high poisson s ratio of earth s inner core explained by carbon alloying earth s core exhibits similar elastic properties to rubber experiments show that a high pressure phase of iron carbide modifies iron s elastic properties under inner core conditions suggesting that carbon is the light element in the core

sound velocity measurements in dhcp feh up to 70 gpa with inelastic x ray scattering implications for the composition of the earth s core abstract we have determined the density evolution of the sound velocity of dhcp fehx x 1 up to 70 gpa at room temperature by inelastic x ray scattering and by x ray diffraction we find that the variation of vp with density is different for the ferromagnetic and nonmagnetic dhcp fehx and that only nonmagnetic dhcp fehx follows birch s law combining our results with birch s law for iron and assuming an ideal two component mixing model we obtain an upper bound of the hydrogen content in the earth s inner core 0 23 6 wt h corresponding to feh0 13 3 the iron alloy with 0 23 6 wt h can satisfy the density and compressional and shear sound velocities of the prem inner core assuming that there are no other light elements in the inner core

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

little ice age cold interval in west antarctica evidence from borehole temperature at the west antarctic ice sheet wais divide 1 the largest climate anomaly of the last 1000 years in the northern hemisphere was the little ice age lia from 1400 1850 c e but little is known about the signature of this event in the southern hemisphere especially in antarctica we present temperature data from a 300 m borehole at the west antarctic ice sheet wais divide results show that wais divide was colder than the last 1000 year average from 1300 to 1800 c e the temperature in the time period 1400 1800 c e was on average 0 52 0 28 c colder than the last 100 year average this amplitude is about half of that seen at greenland summit grip this result is consistent with the idea that the lia was a global event probably caused by a change in solar and volcanic forcing and was not simply a seesaw type redistribution of heat between the hemispheres as would be predicted by some ocean circulation hypotheses the difference in the magnitude of the lia between greenland and west antarctica suggests that the feedbacks amplifying the radiative forcing may not operate in the same way in both regions

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

experimental constraints on the sound velocities of cementite fe3c to core pressures abstract sound velocities of cementite fe3c have been measured up to 1 5 mbar and at 300 k in a diamond anvil cell using the nuclear resonant inelastic x ray scattering nrixs technique from the partial phonon density of states pdos and equation of state eos of fe3c we derived its elastic parameters including shear modulus compressional v p and shear wave v s velocities to core pressures a pressure induced spin pairing transition in the powdered fe3c sample was found to occur gradually between 10 and 50 gpa by the x ray emission spectroscopy xes measurements following the completion of the spin pairing transition the v p and v s of low spin fe3c increased with pressure at a markedly lower rate than its high spin counterpart our results suggest that the incorporation of carbon in solid iron to form iron carbide phases fe3c and fe7c3 could effectively lower the v s but respectively raise the poisson s ratio by 0 05 and 0 07 to approach the seismically observed values for the earth s inner core the comparison with the preliminary reference earth model prem implies that an inner core composition containing iron and its carbon rich alloys can satisfactorily explain the observed seismic properties of the inner core

a new high precision borehole temperature logging system used at gisp2 greenland and taylor dome antarctica we describe a high precision 0 1 1 0 mk borehole temperature bt logging system developed at the united states geological survey usgs for use in remote polar regions we discuss calibration operational and data processing procedures and present an analysis of the measurement errors the system is modular to facilitate calibration procedures and field repairs by interchanging logging cables and temperature sensors measurements can be made in either shallow air filled boreholes or liquid filled holes up to 7 km deep data can be acquired in either incremental or continuous logging modes the precision of data collected by the new logging system is high enough to detect and quantify various thermal effects at the milli kelvin level to illustrate this capability we present sample data from the 3 km deep borehole at gisp2 greenland and from a 130m deep air filled hole at taylor dome antarctica the precision of the processed gisp2 continuous temperature logs is 0 25 0 34 mk while the accuracy is estimated to be 4 5 mk the effects of fluid convection and the dissipation of the thermal disturbance caused by drilling the borehole are clearly visible in the data the precision of the incremental taylor dome measurements varies from 0 11 to 0 32 mk depending on the wind strength during the experiments with this precision we found that temperature fluctuations and multi hour trends in the bt measurements correlate well with atmospheric pressure changes

elastic anisotropy in textured hcp iron to 112 gpa from sound wave propagation measurements we report the first experimental determination of elastic anisotropy in highly textured polycrystalline hexagonal closed packed hcp iron obtained at room temperature and 112 gpa by inelastic x ray scattering ixs in a diamond anvil cell dac the compressional sound velocity vp at 50 and 90 from the c axis was determined to be vp 50 9900 200 m s and vp 90 9450 150 m s respectively the difference of 4 5 between the two velocities is of the same order of the seismic observations of the anisotropy in earth s inner core combining our new results with the equation of state of hcp iron we derive the pressure dependence of the shear velocity vs the vs values extrapolated to inner core densities are 30 higher than the prem results the extrapolated vp values are instead in fair agreement with the prem seismic model though differences in the slope remain furthermore assuming a strong texture characterized by cylindrical symmetry we provide an estimate for the single crystal elastic modulus c11 as a function of pressure while our results are in general agreement with the predominant existence of hcp iron in earth s inner core the remaining differences might be assigned to the presence of another solid iron phase light elements or liquid inclusions as well as anharmonic high temperature effects

twentieth century sea ice trends in the ross sea from a high resolution coastal ice core record we present the first proxy record of sea ice area sia in the ross sea antarctica from a 130 year coastal ice core record high resolution deuterium excess data show prevailing stable sia from the 1880s until the 1950s a 2 5 reduction from the mid 1950s to the early 1990s and a 5 increase after 1993 additional support for this reconstruction is derived from ice core methanesulphonic acid concentrations and whaling records while sia has continued to decline around much of the west antarctic coastline since the 1950s concurrent with increasing air and ocean temperatures the underlying trend is masked in the ross sea by a switch to positive sia anomalies since the early 1990s this increase is associated with a strengthening of southerly winds and the enhanced northward advection of sea ice

recent surface temperature trends in the interior of east antarctica from borehole firn temperature measurements and geophysical inverse methods 1 we use measured firn temperatures down to depths of 80 to 90 m at four locations in the interior of dronning maud land east antarctica to derive surface temperature histories spanning the past few decades using two different inverse methods we find that the mean surface temperatures near the ice divide the highest elevation ridge of east antarctic ice sheet have increased approximately 1 to 1 5 k within the past 50 years although the onset and rate of this warming vary by site histories at two locations nus07 5 78 65 s 35 64 e and nus07 7 82 07 s 54 89 e suggest that the majority of this warming took place in the past one or two decades slight cooling to no change was indicated at one location nus08 5 82 63 s 17 87 e off the divide near the recovery lakes region in the most recent decade inversion results indicate both cooler and warmer periods at different sites due to high interannual variability and relatively high resolution of the inverted surface temperature histories the overall results of our analysis fit a pattern of recent climate trends emerging from several sources of the antarctic temperature reconstructions there is a contrast in surface temperature trends possibly related to altitude in this part of east antarctica

the effect of ferromagnetism on the equation of state of fe3c studied by first principles calculations first principles calculations have been used to determine the equation of state of fe3c in both its low pressure magnetically ordered and high pressure non magnetically ordered states at 0 k the ferromagnetic transition was found to occur at about 60 gpa in the high pressure non magnetically ordered regime at 0 k the material may be described by a birch murnaghan third order equation of state with v 0 8 968 7 angstrom 3 per atom k 0 316 62 2 gpa and k 4 30 2 at atmospheric pressure the ferromagnetic phase transition in fe3c occurs at similar to483 k preliminary measurements of the thermal expansion by powder neutron diffraction show that this transition produces a large effect on thermoelastic properties the volumetric thermal expansion coefficient in the paramagnetic phase was found to be 4 34 x 10 5 k 1 at t similar to 550 k by applying a thermal expansion correction to the calculated equation of state at 0 k predicted values for the density and adiabatic incompressibility of this material at core pressures and temperatures were obtained these results appear to be sufficiently different from seismological data so as to preclude fe3c as the major inner core forming phase c 2002 elsevier science b v all rights reserved

ab initio calculations of the elasticity of iron and iron alloys at inner core conditions evidence for a partially molten inner core abstract ab initio finite temperature molecular dynamics simulations have been used to calculate the elasticity of hcp fe bcc fe fes and fesi at core conditions the calculated compressional wave velocities are in excellent agreement with the most recent experimental data however the calculated shear wave velocities of all phases studied are significantly higher than those inferred from seismology this discrepancy can only be explained if the inner core is partially molten containing more than 8 liquid

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

implicit ice in the global theory of glacial isostatic adjustment the inference of ice sheet paleo topography with respect to sea level is herein shown to require accounting for an accurately calculable additional ice mass beyond that which is explicitly required as input to the integral equation for relative sea level history

terminating the 100 kyr ice age cycle we report a simulation of the most recent 100 000 year glaciationdeglaciation cycle of the late pleistocene ice age a simulation that delivers an ice sheet chronology that is in close accord with that inferred from the geological record our analyses are performed with a reduced model of the climate system that incorporates significant improvements to the representation of both climate forcing and mass balance response in a previously described theory based upon a coupled one level energy balance model ebm and vertically integrated ice sheet model ism the theory fully incorporates the influences of orbital insolation forcing glacial isostatic adjustment and variations in the atmospheric concentrations of greenhouse gases it correctly predicts the main geographical regions of the northern hemisphere that were glaciated at last glacial maximum 21 000 years ago as well as the abrupt termination of the glacial epoch that occurred subsequently the latter feature of the ice age cycle is obtained without the need to incorporate unconstrained and therefore controversial physical processes into the model a limitation of all previous attempts to understand this global scale climate cycle our analyses suggest that the radiative impact on surface glaciation due to the changing atmospheric concentration of co2 is critical to the ability of the model to deliver a synthetic history of glaciation and deglaciation that is in accord with inferences based upon surface geological and geomorphological evidence with the incorporation of this influence model predicted ice thickness distributions at last glacial maximum lgm are very similar to those of the recently described ice 4g reconstruction that was based upon the inversion of postglacial relative sea level histories

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

mantle viscosity and ice age ice sheet topography ice age paleotopography and mantle viscosity can both be inferred from observations of earth s response to the most recent deglaciation event of the current ice age this procedure requires iterative application of a theoretical model of the global process of glacial isostatic adjustment results demonstrate that the iterative inversion procedure converges to a paleotopography that is extremely close to that from the ice 4g model the accompanying mantle viscosity profile is furthermore shown to reconcile the requirements of aspherical geoid anomalies related to the mantle convection process thus resolving a fundamental issue concerning mantle rheology the combined model also explains postglacial sea level histories for the east coast of the united states

twentieth century surface temperature trends in the western ross sea antarctica evidence from a high resolution ice core abstracta 125 yr ice core record of climate from the whitehall glacier ice divide provides exceptionally high resolution stable isotope data from the northwest margin of the ross sea antarctica this is the only proxy data available to extend the instrumental record of temperature in this region where little is known about climate variability over the past two centuries using ecmwf interim re analysis era interim data this study develops a precipitation weighted 18o temperature transfer function of 0 62 c 1 which is comparable to other proximal ice cores such as taylor talos and law domes reconstructed mean annual temperatures show no significant change between 1882 and 2006 however a decrease in cold season april september amjjas temperatures of 1 59 0 84 c decade 1 at 90 confidence is observed since 1979 this cooling trend is in contrast to a surface temperature record from ross island scott base where significant spring warming is observed it is also coincident with a pos

magnitude and temporal evolution of dansgaard oeschger event 8 abrupt temperature change inferred from nitrogen and argon isotopes in gisp2 ice using a new least squares inversion abstract polar temperature is often inferred from water isotopes in ice cores however non temperature effects on 18 o are important during the abrupt events of the last glacial period such as changes in the seasonality of precipitation the northward movement of the storm track and the increase in accumulation these effects complicate the interpretation of 18 o as a temperature proxy here we present an independent surface temperature reconstruction which allows us to test the relationship between 18 o ice and temperature during dansgaard oeschger event 8 38 2 thousand yrs ago using new 15 n and 40 ar data from the gisp2 ice core in greenland this temperature reconstruction relies on a new inversion of inert gas isotope data using generalized least squares and includes a robust uncertainty estimation we find that both temperature and 18 o increased in two steps of 20 and 140 yrs with an overall amplitude of 11 80 1 8 c between the stadial and interstadial centennial mean temperature the coefficient d o 18 d t changes with each time segment which shows that non temperature sources of fractionation have a significant contribution to the 18 o signal when measured on century averaged values we find that d o 18 d t 0 32 0 06 c which is similar to the glacial holocene value of 0 328 c

multidecadal variability of atmospheric methane 1000 1800 c e 1 we present a new high precision high resolution record of atmospheric methane from the west antarctic ice sheet wais divide ice core covering 1000 1800 c e a time period known as the late preindustrial holocene lpih the results are consistent with previous measurements from the law dome ice core the only other high resolution record of methane for this time period and confirm most of the observed variability multidecadal variability in methane concentrations throughout the lpih is weakly correlated or uncorrelated with reconstructions of temperature and precipitation from a variety of geographic regions correlations with temperature are dominated by changes in northern hemisphere high latitude temperatures between 1400 and 1600 c e during the onset of the little ice age times of war and plague when large population losses could have reduced anthropogenic emissions are coincident with short periods of decreasing global methane concentrations

eight centuries of volcanic signal and climate change at talos dome east antarctica 1 during the 1996 programma nazionale di ricerche in antartide international trans antarctic scientific expedition traverse two firn cores were retrieved from the talos dome area east antarctica at elevations of 2316 m td 89 m long and 2246 m st556 19 m long cores were dated by using seasonal variations in non sea salt nss so42 concentrations coupled with the recognition of tritium marker level 1965 1966 and nss so42 spikes due to the most important volcanic events in the past pinatubo 1991 agung 1963 krakatoa 1883 tambora 1815 kuwae 1452 unknown 1259 the number of annual layers recognized in the td and st556 cores was 779 and 97 respectively the d record obtained from the td core has been compared with other east antarctic isotope ice core records dome c epica south pole taylor dome these records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries which might be related to the little ice age lia cold period because of the high degree of geographical variability the strongest lia cooling was not temporally synchronous over east antarctica and the analyzed records do not provide a coherent picture for east antarctica the accumulation rate record presented for the td core shows a decrease during part of the lia followed by an increment of about 11 in accumulation during the 20th century at the st556 site the accumulation rate observed during the 20th century was quite stable

rapid recent warming on rutford ice stream west antarctica from borehole thermometry 1 the antarctic peninsula has warmed faster than the global average rate of warming during the last century due to limited availability of long term meteorological records the geographical extent of this rapid warming is poorly defined we collected borehole temperature measurements in the upper 300 m of rutford ice stream west antarctica and employed an inverse modeling scheme with a heat diffusion advection equation to determine the recent surface temperature history of the borehole position our results reveal recent warming of 0 17 0 07 c decade 1 since 1930 this result suggests that at least in an attenuated form the rapid warming observed over the antarctic peninsula extends as far south as rutford ice stream this result agrees with other recent results that show a warming trend across much of the west antarctic ice sheet

new reconstruction of antarctic near surface temperatures multidecadal trends and reliability of global reanalyses a reconstruction of antarctic monthly mean near surface temperatures spanning 1958 2012 is presented itsprimarygoalistotakeadvantageofarecentlyrevisedkeytemperaturerecordfromwestantarctica byrd to shed further light on multidecadal temperature changes in this region the spatial interpolation relies on a kriging technique aided by spatiotemporal temperature covariances derived from three global reanalyses the european centre for medium range weather forecasts ecmwf interim re analysis erainterim modern era retrospective analysis for research and applications merra and climate forecast system reanalysis cfsr for 1958 2012 the reconstruction yields statistically significant annual warming in the antarctic peninsula and virtually all of west antarctica but no significant temperature change in east antarctica importantly the warming is of comparable magnitude both in central west antarctica and in most of the peninsula rather than concentrated either in one or the other region as previousreconstructions have suggested the transantarctic mountains act for the temperature trends as a clear dividing line between east and west antarctica reflecting the topographic constraint on warm air advection from the amundsen sea basin the reconstruction also serves to highlight spurious changes in the 1979 2009 time series of the three reanalyses that reduces the reliability of their trends illustrating a longstanding issue in high southern latitudes the study concludes with an examination of the influence of the southern annular mode sam on antarctic temperature trends the results herein suggest that the trend of the sam toward its positive phase in austral summer and fall since the 1950s has had a statistically significant cooling effect not only in east antarctica as already well documented and but also only in fall in west antarctica

expression of the bipolar see saw in antarctic climate records during the last deglaciation ice core records of climate from greenland and antarctica show asynchronous temperature variations on millennial timescales during the last glacial period 1 the warming during the transition from glacial to interglacial conditions was markedly different between the hemispheres a pattern attributed to the thermal bipolar see saw 2 however a record from the ross sea sector of east antarctica has been suggested to be synchronous with northern hemisphere climate change 3 here we present a temperature record from the talos dome ice core also located in the ross sea sector we compare our record with ice core analyses from greenland based on methane synchronization 4 and find clearly asynchronous temperature changes during the deglaciation we also find distinct differences in antarctic records pointing to differences in the climate evolution of the indo pacific and atlantic sectors of antarctica in the atlantic sector we find that the rate of warming slowed between 16 000 and 14 500 years ago parallel with the deceleration of the rise in atmospheric carbon dioxide concentrations and with a slight cooling over greenland in addition our chronology supports the hypothesis that the cooling of the antarctic cold reversal is synchronous with the bolling allerod warming in the northern hemisphere 14 700 years ago 5 the period from about 8 to 25kyr before present bp includes the climate transition from the last glacial to the holocene as documented from polar ice cores and other climate archives the pattern of climate changes throughout this transition is different between antarctica and the surrounding southern ocean and the northern hemisphere the steady antarctic deglacial warming reaches a first maximum antarctic isotopic maximum aim1 ref 1 followedbyaninterruptiontowardscoolerconditionsduring the antarctic cold reversal acr conversely greenland records show two rapid warming phases at the onset of the dansgaard oeschger 1 do1 event bllingaller dinterstadial b a andthe

satellite data analysis and numerical simulation of tropical cyclone formation 1 forecast of tropical cyclone tc formation has long been a great challenge owing to lack of reliable observations over vast open oceans recent satellite products provide a unique opportunity to reveal detailed atmospheric wave structures prior to tc formation using the quikscat surface wind and the tropical rainfall measurement mission microwave image data we document temporal and spatial structures of rossby wave trains induced by energy dispersion from a pre existing tc and easterly wave propagation characteristics prior to cyclogenesis in the western north pacific using a baroclinic model we further simulate cyclogenesis processes associated with the tc energy dispersion and easterly waves