biogenic silica accumulation in the ross sea and the importance of antarctic continental shelf deposits in the marine silica budget abstract thirty five box cores were collected from the continental shelf in the ross sea during cruises in january and february 1983 pb 210 and pu 239 240 geochronologies coupled with biogenic silica measurements were used to calculate accumulation rates of biogenic silica sediment in the southern ross sea accumulates at rates ranging from 0 6 to 2 7 mm y with the highest values occurring in the southwestern ross sea biogenic silica content in surface sediments ranges from 2 by weight in sulzberger bay and the eastern ross sea to 41 in the southwestern ross sea biogenic silica accumulation in the southwestern ross sea averages 2 7 10 2 g cm2 y and is comparable to accumulation rates in high productivity upwelling environments from low latitude continental margins e g gulf of california coast of peru the total rate of biogenic silica accumulation in the southern ross sea is approximately 0 2 1014 g y with most of the accumulation occurring in basins 500 1000 m water depth if biogenic silica accumulation in the southern ross sea continental shelf is typical of other basins on the antarctic continental shelf as much as 1 2 1014 g y of silica could be accumulating in these deposits biogenic silica accumulation on the antarctic continental shelf may account for as much as a fourth of the dissolved silica supplied to the world ocean by rivers and hydrothermal vents

a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

solar cycle variations of the equatorial ionospheric anomaly in total electron content in the asian region daily equatorial ionospheric anomaly eia contour charts in total electron content teg were obtained by receiving simultaneously two coherent radio signals transmitted from the u s navy navigation satellite system satellite at lunping observatory 25 00 n 121 17 e from september 1985 to december 1994 the latitude occurrence time and strength of the most developed eia crest obtained from daily tec contour charts have been used to study the solar cycle variations of eia in the asian region no significant solar cycle effect can be seen in the occurrence time and latitude of the most developed eia crest seasonally the winter crest appears larger and earlier than the summer crest and the summer crest appears in lower latitude than other seasons these seasonal changes are mainly accounted for by the effect of daytime meridional wind the strength of eia crest increases with the increasing of solar activity and exhibits winter anomaly with the winter strength larger than the summer one positive correlation is found between the 12 month smoothed eia crest strength and sunspot number no saturation effect can be seen during the high solar activity period the 12 month smoothed eia crest strength exhibits a hysteresis variation about the solar cycle variation monthly mean tec contour charts for the latitude from 15 n to 35 n are also obtained from those daily contour charts by using linear regression analysis the monthly mean tec i at a given month is linearly correlated with smoothed sunspot number r by a formula i a br these results can be used to construct the monthly eia contour chart in tec for any given sunspot number

holocene dust in east antarctica provenance and variability in time and space in this paper we provide a comprehensive overview of the state of knowledge of dust flux and variability in time and space in different sectors of east antarctica during the holocene by integrati

lead isotopic evidence for an australian source of aeolian dust to antarctica at times over the last 170 000 years abstract systematic analysis of pb sr and nd isotopes of 32 fluvial clay samples 6 km 2 murray darling basin mdb located in semiarid southeastern australia displays similar isotopic values between some mdb clays and dust from several ice core samples from the epica dome c in antarctica close scrutiny of several ratios of the four pb isotopes and in particular 208 pb 207 pb versus 206 pb 207 pb shows that several samples from the darling sub basin of the mdb display similar values for the same isotopes for dome c samples from different ages and more particularly during wet phases in australia marine isotopic stages 5e 3 and 1 the combination of nd and sr isotopic ratios from the same mdb fluvial clays clearly eliminates the murray sub basin and supports the darling sub basin as a potential source of aeolian material to antarctica overall the australian dust supply to antarctica predominantly occurred during interglacial periods the work presented here shows that aerosols generated in southeastern australia can travel to parts of west antarctica and this is supported by atmospheric observations and models in addition evidence of australian dust in antarctic ice cores further implies dust deposition in the southern ocean would have occurred in the past current meteorological observations also imply that the western pacific and indian ocean sector of the southern ocean would frequently receive aeolian dust components originating from southeastern australia

stratigraphic architecture of the cenozoic succession in the mcmurdo sound region antarctica an archive of polar palaeoenvironmental change in a failed rift setting the victoria land basin forms part of the failed west antarctic rift and preserves a cenozoic succession up to 4 km thick that records the onset of cenozoic glaciation and the history of antarctic glaciation over the past 34 myr this succession is relevant both to investigations of modern climate change and to studies of long term palaeoclimate change in general this study provides a sedimentological and stratigraphic review of the victoria land basin succession based on analysis of several continuous drillcores acquired since the 1970s and supported by seismic stratigraphic analysis of a large array of seismic reflection data an array of fifteen lithofacies is recognized within the victoria land basin cenozoic succession including fossiliferous and diversely bioturbated mudrocks and diatomites texturally mature sandstones and conglomerates mixed mudstones and sandstones with dispersed gravel with restricted bioturbation and diamictites and associated lithologies these facies record a variety of marine glaciomarine proglacial and subglacial environments locally volcanic and volcaniclastic deposits are interbedded in the succession lithofacies are arranged in repetitive vertical stacking patterns depositional sequences that record glacial advance retreat cycles with attendant relative sea level changes seven varieties of depositional sequences stratigraphic motifs are recognized within the succession as a whole and interpreted to record a range of depositional settings from rifts unaffected by glacial ice motif 7 through varying degrees of glacial influence with abundant meltwater contributions motifs 6 to 3 to cold polar glaciated environments such as that of today motifs 2 and 1 overall there is a gradual trend upward through the succession from motif 7 at the base towards motif 1 at the top but the trend is not monotonic a significant conclusion of this work is that a record of dynamic climate and glacial conditions is preserved through the entire 34 myr period of the cenozoic icehouse at least in the victoria land basin intervals characterized by consistent stratigraphic style motifs are recognized throughout the victoria land basin succession these intervals are of 1 to 6 myr duration each containing numerous depositional sequences they are one to two orders of magnitude longer than glacial interglacial cycles and record periods during which environmental conditions varied in an internally consistent manner these intervals are considered to reflect convolutions of orbital parameters that remained stable for periods of 106 a and then switched to alternative configurations such intervals are directly analogous to 1 to 8 myr intervals characterized by glaciogenic strata that are preserved within the late palaeozoic of eastern australia among other areas and may be a recurring stratigraphic response to icehouse climate regimes through geological time

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

equatorial spread f instability conditions as determined from ionograms conditions of plasma irregularity or spread f generation under the rayleigh taylor mechanism in the nighttime equatorial ionosphere are examined from ionogram data registered over fortaleza 4 s 38 w mag dip lat 1 7 brazil for a one year period the results show that local ionospheric conditions such as the bottomside f region electron density scale length and the ion neutral collision frequency at the base of the layer at sunset hours determine the generation of the spread f irregularities over the equator in the post sunset hours

reexamination of the near surface airflow over the antarctic continent and implications on atmospheric circulations at high southern latitudes abstract previous work has shown that winds in the lower atmosphere over the antarctic continent are among the most persistent on earth with directions coupled to the underlying ice topography in 1987 parish and bromwich used a diagnostic model to depict details of the antarctic near surface airflow a radially outward drainage pattern off the highest elevations of the ice sheets was displayed with wind speeds that generally increase from the high interior to the coast these winds are often referred to as katabatic with the implication that they are driven by radiational cooling of near surface air over the sloping ice terrain it has been shown that the antarctic orography constrains the low level wind regime through other forcing mechanisms as well dynamics of the lower atmosphere have been investigated increasingly by the use of numerical models since the observational network over the antarctic remains quite sparse real time numerical weather prediction for the u s antarctic program has been

pathways of high latitude dust in the north atlantic abstract the contribution of mineral dust from high latitude sources has remained an under examined feature of the global dust cycle dust events originating at high latitudes can provide inputs of aeolian sediment to regions lying well outside the subtropical dust belt constraining the seasonal variability and preferential pathways of dust from high latitude sources is important for understanding the potential impacts that the dust may have on wider environmental systems such as nearby marine or cryospheric domains this study quantifies dust pathways from two areas exhibiting different emission dynamics in the north and south of iceland which is a prominent northern hemisphere dust source the analysis uses air parcel trajectory modelling and for the first time for high latitude sources explicitly links all trajectory simulations to time specific meteorological observations of suspended dust this approach maximises the potential for trajectories to represent dust and illustrates that trajectory climatologies not limited to dust can grossly overestimate the potential for dust transport preferential pathways emerge that demonstrate the role of iceland in supplying dust to the northern atlantic and sub arctic oceans for dust emitted from northern sources a dominant route exists to the northeast into the norwegian greenland and barents seas although there is also potential for delivery to the north atlantic in summer months from the southern sources the primary pathway extends into the north atlantic with a high density of trajectories extending as far south as 50 n particularly in spring and summer common to both southern and northern sources is a pathway to the west southwest of iceland into the denmark strait and towards greenland for trajectories simulated at 500 m the vertical development of dust plumes from iceland is limited likely due to the stable air masses of the region suppressing the potential for vertical motion trajectories rarely ascend high enough to reach the central portions of the greenland ice sheet the overall distribution of trajectories suggests that contributions of icelandic dust are relatively more important for neighbouring marine environments than the cryosphere

plio pleistocene sedimentation in ferrar fiord antarctica a 166 m thick plio pleistocene sequence of glacial sediments has been cored in ferrar fiord in the southwestern corner of the ross sea antarctica the core has the following lithofacies massive diamictite 33 of the core interpreted as lodgement or waterlain till weakly stratified diamictite 25 waterlain till or proximal glaciomarine sediment well stratified diamictite 8 proximal glaciomarine or glaciolacustrine sediment sandstone 25 sand of aeolian or supraglacial origin mudstone 7 derived from subglacial debris and transported offshore in suspension and minor amounts of rhythmite and tuff the range of facies in this polar setting differs from those normally found in subpolar and temperate glacier fiord settings in the high proportion of aeolian derived sand and the low proportion of mudstone facies the core can be divided into two sequences based on composition and texture the sequence from 162 to 100 mbsf metres below the sea floor comprises alternations of diamictite dominated by basement lithologies and thin marine mudstone beds it is pliocene in age 4 9 2 0 ma and records several advances and retreats of ice through the transantarctic mountains and across the drill site from the west the sequence from 100 mbsf to the sea floor of pleistocene age consists of alternations of diamictite interpreted as lodgement and waterlain till and sandstone of aeolian origin deposited in a glaciolacustrine setting similar to ice covered lakes in the dry valleys today these sediments have a high volcanic component and hence are thought to have been derived by the grounding and advance of the ross ice shelf from the east past volcanic ross island this change in source is attributed to the rising transantarctic mountains increasingly containing east antarctic ice the pleistocene sequence above 100 mbsf clearly represents polar glacial sedimentation with alternations of till and glaciolacustrine sand mudstones from the pliocene sequence beneath include palynomorphs indicating times when the landscape was at least partially vegetated but contain no evidence of meltwater influence

regulation of algal blooms in antarctic shelf waters by the release of iron from melting sea ice during summer 1995 96 we measured iron in the water column and conducted iron enrichment bottle incubation experiments at a station in the central ross sea 76 30 s 170 40 w first in the presence of melting sea ice and 17 days later in ice free conditions we observed a striking temporal change in mixed layer dissolved iron concentrations at this station from 0 72 2 3 nm with sea ice present to 0 16 0 17 nm in ice free conditions these changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal diatom biomass our incubation experiments suggest that conditions were iron replete in the presence of sea ice and iron deficient in the absence of sea ice we surmise that bioavailable iron was released into seawater from the melting sea ice stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer until iron limited conditions developed these observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production particularly ice edge blooms in seasonally ice covered antarctic waters

seasonal variations of the ionospheric total electron content in asian equatorial anomaly regions the ionospheric total electron contents tec in both northern and southern equatorial anomaly regions are examined by using the global positioning system gps in asian area the tec contour charts obtained at ymsm 25 2 n 121 6 e 14 0 n geomagnetic and dgar 7 3 s 72 4 e 16 2 s geomagnetic stations in 1997 solar minimum are investigated it is found that the ionospheric crests manifest remarkable seasonal variations the tec values on both northern and southern equatorial anomaly crests yield their maximum values during the vernal and autumnal months but the winter anomaly does not appear in the southern region results show that both crests are fully developed around midday in winter postnoon in equinoxes and late afternoon in summer and the two crests move significantly equatorward in winter but slightly poleward in summer and autumn these phenomena can be fully explained by a combined theory of the transequatorial netural wind the subsolar point and the auroral equatorward wind

additional stratifications in the equatorial f region at dawn and dusk during geomagnetic storms role of electrodynamics 1 the role of electrodynamics in producing additional stratifications in the equatorial f region f 3 layer at dawn and dusk during geomagnetic storms is discussed two cases of f 3 layer at dawn 0600 0730 lt on 5 october 2000 and 8 december 2000 and one case of f 3 layer at dusk 1600 1730 lt on 5 october 2000 are observed for the first time by the digital ionosonde at the equatorial station trivandrum 8 5 n 77 e dip 0 5 n in india the unusual f 3 layers occurred during the geomagnetic storms and are associated with southward turning of interplanetary magnetic field b z suggesting that eastward prompt penetration electric field could be the main cause of the f 3 layers the dawn f 3 layer on 5 october is modeled using the sheffield university plasmasphere ionosphere model by using the e x b drift estimated from the real height variation of the ionospheric peak during the morning period the model qualitatively reproduces the dawn f 3 layer while the existing f 2 layer rapidly drifts upward and forms the f 3 layer and topside ledge a new layer forming at lower heights develops into the normal f 2 layer

long term rates of denudation in t he dry valleys transantarctic mountains southern victoria land antarctica bases on in situ produced cosmogenic 21ne abstract concentrations of cosmogenic 21 ne 21 ne c measured in quartz have been used to estimate long term rates of denudation for contrasting landscape components in the dry valleys area of the transantarctic mountains southern victoria land antarctica samples of beacon supergroup sandstones and granitic basement were collected from two contrasting landscape elements low relief high elevation surfaces and rectilinear slopes to assess variations in rates of denudation with topographic position the sample sites for rectilinear slopes were selected because of proximity to 40 ar 39 ar dated lavas and ash avalanche deposits all 21 ne 20 ne ratios are significantly greater than the atmospheric value and concentrations of 21 ne c were calculated from the measured 21 ne values assuming an atmospheric composition for the trapped component apparent exposure ages calculated from the concentrations of 21 ne c assuming no denudation since exposure range from 3 78 4 66 ma for samples from the high elevation plateau surface and 0 61 2 48 ma for samples from the rectilinear slopes exposure ages for 3 he c were 2 to 42 times lower than those derived from the abundances of 21 ne c because of preferential diffusive loss of 3 he c from the quartz lattice concentrations of 3 he c were therefore not used in the calculation of rates of denudation we interpret the abundances of 21 ne c as reflecting variations in the rates of denudation rather than exposure age in view of independent evidence for prolonged exposure 15 ma of bedrock surfaces at the sample sites calculated maximum rates of denudation range from 0 26 1 02 m ma 1 for the rectilinear slopes down to only 0 133 0 164 m ma 1 for the high elevation surface sites these rates are comparable to other estimates of denudation rates for the dry valleys derived from analyses of cosmogenic isotopes but are around two orders of magnitude lower than the long term mean rate over the past 50 ma estimated from fission track thermochronology combined with the preservation of volcanic deposits dating back to the mid miocene these 21 ne c data demonstrate that only minimal modification of the landscape has occurred in the dry valleys over at least the past 15 ma this significant conclusion supports the view that the east antarctic ice sheet has been essentially stable over this period rather than experiencing major fluctuations as late as the pliocene as has previously been suggested

diatoms of the mcmurdo ice shelf antarctica implications for sediment and biotic reworking abstract in the course of investigations of the origin of the mcmurdo ice shelf mis we analyzed diatoms in 59 sediment samples collected from its upper surface fragments of centric marine species most of which occur in the ross sea today were found in all samples but identifiable marine taxa dominated the total diatom flora in only two samples in contrast non marine diatoms are abundant and diverse in most mis samples these non marine species probably live in the numerous melt ponds which are distributed widely over the shelf surface during the warmest few weeks of each austral summer non marine diatoms are clustered in four assemblages which are probably related in a complex way to geographic position on the ice shelf sediment age local geochemical variations and seasonal blooms the presence of marine diatoms in mis sediments is consistent with isotopic evidence that the mis consists of frozen seawater and with debenham s hypothesis that transport of marine macrofossils to its surface is accomplished by freezing on at the base and upward movement through the shelf caused by surface melting the combined marine and non marine diatom floras of the mis suggest a new mechanism to explain mixed diatom floras and sediments observed in antarctic cores these composite floras and sediments may be introduced or reintroduced to the marine environment during austral summers by melt water streaming off the front of the mis or through crevasses additionally icebergs calved from the mis release theie load of mixed biota and sediment when they melt these observations may pertain to oher present and former antarctic ice shelves that are characterized by surface ablation and basal freezing

frequency magnitude and characteristics of aeolian sediment transport mcmurdo dry valleys antarctica 1 due in part to the challenging environment of earth s high latitude regions available information on cold climate effects on aeolian processes in these areas remains limited data from these areas however provide insight into the physics of sediment transport by wind and the controls on erosive winds in proximity to ice caps and topographic influences this study presents a 2 year record of meteorological saltation activity horizontal saltation flux and particle size distribution data from four sites in the mcmurdo dry valleys of antarctica 2008 to 2010 saltation measurements revealed daily and seasonal patterns with spring and summer sediment transport events occurring between 09 00 and 24 00 hours due to thermally generated winds fall and winter events occur at any time of day with the strongest associated with foehn winds threshold wind speed at 4 2 m in all seasons for all locations was 10 m s 1 saltation occurred in the temperature range 40 c to 5 c westerly winds in the fall winter and easterly winds in spring summer are associated with the majority of transport events the sand in transport is mainly 250 to 500 m in diameter and poorly sorted the integrated saltation flux varies over three orders of magnitude among the sites with the lowest mean flux recorded in the taylor valley 2 9 kg m 1 day 1 and the highest in the eastern victoria valley 2271 kg m 1 day 1 for 24 hours of continuous saltation the percentage of time saltation active at these locations annually is 2 4 and 13 respectively for the victoria taylor and wright valleys

sea ice derived dissolved iron and its potential influence on the spring algal bloom in the bering sea 1 observational and modeling studies in the bering sea indicate that changes in the seasonal ice cover and time of ice retreat influence open water productivity in particular the timing of the spring bloom and its phytoplankton community composition are affected dissolved iron dfe data in the water column and ice cores collected during the 2007 bering ecosystem study best cruise indicate that the melting ice provided substantial dfe to the water column the additional dfe input from melting sea ice could be biologically important along the outer shelf and shelf break where in ice free areas insufficient dfe 20 m variability in sea ice dynamics are likely to result in a varying supply of dfe to the outer shelf and shelf break in early spring and to contribute to the observed changes in the timing and community composition of the spring phytoplankton bloom

statistical analysis of an ionospheric parameter as a base for earthquake prediction 1 this paper is related to the use of ionospheric density variations to tentatively predict earthquakes the results of this statistical analysis are presented as a function of various parameters the ion density was recorded by the low altitude satellite demeter during more than 6 years and a search for anomalies was automatically conducted with the complete data set in a second time a software checked if each anomaly could correspond to an earthquake the search was conducted at less than 1500 km from the anomaly positions and until 15 days after the anomaly time the earthquakes have been classified depending on their magnitude depth and position below the sea or inland this attempt to predict earthquakes of course generates a lot of false alarms and wrong detections nevertheless it is shown that the number of good detections increases with the magnitude of the earthquakes in average the number of perturbations is higher the day of the earthquake and then smoothly decreases for the days before earthquakes below the sea are better detected there are seismic areas close to the south atlantic magnetic anomaly and at high latitudes where the number of natural perturbations is too important to expect a high number of good detections finally when there are several perturbations corresponding to a single earthquake it is possible to combine their positions to have a better estimation of the location of the future epicenter however uncertainties about the time and the magnitude are large

factors controlling the near surface wind field in antarctica abstract using data from the regional atmospheric climate model racmo ant1 the momentum budget of the antarctic atmospheric surface layer sl taken as the lowest model layer located at 6 7 m above the surface is presented in july winter the katabatic pressure gradient force pgf dominates the sl momentum budget over the steep coastal slopes which results in strong 10 15 m s 1 and directionally constant katabatic winds farther inland where surface slopes are more gentle the large scale pgf may become equally important with the circumpolar pressure trough north of the antarctic coastline the large scale pgf acts along with the katabatic pgf in the downslope direction in wilkes land dronning maud land and on the western ross ice shelf the large scale pgf causes equivalent geostrophic winds in excess of 10 m s 1 thermal wind effects that oppose the downslope acceleration are especially strong in areas where large scale forcing is weak which allows cold air to pile up over the flat ice she

high latitude dust deposition in snow on the glaciers of james ross island antarctica high latitude dust hld depositions on four glaciers of james ross island the ulu peninsula were analysed the deposition rate on the selected glaciers varies from 11 8 to 64 0 g m 2 which is one order of magnitude higher compared to the glaciers in antarctica or elsewhere in the world a strong negative relationship between the sediment amount and altitude of a sampling site was found this is most likely caused by the higher availability of aeolian material in the atmospheric boundary layer general southerly and south westerly wind directions over the ulu peninsula with exceptions based on local terrain configuration help to explain the significantly lower level of sediment deposition on san jose glacier and the high level on triangular glacier x ray fluorescence xrf spectrophotometry was used to estimate the relative proportions of the main and trace lithophile elements in the sediment samples both the sediment amount and the xrf results are analysed in a depth profile at each locality and compared among the glaciers suggesting long range transport of fine mineral material from outside james ross island the distribution of aeolian sediment among the glaciers corresponds well with the prevailing wind direction on the ulu peninsula

a comparison of nighttime tid characteristics between equatorial ionospheric anomaly crest and midlatitude regions related to spread f occurrence the occurrence characteristics of tids with enhanced wave amplitudes as detected by spread traces on ionograms has been investigated for an equatorial ionospheric anomaly crest station chung li for comparison with results from midlatitudes two distinct types of distributions are found one set type 1 is directly related to sunspot number while the other type 2 is indirectly related their semiannual variations are also inversely distributed the type 2 variations are the same as those found for midlatitudes type 1 events occur mainly before midnight being influenced by the significant postsunset height rises while type 2 events predominate after midnight the influence of large scale traveling ionospheric disturbances ls tids at both latitude regions has been considered particularly relating to the spread f associated with their passage the results presented for chung li have revealed characteristics similar to those found in midlatitudes thus an alternative explanation is available to explain at least in terms of ionogram recorded spread f events the direct relationship which exists between equatorial spread f and geomagnetic activity in the presunrise hours

sediments beneath multi year sea ice delivery by deltaic and eolian processes abstract little is known about land to sea sediment transport and deposition in polar regimes with multi year sea ice such as at the mouth of the taylor valley one of the dry valleys in antarctica this study integrates textural analysis of 574 coastal subaerial and nearshore submarine sediment samples with data from sediment traps and with published grain size analyses of offshore sea ice surface and submarine sediments to reconstruct transport and depositional processes from the shoreline to 8 km offshore sediment primarily sand sized is transferred into the marine environment via two processes 1 erosion transport and deposition of till by ephemeral meltwater streams that deliver sediment to the subaqueous part of the delta built over the last 7 500 years and 2 onshore to sea ice sediment transport by wind during rare but powerful foehn wind events because the distributaries flow into quiet water beneath the sea ice most of their load is dropped close to shore but a small amount of fine grained sediment mostly silt is carried kilometers offshore probably by low density low salinity plumes wind deposits sediment on the sea ice with median grain size decreasing from medium to fine sand within 1 5 km of the shoreline even offshore sea ice sediment contains very little silt and almost no clay nearshore the sea ice sediment is coarser than that on the underlying seafloor but in a few kilometers offshore the median grain sizes of the seafloor and sea ice sediments are similar this reflects a mixture of sea ice rafted eolian sediment and fine grained delta derived sediment transported beneath the sea ice this system is unusual in the relative effectiveness of the transport systems the feeble distributaries deposit their sediment load immediately upon entering the quiet water and only a minor amount of silt and clay is carried seaward under the ice in contrast winds deposit coarser sediment on the nearshore sea ice and carry fine sand 7 km offshore although the amount and grain size of sediment is attenuated within 1 5 km of shore melting of the sea ice drops sediment onto the seafloor where it mixes with the delta derived silt and clay similar combinations of eolian and fluvial transport processes may have operated in polar regimes dominated by multi year sea ice in the past understanding of the modern processes in explorers cove may aid recognition of ancient sediments deposited under multi year sea ice as well as help predict future changes in processes around antarctica as the distribution of multi year sea ice shifts in response to climate change

equatorial anomaly in ionospheric electron content and its relation to dynamo currents using the ats 6 satellite radio beacon data collected over a chain of stations in the indian zone a study has been made of the equatorial anomaly in total electron content tec and its relation to the e region currents two parameters hd the difference in the magnetic field perturbation between the equator and a low latitude station and vd the backscatter radar measurement of the draft velocity of the electrojet irregularities are used to represent the equatorial current strength the results presented in the form of regression plots relating the strength of the anomaly and that of the current indicate that the anomaly dependence on the current strength is about the same for all the three seasons it is also noted that regardless of the season the anomaly crest moves toward a farther latitude from the equator with increasing current strength the total ionization inventory tec of the anomaly belt is found to increase linearly with the strength of the equatorial current and this result seems to bear some significance for the correlation observed between tecmax and hdmax at the equator

ionospheric disturbances during low latitude auroral events and their association with magnetospheric processes ionospheric disturbances associated with low latitude auroral events that occurred during geomagnetic storms on october 21 1989 and may 10 1992 are investigated from measurements of the total electron content tec by the u s navy navigation satellite system nnss and ionosonde data from the japanese meridian chain features of the ionospheric disturbances are then associated with the progression of geomagnetic disturbances during the storms after the onset of the main phase of each storm anomalous tec distributions characterized by depressed tec distributions on the high latitude side 35 geographic latitude and an enhanced equatorial ionization anomaly eia on the low latitude side 35 geographic latitude were observed over japan both by the nnss and by the meridian chain of ionosonde stations this enhancement of the eia suggests the penetration of magnetospheric electric fields during the storms corresponding to the anomalous tec decreases in the northern part of japan ionosonde stations in this region observed specific disturbances of ionospheric variation characterized by simultaneous decreases of 0f2 and increases of h f these features of ionospheric variations on the high latitude side can be attributed to the upward escape of ionospheric plasma caused by the heating and evacuation mechanisms which are induced by depletion of the plasmasphere and the resulting access of ring current particles to low latitudes after the appearance of the characteristic ionospheric variations mentioned above low latitude aurorae were observed at the maximum development stage of the dst associated with the recovery of midlatitude geomagnetic horizontal h components prior to the appearance of the low latitude aurorae magnetic disturbances in the auroral region increased with the decrease of midlatitude h components as a natural consequence of magnetic storms however they showed a recovery before the start of the low latitude aurorae while the magnitude of the low latitude magnetic field continued to decrease these observed features of the magnetic disturbances suggest that the position of the auroral oval shifted toward the equator before the appearance of the low latitude aurorae consequently these observations are consistent with the plasmapause and auroral zone moving toward the equator before the onset of low latitude aurorae we conclude that the convection electric field penetrating toward low latitudes causes the enhancement of the eia the shrinkage of the plasmasphere and the penetration of high energy particles toward the low latitude region

modern and holocene aeolian dust variability from talos dome northern victoria land to the interior of the antarctic ice sheet abstract high elevation sites from the inner part of the east antarctic plateau sample windborne dust representative of large portions of the southern hemisphere and are sensitive to long range atmospheric transport conditions to polar areas on the periphery of the ice sheet conversely the aeolian transport of particles from high elevation ice free areas can locally represent a relatively important additional input of dust to the atmosphere and the interplay of atmospheric dynamics dust transport and deposition is strictly related to the regional atmospheric circulation behaviour both at present day and in the past the understanding of the spatial extent where local sources can influence the mineral dust budget on the ice sheet is fundamental for understanding the atmospheric dust cycle in antarctica and for the interpretation of the dust history in marginal glaciological settings in this work we investigate the spatial variability of dust flux and provenance during modern pre industrial and holocene times along a transect connecting talos dome to the internal sites of the antarctic plateau and we extend the existing documentation of the isotopic sr nd fingerprint of dust sized sediments from victoria land source areas dust flux grain size and isotopic composition show a marked variability between talos dome mid point d4 and dome c vostok suggesting that local sources play an important role on the periphery of the ice sheet microscope observations reveal that background mineral aerosol in the taldice core is composed by a mixture of dust volcanic particles and micrometric sized fragments of diatoms these latter representing a small but pervasive component of antarctic sediments a set of samples from victoria land mostly consisting of regolith and glacial deposits from high elevation areas was collected specially for this work and the isotopic composition of the dust sized fraction of samples was analyzed results reveal a close relationship with the parent lithologies but direct comparison between source samples and firn ice core dust is problematical because of the ubiquitous volcanic contribution to the environmental particulate input in the talos dome area the frequency of events potentially suitable for peripheral dust transport to talos dome appears relatively high for present day conditions according to back trajectories calculations and the related air flow pattern well defined from a seasonal and spatial perspective also as expected from palaeo data these events appear extremely uncommon for internal sites

cenozoic landscape evolution of the convoy range to mackay glacier area transantarctic mountains onshore to offshore synthesis on the basis of geomorphic mapping we reconstruct the landscape evolution of the convoy range to mackay glacier area of the rifted margin of the transantarctic mountains and compare the land record with that obtained from offshore marine sedimentary rocks in the ross sea three landform assemblages reflect 1 fluvial planation and dissection 2 local glaciation under temperate conditions and 3 overriding by the east antarctic ice sheet overall landscape evolution is typical of a passive continental margin contrasts in morphology between the convoy range and the adjacent dry valleys and royal society mountains reflect the varying location of the initial drainage divide in relationship to the rifted coast in a wider synthesis we draw the following conclusions for the 260 km long mcmurdo sector of the transantarctic mountains denudation since rifting at ca 55 ma has removed a wedge 4 7 km thick at the coast declining inland to 1 km most denudation occurred in the eocene from planation and incision of river valleys near the coast a subsequent pulse of denudation most rapid at 34 31 ma and declining until ca 17 ma coincided with further crustal extension and a change from cool temperate to polar climate during the same interval there was a progressive decrease in landscape modification by warm based glaciers and or rivers between 14 8 and 13 6 ma the maximum overriding antarctic ice sheet flowed northeastward across the mountains leaving meltwater features crossing high altitude saddles and areally scoured bedrock near the coast since 13 6 ma the landscape has seen little change under a hyperarid polar climate either by local glaciers or subaerially fragile middle miocene surficial deposits still survive there has been tectonic stability since the middle miocene

first simultaneous observations of f3 layer and e b drift in indian sector and modeling 1 although the basic mechanism of an additional stratification of the daytime equatorial f region called the f3 layer has been explained two observational aspects that remain not so clear are its summer winter differences and simultaneous occurrences on either side of the geomagnetic equator in this paper we address these two aspects using simultaneous observations of the f3 layer and vertical e b drift velocity made for the first time in an indian station gadanki 6 5 n mag lat during the low solar activity period 2008 2009 and making model computations using the sheffield university plasmasphere ionosphere model the observations confirm the frequent occurrence of the f3 layer in summer months compared to winter months the observations also reveal the occasional occurrence of clear and distinct f3 layer in winter although such a layer is frequent in summer in addition a threshold vertical plasma velocity involving the e b drift and neutral wind and its time integrated value are found to be important for the formation of the f3 layer the model results qualitatively reproduce the observations and show that irrespective of season the formation of the f3 layer is centered on that side of the equator where the equatorward neutral wind reduces the downward field aligned flow of plasma and the latitude band of the layer can extend to the opposite hemisphere especially when the vertical plasma velocity is large

f3 layer during penetration electric field 1 the occurrence of an additional layer called f3 layer in the equatorial ionosphere at american indian and australian longitudes during the super double geomagnetic storm of 7 11 november 2004 is presented using observations and modeling the observations show the occurrence reoccurrence and quick ascent to the topside ionosphere of unusually strong f3 layer in australian longitude during the first super storm 8 november and in indian longitude during the second super storm 10 november all with large reductions in peak electron density nmax and total electron content gps tec the unusual f3 layers can arise mainly from unusually strong fluctuations in the daytime vertical e b drift as indicated by the observations and modeling in american longitude the strongest upward e b drift or eastward prompt penetration electric field ppef ever recorded at jicamarca produces unusually strong f3 layer in the afternoon hours 1400 1600 lt of ppef with large reductions in nmax and tec the layer also reappears in the following evening 1700 1800 lt owing to an unusually large downward drift at night when the drift is unusually upward and strong the f region splits into two layers

a dynamical investigation of the may 2004 mcmurdo antarctica severe wind event using amps on 15 16 may 2004 a severe windstorm struck mcmurdo antarctica the antarctic mesoscale prediction system amps is used along with available observations to analyze the storm a synoptic scale cyclone weakens as it propagates across the ross ice shelf toward mcmurdo flow associated with the cyclone initiates a barrier jet along the transantarctic mountains forcing terms from the horizontal equations of motion are computed in the barrier wind to show that the local time tendency and momentum advection terms are key components of the force balance the barrier jet interacts with a preexisting near surface radiation inversion over the ross ice shelf to set up conditions favorable for the development of large amplitude mountain waves leading to a downslope windstorm in the ross island area hydraulic theory can explain the structure of the downslope windstorms with amplification of the mountain waves possibly caused by wave breaking events the underestimation of amps wind speed at mcmurdo is caused by the misplacement of a hydraulic jump downstream of the downslope windstorms the dynamics associated with the cyclone barrier jet and downslope windstorms are analyzed to determine the role of each in development of the severe winds

equatorial f region vertical plasma drifts seasonal and longitudinal asymmetries in the american sector longitudinal and seasonal asymmetries in the evening ionospheric f region plasma vertical drift v sub z enhancements between two longitudinally separated stations situated along the magnetic equator in the american sector are investigated under solar maximum conditions based on results obtained from the analysis of ionosonde data for these stations the two stations are huancayo peru and fortaleza brazil which have markedly different magnetic declination angles the observed asymmetries are interpreted using a detailed numerical simulation of the e and f region electrodynamic coupling process that takes into account also its asymmetry about the magnetic equator arising from the finite magnetic declination angle the results of the simulation show in agreement with observations that the occurrence time of the evening f region vertical drift prereversal peak and its seasonal variation at a station are controlled by the magnetic declination angle at that station which determines the seasonal variation of the sunset times and hence the integrated pedersen conductivity longitudinal gradient at its magnetic conjugate e layers the amplitude of the prereversal peak on the other hand undergoes the influence of the magnetic declination angle as well as of the thermospheric zonal wind component

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

multiple sources supply eolian mineral dust to the atlantic sector of coastal antarctica evidence from recent snow layers at the top of berkner island ice sheet the sr and nd isotopic composition of dust extracted from recent snow layers at the top of berkner island ice sheet located within the filchner ronne ice shelf at the southern end of the weddell sea enables us for the first time to document dust provenance in antarctica outside the east antarctic plateau eap where all previous studies based on isotopic fingerprinting were carried out berkner dust displays an overall crust like isotopic signature characterized by more radiogenic 87sr 86sr and much less radiogenic 143nd 144nd compared to dust deposited on the eap during glacial periods differences with eap interglacial dust are not as marked but still significant indicating that present day berkner dust provenance is distinct at least to some extent from that of the dust reaching the eap the fourteen snow pit sub seasonal samples that were obtained span a two year period 2002 2003 and their dust sr and nd isotopic composition reveals that multiple sources are at play over a yearly time period southern south america patagonia in particular likely accounts for part of the observed spring summer dust deposition maxima when isotopic composition is shifted towards younger isotopic signatures in the spring possible additional inputs from australian sources would also be supported by the data most of the year however the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in east antarctica which carry old crust like isotopic fingerprints whether the restricted east antarctic ice free areas produce sufficient eolian material has yet to be substantiated however the fact that large 5 mu m particles represent a significant fraction of the samples throughout the entire time series supports scenarios that involve contributions from proximal sources either in patagonia and or antarctica possibly including snow free areas in the antarctic peninsula and other areas as well this also indicates that additional dust transport which does not reach the eap must occur at low tropospheric levels to this coastal sector of antarctica

a study of tomographically reconstructed ionospheric images during a solar eclipse the low latitude ionospheric tomography network litn consists of a chain of six naval navigation satellite system nnss receiving stations established along 121 e longitude from a geographic latitude of 14 6 n to 31 n it is specifically designed to observe large scale ionospheric variations over the equatorial anomaly region by using tomographic imaging techniques recently the network litn was applied to observations of the october 24 1995 solar eclipse two dimensional images of ionospheric electron density during the eclipse period were reconstructed these images and the corresponding results from a nearby ionosonde were compared with those for a reference day it is shown that during the eclipse day the ionosphere experienced some large scale changes in particular four episodes of electron density enhancement or depression have been identified 1 the maximum enhancement occurred before the maximum phase of the solar eclipse at approximately 7 10 n geomagnetic latitude at the 275 300 km ionospheric height 2 the second enhancement appeared roughly 3 1 2 hours after the maximum obscuration at 15 22 n geomagnetic latitude and 300 325 km ionospheric height 3 the largest electron density depression occurred roughly 2 hours after the maximum obscuration at approximately 9 15 n geomagnetic latitude and on both the bottom and topside ionosphere 4 the second depression occurred about 4 hours after the maximum obscuration at approximately 5 5 n geomagnetic latitude and mainly on the topside ionosphere more detailed study suggests that the two enhancements have their origins in the ionospheric day to day variations the first depression is related to the combined photochemical and the equatorial fountain effects and the second depression may have its origin in geomagnetic coupling between conjugate ionospheres these observations are interpreted within the framework of ionospheric dynamics in the equatorial anomaly region

stratigraphy and paleoceanography of pliocene deposits of karaginsky island eastern kamchatka u s s r abstract the lithology and paleontology of pliocene deposits from karaginsky island off eastern kamchatka peninsula u s s r are described in order to provide a paleoceanographic reconstruction of this region of the eastern north pacific ocean the stratigraphic sequence is divided into three suites the limimtevayamian the ust limimtevayamian and the tusatuvayamian which correspond to three standard pacific diatom zones the thalassiosira oestrupii neodenticula koizumi n kamtschatica and n koizumi the entire sequence is further subdivided into six members and 18 distinct beds on the basis of molluscan assemblages and three members and seven beds on the basis of benthic foraminiferal assemblages marine ostracodes are described from the limimtevayamian suite the marine invertebrate assemblages from karaginsky island provide evidence that 1 ocean water temperatures were warmer than today about 4 ma and again about 3 5 3 0 ma 2 several arctic atlantic species of molluscs and ostracodes migrated to the eastern north pacific between 4 2 3 0 ma presumably through the proto bering strait 3 many species found in the karaginsky island pliocene represent pacific taxa which migrated through the arctic into the north atlantic during the late pliocene

sediment transport by wind toward a general model a general model of eolian sediment transport by both saltation and suspension is developed saltation is analyzed through calculations of single trajectories given initial conditions of liftoff speed angle and spin profiles of particle concentration and mass flux generated by assuming that all trajectories are identical display distinct maxima at the top of the trajectory by incorporating the realistic distribution of trajectories that arises from the stochastic nature of grain impacts with a granular bed the model yields monotonic decreases in particle concentration and mass flux with height in accordance with published empirical data the analysis of suspension as the balance between downward advective flux as a result of the settling of grains and their upward diffusive flux as a result of turbulence results in concentration profiles that fall off as power laws with height also in accordance with empirical data a relation for reference level concentrations is presented for both blowing snow and dust profiles the solutions for saltation and suspension are combined to yield mass flux profiles for the entire range of grain sizes in the bed the saltation layer emerges naturally as that region where the total flux of saltating grains exceeds that of suspended grains the model points clearly to the need for further research on the stochastic grain bed interactions which control both the probability distribution of liftoff velocities in saltation and the production of fine particles in suspension

characteristics of intense space weather events as observed from a low latitude station during solar minimum 1 using a dual frequency high resolution software based gps receiver tec and phase have been monitored from calcutta india situated near the northern crest of the equatorial ionization anomaly for studying some space weather events during 2008 2010 data from a dual frequency ionospheric tec and scintillation monitor operational at this station under the international scinda program of the u s air force have also been used this paper presents two cases of intense space weather events occurring in the equatorial latitudes under magnetically quiet conditions during the abnormally prolonged minimum of solar cycle 24 high values of s4 with maximum 0 8 were noted on gps links located almost due south of calcutta 22 58 n 88 38 e geographic magnetic dip 32 n when the look angles of the satellites are more or less aligned with the axis of the anisotropic field aligned irregularities over the magnetic equator associated bite outs in tec of amplitude 40 units were recorded in the local post sunset hours well defined patches of phase scintillations and associated cycle slips were identified on these days higher values of ambient ionization were noted and the diurnal maximum of the electrojet strength was found to be delayed followed by a significant rise of the f region with a high upward drift velocity over the magnetic equator around sunset indicated by ionosonde measurements of in situ ion density using leo dmsp corroborate the f region height rise presence of irregularities in ionization density distributions around 450km was found from c nofs measurements

retreat history of the ross ice sheet shelf since the last glacial maximum from deep basin sediment cores around ross island abstract radiocarbon dated sediment cores from deep basins beneath the mcmurdo ice shelf and seasonally open water north of ross island mcmurdo sound display a characteristic succession of sedimentary facies that document the retreat of the ross ice sheet at the last glacial maximum to its present ice shelf configuration the facies succession records a transition from a nearly grounded ice sheet to open marine environments north of ross island that comprises in ascending stratigraphic order 1 slightly consolidated clast rich muddy diamict dominated by basement clasts from the transantarctic mountains and interpreted as melt out from the basal layer debris proximal to a retreating grounding zone 2 sparsely fossiliferous reworked diatom frustules and non bioturbated mud lacking lonestones interpreted as a sub ice shelf facies and 3 diatom mud and diatom ooze indicative of open marine conditions with evidence of iceberg rafting the succession in the open marine lewis basin north of ross island is similar though the diamict is much sandier and sedimentation rates 1 2 orders of magnitude higher we present a radiocarbon chronology from total organic carbon which implies that lift off of grounded ice in the 900 m deep marine basins surrounding ross island occurred by 10 100 14c years bp following lift off an ice shelf was maintained to the north of ross island until 8900 14c years bp we identify a phase of accelerated retreat at that time between the drygalski trough and ross island immediately preceding the timing of meltwater pulse 1b at 8900 14c years bp the calving line became pinned to ross island significantly decoupling from the grounding line and marking the transition from a retreating ice sheet to the development of the present ice shelf

equatorial plasma fountain and its effects over three locations evidence for an additional layer the f 3 layer the equatorial plasma fountain and equatorial anomaly in the ionospheres over jicamarca 77 w trivandrum 77 e and fortaleza 38 w are presented using the sheffield university plasmasphere ionosphere model under magnetically quiet equinoctial conditions at high solar activity the daytime plasma fountain and its effects in the regions outside the fountain lead to the formation of an additional layer the f3 layer at latitudes within about plus or minus 10 of the magnetic equator in each ionosphere the maximum plasma concentration of the f3 layer which occurs at about 550 km altitude becomes greater than that of the f2 layer for a short period of time before noon when the vertical e b drift is large within the f3 layer the plasma temperature decreases by as much as 100 k the ionograms recorded at fortaleza on january 15 1995 provide observational evidence for the development and decay of an f3 layer before noon the neutral wind which causes large north south asymmetries in the plasma fountain in each ionosphere during both daytime and nighttime becomes least effective during the prereversal strengthening of the upward drift during this time the plasma fountain is symmetrical with respect to the magnetic equator and rises to over 1200 km altitude at the equator with accompanying plasma density depletions in the bottomside of the underlying f region the north south asymmetries of the equatorial plasma fountain and equatorial anomaly are more strongly dependent upon the displacement of the geomagnetic and geographic equators jicamarca and trivandrum than on the magnetic declination angle fortaleza

geographic distribution of the late cenozoic bivalve fortipecten in the northwestern pacific abstract the distribution and migration history of the genus fortipecten a characteristic late cenozoic bivalve is evaluated on the basis of specimens from hokkaido northern japan fossil occurrences indicate that fortipecten species lived in hokkaido from about 7 0 to 1 2 ma the geological occurrences and age of fortipecten in the northwestern pacific imply that the biogeographic history of the species was strongly influenced by climatic fluctuations the latest miocene migration of its geographic range from central hokkaido southward to northern honshu was caused by global cooling its early pliocene expansion northward to kamchatka resulted from warm high stand conditions and its subsequent range contraction resulted from stepwise cooling in the late pliocene to early pleistocene the species became extinct at about 1 2 ma as the result of extreme climatic cooling four species of astartidae co occurred with fortipecten takahashii from three horizons of hokkaido the lowermost horizon about 6 5 ma in the atsuga formation is correlated with the astartidae bearing horizon 5 5 4 8 ma in the bear lake formation in southwestern alaska and indicates the timing of the initial opening of bering strait

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

daytime additional f layer stratification over low midlatitude station of the indian sector under geomagnetic disturbed conditions 1 in this paper the observations of additional f layer stratification are presented in a region which is situated at the outer edge of equatorial ionization anomaly eia zone the digital ionosonde data observed over delhi 28 6 n 77 2 e dip 42 44 n during march april 2001 has been used to carry out the present work the observational period was geomagnetically disturbed and represents the high solar activity phase of 23rd solar cycle the additional transient cusp is frequently observed in the considered months before the noon hours however in this paper only five prominent cases are presented from the analysis of ionograms it is observed that the transient additional cusp is formed between the pre existing f1 and f2 layer hence named as the cusp of f1 5 study reveals that the traveling atmospheric disturbances tads along with the vertical expansion of f layer provides the necessary condition for the existence of this transient feature the intensification of f1 layer along with increased altitude immediately after the disappearance of additional stratification remains one of the fascinating features of the present results the present investigation demonstrates that the daytime f1 and f2 region over low midlatitude station is strongly modulated by the passage of tids originating at high latitudes or by atmospheric disturbances of local origin during the high solar activity period the concurrent presence of tads and the associated disturbance composition appears to be plausible reason behind the present observations

the contribution of aeolian sand and dust to iron fertilization of phytoplankton blooms in southwestern ross sea antarctica iron is a limiting micronutrient for primary production in the ross sea antarctica recent observations reveal low dissolved fe dfe concentrations in the ross sea polynya following high initial rates of primary production in summer after the dfe winter reserve has been consumed significant new sources of dfe are therefore required to further sustain phytoplankton blooms iron from aeolian sand and dust asd released from melting sea ice is one potential source to constrain aeolian fe inputs we determined asd mass accumulation rates and the total and soluble fe content of asd on sea ice in mcmurdo sound southwestern sw ross sea the mean mass accumulation rate was 1 5 g m 2 yr 1 total fe content of this asd was 4 1 wt and the percentage of soluble fe was 11 1 our mean estimate of the bulk aeolian dfe flux of 122 1 mol m 2 yr 1 for the mcmurdo sound region suggests that aeolian fe can support between 9 0 109 and 4 1 1011 mol c yr 1 0 1 4 9 tg c yr 1 of new primary production this equates to only 15 of new primary production in the sw ross sea suggesting that aeolian dfe is a minor component of seasonal fe supply the very high asd accumulation on sea ice in mcmurdo sound compared to other regions of antarctica suggests that our results represent the upper limit of dfe supply to the ocean from this source in the ross sea

aeolian sediment transport and deposition in a modern high latitude glacial marine environment aeolian sand and dust in polar regions are transported offshore over sea ice and released to the ocean during summer melt this process has long been considered an important contributor to polar sea floor sedimentation and as a source of bioavailable iron that triggers vast phytoplankton blooms reported here are aeolian sediment dispersal patterns and accumulation rates varying between 0 2 g m 2 yr 1 and 55 g m 2 yr 1 over 3000 km2 of sea ice in mcmurdo sound south west ross sea adjacent to the largest ice free area in antarctica sediment distribution and the abundance of southern mcmurdo volcanic group derived glass show that most sediment originates from the mcmurdo ice shelf and nearby coastal outcrops almost no sediment is derived from the extensive ice free areas of the mcmurdo dry valleys due to winnowed surficial layers shielding sand sized and silt sized material from wind erosion and because of the imposing topographic barrier of the north south aligned piedmont glaciers southerly winds of intermediate strength ca 20 m sec 1 are primarily responsible for transporting sediment northwards and offshore the results presented here indicate that sand sized sediment does not travel more than ca 5 km offshore but very fine sand and silt grains can travel 100 km from source for sites 10 km from the coast the mass accumulation rate is relatively uniform 1 14 0 57 g m 2 yr 1 three orders of magnitude above estimated global atmospheric dust values for the region this uniformity represents a sea floor sedimentation rate of only 0 2 cm kyr 1 well below the rates of 9 cm kyr 1 reported for biogenic dominated sedimentation measured over much of the ross sea these results show that even for this region of high windblown sediment flux aeolian processes are only a minor contributor to sea floor sedimentation excepting areas proximal to coastal sources

foehn winds in the mcmurdo dry valleys antarctica the origin of extreme warming events abstract foehn winds resulting from topographic modification of airflow in the lee of mountain barriers are frequently experienced in the mcmurdo dry valleys mdvs of antarctica strong foehn winds in the mdvs cause dramatic warming at onset and have significant effects on landscape forming processes however no detailed scientific investigation of foehn in the mdvs has been conducted as a result they are often misinterpreted as adiabatically warmed katabatic winds draining from the polar plateau herein observations from surface weather stations and numerical model output from the antarctic mesoscale prediction system amps during foehn events in the mdvs are presented results show that foehn winds in the mdvs are caused by topographic modification of south southwesterly airflow which is channeled into the valleys from higher levels modeling of a winter foehn event identifies mountain wave activity similar to that associated with midlatitude foehn winds these events are found to be caused by str

seasonal variations of the ionospheric electron densities retrieved from constellation observing system for meteorology ionosphere and climate mission radio occultation measurements 1 we collected the ionospheric electron density ne profiles from the formosat 3 cosmic f3 c radio occultation measurements to investigate the seasonal behaviors of daytime ne in the altitude range of 200 560 km harmonic analysis of the ne at different altitudes provides unprecedented detail of the seasonal behaviors of ne at low solar activity lsa global maps of seasonal harmonic components indicate that there are strong annual and semiannual variations in daytime ne which have distinct latitudinal and altitudinal dependency the semiannual component predominates over the annual variation in the equatorial regions and at high latitudes in the east asian and south atlantic sectors at low altitudes and at higher altitudes the semiannual component predominates in the equatorial region but recedes in other regions the semiannual variation peaks in equinoctial months in most regions while it has maxima in solstice months first in the south pacific region around 30 s 120 w at 250 km altitude and expanding over the south pacific and south atlantic oceans at higher altitudes moreover there is a region around 45 s 30 w with a dominant semiannual component moving toward east north with increasing altitude in the range of 200 270 km these two interesting features are novel but are not reported yet the relative amplitude of the annual component of ne has hemispheric asymmetry which is prominent at high altitudes in the southern hemisphere the winter seasonal anomaly widely exists in the northern hemisphere and southern low latitudes and in indian ocean region at low altitudes but gradually disappears at higher altitudes further in equatorial regions a new finding is the obvious wave like pattern in the longitudinal structure of the amplitudes of seasonal harmonic components in equatorial regions which supports possible couplings of sources with lower atmospheric origins in the longitudinal variations of ne

meteorological controls on sand transport and dune morphology in a polar desert victoria valley antarctica the hyperarid polar desert of the mcmurdo dry valleys contains an abundance of aeolian sedimentary deposits the largest in antarctica providing a unique setting for studying cold climate aeolian processes and dune morphology meteorological controls on sand transport and changes in dune morphology were monitored for 11 days in november december 2004 on a barchan dune in the victoria valley mcmurdo dry valleys sand transport in this environment was found to be influenced by 1 interparticle cohesion ice bonding 2 diurnal variations in the speed of thermally driven easterly valley winds due to reduced solar heating by night and 3 topographically modified foehn southwesterly winds the threshold entrainment velocity during easterly valleys winds was 5 3 m s at 0 4 m 0 21 m s warm dry and gusty foehn southwesterly winds were found to promote aeolian processes by dislodging surface sediments with dune morphology responding rapidly importantly no diurnal signal in sand transport was observed under these conditions when wind speed and sand transport occurred independently of solar heating measured changes in dune morphology indicate that the dune field of the victoria valley under current environmental conditions is in dynamic equilibrium with frequent up valley sand transport by thermally generated valley winds balanced by less frequent but greater magnitude down valley sand transport by moderate to strong foehn southwesterlies this results in little net movement of dunes and subsequent change in the position of the dune field accordingly we believe that regional scale shifts in climate that cause change in the synoptic circulation patterns of the ross sea region that affect the frequency of either the up valley easterlies or down valley foehn winds will result in a net change in the morphology of the victoria valley s dune field such change in circulation may become apparent early as change in the morphology of the victoria valley sand dunes we therefore suggest this site should be monitored as an indicator site for identifying change in regional weather and climate

debris characteristics and ice shelf dynamics in the ablation region of the mcmurdo ice shelf antarctica this paper presents observations and measurements of debris characteristics and ice shelf dynamics in the ablation region of the mcmurdo ice shelf in the ross sea sector of antarctica ice shelf surface processes and dynamics are inferred from a combination of sedimentological descriptions ground penetrating radar investigations and through ablation velocity and ice thickness measurements field data show that in the study area the ice shelf moves relatively slowly 1 5 18 3 m a 1 has high ablation rates 43 441 mm during 2003 04 summer and is thin 6 22 m the majority of debris on the ice shelf was originally transported into the area by a large and dynamic ice sheet ice shelf system at the last glacial maximum this debris is concentrated on the ice shelf surface and is continually redistributed by surface ablation creating an ice cored landscape of large debris rich mounds ice shelf flow forming medial moraines and meltwater streams locally reworking material and redistributing it across the ice shelf surface a conceptual model for supraglacial debris transport by contemporary antarctic ice shelves is presented which emphasizes these links between debris supply surface ablation and ice shelf motion low velocity ice shelves such as the mcmurdo ice shelf can maintain and sequester a debris load for thousands of years providing a mechanism by which ice shelves can accumulate sufficient debris to contribute to sediment deposition in the oceans

multiple sources of soluble atmospheric iron to antarctic waters the ross sea antarctica is a highly productive region of the southern ocean significant new sources of iron fe are required to sustain phytoplankton blooms in the austral summer atmospheric deposition is one potential source the fractional solubility of fe is an important variable determining fe availability for biological uptake to constrain aerosol fe inputs to the ross sea region fractional solubility of fe was analyzed in a snow pit from roosevelt island eastern ross sea in addition aluminum dust and refractory black carbon rbc concentrations were analyzed to determine the contribution of mineral dust and combustion sources to the supply of aerosol fe we estimate exceptionally high dissolved fe dfe flux of 1 2 10 6 g m 2 y 1 and total dissolvable fe flux of 140 10 6 g m 2 y 1 for 2011 2012 deposition of dust fe al and rbc occurs primarily during spring summer the observed background fractional fe solubility of 0 7 is consistent with a mineral dust source radiogenic isotopic ratios and particle size distribution of dust indicates that the site is influenced by local and remote sources in 2011 2012 summer relatively high dfe concentrations paralleled both mineral dust and rbc deposition around half of the annual aerosol fe deposition occurred in the austral summer phytoplankton growth season however the fractional fe solubility was low our results suggest that the seasonality of dfe deposition can vary and should be considered on longer glacial interglacial timescales

atmospheric regime of dust and salt through 75 000 years of taylor dome ice core refinement by measurement of major minor and trace metal suites measurement of absolute and relative amounts of dust and salt deposited in the polar ice record is central to several fields of study including nutrient delivery atmospheric deposition of trace elements past wind strengths dust provenance and other aspects of climate and geochemical history we present a method intended to give a more accurate picture than has been possible before of the total amounts and relative proportions of the dust and salt deposited by the atmosphere into polar ice it also permits us to distinguish different compositional types of dust in the ice the method is based on precise measurement of a suite of several metals whose proportions contrast strongly between dust and salt and vary substantially between dust types we apply the method to a small suite of ice samples from the taylor dome core in coastal west antarctica in full glacial times when total impurities were high and dust dominated over salt wind strength in the west antarctic region was apparently high and extensive sea ice cover prevented incorporation of salt into the atmospheric load at the termination of the glacial period increased salt in the dust salt mixture indicates that sea ice diminished but wind strength continued high and unchanged dust composition indicates unchanged source areas at about 10 000 11 000 y b p sea ice cover appears to have briefly returned to glacial conditions but wind conditions remained in the milder postglacial condition soon after sea ice retreated and an abrupt change in dust composition indicates changed source materials or terranes if extended by analysis of more samples from more sites such information on salt and dust could provide firm constraints on past wind strengths extent of sea ice cover deposition fluxes of salt and dust and changing continental source areas of dust for both polar regions of the earth

the vertical flux of biogenic and lithogenic material in the ross sea moored sediment trap observations 1996 1998 abstract as part of the usjgofs aesops program we deployed an array of moored sediment traps and determined the composition and vertical flux of particulate matter through the water column of the continental shelf environment of the ross sea we deployed two moorings with two traps each one mooring was located in the southcentral ross sea along the line of aesops process studies the other mooring was located in the northcentral ross sea the flux in the southern ross sea was generally double that in the north and there was a significant increase in flux into the deep traps indicating horizontal transport and possible focusing of particulate matter the particles are primarily biogenic although lithogenic contributions can increase to over 30 of the flux in the near bottom trap nearer to the ice shelf the fluxes collected by the traps were generally low but within the range of previous observations several unique observations stand out from these data 1 the export of organic matter to 200 m during the spring and summer was extremely low consistent with observations that the ongoing phytoplankton bloom was being stored or recycled in the upper water column 2 a major pulse of biogenic silica export occurred in the fall just as ice was reforming the correlation of this event with lithogenous particles excess fe and with the early breakout of katabatic winds suggests that this event might be related to fe fertilization of diatom production and export 3 the largest flux of organic matter during 1996 1997 was carried by the pteropod limacina helicina and was observed at both moorings under the ice in the late fall just after the diatom pulse although it is difficult to estimate the proportion of these organisms that were swimmers contaminating the flux we believe that a significant fraction settled into the traps and may represent the die out of this herbivore population after the suspended pom concentration had dropped to very low levels fluxes to the upper traps were much lower than estimates of export flux made by other methods during synoptic ship studies these differences are discussed and the fluxes are compared with preliminary data from the roaverrs trap program which was simultaneously deployed in the ross sea

new evidence for the age of bering strait abstract the earliest known opening of bering strait in signaled by the presence in southern alaskan neogene strata of the marine bivalve mollusk astarte which had dwelled throughout the cenozoic in the arctic and north atlantic oceans astarte occurs with age diagnostic marine diatoms in the middle and upper miocene bear lake formation of the alaska peninsula southwestern alaska the diverse diatom flora of more than 100 taxa contains species characteristic of subzone b of the neodenticula kamtchatica zone of the north pacific diatom biochronology which has an age range of 4 8 5 5 ma this inferred age for an early opening of bering strait predates the generally cited ages of 3 1 4 1 ma stratigraphic data suggest that the first opening of the strait may have occurred even earlier

evidence for an early opening of the bering strait the first opening of the bering strait was an important palaeogeographical and biogeographical event for marine and terrestrial biotas in asia and north america1 2 3 and an oceanographic event of global importance4 5 6 this event however has never been precisely dated so it has not been accurately incorporated into models of global biogeography and oceanography a recent find of the bivalve mollusc astarte in southern alaska is a clear signal that the strait had opened by at least the late miocene or earliest pliocene epochs because this genus otherwise dwelled only in the arctic and north atlantic oceans at that time1 2 here we show that marine diatoms with astarte are correlative with subzone b of the neodenticula kamtschatica zone of the north pacific diatom biochronology yielding an age range of 4 8 5 5 myr refs 7 8 stratigraphic information suggests that this may be a minimum age range for the strait s first opening which evidently occurred between 4 8 and 7 3 7 4 myr ago our results contrast with past studies9 10 11 12 13 that suggested an age of 3 1 4 1 myr for the initial opening of the bering strait

observations of flow and ice ocean interaction beneath the mcmurdo ice shelf antarctica 1 the first oceanographic data from beneath the mcmurdo ice shelf antarctica are presented here with synchronous observations from southern mcmurdo sound multilevel current profiles at three sites over spring tide revealed primarily k1 diurnal tides with net transport from mcmurdo sound into the basin beneath the mcmurdo ice shelf the time series in southern mcmurdo sound captured the 14 day tidal phase shift and showed that transport into the subice shelf cavity was even greater over neap tide with average transport 1 8 sv mcmurdo sound sea ice cover during this period was the heaviest in 25 years of satellite record and was associated with the proximity of two massive icebergs b 15a and c 19 the warmest waters observed beneath the ice shelf were set at the surface freezing temperature probably through recent interaction with this extensive sea ice cover observed ranges of temperature and salinity were narrowed to the extent that neither antarctic surface water nor high salinity shelf water were observed beneath the ice shelf we anticipate that in years with more typical summer sea ice cover surface waters swept beneath the ice shelf will be significantly warmer having even greater potential for basal melt near the ice shelf front our observations also exhibit some of the interactions particular to the subice shelf ocean environment these include occurrence of platelet ice in ice shelf meltwater boundary layer friction effects from the ice cover on the ocean and tidal currents driving enhanced melting near the ice shelf front

characteristics of the ross ice shelf air stream as depicted in antarctic mesoscale prediction system simulations 1 streamlines of the mean annual near surface winds over the antarctic continent suggest a confluent channeling of the drainage flows off the ice sheets and onto the ross ice shelf a persistent cyclonic circulation to the north of the ice shelf supports a large scale pressure field that reinforces the continental drainage flows owing to these two processes an enhanced low level airflow is present along the southern and western sections of the ross ice shelf the resulting air stream known as the ross ice shelf air stream ras is one of the persistent and prominent low level wind features seen in the antarctic real time mesoscale simulations of the antarctic atmosphere and high southern latitudes using a modified version of the pennsylvania state university national center for atmospheric research mesoscale modeling system have been ongoing since the 1999 2000 austral field season model results from the 1 year period november 2001 to october 2002 have been analyzed to investigate the mean structure and modulation of the ross ice shelf air stream analyses of model results show the low level air stream over the western ross ice shelf has a wind speed maxima that is linked to the steep topography to the west individual cases of strong wind events appear to contain a significant barrier wind component that arises from cold air damming against the transantarctic mountains cyclones that frequently form in the ross sea are shown to establish conditions that promote barrier wind dynamics and thus significantly modulate the intensity of the ras

comparing the epica and vostok dust records during the last 220 000 years stratigraphical correlation and provenance in glacial periods a new aeolian dust record from the first 2200 m of the epica dome c ice core 75 06 s 123 21 e covering about 220 000 years of climatic history is compared to the vostok 78 28 s 106 48 e ice core nature 399 1999 429 the two dust profiles are very similar and several common dust events allow to establish stratigraphical links the late quaternary period is characterized at both sites and likely overall east antarctic plateau by high dust input during glacial periods in the epica dome c ice core the dust flux rises by a factor of 25 20 and 12 in glacial stages 2 4 and 6 with respect to interglacial periods holocene and stage 5 5 the magnitude and pattern of changes are comparable in the vostok ice core in this study the geographical origin of ice core dust icd in cold periods has been investigated at both sites through 87sr 86sr versus 143nd 144nd isotopic tracers following the previous studies of grousset et al earth planet sci lett 111 1992 175 and basile et al earth planet sci lett 146 1997 573 the new data and the existing ones allow to define the isotopic fields for dust at the two antarctic sites that are almost identical and restricted into the 0 708 87sr 86sr 0 711 and 5 end 0 5 ranges this suggests a common geographical provenance for dust at vostok and dome c and for all the glacial periods of the late pleistocene to decipher the icd provenance more than 50 samples of loess and aeolian deposits sands and fluvioglacial sediments from the potential source areas psas of the southern hemisphere have been collected however the methodology has been refined with respect to former studies first the isotopic fractionation that can occur in function of grain size has been taken into account and the psa s signature has been defined in the 5 m size range within which fine grained dust reaching antarctica is found moreover a possible contribution from carbonates on the samples from psas has also been also considered south africa and australia can be excluded as dominant sources but a partial overlap arises among southern south america new zealand and the antarctic dry valleys isotopic fields these latter two documented for the first time a possible contribution from all these three sources cannot be excluded but complementary arguments suggest the dominant contribution to east antarctic dust in glacial times deriving from the southern south american region of patagonia and the pampas this study shows a first order uniformity in the dust flux and geographical provenance to the east antarctica plateau during glacial periods

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

on the equatorial anomaly of the ionospheric total electron content near the northern anomaly crest region daily contour charts of the ionospheric total electron content in latitude versus local time coordinates have been used to study the behavior of the development of the equatorial anomaly around the northern anomaly crest region the daily development of the equatorial anomaly shows quite large day to day variabilities not only on magnetically disturbed days but also on quiet days the daily maximum anomaly crest moves poleward as the magnitude of the total electron content of the daily maximum anomaly crest increases the increase of the equatorial electrojet strength also results in a poleward movement of the anomaly crest no significant correlation exists between the anomaly crest and the magnetic ital ap index the monthly mean diurnal development of the equatorial anomaly shows a remarkable seasonal difference with the anomaly largest in equinoxes and slightly larger in winter than in summer copyright american geophysical union 1989

new occurrences of fortipecten hallae dall 1921 mollusca bivalvia in the pliocene of the north pacific abstract the large north pacific bivalve mollusk index fossil fortipecten hallae dall 1921 is present in a well dated stratigraphic section of the milky river formation alaska peninsula southwestern alaska co occurring marine diatoms belong to the upper part of the subzone b of the neodenticula kamtschatica diatom zone of the north pacific diatom chronostratigraphy with an age range of 4 8 5 1 ma early pliocene based on coeval occurrences in northeastern kamchatka russia and synchronous changes in the two molluscan assemblages f hallae is a useful indicator of early pliocene climatic warming along the high latitude north pacific margin

investigation of the age and migration of reversing dunes in antarctica using gpr and osl with implications for gpr on mars gpr provides high resolution images of aeolian strata in frozen sand in the mcmurdo dry valleys of antarctica the results have positive implications for potential gpr surveys of aeolian strata on mars within the lower victoria valley seasonal changes in climate and a topographically constrained wind regime result in significant wind reversals as a consequence dunes show reversing crest lines and flattened dune crests ground penetrating radar gpr surveys of the dunes reveal sets of cross strata and low angle bounding surfaces produced by reversing winds summer sand transport appears to be dominant and this is attributed to the seasonal increase in solar radiation solar radiation which heats the valley floor melts ice cements making sand available for transport at the same time solar heating of the valley floor generates easterly winds that transport the sand contributing to the resultant westward dune migration the location of the dune field along the northern edge of the lower victoria valley provides some shelter from the powerful foehn and katabatic winds that sweep down the valley topographic steering of the winds along the valley and drag against the valley wall has probably aided the formation migration and preservation of the dune field optically stimulated luminescence osl ages from dune deposits range from 0 to 1 3 kyr showing that the dune field has been present for at least 1000 yr the osl ages are used to calculate end point migration rates of 0 05 to 1 3 m yr which are lower than migration rates reported from recent surveys of the packard dunes and lower than similar sized dunes in low latitude deserts the relatively low rates of migration are attributed to a combination of dune crest reversal under a bimodal wind regime and ice cement that reduces dune deflation and restricts sand entrainment

eolian input into the late ordovician postglacial soom shale south africa the soom shale member of the cedarberg formation south africa is a key early paleozoic lagerstatte that directly overlies glacigenic deposits of the late ordovician glacial maximum it was deposited on the gondwanan craton during deglacial transgression we show that it contains a substantial coarse silt to fine sand component that occurs in discrete laminae intimately associated with plankton derived organic material we interpret this component as loess sourced from glacially derived debris and blown into the sea either directly or across seasonal sea ice as happens today on the mcmurdo ice shelf antarctica falling through the water column this material likely stimulated production of phytoplankton which then sank as sediment loaded aggregates in marked sedimentary partitioning these silt and or organic laminae alternate with fine organic poor mud laminae that likely represent river derived nepheloid plumes and that sporadically thicken into centimeter scale mud turbidites sustained eolian input directly into the surface water may have been key to maintaining the high productivity of the soom sea and then via eutrophication and anoxia to the exceptional preservation of its biota

antarctica s dry valleys a potential source of soluble iron to the southern ocean the soluble iron content and dust emission potential of sediment samples collected from the taylor valley in the mcmurdo dry valleys mdvs and sea ice in the mcmurdo sound were evaluated to determine whether inputs to the southern ocean may be sufficient to affect ocean productivity our results show that the dust generating potential from the mdvs soils are comparable to those of sediments from other major dust sources in the southern hemisphere sediments from the mdvs and sea ice are one order of magnitude richer in soluble iron than those in other dust sources in the southern hemisphere forward trajectory analyses show that the dust from the mdvs is likely to be deposited in the southern ocean these results provide evidence of the possible supply of soluble iron to the southern ocean associated with dust transport from the mdvs should climate change expand the exposed areas of the continent

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

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 2 sedimentologic and stratigraphic signature sedimentologic geotechnical geochemical and accelerator mass spectrometer ams radiocarbon data from two marine geologic cruises in the ross sea have allowed us to constrain facies relationships and temporal changes in the west antarctic ice sheet the selection of core sites was facilitated by the use of multibeam bottom imagery and a good quality chirp subbottom reflection system a complex but consistent succession of facies documents a number of environments from subglacial to open marine massive mud rich diamictons have low water contents contain in places a calcareous microfossil assemblage show minimal textural variation and contain low and uniform total organic carbon values this reflects a subglacial setting this unit passes upward into a stratified thin granulated facies consisting of pelletized sandy muddy gravel that is loosely compacted and contains a variable water content and concentrated horizons of pebble sized clasts this facies reflects the lift off zone or thin water film between the basal debris and sea floor overlying this unit are silty clays that contain a well sorted very fine grained sand component there are no coarse grains within this unit this facies is in part laminated and reflects deposition beneath an ice shelf near and away from the grounding line zone the ice shelf facies passes upward into a siliceous mud and ooze unit that represents deposition in an open marine setting a sandy volcaniclastic rich subfacies marks the transition from ice shelf to open marine environments found at the calving line the 86 ams radiocarbon dates on organic matter provide an accurate chronology for 19 cores ice shelf conditions were established in the outer drygalski trough by 11 0 25 ka and perhaps earlier this transition took place in the joides basin by 10 8 ka the calving front of the ross ice shelf passed over the drygalski trough at 74 s by 9 5 0 25 ka the timing of deglaciation in the ross sea calls into question current models for the contribution of antarctic glacial ice to holocene sea level rise and suggests that recession was relatively gradual and more closely aligned with northern hemisphere deglaciation and its associated eustatic pulse

longitudinal structure of the equatorial ionosphere time evolution of the four peaked eia structure 1 longitudinal structure of the equatorial ionosphere during the 24 h local time period is observed by the formosat 3 cosmic f3 c satellite constellation by binning the f3 c radio occultation observations during september and october 2006 global ionospheric total electron content tec maps at a constant local time map local time tec map referred as lt map can be obtained to monitor the development and subsidence of the four peaked longitudinal structure of the equatorial ionosphere from lt maps the four peaked structure starts to develop at 0800 1000 lt and becomes most prominent at 1200 1600 lt the longitudinal structure starts to subside after 2200 2400 lt and becomes indiscernible after 0400 0600 lt in addition to tec ionospheric peak altitude also shows a four peaked longitudinal structure with variation very similar to tec during daytime the four peaked structure of the ionospheric peak altitude is indiscernible at night with global local time maps of ionospheric tec and peak altitude we compare temporal variations of the longitudinal structure with variations of e b drift from the empirical model our results indicate that the observations are consistent with the hypothesis that the four peaked longitudinal structure is caused by the equatorial plasma fountain modulated by the e3 nonmigrating tide additionally the four maximum regions show a tendency of moving eastward with propagation velocity of several 10 s m s

early season depletion of dissolved iron in the ross sea polynya implications for iron dynamics on the antarctic continental shelf 1 the ross sea polynya is among the most productive regions in the southern ocean and may constitute a significant oceanic co2 sink based on results from several field studies this region has been considered seasonally iron limited whereby a winter reserve of dissolved iron dfe is progressively depleted during the growing season to low concentrations 0 1 nm that limit phytoplankton growth in the austral summer december february here we report new iron data for the ross sea polynya during austral summer 2005 2006 27 december 22 january and the following austral spring 2006 16 november 3 december the summer 2005 2006 data show generally low dfe concentrations in polynya surface waters 0 10 0 05 nm in upper 40 m n 175 consistent with previous observations surprisingly our spring 2006 data reveal similar low surface dfe concentrations in the polynya 0 06 0 04 nm in upper 40 m n 69 in association with relatively high rates of primary production 170 260 mmol c m 2 d 1 these results indicate that the winter reserve dfe may be consumed relatively early in the growing season such that polynya surface waters can become iron limited as early as november i e the seasonal depletion of dfe is not necessarily gradual satellite observations reveal significant biomass accumulation in the polynya during summer 2006 2007 implying significant sources of new dfe to surface waters during this period possible sources of this new dfe include episodic vertical exchange lateral advection aerosol input and reductive dissolution of particulate iron

aeolian dust in the talos dome ice core east antarctica pacific ross sea sector victoria land versus remote sources over the last two climate cycles a new ice core taldice drilled at talos dome east antarctica ross sea sector preserves a ca 250 ka long record of palaeoclimate and atmospheric history we investigate dust variability and provenance at the site during glacial periods and the holocene through the sr nd isotopic composition of ice core dust and potential source areas psa we provide new isotopic data on dust sources from victoria land such as regoliths glacial drifts aeolian sands and beach deposits some of these sources are located at high altitude and are known to have been ice free throughout the pleistocene the major features of the taldice dust record are very similar to those from central east antarctica during glacial times south america was the dominant dust supplier for talos dome as well as for the entire east antarctic plateau conversely during the holocene the principal input of mineral dust at talos dome probably derives from proximal sources which are the ice free areas of northern victoria land located at similar altitude with respect to the drilling site atmospheric mobilisation of dust from these neighbouring areas and transport inland to talos dome can be ultimately associated with advection of maritime air masses from the pacific ross sea region copyright 2010 john wiley sons ltd supporting information can be found in the online version of this article

sand transport by wind on complex surfaces field studies in the mcmurdo dry valleys antarctica 1 field experiments on boundary layer winds and sand transport in the victoria valley antarctica have provided information on the spatial and temporal variability of sand transport across coarse sand surfaces covered with isolated roughness elements rock clusters five sand transport events with a duration ranging between 9 6 and 22 h were studied sand transport threshold velocity was determined using the time faction equivalence method and varied between 0 30 and 0 35 m s 1 mean rates of sand transport ranged from 0 008 to 0 072 g cm s 1 sand transport was variably intermittent with continuous saltation intermittency 1 occurring from 11 to as much as 31 of the time for all events there is a close temporal correspondence between intermittency values shear velocity u m s 1 and the ratio u u t u t is threshold shear velocity sand flux and sand transport intensity as measured by piezoelectric saltation sensors although the roughness density of this site is low partitioning of shear stress between the rock clusters and the intervening sand surface is important to the spatial pattern of sand transport and acts to increase the mean threshold wind shear velocity or shear stress for sediment transport by approximately 1 2 times compared to a bare sand surface the effective local threshold wind shear velocity however varies by up to 6 times from the smoother sand areas to the most protected areas of the rock clusters as a result continuous and widespread sand transport will only occur at this site when the overall wind shear velocity exceeds 0 58 m s 1 1 6 u t minimum

a refined age for the earliest opening of bering strait abstract biostratigraphically and chronostratigraphically important diatoms from the milky river formation alaska peninsula southwestern alaska imply an age range of 5 4 5 5 ma for the oldest north pacific cenozoic occurrence of the marine bivalve mollusk astarte which migrated from the arctic ocean into the north pacific when bering strait first flooded the data presented here are a refinement of the age range of 4 8 5 5 ma reported earlier and imply that bering strait first opened very near the end of the miocene at 5 32 ma

motions of the equatorial ionization anomaly crests imaged by formosat 3 cosmic 1 the equatorial ionization anomaly eia structures and evolutions are imaged using radio occultation observation of the newly launched formosat 3 cosmic f3 c satellite constellation three dimensional ionospheric images provide unprecedented detail of the eia structure globally this paper presents images of the eia structures during july august 2006 and discusses the development and subsidence of the eia clear seasonal asymmetries in both ionospheric electron density and layer height are observed two dimensional cross section maps at a meridian provide dynamic variations and motions of the northern and southern eia crests results suggest that in addition to the asymmetric neutral composition effect interactions between the summer to winter transequatorial neutral winds and strength of the equatorial plasma fountain effect play important roles in producing asymmetric development of the eia crests as imaged by the f3 c

ikaite abundance controlled by porewater phosphorus level potential links to dust and productivity abstractglendonites are pseudomorphs of the mineral ikaite caco3 6h2o after loss of hydration water and occur in distinctive euhedral crystalline forms sometimes clustered as rosettes of up to tens of centimeters in diameter while it is generally accepted that organic rich environments methane seeps and high phosphate levels are important for ikaite formation glendonite occurrences in ancient sedimentary sequences are widely considered to reflect near freezing temperatures even at high latitudes during periods of greenhouse climates to fully understand the paleoenvironmental significance of glendonites a comprehensive examination of the modern ikaite setting is necessary temperature is the most important parameter that has been quantitatively constrained for the presence of ikaite low bottom water temperature while a required condition for formation of the mineral is not adequate for its growth other controls are necessary to explain the absence of ikaite in many cold environments in this