolo marine dust deposits in the subtropical eastern atlantic enables the strength of the major wind patterns during the late quaternary to be evaluated and gives an insight into the climate of north africa

variability of the path of the kuroshio ocean current over the past 25 000 years the kuroshio current is the strong northwestern component of the subtropical north pacific ocean gyre and advects a large amount of heat from the tropics to northern mid latitudes the kuroshio has bimodal stationary flow patterns with small and large meander paths east of central japan1 2 which switch on annual and decadal timescales3 4 these switches seem to be caused by changes in current velocity and volume transport of the north equatorial current that are associated with variations in the trade wind intensity in the eastern equatorial north pacific ocean5 6 here we present alkenone derived sea surface temperature records at multicentennial resolution from sediment cores from the nishishichitou ridge off central japan these 25 000 year records show that the kuroshio path has also fluctuated on millennial timescales this variability resembles that of the subtropical high pressure of the north pacific reconstructed from terrestrial pollen distributions water levels in north american lakes and marine micropalaeontological records7 together these data indicate that climate variability off central japan over the past 25 000 years may be part of a circum pacific phenomenon reflecting the rate of subtropical surface circulation in the north pacific ocean

small changes in the sea surface temperature during the last 20 000 years molecular evidence from the western tropical pacific one of the most controversial problems of glacial paleoclimatology is the conservative change in tropical sea surface temperature sst in contrast with the large high altitude temperature change in the western tropical pacific in this report sst was estimated for the last 20 000 years using alkenones preserved in marine sediments recovered from a site 800 km north of new guinea the uk37 unsaturation degree of long chain alkenones synthesized by planktonic prymnesiophyte algae record suggests that sst decreased at most 1 5 c at the last glacial maximum this small changes in sst of the western tropical pacific is concordant with results previously reported in uk37 studies from the eastern equatorial pacific and the equatorial atlantic the uk37 based sst estimates are in good agreement with the climap results and planktonic foraminifera 18o but much smaller than those ca 5 c obtained from coral sr ca and 18o thermometries and glacial vegetation reconstruction

tropical pacific ocean thermocline depth reconstructions for the last glacial maximum we evaluate the relationship between ten surface ocean 0 300 m hydrographic parameters and the spatial distribution of factor analyzed core top planktonic foraminiferal abundances in the tropical pacific ocean 24 n 24 s for core tops 3800 m the spatial distribution of the first three faunal factor loadings 88 of the variance are most highly correlated to subsurface variability mixed layer depth thermocline depth and resistant species percent rsp however rsp is not related to dissolution but is related to thermocline depth factor i mixed layer species g glutinata g ruber and factor iii g ruber can be distinguished from each other by low abundances of g glutinata in factor iii both assemblages spatially comprise the deep mixed layer region of the western tropical and equatorial pacific ocean but are associated with distinct water mass properties a combination of factor i and iii loadings shows a higher correlation to thermocline depth r 0 70 factor ii loadings dominated by thermocline dwelling species n dutertrei are most significantly correlated with the thermocline depth r 0 73 most factors show only marginally significant correlation to sea surface temperatures ssts indicating that sst is not the primary forcing factor on the planktonic foraminiferal species distributions in the tropical pacific a new transfer function was calculated to predict tropical pacific thermocline depth from planktonic foraminifera abundances using the imbrie kipp method ikm standard deviation of residuals 22 m 1 an additional 5 m error is attributed to low species counts in the core top database the modern analog technique mat was also used to predict thermocline depth standard deviation of residuals 21 m while last glacial maximum lgm thermocline depth changes by ikm and mat were generally within error estimated changes were geographically uniform suggesting an oceanographic response to climate forcing we estimate that the thermocline depth of the lgm was shallower than present by 20 m south of 8 s possibly due to a shift in the south pacific anticyclone to the northeast both the ikm and mat estimate a steeper east west thermocline slope along the equator suggesting that zonal wind stress walker circulation was intensified during the lgm collectively the thermocline estimates for the lgm suggest an equatorward compression of the climate zones in both hemispheres

assessment of sea surface temperature at 42 n in the california current over the last 30 000 years assessment of changes in surface ocean conditions in particular sea surface temperature sst is essential to understand long term changes in climate especially in regions where continental climate is strongly influenced by oceanographic processes to evaluate changes in sst in the northeast pacific we have analyzed long chain alkenones of prymnesiophyte origin at 38 depths in a piston and associated trigger core collected beneath the contemporary core of the california current system at 42 n 270 km off the coast of oregon california the samples span 30 000 years of deposition at this location unsaturation patterns u37k in the alkenone series display a statistically significant difference p 0 001 between interglacial 0 44 0 02 n 11 and glacial 0 29 0 04 n 20 intervals of the cores detailed examination of other compositional features of the c37 c38 c39 alkenone series and a related c36 alkenoate series measured downcore suggests the published u37k temperature calibration u37k 0 034 t 0 039 defined for cultures of a strain of emiliania huxleyi isolated from the subarctic pacific provides best estimates of winter sst at our study site this inference is purely statistical and does not imply however that the phytoplankton source of these biomarkers is most productive in winter or at the ocean surface the temperature record for u37k implies 1 an 4 c shift occurred in winter sst from 7 5 1 1 c at the last glacial maximum to 11 7 0 7 c in the present interglacial period and 2 this warming trend was confined to the time frame 14 10 ka within the glacial to interglacial transition period these conclusions are corroborated entirely by results from an independent sst transformation of radiolarian species assemblage data obtained from the same core materials

preliminary vegetation maps of the world since the last glacial maximum an aid to archaeological understanding abstract a set of preliminary broad scale vegetation map reconstructions for use by archaeologists and anthropologists is presented here for the world at the last glacial maximum 18 000 years ago the early holocene 8000 years ago and the mid holocene 5000 years ago for comparison we also give present potential maps which may be regarded as approximating the late holocene vegetation as it would or might be without agricultural modification the maps were produced through consultation with an extensive network of experts and a range of literature and map sources accompanying each regional map is a bibliography detailing the principal literature sources of evidence on late quaternary palaeovegetation and climates the maps presented here are not intended as the last word on the distribution of vegetation at each time slice they are merely a preliminary attempt at appraisal of current knowledge and opinion nevertheless together with the accompanying citation summary they should provide a valuable and readily accessible source of information on current opinion in the quaternary community it is also hoped that the maps will themselves act as a catalyst for archaeologists to use their own data to contribute to the broader climatic palaeovegetational picture

comparing simulated glacial climate and paleodata a reexamination glacial sea surface temperatures ssts simulated by an atmosphere mixed layer ocean model are compared with those reconstructed by the climate long range investigation mapping and prediction climap project using planktonic microfossils two methods of comparison are employed the first is global and uses the subjectively analyzed i e hand contoured then digitized data set published by climap the second is restricted to only those discrete locations where the climap sediment cores were taken both methods indicate that many aspects of the reconstructed glacial sst changes are simulated reasonably well by the model although there are areas of disagreement the extent of the disagreement appears smaller when the ssts are sampled at discrete locations because the largest discrepancies occur in the subtropical pacific where data are sparse when examined separately for each ocean the magnitude of the disagreement in low latitudes roughly corresponds to the magnitude of the uncertainties in sst estimation using planktonic microfossils being largest in the pacific and smallest in the atlantic because the largest discrepancies occur where uncertainties in estimation are large no clear determination of whether the climate model exaggerates or underestimates low latitude climate sensitivity appears possible nonetheless sampling at discrete locations may be the best procedure for evaluating climate model performance because errors associated with extending analyses to data void areas can be avoided and uncertainties associated with inadequate spatial sampling made more evident

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

sea ice and polar climate in the ncar csm the climate system model csm consists of atmosphere ocean land and sea ice components linked by a flux coupler which computes fluxes of energy and momentum between components the sea ice component consists of a thermodynamic formulation for ice snow and leads within the ice pack and ice dynamics using the cavitating fluid ice rheology which allows for the compressive strength of ice but ignores shear viscosity the results of a 300 yr climate simulation are presented with the focus on sea ice and the atmospheric forcing over sea ice in the polar regions the atmospheric model results are compared to analyses from the european centre for medium range weather forecasts and other observational sources the sea ice concentrations and velocities are compared to satellite observational data the atmospheric sea level pressure slp in csm exhibits a high in the central arctic displaced poleward from the observed beaufort high the southern hemisphere slp over sea ice is generally 5 mb lower than observed air temperatures over sea ice in both hemispheres exhibit cold biases of 2 4 k the precipitationminus evaporation fields in both hemispheres are greatly improved over those from earlier versions of the atmospheric gcm the simulated ice covered area is close to observations in the southern hemisphere but too large in the northern hemisphere the ice concentration fields show that the ice cover is too extensive in the north pacific and subarctic north atlantic oceans the interannual variability of the ice area is similar to observations in both hemispheres the ice thickness pattern in the antarctic is realistic but generally too thin away from the continent the maximum thickness in the arctic occurs against the bering strait not against the canadian archipelago as observed the ice velocities are stronger than observed in both hemispheres with a consistently greater turning angle to the left in the southern hemisphere they produce a northward ice transport in the southern hemisphere that is 3 4 times the satellite derived value sensitivity tests with the sea ice component show that both the pattern of wind forcing in csm and the air ice drag parameter used contribute to the biases in thickness drift speeds and transport plans for further development of the ice model to incorporate a viscousplastic ice rheology are presented in spite of the biases of the sea ice simulation the 300 yr climate simulation exhibits only a small degree of drift in the surface climate without the use of flux adjustment this suggests a robust stability in the simulated climate in the presence of significant variability

cool surface waters of the subtropical north pacific ocean during the last glacial one of the most controversial results of the climap12 project s reconstruction of past sea surface temperature sst is that large areas of the subtropical pacific ocean were warmer during the last glacial period than they are today this finding has important implications because sst patterns at low to subtropical latitudes strongly influence climate and sst changes are closely linked with climate fluctuations3 4 5 until now a lack of well preserved high resolution marine sediment cores from the region has hindered efforts to confirm these unexpectedly high ice age sst estimates here we use both the oxygen isotope compositions and species assemblages of planktonic foraminifera in a shallow water core with high deposition rates near hawaii to estimate glacial sst of the subtropical north pacific ocean contrary to the climap results2 our data indicate that the annual average sst in this region was 2 c cooler during the last glaciation than it is today these results help to reconcile the marine sst record with inferences drawn from snowline depressions on hawaii during the last glacial3 6 and should ultimately yield improved estimates of global climate sensitivity by providing important new constraints on climate model simulations of ice age cycles

modern hydrology and late holocene history of lake karakul eastern pamirs tajikistan a reconnaissance study abstract lake karakul in the pamirs tajikistan is a deep brackish water lake in a closed basin at almost 4000 m above sea level water samples from the catchment area and lake karakul and a 104 cm sediment core from its shallow eastern sub basin were investigated and provide a first lake record from the region spanning the last 4200 cal yr bp multi proxy analyses revealed the following a relatively high meltwater inflow from glaciers snow fields and frozen ground in the catchment as a result of relatively warm conditions was reconstructed for the period between 4200 and 3500 cal yr bp the shift to colder climatic conditions around 3500 cal yr bp was probably abrupt total organic carbon values displayed the most dramatic drop for the entire core within less than 40 years in contrast the subsequent re establishment of warmer conditions occurred gradually over several centuries a higher meltwater supply to the lake and warmer conditions were recorded since ca 1900 cal yr bp with two slightly colder intervals between 1200 and 800 cal yr bp and between 400 and 100 cal yr bp the abrupt shift to significantly colder and drier conditions around 3500 cal yr bp in the eastern pamirs is seen also in records from the aral sea and the guliya ice core from the western tibetan plateau however more palaeoclimate studies in this highly continental part of central asia are needed to assess the spatial and temporal patterns of the holocene climate in the region

application of modern analog technique to marine antarctic diatoms reconstruction of maximum sea ice extent at the last glacial maximum modern analog technique mat applied to antarctic diatoms is a new approach for quantitative sea ice paleoreconstructions in the southern ocean in a first step we show that mat is a better approach than the imbrie and kipp method to reconstruct the modern sea ice pattern we then use this approach to reconstruct sea ice presence in number of months per year during the last glacial maximum lgm at this time sea ice presence was greater than today leading to a shorter diatom growing season the maximum sea ice extent inferred from quantitative values of sea ice presence was located 5 8 north of its actual position leading to double the surface of modern winter sea ice this greater sea ice extent may have played a significant role on atmospheric and surface oceanic circulations and therefore on southern mid latitude and high latitude climates it may also have reduced the amount of heat moisture and co2 from the ocean to the atmosphere thus participating in the lowering of atmospheric co2 during the lgm

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

weaker gulf stream in the florida straits during the last glacial maximum as it passes through the florida straits the gulf stream consists of two main components the western boundary flow of the wind driven subtropical gyre and the northward flowing surface and intermediate waters which are part of the global conveyor belt compensating for the deep water that is exported from the north atlantic ocean1 the mean flow through the straits is largely in geostrophic balance and is thus reflected in the contrast in seawater density across the straits2 here we use oxygen isotope ratios of benthic foraminifera which lived along the ocean margins on the boundaries of the florida current during the last glacial maximum to determine the density structure in the water and thereby reconstruct transport through the straits using the geostrophic method a technique which has been used successfully for estimating present day flow3 our data suggest that during the last glacial maximum the density contrast across the florida straits was reduced with the geostrophic flow referenced to the bottom of the channel at only about two thirds of the modern value if the wind driven western boundary flow was not lower during the last glacial maximum than today these results indicate a significantly weaker conveyor belt component of the gulf stream compared to present day values whereas previous studies based on tracers suggested that deep waters of north atlantic origin were not widespread during glacial times indicating either a relatively weak or a shallow overturning cell our results provide evidence that the overturning cell was indeed weaker during glacial times

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

simulated influence of carbon dioxide orbital forcing and ice sheets on the climate of the last glacial maximum a coupled atmosphere ocean sea ice model is used to investigate the climate of the last glacial maximum 21 000 years ago and the relative climate forcing effects of atmosphere co2 the earth s orbital parameters and ice sheet albedo tropical temperatures are found to be 2 2 c less than today s slightly colder than indicated by the climap palaeoclimate reconstruction this result is consistent with a low to medium climate sensitivity to radiative perturbations temperatures are colder still in the northern north atlantic region owing to a weakening and shallowing of the thermohaline circulation a sensitivity analysis suggests that changes in ocean circulation since the last glacial maximum have not contributed directly to the global mean temperature change since that time

foraminiferal faunal estimates of paleotemperature circumventing the no analog problem yields cool ice age tropics the sensitivity of the tropics to climate change particularly the amplitude of glacial to interglacial changes in sea surface temperature sst is one of the great controversies in paleoclimatology here we reassess faunal estimates of ice age ssts focusing on the problem of no analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods a new calibration strategy developed here which uses past variability of species to define robust faunal assemblages solves the no analog problem and reveals ice age cooling of 5 o to 6oc in the equatorial current systems of the atlantic and eastern pacific oceans classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core top assemblages misrepresented the ice age faunal assemblages our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by climate long range investigation mapping and prediction climap 1981 and thus may help to resolve a long standing controversy our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems however and supports climap s inference of stability of the subtropical gyre centers

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases