r selected benthic foraminifera with associated bacterial colonies in upper pleistocene sediments of the ross sea antarctica implications for calcium carbonate preservation investigations on foraminifera from upper pleistocene holocene sediments cored in the continental slope of the western ross sea 2383 m water depth revealed that the record of calcareous assemblages was restricted to a limited time interval approximately 6 kyr and characterized by a dominance of phytodetritus exploiting taxa such as alabaminella weddellensis and epistominella exigua rod shaped calcified fossil bacteria infest the partially dissolved calcareous foraminiferal surfaces either as clusters or as isolated cells suggesting that significant changes from underto oversaturated conditions with respect to calcium carbonate in the chemistry of the seawater developed before the final burial of the foraminiferal tests we postulate that bacterial activity on a microenvironmental scale interface and pore water in the sea floor could influence pore water conditions in such a way as to preserve carbonate in deep marine regions where environmental conditions usually prevent the establishment of carbonate secreting communities 1999 elsevier science b v all rights reserved

seeing the wood from the trees reconstructing past climates is important if we are to distinguish anthropogenic warming from natural variability in the climate system briffa and osborn 1 discuss a recent study by mann et al that has extended their northern hemisphere climatic reconstruction to a d 1000 and explain why there are large uncertainties in the reconstruction of medieval and earlier temperatures on large spatial scales thus although the 20th century was almost certainly the warmest of the millennium the amount of anthropogenic warming remains uncertain 1 http www sciencemag org cgi content full 284 5416 926

glacial northeast atlantic surface water pco2 productivity and deep water formation abstract the carbon isotopic composition of bound organic material within the crystal lattice of planktonic foraminiferal calcite is a valuable proxy for the isotopic composition of primary photosynthate in surface waters this proxy can be used to estimate pco2 in the surface waters of the northeast atlantic during the last glacial period if combined with data on the carbon isotopic composition of foraminiferal calcite our first estimates of surface water pco2 at the location of biogeochemical ocean flux studies core 5k 50 41 3 n 21 51 9 w indicate that this region was probably a more important sink for co2 during the glacial than during the holocene this increased sink could not have been caused by local high primary productivity because glacial primary productivity as estimated from benthic foraminiferal data was extremely low at 5k we thus conclude that the enhanced sink at these latitudes resulted from increased convection of surface water to intermediate or greater depths i e from the southward shift of an important centre of deep intermediate water formation as confirmed by computer simulation

a thousand year speleothem proxy record of north atlantic climate from scotland luminescent organic matter in stalagmites may form annual bands allowing growth rate to be precisely determined stalagmite growth rate is controlled by precipitation so annual bands can be used to derive long precipitation records a continuously banded stalagmite from a cave in nw scotland was used to provide a 1100 year high resolution record of precipitation the location of the cave means that precipitation is closely linked to the north atlantic oscillation for which a record is also derived this suggests that changes in the north atlantic oscillation state was an important control on european climate over the past millennium

benthic foraminiferal response to changes in bottom water oxygenation and organic carbon flux in the eastern mediterranean during lgm to recent times abstract we present a high resolution study of benthic foraminiferal abundances in 4 cores from the central aegean and ne levantine seas spanning the interval from 30 ka bp to the present the benthic foraminiferal faunas indicate that during lgm times bottom waters were well ventilated while organic flux to the sea floor was significantly higher than today from 30 to 10 2 ka bp faunal density and composition suggest a gradual decrease in organic flux to the sea floor this trend is interrupted by a short return to higher organic flux levels during the younger dryas 12 8 11 5 ka bp the faunas immediately preceding the early to middle holocene organic rich layer sapropel s1 are very similar to late holocene faunas indicating oligotrophic conditions the transition from well ventilated bottom waters to anoxic levantine basin or strongly dysoxic aegean sea bottom waters appears to take place within a time span of only 600 years from 10 8 to 10 2 ka bp sapropel s1 10 2 6 4 ka bp is characterized by extended periods of bottom water anoxia in the levantine basin and by strongly dysoxic conditions punctuated by episodic re ventilation events in the aegean sea re establishment of fully oxygenated bottom water conditions after sapropel s1 was extremely rapid the ensuing late holocene faunas are very similar to recent faunas found in the aegean sea suggesting much lower fluxes of organic matter to the sea floor than during glacial times

precessionally forced productivity variations across the equatorial pacific 1 measurements of combustion oxygen demand cod in two sediment cores provide a record of paleoproductivity driven by surface ocean dynamics in the equatorial eastern and western pacific for the past 400 000 years the cod time series are well correlated with each other over this time span and show pronounced precessionally forced peaks of higher productivity during globally colder periods the phase of this signal in the two cores is identical to within chronological uncertainties suggesting a common insolation forcing mechanism for the upper ocean across the equatorial pacific cod is also in phase with the precessionally forced component of global ice volume as indicated by oxygen isotopes and with atmospheric methane in the vostok ice core these relationships imply that the cod relative paleoproductivity index provides an important diagnostic measure of the mechanisms of tropical ocean dynamics and climate change

paleoenvironmental evolution in a high stressed cold seep system vicchio marls miocene northern apennines italy abstract excellent exposures of miocene seep carbonates enclosed in marine marly sediments vicchio outcrops in the northern apennines italy offer the opportunity to highlight the evolution of a fossil seep ecosystem and the response of benthic communities to high stressed environmental conditions for this purpose seep related facies and molluscs within carbonate bodies have been studied coupled with benthic foraminiferal assemblages and carbon and oxygen isotopes in the enclosing marls the integrated planktonic foraminiferal and calcareous nannofossil biostratigraphy has allowed us to constrain the seepage within well calibrated bioevents and to stress the relationships with paleoclimatic and paleoceanographic variations during the middle miocene in the mediterranean area our biostratigraphic data indicate that the onset of the seepage approximates the mi3b cooling event 13 82 ma and the seepage system lasts for 400 kyr the evolution of the vicchio cold seep system passes through four phases 1 the onset of the seepage characterized by a pervasive flow of methane rich fluids is inferred by 13c depletion of marly sediments and by prevailing benthic foraminifera indicative of suboxic conditions at the sea floor 2 the methane flow becomes focused causing the precipitation of wide pinnacle like carbonate bodies which contain giants lucinids enclosing marls indicate well oxygenated conditions possibly enhanced by paleoceanographic variations connected to the mi3b cooling event 3 the appearance of the vesicomyid christineconcha cf c regab and the absence of lucinids in seep carbonates suggest stable methane rich fluid emissions higher flow rates locally favoured the flourishment of bacterial mats benthic foraminifera show abundance peaks of organic matter depending taxa 4 the reduced intensity of methane rich fluid flows favours the precipitation of stratiform carbonate bodies along strike the macrofauna is characterized by the presence of both vesicomyidae and giant lucinids foraminiferal assemblages in the enclosing marls indicate the restoration of well oxygenated conditions

contribution of asian dust and volcanic material to the western philippine sea over the last 220 kyr as inferred from grain size and sr nd isotopes asian dust and volcanogenic materials are two major components in the northwestern pacific quantitatively distinguishing them and estimating their mass accumulation rates mars are very important for understanding regional and global climate change here we present the grain size composition of detrital sediments and the radiogenic strontium sr and neodymium nd isotopic compositions of different grain size fractions of detrital sediments that were recovered from the western philippine sea these new records show that the different grain size distributions can be associated with 1 asian dust from the western and central chinese deserts and chinese loess and 2 volcanogenic materials that were derived from the luzon islands the mars of this asian dust and volcanic materials are obtained by using weibull function fitting the mars of asian dust and volcanic materials are coupled with the glacial interglacial cycle these values are found to have been higher and more variable during the glacial period than during the interglacial period we argue that the strengthening aridity of the asian continent which is connected to solar insolation and ice volume variations from orbital eccentricity constitutes an important mechanism that drives the high mars of glacial dust in the western philippine sea the internal positive feedback of dust may be another important mechanism the significant increase in volcanic material during the glacial period was caused by sea level changes which were driven by the ice volume and solar insolation at high latitudes and by strengthened precipitation from the el nino southern oscillation enso which is driven by orbital eccentricity and precession cycles on the luzon islands

orbitally paced paleoproductivity variations in the timor sea and indonesian throughflow variability during the last 460 kyr 1 a high resolution 1 2 kyr multiproxy record from the timor sea in the easternmost indian ocean international marine global change images program core md01 2378 latitude 13 04 95 s longitude 121 47 27 e 1783 m water depth closely tracks changes in intermediate water ventilation and paleoproductivity over the last 460 kyr within one of the main outflow passages of the indonesian throughflow spectral analysis of five different flux based productivity proxies indicates spectral power concentrated in the 100 kyr glacial interglacial and the 23 kyr and 19 kyr precessional periods paleoproductivity maxima lead ice volume benthic 18o maxima by 20 to 40 1300 to 2600 years at the precession band the spectral differences in tropical paleoproductivity records from the pacific and indian oceans suggest that local processes wind and circulation patterns driven by insolation are dominant in driving productivity rather than large scale tropical features in the timor sea productivity fluctuations over the last 460 kyr were strongly influenced by monsoonal wind patterns offshore nw australia 23 and 19 kyr and were also modulated by sea level related variations in the intensity of the indonesian throughflow 100 kyr

a reconstruction of the north atlantic oscillation using tree ring chronologies from north america and europe tree ring records six from eastern north america and four from northwestern europe are used to develop the first reconstruction of the winter north atlantic oscillation nao the reconstructed series spans the interval ad 1701 1980 and explains 41 of the variance in the nao over the ad 1874 1980 calibration period the reconstruction also captures the spectral properties of this index suggesting that the oscillatory character of the nao is a long term feature of the north atlantic climate system

nao signal recorded in the stable isotopes of greenland ice cores 1 the winter 18o signal is extracted from 7 greenland ice cores covering the past 700 years to filter out noise and local variations in the 7 isotope records a principal component analysis is carried out on the ice core data a comparison between the time series of the first principal component pc1 with 67 years of winter december to march temperature measurements from 3 southern greenland synoptic stations shows highly significant correlations southern greenland winter temperatures are known to be greatly influenced by the north atlantic oscillation nao a good proxy for southern greenland temperatures is therefore expected to reveal at least parts of the nao signal it is shown that the pc1 time series indeed is significantly correlated to the nao during the winter months the inclusion of ice core winter season 18o time series in future multiproxy nao reconstructions is therefore recommended

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

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

snow anomaly events from historical documents in eastern china during the past two millennia and implication for low frequency variability of ao nao and pdo 1 models and instrumental data indicate that the spatial and temporal variations of snow cover are significantly related to atmospheric circulation e g the ao nao here we present historical snow anomaly events during the past two millennia that provide a unique temporal window to studying long term ao nao a prominent phenomenon in wintertime direct descriptions such as no snow during the winter and pray god for snow are interpreted as convincing evidence for snow anomalies the variations of positive negative snow abnormal events show clear decadal to century variations during the past two millennia based on the previous instrumental research and comparison with other reconstruction data we suggest the index of abnormal snow ias may be an ao like atmospheric variability the winter during the medieval warm period mwp ad 900 1300 might be strongly influenced by a predominantly positive ao with less snow condition whereas the little ice age lia ad 1300 1900 by negative ao concomitant with heavier snowfalls in east asia our data show that a warm climate period the mwp a cold period the lia can be perturbed by a cold spell a warm spell which are linked with a change in atmospheric circulation low frequency variability of snow records may be intrinsic to the natural climate system although the dynamic mechanisms linking snow anomalies with atmospheric circulation the ao nao the pdo is unclear on the decadal to century time scales pacific ocean may play an important role in regulating atmospheric circulations since the ias is highly correlated with the reconstruction of pdo

deep sea benthic foraminifera and biogenic opal glacial to postglacial productivity changes in the western equatorial pacific the accumulation rate of benthic foraminifera in deep sea sediments is strongly correlated with the productivity of the surface ocean core tops from diverse deep sea settings straddling different export production levels are used in this study for the calibration between the organic carbon flux to the seafloor jsf flux and the benthic foraminifera accumulation rate bfar the correlation can be used to reconstruct organic carbon flux to the seafloor in the past and hence the productivity of past oceans these results are compared with the accumulation rates of carbonate and biogenic opal in the sediments it is found that biogenic opal is more sensitive to productivity changes in the modern ocean than is carbonate the appropriate equations are derived for the equatorial pacific using core material fromeurydice erdc indomed inmd andpleiades plds expeditions these equations are then applied to two selected time horizons in sediments from the ontong java plateau a western equatorial pacific pelagic depth transect the last transition lt and the last glacial lg it is found that productivity was higher during the last glacial relative to the late holocene by a factor between 1 6 and 2 during the last transition productivity was intermediate between glacial and recent values we do not see any corresponding increase in the rates of accumulation of carbonate or biogenic opal during the last glacial this observation questions the importance of ocean productivity as the main controlling factor of carbonate and biogenic opal accumulation rates back through geological time

north atlantic oscillation dynamics recorded in greenland ice cores carefully selected ice core data from greenland can be used to reconstruct an annual proxy north atlantic oscillation nao index this index for the past 350 years indicates that the nao is an intermittent climate oscillation with temporally active coherent and passive incoherent phases no indication for a single persistent multiannual nao frequency is found in active phases most of the energy is located in the frequency band with periods less than about 15 years in addition variability on time scales of 80 to 90 years has been observed since the mid 19th century

simulation of the last 21 000 years using accelerated transient boundary conditions abstract the earth system model of intermediate complexity ecbilt clio has been used for transient simulations of the last deglaciation and the holocene the forcing effects of the ice sheets greenhouse gas concentrations and orbital configurations are prescribed as time varying boundary conditions in this study two key aspects of the transient simulations are investigated which are of broader relevance for long term transient paleoclimate modeling the effect of using accelerated boundary conditions and of uncertainties in the initial state simulations with nonaccelerated boundary conditions and an acceleration factor 10 were integrated these simulations show that the acceleration can have a significant impact on the local climate history in the outcropping regions of the high southern latitudes and the convective regions in the north atlantic the acceleration leads to damped and delayed temperature response to the boundary conditions furthermore uncertainties in the initial state can strongly

quaternary ostracods as palaeoceanographic indicators a case study off southern australia abstract there is increasing use of ostracods in palaeoceanographic interpretation yet few comparisons have been made with existing foraminiferal indicators this paper examines ostracod records from two cores taken off southern australia and compares them with foraminiferal records of abundance and dissolution core e55 6 from the continental margin of victoria is located in 2346 m water depth core e27 30 located south of tasmania in a water depth of 3552 m lies to the north of the present position of the subtropical convergence while benthic foraminiferal abundances parallel ostracod abundances in core e55 6 this is not the case in core e27 30 in the latter core peaks in ostracod abundance are offset from peaks in foraminiferal abundance this is attributed to high phytodetrital input associated with the subtropical convergence an ostracod based dissolution index is compared with foraminiferal dissolution data from both cores the ostracod dissolution index shows greater sensitivity than foraminiferal fragmentation in water depths well above the lysocline and suggests that carbonate dissolution at these depths may be underestimated using foraminiferal indices the impact of dissolution on ostracods can also be seen as a reduction in abundance this is evident in both cores although the impact is greater in the shallower core suggesting that carbonate saturation may be a factor in the distribution of ostracods in the deep sea further investigation of the effects of carbonate saturation on individual ostracod taxa will enhance their utility as palaeoceanographic tools

impact of late quaternary environmental changes on deep sea benthic foraminiferal faunas of the red sea abstract fluctuations in abundance diversity and species composition of benthic foraminifera from two sites of the northern and southern red sea indicate strong variability of deep sea ecosystems during the last four glacial to interglacial cycles in total five and four different benthic foraminiferal assemblages have been identified in the northern core and southern core respectively comparison with recent faunas from the red sea and adjacent oceans allowed the reconstruction of temporal changes in deep water ventilation salinity and food availability at the seafloor generally the abundance of infaunal and miliolid taxa increase during glacial intervals indicating increased organic matter fluxes oxygen decrease and salinity increase in deep waters during these times these fluctuations are attributed to enhanced oxygen consumption rates and temporarily reduced deep water formation in the northern red sea during glacial intervals the recorded environmental changes are a reflection of both high and low latitude climate changes the northern red sea is mainly influenced by glacio eustatic sea level fluctuations that control deep water formation rates and by mid latitude climate changes of the mediterranean region that control surface productivity in contrast deep sea ecosystem variability of the southern red sea is additionally influenced by low latitude climate changes attributed to the ne monsoon intensity that drives the inflow of nutrient rich surface waters from the gulf of aden these results demonstrate the high sensitivity of deep sea ecosystems of the red sea to both global and regional climate changes

palaeoclimate north atlantic climate swings the north atlantic oscillation has shown high variability over the past few decades a two hundred year long temperature reconstruction from a bermuda coral suggests a link to recent climate warming

generation of the benthic foraminiferal assemblage theory and preliminary data abstract the production of benthic foraminiferal communities is filtered through taphonomic mainly destructive processes within the sediments to generate the fossil assemblage both the production and the taphonomy depend on bottom water oxygen content and flux of organic carbon to the seabed an examination of the relationships of processes generating the fossil assemblage to oxygen and organic carbon supply is made using pore water geochemical measurements to estimate carbon flux for locations in the gulf of mexico and the central california margin the locations are plotted in a three dimensional field with bottom water oxygen content organic carbon flux and sediment depth as the axes then the response of foraminiferal standing stock taphonomic processes and the developing fossil assemblage to the field is investigated variation in the vertical stratification of foraminiferal standing stock and test production species stratification taphonomic process intensity and stratification and sediment bioturbation lead to marked differences in the way the fossil assemblage is generated across the oxygen content organic carbon flux field the result is that the oxygen carbon flux field has a significant impact on the fossil assemblage through the interaction of biological and biogeochemical processes in the sediments a model of this interaction is investigated to show how its elements change across the oxygen carbon flux field and how these affect the generation of the fossil assemblage

an ocean model s response to north atlantic oscillation like wind forcing the response of the atlantic ocean to north atlantic oscillation nao like wind forcing was investigated using an ocean only general circulation model coupled to an atmospheric boundary layer model a series of idealized experiments was performed to investigate the interannual to multi decadal frequency response of the ocean to a winter wind anomaly pattern overall the strength of the sst response increased slightly with longer forcing periods in the subpolar gyre however the model showed a broad response maximum in the decadal band 12 16 years

perturbation at the sea floor during the paleocene eocene thermal maximum evidence from benthic foraminifera at contessa road italy abstract detailed analyses of the benthic foraminiferal assemblages extracted with the cold acetolyse method together with high resolution geochemical and mineralogical investigations across the paleocene eocene p e boundary of the classical succession at contessa road western tethys allowed to recognize and document the paleocene eocene thermal maximum petm interval the position of the benthic extinction event bee and the early recovery of benthic faunas in the aftermath of benthic foraminiferal extinction the stratigraphical interval spanning the p e boundary consists of dominantly pelagic limestones and two prominent marly beds benthic foraminifera indicate that these sediments were deposited at lower bathyal depth not deeper than 1000 1500 m the carbon isotope excursion cie interval is characterized by high barite abundance with a peak at the base of the same stratigraphic interval indicating a complete although condensed record of the early cie a succession of events and changes in the taxonomic structure of benthic foraminifera has been recognized that may be of use for supra regional stratigraphic correlation across the p e boundary interval the composition of the benthic foraminiferal assemblages dominated by infaunal taxa indicates mesotrophic and changing conditions on the sea floor during the last 45 kyr of the paleocene the bee occurs at the base of the cie within the lower marly bed and it is recorded by the extinction of several deep water cosmopolitan taxa then the lysocline ccd rose and severe carbonate dissolution occurred preservation deteriorated the faunal density and simple diversity dropped to minimum values and a peak of glomospira spp has been observed stress tolerant and opportunistic groups represented mainly by bi and triserial taxa dominate the low diversity post extinction assemblages indicating a benthic foraminiferal recovery under environmental unstable conditions probably within a context of sustained food transfer to the bottom a three phase pattern of faunal recovery is recognizable at first the lysocline ccd started to descend and then recovered small sized bulimina oridorsalis umbonatus and tappanina selmensis rapidly repopulated the severely stressed environment later on siphogenerinoides brevispinosa massively returns dominating the assemblage together with other buliminids nuttallides truempyi and anomalinoides sp 1 finally a marked drop in abundance of s brevispinosa is followed by a bloom of the opportunistic and recolonizer agglutinated pseudobolivina that for the first time is recorded within the main cie a second interval of dissolution but less severe than the previous one has been recognized within the upper marly bed uppermost part of the main cie interval and it is interpreted as a renewed less pronounced shoaling of the lysocline ccd that interrupted the recovery of benthic faunas this further rise likely represents a response to persistent instability of ocean geochemistry in this sector of the tethys before the end of the cie in the cie recovery and post cie intervals the composition of the benthic foraminiferal assemblages suggests mesotrophic and unstable conditions at the sea floor according to the geochemical proxy for redox conditions the deposition of the petm sediments at contessa road occurred in well oxygenated waters leading out a widespread oxygen depletion as major cause of the bee changing oceanic productivity carbonate corrosivity and global warming appear to have played a much more important role in the major benthic foraminiferal extinction at the p e boundary

modes of climate variability synthesis and review of proxy based reconstructions through the holocene abstract modes of climate variability affect global and regional climates on different spatio temporal scales and they have important impacts on human activities and ecosystems as these modes are a useful tool for simplifying the understanding of the climate system it is crucial that we gain improved knowledge of their long term past evolution and interactions over time to contextualise their present and future behaviour we review the literature focused on proxy based reconstructions of modes of climate variability during the holocene i e the last 11 7 thousand years with a special emphasis on i proxy based reconstruction methods ii available proxy based reconstructions of the main modes of variability i e el nino southern oscillation pacific decadal variability atlantic multidecadal variability the north atlantic oscillation the southern annular mode and the indian ocean dipole iii major interactions between these modes and iv external forcing mechanisms related to the evolution of these modes this review shows that modes of variability can be reconstructed using proxy based records from a wide range of natural archives but these reconstructions are scarce beyond the last millennium partly due to the lack of robust chronologies with reduced dating uncertainties technical issues related to proxy calibration and difficulty elucidating their stationary impact or not on regional climates over time while for each mode the available reconstructions tend to agree at mutidecadal timescales they show notable disagreement on shorter timescales beyond the instrumental period the reviewed evidence suggests that the intrinsic variability of modes can be modulated by external forcing such as orbital solar volcanic and anthropogenic forcing the review also highlights some modes experience higher variability over the instrumental period which is partly ascribed to anthropogenic forcing these features stress the paramount importance of further studying their past variations using long climate proxy records for the progress of climate science

benthic foraminiferal abundance and stable isotope changes in the indian ocean sector of the southern ocean during the last 20kyr paleoceanographic implications abstract benthic foraminiferal faunas and benthic stable isotopes during the last 20 kyr were investigated in core md02 2488 46 28 8 s 88 01 3 e 3420 m water depth from the southeast indian ocean sector of the southern ocean in order to document paleoceanographic changes from the last glacial through deglaciation and into the holocene variations occurred in the accumulation rates species composition diversity and stable isotopes during the last 20 kyr the benthic 18o and 13c records during the last 28 kyr show that no significant deep water circulation changes took place before 15 6 calendar kyr ka the 13c increase at 15 6 ka is interpreted as reflecting the arrival of better ventilated deep waters at the site and is associated with the progressive increase in of miliolids from 15 ka to 0 ka an interval 16 15 ka of low benthic foraminiferal accumulation rates bfars and an increase in the relative abundance of stainforthia complanata deep waters were 2 2 0 4 c colder during the last glacial than at present carbonate dissolution proxies indicate that carbonate dissolution was higher during the last glacial than during the last deglacial and holocene bfars and the percentage of species indicative of high productivity suggest that the flux of organic matter resulting from surface water productivity was generally higher between 20 and 13 ka than between 12 and 0 ka consistent with the observed higher proportion of biosiliceous sediment at 20 14 ka and published records the combined percentages of the two most abundant species alabaminella weddellensis and epistominella exigua phytodetritus species suggest that seasonality of productivity intermittency of primary productivity fluctuated over the last 20 kyr and was higher during the last glacial and deglaciation 20 10 ka compared with the holocene 10 0 ka the relative abundances of a weddellensis and e exigua do not covary over the last 20 kyr an observation also reported from other areas

five hundred years of gridded high resolution precipitation reconstructions over europe and the connection to large scale circulation we present seasonal precipitation reconstructions for european land areas 30 w to 40 e 30 71 n given on a 0 5 0 5 resolved grid covering the period 1500 1900 together with gridded reanalysis from 1901 to 2000 mitchell and jones 2005 principal component regression techniques were applied to develop this dataset a large variety of long instrumental precipitation series precipitation indices based on documentary evidence and natural proxies tree ring chronologies ice cores corals and a speleothem that are sensitive to precipitation signals were used as predictors transfer functions were derived over the 1901 1983 calibration period and applied to 1500 1900 in order to reconstruct the large scale precipitation fields over europe the performance quality estimation based on unresolved variance within the calibration period of the reconstructions varies over centuries seasons and space highest reconstructive skill was found for winter over central europe and the iberian peninsula precipitation variability over the last half millennium reveals both large interannual and decadal fluctuations applying running correlations we found major non stationarities in the relation between large scale circulation and regional precipitation for several periods during the last 500 years we identified key atmospheric modes for southern spain northern morocco and central europe as representations of two precipitation regimes using scaled composite analysis we show that precipitation extremes over central europe and southern spain are linked to distinct pressure patterns due to its high spatial and temporal resolution this dataset allows detailed studies of regional precipitation variability for all seasons impact studies on different time and space scales comparisons with high resolution climate models as well as analysis of connections with regional temperature reconstructions

correlation between faunal transitions of benthic foraminifera and ballasting of particulate organic carbon by siliceous plankton during the holocene off san in district southwestern japan we investigated the biotic response of benthic foraminifera rhizaria to holocene paleoceanographic changes in a upper bathyal environment by examining fossil benthic foraminifera younger than 13

spatial and temporal organic carbon burial along a fjord to coast transect a case study from western norway we investigated spatial and temporal changes in accumulation rate and source of organic carbon on a gradient along the lysefjord and the more coastal hogsfjord western norway this was achieved th

observed impact of atlantic sst anomalies on the north atlantic oscillation the large scale patterns of covariability between monthly sea surface temperature sst and 500 mb height anomalies z500 in the atlantic sector are investigated as a function of time lag in the ncep ncar reanalysis 1958 97 in agreement with previous studies the dominant signal is the atmospheric forcing of sst anomalies but statistically significant covariances are also found when sst leads z500 by several months in winter a panatlantic sst pattern precedes the north atlantic oscillation nao by up to 6 months such long lead time covariance is interpreted in the framework of the stochastic climate model reflecting the forcing of the nao by persistent atlantic sst anomalies a separate analysis of midlatitudes 208 708n and tropical 208s 208n sst anomalies reveals that the bulk of the nao signal comes from the midlatitudes a dipolar anomaly with warm sst southeast of newfoundland and cold sst to the northeast and southeast precedes a positive phase of the nao and it should provide a prediction of up to 15 of its monthly variance several months in advance since the forcing sst pattern projects significantly onto the tripole pattern generated by the nao these results indicate a positive feedback between the sst tripole and the nao with a strength of up to 25 mk 21 at 500 mb or 2 3 mb k21 at sea level additionally a warming of the tropical atlantic 208s 208n roughly symmetric about the equator induces a negative nao phase in early winter this tropical forcing of the nao is nearly uncorrelated with and weaker than that resulting from the midlatitudes and is associated with shorter lead times and reduced predictive skill

global sst influence on twentieth century nao variability recent studies have suggested that sea surface temperature sst is an important source of variability of the north atlantic oscillation nao here we deal with four basic aspects contributing to this issue 1 we investigate the characteristic time scales of this oceanic influence 2 quantify the scale dependent hindcast potential of the nao during the twentieth century as derived from sst driven atmospheric general circulation model agcm ensembles 3 the relevant oceanic regions are identified corresponding sst indices are defined and their relationship to the nao are evaluated by means of cross spectral analysis and 4 our results are compared with long term coupled control experiments with different ocean models in order to ensure whether the spectral relationship between the sst regions and the nao is an intrinsic mode of the coupled climate system involving the deep ocean circulation rather than an artefact of the unilateral sst forcing the observed year to year nao fluctuations are barely influenced by the sst on the decadal time scales the major swings of the observed nao are well reproduced by various ensembles from the middle of the twentieth century onward including the negative state in the 1960s and part of the positive trend afterwards a six member echam4 t42 ensemble reveals that the sst boundary condition affects 25 of total decadal mean and interdecadal trend nao variability throughout the twentieth century the most coherent nao related sst feature is the well known north atlantic tripole additional contributions may arise from the southern pacific and the low latitude indian ocean the coupled climate model control runs suggest only the north atlantic sst nao relationship as being a true characteristic of the coupled climate system the coherence and phase spectra of observations and coupled simulations are in excellent agreement confirming the robustness of this decadal scale north atlantic air sea coupled mode

decoupling of carbonate preservation carbonate concentration and biogenic accumulation a 400 kyr record from the central equatorial pacific ocean in order to investigate the paleoceanographic record of dissolution of calcium carbonate caco3 in the central equatorial pacific ocean we have studied the relationship between three indices of foraminiferal dissolution and the concentration and accumulation of caco3 opal and corg in core wec8803b gc51 1 3 n 133 6 w 4410 m this core spans the past 413 kyr of deposition and moved in and out of the lysoclinal transition zone during glacial interglacial cycles of caco3 production and dissolution the record of dissolution intensity provided by foraminiferal fragmentation the proportion of benthic foraminifera and the foraminiferal dissolution index consistently indicates that the past corrosion of pelagic caco3 in the central equatorial pacific does not vary with the observed sedimentary concentration of caco3 although there is a weak low frequency variation 100 kyr in dissolution intensity it is unrelated to sedimentary caco3 concentration there are many shorter lived episodes where high caco3 concentration is coincident with poor foraminiferal preservation and where conversely low caco3 concentration is coincident with superb foraminiferal preservation spectral analyses indicate that dissolution maxima consistently lagged glacial maxima manifest by the specmap 18o stack in the 100 kyr orbital band additionally there is no relationship between dissolution and the accumulation of biogenic opal or corg or between dissolution and the burial ratio of corg cinorg calculated from corg and caco3 because previous studies of this core strongly suggest that surface water productivity varied closely with caco3 accumulation both the mechanistic decoupling of carbonate dissolution from caco3 concentration and from biogenic accumulation and the substantial phase shift between dissolution and global glacial periodicity effectively obscure any simple link between export production caco3 concentration and dissolution of sedimentary caco3

upwelling intensity and ocean productivity changes off cape blanc northwest africa during the last 70 000 years geochemical and micropalaeontological evidence abstract the accumulation of biogeochemical organic carbon calcium carbonates molybdenum and iodine micropalaeontological benthic foraminifera and terrigenous markers grain size si al zr al k al over the last 70 000 years in one core sedorqua 11k on the northwest african margin off cap blanc has been used to reconstruct past variations of local upwelling intensity and oceanic productivity the study demonstrates that productivity in this area increased during stage 3 particularly between 40 000 and 50 000 yr b p and during the last deglaciation between 6000 and 15 000 yr b p during most of isotopic stage 2 and particularly during the last glacial maximum productivity was much lower these variations can be attributed to changes in local wind stress and seasonality that are related to variability in monsoon pressure intensity because of the establishment of upwelling cells over the shelf due to high sea level the conditions of sedimentation during the last 5 6 thousend years on the upper slope site 11k are largely dominated by advection from the shelf leading to strong sorting prior to deposition advection seems to have been minor during the other periods of enhanced productivity a conceptual model is proposed to link the productivity variations to atmospheric circulation in particular to the wind stress direction and seasonality

glaciological investigations in the crete area central greenland a search for a new deep drilling site the results of the 1984 85 post gisp campaigns in central greenland are presented eight ice cores were obtained some spanning up to 360 years we present i geographical positions and elevations at the drill sites

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

northeastern atlantic benthic foraminifera during the last 45 000 years changes in productivity seen from the bottom up we studied benthic foraminifera from the last 45 kyr in the 63 mu m size fraction in biogeochemical ocean flux studies bofs cores 5k 50 degrees 41 3 n 21 degrees 51 9 w depth 3547 m and 14k 58 degrees 37 2 n 19 degrees 26 2 w depth 1756 m at a time resolution of several hundreds to a thousand years the deepest site showed the largest fluctuations in faunal composition species richness and benthic foraminiferal accumulation rates the fluctuations resulted from changes in abundance of epistominella exigua and alabaminella weddellensis in the present oceans these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor the phytodetritus species had very low relative abundances and accumulation rates during the last glacial maximum a strong increase in absolute and relative abundance of e exigua and a weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer neogloboquadrina pachyderma s and the increase in abundance of warmer water planktonic species such as globigerina bulloides this strong increase in relative abundance of the phytodetritus species and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor and thus probably of surface productivity when the polar front retreated to higher latitudes the abundance of phytodetritus species decreased during the younger dryas but not to the low levels of fully glacial conditions during heinrich events periods of excessive melt water formation and ice rafting benthic accumulation rates were very low as were the absolute and relative abundances of the phytodetritus species supporting suggestions that surface productivity was very low during these events in both cores pullenia and cassidulina species were common during isotope stages 2 3 and 4 as were bolivinid buliminid and uvigerinid species high relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor in our cores relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates and we can thus not interpret them as indicative of increased productivity during glacials the percentage of these low oxygen species calculated on a phytodetritus species free basis decreased slightly at deglaciation at 5k but not at 14k this suggests that decreased production of north atlantic deep water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern north atlantic at 3547 m depth but not at 1756 m in conclusion major changes in deep sea benthic foraminiferal faunas over the last 45 000 years in our cores from the northeastern atlantic were the result of changes in surface water productivity not of changes in deep water circulation productivity was lower during the glacial probably because of extensive ice cover

glacial and holocene stable isotope distributions in the southeastern indian ocean we have reconstructed glacial interglacial variations in cibicidoides wuellerstorfi 13c and 18o in the southeastern indian ocean using depth transects of cores from off western and southern australia we compare these new results with published stable isotope records to constrain glacial interglacial changes in indian ocean chemistry and circulation the strong last glacial maximum lgm deep water 13c depletions previously observed for the northeastern indian ocean did not extend throughout the low latitude glacial indian ocean we observe only a small lgm 13c decrease off southern australia in marked contrast to the strong lgm 13c depletions observed in many cores from the atlantic and western indian sectors of the southern ocean it is not yet clear whether the very low lgm 13c values in the deep northern and southwestern indian ocean are an artifact of surface ocean productivity or whether they reflect real gradients in deep water chemistry

the late miocene onset of high productivity in the benguela current upwelling system as part of a global pattern abstract we have examined the history of the elevated primary productivity associated with the benguela current upwelling system off southwest africa using sediments from 7 5 to 4 8 ma at ocean drilling program site 1085 in the middle cape basin sedimentation rates are low until 6 9 ma low accumulation rates of benthic foraminifers and organic carbon indicate that biological productivity was also low paleoproductivity dramatically increased at 6 7 6 5 ma and was highly variable until 4 8 ma with productivity maxima during cooler periods the presence of radiolarian opal only between 5 8 and 5 2 ma suggests an interlude of silica rich intermediate water in the cape basin the onset of heightened productivity under the benguela current is mirrored by similar increases reported between 6 9 and 6 7 ma in the tropical eastern pacific the western and northern pacific and the indian ocean the similarity between the patterns at site 1085 and in the pacific and indian oceans suggests that the dramatic productivity increase off southwest africa is part of a global response to paleoceanographic changes

a well verified multiproxy reconstruction of the winter north atlantic oscillation index since a d 1400 abstract a new well verified multiproxy reconstruction of the winter north atlantic oscillation nao index is described that can be used to examine the variability of the nao prior to twentieth century greenhouse forcing it covers the period a d 1400 1979 and successfully verifies against independent estimates of the winter nao index from european instrumental and noninstrumental data as far back as 1500 the best validation occurs at interannual timescales and the weakest at multidecadal periods this result is a significant improvement over previous proxy based estimates which often failed to verify prior to 1850 and is related to the use of an extended reconstruction model calibration period that reduced an apparent bias in selected proxies associated with the impact of anomalous twentieth century winter nao variability on climate teleconnections over north atlantic sector land areas although twentieth century nao variability is somewhat unusual comparable periods of persistent positive phase

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

the sedimentary record of pelagic biogeography abstract sedimentary remains of fossilizable marine organisms chiefly microplanktonic ones coccolithophorids silicoflagellates diatoms dinoflagellates radiolarians foraminifers have long been used for biogeographic surveys usually with the aim of unravelling paleoenvironmental settings utilization of bottom deposits rather than plankton samples has some advantages for this purpose thanatocoenoses require smaller sample sizes materials are more readily available and they eliminate the small time scale variability which obscures long term trends on the other hand the sedimentary imprint of planktonic distributional patterns is often severely distorted by fragmentation and dissolution of the biogenic remains reworking of sediments winnowing and lateral advection of shells especially toward lower latitudes seasonally and interannually variable output rates and the integration of vertically heterogeneous assemblages the biases derived from these processes are reviewed and the need for more information on selective dissolution vertical distribution patterns and planktonic reproduction and output rates is stressed given the assumptions used in paleoenvironmental studies distributional information drawn from sediment samples is less prone to yielding biased information when applied to these surveys than to bio or paleobiogeographic investigations albeit the former can also be significantly affected as a result of changes in the traits that govern the formation of biogenic sediments

a 35 000 year record of changes in the eastern indian ocean offshore sumatra article i nfo we have examined the upper 276 cm of deep sea core bar9403 taken at a water depth of 2034 m offshore the southern portion of sumatra in the eastern indian ocean using several micropalaeontological proxies faunal counts and stable isotopes of oxygen and carbon of planktic and benthic foraminifers as well as floral counts of dinoflagellates were obtained to reconstruct conditions in the oceans over the last 35 000 years at times we found that when benthic foraminifers indicate high organic content values at the bottom of the ocean this is not paralleled by high productivity signals at the sea surface but instead must relate to changes in bottom water circulation as a result of slower water circulation the marine isotopic stages mis 3 1 are clearly differentiated by benthic and foraminiferal assemblages as well as dinoflagellates and their cysts mis 3 is characterised by a much sharper than today thermocline that was closer to the sea surface and by the absence of a low salinity barrier layer which today results from high monsoonal rains the absence of the latter persisted during the last glacial period mis 2 when bottom circulation must have been reduced and high percentages of organic matter occurred on the sea floor combined with low dissolved oxygen levels the deglaciation is marked by a change in salinity at the sea surface as seen by the dinoflagellates and planktic foraminifers and progressive alteration of the thermocline was detected by foraminifers suggesting a less productive deep chlorophyll maximum in contrast with mis 3 and 2 monsoonal activity commenced around 15 000 cal years ago and was well established 2000 years later the holocene is marked by a significant increase in river discharge to the ocean pulsed by the delivery of organic matter to the sea floor despite overall oligotrophic conditions at and near the sea surface induced by a permanent low salinity cap we did not identify obvious and persistent upwelling conditions offshore sumatra for the last 35 000 years

do benthic foraminifer records represent a productivity index in oxygen minimum zone areas an evaluation from the oman margin arabian sea abstract benthic foraminifer accumulation rates bfar and benthic to planktic foraminifer ratios b p have been suggested to represent an index of paleoproductivity in the world oceans it is shown here however that bfar and b p do not record the surface water productivity signal in the intense upwelling and oxygen minimum zone omz along the oman margin greater bfar and b p values are noticed during the last glacial period when the monsoon and upwelling strength were weaker and the surface water productivity was reduced this is in contrast to the suggestion that bfar and b p values are an indication of enhanced productivity on the other hand bfar and b p values were lower during the holocene as a consequence of intensified monsoon and upwelling and resulting enhanced productivity in the arabian sea this appears to suggest that bfar and b p do not reflect the productivity variations in the omz of the arabian sea we speculate that dissolved oxygen concentrations might instead be controlling the benthic foraminifer abundance

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

warming driven mass extinction in the early toarcian early jurassic of northern and central spain correlation with other time equivalent european sections abstract causes of the major mass extinction recorded during the early toarcian early jurassic are controversial many authors have concluded that the mass extinction is caused by the widespread oceanic anoxia derived from a postulated early toarcian oceanic anoxic event etoae supposedly synchronous in all basins and global in extent another group of papers links the mass extinction with a major climate change that occurred synchronously with the mass extinction the results of the study of five sections of the uppermost pliensbachian and lower middle toarcian deposits located in northern and central spain are presented detailed ammonite based biostratigraphy coupled with stable isotope analysis of belemnite calcite and bulk carbonates as well as total organic carbon toc analyses have been performed in all sections records of the vertical distribution of mainly benthic fossils have been compiled in four of the studied sections results obtained in the spanish outcrops have been compared and correlated with other european sections the excellent mutual relation between the patterns of the early toarcian progressive warming and the concomitant progressive losses of species evidences a cause and effect relationship between the increase of temperature and the mass extinction from an uppermost pliensbachian cooling interval warming started at the lower toarcian tenuicostatum zone increase of average seawater palaeotemperature is associated with a progressive and substantial drawdown in the number of species of nektonic planktonic and benthic organisms representing the extinction interval a prominent increase in seawater temperature occurred around the lower toarcian tenuicostatum serpentinum zonal boundary average temperatures at the serpentinum zone increased about 7 c marking the extinction boundary the high temperatures continued during the middle toarcian bifrons chronozone representing the repopulation interval the anoxia linked to the postulated etoae cannot be the responsible for the mass extinction because it has been synchronously recorded in the oxygenated environments of many european and northern african platforms deposition of laminated organic rich black shale facies above 5 wt toc indicating anoxic environments was mostly confined geographically to the western europe euxinic basin and mainly deposited after the extinction event during the interval of faunal recovery

oxygenation changes in the deep western arabian sea during the last 190 000 years productivity versus deepwater circulation 1 fluctuations in the abundance of selected foraminiferal indicator species and diversity allowed the reconstruction of changes in deepwater oxygenation and monsoon driven organic matter fluxes in the deep western arabian sea during the last 190 kyr times of maximum surface production coincide with periods of intensified sw monsoon as shown by the abundance of globigerina bulloides and enhanced carbonate corrosion benthic ecosystem variability in the deep arabian sea is not exclusively driven by variations in monsoonal upwelling and related organic matter supply to the seafloor but also by changes in deepwater ventilation deepening of the base of the oxygen minimum zone omz below 1800 m water depth is strongly coherent on the precessional band but lags proxies of sw monsoon strength by 4 to 6 kyr the out of phase relationship between omz deepening and maximum sw monsoon strength is explained by temporal changes in the advection of oxygen rich deepwater masses of north atlantic and antarctic origin this process affected the remineralization and burial efficiency of organic matter in the deep arabian sea resulting in the observed phase lag between maximum monsoon strength and organic carbon preservation

long term characteristics of simulated ice deformation in the baltic sea 1962 2007 1 the north atlantic oscillation nao index is a frequently used measure for the mean winter conditions in northern europe a positive high index is associated with strong westerlies and anomalous warm temperatures the effects on sea ice conditions in the baltic sea are twofold warm temperatures prevent sea ice formation if ice is present nevertheless the strong winds can promote the formation of ice ridges which hinders ship traffic we use an ocean sea ice model to investigate the nao impact on the ridged ice area fraction in the baltic during 1962 2007 our simulations indicate that in the northern bothnian bay a high nao index is related to an anomalous accumulation of ridges while in the rest of the baltic sea the relationship is contrary the nao explains locally at most only 20 25 of the ridged ice fraction interannual variability which indicates the systems complexity however we find high skill with local correlations around 0 8 for annually averaged ridged ice fraction reconstructed from multilinear regression using winter averaged wind extremes surface air temperature and sea surface temperature sst this suggests that the amount of ridged ice in late winter can be derived from these routinely measured quantities in large parts of the basin it is sufficient to use the atmospheric parameters as a predictor while in the eastern bothnian bay and southern gulf of finland the sst is required to reconstruct the bulk of the ridged ice fraction

primary productivity in the western tropical atlantic follows neogene amazon river evolution the amazon river nutrient rich plume currently triggers large scale phytoplankton blooms in the otherwise oligotrophic western tropical atlantic ocean little is known about the onset and development of this high productivity system although a direct link to the transcontinental amazon river evolution can be expected the amazon submarine fan located on the brazilian equatorial margin bem contains a unique sediment archive of the river s history and associated environmental changes in the marine realm this study represents the first marine microfossil multi proxy approach applied to any sedimentary record in the submarine fan area for the time interval encompassing the onset and development of the transcontinental amazon river system to reconstruct miocene to pleistocene changes in surface and bottom water conditions we analyzed organic walled dinoflagellate cyst and benthic foraminiferal assemblages respectively moreover terrestrial and freshwater palynomorph abundances were studied to provide a link between fluvial input and marine environmental changes in addition a planktonic foraminiferal biostratigraphy is constructed to verify the available calcareous nannofossil based age model our data show that in the early mid miocene up to 13 ma limited fluvial input reached the bem and primary productivity was elevated after which distinctly low productivity conditions prevailed after the birth of the transcontinental amazon at 9 ma surface water productivity initially increased slightly consistently high surface water productivity and decreased bottom water oxygenation followed increasing terrestrial input after the early pliocene the temporal consistency between records from the amazon fan and the more distant ceara rise reflects large scale marine environmental changes followed the development of the amazon river likely related to increased climatic variability in the amazon basin during the plio pleistocene

sea surface temperatures of southern midlatitudes 0 160 kyr b p 1 late quaternary climate fluctuated between extremes of glaciations lasting 90 kyr on average and interglacial episodes lasting 10 kyr still largely unknown are the spatial and temporal evolution of these global climate states with vigorous debate still underway on the mechanisms responsible for glacial inceptions and terminations though it is widely believed that the southern hemisphere oceans play a central role in global climate changes few paleoclimate records exist from there here we present three new alkenone derived sst records from the midlatitude southern hemisphere spanning the last 160 kyr a full glacial interglacial cycle our subtropical sst records from the last glacial period are characterized by 1 warming 47 23 kyr b p when high latitudes in both hemispheres cooled and 2 milder temperatures during the penultimate glacial period than during the last glacial interval these sst features are found to be of tropical to subtropical wide extent implying increased thermal gradients at times of high latitude ice sheet growth this has implications for the vigor of atmospheric and upper ocean circulation and the transport of heat and moisture to the poles that may have been instrumental in the growth and maintenance of polar ice sheets during glacial periods

biogenic sedimentation and surface productivity changes in the southern california borderlands during the last glacial interglacial cycle abstract a variety of geochemical evidence suggests that surface productivity in the california borderlands region was 1 5 2 times higher during the last glacial relative to the holocene high accumulation rates of opaline silica and organic carbon suggest increased glacial productivity while carbonate accumulation records and c org c co 3 ratios point toward a dominantly siliceous plankton community at that time the observed productivity changes are attributed to a southerly migration of the north pacific high pressure cell which resulted in an intensification of the california current and enhanced upwelling south of 40 n during the last glacial

scale dependent reconstruction of the nao index a method is presented to reconstruct decadal variations of the north atlantic oscillation nao the spectral characteristics of the nao on time scales of decades and longer are of particular interest for the understanding of north atlantic ocean atmosphere interactions the reconstruction is based on a transfer model calibration that uses bandpass filtered time series the maximum overlap discrete wavelet transform modwt is applied for decomposing the time series variance into different time scales a total of 43 proxies including greenland ice cores and european tree ring chronologies are selected and regionally grouped providing four independent reconstructions for the period 1700 1978 the mean reconstruction agrees well with two recently published reconstructions during most of the time period however there are considerable differences in the earliest part before 1750 running correlations between the reconstructions indicate that time dependent relations exist among the different nao reconstructions the results suggest that the geographical distribution of proxies strongly affects the reconstruction and could explain some of the apparent discrepancies among the reconstructions recently published in literature in the early eighteenth century external forcing solar volcanic seems to mask the nao signature within the proxies

multiproxy reconstructions of the north atlantic oscillation multiproxy composite reconstructions of north atlantic oscillation nao indices are presented spanning the last three centuries these composite time series draw on four nearly independent reconstructions derived from different combinations of global and north atlantic sector climate proxy data e g tree rings and ice cores as well as long instrumental records a composite reconstruction based on all four series r4 extends from 1750 to 1979 while another version based on only three series r3 extends from 1701 to 1979 both composite reconstructions outperform the individual series based on correlation and verification statistics these results suggest that each individual series reflects different aspects of the nao such that when combined they yield more robust reconstructions as to be expected these composite reconstructions based on both proxy and long instrumental data yield more optimal results than individual or composite reconstructions based on proxy data alone the reconstructions presented here provide an improved means of addressing features evident in the instrumental record with respect to those of prior centuries one such feature evident in the reconstructions is an apparent increase in variance in the instrumental period relative to the past record

early oligocene glaciation and productivity in the eastern equatorial pacific insights into global carbon cycling the onset of sustained antarctic glaciation across the eocene oligocene transition eot marks a pivotal change in earth s climate but our understanding of this event particularly the role of the

spring temperature variability relative to the north atlantic oscillation and sunspots a correlation analysis with a monte carlo implementation abstract a reconstruction of past spring temperatures was analysed and compared to long term records of the north atlantic oscillation nao and sunspots this palaeoclimate reconstruction built previously using multiple proxy evidence of historical and natural sources from southwest finland explained approx 70 of the instrumental temperature variance over a spring season february june and covered the time period from 1750 to the present correlations between the nao and sunspots appear markedly high and based on monte carlo tests statistically significant p

north atlantic interdecadal variability oceanic response to the north atlantic oscillation 1865 1997 abstract in contrast to the atmosphere knowledge about interdecadal variability of the north atlantic circulation is relatively restricted it is the objective of this study to contribute to understanding how the north atlantic circulation responds to a forcing by the north atlantic oscillation nao on interdecadal timescales for this purpose the authors analyze observed atmospheric and sea surface temperature sst data along with the response of an ocean general circulation model to a realistic monthly surface flux forcing that is solely associated with the nao for the period 1865 1997 in agreement with previous studies it is shown that the relationship between the local forcing by the nao and observed sst anomalies on interdecadal timescales points toward the importance of oceanic dynamics in generating sst anomalies a comparison between observed and modeled sst anomalies reveals that the model results can be used to assess interdecadal variability of the north atlantic circulation the observed

summer temperature variations in the european alps a d 755 2004 abstract annually resolved summer temperatures for the european alps are described the reconstruction covers the a d 755 2004 period and is based on 180 recent and historic larch larix decidua mill density series the regional curve standardization method was applied to preserve interannual to multicentennial variations in this high elevation proxy dataset instrumental measurements from high low elevation grid boxes back to 1818 1760 reveal strongest growth response to current year june september mean temperatures the reconstruction correlates at 0 7 with high elevation temperatures back to 1818 with a greater signal in the higher frequency domain r 0 8 low elevation instrumental data back to 1760 agree with the reconstruction s interannual variation although a decoupling between warmer instrumental and cooler proxy data before 1840 is noted this offset is larger than during any period of overlap with more recent high elevation instrumental data even though the proxy time series

reconciling pollen stratigraphical and tree ring evidence for high and low frequency temperature variability in the past millennium abstract climate change and variability assessments require an understanding of their long term and period low frequency and short term and period high frequency variations pollen data have conventionally been thought of as a proxy of low frequency variation of past climates but of more limited applicability for studying high frequencies likewise tree rings are commonly supposed to reflect faithfully high frequency variations with additional uncertainties attributable to variations at lower frequencies here we challenge this view in the context of pollen and tree ring based temperature reconstructions from high latitude europe the two types of records are compared and it is shown that the pollen and tree ring based reconstructions exhibit similar temperature variability on centennial and longer scales these can be revealed using timescale dependent filtering the same method surmounts geochronological discrepancies thus enabling reconciliation of the proxies resulting new reconstructions validate over the instrumental period over longer intervals our new proxy fusions cover the climatic reversals of the medieval climate anomaly during the 10th to 13th centuries little ice age during the 14th to 19th centuries and 20th century warming the warmest spells occurred in association with the medieval climate anomaly and during the 20th century the coolest intervals occurred in relation to little ice age conditions the new reconstructions show that decadal temperature amplitude has been approximately 2 5 c in the past and thus considerably larger than inferred from spatially large scale estimates of temperature anomalies

ecology of deep sea benthic foraminifera in the north atlantic during the last glaciation food or temperature control abstract in this study we explore the paleoecology of nineteen species and two species groups of deep sea benthic foraminifera in relation to bottom water temperature and food supply in the central north atlantic during the last glaciation 60 000 28 000 years bp the study is based on core so82 02ggc taken from 1730 m water depth on the western flank of reykjanes ridge the climate of the investigated period was extremely unstable interrupted by thirteen warmings and coolings the so called dansgaard oeschger events at so82 02ggc surface and bottom water temperatures varied with up to 5 c between the warm interstadials and the cold stadials surface productivity as indicated by the flux of planktic foraminifera varied with a factor of up to ten the dansgaard oeschger events had a significant impact on the benthic foraminiferal faunas which experienced up to 70 replacement between the interstadials and stadials multivariate analysis reveals that the investigated species can be separated into two groups group 1 including bulimina costata brizalina subspinescens epistominella decorata and trifarina angulosa was attracted to higher temperatures and high food supply group 2 including pullenia bulloides valvulineria laevigata and melonis barleeanus was attracted to colder water and low food supply three species belonging to the cold group cibicidoides wuellerstorfi oridorsalis umbonatus and eponides tumidulus are almost exclusively confined to sediments rich in ice rafted detritus a few species including nonionella iridea and epistominella vitrea show opportunistic behaviour most species are epifaunal to shallow infaunal and live today in oligotrophic to mesotrophic habitats our investigations indicate that temperature was the primary factor responsible for the relative abundance and main grouping of species however four species show little influence by temperature and several perhaps most were clearly also affected by food supply

benthic environmental changes in the eastern mediterranean sea during sapropel s5 deposition abstract high resolution benthic foraminiferal analyses of sediment cores collected at different sites in the eastern mediterranean sea revealed that profound changes occurred in deep sea ventilation over the past 124 119 ka bp the three cores sin97 gc01 ban89 gc09 bd02 gc01 were selected in order to investigate middle and deep bathyal ecosystems in the eastern mediterranean basin at site sin97 gc01 933 m water depth urania basin the presence of benthic fauna in the sapropel layer and the gradual increase in benthic foraminiferal abundance from the middle part of the sapropel suggest that the sea floor was partially ventilated and that re oxygenation had increased considerably during the late phase of s5 deposition cores ban89 gc09 2011 m water depth napoli dome and bd02 gc01 2470 m water depth ionian sea show a different pattern during sapropel s5 benthic abundance and diversity strongly decrease and microfauna even disappears in some levels suggesting the establishment and maintenance of stagnant and anoxic conditions at the seafloor until the end of s5 deposition in the deepest part of the basin the re establishment of the benthic foraminiferal community at the top of the s5 layer indicates a relatively slow bottom re oxygenation at the southernmost site the foraminiferal assemblage records a short oxygenation pulse during the deposition of sapropel s5 linked to a short cold spell the results of this study suggest that the evolution of the dysoxic anoxic conditions as well as the re oxygenation pattern at the end of the stagnant period were characterised by spatial and temporal variability possibly controlled by basin physiography

temperature accumulation and ice sheet elevation in central greenland through the last deglacial transition we present a combined heat and ice flow model constrained by measurements of temperature in the greenland ice sheet project 2 gisp2 borehole and by the gisp2 18o record and depth age scale which determines a history of temperature accumulation rate and ice sheet elevation for the past 50 000 years in central greenland important results are that the temperature increase from average glacial to holocene conditions was large approximately 15 c with a 20 c warming from late glacial to holocene that the average accumulation rate during the last glacial maximum between 15 and 30 kyr b p was 5 5 to 7 cm yr 1 approximately 25 of the modern accumulation rate that long term 500 1000 years averaged accumulation rate and temperature have been inversely correlated during the most recent 7 millennia of the holocene and that the greenland ice sheet probably thickened during the deglacial transition the inverse correlation of accumulation rate and temperature in the mid and late holocene suggests that the greenland ice sheet is more prone to volume reduction in a warmed climate than previously thought and demonstrates that accumulation rate is not a reliable proxy for temperature the elevation history of the ice sheet is poorly constrained by the model and independent evidence is needed we also present a simple estimate of the response time for thinning of the interior region of an ice sheet due to retreat of its margins this was approximately 1900 years for central greenland during deglaciation

a comparison of multiple proxies for export production in the equatorial pacific 1 several commonly used paleoproductivity proxies were compared to evaluate the validity of assumptions and limitations associated with each proxy export production fluxes cexport over glacial interglacial timescales were calculated from previously developed proxy specific algorithms at ttn013 pc72 and ttn013 pc114 both located in the equatorial pacific comparison of data from the same core intervals yields conflicting results despite calibrations based on the same core top samples the periodicity of marine barite excess ba and excess al based cexport records is similar the relative magnitude of cexport when calculated using excess ba and algorithms based on sediment trap data is significantly different than records based on core top calibrations particularly during glacial intervals at both sites bulk sedimentary al ti and ba ti ratios covary however these ratios do not correspond with the downcore records of their respective excess concentrations and their accumulation rates or with contemporaneous records based on marine barite excess ba and excess al accumulation although downcore records based on sediment mass accumulation rates may be compromised by sediment focusing this process cannot explain all the differences observed among the various data sets presented here this implies that some or all of these proxies do not exclusively respond to changes in export production the contradictions among these data highlight the importance of addressing inconsistencies among paleoproxies and re examining assumptions imbedded in proxy fundamentals prior to applying paleoproductivity proxies and interpreting paleoceanographic records

oceanic influence on the north atlantic oscillation and associated northern hemisphere climate variations 1959 1993 the north atlantic oscillation nao ex hibits variations at interannual to multidecadal time scales and is associated with climate variations over eastern north america the north atlantic europe and north africa therefore it is very important to understand causes of these nao variations and assess their predictability it has been hypothesized based on observations that sea surface temperature sst and sea ice variations in the north atlantic ocean influ ence the nao we describe results of an ensemble of sixteen experiments with an atmospheric general cir culation model in which we used observed sst and sea ice boundary conditions globally during 1949 1993 we show that multiyear nao and associated climate variations can be simulated reasonably accurately if re sults from a large number of experiments are averaged we also show that the ambiguous results of previous nao modeling studies were strongly influenced by the ensemble size which was much smaller than that in the present study the implications of these results for understanding and predictability of the nao are dis cussed