evidence for nonlinear climate change two stratospheric regimes and a regime shift two regimes are found in the interannual variability of the large scale stratospheric flow in the northern hemisphere cold season the regimes are identified by studying the probability distribution of the leading principal component of the geopotential height which explains approximately 50 of the variance the probability distribution has a bimodal structure with two clearly separated peaks corresponding to two circulation regimes the two regimes are characterized by a strong and a weak vortex respectively and they therefore resemble the two phases of the stratospheric part of the arctic oscillation while the upper troposphere and the lower stratosphere are colder in the strong vortex regime than in the weak vortex regime the lower troposphere is warmer in particular over the continents an abrupt regime shift took place in the last half of the 1970s in favor of the more zonal regime the shift is manifested by a substantial change in the frequencies of the two regimes strong statistical significance for the two separate regimes is obtained by a monte carlo approach the regimes and the regime shift are found in two different datasets reducing the possibility that the results are due to inhomogeneities in the data the results support the nonlinear dynamical perspective on climate change suggested by t n palmer according to this idea the response to a weak forcing would be seen mainly in a change of the frequencies of the climate regimes while the spatial structure of the regimes would be relatively insensitive to the forcing

detecting the near surface redox front in crystalline bedrock using fracture mineral distribution geochemistry and u series disequilibrium oxidizing conditions normally prevail in surface waters and near surface groundwaters but there is usually a change to reducing conditions in groundwater at greater depth dissolved o2 originally present is consumed through biogenic and inorganic reactions along the flow paths fracture minerals participate in these reactions and the fracture mineralogy and geochemistry can be used to trace the redox front an important task in the safety assessment of a potential repository for the disposal of nuclear waste in crystalline bedrock at an approximate depth of 500 m in sweden is to demonstrate that reducing conditions can be maintained for a long period of time oxygen may damage the cu canisters that host nuclear waste additionally in the event of a canister failure oxidizing conditions may increase the mobility of some radionuclides the present study of the near surface redox front is based on mineralogical redox sensitive minerals geochemical redox sensitive elements and u series disequilibrium investigations of mineral coatings along open fractures the fractures have been sampled along drill cores from closely spaced 100 m deep boreholes which were drilled during the site investigation work in the laxemar area south eastern sweden carried out by the swedish nuclear fuel and waste management co skb the distribution of the redox sensitive minerals pyrite and goethite in open fractures shows that the redox front switch from mainly goethite to mainly pyrite in the fractures generally occurs at about 15 20 m depth calcite leaching by recharging water is indicated in the upper 20 30 m and positive ce anomalies suggest oxidation of ce down to 20 m depth the u series radionuclides show disequilibrium in most of the samples indicating mobility of u during the last 1 ma in the upper 20 m u is mainly removed due to oxidation or has experienced complex removal and or deposition at depths of 35 55 m both deposition and removal of u are indicated below 55 m recent deposition of u is generally indicated which suggests removal of u near surface oxidation and deposition of u below the redox front scattered goethite occurrences below the general redox front down to ca 80 m and signs of u removal at 35 55 m mostly correlate with sections of high transmissivity and or high fracture frequencies this shows that highly transmissive fractures are generally required to allow oxygenated groundwaters at depth greater than ca 30 m removal of u oxidation below 55 m within the last 300 ka is not observed although penetration of glacial waters to great depths has been confirmed in the study area their potential o2 load seems to have been reduced near the surface

field observations of slush ice generated during freeze up in arctic coastal waters abstract in some years large volumes of slush ice charged with sediment are generated from frazil crystals in the shallow beaufort sea during strong storms at the time of freeze up such events terminate the navigation season and because of accompanying hostile conditions little is known about the processes acting the water saturated slush ice which may reach a thickness of 4 m exists for only a few days before freezing from the surface downward arrests further wave motion or pancake ice forms movements of small vessels and divers in the slush ice occurs only in phase with passing waves producing compression and rarefaction and internal pressure pulses where in contact with the seafloor the agitated slush ice moves cobble size material generates large sediment ripples and may possibly produce a flat rampart observed on the arctic shoreface in some years processes charging the slush ice with as much as 1000 m 3 km 2 of sediment remain uncertain but our field observations rule out previously proposed filtration from turbid waters as a likely mechanism sedimentary particles apparently are only trapped in the interstices of the slush ice rather than being held by adhesion since wave related internal pressure oscillations result in downward particle movement and cleansing of the slush ice this loss of sediment explains the typical downward increase in sediment concentration in that part of the fast ice canopy composed largely of frazil ice the congealing slush ice in coastal water does not become fast ice until grounded ridges are formed in the stamukhi zone one to two months after freeze up begins during this period of new ice mobility long range sediment transport occurs the sediment load held by the fast ice canopy in the area between the colville and sagavanirktok river deltas in the winter of 1978 1979 was 16 times larger than the yearly river input to the same area this sediment most likely was rafted from canada more than 400 km to the east during a brief time period in the previous fall ocean turbulence is greatly reduced while the congealing slush ice drifts about therefore new ice then forming in intervening open water areas is clean these events explain the patchy appearance of the fast ice after the summer snowmelt more work on the important phenomena reported here is needed to close a major gap in the knowledge of the arctic marine environment

frazil ice entrainment of sediment large tank laboratory experiments laboratory experiments that simulate natural ice formation processes and sediment entrainment in shallow water are presented a 10 30 cm s 1 current was forced with impellers in a 20 m long 1 m deep indoor tank turbulence in the flow maintained a suspension of sediments at concentrations of 10 20 mg l 1 at 0 5 m depth low air temperatures 15 c and 5 m s 1 winds resulted in total upward heat fluxes in the range 140 260 w m 2 the cooling produced frazil ice crystals up to 2 cm in diameter with concentrations up to 4 5 g l 1 at 0 5 m depth considerable temporal variability with time scales of 1 min was documented a close to constant portion of the smaller frazil crystals remained in suspension after some hours the larger crystals which made up most of the ice volume accumulated as slush at the surface current measurements were used to calculate the turbulent dissipation rate and estimates of vertical diffusion were derived after 5 8 hours sediment concentrations in the surface slush were normally close to those of the water after 24 hours however they were 2 4 times higher data indicate that sediment entrainment depends on high heat fluxes and correspondingly high frazil ice production rates as well as sufficiently strong turbulence waves do not seem to increase sediment entrainment significantly

importance of lateral transport processes to 210pb budget in the eastern chukchi sea during summer 2003 chinese ipy research program national natural science foundation of china 41125020 fujian natural science foundation 2009j06026 state oceanic administration of china 201105022 4 ministry of education of china

coastal retreat and shoreface profile variations in the canadian beaufort sea the coastline of the southern canadian beaufort sea consists primarily of unconsolidated bluffs although the sea is ice free for 3 months of the year and wave energy is restricted by pack ice the coast is undergoing regional retreat with erosion rates as high as 10 m a 1 in some locations simple and multiple regression analyses were carried out to determine the degree of correlation between the mean retreat rate measured at various locations and the different parameters that may control shoreline recession sediment texture ground ice content cliff height wave energy and shoreface gradient revealed medium to poor correlation with erosion rates showing that the recessive evolution of the coastline can not be explained solely by wave induced and subaerial processes the comparison of nearshore echo sounding records from 1987 with bathymetry from 1971 showed substantial erosion up to 1 m of the submarine profile between 12 and 15 m of water there is strong evidence that this erosion has been caused by sea ice gouging on the seafloor from depths of 5 to 9 m accretion has taken place possibly induced by ice push processes and inshore of the 5 m isobath wave and current erosion of the shoreface has occurred these results suggest that the erosion of the inner shelf by ice gouging drives the erosion observed inshore on the coastal bluffs and nearshore zone as the shoreface profile strives for a state of dynamic equilibrium

experimental studies of sediment enrichment of arctic ice covers due to wave action and frazil entrainment two processes are investigated that are believed to contribute to the sediment enrichment of ice covers in coastal arctic waters one process results from wave action which pumps sediment rich underlying water into the surface cover the other enriching mechanism is produced by rising frazil that entrains suspended sediment which subsequently becomes incorporated in the surface ice layer in both processes the sediment enrichment of the ice cover is found to depend upon the sediment size and concentration in the underlying water column in the wave dependent process the rate of sediment enrichment is influenced by the period amplitude and duration of the wave action as well as the size of the ice particles and motion of the cover frazil rising through sediment laden water was found to entrain particles of sand far more effectively than silt sand laden frazil floe would often become so loaded with sediment that the floe would eventually settle to the floor of the water column

sea ice sediment entrainment and rafting in the arctic abstract large areas of first year sea ice containing disseminated loads of silt and clay sized materials are common off the northern coast of alaska sand and coaser material is also found in this ice in the form of distinct masses of sediment laden ice sediment is entrained into the sea ice cover during fall storms when frazil or small discs of ice in suspension is actively forming in the supercooled water column at this time sea ice is unconsolidated and very mobile making long range ice rafting possible sediment rich ice may be advected off the shelf and upon melting deposit material in the deep arctic basin the amount of sediment incorporated into the ice cover varies considerably from year to year depending on the location and severity of storms accompanying freezeup in 1978 the seasonal ice cover in an area off northern alaska carried 16 times as much sediment as the total annual suspended sediment input from adjacent coastal rivers sea ice sediment transport is important in the overall sediment budget in northern polar regions particularly the transport of fine grained material but entrainment mechanisms are poorly understood

sediment transport by sea ice in the chukchi and beaufort seas increasing importance due to changing ice conditions abstract sediment laden sea ice is widespread over the shallow wide siberian arctic shelves with off shelf export from the laptev and east siberian seas contributing substantially to the arctic ocean s sediment budget by contrast the north american shelves owing to their narrow width and greater water depths have not been deemed as important for basin wide sediment transport by sea ice observations over the chukchi and beaufort shelves in 2001 02 revealed the widespread occurrence of sediment laden ice over an area of more than 100 000 km2 between 68 and 74 n and 155 and 170 w ice stratigraphic studies indicate that sediment inclusions were associated with entrainment of frazil ice into deformed multiple layers of rafted nilas indicative of a flaw lead environment adjacent to the landfast ice of the chukchi and beaufort seas this is corroborated by buoy trajectories and satellite imagery indicating entrainment in a coastal polynya in the eastern chukchi sea in february of 2002 as well as formation of sediment laden ice along the beaufort sea coast as far eastward as the mackenzie shelf moored upward looking sonar on the mackenzie shelf provides further insight into the ice growth and deformation regime governing sediment entrainment analysis of radarsat synthetic aperture sar imagery in conjunction with bathymetric data help constrain the water depth of sediment resuspension and subsequent ice entrainment 20 m for the chukchi sea sediment loads averaged at 128 t km 2 with sediment occurring in layers of roughly 0 5 m thickness mostly in the lower ice layers the total amount of sediment transported by sea ice mostly out of the narrow zone between the landfast ice edge and waters too deep for resuspension and entrainment is at minimum 4 106 t in the sampling area and is estimated at 5 8 106 t over the entire chukchi and beaufort shelves in 2001 02 representing a significant term in the sediment budget of the western arctic ocean recent changes in the chukchi and beaufort sea ice regimes reduced summer minimum ice extent ice thinning reduction in multi year ice extent altered drift paths and mid winter landfast ice break out events have likely resulted in an increase of sediment laden ice in the area apart from contributing substantially to along and across shelf particulate flow an increase in the amount of dirty ice significantly impacts sub ice algal production and may enhance the dispersal of pollutants

a link between reduced barents kara sea ice and cold winter extremes over northern continents the recent overall northern hemisphere warming was accompanied by several severe northern continental winters as for example extremely cold winter 2005 2006 in europe and northern asia here we show that anomalous decrease of wintertime sea ice concentration in the barents kara b k seas could bring about extreme cold events like winter 2005 2006 our simulations with the echam5 general circulation model demonstrate that lower troposphere heating over the b k seas in the eastern arctic caused by the sea ice reduction may result in strong anti cyclonic anomaly over the polar ocean and anomalous easterly advection over northern continents this causes a continental scale winter cooling reaching 1 5 c with more than three times increased probability of cold winter extremes over large areas including europe our results imply that several recent severe winters do not conflict the global warming picture but rather supplement it being in qualitative agreement with the simulated large scale atmospheric circulation realignment furthermore our results suggest that high latitude atmospheric circulation response to the b k sea ice decrease is highly nonlinear and characterized by transition from anomalous cyclonic circulation to anticyclonic one and then again back to cyclonic type of circulation as the b k sea ice concentration gradually reduces from 100 to ice free conditions we present a conceptual model which may explain the nonlinear local atmospheric response in the b k seas region by counter play between convection over the surface heat source and baroclinic effect due to modified temperature gradients in the vicinity of the heating area

role of planetary waves in the stratosphere troposphere coupled variability in the northern hemisphere winter the role of planetary waves in stratosphere troposphere coupled variability is investigated using an extended singular value decomposition analysis of zonal mean zonal wind and the vertical component of the eliassen palm e p flux for the winters from 1979 80 to 1995 96 the results suggest a close relationship between anomalies of zonal mean zonal wind and the convergence zone of e p flux which together shift poleward and downward from the stratosphere to the troposphere as time advances following enhanced vertical propagation of waves into the stratosphere the arctic oscillation ao pattern is seen in the 500 hpa geopotential height field in association with an increased poleward propagation of tropospheric waves

ice rafting of fine grained sediment a sorting and transport mechanism beaufort sea alaska abstract the presence of turbid sediment rich fast ice in the arctic is a major factor affecting transport of fine grained sediment turbid ice was found to be present in a zone 10 to 20 km wide along the coast of the beaufort sea sediment concentrations observed in cores taken in seasonal fast ice ranged from 3 to more than 1 600 g m3 finely disseminated silt and clay sized particles dominated discoloring the upper segments of the cores in a layer up to 1 m thick in almost all of the cores the upper most 10 cm of ice was relatively less turbid and the relief at the base of the turbid layer was 10 to 20 cm over distances of 1 to 2 m observers have documented the widespread sporadic occurrence of sediment rich fast ice in both the beaufort and bering seas the known sources a d transport relations of suspended sediment did not explain this distribution of turbid ice the occurrence of sediment in only the upper part of the seasonal fast ice indicates that sediment rich ice forms early during ice growth the most likely mechanism for the formation of sediment laden ice and preferential sorting of fine sediments requires resuspension of nearshore bottom sediment during storms accompanied by formation of frazil ice and subsequent lateral advection before the fast ice is stabilized we estimate that the sediment incorporated in the beaufort ice canopy formed a significant proportion of the seasonal influx of terrigenous fine grained sediment the dominance of fine grained sediment suggests that in the arctic and sub arctic these size fractions may be ice rafted in greater volumes than the coarse fraction of traditionally recognized ice rafted sediment the incorporation and transport mechanism may be a significant factor in the transport of fine grained sediments in the arctic basin

anchor ice seabed freezing and sediment dynamics in shallow arctic seas diving investigations confirm previous circumstantial evidence of seafloor freezing and anchor ice accretion during freeze up storms in the alaskan beaufort sea these related bottom types were found to be continuous from shore to 2 m depth and spotty to 4 5 m depth spotty anchor ice occurred as pillow shaped crystal aggregates on buried slabs of frozen sand surrounded by unfrozen sand considerations of required conditions for ice bonding and anchor ice growth allows regional extrapolation and suggests the possibility of anchor ice growth out to 20 m depth the estimated maximum depth of supercooling during fall storms anchor ice and seabed freezing apparently do not develop during a calm freeze up because of the abrupt growth of anchor ice during a freezing storm and its release soon after formation of a surface ice cover this ice type has not been documented before the concretelike nature of frozen bottom where present should prohibit sediment transport by any conceivable wave or current regime during the freezing storm but elsewhere particularly where the bonded crust is broken by grounded ice anchor ice lifts coarse material off the bottom and incorporates it into the ice canopy thereby leading to significant ice rafting of shallow shelf sediment and likely sediment loss to the deep sea

northern hemisphere winter circulation associated with the north atlantic oscillation and stratospheric polar night jet the interannual variability of the atmospheric winter circulation as characterized by the geopotential height at 500 hpa and temperature at 850 hpa associated with the north atlantic oscillation nao and stratospheric polar night jet pnj is examined it is suggested that the wintertime atmospheric circulation related to the nao index can be separated into two different modes of variability one is a regional mode characterized by a meridional dipole type pattern in the 500 hpa geopotential height anomaly field over the atlantic region the other having more zonal structure extends over wider region of the northern hemisphere this is also related to the lower stratospheric polar night jet air temperature near the surface over the eastern part of the eurasian continent is more closely correlated with the above mentioned hemispheric mode of variability than the regional nao

geochemical modelling of the weathering zone of the mina fe u deposit spain a natural analogue for nuclear spent fuel alteration and stability processes in radwaste disposal abstract the mina fe u deposit salamanca spain has been studied in the context of enresa s programme for u mine sites restoration and also as a natural analogue for processes in high level nuclear waste hlnw geological disposal the investigations encompassed an array of geoscience disciplines such as structural geology mineralogy hydrogeology and elemental and isotopic geochemistry and hydrogeochemistry of the site based on the obtained results a conceptual mineralogical and geochemical model was performed integrating the main geochemical processes occurring at the site the interaction between oxidised and slightly acidic water with pyrite pitchblende calcite and dolomite as essential minerals of the u fracture filling mineralisation and hydroxyapatite from the host rock as the main source of p this conceptual model has been tested in a systematic numerical model which includes the main kinetic pyrite and pitchblende dissolution and equilibrium processes carbonate mineral dissolution and goethite schoepite and autunite secondary precipitation the results obtained from the reactive transport model satisfactorily agree with the conceptual model previously established the assumption of the precipitation of coffinite as a secondary mineral in the system cannot be correctly evaluated due to the lack of hydrochemical data from the reducing zone of the site and valid thermodynamic and kinetic data for this hydrated u iv silicate this precipitation can also be hampered by the probable existence of dissolved u iv organic matter and or uranyl carbonate complexes which are thermodynamically stable under the alkaline and reducing conditions that prevail in the reducing zone of the system finally the intense downwards oxic and acidic alteration in the upper part of the system is of no relevance for the performance assessment of a hlnw disposal however the acidic and oxidised conditions are quickly buffered to neutral alkaline and reducing at very shallow depths of relevance for the performance assessment of a hlnw repository even in a natural or artificially perturbed geological environment as mina fe

langmuir circulation driving sediment entrainment into newly formed ice tank experiment results with application to nature lake hattie united states kara sea siberia 1 langmuir circulation lc was generated under freezing conditions in saltwater tank experiments through surface wind stress and cross waves interacting with subsurface return flow fine grained sediments distributed in the tank prior to frazil crystal formation were aligned in parallel streaks in lc bottom convergence zones downwelling at lc surface convergence zones aligned floating frazil in wind parallel rows and individual crystals rotated on helical paths down to the tank bottom and up again to the surface the crystals interacted with suspended particles in the water column and with sediment on the tank bottom preferentially collecting fine grained particles and enhancing their entrainment into new ice evidence includes higher sediment concentrations in ice and ice interstitial water ice pore water as compared to the tank water both tank ice and ice interstitial water contain more silt sized particles than tank water suspension load and tank bottom sediment sand is reduced in the ice and clay is about the same concentration in all samples this points to preferential entrainment of fine particles in newly formed ice supported by lc driven circulation comparable results of lc supported ice particle entrainment were found in lake hattie comparison of ice sediment from tank experiments run with kara sea material to ice particles from the natural kara setting showed both types of ice sediment have very similar grain size distributions and mineralogical compositions results from experiments and nature help to better understand the potentially lc driven entrainment of sediment into ice formed in shallow freezing waters

recent temperature changes in the western arctic during spring abstract the lower troposphere of the western arctic eastern siberia to northern canada was relatively warm during spring in the 1990s based on the ncep ncar reanalysis supplemented by the television infrared observational satellite tiros operational vertical sounder tovs polar pathfinder dataset this warmth is a result of a recent increase in the frequency of warm months compared to the previous four decades the primary difference between four notably warm springs in the 1990s and four cold springs in the 1980s was the sense of the horizontal advection term in a lower tropospheric heat budget for northern alaska southern beaufort sea while the horizontal advection of heat was highly episodic it was related to changes in the mean circulation at low levels in particular a shift from anomalous northeasterly flow in the 1980s to anomalous southwesterly flow in the 1990s during march and april this change in the low level winds in the western arctic coincided with a systematic shift in the arct

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

arctic perennial ice cover over the last 14 million years knowledge of the long term history of the perennial ice is an important issue that has eluded study because the cenozoic core material needed has been unavailable until the recent arctic coring expedition acex detrital fe oxide mineral grains analyzed by microprobe from the last 14 ma 164 m of the acex composite core on the lomonosov ridge were matched to circum arctic sources with the same mineral and 12 element composition these precise source determinations and estimates of drift rates were used to determine that these sand grains could not be rafted to the acex core site in less than a year thus the perennial ice cover has existed since 14 ma except for the unlikely rapid return to seasonal ice between the average sampling interval of about 0 17 ma both north america and russia contributed significant fe grains to the acex core during the last 14 ma

hydrogeochemical evolution and c isotope study of groundwaters from mina fe u deposit salamanca spain implications for processes in radwaste disposal within the framework of the enresa natural analogue programme the u ore deposit of mina fe western spain has been studied as a natural analogue of radioactive spent fuel behaviour after burial in spite of being an extremely perturbed geological environment due to mining activities the main objectives of this project are to determine the hydrogeochemical evolution of the system and identify the main water rock interaction processes that control the physicochemical variables ph and eh of groundwaters including the role played by the organic matter the hydrogeochemical results from 3 consecutive groundwater sampling campaigns separated by a phase of restoration works indicate that the groundwater of the site shows an evolutionary trend from ca so42 acid oxidising waters towards alkaline reducing waters though their evolution with respect to the alkaline and alkaline earth elements is not clear the so42 acid waters are the result of the oxidation processes affecting the primary sulphide rich u mineralisation while the alkaline reducing waters result from the buffer capacity of carbonates from fracture filling materials as the 13c values of dic demonstrate the reducing character of these waters mainly results from the microbiologically mediated partial oxidation of the abundant organic matter existing in the clayey walls of the major faults at the site since other dissolved inorganic redox pairs are insufficient to explain the in situ measured redox potential thus the high content in doc of these waters is also explained since the soil at the site is poorly developed doc dic or both can be responsible for the high u concentration measured in these groundwaters in spite of its reducing character the restoration works performed in the exploitation quarry have also restored the aforementioned evolutionary trend which was the normal evolution of groundwater in the site before mining finally the results are discussed in terms of the geochemical processes expected in a radioactive disposal site after closure

north pacific north atlantic relationships under stratospheric control 1 based on a linear regression correlation analysis of monthly mean atmospheric sea level pressure slp data from the national centers for environmental prediction ncep reanalysis 1948 2000 we find a significant anticorrelation between pressure in the northern north atlantic and north pacific only if the stratospheric circulation is in the strong polar vortex regime but not when the vortex is weak since some general circulation models gcms e g european center hamburg echam4 are biased toward the strong vortex regime svr they tend to reproduce this anticorrelation already in the mean the pattern of the arctic oscillation ao is shown to be consistent with the mean surface pressure differences between the two stratospheric regimes the typical sw ne tilt of the node line of the north atlantic oscillation nao found with linear analyses i e with such that do not take the regime character of the stratospheric circulation into account in northern hemisphere winter is due to a superposition of correlation patterns based on physical processes working in the troposphere a strictly meridional dipole and the pattern resulting from planetary wave refraction in the strong vortex regime and those produced by the rapid transition from one stratospheric regime to the other with subsequent downward propagation of the signal this result underlines the necessity of the application of nonlinear statistics or the restriction of linear statistics to variations in the stable quasi linear environment of natural regimes

grain size separation and sediment mixing in arctic ocean sediments evidence from the strontium isotope systematic the 87 rb 86 sr and 87 sr 86 sr ratios of laptev sea sediments of arctic ocean sediments and of suspended particulate matter spm from siberian rivers lena and khatanga form pseudo isochrons due to grain size separation processes which are referred to as lena mixing envelope lme and as flood basalt envelope fbe at the land ocean transition the reduction of the particle velocity causes a deposition of coarser grained material and the contact with saline water enhances a precipitation of finer grained material the coarse grained material is enriched in sr showing less radiogenic 87 sr 86 sr ratios whereas fine grained material is depleted in sr relative to rb showing more radiogenic 87 sr 86 sr ratios the experimentally determined spread of the 87 rb 86 sr and 87 sr 86 sr ratios as a function of grain size in one sediment sample is on the same order as the natural spread of the 87 sr 86 sr ratios observed in all samples from the arctic ocean chemical index of alteration cia for the lena river spm tend to confirm previous observations that chemical alteration is negligible in the arctic environment thus these pseudo isochrons reflect an average age and the average isotope composition in the river drainage area calculated apparent ages from the fbe reflect the age of the siberian flood basalt of about 220 ma and the initial ratio of 0 707 1 reflects their mantle origin the age calculated from the lme of about 125 ma reflects accidentally the jurassic and cretaceous age of the sediments drained by the lena river and the initial ratio of 0 714 1 reflects the crustal origin of their source rocks comparison of geographical locations reveals that all samples from the eastern laptev sea east of 120 degrees e fall along the lme whereas all samples from the western laptev sea west of 120 degrees e fall between lme and fbe mixing calculations based on 143 nd 144 nd measurements not influenced by grain size show that about 75 of the western laptev sea sediments originate from the lena drainage area whereas about 25 of the sediments are delivered from the siberian flood basalt province sediments from the central arctic ocean are isotopically related to the lena drainage area and the siberian flood basalt province however sediments from the arctic ocean margins close to novaya semlya greenland the fram strait and svalbard originate from sources not yet identified c 1999 elsevier science b v all rights reserved

deposition of organic carbon in arctic ocean sediments terrigenous supply vs marine productivity during the arctic 91 expedition with rv polarstern several kastenlot cores were recovered along a profile crossing the eastern part of the arctic ocean in this paper we present results of detailed sedimentological and organic geochemical investigations on three of these cores which have yielded a wide range of data for the interpretation of the flux and type of organic matter in general the high organic carbon content of the sediments is derived from a high input of terrigenous organic matter the variation in content and composition of the organic carbon in the sediments of core ps2174 5 reflect glacial interglacial changes interglacial stages 7 and 5e reveal a low organic carbon content 0 5 and as indicated by high hydrogen indices low c n ratios higher content of n alkanes c 17 and c 19 and a high opal content reflect higher marine productivity during the glacial stages stages 6 upper 5 and 4 organic carbon values are significantly higher 0 7 1 3 low hydrogen indices high c n ratios low short chain n alkanes and low opal contents provide evidence for a higher input of terrigenous organic matter and reduced marine productivity changes in the content and composition of the organic carbon are believed to vary with the fluctuations in sea level and sea ice coverage

suspension freezing of bottom sediment and biota in the northwest passage and implications for arctic ocean sedimentation ice observations and sediment collected in a summer transit through the northwest passage provide insights on suspension freezing the most important sediment entrainment mechanism for the arctic ocean no evidence was seen for entrainment by bottom adfreezing bluff slumping river flooding dragging ice keels or significant eolian transport from land to sea lack of eolian sediment loading in the northwest passage together with that already reported for northern alaska eliminates wind as an important source for fine sediment in the pack of the beaufort gyre and related parts of the transpolar drift muddy sediment with pebbles and cobbles algae with holdfasts ostracodes with appendages and well preserved mollusks and sea urchins were collected from two sites in a 50 km long stretch of turbid ice these materials indicate that suspension freezing reaching to a water depth of 25 30 m during the previous fall was responsible for entrainment this mechanism requires rapid ice formation in open shallo

the origin of breccia hosted uranium deposits in carbonaceous metasediments of the iberian peninsula u pb geochronology and stable isotope studies of the fe deposit salamanca province spain the upper proterozoic lower cambrian schist graywacke complex of the iberian peninsula hosts several important uranium deposits which are characterized by their occurrence in fracture and breccia zones and by the mineral association pitchblende coffinite carbonates adularia fe sulfides the fe mine in salamanca province is not only the largest known deposit of this type but also the most important uranium deposit in spain with current reserves in excess of 16 000 metric tons of u 3 o 8 primary mineralization occurs as narrow veins occupying fractures and in cavities as finely laminated sediments showing a variety of geopetal textures three stages of primary mineralization separated by episodes of fracturing and brecciation are recognized the early stage commenced with chloritization of wall rocks in narrow zones adjacent to fractures followed by deposition of an assemblage dominated by ankerite and iron sulfides the second main stage mineralization is the most important for uranium and consists mainly of pitchblende coffinite carbonates iron sulfides and adularia the final stage is characterized by repeated episodic deposition of carbonates iron sulfides pitchblende and coffinite as layered cavity filling material chlorite compositions and fluid inclusion data show that wall rock alteration and ore deposition took place over a temperature range of approximately 280 degrees to less than 60 degrees c probably to subsurficial temperatures in the final stage of mineralization the uranium mineralization has been dated by u pb analyses of pitchblende samples at 34 8 or 1 6 ma indicating formation during the pyrenean phase of the alpine orogeny the u pb data also suggest the possibility of a two stage model for the uranium mineralization with the 34 8 or 1 6 ma event representing remobilization of an earlier pre tertiary mineralization calculated delta 18 o sub h 2 o values of the ore forming fluid range from approximately 14 5 per mil for early stage to near zero per mil for late stage fluid the delta 13 c values vary between 7 3 and 9 6 per mil for early and main stage carbonates and show a sharp progressive decline to 23 6 per mil at the end of the final stage the delta 34 s values of sulfides also decrease from the early stage around 10ppm to later stages down to 51 3ppm the combined geologic evidence suggests deposition of the ore from a hydrothermal system that formed in response to the effects of alpine tectonics on the variscan basement meteoric water descended via steeply dipping faults and as well as undergoing extensive isotope exchange with also leached uranium and other components from the metasediments of the schist graywacke complex particularly carbonaceous slates the fluid was probably expelled toward the surface through the fracture and breccia system by seismic pumping the episodic nature of the mineralization may have been controlled by fault movements that initiated brecciation and release of fluid pressure leading to ore deposition in fractures and cavities

variability of the winter wind waves and swell in the north atlantic and north pacific as revealed by the voluntary observing ship data this paper analyses secular changes and interannual variability in the wind wave swell and significant wave height swh characteristics over the north atlantic and north pacific on the basis of wind wave climatology derived from the visual wave observations of voluntary observing ship vos officers these data are available from the international comprehensive ocean atmosphere data set icoads collection of surface meteorological observations for 1958 2002 but require much more complicated preprocessing than standard meteorological variables such as sea level pressure temperature and wind visual vos data allow for separate analysis of changes in wind sea and swell as well as in significant wave height which has been derived from wind sea and swell estimates in both north atlantic and north pacific midlatitudes winter significant wave height shows a secular increase from 10 to 40 cm decade 1 during the last 45 yr however in the north atlantic the patterns of trend changes for wind sea and swell are quite different from each other showing opposite signs of changes in the northeast atlantic trend patterns of wind sea swell and swh in the north pacific are more consistent with each other qualitatively the same conclusions hold for the analysis of interannual variability whose leading modes demonstrate noticeable differences for wind sea and swell statistical analysis shows that variability in wind sea is closely associated with the local wind speed while swell changes can be driven by the variations in the cyclone counts implying the importance of forcing frequency for the resulting changes in significant wave height this mechanism of differences in variability patterns of wind sea and swell is likely more realistic than the northeastward propagation of swells from the regions from which the wind sea signal originates

u series in fe u rich fracture fillings from the oxidised cap of the mina fe uranium deposit spain implications for processes in a radwaste repository abstract within the framework of the enresa spain natural analogue programme the u ore deposit of mina fe is being studied as a natural analogue of radioactive spent fuel behaviour in this context the knowledge of the role played by fracture minerals as scavengers of certain analogue elements mainly u and the establishment of the time scale of the rock water interaction processes controlling the uptakes or losses of u in the system are two relevant objectives fracture infill materials from the site have first been mineralogically characterised then the upper part of the u series determined in both bulk samples and u rich leachates obtained by sequential leaching uranium series of the bulk samples indicate that most of the fractures remained as closed systems in the last 1 6 ma while in other fractures water rock interaction processes affecting the upper part of the u series have been identified these processes indicate recent or rapid u accumulation or losses 102 ka or 234u 230th recoil gain the apparently random distribution in depth of fractures where these processes occurred corroborates the different hydraulic behaviour of fractures as a result of their varying degree of sealing uranium concentrations and 234u 238u ars of the leachates obtained with morgan s solution and 6n hcl indicate that minerals dissolved with these reagents u iv vi oxyhydroxides and goethite clays respectively are responsible for the retention of almost all of the u in the bulk samples furthermore the 234u lost by the u minerals dissolved with morgan s solution seems to be fixed onto goethite clay mixtures the intersticial water being the vehicle for the isotopic transfer which in turn is a recent or recent past process

characteristics of the recent eastward shift of interannual nao variability recent observational studies have shown that the centers of action of interannual variability of the north atlantic oscillation nao were located farther eastward during winters of the period 1978 97 compared to previous decades of the twentieth century in this study which focuses on the winter season december march new diagnostics characterizing this shift are presented further the importance of this shift for nao related interannual climate variability in the north atlantic region is discussed it is shown that an nao related eastward shift in variability can be found for a wide range of different parameters like the number of deep cyclones near surface air temperature and turbulent surface heat flux throughout the north atlantic region by using a near surface air temperature dataset that is homogenous with respect to the kind of observations used it is shown that the eastward shift is not an artifact of changes in observational practices that took place around the late 1970s finally an eof based monte carlo test is developed to quantify the probability of changes in the spatial structure of interannual nao variability for a relatively short 20 yr time series given multivariate white noise it is estimated that the likelihood for differences in the spatial structure of the nao between two independent 20 yr periods which are similar as measured by the angle and pattern correlation between two nao patterns to the observed differences to occur just by chance is about 18 from the above results it is argued that care has to be taken when conclusions about long term properties of nao related climate variability are being drawn from relatively short recent observational data e g 1978 97

a model for entrainment of sediment into sea ice by aggregation between frazil ice crystals and sediment grains avertical numerical model has been developed that simulates tank experiments of sediment entrainment into sea ice physical processes considered were turbulent vertical diffusion of heat salt sediment frazil ice and their aggregates differential growth of frazil ice crystals secondary nucleation of crystals and aggregation between sediment and ice the model approximated the real size distribution of frazil ice and sediment using five classes of each frazil crystals 25 m to 1 5 cm were modelled as discs with a constant thickness of their diameter each class had a constant rise velocity based on the density of ice and drag forces sediment grains 1 600 m were modelled as constant density spheres with corresponding sinking velocities the vertical diffusion was set constant for experiments based on calculated turbulent rms velocities and dissipation rates from current data the balance between the rise sinking velocities and the constant vertical diffusion is an important feature of the model the efficiency of the modeled entrainment process was estimated through a an aggregation factor values for a are in the range but average values are often close to 0 01 entrainment increases with increasing sediment concentration and turbulence of the water and heat flux to the air

numerical model of frazil ice and suspended sediment concentrations and formation of sediment laden ice in the kara sea a one dimensional vertical numerical model of currents mixing frazil ice concentration and suspended sediment concentration has been developed and applied in the shallow southeastern kara sea the objective of the calculations is to determine whether conditions suitable for turbid ice formation can occur during times of rapid cooling and wind and wave induced sediment resuspension although the model uses a simplistic approach to ice particles and neglects ice sediment interactions the results for low stratification shallow 20 m freeze up conditions indicate that the coconcentrations of frazil ice and suspended sediment in the water column are similar to observed concentrations of sediment in turbid ice this suggests that wave induced sediment resuspension is a viable mechanism for turbid ice formation and enrichment mechanisms proposed to explain the high concentrations of sediment in turbid ice relative to sediment concentrations in underlying water may not be necessary in energetic conditions however salinity stratification found near the ob and yenisey rivers damps mixing between ice laden surface water and sediment laden bottom water and probably limits incorporation of resuspended sediment into turbid ice until prolonged or repeated wind events mix away the stratification sensitivity analyses indicate that shallow 20 m unstratified waters with fine bottom sediment settling speeds of 1 mm s 1 or less and long open water fetches 25 km are ideal conditions for resuspension

arctic oscillation or north atlantic oscillation abstract the definition and interpretation of the arctic oscillation ao are examined and compared with those of the north atlantic oscillation nao it is shown that the nao reflects the correlations between the surface pressure variability at its centers of action whereas this is not the case for the ao the nao pattern can be identified in a physically consistent way in principal component analysis applied to various fields in the euro atlantic region a similar identification is found in the pacific region for the pacific north american pna pattern but no such identification is found here for the ao the ao does reflect the tendency for the zonal winds at 35 and 55 n to anticorrelate in both the atlantic and pacific regions associated with the nao and pna because climatological features in the two ocean basins are at different latitudes the zonally symmetric nature of the ao does not mean that it represents a simple modulation of the circumpolar flow an increase in the ao or nao implies stro

key role of organic complexation of iron in sustaining phytoplankton blooms in the pine island and amundsen polynyas southern ocean primary productivity in the amundsen sea southern ocean is among the highest in antarctica the summer phytoplankton bloom in 2009 lasted for 470 days in both the pine island and amundsen polynyas such productive blooms require a large supply of nutrients including the trace metal iron fe the organic complexation of dissolved fe was investigated in the amundsen sea during the spring of 2009 to better understand the potential role of ligands in enhancing the local stock of dissolved fe the main sources of fe and ligands to the amundsen sea are thought to be melting sea ice and the circumpolar deep water cdw which is modified mcdw on the continental shelf and upwells beneath the coastal glaciers and ice shelves upwelling of relatively warm mcdw is also responsible for the rapid melting of the pine island glacier pig and surrounding ice shelves resulting in additional release of fe into surface waters at upwelling stations near ice shelves organic ligands were nearly saturated with fe thus enhancing the stock of fe and its availability to the phytoplankton community however ligands had little capacity to buffer additional fe input from glacial melt in these coastal upwelling regions much of the glacial fe supply is lost due to vertical export of fe via scavenging and precipitation conversely within the phytoplankton bloom in the nearby coastal polynyas the uptake of fe combined with the production of organic matter enhanced the abundance of relatively unsaturated organic ligands capable of stabilizing additional fe supplied from glacial melt these unsaturated dissolved organic ligands combined with the continuous input of fe dissolved and particulate from glacial melt appear to favor the solubilization of fe thus increasing the stock of bioavailable fe and fueling the phytoplankton bloom

microfeatures of modern sea ice rafted sediment and implications for paleo sea ice reconstructions distinguishing sea ice rafted debris sird from iceberg rafted debris is crucial to an interpretation of ice rafting history however there are few paleo sea ice proxies this study characterizes quartz grain microfeatures of modern sird from the arctic ocean and compares these results with microfeatures from representative glacial deposits to potentially differentiate sird from ice rafted sediments which have been recently subjected to glacial processes this allows us to evaluate the use of grain microfeatures as a paleo sea ice proxy sird grains were largely subrounded with medium relief pervasive silica dissolution and a high abundance of breakage blocks and microlayering the glacial grains were more angular with lower relief and higher abundances of fractures and striations gouges discriminate analysis shows a distinct difference between sird and glacial grains with 7 of the sird grains containing typical glacial microtextures suggesting this method is a useful means of inferring paleo sea ice presence in the marine record we propose that differences in microfeatures of sird and glacial ice rafted debris reflect differences in sediment transport and weathering histories sediment transported to a coastal setting and later rafted by sea ice would be subject to increased chemical weathering whereas glaciers that calve icebergs would bypass the coastal marine environment thus preserving their glacial signature

interdecadal changes of surface temperature since the late nineteenth century we present global fields of decadal annual surface temperature anomalies referred to the period 1951 1980 for each decade from 1881 1890 to 1981 1990 and for 1984 1993 in addition we show decadal calendar seasonal anomaly fields for the warm decades 1936 1945 and 1981 1990 the fields are based on sea surface temperature sst and land surface air temperature data the ssts are corrected for the pre world war ii use of uninsulated sea temperature buckets and incorporate adjusted satellite based ssts from 1982 onward our results extend those published in the 1990 intergovernmental panel on climate change scientific assessment and its 1992 supplement we assess the impact of various sources of error in the fields despite poor data coverage initially and around the two world wars the generally cold end of the nineteenth century and start to the twentieth century are confirmed together with the substantial warming between about 1920 and 1940 slight cooling of the northern hemisphere took place between the 1950s and the mid 1970s although slight warming continued south of the equator recent warmth has been most marked over the northern continents in winter and spring but the 1980s were warm almost everywhere apart from greenland the northwestern atlantic and the midlatitude north pacific parts of the middle to high latitude southern ocean may also have been cool in the 1980s but in this area the 1951 1980 climatology is unreliable the impact of the satellite data is reduced because the record of blended satellite and in situ sst is still too short to yield a climatology from which to calculate representative anomalies reflecting climatic change in the southern ocean however we propose a method of using existing satellite data in a step toward this target the maps are condensed into global and hemispheric decadal surface temperature anomalies we show the sensitivity of these estimated anomalies to alternative methods of compositing the spatially incomplete fields running decadal zonal means and annual global and hemispheric time series are also shown finally we discuss some salient features in terms of observed atmospheric circulation changes and of the results of climate model integrations with increasing atmospheric greenhouse gases

okhotsk sea ice coverage and kamchatka glaciation over the last 350ka evidence from ice rafted debris and planktonic δ18o high resolution records of ice rafted debris ird and oxygen isotope records spanning an e w trending transect across the okhotsk sea unravel the marine and terrestrial cryogenic history of ne siberia over the last 350 kyr ird predominantly dispersed basin wide by sea ice shows lowest fluxes during interglacial periods implying a reduced and seasonal sea ice coverage highest ird accumulation rates are observed during glacial and deglacial periods with a more extended but highly dynamic ice cover although being rather synchronous ird fluxes are on average higher in the western okhotsk sea than in the eastern part pointing to a persistent but mobile particle supplying sea ice cover even during full glacial conditions presumably less dense in the eastern parts mis 6 is exceptional in this respect asynchronous fluxes of ird which vary spatially reflect rapid paleoclimatic and paleo glaciomarine changes ird accumulation rates were by factor 2 3 higher during mis 6 as compared to the last glacial maximum and the ird depositional center shifted from the western okhotsk sea early mis 6 toward kamchatka late mis 6 synchronous to a distinct change in the ird mineral composition both the characteristic composition of late mis 6 ird originating from the sredinny mountain range of kamchatka and their significantly enhanced accumulation rates refer to intensified iceberg dispersal across the eastern part of the okhotsk sea at 138 ka 135 ka 129 ka and 128 ka bp this scenario affords the presence of extended mountain glaciers protruding down to sea level on the western side of kamchatka anomalously light planktonic stable oxygen isotopes during mis 6 3 termination ii and mis 5 5 5 4 suggest significant freshwater supply related to the westward drainage of kamchatka glaciers the intensified kamchatka glaciation observed during late mis 6 was repeated during mis 3 iceberg discharges into the eastern okhotsk sea are observed at 60 ka 51 ka 42 ka 38 ka 36 ka and 31 ka and may partly correspond to n atlantic heinrich events

variability of the baroclinic and barotropic transient eddy forcing associated with monthly changes in the midlatitude storm tracks abstract the heat and vorticity transports by synoptic scale eddies at various levels between 1000 and 100 mb have been compiled for each winter month of the 1966 84 period using time filtered daily analyses produced by the u s national meteorological center these circulation statistics were used to compute the three dimensional distributions of the quasigeostrophic geopotential tendency and vertical motion induced by baroclinic and barotropic eddy processes in individual months the latter fields serve as the basis for describing the synoptic scale eddy forcing associated with the leading modes of month to month variability of the storm tracks over the north pacific and north atlantic these modes are associated with the meridional displacements of the storm track axes from their climatological positions the placement of a storm track at a certain latitude in a certain month is accompanied by enhanced convergence of eddy heat fluxes poleward of in the tropospheric column poleward of the storm tra

distribution of trace elements in fracture fillings from the mina fe uranium deposit spain by sequential leaching implications for the retention processes abstract sequential leaching methods have been used to determine the mineralogical distribution of some trace elements for environmental purposes such as radiological contamination of soils and sediments bioavailability studies and natural analogues of deep geological radwaste disposals in this context a 7 step sequential leaching protocol is applied to fe iii u vi rich fracture filling materials from the oxidised zone of the mina fe u deposit to identify and evaluate the main sinks of natural nuclides and other analogue trace elements since it is crucial in the performance assessment of a nuclear waste repository after a careful characterisation of the samples the analytical data from each leaching step were statistically analysed and then interpreted in light of the mineralogical and geochemical features of the samples precise knowledge of the mineralogical distribution of trace elements by sequential leaching methods is quite complex mainly due to cross contamination throughout the different steps of the experiments thus the results obtained suggest that u is retained as u minerals mainly oxides closely associated with crystalline fe oxyhydroxides though ce and la also form independent compounds such as ce oxides and la nd phosphates they are mainly retained by the amorphous mn oxyhydroxides however the crystalline mn oxyhydroxides are the main sink for ni and crystalline fe oxyhydroxides mainly retain p

the uranium ore from mina fe salamanca spain as a natural analogue of processes in a spent fuel repository abstract in the frame of the enresa natural analogue programme the uranium ore from the mina fe salamanca spain has been studied as a natural analogue of radioactive spent fuel behaviour this uranium mine is hosted in highly fractured schistose rocks a geological setting that has not been envisaged in the spanish options for radioactive waste burial however some analogies with the processes that might be involved in the evolution of these geological repositories suggested this investigation the pitchblende pyrite carbonate paragenesis has been studied in situ as natural analogue of the nuclear spent fuel behaviour under extremely oxidative dissolution conditions similarly secondary fe oxyhydroxides and clay minerals have also been considered as relevant analogue materials for the retention of uranium and other analogous trace metals a multidisciplinary characterisation of the site has been performed in order to study these processes though the intense mining activities in the site hindered precise determination of the original hydrogeological and hydrochemical features of the investigated zone boa fault zone the mineralogy and geochemistry of fracture fillings mineralisation and associated clayey materials have allowed the geochemical evolution of the system to be established three geochemical zones have been clearly differentiated i the oxidised zone from the surface to approximately 20 m depth ii the redox transition zone from 20 to 50 m depth and iii the reduced zone located below the transition zone the oxidised zone is characterised by the presence of the typical mineral association resulting from the strong acid conditions caused by the total oxidation of pyrite and other sulphides the total oxidation dissolution and leaching of u iv as uranyl sulphate aqueous complexes prevailed in this oxidised zone the redox transition zone is characterised by the coexistence of the primary uranium paragenesis oxidised minerals as well as numerous secondary solid phases as a result of the physico chemical changes in the environment the optimal physico chemical conditions for the coffinitisation of pitchblende and the co precipitation of fe iii u vi took place in this zone in the reduced zone where the primary uranium paragenesis is present we currently find the necessary physico chemical conditions to stabilise pitchblende pyrite and carbonates the physico chemical conditions of the oxidised zone are not relevant to disposal conditions in the transition zone two main geochemical processes take place i the coffinitisation of pitchblende which may be an important process for the stability of spent fuel in reducing conditions and ii the co precipitation of the fe iii and u vi as oxyhydroxides another relevant mechanism for the retention of uranium the physico chemical conditions that prevail below 50 m depth should be sufficient to stabilise a spent nuclear fuel repository in the same way as they have been able to preserve the 34 ma old uranium deposit of the mina fe

influence of volcanic eruptions on the troposphere through stratospheric dynamical processes in the northern hemisphere winter it has been suggested that the zonal mean stratospheric zonal wind anomalies can propagate downward into the troposphere producing considerable changes on the other hand volcanic aerosols are thought to produce a stronger polar vortex in the winter stratosphere if these suggestions are correct the influence of volcanic eruptions can be expected to produce changes in the northern hemisphere winter troposphere through stratospheric process in the present study this idea is examined by analyzing changes in the january circulation after three recent volcanic eruptions regional features of observed changes in tropospheric temperatures due to volcanic eruptions can be explained by the changes in the propagation of stationary waves associated with dipole type anomalies in the zonal mean zonal winds which are similar to those observed in a previous work on the influence of polar night jet

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

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

entrainment and export of laptev sea ice sediments siberian arctic sea ice sediments sis sediments rafted by ice and shelf surface deposits from the siberian laptev sea were analyzed to study turbulent entrainment processes this study focused on the silt and clay fractions on average representing 63 4 and 30 4 total 93 7 of the bulk sis respectively generally the sis contains 50 more silt than the shelf deposits while the clay percentages in both sample groups are similar sand sized particles are less abundant in sis than in bottom sediment although sis is clearly enriched in silt no evidence was found for preferential ice entrainment of any silt subfraction coarse medium fine statistical tests of sis and shelf silt parameters and the similar clay mineral compositions of both sample groups provide evidence for entrainment of laptev bottom deposits into newly forming ice the entrainment is related to the mechanism known as suspension freezing accordingly coarser clasts sand and plant debris may be lifted upward by buoyant anchor ice while coarse silt particles are supposed to be transported to the surface by rising frazil aggregates additionally turbulent interaction of convergent langmuir circulation and near surface frazil ice streaks is proposed to support ice entrainment of the finest particles 6 4 phi 12 m entrainment and export of sis from the laptev sea were assessed for ten individual flaw leads extended narrow polynyas separating fast and drifting ice using particle concentrations in ice samples and new ice formation rates the results show that roughly 20 mt of sis can be annually exported from the laptev sea by lead ice only thus formation and export of sediment laden lead ice may play a major geological role in siberian arctic shelf erosion and coastal retreat

assessing patterns of annual change to permafrost bluffs along the north slope coast of alaska using high resolution imagery and elevation models abstract coastal permafrost bluffs at barter island on the north slope beaufort sea coast of alaska are among the most rapidly eroding along alaska s coast having retreated up to 132 m between 1955 and 2015 here we quantify rates and patterns of change over a single year using very high resolution orthophotomosaics and co registered surface elevation models derived from a survey grade form of structure from motion photogrammetry from a fixed wing manned aircraft the resulting elevation models were validated with over 10 000 ground check points and found that 95 agreed to within 20 cm before accounting for real differences in the ground surface due to seasonality vegetation and checkpoint acquisition errors this data set provides the most detailed and accurate measurements of coastal change to date along the alaskan coast and the method is scalable to more extensive coastlines between july 2014 and july 2015 the bluffs retreated an average of 1 3 m and a maximum of 8 1 m with an associated net volume loss of 38 100 300 m3 1 3 m3 m this average retreat over this single year was slightly less than the 60 year mean rate of change of 1 5 0 1 m yr suggesting the 2014 2015 year represented relatively typical to slightly below average conditions most of the bluff material 70 was lost during the 3 summer months july to sept of 2014 and the remaining 30 between the late summer and following winter spring the pattern of change was predominantly landward retreat of the top of the bluffs removal of the debris apron and subsequent niching at the base of the bluffs during mid to late summer july to sept followed by erosion of the bluff face and deposition of debris at the base of the bluff through the remainder of the year sept to the following july drivers of the observed change are likely a combination of thermal erosion on the bluff face throughout the summer and episodic thermo mechanical removal of material niching and undercutting of the base associated with high water levels driven by low pressure storms and westerly winds these patterns and high rates of change are believed to be broadly representative of coastal permafrost bluffs found along many high latitude coastlines worldwide

a shape and compositional analysis of ice rafted debris in cores from iodp expedition 323 in the bering sea abstract sediment cores recovered during iodp expedition 323 in the bering sea northern pacific contained numerous ice rafted debris ird clasts up to 85 mm in length the physical properties including roundness and sphericity of 136 clasts from the working half of the cores a subsample of the total clast number were analysed and their composition determined using standard petrographic techniques after removal of pumice and possible fall in derived material from the clast population a total of 86 clasts from the original collection were considered to be ird while roundness and sphericity vary greatly in the clast population the ird are predominately discoid in shape with oblate prolate indices typically between 5 and 5 there are four time periods over the approximately 4 5 ma sample interval 0 36 0 67 ma 0 82 1 06 ma 1 54 1 77 ma and 3 28 ma where there are no ird in the sample set for sites of the bering slope suggesting that these times may have been ice free most clasts show some rounding and are likely to have spent time on beaches with wave action wave action on beaches suggests periods of no ice or only seasonal sea ice the low roundness values of other clasts however suggest they underwent little working and therefore the presence of glaciers or more permanent sea ice at times in those locations the abundance of rounded and unfaceted clasts as ird suggests a lack of large ice sheets in the area during cool periods clast composition of the ird is divided into four broad groups basalt and andesite granite and metamorphic sedimentary and felsic volcanic the granite and metamorphic and more mature sedimentary lithologies are most likely derived from the alaskan continental margin while the extrusive igneous clasts could be derived from a variety of volcanic sources surrounding the bering sea both emergent now or emergent at times of lower sea level there is only a poor correlation with ird abundance and marine isotope stages mis for the time period 2 mm transported by sea ice may not be a good indicator of past climate conditions