snow grain size profiles deduced from microwave snow emissivities in antarctica spaceborne microwave radiometers are an attractive tool for observing antarctic climate because their measurements are related to the snow temperature however the conversion from microwave emission to snow temperature is not simple and strongly depends on the emissivity through snow properties this difficulty in predicting the snow property profile for antarctic conditions is the main bottleneck in the retrieval of accurate climate information from microwave radiometers we attempt to explain the vertically polarized emissivity at 19 3 and 37 ghz derived from brightness temperatures acquired by the special sensor microwave imager ssm i and physical temperature from the era 40 re analysis in antarctica the snow emissivities at 19 3 and 37 ghz are nearly equal although a decrease with frequency is expected to explain this we consider various profiles of snow grain size and density and predict their emissivity using a dense medium radiative transfer dmrt model the results show that the emissivities cannot be explained by constant profiles of grain size and density heterogeneous snowpacks need to be considered we first test random variations of snow density and grain radius with depth and then monotonic and continuous variations in the snow grain radius in both cases we show that an overall increase of the snow grain radius with depth is required to match the observed emissivity in antarctica in addition two parameters characterizing the snow grain profiles are retrieved and compared with 1 in situ measurements of grain size at various locations in east antarctica 2 grain size estimated using visible spaceborne radiometers and 3 a semi empirical relationship for grain growth

226ra in marine barite new constraints on supported 226ra abstract following the pioneering work of paytan et al a paytan et al geochim cosmochim acta 60 1996 4313 4319 new investigations have been undertaken on marine barite separated from central and western equatorial pacific sediments these investigations are designed to achieve a better quantification of supported 226 ra activities in the separated samples enabling the use of excess 226 ra 226 ra ex in marine barite as a tool for dating holocene sediments instrumental neutron activation analysis allowed first to measure significant 238 u activities in the separated samples attributable to highly insoluble minerals that like barite are resistant to the chemical treatment used in this study tio 2 minerals zircon monazite within these u rich minerals 226 ra activities are in secular equilibrium with 238 u second the study of the 226 ra signal in old barite samples that do not contain any residual 226 ra ex activities provided accurate constraints on the amount of 226 ra produced by unsupported 230 th the remaining 226 ra activities corrected for the 238 u contribution appeared to decrease with depth with a slope comparable to that defined by the bulk 230 th ex activities the consistency of this deep trend allowed its extrapolation upwards to the sediment top in order to obtain an estimate of the 226 ra activities produced by unsupported 230 th in the holocene barite samples the total correction for supported 226 ra in the holocene barite samples used in this study therefore consists of the sum of 226 ra activities in secular equilibrium with 238 u within minerals and 226 ra activities produced by unsupported 230 th thus estimated the resulting correction is low for samples separated from central equatorial pacific sediments compared with both the total 226 ra activities measured in barite and results of previous studies the magnitude of the correction is nevertheless higher for samples from western equatorial pacific sediments which display a lower barite purity the corrected 226 ra in barite profiles are in agreement with the general trend observed for long half life radionuclides with a similar mixed layer in the sediment top thus adding confidence in the use of this tool below the mixed layer the exponential decay of 226 ra ex activities in barite allowed the determination of sedimentation rates that agree with the estimates for the two investigated sites ultimately one of the main uses for the 226 ra in barite dating method will be its application to holocene sediments from the southern ocean where dating is often problematic

revisiting the rare earth elements in foraminiferal tests are the rare earth elements rees in foraminifera a valuable proxy for use in paleoceanographic and climate change studies in order to investigate this we attempted a comprehensive study of rees in planktonic and benthic foraminifera several different cleaning protocols were tested although the hydroxylamine used to clean all foraminifera in this study removes an unidentified source of ree contamination it seems to remobilize metal oxides that are otherwise unaffected in flow through dissolution the calculated ree distribution coefficients kd ree s are between 100 and 500 for both planktonic and benthic foraminifera these kds are high compared to other elements in biogenic calcite but can be explained through a general model of element incorporation during foraminiferal calcification from data taken from eight core tops in the southeast pacific we conclude that the rees in planktonic foraminifera are indeed useful as a proxy for upper ocean water mass and mixed layer biogenic productivity alternatively the rees in benthic foraminifera are useful as a proxy for carbon flux to the sea floor these proxies should be robust down core unless the sediments have undergone anoxic diagenesis which stabilizes fe carbonate thus overprinting the primary ree signature however it is clear from ree distributions in foraminiferal tests if anoxic conditions have occurred

climate and oceanographic variability in the sw barents sea during the holocene the holocene section of the marine sediment core psh 5159n located in the sw barents sea has been studied at high resolution with a multiproxy approach a well stratified water column occurred at the site 11 9 8 ka bp the stratification was probably a result of a winter sea ice cover and or fresh warm surface waters during summer stratification and resultant reduction in air sea interaction allowed for warmer bottom water temperatures the general situation 11 9 8 ka bp could have been associated with an anomalous high pressure system over the nordic seas and the arctic ocean during the 11 10 5 ka bp interval the polar front was located close to the barents sea margin the polar front moved towards the site from 10 5 ka bp and from 9 8 to 7 5 ka bp it was probably located close to the site at 7 5 ka bp the polar front retreated eastwards as the present day oceanographic pattern established the mid holocene was in general characterized by rather stable conditions in contrast highly variable cond

a precise high throughput method for determining sr ca sr ba and ca ba ratios in marine barite 1 recent evidence suggests that marine barite an inorganic phase preserved in oxic deep sea sediments may record seawater sr and ca concentrations here we describe a novel method for determining sr ca sr ba and ca ba ratios of discrete marine barite separates marine barite separated from deep sea sediments is dissolved in a basic ethylene diamine tetra acetic acid edta solution and subsequently analyzed using an inductively coupled plasma optical emission spectrometer icp oes since dissolution occurs within 2 5 days and 15 samples can be analyzed on the icp oes per hour data acquisition is rapid compared with other procedures the method yields precisions of 0 7 sr ca 0 6 sr ba and 1 0 ca ba which are reproducible within 1 7 sr ca 1 7 sr ba and 2 5 ca ba precise determination of trace element incorporation in marine barite has implications for paleoceanography development of seawater sr and ca concentration curves and calculation of barite solubility in both the modern and ancient ocean

evidence for warming of atlantic water in the southern canadian basin of the arctic ocean results from the larsen 93 expedition potential temperature and salinity s data obtained along the perimeter of the southern canadian basin north of the east siberian sea in 1993 aboard the ccgs henry larsen show higher temperatures in waters of atlantic origin than in available climatological data for the canadian basin in particular a front is observed near the mendeleyev ridge which separates the cooler atlantic waters of the canada basin from the warmer atlantic waters observed in the makarov basin the front is further characterized by a change in the s slope of arctic thermocline water and by thermohaline intrusions and s reversals within the atlantic layer the idea that this warm variety of atlantic water has come recently from the eurasian basin is supported by its higher level of the tracer cfc 11

strontium calcium ratios in modern porites corals from the great barrier reef as a proxy for sea surface temperature calibration of the thermometer and monitoring of enso high precision sr ca ratios are reported for porites corals from davies reef at 19 s on the midshelf of the great barrier reef australia skeletal growth parameters were also determined from coral slabs using x ray photographs and densitometry measurements a calibration of the sr ca thermometer has been obtained using in situ measured sea surface temperatures which gives sr ca 10 10 48 0 01 0 0615 0 0004 t wheret is in c this calibration applies to different species of porites and a large range of annual extension and calcification rates provided sampling follows a major growth axis biases of 1 2 c have been observed in the low density margins where growth is hampered by interfering fans of corallites the analytical and the long term reproducibility of sr ca derived temperatures are both better than 0 3 c 2 coral growth parameters such as the extension rate or density generally appear to respond to environmental changes such as rainfall but do not affect the sr ca partitioning between coralline aragonite and seawater no correlation has been found between calcification rate and sr ca variations consistent with sr ca being mainly controlled by temperature in the great barrier reef the interannual variability in sst is primarily related to the el nino southern oscillation phenomenon and is typically marked by a cold anomaly during the winter preceding the mature warm phase instrumental records show that the surface waters of the coral sea around 19 s have experienced a significant cooling associated with the el ninos of 1965 1972 and 1982 1983 which the porites corals record faithfully the coral derived temperatures for the period from 1965 to 1993 show an increase of 1 3 c which has occurred mainly since 1979 this warming is larger in magnitude but consistent with the trend for the southern hemisphere land and marine temperature records which shows an increase of around 0 4 c

smos sea ice product operational application and validation in the barents sea marginal ice zone brightness temperatures at 1 4 ghz l band measured by the soil moisture and ocean salinity smos mission have been used to derive the thickness of sea ice the retrieval method is applicable only for relatively thin ice and not during the melting period hitherto the availability of ground truth sea ice thickness measurements for validation of smos sea ice products was mainly limited to relatively thick ice the situation has improved with an extensive field campaign in the barents sea during an anomalous ice edge retreat and subsequent freeze up event in march 2014 a sea ice forecast system for ship route optimisation has been developed and was tested during this field campaign with the ice strengthened research vessel rv lance the ship cruise was complemented with coordinated measurements from a helicopter and the research aircraft polar 5 sea ice thickness was measured using an electromagnetic induction em system from the bow of rv lance and another em system towed below the helicopter polar 5 was equipped among others with the l band radiometer emirad 2 the experiment yielded a comprehensive data set allowing the evaluation of the operational forecast and route optimisation system as well as the smos derived sea ice thickness product that has been used for the initialization of the forecasts two different smos sea ice thickness products reproduce the main spatial patterns of the ground truth measurements while the main difference being an underestimation of thick deformed ice ice thicknesses derived from the surface elevation measured by an airborne laser scanner and from simultaneous emirad 2 brightness temperatures correlate well up to 1 5 m which is more than the previously anticipated maximal smos retrieval thickness

arctic ocean warming and its consequences for the denmark strait overflow 1 two anomalously warm inflow pulses into the atlantic water layer of the arctic ocean have occurred since the late 1980s as a consequence temperatures of the arctic basins at 200 800 m depth have increased considerably in comparison to earlier decades the warm inflow pulses also had a low density owing to the decadal time scale of the circulation in the atlantic water layer large pools of anomalously light water have thereby formed in the arctic ocean these will slowly drain back south into the nordic seas we submit that they will be able to influence the overflows into the atlantic across the greenland scotland ridges the atlantic meridional overturning is fed by these overflows our model experiments indicate that the low density anomalies from the arctic ocean may be able to reduce the denmark strait overflow 15 25 years after the entrance of the original signal through fram strait into the arctic ocean the actual size of the reduction depends on the exact path and speed of the anomalies inside the arctic proper and on local processes in the arctic ocean and the nordic sea

sr ca variations in cretaceous carbonates relation to productivity and sea level changes abstract we present high resolution sr ca measurements on coccolith dominated pelagic carbonates of berriasian valanginian albian santonian and campanian maastrichtian age from dsdp sites and tethyan land sections carbonate sr ca varies by up to 80 over both long and short timescales and may reflect either temporal variations in seawater sr ca or variable sr partitioning in biogenic carbonates numerical models of seawater sr and ca budgets indicate that while sea level changes can cause comparably large variations in the seawater sr ca ratio the timing and pattern of predicted sr ca variations agrees poorly with the carbonate record reef crises unrelated to sea level changes may also elevate seawater sr ca and in some cases the record of reef crises corresponds to increasing carbonate sr ca changes in sr partitioning likely due to changes in calcareous nannoplankton productivity also appear to control carbonate sr ca in these records cretaceous carbonate sr ca broadly covaries with indicators of productivity derived from microfossil ecology recent studies in sediment core tops and cultures have shown that sr partitioning in coccolith carbonate is strongly influenced by changes in coccolithophorid growth and calcification rate where the effects of changing seawater sr ca can be constrained by independent geological data carbonate sr ca measurements could provide a valuable perspective on changes in the productivity of calcareous nannoplankton and variations in the carbonate and carbon cycle in the cretaceous

spatial and temporal characterization of hoar formation in central greenland using ssm i brightness temperatures the summertime formation and burial of low density coarse grained hoar layers in the snow of central greenland can be mapped using satellite passive microwave data variations in a signal derived from special sensor microwave imager ssm i brightness temperature trends correlate temporally and spatially with hoar complex evolution over 120 000 km of the greenland ice sheet s dry firn facies observations at the greenland ice sheet project ii gisp2 site indicate that changes in surface conditions and brightness temperatures correspond to four hoar events over two summers as expected from theory following a snowfall the smooth high density surface reflects some emitted 37 ghz horizontally polarized h radiation but little vertically polarized v radiation progressive surface roughness increases and density decreases during hoar formation cause a gradual decrease in h reflection formation and burial of a hoar layer thus causes a slow decrease followed by an abrupt increase in the v h ratio hoar layers have been used to date the gisp2 ice core through the entire holocene archived microwave data now can be used to assess the timing and frequency of the formation of these stratigraphic markers in central greenland

physical and geochemical properties across the atlantic pacific water mass front in the southern canadian basin temperature salinity nutrients oxygen and halocarbon data collected in the arctic ocean reveal a frontal structure previously unrecognized in the hydrography of the canadian basin samples were collected on a 1300 km section extending from the beaufort sea in the canada basin to the east siberian sea in the makarov basin these data collected in 1993 aboard the ccgs henry larsen reveal a lateral boundary between water masses of atlantic and pacific origin the term water mass assembly is introduced to describe the basic arrangement or vertical stacking of water masses found in the arctic ocean recognizing that water mass components within each assembly may differ from basin to basin using historical data two primary water mass assemblies are defined each consisting of three layers an upper layer an atlantic layer and a deep layer these two assemblies are marked by important differences one assembly here defined as the western arctic wa assembly is characterized by an upper layer of relatively fresh high nutrient water of pacific origin below this by an atlantic layer with a core temperature generally below 0 5 c and finally by a deep layer of higher salinities and colder temperatures about 0 5 c than found in the overlying atlantic layer the second assembly here defined as eastern arctic ea assembly is characterized by the absence of pacific water in the upper layer below this by an atlantic layer core as warm as 2 to 3 c and by a colder about 0 9 c deep layer because the presence or absence of pacific origin water is a key characteristic distinguishing the two assemblies we will refer to the water mass boundary between the two assemblies as the atlantic pacific front earlier research indicated that water masses in the arctic ocean were separated by a front above the lomonosov ridge into the canadian and eurasian basins although all larsen 93 stations from the canada basin a1 d1 display classic wa assembly characteristics the makarov basin station e1 shows ea assembly characteristics in the upper and atlantic layers and a wa assembly deep layer this suggests a relocation in the position of the atlantic pacific boundary away from the lomonosov ridge further larsen 93 data show the transition region between the atlantic and deep layers is fresher in the makarov basin than corresponding water in either the canada or eurasian basins implying a source of cold low salinity water perhaps from the laptev and east siberian shelves the front separating these two assemblies lies above the mendeleyev ridge and is marked by large lateral gradients in all measured properties in particular the penetration of anthropogenic halocarbons is 2 to 3 times deeper in the makarov basin than in the canada basin implying enhanced rates of ventilation this suggests that direct exchange between the canadian and eurasian basins has occurred recently near the perimeter and that physical and chemical properties including contaminants may have been transported by boundary currents more quickly from one basin to the other

on the dynamics of atlantic water circulation in the arctic ocean 1 we use a subset of models from the coordinated experiment of the arctic ocean model intercomparison project aomip to analyze differences in intensity and sense of rotation of atlantic water circulation we focus on the interpretation of the potential vorticity pv balance results differ drastically for the eurasian and the amerasian basins of the arctic ocean we find indications that in the eurasian basin the lateral net flux of pv is a significant factor for the determination of the sense of rotation of atlantic water circulation on timescales beyond pentades the main source of high pv causing cyclonic circulation in the eurasian basin is the barents sea where the seasonal cycle of surface buoyancy fluxes forms stratified water that leaves the shelf and feeds the atlantic water layer awl in the arctic basins however in the amerasian basin vertical pv fluxes are the more important factor these are closely related to wind field changes we find an intense response of the awl flow to wind forcing approximated by the sea level pressure difference between the bering sea and the central canadian basin which describes about half the variance of awl flow of the amerasian basin an experiment driven with a repeated atmospheric climatology exhibits an extreme case where a permanent high pressure system over the beaufort sea dominates the circulation in the amerasian basin demonstrating the potential of the beaufort gyre to adjust in such a way as to suppress a cyclonic awl flow in the amerasian basin in more realistic cases the beaufort gyre still modulates the amerasian basin awl circulation significantly

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

rapid analysis of high precision sr ca ratios in corals and other marine carbonates a method for rapid determination of high precision sr ca ratios in scleractinian corals is presented using an inductively coupled plasma atomic emission spectrophotometer samples are corrected for instrument drift using a reference solution similar to the approach used for analysis of stable isotopes using gas source mass spectrometry further correction for variation of the sr ca ratio with ca concentration is accomplished using internal standards the precision once all corrections have been made is better than 0 1 relative standard deviation 1 for samples of similar ca concentration and better than 0 2 for samples with variable ca concentrations this method increases the sample throughput by approximately a factor of 20 relative to thermal ionization mass spectrometry and significantly reduces instrument and per sample costs comparison of sr ca data for a coral from the galapagos islands with an instrumental temperature record shows excellent agreement and demonstrates the potential for application of this technique to samples of modern and fossil scleractinian corals and other marine carbonates including foraminifera

mechanisms for the variability of dense water pathways in the nordic seas 1 interannual changes in simulated flow fields of the nordic seas are analyzed with respect to their dynamic causes and consequences regarding the flow of dense water from the nordic seas into the subpolar north atlantic across the greenland iceland scotland ridge the simple case of pure density driven outflow with closed northern boundaries shows that dense water mainly originates in the northern lofoten basin and flows southward in three branches namely along the norwegian continental slope along the mohn and jan mayen ridges and a weak current along the east greenland continental slope adding variable exchange through fram strait shows a strengthening of the most western branch and strong recirculations that may reverse the other two branches for this case we find in phase modulation of the denmark strait overflow dso by a changing fram strait supply and a faroe shetland transport that is in opposite phase the scaling of this relation provides a potential explanation of recently observed dso changes however details of the changes in the simulated pathways suggest in accord with the size of the prescribed varying fram strait supply basin wide wind stress curl and local convection which feeds water from different source regions into the outflow pathways as the primary cause for the upstream flow field reorganizations

covariance of optimal parameters of an arctic sea ice ocean model abstractthe uniqueness of optimal parameter sets of an arctic sea ice simulation is investigated a set of parameter optimization experiments is performed using an automatic parameter optimization

renewal and circulation of intermediate waters in the canadian basin observed on the scicex 96 cruise during the summer of 1996 the nuclear submarine uss pogy occupied a line of stations extending through the middle of the canadian basin between about 88 n 44 w lomonosov ridge and about 78 n 144 w center of the canada basin ctd niskin bottle casts extending to 1600 m were carried out at eight stations providing the first high quality temperature salinity cfc tritium and 3he data obtained from this region although xctd data had previously been collected in this region these data along with data from stations at the basin boundary to the south and west reveal the presence of well ventilated intermediate water beneath the halocline in the center of the canada basin indicating renewal times of the order of 1 2 decades the least ventilated intermediate water was observed at the northern end of the canada basin along the southern flank of the alpha ridge intermediate water is derived from the atlantic ocean and enters the arctic ocean through fram strait and the barents sea it flows around the arctic basins in boundary currents and splits in the eastern amundsen basin with one branch crossing the lomonosov ridge and flowing along the east siberian continental slope and the other flowing along the eurasian flank of the lomonosov ridge from the 1996 scientific ice expedition scicex 96 observations we conclude that the branch that flows along the east siberian continental slope transports this water to the chukchi rise where it apparently enters the central canada basin with some flow continuing along the boundary to the southern canada basin the fram strait branch water mixes extensively with waters from the canadian basin during its transit along the east siberian continental slope being diluted by a factor of about 5 by the time it reaches the central canada basin the barents sea branch water does not undergo such extensive mixing and is diluted by a factor of only about 2 when it reaches the central canada basin

visual stratigraphic dating of the gisp2 ice core basis reproducibility and application annual layers are visible in the greenland ice sheet project 2 ice core from central greenland allowing rapid dating of the core changes in bubble and grain structure caused by near surface primarily summertime formation of hoar complexes provide the main visible annual marker in the holocene and changes in cloudiness of the ice correlated with dustiness mark wisconsinan annual cycles both markers are evident and have been intercalibrated in early holocene ice layer counts are reproducible between different workers and for one worker at different times with 1 error over century length times in the holocene reproducibility is typically 5 in wisconsinan ice age ice and decreases with increasing age and depth cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50 000 years visible observations are not greatly degraded by brittle ice or many other core quality problems allowing construction of long consistently sampled time series high accuracy requires careful study of the core by dedicated observers

impact of north atlantic current changes on the nordic seas and the arctic ocean 1 the impact of north atlantic current nac volume heat and salt transport variability onto the nordic seas and the arctic ocean is investigated using numerical hindcast and sensitivity experiments the ocean sea ice model reproduces observed propagation pathways and speeds of sst anomalies signals reaching the entrance to the nordic seas between iceland and scotland originate partly in the lower latitude north atlantic response experiments with different prescribed conditions at 50 n show that changes in the barotropic flow across 50 n have no impact on the seas north of the greenland scotland ridge because of the strong deformation of the f h field a temperature anomaly inserted in the upper 500 m at 50 n on the other hand has a widespread effect on the temperature distribution and the circulation in the high latitude north atlantic nac induced variability in the nordic seas and locally induced variability have similar magnitude the local atmospheric influence and the complexity of north atlantic nordic seas advection pathways make it unlikely that detection of signal propagation in the nac could lead to a prediction of oceanic conditions in the nordic seas and the arctic ocean with several years lead time

empirical partition coefficients for sr and ca in marine barite implications for reconstructing seawater sr and ca concentrations 1 a robust record of fluctuations in seawater sr and ca concentrations is critical for understanding the long term global carbon cycle as it is influenced by the history and location of carbonate precipitation chemical weathering and hydrothermal activity such a record is also necessary for interpretation of paleoceanographic records temperature productivity derived from carbonate sources e g sr ca mg ca li ca marine barite an inorganic phase preserved in oxic deep sea sediments may record seawater sr and ca concentrations using core top barite samples we have derived the partition coefficients for sr dsr 2 9 10 5 ca dca 1 9 10 8 and sr ca dsr ca 1 6 103 in barite the natural variability of core top marine barite sr ca sr ba and ca ba ratios selected from different ocean basins is 10 1 15 0 and 16 3 respectively since estimates of cenozoic fluctuations in seawater sr ca ratios are large possibly greater than 80 relative to the variability recorded in core tops marine barite may be used to reconstruct seawater sr ca ratios and sr and ca concentrations using empirically derived partition coefficients

interannual variability in the hydrography of atlantic water northwest of svalbard using data from 1910 to 1997 we study the mean structure as well as the interannual variability in the autumn hydrography of the part of the west spitsbergen current wsc confined over the upper continental slope and of its continuation the svalbard branch this is known to provide a major pathway for warm and saline atlantic water to the arctic ocean we focus our study on the area northwest of svalbard around 80 n the time series of subsurface hydrography 100 300 m layer show interannual variations which are in the 1980s and 1990s quite coherent with hydrographic time series obtained upstream in the wsc around 76 n as well as with variations in the large scale atmospheric patterns as indicated by the north atlantic oscillation nao index however in the 1970s the coherence is poorer our results suggest that it may be important to focus on the narrow domain of the part of the wsc confined over the upper continental slope in order to get consistent estimates of the arctic ocean inflow signal in the fram strait the warming in this inflow signal in 1970 1996 does not seem to have been as strong as previously suggested

model simulation of greenland sea upper ocean variability 1 observations indicate that the occurrence of dense upper ocean water masses coincides with periods of intense deep water formation in the greenland sea this paper focuses on the upper ocean hydrography of the area and its simulation in models we analyze properties that reside below the summer mixed layer at 200 m and carry the winter mixing signal the analysis employs numerical simulations from four different models all of which are forced as specified by the arctic ocean model intercomparison project aomip the models exhibit varying degrees of success in simulating upper ocean properties observed in the greenland sea including very dense saline water masses in the 1950s 1960s and 1970s two of the models predict the importance of salinity in determining the maximum density in the upper waters of the central gyre the circulation pattern of atlantic water was captured well by two high resolution models as measured by temperature salinity density relationships the simulated temporal variability of atlantic water properties was less satisfactory particularly in the case of salinity

analyzing and modeling the smos spatial variations in the east antarctic plateau abstract the smos brightness temperature t b collected on the east antarctic plateau revealed spatial signatures at l band that have never before been observed when only higher frequency passive microwave observations were available and this has opened up a new field of research because of the much greater penetration depth modeling the microwave ice sheet emission requires taking into account not only snow conditions on the surface but should also include glaciological information even if the penetration depth of the l band is not well known due to the uncertainty on the imaginary part of the ice permittivity it is likely to be of the order of several hundreds of meters which means that the temperature of the ice over a depth of nearly 1000 m influences the emission over such a depth the temperature is related to both the surface conditions and to the ice sheet thickness which in turn depends on the bedrock topography and on other glaciological variables the present paper aims to provide a thorough theoretical explanation of the observed t b spatial variation close to the brewster angle at vertical polarization in order to limit the effect of surface and vertical density variability in the firn in order to provide reliable inputs to the microwave emission models used for simulating t b data an in depth analysis of the temperature profiles was performed by means of glaciological models the comparison between simulated and observed data over three transects totalling 2000 km in east antarctica pointed out that whereas the emission models are capable of explaining the t b spatial variations of several kelvins 0 7 and 2 9 k they are unable to predict its absolute value correctly this study also shows that the main limiting factor in simulating low frequency microwave data is the uncertainty in the currently available imaginary part of the ice permittivity

a comparison between excess barium and barite as indicators of carbon export 1 since dymond et al 1992 proposed the paleoproductivity algorithm based on bio ba which relies on a strong correlation between ba and organic carbon fluxes in sediment traps this proxy has been applied in many paleoproductivity studies barite the main carrier of particulate barium in the water column and the phase associated with carbon export has also been suggested as a reliable paleoproductivity proxy in some locations we demonstrate that baexcess total barium minus the fraction associated with terrigenous material frequently overestimates babarite barium associated with the mineral barite most likely due to the inclusion of barium from phases other than barite and terrigenous silicates e g carbonate organic matter opal fe mn oxides and hydroxides a comparison between overlying oceanic carbon export and carbon export derived from baexcess shows that the dymond et al 1992 algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 c and chlorophyll a measurements of primary production this relationship varies by ocean basin but with the application of the appropriate f ratio to 14 c and chlorophyll a primary production estimates the plot of babarite accumulation and carbon export for the equatorial pacific atlantic and southern ocean converges to a global relationship that can be used to reconstruct paleo carbon export index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 4825 oceanography biological and chemical geochemistry keywords paleoproductivity barite export production excess barium marine sediments citation eagle m a paytan k r arrigo g van dijken and r w murray a comparison between excess barium and barite as indicators of carbon export paleoceanography 18 1 1021 doi 10 1029 2002pa000793 2003

modeling time series of microwave brightness temperature in antarctica this paper aims to interpret the temporal variations of microwave brightness temperature at 19 and 37 ghz and at vertical and horizontal polarizations in antarctica using a physically based snow dynamic and emission model sdem sdem predicts time series of top of atmosphere brightness temperature from widely available surface meteorological data era 40 re analysis to do so it successively computes the heat flux incoming the snowpack the snow temperature profile the microwaves emitted by the snow and finally the propagation of the microwaves through the atmosphere up to the satellite since the model contains several parameters whose value is variable and uncertain across the continent the parameter values are optimized for every 50 km 50 km pixel simulation results show that the model is inadequate in the melt zone where surface melting occurs on at least a few days a year because the snowpack structure and its temporal variations are too complex in contrast the accuracy is reasonably good in the dry zone and varies between 2 and 4 k depending on the frequency and polarization of observations and on the location at the antarctic scale the error is larger where wind is usually stronger suggesting either that meteorological data are less accurate in windy regions or that some neglected processes e g windpumping surface scouring are important at dome c in calm conditions a detailed analysis shows that most of the error is due to inaccuracy of the era 40 air temperature 2 k finally the paper discusses the values of the optimized parameters and their spatial variations across the antarctic

a comparison between active and passive microwave measurements of the antarctic ice sheet and their association with the surface katabatic winds the intensity of the seasat altimeter return power over antarctica varies in strong correlation with the intensity of model katabatic winds it is also strongly correlated with the polarization of the passive microwave signal at 37 ghz of the nimbus 7 smmr data it is shown that this is most likely the result of the wind induced micro roughness of the ice surface

simultaneous parameter optimization of an arctic sea ice ocean model by a genetic algorithm abstractimprovement and optimization of numerical sea ice models are of great relevance for understanding the role of sea ice in the climate system they are also a prerequisite for meaningful pred

the layered character of snow covers snow studies have generally ignored the layered nature of snow covers having achieved a good understanding of the properties and processes in homogeneous snow snow scientists should develop more insight into the evolution of the layers and their effects on overall snow response many of the outstanding problems in snow studies can only be solved by dealing with snow as a layered medium the various mechanisms by which layers are generated their effects and some of the outstanding research problems are described here

arctic warming evolution and spreading of the 1990s warm event in the nordic seas and the arctic ocean 1 observations in the arctic ocean revealed changes in oceanic temperature salinity and ice cover of the 1990s as compared with earlier data with a numerical model we favorably reproduce the development and subsequent propagation of temperature anomalies in water of atlantic origin in the 1980s and 1990s these propagated into the arctic ocean via the barents sea and the fram strait two warm anomalies entered the arctic ocean through these passages while the first smaller anomaly only warmed up the western eurasian basin the second large anomaly spread far into the eastern eurasian basin and across the lomonossov ridge into the western arctic basins intensified boundary currents during the high nao state in the first half of the 1990s significantly influenced the amplitude and speed of propagation of the temperature anomalies inside the arctic ocean in contrast to the notion of a continuous warming process during the 1990s our model results suggest the warming of the atlantic layer in the arctic ocean occurred in the form of events the event with the largest anomalous heat input during the modeled period entered the arctic between 1989 and 1994 it is possible to trace back the additional heat input into the arctic to an increased volume inflow via the faroer scotland passage and reduced heat loss to the atmosphere in the early 1990s after a weaker warm inflow in the second half of the 1990s the most recent observations and the model results point to a recurring warm anomaly in the inflow from 1999 onward

determination of carbonate bound barium in foraminifera and corals by isotope dilution plasma mass spectrometry abstract the trace metal content of biogenic carbonates reflects seawater concentrations only if one can selectively determine the portion of metal bound into the ca lattice site we have developed a procedure to purify benthic foraminifera shells of extraneous sedimentary organic and diagenetic ba the purification procedure involves treatment similar to those developed for the determination of cd in foraminifera shells but with the addition of an alkaline dtpa step to dissolve away sedimentary barite associated with the shells paired sample studies and partial dissolution of benthic foraminifera confirm the effectiveness of this procedure ba ca is determined on the purified shells by measurement of ba by isotope dilution inductively coupled plasma mass spectrometry id icp ms and ca by flame atomic absorption long term precision of the foraminifera ba ca determinations is between 2 and 3 we have also developed a rapid procedure for id icp ms determination of ba in aragonite coral samples with routine precisions of

dating annual layers of a shallow antarctic ice core with an optical scanner this study tests novel methods for automatically identifying annual layers in a shallow antarctic ice core wdc05q using images that were collected with an optical scanner at the us national ice core laboratory a new method of optimized variance maximization ovm modeled the density related changes in annual layer thickness directly from image variance this was done by using multi objective complex mocom parameter optimization to drive a low pass filtering scheme the ovm derived changes in annual layer thickness corresponded well with the results of an independent glaciochemical interpretation of the core individual annual cycles in image brightness were then identified by using ovm results to apply a depth varying low pass filter and fitting a second order polynomial to a locally detrended neighborhood the resulting map of annual cycles agreed to within 1 of the overall annual count of the glaciochemical interpretation agreement on the presence of specific annual layer features was 96 it was also shown that the mocom parameter optimization could calibrate the image based results to match directly the date of a specific volcanic marker

towards quantitative sea ice reconstructions in the northern north atlantic a combined biomarker and numerical modelling approach article i nfo organic geochemical analyses of marine surface sediments from the continental margins of east greenland and west spitsbergen provide for a biomarker based estimate of recent sea ice conditions in the northern north atlantic by means of the sea ice proxy ip25 and phytoplankton derived biomarkers e g brassicasterol and dinosterol we reconstruct sea ice and sea surface conditions respectively the combination of ip25 with a phytoplankton marker in terms of a phytoplankton marker ip25 index pip25 proves highly valuable to properly interpret the sea ice proxy signal as an under or overestimation of sea ice coverage can be circumvented a comparison of this biomarker based assessment of the sea ice distribution in the study area with 1 modern remote sensing data and 2 numerical modelling results reveal a good agreement between organic geochemical satellite and modelling observations the reasonable simulation of modern sea ice conditions by means of a regional ocean sea ice model demonstrates the feasibility to effectively integrate the complex atmospheric and oceanic circulation features as they prevail in the study area the good correlation between modelled sea ice parameters and the biomarker based estimate of sea ice coverage substantiates that linking proxy and model data occurs to be a promising concept in terms of a cross evaluation this combinatory approach may provide a first step towards quantitative sea ice reconstructions by means of ip25 future ip25 studies on marine surface sediments from the arctic realm however are recommended to extend and validate this new attempt of using ip25 in combination with a phytoplankton marker as a quantitative measure for sea ice reconstructions

windsat passive microwave polarimetric signatures of the greenland ice sheet windsat has systematically collected the first global fully polarimetric passive microwave data over both land and ocean as the first spaceborne polarimetric microwave radiometer it was designed to measure ocean surface wind speed and direction by including the third and fourth stokes parameters which are mostly related to the asymmetric structures of the ocean surface roughness although designed for wind vector retrieval windsat data are also collected over land and ice and this new data has revealed for the first time significant land signals in the third and fourth stokes parameter channels particularly over greenland and the antarctic ice sheets the third and fourth stokes parameters show well defined large azimuth modulations that appear to be correlated with geophysical variations particularly snow structure melting and metamorphism and have distinct seasonal variation the polarimetric signatures are relatively weak in the summer and are strongest around spring this corresponds well with the formation and erosion of the sastrugi in the dry snow zone and snowmelt in the soaked zone in this paper we present the full polarimetric signatures obtained from windsat over greenland and use a simple empirical observation model to quantify the azimuthal variations of the signatures in space and time

on improving the simulation of atlantic water circulation in the arctic ocean 1 we performed a set of numerical experiments in order to better simulate the circulation of atlantic water in the arctic ocean by employing a coupled ice ocean arctic regional model we found that the inflow of atlantic water via fram strait is weak in the case of high viscosity and diffusivity coefficients 1 108 cm2 s and 1 107 cm2 s and creates an anticyclonic circulation in the eurasian basin this flow increases significantly when both coefficients are scaled down to 1 107 cm2 s and 0 5 106 cm2 s but the current path is then unstable and it becomes mostly anticyclonic after about a decade of integration a further reduction of these coefficients leads to growing instabilities due to insufficient grid resolution short term integration of the model with doubled space resolution shows better agreement with observations but long term calculation is still restricted by simulation time alternatively a lower resolution version of this model benefits from parameterizations of subscale processes incorporation of the neptune parameterization of eddy topography interaction into the model intensifies the current steered by subsurface topography and results in cyclonic circulation of the atlantic water in every subbasin and in the whole arctic region in the absence of salinity restoring there was strong salinity drift at the surface resulting in a salinity increase in the central arctic by 3 units from 1960 to 2005 the arctic freshwater content is driven basically by year to year variations of convective mixing involving more saline water from lower layers after cooling and increasing in salinity through brine rejection the surface water becomes denser leading to even stronger convective mixing one dimensional model tests showed how model performance could be improved by implementing a lower vertical diffusion coefficient and higher vertical resolution

variation of foraminiferal sr ca over quaternary glacial interglacial cycles evidence for changes in mean ocean sr ca 1 records of sr ca changes in planktonic and benthic foraminifera from diverse hydrographic settings reveal coherent variability 5 1 between ocean basins and between surface and deep waters over the past 300 kyr there is a general increase in foraminiferal sr ca over the penultimate glaciation declining to minimum values during stage 5 and an increase in sr ca from stage 5 through stage 2 coincident changes in benthic foraminifera records from the atlantic and pacific basins imply that sr ca variations are not dominated by dissolution planktonic culturing data provide evidence that the downcore sr ca variations are not controlled by temperature changes and suggest only a small influence of salinity and ph variation common to the records is most readily explained by changes in mean ocean sr ca if fossil foraminifera reliably record higher glacial seawater sr ca coral sr paleothermometry would underestimate sea surface temperature during glacialepisodes

causes and development of repeated arctic ocean warming events 1 a model hindcast for 1948 2002 shows several warming events in the atlantic layer of the arctic ocean the most recent warming event in the 1990s spread from fram strait to the lomonosov ridge and into the canadian basin only a warming event in the 1960s can also be followed into the eastern eurasian basin these two warming events are reinforced by anomalously warm flow from the barents sea while warming events in the 1970s and 1980s encounter average or below normal temperatures in the barents sea branch of the atlantic water the warm barents sea outflow in the 1960s is caused by extensive ice cover and a melt water induced halocline in the barents sea that reduced heat loss from the atlantic water in the 1990s however the warm inflow from the nordic seas was responsible for warmer than normal flow from the barents sea into the arctic ocean

arctic ocean change heralds north atlantic freshening 1 a large pool of freshwater formed of ice and runoff is hosted by the arctic ocean it exits through the canadian archipelago and fram strait to enter the north atlantic deep water production regions using a numerical model and observations we trace a strong freshwater release to subpolar waters in the mid 1990s in contrast to the ice export driven 1970 s great salinity anomaly its source was a large additional liquid freshwater release from the arctic ocean in fact it was a consequence of a change of the arctic ocean s thermohaline structure in response to the very intense north atlantic oscillation in the early 1990s our results show a strong link of large scale arctic ocean changes with the freshwater flux to subpolar waters

li sr mg and na in foraminiferal calcite shells from laboratory culture sediment traps and sediment cores abstract constant temperature laboratory culture experiments of the planktonic foraminiferal species globigerinoides sacculifer brady suggest that the ratios of li and sr to ca in the shells are a function of these ratios in the culture solutions mg ca and na ca in the shells did not vary with changes of these ratios in the culture solution these are the first direct determinations of the relationship between foraminiferal shell chemistry and solution composition the possibility of temperature dependence for the minor elemental composition of foraminiferal shells was also investigated in the laboratory and by analysis of several planktonic and one benthic foraminiferal species from sediment trap and sediment core samples the sr ca mg ca and na ca ratios in the natural samples roughly correlate with calcification temperature whereas differences in the li ca ratios are small and not systematically related to temperature however laboratory culture experiments at 20 c and 30 c showed no variation in the li ca sr ca mg ca and na ca ratios with calcification temperature for the planktonic foraminifera g sacculifer and orbulina universa therefore observed differences in the sr ca mg ca and na ca ratios for the sediment trap and core foraminiferal samples cannot be ascribed to direct effects of calcification temperature but may be due to some other environmental factor which is correlated with temperature

temperature history and accumulation timing for the snowpack at gisp2 central greenland previous research has documented a close association between high resolution snow pit profiles of hydrogen and oxygen stable isotope ratios and multi year special sensor microwave imager ssm i 37 ghz brightness temperature data in central greenland comparison of the ssm i data to profiles obtained during the 1989 91 field seasons indicated that d and 18 o data from the near surface snow at the greenland summit are a reliable high resolution temperature proxy to test this new technique further additional stable isotope data were obtained from a 2 m snow pit constructed during late june 1995 near the gisp2 site this new profile supported by pit stratigraphy and chemistry data confirms the utility ofcomparing stable isotope records with ssm i brightness temperatures the sub annual variation of the d record at the gisp2 site was determined using 15 match points from approximately december 1991 through june 1995 and was guided in part by time constrained hoar layers the close association of these temperature proxies supports the assertion that snow accumulation occurs frequently through the year and that the isotope record initially contains temperature information from many times of the year this is also independently confirmed by analysis of h 2 o 2 data the slope of the multi year t vs 6 correlation was evaluated along with the sub annual variation in the amount rate and timing of accumulation these new results are consistent with those from the previous study and they also demonstrate that the snow in this area initially contains temperature and chemical records with sub annual resolution this encourages confident interpretation of the paleoclimatic signal variations in the gisp2 and grip deep cores

detection and monitoring of stratigraphic markers and temperature trends at the greenland ice sheet project 2 using passive microwave remote sensing data satellite passive microwave sensors provide a sensitive means of studying ice sheet surface processes that assists ice core interpretation and can extend local observations across regional scales analysis of special sensor microwave imager ssm i brightness temperature tb data supports ice core research in two specific ways first the summer hoar complex layers used to date the holocene portion of the greenland ice sheet project 2 ice core can be defined temporally and spatially by ssm i 37 ghz vertically v and horizontally h polarized b ratio v h trends second comparison of automatic weather station temperatures to ssm i 37 ghz v tb data shows that they are an effective proxy temperature record in this region also the tb data can be correlated with proxy temperature trends from stable isotope ratio 18o and d profiles from snow pits and this allows the assignment of dates to specific snow depths

freshwater distribution in the arctic ocean simulation with a high resolution model and model data comparison 1 a high resolution numerical simulation of the arctic ocean is analyzed in order to study the fate of river runoff and freshwater fluxes in the arctic ocean the model is driven by realistic winds and thermodynamic forcing from the european centre for medium range weather forecasting ecmwf reanalysis data set dye tracers have been added to visualize the pathways followed by low salinity water from the major arctic rivers and bering strait inflow the model is spun up using repeated forcing with the 1979 annual cycle for 20 years then the 1979 through 1998 atmospheric forcing is applied under the influence of the 1979 through early 1980s winds a large plume of river runoff exits the broad eurasian shelf seas along the lomonosov ridge starting in about 1985 the locus of shelf to basin transport shifts eastward to the alpha mendeleyev ridge complex this shift in the model output is related to changes in the sea surface height ssh fields which we attribute primarily to shifts in surface wind stresses model resolution runoff inputs and relaxation terms in the lena river delta region are analyzed in detail to expose issues with model performance at boundaries with freshwater inflow suggestions are made for improving future simulations of river runoff in basin scale models

accumulation and hoar effects on microwave emission in the greenland ice sheet dry snow zones the relationships between accumulation and microwave emissivity in the dry snow regions of the greenland ice sheet are studied with special focus on hoar formation with the use of a discrete ordinate radiative transfer model the relative contributions of hoar and accumulation to microwave emission are examined the results show that the link between microwave emission and accumulation rates in the dry snow area ofthe greenland ice sheet is significant however the emissivity is also dependent on the extent of hoar development as a result accumulation estimates based on passive microwave observations in the low accumulation dry snow areas will require successful parameterization of hoar formation furthermore the increasing t b trends that were observed during the 1980s which have been hypothesized to be related to accumulation changes may be strongly related to variations in hoar development other possible explanations for these observed trends such as slight surface melt or atmospheric conditions are also discussed

precipitation over the interior east antarctic ice sheet related to midlatitude blocking high activity abstract intermittent atmospheric blocking high activity in the south tasman sea is shown to play a key role in delivering substantial snowfall as far south as at least 75 s on the central east antarctic ice sheet plateau typically cyclones fail to penetrate this far 1000 km inland and accumulation was thought to be dominated by clear sky precipitation in east antarctica the meridional cloud bands delivering the moisture originate from as far north as 35 40 s and appear to preferentially pass over the east antarctic coast in a corridor from 120 to 160 e comparison of surface observations model and satellite data suggests that a few such episodes contribute a significant proportion of the low mean annual accumulation of the central east antarctic ice sheet e g an estimated 44 at dome c over 18 days in december 2001 january 2002 blocking high related incursions also cause abrupt increases in the surface wind speed snow redistribution and air temperature this has implications for th

a cenozoic seawater sr ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes a cenozoic multi species record of benthic foraminiferal calcite sr ca has been produced and is corrected for inter specific offsets typically less than 0 3 mmol mol and for the linear relationship between decreasing benthic foraminiferal sr ca and increasing water depth the water depth correction determined from holocene late glacial maximum and eocene paleowater depth transects is not vert similar0 1 mmol mol km the corrected cenozoic benthic foraminiferal sr ca record ranges from 1 2 to 2 0 mmol mol and has been interpreted in terms of long term changes in seawater sr ca enabling issues related to higher resolution variability in sr ca to be ignored we estimate that seawater sr ca was not vert similar1 5 times modern values in the late cretaceous but declined rapidly into the paleogene following a minimum in the eocene seawater sr ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late miocene by assuming scenarios for changing seawater calcium concentration and using published carbonate accumulation rate data combined with suitable values for sr partition coefficients into carbonates the seawater sr ca record is used to estimate global average river sr fluxes these fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity tectonic outgassing to calculate changes in global average river 87sr 86sr through the cenozoic the absolute magnitude of sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties nevertheless our results suggest that river sr flux increased from 35 ma to the present day roughly two fold accompanied by an overall increase in 87sr 86sr by not vert similar0 to 0 001 between 75 and 35 ma river 87sr 86sr also increased by not vert similar0 001 to 0 002 but was accompanied by a decrease two to three fold in river sr flux

barite accumulation ocean productivity and sr ba in barite across the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm ca 55 ma was a period of extreme global warming caused by rapid emission of greenhouse gases it is unknown what ended this episode of greenhouse warming but high oceanic export productivity over thousands of years as indicated by high accumulation rates of barium ba may have been a factor in ending this warm period by carbon sequestration however ba has a short oceanic residence time 10 k y so a prolonged global increase in ba accumulation rates requires an increase in input of ba to the ocean increasing barite saturation we use a novel proxy for barite saturation sr ba in marine barite to demonstrate that the seawater saturation state with respect to barite did not change across the petm the observations of increased barite burial no change in saturation and the short residence time can be reconciled if ba burial decreased at continental margin and shelf sites due to widespread occurrence of suboxic conditions leading to ba release into the water column combined with increased biological export production at some pelagic sites resulting in ba sink reorganization

effect of snow surface metamorphism on aquarius l band radiometer observations at dome c antarctica the antarctic plateau presents ideal characteristics to study the relationship between microwave observations and snow ice properties it is also a promising target for radiometer calibration and sensor intercalibration which are critical for applications requiring subkelvin accuracy such as sea surface salinity retrievals this paper presents the spaceborne aquarius l band radiometric observations collected since august 2011 over the antarctic plateau and it focuses on their temporal evolutions at dome c 75 1 circ hbox s 123 35 circ hbox e aquarius operates three radiometers with a sensitivity of 0 15 k over the oceans allowing us to analyze small variations in brightness temperature tb and changes with incidence angles over the antarctic plateau aquarius tbs have a relatively low annual standard deviation 0 2 0 9 k where melting never occurs however the analysis of the tb time series at dome c revealed significant variations up to 2 5 k in summer first these variations are compared with a remote sensing grain index gi based on high frequency 89 and 150 ghz shallow penetration tb channels variations in the ratio of tbs observed at horizontal and vertical polarizations are synchronous with gi changes second aquarius tb variations are compared with the presence of hoar crystals on the surface identified using surface based near infrared photographs the largest and longest changes in tbs correspond to periods with hoar crystals on the surface therefore in spite of the deep penetration of the l band radiation evolutions of the snow properties near the surface which usually change rapidly and irregularly do influence l band observations collection of accurate snow surface measurements and thorough analyses of the l band observations are thus needed to use the antarctic plateau as a calibration inter calibration target

atlantic water circulation over the mendeleev ridge and chukchi borderland from thermohaline intrusions and water mass properties 1 hydrographic and tracer data from 2002 illustrate atlantic water pathways and variability in the mendeleev ridge and chukchi borderland cblmr region of the arctic ocean thermohaline double diffusive intrusions zigzags dominate both the fram strait fsbw and barents sea branch waters bsbw in the region we show that details of the zigzags temperature salinity structure partially describe the water masses forming the intrusions furthermore as confirmed by chemical tracers the zigzags peaks contain the least altered water allowing assessment of the temporal history of the atlantic waters whilst the fsbw shows the 1990s warming and then a slight cooling the bsbw has continuously cooled and freshened over a similar time period the newest boundary current waters are found west of the mendeleev ridge in 2002 additionally we show the zigzag structures can fingerprint various water masses including the boundary current using this tracer data and the advection of the 1990s warming we conclude the strongly topographically steered boundary current order 50 km wide and found between the 1500 m and 2500 m isobaths crosses the mendeleev ridge north of 80 n loops south around the chukchi abyssal plain and north around the chukchi rise with the 1990s warming having reached the northern but not the southern northwind ridge by 2002 pacific waters influence the atlantic layers near the shelf and over the chukchi rise the northwind abyssal plain is comparatively stagnant being ventilated only slowly from the north there is no evidence of significant boundary current flow through the chukchi gap

arctic salinity anomalies and their link to the north atlantic during a positive phase of the arctic oscillation abstract many of the changes observed during the last two decades in the arctic ocean and adjacent seas have been linked to the concomitant abrupt decrease of the sea level pressure in the central arctic at the end of the 1980s the decrease was associated with a shift of the arctic oscillation ao to a positive phase which persisted throughout the mid 1990s the arctic salinity distribution is expected to respond to these dramatic changes via modifications in the ocean circulation and in the fresh water storage and transport by sea ice the present study investigates these different contributions in the context of idealized ice ocean experiments forced by atmospheric surface wind stress or temperature anomalies representative of a positive ao index wind stress anomalies representative of a positive ao index generate a decrease of the fresh water content of the upper arctic ocean which is mainly concentrated in the eastern arctic with almost no compensation from the western arctic sea ice contributes to about two third of this salinification another third being provided by an increased supply of salt by the atlantic inflow and increased fresh water export through the canadian archipelago and fram strait the signature of a saltier atlantic current in the norwegian sea is not found further north in both the barents sea and the fram strait branches of the atlantic inflow where instead a widespread freshening is observed the latter is the result of import of fresh anomalies from the subpolar north atlantic through the iceland scotland passage and enhanced advection of low salinity waters via the east icelandic current the volume of ice exported through fram strait increases by 20 primarily due to thicker ice advected into the strait from the northern greenland sector the increase of ice drift velocities having comparatively less influence the export anomaly is comparable to those observed during events of great salinity anomalies and induces substantial freshening in the greenland sea which in turn contributes to increasing the fresh water export to the north atlantic via denmark strait with a fresh water export anomaly of 7 msv the latter is the main fresh water supplier to the subpolar north atlantic the canadian archipelago contributing to 4 4 msv the removal of fresh water by sea ice under a positive winter ao index mainly occurs through enhanced thin ice growth in the eastern arctic winter sat anomalies have little impact on the thermodynamic sea ice response which is rather dictated by wind driven ice deformation changes the global sea ice mass balance of the western arctic indicates almost no net sea ice melt due to competing seasonal thermodynamic processes the surface freshening and likely enhanced sea ice melt observed in the western arctic during the 1990s should therefore be attributed to extra winter atmospheric effects such as the noticeable recent spring summer warming in the canada alaska sector or to other modes of atmospheric circulations than the ao especially in relation to the north pacific variability

microwave emission from density stratified antarctic firn at 6 cm wavelength previous observations have shown spatial covariances between microwave emission from antarctic firn at 6cm wavelength physical firn temperature and firn density stratification such observations motivate us to understand the physics underlying such covariances and based on that understanding to develop estimation methods for firn temperature and layering parameters we present here a model for 6cm emission from firn in which density and therefore dielectric permittivity varies randomly in discrete layers with mean thicknesses on the order of centimeters the model accounts for depth profiles of the physical temperature mean density and variance of random density fluctuations from layer to layer we also present a procedure to estimate emission model input parameters objectively from in situ density profile observations as well as uncertainties in the input parameters and corresponding uncertainties in theoretical brightness temperature predictions we compare emission model predictions with ground based observations at four diverse sites in antarctica which span a range of accumulation rates and other parameters we use coincident characterization data to estimate model inputs at two sites layered medium emission model predictions based on the most probable input parameters i e with no model tuning agree with observations to within 3 5 for incidence angles 50 corresponding figures for the other two sites are 7 5 and 10 however uncertainties in the input parameters are substantial due to the limited length and depth resolution of the characterization data uncertainties in brightness temperature predictions are correspondingly substantial thus brightness temperature predictions for the last mentioned sites based on only slightly less probable input parameters are also in close agreement with observations the significance of agreements and discrepancies could be clarified using characterization measurements with finer depth resolution

mechanisms of summertime upper arctic ocean warming and the effect on sea ice melt 1 in this study we use a numerical sea ice ocean model to examine what causes summertime upper ocean warming and sea ice melt during the 21st century in the arctic ocean our first question is what causes the ocean to warm in the pacific sector during the summer we find that about 80 of total heating over this region comes from ocean surface heat flux with the remaining 20 originating in ocean lateral heat flux convergence the latter occurs mostly within a few hundred kilometers of the northwest alaskan coast in the summer of 2007 the ocean gained just over twice the amount of heat it did over the average of the previous 7 years our second question is what causes sea ice to melt in the pacific sector during summer our analysis shows that top melt dominates total melt early in the summer while bottom melt and in particular bottom melt due to ocean heat transport dominates later in the summer as atmospheric heating declines bottom melt rates in summer 2007 were 34 higher relative to the previous 7 year average the modeled partition of top versus bottom melt closely matches observed melt rates obtained by a drifting buoy bottom melting contributes about 2 3 of total volume melt but is geographically confined to the marginal ice zone while top melting contributes a lesser 1 3 of volume melt but occurs over a much broader area of the ice pack

glacial to interglacial fluctuations in productivity in the equatorial pacific as indicated by marine barite an empirical correlation between marine barite baso4 accumulation rate in core top sediment samples from two equatorial pacific transects at 140 w and 110 w and the estimated primary productivity of the overlying water column were used to evaluate glacial to interglacial changes in productivity fluctuations in barite accumulation rates down core indicate that during glacial periods of the past 450 000 years the productivity in the central and eastern equatorial pacific was about two times that during intervening interglacial periods this result is consistent with other evidence that productivity was high in the eastern and central equatorial pacific during the last glacial

226ra in barite absolute dating of holocene southern ocean sediments and reconstruction of sea surface reservoir ages absolute dating of marine sediments is necessary to achieve reliable correlations of paleoclimate records the 2 2 6 ra decay in barite separated from a deep sea core of the southern ocean was used to determine absolute ages for the holocene epoch comparison with 1 4 c ages measured on planktic foraminifers provides the first past sea surface reservoir ages in the antarctic zone of the southern ocean throughout the middle to late holocene our results indicate a reservoir age of ca 1100 yr comparable to modern estimates a significantly higher reservoir age ca 1900 yr is obtained for the early holocene which suggests a major change in the southern ocean circulation at that time