ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

retreat history of the east antarctic ice sheet since the last glacial maximum the east antarctic ice sheet eais is the largest continental ice mass on earth and documenting its evolution since the last glacial maximum lgm is important for understanding its present day and future behaviour as part of a community effort we review geological evidence from east antarctica that constrains the ice sheet history throughout this period 30 000 years ago to present this includes terrestrial cosmogenic nuclide dates from previously glaciated regions 14c chronologies from glacial and post glacial deposits onshore and on the continental shelf and ice sheet thickness changes inferred from ice cores and continental scale ice sheet models we also include new 14c dates from the george v land terre adelie coast shelf we show that the eais advanced to the continental shelf margin in some parts of east antarctica and that the ice sheet characteristically thickened by 300 400 m near the present day coastline at these sites this advance was associated with the formation of low gradient ice streams that grounded at depths of 1 km below sea level on the inner continental shelf the lambert amery system thickened by a greater amount 800 m near its present day grounding zone but did not advance beyond the inner continental shelf at other sites in coastal east antarctica e g bunger hills larsemann hills very little change in the ice sheet margin occurred at the lgm perhaps because ice streams accommodated any excess ice build up leaving adjacent ice free areas relatively unaffected evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the lgm an observation supported by ice cores which suggest that interior ice sheet domes were 100 m lower than present at this time ice sheet recession may have started 18 000 years ago in the lambert amery glacial system and by 14 000 years ago in mac robertson land these early pulses of deglaciation may have been responses to abrupt sea level rise events such as meltwater pulse 1a destabilising the margins of the ice sheet it is unlikely however that east antarctica contributed more than 1 m of eustatic sea level equivalent to post glacial meltwater pulses the majority of ice sheet recession occurred after meltwater pulse 1a between 12 000 and 6000 years ago during a period when the adjacent ocean warmed significantly large tracts of east antarctica remain poorly studied and further work is required to develop a robust understanding of the lgm ice sheet expansion and its subsequent contraction further work will also allow the contribution of the eais to post glacial sea level rise and present day estimates of glacio isostatic adjustment to be refined

globular ferropicritic rocks at pechenga kola peninsula russia liquid immiscibility versus alteration abstract the uppermost volcanic unit of the early proterozoic pechenga group comprises ferropicritic volcanic and hypabyssal rocks which possess well developed light weathering globular up to 10 cm in size or layer like structures mesoscopicly similar to those found in some archean ocellar komatiites these structures are superficially reminiscent of features attributed to liquid immiscibility including spheroidal aggregates in all stages of coalescence however several lines of field microscopical mineralogical and chemical evidence argue against the immiscibility hypothesis these include identical modal proportions grain sizes morphologies and orientations of crystalline phases in the globules and matrix as strikingly demonstrated for example by the spinifex textured varieties of the globular rocks a solid state hydrothermal metamorphic diffusional process that affected the originally glassy mesostasis is concluded to be the only feasable mechanism for the formation of the globular structures in the pechenga ferropicrites

problems and possible solutions concerning radiocarbon dating of surface marine sediments ross sea antarctica abstract radiocarbon accelerator mass spectrometric ams dates on the acid insoluble fraction from 38 core tops from the western ross sea antarctica are used to address these questions 1 what are the apparent ages of sediments at or close to the present sediment water interface 2 is there a statistically significant pattern to the spatial distribution of core top ages and 3 is there a correction factor that can be applied to these age determinations to obtain the best possible holocene downcore chronologies ages of core top sediments range from 2000 to 21 000 14c yr b p some old core top dates are from piston cores and probably represent the loss of sediment during the coring process but some core top samples 6000 14c yr b p may represent little or no holocene deposition four possible sources of variability in dates 6000 14c yr b p n 28 are associated with 1 different sample preparation methods 2 different sediment recovery systems 3 different geographic regions and 4 within sample lateral age variability statistical analysis on an a posteriori design indicates that geographic area is the major cause of variability there is a difference in mean surface sediment age of nearly 2000 yr between sites in the western ross sea and sites east of ross bank in south central ross sea the systematic variability in surface age between areas may be attributed to a variable sediment accumulation rates sar surface age is inversely related to sar b differences in the percentage of reworked dead carbon between each area and or c differences in the co2 exchange between the ocean and the atmosphere

timing and pathways of east antarctic ice sheet retreat abstract a lack of reliable chronology often leaves antarctic ice sheet reconstructions incomplete despite being the most heavily investigated region of the antarctic continental shelf the post last glacial maximum lgm record of marine based ice sheet dynamics in the ross sea has remained largely elusive and at odds with fringing terrestrial records of ice sheet decay issues with radiocarbon dating stem primarily from poorly preserved carbonate contamination by glacially recycled carbon and insufficient consideration for glacial geomorphic context and sedimentary facies we assess nearly 70 newly acquired and more than 200 published radiocarbon ages in the context of a consistent sedimentary facies and geomorphic framework to interpret the timing of the local glacial maximum and subsequent retreat of the east antarctic ice sheet eais in the ross sea and potential causes of retreat compound specific radiocarbon ages help to provide good constraints on open marine onset and we demonstrate that with proper corrections and considerations acid insoluble organic aio radiocarbon ages can be reliable in open marine sediments and carbonate ages can be reliable in grounding zone proximal sediments we find that the ice flowing through pennell and joides troughs remained at maximum extent for approximately 10 000 years before retreating at 15 1 and 13 cal ka bp respectively an ice shelf covered the outer continental shelf until 9 5 cal ka bp after which it collapsed in joides trough creating deep iceberg furrows retreat through pennell trough was more episodic marked by grounding zone wedges that backstep upstream and onto lateral banks creating deglacial emergent ice rises as ice retreated from 9 to 4 cal ka bp there was considerable reorganization of drainage and at least one episode of readvance through southern joides trough that began drawdown of terrestrial ice near ross island at 7 8 cal ka bp the ice shelf appears to have retreated to a near present configuration by 2 cal ka bp however due to inconsistencies in calendar ages grounding line position must be inferred from relative chronology based on glacial landforms which suggests grounded ice retreated nearly to drygalski ice tongue and lingered atop crary bank where it was maintained by ice from david glacier our reconstruction further suggests that the eais in the western ross sea was not a discernible contributor to meltwater pulse 1a but likely contributed to eustatic sea level rise well through the middle perhaps even late holocene

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 1 geophysical results in the 1994 1995 and 1998 austral field seasons geophysical research efforts in the ross sea focused on acquiring a high resolution database designed to permit 1 reconstruction of the maximum extent and configuration of the ice sheet during the last glacial maximum i e oxygen isotope stage 2 2 reconstruction of conditions at the base of the ice sheet and 3 assessment of the relative retreat history of the ice sheet following the last glacial maximum five seismic facies are distinguished on the basis of external geometry relationships among features bounding surface amplitude intensity of internal acoustic signature and geometry of internal reflectors seismic facies 1 is a transparent draping unit correlated to diatomaceous mud interpreted as being deposited under open marine conditions seismic facies 2 and 3 are comprised of units displaying subdued massive internal signatures with smooth lower bounding surfaces and hummocky upper surfaces characterized by glacial lineations these units are interpreted to be grounding zone proximal deposits overridden by the expanded ice sheet seismic facies 2 may be a deforming till unit seismic facies 4a is characterized by an internally massive to chaotic signature an erosional often flat lower surface and a hummocky upper surface displaying glacial lineations this unit is interpreted to be till and is divided into deposits associated with the most recent glacial expansion 4a and with an earlier pre last glacial maximum expansion 4b seismic facies 5 is an acoustically laminated ponded and draping deposit interpreted to contain proglacial and sub ice shelf materials deposited continuously since the last interglacial period the associations of these units provide context for the interpretation of the ice edge maximum position conditions at the base of the ice sheet and the relative retreat history of the region there is compelling evidence for a much expanded ice sheet in the ross sea during the last glacial maximum in the western ross sea the maximum grounding position is marked by an isolated grounding zone wedge and placed in the vicinity of coulman island approximately 150 km from the continental shelf edge in the central ross sea the maximum grounding position is close to the continental shelf break based primarily on the presence of an extensive 60 m thick sheet like deposit with a fluted upper surface streaming ice may have occupied bathymetric lows on the continental shelf as suggested by 1 the configuration of bathymetry 2 the presence of glacially eroded troughs 3 the concentration of sediment interpreted to be deforming till within the middle to outer shelf reaches of the troughs and 4 the fluted nature of the upper surface absolute rates of streaming ice flow relative to inter ice stream areas are not implied the western ross sea continental shelf deposits record the retreat history of ice derived predominantly from the east antarctic ice sheet and glaciers of the transantarctic mountains ice flow on the continental shelf is interpreted to have remained fixed in position restricted by the walls of the troughs on the inner shelf of the western ross sea the ice flowed over and eroded lithified sedimentary strata slower moving ice occupied flat topped banks a single grounding zone wedge occurs on the western ross sea central shelf no substantial deposits are observed on the inner continental shelf this lack of grounding zone features reflects a restricted sediment supply and a relatively steady rapid retreat of the ice sheet during retreat ice flow acted independently in each major trough and on the bank tops ice retreated from victoria land basin drygalski trough before it retreated from joides basin ice remained on the bank tops shedding material into the abandoned troughs grounded ice in the central ross sea was derived predominantly from an expanded west antarctic ice sheet the ice sheet remained grounded on the continental shelf edge after retreat of ice from the western ross sea expanded ice eroded the inner shelf and deposited sheets of till on the central and outer shelf ice stream drainage shifted laterally as recorded by rounded laterally accreting ridges that separate bathymetric troughs the central ross sea is the repository for larger volumes of sediment derived from ice flow across basins of relatively thick unlithified sedimentary deposits two till sheets mark grounding zone positions in the central ross sea reflecting the higher sediment supply and a stepped deglaciation ice remained grounded on the pennell bank to the west a series of moraines marks the retreat of ice across the bank mega scale glacial lineations and other streamlined subglacial geomorphic features occur across the continental shelf primarily within the troughs the lineations substantiate the maximum reconstruction and support the interpretation of a deforming substrate beneath the outer reaches of the expanded ice sheet this deforming substrate may have contributed to the onset of deglaciation features associated with meltwater are rare or absent suggesting that basal meltwater played a minor role in retreat of the ice sheet

radiocarbon constraints on antarctic peninsula ice sheet retreat following the last glacial maximum lgm abstract we present marine sedimentologic and radiocarbon data for the timing of retreat of the largely marine based antarctic peninsula ice sheet since the last glacial maximum lgm our findings indicate minimum estimates of deglaciation between 18 000 and 9000 calibrated years before present cal yr bp roughly in phase with the northern hemisphere deglaciation and eustatic sea level rise our findings show this retreat occurred progressively from the outer middle and inner continental shelf regions as well as progressively from the north to the south retreat initiated on the outer shelf of the northern peninsula by 18 000 cal yr bp and continued southward by 14 000 cal yr bp on the outer shelf of marguerite bay several thousand years earlier than estimated by numeric models while individual cores yield estimates of glacial retreat that may vary up to 1100 years we note steps in the data occur at 14 000 and possibly 11 000 cal yr bp coincidental to rapidly rising eustatic sea level including the well documented melt water pulses mwp 1a and 1b these data support the hypothesis that rapidly rising sea level is associated with marine ice sheet destabilization although additional dates are necessary to substantiate this finding this study highlights problems with radiocarbon dating acid insoluble organic aio matter in proximal lateglacial sediments as well as the need for more accurate dating techniques

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

quality and durability assessments of the armourstones for two rubble mound breakwaters mersin turkey due to economic reasons natural stones armourstones of various sizes and qualities are very frequently used for the constructions of the breakwaters to protect coastal engineering structures from wave actions deterioration of the armourstones with time in the form of abrasion and disintegration may end up with the damage of the structures therefore it is necessary to investigate the long term performance and quality of the armourstones which should be sound and durable mersin and kumkuyu harbours were constructed using four different limestones obtained from two quarries the limestones have different characters and site performances in this study the material and mass properties of the limestones taken from the quarries with known site performances as armourstones are investigated the site performances and durability of the limestones are compared with the field measurements and laboratory works thus the information obtained is used to assess long term durability of the armourstones the long term performance of the degirmencayi and tirtar upper level limestones are observed to be good whereas it is rather poor for the tirtar middle and lower level limestones comparison between the predicted and observed durabilities of the armourstones indicated that ciria cur rdid rers and wet to dry strength ratio give better results based on their field performances however the prediction of the durability of the limestones is poor in case rdis average pore diameter and saturation coefficient are used

rock for breakwater construction in western australia its availability and influence on design abstract small boat harbours protected by rubble mound breakwaters are currently being built along the exposed western and southern coasts of western australia the properties that rocks must have to be suitable for armour blocks on breakwaters are discussed particular reference is made to the special problems produced by the remoteness of heavy armour material from the sites of 6796 of breakwaters recently built or being considered in western australia fuller geotechnical investigations for quarries are warranted in these circumstances

liquid immiscibility in the caf2 granite system and trace element partitioning between the immiscible liquids abstract the recent discoveries of ca fluoride melt in magmatic systems especially in peralkaline granites with rare earth element enrichment has raised questions about the presence and nature of liquid immiscibility in caf2 granite systems as well as the partitioning behavior of trace elements between such immiscible liquids we have experimentally explored the immiscibility in this system using natural granite fluorite starting materials at fast and slow cooling rates temperatures from 500 c to 1200 c and 1 atmosphere pressure our experiments confirm the presence of a miscibility gap in the caf2 granite system over a wide range of temperatures the two immiscible liquids are a mafic fluorosilicate melt fm with high cao and f and a felsic oxysilicate melt sm with high sio2 and alkalis immiscibility is encountered when the bulk f content exceeds approximately 4 4 wt at 1200 c and then rapidly decreases to only 0 75 wt at low temperature below 900 c this indicates that calcic magmas are able to evolve to the liquid immiscibility domain by the residual enrichment of fluorine resulting from fractional crystallization and that liquid immiscibility should be common the peritectic reaction fm sm fluorite removes the fluorosilicate liquid around 600 c and could explain the absence of fluorosilicate observations in natural granites the compositions of the liquids in fast cooling experiments show a significantly larger miscibility gap which is characterized by compared to slow cooling runs similar sm compositions but higher ca and f content in fm this difference is caused by suppression of fluorite nucleation and is interpreted as a metastable extension of the high temperature liquid immiscibility immiscibility results in strong fractionation of trace elements which is primarily governed by melt structure and the ionic potential z r of the elements the behavior of trace elements can be categorized into three groups 1 network formers si al ga pb b partition into the oxysilicate melt 2 the partitioning of the alkalis and alkali earths is strongly dependent on the ionic potential with the partitioning coefficients d fm sm in the order dcs

spherulitic crystallization in lamprophyric magmas and the origin of ocelli ocelli are rounded structures containing polycrystalline feldspar aggregates and minor amounts of mafic minerals they occur in lamprophyre dykes all over the world ocelli are usually interpreted in terms of liquid immiscibility1 3 in alkaline lamprophyre dykes along the south coast of norway4 ocelli are closely associated with globular structures varioles which i have assumed5 were formed as a result of a splitting of the magma into two fractions the re examination of these norwegian dykes reported here however has shown that varioles ocelli and leucocratic feldspar rich segregations formed by spherulitic and closely related growth mechanisms from under cooled volatile rich magmas without an intervening stage of liquid phase separation

evaluation of andesite source as armourstone for a rubble mound breakwater hisaronu turkey black sea coast line is a hazardous region especially in winter due to the dominant wave action therefore rubble mound breakwaters protected with armourstone used as ship shelters are vital structures especially for the fishermen the deterioration of the armourstone with time in the form of abrasion and disintegration may result in the failure of the breakwater in this study the properties of the armourstone taken from an andesite quarry and used in the hisaronu rubble mound breakwater were studied both in field and laboratory in order to assess their qualities and long term durabilities based on the in situ observations and laboratory tests the andesite is found to be generally marginal rock ciria cur rdis rers and wet dry strength ratio classifications are in good agreement with the in situ observations and the results of the laboratory tests however rdid average pore diameter and saturation coefficient classifications cannot correctly predict long term durability of the armourstone field studies reveal that block size of the andesite in the quarry increases with depth due to the increase in spacing of the cooling joints of the rock

compositional and kinetic controls on liquid immiscibility in ferrobasalt rhyolite volcanic and plutonic series we present major element compositions of basalts and their differentiation products for some major tholeiitic series the dry low pressure liquid lines of descent are shown to approach or intersect the experimentally defined compositional space of silicate liquid immiscibility ferrobasalt rhyolite unmixing along tholeiitic trends in both volcanic and plutonic environments is supported by worldwide occurrence of immiscible globules in the mesostasis of erupted basalts unmixed melt inclusions in cumulus phases of major layered intrusions such as skaergaard and sept iles and oxide rich ferrogabbros closely associated with plagiogranites in the lower oceanic crust liquid immiscibility is promoted by low pressure anhydrous fractional crystallization that drives the low al2o3 high feo liquids into the two liquid field kinetic controls can be important in the development of two liquid separation the undercooling that occurs at the slow cooling rates of plutonic environments promotes early development of liquid immiscibility at higher temperature in contrast rapid cooling in erupted lavas leads to large undercoolings and liquid immiscibility develops at significantly lower temperatures unmixing leads to the development of a compositional gap characterized by the absence of intermediate compositions a feature of many tholeiitic provinces the compositions of experimental unmixed silica rich melts coincide with those of natural rhyolites and plagiogranites with high feotot and low al2o3 suggesting the potential role of large scale separation of immiscible si rich liquid in the petrogenesis of late stage residual melts no trace of the paired ferrobasaltic melt is found in volcanic environments because of its uneruptable characteristics instead fe ti p rich gabbros are the cumulate products of immiscible fe rich melts in plutonic settings the immiscibility process may be difficult to identify because both melts crystallize the same phases with the same compositions the two liquids might form incompletely segregated emulsions so that both liquids continue to exchange as they crystallize and remain in equilibrium even if segregated both melts evolve on the binodal surface and exsolve continuously with decreasing temperature the two liquids do not differentiate independently and keep crystallizing the same phases with differentiation further evolution by fractional crystallization potentially drives the bulk liquid out of the twoliquid field so that very late stage liquids could evolve into the single melt phase stability field

immiscible silicate liquid partition coefficients implications for crystal melt element partitioning and basalt petrogenesis this study investigates partitioning of ele ments between immiscible aluminosilicate and boro silicate liquids using three synthetic mixtures doped with 32 trace elements in order to get a good spatial separation of immiscible liquids we employed a high temperature centrifuge experiments were performed at 1 050 1 150 c 1 atm in sealed fe and pt containers quenched products were analysed by electron micro probe and la icp ms nernst partition coefficients d s between the fe rich and si rich aluminosilicate immiscible liquids are the highest for zn 3 3 and fe 2 6 and the lowest for rb and k 0 4 0 5 the plots of d values against ionic potential z r in all the composi tions show a convex upward trend which is typical also for element partitioning between immiscible silicate and salt melts the results bear upon the speciation and structural position of elements in multicomponent silicate liquids the ferrobasalt rhyolite liquid immis cibility is observed in evolved basaltic magmas and may play an important role in large gabbroic intrusions such as skaergaard and during the generation of unusual lavas such as ferropicrites

mid holocene grounding line retreat and readvance at whillans ice stream west antarctica author s venturelli ra siegfried mr roush ka li w burnett j zook r fricker ha priscu jc leventer a rosenheim be

retreat of the east antarctic ice sheet during the last glacial termination the east antarctic ice sheet retreated at the end of the last glacial period terrestrial and marine data suggest that the retreat began 14 000 years ago indicating that the east antarctic ice sheet probably did not contribute to meltwater pulse 1a 14 700 years ago

experiments on liquid immiscibility along tholeiitic liquid lines of descent crystallization experiments have been conducted on compositions along tholeiitic liquid lines of descent to define the compositional space for the development of silicate liquid immiscibility starting materials have 46 56 wt sio2 11 7 17 7 wt feotot and mg number between 0 29 and 0 36 these melts fall on the basaltic trends relevant for mull iceland snake river plain lavas and for the sept iles layered intrusion where large scale liquid immiscibility has been recognized at one atmosphere under anhydrous conditions immiscibility develops below 1 000 1 020 c in all of these compositionally diverse lavas extreme iron enrichment is not necessary immiscibility also develops during iron depletion and silica enrichment variations in melt composition control the development of silicate liquid immiscibility along the tholeiitic trend elevation of na2o k2o p2o5 tio2 promotes the development of two immiscible liquids increasing melt cao and al2o3 stabilizes a single liquid field new data and published phase equilibria show that anhydrous low pressure fractional crystallization is the most favorable condition for unmixing during differentiation pressure inhibits immiscibility because it expands the stability field of high ca clinopyroxene which reduces the proportion of plagioclase in the crystallizing assemblage thus enhancing early iron depletion magma mixing between primitive basalt and fe ti p rich ferrobasalts can serve to elevate phosphorous and alkali contents and thereby promote unmixing water might decrease the temperature and size of the two liquid field potentially shifting the binodal solvus below the liquidus leading the system to evolve as a single melt phase

retreat history of the ross ice sheet shelf since the last glacial maximum from deep basin sediment cores around ross island abstract radiocarbon dated sediment cores from deep basins beneath the mcmurdo ice shelf and seasonally open water north of ross island mcmurdo sound display a characteristic succession of sedimentary facies that document the retreat of the ross ice sheet at the last glacial maximum to its present ice shelf configuration the facies succession records a transition from a nearly grounded ice sheet to open marine environments north of ross island that comprises in ascending stratigraphic order 1 slightly consolidated clast rich muddy diamict dominated by basement clasts from the transantarctic mountains and interpreted as melt out from the basal layer debris proximal to a retreating grounding zone 2 sparsely fossiliferous reworked diatom frustules and non bioturbated mud lacking lonestones interpreted as a sub ice shelf facies and 3 diatom mud and diatom ooze indicative of open marine conditions with evidence of iceberg rafting the succession in the open marine lewis basin north of ross island is similar though the diamict is much sandier and sedimentation rates 1 2 orders of magnitude higher we present a radiocarbon chronology from total organic carbon which implies that lift off of grounded ice in the 900 m deep marine basins surrounding ross island occurred by 10 100 14c years bp following lift off an ice shelf was maintained to the north of ross island until 8900 14c years bp we identify a phase of accelerated retreat at that time between the drygalski trough and ross island immediately preceding the timing of meltwater pulse 1b at 8900 14c years bp the calving line became pinned to ross island significantly decoupling from the grounding line and marking the transition from a retreating ice sheet to the development of the present ice shelf

relationship between density compressive strength tensile strength and aggregate properties of andesites from hungary aggregate properties and strength parameters of four andesites from two operating hungarian quarries of nogradkovesd one lithotype and gyongyossolymos three lithotypes are presented in this paper air dry water saturated and freeze thaw subjected specimens were tested on core drilled cylindrical specimens and the aggregate properties were also determined from the remaining part of the drilled rock blocks tensile strength values rapidly decreased from air dry to water saturated and finally to freeze thaw subjected specimens linear relationships between air dry and water saturated bulk densities and between ucs and modulus of elasticity were found micro fabric influences strength and aggregate parameters of studied andesites fine porphyritic andesite has the highest ucs and tensile strength and the best micro deval results while coarser porphyritic andesite has lower strength and aggregate parameters test results were compared with previously published rock mechanical data of intermediate and basic igneous rocks a good exponential correlation was found between micro deval and ucs values of this paper and previously published data sets but there was no indication that micro deval values correlate well with los angeles values

sediment chronology in antarctic deglacial sediments reconciling organic carbon 14c ages to carbonate 14c ages using ramped pyrox we present the first study which directly compares carbonate radiocarbon 14c dates with the ramped pyrox rp radiocarbon dating technique within a single sediment core and we confirm the utilit

immiscible iron and silica rich liquids in the upper zone of the bushveld complex the bushveld complex south africa is the largest layered intrusion on earth and plays a considerable role in our understanding of magmatic differentiation and ore forming processes in this study we present new geochemical data for apatite hosted multiphase inclusions in gabbroic cumulates from the bushveld upper zone inclusions re homogenized at high temperature 1060 1100 c display a range of compositions in each rock sample from iron rich 35 wt feotot 28 wt sio2 to silica rich 5 wt feotot 65 wt sio2 this trend is best explained by an immiscible process and trapping of contrasted melts in apatite crystals during progressive cooling along the binodal of a two liquid field the coexistence of both si rich and fe rich immiscible melts in single apatite grains is used to discuss the ability of immiscible melts to segregate from each other and the implications for mineral and bulk cumulate compositions we argue that complete separation of immiscible liquids did not occur resulting in crystallization of similar phases from both melts but in different proportions however partial segregation in a crystal mush and the production of contrasting phase proportions from the fe rich melt and the si rich melt can be responsible for the cyclic evolution from melanocratic fe ti p rich to leucocratic plagioclase rich gabbros which is commonly observed in the upper zone of the bushveld complex where it occurs at a vertical scale of 50 to 200 m

antarctic sediment chronology by programmed temperature pyrolysis methodology and data treatment 1 we report a detailed programmed temperature pyrolysis combustion methodology for radiocarbon 14c dating of antarctic sub ice shelf sediments the method targets the autochthonous organic component in sediments that contain a distribution of acid insoluble organic components from several sources of different ages the approach has improved sediment chronology in organic rich sediments proximal to antarctic ice shelves by yielding maximum age constraints significantly younger than bulk radiocarbon dates from the same sediment horizons the method proves adequate in determining isotope ratios of the pre aged carbon end member however the isotopic compositions of the low temperature measurements indicate that no samples completely avoided mixing with some proportion of pre aged organic material dating the unresolved but desired young end member must rely on indirect methods but a simple mixing model cannot be developed without knowledge of the sedimentation rate or comparable constraints a mathematical approach allowing for multiple mixing components yields a maximum likelihood age a first order approximation of the relative proportion of the autochthonous component and the temperature at which allochthonous carbon begins to volatilize and mix with the autochthonous component it is likely that our estimation of the cutoff temperature will be improved with knowledge of the pyrolysis kinetics of the major components chronology is improved relative to bulk acid insoluble organic material ages from nine temperature interval dates down to two but incorporation of inherently more pre aged carbon in the first division becomes more apparent with fewer and larger temperature intervals

quality assessment of armourstone for a rubble mound breakwater sinop turkey helaldi is a fishing town in the central black sea region where construction of a rubble mound breakwater is being planned the construction of the breakwater requires good quality durable armourstone several laboratory tests are performed for the quality assessment of the two potential armourstone namely limestone and sandstone the quality evaluation of the stones is done on the basis of ciria cur criteria saturation coefficient wet to dry strength ratio and the rock durability index the quality evaluations are then compared with the field performance of both rocks laboratory test results durability assessments and field performance of the rocks indicate that the limestone is a good quality armourstone and it can be used for the breakwater construction however the sandstone is marginal to poor material with very poor field performance and should not be used for the breakwater construction

age discrepancy between molecular biomarkers and calcareous foraminifera isolated from the same horizons of northwest pacific sediments abstract recent observations show that establishment of molecular level radiocarbon stratigraphy is increasingly critical for paleoceanographic studies especially to enable comparable discussion about past ocean and climate changes inferred from multiple proxy records based on lipid biomarkers and calcareous foraminiferal microfossils so far although we have interesting evidence that there are temporal and spatial age offsets between the algal alkenone biomarker used for sst sea surface temperature estimates and planktonic foraminifera in regions with high sedimentation rates less is known about such age offsets in the settings of lower sedimentation in this study to investigate the potential of biomarkers as an alternative dating proxy to foraminifera in a low sedimentation rate setting we measured radiocarbon ages of 17 different lipid biomarkers fatty acids fas n alkanes and alkenones bulk total organic matter toc and foraminifera from two sections 12 15 cm and 21 24 cm depth of a surface sediment core in the northwest pacific the sedimentation rate estimated from the toc ranged from 10 5 cm kyr in the core top to 0 9 cm kyr in the lower part of the core the ages of the fas detected at 12 15 cm depth ranged from 530 yr bp c 18 to 3250 yr bp c 28 the 14 c analysis of the fas could be divided into two groups fas c 16 c 18 derived from marine organisms and those c 24 c 26 c 28 derived from terrestrial higher plants the high molecular weight hmw fas ages were older 2550 yr bp c 24 to 3250 yr bp c 28 than those of the low molecular weight lmw fas 530 yr bp c 18 to 1820 yr bp c 16 at 21 24 cm depth the alkenone ages were 7100 7300 yr younger than those of the planktonic foraminifera in this horizon the alkenone 14 c age 7500 yr bp and the alkenone estimated sst 15 3 c suggest that these alkenones were produced in this region during the holocene the alkenone 14 c age was also in good agreement with those of the lmw fas c 14 ic 15 aic 15 c 16 and c 18 1 derived from marine plankton and bacteria similarly the toc age was 5700 yr younger than that of the planktonic foraminifera these age differences are large compared with those estimated for the horizon at 12 15 cm depth which was characterized by a relatively higher sedimentation rate these trends between ages of alkenones toc and planktonic foraminifera are not comparable to the results from sites with high sedimentation rates such as the benguella upwelling system mollenhauer g eglinton t i ohkouchi n schneider r r muller p j grootes p m et al 2003 asynchronous alkenone and foraminifera records from the benguela upwelling system geochim cosmochim acta 67 2157 2171 or the bermuda rise drift deposit ohkouchi n eglinton t i keigwin l d hayes j m 2002 spatial temporal offsets between proxy records in a sediment drift science 289 1224 1227 which are significantly different sedimentary settings from our site the radiocarbon results from these high sedimentation rate regions suggest that the alkenones are several thousand years older than the coexisting planktonic foraminifera on the other hand the age offsets between alkenones and planktonic foraminifera at our site are larger than those from the other sites and the alkenones are younger than the planktonic foraminifera

widespread collapse of the ross ice shelf during the late holocene the stability of modern ice shelves is threatened by atmospheric and oceanic warming the geologic record of formerly glaciated continental shelves provides a window into the past of how ice shelves responded to a warming climate fields of deep 560 m linear iceberg furrows on the outer western ross sea continental shelf record an early post last glacial maximum episode of ice shelf collapse that was followed by continuous retreat of the grounding line for 200 km runaway grounding line conditions culminated once the ice became pinned on shallow banks in the western ross sea this early episode of ice shelf collapse is not observed in the eastern ross sea where more episodic grounding line retreat took place more widespread 280 000 km2 retreat of the ancestral ross ice shelf occurred during the late holocene this event is recorded in sediment cores by a shift from terrigenous glacimarine mud to diatomaceous open marine sediment as well as an increase in radiogenic beryllium 10be concentrations the timing of ice shelf breakup is constrained by compound specific radiocarbon ages the first application of this technique systematically applied to antarctic marine sediments breakup initiated around 5 ka with the ice shelf reaching its current configuration 1 5 ka in the eastern ross sea the ice shelf retreated up to 100 km in about a thousand years three dimensional thermodynamic ice shelf ocean modeling results and comparison with ice core records indicate that ice shelf breakup resulted from combined atmospheric warming and warm ocean currents impinging onto the continental shelf

boundary condition of grounding lines prior to collapse larsen b ice shelf antarctica grounding zones where ice sheets transition between resting on bedrock to full floatation help regulate ice flow exposure of the sea floor by the 2002 larsen b ice shelf collapse allowed detailed morphologic mapping and sampling of the embayment sea floor marine geophysical data collected in 2006 reveal a large arcuate complex grounding zone sediment system at the front of crane fjord radiocarbon constrained chronologies from marine sediment cores indicate loss of ice contact with the bed at this site about 12 000 years ago previous studies and morphologic mapping of the fjord suggest that the crane glacier grounding zone was well within the fjord before 2002 and did not retreat further until after the ice shelf collapse this implies that the 2002 larsen b ice shelf collapse likely was a response to surface warming rather than to grounding zone instability strengthening the idea that surface processes controlled the disintegration of the larsen ice shelf

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

sub ice shelf sediment geochronology utilizing novel radiocarbon methodology for highly detrital sediments sub ice shelf sediments near larsen c ice shelf lis c show fine scale rhythmic laminations that could provide a near continuous seasonal resolution record of regional ice mass changes despite the great potential of these sediments a dependable late quaternary chronology is difficult to generate rendering the record incomplete as with many marginal antarctic sediments in the absence of preserved carbonate microfossils the reliability of radiocarbon chronologies depends on presence of high proportions of autochthonous organic carbon with minimized detrital organic carbon consequently acid insoluble organic aio 14c dating works best where high productivity drives high sediment accumulation rates but can be problematic in condensed sequences with high proportions of detrital organic carbon ramped pyrox 14c dating has progressively been shown to improve upon aio 14c dates to the point of matching foraminiferal carbonate 14c dates through differential thermochemical degradation of organic components within samples but in highly detrital sediments proportions of contemporaneously deposited material are too low to fully separate autochthonous organic carbon from detrital carbon in samples large enough to 14c date we introduce two modifications of the ramped pyrox 14c approach applied to highly detrital sediments near lis c to maximize accuracy by utilizing ultra small fractions of the highly detrital aio material with minimization of the uncertainty cost these techniques allow us to generate chronologies for cores that would otherwise go undated pushing the limits of radiocarbon dating to regions and facies with high proportions of pre aged detritus wider use of these techniques will enable more coordinated a priori coring efforts to constrain regional glacial responses to rapid warming where sediments had previously been thought too difficult to date

chronology of the palmer deep site antarctic peninsula a holocene palaeoenvironmental reference for the circum antarctic palmer deep sediment cores are used to produce the first high resolution continuous late pleistocene to holocene time series from the antarctic marine system the sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite fifty four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka bp reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error i e 50 years in addition surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the antarctic peninsula spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400 200 and 50 70 year frequency bands similar to other high resolution records from the holocene but so far unique f

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 2 sedimentologic and stratigraphic signature sedimentologic geotechnical geochemical and accelerator mass spectrometer ams radiocarbon data from two marine geologic cruises in the ross sea have allowed us to constrain facies relationships and temporal changes in the west antarctic ice sheet the selection of core sites was facilitated by the use of multibeam bottom imagery and a good quality chirp subbottom reflection system a complex but consistent succession of facies documents a number of environments from subglacial to open marine massive mud rich diamictons have low water contents contain in places a calcareous microfossil assemblage show minimal textural variation and contain low and uniform total organic carbon values this reflects a subglacial setting this unit passes upward into a stratified thin granulated facies consisting of pelletized sandy muddy gravel that is loosely compacted and contains a variable water content and concentrated horizons of pebble sized clasts this facies reflects the lift off zone or thin water film between the basal debris and sea floor overlying this unit are silty clays that contain a well sorted very fine grained sand component there are no coarse grains within this unit this facies is in part laminated and reflects deposition beneath an ice shelf near and away from the grounding line zone the ice shelf facies passes upward into a siliceous mud and ooze unit that represents deposition in an open marine setting a sandy volcaniclastic rich subfacies marks the transition from ice shelf to open marine environments found at the calving line the 86 ams radiocarbon dates on organic matter provide an accurate chronology for 19 cores ice shelf conditions were established in the outer drygalski trough by 11 0 25 ka and perhaps earlier this transition took place in the joides basin by 10 8 ka the calving front of the ross ice shelf passed over the drygalski trough at 74 s by 9 5 0 25 ka the timing of deglaciation in the ross sea calls into question current models for the contribution of antarctic glacial ice to holocene sea level rise and suggests that recession was relatively gradual and more closely aligned with northern hemisphere deglaciation and its associated eustatic pulse

assessment of deterioration and collapse mechanisms of dolomitic limestone at hasankeyf antique city before and after reservoir impounding turkey the hasankeyf antique city located in southeastern anatolia turkey includes several historical heritages and man made caves it is mainly located in dolomitic limestone the city will be partly under water after reservoir impounding of the ilisu dam and the limestone will be subjected to cyclic processes such as wetting drying and freezing thawing although a new town is formed and part of the city is transported to a nearby area this cannot be done for many existing historical and cultural values at the site the behavior of the limestone under cyclic processes is not known in this study deterioration mechanisms of the limestone were investigated with field and laboratory studies it is found that the rock is not durable very thin surficial deterioration zone exists on the rock surface discontinuity controlled block failures associated with collapse of man made caves occur at the site before reservoir impounding further discontinuity controlled block failures are expected to occur after reservoir impounding by aggravated deterioration and surface erosion of the rock within the fluctuation zone of the reservoir

radiocarbon constraint on relict organic carbon contributions to ross sea sediments we estimate the relative contribution of relict organic matter to the acid insoluble organic carbon aioc fraction of surface sediments from ross sea antarctica on the basis of 14c abundance the bulk isotopic characteristics of aioc can largely be explained by simple two source models of modern and relict organic carbon when samples are grouped according to two geographical regions namely southwestern and south central ross sea this spatial variability in relict organic carbon could be controlled by proximity to the edge of the ross ice shelf and ice drainage areas radiocarbon abundance in the aioc is potentially an excellent tool to estimate the contribution of relict organic carbon in the antarctic margin sediments

holocene history of the larsen a ice shelf constrained by geomagnetic paleointensity dating a sedimentary record collected from beneath the former lar sen a ice shelf reveals the holocene history of the larsen a re gion the record begins with the transition from grounded ice to a floating ice shelf completed by 10 7 6 0 5 ka and ends with the modern recession the record contains several late holocene dia tomaceous ooze layers that suggest proximity to productive open water events radiocarbon ages obtained from these sediments were complicated by the presence of detrital and reworked carbon we have eliminated these complications and constructed a chro nology for the larsen a ice shelf history via tuning of the geo magnetic field paleointensity record with a reference curve this approach provides chronological control to sediment sequences that lack appropriate material for radiocarbon dating geomag netic paleointensity features with wavelengths of 2 3 k y can be recognized and interhemispherically correlated illustrating the po tential to use geomagnetic paleointensity variations as a global cor relation and dating tool at sub milankovitch time scales

immiscibility synthesis as an indication of cooling rates of basalts abstract silicate liquid immiscibility of iron rich and silica rich compositions have been experimentally reproduced at various cooling rates to evaluate the possible effect of cooling rate on the size of the globules the experiments were performed at constant cooling rates from 1 to 32 c hr under atmospheric pressure and controlled oxygen fugacity a tholeiitic basalt which occurs as a 36 cm thick dike in the izu peninsula japan was used as starting material the sample was melted at the liquidus temperature 1190 5 c and cooled to 1000 c two immiscible liquids occur in the charges as do in the dike in the experiments the size of the globules is strongly related to the cooling rate the diameter of the globules decreases exponentially with increasing cooling rate and the number of globules decreases with decreasing cooling rate these facts together with the typical coalescence shape suggests a growth of globules by coalescence rather than a decrease of the nucleation rate compositional variations of the liquid just prior to splitting within each charge do not affect those of the two immiscible liquids however the compositional differences between the two liquids slightly increase with decreasing cooling rate using the cooling rate vs size relationships the size of globules in basalts allows a cooling rate estimate in the izu dike the 10 largest silica rich globules range from 2 3 m to 0 8 m in the center and the margin suggesting cooling rates of about 15 c hr and greater than 32 c hr respectively at temperatures near 1000 c other estimates from natural samples show a good agreement between deduced cooling rates and observed textures