eddy formation near the west coast of greenland abstract this paper extends a bracco and j pedlosky s investigation of the eddy formation mechanism in the eastern labrador sea by including a more realistic depiction of the boundary current the quasigeostrophic model consists of a meridional coastally trapped current with three vertical layers the current configuration and topographic domain are chosen to match as closely as possible the observations of the boundary current and the varying topographic slope along the west greenland coast the role played by the bottom intensified component of the boundary current on the formation of the labrador sea irminger rings is explored consistent with the earlier study a short localized bottom trapped wave is responsible for most of the perturbation energy growth however for the instability to occur in the three layer model the deepest component of the boundary current must be sufficiently strong highlighting the importance of the near bottom flow the model is able to reproduce important features o

eddies in the labrador sea as observed by profiling rafos floats and remote sensing abstract data from profiling rafos floats topex poseidon altimetry and the alongtrack scanning radiometer atsr aboard ers 1 have been used to describe the spatial and seasonal patterns of eddy variability in the labrador sea peaks in sea surface height ssh variability appear in two regions off the west greenland shelf near 61 5 n 52 w where the 3000 m isobath separates from the shelf and in the center of the basin at 58 n 52 w both locations show seasonal ranges in ssh variability of up to 40 mm with the greenland site having largest variability in january march leading the central site by 50 days a sea surface temperature image from the atsr at the greenland site shows numerous eddies both cyclonic and anticyclonic being formed by injection of west greenland current water into the labrador sea interior data from profiling rafos floats launched in 1997 as part of the labrador sea deep convection experiment are used to describe three of the west greenland current eddies in detail one of

stratigraphic context of old crow tephra holitna lowland interior southwest alaska abstract a thick deposit of old crow tephra was discovered in a bluff exposure along the middle holitna river near the kulukbuk hills 61 20 n latitude 157 10 w longitude in interior southwest alaska this locality is the southwesternmost known deposit of old crow tephra in alaska thickness and grain size data from this site support a source volcano in the eastern aleutian arc pleistocene stratigraphic sequences in the lowland are dominated by upward fining eolian sand sheet deposits and loess separated by organic silt these deposits record at least two episodes of regional glaciation and an intervening nonglacial period marine oxygen isotope stage 3 stage 5 or both old crow tephra crops out near the top of the lower upward fining eolian unit indicating that the ash erupted near the end of an interval of periglacial eolian sedimentation the sequence of eolian deposits that contain old crow tephra probably accumulated during the latter part of marine oxygen isotope stage 6 whereas the overlying eolian sequence formed during the last glaciation stage 2 this stratigraphic position is consistent with other stratigraphic contexts for the tephra and with fission track and thermoluminescence ages of ca 140 000 10 000 yr b p

frequency response properties of forced climatic sst anomaly variability in the north atlantic abstract frequency response properties of north atlantic 5 57 n sea surface temperature anomaly tsa variability with periods of several months to 20 years are characterized using the comprehensive ocean atmosphere data set coads significant direct forcing of tsa variability by the anomalous wind field primarily through the resulting anomalous surface turbulent heat flux is observed in the westerly wind and trade wind belts to characterize properties of the large scale climatic tsa response to this forcing over the entire frequency band resolved it is necessary to consider the dual role of anomalous surface heat flux as both the dominant local forcing mechanism and the dominant damping mechanism the latter through a negative linear feedback newtonian relaxation at frequencies where wind forcing is important good agreement exists between the frequency response function estimated from data and the same function theoretically predicted by a simple stochastic forcing model where the locally fo

restratification after deep convection abstract an important yet poorly understood aspect of the water mass transformation process in the ocean is the manner in which the convected fluid once formed is accommodated and drawn into the general circulation following violent mixing in the open ocean that creates a deep homogenous body of fluid restratification of the surface 500 m layer is observed to occur rapidly sealing over the convection patch recent hydrographic casts and tomography inversions in the gulf of lions by send et al for example show that very quickly within a week or so of the cessation of cooling a stratified near surface layer develops on top of the mixed patch this restratification occurs much more rapidly than can be accounted for by air sea fluxes by analytical and numerical study the authors argue that advection by geostrophic eddies spawned by the baroclinic instability of the mixed patch is likely to be a principal mechanism by which restratification occurs a restratification timescale restrat 56r

surprising return of deep convection to the subpolar north atlantic ocean in winter 2007 2008 in the process of open ocean convection in the subpolar north atlantic ocean surface water sinks to depth as a distinct water mass the characteristics of which affect the meridional overturning circulation and oceanic heat flux in addition carbon is sequestered from the atmosphere in the process in recent years this convection has been shallow or non existent which could be construed as a consequence of a warmer climate here we document the return of deep convection to the subpolar gyre in both the labrador and irminger seas in the winter of 2007 2008 we use profiling float data from the argo programme to document deep mixing analysis of a variety of in situ satellite and reanalysis data shows that contrary to expectations the transition to a convective state took place abruptly without going through a phase of preconditioning changes in hemispheric air temperature storm tracks the flux of fresh water to the labrador sea and the distribution of pack ice all contributed to an enhanced flux of heat from the sea to the air making the surface water sufficiently cold and dense to initiate deep convection given this complexity we conclude that it will be difficult to predict when deep mixing may occur again

boundary current eddies and their role in the restratification of the labrador sea an idealized model is used to study the restratification of the labrador sea after deep convection with emphasis on the role of boundary current eddies shed near the west coast of greenland the boundary current eddies carry warm buoyant irminger current water into the labrador sea interior for a realistic end of winter state it is shown that these irminger current eddies are efficient in restratifying the convected water mass in the interior of the labrador sea in addition it is demonstrated that irminger current eddies can balance a significant portion of the atmospheric heat loss and thus play an important role for the watermass transformation in the labrador sea

spectral characteristics of the excitation and propagation of lg from underground nuclear explosions in central asia the nonlinear inverse method of xie 1993 is applied to analyze lg spectra from many recent underground nuclear explosions in central asia the analysis simultaneously determines lg seismic moments m0 and corner frequencies fc of events as well as path variable lg q values and their frequency dependences at 1 hz lg q at 1 hz estimated for many paths from the lop nor and balapan test sites to various broadband incorporated institution for seismology chinese digital seismic network and kyrghizstan network stations agree well with path averaged lg coda q values from previously obtained tomographic maps for eurasia this suggests that the lg q values obtained in this inversion have not been significantly affected by focusing defocusing or other effects of three dimensional structural complexities the logarithms of lg m0 values obtained in this study correlate linearly with a slope of about 1 2 with international seismological centre isc body wave magnitudes mb the linear relationship is consistent with a previous empirical relationship found between the logarithm of p wave seismic moments and isc mb values the slope of the linear relationship also suggests that the logarithm of lg m0 is a more direct measure of event size than is mb which for larger events is affected by high frequency amplitude falloff another important finding of this study is that the m0 values for the explosions scale with fc 4 rather than with fc 3 as would be expected if stress drops were constant this is consistent with previous scaling relations derived using lg from earthquake sources and suggests that the difference between lg and local s excitation by the same source types explosion or earthquake may overwhelm that between the excitation of lg by different source types a comparison between lg m0 and fc values obtained using an explosion source model with those obtained using an earthquake source model suggests that the m0 values estimated using the explosion source model are systematically lower by a factor of 0 27 than those estimated using the earthquake source model this occurs even though the data used are the same in the inversions with the two types of source model the factor of 0 27 is therefore due to the source model dependence of the m0 fc estimates the overshoot and lower spectral levels at lower frequencies in the explosion source model tend to reduce both the estimated m0 and fc values this suggests that in any nuclear monitoring program the same type of source model either an earthquake or explosion should always be used to discriminate explosions using lg the source model dependence also suggests that more effort should be made to estimate the amount of overshoot in the lg excitation caused by various source types

dynamical response of the oceanic eddy field to the north atlantic oscillation a model data comparison abstract observational studies have shown that in many regions of the world ocean the eddy kinetic energy eke significantly varies on interannual time scales comparing altimeter derived eke maps for 1993 and 1996 stammer and wunsch have mentioned a significant meridional redistribution of eke in the north atlantic ocean and suggested the possible influence of the north atlantic oscillation nao cycle this hypothesis is examined using 7 yr of ocean topography experiment topex poseidon altimeter data and three resolution atlantic ocean model simulations performed over the period 1979 2000 during the french clipper experiment the subpolar subtropical meridional contrast of eke in the real ocean appears to vary on interannual time scales and the model reproduces it realistically the nao cycle forces the meridional contrast of energy input by the wind the analysis in this paper suggests that after 1993 the large amplitude of the nao cycle induces changes in the transport of the baroclinically

on the connection between dense water formation overturning and poleward heat transport in a convective basin an isopycnal two layer idealized model for a convective basin is proposed consisting of a convecting interior region and a surrounding boundary current buoyancy and wind driven parameterized eddy fluxes govern the exchange between the two to balance the interior buoyancy loss the boundary current becomes denser as it flows around the basin geostrophy imposes that this densification be accompanied by sinking in the boundary current and hence by an overturning circulation the poleward heat transport associated with convection in the basin can thus be viewed as a result of both an overturning and a horizontal circulation when adapted to the labrador sea the model is able to reproduce the bulk features of the mean state the seasonal cycle and even the shutdown of convection from 1969 to 1972 according to the model only 40 of the poleward heat buoyancy transport of the labrador sea is associated with the overturning circulation an exact solution is presented for the linearized equations when changes in the boundary current are small numerical solutions are calculated for variations in the amount of convection and for changes in the remotely forced circulation around the basin these results highlight how the overturning circulation is not simply related to the amount of dense water formed a speeding up of the circulation around the basin due to wind forcing for example will decrease the intensity of the overturning circulation while the dense water formation remains unvaried in general it is shown that the fraction of poleward buoyancy or heat transport carried by the overturning circulation is not an intrinsic property of the basin but can vary as a result of a number of factors

buoyant eddies entering the labrador sea observed with gliders and altimetry abstract intense buoyant anticyclonic eddies spawned from the west greenland boundary current were observed with high resolution autonomous seaglider hydrography and satellite altimetry as they entered the labrador sea interior surveys of their internal structure establish the transport of both low salinity water in the upper ocean and warm saline irminger water at depth the observed eddies can contribute significantly to the rapid restratification of the labrador sea interior following wintertime deep convection these eddies have saline cores between 200 and 1000 m low salinity cores above 200 m and a velocity field that penetrates to at least 1000 m with 0 1000 m average speeds exceeding 40 cm s 1 their trajectory together with earlier estimates of the gyre circulation suggests why the observed region of deep convection is so small and does not occur where wintertime cooling by the atmosphere is most intense the cyclostrophic surface velocity field of the anticylones from satellite altimetry

lateral heat exchange after the labrador sea deep convection in 2008 abstractthe mechanisms through which convected water restratifies in the labrador sea are still under debate the labrador sea restratification after deep convection in the 2007 08 winter is studied with an eddy resolving numerical model the modeled mixed layer depth during wintertime resembles the argo observed mixed layer very well and the lateral heat flux during the subsequent restratification is in line with observations the irminger rings irs are reproduced with fresher caps above the 300 m depths and they are identified and tracked automatically the model underestimates both the number of irs in the convection area and the heat they carry the underestimation is most likely caused by the errors in the direction of the west greenland currents in the model which causes more irs propagating westward and only the irs originating south of 61 5 n are able to propagate southward yet with speed much slower than observed speed the model still observed three eddies propagating into the convection

pattern formation at the ocean surface sargassum distribution and the role of the eddy field positively buoyant organisms such as the macroalga sargassum and the cyanobacterium trichodesmium often form surface accumulations visible in satellite imagery that have lateral scale separation of tens of kilometers and cannot be explained by langmuir circulation here we discuss the accumulation of floating materials in the ocean in presence of meso and submesoscale activity using high resolution simulations of the ocean mesoscale in both idealized a 3 dimensional box where coherent eddies are forced by small scale winds and realistic domains western gulf of mexico where extensive concentrations of floating sargassum have been recorded in satellite images we show that the distribution of tracers at the ocean surface departs rapidly from that observed a few tens of meters below it such distribution does not resemble that observed for passive tracers in quasi geostrophic turbulence the strong divergence and convergence zones generated at the surface by ageostrophic processes in the submesoscale range are responsible for the creation of areas where the floating material accumulates floating particles are expelled from the core of mesoscale eddies and concentrate in convergence regions in patterns comparable to the ones observed through the satellite images in light of those results sargassum and or trichodesmium may provide a useful proxy to track convergence divergence processes resulting from ageostrophic processes at the ocean surface

the 1982 enola arkansas swarm and scaling of ground motion in the eastern united states abstract the north central arkansas swarm which began in january of 1982 and was still active as of december 1983 has produced over 30 000 events three of these events had duration magnitudes greater than 4 0 fifty three locatable events in the magnitude range 3 8 and below were recorded during the 2 1 2 weeks our 10 digital seismographs were in place the hypocentral locations are confined to a tight cluster with a radius of approximately 1 km depths range between 4 and 7 km focal mechanisms determined for 10 of the events show a combination of strike slip and normal faulting source parameters seismic moment source radius and stress drop were calculated for 48 of the events the seismic moments range from 10 18 to 10 21 dyne cm while the stress drops range from 0 2 to 60 bars acceleration spectra are band limited at the high end at 30 hz the stress drops increase with seismic moment up to 10 20 dyne cm but appear to be constant at greater moment values the arkansas source parameters are similar to other body wave source parameters determined from near source investigations of earthquakes in eastern and central north america e g new brunswick and south carolina and in california e g mammoth lakes oroville and anza but differ substantially from lg wave source parameters estimated for earthquakes in the eastern and central united states

laboratory experiments on eddy generation by a buoyant coastal current flowing over variable bathymetry irminger rings are warm core eddies formed off the west coast of greenland recent studies suggest that these eddies which are implicated in the rapid springtime restratification of the labrador sea are formed by an internal instability of the west greenland current wgc triggered by bathymetric variations this study seeks to explore the effect of the magnitude and downstream length scale of bathymetric variations on the stability of a simple model of the wgc in a series of laboratory experiments in which a buoyant coastal current was allowed to flow over bathymetry consisting of piecewise constant slopes of varying magnitude the currents did not form eddies over gently sloping bathymetry and only formed eddies over steep bathymetry if the current width exceeded the width of the sloping bathymetry eddying currents were immediately stabilized if they flowed onto gently sloping topography bathymetric variations that persisted only a short distance downstream perturbed the flow locally but did not lead to eddy formation eddies formed only once the downstream length of the bathymetric variations exceeded a critical scale of about 8 rossby radii these results are consistent with the observed behavior of the wgc which begins to form irminger rings after entering a region where the continental slope abruptly steepens and becomes narrower than the wgc itself in a region spanning about 20 80 rossby radii of downstream distance

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

some recent lg phase displacement spectral densities and their implications with respect to the prediction of ground motions in eastern north america abstract lg phase displacement spectral density corner periods of recent earthquakes in central new brunswick and central arkansas are used to point out a potential source of dispersion in the relative scaling of eastern north american strong motion data the corner periods of one of the central new brunswick and several of the larger central arkansas earthquakes are atypical of other events of similar magnitude and seismic moment in the region the maximum far field ground motion of an earthquake is a function of its corner period therefore strong motion data of earthquakes that exhibit atypical characteristics such as a displaced corner period are a source of dispersion in the scaling of that strong motion data if plotted as a function of magnitude or seismic moment

deep convection in the irminger sea forced by the greenland tip jet open ocean deep convection one of the processes by which deep waters of the world s oceans are formed is restricted to a small number of locations for example the mediterranean and labrador seas recently the southwest irminger sea has been suggested as an additional location for open ocean deep convection the deep water formed in the irminger sea has the characteristic temperature and salinity of the water mass that fills the mid depth north atlantic ocean which had been believed to be formed entirely in the labrador basin here we show that the most likely cause of the convection in the irminger sea is a low level atmospheric jet known as the greenland tip jet which forms periodically in the lee of cape farewell greenland and is associated with elevated heat flux and strong wind stress curl using a history of tip jet events derived from meteorological land station data and a regional oceanic numerical model we demonstrate that deep convection can occur in this region when the north atlantic oscillation index is high which is consistent with observations this mechanism of convection in the irminger sea differs significantly from those known to operate in the labrador and mediterranean seas

pleistocene ice and sand wedges hooper island northwest territories buried ice and sand wedges have been found in glacially deformed sediments that can be no younger than the early wisconsinan the environmental conditions at the time of ice wedge cracking have been inferred from the number of elementary ice veinlets the vertical extent of the wedges collapse structures oxygen isotope ratios and macrofossils of plants and insects the winter ground and summer climates were probably as warm or warmer than the present the preservation of the ice in the ice wedges shows that permafrost has been present at hooper island since at least the early wisconsinan

sources of eddy kinetic energy in the labrador sea experiments with a suite of north atlantic general circulation models are used to examine the sources of eddy kinetic energy eke in the labrador sea a high resolution model version 112 quantitatively reproduces the observed signature a particular feature of the eke in the labrador sea is its pronounced seasonal cycle with a maximum intensity in early winter as already found in earlier studies based on altimeter data in contrast to a previously advanced hypothesis the seasonally varying eddy field is not related to a forcing by high frequency wind variations but can be explained by a seasonally modulated instability of the west greenland current wgc the main source of eke in the labrador sea is an energy transfer due to reynolds interaction work barotropic instability in a confined region near cape desolation where the wgc adjusts to a change in the topographic slope geostrophic contours tend to converge upstream of cape desolation such that the topographically guided wgc narrows as well and becomes barotropically unstable the eddies spawned from the wgc instability area dominating the eke in the interior labrador sea are predominantly anticyclonic with warm and saline cores in the upper kilometer of the water column while the few cyclones originating as well from the instability area show a more depth independent structure companion experiments with a model exhibit the strength of the wgc influenced by either changes in the wind stress or heat flux forcing as a leading factor determining seasonal to interannual changes of eke in the labrador sea

climatic control on quaternary fluvial sedimentation in the kleszczow graben central poland abstract the pleistocene sequence of the kleszczow graben central poland comprises seven fluvial series ranging in age from pre tiglian to holocene these sequences are investigated in terms of graben tectonics that existed up to the middle pleistocene and climate change ranging from periglacial to cool temperate warm temperate interglacial fluvial deposits are virtually absent there is no evidence for tectonic control of fluvial sedimentation although this is the factor that has controlled sediment preservation deformation and erosion in contrast sedimentation has been influenced greatly by climatic conditions and climatic change mainly as a response to changes in vegetation cover similar responses in the form of typical sedimentary successions are observed in fluvial series of different ages this paper outlines the sequences of erosion and sedimentation and discusses their relation to the regional history of climatic changes the geomorphic positions of river valleys and the positions of advancing ice sheets

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

the seasonality of convective events in the labrador sea abstractmodeling deep convection is a key challenge for climate science here two simulations of the labrador sea circulation obtained with the regional ocean modeling system roms run at a horizontal resolution of 7 5 km are used to characterize the response of convection to atmospheric forcing and its seasonal variability over the period 1980 2009 the integrations compare well with the sparse observations available the modeled convection varies in three key aspects over the 30 years considered first its magnitude changes greatly at decadal scales this aspect is supported by the in situ observations second the initiation and peak of convection i e initiation and maximum shift by 2 3 weeks between strong and weak convective years third the duration of convection varies by approximately one month between strong and weak years the last two changes are associated with the variability of the time integrated surface heat fluxes over the labrador sea during winter and spring while the first resu

the nature of eddy kinetic energy in the labrador sea different types of mesoscale eddies their temporal variability and impact on deep convection abstractoceanic eddies are an important component in preconditioning the central labrador sea ls for deep convection and in restratifying the convected water this study investigates the differen

winter mixed layer development in the central irminger sea the effect of strong intermittent wind events abstract the impact of the greenland tip jet on the wintertime mixed layer of the southwest irminger sea is investigated using in situ moored profiler data and a variety of atmospheric datasets the mixed layer was observed to reach 400 m in the spring of 2003 and 300 m in the spring of 2004 both of these winters were mild and characterized by a low north atlantic oscillation nao index a typical tip jet event is associated with a low pressure system that is advected by upper level steering currents into the region east of cape farewell and interacts with the high topography of southern greenland heat flux time series for the mooring site were constructed that include the enhancing influence of the tip jet events this was used to force a one dimensional mixed layer model which was able to reproduce the observed envelope of mixed layer deepening in both winters the deeper mixed layer of the first winter was largely due to a higher number of robust tip jet events which in turn was caused by the stee

intrinsic and forced interannual variability of the gulf of alaska mesoscale circulation abstract the response of the gulf of alaska goa circulation to large scale north pacific climate variability is explored using three high resolution 15 km regional ocean model ensembles over the period 1950 2004 on interannual and decadal timescales the mean circulation is strongly modulated by changes in the large scale climate forcing associated with pdo and enso intensification of the model gyre scale circulation occurs after the 1976 1977 climate shift as well as during 1965 1970 and 1993 1995 from the model dynamical budgets we find that when the goa experiences stronger southeasterly winds typical during the positive phase of the pdo and enso there is net large scale ekman convergence in the central and eastern coastal boundary the geostrophic adjustment to higher sea surface height ssh and lower isopycnals lead to stronger cyclonic gyre scale circulation the opposite situation occurs during stronger northwesterly winds negative phase of the pdo along the eastern side of the goa basin interannual changes in the surface winds also modulate the seasonal development of high amplitude anticyclonic eddies e g haida and sitka eddies large interannual eddy events during winter spring are phase locked with the seasonal cycle the initial eddy dynamics are consistent with a quasi linear rossby wave response to positive ssh anomalies forced by stronger downwelling favorable winds e g southwesterly during el nino however because of the fast growth rate of baroclinic instability and the geographical focusing associated with the coastal geometry most of the perturbation energy in the rossby wave is locally trapped until converted into large scale nonlinear coherent eddies coastally trapped waves of tropical origin may also contribute to positive ssh anomalies that lead to higher amplitude eddies however their presence does not appear essential the model ensembles which do not include the effects of equatorial coastally trapped waves capture the large haida and sitka eddy events observed during 1982 and 1997 and explain between 40 and 70 of the tidal gauges variance along the goa coast in the western side of the goa basin interannual eddy variability located south of the alaskan stream is not correlated with large scale forcing and appears to be intrinsic a comparison of the three model ensembles forced by ncep winds and a multi century long integration forced only with the seasonal cycle shows that the internal variability alone explains most of the eddy variance the asymmetry between the eddy forced regime in the eastern basin and the intrinsic regime in the western basin has important implications for predicting the goa response to climate change if future climate change results in stronger wintertime winds and increased downwelling in the eastern basin then increased mesoscale activity perhaps more or larger eddies might occur in this region conversely the changes in the western basin are not predictable based on environmental forcing eastern eddies transport important biogeochemical quantities such as iron oxygen and chlorophyll a into the gyre interior therefore having potential upscale effects on the goa high nutrient low chlorophyll region

seasonal and interannual variations of irminger ring formation and boundary interior heat exchange in flame abstractthe contribution of warm core anticyclones shed by the irminger current off west greenland known as irminger rings to the restratification of the upper layers of the labrador sea is investigated in the 1 12 family of linked atlantic models experiment flame model the model output covering the 1990 2004 period shows strong similarities to observations of the irminger current as well as ring observations at a mooring located offshore of the eddy formation region in 2007 09 an analysis of fluxes in the model shows that while the majority of heat exchange with the interior indeed occurs at the site of the irminger current instability the contribution of the coherent irminger rings is modest 18 heat is provided to the convective region mainly through noncoherent anomalies and enhanced local mixing by the rings facilitating further exchange between the boundary and interior the time variability of the eddy kinetic energy and the boundary to interior heat flux in the model are strongly corr

the vistulian aeolian succession in central poland abstract central poland is situated in the centre of the late pleistocene and holocene european aeolian sand belt this area has the highest frequency of round mat grains of all europe due to intense aeolian abrasion aeolian processes were very active during several glaciations but the changes in aeolian activity in the course of an entire glaciation can be studied only for the vistulian weichselian wisconsinan the reason is that a continuous blanket of glacial sediments either covered or partly eroded older aeolian sediments in central poland during the wartanian saalian ii aeolian processes began just after deglaciation and became intense under the periglacial conditions of the late wartanian and the whole vistulian the evolution of these processes is reconstructed especially for the interval of the highest and most effective aeolian activity i e the late plenivistulian oxygen isotope stage 2 the coldest stage of the last glaciation a model of the sequence of periglacial aeolian events during an entire glaciation is presented this model may be used for the reconstruction of older pleistocene cycles of high periglacial aeolian activity

pleistocene epigenetic and syngenetic frost fissures belchatow poland pseudomorphs of cryogenic fissures in stratified medium to fine silty sand and sand at belchatow poland indicate both epigenetic and syngenetic freezing of sediments at various times during the pleistocene syngenetic fissures are more frequent they are typically 0 5 2 0 m in vertical dimension range in width from 5 to 20 cm exhibit both upwarps and downwarps of enclosing sediments and are offset from each other in the stratigraphic sequence epigenetic fissures are larger generally increase in width upwards and are related to an inferred ground surface it is difficult to distinguish between syngenetic fissures that penetrate permafrost and soil ground veins or wedges that require only deep seasonal frost for their formation cold continental environments characterized by rapid sedimentation and permafrost aggradation appear most conducive for formation of syngenetic fissures today both large and small syngenetic fissures are known to exist in the permafrost regions of siberia but are rarely

basal glacier ice and massive ground ice different scientists same science whilst glaciologists and permafrost researchers investigate ice bodies using similar techniques there has been surprisingly little collaboration between the two communities this paper examines the potential benefits of interdisciplinary research into the formation of basal ice beneath glaciers and the origin of massive ice in glaciated permafrost regions active collaboration in these areas has already improved our understanding of the formation of basal ice beneath cold based glaciers the critical role played by basal freezing in controlling the dynamic behaviour of stagnating ice streams and the significance of glacier permafrost interactions at the margins of pleistocene ice sheets however in order to promote future collaboration certain obstacles need to be overcome the contrasting ice classification schemes employed by glaciologists and permafrost scientists for example need to be unified in order to allow detailed comparisons of ice rich sequences in both environments this could in turn enable exciting research advances most notably by facilitating the identification of preserved remnants of pleistocene ice sheets within permafrost regions that provide a potentially invaluable and currently largely untapped source of palaeoglaciological information

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

boundary currents and watermass transformation in marginal seas the properties of watermass transformation and the thermohaline circulation in marginal seas with topography and subject to a spatially uniform net surface cooling are discussed the net heat loss within the marginal sea is ultimately balanced by lateral advection from the open ocean in a narrow boundary current that flows cyclonically around the basin heat loss in the interior is offset by lateral eddy fluxes originating in the boundary current the objectives of this study are to understand better what controls the density of waters formed within the marginal sea the temperature of the outflowing waters the amount of downwelling and the mechanisms of heat transport within the marginal sea the approach combines heat budgets with linear stability theory for a baroclinic flow over a sloping bottom to provide simple theoretical estimates of each of these quantities in terms of the basic parameters of the system the theory compares well to a series of eddy resolving primitive equation model calculations the downwelling is concentrated within the boundary current in both a diffusive boundary layer near topography and an eddy driven region on the offshore edge of the boundary current for most high latitude regions the horizontal gyre is expected to transport more heat than does the overturning gyre

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

hydrography of the labrador sea during active convection the hydrographic structure of the labrador sea during wintertime convection is described the cruise part of the deep convection experiment took place in february march 1997 amidst an extended period of strong forcing in an otherwise moderate winter because the water column was preconditioned by previous strong winters the limited forcing was enough to cause convection to approximately 1500 m the change in heat storage along a transbasin section relative to an occupation done the previous october gives an average heat loss that is consistent with calibrated national centers for environmental prediction surface heat fluxes over that time period 200 wm 22 deep overturning was observed both seaward of the western continental slope which was expected as well as within the western boundary current itself something that had not been directly observed previously these two geographical regions separated by roughly the 3000 m isobath produce separate water mass products the offshore water mass is the familiar cold fresh dense classical labrador sea water lsw the boundary current water mass is a somewhat warmer saltier lighter vintage of classical lsw though in the far field it would be difficult to distinguish these products the offshore product was formed within the cyclonic recirculating gyre measured by lavender et al in a region that is limited to the north most likely by an eddy flux of buoyant water from the eastern boundary current the velocity measurements taken during the cruise provide a transport estimate of the boundary current throughput and offshore recirculation finally the overall trends in stratification of the observed mixed layers are described

the interannual variability of the surface eddy kinetic energy in the labrador sea abstract the variability of the surface eddy kinetic energy eke in the labrador sea is investigated with a suite of numerical integrations using a regional ocean model simulations are performed over the period 1980 2001 and are compared to satellite observations over the last 9 years the surface eke pattern in the basin is dominated by a region along the west coast of greenland where eddies mainly anticyclonic are formed by instability of the main currents flowing over the continental slope consistent with previous idealized results here the interannual changes are linked to the shear of the incoming boundary current system imposed as boundary condition to the model domain the highly variable strength of the east greenland current at the northeast boundary derived from the simple ocean data assimilation soda reanalysis strongly influences the vortex formation in the center of the labrador sea where deep convection occurs a statistically significant portion of the modeled interannual surface eke variability is correlated with the local atmospheric forcing and both heat and wind fluxes play an important role and can be adopted as predictors at a lag of 2 3 months the arctic oscillation index can also be used as a remote indicator of the atmospheric fluxes but with lower skill than local measurements in contrast the north atlantic oscillation index does not correlate significantly with the surface eke at intraseasonal and interannual scales the analysis of altimeter data over the 1993 2001 supports the existence of this asymmetry between the regime locally forced by the atmosphere in the central basin and the regime remotely forced by the incoming boundary current along the west greenland coast those results have important implications for monitoring and predicting the surface eddy kinetic energy variability in the labrador sea

steppe mammoth mammuthus trogontherii remains in their geological and cultural context from belchatow poland a consideration of human exploitation in the middle pleistocene abstract in 1981 and 1991 mammoth remains and associated fauna were found in central poland at the belchatow opencast mine in sandy gravel deposits most of them lay at approximately 160 175 m above mean sea level a s l located in the lower and upper members of the alluvial chojny formation this formation belongs to the middle pleistocene and can be connected with the mazovian mis 11 holsteinian or zbojnian mis 9 reinsdorf interglacial the belchatow mammoth assemblage described here consists of cranial and postcranial elements analysis of their morphological characteristics and osteometrics are used to demonstrate that at least two molars and one tusk belong to mammuthus trogontherii and that the tusk belonged to a male on the basis of the minimum number of elements of the most common element left incisors the mammoth remains represent at least two individuals based upon the different ages of death for the various elements it appears that they represent several individuals the bulk of the mammoth remains were recovered from the oldest depositional cycle in the lower member of chojny formation and are therefore coincident with a shrub tundra environment and cool temperate conditions they were deposited in sediments formed by a meandering river with a fairly low power of flow and were buried soon after transport over a short distance this conclusion is also supported by the palaeobotanical data an additional element a costa was recovered from the upper member of the chojny formation which is associated with the cooling conditions the enveloping deposit appears to be the result of a series of more rapid discharge events by a braided river this element is distinguished from those elements recovered from the lower member due to the presence of a series of unusual striations sem analysis suggests that some of the striations were probably made by chipped stone tools used in a slicing action as if the result of the filleting of flesh from the rib area the time frame for the depositional context of the costa suggests that the striations may have been made by one of several possible human taxa that occurred in central europe during this period including homo heidelbergensis given the dearth of human skeletal remains from this region and time period this represents the earliest and only example of middle pleistocene human butchering activity in poland the remains discussed in this paper are presented in light of their depositional and cultural contexts which not only increases our knowledge of the occurrence of m trogontherii in poland but also provides increased evidence for lower palaeolithic human activity in central europe during an early interglacial

an outline of the pleistocene stratigraphy of the kleszczow graben bechatow outcrop central poland abstract the pleistocene sequence of the kleszczow graben central poland is located in a brown coal quarry 8 km long and 4 km wide it contains ten separate organic horizons in part stacked one above another and in part correlated by reference to associated inorganic units using heavy minerals and gravel petrography three of the organic horizons represent interglacials ferdynandovian mazovian holsteinian and eemian others represent interstadial or periglacial deposits the tertiary quaternary boundary is recorded at the site by reuverian c and prae tiglian biostratigraphy occurring in a single section a major hiatus exists above the prae tiglian and lower pleistocene and cromerian deposits are absent glacial deposits are represented by three elsterian tills five saalian tills and glaciofluvial and glaciolacustrine deposits the czyzow formation lies between the elsterian and saalian deposits and contains at least two interglacials the ferdynandovian and mazovian and several interstadial units without glacial intervening deposits the lower saalian odranian drenthe deposits are separated from the middle saalian wartanian 1 by fluvial sands and organic deposits of the pilica interstadial the middle wartanian 1 and upper saalian wartanian 2 also may be separated by an interstadial palaeosol the evidence from the kleszczow graben supported by other central european quaternary sequences suggest that only four glaciations occurred within the region during the middle pleistocene and that these glaciations were separated by long periods with a complex climate ranging from temperate to periglacial

thaw modification of frost fissure wedges richards island pleistocene mackenzie delta western arctic canada thaw modification is the general process whereby frost fissure wedges are modified during thaw and by which frost fissure pseudomorphs may develop specific processes of thaw modification are inferred from ice wedge pseudomorphs composite wedge pseudomorphs and deformed sand wedges in the pleistocene mackenzie delta i e thermal erosion collapse subsidence refreezing loading buoyancy spreading folding and shearing thaw modification is believed to result in selective preservation of pseudomorphs and wedges sand wedges are more likely to be preserved than are ice wedge pseudomorphs or compositewedge pseudomorphs because only those sand wedges that penetrate massive ice or icy sediments are prone to thaw modification furthermore whereas ice wedges preferentially develop in ice rich fine grained sediments thaw sensitive their pseudomorphs appear to be selectively preserved in ice poor coarse grained sediments thaw stable

observations of the labrador sea eddy field this paper is an observational study of small scale coherent eddies in the labrador sea a region of dense water formation thought to be of considerable importance to the north atlantic overturning circulation numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat yet their small size has hindered observational progress a large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms current meter moorings and satellite altimetry details of the current and water mass structure of individual eddy events as they are swept past by an advecting flow can then be extracted from the mooring data a transition is seen during mid 1997 with long lived boundary current eddies dominating the central labrador sea year round after this time and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time the topex poseidon altimeter covers the labrador sea with a loose net of observations through which coherent eddies can seem to appear and disappear by concentrating on locating and describing anomalous events in individual altimeter tracks a portrait of the spatial and temporal variability of the underlying eddy field can be constructed the altimeter results reveal an annual pulsation of energy and of coherent eddies originating during the late fall at a particular location in the boundary current pinpointing the time and place of the boundary current type eddy formation the interannual variability seen at the mooring is reproduced but the mooring site is found to be within a localized region of greatly enhanced eddy activity notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling these eddy observations as well as hydrographic evidence suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region

seasonal to interannual variability of the eddy field in the labrador sea from satellite altimetry sea level anomalies measured by the altimeters aboard the topex poseidon and ers satellites for the periods 1993 2001 and 1997 2001 respectively are used to investigate the eddy field in the subpolar north atlantic and in the labrador sea a quadratic correction of the obtained eddy kinetic energy eke with respect to significant wave height is applied that led to an increased correlation between moored and altimetric eke in the central labrador sea the mean eke field shows higher levels associated with the main currents and a strong seasonality in the labrador sea the annual cycle of the eke shows a propagation of west greenland current wgc eke into the central labrador sea with a mean southward propagation speed of about 3 cm s 1 while the eke maximum in the labrador current is well separated from the interior by local eke minima the interannual variability of the eke in the labrador sea shows distinct regional differences in the wgc region strong early winter maxima are found during 1993 and 1997 1999 in the central labrador sea maxima are found during march april 1993 1995 and 1997 variations in the annual cycle of the wgc eke are observed while there is a weak annual cycle in the wgc region during 1994 1996 with more continuous eke generation during 1997 2000 there is a strong seasonal cycle with maximum eke during january and particularly low eke during summer the propagation of wgc eke into the central labrador sea is enhanced during 1997 2000 leading to a long persistence of eke in the central labrador sea during 1993 1995 and 1997 the central labrador sea eke almost instantaneously increased during march april followed in the earlier years by a relatively fast destruction of the winterly generated eke

revision of the late middle pleistocene stratigraphy and palaeoclimate in poland abstract the aim of this paper is a critical verification of the late middle pleistocene stratigraphy in poland in connection with stratigraphical schemes in the neighbouring countries although a terrestrial record of the middle pleistocene is almost complete in western and southern europe it is full of gaps in central and eastern europe eight key sites in poland and one in belarus were selected to compile environmental and palaeoclimate data for a revised stratigraphy from the termination of mis 12 to mis 6 and the chronology was based on correlation with oxygen isotope stratigraphy and osl ages the late middle pleistocene record starts with the holsteinian lake sequences some of which have been initiated already at the end of mis 12 persisted through mis 11 and terminated in mid mis 10 in the examined sites mis 11 is represented also by deposits of meandering rivers in a temperate climate in contrast there is no evidence for deposition in most of mis 10 and in mis 9 a warmer and presumably wet episode at the beginning of mis 8 lead to local erosion followed by development of small lakes modest ice sheet advance into central europe occurred in the second part of mis 8 as reflected by a till glaciofluvial and glaciolacustrine deposits and presumably also by permafrost and ice wedges in western belarus mis 7 seems to have been generally warm and wet when small lakes and meandering rivers could develop such mild conditions were interrupted with cool and probably drier episodes when braided rivers and limited pedogenesis occurred saalian ice sheet cover of central europe in mis 6 was widespread but even more importantly in this stage periglacial environments were dominant as shown by continuous permafrost intensive aeolian activity and development of ice wedges and involutions braided rivers developed during short wetter intervals

regional magnitude scaling transportability and ms mb discrimination at small magnitudes data sets of mb pn and mb lg measurements are presented for three continental regions in order to investigate scaling relationships with moment magnitude w and event discrimination at small magnitudes compilations of published measurements are provided for eastern north american and central asian earthquakes and new measurements are reported for earthquakes located in western united states statistical tests on w mb relationships show that the mb lg scale of nurru 1973 is transportable between tectonic regions and a single unified w mb lg relationship satisfies observations for m 6 5 in all regions a unified relationship is also developed for nuclear explosions detonated at the nevada test site and test sites of the former soviet union regional mb for explosions scale at higher rates than for earthquakes and of significance is the finding that mb pn for explosions scales at a higher rate than mb lg a model is proposed where differences in scaling rates are related to effects of spectral overshoot and near field rg scattering on the generation of pn and lg waves by explosions for earthquakes mb pn and mb lg scale similarly showing rates near 1 0 or 2 3 log1omo seismic moment

boundary circulation at the exit of the labrador sea the deep circulation and related transports of the southern labrador sea are determined from direct current observations from ship surveys and a moored current meter array the measurements covered a time span from summer 1997 to 1999 and show a well defined deep boundary current extending approximately out to the 3300 m depth contour and weak reverse currents farther offshore the flow has a strong barotropic component and significant baroclinic flow is only found in the shallow labrador current at the shelf break and associated with a deep core of denmark strait overflow water the total deep water transport below 27 74 kg m 3 was 26 5 sv sv 106 m3 s 1 comprising labrador sea water lsw gibbs fracture zone water gfzw and denmark strait overflow water dsow intraseasonal variability of the flow and transport was high ranging from 15 to 35 sv and the annual means differed by 17 a seasonal cycle is confined to the shallow labrador current in its deeper part where the mean flow is still strong no obvious seasonality could be detected the transport of the interior anticyclonic recirculation was estimated from lowered acoustic doppler current profiler stations and geostrophy yielding about 9 sv thus the net deep water outflow from the labrador sea was about 17 sv the baroclinic transport of gfzw and dsow referenced to the depth of the isopycnal 27 80 kg m 3 is only about one third of the total transport in these layers longer term variations of the total transports are not represented well by the baroclinic contribution

ice wedges growth thaw transformation and palaeoenvironmental significance frost cracking and ice wedge growth are fundamental processes within the permafrost environment extensive areas of contemporary permafrost terrain are characterised by frost fissure polygons formed by repeated thermal contraction cracking of the ground the incremental growth of ice veins and wedges along the axes of contraction cracks contributes significantly to the volume of ground ice in near surface permafrost in areas beyond the present limit of permafrost the recognition of ice wedge pseudomorphs provides one of the few unambiguous indications of the former existence of permafrost conditions an understanding of the processes of ice wedge growth and thaw transformation is essential if contemporary ice wedges are to be used as analogues for pleistocene frost fissure structures in palaeoenvironmental reconstructions

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

quaternary climates and sea levels of the u s atlantic coastal plain uranium series dating of corals from marine deposits of the u s atlantic coastal plain coupled with paleoclimatic reconstructions based on ostracode marine and pollen continent data document at least five relatively warm intervals during the last 500 000 years on the basis of multiple paleoenvironmental criteria we determined relative sea level positions during the warm intervals relative to present mean sea level were 7 5 meters at 188 000 years ago 7 5 1 5 meters at 120 000 years ago 6 5 3 5 meters at 94 000 years ago and 7 3 meters at 72 000 years ago the composite sea level chronology for the atlantic coastal plain is inconsistent with independent estimates of eustatic sea level positions during interglacial intervals of the last 200 000 years hydroisostatic adjustment from glacial interglacial sea level fluctuations lithospheric flexure and isostatic uplift from sediment unloading due to erosion provide possible mechanisms to account for the discrepancies alternatively current eustatic sea level estimates for the middle and late quaternary may require revision

numerical modelling of sh lg waves in and near continental margins summary the effect of transition regions between continental and oceanic structures on the propagation of l waves from continental sources is examined in particular the attenuation due to variations in layer thickness in such transition regions is calculated and explained for a suite of simple models the measured attenuation due tq the geometry of the transition regions between the oceanic and continental structures within a partially oceanic path with source and receiver in a continental structure is at most a factor of four for frequencies from 0 01 to 1 hz this is inadequate to explain the observed extinction of l along such paths this extinction has previously been attributed to the effects of the transition region geometry the method used to calculate the results presented in this study is developed and its validity and accuracy are demonstrated propagator matrix seismograms are coupled into a finite element calculation to produce hybrid teleseismic sh mode sum seismograms these hybrid synthetics can be determined for paths including any regional transition zone or other heterogeneity that exists as part of a longer mostly plane layered path numerical results presented for a suite of transition models show distinct trends in each of the regions through which the wavefield passes the wavefield passes through a continent ocean transition region then a region of oceanic structure and finally through an ocean continent transition region when an l wavefront passes through a continent ocean transition the amplitude and coda duration of the l wave at the surface both increase at the same time much of the modal l energy previously trapped in the continental crust is able to escape from the lower crust into the subcrustal layers as body waves the magnitude of both these effects increases as the length of the transition region increases when the wavefront passes through the region of oceanic structure further energy escapes from the crustal layer and produces a decrease in l amplitude at the surface the rate of amplitude decrease is maximum near the transition region and decreases with distance from it when the wavefield passes through the oceancontinent transition region a rapid decrease in the l amplitude at the surface of the crust results the energy previously trapped in the oceanic crustal layer spreads throughout the thickening crustal layer some of the body wave phases produced when the wavefield passes through the continent ocean transition region are incident on the continental crust in the ocean continent transition region these waves are predominantly transmitted back into the crust the other body wave phases reach depths below the depth of the base of the continental crust before reaching the ocean continent transition and thus escape from the system

the frequency of ice wedge cracking 1967 1987 at garry island western arctic coast canada the frequency of ice wedge cracking has been studied at garry island northwest territories for the 1967 1987 period sites have included low centre polygons intermediate centre polygons and polygons that do not fit any classification system analyses of crack frequency have included trough characteristics polygon characteristics and ice wedge types the results show that crack frequencies are highly variable within one site and also between two adjacent sites the correlation between crack frequency and a low air temperature is poor crack frequencies for a site with 59 wedges ranged from 8 to 42 between 1967 and 1979 and for a nearby site with 32 wedges from 22 to 75 between 1967 and 1987 in view of the wide range in crack frequencies at a given site the use of mean ice wedge growth rates for estimating ages of ice wedges and their casts in environmental reconstruction may be hazardous the data show that the common twofold classification into active and inactive wedges is difficult to apply be

structure formation and geochronology of the late pleistocene and holocene cover deposits in south eastern lithuania article the available data of earlier investigations basalykas 1965 basalykas et al 1976a b kudaba 1983 show that deposits of various origin and age are widespread in asmena upland and lyda plateau south eastern lithuania they overlie a polygenetic dislodged marginal formations of the penultimate medininkai warthe glaciation pleistocene deposits in this area are often deformed by solifluction and fluvial erosion and penetrated by cryogenic ice wedge pseudomorphs granulometric geochemical and petrographic investiga tions of the deposits have demonstrated that they are characterized by different sources of sedimentary material supply as well as different degrees of physical and chemical weathering the alternate deposits preserved in the study area imply palaeoenvironmental changes associated with the different palaeoclimatic events the ca zr ratios in cover deposits testify that the upper beds usually experienced stronger chemical weathering that is associated with warmer climate the cases of weaker weathering can be explained by

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

oceanic transport of surface meltwater from the southern greenland ice sheet meltwater runoff from the greenland ice sheet alters ocean surface salinity numerical simulations show that meltwater from southeastern greenland is transported to the labrador sea more efficiently than that from southwestern greenland

average seismic source parameter relations for mid plate earthquakes mid plate earthquakes which are defined as having their epicenters at least 500 km from plate margins represent a small portion of the total global seismicity however because those occurring within continental interiors are characterized by anomalously large damage areas they are of particular interest empirical mb ms and m o data are used to develop scaling relations for mid plate earthquakes from them it is found that the corner period t o2 of their far field displacement spectra varies as the one fourth power of the seismic moment which indicates that average stress drop increases as seismic moment increases by use of savage s 1972 rectangular bilateral dislocation model the derived spectra of mid plate earthquakes yield estimates of fault rupture length and width average fault displacement and source rise time as a function of seismic moment these relations show that large mid plate earthquakes such as the 1886 south carolina and 1811 and 1812 new madrid events do not require large fault rupture length

labrador sea boundary currents and the fate of the irminger sea water abstract the general circulation of the labrador sea is studied with a dataset of 53 surface drifters drogued at 15 m and several hydrographic sections done in may 1997 surface drifters indicate three distinct speed regimes fast boundary currents a slower crossover from greenland to labrador and a slow eddy dominated flow in the basin interior mean eulerian velocity maps show several recirculation cells located offshore of the main currents in addition to the cyclonic circulation of the labrador sea above the northern slope of the basin the surface drifters have two preferential paths one between the 1000 m and 2000 m isobaths and the other close to the 3000 m isobath the vertical shear estimated from ctd data supports the presence of two distinct currents around the basin one current more baroclinic flows between the 1000 m and 2000 m isobaths the other one more barotropic flows above the lower continental slope the irminger sea water carried by the boundary currents is altered as it tr

quaternary aeolian activity of eastern europe a poland case study abstract the emergence of the pleistocene aeolian processes and their intensity was revealed through morphoscopy the observation and analysis of quartz grain shape and microtexture sediments from 39 cored boreholes and three outcrops located in central and eastern poland were analysed using methodology developed in 1942 by cailleux to identify past wind action this method is based on the recognition of the degree of roundness observed on quartz grains along with their surface typology matt or shiny the obtained results allowed us to separate seven distinct periods where the content of quartz grains with matt surfaces and varying degrees of roundness increased indicating the presence of an aeolian environment these processes were different in their nature and intensity with the wind action periods varying from long lasting and very intense identified across the entire research area to periods with low intensity and local wind action events these periods can be correlated with the advance of oldest glacials the narevian nidanian mis 36 34 mis 22 the sanian 1 mis 16 the sanian 2 mis 12 the advance and retreat of the odranian ice sheet mis 6 maximum stadial and the odranian glaciation mis 6 post maximum stadial wartanian these aeolian processes lead to the formation of coversands and fluvial sediments that are rich in aeolianized grains

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

weichselian late pleniglacial and late glacial depositional environments coleoptera and periglacial climatic records from central poland belchatow environmental conditions during the weichselian have been studied at the belchatow brown coal pit in central poland palaeoclimate has been reconstructed by a multiproxy approach based on sedimentary environments periglacial structures and coleoptera remains the weichselian middle to late pleniglacial sequence reveals a change from lacustrine to fluvial deposition during the late pleniglacial deposition by ephemeral streams with relatively stable channels was abruptly replaced by braided river deposition an increased aridity and the disappearance of the vegetation are held reponsible for this change in river style the increase of aridity in the second part of the late pleniglacial has been inferred from the absence of organic material in the braided deposits and the extension of aeolian environments at the expense of the braided environment a return towards wetter conditions during the late glacial has been inferred from lake marl deposition and local fluvial reworking of dunes special attention has been given to the climate reconstruction of the early late pleniglacial 26 24 ka permafrost conditions during this period in combination with local strong relief and intensive slope processes resulted in rapid aggradation by ephemeral streams with relatively stable channels the climate during the early late pleniglacial was extremely harsh the habitat was in many ways analogous to the true tundra of the present day arctic the periglacial features indicate a mean annual air temperature lower than 4 c the coleopteran assemblage from belchatow is one of the most cold adapted faunas so far recorded from europe the mean temperatures of the warmest and coldest months were respectively 8 c and 27 c it is concluded that a strong temperature decline especially of the winter temperature occurred at the transition from the middle to the late pleniglacial at the onset of the late glacial younger dryas period a cooling of the climate has been inferred from the presence of small ice wedge casts at the base of overlying dune sands a mean annual air temperature between 2 and 5 c is postulated 1998 john wiley sons ltd

mesoscale eddies in the labrador sea and their contribution to convection and restratification abstract the cycle of open ocean deep convection in the labrador sea is studied in a realistic high resolution 4 km regional model embedded in a coarser north atlantic setup this configuration allows the simultaneous generation and evolution of three different eddy types that are distinguished by their source region generation mechanism and dynamics very energetic irminger rings irs are generated by barotropic instability of the west greenland and irminger currents wgc ic off cape desolation and are characterized by a warm salty subsurface core they densely populate the basin north of 58 n where their eddy kinetic energy eke matches the signal observed by satellite altimetry significant levels of eke are also found offshore of the west greenland and labrador coasts where boundary current eddies bces are spawned by weakly energetic instabilities all along the boundary current system bcs baroclinic instability of the steep isopycnal slopes that result from a deep convective over

the dependence of peak horizontal acceleration on magnitude distance and site effects for small magnitude earthquakes in california and eastern north america abstract one hundred and ninety free field accelerograms recorded on deep soil 10 m deep were used to study the near source scaling characteristics of peak horizontal acceleration for 91 earthquakes 2 5 m l 5 0 located primarily in california of the six attenuation relationships developed in this study the one considered most reliable is given by the expression ln p h a 2 5 0 1 0 6 2 3 m l 1 0 ln r 7 2 8 where pha is the mean of the two horizontal components of peak acceleration in g m l is local magnitude r is epicentral distance in kilometers and is a random error term with mean of zero and standard deviation of 0 506 an analysis of residuals based on an additional 171 near source accelerograms from 75 earthquakes indicated that accelerograms recorded in building basements sited on deep soil have 30 per cent lower accelerations and that free field accelerograms recorded on shallow soil 10 m deep have 82 per cent higher accelerations than free field accelerograms recorded on deep soil accelerations recorded on rock were found to be similar in amplitude to those recorded on deep soil a separate analysis of site effects for the imperial valley and oroville regions of california indicated that peak accelerations from individual sites can depart significantly from predictions based on broad site classifications an analysis of residuals based on 27 selected strong motion recordings from 19 earthquakes in eastern north america indicated that near source accelerations associated with frequencies less than about 25 hz are consistent with predictions based on attenuation relationships derived for california once site effects and differences in regional magnitude scales are taken into account

strong motion seismology strong motion seismology is concerned with earthquake ground motion in the amplitude range that poses the threat of human injury or property damage because the occurrence of strong motion cannot be predicted in advance and because the time between significant events at any one place may range from tens to thousands of years strong motion data is recorded on triggered instruments that typically must be maintained in readiness for years between periods of significant recording as a consequence the strong motion data set is sparse because of the engineering need for estimates of future ground motion the scope of the field of strong motion seismology encompasses seismic source theory and any other aspect of seismology that can provide insights helpful in making the best possible estimates given the limited data this relationship with the rest of seismology is a reciprocal one in that strong motion data gives perhaps the best information available on earthquake source processes

hydrographic changes in the labrador sea 1960 2005 abstract the labrador sea has exhibited significant temperature and salinity variations over the past five decades the whole basin was extremely warm and salty between the mid 1960s and early 1970s and fresh and cold between the late 1980s and mid 1990s the full column salinity change observed between these periods is equivalent to mixing a 6 m thick freshwater layer into the water column of the early 1970s the freshening and cooling trends reversed in 1994 starting a new phase of heat and salt accumulation in the labrador sea sustained throughout the subsequent years it took only a decade for the whole water column to lose most of its excessive freshwater reinstate stratification and accumulate enough salt and heat to approach its record high salt and heat contents observed between the late 1960s and the early 1970s if the recent tendencies persist the basin s storages of salt and heat will fairly soon likely by 2008 exceed their historic highs the main process responsible for the net cooling and freshening of the labrador sea between 1987 and 1994 was deep winter convection which during this period progressively developed to its record depths it was caused by the recurrence of severe winters during these years and in its turn produced the deepest densest and most voluminous labrador sea water lsw1987 1994 ever observed the estimated annual production of this water during the period of 1987 1994 is equivalent to the average volume flux of about 4 5 sv with some individual annual rates exceeding 7 0 sv once winter convection had lost its strength in the winter of 1994 1995 the deep lsw1987 1994 layer lost communication with the mixed layer above consequently losing its volume while gaining heat and salt from the intermediate waters outside the labrador sea while the 1000 2000 m layer was steadily becoming warmer and saltier between 1994 and 2005 the upper 1000 m layer experienced another episode of cooling caused by an abrupt increase in the air sea heat fluxes in the winter of 1999 2000 this change in the atmospheric forcing resulted in fairly intense convective mixing sufficient to produce a new prominent lsw class lsw2000 penetrating deeper than 1300 m this layer was steadily sinking or deepening over the years following its production and is presently overlain by even warmer and apparently less dense water mass implying that lsw2000 is likely to follow the fate of its deeper precursor lsw1987 1994 the increasing stratification of the intermediate layer implies intensification in the baroclinic component of the boundary currents around the mid depth perimeter of the labrador sea the near bottom waters originating from the denmark strait overflow exhibit strong interannual variability featuring distinct short term basin scale events or pulses of anomalously cold and fresh water separated by warm and salty overflow modifications regardless of their sign these anomalies pass through the abyss of the labrador sea first appearing at the greenland side and then about a year later at the labrador side and in the central labrador basin the northeast atlantic deep water 2500 3200 m originating from the iceland scotland overflow water reached its historically freshest state in the 2000 2001 period and has been steadily becoming saltier since then it is argued that lsw1987 1994 significantly contributed to the freshening density decrease and volume loss experienced by this water mass between the late 1960s and the mid 1990s via the increased entrainment of freshening lsw the hydrostatic adjustment to expanding lsw or both

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

role of resolved and parameterized eddies in the labrador sea balance of heat and buoyancy abstractdeep convection in the labrador sea is an important component of the global ocean ventilation the associated loss of heat to the atmosphere from the interior of the sea is thought to be mostly supplied by mesoscale eddies generated either remotely or as a result of convection itself processes that are not resolved by low resolution ocean climate models the authors first employ a high resolution ocean model forced with high resolution 33 km 3 h atmospheric fields to further elaborate on the role of mesoscale eddies in maintaining the balance of heat and buoyancy in the labrador sea in general agreement with previous studies it is found that eddies remove heat along the coast and supply it to the interior some of the eddies that are generated because of the barotropic instability off the west coast of greenland are recaptured by the boundary current in the region of deep convection the convergence of heat and buoyancy by eddies significantly increases with the deepening of the winter

ground ice investigations klondike district yukon territory massive bodies of ground ice 2 0 4 0 m thick are regularly exposed in small placer mining operations in the klondike district yukon at mayes claim hunker creek the ice is underlain by 2 0 3 0 m of creek gravels and overlain by 10 0 15 0 m of organic rich and ice rich muck deposits the crystallographic and petrographic characteristics of the ice and its stratigraphic occurrence suggest that the ice body either had a segregation origin or was a residual snowbank subsequently buried by muck deposits and recrystallized

spectral inversion of lg from earthquakes a modified method with applications to the 1995 western texas earthquake sequence spectral inversion of lg from earthquake sources is subject to significant errors due to random and systematic deviation of the lg spectra from idealized theoretical models i present an analysis of these errors and demonstrate that their effects tend to increase with decreasing frequency and recording distance i propose modifications to the inverse method of xie 1993 to reduce these errors the modifications include a more robust q estimator and the added capability of incorporating a priori knowledge into the inversion the modified method is applied to lg spectra from the 1995 western texas earthquake mw 5 7 i measured average two station q values for selected station pairs as well as the source rise time of the mainshock with an empirical green s function approach these served as a priori knowledge for the simultaneous inversion for lg seismic moment m corner frequency fc and path q the result of the inversion indicates that lg source radiation is nearly isotropic the m and fc values estimated using lg from the mainshock and two aftershocks are typical for lg from central and eastern north american earthquakes with m scaling with fc 4 and m and fc being 3 3 1016 n m and 0 3 hz respectively for the mainshock the 1 hz lg q correlates with tectonic environments increasing from about 200 for westerly paths to above 700 for easterly paths two station q measurements suggest that as previously discovered for eurasia the frequency dependence of lg q may be variable with distance if the distance spans a wide range 103 km

excitation and propagation of lg from earthquakes in central asia with implications for explosion earthquake discrimination broadband lg records from 52 shallow earthquakes that occurred near the balapan and lop nor nuclear test sites have been used to study spectral characteristics of the excitation and propagation of the lg phase in central asia using a source model that falls off as 2 at high frequencies and a nonlinear inversion method we simultaneously inverted for lg seismic moments m0 corner frequencies fc and path variable values of q0 and qlg at 1 hz and its power law frequency dependence the logarithms of m0 obtained using lg correlate linearly with logarithms of fc the slope being about 3 56 when all data are used and 4 04 when data were sufficient that full inversions could be performed these slopes differ only slightly from the slope of 3 83 obtained in our earlier studies using underground nuclear explosions the fc values in this study are systematically lower than those found for explosions at the same m0 level a comparison of corner frequencies and lg moment values for unknown events with the plots for known events of this study therefore provides means to discriminate between earthquakes and explosions the mb values are systematically lower for earthquakes of this study than for previously studied explosions at the same seismic moment moreover the logarithms of lg moments obtained in this study correlate linearly with a slope of 1 04 with mb values when all data are used and 1 21 when only well recorded events are used these slopes are close to the slope of 1 19 obtained for explosions the average qlg values along the paths used in this study agree well with those obtained using explosion data in central asia and with reported lg coda q values

soft sediment deformations in the kleszczow graben central poland abstract a wide variety of soft sediment deformation structures is found in the quaternary overburden of a giant open cast browncoal mine near belchatow sw of od central poland situated within a graben the deformation structures range in size from tens of meters to only millimeters it is remarkable that their size is often related to a specific type of genesis most large scale deformations appear to result from tectonic activity other structures commonly of intermediate size result from exogenic processes such as glaciotectonism and overburden induced diapirism penecontemporaneous and other early diagenetic deformational processes among which bioturbation and cryoturbation are commonly of small size only they are nevertheless important because their analysis allows a reconstruction of not only the depositional environment but also the deformational history of the sedimentary succession in spite of the different types of genesis many of the soft sediment deformation structures are in one way or another related to the graben activity since the tectonic conditions in the quaternary deposits within the graben are in many respects comparable to those in rift valleys the deformation structures in the graben might be considered as representative for rift valleys as well the analysis of the structures resulting in an improved insight into their genesis may thus contribute to a better understanding of the conditions to which sediments in rift valleys can be exposed

subglacial meltwater channels and glaciofluvial deposits in the kimberley basin western australia 1 8 ga low latitude glaciation coeval with continental assembly a late palaeoproterozoic unconformity surface developed on low dipping sandstone in the kimberley region northwestern australia exhibits numerous linear parallel grooves 10 50 mm deep 40 80 mm wide and tens of metres long and other erosional forms including sichelwannen these features are interpreted as nye channels and sculpted forms eroded by subglacial meltwaters sandstone filled cracks exposed at the unconformity are viewed as periglacial frost fissures an overlying conglomerate facies 1 15 m thick at the base of the c 1800 ma king leopold sandstone kimberley basin succession contains poorly sorted pebble to boulder conglomerate and is interpreted as glaciofluvial in origin the orientation of the nye channels and sculpted forms and the palaeocurrent direction for the glaciofluvial deposits indicate westward ice flow the conformably following locally glauconitic quartzarenite of the king leopold sandstone probably accumulated in an epeiric sea implying that glaciation reached close to sea level transgression in northwestern and central australia at c 1800 ma may have been partly glacio eustatic glaciation was initiated to the east of the kimberley basin evidently in the halls creek orogen during a major phase of continental collision in australia and worldwide supercontinental assembly recognition of the king leopold glaciation which occurred in low palaeolatitudes c 2200 and 800 ma