snow megadune fields on the east antarctic plateau extreme atmosphere ice interaction large dune fields occupy more than 500 000 km 2 of the east antarctic plateau the megadunes or long wavelength surface ripples have amplitudes of only a few meters wavelengths of a few kilometers and parallel crests which can extend one hundred kilometers they occur in areas characterized by low accumulation extensively recrystallized snow and strong scattering of the microwave part of the spectrum dune crests are oriented perpendicular to the regional katabatic wind direction snow megadunes are unlikely to be formed by simple wind transport of snow particles

active and passive microwave signatures of antarctic firn by means of field measurements and satellite data the angular dependence and polarization behaviour of back scattering and emission of polar firn at 5 2 ghz and 10 3 ghz were measured during an oversnow traverse in dronning maud land antarctica the signatures emphasize the importance of snow stratification in the interpretation of microwave remote sensing measurements highest backscattering coefficients and little angular variations were observed for refrozen firn near the coast in permanently dry snow areas with high accumulation rates and homogeneous snow morphology showed low backscattering coefficients and high emissivities pronounced layering and related density variations in low accumulation zones resulted in increased polarization differences of brightness temperatures and increased like polarized backscattering coefficients this behaviour is confirmed by the analysis of c band scatterometer measurements of the active microwave instrument aboard the european space agency s ers 1

the time averaged geomagnetic field global and regional biases for 0 5 ma summary palaeodirectional data from lava flows and marine sediments provide information about the long term structure and variability in the geomagnetic field we present a detailed analysis of the internal consistency and reliability of global compilations of sediment and lava flow data time averaged field models are constructed for normal and reverse polarity periods for the past 5 ma using the combined data sets nonzonal models are required to satisfy the lava flow data but not those from sediments alone this is in part because the sediment data are much noisier than those from lavas but is also a consequence of the site distributions and the way that inclination data sample the geomagnetic field generated in the earth s core different average field configurations for normal and reverse polarity periods are consistent with the palaeomagnetic directions however the differences are insignificant relative to the uncertainty in the average field models thus previous inferences of non antipodal normal and reverse polarity field geometries will need to be re examined using recently collected high quality palaeomagnetic data our new models indicate that current global sediment and lava flow data sets combined do not permit the unambiguous detection of northern hemisphere flux lobes in the 0 5 ma time averaged field highlighting the need for the collection of additional high latitude palaeomagnetic data anomalous time averaged field structure is seen in the pacific hemisphere centred just south of hawaii the location of the anomaly coincides with heterogeneities in the lower mantle inferred from seismological data the seismic observations can be partly explained by lateral temperature variations however they also suggest the presence of lateral compositional variations and or the presence of partial melt the role of such heterogeneities in influencing the geomagnetic field observed at the earth s surface remains an unresolved issue requiring higher resolution time averaged geomagnetic field models along with the integration of future results from seismology mineral physics and numerical simulations

late quaternary geomagnetic secular variation from historical and 14c dated lava flows on hawaii a paleomagnetic record of geomagnetic paleosecular variation psv is constructed for the last 4400 years based on 191 sites in historical and 14c dated lava flows from mauna loa kilauea and hualalai volcanoes on the island of hawaii the features of this new record are similar to those recorded by sediments from lake waiau near the summit of mauna kea volcano but overall mean inclinations for the lava flows 31 to 33 depending on window size are nearer the expected dipole field value 35 than is that for the sediments 27 divergence of the inclination records with increasing age suggests that the lake waiau values at depths below 2 m have been affected by compaction related inclination shallowing although magnetic terrain effects cannot be ruled out the rate of psv indicated by the record presented here is highly variable 20 century and a pronounced shift in inclination from 25 to 40 occurred between 1030 and 975 years b p paleomagnetic directions from undated materials can be correlated with our calibrated curve but the resolution is largely dependent on the psv rate and data densities for both the reference and unknown directions the upper part of the puna basalt 18 lava flows previously sampled for paleomagnetism along the northern wall of kilauea s caldera uwekahuna bluff was likely deposited sometime between 1030 and 750 years b p but the lowest two flows beneath the uwekahuna ash 2100 years b p are correlated with an age of 3034 years b p paleomagnetic data for 54 lava flows of the ka u basalt exposed in the northwest wall of mauna loa s summit caldera mokuaweoweo indicate that they probably accumulated over a relatively short time interval 200 years and are assigned to a 1000 to 1199 year b p time window the mean of ages within this window is 1030 years b p but mapping and other 14c dates indicate that these summit overflows are probably closer to 1200 years b p in age

rejuvenated volcanism along the southwest rift zone east maui hawai i east maui volcano is the younger and larger of two volcanoes that form the island of maui hawai i rejuvenated stage h na volcanics lava flows along the southwest rift zone form a veneer lying disconformably on top of the postshield kula volcanics 0 93 0 36 ma most of the 59 documented h na eruptions produced a flows from large cinder cones fourteen new 14c ages and stratigraphic relationships suggest that the onset of rejuvenated volcanism on the southwest rift zone began at least 50 ka showing that the quiescent period between the postshield and rejuvenated stage on east maui was 300 000 years long the shortest yet documented on any hawaiian volcano eruption frequency on the southwest rift zone steadily increased during the past 4800 years there have been at least six eruptions within the past 960 years h na volcanic activity on the southwest rift zone during the past 4800 years may have occurred in three episodes each lasting as long as 1000 years separated by quiescent periods 500 800 years long geochemical data ages and geologic relations provide evidence for five multi flow sequences that were erupted during single events helping to define the eruptive character or style of rejuvenation stage volcanic activity on the southwest rift zone areas covered by the products of individual eruptions vary from 0 14 to 40 km2 and volumes from 0 0003 to 0 40 km3 geochemical evidence shows that the h na lavas are derived from a small range of parental melts that undergo varying degrees of fractional crystallization melts crystallization simulations suggest that h na magmatic evolution occurs at a pressure of 3 kbar 10 11 km depth just above the interface between the volcanic edifice and the oceanic plate the h na volcanics are unique among hawaiian rejuvenation suites in having been erupted along rift zones with a relatively high eruption frequency from a quasi steady state deep crustal magma reservoir

latest pleistocene and holocene geomagnetic paleointensity on hawaii geomagnetic paleointensity determinations from radiocarbon dated lava flows on the island of hawaii provide an estimate of broad trends in paleointensity for holocene time and offer a glimpse of intensity variations near the end of the last glacial period when the data from hawaii are compared with others worldwide the intensity of the geomagnetic field seems to have been reduced from the holocene average by about 35 percent between 45 000 and 10 000 years ago a long term reduction of this magnitude is compatible with reported increases in the production rate of cosmogenic nuclides during the same interval

broad trends in geomagnetic paleointensity on hawaii during holocene time paleointensity determinations have been obtained from 22 basaltic lava flows on the island of hawaii using the thelliers method radiocarbon dating indicates that these flows erupted at intervals ranging from about 200 to 1000 years and results of the experiments provide an estimate of broad trends in geomagnetic paleointensity during holocene time in the vicinity of hawaii most of the samples were obtained from quickly cooled flow margins and as a consequence typically contain two titanomagnetite populations only two of the 79 samples analyzed failed to yield an estimate of the paleofield demonstrating that paleointensities can be obtained from such samples if carefully selected virtual dipole moments calculated for the flows are compared with a published curve of dipole field intensity that was constructed using worldwide archeomagnetic data the large nondipole fields that were previously postulated for the vicinity of hawaii are confirmed and the present data indicate that they were present from about 5000 years b p to perhaps as recently as the past 200 years the data indicate however that these nondipole sources must have been virtually absent between about 12 000 and 5000 years b p as they are at the present time

geomagnetic paleosecular variation in easter island the southeast pacific abstract we collected more than 250 samples from 45 sites in lava flows of the three volcanoes on easter island the k ar whole rock dating was attempted on 13 sites all of the ages obtained are younger than 0 8 ma reliable paleomagnetic directions were obtained from 34 sites the mean vgp position is 89 2 n and 239 1 e with a 95 confidence value of 3 8 the angular dispersion value of easter island vgps was calculated to be 11 8 with an upper limit of 14 1 and a lower limit of 9 8 the angular dispersion value is significantly lower than the values predicted by the theoretical secular variation models the pacific dipole window appears to exist also in the southeast pacific

paleomagnetic correlation of late quaternary lava flows in the lower east rift zone of kilauea volcano hawaii paleomagnetic data reflecting paleosecular variation psv of the geomagnetic field are used to correlate individual lava flows in the lower east rift zone of kilauea volcano this area has been recently mapped based on petrography stratigraphy soil development and degree of weathering of the flows eight 14c dates also provide a framework for the relative age assignments site mean directions of remanent magnetization for historic flows in this region indicate that local magnetic anomalies do not mask the psv signal that within flow angular differences are generally 5 and that temporal resolution of the paleomagnetic directions is of the order of 100 years the paleomagnetic correlations do not conflict with the observed stratigraphic relationships and psv reference curves from dated lava flows and lake sediments have also been used to help determine the sequence of directional groups paleomagnetic grouping of flows into eruptive events indicates a different and perhaps more refined eruptive history for the lower east rift zone than implied by the geologic mapping alone the number of individual flows based on petrographic distinctions is likely the same but the frequency of events including petrographically distinct flows is apparently lower than previously thought flows from ridge crest vents bifurcated by the rift indicate formation of the central graben in this region after 300 years ago possibly related to the 1790 eruptions along dual fractures

paleomagnetic secular variation of the honolulu volcanic series 33 700 ka o ahu hawaii abstract thirty years after the precursory study j geophys res 13 1972 2129 19 dated sites with ages between 33 and 700 ka from the honolulu volcanic series hvs southeastern part of the island of o ahu in hawaii have been revisited a minimum of 16 samples per site have been studied using alternating field and thermal demagnetization both techniques yielded similar results coeval flows could be identified by relying on their k ar ages similar rock magnetic parameters and identical directions reliable paleomagnetic directions have been obtained for all sites two site mean directions which deviate significantly from the geocentric axial dipole gad correspond to periods of low dipole intensity and may thus reflect a larger proportion of non dipole components the average value of the site mean declinations is 358 6 while the mean inclination of 34 5 is 3 5 lower than the value of the geocentric dipole at the site the north geographic pole is largely contained within the uncertainties surrounding the position of the mean virtual geomagnetic poles vgp latitude the deviation of 2 3 in latitude is further reduced by 1 if we consider the existence of a standing small quadrupole component that would represent 5 of the dipole the angular dispersion of the virtual geomagnetic poles 12 is only 1 7 smaller than expected at the site latitude and thus not a firm indication of low secular variation thus there is no significant difference with the global time averaged field for the same period other recent results from the same island for an older time period display similar characteristics but with reverse and normal polarities that are not perfectly antipodal it is suggested that this could result from changes in the mean dipole field intensity during these time intervals this points out to the importance of scrutinizing the entire field vector in any analysis of paleosecular changes these results do not bring any evidence for a persistent field anomaly under hawaii

absolute paleointensity and reversal records from the waianae sequence oahu hawaii usa abstract paleointensity experiments were performed on samples from four parallel sections of the waianae volcanics of oahu hawaii that document 0 4 myr of geomagnetic field variations the records of the three successive gilbert gauss lower and upper mammoth reversals confirm that large oscillations of directions precede or follow the reversals which are similar to waveforms generated by paleosecular variation with their amplitude being considerably amplified by the decrease of the dipole determinations of absolute paleointensity were attempted on 546 samples we only selected data which were obtained from segments covering a large part of the remanent magnetization more than 70 on the average and without concave up arai diagrams this procedure limited the success rate to 14 but provided consistent and reliable paleointensities in addition to other time intervals the results document the field variations surrounding the lower mammoth transition a weak field period dominated before the reversal then the transition was initiated by a transit from normal to reverse polarity followed by a short restoration of the field intensity in reverse polarity a second episode of a very weak field was accompanied by a return to positive inclinations before definitely reaching the reverse polarity a strong and apparent rapid recovery of the dipole following the completion of the reversal culminated at a value of 16 1022 am2 similar to field intensities reported for the other detailed volcanic records of reversals studied so far the asymmetry between the pre and the post reversal phases indicates the importance of field regeneration to initiate a new stable polarity interval

surface lithofacies biofacies and diatom diversity patterns as models for delineation of climatic change in the southeast atlantic ocean abstract distribution of diatom species in surface sediments of the southeast atlantic ocean is regulated by present day oceanographic and hydrodynamic processes five assemblages vectors defined by factor vector analysis reflect different environments and conditions assemblage a is a high diversity flora associated with the nutrient rich relatively cold waters south of the polar front in the diatom ooze belt occurrence of this flora on maud rise and vicinity may reflect periodic occurrence of a polynya in that area assemblage b is a reworked assemblage that dominates the southern portion of the study area productivity there is low reflecting sea ice cover during most of the year the area north of the polar front is dominated by assemblage c whose characteristic species reflect the relatively warm subantarctic surface water winnowing and frustule breakage have altered assemblage d found in three isolated samples by removing relatively delicate forms leaving lag deposits of more robust species assemblage e is a low diversity stress flora reflecting unstable unpredictable environments along the polar front antarctic slope and the northern boundary of winter sea ice these sites are characterized by the sinking of cold water downcore analysis of cores lying adjacent to the polar front and the diatom ooze pelagic clay boundary show evidence for past climatic variation the low trophic level occupied by diatoms and the subsequent sensitivity of these organisms to abiotic environmental parameters such as light quality make relative diatom abundance a useful tool for monitoring fluctuations of winter sea ice and the temperature changes responsible for these fluctuations the position of the polar front has migrated at least three times within the last 0 015 m y b p within the last 0 3 m y b p warm maxima have occurred at approximately 0 0 0 015 0 125 and 0 3 m y b p

biostratigraphic characterization and quaternary microfossil palaeoecology in sediment drifts west of the antarctic peninsula implications for cyclic glacial interglacial deposition abstract the sedano project recovered 19 gravity cores on sediment drifts from the pacific continental margin of the antarctic peninsula camerlenghi et al 1997a high resolution terrigenous sedimentary record of the sediment drifts on the antarctic peninsula pacific margin in ricci c a ed the antarctic region museo nazionale dell antartide siena pp 705 710 fifteen cores were sampled with the aim of developing an integrated biostratigraphy and palaeoecology based on calcareous nannofossils diatoms planktonic and benthic foraminifera framed in a depositional process reconstruction barren gray laminated and brown bioturbated hemipelagic sediments characterize glacial and interglacial cycles respectively analyses from both intervals allow comparison between microfossil occurrence in glacial and interglacial cycles the unit boundaries were drawn more accurately by means of the microfossil distribution on the basis of micropalaeontological and sedimentological evidence interglacial unit c is correlated to oxygen isotope stage 5 thus dating the unit boundaries at 127 and 70 ka peaks in diatom abundance correlate well with interglacial units and indicate high productivity and an open ocean environment a calcareous nannofossil cold taxa association is present in most cores examined and its consistent distribution within interglacial unit c indicates key environmental relationships the occurrence of calcareous nannofossils has been related to temperature tolerance sea ice cover reduction nutrient availability and factors limiting primary productivity our results confirm that coccolithophorids occurred at southern high latitudes in the western marginal basins of the antarctic peninsula during short periods of the late quaternary a foraminiferal assemblage made up of sinistral neogloboquadrina pachyderma and few benthics occurs only in interglacial units correlation of microfossil occurrences with climatic cycles adds information on their palaeoecology and palaeoproductivity in the southern high latitudes

a late quaternary geomagnetic secular variation record from lake waiau hawaii and the question of the pacific nondipole low a continuous paleomagnetic record for the last 13 000 years was obtained from the sediments of lake waiau located near the summit of mauna kea volcano on the island of hawaii the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the hypothesis that there has been anomalously low geomagnetic sv in the central pacific was tested using angular dispersion analysis the inclination record has a mean value of 27 that is much lower than the 35 predicted by the geocentric axial dipole hypothesis the spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100 2000 3300 and 7800 years the approximately 8000 and 3500 year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation respectively the approximately 1100 and 2000 year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections in addition bauer plots of the magnetic vector are dominated by clockwise motion the angular dispersion calculated from lake sediments is 5 9 with respect to the mean virtual geomagnetic pole vgp and 9 1 with respect to the geographic pole both values are much lower than the 13 5 expected from paleosecular variation model g which separates the angular dispersion into components from the dipole and the quadruple families our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central pacific furthermore this geomagnetic behavior persists on time scales of 104 years regional anomalies in temperature topography or electrical conductivity at the core mantle boundary are inferred to cause the low sv

palaeosecular variation over the past 5 myr based on a new generalized database summary a generalized database of global palaeomagnetic data from 3719 lava flows and thin dykes of age 0 5 ma has been constructed for use with a relational database management system the database includes all data whose virtual geomagnetic poles vgp lie within 45 of the spin axis and can be used for studies of palaeosecular variation and for geomagnetic field modelling because many of these data were collected and processed more than 15 20 years ago each result has been characterized according to the demagnetization procedures carried out analysis of these data in terms of the latitude variation of the angular dispersion of vgps palaeosecular variation from lavas strongly suggests that careful data selection is required and that many of the older studies may need to be redone using more modern methods differences between the angular dispersions for separate normal and reverse polarity data sets confirm that many older studies have not been adequately cleaned magnetically therefore the use of the database for geomagnetic field modelling should be carried out with some caution using a vgp cut off angle that varies with latitude the best data set consists of 2636 results that show a smooth increase of vgp angular dispersion with latitude model g for palaeosecular variation which is based on modelling of the antisymmetric dipole and symmetric quadrupole dynamo families provides a good fit to these results

an absolute palaeointensity record from soh1 lava core hawaii using the microwave technique absolute palaeointensity results were obtained from 392 samples 166 of 241 flows from the upper 779 m of the scientific observation hole 1 soh1 basalt core kilauea volcano hawaii using the microwave palaeointensity technique based on k ar dates and a previously published age model this covers the last 45 ka thus giving a high resolution record of geomagnetic intensity in hawaii comparisons with other hawaiian absolute palaeointensity data show similar trend of higher intensity than present day for the last 3 ka and then a general decrease in intensity over the last 45 ka though this study reports consistently lower palaeointensity values direct comparison with previous thellier data from the soh1 core shows some discrepancies between the two methods with the thellier data yielding generally higher palaeointensity estimates than the microwave data in view of these discrepancies between the two methods the introduction of raw palaeointensity data into the public domain is suggested

deflection of paleomagnetic directions due to magnetization of the underlying terrain in the summers of 1989 and 1991 we made 344 near ground level measurements of the ambient geomagnetic field above recent basalts on the island of hawaii using a three component fluxgate magnetometer we studied 12 surface features including a lava pond lava channels long tilted blocks smooth sloping surfaces two fissures and a deep u shaped road cut we observed substantial differences up to 20 between the observed and expected international geomagnetic reference field igrf magnetic field directions over these features except those composed of shelly pahoehoe and a flat horizontally thin lava pond we also observed inclinations that were systematically shallower than the igrf field by up to 5 we show that these shallower inclinations can be explained by the magnetization of the regionally sloping surface of the southern side of the island we found that all of the observed inclination deflections can be explained by simple two dimensional models which assume uniform induced and remanent magnetization parameters in the local terrain our observations imply that the inclination deflections cannot be corrected without a complete knowledge of the preexisting terrain and the remanence in the underlying flows upon which the lavas cooled since this information is rarely available it is difficult or impossible to discriminate between dispersion of paleomagnetic directions caused by the magnetic terrain effect and dispersion due to other factors such as paleosecular variation psv we therefore conclude that psv dispersion parameters cannot be accurately determined from paleomagnetic measurements on highly magnetic volcanic flows we also suggest that some of the geomagnetic excursions inferred from measurements on volcanic rocks may be at least in part due to the magnetic terrain effect it is unnecessary to invoke ad hoc mechanisms such as clastic block or crustal rotations distortion of the top crust or flow deformation to explain the large between site dispersions or inclination anomalies observed in many of the paleomagnetic data from volcanic rocks our observations also bring into question the general reliability of paleomagnetic pole positions inferred from volcanic rocks as a systematic inclination deflection due to local and regional slopes and irregular terrain such as those we observed would lead to a corresponding error in the inferred paleolatitude the magnetic terrain effects also offer alternative explanations for anomalous paleomagnetically inferred plate motions

diatom distribution and paleoceanographic reconstruction in the southern ocean present and last glacial maximum abstract diatom assemblage and preservational data are used to reconstruct paleoceanographic conditions at the last glacial maximum 18 000 yrs bp in the southern ocean from these data the following points can be made about the last glacial maximum in this region 1 contraction and slight northern shift of the belt of well preserved diatoms appears to be related to the northward shift of late spring early summer sea ice cover 2 presence of open ocean though poorly preserved diatom assemblages to the south of this belt strongly suggest that during many summers large areas of the southern ocean were ice free 3 the distribution of thenitzschia kerguelensis factor both in surface sediments and at the last glacial maximum indicates that the gyre systems particularly the weddell gyre were intensified during glacial times 4 although data are sparse in the higher latitude south atlantic there is an indication that the weddell polynya also existed during glacial times although it was shifted a few degrees northward

a holocene paleosecular variation record from 14c dated volcanic rocks in western north america 1 a paleosecular variation psv curve for western north america is presented on the basis of 94 virtual geomagnetic poles vgps from dated volcanic rocks sampled at 446 sites approximately 60 of the paleomagnetic database has been previously published a curve defined by spherical smoothed splines is fitted to the vgps ranked by the quality of the age determinations where the data density is highest between 3690 and 30 years before present b p a d 1950 between 7800 and 7050 years b p and between 14 060 and 12 700 years b p the younger segments of the curve derived from volcanic rocks are similar but less complex than other high resolution psv curves derived from lacustrine sediments particularly the record at fish lake oregon the psv record from lava flows psvl however is perhaps more reliable in its general shape and chronology because of the higher fidelity of volcanic rocks as magnetic field recorders and because of the greater density of 14c dates the new psvl record provides a partial holocene master curve for western north america and will be of particular value in dating geological and archeological materials using paleomagnetic directions

the time averaged geomagnetic field as recorded by lava flows over the past 5 myr summary a recently compiled lava flow data base spanning the last 5 million years is used to investigate properties of the time averaged geomagnetic field more than 90 per cent of the power in the palaeofield can be accounted for by a geocentric axial dipole however there are significant second order structures in the field declination and inclination anomalies for the new data base indicate that the main second order signal is the far sided effect and there is also evidence for non zonal structure vgp virtual geomagnetic pole latitude distributions indicate that over the last 5 million years normal and reverse polarity morphologies are different and that any changes in the normal polarity field morphology are undetectable given the present data distribution regularized non linear inversions of the palaeomagnetic directions support all these observations we test the hypothesis that zonal models for the time averaged field are adequate to describe the data and find that they are not non zonal models are needed to fit the data to within the required tolerance level normal and reverse polarity field models obtained are significantly different field models obtained for the brunhes epoch data alone are much smoother than those obtained from combining all the normal polarity data simulations indicate that these differences can be explained by the less extensive data distribution for the brunhes epoch the field model for all of the normal polarity data ln1 contains features observed in the historical field maps although the details differ ln1 suggests that although the two northern hemisphere flux lobes observed in the historical field are stationary to a first order approximation they do show changes in position and amplitude a third less pronounced flux lobe is observed in ln1 over central europe the lack of structure in the southern hemisphere is due in part to the paucity of data jackknife estimates of the field models for different subsets of the data suggest that a few sites contribute significant structure to the final field models more conservative estimates of the time averaged field morphology are obtained by removing these sites

last glacial maximum sea surface temperature and sea ice extent in the pacific sector of the southern ocean sea surface temperatures and sea ice extent are most critical variables to evaluate the southern ocean paleoceanographic evolution in relation to the development of the global carbon cycle atmospheric co2 and ocean atmosphere circulation here we present diatom transfer function based summer sea surface temperature ssst and winter sea ice wsi estimates from the pacific sector of the southern ocean to bridge a gap in information that has to date hampered a well established reconstruction of the last glacial southern ocean at circum antarctic scale we studied the last glacial maximum lgm at the epilog time slice 19 000e23 000 calendar years before present in 17 cores and consolidated our lgm picture of the pacific sector taking into account published data from its warmer regions our data display a distinct east west differentiation with a rather stable wsi edge north of the pacific antarctic ridge in the ross sea sector and a more variable wsi extent over the amundsen abyssal plain the zone of maximum cooling 4 k during the lgm is in the present subantarctic zone and bounded to its south by the 4 c isotherm the isotherm is in the ssst range prevailing at the modern antarctic polar front representing a circum antarctic feature and marks the northern edge of the glacial antarctic circum polar current acc the northward deflection of colder than modern surface waters along the south american continent led to a significant cooling of the glacial humboldt current surface waters 4e8 k which affected the temperature regimes as far north as tropical latitudes the glacial reduction of acc temperatures may also have resulted in significant cooling in the atlantic and indian southern ocean thus enhancing thermal differentiation of the southern ocean and antarctic continental cooling the comparison with numerical temperature and sea ice simulations yields discrepancies especially con cerning the estimates of the sea ice fields but some simulations reproduce well our proxy based tem perature data

fluctuations in late quaternary diatom abundances stratigraphic and paleoclimatic implications from subantarctic deep sea cores abstract we determined relative abundance of the marine diatoms eucampia antarctica and hemidiscus karstenii for the late quaternary in four deep sea cores from the subantarctic region of the southeast indian sector of the southern ocean abundance variations of the former species are shown to be a close proxy for the oxygen isotope record where increased relative abundance approximates glacial intervals and low relative abundance approximates interglacials these abundance variations which reflect orbital forcing are believed to be due to increased presence of sea ice or icebergs during glacial intervals

persistent anomalous inclinations recorded in the koolau volcanic series on the island of oahu hawaii usa between 1 8 and 2 6 ma abstract ten sites of basaltic lava flows from the koolau series island of oahu hawaii were selected to improve the determination of the matuyama time averaged geomagnetic field between 1 8 and 2 6 ma identical primary directions with reverse polarity carried by magnetite were isolated by alternating field and thermal demagnetization in 13 16 specimens from each site the final mean direction points south while the inclination is 7 lower than the inclination of the geocentric axial dipole gad this offset is reduced after correcting the site latitude for the pacific plate motion which has been neglected so far in most studies the mean corrected direction is almost perfectly antipodal to the brunhes mean direction derived from the honolulu series in the same island despite this correction the inclination remains 3 6 larger than the inclination of the axial dipole and cannot be accounted for by a small axial quadrupole which would reverse with the dipole the mean inclinations of other hawaiian records mostly younger than 1 ma involving long sequences of lava flows exhibit similar deviations from the gad which are too large to be accounted for by a small axial quadropole tilting of all sections is difficult to defend for so many localities and persistant secondary components have not been detected thus these inclination anomalies would reflect the presence of a long term standing component under hawaii but crustal magnetization linked to the volcanic edifice cannot be completely ruled out

the myth of the pacific dipole window the angular dispersion of virtual geomagnetic poles vgp from lava flows is often cited as having been anomalously low in the pacific during the brunhes epoch because the dispersion from hawaiian lavas is said to be much lower than measured elsewhere this led to the concept of the pacific dipole window or pacific non dipole low because lavas tend to be erupted in bursts of activity many of the hawaiian data are serially correlated and thus cannot necessarily be treated as independent observations geochronological controls as are available for hawaii have been used in a previous analysis to thin the data to try to avoid repeated sampling of the same geomagnetic field unfortunately in that analysis the angular dispersion of vgps was calculated about the mean vgp instead of about the spin axis and thus underestimated the dispersion we have therefore reanalyzed the relevant data using the following criteria 1 only those lavas with 95 10 have been considered 2 a latitude dependent cut off angle is used to eliminate those vectors that are not part of the normal secular variation 3 we have developed a statistical method to rationalise those flows that have repeatedly sampled the same geomagnetic field vector because suitable geochronological controls are rarely available application of this new method to the hawaiian data shows excellent agreement with the results from using geochronological controls where possible we have therefore included this method in our overall analysis as expected the resulting global data are compatible with a fisher distribution about the spin axis brunhes age data from hawaii n 96 independent measurements give a vgp angular dispersion about the spin axis of sf 12 4 and for the pacific region as a whole sf 12 5 n 190 between latitudes 15 and 30 north or south these values are the same as sf 12 4 n 160 calculated for the rest of the world in the same latitude range this clearly demonstrates that the hypothesis of the pacific dipole window may confidently be rejected

the geomagnetic field over the past 5 million years summary the modern geomagnetic field is usually expressed as a spherical harmonic expansion although the palaeomagnetic record is very incomplete in both space and time sufficient data are available from a span of ages to generate time averaged spherical harmonic field models with many degrees of freedom here three data sets are considered directional measurements from lavas inclination measurements from ocean sediments and intensity measurements from lavas individual data are analysed as well as siteaverages using the same methods that have been developed for the modern field to give models for the past 5 myr the normal polarity field model has an axial dipole intensity similar to that of the modern day field whilst the equatorial dipole component is very much smaller the field is not axisymmetric but shows flux concentrations at the core s surface under canada and siberia similar to those observed in the field over historical timescales tests on synthetic data show that it is unlikely that these similarities result from the overprinting of the palaeomagnetic field due to inadequate cleaning of the samples the reverse polarity field model does not show such obvious features but this may be due to the sparsity of the data the patterns observed in the normal polarity field with persistent features in the northern hemisphere and a smooth southern hemisphere could be explained if the present pattern of secular variation is typical of the past several million years this would reveal itself as large variations over time in the direction of the magnetic vector in regions of high secular variation with relatively little change over quieter regions however we have been unable to find any evidence for a geographical pattern of secular variation in the data

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

archaeomagnetic results from mural paintings and pyroclastic rocks in pompeii and herculaneum abstract this work investigates the magnetic remanence associated with red pigments from murals at pompeii and compares their directions to those of the pyroclastic rocks from the vesuvius ad 79 eruption the remanence of the murals is shown using x ray analyses to be carried by haematite murals in thermae stabianae known to have been painted a few years before ad 79 yield an archaeomagnetic direction d 1 2 i 58 0 95 5 5 indistinguishable from that of a nearby kiln d 358 0 i 59 1 95 1 7 evans and mareschal 1989 probably last used immediately prior to the eruption the directions are also consistent with those of fine grained pyroclastic rocks from the eruption d 351 2 i 57 9 95 3 4 and lithic and tile fragments embedded within them d 358 5 i 60 4 95 8 5 other paintings of the 1st century ad yield similar directions with a lower statistical definition this study shows that murals can retain their remanent magnetization for centuries and demonstrates the viability in principle of pictorial remanence as an archaeomagnetic tool

a map of the pacific geomagnetic anomaly during the brunhes chron abstract the persistence of an anomaly of the geomagnetic field in the central pacific ocean has been suggested by many authors however the amplitude and the extent of this feature remain poorly constrained due to insufficient spatial and temporal coverage of the volcanic database records from marine sediments are appropriate to document the long term behavior of the geomagnetic field we studied 11 piston cores from the central and southwestern pacific in order to document the anomaly during the past 800 kyr ten records were retained after applying selection criteria dealing with physical disturbances deformations and any possible sources of inclination errors the results have been integrated into a new data set for the pacific ocean and the eastern indian ocean which combines sedimentary and volcanic records a strong negative inclination anomaly 10 in the southwestern pacific is the main characteristic of the new map in contrast the sedimentary records from the hawaiian area do not indicate any stable feature but rather alternating positive and negative anomalies the new inclination map of the brunhes chron bears striking similarities with the configuration of the historical field particularly the presence of a negative anomaly centered in the eastern indian ocean and southwestern pacific ocean detailed records constraining the archeological period in the southwestern pacific and documenting the spatial extension of the anomaly are now needed to establish a direct link with the present field

geomagnetic field inclinations for the past 400 kyr from the 1 km core of the hawaii scientific drilling project a volcanic record of geomagnetic field inclination for the past 400 kyr at hilo hawaii has been obtained from the 941 5 m of core recovered by the hawaii scientific drilling project the analysis of 195 lava flows reveals six instances of near zero inclination and two instances of fully negative inclination reverse polarity within an otherwise normal polarity core in particular flow unit 23 178 m depth records a horizontal inclination and may be associated with the laschamp event flow units 40 and 42 260 m depth record negative inclinations and are close in age to the blake event and flow unit 55 320 m depth records a negative inclination with a relative declination change of 75 with respect to the overlying flow and is probably the jamaica biwa i pringle falls event the five instances of shallow inclination found below 400 m depth appear to have resulted from long term secular variation as they are part of inclination swings between 0 and 60 with a periodicity of 10 50 kyr in contrast the inclination shifts at 178 m and 320 m depths significantly deviate from long term trends suggesting the existence of at least two independent processes producing time variations of the geomagnetic field the secular variation has a mean of 30 9 95 2 27 which is significantly shallower than the expected dipole mean of 36 the dispersion 12 5 agrees with global paleosecular variation data for 0 5 ma and secular variation models

particle size measurement of diatoms with inference of their properties comparison of three techniques abstract diatom rich sediments are common in several oceanic regions especially the southern ocean some of these are strongly affected by bottom currents and are expected to be sorted by the flow examination of data on diatoms response by instruments commonly used for size measurement is presented here diatoms are silt to fine sand size filigree silica structures of many shapes with high porosity thus both the bulk density and shape strongly influence the size that is calculated from measurements we document the particle size of diatoms measured by instruments based on settling velocity sedigraph electrical resistance pulse counting coulter counter and laser diffraction malvern laser sizer the malvern laser consistently measures the largest diameters followed by the coulter counter and then settling based techniques relationships between these inferred sizes all expressed as quartz equivalent spherical diameters have implications for the physical properties of diatom tests earlier work has demonstrated that laser diffraction responds to the particles external projected area the effects of both low effective density and irregular shape of diatoms compared with terrigenous grains on their settling velocity causes the sedigraph to indicate relatively small diameters shape effects are less pronounced for quasi spherical diatom species the coulter counter records the diatoms solid volume and is relatively unaffected by their density or shape the measurement of different physical parameters by these instruments offers a basis for estimation of diatom porosity fluid occupied volume within the test measurements of the external diameter and solid volume allow estimates of porosity for laser sizes 20 m this is 75 95 which can be quite well modeled as a perforated spherical shell of wall thickness 1 1 5 m for paleocurrent interpretations a settling based technique makes sedigraph measurements of particle size the most useful but the visual size is best given by laser

paleomagnetic constraints on fault motion in the hilina fault system south flank of kilauea volcano hawaii movement of the south flank of kilauea volcano in hawaii has been associated with catastrophic landslide events the surface expression of this former movement is the hilina fault system with fault scarps as high as 500 m paleomagnetic directions for lava flows exposed in the hilina fault scarps at puu kapukapu and keana bihopa on the hilina pali are used to determine the average rate of movement along faults slip surfaces separating the two sections this paper reports results from two independent paleomagnetic studies within the hilina pali area twenty one paleomagnetic sites 143 cores were sampled by the michigan technological university group from lava flows between the mo o ash and middle pohakaa ash at keana bihopa in the footwall block of the 500 m high hilina pali fault scarp thirty paleomagnetic sites 152 cores were collected by the california institute of technology group from lava flows between the mo o ash and middle pohakaa ash in the 300 m high puu kapukapu section the hanging wall block a comparison of site mean directions show that lava flows in the lower part of the puu kapukapu section have been tilted more than lava flows in the upper part with respect to the keana bihopa section the systematic steepening of remanent directions downsection at puu kapukapu indicates that slippage of this block occurs along listric normal faults the average amount of backward tilt of the puu kapukapu block based on a comparison of mean directions from the two sections is 7 8 7 7 using slope stability methods the average rate of movement of the puu kapukapu block since deposition of the middle pohakaa ash is 1 7 2 4 cm yr and the average displacement subsidence is 680 740 m assuming that the average displacement resulted from a series of earthquakes producing subsidence equal to that observed in the 1975 kalapana earthquake 3 m of subsidence along a 40 km segment of coastline on the south flank of kilauea volcano one kalapana size earthquake occurring every 200 years would account for this displacement lastly overall mean directions for the two sections indicate that puu kapukapu has rotated counterclockwise with respect to the hilina pali by 14 8 8 5 about a nearby vertical axis this also suggests that slippage between the two blocks occurs along listric normal faults

paleosecular variation during sequential geomagnetic reversals from hawaii abstract paleomagnetic directions measured from 175 flows in four volcanic sequences on the island of o ahu hawaii cover about 0 3 m y of geomagnetic field changes and include detailed records of the successive gilbert gauss 3 57 ma and lower mammoth reversals 3 33 ma the dominant pattern of the directional changes is the presence of large inclination variations with increasing amplitude and steep values during the transitional periods the morphology of these recurring features during different transitions is reminiscent of the characteristics of the non dipole field inferred from studies of paleosecular variation in the pacific these observations are consistent with transitional mechanisms yielding the emergence of non dipole components with characteristics similar to those during periods of stable polarity the three different records of the lower mammoth reversal show that clusters of transitional pole positions are not reproducible between parallel sections and are thus linked to local eruptions and not to long lived states of the transitional field

a record of holocene glacial and oceanographic variability in neny fjord antarctic peninsula analyses of a 12 m marine sediment core from neny fjord marguerite bay antarctic peninsula 68 2571 s 66 9617 w yield a high resolution record of holocene climate variability the sediments preserve signals of past glacial and marine environments and offer a unique insight into atmospheric and oceanic forcings on the western antarctic peninsula climate dating of basal material reveals that deglaciation of the fjord occurred prior to 9040 cal yr bp and provides a minimum constraint on the timing of deglaciation close to the southern antarctic peninsula ice divide continuous deposition of ice distal sediments and seasonally open water diatoms indicates that the site has not been over ridden by glacier ice during the holocene a facies of sand rich material offers the only evidence of a localized glacier advance during the mid holocene statistical analysis of diatom assemblage data reveals several climatic episodes of varying magnitude and duration these include an early holocene warm period 9000 and 7000 cal yr bp potentially associated with influx of circumpolar deep water onto the continental shelf and coinciding with widespread glacial retreat and holocene collapse of the george vi ice shelf the mid holocene 7000 to 2800 cal yr bp sediments are characterized by diatom assemblages indicative of less pervasive sea ice cover and prolonged growing seasons with evidence of increased meltwater discharge from 4000 cal yr bp the youngest sediments 2800 cal yr bp to present contain a record that is consistent with the widely documented neoglacial period followed by an abrupt reversal and climate amelioration from sometime after 200 cal yr bp

magnetic anomalies of lava fields in the canary islands possible consequences for paleomagnetic records abstract measurements of the total magnetic field have been performed above the surface of 12 lava flows in the canary islands of la palma and tenerife directions can differ by up to 15 and intensity changes reach 20 the mean flow directions do not coincide and the mean flow virtual dipole moments vdms differ by more than 10 the deviations are linked to topographic features at the surface of the flows and should persist during emplacement of the next overlying flow such effects can thus limit the resolution of paleomagnetic records of detailed geomagnetic features and the field intensity variations above the flows and between the mean flow values could explain a significant part of the scatter inherent to many paleointensity studies historical field variations have been recorded from the same flows and are in agreement with the european curve for the same period however there is also some correlation with the present field which suggest that the underlying magnetized bodies could have affected the paleomagnetic records biases induced by the crustal field would increase considerably during periods of reduced field intensity like during reversals and induce erroneous records samplings performed over large distances within each lava flow would provide the best way to average out the contribution of the anomalies in any case such effects should not be neglected in paleomagnetic studies

geomagnetic intensity and inclination variations at hawaii for the past 98 kyr from core soh 4 big island a new study and a comparison with existing contemporary data abstract reliable thellier thellier paleointensity determinations were obtained from 321 out of 766 examined samples from the upper 200 units 675 m of core soh 4 drilled in the kilauea volcano the main trend of the soh 4 record is a marked decrease from values higher than present in the last 4 kyr to values about 40 smaller from about 20 kyr to the bottom of the sampled interval three main lows coinciding with shallow or negative inclinations observed in the record were identified with an excursion previously documented in hawaii and the mono lake and laschamps events for the last 15 kyr the soh 4 intensities are largely in agreement with the worldwide distribution of volcanic data in the 15 75 kyr interval the general lack of volcanic data makes comparison with the soh 4 data difficult the soh 4 record is similar to a composite record of paleointensity largely based on a recent north atlantic sedimentary paleointensity stack napis 75 the soh 4 record is also generally consistent with a record of geomagnetic field intensity obtained from a study of 36 cl in the grip ice core calculated with the assumption that the production rate of 36 cl is controlled only by the geomagnetic field one pronounced discrepancy between the different records is observed around 50 kyr bp when the sedimentary and cosmogenic based records document high intensities which are not observed in soh 4 these high intensities are also absent in a recent record based on the analyses of sea floor magnetic anomalies the histogram of vadms obtained from soh 4 is different from that obtained from the sedimentary or 36 cl based records and is more skewed than the distribution given by kono and tanaka for the last 2 5 million years

a detailed palaeointensity and inclination record from drill core soh1 on hawaii abstract a new record of absolute palaeointensity was obtained from drill core scientific observation hole 1 soh1 on kilauea volcano hawaii kilauea s high eruption rate resulted in a relatively continuous record and stratigraphic constraints preserved the chronological order three hundred and sixty samples were studied with the thellier thellier technique which gave 195 successful palaeointensity and 271 successful inclination determinations three geomagnetic excursions were observed which exhibited intensity reductions of about 50 initial age control from k ar and ar ar dating only constrained the total age between 20 and 120 ka the final age model was obtained by stretching the soh1 record relative to other hawaiian palaeomagnetic data this gave an age range of 0 45 ka for the flows and identified the excursions as the hilina pali mono lake and laschamp events the soh1 record of the hilina pali event is the most detailed ever incorporating data from around 40 flows this age model suggests that kilauea had a burst of activity at the soh1 site around 20 ka all available data was combined to form a composite record of palaeointensity and inclination on hawaii for 0 45 ka

new tools for the reconstruction of pleistocene antarctic sea ice abstract based on the quantitative analysis of diatom assemblages preserved in 274 surface sediment samples recovered in the pacific atlantic and western indian sectors of the southern ocean we have defined a new reference database for quantitative estimation of late middle pleistocene antarctic sea ice fields using the transfer function technique the detrended canonical analysis dca of the diatom data set points to a unimodal distribution of the diatom assemblages canonical correspondence analysis cca indicates that not only winter sea ice wsi but also summer sea surface temperature ssst represent the most prominent environmental variables that control the spatial species distribution to test the applicability of transfer functions for sea ice reconstruction in terms of concentration and occurrence probability we applied four different methods the imbrie and kipp method ikm the modern analog technique mat weighted averaging wa and weighted averaging partial least squares wapls using logarithm transformed diatom data and satellite derived 1981 2010 sea ice data as a reference the best performance for ikm results was obtained using a subset of 172 samples with 28 diatom taxa taxa groups quadratic regression and a three factor model ikm d172 28 3q resulting in root mean square errors of prediction rmsep of 7 27 and 11 4 for wsi and summer sea ice ssi concentration respectively mat estimates were calculated with different numbers of analogs 4 6 using a 274 sample 28 taxa reference data set mat d274 28 4an 6an resulting in rmsep ranging from 5 52 4an to 5 91 6an for wsi as well as 8 93 4an to 9 05 6an for ssi wa and wapls performed less well with the d274 data set compared to mat achieving wsi concentration rmsep of 9 91 with wa and 11 29 with wapls recommending the use of ikm and mat the application of ikm and mat to surface sediment data revealed strong relations to the satellite derived winter and summer sea ice field sea ice reconstructions performed on an atlantic and a pacific southern ocean sediment core both documenting sea ice variability over the past 150 000 yr mis 1 mis 6 resulted in similar glacial interglacial trends of ikm and mat based sea ice estimates on the average however ikm estimates display smaller wsi and slightly higher ssi concentration and probability at lower variability in comparison with mat this pattern is a result of different estimation techniques with integration of wsi and ssi signals in one single factor assemblage by applying ikm and selecting specific single samples thus keeping close to the original diatom database and included variability by mat in contrast to the estimation of wsi reconstructions of past ssi variability remain weaker combined with diatom based estimates the abundance and flux pattern of biogenic opal represents an additional indication for the wsi and ssi extent

submillennial variations in ocean conditions during deglaciation based on diatom assemblages from the southwest atlantic we present a high resolution paleoceanographic record of deglaciation based on diatom assemblages from a core located just south of the polar front in the southwest atlantic core kc073 is from a sediment drift at the mouth of the falkland trough and contains sediments from the last glacial maximum lgm to present dated using radiocarbon dates on bulk organic matter and radiolarian stratigraphy the site lies along the path of the antarctic circumpolar current acc and immediately downstream of where north atlantic deep water nadw is entrained into the acc significant variations in ocean conditions are reflected in high amplitude changes in diatom concentrations and assemblage composition the diatom assemblage at the lgm indicates that winter sea ice extent was at least 5 farther north than present until at least 19 0 ka calendar years and summer sea ice may have occasionally extended over the site but for the most part it lay to the south during deglaciation chaetoceros resting spores crs dominate the diatom assemblage with valve concentrations in excess of 500 106 valves per gram submillennial scale variations in the numbers of crs and thalassiosira antarctica occur throughout the late deglacial and dominate the changes in diatom concentration we propose that the influx of crs is controlled by the flow of nadw over the falkland plateau as such our data provide unique evidence that nadw impacted on this sector of the southern ocean during deglaciation during the holocene the sedimentation rate dramatically reduced we suggest that the acc flow increased over the site and inhibited settling and winnowed the surface sediments

similar glacial and holocene southern ocean hydrography we present new holocene and glacial d 18 o data measured on planktonic foraminifera neogloboquadrina pachyderma and benthic foraminifera cibicidoides species from the atlantic and pacific sectors of the southern ocean in order to better understand its glacial hydrography combined with previously published data the latitudinal d 18 o distributions of these foraminifera show no appreciable difference during the holocene and the last glacial maximum this suggests that the basic southern ocean hydrography including stratification and the mean position of the antarctic circumpolar current frontal system remained largely unchanged although the small number of pacific data render any conclusion in that sector preliminary the southern ocean is a critical part of the global climate system the continental shelves of the weddell and ross seas are sites of antarctic bottom water aabw formation the highly barotropic antarctic circumpolar current acc reaches the ocean floor and is able to mix efficiently the north atlantic deep water nadw and deep waters from the indian and pacific oceans the mixture of these deep waters the circumpolar deep water cdw then spreads back into the other ocean basins in one form or another the formation of antarctic intermediate water aaiw by ekman pumping occurs in the convergence zone at the polar front and to the north in the subantarctic zone the northward advection of temperatures and salinities of aabw cdw and aaiw from the southern ocean to other ocean basins has a profound effect on the global ocean circulation and thus on global climate in addition the surface waters of the southern ocean are key in controlling the atmospheric co2 content because they link the atmosphere and the large carbon reservoir of the world deep ocean the southern ocean surface waters have thus been a focus of attention in connection with the investigations of low atmospheric co2 content during the last glacial maximum lgm barnola et al 1987 as well as with the forecasts of future atmospheric pco2 levels e g sarmiento et al 1998 specifically the relatively abundant surface macronutrients of the modern southern ocean provide an opportunity for enhanced biological pump export of surface nutrients and co2 to the deep ocean to reduce the atmos phericco2content martinandfitzwater 1988 also reducingthe vertical mixing of southern ocean surface waters can lower the atmospheric pco2 by limiting the transfer of co2 from the deep ocean to the atmosphere ennever and mcelroy 1985 toggweiler and sarmiento 1985 wenk and siegenthaler 1985 in order to better understand the glacial southern ocean hydrog raphy near the surface and at depth we examine the latitudinal distributions of d 18 o in the calcite test of planktonic foraminifera neogloboquadrina pachyderma and benthic foraminifera cibici doides species their d 18 o reflects the seawater temperature and salinity in which they calcify their shells the planktonic fora miniferal carbon isotope ratios associated with this data set are discussed extensively by kohfeld 1998 also benthic foramini feral carbon isotope ratios in the southern ocean have been discussed recently at length matsumoto and lynch stieglitz 1999 ninnemann and charles 1997 oppo and horowitz 2000 our new data in combination with those in the literature show that the spatial distribution ofd 18 o in planktonic and benthic foraminiferal tests remained nearly the same during the lgm as during the holocene a conclusion similar to that reached by charles and fairbanks 1990 on the basis of a subset of the planktonic foraminiferal d 18 o data shown here the additional work in the southern ocean since that of charles and fairbanks 1990 more strongly constrains the lgm southern ocean hydrog raphy and we also infer that the circulation was similar during the holocene and the lgm

distribution of diatoms in surface sediments of prydz bay antarctica abstract four diatom assemblages are identified from the surface sediments of prydz bay and the mac robertson shelf using multivariate analysis a coastal assemblage is characterised by the sea ice diatoms fragilariopsis curta f angulata f cylindrus and pseudonitzschia turgiduloides a continental shelf assemblage is characterised by sea ice and ice edge diatoms and an oceanic assemblage is characterised by the open water diatoms fragilariopsis kerguelensis thalassiosira lentiginosa t gracilis var expecta and trichotoxin reinboldii the cape darnley assemblage contains both sea ice and open water diatoms but all are characteristically large and heavily silicified multiple regression has been used to identify the relationships between the diatom assemblages and known environmental variables there are strong correlations between the coastal shelf and oceanic assemblages and ecological conditions including latitude sea ice distribution and ocean currents the cape darnley assemblage is thought to represent an assemblage from which the smaller and more lightly silicified species have been removed by current winnowing

late pleistocene oxygen isotope records of biogenic silica from the atlantic sector of the southern ocean we determined the isotopic composition of oxygen in marine diatoms in eight deep sea cores recovered from the atlantic sector of the southern ocean the analytical reproducibility and core to core consistency of the isotopic signal suggests that diatom 18o can be used as a new paleocenographic tool to reconstruct past variations in surface water characteristics and to generate 18o isotope based stratigraphy for the southern ocean the data indicate that diatom 18o reflects sea surface temperature and seawater isotopic composition and that diatoms retain their isotopic signal on timescales of a least 430 ka the 18o analyses of different diatom assemblages reveal that the isotopic signal is free of species effects and that the common antarctic species have the same water opal fractionation the transition from the last glacial maximum lgm to the holocene is fully recorded in high sedimentation rate cores an 18o enrichment during the lgm a post lgm meltwater spike and an input of meltwater during the late holocene are the main isotopic features observed in down core records the origin of this meltwater was very likely melting icebergs and or continental ice or by melting sea ice that had accumulated snow the most pronounced meltwater effects are recorded in cores that are associated with the weddel gyre our results provide the basis for extending isotope studies to oceanic regions devoid of carbonate further isotopic stratigraphies may be constructed for records and regions where they were previously not possible

the time averaged paleomagnetic field 0 5 ma persistent departures from the geocentric axial dipole field model of the time averaged paleomagnetic field over the past 5 myr have been analyzed using oceanic data from deep sea cores and continental data from igneous rocks and sediments the data set comprises the equivalent of 9490 spot readings of the field 5831 normal and 3659 reverse from 930 groups of data variations in declination anomalies between groups of data strongly suggest the existence of second order tectonic effects small rotations that make it difficult if not impossible to identify any nonzonal terms that might exist inclination anomalies have therefore been modeled in terms of low degree zonal harmonics the calculated inclination anomalies within 10 latitude bands are widely scattered for both oceanic and continental data and do not appear to have been drawn from distributions with common means we attribute this large scatter to previously undetected or uncorrected second order tectonic effects in the continental data or in the oceanic data to small departures from the vertical in deep sea cores if it is assumed that these effects are random between groups of data and without a systematic bias they can be averaged out to a large extent if there are sufficient numbers of groups within each latitude band this method also has the major advantage that it maximizes time averaging of the field when this is done an acceptable fit to the inclination anomaly data is found using a zonal harmonic model although the point estimates for the reverse polarity zonal quadrupole term are consistently larger than those for the normal polarity zonal quadrupole term the difference is not significant and is likely due to contamination effects this finding is true for a combination of all the data or for separate combinations of continental igneous rocks and ocean sediments this conclusion differs from all previous analyses the major differences occur in model estimates of the zonal octupole term the estimates varying widely depending on the particular data combination we show that false octupole terms can be introduced by several factors including inclination errors in sediments and lavas the use of unit vectors in the analyses and incomplete magnetic cleaning particularly of reversely magnetized rocks thus we cannot impute a geomagnetic significance to the estimates of a zonal octupole term we suggest that the best estimates for the zonal quadrupole g2 g20 g10 are obtained from the combined brunhes age igneous rocks and oceanic normal data 0 033 0 019 and for the combined matuyama age igneous rocks and oceanic reverse data 0 042 0 022 when these two sets are combined the overall best estimate of g2 is 0 038 0 012

geomagnetic field secular variation in pacific ocean a bayesian reference curve based on holocene hawaiian lava flows abstract hawaii is an ideal place for reconstructing the past variations of the earth s magnetic field in the pacific ocean thanks to the almost continuous volcanic activity during the last 10 000 yrs we present here an updated compilation of palaeomagnetic data from historic and radiocarbon dated hawaiian lava flows available for the last ten millennia a total of 278 directional and 66 intensity reference data have been used for the calculation of the first full geomagnetic field reference secular variation sv curves for central pacific covering the last ten millennia the obtained sv curves are calculated following recent advances on curve building based on the bayesian statistics and are well constrained for the last five millennia while for older periods their error envelopes are wide due to the scarce number of reference data the new bayesian sv curves show three clear intensity maxima during the last 3000 yrs that are accompanied by sharp directional changes such short term variations of the geomagnetic field could be interpreted as archaeomagnetic jerks and could be an interesting feature of the geomagnetic field variation in the pacific ocean that should be further explored by new data

development of an antarctic digital elevation model by integrating cartographic and remotely sensed data a geographic information system based approach we present a high resolution digital elevation model dem of the antarctic it was created in a geographic information system gis environment by integrating the best available topographic data from a variety of sources extensive gis based error detection and correction operations ensured that our dem is free of gross errors the carefully designed interpolation algorithms for different types of source data and incorporation of surface morphologic information preserved and enhanced the fine surface structures present in the source data the effective control of adverse edge effects and the use of the hermite blending weight function in data merging minimized the discontinuities between different types of data leading to a seamless and topographically consistent dem throughout the antarctic this new dem provides exceptional topographical details and represents a substantial improvement in horizontal resolution and vertical accuracy over the earlier continental scale renditions particularly in mountainous and coastal regions it has a horizontal resolution of 200 m over the rugged mountains 400 m in the coastal regions and approximately 5 km in the interior the vertical accuracy of the dem is estimated at about 100 130 m over the rugged mountainous area better than 2 m for the ice shelves better than 15 m for the interior ice sheet and about 35 m for the steeper ice sheet perimeter the antarctic dem can be obtained from the authors

holocene palaeomagnetic secular variation recorded in multiple lake sediment cores from eastern finland summary holocene palaeomagnetic secular variation psv in inclination and declination recorded in the sediment remanent magnetization of two small lakes lake lehmilampi 63 37 n 29 06 e and lake kortejarvi 63 37 n 28 56 e in eastern finland is presented as an outcome of systematic coring eight cores 300 753 cm in length were investigated all samples lehmilampi n 1320 kortejarvi n 943 were subjected to palaeo and mineral magnetic analyses the directions of the characteristic remanent magnetization chrm were obtained from progressive alternating field demagnetization of the natural remanent magnetization nrm followed by principle component analysis the younger sections of the sediment columns in the studied lakes are annually laminated providing detailed chronologies for dating psv features back to 5100 cal bp the underlying older sections of the cores were dated by palaeomagnetic pattern matching in respect to varve dated lake nautajarvi psv data ojala saarinen 2002 thus yielding a composite age model covering nearly the whole holocene epoch average sedimentation rates ranging from 0 68 to 0 74 mm yr 1 enabled recording of changes in the geomagnetic field at decadal resolution the carriers of remanence are dominantly magnetite of stable single domain to pseudo single domain grain size accompanied by magnetic minerals of harder coercivity the sediments from both lakes exhibit strong and stable single component magnetizations nearly throughout the whole cores the sediment magnetization lock in delay is estimated to range between 80 and 100 yr psv data were transformed into time series and subsequently stacked to comprise north karelian stack and fisher statistics were used to calculate mean directions together with the 95 per cent confidence level 95 a comparison of declination and inclination features of the north karelian stack with previously published data expresses remarkable similarity therefore confirming the similar source behind the changes in the nrm directional records the high quality of the psv data extracted from lehmilampi and kortejarvi in terms of dating as well as amplitude reconstruction have a high potential to improve existing and future geomagnetic field models

high resolution diatom stratigraphy of quaternary sediments from the scotia sea upper quaternary pelagic and hemipelagic sediments from the scotia sea and south scotia ridge range from diatom ooze to diatom bearing mud diatom content increases northwards and at most sites diatom rich and diatom poor sediments alternate downcore on a scale of metres a local stratigraphy is based on relative abundance of six prominent diatom taxa eucampia antarctica rhizosolenia spp thalassiosira spp chaetoceros spores nitzschia kerguelensis and othernitzschia species and one silicoflagellate species distephanus speculum these stratigraphic units defined using diatoms are correlated with radiolarian abundance stratigraphy cycladophora davisiana and with palaeomagnetic stratigraphy information from modern environments phytoplankton and sediment trap studies indicates that changes in diatom species composition are related to n s movement of the winter ice edge and of the antarctic convergence

a new technique for firn grain size measurement using sem image analysis firn microstructure is accurately characterized using images obtained from scanning electron microscopy sem visibly etched grain boundaries within images are used to create a skeleton outline of the microstructure a pixel counting utility is applied to the outline to determine grain area firn grain sizes calculated using the technique described here are compared to those calculated using the techniques of gow 1969 and gay and weiss 1999 on samples of the same material and are found to be substantially smaller the differences in grain size between the techniques are attributed to sampling deficiencies e g the inclusion of pore filler in the grain area in earlier methods the new technique offers the advantages of greater accuracy and the ability to determine individual components of the microstructure grain and pore which have important applications in ice core analyses the new method is validated by calculating activation energies of grain boundary diffusion using predicted values based on the ratio of grain size measurements between the new and existing techniques the resulting activation energy falls within the range of values previously reported for firn ice

a 17 000 yr paleomagnetic secular variation record from the southeast alaskan margin regional and global correlations high resolution sedimentary records on two cores from the gulf of alaska margin allow development of a 17 400 yr reconstruction of paleomagnetic secular variation psv general agreement between the two records on their independent chronologies confirms that local psv is recorded demonstrating that such archives notwithstanding complexities due to variable sedimentary regimes deposition rates and diagenetic conditions provide meaningful information on past changes of the geomagnetic field comparisons with other independently dated sedimentary paleomagnetic records from the ne pacific indicate largely coherent inclination records that in combination create a ne pacific sedimentary inclination anomaly stack nepsias capturing the common signal over an area spanning 30 longitude and latitude from alaska through oregon to hawaii comparisons of nepsias with high quality declination records from the northern north atlantic nna show that negative shallow inclination anomalies in nepsias are associated with eastward nna declinations while positive steep inclination anomalies in nepsias are associated with westward nna declinations comparison of these directional records to regional geomagnetic intensities over the past 3000 yrs in north america and back nearly 8000 yrs in the euro mediterranean region are consistent with a driving mechanism of oscillations in the relative strength of the north american and euro mediterranean flux lobes the persistence of these dynamics through the holocene implicates a long lived organizing structure likely imposed on the geomagnetic field by the lower mantle and or inner core these observations underscore a fundamental connection between directional psv in the north pacific with that of the north atlantic supporting the potential for long distance correlation of directional psv as a chronostratigraphic tool

paleosecular variation and the average geomagnetic field at 20 latitude we assembled a new paleomagnetic directional data set from lava flows and thin dikes for four regions centered on 20 latitude hawaii mexico the south pacific and reunion we investigate geomagnetic field behavior over the past 5 myr and address whether geographical differences are recorded by our data set we include inclination data from other globally distributed sites with the 20 data to determine the best fitting time averaged field taf for a two parameter longitudinally symmetric zonal model values for our model parameters the axial quadrupole and octupole terms are 4 and 6 of the axial dipole respectively our estimate of the quadrupole term is compatible with most previous studies of deviations from a geocentric axial dipole gad field our estimated octupole term is larger than that from normal polarity continental and igneous rocks and oceanic sediments but consistent with that from reversed polarity continental and igneous rocks the variance reduction compared with a gad field is 12 and the remaining signal is attributed to paleosecular variation psv we examine psv at 20 using virtual geomagnetic pole vgp dispersion and comparisons of directional distributions with simulations from two statistical models regionally the hawaii and reunion data sets lack transitional magnetic directions and have similar inclination anomalies and vgp dispersion in the pacific hemisphere hawaii has a large inclination anomaly and the south pacific exhibits high psv the deviation of the taf from a gad contradicts earlier ideas of a pacific dipole window and the strong regional psv in the south pacific contrasts with the generally low secular variation found on short timescales the taf and psv at hawaii and reunion are distinct from values for the south pacific and mexico demonstrating the need for time averaged and paleosecular variation models that can describe nonzonal field structures investigations of zonal statistical psv models reveal that recent models are incompatible with the empirical 20 directional distributions and cannot fit the data by simply adjusting relative variance contributions to the psv the 20 latitude data set also suggests less psv and smaller persistent deviations from a geocentric axial dipole field during the brunhes

results of a stratified snow emissivity model based on the wave approach application to the antarctic ice sheet the results from a snow emissivity model are used to help with the interpretation of the scanning multichannel microwave radiometer data aboard the satellite nimbus 7 1978 1986 over antarctica the model is based on the solution of maxwell s equations through strong fluctuation theory stogryn 1986 the snow is considered isothermal with horizontal stratification isotropic inside each stratum and with smooth interfaces to wipe out the interference pattern created by plane stratification and in order to take into account the spatial variability of the snow characteristics the final result is a mean value of many computations done with many stratigraphies randomly distributed around a mean profile the spatial distribution of the microwave signatures over antarctica reveals three areas with typical spectral signatures these areas are identified from the point of view of snow characteristics through a ground data set surdyk and fiiy 1993 the model reproduces well the effect of the stratification on the polarization differences as observed the strong gradient of emissivity versus frequency observed on one of the test sites is not completely understood depth hoar layers characterized by faceted and cup shaped coarse snow grains seem to have a particular scattering behavior compared with that of the usual grains when those coarse grains are replaced by fine grains the model results are closer to the measured data the presence of crusts the roughness at the snow ice interfaces and crystal orientation may also have significant effects

quaternary surface water temperature estimations calibration of a diatom transfer function for the southern ocean the quantitative diatom analysis of 218 surface sediment samples recovered in the atlantic and western indian sector of the southern ocean is used to define a base of reference data for paleotemperature estimations from diatom assemblages using the imbrie and kipp transfer function method the criteria which justify the exclusion of samples and species out of the raw data set in order to define a reference database are outlined and discussed sensitivity tests with eight data sets were achieved evaluating the effects of overall dominance of single species different methods of species abundance ranking and no analog conditions e g eucampia antarctica on the estimated paleotemperatures the defined transfer functions were applied on a sediment core from the northern antarctic zone overall dominance of fragilariopsis kerguelensis in the diatom assemblages resulted in a close affinity between paleotemperature curve and relative abundance pattern of this species downcore logarithmic conversion of counting data applied with other ranking methods in order to compensate the dominance of f kerguelensis revealed the best statistical results a reliable diatom transfer function for future paleotemperature estimations is presented

holocene paleosecular variation from dated lava flows on maui hawaii ow inclination and low secular variation seem to be present for at least the past 5 myear in central pacific the period covering the past 10 kyear is crucial to the study of the field variability and to fill the gap between historical field measurements and long term paleomagnetic records we have conducted a paleomagnetic study of 13 sites of basaltic lava flows from maui island with 14c ages between 10 3 and 0 2 ka two other sites dated at 45 and 730 ka were also sampled eight to 10 samples from each site were demagnetized using thermal treatment and companion specimens from the same samples were demagnetized by alternating fields af thermomagnetic and hysteresis measurements indicated that magnetite 575 c in fine grains was the dominant magnetic carrier although in many cases we also observed a low temperature phase which is likely carried by titanomagnetite with low titanium content the existence of relatively high coercivities associated with these two mineralogical phases generated overlapping components which could not be properly isolated using af demagnetization successful results were obtained after thermal demagnetization for 13 sites with a mean inclination of 36 9 4 the mean inclination inc 36 3 of the eleven sites younger than 10 5 ka is also very close to the value 37 of the geocentric axial dipole gad at the site latitude but the angular dispersion of the virtual geomagnetic poles vgps about the spin axis 9 with n 13 and 6 7 with n 11 is significantly lower than the predictions of the models of paleosecular variation at this latitude the inclination variations for the past 10 kyear are in excellent agreement with the very detailed dataset which has previously been obtained from the big island of hawaii the mean inclination of all volcanic records n 132 is 1 8 lower than expected but this is likely caused by the lack of records between 5 and 7 ka b p we note also that the inclinations from lake waiau sediments big island are shallower than those of the volcanic records mauna kea hawaii and were thus probably affected by compaction we infer that there is no striking evidence for an inclination anomaly under hawaii during this period being aware of the need for additional records covering at least the 5 7 ka b p time interval the absence of a systematic deviation going beyond the dispersion of the inclinations obtained for the past millions of years neither pleads for a significant long term persistent anomaly however all studies report a low dispersion of the vgps which must reflect low secular variation

late neogene history of deepwater ventilation in the southern ocean we compiled carbon isotope records from the north atlantic south atlantic and pacific oceans to estimate changes in vertical and interbasinal 13c gradients for the last 9 myr benthic 13c values of deep water in the south atlantic decreased in a series of steps at 7 2 75 and 1 55 ma away from the north atlantic and toward the pacific the benthic 13c of intermediate water in the south atlantic evolved differently from deep waters resulting in an increase in the intermediate to deep 13c gradient 13cid the 13cid increased in steps at 2 75 and 1 55 ma marking the development and intensification of a chemical divide in the atlantic ocean between well ventilated intermediate water and poorly ventilated deep water we suggest these changes in interbasinal and vertical gradients resulted from decreasing northern component water and reduced ventilation of southern component water scw the latter was caused by several interrelated processes in antarctic sources areas including increased sea ice cover enhanced surface water stratification decreased ekman induced upwelling and reduced vertical mixing across the thermocline because antarctic surface water processes and deepwater ventilation rates ultimately influence atmospheric co2 concentration these processes may have acted as a positive feedback that contributed to the major cooling steps in late neogene climate

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

the biogeography of major diatom taxa in southern ocean surface sediments 3 tropical subtropical species abstract this paper gives a modern circumscription of tropical subtropical diatoms regarding their relationship with sea surface temperatures sst and sea ice cover diatoms from 228 core top sediment samples collected from the southern ocean were studied to determine the geographic distribution of eight major diatom species taxa preserved in surface sediments generally located north of the subantarctic front the comparison of the relative contribution of diatom species with modern february sst and sea ice cover reveals species specific sedimentary distributions regulated both by water temperatures and sea ice conditions although selective preservation might have played some role their presence in surface and downcore sediments from the southern ocean are reliable indicators of high sst and poleward transport of waters from the tropical subtropical atlantic our work supports the use of diatom remains to reconstruct past variations of these environmental parameters via qualitative and transfer function approaches

southern ocean pliocene paleotemperature variation from high resolution silicoflagellate biostratigraphy abstract applying the modern biogeographic distribution of silicoflagellate genera dictyocha and distephanus and calcareous nannoplankton as an analog the biostratigraphic record of these phytoplankton can be used qualitatively to examine past changes in surface temperature in the southern ocean the antarctic polar frontal zone pfz is a major biogeographic barrier limiting dictyocha and calcareous nannoplankton to areas north of this zone ocean drilling project odp holes 748b and 751a on the southern kerguelen plateau 900 km south of the present location of the pfz contain expanded pliocene sections through four time intervals 4 5 to 4 2 ma hole 751a 3 7 to 3 1 ma hole 748b 3 6 to 3 5 ma hole 751a and 3 2 to 3 0 ma hole 751a three distinct peaks in dictyocha and calcareous nannofossil abundance reflect surface water warming of at least 4 c through either southward migration of the pfz or a weakening of the thermal gradient across this zone peak warming in the intervals studied is centered near 4 3 ma with other brief yet significant warming events near 4 5 4 2 and 3 6 ma cooling as a result of northward migration of the pfz or intensified thermal gradient is indicated by the absence of dictyocha and calcareous nannofossils in other stratigraphic intervals these data support previous studies indicating pliocene oceanic and climatic variability in the southern high latitudes silicoflagellate abundance patterns from hole 751a identify taxonomic relationships between several morphotypes the simultaneous appearance and proportional occurrence of five sided and four sided dictyocha specimens suggests a close relationship between these two forms distephanus crux s l and dictyocha aspera var pygmaea also show a near mutually exclusive abundance pattern in hole 751a and are similar in basal ring size and morphology indicating they are conspecific they differ only in apical structure whereby distephanus crux s l may have formed an apical bar under fluctuating environmental conditions in the early pliocene these variations in silicoflagellate architecture appear to be related to paleoenvironmental changes indicating that silicoflagellate morphology may represent a more useful paleoceanographic tool that has been noted previously

ecology and paleoecology of the marine diatomeucampia antarctica castr mangin abstract the distribution of eucampia antarctica both in the water column and in the sediments of the southern ocean is discussed on the basis of these data it is concluded that although this species is widely distributed in the southern ocean it is most abundant in a near shore and or neritic environment however a pseudoneritic environment provided by floating ice may also provide a suitable substrate for the proliferation of this species

accumulation and hoar effects on microwave emission in the greenland ice sheet dry snow zones the relationships between accumulation and microwave emissivity in the dry snow regions of the greenland ice sheet are studied with special focus on hoar formation with the use of a discrete ordinate radiative transfer model the relative contributions of hoar and accumulation to microwave emission are examined the results show that the link between microwave emission and accumulation rates in the dry snow area ofthe greenland ice sheet is significant however the emissivity is also dependent on the extent of hoar development as a result accumulation estimates based on passive microwave observations in the low accumulation dry snow areas will require successful parameterization of hoar formation furthermore the increasing t b trends that were observed during the 1980s which have been hypothesized to be related to accumulation changes may be strongly related to variations in hoar development other possible explanations for these observed trends such as slight surface melt or atmospheric conditions are also discussed

effect of snow surface metamorphism on aquarius l band radiometer observations at dome c antarctica the antarctic plateau presents ideal characteristics to study the relationship between microwave observations and snow ice properties it is also a promising target for radiometer calibration and sensor intercalibration which are critical for applications requiring subkelvin accuracy such as sea surface salinity retrievals this paper presents the spaceborne aquarius l band radiometric observations collected since august 2011 over the antarctic plateau and it focuses on their temporal evolutions at dome c 75 1 circ hbox s 123 35 circ hbox e aquarius operates three radiometers with a sensitivity of 0 15 k over the oceans allowing us to analyze small variations in brightness temperature tb and changes with incidence angles over the antarctic plateau aquarius tbs have a relatively low annual standard deviation 0 2 0 9 k where melting never occurs however the analysis of the tb time series at dome c revealed significant variations up to 2 5 k in summer first these variations are compared with a remote sensing grain index gi based on high frequency 89 and 150 ghz shallow penetration tb channels variations in the ratio of tbs observed at horizontal and vertical polarizations are synchronous with gi changes second aquarius tb variations are compared with the presence of hoar crystals on the surface identified using surface based near infrared photographs the largest and longest changes in tbs correspond to periods with hoar crystals on the surface therefore in spite of the deep penetration of the l band radiation evolutions of the snow properties near the surface which usually change rapidly and irregularly do influence l band observations collection of accurate snow surface measurements and thorough analyses of the l band observations are thus needed to use the antarctic plateau as a calibration inter calibration target

the influence of high latitude flux lobes on the holocene paleomagnetic record of iodp site u1305 and the northern north atlantic 1 paleomagnetic analysis and radiocarbon dating of an expanded holocene deep sea sediment sequence recovered by integrated ocean drilling program iodp expedition 303 from labrador sea site u1305 lat 57 28 5 n long 48 31 8 w water depth 3459 m provides insights into mechanisms that drive both paleomagnetic secular variation psv and magnetization acquisition in deep sea sediments seventeen radiocarbon dates on planktonic foraminifera define postglacial ca 8 ka sedimentation rates as ranging from 35 to 90 cm kyr alternating field af demagnetization of u channel samples show that these homogeneous sediments preserve a strong stable and consistently well defined component magnetization normalized remanence records pass reliability criteria for relative paleointensity rpi estimates assuming that the age of magnetization is most accurately defined by well dated psv records with the highest sedimentation rates allows us to estimate and correct for temporal offsets at site u1305 interpreted to result from postdepositional remanence acquisition at a depth of 20 cm comparisons indicate that the northern north atlantic psv and rpi records are more consistent with european than north american records and the evolution of virtual geomagnetic poles vgp are temporally and longitudinally similar to global reconstructions though with much larger latitudinal variation the largest deviations from a geocentric axial dipole gad are observed during times of the highest intensities in contrast to the usual assumption these observations are consistent with the idea that psv in the north atlantic and elsewhere during the holocene results from temporal oscillations of high latitude flux concentrations at a few recurrent locations

new k ar ages and the geologic evidence against rejuvenated stage volcanism at haleakalā east maui a postshield stage volcano of the hawaiian island chain the postshield and previously inferred rejuvenated stage history of haleakal volcano is reevaluated on the basis of 52 new k ar ages 42 from the postshield kula volcanics and 10 from the overlying h na volcanics postshield extrusion was robust from 0 93 to 0 76 ma a period of low extrusion rate or volcanic quiescence occurred between 0 76 and 0 65 ma well within kula time a chemical change to increasingly alkalic lava occurred at this time as the volcano changed from broadly hawaiitic to basanitic in its eruptive products and robust extrusion resumed a slightly longer period of low extrusion rate or quiescence occurred after ca 0 4 ma but only trifling change in geochemical character is observed geochemically the h na volcanics unit chiefly basanitic overlaps greatly with the upper part of the kula volcanics there is a weak tendency to slightly more alkaline character among the h na volcanics the age of the kula h na boundary is ca 0 15 0 12 ma thus volcanic quiescence of only 0 03 m y separates the two formations much shorter than the previously known limit of 0 25 0 30 m y the brevity of this hiatus coupled with coincident vent loci and broadly similar geochemical characteristics for the h na and the upper part of the kula volcanics indicates that the h na volcanics unit comprises deposits of postshield stage volcanism that has waned substantially since ca 0 4 0 3 ma haleakal has not yet begun a classically defined rejuvenated stage our findings support recent numerical modeling of plume lithosphere interactions that predict that haleakal is near the end of its postshield growth

very high resolution paleosecular variation record for the last 1200 years from the aral sea 1 a record of geomagnetic paleosecular variation psv spanning the last 1200 years has been obtained from two lacustrine sediment cores from the north part of aral sea kazakhstan magnetic susceptibility and nrm intensity have been used for correlating between cores and reconstructing composite core data the main swings and fine details of declination and inclination records correlate well between both cores a very high sedimentation rate up to 25 mm per year due to recent tectonic activity of the region provides a very high resolution psv record for the interval from 450 100 years bp to 655 65 years bp the results which have been dated by eight ams radiocarbon age determinations suggest that a 200 400 years secular variation period with amplitudes in declination and inclination up to 10 15 existed regularly during the time interval 0 1200 bp amplitudes of the psv record from aral sea are not reduced and smoothed by postdetrital magnetization processes they adjoin to the historical data model and are considered to represent a reliable paleosecular variation record for the aral sea region for the last 1200 years

the reconstruction of late quaternary antarctic sea ice distribution the use of diatoms as a proxy for sea ice the study of annual diatom transfer from the southern ocean surface to the sea floor using time series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea ice extent the application and robustness of the proposed proxy are demonstrated by the study of late pleistocene sediment cores recovered from different environmental regimes in the southern ocean relative amounts of the sea ice indicator diatoms fragilariopsis cylindrus and fragilariopsis curta of 3 in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea ice summer sea ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export in the presence 3 of diatom assemblage of the deep temperature diatom fragilariopsis obliquecostata the spatial and temporal distribution pattern of the sea ice proxy indicates significant sea ice variations during marine isotope stages 1 and 5 in the present antarctic zone of the southern ocean during glacial maxima the antarctic winter sea ice was extended into the present polar front zone while the antarctic summer sea ice was most probably expanded into the area of the present winter sea ice edge during the short climatic optima at the onset of interglacial periods the winter sea ice extent was distinctly reduced

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

paleomagnetic study of the ages of lavas on the island of lanai i hawai i abstract a detailed paleomagnetic study of tholeiitic basaltic of eight sites drilled from kaumalapau harbor manele bay and maunalei gulch areas was conducted to investigate the volcanic evolution of the island of lana i stepwise alternating field af demagnetizations accompanied by investigations of rock magnetic properties such as low field susceptibility versus temperature k t and saturation isothermal remanent magnetization sirm indicate that the characteristic remanent magnetization chrm is primarily carried by ti poor magnetite demagnetization experiments have identified eight mean flow directions characterized by negative polarities our paleomagnetic results along with the radiometric age determinations of the lavas in question indicate that the tholeiitic flows that formed the lanai volcano were erupted very rapidly and only during the matuyama polarity chron 0 780 2 58 ma and not during the brunhes chron 0 0 78 ma as reported previously for the k ar dated lavas in the maunalei gulch

microfossil and stable isotope evidence for changes in late holocene palaeoproductivity and palaeoceanographic conditions in the prydz bay region of antarctica microfaunal and microfloral data from two gravity cores and stable isotope results from one of these cores taken on fram bank near prydz bay antarctica indicate changes in sea ice patterns and oceanographic conditions which may have been linked to regional and global climate changes that occurred over the past 8000 yr modern diatom assemblages indicative of ice free conditions 1 2 months of the year and dominated by nitzschia species became prevalent some time around 2000 2700 yr b p the occurrence of chaetoceros spp diatom spore dominated assemblages and increased abundances of benthic and planktonic foraminifera ostracods and diatoms coupled with carbon and oxygen isotope changes around 2700 3400 yr b p strongly suggests that this area of the shelf experienced conditions conducive to increased productivity during this time period based on diatom assemblage associations recognized in modern environments the upper water column of fram bank shelf waters was probably stratified during that time due to the presence of low salinity melt water and a very shallow mixed layer protected from storms with sea ice cover for less than 10 months per year the close correspondence of 13c and 18o values from n pachyderma r2 0 74 throughout one core suggests that whatever oceanographic conditions influenced 18o also influenced 13c changes in prydz bay microfossil abundances and isotopes may result from alterations in circulation patterns upwelling conditions or sea ice patterns which significantly affected benthic and planktonic productivity in the area the environmental conditions indicated by older sediments in the cores are less clear but an ice tongue may have been in place 3200 3800 yr b p and minor fluctuations in productivity are indicated around 6000 and 7000 7500 yr b p the lower 100 cm of both cores may not represent in situ deposition but if the corrected ams dates reflect the actual age of the sediments analyzed microfossil and isotope data indicate that productivity and oceanographic conditions were very variable around 8500 8600 yr b p the chronology adopted herein must be regarded as tentative until further study of the area has been undertaken

normal amplitude brunhes paleosecular variation at low latitudes a paleomagnetic record from the trans mexican volcanic belt ancient secular variation in central mexico was determined from paleomagnetic measurements on 45 independent lava flows ranging in age 14c and k ar dates from 2 500 to 580 000 years b p all the analyzed flows are characterized by a normal polarity placing them within the brunhes chron the paleosecular variation analysis yielded an angular standard deviation from the field of an axial dipole of 15 3 with 95 confidence limits of 13 4 and 17 9 and that of the corresponding virtual geomagnetic poles vgps of 13 9 with confidence limits of 12 1 and 16 1 these values are in agreement with those predicted by most statistical models of secular variation but divergent from those obtained from low latitudes 19 n such as hawaii and pagan is