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

partition coefficients for calcic plagioclase implications for archean anorthosites by the use of a multiple aliquot technique combined with statistical calculations to overcome effects of alteration and contamination we have determined partition coefficients d s for rare earth elements rees between natural high ca plagioclase megacrysts and their basaltic matrices some of the basalts that we investigated are shown experimentally to crystallize only high ca plagioclase over approximately a 20 30 c temperature interval below the liquidus the ree d s agree well with experimentally determined values and predict equilibrium melts for archean anorthosites that agree well with coeval basaltic flows and dikes furthermore the d s appear to be valid for both tholeiitic and alkali basalts over a range of mg numbers 34 58 and ree concentrations la from 3 50 ppm similarly calculated d s for co sc cr rb sr cs ba hf ta and th also predict equilibrium melts for anorthosites that agree reasonably well with coeval basaltic flows and dikes the apparent values for co sc and ta seem good to better than 50 whereas the standard deviations for rb and th are equal to their means making the d s of questionable value the others are useful probably to within a factor of 2 experimental studies of the d for total fe as feot indicate a value of about 04 at an oxygen fugacity slightly below that of the qfm buffer a by product of the feot experiments was the experimental d s for mgo tio2 and k2o which could be compared with the d s from natural assemblages from the d s that were determined we suggest that plagioclase megacrysts in the bad vermilion lake anorthosite were in equilibrium with melts having the composition of tholeiitic basalts at an oxygen fugacity slightly below the qfm buffer the predicted melts have an feot content of about 13 k2o of about 15 tio2 of about 1 3 a chondrite normalized ree pattern that is nearly flat at 10 to 20 chondrites with a slight depletion of lrees other incompatible trace elements at 10 to 20 chondrites and cr and co at 0 01 to 0 1 chondrites this range of compositions is essentially identical to the tholeiitic flows and dikes in archean greenstone belts we therefore suggest that the moderately fe rich tholeiites that are hosts to plagioclase megacrysts in greenstone belts form the parental melts for megacrysts which make up the bad vermilion lake anorthositic complex and probably other similar archean anorthositic complexes

abandoned penguin rookeries as holocene paleoclimatic indicators in antarctica penguins are sensitive indicators of the antarctic climate and of the environmental parameters that limit their presence and distribution paleoenvironmental data obtained from the study of abandoned penguin rookeries pygoscelis adeliae along the victoria land coast in antarctica indicate 14c date of 11 13 ka for the oldest abandoned rookery and supply new information about the timing of glacier retreat in southern victoria land after the last glacial maximum the continuous presence of the adelie penguins is documented from 7 ka according to our data the limiting factors that control the presence of penguins along the coast of victoria land changed during the holocene whereas several colonies were occupied for very long periods other sites were used for more or less extended periods and then abandoned the greatest diffusion of rookeries occurred between 3 and 4 ka a period of particularly favorable environmental conditions that has never been repeated it was followed by a sudden decrease in the number of penguin rookeries shortly after 3 ka this event has been attributed to an increase of the sea ice extension and may have been correlated to a worldwide phase of climate change near the subboreal subatlantic boundary a minor phase of penguin reoccupation occurred locally in the eighth to fourteenth centuries a d because the presence and number of penguins reflect the state of health of the antarctic marine ecosystem it is important to evaluate the variations in their distribution in the past in the absence of human induced changes

holocene elephant seal distribution implies warmer than present climate in the ross sea we show that southern elephant seal mirounga leonina colonies existed proximate to the ross ice shelf during the holocene well south of their core sub antarctic breeding and molting grounds we propose that this was due to warming including a previously unrecognized period from 1 100 to 2 300 14c yr b p that decreased coastal sea ice and allowed penetration of warmer than present climate conditions into the ross embayment if as proposed in the literature the ice shelf survived this period it would have been exposed to environments substantially warmer than present

late quaternary diatom assemblages from prydz bay eastern antarctica abstract the paleo depositional environment of inner prydz bay east antarctica has been reconstructed for the past 21 320 14c yr b p using diatom assemblages and sediment facies from a short 352 cm long gravity core between 21 320 and 11 650 14c yr b p compact tillite and diamicton are present in the core and diatom frustules are rare to absent these data suggest that an ice sheet grounded over the site during the last glacial maximum following glacial retreat siliceous muddy ooze was deposited from 11 650 to 2600 14c yr b p in an open marine setting during this stage diatom frustules are abundant and well preserved and thalassiosira antarctica resting spores and fragilariopsis curta dominate the assemblage this assemblage suggests open marine deposition in an environment where the spatial and temporal distribution of sea ice is less than today since 2600 14c yr b p sea ice and ice edge diatom species have become more abundant and neoglacial cooling is inferred the assemblage is similar to that forming currently in prydz bay where sea ice is absent

radiocarbon distribution and the effect of legacy in lakes of the mcmurdo dry valleys antarctica the water of the ice covered lakes of the mcmurdo dry valleys is derived primarily from glacial melt streams and to a lesser extent permafrost seeps and subglacial outflow the result is a mixture of radiocarbon ages that reflect both the end member water source and the biogeochemical processing of waters as they migrate to the lake water column samples were collected from various locations within perennially ice covered antarctic lakes and the streams that feed them and they were analyzed for radiocarbon abundance of organic and inorganic carbon stream gradient and length were shown to affect the degree of equilibration of water with the modern atmosphere prior to entering the lakes stream microbial mats assimilate inorganic carbon flowing over them seasonal ice free moat water dissolved inorganic carbon dic is largely dependent on the amount of meltwater input from streams modern vs that from direct glaciers input old under the ice cover 14c ages of lake water dic and organic matter are dependent on lake history composition and quantity of particulate matter fallout bottom waters of the west lobe of lake bonney have a dic age of 27 000 14c yr before present which we believe are the most radiocarbon deficient lake waters on earth comparison of the radiocarbon profiles in the two lobes of lake bonney along with previously published geochemical data provides a new chronology of the evolution of these two waterbodies and shows that currently deep saline water is being displaced over the sill separating them

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

multiple cosmogenic nuclides document complex pleistocene exposure history of glacial drifts in terra nova bay northern victoria land antarctica geomorphological and glacial geological surveys and multiple cosmogenic nuclide analyses 10be 26al and 21ne allowed us to reconstruct the chronology of variations prior to the last glacial maximum of the east antarctic ice sheet eais and valley glaciers in the terra nova bay region glacially scoured coastal piedmonts with round topped mountains occur below the highest local erosional trimline they represent relict landscape features eroded by extensive ice overriding the whole coastal area before at least 6 ma pre dating the build up of the mt melbourne volcanic field since then summit surfaces were continuously exposed and well preserved under polar condition with negligible erosion rates on the order of 17 cm ma complex older drifts rest on deglaciated areas above the younger late pleistocene glacial drift and below the previously overridden summits the combination of stable and radionuclide isotopes documents complex exposure histories with substantial periods of burial combined with minimal erosion the areas below rounded summits were repeatedly exposed and buried by ice from local and outlet glaciers the exposure ages of the older drift s indicate multiple pleistocene glacial cycles which did not significantly modify the pre existing landscape

honeycomb development on alexander island glacial history of george vi sound and palaeoclimatic implications two step cliffs mars oasis w antarctica abstract analysis of three generations of glacial deposits and of a range of geomorphic features including widespread honeycombs and tafonis at two step cliffs mars oasis 71 52 s 68 15 w provides new insights into the geomorphological evolution of west antarctica with special respect to alveolar weathering at two step terrace indicators of the inherited character of cavernous weathering were found such as 97 non flaking and varnished backwalls and 80 tafoni floors that are till covered and or sealed by lithobiontic coatings based on the ne predominant aspect of the alveolized boulder faces tafoni initiation is attributed to coastal salt spray weathering by halite coming from the george vi sound during the 6 5 ka bp open water period the present day activity of these inherited cavities is restricted to roof flaking attributed to a combination of processes involving thermal stresses this 6 5 ka bp phase of coastal alveolization is the first step of a six stage holocene geomorphological scenario that includes alternatively phases of glacial advance or stationing and phases of vegetal colonization and or rock weathering and aeolian abrasion on the deglaciated outcrops this geomorphic scenario is tentatively correlated with the available palaeoenvironmental record in the antarctic peninsula region with two potential geomorphic indicators of the holocene optimum being identified 1 clusters of centimetric honeycombs facing the sound marine optimum at 6 5 ka bp 2 salmon pink lithobiontic coatings preserved inside cavities and at the boulder surface terrestrial optimum at 4 3 ka bp

holocene glacial history of antarctica and the sub antarctic islands abstract a history of holocene glaciation in the antarctic and sub antarctic affords insight into questions concerning present and future ice sheet and mountain glacier behavior and global climate and sea level change existing records permit broad correlation of holocene ice fluctuations within the region in several areas ice extent was less than at present in mid holocene time an important exception to this is the west antarctic ice sheet which has undergone continued recession throughout the holocene probably in response to internal dynamics the first neoglacial ice advances occurred at 5 0 ka although some sites e g western ross sea lack firm evidence for glacial expansion at that time glaciers in all areas underwent renewed growth in the past millennium and most have subsequently undergone recession in the past 50 years ranging from near catastrophic in parts of the antarctic peninsula to minor in the western ross sea region and sections of east antarctica this magnitude difference likely reflects the much greater warming that is taking place in the antarctic peninsula region today as compared to east antarctica

pre holocene raised beaches at cape ross southern victoria land antarctica raised marine beach deposits along the coast of the ross embayment are important for relative sea level reconstructions and for determining the timing of deglaciation following the last glacial maximum lgm flights of beaches from mcmurdo sound to terra nova bay long have been thought to be of holocene age however new data from cape ross indicate that pre holocene beach material is common and may be predominant at elevations greater than 23 m above mean sea level this discovery leads to unanswered questions regarding the full spatial extent of pre holocene beaches in the antarctic and other formerly glaciated areas more important it indicates that undated raised beaches cannot be assumed to result from isostatic uplift following the lgm and should not be used for relative sea level reconstructions

holocene depositional environments and surface level changes at lake fryxell antarctica we report on holocene surface level variations of lake fryxell antarctica as determined from multiproxy analyses of 18 sediment cores during this time accumulating sediments were predominantly aeolian sand with algal and carbonate laminae based on stratigraphy mineralogy and diatom assemblages we suggest some carbonate laminae were deposited when lake level dropped leading to concentration and subsequent precipitation of salts although lake level appears to have remained relatively stable throughout the holocene minor 4 5 m below present lowstands occurred at approximately 6400 4700 3800 and 1600 cal yr bp the stability of lake fryxell during the holocene contrasts with large scale variability at other dry valleys lakes eg lake vanda and with suggestions from chemical diffusion models of a near desiccation at 1200 cal yr bp the reason for the comparative stability of lake fryxell is uncertain but may be the result of basin morphology and the number aspect and proximity of meltwater sources

late pleistocene and holocene sedimentation on the george v continental shelf east antarctica abstract climatically controlled glaciological and oceanographic environmental changes off the george v coast during the late pleistocene and holocene have been reconstructed from changes in sedimentation processes the evolution of a sediment drift deposit mertz drift located in the deep trough on the shelf has been assessed using a sedimentological approach up to 5 5 m long cores have been collected four late pleistocene to holocene sediment units have been distinguished on the basis of their physical properties grain size distributions geochemical characteristics and ages the basal unit 1 is a grey sandy clayey diamicton 27 37 wt sand deposited before 14 000 14 c yr before present 14 c yr bp unit 1 represents a late pleistocene sub ice shelf water lain till overlain by a thin current winnowed sandy sub unit unit 2 is a massive siliceous sandy mud 11 30 wt sand rich in ice rafted debris deposited between about 14 000 and 5000 14 c yr bp it likely represents an open marine setting proximal to a retreating ice front where strong bottom currents were frequent the overlying unit 3 is a laminated siliceous mud and diatomaceous ooze with less terrigenous material 4 5 wt average sand deposited between 5000 and 3000 14 c yr bp the low wet bulk density values 3 and mass specific magnetic susceptibility values 8 m 3 kg of sediments of unit 3 are a consequence of the high content of biogenic material c org content 1 wt biogenic opal averaging 55 wt unit 3 is probably related to a phase of increased sediment accumulation on the drift site and low bottom current activity on the shelf with a stratified upper water column that could have lead to an enhanced primary productivity occurrence of crossed lamination indicates episodes of slightly enhanced bottom currents probably with velocities up to 3 5 cm s the top unit 4 is a bioturbated siliceous sandy mud on average 50 cm thick deposited under an energetic bottom current regime after about 3000 14 c yr bp this regime is probably related to the activation of a brine rejection mechanism and is linked to the formation of high salinity shelf water hssw in a coastal polynya which causes winnowing of the shelf deposits in contrast the mid holocene setting was characterised by weaker bottom currents that together with high inputs of organic material from the photic zone allowed for the deposition of thick fine grained sediments of unit 3 resulting in an anoxic environment

holocene history of the wilson piedmont glacier along the southern scott coast antarctica geometric and cross cutting relationships between the wilson piedmont glacier and raised beach ridges indicate that the glacier margin has undergone holocene uctuations during mid holocene time the wilson piedmont glacier retreated to a position less extensive than at present a subsequent readvance culmi nated less than 250 years ago since ad 1956 the glacier and adjacent large snow ramps have retreated up to 600 m in some locations large snowbanks have also disappeared although the cross cutting relationships and chronology indicate a late holocene advance at approximately the same time as the little ice age event the magnitude and style of that advance differ from those of the classic little ice age glacier uctuations in the northern hemisphere

insights into the holocene environmental setting of terra nova bay region ross sea antarctica from oxygen isotope geochemistry of adelie penguin eggshells an oxygen isotope record of adelie penguin pygoscelis adeliae eggshells from terra nova bay victoria land antarctica has been reconstructed in order to provide insights into the palaeoenviroment of this region during the last 8000 years the 18o values measured in eggshell carbonate show a great variability over the course of the studied period with maximum values consistently around 27 5 adopting a metabolic enrichment relative to water source of 28 5 eggshell 18o values can be interpreted in terms of marine water uptake by the penguins the spread in 18o of eggshell carbonate at any given time toward more negative values reflects the existence of a low 18o water end member most plausibly snow or snowmelt samples younger than 2000 years are characterized by a general lack of very negative 18o values as also attested by other proxies this shift toward more positive isotopic values is likely to be related both to a decreasing contribution of snow or meltwater in the seawaters and con

a review of the australian new zealand sector of the southern ocean over the last 30ka aus intimate project the australia new zealand region of the southern ocean is influenced by several of the major global water masses of the oceans and is the prime entry point for cold deep waters into the pacific basin during the last glacial there was increased sea ice extent around antarctica as far north as 55 s as well as increased iceberg presence inferred from ice rafted debris evidence from microfossil assemblages suggests that sea surface temperatures sst were up to 7 c cooler consistent with recent estimates of cooling for new zealand derived from glacier modelling and other terrestrial proxies the subtropical front stf subantarctic front saf and polar front pf had migrated north except where the position of the fronts were controlled bathymetrically despite the potential for iron fertilisation by increased dust input into the ocean during the glacial there is limited evidence for higher total biological productivity in the pacific sector of the southern ocean the altered oceanic circulation during the glacial also decreased nutrients in the surface waters and affected the outgassing of co 2 this contributed to an increased storage of co 2 in the deep waters and lowering of the carbonate lysocline during the deglaciation sea ice retreat and sst increased rapidly at 18 ka roughly synchronous with the reinvigoration of deep water circulation in the southern ocean and the release of co 2 stored in the deep waters the gradient in carbon isotopes 13 o benthic between antarctic intermediate water aaiw and lower circumpolar deep water lcdw was greatest at the start of the deglaciation suggesting that the aaiw ventilation preceded lcdw ventilation or there was a significant change in air sea fractionation of 13 o benthic there was a slight enrichment in 18 o planktic decrease in ssts and a reduction in intermediate and deep water circulation between 14 and 12 5 ka bp during the antarctic cold reversal acr coincident with glacier advances in the new zealand southern alps and other terrestrial records of cooling following the acr there was a second more minor release of deep water co 2 most likely related to reinvigoration of north atlantic deep water nadw from 10 ka onwards the modern intermediate and deep water circulation was established air temperatures and ssts reached a maximum in the early holocene with the stf located at its most southerly position and there was a widespread retreat of antarctic ice sheets to their modern position a decline to modern sst and air temperatures in the mid to late holocene followed while millennial cycles overprinted on the sst and 18 o planktic records may be the result of subtle changes in the position and strength of the westerly winds during the holocene

late pleistocene holocene marine conditions in the ross sea antarctica evidence from the diatom record statistical analyses of diatom assemblages from radiocarbon dated sediment cores were used to reconstruct changing palaeoceanographic conditions in the western and west central ross sea antarctica from c 12 14c kyr bp to the present data from three kasten cores support a north to south time transgressive glacial interglacial transition assemblages at the base of each core suggest that glacial processes affecting frustule preservation were significant during the late pleistocene increasing biogenic silic and decreasing per centages of reworked species suggest that upper water column productivity instead of preservational processes increasingly dominates diatom assemblages during grounding line recession c 12to c 6 14c kyr bp a warm ing during the middle to late holocene c 6to c 3 14c kyr bp may have resulted in a spring sea ice melting prior to the annual inception of the ross sea polynya in the west central ross sea and b increased plateletice delivery due to increased melting beneath t

the high temperature behavior of trace hydrous componentsin silicate minerals we have studied the high temperature behavior of water and hydroxide in quartz feldspar topaz zircon muscovite cordierite and beryl using high temperature infrared spectroscopy we have directly observed processes such as dehydration and changes in hydrogen speciation in some minerals trace hydroxyl and water speciation and properties at temperatures of geologic interest can be dramatically different from those at 25 c in muscovite no changes in speciation occur prior to dehydration at 750 c whereas in topaz hydroxyl sites interconvert at 500 c in metamict zircon strongly hydrogen bonded hydroxyl is preferentially lost from a continuum of sites during continuous dehydration occurring from 400 to 900 c there are only minor changes in the o h region spectrum of natural quartz at the transition point in feldspar one type of molecular water is lost at 200 c and at 600 to 800 a second water type converts irreversibly to a new hydrous species changes at high temperature common to the infrared absorption bands of all minerals studied are broadening a shift to lower wave numbers and a slight decrease in integral intensity temperature coefficients for 0 h stretching peak shifts range from 0 to 0 045 cm 1 c lattice modes also broaden and shift to lower wave numbers typically with temperature coefficients of about 0 03 cm 1 c

a new holocene relative sea level curve for terra nova bay victoria land antarctica more than 100 radiocarbon dates of penguin guano and remains shells and seal skin afford ages for raised beaches adjacent to terra nova bay antarctica these dates permit construction of a new relative sea level curve that bears on the timing of deglaciation recession of the ross sea ice sheet grounding line from terra nova bay occurred no earlier than 7200 14c yr 8000 cal yr bp retreat along the victoria land coast may have been rapid possibly contributing to eustatic sea level rise centred at ca 7600 cal yr bp the presence of a significant amount of ice remaining in the ross sea embayment in holocene time lessens the chance that antarctica contributed significantly to meltwater pulse 1a several thousand years earlier copyright 2004 john wiley sons ltd

granulite facies amphibole and biotite equilibria and calculated peak metamorphic water activities samples located near the oregon dome anorthosite massif in the south central adirondack mountains new york contain the fluid buffering mineral assemblages amphibole clinopyroxene orthopyroxene quartz or biotite quartz orthopyroxene k feldspar these rocks were metamorphosed under granulite facies conditions t 725 750 c p 7 5 kbar during the grenville orogeny the mg rich nature of amphiboles micas and pyroxenes allow accurate calculation of water activities because corrections for the effects of solid solution are relatively small the activity of water was low during the peak of granulite facies metamorphism with h2o 0 15 0 14 wollastonite occurrences indicate that the co2 was low 0 3 in nearby rocks demonstrating that large quantities of co2 did not infiltrate in a pervasive manner the combination of low h2o with low co2 is consistent with the hypothesis that magmatic processes were dominant generating dry fluid absent conditions

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

a 45 000 yr record of adelie penguins and climate change in the ross sea antarctica well preserved remains of bone tissue and eggshell of adelie penguin pygoscelis adeliae have been recovered from numerous abandoned colonies in the ross sea region antarctica radiocarbon dates on these remains provide an occupation history for this species ranging from hundreds to tens of thousands of years ago we completed 62 new radiocarbon dates on these remains which now indicate that an open water marine environment existed in the ross sea from ca 45 000 to 27 000 14 c yr before present b p and provide constraints for the timing of the last advance of the ross ice sheet penguins did not recolonize the ross sea until ca 8000 calendar years cal yr b p after the early holocene retreat of the ross ice sheet two subsequent periods of abandonment at 5000 4000 and 2000 1100 cal yr b p correlate with cooling episodes that caused unfavorable marine conditions for breeding penguins most modern colonies were established only within the past 2000 yr

lunar ferroan anorthosites mineralogy compositional variations and petrogenesis detailed petrologic study of a suite of lunar ferroan anorthosites indicates that their mineral compositional variations are generally consistent with derivation of these anorthosites from a common parent magma there are continuous compositional variations in major elements and smooth trends in minor elements mg fe in plagioclase al ti cr in pyroxene relict textures zoning and possible primary trends of mineral compositional variations are preserved in many of the anorthosites the presence of heterogeneous bimodal and or trimodal pyroxene compositions suggests that some of the anorthosites are polymict rocks however they are composed entirely of ferroan anorthosite suite lithologies some aspects of the mineral composition data suggest that complex processes operated during formation of the ferroan anorthosites the lack of a well defined positive or negative trend of pyroxene mg mg fe versus plagioclase anorthite content the homogenization of mineral compositions in some anorthosites and the varied and apparently enriched mn contents of pyroxenes in some anorthosites suggest that original igneous compositional characteristics have been altered during and or after crystallization processes operative during anorthosite formation may have included some mixing of different melts trapping of variable amounts of intercumulus liquid postcrystallization redistribution of elements or perturbations both during adcumulus growth and subsequent to crystallization by impact events feo and mgo contents of the highly calcic plagioclase typical of these anorthosites suggest that the plagioclase melt distribution coefficients for these elements need to be reassessed

the colors of sillimanite sillimanite occurs in three colored varieties yellow brown and blue the yellow color is characteristic of unaltered single crystals of sillimanite from high grade metamorphic rocks and associated pegmatites such sillimanites contain up to 1 8 wt fe 2o 3 and up to 0 3 cr 2o 3 the yellow color is due to fe 3 or in a few cases to cr 3 the ion dominant in the optical spectrum of sillimanite containing negligible cr 3 is fe 3 in tetrahedral coordination however mossbauer data suggest that about 80 of the iron is in octahedral coordination and only 20 in tetrahedral coordination the salient features in the optical spectrum from fe 3 are absorption bands at 462 440 and 412 nm in 616 474 and 438 nm in y and 361 nm in and y no evidence for fe 2 was found absorption from cr 3 occurs near 620 and 423 nm the brown variety is also formed in high grade metamorphic rocks and associated pegmatites some brown sillimanite is chatoyant from abundant acicular inclusions oriented parallel to c brown sillimanite generally contains 1 or more wt fe 2o 3 optical absorption spectra of brown sillimanite include some of the iron features characteristic of yellow sillimanite and prominent bands at 452 nm and 542 nm these last two bands may be due to incipient exsolution of an iron rich phase which appears to constitute the inclusions blue sillimanite has been documented from crustal xenoliths in basalt at two localities and from alluvial deposits at two other localities blue sillimanite contains no more than 1 wt fe 2o 3 the prominent absorption features restricted to y consist of two bands at 595 and 836 nm the spectra are similar to those of blue kyanite as with kyanite it is likely that the coloration is the result of intervalence charge transfer although the intensity of the absorption bands is not correlated with either fe or ti content

is climate change affecting rates of dune migration in antarctica antarctica is the coldest driest and windiest continent on earth and contains sand dunes like deserts elsewhere the structure and age of the cold climate dunes found in the victoria valley antarctica are described in the light of changing climate in the ross sea region of antarctica during the late holocene ground penetrating radar gpr was used to image sand dune stratigraphy and optically stimulated luminescence osl was used to determine when the sands were deposited the timing of sand dune accretion identified from the gpr stratigraphy ranges from the present day to ca 1 3 kyr b p the osl ages were used to calculate end point migration rates of 0 05 1 5 m yr lower than migration rates from photogrammetry and field surveys undertaken over the past 50 yr the earliest recorded dune development ca 1 3 kyr b p was probably controlled by intensification of circumpolar westerlies at that time as well as by drier conditions and lower temperatures that promoted dune stabilization the dune reactivation ca 300 yr ago coincides with cooling ca a d 1700 1850 and strengthening of southern circumpolar westerlies the increase in rate of dune migration after this period and especially the past 200 yr may coincide with the modern rise in co 2 and the warmest temperatures in antarctica during the past 800 kyr

assessing the link between coastal morphology wave energy and sea ice throughout the holocene from antarctic raised beaches post glacial rebound has preserved beaches across many ice free parts of the antarctic coastline these beaches typically contain gravel to boulder sized deposits and are built by high magnitude waves five new ages from the western antarctic peninsula were added to a compilation of 282 published ages from antarctic beaches a reduced compilation based solely on those ages that date beach formation is used to assess variations in beach formation throughout the holocene around antarctica we suggest the clustering of beach ages centered at 0 8 and 2 4 ka in the antarctic peninsula 1 5 3 6 and 6 0 ka in the ross sea and a broad peak from 2 7 to 6 3 ka in east antarctica indicates periods of heightened wave exposure leading to increased beach formation measurements of clast roundness from raised beaches show more rounded material is coincident with periods of heightened beach formation providing an independent means of assessing wave climate a comparison of periods of increased beach formation with available sea ice proxies suggests beach formation is synchronous with reduced sea ice conditions and thus higher wave climate as the presence or absence of sea ice determines open water conditions the factors that control sea ice directly influence antarctic coastal evolution

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

holocene deglaciation and climate history of the northern antarctic peninsula region a discussion of correlations between the southern and northern hemispheres holocene deglaciation and climate history of the northern antarctic peninsula region a discussion of correlations between the southern and northern hemispheres

post glacial regional climate variability along the east antarctic coastal margin evidence from shallow marine and coastal terrestrial records we review the post glacial climate variability along the east antarctic coastline using terrestrial and shallow marine geological records and compare these reconstructions with data from elsewhere nearly all east antarctic records show a near synchronous early holocene climate optimum 11 5 9 ka bp coinciding with the deglaciation of currently ice free regions and the optimum recorded in antarctic ice and marine sediment cores shallow marine and coastal terrestrial climate anomalies appear to be out of phase after the early holocene warm period and show complex regional patterns but an overall trend of cooling in the terrestrial records a mid to late holocene warm period is present in many east antarctic lake and shallow coastal marine records although there are some differences in the regional timing of this warm period it typically occurs somewhere between 4 7 and 1 ka bp which overlaps with a similar optimum found in antarctic peninsula terrestrial records the differences in the timing of these sometimes abrupt warm events in different records and regions points to a number of mechanisms that we have yet to identify nearly all records show a neoglacial cooling from 2 ka bp onwards there is no evidence along the east antarctic coastline for an equivalent to the northern hemisphere medieval warm period and there is only weak circumstantial evidence in a few places for a cool event crudely equivalent in time to the northern hemisphere s little ice age there is a need for well dated high resolution climate records in coastal east antarctica and particularly in terre adelie dronning maud land and enderby land to fully understand the regional climate anomalies the disparity between marine and terrestrial records and to determine the significance of the heterogeneous temperature trends being measured in the antarctic today 2010 elsevier b v

penguin colonization following the last glacial interglacial transition in the vestfold hills east antarctica abstract the population history of the adelie penguin pygoscelis adeliae and its response to climatic and environmental changes have been widely studied in maritime antarctica and several glacial refugia of adelie penguins were dated back to the last glacial maximum however the process of colony expansion during the subsequent glacial interglacial transition was less well documented in this paper we investigate an ornithogenic core from vestfold hills east antarctica to improve knowledge of postglacial penguin colonization local deglaciation occurred around 15 6 kyr bp based on a coarse grained detrital layer a date that is earlier than most of those reported in other studies from the same region geochemical analysis of the core suggests penguins started colonizing the northern vestfold hills around 14 6 kyr bp the oldest geological record in east antarctica on penguin occupation and their population exhibited a broadly increasing trend thereafter the population expanded at approximately 6740 yr bp in the mid holocene which corresponds to a local climatic optimum although this inference is based on population changes of local sub colonies it corresponds well to reconstructions of regional climate change and changes in the penguin population based on genetic studies from a consideration of the results of previous studies of the occupation history of sea birds following deglaciation in the arctic as well as other parts of antarctica we propose that sea birds colonized the emerging ice free areas shortly after local glacier retreat over geological time scales the availability of breeding habitat is a key factor controlling the population size and activity range of antarctic adelie penguins

adelie penguin dietary remains reveal holocene environmental changes in the western ross sea antarctica carbon and nitrogen stable isotope analyses were performed on modern and holocene adelie penguin guano samples collected from ornithogenic soils along the scott coast southern victoria land antarctica from cape irizar to dunlop island and at cape bird ross island guano samples also were sieved and sorted under stereomicroscope in order to select penguin dietary remains such as fish bones and otoliths carbon and nitrogen stable isotope composition coupled with the taxonomic identification of fish otoliths from scott coast holocene samples indicated a mainly fish based diet for this area with pleuragramma antarcticum as the most eaten prey throughout the investigated period from 390 cal bp to ca 7300 cal bp the isotopic values of ross island samples from modern to 3850 cal bp showed a krill consumption increase in the samples younger than 2000 cal bp with the maximum in modern samples scott coast and ross island holocene samples showed 13c and 15n trends similar to those previously published from terra nova bay northern victoria land whereas modern samples from ross island have similar 15n composition but different 13c values this 13c divergence started at ca 2000 bp and follows the abandonment of the scott coast colonies the 13c trend observed in ross island and terra nova bay samples and the abandonment of the scott coast colonies could suggest the stability and the persistence of the previous oceanographic conditions i e polynya for the terra nova bay area and the establishment of new conditions for water circulation in the southern ross sea since 2000 bp when persistent sea ice sealed the scott coast

holocene glacial history and sea level changes on james ross island antarctic peninsula a reconstruction of deglaciation and associated sea level changes on northern james ross island antarctic peninsula based on lithostratigraphical and geomorphological studies shows that the initial deglaciation of presently ice free areas occurred slightly before 7400 14 c yr bp sea level in connection with the deglaciation was around 30 m a s l a glacier readvance in brandy bay of at least 7 km with the initial 3 km over land reached a position off the present coast at ca 4600 yr bp the culmination of the advance was of short duration and by 4300 yr bp the coastal lowlands again were ice free a distinct marine level at 16 18 m a s l was contemporaneous with or slightly post dates the brandy bay advance thus indicating the relative sea level around 4600 4500 yr bp our results from james ross island confirm that over large areas in this part of antarctica the last deglaciation occurred late 1997 by john wiley sons ltd

the medieval climate anomaly in antarctica abstract the medieval climate anomaly mca is a well recognized climate perturbation in many parts of the world with a core period of 1000 1200 ce here we are mapping the mca across the antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites in addition to the conventionally used ice core data we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies a generally warm mca compared to the subsequent little ice age lia was found for the subantarctic islands south of the antarctic convergence the antarctic peninsula victoria land and central west antarctica a somewhat less clear mca warm signal was detected for the majority of east antarctica mca cooling occurred in the ross ice shelf region and probably in the weddell sea and on filchner ronne ice shelf spatial distribution of mca cooling and warming follows modern dipole patterns as reflected by areas of opposing temperature trends main drivers of the multi centennial scale climate variability appear to be the southern annular mode sam and el nino southern oscillation enso which are linked to solar activity changes by nonlinear dynamics

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

δ13c and δ15n in the ornithogenic sediments from the antarctic maritime as palaeoecological proxies during the past 2000 yr abstract in this paper we have examined carbon and nitrogen isotopic compositions in two ornithogenic sediment profiles from the ardley island and barton peninsula of antarctica for palaeoecological changes during the past 2000 yr the 13 c values of the two sediment profiles range from 22 26 to 19 15 pdb in core g and from 24 01 to 19 87 in profile a showing that the predominant carbon source in the sediments plausibly comes from terrestrial and aquatic plants in antarctic such as mosses lichens and algae in lakes as these 13 c values are also close to those in the fresh lake sediments that are not influenced by penguin guano one may not use the 13 c values as evidence for the influence of guano on the sediments the 15 n values of the two profiles range from 4 75 to 18 34 air and from 5 17 to 10 38 for core g and core a respectively the 15 n variations have positive correlations with the trends of the bio element contents in the sediments as the levels of these bio elements in ornithogenic sediments had been used to reconstruct the changes of historical penguin population and tundra vegetation abundance and diversity we then suggest that the 15 n records can be utilized to study palaeoecological processes of penguin our results show that penguin population and activity has generally decreased over the past 2000 yr from 1300 to 900 yr bp and from 1790 to 1860 ad penguin population and activity experienced two strong decreases it will be interesting to understand the cause of these decreases

glaciomarine sedimentation and its paleoclimatic implications on the antarctic peninsula shelf over the last 15 000 years abstract analyses of sedimentological geochemical and micropaleontological parameters from radiocarbon dated sediment cores retrieved from the antarctic peninsula s western continental shelf reveal a detailed paleoclimatic and or paleoceanographic history over the last 15 000 radiocarbon years deglaciation of the outer shelf off anvers island commenced prior to at least 15 000 yr bp marked by the deposition of distal glaciomarine diamicton facies 2 beneath a floating ice shelf and lasted for 3800 years with increasing diatom abundance and total organic carbon toc over time a return to colder conditions occurred between 12 800 and 11 600 yr bp with a drop in toc content and diatom abundance which is coincident with the younger dryas event in the north atlantic region at this time an abrupt increase in percentage sea ice taxa as well as in the ratio of fragilariopsis curta fragilariopsis cylindrus thalassiosira antarctica suggests renewed ice shelf advance in contrast the inner shelf was deglaciated somewhat later about 11 000 yr bp that is 3000 years after the outer shelf prior to 11 000 yr bp deposition of proximal glaciomarine diamicton facies 1 close to the grounding line under a floating ice shelf and or persistent sea ice may have occurred on the inner shelf after this date deposition of distal glaciomarine diamicton facies 2 followed a climatic optimum is recognized between 6000 and 2500 yr bp coinciding with a mid holocene climatic optimum from several other antarctic sites e g the palmer deep during this time as the glacial system receded from the shelf greatly enhanced primary productivity occurred in open marine conditions resulting in the deposition of diatomaceous mud facies 3 and causing post depositional dissolution of calcareous benthic and planktonic foraminifers in sediment around 2500 yr bp the onset of the neoglacial diatomaceous sandy mud facies 4 characterized by a decrease in toc and diatom abundance reflects the formation of more extensive and seasonally persistent sea ice as evidenced by an increase in percentage of sea ice taxa and in the ratio of f curta f cylindrus t antarctica our results provide evidence of climatic change on the antarctic peninsula s western shelf that helps to refine the existence and timing of late pleistocene and holocene millennial scale climatic events in the southern hemisphere

postglacial marine diatom record of the palmer deep antarctic peninsula odp leg 178 site 1098 1 total diatom abundance 1 late pleistocene to holocene climate variability in the antarctic peninsula is described from ocean drilling program odp leg 178 site 1098 palmer deep using total diatom abundance valves per gram dry sediment as a paleoproductivity proxy diatom frustules are absent in the diamicton at the base of the core which was deposited prior to age calibrated circa 13 2 ka immediately above the diamicton frustules are in low abundance as rare fragments and become increasingly more abundant and well preserved up core a rapid and major increase in productivity after circa 12 8 ka is evident from distinctly laminated sediments that overlie the diamicton the strongly laminated section was deposited during a deglaciation phase that followed the retreat of grounded ice after the last glacial maximum diatom productivity decreased during a climatic cooling and or change in meltwater supply until circa 9 0 ka between 9 0 and 4 4 ka productivity increased steadily again with diatom abundance maxima reached during a mid holocene climatic optimum the optimum is interrupted by a brief cold event of 1000 years duration 6 0 5 0 ka after 4 4 ka productivity generally decreased and the last 500 years have experienced the lowest diatom productivity of the postglacial period the palmer deep sediment is compared to ice core and lake sediment records from other regions around the antarctic peninsula these diverse data sets confirm that the antarctic peninsula has been a region of rapid and variable climate fluctuation since the last glacial maximum

early differentiation of the moon evidence from trace elements in plagioclase bulk samples and plagioclase mineral grains from lunar cataclastic ferroan anorthosites were analyzed for trace elements by instrumental neutron activation analysis some pure plagioclase crystals have lower concentrations of cr co sc and heavy rees than previous analyses indicated concentrations of sr eu na ga and the rees in plagioclases from different anorthosites vary in a systematic way and the trace element patterns of plagioclases from pristine norites and troctolites are very different from the plagioclase pattern of anorthosites the following model is suggested to account for these observations 1 melting of a large fraction of the moon formation of a magma ocean precipitation of olivine and later pyroxene followed by flotation of cumulus plagioclase 2 mixing of kreep with a mafic component enriched in mg cr and co 3 precipitation of noritic and troctolitic cumulates and metallic iron from this magma and 4 eruption of these kreep and mg rich lavas and or distribution of these materials over the front side of the moon by basin forming impacts 3 9 4 0 b y ago

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

postglacial marine diatom record of the palmer deep antarctic peninsula odp leg 178 site 1098 2 diatom assemblages 1 the distribution of late pleistocene to holocene diatom assemblages from ocean drilling program odp leg 178 site 1098 palmer deep is described and compared using multivariate statistical methods cluster analysis and analysis of variance five assemblages are identified from site 1098 which are correlated with the climatic zones identified previously in the palmer deep domack et al 2001 a thalassiosira diatom assemblage characterizes the deglaciation phase 13 2 11 0 ka and was deposited during glacial retreat at the end of the regional last glacial maximum a well preserved rhizosolenia assemblage was deposited during a climatic reversal 11 0 9 0 ka and indicates periods of seasonally open water with diatom blooms an open water fragilariopsis kerguelensis assemblage characterizes the mid holocene climatic optimum 9 0 3 7 ka in the neoglacial late holocene 3 7 ka climatic cooling increased sea ice cover and increased wind are inferred from a cocconeis assemblage during the climatic optimum neoglacial transition 4 4 1 8 ka laminae characterized by corethron criophilum were preserved it is uncertain whether the laminae represent short lived interannual bloom events with high settling rates or have been deposited over longer time periods

the hydrous component of sillimanite polarized infrared spectra of a suite of sillimanite samples from high grade regionally metamorphosed rocks and associated quartz veins and pegmatites upper amphibolite to pyroxene granulite facies from xenoliths in basaltic rocks and from alluvial deposits indicate that hydroxyl is the dominant hydrous species bound in sillimanite absorption bands at 3556 3329 3300 and 3248 cm 1 are characteristic of many of the samples heating experiments indicate that only above 700 c is weight loss primarily due to loss of structurally bound oh complete dehydration required heating to 1400 c the maximum content of bound oh in the sillimanites was 0 02 wt h 2o equivalent the intensities of the oh features generally decrease with increasing temperatures estimated for metamorphism consistent with the expectation that water activities decrease with increasing temperature however notable exceptions to this trend suggest that secondary hydration at the unit cell scale is also a viable explanation for oh incorporation in sillimanite

ripple cross laminated sediments on the east antarctic shelf evidence for episodic bottom water production during the holocene abstract biosiliceous sediments sampled from a submarine valley system on the continental shelf of east antarctica contain intervals of ripple cross lamination interspersed with massively bedded units based on radiocarbon dates from one core collected on the mac robertson shelf the most intensely cross laminated sediments were deposited between 6 and 3 5 kyr bp with isolated cross laminae deposited at other times in the holocene the cross laminated sediments are interpreted here as a signal of episodic density currents flowing across the outer shelf which result from the formation of high salinity shelf water hssw this hssw is formed in winter by brine rejection during sea ice formation and by the exchange and cooling of upwelled saline slope water and it contributes to the bottom water produced along the continental margin of antarctica if this interpretation of the cross laminae is correct then bottom water formation and export from the east antarctic shelf has exhibited temporal and probably also spatial variability throughout the holocene such variability would have implications for oceanographers attempting to quantify antarctic bottom water production rates based only on present day observations

ft ir spectroscopic investigation of hydrous components in sillimanite from eastern ghat granulite belt india abstract ft ir spectra of sillimanite samples from high grade regionally metamorphosed rocks belonging to the granulite terrain amphibolite to pyroxene granulite facies deciphers prominent oh features heating experiments indicate growth of prominent band at 3161cm 1 heating above 1000 c all oh features disappear in intensity into broad features with slight shift of bands towards lower energies complete dehydration requires temperatures above 1000 c coexistence of boron and oh features are also observed in all sillimanite samples the high temperature behaviour of sillimanite from the granulite terrain discerns that the hydrous species in sillimanite were incorporated much below 700 c however secondary hydration due to pegmatite activity retrograde metamorphism and migmatisation is not ruled out thus a near anhydrous condition were probably not achieved during the granulite facies metamorphism in eastern ghat granulite terrain

glacial and postglacial sedimentation in the fryxell basin taylor valley southern victoria land antarctica abstract a 9 14 m long sediment sequence was recovered from lake fryxell taylor valley southern victoria land antarctica and investigated for its chronology and sedimentological mineralogical and biogeochemical changes the basal part of the sequence is dominated by coarse clastic matter i e mainly sand the sediment composition suggests that a lake existed in fryxell basin during the middle weichselian by ca 48 000 cal year bp after a short period of lake level lowstand ca 43 000 cal year bp lower taylor valley became occupied by the proglacial lake washburn which was at least partly supplied by meltwater and sediments from the ross ice sheet that was advanced to the mouth of taylor valley evaporation of lake washburn to lower levels started during the last glacial maximum at ca 22 000 cal year bp long before the ross ice sheet retreated significantly lake level lowering was discontinuous with a series of high and low stands from ca 4000 cal year bp environmental conditions were similar to those of today and lower fryxell basin was occupied by a small lake this lake evaporated to a saline or hypersaline pond between ca 2500 and 1000 cal year bp and refilled subsequently

environmental implication of nitrogen isotopic composition in ornithogenic sediments from the ross sea region east antarctica δ15n as a new proxy for avian influence abstract we analyzed 15n in both acid treated and untreated sediment profiles from mcmurdo sound of the ross sea region east antarctica that were influenced by penguin guano the difference between treated and untreated 15n 15n was significant in three profiles which were heavily impacted by guano and minor in two profiles with less guano influence we determined that the total nitrogen in the sediments is primarily derived from penguin guano and algae and used an n species test to explain the variation of 15n in two profiles it was found that post depositional decomposition and ammonia volatilization which have important roles in the cold and arid environment of east antarctica would render an elevated 15n through kinetic isotopic fractionation in the inorganic nitrogen from guano n species analysis revealed that the percentage of inorganic nitrogen in total nitrogen indicative of the degree of guano influence is the key factor controlling 15n in the sediments this hypothesis successfully explained the nitrogen isotopic composition in the remaining three sediment profiles we conclude that the parameter 15n rather than traditionally used untreated 15n can be taken as an effective proxy for the strength of avian influence on ornithogenic sediments in east antarctica

lunar anorthosite 60025 the petrogenesis of lunar anorthosites and the composition of the moon systematic variations of the mineral chemistry of ferroan anorthosite 60025 which is probably a mixture of closely related materials suggest that lunar anorthosites formed by strong fractional crystallization and near perfect adcumulate growth without trapping liquid the parent liquid for the most primitive samples was saturated with olivine plagioclase pigeonite and chromite and evolved to one saturated with plagioclase pigeonite high ca pyroxene and ilmenite the parent liquid also had a very low na2o content and combined with strong fractional crystallization this explains the steep trend of anorthosites on an mg atomic 100 mg mg fe v an diagram the mineral and chemical data for other anorthosites are consistent with such a model near perfect adcumulation can occur if growth takes place at the crystal liquid interface without the physical accumulation of crystals grown elsewhere and is encouraged by the shifts in phase boundaries with pressure anorthosites are probably the remnants of a crust floating on and crystallizing at the surface of a magma ocean originally of bulk moon composition mineralogical and trace element data suggest that the parental liquid for the most primitive anorthosites had previously crystallized no plagioclase and some but perhaps very little pyroxene hence the bulk moon appears to be similar to that proposed by ringwood 1976 but to have even lower alkalis a subchondritic caal ratio and ree abundances and patterns close to chondritic the mare basalt sources are not directly complementary to the feldspathic crust because experimental and trace element data indicate that they are too magnesian and contain too much high ca pyroxene other crustal rocks such as the mg suite samples are not closely related to anorthosites in addition to their chemical differences they have a different crystallization sequence ol plag px in contrast with the ol px plag inferred for anorthosite parental liquid evolution

holocene climate variability in antarctica based on 11 ice core isotopic records a comparison is made of the holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east antarctica vostok dome b plateau remote komsomolskaia dome c taylor dome dominion range d47 km105 and law dome and west antarctica byrd with temporal resolution from 20 to 50 yr the long term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations all the records confirm the widespread antarctic early holocene optimum between 11 500 and 9000 yr in the ross sea sector a secondary optimum is identified between 7000 and 5000 yr whereas all eastern antarctic sites show a late optimum between 6000 and 3000 yr superimposed on the long time trend all the records exhibit 9 aperiodic millennial scale oscillations climatic optima show a reduced pacing between warm events typically 800 yr whereas cooler periods are associated with less frequent warm events pacing 1200 yr

mineral compositions in pristine lunar highland rocks and the diversity of highland magmatism high precision electron microprobe analyses of olivine and pyroxene in pristine lunar highland rocks confirm the dichotomy between ferroan anorthosites and the mg suite ferroan anorthosites plot as coherent trends consistent with formation in a complex global magma system lack of coherent compositional trends in the mg suite rocks indicates derivation from numerous magmas

history of the grounded ice sheet in the ross sea sector of antarctica during the last glacial maximum and the last termination knowledge of variations in the extent and thickness of the antarctic ice sheet is key for understanding the behaviour of southern hemisphere glaciers during the last ice age and for addressing issues involving global sea level ocean circulation and climate change insight into past ice sheet behaviour also will aid predictions of future ice sheet stability here we review ter restrial evidence for changes in ice geometry that occurred in the ross sea sector of antarctica at the last glacial maximum lgm and during subsequent deglaciation during the lgm a thick grounded ice sheet extended close to the continental shelf edge in the ross embayment this ice reached surface elevations of more than 1000 m along the coast of the central and southern trans antarctic mountains and marie byrd land the local lgm occurred by 18 ka on the coast but as late as 7 10 ka inland the first significant thinning took place at roughly 13 ka with most ice loss happening in the holocene this history makes it unlikely that the ross sea sector was a major contributor to meltwater pulse 1a mwp 1a resolution of a possible antarctic origin for mwp 1a awaits detailed reconstructions from all sectors of the ice sheet the antarctic ice sheet contains the world s larg est reservoir of fresh water and is a major control on southern hemisphere climate a history of changes in ice sheet extent and thickness is vital for answering questions involving the initiation of southern hemisphere glaciation and deglaciation

dynamics of penguin population size and food availability at prydz bay east antarctica during the last millennium a solar control abstract the paleoecology of the adelie penguin pygoscelis adeliae is controlled by multiple factors in this study we analyzed two millennial scale ornithogenic sediment cores rnl and rl from the vestfold hills east antarctica using the al normalized phosphorus content of the bulk sediment and carbon nitrogen fractions in penguin remains we reconstructed relative changes in the penguin population size of each sub colony and relative krill abundance in the summer prydz bay polynya both records are correlated to solar irradiance at the centennial scale the penguin population recorded in core rnl decreased from 1120 860 yr bp reached a peak from 860 630 yr bp remained at a low level from 630 320 yr bp and then increased with large fluctuations during the past 400 years these changes are all in phase with the trend of solar irradiance at the decadal scale penguin population minima correspond to solar minima from 490 400 yr bp sporer minimum 290 220 yr bp maunder minimum and from 160 120 yr bp dalton minimum whereas population maxima correspond to solar maxima from 1030 980 yr bp 350 290 yr bp 210 160 yr bp 120 70 yr bp the population recorded in core rl exhibited the same changes as in rnl during the last 480 years the reconstructed krill abundance also corresponds to these trends when data are available this correspondence demonstrates a food chain mechanism that is related to solar activity and light availability at the ocean surface which influence the intensity of photosynthesis and phytoplankton productivity and thus the abundance of krill and apex predators such as penguins our findings highlight the fact that despite the various climatic impacts on penguin populations their effects on the base of the food chain are usually the direct drive