isotopic composition of old ground water from lake agassiz implications for late pleistocene climate a uniform oxygen isotope value of 25 per mil was obtained from old ground water at depths of 20 to 30 meters in a thick deposit of clay in the southern part of the glacial lake agassiz basin the lake occupied parts of north dakota and southern manitoba at the end of the last glacial maximum and received water from the ice margin and the interior plains region of canada ground water from thick late pleistocene age clay deposits elsewhere a till in southern saskatchewan and a glaciolacustrine deposit in northern ontario show the same value at similar depths these sites are at about 50 n latitude span a distance of 2000 kilometers and like the lake agassiz sites have a ground water velocity of less than a few millimeters per year the value of 25 per mil is characteristic of meltwater impounded in the southern basin of lake agassiz this value corresponds to an estimated air temperature of 16 c compared with the modern temperature of 0 c for this area

influence of changing atmospheric circulation on precipitation δ18o temperature relations in canada during the holocene postglacial precipitation 18o history has been reconstructed for two regions of canada long term shifts in the oxygen isotope composition of annual precipitation 18op in southern ontario appear to have occurred with a consistent isotope temperature relation throughout the past 11 50014c yr the modern isotope temperature relation in central canada near present boreal treeline evidently became established between 5000 and 4000 years ago although the relation during the last glacial maximum and deglaciation may also have been similar to present in the early holocene however unusually high 18opapparently persisted in spite of low temperature locally probably associated with high zonal index a rudimentary sensitivity analysis suggests that a small reduction in distillation of moisture in pacific air masses traversing the western cordillera perhaps accompanied by a higher summer winter precipitation ratio could have been responsible for the observed effect equivalent isotope temperature anomalies apparently occurred elsewhere in western north america in response to changing early holocene atmospheric circulation patterns suggesting that a time slice map of 18opfor north america during this period might provide a useful target for testing and validation of atmospheric general circulation model simulations using isotopic water tracers

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

isotopic evidence of holocene climatic change in the san juan mountains colorado abstract the d of cellulose from 14c dated wood collected in the san juan mountains of southwestern colorado decreased by about 45 from 9600 to 3100 yr b p and an additional 25 to the present the wood samples are from trees that grew above present day tree line and reflect a time of warmer average summer temperatures these changes in d are interpreted to indicate a major change during the holocene in the sources of moisture in the seasonality of precipitation or in both

temperature and vapour trajectory controls on the stable isotope signal in canadian rocky mountain snowpacks the effects of temperature and seasonal air mass trajectories on stable water isotopes in alpine snowpacks are investigated using meteorological and snow pit data at two alpine field sites in the canadian rocky mountains haig glacier alberta and opabin glacier british columbia snow pits were sampled through three accumulation seasons october june 2004 05 2005 06 and 2006 07 for 18 o d temperature and density the isotopic characteristics of precipitation over these time periods including the local meteoric waterline and average 18 o d and deuterium excess were defined using this dataset individual snowfall events over the three seasons were identified in the accumulation records from both sites and then fit to snow pit stratigraphies to determine their mean isotopic characteristics a trajectory classification was produced for all events and the key meteorological characteristics of each trajectory class were investigated using data from alpine field sites and a suite of meteorological records from the region an analysis of the relative influences of temperature and air mass trajectory on snow isotope ratios reveals some separation in mean 18 o between storm classes however the separation appears to be driven primarily by the mean temperature of each class rather then being a direct effect of vapour pathway

holocene environments from stable isotope stratigraphy of ostracods and authigenic carbonate in chilean altiplano lakes abstract sediment cores from three shallow 4000 m a s l paleoclimatic profiles show coherency within tropical subtropical circulation patterns climatic signals however are partially masked by local environmental systems results suggest similar arid mid holocene to less arid late holocene trends in the three lakes although each lake shows distinct response characteristics linked to differences in regional moisture balance isotopic signatures for each lake group in discrete 18o vs 13c populations high isotopic variability results from episodic flooding and brine evolution in the shallow lakes laguna seca 18 11 s 69 14 w 4500 m a s l is characterized by a diverse ostracod assemblage of at least 8 species indicating highest moisture levels among the three sites high 13c values are the result of continuous evasion of co2 derived from volcanically charged groundwaters and springs plus the formation of travertine and photosynthetic activity in the lake a 3 decrease in 18o about 4 7 m suggests an abrupt shift to wetter conditions at the transition from mid to late holocene lagunas miscanti 23 44 s 67 46 w 4140 m a s l and del negro francisco 27 28 s 69 14 w 4125 m a s l each contain only one ostracod species limnocythere sappaensis attesting to higher salinities although sediment facies and ostracod continuity and abundances imply a history of higher effective moisture at laguna del negro francisco sediment cores from each lake document more arid conditions in the lower sections with a sharp shift to wetter conditions in the upper sections highly variable isotope values at the transition from mid to late holocene suggest rapid short term climate shifts during this transition this overall trend can be correlated from laguna seca laguna miscanti and laguna del negro francisco to lago titicaca implying climatic coherency along the altiplano isotopic profiles show second order fluctuations and drought events that suggest short term variability along the transect in order to explain differences in the effective moisture among the three sites we postulate interactions of regional air masses in the north convective tropical precipitation dominates laguna seca as for lakes in the titicaca region effective moisture for lagunas del negro francisco and miscanti follows a south to north gradient generated by cold air masses from cut offs of pacific westerlies colliding with moist tropical air masses coherent shifts in the past therefore imply changes in available tropical air mass moisture

peatland succession and long term apparent carbon accumulation in central and northern ontario canada despite their importance as globally significant carbon c stores basic knowledge of post glacial peatland history and c accumulation are lacking for the canadian boreal shield and james bay lowland jbl of central and northern ontario canada radiocarbon dates plant macrofossil analysis and soil c estimates from an eight core transect of the jbl and surrounding regions are used to reconstruct the timings and patterns of fen to bog transitions and the ranges and patterns of long term apparent rate of c accumulation larca peatland initiation lagged the retreat of the laurentide ice sheet the drainage of glacial lakes and isostatic uplift by 810 6050 years transition from carex dominated fen to sphagnum dominated bog had a median timing of 3500 years following peatland establishment and ranged from 640 to 6970 years larca was variable geographically and over time with median values ranging from 13 4 to 31 6 g c m2 yr larca anomalies were generally high 6 1 kyr kyr 1000 calibrated years be

holocene climatic change in the northern midwest pollen derived estimates mapping of holocene pollen data in the midwestern united states has revealed several broadscale vegetational changes that can be interpreted in climatic terms these changes include 1 the early holocene northward movement of the spruce dominated forest and its later southward movement after 3000 yr b p and 2 the eastward movement of the prairie forest border into southwestern wisconsin by 8000 yr b p and its subsequent westward retreat after 6000 yr b p when certain basic assumptions are met multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation to maximize the reliability of the regression equations we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis reconstructions of precipitation during the holocene indicated that from 9000 to 6000 yr b p precipitation decreased by 10 to 25 over much of the midwest while mean july temperature increased by 0 5 to 2 0 c at 6000 yr b p precipitation was less than 80 of its modern values over parts of wisconsin and minnesota after 6000 yr b p precipitation generally increased while mean july temperature decreased in the north and increased in the south the time of the maximum temperature varies within the midwest and is earlier in the north and later in the south

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

holocene climate change in arctic canada and greenland abstract this synthesis paper summarizes published proxy climate evidence showing the spatial and temporal pattern of climate change through the holocene in arctic canada and greenland our synthesis includes 47 records from a recently published database of highly resolved holocene paleoclimate time series from the arctic sundqvist et al 2014 we analyze the temperature histories represented by the database and compare them with paleoclimate and environmental information from 54 additional published records mostly from datasets that did not fit the selection criteria for the arctic holocene database combined we review evidence from a variety of proxy archives including glaciers ice cores and glacial geomorphology lake sediments peat sequences and coastal and deep marine sediments the temperature sensitive records indicate more consistent and earlier holocene warmth in the north and east and a more diffuse and later holocene thermal maximum in the south and west principal components analysis reveals two dominant holocene trends one with early holocene warmth followed by cooling in the middle holocene the other with a broader period of warmth in the middle holocene followed by cooling in the late holocene the temperature decrease from the warmest to the coolest portions of the holocene is 3 0 1 0 c on average n 11 sites the greenland ice sheet retracted to its minimum extent between 5 and 3 ka consistent with many sites from around greenland depicting a switch from warm to cool conditions around that time the spatial pattern of temperature change through the holocene was likely driven by the decrease in northern latitude summer insolation through the holocene the varied influence of waning ice sheets in the early holocene and the variable influx of atlantic water into the study region

holocene climate of the kola peninsula evidence from the oxygen isotope record of diatom silica holocene climate variability was studied in a lake sediment record covering the last c 9000 years from lake chuna on the kola peninsula north west russia using the oxygen isotope composition of diatom silica 18odiatom the evaporation of the lake waters is likely to be minimal and thus the isotopic composition of the lake waters recorded by the 18odiatom reflects the isotopic composition of summer precipitation overall the 18odiatom signal seems to record a predominance of the polar arctic air mass bringing cold summer air temperatures immediately after the last glaciation and again after 4000 years to present time the atlantic maritime air mass is likely to have supplied warm summer rainfall especially in the mid holocene the pattern is broadly consistent with a quantitative pollen reconstruction from chuna lake which suggests higher mean july temperatures from deglaciation to 5500 years bp with a rather steep decline to lower temperatures after 4000 years bp our results support the general regional scenario of a mid holocene warm period deduced from the higher tree line vegetation changes and glacier fluctuations in fennoscandia however the 18odiatom record from the kola peninsula suggests a relatively cold early holocene with a gradual shift to warmer conditions to a maximum at around 5000 4000 years bp assuming that the modern precipitation temperature relationship has been constant throughout the holocene

isotopic evolution of glacial lake agassiz new insights from cellulose and porewater isotopic archives abstract significantly differing estimates of the oxygen isotope composition of lake agassiz have been obtained from two co existing isotopic archives within a sediment core originating from montcalm manitoba in the southern basin of the ancient proglacial lake oxygen isotope analysis of cellulose extracted from the sediments which originated during the lockhart phase 11 700 11 000 14 c yr bp suggests that phytoplankton lived in surface waters having 18 o around 18 1 vsmow substantially enriched relative to connate porewaters in the same core which indicate bottom waters had much lower values of around 24 5 0 5 vsmow this difference may be attributable to seasonal isotopic stratification of the upper part of the water column in the 250 m deep lake modern observations from analogous environments in northern canada suggest that inflow of evaporatively enriched runoff from the large area of deglaciated terrain contributing to lake agassiz possibly enhanced by evaporation from the surface of the lake itself could readily account for sufficient seasonal 18 o enrichment in the epilimnion sediment porewaters in contrast have preserved the isotopic signature of hypolimnion waters supplied by a mixture of glacial meltwater and precipitation derived runoff from the laurentide ice sheet and lack discernable isotopic alteration by evaporation these new estimates are combined with inferred lake water compositions from other isotopic archives to develop a speculative framework for the isotopic evolution of the lake providing improved constraints on the probable isotopic composition of lake agassiz outflow over time which has important implications for efforts to trace and model its changing discharge

interpreting paleoclimate from l8o and 2h in plant cellulose comparison with evidence from fossil insects and relict permafrost in southwestern ontario the oxygen isotope content of terrestrial plant cellulose is related to that of the source waters by a two step process involving evapotranspirative leaf water enrichment and equilibrium isotopic exchange between leaf water and atmospheric carbon dioxide a combination of two models that describe these steps yields consistent agreement between measured and predicted climatic and isotopic data humidity is the dominant influence on variations in the cellulose 18o enrichment relative to the source water a good first order approximation of the average daytime relative humidity during the growth season at a site can be based on the linear correlation that exists between humidity and cellulose enrichment without explicit consideration of factors such as temperature 18o of atmospheric vapour and leaf boundary layer dynamics the value of the combined model for paleoclimatic reconstruction has been tested using fossil wood from a late glacial site at brampton ontario estimates of the past relative humidity

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

postglacial palaeoecology of the subalpine forest grassland ecotone of southwestern alberta new insights on vegetation and climate change in the canadian rocky mountains and adjacent foothills postglacial vegetation change at the subalpine forest grassland ecotone in the foothills of southwestern alberta is reconstructed from fossil pollen plant macrofossils and fossil charcoal the fossils were obtained from the sediments of a small lake chronological control for the record is provided by tephra analysis and the 14c dating of terrestrial plant macrofossils the fossil record is compared with the results from similar studies at sites in the rocky mountains and foothills of alberta and british columbia the comparison of vegetation change at the upper and lower elevational limits of the subalpine forest provides a record of changes in temperature and aridity over the holocene at 10 000 yr b p the study site supported a shrub and herb dominated vegetation picea pinus abies forests were present at mid to high elevations in the mountains and in the northern foothills by this time the climate in the southern foothills was likely arid but not severely cold a relatively open picea and pinus forest was established in the study area between 9400 yr b p and 8000 yr b p fire activity in the region was at a postglacial maximum during this period the transition to forest suggests moister conditions by 8000 yr b p the importance of members of the chenopodiaceae amaranthaceae and typha latifolia increased suggesting an onset of arid conditions characterised by low and fluctuating water levels in lakes between 8000 yr b p and 5000 yr b p the picea and pinus contorta forest at the study site was largely replaced by grassland and pinus flexilis at high elevation sites treeline was located above its modern position during this period little vegetation change is recorded at sites in the northern foothills and at mid elevations at this time the vegetation change in the southern foothills and at high elevations suggests both an elevational and latitudinal displacement of vegetation zones during the mid holocene warm and arid conditions were prevalent in southwestern alberta picea glauca pinus contorta populus tremuloides forest has occupied the site since 5000 yr b p when cooler and moister conditions were established

impacts of climate and river flooding on the hydro ecology of a floodplain basin peace athabasca delta canada since a d 1700 abstract multi proxy paleolimnological analyses on lake sediment cores from spruce island lake 58 50 82 n 111 28 84 w a perched basin in the northern peace sector of the peace athabasca delta pad canada give insights into the relative roles of flow regulation of the peace river and climatic variability on the basin hydro ecology results indicate substantial variability in basin hydro ecology over the past 300 years ranging from seasonal to periodic desiccation in the 1700s to markedly wetter conditions during the early 1800s to early 1900s the reconstruction is consistent with 1 dry climatic conditions that defined the peak of the little ice age and subsequent amelioration evident in conventional ring width and isotopic analyses of tree ring records located hydrologically and climatically upstream of the pad and 2 peace river flood history inferred from sub annual magnetic susceptibility measurements from another lake sediment record in the peace sector of the pad although regulation of the peace river for hydroelectric power generation since 1968 has long been considered a major stressor of the pad ecosystem leading to reduced frequency of ice jam and open water flooding and an extended period of drying our results show that current hydro ecological status is not unprecedented as both wetter and drier conditions have persisted for decades in the recent past under natural climatic variability furthermore paleolimnological evidence from spruce island lake indicates that recently observed dryness is part of a longer trend which began some 20 40 years prior to peace river regulation

holocene paleohydrology of central alberta testing the general circulation model climate simulations paleoecological investigations of 28 lakes and bogs provide the basis for a holocene paleohydrological record for central alberta shallow basins empty during the early holocene began flooding shortly after 8000 years ago most filled from 6500 to 4500 years ago and none filled later than 3000 years ago pollen of a hypersaline indicator genus ruppia was found in cores of lakes where the plant does not presently grow indicating lower lake levels evaporation stress and increased salinity from 8000 to 3000 years ago moore lake 54 30 n 100 30 w may have dropped 15 m from 9200 to 5900 years ago and lofty lake 54 44 n 112 29 w largely dried up between 8700 and 6300 years ago lower water levels are suggested for several lakes by shifts in fossil diatom populations from planktonic to benthic particularly epipelic species including pioneering taxa these shallow warm lakes were highly productive and sedimentary pigment levels reached maximum values between about 9000 and 4000 years ago the pale

oxygen isotope variations in post glacial lake ontario abstract the role of glacial meltwater input to the atlantic ocean in triggering the younger dryas yd cooling event has been the subject of controversy in recent literature lake ontario is ideally situated to test for possible meltwater passage from upstream glacial lakes and the laurentide ice sheet lis to the atlantic ocean via the lower great lakes here we use the oxygen isotope compositions of ostracode valves and clam shells from three lake ontario sediment cores to identify glacial meltwater contributions to ancient lake ontario since the retreat of the lis 16 500 cal 13 300 14c bp differences in mineralogy and sediment grain size are also used to identify changes in the hydrologic regime the average lakewater 18o of 17 5 determined from ostracode compositions indicates a significant contribution from glacial meltwater upon lis retreat from the st lawrence lowlands ancient lake ontario glacial lake iroquois lakewater 18o increased to 12 largely because of the loss of low 18o glacial meltwater input a subsequent decrease in lakewater 18o from 12 to 14 accompanied by a median sediment grain size increase to 9 m indicates that post glacial lake ontario received a final pulse of meltwater 13 000 12 500 cal 11 100 10 500 14c bp before the onset of hydrologic closure this meltwater pulse which is also recorded in a previously reported brief freshening of the neighbouring champlain valley cronin et al 2012 may have contributed to a weakening of thermohaline circulation in the atlantic ocean after 12 900 cal 11 020 14c bp the meltwater presence in the ontario basin continued to inhibit entry of champlain seawater into early lake ontario opening of the north bay outlet diverted upper great lakes water from the lower great lakes causing a period 12 300 8300 cal 10 400 7500 14c bp of hydrologic closure in lake ontario anderson and lewis 2012 this change is demarcated by a shift to higher 18olakewater 7 driven in part by strong evaporative conditions in the ontario basin and in part by increasing 18oprecipitation at this time the 18olakewater then fluctuated only slightly upon the eventual return of the upper great lakes water during the nipissing phase at 5800 cal 5090 14c cal bp anderson and lewis 2012 after which shelly fauna are no longer preserved in the sediment record

paleohydrology of a canadian shield lake inferred from 18o in sediment cellulose oxygen and carbon isotope analyses on cellulose in the postglacial sediment of weslemkoon lake southern ontario show that the cellulose came mainly from aquatic plants or algae rather than from terrestrial sources if a wholly aquatic source is assumed the oxygen isotope content permits inferences of lake water 18o values over the past 10 000 years by accounting for the isotopic fractionation that occurs during cellulose synthesis chronological control is provided by pollen analysis and six 14c dates our reconstruction shows lake water 18o fluctuated from about 5 lower than present in the early postglacial to 5 or more above present values during the mid postglacial these broad secular shifts reflect a combination of fluctuating mean annual 18o of local precipitation evaporative isotopic enrichment of surface waters and snowmelt bypass effects the first two factors reflect the changing paleotemperature and paleohydrology respectively whereas the third factor is a more speculative interp

surface ocean mixing inferred from different multisatellite altimetry measurements abstract two sea surface height ssh anomaly fields distributed by archiving validation and interpretation of satellite oceanographic aviso altimetry are evaluated in terms of the effects that they produce on mixing one ssh anomaly field tagged ref is constructed using measurements made by two satellite altimeters the other ssh anomaly field tagged upd is constructed using measurements made by up to four satellite altimeters advection is supplied by surface geostrophic currents derived from the total ssh fields resulting from the addition of these ssh anomaly fields to a mean ssh field emphasis is placed on the extraction from the currents of lagrangian coherent structures lcss which acting as skeletons for patterns formed by passively advected tracers entirely control mixing the diagnostic tool employed to detect lcss is provided by the computation of finite time lyapunov exponents it is found that currents inferred using upd ssh anomalies support mixing with characteristics similar t

stable isotope variations in stalagmites from northwestern sweden document changes in temperature and vegetation during the early holocene a comment on sundqvist et al 2007a we offer an alternative palaeoenvironmental interpretation of oxygen isotope data obtained on two early holocene stalagmite records from caves in the scandes mountains of northern sweden korallgrottan and labrintgrottan and the well known soylegrotta norway sg93 record with which they are compared that differs in several respects from that proposed by the authors contrary to viewing these as inverted palaeotemperature records we suggest that they primarily reflect changes in the delta o 18 of local annual precipitation modified by secondary temperature dependent variation in water calcite oxygen isotope fractionation at each of the three sites this is supported by the striking similarity over the entire holocene between the sg93 calcite delta o 18 record and the lacustrine carbonate delta o 18 record from lake tibetanus northern sweden which implies straightforward transfer of annual precipitation delta o 18 signals into cave drip waters recent studies of drip waters in korallgrottan also support this model this further enhances the value of cave deposits as palaeoclimate archives in this region and provides additional evidence of the sensitivity of the precipitation isotope thermometer to changes in atmospheric circulation patterns less

seasonality and the isotope hydrology of lochnagar a scottish mountain lake implications for palaeoclimate research the relationship between isotope ratios in precipitation and lake waters was monitored by bi weekly measurements taken over a five and a half year period between may 2000 and september 2005 a period of 1964 days at lochnagar a remote mountain lake in eastern scotland short term changes in the oxygen isotope composition of lake water 18ol at lochnagar follow a seasonal pattern similar to isotopes in local precipitation 18op however changes in catchment residence time snow accumulation lake ice cover and lake stratification modify the temporal structure of 18ol over the seasonal cycle of particular importance is precipitation amount which controls catchment and lake residence times and determines the degree of phase lag and amplitude change between 18ol and 18op a simple mass balance model replicates these effects and demonstrates that the degree of phase lag and amplitude reduction is predictable given known input volume ratio the implications of these observations for the use of 18o

assessing meteoric water composition and relative humidity from18o and2h in wood cellulose paleoclimatic implications for southern ontario canada abstract an empirical model is presented that derives the initial isotopic composition of water used by terrestrial plants and the relative humidity that prevailed during photosynthesis from the isotopic composition of oxygen and carbon bound hydrogen in the plant cellulose the model uses fixed values for the fractionation factors that describe the evapotranspirative isotopic enrichment of leaf waters and the biochemical fractionations occurring during cellulose synthesis when applied to cellulose extracted from fossil plant matter the model can be used to generate quantitative estimates of the temperature and moisture regimes of the past the application of the model is demonstrated by consideration of 18o and 2h results on cellulose from fossil wood collected at brampton ontario the brampton data yield records of systematic changes in the temperature and moisture regimes of the eastern great lakes region over the past 11 500 a both mean annual temperature and photosynthetic humidity increased substantially from values much lower than the present at the end of the wisconsin stage to values higher than the present in the mid holocene the phase relation of the paleotemperature and paleohumidity curves engenders differentiation of the climatic history at brampton into four characteristic zones i a period of ameliorating climate predominantly much colder and drier than now lasting until about 7400 b p ii an early hypsithermal period of warm and dry conditions that transformed after 6000 a b p into iii the main hypsithermal time of warmth and pronounced moistness subsequent climatic detrioration led to establishment of iv cool moist conditions like the present sometime within the last few thousand years

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

early holocene climate at castle peak southern coast mountains british columbia canada clague j j mathewes r w buhay w m and edwards t w d 1992 early holocene climate at castle peak southern coast mountains british columbia canada palaeogeogr palaeoclimatol palaeoecol 95 53 67 new palynological radiocarbon and stable isotope data from castle peak m the southern coast mountains indicate that the earl holocene climate of southern british columbia was warmer and perhaps drier than today fossil wood fragments are common above timberline at castle peak and have yielded 13 radiocarbon ages ranging from 9 1 ka to 8 i ka this evidence for higher timberline during the early holocene is in agreement with pollen data indicating a warmer and possibly longer summer growing season in this area during the early holocene and is consistent with theoretical considerations based on milankovitch forcing of climate change the oxygen and hydrogen stable isotope composition of fossil wood cellulose is similar to that of living trees in the same area growing season relative humidity values derived from the isotopic data provide some support for episodes of dryness at times of elevated timberline although the majority of paleohumidity estimates fall within the range of modern moisture levels

isotopic evidence for shifts in atmospheric circulation patterns during the late quaternary in mid north america wyoming is now at the eastern margin of westerlies originating in the pacific but in the pleistocene appears to have received moisture from elsewhere possibly the gulf of mexico oxygen isotope ratios of pedogenic carbonate in postglacial terraces correspond to ratios in equilibrium with present meteoric waters which show a strong relation to precipitation seasonality and storm sources in contrast the oxygen isotope ratios of all pre holocene soils are significantly more positive even though the carbon isotope composition of coexisting organic matter suggests that the carbonate formed in temperatures cooler than today the oxygen isotope ratios of paleowaters in mid north america appear to be more useful for identifying past storm sources than for estimating paleotemperatures

effect of varying oceanicity on early to mid holocene palaeohydrology kola peninsula russia isotopic evidence from treeline lakes the stable isotope stratigraphy of sedimentary organic matter and algal cellulose in cores from two lakes near treeline on the kola peninsula indicate changes in water and nutrient balance that correlate with inferred expansion of pinus sylvestris during the early to mid holocene trends in cellulose inferred lakewater 18o values for both lakes suggest that moist conditions after deglaciation were followed by progressive drying from about 9500 to between 8000 and 7500 14c yr bp although pine appeared in the area by 8000 14c yr bp the maximum density of trees locally as suggested by stomate evidence occurred during subsequent moistening between 7500 and 6000 14c yr bp this is c 1000 years later than in other regions of northern russia and is possibly attributable to limitations on seedling establishment and survival due to root desiccation during dry winters changes in nutrient balance and productivity in the lakes as inferred from variations in sediment carbon and nitrogen elemental abundances an

crystal residence times from trace element zoning in plagioclase reveal changes in magma transfer dynamics at mt etna during the last 400 years abstract trace element zoning in plagioclase of selected alkaline lavas from the historic 1607 1892 ad and recent 1983 2013 ad activity of mt etna volcano has been used to explore the possible role that volcano tectonics exert on magma transfer dynamics the observed textural characteristics of crystals include near equilibrium textures i e oscillatory zoning and textures with variable extent of disequilibrium patchy zoning coarse sieve textures and dissolved cores historic crystals exhibit lower k concentrations at lower anorthite contents a feature in agreement with the general more potassic character of the recent lavas if compared to the historic products historic plagioclases have statistically higher ba and lower sr concentrations than the recent crystals which result in different sr ba ratios for the two suites of plagioclase variations in the anorthite content along core to rim profiles obtained on crystals with different types of textures for both the historic and recent eruptive periods were evaluated particularly versus sr ba at comparable average an contents crystals characterized by oscillatory zoning which are representative of near equilibrium crystallization from the magma display distinct sr ba ratios we suggest that these features are primarily related to recharge of a new geochemically distinct magma into the storage and transport system of the volcano in addition to distinct trace element and textural characteristics of plagioclase sr diffusion modeling for plagioclase suggests that residence times are generally shorter for crystals found in recently erupted lavas 25 77 years average 43 years compared to those of the historic products 43 163 years average 99 years shorter residences times correlate with gradual increases in eruption volume and eruption frequency rates through time we attribute these features to an increasing influence since the 17th century of extensional tectonic structures within the upper 10 km of the etnean crust which have promoted shorter residence times and higher eruption frequency

stable isotope paleoclimate records for southern ontario canada comparison of results from marl and wood profiles of 18o in two marl cores from southern ontario canada are compared in detail with the records of meteoric water isotopic composition and photosynthetic humidity obtained from previous isotopic studies using wood cellulose at brampton ontario by accounting for the inferred changes in meteoric water composition and temperature the changes in the oxygen isotope content of the marl arising from fluctuations in the evaporative enrichment of the lakewater can be estimated the resulting synthetic profiles of relative evaporative enrichment from both marl cores exhibit strong correspondence to the photosynthetic humidity profile generated from the studies at brampton which substantiates the importance of evaporation in the water budgets of these two lakes a striking analogy exists between the isotopic evaporative enrichment response of such lakewaters and that of the waters in terrestrial plants both of the marl lakes approach close to isotopic steady state during the summer season when carbon