a parametrization based on sea ice morphology of the neutral atmospheric drag coefficients for weather prediction and climate models 1 a hierarchy of parametrizations of the neutral 10 m drag coefficients over polar sea ice with different morphology regimes is derived on the basis of a partitioning concept that splits the total surface drag into contributions of skin drag and form drag the new derivation which provides drag coefficients as a function of sea ice concentration and characteristic length scales of roughness elements needs fewer assumptions than previous similar approaches it is shown that form drag variability can explain the variability of surface drag in the marginal sea ice zone miz and in the summertime inner arctic regions in the miz form drag is generated by floe edges in the inner arctic it is generated by edges at melt ponds and leads due to the elevation of the ice surface relative to the open water surface it is shown that an earlier fit of observed neutral drag coefficients is obtained as a special case within the new concept when specific simplifications are made which concern the floe and melt pond geometry due to the different surface morphologies in the miz and summertime arctic different functional dependencies of the drag coefficients on the sea ice concentration result these differences cause only minor differences between the miz and summertime drag coefficients in average conditions but they might be locally important for atmospheric momentum transport to sea ice the new parametrization formulae can be used for present conditions but also for future climate scenarios with changing sea ice conditions

variability of arctic sea ice topography and its impact on the atmospheric surface drag over the polar oceans near surface atmospheric transport of momentum is strongly influenced by sea ice surface topography the latter is analyzed on the basis of laser altimeter data obtained during airborne campaigns between 1995 and 2011 over more than 10 000 km of flight distance in different regions of the arctic ocean spectra of height and spacing between topographic features averaged over 10 km flight sections show that typical values are 0 45 m for the mean height and about 20 m for the mean spacing nevertheless the variability is high and the spatial variability is stronger than the temporal one the total topography spectrum is divided into a range with small obstacles between 0 2 m and 0 8 m height and large obstacles 0 8 m results show that large pressure ridges represent the dominant topographic feature only along the coast of greenland in the central arctic the concentration of large ridges decreased over the years accompanied by an increase of small obstacles concentration and this might be related to decreasing multiyear ice the application of a topography dependent parameterization of neutral atmospheric drag coefficients reflects the large variability in the sea ice topography and reveals characteristic differences between the regions based on the analysis of the two spectral ranges we find that the consideration of only large pressure ridges is not enough to characterize the roughness degree of an ice field and the values of drag coefficients are in most regions strongly influenced by small obstacles

a parameterization of the ice ocean drag coefficient 1 a parameterization of the ice ocean drag coefficient cw was developed through partitioning the oceanic drag force into three components 1 form drag on the floe edge 2 form drag on the ridge keel and 3 skin friction on the ice bottom through these quantities cw was expressed as a function of observable sea ice geometric parameters sensitivity studies were carried out to investigate the influence of varying sea ice conditions on cw the results revealed that cw increases first and then decreases with increasing ice concentration a similar to the observations of the air ice drag coefficient and which is mainly attributed to the nonmonotonic variation of the form drag on the floe edge with ice concentration moreover the form drag on the floe edge is always the dominant component having a proportion of more than 60 in sea ice with a large aspect ratio draft length 1 100 indicating the necessity of including this term in sea ice dynamic models particularly for the marginal ice zone miz the form drag on the ridge keel becomes dominant only when the ridging intensity is extremely high depth spacing 1 20 additionally a large value of cw cannot be caused only by the inclusion of form drag terms but also by large skin friction over rough ice bottoms finally for typical situations in the miz with moderate ridging intensity the parameterization will underestimate cw by approximately 30 for a rough ice bottom and by over 80 for a smooth ice bottom if no form drags are considered

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

cultivation and human impact at 6000 cal yr b p in tropical lowland forest at niah sarawak malaysian borneo this paper describes palynological evidence for what appears to be comparatively large scale human impact in the catchment of the sungai niah in the wet tropical lowland swamp forests of sarawak malaysian borneo close to the great cave of niah pollen associated with cleared landscapes and rice cultivation is evident in the sedimentary record from before 6000 cal yr b p human activity seems to have been associated with changes in sedimentary regime with peat dominated environments being replaced diachronously by clay dominated deposition this may reflect anthropogenic soil erosion in the catchment of the sungai niah

surface and deep ocean circulation in the subpolar north atlantic during the mid pleistocene revolution 1 we investigated surface and deep ocean variability in the subpolar north atlantic from 1000 to 500 thousand years ago ka based on two ocean drilling program odp sites feni drift site 980 55 29 n 14 42 w and bjorn drift site 984 61 25 n 24 04 w benthic foraminiferal stable isotope data planktic foraminiferal faunas ice rafted debris data and faunally based sea surface temperature estimates help test the hypothesis that oceanographic changes in the north atlantic region were associated with the onset of the 100 kyr world during the mid pleistocene revolution based on percentage of neogloboquadrina pachyderma s records from both sites surface waters during interglacials and glacials were cooler in the mid pleistocene than during marine isotope stages mis 5 and 6 in particular interglaciations at bjorn drift site 984 were significantly cooler faunal evidence suggests that the interglacial arctic front shifted from a position between the two sites to a position northwest of bjorn drift site 984 after ca 610 ka as during the late pleistocene we find faunal evidence for lagging surface warmth at most of the glacial initiations during the mid pleistocene each initiation is associated with high benthic 13c values that are maintained into the succeeding glaciation which we term lagging nadw production these findings indicate that lagging warmth and lagging nadw production are robust features of the regional climate system that persist in the middle to late pleistocene

onset of hudson strait heinrich events in the eastern north atlantic at the end of the middle pleistocene transition 640 ka 1 heinrich events are well documented for the last glaciation but little is known about their occurrence in older glacial periods of the pleistocene here we report scanning xrf and bulk carbonate 18o results from integrated ocean drilling program site u1308 reoccupation of deep sea drilling project site 609 that are used to develop proxy records of ice rafted detritus ird for the last 1 4 ma ca sr is used as an indicator of ird layers that are rich in detrital carbonate i e heinrich layers whereas si sr reflects layers that are poor in biogenic carbonate and relatively rich in detrital silicate minerals a pronounced change occurred in the composition and frequency of ird at 640 ka during marine isotope stage mis 16 coinciding with the end of the middle pleistocene transition at this time hudson strait heinrich layers suddenly appeared in the sedimentary record of site u1308 and the dominant period of the si sr proxy shifted from 41 ka prior to 640 ka to 100 ka afterward the onset of heinrich layers during mis 16 represents either the initiation of surging of the laurentide ice sheet lis off hudson strait or the first time icebergs produced by this process survived the transport to site u1308 we speculate that ice volume i e thickness and duration surpassed a critical threshold during mis 16 and activated the dynamical processes responsible for lis instability in the region of hudson strait we also observe a strong coupling between ird proxies and benthic 13c variation at site u1308 throughout the pleistocene supporting a link between iceberg discharge and weakening of thermohaline circulation in the north atlantic

modern stable isotopic δ18o δ2h δ13c variation in terrestrial fluvial estuarine and marine waters from north central sarawak malaysian borneo stable isotope data on humid tropical hydrology are scarce and at present no such data exist for borneo delta18o 2h and 13c were analysed on 22 water samples from different parts of the sungai river niah basin rain cave drip rainforest pool tributary stream river estuary sea in north central sarawak malaysian borneo this was done to improve understanding of the modern stable isotope systematics of the sungai niah basin essential for the palaeoenvironmental interpretation of the late quaternary stable isotope proxies preserved in the great cave of niah the niah hydrology data are put into a regional context using the meteoric water line for southeast asia as derived from international atomic energy agency world meteorological organization isotopes in precipitation network data although the niah hydrological data set is relatively small spatial isotopic variability was found for the different subenvironments of the sungai niah basin a progressive enrichment occurs towards the south china sea 18o 4 6 2h 29 3 13c 4 8 from the tributary stream 18o 8 4 2h 54 7 13c 14 5 to up river 18o c 8 2h c 51 13c c 12 and down river values 18o c 7 5 2h c 45 13c c 11 this is thought to reflect differential evaporation and mixing of different components of the water cycle and a combination of depleted biogenic 13c plant respiration and decay with enriched 13c values due to photosynthesis atmospheric exchange mixing with limestone and marine waters downstream cave drip waters are relatively enriched in 13c as compared to the surface waters this may indicate rapid degassing of the cave drips as they enter the cave atmosphere copyright 2005 john wiley sons ltd

four climate cycles of recurring deep and surface water destabilizations on the iberian margin centennial climate variability over the last ice age exhibits clear bipolar behavior high resolution analyses of marine sediment cores from the iberian margin trace a number of associated changes simultaneously proxies of sea surface temperature and water mass distribution as well as relative biomarker content demonstrate that this typical north south coupling was pervasive for the cold phases of climate during the past 420 000 years cold episodes after relatively warm and largely ice free periods occurred when the predominance of deep water formation changed from northern to southern sources these results reinforce the connection between rapid climate changes at mediterranean latitudes and century to millennial variability in northern and southern polar regions

influence of a sea ice ridge on low level airflow the influence of a single pressure ridge of 4 5 m height on the structure of the atmospheric surface layer is studied the field of the mean wind velocity is governed by typical features of a bernoulli effect with a speedup over the crest and a shadowing effect downwind of the ridge it is found that the turbulence generated by the ridge compensates for the deformation of the flow field by mixing momentum downward both mean and turbulent fields are restored to their upwind values at a distance of 300 m downwind of the ridge which is equivalent to an aspect ratio of 0 015 the level of maximum turbulence generated by the ridge is characterized by a linear relationship a formulation for the determination of the form drag of a single ridge is proposed and generalized toward an ensemble of ridges we estimate that the form drag contributes 50 to the total drag exerted by a typically ice covered sea surface on the atmospheric flow

reconstructing the southern south china sea upper water column structure since the last glacial maximum implications for the east asian winter monsoon development difference in the stable oxygen isotopes dd 18 o and mg ca based temperatures dt of surface dwelling g ruber and thermocline dwelling p obliquiloculata planktonic foraminifera and the temperature difference between alkenone and p obliquiloculata mg ca based temperatures to estimate the upper ocean thermal gradient at international marine past global change study images core md01 2390 estimates of the upper ocean thermal gradient were used to reconstruct mixed layer dynamics we find that our dd 18 o estimates are biased by changes in salinity and thus do not display a true upper ocean thermal gradient the d to fg ruber and p obliquiloculata as well as the alkenone and p obliquiloculata suggest increased surface water mixing during the late glacial likely due to enhanced eawm winds surface water mixing was weaker during the late holocene indicating a weaker influence of winter monsoon winds the weakest winter monsoon activity occurred between 6 5 ka and 2 5 ka inferred eawm changes since the last glacial maximum coincide with eawm changes as recorded in chinese loess sediments we find that the intensity of the eawm and the east asian summer monsoon show an inverse behavior during the last glacial and deglaciation but covaried during the middle to late holocene

biogenic carbonate and ice rafted debris heinrich layer accumulation in deep sea sediments from a northeast atlantic piston core abstract biogenic carbonate mass accumulation rates show distinct quaternary glacial interglacial changes in a mid latitude northeast atlantic deep sea core during the last 208 kyr these were generally higher during interglacials averaging 2 2 g cm 2 kyr than during glacial periods with a maximum average of 1 2 g cm 2 kyr intervals containing high ice rafted debris have very low biogenic carbonate accumulation rates paleo primary productivity estimates based on biogenic carbonate accumulation rates are generally higher during interglacials averaging 80 gc m 2 yr than during glacials which average 49 gc m 2 yr maximum estimate short intervals with possibly reduced primary productivity correspond to heinrich layers which are the result of pulses of massive iceberg production and rapid melting in the north atlantic we identified thirteen heinrich layers in isotopic stages 7 to 2 they have calendar ages of about 201 189 182 183 164 167 146 149 142 128 131 64 67 52 54 40 43 29 31 21 and 15 kyr these heinrich layers contain large amounts of ice rafted debris including detrital carbonate low amounts of coccoliths and planktic foraminifera mainly neogloboquadrina pachyderma sinistral the upper five heinrich layers are almost barren of coccoliths and the fourth layer is also free of foraminifera the virtual absence of coccoliths is interpreted to reflect reduced coccolithophorid productivity in the photic zone due to low salinity of surface waters and to blockage of light by ice and suspended materials shed off by melting icebergs considering the limited use of other proxies such as organic carbon diatom and benthic foraminifera due to their very low content abundance in the sediments biogenic carbonate mass accumulation rates offer a workable paleo primary productivity proxy in open ocean sediments of the carbonate dominated northeast atlantic

study of the diet effect on δ13c of shell carbonate of the land snail helix aspersa in experimental conditions abstract this study aims to demonstrate the influence of the metabolic co2 derived from the diet and of the atmospheric co2 on the shell carbonate 13c of the pulmonate snail helix aspersa maxima raised under controlled conditions adult snails were analyzed and compared with three hatching and 1 day old young snails stemming from the same breeding one day after the 2 day old individuals were raised during 1 month three groups of gastropods were fed with fresh lettuce c3 plant 13c 27 49 three groups with corn c4 plant 13c 11 7 and three groups ate alternately both c3 c4 the difference between the average 13c values of the adult snails on the one hand and the hatched and 1 day old snails on the other hand indicates a depletion of 2 47 therefore the isotopic parents offspring signal is not preserved the depleted ingested albumen by the snail embryo in the egg during the building of the shell could explain this depletion the c3 diet experiment gave the expected isotopic composition difference between the diet lettuce and the shells average 13cshell lettuce 13 75 0 52 this result shows a clear diet effect on the isotopic composition of the snail shells for the c4 experiment the difference in carbon isotope composition between the corn and the shell 13cshell corn yielded an average value of 4 89 0 87 the main result is that 13c is not constant and appears to depend on the type of ingested food several hypotheses can arise from this study to explain the different fractionations a differences in the quality of the two diets b differences in turnover rate for c3 and c4 feeders the groups regularly fed with mixed diet yielded 13c values showing a preferential use of c3 food for most values the c3 c4 mixed dietary alternation probably led snails to use mainly the lettuce instead of the corn powder

weddell gyre temperature maximum stratum at depths below 200 m relatively warm salty water spreads poleward from the antarctic circumpolar current acc this deep water mass is cooled through interaction with the atmosphere feeding the formation of dense bottom water which in turn influences much of the world ocean significant poleward spreading is accomplished within the weddell gyre of the atlantic sector of the southern ocean an extensive data set obtained in the 1980s within the weddell gyre provides a detailed view of the subsurface temperature maximum t max stratum defining the top of the deep water mass the seasonal sea ice growth and retreat pattern reflects the t max distribution there is evidence for subdivision of the t max into two cold centers which may reflect secondary circulation features within the gyre the primary inflow of warm deep water is derived from the southern edge of the acc near 20 30 e the inflow spreads to the west along 65 s and is divided into smaller pools of relatively warm water west of maud rise with a cold feature directly over the rise in a manner shown by models of topographically generated eddies variability of the t max stratum in the vicinity of maud rise arising from changes in the vigor of the large scale circulation may influence the regional vertical heat fluxes and be related to interannual variability of the sea ice cover and to the recurring polynya feature typical of the region

reconstructing estuarine conditions oyster shells as recorders of environmental change southwest florida abstract live collected shells of the oyster crassostrea virginica contain geochemical records of modern temperature and salinity so records of prehistoric conditions may be obtained from subfossil shells restoration of channelized watersheds in florida is receiving much attention and plans for targeted watersheds require information about estuarine conditions before channelization lack of historical records necessitates alternative methods to understand pre disturbance conditions a 14c calibrated amino acid geochronology based on racemization of glutamic acid yielded ages ranging from 190 1220 ad and from 1270 1860 ad for subfossil oysters from blackwater river near natural watershed and for faka union bay channelized watershed respectively 18o and 13c values of subfossil shells from blackwater river indicate salinity and summer temperatures similar to present winter temperatures recorded in shells from 190 590 720 and 1050 ad appear 1 5 c colder than present winter temperatures whereas the shell from 1220 ad records winter temperatures similar to modern winter temperatures these temperature shifts may indicate change in climate or natural seasonal variation of winter temperature from year to year subfossils from faka union bay may reflect a complicated hydrology which cannot be evaluated by isotopic compositions alone and demonstrates the need for development of independent elemental proxies for temperature and salinity decreases in 13c from subfossil to modern shells may in part result from co2 added to the atmosphere from fossil fuel burning the suess effect subfossil 13c that is 1 more positive than modern shells suggest a change in the dominant carbon sources from terrestrial c4 or aquatic plants to c3 plants mangroves

millennial scale fluctuations in north atlantic heat flux during the last 150 000 years abstract surface water and deep ocean palaeoclimate records obtained from north atlantic core su90 03 40 n 32 w exhibit pronounced fluctuations at sub orbital time scales surface temperature variability in the mid latitude atlantic over the last 150 kyr is dominated by forcing at precession 21 kyr and semi precession harmonics 11 kyr abrupt changes in sea surface temperatures show that the northward transport of heat by the north atlantic current was curtailed during ice rafting events sea surface temperatures were about 12 c colder than modern values during the most intense cooling episodes associated with major ice rafting events heinrich events 1 4 6 and 11 and 10 c below modern values during the later part of isotope stage 3 40 30 ka during these cold intervals the north atlantic current was displaced to south of 40 n as the cold meltwaters penetrated southwards into what is now the subtropical ocean these changes in surface ocean heat exchange were most probably allied to a latitudinal migration and increase in zonality of atmospheric circulation patterns concurrent shifts in ird concentration sea surface temperatures and benthic 13 c values provide evidence of coupling between sea surface processes and the deep water circulation and suggest that decreases in surface temperature and salinity during ice rafting events culminated in a significant reorganisation of north atlantic deep water production

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

shell gathering from mangroves and the seasonality of the southeast asian monsoon using high resolution stable isotopic analysis of the tropical estuarine bivalve geloina erosa from the great cave of niah sarawak methods and reconnaissance of molluscs of early holocene and modern times this paper describes a reconnaissance high resolution study of stable isotopes 18o and 13c from modern shells of the estuarine bivalve geloina erosa and those dated to the early holocene that were harvested by people from mangroves near the great cave of niah on the north coast of borneo this reconnaissance study provides high resolution palaeoclimatic palaeohydrological information concerning early human activity in the region and the past character of the southeast asian monsoon laser ablation continuous flow isotope ratio mass spectrometry la cf irms on modern shells of geloina erosa revealed saw tooth stable isotopic profiles that bear a close resemblance to peaks and troughs of trends in recent local rainfall including the 1998 el nino drought highlighting the potential of geloina erosa for reconstructing seasonality of the southeast asian palaeomonsoon la cf irms analysis of prehistoric shells of geloina erosa held in the harrisson archives of the sarawak museum revealed cyclical shifts in 18o with similar amplitudes of variation as found in modern shells of geloina erosa as at the present day this probably reflects the changing seasonality of the monsoon rains with shifts to negative 18o values during periods of high runoff lighter mean 18o values of the prehistoric shells however may indicate a greater annual surplus of rainfall and possibly consistent with the early holocene strengthening of the summer monsoon at that time the similarity of the last growth increment 18o of the prehistoric shells to their mean 18o profile values suggests that gathering took place during times of moderate runoff

late paleocene arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios abstract characterizing polar climates during past warm intervals is important for understanding greenhouse climate dynamics because high latitude surface temperatures and precipitation patterns are extremely sensitive to global climatic conditions model data comparisons of high latitude climates during past warm intervals cretaceous eocene pliocene are currently at odds specifically simulations of past warm climates produce polar regions characterized by sub freezing temperatures and significant seasonality whereas limited fossil proxy data indicate higher mean annual temperatures and low seasonality i e an equable climate we have constructed a data set to infer northern hemisphere polar marine temperatures during the late paleocene seasonal and mean annual temperature and the oxygen isotopic composition of precipitation are reconstructed for an arctic coastal setting during the thanetian 57 58 ma using fossil shell stable isotope profiles we estimate that coastal water temperatures varied between 10 and 15 c during the seasons of growth presumably spring summer and fall these findings support paleontological evidence implying northern hemisphere polar climates were seasonally warm during the late paleocene in addition estuarine fossil oxygen isotope profiles show periodic excursions to low values as low as 19 vpdb which indicate seasonal pulses of isotopically depleted freshwater

variation in isotopic composition c o and sr of holocene mactra isabelleana bivalvia from the coast of buenos aires province argentina the 13c 12c and 18o 16o ratios of carbonate incremental growth bands and whole shells of the bivalve mactra isabelleana collected from holocene including modern littoral deposits along the coastal area of buenos aires province close to the rio de la plata river reflect different environments which stayed relatively constant throughout the holocene differences in 13c 12c and 18o 16o ratios along the growth axis of two shells from the modern estuarine and marine situations constrain the differences between the two types of environment the data show a marked cyclicity from both sites but the increase in river flow during the winter is reflected by very low d18o and d13c values in the estuarine shell in contrast the shell from the marine site has fewer cycles with lower amplitude which are consistent with seasonal temperature variations away from the influence of river input the differences in the isotopic cyclic variations between the marine and estuarine sites average out in the whole shell analys

post depositional alteration of humid tropical cave sediments micromorphological research in the great cave of niah sarawak borneo the post depositional alteration of cave sediments is of critical importance for the recognition identification and investigation of geoarchaeological and palaeoenvironmental evidence there have been relatively few studies of tropical cave sediments using micromorphology and this work represents one of the most detailed with 26 samples taken from deposits in the west mouth of the great cave of niah that cover the last 55 000 bp and contain the earliest known evidence for the remains of modern humans in southeast asia cave sediments situated in the humid tropics are subject to relatively high temperatures and moisture conditions that promote high rates of chemical alteration and geomorphic change this paper outlines those post depositional features that occurred in situ in the west mouth and include translocation and concentration bioturbation excrement bone alteration plant alteration clast alteration and guano decomposition it examines their implications for recognising past human activities e g fire altered materials the preservation of archaeological remains the nature of palaeoenvironments and of localised physical and bio geochemical processes

biological markers and their carbon isotopes as an approach to the paleoenvironmental reconstruction of nansha area south china sea during the last 30 ka paleoenvironmental changes over the last 30 ka have been documented for the nansha area south china sea from the biomarkers and their carbon isotopic composition of 314 sediment samples from core 17962 the concentrations of marine lipids indicate that the paleoceanographic and paleoclimatic conditions were not stable in the nansha area during the last glacial period the accumulation rates of c37 alkenones and c30 alkyl diols show that marine paleoproductivity was higher during the last glaciation than in the holocene and correlate well with those of terrestrial biomarkers simultaneous variations in accumulation rates of marine biomarkers and terrigenous long chain compounds during the last glacial period suggest that this enhancement of marine productivity was caused by an increase in terrestrial nutrient supply from the sunda shelf the stable carbon isotopic composition of terrigenous long chain compounds such as n alkanes 13 c 28 6 34 2 n alkanoic acids 13 c 27 1 31 8 and n alkanols 13 c 26 6 35 3 indicates that these compounds were derived from c3 plants and the surrounding area of southern south china sea was not dry during the last glacial 2002 elsevier science ltd all rights reserved

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

persistent suborbital climate variability in marine isotope stage 5 and termination ii new surface water records from two high sedimentation rate sites located in the western subtropical north atlantic near the axis of the gulf stream provide clear evidence of suborbital climate variations through marine isotope stage mis 5 persisting even into the warm peak of the interglaciation substage 5e we found that the amplitude of suborbital climate oscillations did not vary significantly for the whole of mis 5 implying that ice volume has little or no influence on the amplitude of suborbital climate variability in this region although some records suggest that longer suborbital variations 4 10 kyr during mis 5 are linked to deepwater changes none of the existing records is of sufficient resolution to assess if a linkage occurred for oscillations shorter than 4 kyr however when examined in conjunction with published data from the norwegian sea new evidence from the subpolar north atlantic suggests that coupled surface deepwater oscillations occurred during the penultimate deglaciation this supports the hypothesis that during glacial and deglacial times ocean ice interactions and deepwater variability amplify suborbital climate change at higher latitudes we suggest that during the penultimate deglaciation the north atlantic deepwater source varied between nordic sea and open north atlantic locations in parallel with surface temperature oscillations

u channel track for susceptibility measurements 1 a lightweight transportable and inexpensive magnetic susceptibility track for u channel samples is described the track utilizes a sapphire instruments 3 3 cm square coil having a response function of shape similar to that of the 2g enterprises u channel magnetometer and a half peak width of 3 cm the instrument has been calibrated using a u channel standard made of manganese dioxide the software incorporates automated track control and measurement drift correction susceptibility measurements on this system compare favorably with the 45 mm circular bartington loop used for u channel samples at the laboratoire des sciences du climat et de l environnement gif sur yvette france and with data from the whole core susceptibility track aboard the ocean drilling program research vessel joides resolution

the shell of the queen scallop aequipecten opercularis l as a promising tool for palaeoenvironmental reconstruction evidence and reasons for equilibrium stable isotope incorporation abstract the queen scallop aequipecten opercularis has been an important part of the marine fauna of the northeast atlantic region since the miocene and is a suitable candidate for palaeoenvironmental studies using stable isotopes modern shells were investigated to determine if carbonate is precipitated in isotopic equilibrium in this species and to confirm that growth continues through the year specimens of a opercularis were cultured under monitored semi natural conditions over an autumn winter period and the analyses of these specimens were supplemented with isotope data from preserved indigenous north sea specimens the results indicated that the cultured specimens grew in relatively low temperatures that oxygen isotopes of shell exterior carbonate were precipitated in isotopic equilibrium and that a large proportion of the ambient temperature range was recorded in shell carbonate the indigenous north sea specimens exhibited a good correspondence to predicted oxygen isotope values for summer the isotopic record related to winter was however somewhat truncated due to growth decelerations in the specimens carbon isotopes of shell exterior carbonate were calculated as being derived primarily from external sources and showed comparatively little influence from metabolically derived carbon this suggests that carbon isotopes were at least close to equilibrium with ambient waters the limited incorporation of metabolic products suggests that a opercularis would be a good monitor of changing carbon isotope ratios in seawater dissolved inorganic carbon the occurrence of equilibrium shell precipitation is explained using a pteriomorph shell calcification model which proposes that transport of ions through the periostracum caused the composition of the extrapallial fluid to be effectively the same as seawater carbonate secretion is therefore not influenced significantly by biological vital effects

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

progressive reduction in ne atlantic intermediate water ventilation prior to heinrich events response to nw european ice sheet instabilities we present high resolution benthic 13c records from intermediate water depth core site md01 2461 1153 m water depth from the porcupine seabight ne atlantic spanning 43 to 8 kyr b p at an average proxy time step of 160 56 years this core provides information on the linkage between records from the portuguese margin and high latitude north atlantic basin allowing additional insights into north atlantic thermohaline circulation thc variability during millennial scale climatic events of the last glacial together these records document both discrete and progressive reductions in glacial north atlantic intermediate water gnaiw formation preceding heinrich h events 1 2 and 4 recorded through the apparent interchange of glacial northern and southern sourced intermediate water signatures along the european margin close coupling of nw european ice sheet nweis instability and gnaiw formation is observed through transient advances of scw along the european margin concurrent with pulses of ice rafted debris and meltwater release into the ne atlantic between 27 and 16 kyr b p when the nweis was at maximum extent and proximal to last glacial maximum convection zones in the open north atlantic it is such nweis instability and meltwater forcing that may have triggered reduced north atlantic thc prior to collapse of the laurentide ice sheet at h1 and h2 precursory reduction in gnaiw formation prior to h4 may also be inferred however limited nweis ice volume prior to h4 and convection occurring in the norwegian greenland sea require that if a meltwater trigger is invoked as appears to be the case at h1 and h2 the source of meltwater prior to h4 is elsewhere likely higher latitude ice sheets clarification of the sequencing and likely mechanisms of precursory decrease of the north atlantic thc support theories of h event initiation relating to ice shelf growth during cold periods associated with reduced north atlantic thc and subsequent ablation through subsurface warming and sea level rise associated with further reductions in meridional overturning

modern humans in sarawak malaysian borneo during oxygen isotope stage 3 palaeoenvironmental evidence from the great cave of niah abstract during recent reinvestigations in the great cave of niah in borneo the hell trench sedimentary sequence seen by earlier excavators was re exposed early excavations here yielded the earliest anatomically modern human remains in island southeast asia calibrated radiocarbon dates pollen algal microfossils palynofacies granulometry and geochemistry of the hell trench sequence provide information about environmental and vegetational changes elements of geomorphic history and information about human activity the hell sediments were laid down episodically in an ephemeral stream or pool the pollen suggests cyclically changing vegetation with forest habitats alternating with more open environments indicating that phases with both temperatures and precipitation reduced compared with the present these events can be correlated with global climate change sequences to produce a provisional dating framework during some forest phases high counts of justicia a plant which today colonises recently burnt forest areas point to fire in the landscape this may be evidence for biomass burning by humans presumably to maintain forest edge habitats there is evidence from palynofacies for fire on the cave floor in the hell area since the area sampled is beyond the limit of plant growth this is evidence for human activity the first such evidence is during an episode with significant grassland indicators suggesting that people may have reached the site during a climatic phase characterised by relatively open habitats 50 ka thereafter people were able to maintain a relatively consistent presence at niah the human use of the hell area seems to have intensified through time probably because changes in the local hydrological regime made the area dryer and more suitable for human use

influence of the water content on x ray fluorescence core scanning measurements in soft marine sediments the x ray fluorescence xrf core scanner provides bulk sediment chemistry data measured nondestructively at the split core sediment surface although this method is widely accepted there is little known about the effects of physical properties such as density and water content on xrf core scanner data comparison of xrf scanner measurements from the sediment surface and dry powder samples of sediment core geob7920 indicates strongly reduced element intensities for the lighter elements al and si we relate the lower element intensities of the measurements taken at the sediment surface to the amount of water in the sample volume analyzed by the xrf core scanner the heavier elements k ca ti and fe remain relatively unaffected by the variation of any physical property within sediment core geob7920 additionally we successfully use the elemental intensity of cl as a proxy for the seawater content in the sample volume analyzed by the xrf core scanner this enables the establishment of a correction function for the elements al and si that corrects for the radiation absorption of the water content in sediment core geob7920 off cape blanc nw africa

origin of the middle pleistocene transition by ice sheet erosion of regolith the transition in the middle pleistocene 0 9 ma seen in 18o deep sea core records from relatively low amplitude high frequency 41 kyr to high amplitude low frequency 100 kyr ice volume variations under essentially the same orbital forcing can be attributed to a change from an all soft bedded to a mixed hard soft bedded laurentide ice sheet through glacial erosion of a thick regolith and resulting exposure of unweathered crystalline bedrock a one dimensional ice sheet and bedrock model which includes transport of sediment and ice by subglacial sediment deformation demonstrates that a widespread deforming sediment layer maintains thin ice sheets before the transition which respond linearly to the dominant 23 and 41 kyr orbital forcing progressive removal of the sediment layer eventually causes a transition to thicker ice sheets whose dominant timescale of change 100 kyr reflects nonlinear deglaciation processes in model simulations over the last 3 ma initialized with no ice and a uniform 50 m sediment layer the time series of ice volume and extent agree in several important aspects with the observed records

macroscopic approaches to the identification of expedient bivalve tools a case study investigating polymesoda geloina coaxans bivalvia corbiculidae shell valves from princess charlotte bay queensland australia the identification of expedient bivalve tools recovered from archaeological deposits is currently hindered by a lack of analytical frameworks in order to identify those shell valves which have been used as expedient tools analysts must be able to identify and distinguish between pre mortem and post depositional modifications and use wear from tool use central to this difficulty is a lack of experimental analogues for comparison with archaeological material here we present an analytical framework for the identification of expedient bivalve tools made from polymesoda geloina coaxans valves recovered from australian archaeological sites this analytical framework consists of a series of actualistic experiments designed to determine those variables useful for distinguishing between modifications produced via pre mortem and post depositional processes that can damage molluscan shell and damage produced via use as an expedient tool trampling flaking and scraping experiments and use wear analysis are used as a reference for comparison with an assemblage of p coaxans valves recovered from archaeological sites in princess charlotte bay north queensland australia we demonstrate that an analytical framework consisting of an analysis of shell area loss shell fracture paths and use wear can be successfully applied to archaeological samples to confidently distinguish between those valves which have been used as expedient tools and those which have not this research has wider implications for the identification of this often overlooked class of shell tools from archaeological sites in australia and other regions allowing a more comprehensive understanding of the place of shell tools in coastal economies of the past

calcification depths and temperatures of planktonic foraminifera off southwest hainan island and their paleoceanographic implications abstract the east asian monsoon system influences the local oceanographic and climatic conditions of south china sea scs making the habitat depths of planktonic foraminifera pf specific for this region the previous paleo ocean reconstructions of scs have been based on calcification habitat depths derived from other oceans which may have affected the accuracy of interpretations in this study the calcification depths of globigerinoides ruber globigerinoides sacculifer and neogloboquadrina dutertrei from sediment traps deployed at 1000 m depth off southwest hainan island from july 2012 to april 2013 were analyzed with regard to the stable isotopes of oxygen 18o and carbon 13c to calculate their regional apparent calcification depths acds with the overall aim to improve the reconstruction of the upper ocean thermal structure acds and temperature estimated from foraminifera 18o ranged from 0 to 42 m and 25 c for g ruber 30 65 m and 23 3 c for g sacculifer and 75 100 m and 20 3 c for n dutertrei respectively the difference between the thermocline species n dutertrei and mixed layer species g ruber and g sacculifer 18o 18oth ml and the temperature t shows water column stratification the periods of lower and higher t and 18o were in phase with the changes in regional overlying wind speed additionally this study reveals that n dutertrei lives and calcifies its shells within the base of the mixed layer depth mld and upper thermocline depth in scs overall the results from this study provide a new insight to understand the mixed layer and thermocline depth in the northern scs

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

inter site variability in the season of shellfish collection on the central coast of british columbia high resolution stable oxygen isotope analysis of the bivalve saxidomus gigantea from shell midden sites was applied to identify seasonal patterns of resource procurement on the central coast of british columbia canada a total of 90 archaeological shells were examined from eight distinct sites spanning a 4500 year period combining micro growth pattern analysis with high resolution stable oxygen isotope sampling allows for a precise season of collection to be determined in estuarine bivalves recovered from archaeological sites the results of the stable oxygen isotope analysis provide insights into seasonally structured harvest of s gigantea butter clam which is associated with different types of sites the results show a variety of patterns including multi seasonal collection intensive seasonal harvesting and casual supplemental use of butter clams at different locations

late pleistocene monsoon variability in northwest thailand an oxygen isotope sequence from the bivalve margaritanopsis laosensis excavated in mae hong son province abstract long continuous records of late quaternary environmental change are rare in southeast asia yet they are crucial for understanding the nature of early human dispersal and occupation in the australasian region we present a new record of palaeomonsoon activity extending back to 35 000 bp years before the present based on the analysis of oxygen isotope ratios 18 o in the freshwater bivalve margaritanopsis laosensis excavated from the tham lod and ban rai rockshelters in mae hong son province northwest thailand long term changes in the m laosensis 18 o record reflect changes in the 18 o of the river water in which these organisms grew and correlate well with changes in speleothem 18 o records of east asian monsoon rainfall from hulu cave and dongge cave in china the new northwest thailand 18 o sequence indicates wetter and relatively unstable climatic conditions from 35 000 to 20 000 bp followed by drier conditions from 20 000 to 11 500 bp a period of peak aridity occurred around 15 600 bp during heinrich event 1 suggesting that the intertropical convergence zone shifted southward when the north atlantic region cooled however there is little evidence for the younger dryas event at 12 800 11 500 bp after 9 800 bp precipitation increased substantially and climatic variability declined our findings provide an improved baseline against which to gauge interactions between early humans and climate change in southeast asia for example there was no significant change in the prehistoric flake stone technology used at tham lod and ban rai despite the bivalve 18 o evidence for substantial climate change in the region also the climatic impact of the younger dryas event appears to have been less intense in northwest thailand compared to the cooling and drying observed in china and may explain why agriculture made a relatively late appearance in thailand possibly involving migrants from china

ecological and paleoenvironmental information using stable isotope profiles from living and fossil molluscs stable oxygen and carbon isotopic profiles from recent specimens of spisula solidissima and placopecten magellanicus collected off the virginia coast are used to calibrate annual temperature controlled cycles in the 18o profile and shell growth characteristics the amplitude of the annual 18o cycles decreases with increasing water depth and may be used as a relative depth indicator the isotopic of profiles of two fossil specimens of pleistocene spisula are very similar in amplitude and character to modern analogues and verify the formation of annual growth increments in these fossil specimens offsets between the 18o profiles of the fossil and modern specimens are related to known temperature and ice volume effects during the late pleistocene and support the utility of mollusc isotope records as a stratigraphic tool carbon isotopic profiles from all specimens show light values in the spring and or fall associated with seasonal phytoplankton productivity offsets in the carbon isotopic composition between infaunal and epifaunal species may be related to sediment porewater geochemistry and oxidation of organic matter trends toward lighter 13c values through ontogeny suggest the effects of metabolic changes from a fast growing juvenile into a slower growing sexually mature adult anomalies in both the oxygen and carbon isotopic profiles identify the formation of minor shell growth increments as corresponding to hydrographic perturbations and to winter cold temperatures

sea surface temperatures for the last 7200 years from the eastern sunda shelf south china sea climatic inferences from planktonic foraminiferal mg ca ratios abstract to test whether low latitude shallow shelf deposits can provide high resolution paleoclimatic records we utilized two cores from the holocene sedimentary fill of incised valleys on the sunda shelf off sarawak malaysia we developed a new sea surface temperature sst record based on planktonic foraminiferal mg ca for the last 7200 years this record reveals several significant shifts between warmer and colder conditions temperatures averaged 27 5 c ca 7200 cal years bp then climbed to 28 2 c from 6500 to 5500 cal years bp at 5500 4500 cal years bp we identified the coldest period 26 8 c of the analyzed period for the last 4500 years sst again averaged 27 5 c but the profile is rather variable the last ca 1000 years recorded the warmest sst averaging 28 5 c we record for the first time in this region a cool interval ca 1000 years in duration centered on 5000 cal years bp concomitant with a wet period recorded in borneo the record also reflects a warm interval from ca 1000 to 500 cal years bp that may represent the medieval climate anomaly variations in the east asian monsoon eam and solar activity are considered as potential drivers of sst trends however hydrology changes related to the el nino southern oscillation enso variability shifts of the western pacific warm pool and migration of the intertropical convergence zone are more likely to have impacted our sst temporal trend our findings indicate that climatic patterns in the region might be in phase with enso and out of phase with the eam

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

fine grained sediment lofting from meltwater generated turbidity currents during heinrich events turbidity currents generated from sediment carrying freshwater discharges into the sea contain a fluid that is less dense than ambient seawater from experiments it is known that such currents will eventually lift from their substrate either in part or as a whole through buoyancy reversal this ascent will happen when their density is lowered below that of seawater through settling of suspended sediment from the top or deposition from the bottom of the flows evidence for large scale lofting of suspended sediment from the top of giant sand and gravel carrying turbidity currents in the labrador sea comes from two independent lines of observations 1 the first is a distinct sedimentary facies consisting of stacked centimeter thick graded mud layers that contain grains of ice rafted debris ird supported by the mud deposition of these unusual layers requires a gradedlayer forming process that is slow enough to allow the incorporation of ird this is not possible with normal mud carrying turbidity currents 2 the second observation is the presence of a huge abyssal sand and gravel plain in the central labrador sea that received its sediment from bed load rich meltwater discharges from the hudson strait outlet of the pleistocene laurentide ice sheet these discharges turned into turbidity currents that released rising columns of freshwater that carried fine grained suspended sediment and spread out at a water level where their density equaled that of ambient seawater deposition from these slow turbid interflows would allow the incorporation of ird in the accumulating graded mud deposits the ird spiked graded mud facies is restricted to heinrich layers within 300 km radius of the hudson strait ice stream terminus tying the sand carrying turbidity currents via fine grained sediment lofting to heinrich events estimated total discharge volumes of individual currents are on the order of 10 3 km 3 supporting the notion that heinrich ice rafting events were times of maximum meltwater generation

millennial scale trends in west pacific warm pool hydrology since the last glacial maximum models and palaeoclimate data suggest that the tropical pacific climate system plays a key part in the mechanisms underlying orbital scale and abrupt climate change atmospheric convection over the western tropical pacific is a major source of heat and moisture to extratropical regions and may therefore influence the global climate response to a variety of forcing factors the response of tropical pacific convection to changes in global climate boundary conditions abrupt climate changes and radiative forcing remains uncertain however here we present three absolutely dated oxygen isotope records from stalagmites in northern borneo that reflect changes in west pacific warm pool hydrology over the past 27 000 years our results suggest that convection over the western tropical pacific weakened 18 000 20 000 years ago as tropical pacific and antarctic temperatures began to rise during the early stages of deglaciation convective activity as inferred from oxygen isotopes reached a minimum during heinrich event 1 ref 10 when the atlantic meridional overturning circulation was weak pointing to feedbacks between the strength of the overturning circulation and tropical pacific hydrology there is no evidence of the younger dryas event in the stalagmite records however suggesting that different mechanisms operated during these two abrupt deglacial climate events during the holocene epoch convective activity appears to track changes in spring and autumn insolation highlighting the sensitivity of tropical pacific convection to external radiative forcing together these findings demonstrate that the tropical pacific hydrological cycle is sensitive to high latitude climate processes in both hemispheres as well as to external radiative forcing and that it may have a central role in abrupt climate change events

new insights into the glacial latitudinal temperature gradients in the north atlantic results from uk 37 sea surface temperatures and terrigenous inputs abstract sea surface temperatures sst and input of continental materials have been reconstructed from the study of the long chain alkenones and n alkanes respectively in a core located in the western side of the mid atlantic ridge md952037 37 05 n 32 02 w 2630 m depth both the long and short term variability recorded by the temperatures and the planktonic 18o are basically the same over the last 280 kyr showing a clear glacial interglacial evolution comparison with core su90 08 located only 6 north and directly influenced by the cold polar waters associated with the polar front during glacial times revealed different climatic conditions during glacial periods at both locations whereas core md952037 recorded similar sst values during the last two glacial periods ca 14 15 c the northern core displayed colder conditions during isotopic stage 2 8 10 c than in stage 6 13 15 c these results indicate the existence of a well developed steep north south gradient between 37 and 43 n during the last glacial period but not during stage 6 which suggests a southern expansion of the polar front during the last glacial maximum

high resolution geochemical investigation of the bivalve shells glycymeris sp from shell mounds in jeju island korea late holocene paleoclimatic implications related to east asian monsoon climate abstract recent and shell mound bivalves glycymeris sp were collected from two sites sangmori and udo jeju island to investigate paleoceanographic conditions using high resolution stable isotope and trace element data the radiocarbon ages are about 3210 50 and 4210 60 bp for the sangmori and udo shell mounds respectively both oxygen and carbon isotopic compositions of the shell mound bivalve shells show clear seasonal cycles with depleted values during summer and the coeval trend which indicates that they were controlled by freshwater input similar ranges of both isotopes indicate that shallow seawater conditions near the sangmori and udo shell mounds are more or less similar however more negative oxygen and carbon isotope values of the shell mound bivalves than the recent counterpart suggest that surface seawater salinity near jeju island was lower due to the increase in changjiang river discharge mg contents of the recent bivalve reflect surface seawater temperature changes whereas sr and ba contents were controlled by nutrient concentrations directly influenced by changjiang river discharge geochemical data of the recent and shell mound bivalves may imply higher precipitation more intense east asian summer monsoon activity at 3 2 and 4 2 ka under the influence of the terminal stage of holocene climatic optimum in south china or may reflect smaller fluctuating peaks during its decline

oxygen isotopic analysis of archaeological shells to detect seasonal use of wetlands on the southern pacific coast of mexico abstract oxygen isotopic ratios in modern and archaeological marsh clam shells polymesoda radiata from the acapetahua estuary in southwestern mexico record large scale salinity fluctuations caused by alternating wet and dry seasons thus prehistoric patterns of rainfall can be reconstructed and the season of molluscan death can be estimated changes in the oxygen isotopic patterns preserved in marsh clam shells from late archaic period c 3000 1800 bc archaeological deposits indicate that the season of shellfish harvesting changed dynamically through time in this region based on this study and other lines of archaeological evidence we argue that hunter gatherers during the early stages of the late archaic period visited locations in the littoral zone throughout the year with a focus during dry season months through the late archaic period a general trend occurred toward wet season use of these locations this culminated at the end of the late archaic period with the exclusive use of the littoral zone during wet season months these data indicate a fundamental shift in the way these estuarine locations were being used we argue that people living in this region altered their overall subsistence strategy during the late archaic period due to scheduling conflicts that occurred with the adoption of maize agriculture

reconstructing the duration of the west african monsoon season from growth patterns and isotopic signals of shells of anadara senilis saloum delta senegal abstract long term reconstructions of the seasonality of the west african monsoon are limited by the lack of seasonally resolved paleoclimate archives in this region we present an application based on the growth patterns and monthly resolved 18o profiles of anadara senilis bivalve shells to quantitatively estimate the duration of the rainy and dry seasons in the hypersaline saloum delta senegal fortnightly growth patterns are used to estimate changes of the growth rate and to place the shell isotope record into a temporal context based on fortnightly growth patterns and sharply declining 18o values the duration of the rainy season was estimated as an illustrative example we quantitatively estimated the duration of two rainy seasons and two dry seasons that occurred about 1500 years ago from a fossil shell of the dioron boumak archaeological site to the nearest month this precision can be statistically improved by the analysis of a larger shell number or by higher resolution isotope sampling our results open the possibility of using large fossil shell accumulations in the saloum delta for quantitative studies of the long term variability of the west african monsoon seasonality

stable isotope microsampling of speleothems for palaeoenvironmental studies a comparison of microdrill micromill and laser ablation techniques three different techniques are currently in use to microsample speleothem and tufa specimens at moderate to high spatial resolution manual microdrilling using a dentist drill semi automated micromilling and laser ablation while a separate handling step is involved in the first two techniques transferring the sample powder to an on line carbonate preparation system linked to an isotope ratio mass spectrometer the laser is directly interfaced with the mass spectrometer via a gas preparation device in this study we compare stable c and o isotope results obtained by these three preparation techniques using continuous he flow mass spectrometry on the same speleothem samples the overall consistency of the results is satisfactorily high in particular between the micromill and the laser data although the precision of the laser data is slightly lower than analyses obtained by the other two methods in particular with respect to 18o the speed of acquisition renders laser ablation a useful reconnaissance technique for rapidly analyzing long sections of speleothems micromilling is the method of choice to obtain highly spatially resolved isotope data of high analytical precision while microdrilling is still an low cost alternative for sampling at comparably low resolution e g of fast growing stalagmites

shell midden sclerochronology abstract sclerochronological analysis of shell midden faunal remains offers a unique opportunity to study climate and environmental change in relation to human activity middens exist near most aquatic habitats almost worldwide for much of the late pleistocene and holocene they afford good preservation of accretionary calcium carbonate remains such as mollusk shells and fish otoliths in comparatively well dated contexts as such midden samples are a source of sequential proxy records of past climate and environmental conditions and may provide detailed pictures of human environment interaction however midden samples present several challenges to the development and application of sclerochronological proxies including unique taphonomic concerns here these challenges are outlined within descriptions of the major applications of midden sclerochronology archeological concerns including season of capture reconstructing the history of anthropogenic environmental impacts and paleoclimate environment proxy reconstructions

evidence for an additional heinrich event between h5 and h6 in the labrador sea 1 an additional heinrich ice rafting event is identified between heinrich events 5 and 6 in eight cores from the labrador sea and the northwest atlantic ocean it is characterized by sediment rich in detrital carbonate 40 caco3 with high concentration of floating dropstones high coarse fraction 150 m content and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment it also shows lighter 18onpl values indicating freshening due to iceberg rafting and or meltwater discharge this event is correlated with dansgaard oeschger event 14 and interpreted as an additional heinrich event h5a the thickness of h5a in the labrador sea reaches up to 220 cm this additional heinrich event has also been reported in cores ps2644 and so82 5 from the northern north atlantic with the recognition of h5a the temporal spacing between heinrich events 1 to 6 becomes more uniform 7 ka

millennial scale climate instability during the early pleistocene epoch climate proxy records of the past 100 000 years show that the earth s climate has varied significantly and continuously on timescales as short as a few thousand years 1 7 similar variability has also recently been observed for the interval 340 500 thousand years ago8 these dramatic climate shifts expressed most strongly in the north atlantic region may be linked to and possibly amplified by alterations in the mode of ocean thermohaline circulation4 5 6 7 8 9 here we use sediment records of past iceberg discharge and deep water chemistry to show that such millennial scale oscillations in climate occurred over one million years ago this was a time of significantly different climate boundary conditions not only was the early pleistocene epoch generally warmer but global climate variations were governed largely by changes in earth s orbital obliguity our results suggest that such millennial scale climate instability may be a pervasive and long term characteristic of earth s climate rather than just a feature of the strong glacial interglacial cycles of the past 800 000 years

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

aspartic acid racemisation dating of mid holocene to recent estuarine sedimentation in new south wales australia a pilot study abstract the degree of aspartic acid racemisation measured in radiocarbon dated specimens of fossil estuarine molluscs collected from lake illawarra a holocene barrier estuary in new south wales australia is evaluated in the context of results of laboratory induced racemisation established in heating simulated ageing experiments the general kinetic trend of aspartic acid racemisation in both heating experiments and fossil molluscs anadara trapezia and notospisula trigonella conforms to a model of apparent parabolic kinetics using the apparent parabolic kinetic model numeric ages based on the degree of aspartic acid racemisation in the fossil molluscs have been calculated an aminostratigraphy of the lake illawarra holocene basin fill has been established based on the extent of aspartic acid racemisation measured in 29 specimens of fossil molluscs aspartic acid d l ratios in a trapezia and n trigonella range from 0 079 0 005 to 0 436 0 004 representing an age range from

regional scale climate influences on temporal variations of rainwater and cave dripwater oxygen isotopes in northern borneo this study investigates the relationship between large scale climate variability rainfall oxygen isotopic composition 18 o and cave dripwater 18 o at gunung mulu and gunung buda national parks in northern borneo 4 n 115 e on intraseasonal to interannual timescales a 3 yr timeseries of rainfall 18 o contains prominent seasonal and interannual variability the seasonal cycle in rainfall 18 o is defined by lighter values of 10 during late boreal summer and heavier values of 4 during late boreal winter and is poorly correlated to local precipitation which displays very weak seasonality seasonally varying moisture trajectories likely play a key role in the observed seasonal cycle of rainfall 18 o driving enhanced fractionation during boreal summer and less fractionation during boreal winter dripwater 18 o timeseries display 2 seasonal cycles that follow the rainfall 18 o seasonal cycles with a mean 18 o value equivalent to the mean 18 o of rainfall large surveys of cave dripwaters conducted during three fieldtrips to gunung mulu buda reveal a system wide response to rainfall 18 o seasonality that supports a relatively short less than 6months response time for most drips during the weak 2005 2006 la nina event sustained positive precipitation anomalies are associated with rainfall 18 o values that are 4 to 5 lighter than previous years values consistent with the tropical amount effect observed in both models and data dripwater 18 o values are 1 to 2 lighter during the weak la nina event the importance of the amount effect in driving intraseasonal rainfall 18 o anomalies at our site is supported by an 8 increase in rainfall 18 o that occurred over the course of two weeks in response to a pronounced decrease in regional convective activity dripwater discharge rates underwent a ten fold decrease during the extended dry period but dripwater 18 o values remained constant this study supports the interpretation of stalagmite 18 o records from gunung mulu buda as paleo precipitation records that are sensitive to the location and strength of deep convection in the west pacific warm pool 2007 elsevier b v all rights reserved

seasonal discharge of estuarine freshwater to the western chukchi sea shelf identified in stable isotope profiles of mollusk shells 1 oxygen and carbon isotope profiles of bivalve mollusks serripes groenlandicus and macoma calcarea record distinct changes of water mass properties in the bering strait region associated with the seasonal discharge of estuarine freshwater from kolyuchin bay into the western chukchi sea cycles in the 18o profiles are correlated with shell growth bands and interpreted as annual maximum 18o values corresponding to coldest water temperatures coincide with dark internal bands in the shell that mark slower growth during winter a 0 5 offset between the baseline winter 18o values of two specimens hx68 and hx65 at different distances from the estuarine discharge is attributed to a difference in seawater 18o between the two sites and indicates that the influence of the estuarine water persists through much of the year the isotope profiles of specimen ak55 collected north of bering strait in the chukchi sea reflect the bering shelf anadyr water flowing from south of bering strait comparison of the 13c profiles shows that hx68 collected closer to kolyuchin bay has high amplitude negative 13c excursions associated with incorporation of dissolved inorganic carbon that is isotopically depleted in 13c probably from terrestrial runoff the significant positive correlation between 18o and 13c values in these specimens suggests that the properties of the ambient water masses are reflected in the stable isotope profiles these results show that the stable isotope profiles of mollusk shells can serve as proxy indicators of water mass properties particularly during runoff events in arctic coastal regions that are logistically difficult to sample directly

evolution of millennial scale climate variability during the mid pleistocene 1 we use the oxygen isotopic composition of planktonic foraminifera globigerinoides ruber white from ocean drilling program site 1058 in the subtropical northwestern atlantic to construct a high resolution 800 year climate record spanning the mid pleistocene climate transition 410 ka to 1350 ka we investigate whether or not millennial scale instabilities in the proxy record are associated with the extent of continental glaciation g ruber 18o values display high frequency fluctuations throughout the record but the amplitude about mean glacial and interglacial 18o values increases at marine isotope stage mis 22 880 ka and is highest during mis 12 these observations support that millennial scale climate instabilities are associated with ice sheet size time series analysis illustrates that these variations have significant concentration of spectral power centered on periods of 10 12 ka and 5 ka the timing of these fluctuations agrees well or coincides with the periodicities of the second and fourth harmonics respectively of precessional forcing at the equator an insolation based origin of the millennial scale instabilities would be independent of ice volume and explains the presence of these fluctuations before the mid pleistocene climate transition as well as during interglacial intervals e g mis 37 and 17 because the amplitude of the millennial scale variations increases during the mid pleistocene transition feedback mechanisms associated with the growth of large 100 ka paced polar ice sheets may be important amplifiers of regional surface water hydrographic changes

evolution and demise of the last interglacial warmth in the subpolar north atlantic detailed faunal isotopic and lithic marine records provide new insight into the stability and climate progression of the last interglacial period marine isotope stage mis 5 which peaked approximately 125 000 years ago in the eastern subpolar north atlantic at the latitude of ireland interglacial warmth of the ice volume minimum of substage 5e mis 5e lasted 10 000 years 10 ka and its demise occurred in two cooling steps the first cooling step marked the end of the climatic optimum which was 2 3 ka long minor ice rafting accompanied each cooling step the second larger step encompassing cold events c26 and c25 was previously identified in the northwestern atlantic approximately 41c of cooling occurred between peak interglacial warmth and c25 and the region experienced an additional temporary cooling of at least 1 21c during c24 a cooling event associated with widespread ice rafting in the north atlantic beginning with c24 mis 5 was characterized by oscillations of at least 1 21c superimposed on a generally cool baseline the results of this study imply that the marine climatic optimum of the last interglacial was shorter than previously thought the finding that the eastern subpolar north atlantic cooled significantly before c24 reconciles terrestrial evidence for progressive climate deterioration at similar and lower latitudes with marine conditions our results also demonstrate a close association between modest ice rafting cooling and deep ocean circulation even during the peak of mis 5e and in the earliest stages of ice growth