high pressure 2000 mpa kyanite and glaucophane bearing pelitic schist and eclogite from cordillera de la costa belt venezuela in the cretaceous melange of the cordillera de la costa belt introduction north central venezuela there are knockers of eclogite barroisitetwo belts of high pressure hp low temperature lt bearing eclogite and pelitic glaucophane schist these occur in a metamorphic rocks are exposed in the caribbean mounmetamorphic melange matrix that locally consists of marble sertain system of northern venezuela which is part of the pentinite amphibolite actinolite schist feldspathic schist and gneiss complex east west trending boundary zone between the graphitic schist chloritoid schist and garnet bearing mica schist caribbean and south american plates e g menendez the protoliths for these various rock types exhibit a wide age range 1966 1967 these two belts are the cordillera de la cambrian to early cretaceous recently discovered knockers of costa and villa de cura belts both of which were pelitic glaucophane schist contain mg glaucophane paragonite metamorphosed during the mid cretaceous presumably kyanite garnet talc graphite rutile quartz in a subduction zone related to the mid cretaceous the coexistence of kyanite and mg glaucophane suggests minimum leeward antilles volcanic arc e g pindell 1993 from p 2000 mpa at t 600 c eclogite knockers from the same jurassic to eocene time north and south america were outcrop contain garnet and clinopyroxene which yield 500 c for diverging and new proto caribbean sea floor was created cores 700 c for rims and p 1200 mpa the assemblage between them e g pindell 1993 therefore the leegarnet biotite phengite albite within schists of the melange matrix ward antilles arc as well as the entire caribbean mounof this locality indicates metamorphic conditions of t tain system are allochthonous and formed far to the 450 520 c at p 1800 mpa because all lithologies in this west as part of the farallon north south american plate outcrop record high p conditions this metamorphic melange formed boundary zone e g pindell 1993 before or during peak metamorphism in a mid cretaceous subduction although the two hp lt belts have similar metazone morphic ages they differ greatly in lithology and metamorphic history the cordillera de la costa belt consists of oceanic and passive continental margin rocks intermixed with paleozoic granites and granitic gneisses in this belt the eclogites and blueschists were retrograded to epidote amphiboliteand greenschist facies assemblages following an apparent p t path typical for

mis 3 to mis 1 temporal and lgm spatial variability in arctic ocean sea ice cover reconstruction from biomarkers using the sea ice proxy ip25 and phytoplankton derived biomarkers brassicasterol and dinosterol arctic sea ice conditions were reconstructed for marine isotope stage mis 3 to 1 with special emphasis on the last glacial maximum lgm in sediment cores from the northern barents sea continental margin across the central arctic ocean to the southern mendeleev ridge our results suggest more extensive sea ice cover than present day during latter part of mis 3 increasing sea ice growth during mis 2 and decreased sea ice cover during the last deglacial the summer ice edge remained north of the barents sea even during extremely cold i e last glacial maximum lgm as well as warm periods i e bolling allerod during the lgm the western svalbard margin and the northern barents sea margin areas were characterized by high concentrations of both ip25 and phytoplankton biomarkers interpreted as a productive ice edge situation caused by the inflow of warm atlantic water in contrast the lgm central arctic ocean north of 84 n was covered by thick permanent sea ice throughout the year with rare break up indicated by zero or near zero biomarker concentrations the spring summer sea ice margin significantly extended southwards to the laptev sea shelf southern lomonosov ridge and southern mendeleev ridge during the lgm our proxy reconstructions are very consistent with published model results based on the north atlantic arctic ocean sea ice model naosim

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

arctic sea ice variability in the context of recent atmospheric circulation trends abstract forty years 1958 97 of reanalysis products and corresponding sea ice concentration data are used to document arctic sea ice variability and its association with surface air temperature sat and sea level pressure slp throughout the northern hemisphere extratropics the dominant mode of winter january march sea ice variability exhibits out of phase fluctuations between the western and eastern north atlantic together with a weaker dipole in the north pacific the time series of this mode has a high winter to winter autocorrelation 0 69 and is dominated by decadal scale variations and a longer term trend of diminishing ice cover east of greenland and increasing ice cover west of greenland associated with the dominant pattern of winter sea ice variability are large scale changes in sat and slp that closely resemble the north atlantic oscillation the associated sat and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the tr

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

dynamical link between the barents kara sea ice and the arctic oscillation abstractthe recent accelerated arctic sea ice decline has been proposed as a possible forcing factor for midlatitude circulation changes which can be projected onto the arctic oscillation ao and or north atlantic oscillation nao mode however the timing and physical mechanisms linking ao responses to the arctic sea ice forcing are not entirely understood in this study the authors suggest a connection between november sea ice extent in the barents and kara seas and the following winter s atmospheric circulation in terms of the fast sea ice retreat and the subsequent modification of local air sea heat fluxes in particular the dynamical processes that link november sea ice in the barents and kara seas with the development of ao anomalies in february is explored in response to the lower tropospheric warming associated with the initial thermal effect of the sea ice loss the large scale atmospheric circulation goes through a series of dynamical adjustment processes the decelerated zonal mean zonal

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

sediment flux dynamics over the shallow 25 m depth shelf of the mediterranean sea along the israeli coast abstract in order to study the dynamics of sediment fluxes at the northern end of the nile littoral cell sediment traps were deployed for one year over the shallow shelf of the mediterranean sea offshore israel the sediment traps replaced monthly were suspended on a mooring line two kilometers offshore of the hadera power station 10 m above a 25 m deep seafloor sea state conditions near the traps were measured by an acoustic doppler profiler that provided the bottom water temperature wave heights and current s velocities and direction the measured sediment fluxes greatly varied between sampling periods with a minimum value of 1 8 g m 2 d 1 in autumn and a maximum value of 83 g m 2 d 1 in winter this variation was mostly effected by wave induced resuspension of sediment a strong correlation r2 0 97 was found between integrated wave heights that exceeded 1 5 m and the measured sediment fluxes based on the sea state conditions and sediment trap data we conclude that the direction of sand transport at the study area was strictly northwards and that almost all of the annual sand transport occurred during several high energy events in the winter fine particles that consisted the majority of the mass flux were absent in the underlying 25 m deep seafloor suggesting that they are very effectively winnowed off beyond the sand strip

seasonal and interannual variability of fast ice extent in the southeastern laptev sea between 1999 and 2013 along with changes in sea ice extent thickness and drift speed arctic sea ice regime is characterized by a decrease of fast ice season and reduction of fast ice extent the most extensive fast ice cover in the arctic develops in the southeastern laptev sea using weekly operational sea ice charts produced by arctic and antarctic research institute aari russia from 1999 to 2013 we identified five main key events that characterize the annual evolution of fast ice in the southeastern laptev sea linking the occurrence of the key events with the atmospheric forcing bathymetry freezeup and melt onset we examined the processes driving annual fast ice cycle the analysis revealed that fast ice in the region is sensitive to thermodynamic processes throughout a season while the wind has a strong influence only on the first stages of fast ice development the maximal fast ice extent is closely linked to the bathymetry and local topography and is primarily defined by the location of shoals where fast ice is likely grounded the annual fast ice cycle shows significant changes over the period of investigation with tendencies toward later fast ice formation and earlier breakup these tendencies result in an overall decrease of the fast ice season by 2 8 d yr which is significantly higher than previously reported trends

estimates of sea ice mechanical properties in the kara sea on the basis of available public data an approximate theoretical approach for characterizing the arctic sea ice engineering properties is explored and discussed in the kara sea the corrected era interim sea ice thickness and orap5 sea ice temperature database are selected as the basic ice physical parameters the formulas recommended by iso 19906 are chosen as the estimation criteria for the ice mechanical properties the generalized extreme value theory is used to analyze the ice extreme statistics specifically the typical mechanical properties including compressive strength flexural strength shear strength and elastic modulus are comprehensively studied the results reveal that all the mechanical properties show higher levels in the northeastern zone than in the southwestern zone with the heaviest ice regime around the southwestern severnaya zemlya in addition an uncertainty analysis is provided compared to the published measurements the snowless flexural strength values obtained are relatively conservative additionally the shear equation in iso 19906 should be pre corrected before practical application

impact of the atlantic meridional overturning circulation amoc on arctic surface air temperature and sea ice variability abstractthe simulated impact of the atlantic meridional overturning circulation amoc on the low frequency variability of the arctic surface air temperature sat and sea ice extent is studied with a 1000 year long segment of a control simulation of the geophysical fluid dynamics laboratory climate model version 2 1 the simulated amoc variations in the control simulation are found to be significantly anticorrelated with the arctic sea ice extent anomalies and significantly correlated with the arctic sat anomalies on decadal time scales in the atlantic sector of the arctic the maximum anticorrelation with the arctic sea ice extent and the maximum correlation with the arctic sat occur when the amoc index leads by one year an intensification of the amoc is associated with a sea ice decline in the labrador greenland and barents seas in the control simulation with the largest change occurring in winter the recent declining trend in the satellite observed sea ice extent also shows a similar pattern in t

arctic sea ice variability on a timescale of weeks and its relation to atmospheric forcing abstract northern hemisphere sea ice concentration 500 hpa height sea level pressure and 1000 500 hpa thickness at 7 day intervals are examined for the period 1972 1989 with emphasis on the winter season the temporal variability of sea ice concentration is largest along the climatological mean ice edge where its frequency distribution is strongly bimodal with ice free and ice covered conditions being observed much more frequently than partial ice cover these results confirm impressions based on visual inspection of satellite imagery that most of the variability in these regions is associated with the advance and retreat of the ice edge relationships between large scale patterns of atmospheric variability and sea ice variability are investigated making use of singular value decomposition of the temporal covariance matrix the analysis is conducted separately for the atlantic and pacific sectors in agreement with earlier studies based upon monthly mean data on sea ice concentration the strongest

longshore sand transport estimates along the mediterranean coast of israel in the holocene abstract the nile littoral cell one of the world s longest runs 650 km along the southeastern mediterranean from abu quir bay near alexandria egypt to haifa bay on the northern israeli coast haifa bay constitutes the northernmost final depositional sink of nile derived quartz sand transported from the nile delta by longshore currents generated by approaching breaking waves the northward net sand transport along the mediterranean coast of israel results from larger waves approaching from west south west and south west compared to their counterparts from west north west and north west this study utilizes an extensive new database gathered from sediment drill cores marine geophysical maps and field observations to measure the volume of sand deposited in haifa bay and the adjacent zevulun plain during the holocene it then compares this volume to recent data including measurements of sand accumulation along haifa port s main breakwater constructed in the southern entrance of the bay as well as longshore sand transport estimates along the northern carmel coast research findings estimate the annual average quantity of sand transported to haifa bay throughout the period at 80 000 90 000 m3 the findings further conclude that this amount has not changed appreciably over the past 75 years evaluating calculated values over the long term it is suggested that the characteristics of longshore sand transport along the coast of israel have not changed significantly during the past 7900 8500 years it is obvious that this conjecture should be treated with reservations

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

decadal climate oscillations in the arctic a new feedback loop for atmosphere ice ocean interactions a combined complex empirical orthogonal function analysis of 40 years of annual sea ice concentration sic and winter sea level pressure slp data reveals the existence of an approximately 10 year climate cycle in the arctic and subarctic the cycle is characterized by a clockwise propagating signal in the sic anomalies and a standing oscillation in the slp anomalies the latter being linked to a fluctuation between the two phases of the north atlantic oscillation to describe the formation and evolution of the sic and slp anomalies associated with the cycle a simple feedback loop is proposed

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

historical variability of sea ice edge position in the nordic seas 1 historical ice observations in the nordic seas from april through august are used to construct time series of ice edge position anomalies spanning the period 1750 2002 while analysis showed that interannual variability remained almost constant throughout this period evidence was found of oscillations in ice cover with periods of about 60 to 80 years and 20 to 30 years superimposed on a continuous negative trend the lower frequency oscillations are more prominent in the greenland sea while higher frequency oscillations are dominant in the barents the analysis suggests that the recent well documented retreat of ice cover can partly be attributed to a manifestation of the positive phase of the 60 80 year variability associated with the warming of the subpolar north atlantic and the arctic the continuous retreat of ice edge position observed since the second half of the 19th century may be a recovery after significant cooling in the study area that occurred as early as the second half of the 18th century

the occurrence and timing of high pressure metamorphism on margarita island venezuela a constraint on caribbean south america interaction the metamorphic rock sequences exposed on the island of margarita venezuela located in the southeastern corner of the caribbean plate margin are composed of a high pressure lowtemperature hp lt nucleus subducted to at least 50 km depth now structurally overlain by lower grade greenschist facies units lacking any sign of high pressure subduction zone metamorphism the hp lt nucleus involves protoliths of both oceanic metabasalts and intimately associated carbonaceous schists of the la rinconada unit peridotite massifs and continental affinity metapelites marbles and gneisses of the juan griego unit all hp lt units were joined together prior to the peak of high pressure metamorphism as shown by their matching metamorphic pressure temperature evolution the metamorphic grade attained produced barroisite as the regional amphibole glaucophane is not known from margarita contrary to a widely propagated assumption there are no major nappe structures post dating

biomarker distributions in surface sediments from the kara and laptev seas arctic ocean indicators for organic carbon sources and sea ice coverage studies of spatial and temporal changes in modern and past sea ice occurrence may help to understand the processes controlling the recent decrease in arctic sea ice cover here we determined concentrations of ip25 a novel biomarker proxy for sea ice developed in recent years phytoplankton derived biomarkers brassicasterol and dinosterol and terrigenous biomarkers campesterol and sitosterol in the surface sediments from the kara and laptev seas to estimate modern spatial seasonal sea ice variability and organic matter sources c25 hbi dienes and trienes were determined as additional palaeoenvironmental proxies in the study area furthermore a combined phytoplankton ip25 biomarker approach pip25 index is used to reconstruct the modern sea ice distribution more quantitatively the terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries reflecting the huge discharge by the major rivers ob yenisei and lena maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice free central part of the kara and laptev seas neither ip25 nor pip25 however shows a clear and simple correlation with satellite sea ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea ice diatom in the water column differences in the diene ip25 and triene ip25 ratios point to different sources of these hbis and different environmental conditions the diene ip25 ratio seems to correlate positively with sea surface temperature while negatively with salinity distributions

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

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

trace element geochemistry of iron titanium rich eclogitic rocks gruppo di voltri western liguria new analyses of rare earth and transition elements are summarized for 29 high pressure metamafic rocks which occur as lenses and layers in the beigua serpentinite of the ligurian alps included are data for 2 metarodingites 8 eclogites 5 glaucophanic eclogites 7 barroisitic amphibolites and 7 porphyroblastic greenschists trace element data similar to major element compositions previously presented show broadly intergradational chemistries among the several lithologies rare earth distributions are relatively flat at 10 30xchondrite with lree relative depletions transition elements exhibit a marked decrease in abundance with increasing atomic number but patterns are characterized by positive anomalies for ti mn fe and ni the bulk rock trace element concentrations are analogous to those of oceanic tholeiites similar ree patterns and overlapping ranges and sensibly identical transition element patterns demonstrate that a continuous spectrum of compositions is present in the analyzed rocks

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

the ecologite bearing metabasaltic sequence of isla margarita venezuela a geochemical study abstract xrf analyses for twenty elements in 41 samples and rnaa for eight ree in ten samples have been carried out as part of a continuing project to elucidate the geological history of the la rinconada group metabasites of margarita island venezuela through the study of continuous and discontinuous metamorphic reactions the study of variations in amphibole composition and by means of a large scale survey of bulk rock geochemistry all together twelve sampling points taken along a continuous metamorphic profile were considered with grade increasing from chlorite bearing amphibolites to paragonite bearing amphibolites to end up into amphibole bearing eclogites the entire section lies within the p t field of conditions of the epidote amphibolite facies the la rinconada group as a whole has a basaltic character although sio 2 may reach as much as 54 despite being macroscopically monotonous the metabasites are chemically variable with fractionation indices i e feo mgo varying by a factor of 5 from 0 48 to 2 66 there is no correlation between the zonation in the metamorphic mineral assemblages and the bulk rock chemistry so that this zonation must reflect only variations in the intensive parameters of metamorphism a definitive distinction between morb and iat or the pia classification of donnelly and rogers 1978 is not yet possible on the basis of the present partial data set the lil elements which are notoriously mobile suggest an iat affinity however the relatively immobile elements ti cr zr and y favour morb ree patterns and enrichment factors which are also considered fairly reliable criteria display characteristics between those typical of morb and pia

ice core data evidence for a prominent near 20 year time scale of the atlantic multidecadal oscillation 1 using five ice core data sets combined into a single time series we provide for the first time strong observational evidence for two distinct time scales of arctic temperature fluctuation that are interpreted as variability associated with the atlantic multidecadal oscillation amo the dominant and the only statistically significant multidecadal signal has a time scale of about 20 years the longer multidecadal variability of 45 85 years is not well defined and none of the time scales in this band is statistically significant we compare these observed temperature fluctuations with results of coupled climate model simulations hadcm3 and gfdl cm2 1 both the 20 25 year and a variable longer amo time scale are prominent in the models long control runs this periodicity supports our conjecture that the observed ice core fluctuations are a signature of the amo the robustness of this short time scale period in both observations and model simulations has implications for understanding the dominant amo mechanisms in climate

seasonal and regional manifestation of arctic sea ice loss abstractthe arctic ocean is currently on a fast track toward seasonally ice free conditions although most attention has been on the accelerating summer sea ice decline large changes are also occu

interannual variability of summer sea ice thickness in the siberian and central arctic under different atmospheric circulation regimes extensive drill hole and electromagnetic induction measurements of sea ice thickness in the siberian and central arctic seas in the summers of 1993 1995 and 1996 reveal significant interannual variability in the laptev sea minimum and maximum modal first year ice thicknesses amounted to 1 25 and 1 85 m in 1995 and 1996 respectively ice thickness correlates with ice extent which reached a record minimum in august 1995 and was well above average in 1996 these differences are explained by the strength and location of a summer cyclonic atmospheric circulation pattern affecting both ice advection and surface melt from drifting buoys deployed in 1995 and satellite radar backscatter data first and second year ice regimes are delineated differences in first year ice backscatter coefficients between 1993 1995 and 1996 are explained by differences in level ice surface roughness the lagrangian evolution of ice thickness between 1995 and 1996 is studied while the shape of the thickness distribution does not change significantly the mean modal ice thickness of the ice field increases from 1 80 m 1 25 m in 1995 to 2 86 m 2 25 m in 1996 the thickness distribution of second year ice in 1996 closely agrees with that of level multiyear ice downstream in the transpolar drift obtained in 1991 in 1996 mean level ice thickness increases at 0 23 and 0 16 m deg 1 with latitude in the kara and laptev sea sectors of the arctic ocean respectively

the eclogite bearing series of isla margarita venezuela geochemistry of metabasic lithologies in the la rinconada and juan griego groups abstract xrf analysis for major and minor elements in 94 samples of the metabasic la rinconada group and in 28 samples of metabasic lithologies in the predominantly metasedimentary overlying juan griego group of isla margarita venezuela has been carried out to compare the bulk compositions of the two eclogite bearing metabasic suites the two units differ in the age and geological setting of the protolith the la rinconada group has a monotonous basaltic character but shows irregular variations in bulk composition which are interpreted to reflect variations in the type of protolith ranging from basaltic lava flow to gabbroic cumulitic dyke as a whole the la rinconada group is related to a source of tholeiitic composition in a morb type volcanic hypabyssal environment the juan griego metabasic rocks are compositionally more homogeneous and uniformly basaltic in their major elements again reflecting a tholeiitic source and a morb type environment despite their contrasting geological setting the two suites of metabasic rocks can be inferred to have had a similar source and have probably developed in a passive atlantic type continental margin setting we infer that the la rinconada group represents early oceanic crust later covered by the siliceous continent derived clastics of the juan griego group in which the minor basaltic intrusions represent the last stages of waning magmatic activity

energetics of multidecadal atlantic ocean variability abstractoscillatory behavior of the atlantic meridional overturning circulation moc is thought to underlie atlantic multidecadal climate variability while the energy sources and sinks driving the mean moc have received intense scrutiny over the last decade the governing energetics of the modes of variability of the moc have not been addressed to the same degree this paper examines the energy conversion processes associated with this variability in an idealized north atlantic ocean model in this model the multidecadal variability arises through an instability associated with a so called thermal rossby mode which involves westward propagation of temperature anomalies applying the available potential energy ape framework from stratified turbulence to the idealized ocean model simulations the authors study the multidecadal variability from an energetics viewpoint the analysis explains how the propagation of the temperature anomalies leads to changes in ape which are subsequently converted into t

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

equilibration conditions of eclogite lenses from isla margarita venezuela implications for the tectonic evolution of the metasedimentary juan griego group abstract the constituent primary and secondary minerals in a suite of fifteen samples of eclogite amphibole eclogite and garnet amphibolite scattered as boudins and pods in metapelitic schists and gneisses on isla margarita venezuela have been analysed by electron microprobe to augment existing bulk rock chemical data the large sample population available allows spurious effects of stoichiometric fe3 calculation procedures and bulk rock influence to be recognised and eliminated all samples belong to one population with a relatively homogeneous character the equilibration temperatures are derived from fe 2 mg fractionation between garnet and clinopyroxene and range from 525 650 c jadeite contents of clinopyroxene and the persistence of minor stable albite constrain pressures to between 13 and 19 kbar combined with new evidence for high pressure metamorphism in the enclosing metapelites and with existing data on an eclogitic metabasic unit exposed in north eastern isla margarita la rinconada group these data show convincingly that the margarita crustal block is and has been a relatively coherent unit ever since the entire complex suffered high pressure metamorphism in late mesozoic times

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

desert flash floods form hyperpycnal flows in the coral rich gulf of aqaba red sea abstract running rivers are very scarce in globally distributed hyperarid and arid coastlines 28 000 km worldwide and it is ephemeral rivers that carry most terrestrial sediment into the sea in these regions however there is very little information regarding the contribution of terrestrial sediment and dynamics of transport of sediment that enter marine basins from these rivers one hyperarid region the gulf of aqaba received an exceptional number of flashflood events during the winter of 2012 2013 the results illustrate for the first time how the high volume of flashflood sediment influences the distribution of coral reefs dwarfs the contribution of airborne dust elevates floodwater densities to produce hyperpycnal flows despite highest ocean salinities and is subsequently transported to the deep basin where it may be preserved as a climate archive

arctic sea ice thickness remained constant during the 1990s the ice cover of the arctic ocean is considered to be a sensitive indicator of global climate change recent research using submarine based observations suggests that the arctic ice cover was thinner in the 1990s compared to an earlier period 1958 1979 and that it continued to decrease in thickness in the 1990s here i analyze subsurface ice thickness draft of arctic sea ice from six submarine cruises from 1991 to 1997 this extensive data set shows that there was no trend towards a thinning ice cover during the 1990s data from the north pole shows a slight increase in mean ice thickness whereas the beaufort sea shows a small decrease none of which are significant transects between the two areas from 76 n to 90 n also show near constant ice thicknesses with a general spatial decrease from the pole towards the beaufort sea combining the present results with those of an earlier study i conclude that the mean ice thickness has remained on a near constant level around the north pole from 1986 to 1997

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

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

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

the interior shelves of the arctic ocean physical oceanographic setting climatology and effects of sea ice retreat on cross shelf exchange abstract the interior shelves of the arctic mediterranean are the shelves of the kara sea laptev sea east siberian sea and beaufort sea they comprise approximately 40 of the total arctic shelf area 2 5 10 6 km 2 and are distinguished from inflow and outflow shelves by their principal forcing dynamics along their southern continental boundary the interior shelves are dominated by the major arctic rivers receiving over 80 of the total freshwater input to the arctic ocean in the mid shelf region wind and ice motion surface stresses dominate mixing and circulation resulting in high variability along their northern seaward boundary they are forced by upwelling and downwelling favourable surface stresses which drive shelf basin exchanges with atlantic and pacific origin cyclonic boundary currents over the upper slope shelf basin exchange is further modified by shelf break morphometry e g canyons valleys headlands and bottom slope here we review the physical oceanographic settings and forcing of the interior shelves and then focus on shelfbreak exchange and supply of nutrients for new primary production due to upwelling across the shelfbreak as a proxy for this nutrient supply we show seasonal and annual time series of along shelfbreak surface stress due to wind and ice motion from 1979 to 2011 we apply this analysis to the shallow shelves from the kara sea to the beaufort sea and comment on recent increases due to atmospheric changes and sea ice retreat

unprecedented low twentieth century winter sea ice extent in the western nordic seas since a d 1200 we reconstructed decadal to centennial vari ability of maximum sea ice extent in the western nordic seas for a d 1200 1997 using a combination of a regional tree ring chronology from the timberline area in fennoscandia and d 18 o from the lomonosovfonna ice core in svalbard the reconstruction successfully explained 59 of the variance in sea ice extent based on the calibration period 1864 1997 the significance of the reconstruction statistics reduction of error coefficient of efficiency is computed for the first time against a realistic noise background the twentieth century sustained the lowest sea ice extent values since a d 1200 low sea ice extent also occurred before mid seventeenth and mid eighteenth centuries early fifteenth and late thirteenth centuries but these periods were in no case as persistent as in the twentieth century largest sea ice extent values occurred from the seventeenth to the nineteenth centuries during the little ice age lia with relatively smaller sea ice covered area during the sixteenth century mod erate sea ice extent occurred during thirteenth fifteenth centuries reconstructed sea ice extent variability is dominated by decadal oscillations frequently associated with decadal components of the north atlantic oscilla tion arctic oscillation nao ao and multi decadal lower frequency oscillations operating at 50 120 year sea ice extent and nao showed a non stationary rela tionship during the observational period the present low sea ice extent is unique over the last 800 years and results from a decline started in late nineteenth century after the lia

cyclone climatology of the bering sea and its relation to sea ice extent abstract a monthly storm track climatology is derived from monthly maps of cyclone tracks for the winter season october through march averaged over 23 years 1957 58 1979 80 for a 2 latitude 4 longitude grid bounded by 51 n 65 n 157 w and 171 e there is a decrease in the number of cyclones with latitude in all months and division into two storm tracks one propagating north northeast along the siberian peninsula and one entering the southern bering sea on a northeasterly course and either curving northward into the central bering sea or continuing parallel to the aleutian island chain monthly average ice extents are established for february and march 1958 80 along a line from norton sound southwest toward the ice edge perpendicular to the average maximum extent comparison of composite cyclone charts summed over the winter season and over the five heaviest and five lightest ice years shows a shift in cyclone centers toward the west in light ice years the correlation between maximum seasonal ice

observed sea ice extent in the russian arctic 1933 2006 1 we present a time series of sea ice extent in the russian arctic based on observational sea ice charts compiled by the arctic and antarctic research institute aari these charts are perhaps the oldest operational sea ice data in existence and show that sea ice extent in the russian arctic has generally decreased since the beginning of the chart series in 1933 this retreat has not been continuous however for the russian arctic as a whole in summer there have been two periods of retreat separated by a partial recovery between the mid 1950s and mid 1980s the aari charts combined with air temperature records suggest that the retreat in recent decades is pan arctic and year round in some regions whereas the early twentieth century retreat was only observed in summer in the russian arctic the aari ice charts indicate that a significant transition occurred in the russian arctic in the mid 1980s when its sea ice cover began to retreat along with that of the rest of the arctic summertime sea ice extents derived from the aari data set agree with those derived from passive microwave including the hadley centre s global sea ice coverage and sea surface temperature hadisst data set the hadisst results do not indicate the 1980s transition or the partial recovery that took place before it the aari charts therefore add significantly to our understanding of the variability of arctic sea ice over the last 8 decades and we recommend their inclusion in future historical data sets of arctic sea ice

a signal of persistent atlantic multidecadal variability in arctic sea ice satellite data suggest an arctic sea ice climate system in rapid transformation yet its long term natural modes of variability are poorly known here we integrate and synthesize a set of multicentury historical records of atlantic arctic sea ice supplemented with high resolution paleoproxy records each reflecting primarily winter spring sea ice conditions we establish a signal of pervasive and persistent multidecadal 60 90 year fluctuations that is most pronounced in the greenland sea and weakens further away covariability between sea ice and atlantic multidecadal variability as represented by the atlantic multidecadal oscillation amo index is evident during the instrumental record including an abrupt change at the onset of the early twentieth century warming similar covariability through previous centuries is evident from comparison of the longest historical sea ice records and paleoproxy reconstructions of sea ice and the amo this observational evidence supports recent modeling studies that have suggested that arctic sea ice is intrinsically linked to atlantic multidecadal variability this may have implications for understanding the recent negative trend in arctic winter sea ice extent although because the losses have been greater in summer other processes and feedbacks are also important

115 year ice core data from akademii nauk ice cap severnaya zemlya high resolution record of eurasian arctic climate change from 1999 to 2001 a 724 m deep ice core was drilled on akademii nauk ice cap severnaya zemlya to gain high resolution proxy data from the central russian arctic despite strong summertime meltwater percolation this ice core provides valuable information on the regional climate and environmental history we present data of stable water isotopes melt layer content and major ions from the uppermost 57 m of this core covering the period 1883 1998 dating was achieved by counting seasonal isotopic cycles and using reference horizons multi annual 18 o values reflect eurasian sub arctic and arctic surface air temperature variations we found strong correlations to instrumental temperature data from some stations e g r 0 62 for vardo northern norway the 18 o values show pronounced 20th century temperature changes with a strong rise about 1920 and the absolute temperature maximum in the 1930s a recent decrease in the deuterium excess time series indicates an increasing role of the kara sea as a regional moisture source from the multi annual ion variations we deduced decreasing sea salt aerosol trends in the 20th century as reflected by sodium and chloride whereas sulphate and nitrate are strongly affected by anthropogenic pollution

picrites as parental magma of morb type tholeiites recent experimental work on peridotites and basalts1 3 and a reappraisal of ophiolite complexes4 supports the concept that basalts are derived from picritic parents5 7 the occurrence of a density minimum in the liquid line of descent8 10 explains why mid ocean ridge tholeiites fall in a restricted compositional range and parental picrites can only be found in the exceptional case when eruption is not yet controlled by a steady state magma chamber7 11 we present here a preliminary account of a natural example of such a case from the caribbean