holocene coastal glaciation of alaska holocene uctuations of the three cirque glaciers on the seward peninsula and ve groups of tidewater and land terminating glaciers along the northernmost gulf of alaska provide a proxy record of late holocene climatic change furthermore the movements of the coastal glaciers were relevant to late holocene native american migration the earliest expansion was recorded about 6850 yr bp by hubbard glacier at the head of yakutat bay in the gulf of alaska however its down fjord advance to the bay mouth was delayed until 2700 bp similarly expansions of the icy bay bering and mccarty glaciers occurred near their present termini by 3600 3000 bp compatible with marked cooling and precipitation increases suggested by the alaskan pollen record decrease in glacier activity 2000 bp was succeeded by advances of gulf coastal glaciers between 1500 and 1300 bp correlative with early medieval expansions across the northern hemisphere a medieval optimum encompassing at least a few centuries prior to ad 1200 is recognized by general retreat of land terminating glaciers but not of all tidewater glaciers little ice age advances of land based glaciers many dated with the precision of tree ring cross dating were centered on the middle 13th or early 15th centuries the middle 17th and the last half of the 19th century a d strong synchrony of these events across coastal alaska is evident 2000 elsevier science ltd all rights reserved

alongshelf variability of inner shelf circulation along the central oregon coast during summer the spatial and temporal variability of inner shelf circulation along the central oregon coast during the 2004 upwelling season is described using a 70 km long array of moorings along the 15 m isobath circulation at three stations located onshore of a submarine bank differed from that of a station north of the bank despite the relatively uniform wind forcing and inner shelf bathymetry present during upwelling favorable winds strong southward alongshelf flow occurred north of the bank no alongshelf flow occurred onshore of the northern part of the bank and increasing southward flow occurred onshore of the southern part of the bank during downwelling favorable winds strong northward flow occurred in the inner shelf onshore of the bank while weak flow occurred north of the bank these alongshelf differences in inner shelf circulation were due to the effects of the bank which isolated the inner shelf onshore of the bank from the regional upwelling circulation that was evident at the northernmost station as a result circulation onshore of the bank was drivenprimarily by local wind forcing whileflow north of the bank was only partiallydriven by local winds a secondary mode of variability attributed to the movement of the regional upwelling jet due to remote forcings contributed the bulk of the variability observed north of the bank with the time dependent wind forcing present acceleration was an important term in the depth averaged alongshelf momentum equation at all stations during upwelling bottom stress and acceleration opposed the wind stress north of the bank while bottom stress was weaker onshore of the bank where the across shelf momentum flux and the alongshelf pressure gradient balanced the residual of the acceleration and stresses during downwelling waters onshore of the bank surged northward at magnitudes much larger than that found north of the bank these spatial variations developed as the season progressed and the regional upwelling circulation intensified explaining known variations in growth and recruitment of nearshore invertebrate species

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

continental extension from core complexes to rigid block faulting extension of overthickened continental crust is commonly characterized by an early core complex stage of extension followed by a later stage of crustal scale rigid block faulting these two stages are clearly recognized during the extensional destruction of the alpine orogen in northeast corsica where rigid block faulting overprinting core complex formation eventually led to crustal separation and the formation of a new oceanic backarc basin the ligurian sea here we investigate the geodynamic evolution of continental extension by using a novel fully coupled thermomechanical numerical model of the continental crust we consider that the dynamic evolution is governed by fault weakening which is generated by the evolution of the natural state variables i e pressure deviatoric stress temperature and strain rate and their associated energy fluxes our results show the appearance of a detachment layer that controls the initial separation of the brittle crust on characteristic listric faults and a core complex formation that is exhuming strongly deformed rocks of the detachment zone and relatively undeformed crustal cores this process is followed by a transitional period characterized by an apparent tectonic quiescence in which deformation is not localized and energy stored in the upper crust is transferred downward and causes self organized mobilization of the lower crust eventually the entire crust ruptures on major crosscutting faults shifting the tectonic regime from core complex formation to wholesale rigid block faulting

weak zone formation for initiating subduction from thermo mechanical feedback of low temperature plasticity abstract we have addressed the problem of subduction initiation with a solid mechanical and fluid dynamical approach using a finite element method the setup has been extended by a rate sensitive coupling at the bottom of a semi brittle lithosphere and a fully coupled thermo mechanical model the central element of our model is a broad asymmetric sedimentary loading function at the passive continental margin which grows with time to 15 km two fundamentally different modes of shear zone formation have been found depending on the rheology of the creep layer mode 1 for cases of low or absent yield stress in the creep layer only the semi brittle top develops a weak zone while the rate sensitive layer acts as a decoupling shear zone mode 2 for cases with a yield strength in the creep layer strain rates above 10 15 s 1 after yielding the entire mechanical lithosphere fails on a major shear zone mode 1 fails to model subduction initiation while mode 2 creates a weak major shear zone that severs through the entire lithosphere

imaging surface contacts power law contact distributions and contact stresses in quartz calcite glass and acrylic plastic a procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials while the surfaces are subjected to static loads or undergoing frictional slip static loading experiments with quartz calcite soda lime glass and acrylic plastic at normal stresses to 30 mpa yield power law distributions of contact areas from the smallest contacts that can be resolved 3 5 m2 up to a limiting size that correlates with the grain size of the abrasive grit used to roughen the surfaces in each material increasing normal stress results in a roughly linear increase of the real area of contact mechanisms of contact area increase are by growth of existing contacts coalescence of contacts and appearance of new contacts mean contacts stresses are consistent with the indentation strength of each material contact size distributions are insensitive to normal stress indicating that the increase of contact area is approximately self similar the contact images and contact distributions are modeled using simulations of surfaces with random fractal topographies the contact process for model fractal surfaces is represented by the simple expedient of removing material at regions where surface irregularities overlap synthetic contact images created by this approach reproduce observed characteristics of the contacts and demonstrate that the exponent in the power law distributions depends on the scaling exponent used to generate the surface topography

multiscale brittle ductile coupling and genesis of slow earthquakes we present the first attempt to explain slow earthquakes as cascading thermal mechanical instabilities to attain this goal we investigate brittle ductile coupled thermal mechanical simulation on vastly different time scales the largest scale model consists of a cross section of a randomly perturbed elasto visco plastic continental lithosphere on the order of 100 9 100 km scale with no other initial structures the smallest scale model investigates a km scale subsection of the large model and has a local resolution of 40 9 40 m the model is subject to a constant extension velocity applied on either side we assume a free top surface and with a zero tangential stress along the other boundaries extension is driven by velocity boundary conditions of 1 cm a applied on either side of the model this is the simplest boundary condition and makes it an ideal starting point for understanding the behavior of a natural system with multiscale brittle ductile coupling localization feedback is observed as faulting in the brittle upper crust and ductile shearing in an elasto viscoplastic lower crust in this process brittle faulting may rupture at seismogenic rates e g at 10 2 10 3 ms 1 whereas viscous shear zones propagate at much slower rates up to 3 9 10 9 ms 1 this sharp contrast in the strain rates leads to complex short time scale interactions at the brittle ductile transition we exploit the multiscale capabilities from our new simulations for understanding the underlying thermo mechanics spanning vastly different time and length scales

geomorphic processes influence human settlement on two islands in the islands of four mountains alaska the islands of four mountains island group of the aleutian island arc is remote and difficult to access consequently little fieldwork has focused on geomorphic processes and their relationship to island morphology climatic change and human settlement we investigated glacial fluvial and slope processes on the morphologically different carlisle cleveland and tana volcanoes the islands were extensively glaciated at the last glacial maximum lgm and there is evidence for a neoglacial advance on the highly dissected tana volcano a large basin is likely the result of a pre lgm sector collapse and subsequent glacial erosion into weak hydrothermally altered rock valley and moraine morphology is also influenced by hydrothermal alteration on both tana and carlisle there are sediment fans composed dominantly of thick debris flow deposits mantled by 3 m of layered tephras fine grained alluvium and anthropogenic deposits debris flow deposition was favored during the unstable paraglacial landscape of the early holocene latest pleistocene the earliest direct archaeological evidence for settlement is 3 8 cal ka bp but soil geochemical evidence suggests that the islands were inhabited by 7 3 cal ka bp this discrepancy in the archaeological record may be explained by geomorphic processes including coastal erosion and unstable geomorphic surfaces

seasonal circulation over the catalan inner shelf northwest mediterranean sea 1 this study characterizes the seasonal cycle of the catalan inner shelf circulation using observations and complementary numerical results the relation between seasonal circulation and forcing mechanisms is explored through the depth averaged momentum balance for the period between may 2010 and april 2011 when velocity observations were partially available the monthly mean along shelf flow is mainly controlled by the along shelf pressure gradient and by surface and bottom stresses during summer fall and winter the along shelf momentum balance is dominated by the barotropic pressure gradient and local winds during spring both wind stress and pressure gradient act in the same direction and are compensated by bottom stress in the cross shelf direction the dominant forces are in geostrophic balance consistent with dynamic altimetry data

paradoxical pseudotachylyte fault melt outside the seismogenic zone abstract fault generated melt pseudotachylyte is an established indicator of palaeoseismic faulting the existing consensus that frictionally induced melting occurs within the classic seismogenic zone contrast the contention over how pseudotachylyte forms within the ductile regime central to this issue is whether all pseudotachylyte originates as pressure dependent frictional melt along slip surfaces or if pressure independent processes have roles in its formation propagation of high velocity slip into deeper crustal levels provides a satisfactory explanation for pseudotachylyte at depth but does not of itself rationalize earthquake nucleation outside the classic seismogenic zone pseudotachylyte from the minas fault zone nova scotia canada is used to demonstrate the formation and preservation of fault related melt under lower crustal conditions microstructures retain evidence of intense dislocation glide with minimal climb and ductile disaggregation of the host the latter are consistent with intracrystalline deformation in the peierls stress controlled glide regime it remains unclear whether the crystal plasticity serves only as a precursory stage to rupture and high velocity slip or is itself responsible for both instability and the thermal transient there are similarities between accelerating plastic slip leading to rupture and aseismic creep bursts tremor that emphasize the mechanistic complexity of deep faulting and the need to extend consideration beyond that of a simple brittle ductile response the occurrence of tremor bursts fall within the depth range of paradoxical pseudotachylyte and provides a circumstantial link between active tectonics and the geologic record that merits examination

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

temporal distribution of suspended sediment transport in a mediterranean basin the lower tordera ne spain abstract suspended sediment dynamics are still imperfectly understood especially in areas of mediterranean climate with strong seasonal contrasts where few studies have been conducted the aim of this study is to analyze the variability in the suspended sediment load at different temporal scales within flood variability monthly seasonal and annual in the tordera river 894 km 2 located in northeastern spain suspended sediment samples were obtained during base flows q 3 5 m 3 s 1 and flood events q 3 5 m 3 s 1 the analysis of the variability in the suspended sediment is structured in two consecutive steps i the construction of statistical relations between suspended sediment concentrations c and discharge q and ii the application of those relations to assess the suspended sediment yield the results show that in a single event the sediment peak generally precedes the peak discharge following a clockwise hysteretic loop furthermore it was observed that the reduction in the suspended sediment concentrations in a sequence of events can be mainly associated with a phenomenon of sediment exhaustion the total amount of suspended sediment transported during a single flood is thus related to its duration and time during the year as well as to its magnitude at a seasonal scale the export of suspended sediment takes place in two phases i sediment preparation and ii sediment transfer and exhaustion during the latter phase the exhaustion of the sediment load is primarily related to the sequence of flood events at the annual scale the results show high inter annual variability according to the number of floods recorded yearly since almost all the suspended load is transported during those events

crustal rheology from focal depths in the north china basin abstract in order to investigate earthquakes in the lower crust of north china basin ncb we develop a new method of resolving very accurately the focal depth for local earthquakes in the sedimentary regions by using p and s to p converted wave sp at the sedimentary interface theoretical analysis shows clearly that the travel time difference between the sp and p wave almost linearly correlates with the focal depth this finding provides tight constraints on the depth with this method we obtain well constrained depths of 44 events in the ncb with uncertainties in the depth of about 2 km such a fine resolution can have great potential in asking questions regarding the crustal rheology the depth distribution shows abundance of earthquakes in depth interval of 20 km with some events in the lower crust but also reveals the absence of seismicity deeper than 25 km we find a good fit between the depth frequency distribution in this region and the yield strength envelope yse in the baikal rift systems brs we infer that the seismogenic thickness is 25 km in the ncb and the main deformation mechanism is brittle fracture we further hypothesize that 1 the rheological layering of dominant rheology in the ncb is similar to that of the brs which can be explained with a quartz rheology at 0 10 km depth and a diabase rheology at 10 35 km depth 2 the temperature is moderate in the seismogenic zone of crust we emphasize that many accurately resolved earthquake locations can shed light on the local nature of the crustal rheology and this strategic method can be employed in other sedimentary regions which are seismically active

energetics of a two phase model of lithospheric damage shear localization and plate boundary formation summary the two phase theory for compaction and damage proposed by bercovici et al 2001a j geophys res 106 8887 8906 employs a nonequilibrium relation between interfacial surface energy pressure and viscous deformation thereby providing a model for damage void generation and microcracking and a continuum description of weakening failure and shear localization here we examine further variations of the model which consider 1 how interfacial surface energy when averaged over the mixture appears to be partitioned between phases 2 how variability in deformational work partitioning greatly facilitates localization and 3 how damage and localization are manifested in heat output and bulk energy exchange microphysical considerations of molecular bonding and activation energy suggest that the apparent partitioning of surface energy between phases goes as the viscosity of the phases when such partitioning is used in the two phase theory it captures the melt compaction theory of mckenzie 1984 j petrol 25 713 765 exactly as well as the void damage theory proposed in a companion paper ricard bercovici submitted calculations of 1 d shear localization with this variation of the theory still show at least three possible regimes of damage and localization at low stress is weak localization with diffuse slowly evolving shear bands at higher stress strong localization with narrow rapidly growing bands exists and at yet higher shear stress it is possible for the system to undergo broadly distributed damage and no localization however the intensity of localization is strongly controlled by the variability of the deformational work partitioning with dilation rate represented by the parameter f or 1 extreme localization is allowed with sharp profiles in porosity weak zones nearly discontinuous separation velocities and effectively singular dilation rates finally the bulk heat output is examined for the 1 d system to discern how much deformational work is effectively stored as surface energy in the high stress distributed damage cases heat output is reduced as more interfacial surface energy is created yet in either the weak or strong localizing cases the system always releases surface energy regardless of the presence of damage or not and thus slightly more heat is in fact released than energy is input through external work moreover increased levels of damage represented by the maximum work partitioning f make the localizing system release surface energy faster as damage enhances phase separation and focusing of the porosity field thus yielding more rapid loss of net interfacial surface area however when cases with different levels of damage are compared at similar stages of development say the peak porosity of the localization it is apparent that increased damage causes smaller relative heat release and retards loss of net interfacial surface energy the energetics and energy partitioning of this damage and shear localization model are applied to estimating the energy costs of forming plate boundaries and generating plates from mantle convection

along shelf current variability on the catalan inner shelf nw mediterranean 1 we examine the circulation over the inner shelf of the catalan sea using observations of currents obtained from three acoustic doppler current profilers two at 24 m and one at 50 m during march april 2011 the along shelf current fluctuations during that period are mainly controlled by local wind stress on short time scales and by remote pressure gradients on synoptic time scales different forcing mechanisms are involved in the along shelf momentum balance during storm conditions wind stress sea level gradients and the nonlinear terms dominate the balance during weak wind conditions the momentum balance is controlled by the pressure gradient while during periods of moderate wind in the presence of considerable stratification the balance is established between the coriolis and wind stress terms vertical variations of velocity are affected by the strong observed density gradient the increased vertical shear is accompanied by the development of stratified conditions due to local heating when the wind is not able to counteract and break stratification the occasional influence of the besos river plume is observed in time scales of hours to days in a limited area in near the city of barcelona the area affected by the plume depends on the vertical extent of the fresher layer the fast river discharge peak and the relaxation of cross shore velocities after northeast storm events this contribution provides a first interpretation of the inner shelf dynamics in the catalan sea

flocculation and sedimentation on the po river delta with the goal of improving understanding of the effect of flocculation on the formation of fine grained deposits on continental shelves hydrographic profiling in situ imaging of suspended matter and collection of surficial sediment samples were conducted at the po river delta in june 2001 these data show that during medium flow conditions 1920 m3 s sedimentation occurs rapidly immediately offshore of the main distributary po della pila rapid sedimentation is promoted by large rapidly sinking flocs forming in the river well upstream of the mouth the delivery of fine sediment to the seabed at the mouth of the po is sufficient to overwhelm the erosive effects of waves and currents leading to accumulation of mud in water depths as shallow as 4 m on cross shelf transects 2 km north and south of the mouth however suspended sediment supply from the river is reduced to the point that mud accumulates only seaward of the 8 m isobath along the central transect suspended sediment concentration decreases rapidly seaward of the 6 m isobath where the emergence of a more organic rich population of flocs along a mid water density interface is suggested energetic activity along the 15 m isobath likely promotes resuspension with the potential for removal of material from the delta further investigation of floc properties namely the relationship of floc size to settling velocity is necessary to establish the degree to which the suspension is flocculated during transport and deposition

seismology energy radiation from the sumatra earthquake we determined the duration of high frequency energy radiation from indonesia s great sumatra andaman earthquake 26 december 2004 to be about 500 seconds this duration can be translated into a rupture length of about 1 200 km which is more than twice as long as that inferred from body wave analyses performed soon after the event our analysis was able rapidly to define the extent of rupture thereby aiding the assessment of seismic hazard in the immediate future

landslides ice quakes earthquakes a thermodynamic approach to surface instabilities the total rate of rock deformation results from competing deformation processes including ductile and brittle mechanisms particular deformation styles arise from the dominance of certain mechanisms over others at different ambient conditions surprisingly rates of deformation in naturally deformed rocks are found to cluster around two extremes representing coseismic slip rates or viscous creep rates classical rock mechanics is traditionally used to interpret these instabilities these approaches consider the principle of conservation of energy we propose to go one step further and introduce a nonlinear far from equilibrium thermodynamic approach in which the central and explicit role of entropy controls instabilities we also show how this quantity might be calculated for complex crustal systems this approach provides strain rate partitioning for natural deformation processes occurring at rates in the order of 10 3 to 10 9 s 1 we discuss these processes using examples of landslides and ice quakes or glacial surges we will then illustrate how the mechanical mechanisms derived from these near surface processes can be applied to deformation near the base of the seismogenic crust especially to the phenomenon of slow earthquakes

sediment dynamics during wet and dry storm events on the tet inner shelf sw gulf of lions abstract the importance of short term processes such as floods and storms on sediment delivery and reworking on the tet inner shelf was investigated the tet inner shelf is a small event dominated system located in the south western part of the gulf of lions the expected sedimentary scenario in this environment is that fluvial sediment should be deposited on the prodelta and later dispersed around the shelf and slope by wave and current reworking during storms this paper investigates differences in inner shelf sediment dynamics between storm events occurring during usual river discharges and those occurring during river floods waves current velocities near bottom water turbidity bottom sediment grain size and sea floor erosion accretion were concurrently measured at 28 m water depth on the tet inner shelf from november 2003 to march 2004 two major storms took place on 4 december 2003 and 21 february 2004 and two moderate storms occurred on 8 december 2003 and 14 march 2004 the two major storms displayed similar wave characteristics maximum significant wave height h s 7 m peak period t p 12 s and wave direction around 90 the main environmental differences during the two major storm events correspond to the amount of sediment discharged from the tet river about 2 10 4 t of sediment was delivered by the river during the 4 december flood wet storm and less than 5 10 2 t during the 21 february storm dry storm sediment dynamics were quite similar during the storm events resuspension caused by waves and sediment advection towards the southeast due to near bottom shelf currents were the dominant sedimentary processes the result was a bottom sediment erosion of several centimetres at the study site during both the wet and dry events the main differences between the wet and dry events arose after the storm immediately after the peak of the wet storm sediment supplied by the tet river and probably from other rivers was deposited around the river mouth a few days later during a moderate storm this unconsolidated sediment was resuspended transported offshore and deposited on the inner shelf in contrast a moderate storm which occurred some days after the dry february storm caused bottom erosion on the inner shelf because no fresh sediment was available on the shallower area the results from this study indicate that the tet inner shelf at 28 m water depth is mainly a bypass zone for sediment that is transported s se towards the middle outer shelf and slope although ephemeral sediment deposits may be favoured by the sediment supplied from flood events sediment transport across the shelf from the river to the slope follows a complex multi step pattern that needs to be addressed using a multi event approach

formation of fine sediment deposit from a flash flood river in the mediterranean sea we identify the mechanisms controlling fine deposits on the inner shelf in front of the besos river in the northwestern mediterranean sea this river is characterized by a flash flood regime discharging large amounts of water more than 20 times the mean water discharge and sediment in very short periods lasting from hours to few days numerical model output was compared with bottom sediment observations and used to characterize the multiple spatial and temporal scales involved in offshore sediment deposit formation a high resolution 50 m grid size coupled hydrodynamic wave sediment transport model was applied to the initial stages of the sediment dispersal after a storm related flood event after the flood sediment accumulation was predominantly confined to an area near the coastline as a result of preferential deposition during the final stage of the storm subsequent reworking occurred due to wave induced bottom shear stress that resuspended fine materials with seaward flow exporting them toward the midshelf wave characteristics sediment availability and shelf circulation determined the transport after the reworking and the final sediment deposition location one year simulations of the regional area revealed a prevalent southwestward average flow with increased intensity downstream the circulation pattern was consistent with the observed fine deposit depocenter being shifted southward from the river mouth at the southern edge bathymetry controlled the fine deposition by inducing near bottom flow convergence enhancing bottom shear stress according to the short term and long term analyses a seasonal pattern in the fine deposit formation is expected

seismology speed and size of the sumatra earthquake we now have a clearer picture of the seismic features of last year s gigantic event our seismological results reveal that indonesia s devastating sumatra andaman earthquake on 26 december 2004 was 2 5 times larger than initial reports suggested second only to the 1960 chilean earthquake in recorded magnitude they indicate that it slowly released its energy by slip along a 1 200 km fault generating a long rupture that contributed to the subsequent tsunami now that the entire rupture zone has slipped the strain accumulated from the subduction of the indian plate beneath the burma microplate has been released and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary although large earthquakes on segments to the south still present a threat

chronology of holocene glaciation central brooks range alaska the central brooks range was glacierized in the highest north facing cirques during late middle to late holocene neoglacial time this neoglaciation involved at least 5 major cirque glacier expansions of similar magnitude as based on lichenometric mapping of more than 50 glaciers and radiocarbon dates directly associated with 5 moraines initial stabilization of debris covered glaciers took place by early holocene time but evidently no moraines formed during this interval few morainal ridges are preserved that date from the older expansions but they have been lichenometrically dated 20 age reliability to 3 separate intervals 4400 3500 and 2900 yr b p twelve morainal complexes have ridges indicative of glacial advance that lichenometrically date at 1800 500 yr b p relict lichens that are now emerging undisturbed from beneath a receding glacier toe imply that this time was one of prolonged recession in at least some parts of the brooks range however radiocarbon analysis of dead moss at this same site dates a subsequent neoglacial advance across the cirque floor at 1120 180 yr b p our data suggest that for the past 1 100 yr cirque glaciers have been continuously in more extended positions than they are today during this glaciologically favorable interval the last two major advances occurred at 800 150 and 390 90 yr b p a d 1410 1600 glaciers across the central brooks range stayed close to their maxima until a d 1640 1750 historical photographs and lichenometry show that retreat was most rapid after a d 1870 and decelerated after the mid 1900s recession from this most recent neoglacial maximum has amounted to 150 700 m and continues at present the cirque glacier advances were accompanied by equilibrium line altitude ela depressions of 100 to 200 m below levels maintained in the late 1970s environmental lapse rate estimates and 1977 1981 glaciologic meteorologic measurements suggest that summer air temperatures accompanying neoglacial maxima were respectively 1 c or 3 to 4 c cooler than those of the late 1970s across the central brooks range the neoglacial maxima elas rise northeastward and northward from 2 to 5 m km 1

investigating the function of prehistoric stone bowls and griddle stones in the aleutian islands by lipid residue analysis the earliest durable cooking technologies found in alaska are stone bowls and griddle stones recovered from the aleutian islands this paper aims to identify the function of these artefacts molecular and chemical analysis of carbonised residues found on their surfaces confirm that these artefacts were used to process marine resources both artefacts have high lipid content and c n ratios suggesting they were used to process oily substances stable isotope results of individual lipids suggest that they were used to process different sets of resources within the aquatic spectrum as griddle stones have slightly more 13c depleted lipids than stone bowls possibly indicating more variable use integration of these results with archaeological and ethnographic data lead us to infer that griddle stones were used for the cooking of a diversity of aquatic resources possibly with the addition of plant foods whereas stone bowls were specifically used to render marine mammal fats we further hypothesize that a sudden peak in stone bowl frequencies at 4000 3000 cal yr bp was connected to a neoglacial cold spell bringing sea ice conditions to the aleutian islands this may have led to new subsistence strategies in which the rendering of marine mammal fats played a central role

dynamics of sea mammal and bird populations of the bering sea region over the last several millennia abstract the secular dynamics of sea mammal and bird populations of the bering sea region over the last several millennia are reconstructed we identify osteological material from the cultural layers of ancient sea mammal hunter settlements as well as natural deposits in chukotka kamchatka and the aleutian and commandor islands changes in species composition of mammals and birds of this region are identified climatic changes are reconstructed from complex investigations of peat and coastal deposits in chukotka and the aleutian islands all material was radiocarbon dated about 400 dates it was found that the main factors affecting the dynamics of sea mammal and bird populations in the northern part of the region over the last several thousand years were summer precipitation and sea ice conditions whereas in the southern part precipitation and summer temperature dominated

quartz rheology and short time scale crustal instabilities we present numerical results of thermal mechanical feedback in crustal quartz rheology and contrast this behavior to the vastly different character of an olivine mantle in the numerical experiments quartz is found to have a very strong tendency for short time scale instabilities while our numerical experiments show that olivine has a decisive tendency for a stable thermally lubricated slip at the same time olivine can also go through a transitional period of creep bursts which are physically caused by multiple interacting ductile faults at various length and time scales which collocate quickly into a major shear zone since olivine has this strong propensity to self organize in a large apparently stable fault system it lacks the dynamics of interacting ductile faults evident in other minerals quartz behaves totally different and keeps its jerky slip behavior for prolonged deformation an example is shown here in which a 30 50 km piece of a wet quarzitic crust is extended for about 2 ma the associated total displacement field clearly shows the unstable slipping events which have a characteristic time frame of one to several years in contrast olivine is very stable and has a much longer time scale for thermal instability of 100 kyrs

the role of global and local factors in determining the middle to late holocene environmental history of the south kurile and komandar islands northwestern pacific abstract the study of holocene deposits from northwestern pacific islands is very important for understanding the natural development of the area in the context of oceanic climate strong microclimate variability and the influence of contrasting marine currents holocene sections from bering island record the following events cooling at about 4600 4500 yr bp warming at about 3500 3400 yr bp cooling at about 3000 yr bp sea level rise up to 1 5 m at about 2700 bp cooling at about 1800 1400 yr bp and sea level rise at about 1000 yr bp on the south kuriles a dry and cool climate changed to warm and moist about 7000 6500 yr bp later than on hokkaido island at this time the kuroshio current system became more active and birch assemblages were replaced by cool temperate broadleaf forests and mixed coniferous broadleaf forests at the holocene optimum about 6000 yr bp temperate broadleaf forest occupied almost all of kunashir and the okhotsk side of iturup and the climate was warmer than present the highest sea level position reached was 2 5 3 m above present level about 6500 6300 yr bp during the cooling about 4700 4500 yr bp island vegetation changed slightly due to the influence of warm currents major sea level regression during this period led to the formation of extensive coastal dune fields the warming at the beginning of the late holocene was almost as great as that of the holocene optimum two minor transgressions are recorded the vegetation changes and climatic deterioration that took place in the second half of the late holocene resulted in either a disappearance of thermophylous taxa or in a southward shift of their natural habitats during the cooling from 1700 to 1300 yr bp the isthmus area increased coastal wetlands with lakes and coastal dunes with paleosols were formed and grassland and swamp landscapes developed late holocene warming was not intensive volcanic impact on environments led to changes in vegetation assemblage swamping of the area and thick soil profile formation

patterns of faunal extinction and paleoclimatic change from mid holocene mammoth and polar bear remains pribilof islands alaska abstract qagnax cave a lava tube cave on st paul island in the pribilofs has recently produced a mid holocene vertebrate faunal assemblage including woolly mammoth polar bear caribou and arctic fox several dates on the mammoth remains converge on 5700 14c yr bp these dates 2300 yr younger than mammoth dates previously published from the pribilof islands make these the youngest remains of proboscideans and of non extinct quaternary megafauna recovered from north america persistence of mammoths on the pribilofs is most parsimoniously explained by the isolation of the pribilofs and the lack of human presence in pre russian contact times but an additional factor may have been the local existence of high quality forage in the form of grasses enriched by nutrients derived from local holocene tephras this interpretation is reinforced by stable carbon and nitrogen isotope values obtained from the mammoth remains the endpoint of mammoth survival in the pribilofs is unknown but maybe coterminous with the arrival of polar bears whose remains in the cave date to the neoglacial cold period of 4500 to 3500 14c yr bp the polar bear record corroborates a widespread cooling of the bering sea region at that time

arctic siberia refuge of the mammoth fauna in the holocene abstract global climate change at the end of pleistocene led to extinction in the huge territories of northern eurasia of the typical representatives of the mammoth fauna mammoth woolly rhinoceros wild horse bison musk ox and cave lion undoubtedly the mammoth fauna underwent pressure from upper paleolithic humans whose hunting activity could also have played a role in decreasing the number of mammoths and other representatives of megafauna formerly it was supposed that the megafauna of the mammoth complex had become extinct by the beginning of the holocene nevertheless the latest data indicate that extinction of the mammoth fauna was significantly delayed in the north of eastern siberia in the 1990s some radiocarbon dates established that mammoths existed in the holocene on wrangel island from 7700 until 3700 ybp radiocarbon data show that wild horses inhabited the north of eastern siberia 4600 2000 ybp muskoxen lived here about 3000 ybp some bison remains from eastern siberia belong to the holocene the following circumstances could promote the survival of representatives of mammoth fauna cool and dry climate in this region promotes the maintenance of steppe associations the habitats of those mammals late paleolithic and mesolithic settlements are not found in the arctic zone of eastern siberia from taimyr peninsula to the lower yana river they are very rare in basins of the indigirka and kolyma rivers the small number of stone age hunting tribes in the northern part of eastern siberia was probably another factor that contributed to the survival of some mammoth fauna representatives

syn convergent extension observed using the retreat gps network northern apennines italy 1 we present crustal deformation results from a geodetic experiment retreating trench extension and accretion tectonics retreat focused on the northern apennines orogen in italy the experiment centers on 33 benchmarks measured with gps annually or more frequently between 2003 and 2007 supplemented by data from an additional older set of 6 campaign observations from stations in northern croatia and 187 continuous gps stations within and around northern italy in an attempt to achieve the best possible estimates for rates and their uncertainties we estimate and filter common mode signals and noise components using the continuous stations and apply these corrections to the entire data set including the more temporally limited campaign time series the filtered coordinate time series data are used to estimate site velocity we also estimate spatially variable seasonal site motions for stations with sufficient data the rms scatter of residual time series are generally near 1 mm and 4 mm horizontal and vertical respectively for continuous and most of the new campaign stations but scatter is slightly higher for some of the older campaign data velocity uncertainties are below 1 mm yr for all but one of the stations maximum rates of site motion within the orogen exceed 3 mm yr directed ne relative to stable eurasia this motion is accommodated by extension within the southwestern and central portions of the orogen and shortening across the foreland thrust belt to the northeast of the range the data set is consistent with contemporaneous extension and shortening at nearly equal rates the northern apennines block moves northeast faster than the northern adria microplate convergence between the northern apennines block and the northern adria microplate is accommodated across a narrow zone that coincides with the northeastern apennines range front extension occurs directly above an intact vertically dipping slab inferred by previous authors from seismic tomography the observed crustal deformation is consistent with a buried dislocation model for crustal faulting but associations between crustal motion and seismically imaged mantle structure may also provide new insights on mantle dynamics

a mid holocene shift in arctic sea ice variability on the east greenland shelf records of iceberg rafting and palaeohydrography from two east greenland shelf cores jm96 1206 1 gc and jm96 1207 1 gc are reported benthic foraminifera stable isotopes and ird e uxes indicate a shift toward colder lower salinity polar conditions c 5 cal ka a new proxy of iceberg rafting on the east greenland shelf is the e ux of calcium carbonate tic thought to be derived from glacial erosion of cretaceous calcareous mudstones a change in the regularity and spacing of carbonate e ux peaks at c 4 7 cal ka in jm96 1207 coincides with the onset of neoglacial cooling in the renland ice core d 18 o record we propose that the carbonate e ux peaks between 4 7 and 0 4 cal ka are related to sea surface coolings associated with increased e ux of polar water and sea ice in the east greenland current these peaks are synchronous with sea surface coolings interpreted from north atlantic deep sea cores but additional peaks centred around 2 4 and 3 8 cal ka in jm96 1207 suggest that the shelf site captures higher frequency events the data indicate that severe arctic sea ice events began in the neoglacial interval and that earlier holocene cool events in deep sea records are associated with other processes such as release of meltwater from residual glacier ice and glacial lakes

observations and a model of undertow over the inner continental shelf abstract onshore volume transport stokes drift due to surface gravity waves propagating toward the beach can result in a compensating eulerian offshore flow in the surf zone referred to as undertow observed offshore flows indicate that wave driven undertow extends well offshore of the surf zone over the inner shelves of martha s vineyard massachusetts and north carolina theoretical estimates of the wave driven offshore transport from linear wave theory and observed wave characteristics account for 50 or more of the observed offshore transport variance in water depths between 5 and 12 m and reproduce the observed dependence on wave height and water depth during weak winds wave driven cross shelf velocity profiles over the inner shelf have maximum offshore flow 1 6 cm s 1 and vertical shear near the surface and weak flow and shear in the lower half of the water column the observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the su

deposition and flux of sediment from the po river italy an idealized and wintertime numerical modeling study abstract recent studies of sediment dynamics and clinoform development in the northern adriatic sea focused on winter 2002 2003 and provided the data and motivation for development of a detailed sediment transport model for the area near the po river delta we used both idealized test cases and more realistic simulations to improve our understanding of seasonal sediment dynamics there we also investigated the relationship between physical processes and the observed depositional products e g the accumulation of sediment very near the po river distributary mouths sediment transport near the po river was evaluated using a three dimensional ocean model coupled to sediment transport calculations that included wave and current induced resuspension suspended sediment transport multiple grain classes and fluvial input from the po river high resolution estimates from available meteorological and wave models were used to specify wind wave and meteorological forcing model results indicated that more than half of the discharged sediment remained within 15 km of the po river distributary mouths even after two months of intensive reworking by winter storms during floods of the po river transport in the middle to upper water column dominated sediment fluxes otherwise sediment fluxes from the subaqueous portion of the delta were confined to the bottom few meters of the water column and correlated with increases in current speed and wave energy spatial and temporal variation in wind velocities determined depositional patterns and the directions of sediment transport northeasterly bora winds produced relatively more eastward transport while southwesterly sirocco winds generated fluxes towards both the north and the south eastward transport accounted for the majority of the sediment exported from the subaqueous delta most likely due to the frequent occurrence of bora conditions progradation of the po river delta into the adriatic sea may restrict the formation of the western adriatic coastal current increasing sediment retention at the po delta and reducing the supply of sediment to the apennine margin a positive morphodynamic feedback may therefore be present whereby the extension of the delta into the adriatic increases sediment accumulation at the delta and facilitates further progradation

fast mechanisms for the formation of new plate boundaries abstract we demonstrate the important role played by non linear feedback in promoting the fast breakup of the continental lithosphere and the formation of new plate boundaries we compare the difference in fluid dynamic and elasto visco plastic approaches and emphasize the advection of stresses in finite element models with large strain lagrangian formulation two types of instabilities were found at multiple time length scales ranging from 100 years and km scale to 0 1 myr and 100 km scale one mechanism relies on the thermo mechanical elasto plastic energy conversion and the other stems from the void volatile interaction elasticity takes on a guiding role in the propagation of shear zones closely followed by a thermal wave which is again followed by a wave of volatiles this last mechanism consolidates the fault zones and establishes the plate boundary for a geological time scale using a fully coupled thermal mechanical approach we obtain for the first time a two dimensional solution which shows that the constant velocity boundary conditions can lead to episodic avalanche type tectonic phases within

holocene history of the bering sea bowhead whale balaena mysticetus in its beaufort sea summer grounds off southwestern victoria island western canadian arctic abstract the fossil remains of 43 bowhead whales were mapped on the raised beaches of western wollaston peninsula victoria island canadian arctic near the historic summer range limit of the bering sea stock in the beaufort sea the elevations and radiocarbon ages of the remains demonstrate that the bowhead ranged commonly into the region following the submergence of bering strait at ca 10 000 14c yr b p until ca 8500 14c yr b p during the same interval bowheads ranged widely from the beaufort sea to baffin bay subsequently no whales reached wollaston peninsula until ca 1500 14c yr b p late holocene populations evidently were small or occupations were brief in comparison to those of the early holocene although the late holocene recurrence may relate to the expansion of pioneering thule whalers eastward from alaska there are few thule sites and limited evidence of thule whaling in the area surveyed to support this suggestion

water and sediment fluxes on the ebro delta shoreface on the role of low frequency currents abstract field measurements of water and sediment fluxes were acquired on the ebro delta shoreface at depths of 8 5 and 12 5 m during winter this period was characterised by high river discharges a dominant nw wind and the presence of six wave storms the survey can be considered as being typical of high energy conditions water fluxes on the shoreface were jointly dominated by mesoscale shelf processes anticyclonic gyre on the ebro shelf inducing a dominant northward flow and by local meteorological forcing n ne winds inducing southward current reversals which were coupled with the presence of e wave storms the concentration of suspended sediment in the water column was associated with wave activity i e wave induced near bottom velocity moreover a lag of 6 h was found between the concentration time series at both locations which was associated with a slow seaward advection of fine sediment as a result of this advection an increase of 30 in the content of fines of the bottom sediment at the deepest location was detected during the survey period measured sediment fluxes presented a pulsating structure related to mean current fluctuations and fluctuations in sediment concentration induced by waves longshore transport rates were dominant over cross shore rates when time integrated the net cross shore fluxes were offshore at the outer site and onshore at the inner site due to differences in current direction since it shifted towards the coast at the shallower location net longshore transport was almost nil when current reversals were present and when disappeared transport at the inner shelf was northward

thermal mechanical effects of low temperature plasticity the peierls mechanism on the deformation of a viscoelastic shear zone we studied for the first time the effects of low temperature plasticity on the formation of shear zones a thermal mechanical model has been developed for describing the shear deformation of maxwell viscoelastic material with a rheology close to dry olivine we employed a one dimensional model with a half width of l deforming under a constant velocity u at the boundary and the spatially averaged strain rate u l was set to o 10 14 s 1 in addition to diffusion and power law creep we included deformation by low temperature plasticity called the peierls mechanism which is significant at low temperatures and has a strong exponential dependence on the stress when a sufficient magnitude of heat is generated by the rapid conversion from elastically stored energy into viscous dissipation thermal instability takes place and the deformation localizes in a narrow region by comparing the condition for thermal instability we found that the low temperature plasticity inhibits the development of thermal instability in shear zones in case of constant strain rate the peierls mechanism enhances deformation at a significantly lower stress compared to the rheology with solely diffusion creep and power law creep the enhanced deformation by low temperature plasticity produces lower amount of dissipative heating and thus stabilizes the shear zone comparing the stability between constant strain rate and constant stress boundary conditions we found that the peierls mechanism exerts an opposite destabilizing effect in the case of constant stress for dry olivine rheology and realistic magnitude of the strain rate the effect of low temperature plasticity is significant for temperatures between around 800 k and 1000 k this finding suggests that the low temperature plasticity may be crucial in determining the thermal mechanical stability in the shallow portion of slabs

temperature and precipitation history of the arctic as the planet cooled from peak warmth in the early cenozoic extensive northern hemisphere ice sheets developed by 2 6 ma ago leading to changes in the circulation of both the atmosphere and oceans from not vert similar2 6 to not vert similar1 0 ma ago ice sheets came and went about every 41 ka in pace with cycles in the tilt of earth s axis but for the past 700 ka glacial cycles have been longer lasting not vert similar100 ka separated by brief warm interglaciations when sea level and ice volumes were close to present the cause of the shift from 41 ka to 100 ka glacial cycles is still debated during the penultimate interglaciation not vert similar130 to not vert similar120 ka ago solar energy in summer in the arctic was greater than at any time subsequently as a consequence arctic summers were not vert similar5 c warmer than at present and almost all glaciers melted completely except for the greenland ice sheet and even it was reduced in size substantially from its present extent with the loss of land ice sea level was about 5 m higher than present with the extra melt coming from both greenland and antarctica as well as small glaciers the last glacial maximum lgm peaked not vert similar21 ka ago when mean annual temperatures over parts of the arctic were as much as 20 c lower than at present ice recession was well underway 16 ka ago and most of the northern hemisphere ice sheets had melted by 6 ka ago solar energy reached a summer maximum 9 higher than at present not vert similar11 ka ago and has been decreasing since then primarily in response to the precession of the equinoxes the extra energy elevated early holocene summer temperatures throughout the arctic 1 3 c above 20th century averages enough to completely melt many small glaciers throughout the arctic although the greenland ice sheet was only slightly smaller than at present early holocene summer sea ice limits were substantially smaller than their 20th century average and the flow of atlantic water into the arctic ocean was substantially greater as summer solar energy decreased in the second half of the holocene glaciers re established or advanced sea ice expanded and the flow of warm atlantic water into the arctic ocean diminished late holocene cooling reached its nadir during the little ice age about 1250 1850 ad when sun blocking volcanic eruptions and perhaps other causes added to the orbital cooling allowing most arctic glaciers to reach their maximum holocene extent during the warming of the past century glaciers have receded throughout the arctic terrestrial ecosystems have advanced northward and perennial arctic ocean sea ice has diminished here we review the proxies that allow reconstruction of quaternary climates and the feedbacks that amplify climate change across the arctic we provide an overview of the evolution of climate from the hot house of the early cenozoic through its transition to the ice house of the quaternary with special emphasis on the anomalous warmth of the middle pliocene early quaternary warm times the mid pleistocene transition warm interglaciations of marine isotope stages 11 5e and 1 the stage 3 interstadial and the peak cold of the last glacial maximum

near bottom suspended sediment variability caused by storms and near inertial internal waves on the ebro mid continental shelf nw mediterranean abstract near bottom currents and suspended sediment concentrations ssc recorded on the ebro continental shelf at 60 m depth during the transition between fair and stormy weather have revealed some of the major processes controlling the sediment re suspension and transport at mid shelf depths in this nw mediterranean area storm waves were the main contributor to the transport of sediment although they only resuspended surface sediments during extreme wave conditions h s 4 5 m and t s 11 s during the recording period the net suspended sediment flux along the shelf was one order of magnitude higher than the net suspended sediment flux across the shelf and the resultant transport was towards the sw and seaward fluctuations of the near bottom ssc during fair weather showed a periodicity around 17 h and were related to the occurrence of near inertial internal waves caused by wind pulses during storm events the energy propagation of these internal waves reached critical angles at the mid and outer shelf which could favor the development and maintenance of the bottom nepheloid layer on the ebro continental shelf as well as on other mediterranean continental shelves

sea ice expansion in the bering sea during the neoglacial evidence from archaeozoology the neoglacial was a period of cold that lasted more than 2000 years during the mid holocene from approximately 4700 to 2500 years ago although proxy data from a number of sources document the re

wave climate sediment supply and the depth of the sand mud transition a global survey abstract the influences of wave climate and sediment supply on the depths of sand mud transitions hsmt are investigated depths of sand mud transitions smt are based on published granulometric data from surface samples gathered from 14 sites in different wave dominated coastal environments with fluvial input including high energy columbia eel russian san lorenzo copper and nepean rivers moderate energy ebro nile santa clara tseng wen and kao ping rivers and low energy po pescara and tronto rivers regimes geometric mean diameter gmd and mud percent are compiled from samples along shore normal transects and significant correlation is found between these two textural descriptors nominally the smt is defined as the transition from gmd 63 m to 25 mud this dual definition is applied to the 14 systems and hsmt is tabulated for each system correlation is found between hsmt and the depth at which wave induced bottom shear stress equals the critical erosion shear stress of the largest mud particles and also between hsmt and significant wave height lack of correlation between hsmt and sediment load of nearby rivers indicates either that the influence of sediment supply on depth of the sand mud transition is small or is not adequately represented in this study shelf width and slope do not correlate with residuals from a formalized linear relationship between hsmt and significant wave height the relationship between hsmt and wave climate is useful for calibration of numerical models of erosion and deposition in wave dominated coastal environments for prediction of seabed properties in remote or inaccessible areas and for reconstruction of paleodepth based on facies changes from sand to mud in ancient rocks

dynamic recrystallization near the brittle plastic transition in naturally and experimentally deformed quartz aggregates the electron backscattering diffraction technique ebsd was used to analyze bulging recrystallization microstructures from naturally and experimentally deformed quartz aggregates both of which are characterized by porphyroclasts with finely serrated grain boundaries and grain boundary bulges set in a matrix of very fine recrystallized grains for the tonale mylonites we investigated a temperature range of 300 380 c 0 25 gpa confining pressure a flow stress range of 0 1 0 2 gpa and a strain rate of 10 13 s 1 were estimated experimental samples of black hills quartzite were analyzed which had been deformed in axial compression at 700 c 1 2 1 5 gpa confining pressure a flow stress of 0 3 0 4 gpa a strain rate of 10 6 s 1 and to 44 to 73 axial shortening using orientation imaging we investigated the dynamic recrystallization microstructures and discuss which processes may contribute to their development our results suggest that several deformation processes are important for the dismantling of the porphyroclasts and the formation of recrystallized grains grain boundary bulges are not only formed by local grain boundary migration but they also display a lattice misorientation indicative of subgrain rotation dynamic recrystallization affects especially the rims of host porphyroclasts with a hard orientation i e with an orientation unsuitable for easy basal slip in addition dauphine twins within porphyroclasts are preferred sites for recrystallization we interpret large misorientation angles in the experimental samples which increase with increasing strain as formed by the activity of fluid assisted grain boundary sliding

sediment dispersal in the northwestern adriatic sea 1 sediment dispersal in the adriatic sea was evaluated using coupled three dimensional circulation and sediment transport models representing conditions from autumn 2002 through spring 2003 the calculations accounted for fluvial sources resuspension by waves and currents and suspended transport sediment fluxes peaked during southwestward bora wind conditions that produced energetic waves and strengthened the western adriatic coastal current transport along the western adriatic continental shelf was nearly always to the south except during brief periods when northward sirocco winds reduced the coastal current much of the modeled fluvial sediment deposition was near river mouths such as the po subaqueous delta nearly all po sediment remained in the northern adriatic material from rivers that drain the apennine mountains traveled farther before deposition than po sediment because it was modeled with a lower settling velocity fluvial sediment delivered to areas with high average bed shear stress was more highly dispersed than material delivered to more quiescent areas modeled depositional patterns were similar to observed patterns that have developed over longer timescales specifically modeled po sediment accumulation was thickest near the river mouth with a very thin deposit extending to the northeast consistent with patterns of modern sediment texture in the northern adriatic sediment resuspended from the bed and delivered by apennine rivers was preferentially deposited on the northern side of the gargano peninsula in the location of thick holocene accumulation deposition here was highest during bora winds when convergences in current velocities and off shelf flux enhanced delivery of material to the midshelf

modeling shear zones in geological and planetary sciences solid and fluid thermal mechanical approaches abstract shear zones are the most ubiquitous features observed in planetary surfaces they appear as a jagged network of faults at the observable brittle surface of planets and in geological exposures of deeper rocks they turn into smoothly braided networks of localized shear displacement leaving centimeter wide bands of mylonitized reduced grain sizes behind the overall size of the entire shear network rarely exceeds kilometer scale at depth although mylonitic shear zones are only visible to the observer when uplifted and exposed at the surface they govern the mechanical behavior of the strongest part of the lithosphere below 10 15 km depth mylonitic shear zones dissect plates thus allowing plate tectonics to develop on the earth we review the basic multiscale physics underlying mylonitic ductile shear zone nucleation growth and longevity and show that grain size reduction is a symptomatic cause but not necessarily the main reason for localization we also discuss a framework for analytic and numerical modeling including the effects of thermal mechanical couplings thermal elasticity the influence of water and void volatile feedback the physics of ductile shear zones relies on feedback processes that turn a macroscopically homogenously deforming body into a heterogeneously slipping solid medium positive feedback can amplify strength heterogeneities by cascading through different scales we define basic intrinsic length scales of strength heterogeneity such as those associated with plasticity grain size fluid inclusion and thermal diffusion length scale for an understanding ductile shear zones we need to consider the energetics of deformation shear heating introduces a jerky flow phenomenon potentially accompanied by ductile earthquakes additional focusing due to grain size reduction only operates for a narrow parameter range of cooling rates for the long time scale deformational energy stored inside the shear zone through plastic dilation or crystallographic and shape preferred orientation consumes only a maximum of 10 of energy dissipated in the shear zones but creates structural anisotropy shear zones become long living features with a long term memory a special role is attributed to the presence of water in nominally anhydrous minerals we show that water directly affects the mechanical equation of state and has the potential to synchronize viscous and plastic flow processes at geological time scale we have shown that fully coupled finite element calculations using mechanical data from the laboratory can reproduce the basic mode of deformation of an entire mylonitic shear zone the next step of modeling lies in benchmarking basic feedback mechanism in field studies and zooming into the braided network of shear zone structure without losing the large scale constraint numerical methods capable of fulfilling the goal are emerging these are adaptive wavelet techniques and hybrid particle finite element codes which can be run over a computational grid across the net

tracking the rupture of the mw 9 3 sumatra earthquake over 1 150 km at teleseismic distance on 26 december 2004 a moment magnitude mw 9 3 earthquake occurred along northern sumatra the nicobar and andaman islands resulting in a devastating tsunami in the indian ocean region the rapid and accurate estimation of the rupture length and direction of such tsunami generating earthquakes is crucial for constraining both tsunami wave height models as well as the seismic moment of the events compressional seismic waves generated at the hypocentre of the sumatra earthquake arrived after about 12 min at the broadband seismic stations of the german regional seismic network grsn located approximately 9 000 km from the event here we present a modification of a standard array seismological approach and show that it is possible to track the propagating rupture front of the sumatra earthquake over a total rupture length of 1 150 km we estimate the average rupture speed to be 2 3 2 7 km s 1 and the total duration of rupture to be at least 430 s and probably between 480 and 500 s

sediment transport events on the northern california continental shelf abstract a long term monitoring tripod has been maintained in 60 m water depth at the northern end of the strataform study site on the northern california continental shelf as part of this ongoing study tripod data for 1 year beginning 24 september 1995 are used to provide a sediment transport analysis on an event by event basis the objective of this paper is to highlight the energetic nature of this shelf region in terms of the frequency duration and magnitude of sediment suspension events and the associated particle flux analyses are based on measurements from two current meters and two optical backscatterance sensors located at 30 and 100 cm above the bed data from these instruments and a pressure sensor were averaged over 7 5 min every hour during the year of record 41 distinct sediment suspension events occurred i e sustained suspended sediment concentrations greater than 20 mg l above background level at 100 cm above bed suspended sediment events were associated with significant wave activity tidal currents and river discharge the average duration of a sediment suspension event was 3 1 days and varied from 0 7 to 8 days during events mean suspended sediment concentrations of 110 mg l were observed with peak hourly observations exceeding 1000 mg l concentrations between events averaged 35 mg l the overall sediment flux for the period of record was directed seaward and southward the distribution and magnitude of sediment suspension events and particle flux showed a strong seasonality for example of the sediment transport during events 98 of the net along shelf and 73 of the net across shelf sediment transport occurred in the winter three major winter storms could account for 72 of the total along shelf transport but only 10 of the across shelf transport the across shelf flux was more evenly distributed over the year and occurred as a result of mean currents and very low frequency seaward flows associated with mesoscale circulation patterns

deterministic coastal morphological and sediment transport modeling a review and discussion 1 modern coastal ocean modeling systems are now capable of numerically simulating a variety of coastal and estuarine problems and can thus provide useful information for managing coastal zones here we review state of the art eulerian implementations of bottom up sediment transport and morphological change in coastal ocean hydrodynamic models in order to investigate the fate of suspended sediment in coastal and estuarine waters as well as the evolution of sea or river beds sediment dynamics need to be represented at a scale relevant to the numerical discretized solution and significant effort is devoted to parameterize sediment processes we discuss boundary layer hydrodynamics and the computation of the bed shear stress we also focus on approaches used to represent near bed processes such as bed load transport and sediment erosion and deposition sediment diffusivities settling velocities and cohesive processes such as flocculation all have an impact on suspended sediment throughout the water column we then describe the implementation of process parameterizations in coastal hydrodynamic models explicitly reviewing five widely used systems the approaches implemented in these coastal models may present distinct strengths and shortcomings with regard to some important issues for coastal zones both numerical and physical while these detailed limitations need to be considered as part of model assessment more general issues also hinder present state of the art models in particular sediment transport is inherently highly empirical which is further compounded by issues arising from turbulence closure schemes we conclude by suggesting some possible directions toward improving sediment dynamics understanding and coastal scale predictive ability

fabric controls on strain accommodation in naturally deformed mylonites the influence of interconnected micaceous layers abstract we present microstructural analyses demonstrating how the geometrical distribution and interconnectivity of mica influences quartz crystallographic preferred orientation cpo development in naturally deformed rocks we use a polymineralic qtz pl kfs bt ms grt tur mylonite from the zanskar shear zone a section of the south tibetan detachment nw himalaya to demonstrate how quartz cpo intensity decreases from quartz dominated domains to micaceous domains independently of whether or not quartz grains are pinned by mica grains we then use a bimineralic qtz ms mylonite from the main central thrust nw himalaya to show how increasing mica grain connectivity is concomitant with a systematic weakening of quartz cpo our results draw distinctions between cpo weakening due to i second phase drag leading to ineffective recovery in quartz and ii increased transmission and localisation of strain between interconnected mica grains in the latter case well connected micaceous layers take up most of the strain weakening the rock and preventing straining of the stronger quartz matrix our findings suggest that rock weakening in quartz rich crustal rocks is influenced not only by the presence of mica rich layers but also the degree of mica grain connectivity which allows for more effective strain localization through the entire rock mass

distribution and sources of organic matter in size fractionated nearshore sediments off the barcelona city nw mediterranean abstract continental shelves are recognized to play a key role in the biogeochemical cycle of carbon linking terrestrial and marine carbon reservoirs in this study we investigate the physical and biogeochemical processes that control the source transport and fate of organic carbon oc in the continental shelf off barcelona city in the nw mediterranean sea surface sediment samples were collected from depths of 10 40 m during late summer and autumn 2012 grain size and biogeochemical parameters such as oc its stable isotope 13 c total nitrogen tn and oc tn ratios were analysed in size fractionated sediments the influence of environmental factors over the study area was determined using hydrological and oceanographic time series together with video images of the barcelona coast line and nearshore region we have found a wide range of oc contents from 0 13 to 8 68 depending on water depth and sediment particle size the highest oc concentration was always found in the clay fraction 63 m that contained terrestrial plant debris wave activity discharge of the besos river and the espigo de ginebra outfall were the main mechanisms controlling the sorting of sediments by their grain size and thus the distribution of oc in the inner shelf off barcelona in addition we observed that the organic matter in clay particles was progressively degraded seawards probably because these particles remain suspended in the water column much more time compared to those that are heavier and therefore they are exposed for longer time periods to oxygenated conditions both oc tn ratios and 13 c values found suggest that the organic matter preserved was predominantly land supplied

lateglacial and holocene climate disturbance and permafrost peatland dynamics on the seward peninsula western alaska abstract northern peatlands have accumulated large carbon c stocks acting as a long term atmospheric c sink since the last deglaciation how these c rich ecosystems will respond to future climate change however is still poorly understood furthermore many northern peatlands exist in regions underlain by permafrost adding to the challenge of projecting c balance under changing climate and permafrost dynamics in this study we used a paleoecological approach to examine the effect of past climates and local disturbances on vegetation and c accumulation at a peatland complex on the southern seward peninsula alaska over the past 15 ka 1 ka 1000 cal yr bp we analyzed two cores about 30 m apart nl10 1 from a permafrost peat plateau and nl10 2 from an adjacent thermokarst collapse scar bog for peat organic matter om c accumulation rates macrofossil pollen and grain size analysis a wet rich fen occurred during the initial stages of peatland development at the thermokarst site nl10 2 the presence of tree pollen from picea spp and larix laricinia at 13 5 12 1 ka indicates a warm regional climate corresponding with the well documented bolling allerod warm period a cold and dry climate interval at 12 1 11 1 ka is indicated by the disappearance of tree pollen and increase in poaceae pollen and an increase in woody material likely representing a local expression of the younger dryas yd event following the yd the warm holocene thermal maximum htm is characterized by the presence of populus pollen while the presence of sphagnum spp and increased c accumulation rates suggest high peatland productivity under a warm climate toward the end of the htm and throughout the mid holocene a wet climate induced several major flooding disturbance events at 10 ka 8 1 ka 6 ka 5 4 ka and 4 7 ka as evidenced by decreases in om and increases in coarse sand abundance and aquatic fossils algae chara and water fleas daphnia the initial peatland at permafrost site nl10 1 is characterized by rapid c accumulation 66 g c m 2 yr 1 high om content and a peak in sphagnum spp at 5 8 4 6 ka suggesting the lack of permafrost a transition to extremely low c accumulation rates of 6 3 g c m 2 yr 1 after 4 5 ka at this site suggests the onset of permafrost aggradation likely in response to neoglacial climate cooling as documented across the circum arctic region a similar decrease in c accumulation rates also occurred at non permafrost site nl10 2 time weighted c accumulation rates are 21 8 g c m 2 yr 1 for core nl10 1 during the last 6 5 ka and 14 8 g c m 2 yr 1 for core nl10 2 during the last 15 ka evidence from peat core analysis and historical aerial photographs shows an abrupt increase in sphagnum spp and decrease in area of thermokarst lakes over the last century suggesting major changes in hydrology and ecosystem structure likely due to recent climate warming our results show that the thermokarst permafrost complex was much more dynamic with high c accumulation rates under warmer climates in the past while permafrost was stabilized and c accumulation slowed down following the neoglacial cooling in the late holocene furthermore permafrost presence at local scales is controlled by both regional climate and site specific factors highlighting the challenge in projecting responses of permafrost peatlands and their c dynamics to future climate change

quartz deformation across interlayered monomineralic and polymineralic rocks a comparative analysis abstract given the increased availability of ebsd and fabric analyzer facilities quartz microstructural and cpo analysis have become tools of the trade for studies investigating crustal tectonics therefore improved understanding of the complexities of quartz deformation is needed to ensure that such analyses distinguish primarily between tectonic outcomes and artefacts of the quartz deformation behaviours in different deformed rock volumes we contribute to this understanding by comparing quartz deformation between monomineralic rocks which have simple compositions and polymineralic rocks which are more complex and representative of the crust mylonite quartzites and gneisses of the main central thrust nw himalaya are used for comparison under similar deformation conditions quartz inside monomineralic rocks forms well developed cpos and dynamically recrystallized microstructures typical of grain size insensitive gsi creep mechanisms quartz inside polymineralic rocks by contrast exhibits weak cpos and fine grained microstructures commonly interpreted as grain size sensitive creep but also exhibits lattice distortions e g undulose extinction sub grain boundaries associated with gsi creep we postulate that intrinsic factors such as interphase boundaries cause these ambiguous results the lack of clear evidence for deformation mechanisms in polymineralic rocks casts doubt on the reliability of quartz microstructures and cpos for rapid diagnoses of their rheology and broader tectonic significance

rapid conversion of elastic energy into plastic shear heating during incipient necking of the lithosphere an important and novel mechanism for ductile failure of the lithosphere is identified here which is intrinsic to the thermal mechanical feedback in a temperature dependent plastic body with coupled elastic fields both a temperature dependent power law visco elasto plastic rheology and a temperature dependent elasto plastic rheology are employed to study in a self consistent fashion the deformation of the lithosphere subject to extension by means of a two dimensional finite element code a structural perturbation initially localizes elasto plastic deformation only in its immediate vicinity however after 800 000 years have elapsed the localized zone of deformation takes off in a crack like fashion and travels to the bottom of the lithosphere in about 50 000 years time when the plate is severed thermal runaway is caused by mechanical heating triggered by the rapid energy transfer of the globally stored elastic energy into localized plastic dissipation in the ductile fault

subtidal inner shelf circulation near point conception california 1 we discuss connections between inner shelf and mid shelf circulation near point conception california as well as the wind forcing of inner shelf circulation point conception marks the southern edge of a major upwelling zone that extends from oregon to central california the coastline makes a sharp eastward turn at point conception and the santa barbara channel to the east is generally assumed to be an upwelling shadow consistent with this regional division inner shelf currents are strongly correlated with wind north of point conception but not in the santa barbara channel one exception to this generalization is a location in the santa barbara channel near a pass that cuts through the coastal mountains where local winds have a dominant cross shore component and directly drive cross shore currents over the inner shelf inner shelf currents in the santa barbara channel when compared with mid shelf currents in that area are weaker but strongly correlated by contrast inner shelf currents north of point conception show a far greater incidence of poleward flow than is seen over the mid shelf in that area poleward flow events lasting 1 5 days transport warm water from the santa barbara channel around point conception to the central california coast these events are associated with relaxation of the generally equatorward wind but not always with mid shelf flow reversals