statistical analysis of atmospheric forcing of north pole ice draft variations a series of correlation experiments and regression models are used to explore the atmospheric forcing of observed interannual variability in north pole ice drafts as measured by u s navy submarine sonar from 1982 to 1992 mean ice drafts as well as ice draft distributions are used in the analysis nearby drifting buoys are used to approximate a full 2 year motion history of the north pole ice parcels prior to submarine underpass drawing from theoretical work and empirical observation predictors of north pole ice draft variation are selected which embody accumulated ice exposure to subfreezing air temperature ice divergence and patterns of ice motion the timescales of the predictors are based on systematic evaluations of the lag dependence of the predictor predictand relationships linear correlation of each predictor with the observed ice draft distribution shows accumulated ice exposure to subfreezing air temperature is weakly correlated with reductions in shallow 0 to 2 5 m drafts ice divergence a week prior to draft measurement correlates most closely with the redistribution of ice drafts shallower than 3 5 m ice divergence and ice deflection from its wind forced motion during the 6 months prior to observation correlate with deeper ice drafts deeper than 6 8 and 4 6 m respectively together these two parameters explain more than 80 of the variance of the observed mean ice draft the accumulated ice exposure to subfreezing air temperatures colder than the 1980 1992 mean in the 2 years prior to ice arrival at the north pole adds little to an explanation of the interannual variance of the mean ice draft the results imply that 1 a realistic formulation of sea ice dynamics is a first order priority for model simulations of ice draft and 2 north pole ice thickness is not a simple function of arctic air temperature

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

sea ice production over the laptev sea shelf inferred from historical summer to winter hydrographic observations of 1960s 1990s the winter net sea ice production nsip over the laptev sea shelf is inferred from continuous summer to winter historical salinity records of 1960s 1990s while the nsip strongly depends on the assumed salinity of newly formed ice the nsip quasi decadal variability can be linked to the wind driven circulation anomalies in the laptev sea region the increased wind driven advection of ice away from the laptev sea coast when the arctic oscillation ao is positive implies enhanced coastal polynya sea ice production and brine release in the shelf water when the ao is negative the nsip and seasonal salinity amplitude tends to weaken these results are in reasonable agreement with sea ice observations and modeling

alaska landfast sea ice links with bathymetry and atmospheric circulation 1 using radarsat synthetic aperture radar sar imagery of northern alaska and northwestern canada we calculated a mean climatology of the annual landfast ice cycle for the period 1996 2004 we also present the monthly minimum mean and maximum landfast ice extents throughout the study area these data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge slie into waters around 18 m deep isobaths near this depth are a good approximation for midseason landfast ice extent comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the arctic due to later formation and earlier breakup this will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities which are intimately linked to the timing of marine mammal migration patterns interannually landfast ice formation correlates with the incursion of pack ice into coastal waters suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge the timing of breakup correlates well with onset of thawing air temperatures analysis of regional data shows a multidecadal trend toward earlier thaw onset which suggests that the observed change in breakup dates may be part of a longer term trend

possible dynamic and thermal causes for the recent decrease in sea ice in the arctic basin 1 a dynamic thermodynamic sea ice model with 50 km spatial and 24 hour temporal resolution was used to investigate the spatial and temporal variability of the sea ice cover and the surface energy exchange in the arctic basin daily surface level air temperature and pressure data from national centers for environmental prediction for 1958 1997 and climatic data for cloudiness relative humidity snow precipitation and the heat flux from the deep ocean in the greenland barents and bering seas were used as external forcing the model is integrated using the method of large particles belotserkovskii 1984 the model satisfactorily reproduces the seasonal and interannual variability of the main characteristics of the sea ice the sea ice extent and exchange through the main straits and the surface heat exchange for different parts of the arctic basin in particular estimates of the year to year difference between mean sea ice thickness in september show good agreement with the essential thinning of sea ice in the canadian basin that rothrock et al 1999 found most of the decrease in sea ice thickness is caused by a decrease in ridge concentration and an increase in the area covered by undeformed ice numerical experiments show that only 20 of the ice decrease can be explained by an increase in surface level air temperature model results for the canadian and eurasian basins allow us to determine the main trends in the temporal variability of ice thickness in these regions our model results suggest that the recent thinning of the sea ice correlates with a decrease in the concentration of ridged ice in turn the concentration of ridged ice and the total sea ice volume in the canadian basin correlate with cyclonic and anticyclonic regimes of the wind driven ice motion the sharp decrease in modeled ice volume in the canadian basin after 1987 also coincides with a significant increase in the mean atmospheric vorticity index for the central arctic ocean

long term ice variability in arctic marginal seas abstract examination of records of fast ice thickness 1936 2000 and ice extent 1900 2000 in the kara laptev east siberian and chukchi seas provide evidence that long term ice thickness and extent trends are small and generally not statistically significant while trends for shorter records are not indicative of the long term tendencies due to large amplitude low frequency variability the ice variability in these seas is dominated by a multidecadal low frequency oscillation lfo and to a lesser degree by higher frequency decadal fluctuations the lfo signal decays eastward from the kara sea where it is strongest in the chukchi sea ice variability is dominated by decadal fluctuations and there is no evidence of the lfo this spatial pattern is consistent with the air temperature north atlantic oscillation nao index correlation pattern with maximum correlation in the near atlantic region which decays toward the north pacific sensitivity analysis shows that dynamical forcing wind or surfac

interception of atmospheric fluxes by arctic sea ice evidence from cosmogenic 7be 1 the natural cosmogenic radionuclide 7be t1 2 53 4 d is supplied to the surface ocean from the atmosphere and in the arctic ocean can be used as a tracer of the efficiency with which sea ice intercepts the atmospheric fluxes of chemical species and of the importance of ice as a transport mechanism for particulate matter and chemical species analyses of 7be in samples of surface water surface sea ice water beneath the ice sea ice sediments and precipitation from the eurasian basin of the arctic ocean show that the fraction of sea ice coverage determines the amount of 7be in the surface water when sea ice coverage is 80 the water column inventory drops to 58 20 bq m 2 the 7be inventory in sea ice is 39 23 bq m 2 and mass balance calculations show that sea ice can intercept 30 18 of the atmospheric flux of 7be during the studied period we suggest that other atmospherically transported contaminants should be similarly intercepted 7be in the ice also can be used to estimate that the annual transport and release of sediment to the ablation area of the fram strait is 500 g m 2 a value comparable to previously measured fluxes in sediment traps deployed in the area

oxygen isotope exchange and closure temperatures in cooling rocks retrograde exchange of oxygen isotopes between minerals in igneous and metamorphic rocks by means of diffusion is explored using a finite difference computer model which predicts both the zonation profile of 18o within grains and the bulk 18o value of each mineral in the rock apparent oxygen isotope equilibrium temperatures that would be observed in these rocks are calculated from the 18o values of each mineral pair within the rock in systems which cool linearly from a sufficiently high temperature or at a low enough cooling rate such that the final oxygen isotope values are not dependent upon the initial oxygen isotope values slow cooling the apparent oxygen isotope temperature derived for a rock composed of a single mineral pair can be shown to be simply related to the dodson closure temperatures tc for the two phases and the mode of the rock adding a third phase into a system which undergoes slow cooling will cause the apparent temperature derived for the two minerals already present to differ from the simple relationship for a two phase system in some systems oxygen isotope reversals can be developed if cooling is not slow then the mineral 18o values resulting from cooling will be partly dependent upon the initial temperature of the system concerned the model successfully simulates the mineral 18o values that are often observed in granitic rocks application of the model will help in assessing the validity of oxygen isotope thermometry in different geological settings and allows quantitative prediction of the oxygen isotope fractionations that are developed in cooling closed systems

optical properties in waters around the mendeleev ridge related to the physical features of water masses abstract irradiance profiles were measured during the korean 2012 summer arctic ocean cruise and optical properties were studied the optical attenuation coefficient in all surface waters was low as the nutrients in the surface layers became exhausted and phytoplankton growth was only possible at the subsurface where optimal conditions of nutrients and sufficient illumination existed this high attenuation zone was at about 40 60 m the attenuation properties were categorized to three types type 1 waters had weaker maximum attenuation coefficients and were located at the chukchi plateau and the north margin of the study region type 2 water had an intense maximum of attenuation coefficient up to 0 56 m located on west flank of mendeleev ridge and continental slope of east siberian sea two integral parameters attenuation depth and optical thickness were mapped by spatial distribution the attenuation depth was basically shallower 40 m to the west and deeper to the east 100 m the averaged optical thickness at the level of 30 60 m was the main zone of high attenuation both the optical attenuation property and the physical features of the water indicated two subsurface water masses one is the cold shelf water well mixed with river water and transported to the east by a subsurface current along the east siberian slope the other is the warmer water from the pacific with lower nutrients and transported to the northwest along the north margin of the observed region a cyclonically re circulated branch of shelf water passing over the chukchi abyssal plain was described in this study

evidence of arctic sea ice thinning from direct observations the arctic sea ice cover is rapidly shrinking but a direct longer term assessment of the ice thinning remains challenging a new time series constructed from in situ measurements of sea ice thickness at the end of the melt season in fram strait shows a thinning by over 50 during 2003 2012 the modal and mean ice thickness along 79 degrees n decreased at a rate of 0 3 and 0 2 m yr 1 respectively with long term averages of 2 5 and 3 m airborne observations reveal an east west thickness gradient across the strait in spring but not in summer due to advection from more different source regions there is no clear relationship between interannual ice thickness variability and the source regions of the ice the observed thinning is therefore likely a result of arctic wide reduction in ice thickness with a potential shift in exported ice types playing a minor role

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

ice floe tracker an algorithm to automatically retrieve lagrangian trajectories via feature matching from moderate resolution visual imagery abstract satellite observations of sea ice along marginal ice zones suggest a strong coupling between sea ice transport and the underlying ocean turbulent eddy field moderate resolution imaging spectroradiometer modis satellite imagery spanning over almost two decades of daily observations at a resolution of up to 250 m provides a good resource for deriving long term ocean kinematics from sea ice dynamics in this paper we present a newly developed automatic algorithm to retrieve dynamic measurements of sea ice from these images we describe the methodology by presenting results acquired along the east greenland current ecg for 6 5 weeks in the spring of 2017 during this period our ice floe tracker was used to identify and track ice floes with length scales ranging from 8 to 65 km by effectively filtering atmospheric conditions from modis images ice floes were tracked for up to ten consecutive days and a total of 1061 trajectories were retrieved a southward mean sea ice flow associated with the ecg was observed along with deviations in both direction and magnitude suggesting the effect of an underlying turbulent eddy field the absolute position and tracking errors associated with our method are 255 m and 0 65 cm s respectively each derived from a comparison between manually and automatically identified ice floes going forward our methodology will be employed to process longer time sequences to analyze nonlinear interactions between drifting ice floes and the upper ocean turbulent eddy field in the ecg as well as to investigate other prominent regions of the arctic ocean

wind shear generated high frequency internal waves as precursors to mixing in a stratified lake field data were used to estimate the wavelength phase speed direction of propagation frequency and the vertical structure of high frequency internal waves observed on the crests of basin scale waves of lake kinneret during periods of strong wind shear stability analysis indicates that these waves were generated by shear in the surface mixing layer the characteristics of the high frequency internal waves changed within a wind event as the result of the evolution of the background flow conditions following the deepening of the surface layer and the propagation of the basin scale internal waves when the background conditions were appropriate the vertical structure of the unstable mode was such that the perturbations generated visible sinuous internal waves that in turn modified the density profile in the metalimnion in such a way that secondary shear instabilities were triggered the high frequency internal waves were observed over larger distances but poor coherence in temperature records from stations 200 m apart indicated that individual high frequency internal waves were dissipated locally these waves are thus a local mechanism allowing energy to be drawn from the energized surface layer and transported to the metalimnion where it sustains turbulence part of the energy extracted from the surface layer was also returned to the mean flow in the metalimnion high frequency internal waves are therefore also a source of momentum for the metalimnetic currents the vertical excursions of the waves also indicate that they could potentially play a role in phytoplankton growth by significantly altering the light regime at relatively high frequencies

determination of oxygen diffusion rates in magnetite from natural isotopic variations the oxygen isotope compositions of magnetite grains hosted in a calcite marble from the bancroft terrane of the ontario grenville province vary systematically with grain size the 18 o values of magnetite and corresponding closure temperatures t c based on calcite magnetite range from 18 o 2 6 t c 505 c for a grain radius of 0 075 mm to 18 o 5 5 t c 660 c for a grain radius of 1 15 mm the 18 o of the calcite is constant within a scale of 100 m at a value of 12 3 the observed isotopic variations can be fit to the diffusion model of dodson by the method of least squares r 0 98 to yield an activation energy q 211 20 kj mole and a pre exponential factor d o 4 3 3 3 1 9 x 10 7 cm 2 s for a cooling rate of 4 c m y the activation energy estimate is independent of the assumed cooling rate but the calculated pre exponential factor varies as follows d o cm 2 s d t d t x 1 08 x 10 7 note d t d t is in c m y the activation energy is identical to an experimental determination by giletti and hess but the pre exponential factor is 100 times lower the difference is attributed to the water rich conditions in the experiments and the absence of fluid in the slowly cooled marbles investigated in this study the strong dependence of diffusion rate on water presence or f h 2 o may be used as a sensor for water rich fluids during cooling in natural systems

a comparison between multiproxy and historical data ad 1990 1840 of drift ice conditions on the east greenland shelf 66 n the reduction in sea ice along the se greenland coast during the last century has severely impacted ice rafting to this area in order to reconstruct ice rafting and oceanographic conditions in the area of denmark strait during the last 150 years we conducted a multiproxy study on three short 20 cm sediment cores from outer kangerdlugssuaq trough 300 m water depth the proxy based data obtained have been compared with historical and instrumental data to gain a better understanding of the ice sheet ocean interactions in the area a robust chronology has been developed based on 210pb and 137cs measurements on core po175gkc 9 66 2 n 32 w and expanded to the two adjacent cores based on correlations between calcite weight percent records our proxy records include sea ice and phytoplankton biomarkers and a variety of mineralogical determinations based on the 2 mm sediment fraction including identification with quantitative x ray diffraction ice rafted debris counts on the 63 150 m sand fraction

north pole ice thickness and association with ice motion history 1977 1992 ice drafts measured by u s navy submarine sonar near the north pole from 1977 to 1992 were used together with arctic ocean drifting buoy data from 1979 to 1992 to investigate north pole ice thickness changes during this 15 year period a primary objective was to determine dynamical forcing mechanisms and associated time scales relevant to ice thickness variation north pole ice thickness showed much interannual variability and no systematic decrease of ice thickness was observed changes in ice thickness were closely associated with long term directional deviation of ice motion from geostrophic wind forcing and with ice convergence and divergence at the north pole during the 1 2 weeks prior to submarine measurement the geographic origin of ice within the arctic ocean was not associated with its eventual thickness at the north pole

sea ice motion as a drunkard s walk observations of sea ice displacement over short periods of time are used to deduce some statistics of the ice motion over long periods of time the objective is to follow the trajectory of a piece of ice starting at a randomly selected time and location and ending when the ice either melts or leaves the arctic basin trajectories are also followed backward in time to the time and location where the piece of ice was formed statistical properties considered are the age and remaining lifetime of ice in various locations and the probability that ice presently occupying a particular location was originally created or will ultimately melt in certain regions possible applications are to the distribution of pollutants by sea ice and to the design of experiments involving drifting measurement platforms

variability in arctic sea ice drift 1 analysis of arctic sea ice drift from 1979 1997 using a lagrangian perspective shows the complexities of ice drift response to variations in atmospheric conditions changes in ice dynamics influence the redistribution of ice and any transported material from different source areas sources of ice exported to fram strait shifted in about 1986 87 from dominance of the kara sea and severnaya zemlya to the new siberian islands east siberian sea and chukchi sea average travel time of multiyear ice within the perennial pack of the central arctic basin reached a maximum in 1987 88 and decreased by at least 1 year between 1984 1989 and 1990 1997 consistent with the observations of other investigators this decrease in ice travel time occurred following a major export or surge of old ice to fram strait from the beaufort gyre in 1988 through 1990 which decreased the fraction of thick ridged ice within the central basin

recent changes in arctic ocean sea ice motion associated with the north atlantic oscillation examination of a new ice motion dataset of the arctic ocean over a recent eighteen year period 1978 1996 reveals patterns of variability that can be linked directly to the north atlantic oscillation the intensity of the icelandic low one of its centers of action modulates the sea level pressure distribution over a broad region of the arctic ocean and the greenland iceland norwegian and barents seas over the winters of 1988 through 1995 the oscillation has remained in its positive phase contributing to coherent large scale changes in the intensity and character of ice transport in the arctic ocean the significant changes include the weakening of the beaufort gyre the increase in ice export through the fram strait the increase in ice import from the barents kara seas the enhanced eastward transport of sea ice from the laptev sea the weakening of the transpolar drift stream and the reduction in ice extent in the nordic seas all of these changes affect the regional and total sea ice mass balance of the arctic ocean

arctic contribution to upper ocean variability in the north atlantic abstract because much of the deep water of the world s oceans forms in the high latitude north atlantic the potential climatic leverage of salinity and temperature anomalies in this region is large substantial variations of sea ice have accompanied north atlantic salinity and temperature anomalies especially the extreme and long lived great salinity anomaly of the late 1960s and early 1970s atmospheric pressure data are used hem to show that the local forcing of high latitude north atlantic ocean fluctuations is augmented by antecedent atmospheric circulation anomalies over the central arctic these circulation anomalies are consistent with enhanced wind forcing of thicker older ice into the transpolar drift stream and an enhanced export of sea ice fresh water from the arctic into the greenland sea prior to major episodes of ice severity in the greenland and iceland seas an index of the pressure difference between southern greenland and the arctic asian coast reached its highest value of the twe

ice thickness in the arctic ocean the statistical reliability of experimental data the statistical reliability of ice thickness distributions derived from submarine sonar data sets of finite length is examined focusing on the standard error eh l in the mean ice draft h derived from a record of length l km this is important in assessing the significance or otherwise of quoted temporal or spatial differences in mean ice draft estimates for eh 50 are derived from four different submarine surveys each of which involved repeated sampling of apparently homogeneous ice fields values ranged from 7 18 to 15 29 of the mean for climate related comparisons of data sets from different years in the same location a value of 12 75 is recommended derived from data gathered at the north pole this value is used to reassess the significance of published data on ice draft variability quoted variability at the north pole over the 1977 1990 period is found to be not statistically significant but a difference in area averaged ice draft over the eurasian basin between 1976 and 1987 remains highly significant using hitherto unreported 1987 data from the north pole area the statistical variability of other parameters of the ice cover is examined the frequency of lead occurrence the width of leads the fractional cover of smooth ice and the frequency of keel occurrence all show standard errors of 22 24 in their mean values while mean keel draft has a 4 error all over a 50 km track length finally unreported 1987 data for an area extending from the pole to 72 n along the prime meridian and the east greenland shelf break are examined in 1 bins using eh l to assess the significance of variations in the mean a statistically significant decline in mean ice draft is observed starting at 86 n and continuing to 72 n a linear regression gives a thinning rate of 0 22 m deg the decline within the arctic basin itself is tentatively ascribed to a mixture of under ice melt and mixing of ice types since data on young ice occurrence show that divergence did not occur north of fram strait

has arctic sea ice rapidly thinned abstract reports based on submarine sonar data have suggested arctic sea ice has thinned nearly by half in recent decades such rapid thinning is a concern for detection of global change and for arctic regional impacts including atmospheric time series ocean currents and river runoff into an ocean ice snow model show that the inferred rapid thinning was unlikely the problem stems from undersampling varying winds that readily redistribute arctic ice create a recurring pattern whereby ice shifts between the central arctic and peripheral regions especially in the canadian sector timing and tracks of the submarine surveys missed this dominant mode of variability although model derived overall thinning from the 1960s to the 1990s was less than hitherto supposed there is also indication of accelerated thinning during the early mid 1990s

changes in the thickness distribution of arctic sea ice between 1958 1970 and 1993 1997 1 submarine sonar data collected in the central arctic basin during middle and late summer were used to examine differences in the sea ice thickness distribution function g h between the periods 1958 1970 and 1993 1997 cruises during the former period were made in july and august whereas the 1993 1997 cruises were made in september and october seasonal correction was applied to adjust for the differences in thickness while ice drafts were from only seven submarine cruises and somewhat spatially limited results indicate that the fractional area covered by open water and first year ice increased from 0 19 to 0 30 during the time interval this was balanced by an 11 reduction of level multiyear and ridged ice substantial losses occurred in ice thicker than 2 m with an increase in the amount of 1 2 m ice the volume of ice less than 4 m thick remained nearly the same and the total volume decreased about 32 losses in the volume of thicker ice increased with increasing thickness part of the change in g h is likely caused by increased ice area export through fram strait in the late 1980s and early 1990s because decadal variations in the north atlantic oscillation and arctic oscillation indices correlate with ice export anomalies export induced changes in g h probably tend to be cyclical in nature however a substantial shift in the peak of g h suggests that changes in thermal forcing were also a major factor in the observed thinning

modeling linear kinematic features in sea ice abstract sea ice deformation is localized in narrow zones of high strain rate that extend hundreds of kilometers for example across the arctic basin this paper demonstrates that these failure zones may be modeled with a viscous plastic sea ice model using an isotropic rheology if the ice is assumed to be heterogeneous at the grid scale and allowed to weaken in time intersecting failure zones propagate across the region the direction of failure propagation depends upon the stress applied to the ice wind stress and boundary conditions and the rheological model describing plastic failure of the ice the spacing between failure zones is controlled by the magnitude of the wind stress and the distribution describing spatial variability of ice strength sea ice motion and deformation oscillate at close to a 12 h period throughout the arctic and antarctic pack ice this oscillation is found at all spatial scales from hundreds of kilometers to the lead scale it is shown that with an inertial embedded mo

the rayner complex of east antarctica complex isotopic systematics within a proterozoic mobile belt new isotopic rb sr u pb zircon and sm nd and petrological data are presented for part of an extensive proterozoic mobile belt locally known as the rayner complex in east antarctica much of the belt is the product of mid proterozoic 1800 2000 ma juvenile crustal formation melting of this crust at about 1500 ma ago produced the felsic magmas from which the dominant orthogneisses of this terrain were subsequently derived deformation and transitional granulite amphibolite facies conditions which peaked at 750 50 c and 7 8 kbar 0 7 0 8 gpa produced open to tight folding about e w axes and syn tectonic granitoids about 960 ma ago subsequent felsic magmatism occurred at about 770 ma and not as has been widely advocated at 500 550 ma which appears to have been a time of widespread upper greenschist facies 400 500 c metamorphism localized shearing and faulting sm nd model ages of 1 65 2 18 ga disprove a previously favoured hypothesis that the rayner complex mostly represents reworked archaean rocks from the neighbouring craton napier complex models that involve rehydration of the napier complex are no longer required since the rayner complex was its own source of water two episodes of proterozoic crustal growth are identified the later of which occurred between about 1200 ma and 1000 ma and was relatively minor sedimentation took place only shortly before late proterozoic orogenesis the multiphase history of the rayner complex has resulted in complex isotopic behaviour three temporally discrete episodes of pb loss from zircon have been identified the earliest two of which are responses to the c 960 ma and 540 ma tectonothermal events fluid leaching was operative during the later event for there is a good correlation between degree of isotopic discordance and secondary mineral growth pb loss during the high grade event was probably governed by the same process or by lattice annealing some zircon suites also document recent pb loss most lower concordia intercepts have no direct geological meaning and are explicable as mixed ages produced by incomplete pb loss during two or more secondary events whereas all zircon separates from the orthogneisses produce u pb isotopic alignments zircons from the only analysed paragneiss produce scattered data in part reflecting a range of provenance the 960 ma event was also associated with the growth of a characteristically low u zircon 300 g g in rocks of inferred high zr content there is ubiquitous evidence for the resetting of rb sr total rock isochrons even samples separated by up to 10 km fail to produce igneous crystallization ages minor mineralogical changes produced by the 540 ma upper greenschist facies metamorphism were sufficient to almost completely reset some rb sr isochrons and to produce open system conditions on outcrop scale at least in one location

an estimate of the mean field of arctic sea ice motion the observational basis for our understanding of sea ice motion comes from the trajectories of particular ice floes these ice floes may have been marked by a manned research station or more recently by an automatic data buoy since 1893 almost 100 station years of drift data have been recorded using the principles of optimal linear estimation these data are used to obtain a quantitative estimate of the field of mean motion

sea ice thickness variability in the chukchi sea spring and summer 2002 2004 abstract measurements of sea ice thickness were obtained from drill holes an ice based electromagnetic induction instrument iem and a ship borne electromagnetic induction instrument sem during the early melt season in the southern chukchi sea in 2002 and 2004 and in late summer 2003 at the time of minimum ice extent in the northern chukchi sea an ice roughness criterion was applied to distinguish between level and rough or ridged ice ice thickness modes in the probability density functions pdfs derived from drill hole and iem measurements agreed well with modes at 1 5 1 6 and 1 8 1 9 m for all data from level ice the pdfs derived from sem measurements show that the primary modes are at 0 1 and 1 1 m in 2003 and 0 7 m in 2004 in 2002 and 2004 significant fractions between one third and one half of level ice were found to consist of rafted ice segments snow depth varied significantly between years with 2004 data showing more than half the snow cover on level ice to be at or below 0 05 m depth in late spring ice growth simulations and examination of ice drift and deformation history indicate that impacts of atmospheric and oceanic warming on level ice thickness in the region over the past few decades are masked to a large extent by variability in snow depth and the contribution of deformation processes in comparison with submarine sonar ice thickness data from previous decades a reduction in ice thickness by about 0 5 1 m is in part explained by the replacement of multi year with first year ice over the chukchi and beaufort shelves

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

recent changes in arctic sea ice the interplay between ice dynamics and thermodynamics abstract it is well established that periods of high north atlantic oscillation nao index are characterized by a weakening of the surface high pressure and surface anticyclone in the beaufort sea and the intensification of the cyclonic circulation in the eastern arctic ocean the response of arctic sea ice to these atmospheric changes has been studied with a thickness distribution sea ice model coupled to an ocean model during a period of high nao 1989 96 the model shows a substantial reduction of ice advection into the eastern arctic from the canada basin and an increase of ice export through fram strait both of which tend to deplete thick ice in the eastern arctic ocean and enhance it in the western arctic in an uneven dipolar pattern we call the east west arctic anomaly pattern ewaap from the period 1979 88 with a lower nao index to the period 1988 96 with a high nao index the simulated ice volume in the eastern arctic drops by about a quarter while that in the western arctic increases by

the climatology of internal waves in a deep temperate lake kootenay lake is a long 100 km deep 140 m dimictic lake in southeastern british columbia internal waves were observed over an 18 month period using three thermistor chains moored along the major axis of the lake to characterize their seasonal aspects four types of oscillations are recognized 1 classical seiches with amplitudes of 10 30 m and periods of 1 2 weeks 2 intrabasin waves with periods of 2 4 days 3 large amplitude waves resembling nonlinear surges and 4 high frequency waves associated with both the internal surge and large amplitude internal seiche motions the periods of the major components of the internal wave field are determined mainly by morphometry but vary seasonally with stratification thus the wind which not only forces internal waves but can also modify stratification is important in large lakes like kootenay the thermal structure may vary not only spatially but also temporally at periods comparable to those of the internal waves themselves hence the shape and frequency of these waves may be altered as they pass through the lake

contrasting oxygen diffusion in nepheline diopside and other silicates and their relevance to isotopic systematics in meteorites oxygen self diffusion coefficients have been determined in natural nepheline na3 na k al4si4o16 and synthetic diopside camg sio3 2 at one atmosphere by monitoring the rate of 18o exchange between co2 gas and minerals of pre determined grain size 10 12 5 and 15 m radius oxygen self diffusion in nepheline between 1000 and 1300 c fits a linear arrhenius relation of the form d 5 9 10 9 exp 25 0 2 5 103calrt and for diopside between 1150 and 1350 c d 6 3 exp 96 7 5 8 103calrt the activation energy for oxygen diffusion in nepheline is similar to that of melilite 31 9 0 1 kcal mol but the oxygen diffusivity is lower by two orders of magnitude the diffusion of oxygen in diopside is similar to that of nepheline at 1375 c however the activation energy is almost four times higher this contrast suggests a difference in the crystal chemical and structural controls of the minerals both nepheline and melilite are characterized by strongly distorted alkali sites within their frameworks which could account for their relatively low activation energies and high diffusivities more importantly nepheline and melilite have sheet like structures and high anionic porosities which may provide ready migration paths for oxygen the concentration of open space between the silicate sheets in melilite may explain the greater diffusivity of oxygen in melilite than in nepheline diopside forsterite anorthite spinel are characterized by high activation energies 80 to 100 kcal and are refractory with very stable bonds and low anion porosities furthermore these minerals are much denser and closer packed than nepheline or melilite making it difficult for oxygen to migrate within the crystalline structure and have access to the cation oxygen bonds oxygen diffusion studies constrain interpretations of post solidus oxygen exchange among minerals and may be used to explain the stable isotope systematics observed in ca al rich inclusions of carbonaceous chondrites the slow exchange and diffusion of oxygen in diopside suggests that the isotopic composition of clinopyroxenes in ca al rich inclusions of carbonaceous chondrites has not changed appreciably since their incorporation into the meteorite however minerals such as nepheline and melilite which readily exchange oxygen record the isotopic composition of the last nebular gas to which they were exposed

the concept of model temperature in oxygen isotope geochemistry an example of a single outcrop from the rayner complex enderby land east antarctica abstract oxygen isotope distribution among rocks of different lithologies from one outcrop of the polymetamorphic rayner complex east antarctica was used to estimate the model temperatures t m which correspond to the change of fluid behavior from the large scale migration to small scale exchange open system vs closed system during waning stages of regional metamorphism t m are deduced assuming 1 1 isotopically homogeneous fluid before isolation of a sample scale system from its surroundings and 2 2 mass balance control of the fluid isotopic composition after the isolation an estimated t m of about 720 c fits data on cationic geothermometers and equals the peak conditions of the major rayner event conventional oxygen geothermometry applied to the same samples gives equilibrium temperatures that are generally lower down to 565 c though the local scale oxygen transport among minerals mostly caused disequilibrium in isotope distribution

distribution and biomass transport of ice amphipods in drifting sea ice around svalbard abstract diversity and distribution of ice amphipods were determined in drifting sea ice around svalbard during may august 2003 2005 sea ice concentrations were determined visually and by satellite recordings backward trajectories for ice drift based on satellite observations indicated that multi year ice in the area had originated 3 5 years earlier in the kara sea and western laptev sea whereas some of the younger ice 1 2 years may have originated in franz josef land area quantitative collections of ice amphipods were obtained by scuba divers from flat areas and ridges below sea ice the abundance and biomass were generally higher on ridges particularly for the large gammarus wilkitzkii whereas apherusa glacialis was more abundant on flat areas abundance and biomass varied among seasons may august and years with low values in may and higher values in july the high values were similar to abundance and biomass values from july 1996 redundancy analysis showed that 33 and 52 of the variability in respective species abundance and biomass could be explained by environmental variables with ice draft and snow cover being the most important the overall mean biomass for flats 0 30 0 05 g m 2 and ridges 1 64 0 46 g m 2 were used to calculate ice associated biomass transport based on revised mean annual ice flux through fram strait 662 000 km2 yr 1 and into the barents sea total 228 000 km2 yr 1 about 478 103 t ww 57 103 t c of ice amphipods are transported annually through fram strait and 194 103 t ww 23 103 t c into the northern barents sea implying that 71 of the amphipod biomass in drifting sea ice passes through fram strait and 29 enters the barents sea climate induced reduction in ice thickness and extent will likely decrease this southward biomass transport and thus the current carbon input of about 80 103 t c yr 1 into these marginal seas ice amphipod populations probably cannot be sustained if the summers become ice free in the arctic ocean and particularly reduction of multi year ice in the arctic ocean will affect long lived species such as gammarus wilkitzkii

the under ice thickness distribution of the arctic basin as recorded in 1958 and 1970 the uss nautilus ssn 571 was the first vessel to cross the arctic basin via the north pole in early august 1958 during this expedition almost continuous acoustic under ice thickness profiles were recorded in august 1970 uss queenfish ssn 651 retraced nautilus route yielding the only duplicate transect of under ice topography across the arctic basin comparisons of the statistical analysis of the under ice draft measurements obtained through use of wide beam and narrow beam and narrow beam only acoustic profilers by nautilus and queenfish respectively along the coincidental route are presented geographic areas found to have distinct under ice characteristics and ice composition are identified the under ice statistics of both cruises are considered in relation to representative field observations and modeling results of other researchers principal findings are 1 nautilus recorded generally more severe ice conditions within the canada basin than did queenfish 12 years later overall mean drafts were 3 08 and 2 39 m respectively 2 the under ice topography becomes progressively more severe when proceeding from the canadian to the eurasian side of the arctic basin 3 the canada basin may contain the most moderate under ice topography and the greatest number of open water and refrozen polynyas and leads within the central arctic basin 4 the makarov and amundsen basins and the arctic mid ocean ridge may contain some of the most severe under ice topography within the arctic basin and 5 the present study indicates an overall arctic basin mean of 3 4 open water new ice less than 30 cm in summer

thickness and surface properties of different sea ice regimes within the arctic trans polar drift data from summers 2001 2004 and 2007 1 large scale sea ice thickness and surface property data were obtained in three summers and in three different sea ice regimes in the arctic trans polar drift tpd by means of helicopter electromagnetic sounding distribution functions p of sea ice thickness and of the height spacing and density of sails were analyzed to characterize ice regimes of different ages and deformations results suggest that modal ice thickness is affected by the age of a sea ice regime and that the degree of deformation is represented by the shape of p mean thickness changes with both age and deformation standard error calculations showed that representative mean and modal thickness could be obtained with transect lengths of 15 km and 50 km respectively in less deformed ice regimes such as those around the north pole in heavier deformed ice regimes closer to greenland 100 km transects were necessary for mean thickness determination and a representative modal thickness could not be obtained at all mean sail height did not differ between ice regimes whereas sail density increased with the degree of deformation furthermore the fraction of level ice open melt ponds and open water along the transects were determined although overall ice thickness in the central tpd was 50 thinner in 2007 than in 2001 first year ice fyi was not significantly thinner in 2007 than fyi in 2001 with a decrease of only 0 3 m thinner fyi in 2007 only occurred close to the sea ice edge where open water covered more than 10 of the surface melt pond coverage retrieved from laser measurements was 15 in both the 2004 myi regime and the 2007 fyi regime

contour mapping of arctic basin ice draft and roughness parameters a data base of ice draft and roughness parameters has been constructed for selected portions of the arctic ocean based upon analysis of under ice draft distribution data acquired by inverted echo sounder systems on submarines from the voyages of 12 submarines which traversed the alaskan canadian and central arctic regions of the arctic ocean during the summer and winter seasons a series of mean ice draft and deep draft keel statistics was calculated for 50 km segments along each submarine track contour maps of the mean ice draft its standard deviation the mean keel draft and the spatial frequency of ice keels were constructed they show that the greatest ice drafts the roughest ice and the greatest number of deep draft keels are found off the north coasts of the canadian archipelago and greenland due to ice convergence on these land barriers

diffusion effects on oxygen isotope temperatures of slowly cooled igneous and metamorphic rocks recently obtained data on oxygen diffusion in feldspars quartz and hornblende permit the prediction of the apparent18o16o temperatures that would be measured in a rock that consisted only of those three minerals and cooled slowly from high temperature the computed temperatures would be based on the differences in the18o16o ratios between coexisting pairs of minerals the present calculation takes into account the diffusion rates for oxygen as a function of temperature the cooling rate of the rock the mineral grain sizes and the mode of the rock for mineral grains 1 mm in radius and a cooling rate of 10 c m y the minimum difference in apparent temperature between quartz feldspar and feldspar hornblende pairs will be 115 c despite the assumption of a normal uneventful slow cooling history to room temperature further the apparent quartz hornblende temperature will range over 30 c 590 620 c depending on the mode of the rock for a cooling rate of 1000 c m y the apparent difference in temperature can be as much as 400 c consequently consistency in temperatures obtained by oxygen isotope analysis should not be expected in most high grade metamorphic rocks or igneous rocks which are cooled slowly departures from the pattern of temperatures obtained in this model would imply a very rapid quench from high temperature or a complex history for the rock for some minerals including hornblende the relation between temperature and the equilibrium fractionation of oxygen isotopes between coexisting phases has been derived from observed relations in natural specimens the choice of the specimens used for such calibrations needs to be re evaluated in light of these findings this may result in a change in the equilibrium equation constants an example from the literature the san jose tonalite baja california mexico was modelled and yields 18o concentrations in the minerals that correspond closely with the measured values this suggests that the model used is appropriate that the rock has had a simple thermal history and that it cooled at 100 200 c m y over the temperature range 800 500 c the set of paleotemperatures obtained for a rock will in general yield neither the mineral closure temperatures nor the formation or crystallization temperatures on the other hand the cooling rate of the rock may be derived from the data this in turn may have important tectonic implications with regard to denudation and uplift rates

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

changes in the 18o 16o ratios of fluids as evidence for different metamorphic episodes in high grade gneisses from the konovalov mountains area rayner complex east antarctica abstract rocks of the rayner complex in east antarctica have suffered a complex multiphase metamorphic evolution radiogenic age constraints taken from the literature suggest at least two metamorphic events the main rayner event accompanied by charnockite emplacement 963 myr ago and an amphibolite facies overprint 500 550 myr ago some authors have suggested that a second high temperature metamorphic event was connected with the widespread intrusion of granitic magmas at about 770 myr petrological and stable isotope thermometry is consistent with three metamorphic events i a first granulite facies metamorphism as preserved in the cationic equilibria of minerals in enderbitic gneisses yielding 810 c and 6 9 kbar ii a regionally pervasive overprint also at high temperatures 730 c and 5 9 kbar previously regarded as the main rayner event and iii an amphibolite facies overprint followed by a greenschist facies retrogression which is especially pronounced in late shear zones we show that the two older events can be distinguished by the isotopic composition of the metamorphic fluids during the first granulite facies event the rocks preserved their inherited isotopic signatures whereas the second granulite facies overprint was accompanied by pervasive flux of fluids of magmatic possibly mantle origin during the third amphibolite grade event the fluids trapped during the second event were remobilised and led to partial reequilibration

the role of fluids in granulite facies metamorphism as deduced from oxygen and carbon isotopic compositions abstract based on stable isotope data of whole rock samples the main fluid rock exchange reactions in the high grade rocks of the crystalline basement of sri lanka is deduced to have occurred prior to granulite facies metamorphism the influx of external fluids during and after granulite facies conditions was only channellized and did not give rise to the formation of interconnected fluid films in rock volumes larger than several cm3 fluid present conditions were thus only manifest for relatively short periods of time much less than 106 y so that the conditions of granulite facies metamorphism of the sri lankan basement rocks in general can be characterized as fluid absent

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

o isotope variations in a porphyroclastic meta anorthosite diffusion effects and false isotherms a detailed o isotope study of annealed porphyroclastic meta anorthosite was performed to assess the degree of postpeak metamorphic and postshearing reequilibration stable isotope and petrologic evidence indicate that the whitestone anorthosite ontario was infiltrated by an sqand cor rich fluid subsequent to peak grenville granulite facies metamorphism ductile shearing occurred during and following peak metamorphism relict igneous plagioclase phenocrysts an o occur as coarse grained porphyroclasts in a finegrained recrystallized matrix of plagioclase anoo hornblende garnet scapolite epidote ilmenite the 6 80 values of mineral fragments as small as 200 pm were analyzed to assess constituents developed at different stages of the rock s history the 6r8o ro n values 7oo are as follows porphyroclastic plagioclase 8 1 8 5 av 8 38 0 14 2o matrix plagioclase 8 2 9 2 av 8 65 0 32 garnet 6 87 0 02 n 2 hornblende 6 44 0 00 n 2 ilmenite 1 93 0 18 n 2 in situ analyses agree within error but are far more scattered av 8 2 0 5 the plagioclase porphyroclasts are isotopically homogeneous a result of rapid difitsion of 180 160 at hlgh z and slow cooling rates the theoretical d 8o values of all minerals were calculated on the basis of o volume diffi rsional considerations using diffusion rate data for both hydrous and anhydrous conditions the whitestone data set is in far better agreement with the diftrsion data obtained in hydrothermal experiments indicating that cooling probably occurred in the presence of a hydrous fluid similar calculations made for other granulite terranes are generally consistent with cooling under anhydrous conditions the observed d 8o values of all phases from the whitestone anorthosite yield an enoneous equilibration temperature of 470 l 30 c that can be explained by an infinite reservoir model involving postpeak metamorphic o isotope exchange with an infinite reservoir of plagioclase comparable false isotherms are characteristic of other granulite terranes as well

sea ice transport a highly variable link between arctic and north atlantic the variability of the ice volume flux into the northeast atlantic is investigated with an optimized dynamic thermodynamic sea ice model using 40 years 1958 1997 of atmospheric forcing fields derived from the ncep ncar reanalysis project the simulated sea ice export from the arctic exhibits considerable interannual to decadal variability and is primarily a linear response to sea level pressure anomalies over greenland and over the barents and kara seas our model results suggest that ice export anomalies such as in 1968 which supposedly caused the so called great salinity anomaly in the northern north atlantic are not unique but rather frequent events as part of the variability of the arctic climate system

simulation of the interannual variability of the wind driven arctic sea ice cover during 1958 1998 a thermodynamic dynamic sea ice model based on a granular material rheology developed by tremblay and mysak is used to study the interannual variability of the arctic sea ice cover during the 41 year period 1958 98 monthly wind stress forcing derived from the national centers for environmental prediction ncep reanalysis data is used to produce the year to year variations in the sea ice circulation and thickness we focus on analyzing the variability of the sea ice volume in the arctic basin and the subsequent changes in sea ice export into the greenland sea via fram strait the relative contributions of the fram strait sea ice thickness and velocity anomalies to the sea ice export anomalies are first investigated and the former is shown to be particularly important during several large export events the sea ice export anomalies for these events are next linked to prior sea ice volume anomalies in the arctic basin the origin and evolution of the sea ice volume anomalies are then related to the sea ice circulation and atmospheric forcing patterns in the arctic large sea ice export anomalies are generally preceded by large volume anomalies formed along the east siberian coast due to anomalous winds which occur when the arctic high is centered closer than usual to this coastal area when the center of this high relocates over the beaufort sea and the icelandic low extends far into the arctic basin the ice volume anomalies are transported to the fram strait region via the transpolar drift stream finally the link between the sea ice export and the north atlantic oscillation nao index is briefly discussed the overall results from this study show that the arctic basin and its ice volume anomalies must be considered in order to fully understand the export through fram strait

interannual variability of arctic landfast ice between 1976 and 2007 abstractanalysis of weekly sea ice charts produced by the u s national ice center from 1976 to 2007 indicates large interannual variations in the averaged winter landfast ice extent around the arctic basin during the 32 yr period of the record landfast ice cover was relatively extensive from the early to mid 1980s but since then has declined in many coastal regions of the arctic particularly after the early 1990s while the barents baltic and bering seas show increases in landfast ice area the overall change for the northern hemisphere is negative about 12 27 2 8 103 km2 yr 1 or 7 1 5 decade 1 relative to the long term mean except in a few coastal regions the seasonal duration of landfast ice is shorter overall particularly in the laptev east siberian and chukchi seas the decreased winter landfast ice extent is associated with some notable changes in ice growth and melt patterns in particular the slowed landfast ice expansion during fall and early winter since 1990 the observed

evidence for rapid thinning of sea ice in the western arctic ocean at the end of the 1980s examination of springtime ice drafts obtained from submarine profiles in a narrow band of the western arctic ocean from offshore alaska to 89 n indicates that the mean ice draft decreased 1 5 m between the mid 1980s and early 1990s no similar trend was evident in ice drafts near the north pole the 1980s drafts were composed largely of ice exceeding 3 5 m while the early 1990s drafts contained more ice in thinner categories the differences in drafts between the two periods appear to be related largely to ice dynamics effects associated with the presence and strength of the beaufort gyre which weakened considerably in the early 1990s

thinning of arctic sea ice observed in fram strait 1990 2011 1 time series 1990 2011 of sea ice thickness observed by moored sonars in the transpolar drift in fram strait are examined contrasting the post 2007 years against the 1990s three remarkable changes in the monthly ice thickness distributions are highlighted 1 the thickness of old level ice modal thickness is reduced by 32 2 the old ice modal peak width is reduced by 25 and 3 the fraction of ridged ice thicker than 5 m is reduced by 50 the combined effect on the mean ice thickness is a reduction from an annual average of 3 0 m during the 1990s to 2 2 m during 2008 2011 most of the thinning took place after 2005 2006 while the old ice modal thickness and peak width show signs of recovery after 2008 the decreasing trend in fraction of ridged ice and mean ice thickness persists until the end of the record in 2011 the ice observed in fram strait carries an integrated signal of arctic change due to the advection of ice from many sites in the arctic based on concurrence in timing we conclude that much of the thinning quantified here is reflecting recent change in the age composition of the arctic ice cover toward younger ice the old level ice remains thin and as such the ice cover remains preconditioned for new summers of very low sea ice extent

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

on the arctic ocean ice thickness response to changes in the external forcing submarine and satellite observations show that the arctic ocean ice cover has undergone a large thickness reduction and a decrease in the areal extent during the last decades here the response of the arctic ocean ice cover to changes in the poleward atmospheric energy transport fwall is investigated using coupled atmosphere ice ocean column models two models with highly different complexity are used in order to illustrate the importance of different internal processes and the results highlight the dramatic effects of the negative ice thickness ice volume export feedback and the positive surface albedo feedback the steady state ice thickness as a function of fwall is determined for various model setups and defines what we call ice thickness response curves when a variable surface albedo and snow precipitation is included a complex response curve appears with two distinct regimes a perennial ice cover regime with a fairly linear response and a less responsive seasonal ice cover regime the two regimes are separated by a steep transition associated with surface albedo feedback the associated hysteresis is however small indicating that the arctic climate system does not have an irreversible tipping point behaviour related to the surface albedo feedback the results are discussed in the context of the recent reduction of the arctic sea ice cover a new mechanism related to regional and temporal variations of the ice divergence within the arctic ocean is presented as an explanation for the observed regional variation of the ice thickness reduction our results further suggest that the recent reduction in areal ice extent and loss of multiyear ice is related to the albedo dependent transition between seasonal and perennial ice i e large areas of the arctic ocean that has previously been dominated by multiyear ice might have been pushed below a critical mean ice thickness corresponding to the above mentioned transition and into a state dominated by seasonal ice

reconstructing the origin and trajectory of drifting arctic sea ice recent studies have indicated that drifting arctic sea ice plays an important role in the redistribution of sediments and contaminants here we present a method to reconstruct the back ward trajectory of sea ice from its sampling location in the eurasian arctic to its possible site of ori gin on the shelf based on historical drift data from the international arctic buoy program this method is verified by showing that origins derived from the backward trajectories are generally con sistent with other indicators such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions the trajectories are then used to identify regions where sediment laden ice is exported to the transpolar drift stream from the new siberian islands and the central kara plateau calculation of forward trajectories shows that the kara sea is a major contributor of ice to the barents sea and the southern limb of the transpolar drift stream

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

late summer sea ice thickness variability in the arctic transpolar drift 1991 2001 derived from ground based electromagnetic sounding 1 late summer thickness distributions of large ice floes in the transpolar drift between svalbard and the north pole in 1991 1996 1998 and 2001 are compared they have been derived from drilling and electromagnetic em sounding results show a strong interannual variability with significantly reduced thickness in 1998 and 2001 the mean thickness decreased by 22 5 from 3 11 m in 1991 to 2 41 m in 2001 and the modal thickness by 22 from 2 50 m in 1991 to 1 95 m in 2001 since modal thickness represents the thickness of level ice the observed thinning reflects changes in thermodynamic conditions together with additional data from the laptev sea obtained in 1993 1995 and 1996 results are in surprising agreement with recently published thickness anomalies retrieved from satellite radar altimetry for arctic regions south of 81 5 n this points to a strong sensitivity of radar altimetry data to level ice thickness

intercrystalline stable isotope diffusion a fast grain boundary model we formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals and the intragranular distribution of stable isotopes in each mineral as functions of mineral grain sizes and shapes diffusivities modes equilibrium isotopic fractionations and the cooling rate of a rock one of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes this fast grain boundary fgb model describes interdiffusion between any number of mineral grains assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled the model can be used for a rock containing any number of minerals and number of grain sizes of each mineral several grain shapes and any thermal history or domain size desired previous models describing stable isotope interdiffusion upon cooling have been based on dodson s equation or an equivalent numerical analogue the closure temperature of dodson is the average bulk temperature recorded between a mineral and an infinite reservoir by using dodson s equation these models have treated the closure temperature as an innate characteristic of a given mineral independent of the amounts and diffusion rates of other minerals such models do not accurately describe the mass balance of many stable isotope interdiffusion problems existing models for cation interdiffusion could be applied to stable isotopes with some modifications but only describe exchange between two minerals under specific conditions the results of fgb calculations differ considerably from the predictions of dodson s equation in many rock types of interest actual calculations using the fgb model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient and may differ from that predicted by dodson s equation by hundreds of degrees c either or both of two minerals may preserve detectable zonation which may in some instances be larger in the faster diffusing mineral rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone the results of fgb diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations concordant or discordant recorded within any rock in which diffusion could have acted over observable scales the predictions of this model are applicable to thermometry evaluation of open or closed system retrogression and determination of cooling rates or diffusion coefficients

dynamic thermodynamic sea ice model ridging and its application to climate study and navigation abstract a dynamic thermodynamic sea ice model with the ocean mixed layer forced by atmospheric data is used to investigate spatial and long term variability of the sea ice cover in the arctic basin the model satisfactorily reproduces the averaged main characteristics of the sea ice and its extent in the arctic basin as well as its decrease in the early 1990s employment of the average ridge shape for describing the ridging allows the authors to suggest that it occurs in winter and varies from year to year by a factor of 2 depending on an atmospheric circulation pattern production and horizontal movement of ridges are the focus in this paper as they show the importance of interannual variability of the arctic ice cover the observed thinning in the 1990s is a result of reduction in ridge formation on the pacific side during the cyclonic phase of the arctic oscillation the model yields a partial recovery of sea ice cover in the last few years of the twentieth century in addition to the sea ice cover

on the origin and evolution of sea ice anomalies in the beaufort chukchi sea the origin and space time evolution of beaufort chukchi sea ice anomalies are studied using data and a recently developed dynamic thermodynamic sea ice model first the relative importance of anomalies of river runoff atmospheric temperature and wind in creating anomalous sea ice conditions in the beaufort chukchi sea is investigated the results indicate that wind anomalies are the dominant factor responsible for creating interannual variability in the beaufort chukchi sea ice cover temperature anomalies appear to play a major role for longer time scale fluctuations whereas the effects of runoff anomalies are small the sea ice model is then used to track the position of a positive sea ice anomaly as it is transported by the beaufort gyre toward the transpolar drift stream and then exported out of the arctic basin into the greenland sea via fram strait the model integration shows that sea ice anomalies originating in the western beaufort sea can survive a few seasonal cycles as they propogate through the arctic basin and can account for a notable amount of anomalous ice export into the greenland sea these anomalies however represent a small contribution to the fresh water budget in this area when compared with sea ice fluctuations generated by interannually varying local winds

oxygen diffusion in magnetite the diffusion rate of oxygen in magnetite fe3o4 has been measured under hydrothermal conditions between 800 and 500 c at 1000 bars pressure and yields the arrhenius relation d 3 5 10 6 exp 45 000rt kcal g atom o the diffusion rate was found to be the same within the estimated uncertainty of a factor of 2 for measurements at 100 1000 and 2000 bars 20 200 mpa water pressure and for oxygen fugacities buffered by magnetite hematite and approximately ninio the activation energy and diffusion mechanism probably change to that given by castle and surman 10 at temperatures below 460 c the oxygen diffusion rate in magnetite is between those of quartz and hornblende closure temperatures fall in the range 380 c for 0 1 mm radius grains cooling at 1 c m y to 675 c for 1 mm radius and cooling at 1000 c m y if the present data are used but will be lower for the fine grain sizes and slow cooling rates if the castle and surman data are used

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

arctic sea ice seasonal prediction by a linear markov model abstracta linear markov model has been developed to predict sea ice concentration sic in the pan arctic region at intraseasonal to seasonal time scales which represents an original effort to use a reduced dimension statistical model in forecasting arctic sea ice year round the model was built to capture covariabilities in the atmosphere ocean sea ice system defined by sic sea surface temperature and surface air temperature multivariate empirical orthogonal functions of these variables served as building blocks of the model a series of model experiments were carried out to determine the model s dimension the predictive skill of the model was evaluated by anomaly correlation and root mean square errors in a cross validated fashion on average the model is superior to the predictions by anomaly persistence damped anomaly persistence and climatology the model shows good skill in predicting sic anomalies within the arctic basin during summer and fall long term trends partially contribute to the

a parametric study of the generation and degeneration of wind forced long internal waves in narrow lakes the generation and energy downscaling of wind forced long internal waves in strongly stratified small to medium sized narrow lakes are studied a two layer nonlinear model with forcing and damping is employed even though the wave field is fundamentally bidirectional in nature a domain folding technique is employed to simulate the leading order internal wave field in terms of a weakly nonlinear weakly dispersive model equation of korteweg devries type parametric effects of wind forcing and environmental conditions including variable topography and variable basin width are examined energy downscaling from basin scale waves to shorter scales are quantified by means of a time evolution of the wave energy spectra it is demonstrated that an internal wave resonance is possible when repetitive wind forcing events arise with a frequency near the linear seiche frequency an attempt is made to apply the model to describe the shoaling of long waves on sloping endwall boundaries modelling of the energy loss and energy reflection during a shoaling event is calibrated against laboratory experiments

oxygen diffusion rates in quartz exchanged with co2 oxygen self diffusion rates were determined in quartz samples exchanged with18o enriched co2 between 745 and 900 c and various pressures and the diffusion profiles were measured using an ion microprobe the activation energy q and preexponential factor d0 at p co2 p tot 100 bar for diffusion parallel to the c axis are 159 13 kj g atom and 2 10 0 75 0 55 10 8 cm2 s this rate is approximately 100 times slower than that obtained from hydrothermal experiments and 100 times faster than a previous 1 bar quartz o2 exchange experiment the oxygen diffusion rate measured at 0 6 bar 888 c and at 900 c in vacuum is in agreement with the previous 1 bar exchange experiments with18o2 the effect of higher co2 pressures is small at 900 c the diffusion rate exchanged with co2 is 2 35 10 15 cm2 s at 100 bar 2 24 10 15 cm2 s at 3 45 kbar and 8 13 10 15 cm2 s at 7 2 kbar there is probably a diffusing species other than oxygen that enhances the oxygen diffusion rate in these quartz co2 systems relative to that occurring at very low pressures or in a vacuum the effect of this diffusing species however is not as strong as that associated with h2o preserved oxygen isotope fractionations between coexisting minerals in a slowly cooled high grade metamorphic terrane will vary depending upon whether a water rich phase was present or not closure temperatures will be approximately 100 c higher in rocks where no water rich phase was present during cooling the measured fractionations between coexisting minerals in metamorphic rocks may potentially be used as a sensor of water presence during retrogression

downscaling model resolution to illuminate the internal wave field in a small stratified lake this paper presents the application of hydrostatic and nonhydrostatic three dimensional hydrodynamic models to a stratified lake focus was given to the multiscale response of the internal wave field to strong wind gusts exceeding 20 m s 1 simulations were performed using different horizontal grid resolutions with uniform grid sizes varying from 100 100 to 10 10 m results of the hydrostatic models were used to investigate the large scale features of the internal wave motion with the intent of investigating the high frequency waves observed results of these simulations were used as initial conditions for nonhydrostatic simulations using smaller grids wavelength of the high frequency waves decreased with grid resolution however none of the uniform grids were sufficiently fine to capture the waves of the highest frequency simulations performed using a nonuniform grid produced internal waves of similar frequency of the waves observed in the field the simulations showed that these waves were shear u

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

uncertainty in modeled arctic sea ice volume 1 uncertainty in the pan arctic ice ocean modeling and assimilation system piomas arctic sea ice volume record is characterized a range of observations and approaches including in situ ice thickness measurements icesat retrieved ice thickness and model sensitivity studies yields a conservative estimate for october arctic ice volume uncertainty of 1 35 103 km3 and an uncertainty of the ice volume trend over the 1979 2010 period of 1 0 103 km3 decade 1 a conservative estimate of the trend over this period is 2 8 103 km3 decade 1 piomas ice thickness estimates agree well with icesat ice thickness retrievals 0 1 m mean difference for the area for which submarine data are available while difference outside this area are larger piomas spatial thickness patterns agree well with icesat thickness estimates with pattern correlations of above 0 8 piomas appears to overestimate thin ice thickness and underestimate thick ice yielding a smaller downward trend than apparent in reconstructions from observations piomas ice volume uncertainties and trends are examined in the context of climate change attribution and the declaration of record minima the distribution of 32 year trends in a preindustrial coupled model simulation shows no trends comparable to those seen in the piomas retrospective even when the trend uncertainty is accounted for attempts to label september minima as new record lows are sensitive to modeling error however the september 2010 ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

patterns of sea ice retreat in the transition to a seasonally ice free arctic abstractthe patterns of sea ice retreat in the arctic ocean are investigated using two global climate models gcms that have profound differences in their large scale mean winter atmospheric circulation and sea ice drift patterns the community earth system model large ensemble cesm le presents a mean sea level pressure pattern that is in general agreement with observations for the late twentieth century the community climate system model version 4 ccsm4 exhibits a low bias in its mean sea level pressure over the arctic region with a deeper icelandic low a dynamical mechanism is presented in which large scale mean winter atmospheric circulation has significant effect on the following september sea ice extent anomaly by influencing ice divergence in specific areas a lagrangian model is used to backtrack the 80 n line from the approximate time of the melt onset to its prior positions throughout the previous winter and quantify the divergence across the pacific and eurasian sectors of the arctic i

the degeneration of internal waves in lakes with sloping topography in a laboratory study we quantified the temporal energy flux associated with the degeneration of basin scale internal waves in closed basins the system is two layer stratified and subjected to a single forcing event creating available potential energy at time zero a downscale energy transfer was observed from the wind forced basin scale motions to the turbulent motions where energy was lost due to high frequency internal wave breaking along sloping topography under moderate forcing conditions steepening of nonlinear basin scale wave components was found to produce a high frequency solitary wave packet that contained as much as 20 of the available potential energy introduced by the initial condition the characteristic lengthscale of a particular solitary wave was less than the characteristic slope length leading to wave breaking along the sloping boundary the ratio of the steepening timescale required for the evolution of the solitary waves to the travel time until the waves shoaled controlled their development and degeneration within the domain the energy loss along the slope the mixing efficiency and the breaker type were modeled using appropriate forms of an internal iribarren number defined as the ratio of the boundary slope to the wave slope amplitude wavelength this parameter allows generalization to the oceanographic context analysis of field data shows the portion of the internal wave spectrum for lakes between motions at the basin and buoyancy scales to be composed of progressive waves both weakly nonlinear waves sinusoidal profile with frequencies near 10 24 hz and strongly nonlinear waves hyperbolic secant squared profile with frequencies near 10 23 hz the results suggest that a periodically forced system may sustain a quasi steady flux of 20 of the potential energy introduced by the surface wind stress to the benthic boundary layer at the depth of the pycnocline

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

winter coastal divergence as a predictor for the minimum sea ice extent in the laptev sea abstractseasonal predictability of the minimum sea ice extent sie in the laptev sea is investigated using winter coastal divergence as a predictor from february to may the new ice forming in wi

fluids in granulite facies metamorphism a comparative oxygen isotope study on the south india and adirondack high grade terrains oxygen isotope compositions have been determined for samples from the south india archean to pro terozoic and northwest adirondack late proterozoic high grade terrains delta 18 o values of charnockites and related orthogneiss protolith from the prograde amphibolite facies to granulite facies transition zone in south india range from 5 9 to 8 4 charnockites khondalites sillimanite gneisses and retrogressed gneisses from the interior of the granulite facies terrain average 2 higher than orthogneisses of the transition zone individual minerals in incipient charnockitic net veins as at kabbaldurga karnataka and ponmudi kerala have delta 18 o identical to minerals of their non charnockitic host rocks quartz delta 18 o values of the northwestern adirondack granites and gneisses average 3 4 higher than those from the indian rocks the two terrains are thus isotopically distinct which may reflect differences in premetamorphic history or different degrees of communication with external

the arctic ice thickness anomaly of the 1990s a consistent view from observations and models 1 observations of sea ice draft from submarine cruises in much of the arctic ocean show that the ice cover was unusually thin in the mid 1990s here we limit our examination to digitally recorded draft data from eight cruises spanning the years 1987 to 1997 and find a decrease of about 1 m over the 11 year span comparisons of our modeled draft with observed draft show good agreement in the temporal change comparing average draft over entire cruises the rms discrepancy between modeled and observed draft is 0 3 m and the correlation is 0 98 agreement in the spatial patterns of draft is somewhat lower the rms discrepancy of 50 km averages of draft is 0 7 m and the correlation is 0 73 we review reports of interannual variations of ice thickness or volume from other model studies all models agree that thickness decreased by between 0 6 and 0 9 m from 1987 to 1996 our model shows a modest recovery in thickness from 1996 to 1999 for the 1950s 1960s and 1970s models tend to disagree on the size and to a lesser extent the timing or phase of interannual variations

spatial and temporal variations in the age structure of arctic sea ice 1 spatial and temporal variations in the age structure of arctic sea ice are investigated using a new reverse chronology algorithm that tracks ice covered pixels to their location and date of origin based on ice motion and concentration data the beaufort gyre tends to harbor the oldest 10 years old sea ice in the western arctic while direct ice advection pathways toward the transpolar drift stream maintain relatively young 5 years ice in the eastern arctic persistent net losses 4 2 yr 1 in extent of ice 10 years old 10 year age class were observed during 1989 2003 since the mid 1990s losses to the 10 year age class lacked compensation by recruitment due to a prior depletion of all mature 6 10 year age classes survival of the 1994 and 1996 1998 sea ice generations reestablished most mature age classes and thereby the potential to increase extent of the 10 year age class during the mid 2000s

lake of lugano and topographic waves during the summer of 1979 wind water temperature and current measurements were made in the lake of lugano switzerland to study its response to meteorological forcing analysis of the collected data revealed the presence of wind induced internal gravity wave seiches with periods of 24 h and less1 however during this study an intriguing 3 day oscillation in the temperature and horizontal current records was also noted1 we present here evidence which suggests that this low frequency oscillation is a free topographic rossby wave that travels around the lake in an anticlockwise direction