environmental control on mediterranean salinity and δ18o a box model is presented to simulate changes in mediterranean long term average salinity and 18o over the past 20 000 years simulations are validated by comparison with observations sensitivity tests illustrate robustness with respect to the main assumptions and uncertainties the results show that relative humidity over the mediterranean remained relatively constant around 70 apparently narrowly constrained to the lower end of the range observed globally over sea surfaces by the basin s land locked character isotopic depletion in run off relative to the present is identified as the main potential cause of depletions in the mediterranean 18o record also slight increases in relative humidity of the order of 5 might have caused very pronounced isotopic depletions such as that in sapropel s5 of the penultimate interglacial maximum the model shows distinctly non proportional responses of 18o and salinity to environmental change which argues against the use of isotope residuals in mediterranean paleosalinity reconstructions

assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

mid holocene el nino southern oscillation enso attenuation revealed by individual foraminifera in eastern tropical pacific sediments holocene reconstructions of the el nino southern oscillation enso provide valuable perspective on its recent evolution and can be important for assessing its future optimal assessment of past enso variability requires observations from its center of action in the eastern equatorial pacific but these are limited due to paucity of high resolution paleoceanographic archives e g corals here we use a new approach to quantify past enso variance based on the oxygen isotopic composition 18 o of individual foraminifera globigerinoides ruber from deep sea sediments in the enso source region individual g ruber foraminifera behave as monthly recorders of sea surface conditions including enso extremes circumventing the lack of annual resolution in the sediments intrapopulation 18 o distributions derived with this method from a core near the galapagos islands reveal mid holocene reductions in variance of 50 requiring drastic attenuation of the enso amplitude furthermore mg ca thermometry indicates that mid holocene background conditions were accompanied by a stronger zonal temperature gradient that coincided with a northward displaced intertropical convergence zone itcz the results suggest that the position of the itcz is an important factor in the low frequency modulation of enso and could influence its future evolution

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

distribution patterns of live planktic foraminifers as related to regional hydrography and productive systems of the mediterranean sea abstract distribution patterns of live planktic foraminifers are examined at two times of the year late summer and late winter through horizontal plankton towing along a nw se transect across the west and east mediterranean basins and in the alboran sea french oceanographic cruises vicomed i ii and iii respectively foraminiferal production is significantly different in the two sampling periods and across the west and east mediterranean foraminiferal density is higher in winter than summer e g in the western basin 3700 specimens 1000 m3 in winter against 200 600 specimens 1000 m3 in summer the production averaged for the two sampling sets is higher in the western basin than in the eastern one however in late summer peaks of maximal production are observed in the central mediterranean strait of sicily and ionian basin 1000 to 2000 specimens 1000 m3 where the assemblages are dominated by globigerinoides ruber rosea and g ruber alba in the mediterranean sea frontal regions and semipermanent eddies which are essentially controlled by regional hydrography represent a significant portion of the regional production they also elicit a higher diversity of species their influence is observed in summer as well as in winter at the end of summer the rather shallow mixed layer hosts spinose symbiont bearing species such as g ruber alba g ruber rosea o universa and g trilobus at that season in the western basin the nutrient content of the mixed layer is generally low and the surface layer is rapidly nutrient depleted summer foraminiferal production remains low at the surface with respect to the winter production in the eastern basin late summer and autumn correspond to the biological spring summer foraminiferal production in surface waters is higher than in winter but standing crops are lower than in the western basin for the same species at the same period in summer however frontal structures and eddies are generally better developed than in winter in some particular cases frontal boundaries in the western basin eddies south of cyprus nutrients from intermediate layers can be upwelled through isopycnal or diapycnal mixing to the photic zone and allow for secondary blooms in the western basin these blooms favour the development of grazers at depth globorotalia truncatulinoides g inflata south of cyprus in the eastern basin oligotrophic conditions promote the development of heterotrophic organisms and predatory foraminifers have higher standing stocks g ruber alba g ruber rosea in winter the break down of the thermocline combined with deep turbulent mixing in the northwestern basin and the deepening of the mixed layer in the alboran sea and along the north african coast result in increased phytoplankton biomass and favour reproduction and proliferation of species such as g truncatulinoides or g inflata our observations indicate that the geographic and depth distribution of live foraminiferal species cannot be entirely explained by the general temperature and salinity differences among the different mediterranean basins but that they are strongly related to regional hydrographic patterns hydrography controls the seasonality and depth of the turbulent mixing which differ between the western and the eastern basins the depth of the mixed layer and its seasonal stratification and the strength of the pycnocline nutrient supply and primary production are mostly regulated by these dynamics one may therefore expect that the species assemblages on the sea floor and in deep sea cores will also correlate to the various hydrographic parameters of the overlying water masses

life and extinction of megafauna in the ice age arctic understanding the population dynamics of megafauna that inhabited the mammoth steppe provides insights into the causes of extinctions during both the terminal pleistocene and today our study area is alaska s north slope a place where humans were rare when these extinctions occurred after developing a statistical approach to remove the age artifacts caused by radiocarbon calibration from a large series of dated megafaunal bones we compare the temporal patterns of bone abundance with climate records megafaunal abundance tracked ice age climate peaking during transitions from cold to warm periods these results suggest that a defining characteristic of the mammoth steppe was its temporal instability and imply that regional extinctions followed by population reestablishment from distant refugia were characteristic features of ice age biogeography at high latitudes it follows that long distance dispersal was crucial for the long term persistence of megafaunal species living in the arctic such dispersal was only possible when their rapidly shifting range lands were geographically interconnected the end of the last ice age was fatally unique because the geographic ranges of arctic megafauna became permanently fragmented after stable interglacial climate engendered the spread of peatlands at the same time that rising sea level severed former dispersal routes

field examination of the oceanic carbonate ion effect on stable isotopes in planktonic foraminifera we determined the 18o and 13c of individual globigerinoides ruber and pulleniatina obliquiloculata from sediment traps located from 5 n to 12 s along 140 w in the pacific ocean to evaluate the effects of varying co3 on shell 18o and 13c variations in the offset between shell 13c and 13cdic 13cs dic are attributed to differences in co3 temperature and shell size between sample sites when 13cs dic of g ruber was corrected for variations in co3 using the experimental slope of bijma et al 1998 the residual 13cs dic was correlated with mixed layer temperature 0 10 0 04 c 1 the slope of this temperature effect is consistent with experimental results in p obliquiloculata 13cs dic and temperature were strongly anticorrelated 0 14 0 03 c 1 we are unable to separate the influences of co3 and temperature in this species without independent experimental data correcting for co3 variability on 18os of g ruber improves the accuracy of estimated sea surface temperatures

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

reconstructing the stable isotope geochemistry and paleotemperatures of the equatorial atlantic during the last 150 000 years results from individual foraminifera this study represents an attempt to extract paleoclimatic data from the deep sea record by analyzing foraminiferal shells individually using the oxygen 18o and carbon 13c isotopic composition of individual orbulina universa and neogloboquadrina dutertrei we present an approach to reconstruct the 18o of seawater 18ow the 13c of co2 and seasonal maximum sea surface temperatures sst in the western and eastern equatorial atlantic we examine the glacial and interglacial extremes of the last 150 000 years isotope stages 1 2 5e and 6 comparison of recent water column hydrography with reconstructions from core top assemblages shows that o universa and n dutertrei 18o and 13c values accurately record hydrographic conditions in the mixed layer and upper thermocline at both sites by analyzing shells individually we can evaluate the effect of bioturbation on the range of 18o and 13c values in each interval and take it into consideration in our data interpretations downcore results show that n dutertrei 18o values in the western equatorial atlantic reflect glacial to interglacial changes in 18ow due to continental ice formation 18o 1 30 we use changes in n dutertrei 18o values between core intervals to estimate the ice volume effect in paleotemperature calculations for the mixed layer to validate the use of o universa for mixed layer reconstructions we have added individual globigerinoides sacculifer data for stages 1 and 2 at both sites paleotemperature reconstructions from o universa 18o values indicate that maximum seasonal mixed layer temperatures in the equatorial atlantic decreased by at most 2 6 c between isotope stages 1 and 2 and by no more than 3 4 c between stages 1 and 6 individual shell data from g sacculifer yield similar results indicating that maximum o universa 18o values reflect the mixed layer environment in agreement with climate long range investigation mapping and prediction climap 1981 sst reconstructions for stage 2 these data indicate little change between glacial and interglacial paleotemperatures in the equatorial atlantic an electronic supplement of this material may be obtainedon a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as theusername and guest as the password go to the rightdirectory by typing cd apend type ls to see what files areavailable type get and the name of the file to get it finally type exit to leave the system paper 95pa03773 reconstructing the stable isotope geochemistry andpaleotemperatures of the equatorial atlantic during the last150 000 years results from individual foraminifera katharina billups and howard j spero diskette may beordered from american geophysical union 2000 floridaavenue n w washington dc 20009 15 00 paymentmust accompany order

variability of mg ca and sr ca between and within the planktonic foraminifers globigerina bulloides and globorotalia truncatulinoides the variability in mg ca and sr ca within individual tests and chambers of tests and samples consisting of differing numbers of individuals was determined for globigerina bulloides and globorotalia truncatulinoides in a north atlantic core top sample 52 918 n 16 917 w the variability in mg ca and sr ca within individual tests and chambers was determined by electron microprobe and samples consisting of variable sample size were measured using inductively coupled plasma optical emission spectrometer icp oes large compositional heterogeneity was found within individual chambers and within the test as a whole of the two species and the presence of regions with up to 10 mmol mol mg ca especially in g bulloides mean mg ca decreases in successive chambers of g bulloides especially the 300 355 m fraction and is accompanied by decreasing variance but is not statistical significant sr ca is much more homogeneously distributed with a normal distribution and shows no differences from chamber to chamber the variability of mg ca and sr ca decreases with increasing sample size from single to five to twenty tests per sample approximately as for a normal distribution with greater variability for g bulloides than for g truncatulinoides equivalent to uncertainties in temperature n 20 of 1 1 c and 0 7 c for the two species within the whole of the sediment mixed layer

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

grain size properties and organic carbon stock of yedoma ice complex permafrost from the kolyma lowland northeastern siberia the organic carbon stock in permafrost is of increasing interest in environmental research because during the late quaternary a large pool of organic carbon accumulated in the sedimentary deposits of arctic permafrost because of its potential to degrade and release organic carbon the organic matter inventory of yedoma ice complex deposits is relevant to current concerns about the effects of global warming in this context it is essential to improve the understanding of preserved carbon quantities and characteristics the paper aims to clarify the yedoma ice complex origin and to develop an approach for volumetric organic matter quantification therefore we analyzed the grain size and the organic matter characteristics of the deposits exposed at the stratigraphic key site duvanny yar lower kolyma river northeast siberia a distinct bimodal grain size distribution confirms a polygenetic origin of the frozen sediments from a flood plain environment the total organic carbon content averages 1 5 1 4 wt while the volumetric organic carbon content averages 14 8 kg m however large scale extrapolations for yedoma ice complex deposits in general are not reasonable yet because of their rather unclear spatial distribution we conclude that yedoma ice complex formation at duvanny yar was dominated by water related alluvial fluvial lacustrine as well as aeolian processes the total organic carbon content of the studied deposits is low if compared to other profiles but it is still a significant pool

the gin sea a synthesis of its physical oceanography and literature review 1972 1985 abstract a synthesis and review of the physical oceanography of the gin sea greenland iceland and norwegian seas is presented an accompanying bibliography is included from 1972 through 1985 some 1986 works are also noted emphasis is placed on describing the gin sea as a major semi enclosed basin that plays a role unique among the world s oceans by providing a strong two way advective exchange between the ice covered polar sea and the north atlantic ocean and at the same time acting as the primary site for northern hemisphere bottom water formation the water masses for the gin sea are defined in a manner as consistent as possible with the literature the large scale oceanographic and meteorological factors influencing the water mass formation and circulation are described a sample calculation of the various horizontal and vertical thermohaline driven exchanges is given

recent terrestrial and carbonate fluxes in the pelagic eastern mediterranean a comparison between sediment trap and surface sediment a sediment trap mooring was deployed in the central eastern mediterranean from november 1991 to august 1994 at 3000 m water depth total mass al ca mg sr and 230th fluxes recovered by the sediment trap are highly seasonal with highest fluxes during early spring in 1992 and 1993 and during late spring early summer in 1994 comparison of historic annual satellite derived chlorophyll records coastal zone colour scanner with the trap flux time series indicates a lag of 4 6 months between maximum primary production in the surface ocean and maximum flux recorded by the trap only the flux of coccospheres to the trap is at a maximum 1 month after maximum pigment concentrations in surface waters a value commonly found in other areas quantification of the inorganic lithogenic flux to the trap indicates that saharan dust is likely to be the major contributor to the trap mass flux the trapping efficiency of the sediment trap as calculated from the intercepted 230th flux is only 23 and the trap al flux is similarly 4 lower than al fluxes measured in nearby uppermost sediments compared with surface sediments the trap intercepted carbonate fluxes are even lower 9 than the corresponding lithogenic fluxes this is partly due to the very low abundance of large 32 m foraminifera and pteropods found in the trap material compared to the surface sediment we speculate that the period of our sediment trap deployment was insufficiently long to recover episodical large fluxes such as may be triggered by north atlantic oscillation variations

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

late pleistocene mis 3 2 palaeoenvironments as recorded by sediments palaeosols and ground squirrel nests at duvanny yar kolyma lowland northeast siberia abstract a detailed study of the duvanny yar section in the kolyma lowland yakutia provides the most extensive knowledge to date about late pleistocene soil formation processes and environments in the north east siberian arctic late quaternary palaeoenvironmental changes were reconstructed using paleopedological data and a range of palaeoecological bio indicators palynomorphs plant macrofossils and insects the frozen sediments representing marine isotope stage 3 mis 3 which encompasses the karginsky interstadial include profiles of four palaeosols of different ages the oldest palaeosol is early karginskian and three overlying soil horizons represent a late karginskian pedocomplex palaeopedological data indicate a change of from synlithogenic soil formation processes to epigenic ones during these intervals the intervening periods of synlithogenic pedogenesis were accompanied by active accumulation of eolian deposits the earlier karginskian period of pedogenesis occurred in the absence of eolian sedimentation and when summer conditions were warm the wide spectrum of peaty and peaty gley soils observed in the late karginskian deposits developed under conditions of progressive cooling the structure and content of fossil rodent burrows dated to approximately 30 000 yr bp from frozen late pleistocene deposits at duvanny yar indicate an arid and severe climate a depth of active layer of 60 80 cm and a wide distribution of disturbed habitats with pioneer and steppe vegetation

planktonic response to main oceanographic changes in the alboran sea western mediterranean as documented in sediment traps and surface sediments abstract in order to determine the influence of seasonal oceanographic changes to the export of particulates and the flux of organisms as well as its corresponding integrated signal left in the bottom sediments of the alboran sea western mediterranean two mooring lines alb 1f and alb 1d were deployed from july 1997 to may 1998 on the continental slope south of malaga at 36 01 n 04 16 w and 36 14 n 04 28 w and a water depth of 1004 and 958 m respectively the mooring locations are under the influence of the incoming atlantic surface water asw at the northern and productive edge of the western alboran gyre wag and of the wind induced upwelling offshore the spanish coast additionally a total of five core tops located in the same area were studied the results are compared to information based on seawifs images of chlorophyll a concentration sst meteorological data on wind direction and intensity and fluvial discharges from the main rivers of the alboran basin the temporal oceanographic evolution of the alboran sea during the studied period was divided into five episodes e1 july 1997 e2 august october 1997 e3 november to mid december 1997 e4 december march 1998 and e5 april may 1998 the episodes represent different oceanographic conditions in the alboran sea during the studied period detailed analyses of the recorded pattern of bulk components calcareous nannoplankton planktonic foraminifera diatoms and phytoliths reflect seasonal changes in the main hydrographic regimes in the western alboran sea all biogenic bulk components as well as the annual evolution of the floral and faunal assemblages follow a tri modal pattern with maximum fluxes recorded during e1 e3 and e5 representing periods of higher productivity and wind induced upwelling during these periods species such as the small gephyrocapsa group gephyrocapsa muellerae and calcidiscus leptoporus the foraminifer globigerina bulloides and the diatom chaetoceros resting spores rs were dominant gephirocapsa oceanica and globorotalia inflata were coupled to the evolution of the atlantic surface water asw or related to surface water stability e2 and e4 the diatom leptocylindrus danicus responded to upwelling relaxation and water stratification e1 e2 and e4 and benthic diatoms were related to eddy intensity at bottom phytolith fluxes were directly related to wind intensities and the prevailing westerly winds e3 and e5 the distribution of microfossils in surface sediments differs from the biogenic assemblages recorded in the sediment traps in this sense during 1997 1998 the strongest el nino event in the last century took place which could have forced an unusual seasonality in the alboran sea reflecting an exceptional micropaleontological signal not observed in the surface sediments

uncertainties in seawater thermometry deriving from intratest and intertest mg ca variability in globigerinoides ruber intertest mg ca variability within these deep sea core top samples is a source of significant uncertainty in mg ca seawater temperature estimates and is notable for being site specific our results indicate that widely assumed uncertainties in mg ca thermometry may be underestimated we show that statistical power analysis can be used to evaluate the number of tests needed to achieve a target level of uncertainty on a sample by sample case a varying bias also arises from the presence and varying mix of two morphotypes g ruber ruber and g ruber pyramidalis which have different mean mg ca values estimated calcification temperature differences between these morphotypes range up to 5c and are notable for correlating with the seasonal range in seawater temperature at different sites

beringian climate during the late pleistocene and holocene abstract the difference between the climates of the bering land bridge and asiatic western beringia 18 20 ka ago is discussed the climatic reconstructions of the bering land bridge and western beringia are based upon two methods first we discuss the ecological and thermal requirements of the thermophilic weevils coleoptera curculionidae in the genus stephanocleonus second we discuss the effect of climatic continentality on soil temperatures we suggest that for western beringia the climate was suitable for the warm steppe environment mean july air temperatures were at least 10 11 c and an annual sum of daily temperatures above 0 c sdd at the soil surface was up to 2500 c in contrast to these conditions the climate of the bering land bridge was very similar to that found in the modern arctic tundra zone

opening the carbon isotope vital effect black box 1 seasonal temperatures in the euphotic zone recent laboratory experiments with orbulina universa show that the carbon and oxygen isotope signals from this symbiont bearing planktonic foraminifera record distinct environmental parameters irradiance and temperature since light levels are correlated with depth in the marine environment the carbon isotopic composition of o universa can be utilized to differentiate individuals from different depth habitats by combining 18o and 13c data from individuals in an assemblage estimates of seasonal temperature ranges are possible for the upper and lower euphotic zone of the ocean reconstruction of seasonal temperatures using individual holocene o universa from western equatorial pacific ocean boxcore erdc 83 yields ranges of 23 5 to 29 9 c and 20 1 to 24 5 c for the shallow and deep euphotic zone respectively these values are in excellent agreement with recent temperature measurements from this region analyses of individual late glacial 12 000 13 000 years b p o universa from this site suggest the seasonal upper euphotic zone temperature range was approximately 2 5 c lower than it is today a function of cooler summers

controls on shell mg ca and sr ca in cultured planktonic foraminiferan globigerinoides ruber white mg ca and sr ca ratios were determined on a single species of planktonic foraminiferan globigerinoides ruber white collected from the gulf of eilat and cultured in seawater at five different salinities 32 to 44 five temperatures 18 to 30 c and four ph values 7 9 to 8 4 the mg ca temperature calibration of cultured g ruber with an exponential slope of 8 3 c agrees well with previously published calibrations from core tops and sediment traps however the dependence of mg ca on salinity with an exponential slope of 5 3 psu is also significant and should be included in the calibration equation with this purpose we calculated a calibration equation for g ruber dependent on both temperature and salinity within the 95 confidence limits mg ca mmol mol exp 0 06 0 02 s psu 0 08 0 02 t c 2 8 1 0 r2 0 95 the influence of ph on mg ca ratios is negligible at ambient seawater ph 8 1 to 8 3 however we observe a dominating ph control on shell mg ca when the ph of seawater is lower than 8 0 sr ca in g ruber shows a significant positive correlation with average growth rate presumably part of the variability in shell sr ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions

the isotopic signature of planktonic foraminifera from ne atlantic surface sediments implications for the reconstruction of past oceanic conditions the stable isotope compositions of the planktonic foraminifera globigerina bulloides globigerinoides ruber white and pink varieties globigerinoides trilobus globorotalia inflata and globorotalia truncatulinoides right and left coiling types were examined as recorders of north atlantic surface water properties based on 40 box core surface sediments between 60 and 30 n while g ruber white and pink varieties and g trilobus mainly reflect summer surface water conditions in their oxygen isotope composition g bulloides reflects temperatures of the northward migrating spring bloom february march in the south to may june in the north our data show that g bulloides cannot be regarded as an indicator for summer temperatures as deduced from duplessy et al s data gt inflata and gt truncatulinoides right and left coiling build their shells in the coldest waters compared with the other species and reflect temperatures between 100 and 400 m water depth the difference in oxygen isotope composition between g bulloides and g inflata serves as a proxy for water mass stratification g bulloides is the only species that gives a distinct pattern in its carbon isotopic composition showing a high correlation with the surface water phosphate values along the transect and may serve as a proxy for palaeonutrients and or productivity

paleoecology of beringian packrat middens from central yukon territory canada rodent middens from ice rich loess deposits are important new paleoenvironmental archives for eastern beringia plant macrofossils recovered from three middens associated with dawson tephra ca 24 000 14 c yr b p at two sites in yukon territory include diverse graminoids forbs and mosses these data suggest substantial local scale floristic and habitat diversity in valley settings including steppetundra on well drained soils moist streamside meadows and hydric habitats fossil arctic ground squirrel burrows and nesting sites indicate that permafrost active layers were thicker during pleistocene glacial periods than at present on north facing slopes d 2004 university of washington all rights reserved

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

forest or no forest implications of the vegetation record for climatic stability in western beringia during oxygen isotope stage 3 abstract two conflicting stratigraphic schemes describe the siberian karginskii interstade oxygen isotope stage 3 equivalent as having 1 relatively stable climate with environments more similar to the full glaciation or 2 variable climate with landscapes that more closely approximate contemporary ones new data from continuous lake cores and a nearly continuous section from western beringia wb suggest that both schemes are valid herb dominated communities possibly with isolated populations of larix characterized northern wb with only a slight shift from relatively warm to cool summers during the mid interstade in contrast herb and shrub tundra steppe forest tundra and modern larix forest occurred at various times in areas of southern wb suggesting greater climatic instability a thermal optimum is evident in the south during the mid interstade with modern vegetation in southeastern wb and larix forest tundra in the southwest variations in pinus pumila pollen indicate summer warm winter dry and summer warm winter wet conditions in southeastern wb these fluctuations contrast to other areas of wb where summers and probably winters were consistently arid although the interstade presents a unique interval within the late pleistocene paleodata and paleoclimatic models suggest that changes in marine conditions including sea level were likely key drivers in the regional climate history

effect of salinity and seawater calcite saturation state on mg and sr incorporation in cultured planktonic foraminifera abstract trace elements incorporated in planktonic foraminiferal test carbonate are commonly used as paleoproxies for instance mg ca ratios are frequently used for reconstructing sea surface temperature and together with the foraminiferal stable oxygen isotope ratios are also used as paleosalinity proxy foraminiferal sr ca ratios constitute another example of the application of trace elements in paleostudies since they may reflect the sr ca values of seawater however over the past few decades it has been proven that the incorporation of trace elements in foraminiferal calcite is controlled by more than one environmental parameter to quantify the effect of salinity on mg and sr incorporation planktonic foraminifera globigerinoides sacculifer sensu stricto were grown in the laboratory under different environmental conditions laboratory experiments allowed us to separate a direct salinity effect from a possible independent impact through differences in the calcite saturation state of the seawater although the temperature effect is more important than the salinity effect a change of 4 salinity units is equivalent to a 1 c bias on mg ca based temperatures this effect of salinity on mg incorporation is minor however when using mg ca based temperatures in combination with foraminiferal 18o to calculate salinity it cannot be neglected the present study shows salinity as the overriding control on mg incorporation within the range of studied between 5 25 and 6 50 co32 between 218 and 270 mol kg at a constant temperature of 26 c in contrast appears to be the main control on foraminiferal sr incorporation 0 10 mmol mol per 100 mol kg rise in co32 whereas salinity has a non significant influence on sr ca

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

do planktic foraminifera accurately record shifts in the carbon isotopic composition of seawater σco2 abstract both the carbon isotopic composition of seawater and physiological vital effects such as respiration and symbiont photosynthesis influence the 13 c value of foraminiferal calcite the symbiont bearing planktic foraminifera orbulina universa was grown in a series of laboratory experiments to determine whether vital effects differentially obscure the 13 c signal such that changes in the 13 c of seawater co 2 cannot be quantitatively evaluated foraminifera were cultured under three different irradiance levels to elicit a full range of symbiont photosynthetic effects and in seawater with 13 c values ranging between 1 77 ambient and 5 76 power regression analysis of isotope data from individual shells plotted against culture irradiance yields three curves which are nearly parallel but are offset by the difference between the carbon isotopic composition of the culture waters when irradiance groups are combined and o universa 13 c values are plotted against seawater 13 c three parallel linear regressions are obtained with slopes ranging between 0 93 and 0 96 because the slopes are near unity it is concluded that the 13 c of o universa accurately tracks changes in the carbon isotopic composition of seawater regardless of the magnitude of its physiological vital effect o universa oxygen isotope data show that individuals maintained in the low and medium irradiance groups secrete their shells in isotopic equilibrium according to established paleotemperature equations in contrast individuals grown under high irradiance levels maximum symbiont photosynthetic rates are on average 0 35 depleted in 18 o relative to equilibrium symbiont enhanced calcification rates in the high light group may be responsible for the observed 18 o difference

ice complex formation in arctic east siberia during the mis3 interstadial abstract a continuous 15 m long sequence of ice complex permafrost yedoma exposed in a thermo cirque at the southern coast of bol shoy lyakhovsky island new siberian archipelago dmitry laptev strait was studied to reconstruct past landscape and environmental dynamics the sequence accumulated during the marine isotope stage 3 mis3 interstadial between 49 and 29 ka bp in an ice wedge polygon the frozen deposits were cryolithologically described and sampled on a vertical bluff between two ice wedges according to sedimentological and geochronological data the section is subdivided into three units which correlate with environmental conditions of the early middle and late mis3 period palynological data support this stratification the stable isotope signature of texture ice in the polygon structure reflects fractionation due to local freeze thaw processes while the signature of an approximately 5 m wide and more than 17 m high ice wedge fits very well into the regional stable water isotope record regional climate dynamics during the mis3 interstadial and local landscape conditions of the polygonal patterned ground controlled the ice complex formation the sequence presented here completes previously published mis3 permafrost records in northeast siberia late quaternary stadial interstadial climate variability in arctic west beringia is preserved at millennial resolution in the ice complex a mis3 climate optimum was revealed between 48 and 38 ka bp from the ice complex on bol shoy lyakhovsky island

paleosalinity and δ18o a critical assessment in paleoceanography a traditional application of oxygen isotope ratios in fossil carbonate from deep sea cores concerns the reconstruction of paleotemperatures recently isotopic data have been increasingly employed in the reconstruction of paleosalinities as well this application involves a number of basic assumptions a critical review of which is presented here as the calculation of paleosalinity from 18o residuals assumes constant and linear surface water salinity s 18o relationships we investigate this basic assumption for areas with important and variable freshwater budget and or sea ice influences we show that it is particularly unwarranted to assume such temporally invariant linearity in temperate and subpolar seas because of the effects of freezing and melting more critically we argue that the determinant of many regions s 18o is advection not the local water balance so that the basic 18o of seawater in many regions of the world ocean would likely have changed in a manner somewhat different from that expected from the ice volume record although the differences may not be significant for the gross reconstruction of such features as past sea level we believe they do potentially bias paleosalinity reconstructions mostly toward high salinities to fully exploit the potential of oxygen isotope records as quantitative paleosalinity indicators both the spatial and temporal variabilities need to be constrained hence we recommend that 1 for any time slice of specific interest to paleoceanographic and paleoclimatological studies a coupled ocean atmosphere isotope model or at least an ocean isotope model driven by a paleoclimate isotope model should be used to define the distribution of the base mixing end member 18o of sea water 2 much further regional scale research is needed on flux rates and isotopic compositions of the various terms in the freshwater budget as well as on the variability in the various advective terms the latter variability may be assessed from reconstructions of past seaice distributions and of volume fluxes isotopic compositions of outflow from marginal seas and through sea straits passages

some geometrical aspects of uncertainties in combined plate reconstructions the uncertainties in both the position of a pole of rotation and the rotation angle describing a plate reconstruction depend not only on the number and quality of data used but also on two geometrical factors the length of plate boundary represented by the data and the distance from the best fit pole to the center of the data region we describe a simple geometrical method that can be used to calculate minimum uncertainties in reconstructions based on positions of magnetic anomalies and fracture zones with finite uncertainties uncertainties in pole positions and angles corresponding to 10 km uncertainty in individual data points can when combined yield uncertainties in reconstructed positions greatly in excess of 10 km per rotation for example an uncertainty of 10 km in anomaly 6 reconstructions in the south pacific southeast indian northwest indian and north atlantic oceans would result in uncertainty of up to 190 km in the reconstructed position of the pacific plate with respect to north america at 19 8 m y b p existing data show that the realistic uncertainties for this case are twice as large as the calculated minimum uncertainties

mis3 paleosols in the center north of eastern europe and western siberia reductomorphic pedogenesis conditioned by permafrost abstract the mis3 paleosol units comprise a prominent element of the loess paleosol sequences throughout the eurasian loess belt to the north of the loess regions the findings of mis3 paleosols were few it was supposed that geomorphic processes related to the extensive ice cover of the last glacial maximum destroyed the earlier soil mantle recently much smaller extent of continental ice in the east of northern europe and ice free west siberian plain during mis2 has been hypothesized supposing preservation of mis3 and earlier paleopedological records we discovered in the center north of european russia upper volga basin and western siberia middle ob basin mis3 paleosols within the late pleistocene alluvial and lacustrine sequences and correlated the studied profiles on the basis of macro and micromorphological characteristics and radiocarbon datings of the paleosol organic materials paleosols are represented by hydromorphic profiles with histic horizons and gleyic color pattern conspicuously they are developed in the well drained geomorphic positions where modern soils are non gleyic we suppose that the presence of permafrost was responsible for water logging and generation of reductomorphic soil environment we further hypothesize a northern zone of mis3 soil mantle comprised of histic and reductaquic cryosols different from synchronous cambisols and chernozems formed within loess sequences to the south

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

mediterranean quaternary sapropels an immediate response of the african monsoon to variation of insolation abstract in the subsurface of the east mediterranean sea eleven discrete basin wide organic rich black sapropels were deposited during the last 465 000 years they are dated by oxygen isotopic chronostratigraphy the most recent sapropel has been shown to be the consequence of heavy nile river summer floods due to increased monsoonal summer precipitation over ethiopia and not of scandinavian ice sheet meltwater influx into the east mediterranean sea as was previously believed while most sapropels were deposited during interglacials two thick sapropels formed during glacial periods as shown by their position in the oxygen isotopic stratigraphy and by their pollen record in core rc9 181 the new evidence presented here is that the sapropel sequence in this core including the two glacial sapropels correlates on a one to one basis with the highest values of an index of insolation on top of the atmosphere the concept of this index derives from an analysis of the african monsoon process the index variation is computed for the last 465 000 years from the caloric northern summer insolation in the tropical latitudes controlled by variations of the earth s orbital parameters it is conjectured that this index might be linked through the climate system to the monsoonal precipitation which in africa produces the nile river summer flood

environmental versus biomineralization controls on the intratest variation in the trace element composition of the planktonic foraminifera g inflata and g scitula the intratest variation in the chemical composition of globorotalia scitula and g inflata recovered from a sediment trap sample collected at 3000 m in the north atlantic in early spring has been investigated using laser ablation inductively coupled plasma mass spectrometry and electron microprobe mg ca li ca b ca mn ca and ba ca vary by up to a factor of 10 through the test walls water column properties including temperature and salinity are well documented at the trap site and the observed variations are too large to be explained by vertical migration of the foraminifera however changes in calcite precipitation rate crystal structure or the chemical composition of the internal calcification reservoir also cannot by themselves fully account for the pattern of intratest variability nevertheless the average mg ca for each chamber generally produces a mg ca temperature that matches that measured in the water column the exception is small morphologically distinct g inflata tests that have anomalously high mg ca

approaches to unravel seasonality in sea surface temperatures using paired single specimen foraminiferal δ18o and mg ca analyses 1 seasonal changes in surface ocean temperature are increasingly recognized as an important parameter of the climate system here we assess the potential of analyzing single specimen planktonic foraminifera as proxy for the seasonal temperature contrast seasonality oxygen isotopes and mg ca ratios were measured on single specimens of globigerinoides ruber extracted from surface sediment samples of the mediterranean sea and the adjacent atlantic ocean variability in 18o and mg ca was then compared to established modern seasonal changes in temperature and salinity for both regions the results show that 1 average 18o derived temperatures correlate with modern annual average temperatures for most sites 2 the range in 18o and mg ca derived temperature estimates from single specimen analysis resembles the range in seasonal temperature values at the sea surface 0 50 m in the mediterranean sea and the atlantic ocean and 3 there is no strong correlation between mg ca and 18o derived temperatures from the same specimens in the current data set indicating that other parameters salinity carbonate ion concentration symbiont activity ontogenesis and natural variability potentially affect these proxies

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection

persistent summer expansion of the atlantic warm pool during glacial abrupt cold events palaeoclimate records and numerical model simulations indicate that changes in tropical and subtropical sea surface temperatures and in the annual average position of the intertropical convergence zone are linked to high latitude climate changes on millennial to glacial interglacial timescales it has recently been suggested that cooling in the high latitudes associated with abrupt climate change events is evident primarily during the northern hemisphere winter implying increased seasonality at these times8 however it is unclear whether such a seasonal bias also exists for the low latitudes here we analyse the mg ca ratios of surface dwelling foraminifera to reconstruct sea surface temperatures in the northeastern gulf of mexico for the past 300 000 years we suggest that sea surface temperatures are controlled by the migration of the northern boundary of the atlantic warm pool and hence the position of the intertropical convergence zone during boreal summer and are relatively insensitive to winter conditions our results suggest that summer atlantic warm pool expansion is primarily affected by glacial interglacial variability and low latitude summer insolation because a clear signature of rapid climate change events such as the younger dryas cold event is lacking in our record we conclude that high latitude events seem to influence only the winter caribbean climate conditions consistent with the hypothesis of extreme northern hemisphere seasonality during abrupt cooling events