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

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

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

sedimentary pyrite a window into the microbial past early diagenetic pyrite forms as a result of microbial processes in sediments but has received little attention as a potential source of microbial fossils sedimentary pyrite grains archean to jurassic in age were examined by scanning and transmission electron microscopy tem ion milling was essential for the preparation of electron transparent tem samples most pyrite grains revealed coccoid rod shaped and even filamentous features that are interpreted as microbial identification of microbial remains in sedimentary pyrite may greatly expand our knowledge of microbial life in the sedimentary record combined with geochemical characterization the study of pyritized microbes in the geologic record may in the future enable us to interpret changes in geochemical signatures more realistically in terms of different sulfate reducing communities sedimentary pyrite grains may also represent a good prospect to further our knowledge of past life on mars

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

spatial variation in the influence of the north atlantic oscillation on precipitation across greenland 1 ice core derived accumulation records from greenland have been proposed as proxies for north atlantic oscillation nao reconstruction in a series of single site analyses accumulation records from ice cores drilled in western greenland were found to exhibit the strongest linear association with nao in this paper we expand on these findings by proposing a spatiotemporal statistical model to explore further the relationship between nao and the accumulation records from 35 firn and ice cores drilled in western and southern greenland in particular we propose a temporal extension of the bayesian spatially varying coefficient regression model which is fit using a markov chain monte carlo algorithm this model readily accommodates the irregular features of the data i e variation in record lengths and irregular spacing among ice core locations and the serial dependence within individual records using our statistical model we are able to exploit the spatial dependence structure of the derived accumulation nao relationship to explore the regional patterns in the strength of this relationship our findings support previous work that identified a region in western greenland where derived accumulation is most correlated with nao however we also identify a region further inland to the east and south where the estimated strength of the linear accumulation nao relationship is weaker but more certain than in the previously identified region thus our findings can be used to guide decisions regarding where to locate future drilling efforts in greenland by weighing the trade off between the potential strength of the accumulation nao relationship and its uncertainty

a pathway connecting the monsoonal heating to the rapid arctic ice melt abstractthis study provides a monsoonal link to the rapid arctic ice melt each year the planetary scale african asian monsoonal outflow near the tropopause carries a large anticyclonic gyre that has a longitudinal spread that occupies nearly half of the entire tropics in recent years the south asian summer monsoon has experienced increased rainfall over northwestern india and pakistan and it has also contributed to more intense local anticyclonic outflows from this region the western lobes of these intense upper high pressure areas carry outflows with large heat fluxes from the monsoon belt toward central asia and eventually to the region of the rapid ice melt of the canadian arctic in this study this spectacular pathway has been defined from airflow trajectories heat content and heat flux anomalies most of these show slow increasing trends in the last 20 years the monsoonal connection to the rapid arctic ice melt is a new contribution of this study this is shown from the passage of a vertical c

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

amino acids of proterozoic and ordovician sulphide coated grains from western canada record of biologically mediated pyrite precipitation abstract early diagenetic sulphide coated grains from a quartz arenite of the helikian siyeh formation of southern alberta and british columbia and from sandstones of the ordovician winnipeg formation of saskatchewan contain 9 17 26 10 mol g 1 protein amino acids and 3 74 18 19 mol g 1 non protein amino acids the protein amino acid content of the whole rock varies from 120 07 to 315 36 nmol g 1 and the non protein from 91 31 to 241 29 nmol g 1 the sulphide coated grains contain approximately three times the amount of amino acids reported in modern carbonate ooids and 100 times that in jurassic ooids from italy the abundance of total amino acids and the relative abundance of the s containing methionine supports the previously proposed genesis of these grains involving bacterial reduction of seawater sulphate the occurrence of unstable and non racemized amino acids in the sulphide coated grains and their low concentration in the matrix is interpreted as evidence of exceptional preservation and not of contamination the virtually identical average amino acid content and composition of proterozoic and ordovician sulphide coated grains suggest similar processes of sulphide precipitation and also a uniquely similar preservation of the amino acids due to the differences in age and geological history of the two formations

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

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

multiple flow regimes in the northern hemisphere winter part i methodology and hemispheric regimes abstract recurrent and persistent flow patterns are identified by examining multivariate probability density functions pdfs in the phase space of large scale atmospheric motions this idea is pursued systematically here in the hope of clarifying the extent to which intraseasonal variability can be described and understood in terms of multiple flow regimes bivariate pdfs of the northern hemisphere nh wintertime anomaly heights at 700 mb are examined in the present paper using a 37 year dataset the two dimensional phase plane is defined by the two leading empirical orthogonal functions eofs of the anomaly fields pdfs on this plane exhibit synoptically intriguing and statistically significant inhomogeneities on the periphery of the distribution it is shown that these inhomogeneities are due to the existence of persistent and recurrent anomaly patterns well known as dominant teleconnection patterns that is the pacific north american pna pattern its reverse and zonal and blocked phases of the

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

observed interaction between pacific sea ice and the western pacific pattern on intraseasonal time scales the relationship between north pacific sea ice and the western pacific wp pattern is examined using wintertime observational data between 1978 and 2008 weekly averaged data are chosen to capture the characteristically short time scale of the wp a clear relationship is found between the wp and sea ice concentrations in the bering sea where the positive polarity of the wp is accompanied by increasing sea ice concentrations and the negative wp by decreasing sea ice concentrations sea ice concentrations in the sea of okhotsk however are shown to be largely insensitive to the strength of the wp feedback of bering sea sea ice concentrations onto the wp is tested by fitting weekly averaged observations to a vector autoregressive var model results from the var model indicate that feedback of bering sea sea ice onto the wp plays a significant role in the dynamics of the wp and that this feedback is positive that is wp induced changes in bering sea sea ice concentrations help sustain existing wp conditions thereby lengthening the time scale of variability of the wp

variability of north pacific sea ice and east asia north pacific winter climate abstract sea ice variability in the north pacific and its associations with the east asia north pacific winter climate were investigated using observational data two dominant modes of sea ice variability in the north pacific were identified the first mode features a dipole pattern between the sea of okhotsk and the bering sea the second mode is characterized by more uniform ice changes throughout the north pacific using the principal components of the two dominant modes as the indices pc1 and pc2 analyses show that the positive phases of pc1 feature a local warming cooling in the sea of okhotsk the bering sea which is associated with the formation of the anomalous anticyclone extending from the northern pacific to siberia accompanied by a weakening of the east asian jet stream and trough the associated anomalous southeasterlies easterlies reduce the climatological northwesterlies westerlies leading to warm and wet conditions in northeast china and central siberia the positive phases of pc2

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

structural collapse in kaolinite montmorillonite and illite clay and its role in the ceramic rehydroxylation dating of low fired earthenware the rehydroxylation dating of ancient pottery estimates the age of ceramic manufacture based upon the total hydroxyl oh accumulation since initial firing the diffusion of oh is impacted by the structural porosity of the ceramic that becomes progressively or suddenly closed with increasing temperature as the clay structure collapses changes in ceramic mineral structure along the temperature continuum occur at certain thermal set points infrared spectroscopic analysis of heat treated kaolin illite and montmorillonite reveals that shifts in the si o band correlate with the extent of structural collapse occurring between 600 and 1000 c accelerated rehydroxylation experiments reveal that the activation energy of rehydroxylation decreases with greater structural collapse and indicates that the rate of rehydroxylation will be faster for ceramics fired at more elevated temperatures

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

sea ice anomalies observed in the greenland and labrador seas during 1901 1984 and their relation to an interdecadal arctic climate cycle two independent ice data sets from the greenland and labrador seas have been analyzed for the purpose of characterizing interannual and decadal time scale sea ice extent anomalies during this century sea ice concentration data for the 1953 1984 period revealed the presence of a large positive anomaly in the greenland sea during the 1960s which coincided with the great salinity anomaly an upper ocean low salinity water mass that was observed to travel cyclonically around the northern north atlantic during 1968 1982 this ice anomaly as well as several smaller ones propagated into the labrador sea and then across to the labrador and east newfoundland coast over a period of 3 to 5 years a complex empirical orthogonal function analysis of the same data also confirmed this propagation phenomenon an inverse relation between sea ice and salinity anomalies in the greenland labrador sea region was also generally found an analysis of spring and summer ice limit data obtained from danish meteorological institute charts for the period 1901 1956 indicated the presence of heavy ice conditions i e positive ice anomalies in the greenland sea during 1902 1920 and in the late 1940s and generally negative ice anomalies during the 1920s and 1930s only limited evidence of the propagation of greenland sea ice anomalies into the labrador sea was observed however probably because the data were from the ice melt seasons on the other hand several large ice anomalies in the greenland sea occurred 2 3 years after large runoffs in the early 1930s and the late 1940s from northern canada into the western arctic ocean similarly a large runoff into the arctic during 1964 1966 preceded the large greenland sea ice anomaly of the 1960s these facts together with recent evidence of climatic jumps in the northern hemisphere tropospheric circulation suggest the existence of an interdecadal self sustained climate cycle in the arctic in the greenland sea this cycle is characterized by a state of large sea ice extent overlying an upper layer of cool relatively fresh water that does not convectively overturn which alternates every 10 15 years with a state of small sea ice extent and relatively warm saline surface water that frequently overturns

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

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

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

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

low frequency variability in the northern hemisphere winter geographical distribution structure and time scale dependence abstract low frequency variability in wintertime 500 mb height is examined with emphasis on its structure geographical distribution and frequency dependence a 39 year record of 500 mb geopotential height fields from the nmc analyses is time filtered to partition the fluctuations into frequency bands corresponding to periods of 10 60 days 60 180 days and 180 days winter is defined as the six month period november through april variance teleconnectivity and anisotropy fields and selected loading vectors derived from orthogonal and oblique rotations of the eigenvectors of the temporal correlation matrix for each band are shown and discussed the variability in all frequency bands exhibits substantial anistropy with meridionally elongated features arranged as zonally oriented wave trains prevailing over the continents and zonally elongated features organized in the form of north south oriented dipole patterns prevailing over the oceanic sectors of the hemisphere the wave trains are most pronounc

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

atmosphere ocean coupled variability in the south atlantic abstract the climate variability of the south atlantic region is determined from 40 yr 1953 92 of comprehensive ocean atmosphere data set monthly sea surface temperature sst and sea level pressure slp data using the empirical orthogonal function eof and the singular value decomposition svd analysis methods the eof method is applied to each field separately whereas the svd method is applied to both fields simultaneously the significance of the atmosphere ocean interaction is revealed by a strong resemblance between individual eof and coupled svd modes of sst and slp the three leading modes of coupled variability on interannual and interdecadal timescales are discussed in some detail the first coupled mode which accounts for 63 of the total square covariance represents a 14 16 yr period oscillation in the strength of the subtropical anticyclone accompanied by fluctuations of a north south dipole structure in the sst the atmosphere ocean coupling is strongest during the southern summe

sulphide ooids from the proterozoic siyeh formation of alberta canada sulphide ooids from 0 5 to 4 mm in diameter occur over a large area in a thin arenite bed near the base of the proterozoic siyeh formation in southwestern alberta examination by optical microscope scanning electron microscope and electron microprobe reveals that the ooids are composed of concentric layers a few micrometers to a few tens of micrometers thick of pyrite and chalcopyrite covellite is also present in several ooids copper sulphides are more abundant towards the centre of the ooids than in the outer shells where pyrite is predominant a slightly eccentric nucleus of chalcopyrite and or titanium oxide occurs in several ooids it is speculated that the ooids grew during early diagenesis of the arenite and that the source of metals were black argillaceous sediments above and below the arenite the nucleation of sulphides around detrital grains of chalcopyrite and titanium oxide has an important bearing on metallogenetic models of stratiform copper deposits

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

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

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

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

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

bacteria as nucleation sites for authigenic minerals in a metal contaminated lake sediment abstract sediment samples contaminated with metals arising from mine tailings drainage were obtained from lower moose lake in the onaping region near sudbury ontario canada the samples were examined by electron microscopy selected area electron diffraction and energy dispersive x ray spectroscopy individual bacterial cells and their remains were prominent as nucleation sites for both metal sulfides and a complex polymorphic fe al silicate the principal metal sulfide species associated with the bacteria were amorphous mackinawite fes 1 x and microcrystalline millerite nis trace amounts of cu and zu were also detected in some of the sulfide precipitates at least two structural forms of the fe al silicate were present and energy dispersive x ray spectroscopy point analyses revealed corresponding differences in chemical composition poorly ordered limonitic clay type phases had a granular morphology and contained less fe than well developed crystalline material which generated hexagonal diffraction patterns with reflections d 4 60 and 2 55 characteristic of an interstratified chamositic clay

the atmospheric response to realistic arctic sea ice anomalies in an agcm during winter abstract the influence of realistic arctic sea ice anomalies on the atmosphere during winter is investigated with version 3 6 of the community climate model ccm3 6 model experiments are performed for the winters with the most 1982 83 and least 1995 96 arctic ice coverage during 1979 99 when ice concentration estimates were available from satellites the experiments consist of 50 member ensembles using large ensembles proved critical to distinguish the signal from noise the local response to ice anomalies over the subpolar seas of both the atlantic and pacific is robust and generally shallow with large upward surface heat fluxes 100 w m 2 near surface warming enhanced precipitation and below normal sea level pressure where sea ice receded and the reverse where the ice expanded the large scale response to reduced enhanced ice extent to the east west of greenland during 1982 83 resembles the negative phase of the arctic oscillation north atlantic oscillation ao nao with a ridge over t

variability in bering sea ice cover as affected by a regime shift in the north pacific in the period 1947 1996 in the late 1970s a regime shift or step occurred in the climate of the north pacific causing among many other effects a 5 reduction in the ice cover in the eastern bering sea as well as shifts in the position of the aleutian low analyses of the aleutian low from monthly mean northern hemisphere sea level pressure for winters december march for 1947 1996 are presented and compared with monthly mean ice cover from the bering sea for 1952 1996 the southern oscillation index and the western pacific oscillation before the regime shift below normal ice cover in the bering sea was typically associated with el nino conditions which caused the aleutian low to move eastward of normal carrying warm pacific air over the bering sea conversely above normal ice cover was associated with la nina conditions which caused the aleutian low to move westward of normal allowing higher pressure to move over the bering sea since the regime shift during el ninos the aleutian low has been moving even farther east causing winds to blow from the east and north off alaska and resulting in above normal ice in the bering sea before the regime shift the occurrence of el nino and la nina conditions was about even since the regime shift el nino conditions are about 3 times more prevalent in recent work e g mantua et al 1997 minobe 1997 there is evidence that this regime shift is the latest in a series of climate shifts going back to at least the late 1800s and may be due to a 50 to 70 year oscillation in a north pacific atmospheric ocean coupled system

are the intensities and durations of small scale pottery firings sufficient to completely dehydroxylate clays testing a key assumption underlying ceramic rehydroxylation dating rehydroxylation rhx dating was recently suggested as a simple cheap and accurate method for dating ceramics it depends on the constant rate of rehydroxylation the slow reintroduction of oh of clays after they are fired and dehydroxylated purged of oh during the production of pots bricks or other ceramics the original firing of the ceramic artifact should set the dating clock to zero by driving all hydroxyls out of the clay chemical structure to examine whether this assumption holds especially for pot firings of short duration and low intensity as those in small scale traditional settings we performed thermogravimetric analysis of clay samples of known mineralogy at temperatures and for durations reported from traditional sub saharan american and south asian pottery firings results demonstrate that in the majority of samples complete dehydroxylation dhx did not occur within or even beyond the conditions common in traditional firings consequently between 0 01 and 1 5 of a sample s mass in residual oh may remain after firings analogous to those observed in the ethnographic record lack of complete dhx at the scales we have observed can result in the over estimation of ceramic ages by decades to tens of thousands of years depending largely on the age of the sample and the amount of residual oh present thus in many cases a key assumption underlying current rhx dating methods is unlikely to have been met introducing considerable error in dates

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

early biodegradation of ligneous organic materials and its relation to ore deposition in the treves zn pb ore body gard france abstract previous petrographical and geochemical studies on the organic content of mineralized and non mineralized carbonate series in the treves zn pb stratiform deposit led to the conclusion that ore deposition occurred during the diagenetic history of the sediments in a mixed fresh hydrothermal system gauthier and disnar 1984 gauthier et al 1985a these circulations of fluids are probably responsible for the dolomitization of the original limestones and for the deposition of the ore through microbial activity gauthier 1984 gauthier el al 1985b the occurrence of this activity is supported by the formation of two kinds of organic components which are attributable to this uncommon bio alteration process alphatic rich bitumen like products and aromatic polyethers the chemical composition of these two types of compounds suggests that they were produced from ligneous debris by sulfate reducing bacteria other indications of the occurrence of a biological activity have been found in the nature and relative abundance of microbial amino compounds however these constituents are thought to have been introduced only recently into the sediments whereas other evidence supports the idea that ore deposition occurred before diagenesis

organic microfacies and basinal tectonic control on source rock accumulation a microscopic approach with examples from an intracratonic and extensional basin abstract relationships among organic petrographic maceral assemblages and hydrocarbon source rock depositional environments distinguish broad marine terrestrial and mixed kerogen accumulation settings organic microfacies from paleozoic and mesozoic source rock intervals in the intracratonic williston basin and the extensional sverdrup basin have been studied using incident white and fluorescent light microscopy distinct anoxic organic microfacies are defined in upper ordovician bighorn group subtidal platformal kukersites and middle devonian upper elk point group carbonate lithologies that preserve a progression of depositional environments from platformal to starved basinal paleozoic carbonate platform microfacies are characterized by well preserved cyanophyceae alginite stromatolitic mats displaying upper surface textural features such as pustules pinnacles endolithic algal borings and interlaminated vertical and horizontal alginite resulting from phototactic growth potential source intervals in middle and upper triassic shelf shales from the sverdrup basin and middle devonian carbonate platform marginal mudstones in the williston basin are both characterized by high concentrations of sapropelic bituminite kerogen hosting unicellular marine alginite similar bituminite rich organic microfacies occur in middle devonian basinal settings associated with larger more abundant alginite and significant amounts of dasycladacean calcareous algae the main controls on source rock accumulation are water depth and chemistry as controlled by depositional setting and basin restriction

on the effect of organic carbon on rehydroxylation rhx dating scientific dating is an invaluable tool to understand the development of human civilizations from prehistoric to historic times ceramics is the most abundant material recovered from archaeological excavations but a satisfactory scientific dating method is still lacking so called rehydroxylation rhx dating promises precise age information but the validity of the method still has to be proven we have investigated one possible obstacle imposed by the presence of organic carbon in the samples such a contamination can lead to significant deviations of the dating result the amount of co2 released from the following samples was determined a medieval clay brick from alkoven austria two authentic archaeological samples from the iron age from megiddo israel a 1600 ad earthenware sherd from enkhuizen netherlands which had been successfully dated with rhx at another laboratory we investigated several possibilities to remove such contamination