weak tidal correlation of nw bohemia vogtland earthquake swarms we analyze the possible effect of solid earth tidal stresses upon a vertical strike slip fault in nw bohemia vogtland central europe typical by occurrence of swarm earthquakes the horizontal components of solid earth tidal stresses were found strongly to prevail and to reach the level of 2 kpa we examined tidal triggering as influence of tidal stresses to launching the swarm activity in relative absence of other stress disturbances the onset times of 46 swarms of mostly ml 3 earthquakes that occurred in the period 1991 2005 displayed an increased occurrence near the fortnightly maximum of tidal extensive normal stress the statistical test however did not prove a statistically significant correlation indicating a triggering effect of fault extension due to tidal loading we also examined tidal effects to the already running seismic activity of the prominent 2000 swarm by comparing the tidal stress distribution in the investigated period with the distribution of tidal stresses in the occurrence times of each earthquake the results show that these distributions are almost similar which indicates that individual earthquakes occur independent of tidal stresses the unclear tidal correlation of the swarm seismicity may be interpreted by small amplitudes and rates of tidal stress changes compared to the amplitudes and rates of coseismic stress perturbations and of pressure bursts of deep generated fluids

spatial variability of antarctic peninsula net surface mass balance 1 measurements from ice cores and snow pits collected over the last 50 years are used to examine how net surface mass balance varies across the antarctic peninsula to give the first detailed map of mass balance for the region a total of 211 reliable mass balance measurements were available for the preparation of the map but some areas were found to be very data sparse the analysis suggests that the largest values of mass balance are found along the spine of the northern part of the peninsula where over 2 5 m yr 1 water equivalent we has been measured a secondary peak of more than 2 0 m yr 1 we is determined along the mountains of eastern alexander island precipitation minus evaporation p e fields from the european centre for medium range weather forecasts reanalysis project are compared with our analysis of in situ data the model fields are found to have peak values of p e of only half the amounts found from the measurements the greatest model values are located on the western side of the peninsula areas where a high density of in situ data is available including king george vi sound and the high south central plateau part of the peninsula show a high spatial variability of net surface mass balance suggesting that local orographic features play a major part in dictating the mass balance

seasonal study of d18o and d13c in living stained benthic foraminifera from two swedish fjords in a previous 16 month seasonal study on living stained benthic foraminifera from two fjords on the swedish west coast it was reported that foraminifera proliferated in response to phytodetritus input the strongest response came from the opportunistic species stainforthia fusiformis in this study our objective was to find out if that phytodetritus input resulted in a change in the carbon isotopic composition of the foraminiferal tests we also wanted to examine if variations in salinity and temperature due to seasonality or deep water exchanges were reflected in the 18o values from s fusiformis that were obtained from the havstens fjord 20 m and the gullmar fjord 119 m during the 16 month study we developed a time series of 18o and 13c after the spring blooms in the havstens and the gullmar fjord decreases of about 0 2 to 0 3 in the foraminiferal 13c values were noted in the gullmar fjord after the autumn blooms decreases of the same order were also noted comparing the havstens and the gullmar fjord we found a 1 difference in both 13c and 18o we attribute this to hydrographic differences between the two fjords using calculated values of 18o together with the measured ones we noticed that s fusiformis in the gullmar fjord seems to calcify close to equilibrium with respect to the oxygen isotopes during autumn water temperatures were relatively high in the havstens fjord and foraminiferal abundance in the fjord was also high after a phytodetritus input but the measured 18o values do not reflect these higher temperatures this apparently contradictory combination of results might be explained by a varying 18o composition of the water during the year which counterbalances the temperature effect

tidal triggering of earthquakes in the subducting philippine sea plate beneath the locked zone of the plate interface in the tokai region japan we found a characteristic space time pattern of the tidal triggering effect on earthquake occurrence in the subducting philippine sea plate beneath the locked zone of the plate interface in the tokai region central japan where a large interplate earthquake may be impending we measured the correlation between the earth tide and earthquake occurrence using microearthquakes that took place in the philippine sea plate for about two decades for each event we assigned the tidal phase angle at the origin time by theoretically calculating the tidal shear stress on the fault plane based on the distribution of the tidal phase angles we statistically tested whether they concentrate near some particular angle or not by using schuster s test in this test the result is evaluated by pvalue which represents the significance level to reject the null hypothesis that earthquakes occur randomly irrespective of the tidal phase angle as a result of analysis no correlation was found for the data set including all the earthquakes however we found a systematic pattern in the temporal variation of the tidal effect the p value significantly decreased preceding the occurrence of mz4 5 earthquakes and it recovered a high level afterwards we note that those mz4 5 earthquakes were considerably larger than the normal background seismicity in the study area the frequency distribution of tidal phase angles in the pre event period exhibited a peak at the phase angle where the tidal shear stress is at its maximum to accelerate the fault slip this indicates that the observed small p value is a physical consequence of the tidal effect we also found a distinctive feature in the spatial distribution of p values the small p values appeared just beneath the strongly coupled portion of the plate interface as inferred from the seismicity rate change in the past few years d 2005 elsevier b v all rights reserved

lithogenic and biogenic particle deposition in an antarctic coastal environment marian cove king george island seasonal patterns from a sediment trap study abstract particulate suspended material was recovered over a 23 month period using two sediment traps deployed in shallow water 30 m deep off the king sejong station located in marian cove of king george island west antarctica variability in seasonal flux and geochemical characteristics of the sediment particles highlights seasonal patterns of sedimentation of both lithogenic terrigenous and biogenic particles in the coastal glaciomarine environment all components including total mass flux lithogenic particle flux and biogenic particle flux show distinct seasonal variation with high recovery rates during the summer and low rates under winter fast ice the major contributor to total mass flux is the lithogenic component comprising from 88 during the summer months about 21 g m 2 d 1 up to 97 during the winter season about 2 g m 2 d 1 the lithogenic particle flux depends mainly on the amount of snow melt snow accumulation delivered into the coastal region as well as on the resuspension of sedimentary materials these fine grained lithogenic particles are silt to clay sized composed mostly of clay minerals weathered on king george island biogenic particle flux is also seasonal winter flux is 0 2 g m 2 d 1 whereas the summer contribution increases more than tenfold up to 2 6 g m 2 d 1 different biogenic flux between the two summers indicates inter annual variability to the spring summer phytoplankton bloom the maximum of lithogenic particle flux occurs over a short period of time and follows the peak of biogenic particle flux which lasts longer the seasonal warming and sea ice retreat result in change in seawater nutrient status and subsequent ice edge phytoplankton production meanwhile the meltwater input to marian cove from the coastal drainage in january to february plays a major role in transporting lithogenic particles into the shallow water environment although the tidal currents may be the main agents of resuspension in this kind of sheltered bay

high resolution holocene climate record from maxwell bay south shetland islands antarctica the highest resolution holocene sediment core from the antarctic peninsula to date was collected during the first shaldril cruise nbp0502 drilling yielded a 108 2 m long core 87 recovery site nbp0502 1b from maxwell bay south shetland islands this high resolution sediment record comes from a region that is currently experiencing dramatic climate change and associated glacial retreat such records can help to constrain the nature of past climate change and causal mechanisms and to provide a context for evaluating current climate change and its impacts the base of the drill site sampled till and or proximal glacimarine sediments resting directly on bedrock glacimarine suspension deposits composed of dark greenish gray silty mud with variable diatom abundance and scattered very fine sand laminations make up the majority of the sedimentary section detailed sedimentological and geochemical analyses including magnetic susceptibility total organic carbon toc content carbon and nitrogen isotopic composition pebble content and biogenic silica content allow subdivision of the glacimarine section into nine units and seismic facies analyses resulted in the identification of six distinct seismic units we used 29 radiocarbon ages to construct an age model and calculate sedimentation rates that vary by two orders of magnitude from 0 7 mm a to 30 mm a radiocarbon ages from glacimarine sediments just above the till date back to between 14 1 and 14 8 ka thus ice was grounded in the fjord during the last glacial maximum and eroded older sediments from the fjord following initial retreat of grounded ice from maxwell bay the fjord was covered by a permanent floating ice canopy probably an ice tongue the highest sedimentation rate corresponds to an interval that contains abundant sand laminations and gravelly mud intervals and likely represents a melt out phase or period of rapid glacial retreat from 10 1 ka to 8 2 ka there is no evidence for an early holocene climatic reversal as recorded farther south at the palmer deep drill site minimum sea ice cover and warm water conditions occurred between 8 2 and 5 9 ka from 5 9 to 2 6 ka there was a gradual cooling and more extensive sea ice cover in the bay after 2 6 ka the climate varied slightly causing only subtle variation in glacier grounding lines there is no compelling evidence for a little ice age readvance in maxwell bay the current warming and associated glacial response in the northern antarctic peninsula appears to be unprecedented in its synchroneity and widespread impact

a 3 d hydrodynamic model of river flow in a delta region in this paper an application of telemac 3d to simulate the hydrodynamics of the river po delta flow is presented the po delta is a particular hydrological system in which the morphological configuration is in continuous evolution owing to natural and human activities a large amount of field data collected during several years has been used to test the 3 d mathematical model in the present article the main characteristics of the delta the data and hypotheses assumed in the calculations and the main results in terms of hydrodynamic and environmental variables are described copyright 2000 john wiley sons ltd

a three dimensional tidal model in boundary fitted curvilinear grids abstract in hydrodynamic models of marine and estuarine currents the use of boundary fitted curvilinear grids not only makes the model grids fit to the coastline and bathymetry well but also makes the kinetic boundary conditions simple and more accurate because of these advantages a three dimensional tidal model with boundary fitted curvilinear grids has been developed to simulate both tide and current in estuarine and shelf water the basic idea is to use a set of coupled stretched and elliptic transformations to map the physical space into a corresponding transformed space such that all boundaries are coincident with co ordinate lines and the transformed grids are rectangular the hydrodynamic equations in the transformed space are solved in a rectangular mesh of the transformed grid system the application of the model in the simulation of the m 2 s 2 k 1 and o 1 tidal waves in the bohai sea china shows that the numerical results are in good agreement with the observations the method of boundary fitted curvilinear grids is effective for improving simulation accuracy of current in the estuarine and shallow seas especially at the coastal regions where the current was usually impractical by a uniform cartesian grid system with the shoreline and bathymetry represented by numerous stair steps

distribution of the lunisolar tidal elastic stress tensor components within the earth s mantle a set of second order spheroidal love shida numbers h r k r l r and their radial derivatives were determined for the case of a symmetric non rotating elastic isotropic snrei earth with a liquid core by these means the stress tensor components from the surface to the core mantle boundary cmb were calculated for the case of zonal tesseral and sectorial tides the possible dependence of geophysical phenomena on the lunisolar effect is discussed for the three different kinds of tides the case of tidal triggering of earthquakes is discussed in more detail since the tidal potential and its derivatives are coordinate dependent and the zonal tesseral and sectorial tides have different distributions on and within the earth the lunisolar stress cannot influence the break out of every seismological event in the same degree a correlation between earthquake energy release and the lunisolar effect can exist in some cases where the seismic area is well determined and has either one seismic source or severe similar ones particularly in volcanic areas where the seismic activity is connected to the volcano s activity or in the case of some aftershock swarms significant correlation was found by different authors

oceanographic controls on benthic foraminifers from the bellingshausen margin of the antarctic peninsula abstract surface sediment samples collected from the bellingshausen sea continental margin of the antarctic peninsula were analyzed for benthic foraminifers a total fauna including live and dead specimen counts was used to statistically identify discrete benthic foraminifer assemblages two major assemblages were defined the bulimina aculeata and fursenkoina spp assemblages the distribution of the bulimina aculeata and fursenkoina spp assemblages are closely associated with the distribution of the two dominant bottom water masses on the continental margin the circumpolar warm deep water and weddell sea transitional water respectively their distributions cannot be related to organic carbon content or sediment texture of the surface sediments the faunal composition of the bellingshausen sea margin assemblages and their water mass associations are similar to faunal water mass relationships observed in the weddell sea and south atlantic ocean where bulimina aculeata is associated with circumpolar deep water and nonionella iridea n bradii and trifarina earlandi are associated with eastern shelf and modified weddell sea water

three dimensional hydrodynamic and salinity transport modelling of danshuei river estuarine system and adjacent coastal sea taiwan a three dimensional time dependent hydrodynamic and salinity model was applied to the danshuei river estuarine system and adjacent coastal sea in taiwan the model forcing functions consist of tidal elevations along the open boundary and freshwater flows from the main stem and tributaries in the danshuei river system the bottom roughness height was calibrated and verified with model simulation of barotropic flow and the turbulent diffusivities were calibrated through comparison of time series of salinity distributions the overall model verification was achieved with comparisons of residual current and salinity distribution the model simulation results are in qualitative agreement with the available field data the model was then used to investigate the tidal current residual current and salinity patterns under the low freshwater flow condition in the modelling domain the results reveal that the extensive intrusion of saline water imposes a significant baroclinic forcing and induces a strong residual circulation in the estuary the downriver net velocity in the upper layer increases seaward despite the enlargement of the river cross section in that direction strong residual circulation can be found near the kuan du station this may be the result of the deep bathymetric features there copyright 2007 john wiley sons ltd

stable oxygen and carbon isotope information on the establishment of a new opportunistic foraminiferal fauna in a swedish skagerrak fjord basin in 1979 1980 significant faunal changes reported fromrecent coastal environments which are not directly influenced by urban and industrial impact are rarely seen in gullmar fjord on the swedish west coast a significant foraminiferal fauna change occurred in connectionwith severe low oxygen conditions that evolved in thewinter of 1979 1980 a foraminiferal fauna marked by common skagerrak kattegat species which had previously characterised the deep fjord basin was replaced by the opportunistic low oxygen tolerant species stainforthia fusiformis williamsson to study this phenomenon further we performed stable oxygen and carbon isotope analyses on the indicator species itself s fusiformis both on specimens from sediment cores representing approximately the last 85 years and on living stained individuals taken from a transect across the deep fjord basin our purpose was to detail how and why s fusiformis came to dominate the fauna the oxygen isotope results suggest that salinities and temperatures in the deep basin have been relatively constant over the last c 85 years while the carbon isotopes show a significant change towards more negative values in association with the faunal shift of 1979 1980 the combined results from both the cores and the surface sediments suggest that s fusiformis did not inhabit the deep basin until 1980 before then almost all specimens of s fusiformis were small sized and their carbon isotope values suggest they were re deposited shallow water specimens that had been transported down to the central deep basin as part of a suspension load after a major faunal extinction in 1979 1980 s fusiformis of all sizes suddenly appeared in large numbers and their carbon isotopic values were similar to the signal from registered in the recent living fauna within the deep basin this suggests that the opportunistic s fusiformis established itself in the deep basin as a consequence of the severe low oxygen event and the faunal crash of the previously dominating skagerrak kattegat fauna less

sediments in palaeo notches potential proxy records for palaeoclimatic changes in antarctica abstract many climatic proxy materials such as ice cores coastal and lacustrine sediments and abandoned penguin rookeries have been used to study palaeoclimatic changes and the palaeoenvironmental evolution of antarctica in this paper we report another geological record well preserved sedimentary sequences in the palaeo notches in marine terraces of fildes peninsula king george island based upon grain size distribution and microtexture geochemical element compositions and radiocarbon dating we identified the sediments in one palaeo notch as lacustrine sediments most likely deposited in a small palaeo lake from these data we inferred that between 4000 and 3000 yr b p a moderate chemical weathering occurred and the climate was warmer and more humid than present in good agreement with the findings from other climatic proxy materials we believe that the sediments in palaeo notches provide another reliable proxy material for studying the palaeoclimate and the palaeoenvironment in antarctica

foraminiferal assemblages and caco3 dissolution since the last deglaciation in the maxwell bay king george island antarctica abstract three sediment cores a10 01 02 and 08 from the maxwell bay king george island antarctica were quantitatively analyzed for foraminiferal fauna planktonic foraminifera of three cores are rare due to the special antarctica environment benthic foraminifera is mainly composed of globocassidulina biora globocassidulina crassa rossensis cassidulinoides parkerianus and miliammina arenacea g biora and g crassa rossensis show high percentages in the shallower core a10 08 while m arenacea displays obviously high percentage in deeper core a10 02 the lower parts of the cores have a lower abundance of foraminifera while the upper parts have a relatively higher abundance the down core variations of benthic foraminifera reflect the contrast of surface water environment between the last deglaciation and post glacial during the last deglaciation lower parts of the cores the lower abundant foraminifera was consistent with the lower toc which reflected that the extensive sea ice prevented the production of primary organisms and therefore lower flux of organic particles was delivered to the sea floor abundant foraminifera together with higher toc in the upper parts of the cores suggested a higher primary productivity after the glaciation the shallowest water depth core a10 08 45 m displayed a better carbonate preservation than the other two cores a10 01 and 02 from the depths of 85 and 105 m respectively the disparity in carbonate dissolution reflected the remarkable shallow lysocline and carbonate compensation depth ccd in the antarctic area and also reflected significant variations in water properties even within such a difference only about 60 m in water depth down core variations of benthic foraminifera dissolution index bdi and caco 3 content indicated the existence of stronger carbonate dissolution in the upper parts than those in the lower parts of the cores the down core variations of carbonate dissolution suggested changes of water properties linked to the shallow ccd in this area it was supposed that the less influence of the saline shelf water during the last deglaciation enhanced the carbonate preservation with the sea level increasing and retreat of the coastal ice after the glacial erosive water masses and the higher co 2 accumulated by the increased flux of organic material led to severe dissolution of caco 3 and foraminiferal shells in the sediment

late holocene cyclic glaciomarine sedimentation in a subpolar fjord of the south shetland islands antarctica and its paleoceanographic significance sedimentological geochemical and paleontological evidence the glaciomarine sedimentary record of the fjord head collins harbor in maxwell bay south shetland islands west antarctica a large marine calving embayment contains repeating couplets of organic rich massive diamicton and organic poor stratified diamicton the massive diamicton is characterized by high total organic carbon toc content and carbon to nitrogen c n ratios and was deposited in a cold climate regime by iceberg rafted sedimentation from coastal fast ice in which algal plants as well as gravels were entrained the stratified diamicton is characterized by low toc content and c n ratios and was formed in a warmer climate regime when the flux of icebergs was suppressed but turbid meltwater discharge continued to produce lamination when the meltwater discharge decreased in cold climatic conditions and resultant phytoplankton productivity was reduced due to the increased sea ice coverage ice rafting from shorefast sea ice might have played a major role in entraining benthic algae as well as loads of sand and gravel along the coastal area resulting in an increased c n ratio and gravel content in the massive diamicton accelerator mass spectrometry ams radiocarbon analyses conducted on well preserved calcite shells were used to construct a chronology for the past 3000 years fluctuations in toc are recorded approximately four cycles over this time period with the average duration of a cooling cycle being 500 years these cycles may be correlative with the high frequency 550 yr variability in reduced circumpolar deep water cdw on the west antarctic peninsula shelf because a decrease in cdw may be related to reduced deep water production in the north atlantic during colder periods as demonstrated for glacial intervals throughout the pleistocene

glaciomarine sedimentation and palaeo glacial setting of maxwell bay and its tributary embayment marian cove south shetland islands west antarctica abstract high resolution 3 5 khz and multi channel seismic profiles and piston cores were collected from maxwell bay and its tributary embayment marian cove in the south shetland islands antarctica during the korea antarctic research program 1992 93 and 1995 96 to elucidate the glaciomarine sedimentation processes and recent glacial history of the area seismic data from maxwell bay reveal a rugged bay margin and flattened basin floor covered with well stratified hemipelagic muds on the base of slope acoustically transparent debris flows occur indicating downslope resedimentation of glaciomarine sediments despite the subpolar and ice proximal settings of marian cove the seafloor is highly rugged with a thin sediment drape suggesting that much of the area has been recently eroded by glaciers sediment cores from the cove penetrated three distinct fining upward lithofacies 1 basal till in the lower part of the core accumulated just seaward of the grounding line of the tidewater glacier 2 interlaminated sand and mud in the middle part deposited in ice proximal zone by a combination of episodic subglacial meltwater inflow and iceberg dumping and 3 pebbly mud in the upper part deposited in ice distal zone by both surface meltwater plume and ice rafting from the glacier front a reconstruction of the glacial history of these areas since the late glacial maximum shows an ice sheet filling maxwell bay in late wisconsin time and grounding of the tidewater glacier in marian cove until about 1300 yr bp

holocene paleoclimate change in the antarctic peninsula evidence from the diatom sedimentary and geochemical record abstract holocene marine deposition in lallemand fjord antarctic peninsula is reinterpreted using statistical analyses cluster analysis analysis of variance nonmetric multidimensional scaling and multiple regression to compare diatom assemblages and the primary sedimentological proxies the assemblages have been deposited in a variable sea ice zone over the last ca 10 500 yr bp in response to a climate change in the late pleistocene early holocene 10 580 7890 yr bp a sea ice diatom assemblage was deposited in the presence of a retreating ice shelf at the head of the fjord in the mid holocene 7890 3850 yr bp an open water assemblage was deposited and sea ice cover was at a minimum we associate the assemblage with climatic warming which characterizes much of the antarctic peninsula during this time a second sea ice assemblage different from that deposited in the early holocene has been deposited in lallemand fjord since the late holocene

strong thermodynamic imprint on recent bottom water and epibenthic δ13c in the weddell sea revealed implications for glacial southern ocean ventilation abstract paleonutrient proxies are widely used to reconstruct the geometry of deep water masses during the last glacial maximum lgm epibenthic 13 c provides best spatial coverage and artifacts are well investigated discrepancies between reconstructed lgm circulation patterns derived from models or different benthic nutrient proxies can partly be resolved by varying air sea signatures of 13 c i e 13 c as however there are very few data available to calculate a 13 c as of modern bottom water dissolved inorganic carbon dic 13 c and to document how this signal is recorded in benthic foraminiferal 13 c here i show that today bottom water in the atlantic sector of the southern ocean is 13 c enriched with 13 c dic values between 0 4 and 1 0 and 13 c as values 0 4 and that this signal is recorded in live and dead epibenthic 13 c this is in contrast to a uniform modern antarctic circumpolar 13 c dic of rather 0 4 which hitherto is used as modern framework to compare to low lgm 13 c dic of southern sourced bottom water and glacial inter basin differences i conclude that a potential reduction of the strong recent thermodynamic imprint during bottom water generation in glacial times could explain depleted circum antarctic 13 c dic without associated co 2 enrichment and anoxia in antarctic bottom waters the present synoptic compilation of 13 c dic and live benthic foraminifera 13 c is in support of hypotheses that explain low lgm 13 c by a depletion of southern end member 13 c dic due to extensive sea ice formation with low 13 c as brine rejection and diminished air sea gas exchange

productivity cycles of 200 300 years in the antarctic peninsula region understanding linkages among the sun atmosphere oceans sea ice and biota compared to the rest of the world9s oceans high resolution late holocene paleoclimatic data from the southern ocean are still rare we present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the antarctic peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr analyses completed include measurement of magnetic susceptibility and granulometry bed thickness particle size percent organic carbon bulk density and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances downcore variability of these parameters demonstrates the significance of both short term cycles which recur approximately every 200 yr and longer term events 2500 yr cycles that are most likely related to global climatic fluctuations in the upper 600 cm of the core lower values of magnetic susceptibility ms are correlated with lower bulk density the presence of thinly laminated units specific diatom assemblages and generally higher total organic carbon content below 600 cm magnetic susceptibility is uniformly low though variability in other parameters continues the magnetic susceptibility signal is controlled primarily by dilution of ferromagnetic phases with biosiliceous material this signal may be enhanced further by dissolution of magnetite in the magnetic susceptibility lows high total organic carbon the role of variable primary productivity and its relationship to paleoclimate is assessed through the diatom data in particular magnetic susceptibility lows are characterized by higher than normal abundances of chaetoceros resting spores corethron criophilum and or rhizosolenia spp also are found as is a higher ratio of the most common species of fragilariopsis versus species of thalassiosira these assemblages are indicative of periods of high primary productivity driven by the presence of a meltwater stabilized water column the 200 yr cyclicity noted in other paleoclimatic records around the world suggests a global forcing mechanism possibly solar variability in addition to the cyclic changes in productivity overall elevated productivity is noted below 600 cm or prior to ca 2500 yr b p this increased productivity may represent the tail end of a holocene climatic optimum which is widely recognized in other parts of the world but as yet is poorly documented in antarctica

application of three dimensional boundary fitted circulation model to providence river a three dimensional boundary fitted circulation model by muin and spaulding in 1996b was applied to simulate tidal and wind driven flow in upper narragansett bay and the providence and seekonk rivers the model employs a split mode solution technique the exterior mode vertically averaged was solved using a semiimplicit method the interior mode vertical structure was solved explicitly except for the vertical diffusion term that is implicit the vertical eddy viscosity was calculated from a one equation turbulence model model predicted tidal currents for the principal constituents were in good agreement with field observations the im d2 dominated the tidal currents accounting for 80 of the total tidal energy a combination of bottom friction coefficient of 0 0025 and constant 0 3 in the mixing length formulation of the turbulence model provided the best fit to the available observations the model predicted a cooscillating wave pattern with the im d2 water elevation about three hours out of phase with the current an approximate one hour phase difference between the currents in the deep dredged channel and the shallow water on either side was predicted wind driven flow was simulated under constant wind forcing of 0 01 n m ua 0 1 dyne cm along and across the river axis the steady state flow patterns are consistent with observations showing flows against the wind direction in the dredged channel the model predicted steady state currents in the dredged channel have maximum values of 3 4 cm s for winds along the channel axis and 1 cm s for winds across the channel axis

late holocene palaeoclimatic records from lake sediments on james ross island antarctica sediment profiles from several lakes ponds in the northern ice free area of james ross island antarctica were the subject of a multi disciplinary palaeoenvironmental investigation the results obtained from lithological geomagnetic geochemical and diatom analyses and the frequency of branchinecta eggs were evaluated with multivariate statistics and provide a fairly detailed picture of climate change during the last 5000 years new radiocarbon dates are combined with previously published 14c dates so as to date the palaeoenvironmental and palaeohydrological changes identified by the stratigraphic studies in combination with the findings of glacial geological studies our data suggest that the brandy bay glacier began to recede rapidly just before 5000 yr b p due to calving and moisture starvation caused by cold and arid conditions in one of the ponds studied gypsum began to precipitate as a consequence of these conditions when the influence of glacial meltwater ceased this hypothesis was tested by hydrochemical modeling at approximately 4200 yr b p the climate became more humid and warmer and the pond supported a fairly diverse biota which included a variety of diatom species and for example branchinecta gaini a crustacean that feeds on benthic cyanobacterial mats the brandy bay glacier probably advanced during this humid period but the advance was interrupted by subsequent arid conditions which started at 3000 yr b p during this arid phase glaciers became completely absent from the study area as a result formerly large lakes fed by glacial meltwater transformed into small enclosed brackish water bodies that contained b gaini the arid and fairly cold conditions lasted for 1500 2000 years until approximately 1200 yr b p when the aquatic systems expanded and their salinity was lowered as a result of increased snow accumulation and glacial expansion the increased deposition of minerogenic matter caused by glacial erosion and meltwater inflow probably caused the disappearance of branchinecta on james ross island we regard this most recent phase as a period of increased humidity and warmth compared to the previous period although the conditions appear to be less warm and humid than those which prevailed during the climatic optimum between 4200 and 3000 yr b p in spite of certain correlation problems we tentatively correlate our results to other studies of holocene environments in antarctica and from that it can be suggested that the climatic optimum was of circumpolar significance therefore the climatic oscillations recorded in sediments on james ross island may reflect oscillations in the anticyclonic stormtracks and the strength of the high pressure cell over the inland ice sheet

a variable parameter bidirectional stage routing model for tidal rivers with lateral inflow abstract water stage variations are complicated in tidal rivers due to the combination of upstream flood and downstream tide this study proposed a bidirectional stage routing model bsr for tidal rivers by considering the stage hydrograph as the overlay of bidirectional propagation of upstream flood wave and downstream tidal wave the basic stage routing equations derived from the storage equation and water balance equation are used to calculate the upstream flood wave routing and the downstream tidal wave propagation respectively the lateral inflow can be directly specified as an additive term in the basic equation of bsr model or indirectly estimated by a lateral flow rate reflecting the proportion of lateral inflow to the upstream water parts of the model parameters are time variable to account for the effect of water surface slope on water stage the model inputs include stage hydrographs at the upstream and downstream boundaries the channel geometric characteristics data are not required when the average channel width is estimated as a parameter the case study results in the tidal reaches of the caoe river and qiantang river in china demonstrate that the bsr model performs well in water stage simulation with relatively simple structure modest data requirement and stable performance the physically based bsr model has the potential for water stage routing in tidal rivers when channel geometry data are not available

recent benthic foraminifera from the eastern south atlantic ocean dependence on food supply and water masses abstract sixty surface sediment samples from the eastern south atlantic ocean including the walvis ridge the angola and cape basins and the southwest african continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences live stained with rose bengal and dead faunas were counted separately and then each grouped by q mode principal component analysis into seven principal faunal end members then multiple regression technique was used to correlate recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages 1 seasonality of food supply and organic carbon flux rates together with oxygen content in the pore and bottom waters 2 lateral advection of deep water masses 3 bottom water carbonate corrosiveness and 4 energetic state at the benthic boundary layer and grain size composition of the substrate food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the recent benthic foraminifera at the continental margin in the zone of coastal upwelling and its mixing area benthic foraminiferal assemblages are dominated by stenobathic high productivity faunas characterized by elevated standing stocks low diversities and a large number of endobenthic living species at the continental shelf and upper continental slope the live assemblages are characterized by rectuvigerina cylindrica uvigerina peregrina s 1 uvigerina auberiana and rhizammina spp while the dead assemblages are characterized by cassidulina laevigata bolivina dilatata bulimina costata and b mexicana at the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the cunene river mouth where the live assemblage is dominated by uvigerina peregrina s 1 the corresponding dead assemblage by melonis barleeanum and m zaandamae in the adjacent areas of the lower continental slope the biocoenosis is characterized by reophax bilocularis and epistominella exigua which becomes dominant in the corresponding dead assemblage at the walvis ridge and in the abyssal angola and cape basins where organic matter fluxes are low and highly seasonal benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration the top and flanks of the walvis ridge are inhabited by the rhizammina psammosphaera and r bilocularis live assemblages the corresponding dead assemblages are dominated by g subglobosa on the ridge top and e exigua on the flanks within the highly diverse e exigua dead assemblage several associated epibenthic species coincide with the core of nadw between about 1600 and 3700 m water depth these species include osangularia culter cibicidoides kullenbergi melonis pompilioides bolivinita pseudothalmanni and bulimina alazanensis the assemblages of the abyssal cape and angola basins are characterized by nuttallides umbonifer and a high proportion of agglutinated species these species are adapted to very low organic matter fluxes and a carbonate corrosive environment

correlation between the phase of the moon and the occurrences of microearthquakes in the tamba region through point process modeling 1 we study the correlation between the phase of the moon and the occurrence of microearthquakes in the tamba region close to the fault of the 1995 kobe earthquake the existence of the correlation during the two year period following the kobe earthquake was suggested in a previous study first in this study we investigate the statistical significance of such correlation using point process modeling and aic akaike information criterion we confirm that the existence of the correlation is statistically significant second we investigate the temporal variation of the correlation during the four year period following the kobe earthquake the result of the second analysis indicates that the correlation is strongest just after the kobe earthquake and that it then becomes weaker year by year

the marine record of deglaciation of the south shetland islands antarctica since the last glacial maximum abstract the marine geological record of the glacial retreat history of the south shetland islands is derived from the integration of seismic data core lithofacies radiocarbon ages and geomorphological data from two study areas on the northern shelf we present one of the first published multibeam bathymetric images of the seafloor this new image combined with descriptions of new and existing short sediment cores and high resolution seismic data from the continental shelf north of king george island are used to map a grounding zone wedge that marks the minimum seaward extent of the south shetland ice cap during the last glacial maximum seismic data multibeam bathymetry and sediment cores from maxwell bay on the opposite side of king george island are used to provide further spatial constrains on the history of grounding and retreat of the ice cap along the southern margin of the south shetland islands during the last glacial maximum the south shetland ice cap extended onto the outer continental shelf some 50 km north of its present location the ice grounded on the shelf in troughs in present water depths of almost 400 m it had a minimum thickness of 570 m and was also grounded in the deepest part of fjords and straits between the islands to the south the ice cap extended seaward of the mouths of fjords and straits to the steep northern boundary of the bransfield strait sediment eroded from the fjords and straits was deposited in prominent fans that extend into the bransfield strait and show evidence for an ice shelf that covered the bransfield strait during the last glacial maximum a long drill core shaldril in maxwell bay and several jumbo piston cores yielded carbonate material used to constrain the timing and spatial extent of glacial retreat within maxwell bay the oldest glacimarine sediments in the fjord date back to 14 1 to 14 8 ka and suggest an initial deglaciation earlier than most previous studies of the south shetland islands upper maxwell bay was ice free by 9 1 ka and most of maxwell bay proper was ice free by 5 9 ka except for the smaller tributary fjords of maxwell bay these smaller tributary fjords were ice free by 1 7 ka but may have been ice free earlier but reoccupied by a neoglacial advance that ended approximately 1 7 ka

bransfield basin fine grained sediments late holocene sedimentary processes and antarctic oceanographic conditions the antarctic peninsula is sensitive to climatic change due to its northerly position and to the relatively reduced volume and character of its ice cover high resolution palaeoclimatic records from the ant arctic peninsula ice cores extend back only 500 years a climatic record of 2850 years in the bransfield basin is investigated through the analysis of sediment gravity cores from the floor of the central subbasin core gebra 1 and the slope of the eastern subbasin core gebra 2 sedimentological mineralogical and geo chemical properties have been systematically measured together with accelerator mass spectrometry ams radiocarbon dating the fine grained sediments result from two main processes hemipelagic settling from resuspensions and primary productivity and turbidity currents hemipelagic sediments were selected to investi gate the oceanographic and climatic conditions of the northern antarctic peninsula region during the last three millennia cold climatic periods are characterized by millimetric laminations and or black layers with higher organic carbon nitrogen and opal contents warm periods are recorded as massive to diffuse laminated facies with lower biogenic contents the results include the little ice age lia cold pulse as well as several 200 300 year long fluctuations within the lia and before this major climatic event of the holocene

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

unstable climate oscillations during the late holocene in the eastern bransfield basin antarctic peninsula core a9 eb2 from the eastern bransfield basin antarctic peninsula consists of pelagic diatom ooze clay couplets and bioturbated diatom ooze and hemipelagic bioturbated mud sediments interbedded with turbidites homogeneous mud and silt clay couplets the cyclic and laminated nature of these pelagic sediments represents alternation between the deposition of diatom rich biogenic sediments and of terrigenous sediments sediment properties and geochemical data explain the contrasting lamination with light layers being finer grained and relatively rich in total organic carbon and biogenic silica content also the high resolution magnetic susceptibility ms variations highlight distinct features high ms values coincide with clastic rich sections and low ms values correspond to biogenic sections the chronology developed for core a9 eb2 accounts for anomalous ages associated with turbidites and shows a linear sedimentation rate of approximately 87 cm 103 yr which is supported by an accumulation rate of 80 cm 103 yr calculated from 210pb activity the late holocene records clearly identify neoglacial events of the little ice age lia and medieval warm period mwp other unexplained climatic events comparable in duration and amplitude to the lia and mwp events also appear in the ms record suggesting intrinsically unstable climatic conditions during the late holocene in the bransfield basin of antarctic peninsula

retreating glacier fronts on the antarctic peninsula over the past half century the continued retreat of ice shelves on the antarctic peninsula has been widely attributed to recent atmospheric warming but there is little published work describing changes in glacier margin positions we present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years of these glaciers 87 have retreated and a clear boundary between mean advance and retreat has migrated progressively southward the pattern is broadly compatible with retreat driven by atmospheric warming but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region

oceanic and atmospheric forcing of early holocene ice shelf retreat george vi ice shelf antarctica peninsula we use lake sediment records from an epishelf lake on alexander island to provide a detailed picture of the holocene history of george vi ice shelf gvi is core analyses included micropaleontology diatoms foraminifera stable isotope 18o 13c geochemistry total organic carbon toc total nitrogen tn c n ratios and grain size analyses these data provide robust evidence for one period of past ice shelf absence during the early holocene the timing of this period has been constrained by 10 ams 14c dates performed on mono specific foraminifera samples these dates suggest that gvi is was absent between c 9600 cal yr bp and c 7730 cal yr bp this early holocene collapse immediately followed a period of maximum holocene warmth that is recorded in some antarctic ice cores and coincides with an influx of warmer ocean water onto the western antarctic peninsula ap shelf at c 9000 cal yr bp the absence of a currently extant ice shelf during this time interval suggests that early holocene ocean atmosphere variability in the ap was greater than that measured in recent decades

foraminiferal assemblages from ice proximal paleo settings in the whales deep basin eastern ross sea antarctica abstract reconstructions of ross sea paleoenvironments based on foraminifera are hindered by the dearth of actualistic data especially from below the ross ice shelf to fill this gap we used a recently developed well resolved deglaciation record from the whales deep basin of the eastern ross sea to understand the ecological affinities of different foraminiferal assemblages during open water conditions similar to the present two benthic foraminiferal communities are strongly dominated by agglutinated species however in the underlying sediments that represent sub ice shelf and grounding zone proximal settings on the outer continental shelf we identified five different assemblages of calcareous foraminifera by antarctic margin standards these calcareous assemblages are periodically truly abundant along with assemblages dominated by benthic calcareous species that are well known from many antarctic settings i e globocassidulina biora trifarina earlandi and astrononion echolsi two important assemblages are dominated by a heretofore undescribed pustulose morphotype of g biora and poorly known spinose morphotype of t earlandi based on our correlations to the deglacial record these two assemblages live near the grounding line or in environments with especially intense bottom water currents as grounded and floating ice retreated south to the middle continental shelf these later sub ice shelf and grounding zone proximal settings were largely devoid of calcareous foraminifera and instead were inhabited by agglutinated taxa this improved understanding of foraminiferal assemblage distributions from a variety of environments within the eastern ross sea may contribute to better use of foraminiferal data to investigate the evolution of environmental changes in grounding line proximal environments

benthic foraminiferal record of holocene deep water evolution in the palmer deep western antarctic peninsula benthic foraminiferal data from ocean drilling program site 1098 indicate significant changes in deep water conditions of the palmer deep western antarctic peninsula margin throughout the holocene 13 ka to present the earliest holocene represents a period of transition from the last glacial maximum lgm cold bottom waters similar to saline shelf water ssw dominated the middle holocene the late holocene in the palmer deep has been characterized by alternating dominance of circumpolar deep water cdw and saline shelf water these changes have global oceanographic and climatic implications we suggest that the middle holocene bottom water record in the absence of circumpolar deep water on the western antarctic peninsula shelf indicates high saline shelf water production and or weakened circumpolar deep water production during the middle holocene climatic optimum the late holocene benthic foraminiferal record indicates rapidly fluctuating sea ice conditions and may indicate a teleconnection between the south pacific and southern ocean thus having implications related to the southern oscillation index

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

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

a new holocene relative sea level curve for the south shetland islands antarctica abstract precise relative sea level rsl data are important for inferring regional ice sheet histories as well as helping to validate numerical models of ice sheet evolution and glacial isostatic adjustment here we develop a new rsl curve for fildes peninsula south shetland islands ssis a sub antarctic archipelago peripheral to the northern antarctic peninsula ice sheet by integrating sedimentary evidence from isolation basins with geomorphological evidence from raised beaches this combined approach yields not only a holocene rsl curve but also the spatial pattern of how rsl change varied across the archipelago the curve shows a mid holocene rsl highstand on fildes peninsula at 15 5 m above mean sea level between 8000 and 7000 cal a bp subsequently rsl gradually fell as a consequence of isostatic uplift in response to regional deglaciation we propose that isostatic uplift occurred at a non steady rate with a temporary pause in ice retreat ca 7200 cal a bp leading to a short lived rsl rise of 1 m and forming a second peak to the mid holocene highstand two independent approaches were taken to constrain the long term tectonic uplift rate of the ssis at 0 22 0 48 m ka placing the tectonic contribution to the reconstructed rsl highstand between 1 4 and 2 9 m finally we make comparisons to predictions from three global sea level models

holocene oceanographic and glacial changes recorded in maxwell bay west antarctica abstract three holocene core sections from maxwell bay south shetland islands west antarctica are investigated using ms grain size toc foraminifera 18o and 13c 14c and 210pb in order to examine holocene oceanographic glacial and climatic changes in the region they come from 190 221 and 333 m water depths and the bay margin proximal locations complementing earlier studies from the deep central part the three records vary between locations and reflect combined marine and terrigenous influence from the open ocean and surrounding islands respectively the longest and best dated composite section comes from the inner part of the bay core jtc jpc 17 and extends back to 6 3 cal kyr bp close to the termination of the holocene climatic optimum a combination of dating problems and mixed foraminiferal assemblages prevented reliable interpretation of core jpc 15 from the outer part of the bay core jpc 16 collected from the inner bay near the inlet between king george and nelson islands revealed repeated highs in planktonic neogloboquadrina pachyderma occurrence during last 3000 yr these highs are interpreted as indicating periods of decreased meltwater flow into the bay and thus greater influence of open marine surface waters core jtc jpc 17 located closest to king george island and the collins ice cap records increased glacial conditions at 2000 cal yr bp this event is recorded by turbidite deposition at core site jpc 16 major components of the benthic foraminiferal assemblage indicate decreasing tolerance to near glacier or near shore conditions however local climate variability appears to have overall little impact on benthic foraminiferal biota thus it is unlikely that in similar settings recent warming would be strongly manifest as changes in benthic foraminiferal communities stable isotopic analysis is based on cassidulinoides parkerianus and globocassidulina biora subtle decrease in 18o at 3500 cal yr bp followed by episodic increases at 1000 cal yr bp and in the youngest part of the record appear to correlate with the period prior to the beginning of the neoglacial with medieval warm period and with post little ice age warming respectively the latest event is also marked by a significant increase in sediment accumulation rate in the second half of the 20th century

precipitation sublimation and snow drift in the antarctic peninsula region from a regional atmospheric model 1 a regional atmospheric model with a horizontal grid spacing x of 14 km is used to study the surface mass balance components precipitation sublimation and snow drift in the region of the antarctic peninsula ap an integration is performed for the 7 year period 1987 1993 using a realistic forcing at the lateral model boundaries and at the sea surface output from this integration indicates that the precipitation reaches its maximum value on the northwestern slope of the ap where the upward motion in the atmosphere is largest uplift occurs upstream of the barrier affecting the precipitation distribution over sea the effect of the barrier on the precipitation distribution over the bellingshausen sea might have important implications for the ocean circulation in this region the mean precipitation over the grounded ice of the ap 1 20 m water eq yr 1 is 6 times larger than the mean value over all the grounded ice of antarctica our estimates for the surface sublimation and wind transport of snow over the grounding line toward the sea are 9 and 6 1 of the precipitation respectively in situ data of the wind distribution at three coastal sites located on the northern eastern and western sides of the ap are used to evaluate the modeled wind field which is important for the snow drift calculations for two of the three sites considered the prevailing wind direction and bimodal wind distribution are correctly represented by the model the calculated distribution of accumulation and ablation due to snow drift shows a complex pattern the wind removes snow from the spine of the ap where the near surface flow field diverges whereas deposition occurs mainly on the eastern slopes where the near surface flow field converges an intercomparison between two 7 year integrations at different horizontal resolution x 14 km and x 55 km shows that the precipitation on the northwestern slope is very sensitive to the model resolution in the x 14 km integration precipitation on the northwestern slope is higher than in x 55 km because of higher vertical velocities resulting in a 35 increase in average precipitation over the grounded ice of the ap

three dimensional modelling of stratified coastal waters abstract an implicit baroclinic 3 d model developed to simulate the circulation in coastal waters is presented the model has hydrodynamic transport and turbulence model components it is a composite finite difference finite element model in the horizontal plane second order central finite differences on a staggered scheme and in the vertical galerkin method with linear shape functions are used implicit equations are solved by crank nicholson method which has second order accuracy in time also developed model predictions are compared with the analytical solutions of steady wind driven circulatory flow and tidal flow model predictions are tested with an experiment performed on the buoyant surface jet discharge then the model is applied to the goksu lagoon system located on the mediterranean coast of turkey where there exist some measurements of salinity temperature and velocity model predictions are in good agreement with the field data

formation of the density currents in the zone of confluence of two rivers summary the peculiarities of the formation of density currents in the zone of confluence of two rivers with strongly different hydrochemical regimes are studied numerically and experimentally the three dimensional numerical simulation shows that the water of the river of higher mineralization and density flows under the water of the river of lower mineralization and density and vice versa and besides such overlapping of the water streams is observed both upstream and downstream of the confluence of two rivers the results of numerical simulation are supported by the data of expedition observations and in situ measurements a similar phenomenon namely a flow of two overlapped oppositely directed water streams was previously discovered in the mouth zone of the rivers flowing in the sea our study reveals the existence of a new type of the hydrological systems in which such a phenomenon occurs

evidence for tidal triggering of earthquakes as revealed from statistical analysis of global data 1 we observe tidal triggering of earthquakes by measuring the correlation between the earth tide and earthquake occurrence we used the times locations and focal mechanisms of the 9350 globally distributed earthquakes with magnitude 5 5 or larger from the harvard centroid moment tensor catalog the tidal stress was theoretically computed by using the preliminary reference earth model and a recent ocean tide model nao 99b we considered the shear stress on the fault plane and the trace of stress tensor j1 defining the tidal phase angle at the occurrence time for each earthquake we statistically tested the phase selectivity using the schuster s method for all the earthquakes no significant correlation is found between the earth tide and earthquake occurrence both for the shear stress and for j1 by classifying the data set according to fault types however we find a high correlation with the shear stress for reverse fault type the correlation is particularly clear for shallow and smaller earthquakes of this type significant correlation with j1 also appears for larger earthquakes of reverse fault type and for shallow and larger ones of normal fault type we find no correlation for strike slip type for all the cases of high correlation earthquakes tend to occur when the tidal stress accelerates the fault slip indicating that high correlation is not coincidental but is physically justified this result strongly suggests that a small stress change due to the earth tide encourages earthquake occurrence when the stress in the future focal area is near a critical condition

geometry and thermal regime of the king george island ice cap antarctica from gpr and gps king george island is the largest of the south shetland islands close to the tip of the antarctic peninsula the annual mean temperature on the island has increased by 1 c during the past three decades and the ice cap that covers the majority of the island is sensitive to climatic change we present data from two field campaigns 1997 and 2007 700 km of global positioning system gps and ground penetrating radar gpr profiles were collected on arctowski icefield and on the adjacent central part the data were analysed to determine the surface and bed topography and the thermal regime of the ice average ice thickness is 250 m and maximum thickness is 420 m the gpr profiles show isochrones throughout the ice cap which depict the uparching of raymond bumps beneath or close to the ice divides a water table from percolation of meltwater in the snowpack shows the firn ice boundary at 35 m depth the firn layer may be temperate due to the release of latent heat in the area below 400 m a s l backscatter by water inclusions is abundant for ice depths below the water table we interpret this as evidence for temperate ice scatter decreases significantly above 400 m ice temperatures below the water table in this part of the ice cap are subject to further field and modelling investigations

sediment accumulation rates in subpolar fjords impact of post little ice age glaciers retreat billefjorden svalbard abstract the little ice age 1600 1900 ad and 20th century sediment accumulation rates in billefjorden a subpolar fjord on svalbard were reconstructed by applying 210 pb 137 cs and ams 14 c datings the modern sediment accumulation rate decreases from more than 0 39 cm y 1 at the fjord head to 0 08 cm y 1 close to the fjord mouth however during the little ice age the sediments accumulated at a much lower rate of 0 02 cm y 1 in the central fjord basin this difference is most likely related to the rapid retreat of glaciers during the 20th century when most of them withdrew up to 2 km the post little ice age increases in temperature and a negative glacier mass balance resulted in a larger meltwater discharge transferring substantial amounts of sediments released from the glaciers as well as those eroded from previously stored unconsolidated glacial sediments a comparison of data from the subpolar fjords of svalbard suggests that the increase in the sediment accumulation rate is a common trend and further increases might be expected if climate warming continues the properties of the fjord sediments grain size ird coarse fraction composition clay mineralogy from the little ice age and the 20th century showed no distinct differences the change in the accumulation rate may be the most evident sedimentary record of this climatic change

variability in the freshwater balance of northern marguerite bay antarctic peninsula results from δ18o abstract we investigate the seasonal variability in freshwater inputs to the marguerite bay region western antarctic peninsula using a time series of oxygen isotopes in seawater from samples collected in the upper mixed layer of the ocean during 2002 and 2003 we find that meteoric water mostly in the form of glacial ice melt is the dominant freshwater source accounting for up to 5 of the near surface ocean during the austral summer sea ice melt accounts for a much smaller percentage even during the summer maximum around 1 the seasonality in meteoric water input to the ocean around 2 of the near surface ocean is not dissimilar to that of sea ice melt around 2 in 2002 and 1 in 2003 contradicting the assumption that sea ice processes dominate the seasonal evolution of the physical ocean environment close to the antarctic continent three full depth profiles of oxygen isotopes collected in successive decembers 2001 2003 indicate that around 4 m of meteoric water is present in the water column at this time of year and around 1 m of sea ice formed from this same water column the predominance of glacial melt is significant since it is known to be an important factor in the operation of the ecosystem for example by providing a source of nutrients and modifying the physical environment to control the spatial extent and magnitude of phytoplankton blooms the western antarctic peninsula is undergoing a very rapid change in climate with increasing ocean and air temperatures retreating glaciers and increases in precipitation associated with changes in atmospheric circulation as climate change continues we expect meteoric water inputs to the adjacent ocean to rise further sea ice in this sector of the antarctic has shown a climatic decrease and we expect a reduction in oceanic sea ice melt fractions if this change continues continued monitoring of the oceanic freshwater budget at the western peninsula is needed to track these changes as they occur and to better understand their ecological consequences

influence of rapid glacial retreat on the rate of erosion by tidewater glaciers glacial erosion rates inferred from total sediment budgets in recently deglaciated fjords which are the highest reported erosion rates worldwide have received considerable attention in fields as diverse as tectonics glacial sedimentation and climate these record rates however are representative only of tidewater glaciers during their extensive retreat of the post little ice age period erosion rates averaged over glacial interglacial cycles and longer periods are likely to be substantially smaller we examine the influence of retreat rate on sediment yields from tidewater glaciers by reconstructing the history of sediment output from retreating glaciers necessary to produce sediment packages observed in contemporary fjords using a simple numerical model of proglacial sedimentation in front of a retreating glacier seismic profiles of proglacial sediments and the history of terminus retreat of muir glacier glacier bay alaska we calculate the sediment flux as a function of time from this glacier between 1900 and 1979 and conclude that sediment flux scales with retreat rate the corresponding basin wide erosion rate during this 79 yr period averages 37 mm yr and exceeds long term erosion rates by a factor of 5 1 for muir glacier and by inference for other calving glaciers the general drastic retreat and the marked regional drawdown of ice since the little ice age are both linked to unusually rapid calving and fast ice motion which is conducive to rapid erosion

holocene changes in the position and intensity of the southern westerly wind belt the position and intensity of the southern westerly wind belt varies seasonally as a consequence of changes in sea surface temperature during the austral winter the belt expands northward and the wind intensity in the core decreases conversely during the summer the belt contracts and the intensity within the core is strengthened reconstructions of the westerly winds since the last glacial maximum however have suggested that changes at a single site reflected shifts throughout the entire southern wind belt 1 4 here we use sedimentological and pollen records to reconstruct precipitation patterns over the past 12 500 yr from sites along the windward side of the andes precipitation at the sites located in the present core and northern margin of the westerlies is driven almost entirely by the wind belt 5 and can be used to reconstruct its intensity rather than varying coherently throughout the holocene epoch we find a distinct anti phasing of wind strength between the core and northern margin over multi millennial timescales during the early holocene the core westerlies were strong whereas the northern margin westerlies were weak we observe the opposite pattern in the late holocene as this variation resembles modern seasonal variability we suggest that our observed changes in westerly wind strength can best be explained by variations in sea surface temperature in the eastern south pacific ocean chile is ideally located to reconstruct past variability of the southern westerly wind belt sww as the sww almost entirely controls precipitation on the western side of the andes in southern south america with an extreme northsouth

glaciomarine sedimentation and its paleoceanographic implications along the fjord margins in the south shetland islands antarctica during the last 6000 years abstract two 3 m long cores were collected from maxwell and admiralty bays on king george island one of the south shetland islands west antarctica these cores were examined for their benthic foraminifer globocassidulina biora 18o and 13c records diatom abundance counts and biogenic constituents carbon and silica these high resolution data were used to reconstruct the paleoceanography of the bays and to link the marine record with deglaciation of the south shetland islands ice cap in maxwell bay extremely low diatom abundance the depletion of total organic carbon toc and biogenic silica biosi and enriched 18o between 6200 and 4000 bp indicate that this period was characterized by cold conditions with deposition of waterlain till unit 1 just seaward of the grounding line low sedimentation limitation of primary production on surface water and lack of meltwater supply deglaciation along the maxwell bay margin was dated from about 4000 bp until at least 2700 bp with increasing toc biosi and diatom abundance and decreasing the c n ratio up core at this time subglacial meltwater streams began to emanate from the glacier front sediment laden meltwater plumes from these streams deposited interlaminated sand and mud unit 2 in the ice proximal zone deglaciation was followed by marked climatic warming at around 2700 bp with evidence of toc and biosi maxima depleted 18o and markedly increased diatom valves with further glacier recession diatomaceous pebbly mud unit 3 was deposited in open marine conditions a large influx of organic materials by enhanced production during this period caused both rapid depletion of caco3 in sediment and resulted in marked increase in sedimentation since 2700 bp at 200 m water depth along the maxwell bay margin core s 19 in contrast the shallower platform along the admiralty bay margin core s 2 was deglaciated later about 1900 bp that is 2000 years after the maxwell bay margin this is possible as core s 19 is situated 200 m water depth more distal to the fjord head glacier while core s 2 in admiralty bay lies on a shallower platform

holocene climate and glacial history of the northeastern antarctic peninsula the marine sedimentary record from a long shaldril core abstract a high resolution record of holocene deglacial and climate history was obtained from a 77 m sediment core from the firth of tay antarctic peninsula as part of the shaldril initiative this study provides a detailed sedimentological record of holocene paleoclimate and glacial advance and retreat from the eastern side of the peninsula a robust chronostratigraphy was derived from thirty three radiocarbon dates on carbonate material this chronostratigraphic framework was used to establish the timing of glacial and climate events derived from multiple proxies including magnetic susceptibility electric resistivity porosity ice rafted debris content organic carbon content nitrogen content biogenic silica content and diatom and foraminiferal assemblages the core bottomed out in a stiff diamicton interpreted as till gravelly and sandy mud above the till is interpreted as proximal glaciomarine sediment that represents decoupling of the glacier from the seafloor circa 9400 cal yr bp and its subsequent landward retreat this was approximately 5000 yr later than in the bransfield basin and south shetland islands on the western side of the peninsula the firth of tay core site remained in a proximal glaciomarine setting until 8300 cal yr bp at which time significant glacial retreat took place deposition of diatomaceous glaciomarine sediments after 8300 cal yr bp indicates that an ice shelf has not existed in the area since this time the onset of seasonally open marine conditions between 7800 and 6000 cal yr bp followed the deglacial period and is interpreted as the mid holocene climatic optimum open marine conditions lasted until present with a minor cooling having occurred between 6000 and 4500 cal yr bp and a period of minor glacial retreat and or decreased sea ice coverage between 4500 and 3500 cal yr bp finally climatic cooling and variable sea ice cover occurred from 3500 cal yr bp to near present and it is interpreted as being part of the neoglacial the onset of the neoglacial appears to have occurred earlier in the firth of tay than on the western side of the antarctic peninsula the medieval warm period and little ice age were not pronounced in the firth of tay the breadth and synchroneity of the rapid regional warming and glacial retreat observed in the antarctic peninsula during the last century appear to be unprecedented during the holocene epoch

benthic foraminiferal assemblages from the eastern weddell sea between 68 and 73 s distribution ecology and fossilization potential surface sediment samples taken with a vented box corer from the eastern weddell sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content the live fauna was differentiated from empty tests comprising the foraminiferal death assemblage based on the dead assemblages potential fossil assemblages were calculated to facilitate the analogy with late neogene core material five distinct live assemblages inhabit the continental margin today six dead assemblages and five potential fossil assemblages respectively correspond to these biocoenoses a predominantly calcareous live fauna dominated by trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope below this on the upper slope down to 2000 m water depth the predominantly calcareous bulimina aculeata assemblage coincides with the core of warm 0 c weddell deep water and with fine and more organic rich sediments these calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment which depends largely on the grain size distribution of the sediment and the fluxes of organic matter therefore a still calcareous t angulosa dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by martinottiella nodulosa the characteristic arenaceous fossil remnant of the former predominantly calcareous live b aculeata fauna on a continental terrace between 2500 and 3500 m water depth cribrostomoides subglobosus dominates the live fauna but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by oridorsalis umbonatus and epistominella exigua comprises the dead assemblage and the potential fossil assemblage respectively on the lower continental slope between the carbonate lysocline 3500 m and the carbonate compensation depth 4000 m tests of nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna which is associated with the lower part of the antarctic bottom water aabw this corroborates earlier investigations suggesting a relationship between the carbonate corrosiveness of water masses and the distribution of n umbonifer this is important for inferring paleo routes and estimates of paleo production rates of aabw during the neogene

holocene southern ocean surface temperature variability west of the antarctic peninsula the antarctic peninsula is currently one of the fastest warming locations on earth but its long term variability has remained unclear amelia shevenell and colleagues now use the tex86 proxy a palaeothermometer that tracks membrane lipids of the marine picoplankton crenarchaeota to show that a long term cooling of about 4 c occurred in waters near the tip of antarctic peninsula over the past 12 000 years this is consistent with orbitally controlled changes in insolation shorter term variability in temperature seems to have been strongly influenced by the position of the westerly winds this work suggests that the present influence of the el nino southern oscillation system on the antarctic peninsula is a relatively recent phenomenon dating to the late holocene the antarctic peninsula is currently one of the fastest warming locations on earth but its long term variability has remained unclear this study uses tex86 sea surface temperature proxy evidence to show that a long term cooling of about 3 4 c occurred in waters near the tip of the antarctic peninsula over the past 12 000 years consistent with orbitally controlled changes in insolation shorter term variability in temperature at the antarctic peninsula appears to have been strongly influenced by the position of westerly winds the present influence of the el nino southern oscillation system on the antarctic peninsula may have arisen only during the late holocene the disintegration of ice shelves reduced sea ice and glacier extent and shifting ecological zones observed around antarctica1 2 highlight the impact of recent atmospheric3 and oceanic warming4 on the cryosphere observations1 2 and models5 6 suggest that oceanic and atmospheric temperature variations at antarctica s margins affect global cryosphere stability ocean circulation sea levels and carbon cycling in particular recent climate changes on the antarctic peninsula have been dramatic yet the holocene climate variability of this region is largely unknown limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms here we show that surface ocean temperatures at the continental margin of the western antarctic peninsula cooled by 3 4 c over the past 12 000 years tracking the holocene decline of local 65 s spring insolation our results based on tex86 sea surface temperature sst proxy evidence from a marine sediment core indicate the importance of regional summer duration as a driver of antarctic seasonal sea ice fluctuations7 on millennial timescales abrupt sst fluctuations of 2 4 c coincide with globally recognized climate variability8 similarities between our ssts southern hemisphere westerly wind reconstructions9 and el nino southern oscillation variability10 indicate that present climate teleconnections between the tropical pacific ocean and the western antarctic peninsula11 strengthened late in the holocene epoch we conclude that during the holocene southern ocean temperatures at the western antarctic peninsula margin were tied to changes in the position of the westerlies which have a critical role in global carbon cycling9 12

diatom assemblages from coastal settings of west antarctica abstract diatom assemblages from 33 core tops collected along a 2500 km transect of the northern antarctic peninsula and pine island bay areas were examined for their use as paleoenvironmental proxies environmental affinities of assemblages were interpreted within a broad geographical context and a wide range of ecological conditions four major assemblages were identified three pelagic assemblages related to different sea ice duration sst and other conditions affecting primary production and one benthic and epiphytic dominated assemblage typical of near shore shallow water habitats chaetoceros resting spores are an important component of diatom assemblages their high concentrations may reflect increased primary production and are associated with low total assemblage diversities the lowest diversities are observed at sites with increased resting spore percentages along the nw coast of the antarctic peninsula sedimentation rates strongly influence total diatom concentrations by contrast relative abundances of chaetoceros resting spores remain mostly unaffected by terrigenous flux and may serve as a reliable proxy for primary production this broad sampling of antarctic coastal environments fills a gap in our knowledge of phytoplankton communities in polar regions and helps establish the framework for reconstructing paleoenvironments from the paleorecord

variations in sediment yield over the advance and retreat of a calving glacier laguna san rafael north patagonian icefield abstract bathymetric and sub bottom acoustic data were collected in laguna san rafael chile to determine sediment yields during the little ice age advance and subsequent retreat of san rafael glacier the sediment volumes and subaqueous landforms imaged are used to interpret the proglacial dynamics and estimate erosion rates from a temperate tidewater glacier over a complete advance retreat cycle sediment yields from san rafael glacier averaged 2 7 107 m3 a since the end of the little ice age circa ad 1898 corresponding to average basin wide erosion rates of 23 9 mm a the highest erosion rates 68 23 mm a occurred at the start of the retreat phase and have since been steadily decreasing erosion rates were much lower during glacial advance averaging at most 7 mm a than during retreat such large glacial sediment yields over two centuries of advance and retreat suggest that the contribution of sediments stored subglacially cannot account for much of the sediment being delivered to the terminus today the detailed sub bottom information of a proglacial lagoon yields important clues as to the timing of erosion deposition and transfer of glacigenic sediments from orogens to the continental shelves and the influence of glacier dynamics on this process

environmental connotations of benthic foraminiferal assemblages from coastal west antarctica abstract this paper examines the variability in foraminiferal assemblages in surface samples from coastal settings along the northwestern antarctic peninsula as well as in the pine island bay area material comes from water depths ranging between 20 and 1257 m latitudes between 62 and 73 s and bottom water temperatures from 1 5 to 1 2 c the microfossil analysis within this broad geographical and environmental context provides a basis for paleo environmental studies environmental affinities of the assemblages were interpreted based on a wide array of ecological conditions including ctd data as well as on faunal indices and ecological affinities of the key taxa six foraminiferal assemblages are dominated by calcareous taxa among other factors they correspond to variable food supply terrigenous sedimentation and water mass properties another two assemblages are dominated by arenaceous foraminifera and reflect conditions corrosive to carbonate our findings indicate that preserved fossil assemblages in cores from these locations may not be accurate representations of living assemblages

antarctic holocene climate change a benthic foraminiferal stable isotope record from palmer deep the first moderate to high resolution holocene marine stable isotope record from the nearshore antarctic continental shelf ocean drilling program odp hole 1098b suggests sensitivity of the western antarctic peninsula hydrography to westerly wind strength and el nino southern oscillation enso like climate variability despite proximity to corrosive antarctic water masses sufficient caco3 in palmer deep sediments exists to provide a high quality stable isotopic record especially in the late holocene coherence of benthic foraminifer delta 18 o delta 13 c sedimentologic and caco3 fluctuations suggests that rapid 20 years palmer deep bottom water temperature fluctuations of 1d 1 5dc are associated with competitive interactions between two dominant oceanographic climatic states an abrupt shift from a warmer stable upper circumpolar deep water ucdw state to a cooler variable shelf water state occurred at s3 6 ka palmer deep bottom waters oscillated between ucdw and shelf water dominated states between s3 6 and 0 05 ka cool shelf water intervals correlate with neoglacial events the most recent and largest being the little ice age lia s0 7 0 2 ka similarities between palmer deep and global holocene records and the rapidity of inferred bottom water fluctuations suggest that western antarctic peninsula shelf hydrography has not been controlled by thermohaline reorganizations but by variable strength and or position of the southern hemisphere westerly wind field we suggest that these atmospheric perturbations may have originated in the low latitude tropical pacific

210pb sediment radiochronology an integrated formulation and classification of dating models abstract environmental archives such as sediments banded corals and tree rings are widely used to reconstruct past environmental conditions of ecosystems in particular 210 pb has been used during more than 4 decades through dating of undisturbed sediment cores to study ecosystem changes during the last 100 yr since its inception diverse dating models have been proposed developed used and validated in numerous environments but their nomenclature and formulation is not homogenous in this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation which relates excess 210 pb concentration in sediment its flux to the sediment surface and mass accumulation rate from this equation models were consistently named based on the main hypothesis used and using a unified and logical nomenclature dating equations were derived in detail we applied in detail most of the described models to a sediment core from mexico and uncertainty expressions were also included finally some recommendations to use the models are proposed we believe that this work can facilitate the use of 210 pb as a tool to date sediment cores in a more homogeneous way

3d numerical model for pearl river estuary a 3d numerical model with an orthogonal curvilinear coordinate in the horizontal direction and sigma coordinate in the vertical direction has been developed this model is based on pom princeton ocean model in this model a second moment turbulence closure submodel is embedded and the stratification caused by salinity and temperature is considered furthermore to adapt to estuary locations where the flow pattern is complex the horizontal time differencing is implicit with the use of a time splitting method instead of the explicit method in pom this model is applied to the pearl river estuary which is the largest river system in south china with hong kong at the eastern side of its entrance the computation is verified and calibrated with field measurement data the computed results mimic the field data well

late holocene advance of the collins ice cap king george island south shetland islands radiocarbon dates of incorporated moss indicate advance of the collins ice cap on fildes peninsula king george island after 650 cal yr bp ad 1300 broadly contemporaneous with the little ice age as defined in europe during that time the glacier extended less than 400 500 m beyond its present day margin moreover radiocarbon data indicate that this was the most extensive advance of the last 3500 cal years prior to 650 cal yr bp the ice must have been at or behind its present position furthermore the data indicate that climate conditions prior to the late holocene advance may have been similar to or possibly warmer than today