the role of ice thickness and bed properties on the dynamics of the enhanced flow tributaries of bailey ice stream and slessor glacier east antarctica

switch off of a major enhanced ice flow unit in east antarctica 1 the east antarctic ice sheet eais is the largest reservoir of ice on the planet by an order of magnitude compared with the west antarctic ice sheet wais it is traditionally considered to be relatively stable with only minor adjustments to its configuration over glacial interglacial cycles here we present the results of a radio echo sounding survey from coats land east antarctica which suggests that parts of the eais outlet drainage system may have changed significantly since the last glacial maximum we have identified an enhanced flow unit from buckled internal layering and smooth bed morphology that is no longer active we believe this feature to have shut down at some point since the last glacial maximum 20 ka bp

seismic measurements reveal a saturated porous layer beneath an active antarctic ice stream seismic reflection studies recently conducted on ice stream b part of the marine ice sheet of west antarctica show a metres thick layer immediately beneath the ice in which both compressional p and shear s wave speeds are very low these low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure from this and from arguments presented in an accompanying paper1 to the effect that the layer would be too weak to support the shear stress exerted by the overlying ice we conclude that the layer is deforming and that the ice stream probably moves principally by such deformation

the evolution of the subglacial landscape of antarctica the aim is to investigate the evolution of the subglacial landscape of antarctica using an ice sheet and erosion model we identify different stages of continental glaciation and model the erosion processes associated with each stage the model links erosion to the basal thermal regime and indicates that much of the antarctic interior may have been subject to less than 200 m of erosion the depth of erosion reflects the presence or absence of warm based ice and the consistency of ice flow direction this information linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography is used to generate a map of the subglacial antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the laurentian and scandinavian shields near the continental margins selective linear erosion has overdeepened pre existing river valleys by as much as 2 8 km high elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold based ice high erosion rates result from steep thermal gradients in basal ice mountain regions such as the gamburtsev mountains uplands in dronning maud land and massifs in west antarctica are likely to bear features of local alpine glaciation such landscapes may have been protected under cold based ice for the last 34 myrs or possibly longer

predicting radar attenuation within the antarctic ice sheet abstract to better understand the ability of ice penetrating radar to diagnose the subglacial environment from bed returned power we model the englacial radar attenuation of antarctic ice first we use a one dimensional thermo mechanical model to evaluate the sensitivity of the depth averaged attenuation rates to ice temperature as a function of surface accumulation rate geothermal flux and ice thickness we find that attenuation is most sensitive to variations in geothermal flux and accumulation rate when the bed temperature is close to the pressure melting point but even if geothermal flux and accumulation rate remain fixed attenuation can easily vary with ice thickness such high sensitivities show that one should not assume a uniform attenuation rate in the radar data analysis then using ensembles of modeled ice temperatures with different boundary conditions we generate multiple attenuation predictions for the antarctic ice sheet and evaluate the resulting uncertainties the largest contributor to uncertainty in these predictions is the geothermal flux this uncertainty is localized within the deeper half of the ice sheet by combining these temperature ensembles with ice core chemistry data we show that the sea salt adds little to the attenuation but the contribution from acids accounts for 29 inland to 53 coast of the total attenuation we conclude that improving radar diagnosis of the subglacial environment using bed returned power requires both 1 better data interpretation algorithms that account for attenuation variations and 2 better constraints of geothermal flux and bulk chemistry

tributaries of west antarctic ice streams revealed by radarsat interferometry interferometric radarsat data are used to map ice motion in the source areas of four west antarctic ice streams the data reveal that tributaries coincident with subglacial valleys provide a spatially extensive transition between slow inland flow and rapid ice stream flow and that adjacent ice streams draw from shared source regions two tributaries flow into the stagnant ice stream c creating an extensive region that is thickening at an average rate of 0 49 meters per year this is one of the largest rates of thickening ever reported in antarctica

pitfalls in radar diagnosis of ice sheet bed conditions lessons from englacial attenuation models 1 radar power returned from ice sheet beds has been widely accepted as an indicator of bed conditions however the bed returned power also depends on englacial attenuation which is primarily a function of ice temperature here using a one dimensional attenuation model it is demonstrated that in most cases variations in bed returned power are dominated by variations in englacial attenuation rather than bed reflectivity both accumulation rate and geothermal flux anomalies can interfere with the interpretation with the consequence analytical radar algorithms that have been widely accepted likely yield false delineations of wet dry beds more careful consideration is needed when diagnosing bed conditions spatial patterns of shallow englacial radar reflectors can be used as a proxy for accumulation rates which affect ice temperature and thus returned power i argue that it is necessary to simultaneously interpret the returned power and englacial reflector patterns to improve the bed diagnosis

dependence of antarctic surface mass balance on temperature elevation and distance to open ocean the latest compilations of surface mass balance mean annual surface temperature and elevation for the antarctic ice sheet derived from data sets of approximately 1500 700 and 105 points respectively have been used to obtain areally integrated means for 24 ice drainage systems and 329 grid point values covering the whole ice sheet monthly summaries of remotely sensed sea ice data for 1973 1976 have been used to obtain mean annual distance to open ocean linear and second order regression analyses of surface balance on 1 temperature for the entire ice sheet 2 elevation for the conterminous grounded ice and 3 distance to the open ocean for the ice shelves including ice rises and attached islands have been made using both system means and grid point values these analyses show correlation coefficients of between 0 63 and 0 81 and they provide bases for descriptive models of the present antarctic ice sheet as well as for predictive models of the response of the ice sheet to air temperature changes and variations in meridional mass and energy transfers extrapolation to other ice sheets past and present may be possible but should be made cautiously linear models are recommended for paleoclimatic reconstructions of ice sheets in upper mid latitudes and second order models are recommended for those in high latitudes system means are shown to be reliable for these purposes incidental results are new estimates of the mean annual surface temperature for the whole ice sheet 36 c and mean surface elevation for the conterminous grounded ice 2290 m

gelifluction viscous flow or plastic creep this paper reports results from two scaled centrifuge modelling experiments designed to simulate thaw related gelifluction a planar 12 prototype slope was modelled in each experiment using the same natural fine sandy silt soil however two different scales were used in experiment 1 the model scale was 1 10 tested in the centrifuge at 10 gravities g and in experiment 2 the scale was 1 30 tested at 30 g centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is n2 where n is the number of gravities under which the model was tested however the equivalent time scaling for viscous flow is 1 1 if gelifluction is a viscosity controlled flow process scaling conflicts will therefore arise during centrifuge modelling of thawing slopes and rates of displacement will not scale accurately to the prototype if however no such scaling conflicts are observed we may conclude that gelifluction is not controlled by viscosity but rather by elasto plastic soil deformation in which frictional shear strength depends on effective stress itself a function of the thaw consolidation process models were saturated consolidated and frozen from the surface downwards on the laboratory floor the frozen models were then placed in the geotechnical centrifuge and thawed from the surface down each model was subjected to four freeze thaw cycles soil temperatures and pore water pressures were monitored and frost heave thaw settlement and downslope displacements measured pore water pressures displacement rates and displacement profiles reflecting accumulated shear strain were all similar at the two model scales and volumetric soil transport per freeze thaw cycle when scaled to prototype were virtually identical displacement rates and profiles were also similar to those observed in earlier full scale laboratory floor experiments it is concluded therefore that the modelled gelifluction was not a time dependent viscosity controlled flow phenomenon but rather elasto plastic in nature a first approximation flow law is proposed based on the cam clay constitutive model for soils

sedimentological evidence for the formation of an east antarctic ice sheet in eocene oligocene time middle eocene to late oligocene sediments recovered at ocean drilling program sites 689 and 690 on maud rise in the southernmost atlantic ocean and at sites 738 and 744 on kerguellen plateau in the southernmost indian ocean were analysed in order to study the depositional environment and the palaeoclimate special emphasis was placed on the reconstruction of the formation of a cryosphere on the antarctic continent the investigations include quantifications of carbonate and opal contents grain size analyses and studies of clay mineral assemblages the sedimentary sequence at all sites under investigation is highly pelagic with nannofossil oozes and chalks dominant the first indication of probable glacierization at sea level is in the form of isolated gravel and terrigenous sand grains which indicate ice rafting from middle eocene time at c 45 5 ma this is supported by enhanced concentrations of detrital chlorite and reworked kaolinite probably some glaciers reached the sea while most of the continent remained under the influence of a humid and warm to temperate climate the growth of the inland ice resulted in enhanced physical weathering and in increased contents of detrital chlorite and kaolinite from about 40 ma a strengthening of the glacial conditions and the onset of continental east antarctic glaciation is recorded in early oligocene sediments with an age of 36 ma all major sediment parameters document this event the clay mineralogy changed between c 36 3 ma and c 35 5 ma from smectite dominated assemblages to illite and chlorite dominated assemblages the latter being indicative of physical weathering under cooler climates large quantities of ice rafted gravel and sand accumulated on the kerguelen plateau between 36 0 ma and 35 8 ma at the same time an increase in opal content occurred as well as a decrease in carbonate the sediment parameters imply that the east antarctic continent was more or less totally buried beneath the ice during oligocene time the ice sheet however probably did not have a polar but a temperate character as indicated by the occurrence of nothofagus and relatively warm surface water temperatures prohibiting the long distance transport of debris by icebergs

east antarctic ice stream tributary underlain by major sedimentary basin marine and rift sediments exert a fundamental control on ice stream flow in the west antarctic ice sheet and hence on its mass balance and stability in contrast most ice streams in the much larger east antarctic ice sheet are thought to be relatively stable features resting on till perhaps underlain by crystalline rock any geological controls on east antarctic ice sheet enhanced flow remain largely unknown we present aerogeophysical evidence indicating that a region of enhanced ice flow in the interior of the east antarctic ice sheet is underlain by subglacial sediments 3 km thick and that these are influencing the flow regime of the overlying ice we show that subglacial sediments are important in modulating ice dynamics not just for the west antarctic ice sheet but also for its much larger neighbor and suggest that the sedimentary basin identified here may contain information on the neogene glacial history of this part of the east antarctic ice sheet

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

the contribution of discontinuous rock mass failure to glacier erosion geomechanical rock mass properties control the response of bedrock to applied stresses and can be summarized in a linear mohr coulomb equation which defines the principal parameters determining failure nevertheless in studying the erosion of bedrock by glacier ice little attention has been paid to failure criteria though a coincidence of erosion all and forms with fracture systems at regional and local scales has been demonstrated few studies have analysed the precise nature of the fracture geometry or proposed its mechanical impact in association with glacier ice this investigation proposes that since almost all bedrock possesses identifiable fracture systems the properties of discontinuous rock mass drm be regarded as defining primary conditions of stress and stability which are subsequently modified directly and indirectly by glacier ice consequent rock mass failure modes are prescribed by discontinuity geometry and applied stresses and evidence from north wales confirms the validity of the theoretical treatment of rock mass properties and explains the accordance of landforms with structure

subglacial geology in coats land east antarctica revealed by airborne magnetics and radar sounding during the austral summer of 2001 02 five thousand line kilometres of airborne radio echo sounding and aeromagnetic data were collected in the region of three tributaries of slessor glacier east antarctica which drains into the filchner ice shelf basal topography and roughness estimates were obtained from the echo sounding data which have been combined here with the subglacial geological units inferred from an analysis of the aeromagnetic data this analysis included euler and werner deconvolution to determine the location and depth of sills dykes and faults in addition we high pass filtered the magnetic anomaly profiles to obtain information about the near surface subglacial geology this revealed a prominent area of low magnetic susceptibility lying in a deep topographic basin underneath the northern tributary of slessor glacier forward and inverse magnetic models indicate that this area is likely underlain by a 3 km thick sedimentary basin ice flow modelling suggests that this sedimentary basin influences the ice dynamics in the tributary these results have important implications for understanding the dynamics of this and other east antarctic flow features that may be underlain by a weak sedimentary bed

basal conditions beneath enhanced flow tributaries of slessor glacier east antarctica radio echo sounding data are used to investigate bed roughness beneath the three enhanced flow tributaries of slessor glacier east antarctica slow moving inter tributary areas are found to have rough beds while the bed of the northernmost tributary is relatively smooth a reconstruction of potential subglacial drainage routing indicates that water would be routed down this tributary and investigations of basal topography following isostatic recovery reveal that the bed would have been below sea level in preglacial times so marine sediments may have accumulated here together these factors are further support for the dominance of basal motion in this tributary reported elsewhere conversely although the other two slessor tributaries may have water routed beneath them they would not have been below sea level before the growth of the ice sheet so cannot be underlain by marine sediments they are also found to be rough and within the range of uncertainties it is likely that basal motion does not play a major role in the flow of these tributaries perhaps the most interesting area however is a deep trough where flow rates are currently low but the bed is as smooth as the northern slessor trough it is proposed that although ice deformation currently dominates in this trough basal motion may have occurred in the past when the ice was thicker

flow laws for glacier ice comparison of numerical predictions and field measurements ice flow along the 20 km long strain network up stream of the dye 3 bore hole in greenland is studied in detail by solving the force balance equations and using selected flow laws stresses and strain rates are calculated throughout the section of the ice sheet the validity of the results is evaluated by comparison with the velocity profile derived from bore hole tilting measurements and with observed surface strain rates a number of constitutive relations are tried and most predict a velocity profile at the bore hole site that is in good agreement with that observed if appropriate enhancement factors are used however there are major discrepancies between modelled and measured surface strain rates use of nye s generalization of glen s flow law or an anisotropic constitutive relation requires unrealistically large along flow variations in the enhancement factor inclusion of normal stress effects can lead to much better agreement but it is possible that other processes such as dynamic recrystallization or primary creep should be included in the constitutive relation of polar ice

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

isotropic and anisotropic flow relations for ice dynamics a flow relation for the minimum strain rates for isotropic ice is presented this flow relation has been compiled from laboratory tests in shear and compression and covers the temperature and stress ranges typical of natural ice masses however the ice in natural ice masses is mostly anistropic three cores drilled at law dome antarctica are used as examples to illustrate some of the different anisotropies that develop in ice masses in relation to the stress configurations and accumulated strains for the shear or compression stress configurations anistropic flow rates can be derived as enhancements of the minimum isotropic flow rates for the particular stress temperature and stress configuration for compression this enhancement asymptotically approaches 3 for shear the enhancement may be as high as 8 for combinations of shear and compression further tests are required

widespread complex flow in the interior of the antarctic ice sheet it has been suggested that as much as 90 of the discharge from the antarctic ice sheet is drained through a small number of fast moving ice streams and outlet glaciers fed by relatively stable and inactive catchment areas here evidence obtained from balance velocity estimates suggests that each major drainage basin is fed by complex systems of tributaries that penetrate up to 1000 kilometers from the grounding line into the interior of the ice sheet this finding has important consequences for the modeled or estimated dynamic response time of past and present ice sheets to climate forcing

determining basal ice sheet conditions in the dome c region of east antarctica using satellite radar altimetry and airborne radio echo sounding large subglacial lakes manifest themselves as flat regions on the ice surface ers 1 satellite radar altimetry of the dome c region of east antarctica was analyzed to correlate unusually flat areas on the ice surface with known locations of subglacial lakes identified from airborne radio echo sounding res data the mean length of subglacial lakes which have an expression in the ice sheet surface was 8 3 km whilst those that did not exhibit a surface morphological manifestation had a mean length of 3 3 km thus lakes up to about 4 km in length are unlikely to be detected from satellite radar altimetry of the ice surface given that the spacing of radio echo flight tracks within the spri nsf tud antarctic database is 50 100 km in many areas a number ofsubglacial lakes probably lie undetected beneath the ice sheet res information from two large flat surface regions within dome c and a further flat area located at 80 s 127 e indicates the absence ofsubglacial lakes beneath the ice surface features however these areas are characterised by relatively strong radio echo returns which may indicate the presence of water saturated basal sediments we suggest that 1 blankets of water saturated basal sediments may cause similar surface morphological features to those produced by subglacial lakes and 2 misidentification ofsubglacial lakes from satellite altimeter observations of the ice sheet surface is possible without the support of res information relating to the ice sheet base furthermore our study indicates a lack of sub glacial lake signals from res data over relatively thick regions of east antarctica such as the adventure subglacial trough we conclude that subglacial water produced in such regions may be transported by a basal hydrological system driven by overburden pressure to less thick regions of the ice sheet where subglacial lakes have been identified

radar reflections reveal a wet bed beneath stagnant ice stream c and a frozen bed beneath ridge bc west antarctica digital airborne radar data were collected during the 1987 88 antarctic field season in nine gridded blocks covering the downstream portions of ice stream b 6 km spacing and ice stream c 11 km spacing together with a portion of ridge bc between them an automated processing procedure was used for picking onset times of the reflected radar pulses converting travel times to distances interpolating missing data converting pressure transducer readings correcting navigational drift performing crossover analysis and zeroing remanent crossover errors interpolation between flight lines was carried out using the minimum curvature method maps of ice thickness estimated accuracy 20 m and basal reflection strength estimated accuracy 1 db were produced the ice thickness map confirms the characteristics of previous reconnaissance maps and reveals no new features the reflection strength map shows pronounced contrasts between the ice streams and ridge bc and between the two ice streams themselves we interpret the reflection strengths to mean that the bed of ice stream c as well as that of ice stream b is unfrozen that the bed of ridge bc is frozen and that the boundary between the frozen bed of ridge bc and the unfrozen bed of ice stream c lies precisely below the former shear margin of the ice stream

changes in the west antarctic ice sheet the portion of the west antarctic ice sheet that flows into the ross sea is thinning in some places and thickening in others these changes are not caused by any current climatic change but by the combination of a delayed response to the end of the last global glacial cycle and an internal instability the near future impact of the ice sheet on global sea level is largely due to processes internal to the movement of the ice sheet and not so much to the threat of a possible greenhouse warming thus the near term future of the ice sheet is already determined however too little of the ice sheet has been surveyed to predict its overall future behavior

basal topography and ice flow in the bailey slessor region of east antarctica an airborne radio echo sounding campaign carried out in the upper reaches of bailey ice stream and slessor glacier in coats land east antarctica has revealed that tributaries of enhanced flow lie within well defined basal troughs and are separated from each other by bed highs these new data indicate significant differences in ice thickness compared with those estimated in the bedmap database a numerical modeling study has revealed that driving stresses are high enough to account for flow by ice deformation alone in intertributary areas most flow in the enhanced flow tributaries of slessor glacier may also be explained by ice deformation alone however although ice deformation is also significant in the bailey ice stream tributary a large amount of basal motion is also required to fully explain flow velocities here it is proposed that the trough in which bailey tributary lies is sufficiently deep that marine sediments may have accumulated here in preglacial times along with water produced by geothermal heating frictional heating and through a reduction in the pressure melting point basal motion may therefore be facilitated by the presence of a deformable saturated till layer at the bed

influence of subglacial geology on the position of a west antarctic ice stream from seismic observations ice streams drain much of the interior west antarctic ice sheet and buffer the main ice reservoir from oceanic influences1 2 the slow flowing interior feeds the floating ross ice shelf with ice via fast flowing ice streams3 that are believed to modulate sea level change through their control of inland ice storage understanding ice stream behaviour and predicting the response to climate change4 requires a better knowledge of the subglacial geology5 6 it is known that a thawed ice bed and high pressure basal water are necessary but not sufficient conditions to cause ice streaming7 8 moreover it has been hypothesized that a soft sedimentary bed is also required because of its intrinsic low frictional resistance to flow9 and owing to its high erodibility so as to generate till that can deform and lubricate ice motion10 11 or to bury rough features and smooth the bed for sliding here we use seismic observations to provide evidence that one margin of the upglacier part of an ice stream is directly above the boundary of a basin with such sedimentary fill the ice stream is within the basin and the ice outside the basin is slow flowing the basin fill presents an order of magnitude lower frictional resistance to ice flow than the subglacial material outside the basin we conclude that the ice stream position is dependent on subglacial geology

the possible transition from glacial surge to ice stream on vavilov ice cap an edited version of this paper was published by agu copyright 2019 american geophysical union

spatial variation of englacial radar attenuation modeling approach and application to the vostok flowline 1 constraining the spatial variation of englacial radar attenuation is critical for accurate inference of the spatial variation of the englacial and basal properties of ice sheets from radar returned power here we evaluate attenuation models that account for spatial variations in ice temperature and chemistry and test them along the flowline that passes through the vostok ice core site antarctica the simplest model often used but rarely valid assumes a uniform attenuation rate everywhere along the flowline so that total attenuation is proportional to ice thickness the next simplest model uses spatially varying temperatures predicted by an ice flow model and assumes uniform chemistry additional models account for spatially varying chemistry using englacial stratigraphy we find that the roundtrip attenuation to the bed can easily differ by 10 db or more between the uniform attenuation rate model and models that account for variable ice temperature such differences are sufficient to confound the delineation of dry and wet beds also including spatial variations in chemistry produces smaller differences 10 db but the magnitude of these differences depends on the relative importance of dry and wet deposition of impurities in the past accounting for dry deposited impurities requires ice flow modeling and results in larger differences from all other models which assume uniform chemistry or wet deposition only these results indicate that modeling the spatial variation of attenuation requires a spatially varying temperature model in order to infer bed conditions from bed returned power accurately and that both ice core data and radar stratigraphy are also strongly desirable

comparison of organic uk 37 texh86 ldi and faunal proxies foraminiferal assemblages for reconstruction of late quaternary sea surface temperature variability from offshore southeastern australia several proxies have been developed to reconstruct past sea surface temperature sst but different proxies may reflect temperatures of different seasons and each proxy is characterized by certain uncertainties therefore a multiproxy approach is preferred to precisely reconstruct sst here we reconstruct sst of the ocean offshore southeastern australia murray canyons area for the last 135 ka using three independent organic proxies texh86 based on glycerol dialkyl glycerol tetraethers gdgts uk 37 based on alkenones and ldi based on long chain diols in addition to foraminiferal faunal assemblages the organic proxy records show similar trends with the highest temperature 21 c for uk 37 and texh86 and 25 c for ldi during the last interglacial and lowest temperature 8 c for texh86 10 c for uk 37 and 12 c for ldi during the last glacial maximum however the differences in absolute sst estimates obtained by the organic proxies varied over time with differences of up to 9 c between ldi and texh86 the seasonal sst reconstructions based on the modern analogue of foraminiferal assemblages also show similar trends as the organic proxies with highest temperatures during the last interglacial 23 c for the warmest month sst 20 c for mean annual and 18 c for the coolest month and lowest temperature during the last glacial maximum 14 c for the warmest month 11 c for mean annual and 9 c for the coolest month down core comparison between the reconstructed ssts of the organic and inorganic proxies shows that ldi inferred temperatures compare well with the temperature of the warmest month texh86 with the temperature of the coolest month and uk 37 with mean annual temperature an increase in texh86 sst estimates relative to those of other proxies during deglaciations and interglacials suggests that either winter temperatures rapidly warmed possibly due to an invigoration of the leeuwin current over the core site or there was a change in the growth season of the thaumarchaeota the source organism of gdgts our study shows the benefits of a multiproxy approach in the interpretation of sst proxies leading to a more robust knowledge of past ocean temperature changes