slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

northern europe climate variations during late holocene evidence from marine skagerrak abstract granulometric and stable oxygen isotope analyses of four sediment cores from two high accumulation areas in the skagerrak ne north sea were carried out in order to reconstruct climate fluctuations and to evaluate climate impact during the upper holocene extremely high sedimentation rates especially in the eastern skagerrak are explained by increased current activity which is responsible for the transport and deposition of high quantities of suspension load during periods of stormy zonal atmospheric circulation patterns these were most frequent during colder periods while warmer phases are characterized by calmer meridional to zonal atmospheric circulation patterns while the subatlantic climate deterioration and the subboreal climate optimum left only indistinct traces in the sediments the roman climate optimum and a colder period between ca 400 and 700 ad are well documented the following medieval warm period is characterized by a clear temperature increase of the waterbody in connection with less frequent advances of atlantic water masses into the skagerak deep and a decrease in bottom current strength a mode of sedimentation prevails similar to that of recent summer conditions suggesting short and mild winters during that period the onset of the little ice age around 1350 ad however shows an intensified bottom current circulation most probably due to amplifying westerly winds and a decrease in water temperatures in connection with more frequent advances of higher saline atlantic waters the little ice age can be divided into 3 phases a stormy zonal onset a calm meridional maximum and a stormy zonal end the stormy phases are characterized by a sedimentation mode similar to that of recent winter conditions while the little ice age maximum shows conditions comparable to exceptional cold modern winters from 1900 ad at the onset of the modern climate optimum the winter type sedimentation decreases and conditions change again to a level comparable to the medieval warm period

on land ice loss and glacial isostatic adjustment at the drake passage 2003 2009 1 land glacier extent and volume at the northern and southern margins of the drake passage have been in a state of dramatic demise since the early 1990s here time varying space gravity observations from the gravity recovery and climate experiment grace are combined with global positioning system gps bedrock uplift data to simultaneously solve for ice loss and for solid earth glacial isostatic adjustment gia to little ice age lia cryospheric loading the present day ice loss rates are determined to be 26 6 gt yr and 41 5 9 gt yr in the southern and northern patagonia ice fields npi spi and antarctic peninsula ap respectively these are consistent with estimates based upon thickness and flux changes bounds are recovered for elastic lithosphere thicknesses of 35 h 70 km and 20 h 45 km and for upper mantle viscosities of 4 8 1018 pa s and 3 10 1019 pa s using a half space approximation for npi spi and ap respectively using an iterative forward model strategy antarctic peninsula ice models with a prolonged lia extending to a d 1930 are favored in all 2 fits to the gps uplift data this result is largely decoupled from earth structure assumptions the gia corrections account for roughly 20 60 of the space determined secular gravity change collectively the on land ice losses correspond to volume increases of the oceans equivalent to 0 19 0 045 mm yr of sea level rise for the last 15 years

sand invasion along the portuguese coast forced by westerly shifts during cold climate events phases of higher aeolian activity are responsible for the formation and movement of large transgressive dunefields well reported phases of aeolian activity in northwest europe are coincident with global cooling events and were related to enhanced westerly winds and storminess however the extent to which these climatic episodes influenced dunefield dynamics in southwest europe remains an open question ground penetrating radar gpr was used to image the stratigraphy of a cliff top coastal transgressive dunefield in portugal and reconstruct former windfield regimes using optically stimulated luminescence osl five major phases of aeolian activity were dated at 12 6 5 6 1 2 0 4 and 0 3 ka and related to coastal instability and enhanced westerlies these phases were later reconciled to favorable patterns of atmospheric circulation simulated by global and regional climate models at both synoptic and local scales respectively the results prove that major phases of aeolian activity in southwest europe are associated with the onset of cold climate events of global distribution coinciding with aeolian accumulation in northwest europe this implies the dominance of zonal westerlies along the western coast of europe from denmark to portugal during the onset of cold climate events model simulations suggest that the pattern of atmospheric circulation during periods of enhanced aeolian activity is compatible with prolonged negative phases of the north atlantic oscillation nao

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

spatial and temporal evolution of pine island glacier thinning 1995 2006 we use ers 2 and envisat satellite radar altimetry to examine spatial and temporal changes in the rate of thinning of the pine island glacier west antarctica during the period 1995 to 2006 we show that the pattern of thinning has both accelerated and spread inland to encompass tributaries flowing into the central trunk of the glacier within the 5 400 km 2 central trunk the average rate of volume loss quadrupled from 2 6 0 3 km 3 yr 1 in 1995 to 10 1 0 3 km 3 yr 1 in 2006 the region of lightly grounded ice at the glacier terminus is extending upstream and the changes inland are consistent with the effects of a prolonged disturbance to the ice flow such as the effects of ocean driven melting if the acceleration continues at its present rate the main trunk of pig will be afloat within some 100 years six times sooner than anticipated citation wingham d j d w wallis and a shepherd 2009 spatial and temporal evolution of pine island glacier thinning 1995 2006 geophys res lett 36 l17501 doi 10 1029 2009gl039126

primary productivity variability on the atlantic iberian margin over the last 70 000 years evidence from coccolithophores and fossil organic compounds 1 this study analyzes coccolithophore abundance fluctuations e g emiliania huxleyi gephyrocapsa specimens and florisphaera profunda in core md01 2444 sediment strata retrieved at the iberian margin northeastern atlantic ocean coccolithophores are calcareous nannofossils a major component of the oceanic phytoplankton which provide information about past ecological and climatological variability results are supported by data on fossil organic compounds sea surface temperatures alkenones and n hexacosan 1 ol index and geochemical analyses benthic 13ccc and planktonic 18occ isotopes three scenarios are taken into account for this location at centennial scale resolution over the last 70 000 years the holocene and the stadial and interstadial modes the different alternatives are described by means of elements such as nutrients upwelling phenomena temperatures at surface and subsurface level or the arrival of surface turbid fresh and cold waters due to icebergs low sea level increased aridity and dust during the holocene moderate primary productivity was observed mainly concentrated in e huxleyi specimens surface temperatures were at maxima while the water column was highly ventilated by northern sourced polar deep waters and warmer subsurface nutrient poor subtropical waters over most of the last glacial stadials surface productivity weakened higher f profunda and reworked specimen percentages and lower diunsaturated and triunsaturated c37 alkenones the arrival of cold arctic surface waters traced by tetraunsaturated c37 peaks and large e huxleyi together with powerful ventilated southern sourced polar deep waters disturbed in all likelihood the delicate vertical equilibrium while preventing significant upwelling mixing finally during the last glacial interstadials lower f profunda percentages nonreworked material and higher diunsaturated and triunsaturated c37 alkenones a combined signal is observed warm surface temperatures were concurrent with generally low oxygenation of the deep sea floor moderate arrival of northern sourced deep waters and subsurface cold nutrient rich recently upwelled waters probably of polar origin these particular conditions may have promoted vertical mixing while enhancing surface primary productivity mainly of gephyrocapsa specimens

recent sea level contributions of the antarctic and greenland ice sheets after a century of polar exploration the past decade of satellite measurements has painted an altogether new picture of how earth s ice sheets are changing as global temperatures have risen so have rates of snowfall ice melting and glacier flow although the balance between these opposing processes has varied considerably on a regional scale data show that antarctica and greenland are each losing mass overall our best estimate of their combined imbalance is about 125 gigatons per year of ice enough to raise sea level by 0 35 millimeters per year this is only a modest contribution to the present rate of sea level rise of 3 0 millimeters per year however much of the loss from antarctica and greenland is the result of the flow of ice to the ocean from ice streams and glaciers which has accelerated over the past decade in both continents there are suspected triggers for the accelerated ice discharge surface and ocean warming respectively and over the course of the 21st century these processes could rapidly counteract the snowfall gains predicted by present coupled climate models

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

high frequency surface water changes in the tagus prodelta off lisbon eastern north atlantic during the last two millennia abstract a high resolution sedimentary sequence recovered from the tagus prodelta has been studied with the objective to reconstruct multi decadal to centennial scale climate variability on the western iberian margin and to discuss the observations in a wider oceanographic and climatic context between ca 100 bc and ad 400 the foraminiferal fauna and high abundance of globorotalia inflata indicate advection of subtropical waters via the azores current and the winter time warm portugal coastal current between ca ad 400 and 1350 encompassing the medieval climate anomaly mca enhanced upwelling is indicated by the planktonic foraminiferal fauna in particular by the high abundance of upwelling indicator species globigerina bulloides relatively light 18o values and high sea surface temperature sst reconstructed from foraminiferal assemblages point to upwelling of subtropical eastern north atlantic central water between ca ad 1350 and 1750 i e most of the little ice age relatively heavy 18o values and low reconstructed sst as well as high abundances of neogloboquadrina incompta indicate the advection of cold subpolar waters to the area and a southward deflection of the subpolar front in the north atlantic as well as changes in the mode of the north atlantic oscillation in addition the assemblage composition together with the other proxy data reveals less upwelling and stronger river input than during the mca stronger azores current influence on the iberian margin and strong anthropogenic effect on the climate after ad 1750 is indicated by the foraminiferal fauna the foraminiferal assemblage shows a significant change in surface water conditions at ca ad 1900 including enhanced river runoff a rapid increase in temperature and increased influence of the azores current the tagus record displays a high degree of similarity to other north atlantic records indicating that the site is influenced by atmospheric oceanic processes operating throughout the north atlantic as well as by local changes

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

shallow marine sediment cores record climate variability and earthquake activity off lisbon portugal for the last 2000 years abstract sea surface temperature sst river discharge and biological productivity have been reconstructed from a multi proxy study of a high temporal resolution sedimentary sequence recovered from the tagus deposition center off lisbon portugal for the last 2000 years sst shows 2 c variability on a century scale that allows the identification of the medieval warm period mwp and the little ice age lia high iron fe and fine sediment deposition accompanied by high n alkane concentrations and presence of freshwater diatoms during the lia 1300 1900 ad science 292 2001 662 suggest augmented river discharge whereas higher total alkenone concentrations point to increased river induced productivity during the mwp 550 1300 ad science 292 2001 662 larger mean grain size and low values of magnetic susceptibility and concentrations of fe n alkanes and n alcohols are interpreted to reflect decreased runoff at the same time increased benthic and planktonic foraminifera abundances and presence of upwelling related diatoms point to increased oceanic productivity on the basis of the excellent match found between the negative phases of the north atlantic oscillation nao index and the intensified tagus river discharge observed for the last century it is hypothesized that the increased influx of terrigenous material during the lia reflects a negative nao like state or the occurrence of frequent extreme nao minima during the milder few centuries of the mwp stronger coastal upwelling conditions are attributed to a persistent positive nao like state or the frequent occurrence of extreme nao maxima the peak in magnetic susceptibility centered at 90 cm composite core depth ccd is interpreted as the result of the well known 1755 ad lisbon earthquake the lisbon earthquake and accompanying tsunami are estimated to have caused the loss of 39 cm of sediment 355 years of record most of the lia and the instantaneous deposition of a 19 cm sediment bed

late holocene coastal hydrographic and climate changes in the eastern north sea we present a high resolution palaeoenvironmental reconstruction covering the late holocene from the skagerrak and other sites in the north sea area the data which are based on the analyses of marine sediment cores reveal a marked environmental shift that took place between ad 700 and ad 1100 with the most pronounced changes occurring at ad 900 both surface and bottom waters in the skagerrak were subject to major circulation and productivity changes at this time due to an enhanced advection of atlantic waters to the north sea marking the beginning of the mediaeval warm period mwp the observed increase in bottom current strength is especially remarkable as there is hardly any comparable signal in the older part of the record going back to 1000 bc at the transition to the little ice age lia the bottom current strength remains at a high level now probably forced by atmospheric circulation thus despite opposite temperature forcing these two consecutive climate scenarios are apparently able to generate distinctly stronger bottom currents in the skagerrak than observed in the preceding 2000 years and demonstrate the significance of climatic forcing in shaping the marine environment indeed both the mwp and the lia are reported as strong climatic signals in northwest europe being the warmest except the late twentieth century and coldest periods respectively during at least the last 2000 years

diatom assemblages as upwelling indicators in surface sediments off portugal abstract diatom abundance and assemblage composition have been determined for 169 surface sediment samples from the portuguese margin an area where seasonal upwelling occurs each year from april to october absolute diatom abundance distribution patterns reflect the more intense and or persistent and more homogeneous upwelling north of the nazare canyon the position of the inner upwelling front south of lisbon and the eastern continuation of the coastal upwelling jet along the algarve coast distribution patterns of species and of ecologically defined groups meroplanktonic oceanic freshwater and marine benthic support the hypothesis that diatom species and assemblages are good indicators of the changing character of the upwelling system small species of the genus thalassiosira occur in areas of persistent upwelling where availability of nutrients is more constant and or higher paralia sulcata ehr cleve is an abundant species whose mean cell diameter increases as nutrient availability decreases resting spores mainly of chaetoceros ehrenberg record the position of the zone where higher variability occurs the inner upwelling front

increasing rates of ice mass loss from the greenland and antarctic ice sheets revealed by grace 1 we use monthly measurements of time variable gravity from the grace gravity recovery and climate experiment satellite gravity mission to determine the ice mass loss for the greenland and antarctic ice sheets during the period between april 2002 and february 2009 we find that during this time period the mass loss of the ice sheets is not a constant but accelerating with time i e that the grace observations are better represented by a quadratic trend than by a linear one implying that the ice sheets contribution to sea level becomes larger with time in greenland the mass loss increased from 137 gt yr in 2002 2003 to 286 gt yr in 2007 2009 i e an acceleration of 30 11 gt yr2 in 2002 2009 in antarctica the mass loss increased from 104 gt yr in 2002 2006 to 246 gt yr in 2006 2009 i e an acceleration of 26 14 gt yr2 in 2002 2009 the observed acceleration in ice sheet mass loss helps reconcile grace ice mass estimates obtained for different time periods

increased upwelling off portugal during the last glaciation diatom evidence abstract quantitative studies have been carried out on opaline microfossils and diatom assemblage composition and preservation in two latest quarternary 100 ka to p d cores from the continental slope of portugal the sites are located in an area of modern summer coastal upwelling created by northerly trade winds the spatial patterns and intensity of this upwelling system are accurately recorded by the diatom abundances and taxonomic composition in the surface sediments the diatom record in these sequences indicates that coastal upwelling intensity was similar to present day during late holocene interglacial stage 3 and late stage 5 higher during stage 2 and lower in the early holocene paleoproductivity estimates are consistent with the diatom accumulation rates from stage 3 to the recent this indicates that both the diatom and the organic carbon content of the sediments mainly reflect the biological productivity in the euphotic zone

geoacoustic inversion on the new jersey margin along and across the shelf this paper presents results of a range independent perturbative inverse approach applied to data from the shallow water experiment 2006 the inversion technique is based on a linearized relationship between sound speed in the sediment and modal eigenvalues horizontal wave numbers were estimated from data collected from two distinct source receiver tracks oriented along and across the shelf the specific inversion algorithm used is based on qualitative regularization and uses known information about the environment to constrain the solution locations of the r reflector and other layering information are used as a priori information for the inversion to emphasize the layered structure of the sediment

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

snowfall in coastal west antarctica much greater than previously assumed 1 a new antarctic accumulation distribution based on regional model output calibrated with 1900 in situ observations is used to re assess accumulation in 24 antarctic ice drainage basins when compared to the previous compilation good agreement is found for 19 of the 24 basins representing 93 of the ice sheet that is reasonably well covered with observations in contrast the amundsen sea sector of west antarctica and the western antarctic peninsula both data sparse regions are found to receive 80 96 more accumulation than previously assumed for the pine island and thwaites glaciers west antarctica which have recently undergone rapid acceleration and thinning this means a downward adjustment of their contribution to global sea level rise from 0 24 to 0 14 mm per year model time series do not show a significant change in antarctic accumulation over the period 1980 2004

satellite gravity measurements confirm accelerated melting of greenland ice sheet using time variable gravity measurements from the gravity recovery and climate experiment grace satellite mission we estimate ice mass changes over greenland during the period april 2002 to november 2005 after correcting for the effects of spatial filtering and limited resolution of grace data the estimated total ice melting rate over greenland is 239 23 cubic kilometers per year mostly from east greenland this estimate agrees remarkably well with a recent assessment of 224 41 cubic kilometers per year based on satellite radar interferometry data grace estimates in southeast greenland suggest accelerated melting since the summer of 2004 consistent with the latest remote sensing measurements

impact of extended nao buoyancy forcing on the subpolar north atlantic and climate variability over the last millenium 1 we examine the impact of forcing a regional eddy permitting ocean model of the subpolar north atlantic with anomalous buoyancy fluxes corresponding to extended extreme states of the north atlantic oscillation nao we find a weakened enhanced meridional overturning circulation moc in our low high nao simulations such results may be consistent with ideas that suggest the medieval warm period mwp and the little ice age are associated with periods when the nao is predominantly in one phase our results also show multidecadal moc variability with a period of 70 years in our high nao simulation in comparison to an equilibrium like circulation under low nao related forcing a less stable climatic state is therefore suggested to occur under high nao forcing which may be consistent with ideas that suggest the warming associated with the mwp did not occur synchronously over the north atlantic the variability appears to be brought about by internal oceanic processes

late holocene summer temperature reconstruction from chironomid assemblages of lake anterne northern french alps we present a chironomid based reconstruction of late holocene temperature from lake anterne 2060 m a s l in the northern french alps chironomid assemblages were studied in 49 samples along an 8 m long sediment core covering the last 1800 years july air temperatures were inferred using an inference model based on the distribution of chironomid assemblages in 100 swiss lakes the transfer function has a leave one out cross validated coefficient of determination r of 0 88 a root mean square error of prediction rmsep of 1 40 c despite possible biases induced by methodological aspects and the ecological complexity of the chironomid response to both climate and environmental changes the concordance of the lake anterne temperature reconstruction with other alpine records suggests that the transfer function has successfully reconstructed past summer temperature during the last two millennia the twentieth century is the only section of the record which shows a poor agreement with other climate recons

spread of ice mass loss into northwest greenland observed by grace and gps 1 greenland s main outlet glaciers have more than doubled their contribution to global sea level rise over the last decade recent work has shown that greenland s mass loss is still increasing here we show that the ice loss which has been well documented over southern portions of greenland is now spreading up along the northwest coast with this acceleration likely starting in late 2005 we support this with two lines of evidence one is based on measurements fromthegravityrecoveryandclimateexperiment grace satellite gravity mission launched in march 2002 the other comes from continuous global positioning system gps measurements from three long term sites on bedrock adjacent to the ice sheet the grace results provide a direct measure of mass loss averaged over scales of a few hundred km the gps data are used to monitor crustal uplift caused by ice mass loss close to the sites the grace results can be used to predict crustal uplift which can be compared with the gps data in addition to showing that the northwest ice sheet margin is now losing mass the uplift results from both the gps measurements and the grace predictions show rapid acceleration in southeast greenland in late 2003 followed by a moderate deceleration in 2006 because that latter deceleration is weak southeast greenland still appears to be losing ice mass at a much higher rate than it was prior to fall 2003 in a more general sense the analysis described here demonstrates that gps uplift measurements can be used in combination with grace mass estimates to provide a better understanding of ongoing greenland mass loss an analysis approach that will become increasingly useful as long time spans of data accumulate from the 51 permanent gps stations recently deployed around the edge of the ice sheet as part of the greenland gps network gnet citation khan s a j wahr m bevis i velicogna and e kendrick 2010 spread of ice mass loss into northwest greenland observed by grace and gps geophys res lett 37 l06501 doi 10 1029 2010gl042460

measurements of time variable gravity show mass loss in antarctica using measurements of time variable gravity from the gravity recovery and climate experiment satellites we determined mass variations of the antarctic ice sheet during 2002 2005 we found that the mass of the ice sheet decreased significantly at a rate of 152 80 cubic kilometers of ice per year which is equivalent to 0 4 0 2 millimeters of global sea level rise per year most of this mass loss came from the west antarctic ice sheet

thwaites glacier grounding line retreat influence of width and buttressing parameterizations major ice loss has recently been observed along coastal outlet glaciers of the west antarctic ice sheet mainly due to increased melting below the ice shelves however the behavior of this marine ice sheet is poorly understood leading to significant shortcomings in ice sheet models attempting to predict future sea level rise the stability of a marine ice sheet is controlled by the dynamics at the grounding line the boundary between the grounded ice stream and the floating ice shelf one of the largest contributors to current sea level rise is the fast flowing thwaites glacier which flows into the amundsen sea here we use an ice stream ice shelf model and perform a number of experiments along a central flowline to analyze the sensitivity of its grounding line on centennial timescales in the absence of width and buttressing effects we find that the grounding line retreats by 300 km in 200 years from the present day rate of 1 5 km a 1 with variable glacier width implemented in the model flow convergence slows the retreat of thwaites grounding line at 0 3 1 2 km a 1 the parameterization of ice shelf buttressing according to different observed scenarios further reduces the glacier retreat and can even lead to a slight advance in the most buttressed case

rapid changes in ice discharge from greenland outlet glaciers using satellite derived surface elevation and velocity data we found major short term variations in recent ice discharge and mass loss at two of greenland s largest outlet glaciers their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates likely as a result of fast re equilibration of calving front geometry after retreat total mass loss is a fraction of concurrent gravity derived estimates pointing to an alternative source of loss and the need for high resolution observations of outlet dynamics and glacier geometry for sea level rise predictions

mass balance of the greenland ice sheet at dye 3 the mass balance of the greenland ice sheet a t dye 3 is estimated on the basis of 0 bserva tions of ice thickness accumulation rate surface velocities and surface strain rates the calculations indicate a rate of increase of surface elevation of 3 cm year with 95 confidence limits of 3 cm year and 9 cm year previous estimates of the mass balance of the greenland ice sheet by the same method reported large imbalances these are most probably due to lack of precise data and the use of quantities measured at the surface as representative of depth averaged quantities the most reliable observations indicate that the interior regions of the greenland ice sheet are at present thickening at a rate of a few centimetres per year a contributing cause for this may be the slow thinning of a bottom layer of relatively soft wisconsin ice resume bilan de masse de l lndlandsis groenlandais a dye 3 le bilan de masse est estime it partir des mesures d epaisseur taux d accumulation vitesses et vitesses de deformation superficielles le calcul don ne un epalss lssement de 3 cm an 1 avec un intervalle de confiance au seuil de 95 allant de 3 cm an 1 it 9 cm an i les estimations anterieures du bilan de l lndlandsis obtenues par la meme methode sont examinees on en deduit que les valeurs de bilan tres eloignees de l equilibre sont certainement dues au manque de donnees preclses et ou a i utilisation de donnees superficielles comme valeurs moyennes sur une

climate change and coastal hydrographic response along the atlantic iberian margin tagus prodelta and muros ria during the last two millennia the tagus prodelta w portugal and the muros ro a nw spain are areas of high deposition rates registering high resolution palaeoclimatic records for western iberia we compare the climatic conditions of the two areas over the last two millennia based on proxies of temperature sea surface temperatures and oxygen isotopes continental input grain size iron and magnetic susceptibility and productivity inorganic and organic carbon carbon isotopes benthic foraminifera and diatoms biogeochemical changes in the tagus prodelta reflect widely recognized north atlantic climatic periods encompassing the roman period ad 0 350 the dark ages ad 400 700 the mediaeval warm period mwp ad 800 1200 and the little ice age lia ad 1300 1750 the atmospheric north atlantic oscillation nao drives the tagus prodelta multidecadal long term variability in precipitation river input during cold periods negative nao and marine upwelling during warmer periods positive nao a scheme that is reversed in the galician region the muros ro a shows only local hydrodynamics until ad 1150 including a suboxic event in the inner ro a around ad 500 700 since ad 1150 atlantic warm upwelled waters have ventilated the outer ro a but only reach the inner ro a at ad 1750 the twentieth century records are also interpreted as a reflex of the inverse nao mode in both areas resulting in amplification of the lia biogeochemical water conditions centennial scale solar activity appears to be another important forcing mechanism or the only one if solar activity drives the nao and bond cycles behind changes in the hydrography of the tagus prodelta and primary production bottom ventilation and organic carbon degradation in the muros ro a

mass balance of glaciers and ice caps consensus estimates for 1961 2004 1 working with comprehensive collections of directly measured data on the annual mass balance of glaciers other than the two ice sheets we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960 mass balance was slightly below zero around 1970 and has been growing more negative since then excluding peripheral ice bodies in greenland and antarctica global average specific balance for 1961 1990 was 219 112 kg m 2 a 1 representing 0 33 0 17 mm sle sea level equivalent a 1 for 2001 2004 the figures are 510 101 kg m 2 a 1 and 0 77 0 15 mm sle a 1 including the smaller greenland and antarctic glaciers global total balance becomes 0 38 0 19 mm sle a 1 for 1961 1990 and 0 98 0 19 mm sle a 1 for 2001 2004 for 1991 2004 the glacier contribution 0 77 0 26 mm sle a 1 is 20 30 of a recent estimate of 3 2 0 4 mm a 1 of total sea level rise for 1993 2005 while our error estimates are not rigorous we believe them to be liberal as far as they go but we also discuss several unquantified biases of which any may prove to be significant

variations in sediment provenance during the past 3000 years off the tagus river portugal marine sediments from the portuguese shelf are influenced by environmental changes in the surrounding continental and marine environment these are largely controlled by the north atlantic oscillation but additional impacts may arise from episodic tsunamis in order to investigate these influences a high resolution multi proxy study has been carried out on a 5 4 m long gravity core and five box cores from the tagus prodelta on the western portuguese margin incorporating geochemical c org n total ratios delta c 13 org delta n 15 delta o 18 c org and caco3 content and physical sediment properties magnetic susceptibility grain size subsurface data of the five box cores indicate no major effect of early postdepositional alteration surface data show a higher fraction of terrigenous organic material close to the river mouth and in the southern prodelta gravity core geob 8903 covers the last 3 2 kyrs with a temporal resolution of at least 0 1 cm yr very high sedimentation rates between 69 and 140 cm core depth indicate a possible disturbance of the record by the ad1755 tsunami although no evidence for a disturbance is observed in the data sea surface temperature and salinity on the prodelta the local budget of marine no3 as well as the provenance of organic matter remained virtually constant during the past 3 2 kyrs a positive correlation between magnetic susceptibility ms and north atlantic oscillation nao is evident for the past 250 years coinciding with a negative correlation between mean grain size and nao this is assigned to a constant riverine supply of fine material with high ms which is diluted by the riverine input of a coarser low ms component during nao negative high precipitation phases end member modelling of the lithic grain size spectrum supports this revealing a third coarse lithic component the high abundance of this coarse end member prior to 2 kyr bp is interpreted as the result of stronger bottom currents concentrating the coarse sediment fraction by winnowing as continental climate was more and prior to 2 kyr bp subboreal the coarse end member may also consist of dust from local sources a decrease in grain size and caco3 content after 2 kyr bp is interpreted as a result of decreasing wind strength the onset of a fining trend and a further decrease in caco3 around ad900 occurs simultaneous to climatic variations reconstructed from eastern north atlantic records a strong increase in ms between ad1400 and ad1500 indicates higher lithic terrigenous input caused by deforestation in the hinterland c 2008 elsevier b v all rights reserved

mountain glaciers and ice caps around antarctica make a large sea level rise contribution the intergovernmental panel on climate change ipcc estimates that the sum of all contributions to sea level rise for the period 1961 2004 was 1 1 0 5 mm a 1 leaving 0 7

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

eight hundred year temperature variability from the norwegian continental margin and the north atlantic thermohaline circulation 1 four cores raised from the eastern norwegian sea and adjacent norwegian fjords at sites influenced by atlantic water have been investigated oxygen isotope analyses in benthic and planktonic foraminifera are used as a proxy for the paleotemperature development spanning the last 800 years the cores have been dated using a combination of 210pb and radiocarbon dates yielding time resolutions of 2 5 years for the last century and 9 25 years beyond this the proxy records have been compared with instrumental time series covering the last 100 years in order to validate the oxygen isotope measurements as a proxy for paleotemperature the comparison shows that the paleotemperature variability derived from the oxygen isotope analyses is generally similar to the amplitudes and trends seen in the instrumental time series in particular a cooling around 1905 1925 followed by a warming until 1955 is evident in all proxy records as well as in the instrumental time series beyond the last century the proxy records show two periods from 1225 1450 and 1650 1905 25 when temperatures were 1 3 1 6 c lower than present separated by a period of temperatures periodically comparable to present the last 80 years represent the modern warming and appear to be the warmest period of the last 800 years we find that that the ocean temperature variability is comparable to terrestrial reconstructions from the region implying a strong link in the ocean atmosphere climate system this suggests that the climate variability in this region beyond the period covered by instrumental time series was also associated with changes in the thermohaline circulation

holocene climatic development in skagerrak eastern north atlantic foraminiferal and stable isotopic evidence a high resolution multiproxy study of core md99 2286 reveals a highly variable hydrographic environment in the skagerrak from 9300 cal yr bp to the present the study includes foraminiferal faunas stable isotopes and sedimentary parameters as well as temperature and salinity reconstructions of a c 29 m long radiocarbon dated core record the multivariate technique fuzzy c means was applied to the foraminiferal counts and it was extremely valuable in defining subtle heterogeneities in the foraminiferal faunal data corresponding to hydrographic changes the major early mid holocene littorina transgression led to flooding of large former land areas in the north sea the opening of the english channel and danish straits and initiation of the modern circulation system this is reflected by fluctuating c n values and an explosive bloom of hyalinea balthica a slight indication of ameliorated conditions between 8000 and 5750 cal yr bp is related to the holocene thermal maximum a subsequent increase in

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

variations in organic carbon flux and stagnation periods during the last 2400 years in a skagerrak fjord basin inferred from benthic foraminiferal δ13c

mass balance of the greenland ice sheet from 1958 to 2007 we combine estimates of the surface mass balance smb of the greenland ice sheet for years 1958 to 2007 with measurements of the temporal variability in ice discharge d to deduce the total ice sheet mass balance during that time period we find a robust correlation r2 0 83 between anomalies in smb and in d which we use to reconstruct a continuous series of total ice sheet mass balance we find that the ice sheet was losing 110 70 gt yr in the 1960s 30 50 gt yr or near balance in the 1970s 1980s and 97 47 gt yr in 1996 increasing rapidly to 267 38 gt yr in 2007 multi year variations in ice discharge themselves related to variations in smb cause 60 20 more variation in total mass balance smb and therefore dominate the ice sheet mass budget copyright 2008 by the american geophysical union

the north atlantic oscillation forcing through the last 2000 years spatial variability as revealed by high resolution marine diatom records from n and sw europe abstract the tagus pro delta portuguese margin and the skagerrak ne of the north sea are two marine systems controlled by atmospheric changes which at present are mainly determined by fluctuations of the north atlantic oscillation nao on the basis of diatom records from marine sediment cores environmental changes primary productivity and salinity are reconstructed for the last 2000 years for both regions these sites are investigated focusing on the regional response to changing nao forcing both studied sites are characterized by sedimentation rates in the order of 0 12 cm year and 0 47 cm year for the most recent deposits off the tagus pro delta allowing high resolution paleoceanographic reconstructions 8 3 and 2 1 years represented per sample the last 2000 years are a period covering in europe the historical climatic periods known as the dark ages da the medieval warm period mwp and the little ice age lia in the skagerrak the cold periods of the da and lia are marked by diatom dissolution stages whereas at the tagus pro delta the da were associated with increased diatom production and possible upwelling and the onset of the lia corresponded to enhanced flow of the tagus river during the mwp better diatom preservation in the skagerrak related to stronger advection of salty atlantic waters is paralleled by dominant upwelling conditions at the tagus pro delta the two most intense upwelling periods at the tagus pro delta at ad 600 and ad 900 correspond to a dissolution stage and a slight change in salinity in the skagerrak respectively although the comparison of the two study sites suggests a common forcing such as the nao the different inferred behaviors for each main climatic period in each region demonstrate that the nao by its own is not sufficient to explain the climatic variability at a regional scale

seasonal variation in velocity before retreat of jakobshavn isbrae greenland 1 using repeat pass satellite feature tracking the dynamic behaviour of jakobshavn isbrae which drains around 7 of the greenland ice sheet is investigated in improved detail through its recent period of thinning acceleration and retreat the departure in 1995 from the normal seasonal invariance in velocity near the grounding line suggests a possible change in dynamics well before the subsequent thinning phase the initiation of the acceleration and retreat is pinpointed to spring 1998 and may have been prompted by the same mechanism that gave rise to the spring 1995 flow increase

changes in west antarctic ice stream dynamics observed with alos palsar data the advanced land observation system alos phased array synthetic aperture radar palsar is an l band frequency 1 27 ghz radar capable of continental scale interferometric observations of ice sheet motion here we show that palsar data yield excellent measurements of ice motion compared to c band 5 6 ghz radar data because of greater temporal coherence over snow and firn we compare palsar velocities from year 2006 in pine island bay west antarctica with those spanning years 1974 to 2007 between 1996 and 2007 pine island glacier sped up 42 and ungrounded over most of its ice plain smith glacier accelerated 83 and ungrounded as well their largest speed up are recorded in 2007 thwaites glacier is not accelerating but widening with time and its eastern ice shelf doubled its speed total ice discharge from these glaciers increased 30 in 12 yr and the net mass loss increased 170 from 39 15 gt yr to 105 27 gt yr longer term velocity changes suggest only a moderate loss in the 1970s as the glaciers unground into the deeper smoother beds inland the mass loss from this region will grow considerably larger in years to come copyright 2008 by the american geophysical union

mass balance of polar ice sheets recent advances in the determination of the mass balance of polar ice sheets show that the greenland ice sheet is losing mass by near coastal thinning and that the west antarctic ice sheet with thickening in the west and thinning in the north is probably thinning overall the mass imbalance of the east antarctic ice sheet is likely to be small but even its sign cannot yet be determined large sectors of ice in southeast greenland the amundsen sea embayment of west antarctica and the antarctic peninsula are changing quite rapidly as a result of processes not yet understood

estimating phytolith influx in lake sediments abstract so far no phytolith extraction protocols have been tested for accuracy and repeatability here we aim to display a phytolith extraction method combining the strengths of two widely used protocols supplemented with silica microspheres as exogenous markers for quantifying phytolith concentrations phytolith concentrations were estimated for samples from two sedimentary sequences in which numerical age depth models make it possible to calculate phytolith influxes phytolith numbers per cm2 per yr analysis of replicates confirmed the statistical robustness the repeatability and the very few biases of our extraction technique for small phytoliths since the relationship between grass silica short cells and microspheres was kept stable furthermore we demonstrated that silica microspheres are robust exogenous markers for estimating phytolith concentrations the minimum number of items i e phytoliths plus silica microspheres that must be counted to estimate phytolith concentrations and thus influxes depends on the ratio of phytoliths to microspheres r and is minimized when r 1 nevertheless we recommend using ratios r 1 in order to avoid having the counting process become excessively time consuming because microspheres are easier to identify and count than phytoliths

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100