interglacial collapse of crary trough mouth fan weddell sea antarctica implications for antarctic glacial history abstract in this study we investigate the stratigraphy of a trough mouth fan in the weddell sea to determine possible relationships between basin floor stratigraphy and glaciation on antarctica seismic data from the basin floor show a deep broad and elongate erosional channel filled by thick chaotic facies deposits basin floor fans and channel levee deposits from seismic stratigraphy analysis of basin floor stratigraphy we infer that this channel formed by large volume mass wasting sourced from poorly sorted glacial sediments from crary trough mouth fan and dronning maud land slopes correlation to odp leg 113 site 693 suggests that the mass wasting of the slopes occurred in the early pliocene we surmise that collapse occurred during an early pliocene interglacial and was related to major drawdown of the antarctic ice volume collapse was probably triggered by rebound and relative sea level fall a mathematically predicted geoidal effect related to antarctic ice volume reduction the record of this major ice volume reduction is not manifest in the trough mouth fan but rather is manifest in the basin floor stratigraphy as a major backfilled erosional channel which extends far beyond the trough mouth fan

late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

resolving a late oligocene conundrum deep sea warming and antarctic glaciation abstract changes in ice volume and resulting changes in sea level were determined for the late oligocene 26 23 ma astronomical timescale ats by applying 18 o to sea level calibrations to deep sea 18 o records from odp sites 689 690 929 1090 and 1218 our results show that maximum global ice volume occurred during two late oligocene 18 o events oi2c 24 4 ma and mi1 23 0 ma inferred glacioeustatic lowering with volumes up to 25 greater than the present day east antarctic ice sheet eais ice volume during glacial minima was on the order of about 50 of the present day eais this is supported by late oligocene stratigraphic records from antarctica that contain evidence of cold climates and repeated episodes of glaciation at sea level and grounding lines of glacial ice on the antarctic continental shelf in the ross sea and prydz bay in contrast composite deep sea 18 o records show a significant decrease 1 between 26 7 and 23 5 ma which have long been interpreted as bottom water warming combined with deglaciation of antarctica however a close examination of individual 18 o records indicates a clear divergence after 26 8 ma between records from southern ocean locations i e ocean drilling program sites 689 690 744 and those of other ocean basins high 18 o values 2 9 3 3 from these southern ocean 18 o records are consistent with an ice sheet on the east antarctic continent equivalent to present day values and cold bottom water temperatures 2 0 c these differences suggest a reduction in deep water produced near the antarctic continent i e proto antarctic bottom water proto aabw which were quickly entrained and mixed with warmer and presumably more saline bottom water originating from lower latitudes expansion of a warmer deep water mass and the weakening of the proto aabw may explain the large intra basinal isotopic gradients that developed among late oligocene benthic 18 o records these conclusions are also supported by ocean modeling suggesting a reduction of deep water formed in the southern ocean strengthening of deep water from the northern hemisphere and decreasing temperatures in high southern latitudes occurred as the drake passage opened to deep water low 18 o values reported from deep sea locations other than the southern ocean are shown to bias estimates of antarctic ice volume calling for a re evaluation of the notion that antarctic ice volume was significantly reduced during the late oligocene

substrate control on distribution of subglacial and glaciomarine seismic facies based on stochastic models of glacial seismic facies deposition on the ross sea continental margin antarctica abstract a quantitative approach was utilized to establish the nature of spatial and temporal variations of glaciomarine and subglacial seismic facies deposition in the ross sea the ross sea is an excellent area to study antarctic ice sheet volume variations because it receives ice sheet drainage from approximately 25 of the continent and it contains subsiding basins to preserve the stratigraphic record of the ice sheet volume fluctuations this region receives most of the influence on deposition from the marine based west antarctic ice sheet which is believed to have been subject to catastrophic surges hollin j t 1962 on the glacial history of antarctica journal of glaciology 4 173 195 the eastern basin in particular has been subsiding creating accommodation space in which to preserve the plio pleistocene record of ice sheet fluctuations evidence from high resolution seismic data in conjunction with dsdp leg 28 drilling results are used to test hypotheses of paleo ice sheet behavior here we present quantitative evidence for a dynamic polar style of glaciation meaning that the ice sheets have had dynamic or large ice volume change not merely in the plio pleistocene but back to the late oligocene high resolution seismic data correlated to dsdp sites 270 273 shows evidence of multiple ice sheet grounding events in central and eastern ross sea strata a recipient of both west and east antarctic ice sheets from the late oligocene until the present we suggest that the west and east antarctic ice sheets are dynamic and have gone through a full spectrum of thermal states temperate through polar since the late oligocene and not necessarily in any particular preferred temporal order statistical analysis of the spatial distribution of seismic facies within seismic cores indicates that tectonic influence on distribution of basal substrate is a significant contributor to spatial variability of subglacial depositional processes and therefore distribution of subglacial facies

late pliocene margin development and mega debris flow deposits on the antarctic continental margins evidence of the onset of the modern antarctic ice sheet abstract major global climatic changes in the cenozoic coincided with major changes in volume of polar ice sheets which are reflected in the sedimentary regime of polar continental margins we compile and review the most recent evidences of the neogene architectural change in the sedimentary units of the antarctic continental margins to provide a comprehensive interpretation of timing and circumstances of the last of these changes we review and interpret the seismic stratigraphy and the borehole data where available from 6 key sectors of east and west antarctica the continental margins of the antarctic peninsula prydz bay wilkes land weddell sea eastern and western ross sea in these margins we identify the following change in the geometry of the sedimentary deposits margin wide erosion and subsequent progradation on the continental shelf stratal downlap on the continental slope major mass wasting deposits on the continental rise the change is apparently synchronous and dated about 3 ma in the antarctic peninsula and prydz bay margins and broadly concomitant in the others sectors this suggests a common driving force which we suggest to be the late pliocene climatic change that induced the transition of the antarctic ice sheet regime from polythermal to present polar cold dry based conditions we infer that in consequence of the late pliocene global cooling meltwater decreased in quantity and focussed within the main ice troughs where large ice streams began to flow the regional erosion was followed by focussing of the sedimentary transport at the base of the large ice streams and faster progradation of sedimentary wedges at the mouth of the ice troughs this induced large failures of the continental slope while the continental rise was progressively deprived of terrigenous sediments

a comparison of the nw european glaciated margin with other glaciated margins the present paper provides an overview of glacial related seabed features and sedimentary sequences found along the formerly glaciated nw european margin and compare it with those found on contemporary glaciated margins from both the southern and northern hemispheres a brief review of the seabed physiography and strata architecture of the margins under consideration is followed by comparison of the most relevant similarities and differences comparison of the present day bathymetric setting of both former and contemporary glaciated margins reveals no clear link to the effect of neither ice sheet or sediment load three different types of glacially eroded shelf transverse troughs have been identified while marginal troughs seem connected to similar geological settings everywhere beyond the shelf edge interaction between downslope and alongslope processes has occurred resulting amongst others in the formation of large sedimentary mounds on the rise more frequent large scale mass wasting occurs on the former glaciated nw european margin than the greenland and antarctic margins in the latest neogene to recent times a two stage evolution of the shelf prograding wedges is observed on all margins under consideration which may reflect a general development of an ice cover from an initial phase of non to restricted glaciation evolving to a mature stage of expansive glaciation

seismic stratigraphy and sediment distribution on the wilkes land and terre adelie margins east antarctica abstract seismic reflection data show the existence of two major sedimentary basins along the continental margin of wilkes land and terre adelie east antarctica that contain more than 5 s twt 9 km of sediments four seismic megasequences are identified ms4 to ms1 that are bounded by basement unconformities of interpreted turonian maastrichtian and early middle eocene age and the seafloor the 4 5 km thick rift and pre rift sediments are concentrated in a margin parallel basin sabrina basin on the basis of seismic correlation with the australian margin this basin is interpreted to be of late jurassic to mid cretaceous age the post rift sediments are generally thick along the margin and in the adjacent deep ocean basin but are particularly thick in a major depocentre off west wilkes land named here the budd coast basin bcb the bcb contains a maximum observed thickness of 5 s twt 9 km of post rift sediments and its location suggests that the sediments were largely derived from a sub glacial basin currently occupied by the totten glacier within the post rift sediments a major regional unconformity is identified that is interpreted to be of early middle eocene age 45 ma while some previous interpretations have suggested that this unconformity marks the onset of the glaciation of east antarctica the unconformity is interpreted here to be the product of the major global plate reorganisation in the middle eocene and the coincident sharp increase in the sea floor spreading rate between australia and antarctica a seismic unconformity that can be correlated with the onset of glaciation is not identified and the position of glacial onset within the sedimentary section can only be estimated through the extrapolation of sedimentation rates from the underlying section and from deep sea drilling project site 269 the post middle eocene section is much thicker than the underlying post rift section and this is interpreted to be largely due to the very high sediment fluxes associated with the period of polythermal glaciation from 34 9 ma sediment isochron and isopach maps derived from a regional seismic grid show that the depocentre of the bcb trends approximately north south beneath the continental slope but is deflected to the east beneath the deep ocean basin this distribution indicates that deep marine processes were important in lateral along margin sediment transport a west to east direction of movement is inferred by the sediment distribution this direction is opposite to the present day marginal currents along the continental slope and rise

depositional processes beneath coastal multi year sea ice the extent of multi year sea ice impacts climate processes worldwide such as ocean atmosphere carbon dioxide exchange and deep ocean current formation reconstructing these processes in the past and assessing the distribution of ecologically and climatically significant features such as polynas requires recognition of sediments deposited under multi year sea ice but little is known about their characteristics textural analysis of subaerial and sea floor sediment in explorers cove mcmurdo sound at the mouth of taylor valley antarctica augmented with observations of sedimentary structures and faunal components elucidates how sediment is transported to the sea floor and allows characterization of the deposits comparison of grain size characteristics of subaerial moraine delta and sea ice surface sediment and sea floor sediment from short cores taken at depths of 7 to 25 m indicates that the likely source of the moderately to poorly sorted sea floor sand is deltaic sediment small glacial meltwater streams have built deltas since taylor valley became ice free ca 7000 years ago windblown sediment accumulating on the multi year sea ice close to the coast typically is coarser grained than sediment on the sea floor this suggests that the transport of sediment through the ice to the sea floor is not the predominant mode of sediment transfer however supra sea ice sediment does move to the sea floor through local fractures the rate of sedimentation under multi year sea ice is low because of limited stream flow and biogenic sedimentation the ice cover inhibits primary productivity and dampens waves precluding physical re suspension the upper centimetres of sea floor sediment are churned by epifaunal scallops and brittle stars that leave no telltale biogenic structures and whose calcite ossicles and shells may be poorly preserved the resulting deposits under multi year sea ice are poorly sorted massive sand that provides little evidence of the bioturbators that have masked the indicators of the original physical depositional processes

structure of the carbon isotope excursion in a high resolution lacustrine paleocene eocene thermal maximum record from central china abstract the carbon isotope excursion cie associated with the paleocene eocene thermal maximum petm has been recognized for the first time in the micritic carbonate total organic carbon toc and black carbon bc contained within the lacustrine sediments from the nanyang basin central china the remarkably large excursion 6 in the 13ctoc and 13cbc values is possibly attributable to increased humidity and elevated pco2 concentration the 4 cie recorded in the 13ccalcite reflecting the average isotope change of the watershed system is consistent with that observed in planktonic foraminifera this correspondence suggests that the true magnitude of the carbon isotope excursion in the ocean atmosphere system is likely close to 4 the 10 m excursion onset in our multi proxy 13c records demonstrates that the large input of 13c depleted carbon into the ocean atmosphere system was not geologically instantaneous despite difference and somewhat smoothness in detailed pattern of the cie due to localized controls on different substrates inorganic and organic 13c data generally depict a gradual excursion onset at least over timescales of thousands of years in addition continental temperature reconstruction based on the distribution of membrane lipids of bacteria suggests a warming of 4 c prior to the petm and 7 c increase in temperature during the petm the temperature data are overall similar in pattern and trend to the 13c change across the petm these observations combined with pre cie warming are in line with the idea that 13c depleted carbon release operated as a positive feedback to temperature suggesting supply from one or more large organic carbon reservoirs on earth s surface

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

on the duration of west antarctic ice sheet grounding events in ross sea during the quaternary abstract a back stepping succession of three seismically defined grounding zone wedges gzws in the glomar challenger basin palaeo ice stream trough is usually assigned to the short time that elapsed since the west antarctic ice sheet retreat began at 11 ka 14c bp recent radiocarbon dates have however suggested an alternate interpretation in which the youngest of these three gzws the gray unit gzw on the middle shelf corresponds to deposition during the last glacial maximum lgm if so then the gray unit must represent an amalgamation of erosion and deposition spanning a much longer time interval i e the 100 ky interval between the last interglacial and the lgm to test these conflicting interpretations the gray unit sediment volume was mapped from seismic and multibeam data two end member durations were calculated because flux during ice sheet retreat is significantly higher than flux during ice sheet advance using the retreat mode flux the 1 47 ky grounding event estimate shows that the middle shelf gzw could have been deposited during the post lgm retreat however the 147 34 ky grounding event estimate based on the advance mode flux also demonstrates that the gzw might reasonably represent an amalgamation of erosion and deposition as grounded ice gradually advanced between mis5e and mis2 i e from the last interglacial to the last glacial maximum these data thus require that both interpretations of how the near surface stratigraphy relates to grounding line translations in the last glacial cycle be considered feasible working hypotheses

margin architecture reveals the transition to the modern antarctic ice sheet ca 3 ma seismic reflection data collected primarily on the continental slope of the pacific margin of the antarctic peninsula after drilling ocean drilling program odp leg 178 allow us to date a regional change in the style of margin accretion to ca 3 ma late pliocene deep erosion of continental shelf and slope which likely included the emplacement of a megadebris flow deposit was followed by prominent growth of steep relatively stable continental slope prograding wedges while the deep distal margin sedimentation rate was significantly reduced a review of the available stratigraphy from deep sea drilling project odp drilling and correlation with available seismic stratigraphic information allowed us to recognize comparable changes in terms of age and trends in continental margin evolution in several places around antarctica we argue that this late pliocene architectural change of the antarctic margin reflects a change in the texture and water content of the sediment delivered by the antarctic ice sheet following the transition from wet to dry based ice regimes this circum antarctic change coincides with the late pliocene ca 3 ma global cooling and is proposed as the marker event of the transition to the modern cold polar dry based antarctic ice sheet

the crary fan a trough mouth fan on the weddell sea continental margin antarctica abstract multichannel seismic investigations show the presence of a large trough mouth fan deposit on the continental margin in the southern weddell sea a characteristic feature of the fan is relatively few but large canyons and or channels which appear to have been stable for long periods levees associated with the channels may reach thicknesses of more than 1 km drilling during odp leg 113 recorded the presence of glaciers in east antarctica since early oligocene time and the seismic stratigraphic evidence suggests that the submarine fan is largely composed of glacigenic sediments the channel levee systems and complexes indicate several growth phases apparently controlled by glacial interglacial climate fluctuations with maximum fan growth during glacial periods the present interglacial period is characterized by strong and erosive flow of ice shelf water running down the western slope of the fan and carrying only minor amounts of suspended matter the fan is essentially sediment starved during interglacial periods the dimensions of the channel levee complexes and the persistent loci of sediment supply suggest that turbidite sedimentation resulted from melting of wet based glaciers at or near the shelf edge which has consequently prograded 70 80 km seaward

seismic stratigraphy of the antarctic peninsula pacific margin a record of pliocene pleistocene ice volume and paleoclimate multichannel seismic profiles across the pacific margin of the antarctic peninsula show a series of oblique progradational sequences these sequences exhibit a variety of unusual characteristics that suggest they were produced by the action of ice sheets grounded out to the shelf edge at times of glacial maximum reflection events from deeper stratigraphic levels followed down the continental slope and onto the rise overlie ocean crust of known age showing that at least eight such glacial sequences have been deposited within the past 6 m y similar groundings have probably occurred on most antarctic margins but the depositional record is particularly well preserved at this margin because of pliocene pleistocene thermal subsidence neogene global sea level fluctuations have been attributed to changes in volume of continental ice sheets the depositional sequences on the pacific margin of the antarctic peninsula are thought to record west antarctic ice sheet fluctuations directly further investigation of these sequences would assess the relation between fluctuations in ice volume and the low latitude record of global sea level change

vegetation and climate from two oligocene glacioeustatic sedimentary cycles 31 and 24 ma cored by the cape roberts project victoria land basin antarctica abstract the cape roberts project recovered over 1500 m of coastal glaciomarine sediments of oligocene and early miocene age off the ross sea margin of antarctica the strata are characterised by cyclic repetition of facies in a glaciomarine setting and are interpreted to be a record of glacial interglacial episodes involving significant changes in eustatic sea level on milankovitch frequencies we have undertaken a detailed study of pollen and spores miospores from an early oligocene 31 ma and a late oligocene 24 ma cycle although miospores are sparse in the core averaging only 1 grain per gram of sediment processed over 1200 cenozoic miospores were recovered for this study previous studies of miospores from ross sea sediments have encountered problems differentiating between reworked and in situ palynomorphs here only samples containing a low relative abundance of an eocene dinoflagellate cyst assemblage the transantarctic flora have been used to infer the contemporaneous oligocene miospore flora the flora of the early oligocene cycle is dominated by three species of nothofagidites and four types of podocarpidites the assemblage from the upper oligocene cycle is also dominated by nothofagidites and podocarpidites but with the addition of two distinctive taxa an angiosperm pollen and a bryophyte spore notwithstanding these additions there is a slight decrease in floral diversity between the two cycles while this study confirms that some floristic changes did occur between early and late oligocene time on the victoria land coast the present data suggest that the changes were not extensive it is likely that the vegetation of both cycles was a low diversity scrub of low stature consisting of mainly nothofagus podocarps and bryophytes modern analogues suggest that this vegetation was growing in a climate significantly warmer mean summer monthly temperature 4 12 c than is found on the present day victoria land msmt 5 c although colder that the temperate climate suggested by the diverse flora found in ross sea sediments of eocene age

cenozoic marine sedimentation and ice volume variation on the east antarctic craton recycled cretaceous and cenozoic marine microfossils have been recovered from samples of the pliocene sinus formation samples were collected from outcrops in the reedy beardmore and ferrar glacier areas of the transantarctic mountains between lat 77 and 86 s the glaciogene sediments contained diatoms foraminifera calcareous nannoplankton silicoflagellates radiolarians sponge spicules palynomorphs and ostracodes of late cretaceous paleocene eocene late oligocene late miocene and pliocene age this suggests the presence of open marine basins on the east antarctic craton during late mesozoic and cenozoic time the apparent absence of early oligocene and early through middle and earliest late miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times the high elevation setting of sirius formation outcrops suggests one of two hypotheses for their origin 1 they are in situ pliocene glaciomarine deposits that were uplifted 1 750 2 500 m with the transantarctic mountains to their present elevation 2 the sirius formation deposits are a mixture of derived sediments stripped from sub ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the transantarctic mountains we favor the second hypothesis with transport to sites sometime within the past 3 m y

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

relative temporal stability of the antarctic ice sheets during the late neogene based on the minimum frequency of outer shelf grounding events abstract the stability of the antarctic cryosphere involves two fundamental aspects the magnitude of ice volume changes and the frequency of ice volume changes in this article we synthesize results from three regional seismic stratigraphic studies of the continental shelf to evaluate the relative frequency of extreme advances of the ice sheets during the late neogene for different sectors of the antarctic ice sheet detailed analyses of glacial unconformities on the eastern and western ross sea outer continental shelf indicate that there were at least eight episodes during the late neogene when the east antarctic ice sheet eais and the west antarctic ice sheet wais were significantly larger the seismic results from the shelf do not support the conventional view that the land based eais was relatively stable and that the marine based wais was relatively dynamic glacial unconformities on the pacific continental shelf of the antarctic peninsula indicate that there were at least 30 outer shelf ice sheet expansions during the late neogene this suggests that the small land based antarctic peninsula ice cap apic may have been the most dynamic component of the antarctic cryosphere conversely the greater number of grounding events on the antarctic peninsula shelf may be a result of the margin s younger thermal age and hence greater potential to preserve units and unconformities during the late neogene we acknowledge that the available chronostratigraphic control from the antarctic margin is poor and that more chronological data are needed to confirm our late neogene age assignments

pliocene pleistocene glaciomarine sedimentation in eastern prydz bay and development of the prydz trough mouth fan odp sites 1166 and 1167 east antarctica abstract lithostratigraphy grain sizes and down hole logs of site 1166 on the continental shelf and site 1167 on the upper slope are analyzed to reconstruct glacial processes in eastern prydz bay and the development of the prydz trough mouth fan in eastern prydz bay upper pliocene lower pleistocene glaciomarine sediments occur interbedded with open marine muds and grade upward into waterlaid tills and subglacial tills lower pleistocene sediments of the trough mouth fan consist of coarse grained debrites interbedded with bottom current deposits and hemipelagic muds indicating repeated advances and retreats of the lambert glacier amery ice shelf system with respect to the shelf break systematic fluctuations in lithofacies and down hole logs characterize the upper pliocene lower pleistocene transition at sites 1166 and 1167 and indicate that an ice stream advanced and retreated within the prydz channel until the mid pleistocene the record from site 1167 shows that the grounding line of the lambert glacier did not extend to the shelf break after 0 78 ma published ice rafted debris records in the southern ocean show peak abundances in the pliocene and the early pleistocene suggesting a link between the nature of the glacial drainage system as recorded by the trough mouth fans and increased delivery of ice rafted debris to the southern ocean

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

piston core based biostratigraphic constraints on pleistocene oscillations of the west antarctic ice sheet in western ross sea between north basin and and 1b drill site abstract new diatom biostratigraphic age data derived from piston core were used to constrain the chronology for a seismic based interpretation of west antarctic ice sheet wais advance and retreat from the north basin outer shelf in western ross sea the data demonstrates that grounded ice occupied the outer shelf on at least ten occasions during the last 2 0 ma of the pleistocene although the biostratigraphic resolution is low the constraints permit correlations to coeval section recently drilled in south mcmurdo sound at the and 1b drill site our interpretation of regional scale correlations suggests that the pleistocene dynamics of the wais involved grounding line translations in excess of 600 km however the data also suggests that only two major advances of grounded ice occurred since 0 71 ma in other words several of the late pleistocene sediment cycles at and 1b must represent only minor advance and retreat of grounded ice to and from south mcmurdo sound the results prove false the long standing tacit assumption that the wais experienced major advances in association with peak glacials and eustatic lowstands during the last 700 ka of the pleistocene these results show that piston cores can be used to constrain the timing of pre holocene grounding events these data also highlight the need for regional scale correlations to distinguish between major versus minor grounding line translations of grounded ice in the marine setting

late cenozoic glacial history of the ross embayment antarctica abstract knowledge of the cenozoic terrestrial and marine glacial history of antarctica has been developed through studies of on land surface outcrops and subsurface drillcores and through examination of drillcores and piston cores obtained from a variety of offshore marine geological settings these field and laboratory endeavors have been a major target of the antarctic earth science community for more than thirty years the ross sea sedimentary basins including the byrd basin west antarctica wilkes and pensacola basins east antarctica and the transantarctic mountains provide significant data on the cenozoic glacial record a record that has been traced back to at least 38 ma close to the eocene oligocene boundary this paper reviews the late cenozoic history of the transantarctic mountains and flanking sedimentary basins with emphasis on the debate between the stabilist view of antarctic ice sheet history see clapperton and sugden 1990 and our favored multi glacial dynamic ice sheet model

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

the age and origin of the labyrinth western dry valleys antarctica evidence for extensive middle miocene subglacial floods and freshwater discharge to the southern ocean a 50 km long network of bedrock channels and scoured terrain occupies the ice free portion of a major trough that crosses the transantarctic mountains in southern victoria land the channels collectively termed the labyrinth emerge from beneath the margin of the east antarctic ice sheet wright upper glacier and are incised into a 300 m thick sill of ferrar dolerite at the head of wright valley upper and intermediate elevation erosion surfaces of the labyrinth exhibit striations and molding characteristic of glacial erosion channels and canyons on the lower surface are as much as 600 m wide and 250 m deep have longitudinal profiles with many reverse gradients and contain potholes 35 m deep at tributary junctions these characteristics are most consistent with incision from fast flowing subglacial meltwater estimated discharge is on the order of 1 6 2 2 10 6 m 3 s 1 our 40 ar 39 ar analyses of volcanic tephra from the labyrinth show that the chan nels are relict that major channel incision predates 12 4 ma and that the last major subglacial flood occurred sometime between 14 4 ma and 12 4 ma the most plausible origin for the labyrinth is erosion associated with episodic drainage of subglacial lakes in east antarctica one compelling possibility is that discharge of large volumes of sub glacial meltwater to the southern ocean and to the ross sea in particular may have coincided with and contributed to oscillations in regional and or global climate during the middle miocene

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

seismic stratigraphy of the central basin in northwestern ross sea slope and rise antarctica clues to the late cenozoic ice sheet dynamics and bottom current activity abstract sedimentation processes influenced by late cenozoic ice sheet dynamics and bottom current activity can be extracted from the seismic stratigraphic record of the ross sea continental slope and rise where more continuous sedimentary successions are preserved compared to the continental shelf in this study we present a seismic stratigraphic analysis of the central basin that lies in the northwestern ross sea using newly acquired and existing legacy seismic reflection data that are correlated to adjacent scientific drill sites the chronostratigraphy of ross sea seismic sequences lying above the mid miocene sequence boundary rsu4 ca 16 5 15 5 ma is based on the former antarctic offshore stratigraphy antostrat project depth contour and isopach maps of sedimentary sequences bounded by two major unconformities of rsu4 and rsu2 the late pliocene boundary ca 4 0 2 8 ma and the present day seafloor were produced to illustrate the evolution of paleo seafloor morphology distribution of sediments and depocenter migration in the western ross sea outer margin the results of seismic stratigraphic analysis indicate that gravity sedimentation processes dominated the central basin infill up to the mid miocene and then downslope sediment supply gradually diminished through the late miocene and quaternary likely reflecting a shift toward a cooler less erosive glacial regime change since the late pliocene a topset truncated glacial prograding wedge developed in the upper continental slope at the mouth of the joides basin and the sediment depocenter was shifted from the basin floor to the upper slope suggesting the more persistent occurrence of grounded ice sheets on the outer continental shelf meanwhile persistent along slope bottom current processes formed contourites on the slope and over the crests of banks surrounding the central basin since the mid miocene in the late pliocene the contourites that formed off the joides basin mouth were overlain by glaciogenic debris flows while the growth of contourites continued over and along the flanks of banks farther to the north this suggests that along slope bottom current processes near the joides basin mouth were diminished or dominated by the glacial discharge to the continental shelf edge the sediment stacking patterns differ between the joides central basins and the drygalski adare basins located on the westernmost ross sea margin suggesting that distinctive glacial interglacial behavior of the former grounded ice streams and sediment supplies in the troughs feeding these basins were largely controlled by the paleo seafloor morphology of the western ross sea continental shelf

cenozoic prograding sequences of the antarctic continental margin a record of glacio eustatic and tectonic events abstract sedimentary sections up to 6 14 km thick lie beneath many areas of the antarctic continental margin the upper parts of the sections contain up to 6 km of cenozoic glacial and possibly non glacial sequences that have prograded the continental shelf up to 85 km we describe the cenozoic sequences using two general categories based on their acoustic geometries type ia sequences which account for most prograding of the antarctic continental shelf have complex sigmoidal geometries and some acoustic characteristics atypical of low latitude margins such as troughs and mounds lying parallel and normal to the shelf edge and high velocities 2 0 2 6 km s for flat layers within 150 m of the seafloor type iia sequences which principally aggrade the paleoshelf lie beneath type ia sequences and have mostly simple geometries and gently dipping reflections the prograding sequences are commonly located near the seaward edges of major mesozoic and older margin structures relatively rapid cenozoic subsidence has occured due to the probable rifting in the ross sea thermal subsidence in the antarctic peninsula and isostatic crustal flexure in wilkes land in prydz bay and the weddell sea prograding sequences cover mesozoic basins that have undergone little apparent cenozoic tectonism grounded ice sheets are viewed by us and others as the principal mechanism for depositing the antarctic prograding sequences during the initial advance of grounded ice the continental shelf is flexurally overdeepened the inner shelf is heavily eroded and gently dipping glacial strata are deposited on the shelf i e type iia sequences the overdeepened shelf profile is preserved a during glacial times by grounded ice sheets episodically crossing the shelf eroding sediments from onshore and inner shelf areas and depositing sediments at the front of the ice sheet as outer shelf topset banks and continental slope foreset aprons i e type ia sequences and b during interglacial times like today by little or no clastic sedimentation on the continental shelf other than beneath retreated ice shelves lying far from the continental sheld edge ice streams carve broad depressions across the shelf and carry abundant basal sediments directly to the continental shelf edge thereby creating troughmouth fans and sheet like prograding sequences i e type ia sequences numerous acoustic unconformities and multiple overcompacted layers within the prograding sequences suggest major fluctuations of the antarctic ice sheet the available drilling and seismic interpretations provide the following history 1 cenozoic ice sheets have existed in places near the continental shelf since middle to late eocene time 2 a grounded antarctic ice sheet first expanded to the continental shelf edge with probable overdeepening of the outer shelf in late eucene to early oligocene time in prydz bay possibly in early miocene time in the ross sea and at least by middle miocene time in the weddell sea 3 the relative amounts of shelf prograding and inferred ice volume variations and related sea level changes have increased since middle to late miocene time in the eastern ross sea prydz bay and possibly weddell sea our analysis is preliminary further acoustic surveys and scientific drilling are needed to resolve the proximal antarctic record of glacio eustatic climatic and tectonic events recorded by the prograding sequences

effect of cenozoic ice sheet fluctuations in antarctica on the stratigraphic signature of the neogene stratigraphic successions from the gulf of mexico offshore alabama northeast java indonesia ross sea antarctica and several other continental margins have been examined all are characterized by very similar neogene stratal geometries in seismic profiles and well log cross sections from these areas a large mid oligocene i e latest early oligocene earliest late oligocene basinward shift in coastal onlap is followed by a major early miocene transgression and aggradation which is in turn followed by early middle miocene transgressions and late middle and late miocene progradational episodes the succession culminates in plio pleistocene high frequency progradations and transgressions the interregional character of the neogene stratal signature and its similarity to the stratal geometry found in seismic data from the ross sea continental shelf antarctica suggest that the neogene stratal signature is a manifestation of glacioeustatic fluctuations a review of the literature and an analysis of recently acquired and published data indicate that the first major ice sheet grounding event in the ross sea occurred during middle to late oligoce time the ross sea is the repository for ice flowing from a major portion of the continental interior thus the glacial record of the ross sea should serve as a gage of ice volume changes on the continent that were large enough to influence global eustasy the ice advance onto the ross sea continental shelf during middle to late oligocene time may have been the result of a decrease in the rate of shelf subsidence as rifting in the ross sea slowed or ceased advance of the ice sheet resulted in widespread erosion of the continental shelf and shelf overdeepening it is hypothesized that metastable marine based ice sheets have waxed and waned on the antarctic continental shelf since at least the oligocene and that the these waxing and waning events were responsible for the development of a global neogene stratigraphic signature

neogene glacigenic debris flows on james ross island northern antarctic peninsula and their implications for regional climate history detailed sedimentological and microtextural analyses of newly discovered late neogene diamictites and other coarse grained facies mostly sandwiched between hyaloclastite of the james ross island volcanic group and cretaceous sandstone and mudstone indicate deposition mainly by glacigenic debris flows the deposits on james ross island northern antarctic peninsula constrain the depositional setting ice bed dynamics and regional palaeoclimate the sequences on james ross island vary in age but are mainly late miocene and pliocene unlike neogene sedimentary sequences elsewhere in antarctica those on james ross island are unusually well dated by a combination of 40ar 39ar and 87sr 86sr analyses on fresh interbedded lavas and pristine bivalve molluscs respectively the sr isotopic ages of the debris flows cluster around 4 74 4 89 5 44 5 78 and 6 31 ma and probably date relatively warm periods in the northern antarctic peninsula region when the bivalves lived under ice poor or seasonally ice free conditions the bivalves are often remarkably well preserved lack adhering lithified sediment and in at least two locations are large mainly unfragmented and sometimes articulated suggesting that they were alive immediately prior to their incorporation in subaqueous debris flows at the margins of an advancing glacier these fossiliferous glacigenic debris flows signify episodes of ice expansion during relatively warm periods or interglacials of the late miocene and pliocene the james ross island glacigenic sedimentary successions attain thicknesses of up to 150 m and extend over 4 km laterally the high volume of glacigenic sediment delivery implicit in the james ross island successions indicates that a series of dynamic ice fronts crossed the region during the late miocene and pliocene epochs associated evidence in the form of clast abrasion including striations and faceting and bedrock erosion is indicative of basal sliding and subglacial sediment deformation active at the ice bed interface and wet based temperate or polythermal regimes prior to remobilisation the evidence further suggests two local ice caps on james ross island during the warm periods as well as ice overriding by the antarctic peninsula ice sheet from the west and northwest

late oligocene to early miocene geochronology and paleoceanography from the subantarctic south atlantic mi2 as well as several other distinctive isotope events our data suggest that the d 18 o maximum commonly associated with the oligocene miocene o m boundary falls within c6cn 2r 23 86 ma the d 13 c maximum coincides within the temporal resolution of our record with c6cn 2n r boundary and hence to the o m boundary comparison of the stable isotope record from site 1090 to the orbitally tuned stable isotope record from odp site 929 across the o m boundary shows that variability in the two records is very similar and can be correlated at and below the o m boundary site 1090 stable isotope records also provide the first deep southern ocean end member for reconstructions of circulation patterns and late oligocene to early miocene climate change comparison to previously published records suggests that basin to basin carbon isotope gradients were small or nonexistent and are inconclusive with respect to the direction of deep water flow oxygen isotope gradients between sites suggest that the deep southern ocean was cold in comparison to the north atlantic indian and the pacific oceans dominance of cold southern component deep water at site 1090 at least until 17 ma suggests that relatively cold circumpolar climatic conditions prevailed during the late oligocene and early miocene we believe that a relatively cold southern ocean reflects unrestricted circumpolar flow through the drake passage in agreement with bathymetric reconstructions index terms 4267 oceanography general paleoceanography 1035 geochemistry geochronology 4870 oceanography biological and chemical stable isotopes keywords paleoceanography 1035 geochronology stable isotopes

glaciation across the oligocene miocene boundary in southern mcmurdo sound antarctica new chronology from the ciros 1 drill hole few palaeogene and neogene sediment cores from the antarctic continental margin have been dated with sufficient precision to enable establishment of direct linkages between glacial events on the antarctic continent and marked events in deep sea delta 18o records as a result much of our knowledge of the gradual but stepwise shift from greenhouse climates of the cretaceous to the ice house climates of the quaternary is inferred from well dated and more continuously deposited deep sea sediments in this study we present new magnetostratigraphic results from the ciros 1 drill core from mcmurdo sound antarctica along with a reinterpretation of a published diatom biostratigraphic zonation that is constrained by correlation to a high precision age model from the nearby crp 2 2a drill core our results suggest that most of the upper 350 m of the ciros 1 drill core represents rapid sediment accumulation during a short time interval spanning the oligocene miocene boundary chronostratigraphic control is precise enough to enable correlation of this interval of glacimarine sedimentation with the mi 1 deep sea delta 18o event which confirms that the mi 1 event was related to a major expansion of antarctic ice a major unconformity at 366 m in the ciros 1 drill core which is widely observed in regional seismic reflection studies represents 9 myr of missing time this unconformity can be traced offshore into the ross sea using seismic stratigraphy and is interpreted to indicate significant east antarctic ice sheet development during the mi 1 glaciation the stratigraphic expression of this 400 kyr glacial event is evidently multiphase and complex in the victoria land basin probably because it was punctuated by higher frequency orbitally induced glacial oscillations the presence of nothofagidites pollen throughout the ciros 1 drill core and the presence of a nothofagus southern beech leaf within the early miocene portion of the core indicate that antarctic mean summer temperatures did not decrease below 5 deg c throughout the mi 1 glaciation these temperatures are significantly warmer than present day mean summer temperatures at sea level in mcmurdo sound the persistence of a nothofagus forest in coastal southern victoria land throughout this time interval suggests that the present state of deep refrigeration was not reached until some time after the mi 1 glaciation

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

late pleistocene interactions of east and west antarctic ice flow regimes evidence from the mcmurdo ice shelf we present new interpretations of deglaciation in mcmurdo sound and the western ross sea with observationally based reconstructions of interactions between east and west antarctic ice at the last glacial maximum lgm 16000 12 000 8000 and 4000 bp at the lgm east antarctic ice from mulock glacier split one branch turned westward south of ross island but the other branch rounded ross island before flowing southwest into mcmurdo sound this flow regime constrained by an ice saddle north of ross island is consistent with the reconstruction of stuiver and others 1981a after the lgm grounding line retreat was most rapid in areas with greatest water depth especially along the victoria land coast by 12 000 bp the ice flow regime in mcmurdo sound changed to through flowing mulock glacier ice with lesser contributions from koettlitz blue and ferrar glaciers because the former ice saddle north of ross island was replaced by a dome the modern flow regime was established 4000 bp ice derived from high elevations on the polar plateau but now stranded on the mcmurdo ice shelf and the pattern of the transantarctic mountains erratics support our reconstructions of mulock glacier ice rounding minna bluff but with all ice from skelton glacier ablating south of the bluff they are inconsistent with drewry s 1979 lgm reconstruction that includes skelton glacier ice in the mcmurdo sound through flow drewry s 1979 model closely approximates our results for 12 000 4000 bp ice sheet modeling holds promise for determining whether deglaciation proceeded by grounding line retreat of an ice sheet that was largely stagnant because it never approached equilibrium flowline profiles after the ross ice shelf grounded or of a dynamic ice sheet with flowline profiles kept low by active ice streams that extended northward from present day outlet glaciers after the ross ice shelf grounded

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

a major trough mouth fan on the continental margin of the bellingshausen sea west antarctica the belgica fan a 330 km length of the little known continental shelf edge and slope of the bellingshausen sea west antarctica is investigated using multibeam swath bathymetric and sub bottom profiler evidence the shelf break is at 650 700 m across the 150 km wide belgica trough and to either side is about 500 m when full glacial ice advanced across the shelf to reach the shelf break it was partitioned into fast and slow flowing elements with an ice stream filling the trough this had important consequences for the nature and rate of sediment delivery to the adjacent continental slope off belgica trough the upper continental slope has convex outward contours indicating a major sedimentary depocentre of gradient 1 2 degrees acoustic profiles and cores from the depocentre show a series of diamictic glacigenic debris flows the depocentre is interpreted as a trough mouth fan built largely by debris delivered from the ice stream the slope is steeper beyond the trough margins at up to 6 degrees the main morphological features on the bellingshausen sea slope are gully systems and channels major canyons and late quaternary slides are absent most gullies and channels are found on the fan gullies are about 15 25 m deep a few hundred metres wide and some are 25 km long the largest channel is over 60 km long about a kilometre wide and 10 to 15 m deep the channels provide pathways for sediment by passing of the upper slope and transfer to the continental rise and beyond by turbidity currents gullies on the bellingshausen sea margin cut through debris flows on the slope assuming the debris flows are linked mainly to downslope transport of diamictic debris when ice was at the shelf edge under full glacial conditions then those gullies cut into them formed during deglaciation belgica fan is 22 000 km 2 in area and about 60 000 km 3 in volume it is the largest depocentre identified to date on the continental margin of the west antarctic ice sheet fed by an interior ice sheet basin of approximately 200 000 km 2 c 2008 elsevier b v all rights reserved

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

glaciology and geological signature of the last glacial maximum antarctic ice sheet dynamical changes in contemporary ice sheets account for significant proportions of their current rates of mass loss but assessing whether or not these processes are a natural part of ice sheet evolution requires inference from palaeo glaciological records however a robust mechanism for translating sparse geological data into meaningful interpretations of past glacier dynamics at the continental scale is lacking since geological archives can be ambiguous and often their chronology is only poorly constrained to address this we combine the interpretation of high resolution antarctic ice sheet model results with continent wide geological evidence pertinent to the dynamical configuration of the ice sheet during the last and possibly preceding glacial maxima we first focus on the thermal regime of the ice sheet its pattern and velocity of flow variability in likely subglacial erosion and sediment transport and how these characteristics evolve during glacial transitions we show that rapid basal sliding was restricted to discrete outlets that eroded and advected sediment toward and across the continental shelf primarily during the early stages of advance and retreat of the ice sheet highlighting the need to consider time transgressive behaviour in the interpretation of geological archives secondly we present new modelling that attempts to improve the fit of our numerical model to geologically based reconstructions in the ross sea by accounting for locally enhanced ablation in mcmurdo sound our new simulation achieves a much closer fit to empirically derived flow patterns than previously growth of the modelled last glacial maximum ice sheet takes place primarily by marine ice accretion in the major embayments as a consequence of cooler ocean temperatures and reduced sub ice shelf melting and at its maximal extent represents a grounded ice volume excess above present of approximately 8 3 m sea level equivalent this figure thus provides an upper bound on the possible antarctic contribution to deglacial meltwater pulses

morphology and sedimentary processes on the continental slope off pine island bay amundsen sea west antarctica morphology and sedimentation on the pine island bay continental margin eastern amundsen sea is investigated using swath bathymetry parametric subbottom profiler topas records and sediment cores a major cross shelf trough extends to the continental shelf edge at 114 w through which fast flowing ice drained the west antarctic ice sheet under full glacial conditions the slope adjacent to the trough mouth is 4 whereas to the east and west it is steeper a bulge in bathymetric contours beyond and east of the trough mouth indicates some slope progradation elsewhere seismic reflection profiles indicate major shelf aggradation and minor slope progradation networks of gullies and channels dominate the slope adjacent to pine island bay in front of the trough mouth gullies at the shelf edge and uppermost slope connect directly with channels that continue to the continental rise other gullies connect indirectly with channels further downslope topas records indicate that gully channel systems acted as conduits for coarse grained sediment transfer cores comprise turbidites representing channel deposits and diamicton facies deposited by debris flows sandy turbidites interbedded with hemipelagic muds occur on the rise and abyssal plain the west antarctic ice sheet extended to the shelf edge during full glacials delivering water saturated till and turbid water directly to the continental slope along a line source gully channel systems are probably a product of sediment gravity flows derived from the release of water saturated till and turbid water along the ice sheet margin perhaps augmented subsequently by downslope flow of dense cold and saline water associated with sea ice production during the holocene the gully channel systems enable sediment to bypass the continental slope spatial variations in gully channel system morphology along the amundsen sea continental slope are probably linked to differences in sediment gravity flow processes and the rate and composition of sediment delivered to the shelf edge from the ice sheet cored sediments on the slope and abyssal plain record the widespread presence of turbidite sands indicating that downslope transfer of glacier derived sediments has taken place this supports our interpretation that submarine channels are derived from and are conduits for mass wasting submarine channels on the upper slope continue into the abyssal plain as far north as 67 s they are separated by sediment drifts and sediment waves resulting from the interaction between downslope turbidity current processes and along slope bottom currents similar deep sea sedimentary processes operate along much of west antarctica and the western side of the antarctic peninsula

early stall of west antarctic ice sheet advance on the eastern ross sea middle shelf followed by retreat at 27 50014cyrbp abstract marine geological and geophysical data suggest that the west antarctic ice sheet wais deposited three thick seismically resolvable units in the eastern ross sea since the last glacial maximum lgm but the chronology of these grounding events is debated existing ice retreat chronologies for the eastern ross sea are considered suspect because nearly all have been developed using radiocarbon dating of acid insoluble organics aio from bulk sediment we used a new strategy to isolate in situ forams from diamict sediment deposited at the middle shelf grounding zone wedge gzw a subaqueous ice marginal landform previously interpreted to represent deposition during the third grounding event since the lgm advance to the shelf edge here we present a synthesis of our new radiocarbon dates of foram tests and aio with previously published radiocarbon dates we propose that the wais s lgm advance in the eastern ross sea sector reached the middle shelf circa 27 500 14c yr bp and that open marine sedimentation began shortly thereafter there is as of yet no clear explanation for why wais retreat in this sector of antarctica apparently began prior to the peak of the last glacial cold period a precipitation deficit localized warm water intrusion an ice dynamic response in the absence of climate forcing or another as of yet unknown forcing mechanism could be responsible

pliocene paleoclimate and east antarctic ice sheet history from surficial ash deposits the preservation age and stratigraphic relation of an in situ ashfall layer with an underlying desert pavement in arena valley southern victoria land indicate that a cold desert climate has persisted in arena valley during the past 4 3 million years these data indicate that the present east antarctic ice sheet has endured for this time and that average temperatures during the pliocene in arena valley were no greater than 3 c above present values one implication is that the collapse of the east antarctic ice sheet due to greenhouse warming is unlikely even if global atmospheric temperatures rise to levels last experienced during mid pliocene times

direct constraints on antarctic peninsula ice sheet grounding events between 5 12 and 7 94 ma 1 how has the antarctic ice sheet responded to or influenced global climate change this simple question has been difficult to address because the long term records of the ice sheet s fluctuations are poorly constrained with geologic data from antarctica thus studies to date have not convincingly established how specific antarctic ice sheet events correlate with climatic eustatic or other phenomena known from low latitude and deep sea records this study focused on documenting the direct record of ice sheet advance and retreat to the antarctic peninsula s shelf edge on the peninsula s outer shelf seismic reflectors interpreted to be subglacial unconformities were correlated with published results from ocean drilling program leg 178 lithologic and chronologic control at two drill sites provided ground truth for the seismic interpretation and the timing of the antarctic peninsula ice sheet grounding events this synthesis showed that grounded ice advanced to the shelf edge on at least 12 occasions between 5 12 and 7 94 ma

an ice grounding line wedge from the ghaub glaciation 635 ma on the distal foreslope of the otavi carbonate platform namibia and its bearing on the snowball earth hypothesis our detailed examination of the ghaub formation possibly 635 ma on the distal foreslope of the otavi carbonate platform is part of a regional study of the congo paleocontinental margin in northwestern namibia detrital carbonates of the ghaub formation disconformably overlie the franni aus member of the ombaatjie formation a coarsening upward stack of carbonate turbidites and oolite clast debris flow breccias interpreted to be a glacioeustatic falling stand wedge within the main ghaub formation carbonate diamictites are interleaved with mesoscale laminated to cross laminated climbing rippled grainstones and mudstones and conglomeratic carbonates amalgamation of diamictite units is observed where interleaved facies grainstones mudstones are laterally discontinuous due to reactivation of erosion followed by renewed deposition the diamictite package is progradational overall and 80 m thick on average it is overlain by the 5 15 m thick bethanis member which is unique in its lateral continuity composite fining upward trend and distinctive interbedding of turbidite grainstones argillaceous siltstones climbing rippled mudstones and meter scale stromatolite dropstones dropstones are ubiquitous within the finer grained ghaub lithofacies and their presence along with the facies context for subglacial and near grounding line deposition indicates a glacigenic origin for the ghaub formation despite its subtropical paleolatitude and distal foreslope setting we infer a glacial maximum represented by the sub ghaub disconformity followed by the main ghaub interval when an ice grounding line on the distal foreslope experienced abrupt step backs and readvances of limited magnitude terminated by the bethanis episode of unusually widespread iceberg calving and slope instability the bethanis member is overlain conformably by the keilberg member of the maieberg formation reconstruction of the foreslope places the ghaub grounding line wedge 1 3 km vertically below the rim of the platform implying an enormous base level change upon deglaciation when the platform was drowned below wave base for a period far exceeding the time scale for isostatic adjustment the magnitude of base level change supports the pan glacial hypothesis that dynamic thick ice sheets existed simultaneously on virtually all continents the snowball hypothesis that the oceans were also covered by glacial ice sea glacier provides a simple explanation for the main ghaub to bethanis transition terminal deglaciation was triggered by collapse of the sea glacier

a lost world archaic crinoid dominated assemblages on an antarctic seamount abstract the previously unsurveyed admiralty 67 s 171 e and scott island 67 22 s 179 55 e seamounts to the north of the ross sea were explored using cameras and physical sampling gear during the new zealand ipy caml research voyage tan0802 in february 2008 a striking assemblage dominated by stalked crinoids and brachiopods was found at 580 600 m depths on isolated knolls at the northwest and southeast extremities of admiralty seamount the seabed at these sites was littered with crinoid ossicles and crinoid stalk bases were conspicuous on exposed rocks suggesting that these assemblages have persisted for a considerable period of time the crinoid sites were limited to the isolated knolls but large areas of the flanks of the main seamount were covered by dense populations of suspension feeding ophiuroids these assemblages are more similar in structure to those preserved in fossil strata from the palaeocene and late eocene than to any extant assemblages yet described from the antarctic in comparisons with faunal assemblages on scott island seamount the abundance of stalked crinoids was strongly inversely correlated with the abundance of echinoid asteroid and lithodid crab predators and both asteroids and echinoids were photographed feeding on crinoids these observations are consistent with the prevailing hypotheses that crinoid and ophiuroid dominated assemblages which were widespread in the palaeocene were displaced by the radiation of mobile predators and that conditions in isolated habitats in the southern ocean may have acted as refugia allowing the persistence of archaic benthic assemblages

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

late cenozoic environments in the barents sea we examine the paleoceanography and paleogeography of the barents sea during the late cenozoic glacial regime by seismostratigraphy and core analysis during the smaller glaciations which probably dominated the first period of the glaciogenic regime approximately 2 5 0 8 ma glaciomarine processes with sediment influx from the adjacent mainland prevailed the barents sea has been covered by grounded ice sheets several five to 10 times during the late cenozoic we speculate that these glaciations occurred during the last 0 8 ma during these larger glaciations the margin of the ice sheet expanded to the shelf edge and the continental shelf break and slope acted as a depocenter and prograded rapidly frequent sediment gravity flows accumulated on the lower continental slope during interglacials the barents sea was converted to a starved continental margin most of the barents sea was glaciated during the maximum of the last glaciation 19 16 ka a two stepped deglaciation 16 to 13 ka and 13 to 10 ka occurred incipient atlantic water reached the western areas about 13 ka and totally replaced the arctic water by 10 ka these paleoceanographic events were delayed in the eastern barents sea

sedimentation on the ross sea continental shelf antarctica abstract glacial marine sedimentation has prevailed throughout most of the early glacial history of the ross sea region however since late miocene to early pliocene time the west antarctic ice sheet has advanced onto the continental shelf perhaps several times glacial troughs of the western ross sea may also have formed at this time these glacial troughs border outlet glaciers of the east antarctic ice sheet a widespread lodgement till facies was deposited during this glacial advance holocene retreat of this expanded ice sheet left no conspicuous meltwater record so decoupling of the ice sheet from the seafloor rather than rapid melting is implied modern glacial sediment is far less prevalent than biogenic sediment and reworked glacial sediment except in coastal areas adjacent to small ice shelves and ice tongues little or no debris is being transported beyond the calving line of the ross ice shelf siliceous mud and ooze occurs in the western ross sea where surface circulation is most vigorous and warm deep waters up well this siliceous sediment along with terrigenous silt and clay blankets the seafloor below approximately 300 m water depth most of the ross sea continental shelf is deeper than this surface sediments on shallow banks and coastal platforms have clearly been reworked by marine currents the most vigorous bottom current activity occurs in those areas where geostrophic currents impinge onto the shelf debris flows and turbidity currents are also important in eroding and redistributing glacial sediments on the shelf terrigenous silt and clay are more abundant in surface sediment than basal till the source of this silt and clay is problematic the most plausible sources being onshore transport of suspended sediment by impinging currents and subglacial meltwater input

late neogene geomorphological and glacial reconstruction of the northern victoria land coast western ross sea antarctica abstract this study is a contribution to the reconstruction of the geomorphology and the glacial history of the northern victoria land coastal glaciers high resolution single channel reflection seismic lines were collected in 2002 within the framework of the italian antarctic programme pnra in wood bay and lady newnes bay north to cape washington western ross sea antarctica the data provide evidence of overdeepened marine subglacial valleys more than 1 km deep and 1 2 km wide formed along the seaward extension of the tinker aviator fitzgerald and icebreaker glaciers and converging into the major sw ne ice stream system the spatial distribution and the geometry of the seismic facies as well as the direct correlation with the seismic sequences in the northern basin are interpreted to document 1 the depositional activity of a coastal glacial system seaward of northern victoria land nvl after 18 ma based on the seismic correlation with the base of dsdp 273 and possibly in the early pliocene in coalescence with expanded ice streams coming from the south along the drygalski basin possibly draining from the wais as documented at and 1b in the mcmurdo sound naish et al 2007 2008 2009 followed by 2 the development of tam tidewater glaciers that carved sea valleys near the victoria land coast onto the shelf the transition from a dynamic thick ice sheet covering the coastal area of nvl to the nvl valley glaciers advancing and retreating up to about 100 km from the coast in the middle pliocene would represent a significant environmental change possibly from interglacial conditions more temperate than today and gradually cooling to a cold and dry coastal regime

seismic data from the northern basin ross sea record extreme expansions of the east antarctic ice sheet during the late neogene abstract approximately 3700 km of intermediate resolution single channel seismic data from the northern basin were analyzed to investigate the late neogene history of east antarctic ice sheet eais grounding events on the shelf and to evaluate how glacial unconformities on the shelf are manifested on the upper slope the northern basin was chosen as the site of this study because ice sheet reconstructions show that the basin received sediment by ice emanating from east antarctica in addition seismic correlations to dsdp site 273 suggest that a relatively thick late neogene section exists on the basin s outer shelf and upper slope on the northern basin shelf glacial unconformities exhibiting broad low angle relief topset truncation and cross cutting relationships reveal a dynamic history of expansions and contractions during which the eais was larger than present on at least eight occasions during the late neogene on the upper slope the correlative conformities of the glacial unconformities are indistinct reflections within thick trough mouth fan tmf depocenters at the mouths of drygalsky and joides basins the glacial unconformities and correlative conformities define tmf sequences and each tmf sequence contains several topset truncated prograding slope reflectors we infer that the correlative conformities on the continental slope correspond to the interface between prograding glaciogenic deposits glacial maximum and diatomaceous glacial marine sediments glacial minimum the seismic stratigraphic analysis and regional mapping indicate that the upper slope does not contain a more complete late neogene section than that which exists on the shelf we infer that diatomaceous glacial marine sediments on the slope may be relatively undisturbed and hence may provide a means of dating the tmf sequences it is hoped that these results will stimulate efforts to core the late neogene section in the northern basin tmfs to investigate how these eais expansions and contractions relate to other records of late neogene climate and eustasy

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

a coupled climate ice sheet modeling approach to the early cenozoic history of the antarctic ice sheet abstract the sudden widespread glaciation of antarctica and the associated shift toward colder temperatures near the eocene oligocene boundary 34 ma represents one of the most fundamental reorganizations of the global climate system recognized in the geologic record this glacial inception and the subsequent evolution of the early east antarctic ice sheet eais are simulated using a new coupled global climate dynamical ice sheet model accounting for the paleogeography greenhouse gas concentrations changing orbital parameters and varying ocean heat transport suites of long 105 yr climate ice sheet simulations are used to investigate the effects of declining atmospheric co2 compared to those of the tectonic opening of southern ocean gateways and the timing of mountain uplift in the antarctic interior in contrast to the established paradigm for the glaciation of antarctica which centers on the opening of the southern ocean gateways and the thermal isolation of the continent our results show that declining cenozoic pco2 may have played the dominant role first small isolated ice caps formed on the highest antarctic plateaus then as a co2 threshold between 3 and 2 pre industrial level pal was crossed height mass balance feedbacks were initiated during orbital periods with cold austral summers triggering much larger highly dynamic terrestrial ice sheets as co2 continued to decline these isolated ice caps eventually merged into a permanent continental scale eais in our model neither the opening of the southern ocean gateways nor mountain uplift significantly affected the timing of the major ice sheet transition given a scenario of gradually declining co2 from 4 to 2 pal over 10 million years around the eocene oligocene boundary

late wisconsin and early holocene glacial history inner ross embayment antarctica abstract lateral drift sheets of outlet glaciers that pass through the transantarctic mountains constrain past changes of the huge ross ice drainage system of the antarctic ice sheet drift stratigraphy suggests correlation of reedy iii reedy glacier beardmore beardmore glacier britannia hatherton darwin glaciers ross sea mcmurdo sound and younger terra nova bay drifts radiocarbon dates place the outer limits of ross sea drift in late wisconsin time at 24 000 13 000 yr b p outlet glacier profiles from these drifts constrain late wisconsin ice sheet surface elevations within these constraints we give two extreme late wisconsin reconstructions of the ross ice drainage system both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner ross embayment however in the central ross embayment one reconstruction shows floating shelf ice whereas the other shows a grounded ice sheet massive late wisconsin holocene recession of grounded ice from the western ross embayment which was underway at 13 040 yr b p and completed by 6600 6020 yr b p was accompanied by little change in plateau ice levels inland of the transantarctic mountains sea level and basal melting probably controlled the extent of grounded ice in the ross embayment the interplay between the precipitation low late wisconsin and high holocene values and the influence of grounding on outlet glaciers late wisconsin thickening and late wisconsin holocene thinning with effects dying out inland probably controlled minor elevation changes of the polar plateau

late neogene ice drainage changes in prydz bay east antarctica and the interaction of antarctic ice sheet evolution and climate abstract during the late neogene the lambert glacier amery ice shelf drainage system flowed across prydz bay and showed several changes in flow pattern in the early pliocene the lambert glacier ice stream reached the shelf edge and built a trough mouth fan on the upper continental slope this was associated with an increase in ice discharge from the princess elizabeth land coast into prydz bay the trough mouth fan consists mostly of debris flow deposits derived from the melting out of subglacial debris at the grounding line at the continental shelf edge the composition of debris changes at around 1 1 ma bp from material derived from erosion of the lambert graben and prydz bay basin to mostly basement derived material this probably results from a reduction in the depth of erosion and hence the volume of ice in the system in the trough mouth fan debris flow intervals are separated by thin mudstone horizons deposited when the ice had retreated from the shelf edge age control in an ocean drilling program hole indicates that most of the trough mouth fan was deposited prior to the brunhes matuyama boundary 780 ka bp this stratigraphy indicates that extreme ice advances in prydz bay were rare after the mid pleistocene and that ice discharge from princess elizabeth land became more dominant than the lambert glacier ice in shelf grounding episodes since the mid pleistocene mechanisms that might have produced this change are extreme inner shelf erosion and or decreasing ice accumulation in the interior of east antarctica we interpret this pattern as reflecting the increasing elevation of coastal ice through time and the increasing continentality of the interior of the east antarctic ice sheet the mid pleistocene change to 100 ka climatic and sea level cycles may also have affected the critical relationship between ice dynamics and the symmetry or asymmetry of the interglacial glacial climate cycle duration

architecture and sedimentary processes on the mid norwegian continental slope a 2 7 myr record from extensive seismic evidence abstract quaternary architectural evolution and sedimentary processes on the mid norwegian continental slope are investigated using margin wide three and two dimensional seismic datasets of 100 000 km3 sediments delivered to the mid norwegian shelf and slope over the quaternary 75 000 km3 comprise the slope succession the structural high of the voring plateau characterised by initially low 1 2 slope gradients and reduced accommodation space exerted a strong control over the long term architectural evolution of the margin slope sediment fluxes were higher on the voring plateau area increasing up to 32 km3 ka 1 during the middle pleistocene when fast flowing ice streams advanced to the palaeo shelf edge resulted in a more rapid slope progradation on the voring plateau these rates of sediment delivery are high compared to the maximum of 7 km3 ka 1 in the adjacent sectors of the slope characterised by steeper slope 3 5 more available accommodation space and smaller or no palaeo ice streams on the adjacent shelves in addition to the broad scale architectural evolution identification of more than 300 buried slope landforms provides an unprecedented level of detailed process based palaeoenvironmental reconstruction channels dominate the early pleistocene record 2 7 0 8 ma during which glacimarine sedimentation on the slope was influenced by dense bottom water flow and turbidity currents morphologic signature of glacigenic debris flows appear within the middle late pleistocene 0 8 0 ma succession their abundance increases towards late pleistocene marking a decreasing role for channelized turbidity currents and dense water flows this broad scale palaeo environmental shift coincides with the intensification of northern hemispheric glaciations highlighting first order climate control on the sedimentary processes in high latitude continental slopes