observations and geologic significance of marine snow in a shallow water partially enclosed marine embayment because of their fragile nature marine snow sized aggregates aggregates 0 5 mm in longest dimension have been generally overlooked in shallow water environments we report in situ observations and measurements in cape lookout bight north carolina that indicate that marine snow is probably always present and usually abundant underwater photographs show that over a period of hours marine snow varies in size from 8 to 71 10 5 ml and in abundance from 291 to 489 l 1 but that such variations in size and abundance are not obviously related to tide total suspended sediment concentration or current speeds in the 10 to 20 cm s 1 range photographs and concurrent transmissometer records suggest that variations in size shape and abundance of marine snow may be sufficiently great that particulates do not remain optically constant and thus affect beam transmission irrespective of total suspended sediment concentration levels marine snow is significant geologically in that it has high settling rates 50 to 200 m per day and may be the package in which much of the vertical mass flux occurs if so it offers an explanation for the high accumulation rates observed in coastal and estuarine fluid mud deposits

cold water coral habitats of rockall and porcupine bank ne atlantic ocean sedimentary facies and benthic foraminiferal assemblages the extent of the cold water coral mounds in the modern ocean basins has been recently revealed by new state of the art equipment however not much is known about their geological extent or development through time in the facies model presented here seven different types of seabed substrate are distinguished which may be used for reconstruction of fossil coral habitats the studied substrates include off mound settings foram sands hardgrounds dead coral debris and substrates characterized by a variable density of living coral framework whereas sediment characteristics only provide a basis for distinguishing on and off mound habitats and the loci of most prolific coral growth benthic foraminiferal assemblages are the key to identifying different mound substrates in more detail specific foraminiferal assemblages are distinguished that are characteristic of these specific environments assemblages from off mound settings are dominated by attached epifaunal species such as cibicides refulgens and cibicides variabilis the attached epibenthic species discanomalina coronata is also common in off mound sediments but it is most abundant where hardgrounds have formed in contrast the settings with coral debris or living corals attract shallow infaunal species that are associated with more fine grained soft sediments the typical living coral assemblage is composed of cassidulina obtusa bulimina marginata and cassidulina laevigata the abundance of these species shows an almost linear increase with the density of the living coral cover the benthic foraminifera encountered from off mound to top mound settings appear to represent a gradient of decreasing current intensity and availability of suspended food particles and increasing availability of organic matter associated with fine grained sediment trapped in between coral framework

tsunami generation by a rapid entrance of pyroclastic flow into the sea during the 1883 krakatau eruption indonesia 1 the 1883 eruption of krakatau volcano in indonesia was one of the most explosive volcanic events in history it was a marine caldera forming eruption that resulted in voluminous ignimbrite deposits and huge tsunamis we have used numerical simulations to investigate three major mechanisms for tsunami generation caldera collapse phreatomagmatic explosion and pyroclastic flow and have constrained the source parameters computed tsunami characteristics for each hypothesis are compared with observations at locations along the coasts of the sunda strait where tsunami data were obtained immediately after the eruption for the pyroclastic flow hypothesis two types of two layer shallow water models dense and light type models were used under different initial conditions pyroclastic flows are erupted from a circular source following a sine function that assumes waning and waxing phases caldera collapse was performed using a simple piston like plunger model in which collapse duration was assumed to be up to 1 h the phreatomagmatic explosion hypothesis was examined using simple empirical models for underwater explosions in shallow water with explosion energy between 1016 and 1017 j the results show that when a pyroclastic flow with a volume of 5 km3 and an average discharge rate of the order of 107 m3 s enters the sea the computed tsunami heights are broadly consistent with historical records in coastal areas including a tide gauge record at batavia now jakarta we conclude that a pyroclastic flow entering the sea is the most plausible mechanism of the 1883 krakatau tsunami

climate controlled multidecadal variability in north african dust transport to the mediterranean high resolution laser ablation inductively coupled plasma mass spectroscopy scanning of resin embedded laminated sediments is used to detail variability in the composition and magnitude of recent eolian dust deposition in the eastern mediterranean the composition of dust accumulating in the anoxic atalante basin varies in response to the strength of the summer blocking mode of mediterranean climate dust sources located upwind on the westerly airflow are favored during phases of weaker blocking hence stronger summer westerlies this mode is in turn correlated to the pronounced multidecadal oscillation in mediterranean sea surface temperature related to the atlantic multidecadal oscillation suggesting that coupled ocean atmosphere dynamics control the large scale transport of dust in the region variable precipitation in dust source regions may also exert an influence on the relative flux of dust from each source and hence the net composition of dust deposited in the basin persistent oscillations in the composition of deeper sediments indicate that the basin offers a high potential archive for reconstruction of climate controlled variability in dust transport prior to the instrumental era

the composition and emplacement of basaltic magmas produced during the development of continental margin basins the gulf of california mexico the gulf of california is a region of active ensialic basin development and transform faulting legs 64 and 65 of the deep sea drilling project have demonstrated the diversity of basement stratigraphy drilling at sites 474 482 483 and 485 at the mouth of the gulf recovered massive basaltic flows and occasional pillow lavas and sills whereas drilling in the central part of the gulf in the guaymas basin recovered a sequence of sediments and massive doleritic sills very high sedimentation rates over 1000 m ma are characteristic of the guaymas basin and prevent extrusion of the basaltic magma onto the seafloor thus resulting in at least partial intercalation of oceanic layers 1 and 2 such a process of ocean crust formation could be locally important during the early stages of ocean and marginal basin development when sedimentation rates may be very high over 200 samples of basalts and dolerites from the gulf of california have been analysed by x ray fluorescence and neutron activation techniques basalts from the mouth of the gulf are tholeiitic and contain very low abundances of the more hygromagmatophile more hyg elements k rb ba th ta nb and light ree relative to the hyg elements y zr ti and heavy ree thus resembling depleted n type morb from elsewhere along the e pacific rise epr dolerites from the guaymas basin also have a tholeiitic chemistry and some epr basalt characteristics e g la n sm n

the relative mobility of natural th pb and po and fallout pu am cs radionuclides in the coastal marine environment results from model ecosystems merl and narragansett bay the relative mobility of nuclides of pb th pu and cs which are widely used as geochemical tracers for sedimentation and bioturbation was investigated in artificial microcosm tanks merl and in narragansett bay their mobility was characterized by their removal rates from the water column their affinity toward particles and their degree of penetration into the surface sediments pb th and pu transport was controlled predominantly by the affinity of these elements to particles and the transport parameters of the particles themselves i e sediment resuspension and mixing rates because of its low distribution coefficient transport of cs was controlled by molecular diffusion through pore water in the winter while in summer cs transport was enhanced due to bioturbation the increase with depth of the cspu ratio in core profiles of merl and narragansett bay sediments is thus caused primarily by the higher mobility of cs

interaction of faults and perturbation of slip influence of anisotropic stress states in the presence of fault friction and comparison between wallace bott and 3d distinct element models abstract two decades after their birth the validity of fault slip inversion methods is still strongly debated these methods are based upon a very simplified mechanical background the wallace bott hypothesis following previous studies the 3d distinct element method 3dec software is used to explore the effect of varying stress anisotropy i e the shape ratio on slip perturbation along pairs of faults two end member configurations are modelled in taking into account fault friction and internal deformation of faulted blocks the first model deals with a relatively simple case where two nonintersecting conjugate normal faults are reactivated in an oblique normal stress regime the second one simulates an extreme situation where two perpendicular intersecting faults are submitted to oblique extension the average direction of fault slip predicted by 3dec models is compared to the corresponding slip predicted by the simplified wallace bott model for the two simulated cases it is shown that results from 3dec and wallace bott models are mutually consistent and argue for the validity of fault slip data inversion methods consistency remains even if slip is significantly deviated near the intersection line of faults these deviations depend on the degree of anisotropy of applied stresses in presence of fault friction furthermore modelling results suggest that for intersecting faults with convergent slip directions consideration of fault friction in the models leads to reduction of slip perturbation in other words modelling results lead to the nonintuitive conclusion that the validity of the simplified wallace bott model is strengthened when 3dec model s complexity i e the number of parameters incorporated increases

particle mixing rates in sediments of the northeast tropical atlantic evidence from 210pbxs 137cs 228thxs and 234thxs downcore distributions particle mixing rates were estimated from distribution of 137cs and excess activities of 210pb 228th and 234th measured in nine sediment cores taken from the northeast tropical atlantic i e at the three sites of the french eumeli eutrophic mesotrophic and oligotrophic programme at the oligotrophic site activities of 137cs and excess 210pb decrease smoothly with depth on the other hand at the mesotrophic and eutrophic sites 210pbxs and 137cs profiles suggest a mixing process with three different regimes with subsurface sediments being mixed more rapidly than those at the surface bioturbation rates were found to be slowest at the oligotrophic site intermediate at the mesotrophic site and fastest at the eutrophic site these mixing intensities appear closely linked to benthic fauna abundance organic carbon flux to the sediments and primary production in overlying surface waters the use of a multitracer approach for studying sediment particle reworking has allowed bioturbation rates to be better constrained and an assessment of whether radionuclide distributions in surface sediments are in steady state for only one core from the mesotrophic site were surface sediments not in steady state perhaps because of the occurrence of a benthic animal i e a xenophyophore at the surface of this core

estimates of particle flux and reworking at the deep sea floor using234th 238u disequilibrium abstract because of high specific activities of excess234th t1 2 24 1 days on suspended particles in the deep sea this nuclide is potentially an extremely sensitive indicator of particle inputs and dynamics at the seafloor measurements were made at two deep sea sites in order to examine this potential inventories of excess234th at a low current hemipelagic mud site 3990 m in the panama basin were 1 5 september 81 and 2 5 june 82 dpm cm2 the steady state fluxes to the seafloor calculated from these inventories are in rough agreement with radionuclide fluxes measured in sediment traps small scale 100m spatial variability in inventories implies biologically significant heterogeneity in particle inputs sediment from the continental rise site in the northwest atlantic 2800 m a site with higher current velocities than the panama basin had an inventory of 1 9dpm cm2 this inventory is also in rough agreement with predictions made on the basis of nearby sediment trap data particle mixing coefficients of 30cm2 yr calculated at the pacific and atlantic sites are similar to those in shallow water deposits but could reflect disturbance during handling based on210pb data from the panama basin sediment from below 6cm is mixed at a rate 10 slower than the near surface sediment to a depth of at least 20 cm agreement between234th predicted mixing rates at the panama basin site with210pb profiles and in situ experiments with glass bead tracers implies that these rates are real although the diffusion of dissolved234th into deep sea sediments complicates interpretations 234thxs distributions in bottom sediments offer a useful adjunct to sediment traps for investigation of particle dynamics near the deep sea floor

laboratory experiments of tsunami runup on a circular island laboratory experiments of a 7 2 m diameter conical island were conducted to study three dimensional tsunami runup the 62 5 cm tall island had 1 on 4 side slopes and was positioned in the center of a 30 m wide by 25 m long flat bottom basin solitary waves with height to depth ratios ranging from 0 05 to 0 20 and source lengths ranging from 0 30 to 7 14 island diameters were tested in water depths of 32 and 42 cm twenty seven capacitance wave gages were used to measure surface wave elevations at incident and four radial transects on the island slope maximum vertical runup measurements were made at 20 locations around the perimeter of the island using rod and transit a new runup gage was located on the back or lee side of the island to record runup time series

physical processes and fine grained sediment dynamics coast of surinam south america abstract the prograding holocene mud wedge between the amazon and orinoco rivers in the trade wind belt of northeastern south america provides a modern day example of muds accumulating under moderate wave energy conditions gigantic shore attached mudbanks 10 km 20 km composed partly of thixotropic fluid mud gel front this coast every 30 60 km to form a buffer to wave attack and a temporary storage for fine grained sediments this mesotidal coast tide range 2 0 m with gentle offshore slope 0 0006 allows the exposure twice a day of extensive tidal flat deposits which are backed by mangrove swamps on a well developed chenier plain complex field experiments were conducted in surinam du ing 1975 and 1977 to provide new information on process form relationships in this interesting but unusual muddy environment simultaneous measurements of waves currents tide elevation suspended sediment concentration and variations in mud density show that soft intertidal and subtidal muds are suspended at both tide and wave frequency suspended sediment concentrations typically exceed 1 000 mg l at the surface as incoming solitary like waves partially disperse fluid mud into overlying water on a falling or rising tide redeposition of mud may occur near time of high tide the strong attenuation of shallow water waves by these muds provides conditions that are favorable for further sedimentation high concentrations of suspended fluid mud together with solitary like waves from the northeast throughout the year can lead to extraordinarily high net sediment transport rates in the nearshore zone calculations based on solitary wave theory and on data obtained from this study indicate that 15 65 106 m3 of mud can move along shore each year without involving breaking waves the concept of radiation stress and a nearshore circulation cell or bedload transport farther offshore outside the zone of wave dominance wind driven currents and the guiana current combine to transport muds to the northwest consistent with the observed direction of mudflat migration

seasonality variations in the central mediterranean during climate change events in the late holocene abstract holocene rapid climate change rcc events such as the little ice age lia are thought to have influenced average annual temperatures only marginally but to have affected winter temperatures relatively strongly with summer temperatures relatively unaffected reconstructing climate change at a seasonal resolution is crucial to fully capture holocene climate variability mediterranean climate is highly seasonal being influenced by the subtropical high pressure belt in summer and the mid latitude westerlies combined with outbreaks of polar winds in winter we identified events of high and low detrital input to the gulf of taranto central mediterranean sea anticipated to be linked to humid and dry conditions respectively and thereby potentially reflecting seasonal contrasts these events represent the bronze age ba roman humid period rhp medieval climate anomaly mca lia and present day and were selected for the analysis of single specimen globigerinoides ruber white carbonate chemistry mg ca 18o and 13c the dynamic range found for these parameters for the measured single individuals in the most recent interval reflects the present day seasonal contrasts in temperature and precipitation albeit with a bias towards the summer season these results are compared with high resolution 15 years sample sea surface temperature sst and bottom water temperature bwt reconstructions based on the 18o of g ruber white and mg ca of benthic foraminifer hyalinea balthica although the seasonal temperature contrast remains relatively stable significant winter cooling is observed during the ba and lia connections between high latitude climate winter conditions and low latitude climate summer conditions appear not straightforward during rcc events this results in changes in the moisture balance and in shifts in seasonal dominance between rccs during the lia winter like conditions cold and humid prevail throughout the year in contrast winters are dry and cold during the ba and are accompanied by dry and warm summers suggesting year round aridity and a relatively high seasonal temperature contrast this could have had a profound impact on early agriculture in southern italy

tsunami sedimentation associated with the 1923 kamchatka earthquake abstract the kuril kamchatka region is notorious for the occurrence of earthquake tsunamis and historical documents show that they have caused repeatedly considerable damage since the 1750s the great tsunami generated in april 1923 around the northern kamchatka trench flooded the coast of ust kamchatsk depositing a thin sand layer which is traceable up to 3 km or more inland beyond the present coastline local government documents indicate that the 1923 tsunami flooded low lying coastal areas covered by thick snow the unusual process of tsunami run up without loss of tractive load is interpreted to have resulted from the smoothing of fields by the ice covered surface we conclude that the tsunami flooded snowfields and deposited an extensive sheet of sand a mixture of snow and seawater flooded over the area and caused damage to vegetation

catastrophic event recorded among holocene eolianites sidi salem formation se tunisia a high energy deposit cuts through the early holocene eolianites of the sidi salem formation which forms a ridge along the southeastern coast of tunisia the sedimentary structures as well as the paleo altitude and paleo location of the outcrop state for a subaqueous deposition by an unusually large catastrophic event regarding its age and the related uncertainties it could be either an exceptional storm or a landslide or impact triggered tsunami the mega tsunami of the 8000 bp collapse of the valle del bove valley etna volcano could be this event for its matching age and calculated run up height

live and dead benthic foraminiferal faunas from whittard canyon ne atlantic focus on taphonomic processes and paleo environmental applications abstract dead benthic foraminiferal assemblages were studied in the 150 m fraction of 4 5 cm deep sediment levels at 18 stations in the whittard canyon area in june 2007 this sediment layer is composed of fairly recent sediment in both canyon branches the population dynamics such as seasonal response to phytodetritus deposition certainly contribute to differences between live and dead faunas for instance bulimina marginata which is usually considered as an opportunistic species is over represented in the dead assemblage the fragility of the tests of some species can explain their total absence in the thanatocoenoses this concerns many organic cemented arenaceous tests miliolid tests sensitive to dissolution and perforate taxa with thin tests furthermore transport e g sediment gravity flows active in both canyon branches leads to an increasing relative contribution of allochthonous individuals originating from outer shelf and upper canyon sites towards the deeper canyon stations consequently the dead faunas do no reflect local environmental conditions the high abundance of transported dead foraminifera in both canyon branches leads to important biases in the foraminiferal assemblage composition but may also significantly bias the interpretation of 13 c 18 o trace elements and 14 c concentration in foraminiferal shells it may therefore strongly complicate the reconstruction of environmental parameters such as bottom water temperature or exported paleoproductivity and radiocarbon dating of the foraminiferal assemblages therefore in both canyon axes the use of dead foraminiferal faunas to reconstruct paleoenvironmental in situ conditions is precluded however the study of dead assemblages in the canyon branches in particular the quantity of allochthonous foraminifera can give important clues about the downslope sedimentary dynamics on both open slopes despite taphonomic test destruction and biological processes population dynamics the distribution and the composition of the live fauna resemble those of the dead assemblage in these areas dead foraminiferal faunas include much less material derived from downslope transport consequently on the open slope dead assemblages appear to better reflect local conditions therefore the ecological information obtained from fossil open slope samples can be more reliably used to reconstruct paleoenvironmental conditions

the interaction of plankton and suspended sediment in fjords abstract the interaction of plankton with suspended sediment affects both the plankton and the sediment trace metals organics and nutrients that are adsorbed onto suspended particles affect the supply of these materials to phytoplankton and zooplankton ingestion of suspended sediment by zooplankton exposes the particulate minerals to physical and chemical breakdown occasionally strong enough to produce changes in particle mineralogy fecal pellets produced from undigested material package fine particulate material and thus increase their rate of sedimentation this is particularly important in fjords an aqueous environment that is dominated by the vertical flux of suspended sediment pelletization also allows the transport of undigested food to greater depths providing an important source of organic material to benthic sediments and food to deep water organisms

coupling bedform roughness and sediment grain size sorting in modelling of tidal inlet incision abstract a key problem in the decadal morphodynamic modelling of tidal inlet system is on the evolution of the inlet channels especially the unrealistic channel incision the present study attempts to couple two processes including the bedform roughness and sediment grain size sorting in the two dimensional depth averaged process based model to solve the problem based on the comparison of the modelling results and relevant field observations in the dutch wadden sea it is suggested that bedform roughness height predictor is a useful tool for determining spatial and temporal heterogeneous bed frictions within tidal channels bedform roughness is dominated by dune roughness in order to represent the memory of old bedforms a relaxation time method was implemented the corresponding large relaxation time 2 m2 tidal periods smooths the tidal variations of dune roughness and makes it respond to hydrodynamic changes on a longer time scale when decadal morphological modelling is carried out the model performance can be significantly improved by introducing either bedform dune roughness predictor or sediment sorting processes the mechanisms are twofold first in the deep channels where flow velocities are high large dunes develop and cause large bed drag coefficients second coarser bed sediments within the channel area induced by sorting prevent the channel incision if both effects are coupled in the morphodynamic modelling the inlet channel incision is further controlled which is not just a result of the linear superposition of both effects because sorting can further promote the development of dunes within the deep channels

origin of inner shelf mud deposit in the southeastern yellow sea huksan mud belt abstract a variety of previous sedimentological results together with newly obtained hydrodynamic data are summarized and reinterpreted with respect to the most likely origin of the huksan mud belt hmb in the southeastern yellow sea the hmb consists of two mud units that have similar grain texture and clay mineralogy but can be differentiated on seismic profiles because the lower unit is generally harder than the watery upper unit the hydrographic measurements together with satellite imagery clearly indicate that the suspended plume covering the hmb originates from the west coast of korea the suspended plume becomes enhanced by winter monsoon winds beginning in late fall most of the studies of clay mineralogy geochemistry and isotherm distribution also suggest that the hmb has been derived from the west coast of korea particularly from the keum river an approximate evaluation of the depositional time for the hmb based on its dimensions and the discharge rate of the keum river suggests a time duration of the order of 14 000 years hydrodynamic measurements across two transects over the northernmost hmb reveal that suspended matter travels southwest toward the main body of the hmb in a well constrained corridor ultimately connected with the keum river time series 12 5 h hydrodynamic measurements at a site over the hmb suggest that the winter season suspended plume carries concentrations of suspended matter one to two orders of magnitude higher than those of the summer silt grains of 5 6 well sorted through numerous resuspension events settle out onto the hmb forming distinctive silt laminae alternating with clay rich laminae

recent sedimentation and sediment accumulation rates of the ba lat prodelta red river vietnam abstract the ba lat river is the major distributary of the red river system in north vietnam to assess the recent to subrecent depositional processes in the ba lat prodelta a detailed sediment analysis was conducted bottom samples were collected during two field surveys one in the dry season winter and one in the wet season summer a steep frontal prodelta slope is characterized by very rapid sedimentation tens of cm per year of muddy sediments under influence of the turbid river plume beyond direct influence of the river plume the bottom slope decreases and bottom transport by the prevailing southward directed currents becomes important coarse grained tempestites alternate with the dominating muddy sediments downcore changes in the 234 th activities indicate that the subaqueous delta progrades to the southwest with erosion and reworking of older sediments occurring north of the present outlet the southwestward progradation is also encountered in the trend of 210 pb activities indicating that this process has continued for at least 100 years avulsion of the ba lat outlet in 1973 has led to a decrease in sedimentation rates north of the ba lat outlet

development of stratigraphy and sediment distribution in the northeastern yellow sea during holocene sea level rise abstract a succession of holocene deposits in the northeastern yellow sea were interpreted in a sequence stratigraphic context and sedimentology of each deposit was characterized based on analyses of high resolution seismic profiles and sediment cores taken along a transect thin 3 m transgressive sediments that accumulated through shoreface erosion during the rapid sea level rise in the early holocene overlie a subaerially eroded low gradient late pleistocene platform on the present day inner shelf region cores reveal marine sands over tidal estuarine sandy muds with an intervening rather indistinct ravinement surface in the deepest shelf area these early holocene tidal estuarine deposits remain exposed at the seabottom in the mid o late holocene two contrasting deposits of the highstand type deltaic clayey mud and tidal sand ridges began to accumulate in response to slower rates of sea level rise a series of tidal sand ridges in the nearshore area migrated offshore over the transgressive sand sheet and a deltaic watery mud prograded discordantly over consolidated tidal estuarine deposits in the central shelf the transgressive facies relationships present a model for macrotidal epicontinental sea settings subject to low wave energy and reduced sediment supply

climate of the past 2500 years in the gulf of taranto central mediterranean sea a high resolution climate reconstruction based on δ18o and δ13c of globigerinoides ruber white we present a high resolution isotope stratigraphy based on globigerinoides ruber white over the past 2500 years in the gulf of taranto central mediterranean g ruber white reflects summer conditions in the gulf of taranto but is influenced by two major surface water masses the western adriatic current wac and the ionian surface water isw and their variations on a decadal to multicentennial scale our analysis of the 13c and 18o of g ruber white allows the distinction of several climatic periods the roman warm period rwp 450 0 bc with relatively wet and warm conditions and a higher influence of the wac the roman classical period rcp ad 1 200 characterized by salinity increase resulting from circulation changes the dark ages cold period dcp ad 500 750 where wetter conditions in the gulf of taranto region are coherent with an increase dominance of the wac the medieval warm period mwp with wet and warm conditions in the first and a gradual drying in the second half and finally the transition from the mwp to the little ice age lia which is characterized by continuing dry conditions

solar forcing of nile discharge and sapropel s1 formation in the early to middle holocene eastern mediterranean we present high resolution records for oxygen isotopes of the planktic foraminifer globigerinoides ruber 18oruber and bulk sediment inorganic geochemistry for holocene age sediments from the southeast mediterranean our 18oruber record appears to be dominated by nile discharge rather than basin scale salinity temperature changes nile discharge was enhanced in the early to middle holocene relative to today the timing of the long term maximum in nile discharge during the early holocene corresponds to the timing of maximum intensity of the indian ocean influenced southwest indian summer monsoon sim this coincidence suggests a major influence of an indian ocean moisture source on nile discharge in the early to middle holocene while presently the atlantic ocean is the main moisture source nile discharge was highly variable on multicentennial time scale during the early to middle holocene being strongly influenced by variable solar activity this solar driven variability is also recorded in contemporaneous sim records however not observed in an atlantic ocean derived west african summer monsoon record from the holocene this supports the hypothesis that the indian ocean moisture source predominantly controlled nile discharge at that time solar driven variability in nile discharge also influenced paleoenvironmental conditions in the eastern mediterranean bulk sediment ba al and v al used as indicators for export productivity and redox conditions respectively varied both in response to solar forcing on multicentennial time scales we suggest that changes in nile discharge on these time scales have been concordant with nutrient inputs to and shallow ventilation of the eastern mediterranean

the influence of the sunda strait opening on paleoenvironmental changes in the eastern indian ocean abstract with sea level rise in the early holocene the warm and low salinity sea water from the java sea was transported into the eastern indian ocean after the opening of the sunda strait however the impact of this process on sediment provenance and paleoproductivity is rarely known in this study we analyzed the grain size sr nd pb isotopic compositions and biogenic elements of core cj01 185 1538 m water depth in the eastern indian ocean off the sunda strait our new results reveal a large volcanic eruption in the west of java at 2 1 ka and the krakatau eruption at 1883 ce on the basis of the pb isotopic compositions 87 sr 86 sr ratios and e nd values we infer that sediments from core cj01 185 were derived primarily from java island there is a distinct change in sr nd pb isotopic compositions of the sediments from the last glacial period to the holocene indicating less radiogenic nd isotopes from the java sea into the eastern indian ocean after the opening of the sunda strait at 10 ka moreover the sedimentation rate increased significantly from 6 5 cm kyr 1 during the last glacial period to 20 cm kyr 1 in the holocene the input of additional terrigenous nutrients from the java sea induced paleoproductivity with higher toc and tn concentrations after the opening of the sunda strait our results thus suggest that the paleoproductivity was mainly influenced by terrigenous materials input in the holocene other than southeast monsoon or upwelling in the last glacial period

sediment distribution dispersal and budget in the yellow sea abstract information on the surface sediment distribution in the yellow sea is newly compiled based on all available data produced by chinese and korean workers and is used to refine the dispersal patterns and budget of sediments derived from the adjoining landmass the central yellow sea is largely covered with fine grained sediments originating from the huanghe river 2 2 10 8 t yr about 20 of the total discharge thick sediment accumulation exceeding 5 mm yr occurs in the gulf of bohai and around the shandong peninsula about two thirds of the total huanghe river discharge the old huanghe delta suffers from reworking by strong tides and waves and forms a mud patch southwest of cheju island accumulation rate 2 10 7 t yr more than half of the sediments derived from the changjiang river are deposited along the coast of the east china sea the remainder accumulate on the inner shelf off the river mouth in the southeastern yellow sea the keum river dominates sediment discharge forming a holocene mud belt along the southwestern coast of korea accumulation rate 5 10 6 t yr turbid water plumes occur nearshore throughout the year and their suspended sediments are transported along the tip of the peninsula to the western coastal embayments in the south sea the nakdong river discharge of 1 10 7 t yr is responsible for the eastern nearshore mud of the south sea relict sands occur in the northern part of the yellow sea in the northern east china sea and in the korea strait

origin and transport of trace metals deposited in the canyons off lisboa and adjacent slopes portuguese margin in the last century abstract submarine canyons play an important role in the transfer of contaminated sediments from shelf areas to the deeper ocean to evaluate the importance of submarine canyons adjacent to the tagus and sado estuaries portuguese margin as sediment pathway major and trace elements 210 pb radionuclides organic carbon calcium carbonate and grain size were analyzed in fifteen short sediment cores from the cascais and lisboa setubal submarine canyons and neighbor slopes at the estremadura spur and off sines mass accumulation rates mar vary between 0 02 and 0 40 g cm 2 y 1 with the highest values in the upper cascais and lisboa canyons mercury and pb enrichment factors exceed 2 and show a continuously increasing trend since 1950 ad in the upper sections of the cascais canyon and in the lisboa setubal canyon system implying an anthropogenic source mercury and pb anthropogenic inventories also present highest values in the canyon heads which is consistent with its proximity to the tagus and sado river mouths to a lesser extent the estremadura and sines slopes and the deeper sections of the canyons also have slightly increasing hg and pb enrichment factor trends towards the present day for these areas with a major influence of pelagic sedimentation we infer atmospheric transport as a complementary source of contaminants therefore our data suggest that although canyons are preferential conduits to transport sediments to the deep sea when compared to the slopes hg and pb derived from human activities have reached both domains with different intensities down to a depth of 2000 mwd

dispersal of fine grained sediments in the southeastern yellow sea a steady state model a large portion of the yellow sea is floored by fine grained clastics derived largely from the hwangho and yangtze rivers in the southeastern yellow sea however coarse grained sediments prevail derived probably from the short and steep korean rivers farther east the coarse grained sediments contain substantial amounts of fine fractions near the keum estuary detrital clays such as kaolinite and chlorite are abundant in the free fractions and this trend extends for about 120 km both toward the northwest and the southwest illite appears to be dominant in the rest of the yellow sea the data suggest that the bulk of fine grained sediments in the southeastern yellow sea originates from the keum river the sediments are subsequently transported by prevailing nearshore currents both northwestward during summer and southwestward in winter the tidal currents may also play a role the close correspondance between the oceanographic data and the mineralogic evidence suggests that the dispersal of fine grained sediments in the southeastern yellow sea occurs largely under the steady state conditions

compositional data analysis coda as a tool to study the paleo ecology of coccolithophores from coastal neritic settings off central portugal abstract whereas using the species percentages is the standard analytical procedure used to infer species ecological preferences independently of taphonomical effects the closure problem associated with closed number systems and subsequent inconsistency of determining percentages may lead to spurious correlations biased statistical analysis and misleading interpretations to avoid these problems we applied compositional data analysis coda to investigate the paleo ecological preferences and spatial distribution of coccolith assemblages preserved in seafloor sediments using as a case study the central portuguese submarine canyons and adjacent shelf slope areas results from using the isometric log ratio ilr approach from coda are compared with results from using classical analytical methods and further discussed while providing scale invariance and subcompositional coherence coda is revealed to be a consistent statistical tool to infer the paleo ecological preferences of coccolithophores corroborating earlier work based on from percentage determinations results of this study clearly confirmed the coastal neritic distribution of coccoliths from gephyrocapsa oceanica helicosphaera carteri and coronosphaera mediterranea whereas coccoliths from calcidiscus leptoporus umbilicosphaera sibogae umbellosphaera irregularis and rhabdosphaera spp more typically occur offshore differences between canyons and adjacent shelf and slope areas were also confirmed namely the a greater importance of the coastal neritic assemblage possibly resulting from local and persistent nutrient pumping in these areas and b stronger mixing of coccoliths from coastal and oceanic species in upper canyon reaches resulting from the focused coastward advection of more oceanic water masses along their axes unlike the results from both ilr coordinates and the percentage approaches both coccolith concentrations and fluxes showed that spatial trends in which the species ecological inter relationships appear to be masked by taphonomical phenomena especially towards the coast and in the canyons suggesting the two latter approaches are not suitable to perform paleo ecological inferences in more dynamic coastal neritic settings our study suggests that the paleo ecological signal preserved in the studied sediment samples is persistent enough to be revealed by both coda and percentages yet given that coda provides the only statistical solution to coherently draw paleo ecological interpretations from compositional data our recommendation is that coda should always be used to test and validate any ecological signals obtained from percentage distributions

pitfalls of normalization of marine geochemical data using a common divisor abstract normalization of trace element contents of sediment through division by the content of an immobile element usually aluminum is common practice in marine geochemical studies this might appear to be a simple way of correcting for dilution by sedimentary phases barren of a particular trace element for instance carbonates or silica and for comparison with its content in a standard clay or shale the purpose of this paper is to revive the awareness of the pitfalls of this practice by giving numerical examples of the often unexpected results of normalization taking a statistical perspective it is first shown that uncorrelated variables acquire spurious correlations when normalized but normalization can also increase decrease change sign of or even blur the correlations between unmodified variables next a number of realistic scenarios are worked out to show that the correlations between normalized element contents still suffer from the closure effect only in a few simple cases it is possible to extract from the normalized data realistic estimates of trace element contents in distinct sedimentary phases such as organic matter this is ascertained from data on copper contents in sediment from the black sea and arabian sea when the coefficient of variation i e standard deviation divided by the mean of the aluminum data is relatively low and much lower than for the original values of the trace elements comparisons of correlations can equally well or even better be made on the basis of the unmodified values then the comparison of trace element data with their values for standard shales is discussed the inherent problem is that the composition of the commonly used standard shale and consequently the reference values of normalized elements are not necessarily representative of the local or regional sediments in the study area also this method falls short of identifying the processes responsible for enrichment or diminution in trace element contents finally consideration is given to some aspects of a proper use of al normalization

the effect of bioturbation in pelagic sediments lessons from radioactive tracers and planktonic foraminifera in the gulf of aqaba red sea abstract studies of recent environmental perturbations often rely on data derived from marine sedimentary records these records are known to imperfectly inscribe the true sequence of events yet there is large uncertainty regarding the corrections that should be employed to accurately describe the sedimentary history here we show in recent records from the gulf of aqaba red sea how events of the abrupt disappearance of the planktonic foraminifer globigerinoides sacculifer and episodic deposition of the artificial radionuclide 137 cs are significantly altered in the sedimentary record compared to their known past timing instead of the abrupt disappearance of the foraminifera we observe a prolonged decline beginning at core depth equivalent to 30 y prior to its actual disappearance and continuing for decades past the event we further observe asymmetric smoothing of the radionuclide peak utilization of advection diffusion reaction models to reconstruct the original fluxes based on the known absolute timing of the events reveal that it is imperative to use a continuous function to describe bioturbation discretization of bioturbation into mixed and unmixed layers significantly shifts the location of the modeled event when bioturbation is described as a continuously decreasing function of depth the peak of a very short term event smears asymmetrically but remains in the right depth when sudden events repeat while the first spike is still mixed with the upper sediment layer bioturbation unifies adjacent peaks the united peak appears at an intermediate depth that does not necessarily correlate with the timing of the individual events in a third case a long lasting sedimentary event affected by bioturbation the resulting peak is rather weak compared to the actual event and appears deeper in the sediment column than expected based on the termination of the event the model clearly shows that abrupt changes can only endure in the record if a thick sediment layer settled on the sediment water interface at once or if bioturbation rates decreased to very low values for a prolonged period of time in any other case smearing by bioturbation makes an abrupt event appear to have started shortly before the real timing and end long after its true termination

the glacial interglacial transition and holocene environmental changes in sediments from the gulf of taranto central mediterranean abstract an extensive high resolution sedimentological geochemical survey was done using geo acoustics xrf core scans icp aes ams 14c dating and grain size analyses of sediments in 11 cores from the gulf of taranto the southern adriatic sea and the central ionian sea spanning the last 16 cal ka bp comparable results were obtained for cores from the gallipoli shelf eastern gulf of taranto and the southern adriatic sea suggesting that the dominant provenance of gallipoli shelf sediments is from the western adriatic mud belt the 210pb and 14c dated high accumulation rate sediments permit a detailed reconstruction of climate variability over the last 16 cal ka bp although the glacial interglacial transition is generally dry and stable these conditions are interrupted by two phases of increased detrital input during the bolling allerod and the late younger dryas the event during the younger dryas period is characterized by increased sediment inputs from southern italian sources this suggests that run off was higher in southern compared to northern italy at approximately 7 cal ka bp increased detrital input from the adriatic mud belt related to sea level rise and the onset of deep water formation in the adriatic sea is observed and is coincident with the end of sapropel s1 formation in the southern adriatic sea during the mid to late holocene we observed millennial scale events of increased detrital input e g during the roman humid period and of decreased detrital input e g medieval warm period these dry wet spells are consistent with variability in the north atlantic oscillation nao a negative state of the nao and thus a more advanced penetration of the westerlies into the central mediterranean that result in wet conditions in the research area concord with events of high detrital input e g during the roman humid period in contrast a positive state of the nao resulting in dry conditions in the mediterranean dominated during events of rapid climate change such as the medieval warm period and the bronze age

desert flash floods form hyperpycnal flows in the coral rich gulf of aqaba red sea abstract running rivers are very scarce in globally distributed hyperarid and arid coastlines 28 000 km worldwide and it is ephemeral rivers that carry most terrestrial sediment into the sea in these regions however there is very little information regarding the contribution of terrestrial sediment and dynamics of transport of sediment that enter marine basins from these rivers one hyperarid region the gulf of aqaba received an exceptional number of flashflood events during the winter of 2012 2013 the results illustrate for the first time how the high volume of flashflood sediment influences the distribution of coral reefs dwarfs the contribution of airborne dust elevates floodwater densities to produce hyperpycnal flows despite highest ocean salinities and is subsequently transported to the deep basin where it may be preserved as a climate archive

recent sediment transport and deposition in the nazare canyon portuguese continental margin processes pathways and fluxes of sediment transport and deposition in the nazare submarine canyon portuguese continental margin were investigated by water column profiling of suspended particulate matter recording of near bottom currents and suspended particulate matter fluxes with benthic landers and by analysis of surface sediment cores the results show that fine grained suspended sediment from the adjacent shelf is captured in the upper canyon and actively transported through the canyon to the abyssal plain under influence of tidal currents and intermittent sediment gravity flows tidal currents are actively resuspending and transporting sediment in the upper to middle canyon as reflected by high concentration of suspended particles in bottom waters high horizontal and vertical sediment fluxes in the bottom water layer and high sediment accumulation rate on the seabed diminishing strength of tidal currents leads to focussed sediment deposition in the middle canyon further transport of sediments toward the lower canyon takes place predominantly by sediment gravity flows occurring on yearly or longer timescale turbidity currents strong enough to transport sand sized material to the lower canyon occur only on centennial or longer timescales

role of the giant saemangeum dyke in sedimentation at the mouth of an estuarine complex abstract the saemangeum dyke is an enormous offshore structure 33 km long that dams the combined estuary of two rivers on the mid west coast of korea among the numerous environmental issues associated with the dyke construction it has been of special interest whether the tidal flats in the most reentrant area daehangri just outside the beginning part of the dyke will actively grow or not this lies in the center of the arguments about positive negative functions of the dyke field measurements concentrated on hydrodynamics within the bottom boundary layer and sediment transport evaluations were conducted in the coastal areas around the daehangri tidal flats to examine sediment transport and thus source sink relationships of sediments therein deployments of autonomous benthic instruments tisdos during 1 3 weeks indicate that the nearshore sands and muds are transported toward the dyke whereas sands on tidal flats and beaches are transported from the dyke along the shoreline most of the nearshore sediments eventually deposit to form a shallow shoal near the garyuk opening located in the opposite direction to the daehangri tidal flats the rates of sediment transport increase greatly by high waves as compared to those caused by even spring peak tidal currents alone as a result the scheme of sediment transport over the study area clearly rules out the daehangri tidal flats from the newly forming active sinks of the nearshore sediments triggered artificially by the construction of the saemangeum dyke

validation of accumulation rates in teluk banten indonesia from commonly applied 210pb models using the 1883 krakatau tephra as time marker abstract teluk banten is a tropical shallow marine embayment on the north coast of java close to the krakatau volcanic complex the tsunami generated by the 1883 krakatau eruption resulted in the deposition of a tsunamite tephra layer on the bottom of teluk banten the krakatau event layer has been used as a time marker to validate 210 pb geochronological dating models this validation was performed to answer the question why should we believe excess 210 pb derived mass accumulation rates the commonly used models have therefore been applied to 210 pb activity profiles from 25 gravity cores models that have been validated are the constant flux and constant sedimentation cf cs with and without a surface mixed layer the constant initial concentration cic the constant rate of supply crs and the flux balance model after comparison of the mass accumulation rates mars of the different models with the mars obtained from the krakatau layer the following could be concluded firstly activity profiles without a surface mixed layer gave cf cs mars which were on average a factor 1 4 0 3 n 8 too high including a mixing rate of 0 5 0 4 cm 2 yr 1 into the model could explain this overestimation secondly for 210 pb activity profiles with a surface mixed layer the mars were in good comparison 1 0 0 3 n 12 with the mars derived from the krakatau event layer thirdly increased accumulation instead of reworking had to be the main cause of the comparatively thick upper layer of five cores with very high inventories fourthly assuming a variable accumulation rate and applying the cic model and crs model for these five cores the weighted average cic mars were in general more accurate than the crs mar finally the flux balance model which is not often used gave mars that were a factor 1 3 0 2 n 25 too high the advantage of this model is that it is independent of the profile shape the disadvantage is that a reliable and accurate initial activity over longer time scales has to be obtained

seasonal variation of sedimentary processes in a semi enclosed bay hampyong bay korea abstract multi annual sedimentological observations on tidal flat sediments were carried out in hampyong bay southeastern yellow sea to infer the budget of modern muddy sediments in the bay sedimentation rates over a four year period show contrasting types of seasonal sedimentary cycles occurring in the tidal flats within the elongated bay both sides of the bay are largely sheltered from winter waves resulting in surface mud deposition during winter and erosion during summer in contrast tidal flats along the head of the bay are influenced by winter waves resulting in a reversed trend where erosion occurs during winter and deposition during summer tidal flats near the bay mouth however show a sedimentary cycle disrupted by the construction of sea walls undergoing consistent erosion throughout the observational period the shoreline artificially straightened seems to cause tidal currents to bypass the tidal flat and hence to be much stronger these differences in sedimentary cycles suggest the critical importance of the orientation of tidal flats relative to the propagating direction from n nw of the monsoon winter storm waves on the tidal flat sedimentation in the eastern coastal area of the yellow sea the preliminary budget estimation for the tidal flat mud suggests that the tidal flats in hampyong bay are subject to the slight but consistent erosion as a whole

evaluation of tsunami impacts on shallow marine sediments an example from the tsunami caused by the 2003 tokachi oki earthquake northern japan abstract a combined approach of field geology and numerical simulation was conducted for evaluating the tsunami impacts on the shelf sediments the 2003 tokachi oki earthquake m 8 0 that occurred on 25 september 2003 off southeastern hokkaido northern japan generated a locally destructive tsunami maximum run up height of the tsunami waves reached 4 m above sea level in order to estimate the tsunami impacts on shallow marine sediments we compared pre and post tsunami marine sediments in water depths of 38 112 m in terms of grain size sedimentary structure and microfossil content decreases of fine fractions especially finer than very fine sand which led to coarsen the mean grain size were detected in the inner shelf of the northern part of the study area foraminiferal assemblages also changed in the coarsened sediments on the other hand the other shelf sediments largely unchanged or slightly fined we also simulated the tsunami wave velocity and direction and grain size entrained by the modeled tsunami the numerical simulation resulted in that the 2003 tsunami could transport very fine sand in water depths shallower than 45 95 m at the northern part of the study area this is comparable with the actual grain size changes after the tsunami had passed however some storms and tidal currents might also be possible to stir the surface sediments after the pre tsunami survey so we could not conclude that the grain size changes had been caused only by the tsunami nevertheless a combined approach of sampling and modeling was powerful for estimating the tsunami impacts under the sea

manzala lagoon nile delta egypt modern sediment accumulation based on radioactive tracers this study was undertaken to determine whether recent anthropogenic changes in the nile basin have affected the modern rate of sediment accumulation in the nile delta excess 210pb 137cs and 239 240pu were used to develop a sediment chronology for a core from central manzala lagoon the delta sector which has had the highest average rate of sediment accumulation during the holocene to about 0 7 cm year 1 excess 210pb was detected in the top 32 cm of the core yielding an accumulation rate of 1 2 cm year 1 higher than the mean rate for the holocene a high 137cs 239 240pu ratio requires a reactor source possibly chernobyl for these nuclides low concentrations of excess 210pb and weapons fallout nuclides precluded recognition of changes in sediment accumulation rate in manzala lagoon during this century and may limit the use of tracer radionuclides for modern sediment chronology in the nile delta

the tsunamite problem the genetic term tsunamite is used for a potpourri of deposits formed from a wide range of processes overwash surges backwash flows oscillatory flows combined flows soft sediment deformation slides slumps debris flows and turbidity currents related to tsunamis in lacustrine coastal shallow marine and deep marine environments tsunamites exhibit enormous variability of features e g normally graded sand floating mudstone clasts hummocky cross stratification etc these sedimentary features may also be interpreted as deposits of turbidity currents turbidites debris flows debrites or storms tempestites however sedimentary features play a passive role when these same deposits are reinterpreted as tsunamites on the basis of historical evidence for tsunamis and their triggering mechanisms e g earthquakes volcanic explosions landslides and meteorite impacts this bipartite sedimentological vs historical approach which allows here classification of the same deposit as both turbidite and tsunamite has blurred the distinction between shallow marine and deep marine facies a solution to this problem is to classify deposits solely by a descriptive sedimentological approach the notion that tsunami waves can directly deposit sediment in the deep sea is unrealistic because tsunami waves represent transfer of energy and they are sediment starved during tsunamis and major storms submarine canyons serve as the physical link between shallow water and deep water environments for sediment transport tsunami related deposition involves four progressive steps 1 triggering stage offshore 2 tsunami stage incoming waves 3 transformation stage near the coast and 4 depositional stage outgoing sediment flows in this progression deep water deposition can commence only after the demise of incoming tsunami waves due to their transformation into outgoing sediment flows deposits of these sediment flows already have established names e g debrite and turbidite therefore the term tsunamite for these deposits is obsolete

tsunami deposits from major explosive eruptions an example from the 1883 eruption of krakatau inundation of coastal areas by tsunamis during the 1883 eruption of krakatau volcano led to the deposition of unusual pumice enriched deposits fractal analysis of pumice shapes and lithologic characterization of the deposits suggest that the source of the abundant pumiceous material was widespread pumice rafts on the surface of the sunda straits that formed by fallout and pyroclastic flow activity the rafts contained pumices rounded by particle to particle abrasion and were strongly depleted in dense components such as lithics and crystals by differential settling stranding of the floating pumice is inferred to have occurred during the receding phase of tsunamis after they had inundated low lying coastal areas other pumice bearing tsunami deposits contain significant amounts of coral fragments and nonvolcanic beach sediment these units represent redeposition of beach and shallow water sediments that were mixed with varying proportions of primary pyroclastic material the krakatau example illustrates the great diversity of lithofacies that may occur in deposits formed from volcanogenic tsunamis recognition of such deposits in coastal areas near centers of active explosive volcanism may provide an additional criterion with which to assess volcanic hazards

sequence of sedimentation processes caused by the 1992 flores tsunami evidence from babi island sedimentation processes caused by a modern tsunami have been discussed from the point of view of geologic and numerical investigations of the 1992 flores tsunami in indonesia geologic evidence on babi island shows an invasion of two waves of different direction and magnitude which resulted in widespread deposition of marine sand on the north and south southwest shores on the latter coarse and well sorted carbonate sand containing molluscan shells suggests that much more destructive waves swept across the southern coast as compared with the northern coast where the deposit included medium carbonate sand with a silty component a physical explanation for such destructive waves on the southern coast of babi is provided by a numerical simulation of the tsunami generation and propagation the geologic and numerical results indicate that an isolated island surrounded by a circular shoreline or reef edge will be subject to the most destructive waves on the coast on the back side of the island relative to the tsunami source

sea level changes in the tectonically stable malay thai peninsula abstract the malay thai peninsula is part of sundaland a geological region of relative crustal stability therefore the positions of old shorelines of the past 20 000 years or so can be considered to indicate positions of actual past sea levels over 200 shoreline indicators at positions below as well as above present sea level have been radiocarbon dated these dated positions indicate that prior to 6 ka the sea rose from at least 90 m below present sea level at rates that initially amounted to 15 mm year and later became 6 mm year at ca 6 ka the rising sea surpassed its current position and at ca 5 ka it reached 5 m during this maximum marine inundation the peninsula was narrower since the low coastal plains did not yet exist in the period following this maximum transgression the available shoreline data indicate that regional sea level subsided through a series of fluctuations that were characterized by amplitudes of 2 m and periods of about 2000 years the peaks and troughs of the fluctuations became progressively lower the latest peak was at about 1 7 m or 0 7 m above present high tide a few hundred years ago the cause of these fluctuations is not yet known but the trend suggests that in the near future regional sea level may subside at annual rates between 1 5 mm and 2 mm this rate of descent is 25 to 30 of the estimated rate of sea level rise that may result from global warming in other words for the malay thai peninsula the effect of sea level rise on account of manmade greenhouse gases will be partly compensated by actual subsidence of regional sea level

enhanced short term sediment deposition within the nazare canyon north east atlantic abstract in january and may 1999 interface sediments were sampled within the nazare canyon a large submarine canyon that deeply indents the western iberian continental margin ne atlantic at around 39 35n excess 234th profiles were established with high resolution to calculate inventories and bioturbation coefficients a northern transect at 42 n is briefly presented as a reference for the western iberian margin synthesis of these parameters is used to examine short term deposition within the nazare canyon 234thxs was always detected with significant activities on surface in most of the samples along the reference transect and in the adjacent area surface 234th excesses are about 10 20 dpm g 1 in contrast 234thxs reaches very high levels up to 170 dpm g 1 in the canyon there is a large range of variability in inventories and bioturbation rates in relation with depth and location these results show a preferential deposition in the canyon and focus in the upper and middle part of the canyon on a monthly time scale the nazare canyon appears as a significant locus of sedimentation for the western iberian margin

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

osl over dispersion a pilot study for the characterisation of extreme events in the shallow marine realm abstract identification of extreme events in the sedimentary record relies on the correct characterisation of the deposit by means of multiple parameters and different diagnostic criteria multiple proxies based on well tested geological biological and chemical analyses have been used to distinguish tsunami layers from other marine extreme events however few proxies distinguish or compare the degree of sedimentary chaos of an event relative to background sediments and between other extreme events in this pilot study the potential of optically stimulated luminescence osl normally used as a dating method is demonstrated and a new potential sedimentological proxy is proposed when analysing in depth the osl signal from single grain measurements to distinguish between underwater deposits derived from marine extreme events embedded in the texturally and compositionally homogeneous shallow shelf archive of the eastern mediterranean newly and previously collected sediment samples from underwater excavations and a sediment core offshore caesarea maritima israel were used in this experiment each sample was associated with either tsunami storm or fair weather normal marine conditions based on multiple proxies in this study single grain over dispersion sg od values and ranges are used as a potentially novel way to quantify the degree of sedimentary chaos thus the degree of scatter of the dose distribution as a function of the efficiency of exposure to sunlight zeroing of the quartz grains entrained during transport and deposition given that turbidity of a fluid should be associated with lower light penetration and higher energy flow with greater sediment density as can occur in tsunamis relative to storms these conditions should be reflected in variations in single grain over dispersion values hence identifying luminescence distribution patterns related to known depositional conditions this quantification is coupled with detailed statistical analysis of the resulting single grain equivalent dose distributions minimally used in osl dating three types of underwater deposits were categorised based on three distribution typologies to which preliminary conservative single grain over dispersion ranges were assigned 60 for tsunami related deposits showing asymmetric distributions with strong positive skewness this new tool provides a means to study offshore extreme marine events without potential dismissal of other identification criteria and proxies based on these results single grain over dispersion osl could be considered as a potential new sedimentological proxy for identification comparison and characterisation of marine derived extreme events in the shallow shelf such as tsunami deposits as it is intrinsic to the sediment grain and the degree of sedimentary chaos of the event itself

a holocene tsunami deposit in eastern scotland a thin regionally extensive laterally persistent sand layer identified within the holocene coastal sequences of eastern scotland dated to 7000 years bp is suggested to be a tsunami deposit the likely source of the tsunami wave is the earthquake induced second storegga slide on the norwegian continental slope at least 750 km northeast of the deposit

distribution of suspended sediment in the korea strait and southeastern yellow sea onset of winter monsoons abstract high energy conditions in the yellow sea begin each year with the onset of monsoon winds in late october these transitional season surges of cold air initiate sediment resuspension vertical mixing of suspended sediments and a wind driven coastal current that flows to the south during the summer to winter transition suspended sediment concentrations in the southeastern yellow sea range from 5 100 mg l 1 at the surface and 5 500 mg l 1 at the bottom the highest concentrations occur off the southwest tip of the korean peninsula and the lowest occur in the central part of the korea strait the rate of transitional season destratification may depend on the timing and intensity of monsoonal surges whereas a late onset of monsoon winds allows waters to remain longer in their moderately stratified summer condition an early onset of monsoon winds tends to destratify the water column by mid november resulting in a nearly uniform high concentration of suspended sediments from surface to bottom the band of more turbid coastal water ends abruptly 25 50 km offshore as a turbidity front in waters 20 80 m deep a wind driven residual flow to the south appears to transport large volumes of this turbid water into the korea strait and perhaps as far as the sea of japan

tsunami sedimentary facies deposited by the storegga tsunami in shallow marine basins and coastal lakes western norway sedimentary successions in small coastal lakes situated from 0 to 11 m above the 7000 year bp shoreline along the western coast of norway contain a distinctive deposit very different from the sediments above and below the deposit is interpreted to be the result of a tsunami inundating the coastal lakes an erosional unconformity underlies the tsunami facies and is traced throughout the basins with most erosion found at the seaward portion of the lakes the lowermost tsunami facies is a graded or massive sand that locally contains marine fossils the sand thins and decreases in grain size in a landward direction above follows coarse organic detritus with rip up clasts here termed organic conglomerate and finer organic detritus the tsunami unit generally fines and thins upwards the higher basins 6 11 m above the 7000 year shoreline show one sand bed whereas basins closer to the sea level 7000 years ago may show several sand beds separated by organic detritus these alternations in the lower basins may reflect repeated waves of sea water entering the lakes in basins that were some few metres below sea level at 7000 years bp the tsunami deposit is more minerogenic and commonly present as graded sand beds but also in some of these shallow marine basins organic rich facies occur between the sand beds the total thickness of the tsunami deposit is 20 100 cm in most studied sites an erosional and depositional model of the tsunami facies is developed

a simplified model of stress slip relationships application to the froy field northern north sea abstract we apply an analytical method sortan to determine fault slip as induced by far field stress the sortan method is based on the wallace bott hypothesis the method is applied to all major faults of the froy oil field located at the eastern margin of the southern viking graben north sea the purpose was to quantify the most likely senses of motion experienced by the faults during the late jurassic early cretaceous rifting event because strike slip displacement is generally difficult to determine based on classical exploration methods particular attention was paid to the simulated strike slip component along the major faults depth converted structural maps were used to determine fault attitudes the presence at the northern edge of the field of a major syn rift dextral strike slip fault the north froy fault allowed us to constrain the most likely characteristics of the prevailing stress field during rifting according to different possible stress states different models were run the results from the sortan modelling indicate that the strike slip component of motion was in general minor on the major faults within the oil field the inferred stress state is found consistent with rifting involving fault related displacement strongly dependent on 3 orientation this stress state prevailed at least during the latest stages of rifting latest jurassic early cretaceous of the northern north sea this case study shows that where paleostress inversion methods cannot be applied in the absence of direct observation the sortan method has the potential to constrain the slip behaviour of the brittle structure it also enables one to rapidly check the overall mechanical consistency of tectonic interpretations

sediment mixing and accumulation rate effects on radionuclide depth profiles in hudson estuary sediments measured anthropogenic radionuclide profiles in sediment cores from the hudson river estuary were compared with profiles computed by using known input histories of radionuclides to the estuary and mixing coefficients which decreased exponentially with depth in the sediment observed sup 134 cs sediment depth profiles were used in the mixing rate computation because reactor releases were the only significant source for this nuclide whereas the inputs of sup 137 cs and sup 239 240 pu to the estuary were complicated by runoff or erosion in upstream areas in addition to direct fallout from precipitation our estimates for the rates of surface sediment mixing in the low salinity reach of the estuary range from 0 25 to 1 cm sup 2 yr or less in some areas of the harbor adjacent to new york city were fine particle accumulation rates are generally 3 cm yr and often as high as 10 to 20 cm yr sediment mixing rates as high as 10 cm sup 2 yr would have little effect on radionuclide peak distributions consequently anthropogenic radionuclide maximum activities in subsurface sediments of the hudson appear to be useful as time stratigraphic reference levels which can be correlated with periods of maximum radionuclide inputs for estimating rates and patterns of sediment accumulation

tectonic history of the western tethys since the late triassic the tectonic history of the western tethys since the late triassic is illustrated through a set of computer generated plate reconstructions which are based on a rigorous plate motions model of this region the model is constrained by the atlantic plate kinematics and on land geologic evidence and defines 13 tectonic phases spanning the time interval from the late ladinian 230 ma to the present the kinematics associated with the late triassic western tethyan rifts produced the detachment of a large composite fragment from the northern margin of gondwana it can be considered as the eastern propagation of the central pangea breakup during the early jurassic these rift zones became inactive while new zones of extension formed along the southern margin of eurasia the eastern margin of iberia and within the rifted northern gondwana fragment itself plate motions associated with the first two extensional centers can still be considered as an eastern branch of the central atlantic plate kinematics conversely the kinematic parameters of the latter rift result from the composition of the euler rotation describing the central pangea breakup and the euler pole of closure of the paleo tethys ocean the late triassic early jurassic rifting phases determined the formation of a number of independent microplates at the interface between africa and eurasia starting from the early cretaceous convergence between africa and eurasia triggered further deformation within the dispersed continental fragments and the formation of backarc basins at the active margins ultimately leading to an increase in the number of tectonic elements that were moving independently in the western tethyan region during the late cretaceous and the cenozoic the proposed tectonic evolution of the western tethys area is compatible with both global scale plate kinematics and geological constraints from on land data observed across the present day mosaic of displaced terranes surrounding the mediterranean region

depositional age and triggering event of turbidites in the western kumano trough central japan during the last ca 100 years abstract for correlating a turbidite record with a detailed land record of natural disasters during the last ca 100 years the depositional age of the surface hemipelagic sediments of the kumano trough located in central japan were estimated we attempted to extract mass accumulation rate of hemipelagic fallout from hemipelagic intervals on the basis of 137 cs geochronology x radiograph dry bulk density and grain size distribution based on assumptions of the biogenic mixing effect on the 137 cs appearance horizon and hemipelagite erosion by turbidity current the reconstructed turbidite record from hemipelagic fallout mass accumulation rate is well correlated with the record of major natural disasters in the kumano area based on the correlation most of turbidite layers are flood storm origin except for a well sorted seismo turbidite induced by the tonankai earthquake that occurred the mid 20th century although the wide distribution of a flood induced turbidite layer due to the 19th century tostukawa flood which was a huge disaster in the area caused by heavy rain and dams breaching it does not show a hyperpycnite succession the flood by dams breaching may cause surge like flow angular to subangular sand sized lithic fragments in the turbidite show that sand grains were transported from the kumano river directly plant debris and microfossils are common in both seismo turbidite and flood storm induced turbidites

particle mixing rates in deep sea sediments determined from excess 210pb and 32si profiles particle mixing rates have been determined for 5 south atlantic antarctic and 3 equatorial pacific deep sea cores using excess 210 pb and 32 si measurements radionuclide profiles from these siliceous calcareous and clay rich sediments have been evaluated using a steady state vertical advection diffusion model in antarctic siliceous sediments 210 pb mixing coefficients 0 04 0 16 cm 2 y are in reasonable agreement with the 32 si mixing coefficient 0 2 or 0 4 cm 2 y depending on 32 si half life in an equatorial pacific sediment core however the 210 pb mixing coefficient 0 22 cm 2 y is 3 7 times greater than the 32 si mixing coefficient 0 03 or 0 07 cm 2 y the difference in 210 pb and 32 si mixing rates in the pacific sediments results from 1 non steady state mixing and differences in characteristic time and depth scales of the two radionuclides 2 preferential mixing of fine grained clay particles containing most of the 210 pb activity relative to coarser particles large radiolaria containing the 32 si activity or 3 the supply of 222 rn from the bottom of manganese nodules which increases the measured excess 210 pb activity relative to 226 ra at depth and artificially increases the 210 pb mixing coefficient based on 32 si data and pore water silica profiles dissolution of biogenic silica in the sediment column appears to have a minor effect on the 32 si profile in the mixed layer deep sea particle mixing rates reported in this study and the literature do not correlate with sediment type sediment accumulation rate or surface productivity based on differences in mixing rate among three antarctic cores collected within 50 km of each other local variability in the intensity of deep sea mixing appears to be as important as regional differences in sediment properties

spatial and temporal variability in the holocene sea level record of the south australian coastline abstract studies of past sea levels based on radiocarbon dated field samples suffer variously from compilation of information from disparate locations and the imprecise nature of the dated indicators geographic segregation and systematic elimination of poor samples from time depth data sets leads to improved interpretation of holocene sea level history an example is presented from southern australia where this is achieved through selection of higher resolution palaeoenvironmental indicators separation of transgressive from regressive populations and geographic regionalisation of data in southern australia fossil sea level indicators preserved in prograding coastal plain settings include seagrass sandflat mangrove samphire and chenier ridge organo sedimentary remains these provide sea level time depth data points with a variety of elevational and dating errors preserved organic remains at the transition from posidonia seagrass to intertidal sandflat environment and from sandflat to avicennia mangrove environment provide the most precise local data for tracing sea level change time depth plots of 233 dated sea level indicators from south australia generate a broad sea level envelope tracing the southern australian transgression from 10 000 to ca 6000 radiocarbon years bp followed by a more or less consistent level to the present finer details of sea level behaviour are only apparent after systematic selection separation and regionalisation of the data the data indicate a very rapid sea level rise in the early holocene at about 16 mm year reaching present levels at 6400 years bp this was followed by regionally variable regression and emergence of the land of 1 3 m a process that continues to the present the systematic increase from 1 to 3 m in the elevation of the 6400 year bp highstand with distance away from the shelf margin is consistent with a hydro isostatic origin for the emergence as predicted by geophysical models

fallout plutonium and natural radionuclides in annual bands of the coral montastrea annularis st croix u s virgin islands abstract we have investigated the banded coral montastrea annularis as a recorder of the history of fallout pu in surface seawater thirty annual growth bands representing growth during coral years 1951 1980 were subsampled from m annularis collected at st croix u s virgin islands coral years begin and end in late summer early autumn and are designated for the calendar year in which they end 239 240 pu was finite in coral years 1954 1980 and the coral pu record is very simply related to the fallout history of 90 sr peaks in coral pu in coral years 1959 and 1964 correspond to fallout peaks in 1959 and 1963 respectively peak broadening and time lags in the coral pu record as compared to the 90 sr fallout record are consistent with retention of fallout pu in surface seawater for about two years characteristic removal time during the period of major fallout and possibly longer thereafter the simplicity of the coral pu record and its close correspondence with fallout history suggest that 239 240 pu was incorporated into the coral skeleton with constant discrimination relative to ca the effects of speciation and oxidation state upon pu incorporation are presently unknown to aid the pu interpretation ca mg sr na and natural radionuclides 238 u 228 ra 232 th and 210 pb were also determined in the annual bands in small samples 0 5 g ca mg and na show correlated variations which could be due to seasonal variability in uptake the 238 u and 228 ra records were generally consistent with uptake at constant discrimination from surface water reservoirs of nearly constant concentration although one sample showed probable diagenetic addition of u 232 th was not detected with certainty this implies that terrigenous particles were not consistently entrapped within the coral skeleton interpretation of 210 pb was difficult because 226 ra was not measured montastrea annularis preserves a record of fallout pu to make this record useful it must be considered in the broadest possible geochemical context

structural evolution metamorphism and restoration of the arabian continental margin saih hatat region oman mountains abstract 170 m y of relatively stable passive margin sedimentation along the northern continental margin of arabia was abruptly terminated during the cenomanian turonian 95 ma when the oman continental margin collapsed and subsided rapidly aruma basin to accommodate obduction of the semail ophiolite complex and underlying thrust sheets haybi and hawasina complexes in the oman mountains the ophiolite was emplaced at least 200 km over the passive margin probably over 450 km in total from ne to sw during the later stages of obduction the leading edge of the continental margin was subducted to depths where carpholite bearing rocks 6 8 kbar blueschist 12 15 kbar and eclogite ca 20 kbar facies metamorphism formed in a ductile deforming ne dipping subduction zone along the northeastern margin of the saih hatat culmination in ne oman the mesozoic shelf carbonates are deformed by recumbent folding on all scales the present day structure is dominated by four sw vergent thrust slices in carpholite grade rocks at higher structural levels overlying lower units of crossite bearing blueschist hulw unit garnet glaucophane chloritoid blueschists and garnet clinopyroxene phengite glaucophane eclogites 15 20 kbar the largest shear zone separates 7 8 kbar hulw unit blueschists above from 12 15 kbar retrogressed eclogites and ca 20 kbar eclogites of the as sifah unit below further inboard sw a major shear zone separates the lower plate hulw blueschist facies rocks from the upper plate sedimentary rocks upper plate lower plate discontinuity which also show carpholite grade hp metamorphism towards the ne restoration of the entire saih hatat continental margin shows that the upper plate lower plate discontinuity cuts down section to the sw as far as the proterozoic hatat schists ne directed extensional crenulation schistosity and nne oriented stretching lineations in the eclogite and blueschist facies rocks are consistent with sw directed exhumation of footwall hp rocks ne facing folds and spectacular sheath folds with greatly attenuated limbs in the upper plate sediments are interpreted as antithetic backfolds with shortening in the upper plate balanced by the subduction of the lower plate consistent with a ne directed subduction of the continental margin rocks beneath the sw obducting ophiolite haybi and hawasina thrust sheets recent suggestions of a nascent sw directed subduction beneath the oman margin are not consistent with the sedimentary evolution of the shelf and slope carbonates or the geological structure of saih hatat two main phases of tectonic uplift of saih hatat and jebel akhdar are firstly the latest cretaceous ramp culmination associated with foreland propagating thrusts in the sw and backfolds in the ne and secondly post late eocene oligocene uplift by ca 2000 m

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

shallow marine tsunami deposits in teluk banten nw java indonesia generated by the 1883 krakatau eruption teluk banten tb is a tropical shallow marine embayment with coral reef islands close to the krakatau volcanic complex the 1883 krakatau eruption generated a tsunami which had a devastating effect on the neighboring coastal areas the effects of the 1883 krakatau eruption and the associated tsunami on the bottom sediments in tb are assessed using textural compositional and 210 pb geochronological data an important diagnostic criterion consists of the occurrence of tephra conform descriptions of the 1883 eruption tephra the tsunamite consists of a sandy layer with abundant reworked shell and other carbonate fragments coarse components in the tsunamite consist of locally derived material eroded from the seabed land derived components are incorporated in the tsunamite only in close proximity to the coast the tsunamite is thickest in localized areas of the central part of the bay along the northern open sea facing slope of tb the tsunamite is relatively thin 6 7 cm thick but well preserved as little postdepositional modifications have occurred in the eastern bay area recent erosion since the redirection of the ciujung river in the 1920s has removed the krakatau tsunamite along the west coast of tb the only signature of the 1883 krakatau eruption consists of tephra and evidence for a high energy event is lacking presumably the western area was sheltered from the tsunami wave coming from the northwest at the shallower stations with low accumulation rates the tephra has been thoroughly mixed by bioturbation 2003 elsevier science b v all rights reserved

sedimentation and hydrodynamic processes associated with the tsunami generated by the 1755 lisbon earthquake abstract an unusual sedimentary horizon believed to have been deposited by the tsunami associated with the 1755 lisbon earthquake has been identified at boca do rio in southern portugal this horizon marks a distinct sedimentological and micropalaeontological break from the deposits enclosing it the sedimentary characteristics of the horizon which consists of several distinct sub units vary greatly in both vertical and horizontal section detailed textural analysis through vertical sections of these sub units shows abrupt changes in particle size characteristics the highly variable nature of the horizon appears to be due to rapid variation in the hydrodynamic characteristics of the depositional event the lowermost section of the deposit appears to have been deposited from a highly turbulent water mass which was able to transport gravel sized clasts as well as gravel sized mud balls eroded from underlying material the water mass rapidly lost energy leading to the deposition of predominantly sand silt and clay particles sharp breaks in textural characteristics are likely to be due to changes in current direction caused by wave reflection or swash backwash interference the main sources of sand sized material within the deposit are the seaward barrier beach foredune system the tsunami deposit at boca do rio shares many of the sedimentary characteristics of tsunami deposits from other sites around the world

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

tsunami deposits in holocene bay mud in southern kanto region pacific coast of central japan abstract tsunami have probably deposited sand sheets that are intercalated in holocene bay floor mud exposed on the boso and miura peninsulas facing the convergent boundary of the pacific philippine sea and eurasian plates we have identified seven sand sheets at four drowned valleys and correlated these by 137 radiocarbon dates of shells and wood the sheets consist of poorly sorted muddy sand and well sorted sand layers in fining upward sequences containing abundant transported shells rip up clasts and wood fragments the sheets erosionally overlie bioturbated bay floor mud that contains molluscan shells in life position most of the sheets are less than 20 cm thick and rarely more than 50 cm thick some molluscan shells are older in these layers than in underlying mud both landward and seaward paleocurrents are shown in a few cases by imbrication of shells and by low angle wedge shaped lamination at least five of the sand sheets contain molluscan fossils derived from rocky coasts or shore platforms although they intercalated in mud deposited within bays at depths of 10 15 m two other sand sheets are dominated by open seashore ostracode assemblages although they were deposited in the brackish inner bay and muddy central bay five of the layers may correlate with emergences recorded by nearby holocene marine terraces these correlations suggest that great earthquakes triggered the inferred tsunami the tsunami occurred at intervals of 300 2000 years beginning about 10 000 years ago

mixing depths and sediment accumulation rates on an arid tropical shelf based on fine fraction 210pb analysis abstract continental shelves in arid tropical settings present particular challenges to 210pb based analysis of sedimentation rates and surface mixing owing to the combination of coarse sediment deep and year round bioturbation and lower atmospheric flux of 210pb the modern continental shelf at the northern terminus of the hyper arid gulf of eilat aqaba goe receives flood runoff of siliciclastics producing a mixed seabed with 20 carbonate that is dominated by larger benthic foraminifera and mollusks focusing analysis on only the fine fraction of deep penetrating cores 70 cm from 15 to 40 m water depths yields reliable 210pb profiles in contrast to analysis of bulk sediment graphical abstract sedimentation rates increase offshore five fold from 0 01 0 04 cm y in 15 m water depth to 0 21 0 27 cm y in 30 40 m depths reflecting offshore redistribution of flood delivered siliciclastic sediments away from the wadi mouth a result also supported by an offshore increase in the inventory of excess 210pb in contrast the thickness of the surface mixed layer sml decreases from 30 cm to 20 cm with proximity to anthropogenic stressors channelized flood runoff historic release of sewage and operation of fish cages which we attribute to the suppression of macrobenthic burrowers the rate of sedimentation on the gulf shelf away from dynamic bypassing in the 15 m shoreface is comparable to other tropical carbonate shelves rich in large benthic foraminifera and is higher than rates documented on the adjacent slope increasing confidence in this approach to 210pb analysis using only the fine fraction analysis of the fine fraction rather than bulk sediment would be a useful adjustment to 210pb methodology in any area with scarce fine grained sediment

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

fresh pumice from the central indian basin a krakatau 1883 signature the occurrence of pumice in the central indian basin cib has been a controversy some are of the opinion that these pumices are erupted from a volcano along the ninetyeast ridge while others suggest the indonesian arc volcanism as their probable source recently it is also suggested that the pumice are the products of in situ silicic volcanism in the cib this study was initiated in order to resolve this controversy about the origin of the fresh pumice from the cib the fresh pumice pieces of different sizes and shapes were collected from the surficial sediments of the cib from an average depth of about 5000 m 12 s 76 e glass is the main phase comprising about 95 volume and resembles the matrix glass in krakatau 1883 dacitic pumice which is also very poor 5 in the modal mineral composition the mineral and glass analyses were carried out with the help of the electron microprobe the orthopyroxenes clinopyroxenes plagioclases and spinels are the mineral phases present in these pumices the pyroxenes have similar wo en and fs components to those previously reported from the 1883 krakatau eruption products geochemically these fresh pumices have a high sio2 content 71 and high total alkali content 8 similar to 1883 eruption products of krakatau thus based on the similarities in mineralogy and glass chemical composition it is inferred that these fresh pumices are the products of the fierce 1883 eruption of the krakatau volcano in the sunda strait of the indonesian arc

signatures of natural catastrophic events and anthropogenic impact in an estuarine environment new zealand the sedimentary record of known natural catastrophic events and anthropogenic activity in an estuarine environment is assessed using sedimentological chemical and geochronological techniques shallow cores collected from intertidal and salt marsh sediments in ahuriri estuary hawke s bay reveal a variety of signatures of natural and human disturbance evidence for the 1931 hawke s bay earthquake which resulted in an uplift of one to two metres in the napier area is given by a change from silt to sand dominated sediment in the lower estuary which is consistent with a shift toward higher energy depositional conditions following uplift however based on physical properties of sediments the 1931 uplift event does not appear to have caused major changes in depositional conditions in the upper estuary similarly no changes were recorded at one site in the lower estuary which seems to represent an area of low energy depositional environment although the 1960 chilean tsunami resulted in structural damage in napier it did not produce any recognisable sedimentological and geochemical signature in the sedimentary record suggesting that the study sites were possibly beyond the limit of sedimentation of the tsunami post european settlement impact is mainly restricted to the lower estuary where increased concentrations of zn cr pb and cu are attributed to industrial discharges evidence of agricultural runoff is shown by an increase in cu concentrations within a fine grained depositional environment that is distal from industrial sources in the town of napier chemical data cl and s suggest a change in the depositional environment in the upper estuary due to increased freshwater influx and or decrease in seawater influence dating by 210pb suggests that this occurred around the middle part of the 19th century and might be attributed to river flooding in the region at that time

particle interaction in fjord suspended sediment abstract glacial flour enters the surface layer of howe sound a fjord in southwestern british columbia as a sediment plume which moves quickly down inlet while gradually mixing with the sea water flocculation occurs in the lower brackish waters of the surface layer although mixing and diffusion are the dominant processes for sediment to enter the marine water once in the underlying marine water zooplankton pelletization and biologic agglomeration of inorganic floccules predominate this generates a response in the order of days between the two layers in terms of sedimentation of particulate matter most particles settling in the fjord environment fall as 1 sand and silt grains containing attached clay particles 2 clay clasts possibly related to river mudballs 3 mineral bearing fecal pellets from pelagic zooplankton 4 large grain inorganic and colloidal floccules and 5 inorganic biogenic agglomerates analysis of sediment trap data has led to the following conclusions 1 water turbidity cannot be used to infer the downward flux of particles 2 size distributions of sediment deposited on the sea bed are a function of non lognormal size distributions from particles composing sub laminae

tidal computations for morecambe bay summary a numerical finite difference technique for computing tides in areas of shoaling water has been established and used to calculate the m2 tide in morecambe bay an essential feature of the method is the representation of drying banks which appear as the water level falls on the ebb and which are re submerged on the flood as the level rises again since the non linear advective acceleration should be important in shallow water schemes for incorporating these terms are examined and the influence of advection on the tide assessed in a series of tests the open sea tides applied to the outer boundary of the numerical bay model were taken first from existing tidal charts then from calculations with a larger scale encompassing model and finally from observations of current in each case the computed tidal elevations within the bay turned out to be in satisfactory agreement with those obtained from observations however it is significant that in the first case inaccuracy of the input tidal distribution deduced from charts gives rise to erroneous currents near the boundary

sedimentological record of tsunamis on shallow shelf areas the case of the 1969 ad and 1755 ad tsunamis on the portuguese shelf off lisbon one of the aims of the sedport project esf euromargins eurocores program was to investigate the depositional features on the shelf and upper slope of the portuguese margin tagus system during the holocene to fulfill the objectives two shallow box cores and two sedimentary sequences were studied po287 26b and the spliced sequence of sites d13902 po287 26g recovered on the portuguese continental shelf ssw off the tagus river mouth and the box po287 28b and gravity core geob8903 collected towards the w of the river mouth magnetic susceptibility grain size and xrf fe data as well as 210 pb and ams 14 c dating of these sedimentary sequences have allowed the identification of an instantaneous deposit at about 20 cm in the box cores downcore we could establish a hiatus corresponding to 355 yr of sedimentation at both sites a 39 cm instantaneous deposit of coarse material including carbonate broken shells on the ssw site and a 1 5 m instantaneous deposit of fine material on the w site both hiatus and instantaneous deposits are considered to be of tsunamigenic origin the box cores deposit has an estimated age of 1969 ad and it is attributed to the 1969 earthquake caused tsunami the hiatus and deposits found downcore are due to the age limits encountered believed to represent the tsunami related to the 1755 lisbon major earthquake these data further indicate a sediment deposit similar in type and thickness on both ssw and w sites in 1969 while the 1755 ad record indicates a higher energy backwash along the ssw and a preferential deposition of fine suspended matter towards the w c 2007 elsevier b v all rights reserved

trace metal enrichments in portuguese submarine canyons and open slope anthropogenic impact and links to sedimentary dynamics abstract in order to evaluate the role of submarine canyons as transport routes for the particulate matter including anthropogenic trace metals from coastal areas to the deep sea we analysed contents of ca al fe mn zn cr pb ni and cu organic carbon and calcium carbonate in surface sediments and sediment trap particulate material from canyon and open slope areas of the central portuguese continental margin the contribution of trace metals from anthropogenic sources was assessed by comparing present day concentrations and average elemental concentrations for the industrial period last 150 years with pre industrial baseline values baseline elemental concentrations are very similar for the lisbon setubal and nazare canyons but varying degrees of anthropogenic trace metal enrichments are recorded in more recent sediments the upper lisbon and cascais canyons appear the most affected by anthropogenic trace metal deposition excess pb zn and cu amount 55 57 and 21 respectively of total inventories over the last 150 years the upper nazare canyon follows with 42 21 and 17 respectively lower contributions of anthropogenic trace metals were found for the lower reaches of the canyons and adjacent open slopes indicating that the upper canyon areas act as trace metal depocentres whereas dispersal to deeper canyon and slope areas is limited the tagus and to a lesser extent the sado river appear the main sources of pb zn and cu to the canyons but atmospheric dispersal of pb seems also important especially in the southern area anthropogenic enrichment of pb and zn in the cascais and lisbon canyons is comparable to values published for canyons in the nw mediterranean and off taiwan located in close proximity to industrialized areas different from pb and zn present day cu enrichment appears to increase toward deeper water where pelagic sedimentation is predominant suggesting that dispersal of this trace metal is at least partly linked with surface water plankton production

an overview of distal tephrochronology in northern europe during the last 1000 years several tephra layers from the last millennium have been identified in distal peat and lake sediment sequences in northern europe forming a framework of volcanic events of great value for palaeoenvironmental investigations most of the tephras within this framework have an origin in iceland but distal layers from jan mayen have also been identified the predominant transport pathway in an easterly southeasterly direction has led to the deposition of these tephras in a number of terrestrial deposits in northern europe ash from silicic eruptions 63 sio2 dominate at these sites even though many of the documentary records in distal areas report tephra fall from several basaltic eruptions here we provide an overview of the distribution shard concentration and geochemistry of these tephras to highlight the most important isochrones for addressing key dating issues in particular three horizons hekla 1 ad 1104 oraefajokull ad 1362 and askja ad 1875 are found at a number of different locations in northern europe and as such are valuable tie points for improving and validating chronological models and for synchronisation of records spanning the last 1000 years in addition we present new data identifying tephra from the grimsvotn volcanic system within the lomonosovfonna ice cap on svalbard demonstrating that some tephras have been transported 2000 km to as far north as 798 n along a northeasterly trajectory this discovery highlights the potential for utilising tephrochronology as a correlation tool for palaeoarchives located in more northerly areas and the complex nature of fall out from different eruptions copyright 2009 john wiley sons ltd

paleostress inversion a multi parametric geomechanical evaluation of the wallace bott assumptions wallace 1951 and bott 1959 were the first to introduce the idea that the slip on each fault surface has the same direction and sense as the maximum shear stress resolved on that surface however this simplified hypothesis is questionable since fault mechanical interactions may induce slip reorientations earlier numerical geomechanical models confirmed that the slickenlines slip vectors are not necessarily parallel to the maximum resolved shear stress but are consistent with local stress perturbations this leads us to ask as to what extent the wallace and bott simplifications are reliable as a basis hypothesis for stress inversion from fault slip data here a geomechanical multi parametric study using a 3d boundary element method covering i fault geometries such as intersected faults or corrugated fault surfaces ii the full range of andersonian state of stress iii fault friction iv fault fluid pressure v half space effect and vi rock properties is performed in order to understand the effect of each parameter on the misfit angle between geomechanical slip vectors and the resolved shear stresses it is shown that significant misfit angles can be found under specific configurations invalidating the wallace and bott assumptions even though fault friction tends to minimize the misfit we therefore conclude that in such cases stress inversions based on fault slip data should be interpreted with care

the sedimentology of middle holocene tsunami facies in northern sutherland scotland uk abstract lagoonal sediments attributed to the main holocene marine transgression in strath halladale northern sutherland contain a complex coarser layer believed to have been deposited during the tsunami associated with the second storegga slide off south west norway the coarser sequence is dated at between 7590 50 and 7290 50 radiocarbon years bp 6507 6260 cal bc and 6228 6029 cal bc detailed stratigraphical analysis has determined a distinctive suite of sedimentary sub units within the coarser layer in marked contrast to the sediments which occur above and below a pronounced erosional unconformity with the underlying sediments is recorded with the base of the tsunami layer characterised by eroded material from the underlying peat the presence of a mixed diatom assemblage although fragmentary indicates a chaotic accumulation of the deposit with all habitats represented variations in particle size within the sequence disclose striking similarities with those from contemporary tsunami deposits the run up of the tsunami sediments is calculated at a minimum of 4 6 m this is the first occasion on which a deposit of the second storegga slide tsunami has been found outside the north sea basin and indicates that the area affected by the tsunami may have been larger than has been previously described

geologic evidence for earthquakes during the past 2000 years along the copalis river southern coastal washington evidence for several prehistoric earthquakes is present in deposits less than 2000 years old that crop out at the copalis river estuary 47 07 2 n 124 09 7 w the deposits show that land subsided decimeters into the intertidal zone on as many as three occasions and that sand vented while the land underwent little or no subsidence on another occasion the evidence for earthquake induced subsidence consists of buried marsh and forest soils that evince sudden estuarine submergence attended on at least one occasion by a landward directed surge of sandy water this combination of submergence and surge implies subsidence and tsunami exposed evidence for subsidence and tsunami along the copalis river is strong for a time within a few decades of 300 years ago moderate for a time 1400 1900 years ago and weak subsidence or lacking tsunami for an intermediate time also about 1400 1900 years ago the history of sudden submergence and tsunami in the past 2000 years at the copalis river estuary resembles that shown by buried soils farther south in coastal washington at grays harbor and willapa bay the history can be explained most simply by great mw of 8 or 9 thrust earthquakes at the boundary between the juan de fuca and north america plates with one or two earthquakes occurring 1400 1900 years ago and another close to 300 years ago the evidence for earthquake induced venting along the copalis river consists of sand intrusions and vented sand volcanoes the sand rose through muddy estuarine deposits at least 3 m thick entraining these deposits in fragments as much as 0 3 m long intrusion occurred at one or more times in the past 2000 years and at least some of the venting occurred 900 1300 years ago the sand bodies do not imply artesian flow of flood pressured groundwater because the sand vented forcefully and infrequently through a lowland that probably lacked natural levees the earthquake implied by the venting of sand 900 1300 years ago could have come from a source below above or at the boundary between the juan de fuca and north america plates if from the subducted juan de fuca plate the implied earthquake was farther west or larger than the largest earthquakes within that plate during the past 100 years evidence permitting a source within the north america plate includes a fault scarp an uplifted tideflat and landslides near puget sound dating from the interval 700 1700 years ago a plate boundary source would explain buried soils whose estuarine submergence and burial imply coseismic subsidence for parts of coastal washington in the interval 600 1300 years ago however stratigraphy shows that little or no coseismic subsidence occurred along the copalis river during the venting 900 1300 years ago if a plate boundary earthquake struck coastal washington 900 1300 years ago the earthquake produced a different distribution of land level change than did the plate boundary earthquakes inferred for 1400 1900 and 300 years ago

late holocene 0 2 4 ka bp surface water temperature and salinity variability feni drift ne atlantic ocean abstract planktonic foraminiferal mg ca ratios and oxygen isotopic compositions of a spliced sediment record from feni drift ne atlantic ocean box core m200309 and piston core enam9606 trace late holocene sea surface temperature sst and salinity changes over the past 2400 years at this location the variability of sst and oxygen isotopic composition of seawater 18 o w reflects variable northward advection of warm and saline surface waters which appears linked to climate variability over the adjacent european continent our records reveal a general long term cooling trend superimposed on this overall trend partly higher temperatures and salinities from 180 to 560 ad and 750 to 1160 ad may be ascribed to the roman and medieval warm periods respectively subsequently our record displays highly variable surface water conditions the main little ice age sst minimum is restricted to the 15th and 16th centuries ad pervasive multidecadal to centennial scale variability throughout the sedimentary proxy records can be partly attributed to solar forcing and or variable heat extraction from the surface ocean caused by shifts in the prevailing state of the north atlantic oscillation nao high salinities in the 17th and 18th centuries are considered to reflect tropical anomalies linked to a southward shift of the intertropical convergence zone propagating across the north atlantic ocean

discovery of minoan tsunami deposits the hellenic arc is a terrane of extensive quaternary volcanism one of the main centers of explosive eruptions is located on thera santorini and the eruption of the thera volcano in late minoan time 1600 1300 b c is considered to have been the most significant aegean explosive volcanism during the late holocene the last eruptive phase of thera resulted in an enormous submarine caldera which is believed to have produced tsunamis on a large scale evidence suggesting seawater inundation was found previously at some archaeological sites on the coast of crete however the cause of the tsunami and its effects on the area have not been well understood on the aegean sea coast of western turkey didim and fethye and crete gouves we have found traces of tsunami deposits related to the thera eruption the sedimentological consequences and the hydraulics of a thera caused tsunami indicate that the eruption of thera volcano was earlier than the previous estimates and the tsunami did not have disruptive influence on minoan civilization

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

tidal characteristic adjustment due to dyke and seawall construction in the mokpo coastal zone korea the results of tidal analyses of long term 1971e2001 sea level elevation records at the mokpo observation station on the western tip of the southwest coast of korea showed significant changes in tidal amplitudes together with advance in phases for the major constituents as a result of constructing a dyke and two seawalls in the mokpo coastal zone mcz according to the stages of construction the amplitudes of each tidal constituent rather than the phases showed different variability patterns the semidiurnal m2 and s2 and fourth diurnal m4 and ms4 amplitudes increased significantly post dyke construction whereas the diurnal k1 and o1 amplitudes decreased slightly post seawall construction that is the semidiurnal and fourth diurnal amplitudes were markedly affected by the dyke construction and less affected by the construction of the two seawalls in contrast the diurnal amplitudes were little influenced by the dyke construction and slightly influenced by the construction of the two seawalls three numerical simulations with different stages of construction reveal that an increase advance in tidal amplitudes phases in mokpo harbour is closely related to change in the mcz from a choked coastal system to a non choked system before the construction amplitudes phases inside the mcz were lower more delayed than those that are outside due to narrow channels in comparison with large capacity of water storage inside the mcz in addition to results of the numerical model a simple analytic model showed that semidiurnal tides are more affected than the diurnal tides under the choked system because of their different frequencies tidal amplitudes increase in the shallow youngam and geumho basins due to the shoaling effect while remaining low in the youngsan river estuary due to intensive tidal dissipation within the river the presence of the aphae channel together with relatively active tidal dissipation in the muan basin accounts for the low amplitudes compared to those of the youngam and geumho basins reduction in capacity of water storage induced by the series of constructions in the mcz shifts the complex hydraulic system to a simple non choked system therefore the difference in tidal amplitudes and phases between inside and outside of the mokpogu channel was significantly reduced after construction 2003 elsevier ltd all rights reserved

tidally induced clouds of suspended sediment connected to shallow water coral reefs abstract the bay of banten west java indonesia represents a shallow coastal embayment harboring coral reefs subject to extremely turbid conditions the sedimentary regime and flow structure of two contrasting coral reef islands in the embayment were investigated to identify the mechanisms responsible for mean and peak levels of suspended sediment concentration ssc around the reefs arrays of in situ calibrated optical backscatter obs sensors were deployed across the reef slopes far field conditions were simultaneously monitored using an acoustic doppler current profiler adcp and a conductivity temperature and depth ctd probe equipped with an obs sensor in addition hydrographic surveys were conducted using the adcp attached to a small fishing boat navigating transects perpendicular to the reef islands the direct influence of river plumes was found to be insignificant waves act only in the uppermost few meters of the reef slopes where coral growth is most abundant and little sediment is available for resuspension tidal currents are the primary cause of high turbidity which was inferred from peaks in the diurnal and semidiurnal frequency bands of ssc spectra and the large depths where the turbidity variation sometimes initiates the entrained sediment disperses upward across the reef slopes which is likely due to a secondary current associated with bending of the flow along the curved hydraulically rough reef slopes in weakly stratified ambient waters changes in sediment availability variable critical shear stresses for erosion and deposition and the formation and evanescence of island wakes may explain the high variability of ssc at the reef slopes

deposition rates mixing intensity and organic content in two contrasting submarine canyons the hydrographically different conditions characterising the western iberian margin ne atlantic and the gulf of lions mediterranean may play an important role in determining the biogeochemical characteristics of the sediments to investigate this we compared the nazare and cap de creus canyons and their respective adjacent open slopes in terms of the organic carbon corg contents chlorophyll a chl a concentrations c n and chl a phaeopigment ratios and also in terms of modelled mixing intensities chl a and 210pb deposition and background concentrations in sediments chlorophyll a and 210pb profiles were fitted simultaneously with a reactive transport model to estimate mixing intensity deposition and background concentrations further to account for the possibility that the decay of chl a may be lower in the deep sea than in shallow areas we estimated the model parameters with two models in one approach model 1 the temperature dependent decay rate of chl a as given by sun et al sun m y lee c aller r c 1993 laboratory studies of oxic and anoxic degradation of chlorophyll a in long island sound sediments geochimica et cosmochimica acta 57 147 157 for estuaries was used in the other approach model 2 an extra parameter was estimated to derive the chlorophyll a degradation rate an f test taking into account the different number of parameters in the models was used to single out the model that significantly fitted the data best in most cases the model parameters were best explained with model 1 indicating the empirical relationship by sun et al 1993 is a valid means to estimate the chlorophyll a degradation rate in deep sea sediments to assess the robustness with which the model parameters were estimated we provide a first application of bayesian analysis in the modelling of tracers in sediments bayesian analysis allows calculating the mean and standard deviation for each model parameter and correlations among parameters the model parameters for stations for which 210pb and chlorophyll a profiles were available were robustly fitted as evidenced by an average coefficient of variation of 0 22 corg contents chl a concentrations chl a phaeo ratios mixing intensities depositions and background concentrations of chl a and 210pb indicated that the cap de creus canyon and adjacent slope were less active in terms of organic matter accumulation and burial than the nazare canyon and respective open slope

sedimentary processes of fine grained material and the effect of seawall construction in the daeho macrotidal flat nearshore area northern west coast of korea abstract sedimentary processes on the lower tidal flat of the reclaimed seosan bay daeho tidal flat at the west coast of korea have undergone significant changes since 1984 when seawalls over 8 km long were constructed at the bay mouth comparison of pre and post construction tidal flow models indicates that in general tidal currents have increased considerably in front of the daeho tidal flat with tidal flow directions having changed from shore normal to shore parallel the 12 h measurements of currents and suspended sediment concentrations at four anchored hydrographic stations show nearshore suspended sediments drifting southward throughout the year bypassing the daeho tidal flat cyclic seasonal variations occur prominently in the grain texture of the tidal flat sediments and associated sedimentation rates in summer fine grained sediments deposit at a rate of 2 6 mm month particularly in sheltered places during the winter monsoon erosional processes are greatly enhanced by the interplay of tidal currents and waves up to 30 mm month this sedimentary seasonality is reflected in the variations in the concentration of nearshore suspended matter the concentration of suspended matter is much higher in winter 60 80 mg l because of vigorous resuspension activities compared with the summer concentration 10 30 mg l the direct effect of seawall construction coupled with strong natural seasonality can be seen from the continuous monitoring of sedimentation rates on the tidal flat the 2 year 1993 1995 measurements indicate that the entire daeho tidal flat was eroded during that period at the abnormally high average rate of 10 cm year the causal blocking of bayward sediment and water movements by any artificial structure might lead to similar erosional conditions to many other bays facing the yellow sea on the both chinese and korean coastlines subjected to energetic winter wave attack