extreme detached dust layers near martian volcanoes evidence for dust transport by mesoscale circulations forced by high topography modeling suggests that thermal circulations over mars s highest volcanoes transport water vapor and dust from the surface into the middle atmosphere forming detached layers in these constituents intense vertical mixing also takes place in regional and global dust storms which can generate detached layers that are extreme in both altitude and magnitude here we employ observations by the mars climate sounder mcs on board mars reconnaissance orbiter taking advantage of improved vertical coverage in mcs s aerosol retrievals to discover a new class of extreme detached dust layers eddls observed during minimal dust storm activity and furthermore distinguished by their potentially large and measurable horizontal extent 1000 km these eddls cluster near olympus mons and the tharsis montes from which they likely originate the existence of these eddls suggests that vertical mixing by topographic circulations can be much stronger than previously modeled and more frequent than previously observed

clues to variability in arctic minimum sea ice extent received 11 august 2005 revised 20 september 2005 accepted 26 september 2005 published 2 november 2005 1 perennial sea ice is a primary indicator of arctic climate change since 1980 it has decreased in extent by about 15 analysis of new satellite derived fields of winds radiative forcing and advected heat reveals distinct regional differences in the relative roles of these parameters in explaining variability in the northernmost ice edge position in all six peripheral seas studied downwelling longwave flux anomalies explain the most variability approximately 40 while northward wind anomalies are important in areas north of siberia particularly earlier in the melt season anomalies in insolation are negatively correlated with perennial ice retreat in all regions suggesting that the effect of solar flux anomalies is overwhelmed by the longwave influence on ice edge position citation francis j a e hunter j r key and x wang 2005 clues to variability in arctic minimum sea ice extent geophys res lett 32 l21501 doi 10 1029 2005gl024376

increased surface ocean heating by colored detrital matter cdm linked to greater northern hemisphere ice formation in the gfdl cm2mc esm abstractrecent observations of arctic ocean optical properties have found that colored dissolved organic matter cdom is of primary importance in determining the nonwater absorption coefficient of light in this region although cdom is an important optical constituent in the arctic ocean it is not included in most of the current generation of earth system models esms in this study model runs were conducted with and without light attenuation by colored detrital matter cdm the combined optical contribution of cdom and nonalgal particles the fully coupled gfdl cm2 with modular ocean model version 4p1 mom4p1 at coarse resolution cm2mc esm was used to examine the differences in heating and ice formation in the high northern latitudes the annual cycle of sea surface temperature sst is amplified in the model run where the optical attenuation by cdm is included annually averaged integrated ice mass is 5 greater and total ice extent is 6 greater owing to colder wintertime ssts differences in o

hyperspectral imaging of convective co2 ice clouds in the equatorial mesosphere of mars 1 a unique feature of the martian climate is the possibility for carbon dioxide the main atmospheric constituent to condense as ice co2 ice is usually detected as frost but is also known to exist as clouds this paper presents the first unambiguous observation of co2 ice clouds on mars these images were obtained by the visible and near infrared imaging spectrometer omega on board mars express the data set encompasses 19 different occurrences compositional identification is based on the detection of a diagnostic spectral feature around 4 26 m which is produced by resonant scattering of solar photons by mesospheric co2 ice particles in a spectral interval otherwise dominated by saturated gaseous absorption observed clouds exhibit a strong seasonal and geographic dependence concentrating in the near equatorial regions during two periods before and after northern summer solstice ls 45 and 135 radiative transfer modeling indicates that the 4 26 m feature is very sensitive to cloud altitude opacity and particle size thereby explaining the variety of spectra associated with the cloud images on two orbits the simultaneous detection of clouds with their shadow provides straightforward and robust estimates of cloud properties these images confirm the conclusions established from modeling clouds are thick with normal opacities greater than 0 2 in the near infrared and are lofted in the mesosphere above 80 km the mean radius of co2 ice crystals is found to exceed 1 m an unexpected value considering this altitude range this finding implies the existence of high altitude atmospheric updrafts which are strong enough to counteract the rapid gravitational fall of particles this statement is consistent with the cumuliform morphology of the clouds which may be linked to a moist convective origin generated by the latent heat released during co2 condensation

a 21 year record of arctic sea ice extents and their regional seasonal and monthly variability and trends satellite passive microwave data have been used to calculate sea ice extents over the period 1979 1999 for the north polar sea ice cover as a whole and for each of nine regions over this 21 year time period the trend in yearly average ice extents for the ice cover as a whole is 32 900 6 100 sq km yr 2 7 0 5 decade indicating a reduction in sea ice coverage that has decelerated from the earlier reported value of 34 000 8 300 sq km yr 2 8 0 7 decade for the period 1979 1996 regionally the reductions are greatest in the arctic ocean the kara and barents seas and the seas of okhotsk and japan whereas seasonally the reductions are greatest in summer for which season the 1979 1999 trend in ice extents is 41 600 12 900 sq km yr 4 9 1 5 decade on a monthly basis the reductions are greatest in july and september for the north polar ice cover as a whole in september for the arctic ocean in june and july for the kara and barents seas and in april for the seas of okhotsk and japan only two of the nine regions show overall ice extent increases those being the bering sea and the gulf of st lawrence for neither of these two regions is the increase statistically significant whereas the 1079 1999 ice extent decreases are statistically significant at the 99 confidence level for the north polar region as a whole the arctic ocean the seas of okhotsk and japan and hudson bay

marsis remote sounding of localized density structures in the dayside martian ionosphere a study of controlling parameters enhanced topside electron densities in the dayside martian ionosphere have been repetitively observed in areas of near radial crustal magnetic fields for periods of tens of days indicating their long term spatial and temporal stability despite changing solar wind conditions we perform a statistical study of these density structures using the ionospheric mode of the mars advanced radar for subsurface and ionosphere sounding marsis onboard mars express we estimate the apparent extents of these structures relative to the altitude of the surrounding ionosphere the apex of the density structures often lies higher than the surrounding ionosphere median vertical extent of 18 km which indicates upwellings these structures are much wider than they are high with latitudinal scales of several degrees the radar reflector regions are observed above both moderate and strong magnetic anomalies and their precise locations and latitudinal extents match quite well with the locations and latitudinal extents of magnetic structures of given magnetic polarity oblique to vertical fields which happen to be regions where the field lines are open part of the time the majority of the density structures occur in regions where ionospheric plasma is dominant indicating closed field regions shielded from shocked solar wind plasma

atmospheric forcing on the barents sea winter ice extent abstract the atmospheric forcing on the barents sea ice extent during winter december february djf has been investigated for the period 1967 2002 the time series for the sea ice extent is updated and includes the winter of 2005 which marks a new record low in the wintertime barents sea ice extent and a linear trend of 3 5 decade 1 in the ice extent was found covariability between the barents sea ice extent and the atmospheric mean seasonal flow and the synoptic cyclones has been discussed separately for the mean flow linear correlations and regression analysis reveal that anomalous northerly southerly winds prevail in the nordic seas during winters with extensive sparse barents sea ice extent some of the variability in the mean flow is captured by the north atlantic oscillation nao however the wintertime link between the barents sea ice extent and the nao is moderate by studying the cyclone activity in the high latitude northern hemisphere using a dataset of individual cyclones two

oblique reflections in the mars express marsis data set stable density structures in the martian ionosphere the mars advanced radar for subsurface and ionospheric sounding marsis onboard the european space agency s mars express mex spacecraft routinely detects evidence of localized plasma density structures in the martian dayside ionosphere such structures likely taking the form of spatially extended elevations in the plasma density at a given altitude give rise to oblique reflections in the active ionospheric sounder data these structures are likely related to the highly varied martian crustal magnetic field in this study we use the polar orbit of mex to investigate the repeatability of the ionospheric structures producing these anomalous reflections examining data taken in sequences of multiple orbits which pass over the same regions of the martian surface under similar solar illuminations within intervals lasting tens of days presenting three such examples or case studies we show for the first time that these oblique reflections are often incredibly stable indicating that the underlying ionospheric structures are reliably reformed in the same locations and with qualitatively similar parameters the visibility or lack thereof of a given oblique reflection on a single orbit can generally be attributed to variations in the crustal field within the ionosphere along the spacecraft trajectory we show that within these examples oblique reflections are generally detected whenever the spacecraft passes over regions of intense near radial crustal magnetic fields i e with a cusp like configuration the apparent stability of these structures is an important feature that must be accounted for in models of their origin

hf radio wave attenuation due to a meteoric layer in the atmosphere of mars in the atmosphere of mars the effect of an ionospheric layer of meteoric origin on an hf radio wave propagation is investigated we consider the putative magnesium ion layer which results from the ablation of sporadic meteors from a work recently published to account for day night variability two electron profiles are considered in an altitude range around 80 km first we argue that there may be some observational evidence of this magnesium layer in early mars observations that were not noticed before then we study the effect of this ionospheric layer on the attenuation of hf waves for a propagation path through the ionosphere as envisaged for hf subsurface sounding on future mars missions the one way attenuation may range from up to 360 db s at 1 8 mhz and up to 18 db s at 9 mhz

plasma observations during the mars atmospheric plume event of march april 2012 we present initial analyses and conclusions from plasma observations made during the reported mars plume event of march april 2012 during this period multiple independent amateur observers detected a localized high altitude plume over the martian dawn terminator the cause of which remains to be explained the estimated brightness of the plume exceeds that expected for auroral emissions and its projected altitude greatly exceeds that at which clouds are expected to form we report on in situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by mars express obtained over the same surface region but at the opposing terminator measurements in the ionosphere at the corresponding location frequently show a disturbed structure though this is not atypical for such regions with intense crustal magnetic fields we tentatively conclude that the formation and or transport of this plume to the altitudes where it was observed could be due in part to the result of a large interplanetary coronal mass ejection icme encountering the martian system interestingly we note that the only similar plume detection in may 1997 may also have been associated with a large icme impact at mars

modeled winter sea ice variability and the north atlantic oscillation a multi century perspective the relationship between winter sea ice vari ability and the north atlantic oscillation nao is examined for the time period 1860 2300 this study uses model output to extend recently reported observational results to multi century time scales nine ensemble members are used in two global climate models with forcing evolving from pre industrial conditions through the so called a1b scenario in which carbon dioxide stabilizes at 720 ppm by 2100 throughout the nao generates an east west dipole pattern of sea ice concentration sic anomalies with oppositely signed centers of action over the labrador and barents seas during the positive polarity of the nao sic increases over the labrador sea due to wind driven equatorward advection of ice and sic decreases over the barents sea due to wind driven poleward transport of heat within the mixed layer of the ocean although this nao driven sic variability pattern can always be detected it accounts for a markedly varying fraction of the total sea ice variability depending on the strength of the forced sea ice extent trend for the first half of the 20th century or 1990 control conditions the nao driven sic pattern accounts for almost a third of the total sic var iance in the context of the long term winter sea ice retreat from 1860 to 2300 the nao driven sic pattern is robustly observable but accounts for only 2 of the total sic vari ance the nao driven sic dipole retreats poleward with the retreating marginal ice zone and its barents sea center of action weakens results presented here underscore the idea that the nao s influence on arctic climate is robustly observable but time dependent in its form and statistical importance

variability of north pacific sea ice and east asia north pacific winter climate abstract sea ice variability in the north pacific and its associations with the east asia north pacific winter climate were investigated using observational data two dominant modes of sea ice variability in the north pacific were identified the first mode features a dipole pattern between the sea of okhotsk and the bering sea the second mode is characterized by more uniform ice changes throughout the north pacific using the principal components of the two dominant modes as the indices pc1 and pc2 analyses show that the positive phases of pc1 feature a local warming cooling in the sea of okhotsk the bering sea which is associated with the formation of the anomalous anticyclone extending from the northern pacific to siberia accompanied by a weakening of the east asian jet stream and trough the associated anomalous southeasterlies easterlies reduce the climatological northwesterlies westerlies leading to warm and wet conditions in northeast china and central siberia the positive phases of pc2

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

30 year satellite record reveals contrasting arctic and antarctic decadal sea ice variability a 30 year satellite record of sea ice extents derived mostly from satellite microwave radiometer observations reveals that the arctic sea ice extent decreased by 0 30 0 03 x 10 exp 6 square kilometers per 10 yr from 1972 through 2002 but by 0 36 plus or minus 0 05 x 10 exp 6 square kilometers per 10yr from 1979 through 2002 indicating an acceleration of 20 in the rate of decrease in contrast the antarctic sea ice extent decreased dramatically over the period 1973 1977 then gradually increased over the full 30 year period the antarctic ice extent decreased by 0 15 plus or minus 0 08 x 10 exp 6 square kilometers per 10 yr the trend reversal is attributed to a large positive anomaly in antarctic sea ice extent in the early 1970 s an anomaly that apparently began in the late 1960 s as observed in early visible and infrared satellite images

recent changes in arctic ocean sea ice motion associated with the north atlantic oscillation examination of a new ice motion dataset of the arctic ocean over a recent eighteen year period 1978 1996 reveals patterns of variability that can be linked directly to the north atlantic oscillation the intensity of the icelandic low one of its centers of action modulates the sea level pressure distribution over a broad region of the arctic ocean and the greenland iceland norwegian and barents seas over the winters of 1988 through 1995 the oscillation has remained in its positive phase contributing to coherent large scale changes in the intensity and character of ice transport in the arctic ocean the significant changes include the weakening of the beaufort gyre the increase in ice export through the fram strait the increase in ice import from the barents kara seas the enhanced eastward transport of sea ice from the laptev sea the weakening of the transpolar drift stream and the reduction in ice extent in the nordic seas all of these changes affect the regional and total sea ice mass balance of the arctic ocean

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

climate change triggered sedimentation and progressive tectonic uplift in a coupled piedmont axial system cuyama valley california usa channels on the north facing piedmont of the sierra madre range in cuyama valley california have alternated between three process regimes during the late quaternary 1 vertical incision into piedmont alluvium and older sedimentary deposits 2 lateral erosion and 3 sediment accumulation the state of the piedmont system at a given time has been controlled by upstream sediment flux regional tectonic uplift and incision of the axial cuyama river to better understand the timing and to attempt to interpret causes of past geomorphological processes on the sierra madre piedmont we mapped the surficial geology and dated alluvial deposits using radiocarbon cosmogenic and optical dating methods four primary episodes of sedimentation have occurred since ca 100 ka culminating in the most recent period of extensive piedmont sedimentation between 30 and 20 ka fill terraces in cuyama valley formed by piedmont sediment accumulation followed by vertical incision and lateral erosion are fairly planar and often mantle strath bedrock surfaces their vertical spatial arrangement is a record of progressive regional tectonic uplift and concomitant axial cuyama river channel incision migrating up tributary piedmont channels subparallel longitudinal terrace profiles which have a linear age elevation relationship indicate that multiple episodes of climatically controlled sedimentation overprints 1 m kyr 1 of regional uplift affecting the cuyama river and its tributaries sedimentation was probably a result of increased precipitation that caused saturation landsliding in steep catchments it is possible that increased precipitation during the last glacial maximum was caused by both continental scale circulation pattern reorganization and increased pacific storm frequency and intensity caused by early warming of nearby pacific ocean surface waters older episodes of piedmont sedimentation are difficult to correlate with specific climate regimes but may correlate with previous periods of increased precipitation copyright 2007 john wiley sons ltd

mapping the mesospheric co2 clouds on mars mex omega and mex hrsc observations and challenges for atmospheric models this study presents the latest results on the mesospheric co2 clouds in the martian atmosphere based on observations by omega and hrsc onboard mars express we have mapped the mesospheric co2 clouds during nearly three martian years of omega data yielding a cloud dataset of 60 occurrences the global mapping shows that the equatorial clouds are mainly observed in a distinct longitudinal corridor at seasons ls 0 60 and again at and after ls 90 a recent observation shows that the equatorial co2 cloud season may start as early as at ls 330 three cases of mesospheric midlatitude autumn clouds have been observed two cloud shadow observations enabled the mapping of the cloud optical depth 0 01 0 6 with median values of 0 13 0 2 at 1 m and the effective radii mainly 1 3 m with median values of 2 0 2 3 m of the cloud crystals the hrsc dataset of 28 high altitude cloud observations shows that the observed clouds reside mainly in the altitude range 60 85 km and their east west speeds range from 15 to 107 m s two clouds at southern midlatitudes were observed at an altitude range of 53 62 km the speed of one of these southern midlatitude clouds was measured and it exhibited west east oriented speeds between 5 and 42 m s the seasonal and geographical distribution as well as the observed altitudes are mostly in line with previous work the lmd mars global climate model shows that at the cloud altitude range 65 85 km the temperatures exhibit significant daily variability caused by the thermal tides with the coldest temperatures towards the end of the afternoon the gcm predicts the coldest temperatures of this altitude range and the season ls 0 30 in the longitudinal corridor where most of the cloud observations have been made however the model does not predict supersaturation but the gcm predicted winds are in fair agreement with the hrsc measured cloud speeds the clouds exhibit variable morphologies but mainly cirrus type filamented clouds are observed nearly all hrsc observations and most of omega observations in 15 of omega observations clumpy round cloud structures are observed but very few clouds in the hrsc dataset show similar morphology these observations of clumpy cumuliform type clouds raise questions on the possibility of mesospheric convection on mars and we discuss this hypothesis based on convective available potential energy calculations

an extremely high altitude plume seen at mars morning terminator examination of amateur observations of mars shows atmospheric plumes 200 to 250 kilometres high that are observed in the morning but not in the evening over a period of more than a week our current understanding of martian atmospheric dynamics and plume formation cannot account for the creation of such enormous plumes in march and april 2012 amateur astronomers observing mars recorded what seemed like an eruption of some kind a protrusion from the planet s disk that took about 10 hours to develop and lasted for more than a week agustin sanchez lavega and colleagues have now analysed these observations in detail and describe the highest reaching plume like feature ever detected on mars it reached an altitude of 250 kilometres previous high altitude features reached no higher than 100 kilometres and extended more than 500 kilometres in both the north south and east west directions suggested explanations for this mysterious plume include clouds of co2 or h2o ice or a phenomenon related to auroral emissions but our current understanding of martian atmospheric dynamics and plume formation cannot account for the creation of such enormous plumes the martian limb that is the observed edge of the planet represents a unique window into the complex atmospheric phenomena occurring there clouds of ice crystals co2 ice or h2o ice have been observed numerous times by spacecraft and ground based telescopes showing that clouds are typically layered and always confined below an altitude of 100 kilometres suspended dust has also been detected at altitudes up to 60 kilometres during major dust storms1 2 3 4 5 6 highly concentrated and localized patches of auroral emission controlled by magnetic field anomalies in the crust have been observed at an altitude of 130 kilometres7 here we report the occurrence in march and april 2012 of two bright extremely high altitude plumes at the martian terminator the day night boundary at 200 to 250 kilometres or more above the surface and thus well into the ionosphere and the exosphere8 9 they were spotted at a longitude of about 195 west a latitude of about 45 at terra cimmeria extended about 500 to 1 000 kilometres in both the north south and east west directions and lasted for about 10 days the features exhibited day to day variability and were seen at the morning terminator but not at the evening limb which indicates rapid evolution in less than 10 hours and a cyclic behaviour we used photometric measurements to explore two possible scenarios and investigate their nature for particles reflecting solar radiation clouds of co2 ice or h2o ice particles with an effective radius of 0 1 micrometres are favoured over dust alternatively the plume could arise from auroral emission of a brightness more than 1 000 times that of the earth s aurora over a region with a strong magnetic anomaly where aurorae have previously been detected7 importantly both explanations defy our current understanding of mars upper atmosphere

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

temporal and regional variability of arctic sea ice coverage from satellite data with rapid and accelerated arctic sea ice loss it is beneficial to update and baseline historical change on the regional scales from a consistent intercalibrated long term time series of sea ice data for understanding regional vulnerability and monitoring ice state for climate adaptation and risk mitigation in this paper monthly sea ice extents sies derived from a passive microwave sea ice concentration climate data record for the period of 1979 2015 are used to examine arctic wide and regional temporal variability of sea ice cover and their decadal trends for 15 regions of the arctic three unique types of sie annual cycles are described regions of vulnerability within each of three types to further warming are identified for the arctic as a whole the analysis has found significant changes in both annual sie maximum and minimum with 2 41 0 56 per decade and 13 5 2 93 per decade change relative to the 1979 2015 climate average respectively on the regional scale the calculated trends for the annual sie maximum range from 2 48 to 10 8 decade 1 while the trends for the annual sie minimum range from 0 to up to 42 decade 1

radar soundings of the ionosphere of mars we report the first radar soundings of the ionosphere of mars with the marsis mars advanced radar for subsurface and ionosphere sounding instrument on board the orbiting mars express spacecraft several types of ionospheric echoes are observed ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere to a wide variety of oblique and diffuse echoes the oblique echoes are believed to arise mainly from ionospheric structures associated with the complex crustal magnetic fields of mars echoes at the electron plasma frequency and the cyclotron period also provide measurements of the local electron density and magnetic field strength

recent arctic sea ice variability connections to the arctic oscillation and the enso 1 trends in the satellite derived arctic sea ice concentrations 1978 2002 show pronounced decreases in the barents kara seas between the chukchi and beaufort seas the central sea of okhotsk and a portion of the hudson baffin bay by 2 8 per decade exceeding the 95 confidence level qualitatively speaking positive phases of the arctic oscillation ao and el nino southern oscillation enso produce similar ice changes in the western arctic but opposite ice changes in the eastern arctic the manner in which the ice changes are related to the ao and enso are demonstrated over the last 24 years the magnitude of the ice changes associated with the positive ao trend and the negative enso trend is much smaller than the regional ice trends thus more local or less understood large scale processes should be investigated for explanations

late holocene paleoceanography and climate variability over the mackenzie slope beaufort sea canadian arctic abstract late holocene paleoceanography and climate variability of the southeastern beaufort sea canadian arctic have been investigated on the basis of sedimentary cores collected over the mackenzie slope piston trigger and box cores were sampled at station 803 in 2004 aboard the ccgs amundsen at 218 m water depth the chronology of the piston core is constrained by 4 ams 14 c dates as the sedimentation rate in the box core is assessed from 210 pb data we obtain a continuous composite sequence covering the last 4600 years with a sedimentation rate of 140 cm kyr 1 transfer functions modern analogue technique based on dinoflagellate cyst dinocyst assemblages were used to reconstruct the evolution of sea surface conditions over the time period covered by the cores palynological data reveal that dinocyst assemblages are dominated by operculodinium centrocarpum sensu lato mean of 43 3 throughout the core with the accompanying taxa brigantedinium spp 19 6 islandinium minutum 15 6 and cysts of pentapharsodinium dalei 13 7 four zones have been established on the basis of dinocyst relative abundances dinocyst assemblage zone 1 d1 from 4600 to 2700 cal years bp is dominated by o centrocarpum mean of 49 0 in zone d2 2700 1500 cal years bp the relative abundances of o centrocarpum decrease 34 4 in favour of the opportunistic heterotrophic taxa brigantedinium spp 28 8 and cysts of polykrikos sp var arctic quadratus 2 8 dinocyst zone d3 1500 30 cal years bp or 450 1920 ad is characterised by the high relative abundance of the peridinioid taxa i minutum 19 9 the last zone d4 spanning from 1920 to 2004 ad is again dominated by o centrocarpum 44 5 and shows low relative abundances of brigantedinium spp and cf echinidinium karaense quantitative reconstructions of past sea surface parameters august sea surface temperature sst august sea surface salinity sss and duration of sea ice cover indicate relatively stable conditions over the last 4 6 kyr with episodic cooling events sst of 1 5 c below the modern value of 6 c that took place between 700 and 1820 ad we associate the last and the longest of these cooling events 1560 1820 ad with the little ice age reconstructed sss shows decadal oscillations since 1920 ad that we tentatively associate with the accumulation of freshwater by the beaufort gyre and the subsequent great salinity anomalies our data suggest that similar salinity anomalies could have occurred ca 1860 and 1790 ad stable isotopic data show a slight increase in 13 c values from 27 1 at the base to 25 8 at the top over the last 4 6 kyr that we associate with the gradual increase in atmospheric co 2 concentration as recorded by antarctic ice cores variations in the 15 n profile suggest variations in pacific water influence from 4600 to 1300 cal years bp associated with centennial scale shifts of the arctic oscillation phases

magnetically controlled structures in the ionosphere of mars 1 the ionospheric sounding data obtained by the marsis mars advanced radar for subsurface and ionospheric sounding instrument on the mars express spacecraft show that the dayside ionosphere has considerable structure over regions of strong crustal magnetic fields this structure is typically seen as a hyperbola shaped trace in a display of echo intensity versus apparent altitude and time the hyperbola shapes are consistent with oblique reflections from regions of enhanced electron density that are fixed with respect to mars comparisons with the cain et al 2003 model for the crustal magnetic field of mars show that the apexes of the hyperbolas which identify the closest approach to the regions of enhanced electron density usually coincide with regions where the crustal magnetic field is strong and nearly vertical the electron density enhancements which extend as much as 50 km above the surrounding ionosphere are believed to arise from increases in the scale height of the ionosphere possibly due to heating of the ionosphere by solar wind electrons that reach the base of the ionosphere along the nearly vertical open magnetic field lines statistical analyses of the apparent altitudes of the apexes of the hyperbolas as well as analyses of repeated passes over the same region indicate that the electron density enhancements usually consist of horizontal cylinder like structures rather than isolated hemispherical structures in many cases the axes of the cylindrical density structures are aligned with the symmetry axes of adjacent cylindrical magnetic field structures with opposite polarity

overlapping ionospheric and surface echoes observed by the mars express radar sounder near the martian terminator 1 radar soundings from the mars express spacecraft occasionally show ionospheric and surface echoes that overlap in frequency for specular reflection from a horizontally stratified ionosphere such a frequency overlap is not possible since ionospheric and surface reflections can only occur at frequencies below and above the maximum ionospheric plasma frequency respectively in this paper we show that such overlapping echoes are only observed near the terminator where strong horizontal gradients are present in the ionosphere using a simple ionospheric propagation model we show that the observed frequency overlaps are consistent with current estimates of the horizontal gradients near the terminator

enhanced ionization of the martian nightside ionosphere during solar energetic particle events electron densities in the martian nightside ionosphere are more than 90 of time too low to be detected by the mars advanced radar for subsurface and ionosphere sounding radar sounder on board the mars express spacecraft however the relative number of ionograms with peak electron density high enough to be detected represents a good statistical proxy of the ionospheric density we focus on solar energetic particle sep events and we analyze their effects on ionospheric formation sep time intervals were identified in situ using the background counts recorded by the ion sensor of the aspera 3 instrument on board mars express we show that peak electron densities during the sep events are large enough to be detected in more than 30 of measurements and moreover the reflections of the sounding signal from the ground almost entirely disappear nightside electron densities during sep events are thus substantially increased as compared to normal nightside conditions

continuous monitoring of nightside upper thermospheric mass densities in the martian southern hemisphere over 4 martian years using electron reflectometry details are presented of an improved technique to use atmospheric absorption of magnetically reflecting solar wind electrons to constrain neutral mass densities in the nightside martian upper thermosphere the helical motion of electrons on converging magnetic field lines through an extended neutral atmosphere is modeled to enable prediction of loss cone pitch angle distributions measured by the magnetometer electron reflectometer mag er experiment on mars global surveyor at 400 km altitude over the small fraction of mars southern hemisphere 2 5 where the permanent crustal magnetic fields are both open to the solar wind and sufficiently strong as to dominate the variable induced martian magnetotail field spherical harmonic expansions of the crustal fields are used to prescribe the magnetic field along the electron s path allowing least squares fitting of measured loss cones in order to solve for parameters describing the vertical neutral atmospheric mass density profile from 160 to 230 km results are presented of mass densities in the southern hemisphere at 2 a m lst at the mean altitude of greatest sensitivity 180 km continuously over four martian years seasonal variability in densities is largely explained by orbital and latitudinal changes in dayside insolation that impacts the nightside through the resulting thermospheric circulation however the physical processes behind repeatable rapid late autumnal cooling at mid latitudes and near aphelion warming at equatorial latitudes is not fully clear southern winter polar warming is generally weak or nonexistent over several mars years in basic agreement with mgs and mro accelerometer observations the puzzling response of mid latitude densities from 160 to 200 e to the 2001 global dust storm suggests unanticipated localized nightside upper thermospheric lateral and vertical circulation patterns may accompany such storms the downturn of the 11 year cycle of solar euv flux is likely responsible for lower aphelion densities in 2004 and 2006 mars years 27 and 28

impacts of holocene climatic variations on alluvial fan activity below snowpatches in subarctic quebec abstract in the lake guillaume delisle area of subarctic quebec storm generated alluvial fans have been active sporadically throughout the holocene in this study we propose that the persistence of late lying snowpatches in fan catchments during holocene cold episodes promoted alluvial fan activity by lowering the precipitation threshold required to trigger a torrential event this hypothesis was tested by characterizing the depositional processes responsible for alluvial fan formation below snowpatches and by reconstructing the holocene alluvial fan activity stratigraphic and sedimentary analyses conducted on seven alluvial fans revealed that they were deposited by torrential activity leading to waterlaid transient or hyperconcentrated deposition the chronology of the storm generated alluvial fans based on 22 radiocarbon dates indicates that torrential activity was enhanced during the cooler late holocene i e after ca 3500 cal yr bp snowier winters and cooler summers were beneficial to nival activity allowing the persistence of larger snowpatches throughout the summer and fall seasons rainfall induced thaw of such snowpatches during rainstorm events is inferred to have contributed to alluvial fan activity by increasing water availability three peaks of alluvial activity occurred during the late holocene 2950 2750 1900 1400 and 800 300 cal yr bp and are indicative of increased storminess resulting in higher fan activity increased fan activity during cooler episodes was concurrent with increased runoff activity in the immediate pronival area this stresses the importance of nivation below snowpatches and pinpoints the role of nivation in enhancing geomorphological activity during period of cooler and more humid climate in subarctic environments

divergent patterns of recent sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region abstract over the past three decades of the observed satellite record there have been significant changes in sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region par satellite data reveal that patterns in sea ice cover have been spatially heterogeneous with significant declines in the chukchi and beaufort seas yet more complex multi year variability in the bering sea south of st lawrence island these patterns in the chukchi and beaufort seas have intensified since 2000 indicating a regime shift in sea ice cover across the northern portion of the par in particular satellite data over 1979 2012 reveal localized decreases in sea ice presence of up to 1 64 days year canada basin and 1 24 days year beaufort sea which accelerated to up to 6 57 days year canada basin and 12 84 days year beaufort sea over the 2000 2012 time period in contrast sea ice in the bering sea shows more complex multi year variability with localized increases in sea ice presence of up to 8 41 days year since 2000 the observed increases in sea ice cover since 2000 in the southern bering sea shelf region are observed in wintertime whereas sea ice losses in the canada basin and beaufort sea have occurred during summer we further compare sea ice variability across the region with the national centers for environmental prediction ncep north american regional reanalysis narr wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs wind driven processes results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover those in the beaufort sea are primarily wind driven those offshore in the canada basin are primarily thermally driven and those in the bering sea are influenced by elements of both sea ice variability and its drivers across the par provides critical insight into the forcing effects of recent shifts in climate and its likely ultimate profound impacts on ecosystem productivity across all trophic levels

rock varnish evidence for latest pleistocene millennial scale wet events in the drylands of western united states rock varnish from late to latest pleistocene geomorphic features in the drylands of the western u s provides evidence of nine millennial scale wet events from 11 500 18 000 calendar yr b p represented by regionally replicable and approximately evenly spaced manganese and barium rich dark bands in varnish microstratigraphy preliminary radiometric age calibration indicates that these events appear to be broadly coeval with millennial scale cooling events identified in the greenland ice sheet project 2 gisp2 ice core record six of these wet events are associated with the cold intervals of the younger dryas and heinrich event h1 and the other three with the short lived cooling phases of the intra allerod cold period the older dryas and the oldest dryas these results combined with our previous documentation of millennial scale wet events in the holocene varnish record for the same region indicate that such wet oscillations in the western u s may be parts of regionally widespread manifestation of well documented pervasive millennial scale cycles of the north atlantic climate

antarctic sea ice extent during the holocene reconstructed from inland ice core evidence 1 interannual fluctuations in the antarctic sea ice extent sie affect the global albedo and heat balance and they may affect global co2 levels we found that the annual trend of sodium ion fluxes in the snowpack in the dome fuji region of east antarctica can serve as a proxy for the present day sie in the southern indian ocean and weddell sea sectors we then used sodium ion profiles obtained from the dome fuji ice core to reconstruct the sie during the holocene we observed that 1 the beginnings of both the climatic optimum 12 0 ka bp and neoglaciation 5 4 ka bp in the southern ocean indicated by siliceous microfossil records are consistent with decreases 11 8 ka bp and increases 5 4 ka bp in the sodium ion fluxes in the dome fuji ice core and 2 the interannual fluctuation in the sie during some periods of the neoglaciation was greater than the interannual fluctuation during the climatic optimum

millennial scale varnish microlamination dating of late pleistocene geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a climate based correlative age determination technique used to correlate and date various geomorphic features in deserts in this study we establish a generalized late pleistocene 18 74 ka millennial scale microlamination sequence in fine grained fast accumulating rock varnish for the drylands of western usa radiometrically calibrate the sequence and correlate it with the 18 o record in the gisp2 greenland ice core we then use this climate correlated varnish microstratigraphy to estimate surface exposure ages for radiometrically dated late pleistocene geomorphic features in the study region the vml dating of debris flow deposits on the sehoo recessional shorelines of lake lahontan at the jessup embayment of central nevada yields a minimum limiting age of 14 95 15 95 ka in good agreement with a calibrated 14 c age of 15 22 0 12 ka for the timing of the lake recession the vml dating of a giant ejecta block on the rim of meteor crater in northern arizona yields a minimum limiting age of 49 15 ka closely matching a thermoluminescence tl age of 49 3 ka and slightly younger than a recently updated cosmogenic 36 cl age of 56 0 2 4 ka for the meteor impact event the vml dating of distal q2c fan surfaces on hanaupah canyon alluvial fan in death valley california yields a minimum limiting age of 73 55 ka in accord with cosmogenic 36 cl depth profile ages of 66 22 14 ka and 72 24 20 ka for the same fan deposits the close agreement between the vml age estimates and the independently derived radiometric ages for these geomorphic features attests to the validity and reliability of millennial scale vml dating to further assess its potential in desert geomorphological research we use the vml method to study alluvial fan responses to millennial scale climatic changes the vml dating of a small tributary fan in death valley reveals two episodes of fan aggradation one ceasing at 73 55 86 75 ka during the dry period of the last interglacial mis 5a and the other finishing at 66 15 ka during the wet period of the last glacial mis 4 the vml and 36 cl dating of the distal q2c fan surfaces on hanaupah canyon fan reveal two episodes of large scale fan aggradation ended at 72 24 20 ka and 73 55 ka during the wet period of mis 4 fanhead incision and associated within channel or fantoe aggradation are found to take place during the relatively dry period of the glacial to interglacial climatic transition 12 24 ka and the holocene interglacial dry period 0 12 ka these data indicate that on the millennial to sub milankovitch timescale 10 3 10 4 years fan aggradation is a discrete sedimentational process under various climatic conditions because fan aggradation is ultimately controlled by the intensity and frequency of precipitation events which in turn are modulated by major climatic oscillations such as heinrich events dansgaard oeschger do events and glacial interglacial shifts these major climatic changes could be the pacemaker of regionally contemporaneous large area fan segmentation