nd sr isotopic composition of granulites and constraints on the evolution of the lower continental crust in a statistical study of granulite facies rocks we have analysed 32 samples with ages ranging from 2 900 to 200 myr for sm nd rb and sr and 143nd 144nd and 87sr 86sr ratios the sm nd ratio is found to be constant compared with the highly variable rb sr ratio using the model age formalism we show that in many cases internal differentiation of continental crust follows external differentiation with a large time interval

exchange of neodymium and its isotopes between seawater and small and large particles in the sargasso sea the concentrations and isotopic ratios of nd were measured in small 1 53 m and large 53 m in situ filtered particles sediment trap material sediment and aerosol samples collected during oligotrophic and productive conditions in the sargasso sea atmospheric input is the main source of exogeneous nd into the sargasso sea based on ndal ratios in trapped material we suggest that up to 50 of atmospheric nd could dissolve at the air sea interface the concentration and isotopic composition of nd vary with both depth and the particle size neodymium concentrations of small and large particles increase with depth from 2 9 12 g g and 5 8 11 8 g g respectively at 40 m the nd signature of large particles is significantly more negative nd 0 13 1 0 2 than that of the small ones nd 0 11 7 0 3 and the particles filtered deeper below 237 m the nd 0 values for small particles match the seawater whereas the nd 0 values of large particles remain less radiogenic these differences are related to the different behaviors of the particulate fractions small particles apparently exchange nd with seawater and then sink rapidly to depth as biologically formed aggregates large particles these aggregates isolate the small particles slowing the exchange with the water to produce different signatures between large particles and seawater since these exchange processes modify the particulate nd signature the shallow radiogenic nd 0 signature observed in the surface and subsurface waters in the nw atlantic is not due to external contributions and is likely of advective origin at depth below 800 m the magnitude of the aggregation disaggregation process varies significantly with season the fraction of small particles repackaged into large aggregates can vary from 0 8 to 80 100 in productive and oligotrophic conditions respectively this seasonal variation may correspond to sinking particles of different zooplanktonic origin vertical fluxes of nd into and out of the sargasso sea as well as exchange fluxes in the water column are examined about 50 of the particulate flux from the surface is remineralized at depth a net scavenging flux of 0 8 10 4 g m2 y is required this value corresponds to a scavenging nd residence time of 1900 y considerably longer than previous estimates of global oceanic residence time of nd on the order of 400 y

increased arctic sea ice volume after anomalously low melting in 2013 changes in arctic sea ice volume are difficult to quantify five years of satellite data reveal a reduction in autumn sea ice volume in 2010 2012 but a sharp increase in 2013 and 2014 suggesting that ice volume can recover quickly

variations in the nd isotopic composition of foraminifera from atlantic ocean sediments 143nd 144nd ratios have been measured in recent core top foraminifera from 25 sites throughout the atlantic ocean the average nd 0 value from this study agrees well with previous estimates of the average nd isotopic composition of the atlantic based on analyses of ferromanganese deposits and seawater samples however the larger data base and the nature of the samples have allowed us to identify distinct provenances of nd isotopes in the atlantic

ku band radar penetration into snow cover on arctic sea ice using airborne data satellite radar altimetry provides data to monitor winter arctic sea ice thickness variability on interannual basin wide scales when using this technique an assumption is made that the peak of the radar return originates from the snow ice interface this has been shown to be true in the laboratory for cold dry snow as is the case on arctic sea ice during winter however this assumption has not been tested in the field we use data from an airborne normal incidence ku band radar altimeter and in situ field measurements collected during the cryosat validation experiment cryovex bay of bothnia 2006 and 2008 field campaigns to determine the dominant scattering surface for arctic snow covered sea ice in 2006 when the snow temperatures were close to freezing the dominant scattering surface in 25 of the radar returns appeared closer to the snow ice interface than the air snow interface however in 2008 when temperatures were lower the dominant scattering surface appeared closer to the snow ice interface than the air snow interface in 80 of the returns

records of the nd isotope composition of seawater from the bay of bengal implications for the impact of northern hemisphere cooling on itcz movement abstract this study presents a record of planktonic foraminiferal neodymium isotopic gradients along a north south transect in the bay of bengal during time slices of late holocene and last glacial maximum lgm age together with a record of planktonic foraminiferal variation in the northern bay of bengal 15 n over the last 195 ky in late holocene core top planktonic foraminifera the north south end gradient rises from nonradiogenic values of 12 at 20 n to 10 at 5 n in parallel with the modern surface salinity gradient controlled by discharge of himalayan rivers in the northern bay during the lgm end increased throughout the bay the contrast between northernmost and southernmost sites decreased and maximum end values of 6 5 occurred between 12 and 15 n a small part of the shift to higher mean end throughout the bay during the glacial may arise from a uniform increase in deposition of far field dust from arabian and persian gulf regions however the spatial pattern of end variation between lgm and late holocene also suggests a shift from modern dominance of nonradiogenic nd sources from the ganges brahmaputra basin to lgm dominance of more radiogenic nd sources from arakan coastal rivers over the last 195 ky at 15 n the most radiogenic end values of 7 occur at glacial maxima and the most nonradiogenic values of 11 occur during interglacials end values are highly correlated with glacial interglacial variations in planktonic foraminiferal 18o in this record shifts in river sources from the more northerly ganges brahmaputra watershed to the more southerly arakan coastal river systems respond dominantly to inter tropical convergence zone itcz movement driven by northern hemisphere cooling during 100 ky glacial interglacial cycles with a small component of variation on precessional timescales the nonlinear correlation of end with ice volume suggests that itcz movement responds to aerial coverage of ice sheets and snow rather than to ice thickness and volume these data add support to recent general circulation models of itcz response to northern hemisphere ice sheets which simulate decreased glacial precipitation in the ganges brahmaputra basin and increased glacial precipitation in the southern arakan coastal basin

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

assessment of radar derived snow depth over arctic sea ice knowledge of contemporaneous snow depth on arctic sea ice is important both to constrain the regional climatology and to improve the accuracy of satellite altimeter estimates of sea ice thickness we assess new data available from the nasa operation icebridge snow radar instrument and derive snow depth estimates across the western arctic ice pack using a novel methodology based on wavelet techniques that define the primary reflecting surfaces within the snow pack we assign uncertainty to the snow depth estimates based upon both the radar system parameters and sea ice topographic variability the accuracy of the airborne snow depth estimates are examined via comparison with coincident measurements gathered in situ across a range of ice types in the beaufort sea we discuss the effect of surface morphology on the derivation and consequently the accuracy of airborne snow depth estimates we find that snow depths derived from the airborne snow radar using the wavelet based technique are accurate to 1 cm over level ice over rougher surfaces including multiyear and ridged ice the radar system is impacted by ice surface morphology across basin scales we find the snow radar derived snow depth on first year ice is at least 60 of the value reported in the snow climatology for the beaufort sea canada basin and parts of the central arctic since these regions were previously dominated by multiyear ice during the measurement period of the climatology snow on multiyear ice is more consistent with the climatology

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

higher erosion rates in the himalaya geochemical constraints on riverine fluxes the modern erosion rate of continental scale mountains is difficult to estimate and is usually based on measurement of the suspended load flux of rivers combined with assumptions about river bedload transport and sedimentation in flood plains these two parameters are very difficult to measure directly in continental scale basins in this paper we examine the chemical composition of the suspended load bedload and dissolved load of the ganga and brahmaputra rivers and compare them with the average composition of himalayan source rocks a mass balance equation of erosion fluxes shows that a si rich component is needed in addition to suspended and dissolved load fluxes to account for the composition of the source rock it corresponds to bedload sediment and flood plain deposits which are enriched in quartz by mineral sorting during transport the combined budget of si al and fe in the river system allows us to estimate this si rich flux by this method the total himalayan erosion is estimated to be twice the measured flux of suspended load the comparison between the brahmaputra and the ganga shows that the eastern himalaya has a higher erosion rate 2 9 mm yr than the western himalaya 2 1 mm yr this is likely the result of the higher runoff in the brahmaputra basin the intensity of the monsoon acts as a first order control of the erosion rate in the range

chemical evolution of rare earth elements fractionation between colloidal and solution phases of filtered river water abstract within the dissolved fraction of connecticut river water there is large scale fractionation of rare earth elements between colloidal and solution phases colloidal particles carry a large part of the dissolved ree pool filtration through filters with progressively smaller pore size 0 45 0 22 and 0 025 m results in filtrates with lower absolute concentrations of ree and more fractionated compositions with decreasing pore size the filtrates have shale normalized abundances which become systematically more depleted in the lree relative to the hree hence both the solution and colloidal phases are significantly fractionated with respect to the dissolved fraction these conclusions are consistent with previous studies of ree in rivers estuaries and soils and with surface solution speciation models colloids play an important role in the aquatic geochemistry of rare earth elements they are responsible for the fractionation of ree during the estuarine removal of ree the removal of suspended and colloidal particles from river water leaves the solution phase of river water with compositions of ree as evolved as those of surface seawater hence the evolution of the composition of ree in river water and seawater is significantly influenced by colloid formation during chemical weathering on the continents

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

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

combined airborne laser and radar altimeter measurements over the fram strait in may 2002 knowledge of sea ice thickness is critical for the prediction of future climate and for assessing the significance of changes in thickness sea ice thickness can be calculated from radar or laser satellite altimetry measurements of freeboard however a lack of knowledge of snow depth introduces significant uncertainties into these calculations this paper compares the first coincident airborne laser and radar altimetry data over sea ice collected during the laser radar altimetry lara field campaign lara was a flight of opportunity that provided valuable data to explore techniques to validate satellite measurements of ice freeboard and the possibility of combining laser and radar measurements over snow covered sea ice to calculate the snow depth two new methods were created to analyse these data sets a new radar retracker and a radar power simulator which models radar returns from the laser data we present the first quantitative analysis of data from the lara laser and radar altimeters and demonstrate the potential of combining laser and radar altimetry to estimate snow depth lara elevation estimates compare well with elevations from the radar altimeter onboard ers 2 at the sub meter level and the study provides lessons for future validation of satellite altimetry data over sea ice laser elevations are consistently higher than the radar elevations over snow covered sea ice as lara was a flight of opportunity no coincident in situ measurements were available nevertheless the difference between the reflecting surface of the laser and radar is consistent with snow depth from climatology and the analysis techniques developed in this paper will be useful for future radar and laser altimetry comparisons

large scale ice thickness distribution of first year sea ice in spring and summer north of svalbard the large scale thickness distribution of sea ice was measured during several campaigns in the european arctic north of svalbard from 2007 using an airborne electromagnetic induction device in august 2010 and april may 2011 this was complemented by extensive on ice work including measurements of snow thickness and freeboard ice thicknesses show a clear difference between the seasons with thicker ice during spring than in summer in spring 2011 negative freeboard and flooding were observed as a result of the extensive snow cover we find that the characteristics of the first year sea ice allow combining observations from different years the ice thickness in the marginal ice zone increases with increasing latitude and increasing distance to the ice edge however in the inner ice pack from 100 km from the ice edge the thickness remains almost constant modal ice thickness in spring reaches 2 4 m whereas in summer it is 1 0 1 4 m our study provides new insight into ice thickness distributions of a typical ice cover consisting of mainly first and second year ice which may become the dominant ice type in the arctic in the future

thickness and density of snow covered sea ice and hydrostatic equilibrium assumption from in situ measurements in fram strait the barents sea and the svalbard coast modern satellite measurements of sea ice thickness are based on altimeter measurements of the difference in elevation between the snow or ice surface and the local sea surface for retrieval of sea ice thickness it is assumed that the ice is in hydrostatic equilibrium and that the snow load on the ice and the density of the sea ice and sea water are known this study presents data from in situ sea ice thickness drillings and snow and ice density measurements from fram strait the barents sea and the svalbard coast in the european arctic the error in the altimetry ice thickness products is assessed based on the spatial variability of snow and ice density and snow thickness data ice thickness uncertainty related to snow depth was found to be 40 cm radar altimeter and 90 cm laser altimeter while uncertainty related to ice density is 25 cm for both techniques the assumption of hydrostatic equilibrium at the scales of the measurements 10 100 m was found to hold better in the case of level landfast ice near svalbard than for fram strait drift ice which consists of mixed ice types where the deviation between the calculated and measured ice thicknesses was on average 0 5 m

warm atlantic water explains observed sea ice melt rates north of svalbard warm atlantic water aw that flows northward along the svalbard west coast is thought to transport enough heat to melt regional arctic sea ice effectively despite this common assumption quantitative requirements necessary for aw to directly melt sea ice fast enough under realistic winter conditions are still poorly constrained here we use meteorological data satellite observations of sea ice concentration and drift and model output to demonstrate that most of the sea ice entering the area over the yermak plateau melts within a few weeks simulations using the los alamos sea ice model cice in a 1 d vertically resolved configuration under a relatively wide range of in situ observed atmospheric and ocean forcing show a good fit to observations simulations require high frequency atmospheric forcing data to accurately reproduce vertical heat fluxes between the ice or snow and the atmosphere moreover we switched off hydrostatic equilibrium to properly reproduce ice and snow thickness when observations showed that ice had a negative freeboard without surface flooding and snow ice formation this modeling shows that realistic melt rates require a combination of warm near surface aw and storm induced ocean mixing however if aw is warmer than usual 5 c then lower mixing rates are sufficient our results suggest that increased winter storm frequency and increased heat content of the aw may work together in reducing future sea ice cover in the eurasian basin

spring snow conditions on arctic sea ice north of svalbard during the norwegian young sea ice n ice2015 expedition snow is crucial over sea ice due to its conflicting role in reflecting the incoming solar energy and reducing the heat transfer so that its temporal and spatial variability are important to estimate during the norwegian young sea ice n ice2015 campaign snow physical properties and variability were examined and results from april until mid june 2015 are presented here overall the snow thickness was about 20 cm higher than the climatology for second year ice with an average of 55 27 cm and 32 20 cm on first year ice the average density was 350 400 kg m 3 in spring with higher values in june due to melting due to flooding in march larger variability in snow water equivalent was observed however the snow structure was quite homogeneous in spring due to warmer weather and lower amount of storms passing over the field camp the snow was mostly consisted of wind slab faceted and depth hoar type crystals with occasional fresh snow these observations highlight the more dynamic character of evolution of snow properties over sea ice compared to previous observations due to more variable sea ice and weather conditions in this area the snowpack was isothermal as early as 10 june with the first onset of melt clearly identified in early june based on our observations we estimate than snow could be accurately represented by a three to four layers modeling approach in order to better consider the high variability of snow thickness and density together with the rapid metamorphose of the snow in springtime

tracing the distribution of erosion in the brahmaputra watershed from isotopic compositions of stream sediments bank sediments and suspended loads of the brahmaputra river and its important tributaries were collected from the himalayan front to bangladesh along with most of the important tributaries chemical and isotopic compositions of the sediments are used to trace sediment provenance and to understand erosion patterns in the basin overall isotopic compositions range from 0 7053 to 0 8250 for sr and nd from 20 5 to 6 9 this large range derives from the variable proportions of sediments from himalayan formations with high sr isotopic ratios and low nd and transhimalayan plutonic belt with lower sr isotopic ratios and higher nd the latter are exposed to erosion in the tsangpo and in the eastern tributary drainages overall erosion of the himalayan rocks is dominant representing ca 70 of the detrital influx compositions of the brahmaputra main channel are rather stable between 0 7177 and 0 7284 for sr and between 14 4 and 12 5 for nd throughout its course in the plain from the siang tsangpo at the foot of the himalayan range down to the delta this stability despite the input of large himalayan rivers suggests that the siang tsangpo river represents the major source of sediment to the whole brahmaputra geochemical budget implies that erosion of the namche barwa zone represents about 45 of the total flux at its outflow before confluence with the ganga from only 20 of the mountain area higher erosion rates in the eastern syntaxis compared to the other himalayan ranges is related to the rapid exhumation rates of this region possibly triggered by higher precipitation over the far eastern himalaya and the high incision potential of the tsangpo river due to its very high water discharge

northern hemisphere climate control of the bengali rivers discharge during the past 4 ma abstract nd isotopes are useful tracers for paleoceanography due to the short nd residence time in seawater and the large differences between the isotopic signatures of various geological reservoirs therefore nd variations reflect the geological history of individual oceanic basins using a differential dissolution technique which extracts nd isotopes of seawater trapped in mno2 coatings and carbonates in marine sediment we measured almost two hundred samples from odp sites 758 and 757 in the northern bay of bengal covering the last 4 ma for the first time we have shown a covariation between nd and 18o over at least the last 800 ka we also show that from 4 ma to 2 6 ma nd is almost constant and starts to fluctuate at 2 6 ma when northern glaciations increased from 2 6 ma to 1 ma the fluctuation period is close to 40 ka while from 1 ma to present it is dominantly 100 ka we attribute these findings to mixing between himalayan river water that ultimately originates as indian summer monsoon rain and normal bay of bengal seawater previous studies on seawater using nd 18o analyzed on planktonic foraminifera and sedimentary data can be integrated into this model a simple quantitative binary mixing model suggests that the summer monsoon rain was more intense during interglacial than glacial periods during last glacial episode the monsoon trajectory was deviated to the east at a large scale the indian monsoon is fully controlled by the variations in northern hemisphere climate but with a complex response function to this forcing our study clearly establishes the large potential of nd isotope data to evaluate the hydrological river regime during the quaternary and its relationship with climate fluctuations particularly when the sediment archive is sampled close to sediment sources

extraction of nd isotopes from bulk deep sea sediments for paleoceanographic studies on cenozoic time scales abstract nd isotopes preserved in fossil fish teeth and ferromanganese crusts have become a common tool for tracking variations in water mass composition and circulation through time studies of nd isotopes extracted from pleistocene to holocene bulk sediments using hydroxylamine hydrochloride hh solution yield high resolution records of nd isotopes that can be interpreted in terms of deep water circulation but concerns about diagenesis and potential contamination of the seawater signal limit application of this technique to geologically young samples in this study we demonstrate that nd extracted from the 63 m decarbonated fraction of older ocean drilling program odp sediments using a 0 02 m hh solution produces nd isotopic ratios that are within error of values from cleaned fossil fish teeth collected from the same samples indicating that the hh extractions are robust recorders of deep sea nd isotopes this excellent correlation was achieved for 94 paired fish teeth and hh extraction samples ranging in age from the miocene to cretaceous distributed throughout the north tropical and south atlantic and composed of a range of lithologies including carbonate rich oozes chalks and black shales the strong nd signal recovered from cretaceous anoxic black shale sequences is unlikely to be associated with ferromanganese oxide coatings but may be derived from abundant phosphatic fish teeth and debris or organic matter in these samples in contrast to the deep water nd isotopic signal sr isotopes from hh extractions are often offset from seawater values suggesting that evaluation of sr isotopes is a conservative test for the integrity of nd isotopes in the hh fraction however rare earth elements ree from the hh extractions and fish teeth produce distinctive middle ree bulge patterns that may prove useful for evaluating whether the nd isotopic signal represents uncontaminated seawater alternatively a few paired hh extraction and cleaned fish teeth samples from each site of interest can be used to verify the seawater composition of the hh extractions the similarity between isotopic values for the hh extraction and fish teeth illustrates that the extensive cleaning protocol applied to fish teeth samples is not necessary in typical carbonate rich deep sea sediments

snow contribution to first year and second year arctic sea ice mass balance north of svalbard the salinity and water oxygen isotope composition 18o of twenty nine first year fyi and second year syi arctic sea ice cores total length 32 0 m from the drifting ice pack north of svalbard were examined to quantify the contribution of snow to sea ice mass five cores total length 6 4 m were analyzed for their structural composition showing variable contribution of 10 30 by granular ice in these cores snow had been entrained in 6 to 28 of the total ice thickness we found evidence of snow contribution in about three quarter of the sea ice cores when surface granular layers had very low 18o values snow contributed 7 5 9 7 to sea ice mass balance on average including also cores with no snow using 18o mass balance calculations in syi cores snow fraction by mass 12 7 16 3 was much higher than in fyi cores 3 3 4 4 while the bulk salinity of fyi 4 9 was distinctively higher than for syi 2 7 we surmise that oxygen isotopes and salinity profiles can give information on the age of the ice and allows to distinguish between fyi and syi or older ice in the area north of svalbard this article is protected by copyright all rights reserved

thin ice and storms sea ice deformation from buoy arrays deployed during n ice2015 arctic sea ice has displayed significant thinning as well as an increase in drift speed in recent years taken together this suggests an associated rise in sea ice deformation rate a winter and spring expedition to the sea ice covered region north of svalbard the norwegian young sea ice2015 expedition n ice2015 gave an opportunity to deploy extensive buoy arrays and to monitor the deformation of the first year and second year ice now common in the majority of the arctic basin during the 5 month long expedition the ice cover underwent several strong deformation events including a powerful storm in early february that damaged the ice cover irreversibly the values of total deformation measured during n ice2015 exceed previously measured values in the arctic basin at similar scales at 100 km scale n ice2015 values averaged above 0 1 d 1 compared to rates of 0 08 d 1 or less for previous buoy arrays the exponent of the power law between the deformation length scale and total deformation developed over the season from 0 37 to 0 54 with an abrupt increase immediately after the early february storm indicating a weakened ice cover with more free drift of the sea ice floes our results point to a general increase in deformation associated with the younger and thinner arctic sea ice and to a potentially destructive role of winter storms

manganese and iron in indian ocean waters abstract the first vertical profiles of dissolved mn and fe for the nw indian ocean are reported the area is characterized by seasonal upwelling and a broad oxygen minimum zone in intermediate waters the dissolved fe profile exhibits a maximum 5 1 nm in the oxygen minimum zone with low values both in surface waters 0 3 nm and deep waters around 1 nm mn concentrations in the surface waters are elevated 2 0 4 3 nm and decrease rapidly in an offshore direction below the first 25 m concentrations decrease dramatically 0 5 1 3 nm indicating removal by oxidation and particle scavenging further down various mn maxima are observed which can be related to hydrographic features sigma 1 1 intermediate water originating from the red sea lost its dissolved o2 while flowing northward along the omani coast and exhibits a strong mn maximum 4 6 6 5 nm coincident with the deep o2 minimum 2 2 at the two inshore stations in the gulf of oman this is overlain by relatively modest mn maxima 2 7 nm related to arabian gulf overflow water 3 3 finally the strong mn maxima 4 4 5 6 nm in the oxygen minimum zone at the two offshore stations are related to yet another watermass below these various maxima concentrations decrease gradually to values as low as 90 pm at 2000 meters depth towards the seafloor concentrations increase again leading to a modest bottom water maximum 0 7 1 5 nm the overall vertical distributions of mn and fe are strikingly similar also in actual concentrations to those previously reported for the eastern equatorial pacific an area also characterized by an extensive o2 minimum zone

neodymium isotopes in planktonic foraminifera a record of the response of continental weathering and ocean circulation rates to climate change the neodymium nd isotope composition of ancient seawater is a potentially useful tracer of changes in continental inputs and ocean circulation on timescales of a few ka here we present the first nd isotope record for seawater using sedimentary foraminifera cleaned using standard oxidative reductive techniques the data along with mn ca ratios suggest that cleaned foraminifera provide a reliable record of nd in seawater and hold out the prospect of using nd in foraminifera to examine changes in seawater that accompany glacial interglacial climatic cycles the principal potential problem to be overcome with the use of forams as records of trace elements in ancient seawater is their diagenetic fe mn coatings these contain large amounts of nd and other trace elements but can be cleaned off using highly reducing reagents mn ca ratios for the majority of the cleaned sedimentary foraminifera analysed here lie within the range 10 100 mol mol that has yielded success in studies of transition elements in forams mass balance modelling suggests that for residual mn ca ratios 100 mol mol nd added to the foram in the coating will never shift the measured nd isotope composition significantly away from the seawater value acquired by the foram test in the water column additionally nd concentrations measured in cleaned sedimentary foraminifera are comparable with those for a modern sample that has never encountered diagenetic fluids finally core top planktonic foraminifera for two sites have nd isotope compositions that are identical to local surface seawater the data we present here for labrador sea forams over the past 2 5 m y are interpreted in terms of changes in the seawater isotopic composition the data show a pronounced shift from end values of 12 to 19 in the period 2 5 1 5 ma this change is interpreted to result from the initiation of northern hemisphere glaciation and the increased derivation of labrador sea nd via ice rafting from archaean terranes in central canada in combination with stable isotope and foraminiferal relative species abundance data the new nd data are consistent with the surface hydrography of the labrador sea being dominated by a fluctuating balance between cold polar waters containing unradiogenic nd and warm subtropical waters containing more radiogenic nd the major change in labrador sea nd that is observed in the past 2 5 ma can on its own account for the change in the nd isotope composition of north atlantic deep water over the same time period

enhanced arctic sea ice drift estimation merging radiometer and scatterometer data satellites enable daily and global coverage of the polar oceans and provide a unique monitoring capability of sea ice dynamics sea ice drift maps can be estimated in arctic from several satellite sensors particularly from scatterometers and radiometers this study presents the benefits of combining single drift fields at the same resolution into a merged field built at three and six day lags during winters with a 62 5 km resolution it is shown that combining these drift fields not only increases the reliability of the displacement estimation and the number of estimated vectors to almost a full ice covered area but also expands the time period over which these estimations are reliable from freeze until the melt onset the autumn winter spring sea ice drift fields presented here are systematically produced at institut francais de recherche pour l exploitation de la mer centre d exploitation et de recherche satellitaire the sea ice drift 1992 2011 time series is available and the processing is ongoing these data are available for operational use and for the scientific community

interdecadal changes in snow depth on arctic sea ice snow plays a key role in the growth and decay of arctic sea ice in winter it insulates sea ice from cold air temperatures slowing sea ice growth from spring to summer the albedo of snow determines how much insolation is absorbed by the sea ice and underlying ocean impacting ice melt processes knowledge of the contemporary snow depth distribution is essential for estimating sea ice thickness and volume and for understanding and modeling sea ice thermodynamics in the changing arctic this study assesses spring snow depth distribution on arctic sea ice using airborne radar observations from operation icebridge for 2009 2013 data were validated using coordinated in situ measurements taken in march 2012 during the bromine ozone and mercury experiment bromex field campaign we find a correlation of 0 59 and root mean square error of 5 8 cm between the airborne and in situ data using this relationship and icebridge snow thickness products we compared the recent results with data from the 1937 1954 1991 soviet drifting ice stations the comparison shows thinning of the snowpack from 35 1 9 4 to 22 2 1 9 cm in the western arctic and from 32 8 9 4 to 14 5 1 9 cm in the beaufort and chukchi seas these changes suggest a snow depth decline of 37 29 in the western arctic and 56 33 in the beaufort and chukchi seas thinning is negatively correlated with the delayed onset of sea ice freezeup during autumn

glacial interglacial variations in the neodymium isotope composition of seawater in the bay of bengal recorded by planktonic foraminifera this study presents neodymium isotope and elemental data for cleaned planktonic foraminifera from odp site 758 in the southernmost reaches of the bay of bengal in the north east indian ocean cleaning experiments using oxidative reductive techniques suggest that diagenetic fe mn oxyhydroxide coatings can be effectively removed and that the measured nd isotope composition reflects the composition of seawater from which the foraminiferal calcium carbonate was precipitated modern core top pulleniatina obliquiloculata and globorotalia menardii give end values of 10 12 0 16 and 10 28 0 16 respectively indistinguishable from recent direct measurements of surface seawater in this area a high resolution nd isotope record obtained from g menardii for the past 150 kyr shows systematic variations end 3 on glacial interglacial timescales the timing of those variations shows a remarkable correspondence with the global oxygen isotope record which suggests a process controlling the nd isotope composition that responds in phase with global climate cycles palaeoclimate reconstruction indicates that during the last glacial maximum changes in monsoon circulation resulted in a reduction in rainfall over the indian subcontinent and a decrease in the flux of river water delivered to the bay of bengal thus changes in the riverine input of nd a change in either flux or composition most likely caused the isotope variations although changes in dust source or local ocean circulation may have also played a role these results clearly establish a link between climate change and variations in radiogenic isotopes in the oceans and illustrate the potential of nd isotopes in foraminifera for high resolution palaeoceanographic reconstruction

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

comparison of sea ice thickness measurements under summer and winter conditions in the arctic using a small electromagnetic induction device drillhole determined sea ice thickness was compared with values derived remotely using a portable smalloffset loop loop steady state electromagnetic em induction device during expeditions to fram strait and the siberian arctic under typical winter and summer conditions simple empirical transformation equations are derived to convert measured apparent conductivity into ice thickness despite the extreme seasonal differences in sea ice properties as revealed by ice core analysis the transformation equations vary little for winter and summer thus the em induction technique operated on the ice surface in the horizontal dipole mode yields accurate results within 5 to 10 of the drillhole determined thickness over level ice in both seasons the robustness of the induction method with respect to seasonal extremes is attributed to the low salinity of brine or meltwater filling the extensive pore space in summer thus the average bulk ice conductivity for summer multiyear sea ice derived according to archie s law amounts to 23 ms m compared to 3 ms m for winter conditions these mean conductivities cause only minor differences in the em response as is shown by means of 1 d modeling however under summer conditions the range of ice conductivities is wider along with the widespread occurrence of surface melt ponds and freshwater lenses underneath the ice this causes greater scatter in the apparent conductivity ice thickness relation this can result in higher deviations between em derived and drillhole determined thicknesses in summer than in winter

sea ice thickness from airborne laser altimetry over the arctic ocean north of greenland 1 we present a new method to measure ice thickness of polar sea ice freeboard heights using airborne laser altimetry combined with a precise geoid model giving estimates of thickness of ice through isostatic equilibrium assumptions in the paper we analyze a number of flights from the polar sea off northern greenland and estimate accuracies of the estimated freeboard values to be at a 13 cm level corresponding to about 1 m in absolute thickness

the role of moist intrusions in winter arctic warming and sea ice decline abstractthis paper examines the trajectories followed by intense intrusions of moist air into the arctic polar region during autumn and winter and their impact on local temperature and sea ice concentration it is found that the vertical structure of the warming associated with moist intrusions is bottom amplified corresponding to a transition of local conditions from a cold clear state with a strong inversion to a warm opaque state with a weaker inversion in the marginal sea ice zone of the barents sea the passage of an intrusion also causes a retreat of the ice margin which persists for many days after the intrusion has passed the authors find that there is a positive trend in the number of intrusion events crossing 70 n during december and january that can explain roughly 45 of the surface air temperature and 30 of the sea ice concentration trends observed in the barents sea during the past two decades

effect of frequent winter warming events storms and snow on sea ice growth a case from the atlantic sector of the arctic ocean during the n ice2015 campaign

neodymium in modern foraminifera from the indian ocean implications for the use of foraminiferal nd isotope compositions in paleo oceanography abstract the use of the nd isotope composition of planktic foraminifera as a proxy for sea surface water is based on the assumption that nd is incorporated during initial calcification and preserved after foraminifera death subsequent transport through the water column and storage in the sediment pile to test this assumption nd concentrations are reported from foraminiferal tests collected from 20 to 3045 m depth multinets and sediment traps from offshore somalia and in the somali basin of the indian ocean nd partition coefficients calculated for two species globigerinoides ruber and globigerina bulloides sampled in the uppermost water column 100 m are 16 52 the measured nd ca ratio of living foraminifera is 8 nmol mol which is 8 190 times lower than reported in cleaned foraminifera from sediment cores 61 1500 nmol mol moreover the nd content of foraminiferal tests varies markedly within the water column 8 220 nmol mol ca recording a positive correlation with mn content r2 0 91 the observed changes in the nd concentration after foraminiferal death appear to reflect nd addition from deeper in the water column and imply a major disturbance of the primary nd isotope composition formed at the surface the high nd ca reported for cleaned foraminifera from sediment cores are interpreted to be a consequence of current cleaning techniques although cleaning successfully removes organics and secondary mn coatings into solution any released rare earth elements ree are subsequently re adsorbed onto the calcite cleaning removes elements with a 2 valency state into solution e g cd and mn but more reactive elements with higher valency states e g ree3 th4 are re absorbed onto residual carbonate it is concluded that although foraminifera clearly record temporal variations in nd isotope composition the relationship between these variations and changes in the sea surface nd isotope composition has yet to be established unambiguously further work is required to rule out the possibility that the nd in foraminifera represents a mixed signal derived from surface sediments and bottom and pore waters

glacial to interglacial contrasts in the northern indian ocean differences between the 18o 16o ratios of planktonic foraminifera deposited during the last glacial maximum about 18 000 yr ago and those deposited during the holocene show that in the indian ocean the south west monsoon was weaker than today but that the north east monsoon was stronger the upwelling observed in modern conditions along the southern coast of arabia had disappeared because of the low speed of the southwestern winds during glacial summers the reduction in rainfall and runoff over the continent caused a reduction of the salinity gradient in the bay of bengal and along the western coast of india increased precipitation fell on the sea south of 10 n while strong evaporation over the northernmost arabian sea produced an enhanced salinity gradient in that area

nd ca ratios in plankton towed and core top foraminifera confirmation of the water column acquisition of nd planktic foraminifera have been used as recorders of the neodymium nd isotopic composition of seawater although there is still controversy over the precise provenance of the nd signal we present an extensive multispecific plankton tow nd ca data set from several geographic locations se atlantic ne atlantic norwegian sea and western mediterranean together with core top samples from the mediterranean region the range of nd ca ratios in plankton towed foraminifera cleaned only of organic material from all regions 0 01 0 7 mol mol is similar to previously published analyses of sedimentary foraminifera cleaned using both oxidative and reductive steps with distribution coefficients kd ranging between 4 and 302 for the mediterranean where core top and plankton tow data are both available the range for plankton tows 0 05 0 7 mol mol is essentially identical to that for the core tops 0 1 0 5 mol mol readsorption of nd during cleaning is ruled out by the fact that the plankton tow samples underwent only an oxidative cleaning process we find a relationship between manganese mn and nd in plankton tow samples that is mirrored by a similar correlation in core top samples this relationship suggests that fe mn coatings are of negligible importance to the nd budgets of foraminifera as the nd mn ratio it implies is over an order of magnitude greater than that seen in other fe mn oxide phases rather since both plankton tows and core tops present a similar behavior the nd mn relationship must originate in the upper water column the data are consistent with the acquisition of nd and mn from the water column by binding to organic material and the fact that intratest organic material is shielded from both aggressive cleaning and diagenetic processes collectively the results help to explain two abiding puzzles about nd in sedimentary planktic foraminifera their high ree contents and the fact that they record a surface water nd isotopic signal regardless of the cleaning procedure used

meteorological conditions in a thinner arctic sea ice regime from winter to summer during the norwegian young sea ice expedition n ice2015 atmospheric measurements were made over arctic sea ice north of svalbard from winter to early summer january june 2015 during the norwegian young sea ice n ice2015 expedition these measurements which are available publicly represent a comprehensive meteorological data set covering the seasonal transition in the arctic basin over the new thinner sea ice regime winter was characterized by a succession of storms that produced short lived less than 48 h temperature increases of 20 to 30 k at the surface these storms were driven by the hemispheric scale circulation pattern with a large meridional component of the polar jet stream steering north atlantic storms into the high arctic nonstorm periods during winter were characterized by strong surface temperature inversions due to strong radiative cooling radiatively clear state the strength and depth of these inversions were similar to those during the surface heat budget of the arctic ocean sheba campaign in contrast atmospheric profiles during the opaquely cloudy state were different to those from sheba due to differences in the synoptic conditions and location within the ice pack storm events observed during spring summer were the result of synoptic systems located in the barents sea and the arctic basin rather than passing directly over n ice2015 these synoptic systems were driven by a large scale circulation pattern typical of recent years with an arctic dipole pattern developing during june surface temperatures became near constant 0 c on 1 june marking the beginning of summer atmospheric profiles during the spring and early summer show persistent lifted temperature and moisture inversions that are indicative of clouds and cloud processes

oxygen isotope salinity relationship in the northern indian ocean we analyze the surface 18o salinity relationships of the bay of bengal and the arabian sea in the northern indian ocean known for their contrasting hydrological conditions new measurements of these tracers show a very low 18o salinity slope associated with the strong dilution in the bay of bengal but a slope more typical of this latitude in the arabian sea although this region is marked by a complex monsoonal regime numerical modeling using a box model and a general circulation model is able to capture the 18o salinity slope and its geographical variation both models clearly show that the low 18o salinity slope is due to the evaporation minus precipitation balance with an important contribution of the continental runoff in the bay of bengal although the low value of these slopes 0 25 makes past salinity reconstructions uncertain insight into the last glacial maximum conditions shows a probable stability of these slopes and limited error on paleosalinity

oxygen isotope evidence for a stronger winter monsoon current during the last glaciation a variety of palaeoclimate data from the northern indian ocean has shown that the asian summer monsoon was weaker during the last glacial maximum 18 000 years ago than it is today1 5 it has also been inferred from these data that the winter monsoon was stronger at that time5 here we present evidence that the transport of low salinity water from the bay of bengal to the arabian sea caused by the winter monsoon6 was higher during the last glacial maximum this inference is based on a negative excursion up to about 1 in magnitude in the oxygen isotope ratios of three planktonic foraminiferal species detected in a sediment core from the arabian sea by high resolution 1 2 cm sampling our results place an upper limit of about 4 000 years on the length of time during which the winter monsoon was stronger than today

intensification and variability of ocean thermohaline circulation through the last deglaciation neodymium isotope ratios in the authigenic ferromanganese oxide component in a southeastern atlantic core reveal a history of the global overturning circulation intensity through the last deglaciation from a minimum during the last glacial maximum lgm north atlantic deep water nadw began to strengthen between 18 and 17 kyr cal bp approximately 2000 3000 years before the bolling warming it exhibits a gradually increasing baseline intensity that plateaus in the early holocene tracks increasing northern hemisphere insolation and parallels atmospheric co2 concentration millennial scale fluctuations are superimposed on this baseline nadw increase corresponding to events in northern hemisphere climate records the millennial excursions show sharp increases associated with the pre bolling retreat of continental glaciers and the bolling warming itself a decrease with allerod cooling and a recovery through the younger dryas and early holocene the data confirm a close link between deep ocean circulation and north atlantic climate changes there is no clear linkage with meltwater pulses indicating that rapid meltwater additions did not trigger observable mode changes in nadw production however rapid changes in north atlantic sea ice cover show a strong relationship with the millennial perturbations of nadw flux to the deep southern ocean the data indicate that the baseline intensity of nadw reaching the cape basin is paced by northern hemisphere insolation and that north atlantic sea ice coverage acts as a major amplifying link between the oceans and the atmosphere d 2004 elsevier b v all rights reserved

seasonal evolution of the geostrophic circulation in the northern gulf of california abstract an improved description of the seasonal variability of the geostrophic circulation in the northern gulf of california is obtained from a historical hydrographic database larger than in previous studies the evolution of the geostrophic circulation consists of a cyclonic summer period an anticyclonic winter period and two transition periods the cyclonic summer period lasts from june to september four months and is characterized by a strongly baroclinic cyclonic gyre which dominates the circulation the anticyclonic winter period starts in november and persists until april six months the anticyclonic geostrophic circulation is less robust than that in summer the transition periods take of the order of one month occurring around october and april may and are characterized by the simultaneous presence of both types of gyres empirical orthogonal function analysis shows a strong seasonal signal in the dynamic height for the first mode 97 2 of the total variance whose spatial structure is a closed gyre which oscillates between cyclonic during the summer months and anticyclonic the rest of the year the results strengthen and extend those from previous work based on analysis of hydrographic data on limited direct observations on satellite image analysis and on numerical modelling

variability of arctic sea ice thickness and volume from cryosat 2 we present our estimates of the thickness and volume of the arctic ocean ice cover from cryosat 2 data acquired between october 2010 and may 2014 average ice thickness and draft differences are within 0 16 m of measurements from other sources moorings submarine electromagnetic sensors icebridge the choice of parameters that affect the conversion of ice freeboard to thickness is discussed estimates between 2011 and 2013 suggest moderate decreases in volume followed by a notable increase of more than 2500 km 3 or 0 34 m of thickness over the basin in 2014 which could be attributed to not only a cooler summer in 2013 but also to large scale ice convergence just west of the canadian arctic archipelago due to wind driven onshore drift variability of volume and thickness in the multiyear ice zone underscores the importance of dynamics in maintaining the thickness of the arctic ice cover volume estimates are compared with those from icesat as well as the trends in ice thickness derived from submarine ice draft between 1980 and 2004 the combined icesat and cryosat 2 record yields reduced trends in volume loss compared with the 5 year icesat record which was weighted by the record setting ice extent after the summer of 2007

plate tectonics radiogenic isotopic tracers and paleoceanography the case of the manganese crusts in the pacific abstract hydrogenous ferromanganese crust deposits on seafloor and volcanic seamounts are archives of past isotopic compositions of the ocean isotopic compositions of long life radiogenic isotopes that are dissolved in the ocean such as nd and pb are mixtures of different erosion products continents volcanics arcs ridges etc transported by oceanic currents or winds isotopic studies on mn crusts are thus potential paleogeographic and paleoceanographic tracers however global paleogeography can drastically evolve over the period of growth of crust as well as the latitude longitude and water depth of the mn crust thus each crust sampled a succession of geographic sites related to its spatial evolution through time for this reason valid information about the past ocean isotopic composition can only be extracted from mn crust under the condition that the successive paleogeographic and paleodepth positions can be reconstructed for each mn crust we followed this approach for six hydrogenous mn crusts from the pacific ocean that have recorded pb and nd isotopic signals for the past 80 myr the evolution of the isotopic data was considered within a proper geodynamical framework that takes into account the paleopositions of the pacific plate and surrounding continents of the hot spots and ridges as well as the paths of the six crusts the differences and similarities between the pb and nd revealed by our analysis emphasize their complementarity as paleoceanographic tracers the nd isotopes are strongly influenced by the exchange between indian and pacific waters specifically by the progressive closure of the indonesian gateway the closed central pacific characteristics are defined from the extrapolation of the isotopic trend this highlights the important role played by erosion of volcanic arcs in the nd isotopic value of seawater our approach also stresses the influence of local volcanic activity ridges or active hot spot for lead isotopes

large scale surveys of snow depth on arctic sea ice from operation icebridge 1 we show the first results of a large scale survey of snow depth on arctic sea ice from nasa s operation icebridge snow radar system for the 2009 season and compare the data to climatological snow depth values established over the 1954 1991 time period for multiyear ice the mean radar derived snow depth is 33 1 cm and the corresponding mean climatological snow depth is 33 4 cm the small mean difference suggests consistency between contemporary estimates of snow depth with the historical climatology for the multiyear ice region of the arctic a 16 5 cm mean difference climatology minus radar is observed for first year ice areas suggesting that the increasingly seasonal sea ice cover of the arctic ocean has led to an overall loss of snow as the region has transitioned away from a dominantly multiyear ice cover

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

field investigations of ku band radar penetration into snow cover on antarctic sea ice monitoring long term large scale changes in the antarctic sea ice thickness is not currently possible due to the sampling constraints of the ship based and airborne observations which comprise most of the available thickness data satellite radar altimetry has been used to measure sea ice thickness variability in the arctic where it is assumed that the highest amplitude radar return originates from the snow ice interface as the arctic snow is cold and dry however this may not be the case in the antarctic due to more complex snow stratigraphy caused by warmer winter temperatures and frequent snow flooding we present the first measurements of radar penetration into snow cover on antarctic sea ice in the ku band at which satellite radar altimeters operate data were taken using a sled borne radar on sea ice off east antarctica during september and october 2007 radar data and field measurements of snow density thickness wetness and layers were taken over a range of locations including snow packs with flooding hard crusts and icy layers detailed snow pit studies showed that the snow ice interface was the dominant scattering surface only for snow without morphological features or flooding analysis of transect data showed that the mean depth of the dominant scattering surface of the radar was only around 50 of the mean measured snow depth indicating that the dominant scattering surface was not always the snow ice interface for the antarctic sea ice surveyed

the namche barwa syntaxis evidence for exhumation related to compressional crustal folding abstract geological observation in the eastern end of the himalayas shows that the asia india suture is folded and continues southward into india and burma where the continuation of the transhimalayan plutonic complex can be identified metamorphic rocks derived from india occur structurally below the suture in the core of a regional antiform isotopic and fission track dating are consistent with the geological interpretation in addition they establish cooling exhumation of rocks from c 30 km depth within the last 4 ma rapid exhumation of deep crustal levels in mountain systems is generally related to extension subsequent to thermal softening of a thickened continental lithosphere however in the eastern himalayas we argue that exhumation is caused by c 10 mm yr 1 erosion coeval with crustal scale folding the general history of this syntaxis resembles the evolution of the western himalayas syntaxis in pakistan

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

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

comparison of freeboard retrieval and ice thickness calculation from als asiras and cryosat 2 in the norwegian arctic to field measurements made during the n ice2015 expedition we present freeboard measurements from airborne laser scanner als the airborne synthetic aperture and interferometric radar altimeter system asiras and cryosat 2 siral radar altimeter ice thickness measurements from both helicopter borne and ground based electromagnetic sounding and point measurements of ice properties this case study was carried out in april 2015 during the n ice2015 expedition in the area of the arctic ocean north of svalbard the region is represented by deep snow up to 1 12 m and a widespread presence of negative freeboards the main scattering surfaces from both cryosat 2 and asiras are shown to be closer to the snow freeboard obtained by als than to the ice freeboard measured in situ this case study documents the complexity of freeboard retrievals from radar altimetry we show that even under cold below 15 c conditions the radar freeboard can be close to the snow freeboard on a regional scale of tens of kilometers we derived a modal sea ice thickness for the study region from cryosat 2 of 3 9 m compared to measured total thickness 1 7 m resulting in an overestimation of sea ice thickness on the order of a factor 2 our results also highlight the importance of year to year regional scale information about the depth and density of the snowpack as this influences the sea ice freeboard the radar penetration and is a key component of the hydrostatic balance equations used to convert radar freeboard to sea ice thickness

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

simulated effects of a snow layer on retrieval of cryosat 2 sea ice freeboard the impact of a snow layer on the location of the tracking point rp for ranging to the sea ice surface in cryosat 2 synthetic aperture interferometric radar altimeter waveforms is simulated with a range resolution of 47 cm the response of the air snow a s interface broadens the response of the snow ice s i interface and displaces the rp toward the altimeter this effect is largest when the strengths of their returns are comparable and when snow thicknesses are 20 cm on the other hand the rp is displaced away from the altimeter when the reduced propagation speed in the snow layer is not accounted for this analysis examines the dependence of these competing corrections on snow thickness and the relative scattering strengths of the interfaces and the sensitivity of two different tracking approaches leading edge and centroid to these snow parameters expected errors depend on a better understanding of the relative scattering strengths of the interfaces and snow layer

tectonically driven changes in the indian ocean circulation over the last 25 ma neodymium isotope evidence abstract changes in ancient oceanic current patterns have been strongly influenced by plate tectonics particularly by the opening or closing of gateways between different oceans such modifications of oceanic circulation have important consequences on climate we studied the nd seawater isotopic composition of indian and pacific ocean cores using nd isotopes which are good paleo oceanographic tracers we focused on the past 25 ma which are marked by the closure of the indonesian gateway as well as the mediterranean connection we show that a strong westerly oceanic surface current which we refer to the miocene indian ocean equatorial jet miojet linked the eastern and western indian ocean from 14 ma to 3 ma and infer that this major change in oceanic circulation probably induced important variations of global climate

taking a look at both sides of the ice comparison of ice thickness and drift speed as observed from moored airborne and shore based instruments near barrow alaska data from the seasonal ice zone observing network sizonet acquired near barrow alaska during the 2009 10 ice season allow novel comparisons between measurements of ice thickness and velocity an airborne electromagnetic survey that passed over a moored ice profiling sonar ips provided coincident independent measurements of total ice and snow thickness and ice draft at a scale of 10 km once differences in sampling footprint size are accounted for we reconcile the respective probability distributions and estimate the thickness of level sea ice at 1 48 0 1 m with a snow depth of 0 12 0 07 m we also complete what we believe is the first independent validation of radar derived ice velocities by comparing measurements from a coastal radar with those from an under ice acoustic doppler current profiler adcp after applying a median filter to reduce high frequency scatter in the radar derived data we find good agreement with the adcp bottom tracked ice velocities with increasing regulatory and operational needs for sea ice data including the number and thickness of pressure ridges coordinated observing networks such as sizonet can provide the means of reducing uncertainties inherent in individual datasets

microfossil evidence for changing salinity patterns in the bay of bengal over the last 20 000 years the monsson climate characterizing the northern indian ocean produces salinity gradients that are large compared with those in other open ocean areas these gradients are substantially independent of thermal and other ecologically important gradients this situation makes it possible not only to isolate the effect of salinity on sea bed distribution patterns of planktonic foraminifera but also to investigate past salinity changes along a north south transect of piston cores in the bay of bengal analysis of 152 surface sediment samples reveals that at least three factors other than salinity are important in controlling foraminiferal distribution sea bed dissolution surface productivity and surface temperature of these dissolution is the most important therefore in order to reconstruct past salinity patterns in the bay of bengal faunal indices need to be developed that isolate the effect of salinity we have developed two independent approaches the first uses ternary diagrams of the three dominant dissolution resistant species globoquadrina dutertrei globorotalia menardii pulleniatina obliquiloculata high values of g dutertrei are associated with low surface salinities the second approach uses dissolution buffered salinity transfer functions based on the total foraminiferal fauna in the 152 surface samples from the northern indian ocean applied to downcore samples these methods show the same basic historical pattern of salinity variation which is in turn consistent with independent inferences based on preliminary oxygen isotope data duplessy 1980 historical changes in the bay of bengal salinity are reconstructed along a north south transect of seven cores at 90 e the stratigraphy of the transect is controlled by oxygen isotope profiles that are similar to the generalized patterns observed in other areas over the past 20 000 yr salinity gradients are reconstructed for three time intervals 1 the last glacial maximum lgm 2 the mid termination mt and 3 the holocene during the lgm interval salinity was highger in the bay of bengal particularly in the north thus reducing the north south salinity gradient during the mt the middle of the transition from glacial to interglacial global climatic regimes northern bay of bengal surface salinity was considerably reduced while salinity to the south was generally similar to today thus the salinity gradient between 10 n and 15 n was considerably steeper than today in contrast the holocene gradient was approximately the same as the modern gradient with absolute values along the transect being slightly but uniformly higher these changes in the pattern of salinity are explained in terms of changes in the local patterns of precipitation and river run off during the lgm the salinity pattern probably results from decreased precipitation and decreased run off by the ganges brahmaputra river system during the mt decreased salinity in the northern bay of bengal is caused by increased precipitation and run off rather than by the influx of glacial meltwater the steeper mt salinity gradient in the central bay of bengal suggests increased eastward advection of equatorial surface waters by a southwest monsoon current somewhat more vigorous than today these patterns can be correlated with faunal evidence from the western arabian sea that suggest decreased upwelling during the lgm and increased upwelling during the mt this coupling of events may be associated with changes in the pattern or intensity of circulation during the southwest monsoon decreased intensity at the lgm 18 000 b p and increased intensity at the mt 10 500 to 12 500 b p

reduced ice thickness in arctic transpolar drift favors rapid ice retreat 1 helicopter borne electromagnetic sea ice thickness measurements were performed over the transpolar drift in late summers of 2001 2004 and 2007 continuing ground based measurements since 1991 these show an ongoing reduction of modal and mean ice thicknesses in the region of the north pole of up to 53 and 44 respectively since 2001 a buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi and second year ice in earlier years to first year ice in 2007 which had modal and mean summer thicknesses of 0 9 and 1 27 m measurements of second year ice which still persisted at the north pole in april 2007 indicate a reduction of late summer second year modal and mean ice thicknesses since 2001 of 20 and 25 to 1 65 and 1 81 m respectively the regime shift to younger and thinner ice could soon result in an ice free north pole during summer

the pb isotope geochemistry of granitoids from the himalaya tibet collision zone implications for crustal evolution abstract pb isotopic data on 80 k feldspars from six individual granitoid belts of the himalaya tibet collision zone are reported the isotopic trends observed in the trans himalayan complex which outcrops along the indus zangpo suture zone are best explained by a mixture of mantle derived pb component s with crustal derived pb these confirm that the batholith was built upon sialic continental crust as a result of the northward subduction of mesozoic oceanic crust beneath southern tibet the pb isotopic compositions of k feldspars from the three granitoid belts located within the lhasa block to the north of the indus zangpo suture zone are all radiogenic and indistinguishable from those of k feldspars extracted from basement rocks no pristine mantle derived component was identified and the granitoids are interpreted as being wholly derived from the partial melting of the continental crust furthermore the isotopic compositions of the granitoids are remarkably similar over the entire lhasa block implying that they were equilibrated by fluid remobilization during granulite facies metamorphism in the lower crust to the south of the indus zangpo suture zone and within the indian shield the lead isotopic composition of k feldspars from two granitoid belts although significantly more radiogenic than those of the lhasa block are identical to that of the basement gneisses indicating also that the granitic melts are the products of the anatexis of the continental crust in both the lhasa block and the indian shield the generation of granitic melts occurred as a consequence of large scale intracontinental thrusting events that created crustal repetition and induced the development of thermal anomalies at depths due to the burial of meta sedimentary rocks rich in water and radioactive heat producing elements the lhasa block and the indian shield define two distinct pb isotopic provinces which have undergone complex episodes of u th pb fractionation and are largely composed of precambrian material furthermore the correspondence between distinct pb isotopic provinces and discrete continental segments might indicate that the blocks originated from different sectors of the gondwanian continent