mississippi river subaqueous delta is entering a stage of retrogradation abstract the subaqueous delta of the mississippi river the largest river system in the conterminous u s has entered a stage of retrogradation caused by multiple natural and anthropogenic activities since the 1950s the suspended sediment load of the mississippi river has decreased by 50 due primarily to the construction of 50 000 dams in the mississippi basin the impact of this decreased sediment load has been observed in subaerial environments but the impact on sedimentation and geomorphology of the subaqueous delta front has yet to be examined to identify historic trends in sedimentation patterns we compiled bathymetric datasets including historical charts industry and academic surveys and national oceanic and atmospheric administration hydrographic data collected between 1764 and 2009 the progradation rate measured at the 10 m depth contour of southwest pass which receives 69 of the suspended sediment load reaching head of passes has decreased from 67 m yr between 1874 and 1940 to 26 m yr between 1940 and 1979 with evidence of further deceleration from 1979 to 2009 at south pass and pass a loutre the delta front has entered the destructive phase with the 10 m contour retreating at rates 20 m yr at both passes since 1979 advancement of the delta front also decelerated in deeper water in some areas out to 180 m depth except locally where mudflow lobes are advancing deeper contours show a pattern of decreasing progradation rate between 1874 1940 and 1979 2005 time periods furthermore based on differences measured between available bathymetric datasets the sediment accumulation rate across the delta front decreased by 73 for the same period the retention rate of mississippi river sediment on the delta front ranged from 67 to 81 for the time periods assessed with total sediment load stored on the delta front equal to 317 54 mt yr from 1874 to 1940 145 25 mt yr from 1940 to 1979 and 87 15 mt yr from 1979 to 2005 we document for the first time that the mississippi river delta front has entered a phase of retrogradation which will likely be accelerated by future upstream activities that divert a portion of the sediment load to the upper delta for coastal protection and restoration projects the decline of the subaqueous mississippi river delta has critical implications for biogeochemical cycling subaqueous mass wasting and sediment dispersal to the coastal ocean

mud capped dredge pits an experiment of opportunity for characterizing cohesive sediment transport and slope stability in the northern gulf of mexico abstract mud capped dredge pits mcdps defined as sand borrow sites from paleo river channels with cohesive sediment capped walls are used for northern gulf of mexico ngom coastal restoration projects due to lower cost than more distal restoration resources mcdp evolution including infilling and pit wall slope stability is poorly understood in relation to sandy borrow areas we present and interpret bathymetric data from sandy point mcdp which was constructed in 2012 about 20 km northwest of southwest pass the most active mississippi river distributary in water depths of 11 m repeat bathymetric surveys show the pit is infilling 54 cm or volumetrically 200 000 m3 per year which is on the same order as seasonal scale and an order of magnitude higher than the decadal scale vertical accretion rates observed seaward of southwest pass this infilling rate is higher than predicted based solely on excavated volume when compared with other dredge pits in sandy substrate sediment starved settings mcdp infill is volumetrically dominated by far field here defined as river plume or shelf bed resuspension sediment with only 9 of pit infill from pit wall failure geomorphic comparison of sandy point mcdp walls with southwest pass mudflow gully walls shows that the mcdp is oversteepened relative to natural depression features in this setting the convergence of mcdp and mudflow gully gradients towards a common value 4 5 may represent an angle of repose in lieu of decadal scale forcings findings from this experiment of opportunity show that mcdps 1 are effective sediment traps 2 have steep but relatively laterally stable walls 3 do not represent significant risk to infrastructure in a 3 year time scale and 4 are predicted to infill within about 2 decades provided a proximal sediment source exists

the seal edge coombes north derbyshire a study of their erosional and depositional history periglacial landforms and deposits of devensian age are commonly observed on the higher hill slopes of north derbyshire but to date very few glacial features or sediments have been recognised at seal edge the escarpment slope has been sculptured by both frost and nivational processes but at middle seal clough there are lobate ridges located beyond the talus foot that are probably moraines formed during the dimlington stadial of the late devensian by a small corrie glacier the history of the coombe has been interpreted from a study of both the inorganic and organic sediments and although the results are not conclusive they indicate that ice and snow were important in the development of the coombe and that the peat formations in the basin also provide the earliest record to date for events in the vegetation history of the southern pennine moorlands

which triggers produce the most erosive frequent and longest runout turbidity currents on deltas subaerial rivers and turbidity currents are the two most voluminous sediment transport processes on our planet and it is important to understand how they are linked offshore from river mouths previously it was thought that slope failures or direct plunging of river flood water hyperpycnal flow dominated the triggering of turbidity currents on delta fronts here we re analyse the most detailed time lapse monitoring yet of a submerged delta comprising 93 surveys of the squamish delta in british columbia canada we show that most turbidity currents are triggered by settling of sediment from dilute surface river plumes rather than landslides or hyperpycnal flows turbidity currents triggered by settling plumes occur frequently run out as far as landslide triggered events and cause the greatest changes to delta and lobe morphology for the first time we show that settling from surface plumes can dominate the triggering of hazardous submarine flows and offshore sediment fluxes

origin chronology and environmental significance of holocene aeolian and alluvial sands at blue mountain falkland islands extensive and thick sand accumulations containing organic rich horizons at blue mountain falkland islands are most probably derived from weathering of local bedrock under late pleistocene periglacial conditions weathering and subsequent deflation produced several shallow basins that are now occupied by lakes sand morphology sedimentary structures and site characteristics indicate that the sand deposits are predominantly aeolian although some alluvial sands are also present deflation occurred either before the lakes existed or at times of lower lake levels sixteen 14c dates from organic rich horizons show that some sand accumulated in the early holocene or late pleistocene but that most is of mid to late holocene age landscape stability instability phases were not synchronous between sites and cannot be explained by the regional trends of holocene climate change a period of significantly lower lake levels and major aeolian erosion at c 5000 4500 bp is proposed but is not supported by regio

stone run block stream formation in the falkland islands over several cold stages deduced from cosmogenic isotope 10be and 26al surface exposure dating cosmogenic isotope 10be and 26al surface exposure dating has been applied to valley axis and hillslope stone runs relict periglacial block streams and their source outcrops in the falkland islands south atlantic the data indicate that stone runs are considerably older landforms than previously envisaged and afford no evidence that they are a product of the last glacial maximum the samples range in apparent 10be age from 42k to 731k yr bp but some of these are minima the results indicate that valley axis stone runs may be up to 700 800k yr old have simple exposure histories and are composite landforms that developed over several cold stages analyses of some hillslope and outcrop samples also demonstrate simple exposure histories with 10be ages from 42k to 658k yr bp in contrast isotopic ratios from other hillslope and outcrop samples reveal they have had a complex exposure history involving periods of burial or shielding the samples range in 10be age from 59k to 569k yr bp and these are regarded as minimum age estimates larger stone runs may be older than smaller runs and there is a possibility that stone runs older than 800k yr exist in other parts of the falklands the assertion that glaciation in the falklands was restricted to the highest uplands is supported by the data and the potential for age determination of other boulder strewn and bedrock landforms using cosmogenic isotope analysis in order to extend the geochronology of quaternary events and processes is noted

holocene glacier fluctuations in south america and antarctica abstract glacial geologic evidence indicates that glaciers throughout the andes and antarctica fluctuated during the holocene radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka reaching positions from several 100 m to a few kilometres beyond their present limits in south america tenuous evidence from radiocarbon dates with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of neoglacial advance culminating 5000 4000 bp 3000 2000 bp 1300 1000 bp and 15th late 19th centuries smaller advances may have occurred at ca 8400 bp ca 7500 bp and ca 6300 bp the meagre data are consistent in indicating broad synchrony throughout the andes during the last 5 ka suggesting response to global climatic changes anomalies exist in patagonia where some tide water glaciers reached their maximal holocene limits recently this century the broad spectrum of differing antarctic environments produces interesting contrasts some local glaciers in the mcmurdo sound area of the east artarctic continent are more extensive now than during the global glacial maximum ca 18 ka bp when they were starved of precipitation consistent agreement among 14 radiocarbon dates from the south shetland islands indicates two main holocene glacier advances the most extensive 2 3 km peaking in the 12th century the other culminating in the 18th 19th century glaciers in south georgia reached their most advanced holocene limits before 2200 bp moraine fjord glacier which culminated as a 6 km advance between 1460 1700 radiocarbon bp may have lagged 400 650 years behind the climatic forcing because it could only advance in its deep water fjord by building a moraine bank smaller advances in south georgia culminated in the 17th 19th centuries and during the 1920s 30s there is no firm evidence of glacier advances before 3 ka bp in the southern ocean sub antarctic domain but broad synchrony in glacier advances during the last ca 3000 years appears to have occurred throughout the andes antarctic transect caution is required in the interpretation and correlation of moraines associated with calving glaciers and of those with poorly constrained dating

understanding fine grained river sediment dispersal on continental margins studies of fine grained sediment dispersal in the marine environment have documented diversity in the behavior of depositional systems on continental margins with different oceanographic conditions and morphologies based on the pattern and nature of sediment accumulation for twenty three case studies we propose there are five basic types of dispersal systems and these are related to river wave tide and margin characteristics data suggest that the type of dispersal system on any margin can be predicted with knowledge of sediment load mean significant wave height tidal range and continental shelf width at a river mouth and from these a hierarchical decision tree is developed analysis of the dispersal system type of more than 100 river mouths reveals that proximal accumulation dominated pad and marine dispersal dominated mdd systems are most abundant but estuarine accumulation dominated ead systems also are anticipated to be numerous globally research quantifying marine sediment dynamics in these system types is needed although less common the size and nature of subaqueous delta clinoform sdc and canyon captured cc systems also warrant future attention to their study strong correlations between physical characteristics i e significant wave height and tidal range and the depth and distance to the nearest maximum shelf depocenter provide evidence that in reality a continuum exists between the system types the process related partitioning of sediment in the five different types of marine dispersal systems has important implications for understanding the stratigraphic record and the cycling of carbon

226ra in the black sea and sea of marmara water column distributions of226ra were determined at stations in the sea of marmara and the black sea as part of the 1988 joint u s turkish black sea expedition black sea surface water226ra concentrations were a factor of three to four lower than measurements made 20 years earlier the most likely cause is increased removal of226ra and ba 35 due to increased surface biological activity a secondary effect is decreased fluvial discharge and related dimunition of inputs by desorption from fluvial suspended sediments the amount of226ra missing from the surface waters of the black sea over this period is accounted for in the high porosity surficial fluff sediment layer throughout the black sea depth profiles of226ra exhibited pronounced maxima of approximately 25 dpm 100 l at about 16 2 16 3 in the vicinity of a bacterial maximum but slightly shallower than the total dissolved mn and fe maxima 16 4 16 5 reported by lewis and landing 38 while the226ra maximum may in part be linked to the cycling of mn and fe oxyhydroxides near theo2h2s interface its distribution appears to be more plausibly explained as a result of the microbial breakdown of particulate organic matter and the subsequent release and partial dissolution of associated barite in this region a simple steady state two model has been used to obtain a semiquantitative understanding of the behavior of226ra in the black sea by incorporating reasonable estimates for the input and removal of226ra in the black sea an excellent agreement between predicted and observed 1988 226ra concentrations was achieved the model suggests that the dominant variables controlling the distribution of226ra in the black sea are riverine input and cycling with ba

palaeoclimates in central and south america since 18 000 bp based on pollen and lake level records abstract the last 18 ka of palaeoclimates are discussed at 3 ka intervals based on palaeoenvironmental changes shown in pollen and lake level records from central and south america a total of 61 pollen records fulfill the requirements of continuity and chronology to be used in this synthesis 8 records from tropical and subtropical lowlands in central and south america 7 records from the central american highlands 26 records from the high andes north and south of the equator 2 records from the southern subtropics and 18 from the southern andes and subantarctic islands palaeoclimatic interpretation of the pollen records is semiquantitative based on bioclimatic parameters such as e g elevational temperature gradients or latitudinal precipitation gradients that can be related to vegetation zonation additional palaeoclimatic information is obtained from lake level records derived either from dated shorelines or from the limnological history of lake sediment sections large scale palaeoclimatic comparison of the proxy data records indicates that full and late glacial climates throughout central and south america were cooler than today by about 4 to 5 c but that moisture patterns showed regional differentiation thus in both the southern subtropics and high latitudes in southern chile conditions were substantially moister than today during full and late glacial times whereas everywhere else conditions were far drier than today in terms of palaeocirculation this scenario can be interpreted as a poleward shift of the subtropical as well as the westerly circulation a scenario that has been suggested by palaeoclimatic simulations from general circulation models gcm another major palaeoclimatic aspect predicted by the gcm simulations is the suppressed early holocene summer monsoon in the southern subtropics although proxy records are few from this zone their palaeoenvironmental history during that time shows a period of aridity that would support the model one of the most controversial aspects of south american palaeoclimates concerns the existence of a younger dryas equivalent a cold period between 11 and 10 ka bp based on the existing data from south america that show a great diversity of palaeoclimatic trends the concept of an interval that is characterized by the same climatic signal as documented for the north atlantic seems too simplistic moreover at this point only very few records have been analysed in sufficient detail to yield unambiguous climatic information for the interval in question the principal outcome of this palaeoenvironmental and palaeoclimatic synthesis is the better understanding of the type and quality of data available at present and the realization of regions and periods where much more and concerted effort is needed to address problems of intra and interhemispheric palaeoclimatic correlations only then can questions concerning the mechanism of climatic change be tackled successfully

sand veins and wedges in cold aeolian environments sedimentary structures formed by the progressive primary infilling of thermal contraction cracks with sand are termed primary sand veins and sand wedges in addition to simple vein or wedge shapes irregularities can be caused by sand veins branching from their sides and toes primary sand wedges form widely in sandy polar deserts locally in sandy areas of tundra and probably in seasonally frozen ground there are no unique criteria for distinguishing primary sand veins and wedges from sand veins and wedges of other origins identification of the former depends on the occurrence of distinctive features not always present and on evaluation of their lithofacies and palaeoenvironmental contexts care and caution are advocated in the use of ancient relict primary sand veins and wedges as quantitative palaeoenvironmental indicators because modern active wedge distribution is poorly known and hence inferred thermal climatic threshold values are questionable it is suggested that ancient relict primary sand wedges exceeding 2 m in depth and with well developed vertical lamination probably indicate the former occurrence of continuous permafrost whereas sand veins and narrow sand wedges frost cracks are potentially ambiguous as they may form not only in the active layer above and within continuous permafrost but also in seasonally frozen ground in non permafrost areas

storm wave reactivation of a submarine landslide submarine landslides move large amounts of sediment and are often hazardous to offshore installations marine surveying techniques effectively define landslide locations and geometries for example refs 1 4 in various underwater geological settings including deltas fjords and earthquake prone areas1 5 movement rates and mechanics are generally inferred from indirect evidence such as cable breaks and damage to sea floor structures for example refs 6 8 but actual measurements of landslide behaviour are sparse using bottom deployed pressure sensors tiltmeters and accelerometers we have collected data on sea floor landslide reactivation involving sediment collapse and remoulding on the submarine slopes of the huanghe delta china the sensors were emplaced into sea floor clayey silts on 4 october 1987 and recovered on 16 october after the passage of three severe storms

sub decadal submarine landslides are important drivers of deltaic sediment flux insights from the mississippi river delta front submarine mass failures triggered by energetic forcing events such as hurricanes and earthquakes are relatively well studied due to the potential for infrastructure damage and tsunami generation such failures are common on heavily sedimented margins where underconsolidated deposits are preconditioned to fail however studies of seafloor sediment movement between large events remain scarce using repeat bathymetric surveys of the mississippi river delta front mrdf we document substantial seafloor movement in absence of major hurricanes about 1 m yr of deepening was observed within preexisting failures with downslope sediment transport on the order of 10 5 m 3 yr outside failure features seafloor depths remained stable or showed minor 20 cm yr accretion mrdf volumetric sediment flux during hurricane driven mass failures is an order of magnitude greater than the annual flux during a quiescent interval when normalized by time however sediment flux during the quiescent interval 5 5 10 5 m 3 yr was half that of hurricane driven mass failures 1 1 10 6 m 3 yr these observations corroborate our wave modeling results which infer that even waves of 1 yr recurrence interval can generate differential seafloor pressures sufficient to trigger submarine landslides this does not exclude the possibility of river floods also being agents of failure these findings indicate that sub decadal submarine landslides are important to mrdf dynamics comparable to the role of major hurricanes and observation during seemingly quiescent periods is necessary to holistically assess sediment flux the periodicity and prevalence of moderate scale mass transport documented here corroborates similar recent studies offshore other deltas globally indicating that highstand mass and time budgets of shelf to deep sea sediment flux in addition to organic carbon and bioreactive particles may need to be revised

submarine slide initiation and evolution offshore pointe odden gabon analysis from annual bathymetric data 2004 2009 abstract time serial bathymetric data acquired between 2004 and 2009 are used to evaluate the morphological evolution of the coastal area offshore pointe odden located on the mandji island gabon data analysis highlights the alternation between fast sedimentation periods at shallow water depth related to intense longshore drift and catastrophic erosional events because of sediment overloading and slope oversteepening small scale instabilities are generated successive slide scars channel formation and growth by retrogressive erosion however when critical stability conditions are reached large failures occur 2005 submarine slide geotechnical measurements and sedimentological analyses on the study area suggest that flow liquefaction would be the triggering mechanism of the 2005 event moreover our analysis shows that the associated slide scar is rapidly filled by compensation and that failure morphology could disappear from the seafloor in about 15 20 years

fluvial aeolian interactions part i modern systems two modern fluvial aeolian depositional systems great sand dunes national monument colorado and the mojave river wash california are remarkably similar in spite of different climates sizes fluvial sediment textures and relative directions of aeolian and fluvial transport dune growth and migration and deflation of blowouts create 8 10 m of local relief in unflooded aeolian landscapes there are six prominent fluvial aeolian interactions 1 fluvial flow extends into the aeolian system until it is dammed by aeolian landforms 2 interdune areas overbank interdunes upstream of aeolian dams and alongside channels are flooded 3 water erodes dunes alongside channels and interdunes 4 flood waters deposit sediment in interdune areas 5 fluvially derived groundwater floods interdunes interdune playas 6 wind erodes fluvial sediment and redeposits it in the aeolian system unique and characteristic sediments are deposited in overbank interdunes and in interdune playas reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions these fluvial aeolian interdune deposits are characterized by irregular concave up bases and flat upper surfaces containing mudcracks or evaporite cement characteristic low relief surfaces form in aeolian systems as an effect of flooding fluvial deposits are resistant to aeolian deflation aeolian sand is preserved when flood sediments are deposited around the bases of the dunes thus repetitive fluvial and aeolian aggradation tends to be stepwise as interdune floors are suddenly raised during floods the effects of flooding should be easy to recognize in ancient aeolianites even beyond the area covered with overbank muds

quaternary glaciations of the southern andes abstract the southern andes comprise the southernmost portion of the andean cordillera beginning at the edge of the puna altiplano lat 27 s and ending at isla de los estados lat 55 s the late cainozoic glacial record of these mountains spans the interval from the late miocene to the present and is one of the most complete to be found anywhere in the world this has arisen for several reasons i the conterminous mountain ice cap extended to the piedmont zone on both flanks of the range where the sedimentary and morphological record has been well preserved ii periodic volcanism mainly from monogenetic fissure eruptions of basalt east of the range and from central tephra producing cones along the mountain crest has provided opportunity for the preservation and radiometric dating of interbedded glacial deposits iii a tectonically induced interval of stream incision in the mid pleistocene and simultaneous uplift has preserved glacial sediments on interfluves iv in the chilean lakes region west of the mountains late quaternary glaciers terminated in a well vegetated landscape thus creating scope for radiocarbon dating of interbedded and incorporated organic materials consequently the last glaciation in the llanquihue area of chile is one of the best dated sequences in south america thus the llanquihue glaciation is proposed as the south american equivalent of the wisconsin and weichsel glaciations of north america and north west europe respectively

immobility of 210pb in black sea sediments we measured 210pb in a core from the deep black sea which contained a turbidite of low 210pb activity surrounded above and below by pelagic sediments of much higher activity to evaluate in situ210pb mobility under the anoxic moderately sulfidic conditions by measuring at millimeter scales across the distinct laminae turbidite contacts and modeling the observed profile we estimated a lower limit of the kd of 107 deff 5 10 13 this result increases confidence in sediment chronologies from the black sea based on 210pb because it implies that profiles will not be altered significantly by diffusive transport of 210pb below the turbidite the 210pb inferred accumulation rate was 50 g m2 a which is lower than laminae based estimates by a factor of 3 4

hydrodynamic controls on muddy sedimentary fabric development on the southwest louisiana subaqueous delta abstract this study examines the sedimentary products of current wave enhanced sediment gravity flows cwesgfs on the muddy southwest louisiana swla subaqueous delta where the combined effects of gravity currents and wave orbital velocity exert a strong control on sedimentary fabric development and contribute to development of a muddy inner shelf clinothem cwesgf microstratigraphy from the swla subaqueous delta displays an overall structure similar that is similar to the tripartite layering of wesgfs previously documented on the eel shelf where wave enhanced sediment gravity flow deposits were first described basal crossbeds intermediate planar interlaminations of clay and silt topmost clay rich drape however on the swla subaqueous delta a shorter wave period appears to impart more rapid alternations in turbulent and laminar conditions than for the eel shelf reducing the prominence of the intermediate planar laminations that are thought to develop during laminar flow conditions only a novel framework for relating the sedimentary products of cwesgfs to interacting unidirectional wave driven and gravity driven flow is used to place our results in a global context with respect to other modern examples this is an important contribution as it may provide insights into paleo depositional conditions represented by sedimentary structures in ancient strata and provide the basis for developing additional recognition criteria for cwesgfs an important and diverse class of sediment gravity flows

sediment accumulation in the central western black sea over the past 5100 years the postdepositional particle flux accumulation rate over the last 5100 years was studied in the anoxic sediment units i and ii from the central western black sea deposition of unit ii sapropel in the deep black sea basin was divided further into two subunits the beginning of the deposition of the sapropel in the black sea 5100 3100 years b p subunit iib was characterized by higher organic carbon accumulation rates due largely to higher primary production accumulation rates of lithogenic matter were at a minimum compared to younger units during the subsequent 2100 years 3100 1000 years b p subunit iia organic carbon accumulation rates decreased considerably while accumulation rates of lithogenic matter increased to the present level at 1000 years b p unit i total mass accumulation rates increased by a factor of 3 this increase was largely a result of an increase in carbonate accumulation rates by a factor of 11 which was caused by the rapid appearance of emiliania huxleyi in the black sea higher carbonate accumulation rates in unit i are mainly the cause for the considerably lower organic carbon content compared to unit ii since the organic carbon accumulation rate in unit i did not decrease general correspondence of accumulation rates of lithogenic matter in different cores through time suggests overregional long term 100 year scale climatic effects on the terrigenous particle supply to the black sea

large scale mass wasting events on the fraser river delta front near sand heads british columbia although the fraser river delta front supports coastal structures including ports a lighthouse jetties submarine power cables and sewage pipelines the stability of the delta front is little understood five large scale mass wasting events at the mouth of the main channel near sand heads have been detected by comparing successive bathymetric surveys conducted by public works canada between 1970 and 1986 these events can involve the downslope movement of more than 1 106 m3 of silty sand and the landward retrogression of the delta front crest of up to 350 m or more morphologic and sedimentologic evidence suggests that these events are slope failures which result from the liquefaction of silty sand rapid deposition at the river mouth is likely a prerequisite for failure although interstitial gas tidal currents waves and earthquakes also may contribute to failure these results have important implications for the foundation stability of the sand heads lighthouse and future coastal structures in t

a relationship between dunes fire and climate recorded in the holocene deposits of quebec during the past 5 000 yr bp the tropics have experienced an increase in aridity and aeolian activity in both maritime and continental areas1 4 in contrast the onset and subsequent development of post hypsithermal climates in northern latitudes were primarily conducive to global cooling it is suggested here that aeolian activity in cold environments represents a direct response to this long term cooling trend that began after 6 000 5 000 yr bp at the end of the climatic optimum5 9 this study establishes the holocene chronology of sand dunes near the outer forest limit in northern quebec fig 1 i show here that fires initiate the aeolian activity and that the fire dune relationship is typical of cooling period on this basis a palaeoclimatic reconstruction since the climatic optimum is proposed

iunconsistencies in accumulation rates of black sea sediments inferred from records of laminae and 210pb recently published estimates for the age of the unit 1 unit 2 contact in black sea sediments based on accelerator mass spectrometry ams 14c measurements jones 1990 calvert et al 1991 appear to be older than those based on the previously published chronology based on lamina couplets degens et al 1980 hay 1988 by a factor of 2 to 3 to help reconcile the differences we compare sediment accumulation rates based on the 210pb method with estimates based on lamina counts for two cores from the black sea abyssal plain accumulation rates estimated using the 210pb technique have varied little over the last 150 years from the averages of 55 and 50 g m 2 yr 1 at stations in the western and eastern basins respectively these values are about a factor of 2 lower than accumulation rates derived by counting lamina couplets over the dated intervals close examination of the laminae suggests that the discrepancy exists both because it is difficult to count the very fine laminae and because a complete couplet is not deposited every year in order to provide a useful stratigraphic horizon for future investigators studying sedimentary records of the black sea we estimate the age of a distinct black marker horizon which can be easily identified across the entire abyssal plain to be 150 8 years deposited in 1838 8 a d

late pleistocene sediments and environmental change at plaza creek falkland islands south atlantic late pleistocene organic rich sediments exposed in coastal bluffs near the head of plaza creek east falkland have yielded conventional and ams 14c dates of between 36 and 28 ka bp and possess a pollen spectrum dominated by grasses indicating a vegetation assemblage similar to that of the present day although some sample dates are anomalous and contamination by non contemporaneous carbon cannot be ruled out entirely the age estimates are consistent with evidence and dates from antarctica south america and the amphi north atlantic for climate shifts to interstadial conditions at around that time the organic rich units are developed in and enclosed by deposits attributed to processes of periglacial mass wasting grain size characteristics suggest that these sediments may have been emplaced by solifluction shallow translational landsliding and surface wash in at least five mass wasting episodes some of the mass wasting sediments might correlate with solifluction deposits above and below a podsolic soil dated to 26 ka bp at san carlos east falkland and with periods of cirque and valley glaciation identified in the uplands of the falkland islands the similarity between late pleistocene interstadial holocene and present day pollen assemblages and the lack of vegetation change within these periods is characteristic of most cool temperate southern ocean islands and may reflect the lack of sensitivity of the vegetation to climate change and or a lack of climate variability for the time intervals covered 1998 john wiley sons ltd

mass wasting on the mississippi river subaqueous delta abstract the mississippi river delta front mrdf is an excellent natural laboratory for studying seafloor instability and evaluating the preconditioning factors and triggering mechanisms that lead to seafloor failures the occurrence of seafloor landslides on the mrdf has been recognized since the 1950s but the bulk of research on the topic was conducted in the 1970s 80s after seafloor landslides triggered by hurricane camille damaged offshore infrastructure through these efforts it was recognized that seafloor instability features are present across the entire delta front that rapid sediment delivery from the mississippi river is a primary preconditioning factor for failures and that cyclic loading from hurricane waves is the main triggering mechanism for deep seated catastrophic events however mounting evidence shows that mrdf seafloor motion occurs even during periods of no hurricane activity which could be attributed to creep like motion of underconsolidated sediment or smaller episodic flows triggered by winter storms or mississippi river floods given the extensive spatial distribution of instabilities on the mrdf the multiple mechanisms of failure and variety of resulting morphology and the range of potential triggering mechanisms with short recurrence the mrdf is an exceptional location to assess the complex problem of seafloor landslides an improved understanding of seafloor landslides is crucial for understanding global sediment budgets and associated biogeochemical cycling as they can evacuate large volumes of sediment into deep water over short time periods additionally seafloor landslides pose a hazard to offshore infrastructure and to coastal communities through possible tsunami inundation and advancing research on preconditioning factors and triggering mechanisms would improve hazard assessments this paper presents a review and synthesis of geological and geotechnical research on the mrdf particularly with respect to seafloor landslides their occurrence geological and geotechnical controls triggering mechanisms and knowledge gaps related thereto this synthesis is conducted at times of rapidly developing technologies for studying seafloor instability and as the mrdf enters a stage of degradation characterized by reduced sediment delivery and accumulation

tracing seafloor methane emissions with benthic foraminifera results from the ana submarine landslide eivissa channel western mediterranean sea article the hypothesis that benthic foraminifera are useful proxies of local methane emissions from the seafloor has been verified on sediment core ks16 from the headwall of the ana submarine landslide in the eivissa channel western mediterranean sea the core ms312 from a nearby location with no known methane emis sions is utilised as control the core was analysed for biostratigraphy benthic foraminiferal assemblages hyalinea balthica and uvigerina peregrina carbon and oxygen stable isotope composition and sedimentary structures the upper part of the core records post landslide deglacial and holocene normal marine hemipe lagic sediments with highly abundant benthic foraminifera species that are typical of outer neritic to upper bathyal environment in this interval the 13 c composition of benthic foraminifera indicates normal marine environment analogous to those found in the control core below the sedimentary hiatus caused by the em placement of the slide the foraminiferal assemblages are characterised by lower density and higher shannon index markedly negative 13 c shifts in benthic foraminifera are attributed to the release of methane through the seabed the mean values of the 13 c anomaly in u peregrina are 0 951 0 208 in the pre landslide sediments and 0 269 0 152 in post slide reworked sediments deposited immediately above the hiatus the 13

late pleistocene and holocene landscape evolution and environmental change in the lake sulivan area falkland islands south atlantic abstract late pleistocene and holocene landscape evolution around lake sulivan falkland islands south atlantic is assessed using morphological stratigraphical palaeoecological and 14c dating evidence data indicate a complex landscape history involving frost related activity ventifact development growth and degradation of peat terrain expansion and contraction of lakes and the development stabilisation and subsequent reworking of alluvial and aeolian sand bodies late pleistocene cold conditions favoured production of sandy diamicts on hillslopes and ventifacts on outcrops and blockfield clasts lateglacial climatic amelioration was marked by early growth of peat ca 16 500 cal yr bp since then peat accumulation changes in lake areas and depths and alluvial and or aeolian sand deposition have been recurring and dominant features of landscape change which throughout the late pleistocene and early holocene may have been a response to near synchronous climatic fluctuations along the south america antarctica axis marked landscape changes around lake sulivan coincided with intervals of glacier readvance in south america and south georgia at ca 3200 1900 and 700 100 cal yr bp with lower lake levels and aeolian sand transport from exposed lakebeds and shorelines implying greater aridity in the falklands than at present

stratigraphic charcoal analysis on petrographic thin sections application to fire history in northwestern minnesota results of stratigraphic charcoal analysis from thin sections of varved lake sediments have been compared with fire scars on red pine trees in northwestern minnesota to determine if charcoal data accurately reflect fire regimes pollen and opaque spherule analyses were completed from a short core to confirm that laminations were annual over the last 350 yr a good correspondence was found between fossil charcoal and fire scar data individual fires could be identified as specific peaks in the charcoal curves and times of reduced fire frequency were reflected in the charcoal data charcoal was absent during the fire suppression era from 1920 a d to the present distinct charcoal maxima from 1864 to 1920 occurred at times of fire within the lake catchment fire was less frequent during the 19th century and charcoal was substantially less abundant fire was frequent from 1760 to 1815 and charcoal was abundant continuously fire scars and fossil charcoal indicate that fires did not occur during 1730 1750 and 1670 1700 several fires occurred from 1640 to 1670 and 1700 to 1730 charcoal counted from pollen preparations in the area generally do not show this changing fire regime simulated sampling of the thin section data in a fashion comparable to pollen slide methods suggests that sampling alone is not sufficient to account for differences between the two methods integrating annual charcoal values in this fashion still produced much higher resolution than the pollen slide method and the postfire suppression decline of charcoal characteristic of my method but not of pollen slides is still evident consideration of the differences in size of fragments counted by the two methods is necessary to explain charcoal representation in lake sediments

carbon accumulation rates and the origin of the holocene sapropel in the black sea a detailed radiocarbon chronology obtained by accelerator mass spectrometry together with organic carbon and carbonate measurements on two black sea cores has been used to compare and contrast the burial fluxes of organic carbon in the holocene sapropel and the modern sediment at both deep water and eastern slope sites the sapropel is separated from the modern facies by a variable thickness of compositionally homogeneous sediment with low levels of organic carbon and anomalously old radiocarbon ages this homogeneous unit probably represents deposition by slumping or mudflow the age limits of the sapropel are 1600 6600 b p at the deep water site and 4000 6000 b p radiocarbon years before 1950 a d at the shallow water site the carbon accumulation rate in the deep water sapropel is higher than that in the modern deep water facies by a factor of 2 and is approximately the same as that in the modern sediment in shallow water the revised chronology of sapropel formation and the differences in the carbon accumulation rates probably indicate that the sapropel was formed by increased production during the transition from the premodern lake to the modern marine phases of the black sea this conclusion is consistent with the clear marine carbon isotope signal in the organic mattermore in the sapropel in both cores results to be reported elsewhere in contrast to the mixed source of carbon in the other facies less

late glacial and holocene glacier fluctuations and environmental change on south georgia southern ocean south georgia provides a terrestrial record of postglacial environmental change from a largely oceanic zone of the earth the record is representative of the southern westerlies and provides a link between antarctica and the temperate zones of southern south america evidence from glacial geomorphology slope stratigraphy and analyses of environmental indicators in peat and lake cores is used to interpret this record wastage of the full glacial ice cap was interrupted by a late glacial stade of the outlet and valley glaciers before ca 10 000 yr b p plant growth had begun at low altitude 50 m on the sheltered lee side northeast coast within the late glacial moraine limits by 9700 yr b p environmental conditions on slopes above 80 m probably were too rigorous for a stable vegetation cover until ca 6400 yr b p this was followed by a period from 5600 to 4800 yr b p when conditions were warmer than at present by up to 0 6 c periods of climatic cooling occurred at ca 4800 3800 yr b p ca 3400 1800 yr b p and within the last 1400 yr the most extensive holocene advance of south georgia glaciers culminated just before 2200 yr b p these holocene temperature changes of between 0 5 and 1 0 c are comparable in scale and timing to those identified from recent analyses of vostok ice cores from the antarctic ice sheet

rate and nature of podzolisation in aeolian sands in the falkland islands south atlantic abstract the rate and nature of podzolic soil development in aeolian sands in the cool temperate falkland islands south atlantic have been evaluated using 14c dating and morphological and chemical criteria in freely drained sands a carbic podzol developed over a minimum period of ca 2500 3000 years in sands with some drainage restriction a carbi ferric podzol developed within 300 500 years the shorter time span is consistent with results for podzolisation from other locations morphological and chemical contrasts between the profiles are inversely related to soil age the younger soil exhibits more complex podzolic horizonation and is attributed to pedogenesis in association with wetter profile conditions

a review of sediment diversion in the mississippi river deltaic plain abstract one of the proposed methods for restoring the disappearing mississippi delta is sediment diversion which uses channels and structures to divert water and sediment from the mississippi and atchafalaya rivers into adjacent basins this study presents a comprehensive review of geological and physical aspects of sediment dynamics in the mississippi river deltaic plain mrdp with special reference to diversion studies over the past two decades we synthesize these studies present the current understanding of sediment diversions in the context of sediment dynamics identify multiple key knowledge gaps and make recommendations for future studies to maximize net land building in the mrdp management strategies should be focused on a enhancing river sediment delivery both mud and sand b increasing sediment retention in receiving basins and c minimizing erosion in bays and estuaries compared with extensive studies of land building there have been relatively fewer studies of erosional processes a heterogeneous coastal geological framework cohesive sediment erodibility and subsidence together play complicated yet critical roles in future sediment dynamics in bays and estuaries of the mrdp sediment retention rates are highly sensitive to spatial and temporal scales types of sediments and delivery season sediment diversions to seaward receiving basins provide more surge protection but tend to have lower sediment retention due to active coastal processes structures and devices that improve sediment retention trap sediments dissipate waves and build living shorelines should be explored and cost to benefit analysis is needed long term planning should consider more landward diversions strategic community relocation and nonlinear response of the complex sedimentary system of the mrdp

frequency and triggering of small scale submarine landslides on decadal timescales analysis of 4d bathymetric data from the continental slope offshore nice france time series bathymetric data acquired from 1967 to 2011 are used to evaluate the morphological evolution of the continental shelf and upper continental slope off the city of nice se france ligurian sea mapping in water depths of 0 300 m was undertaken to identify the changing morphology of landslide scars and their erosive chutes quantitative digital terrain model dtm comparisons reveal areas of erosion and deposition over intervals of 5 8 years sediment remobilization events on the upper slope above depths of 200 m are frequent and significant landslide scars with volumes 25 000 m3 can occur with frequencies of 200 m periods of quiescence 1980 1990 and 2006 2011 are seen to alternate with periods when rapid retrogressive failure increase sediment volumes eroded from the upper slope shelf transition by an order of magnitude 1999 2006 temporal variations in landslide activity were correlated to several potential triggering factors that individually would not induce failures including earthquake activity rapid deposition of fine grained sediments on a steep slope and rainfall leading to fresh groundwater circulation below the shelf this 4d bathymetric study suggests that over the last 50 years the most important factor triggering landslides offshore nice is overpressure due to freshwater outflows

extreme waves under hurricane ivan hurricane ivan a category 4 storm passed directly over six wave tide gauges deployed by the naval research laboratory on the outer continental shelf in the northeastern gulf of mexico waves were observed with significant wave heights reaching 17 9 meters and maximum crest to trough individual wave heights of 27 7 meters 91 feet analysis suggests that significant wave heights likely surpassed 21 meters 69 feet and that maximum crest to trough individual wave heights exceeded 40 meters 132 feet near the eyewall

quaternary glaciations in the southern ocean and antarctic peninsula area abstract there are three main difficulties in constructing detailed time series for late quaternary glacier fluctuations in the southern ocean sub antarctic region sea level control on ice extent differential tectonics and lack of material for radiometric dating south of 60 s the glacial equilibrium line altitude is low enough for glaciers to expand without a decrease in temperature if sea level falls thus most tidewater glaciers in this region are not reliable indicators of small scale fluctuations in climate tectonic uplift during the quaternary may explain why the falkland islands did not develop most of their glacial and nivoglacial features until the last glaciation the south shetland islands have a unique assemblage of raised marine features in the sub antarctic possibly because the crustal block overlies a zone of magmatism and may respond sensitively to isostatic changes imposed by fluctuating ice masses despite the lack of vegetation some radiometric dates have been obtained from peat seaweed and fossil remains of marine shells and bones associated with glacial and raised beach deposits together with relative weathering criteria and drift distribution these suggestthat glaciers in the southern ocean and sub antarctic region have fluctuated synchronously with glaciers elsewhere in the southern hemisphere during the last 100 ka the last glaciation maximum culminated after 26 ka bp and glacier advances are inferred for the late glacial intervals 15 14 ka and 12 10 ka bp and the neoglacial interval last 5 ka

preconditioning and triggering of offshore slope failures and turbidity currents revealed by most detailed monitoring yet at a fjord head delta rivers and turbidity currents are the two most important sediment transport processes by volume on earth various hypotheses have been proposed for triggering of turbidity currents offshore from river mouths including direct plunging of river discharge delta mouth bar flushing or slope failure caused by low tides and gas expansion earthquakes and rapid sedimentation during 2011 106 turbidity currents were monitored at squamish delta british columbia this enables statistical analysis of timing frequency and triggers the largest peaks in river discharge did not create hyperpycnal flows instead delayed delta lip failures occurred 8 11 h after flood peaks due to cumulative delta top sedimentation and tidally induced pore pressure changes elevated river discharge is thus a significant control on the timing and rate of turbidity currents but not directly due to plunging river water elevated river discharge and focusing of river discharge at low tides cause increased sediment transport across the delta lip which is the most significant of all controls on flow timing in this setting