planktonic foraminiferal mg ca as a proxy for past oceanic temperatures a methodological overview and data compilation for the last glacial maximum as part of the multi proxy approach for the reconstruction of the glacial ocean margo incentive published and unpublished temperature reconstructions for the last glacial maximum lgm based on planktonic foraminiferal mg ca ratios have been synthesised and made available in an online database development and applications of mg ca thermometry are described in order to illustrate the current state of the method various attempts to calibrate foraminiferal mg ca ratios with temperature including culture trap and core top approaches have given very consistent results although differences in methodological techniques can produce offsets between laboratories which need to be assessed and accounted for where possible dissolution of foraminiferal calcite at the sea floor generally causes a lowering of mg ca ratios this effect requires further study in order to account and potentially correct for it if dissolution has occurred mg ca thermometry has advantages over other paleotemperature proxies including its use to investigate changes in the oxygen isotopic composition of seawater and the ability to reconstruct changes in the thermal structure of the water column by use of multiple species from different depth and or seasonal habitats presently available data are somewhat limited to low latitudes where they give fairly consistent values for the temperature difference between late holocene and the lgm 2 3 5 c data from higher latitudes are more sparse and suggest there may be complicating factors when comparing between multi proxy reconstructions

seasonal changes in planktonic foraminifera in the northwestern north pacific ocean sediment trap experiments from subarctic and subtropical gyres abstract upper ocean environments such as seawater temperature salinity thermal structure in the water column light intensity and food supply affect the assemblage of planktonic foraminifera since detailed information on planktonic foraminifera was not available for the northwestern north pacific we examined seasonal changes in fluxes and composition of planktonic foraminifera there data were collected by sediment traps deployed at three sites site 50n 50 01 n 165 02 e site knot 43 58 n 155 03 e and site 40n 39 60 n 165 00 e in this area in order to better understand the relationship between the foraminiferal assemblage and surface ocean environments although each planktonic foraminiferal species showed specific seasonal variations in flux some exhibited similar flux profiles in order to define these more accurately correlations among species were calculated and the foraminiferal species classified into four groups 1 group a subpolar species neogloboquadrina pachyderma globigerina quinqueloba globigerina bulloides and globigerinita glutinata 2 group b subtropical and tropical species globigerinoides ruber and globigerinoides sacculifer 3 group c post upwelling species neogloboquadrina dutertrei and 4 group d deep water species globorotalia scitula and globorotalia truncatulinoides the common environments for each period based on foraminiferal production and composition were observed among the three sites based upon predominant foraminiferal groups total foraminiferal fluxes tffs organic matter om fluxes and hydrographic conditions including sea surface temperatures sst and thermal structure the surface ocean environments in the northwestern north pacific could be generalized into five types type i is characterized by a dominance of group b with low tffs under high sst and type ii is marked by a high flux of group a on the other hand type iii shows low tffs and low om fluxes due to low insolation during winter type iv represents a high flux of group a and group d at site 40n under a well mixed surface ocean and type v is characterized by a prominent peak of group c under a developed thermocline a comparison of annual mean foraminifera fluxes at 50 n between the northwestern site 50n and the northeastern north pacific station papa during the normal cold mode demonstrated higher fluxes of foraminifera at site 50n due to higher nutrient concentrations the results also showed that g bulloides is not always a proxy for upwelling and that n pachyderma is not solely controlled by seawater temperature in the northwestern pacific where the surface water is enriched in nutrients the fluxes and composition of foraminifera suggest that similar ocean environments are expected in large areas of the northern north pacific from site knot to station papa during the warm mode which is affected by el nino events

seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic blooms this annual population overturning is marked by a 0 7 increase in d 18 o in both species the shell flux of n pachyderma peaks during the spring bloom and in late summer when stratification is close to its minimum and maximum respectively both export periods contribute about equally and account for 95 of the total annual flux shell fluxes of t quinqueloba show only a single broad pulse in summer thus following the seasonal stratification cycle the d 18 oo fn pachyderma reflects temperatures just below the base of the seasonal sml without offset from isotopic equilibrium the d 18 op attern oft quinqueloba shows a nearly identical amplitude and correlates highly with the d 18 oo fn pachyderma therefore t quinqueloba also reflects temperature near the base of the sml but with a positive offset from isotopic equilibrium these offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species in the irminger sea the species consistently show a contrast in their flux timings their flux weighted dd 18 o will thus dominantly be determined by seasonal temperature differences at the base of the sml rather than by differences in their depth habitat consequently their sedimentary dd 18 o may be used to infer the seasonal contrast in temperature at the base of the sml citation jonkers l g j a brummer f j c peeters h m van aken and m f de jong 2010 seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic paleoceanography 25 pa2204 doi 10 1029 2009pa001849

stable isotope signals from brines in the barents sea implications for brine formation during the last glaciation the 18 o and 13 c values of benthic foraminifera from the cold stadials of the last glacial period in the nordic seas are low whereas the values from the warm interstadials are high the low values have been attributed to brine formation carrying a low stable isotope signal from the surface water into deep water as occurs around antarctica today brines are often considered to have played a major role for the abrupt millennial scale climate shifts during the last glaciation however very little is known of the isotopic composition of modern brines in the northern hemisphere greatly hampering the interpretation of past data here we report on the oxygen and carbon isotope composition of benthic foraminifera in two cores from a brine influenced shelf environment in storfjorden svalbard in the barents sea the results indicate that brines with sufficient density to contribute significantly to intermediate and deep water are formed from cold salty waters and have high 18 o and 13 c values brines with low 18 o values formed from cold fresher water have relatively low density and they are unable to penetrate the deeper parts of the arctic and nordic seas this indicates that the low benthic 18 o and 13 c values obtained from the nordic seas during stadials cannot be attributed to brines the implication is that brines did not contribute significantly to the millennial scale climate shifts

spatial and temporal distribution of holocene temperature maxima in the northern nordic seas interplay of atlantic arctic and polar water masses abstract subsurface and bottom water temperatures on the western shelf of svalbard at 79 n are reconstructed in order to investigate the relative influence of warm atlantic water cold arctic polar water and meltwater during the holocene the study is based on sediment core np05 21gc which has been investigated for the distribution of planktic foraminiferal species oxygen and carbon isotopes measured in benthic and planktic foraminifera and subsurface and bottom water temperatures calculated from transfer functions the data are compared to several other records from the western margin of svalbard the results indicate that until 9600 years bp the water column west of svalbard was stratified by a pycnocline situated at a water depth of c 100 m on the shelf and at c 30 m on the slope the water mass above the pycnocline consisted of cold arctic polar water and meltwater whereas the water mass below the pycnocline consisted of warm atlantic water after 9600 the supply of arctic polar water and meltwater diminished weakening the pycnocline and from 9000 to 6000 years bp warm atlantic water occupied the entire water column the upper and deeper water masses experienced different holocene temperature maxima in the atlantic water the temperature maximum occurred during the early holocene 11 500 8200 years bp only interrupted by the cold pre boreal oscillation c 11 300 10 800 years bp the maximum was followed by a gradual temperature decrease until c 5000 years bp in the upper water masses the temperature maximum occurred from c 9000 6000 years bp the timing of the maximum here is influenced by the decreasing supply of cold arctic polar water versus the increasing dominance of atlantic water the temperatures of both the surface and bottom water decreased to a minimum from c 5000 2000 years bp during the last 2000 years conditions have been increasingly unstable although with slightly increasing subsurface temperatures

oxygen isotopic composition of multiple species of planktonic foraminifera recorders of the modern photic zone temperature gradient abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected as expected from previous work in the tropics all dominant tropical species occur in greatest abundance within the photic zone many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration while a few algal symbiont bearing species occur in greatest abundance in the mixed layer the 18o measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by ravelo et al 1990 comparison between the measured 18o values of planktonic foraminifera with the predicted 18o profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year species which calcify below the photic zone have only trace relative abundances finally it appears that the total range of 18o values of the dominant species approximates the predicted annual 18o of calcite range in the upper 80 m of the water column

climate and oceanographic variability in the sw barents sea during the holocene the holocene section of the marine sediment core psh 5159n located in the sw barents sea has been studied at high resolution with a multiproxy approach a well stratified water column occurred at the site 11 9 8 ka bp the stratification was probably a result of a winter sea ice cover and or fresh warm surface waters during summer stratification and resultant reduction in air sea interaction allowed for warmer bottom water temperatures the general situation 11 9 8 ka bp could have been associated with an anomalous high pressure system over the nordic seas and the arctic ocean during the 11 10 5 ka bp interval the polar front was located close to the barents sea margin the polar front moved towards the site from 10 5 ka bp and from 9 8 to 7 5 ka bp it was probably located close to the site at 7 5 ka bp the polar front retreated eastwards as the present day oceanographic pattern established the mid holocene was in general characterized by rather stable conditions in contrast highly variable cond

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

glacial to deglacial changes in north atlantic meltwater advection and deep water formation centennial to millennial scale 14c records from the azores plateau abstract the last deglacial was marked by tremendous changes in ocean temperature and circulation as well as atmospheric co2 and 14c we employed the 14c plateau tuning technique to a centennial scale planktic 14c record of core md08 3180 retrieved s w of the azores islands at 3060 m water depth to establish both a new standard of absolute age control and a record of past 14c reservoir ages of ocean surface waters both 18o minima of g bulloides and high planktic reservoir ages of 1600 to 2170 yr suggest two major melt water incursions that reached from the labrador sea up to the subtropics over heinrich stadial 1 hs 1 in parallel we established a record of apparent benthic ventilation ages that add the planktic 14c reservoir ages together with the benthic planktic 14c age difference at the site and time of deposition a sum finally adjusted to past changes in atmospheric 14c that occurred since the time of deep water formation near the azores apparent deep water ages of the last glacial maximum were as low as 340 740 yr which suggests a lateral advection of young north atlantic deep waters nadw from subpolar regions south of iceland in harmony with recent model simulation and in contrast to a widely assumed major shoaling of glacial deep water formation during hs 1 local benthic ventilation ages increased up to 2200 2550 yr thus suggest an incursion of old southern source deep waters an unstable regime that was interrupted by brief pulses of nadw incursion near 16 15 6 cal ka and most salient near 14 9 14 7 ka

estimation of the catchment area of a sediment trap by means of current meters and foraminiferal tests abstract between june 1989 and july 1990 a mooring equipped with four current meters and one sediment trap was deployed in the fram strait 79 n from the material collected by the sediment trap two species of planktic foraminifera turborotalita quinqueloba and neogloboquadrina pachyderma were used to estimate the catchment area of the sediment trap for each species and size class the individual sinking velocity was used to determine the residence time in the water column the residence time is the major factor that determines the drift of the tests using current meter data trajectories were calculated to estimate the catchment area and the area of sedimentation the maximum distance the smallest tests have been transported while sinking from the surface 100 m to the sediment trap 1125 m is approximately 275 km with maximum trajectory lengths of up to 300 km depending mainly on the grain size of the tests the distances and trajectories have means lying between 25 and 50 km for n pachyderma and 50 and 100 km for t quinqueloba respectively considering the whole sampling period the estimated catchment areas are 23 900 km 2 for all n pachyderma tests and 33 300 km 2 for all t quinqueloba tests respectively the respective areas of sedimentation are estimated to range from 3400 km 2 to 3500 km 2

oxygen and carbon isotopic composition of living planktonic foraminifera from the northeast pacific ocean abstract stable isotopic analyses were performed on the tests of five species of living planktonic foraminifera which are important in paleoclimatic studies of high latitude late cenozoic sequences all but two of the samples used are from horizontal plankton tows of known depths between 0 500 m in the northeastern pacific ocean 50 n 145 w in situ hydrographic seawater stable isotopic and quantitative species distribution data are used in the interpretation of the results all of the species show depletions in both 18 o and 13 c in their calcite tests relative to calcite precipitated in isotopic equilibrium with ambient seawater estimates of the departures from isotopic equilibrium range from 0 35 in globigerinita glutinata to 2 24 in neogloboquadrina pachyderma sinistral with respect to 18 o and from 0 5 in orbulina universa to 4 34 globigerina bulloides with respect to 13 c the 18 o data suggest that primary test growth for individual species is not restricted to the depth interval where highest total standing crop values occur oxygen and carbon isotopic depth rankings for g bulloides n pachyderma and g glutinata reflect the relative magnitude of the vital effect in these species and not necessarily different depth habitats the vital effect for 18 o in these species remains approximately constant with changing temperature water depth while the vital effect for 13 c strongly decreases with increasing depth temperature also does not appear to directly affect the coiling ratios of g bulloides but a significant negative correlation exists between the percentage of sinistrally coiled g glutinata and water temperature

seasonal variation in the oxygen isotopic composition of different sized planktonic foraminifer neogloboquadrina pachyderma sinistral in the northwestern north pacific and implications for reconstruction of the paleoenvironment 1 the oxygen isotope value 18o of planktonic foraminifer shells is one of the most commonly used proxies to reconstruct the paleoenvironment neogloboquadrina pachyderma sinistral n pachyderma sin is a dominant foraminifer in subpolar and polar region that is used extensively for high latitude paleoreconstruction the present study examined seasonal variation in 18o of n pachyderma sin using sediment trap samples collected over 3 5 years in the northwestern north pacific ocean the vital offset value was about 1 which agrees with previous plankton tow studies large shell individuals 180 250 m secrete their shells in a shallower and warmer environment than small ones 125 180 m and the difference in 18o between shell size showed seasonal variation although large individuals calcify at a slower rate with slightly heavier 18o than small individuals differences between size classes mainly reflect different habitation in the water column and are related to seasonal changes in stratification during summer large individuals would calcify mainly at 25 35 m depth while small individuals calcify near the pycnocline at 45 m during winter both size classes calcify at or slightly above the weak pycnocline at 45 65 m thus the shell 18o could record the oceanographic environment around pycnocline depth and size specific differences in 18o reflect water column stratification the annual flux weighted 18o corresponded to non flux weighted mean 18o value due to the equal contribution of two flux peaks and differences between size classes also related to the stratification it suggests that fossil 18o data could represent the annual mean environment around pycnocline and past stratification

spatio temporal dynamics of hydrographic reorganizations and iceberg discharges at the junction between the northeast atlantic and norwegian sea basins surrounding heinrich event 4 abstract dansgaard oeschger and heinrich events constitute ones of the most enigmatic features of the last glacial period many studies have focused on their characteristic millennial climatic variability testing atmospheric cryospheric oceanic couplings but major uncertainties and discrepancies still remain a new scenario robustly supported by an approach coupling paleoreconstructions and freshwater hosing experiments simulating heinrich type perturbations has recently emerged reconciling most of the up to now hypothesized theories it suggests the occurrence of a regional seesaw between a cooled down north atlantic ocean and warmed up nordic seas during cold atmospheric phases in relation to enhanced subsurface advection of warm atlantic waters re emerging in the norwegian sea the associated ocean warming thus reaching nordic basins at a critical location beyond the faeroe shetland sill is proposed to be involved in the concomitant release of european icebergs here we further investigate this promising scenario over the 35 41 ka bp interval by i outlining its precise spatial pattern in a crucial area i e the junction between the north atlantic and the norwegian sea close to european ice sheets ii resolving its very fine temporal and regional evolution during critical transitions associated with the onset of warm advection i e greenland interstadial to greenland stadial and greenland interstadial to heinrich stadial and iii assessing its impact on the spatio temporal dynamic of iceberg discharges from the european and laurentide ice sheets during cold stadial episodes especially including heinrich event 4

oxygen isotope composition of living neogloboquadrina pachyderma sin in the arctic ocean data from the nansen basin of the arctic ocean are used to investigate the habitat and conditions under which the polar planktic foraminifer neogloboquadrina pachyderma sin calcifies the vertical distribution of 18o values of net sampled speciments together with their abundances and proportion of calcification are compared with 18o values from both water samples and foraminiferal tests from core top sediments within the nansen basin the average depth of habitat of n pachyderma sin changes from about 150 m in the southern part to about 80 m in the northern the average depth of calcification however in both regimes varies between 100 and 200 m water depth 18o data from net sampled n pachyderma sin are directly reflected in the core top sediment data but compared to equilibrium calcite 18o values derived from measurements of the ambient water a consistent offset of about 1 over all depth intervals is observed while in the southern part of the nansen basin advection through fram strait of planktic foraminifers from further south may play a role the data from the northern part of the nansen basin give clear evidence that the observed offset in 18o values is caused by a vital effect of n pachyderma sin

accidental gas emission from shallow pressurized aquifers at alban hills volcano rome italy geochemical evidence of magmatic degassing abstract recent studies suggested that alban hills rome is a quiescent and not an extinct volcano as it produced holocene eruptions and several lahars until roman times by water overflow from the albano crater lake alban hills are presently characterized by high p co2 in groundwaters and by several cold gas emissions usually in sites where excavations removed the superficial impervious cover gas consists mostly of co 2 with minor h 2 s and the diffuse co 2 soil flux is locally very high accidental gas blowouts occurred during shallow well drillings tens to hundreds m depth in zones with no surface gas manifestations indicate the presence of gas pressurized aquifers confined underneath impermeable layers within both the volcanic rock pile and the underlying pleistocene loose sediments degassing mostly occurs in correspondence of bordering faults of buried horsts cut in the mesozoic carbonate basement hosting the main aquifer carbon isotopic composition 13 c co2 suggests that co 2 is at least partly originated by thermal decarbonation of these limestones 3 he 4 he isotopic ratio of the gas up to 1 9 ra is the same or even slightly higher than that of olivine and clinopyroxene fluid inclusions of the alban hills volcanic products indicating a possible magmatic source for the gas low r ra values compared to morb and island arc magmas are characteristic of the potassic roman comagmatic province and reflect a deep involvement of crustal material in the magma genesis the lack of high temperature fumaroles can be explained by an efficient meteoric cold water penetration and circulation in the volcano permeable terrains

lateral and vertical variability in crustal velocity structure in a small area of the north atlantic abstract the detailed velocity structure of a 70 by 35 km area of 6 10 ma old crust on the flank of the mid atlantic ridge at 24 n was studied using 358 explosive charges and several hundred 16 4 1 airgun shots fired into an array of eight ocean bottom hydrophones inversion of the first arrival refracted travel times shows that the crust comprises a normal oceanic section about 5 km thick with a steep velocity gradient in the upper crust increasing from about 3 5 km sec at the seafloor overlying a typical oceanic layer 3 and a probably anisotropic mantle delay time function mapping using two datasets containing arrivals from layer 3 and from the mantle show that lateral variability is generally low over most of the survey area with a small region of high delay times in the northwest corner caused by the presence of abnormal crust probably associated with a minor fracture zone we find that the topography of the base of layer 2 is similar to that of the top indicating that the normal faulting which occurs along the margins of the median valley extends down at least into layer 3 our observations from mantle arrivals are consistent with a much flatter moho which constrains possible models of crustal formation at the spreading centre

ventilation history of nordic seas overflows during the last de glacial period revealed by species specific benthic foraminiferal 14c dates formation of deep water in the high latitude north atlantic is important for the global meridional ocean circulation and its variability in the past may have played an important role in regional and global climate change here we study ocean circulation associated with the last de glacial period using water column radiocarbon age reconstructions in the faroe shetland channel southeastern norwegian sea and from the iceland basin central north atlantic the presence of tephra layer faroe marine ash zone ii dated to 26 7 ka enables us to determine that the middepth 1179 m water depth and shallow subsurface reservoir ages were 1500 and 1100 14c years respectively older during the late glacial period compared to modern suggesting substantial suppression of the overturning circulation in the nordic seas during the late last glacial maximum and the onset of deglaciation 20 18 ka nordic seas overflow was weak but active during the early deglaciation 17 5 14 5 ka our data reveal large differences between 14c ventilation ages that are derived from dating different benthic foraminiferal species pyrgo and other miliolid species yield ventilation ages 6000 14c years while all other species reveal ventilation ages 2000 14c years these data either suggest subcentennial regional circulation changes or that miliolid based 14c ages are biased due to taphonomic or vital processes implications of each interpretation are discussed regardless of this enigma the onset of the bolling allerod interstadial 14 5 ka is clearly marked by an increase in middepth nordic seas ventilation and the renewal of a stronger overflow

northward oceanic heat transport in the main branch of the norwegian atlantic current over the late holocene the norwegian atlantic current represents the northernmost reaches of the sub surface limb of the atlantic meridional overturning circulation its shelf edge branch the norwegian atlantic slope c

insights into north atlantic deep water formation during the peak interglacial interval of marine isotope stage 9 mis 9 foraminifera abundance and stable isotope records from odp site 984 61 25 n 24 04 w 1648 m in the north atlantic are used to reconstruct surface circulation variations and the relative strength of the north atlantic deep water nadw formation over the period spanning the peak warmth of marine interglacial stage mis 9e 324 336 ka this interval includes the preceding deglaciation termination 4 t4 and the subsequent glacial inception of mis 9d the records indicate a greatly reduced contribution of nadw during t4 as observed in more recent deglaciations in contrast with the most recent deglaciation the lack of a significant nadw signal extended from t4 well into the peak interglacial mis 9e and persisted nearly until the transition to the subsequent glacial stage mis 9d although nadw formation resumed during mis 9e only depths greater than 2000 m appear to have been ventilated the poorly ventilated intermediate depth of site 984 2000 m may have resulted on one hand from a general reduction of deep water ventilation by nadw during the study interval or on the other hand from different pathways of the spread of newly formed nadw that bypassed the study location the intermediate depths may have also been invaded by southern sourced waters as the formation of intermediate depth nadw weakened the absence of any significant nadw signal at the water depth of site 984 during the climatic optimum contrasts sharply with subsequent interglacial peaks mis 5e and the holocene despite the perturbed intermediate depth circulation oceanic heat transport northeastward was not interrupted and may have contributed to the relatively mild interglacial conditions of mis 9e

reassessing mg ca temperature calibrations of neogloboquadrina pachyderma sinistral using paired δ44 40ca and mg ca measurements the mg ca temperature calibration of the polar to subpolar planktonic foraminifera neogloboquadrina pachyderma sinistral sinistral indicates left coiling was refined by a multiproxy approach combining hydrographic temperature and salinity data with mg ca delta ca 44 40 and delta o 18 values from holocene nordic seas core top samples reliable mg ca based temperature estimates are limited to foraminiferal tests that calcified in water masses with temperatures above similar to 3 degrees c at habitat depth in these samples mg ca and delta ca 44 40 values are positively correlated mg ca mmol mol 0 77 0 22 x delta ca 44 40 parts per thousand srm 915a 0 52 0 12 n 20 r 2 0 76 both mg ca and delta ca 44 40 derived temperatures projected onto their corresponding depth intervals reveal that the apparent calcification depth of n pachyderma sinistral averaging the specimens whole life cycle is bound to an isopycnal layer defined by water densities sigma t between 27 7 and 27 8 this implies that n pachyderma sinistral prefers gradually deeper habitats with increasing sea surface temperatures thus counterbalancing absolute temperature variations consequently the total temperature range recorded in this foraminiferal species is restricted and only partly reflects environmental changes on the basis of the new mg ca delta ca 44 40 and delta o 18 multiproxy data set we propose a linear mg ca temperature relation for high latitude n pachyderma sinistral mg ca mmol mol 0 13 0 037 t degrees c 0 35 0 17 t 3 degrees c in core top samples from polar waters with peak summer temperatures below similar to 3 degrees c the temperature response in the mg ca and delta ca 44 40 proxy signal is inversed and poorly correlated both mg ca and delta ca 44 40 derived temperature estimates pretend significantly higher calcification temperatures than maximum summer sea surface temperatures of these water masses

oceanographic regimes in the northwest labrador sea since marine isotope stage 3 based on dinocyst and stable isotope proxy records abstract sea surface temperature sst salinity and density gradients in the upper water column of the northwest labrador sea have been reconstructed based on high resolution analysis of a core hu2008 029 004pc spanning the last 36 ka raised off hudson strait the modern analogue technique was applied to dinocyst assemblages and combined with stable isotope data from neogloboquadrina pachyderma left coiled npl for this purpose three oceanographic regimes were identified broadly corresponding to the glacial deglacial and postglacial intervals the site remained under the direct influence of the laurentide ice sheet lis margin until the postglacial and did not record the bolling allerod warming and weakly recorded the younger dryas event the glacial regime lasted until 12 2 cal ka bp it was characterized by generally low concentrations of dinocysts within an assemblage indicative of quasi perennial sea ice the deglacial regime ca 12 2 8 3 cal ka bp was marked by increased biogenic fluxes and more diversified dinocyst assemblages and possibly an enhanced subsurface inflow of north east atlantic deep water warm summer 11 c but low winter 0 c sea surface temperatures sea ice cover during about 3 months per year and low summer salinity 28 suggest strong stratification in the upper water layer in relation to meltwater supply from the lis following the final drainage of glacial lake agassiz through hudson strait which is dated here at 8 3 cal ka bp and the subsequent lis collapse increased summer salinity up to 35 was accompanied by a reduced seasonal gradient of sea surface temperature from winter 3 8 c to summer 8 6 c suggesting enhanced penetration of north atlantic water weakened stratification of the surface water layer then allowed for winter convection and labrador sea water formation which is consistent with increased npl 13c values in response to higher ventilation of the subsurface water layer

water mass exchange between the nordic seas and the arctic ocean on millennial timescale during mis 4 mis 2 1 the climate of the last glaciation circa 65 000 25 000 years ago was interrupted by about 15 abrupt temperature fluctuations the so called dansgaard oeschger events consisting of warm interstadials and cold stadials recorded in greenland ice cores the largest fluctuations occur in the north atlantic region but they have been registered over the most of the world the events are linked to changes in deep water formation in the nordic seas and north atlantic disrupting the thermohaline circulation yet dansgaard oeschger events have so far not been recorded north of the convection areas in the central nordic seas and it is not known if they affected the water exchange between the nordic seas and the arctic ocean in this study we analyze core jm05 31gc from the northern fram strait at the very entrance to the arctic ocean the core contains sediments from marine isotope stages miss 4 2 the results show millennial timescale shifts in all the investigated proxies including the distribution of planktonic and benthic foraminifera planktonic and benthic oxygen and carbon isotopes and several sedimentological parameters in jm05 31gc the interstadials are characterized by relatively high surface and low bottom water temperatures low content of ice rafted debris and well ventilated bottom water stadials are characterized by the presence of icebergs and decreasing surface water and increasing bottom water temperatures due to increased inflow of atlantic subsurface water ventilation decreased during heinrich events and most stadials the results show that the dansgaard oeschger events strongly affected the water exchange between the nordic seas and the arctic ocean

stable isotope clue to episodic sea ice formation in the glacial north atlantic sea ice is a determinant parameter of the climate system which acts as amplifier through positive ice albedo feedbacks and induces deep water formation through brine production it is also one of the most elusive parameters in the paleoclimate record most proxies of sea ice provide information on its presence and extent of e g diatoms or dinocysts but do not permit assessment on its rate of formation however seemingly off equilibrium low 18o values in mesopelagic planktic foraminifer species as observed today in the arctic ocean are thought to relate to the production of isotopically light brines during sea ice formation and might thus provide a clue on the rate of sea ice growth with reference to the isotopic properties of modern planktic foraminifers in the arctic ocean and using multi proxy data sets from the last glacial stage in the northwest north atlantic we re examined some of the current interpretations of planktic isotope records in the glacial nw north atlantic the large amplitude light isotopic excursions recorded in neogloboquadrina pachyderma left coiling during heinrich events 1 for example correspond to extensive sea ice cover as reconstructed from dinocysts and do not seem unequivocally linked to low salinity pulses such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines on the contrary the isotopically heavy planktic foraminifers of the last glacial maximum lgm interval stricto sensu would rather suggest relatively low rates of brine production thus low sea ice growth rates in the area this would imply that the lgm distribution of sea ice in the north atlantic was primarily linked to spreading and drifting from marginal and nordic source areas and not from enhanced in situ production at the scale of glacial interglacial cycles isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18o salinity relationship in deep ocean water masses that might deserve closer examination as it would be independent of continental ice volume changes

controls on stable isotope and trace metal uptake in neogloboquadrina pachyderma sinistral from an antarctic sea ice environment article the polar foraminifera neogloboquadrina pachyderma sinistral dominates assemblages from the high latitude southern ocean which plays a key role in determining past climate due to the tight linkage between antarctic temperature and atmospheric co2 here we use n pachyderma s harvested from sediment traps off the west antarctic peninsula to construct a seasonal time series for the calibration of calcite proxies in a high latitude seasonal sea ice environment where temperature is decoupled from other environmental parameters we have used a combination of 18 ocaco3 and 13 ccaco3 to decipher the calcification temperature and salinity which reflect that n pachyderma s live in surface waters throughout the year and at the ice water interface in austral winter further our results demonstrate that the uptake of trace metals into n pachyderma s calcite is influenced by secondary environmental conditions in addition to temperature during periods of sea ice cover we propose an elevated carbonate ion concentration at the ice water interface resulting from biological utilisation of co2 could influence calcification in foraminifera our calculations suggest that for n pachyderma s mg ca sr ca ratios and li ca ratios are linear functions of calcification temperature and co3 2 n pachyderma s mg ca ratios exhibit temperature sensitivity similar to previous studies 10 20 c and a sensitivity to co3 2 of 1 mol kg 1 sr ca ratios are less sensitive to environmental parameters exhibiting 5 increase c and 0 5 10 mol kg 1 the relationship between li ca ratios and both temperature and co3 2 is less significant with 10 increase in li ca ratio c and 10 mol kg 1 we show how a multi proxy approach could be used to constrain past high latitude surface

modeling the distribution and seasonality of neogloboquadrina pachyderma in the north atlantic ocean during heinrich stadial 1

temperature reconstructions for sw and n iceland waters over the last 10 cal ka based on δ18o records from planktic and benthic foraminifera abstract we have obtained 18 o carb data from planktic n pachyderma s and benthic foraminifera c lobatulu s m barleeanu s from eight cores between 40 and 500 m water depth along the sw core b997 347 and n iceland margins cores b997 321 324 327 328 329 330 and 332 that span the last 10 cal ka sampling resolution varies between centuries to millennial scales over this time range changes in 18 o carb in foraminifera are the product of changes in the global ice volume and the temperature and salinity of the water at the level in which the foraminifera live in order to evaluate the relative roles of these variables we investigate 1 the salinity s and 18 o water values for present day waters off iceland and 2 the present day relationships between 18 o carb or calcite values of foraminifera and water column temperature and salinity data we estimate the average error in the temperature estimate to be 0 3 c based on a monto carlo simulation of the various error terms we argue that around iceland the variations in 18 o carb of both benthic and planktic species over the last 10 cal ka are principally controlled by temperature variations while salinity changes prove less important spatial and temporal changes are examined for both bottom water and 50 m water temperature reconstructions based on six and four cores respectively reconstructed temperatures for sites around sw n iceland indicate that surface and seafloor water temperatures were warmest in the early holocene 10 6 cal ka beginning at 6 cal ka surface and seafloor temperatures began to cool in n iceland and to become less stratified in sw iceland over the last 5000 yrs sea surface temperature variations have been 1 c for 50 of the observations with a maximum range of 2 5 c a profound decrease in temperature of 1 5 c is recorded in our fjord site b997 328 during the little ice age an abrupt earlier cold event is well expressed in at least three n iceland cores around 5 cal ka

unstable younger dryas climate in the northeast north atlantic the younger dryas stadial greenland stadial 1 has long been recognized in proxy records throughout the north atlantic region as a stable cool period that started and ended abruptly however modeling experiments in which the younger dryas cooling was forced by meltwater predict much more unstable climatic conditions compared to the proxy records here we present evidence of a climatically unstable younger dryas based on a decadal resolution marine proxy record from the norwegian continental shelf this record shows that the north atlantic was characterized in the early younger dryas by arctic water and an increasing accumulation of fresh surface water that peaked at 12 500 calendar yr b p for 300 yr during the late younger dryas the sea surface temperatures fluctuated between glacial values 2 c and interglacial values 10 c on a subdecadal to multidecadal time scale this period of extreme instability preceded the more stable and warm holocene starting ca 11 500 calendar yr b p these results are consistent with modeling experiments that link the younger dryas climate changes to fluctuations of the north atlantic thermohaline circulation

constraints on sst estimates for the northern north atlantic nordic seas during the lgm abstract a map of estimated calcification temperatures of the planktic foraminifer neogloboquadrina pachyderma sinistral tnps for the nordic seas and the northern north atlantic for the last glacial maximum was produced from oxygen isotopes with support of mg ca ratios to arrive at the reconstruction several constraints concerning the plausible salinity and 18 o fields were employed the reconstruction indicates inflow of temperate waters in a wedge along the eastern border of the nordic seas and at least seasonally ice free waters the reconstruction from oxygen isotopes shows similarities with mg ca based paleotemperatures in the southern and southeastern sector while unrealistically high mg ca values in the central nordic seas prevent the application of the method in this area the oxygen isotope based reconstruction shows some agreement with temperature reconstructions based on the modern analogue technique but with somewhat lower temperatures and a stronger internal gradient inside the nordic seas all told our results suggest a much more ice free and dynamic high latitude ocean than the climap reconstruction

marine calcium carbonate preservation vs climate change over the last two millennia in the fram strait implications for planktic foraminiferal paleostudies abstract we present a high resolution study of planktic foraminiferal distribution patterns in a deep sea core from the eastern fram strait position 78 55 n 06 46 e water depth 1497 m the sediment core is located below atlantic water masses flowing into the arctic ocean and spans the last 2400 years the investigation is based on planktic foraminiferal species distribution stable isotopes and sedimentological data the mean shell weight of neogloboquadrina pachyderma fragmentation organic and inorganic carbon content and the presence of benthic organic linings were also investigated as an indication of preservation changes the results indicate that the planktic foraminifera are affected by dissolution and point to five periods of especially poor preservation at 200 bce 300 650 ce 700 850 ce 1400 1500 ce and from 1800 ce to present in the last century small and fragile subpolar species turborotalita quinqueloba and globigerinita uvula are preserved the increased percentage of these subpolar species together with increases in the caco 3 toc and total foraminiferal flux would point to surface water warming however our data suggest that these fragile species may not have been preserved in sediments older than 1900 ce due to selective dissolution consequently the magnitude of the previously recorded recent surface water warming in the fram strait may be overestimated

centennial to millennial scale ice ocean interactions in the subpolar northeast atlantic 18 41 kyr ago in order to monitor the evolution of the british irish ice sheet biis and its influence in surface ocean structure during marine isotopic stages mis 2 and 3 we have analyzed the sediments recovered in core md04 2829cq rosemary bank north rockall trough northeast atlantic dated between 41 and 18 ka b p ice rafted debris flux and composition 40ar 39ar ages of individual hornblende grains multispecies planktonic stable isotope records planktonic foraminifera assemblage data and faunal based sea surface temperatures ssts demonstrate a close interaction between biis dynamics and surface ocean structure and water properties in this region the core location lies beneath the north atlantic current nac and is ideal for monitoring the shifts in the position of its associated oceanic fronts as recorded by faunal changes these data reveal a succession of biis sourced iceberg calving events related to low sst usually synchronous with dramatic changes in the composition of the planktonic foraminifera assemblage and with variations in the stable isotope records of the taxa neogloboquadrina pachyderma sinistral coiling and globigerina bulloides the pacing of the calving events from typically dansgaard oeschger millennial timescales during late mis 3 to multicentennial cyclicity from 28 ka b p represents the build up of the biis and its growing instability toward heinrich event he 2 and the last glacial maximum our data confirm the strong coupling between biis instabilities and the temperature and salinity of surface waters in the adjacent northeast atlantic and demonstrate the biis s ability to modify the nac on its flow toward the nordic seas in contrast subsurface water masses were less affected except during the greenland stadials that contain hes when most intense water column reorganizations occurred simultaneously with the deposition of cream colored carbonate sourced from the laurentide ice sheet

reconstructing the upper water column thermal structure in the atlantic ocean 1 the thermal structure of the upper ocean 0 1000m is set by surface heat fluxes shallow wind driven circulation and the deeper thermohaline circulation its long term variability can be reconstructed using deep dwelling planktonic foraminifera that record subsurface conditions here we used six species neogloboquadrina dutertrei globorotalia tumida globorotalia inflata globorotalia truncatulinoides globorotalia hirsuta and globorotalia crassaformis from 66 core tops along a meridional transect spanning the mid atlantic 42 n to 25 s to develop a method for reconstructing past thermocline conditions we estimated the calcification depths from 18 o measurements and the mg ca temperature relationships for each species this systematic strategy over this large latitudinal section reveals distinct populations with different mg ca temperature relationships for g inflata g truncatulinoides and g hirsuta in different areas the calcification depths do not differ among the different populations except for g hirsuta where the northern population calcifies much shallower than the southern population n dutertrei and g tumida show a remarkably constant calcification depth independent of oceanographic conditions the deepest dweller g crassaformis apparently calcifies in the oxygen depleted zone where it may find refuge from predators and abundant aggregated matter to feed on we found a good match between its calcification depth and the 3 2ml l oxygen level the results of this multispecies multiproxy study can now be applied down core to facilitate the reconstruction of open ocean thermocline changes in the past

paired δ18o signals of neogloboquadrina pachyderma s and turborotalita quinqueloba show thermal stratification structure in nordic seas abstract the vertical density gradients in the nordic seas are crucial for the preconditioning of the surface water to thermohaline sinking in winter these gradients can be reconstructed from paired oxygen isotope data in tests of different species of planktonic foraminifera the isotopic signatures of which represent different calcification depths in the water column comparison of 18 o values from foraminiferal tests in plankton hauls sediment traps and nearby core top samples with the calculated 18 o calcite profile of the water column revealed species specific 18 o vital effects and the role of bioturbational admixture of subfossil specimens into the surface sediment on the basis of core top samples obtained along a west east transect across various hydrographic regions of the nordic seas 18 o values of turborotalita quinqueloba document apparent calcification depths within the pycnocline at 25 75 m water depth the isotopic signatures of neogloboquadrina pachyderma s reflect water masses near and well below the pycnocline between 70 and 250 m off norway where the atlantic inflow leads to thermal stratification here temperatures in the calcification depth of n pachyderma s differ from sea surface temperature by approximately 2 5 c in contrast n pachyderma s calcifies very close to the sea surface 20 50 m in the arctic domain of the western nordic seas however further west n pachyderma s prefers somewhat deeper more saline water at 70 130 m well below the halocline that confines the low saline east greenland current this implies that the 18 o values of n pachyderma s do not fully reflect the freshwater proportion in surface water and that any reconstruction of past meltwater plumes based on 18 o is too conservative because it overestimates sea surface salinity minimum 18 o differences n pachyderma s and t quinqueloba may serve as proxy for sea regions with dominant haline and absent thermal stratification whereas thermal stratification leads to 18 o differences of 0 4 to 1 5

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

holocene sea subsurface and surface water masses in the fram strait comparisons of temperature and sea ice reconstructions highlights holocene sea subsurface temperatures after husum hald 2012 estimated from planktic foraminifer fauna in e fram strait biomarkers and ip25 derived indices including dip25 indicate surface water variability delayed onset of early holocene conditions in subsurface 10 6 ka compared to surface 11 7 ka water conditions warm atlantic layer likely occupied uppermost 200 m in eastern fram strait between 10 and 9 ka diverging late holocene trends in surface and subsurface conditions linked to presence of strong pycnocline stratification abstract two high resolution sediment cores from eastern fram strait have been investigated for sea subsurface and surface temperature variability during the holocene the past ca 12 000 years the transfer function developed by husum and hald 2012 has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions and to conclude on the holocene climate and oceanographic variability on the west spitsbergen continental margin results consistently reveal warm sea surface to subsurface temperatures of up to 6 c until ca 5 cal ka bp with maximum seawater temperatures around 10 cal ka bp likely related to maximum july insolation occurring at that time maximum atlantic water aw advection occurred at surface and subsurface between 10 6 and 8 5 cal ka bp based on both foraminiferal and dinocyst temperature reconstructions probably a less stratified ice free nutrient rich surface ocean with strong aw advection prevailed in the eastern fram strait between 10 and 9 cal ka bp weakened aw contribution is found after ca 5 cal ka bp when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka bp cold late holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high 18o values of the subpolar planktic foraminifer species turborotalita quinqueloba while ip25 associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea ice increase since about 7 cal ka bp in surface waters planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface aw influx since ca 3 cal ka bp the observed decoupling of surface and subsurface waters during the later holocene is most likely attributed to a strong pycnocline layer separating cold sea ice fed surface waters from enhanced subsurface aw advection this may be related to changes in north atlantic subpolar versus subtropical gyre activity

stable oxygen and carbon isotopes in planktonic foraminifera neogloboquadrina pachyderma in the arctic ocean an overview of published and new surface sediment data abstract a summary study on oxygen and carbon stable isotopes in planktonic foraminifera from arctic ocean floor appeared in marine geology 20 years ago spielhagen and erlenkeuser 1994 we revisit this topic with a wealth of new data focused on the western amerasian arctic a spotlight in the current climatic and oceanic change neogloboquadrina pachyderma the most abundant polar planktonic foraminiferal species is an important tool for reconstructing surface subsurface water changes in the arctic our new data on n pachyderma 150 250 m from the surface sediments show 18 o and 13 c values of 18 o and 13 c are both influenced by complex water sources water column structure and foraminiferal depth habitat the observed distribution of n pachyderma stable isotopes confirms a shallow habitat of this species in the sea ice covered central arctic especially in the canada basin probably in relation to the shallow chlorophyll maximum the associated light n pachyderma 18 o reflects the long term storage of fresh water at the shelf break a deeper dwelling of n pachyderma with heavier 18 o is supported by a more extensive photic zone and nutrient availability air sea exchange plays an important role in 13 c distribution and is consistent with heavy n pachyderma 13 c in the perennially ice covered central arctic ocean light 13 c composition at the shelf break is additionally influenced by shelf bottom waters enriched in isotopically light remineralized terrestrial carbon distribution of foraminiferal 13 c on the chukchi shelf reflects primary production patterns in the area

distribution of planktic foraminifera at the ice margin in the arctic fram strait planktic foraminifera were collected in net tows 63 m along two east west transects at 78 and 80 n in the fram strait northern nordic seas at five concurrent depth intervals in the upper 200 m of the water column in the ice free zone absolute abundances in the upper 200 m of the water column up to 500 individuals m3 were obtained along the ice margin the absolute abundances reached up to 1250 ind m3 while in the ice covered areas not more than 50 ind m3 have been found surprisingly these strong variations in abundance are not accompanied by significant changes in faunal assemblages between the ice free and the ice covered regions neogloboquadrina pachyderma is the dominant species in most samples making up to 60 of the total faunal assemblage globigerina quinqueloba contributes 38 and all other species combined make up only 2 of the total fauna both absolute and relative abundances of the collected foraminifera are strongly dependent on the mesh size used using smaller mesh sizes provides a wider species spectrum which is of special interest for paleoceanographic reconstructions in the nordic seas where fossil assemblages 150 m often consist of only one species the specific hydrographic conditions in the fram strait with warm atlantic waters underlying cold polar surface waters result in a rather atypical depth distribution of the planktic foraminifera all species seem to prefer the temperate atlantic waters between 50 m and 200 m thus the species composition as well as geochemical tracers do not reflect the surface ocean conditions which again has potentially interesting implications for paleoceanographic reconstructions

neogloboquadrina pachyderma dex and sin mg ca and δ18o records from the norwegian sea magnesium calcium mg ca records based on n pachyderma dex and n pachyderma sin from the last 1200 years have been retrieved from high resolution cores in the norwegian sea comparing temperatures inferred from mg ca and the oxygen isotopic composition of calcite 18oc with instrumental temperature records from ocean weather ship mike suggests that n pachyderma calcifies during the summer season with an offset to oxygen isotope equilibrium of 0 6 in this region summer temperatures below the thermocline are related to the winter season ventilation and breakdown of the seasonal thermocline hence the deeper dwelling n pachyderma sin provides a winter season signal down core n pachyderma dex mg ca temperatures display larger variance than observed in 18oc temperatures record derived from the same morphotype the smaller variance in the 18ocn pachyderma dex temperatures is probably linked to salinity changes in the upper 50 m of the water column the mg ca temperature and 18oc records are used to reconstruct changes in the oxygen isotopic composition of water 18ow during the last 1200 years the reconstructed 18ow records show variation within a realistic range allowing the influence of other water masses than those present at the site today and suggest that the mg ca signal in morphotypes of n pachyderma in the norwegian sea responds to changes in climatic parameters

recent increase in surface water stability during warming off california as recorded in marine sediments warming of surface waters in the california current since the 1950s has coincided with a significant decline in zooplankton volume this has been attributed to reduced upwelling of nutrient rich waters caused by increased thermal stratification across the thermocline proxy microfossil evidence preserved in the santa barbara basin suggests that stability increased early in the 1900s intensified after the early 1940s and became well established by 1960 accumulation of upwelled radiolarians in the basin has steadily declined since 1900 while oxygen isotopes in surface dwelling planktonic foraminifera reflect increasing surface temperatures comparison of the delta sup 18 o records between surface and thermocline dwelling planktonic foraminifera reveals that the temperature difference between surface and thermocline water has increased during the twentieth century instrumental records of surface and thermocline temperatures monitored since 1950 support these results this evidence suggests that relaxation of north pacific anticyclonic gyre circulation deepened isopycnics causing onshore movement of warmer less saline waters and reduced upwelling of cool nutrient rich waters

calcification depths of planktonic foraminifera from the southwestern atlantic derived from oxygen isotope analyses of sediment trap material abstract we present a multi year record of shell fluxes and 18o of six planktonic foraminifera species globigerinoides ruber pink globigerinoides ruber white trilobatus sacculifer orbulina universa neogloboquadrina dutertrei globorotalia menardii from sediment traps located in the southwestern atlantic among the six species only the fluxes of g ruber white and n dutertrei exhibit a significant seasonal component with g ruber white showing a single flux peak in austral summer and n dutertrei exhibiting two flux peaks in spring and autumn to estimate calcification depths of the studied species we then compare their measured 18o to vertical 18o profiles predicted for each collection time from in situ temperature profiles and climatological salinity profiles for the majority of the cases the measured 18o could be accounted for by in situ calcification assuming species specific temperature 18o calibrations the resulting estimates of the calcification depth imply that each species exhibits a characteristic typical mean calcification depth the estimated calcification depths for n dutertrei mode 60 70 m and g menardii mode 70 80 m appear to track the depth of the thermocline in the region whereas the calcification depths of the remaining four species correspond to conditions in the mixed layer among the apparent mixed layer calcifiers g ruber pink and white appeared to calcify consistently shallower mode 30 40 m while t sacculifer calcified deeper mode 50 60 m because of the low flux seasonality the observed oxygen isotope offsets among the species are similar to the flux weighted mean annual 18o offsets indicating that isotopic offsets among the species in sediment samples are mainly due to different calcification depths since the habitat offsets among the species are consistent across seasons 18o in sedimentary shells can be used to track conditions in different parts of the water column and the difference in the oxygen isotope composition between surface species best represented by g ruber pink and thermocline species best represented by n dutertrei can be used as a proxy for stratification in the southwestern atlantic

rapid switches in subpolar north atlantic hydrography and climate during the last interglacial mis 5e plateauing just below early mis 5e values a planktonic d 18 o minimum during the cooling event indicates that marked freshening of the surface waters accompanied the cooling we suggest that switches in the subpolar gyre hydrography occurred during a warmer climate involving regional changes in freshwater fluxes balance and east greenland current influence in the study area the nature of these hydrographic transitions suggests that they are most likely related to large scale circulation dynamics potentially amplified by gis meltwater influences

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

influences on the fractionation of calcium isotopes in planktonic foraminifera for paleoceanographic studies it is important to understand the processes that influence the calcium ca isotopic composition of foraminiferal calcite tests preserved in the sediment record seven species of planktonic foraminifera from coretop sediments collectively exhibited a ca temperature dependent fractionation of 0 013 per c thisisin agreement with previously published estimatesformostspecies ofplanktonic foraminifera as well asbiogenicandinorganiccalciteandaragonite fourspeciesofplanktonicforaminiferacollectedfromasedimenttrapshowedaconsiderableamountof scatterandnoconsistenttemperaturedependentfractionation analyzedsizefractionsofcoretopsamplesshownosignificantrelationshipwith 44 40 ca however preliminary results suggest that the symbiotic and spinose foraminifera globigerinoides sacculifer might exhibit a relationship between test size and 44 40 ca a one box model in which ca isotopes are allowed to fractionate by rayleigh distillation from a biomineralization reservoir internal pool was used to constrain the isotopic composition of the original biomineralization ca reservoir assuming around 85 of the ca reservoir is precipitatedandthefractionationfactorduringprecipitationis0 9985 0 00002 t c toexplaintheforaminiferalcaisotopedata thismodelindicates

variability of north atlantic heat transfer during mis 2 1 short term changes in sea surface conditions controlling the thermohaline circulation in the northern north atlantic are expected to be especially efficient in perturbing global climate stability here we assess past variability of sea surface temperature sst in the northeast atlantic and norwegian sea during marine isotope stage mis 2 and in particular during the last glacial maximum lgm five high resolution sst records were established on a meridional transect 53 n 72 n to trace centennial scale oscillations in sst and sea ice cover we used three independent computational techniques simmax modern analogue technique artificial neural networks ann and revised analog method ram to reconstruct sst from planktonic foraminifer census counts simmax and ann reproduced short term sst oscillations of similar magnitude and absolute levels while ram owing to a restrictive analog selection appears less suitable for reconstructing cold end sst the simmax and ann sst reconstructions support the existence of a weak paleo norwegian current during dansgaard oeschger do interstadials number 4 3 2 and 1 during the lgm two warm incursions of 7 c water to occurred in the northern north atlantic but ended north of the iceland faroe ridge a rough numerical estimate shows that the near surface poleward heat transfer from 53 across the iceland faroe ridge up to to 72 n dropped to less than 60 of the modern value during do interstadials and to almost zero during do stadials summer sea ice was generally confined to the area north of 70 n and only rarely expanded southward along the margins of continental ice sheets internal lgm variability of north atlantic 40 n sst in the glamap 2000 compilation sarnthein et al 2003b pflaumann et al 2003 indicates maximum instability in the glacial subpolar gyre and at the iberian margin while in the nordic seas sst was continuously low

planktonic foraminifera as recorders of past surface water stratification the 18 o difference between shallow and deep living planktonic foraminifera is a proxy for the stratification of surface waters in holocene sediments from the atlantic this difference increases from about 0 in subpolar regions to 3 in the tropics the 18 o values of the shallow dwellers globigerinoides sacculifer and neogloboquadrina pachyderma mainly reflect surface water conditions the calcification depth of the deep living species globorotalia truncatulinoides right coiling is affected by the stratification of the water column in the subtropics shell formation of g truncatulinoides right coiling begins in weakly stratified surface waters in the tropics the initial shell is secreted below the mixed layer this hydrographically induced difference in calcification depth allows the use of the isotopic difference between g truncatulinoides and the shallow species as a proxy for the stratification of surface waters the 18 o between g truncatulinoides and g sacculifer from tropical gravity core geob 1523 1 was significantly lower during isotope stage 2 this suggests that the glacial temperature stratification of western equatorial atlantic surface waters was significantly reduced relative to the holocene

last interglacial mis5e hydrographic shifts linked to meltwater discharges from the east greenland margin abstract proximal evidence of the surface ocean response to size reduction of the greenland ice sheet gis during the last interglacial mis5e and preceding glacial termination t2 remains largely elusive using a new sediment record from the western iceland sea the behavior of the northeastern gis and its relation to the subpolar north atlantic surface hydrography is examined extremely light oxygen isotopic 18o values are found off central east greenland during early mis5e and point to enhanced meltwater release potentially from the northeastern sector of the gis data from downstream the cold east greenland current egc and its eastward branches suggest a far reaching effect of this meltwater not only in the nordic seas but also in the se labrador sea in particular whereas an early mis5e warming at 128 5 126 5 ka in the two regions coincided with the relative reduction of meltwater input into the egc the subsequent cooling noted at 126 5 ka followed a renewed major freshwater event off central east greenland our data further indicate persistent freshwater influence from the east greenland margin over the entire mis5e interval and in addition also reveal a late mis5e meltwater event the latter event occurred just prior to the last glacial inception and emphasizes the importance of greenland meltwater as forcing factor on interglacial climates

new constraints on european glacial freshwater releases to the north atlantic ocean during the late quaternary both external and internal forcings have driven major climatic shifts from glacial to interglacial conditions nonlinear climatic steps characterized the transitions leading to these extrema with intermediate excursions particularly well expressed in the dynamics of the northern hemisphere cryosphere here we document the impact of these dynamics on the north eastern north atlantic ocean focussing on the 35 10 ka interval sea surface salinities have been reconstructed quantitatively based on two independent methods from core md95 2002 recovered from the northern bay of biscay adjacent to the axis of the manche paleoriver outlet and thus in connection with proximal european ice sheets and glaciers quantitative reconstructions deriving from dinocyst and planktonic foraminiferal analyses have been combined within a robust chronology to assess the amplitude and timing of hydrological changes in this region our study evidences strong pulsed freshwater discharges which may have impacted the north atlantic meridional overturning circulation

seasonal patterns of shell flux δ18o and δ13c of small and large n pachyderma s and g bulloides in the subpolar north atlantic past water column stratification can be assessed through comparison of the delta o 18 of different planktonic foraminiferal species the underlying assumption is that different species form their shells simultaneously but at different depths in the water column we evaluate this assumption using a sediment trap time series of neogloboquadrina pachyderma s and globigerina bulloides from the nw north atlantic we determined fluxes delta o 18 and delta c 13 of shells from two size fractions to assess size related effects on shell chemistry and to better constrain the underlying causes of isotopic differences between foraminifera in deep sea sediments our data indicate that in the subpolar north atlantic differences in the seasonality of the shell flux and not in depth habitat or test size determine the interspecies delta delta o 18 n pachyderma s preferentially forms from early spring to late summer whereas the flux of g bulloides peaks later in the season and is sustained until autumn likewise seasonality influences large and small specimens differently with large shells settling earlier in the season the similarity of the seasonal delta o 18 patterns between the two species indicates that they calcify in an overlapping depth zone close to the surface however their delta c 13 patterns are markedly different 1 parts per thousand both species have a seasonally variable offset from delta c 13 dic that appears to be governed primarily by temperature with larger offsets associated with higher temperatures the variable offset from delta c 13 dic implies that seasonality of the flux affects the fossil delta c 13 signal which has implications for reconstruction of the past oceanic carbon cycle citation jonkers l s van heuven r zahn and f j c peeters 2013 seasonal patterns of shell flux delta o 18 and delta c 13 of small and large n pachyderma s and g bulloides in the subpolar north atlantic paleoceanography 28 164 174 doi 10 1002 palo 20018

sub sea surface temperatures in the polar north atlantic during the holocene planktic foraminiferal mg ca temperature reconstructions holocene sea surface temperatures in the eastern fram strait are reconstructed based on mg ca ratios measured on the planktic foraminifer neogloboquadrina pachyderma sin the reconstructed sub sea surface temperatures ssstmg ca fluctuate markedly during the earliest holocene at 11 7 and 10 5 kyr bp this is probably in response to the varying presence of sea ice and deglacial meltwater between 10 5 7 9 kyr bp the ssstmg ca values are relatively high 4 c and more stable reflecting high insolation and intensified poleward advection of atlantic water after 7 9 kyr bp the ssstmg ca values decline to an average of 3 c throughout the mid holocene these changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating arctic water the ssstmg ca values increase and vary between 2 1 c and 5 8 c from 2 7 kyr bp to the present this warming is in contrast to declining late holocene in

paleonutrient and productivity records from the subarctic north pacific for pleistocene glacial terminations i to v our study addresses fundamental questions of the mode and timing of orbital and millennial scale changes in the meridional overturning circulation moc of the subarctic north pacific particular concerns are the vertical mixing the present and past abundance of nutrients in surface waters despite strong stratification and the north pacific north atlantic seesaw of oscillations in sea surface temperature sst we do this by generating and interpreting multiple records for glacial terminations i v down two long piston cores one each from the western and eastern subarctic pacific chlorins and biogenic opal are proxies for surface water productivity delta 13 c of epibenthic foraminifera is a record of deepwater ventilation and the delta 13 c of n pachyderma sin is a tracer of nutrients in subsurface waters that extend up to the sea surface during times of vertical mixing the degree of mixing is traced by pairing sst and delta 18 o records of planktic surface and subsurface pycnocline dwellers tight age control is deduced from a suite of age calibrated 14 c plateau boundaries for termination i and benthic delta 18 o and geomagnetic events for the last 800 ka carbon 14 paleoreservoir ages record the ages of surface and deep waters to uncover short term changes in moc over termination i we have defined a standard sequence of short term productivity events for termination i also evident during terminations ii to v and subsequent interglacials over the last 450 ka the peak glacial regime of stable stratification and low productivity terminated together with the end of ice rafting and melting near 17 ka similar to 2000 years after the onset of termination i pulses of vertical mixing and incursion of warm surface waters from the subtropics followed convected young water masses finally penetrated down to 3600 m water depth at 17 0 to less than 14 5 ka significantly improving bottom water ventilation through the late deglacial and earliest interglacial mixing with upwelled nutrients from the pycnocline induced short term maxima in algal production of chlorins and biogenic opal near 17 15 and 15 12 ka respectively deglacial meltwater incursions in the aleutian current and silica input from north american rivers also promoted east pacific productivity after 15 5 ka productivity decreased during the late deglacial and early interglacial coeval with an exceptional peak in caco 3 preservation caused by both low organic flux and well ventilated deepwater subsequently low salinity and cool surface waters and in turn stratification were gradually restored a second opal dominated productivity maximum marked the ends of interglacials the deglacial pulses of vertical mixing around 17 11 ka imply an important contribution of the north pacific to the coeval release of oceanic co 2 into the atmosphere and support the east west seesaw model of climate change

surface water conditions and calcium carbonate preservation in the fram strait during marine isotope stage 2 28 8 15 4 kyr 1 we present a high resolution record of calcium carbonate preservation alongside the distribution pattern of planktic foraminifera from the fram strait the record covers the marine isotope stage mis 2 28 8 to 15 4 kyr including the last glacial maximum lgm and the early deglaciation in multidecadal temporal resolution the investigation is based on the distribution patterns of planktic foraminifera stable isotopes mean shell weight of neogloboquadrina pachyderma the degree of fragmentation of planktic shells caco3 content and geochemical and sedimentological data the dissolution proxies indicate long lasting periods of markedly reduced preservation of calcium carbonate at 28 8 27 2 24 1 23 2 and 16 6 15 4 kyr in addition to a number of short lasting periods 300 year during the lgm these periods are accompanied by a simultaneous and significant reduction in specimens of subpolar planktic foraminifera indicating a southward expansion of arctic surface water masses prolonged periods with high abundances of subpolar foraminiferal species and good preservation of calcium carbonate are attributed to increased influence of atlantic water masses which appears to persist throughout most of the mis 2 comparison to holocene mis 1 shell weight records shows that the preservation during mis 2 was overall better even during the events of dissolution this was probably a reflection of the low concentration of atmospheric co2 at the time

norwegian sea warm pulses during dansgaard oeschger stadials zooming in on these anomalies over the 35 41 ka cal bp interval and their impacts on proximal european ice sheet dynamics abstract the last glacial millennial climatic events i e dansgaard oeschger and heinrich events constitute outstanding case studies of coupled atmosphere ocean cryosphere interactions here we investigate the evolution of sea surface and subsurface conditions in terms of temperature salinity and sea ice cover at very high resolution mean resolution between 55 and 155 years depending on proxies during the 35 41 ka cal bp interval covering three dansgaard oeschger cycles and including heinrich event 4 in a new unpublished marine record i e the md99 2285 core 62 69 n 3 57s e we use a large panel of complementary tools which notably includes dinocyst derived sea ice cover duration quantifications the high temporal resolution and multiproxy approach of this work allows us to identify the sequence of processes and to assess ocean cryosphere interactions occurring during these periodic ice sheet collapse events our results evidence a paradoxical hydrological scheme where i greenland interstadials are marked by a homogeneous and cold upper water column with intensive winter sea ice formation and summer sea ice melting and ii greenland and heinrich stadials are characterized by a very warm and low saline surface layer with iceberg calving and reduced sea ice formation separated by a strong halocline from a less warm and saltier subsurface layer our work also suggests that this stadial surface subsurface warming started before massive iceberg release in relation with warm atlantic water advection these findings thus support the theory that upper ocean warming might have triggered european ice sheet destabilization besides previous paleoceanographic studies conducted along the atlantic inflow pathways close to the edge of european ice sheets suggest that such a feature might have occurred in this whole area nonetheless additional high resolution paleoreconstructions are required to confirm such a regional scheme

deep dwelling planktonic foraminifera of the northeastern pacific ocean reveal environmental control of oxygen and carbon isotopic disequilibria abstract we assess the utility of four species of living planktonic foraminifera as tracers of thermocline and intermediate water masses in the northern pacific ocean based on their water column distribution and shell isotopic composition assuming oxygen isotopic equilibria with the water column we infer apparent calcification depths this allows an estimate of apparent carbon isotopic disequilibria we then relax the assumption of oxygen isotopic equilibrium to examine habitat effects on kinetic disequilibrium processes in the california current left coiling neogloboquadrina pachyderma and globigerina calida calcify in the upper thermocline globorotalia scitula resides within the shallow salinity minumum potential density 25 1 26 7 while globoquadrina hexagona is associated with the deeper north pacific intermediate water 26 7 26 9 apparent carbon isotopic disequilibria corrected for oxygen isotopic disequilibria range from 1 0 1 9 in these asymbiotic species the carbon isotopic disequilibrium can be modeled as a single exponential function of temperature or a logarithmic function of potential food supply we infer that carbon isotopic disequilibrium increases with metabolic rate related to temperature and or food supply kinetic processes of oxygen and carbon isotopic disequilibria yields reasonable depth habitats if the slope of the oxygen carbon isotopic shift is about 0 35 consistent with culture data our finding of a link between environment metabolism and isotopic disequilibrium observed in oceanic settings suggests the potential to better reconstruct the structure and biological processes of the upper water column from geologic data

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

neogloboquadrina pachyderma sinistral coiling as paleoceanographic tracers in polar oceans evidence from northeast water polynya plankton tows sediment traps and surface sediments the abundance and chemistry of the planktonic foraminifera neogloboquadrina pachyderma sinistral coiling have long been used as tools for monitoring polar surface ocean changes and for correlating these changes to atmospheric and thermohaline circulation fluctuations however due to its remote habitat very little is known about how modern n pachyderma s respond to changing environmental conditions in the polar seas modern samples of n pachyderma s from the northeast water polynya provide a means for studying how environmental conditions affect the vertical distribution and chemistry of this species highest abundances of n pachyderma s were associated with the chlorophyll maximum in the surface 20 80 m where they are exploiting their primary food source evidence suggests that the addition of a calcite crust modifies the calcite tests of some n pachyderma s between 50 and 200 m increasing shell density and modifying shell chemistry the shell mass of encrusted forms is 3 4 times greater than the nonencrusted forms between 50 and 200 m the oxygen isotope composition of n pachyderma s shells increase by 1 5 in response to local water column gradients the 13c values of n pachyderma s are basically invariant with depth in this region are consistently 1 0 depleted in comparison with the 13c for equilibrium calcite and remain basically constant during the shell thickening process mass balance calculations suggest that encrustation occurs at all depths but abundance counts suggest that the process occurs mostly at the depth of the main pycnocline sediment fluxes of n pachyderma s occur during a 2 week bloom event and decrease to almost zero below complete ice cover the decoupling of the processes controlling abundances and shell chemistry explain the discrepancies between transfer function and isotopically derived paleotemperature estimates of surface conditions in some oceanic settings the ability of 18o to record surface ocean conditions will depend on vertical water column gradients as evidenced by the differences in core top calibrations between the north and south atlantic

the north atlantic atmosphere sea surface 14c gradient during the younger dryas climatic event abstract we attempt to quantify the 14c difference between the atmosphere and the north atlantic surface during a prominent climatic period of the last deglaciation the younger dryas event yd our working hypothesis is that the north atlantic may have experienced a measurable change in 14c reservoir age due to large changes of the polar front position and variations in the mode and rate of north atlantic deep water nadw production we dated contemporaneous samples of terrestrial plant remains and sea surface carbonates in order to evaluate the past atmosphere sea surface 14c gradient we selected terrestrial vegetal macrofossils and planktonic foraminifera neogloboquadrina pachyderma left coiling mixed with the same volcanic tephra the vedde ash bed which occurred during the yd and which can be recognized in north european lake sediments and north atlantic deep sea sediments based on ams ages from two norwegian sites we obtained about 10 300 yr bp for the atmospheric 14c age of the volcanic eruption foraminifera from four north atlantic deep sea cores selected for their high sedimentation rates 10 cm kyr 1 were dated by ams 21 samples for each core the raw 14c ages assigned to the ash layer peak is significantly older than the 14c age obtained on land part of this discrepancy is due to bioturbation which is shown by numerical modelling nevertheless after correction of a bioturbation bias the mean 14c age obtained on the planktonic foraminifera is still about 11 000 11 100 yr bp the atmosphere sea surface 14c difference was roughly 700 800 yr during the yd whereas today it is 400 500 yr a reduced advection of surface waters to the north atlantic and the presence of sea ice are identified as potential causes of the high 14c reservoir age during the yd

comparing proxies for the reconstruction of lgm sea surface conditions in the northern north atlantic abstract within the frame of the multiproxy approach for the reconstruction of the glacial ocean margo project sea surface conditions of the last glacial maximum lgm 23 19 ka were reconstructed using different proxies which were calibrated to a standardized modern hydrography in the north atlantic the revised lgm margo data set provides a comprehensive coverage including the nordic seas the data set includes reconstruction based on planktonic foraminifer assemblages dinocyst assemblages alkenone coccolithophorid biomarkers and mg ca ratios in planktonic foraminifers several hydrological features of the lgm north atlantic can be identified that are supported by all four proxies they include an extensive perennial sea ice cover along the eastern canadian and greenland margins seasonally ice free central north atlantic and norwegian sea and the winter sea ice limit being located at about 55 n all proxies also suggest significantly colder than modern sea surface conditions in the southeastern part of the north atlantic and a more zonal temperature pattern than at present with a steep sst gradient of the order of 10 c between 40 n and 45 n however in the nordic seas large discrepancies remain well above the level of uncertainty of the sst reconstructions these discrepancies might be related to stratification of the upper water mass linked to large annual amplitude of temperature with contrasting winter and summer conditions high interannual interdecadal variability or taphonomic processes affecting some of the proxies the average lgm sst in the nordic seas cannot at present be assessed with confidence however the existing evidence suggests that highly variable sea surface conditions and at least occasional advection of north atlantic waters may have characterised the glacial nordic seas

contrasting ocean changes between the subpolar and polar north atlantic during the past 135 ka variations in the poleward directed atlantic heat transfer was investigated over the past 135 ka with special emphasis on the last and present interglacial climate development eemian and holocene both interglacials exhibited very similar climatic oscillations during each preceding glacial terminations deglacial ti and tii like ti also tii has pronounced cold warm cold changes akin to events such as h1 bolling allerod and the younger dryas but unlike ti the cold events in tii were associated with intermittent southerly invasions of an atlantic faunal component which underscores quite a different water mass evolution in the nordic seas within the eemian interglaciation proper peak warming intervals were antiphased between the nordic seas and north atlantic moreover inferred temperatures for the nordic seas were generally colder in the eemian than in the holocene and vice versa for the north atlantic a reduced intensity of atlantic ocean heat transfer to the arctic therefore characterized the eemian requiring a reassessment of the actual role of the ocean atmosphere system behind interglacial but also glacial climate changes key points reduced amoc during the eemian ba yd type warming cooling in termination 1 and 2 comparison of glacial inceptions reveals present climate status

hydrology in the sea of marmara during the last 23 ka implications for timing of black sea connections and sapropel deposition 1 sediments deposited under lacustrine and marine conditions in the sea of marmara hold a late quaternary record for water exchange between the black sea and the mediterranean sea here we report a multiproxy data set based on oxygen and strontium isotope results obtained from carbonate shells major and trace elements and specific organic biomarker measurements as well as a micropaleontological study from a 14c dated sediment core retrieved from the sea of marmara pronounced changes occurred in 18o and 87sr 86sr values at the fresh and marine water transition providing additional information in relation to micropaleontological data organic biomarker concentrations documented the marine origin of the sapropelic layer while changes in n alkane concentrations clearly indicated an enhanced contribution for organic matter of terrestrial origin before and after the event when compared with the black sea record the results suggest that the black sea was outflowing to the sea of marmara from the last glacial maximum until the warmer bolling allerod the first marine incursion in the sea of marmara occurred at 14 7 cal ka b p however salinification of the basin was gradual indicating that black sea freshwaters were still contributing to the marmara seawater budget after the younger dryas which is associated with a high input of organic matter of terrestrial origin both basins were disconnected resulting in a salinity increase in the sea of marmara the deposition of organic rich sapropel that followed was mainly related to enhanced primary productivity characterized by a reorganization of the phytoplankton population

late quaternary sedimentation along a fjord to shelf trough transect east greenland c 68 n the east greenland continental margin between c 66 and 68 n consists of a major fjord trough system that extends from kangerdlugssuaq fjord along kangerdlugssuaq trough to denmark strait measurements of the temperature and salinity of the water column along this transect indicates that warm water 0 2 c underlies the surface polar water of the east greenland current a series of short 1 3 m gravity cores along the fjord trough transect have sufficient numbers of foraminifera that a suite of ams 14c dates has been obtained including both basal and core top age estimates rates of sediment accumulation vary through space and time over the last 1 ka estimates vary from c 3 to 0 1 m these dates and measurements of sediment density together with measurements of the percentages by weight of total organic carbon and biogenic silica are used to show graphs of fluxes of the organic and inorganic sediment components over the last 1 14 ka an analysis of the net flux of foraminifera indicates a reduction in numbers during the younger dryas chronozone and a general similarity with data from the renland east greenland ice core data

evolution of subpolar north atlantic surface circulation since the early holocene inferred from planktic foraminifera faunal and stable isotope records abstract past changes in the surface flow regime of two main eastern north atlantic warm water pathways toward the nordic seas were reconstructed based on faunal analyses in combination with carbon and oxygen stable isotope measurements in planktic foraminifera the investigated sites in the surroundings of the faroe islands are located in the transitional area where surface waters of subpolar and subtropical origin mix before entering the arctic mediterranean in these areas large amplitude millennial variability in the characteristics of the upper water column appears modulated by changes in the intensity of the subpolar gyre circulation from 7 8 to 6 ka bp faunal records indicate a deep mixed layer which in conjunction with lighter 18 o values suggest that the inflowing atlantic waters were dominated by a relatively cooler and fresher water mass reflecting a strengthening of the subpolar gyre under conditions of enhanced positive nao like forcing and reduced meltwater input a shift in the hydrographic conditions occurred during the mid holocene centered at 5 ka bp at this time increasing upper water column stratification and the incipient differentiation of the stable isotopic signal of the iceland faroe and faroe shetland surface water masses suggest increasing influx of warmer more saline surface waters from the subtropical gyre as subpolar gyre circulation weakened the mid holocene decline in subpolar gyre strength is presumably related to a shift toward a low state of the nao like forcing associated with decreased solar irradiance later in the holocene from 4 ka bp to present the increased frequency and reduced amplitude of the surface hydrographic changes reflect corresponding fluctuations in subpolar gyre circulation these high frequency oscillations in subpolar gyre strength suggest increased surface circulation sensitivity to moderate freshwater fluxes to the labrador irminger sea basin highlighting the importance of the salinity balance in modulating subpolar gyre dynamics particularly under conditions of low nao atmospheric forcing

multiproxy fossil comparison reveals contrasting surface ocean conditions in the western iceland sea for the last two interglacials abstract dinoflagellate cyst dinocyst coccolith and planktic foraminiferal assemblages from a core in the western iceland sea were used to reconstruct and compare the surface ocean developments of the holocene and the last interglacial marine isotopic stage or mis 5e while increasing subpolar planktic foraminifers from 10 ka indicate subsurface warming peaking around 7 5 ka the dinocyst data suggest that the uppermost ocean remained dominated by cold waters until 6 5 ka a reduced advection of cold polar waters through the east greenland east icelandic current thereafter entailed warmest and most saline holocene conditions between 6 5 and 5 ka in turn followed by a general cooling trend by contrast both planktic foraminifers and dinocysts show an increased presence of atlantic type waters from 122 ka onward resulting in a mis 5e thermal optimum around 120 5 ka nonetheless occasional freshwater input from melting drift ice created stratified but also seasonally variable conditions during this first half of mis 5e this stratification signature disappeared at 120 ka when a marked repositioning of the oceanographic fronts occurred slightly colder conditions are indicated by both phyto and zooplankton from there on until the end of mis 5e around 117 ka a late mis 5e cooling at the iceland plateau is opposite to a late mis 5e optimum observed in the eastern nordic seas this regional difference is likely explained by various feedback mechanisms following the major reorganisation of the oceanic fronts at 120 ka the holocene and mis 5e interglacial variability is not reflected in the quasi monospecific coccolith assemblages and illustrates the low sensitivity of living coccolithophore communities to subtle temperature changes in the low temperature regions of the nordic seas overall quite different surface water properties appear to have characterised both interglacial intervals with a higher share of warm atlantic elements in the planktic communities during mis 5e this suggests a higher contribution of atlantic waters in the southwestern nordic seas probably due to a more northward expansion of the irminger current under weakened polar east greenland east icelandic currents such a reduced influence of polar waters in the southwestern nordic seas may thus explain other evidence for relatively warm conditions in mis 5e all around southern greenland

planktic foraminiferal dissolution in the twilight zone abstract calcite dissolution of planktic foraminifers that settle from the surface ocean to depths has been assessed using the weight size relationship of tests and correlated to carbonate ion concentration co 3 2 of ambient sea water globigerina bulloides and globigerinita glutinata were sampled from the north atlantic and the arabian sea during different seasons spring and fall and the monsoons respectively test weight has been determined for single tests from narrow size classes 250 8 m and 300 7 m minimum test diameter initial test weight of both species in surface waters differs between regions and seasons weight loss of settling tests in the twilight zone between 100 and 1000 m water depths averaged 19 below the twilight zone 1000 2500 m no weight loss occurs on average and tests may even gain weight remineralization of settling planktic foraminiferal tests is most pronounced at maximum co 3 2 accordingly strong dissolution occurs in the twilight zone at the depth of maximum decrease in co 3 2 it is assumed that dissolution of planktic foraminiferal calcite is caused by co 3 2 under saturation inside the test buffered by diffusive exchange of co 3 2 ions with the ambient sea water through the pores and aperture consequently reconstruction of small scale differences in seawater co 3 2 from test weight alone is not feasible and systematic correlation between test weight and co 3 2 of the ambient sea water is statistically not significant at constant co 3 2 remineralization cannot be deduced from test weight neither at high nor low co 3 2 saturation in total our data suggest that the global vertical planktic foraminiferal caco 3 flux is about 19 lower than calculated by schiebel 2002 planktic foraminiferal sedimentation and the marine calcite budget global biogeochemical cycles 16 4 1065 doi 10 1029 2001gb001459

foraminifer isotope study of the pleistocene labrador sea northwest north atlantic iodp sites 1302 03 and 1305 with emphasis on paleoceanographical differences between its inner and outer basins article i nfo coresraisedduringiodpexpedition303offsoutherngreenland eirikridgesite1305 andoffthelabradorcoast orphanknollsite1302 1303 wereanalyzedtoestablishanisotopestratigraphy respectivelyforthe inner and outer basins of the labrador sea ls these isotopic data also provide information on the atlantic meridional overturning circulation amoc notably with regard to the intensity of the western boundary under current wbuc which is tightly controlled by the production of denmark strait overflow water dsow and the production of labrador sea water lsw in the inner basin through winter cooling and convection the upper 184 m of sediment at eirik ridge spans marine isotope stages mis 32 to 1 at this site two distinct regimes are observed prior to mis 20 the isotopic record resembles that of the open north atlantic records of the interval

stable isotope composition δ 18 o δ 13 c of living planktic foraminifers in the outer laptev sea and the fram strait abstract the upper water column in the fram strait and the outer laptev sea was sampled for water column isotopes and living planktic foraminifer species neogloboquadrina pachyderma sinistral coiling ehrenberg 1861 and turborotalita quinqueloba natland 1938 their shell 18o and 13c values are compared to water oxygen and dissolved inorganic carbon isotope data to determine the environmental influence on the foraminifers isotopic ratio major controls on the oxygen isotope composition of both species are the shallow depth habitat under permanent ice coverage the low salinity surface layer and the rate of metabolic activity none of the specimens precipitated its shell in isotopic equilibrium with the ambient sea water they are all depleted in 13c and 18o attributed to a species specific vital effect for nonencrusted n pachyderma sin in the 125 250 m size class this vital effect amounts to 1 3 in 18o and 2 0 in 13c it increases to higher values in waters under permanent ice cover t quinqueloba reveals a mean vital effect of about 1 3 in 18o and 2 6 in 13c the general isotopic trends are similar for n pachyderma sin and t quinqueloba differences in the species isotope ratio at the same sites are caused by different calcification depths and metabolic activity the oxygen isotope composition of n pachyderma sin shows a relationship to salinity measurements and indicates that it is a good quantitative proxy for salinity reconstructions while no relationship exists in this region between n pachyderma sin oxygen isotopes and water temperature

paleoceanographic evolution of the sw svalbard margin 76 n since 20 000 14c yr bp abstract two cores from the southwestern shelf and slope of storfjorden svalbard taken at 389 m and 1485 m water depth have been analyzed for benthic and planktic foraminifera oxygen isotopes and ice rafted debris the results show that over the last 20 000 yr atlantic water has been continuously present on the southwestern svalbard shelf however from 15 000 to 10 000 14c yr bp comprising the heinrich event h1 interval the bolling allerod interstades and the younger dryas stade it flowed as a subsurface water mass below a layer of polar surface water in the benthic environment the shift to interglacial conditions occurred at 10 000 14c yr bp due to the presence of a thin upper layer of polar water surface conditions remained cold until ca 9000 14c yr bp when the warm atlantic water finally appeared at the surface neither extensive sea ice cover nor large inputs of meltwater stopped the inflow of atlantic water its warm core was merely submerged below the cold polar surface water

arctic ocean record of last two glacial interglacial cycles off north greenland ellesmere island implications for glacial history a sediment record from the practically unknown southernmost part of the lomonosov ridge off north greenland ellesmere island has been studied greenice core 10 encompasses marine isotope stages mis 7 1 and reveals changing paleoceanographic conditions and land ocean connections during the last two glacial interglacial cycles the isotope record of planktic foraminifera neogloboquadrina pachyderma s show large similarities to other arctic ocean key records supporting that the pattern reflect over regional changes of the halocline structure the relatively low 18 o values of subpolar foraminifera turborotalita quinqueloba in the last interglacial unit support that the specimens represent local production related to warm interglacial conditions and a reduced sea ice cover in the interior arctic ocean enhanced deposition of coarse ice rafted debris took place during the mis 8 7 transition periods of mis 6 mis 6 5 transition mis 5d mis 4 and late mis 3 30 40 14 c kyr bp in mis 2 ird flux was low in the area the ird contains detrital carbonate similar to other amerasia basin records the occurrence of finegrained calcite rich detrital carbonate layers at glacial interglacial transitions seems unique to this area we suggest that detrital carbonate was transported and deposited from nepheloid flows during deglaciations of ellesmere island when the atlantic water boundary current along the continental margin was gaining strength 2007 elsevier b v all rights reserved

surface water changes in the norwegian sea during last deglacial and holocene times stable carbon and oxygen isotopes of the polar planktic foraminifera neogloboquadrina pachyderma sinistral from sediment cores of the norwegian sea reveal several anomalous 13c and 18o depletions in the surface water during the last glacial to interglacial transition and during the later holocene the depletions that are observed between the last glacial maximum lgm and the end of the main deglacial phase were caused by massive releases of freshwater from thawing icebergs which consequently resulted in a stratification of the uppermost surface water layer and a non equilibrium between the water below and the atmosphere at 8 5 ka 14c bp this strong iceberg melting activity ceased as defined by the cessation of the deposition of ice rafted detritus after this time the dominant polar and subpolar planktic foraminiferal species rapidly increased in numbers however this post deglacial evolution towards a modern type oceanographic environment was interupted by a hitherto undescribed isotopic event 7 8 ka which on a regional scale is only identified in eastern norwegian sea surface water this event may be associated with the final pulse of glacier meltwater release from fennoscandia which affected the onset of intensified coastal surface water circulation off norway during a time of regional sea level rise all these data indicate that surface water changes are an integral part of deglacial processes in general yet the youngest observed change noted around 3 ka gives evidence that such events with similar effects occur even during the later holocene when from a climatic point of view relativelystable conditions prevailed

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

oceanographic changes through the last millennium off north iceland temperature and salinity reconstructions based on foraminifera and stable isotopes abstract temperature and salinity reconstructions for two 1000 year high resolution sedimentary records located at the boundary between atlantic and arctic surface waters on the north icelandic shelf are based on transfer functions and oxygen isotopes for planktonic and benthic foraminifera there is a general increase of arctic water indicator species at the transition from the medieval warm period into the little ice age lia and a subsequent return of atlantic water indicator species towards the end of the lia and in the 20th century the timing of the reconstructed temperature changes both at the beginning and at the end of the lia appears to be slightly different for the different water masses the earliest temperature change is seen in the bottom and subsurface waters where a cooling is reconstructed as early as ad 1150 1200 at both locations whereas previously published diatom based and alkenone based sea surface temperature reconstructions show a change at ad 1300 coinciding with the air temperature shift in the area our results show the need of a thorough understanding of the oceanography in the study area as well as the different living habitat for the biological proxies used for the temperature estimates

paleoceanographic development in the sw barents sea during the late weichselian early holocene transition abstract the late weichselian early holocene variability of the north atlantic current has been studied with focus on the zonal component of this meridional transport during the transition from glacial to interglacial conditions the investigated sediment core is from 409 m water depth in the sw barents sea eight accelerator mass spectrometry ams 14c dates show that the core covers the last 20 000 cal yr b p with a centennial scale resolution during late weichselian early holocene planktic foraminiferal assemblages were analyzed using the 100 m size fraction and foraminiferal planktic and benthic 13c and 18o isotopes were measured furthermore a range of physical and chemical analyses has been carried out on the bulk sediment samples four time periods have been identified which represent the varying oceanographic conditions in ingoydjupet a glacial trough located off the north coast of norway in the sw barents sea 1 the late glacial before ca 15 000 cal yr b p influenced by the nearby ice sheets with high amounts of sea ice or iceberg transported detritus 2 the late oldest dryas stadial and the bolling allerod interstadial ca 15 000 12 700 cal yr b p with cold surface water conditions influenced by the collapse of the nearby ice sheets high amounts of sea ice or iceberg transported detritus and melt water and weak subsurface inflow of atlantic water 3 the younger dryas cold stadial 12 700 11 650 cal yr b p with low primary productivity and extensive sea ice cover and 4 the preboreal and early holocene 11 650 6800 cal yr b p cal yr b p with strong influx of atlantic water into the area near absence of ice rafted debris and generally ameliorated conditions in both surface and bottom water masses as seen from a high flux of foraminifera and increased marine primary production

seasonal variability of δ18o and δ13c of planktic foraminifera in the bering sea and central subarctic pacific during 1990 2000 we evaluated a 10 year time series of 18o and 13c records from three planktic foraminifers neogloboquadrina pachyderma globigerina umbilicata and globigerinita glutinata in the bering sea and central subarctic pacific with a focus on their responses to environmental changes foraminiferal 18o followed the equilibrium equation for inorganic calcite with species specific equilibrium offsets ranging from nearly zero 0 02 for n pachyderma and 0 01 for g umbilicata to 0 16 g glutinata equilibrium offsets in our sediment trap samples were smaller than those from plankton tow studies implying that foraminiferal 18o was modified by encrustation during settling habitat calcification depths varied from 35 55 m n pachyderma and g umbilicata or 25 45 m g glutinata during warm stratified seasons to around 100 m during winter when the mixed layer depth increases unlike 18o foraminiferal 13c showed species specific responses to environmental changes we found a dependency of 13c in g umbilicata on co32 concentrations in ambient seawater that agreed reasonably well with published laboratory results suggesting that 13c of g umbilicata is subject to vital effects in contrast 13c of n pachyderma and g glutinata are likely affected by other species specific biological activities seasonal flux patterns reveal that fossil records of n pachyderma and g glutinata represent annual mean conditions whereas that of g umbilicata most likely indicates those of a specific season because none of these three taxa was abundant from december to february their fossil records likely do not reflect isotope signals from cold seasons

instabilities in the labrador sea water mass structure during the last climatic cycle in the modern labrador sea the north atlantic deep water components are found below the 2 km deep intermediate labrador sea water lsw mass which is renewed locally through winter convective mixing this water mass structure remained relatively stable since 9 5 14 c ka bp as indicated by isotopic studies of foraminifer assem blages from deep sea cores almost constant differences in 18 o values are observed between major species these av erage 0 5 between the epipelagic species globigerina bulloides and the mesopelagic species neogloboquadrina pachyderma left coiled and 1 between neogloboquadrina pachydermaand the benthic species cibicides wuellerstorfi after correction for cibicides wuellerstorfi specific fractionation these isotopic compositions represent thermohaline conditions in surface waters in the pycnocline with the lsw and in the deep component of the north atlantic deep water respectively a drastically different structure characterized the glacial labrador sea differences in 18 o values of 2 to 2 5 are then observed between globigerina bulloides and benthic species indicative of a strong halocline between the corresponding water masses thus for reduced production of intermediate waters during the same interval neogloboquadrina pachydermashows 13 c and 18 o fluctuations of 1 to 1 5 amplitude in phase with heinrich bond events and higher frequency climate oscillations the 18 o values in neogloboquadrina pachyderma vary between those of globigerina bulloides and of benthic foraminifers suggesting large amplitude bathymetric fluctuations of the halo thermocline above and below the bathymetric range occupied by neogloboquadrina pachyderma minimum 18 o values in neogloboquadrina pachydermamatch intervals of maximum ice rafting deposition such as the late heinrich events thus intervals with a deeper more dilute buoyant surface water layer

oxygen isotope ecology of recent planktic foraminifera at the central walvis ridge se atlantic 1 above the walvis ridge in the se atlantic ocean we collected living plantkic foraminifera from the upper water column using depth stratified plantkon tows the oxygen isotope composition 18oc in shells of foraminifera and shell concentration profiles show seasonal and depth habitats of individual species the tow results are compared with the average annual deposition 18oc from sediment traps and the interannual average 18oc of fossil specimens in top sediments at the same site the species globigerinita glutinata best reflects the austral winter spring sea surface temperature sst its 18oc signal in top sediments remains pristine in contrast tow results also show that globigerinoides ruber continues to calcify below the surface mixed layer sml i e down to the deep chlorophyll maximum dcm hence its 18oc signature of exported specimens reflects the sst only when sml incorporates the dcm deep tow and sediment trap results show that both globorotalia truncatulinoides and globorotalia inflata record the temperature between 150 and 350 m depending on the season and the shell size however for all fossil taxa in sediments apart from globigerinita glutinata we observe a positive 18oc shift with respect to the sediment trap and plankton tow values likely related to the interannual flux changes and deep encrustation