permafrost and climate in europe monitoring and modelling thermal geomorphological and geotechnical responses we present a review of the changing state of european permafrost within a spatial zone that includes the continuous high latitude arctic permafrost of svalbard and the discontinuous high altitude mountain permafrost of iceland fennoscandia and the alps the paper focuses on methodological developments and data collection over the last decade or so including research associated with the continent scale network of instrumented permafrost boreholes established between 1998 and 2001 under the european union pace project data indicate recent warming trends with greatest warming at higher latitudes equally important are the impacts of shorter term extreme climatic events most immediately reflected in changes in active layer thickness a large number of complex variables including altitude topography insolation and snow distribution determine permafrost temperatures the development of regionally calibrated empirical statistical models and physically based process oriented models is described and it is shown that though more complex and data dependent process oriented approaches are better suited to estimating transient effects of climate change in complex mountain topography mapping and characterisation of permafrost depth and distribution requires integrated multiple geophysical approaches and recent advances are discussed we report on recent research into ground ice formation including ice segregation within bedrock and vein ice formation within ice wedge systems the potential impacts of climate change on rock weathering permafrost creep landslides rock falls debris flows and slow mass movements are also discussed recent engineering responses to the potentially damaging effects of climate warming are outlined and risk assessment strategies to minimise geological hazards are described we conclude that forecasting changes in hazard occurrence magnitude and frequency is likely to depend on process based modelling demanding improved understanding of geomorphological process response systems and their impacts on human activity

morphology and geology of the continental shelf and upper slope of southern central chile 33 s 43 s the continental shelf and slope of southern central chile have been subject to a number of international as well as chilean research campaigns over the last 30 years this work summarizes the geologic setting of the southern central chilean continental shelf 33 s 43 s using recently published geophysical seismological sedimentological and bio geochemical data additionally unpublished data such as reflection seismic profiles swath bathymetry and observations on biota that allow further insights into the evolution of this continental platform are integrated the outcome is an overview of the current knowledge about the geology of the southern central chilean shelf and upper slope we observe both patches of reduced as well as high recent sedimentation on the shelf and upper slope due to local redistribution of fluvial input mainly governed by bottom currents and submarine canyons and highly productive upwelling zones shelf basins show highly variable thickness of oligocene quaternary sedimentary units that are dissected by the marine continuations of upper plate faults known from land seismic velocity studies indicate that a paleo accretionary complex that is sandwiched between the present relatively small active accretionary prism and the continental crust forms the bulk of the continental margin of southern central chile

redox chemistry of west antarctic peninsula margin surface sediments abstract continental margin sediments are commonly studied using trace metal enrichments as proxies for characterizing their modern redox conditions and tracking past changes in bottom water ventilation and marine primary productivity currently little is known about the sedimentary redox history of the continental shelf west of the antarctic peninsula yet environmental conditions in the antarctic peninsula region have changed rapidly in recent decades in response to global warming paleoclimate archives including bulk sediment trace metal enrichments can provide insight into both past and future environmental changes in this climatically sensitive region and characterization of redox conditions in surface modern sediments is essential for establishing a framework for paleoredox interpretations in this study we measured concentrations of trace metals ag cd re and mo and productivity proxies total ba organic carbon and biogenic silica in surface sediments from the marguerite bay gerlache strait and bransfield strait areas proxy concentrations suggest that sediments are generally suboxic due to seasonally high export of organic carbon from surface waters comparison of west antarctic peninsula trace metal al ratios to trace metal data from continental margins outside the antarctic region demonstrates that although the west antarctic peninsula water column differs from other locations e g it lacks a strong oxygen minimum zone sedimentary redox chemistry is similarly controlled by organic matter decomposition through slow recycling of highly seasonal export production falling through a cold water column

review of erosion dynamics along the major n s climatic gradient in chile and perspectives abstract chile is an elongated country running in a north south direction for more than 30 along a subduction zone its climate is progressively wetter and colder from north to south this particular geography has been used positively by a growing number of studies to better understand the relationships between erosion processes and climate land use slope tectonics volcanism etc here we review the erosion rates factors and dynamics over millennial to daily periods reported in the literature in addition 21 new catchment mean erosion rates suspended sediment and 10be are provided and previous suspended sediment derived erosion rates are updated a total of 485 local and catchment mean erosion rates are reported erosion rates vary between some of the smallest values on earth 10 5 mm a to moderate values 0 5 mm a compared to other active ranges this review highlights strong limitations concerning the quantification of local erosion factors because of uncertainties in sampling point location slope and rainfall data for the mean erosion rates e for the millennial and decennial catchments a model of the form e s 1 s 0 6 2 r with 0 3 0 8 accounts for 40 to 70 of the erosion variance confirming a primary role of slope s compared to precipitation rate r over this time scale over the long term this review points to the long 5 to 10 ma response time of rivers to surface uplift in north central arid chile over millennia data provide evidence for the progressive contribution of extreme erosion events to millennial averages for drier climates as well as the link between glacier erosion and glacier sliding velocity in this period of time a discrepancy exists between the long term offshore sedimentological record and continental decennial or millennial erosion data for which no single explanation appears still little information is available concerning the magnitude of variation of millennial erosion rates over centuries data show the variable role of groundwater in the dynamics of suspended load and document a decrease in erosion over hundreds of years probably associated with historical harvesting

recent sedimentation and mass accumulation rates based on 210pb along the peru chile continental margin abstract the concentrations of the natural radionuclide 210 pb were measured in sediment samples collected with a multicorer boxcorer and gravity corers along the chilean continental margin 20 45 s in order to estimate sedimentation rate sr and mass accumulation rate this database was compared with previously obtained results from central peru callao 210 pb activities decreased exponentially with core depth and profiles showed a deepening of the 210 pb in excess unsupported in the sediments from north to south 6 18 cm sediment depth off peru and northern chile vs 8 35 cm off central and southern chile an onshore offshore decrease of surface activities was observed off central peru whereas the reverse was true for surface activities along the chilean margin srs increased from north 0 04 0 17 cm yr 1 to south 0 09 0 29 cm yr 1 across the shelf higher rates were observed at deeper sites especially at those close to submarine canyons except off central peru where srs showed similar values through the slope area off northern chile and central peru srs seem to reflect the export of particles over the shelf and redistribution processes such as slumps and lateral transport in contrast srs in central and southern chile seem to be controlled by several additional factors that modulate the settling particles such as onshore precipitation and river runoff in addition the more complex topography of the southern chile margin allows for settling or winnowing areas

how depositional conditions control input composition and degradation of organic matter in sediments from the chilean coastal upwelling region abstract in a comprehensive study we compared depositional conditions organic matter om composition and organic carbon turnover in sediments from two different depositional systems along the chilean continental margin at 23 s off antofagasta and at 36 s off concepcion both sites lie within the chilean coastal upwelling system and have an extended oxygen minimum zone in the water column however the northern site 23 s borders the atacama desert while the southern site 36 s has a humid hinterland eight surface sediment cores up to 30 cm long from water depths of 126 1350 m were investigated for excess 210pb 210pbxs activity total organic and total inorganic carbon concentrations toc and tic respectively c n ratios organic carbon isotopic compositions 13c chlorin concentrations chlorin indices ci and sulfate reduction rates srr sediment accumulation rates obtained from 210pb analysis were similar in both regions 0 04 0 15 cm yr 1 at 23 s 0 10 0 19 cm yr 1 at 36 s although total 210pbxs fluxes indicated that the vertical particle flux was higher at 36 s than at 23 s we propose that sediment focusing in isolated deposition centers led to high sediment accumulation rates at 23 s furthermore there were no indications for sediment mixing at 23 s while bioturbation was intense at 36 s 13c values 24 5 to 20 1 vs vpdb and c n ratios molar 8 6 12 8 were characteristic of a predominantly marine origin of the sedimentary om in both investigated areas the extent of om alteration in the water column was partly reflected in the surface sediments as chlorin concentrations decreased and c n ratios and ci increased with increasing water depth of the sampling site srr were lower at 23 s areal srr 0 12 0 60 mmol m 2 d 1 than at 36 s areal srr 0 82 1 18 mmol m 2 d 1 which was partly due to the greater water depth of most of the sediments investigated in the northern region and consistent with a lower quality of the sedimentary om at 23 s reaction rate constants for toc degradation that were obtained from measured srr ksrr 0 0004 0 0022 yr 1 showed a good correspondence to ktoc that were derived from the depth profiles of toc 0 0003 0 0014 yr 1 both ksrr and ktoc reflect differences in om composition at 36 s they were related to the degradation state of bulk om represented by c n ratios whereas near 23 s they were related to the freshness of a small fraction of labile om represented by ci our study shows that although rates of organic carbon accumulation were similar in both investigated sites the extent and kinetics of organic carbon degradation were closely linked to differing depositional conditions

advection and removal of 210pb and stable pb isotopes in the oceans a general circulation model study abstract natural pb isotope variability in the oceans encodes information about the sources of continental material to the oceans about ocean circulation and about pb removal in order to use this information we must understand the natural cycle of pb in the oceans which is overprinted by large anthropogenic input in this study we use 210 pb which has not been significantly anthropogenically perturbed to investigate oceanic pb geosecs 226 ra and model derived atmospheric fluxes of 210 pb are used to input 210 pb into an ocean general circulation model irreversible scavenging of this 210 pb onto settling biogenic particles and at the seafloor are tuned so that the model replicates the observed pattern of 210 pb in the oceans the best fit model run provides a map of the variability of residence time for pb the global average residence time of pb in this model is 48 yr but there is over an order of magnitude variation between areas of high and low productivity this is expected to enhance provinciality of pb isotope ratios in the oceans because stable pb isotopes are expected to behave in seawater in a similar fashion to 210 pb the pattern of removal of 210 pb derived by the model can be used to investigate the behavior of stable pb isotopes we use a simplified input of pb consisting of five point sources representing major rivers and a disseminated dust input although this simplified input scheme does not allow precise reconstruction of pb concentration and isotopes in the oceans it allows us to answer some first order questions about the behavior of pb as an ocean tracer with a total pb input of 6 3 10 7 mol yr chow t j and patterson c c the occurrence and significance of pb isotopes in pelagic sediments geochim cosmochim acta 26 263 308 1962 the model predicts natural seawater pb concentrations averaging 2 2 pmol kg even in the absence of anthropogenic input the model ocean exhibits a near surface maximum in pb concentration and the model suggests natural pb concentrations in the northern hemisphere an order of magnitude higher than in the southern hemisphere a point source of pb is suggested to dominate the seawater pb inventory close to the source but is reduced to typically less than 10 of the inventory by the time that pb is advected out of the originating ocean this length scale of advection for pb isotope signals confirms their potential as tracers of ocean circulation assuming an 8 dissolution of dust their input to the open ocean are seen to be a significant portion of pb inventory throughout the oceans and make up 50 of the pb inventory in the model s southern ocean finally a preliminary investigation of the response of pb isotope distributions to changes in boundary conditions between glacial and interglacial times illustrates that significant variation in the pb isotopes are expected in some regions even for reasonably small changes in climate conditions

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

fore arc seafloor unconformities and geology insight from 3 d seismic geomorphology analysis peru new 3d seismic data collected over 4870 km2 in the 3 45 12 30 s peruvian segment of the east pacific subduction system image seafloor erosional surfaces that can be mapped across the forearc basins forearc basins experience various stresses from their base where basal tectonic erosion acts to the seafloor which is influenced by aerial shallow and deep water currents driven by waves or thermohaline oceanic currents previously there has been little interest in stresses on the upper layer and there is a lack of documentation of unconformities and the erosive processes in certain bathymetric domains in forearc basins we address this with the study of examples sourced from 3d seismic reflection surveys of the seafloor offshore peru unconformities occur in two distinctive bathymetric domains associated with the continental shelf and the upper slope of the margin identification and characterization of unconformity surfaces yield estimates of the amount of erosion at the modern seafloor that range from 18 to 100 regional physical oceanography allows us to calibrate potential candidates for these two distinctive domains the first control on erosion is the dynamics of deep to intermediate oceanic currents related to the humboldt peru chile water masses while the second is wave action in the shallower erosional surfaces this study illustrates the unseen landscape of the forearc basins of south america and helps to highlight the importance of erosive surficial processes in subduction landscapes

accumulation and biological mixing of peru margin sediments abstract rates of sediment accumulation and biological particle mixing in eight cores from the peru shelf have been estimated by application of uranium series disequilibrium techniques and radiocarbon dating activities of 210pb 226ra 234th and 238u have been determined in closely spaced intervals in each sediment core biological particle mixing coefficients were determined via a two box advection diffusion steady state mixing model based on the distribution profiles of excess 210pb and in some cases excess 234th activities the sedimentation rates estimated were in the order of a few millimeters yr except for cores enriched in phosphatic components which displayed rates a few orders of magnitude slower bioturbation was significant in most cores studied with the exception of one core collected from within the middle of the oxygen minimum zone estimated biological mixing coefficients were in the order of 100 101 cm2 yr 1 for the surface mixed layer and 10 1 100 cm2 yr 1 for the layer below sediment slumping appears to have affected the 210pb distribution of two or three of our cores

high resolution of glacial ice stratigraphy a ground penetrating radar study of pegasus runway mcmurdo station antarctica ground penetrating radar gpr has been used to detect areas of present or potential structural weakness beneath a 3 2 km snow covered ice runway on the ross ice shelf antarctica the bandwidths of the transmitted wavelets were centred near 500 mhz the data show many horizons up to tens of metres long and occurring to about a 9 m depth below which a brine intrusion limits penetration the horizons are interpreted as discrete scatterers because of their diffraction nature and loss of higher frequencies with depth the presence of porous ice or dispersed water is interpreted from wavelet phase the water may be associated with apparent deepening and fading of the brine horizon if the above interpretation is correct water occurs at depths to 3 5m and extends as much as 40 m horizontally which is greater and deeper than known previously at 3 5 m depth the water may be adsorbed on mineral particles rather than remain free migration of the diffractions with a single layer migration scheme shows all horizons above the brine layer to be small dielectric perturbations within the ice stacking and hilbert transformation of the data reveal slight folding along the length of the runway loss of high frequency amplitude in the wavelets suggests that higher frequency radar might improve resolution only in the top few metres

influence of deposition in dam reservoir on the deep marine hemipelagic environment off niigata central japan it has been well known that dam construction on rivers can cause a decrease in sediment supply and serious coastal erosion while influence of dams on the sedimentary environment beyond the coastal area has not been well known the mass accumulation rate mar in the hemipelagic environment 500 700 m water depth off niigata central japan since the early half of the twentieth century was obtained from core samples based on excess 210pb activity decreases in mar during the mid twentieth century were recognized in several core samples located northern off the agano and shinano river mouths using the cic model combining correction for the influence of surface bioturbation based on the ratio of mars decreases in mar were estimated as occurring during 1959 1964 and 1949 1955 these dates correspond with construction of the okutadami dam 1956 1961 possessing the largest capacity and reservoir sediment volume of 3 9 107 m3 in the agano and shinano river systems the other core located nw off the agano river mouth showed constant mar through the mid twentieth century a synchronicity of huge dam construction and decrease in mar in deep marine environment the similarity between silt clay sized grain size of dam reservoir sediment and that seen in the hemipelagic environment and horizontal distribution of decreasing mar in cores according to north northeastward sediment transport on shelf makes it reasonable to interpret that the decrease in mar in hemipelagic environment was caused by entrapment of silt clay grains in the huge dam reservoir

changes in glacier extent on north novaya zemlya in the twentieth century glacier retreat on north novaya zemlya for the past century was documented by registering glacier terminus positions from expedition and topographic maps and remotely sensed images recession of tidewater calving glaciers on north novaya zemlya in the first half of the twentieth century was relatively rapid 300 m yr 1 consistent with post little ice age warming documented by a 122 year instrumental record from malye karmakuly the glaciers completed 75 to 100 of the net twentieth century retreat by 1952 between 1964 and 1993 half of the studied glaciers were stable the remainder retreated modest distances of 0 75 elevated sst in the barents sea appear to reflect increased advecti

characterization of englacial channels by ground penetrating radar an example from austre broggerbreen svalbard 1 ground penetrating radar profiles at 100 mhz have been collected over an englacial channel system on the cold ice glacier austre broggerbreen svalbard analysis and synthetic modeling of the travel times and waveforms of the reflections from the channel have shown that after a near vertical drop of 45 m in a moulin the watercourse flows 900 m subhorizontally the size of the conduit varies from a large semicircular channel 5 m wide at its base close to the moulin to a vertically elongated 2 5 m high channel close to the outlet variations in the depth of water along the channel have been calculated to be between 14 and 90 of the channel height using detailed analysis of waveforms the low channel gradient 2 and results of dye tracing experiments suggest that there is a significant degree of ponding along the channel length this channel geometry was probably created during a period of increased crevassing from the little ice age a descent into the moulin provided direct observations of the channel dimensions close to the moulin and helped verify the interpretations and conclusions drawn from the study thus radar reflections can be successfully used to determine the depth dimensions and water content of englacial watercourses due to the transparency of ice to radar signals and the strong contrast in velocity between water ice and air this technique offers exciting possibilities for the remote monitoring of englacial channels from the glacier surface

high resolution marine record of climatic change in mid latitude chile during the last 28 000 years based on terrigenous sediment parameters abstract marine sediment cores from the continental slope off mid latitude chile 33 s were studied with regard to grain size distributions and clay mineral composition the data provide a 28 000 yr14c accelerator mass spectrometry dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland these variations can be interpreted in terms of the paleoclimatic evolution of mid latitude chile and are compared to existing terrestrial records glacial climates 28 000 18 000 cal yr b p were generally cold humid with a cold semiarid interval between 26 000 and 22 000 cal yr b p the deglaciation was characterized by a trend toward more arid conditions during the middle holocene 8000 4000 cal yr b p comparatively stable climatic conditions prevailed with increased aridity in the coastal range the late holocene 4000 0 cal yr b p was marked by more variable paleoclimates with generally more humid conditions variations of rainfall in mid latitude chile are most likely controlled by shifts of the latitudinal position of the southern westerlies compared to the holocene the southern westerly wind belt was located significantly farther north during the last glacial maximum less important variations of the latitudinal position of the southern westerlies also occurred on shorter time scales

holocene sediments from the southern chile trench a record of active margin magmatism tectonics and palaeoseismicity abstract sedimentology petrography and the provenance of holocene sediments from the southern chile trench 36 47 s were investigated in an integrated approach combining description of a collection of gravity cores measurements of physical properties quantitative x ray petrography and modal analysis the sediments studied were trench hemipelagic sediments fan deposits and more distal hemipelagic sediments from the nazca plate the trench is mostly fed by multiple point sources via submarine canyons sandy turbidites show a southward increase in sediment maturity whereas volcanic lithic fragments and plagioclase represent the dominant fraction in the north quartz content strongly increases in the southern part of the study area in line with source lithologies further north active volcanoes in the main cordillera represent almost the entire provenance signal as a result of a strong contribution of highly erodible volcanic rocks recurrence rates of sandy and silty turbidites in the trench fan sediments indicate a link to the palaeoseismic record on land our study documents the potential usefulness of proximal turbidites to reconstruct palaeoseismicity even at a scale of single segments of the plate boundary

sedimentation rates off sw africa since the late miocene deciphered from spectral analyses of borehole and gra bulk density profiles odp sites 1081 1084 abstract sedimentation rates srs off sw africa were calculated by performing spectral analyses in the depth domain on borehole and gamma ray attenuation gra bulk density data from odp sites 1081 1084 inversion and integration of srs versus depth from spectral analysis yielded detailed sr profiles in the time domain our technique allowed the detection of excursions in calculated srs that not only often differed from those established through coarse scaled biostratigraphic data but also revealed a greater regional variability in the sediment accumulation over time high resolution bulk density data exhibited distinct periodicity in the waveband of milankovitch cycles precession at 19 23 kyr obliquity at 41 kyr eccentricity at 100 kyr the pronounced milankovitch cyclicity suggests that climate variability and trends in srs along the benguela current system bcs were responding to insolation patterns during the past 6 myr we find relatively low srs when evolutive amplitude spectra are dominated by obliquity and eccentricity periods in contrast significant sr peaks at all sites often occur when strong precessional amplitudes coexist with obliquity and eccentricity cycles episodes of high srs often coincide with peaks in organic carbon mass accumulation rates mar c org and reduced sea surface temperature sst in the southern walvis basin which have been associated with increased regional upwelling this suggests that the high srs reflect high productivity high mar c org attributed to strong wind and upwelling intensity during cool climate periods low ssts in accordance with orbital forcing patterns observed in our spectra

out of the woods driftwood insights into holocene pan arctic sea ice dynamics the collation of 913 driftwood samples from across the western arctic with spatiotemporal distribution and available provenance data enabled the production of a high resolution proxy based reconstruction of holocene arctic ocean surface current and sea ice dynamics regionally bounded driftwood based sea ice reconstructions studies suggest spatiotemporally complex past arctic sea ice extent and movement however a large scale compilation of holocene arctic driftwood has not previously been developed sparse driftwood in the early holocene 8 2 cal ka b p deglacial period was followed by increased driftwood deposition in the warmer mid holocene 8 2 4 2 cal ka b p characterized by an enhanced transpolar drift tpd 7 cal ka b p leading to sea ice loss through the fram strait driftwood incursion peaks show spatial e w progression from the eurasian archipelagos to greenland and the canadian arctic archipelago suggesting a progressive shift in the orientation of the tpd on centennial millennial time scales and intermediate phases in the arctic oscillation late holocene cooling 4 2 cal ka b p is indicated by increased influx of probably north american picea via a strengthened beaufort gyre bg which enhanced sea ice recirculation starting in the western arctic and progressing eastward in recent millennia 2 cal ka b p a more variable driftwood record alternates between bg and tpd dominance on centennial time scales to further constrain a spatiotemporal reconstruction of variations in holocene ocean current and sea ice dynamics a more definitive determination of driftwood provenance is recommended to build upon the current framework such as through radiogenic isotope tracing and adna analysis

estimating winter ebullition bubble volume in lake ice using ground penetrating radar freshwater lakes are an important source of atmospheric methane ch4 however uncertainties associated with quantifying fluxes limit the accuracy of climate warming projections among emission pathways ebullition bubbling is the principal and most challenging to account for given its spatial and temporal patchiness when lakes freeze many methane rich bubbles escaping from lake bottom sediments are temporarily trapped by downward growing lake ice as bubble position is then seasonally fixed we postulate that it should be possible to locate bubbles using a geophysical approach sensitive to perturbations in the ice water interface and ice sheet structure generated by bubbles this study utilizes ground penetrating radar gpr to non invasively quantify the amount of ebullition gas present in lake ice to do this requires an appropriate petrophysical transformation that relates radar wave velocity and volumetric gas content we utilized laboratory experiments to show that electromagnetic models and vo

ground penetrating radar reflection profiling of groundwater and bedrock in an area of discontinuous permafrost we have used ground penetrating radar to profile the depth of permafrost to groundwater beneath permafrost and to bedrock within permafrost in alluvial sediments of interior alaska we used well log data to aid the interpretations and to calculate dielectric permittivities for frozen and unfrozen materials interfaces between unfrozen and frozen sediments above permafrost were best resolved with wavelet bandwidths centered at and above 100 mhz the resolution also required consideration of antenna configuration season and surface conditions depths to subpermafrost groundwater were profiled where it was in continuous contact with the bottom of the permafrost except near transitions to unfrozen zones where the contact appeared to dip steeply the complexity of the responses to intrapermafrost bedrock detected at a maximum depth of 47 m appears to distinguish these events from those of subpermafrost saturated sediments the relative dielectric permittivity ranged between 4 4 and 8 3 for the permafro

chlorin index a new parameter for organic matter freshness in sediments 1 total chlorins comprising degradation products of chlorophyll have been used recently to reconstruct paleoproductivity from marine sediment cores here we report on a new index the chlorin index ci that proves to be a helpful tool for rapidly estimating organic matter freshness in marine sediments the ci is a ratio between the fluorescence intensity of a sediment extracted with acetone and treated with hydrochloric acid and the original sediment extract it represents the ratio of chlorophyll and its degradation products deposited in the sediments that could still be chemically transformed and those that are inert to chemical attack the ratio is lower in sediments that include freshly deposited phytoplankton material and higher in older more degraded sediments we measured this new parameter on surface sediments and sediments from several short and a long sediment core from different oceanic settings ci values range from 0 2 for chlorophyll a to 0 36 0 56 for fresh material deposited on the shelf off namibia to values around 0 67 in sediments off chile and peru to values up to 0 97 for sediments in a deep core from the northeastern slope of the arabian sea we have compared the ci to rates of bacterial sulfate reduction as a direct measure of organic matter reactivity and to other degradation indices based on amino acid composition we conclude that the ci is a reliable and simple tool for the characterization of organic material freshness in sediments in respect to its degradation state

suspended sediment transport on the continental shelf near davenport california abstract suspended sediment transport on the shelves off santa cruz and davenport california is studied using field measurements and bottom boundary layer modeling strong transport events mostly occur during storms in winter the volume of winter sediment transport is at least one order of magnitude greater than that of summer spring transport rock outcrops on the inner shelf

thin ice growth the thickening of ice covers has traditionally been calculated using a method in which the thickness is assumed proportional to the square root of the accumulated freezing degree days particularly for newly formed thin ice this method overpredicts the ice thickness consideration of the thermal resistance between the top of the ice and the atmosphere results in a method which predicts linear growth with time for thin ice and transitions to the t growth at large thicknesses the method proposed here is not new but seems to be rarely used even though it requires selection of only one coefficient data from several sources including initial river ice growth sea ice growth and sludge freezing are used to validate the method and bracket the coefficient

ground penetrating radar for determining volumetric soil water content results of comparative measurements at two test sites ground penetrating radar gpr can provide information on the soil water content of the unsaturated zone in sandy deposits via measurements from the surface and so avoids drilling proof of this was found from measurements of radar wave velocities carried out ten times over 13 months at two test sites in the netherlands at these same locations and on the same dates soil water content was measured in access robes using a capacitance probe comparison of gpr and capacitance probe observations revealed that 1 the inferred absolute values of soil water content agree well this is remarkable because the soil water content is deduced entirely differently for the two methods 2 seasonal fluctuations in soil water content established for different general depth zones of radar waves correlate well with the fluctuations observed in the access tubes 3 the various methods to determine the propagation velocities of radar waves are complementary together they produce a realistic and reasonably complete image of the vertical distribution of the soil water content of the entire unsaturated zone high frequency 200 mhz direct groundwaves and refracted waves constitute a particularly attractive complementary combination which provides information on consecutive shallow zones in the underground i e the zones of major soil water content fluctuations 4 lateral variations established at one of the test sites where several access tubes have been placed in a transect also follow from the gpr measurements along that profile this non destructive determination of soil water content in practically continuous and detailed sections is one of the great assets of gpr opening the way to mapping preferential soil water flow paths

germanium silicon fractionation in a river influenced continental margin the northern gulf of mexico abstract in this study we have sampled the water column and sediments of the gulf of mexico to investigate the effects of high riverine terrigenous load and sediment redox conditions on the cycling of ge and si water column ge si ratios across the gulf of mexico continental shelf range from 1 9 to 25 mol mol which is elevated compared to the global ocean value of 0 7 mol mol the ge enrichment in the gulf of mexico seawater is primarily due to anthropogenic contamination of the mississippi river which is the main ge and si source to the area and to a smaller extent due to discrimination against ge during biogenic silica bsi production ge si 1 2 1 8 mol mol especially by radiolarians and siliceous sponges ge si 0 6 1 1 mol mol most sediment pore waters ge si 0 3 4 5 mol mol and sediment incubation experiments benthic flux ge si 0 9 1 2 mol mol indicate precipitation of authigenic phases that sequester ge from pore waters non opal sink this process appears to be independent of oxidation reduction reactions and suggests that authigenic aluminosilicate formation reverse weathering may be the dominant ge sink in marine sediments compilation of previously published data shows that in continental margins non opal ge burial flux is controlled by bsi supply while in open ocean sediments it is 10 100 times lower and most likely limited by the supply of lithogenic material we provide a measurement based estimate of the global non opal ge burial flux as 4 32 mmol yr 1 encompassing the 2 16 mmol yr 1 needed to keep the global marine ge cycle at steady state

geochemical characteristics of chilean upwelling sediments at 36 s abstract we examined the cycling of c s fe and the trace elements te ag cd mo mn re and se in chilean upwelling sediments from water depths of 127 2744 m at 36 s the sediments are clay rich with moderate total organic carbon toc and low biogenic caco3 contents for the shallow site within oxygen minimum zone omz which shows some thioploca biomass highest observed toc contents correspond to highest productivity induced toc flux and or enhanced preservation under o2 deficient conditions pyrite formation may be restricted by the concurrent presence of elemental s in thioploca and or the availability of reactive iron in the other sediments 370 m water depth pyrite formation is strongly restricted due to the low availability of metabolizable toc for sulfate reduction calculations of the degree of bacterially mediated remineralization suggest that more nitrogen than toc was remineralized by sulfate reduction than expected from redfield c n relationship manganese is significantly depleted due to reductive dissolution of mn hydr oxides within all sediments mo is only significantly enriched vs the lithogenic background in the shallow core implying anoxic conditions contents of re and mo as well as re mo ratios indicate suboxic conditions for the other cores cd and re contents decrease with increasing water depth reflecting decreasing reducing conditions in contrast authigenic ag contents increase with water depth suggesting enrichment controlled by seawater availability and or opaline input and not redox conditions elevated se contents in all cores may be either due to bio detrital input or diffusion from seawater accumulation rates of toc ts and te off chile are in the same order as those from the gulf of california and lower than those off peru distinct seasonality in upwelling and dilution of chilean sediments with terrigenous material lead to rather low metabolizable toc contents and lower te trapping capacity

diffraction based velocity estimates from optimum offset seismic data a graphical method is characterized for estimating seismic velocity directly from diffraction patterns observed on common offset records the nature of the resulting estimate is examined by illustrating the connection between the graphical approach and a related method used by practitioners of ground penetrating radar while the latter provides only a crude stacking velocity the graphical technique yields the generalized rms velocity for stratified media associated interval velocities can be derived from two or more diffraction events having their sources within the plane of survey where there is a lack of geological evidence to suggest that scatterers reside in plane we propose a simple strategy for locating a scatterer from its expression on two or more independent records error in the resulting location is directly related to subsurface velocity heterogeneity finally since the diffraction based velocity estimates assume that source and receiver are coincident the error stemming from nonzero off

major asian aeolian inputs indicated by the mineralogy of aerosols and sediments in the western north pacific recent atmospheric chemistry studies have shown that substantial quantities of soil material are being transported out of asia and across large regions of the north pacific1 2 in the central north pacific the estimated1 6 12 1012 g yr 1 and measured2 20 1012 g yr 1 deposition rate of mineral aerosols could account for a substantial fraction of the non biogenic portion of deep sea sediments in this region where sedimentologists have previously estimated that 75 95 3 4 of the surface sediment is derived from atmospheric dust fallout the quantitative importance of wind transported aeolian material to sedimentation in the north pacific would be more firmly established if it could be shown that the composition of the present day soil aerosol is similar to that of mineral particles in the underlying sediments which have been deposited over a period of thousands of years here we compare the compositions of soil aerosols and sediments collected from the western north pacific and find that their mineralogies are identical except for one mineral this supports the hypothesis that the sediments are heavily impacted by aeolian sources

analysis of submarine landsliding in the rupture area of the 27 february 2010 maule earthquake central chile the comparison of bathymetric datasets compiled before and after the mw 8 8 maule earthquake of the 27 february 2010 offshore central chile proves that no new submarine landslides on a size scale detectable with hull mounted bathymetric echosounders features of a horizontal size of 1 km formed as a direct consequence of the ground shaking gravity coring around a pre existing slide feature offshore concepcion biobio slide however documents that 1 a number of events occurred as retrogressive failures of the biobio slide wall the youngest of which is 700 1000 years old and that 2 a very recent small scale slide structure resulted from non destructive imbricate stacking of a thin sediment layer pore water geochemical data show that this event post dates the maule earthquake suggesting that it was triggered by one of the numerous aftershocks the absence of larger failures and the presence of a small slide let us propose that in contrast to apparent logic frequent violent earthquakes at convergent margins do not necessarily pose a particular tsunami risk by landslides the frequent shaking might even limit the slide volume and therefore their tsunami hazard as instead of rare and large slides frequent smaller slides are induced

fluxes and budget of on the continental margin of the bay of biscay northeastern atlantic abstract as part of the ecofer experiment ecomarge program jgofs france concentrations of the natural radionuclide 210 pb were measured in particulate matter collected by sediment traps deployed for a 14 month period june 1990 august 1991 on two mooring lines within the cap ferret canyon on the french continental slope of the bay of biscay northeastern atlantic 210 pb concentrations range 63 218 dpm g 1 and fluxes range 0 1 11 2 dpm cm 2 yr 1 displayed typical gradients increasing with depth at both mooring sites also at equivalent trap depths 210 pb activities were systematically higher on the deep slope mooring 3000 m compared to the shallow one 2300 m fluxes of 210 pb generally decreased seaward and exhibited temporal variations but with no marked seasonal trend essentially matching variations in total mass flux various correlations between 210 pb activities and major constituents of trapped particles were examined 210 pb activities were independent of the particle composition indicating that in this area scavenging of this nuclide from the water column was not directly tied to the quality of settling particles the 210 pb budget as determined by the balance of local supply flux and fluxes to sediment traps and sediments implies important lateral inputs to both mooring sites 65 89 of the flux measured by traps a feature typical of continental margin environments on the basis of annual mean 210 pb activity in traps of the two mooring sites two particle sources are hypothesized the first source located in shallow waters of the shelf and upper slope supplies the entire slope region the second source probably composed of resuspended particles from upper slope sediments feeds essentially the upper and intermediate slope region maximum sedimentation rates determined on seven box cores decreased with bottom depth from 0 3 to 0 4 cm yr 1 at the canyon heads down to 0 06 cm yr 1 at 3000 m a good agreement was observed at both mooring sites between 210 pb fluxes registered by the near bottom traps and excess 210 pb inventories within the underlying sediments suggesting that nuclide fluxes measured by traps during this experiment are representative of fluxes on a longer time scale 10 100 yr nevertheless total mass fluxes measured by traps were 3 4 times lower than 210 pb determined sediment accumulation rates a discrepancy that may be more apparent than real given the possible errors in the latter due to bioturbation

sedimentation in the chile trench petrofacies and provenance abstract the chile trench study area extends over 2 000 km along the andean continental margin from 23 s to 42 s latitude the qfl composition of chile trench sands encompasses the average compositions of modern sands from strike slip continental arc oceanic backarc and oceanic forearc types of active margins valloni and maynard 1981 and spans the complete spectrum from dissected to undissected magmatic arc settings dickinson et al 1983 trench sands along north chile central chile and the glaciated archipelago of south chile are derived from a more plutonic source region or dissected magmatic arc these sands exhibit abnormally low lithic and calcic plagioclase content but high quartz and alkali feldspar in central chile the plutonic provenance is correlated with an ab ence of quaternary volcanism along the chilean archipelago pleistocene glaciation has carved into the magmatic roots of the andes effecting arc dissection in spite of active volcanism in arid north chile the volcanic debris of the high cordillera is trapped onshore in longitudinal forearc basins allowing an exaggerated contribution from crystalline rocks of the coast range the light and heavy mineral and lithic composition of trench sands is described by four ideal petrologic assemblages isolated by q mode factor analysis the basic magmatic arc petrofacies volcanic lithics calcic plagioclase olivine clinopyroxene and orthopyroxene the most chemically unstable and least differentiated assemblage is derived exclusively from basalts and basaltic andesites in the quaternary volcanic arc of south chile the acidic magmatic arc petrofacies volcanic lithics alkali feldspar biotite hornblende and magnetite is derived from andesitic to rhyolitic volcanics and granodioritic plutons emplaced during various mesozoic and cenozoic magmatic episodes in the history of the andean margin the metamorphic magmatic arc petrofacies mica alkali feldspar hlorite actinolite epidote and blue green hornblende is derived from ferromagnesian rocks altered to the greenschist facies in the basal marine section of the andean eugeosyncline and in the paleozoic basement the cratonic block petrofacies quartz and the accessory minerals andalusite garnet and tourmaline is derived from mature platform sediments late stage granitic intrusions and high grade regional metamorphics associated with the south american craton it is most prominent along northern chile where the continental crust is thickest and presumably truncated by subduction erosion actual petrofacies in the chile trench are typically mixtures of the four ideal petrofacies their compositions can be related to 1 the lithology and erodibility of the source terranes 2 the distribution and composition of modern arc volcanism 3 the prevailing climate in the provenance region and 4 the structure and morphology of the continental margin and trench in many cases contemporary volcanism inundates and dominates the petrologic assemblage diluting contributions from all other source rock types and forming a low diversity petrofacies at high latitudes where glaciation was extensive a variety of source rock terranes were actively denuded and petrofacies of high diversity were deposited in the adjacent trench the linear frequency of sediment supply points along the base of the continental slope controls the spatial heterogeneity of petrofacies on the depositional surface in the trench basin the most homogenous petrofacies derived from major submarine canyon systems and extensive subaerial drainage basins may extend hundreds of kilometers along margin due to axial transport processes within the trench

evaluation of sediment trace metal records as paleoproductivity and paleoxygenation proxies in the upwelling center off concepcion chile 36 s a b s t r a c t this study analyzes the records of several trace metals sensitive to redox conditions in continental shelf sediments off concepcion chile 36 s the continental margin off concepcion 36 s 73 w lies beneath an important upwelling center characterized by high primary production rates and consequently high fluxes of organic matter in spring and summer this material settles to the seafloor where it decays pro ducing periods of very low oxygen content in bottom waters 1 ml l y 1 the goals of this study were to determine the input of trace metals to the sediment and to decipher how this information can be used to reveal variations in primary productivity or bottom oxygenation gravity cores collected at two stations vg06 2 over the mid shelf station 88 m water depth upper boundary of the oxygen minimum zone and vg06 3 over the outer shelf 120 m water depth within the oxygen minimum zone were sampled for high resolution profiles 1 cm of trace metals biogenic opal stable isotopes and total organic carbon the results suggest that the variability in the trace metal distribution on the continental shelf off concepcion is determined by redox conditions and the organic carbon flux to the bottom some sections of the sediment cores from the outer shelf showed appreciable authigenic enrichment of u cd and mo ef 5 10 2 5 and 10 16 respectively along with heavier values of d 15

surface sediment distribution along the chilean continental slope related to upwelling and productivity abstract the coastal upwelling system of the peru chile current belongs to the most productive regions in the world oceans in spite of this remarkable fact only very little is known about the sediment distribution in its southern part off the coast of chile to increase the knowledge about this region a multiparameter study of the surface sediment distribution along the chilean continental slope between 27 and 42 s has been carried out detailed analyses of sedimentary data toc and carbonate contents 13corg 15n of the species composition of planktic foraminifera and of the stable isotope composition of the two planktic foraminifera species neogloboquadrina pachyderma dex and globigerina bulloides reveal a close relation to environmental conditions in the region the pattern of a southward increase of surface water productivity known from satellite data is closely reflected in the organic carbon and 15n data information about the water mass distribution especially about varying influences of upwelling waters and warmer subtropical surface waters can be derived from the species composition of the planktic foraminifera while the stable isotope data provide additional clues about water mass characteristics high productivity along the chilean margin north of 40 s is sustained by coastal upwelling while further to the south advection of nutrients with the antarctic circumpolar current and a significant riverine input fuel the highest productivity found in the study area this data set will provide the base for future paleoclimatic and paleoceanographic reconstructions of the southeast pacific region

beyond the black sea paradigm the sedimentary fingerprint of an open marine iron shuttle we present iron fe concentration and fe isotope data for a sediment core transect across the peru upwelling area which hosts one of the ocean s most pronounced oxygen minimum zones omzs the lateral progression of total fe to aluminum ratios fet al across the continental margin indicates that sediments within the omz are depleted in fe whereas sediments below the omz are enriched in fe relative to the lithogenic background rates of fe loss within the omz as inferred from fet al ratios and sedimentation rates are in agreement with benthic flux data that were calculated from pore water concentration gradients the mass of fe lost from sediments within the omz is within the same order of magnitude as the mass of fe accumulating below the omz taken together our data are in agreement with a shuttle scenario where fe is reductively remobilized from sediments within the omz laterally transported within the anoxic water column and re precipitated within the more oxic water below the omz sediments within the omz have increased 56fe 54fe isotope ratios relative to the lithogenic background which is consistent with the general notion of benthic release of dissolved fe with a relatively low 56fe 54fe isotope ratio the fe isotope ratios increase across the margin and the highest values coincide with the greatest fe enrichment in sediments below the omz the apparent mismatch in isotope composition between the fe that is released within the omz and fe that is re precipitated below the omz implies that only a fraction of the sediment derived fe is retained near shore whereas another fraction is transported further offshore we suggest that a similar open marine shuttle is likely to operate along many ocean margins the observed sedimentary fingerprint of the open marine fe shuttle differs from a related transport mechanism in isolated euxinic basins e g the black sea where the laterally supplied reactive fe is quantitatively captured within the basin sediments we suggest that our findings are useful to identify omz type fe cycling in the geological record

sediment accumulation rates and carbon fluxes to bottom sediments at the western bransfield strait antarctica abstract mean sediment and carbon accumulation rates in the western bransfield strait during the last ca 100 years were determined at three sites by using 210 pb as a radiotracer of sedimentation processes rates 210 pb profiles showed moderate mixing in the upper 8 5 12 cm which was attributed to bioturbation sediment accumulation rates calculated assuming no mixing below the surface mixed layer sml were found to be relatively high between 0 03 and 0 09 g cm 2 yr 1 in good agreement with previously reported data based on both 210 pb and 14 c dating in surrounding areas these results together with the calculated excess 210 pb fluxes to the bottom sediments and the 210 pb and 210 po distributions in the water column indicated the presence of a large net advective flux of material in the area highlighting the importance of glacial related sedimentation processes in this semi enclosed sea carbon in bottom sediments was mainly organic and its content was moderately low 0 65 1 25 being slightly higher within the sml reflecting the presence of inhabiting organisms however organic carbon oc accumulation fluxes 3 1 6 7 g c m 2 yr 1 were considerable due to the high sediment accumulation rates 210 pb dated profiles allowed us to estimate the amount of carbon exported from the water column and buried in the bottom sediment which represents about 3 7 of the mean annual primary production in the euphotic layer of the bransfield strait the burial efficiency of oc in the sediment was estimated to be approximately 60 80

upwelling and the distribution of chlorophyll a within the bay of concepcion chile abstract the influence of upwelling on the distribution of chlorophyll a within the bay of concepcion chile is discussed in light of continuous measurements of surface in vivo chlorophyll fluorescence and temperature taken simultaneously along horizontal transects and hydrographic stations data results suggest significant temporal variability both in the distribution of in vivo fluorescence temperature and salinity within the bay and in the characteristics of the exchange between the bay and the adjacent shelf waters induced by variable upwelling upwelling is produced by the predominant south westerly winds during the summer significant variations in the wind direction occur with periods from two to seven days during active upwelling exchange is characterized by a surface outflow through the mouth of the bay and an inflow at depth low chlorophyll fluorescence is confined to the upwelling areas on the eastern shore either within or outside the bay high chlorophyll fluorescence is confined to the central and western bay density data suggest a three layered circulation pattern at the mouth of the bay during the upwelling relaxation involving an inflow both at the surface and bottom and outflow at mid depth associated with this exchange is an active high chlorophyll transport from the bay to the adjacent coastal waters at mid depth and inflow of low chlorophyll water from the adjacent shelf at the surface and near the bottom

seasonal climatology of hydrographic conditions in the upwelling region off northern chile over 30 years of hydrographic data from the northern chile 18os 24os upwelling region are used to calculate the surface and subsurface seasonal climatology extending 400 km offshore the data are interpolated to a grid with sufficient spatial resolution to preserve cross shelf gradients and then presented as means within four seasons austral winter july september spring october december summer january march and fall april june climatological monthly wind forcing surface temperature and sea level from three coastal stations indicate equatorward upwelling favorable winds throughout the year weakest in the north seasonal maximum alongshore wind stress is in late spring and summer december march major water masses of the region are identified in climatological t s plots and their sources and implied circulation discussed surface fields and vertical transects of temperature and salinity confirm that upwelling occurs year round strongest in summer and weakest in winter bringing relatively fresh water to the surface nearshore surface geostrophic flow nearshore is equatorward throughout the year during summer an anticyclonic circulation feature in the north which extends to at least 200 rn depth is evident in geopotential anomaly and in both temperature and geopotential variance fields subsurface fields indicate generally poleward flow throughout the year strongest in an undercurrent near the coast this undercurrent is strongest in summer and most persistent and organized in the south south of 21os a subsurface oxygen minimum centered at 250 m is strongest at lower latitudes low salinity subsurface water intrudes into the study area near 100 m predominantly in offshore regions strongest during summer and fall and in the southernmost portion of the region the climatological fields are compared to features off baja within the somewhat analogous california current and to measurements from higher latitudes within the chile peru current system

holocene north atlantic surface circulation and climatic variability evidence from diatom records diatom analyses have been performed on a 425cm long holocene marine sediment sequence from the north atlantic south of iceland and a 920cm sediment core spanning the last c 7500 years from skalafjord faeroe islands additional core data include stable isotopes and results from magnetic susceptibility measurements while chronostratigraphic control has been provided by ams 14c measurements the diatom records reveal distinct changes in north atlantic surface circulation and climate that have been correlated with published terrestrial and marine records initial holocene warming is dated at 9900 14c years bp and after a preboreal cold spell enhanced north atlantic current activity and warming prevailed from 9600 to 8800 14c years bp from 8800 to 8000 4c years bp the advection of warm atlantic water masses weakened presumably under atmospheric circulation conditions characterized by a dominating negative nao prior to the holocene climatic optimum 6000 5000 14c years bp distinct hydrographic gradient

influence of boundary scavenging and sediment focusing on 234th 228th and 210pb fluxes in the santa barbara basin abstract sediment trap samples were collected from the santa barbara basin to examine the flux of 234 th 228 th and 210 pb mean ratios of measured to predicted fluxes are 2 10 and 21 for 234 th 228 th and 210 pb respectively boundary scavenging may supply a portion of all three radionuclides however sediment focusing supplies additional 228 th and 210 pb but little 234 th sediment temporarily deposited on the shelf around the basin contains little excess 234 th due to its short half life 228 th and 210 pb fluxes to the sediments in the santa barbara basin are several times greater than predicted from their supply in the overlying water column these enhanced fluxes require lateral transport of 228 th and 210 pb to the basin through boundary scavenging and sediment focusing 234 th flux is poorly correlated with 228 th and 210 pb fluxes because individual radionuclide sources to the basin differ i e water column production boundary scavenging and or sediment focusing correlations between 228 th and 210 pb fluxes are high due to the strong influence of sediment focusing on both radionuclides there is a strong correlation between both the 228 th and 210 pb flux and total mass flux and lithogenic flux but a weak correlation with the other major sediment components e g organic carbon carbonate and biogenic opal in the santa barbara basin a large fraction of the total mass flux is lithogenic material 50 80 hence the strong correlation between 228 th and 210 pb fluxes and both total mass and lithogenic fluxes 234 th flux is poorly correlated with total mass and major sediment component fluxes

chlorophyll variability in eastern boundary currents the first three years of seawifs data 199 2000 provide the most complete quantification to date of chlorophyll seasonal variability along the full latitudinal ex tent of the four major eastern boundary currents ebcs comparisons to previously published chlorophyll seasonal climatologies deduced from the relatively sparse coverage provided by the coastal zone color scanner czcs show significant differences in both southern hemisphere ebcs while northern hemisphere regions are qualitatively simi lar comparisons between chlorophyll and cross shelf ek man transport seasonal cycles calculated from coincident satellite scatterometer data show seasonal maxima have similar phases over most of the california current at higher 32os latitudes in the peru chile and benguela currents 30os and at lowest latitudes 20on in the canary current latitudinal zones within which phases diverge are indicative of alternate and or more distant forcing

geochemical characterization of two distinctive systems with evidence of chemosynthetic activity explored at the se pacific margin off chile 46 s and 33 s this study presents the geochemical composition of superficial sediment under oxic and suboxic bottom water conditions along the chilean continental margin se pacific where evidence for benthic chemosynthetic activity associated with diffuse seeping of chemically reduced fluids has been reported the exploration was carried out at 1 the chilean triple junction ctj at a water depth of 2900 m with the additional indication of hydrothermal activity near a methane rich cold seep area 46 s german et al 2010 and 2 the el quisco methane seep site eqss at 340 m water depth 33 s melo et al 2007 krylova et al 2014 while the deeper ctj is located within an oxic environment dissolved oxygen in the bottom waters 164 m the shallower eqss lies within a suboxic environment dissolved oxygen in bottom water 23 m located within the lower limit of the se pacific oxygen minimum zone omz pore water from short cores was analyzed for dissolved major minor and trace elements cl na mg k ca sr si b p ba pb mn fe cd u and mo 13dic sulfide sulfate and methane the solid sediment fraction was likewise analyzed for total organic carbon toc metals and redox potential elevated sediment temperatures were found in superficial sediments 5 13 c at the ctj site which could be due to warm fluids associated with the proximity of the ridge where hydrothermal vents may occur reduced fluids were also present here indicated by higher mn fluxes toward the water column even in oxidized sediments rpd 8 cm which contrasted with the lower fluxes in reduced sediments of the eqss site rpd 2 cm 13c depleted dic anomalously low pore water cl 15 ppb and low concentrations of other major elements may be the result of dilution by fluid seeping and precipitation of major elements producing authigenic enrichment ca mg sr the fluid could also a be diluted by pure water produced during methane hydrate dissociation as observed in other cold seep areas and b correspond to clay mineral dehydration as reported in plate subduction systems the reducing conditions established at the ctj conduct the cd enrichment at a similar magnitude of that seen at the shallower suboxic site eqss evidence of chimney or vent fauna was not observed at the eqss higher toc and total sulfide contents were consistent with enhanced deposition of organic matter and reducing conditions developed in the omz favoring the authigenic enrichment of cd u and pb the geochemical evidence based only on methane concentrations and 13dic is insufficient to establish the presence of methane seeps as previously reported

late holocene environmental change in arctic western siberia the putorana plateau western siberia situated on the boundary of the atlantic and continental siberian climate provinces is sensitive to shifts in atmospheric circulation three lakes on an altitudinal transect were studied using chironomid subfossils to provide the first estimates of late holocene climate in this remote poorly studied region of arctic russia the analysis of sediment cores from three closely located lakes is rare in palaeoenvironmental studies and enables the role of other environmental variables which may be a potential source of error in palaeoclimatic reconstructions to be assessed the chironomid based reconstructions suggest a more maritime climate c 3400 cal bp with july temperatures c 1 5 c warmer than present which cooled rapidly by c 2 c with a more continental climate between 3200 and 2600 cal bp these trends are similar in timing and scale to other northern hemisphere records the recent chironomid records from all three lakes show pronounced faunal changes over the last 50 years probably directly or indirectly because of climate driven changes in catchment hydrology this is particularly evident in the recent record from an open lake within a large wetland habitat which appears relatively insensitive to changes in july air temperatures

constraining spatial variability of methane ebullition seeps in thermokarst lakes using point process models 1 ebullition is an important but highly heterogeneous mode of methane emission in lakes variability in both spatial distribution and temporal flux creates difficulty in constraining uncertainties in whole lake emission estimates analysis of short and long term flux measurements on 162 ebullition seeps in 24 panarctic lakes confirmed that seep classes identified a priori according to bubble patterns in winter lake ice have distinct associated fluxes irrespective of lake or region to understand the drivers of ebullition s spatial variability and uncover ways to better quantify ebullition in field work we combined point process modeling with field measurements of 2679 gps marked and classified ebullition seeps in three alaskan thermokarst thaw lakes that varied by region permafrost type and seep distribution spatial analysis of field data revealed that seeps cluster above thawed permafrost soil mounds in lake bottoms seep density and clustering determined from field observations were used as parameters in a poisson cluster process model to simulate seeps across entire lake surfaces sampling results indicated that 1 applying seep class mean flux values to unmeasured seeps counted on ice bubble surveys does not compromise accuracy of whole lake flux estimates 2 three distributed 50 m2 ice bubble survey transects more accurately estimate mean lake ebullition than 17 dispersed 0 2 m2 bubble traps and 3 the uncertainty associated with whole lake mean ebullition estimated by lake ice survey transects is inversely related to seep density findings suggest that transect field data collected on a large number of widely distributed lakes can be combined to provide a well constrained bottom up estimate of regional lake ebullition

shelfal sediment transport by an undercurrent forces turbidity current activity during high sea level along the chile continental margin terrigenous sediment supply marine transport and depositional processes along tectonically active margins are key to decoding turbidite successions as potential archives of climatic and seismic forcings sequence stratigraphic models predict coarse grained sediment delivery to deep marine sites mainly during sea level fall and lowstand marine siliciclastic deposition during transgressions and highstands has been attributed to sustained connectivity between terrigenous sources and marine sinks facilitated by narrow shelves to decipher the controls on holocene highstand turbidite deposition we analyzed 12 sediment cores from spatially discrete coeval turbidite systems along the chile margin 29 40 s with changing climatic and geomorphic characteristics but uniform changes in sea level sediment cores from intraslope basins in north central chile 29 33 s offshore a narrow to absent shelf record a shut off of turbidite deposition during the holocene due to postglacial aridification in contrast core sites in south central chile 36 40 s offshore a wide shelf record frequent turbidite deposition during highstand conditions two core sites are linked to the biobio river canyon system and receive sediment directly from the river mouth however intraslope basins are not connected via canyons to fluvial systems but yield even higher turbidite frequencies high sediment supply combined with a wide shelf and an undercurrent moving sediment toward the shelf edge appear to control holocene turbidite sedimentation and distribution shelf undercurrents may play an important role in lateral sediment transport and supply to the deep sea and need to be accounted for in sediment mass balances

morphology of san antonio submarine canyon on the central chile forearc a multibeam survey was conducted over san antonio submarine canyon near valparaiso chile in april and may 1993 using the seabeam 2000 system on the r v melville the bathymetric data from this survey reveal a canyon with an overall sinuosity of 1 25 a broad roughly u shaped cross section along most of its length and an almost constant channel slope above the forearc structural high the course of the canyon is deflected to the north by a prominent structural high opposite the town of san antonio seabeam 2000 side scan sonar data reveal high backscatter material on the floor of the canyon with a longitudinal fabric reminiscent of stream braiding and point bars formed on the inside of channel bends we interpret this high backscatter material to be coarse sediment transported down the canyon as turbidity currents the source of these turbidity currents is probably the rio maipo which enters the ocean near the head of the canyon

holocene glacier and climate fluctuations on franz josef land arctic russia 80 n fluctuations in glacier extent provide the first comprehensive record of holocene paleoclimate for franz josef land glacier fluctuations were constrained using 45 14c ages from 16 glacier margins many glaciers were behind present margins before 9 4 kyr possibly as early as 10 3 kyr and probably remained so until at least 4 4 kyr where kyr 14c yr b p 1000 subsequently glaciers expanded probably reaching present margins before 3 2 kyr but certainly by 2 kyr a prominent neoglacial advance occurred ca 1 kyr and was followed by little ice age advances including one in the middle 1600s a d glaciers were larger than present at the turn of the century followed by widespread retreat soon after the holocene glacier record closely mimics that of svalbard 500 to 1000 km to the west suggesting similar glacier mass balance changes over a broad region of the eurasian arctia independent paleoclimate evidence from svalbard indicates higher than present summer air temperatures during the early to middle holocene when glaciers were behind present margins followed by generally cooler summer conditions and intermittent glacier advances and retreats holocene glacier variations were probably more influenced by summer temperature than winter precipitation

accumulation rate and mixing of shelf sediments in the monterey bay national marine sanctuary abstract the distribution of excess 210pb in 31 sediment cores was used to determine modern last 100 yr mass accumulation rates and the depth of sediment mixing on the continental shelf between pacifica and monterey california usa apparent mass accumulation rates average 0 27 g cm 2 yr 1 and range from 0 42 g cm 2 yr 1 to 0 12 g cm 2 yr 1 accumulation rates were highest at mid shelf water depths 60 100 m adjacent to major rivers and near the head of the ascension submarine canyon cores from water depths of less than 65 m had low uniform 210pb activity profiles and sandy textures the uppermost 5 13 cm of 15 cores had uniform 210pb activity profiles above a region of steadily decreasing 210pb activity this phenomenon was attributed to sediment mixing the thickness of this upper layer of uniform 210pb activity decreased southward from 13 cm west of pacifica to less than 5 cm near monterey canyon this southward decrease may be attributed to shallower bioturbation in the southern study area integrated excess 210pb activities were generally higher where sedimentation rates were high they were also higher with increasing distance from major rivers thus sedimentation rate alone does not explain the distribution of integrated excess 210pb in this study area excess 210pb in the seafloor is controlled by other factors such as sediment texture the atmospheric deposition rate of 210pb and the residence time of sediment particles in the water column

organic matter budget in the southeast atlantic continental margin close to the congo canyon in situ measurements of sediment oxygen consumption abstract a study of organic carbon mineralization from the congo continental shelf to the abyssal plain through the congo submarine channel and angola margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling two measurement techniques were coupled on a single autonomous platform in situ benthic chambers and microelectrodes which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters in addition sediment trap fluxes sediment composition org c tot n caco3 porosity and radionuclide profiles provided measurements of respectively input fluxes and burial rate of organic and inorganic compounds the in situ results show that the oxygen consumption on this margin close to the congo river is high with values of total oxygen uptake tou of 4 0 6 3 6 0 5 mmol m 2 d 1 at 1300 and 3100 m depth respectively and between 1 9 0 3 and 2 4 0 2 mmol m 2 d 1 at 4000 m depth diffusive oxygen uptakes dou were 2 8 1 1 2 3 0 8 0 8 0 3 and 1 2 0 1 mmol m 2 d 1 respectively at the same depths the magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel levee system which indicates that cross slope transport processes are active over the entire margin comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5 8 times larger than the vertical flux recorded in traps transfer of material from the congo river occurs through turbidity currents channelled in the congo valley which are subsequently deposited in the lobe zone in the congo fan below 4800 m ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone which agrees with the high organic carbon content 3 and the large sedimentation rate 19 mm y 1 found on this site the lobe region could receive as high as 19 mol c m 2 y 1 1 3 being mineralized and 2 3 being buried and could constitute the largest depocenter of organic carbon in the south atlantic

the giant coastal landslides of northern chile tectonic and climate interactions on a classic convergent plate margin abstract documented for the first time are an extensive suite of late neogene giant terrestrial coastal landslides along the classic convergent margin of western south america 18 to 24 south these are remarkable in terms of their unusual abundance and atypical setting such failures previously being linked with oceanic volcanic edifices or over steepened glaciated coastlines located within the hyper arid coastal cordillera of the atacama desert of northern chile we report the presence of more than 60 individual large scale landslides with individual volumes up to 9 km 3 developed over a horizontal coastline distance of some 650 km these landslides were emplaced as a combination of rock avalanches and multiple rotational failures the majority terminated directly into the pacific likely generating significant tsunami hazard to the chilean and south peruvian coastline in a region which is today considered to be part of a notorious seismic gap the proliferation and scale of these late neogene giant landslides in this actively uplifting hyperarid terrain suggests they are the main geomorphic agent for relief reduction probably triggered by megathrust earthquakes and potentially providing a unique palaeoseismic archive the temporal and spatial distribution of these giant landslides corresponds with a period of surface steepening of the forearc wedge in the central andes and south to north differential uplift associated with factors such as aseismic ridge subduction the resulting surface gradient increases combined with the persistent climatic aridity of the region have served to limit effective relief reducing geomorphic processes in this oversteepened terrain to large scale landsliding the phenomena documented here geospatially link previously recognised large scale slope failures from the off shore environment and higher altitude areas of the andean forearc suggesting that large scale landsliding is capable of transferring sediment on a regional scale to the off shore peru chile trench this has implications for the friction of the subducting nazca plate and associated seismicity and uplift

copper isotope signatures in modern marine sediments abstract the development of metal stable isotopes as tools in paleoceanography requires a thorough understanding of their modern marine cycling to date no cu isotope data has been published for modern sediments deposited under low oxygen conditions we present data encompassing a broad spectrum of hydrographic and redox regimes including continental margin and euxinic sulphide containing settings taken together with previously published data from oxic settings these data indicate that the modern oceanic sink for cu has a surprisingly homogeneous isotopic composition of about 0 3 65cu relative to nist srm976 we suggest that this signature reflects one of two specific water column processes 1 an equilibrium isotope fractionation between soluble isotopically heavy cu complexed to strong organic ligands and an isotopically light pool sorbed to particles that deliver cu to the sediment or 2 an equilibrium isotope fractionation between the same isotopically heavy ligand bound pool and the particle reactive free cu2 species with the latter being scavenged by particulates and thereby delivered to the sediment an output flux of about 0 3 into sediments is isotopically light relative to the known inputs to the ocean at around 0 6 and the seawater value of 0 6 to 0 9 suggesting the presence of an as yet unidentified isotopically light source of cu to the oceans we hypothesize that this source may be hydrothermal or may result from the partial dissolution of continentally derived particles

biogeochemical significance of fatty acid distribution in the coastal upwelling ecosystem off concepcion 36 s chile abstract the distribution of fatty acids fas in the water column and surface sediment of the coastal upwelling ecosystem off concepcion central chile almost monthly from february 2007 to november 2008 was analyzed using gas chromatography mass spectrometry the concentration of fas in the water column ranged from 3 4 to 67 7 g l 1 and showed higher values in surface water than in bottom water and under upwelling vs non upwelling conditions the content in surface sediment ranged from 21 6 to 328 5 g g dw 1 and had a higher abundance in february 2007 and january march and june 2008 in surface water 16 0 18 0 and 16 1n 7 made up ca 47 of the fas during the study period while in bottom water 16 0 18 0 and 18 1n 9 accounted for ca 45 and in surface sediment ca 43 was accounted for by 14 0 16 0 16 1n 7 and 18 1n 7 fas seasonal variability in the relative abundance of saturated and polyunsaturated fas pufas was observed in surface water while in bottom water and surface sediment no major temporal change in fa composition was observed a negative exponential relationship between bacterial fas and pufas from surface water and sediment suggests that bacteria may be responsible for ca 80 of pufa removal during sinking we suggest that the fa composition of the surface sediment of the ocean is a consequence of rapid alteration of the fa pool by biological activity in the water column and sediment driven by the removal of the labile fraction of fas

transuranic nuclides in two coastal marine sediments off peru the fluxes of plutonium isotopes as well as their depth profiles are similar for northern and southern hemispheric varved sediments taken off western american coasts the inventories are in excess of the values predicted for atmospheric fallout in these anoxic sediments there is a general increase in concentration from depths to the near surface these observations are explainable on the bases that anoxic deposits have a substantially higher retentivity of sedimented materials compared to that of their bioturbated oxic counterparts and that there are inputs of resuspended materials previously deposited in the marine environment the 241am distributions are explained by ingrowth from 241pu assuming a substantial input of the parent from the u s thermonuclear tests during the 1950 s and the immobilization of both pu and am in the deposits

temporal variability of 210pb fluxes and bioturbation in shelf sediments beneath the high primary production area off concepcion central southern chile 36 s abstract we estimated monthly fluxes of 210 pb in shelf sediments beneath a high productivity area off central southern chile 36 s during 1 year september 2002 august 2003 sediment cores were obtained using a multiple corer and were analyzed mainly for 210 pb total pigments and macrofauna abundance the 210 pb inventories and fluxes were estimated for surface sediments 0 5 cm and bioturbation coefficients were inferred using chlorophyll a reactive profiles in general 210 pb content was inversely correlated with phytodetritus fluxes high photosynthetic pigment contents in surface sediments were consistently associated with lower 210 pb contents macrofaunal activity responded to oxygen and organic matter supplies at the sediment surface generally concentrated in the first centimeters but particularly so during months of high organic matter fluxes and deficient bottom water oxygen conditions at this study site several processes involved in the 210 pb surface distribution make it difficult to accurately estimate ages at the surface we postulate that the organic fluxes promote changes in the faunal activity which in combination with sediment resuspension and water circulation over the shelf produce seasonal variations in the 210 pb inventories

sedimentation in the chile trench depositional morphologies lithofacies and stratigraphy the depositional bodies of the chile trench trench fans the axial channel sheeted basins ponded basins and axial sediment lobes control the spatial distribution of modem lithofacies in the basin sheeted basins south of 41 s are presumably fed by closely spaced submarine gullies that approximate a line of source of sediment supply along the base of the slope trench fans 41 s 33 s are built at the mouths of major submarine canyon systems which act as point sources of sediment supply the axial channel follows the northward gravitational gradient draining the distributary networks of trench fans into the longitudinal transport system down gradient northern fan lobes are severely dissected by erosional processes evidently periods of proximal deposition alternate with periods of massive sediment remobilization and progradation of the axial dispersal system into more distal environments channelized basins in the canyon mouth areas yield to sheeted basins depositional surface maintains an axial gradient or ponded basins depositional surface is strictly flat in inter canyon areas tectonic disruption of the oceanic basement can locally augment the axial gradient and stimulate flow channelization or reverse the gradient and induce sediment ponding a large margin parallel sediment lobe is built at the base of a high axial escarpment near 33 s where the axial channel crosses a transverse discontinuity at the convergent plate boundary five lithofacies are defined by q mode factor analysis of sediment textures and hydro dynamic structures in 27 cores from the chile trench the channel facies thick amalgamated sand massive to laminated or cross bedded is deposited by high energy processes within the coarse grained bedload of turbidity currents it forms in distributary and axial channels the levee facies rhythmically bedded internally structureless graded sand and graded silt is deposited from concentrated sediment suspensions that quickly lose momentum during channel spillover it forms on channel flanks although constructional levees are not always present the basin 1 facies more complete bouma sequences both upper and lower flow regime structures forms in ponded basins where flows are confined by a high relief seaward trench wall the basin 2 facies graded and laminated silt lower flow regime structures forms in low energy environments such as interchannel areas distal basins trench walls and elevated topographic features the contourite facies silt and sand laminations winnowed from hemipelagic muds and distal turbidites is best developed in sediment starved basins where geostrophic currents are constricted and accelerated between the steep inner and outer trench walls the trench wedge records a coarsening upward sequence as the oceanic plate migrates toward and into the trench during plate convergence and becomes more proximal to sediment sources along the base of the continental margin near canyon mouths prograding trench fans drive the axial channel seaward into the trench wedge and the coarsening upward sequence is truncated by a time transgressive erosional unconformity abandoned axial channel deposits are carried landward beneath prograding fans to record a fining upward sequence above the basal unconformity channel migration and lobe aggradation may produce fining and coarsening upward sequences on depositional fan lobes but sequences on the erosional lobes are fragmented by numerous truncation surfaces

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

late quaternary variability of sedimentary nitrogen isotopes in the eastern south pacific ocean 1 we present high resolution bulk sedimentary 15n data from the southern edge of the present day oxygen minimum zone of the eastern south pacific the record is interpreted as representing changes in water column nitrogen removal during the last 70 000 years we found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales these fluctuations were not related to other millennial scale changes like the northern hemisphere s dansgaard oeschger climate swings or local changes in primary productivity so appear to be dictated by the southern hemisphere s climate rhythm this is preliminarily corroborated by an overall agreement between our 15n data and the sedimentary proxy of ice sheet dynamics in patagonia which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern south pacific intermediate waters finally potential implications on late quaternary changes in atmospheric co2 concentrations are discussed

the competition between coastal trace metal fluxes and oceanic mixing from the 10be 9be ratio implications for sedimentary records at an ocean margin site 37 s offshore chile we use the meteoric cosmogenic 10be 9be ratio to trace changes in terrestrial particulate composition due to exchange with seawater we analyzed the marine authigenic phase in surface sediments along a coast perpendicular transect and compared to samples from their riverine source we find evidence for growth of authigenic rims through coprecipitation not via reversible adsorption that incorporate an open ocean 10be 9be signature from a deep water source only 30 km from the coast overprinting terrestrial 10be 9be signatures together with increasing 10be 9be ratios particulate bound fe concentrations increase which we attribute to release of fe rich pore waters during boundary exchange in the sediment the implications for the use of 10be 9be in sedimentary records for paleodenudation flux reconstructions are the following in coast proximal sites the authigenic record will likely preserve local riverine ratios unaffected by exchange with seawater whereas sites beneath well mixed seawater will preserve global flux signatures

neogene sedimentary and mass wasting processes on the continental margin off south central chile inferred from dredge samples the active continental margin off south central chile 36 to 40 s is transitional between the tectonically erosive empty trench margin north of juan fernandez ridge and the accretionary trench filled margin south of the chile triple junction the small width of the presently active accretionary wedge maximum width of 25 to 50 km argues for past phases of tectonic erosion at present this sector shows indications of contemporaneous accretion subduction and underplating of sediment as well as readjustment of the slope by various mass wasting processes in this context this study aims to examine the neogene sedimentary processes on the continental margin from dredge samples recovered during r v sonne cruise so161 5 within this transitional domain using lithology sandstone petrology shale mineralogy and analysis of sedimentary structures our results yield that the principal transport of material occurs in high energy turbidity currents and debris flows via submarine canyons deeply cutting the continental slope whereas sediment on the shelf is transported by strong coast parallel bottom currents and trapped by submarine canyons cutting into the shelf a wide range of mass wasting processes including slumping debris flows evolving to low density turbidity currents and mud flows rework the slope sediments in contrast thick undisturbed sequences of mostly hemipelagic sediments accumulate in active slope basins which are largely protected from mass movements xrd analyses revealed early diagenetic lithification and overall burial depths of up to 230 mbsf suggesting a shallow subsurface cycle of sedimentation subsidence diagenesis uplift erosion and resedimentation the composition of sandstones is dominated by volcanic rock fragments of andean provenance along strike modal changes reflect a southward increase in glacially denudation and rainfall the combination of which caused more intense erosion of volcanic rocks and exposure weathering and as a result increased fluvial transport of metamorphic and plutonic rocks to the sea

effect of varying oceanicity on early to mid holocene palaeohydrology kola peninsula russia isotopic evidence from treeline lakes the stable isotope stratigraphy of sedimentary organic matter and algal cellulose in cores from two lakes near treeline on the kola peninsula indicate changes in water and nutrient balance that correlate with inferred expansion of pinus sylvestris during the early to mid holocene trends in cellulose inferred lakewater 18o values for both lakes suggest that moist conditions after deglaciation were followed by progressive drying from about 9500 to between 8000 and 7500 14c yr bp although pine appeared in the area by 8000 14c yr bp the maximum density of trees locally as suggested by stomate evidence occurred during subsequent moistening between 7500 and 6000 14c yr bp this is c 1000 years later than in other regions of northern russia and is possibly attributable to limitations on seedling establishment and survival due to root desiccation during dry winters changes in nutrient balance and productivity in the lakes as inferred from variations in sediment carbon and nitrogen elemental abundances an

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

a model for radionuclides in sediments influenced by mixing and compaction a model for the activity of radionuclides in sediments has been set up based on the one dimensional advection diffusion equation the model considers sedimentation mixing and compaction observed distributions of deposit feeding organisms and the nature of physical disturbances indicate that a gaussian diffusion coefficient may be appropriate two layer models with constant and gaussian mixing respectively in the upper layer are compared with measured pb 210 profiles for two cores from green bay lake michigan and it is found that the maximal diffusion coefficient d0 in the gaussian model is considerably greater than the constant d value e g d0 4 versus d 0 2 cm2 year if compaction effects are neglected the solution for the gaussian model is based on an approximate power series method compaction can be taken into account by using an exponential sedimentation rate or bulk sediment density by comparing with measured data for a lake ontario core it is seen that compaction alone can give an appreciable flattening of the activity curves near the top layers

terrigenous sediment supply along the chilean continental margin modern regional patterns of texture and composition the regional patterns of texture and composition of modern continental slope and pelagic sediments off chile between 25 s and 43 s reflect the latitudinal segmentation of geological morphological and climatic features of the continental hinterland grain size characteristics are controlled by the grain size of source rocks the weathering regime and mode of sediment input eolian off northern chile vs fluvial further south bulk mineral assemblages reveal a low grade of maturity regional variations are governed by the source rock composition of the different geological terranes and the relative source rock contribution of the coastal range and andes as controlled by the continental hydrology the relative abundance of clay minerals is also predominantly influenced by the source rock composition and partly by continental smectite neoformation latitudinal variations of illite crystallinities along the chilean continental slope and west of the peru chile trench clearly reflect modifications of the weathering regime which correspond to the strong climatic zonation of chile

peruvian sediments as recorders of an evolving hiatus for the last 22 thousand years highlights review of sediment archives from the peruvian margin since the lgm focus on the evolutionary feature of the hiatus found in archives modern analogue for current dominated environments for paleo reconstructions new results for erosional potential of the non linear internal waves nliws abstract the peruvian continental margin is characterized by the presence of one of the strongest and most distinct oxygen minimum zones omzs in today s oceans therefore it has long been in the focus of oceanographic and geological investigations observations indicate that omzs are expanding in relation with currently changing climate to advance understanding of the temporal evolution of omzs and climate change complete paleoceanographic and palaeoclimatological reconstructions are needed however the development of paleoenvironmental scenarios for the period since the last glacial maximum at this region was hampered by a ubiquitous hiatus and short term interruptions of the stratigraphical record in the present study we combined the stratigraphical information from 31 sediment cores from the peruvian margin located between 3 and 18 s and water depths of 90 to 1300 m within and below today s omz in order to determine the extent of the hiatus and assess the responsible mechanisms a widespread unconformity and related erosional features omission surfaces and phosphorites were observed in sediment cores from the area south of 7 s depicting a prograding feature on the continental slope from south to north during the deglaciation combining recent oceanographic and sedimentological observations it is inferred that tide topography interaction and resulting non linear internal waves nliws shape the slope by erosion carry sediments upslope or downslope and leave widespread phosphoritic lag sediments while the peru chile undercurrent pcuc transports the resuspended sediments southward causing non deposition this exceptional sedimentary regime makes the peruvian margin a modern analogue for such environments overall our compilation of downcore records showed that enhanced bottom currents due to tide topography interaction were progressively evolving and affected a wider area with the onset of the last deglaciation elevated tidal amplitudes and variability of mid depth water masses i e density changes and hydrodynamics in relation with changing climate were potential reasons of this evolving feature of erosion and reworking additionally erosion and non deposition was observed widest and even was encountered on the continental shelf during the early holocene potentially indicating a strong phase of the pcuc mirroring today s el nino like conditions

bioturbation coefficients of deep sea sediments from the peru basin determined by gamma spectrometry of 210pbexc abstract in the investigation of the impact of deep sea mining on the ecosystem the radioactive disequilibrium between 210pb and 226ra was studied in 16 surface sediment cores from the peru basin to obtain a quantitative measure of bioturbation gamma spectrometry was used as a fast non destructive simultaneous assay of 210pb and 226ra buried manganese nodules and geochemical anomalies affect the depth profiles of these two radioisotopes the calculated bioturbation coefficients show a high lateral variability this made it impossible to detect a significant difference in bioturbation between two different study areas

turbidite paleoseismology along the active continental margin of chile feasible or not abstract much progress has been made in estimating recurrence intervals of great and giant subduction earthquakes using terrestrial lacustrine and marine paleoseismic archives recent detailed records suggest these earthquakes may have variable recurrence periods and magnitudes forming supercycles understanding seismic supercycles requires long paleoseismic archives that record timing and magnitude of such events turbidite paleoseismic archives may potentially extend past earthquake records to the pleistocene and can thus complement commonly shorter term terrestrial archives however in order to unambiguously establish recurring seismicity as a trigger mechanism for turbidity currents synchronous deposition of turbidites in widely spaced isolated depocenters has to be ascertained furthermore characteristics that predispose a seismically active continental margin to turbidite paleoseismology and the correct sample site selection have to be taken into account here we analyze 8 marine sediment cores along 950 km of the chile margin to test for the feasibility of compiling detailed and continuous paleoseismic records based on turbidites our results suggest that the deposition of areally widespread synchronous turbidites triggered by seismicity is largely controlled by sediment supply and hence the climatic and geomorphic conditions of the adjacent subaerial setting the feasibility of compiling a turbidite paleoseismic record depends on the delicate balance between sufficient sediment supply providing material to fail frequently during seismic shaking and sufficiently low sedimentation rates to allow for coeval accumulation of planktonic foraminifera for high resolution radiocarbon dating we conclude that offshore northern central chile 29 32 5 s holocene turbidite paleoseismology is not feasible because sediment supply from the semi arid mainland is low and almost no holocene turbidity current deposits are found in the cores in contrast in the humid region between 36 and 38 s frequent holocene turbidite deposition may generally correspond to paleoseismic events however high terrigenous sedimentation rates prevent high resolution radiocarbon dating the climatic transition region between 32 5 and 36 s appears to be best suited for turbidite paleoseismology

relationships between mineral surfaces and organic carbon concentrations in soils and sediments abstract relationships between mineral specific surface area and organic carbon oc concentration are examined for sediments and soil a horizons from throughout the world i found published elsewhere that continental shelf sediments from many different regions exhibit downcore loss of oc to a refractory background level which shows a consistent relationship with mineral surface area slope 0 86 mg m 2 oc this trend is equivalent to a monolayer of organic matter over all surfaces and is termed the monolayer equivalent me level sediments and soils from other environments are compared to this empirically derived relationship several continental slope areas show extension of this relationship to considerable depth marked excesses of oc above this trend which persist downcore were found in sediments with high carbonate mineral content or slope sediments with low dissolved oxygen concentrations in the overlying water column about half of the soils examined also adhered to this relationship while soils with high carbonate content low ph or poor drainage showed oc concentrations higher than the me level oc concentrations below the me level are found in deltaic regions and areas with low organic matter delivery such as the deep sea or arid soils the nature of mineral surfaces was examined using n2 adsorption desorption isotherms and most surface area was found to be present as pores with

velocity variations and water content estimated from multi offset ground penetrating radar the common midpoint cmp processing technique has been shown to be effective in improving the results of ground penetrating radar gpr profiling when radar data are collected with the cmp multioffset geometry stacking increases the signal to noise ratio of subsurface radar reflections and results in an improved subsurface image an important aspect of cmp processing is normal moveout velocity analysis our objectives are to show the effect of multiple velocity analyses on the stacked radar image and particularly to demonstrate that this velocity information can also be used to determine subsurface water content most gpr surveys are very limited in spatial extent and assume that within the survey range radar velocity structure in the shallow subsurface can be adequately approximated by a single velocity function in data processing in this study we show that variation in radar velocity can be quite significant and that the stacked profile improves as the number of velocity analysis locations is increased interval velocities can be calculated from the normal moveout velocities derived in the cmp velocity analysis with some reasonable assumptions about subsurface conditions necessary for radar propagation interval velocity can be converted to an estimate of volumetric water content therefore by collecting gpr data in the multioffset cmp geometry not only is the radar profile improved but it also allows for an interpretation of subsurface variation in water content we show the application of these techniques to multioffset gpr data from the chalk river test area operated by atomic energy of canada limited

early diagenesis of organic matter in peru continental margin sediments phosphorite precipitation abstract pore water chemistry total dissolved co 2 nh 4 no 3 no 2 po 4 si oh 4 ca mg fe mn so 4 h 2 s and f and titration alkalinity solid phase chemistry c org p org c tot n tot f si opal and s ii and sediment characteristics porosity dry bulk density and formation factors were determined on a centimeter scale spacing in the upper 20 40 cm of sediments under intense upwelling areas on the peru continental shelf these data demonstrate that carbonate fluorapatite cfa is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content up to 20 c org very high porosity 0 96 ml cm 3 and very low dry bulk density 3 dissolved phosphate concentrations at the sediment water interface range from 20 to 100 m orders of magnitude higher than bottom water concentrations and much higher than predicted from regeneration of organic matter the mechanism of this interfacial phosphate release is unclear but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments fluoride is incorporated into cfa by diffusion from the overlying seawater and carbonate ions are provided from pore water alkalinity magnesium concentrations in this reaction zone are not significantly different from those of seawater suggesting that magnesium depletion is not a necessary prerequisite for cfa precipitation the environment of precipitation is interface linked rather than driven by organic diagenesis of phosphorus deeper in the sediment most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region but almost all show the precipitation signature near the interface this interface linked early diagenetic porewater environment for the precipitation of cfa explains many of the geochemical characteristics of phosphorites and provides a testable model to compare the modern phosphogenic analog with ancient phosphorite deposits two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites