eastern mediterranean surface water nd during eemian sapropel s5 monitoring northerly mid latitude versus southerly sub tropical freshwater contributions abstract a well developed sapropel s5 was deposited in the eastern mediterranean during the last interglacial eemian 124 119 ka freshwater contributions to the basin at this time can be traced using the isotopic composition of nd in planktonic foraminifera this enables differentiation between radiogenic sources to the south under the influence of the african monsoon and unradiogenic sources to the north relating to the mid latitude westerlies here we compare new nd data from a core in the southeast aegean sea with published data from the ionian and levantine seas shifts towards more radiogenic nd in the lower and middle parts of sapropel s5 are most pronounced in the ionian sea record with nd and 18og ruber co varying more closely here than in the levantine and aegean seas this is consistent with a freshwater source proximal to the ionian sea site likely indicating a substantial reactivation of rivers flowing northward from the central saharan watershed the lack during s5 deposition of a noticeable shift towards more unradiogenic nd in the aegean record would exclude a large influx of water from the northern borders of the eastern mediterranean during sapropel deposition these findings support a scenario whereby the last interglacial eastern mediterranean was influenced strongly by the remote effects of an intensified african monsoon with more local precipitation in the northern borders contributing relatively little to the sea surface composition

balancing rare earth element distributions in the northwestern mediterranean sea abstract elemental concentrations of rare earth elements ree and isotopic compositions of neodymium end have been measured in three water column profiles in the north western mediterranean sea clear enrichments of ree are observed when comparing to adjacent atlantic waters suggesting ree inputs along the circulation in this area for the first time relative proportions of external sources including submarine groundwater discharges sgd have been quantified for the studied area atmospheric deposition is estimated to be the most important external source for all the ree with an average contribution of 44 followed by diffusion from porewaters which provide a 30 dissolved riverine fluxes account for 11 sgd for 10 and dissolution of remobilized surface sediments the remaining 6 mass balances accounting for seawater transport and identified external sources have been delineated for the three main water masses modified atlantic waters levantine intermediate waters and western mediterranean deep waters they show that the balances of ree in this area are dominated by seawater mass mixing superimposed on this hydrography ree vertical profiles are affected by external sources and biogeochemical cycling dissolved ree are correctly balanced in deep waters whereas substantial missing fluxes are identified in the surface and intermediate water masses additional net lree outputs and hree inputs are required in the surface waters while net output fluxes for all the ree are missing at intermediate waters the most likely process suggested here is an active reversible scavenging consistent with a stronger adsorption of lree compared to hree in the particular case of the redox sensitive cerium the most plausible mechanism to explain the net output missing fluxes is ce 3 removal by particle scavenging via oxidation to insoluble ce 4 estimated ce oxidation rates of 0 33 d 1 in surface waters agree well with previously published values exchange fluxes derived from the isotopic nd mass balance indicate higher nd scavenging in surface compared to intermediate waters

an outsider s review of the astronomical theory of the climate is the eccentricity driven insolation the main driver of the ice ages abstract although the astronomical theory of the climate also known as the milankovitch theory explains a number of key features of the paleoclimate time series especially frequency and phase distribution in terms of orbital influence on the waxing and waning of ice sheets it still faces several important unresolved challenges in this review we discuss five main challenges we believe the theory must resolve in order to survive 1 the large amplitude of the 100 ky ice age cycles 2 the switch from 41 ky to 100 ky long glaciations around 0 9 ma bp 3 the absence of significant spectral power at 413 ky over the past 1 2 ma 4 the variation in glacial cycle duration in the last 800 ky and 5 the presence of non orbital spectral peaks in the climate record but in spite of these problems we conclude that the milankovitch theory may still be a viable one at least in the original sense of hays et al science 194 1976 1121 that orbital changes somehow influenced the ice ages many investigators ourselves included appear to see the impact of orbital forcing in the data clear evidence of astronomical forcing as well as evidence which suggests that the climate system responds nonlinearly to all milankovitch orbital frequencies

rare earth element concentrations and nd isotopes in the southeast pacific ocean 1 three vertical profiles of rare earth element concentrations and nd isotopic compositions have been measured in the remote southeast pacific ocean the three stations represent contrasting environments the oligotrophic center of the gyre station gyr the transition zone east of the south tropical front station egy and the peru chile upwelling marked by a pronounced oxygen minimum station upx rare earth concentrations display nutrient like vertical profiles except at upx where surface waters are enriched at this station nd isotopic compositions are clearly more radiogenic than in the open ocean suggesting that boundary exchange process is releasing lithogenic rare earth element from the volcanic andes unexpected radiogenic values end reaching 3 7 are also observed at 2000 m at station gyr in the upper circumpolar deep water that commonly have end values around 6 exchange processes related to hydrothermal activity are suspected to produce this increase in end in the vicinity of the east pacific rise these results provide some guidance for higher resolution studies planned in this region by the international geotraces program

the hafnium neodymium isotopic composition of atlantic seawater the first full water column hafnium isotopic compositions of atlantic seawater have been obtained at seven locations from the labrador sea to the drake passage despite subpicomolar concentrations in seawater a precision of the hf isotopic measurements of 03 epsilon hf units was achieved an overall epsilon hf range between 3 1 in the labrador sea and 4 4 in antarctic bottom water was determined the distribution of which broadly reflects continental weathering inputs within particular water column profiles significant differences of up to 4 epsilon hf units occur combined with nd isotope data of the same samples it is evident that the hf isotopic composition of seawater is too radiogenic for a given nd isotopic composition and that the largest difference between expected and measured hf isotopic compositions in seawater occurs near the oldest continental crust in the labrador sea this corroborates the previous proposition which was mainly based on ferromanganese crust data that the hf isotopic composition of seawater is controlled by incongruent weathering of continental crust and possibly to some extent by hydrothermal contributions hafnium concentrations in the ocean do not increase along the deep ocean conveyer indicating an oceanic residence time of only a few hundred years which is significantly shorter than previously assumed the hf isotopic composition of past seawater can therefore serve as a proxy for short distance basin scale mixing processes and the regime and intensity of nearby continental weathering processes c 2009 elsevier b v all rights reserved

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

the hafnium and neodymium isotope composition of seawater in the atlantic sector of the southern ocean we present the first combined dissolved hafnium hf and neodymium nd concentrations and isotope compositions of deep water masses from the atlantic sector of the southern ocean eight full depth profiles were analyzed for hf and twelve for nd hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0 2 pmol kg and 0 4 pmol kg and increase to relatively constant values of around 0 6 pmol kg in the deeper water column at the stations north of the polar front pf nd concentrations increase linearly from about 10 pmol kg at depths of 200 m to up to 31 pmol kg close to the bottom indicating particle scavenging and release within the weddell gyre wg however nd concentrations are essentially constant at 25 pmol kg at depths greater than 1000 m the distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry hafnium essentially shows invariant isotope compositions with values averaging at ehf 4 6 whereas nd isotopes mark distinct differences between water masses such as modified north atlantic deep water nadw end 11 to 10 and antarctic bottom water aabw end 8 6 to 9 6 but also waters locally advected via the agulhas current can be identified by their unradiogenic nd isotope compositions mixing calculations suggest that a small fraction of nd is removed by particle scavenging during mixing of water masses north of the pf nevertheless the nd isotope composition has apparently not been significantly affected by uptake and release of nd from particles as indicated by mixing calculations a mixing envelope of an approximated north pacific and a north atlantic end member shows that nd isotope and concentration patterns in the lower circumpolar deep water lcdw can be fully explained by 30 70 percentage contributions of these respective end members

rare earth elements and neodymium isotopes in sedimentary organic matter abstract we report rare earth element ree and neodymium nd isotope data for the organic fraction of sediments collected from various depositional environments i e rivers n 25 estuaries n 18 open ocean settings n 15 and cold seeps n 12 sedimentary organic matter som was extracted using a mixed hydrogen peroxide nitric acid solution 20 h2o2 0 02 m hno3 after removal of carbonate and oxy hydroxide phases with dilute hydrochloric acid 0 25 m hcl a series of experimental tests indicate that extraction of sedimentary organic compounds using h2o2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates however this contamination is expected to be minor for ree because measured concentrations in h2o2 leachates are about two orders of magnitude higher than in the above mentioned phases the mean ree concentrations determined in the h2o2 leachates for samples from rivers estuaries coastal seas and open ocean settings yield relatively similar levels with ree 109 86 ppm mean s n 58 the organic fractions leached from cold seep sediments display even higher concentration levels 285 150 ppm mean s n 12 the h2o2 leachates for most sediments exhibit remarkably similar shale normalized ree patterns all characterized by a mid ree enrichment compared to the other ree this suggests that the distribution of ree in leached sedimentary organic phases is controlled primarily by biogeochemical processes rather than by the composition of the source from which they derive e g pore river or sea water the nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions in contrast the som extracted from marine sediments display end values that typically range between the end signatures for terrestrial organic matter inferred from the analysis of the sedimentary detrital fractions and marine organic matter inferred from the analysis of local surface seawater a notable exception is the case of organic matter om fractions leached from cold seep sediment samples which sometimes exhibit end values markedly different from both terrigenous and surface seawater signatures this suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes recycling pore water ree characterized by a distinct isotopic composition overall our results confirm that organic matter probably plays an important role in the oceanic ree budget through direct scavenging and remineralization within the water column both the high ree abundances and the shape of shale normalized patterns for leached som also suggest that om degradation in sub surface marine sediments during early diagenesis could control to a large extent the distribution of ree in pore waters benthic fluxes of organic bound ree could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins neodymium isotopes could provide useful information for tracing the origin terrestrial versus marine and geographical provenance of organic matter with potential applications in paleoceanography in particular future studies should further investigate the potential of nd isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation

simulations of northern hemisphere ice sheet retreat sensitivity to physical mechanisms involved during the last deglaciation a 3 dimensional thermomechanical ice sheet model is used to simulate the evolution of the geometry of northern hemisphere ice sheets through the last deglaciation the ice sheet model is forced by a time evolving climatology provided by the linear interpolation through time of climate snapshots simulated by the lmd5 3 atmospheric general circulation model agcm at different periods of the last deglaciation 21 15 9 6 and 0 kyr bp the agcm is driven by insolation atmospheric co2 content ice sheet configuration and sea surface temperatures although our approach is able to produce the complete continental ice retreat our simulated deglaciation presents a phase lag with reconstructions based on observational evidences this suggests that physical mechanisms related to climate forcing and or ice sheet internal dynamics are not properly represented the influence of millennial scale forcing feedback mechanisms between ice sheet elevation and surface mass balance and parameterization of the ice flow is also tested through a set of sensitivity experiments the rapid variability has a strong impact on the evolution of the ice volume because of nonlinear effects in temperature mass balance relationships fennoscandia appears to be strongly sensitive to the small scale ice sheet instability both ice sheets are to some extent sensitive to an increased basal sliding

warming salting and origin of the tyrrhenian deep water 1 data collected from 1996 to 2001 down to 3 500 m in the tyrrhenian sub basin with ship handled and moored instruments show 5 year t and s trends 0 016 c yr 0 008 yr that are the largest ever evidenced in mediterranean deep waters this is not consistent with the usual hypothesis that tyrrhenian deep water tdw is a mixture of eastern water flowing from the sicily channel and western water flowing from the sardinia channel partly since both are reported to encounter lower trends we argue that tdw might result from a dense water formation process occurring within the tyrrhenian itself in a region never reported up to now east of the bonifacio strait whatever the validity of our hypothesis climatic changes are occurring in the whole sea and are efficiently specified with long time series

tracing past ocean circulation to understand how ocean circulation and climate may change in the future we must first understand how the system operated in the past without man9s influence new inorganic isotopic tracers are now helping to elucidate past ocean circulation patterns but controversies remain regarding the relative influence of ocean circulation and weathering on the isotopic signals

rare earth elements in the mediterranean sea and mixing in the mediterranean outflow abstract mediterranean surface waters contain elevated levels of the rare earth elements compared to similar nutrient depleted open ocean waters application of a flux balance model shows that the mediterranean is a net sink for ce and a net source for the other ree the abundance pattern of the excess ree required for mass balance is enriched in heavy ree and has a negative ce anomaly this supports a marine possibly coastal source for the ree although the magnitudes of the fluxes involved are consistent with aeolian input an aeolian source would require large scale removal of ce and the light ree within the mediterranean sea a mixing model to compute trace metal anomalies in the mediterranean outflow predicts the observed ree concentrations well this implies that ce behaves conservatively in outflow waters over the calculated one month period for mediterranean water to reach the study site application to other trace metals gives good agreement for al cd and mn

on the impact of forced roll convection on vertical turbulent transport in cold air outbreaks we investigated the impact of roll convection on the convective boundary layer and vertical transports in different cold air outbreak cao scenarios using large eddy simulations les the organization of convection into rolls was triggered by upstream heterogeneities in the surface temperature representing ice and water by changing the sea ice distribution in our les we were able to simulate a roll and a nonroll case for each scenario furthermore the roll wavelength was varied by changing the scale of the heterogeneity the characteristics of the simulated rolls and cloud streets such as aspect ratios orientation of the roll axes and downstream extensions of single rolls agreed closely with observations in cao situations the vertical turbulent fluxes calculated for each simulation were decomposed into contributions from rolls and from unorganized turbulence even though our results confirmed that rolls triggered by upstream heterogeneities can substantially contribute to vertical turbulent fluxes the total fluxes were not affected by the rolls

sedimentary fe mn oxyhydroxides as paleoceanographic archives and the role of aeolian flux in regulating oceanic dissolved ree in the marine environment authigenic ferromanganese fe mn oxides precipitate from seawater incorporating many dissolved trace elements such as nd pb whose isotopic composition is a direct proxy for ambient seawater thus isotopic studies of the fe mn oxyhydroxide component leached from sedimentary records can provide information on changes in erosional input or ocean circulation changes such studies may be complicated however by the presence of detrital material containing a fe mn oxide component which may mask the true seawater signal in addition the formation of fe mn oxyhydroxides in the marine environment remains poorly understood in particular the phase carbonates detrital particles that controls the delivery of authigenic fe mn oxides to the sediments has not yet been determined in this study we have analysed the ree and nd isotopic compositions of fe mn oxyhydroxide fractions dispersed in marine sediment cores from the cape and angola basins in the se atlantic cruise images ii for the angola basin deep sea core located at 1000 km south of the congo river mouth both the ree and nd isotopic compositions nd measured in recent fe mn oxyhydroxide fractions are typical of congo river borne fe mn oxides this shows that preformed fe mn oxides associated with detrital fractions can locally contaminate the seawater signal recorded by authigenic oxyhydroxides by contrast examination of ree distributions nd isotope data and mass accumulation rates in cape basin sediments shows paradoxically that the flux of fe mn oxides to sediments is controlled by aeolian particles from the nearby namib desert even though their ree and nd compositions point clearly to an authigenic origin it is proposed that partial dissolution of aeolian dust occurs in the water column releasing into solution its easily leachable fe mn component the dissolved fe2 and mn2 would then fuel the reprecipitation of authigenic fe mn oxyhydroxides scavenging additional dissolved trace elements from the ocean most probably from deep water masses in this case calculations suggest that aeolian deposition acts as a net sink for dissolved nd in the cape basin rather than a source and allows us to estimate the rate of removal of dissolved nd associated with atmospheric deposition yielding a global oceanic residence time for nd nd of between 500 and 1400 years

simulation of the last glacial cycle by a coupled sectorially averaged climate ice sheet model 1 the climate model this paper describes a sectorially averaged seasonal model developed for simulating the long term response of the climate system to the astronomical forcing the model domain covers the northern hemisphere the atmospheric dynamics is represented by an improved zonally averaged quasi geostrophic model it includes a new parameterization of the meridional transport of quasi geostrophic potential vorticity and a parameterization of the hadley sensible heat transport the atmosphere interacts with the other components of the climate system ocean sea ice and land surface covered or not by snow and ice through vertical fluxes of momentum heat and water vapor the model explicity incorporates detailed radiative transfer surface energy balances and snow and sea ice budgets the vertical profile of the upper ocean temperature is computed by an integral mixed layer model which takes into account meridional convergence of heat sea ice is represented by a thermodynamic model including leads and a new parameterization for lateral accretion this paper presents the model climate for present conditions and results of sensitivity experiments obtained by modifying some internal parameters or by deactivating certain parameterizations in the model simulation of the present climate shows that the model is able to reproduce the main characteristics of the general circulation and in particular the surface wind field the seasonal cycles of oceanic mixed layer sea ice and snow cover are also well reproduced sensitivity experiments show the importance of the meridional sensible heat transport by the hadley circulation in the tropics the seasonal cycle of the oceanic mixed layer depth and sea ice formation in latitude bands where the average water temperature is above the freezing point in a forthcoming paper this model will be coupled to an ice sheet model and applied to the simulation of the last glacial cycle in the northern hemisphere

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

submarine groundwater discharge is an important net source of light and middle rees to coastal waters of the indian river lagoon florida usa abstract porewater i e groundwater samples were collected from multi level piezometers across the freshwater saltwater seepage face within the indian river lagoon subterranean estuary along florida s usa atlantic coast for analysis of the rare earth elements ree surface water samples for ree analysis were also collected from the water column of the indian river lagoon as well as two local rivers eau gallie river crane creek that flow into the lagoon within the study area concentrations of rees in porewaters from the subterranean estuary are 10 100 times higher than typical seawater values e g nd ranges from 217 to 2409 pmol kg 1 with submarine groundwater discharge sgd at the freshwater saltwater seepage face exhibiting the highest ree concentrations the elevated ree concentrations for sgd at the seepage face are too high to be the result of simple binary mixing between a seawater end member and local terrestrial sgd instead the high ree concentrations indicate that geochemical reactions occurring within the subterranean estuary contribute substantially to the ree cycle a simple mass balance model is used to investigate the cycling of rees in the indian river lagoon and its underlying subterranean estuary mass balance modeling reveals that the indian river lagoon is approximately at steady state with respect to the ree fluxes into and out of the lagoon however the subterranean estuary is not at steady state with respect to the ree fluxes specifically the model suggests that the sgd nd flux for example exported from the subterranean estuary to the overlying lagoon waters exceeds the combined input to the subterranean estuary from terrestrial sgd and recirculating marine sgd by on average 100 mmol day 1 the mass balance model also reveals that the subterranean estuary is a net source of light rees lree and middle rees mree to the overlying lagoon waters but acts as a sink for the heavy rees hree geochemical modeling and statistical analysis further suggests that this fractionation occurs in part due to the coupling between ree cycling and iron redox cycling within the indian river lagoon subterranean estuary the net sgd flux of nd to the indian river lagoon is 7 fold larger than the local effective river flux to these coastal waters this previously unrecognized source of nd to the coastal ocean could conceivably be important to the global oceanic nd budget and help to resolve the oceanic nd paradox by accounting for a substantial fraction of the hypothesized missing nd flux to the ocean

idealized dry quasi 2 d mesoscale simulations of cold air outbreaks over the marginal sea ice zone with fine and coarse resolution a nonhydrostatic model nh3d is used for idealized dry quasi 2 d simulations of arctic cold air outbreaks using horizontal grid spacings between 1 25 and 60 km despite the idealized setup the model results agree well with observations over fram strait it is shown that an important characteristic of the flow regime during cold air outbreaks is an ice breeze jet ibj with a maximum wind speed exceeding often the large scale geostrophic wind speed according to the present simulations which agree very well with those of another nonhydrostatic mesoscale model metras the occurrence strength and horizontal extent l of this jet depend strongly on the external forcing and especially on the direction of the large scale geostrophic wind relative to the orientation of the ice edge the latter dependency is explained by the effects of the thermally induced geostrophic wind over open water and coriolis force it is found that coarse resolution runs underestimate the strength of the jet this underestimation has important consequences to the surface fluxes of heat and momentum which are also underestimated by about 10 15 on average over the region between the ice edge and 120 180 km downstream our results suggest that a grid spacing of about l 7 is required about 10 30 km to simulate the ibj strength with an accuracy of at least 10 thus the results of large scale models as well might contain uncertainties with regard to the simulated ibj strength which would influence the energy budget in a large region along the marginal sea ice zones

distribution and mixing of intermediate water masses in the channel of sicily mediterranean sea 1 the channel of sicily which represents the only connection between the western and the eastern mediterranean sea can be described as a three layer system where fresher water of atlantic origin modified atlantic water flows eastward in the upper layer levantine intermediate water liw leaves the eastern basin at around 250 350 m and an outflow of transitional ionian deep water tidw is identified below the liw synoptic mesoscale plankton experiment data collected during four surveys in the channel of sicily show that liw and tidw are subject to major modifications when crossing the eastern sill a significant bernoulli aspiration is found there and the bottom water at the sill is composed of modified deep ionian waters coming from 800 m an analysis of the water mass composition proves that liw mixes essentially with tidw and that the tidw flow through the channel must be larger than the expected 0 5 sv the presence of a secondary circulation related to the bottom boundary layer is demonstrated to be the primary factor leading to the dilution and cooling of liw

recent changes in deep water formation and spreading in the eastern mediterranean sea a review abstract observations of the last decade testify that the characteristics of the deep thermohaline circulation in the eastern mediterranean sea have changed thoroughly the source of the most dense waters of the basin has moved from the adriatic to the aegean sea this new source has proved to be very efficient since the estimated formation rate for the period 1989 95 was more than 1 sv about three times more than the dense water formation rate of the adriatic sea these new waters with hydrological characteristics that are warmer and more saline have replaced almost 20 of the older deep waters of the basin and have uplifted the deep isopycnals by about 500 m this major event can be attributed to important meteorological anomalies in the eastern mediterranean and to changes of circulation patterns the extended dry period of 1988 93 and the exceptionally cold winters of 1987 and 1992 93 created favorable conditions for increased formation of dense water in the aegean furthermore changes in the circulation patterns in the intermediate water range levantine intermediate water liw and cretan intermediate water themselves possibly linked to meteorological anomalies appear to have played an important role in the redistribution of salt as a result of an interruption to exchanges between the ionian and levantine basin the salinities in the latter started to rise high salinity waters were diverted into the aegean malanotte rizzoli p manca b b ribera dacala m theocharis a 1998 the eastern mediterranean in the 80s and in the 90s the big transition emerged from the poem bc observational evidence rapport du commission international de la mer medittanee 35 174 175 and the westward transport of liw was reduced an additional effect of the deep water discharge from the aegean and the resulting uplifting of mid depth waters was to lower salinities in the liw layer this effect is most strongly felt in the ionian sea a 3 d primitive equation numerical model for the eastern mediterranean with a 20 km grid size is used to simulate the observed changes and understand the basic mechanisms which caused them under appropriate atmospheric forcing the model successfully reproduces the main characteristics of the transient these results indicate that the observed changes can be at least partially explained as a response of the eastern mediterranean and more specifically of the aegean to atmospheric forcing variability

reconstruction of atmospheric co2 from ice core data and the deep sea record of ontong java plateau the milankovitch chron we provide a reconstruction of atmospheric co2 from deep sea sediments for the past 625000 years milankovitch chron our database consists of a milankovitch template of sea level variation in combination with a unique data set for the deep sea record for ontong java plateau in the western equatorial pacific we redate the vostok ice core data of barnola et al 1987 to make the reconstructions we employ multiple regression between deep sea data on one hand and ice core co2 data in antarctica on the other the patterns of correlation suggest that the main factors controlling atmospheric co2 can be described as a combination of sea level state and sea level change for best results squared values of state and change are used the square of sea level rule agrees with the concept that shelf processes are important modulators of atmospheric co2 e g budgets of shelf organic carbon and shelf carbonate nitrate reduction the square of change rule implies that on short timescales any major disturbance of the system results in a temporary rise in atmospheric co2

saharan dust inputs to the western mediterranean sea depositional patterns geochemistry and sedimentological implications data are presented for a number of parameters for aerosols and rainwaters collected at a station on sardinia the findings are interpreted with special reference to saharan dusts and are compared to other data on these dusts obtained from a variety of sites around the mediterranean sea at the sardinia site the particle size distribution of the saharan outbreaks exhibits a bimodal structure the two modes being between 2 and 4 m and 15 and 30 m the presence of giant particles strongly affects the deposition velocities of the saharan aerosols source markers for the saharan dusts are palygorskite kaolinite calcite dolomite and rounded quartz grains the input of saharan dust has important effects on the chemistry of the mediterranean aerosols these include i increases in the atmospheric concentrations and sea surface fluxes of crust controlled trace metals e g al fe ii decreases in the efcrust values of non crust controlled trace metals e g cu zn and pb in the aerosols and iii changes in the solid state speciation of cu zn and pb which decrease their solubilities in seawater the saharan dusts also affect the composition of rainwater by raising the ph following the dissolution of calcium and by decreasing the solubility of trace metals such as cu zn and pb wet deposition controls the flux of saharan dust to the mediterranean sea but dry deposition can also be important the dust transport occurs in the form of pulses and the annual dust flux can be controlled by a few episodes of saharan outbreaks e g sometimes a single outbreak can account for 40 80 of the flux saharan dust deposition fluxes range from 2 to 25 g m 2 average 10 in the west mediterranean between 39 and 42 n from 6 to 46 g m 2 average 20 in the east mediterranean and from 0 4 to 1 0 g m 2 over the alps on continental europe the present day saharan dust fluxes 1 mg cm 2 year 1 account for about 10 20 of the recent deep sea sedimentation in the western mediterranean 3 15 mg cm 2 year 1

water mass circulation on demerara rise during the late cretaceous based on nd isotopes abstract circulation in the north atlantic during the late cretaceous has implications for poleward heat transport and nutrient distribution during an extreme greenhouse interval with episodes of ocean anoxia nd isotopes of fossil fish teeth and debris represent one of the few water mass tracers that can be used to reconstruct deep ocean circulation we present nd isotopic data interpreted as bottom water values for 290 samples from three ocean drilling program sites on demerara rise sites 1258 1260 and 1261 along with 102 analyses from four other north atlantic sites cape verde goban spur bermuda rise and blake nose that provide additional geographic and bathymetric control our results confirm the presence of a water mass with low end values 14 to 17 that are believed to be influenced by continental material during local water mass formation at low latitudes this demerara bottom water dbw is the primary water mass in the region from the cenomanian to coniacian and from the late campanian through early maastrichtian following a hiatus of 10 my a positive 8 end unit excursion occurs during ocean anoxic event 2 oae2 that cannot be explained by changes in weathering inputs diagenesis or magmatic sources of nd instead it appears to represent an influx of bottom waters sourced from the tethys or north atlantic this replacement of dbw during oae2 argues for decreased production of dbw or enhanced production of tethys north atlantic waters during peak greenhouse conditions from the late campanian through early maastrichtian dbw becomes the only water mass recorded at demerara rise and it appears to expand to abyssal depths at cape verde in the campanian this water mass is ultimately replaced by waters that appear to be sourced from the north atlantic starting in the late maastrichtian observed variations in circulation in the tropical north atlantic during the late cretaceous can account for extensive deposition of black shales in the region prior to the hiatus as well as local warming during a global cooling event in the maastrichtian

circulation changes in the eastern mediterranean sea over the past 23 000 years inferred from authigenic nd isotopic ratios the eastern mediterranean sea ems is a key region to study circulation change because of its own thermohaline circulation in this study we focused on intermediate deep water circulation since the last glacial maximum lgm including the sapropel s1 period two cores from the levantine sea and the strait of sicily respectively collected at 1 780 m and 771 m water depth were studied using 143nd 144nd end of foraminiferal tests and leachates as well as benthic foraminiferal stable isotopes 13c 18o this approach allowed the determination of variations in 1 the north atlantic water contribution to the mediterranean basin 2 water exchanges at the strait of sicily and 3 the influence of the nile river over the last 23 000 years during the lgm high benthic foraminiferal 13c values indicate well ventilated intermediate and deep waters in the ems the end values were more radiogenic than at present reflecting a smaller contribution of unradiogenic north atlantic waters to the ems due to reduced exchange at the strait of sicily the sluggish circulation in the ems initiated during deglaciation was further enhanced by increased nile river freshwater inputs between 15 ka bp and the s1 period partial dissolution of nile river particles contributed to an increase in ems end the large end gradient between the ems and the western mediterranean sea observed during lgm and s1 suggests that each basin had a distinct circulation mode decreasing end values at the strait of sicily after s1 reflected improved water exchange between both basins leading to the modern circulation pattern

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

interbasin deep water exchange in the western mediterranean owing to its nearly enclosed nature the tyrrhenian sea at first sight is expected to have a small impact on the distribution and characteristics of water masses in the other basins of the western mediterranean the first evidence that the tyrrhenian sea might in fact play an important role in the deep and intermediate water circulation of the entire western mediterranean was put forward by hopkins 1988 there an outflow of water from the tyrrhenian sea into the algero provencal basin was postulated in the depth range 700 1000 m to compensate for an observed inflow of deeper water into the tyrrhenian sea however this outflow the tyrrhenian deep water tdw was undetectable since it would have hydrographic characteristics that could also be produced within the algero provencal basin a new data set of hydrographic tracer lowered acoustic doppler current profiler ladcp and deep float observations presented here allows us now to identify and track the tdw in the algero provencal basin and to demonstrate the presence and huge extent of this water mass throughout the western mediterranean it extends from 600 m to 1600 1900 m depth and thus occupies much of the deep water regime the outflow from the tyrrhenian is estimated to be of the order of 0 4 sv sv 10 6 m 3 s 1 based on the tracer balances this transport has the same order of magnitude as the deep water formation rate in the gulf of lions the tyrrhenian sea effectively removes convectively generated deep water western mediterranean deep water wmdw from the algero provencal basin mixes it with levantine intermediate water liw above and reinjects the product into the algero provencal basin at a level between the wmdw and liw thus smoothing the temperature and salinity gradients between these water masses the tracer characteristics of the tdw and the lowered adcp and deep float observations document the expected but weak cyclonic circulation and larger flows in a vigorous eddy regime in the basin interior

variable hfsrnd radiogenic isotopic compositions in a saharan dust storm over the atlantic implications for dust flux to oceans ice sheets and the terrestrial biosphere isotopic characterization of aerosol mineral particles atmospheric dust of varying sizes is essential in classifying source areas and for determining the source of dust deposited over oceans and icesheets however the effect of atmospheric transport on radiogenic isotopic compositions is not well constrained making provenance interpretation difficult in order to investigate the isotopic variability of 176hf 177hf 87sr 86sr and 143nd 144nd we analyzed eight airborne dust samples in two size fractions collected along a cross atlantic transect through a dust storm originating in the sahara in late 2002 past measurements of 176hf 177hf 87sr 86sr and 143nd 144nd of dust have focused primarily on coarse sized particles 30 m whereas far field deposition is primarily finer particles 2 m strontium or neodymium isotopic sorting based on distance is not evident in our dataset however the combined isotopic ratios of the dust collected suggest a saharan origin hafnium isotopic compositions show an east to west trend towards more radiogenic compositions across the atlantic suggesting grain and mineral sorting during dust transport along the 4000 km transect transport models with variable dust particle diameter and wind speed demonstrate the preferential depletion of the high density mineral zircon during transport of dust from the source area the transport model combined with a simple two component mixing model show that the hf isotopic composition changes can be explained by the loss of the mineral zircon during transport modeling of this zircon effect with distance from the dust source in the hf isotopic composition of marine terrestrial and glacial dust deposits may reveal additional information concerning dust transport and sources in the geologic past

entering the glaciation with a 2 d coupled climate model a 2 dimensional model which links the atmosphere the mixed layer of the ocean the sea ice the continents the ice sheets and their underlying lithosphere has been used to test the milankovitch theory over the last glacial interglacial cycle sensitivity tests have shown that the orbital variations can induce in such a system feedbacks sufficient to generate the low frequency part of the climatic variations over the last 122 ka bp these variations at the astronomical time scale are broadly in agreement with ice volume and sea level reconstruction independently obtained from geological data at the beginning of the integration during isotopic substage 5e when there was no northern american nor eurasian ice sheets june insolation at high latitudes seemed to correlate well with summer temperature at the surface of the ice sheets and with the ablation rate the relation is more complicated when large ice sheets exist broadly the june july insolation from 60 to 70 degrees n leads the ice volume by roughly 5000 years over the last glacial interglacial cycle the simulated climate was shown to be sensitive to the ice albedo temperature feedback to the precipitation altitude negative feedback over the ice sheets to the ice sheet slope and continentality effects and to the albedo of the ice sheets as a function of the snowfall frequency at their surface the formation and waxing of the ice sheets are particularly sensitive to ablation more than to snowfalls imperfections in the simulated climate were recognized in particular at the last glacial maximum when the cooling was not large enough and the northern hemisphere ice sheets did not extend far enough to the south weaknesses which are partly solved in a further experiment gallee et al 1989 by using the proper co2 atmospheric concentration given by the vostok ice core in addition to the astronomical forcing

roll and cell convection in wintertime arctic cold air outbreaks abstract cold air outbreaks from the polar ice caps or winterly continents over the open ocean lead to organized convection that typically starts as longitudinal roll patterns and changes to cellular patterns in downstream direction during the field experiments arktis 1991 and arktis 1993 aircraft missions were conducted in 13 cold air outbreak events over the greenland and barents seas to determine the characteristic parameters of both the mean primary flow and the superimposed organized convection secondary flow the measurements are classified into four categories with respect to the convective pattern form longitudinal rolls with small and wider horizontal wavelengths transitional forms between rolls and cells and cells rolls were observed for boundary layer depths h 1 4 km with 8 km and h between 4 and 12 the amplitudes of the secondary flow scale varia

rare earth elements rees in the tropical south atlantic and quantitative deconvolution of their non conservative behavior this study presents new concentration measurements of dissolved rare earth elements drees along a full depth east west section across the tropical south atlantic 12 s and uses these data to investigate the oceanic cycling of the rees enrichment of drees associated with the redox cycling of fe mn oxides is observed in the oxygen minimum zone omz off the african shelf for deeper waters a multi parameter mixing model was developed to deconvolve the relative importance of physical transport i e water mass mixing from biogeochemical controls on the dree distribution in the deep atlantic this approach enables chemical processes involved in ree cycling not apparent from the measurements alone to be distinguished and quantified results show that the measured dree concentrations below 1000 m are dominantly controlled 75 by preformed ree concentrations resulting from water mass mixing this result indicates that the linear correlation between drees and dissolved si observed in atlantic deep waters results from the dominantly conservative behavior of these tracers rather than from similar chemical processes influencing both drees and si minor addition of drees 10 of dnd and 5 of dyb is observed in the deep 4000 m brazil basin resulting from either remineralization of particles in situ or along the flow path greater addition of drees up to 25 for dnd and 20 for dyb is found at 1500 m and below 4000 m in the angola basin near the african continental margin cerium anomalies suggest that different sources are responsible for these dree addition plumes the 1500 m excess is most likely attributed to dree release from fe oxides whereas the 4000 m excess may be due to remineralization of calcite higher particulate fluxes and a more sluggish ocean circulation in the angola basin may explain why the dree excesses in this basin are significantly higher than that observed in the brazil basin hydrothermal venting over the mid atlantic ridge acts as a regional net sink for light rees but has little influence on the net budget of heavy rees the combination of dense ree measurements with water mass deconvolution is shown to provide quantitative assessment of the relative roles of physical and biogeochemical processes in the oceanic cycling of rees

water mass analysis for the u s geotraces ga03 north atlantic sections we present the distributions of hydrographic properties potential temperature salinity dissolved oxygen and micromolar level inorganic macronutrients along two sections occupied in the subtropical north atlantic as part of the first u s geotraces ga03 survey during 2010 and 2011 the purpose of this work is to place subsequent papers in this special issue in a general context and to provide a framework in which the observed distributions of trace elements and isotopes can be interpreted using these hydrographic properties we use a modified optimum multiparameter water mass analysis method to diagnose the relative contributions of various water types along the sections and rationalize their distributions the water mass compositions appear largely consistent with what is understood from previous studies about the large scale circulation and ventilation of the north atlantic with perhaps one exception we found that the north atlantic deep water both east and west of the mid atlantic ridge is more strongly influenced by iceland scotland overflow water relative to denmark straits overflow water about 3 1 than inferred from other tracer studies typically 2 1 it remains unclear whether this is an artifact of our calculation or a real change in deep water composition in the decades between the determinations

clues from mis 11 to predict the future climate a modelling point of view simulations performed with the lln two dimensional northern hemisphere climate model have confirmed that climate is largely triggered by changes in insolation forcing although atmospheric co concentration also plays an important role in particular in the amplitude of the simulated variations marine isotope stage 11 mis 11 some 400 kyr ago and the future share a common feature related to climate forcing i e the insolation at these times displays small similar variations mis 11 can be considered an analogue for future natural climate changes different simulations were performed to identify the conditions constraining the length of the mis 11 simulated interglacial clearly its length strongly depends on the phase relationship between insolation and co2 variations it is only when insolation and co act together towards a cooling i e they both decrease together that the climate enters quickly into glaciation and that the interglacial may be short otherwise each forcing alone is not able to drive the system into glaciation and the climate remains in an interglacial state the same situation applies for the future however we already know that co2 and insolation do not play together indeed insolation has been decreasing since 11 kyr bp and co2 concentration remains above 260 ppmv with a general increasing trend over the last 8000 yr therefore we conclude that the long interglacial simulated for the future is a robust feature and the earth will not enter naturally into glaciation before 50 kyr ap c 2003 elsevier science b v all rights reserved

some features of the algerian current an analysis of infrared images leads to a new conception of the dynamics of the atlantic water in the algerian basin in situ current measurements are not yet available but coherent hypotheses are presented with the aim to initiate further experimental and theoretical works the algerian current flows steadily along the coast near 0 and becomes unstable near 1 2 e eddies of both signs are generated that are advected by the mean current but only the anticyclonic eddies increase in size diameter about 100 km as they extract more energy from the mean current they are advected more slowly and they may detach from the coast and drift for several weeks in the algerian basin they grow as deep as 1000m at least and they are able to pull lenses of intermediate water seaward from the sardinian continental slope coastal upwelling cells are generated near 1 2 e between the cyclonic and the anticyclonic eddies they are also advected by the mean current and are definitively not wind induced these turbulent structures create intense mixing between the atlantic and mediterranean waters which account for the large eastward gradient of salinity encountered in the surface layer therefore the algerian basin is characterized by a large mesoscale variability mainly due to the instability of the algerian current it appears to be a reservoir in which the water of atlantic origin is amassed and it forms a buffer zone which disconnects the flow of atlantic water coming in at gibraltar from the flow of hygly modified atlantic water exiting the basin through the strait of sardinia and into the ligurian sea

neodymium isotopic composition and concentration in the western north atlantic ocean results from the geotraces ga02 section the neodymium nd isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation the modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete here we present new observational data for nd isotopes and concentrations from twelve seawater depth profiles which follow the flow path of north atlantic deep water nadw from its formation region in the north atlantic to the northern equatorial atlantic samples were collected during two cruises constituting the northern part of the dutch geotraces transect ga02 in 2010 the results show that the different water masses in the subpolar north atlantic ocean which ultimately constitute nadw have the following nd isotope characteristics upper labrador sea water ulsw end 14 2 0 3 labrador sea water lsw end 13 7 0 9 northeast atlantic deep water neadw end 12 5 0 6 northwest atlantic bottom water nwabw end 11 8 1 4 in the subtropics where these source water masses have mixed to form nadw which is exported to the global ocean upper nadw is characterised by end values of 13 2 1 0 2sd and lower nadw exhibits values of end 12 4 0 4 2sd while both signatures overlap within error the signature for lower nadw is significantly more radiogenic than the traditionally used value for nadw end 13 5 due to the dominance of source waters from the nordic seas nwabw and neadw comparison between the concentration profiles and the corresponding nd isotope profiles with other water mass properties such as salinity silicate concentrations neutral densities and chlorofluorocarbon cfc concentration provides novel insights into the geochemical cycle of nd and reveals that different processes are necessary to account for the observed nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column while our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension the results for open ocean seawater demonstrate at an unprecedented level the suitability of nd isotopes to trace modern water masses in the strongly advecting western atlantic ocean

high resolution simulations of the turbulent flow in the vicinity of an arctic lead a lead a break in the arctic ice allows contact between the warm ocean and the cold atmosphere because of its importance for the energy budget of the atmosphere many numerical simulations have been made so far to get detailed information about the vertical heat flux and the atmospheric turbulence induced by leads nevertheless the spatial resolution of these simulations is still too coarse to resolve the turbulence directly above the lead where the convective boundary layer cbl may increase to maximum heights of only a few meters whereas in the past spatial resolution was restricted due to insufficient hardware resources today high performance computer architectures allow significant increases in model resolution in this study a large eddy simulation model developed for a massively parallel computer is used to show that an increased model resolution leads to significant changes in the simulation results which are in contrast with earlier studies of flows above and on the leeward side of a single lead the better the model resolution is the earlier the convection starts and this affects the overall cbl structure organized roll like structures on the downstream side of the leads that appeared in earlier studies are shown to be completely caused by insufficient grid resolution the effect of model resolution on the simulation results becomes even greater for higher wind speeds because with increasing geostrophic wind speed and mean wind speed the boundary layer depth decreases and an even finer grid becomes necessary

cell broadening revisited results from high resolution large eddy simulations of cold air outbreaks large eddy simulations les have been carried out in order to investigate the structure and development of organized mesoscale cellular convection mcc during cold air outbreaks caob and to reevaluate results by muller and chlond some limitations of this and other earlier les studies of caobs have been removed by using a parallelized model with both a large horizontal domain and a fine grid resolution these model simulations reveal a hitherto undiscovered insight into the development of mcc it is shown that mcc with aspect ratios larger than 10 only develop in the presence of diabatic heat sources that is latent heat release within the clouds and cloud top radiative cooling which confirms results from previous studies simulated cells are of closed type the wind field is seen to be correlated with the liquid water field and thus dynamic variables are organized on the mesoscale as well updrafts predominantly occur in regions with high liquid water content two dimensional spectral analysis confirms clear peaks at the wavelength of the mcc the dynamic variables are characterized by an organized conglomeration of randomly distributed up and downdrafts where each convective cell can hardly be detected by eye whereas scalar variables like temperature and the liquid water path field are characterized by large scales with aspect ratios of 9 to 11 in the vertical velocity field multiple scales are present simultaneously with small scales having aspect ratios between 1 and 3 contributing most to the total energy but also large scales correlated with scales seen in the thermodynamic variables

new neodymium isotope data quantify nile involvement in mediterranean anoxic episodes the development of widespread anoxic conditions in the deep oceans is evidenced by the accumulation and preservation of organic carbon rich sediments but its precise cause remains controversial the two most popular hypotheses involve 1 circulation induced increased stratification resulting in reduced oxygenation of deep waters or 2 enhanced productivity in the surface ocean increasing the raining down of organic matter and overwhelming the oxic remineralization potential of the deep ocean in the periodic development of deep water anoxia in the pliocene pleistocene mediterranean sea increased riverine runoff has been implicated both as a source for nutrients that fuel enhanced photic zone productivity and a source of a less dense freshwater cap leading to reduced circulation basin wide stagnation and deep water oxygen starvation monsoon driven increases in nile river discharge and increased regional precipitation due to enhanced westerly activity two mechanisms that represent fundamentally different climatic driving forces have both been suggested as causes of the altered freshwater balance here we present data that confirm a distinctive neodymium nd isotope signature for the nile river relative to the eastern mediterranean providing a new tracer of enhanced nile outflow into the mediterranean in the past we further present nd isotope data for planktonic foraminifera that suggest a clear increase in nile discharge during the central intense period of two recent anoxic events our data also suggest however that other regional freshwater sources were more important at the beginning and end of the anoxic events taken at face value the data appear to imply a temporal link between peaks in nile discharge and enhanced westerly activity

late pliocene to pleistocene sensitivity of the greenland ice sheet in response to external forcing and internal feedbacks the timing and nature of ice sheet variations on greenland over the last 5 million years remain largely uncertain here we use a coupled climate vegetation ice sheet model to determine the climatic sensitivity of greenland to combined sets of external forcings and internal feedbacks operating on glacial interglacial timescales in particular we assess the role of atmospheric pco2 orbital forcing and vegetation dynamics in modifying thresholds for the onset of glaciation in late pliocene and pleistocene the response of circum arctic vegetation to declining levels of pco2 from 400 to 200 ppmv and decreasing summer insolation includes a shift from boreal forest to tundra biomes with implications for the surface energy balance the expansion of tundra amplifies summer surface cooling and heat loss from the ground leading to an expanded summer snow cover over greenland atmospheric and land surface fields respond to forcing most prominently in late spring summer and are more sensitive at lower pleistocene like levels of pco2 we find cold boreal summer orbits produce favorable conditions for ice sheet growth however simulated ice sheet extents are highly dependent on both background pco2 levels and land surface characteristics as a result late pliocene ice sheet configurations on greenland differ considerably from late pleistocene with smaller ice caps on high elevations of southern and eastern greenland even when orbital forcing is favorable for ice sheet growth

co2 and northern hemisphere ice volume variations over the middle and late quaternary the atmospheric co sub 2 concentrations have been reconstructed over the past 600 ka based on regression between the vostok co sub 2 data and the specmap oxygen isotope values a lag of 4 5 ka co sub 2 preceding delta sup 18 o gives the best results a polynomial of order 5 explains 66 of the vostok co sub 2 variance over the last 220 ka the northern hemisphere ice sheet volume was simulated over the past 575 ka using the lln 2 d model forced by insolation and these statistically reconstructed atmospheric co sub 2 concentrations the simulated ice volume fluctuations resemble the deep sea oxygen isotope variations co sub 2 of interglacial level is necessary for explaining both the interglacial at oxygen isotopic stage 11 and our present day interglacial

from the subtropics to the central equatorial pacific ocean neodymium isotopic composition and rare earth element concentration variations 1 neodymium isotopic compositions end and rare earth element ree concentrations were measured for filtered surface to deep waters 112 samples in the southern tropical pacific the relatively detailed picture of these tracer distributions allowed us to refine the areas where oceanic end variations occur end values increase for most of the water masses flowing from samoa to the solomon sea and in the papua new guinea png area as already observed furthermore water masses arriving from the eastern equatorial pacific 200 550 m depth also revealed radiogenic values possibly acquired in the vicinity of the south american coasts and galapagos islands these end variations affect the whole water column the most likely process causing such variations is boundary exchange between the numerous radiogenic slopes margins located in this area and seawater flowing past dissolution of atmospheric deposition and or diffuse streaming of volcanic ash are also suggested to explain the radiogenic end observed at the surface in the png area interestingly a positive europium eu anomaly characterizes the normalized ree patterns of most of the studied water masses this anomaly is consistent with the ree patterns of sediment and rock samples that are potential sources for the local waters such consistency reinforces the hypothesis that lithogenic sources play a major role in the oceanic ree budget thanks to boundary exchange the data set presented here is a good basis for further sampling that will be realized in the framework of the ongoing geotraces program www geotraces org

the phase relations among atmospheric co2 content temperature and global ice volume over the past 420 ka the phase relations leads lags among atmospheric co 2 content temperature and global ice volume are key to understanding the causes of glacial interglacial g ig climate transitions comparing the co 2 record with other proxy variables from the vostok ice core and stacked marine oxygen isotope records allows the phase relations among these variables over the last four g ig cycles to be estimated lagged generalized least squares regression provides an e cient and precise technique for this estimation bootstrap resampling allows account to be taken of measurement and timescale errors over the full 420 ka of the vostok record co 2 variations lag behind atmospheric temperature changes in the southern hemisphere by 1 3 1 0 ka and lead over global ice volume variations by 2 7 1 3 ka however signi cant short term changes in the lag of co 2 relative to temperature subsequent to terminations ii and iii are also detected 2001 elsevier science ltd all rights reserved

mid pleistocene revolution and the eccentricity myth the mid pleistocene revolution mpr is the term used to describe the transition between 41 ka and 100 ka glacial interglacial cycles which occurred about one million years ago despite eccentricity having by far the weakest influence on insolation received at the earth s surface of any of the orbital parameters it is often assumed to be the primary driver of the post mpr 100 ka climate cycles the traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity this eccentricity myth is a simplified view of the relationship between global climate and orbital forcing and is in part due to an artefact of spectral analysis our aim here is to clarify the often confused role of eccentricity and review current theories of the mpr we suggest that the post mpr 100 ka glacial interglacial cycles are more closely linked to precession with the saw toothed climate cycles being defined by every four or five precessional cycle because control over the number of precessional cycles involved is determined by eccentricity eccentricity at most paces rather than drives the system if true then one must also question whether the mpr itself defined by an abrupt change in spectral characteristics is not also somewhat misconceived

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

high resolution paleo environmental changes during the sapropel 1 in the north ionian sea central mediterranean high resolution paleoceanographic reconstruction of surface water properties during the most recent sapropel event s1 has been carried out by means of quantitative analyses of planktonic foramini

rare earth elements and yttrium in seawater icp ms determinations in the east caroline coral sea and south fiji basins of the western south pacific ocean abstract using inductively coupled plasma mass spectrometry icp ms vertical profiles of yttrium and all the rare earth elements rees in seawater were obtained at three locations in the western south pacific the east caroline coral sea and south fiji basins based on the data we have analyzed the inter ree iii relationships and found that ree iii s heavier than dy and particularly close neighbors show strong coherencies in their oceanic behavior considering that the heavy ree iii s are less particle reactive than the light and middle ree iii s and that they have very tight correlations with regressions passing almost through the origin the neighboring element ratios of the heavy ree iii s behave virtually conservatively and are suitable as tracers of water masses the dy ho er system is practically good because its dynamic range signal to noise ratio is large in the ocean the highest ho dy ratios 0 31 are found in intermediate and deep waters throughout the western south pacific which overlie the antarctic bottom water with a low ho dy ratio 0 27 these high ho dy waters are probably formed in the polar and subantarctic frontal zone and advect northward ree iii data provide better insights into the deep water recirculation in the south pacific than those discussed based upon the regular oceanographic properties alone

dense water dynamics along the strait of sicily mediterranean sea abstract hydrographic and current meter data gathered in different periods in the strait of sicily and in the southern tyrrhenian sea allow the outflow characteristics from the eastern toward the western mediterranean basin to be analyzed the evolution through the strait of a deep vein of dense water coming from the eastern mediterranean is described together with the dynamic interaction with overlying layers these data are related to a slightly generalized version of recent density current models such as those of emms and those of baringer and price taking into account the dynamic influence of the overlying currents and in particular their friction and mixing this model explains the path of this deep flow and enables estimates of entrainment and bottom friction to be made with these new data a phenomenon of considerable interest namely the dynamics of density currents crossing and outflowing from a strait is examined and discussed

reconstructing deglacial north and south atlantic deep water sourcing using foraminiferal nd isotopes during the last few decades neodymium isotopes have been increasingly used as a paleoceanographic and paleoclimate proxy on million year through millennial time scales the widespread use of the nd isotope proxy depends on whether the nd isotopic composition of past seawater can be reliably extracted from authigenic sediment phases here we show evidence that planktonic foraminifera with authigenic coatings preserve a deep water nd isotopic signature and thus can be used to reconstruct past deep water nd isotopes applying this method downcore on south atlantic deep cape basin core tno57 21 41 1 s 7 9 e 4981 m the nd isotopic composition of the planktonic foraminiferal fe mn oxide coatings is identical with and confirms that of the reductively leached bulk sediment fraction piotrowski et al 2004 2005 2008 as reflecting changes in bottom water sourcing in the case of northeastern north atlantic core bofs 8k 52 5 n 22 1 w 4045 m the planktonic foraminiferal fe mn oxide coatings have different nd isotopes from reductive sediment leaches clearly acid reductive leaching must be tested in more detail we observe that the nd isotopic composition of the deep northeastern atlantic core shifted during the deglaciation from glacial values similar to the south atlantic cape basin towards holocene values similar to the bermuda rise roberts et al 2010 taken as a whole the nd isotope record from foraminiferal authigenic coatings suggests large scale changes in the proportion of northern and southern deep water sources occurred throughout the atlantic ocean with substantial chemical gradients at times during the last deglaciation

rare earth elements and nd isotopes as tracers of modern ocean circulation in the central mediterranean sea abstract seawater rare earth element ree concentrations and nd isotopic composition end are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater however their measurements are basically lacking in the mediterranean sea water column this study analyzes 9 seawater stations around the central mediterranean sea to clarify the relative importance of external sources vertical biogeochemical processes and lateral water mass transport in controlling ree and end distributions concentrations of ree do not show nutrient like profiles with depth likely indicative of relatively young waters with limited accumulation of remineralized ree light ree lree present a non conservative behavior which largely peak at surface waters and rapidly decrease with depth the negative correlation of surface lree enrichment with offshore distance highlights the influence of continental input from the western italian coast to the tyrrhenian surface waters in contrast to other regions with reported boundary exchange this process does not modify the end values here on the other side distributions of dissolved heavy ree hree and end display a conservative behavior that can be explained by mixing of western maw and wmdw and eastern liw and emdw originated waters we test this hypothesis with an optimum multi parameter analysis ompa including hree and end parameters even though the limited data set consistent results of water mass fractions are obtained for the four main water masses although with some particularities while liw takes on major importance when considering hree in the model emdw fractions are preferentially detected with end this latter finding implies a noticeable deep water flux across the sicily strait into the western mediterranean that was not clearly evidenced before

tracing papua new guinea imprint on the central equatorial pacific ocean using neodymium isotopic compositions and rare earth element patterns abstract the nd isotopic composition ic and rare earth patterns of hydrodynamic structures of the equatorial pacific ocean were characterized along 140 w the nd ic of antarctic intermediate water aaiw and of the lower layer of the equatorial undercurrent euc at 140 w 13 c water are much more radiogenic at the equator than at their origin in the south equatorial current 12 s revealing that these water masses have been in contact with the highly radiogenic papua new guinea png slope in both cases only a small fraction less than 9 of the sediment deposited on the png slope is required to be exchanged or dissolved to explain these nd ic variations whereas the hydrographic properties of the same water masses remain unchanged this confirms the usefulness of this tracer to identify pathways of water masses these results emphasize the importance of jets in transporting lithogenic material into the subsurface layers of remote areas where aeolian inputs are particularly weak and corroborate the previous results on fe and al maximum in this area m l wells g k vallis e a silver nature 398 1999 601 604 the nd ic of the upper layer of the euc contrasts strongly to that of the subpycnocline layer indicating that the equatorial upwelling only affects the surface waters and is not effective between 120 and 150 m we calculate that the nd imprint of the png input is likely to vanish from this surface layer as it traverses the basin due to the replacement of upwelled waters by non radiogenic ones

simulation of the last glacial cycle by a coupled sectorially averaged climate ice sheet model 2 response to insolation and co2 variations a two dimensional climate model which links the northern hemisphere atmosphere ocean mixed layer sea ice and continents has been asynchronously coupled to a model of the three main northern ice sheets and their underlying bedrock the coupled model has been used to test the influence of several factors including snow surface albedo over the ice sheets in producing plausible ice age simulations using astronomically derived insolation and co2 data from the vostok ice core the impact of potentially important processes such as the water vapor transport clouds and deep sea circulation was not investigated in this study after several sensitivity experiments designed to identify the main mechanism governing surface temperature and ice accumulation the model is first run with ice sheet feedback by forcing it only with the astronomical insolation over the past 122 kyr large variations of ice volume are simulated between 122 and 55 kyr b p with a rapid latitudinal extension of the north american and eurasian ice sheets starting at 120 kyr b p the simulated last glacial maximum is at 19 kyr b p the model is able to simulate deglaciation as well the simulated evolution of the three northern ice sheets is generally in phase with geological reconstructions the major discrepancy between the simulation and paleoclimate reconstructions lies in the underestimation of temperature variations linked with an underestimation of the ice sheet extent and an excess in the prescribed co2 concentration sensitivity experiments show that ablation is more important to the ice sheet response than snow precipitation variations in the model a key mechanism in the deglaciation after the last glacial maximum appears to be the aging of snow which decreases its albedo the other factors which play an important role are in decreasing level of importance the ice sheet altitude insolation taiga cover and ice sheet extent a final set of experiments addresses the effects of co2 on the simulated climate of the last glacial maximum and on a new long term experiment covering the last 122 kyr this last experiment is made by forcing the model with both insolation and co2 variations this additional forcing improves the temperature and ice volume results despite the limitations inherent to the present modeling approach the sensitivity experiments performed can provide insight into the relative importance of possible mechanism responsible for the building and melting of huge ice sheets during the last glacial interglacial cycle

the role of orbital forcing in the early middle pleistocene transition abstract the early middle pleistocene transition empt is the term used to describe the prolongation and intensification of glacial interglacial climate cycles that initiated after 900 000 years ago during the transition glacial interglacial cycles shift from lasting 41 000 years to an average of 100 000 years the structure of these glacial interglacial cycles shifts from smooth to more abrupt saw toothed like transitions despite eccentricity having by far the weakest influence on insolation received at the earth s surface of any of the orbital parameters it is often assumed to be the primary driver of the post empt 100 000 years climate cycles because of the similarity in duration the traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity this eccentricity myth is due to an artefact of spectral analysis which means that the last 8 glacial interglacial average out at about 100 000 years in length despite ranging from 80 000 to 120 000 years with the realisation that eccentricity is not the major driving force a debate has emerged as to whether precession or obliquity controlled the timing of the most recent glacial interglacial cycles some argue that post empt deglaciations occurred every four or five precessional cycle while others argue it is every second or third obliquity cycle we review these current theories and suggest that though phase locking between orbital forcing and global ice volume may occur the chaotic nature of the climate system response means the relationship is not consistent through the last 900 000 years

tyrrhenian sea circulation and water mass fluxes in spring 2004 observations and model results 1 hydrological and current measurements collected in the tyrrhenian sea during may june 2004 are analyzed with an inverse box model ibm to establish the mean circulation patterns of the basin during spring 2004 these patterns are compared with those provided by a high resolution primitive equation model the princeton ocean model or pom implemented over the area to simulate the mean basin circulation during the survey the good agreement between the two circulation fields despite the differences and the respective limitations of the employed methods represents solid evidence for the reliability of the estimated dynamical structures moreover the pom reveals the short spatial variability of the basin not always resolved by ibm because of the low spatial resolution of the in situ measurements the comparative study indicates the tyrrhenian basin as an extremely active region of the mediterranean sea characterized by a rich mesoscale dynamics this work provides for the first time after more than 25 years a novel qualitative assessment of the tyrrhenian sea spring circulation together with a robust quantitative estimation of the water mass stream fluxes inside the basin and of the exchanges with the adjacent regions

dispersal patterns for hydrothermal plumes in the south pacific using manganese as a tracer abstract manganese profiles over the spreading axis of the east pacific rise epr between 22 15 s and 19 25 s disclose a series of plumes which are formed by buoyant emanations of hot hydrothermal vent fluids the plume ceilings or anomaly maxima can occur several hundred meters above the sea floor these plumes are dispersed laterally and are detectable as mid depth manganese anomalies 2000 km from the spreading axis along this section the plumes are dispersed mainly westward but at 30 s the plumes are advected eastward the asymmetrical dispersal pattern inferred from these data is coincident with the asymmetrical distribution of metalliferous sediments about the epr which suggests that plumes generated by high temperature venting play a dominant role in the formation of these sediments

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

seasonal variability of the tyrrhenian sea surface geostrophic circulation as assessed by altimeter data abstractnew insights into the structure and variability of the tyrrhenian sea s surface circulation are obtained through the analysis of a very long series of altimetric observations 1993 2010 in late winter and part of spring a consistent mean flow is individuated in the eastern tyrrhenian sea formed by a stream of atlantic water that meanders around four anticyclonic structures located along the italian coast which have smaller cyclonic companions offshore the signatures of these vortices are also found in images of chlorophyll and sea surface temperature as well as in modeling results both from a high resolution operational model of the tyrrhenian sea s circulation and from a dedicated numerical simulation analysis of the energy exchange between eddies and mean flow together with numerical evidence suggests that this winter spring circulation pattern may result from basin scale instability of the atlantic stream in summer the dynamic is dominated by a well known dipole located to the east

another description of the mediterranean sea outflow abstract papers about the outflow in the strait of gibraltar assume that i it is composed of only two mediterranean waters mws the levantine intermediate water liw and the western mediterranean deep water wmdw from the eastern and western basins respectively ii both mws are mixed near 6 w hence producing a homogeneous outflow that is then split into veins due to its cascading along different paths and to different mixing conditions with the atlantic water aw a re analysis of 1985 1986 ctd profiles gibraltar experiment indicates two other mws the winter intermediate water wiw from the western basin and the tyrrhenian dense water tdw basically originated from the eastern basin in the central alboran subbasin these four mws are clearly differentiated roughly lying one above the other in proportions varying from north to south proportions also vary with time so that the outflow can be mostly of either eastern or western origin while progressing westward the mws can still be differentiated and associated isopycnals tilt up southward as much as being in the sill surroundings roughly parallel to the moroccan continental slope where the densest mws are the mws at the sill are thus juxtaposed and they all mix with aw leading to an outflow that is horizontally heterogeneous just after the sill 5 45 w before progressively becoming vertically heterogeneous as soon as 6 15 w there can be little liw and or no wmdw outflowing for a while an analysis of new 2003 2008 time series from two ctds moored ciesm hydro changes programme at the sill 270 m and on the moroccan shelf 80 m confirms the juxtaposition of the mws their individual and generally intense mixing with aw as well as the large temporal variability of the outflow composition only liw and tdw were indicated at the sill while on the shelf only liw tdw sometimes denser there than 200 m below and wmdw were indicated but none of the mws has been permanently outflowing at one or the other place the available data can be analyzed coherently intermediate and deep mws are formed in both basins in amounts that although variable from year to year allow their tracing up to the strait four major mws circulate alongslope counterclockwise as density currents and as long as they are not trapped within a basin which is necessarily the case for the deep mws in the alboran the intermediate mws wiw liw and upper tdw circulate in the north while the deep mws lower tdw and wmdw are uplifted hence relatively motionless and mainly pushed away in the south since both the intermediate and deep mws outflow at the sill they are considered as light and dense mws the light dense mws interface possibly intersecting the aw mws interface in the sill surroundings considering an outflow east of the sill composed of only two light dense homogeneous layers gives significant results across the whole strait the outflow has spatial and temporal variabilities much larger than previously assumed the mws are superposed in the sea and lead at the sill to juxtaposed and vertically stratified suboutflows that will cascade independently before forming superposed veins in the ocean these veins can have similar densities and hydrographic characteristics even if associated with different mws which accounts for the features permanency assumed up to now the outflow structure downstream of the sill depends on its composition upstream and more importantly on that of aw in the sill surroundings where fortnightly and seasonal signals are imposed on the whole outflow

sensitivity of the lln climate model to the astronomical and co2 forcings over the last 200 ky the louvain la neuve climate model there referred to as the lln 2 d model has been used extensively to simulate the northern hemisphere ice volume under both the insolation and co2 forcings the period analysed here covers the last 200 ky first sensitivity analyses to constant co2 concentration were performed the model was accordingly forced by insolation changes only the co2 concentration being kept constant to respectively 210 250 and 290 ppmv results show that the simulated ice volume variations are comparable to the geological reconstructions only when the co2 concentration is low 210 ppmv and that the sensitivity of the simulated northern hemisphere ice volume to co2 is not constant through time second three co2 reconstructions were used to force the lln 2 d model in addition to insolation results show 1 a better agreement with the specmap oxygen isotope time series in particular as far as the amplitude of the signal is concerned and 2 that the simulated northern hemisphere ice volume is not very sensitive to the slight differences between these three reconstructions

biogeochemical implications from dissolved rare earth element and nd isotope distributions in the gulf of alaska dissolved rare earth element ree concentrations and nd isotope compositions were measured for surface waters and full water column profiles of the gulf of alaska goa and compared to water mass properties and circulation in order to better understand the mechanisms controlling the input and transport of rees in the ocean the rees display a typical open ocean range of concentrations i e la 12 66 pm lu 0 2 2 5 pm and depth distributions i e surface ocean depletion and enrichment with water depth nd isotope signatures are highly radiogenic as expected for the north pacific margin ranging from 3 8 to 0 2 epsilon nd the most radiogenic values were found in the coastal waters but also in the cores of eddies indicating efficient export of rees from the margins and across the mixed layer this is the first time that distinct nd isotope distributions in near surface waters can be directly assigned to offshore eddy transport a distinct mid depth similar to 2200 m nd isotope signal was found that most likely reflects advection of a water mass that formed through past down welling in the northern pacific subsurface nd isotope compositions appear to behave conservatively and can be explained through a ree distribution model proposed here this model is based on multivariate analysis of the rees and invokes two distinct pools of dissolved rees a passive pool complexed by carbonate ions and a bio reactive pool that is microbially manipulated the latter pool is only significant in the upper water column and most likely reflects the indirect effects of microbial cycling of iron our model of the open ocean ree distribution contributes to explaining the conservative nature of nd isotopes and provides a mechanism linking surface ocean and pore water ree dynamics

is the spectral signature of the 100 kyr glacial cycle consistent with a milankovitch origin spectral analysis techniques traditionally applied to proxy climate records have involved the use of specialized windowing functions because of the finite length of the record available these have the effect of artificially broadening the spectral peaks such that closely spaced peaks may not be fully resolved alternatively use of a simple boxcar window following muller and macdonald 1997b will maximize the spectral frequency resolution this is achieved at the expense of potential truncation artifacts manifested as spurious peaks in the spectra although in the spectral analyses presented here such additional peaks are not significant in addition simple methods like this are not able to place any confidence intervals on the results global ice volume proxy records obtained

the geochemical balance of the rare earth elements and neodymium isotopes in the oceans profiles of ree concentrations and neodymium isotope measurements in the western indian ocean are consistent with published data from the other major oceans ree concentrations show a strong hydrographic control the influence of intermediate water masses is particularly significant surface water concentrations vary with salinity paniculate rees are less than 5 of dissolved concentration except for ce where up to 20 of total rees are present as 0 4 m particles in contrast to dissolved profiles concentration profiles of paniculate rees including ce all increase with depth ree concentrations correlate with silica over all but the deepest waters although in detail correlations are complex the neodymium isotopic composition of indian ocean seawater avg nd 0 8 3 is intermediate between that for the atlantic and pacific oceans comparison of ree data from the major oceans shows that the hrees behave more like si than do the lrees sm nd ratios are near constant for all oceans whereas ernd ratios vary between the atlantic indian and pacific oceans the fractionation of the rees in surface seawaters can be explained by fractionation factors relative to silica from 0 12 for la to 0 05 for er use of a seven box model shows that the interoceanic variations in neodymium isotopic compositions and nd concentrations cannot be reconciled unless particle water exchange is invoked the degree of exchange required is consistent with particle residence times of 1 10 yr

additional evidence of liw entrainment across the algerian subbasin by mesoscale eddies and not by a permanent westward flow abstract the circulation of the levantine intermediate water liw in the algerian subbasin western basin of the mediterranean sea has been much debated for more than fifteen years now together with the old circulation diagrams several numerical models claim that a branch of liw is permanently flowing westwards across the algerian subbasin i e directly from the channel of sardinia towards the strait of gibraltar only a few models support the fact that the unique continuous flow of liw is structured as an alongslope counterclockwise vein which is thus directed northwards off sardinia in the algerian subbasin and hence support the diagram published by millot in 1987 millot c 1987a circulation in the western mediterranean oceanologica acta 10 2 143 149 according to this diagram any little mixed liw found in the central subbasin corresponds to fragments which have been pulled away from the vein and entrained there by mesoscale eddies originated from the algerian current the elisa experiment 1997 1998 as a follow up of other ones conducted since about 15 years was designed partly to validate the diagram in addition to about 40 current meters set in place for one year four main campaigns were conducted with a sampling strategy guided in real time by infrared satellite information the data set we present clearly provides additional evidence that the little mixed liw found in the central algerian subbasin has been entrained there by the mesoscale eddies and not by a permanent westward flow

obliquity forcing with 8 12 times preindustrial levels of atmospheric pco2 during the late ordovician glaciation results from coupled ice sheet and atmospheric general circulation models show that the waxing and waning of ice sheets during the late ordovician were very sensitive to changes in atmospheric p co 2 and orbital forcing at the obliquity time scale 30 40 k y without orbital forcing ice sheets can grow with p co 2 level as high as 10 times preindustrial atmospheric level pal however with orbital forcing ice sheets can grow only with p co 2 levels of 8 times pal or lower these results indicate that the threshold of p co 2 for the initiation of glaciation is on the lower end of previously published estimates of 8 20 times pal the ice sheet model results further indicate that during exceptionally long periods of low summer insolation and low p co 2 levels 8 10 times pal large ice sheets could have formed that were able to sustain permanent glaciation under subsequently higher p co 2 values this finding suggests that in order to end the late ordovician glaciation with a rise in p co 2 atmospheric p co 2 must have risen to at least 12 times pal ice sheets therefore introduce nonlinearities and hysteresis effects to the ordovician climate system these nonlinearities might have also played a role in the initiation and termination of other glaciations in earth history

rare earth elements and nd isotopes tracing water mass mixing and particle seawater interactions in the se atlantic abstract distributions of dissolved and particulate rare earth elements rees and seawater neodymium isotopic composition e nd were established in samples from the bonus goodhope bgh ipy geotraces cruise in the se atlantic sector of the southern ocean 36 s 13 e to 57 s 0 feb mar 2008 close to the south african continent in the subtropical domain particulate rees show the highest concentrations and flat paas normalized patterns clearly tracing their lithogenic origin active cerium oxidation onto suspended particles is evidenced by the mirror image relationship of the cerium anomaly between dissolved and particulate phases unradiogenic dissolved neodymium in surface waters e nd 17 1 traces the influence of old sedimentary material brought by the agulhas current and rings to the cape basin area a mass balance calculation suggests that the release of nd from dissolution of lithogenic material corresponds to a remobilization of 154 10 6 t of sediment per year i e 5 of the total sediment delivered to the southeast african coast annually at open ocean stations both dissolved and particulate rees present negative cerium anomalies indicating that particles have acquired a marine signature the increasing ree concentrations with depth and the strong linear correlations of dissolved ree with silica indicate that surface removal and deep re mineralisation of rees are partially related to the biogeochemical cycle of silicate which involves biogenic silica diatoms combined with marine carbonates these authigenic phases could explain the observed ree patterns in suspended particles except for la we suggest that the positive la anomalies in both phases are linked to the oceanic barium cycle and the partial dissolution of barite crystals especially in the polar frontal zone the e nd composition behaves conservatively in intermediate and deep waters while input processes affect the isotopic signal of subtropical surface waters and weddell gyre bottom waters an indian ocean and an atlantic variety of aaiw have been isotopically differentiated e nd 9 3 0 3 and e nd 8 0 0 5 respectively homogeneous signatures characterize circumpolar waters e nd from 8 2 to 8 4 for cdw a binary mixing model has been used to assess the contribution of undiluted nadw reaching southern latitudes

neodymium isotopes in the mediterranean sea comparison between seawater and sediment signals nine depth profiles of dissolved nd concentrations and isotopic ratios epsilon nd were obtained in the levantine basin the ionian the aegean the alboran seas and the strait of gibraltar thirteen core top sediments and nile river particle samples were also analyzed leached with 1 n hcl acetic acid or hydroxylamine hydrochloride the seawater epsilon nd values become more radiogenic during the eastward circulation in the mediterranean sea the relationship between salinity and the seawater epsilon nd shows that the nd isotopic signature is more conservative than salinity in the mediterranean sea the water mass with the highest epsilon nd 4 8 is found at about 200 m in the easternmost levantine basin the average epsilon nd value for deep waters is 7 0 in the eastern basin 2 5 epsilon units higher than in the western basin by examining the sensitivity of seawater epsilon nd to nd inputs from the nile we conclude that the most significant radiogenic nd source is partially dissolved nile river particles the nd flux from the nile river water has a minor influence on the mediterranean seawater end except for the easternmost levantine basin the leachate epsilon nd values are consistent with the seawater values in the easternmost levantine basin the leachate end values obtained with hcl leaching are systematically higher than the seawater values the relationship between leachate and residual epsilon nd values indicates that the hcl leaching partially dissolves lithogenic nd so the dissolution of nile river particles is the cause of the observed shift some end values obtained with hydroxylamine hydrochloride leaching are higher than those obtained with hcl leaching although the reason for this shift is not clear sr 87 sr 86 successfully detects the presence of a nonmarine component in the leachate our results suggest that leaching performance may vary with the mineralogy of marine sediments at least in the case of the mediterranean sea copyright c 2004 elsevier ltd

carbon isotope records from pacific surface waters and atmospheric carbon dioxide we have stacked planktonic carbon isotope data from three cores in the western equatorial pacific in order to generate a new reconstruction of atmospheric carbon dioxide over the past 450 000 years our new reconstruction resembles that of shackleton et al 1983 based on data from east pacific core v19 30 which successfully predicted features that were subsequently verified by barnola et al 1987 in the record from the vostock ice core in addition the new data confirm the discovery of shackleton and pisias 1985 that changes in atmospheric co2 lead changes in ice volume and hence probably contributed to the glacial interglacial cycles our new reconstruction avoids some of the deficiencies of the previous reconstruction in particular the planktonic species neogloboquadrina dutertrei on which the earlier reconstruction depends does not calcify in truly nutrient free surface water as the model assumes whereas our new reconstruction uses globigerinoides sacculifer which is expected to be more reliable in addition the surface waters in the west pacific are closer to the nutrient free ideal on which the model broecker 1982 depends on the other hand the amplitude of the new reconstruction is significantly smaller than the amplitude observed by barnola et al 1987 it is not clear whether this smaller range is a better estimate of the amplitude of the biological pump effect or whether the true amplitude is reduced by bioturbation in the west pacific cores that we studied

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

modeling the distribution of nd isotopes in the oceans using an ocean general circulation model nd isotopic compositions of authigenic phases in marine archives are increasingly used as a tracer of past changes in ocean circulation such applications assume that water masses are tagged with distinct nd isotope compositions in source regions and that away from these regions the nd isotope ratios observed in deep waters mainly reflect water mass mixing however the degree to which the simple assumption of quasi conservative mixing reflects the complicated reality of general circulation in the oceans is not well understood here we present numerical simulations of the nd isotope distribution in seawater using an offline ocean general circulation model ogcm treating the nd isotopic composition of seawater as a conservative tracer nd isotope data from modern surface waters are used to generate an interpolated map of nd isotope compositions for the entire surface ocean this map is treated as a fixed surface boundary condition that is propagated into the interior ocean by the advective diffusive transport of the ocean model until a steady state is reached this treatment of nd isotopes was chosen because it mimics the behavior of well known and well understood conservative tracers such as potential temperature and salinity the model results for all non surface grid points are then compared to published data this simple approach produces nd isotope estimates for north atlantic deep water that are consistent with observations but produces values lower than observed in the deep pacific and southern oceans indicating the need for a source of radiogenic nd directly to the deep pacific ocean sensitivity tests show this to be a robust result by fixing the return flow of the pacific ocean to the southern ocean with nd isotope ratios that are consistent with modern observations the model results are brought into close agreement with a majority of the available data with the addition of a deep pacific source of radiogenic nd more than half of the simulated values from the interior ocean fall within one e unit of the corresponding observations our results thus indicate that the deep pacific ocean requires a source of radiogenic nd in addition to inputs to the surface ocean and that when the deep waters of the north atlantic and north pacific are set with realistic values a majority of intermediate areas are consistent with quasi conservative mixing of these two end members

modelling northern hemisphere ice volume over the last 3 ma the northern hemisphere ice sheet volumes over the last 3 ma were simulated using the lln 2 d model the forcings were both insolation and co2 concentration different atmospheric co2 scenarios were used because of a lack of co2 reconstruction over this remote past with constant co2 concentrations the simulated ice volume does not show any gradual increase as recorded in the marine sediments moreover its spectrum changes according to the chosen value of co2 when co2 is fixed at 220 ppmv the simulated ice volume is dominated by the similar to 100 ka period if a pre industrial co2 concentration of 280 ppmv is used the simulation is dominated by the similar to 41 ka period by using a linearly decreasing co2 concentration going from 320 ppmv at 3 ma bp to 200 ppmv at present the simulated changes in the power spectrum are in agreement with those obtained from the sedimentary records roughly before 1 ma bp the dominating period is similar to 41 ka afterwards the similar to 100 ka period becomes dominant this transition is accompanied by a gradual increase of the ice volume potential mechanisms for this transition are discussed using cyclic co2 fluctuations over the last 0 6 ma does not change significantly the spectral characteristics of the simulated ice volume but amplifies the amplitude of its variations c 1998 elsevier science ltd all rights reserved

hemispheric roles of climate forcings during glacial interglacial transitions as deduced from the vostok record and lln 2d model experiments the vostok ice contains fingerprints of atmospheric greenhouse trace gases antarctic temperature northern hemisphere temperature and global ice volume sea level changes during the last glacial interglacial cycles and thus allows us to investigate the sequences of these climatic events in particular during the transitions from full glacial to interglacial conditions the use of the updated co2 record presented here and a reexamination of the sea level proxy confirm that the succession of changes has been similar through each of the four marked transitions found at vostok antarctic air temperature and co2 increase in parallel and almost synchronously while the rapid warmings over greenland take place during the last half of their change and coincide with the marked decay in continental ice volume the vostok results thus emphasize a fundamental difference between south and north in terms of climate dynamics our results confirm the role of co2 as an important amplifier of the glacial interglacial warming in the south it appears also that the marked warming observed at high northern latitudes lagging behind the co2 increase by several thousand years is roughly synchronous with the decay of the northern ice sheets suggesting a major role of climatic feedback due to this decay such a climatic scenario is supported by sensitivity experiments performed with the lln 2 d model forced by the northern hemisphere insolation and co2 model results indicate that the decay of the northern ice sheets and the northern hemisphere temperature depend primarily on the northern summer insolation these results nevertheless could be affected if mechanisms specific to the southern hemisphere appear to play a major role in driving the northern hemisphere climate the model also helps to constrain the time response of ice volume to insolation and co2 changes

neodymium isotopic composition of the mediterranean outflow and the eastern north atlantic the neodymium concentration and isotopic composition of the mediterranean outflow in the strait of gibraltar has been directly determined the outflow has a dissolved nd concentration of 23 pmoles kg with nd 0 9 4 these results are in clear disagreement with previous values inferred for the mediterranean this concentration and nd 0 do not sharply contrast with north atlantic deep water nadw values and can produce isotopic anomalies no larger than 1 unit in the north atlantic a new profile in the eastern north atlantic does not exhibit an nd 0 anomaly at the depth of the mediterranean water core in accordance with the above inferences while concentrations and nd 0 at this site indicate that nd is conservative in the deep eastern north atlantic a previously reported nd 0 anomaly in the eastern north atlantic originally associated with the mediterranean outflow has a different source the direct contribution of the mediterranean outflow to the nadw nd budget is small 10 of the high latitude sources however the outflow plus entrained water supply 30 of the total nd associated with northern latitude deep water sources concentrations of dissolved nd in the outflow are enriched compared to the atlantic inflow which has 16 pmoles kg with nd 0 11 8 the principal source of the excess dissolved nd is inferred to be partial dissolution of detrital particles simple mass balance calculations suggest that 0 6 of the nd associated with detrital river transported sediments and or 3 5 of the nd associated with eolian particles delivered to the mediterranean is mobilized during passage into the marine environment if general these mobilization efficiencies imply that the dissolution of detrital particles is a significant source of dissolved nd and other rare earth elements in seawater

is vegetation responsible for glacial inception during periods of muted insolation changes the marine isotope stage 11 interglacial centred at similar to 400 ka appears to be the best candidate for understanding climatic changes in the context of low insolation forcing such as that of our present interglacial direct correlation between terrestrial pollen and marine climatic indicators and ice volume proxy from deep sea core md01 2447 off northwestern iberia shows for the first time the phase relationship between southwestern european vegetation sea surface temperatures in the northeastern atlantic mid latitudes and ice volume during mis 11 a warmest 32 000 years long period and three following warm cold cycles occurred synchronously on land and ocean the end of the warmest period sees the glacial inception which coincides with the replacement of warm deciduous forest by conifer pine fir expansion in northwestern iberia and consequently with the southward migration of the tree line in high latitudes in response to declining summer insolation as weak insolation changes alone cannot account for ice growth the associated vegetation changes must now be considered as a potential major feedback mechanism for glaciation initiation during mis 11 c 2005 elsevier ltd all rights reserved

neodymium budget in the modern ocean and paleo oceanographic implications the oceanic nd budget is calculated using a steady state 10 box model and a compilation of field data this is the first attempt to propose consistent estimates of the nd fluxes entering the ocean as well as indicating possible nd sources and the proportion of nd fluxes exchanged between dissolved and particulate fractions with presently available nd data the best estimates give a total nd influx of 9 x 10 9 g yr which leads to an oceanic nd residence time of 500 years from modeling tests we suggest that the authigenic nd scavenged by particulates is 100 remineralized in the deep ocean the total exchanged nd flux may be as high as 2 x 10 10 g yr the epsilon nd 0 values of the influxes are 22 11 1 and 4 for the north atlantic surface atlantic north pacific and surface indo pacific regions respectively atmospheric and riverine nd fluxes are insufficient to explain the magnitude and regional variability of calculated nd influxes and epsilon nd 0 we propose continental margins as an additional source supplying nd to the ocean using the model calibrated for nd we examine the sensitivity of deep water epsilon nd 0 to variations of nd inputs to the ocean deep water nd concentrations and epsilon nd 0 vary with the changes in nd influxes and their epsilon nd 0 as nd sources to the ocean may change during glacial interglacial periods the epsilon nd 0 shifts recorded in ferromanganese nodules and crusts do not necessarily reflect changes in paleoceanic circulation the effects of continental erosion should be considered in reconstructing patterns of ocean circulation using nd isotopes

four climate cycles in vostok ice core author s petit jr basile i leruyuet a raynaud d lorius c jouzel j stievenard m lipenkov vy barkov ni kudryashov bb davis m saltzman e kotlyakov v

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc