226 ra excess ba growth rates and u th ra ba systematic of baltic mn fe crusts abstract we analyzed 238u 234u 232th 230th and 226ra by thermal ionization mass spectrometry tims and ba by inductively coupled plasma optical emission spectrometry icp oes on eight mn fe crusts from the mecklenburg bay sw baltic and on one from the bothnian bay n baltic to test the 226raex ba ratio as potential geochronometer 226raex ba ratios decrease as a function of depth within the concretions in all analyzed profiles calculated diffusion coefficients are relatively low 9 10 7 cm2 yr for ra and 5 10 7 cm2 yr for ba and suggest that diffusion is negligible for the ra and ba record in addition 226raex ba ages are consistent and independent from the growth rate and growth direction within a crust thus the decline in 226raex ba ratio is most likely due to radioactive decay of 226raex although the influence of varying oxic conditions has still to be evaluated 226raex ba growth rates range from 0 021 to 0 0017 mm yr and tend to be lower than those calculated and based on stratigraphic methods 1 to 0 013 mm yr 226raex ba ages of concretions from shallow water environment 20 m depth mecklenburg bay sw baltic cover a time interval from 990 140 yr to 4310 310 yr bp corresponding to the stabilization of the sea level close to the present position about 5500 to 4500 yr ago one sample from greater depth 70 m bothnian bay n baltic showed a higher 226raex ba age of 6460 520 yr bp

rare earth abundance patterns in ferromanganese concretions from the gulf of bothnia and the barents sea abstract ferromanganese concretions from the svalbard shelf in the barents sea show slightly convex shale normalized ree patterns with no eu anomalies concretions from the gulf of bothnia northern part of the baltic sea exhibit an enrichment of light ree and negative eu anomalies this difference is interpreted as a consequence of different conveyor mechanisms of the ree to the sediment it is suggested that dissolving biogenic debris contributes to the convex pattern obtained in the barents sea whereas an inorganic suspended fraction with scavenged ree is the main carrier in the gulf of bothnia during oxic diagenesis in the sediment the scavenged ree are set free into the porewater and contribute to the distribution pattern in concretions found in the gulf of bothnia small mn rich spheroidal concretions are enriched two to five times in ree compared to average shale whereas mn poor flat concretions are low in ree specific surface area of the concretion and the depth of burial in the oxidized surface sediment are two factors that strongly affect the enrichment of the ree weak ce anomalies are present in the analysed concretions and a redox level dependence is seen

detecting holocene changes in thermohaline circulation throughout the last glacial cycle reorganizations of deep ocean water masses were coincident with rapid millennial scale changes in climate climate changes have been less severe during the present interglacial but evidence for concurrent deep ocean circulation change is ambiguous

multi proxy palaeoecological responses to water level fluctuations in three shallow turkish lakes abstract natural or human induced water level fluctuations influence the structure and function of shallow lakes especially in semi arid to arid climate regions in order to reliably interpret the effect of water level changes from sedimentary remains in the absence of historical data it is crucial to understand the variation in sedimentary proxies in relation to water level measurements here we took advantage of existing water surface elevation data on three large shallow lakes in turkey to elucidate the impact of lake level changes on benthic pelagic primary production over the last 50 100 years sub fossil cladocerans diatoms plant remains and pigments were investigated as biological variables x ray fluorescence xrf and loss on ignition loi analyses were conducted as geochemical physical variables on a set of 210 pb and 137 cs dated cores dating of the cores were robust with the exception of uncertainties in lake marmara littoral core due to low unsupported 210 pb activities and high counting errors results indicated that lake marmara was dominated by benthic species throughout the sediment record while lakes beysehir and uluabat shifted from a littoral dominated system to one with increased pelagic species abundance in all cores there was a stronger response to longer term decadal and pronounced water level changes than to short term annual biennial and subtle changes it was also noted that degree of alteration in proxies differed between lakes through time and among pelagic littoral areas likely emphasising differences in depositional environments and or resolution of sampling and effects of other stressors such as eutrophication our results highlight lake specific changes associated with water level fluctuations difficulties of conducting studies at required resolution in lakes with rather mixed sediment records and complexity of palaeolimnological studies covering recent periods where multiple drivers are in force they further emphasise the need to include instrumental records when interpreting effects of recent water level changes from sediment core data in large shallow lakes

nd and pb isotope time series from atlantic ferromanganese crusts implications for changes in provenance and paleocirculation over the last 8 myr high resolution nd and pb isotope time series for the last 8 myr are reported for four atlantic ferromanganese crusts dated by 10be 9be chronology these are compared to new high resolution and high precision pb isotope time series and recently published nd isotope time series for two previously studied crusts from the nw atlantic ocean these records allow a more detailed examination of atlantic deepwater variability over the time period of intensification of northern hemisphere glaciation nhg changes in the pb isotope time series started after 3 ma but were most dramatic over the last 1 8 myr coinciding with changes of pb isotopes in the arctic ocean this latter change post dates the intensification of nhg at 3 1 to 2 5 ma and reflects an increase in the input of material eroded from the archean shield of canada and greenland shifts in nd and pb isotope compositions in a crust from the blake plateau occur before 5 ma and most prominent at 8 ma suggest that water masses from either the pacific or southern ocean influenced the isotope composition of this crust the relatively high end values around 8 ma recorded by the blake plateau crust are explained by a contribution of eastward flowing pacific water through the panama gateway into the caribbean sea this high end signal decreased between 8 and 5 ma suggesting that the supply of pacific water into the caribbean became restricted this is earlier than the caribbean seawater salinity increase at 4 2 ma deduced from 18o data and may indicate that there was only a surface water connection between the caribbean and pacific between 5 and 4 2 ma the closure of the panama gateway to intermediate and deep water exchange 200 m depth apparently occurred much earlier than the intensification of northern hemisphere glaciation at 3 1 2 5 ma and cannot therefore have been a direct cause of this climatic change but may as recently argued only have been a necessary precondition

contribution of small glaciers to global sea level observed long term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers excluding those in greenland and antarctica to the oceans the average observed volume change for the period 1900 to 1961 is scaled to a global average by use of the seasonal amplitude of the mass balance these data are used to calibrate the models to estimate the changing contribution of glaciers to sea level for the period 1884 to 1975 although the error band is large these glaciers appear to account for a third to half of observed rise in sea level approximately that fraction not explained by thermal expansion of the ocean

a complete formalism for the inversion of post glacial rebound data resolving power analysis summary a formal inverse theory for mantle viscosity based upon the data of glacial isostatic adjustment is here formulated and applied to synthetic data in this theory full account has been taken of the normal mode nature of the forward problem for realistic viscoelastic maxwell models of the planet since it is impossible to accurately infer the excitation and decay constants of the individual normal modes from the observations the formalism is cast in terms of the observed gross earth data in the time domain in this analysis expressions are required for the first order perturbations in both the modal amplitudes and relaxation times that are induced by an arbitrary radial perturbation to the starting viscosity profile a numerical technique is developed which enables us to accurately determine differential kernels for the modal amplitudes the analogous kernels for the modal decay times are derived analytically peltier 1976 and the complete set of kernels is shown to satisfy the physical constraint imposed by the uniqueness of the state of isostatic equilibrium for the viscously incompressible maxwell models that we employ when the problem is parametrized in terms of the logarithm of viscosity the kernels are capable of accurately predicting shifts in the normal mode characteristics for at least an order of magnitude variation in mantle viscosity using bayesian statistics a formal inversion is applied to a set of synthetically generated data these data chosen to reproduce the space time coverage of the actual observables include a subset related to the global gravity field and a large sequence of idealized relative sea level rsl curves it is found that even very weak a priori constraints can provide a stable and accurate inversion a resolving power analysis indicates a spatial resolution of approximately 1200km near the core mantle boundary cmb with a gradual improvement to better than 350km in the middle of the upper mantle subsets of the synthetic data are inverted in order to examine conditions on stability and accuracy and to determine their relative contributions to the spatial resolution data from progressively older beaches are shown to contribute most to the spatial resolution at all depths though the improvement in lower mantle resolution converges for data obtained from beaches formed within the last 5000 yr furthermore the rsl curves in the vicinity of the peripheral bulge of the ancient laurentide ice sheet are significant contributors to lower mantle resolution as demonstrated in previous analyses of the forward problem the inversion of this subset of the data also appears to be encouragingly stable

quantifying holocene lithospheric subsidence rates underneath the mississippi delta abstract the pattern of holocene relative sea level rsl change on the us gulf coast has been a long standing subject of debate featuring opposing scenarios of continuous submergence versus one or more holocene rsl highstands the significance of this debate is that the relative role of eustasy glacial isostatic adjustment gia and lithospheric flexural subsidence associated with mississippi delta sediment loading remains unresolved here we present a new rsl record from the louisiana chenier plain 100 km west of the mississippi delta margin based on ams 14 c dated marsh basal peat this enables us to provide for the first time constraints on holocene lithospheric subsidence rates underneath one of the world s major deltas our new record conclusively shows that no middle holocene rsl highstands occurred on the central us gulf coast rather it exhibits a pattern of progressive rsl rise comparable to that from the mississippi delta suggesting that long wavelength gia is a dominant deformational process driving lithospheric subsidence in the entire region by means of forebulge collapse nevertheless a 0 15 0 07 mm yr differential rate of subsidence between the chenier plain and key portions of the mississippi delta including the new orleans metropolitan area exists this shows that while the sediment loading effect is real it is about an order of magnitude smaller than recent studies have postulated

separating natural and anthropogenic vertical movements in fast subsiding areas the po plain n italy case the geological and the anthropogenic components of vertical movement act on different time scales millions to thousands years and hundreds to tens of years respectively this peculiarity has been used in order to separate the factors controlling sea level changes in the po plain area the component due to long term geological processes is calculated from stratigraphic data commercial wells and seismic lines adding to this long term component the contribution of pleistocene deglaciation obtained from analytical models an estimate of the total natural component of vertical velocities is obtained the validity of these values is confirmed by comparison with velocities obtained from archaeological data and detailed palynological and paleontological analyses the anthropogenic components can be inferred by comparison between the total natural vertical velocities we calculate and vertical velocities obtained from other data sets two applications are proposed using tide gauge records and geodetic data respectively

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

annual climate variability in the holocene interpreting the message of ancient trees abstract over vast areas of the world s landmasses where climate beats out a strong seasonal rhythm tree growth keeps unerring time in their rings trees record many climate melodies played in different places and different eras recent years have seen a consolidation and expansion of tree ring sample collections across the traditional research areas of north america and europe and the start of major developments in many new areas of eurasia south america and australasia from such collections are produced networks of precisely dated chronologies records of various aspects of tree growth registered continuously year by year across many centuries their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space with their extensive coverage high temporal resolution and rigid dating control dendroclimatic reconstructions contribute significantly to our knowledge of late holocene climates most importantly on timescales ranging from 1 to 100 years in special areas of the world where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved work building chronologies covering many millennia continues apace very recently trees have provided important new information about major modes of general circulation dynamics linked to the el nino southern oscillation and the north atlantic oscillation and about the effect of large volcanic eruptions as for assessing the significance of 20th century global warming the evidence from dendroclimatology in general supports the notion that the last 100 years have been unusually warm at least within a context of the last two millennia however this evidence should not be considered equivocal the activities of humans may well be impacting on the natural growth of trees in different ways making the task of isolating a clear climate message subtly difficult

climatic influences on the growth rates of mn crusts during the late quaternary abstract the concentration of 230 th in mn crust va13 2 146 w 9 25 s 4830 m from the pacific ocean was measured with high depth resolution 0 02 mm to a depth of 1 4 mm corresponding to an age of 226 ka b p the mean growth rate estimated from these results is 6 2 0 4 mm ma however the exponential curve obtained shows two drastic events in the 230 th concentration record with durations of 41 4 ka and 37 6 ka which are interpreted as growth standstills the decay corrected 230 th concentration is inversely correlated with those of mn fe and co indicating that the 230 th flux into the crust has been constant throughout time and that the observed fluctuations in 230 th are due to dilution by the main components by applying a constant 230 th flux model high resolution growth rates were derived from every sample investigated a detailed comparison of the growth pattern with the specmap time table reveals that the va13 2 growth rates tend to be higher during interglacial than during glacial periods in particular the observed growth standstills are associated with glacial stages 6 and 8 further investigation of mn crust 72 dk 9 taken from shallower water 170 35 w 20 13 n 1550 m tend to confirm that there is a link between the growth rates of hydrogenetic crusts and the climate of the late quaternary

investigations of fennoscandian glacial isostatic adjustment using modern sea level records we present a new method for determining the rates from a network of regional tide gauge data the method involves using a model for the sea level observations annual averages of relative sea level that explicitly includes a term for the interannual sealevel variations which are assumed to be constant for all sites in the network the resulting simultaneous analysis of all the sea level observations yields sea level rates which are biased by the unknown temporal slope of the interannual variations by differencing sea level rate estimates with respect to one site site referenced sea level rates are calculated which are free from this bias the differencing procedure also removes any signal due to a common sea level rate such as might be associated with eustatic sea level rise the resulting site referenced sea level rates therefore in principle reflect only the relative vertical crustal motions of the tide gauge sites with respect to the geoid these site referenced sea level rates represent a potentially more accurate data set than have previously been used for sea level studies we have used these rates to investigate glacial isostatic adjustment gia in fennoscandia specifically we have used the site referenced sea level rates within the baltic sea to estimate adjustments to the ice history and earth model which are used to calculate vertical rates of adjustment due to gia a method never before used for fennoscandia the parameters selected were lithospheric thickness the viscosities of assumed isoviscous upper and lower mantles and a fennoscandian ice thickness scaling parameter we present the results of this estimation procedure for a specific test ice model we also find evidence that the sea level record for the site nearest the center of uplift furuogrund may be contaminated by systematic errors of unknown origin data from this site have previously been used to determine a rate for the maximum uplift that we find is perhaps 1 mm yr 1 or 10 too large

weathering versus circulation controlled changes in radiogenic isotope tracer composition of the labrador sea and north atlantic deep water geological reconstructions and general circulation models suggest that the onset of both northern hemisphere glaciation 2 7 myr ago and convection of labrador sea water lsw were caused by the closure of the panama gateway 4 5 myr ago time series data that have been obtained from studies of ferromanganese crusts from the northwestern atlantic suggest that radiogenic isotopes of intermediate ocean residence time pb and nd can serve as suitable tracers to reconstruct these events however it has been unclear until now as to whether the changes that have been observed in isotope composition at this time are the result of increased thermohaline circulation or due to the effects of increased glacial weathering in this paper we adopt a box model approach to demonstrate that the shifts in radiogenic isotope compositions are unlikely to be due to changes in convection in lsw but can be explained in terms of increases of erosion levels due to the glaciation of greenland and canada furthermore we provide experimental evidence for the incongruent release of a labile fraction of strongly radiogenic pb and nonradiogenic nd from continental detritus eroding into the labrador sea this can be attributed to the glacial weathering of old continents and accounts for the paradox that one of the areas of the world most deficient in radiogenic pb should provide such a rich supply of radiogenic pb to the oceans an important general conclusion is that the compositions of radiogenic isotopes in seawater are not always a reflection of their continental sources perhaps more importantly the transition from chemical weathering to mechanical erosion is likely to result in significant variations in radiogenic tracers in seawater

space geodetic constraints on glacial isostatic adjustment in fennoscandia analysis of global positioning system gps data demonstrates that ongoing three dimensional crustal deformation in fennoscandia is dominated by glacial isostatic adjustment our comparison of these gps observations with numerical predictions yields an earth model that satis es independent geologic constraints and bounds both the average viscosity in the upper mantle 5 x 10 20 to 1 x 10 21 pascal seconds and the elastic thickness of the lithosphere 90 to 170 kilometers we combined gps derived radial motions with fennoscandian tide gauge records to estimate a regional sea surface rise of 2 1 0 3 mm year furthermore ongoing horizontal tectonic motions greater than 1 mm year are ruled out on the basis of the gps derived three dimensional crustal velocity field

the melting history of the late pleistocene antarctic ice sheet spatial and temporal variations in the sea levels of the past 20 000 years around the globe place constraints on the melting history of the major late pleistocene ice sheets the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9 000 6 000 years ago when it may have lagged behind minor melting of the antarctic ice sheet continued throughout the holocene

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

rare earth elements in river waters we measured rare earth element ree concentrations in river waters to characterize the suspended and dissolved river flux of the ree to the oceans the ree pattern of river suspended materials is sensitive to drainage basin geology a positive correlation is observed between la yb ratios and nd model ages for the rivers studied major rivers have light ree enriched patterns relative to the north american shale composite nasc with la yb n 1 6 2 7 river water dissolved material 0 2 m is heavy ree enriched relative to suspended material and the most pronounced negative ce anomalies occur in rivers of high ph light ree concentrations vary by approximately 3 orders of magnitude and are inversely related to ph and major cation concentrations from these data we estimate that typical major river runoff has heavy ree depleted suspended material with la yb n 1 9 we conclude that the terrigenous input to the oceans from major rivers is heavy ree depleted relative to shales from the available data average river water dissolved material appears to be heavy ree enriched with la yb n 0 4 estuarine removal processes lower the dissolved ree river flux by approximately 60 and result in a flux that is more heavy ree enriched with la yb n 0 2 calculated oceanic residence times with respect to river input range from 2300 to 21 000 years are shortest for ce and greatest for the heavy ree and la such long residence times may suggest the presence of additional sources of ree in seawater

nd and pb isotopes in atlantic and pacific water masses before and after closure of the panama gateway two nd and pb isotope time series of hydrogenous ferromanganese crusts one from the tehuantepec ridge in the deep eastern equatorial pacific and the other from blake plateau in the shallow northwestern atlantic which cover the past 7 8 m y show no variations coincident with the final closure of the panama gateway estimated as ca 3 5 ma the record of the atlantic crust located in the present day gulf stream shows a shift in isotope composition from ca 8 to 5 ma that is explained by a diminishing supply of pacific water it is argued that the major restriction of water mass exchange through the panama gateway occurred before 5 ma and thus cannot serve as a direct cause of the onset of northern hemisphere glaciation the absence of a significant signature in the isotope records from the pacific crust suggests that the volume of water exchanged with the atlantic through shallow archipelagic straits of the gateway during the 3 4 m y prior to closure was too small to influence the radiogenic isotope composition of pacific deep water

distribution and sources of pre anthropogenic lead isotopes in deep ocean water from fe mn crusts abstract the lead isotope composition of ocean water is not well constrained due to contamination by anthropogenic lead here the global distribution of lead isotopes in deep ocean water is presented as derived from dated ca 100 ka surface layers of hydrogenetic fe mn crusts the results indicate that the radiogenic lead in north atlantic deep water is probably supplied from the continents by river particulates and that lead in pacific deep water is similar to that characteristic of island and continental volcanic arcs despite a short residence time in deep water 80 100 a the isotopes of lead appear to be exceedingly well mixed in the pacific basin there is no evidence for the import of north atlantic deep water derived lead into the pacific ocean nor into the north indian ocean this implies that the short residence time of lead in deep water prohibits advection over such long distances consequently any climate induced changes in deep water flow are not expected to result in major changes in the seawater pb isotope record of the pacific ocean

was a change in thermohaline circulation responsible for the little ice age long term 800 year and short term 20 year estimates of the rate of deep water formation in the southern ocean are in serious disagreement this disagreement suggests to me that the rate of deep water formation may have been larger during the little ice age lia than it is now

predicted and observed holocene sea levels on the australian coast what do they indicate about hydro isostatic models in far field sites data relating to holocene sea level elevations and ages obtained by radiocarbon dating of relict calcareous skeletons of intertidal organisms from widely spaced parts of the australian coast a far field region of comparative tectonic stability are divisible into two sets namely pre and post ca 3600 yr bp the older ages are from material consistently between 1 5 m and 2 2 m higher than present sea level whereas the younger ages ca 3600 1500 yr bp generally cluster around 1 m above present sea level the elevations do not display any decline in amplitude from north to south over an extensive transect contrary to predictions by hydro isostatic models also there appears to be little difference between time elevation results for the coasts of north queensland new south wales and the bass strait region adjacent to tasmania despite differences in the width of the continental shelf in these three locations and the expectation of some hydro isostatic warping of the continental shelf subsequent to the onset of the holocene transgression results from the south and southwest coasts of western australia also display similar elevations to the east coast for the same time periods there is sufficient evidence extending over 20 of latitude to suggest that north south differences related to hydro isostatic influence is limited or non existent there is insufficient data to test hydro isostatic models across continental shelves hydro isostasy and the lithological elasticity it reflects may not be as pronounced in far field sites with narrow continental shelves as models predict stable far field passive continental margins may be the best place to measure the ratio of inputs of eustatic and hydro isostatic influences on holocene relative sea levels copyright 2002 john wiley sons ltd journal of quaternary science

fast growing shallow water ferro manganese nodules from the western baltic sea origin and modes of trace element incorporation abstract ferro manganese nodules of the western baltic sea reveal enhanced heavy metal concentrations since the end of the 19th century and are therefore potentially useful for retrospective monitoring of the heavy metal pollution history however only zn shows a significant rise even though cu is also introduced to the western baltic sea by natural and anthropogenic sources this study focused on geochemical considerations to evaluate the mechanism responsible for the predominance of zn in ferro manganese nodules compared to cu the particulate and dissolved metal fractions in the water column in the fluffy layer an approximately 2 cm thick sediment layer situated at the sediment water interface and in the pore water adjacent to ferro manganese nodules were studied the analysis of the dissolved fraction and speciation studies were carried out using cathodic stripping voltammetry csv the particulate fraction and the pore water were analyzed via graphite furnace atomic absorption spectroscopy gf aas and inductively coupled plasma optical emission spectroscopy icp oes the fluffy layer provides high quantities of mn fe zn and cu to the dissolved fraction of the bottom water during the stratification period hence the signal manifested in the ferro manganese nodules consists of newly emitted elements on top of the amount collected in the fluffy layer over many years and remobilized throughout the stratification trace elements with the tendency to form weak inorganic complexes in the water column like zn are more likely to be incorporated in ferro manganese nodules and therewith document the anthropogenic metal input while elements which tend to form strong organic complexes such as cu are scavenged by particulate organic matter in the water column and the fluffy layer

nd isotopes in indian ocean sediments used as a tracer of supply to the ocean and circulation paths abstract neodynium isotopic compositions of eighteen sediments from the indian ocean were measured these quaternary marine sediments were collected in different physiographic provinces with samples being taken from the abyssal plain ridge submarine fan fracture zone and aseismic ridge environments the main results is that there are large areas in the indian ocean which are isotopically homogeneous although the results also enforce the idea that in marine sediments the continent derived material exerts an important control on the nd budget the northeastern part of the indian ocean is influenced by erosion of the indonesian arc the values between e 0 7 and e 0 8 observed in samples from the central indian ocean are nearly constant both in the eastern and western parts of the indian ocean this was interpreted as mixing between two major inputs firstly material coming from the erosion of the indian shield e 0 14 to 17 and secondly from the indonesian arc e 0 0 subsequently all the material is then homogenized by the oceanic circulation the western indian ocean values are more variable perhaps because of the proximity of old continental terrains i e southern africa and the influence of atlantic waters the highest value e 0 2 93 observed in the southern part of the indian ocean may be explained by the influence of the erosion of the crozet basaltic plateau indeed the two samples which exhibit positive nd isotopic values correspond geographically to the area of erosion of the crozet and possibly the kerguelen basaltic plateaus the location of the sample with the lowest isotopic value e 0 18 88 close to antarctica implies that this sediment might have included an old continental component of precambrian or even archaen age this result traces in the case of particle transport the circulation of water masses from antarctica to northern parts of the indian ocean which are known for their deep waters with the exception of the samples located near the crozet plateau where probable destruction of the plateau is occurring we do not observe any nd isotopic variations related to the specific physiographic location of any one sample consequently the nd isotopic variations are principally due to the pathways of water circulation and possibly winds over the indian ocean

effects of mantle flow law stress exponent on postglacial induced surface motion and gravity in laurentia summary recent studies show that power law rheology with stress exponent n 3 in the lower mantle or in a thin zone just beneath the lithosphere are consistent with the sea level observations in and around laurentia in this study the stress exponent n is varied from 2 to 4 and for each value of n a range of creep parameter a is searched to find the earth model that gives the best fit to the sea level observations in and around laurentia the effects of stress exponent on other geophysical observables namely present day uplift rate horizontal velocity free air gravity and the rate of change in gravity are also studied the model used to calculate the postglacial readjustment of the earth is a 3 d finite element model that includes realistic ice histories and eustatic water loads on stratified incompressible viscoelastic maxwell flat earths three types of earth rheology models are considered the first one has nonlinear rheology throughout the mantle and the second has a nonlinear zone at the top of the mantle below the elastic lithosphere and a linear mantle the third one has nonlinear rheology restricted to lie in the lower mantle it is found that the models with nonlinear rheology in the lower mantle give better fits to the sea level data in and around laurentia than the first two types however sea level data when taken as a whole cannot clearly discriminate between the stress exponents 2 3 or 4 present day uplift rate horizontal velocity and rate of gravity change however may be useful in further discriminating mantle rheology

a lead isotopic study of circum antarctic manganese nodules abstract lead isotope ratios in manganese nodules from the circum antarctic ocean display systematic geographical variations eastward in the direction of current movement from south of australia they progressively decrease in the pacific sector and into the western atlantic sector until 30 w from this longitude lead isotope ratios increase in the eastern atlantic sector and reach their highest values in the indian sector near 110 e south of western australia they abruptly decrease these two lead isotope domains correspond closely to the circum antarctic neodymium isotope domains previously recognized by albarede and goldstein 1992 however the intraocean isotopic variations are much clearer for pb than nd reflecting the shorter oceanic residence time of pb 102 y compared with nd 103 y and confirming that pb is a much more sensitive marine tracer throughout the circum antarctic ocean the lead isotopic changes follow the pattern of present day oceanic circulation the pb shows an overall continental signature which is strongest in the indian sector the most probable candidate as the source of the continental signal is north atlantic deep water nadw which enters the circum antarctic in the south atlantic as nadw mixes with circumpolar water lead isotope ratios increase eastward in the indian sector reflecting progressive loss of the pacific derived pb signal the abrupt decrease of lead isotope ratios between the indian and pacific sectors appears to be a consequence of addition of pacific seawater through the pacific lead isotope ratios gradually decrease eastward approaching values of east pacific rise metalliferous sediments ocean ridge basalts and south pacific mn nodules this trend results from an increasing influence of pacific ocean water containing a component derived from pacific volcanism the pacific signature persists into the argentine basin in the southwest atlantic ocean reflecting significant input of water from the drake passage northward into the atlantic the pacific pb component is seen in the atlantic and indian oceans near southern africa as well as in the atlantic and indian sectors of the circum antarctic lead and neodymium isotopes correlate in the atlantic indian sectors but not in the pacific sector reflecting differences in residence times and modes of water mass mixing the renewal of circum antarctic water occurs on a timescale which is short compared to the residence time of nd but long compared to pb as a result dissolved pb is subject to considerable changes over the timescale of circumpolar current movement while nd is less easily affected nadw is added locally in the south atlantic and moves eastward as a water mass as nadw mixes with circumpolar water cpw through the indian sector changes affecting nd pb in nadw and cpw occur in tandem and neodymium and lead isotopes are correlated through the pacific sector gradual addition of pacific seawater occurs over a large region and nd pb relationships are not coupled because simple isotopic mixing systematics are not conserved there neodymium and lead isotopes vary independently the consistency of lead isotope variations with present day ocean bottom water circulation is remarkable considering that the mn nodules as sampled reflect the integrated flux of pb over 105 106 y the oceanic mixing time is 103 y the residence time for pb is 102 y and the circulation time of the circumantarctic ocean is 30 y processes occurring over such different timescales can show such a relationship only if the system is stable over the longest time interval thus on average element sources and ocean circulation through the pleistocene have been similar to the present day despite significant perturbations during glacial periods

multiple processes causing sea level rise in the central mediterranean our analysis of a series of sea level records along the italian coast of the adriatic sea indicates a sea level rise not attributable to a global eustatic signal but rather to the combined effects of active tectonics and glacial isostatic adjustment henceforth gia the highest predicted sea level rise of the order of 0 9 1 0 mm yr occurs in proximity of the city of ravenna in the northern sector of the adriatic sea decreasing to 0 4 0 5 mm yr in the northernmost and southern parts of the adriatic sea while gia is the dominant mechanism of sea level rise in the southern sector of the adriatic sea active tectonics and gia contribute a comparable amount in the north our results are of importance for quantitative estimates of trends of sea level changes in a part of the mediterranean the northern adriatic sea where the historical cities of venice and ravenna are severely exposed to sea level rise

contrasting geochemical cycling of hafnium and neodymium in the central baltic sea the central baltic sea is a marginal brackish basin which comprises anoxic bottom waters and is surrounded by geological source terrains with a wide variety of compositions and ages this allows the investigation of water mass mixing using radiogenic isotope compositions of nd and hf as well as their geochemical cycling across varying redox conditions in the water column in this study we present the distribution of nd and hf concentrations and their isotopic compositions for 6 depth profiles and 3 surface water sites obtained during a cruise in the central baltic sea onboard the rv oceania as a part of the international geotraces program the results obtained indicate that nd isotopes effectively trace the mixing between more radiogenic saline waters from the south and unradiogenic fresh waters from the north which helps to understand the reliability of nd isotopes as water mass tracer in the open ocean in surface waters nd shows higher concentrations and less radiogenic isotope compositions at the northern stations which are progressively diluted and become more radiogenic to the south consistent with the counterclockwise circulation pattern of central baltic sea surface waters in contrast to the variable nd concentrations hf shows much less variability at the gotland deep station the nd concentrations of the euxinic waters are higher by a factor 10 than those of the overlying oxygen depleted waters whereas hf only shows small concentration variations this indicates faster removal of hf from the water column than nd moreover the dissolved hf isotope signatures document great variability but no consistent mixing trends our explanation is that hf has a lower residence time than nd and also that the hf isotope signatures of the sources are highly heterogeneous which is attributed to their differing magmatic and tectonic histories as well as incongruent post glacial weathering around the central baltic sea

on postglacial geoid subsidence over the equatorial oceans we develop two new spectral formalisms for the gravitationally self consistent solution of the sea level equation which governs the redistribution of glacial meltwater on a visco elastic earth the first is a purely spectral technique based on an extension of theory outlined by dahlen 1976 for determining the equilibrium oceanic tide on an elastic planet using this technique with a feasible spherical harmonic truncation level l 30 we can obtain convergence in the computed sea level variations within the degree range l 10 we also develop a second pseudospectral technique however which permits the construction of gravitationally self consistent solutions to much higher degree and order l 100 the pseudospectral formalism is employed here to develop a comprehensive physical explanation for the global pattern of present day sea level variations due to ongoing glacial isostatic adjustment in particular we focus upon a mechanism which we term equatorial ocean syphoning that acts to draw water toward the oceanic portion of the collapsing peripheral bulge that encircles previously glaciated regions the collapse of the forebulge induces a flow of water which is required to maintain hydrostatic equilibrium the syphoning mechanism dominates the relative sea level rsl variation in oceans in the far field of the ice sheets that is beyond the peripheral bulge during periods such as the interglacial of the past 4000 years during which the volume of the ice sheets has not apparently changed appreciably while at the same time isostatic adjustment persists the rsl change in the near field is in contrast dominated by the local vertical displacement of the solid surface finally comparison of gravitationally self consistent predictions of rsl change in the far field with the observational data at small pacific island sites has provided an upper bound of 1 to 2 m for the eustatic sea level rise produced by any recent last 3000 years melting of the antarctic ice sheet

geochemistry and origin of ferromanganese concretions in the gulf of bothnia abstract ferromanganese concretions cover large areas of the gulf of bothnia they are flat to well rounded the rounded ones being richer in oxyhydroxides of iron and manganese rounded and ellipsoidal nodules particularly those in the northern gulf of bothnia are richest in mn ni ba and cu which probably coexist in a mn oxyhydroxide phase flat nodules are enriched in fe p rare earths and as probably associated with an fe oxy hydroxide component aluminum v cr and ti occur in still another phase the sediments of the gulf generally consist of a 10 50 mm thick layer of oxidized surface sediment enriched in mn ba p and ni lying on top of reduced sediments which are diagenetically depleted in these elements the remobilized elements have redeposited in the nodules but this process cannot explain the origin of all the nodular material some released mn ba and ni furthermore enter into suspended phases which eventually leave the baltic sea the economic value of the nodules in the gulf of bothnia is probably limited at present

closure of the central american isthmus and its effect on deep water formation in the north atlantic modern ocean thermohaline driven circulation influences global climate by transporting heat to high latitudes1 2 and by affecting the exchange of co2 between ocean and atmosphere3 north atlantic deep water nadw plays a key role in this circulation and quaternary climate cycles have been linked to changes in nadw flow4 general circulation model simulations indicate that before closure some 3 4 million years ago of the central american isthmus the narrow strip of land linking north and south america the direct flow of low salinity water from the pacific to the atlantic ocean would have led to a smaller nadw flow5 6 sedimentation patterns7 and nutrient proxies8 11 support these model results by indicating an increase in nadw flow around the time of isthmus closure but these records do not allow changes in different nadw sources to be distinguished and the overall effect of closure on global ocean circulation is poorly known here we present nd pb and sr isotope records preserved by a hydrogenous ferromanganese crust from the nadw flow path in the western north atlantic ocean these records indicate that the isotopic signal associated with nadw strengthened around 3 4 million years ago showing that deep water that formed in the labrador sea made a gradually increasing contribution to nadw flow these data taken together with those from the central pacific ocean12 indicate an increased nadw flow since isthmus closure and suggest that the closure established today s general pattern of ocean circulation

actual timing of neodymium isotopic variations recorded by femn crusts in the western north atlantic hydrogenetic ferromanganese femn crusts from the western north atlantic record variations in the nd and pb isotopic composition of cenozoic deep water preserved during their growth the timing and cause of the most striking change have been the subject of debate some have proposed that the shift took place after 4 ma in response to the closure of the panama gateway others have argued that the major change in isotope composition occurred as early as 8 ma this study presents high resolution nd isotope records for crusts previously dated using 10be 9be chronology these data confirm that the shifts in nd occurred after 4 ma consistent with a likely relationship with the closure of the central american isthmus and intensification of northern hemisphere glaciation and in accordance with changes seen in other physical and chemical records these results illustrate the need for both a robust chronological framework and high resolution records before a reliable paleoceanographic interpretation can be made of the variations recorded by femn crusts

total meltwater volume since the last glacial maximum and viscosity structure of earth s mantle inferred from relative sea level changes at barbados and bonaparte gulf and gia induced j2

the lageos constraint on deep mantle viscosity results from a new normal mode method for the inversion of viscoelastic relaxation spectra the recently observed acceleration in the node of the orbit of the lageos satellite has previously been shown to provide a good constraint on the viscosity of the earth s mantle beneath the 670 km seismic discontinuity this paper explores the extent to which the previously inferred lower mantle viscosity may be traded off against variations of other properties of the radial viscoelastic structure we show explicitly that the nontidal acceleration of rotation inferred from the lageos data and predicted as a consequence of the earth s response to the last deglaciation event of the current ice age is relatively insensitive both to variations of lithospheric thickness and to the presence or absence of plausible chemical heterogeneity across the 670 km interface it therefore provides a high quality constraint on the viscosity of the deep mantle with the upper mantle viscosity fixed at the nominal value of 1021 pa s the bounds on lower mantle viscosity lm are such that 2 1021 pa s lm 6 1021 pa s even when allowance is made for the presence of a viscous boundary layer at the base of the upper mantle such as would exist if the mantle convective circulation were layered

late holocene sea level change on rota and guam mariana islands and its constraint on geophysical predictions abstract holocene emergent reefs and notches are well distributed on rota and guam relative sea level changes at these islands are reconstructed based on geomorphological observations and borings on present and emergent reefs together with 54 radiocarbon dates sea level rose gradually to a maximum of 1 8 m between 6000 and 4200 yr b p and reached its highest level by 4200 yr b p on both islands after 3200 yr b p abrupt uplift caused emergence of the reef by subtracting the tectonic effect we obtained the sea level change in the marianas sea level reached its present level by 4200 yr b p and has remained almost stable since then reconstructed late holocene sea level change in the mariana islands provides constraints on geophysical models of sea level variations

global sea level trend in the past century data derived from tide gauge stations throughout the world indicate that the mean sea level rose by about 12 centimeters in the past century the sea level change has a high correlation with the trend of global surface air temperature a large part of the sea level rise can be accounted for in terms of the thermal expansion of the upper layers of the ocean the results also represent weak indirect evidence for a net melting of the continental ice sheets

60 myr records of major elements and pb nd isotopes from hydrogenous ferromanganese crusts reconstruction of seawater paleochemistry we compare the time series of major element geochemical and pb and nd isotopic composition obtained for seven hydrogenous ferromanganese crusts from the atlantic indian and pacific oceans which cover the last 60 myr average crust growth rates and age depth relationships were determined directly for the last about 10 myr using be 10 be 9 profiles in the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial be 10 be 9 ratios due to the lack of additional information co contents have also been used previously to estimate growth rates in co rich pacific and atlantic seamount crusts puteanus and halbach 1988 a comparison of be 10 be 9 and co based dating of three co rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated be 10 be 9 based growth rates back to 60 ma our data show that the flux of co into co poor crusts has been considerably lower the relationship between growth rate and co content for the co poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits manheim 1986 the results suggest that the co content provides detailed information on the growth history of ferromanganese crusts particularly prior to 10 12 ma where the be 10 based method is not applicable the distributions of pb and nd isotopes in the deep oceans over the last 60 myr are expected to be controlled by two main factors a variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and b variability of supply rates or provenance of detrital material delivered to the ocean linked to climate change glaciations or major tectonic uplift the major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust consequently any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution this is because local processes appear to have dominated over more basin wide paleoceanographic effects in this study co is the only element which shows a relationship to pb and nd isotopes in pacific crusts a possible link to changes of pacific deep water properties associated with an enhanced northward advection of antarctic bottom water from about 14 ma is consistent with the pb but not with the nd isotopic results the self consistent profiles of the pb and nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts including phosphatization events have been insignificant for particle reactive elements such as pb be and nd isotope time series of pb and nd show no systematic relationships with major element contents of the crusts which supports their use as tracers of paleo seawater isotopic composition

glacial rebound and relative sea level variations a new appraisal summary late pleistocene and holocene changes in sea level at technically stable shorelines contain information on the melting history of the ice sheets and on the response of the earth to changes in surface loads on time scales of 104yr some separation of parameters defining the ice loads and the earth s response can be achieved by examining sea level change at different sites around the world and at different epochs this paper examines the mathematical requirements for obtaining satisfactory solutions for the sea level equation rather than emphasizing results for the earth s response to the surface loads an examination of the equation expressing the sea level variation on a viscoelastic earth indicates that careful consideration needs to be given to both the definition of the ice load and the geometry of the redistributed water load if geophysically significant earth response parameters are to be deduced from observations of relative sea level the spectrum of the 5 x 5 area mean description of the ice load widely used in glacial rebound studies contains significant power at high degrees n 30 and can result in substantial spatial variations in sea level unless a thick lithosphere is introduced in the earth s response function a smoothed 1 1 description of the ice model avoids these high degree oscillations in relative sea level and produces satisfactory sea level results without requiring a thick lithosphere at far field sites the holocene sea levels are sensitive to the earth s response to the meltwater loading in the vicinity of the site and a high degree spatial resolution of coastline geometry is required to model the mantle flow driven by the differential loading about the site at some sites convergence of the solution to the sea level equation is not obtained even when the solution is expanded to degree 180 convergent solutions at lower degrees can be achieved by introducing earth models with a moderately thick lithosphere if high resolution ice and meltwater load models are not used then the tendency will be to overestimate the effective elastic thickness of the lithosphere estimates of mantle viscosity are also of questionable value if these high resolution models are not used a preliminary examination of sea levels at sites in both the near and far field places an upper limit of about 50 80 km on the effective lithospheric thickness these sea level observations are also consistent with an upper mantle viscosity of about 1021 pas with a lower mantle viscosity in the range of 1021 1023pa s

holocene humidity changes in northern finnish lapland inferred from lake sediments and submerged scots pines dated by tree rings conclusive evidence for a rise in water levels has been found in connection with lake sediment studies undertaken partly in collaboration with the pine megafossil sampling and dendrochronological work in northern finnish lapland the change in lake level stands is shown by slow sedimentation rate in the early to mid holocene and an increase thereafter these data indicate a regional rise in water levels during the latter part of the holocene following a relatively dry period between 8000 and 4000 bp synchronous changes also indicating rising water levels have been observed in the diatom and cladoceran assemblages of the sediment cores subfossil scots pines pinus sylvestris l have been preserved in large quantities in small lakes in lapland because in many cases the rising water level has inundated the trunks after death the position of the subfossil trunks and stumps often indicates that the pines have been growing on dry land at the sides of the lakes in which they are now submerged traces of

constraints on mantle viscosity from relative sea level variations in hudson bay a number of previous analyses have suggested that the relative sea level record in hudson bay constrains the viscosity of the lower mantle to be near 1021 pa s these conclusions have been based on a limited number of forward calculations which have assumed an isoviscous lower mantle region we compute frechet kernels for the rsl data in hudson bay to determine the detailed depth dependent sensitivity of the data to variations in a viscosity profile which is consistent with the past inferences we find that the rsl data provide a robust constraint on the average viscosity in the top half of the lower mantle only the average must be near 1021 pa s the data are less sensitive to variations in the viscosity below approximately 1800 km depth and in the upper mantle forward analyses included herein show that the data admit models whose average viscosity in the deep mantle below 1800 km depth and in the upper mantle can differ significantly from the value near 1021 pa s estimated for the top half of the lower mantle the total variation in the viscosity from the surface to the cmb can exceed an order of magnitude or more and still satisfy the constraint provided by the hudson bay rsl data set the necessity of invoking an isoviscous mantle model in previous studies is thus seen to be a consequence of the limited class of viscosity model solutions employed in those studies

glacial isostatic adjustment and the free air gravity anomaly as a constraint on deep mantle viscosity summary a gravitationally self consistent theory for relative sea level variations forced by pleistocene deglaciation events is employed to explore the extent to which rsl and free air gravity observations together constrain the viscosity of the mantle beneath the seismic discontinuity at 670 km depth a trade off is revealed between errors in the assumed deglaciation history and errors in the inferred value of the viscosity of the lower mantle taking full account of such uncertainty plausible values of the viscosity beneath the transition region are bounded above by 1023 poise cgs units the preferred value is at least a factor of 2 lower than this and is strongly constrained by the observed free air gravity anomaly over hudson bay the calculations described in detail here show for the first time that the relatively large gravity anomalies observed over sites of wurm wisconsin deglaciation do not require any pronounced increase of mantle viscosity with depth in order to explain them

low frequency temperature variations from a northern tree ring density network we describe new reconstructions of northern extratropical summer temperatures for nine subcontinental scale regions and a composite series representing quasi northern hemisphere temperature change over the last 600 years these series are based on tree ring density data that have been processed using a novel statistical technique age band decomposition designed to preserve greater long timescale variability than in previous analyses we provide time dependent and timescale dependent uncertainty estimates for all of the reconstructions the new regional estimates are generally cooler in almost all precalibration periods compared to estimates obtained using earlier processing methods particularly during the 17th century one exception is the reconstruction for northern siberia where 15th century summers are now estimated to be warmer than those observed in the 20th century in producing a new northern hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data and the reliability of each regional series begins to decrease we compare our new hemisphere series to other published large regional temperature histories most of which lie within the 1 confidence band of our estimates over most of the last 600 years the 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period

postglacial sealevels in the pacific implications with respect to deglaciation regime and local tectonics nakiboglu sm lambeck k and aharon p 1983 postglacial sealevels in the pacific implications with respect to deglaciation regime and local tectonics tectonophysics 91 335 358 observations of holocene sealevel fluctuations contain forrnati on the mehing history of the major past ice sheets on the viscosity of the mantle and on vertical motions of tectonic origin seafevel changes at eleven sites in the southwest pacific region have been examined with the following results 1 the ice i model of peltier and andrews 1976 for arctic deglaciation is inadequate to explain all sealevels two alternative modifications of this model are a a forward shift in the deglaciation history with the onset of major melting starting at about 14 000 yrs ago and ending at 6ckto yrs ago fb the ice 1 model for the arctic deglaciation from 17 000 to 7000 yrs b p plus a significant amount of antarctic melt water 2 the effective mantle viscosity is in the range 10 lo22 p although the sealevel results for the locations studied are not strongly dependent on viscosity 3 vertical motions of tectonic origin can be separated from the hydro isostatic sealevel fhtctuations if these motions exceed about 0 5 mm yr i only two locations provide clear evidence for vertical motion consistent with independent geological observations the huon peninsula of new guinea is undergoing uplift of between 1 2 and 1 7 mm yr t while the hawaiian island of oahu is subsiding at a rate of about l 2 mm stations along the southeastern and eastern coast of australia are suggestive of small uplift of perhaps 0 5 i 0 mm yr i the sealevels in new zealand and the mnlacca straits are also found to be in agreement with other observations that point to regional tectonic stability

nd isotope signature of holocene baltic mn fe precipitates as monitor of climate change during the little ice age neodymium nd isotope profiles were analyzed on two baltic mn fe precipitates 99 2 and tl1 from shallow water 20 m of the mecklenburg bay the age range of these mn fe precipitates determined by 226raex ba dating reaches from recent growth back to 4300 and 1000 yr bp respectively over this time range the nd isotope composition varies from end 0 13 1 to 17 5 in the selected baltic precipitates indicating substantial changes in the nd isotope composition of the baltic sea the lowest end values were recorded during the time interval of the little ice age lia ad 1350 to 1850 these minimum values indicate either an increase of the input of less radiogenic nd from scandinavian archean proterozoic sources end about 22 to the baltic sea or a decrease of the input of more radiogenic nd from continental european sources end about 12 and or north sea water end about 10 variations of both erosive continental input and north sea inflow may indicate a direct response of the nd isotope signal in the baltic sea to climate changes during the lia and be related to cyclic shifts in the atmospheric circulation triggered by the north atlantic oscillation nao another aspect that possibly influenced the input of trace elements and nd isotopes into the baltic sea is the population development in the circum baltic area during the lia the lowest end values also correspond to the medieval demographic crises that led to a significant decrease of agricultural activity and farmland the reduction of soil erosion and enhanced regrowth of natural vegetation may have changed the amount and proportions of dissolved and suspended particulate matter transported into the baltic sea by rivers which in turn may have resulted in a change of the nd isotope composition of baltic sea water

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

sea level changes since the last glacial maximum an appraisal of the ipcc fourth assessment report the ipcc fourth assessment report ar4 stated that global sea level rose by about 120 m between the last glacial maximum lgm and 3 2 ka and did not rise again until the late 19th century a review of relevant literature demonstrates that the rise may have been larger by 10 15 m that the timing of stabilisation is poorly constrained within the last 7 ka bp and that the onset of modern rates of sea level rise is not synchronous and uniform across the globe the lgm lowstand as defined in the ar4 is based on the classic barbados sea level history but the sea level curve from this island may not be an accurate eustatic approximation if glacial isostatic adjustment gia processes were significant as suggested by various authors the barbados sea level curve revealed the existence of meltwater pulse mwp 1a at around 14 000 cal a bp questions about the source and causal mechanism of mwp 1a are still being explored by field scientists and gia modellers these problems have direct relevance for contemporary measurements of ice mass changes because space geodetic measurements rely on information provided by gia models to separate land motion from ice mass changes global patterns of holocene sea level change are controlled by regional sea level variability not only through isostatic and tectonic processes but also through steric effects longer wavelength gravitational changes produced by changing ice ocean mass flux and hemispheric scale perturbations in the earth s rotation eustasy is therefore merely a concept not a measurable quantity constraining the late holocene ice melt contribution to global sea level rise and determining regional sea level rise patterns in the 18th and 19th centuries are important future tasks for sea level scientists these will establish the baseline contributions to 20th and 21st century sea level rise and will help to determine the causes of modern rates of sea level rise constraining historical sea level accelerations and short term ice mass flux will aid models of ice sheet dynamics and help to reduce current uncertainties in future sea level predictions the ar4 shows that regional sea level variability is clearly present in sea level change patterns for the past 50 a and an important challenge for the next ipcc assessment is to incorporate this variability into regional future sea level rise scenarios copyright 2009 john wiley sons ltd

continental runoff of osmium into the baltic sea the isotopic composition of osmium os in continental surface waters and shallow ground waters has been determined by analyzing fresh water fe mn nodules and bog ores the isotopic composition of the continental runoff from the precambrian baltic shield is much more radiogenic 187 os 186 os 31 2 65 4 than the runoff from the phanerozoic sedimentary platform to the south of the baltic sea 187 os 186 os 8 6 11 0 fe mn nodules from the baltic sea have intermediate values 187 os 186 os 12 4 21 2 indicating mixture of north sea water and continental fresh water isotope mass balance calculations indicate that the concentration of os in the continental runoff is similar to the os concentration in seawater extrapolating these data to infer the global runoff yields 48 kg yr comparable with previous estimates the residence time of os in seawater relative to continental runoff is calculated at 32 ka the oceanic residence time of os relative to the bulk input to seawater is 16 ka if the mean 187 os 186 os of the continental runoff is 16 the os isotopic composition of the continental runoff is much more variable than previously suggested 187 os 186 os values 30 being characteristic of precambrian shields glaciation of old cratonic shields might therefore modulate riverine supply of this very radiogenic cratonic os linking accelerated increase in the marine os isotope record to glaciations of precambrian shields

influence of glacial isostatic adjustment on tide gauge measurements of secular sea level change modem tide gage records of secular sea level change are strongly contaminated by the ongoing influence of glacial isostatic adjustment in this paper we employ an accurate high resolution model of the glacial isostatic adjustment process to filter this signal from time series consisting of annual mean heights observed on over 500 tide gages from which records of duration longer than 10 years are available these records are all contained in the archive of the permanent service for mean sea level at bidston in the united kingdom prior to removal of the isostatic adjustment contamination from these records the secular sea level change signal is seen to exhibit both rising and falling levels depending upon geographic location with regions of falling level corresponding to those that were ice covered during the last glaciation event of the present ice age after filtering the geographic heterogeneity in rates is considerably reduced so much so that a globally coherent component consisting of a rise of sea level at a rate of 2 4 0 9 mm yr 1 is revealed this could conceivably be driven by the greenhouse effect although no particular mechanism has been unambiguously identified by our analyses we investigate the impact of a number of different variants of the analysis procedure upon the inferred global signal

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

the sources and transport of sr and nd isotopes in the baltic sea we have determined the concentration and isotopic composition of sr and nd in waters from the baltic sea the baltic sea is an intracontinental stratified brackish water estuarine like system and the rivers emptying into it drain a suite of terranes ranging from proterozoic archean in the north to phanerozoic in the south the sampled brackish waters range in salinity from seawater sw at 35 289 to a minimum of 2 460 at the surface in the innermost part of the gulf of bothnia the sr concentrations show generally conservative behavior indicating a simple two component mixing however small deviations 3 70 from a perfect mixing line reveal that the imprints from rivers with different sr concentrations are preserved in the blending strontium concentrations from a depth profile across the redoxcline in the baltic proper indicate that vertical particle transport alters the sr concentration in the water our estimated concentration of sr in the average freshwater input to the baltic is 0 03 ppm which is only about 0 4 of the sw concentration the sr isotopic data range from e sr sw 0 in seawater to e sr bw sw 7 8 in the least saline baltic water bw sample in the gulf of bothnia the isotopic composition of sr versus 1 sr in the baltic sea follows an almost perfect mixing line which shows that seawater sr is mixed with much more radiogenic components calculated end member values of e sr sw for each sample show that the riverine input into the gulf of bothnia has e sr sw 120 200 and 10 50 e units in the baltic proper these values are in general agreement with direct measurements of river waters in each region however the calculated values in the gulf of bothnia are lower than the measured river water input in this region which indicates the presence of less radiogenic sr presumably originating from the river waters draining the southern part of the basin which are partially transported northward and mixed with sr from the gulf of bothnia rivers the nd concentration in the baltic sea is not conservative varying between 5 and 45 ppt with the highest concentrations in the bottom waters due to vertical particulate transport a plot of e nd o in baltic water yields a good correlation with the calculated freshwater end member e sr sw the data show that it is possible to unravel the different freshwater sources into the baltic and to identify the zones of particulate removal of both non conservative species such as the ree and of quasi conservative species such as sr the use of isotopic tracers in this estuarine environment may provide a much better insight into mixing and element transport it should also be possible to trace lateral movements of freshwater inputs

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

induced stresses and fault potential in eastern canada due to a realistic load a preliminary analysis summary in order to understand the causal relation between postglacial rebound and earthquakes a simple disc load model is used to 1 calculate stresses induced in the lithosphere and mantle by glacial loading melting and postglacial rebound and 2 evaluate the effect of glacial loading rebound on the failure potential for earthquakes in the upper crust the dependence of the failure potential and the actual mode of failure on the coefficient of friction the ambient tectonic stress magnitude direction the stress due to the overlying rocks and lithospheric thickness are investigated prominent features of this paper are the inclusion of 1 a viscoelastic mantle and thus the migration of stress and 2 the ambient tectonic stress and overburden stress contributions in the calculation of the total stress field it is assumed that throughout the earth there are optimally oriented pre existing virtual faults that are initially close to but not at failure thus a time dependent quantity called dfsm related to the coulomb mohr failure criterion can be defined such that a negative value of dfsm would advocate faulting or earthquake activities whereas a positive value of dfsm would promote stability the results indicate that under all combinations of tectonic stress magnitude and overburden stress crustal loading promotes fault stability directly underneath the load upon the removal of the load thrust faulting is predicted within the ice margin if the horizontal stress s induced by the overburden is greater than or equal to the vertical component s of the overburden stress 121 where sjs under this condition theory predicts that faulting or earthquake activity should have reached a maximum immediately after deglaciation if the horizontal stress induced by the overburden is less than the vertical component of the overburden stress 1 l then theory predicts fault stability within the ice margin the theory predicts fault instability both north and south of the ice margin the mode of failure however is completely determined by the value of i the trade off between the tectonic stress magnitude and the overburden stress parameter 1 is also investigated it is shown that a larger tectonic stress magnitude can be used to compensate a smaller value of 1 the results of this analysis show that variations in the coefficient of friction lithospheric thickness and a ductile zone below the upper crust do not significantly affect the above conclusions

evolution of nd and pb isotopes in central pacific seawater from ferromanganese crusts abstract hydrogenetic ferromanganese crusts incorporate elements from ambient seawater during their growth on seamounts by analysing nd pb and be isotope profiles within crusts it is possible to reconstruct seawater tracer histories depth profiles of 10be 9be ratios in three pacific ferromanganese crusts have been used to obtain growth rates which are between 1 4 and 3 8 mm ma nd and pb isotopes provide intact records of isotopic variations in pacific seawater over the last 20 ma or more there were only small changes in pb isotope composition in the last 20 ma this indicates a constant pb composition for the erosional sources and suggests further that erosional nd inputs may have been uniform too end values vary considerably with time and most probably reflect changes in ocean circulation the end values of the crusts not only vary as a function of age but also as a function of water depth from 25 to 0 ma crust va13 2 from 4 8 km water depth has a similar pattern of end variation to the two shallower crusts from 1 8 and 2 3 km but about 1 0 to 1 5 units more negative this suggests that end stratification in pacific seawater as demonstrated for the present day has been maintained for at least 20 ma each crust shows a decrease in end from 3 5 ma to the present which is interpreted in terms of an increase in the nadw component present in the pacific from 10 to 3 5 ma ago the crusts show an increase in end this suggests a decreasing role for a deep water source with end less than circum pacific sources in this regard the panamanian gateway restriction from 10 ma with final closure at 3 5 ma may have played an important role in reducing access of atlantic derived nd to the pacific

the little ice age only the latest big chill boston at the spring meeting of the american geophysical union here earlier this month paleoceanographers reported that they had found tiny bits of ice borne rock in north atlantic sediments laid down during the little ice age from about 1400 to 1900 and in older sediments every millennium or two beginning at least 130 000 years ago the finding implies that earth has experienced a long string of little ice ages perhaps driven by variations in the sun or by changes in ocean currents it also suggests that the world will be warming naturally as part of this roughly 1500 year climate cycle on top of any human induced greenhouse effect

glacial isostatic adjustment and the anomalous tide gauge record of eastern north america sea level variations as recorded by the global network of tide gauges represent a rich data set for studying a wide range of natural and anthropogenic phenomena such as the sea level rise induced by possible global warming for this purpose long term sea level trends must be corrected for the contaminating effects of continuing glacial isostatic adjustment1 5 gia the numerical correction procedure has for sites on the east coast of north america yielded a set of highly anomalous sea level rates characterized by systematic geographical trends2 4 5 we demonstrate that these trends are a consequence of inadequacies in the previous standard numerical prediction for gia in particular we find that the well known trends in the gia corrected tide gauge rates are eliminated if the lower mantle viscosity of the earth model used in the gia prediction is increased this result obviates the need to explain the anomalous trend as a manifestation of gulf stream ocean circulation4 or neotectonic processes2

the influence of a finite glaciation phase on predictions of post glacial isostatic adjustment we predict relative sea level rsl variations present day three dimensional 3d crustal deformation rates and baseline velocities and a set of anomalies in the gravitational field of the planet using a suite of models for the space time geometry of the pleistocene ice sheets these models are distinguished on the basis of the details of the glaciation phase and they include the cases of an infinite glaciation phase i e an assumption of isostatic equilibrium at the time of the last glacial maximum lgm a steady uniform glaciation and a glaciation in which the bulk of the accumulation is limited to the final stages of the growth phase comparison of the observational records of postglacial rsl change with predictions based on the assumption of isostatic equilibrium at lgm have commonly been used to infer both the space time geometry of the final deglaciation event and the mantle viscosity we conclude that both these applications may be influenced significantly by the incorporation of a finite glacial cycle as an example rsl predictions which assume isostatic equilibrium at lgm and those which incorporate a relatively rapid glaciation phase can differ by a factor of 2 or more at some sites within previously glaciated regions when an earth model characterized by a lower mantle viscosity of 1022 pa s is adopted we have also found that differences in the adopted model for the glaciation event are capable of explaining entirely the discrepancies 0 2 mm yr between previously published predictions of present day tangential velocities in north america these discrepancies are characterized by a dominant long wavelength signal and hence they do not necessarily influence strongly predictions of baseline velocities variations in the glaciation model can also have an important effect on predictions of peak gravity anomalies over previously glaciated regions and secular variations in the zonal harmonics of the earth s geoid in both cases the effect may be sufficient to alter significantly the signal from other geophysical processes which may need to be invoked to reconcile the observational constraints

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

lithospheric thickness antarctic deglaciation history and ocean basin discretization effects in a global model of postglacial sea level change a summary of some sources of nonuniqueness the global model of postglacial relative sea level variations that has been developed over the past decade is employed to investigate the constraints that it may be invoked to place on the timing of the deglaciation of west antarctica the analyses presented here confirm the suggestion of p wu and w r peltier 1983 geophysical journal of the royal astronomical society74 377 450 that the model of this event employed inj a clark and c s lingle 1979quaternary research11 279 298 may be simply modified to rectify the misfits between theory and observation that are otherwise obtained at southern hemisphere sites a large number of southern hemisphere relative sea level data are shown to require that the retreat of antarctic ice substantially lagged the retreat of northern hemisphere ice if the deglaciation of antarctica was abrupt the time of onset of antarctic deglaciation is thereby shown to coincide with the time of most rapid northern hemisphere deglaciation sensitivity tests are performed which demonstrate that this result is relatively insensitive to the discretization employed to represent the ocean basins the only exception to this general rule obtains at some coastal sites at which a trade off is revealed between the delay of west antarctic melting and the thickness of the lithosphere required to reconcile the observed local variations of relative sea level at such sites which are all in the far field of the ice sheets some attention must be paid to the accuracy of the local finite element representation of the oceans and to the details of the antarctic deglaciation history

isotopic compositions of ce nd and sr in ferromanganese nodules from the pacific and atlantic oceans the baltic and barents seas and the gulf of bothnia abstract ferromanganese nodules from the pacific and atlantic oceans the barents and baltic seas and the gulf of bothnia were analyzed for the isotopic compositions of ce nd and sr and the abundances of ree ba and sr ree patterns of barents baltic and bothnian samples show no ce anomaly or even a negative one in contrast to the positive anomaly observed for the pacific and atlantic samples moreover the baltic and bothnian samples have distinctly low end values average end values of the four regions are as follows pacific 5 barents 10 atlantic 11 and baltic inclusive of gulf of bothnia 19 the characteristic low end values of the baltic samples are indicative of the influence of precambrian rocks from the baltic shield of particular interest is the feature of the ce isotopic composition that ece values of the samples from the pacific are negative and those from the other three regions positive this novel finding might suggest a difference in sources of ce between the pacific and other regions these results demonstrate that ce isotopic ratios can be a useful tracer in marine geochemistry in combination with isotopic compositions of nd and sr

pleistocene deglaciation and the global gravity field the present day global geoid and free air gravity anomaly signals induced by pleistocene deglaciation have been computed along with their secular variations a revised green function has been derived for the free air gravity anomaly and we find that an earth model with a lower mantle viscosity moderately larger than the upper mantle value satisfies observations of the anomaly over both hudson s bay and fennoscandia using this preferred earth model the predicted global geoid anomaly map is characterized by peak negative values of 36 7 9 4 and 21 9 m over hudson s bay northern europe and antarctica respectively and by a smooth small amplitude 2 5 m upwarping over the major ocean basins although the field has an order of magnitude less power than the observed there is a significant spatial correlation between the two inferences of mantle viscosity based upon comparisons between the observed geoid and the computed deglaciation induced anomaly are hampered by the large contribution from the convective circulation in the earth s mantle we have subtracted a predicted convection signal based on seismic tomography from the observed field however the residual geoid thus obtained is still too inaccurate to allow a useful comparison in contrast a filtered version of the observed geoid over canada which retains harmonic coefficients in the degree range 10 22 provides a relatively uncontaminated by convection datum that is indeed satisfied by the preferred earth model secular variations in the earth s gravitational field are naturally dominated by the signal from pleistocene deglaciation in this respect we compute zonal harmonics in the expansion of the present day rate of change of the geopotential and in particular we predict amplitudes comparable to that for the previously analysed j2 for j4 j5 j7 and j9 all of which reflect in large part the response due to the melting of the massive laurentide ice sheet this analysis suggests that measurement of these higher order secular variations of the zonal harmonics based upon analysis of long time series of lageos ranging data could provide very useful additional constraints on the radial variation of mantle viscosity these constraints along with all others described in this paper are shown to be relatively insensitive to assumptions concerning the deflection during the glacial isostatic adjustment process of the 400 and 670 km density discontinuities within the mantle

pleistocene deglaciation and the earth s rotation a new analysis summary this paper is concerned with an analysis of the effect of the pleistocene glacial cycle upon the earth s rotation we demonstrate that two important geophysical observables may be explained as aspects of the rotational response to surface mass loading by ice sheets these are the astronomically observed non tidal component of the acceleration of planetary rotation and the secular drift of the rotation pole relative to the surface geography which is evident in the ils pole path the former observation is shown to provide an unambiguous constraint upon the viscosity of the planetary mantle and requires a depth dependence of this parameter which is the same as that which has previously been inferred in studies of the relative sea level variations and free air gravity anomalies associated with post glacial rebound the observed secular drift of the pole cannot provide an independent estimate of the viscosity of the mantle because it depends jointly upon mantle viscosity and lithospheric thickness with the viscosity profile fixed by the rebound data the observed speed of polar wander suggests a continental lithospheric thickness which is in excess of that appropriate for old ocean basins but nevertheless in accord with independent constraints

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

a new holocene relative sea level curve for western brittany france insights on isostatic dynamics along the atlantic coasts of north western europe abstract this study presents new relative sea level rsl data that were obtained in the finistere region western tip of brittany france and the implications those data have for the understanding of the isostatic dynamics across north western europe and more specifically along the atlantic and channel coasts new stratigraphic sequences were obtained and analyzed to derive 24 new sea level index points in which 6 are basal these new data considerably increase the knowledge we have of the rsl evolution along the coasts of western brittany since the last 8 kyr b p from this new dataset rsl was estimated to rise continuously over the last 8 kyr with a major inflection at ca 6 kyr cal bp our results show large vertical discrepancies between the rsl records of brittany and south western uk with the latter plotting several meters below the new data from this comparison we suggest that the two regions underwent a very different pattern and or amplitude of subsidence during the last 8 kyr which has implications for the spatial and temporal pattern of the peripheral bulge of the european ice sheets we compared our data against predictions from glacio isostatic adjustment models gia models there are large misfits between rsl observations and the predictions of the global ice 5g vm2a peltier 2004 glac1 b tarasov and peltier 2002 tarasov et al 2012 briggs et al 2014 and regional uk models biis bradley et al 2009 bradley et al 2011 kuchar kuchar et al 2012 which can t be resolved through significant changes to the deglaciation history and size of the british irish ice sheet paleo tidal modelling corrections indicate regional changes in the tidal ranges played a negligible role in the data model misfits hence we propose that the misfits are due to some combination of i unaccounted mass loss of far field ice sheets antarctic ice sheet or laurentide ice sheet ii unresolved differences in the deglaciation history and size of the fennoscandian ice sheet or more likely iii significant lateral variations in the earth s structure across the english channel

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

world map of nd isotopes in sea floor ferromanganese deposits the nd isotopic compositions of hydrogenous ferromanganese encrustations and nodules largely reflect those of the overlying seawater integrated over the few millions of years over which they grow available nd isotope data on ocean floor hydrogenous deposits suggest control by nd from particulates blown from the continents and released by volcanic activity associated with subduction zones and midocean ridges the regional nd isotope variations display a marked similarity to the broad patterns of present day deep ocean circulation suggesting that the particulates that are the sources of oceanic nd travel along with water masses despite rapid 10 100 ka perturbations during glacial periods the long term patterns of water mass movements and oceanic fluxes of particulates have remained essentially stable over the last few million years

near field hydro isostasy the implementation of a revised sea level equation summary we describe how the existing sea level equation incorrectly predicts the change in sea level and thus the ocean load in ice covered subgeoidal geographic regions during periods of deglaciation we go on to present a new sea level equation that overcomes this problem and we describe how this equation can be solved in a gravitationally self consistent manner by employing a well known spectral technique application of the new theory to predict relative sea level rsl histories and present day 3 d solid surface deformation rates in northeastern canada based on a single earth model characterized by a lithospheric thickness of 100 km and upper and lower mantle viscosities of 5 1020 and 5 1021 pa s respectively demonstrates that a significant error is introduced when the original theory is employed to predict the oceanic component of the surface load predictions of rsl curves show a discrepancy of 40 per cent at sites where data have been obtained and employed to constrain models of earth viscosity structure and ice sheet histories this error will significantly bias estimates of mantle viscosity structure and ice thicknesses that are based on the original theory in addition predictions of 3 d deformation rates differ by up to 25 per cent in some regions and so future applications that employ these data to constrain models of the glacial isostatic adjustment process should adopt the improved sea level theory in contrast estimates of inverse decay times from the predicted rsl curves are insensitive to within the observational error to the improvement in the surface load introduced by the new theory thus viscosity structure inferences based on this parametrization and the original sea level equation are unaffected by the error in the ocean load finally the new theory predicts a eustatic i e globally uniform rise in sea level over the postglacial period that is 11 m lower than that determined via the original theory therefore estimates of the global ice budget at the last glacial maximum based on far field rsl data and the original sea level theory will be too small by 10 per cent

predictions of secular geoid changes from late pleistocene and holocene antarctic ice ocean mass imbalance summary estimates on ice volume changes in antarctica from both contemporary mass imbalance during the last hundred to thousand years and ice volume changes during the last glacial cycles are difficult to obtain future satellite gravity missions monitoring secular changes in gravity as a proxy of mass changes of the antarctic ice sheet will therefore provide an additional important constraint on the antarctic ice sheet history we assess the contributions from both past ice volume changes during the last glacial cycles and present ice imbalances over antarctica using a variety of published ice models model predictions of secular changes of the geoid anomaly based on plausible mantle viscosity profiles enable us to discuss the importance of past and present ice volume changes and their characteristic signatures while uncertainties arising from the viscosity profile are of secondary importance for model predictions of the secular change of the geoid anomaly we expect significant bias of the observed signal from uncertainties in the timing of the end of deglaciation which is in agreement with previous studies hence the benefit of inferring present day antarctic ice imbalance from satellite gravity missions will depend on improvements to ice models for the last glacial cycle

age and ϵ nd constraints on the palaeoproterozoic tectonic evolution in the baltic sea region abstract the metamorphic precambrian basement in the western part of the east european craton eec has previously been considered to be archaean in age recent u pb and sm nd studies in estonia poland and belarus have however revealed a vast area of palaeoproterozoic crust in order to survey the crustal ages in latvia and lithuania and to establish the relationships of these territories with adjacent regions of the eec particularly those exposed in the baltic and ukrainian shields three new u pb zircon age determinations and 21 nd whole rock analyses were performed in latvia a granodiorite yielded an intrusion age of 1816 5 ma and a felsic metavolcanic rock an age of metamorphism at 1810 2 ma with indications of a minimum protolith age of ca 1840 ma in lithuania a metasediment yielded a multigrain u pb zircon age of 2302 200 100 ma very similar to multigrain zircon ages of svecofennian metasediments in scandinavia the nd survey of various rock types demonstrated relatively little variation with depleted mantle model ages between 2 4 and 1 9 ga for the igneous rocks and between 2 5 and 2 0 ga for the metasedimentary ones this indicates only minor influence of archaean crust but close isotopic similarity to rocks of the same lithologies in the svecofennian domain of sweden and finland together with recent u pb and sm nd results from other parts of the eec the present study suggests a close relationship between the palaeoproterozoic crust in estonia western latvia and western lithuania and the southern part of the svecofennian domain within the baltic shield all these regions have u pb zircon ages of rock formation between 1 90 and 1 82 ga and were subjected to a major metamorphic event between 1 83 and 1 81 ga these ages contrast with ages between 2 0 and 1 9 ga for similar rocks farther east and southeast i e closer to the ukrainian shield altogether the current results reaffirm an accretionary character of the palaeoproterozoic crust in the western part of the eec as previously concluded by other investigators in addition there is basis to suggest that the crust in western latvia and lithuania was formed during the late stages of the svecofennian orogeny and thus can be correlated with juvenile late svecofennian crust in southeastern sweden

trace metal fluxes to ferromanganese nodules from the western baltic sea as a record for long term environmental changes trace element profiles in ferromanganese nodules from the western baltic sea were analyzed with laser ablation inductively coupled plasma mass spectroscopy la icp ms and synchrotron based micro x ray radiation techniques fluorescence msxrf and diffraction mxrd at high spatial resolution in growth direction of the trace elements studied zn cu cd ni co mo ba zn showed the most significant enrichment with values in the outermost surface layers of up to six fold higher than those found in older core parts the high resolution zn profiles provide the necessary temporal resolution for a dating method analogous to dendrochronology profiles in various samples collected during two decades were matched and the overlapping sections used for estimation of the accretion rates assuming a continuous accretion of these relatively fast growing nodules on average 20 mm a 1 over the last century the zn enrichment was thus assessed to have commenced around 1860 70 in nodules from the kiel bight and in 1880 90 from mecklenburg bight reflecting the enhanced heavy metal emissions with rising industrialization in europe apart from the obvious success with zn only as and co show significant but only 1 5 fold enrichments in the most recent growth layers of the nodules other anthropogenic trace metals like cu and cdmore are not at all enriched which together with the distinct early diagenetic fe mn banding weakens the potential of the nodules for retrospective monitoring less

the isotopic composition of nd in a boreal river a reflection of selective weathering and colloidal transport in this study the nd concentrations cnd from 18 months of weekly sampling of filtered water 90 dominated by a colloidal phase primarily composed of organic c and fe the end 0 and 147sm 144nd only vary within a narrow range 27 1 to 24 8 and 0 103 to 0 110 respectively with no obvious relationship to cnd and discharge the end 0 and 147sm 144nd in the river water is significantly lower than in the unweathered till and average bedrock in the catchment and show a closer resemblance with the isotopic characteristics found in humic substances and plant material these data show that the isotopic composition of nd exported from a large boreal drainage basin does not directly reflect that of the bulk bedrock in the catchment the isotopic composition is controlled by selective weathering and the nd transport is dominated by organic colloidal particles

postglacial sea level change on a rotating earth first results from a gravitationally self consistent sea level equation we present and solve a gravitationally self consistent sea level equation which governs postglacial sea level variations on a spherically symmetric self gravitating viscoelastic and rotating earth we find that the inclusion of a glacio isostatically induced rotational excitation can significantly affect previous predictions of both present day sea level rates and postglacial sea level histories which were based on a theory that assumed a non rotating earth model to illustrate we consider present day sea level rates and tide gauge corrections along the us east coast and relative sea level curves in the far field of the late pleistocene ice sheets

transient eddy forcing of the rotational flow during northern winter abstract the total direct transient eddy forcing of the vorticity balance in the upper troposphere during northern winter is examined using 11 years of 2 to 8 day bandpassed global analyses most examinations of the importance of high frequency eddy vorticity fluxes to the maintenance of either the climatological standing waves or low frequency anomalous flows have focused on only the horizontal blow or the rotational component of the horizontal transient flow the latter simplification has been shown to be questionable for planetary scales the vorticity flux by the transient divergent flow produces a forcing of the mean streamfunction that is of comparable magnitude with the equivalent rotational term however the streamfunction forcing by the sum of the transient vertical advection and twisting terms largely balances the fearing by the vorticity flux convergence associated with the divergent flow the result is that the convergence of the eddy vorticity flux by the total transient flow is not a good a

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle