sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

geochemistry of late palaeocene and early eocene tephras from the north sea basin the late palaeocene to early eocene balder and sele formations of the north sea basin contain over 200 air fall water lain tephras these occur over the entire north sea area extending onshore into denmark nw germany the netherlands and se england they have also been recorded in the bay of biscay and goban spur areas of the ne atlantic and offshore mid norway results from cores drilled in two widely separated areas of the north sea have been integrated with earlier work on the northern north sea and danish sequences to demonstrate that the stratigraphic and geochemical development of the tephra sequence is regionally consistent this indicates that a single source or group of sources was responsible rather than a number of geographically separated intrabasinal volcanoes for which little geophysical evidence can be found the sequence comprises a lower group of sporadic thin tephras of variable composition including tholeiitic alkalic trachytic trachyandesitic and peralkaline varieties and an upper group of thicker more abundant tephras almost exclusively of fe ti tholeiitic composition general thickness trends and geochemical evidence indicates that the source volcanoes lay on the proto greenland scotland ridge with the tephras showing several features that ally them to the early palaeogene faeroe greenland igneous province the reasons behind the highly explosive nature of the basaltic magmatism remain enigmatic

a parameterization of the ice ocean drag coefficient 1 a parameterization of the ice ocean drag coefficient cw was developed through partitioning the oceanic drag force into three components 1 form drag on the floe edge 2 form drag on the ridge keel and 3 skin friction on the ice bottom through these quantities cw was expressed as a function of observable sea ice geometric parameters sensitivity studies were carried out to investigate the influence of varying sea ice conditions on cw the results revealed that cw increases first and then decreases with increasing ice concentration a similar to the observations of the air ice drag coefficient and which is mainly attributed to the nonmonotonic variation of the form drag on the floe edge with ice concentration moreover the form drag on the floe edge is always the dominant component having a proportion of more than 60 in sea ice with a large aspect ratio draft length 1 100 indicating the necessity of including this term in sea ice dynamic models particularly for the marginal ice zone miz the form drag on the ridge keel becomes dominant only when the ridging intensity is extremely high depth spacing 1 20 additionally a large value of cw cannot be caused only by the inclusion of form drag terms but also by large skin friction over rough ice bottoms finally for typical situations in the miz with moderate ridging intensity the parameterization will underestimate cw by approximately 30 for a rough ice bottom and by over 80 for a smooth ice bottom if no form drags are considered

role of ice dynamics in anomalous ice conditions in the beaufort sea during 2006 and 2007 1 a new record minimum in summer sea ice extent was set in 2007 and an unusual polynya formed in the beaufort sea ice cover during the summer of 2006 using a combination of visual observations from cruises ice drift and satellite passive microwave sea ice concentration we show that ice dynamics during preceding years included events that preconditioned the beaufort ice pack for the unusual patterns of opening observed in both summers intrusions of first year ice from the chukchi sea to the northern beaufort and increased pole ward ice transport from the western arctic during summer has led to reduced replenishment of multiyear ice older than five years in the western beaufort resulting in a younger thinner ice pack in most of the beaufort we find ice younger than five years melts out completely by the end of summer south of 76n the 2006 unusual polynya was bounded to the south by an ice tongue composed of sea ice older than 5 years and formed when first year and second year ice melted between 76n and the older ice to the south in this paper we demonstrate that a recent shift in ice circulation patterns in the western arctic preconditions the beaufort ice pack for increased seasonal ice zone extent

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

the impact of variable sea ice roughness on changes in arctic ocean surface stress a model study the arctic sea ice cover is thinning and retreating causing changes in surface roughness that in turn modify the momentum flux from the atmosphere through the ice into the ocean new model simulations comprising variable sea ice drag coefficients for both the air and water interface demonstrate that the heterogeneity in sea ice surface roughness significantly impacts the spatial distribution and trends of ocean surface stress during the last decades simulations with constant sea ice drag coefficients as used in most climate models show an increase in annual mean ocean surface stress 0 003 n m2 per decade 4 6 due to the reduction of ice thickness leading to a weakening of the ice and accelerated ice drift in contrast with variable drag coefficients our simulations show annual mean ocean surface stress is declining at a rate of 0 002 n m2 per decade 3 1 over the period 1980 2013 because of a significant reduction in surface roughness associated with an increasingly thinner and younger sea ice cover the effectiveness of sea ice in transferring momentum does not only depend on its resistive strength against the wind forcing but is also set by its top and bottom surface roughness varying with ice types and ice conditions this reveals the need to account for sea ice surface roughness variations in climate simulations in order to correctly represent the implications of sea ice loss under global warming

characteristics of the beaufort sea high abstract characteristics of the arctic ocean s beaufort sea high are examined using fields from the ncep ncar reanalysis at a 2 hpa contour interval the beaufort sea high appears as a closed anticyclone in the long term annual mean sea level pressure field and in spring in winter the beaufort sea region is influenced by a pressure ridge at sea level extending from the siberian high to the yukon high over northwestern canada as assessed from 6 hourly surface winds the mean frequency of anticyclonic surface winds over the beaufort sea region is fairly constant through the year while for all seasons a strong closed high can be interpreted as the surface expression of an amplified western north american ridge at 500 hpa there is some suggestion of a split flow where the ridge linked to the surface high is separated from the ridge to the south that lies within the main belt of westerlies the aleutian low in the north pacific tends to be deeper than normal when there is a strong beaufort sea high in

volcaniclastic rocks of the reydarfjordur drill hole eastern iceland 1 primary features a 1918 m deep bore hole in a late miocene shield basalt central volcano mixed sequence contains 58 stratigraphically distinct volcaniclastic interbeds constituting 8 8 of the extrusive part of the section textural mineral chemical and bulk chemical criteria are applied to identify the original nature composition and origin of these rocks which have been metamorphosed by hydrothermal alteration between 100 c top to ca 300 c base of the section units range from a few centimeters to 18 m excluding a 30 m thick ignimbrite with 75 of the units being less than 1 m thick formerly vitric to tachylitic shards and lapilli lithic fragments and crystals are the main components most thin volcaniclastic units are basaltic vitric to tachylitic tuffs thin felsic air fall tuffs a few millimeters to a few centimeters thick occur as separate layers and interbedded with basaltic tuffs nearly all thicker units are made up dominantly of felsic vitric to lithic clasts and crystals phenocrysts common only in felsic air fall tuffs are clinopyroxene ranging from augite to ferrohedenbergite and plagioclase ranging from an80 20 both of which span the entire range of compositions previously known from iceland bulk chemical analyses of major and 11 trace elements of 65 samples allow texturally indistinct rocks to be compositionally identified even though chemical changes due to mixing and alteration are pronounced in many rocks the rhyolitic ignimbrite cooling unit is composed of four flow units the upper most being slightly more mafic in composition because of admixture of a basaltic component the two central flow units show extensive high temperature devitrification with lensoid tridymite rimmed cavities now laumontite filled representing collapsed pumice lapilli the composition of the clastic units corresponds in a general way to that of the interbedded lava flows these data and evidence for weathering and reworking in some units are used to reconstruct the volcanic history of the area phase a 1918 1306 m dominantly mafic shield basalts contains only few and mostly basaltic tuffs except for sparse rhyolitic air fall tuff from distant central volcanoes phase b 1306 653 m composed dominantly of evolved basalts and icelandites culminating with the rhyolitic ignimbrite 920 950 m probably represents the eastern flank of a nearby central volcanic complex whose center may be situated less than 10 km westward downdip the upper extrusive 500 m of the section phase c are basalt lavas of average tholeiitic composition containing abundant chiefly felsic and reworked clastic units in the interval between 286 and 410m these are tentatively interpreted to reflect a phase of structural basin forming not compensated by extrusive volcanic activity allanite phenocrysts were found for the first time in icelandic rocks and the host pumice tuffs may constitute an important stratigraphic marker horizon that may help to tie the drilled section to the subaerial volcanic series in this part of eastern iceland the alteration of the clastic layers is discussed in a companion paper

late triassic tuff intervals in the ordos basin central china their depositional petrographic geochemical characteristics and regional implications abstract tuff intervals of upper triassic yanchang formation are laterally widespread in the ordos basin central china this paper focuses on magmatic origins and potential source regions of these tuff intervals through detail depositional petrographic and geochemical analyses most of the tuff intervals are well documented at the bottom of the chang7 oil reservoir unit and can be correlated laterally and certain tuff beds are reworked by turbidity current or seismic activity petrographic studies of the chang7 tuffs indicate that they are composed of crystal shards lithic shards and altered glass shards and the crystal shards include plagioclase quartz and biotite alteration of the chang7 tuffs is ubiquitous thus most of these tuffs transformed into illite smectite i s mixed layers which are identified by scanning electron microscopy sem and x ray diffraction xrd less common minerals are also detected in the chang7 tuffs such as zircon hematite siderite anatase major elements are determined by the x ray fluorescence xrf analysis the results indicate that the chang7 tuffs are enriched in k2o average 4 21 the ratio of sio2 al2o3 ranges from 1 73 to 2 85 average 2 17 and the ratio of tio2 al2o3 varies between 0 006 and 0 032 average 0 017 which imply that the chang7 tuffs originated from a felsic parental magma trace elements are determined by inductively coupled plasma mass spectrometry icp ms indicating the total rare earth element ree concentrations are variable and range from 117 46 to 466 83 ppm average 251 88 ppm ree distribution pattern of the chang7 tuffs presents a lree rightward incline with flat hree curve the value of eu ranges from 0 151 to 0 837 average 0 492 suggesting a strong to weak negative eu anomaly the chang7 tuffs show positive anomalies in rb th and u and negative anomalies in nb sr and eu on a primitive mantle normalized spidergram a preliminary analysis of the geochemical composition of the chang7 tuffs suggests a parental magma origin of rhyodacite dacite which came from volcanic arc related setting along an active continental margin combined with the chronology and geochemical studies of the synchronous tianshui rhyolite in the west qinling mountains we propose that the west qinling mountains is one of the potential source regions of these tuffs and the middle late triassic terminal closure of eastern tethys provided the arc related magma

pleistocene mass flow deposits of basaltic hyaloclastite on a shallow submarine shelf south iceland a pleistocene subaqueous volcanic sequence in south iceland consists of flows of basaltic hyaloclastite and lava with interbedded sedimentary diamictite units emplacement occurred on a distal submarine shelf in drowned valleys along the southern coast of iceland the higher sea level was caused by eustatic sea level change probably towards the end of a glaciation this sequence nearly 700 m thick rests unconformably on eroded flatlying lavas and sedimentary rocks of likely tertiary age a standard depositional unit describing the flows of hyaloclastite starts with compact columnar jointed basalt overlain by cubejointed basalt and or pillow lava this in turn is overlain by thick unstructured hyaloclastite containing aligned basalt lobes and bedded hyaloclastite at the top a similar lithofacies succession is valid for proximal to distal locations the flows were produced by repeated voluminous extrusions of basaltic lava from subaquatic fissures on the eastern rift zone of iceland the fissures are assumed to lie in the same general area as the 1783 laki fissure which produced 12 km3 of basaltic lava due to very high extrusion rates the effective water melt ratio was low preventing optimal fragmentation of the melt the result was a heterogeneous mass of hyaloclastite and fluid melt which moved en masse downslope with the melt at the bottom of the flow and increasingly vesicular hyaloclastite fragments above the upper and distal parts of the flow moved as low concentration turbulent suspensions that deposited bedded hyaloclastite

wind driven freshwater buildup and release in the beaufort gyre constrained by mesoscale eddies recently the beaufort gyre has accumulated over 20 km3 of freshwater in response to strong anticyclonic atmospheric winds that have prevailed over the gyre for almost two decades here we explore key physical processes affecting the accumulation and release of freshwater within an idealized eddy resolving model of the beaufort gyre we demonstrate that a realistic halocline can be achieved when its deepening tendency due to ekman pumping is counteracted by the cumulative action of mesoscale eddies based on this balance we derive analytical scalings for the depth of the halocline and its spin up time scale and emphasize their explicit dependence on eddy dynamics our study further suggests that the beaufort gyre is currently in a state of high sensitivity to atmospheric winds however an intensification of surface stress would inevitably lead to a saturation of the freshwater content a constraint inherently set by the intricacies of the mesoscale eddy dynamics

correlation of middle ordovician k bentonites based on chemical fingerprinting six separate k bentonite beds in middle ordovician rocks of southwestern ohio and northern kentucky have been analyzed for three major and 22 trace elements and the data used as a basis for stratigraphie correlation samples from eight cores distributed over a distance of 140 km were analyzed for dy eu mn na k sm la as ga lu sb fe yb cr tb se rb co ce ta th hf cs zn and zr by instrumental neutron activation analysis and x ray fluorescence and the results subjected to stepwise discriminant analysis within layer and between layer variations in composition were assessed and a ranking of elements established on the basis of their ability to characterize individual layers eighteen elements are sufficient to establish 100 classification in a group matrix of the six beds with the principle assignment contributions coming from th ta rb cr fe ga yb and k to test the stratigraphie usefulness of chemical fingerprinting over more extended distances seven samples of k bentonites e

ekman circulation in the arctic ocean beyond the beaufort gyre data derived from satellite based observations with buoy based observations and assimilations are used to calculate ocean ekman layer transport and evaluate long term trends in the arctic ocean over the period 1979 2014 the 36 year mean of upwelling downwelling is 3 6 2 0 4 0 2 2 sv for the entire arctic basin with 0 4 sv net downwelling contributed mostly by the canadian region with regard to long term trends the annual mean upwelling downwelling over the entire arctic basin is increasing at a linear rate of 0 89 0 96 sv decade the canada alaska coasts and beaufort and laptev seas are regions of greatest ekman transport intensification the central arctic ocean and lincoln sea also have an increasing trend in transport the canadian and eurasian regions each account for about half the total vertical ekman variations in the arctic basin this article is protected by copyright all rights reserved

volcaniclastic rocks of the reydarfjordur drill hole eastern iceland 2 alteration volcaniclastic rocks of basaltic to rhyolitic composition interlayered with basaltic to icelanditic lava flows in a 1918 m drill hole in eastern iceland are altered to zeolite and pumpellyite prehnite facies assemblages major alteration minerals are chlorites illite chlorite mixed minerals illites k feldspar laumontite quartz and sphene others include julgoldite and secondary allanite smectites as well as mordenite and heulandite are restricted to the upper 900 m epidote and minor pumpellyite prehnite wairakite and anhydrite are restricted to the core below 900 m the boundary between zeolite and prehnite pumpellyite facies is marked by the appearance of chlorite epidote quartz assemblages at around 900 m the typical paragenesis prehnite pumpellyite epidote chlorite occurs near the base of the drill hole at 1855 m textures indicate generally prograde metamorphic conditions the broad compositional spectrum ranging from basalt to rhyolite abundance of vitric fragments and high initial porosity and permeability of the volcaniclastic rocks were major factors governing alteration the site of growth crystal shard vesicle pore and vein of a secondary phase strongly influences composition habit amount paragenesis and time of crystallization for example sphene and to a lesser degree epidote are less rich in fe and better crystallized in plagioclase than in the adjacent matrix the different mineral assemblages developed within plagioclase crystals through the section most clearly reflect the metamorphic changes the abundance of vitric rhyolitic clasts shards and pumice favored k al si enriched fluids from which phases like illite and adularia crystallized these phases were not found in interlayered basalt flows mehegan et al this issue low ca activity is also indicated by the occurrence of wairakite and pumpellyite rather than prehnite which is common in the basalts secular changes during metamorphism in pore fluid composition are shown by zonations in mineral compositions for example the depletion of epidote and juldoldite pumpellyite in fe with time appears to reflect decreasing o2 bulk rock chemical changes are more intense in the volcaniclastic rocks compared to the basalt lavas h2o fe3 fe2 and in part co2 values are higher in the upper part of the hole reflecting the higher porosity and glass content of the clastic rocks they decrease markedly downhole approaching values of the lava flows due to more pervasive metamorphic alteration and thus similar mineral assemblages and physical properties

complex reservoir geometries in a deep water clastic sequence gryphon field ukcs injection structures geological modelling and reservoir simulation abstract the balder formation sandstone reservoir of the gryphon field was deposited during the late paleocene early eocene while the background sedimentation comprised pelagic shales and tuffs sediment gravity flows transported sands from the shelf area in the west the crawford ridge acted as a barrier to sediment transport in the east causing the sands to be deposited predominantly as massive sand bodies as flow velocities decreased during burial sand remobilisation and injection occurred possibly localised around faults cored intervals show a range of injection structures from thin cm scale dykes to more massive metre scale chaotic intrusive features the cross cutting nature of the injection structures as observed in core and in seismic sections accounts for the high degree of reservoir connectivity observed in the field a study was undertaken with the objective of constructing a 3d geological model for dynamic reservoir simulation in order to evaluate future development activities in the field as previous purely deterministic models had proven unsuitable the complex depositional and post depositional history of the gryphon field reservoir has resulted in a system for which there is no published analogue to aid in 3d reservoir modelling preliminary stochastic models based on analogues chosen to reflect the reservoir sand body geometries did not match the field production history the fact that both the deterministic and fully stochastic models were unsuitable suggested that a novel approach was required to model this field subsequent models constructed using a combination of stochastic and deterministic models have proven successful in matching the production history of the field and evaluating infill opportunities

palaeocene oligocene tectonics of nw europe s u m m a r y during the palaeogene in nw europe a gallic subplate was very nearly created this plate was almost entirely bordered by plate boundaries although not of equivalent ages to the n the n atlantic began to open about 56 ma ago the alpine convergent boundary extended southwestwards to the pyrenean subduction zone on the ne side a n british pataeocene early eocene fracture dyke boundary appears to pass southeastwards across the north sea into a lutetian to burdigalian rift system there is an age disparity between the fracturing and nw dyke intrusion in britain and the fracturing and formation of the rhine graben the last dykes in britain ypresian were intruded not long before the important subsidence of the rhine graben earliest lutetian but their causes were different the british dyke fractures propagated southeastwards via the cleveland dyke towards the north sea whereas the rhine graben propagated northwards towards the zuider zee depression however the structures from both sides converged in the sole pit basin in the north sea with the result that a continuous though not coevally originated fracture system developed from nw scotland to the alps during the early tertiary there was a wide range of tectonic activity throughout nw europe fig 1 in nw britain lavas were extruded and plutonic complexes and extensive dyke swarms were intruded in the north sea tufts were deposited as a result of volcanism along the rockall faeroe rift reactivation of faults con trolled magmatism localization of gas fields devolatilization of coal and inversion of basins caused uplift deformation and erosion along the rhine graben doming subsidence and rift propagation took place in association with alka line volcanism and plutonism coevally with the meso alpine compressive deformations that oc curred in the alps faulting controlled sedimen tation patterns during inversion of basins in southern england the english channel northern france and holland old rift faults were reacti vated in the western approaches basin thrust faults formed in the southern bay of biscay contemporaneously with thrusting in the pyre nees and variscan massifs were tilted and uplifted along steep reverse faults the main tectonic activity lasted from about 60 ma to about 30 ma but it was diachronous generally earlier in the nw and later in the se the igneous activity in northern britain was related to the opening of the n atlantic in the late palaeocene but the formation of the rhine graben and the inversion of sedimentary basins in the north sea and near the english channel were caused by major orogenic events in the alpine region in the late eocene to mid oligocene frisch 1981 tectonic phenomena in the north sea provide the link between those in northern britain and those in the rhine graben the aim of this paper is to demonstrate that these movements from the atlantic and alpine sides almost fragmented the lithospheric plates of nw europe during the creation of a gallic sub block an earlier northern boundary from nw scotland to northern germany being transected by a later eastern boundary along the rhine graben

early opening history of the north atlantic i structure and origin of the faeroe shetland escarpment summary marine geophysical surveys show that the escarpment is the buried feather edge of a thick pile of flood basalts of early eocene age overlying a thinner more widespread layer of basalts of late palaeocene age the escarpment does not therefore define the continent ocean boundary in the southern norwegian sea but instead marks the contemporary shoreline separating terrestrially erupted basalt flows in the north from a restricted shallow water shelf to the south the basalts overlie 5 6 km of mesozoic sediments which have completely buried a large conical flat topped seamount of similar dimensions to anton dohrn and rosemary bank we call this newly postulated body the brendan seamount the mesozoic sediments are at least as old as early cretaceous in age therefore precluding the possibility that the mid cretaceous seafloor spreading episode supposed by some to have created the rockall trough could have also created the thin crust inferred to underlie the faeroe shetland trough and mbre basin

the aerodynamic roughness of different types of sea ice the aerodynamic roughness for all major types of sea ice is specified on the basis of surface layer measurements from ship and ice floe platforms median neutral surface drag coefficients cdn 1000 for grease and nilas ice are 0 7 and 1 6 small medium large and fused pancake ice have cdn equal to 0 9 1 6 2 4 and 1 9 young ice cdn ranges from 2 3 to 3 1 very smooth first year or multiyear ice with no pressure ridges has cdn equal to 1 5 pack ice has median values of 2 0 and 2 2 for first year and multiyear ice marginal ice zone ice averages 3 1 and 3 4 first year multiyear if unaffected by wave action wave affected ice has cdn values of 4 2 and 4 6 first year multiyear extremely rough multiyear ice in intense shear or compaction regions has cdn equal to 8 0 open ocean areas within 100 km of an ice edge averaged 1 8 while ice free water downwind of ice with small or no waves is 1 4 these values can be adjusted if heat fluxes are present the accuracy of the cdn averages is estimated to be 20 or better

mafic volcaniclastic deposits in flood basalt provinces a review flood volcanic provinces are assumed generally to consist exclusively of thick lavas and shallow intrusive rocks mostly sills with any pyroclastic rocks limited to silicic compositions however mafic volcaniclastic deposits mvds exist in many provinces and the eruptions that formed such deposits are potentially meaningful in terms of potential atmospheric impacts and links with mass extinctions the province where mvds are the most voluminous the siberian traps is also the one temporally associated with the greatest phanerozoic mass extinction a lot remains to be learned about these deposits and eruptions before a convincing genetic link can be established but as a first step this contribution reviews in some detail the current knowledge on mvds for the provinces in which they are better known i e the north atlantic igneous province including greenland the faeroe islands the british isles and tephra layers in the north sea basin and vicinity the ontong java plateau the ferrar and the karoo we also provide a brief overview of what is known about mvds in other provinces such as the columbia river basalts the afro arabian province the deccan traps the siberian traps the emeishan and an archean example from australia the thickest accumulations of mvds occur in flood basalt provinces where they underlie the lava pile faeroes n1 km ferrar province z400 m siberian traps 700 m in the faeroes case the great thickness of mvds can be attributed to accumulation in a local sedimentary basin but in the ferrar and siberian provinces the deposits are widespread n310 5 km 2 for the latter on the ontong java plateau over 300 m of mvds occur in one drill hole without any overlying lavas where the volcaniclastic deposits are sandwiched between lavas their thickness is much less in most of the cases reviewed primary mvds are predominantly of phreatomagmatic origin as indicated by the clast assemblage generally consisting of basaltic clasts of variable vesicularity dominantly non to poorly vesicular mixed with abundant country rock debris the accidental lithic components often include loose quartz particles derived from poorly consolidated sandstones in underlying sedimentary basins east greenland ferrar karoo these underlying sediments or sedimentary rocks were not only a source for debris but also aquifers that supplied water to fuel phreatomagmatic activity in the

an unexpected seasonal variability of salinity in the beaufort sea upper layer in 1996 1998 1 the salinity in the upper beaufort sea from the mixed layer to the thermocline layer was observed by drifting buoys from 1996 to 1998 the salinity in this depth range was lower in winter and higher in the summer the exact opposite from what one would expect from the seasonal cycle of the freshwater flux associated with the ice melting freezing and river runoff in this study we calculated the daily ekman transport and upwelling velocity in the beaufort sea using both satellite and buoy data in fall and winter months the offshore transport of low salinity water from the coastal area toward the interior where the buoys were located was observed to be strong this horizontal ekman transport led to the freshening of the surface ekman layer in the buoy location the convergence of the ekman transport resulted in a strong downwelling in the offshore regions and so the halocline and thermocline were pushed downward the downwelling then results in the freshening of the subsurface salinity as observed by buoys other processes such as lateral advection may have also played a role in the subsurface freshening the lack of in situ observations needed to estimate the salinity gradient makes it difficult to assess more accurately the contribution from lateral advection a scaling analysis using the salinity climatology suggests that the lateral salinity advection though considerably smaller than the vertical one may not be negligible

the laptev sea as a source for recent arctic ocean salinity changes this study was motivated by observations of significant salinification of the upper eurasian basin that began around 1989 observational data and modeling results provide evidence that increased arctic atmospheric cyclonicity in the 1990s resulted in a dramatic increase of the salinity in the eurasian basin two mechanisms account for the laptev sea salinization eastward diversion of russian rivers and increased brine formation due to enhanced ice production in numerous leads in the laptev sea ice cover both these mechanisms are linked to changes in wind patterns and were essential to the formation of salinity anomalies the resulting laptev sea salinity anomaly was advected to the central eurasian basin the strong salinization over the eurasian basin altered the formation of cold halocline waters weakened vertical stratification and released heat upward from below the cold halocline layer our analysis suggests that local processes in the laptev sea may have a basin wide impact on the thermohaline structure of the arctic ocean

nannoplankton zonation and the palaeocene eocene boundary beds of nw europe an indirect correlation by means of volcanic ash layers correlation of early palaeogene ash layers in dsdp hole 550 leg 80 goban spur with those of the north sea basin indicates that the base of nannoplankton zone np10 approximates the base of the sele formation of the north sea area the bases of the danish ash series the german ash bearing untereozan 1 and the paris basin sparnacian and the top of the woolwich reading bottom bed of the london basin if as is now common practice the palaeocene eocene boundary is placed at the np9 np10 boundary then the units listed above would constitute the basal units of the eocene in their respective countries the cessation of large scale pyroclastic activity took place at about the middle of the zone np10 interval

salinity trends on the siberian shelves 1 we present an analysis of observed long term 100 year salinity trends on the freshwater dominated siberian continental shelves a multiple regression was performed in the white sea ws the kara sea ks the laptev sea ls and the east siberian sea ess since 1930 the ws has gained freshwater while the ess has lost it consistent with river discharge trends over this period over the past 20 years increases in both river discharge and direct precipitation can explain observed salinity decreases in the ws but not in the ks salinity trends in the ls and ess indicate that ocean circulation plays a dominate role in these areas where in recent years freshwater has been diverted eastward along the coast rather than northward toward the deep ocean

intensification of geostrophic currents in the canada basin arctic ocean abstractcontinuous sampling of upper ocean hydrographic data in the canada basin from various sources spanning from 2003 through 2011 provides an unprecedented opportunity to observe changes occurring in a major feature of the arctic ocean in a 112 km radius circle situated near the center of the traditional beaufort gyre geopotential height referenced to 400 dbar increased by about 0 3 gpm from 2003 to 2011 and by the end of the period had increased by about 65 from the climatological value near the edges of the domain considered the anomalies in dynamic height are much smaller indicating steeper gradients a rough dynamic topography constructed from profiles collected between 2008 and 2011 shows the center of the gyre to have shifted south by about 2 in latitude along the 150 w meridian geostrophic currents are much stronger on the periphery of the gyre reaching amplitudes 5 6 times higher than climatological values at grid points just offshore from the beaufort and chukchi shelf slopes esti

latest on the absolute age of the paleocene eocene thermal maximum petm new insights from exact stratigraphic position of key ash layers 19 and 17 abstract we constructed a precise early eocene orbital cyclostratigraphy for dsdp site 550 leg 80 goban spur north atlantic utilizing precession related cycles as represented in a high resolution x ray fluorescence based barium core log based on counting of those cycles we constrain the exact timing of two volcanic ash layers in site 550 which correlate to ashes 19 and 17 of the fur formation in denmark the ashes relative to the onset of the paleocene eocene thermal maximum petm are offset by 862 kyr and 672 kyr respectively when combined with published absolute ages for ash 17 the absolute age for the onset of the petm is consistent with astronomically calibrated ages using the current absolute age of 28 02 ma for the fish canyon tuff fct standard for calibrating the absolute age of ash 17 is consistent with tuning option 2 in the astronomically calibrated paleocene time scale of westerhold et al 2008 westerhold t rohl u raffi i fornaciari e monechi s reale v bowles j and evans h f 2008 astronomical calibration of the paleocene time palaeogeography palaeoclimatology palaeoecology v 257 p 377 403 using the recently recalibrated absolute age of 28 201 ma for the fct standard is consistent with tuning option 3 in the astronomically calibrated paleocene time scale the new results do not support the existence of any additional 405 kyr cycle in the early paleocene astronomically tuned time scale

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

tertiary volcanism in the kangerdlugssuaq region e greenland trace element geochemistry of the lower basalts and tholeiitic dyke swarms

on the ice and heat balance in fram strait the sea ice margin northwest of spitsbergen is schematically represented by a stationary wedge maintained by opposing ice and warm atlantic water advection ice melt and cooling of the surface water generate a mixed layer with properties approximating those found elsewhere in the arctic basin the heat energy required to melt the advancing ice is roughly comparable to the rate of heat loss of the west spitsbergen current and suggests that direct heat exchange with the atmosphere is less important only a small fraction of the nearly fresh water from ice melt exits through eastern fram strait and most of it appears to return to the arctic basin whether or not it contributes to the formation and maintenance of the arctic mixed layer depends on the largely unknown circulation pattern north of fram strait an example of the large interannual variation of the mean wind stress field is shown to illustrate the likelihood of an equally large variance of the ice and surface water circulation

paleogene tuffaceous intervals grane field block 25 11 norwegian north sea their depositional petrographical geochemical character and regional implications abstract paleogene volcaniclastic rocks from four wells from the grane field block 25 11 southern viking graben on the western flank of the utsira high north sea have been studied the tuffaceous intervals consist of the volcanic phase 1 58 57 ma in the vale and lista formations and the volcanic phase 2 55 52 ma in the sele and balder formations tuff beds of phase 1 are interpreted as having been redeposited by turbidity currents whereas those of phase 2 reflect normal settling of fall out pyroclastics in water two types of fragments occur the most abundant being vesicular pyroclasts with irregular shape and dark microlithic partly vesicular granules representing shallow submarine surtseyan type eruptions the other type of pyroclastic fragments are vitric shards which originate by quenching granulation during subaqueous eruptions the tuffaceous intervals have been subdivided into 1 identified pyroclastics based on textural interpretations and 2 assumed pyroclastics based on geochemical interpretations the majority of the samples are sub alkaline basalts and basaltic andesites the phase 1 tuffs evolved from basalts to rhyolites upwards in the lista formation and phase 2 tuffs consist of sub alkaline basalts and basaltic andesites of within plate origin similar to the contemporaneous lower basalts in east greenland the rockall trough and the middle series on faroes all linked to the opening of the north atlantic ocean

the force balance of sea ice in a numerical model of the arctic ocean the balance of forces in the sea ice model of hibler 1979 is examined the model predicts that internal stress gradients are an important force in much of the arctic ocean except in summer when they are significant only off the northern coasts of greenland and the canadian archipelago a partition of the internal stress gradient between the pressure gradient and the viscous terms reveals that both are significant although they operate on very different timescales the acceleration term is generally negligible while the sum of coriolis plus sea surface tilt is small thus the seasonal average force balance in fall winter and spring is mostly between three terms of roughly equal magnitudes air drag water drag and internal stress gradients this is also true for the monthly average force balance however we find that there is a transition around the weekly timescale and that on a daily basis the force balance at a particular location and time is often between only two terms either between air drag and water drag or between air drag and internal stress gradients the model is in agreement with the observations of thorndike and colony 1982 in that the correlation between geostrophic wind forcing and the model s ice velocity field is high this result is discussed in the context of the force balance we show that the presence of significant internal stress gradients does not preclude high wind ice correlation a breakdown of the internal stress gradient into component parts reveals that the shear viscous force is far from negligible which casts strong doubt on the theoretical validity of the cavitating fluid approximation in which this component is neglected finally the role of ice pressure is examined by varying the parameter p we find a strong sensitivity in terms of the force balance as well as ice thickness and velocity

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

origin and timing of sand injection petroleum migration and diagenesis in tertiary reservoirs south viking graben north sea petrographic fluid inclusion and carbon and oxygen stable isotope studies of tertiary injectite reservoirs in the south viking graben of the north sea allow an understanding of the origin and timing of sand injection petroleum migration and diagenesis injection from shallowly 400 m 1300 ft buried paleocene and eocene unconsolidated sandstones occurred at the end of the eocene probably in response to earthquake activity liquid oil was already present in the parent sands prior to injection and leaked from the injectites to the seabed upward migrating oil and basinal brines mixed with downward invading mixed meteoric marine pore fluids in the injectites causing extensive biodegradation of the oil biodegradation of oil provided the driver for early carbonate cementation in injectites causing diminished reservoir quality however early carbonate cementation also sealed off the injectites as potential escape routes for petroleum from the underlying parent sands oil and gas continued to migrate into the reservoir parent sands upon increased burial causing a mixing of high api oil with the early charged extensively biodegraded low api oil the study of early diagenetic imprints reveals the evolution of injectite reservoirs which forms the basis for understanding how to explore and develop them

cross shelf transport of warm and saline water in response to sea ice drift on the laptev sea shelf 1 oceanographic moorings and conductivity temperature depth ctd surveys from september 2009 to september 2010 are used to describe recent changes in the laptev sea hydrography and to highlight wind and ice driven surface ekman transport as the mechanism to translate these changes from the outer to the inner shelf bottom waters in february 2010 moored oceanographic instruments recorded a sudden increase in temperature 0 8 c and salinity 3 near the bottom of the inner laptev sea shelf such warm and saline waters had not been previously observed on the inner shelf in winter they likely originated from the basin and were first observed during a summer 2009 ctd survey in the northwestern shelf break region subsequently spreading east and shoreward across the laptev sea shelf the changes were introduced to the mooring site by the first of a series of bottom intensified flow events with velocities reaching 20 cm s 1 topographically guided along a relic submarine river valley each of the flow events coincided with negative pressure anomalies at the mooring site and offshore directed upwelling favorable winds and ice drift we suggest that the observations to first order resemble a simplified two dimensional two layered ocean where offshore surface ekman transport is compensated for by a barotropic shoreward response flow near the bottom in this paper we use one of the first comprehensive long term laptev sea datasets to highlight ice ocean atmosphere interactions in early and late winter and discuss the role of freshwater stratification and ice mobility on under ice circulation on the laptev sea shelf

oil source rock correlation for tight oil in tuffaceous reservoirs in the permian tiaohu formation santanghu basin northwest china tight oil in the permian tiaohu formation in the santanghu basin northwest china has a peculiar property such that the reservoir is sedimentary organic matter bearing tuff characterized by high porosity 10 25 and very low permeability mainly in the range of 0 01 0 50 md biomarker and stable carbon isotope compositions of selected crude oils and source rock extracts were analyzed to determine the source rock of the tight oil source rocks in the lucaogou formation consist of various rock types dominated by mudstones containing organic matter with intense yellow green fluorescence mudstones in the lucaogou formation have total organic carbon toc values mainly in the range of 1 0 8 0 wt hydrocarbon generation potential s1 s2 mostly 6 mg g and chloroform extractable bitumen a generally 0 1 the maceral composition is predominantly fluorescing amorphinite the hydrogen index hi varies from 300 to 900 mg hc g toc indicating dominant type i and type ii kerogen compared with the mudston

development of early diagenetic silica and quartz morphologies examples from the siri canyon danish north sea abstract the siri canyon has proved to be a perfect area for investigating various morphologies of diagenetic silica in sandstones the development in silica morphologies can be observed from very shallow 1700 m to increased burial depth 3000 m and increased proximity to the central graben distance from 0 to 65 km hydrocarbons and pore fluids now found in the siri fairway have at least partly originated from the central graben the siri canyon is a submarine canyon system eroded into the uppermost chalk deposits and filled with palaeogene hemipelagic and turbiditic marls and mudstones interbedded with sandstone units deposited from sandy mass flows and sandy turbidites which originated on the stavanger platform several hydrocarbon exploration and production wells have been drilled in the siri canyon seven of which are included in this study nini 3 nini 1 na 2p sofie 1 siri 4 celilie 1a and augusta 1 the reservoir sandstones in these wells all contain authigenic silica of various morphologies identified with a combination of traditional optical microscopy and scanning electron microscopy the silica morphologies in some places are classic and well documented in the literature whereas others at least to our knowledge have never previously been described some of the silica morphologies presented here show gradual transition from one to another and others are stand alone forms without clear relationships to other forms the silica morphologies can be expressed in the following way 1 opal rims characteristic of the initial phase of the silica diagenesis in most sandstone units in the siri canyon thick opal rims characterise the sandstone parts adjacent to the mudstone units in the stine segment of the siri field 2 microquartz quartz crystals with a size of 1 5 m seen as coatings on the opal rims both ordered and random 3 cavity overgrowth found as quartz outgrowths in circular and angular cavities formed by dissolution of early authigenic phases angular cavities in the microquartz coatings origin from dissolution of clinoptilolite possibly with a source in volcanic ash whereas dissolution of lepispheres probably resulted in circular cavities 4 quartz ridges syntaxial quartz overgrowths a few micro millimetre in width in parallel lines defined in this paper 5 quartz mountains syntaxial irregular 5 10 m large quartz crystals defined in this paper developed in the water filled sandstone intervals where fluids from the central graben were introduced possibly together with the hydrocarbon and where the continued growth was not retarded by the presence of hydrocarbons in the pore fluids 6 macroquartz syntaxial quartz overgrowths 20 m seen as continued growths from quartz mountains this takes place in the deeper reservoir sandstones promoted by fluids originating from the central graben and increased burial depth 7 quartz with sutured grain contacts occurring only in the deepest well 3000 m

circulation of summer pacific halocline water in the arctic ocean 1 we present an analysis of arctic ocean hydrographic and sea ice observations from the 1990s with a focus on the circulation of water that originates in the north pacific ocean previous studies have shown the presence of two varieties of relatively warm summer halocline water in the vicinity of the chukchi sea i e the relatively fresh alaskan coastal water acw and the relatively saltier summer bering sea water sbsw here we extend these studies by tracing the circulation of these waters downstream into the arctic ocean we find that acw is generally most evident in the southern beaufort gyre while sbsw is strongest in the northern portion of the beaufort gyre and along the transpolar drift stream we find that this separation is most extreme during the early mid 1990s when the arctic oscillation was at historically high index values this leads us to speculate that the outflow to the north atlantic ocean through the canadian archipelago and fram strait may be similarly separated as arctic oscillation index values fell during the later 1990s acw and sbsw began to overlap in their regions of influence these changes are evident in the area north of ellesmere island where the influence of sbsw is highly correlated with a 3 year lag with the arctic oscillation index we also note the presence of winter bering sea water wbsw which underlies the summer varieties all together this brings the number of distinct pacific water types in our arctic ocean inventory to three acw sbsw and wbsw

persistent artifacts in the nsidc ice motion data set and their implications for analysis in this study we evaluate weekly ease grid sea ice velocities released by the national snow and ice data centre nsidc we identify persistent eulerian and lagrangian features that arise solely as an artifact of the method used in the incorporation of buoy data this in turn significantly impacts calculation of sea ice motion gradients including divergence convergence and shear our numerical experiments and comparison with observations further demonstrate the impact of these artificial features on climatological assessments including age of ice studies in particular we find that age of ice studies using this dataset significantly underestimate multi year ice extent by an average of 0 8 million km2 in the month of march

geochemical and tight reservoir characteristics of sedimentary organic matter bearing tuff from the permian tiaohu formation in the santanghu basin northwest china abstract tuff reservoirs have been found in petroliferous basins but have not been sufficiently studied the discovery of the permian tiaohu formation reservoir in the santanghu basin in northwest china has offered an excellent opportunity to further enhance our knowledge of the tuff s geochemical and reservoir characteristics the tuff reservoir has the peculiar property of being a sedimentary organic matter bearing tuff in this study an integrated analysis of the organic geochemistry elemental and mineral compositions quartz crystallinity pore types and tight reservoir characteristics was conducted based on samples from the 20 30 m thick tuffs the extracted tuff samples have total organic carbon toc values of 0 5 1 0 wt total hydrocarbon yield values of 2 6 mg g and hydrogen index values of 20 336 mg hc g toc the organic matter consists predominantly of type iii and ii 2 kerogens and the temperature of the maximum yield of pyrolysate varies from 420 to 450 c which reflects the oil generating capacity of the rock the physical properties of the tuff are characterised by high porosity varying from 10 to 25 and low permeability the air permeability mainly ranges from 0 01 to 0 50 md the devitrification of vitreous textures within the tuff primarily dictates the reservoir s characteristics i e the greater the degree of devitrification the higher the porosity of the reservoir vitric tuffs have reservoirs with higher porosity than crystal vitric tuffs and the degree of devitrification is generally controlled by the burial depth temperature and organic matter organic acid content vitric tuffs with high porosity and permeability are usually located far from the crater and within the central lower part of the reservoir this research may influence geologists to pay more attention to the exploration value of this special type of reservoir in other regions

mechanisms of pacific summer water variability in the arctic s central canada basin pacific water flows northward through bering strait and penetrates the arctic ocean halocline throughout the canadian basin sector of the arctic in summer pacific summer water psw is modified by surface buoyancy fluxes and mixing as it crosses the shallow chukchi sea before entering the deep ocean measurements from ice tethered profilers moorings and hydrographic surveys between 2003 and 2013 reveal spatial and temporal variability in the psw component of the halocline in the central canada basin with increasing trends in integrated heat and freshwater content a consequence of psw layer thickening as well as layer freshening and warming it is shown here how properties in the chukchi sea in summer control the temperature salinity properties of psw in the interior by subduction at isopycnals that outcrop in the chukchi sea results of an ocean model forced by idealized winds provide support to the mechanism of surface ocean ekman transport convergence maintaining psw ventilation of the halocline

linearity of the earthquake recurrence curve to m 1 from little skull mountain aftershocks in southern nevada laboratory and theoretical studies suggest that there is a minimum patch size for rupture on faults thus limiting observed earthquake sizes to above some moment or magnitude corresponding to this patch dimension this limit most likely being at a much lower magnitude than that which can be observed due to background noise of the earth and to attenuation is difficult to verify for real earthquakes we have recorded earthquakes to as small as m 2 richter local magnitude in the aftershock zone of the m 5 6 little skull mountain earthquake of 29 june 1992 the network threshold for location is below m 0 however by considering all the triggered earthquakes at station lsc which is just above the aftershock zone and combining these with the located events the recurrence curve is extended well below the network threshold we do this by forming a relation between the trace amplitudes of the lsc recordings and the network magnitudes for larger events and then assigning an estimated m to the smaller triggered events the recurrence curve plotted for the combined data shows a constant b value of 0 82 down to roughly m 1 2 we show that this magnitude is somewhat below the detection threshold of lsc the smallest recorded events are similar in appearance to events larger by as much as 3 magnitude units in the aftershock zone partly due to the band limitation of the 100 samples sec data and local attenuation s to p ratios much greater than 1 and broadband signals for these small events are indicative of normal tectonic earthquakes the seismic moments of the very smallest events near m 2 are approximately 5 109 n m larger than observations in deep mines by at least an order of magnitude because the source corner frequency is too high to be seen in the spectrum of the smallest earthquakes we cannot estimate source radii manuscript received 19 february 2003

a hot spot model for early tertiary volcanism in the n atlantic s u m m a r y the initial stages of rifting of the n atlantic were accompanied by massive extrusion of volcanic rocks and the accretion to the lower crust of even greater volumes of igneous rock emplacement of the bulk of the igneous rocks along the 2000 km long continental rift occurred in as little as 2 3 my the pattern and timing of magmatic activity can be explained by partial melting of anomalously hot asthenosphere as it welled up to fill the space left by the stretched and thinned continental lithosphere asthenosphere temperatures were elevated regionally by 100 150 over a 2000 km diameter region by the mushroom shaped head of hot material fed by a mantle plume which at present is centred beneath iceland

original sediment composition of the lower cretaceous lacustrine tight oil mudstone and influences on diagenesis and organic matter content the erennaoer sag in erlian basin ne china abstract the original sediment composition is of great value to providing an understanding of depositional environment and hydrocarbon generation potential but it is easily altered by diagenesis and difficult to recognize in this study we examine carbonate rich tight oil mudstones of the lower cretaceous arshan formation in the erennaoer sag of the erlian basin as an example based on analyses of mineralogy stable carbon and oxygen isotopes and trace rare earth elements the original composition of the arshan mudstones has been reconstructed results show that the original arshan mudstone composition was mainly siliciclastic detritus tuffaceous and clay matrix which has a major impact on diagenesis and organic matter content the erupted volcanic ashes were beneficial to the introduction of nutrients an increase in biomass and an associated increase in to the preservation of organic matter which has been suggested by an improvement of toc of arshan tuffaceous mudstones with average contents of 2 82 the volcanic ashes in the studied mudstones had also enhanced methanogensis during the shallow burial additionally the early alteration products of authigenic minerals include analcime or zeolite most of which is entirely altered to analcime and chlorite the formation of major eogenetic carbonate cements include early dolomite and calcite which were related to volcanic materials and methanogenesis at shallow depths

atmospheric boundary layer structure and drag coefficients over sea ice this paper estimates the air sea drag coefficient for first year ice from recent aircraft measurements and reconciles the range of observed drag coefficients 103cd 1 2 3 7 referenced to 10 m for all sea ice types based on ice roughness and seasonal meteorology for the purpose of sea ice modeling it is necessary to define an effective drag coefficient which relates regional stress to regional wind because sea ice is heterogeneous on scales less than 20 km regional stress is influenced by the distribution of surface roughness the buoyancy flux from quasi periodic leads and external atmospheric conditions principally the inversion height 103cd is 1 3 1 5 for smooth ice but is much greater for nonflat surfaces for wind speeds greater than 5 m s and air temperatures below freezing the effective 103cd is 2 5 3 0 for nearly continuous pack ice such as first year ice in seasonal ice zones and central arctic basin the range of values of 103cd is 3 0 3 7 for unstable boundary layers typical of off ice winds in the marginal ice zone miz or even greater if the ice has been broken by a recent storm cd values at the lower end of these ranges are associated with low inversion heights these coefficients are confirmed by 103cd of 2 9 2 5 and 3 1 for first year sea ice calculated from gust probe data collected by the noaa p 3 aircraft interior to the inner miz in the bering sea during the marginal ice zone experiment mizex west in february 1983 and 103cd of 2 6 for the arctic calculated from arctic ice dynamics joint experiment aidjex aircraft data for february 1976 the effective drag coefficient with the presence of even a small concentration of sea ice is greater than the oceanic value as shown by a 103cd of 2 2 calculated from noaa p 3 gust probe data over a 40 km track of 0 4 ice concentration in the outer miz of the greenland sea in june 1984 during mizex 84 the relation of surface wind and stress to the geostrophic wind for shallow inversion heights typical of high latitudes is reviewed with a turbulent closure atmospheric boundary layer model the winter arctic is typified by low inversions 100 m low geostrophic drag coefficients and large geostrophic surface wind turning angles with low functional dependence on surface roughness seasonal ice zones are typified by a more modest influence of the inversion on boundary layer characteristics

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology