the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

a uranium thorium dated late eemian or early midlandian organic deposit from near kilfenora between spa and fenit co kerry ireland this paper discusses the dating of stratigraphically important quaternary sequences from a site near fenit co kerry which have been the subject of debate since they were first described by mitchell in 1970 the overall stratigraphy of the quaternary deposits have been investigated and detailed analyses of the organic material carried out pollen from biogenic sediments have been analysed and samples of peat dated using the uranium thorium disequilibrium method the pollen assemblages match no others previously recorded in ireland and appear to represent a cool temperate phase following the last interglacial the uranium thorium dates of between 114000 and 123000 yr bp indicate that the deposit dates from oxygen isotope stage 5 possibly post dating the last temperate stage the eemian stage interglacial oxygen isotope substage 5e the dating of this deposit and the realisation that it is not penultimate temperate stage gortian in age invalidates much recent speculation on the age of the gortian interglacial

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

january and july simulations with a spectral general circulation model abstract we describe the results of january and july simulations carded out with a nine level spectral model employing a rhomboidal truncation at wavenumber 15 sea surface temperature sea ice distribution and solar zenith angle are held constant in each simulation the model includes interactive clouds and radiative processes after ramanathan et al 1983 selected fields are shown which highlight the model s strengths and weaknesses the latitude height distribution of the zonal wind is successfully simulated the model captures the separation between the wintertime westerly jets in the troposphere and stratosphere and thus simulates the sign reversal in the vertical wind shear across the jet axis in the upper troposphere in addition to the zonal wind we show also the zonally averaged temperature meridional wind and vertical velocity regional distributions of sea level pressure surface air temperature precipitation and a number of other fields defined at various pressure levels are compared in

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

zonal pressure gradient velocity and transport in the atlantic equatorial undercurrent from focal cruises july 1982 february 1984 the zonal pressure gradient zpg along the atlantic equator and the equatorial undercurrent euc transport are discussed for four cruises representative of each season a very clear sea surface slope reversal occurred in the eastern area during autumn as far west as 14 w an early onset of the equatorial thermocline rising was evident during spring 1983 an eastward equatorial surface jet clearly distinct from the euc was observed at 35 w and 29 w the greatest zpg but the lowest euc transport were observed during summer 1983 a nearly total absence of the zpg and a large surfacing of the euc as far as 10 w characterized the 1984 winter

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

seasonal variations in equatorial atlantic ocean zonal volume transport at 28 w zonal volume transport is examined over the upper 150 m of the water column at 28 w using the seasonal response of the equatorial atlantic experiment moored current meter data at 0 75 s 0 0 and 0 75 n and a time domain empirical orthogonal function eof analysis to improve spatial and temporal resolution gaussian distributions are fit to the mean volume transports per unit width and the fluctuations about these means that are found to be represented by a single eof mode the mean volume transport is distributed symmetrically both about the equator and about 75 m depth with a meridional scale width of 101 km and a magnitude of 20 3 sv the standard deviation for the fluctuations is 4 7 sv and in contrast to the mean the fluctuations are confined to above 100 m depth with a larger meridional scale width the scale width for the mean is consistent with an inertial scale associated with conservation of potential vorticity while the scale width for the fluctuations is consistent with an equatorial rossby radius of deformation associated with equatorially trapped waves these findings support a hypothesis that different physical processes are controlling the volume transport as integrated from the surface across the equatorial undercurrent over different time scales on the time scale of the record length average inertial dynamics appear to be controlling while on the time scales of the seasonal fluctuations linear equatorial long wave dynamics appear to be controlling however given the limited record length there are insufficient degrees of freedom to test this hypothesis statistically

quaternary deposits and glacial stratigraphy in ireland quaternary stratigraphic studies in ireland have been based largely on lithostratigraphy the division of complex sedimentary sequences into the traditional framework of munsterian and midlandian events has created a series of stratigraphic scenarios which cannot be fully substantiated either by biostratigraphy or by facies basin analysis many of the current problems of glacial stratigraphy in ireland therefore arise directly from the field procedures used and the frameworks used to subdivide sedimentary sequences these problems are centred on the selection of type sites the subdivision of sedimentary sequences into unnatural divisions the concepts of direct and indirect stratigraphy classical models of climatically determined ice advance retreat cycles and the genetic inferences of the term till the conceptual basis of various stratigraphic schemes has changed little since the work of farrington 1934 1966 it is argued that a more realistic approach to description and assessment of glacigenic sediments should be based on basinal facies analysis and must include a documentation of the composition and geometry of three dimensional facies variations palaeoenvironmental interpretations of complex glacigenic sequences especially in coastal locations should take account of the influences of marine ice sheets on the sedimentary record in the past most sequences were interpreted in terms of glacioterrestrial models a large body of sedimentary evidence now indicates that shallow glaciomarine environments occurred along the margins of the last ice sheet during its maximum and subsequent retreat phases the locations and patterns of associated icemarginal systems indicate that the magnitude of and patterns of crustal deformation were greater and more complex than formerly realised thus the primary control on sea level variation at successive ice sheet margins was largely a function of glacioisostatic disequilibrium although complex glacial and glacially related sequences are known it is argued here that most of the multiple glacigenic sequences in ireland can be accommodated within the midlandian cold stage the basal units from certain sequences and erratic fans have been attributed to events earlier than the midlandian however it is difficult to compare these traces of earlier events from different sectors of the island due to poor dating correlation and the fact that direct and indirect stratigraphy is not adequately defined or separated the age of the gortian style interglacial sequences the implications of their floristic composition and their relationships to drift stratigraphy remains a major problem in stratigraphic constructions of the irish quaternary the stratigraphic significance of many till units must remain largely unknown until these matters are resolved at present it is not clear if the gortian sequences represent more than one interglacial a series of exposures in ulster provide evidence for major environmental changes during the midlandian cold stage these include an early stadial an early forest biozone 48 1 ka bp an early herb biozone 41 5 ka bp a middle interstadial phase of cold but non glacial aspect 30 5 ka bp a late stadial max 24 22 ka bp and a late glacial climatic oscillation the late midlandian stadial comprises a major glaciation that almost covered the island and a later more restricted phase when drumlins formed in the northern and western parts of the island max 17 ka bp

climate sensitivity to continental ice sheet size and configuration abstract a version of the ncar community climate model ccm has been used to carry out a study of climate sensitivity to the size and distribution of continental ice sheets by comparing two perpetual season fixed sea surface temperature sst winter simulations of the climate at a glacial maximum the two simulations differ only in the size and configuration of the continental ice sheet boundary conditions these conditions represent minimum and maximum ice sheet extent for a glacial maximum as presently constrained by the geologic evidence all other boundary conditions are as specified by climap 1981 for winter surface conditions during the last glacial maximum lgm the ice sheets specified by climap 1981 used by many previous researchers to simulate ice age climate conditions are intermediate in size between the minimum and maximum ice sheets used for the simulations described here the maximum case simulation resulted in unexpected positive temperature anomalies over the northern hemisphere

current understanding of pleistocene temperate stages in ireland abstract research on irish pleistocene temperate stages has been dominated by investigation of deposits with very similar floristic records collectively termed the gortian and traditionally correlated with the continental holsteinian recently detailed investigation of interglacial material from cork harbour suggested the gortian group may contain floristically similar deposits of different ages the pollen record had gortian holsteinian characteristics and dating by measurement of uranium thorium disequilibrium and amino acid racemization suggested that the deposits were younger than stage 11 correlated with the holsteinian by reille and de beaulieu reille de beaulieu quat res 44 1995 205 the suggestion that there may have been more than one holsteinian style temperate stage in europe might explain the floristic similarity of gortian and holsteinian deposits and the apparent younger age of the cork deposits the lack of a last interglacial stratotype is the most outstanding problem in irish quaternary studies the pollen content of sediments at fenit co kerry dated to ca 118 ka bp suggested they may represent a cool temperate phase at the end of the last interglacial recently investigated sub drumlin organic rich deposits at knocknacran co monaghan are also possibly last interglacial in age and these are discussed in detail here

near surface current and temperature variability observed in the equatorial atlantic from drifting buoys we examine data from 23 surface drifters which were deployed between june 1983 and july 1984 at 4 w 1 5 4 s the drifters were equipped with a window shade drogue centered at 15 m depth and in most cases a 117 m long thermistor chain drift data indicate a westward south equatorial current with typical speeds of about 20 cm s 1 south of the equator maximum westward flow of 30 40 cm s 1 occurred in june through september of 1983 and 1984 consistent with climatology near zero westward flow which was significantly weaker than was expected from climatology by about 20 cm s 1 occurred from february to april 1984 this probably represents real interannual variability and may be related to the fact that the equatorial atlantic was warmer than usual in the spring and summer of 1984 energetic variations on time scales of o 1 month and less and space scales of o 100 km and less are ubiquitous in the drift and temperature data kinetic energy levels associated with these variations south of the equator are typically 100 cm2 s 2 with slightly higher values in boreal summer energy levels north of the equator are about 500 cm2 s 2 on the basis of data available only during the boreal summer and fall the sources of this energy include inertia gravity waves instabilities of the general circulation and other phenomena for which there is no simple explanation

freshwater organic deposits and stratified sediments between early and late midlandian devensian till sheets at aghnadarragh county antrim northern ireland the following events have been identified from a complex sequence of midlandian devensian sediments recently exposed at aghnadarragh county antrim 1 a lower till interpreted as early midlandian was deposited by a major lowland ice sheet which moved south eastwards from central ulster across the lough neagh depression 2 deglacial conditions were followed by a periglacial phase characterised by ice wedge growth and sedimentation by gravelly debris flows the latter contain the oldest known remains of mammuthus primigenius in ireland 3 an early midlandian interstadial is represented by a woody detritus peat with evidence of betula pinuos and picea woodlands and a rich beetle fauna wood from this horizon has been shown to be beyond the range of radiocarbon dating 48 180 bp 4 interstadial conditions were succeeded by a cold non glacial phase dominated by in channel gravelly flows and deposition of organic muds which contain plant and insect fossils these horizons are older than 46 850 bp 5 an upper non drumlinised till was deposited during the late midlandian by a major lowland ice sheet which moved generally eastwards across the lough neagh lowlands from central ulster this glaciation probably reached its maximum at ca 20 24 ka 6 drumlin formation occurred in the lough neagh lowlands towards the end of the late midlandian the limiting moraines are dated to 17 ka the lower till at aghnadarragh is the first positive record of a major lowland ice sheet in ireland during the early part of the last cold stage the early midlandian interstadial peats have not been documented elsewhere in ireland and correlate broadly with the chelford interstadial complex of the english midlands related exposures elsewhere in ulster confirm that the middle part of the last cold stage was free of major lowland ice masses but deposits of this period are absent from aghnadarragh

response of the equatorial atlantic ocean to the 1983 1984 wind from the programme francais ocean et climat dans l atlantique equatorial cruise data set variations of the zonal pressure gradient zpg and the equatorial undercurrent euc are described in the equatorial atlantic ocean between 34 30 w and 6 30 e as observed during eight pairs of programme francais ocean et climate dans l atlantique equatorial cruises between october 1982 and august 1984 in 1982 and 1983 the annual cycle of weak trades early in the year followed by comparatively strong and sustained trades were relatively normal in the boreal winter of 1984 the extent of the collapse of the trade winds was exceptional and consequences were observed in the upper layers of the ocean along the equator the 20 c isotherm depth representative of the thermocline depth was unusually deep along the equator in the gulf of guinea a near zero value of the zpg was observed from the greenwich meridian westward an eastward surface current separated from the euc by a layer of reduced velocity was observed over much the same fetch west of 10 w the maximum velocity of the euc showed very little seasonal variation usually between 70 and 80 cm s 1 except in the boreal fall of 1983 when it exceeded 100 cm s 1 during this period in both 1983 and 1984 the euc transport at 23 w reached 25 106 m3 s 1 or twice its annual average which derived not only from the increase in speed but also for a deepening of the current to below 100 m it was also the season when the zpg was strongest and has a similar amplitude at both the surface and 50 dbar relative to 500 dbar the seasonal variations of the euc in the gulf of guinea were even more pronounced during the boreal summer and fall the current weakened while the local zpg reversed direction compared to the west the stronger penetration of the euc into the gulf occurred in the alternate seasons when there was no local reversal in the eastward acting zpg force the large changes in the oceanic and atmospheric circulation during the 1983 1984 period are hypothesized to be related to the suppression of the coastal period are hypothesized to be related to the suppression of the coastal benguela upwelling along the namibia coast this atlantic equivalent to el nino occurred 1 year after the exceptionally strong event in the pacific

abrupt glacial valley incision at 0 8 ma dated from cave deposits in switzerland glacial erosion dramatically alters mountain landscapes but the pace at which glaciers carve a previously fluvial landscape remains poorly defined because long term valley incision rates are difficult to measure here we reconstruct the lowering history of the aare valley switzerland over the past 4 m y by dating cave sediments with cosmogenic 26al and 10be incision accelerated from 120 m m y to 1200 m m y at 0 8 1 0 ma at least 1 m y after the onset of local glaciation rapid incision may have been triggered by lowering of the equilibrium line altitude at the mid pleistocene climate transition

on the baroclinic response of the zonal pressure gradient in the equatorial atlantic ocean temperature time series obtained from surface moorings deployed along the equator in the atlantic ocean during the seasonal response of the equatorial atlantic experiment and the programme francais ocean et climat dans l atlantique equatorial were used to investigate the baroclinic response of the zonal pressure gradient due to the sloping isopycnals the zonal pressure gradient evolved as a complicated function of time depth and zonal position the most rapid and spatially inhomogeneous variations corresponded to periods of rapidly changing easterly wind stress following these periods the baroclinic response due to the sloping isopycnals was observed to overshoot its intended equilibrium before relaxing to it in so doing it tended to buffer pressure gradient variations at the depth of the equatorial undercurrent euc over much of the year the isopycnal slopes opposed the surface slope after the winds relaxed in winter however the isopycnal slopes reversed and acted in concert with the surface slope thereby enhancing the pressure gradient at the depth of the euc relative to that at the surface this reversal might be important in maintaining the euc during times of weak easterly wind stress the vertical structure of the zonal pressure gradient varied with the depth of the thermocline when the winds were weak and the thermocline was shallow the baroclinic response of the zonal pressure gradient due to the sloping isopycnals was primarily effected in the upper 50 m after the winds intensified and the thermocline deepened the baroclinic response extended down to at least 150 m

influence of insolation and glaciation on atmospheric circulation in the north atlantic sector implications of general circulation model experiments for the late quaternary climatology of europe abstract atmospheric general circulation models have been used to simulate the sensitivity of regional climates to late quaternary changes in insolation ice sheets and atmospheric co 2 model results for full glacial conditions 18 ka show the atlantic westerly jet strengthened and shifted south a corresponding southward shift of the icelandic low and a strengthening and northward shift of the subtropical anticyclone sta a glacial anticyclone developed over the european ice sheet and cold dry conditions prevailed over much of europe the full glacial climate anomaly for the north atlantic sector is explained by a combination of low atmospheric co 2 reducing global surface temperatures and circulation changes caused by the ice sheets by the early holocene 9 ka the ice sheets were much reduced while the orbital anomaly was near its maximum producing mid continental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons the jet and the icelandic low were displaced to north of their present position producing strong onshore flow and mild wet winters in northern europe while the sta was also shifted northwards producing offshore flow and dry summers in the same region during the late glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others the model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale

long continental records of climate an introduction abstract the symposium on long continental records presented new information on past climates on land it seems that throughout the last 2 5 million years the climate in the middle latitudes changed in the same complex fashion as during the better known late pleistocene and holocene times over 40 interglacial glacial shifts took place during this interval out of those 40 10 12 glacials were markedly stronger and or longer lasting than the others the apparently abrupt shifts from interglacials to glacials were probably gradual oscillatory coolings interrupted by warming episodes in that respect the detailed anatomy of the past climate changes does not differ substantially from the climate oscillations documented by instrumental weather records in the last two centuries the pronounced expansions of dry and cold steppes on land were accompanied by corresponding increases of the ice volume indicated by the oxygen isotope ratio the two exceptions occurred around 1 4 ma ago and 1 6 ma ago the reason for this discrepancy is not known by far the most expressed change of land environments occurred at about 2 4 ma ago

the beginning of the ice age in europe and its major subdivisions abstract the time range of the quaternary is discussed in terms of the view that this period is essentially the one in the earth s history in which during certain intervals inland ice developed in the northern hemisphere this process first became evident about 2 3 ma bp since then the quaternary thus defined has witnessed many climatic variations although for practical reasons it is not feasible to assign the status of stage to each distinclty warm or cold phase climatic change is nevertheless the most appropriate basis for world wide correlation it seems possible to use both climatic change and other correlation parameters to arrive at a practicable subdivision of the quaternary period into stages before about 1 ma vegetational succession during interglacials in western europe differed from that seen in later times a possible cause for this divergence is discussed in the later part of the quaternary after about 1 ma two distinct types of warm temperate intervals occurred one associated with high sea levels and an oceanic climate the other showing lower sea levels and a cooler and more continental climate the difference between these two types is shown by comparison of the distribution of abies during these time intervals

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

vostok ice core climatic response to co2 and orbital forcing changes over the last climatic cycle vostok climate and co2 records suggest that co2 changes have had an important climatic role during the late pleistocene in amplifying the relatively weak orbital forcing the existence of the 100 kyr cycle and the synchronism between northern and southern hemisphere climates may have their origin in the large glacial interglacial co2 changes

the gortian temperate stage abstract interglacial sediments assigned to the gortian temperate stage are recorded at eleven sites throughout ireland but they remain undated by absolute means however the unique vegetational assemblages found within the gortian appear to belong to the middle pleistocene on biostratigraphic grounds the gortian vegetational records are reviewed and a summary of the possible age of the interglacial is presented along with recent work that has been carried out on stratigraphically important sites within ireland

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

glaciomarine facies within subglacial tunnel valleys the sedimentary record of glacioisostatic downwarping in the irish sea basin coastal exposures of late pleistocene sediments deposited after 19 000 yr bp near dublin ireland provide a window into the infill of a subglacially cut tunnel valley exposures close to the steeply dipping bedrock wall of the valley show boulder gravels within multi storey u shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head gravels are truncated by poorly sorted ice proximal glaciomarine sediments that record the pumping of large volumes of subglacial debris along the tunnel valley to a tidewater ice sheet margin the sedimentary succession is dominated by sediment gravity flow facies comprising interbedded diamict and massive poorly sorted gravel facies interpreted as subaqueous debris flow deposits gravel beds show local inverse and normal coarse tail graded facies recording the restricted development of turbulent flow sediment gravity flow deposits fill broad 2 km shallow 10 m and overlapping channels penetrative deformation structures e g dykes are common at the base of channels the same subglacially eroded topography and glaciomarine infill stratigraphy can be identified on high resolution seismic profiles across nearly 600 km2 of the western irish sea tunnel valleys are argued to have been exposed to glaciomarine processes by the rapid retreat of a calving tidewater ice sheet margin in response to marine flooding caused by glacio isostatic downwarping below the last british ice sheet the facies associations described in this paper comprise an event stratigraphy that may be found on other glaciated continental shelves

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

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

climatic deterioration and the end of the gortian interglacial in sediments from derrynadivva and burren townland near castlebar county mayo ireland pollen and macrofossil analyses of two sequences of organic sediment in western ireland have allowed the recognition of the latter parts of the gortian interglacial a middle pleistocene temperate stage the palaeobotanical information from the two sites identifies the preservation of partial sequences from the gortian interglacial believed to be the equivalent of the hoxnian stage of britain and the holsteinian of europe the pollen and macrofossil data from one of the sites derrynadivva span the middle and latter parts of the temperate stage the results show that fire influenced the vegetation throughout the middle part of the temperate stage and the termination of the organic depositional sequence appears to have been due to environmental deterioration the former is identified through the abundant occurrence of charcoal in the sediments whereas the latter is apparent in the sediment sequence and in the reworking of thermophilous pollen types into the upper part of the deposit the second site burren townland records only part of the later zones of the interglacial but the ericaceous assemblages of the latter part of the gortian interglacial are well developed and well preserved macrofossil analyses and scanning electron microscopy work on the pollen at the latter site has allowed the recognition of rhododendron ponticum adding to previous records of this species which now has a very disjunct european distribution

stationary waves of the ice age climate abstract a linearized steady state primitive equation model is used to simulate the climatological zonal asymmetries stationary eddies in the wind and temperature fields of the 18 000 ybp climate during winter we compare these results with the eddies simulated in the ice age experiments of broccoli and manabe who used climap boundary conditions and reduced atmospheric co2 in an atmospheric general circulation model gcm coupled with a static mixed layer ocean model the agreement between the models is good indicating that the linear model can be used to evaluate the relative influences of orography diabatic heating and transient eddy heat and momentum transports in generating stationary waves we find that orographic forcing dominates in the ice age climate the mechanical influence of the continental ice sheets on the atmosphere is responsible for most of the changes between the present day and ice age stationary eddies this concept of the ice age climate is complicated by the sensitivity of t

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation