seismicity and subterranean sounds in the northwest deccan volcanic province of india abstract the northwestern deccan volcanic province in india is one of the most seismically active intraplate regions of the world in addition the region is associated with episodic swarm activity and reports of sounds whose linkage hitherto remains elusive during the month of january 2016 a swarm activity occurred in the kachchh and saurashtra regions and continued for about two months many of the events were accompanied by audible sounds like blasting that caused severe panic among local residents prompting us to investigate the causative mechanism the events were recorded by our seismic stations and an additional five stations that we were able to deploy at the onset of the swarm the activity produced sounds with good energy in the audible frequency range of humans spectrogram analysis of the events with associated sounds revealed frequencies 20 hz in contrast to the lower frequencies for those that did not generate the sounds in addition to the higher frequencies we observed horizontal particle motion that was dominated by retrograde elliptical motion consistent with rayleigh waves these observations were not recorded from any of the events that did not generate sounds audible sounds generated by earthquakes are consistently reported from shallow earthquakes that generate high frequency surface waves

holocene climatic evolution at the chinese loess plateau testing sensitivity to the global warming cooling events abstract a high resolution petromagnetic analysis demonstrates that pedogenic alterations in holocene loess sand sequences from the regions of the guanzhong basin and the mu us desert on the chinese loess plateau clp were affected by climatic variations in temperature and precipitation three warm humid intervals 8 4 3 7 2 4 1 2 and 0 81 0 48 ka associated with soil formation and relatively high values of petromagnetic parameters occurred during the holocene a substantial paleosol development from 8 4 to 3 7 ka and higher petromagnetic parameter values indicate a generally strong warm humid phase in the mid holocene which can be attributed to the holocene climatic optimum our study demonstrates that the holocene climate in the eastern part of the clp is sensitive to warming and cooling events linked to global changes in temperature and precipitation a complete holocene climate record is constructed correlating well with the other regional climate records along the south to north profile on eastern clp and suggesting that similar climatic changes occurred in eastern monsoonal china during the holocene results are supported by other climate records in different regions of the world and imply that the holocene climatic optimum in the northern hemisphere probably took place at the same time

environmental conditions for the presence of magnetofossils in the last glacial maximum inferred from magnetic parameters of sediments from the ulleung basin east sea abstract magnetic characterization of sediments from the ulleung basin in the east sea japan sea was carried out to decipher changes in environmental conditions over the last 39 000 years magnetic susceptibility intensities of natural remanent magnetization nrm anhysteretic remanent magnetization arm partial arm parm and saturation isothermal remanent magnetization sirm were measured for selected samples irm acquisition hysteresis and first order reversal curve forc measurements were made the ratios of rock magnetic parameters such as arm sirm arm and s ratio were determined to identify magnetic grain size and mineralogical variations along with electron microscope observations of magnetic mineral extracts down core variations in rock magnetic parameters for the 5 21 m long sediment core reveal distinct intervals with different grain size concentration and composition of magnetic minerals the uppermost portion and the high magnetic intensity zone hiz in marine isotope stage mis 2 are characterized by higher concentrations of fine grained magnetite whereas the mis 1 and 3 intervals contain lower concentrations of coarser grained magnetic minerals with increasing influence of hematite and or iron sulphide minerals the hiz interval is inferred to contain high occurrences of fine grained bacterial magnetosomes based on geochemical proxies east sea conditions for the hiz interval coincident with the last glacial maximum lgm can be summarized as having low total organic carbon toc enhanced eolian contributions from terrestrial organic particles and iron bearing minerals under the influence of an intensified east asian winter monsoon along with iron reducing but not sulphidic conditions that favoured growth and preservation of magnetotactic bacteria the delicate balance between reductive dissolution of magnetofossils under sulphidic conditions and production and preservation of magnetotactic bacteria in overlying iron reducing sediments for the hiz interval is responsible for the resultant abundance variations of magnetosomes in the studied sediments

a thermodynamically self consistent damage equation for grain size evolution during dynamic recrystallization summary we employ basic non equilibrium thermodynamics to propose a general equation for the mean grain size evolution in a deforming medium under the assumption that the whole grain size distribution remains self similar we show that the grain size reduction is controlled by the rate of mechanical dissipation in agreement with recent findings our formalism is self consistent with mass and energy conservation laws and allows a mixed rheology as an example we consider the case where the grain size distribution is lognormal as is often experimentally observed this distribution can be used to compute both the kinetics of diffusion between grains and of dynamic recrystallization the experimentally deduced kinetics of grain size coarsening indicates that large grains grow faster than what is assumed in classical normal grain growth theory we discuss the implications of this model for a mineral that can be deformed under both dislocation creep and grain size sensitive diffusion creep using experimental data of olivine our predictions of the piezometric equilibrium in the dislocation creep regime are in very good agreement with the observations for this major mantle forming mineral we show that grain size reduction occurs even when the average grain size is in diffusion creep because the largest grains of the grain size distribution can still undergo recrystallization the resulting rheology that we predict for olivine is time dependent and more non linear than in dislocation creep as the deformation rate remains an increasing function of the deviatoric stress this rheology is not localizing

small scale mantle convection produces stratigraphic sequences in sedimentary basins cyclic sedimentary deposits link stratigraphic sequences that are now geographically distant but were once part of the same depositional environment some of these sequences occur at periods of 2 to 20 million years and eustatic sea level variations or regional tectonic events are likely causes of their formation using numerical modeling we demonstrate that small scale mantle convection can also cause the development of stratigraphic sequences through recurrent local and regional vertical surface movements small scale convection driven stratigraphic sequences occur at periods of 2 to 20 million years and correlate only at distances up to a few hundred kilometers these results suggest that previous sequence stratigraphic analyses may contain erroneous conclusions regarding eustatic sea level variations

lithology sedimentology and genesis of the wadena drumlin field minnesota u s a abstract studies on both the regional and small scales of the lithology sedimentology and stratigraphy of the wadena drumlin field in central minnesota u s a provide insights to the processes that operated within the wadena lobe during the drumlin forming phase horizontal changes in the down glacier direction in the nature of the drumlin till include an increase in the carbonate content decrease in grain size and magnetite content and variations in fine fraction mineralogy these changes also occur with depth at individual sites it is inferred that these patterns reflect progressive incorporation and mixing of the substrate which for much of the drumlin field is a till of northwestern origin with the till already in transit within the base of the wadena lobe derived from the northeast factors contributing to enhanced erosion within the wadena drumlin field include increased vertical strain rates over a major subglacial highland the presence of deformable bed material and a lowered ice profile which permitted elevated rates of bed deformation the patterns of mixing are generally consistent with substrate incorporation either by regelation or in the context of a deforming bed although neither of these processes adequately explain all of the observed features of the drumlin till where localized departures from the generalized pattern exist it can be shown that these are the result of either syn or post depositional processes primarily winnowing or the influence of a different substrate additional data are presented including macrofabric measurements and detailed site descriptions that are consistent with an accretionary progressive build up of the drumlin forms

holocene paleoceanography of the northwest passage canadian arctic archipelago abstract a series of cores box and piston were collected at 2 key locations in lancaster sound cores 2004 804 009 bc and pc and barrow strait cores 2005 804 004 bc and pc in the canadian arctic archipelago to document the evolution of sea surface conditions in the main axis of the northwest passage during the holocene time period reconstruction of sea surface parameters summer temperature and salinity duration of sea ice cover were estimated based on transfer functions using dinoflagellate cyst assemblages as proxy indicators the chronology of these cores is based on calibrated ams 14c dates 210pb analyses and correlations between paleomagnetic secular variations of the geomagnetic field and a predicted spherical harmonic model of the geomagnetic field cals7 k 2 our age models for both cores indicate that 009 pc spans the last 11 100 cal bp while 004 pc encompasses the last 10 800 cal bp calculated sedimentation rates are in the range of 43 140 cm kyr for core 009 pc and 15 118 cm kyr for core 004 pc allowing for a millennial time scale resolution in each core our results indicate relatively harsh conditions in lancaster sound between 10 800 and 9000 cal bp summer temperatures 2 c cooler than at present which we associate with the presence of active ice streams in northernmost baffin bay and a weak west greenland current this is followed by a warming trend up to 3 c higher than present that took place between 8500 and 5500 cal bp which we associate with the holocene thermal maximum and to a large scale atmospheric pattern such as the arctic oscillation operating at the millennial time scale this is concomitant with an increase in the relative abundance of phototrophic dinoflagellate cyst taxa a gradual cooling of sea surface temperature and increased sea ice follow this from 5500 cal bp until the modern period in barrow strait harsh sea surface conditions prevailed from 11 100 to 5500 cal bp with summer temperatures as low as 4 c cooler than at present the warming trend occurred later in this region between 5500 and 1000 cal bp after which a gradual cooling is observed until the modern period the apparent shift or opposite warming trends between lancaster sound and barrow strait after 5500 cal bp could be the result of a change in atmospheric circulation patterns related to a possible shift in the ao mode from ao to ao comparison of ice core 18o record from devon island ice cap and the reconstructed sea surface temperature from core 009 pc suggests a strong atmospheric oceanic coupling throughout the holocene in this area

centroid moment tensor solutions for july september 1998 abstract centroid moment tensor solutions are presented for 214 earthquakes that occurred during the third quarter of 1998 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging plenum new york 19 785 797 a new model of anelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of anelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms

the role of viscoelasticity in subducting plates subduction of tectonic plates into earth s mantle occurs when one plate bends beneath another at convergent plate boundaries the characteristic time of deformation at these convergent boundaries approximates the maxwell relaxation time for olivine at lithospheric temperatures and pressures it is therefore by definition a viscoelastic process while this is widely acknowledged the large scale features of subduction can and have been successfully reproduced assuming the plate deforms by a viscous mechanism alone however the energy rates and stress profile within convergent margins are influenced by viscoelastic deformation in this study viscoelastic stresses have been systematically introduced into numerical models of free subduction using both the viscosity and shear modulus to control the maxwell relaxation time the introduction of an elastic deformation mechanism into subduction models produces deviations in both the stress profile and energy rates within the subduction hinge when compared to viscous only models these variations result in an apparent viscosity that is variable throughout the length of the plate decreasing upon approach and increasing upon leaving the hinge at realistic earth parameters we show that viscoelastic stresses have a minor effect on morphology yet are less dissipative at depth and result in an energy transfer between the energy stored during bending and the energy released during unbending we conclude that elasticity is important during both bending and unbending within the slab hinge with the resulting stress loading and energy profile indicating that slabs maintain larger deformation rates at smaller stresses during bending and retain their strength during unbending at depth

mantle convection with a brittle lithosphere thoughts on the global tectonic styles of the earth and venus summary plates are an integral part of the convection system in the fluid mantle but plate boundaries are the product of brittle faulting and plate motions are strongly influenced by the existence of such faults the conditions for plate tectonics are studied by considering brittle behaviour using byerlee s law to limit the maximum stress in the lithosphere in a mantle convection model with temperature dependent viscosity when the yield stress is high convection is confined below a thick stagnant lithosphere at low yield stress brittle deformation mobilizes the lithosphere which becomes a part of the overall circulation surface deformation occurs in localized regions close to upwellings and downwellings in the system at intermediate levels of the yield stress there is a cycling between these two states thick lithosphere episodically mobilizes and collapses into the interior before reforming the mobile lid regime resembles convection of a fluid with temperature dependent viscosity and the boundary layer scalings are found to be analogous this regime has a well defined nusselt number rayleigh number relationship which is in good agreement with scaling theory the surface velocity is nearly independent of the yield stress indicating that the plate motion is resisted by viscous stresses in the mantle analysis suggests that mobilization of the earth s lithosphere can occur if the friction coeycient in the lithosphere is less than 0 03 0 13 lower than laboratory values but consistent with seismic field studies on venus the friction coeycient may be high as a result of the dry conditions and brittle mobilization of the lithosphere would then be episodic and catastrophic

the upper and lower thvera sedimentary geomagnetic reversal records from southern sicily detailed paleomagnetic records of the upper and lower thvera polarity transitions have been determined from pliocenc marine marls in southern sicily the dominant magnetic mineral is fine grained magnetite the two transitions have vgp paths following a great circle passing south america and the west coast of north america there are strong indications that the vgp paths result from smoothing of the non antipodal stable directions before and after the transitions the upper thvera transitional record is preceded by two excursions and followed by a third one the first excursion is a sedimentary artefact caused by post depositional migration of magnetic minerals and the third one by is caused by weathering of the sediment the upper thvera transition from sicily is compared with the record from calabria about 250 km away the two records show similarities as well as differences both transitions have identical vgp paths but in calabria the transition is recorded lower in the sediment the first and third excursions have different characters and the second one is not present apparently the registration of transitions of the earth s magnetic field in sediments is strongly influenced by smoothing and diagenetic processes after deposition

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

sea surface conditions in northernmost baffin bay during the holocene palynological evidence the analysis of cores collected in northernmost baffin bay from within the area of the north water polynya permits definition of a composite sedimentary sequence ca 12 m thick spanning the last 10 000 14 c yr with only a few discontinuities palynological analyses were performed in order to reconstruct changes in surface water conditions and biogenic production transfer functions using dinocyst assemblages were applied to estimate sea surface temperature sst and salinity as well as the seasonal duration of sea ice cover at the base of the record prior to 9300 14 c yr bp dinocysts and organic linings of benthic foraminifers are sparse indicating harsh conditions and low productivity after ca 9300 14 c yr bp the increased concentration of benthic foraminifers up to 10 3 linings cm 3 and dinocyst fluxes 10 2 10 3 cysts cm 2 yr 1 reveals high biological productivity related to open water conditions the early to middle holocene from ca 9000 to ca 3600 14 c yr bp is marked by relatively high species diversity in dinocyst assemblages and the significant occurrence of autotrophic taxa such as spiniferites elongatus pentapharsodinium dalei and impagidinium pallidum this assemblage suggests conditions at least as warm as at present from ca 6400 to ca 3600 14 c yr bp transfer functions indicate warmer conditions than at present with sst in august fluctuating up to 5 5 c after 3600 14 c yr bp the dinocyst record suggests a trend of decreasing temperature toward modern values marked by recurrent cooling events copyright 2001 john wiley sons ltd

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

deciphering the impact of diagenesis overprint on negative δ13c excursions using rock magnetism case study of ediacaran carbonates yangjiaping section south china rock magnetism is used here to investigate the genesis of one of the puzzling negative carbon isotopic excursions of the neoproterozoic in the yangtze platform south china a detailed characterization of the magnetic mineralogy which includes low temperature and high field magnetometry and classical magnetic measurement arm irm susceptibility was therefore performed along upper doushantuo and lower dengying formations outcropping in the yangjiaping section the derived magnetic parameters show variations that can be interpreted as variations in magnetic grains size and in oxide contents they show that the magnetic content is significantly reduced in samples presenting negative 13ccalcite values we interpret this as a result of magnetite dissolution and secondary carbonate precipitation during early diagenesis bacterial sulfate reduction combined with c and o isotopic data paleomagnetic techniques thus show that the upper doushantuo lower dengying negative excursion of the yangjiaping section is largely due to diagenesis although the preservation of a genuine 13c excursion of lower magnitude from 7 down to 0 instead of down to 9 as usually considered cannot be ruled out a corrected 13ccarbonate chemostratigraphic curve is therefore proposed the unambiguous identification of a strong diagenetic component for this excursion casts doubts on the primary nature of other potentially time equivalent negative excursions of the yangtze platform and thus to its correlation to negative excursions in other cratons i e shuram excursion more generally this study illustrates the potential of magnetic mineralogy characterization a low cost time efficient and non destructive technique as screening tool for diagenetic overprints of 13c and 18o

magnetic mineral tracing of sediment provenance in the central bengal fan abstract we present a comprehensive magnetic mineral analysis of surface sediments from 110 sites in the central bengal fan to trace sediment provenance multiple magnetic parameters including magnetic mineralogy concentration and grain size were generated rock magnetic measurements indicate that the dominant magnetic minerals within the studied sediments are detrital magnetite and titanomagnetite which is further confirmed directly by scanning electron microscope sem and transmission electron microscope tem observations on magnetic extracts fuzzy c means clustering analysis of magnetic parameters indicates that the study area can be divided into three clusters considering the position of active valley we further divide cluster 1 into clusters 1a and 1b cluster 1a primarily covers the west side of the active valley with relatively high magnetic concentrations and dominantly coarse grained magnetic minerals which likely correspond to basaltic materials derived from the deccan plateau from the godavari river mouth to the inner bay of bengal magnetic concentration gradually decreases with a fining trend of magnetic grain size clusters 1b 2 and 3 are on the east side of the active valley where magnetic concentration and magnetic grain size decrease with increasing distance to the active valley combined with published data in the indian region and the upper bengal fan we suggest that the main provenances are the himalayan and the deccan plateau whose contributions to sediment distribution are quantitatively assessed our analysis suggests that the position of active valley plays a key role in sediment distribution in the central bengal fan while the effect of ocean currents is negligible

the sounds of small earthquakes quantitative results from a study of regional macroseismic bulletins an original database of regional bulletins is analyzed to derive first order relationships that link the sounds generated by small earthquakes to the amplitude of ground motions and to local magnitude scales the database is a collection of about 1000 macroseismic observations collected during the 1984 1999 period in the french pyrenees from a staff of regular observers for each observation the main parameters are the qualitative perception of the sound faint or loud the hypocentral distance and the earthquake local magnitude expressed on the scale used by the french laboratoire de detection et de geophysique ldg network a local relationship between the magnitude the hypocentral distance and the amplitude of the p wave vertical ground displacement recorded in local seismological stations is established audibility thresholds of small earthquakes are then expressed as a function of richter m l magnitude and hypocentral distance the values obtained provide lower bounds for human perception of earthquakes

holocene glaciation and climate evolution of baffin island arctic canada abstract lake sediment cores and cosmogenic exposure ce dates constrain the pattern of deglaciation and evolution of climate across baffin island since the last glacial maximum lgm ce dating of erratics demonstrates that the northeastern coastal lowlands became ice free ca 14 ka as the laurentide ice sheet lis receded from its lgm margin on the continental shelf coastal lakes in southeastern baffin island started to accumulate sediment at this time whereas initial lacustrine sedimentation was delayed by two millennia in the north reduced organic matter in lake sediment deposited during the younger dryas chron and the lack of a glacial readvance at that time suggest cold summers and reduced snowfall ice retreated rapidly after 11 ka but was interrupted by a widespread readvance of both the lis and local mountain glaciers 9 6 ka cockburn substage a second readvance occurred just before 8 ka during a period of unusually cold summers corresponding to the 8 2 ka cold event in the greenland ice sheet most local glaciers were behind their present margins before 7 ka and in some instances much earlier although the foxe dome of the lis continued to slowly retract toward the present day barnes ice cap throughout the holocene pollen in lake sediments is rare and dominated by exotic sources prior to 12 ka subsequently grass tundra became established followed by modern tundra vegetation ca 8 ka with subtle changes in pollen assemblages in the late holocene lake primary productivity peaked in the early holocene before terrestrial vegetation or marine surface waters reached their apparent thermal maxima lacustrine marine and glacial proxies all reflect significant late holocene cooling the onset of neoglaciation is well dated in lacustrine records at ca 6 ka with intensification after 2 5 ka the expansion of local glaciers during the little ice age represents the most extensive advance since 7 ka we suggest that the replacement of atlantic surface waters by cold low salinity arctic ocean water coupled with the steady reduction of summer insolation resulted in a significant positive sea ice feedback that produced a larger late holocene summer temperature depression over the baffin region than in the pacific sector of the arctic

robust characteristics method for modelling multiphase visco elasto plastic thermo mechanical problems abstract we have extended our previous 2d method gerya t v yuen d a 2003 characteristics based marker in cell method with conservative finite differences schemes for modeling geological flows with strongly variable transport properties phys earth planet interiors 140 295 320 which is a combination of conservative finite differences with marker in cell techniques to include the effects of visco elasto plastic rheology self gravitation and a self consistently derived evolving curvilinear planetary surface this code is called i2elvis and can solve a new class of computationally challenging problems in geodynamics such as shear localization with large strains crustal intrusion emplacement of magmas bending of realistic visco elasto plastic plates and core formation by vigorous shell tectonics activities related to a global rayleigh taylor instability of a metal layer formed around silicate rich lower density primordial core during planetary accretion we discuss in detail the computational strategy required the rheological constraints to be satisfied at each time step and spatial location we show analytical benchmarks and examples drawn from comparing between numerical and analogue experiments in structural geology subducting slab bending with a visco elasto plastic rheology and equilibrium spherical configurations from self gravitation we have also tested possibilities of future applications by addressing 3d geometries based on multigrid method and including inertial effects in the momentum equation with tracers in order to simulate meteoritic impact events and eventually earthquake instabilities

influence of sediment source and type on the magnetic susceptibility of fiord and shelf deposits baffin island and baffin bay n w t volume and mass magnetic susceptibility are measured on recent and late quaternary sediments from the fiords and shelf of eastern baffin island baffin bay and the northern labrador sea major changes in hinterland bedrock geology are associated with order of magnitude changes in magnetic susceptibility the fiords that head into the proterozoic foxe fold belt have mass magnetic susceptibilities ms of 2 4 10 7 m3 kg compared with 25 60 10 7 m3 kg in sediments derived from archean gneisses and granites another low ms region is the middle reach of frobisher bay ms studies in cambridge mcbeth and itirbilung fiords included analyses of surface samples and samples from lehigh 3 m and piston 11 m cores lehigh cores had higher ms values on average than the piston cores suggesting a coarsening in texture or an increase in the flux of magnetic minerals during the last 0 3 3 ka an analysis of the ms logs of 17 piston cores indicated that six broad patterns of ms can be recognized based on a

mid to late holocene hydrological and climatic variability in disko bugt central west greenland diatom and lithological analyses were carried out on two sediment cores from disko bugt and the adjacent kangersuneq fjord west greenland in order to investigate mid to late holocene 6 9 0 7 kyr bp hydrographic and climatic variability while the disko bugt record is found to reflect mainly west greenland current wgc fluctuations that can be linked to north atlantic circulation variability the fjord record appears to be more representative of local climate conditions the records demonstrate that the period of investigation was marked by a late holocene thermal maximum beginning at c 4 8 kyr and ending between 3 5 and 3 1 kyr bp encompassing a colder period between c 4 0 and 3 8 kyr bp an episode of higher surface water temperature is also indicated in disko bugt between 2 2 and 1 5 kyr bp in contrast the record from kangersuneq fjord suggests persisting cooler summer surface waters for this interval interpreted to be attributable to increased meltwater outflow the warming episode recogni

elasticity yielding and episodicity in simple models of mantle convection we explore the implications of refinements in the mechanical description of planetary constituents on the convection modes predicted by finite element simulations the refinements consist in the inclusion of incremental elasticity plasticity yielding and multiple simultaneous creep mechanisms in addition to the usual visco plastic models employed in the context of unified plate mantle models the main emphasis of this paper rests on the constitutive and computational formulation of the model we apply a consistent incremental formulation of the non linear governing equations avoiding the computationally expensive iterations that are otherwise necessary to handle the onset of plastic yield in connection with episodic convection simulations we point out the strong dependency of the results on the choice of the initial temperature distribution our results also indicate that the inclusion of elasticity in the constitutive relationships lowers the mechanical energy associated with subduction events

centennial scale benthic foraminiferal record of late holocene oceanographic variability in disko bugt west greenland a new centennial scale benthic foraminiferal record of late holocene climate variability and oceanographic changes off west greenland disko bugt highlights substantial subsurface water mass changes e g temperature and salinity of the west greenland current wgc over the past 3 6 ka bp benthic foraminifera reveal a long term late holocene cooling trend which may be attributed to increased advection of cold low salinity water masses derived from the east greenland current egc cooling becomes most pronounced from c 1 7 ka bp onwards at this point the calcareous atlantic benthic foraminiferal fauna decrease significantly and is replaced by an agglutinated arctic fauna superimposed on this cooling trend centennial scale variability in the wgc reveals a marked cold phase at c 2 5 ka bp which may correspond to the 2 7 ka bp cooling event recorded in marine and terrestrial archives elsewhere in the north atlantic region a warm phase recognized at c 1 8 ka bp is likely to correspond to the roman warm period and represents the warmest bottom water conditions during the time period of the medieval climate anomaly we observe only a slight warming of the wgc a progressively more dominant cold water contribution from the egc on the wgc is documented by the prominent rise in abundance of agglutinated arctic water species from 0 9 ka bp onwards this cooling event culminates at c 0 3 ka bp and represents the coldest episode of the little ice age gradually increased influence of cold low salinity water masses derived from the egc may be linked to enhanced advection of polar and arctic water by the egc these changes are possibly associated with a reported shift in the large scale north atlantic oscillation atmospheric circulation pattern towards a more frequent negative north atlantic oscillation mode during the late holocene

revising the 1759 kattegat earthquake questionnaires using synthetic wavefield analysis abstract in aseismic regions the lack of large earthquakes in modern times makes the study of historical earthquakes essential as such events often serve as the yardstick for estimating seismic hazards since the largest earthquakes with few exceptions took place hundreds of years ago we may claim that their recurrence times are very large or alternatively their magnitudes are biased upwards scandinavia is no exception in this regard and one interesting event in particular is the kattegat earthquake of 22 december 1759 it is unique in the sense that a macroseismic questionnaire was circulated in zealand within days of its occurrence the puzzling feature here is that intensity ranges from vii to i across zealand but then given i iii for hamburg and other north german cities we have chosen two avenues in reassessing the magnitude of the kattegat earthquake namely 1 2d finite difference fd waveform modelling to evaluate possible amplitude amplifications due to sub surface basin structures and 2 re assessing the intensity reports of the 1759 kattegat earthquake in light of the new european macroseismic scale ems 98 our 2d fd results show that the presence of the danish and the north german basins led to shear wave amplitude amplification by factors of 10 and 5 respectively this is equivalent to a significant increase or overestimation of the area of perception tied to i iii the re assessment of the macroseismic observations in light of the above results and the ems 98 downgrade the kattegat earthquake ms magnitude from 5 6 to 5 1

spatial patterns of earthquake sounds and seismic source geometry earthquake sounds are heard during or immediately before an event up to several kilometres around the epicentral area sound data as heard by people have been collected by way of macroseismic questionnaires showing that sound audibility does not follow isotropic patterns the explanation of this effect is found in the behaviour of the particular radiation pattern of the p waves for each earthquake in connection with its focal mechanism this result opens the possibility to get more information about the earthquake source parameters in the future and past events making use of non instrumental observations

minimum heat flow from the core and thermal evolution of the earth abstract the role of heat flow coming from the core is often overlooked or underestimated in simple models of earth s thermal evolution throughout most of earth s history the mantle must have been extracting from the core at least the amount of heat that is required to operate the geodynamo in view of recent laboratory measurements and theoretical calculations indicating a higher thermal conductivity of iron than previously thought the above constraint has important implications for the thermal history of the earth s mantle in this work we construct a paramaterized mantle convection model that treats both the top and the core mantle boundary heat fluxes according to the boundary layer theory or alternatively employs the model of labrosse 2015 to compute the thermal evolution of the earth s core we show that the core is likely to provide all the missing heat that is necessary in order to avoid the so called thermal catastrophe of the mantle moreover by analyzing the mutual feedback between the core and the mantle we provide the necessary ingredients for obtaining thermal histories that are consistent with the petrological record and have reasonable initial conditions these include a sufficiently high viscosity contrast between the lower and upper mantle whose exact value is sensitive to the activation energy that governs the temperature dependence of the viscosity

lake level fluctuations at ljustjarnen central sweden and their implications for the holocene climate of scandinavia abstract a detailed reconstruction of water level fluctuations in ljustjarnen a small kettle lake in south central sweden provides a preliminary outline of holocene changes in water balance for that region lake levels were generally high from 9200 to 8000 yr b p falling from then until c 6500 6000 yr b p and rising again by 5000 yr b p temporary lowerings were recorded c 4000 yr b p and c 2000 yr b p and water levels have risen dramatically since c 500 yr b p the reconstruction is based on sedimentologic and fossil analyses of multiple cores as well as on geomorphological evidence comparison of lake level fluctuations in south central sweden with those from southern sweden and western finnish lapland and with records of glacier fluctuations in the scandinavian mountains suggest a distinct north south contrast in water balance from 9000 to 5000 yr b p consistent with strongly zonal atmospheric circulation during that period between 7000 and 5000 yr b p the mid holocene dry period appears to have been time transgressive across scandinavia perhaps as a result of a gradual shift in the position of the atlantic polar front and its associated cyclonic stormtrack since 4000 yr b p however most detectable fluctuations are synchronous across scandinavia with the most prominent and widespread change being increased net moisture during the little ice age

testing the uncertainty of diffuse reflectance spectroscopy methods for estimating marine sediment components by full resolution spectrophotometry and principle component analyses abstract estimating terrestrial and biogenic component variations in marine sediment cores provide essential information in paleoceanographic studies the variations of terrestrial and biogenic components can be used to infer the changes of sediment provenances that are important for understanding what processes have governed the sediment compositional changes in the cores one non destructive technique diffuse reflectance spectroscopy drs is now commonly used to capture high resolution information on sediment component changes the drs method is a quick and cost effective procedure for sediment core analysis that requires no chemical analysis with complicated procedures recently one drs device for capturing visible vis color reflectance data crd 400 700 nm from core surfaces the minolta cm 2600d has become a standard tool in all marine sediment core analysis however by capturing the visible wavelength of crd only there are uncertainties in the crd near the ultraviolet uv and near infrared nir obtained by minolta cm 2600d are poorly known in this study we used a full resolution fr drs device the analytical spectral device asd labspec pro fr ultraviolet visible near infrared uv vis nir spectrometer 250 2500 nm to compare with the crd obtained from the minolta cm 2600d using the marine sediment core md103264 taken from offshore southwestern taiwan we compared the differences in the vis wavelength range of crd between the two devices by analyzing the derivatives and a varimax rotated principle components analysis vpca of the crd from 420 samples from core md103264 our results show significant uncertainties in crd near the wavelengths of 400 450 and 650 700 nm in the data from the minolta cm 2600d these uncertainties could result in biased or erroneous estimates for terrestrial and biogenic components of marine sediment cores our experiments indicate that the crd obtained with any device with vis wavelength range only should be interpreted with caution particularly in the 400 450 and 650 700 nm range

late holocene diatom inferred reconstruction of temperature variations of the west greenland current from disko bugt central west greenland the diatom flora from a high resolution core collected from disko bugt central west greenland records variations in surface water temperature for the late holocene 1600 300 cal bp our data support the existence of a previously identified anti phase relationship between the surface water temperature from west greenland and climate events recorded in the ne atlantic and between surface and subsurface waters identified from benthic foraminifera of the west greenland current wgc the diatom flora record relatively cool surface water conditions during the end of the roman warm period and medieval warm period mwp and relatively warmer surface water conditions during the dark ages cold period and little ice age lia this is particularly pronounced during the mwp experiencing the coldest conditions and the lia experiencing the warmest conditions through the whole sequence studied the most likely explanation for this anti phase relationship is linked to the flux of meltwater delivered to the wgc from sea ice and the greenland ice sheet off the west greenland margin the generally warmer conditions of the mwp resulted in increased melting of sea ice and the greenland ice sheet producing an increased meltwater flux and cooling of the surface waters of the wgc in contrast reduced meltwater flux during the relatively cold lia resulted in reduced meltwater flux to the wgc producing a relative warming of the surface waters recorded by the diatom flora

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

late quaternary sedimentation in baffin bay baffin bay is a small ocean basin that connects the arctic and atlantic oceans the adjacent continental shelves have been extensively reworked during quaternary glaciation the shelf break generally lies between 200 and 500 m the continental slope passes directly into the abyssal plain of baffin bay basin without any major submarine canyon deep sea fan system being present except for a large smooth sediment apron in northern baffin bay on the basis of over 50 piston cores six quaternary sediment facies are distinguished from detrital mineralogy reflected in colour and sediment texture facies a b and c are predominantly ice rafted or are debris flow deposits each with a distinct mineralogy facies d is turbidites and bottom current sorted sands silts and muds facies e is hemipelagic sediment facies f consists of sediments ranging from slumps through debris flow deposits to fine grained turbidites with a distinctive provenance in northern baffin bay these sediment facies appear to be part

the innuitian ice sheet configuration dynamics and chronology abstract portrayal of north american ice cover during the last glacial maximum is dominated by the laurentide ice sheet leaving little detail for the adjacent innuitian ice sheet iis four decades of geological fieldwork across the queen elizabeth islands now warrant specific treatment of the iis including its chronology configuration dynamics and retreat this reconstruction is relevant to the sedimentary history of the arctic ocean and to high latitude climate forcing the iis was composed of both an alpine and lowland sector the advance of the alpine sector occurred as recently as 19 14 c ka bp geological evidence configures outflow from alpine and lowland divides that produced several palaeo ice streams one extending northwestward across the canadian arctic archipelago to the polar continental shelf retreat of the iis commenced along its southwest margin 11 6 14 c ka bp however most of the ice sheet remained on the continental shelf during the younger dryas by 10 14 c ka bp marine based ice experienced widespread calving through the western and central archipelago in response to holocene warming and ongoing eustatic sea level rise the sea penetrated the eastern archipelago by 8 5 14 c ka bp gutting the alpine sector of the iis regional isobases record the glacioisostatic signature of the ice sheet and are congruent with the primary geological evidence the delayed buildup of the iis was out of phase with the growth of the laurentide ice sheet that occasioned climatic and glacio eustatic forcing in the innuitian region recent modelling experiments reinforce the hypothesis that growth of the laurentide ice sheet culminated in a split jet stream that temporarily favoured augmented precipitation and growth of the iis

improvements in long core measurement techniques applications in palaeomagnetism and palaeoceanography we report on new developments in the long core measurement techniques using u channels in connection with new small access cryogenic magnetometers with these new instruments u channel samples allow us to measure a wide range of magnetic parameters along entire core length with a spatial resolution and accuracy virtually equivalent to that obtained using discrete cubic samples an additional advantage is that the sediment disturbance when sampling is significantly less when using u channels we present comparisons of results from both continuous and discrete measurements and examine the effectiveness of minimal deconvolution using various techniques examples of continuous measurements of low field susceptibility nrm arm irm hrc from north atlantic deep sea cores show that it is possible to generate logs of combination of parameters related to rock magnetic characteristics of the sediments useful in palaeoceanography in particular the continuous method allows us to rapidly detect core regions with fast changing magnetic parameters useful for correlation between cores and also for understanding changes in palaeo environmental conditions the fast scan also allows us to detect regions of the core where the rock magnetic parameters are suitable or not suitable for palaeomagnetic studies related to changes in the geomagnetic field such as the relative changes in palaeointensity

a comparison of numerical surface topography calculations in geodynamic modelling an evaluation of the sticky air method summary calculating surface topography in geodynamic models is a common numerical problem besides other approaches the so called sticky air approach has gained interest as a free surface proxy at the top boundary the often used free slip condition is thereby vertically extended by introducing a low density low viscosityfluid layer this allows the air crust interface to behave in a similar manner to a true free surface we present here a theoretical analysis that provides the physical conditions under which the sticky air approach is a valid approximation of a true free surface two cases are evaluated that characterize the evolution of topography on different timescales 1 isostatic relaxation of a cosine perturbation and 2 topography changes above a rising plume we quantitatively compare topographies calculated by six different numerical codes using finite difference and finite element techniques using three different topography calculation methods i direct calculation of topography from normal stress ii body fitting methods allowing for meshing the topography and iii lagrangian tracking of the topography on an eulerian grid it is found that the sticky air approach works well as long as the term st ch hst l 3 is sufficiently small where st and hst are the viscosity and thickness of the sticky air layer and ch and l are the characteristic viscosity and length scale of the model respectively spurious lateral fluctuations of topography as observed in some marker based sticky air approaches may effectively be damped by an anisotropic distribution of markers with a higher number of markers per element in the vertical than in the horizontal direction

fluctuations of local glaciers in greenland during latest pleistocene and holocene time abstract this paper is the first to summarize research on fluctuations of local glaciers in greenland e g ice caps and mountain glaciers independent of the greenland ice sheet during latest pleistocene and holocene time in contrast to the extensive data available for fluctuations of the greenland ice sheet surprisingly little data exist to constrain local glacier extents much of the available research was conducted prior to wide spread use of ams radiocarbon dating and the advent of surface exposure and luminescence dating although there is a paucity of data generally similar patterns of local glacier fluctuations are observed in all regions of greenland and likely reflect changes in paleoclimate which must have influenced at least the margins of the inland ice absolute age data for late glacial and early holocene advances of local glaciers are reported from only two locations disko island and the scoresby sund region subsequent to late glacial or early holocene time most local glaciers were smaller than at present or may have disappeared completely during the holocene thermal maximum in general local glacier advances that occurred during historical time 1200 1940 ad are the most extensive since late glacial or early holocene time historical documents and more recent aerial photographs provide useful information about local glacier fluctuations during the last 100 yrs in all but one area north greenland local glaciers are currently receding from historical extents

environmental changes in baffin bay during the holocene based on the physical and magnetic properties of sediment cores the physical and magnetic properties of four long sediment cores hu2008 029 034pc 038pc 042pc and 070pc sampled in northern smith sound and jones sound and eastern disko bugt baffin bay were analysed to reconstruct the holocene environmental changes in baffin bay radiocarbon dating of each core revealed sedimentation rates of up to 136 cm ka 1 except for specific intervals magnetic properties and ratios reveal that the magnetic remanence is mostly carried by magnetite and that changes in magnetic grain size and concentration are indicative of environmental variations associated with ice rafted debris sea ice meltwater pulses or terrigenous inputs these variations indicate that all four cores which cover a period from 12 360 cal a bp to the present have sedimentary facies that correspond to the major climatic changes of the holocene deglaciation and the climatic optimum in addition two cores hu2008 029 038pc and 070pc present the signal of two climatic events with a local influence during the neoglacial period

a pedogenic model for the magnetic enhancement of late miocene fluvial lacustrine sediments from the xining basin ne tibetan plateau

the magnetic signature of rapidly deposited detrital layers from the deep labrador sea relationship to north atlantic heinrich layers rock magnetic parameters from deep labrador sea piston core p 094 are useful for recognizing rapidly deposited detrital layers some of which correlate with north atlantic heinrich layers variations in magnetic properties and lithology distinguish two classes of rapidly deposited detrital layers during the last ice age 1 seven detrital carbonate dc layers have high carbonate content and mean magnetite grain diameters about 4 times greater than the background sediments 2 six low detrital carbonate ldc layers have very similar magnetic properties to dc layers but low carbonate content similar to the background sediments the magnetite associated with dc and ldc layers is well sorted and relatively uniform within and between layers ice rafted detritus ird recognized by increased percentage of the 125 micron grain size fraction and by high magnetic susceptibility is associated with most dc and ldc layers but is not the dominant detrital constituent the correspondence of dc and ldc layers with increased grain size of well sorted magnetite but not with coarse fraction content precludes ice rafting as the primary depositional mechanism dc and ldc layers may have been deposited from suspended sediment derived from turbidite activity in the nearby northwest atlantic mid ocean channel namoc this interpretation is supported by a piston core p 013 from a greenland rise site largely but not completely outside the influence of the namoc the association of dc layers with ird and the apparent age correlation of dc layers to north atlantic heinrich layers suggest that the ice advances which produced the ird in p 094 and in correlative north atlantic heinrich layers also triggered turbiditic flows down the namoc several dc and ldc layers however do not correlate with recognized heinrich layers but appear to be coeval with recently discovered high frequency ird rich layers in the north atlantic

the circulation water masses and sea ice of baffin bay abstract the oceanographic meteorological and sea ice conditions in baffin bay are studied using historical hydrographic satellite and meteorological data and a set of current meter data from a mooring program of the bedford institute of oceanography baffin bay is partially covered by sea ice all year except august and september the interannual variation of the ice extent is shown to be correlated with winter air temperature available hydrographic data were used to study the water masses and the horizontal and vertical distribution of temperature salinity three water masses can be identified arctic water in the upper 100 300 m of all regions except the southeast west greenland intermediate water at 300 800 m in most of the interior of baffin bay and deep baffin bay water in all regions below 1200 m the temperature and salinity in baffin bay have limited seasonal variability except in the upper 300 m of eastern davis strait northern baffin bay and the mouth of lancaster sound summer data have a temperature minimum at 100 m which suggests winter convection does not penetrate deeper than this depth current meter data and results of a circulation model indicate that the mean circulation is cyclonic the seasonal variation of the currents is complex overall summer and fall tend to have stronger currents than winter and spring at all depths among the different regions the largest seasonal variation occurs at the mouth of lancaster sound and the baffin island slope model generated velocity fields show a basic agreement with the observed currents and indicate strong topographic control in the vicinity of davis strait and on the greenland shelves the model also produces a southward counter current on the greenland slope which may explain the observed high horizontal shears over the greenland slope estimates of the volume and fresh water transports through lancaster jones and smith sounds are reviewed transports through davis strait are computed from the current meter data the balance of freshwater budget and sensitivity of the thermohaline circulation to freshwater transport are discussed

viscoelastic mantle convection and lithospheric stresses summary accurate predictions of stress distribution in the lithosphere are of major importance for approaching more realistic numerical models of the mantle lithosphere system since stress fields in the lithosphere computed in convection models differ substantially between viscous and viscoelastic rheologies it is essential to employ a viscoelastic rheology when accurate stresses are to be predicted in mantle convection models involving the lithosphere this difference in stress distribution and magnitude has important implications for accurate modelling of stress dependent processes like power law creep shear heating and plasticity a further requirement for computation of accurate stress fields is to ensure numerically divergence free solutions in the boussinesq approximation we present the technical background required for implementation of numerically incompressible solutions and for implementation of a maxwell viscoelastic rheology in the frame of the finite element method fem we employ the jaumann invariant stress derivative in our implementation and demonstrate that the choice of the invariant stress derivative is irrelevant for geodynamic simulations we discuss potential numerical advantages of a viscoelastic rheology when large viscosity variations are applied in thermal convection models due to the physical transition from effectively viscous to elastic behaviour in a viscoelastic model the introduction of viscosity cut offs generally applied in viscous models can be avoided

an environmental magnetic fingerprint of periglacial loess records of late pleistocene loess palaeosol sequences from eastern germany a detailed rock magnetic analysis of the last glacial interglacial loess palaeosol sequences was carried out in the framework of a comprehensive stratigraphic study of loess in saxony eastern germany magnetic susceptibility and laboratory induced remanences have been determined to compare individual sections and to identify the specific rock magnetic characteristics of the saxonian loess province according to the model of pedogenic magnetic enhancement an increasing neoformation of ferrimagnetic minerals in the course of pedogenesis was observed only in the uppermost late weichselian lithological units consisting of pure aeolian loess and indicating dryer climatic conditions in contrast the rock magnetic characteristics of the lower middle and early weichselian units exhibit a significant destruction of primary magnetic minerals caused by such secondary processes as climatically controlled waterlogging and reworking this change in magnetic composition with stratigraphic depth was additionally proved by factor analysis in which the main observation an increasing fd with decreasing argues for a general magnetic depletion in conjunction with decreasing magnetic grain sizes caused by weathering of larger primary particles the magnetic fingerprint of the saxonian loess is characterised by prevailing magnetic depletion processes which effectively rules out the application of the wind vigour model moreover the magnetic characteristics differ significantly from that of other loess regions and support a new and independent model which explains the magnetic behaviour of strongly reworked and waterlogged gleyed loess palaeosol sequences in the relatively humid central european periglacial areas

high field magnetic susceptibility χhf as a proxy of biogenic sedimentation along the antarctic peninsula abstract high field mass normalized magnetic susceptibility hf is presented as a proxy for biogenic sedimentation in glacimarine sediment from the western antarctic peninsula hf is measured at field strengths that exceed the saturation field of ferrimagnetic minerals these measurement conditions exclude the contributions of ferrimagnetic iron oxides that dominate low field volume normalized susceptibility k measurements therefore hf allows for closer examination of paramagnetic and diamagnetic minerals the latter of which includes biogenic silica and biogenic calcite in sedimentary sequences from the western antarctic peninsula the main processes affecting the abundance of diamagnetic material in sediment is biological productivity and the subsequent flux of biogenic silica to the seafloor hf profiles were measured on two biosiliceous sediment cores from the western antarctic peninsula comparisons with quantitative biogenic silica measurements indicate that hf tracks opaline silica very well and reveals the presence of century scale cycles in sediment composition in intervals where k appears featureless hf is limited as a quantitative measure of biogenic sediment flux since terrigenous paramagnetic and diamagnetic minerals also contribute to the measurement the interpretation of hf can also be complicated by the presence of unsaturated high coercivity minerals such as hematite and goethite or by the presence of ultra fine superparamagnetic sp particles however in sediment sequences where the condition of saturation is met hf is very well suited for the rapid identification of temporal trends in biogenic sedimentation

control of folding by gravity and matrix thickness implications for large scale folding 1 we show that folding of a non newtonian layer resting on a homogeneous newtonian matrix with finite thickness under influence of gravity can occur by three modes 1 matrix controlled folding dependent on the effective viscosity contrast between layer and matrix 2 gravity controlled folding dependent on the argand number the ratio of the stress caused by gravity to the stress caused by shortening and 3 detachment folding dependent on the ratio of matrix thickness to layer thickness we construct a phase diagram that defines the transitions between each of the three folding modes our priority is transparency of the analytical derivations e g thin plate versus thick plate approximations which permits complete classification of the folding modes involving a minimum number of dimensionless parameters accuracy and sensitivity of the analytical results to model assumptions are investigated in particular depth dependence of matrix rheology is only important for folding over a narrow range of material parameters in contrast strong depth dependence of the viscosity of the folding layer limits applicability of ductile rheology and leads to a viscoelastic transition our theory is applied to estimate the effective thickness of the folded central asian upper crust using the ratio of topographic wavelength to moho depth phase diagrams based on geometrical parameters show that gravity does not significantly control folding in the jura and the zagros mountains but does control folding in central asia applicability conditions of viscous and thin sheet models for large scale lithospheric deformation derived in terms of the argand number have implications for the plate like style of planetary tectonics

the seismic cycle at subduction thrusts 2 dynamic implications of geodynamic simulations validated with laboratory models 1 the physics governing the seismic cycle at seismically active subduction zones remains poorly understood due to restricted direct observations in time and space to investigate subduction zone dynamics and associated interplate seismicity we validate a continuum visco elasto plastic numerical model with a new laboratory approach paper 1 the analogous laboratory setup includes a visco elastic gelatin wedge underthrusted by a rigid plate with defined velocity weakening and strengthening regions our geodynamic simulation approach includes velocity weakening friction to spontaneously generate a series of fast frictional instabilities that correspond to analog earthquakes a match between numerical and laboratory source parameters is obtained when velocity strengthening is applied in the aseismic regions to stabilize the rupture spontaneous evolution of absolute stresses leads to nucleation by coalescence of neighboring patches mainly occurring at evolving asperities near the seismogenic zone limits consequently a crack or occasionally even pulse like rupture propagates toward the opposite side of the seismogenic zone by increasing stresses ahead of its rupture front until it arrests on a barrier the resulting surface displacements qualitatively agree with geodetic observations and show landward and from near the downdip limit upward interseismic motions these are rebound and reversed coseismically this slip increases adjacent stresses which are relaxed postseismically by afterslip and thereby produce persistent seaward motions the wide range of observed physical phenomena including back propagation and repeated slip and the agreement with laboratory results demonstrate that visco elasto plastic geodynamic models with rate dependent friction form a new tool that can greatly contribute to our understanding of the seismic cycle at subduction zones

mantle convection modeling with viscoelastic brittle lithosphere numerical methodology and plate tectonic modeling the earth s tectonic plates are strong viscoelastic shells which make up the outermost part of a thermally convecting predominantly viscous layer brittle failure of the lithosphere occurs when stresses are high in order to build a realistic simulation of the planet s evolution the complete viscoelastic brittle convection system needs to be considered a particle in cell finite element method is demonstrated which can simulate very large deformation viscoelasticity with a strain dependent yield stress this is applied to a plate deformation problem numerical accuracy is demonstrated relative to analytic benchmarks and the characteristics of the method are discussed

paleoenvironments during younger dryas early holocene retreat of the greenland ice sheet from outer disko trough central west greenland paleoenvironments during the late younger dryas through early holocene retreat of the greenland ice sheet from the outer shelf in the disko trough system of central west greenland were investigated via lithofacies foraminifera dinocysts and sediment provenance analyses in radiocarbon dated sediment cores from the upper slope jr175 vc35 and outer shelf jr175 vc20 and hu2008029 070cc core data show that the ice margin retreated rapidly from the outer shelf by calving beginning by 12 2k cal a bp under cold paleoceano graphic conditions with up to 11 months of sea ice ice retreat into disko bugt was well underway by 10 9k cal a bp enhanced ice sheet ablation in disko bugt and elsewhere along the west greenland coast is inferred from cold glacial marine conditions associated with high sedimentation rates between 10 9 and 9 5k cal a bp on the outer shelf glacial marine conditions are recorded on the outer shelf until 7 8k cal a bp detrital carbonate bearing sediments rich in 2 mm clasts deposited between 11 6 and 10 6k cal a bp indicate that icebergs calved from northern baffin bay ice margins were melting and releasing sediments along west greenland while the greenland ice sheet margin was retreating into disko bugt copyright 2013 john wiley sons ltd

rupture directivity of the major shocks in the 1997 umbria marche central italy sequence from regional broadband waveforms we derive the relative moment rate function for the main shocks in the fall 1997 central italy seismic sequence mw 5 7 6 0 5 6 by applying an empirical green function method by using three conveniently placed broad band mednet stations we obtain clear source time functions indicating directivity effects for all of the three earthquakes with southeastward rupture propagation for the two southernmost events and an opposite direction for the other and largest one taking a simple source model forward modeling is utilized for determining fault parameters such as length rupture propagation velocity and direction and slip distribution

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

relationship between median destructive field and remanent coercive forces for dispersed natural magnetite titanomagnetite and hematite summary remanent acquisition curves remanent hysteresis curves and alternating field demagnetization curves were determined for a number of artificial rock specimens containing well defined grain size fractions between 5 and 250 m of natural magnetite titanomagnetite and hematite from these curves the remanent acquisition coercive force h cr the remanent coercive force hcr and the median destructive field of irm h i were determined theoretically these parameters should be the same for an assembly of non interacting homogeneously distributed randomly oriented single domain grains for a given hematite specimen h cr hcr and h i have about the same value in spite of the strong grain size dependence of these parameters for each specimen of magnetite and titanomagnetite the value of h cr is larger than hcr which again is larger than h i however the ratios h cr hcr and h i hcr appear to have a different constant value an interesting relationship which appears to hold for dispersed magnetite titanomagnetite or hematite grains between 5 and 250 m independently of grain size quantity and packing density of the magnetic material is

an extensive and dynamic ice sheet on the west greenland shelf during the last glacial cycle considerable uncertainty surrounds the extent and timing of the advance and retreat of the greenland ice sheet gis on the continental shelf bordering baffin bay during the last glacial cycle here we use marine geophysical and geological data to show that fast flowing ice sheet outlets including the ancestral jakobshavn isbrae expanded several hundred kilometers to the shelf edge during the last glaciation ca 20 ka retreat of these outlets was asynchronous initial retreat from the shelf edge was underway by 14 880 calibrated cal yr b p in uummannaq trough radiocarbon dates from the adjacent disko trough and adjoining trough mouth fan imply later deglaciation of jakobshavn isbrae and significantly an extensive readvance and rapid retreat of this outlet during the younger dryas stadial yd this is notable because it is the first evidence of a major advance of the gis during the yd on the west greenland shelf although the short duration suggests that it may have been out of phase with yd temperatures

diachronous evolution of sea surface conditions in the labrador sea and baffin bay since the last deglaciation assessing changes in sea surface conditions due to the effects of past freshwater outflow through baffin bay and davis strait to the labrador sea hereafter referred to as the baffin bay corridor

early holocene palaeoceanography and deglacial chronology of disko bugt west greenland two new cores from disko bugt a large marine embayment in west greenland are used to assess the deglacial chronology and palaeoceanography of the area during the early holocene deglaciation of the main part of disko bugt is directly dated for the first time to a minimum of ca 10 2 ka cal bp by this time the jakobshavn isbrae ice stream had retreated to the eastern margins of disko bugt initial deglaciation took place before the relatively warm west greenland current wgc was initiated a strengthening in the wgc is identified from ca 9 2 ka cal bp accompanied by retreat of the ice stream to a shallow bank immediately west of the present day jakobshavn isfjord while in this position the calving and melting ice stream produced large volumes of sediment and meltwater the large volumes of meltwater prevented the relatively warm waters of the wgc reaching the eastern margins of disko bugt the ice stream remained grounded on this bank for over a thousand years until ca 7 9 ka cal bp when reduced sedimentation rates and an increase in boreal fauna point to its retreat inside the present day fjord system

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

effects of elasticity on the rayleigh taylor instability implications for large scale geodynamics summary although parts of the lithosphere may be expected to behave elastically over certain timescales this effect is commonly ignored in models of large scale mantle dynamics recently it has been demonstrated that elasticity and in particular viscoelasticity may have a significant effect on the buckling instability and on the creation of lithospheric scale shearzones it is however less clear whether elasticity also has an effect on mantle convection and density driven lithospheric instabilities the focus of this work is therefore to study the effects of elasticity on the twolayer rayleigh taylor rt instability consisting of a maxwell viscoelastic layer overlying a viscous layer of lower density we analyse this problem by performing systematic numerical simulations that are compared with newly derived analytical solutions it is demonstrated that elasticity can be important for certain parameter combinations it leads to a speedup of the rt instability the cause for this speedup is that the rt instability is only sensitive to the viscous fraction of deformation in the viscoelastic layer elasticity reduces the viscous fraction of deformation at timescales shorter than the maxwell relaxation time t m t m g where is the viscosity and g the elastic shear module for plate tectonics on earth the parameters are such that the effect of elasticity on instability growth is negligible for most boundary conditions whereas elasticity does not or only slightly change the timescales for lithospheric detachment of the upper mantle it does significantly alter the response and stress build up in the overlying crust numerical simulations illustrate this effect for lithospheric detachment and show that peak stresses in a viscoelastic crust are smaller than stresses that develop in a viscous crust moreover if the timescale for delamination of the mantle lithosphere is equal or smaller than the maxwell relaxation time of the crust the topography of the crust is increased compared to viscous models

paleomagnetic secular variation and relative paleointensity during the holocene in south china huguangyan maar lake revisited the scarcity of reliable paleomagnetic secular variation psv records from east asia especially from low latitude regions impedes better understanding of global psv mechanisms here we report on a radiocarbon dated holocene psv record from a composite 6 7 m long core collected from the high sedimentation rate huguangyan maar lake hml in subtropical tropical south china rock magnetic results demonstrate that the natural remanent magnetization resides in single domain magnetite alternating field demagnetization experiments at 1 cm spacing on u channel samples reveal six distinct inclination highs at 7 500 bce 5 100 bce 4 600 bce 3 600 3 400 bce 1 600 1 200 bce and 600 800 ce three inclination lows at 4 800 bce 600 300 bce and 1 000 1 300 ce and three eastward declination trends at 3 600 3 200 bce 2 600 2 400 bce and 400 bce to 200 ce the similarity between the hml psv record and other independently dated records from east asia and geomagnetic field models corroborates the robustness of our age model and holocene psv record strikingly centennial to millennial scale psv features of the hml are comparable within age uncertainties with other holocene records from europe north america and canada suggesting that such directional patterns are likely to be hemispheric in scale although relative paleointensity data of hml are affected by environmental factors e g organic matter diagenesis the record still provides a regionally important new psv reference curve whose conspicuous features may serve as stratigraphic markers for east asian paleorecords

rock magnetic carriers of century scale susceptibility cycles in glacial marine sediments from the palmer deep antarctic peninsula abstract a 4200 year long magnetic susceptibility profile from the palmer deep records century and millennial scale variability in paleoenvironmental conditions along the western antarctic peninsula the susceptibility profile shows regularly spaced highs and lows over the last 3360 years b p then drops to uniformly low values these features are formed by the variable dilution of terrigenous material with biogenic sediments and shifts in magnetic mineralogy high susceptibility intervals are characterized by multi domain md pure magnetite low susceptibility intervals are characterized by pseudo single domain psd magnetite and titanomagnetite prior to 3360 years b p the magnetic mineral assemblage is dominated by fine psd titanium rich titanomagnetite and superparamagnetic particles suggesting a change in sediment provenance and or sediment transport processes the absence of md magnetite suggests a cessation in locally derived ice rated debris this horizon represents the transition from the mid holocene climatic optimum to the neoglacial period marked by an increase in glacial sedimentation

earthquake sound perception 1 sound is an effect produced by almost all earthquakes using a web based questionnaire on earthquake effects that included questions relating to seismic sound we collected 77 000 responses for recent shallow italian earthquakes an analysis of audibility attenuation indicated that the decrease of the percentage of respondents hearing the sound was proportional to the logarithm of the epicentral distance and linearly dependent on earthquake magnitude in accordance with the behavior of ground displacement even if this result was based on italian data qualitative agreement with the results of theoretical displacement and of a similar study based on french seismicity suggests wider validity we also found that given earthquake magnitude audibility increased together with the observed macroseismic intensity leading to the possibility of accounting for sound audibility in intensity assessment magnitude influenced this behavior making small events easier to recognize as suggested by their frequency content

a preliminary magnetic study of soil samples from west central minnesota abstract various rock magnetic techniques were applied to characterize magnetically the samples of a soil profile taken from west central minnesota there is a marked change in magnetic properties as a function of depth in the core x ray analysis and curie temperature measurements carried out on the magnetic fractions indicate that magnetite is the dominant iron oxide in both the top soil and the subsoil the intensity of anhysteretic remanent magnetization arm decreases sharply as the depth increases in contrast the stability of arm was found to be higher for the subsoil the surface soil sample was capable of acquiring a significant amount of viscous remanent magnetization vrm the vrm acquisition coefficient s a of the subsoil s a 3 18 10 6 emu g 1 3 18 10 6 a m 2 kg 1 was about ten times weaker than that of the top soil sample s a 3 868 10 7emu g 1 3 868 10 7 a m 2 kg 1 the magnetic domain state indicator the ratio of coercivity of remanence to coercive force h cr h c was 1 5 and 3 85 for the top soil and subsoil respectively it appears that the observed variations in magnetic properties down the present soil core is due only to a difference in grain size we conclude that the magnetic grains in surface soil samples were more single domain sd like whereas the magnetite grains in the subsoil samples were more likely in pseudo single domain psd or small multidomain md range the observed lower stability for the surface soil samples is attributed to the presence of superparamagnetic grains whose presence was confirmed by transmission electron micrographs

magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the eastern mediterranean sea summary magnetic properties irm arm xin s ratio at 0 3 t room temperature rt hysteresis and thermomagnetic curves and geochemical data fe s mn al ti organic c were studied in two eastern mediterranean boxcores abc26 and bc19 at a resolution of 3 5 mm the boxcores contain sapropel s1 9 6 kyr bp at a few decimetres below seafloor the magnetic fraction consists predominantly of single domain sd to pseudo singledomain psd magnetite in the entire cores the original input of magnetic grains comes from two sources aeolian dust both cores and volcanic ash from the minoan eruption of santorini core bc19 only non steady state diagenesis has changed the magnetic mineralogy considerably in these alternating organic rich organic poor sediments during deposition of sapropel s1 reductive diagenesis and pyritization in and just below the sapropel caused lower magnetic intensities coarser magnetic grain sizes and partial maghemitization in thermomagnetic curves two types of pyrite can be identified one oxidizes below 450 uc and the other above 450 uc the higher oxidation temperature is predominantly found below the sapropel this may be related to the microtexture of pyrite which is euhedral below sapropels and mainly framboidal within sapropels since the end of sapropel deposition a downward moving oxidation front has oxidized the upper half c 5 cm of the sapropel the oxidized part of the sapropel is enriched in diagenetically formed fe oxides with relatively high coercivity and arm the maximum coercivity is found in a distinct layer between the present day mn and fe redox boundaries at the top of the unoxidized sapropel the freshly precipitated fe oxides in this centimetre thick layer contain a mixture of superparamagnetic sp grains and high coercivity sd magnetite higher in the oxidized zone the freshly precipitated fe oxides have aged into generally slightly lower coercivity sd grains with relatively high arm in addition to the diagenetic formation of fe oxides at the top of the sapropel formation of a ferrimagnetic fe monosulphide may have occurred within the sapropel during later stages of diagenesis which may have enhanced the arm signal in the organic rich interval in particular

comparison of hysteresis thermomagnetic and low temperature magnetic properties of particle size fractions from loess and palaeosol samples in central asia and the chinese loess plateau

moment tensor analysis of the central italy earthquake sequence of september october 1997 the larger earthquakes in the umbria marche central italy seismic sequence of september october 1997 are analyzed using long period seismograms from the mediterranean seismographic network mednet and additional data from the global seismographic network gsn we modify the harvard centroid moment tensor cmt algorithm to allow moment tensor inversion of long period waveforms primarily rayleigh and love waves for small earthquakes at local to regional distances 5 5 in the sequence moment tensors have previously been determined using teleseismic waveforms and standard methods of analysis our results agree well with those of earlier studies we determine additional moment tensors for the largest foreshock and 10 aftershocks with mw 4 2 the earthquakes are characterized by normal faulting mechanisms with a ne sw tension axis and the presumed fault plane dips towards the sw only one of the fourteen events studied has a different faulting geometry indicating instead right lateral strike slip faulting on a plane oriented approximately e w or left lateral faulting on a plane oriented n s the september 26 mainshock 09 40 ut accounts for only approximately 50 of the total moment release in the sequence

paleomagnetic rock magnetic and geochemical study of the 1755 tsunami deposit at boca do rio algarve portugal abstract a multiproxy study combining paleomagnetic rock magnetic magnetic susceptibility anhysteretic remanent magnetization arm isothermal remanent magnetization irm anisotropy of magnetic susceptibility ams and geochemical xrf data was carried out on trench sediments collected in the area of boca do rio algarve south portugal known to have been stricken by a tsunami wave related to the 1755 lisbon earthquake the magnetic mineral assemblage is dominated by multidomain ferrimagnetic grains with a significant contribution 5 9 of ultra fine magnetic particles related to the presence of pedogenetic magnetite the variable amount of this post depositional magnetite plays a role on the characteristic remanent magnetization chrm of the sediment the primary magnetization recorded at t1 located farthest from the coast is representative of the paleosecular variation of the earth s magnetic field and a comparison of the results with the regional model for the geomagnetic field in europe scha dif 3k was used to constrain the erosional signature of the tsunami layer the result indicates that less than eighty years could be missing in the sedimentary column the eroded sediment thickness 27 40 cm was incorporated in the tsunami layer that is characterized by a low magnetic content and a large increase in the ca content representing allochthonous material sedimentological geochemical magnetic and ams data show that the signature of the tsunami layer reflects at least two waves with an erosive capacity that is controlled by the distance from the shore

holocene break up and reestablishment of the petermann ice tongue northwest greenland abstract over the last decade two major calving events of the petermann ice tongue in northwest greenland have led to speculation on its future stability and contribution to further greenland ice sheet mass loss however it has been unclear if these events are anomalous or typical within the context of limited historical observations we extend the historical record of the floating ice tongue using the stratigraphy of petermann fjord sediments to provide a longer term perspective computed tomography ct scans x ray fluorescence xrf scans ice rafted debris ird counts and the magnetic properties of specific particle size fractions constrain changes in depositional processes and sediment sources at our core sites allowing for reconstructions of past behavior of the petermann ice tongue radiocarbon dating of foraminifera 210pb and paleomagnetic secular variation psv provide age control and help to address uncertainties in radiocarbon reservoir ages a floating ice tongue in petermann fjord formed in late glacial time as petermann glacier retreated from an advanced grounded position this paleo ice tongue broke up during the early holocene when high northern latitude summer insolation was higher than present after gradual regrowth of the ice tongue associated with regional cooling the ice tongue reached its historical extent only within the last millennium little or no ice tongue was present for nearly 5000 years during the middle holocene when decadal mean regional temperatures are estimated to be 0 8 2 9 c higher than preindustrial 1750 ce and seasonal sea ice in the lincoln sea was reduced this pre historical behavior shows that recent anthropogenic warming may already be in the range of ice tongue instability and future projected warming increases the risk of ice tongue break up by the mid 21st century

seismoacoustic recordings of small earthquakes in the pyrenees experimental results an experiment was conducted in the lesponne valley central french pyrenees to record the sounds that frequently accompany earthquakes in this region seismic and acoustic signals of a short period seismometer and a condenser microphone were continuously monitored for ten months during this period four small m l p transmission but also sv to p conversion into the atmosphere are identified thus confirming former hypotheses formulated by hill et al 1976 unambiguous quantitative constraints on the seismic to acoustic conversion are provided by the computation of transmission coefficients the dominant audio frequencies are recorded in the 5 to 60 hz band that is at the boundary between sounds and infrasounds and at the lower bound of human audibility high frequency infrasounds about 8 hz are interpreted as the transmission to the atmosphere of rayleigh waves induced locally by a thin soil layer

towards a self consistent plate mantle model that includes elasticity simple benchmarks and application to basic modes of convection one of the difficulties with self consistent plate mantle models capturing multiple physical features such as elasticity non newtonian flow properties and temperature dependence is that the individual behaviours cannot be considered in isolation for instance if a viscous mantle convection model is generalized naively to include hypo elasticity then problems based on earth like rayleigh numbers exhibit almost insurmountable numerical stability issues due to spurious softening associated with the co rotational stress terms if a stress limiter is introduced in the form of a power law rheology or yield criterion these difficulties can be avoided in this paper a novel eulerian finite element formulation for visco elastic convection is presented and the implementation of the co rotational stress terms is addressed the salient dimensionless numbers of visco elastic plastic flows such as weissenberg deborah and bingham numbers are discussed in a separate section in the context of geodynamics we present an eulerian formulation for slow temperature dependent visco elastic plastic flows a consistent tangent incremental formulation of the governing equations is derived numerical and analytical solutions demonstrating the effect of visco elasticity co rotational terms are first discussed for simplified benchmark problems for flow around cylinders we identify parameter ranges of predominantly viscous and visco plastic and transient behavior the influence of locally high strain rates on the importance of elasticity and non newtonian effects is also discussed in this context for the case of simple shear we investigate in detail the effect of different co rotational stress rates and the effect of power law creep the results show that the effect of the co rotational terms is insignificant if realistic stress levels are considered e g deviatoric invariant smaller than 1 10 of the shear modulus say we also consider the basic convection modes of stagnant lid episodic resurfacing and mobile lid convection as applicable to a cooling planet the simulations show that elasticity does not have a significant effect on global parameters such as the nusselt number and the qualitative nature of the basic convection pattern our simple benchmarks show however also that elasticity plays a significant role for instabilities on the local scale of an individual subduction zone

late paleozoic remagnetization and its carrier in the trenton and black river carbonates from the michigan basin paleomagnetic study of subsurface samples of the upper ordovician trenton and black river limestones collected from six industrial wells in the southern part of the michigan basin yields a well clustered characteristic direction mean dec inc of 170 6 10 9 alpha 95 7 6 circ after rotation of random declinations by aligning a present day field overprint with geographic north the corresponding paleomagnetic pole at 52 4 n 111 0 e is similar to those of the remagnetized carbonates in ontario and new york state suggesting that the michigan formations were also remagnetized in the late paleozoic rock magnetic characterizations suggest that the characteristic magnetization is carried by single and pseudosingle domain magnetite grains very fine rounded single crystal magnetite grains believed to be products of chemical precipitation observed by scanning and scanning transmission electron microscope sem stem are inferred to be the carrier of the remagnetization paired carbon isotope analys

relative variations in geomagnetic intensity from sedimentary records the past 200 000 years abstract eighteen records of relative paleointensity from marine sediments have been compiled in order to retrace the global changes in geomagnetic intensity during the past 200 kyr before dealing with any other source of noise we focused on problems inherent to the depth versus time correlations the accuracy and resolution of dating mostly deduced from isotopic stratigraphy were identified as significant factors of distortion we found also that different time scales have been used by authors after readjustment with respect to the same time scale the records were stacked together and the statistical significance of the results tested by a bootstrap technique seventeen records shown to be coherent were combined into a synthetic curve defined as sint 200 other stacks combining various subsets of data were found to be identical to sint 200 except for changes in dispersion in fact the dispersion around sint 200 could be reduced further by improving the correlations without violating the stratigraphy a procedure which at least for some records emphasizes the need for more detailed depth time correlations another characteristic emerging from the results is that paleointensity features as short as 10 kyr are observed between 120 200 ka and can thus in principle be resolved however subsequent refinement is still necessary for this period which is documented by fewer records than the following 120 kyr finally we compared sint 200 with the records from the labrador sea and the lac du bouchet ldb both of which rely mostly on 14c chronology the two records show satisfactory agreement with sint 200 when transferred with respect to the age model established by correlating their 18o labrador and susceptibility features ldb with the 18o reference record the offset of 7 kyr at 40 ka measured in both cases between the 14c and 18o ages is higher than the value deduced from a recent model of a geomagnetic field control of 14c production 1 but is not inconsistent with recent u th dates

paleoceanographic changes in the disko bugt area west greenland during the holocene micropaleontological analyses of a sediment core raised in disko bugt west of greenland were undertaken in order to document paleoceanographical changes in the eastern baffin bay during the holoc

initiation of subduction by small scale convection 1 the possibility of initiation of subduction by sublithospheric small scale convection is investigated with the help of fowler s theory numerical constraints on the lithospheric stresses generated by convection and direct numerical simulations of subduction the derived scaling laws show that the critical yield stress for initiation of subduction by small scale convection is of the order of 30 mpa this value is comparable with the critical yield stress required for initiation of subduction by plate forces and with the estimates of stresses in the subduction zone this implies that small scale convection can play an important role in the initiation of subduction on the present day earth this also implies that small scale convection can initiate subduction in the absence of already occurring plate tectonics and thus can be a trigger mechanism for plate tectonics on the early earth and other terrestrial planets the critical yield stress for initiation of subduction by either mechanism is at least one order of magnitude smaller than the estimates of the lithospheric strength suggested by laboratory experiments on rock deformation such a low lithospheric strength is most likely caused by a relatively high abundance of water in the interior of the earth since the critical yield stress depends only weakly on planetary parameters water seems to be the key condition required for plate tectonics to occur on a terrestrial planet

decadal to millennial scale periodicities in north iceland shelf sediments over the last 12 000 cal yr long term north atlantic oceanographic variability and solar forcing giant piston core md99 2269 recovered 25 m of sediment in hunafloaall a deep trough on the north iceland margin fronting the iceland sea and the site of a shelf sediment drift the rate of sediment accumulation is 2 m kyr 5 yr cm the core terminated in the vedde tephra v12 cal ka the sediment was sampled at between 5 and 50 yr sample including rock magnetic grain size and sediment properties data reduction was carried out using principal component analysis two pc axes for the 5 yr sample magnetic data are strongly correlated with measures of coercivity arm20 mt arm and magnetic concentrations karm in turn arm20 mt arm is highly correlated negatively with grain size and the mean size of the sortable silt fraction analyses of the two pc axes with mtm spectral methods indicate a series of significant s 99 periodicities at millennial to multidecadal scales including those at v200 125 and 88 yr which are associated with solar variability we also document a strong correlation between the sediment magnetic properties and the d 18 o on benthic foraminifera on the north iceland inner shelf we hypothesize that the links between variations in grain size magnetic concentrations and solar forcing are controlled by atmospheric and oceanographic changes linked to changes in the relative advection of atlantic and polar waters along the north iceland margin today these changes are associated with variations in the deep convection in the greenland and iceland seas the precise linkages are however presently elusive although a combination of coarser sediments and low d 18 o values define a holocene thermal maximum between v8 and 6 cal ka 2003 elsevier science b v all rights reserved

earthquake and flood induced turbidites in the saguenay fjord quebec a holocene paleoseismicity record abstract a 38 m long piston core from the deep basin of the saguenay fjord quebec recorded rapidly deposited layers rdl interpreted to represent major floods and earthquakes over the past 7200 years high resolution physical magnetic and sedimentological analyses revealed at least 14 rdl generally with a sandy base and a light gray color interbedded with hemipelagic sediments digital x radiography and grain size analyses at

use of magnetic and radiometric measurements to investigate erosion and sedimentation in a british upland catchment in response to the potential shortcomings of single technique strategies in the investigation of erosion and sedimentation a combined magnetic and radiometric 13cs and 210pb approach has been undertaken in the upland watershed lake system of howden reservoir derbyshire by combining these techniques some assessment of sediment sources and the erosion status of the catchment has been achieved alone each approach would have been unable to determine unequivocally sediment provenance furthermore the parallel use of these measurements has highlighted limitations and or uncertainties in both the magnetic and 137cs techniques these problems reflect the particular soil characteristics and drainage conditions of this upland catchment despite the documented severity of peat erosion in the region howden reservoir has a mixture of sediment sources and a relatively moderate rate of sedimentation sediment yields total 127 7 t km 2 yr 1 including organic fraction 31 3 t km 2 yr 1 are however higher than in other british upland areas