biogenic silica accumulation in the ross sea and the importance of antarctic continental shelf deposits in the marine silica budget abstract thirty five box cores were collected from the continental shelf in the ross sea during cruises in january and february 1983 pb 210 and pu 239 240 geochronologies coupled with biogenic silica measurements were used to calculate accumulation rates of biogenic silica sediment in the southern ross sea accumulates at rates ranging from 0 6 to 2 7 mm y with the highest values occurring in the southwestern ross sea biogenic silica content in surface sediments ranges from 2 by weight in sulzberger bay and the eastern ross sea to 41 in the southwestern ross sea biogenic silica accumulation in the southwestern ross sea averages 2 7 10 2 g cm2 y and is comparable to accumulation rates in high productivity upwelling environments from low latitude continental margins e g gulf of california coast of peru the total rate of biogenic silica accumulation in the southern ross sea is approximately 0 2 1014 g y with most of the accumulation occurring in basins 500 1000 m water depth if biogenic silica accumulation in the southern ross sea continental shelf is typical of other basins on the antarctic continental shelf as much as 1 2 1014 g y of silica could be accumulating in these deposits biogenic silica accumulation on the antarctic continental shelf may account for as much as a fourth of the dissolved silica supplied to the world ocean by rivers and hydrothermal vents

sedimentation of biogenic constituents during the last century in western bransfield and gerlache straits antarctica a relation to currents primary production and sea floor relief abstract as part of the fruela experiment 11 sediment cores were recovered from the bellingshausen sea the western bransfield and gerlache straits antarctic peninsula to determine the spatial distribution of organic carbon oc biogenic silica bsi and nitrogen n in the sediment under regions of known irregular primary production rates pprs oc bsi and n contents ranged from 0 3 to 1 2 from 5 7 to 20 4 and from 0 03 to 0 17 respectively apparent mean sediment accumulation rates sars varied between 0 25 and 3 11 mm year 1 220 and 1750 g m 2 year 1 central gerlache and western bransfield straits the orleans canyon had the highest biogenic constituents contents and sediment accumulation rates whereas the northern coast off snow island bellingshausen sea showed the lowest values central gerlache strait with the highest primary production rates in the study area was the only region where the oc and bsi contents in the sediment corresponded to the photosynthetic activity in the euphotic zone above it at the extremes of gerlache strait as in western bransfield strait sediment focusing by currents enhanced by depressions in the sea floor contributed to develop regions with high biogenic constituent concentrations whereas at the bellingshausen sea and western gerlache strait winnowing by currents may drift away the biogenic material exported from the euphotic zone apparently bottom relief and currents rather than solely depth determined the modern distribution and accumulation rates of biogenic particulate matter in the study area paleoceanographic interpretations of the sedimentary record from antarctic marginal seas such as gerlache and bransfield straits should consider that focusing due to lateral transport and sea floor morphology and the preferential degradation of oc relative to bsi may increase to an important degree the biogenic contents in the sediment especially the opal oc and bsi accumulation in antarctic marginal seas could be as important as the broad continental shelves despite large spatial differences

characteristics of flow fluctuations in a tide dominated estuary application of triple decomposition technique small tide dominated estuaries are affected by both large scale flow structures manifested as oscillatory residual currents and small scale bed generated turbulence the present understanding of the effects and relative contributions of these factors are inadequate due to limited systematic observations a field study was conducted in a small sub tropical estuary in which high frequency 50 hz turbulence data were recorded continuously for about 48 h a triple decomposition technique was introduced to isolate the contributions of tides slow fluctuations and true turbulence in the flow field a striking feature of the data set was the slow fluctuations which exhibited large velocity amplitudes up to 50 of the tidal amplitude under neap tide conditions the skewness of the fast true turbulence were within the range of 4 and 2 the analysis of the fast fluctuations revealed that variation in the turbulence characteristics are linked with the tidal velocity suggesting that the dispersion and mixing are dependent on some large scale flow properties the results also indicated enhanced mixing associated with the slow fluctuation in the flow field the results provided useful sets of information about the properties of slow and fast fluctuating components and their variations through tidal cycles in a micro tidal estuary

cycling of fallout pu 241am 137cs and natural u th 210pb radionuclides in washington continental slope sediments abstract we report activity profiles of pu isotopes 241am 137cs 210pb u and th isotopes in washington continental slope sediments from 332 1415 m water identify major processes responsible for them and compare results with those previously reported for washington shelf sediments specific activities of all nuclides but 137cs are higher in slope surface sediments than shelf surface sediments these higher specific activities which are due to more efficient scavenging by finer grained particles and higher concentrations of dissolved nuclides in slope waters do not cause proportionally higher slope sediment radionuclide inventories because they are counterbalanced by 5 10 fold lower sediment accumulation rates on the slope profiles of natural u and th series isotopes reveal that fallout nuclide profiles are not markedly affected by greater exchange of pore and overlying waters but they are dependent upon rate and depth of solid phase mixing 239 240pu activities inventories in slope sediments correlate with those of excess 210pb as in shelf sediments but with higher ratios of 210 pb pu in slope deposits 241 am 239 240 pu activity and inventory ratios in slope sediments average twice ratios in shelf sediments due primarily to greater particle affinity and preferential downward transport of 241am am pu activity ratios change little with depth in slope sediments suggesting insignificant separation of the two nuclides during diagenesis 239 240 pu 137 cs ratios are 2 3 times greater in slope than shelf sediments due to a combination of preferential scavenging of pu and greater 137cs loss by decay and desorption pu cs activity ratios decrease with depth in more porous slope sediments due to downward migration of 137cs 137cs is found in slope sediments from all water depths even though it is barely detectable below about 700 m in north pacific waters

ice dammed lateral lake and epishelf lake insights into holocene dynamics of marguerite trough ice stream and george vi ice shelf alexander island antarctic peninsula abstract we present new data regarding the past dynamics of marguerite trough ice stream george vi ice shelf and valley glaciers from ablation point massif on alexander island antarctic peninsula this ice free oasis preserves a geological record of ice stream lateral moraines ice dammed lakes ice shelf moraines and valley glacier moraines which we dated using cosmogenic nuclide ages we provide one of the first detailed sediment landform assemblage descriptions of epishelf lake shorelines marguerite trough ice stream imprinted lateral moraines against eastern alexander island at 120 m at ablation point massif during deglaciation lateral lakes formed in the ablation and moutonnee valleys dammed against the ice stream in george vi sound exposure ages from boulders on these shorelines yielded ages of 13 9 to 9 7 ka following recession of the ice stream george vi ice shelf formed in george vi sound an epishelf lake formed at 15 20 m asl in ablation and moutonnee valleys dated from 9 4 to 4 6 ka suggesting that the lake was stable and persistent for some 5000 years lake level lowering occurred after this with the lake level at 12 m at 3 1 0 4 ka and at 5 m asl today a readvance of the valley glaciers on alexander island at 4 4 0 7 ka is recorded by valley glacier moraines overlying epishelf lake sediments we speculate that the glacier readvance which occurred during a period of warmth may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of george vi ice shelf

recent sedimentation on the new jersey slope and rise radiocarbon dating and sedimentological studies of closely spaced cores indicate movement during the holocene of sediments on the new jersey continental slope and upper rise between wilmington and lindenkohl canyons the uneven time stratigraphic thickness of the late quaternary sediment sections between cores and the nonuniform deposition rate at any given core site and among core sites show that the sediment blanket in canyon and intercanyon areas has been affected by downslope gravity driven pocesses during the holocene to the present the reduced rate of deposition on the slope and upper rise between the late pleistocene and the present is largely due to decreased off shelf transport in response to the eustatic rise in sea level very old radiocarbon dates at core tops result from emplacement of older reworked materials from upslope or from truncation of sections by mass wasting processes exposing older material at the sea floor these processes also account for an irregular sequence of dated sections within cores and stratigraphic irregularities of the surficial cover from core to core marked variability in deposition rates on the slope and upper rise is largely a function of topographic configuration proximity and accessibility to sediment source and transport processes seaward of the shelf break moreover higher accumulation rates on the upper rise are attributed primarily to slope bypassing bypassing prevalent during the late pleistocene has continued periodically to the present

application of tandem accelerator mass spectrometer dating to late pleistocene holocene sediments of the east antarctic continental shelf abstract glacial recession from the antarctic continental shelf is recorded by glacial marine diamictons sands and overlying siliceous oozes in order to clarify the chronology for this sequence use was made of the university of arizona tandem accelerator mass spectrometer tams for 14 c dating small samples of benthic and planktonic foraminifera were selectively removed from diamictons graded sands and surface sediments which were recovered from the wilkes land continental shelf and slope east antarctica organic carbon was also utilized as a source for tams dating of the siliceous oozes and muds uncorrected ages varied from 14 260 140 to 3230 200 yr b p carbon fixed by phytoplankton and foraminifera is strongly influenced by old glacial derived co 2 thus reservoir corrections of up to 5500 yr are needed for the 14 c dates iceberg turbation reworks foraminifera so that dates from resulting deposits diamictons are interpreted as maximum ages the consistency of corrected ages from the shelf along with the sedimentologic interpretation suggests a rather recent recession perhaps mid holocene for this portion of the east antarctic ice sheet further application of the tams method should help clarify other problems concerning the late quaternary glacial history of antarctica

oxygen isotope and total beta radioactivity measurements on 10 m ice cores from the antarctic peninsula as part of the glaciology of the antarctic peninsula gap programme the snow cover at 25 stations was sampled to 10 m depth for oxygen isotope and total radioactivity analysis the mean annual oxygen isotope ratio correlates satisfactorily with 10 m temperature despite the complex topography of the area and suggests on average that climatic trends in the region are fairly systematic the relationship with temperature is similar to that derived from a simple model in which an air mass initially of maritime subtropical characteristics is progressively cooled as it moves towards the region the detailed isotope profiles show that for future deep drilling the most easily interpretable climatic information will be found in the more continental areas on the cast coast and on the plateau in the south of the region the degree of continentality of particular sites is reflected in the amplitude of the annual wave in the upper portion of the isotope ratio profile as well as in the accumulation rate

ice stream retreat and ice shelf history in marguerite trough antarctic peninsula sedimentological and foraminiferal signatures the timing nature and causes of grounded ice sheet retreat following the last glacial maximum lgm in marguerite trough west antarctic peninsula and subsequent early holocene ice shelf decay are presented in this paper we use sedimentological foraminiferal geotechnical and accelerator mass spectrometer ams radiocarbon data from marine cores from the mid continental shelf together with previously published ams dates to establish a sedimentological and chronological model initial ice sheet retreat through the outer and mid shelf sectors of marguerite trough was under way by ca 14 ka b p was rapid and coincided with the sea level rise of meltwater pulse 1a an ice shelf formed during this retreat and fine grained laminated muds reflecting meltwater derived suspension settling and or tidal pumping were deposited during this time the ice sheet remained grounded on the inner shelf ice shelf breakup and retreat of the calving front from ca 13 2 to 12 5 ka b p was slow 100 m a 1 across the outer and mid shelf with calving bay conditions remaining for at least 3 5 ka we interpret this ice shelf decay to have been driven by an incursion of weddell sea transitional water onto the shelf in contrast grounding line and ice shelf retreat in the inner bay occurred from ca 9 3 ka b p and was driven by circumpolar warm deep water encroaching onto the continental shelf at this time the mid shelf was an open marine environment characterized by hemipelagic deposition these findings highlight the importance of oceanographic controls in the breakup of antarctic peninsula ice shelves during the holocene

field studies of velocity salinity and suspended solids concentration in a shallow tidal channel near tidal flap gates abstract the design and operation of mathematical models of solute mixing and sediment transport in estuaries rely heavily on the provision of good quality field data we present some observations of salinity suspended sediment concentration and velocity at one of the tidal limits of a semi enclosed tidal lagoon in southern england pagham harbour west sussex uk where the natural processes of tidal incursion and solute mixing have been heavily modified as a result of the construction of sea walls dating back to the 18th century these observations made immediately downstream of two parallel tidal flap gates by conductivity temperature depth ctd profiler and also using bed mounted sensor frames to measure velocity at 2 fixed depths have yielded a set of results covering 11 tidal cycles over the period 2002 04 it is clear from the results obtained that over a typical tidal cycle the greatest vertical salinity gradients occur in the 1 2 h immediately after the onset of the flood tide and that subsequently energetic mixing acts to rapidly break down this stratification under moderate to high fresh water flows 0 5 m 3 s the break down in vertical salinity gradient is more gradual while under low fresh water flows 3 s the vertical salinity gradient is generally less pronounced estimates of richardson number during the early flood tide period reveal values that vary rapidly between

radiocarbon in the weddell sea as observed in a deep sea coral and in krill radiocarbon measurements were performed on krill and coral samples collected from the weddell sea during iwsoe 80 these are the first radiocarbon measurements available from this area since 1973 these data reveal carbon 14 levels for weddell surface water and southern weddell shelf water these data indicate that the radiocarbon levels in surface waters in 1980 were the same or slightly lower than those present in 1973 in addition an unusually low 14c value for shelf water from coral at 500 m is evidence that warm deep water wdw may penetrate much further and more frequently onto the shelf region than had previously been expected

the sedimentary legacy of a palaeo ice stream on the shelf of the southern bellingshausen sea clues to west antarctic glacial history during the late quaternary a major trough belgica trough eroded by a palaeo ice stream crosses the continental shelf of the southern bellingshausen sea west antarctica and is associated with a trough mouth fan belgica tmf on the adjacent continental slope previous marine geophysical and geological studies investigated the bathymetry and geomorphology of belgica trough and belgica tmf erosional and depositional processes associated with bedform formation and the temporal and spatial changes in clay mineral provenance of subglacial and glaciomarine sediments here we present multi proxy data from sediment cores recovered from the shelf and uppermost slope in the southern bellingshausen sea and reconstruct the ice sheet history since the last glacial maximum lgm in this poorly studied area of west antarctica we combined new data physical properties sedimentary structures geochemical and grain size data with published data shear strength clay mineral assemblages to refine a previous facies classification for the sediments the multi proxy approach allowed us to distinguish four main facies types and to assign them to the following depositional settings 1 subglacial 2 proximal grounding line 3 distal sub ice shelf sub sea ice and 4 seasonal open marine in the seasonal open marine fades we found evidence for episodic current induced winnowing of near seabed sediments on the middle to outer shelf and at the uppermost slope during the late holocene in addition we obtained data on excess pb 210 activity at three core sites and 44 ams c 14 dates from the acid insoluble fraction of organic matter aio and calcareous micro fossils respectively at 12 sites these chronological data enabled us to reconstruct for the first time the timing of the last advance and retreat of the west antarctic ice sheet wais and the antarctic peninsula ice sheet apis in the southern bellingshausen sea we used the down core variability in sediment provenance inferred from clay mineral changes to identify the most reliable aio c 14 ages for ice sheet retreat the palaeo ice stream advanced through belgica trough after similar to 36 0 corrected c 14 ka before present b p it retreated from the outer shelf at similar to 25 5 ka b p the middle shelf at similar to 19 8 ka b p the inner shelf in eltanin bay at similar to 12 3 ka b p and the inner shelf in ronne entrance at similar to 6 3 ka b p the retreat of the wais and apis occurred slowly and stepwise and may still be in progress this dynamical ice sheet behaviour has to be taken into account for the interpretation of recent and the prediction of future mass balance changes in the study area the glacial history of the southern bellingshausen sea is unique when compared to other regions in west antarctica but some open questions regarding its chronology need to be addressed by future work c 2010 elsevier ltd all rights reserved

diatom evidence for late holocene climatic events in granite harbor antarctica downcore diatom data from a deep basin in granite harbor antarctica provide new high resolution information concerning changes in oceanographic and depositional processes that have occurred during approximately the last 1250 years the influence of global scale climatic change during the time of the medieval warm period and possibly the little ice age is revealed by long term changes in floral assemblages as recorded by changes in the relative concentration of nitzschia cylindrus the diatom data suggest that granite harbor experienced less annual ice and pack ice cover during both these periods possibly because of higher temperatures during the medieval warm period and stronger offshore winds during the little ice age the sedimentary record reveals several distinct short lived events in which nearly monospecific blooms of corethron criophilum and chaetoceros spp occurred possibly the result of strong stabilization of the upper water column and were most likely a response to regional rather than global conditions although short lived these events may play a significant role in the delivery of organic carbon and biogenic silica to the seafloor

fine sediment mass balance in the western adriatic continental shelf over a century time scale abstract to obtain a quantitative estimate of the sediment accumulating on the muddy belt extending along the western adriatic continental shelf a budget was calculated based on the mass accumulation rates measured from more than one hundred activity depth profiles of 210 pb 137 cs depth distributions were used when possible to support 210 pb results 210 pb profiles show quasi monotonic declines in the foreset region of the central adriatic clinoform in the prodelta of the rivers po and isonzo 210 pb profiles are characterized by intervals of low and uniform activity which are thought to be produced by flood deposition since the north adriatic is shallow and occasionally affected by storms from bora wind sediments are not in steady state and their accumulation is the net result of recurring deposition resuspension and winnowing events in the western adriatic mass accumulation rates range between 0 04 and 6 6 g cm 2 yr 1 peak values were recorded in the po and isonzo prodeltas and along a narrow belt between pescara and the gargano promontory furthermore the latter depocentre is located immediately seaward of the offlap break 40 50 m water depth and parallels that of the most recent sigmoid of the hst the integration of mass accumulation rates throughout the mud wedge of the north and central adriatic gave a value of 42 0 tg yr 1 of sediment accumulating along the italian coast the balance between sediment accumulation and riverine sediment supply 46 6 tg yr 1 suggests an export of 4 6 tg yr 1 to the south adriatic basin and or the mediterranean sea the along shore sediment transport is very effective and in particular 16 2 tg yr 1 of sedimentary material 35 of the riverine supply is transferred from north to central adriatic through the ancona section

210pb and 137cs in air and soils measure the rate and vertical profile of aerosol scavenging we have determined the deposition rates of sup 210 pb and sup 137 cs from the atmosphere to the landscape of the eastern and mid western united states by measuring their inventories in core samples of undisturbed soils the mean inventories in lowland sites are 27 7 dpm cm sup 2 for sup 210 pb and 21 8 dpm cm sup 2 for sup 137 cs as of january 1984 the mean annual concentration of sup 210 pb in surface air at the 9 sites of the sure network decreases smoothly from about 0 060 dpm m sup 3 near the mississippi river to about 0 030 near the atlantic coast the ratio of deposition rate to surface air concentration is 0 62 0 03 cm s sup 1 for sup 210 pb and 1 36 0 08 cm s sup 1 for sup 137 cs using the activity vs altitude profiles of moore et al 1973 for sup 210 pb and the fission product nuclide sup 90 sr we calculate tropospheric aerosol mean residence times for sup 210 pb and sup 137 cs of 4 8 and 5 5 days respectively this near equality precludes a rapid decrease of the aerosol scavenging rate constant in the mid troposphere the sup 137 cs sup 210 pb ratios in soils from elevations above 1000 m in the appalachian mountains aremore lower than those in adjacent lowland soils indicating the preferential removal of aerosols from the lower layer of the troposphere presumably by cloud droplet impaction or by seeder feeder clouds less

rates of sediment reworking at the hebble site based on measurements of th 234 cs 137 and pb 210 abstract th 234 cs 137 and pb 210 measurements have been made on ten cores from the hebble site on the nova scotian continental rise th 234 mixing coefficients from hebble sediments show substantial lateral variability with values ranging from 1 to 33 cm 2 yr 1 these mixing coefficients are one to two orders of magnitude greater than values from typical continental rise and abyssal sediments because of high densities of benthic macrofauna th 234 data from hebble cores indicate that particles at the sediment water interface are mixed to depths of 1 5 cm on a 100 day time scale cs 137 and pb 210 data indicate that on time scales of 30 100 yrs surface sediments are reworked to depths ranging from 1 to 12 cm based on th 234 profiles from two hebble cores collected less than 200 m apart during consecutive years no temporal variability in mixing rate could be resolved in some hebble sediments there is good agreement between the th 234 mixing coefficient 100 day time scale and the pb 210 mixing coefficient 100 yr time scale in other hebble cores however th 234 data indicate that the pb 210 profile has not reached steady state if steady state solutions are used to model these non steady state profiles the calculated pb 210 mixing coefficient may underestimate the true mixing coefficient by as much as an order of magnitude

climatic control of sedimentation in bays and fjords of the northern antarctic peninsula abstract the northern antarctic peninsula is dominated by strong climatic gradients which are locally enhanced by subsidiary orographic and topographic effects these gradients are reflected in the sediments of the bays and fjords of the region the climate of the south shetland islands is relatively warm with high levels of precipitation this leads to a temperate glacial setting in which many glaciers terminate on land and bay waters which are turbid with terrigenous debris sediments which consist of terrigenous muds and sands with a low ice rafted debris ird content are relatively thick 70 m and have now filled in and almost completely mask the underlying basement topography the palmer archipelago is colder than the south shetland islands and is the wettest area of the antarctic it is heavily glaciated and all major glaciers are grounded below sea level only rarely have sediment plumes been seen the sediments which are primarily terrigenous muds and sands with a variable ird component are thin maximum 40 m but are ponding in every available bathymetric depression the pristine nature of the ice visible above sea level indicates that terrigenous debris is entering the bays from below sea level sediment gravity flows are important in redistributing sediment the danco coast lies within the precipitation shadow of the graham land plateau its climate is slightly colder and is the driest in the study area with less than half of the precipitation of the palmer archipelago nevertheless it is also heavily glaciated with few exceptions sediments here are diatomaceous muds and oozes they are very thin and drape across the rugged basement topography rather than ponding in lows sediment gravity flow deposits are rare these observations indicate a lower rate of production of terrigenous sediment here a consequence of the drier climatic setting

glacial marine sedimentation and quaternary glacial history of marguerite bay antarctic peninsula abstract marguerite bay situated between the subpolar glacial regime of the northern antarctic peninsula and the polar glacial regime of west antarctica is ideally located to test various models of glacial and glacial marine sedimentation and specific scenarios of late wisconsin ice sheet expansion piston cores and single channel seismic reflection data were collected during the deep freeze 85 and 86 expeditions to determine the late quaternary history of the area seismic data in the bay show a rugged seafloor with numerous deep troughs and a very thin layer of sediment over crystalline basement or older sediments glacial erosion is important in modifying existing features although the ultimate repository of the eroded material is not known it is not found within the bay the piston cores are topped by diatomaceous muds which are underlain by terrigenous muds and muddy gravels that imply deposition beneath an ice shelf basal tills were penetrated at three sites reflecting deposition by a grounded marine ice sheet a reconstruction of the glacial history of marguerite bay since the last glacial maximum shows grounded ice filling the bay in late wisconsin time rising sea level caused an uncoupling of the ice sheet and slow retreat of an ice shelf throughout the holocene

sedimentation processes on the antarctic continental margin at kapp norvegia during the late pleistocene sedimentological analyses concerning ice rafted debris grain size distribution biogenous components and clay mineral composition of four sediment cores from the antarctic continental margin off kapp norvegia reveal a cyclical pattern of three different sediment facies these are classified into warm and cold types representing warm and cold a climatic periods and short transition period from cold to warm events

the antarctic ice sheet during the last glacial maximum and its subsequent retreat history a review abstract an emerging body of evidence from studies of the last glacial interglacial cycle suggests that the east and west antarctic ice sheets have not advanced and retreated in concert the west antarctic ice sheet advanced to the outer shelf in most regions during the last glacial maximum lgm the retreat from the shelf commenced shortly after the lgm and continued into the late holocene the west antarctic ice sheet in ross and amundsen seas slid across a deforming bed at least during the final phases of extended glaciation this implies that at this time the ice sheet had a low profile differences in the number and locations of grounding zone wedges and smaller grounding zone features from trough to trough imply that individual west antarctic ice sheet ice streams retreated episodically details concerning the expansion retreat and behavior of the east antarctic ice sheet eais are more sparse the picture emerging is that the eais did not expand to the continental shelf edge during the lgm rather it achieved a maximum extent of a mid shelf position in some locations while in other areas the ice terminus was situated near its present location the timing of retreat along sectors within the eais appears diachronous and in places occurred prior to the lgm the antarctic peninsula shelf contained considerably more ice during the lgm than previously proposed the results presented in this paper support more recent published ice sheet models that call for greater contributions of melting ice from west antarctica including the antarctic peninsula to the post glacial rise in sea level

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

continuous high frequency turbulence and suspended sediment concentration measurements in an upper estuary the present study details new turbulence field measurements conducted continuously at high frequency for 50 hours in the upper zone of a small subtropical estuary with semi diurnal tides acoustic doppler velocimetry was used and the signal was post processed thoroughly the suspended sediment concentration wad further deduced from the acoustic backscatter intensity the field data set demonstrated some unique flow features of the upstream estuarine zone including some low frequency longitudinal oscillations induced by internal and external resonance a striking feature of the data set is the large fluctuations in all turbulence properties and suspended sediment concentration during the tidal cycle this feature has been rarely documented

developing sediment geochronologies for high latitude continental shelf deposits a radiochemical approach during january and february of 1986 47 box cores and 55 piston cores were collected from the bransfield strait gerlache strait and marguerite bay antarctica apparent sediment accumulation rates established for 100 yr time scales with excess 210pb chronologies range from 0 08 to 0 34 cm yr in the bransfield strait 0 15 to 0 51 cm yr in gerlache strait and from 0 10 to 0 27 cm yr in marguerite bay for the antarctic peninsula continental shelf 137cs appears to have a limited usefulness in assessing the effects of deep sediment mixing by benthic fauna on seabed excess 210pb profiles because the observed activities for the regions examined are close to counter detection limits conventional 14c ages of surface sediments from the peninsula region range from 1370 to 2820 yr the spatial variations in the conventional 14c surface ages are thought to be influenced predominantly by inputs of older eroded sediment from lateral transport current winnowing mass wasting and or a variable carbon source on a 1000 yr time scale 14c measurements of five piston cores from the bransfield strait yielded sediment accumulation rates ranging from 0 06 to 0 49 cm yr these data support the assertion by nelson 1988 that the excess 210pb sediment accumulation rates range of 0 08 to 0 34 cm yr for this region represent true rates the two sediment accumulation rates of 0 01 and 0 08 cm yr for the gerlache strait are significantly lower than the observed apparent 210pb accumulation rates mean 0 27 0 12 cm yr for this region likewise two piston cores from marguerite bay yielded 14c sediment accumulation rates of 0 02 and 0 05 cm yr which also are considerably lower than the excess 210pb apparent accumulation rates mean 0 17 0 06 cm yr for this area the one dimensional advection diffusion equation of goldberg and koide geochim cosmochim acta vol 51 1962 was solved simulatneously with 210pb and 14c data for bc18 and bc113 to resolved the effects of sediment mixing and accumulation in bransfield strait and marguerite bay box core samples respectively this model indicates that 210pb and 14c sediment accumulation rates agree within a factor of 2 in the bransfield strait whereas in marguerite bay the apparent 210pb accumulation rates may be as much as an order of magnitude too high in the southern high latitude environments of the antarctic peninsula radiocarbon measurements in the seabed are a better approach than 210pb for establishing accurate rates of sediment accumulation the 14c chronologies when coupled with 210pb data provide more reliable assessments of biological deep mixing and sediment accumulation rates than do excess 210pb data coupled with measurements of bomb produced 137cs the sediment accumulation rates for both 100 yr and 1000 yr time scales tend to decrease southward from the bransfield strait to marguerite bay which is consistent with glacial marine sedimentation processes as modulated by climate for the western antarctic peninsula seabed measurements of 210pb 137cs and 14c also provides valuable insights on water circulation and upwelling atmospheric inputs and sediment depositional processes for the antarctic peninsula region

antarctic palaeo ice streams we review the geomorphological sedimentological and chronological evidence for palaeo ice streams on the continental shelf of antarctica and use this information to investigate basal conditions and processes and to identify factors controlling grounding line retreat a comprehensive circum antarctic inventory of known palaeo ice streams their basal characteristics and minimum ages for their retreat following the last glacial maximum lgm is also provided antarctic palaeo ice streams are identified by a set of diagnostic landforms that nonetheless display considerable spatial variability due to the influence of substrate flow velocity and subglacial processes during the lgm palaeo ice streams extended via bathymetric troughs to the shelf edge of the antarctic peninsula and west antarctica and typically to the mid outer shelf of east antarctica the retreat history of the antarctic ice sheet since the lgm is characterised by considerable asynchroneity with individual ice streams exhibiting different retreat histories this variability allows antarctic palaeo ice streams to be classified into discrete retreat styles and the controls on grounding line retreat to be investigated such analysis highlights the important impact of internal factors on ice stream dynamics such as bed characteristics and slope and drainage basin size whilst grounding line retreat may be triggered and to some extent paced by external atmospheric and oceanic forcing the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

sedimentation of biogenic siliceous particles in antarctic waters from the atlantic sector abstract sediment traps were deployed in the drake passage bransfield strait and west of south orkney islands powell basin during december 1980 january 1981 december 1983 and between march and december 1983 respectively most of the trapped material is biogenic opal except in the lower half of the water column in bransfield strait where large amounts of resuspended aluminosilicates and quartz grains were present frustules and skeletons of siliceous microorganisms diatoms silicoflagellates radiolarians chrysophycean cysts fragments and moults of crustaceans and tests of foraminifera were found quantitatively diatoms are the dominant constituent of the trapped biogenic material alteration of diatom assemblages in the water column is due to mechanical breakdown by grazing zooplankton it mainly affects large frustules e g corethron criophilum castracane in the uppermost part of the water column dissolution of frustules occurs mostly at the sediment water interface and leads to the enrichment of strongly silicified valves e g nitzschia kerguelensis o meara hasle thalassiosira antarctica comber resting spores at the bransfield strait site a large part of biogenic opal was incorporated into fecal pellets of krill and copepods the bulk of pellet content consists of fragmented diatom frustules 1 10 m in size most intact valves found in the sediments have settled through the water column by means other than fecal pellet transport e g settling as solitary particles or incorporated into or attached to marine snow or large amorphous aggregates

rapid deglaciation of marguerite bay western antarctic peninsula in the early holocene glacial geological evidence of rapid ice stream retreat is important for the potential insight it can bring to understanding of contemporary rapid ice sheet change here we report new chronological constraints on the deglacial history of the marguerite trough ice stream which formerly drained part of the western margin of the antarctic peninsula this ice stream has been previously identified on geomorphological grounds as an example of an outlet that underwent rapid retreat following the last glacial maximum but the precise timing of this retreat has not been conclusively determined we obtained cosmogenic surface exposure dates on erratic boulders that record the thinning history of ice flowing into the ice stream these dates show that the ice stream underwent 270 m of thinning very rapidly at 9 6 ka bp the timing of ice stream thinning agrees closely with previously published data on ice shelf retreat the age of the first post glacial beaches and minimum constraining ages for the onset of lacustrine sedimentation and post glacial sedimentation in inner shelf fjords we compare the timing of retreat to the similarly sized anvers trough ice stream further north and find that retreat in marguerite bay was more rapid and earlier than in the anvers trough we argue that the intrusion of circumpolar deep water is the most likely forcing mechanism for retreat in marguerite bay a key finding of this study is that rapid retreat occurred in deep water with reverse continent dipping slope but also in relatively shallow water with a positive slope this may have implications for understanding of oceanographically forced ice sheet change in other parts of west antarctica

turbulence characteristics of a small subtropical estuary during and after some moderate rainfall in natural estuaries scalar diffusion and dispersion are driven by turbulence in the present study detailed turbulence measurements were conducted in a small subtropical estuary with semi diurnal tides under neap tide conditions three acoustic doppler velocimeters were installed mid estuary at fixed locations close together the units were sampled simultaneously and continuously at relatively high frequency for 50 hours the results illustrated the influence of tidal forcing in the small estuary although low frequency longitudinal velocity oscillations were observed and believed to be induced by external resonance the boundary shear stress data implied that the turbulent shear in the lower flow region was one order of magnitude larger than the boundary shear itself the observation differed from turbulence data in a laboratory channel but a key feature of natural estuary flow was the significant three dimensional effects associated with strong secondary currents including transverse shear events the velocity covariances and triple correlations as well as the backscatter intensity and covariances were calculated for the entire field study the covariances of the longitudinal velocity component showed some tidal trend while the covariances of the transverse horizontal velocity component exhibited trends that reflected changes in secondary current patterns between ebb and flood tides the triple correlation data tended to show some differences between ebb and flood tides the acoustic backscatter intensity data were characterised by large fluctuations during the entire study with dimensionless fluctuation intensity ib ib between 0 46 and 0 54 an unusual feature of the field study was some moderate rainfall prior to and during the first part of the sampling period visual observations showed some surface scars and marked channels while some mini transient fronts were observed

preservation efficiencies and accumulation rates for biogenic silica and organic c n and p in high latitude sediments the ross sea rates of biogenic sediment accumulation biogenic silica and organic c n and p and pore water flux have been established for a variety of depositional environments in the ross sea on the basis of 14c measurements in kasten cores sediment accumulation rates ranged from 250 cm kyr 1 in the coastal basin of granite harbor to 1 2 cm kyr 1 in the shelf and slope environments of the northern and eastern ross sea burial of biogenic material was most rapid in the southwestern ross sea where biogenic silica accumulation rates ranged from 2 to 31 g cm 2 kyr 1 and organic carbon accumulation rates ranged from 0 05 to 1 4 g cm 2 kyr 1 in the northern and eastern ross sea biogenic silica and organic carbon accumulation rates typically equaled 0 02 0 03 g sio2 cm 2 kyr 1 and 0 002 0 004 g c cm 2 kyr 1 flux core measurements were used to estimate seabed regeneration rates for biogenic silica organic carbon and phosphorus pore water fluxes in general showed much less variability across the ross sea than did the biogenic accumulation rates pore water silicate fluxes in the study area ranged from 0 6 to 5 3 g sio2 cm 2 kyr 1 whereas carbon fluxes ranged from 0 1 to 1 2 g c cm 2 kyr 1 and phosphate fluxes varied from 0 006 to 0 012 g p cm 2 kyr 1 seabed preservation efficiencies were calculated for biogenic silica organic carbon and phosphorus by combining the solid phase and pore water data the seabed preservation efficiencies for biogenic silica 1 86 were greater than for organic carbon 1 71 at all nine stations examined the preferential preservation of biogenic silica relative to organic carbon also was apparent in ross sea sediments because the biogenic silica organic carbon ratio in the material buried in the seabed generally was 2 times greater than the ratio in sediment particles arriving at the sediment water interface sediment accumulation rate correlated strongly with both the biogenic silica and the organic carbon preservation efficiency data p preservation efficiencies remained relatively high 24 65 even when the accumulation rates were low 1 2 cm kyr 1 because of the near zero phosphate fluxes out of the seabed of the total p in the seabed 0 04 0 09 wt approximately 25 existed in the form of organic p the total amount of biogenic silica accumulating on the ross sea shelf is 2 3 1012 g sio2 yr 1 which is approximately an order of magnitude less than the ledford hoffman et al 1986 estimate that was based on 210pb chronologies biogenic silica accumulation rates in the southern central and western ross sea increased during the mid and late holocene reaching their maximum values during the past 500 to 1000 years

late glacial to holocene climatic and oceanographic record of sediment facies from the south scotia sea off the northern antarctic peninsula two gravity cores were collected from the south scotia sea located off the northern antarctic peninsula during the 2002 2003 korea antarctic research program karp expedition to determine the late quaternary climatic and oceanographic history reassessment of previous sedimentological geochemical and micropaleontological analyses combined with established age model of ams 14c dates represent the reliable record of late pleistocene climatic oceanographic change for the scotia sea region of antarctica during the last glacial maximum lgm the south scotia sea received large amounts of sorted terrigenous sediments and some of the reworked diatom fossils emplaced by bottom currents from an extensively glaciated weddell sea continental margin drifting icebergs calved from the glacial fronts have dispersed glacial dropstones throughout the study area the bottom current deposits during the glacial phase comprise two lithologic units 1 bioturbated gravelly sandy mud facies 1 formed by sluggish bottom current caused by reduced dense water production originated from the ice sheet on the weddell shelf 2 indistinctly layered diatomaceous mud as shown by total organic carbon toc highs in the facies 1 deposited by sporadic bottom currents caused by intensified sea ice formation in polynya during the glacial stage the lgm is characterized by greater and longer sea ice coverage and a restricted weddell scotia summer communication as evidenced by a relative decrease in percentage thalssiosira antarctica and chaetoceros resting spores which are more abundant close to the weddell ice shelf deglaciation about 13 000 9000 14c yr bp in the south scotia sea was characterized by increasing toc diatom abundance and decreasing magnetic susceptibility and sand contents up core at this time subglacial meltwater streams began to emanate from the weddell ice sheet with peak of ice rafting sediment laden turbid plumes from melting glacier and deglaciated weddell shelf have probably been joined into the realm of contour currents weddell gyre circulation ultimately forming indistinctly laminated gravelly mud facies 2 in the south scotia sea these currents probably resulted from water exchange between the weddell ice shelf and circumpolar warm deep water during the retreating phase of the last glaciation the deglaciation was probably followed by a period of open marine conditions with variable extent of sea ice variable toc content between about 9000 and 3000 14c yr bp bottom water production occasionally appears to have diminished or ceased due to the disintegration of some of the weddell ice shelf and biogenic input became increased forming bioturbated diatomaceous mud and ooze facies 3 the climatic amelioration could have restored the weddell scotia communication during the summer as evidenced by a relative increase of t antarctica and c resting spore in facies 3 at the onset of neoglacial about 3000 14c yr bp a decrease in toc and diatom abundance and an increase of sand content reflect the formation of more extensive and seasonally persistent multiyear sea ice the weddell ice shelf advanced with increased sea ice coverage at this time and as a result bottom water might play a role in transporting terrigenous sediments and reworked fossil diatoms into the south scotia sea forming diatomaceous sandy mud facies 4 during this time it is possible that the weddell scotia communication would have been partly restricted as evidenced by a reduction of the numbers of t antarctica and c resting spores our results indicate environmental variability throughout the late quaternary that was consistent across most portions of the maritime antarctic peninsula in addition the timing of climatic transitions correlates with the northern hemisphere indicating the possibility of coherent climatic variability during the late quaternary at least for the higher latitudes

infragravity currents in a small ria estuary amplified coastal edge waves abstract observations are presented of estuarine infragravity oscillations in a very small estuary the ria de santiuste northern spain that discharges into a bay time scale calculations and measurements indicate that the most likely source of amplified infragravity waves within the estuary are coastal edge waves which appear to be resonating between the headlands of the bay and onshore offshore seiching of waters that may be resonating between the beach and the bay s seaward limit infragravity waves in the estuary have a narrow power dominant periodicity range of 4 3 4 8 min generally only very weak waves and at other periodicities occur within the tidal river when it is unaffected by the tide although infragravity water level amplitudes are small in the tidal river typically 0 01 m during high water the corresponding velocity amplitudes are significant typically 0 1 m s 1 despite the occurrence of high runoff conditions during these measurements within the estuary and close to the mouth near bed salinity shows considerable variability that is a consequence of salt wedge oscillations with periodicities that are within the range of 4 3 4 8 min model results for simulated neap to spring high water water levels show that wave periodicities in the range 3 5 4 5 min correspond approximately to 3 4 resonances the model also indicates that an effect of low runoff is to greatly enhance resonant behaviour within the estuary such that water level amplitudes of 0 02 m at the mouth can produce wave currents as fast as 0 4 m s 1 within the estuary compared with 0 1 m s 1 during high runoff

implications of intermittent turbulent bursts for sediment resuspension in a coastal bottom boundary layer a field study in the western yellow sea china abstract previous experiments carried out in the laboratory flumes and open channels have shown that close to the wall sediment resuspension is largely dominated by a sequence of intermittent powerful and large scale motions called coherent structures or burst cycle which mainly account for reynolds stress generation however the difficulties in simultaneously measuring the fluctuations of velocities and sediment concentration close to the seabed during the field observations inhibit the further understanding of this laboratory discovery in the marine regime in the present paper field data sets collected within a coastal bottom boundary layer bbl in the western yellow sea are examined comprehensively to reveal the relationships between coherent structures and sediment resuspension the following results are obtained 1 the bulk of turbulent sediment flux c w is accomplished by ejection 56 and sweep 42 events while contributions coming from outward and inward interactions are negligible 2 wall turbulence containing coherent structures vertically transport momentum more efficiently than suspended sediments 3 spectral scaling of sediment concentration reveals that two types of suspended sediment clouds with different sizes were existent during the peak flood the large size particle clouds contain coarse sediments locally resuspended from seabed whereas the smaller particle clouds consist of silts and clays and act as washload advected from jiaozhou bay and yellow sea by tidal flows 4 wavelet transform can provide a more intuitive way to study and visualize the relationship between the burst cycle and sediment suspension and the results clearly show that the intermittent reynolds stress generation is accompanied by intense sediment resuspension

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

mechanisms of holocene palaeoenvironmental change in the antarctic peninsula region the antarctic peninsula is one of the three fastest warming regions on earth here we review holocene proxy records of marine and terrestrial palaeoclimate in the region and discuss possible forcing mechanisms underlying past change with a specific focus on past warm periods our aim is to critically evaluate the mechanisms by which palaeoclimate changes might have occurred in order to provide a longer term context for assessing the drivers of recent warming two warm events are well recorded in the holocene palaeoclimate record namely the early holocene warm period and the mid holocene hypsithermal mhh whereas there are fewer proxy data for the mediaeval warm period mwp and the recent rapid regional rrr warming we show that the early holocene warm period and mhh might be explained by relatively abrupt shifts in position of the southern westerlies superimposed on slower solar insolation changes a key finding of our synthesis is that the marine and terrestrial records in the ap appear to show markedly different behaviour during the mhh this might be partly explained by contrasts in the seasonal insolation forcing between these records circumpolar deep water cdw has been implicated in several of the prominent changes through the holocene but there are still differences in interpretation of the proxy record that make its influence difficult to assess further work is required to investigate contrasts between marine and terrestrial proxy records east west contrasts in palaeoclimate the history of cdw to retrieve a long onshore high resolution record of the holocene and determine the role of sea ice in driving or modulating palaeoclimate change along with further efforts to study the proxy record of the rrr and the mwp

the radiocarbon record in varved sediments of carmen basin gulf of california a measure of upwelling intensity variation during the past several hundred years the decrease in 14c 12c with depth in a varved sediment core raised from the eastern flank of carmen basin gulf of california is greater than expected from varve and 210pb chronology the discrepancy is ascribed to a virtually monotonic decrease in upwelling intensity from several hundred years ago to the present this radiochemical study presents an approach independent of previously used biostratigraphic techniques for evaluating temporal variations in upwelling intensity in the gulf of california

a mid to late holocene record of vegetation decline and erosion triggered by monsoon weakening and human adaptations in the south east indian peninsula the mid to late holocene monsoon decline led to aridification of the indian peninsula impacting the early agricultural practices in the region our analysis of organic carbon mineral magnetic properties and ams 14c dating of a 54 2 m long sediment core cy from the godavari delta india showed changes in the organic carbon source and sediment provenance which are linked to the changes in vegetation and soil rock erosion caused by widespread aridification and associated human adaptation in central india our results show a decline in the concentration of ferrimagnetic minerals indicating reduced input from the basalts of the deccan plateau after 6 0 cal ka bp in response to the weaker indian monsoon 13c values show a distinct increase from 4 9 cal ka bp indicating an increase in c4 plant sources under the continued weak monsoon phase whereas a higher ferrimagnetic mineral concentration in the sediment suggested an increased deccan basalt source abrupt increase in 13c values and decrease in