major pathways of atlantic water in the northern north atlantic and nordic seas toward arctic 1 the major pathways of near surface atlantic water in the northern north atlantic and nordic seas are identified as current speeds above 30 cm s using 1014 lagrangian drifters combined with previously published hydrography the inflow over the scotland greenland ridge and establishment of the two branch norwegian atlantic current nwac are described in light of the circulation in the northern north atlantic the western branch of the nwac appears as a jet in the polar front topographically guided from the iceland faroe front through the nordic seas toward fram strait the eastern branch starts as a shelf edge current above the irish scottish continental shelf and after passing through the faroe shetland channel it continues northward along the norwegian shelf edge toward the arctic with a branch bifurcating into the barents sea the nwac appears to maintain its two branch structure throughout the nordic seas with the atlantic water confined to a 200 600 km wide wedge

new results and a palaeomagnetic overview of the pontides in northern turkey summary palaeomagnetic results are reported from 16 sites within volcanic and volcano sedimentary rocks of cretaceous and eocene age from the central pontides in northern turkey the sampled area is bounded by the north anatolian fault naf to the south and the black sea to the north the palaeomagnetic data collected demonstrate the presence of both non rotated and anticlockwise rotated regions i declination directions including lower upper cretaceous and eocene sites do not indicate any significant rotations north of where the naf exhibits an arcuate shape ii 20 anticlockwise rotation was observed in the sinop peninsula the northernmost extremity of the central pontides iii in the west of the central pontides two sites with normal and reversed antipodal directions indicate a 20 anticlockwise rotation and iv another region lies to the east of the study area and shows a rotation in an anticlockwise sense of about 5 30 the upper cretaceous and eocene directions reported in this paper and other palaeomagnetic studies show that there is not much difference between the inclination values of the upper cretaceous i 40 1 95 7 2 and the eocene sites i 39 6 95 8 1 furthermore the values of the inclination available from both sedimentary and volcanic upper jurassic lower cretaceous formations are shallower than the upper cretaceous ones this suggests that the entire pontides have undergone a northward drift of over 2000 km since the upper jurassic

response of norwegian sea temperature to solar forcing since 1000 a d abstract we report on a 1000 year long oxygen isotope record in sediments of the eastern norwegian sea which we argue represents the temperature and transport of warm atlantic waters entering the nordic sea basin via the north atlantic drift and the large scale meridional overturning circulation the single sample resolution of the record is 2 5 10 years and age control is provided by pb 210 and cs 137 dating identification of historic tephra and a c 14 wiggle match dating method in which the surface reservoir 14c age in the past is constrained rather than assumed thereby eliminating a large source of chronological uncertainty the oxygen isotope results indicate decade to century scale temperature variations of 1 2 degrees c in the shallow similar to 50 m deep subsurface which we find to be strongly correlated with various proxies of past solar activity the correlations are synchronous to within the timescale uncertainties of the ocean and solar proxy records which vary among the records and in time with a range of about 5 30 years the observed ocean temperature response is larger than expected based on simple thermodynamic considerations indicating that there is dynamical response of the high latitude ocean to the sun correlations of our results with a gridded temperature reconstruction for europe are greater in central europe than in coastal regions suggesting that the temperature and transport of warm atlantic waters entering the nordic basin and the pattern of temperature variability over europe are both the proximate responses to a change in the atmospheric circulation consistent with a forced shift in the primary modes of high latitude atmospheric variability less

estimation of curie point temperature and geothermal structure of island arcs of japan abstract curie depth analysis from aeromagnetic data was performed in a nationwide project to assess the geothermal resources of japan creation of a curie depth map of japan was completed in 1984 and it agrees well with thermal structures such as the high temperature gradient regions of volcanic chains low temperature regions of the forearc basins and the intermediate temperature regions of the backarc basins measured temperature gradient t data were gathered in order to estimate the curie temperature from the t and the curie depths when t is assumed to be constant with respect to depth a remarkable difference is found in the estimated curie temperature t e c of the backarc and forearc side of the basins in the backarc side an average t e c of 450 c is reasonable for both the curie depth estimated from aeromagnetic data average depth of about 10 km in the backarc side and the temperature gradients average gradient of 4 5 c 100 m the average t e c on the forearc side was found to be low at about 300 c the difference in the curie temperatures between the two areas may be due to a regional difference in rock type e g granite as opposed to basalt in the case of the northeast japan arc as suggested by some authors the isotherms may suddenly fall between the volcanic front and the trench based on model studies we recognized that a curie depth map obtained by the algorithm we developed should include an averaging effect this suggests that the inferred curie depth curve across the line marking the sudden fall in the curie isotherm should gradually increase towards the trench therefore the low curie temperature that we estimated may indicate an apparent shallow curie depth caused by the averaging effect against an area bearing deep curie depths hence the reasons for the inconsistency of the estimated curie temperature between the forearc side and backarc side may be as follows 1 the averaging effect of the curie depth estimate which makes the curie depth apparently shallower in the forearc side and 2 the lower curie temperature of basaltic rocks which are assumed to be distributed along the east side of the aseismic front

surface changes in the eastern labrador sea around the onset of the little ice age despite the relative climate stability of the present interglacial it has been punctuated by several centennial time scale climatic oscillations the latest of which are often colloquially referred to as the medieval climatic anomaly mca and the little ice age lia the most favored explanation for the cause of these anomalies is that they were triggered by variability in solar irradiance and or volcanic activity and amplified by ocean atmosphere sea ice feedbacks as such changes in the strength of the atlantic meridional overturning circulation amoc are widely believed to have been involved in the amplification of such climatic oscillations the labrador sea is a key area of deep water formation the waters produced here contribute approximately one third of the volume transport of the deep limb of the amoc and drive changes in the north atlantic surface hydrography and subpolar gyre circulation in this study we present multi proxy reconstructions from a high resolution marine sediment core located south of greenland that suggest an increase in the influence of polar waters reaching the labrador sea close to mca lia transition changes in freshwater forcing may have reduced the formation of labrador sea water and contributed towards the onset of the lia cooling

episodic reductions in bottom water currents since the last ice age although north atlantic deep water formation was greatly reduced during the last glacial maximum bottom water currents were as vigorous as at present however they were weakened during periods of north atlantic surface freshening a strong correlation can be seen between bottom water current strength and greenland air temperature records thus confirming a close connection between ocean circulation and abrupt climate change past changes in the freshwater balance of the surface north atlantic ocean are thought to have influenced the rate of deep water formation and consequently climate1 2 although water mass proxies are generally consistent with an impact of freshwater input on meridional overturning circulation3 there has been little dynamic evidence to support this linkage here we present a 25 000 year record of variations in sediment grain size from south of iceland which indicates vigorous bottom water currents during both the last glacial maximum and the holocene period together with reconstructions of north atlantic water mass distribution vigorous bottom currents suggest a shorter residence time of northern source waters during the last glacial maximum relative to the holocene period the most significant reductions in flow strength occur during periods that have been associated with freshening of the surface north atlantic the short term deglacial oscillations in bottom current strength are closely coupled to changes in greenland air temperature with a minimum during the younger dryas cold reversal and a maximum at the time of rapid warming at the onset of the holocene our results support a strong connection between ocean circulation and rapid climate change

development and hydrocarbon potential of mesozoic sedimentary basins around margins of north atlantic the late triassic early jurassic rift basins of iberia offshore eastern canada and the continental shelf of western europe are fragments of a formerly coherent northeast trending rift system that probably formed as a result of tensional stress between europe africa and north america the separation of europe north america and iberia was preceded by a late jurassic early cretaceous rifting phase that is clearly distinct from the earlier mesozoic rifting episode and was little influenced by it the two periods of rifting are separated by a middle jurassic relatively tectonically quiet period the distribution of hydrocarbon finds within the rift basin suggests that the best prospects are in areas where the two rifting episodes are superimposed lack of mature source r cks in the later mesozoic rift basins and an unfavorable temporal relationship between hydrocarbon generation and tectonic activity in the early mesozoic basins are proposed as explanations for the apparently poor hydrocarbon prospectivity of large areas of the mesozoic basins

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

magnetic model of the subduction zone in the northeast japan arc abstract magnetic modeling of the forearc side of the tohoku northeastern japan arc was carried out using spectral analysis of shipborne magnetic data the original data show anomalies caused by volcanic rocks on the western shallow side and linear marine magnetic anomalies on the eastern deeper side throughout the forearc region as calculated from temperature gradient data of heat flow measurements and deep drilling the curie depth is deeper than the moho on the eastern deeper side this suggests that the moho may correspond to the base of the magnetic layer because analysis of upper mantle xenolith suites indicates that the upper mantle should be non magnetic in addition the conrad discontinuity may correspond to the apparent top of magnetic layer because the lower crustal layer would be more mafic than the upper layer it was estimated by 2d spectral analysis that the magnetic base and surface lie at about 20 km and 10 km respectively this suggests that the moho and the conrad may roughly correspond to the magnetic base and surface the magnetic anomalies in the pacific basin are traced towards and over the inner side of the trench and show a gradual decrease in amplitude disappearing eventually about 100 km west of the trench this reflects the descent of the oceanic slab the 1d spectral analysis indicates that the marine magnetic layer is descending at an angle of about 4 in the japan trench this angle increasing to 20 degrees below the coast where the marine magnetic layer reaches a depth of more than 30 km this agrees with the seismic reflection data from the trench and because the magnetic layer can be traced down to a depth of 30 km it may be suggested that the curie isotherm deepens to more than 30 km just east of the coast

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

interpretation of the gravity and magnetic anomalies of the cappadocia region central turkey the cappadocia region located in central turkey is characterized by widespread lava flows and volcanoclastic deposits dating from miocene to quaternary gravity and aeromagnetic anomalies of the region appear to present similar high and low amplitude regions although the aeromagnetic anomalies exhibit a rather complex pattern which is thought to be caused by remanent magnetization the low pass filtered aeromagnetic map shows a deep seated magnetic anomaly which may be linked to the widespread volcanic activity at the surface the pseudogravity transformation of the upward continued anomaly has been constructed the pseudogravity anomaly demonstrates some form of clockwise rotation this anomaly was modelled by means of a three dimensional method the top and bottom of the body are at 6 3km and 11km including the flight height from the ground surface respectively this deep body is ellipsoidal and extends along an e w direction which is in line with the regional stress direction deduced from gps measurements a new mobilistic dynamo tectonic system appears to explain the body s e w elongation the modelled body may be the source for the inferred geothermal energy of the region magnetic measurements were carried out on oriented rock samples collected from outcrops of ignimbrites and basalts providing directions and intensities of remanent magnetization susceptibilities and koeningsberger q ratios standard deviations of remanent directions of the natural remanent magnetization nrm display a wide scatter implying unreliability of the surface data reduction to pole rtp transformation of magnetic anomalies was successful with the induced magnetization angle despite the complex pattern of magnetic anomalies

north atlantic climate and deep ocean flow speed changes during the last 230 years variations in the near bottom flow speed of iceland scotland overflow water isow are documented in a 230 year long deep sea sediment record from the eastern flank of reykjanes ridge in the subpolar north atlantic at sub decadal time scales for recent decades the isow palaeocurrent reconstructions show similarities with observational hydrographic data furthermore recent isow flow changes fall mostly within the range of its variability of the past 230 years the record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar north atlantic with the north atlantic oscillation nao index with more less vigorous isow flow during negative positive phases of the nao our results suggest that the changes in isow vigor are largely controlled by the transport and characteristics of labrador sea water rather than variations in the overflow itself with implications for the meridional overturning of the atlantic ocean and climate

evidence for a widespread climatic anomaly at around 9 2 ka before present 1 the 8 2 ka event was triggered by a meltwater pulse mwp into the north atlantic and resultant reduction of the thermohaline circulation thc this event was preceded by a series of at least 14 mwps their impact on early holocene climate has remained almost unknown a set of high quality paleoclimate records from across the northern hemisphere shows evidence for a widespread and significant climatic anomaly at 9 2 ka b p this event has climatic anomaly patterns very similar to the 8 2 ka b p event cooling occurred at high latitudes and midlatitudes and drying took place in the northern tropics and is concurrent with an mwp of considerable volume 8100 km3 as the 9 2 ka mwp occurs at a time of enhanced baseline freshwater flow into the north atlantic this mwp may have been despite its relatively small volume sufficient to weaken thc and to induce the observed climate anomaly pattern

freshwater outburst from lake superior as a trigger for the cold event 9300 years ago paleoclimate proxy records reveal a pervasive cooling event with a northern hemispheric extent approximately 9300 years ago coeval changes in the oceanic circulation of the north atlantic imply freshwater forcing however the source magnitude and routing of meltwater have remained unknown located in central north america lake superior is a key site for regulating the outflow of glacial meltwater to the oceans here we show evidence for an approximately 45 meter rapid lake level fall in this basin centered on 9300 calibrated years before the present due to the failure of a glacial drift dam on the southeast corner of the lake we ascribe the widespread climate anomaly approximately 9300 years ago to this freshwater outburst delivered to the north atlantic ocean through the lake huron north bay ottawa river st lawrence river valleys

crustal disequilibrium of the central pontides northern turkey due to oroclinal bending revealed by gravity modelling abstract the turkish pontide orogenic belt belongs to the former eurasian margin which is the result of two major successive processes of the closure of the tethyan oceans subduction followed by collision this almost e w trending large mountain range shows an arc shaped geometric structure in the northern turkey according to previous studies based on geological and paleomagnetic data oroclinal deformation was proposed as a result of the geodynamic evolution due to the africa eurasia convergence in the region the aim of study is to determine how this important evolution is expressed in the lithosphere beneath the region by gravity modelling a bouguer gravity anomaly map was constructed and from this a gravity model is presented that reveals the general crustal structure underneath the northern turkey the results present a significant crustal thickness change that occurs in the n s and as well as in the e w directions from s to n a significant sharp crustal thickness decrease 20 km was found while from e to w the crustal thickness beneath the pontides increases by approximately 7 km while an average thickness of 37 km was calculated in the east it reached a maximum value of 44 km in the west although the reason for the increase in crustal thickness from north to south is logical in terms of the geodynamic evolution the increase from east to west is probably caused by the nature of the continental collision the most plausible explanation is an oblique nw indentation of the kirsehir block into the pontides

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

crustal s wave structure beneath eastern black sea region revealed by rayleigh wave group velocities abstract in this study the crustal s wave structure beneath the eastern black sea region including the eastern black sea basin ebsb and eastern pontides ep has been revealed using inversion of single station fundamental mode rayleigh wave group velocities in the period range of 4 40 seconds we used digital broadband recordings of 13 regional earthquakes that recently occurred in the easternmost ebsb recorded at stations of the kandilli observatory and earthquake research institute koeri the average group velocity dispersion curves were generated from 26 paths for the ebsb and 16 paths for the ep and they were inverted to determine the average 1 d shear wave structure of the region we have created a pseudo section roughly depicting the crustal structure of the region based on the group velocity inversion results of all station earthquake paths the thickness of the sedimentary layer reaches 12 km in the center of ebsb vs 2 5 3 1 km s and decreases 4 km in the ep there is a thin sedimentary layer in the ep vs 2 7 km s a consolidated thin crust that exists in the ebsb possesses a high seismic velocity vs 3 8 km s while a thin 26 km and transitional crust exists beneath the ebsb a thick about 42 km continental crust exists beneath the ep where the conrad is clearly seen at about a 24 km depth thick continental crust in the ep region is clearly distinguished from a gradational velocity change vs 3 4 3 8 km s the moho dips approximately southwards and the vs velocity 4 25 4 15 km s beneath the moho discontinuity decreases from the ebsb to the ep in the n s direction this may be an indication of a southward subduction

crustal model for the middle east and north africa region implications for the isostatic compensation mechanism summary we present a new 3 d crustal model for the middle east and north africa region that includes detailed topography sediment thickness and moho depth values the model is obtained by collecting integrating and interpolating reliable published sedimentary rock thickness and moho depth measurements in the middle east and north africa region to evaluate the accuracy of the model the 3 d gravity response of the model is calculated and compared with available observed bouguer gravity anomalies in the region the gravity modelling shows that the new crustal model predicts large portions of the observed bouguer anomalies however in some regions such as the red sea and caspian sea regions where crustal structure is relatively well determined the residual anomalies are of the order of a few hundred milligals since the new crustal model results in large residual anomalies in regions where reasonably good constraints exist for the model these large residuals cannot simply be explained by inaccuracies in the model to analyse the cause of these residuals further we developed an isostatically compensated airy type moho depth model and calculated its gravity response isostatic gravity anomalies are in nearly perfect agreement with the observed gravity values however the isostatic model differs significantly from the new 3 d crustal model if isostasy is to be maintained crustal and or upper mantle lateral density variations are needed to explain the large observed gravity residuals

holocene thinning of the greenland ice sheet the nature of the response of the greenland ice sheet gis to climate change is a fundamental question in climate science but the details remain unclear during the holocene climate optimum 6 000 to 9 000 years ago for example many locations in the northern hemisphere showed unusual warmth yet changes in greenland appeared inconsistent vinther et al now standardize the previously disparate seeming ice core records of climate history on the gis during the holocene and find consistent evidence for a stronger climate optimum than was previously recognized together with elevation reduction and marginal ice sheet thinning the response of the greenland ice sheet gis to changes in climate remains uncertain during the holocene climatic optimum an unusually warm period from about 9 000 to 6 000 years ago changes in greenland appear inconsistent with the rest of the northern hemisphere here the greenland holocene temperature history and the evolution of gis surface elevation are extracted from four gis locations the results may resolve this disparity on entering an era of global warming the stability of the greenland ice sheet gis is an important concern1 especially in the light of new evidence of rapidly changing flow and melt conditions at the gis margins2 studying the response of the gis to past climatic change may help to advance our understanding of gis dynamics the previous interpretation of evidence from stable isotopes 18o in water from gis ice cores was that holocene climate variability on the gis differed spatially3 and that a consistent holocene climate optimum the unusually warm period from about 9 000 to 6 000 years ago found in many northern latitude palaeoclimate records4 did not exist here we extract both the greenland holocene temperature history and the evolution of gis surface elevation at four gis locations we achieve this by comparing 18o from gis ice cores3 5 with 18o from ice cores from small marginal icecaps contrary to the earlier interpretation of 18o evidence from ice cores3 6 our new temperature history reveals a pronounced holocene climatic optimum in greenland coinciding with maximum thinning near the gis margins our 18o based results are corroborated by the air content of ice cores a proxy for surface elevation7 state of the art ice sheet models are generally found to be underestimating the extent and changes in gis elevation and area our findings may help to improve the ability of models to reproduce the gis response to holocene climate

near surface circulation in the northern north atlantic as inferred from lagrangian drifters variability from the mesoscale to interannual 1 the near surface circulation of the nordic seas is basically cyclonic and consists of jets and recirculation cells which are tightly linked to the bottom topography variable forcing by the large scale rotation of the wind leads to a modulation in the strength of the gyres and their interconnecting jets this is seen in drifter and altimeter data currents are stronger during winter and during phases of high north atlantic oscillation index the exchanges between the north atlantic and the nordic seas do not seem to be directly affected by this variable forcing the narrow boundary currents and the intergyre jets are subject to instability causing mesoscale current fluctuations which contribute to the stirring and mixing of polar and atlantic water masses

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

depth estimation from the scaling power spectrum of potential fields summary depth estimation from potential field power spectra requires a realistic assumption of the statistical properties of the source distributions density and susceptibility distributions in the earth s crust exhibit a long range dependence which is adequately described by scaling random fields with a spectral density proportional to some power of the wavenumber the theoretical power spectrum for a half space model of scaling sources explains the shape of observed power spectra of real potential field data very well minimizing the misfit between the model and the observed power spectrum yields an estimate for the depth to the top of the sources after demonstrating this approach on synthetic magnetic data we reinterpret power spectra of gravity and aeromagnetic data from utah hawaii and saskatchewan finding depth values that differ significantly from earlier interpretations all three power spectra are best explained by source distributions starting at surface level even the power spectrum from an aeromagnetic survey of a sedimentary basin with virtually non magnetic basin fill in the latter case a priori information on the intensity and the scaling exponent of the field caused by the basement had to be included to obtain an approximate estimate of the basin depth in general potential field power spectra are dominated by scaling properties of their source distributions and contain only limited depth information

measurement of the sortable silt current speed proxy using the sedigraph 5100 and coulter multisizer iie precision and accuracy the weight percentage and mean size of the 10 63 m terrigenous silt fraction termed sortable silt of fine grained marine sediments have recently been argued to be proxies for near bottom palaeocurrent intensity this paper details the accuracy and precision of the sedigraph 5100 and the coulter multisizer iie in determining the weight percentage and mean size of the sortable silt at abundances characteristic of deep ocean sediments three sortable silt standards and a fine silt clay diluent were generated from natural deep sea sediment of the iceland basin these were used to produce silty clays with standard additions of sortable silt ranging from 1 to 20 of the total by weight accuracy was measured relative to the size of the pure spike measured by each instrument at sortable silt abundance 5 the sedigraph and the coulter multisizer estimate both weight percentage and mean grain size precisely and accurately while below 5 instrumental noise degrades their performance on the basis of the sedigraph results a series of percentage errors is defined which may be applied to sortable silt mean size and weight percentage estimates used in palaeoceanographic near bottom current reconstruction it is suggested that ideally palaeocurrent reconstructions should be based on sedigraph determinations of the 0 63 m grain size distribution yielding both mean and abundance or on coulter multisizer determinations of the sortable silt grain size mean the coulter multisizer may prove especially useful in regions of very depleted 5 sortable silt component

hydrography and sedimentation under the deep western boundary current on bjorn and gardar drifts iceland basin abstract the interaction of northern component waters overflowing the iceland scotland ridge with sediments further south in the iceland basin has been responsible for highly variable sedimentation patterns since at least the late miocene 5 million years ago and has formed both bjorn and gardar drifts presently this process is maintained by a flux of approximately 3 sv measured along the south icelandic slope of iceland scotland overflow water isow with a mean regional flow direction to the sw which affects sediment transport on bjorn drift below 1350 m depth and over most of the gardar drift coriolis deflection of isow flow causes it to move as a deep western boundary current dwbc in the iceland basin which redistributes sediments under the influence of seabed topography here hydrographic and sedimentological data are used to illustrate the effects and extent of the vigorous dwbc activity the study presents a baseline against which inferred changes in the past can be assessed north of 58 n bottom nepheloid layers with heavy suspended sediment loads are often encountered particularly under the denser and faster flowing core of isow on the eastern slope of gardar drift in this area the presence of migrating regular sedimentary waves is seen on 3 5 khz profiles this is consistent with both the near bottom flow velocity probably in excess of 10 cm s 1 estimated by the geostrophic method and the presence of well sorted foraminiferal sand on the seabed south of 58 n dilute bottom nepheloid layers associated with more tranquil conditions near the seabed inferred from photographic and sedimentological evidence show that currents on gardar drift are weak although most of the south iceland basin is mantled by both regular and irregular non migratory mudwaves the absence of migrating structures with the exception of current intensification associated with discrete basement highs indicates that more sluggish currents characterise this region throughout the region highly variable mean holocene sediment accumulation rates are inferred 2 40 cm ka 1 as a result of the dwbc interacting with the topography

a decadal scale holocene sea surface temperature record from the subpolar north atlantic constructed using diatoms and statistics and its relation to other climate parameters 1 a sediment core from reykjanes ridge has been studied at 10 to 50 year time resolution to document variability of holocene surface water conditions in the western north atlantic and to evaluate effects of holocene ice rafting episodes diatom assemblages are converted to quantitative sea surface temperatures sst using three different transfer functions spectral and scale space methods are also applied on the records to explore variability at different timescales diatom assemblage and sst records clearly show that decaying remnants of the laurentide ice sheet strongly influenced early holocene climate in the western north atlantic this overrode the predominance of milankovitch forcing which played a key role in the development of holocene climate in the eastern north atlantic and nordic seas superimposed on general holocene climate change is high frequency sst variability on the order of 1 3 c the record also documents climatic oscillations with 600 to 1000 1500 and 2500 year periodicities with a time dependent dominance of different periodicities through the holocene a clear change in variability occurred about 5 ka bp the sst record also provides evidence for holocene cooling events hce that in some cases correlate to documented southward intrusions of ice into the north atlantic

curie point depth investigation of central anatolia turkey the residual aeromagnetic total field intensity anomalies in central anatolia were calculated from the regional aeromagnetic anomalies surveyed by the mineral research and exploration mta of turkey the residual aeromagnetic data were analyzed to produce curie point estimates by the method of okubo et al 1985 the curie point depth of central anatolia varies from 7 9 km and 22 6 km the shallowest curie point depths were observed around the cappadocia and erciyes volcanic complexes in central anatolia a good correlation was deduced between the curie point depths and the heat flow data measured previously which is most certainly important for the geothermal resources of the region the shallow curie point depths also correlate well with the hot spring locations in central anatolia

petrology and geochemistry of tertiary volcanic rocks from the ikizce ordu area ne turkey implications for the evolution of the eastern pontide paleo magmatic arc abstract tertiary volcanism in the ikizce region at the western edge of the eastern pontides paleo magmatic arc is represented by basaltic and andesitic rocks associated with sediments deposited in a shallow basin environment the basaltic rocks contain plagioclase an58 80 olivine fo82 84 clinopyroxene wo44 48en35 42fs7 17 hornblende mg 0 68 0 76 phenocrysts and magnetite microcrysts whereas the andesitic rocks include plagioclase an25 61 clinopyroxene wo46 49en38 43fs11 13 hornblende mg 0 48 0 81 biotite mg 0 48 0 60 phenocrysts titanomagnetite apatite and zircon microcrysts geochemical data indicate magmatic evolution from tholeiitic alkaline transitional to calc alkaline characteristics with medium k contents the geochemical variation in the rocks can be explained by fractionation of common mineral phases such as clinopyroxene olivine hornblende plagioclase magnetite and apatite the trace elements distributions of the volcanic rocks show similarities to those of e type morb have a shape that is typical of rocks from subduction related tectonic setting with enrichment in lile and to a lesser extent in lree but depletion in hfse the rocks evolved from a parental magma derived from an enriched source formed by subduction induced metasomatism of basaltic rocks the latter formed through clinopyroxene olivine controlled fractionation in a high level magma chamber the andesitic rocks developed through hornblende plagioclase controlled fractionation in shallow level magma chamber s

curie point depths of the island of kyushu and surrounding areas japan as part of a comprehensive nationwide evaluation of geothermal resources for japan the first of the curie point depth maps covering the island of kyushu has been prepared the map was created by inverting gridded regional aeromagnetic data two satisfactory algorithms were developed to invert the gridded data based upon a distribution of point dipoles the first algorithm estimates x0 y0 and z0 the coordinates of the centroid of the distribution by computing a least squares fit to the radial frequency of the fourier transform the second algorithm estimates centroid depth only by computing a least squares fit to the squared amplitude of the frequency estimates the average depth to the top zt of the collection of point dipoles was estimated by a variation of the second algorithm the depth to the bottom of the dipoles inferred curie point depth is zb 2z0 zt the depth estimates are hand contoured to produce the final map the curie point depth map is then compared to regional geology and heat

two millennia of north atlantic seasonality and implications for norse colonies 18o values of mollusks recovered from near shore marine cores in northwest iceland quantify significant variation in seasonal temperature over the period from 360 b c to a d 1660 twenty six aragonitic bivalve specimens were selected to represent intervals of climatic interest by using core sedimentological characteristics carbonate powder was sequentially micromilled from shell surfaces concordant with growth banding and analyzed for stable oxygen 18o and carbon 13c isotope values because 18o values record subseasonal temperature variation over the lifetime of the bivalves these data provide the first 2 000 year secular record of north atlantic seasonality from ca 360 cal yr b c to cal yr a d 1660 notable cold periods 360 b c to 240 b c a d 410 and a d 1380 to 1420 and warm periods 230 b c to a d 140 and a d 640 to 760 are resolved in terms of contrast between summer and winter temperatures and seasonal temperature variability literature from the viking age ca 790 to 1070 during the establishment of norse colonies and later in iceland and greenland permits comparisons between the 18o temperature record and historical records thereby demonstrating the impact of seasonal climatic extremes on the establishment development and in some cases collapse of societies in the north atlantic

rapid holocene deglaciation of the labrador sector of the laurentide ice sheet abstract retreat of the laurentide ice sheet lis following the last glacial maximum 21 000 yr bp affected regional to global climate and accounted for the largest proportion of sea level rise although the late pleistocene lis retreat chronology is relatively well constrained its holocene chronology remains poorly dated limiting our understanding of its role in holocene climate change and sea level rise here new 10be cosmogenic exposure ages on glacially deposited boulders are used to date the final disappearance of the labrador sector of the lis ls lis these data suggest that following the deglaciation of the southeastern hudson bay coastline at 8 0 0 2 cal ka bp the southwestern margin of the ls lis rapidly retreated 600 km in 140 yr and most likely in 600 yr at a rate of 900 m yr 1 with final deglaciation by 6 8 0 2 10be ka the disappearance of the ls lis 6 8 10be ka and attendant reduction in freshwater runoff may have induced the formation of labrador deep seawater while the loss

surface and deep ocean interactions during the cold climate event 8200 years ago evidence from a north atlantic deep sea sediment core reveals that the largest climatic perturbation in our present interglacial the 8200 year event is marked by two distinct cooling events in the subpolar north atlantic at 8490 and 8290 years ago an associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the atlantic meridional overturning circulation the existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying laurentide ice sheet margin

gulf stream density structure and transport during the past millennium the gulf stream transports approximately 31 sv 1 sv 10 6 m 3 s 1 of water and 1 3 10 15 w of heat into the north atlantic ocean the possibility of abrupt changes in gulf stream heat transport is one of the key uncertainties in predictions of climate change for the coming centuries given the limited length of the instrumental record our knowledge of gulf stream behaviour on long timescales must rely heavily on information from geologic archives here we use foraminifera from a suite of high resolution sediment cores in the florida straits to show that the cross current density gradient and vertical current shear of the gulf stream were systematically lower during the little ice age ad 1200 to 1850 we also estimate that little ice age volume transport was ten per cent weaker than today s the timing of reduced flow is consistent with temperature minima in several palaeoclimate records implying that diminished oceanic heat transport may have contributed to little ice age cooling in the north atlantic the interval of low flow also coincides with anomalously high gulf stream surface salinity suggesting a tight linkage between the atlantic ocean circulation and hydrologic cycle during the past millennium

reconstruction of the late holocene changes in the sub arctic front position at the reykjanes ridge north atlantic changes in the dynamics of the north atlantic subpolar gyre are involved in the modulation of the northward salinity and heat transport in the northern north atlantic via the north atlantic current nac variations in the strength of the east greenland current egc can influence the gyre dynamics by impacting deep convection in the labrador sea oxygen isotope data of three planktonic foraminiferal species surface water neogloboquadrina pachyderma dextral coiling and globigerina bulloides thermocline recorder globorotalia inflata from a site located close to the present sub arctic front at the reykjanes ridge suggest significant strengthening or shifting of the sub arctic front throughout the late holocene the oxygen isotope based inferences are supported by mg ca derived temperature reconstructions from neogloboquadrina pachyderma dextral coiling alkenone derived sea surface temperature and other paleoclimatic proxy data the late holocene strengthening shift of the sub arctic front appears caused

the indian bay formation fossiliferous early ordovician volcanogenic rocks in the northern gander terrane newfoundland and their regional significance the first reported fossiliferous rocks in the northern gander terrane of the newfoundland appalachians occur at indian bay big pond in an area previously mapped as unfossiliferous quartzose sedimentary rocks of the gander group brachiopods trilobites and bryozoans in argillaceous tuff indicate a late arenigian late early ordovician age the rocks associated with the fossils are similar to coeval rocks of the dunnage terrane in newfoundland but are atypical of the gander terrane the sequence that includes the fossiliferous rocks at indian bay big pond is here named the indian bay formation the indian bay formation may overlie the gander group stratigraphically but structural geophysical and geochemical data suggest that the rocks of the indian bay formation are contained in a klippe thrust onto the gander terrane

holocene climate variability reflected in diatom derived sea surface temperature records from the subpolar north atlantic a detailed investigation of two deep sea sediment cores from the gardar drift in the subpolar north atlantic cores md99 2251 and md99 2252 has been undertaken to determine the extent of holocene

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

cenozoic sediment accumulation on drifts in the northern north atlantic the northern north atlantic sediment drifts have a much greater areal extent than has previously been indicated the northern north atlantic extends from the east greenland to european continental shelves and from the charlie gibbs fracture zone to the greenland scotland ridge within this region are seven major sediment drifts containing some of the best clues for pre quaternary bottom water circulation in the north atlantic feni drift is the oldest in the region originating near the eocene oligocene boundary it was followed by accumulation of bjorn gardar hatton and snorri drifts from the late early to middle miocene eirik drift may have started to accumulate in the late miocene and gloria drift in the early pliocene through analysis of the cenozoic sediment mass age distribution and the change in area of seafloor for the study area through time it can be concluded that there is a deficit of oligocene to miocene sediment in the region this could be explained by sediment cycling the erosion of older sediment to produce young sediment the mass of pliocene to quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of eocene and oligocene sediment by deepwater currents the sediment drift portion of the total regional sediment mass increased significantly three times during the cenozoic each of these drift growth phases lasted between 3 and 4 m y the first two growth phases from the late eocene to early oligocene and from the early to middle miocene were accompanied by northward shifts of depocenters to the newly forming sediment drifts the third and largest growth phase occurred between 7 and 3 ma and may have been preceded by the initiation of accumulation on eirik drift 8 7 ma this most recent growth phase was accompanied by high apparent accumulation rates over southern gardar drift as it expanded to the east erosion rates over reykjanes ridge may have been higher during the mid pliocene than in the quaternary there are two main sites where dense water could have formed and flowed south through the rockall trough to start the accumulation of feni drift if the atmosphere were cool enough dense water could have formed in the norwegian sea or on the faeroe shelf dense water may also have formed on the rockall plateau due to salinity increase through evaporation in an arid climate as an alternative to the hypothesis of arctic ocean water overflowing the iceland faeroe ridge in the early middle miocene it is suggested that dense water formed along shallow segments of the iceland faeroe ridge and then flowed into the south iceland basin to begin accumulation of bjorn gardar and snorri drifts the initiation of sediment drift formation in the south iceland basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a middle miocene uplift event along the iceland faeroe ridge a second uplift event along the greenland scotland ridge and a decreased production of northern component water in the early pliocene may be responsible for increased sediment accumulation in bjorn gardar and eirik drifts

amplitude and timing of temperature and salinity variability in the subpolar north atlantic over the past 10 k y paired planktic foraminiferal 18 o and mg ca data reveal trends of increasing temperatures 3 c and salinities in the subpolar north atlantic over the course of the holocene which were punctuated by abrupt events the trends likely refl ect an insolation forced northward retreat of the boundary between polar and north atlantic subsurface waters the superimposed variability does not appear to be periodic but tends to recur within a broad millennial band the records provide convincing evidence of open ocean cooling nearly 2 c and freshening during the 8 2 ka event and suggest similar conditions at 9 3 ka however the two largest temperature oscillations in our record 2 c occurred during the past 4 k y suggesting a recent increase in temperature variability relative to the mid holocene perhaps in response to neoglaciation which began at about this time

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

lithospheric structure of the continent continent collision zone eastern turkey summary we infer the lithospheric structure in eastern turkey using teleseismic and regional events recorded by 29 broad band stations from the eastern turkey seismic experiment etse we combine the surface wave group velocities rayleigh and love with telesesimic receiver functions to jointly invert for the s wave velocity structure moho depth and mantle lid lithospheric mantle thickness we also estimated the transverse anisotropy due to love and rayleigh velocity discrepancies we found anomalously low shear wave velocities underneath the anatolian plateau average crustal thickness is 36 km in the arabian plate 44 km in anatolian block and 48 km in the anatolian plateau we observe very low shear wave velocities at the crustal portion 30 38 km of the northeastern part of the anatolian plateau the lithospheric mantle thickness is either not thick enough to resolve it or it is completely removed underneath the anatolian plateau the shear velocities and anisotropy down to 100 km depth suggest that the average lithosphere asthenosphere boundary in the arabian plate is about 90 and 70 km in anatolian block adding the surface waves to the receiver functions is necessary to constrain the trade off between velocity and the thickness we find slower velocities than with the receiver function data alone the study reveals three different lithospheric structures in eastern turkey the anatolian plateau east of karliova triple junction the anatolian block and the northernmost portion of the arabian plate the boundary of lithospheric structure differences coincides with the major tectonic boundaries

jurassic cretaceous paleomagnetism and paleogeography of the pontides turkey published paleomagnetic data from the pontides indicate anomalously low jurassic and early cretaceous paleolatitudes compatible with the southern neo tethyan african continental margin and significantly different from paleolatitudes predicted for the northern eurasian neo tethyan margin we present a new set of paleomagnetic data from 50 late cretaceous sites mainly from the western pontides and from the eastern pontides and 11 early jurassic sites mainly from the eastern pontides fold tests indicate that the characteristic magnetization components predate eocene folding late cretaceous site mean declinations are northerly in the eastern pontides and rotated to the west by a few tens of degrees in the western pontides late cretaceous site mean declinations are affected by local clockwise rotation in one sampling region close to the north anatolian fault the mean late cretaceous inclinations and resulting paleolatitudes are 41 1 23 5 n and 43 7 25 5 n for the western and eastern pontides respectively for the eastern pontides the early jurassic liassic mean inclination is 60 5 yielding a paleolatitude of 41 4 n considerably further north than previous paleolatitude estimates for the eastern pontides at this time the paleolatitude estimates for the western and eastern pontides are consistent with these units being close to the eurasian continental margin during liassic and late cretaceous time

determination of the crustal and thermal structure of the erzurum horasan pasinler basins eastern turkiye using gravity and magnetic data the erzurum horasan pasinler basin which surrounds miocene rocks is oriented approximately e w and is located in eastern anatolia turkiye east anatolia where ophiolitic and young volcanic rocks are widespread is situated in the alpine himalayan fold thrust fault belt the nw se trending north anatolian transform fault zone and the ne sw trending east anatolian transform fault zone formed by the compressional regime of east anatolia control the main tectonics of the study region while the moho and conrad depths of the study region are 43 0 and 20 9 km respectively the average sedimentary thickness has been determined to be 5 2 km by using the power spectrum method on the other hand it is found that the depth of the moho in the region varies from 41 0 to 44 5 km and the depth of the conrad discontinuity varies between 22 and 26 km as computed using empirical equations the basement of the sedimentary layer is calculated to be 6 km by using inversion results applied to the residual gravity data the curie point depth and average heat flow value in this region are calculated as 18 0 km and 89 1 m wm 2 respectively geotherm calculations reveal that the moho temperature is 1 028 0 c based on the crustal model the high heat flow values obtained are attributed to tectonic activities and melting of the lithospheric mantle caused by upwelling of the asthenosphere

dynamics of north atlantic deep water masses during the holocene high resolution flow speed reconstructions of two core sites located on gardar drift in the northeast atlantic basin and orphan knoll in the northwest atlantic basin reveal a long term decrease in flow speed of northeast atlantic deep water neadw after 6 500 years benthic foraminiferal oxygen isotopes of sites currently bathed in neadw show a 0 2 depletion after 6 500 years shortly after the start of the development of a carbon isotope gradient between neadw and norwegian sea deep water we consider these changes in near bottom flow vigor and benthic foraminiferal isotope records to mark a significant reorganization of the holocene deep ocean circulation and attribute the changes to a weakening of neadw flow during the mid to late holocene that allowed the shoaling of lower deep water and deeper eastward advection of labrador sea water into the northeast atlantic basin

age of the fjord stade moraines in the disko bugt region western greenland and the 9 3 and 8 2 ka cooling events abstract retreat of the western greenland ice sheet during the early holocene was interrupted by deposition of the fjord stade moraine system the fjord stade moraine system spans several hundred kilometers of western greenland s ice free fringe and represents an important period in the western greenland ice sheet s deglaciation history but the origin and timing of moraine deposition remain uncertain here we combine new and previously published 10 be and 14 c ages from disko bugt western greenland to constrain the timing of fjord stade moraine deposition at two locations 60 km apart at jakobshavn isfjord the northern of two study sites we show that jakobshavn isbrae advanced to deposit moraines ca 9 2 and 8 2 8 0 ka in southeastern disko bugt the ice sheet deposited moraines ca 9 4 9 0 and 8 5 8 1 ka our ice margin chronology indicates that the greenland ice sheet in two distant regions responded in unison to early holocene abrupt cooling 9 3 and 8 2 ka as recorded in central greenland ice cores although the timing of fjord stade moraine deposition was synchronous in jakobshavn isfjord and southeastern disko bugt within uncertainties we suggest that jakobshavn isbrae advanced while the southeastern disko bugt ice margin experienced stillstands during the 9 3 and 8 2 ka events based on regional geomorphology and the distribution of 10 be ages at each location the contrasting style of ice margin response was likely regulated by site specific ice flow characteristics jakobshavn isbrae s high ice flux results in an amplified ice margin response to a climate perturbation both warming and cooling whereas the comparatively low flux sector of the ice sheet in southeastern disko bugt experiences a more subdued response to climate perturbations our chronology indicates that the western greenland ice sheet advanced and retreated in concert with early holocene temperature variations and the 9 3 and 8 2 ka events although brief were of sufficient duration to elicit a significant response of the western greenland ice sheet

east anatolian high plateau as a mantle supported north south shortened domal structure an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017858 shtml http atlas geo cornell edu turkey publications sengor et al 2003 htm

centennial to millennial scale holocene climate deep water linkage in the north atlantic the stability of the earth s climate is strongly linked to the steadiness of the atmospheric and oceanic transport of heat from low to high latitudes high resolution holocene sedimentary records from the subpolar north atlantic demonstrate a persistent link between centennial to millennial scale fluctuations in the flow speed of iceland scotland overflow water inferred from granulometric proxy data and both the surface north atlantic current component of the meridional overturning circulation moc and published fennoscandian atmospheric temperature variability however these data also highlight the difficulties associated with the interpretation of geochemical and sedimentological deep water circulation proxies as they do not provide a wholly consistent picture the similarity between surface and deep ocean 13c records suggests a preformed component in the deep ocean 13c signal on the other hand the sedimentological results display a strong linkage to changing conditions in the overlying surface ocean waters suggesting this proxy better reflects the activity of the moc at least during the holocene of this region the most widespread oceanic perturbation coincides with an interval of possibly global climatic deterioration around 2700 years ago these results firmly establish deep water production in the nordic seas as a key component in the assortment of variables affecting climate during the holocene

investigation of crustal thickness in eastern anatolia using gravity magnetic and topographic data the tectonic regime of eastern anatolia is determined by the arabia eurasia continent continent collision several dynamic models have been proposed to characterize the collision zone and its geodynamic structure in this study change in crustal thickness has been investigated using gravity magnetic and topographic data of the region in the first stage two dimensional low pass filter and upward analytical continuation techniques were applied to the bouguer gravity data of the region to investigate the behavior of the regional gravity anomalies next the moving window power spectrum method was used and changes in the probable structural depths from 38 to 52 km were determined the changes in crustal thickness where free air gravity and magnetic data have inversely correlated and the type of the anomaly resources were investigated applying the euler deconvolution method to bouguer gravity data the obtained depth values are consistent with the results obtained using the power spectrum method it was determined that the types of anomaly resources are different in the west and east of the 40 e longitude finally using the obtained findings from this study and seismic velocity models proposed for this region by previous studies a probable two dimensional crust model was constituted

determination of tectonic and crustal structure of the eastern pontide orogenic belt ne turkey using gravity and magnetic data the eastern pontide orogenic belt is one of the most complex geodynamic settings within the alpine belt subduction polarity which is responsible for the formation of the eastern pontide magmatic arc is still under debate because of limited geological geophysical and geochemical data this orogenic belt is mainly divided into three subzones depending on lithological characteristics and facies changes as in northern southern and axial zones from north to south these zones are separated from each other by near vertical faults that display the block faulting tectonic style of this belt in this study the tectonic and crustal structure of the eastern pontides which as yet have not been prospected by using geophysical data has been investigated with potential field data the horizontal gradient map obtained from gravity data shows a number of steep and gentle lineaments it seems that these lineaments e w ne and nw trending correspond to major structural zones of continental crust additionally the moho depth and curie point depth variation maps of the eastern pontide orogenic belt have been computed with the power spectral method of the radial wavenumber carried out by using the fast fourier transform method as a result of this method we estimated that the depths of the moho and curie point varied between 29 0 1 2 47 2 1 9 km and 14 3 0 7 27 9 1 4 km respectively our findings indicate that the moho depth generally increases from north to south in the region however the curie point depth level within the crust has an undulating surface not a horizontal one

faroe bank channel overflow 1995 2005 abstract the faroe bank channel fbc is the deepest passage across the greenland scotland ridge and there is continuous overflow of dense water through the channel which provides a substantial contribution to the global thermohaline circulation since november 1995 acoustic doppler current profilers adcps have been moored at the sill of the channel continuously except for short annual servicing periods in addition to this ctd sections have regularly been occupied across the channel and instruments recording temperature and salinity have been moored for short periods these observations demonstrate that the channel due to its small width can be monitored fairly well with only one adcp mooring and they allow the generation of a time series of overflow volume flux for the 1995 2005 period the kinematic overflow flux defined solely from the velocity field was found to have an average value of 2 1 0 2 sv with a seasonal and with inter annual variations of approximately 10 amplitude but with no discernible trend for the whole period the average flux of water with potential density exceeding 27 8 kg m 3 was found to be 1 9 0 3 sv with average properties 0 25 c s 34 93 28 01 kg m 3 for this period no evidence was found for a weakening overflow flux but the salinity of the fbc overflow especially the warmer parts has increased substantially during the period which implies an increased average density on the order of 0 01 kg m 3 previous observations of a helical cross channel circulation are confirmed and may explain the thin pycnocline layer but shear instability induces intensive mixing that puts a lower limit on the layer thickness critical control at one point of the sill cross section rather than friction seems to govern the overflow dynamics and simple layered models can explain much of the observed features as well as the seasonal variation but potential vorticity as defined for a single overflow layer is not conserved a previously suggested 1950 2000 weakening of the fbc overflow which was partly based on a subset of the data presented here is not supported by the full dataset

volcanic belts as markers of the mesozoic cenozoic active margin of eurasia discussion discussion sur l article de kazmin v g sbortshikov i m ricov l e zonenshain l p bovlin j knipper a l paru dans tectonophysics nld 1986 123 123 152

approximating edges of source bodies from magnetic or gravity anomalies cordell and grauch 1982 1985 discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks the final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes we attempt to automate their final step our method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources the method applies to both local surveys and to continent wide compilations of magnetic and gravity data e g zietz 1982 simpson et al 1983a kane et al 1982

one dimensional thermal modeling of the eastern pontides orogenic belt ne turkey the eastern pontides orogenic belt is one of the most complex geodynamic settings in the alpine himalayan belt due to the lack of systematical geological and geophysical data in this study 1d crustal structure and p wave velocity distribution obtained from gravity modeling and seismological data in the area has been used for the development of the thermal model of the eastern pontides orogenic belt the computed temperature depth profiles suggest a temperature of 590 60 c at a moho depth of 35 km indicates the presence of a brittle ductile transition zone this temperature value might be related to water in the subducted crust of the tethys oceanic lithosphere the curie temperature depth value of 29 km which may correspond to the crustal magma chambers is found 5 7 km below the moho depth surface heat flow density values vary from 66 5 and 104 7 mw m 2 high mantle heat flow density value of 48 mw m 2 is obtained for the area should be related to melting of the lithospheric mantle caused by upwelling of asthenosphere

curie point depth map of turkey summary a curie point isotherm map of the whole of turkey has been prepared from aeromagnetic data by means of a spectral analysis technique the most characteristic signature of this map is that the shallow depths generally correlated with the young volcanic rocks and the thinned crustal thicknesses in the west reveal geothermal fields and several hot springs the orogenic pontide belt of the black sea region in the north the western taurus belt in the south and some high plateaus in eastern turkey show that the deepest curie isotherm depths range between 20 and 29 km depth contour lines elongating in an almost e w direction are due to the overlapping percentage of adjacent data blocks of 50 per cent in the e w direction and to magnetic anomalies trending in the e w direction curie isotherm depths are in the range 6 to 10 km in the aegean region and are characterized by e w and ne sw trending graben structures as expected since the region has crustal thinning and many hot springs and geothermal fields these imply the existence of shallow heat sources that could be utilized for electricity heating of towns and cities greenhouse and health purposes

crustal thickness of turkey determined by receiver function abstract two hundred and sixty seven teleseismic events with a moment magnitude greater than 5 5 which occurred between january 2005 and october 2010 were analyzed to determine the moho depth variation beneath turkey by using the receiver function rf technique the rf technique was applied to 120 broadband seismic stations which were already deployed in the area permanently by the kandilli observatory and earthquake research institute koeri and the disaster and emergency management presidency afad the rfs were stacked considering back azimuth slowness and waveform similarities to enhance the signal noise ratio the genetic algorithm ga was used to obtain both 1 d shear wave speed model and the moho depth beneath each seismic station a data set consisting of 112 shear speed models derived from rfs revealed the crustal structure of turkey for imaging several 2 d profiles of depth migrated rfs were constructed to delineate the fine crustal structure the moho discontinuity is clearly seen on all profiles and the mid crustal velocity discontinuity within the crust is observed in some profiles the depth of the moho varies between 24 and 48 km the thinnest crustal thickness is located on the coast of western turkey and the deepest moho boundary is observed in eastern turkey the shear wave velocities vary between 4 0 km s and 4 5 km s in the uppermost mantle beneath turkey

holocene multidecadal to millennial scale variations in iceland scotland overflow and their relationship to climate the nordic seas overflows are an important part of the atlantic thermohaline circulation while there is growing evidence that the overflow of dense water changed on orbital time scales during the holocene less is known about the variability on shorter time scales beyond the instrumental record here we reconstruct the relative changes in flow strength of iceland scotland overflow water isow the eastern branch of the overflows on multidecadal millennial time scales the reconstruction is based on mean sortable silt ss from a sediment core on the gardar drift 60 19 n 23 58 w 2081 m our ss record reveals that the main variance in isow vigor occurred on millennial time scales 1 2 kyr with particularly prominent fluctuations after 8 kyr superimposed on the millennial variability there were multidecadal centennial flow speed fluctuations during the early holocene 10 9 kyr and one prominent minimum at 0 9 kyr we find a broad agreement between reconstructed isow and regional north atlantic climate where a strong weak isow is generally associated with warm cold climate we further identify the possible contribution of anomalous heat and freshwater forcing respectively related to reconstructed overflow variability we infer that ocean poleward heat transport can explain the relationship between regional climate and isow during the middle to late holocene whereas freshwater input provides a possible explanation for the reduced overflow during early holocene 8 10 kyr

investigation into the regional wrench tectonics of inner east anatolia turkey using potential field data abstract the residual aeromagnetic and gravity anomalies of inner east anatolia surveyed by the mineral research and exploration mta of turkey display complexities some faults which are known and new lineaments are drawn from maxspot map derived from the location of the horizontal gradient of gravity anomalies tectonic lineaments of inner east anatolia exhibit similarities to the direction of east anatolian fault zone anticlockwise rotation approximately 30 defined from disorientations of aeromagnetic anomalies the lineaments obtained from maxspots map produced from the gravity anomalies and disoriented aeromagnetic anomalies are in line with the mobilistic system revealed by the palaeomagnetic data these alpine age continental rotations caused westward wrenching of the global lithosphere and led to significant tectonic reactivation and deformations gps measurements current tectonic knowledge and the results of the evaluation of potential field data were combined in a base map to demonstrate similarities

curie point depths based on spectrum analysis of aeromagnetic data west anatolian extensional province turkey the curie point depth map of western anatolia was constituted from spectral analysis of the aeromagnetic data the curie point depth values from 53 overlapping blocks 90 90 km in size have been estimated from the band pass filtered data the slope of the longest wavelength part of the radially averaged log power spectrum divided by the radial frequency produced the depth to the centroid z0 for the deepest crustal block the depth to the top zt was obtained by the slope of the second longest wavelength part of the spectrum from these depths the curie point depth was then calculated by using zb 2z0 zt the curie point depth estimates for western anatolia range between 8 2 and 19 9 km

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

links between early holocene ice sheet decay sea level rise and abrupt climate change the beginning of the holocene interglacial was marked by ice sheet melting and sea level rise a review of sea level and climate records identifies two sea level jumps associated with the final drainage of glacial lake agassiz and links them to an abrupt cooling event

lithospheric structure of the arabian and eurasian collision zone in eastern turkey from s wave receiver functions summary crustal and upper mantle seismic discontinuities beneath eastern turkey are imaged using teleseismic s to p converted phases three crustal phases are observed the moho with depth ranging between 30 and 55 km indicating variable tectonic regimes within this continental collision zone an upper crustal discontinuity at approximately 10 km depth and various crustal low velocity zones possibly associated with recent quaternary volcanism imaging of the upper mantle is complicated by the 3 d geometry of the region in particular due to the bitlis zagros suture zone however several upper mantle s to p converted phase are identified as being the signature of the lithosphere asthenosphere boundary lab the inferred lab for the eastern anatolian accretionary complex indicates that eastern turkey has an anomalously thin between 60 and 80 km lithosphere which is consistent with an oceanic slab detachment model the observed lab phases for the arabian shield and iranian plateau indicate that lithospheric thickness for these stable regions is on the order of 100 to 125 km thick which is typical of continental margins

the arctic atlantic thermohaline circulation abstractthe atlantic ocean s thermohaline circulation is an important modulator of global climate its northern branch extends through the nordic seas to the cold arctic a region that appears to be particularly influenced by climate change a thermohaline circulation is fundamentally concerned with two degrees of freedom this is in particular the case for the inflow of warm and saline atlantic water through the nordic seas toward the arctic that is balanced by two branches of outflow the authors present an analytical model rooted in observations that constrains the strength and structure of this arctic atlantic thermohaline circulation it is found maybe surprisingly that the strength of atlantic inflow is relatively insensitive to anomalous freshwater input it mainly reflects changes in northern heat loss freshwater anomalies are predominantly balanced by the inflow s partition into estuarine and overturning circulation with southward polar outflow in the surface and dense overflow at depth res

variations in the strength of the north atlantic bottom water during holocene abstract we report here on a multi proxy study of the changes in the dynamics and the properties of bottom water mass in the subpolar north altantic during holocene magnetic properties coupled with sortable silt and benthic carbon isotopes are investigated for holocene marine sedimentary sequences located in the charlie gibbs fracture zone 53 n and in central 57 n and southern gardar drift 59 n all the cores are located at water depths bathed by the iceland scotland overflow water isow mixed at the southernmost locality with southern sourced water masses the long term variations in measured proxies are fitted with similar polynomial curves an early holocene event characterized by a shutdown shoaling of the bottom circulation at the deepest sites is most likely related to the main deglacial freshwater inputs it is followed by a progressive strengthening deepening of the overflow water which culminates around 6 kyr in coincidence with the holocene thermal maximum after 6 kyr corresponding to a drastic hydrological reorganization in the north atlantic a general decline in the bottom flow strength is observed until about 2 kyr b p when it reached its present day state after detrending several short periods of reduced bottom flow strength and sedimentary transport from the northern detrital sources are observed with a periodicity of around 600 yr with no clear relationship at this time scale between surface and deep ocean