stacking paleointensity and oxygen isotope data for the last 1 5 myr piso 1500 coupled relative geomagnetic paleointensity rpi and oxygen isotope records are used to construct rpi and oxygen isotope stacks for the last 1 5 myr the coupled correlations are accomplished using the match algorithm lisiecki l e and lisiecki p a 2002 application of dynamic programming to the correlation of paleoclimate records paleoceanography 17 1049 doi 10 1029 2001pa000733 to simultaneously correlate isotope and rpi records the simultaneous match reduces the degree of freedom associated with correlations using rpi or oxygen isotope records alone the overall compatibility of rpi and oxygen isotopes indicates a dominant global but independent component in both signals the local wavelet power spectrum lwps for the rpi stack indicates little significant orbital power although the accompanying oxygen isotope stack has all the lwps characteristics expected of a high resolution oxygen isotope record containing orbital frequencies the piso 1500 stack represents a new stratigraphic template that can be used to correlate among marine sediment records and link them to polar ice cores via variations in cosmogenic nuclide production scaling the stack to values for virtual axial dipole moment vadm indicate maxima at 15 1022 am2 and minima that imply a threshold of 2 5 1022 am2 below which values are associated with either polarity reversals or magnetic excursions

temperature inversions thermal tides and water ice clouds in the martian tropics 1 we report new results on the structure and dynamics of the tropical atmosphere of mars derived from a combination of radio occultation measurements by mars global surveyor and simulations by a mars general circulation model mgcm radio occultation experiments sounded the equatorial atmosphere at latitudes of 36 n to 30 s during midsummer of the northern hemisphere ls 134 162 sampling the predawn thermal structure at a local time of 0412 elevated temperature inversions are a conspicuous feature of these observations they appear at pressures between 30 and 200 pa well above the surface and their magnitude exceeds 6 k in 34 of the temperature profiles in this latitude band the properties and spatial distribution of these elevated inversions are organized across the tropics on planetary scales inversions are strongest and occur most frequently above elevated terrain achieving a peak magnitude of 30 k near tharsis and their altitude generally increases toward the south according to mgcm simulations which closely resemble the observations these temperature inversions arise from zonally modulated thermal tides the best simulation includes an interactive hydrologic cycle which results in strong coupling between the thermal tides and radiatively active water ice clouds prominent clouds form in response to wave induced adiabatic cooling and evolve in a pattern closely correlated with the thermal structure of the tides the tides in turn are intensified by radiative forcing from the clouds this tide cloud coupling imposes strong diurnal modulation on the properties of clouds in the tropics

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

the time averaged paleomagnetic field we review indications of persistent deviations from the geocentric axial dipole model of the time averaged geomagnetic field and present a zonal harmonic model derived from 185 deep sea sediment piston cores taken from low to middle latitudes to approximately 45 analysis of the paleomagnetic inclination recorded in these cores for the brunhes normal polarity 0 73 ma and matuyama reverse polarity 0 73 2 47 ma chrons after plate motion correction gives well constrained estimates of the dominant long term nondipole contributions the axial quadrupole and axial octupole and shows no significant deviation from axial symmetry the amplitude of the axial quadrupole is found to vary with polarity 2 6 of the geocentric axial dipole for normal 4 6 for reverse while the axial octupole does not show appreciable change 2 9 for normal 2 1 for reverse these estimates of the quadrupole contribution agree well with prior determinations for the plio pleistocene 0 5 ma however the octupole contribution we find is opposite in sign to previous estimates we suggest that a negative octupole is representative of the actual time averaged paleomagnetic field while prior positive octupole estimates probably reflect spurious inclination shallowing the lack of polarity asymmetry in the octupole suggests that this nondipole component may be more closely linked to the main dipole field than is the quadrupole and so supports models of the geodynamo in which dipole and quadrupole families do not interact

geomagnetic field intensity and reversals during the past four million years a long and continuous record of the geomagnetic field intensity shows that intensity variations are dominated by two modes major episodes of field regeneration prevail on timescales of a few thousand years immediately after most reversals whereas stable polarity states are characterized by a slow 0 5 myr relaxation process reversals can be seen as the consequence of a progressive degradation of the dipole field

a survey of martian dust devil activity using mars global surveyor mars orbiter camera images 1 a survey of dust devils using the mars global surveyor mgs mars orbiter camera moc wide and narrow angle wa and na images has been undertaken the survey comprises two parts 1 sampling of nine broad regions from september 1997 to july 2001 and 2 a focused seasonal monitoring of variability in the amazonis region an active dust devil site from march 2001 to april 2004 for part 1 dust devils were identified in na and wa images and dust devil tracks were identified in na images great spatial variability in dust devil occurrence is highlighted with amazonis planitia being the most active region examined other active regions included cimmerium sinai and solis numerous dust devil tracks but very few dust devils were observed in casius this may suggest dust devils here occur at local times other than that of the mgs orbit 2 pm alternatively variations in surface properties may affect the ability of dust devils to leave visible tracks the seasonal campaign within amazonis shows a relatively smooth variation of dust devil activity with season peaking in mid northern summer and falling to zero in southern spring and summer this pattern of activity correlates well with the boundary layer maximum depth and hence the vigor of convection global maps of boundary layer depth and surface temperature do not predict that amazonis should be especially active potentially suggesting a role for mesoscale circulations measurement of observed dust devils yields heights of up to 8 km and widths in excess of 0 5 km

a middle miocene relative paleointensity record from the equatorial pacific abstract we present a high resolution magnetostratigraphy and relative paleointensity rpi record derived from the upper 85 m of iodp site u1336 an equatorial pacific early to middle miocene succession recovered during expedition 320 321 the magnetostratigraphy is well resolved with reversals typically located to within a few centimeters resulting in a well constrained age model the lowest normal polarity interval from 85 to 74 87 m is interpreted as the later part of chron c6n 18 614 19 599 ma thirty three other magnetozones occur from 74 87 to 0 85 m which are interpreted to represent the continuous sequence of chrons onset of chron c5er 18 748 ma to the end of chron c5an 1n 12 014 ma we identify three putative previously unrecognized subchrons within chron c5cn 1n chron 5bn 1r and c5abn sedimentation rates vary from about 7 to 15 m myr with a mean of about 10 m myr we observe rapid apparent changes in the sedimentation rate at geomagnetic reversals between 16 and 19 ma that indicate a calibration error in geomagnetic polarity timescale atnts2004 the remanence is carried mainly by non interacting particles of fine grained magnetite which have forc distributions characteristic of biogenic magnetite given the relative homogeneity of the remanence carriers throughout the 85 m thick succession and the fidelity with which the remanence is recorded we have constructed a relative paleointensity rpi record that provides new insights into middle miocene geomagnetic field behavior the rpi record indicates a gradual decline in field strength between 18 5 ma and 14 5 ma and indicates no discernible link between rpi and either chron duration or polarity state

the distribution of dust devil activity on mars 1 martian dust devil activity inferred from their tracks is mapped globally and compared to surface and atmospheric properties dust devils are estimated to lift 2 3 1 1011 kg of dust each year mostly from two narrow bands near 60 n and 60 s during their respective spring and summer approximately 55 of the dust lifted by dust devils in the northern hemisphere is removed from within 45 and 75 n while 65 of that lifted in the south is from within 45 and 75 s the southern band is an order of magnitude more populated with tracks than in the north likely a result of mars orbital eccentricity the equator is the location of a lesser peak while few dust devil tracks are found at the poles and middle latitudes during the fall and winter in both hemispheres few tracks are observed dust devil and track formation does not appear to be controlled significantly by elevation topographic slope dust cover or surface physical properties dust devils annually lift approximately half as much material as local and regional dust storms and are therefore significant contributors of dust into the martian atmosphere

geomagnetic dipole strength and reversal rate over the past two million years independent records of relative magnetic palaeointensity from sediment cores in different areas of the world can be stacked together to extract the evolution of the geomagnetic dipole moment1 2 and thus provide information regarding the processes governing the geodynamo so far this procedure has been limited to the past 800 000 years 800 kyr ref 3 which does not include any geomagnetic reversals here we present a composite curve that shows the evolution of the dipole moment during the past two million years this reconstruction is in good agreement with the absolute dipole moments derived from volcanic lavas which were used for calibration we show that at least during this period the time averaged field was higher during periods without reversals but the amplitude of the short term oscillations remained the same as a consequence few intervals of very low intensity and thus fewer instabilities are expected during periods with a strong average dipole moment whereas more excursions and reversals are expected during periods of weak field intensity we also observe that the axial dipole begins to decay 60 80 kyr before reversals but rebuilds itself in the opposite direction in only a few thousand years

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

rock magnetic criteria for the detection of biogenic magnetite abstract we report results on the magnetic properties of magnetites produced by magnetotactic and dissimilatory iron reducing bacteria magnetotactic bacterial mtb strains ms1 mv1 and mv2 and dissimilatory iron reducing bacterium strain gs 15 grown in pure cultures were used in this study our results suggest that a combination of room temperature coercivity analysis and low temperature remanence measurements provides a characteristic magnetic signature for intact chains of single domain sd particles of magnetite from mtbs the most useful magnetic property measurements include 1 acquisition and demagnetization of isothermal remanent magnetization irm using static pulse and alternating fields 2 acquisition of anhysteretic remanent magnetization arm and 3 thermal dependence of low temperature 20 k saturation irm after cooling in zero field zfc or in a 2 5 t field fc from 300 k however potentially the most diagnostic magnetic parameter for magnetosome chain identification in bulk sediment samples is related to the difference between low temperature zero field and field cooled sirms on warming through the verwey transition t 100 k intact chains of unoxidized magnetite magnetosomes have ratios of fc zfc greater than 2 where the parameter is a measure of the amount of remanence lost by warming through the verwey transition disruption of the chain structure or conversion of the magnetosomes to maghemite reduces the fc zfc ratio to around 1 similar to values observed for some inorganic magnetite maghemite greigite and gs 15 particles numerical simulations of fc zfc ratios for simple binary mixtures of magnetosome chains and inorganic magnetic fractions suggest that the fc zfc parameter can be a sensitive indicator of biogenic magnetite in the form of intact chains of magnetite magnetosomes and can be a useful magnetic technique for identifying them in whole sediment samples the strength of our approach lies in the comparative ease and rapidity with which magnetic measurements can be made compared to techniques such as electron microscopy

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

palaeomagnetic study of iodp sites u1331 and u1332 in the equatorial pacific extending relative geomagnetic palaeointensity observations through the oligocene and into the eocene

relationship between frontal dust storms and transient eddy activity in the northern hemisphere of mars as observed by mars global surveyor we have compiled a catalog of frontal dust storms in the northern hemisphere using mars orbiter camera daily global maps spanning 2 3 martian years of mars global surveyor mgs observations from 1999 to 2003 the most vigorous frontal storms that flush dust to the low latitudes occur in early mid fall and mid late winter away from the northern winter solstice while many streaks are observed in the polar hood during the winter solstice period no frontal dust storms are observed in the vicinity of the north polar region we have also analyzed simultaneous mgs thermal emission spectrometer tes temperature data and found statistically significant negative temperature anomalies associated with frontal storms in the lowest scale height of the atmosphere the geographical and seasonal distributions of temperature standard deviations associated with transient variations agree well with the distributions of frontal storms the correlation deteriorates with increasing altitude suggesting that lower level temperature waves are associated with the frontal dust storms specifically eastward traveling m 3 waves with periods of 2 3 sols appear to be closely related to the development of flushing frontal storms

oligocene miocene relative geomagnetic paleointensity correlated from the equatorial pacific iodp site u1334 and odp site 1218 to the south atlantic odp site 1090 abstract late oligocene to early miocene relative paleointensity rpi proxies can be correlated from the equatorial pacific iodp site u1334 and odp site 1218 to the south atlantic odp site 1090 age models are constrained by magnetic polarity stratigraphy through correlation to a common geomagnetic polarity timescale the rpi records do not contain significant power at specific orbital frequencies and hence there is no significant coherency between rpi proxies and the normalizers used to construct the proxies although orbital power is present in some normalizers there is no obvious control on rpi proxies from mean sedimentation rate within polarity chrons magnetic grain size proxies or magnetic concentration parameters the salient test is whether the equatorial pacific records can be correlated one to another and to the records from the south atlantic all records are dominated by rpi minima at polarity reversals as expected although the comparison within polarity chrons is compelling enough to conclude that the intensity of the earth s axial dipole is being recorded this is supported by the fit of rpi data from sites u1334 and 1218 after correlation of the two sites using diverse core scanning data rather than polarity reversals alone we do not see a consistent relationship between polarity chron duration and mean rpi and no consistent skewness saw tooth pattern for rpi within polarity chrons stacks of rpi records for 17 5 26 5 ma include long term changes in rpi on myr timescales that are superimposed on rpi minima associated with polarity reversals and shorter term variations in rpi with an apparent pacing of 50 kyr the equatorial pacific to south atlantic correlations indicate that rpi can be used as a global stratigraphic tool in pre quaternary sediments with typical pelagic sedimentation rates of a few cm kyr

dust storms originating in the northern hemisphere during the third mapping year of mars global surveyor abstract data from the third mars global surveyor mgs mapping year my 26 2003 2005 are used to investigate dust storms originating in the northern hemisphere flushing dust storms which originate as frontal dust storms at the northern polar vortex edge and propagate southward through topographic channels are observed immediately before and after a quiescent period that occurs around the northern winter solstice 240 l s 300 both the pre and post solstice active periods can be further divided into two sub periods the most vigorous of these flushing storms occurred during l s 210 220 and l s 310 320 the lifted dust crossed the equator and accumulated in the southern hemisphere these major dust storms enhanced the hadley circulation and suppressed the lower level baroclinic eddies in the northern mid and high latitudes the 2 3 sol wave number m 3 traveling waves show the best correlation with flushing dust storms and can combine with other wave modes to produce storm tracks and fronts within individual sub periods

rock magnetic artifacts on long term relative paleointensity variations in sediments 1 long term changes of geomagnetic field intensity including possible dependence on lengths of polarity intervals provide fundamentally important information for understanding the geodynamo a positive correlation between paleointensity and polarity interval length was previously suggested from an oligocene ca 23 34 ma relative paleointensity record at deep sea drilling program site 522 in the atlantic ocean which is the only continuous paleointensity data set published so far for this age interval we have conducted a paleomagnetic study of eocene to oligocene sediments at three sites in the eastern equatorial pacific ocean our objectives include revisiting the issue of the paleointensity polarity length correlation magnetic properties of the sediments meet the frequently used criteria for reliable relative paleointensity estimation although short wavelength normalized remanence intensity fluctuations associated with polarity boundaries and possible geomagnetic excursions agree among the three sites long term changes are inconsistent apparent positive correlation between normalized intensity and polarity length was observed but the normalized intensity has an obvious anti correlation with the ratio of anhysteretic remanent magnetization arm to isothermal remanent magnetization irm which is mainly controlled by the relative abundance of biogenic and terrigenous magnetic minerals furthermore the normalized intensity correlates with sedimentation rate these facts indicate a lithological contamination on the normalized intensity records the dependence on arm irm and sedimentation rate is also evident at site 522 it is inferred that variations in sedimentation rate and the relative abundance of biogenic magnetite on depositional remanent magnetization acquisition efficiency may not be well compensated by the normalization it is therefore premature to conclude that stronger geomagnetic fields were recorded during longer polarity intervals from currently available normalized intensity records

detection of noninteracting single domain particles using first order reversal curve diagrams we present a highly sensitive and accurate method for quantitative detection and characterization of noninteracting or weakly interacting uniaxial single domain particles unisd in rocks and sediments the method is based on high resolution measurements of first order reversal curves forcs unisd particles have a unique forc signature that can be used to isolate their contribution among other magnetic components this signature has a narrow ridge along the hc axis of the forc diagram called the central ridge which is proportional to the switching field distribution of the particles therefore the central ridge is directly comparable with other magnetic measurements such as remanent magnetization curves with the advantage of being fully selective to sd particles rather than other magnetic components this selectivity is unmatched by other magnetic unmixing methods and offers useful applications ranging from characterization of sd particles for paleointensity studies to detecting magnetofossils and ultrafine authigenically precipitated minerals in sediments

a first look at dust lifting and dust storms near the south pole of mars with a mesoscale model surface wind stresses and dust lifting in the south polar region of mars are examined with a three dimensional numerical model the focus of this study is the middle to late southern spring period when cap edge dust lifting events are observed mesoscale model simulations of high southern latitudes are conducted at three dates within this season l s 225 255 and 310 assuming that dust injection is related to the saltation of sand sized grains or aggregates the mars mm5 mesoscale model predicts surface wind stresses of sufficient strength to initiate movement of sand sized particles 100 m and hence dust lifting during all three periods the availability of dust and or sand sized particles is not addressed within this study instead the degree to which the existence of sufficiently strong winds limit dust injection is examined by eliminating forcing elements from the model the important dynamical modes generating high wind stresses are isolated the direct cap edge thermal contrast and topographic slopes in some locations provides the primary drive for high surface wind stresses at the cap edge while sublimation flow is not found to be particularly important at these three dates simulations in which dust is injected into the lowest model layer when wind stresses exceed a threshold show similar patterns of atmospheric dust to those seen in recent observations comparison between these simulations and those without active dust injection shows no signs of consistent positive or negative feedback due to dust clouds on the surface wind stress fields during the late spring season examined here

north polar dust storms in early spring on mars abstract observations of mars during 1996 1997 by the hubble space telescope covered the entire spring season in the northern hemisphere of mars which was favorably positioned for viewing the north polar region this paper reports observations of dust activity during this period local dust activity occurred near the edge of the subliming north polar cap during early spring this included local dust clouds similar to those seen by viking near the edge of the south polar cap and unusual arc shaped dust features that seem to represent a new type of dust phenomenon these dust arcs may explain the rima tenuis rift which has been occasionally seen by groundbased observers of mars analysis of numerical simulations from a mars general circulation model for the early northern spring season have provided insights into the plausible meteorological background at high latitudes in the vicinity of the retreating north polar cap these hubble observations extend the geographic and seasonal ranges during which local dust activity seems to be common on mars the combination of image analysis and model calculations support the hypothesis that these dust storms are the result of winds associated with fronts moving across the seasonal cap that lift dust exposed on the cap during co 2 sublimation

time variations in geomagnetic intensity 1 after many years spent by paleomagnetists studying the directional behavior of the earth s magnetic field at all possible timescales detailed measurements of field intensity are now needed to document the variations of the entire vector and to analyze the time evolution of the field components a significant step has been achieved by combining intensity records derived from archeological materials and from lava flows in order to extract the global field changes over the past 12 kyr a second significant step was due to the emergence of coherent records of relative paleointensity using the remanent magnetization of sediments to retrace the evolution of the dipole field a third step was the juxtaposition of these signals with those derived from cosmogenic isotopes contemporaneous with the acquisition of records new techniques have been developed to constrain the geomagnetic origin of the signals much activity has also been devoted to improving the quality of determinations of absolute paleointensity from volcanic rocks with new materials proper selection of samples and investigations of complex changes in magnetization during laboratory experiments altogether these developments brought us from a situation where the field changes were restricted to the past 40 kyr to the emergence of a coherent picture of the changes in the geomagnetic dipole moment for at least the past 1 myr on longer timescales the field variability and its average behavior is relatively well documented for the past 400 myr section 3 gives a summary of most methods and techniques that are presently used to track the field intensity changes in the past in each case current limits and potential promises are discussed the section 4 describes the field variations measured so far over various timescales covered by the archeomagnetic and the paleomagnetic records preference has always been given to composite records and databases in order to extract and discuss major and global geomagnetic features special attention has been devoted to discussing the degree of confidence to be put in the data by considering the integration of multiple data sets involving different techniques and or materials

fossil bacterial magnetite in deep sea sediments from the south atlantic ocean the magnetostratigraphy of deep sea sediment cores has proven to be a powerful and high resolution method of dating and comparing sedimentary records in contrast to this widespread application relatively few attempts have been made to analyse and identify the mineralogy grain size and origin of the carrier of the remanent magnetization1 2 it is widely assumed that dominant ferrimagnetic minerals in deep sea sediments are of lithogenic origin that is that they derive from oceanic or continental detritus volcanic ashfalls micrometeorites hydrothermal precipitation or chemical mineralization processes a very different view was taken by kirschvink and lowenstam3 who suggested that fossil remnants of magnetite mineralizing organisms in particular magnetotactic bacteria might play an important part in the magnetization of sediments deposited in certain detritus poor aquatic systems we have used rock magnetic diagnostic methods to characterize the magnetic phases in deep sea sediments from the south atlantic these phases were then extracted and studied with the electron microscope our results indicate that fossil bacterial magnetite is the main carrier of the natural remanent magnetization in sediments ranging in age from quarternary to eocene different types of bacterial magnetosomes were detected most of them occurring in chains of identical particles and nearly all of them falling into the theoretically determined4 size range of single domain magnetitite

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

seasonal changes of the baroclinic wave activity in the northern hemisphere of mars simulated with a gcm 1 seasonal changes in baroclinic wave activity during northern autumns ls 195 225 and winters ls 280 300 are studied with a martian general circulation model for the weak dust load the simulated s 2 harmonic with 3 1 sols period dominates near the surface while s 1 5 5 sols period is more prominent at higher altitudes during autumns in winters the s 1 wave has stronger amplitudes and a deep up to 0 1 mb vertical structure these simulations are consistent with observations from mgs we provide a simple explanation for the planetary wave changes in terms of seasonal variations of the background zonal mean fields in particular the observed and simulated significant reduction of the baroclinic wave activity during strong solstitial season dust storms occurs due to the stabilization of the jet stream with respect to baroclinic disturbances and due to the associated weakening of the wave excitation

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

geomagnetic moment variation and paleomagnetic excursions since 400 kyr bp a stacked record from sedimentary sequences of the portuguese margin abstract a paleomagnetic study was performed in clayey carbonate sedimentary sequences deposited during the last 400 kyr on the portuguese margin northeast atlantic ocean declination and inclination of the stable remanent magnetization present recurrent deviations from the mean geomagnetic field direction the normalized intensity documents a series of relative paleointensity rpi lows recognized in other reference records three directional anomalies occurring during rpi lows chronologically correspond to the laschamp excursion 42 kyr bp the blake event 115 122 kyr bp and the icelandic basin excursion 190 kyr bp a fourth directional anomaly recorded at 290 kyr bp during another rpi low defines the portuguese margin excursion four non excursional rpi lows are recorded at the ages of the jamaica pringle falls mamaku calabrian ridge 1 and levantine excursions the rpi record is characterized by a periodicity of 100 kyr paleointensity lows often coinciding with the end of interglacial stages this record sets the basis of the construction of an authigenic 10be 9be record from the same sedimentary sequences carcaillet et al this issue

padm2m a penalized maximum likelihood model of the 0 2 ma palaeomagnetic axial dipole moment summary we present a new time varying model for palaeomagnetic axial dipole moment padm for the past 2 myr and compare it with earlier virtual axial dipole moment vadm reconstructions which have been based on stacking and averaging scaled relative palaeointensity records the padm is derived from both absolute and relative palaeointensity data and constructed using a new penalized maximum likelihood pml approach to recover a cubic b spline representation of axial dipole field variations on million year timescales the pml method is explicitly intended to reduce bias in estimating the true axial dipole moment that arises in average vadm reconstructions we apply the pml method to a set of 96 032 published data 1800 palaeointensities from igneous rocks 3300 archaeointensities and 86 relative palaeointensity time series of variable lengths and resolutions two models are discussed padm2mp is a trial model based on a subset of the nine longest available sedimentary records padm2m uses a comprehensive data set 76 records 81 446 data 10 records were eliminated and is our preferred model padm2m has a lower mean than existing vadm reconstructions but shows similarities in long period variability some differences in timing amplitude and resolution of certain features can be attributed to variations in age assignments others result from our more comprehensive data set and a reduction in bias attributable to pml modelling padm2m has an average axial dipole moment over 0 2 ma of 5 3 1022 am2 with a standard deviation of 1 5 1022 am2 the brunhes chron average 6 2 1022 am2 is higher than for earlier epochs of matuyama 4 8 1022 am2 as seen in some previous studies the power spectrum for our model agrees with previous estimates of the global palaeomagnetic power spectrum for frequencies up to about 102 myr 1 we see no distinctive evidence in the power spectrum for orbital forcing of geodynamo behaviour

the paleomagnetic field from equatorial deep sea sediments axial symmetry and polarity asymmetry paleomagnetic data from 89 equatorial deep sea sediment cores indicate that the configuration of the time averaged geomagnetic field depends strongly on polarity state but that it remains within 1 degree of axial symmery throughout the pliocene and pleistocene last 5 million years the relative magnitude of the nondipole field was greater by almost a factor of 2 during reverse than during normal polarity intervals these results thus support earlier suggestions that there may be a standing nonreversing component of the geomagnetic dynamo

the mars limited area model and simulations of atmospheric circulations for the phoenix landing area and season of operation 1 the mars limited area model mlam has been used to simulate martian northern polar atmospheric circulation phenomena during the planned season of the phoenix lander touching down on the surface ls 76 initial and boundary conditions are from thermal emission spectrometer observations assimilated via the united kingdom mars general circulation model the higher resolution north pole centric nestings grid lengths about 17 30 km and 8 5 15 km respectively resolve phenomena such as shallow mesoscale katabatic drainage flows spiraling out of the cold polar dome strong valley winds out of chasma borealis and diurnal slope winds embedded on the easterly basic flow e g at phoenix landing area d there conditions appear to be mild for mars and baroclinic activity is low low level jets with wind speeds exceeding 20 m s are however possible but they are most likely nocturnal and would hence not endanger the early afternoon landing of phoenix dust lifting is predicted for strong wind areas near the landing area b where baroclinic activity appears to be high and in the general area of the landing area d primarily east of it

magnetic detection and characterization of biogenic magnetic minerals a comparison of ferromagnetic resonance and first order reversal curve diagrams australian research council grant number dp120103952 australia new zealand iodp consortium anzic grant number le0882854

magnetostatic interactions in deep sea sediments inferred from first order reversal curve diagrams implications for relative paleointensity normalization 1 understanding magnetostatic interactions in sediments is important for paleomagnetism and rock magnetism magnetostatic interactions are known to affect significantly the efficiency of anhysteretic remanent magnetization arm acquisition and hence the ratio of arm susceptibility arm to saturation isothermal remanent magnetization sirm a magnetic grain size proxy widely used for environmental applications can be controlled by magnetostatic interactions relative paleointensity estimations may also be influenced by magnetostatic interactions because arm is often used as a normalizer to correct for the difference in magnetizability of sediments in this study characterization of magnetic grains in deep sea sediments from the north pacific ocean was conducted using first order reversal curve forc diagrams and irm acquisition curves the forc diagrams indicate that the magnetic grains consist mainly of a noninteracting single domain sd component and an interacting sd component and additionally of a multidomain md component the relative abundances of these components were semiquantitatively estimated by curve fitting of cross sections along a line parallel to the axis of local interaction fields hu and through a peak in the coercivity hc three components were fitted assuming a gaussian distribution of interaction fields hu the irm acquisition curves can be described by two dominant components assuming a log gaussian distribution the mean coercivities of the two components are 40 and 100 mt respectively it is estimated that the former component is carried by biogenic magnetite and roughly corresponds to the noninteracting sd component derived from the forc diagrams and that the latter component is carried by eolian maghemite corresponding to the interacting sd component the arm sirm ratio decreases with increasing concentration of the interacting sd component this implies that the arm sirm ratio is significantly affected by magnetostatic interactions and that it does not necessarily reflect magnetic grain size the effect of magnetostatic interactions on natural remanent magnetization acquisition in sediments is not well understood but if it is similarly sensitive to the sirm normalization by arm in relative paleointensity estimations would overcompensate for the concentration of magnetic grains and cause the significant coherence between the normalized intensity and the normalizer that has been reported in the literature

a geomagnetic paleointensity stack between 0 8 and 3 0 ma from equatorial pacific sediment cores 1 we have conducted a paleomagnetic study of six sediment cores taken from the equatorial pacific three from the west caroline basin and three from the manihiki plateau in order to make a relative paleointensity stack during the matuyama and late gauss chrons the age of the bottom of the cores ranges from 1 2 to 3 0 ma the sediments show little downcore changes in the proxies of magnetic grain size and mineralogy and are hence suitable for estimating relative paleointensity the age of the cores is controlled by correlating variations in magnetic concentration magnetic susceptibility and or anhysteretic remanent magnetization arm to target oxygen isotope 18o curves all cores from the manihiki plateau show an upward decrease of the natural remanent magnetization nrm intensity normalized by arm and isothermal remanent magnetization irm with a decrease in sedimentation rate such a trend was removed before being converted to relative paleointensity this observation implies that a sedimentation rate change can affect relative paleointensity estimation relative paleointensity records from the six cores coincide well with each other within uncertainty of age we constructed a stacked curve between 0 8 and 3 0 ma the equatorial pacific paleointensity stack epapis 3ma after adjusting age the number of cores stacked is three to four throughout the record quasiperiodic paleointensity lows occur in the epapis 3ma and corresponding paleointensity lows can be found in previously published records with some shifts in age at least parts of the paleointensity minima seem to be accompanied by geomagnetic excursions the asymmetric sawtooth pattern of paleointensity variations is not observed at the matuyama gauss boundary and thereafter in our record a spectral analysis shows that 100 kyr orbital eccentricity frequency may exist in paleointensity variations during the matuyama and late gauss chrons

interannual variability of water ice clouds over major martian volcanoes observed by moc abstract using mars global surveyor mars orbiter camera daily global maps cloud areas have been measured daily for water ice clouds associated with the topography of the major volcanoes olympus mons ascraeus mons pavonis mons arsia mons elysium mons and alba patera this study expands on that of benson et al benson j l bonev b p james p b shan k j cantor b a caplinger m a 2003 icarus 165 34 52 by continuing their cloud area measurements of the tharsis volcanoes olympus mons and alba patera for an additional martian year august 2001 may 2003 and by also including elysium mons measurements from march 1999 through may 2003 the seasonal trends in cloud activity established by benson et al benson j l bonev b p james p b shan k j cantor b a caplinger m a 2003 icarus 165 34 52 for the five volcanoes studied earlier are corroborated here with an additional year of coverage for volcanoes other than arsia mons interannual variations that could be associated with the large 2001 planet encircling dust storm are minimal at arsia mons where cloud activity was continuous in the first two years clouds disappeared totally for 85 of l s l s 188 275 due to the dust storm elysium mons cloud activity is similar to that of olympus mons however the peak in cloud area is near l s 130 rather than near l s 100

magnetotactic bacteria and single domain magnetite in hemipelagic sediments remanent magnetism in marine sediments has been used extensively over the past twenty years to calibrate the geological time scale study geomagnetic reversals and secular variation and measure the rates of seafloor spreading although these sediments may contain different magnetic minerals magnetite is the most commonly observed and magnetically stable phase and its size shape and post depositional fate affect the magnetic remanence of the sediments biogenic magnetites are single domain with a high natural magnetic remanence nrm and have been suggested as a significant source of magnetic remanence in marine sediments we have studied surface sediments from the santa barbara basin and report the occurrence of living magnetotactic bacteria and the deposition of biogenic ultra fine grained single domain magnetite using a novel extraction technique transmission electron microscopy and squid magnetometry we show that these bacteria and the magnetite they produce are the major source of stable remanent magnetism in these sediments

mars atmospheric dynamics as simulated by the nasa ames general circulation model 2 transient baroclinic eddies a large set of experiments performed with the nasa ames mars general circulation model gcm have been analyzed to determine the properties structure and dynamics of the simulated transient baroclinic eddies the mars gcm simulations span a wide range of seasonal dates and dust loadings and include a number of special sensitivity experiments e g with flat topography there is strong transient baroclinic eddy activity in the extratropics of the northern hemisphere during the northern autumn winter and spring seasons the eddy activity remains strong for very large dust loadings though it shifts northward the eastward propagating eddies are characterized by zonal wavenumbers of 1 4 and periods of 2 10 days in several simulations the eddy variance is dominated by a single zonal wavenumber and a narrow range of periods the longer wavenumbers 1 and 2 transient eddies have a very deep vertical structure exhibiting a maximum kinetic energy density at the model top 45 50 km in many of the simulations in a simulation for early northern spring the eddies are quite shallow however the transient eddies generate the bulk of their energy baroclincally via large meridional and vertical heat fluxes at both lower and upper levels this is despite the fact that their vertical structure is typically close to equivalent barotropic above the lowest 10 km the eddies also appear to generate a substantial amount of energy barotropically via large meridional momentum fluxes at both lower and upper levels in the tropics and northern subtropics at upper levels 25 50 km there are strong transient eddy motions with structures resembling those characteristic of inertially unstable modes this eddy activity appears to be a response to the forcing of a region of marginal inertial stability by the extratropical transient baroclinic eddies as the wavenumbers and periods are the same as those in the extratropics a major surprise is the presence of very weak transient eddy activity in a number of the southern winter simulations it appears that this is partly a consequence of the stabilizing effects of the zonally symmetric topography in the gcm but it also must be associated with certain aspects of the zonal mean circulation in southern winter this is indicated by the presence of relatively large amplitude eddies in simulations for early southern autumn and spring and in a southern winter solstice simulation incorporating a different topography derived from the mars digital terrain model this topography differs from that used in most of the gcm simulations in not being characterized by steep symmetric slopes which are stabilizing to baroclinic instability in southern high latitudes it is hypothesized that the very large extent of the southern seasonal polar cap and high elevations in the south both might contribute to weakening the transient eddy activity large zonally symmetric topography in the northern hemisphere of the mars gcm also appears to have a strong impact on the transient eddies acting to increase the dominant zonal wavenumbers and phase speeds the properties of the gcm baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from viking lander meteorology observations the gcm eddies are found to be very similar to those observed in most respects a notable exception is that the eddy amplitudes in the highly dusty gcm simulations are much larger than those observed by viking during the 1977 winter solstice dust storm this is almost certainly at least partly due to the relatively small latitudinal expansion of the hadley circulation in the highly dusty gcm experiments

isolating climatic and paleomagnetic imbricated signals in two marine cores using principal component analysis high resolution measurements of climatic and magnetic parameters have been performed on two cores from the eastern china sea and the western caroline basin on both cores magnetic parameters show a strong imprint of climatic changes but the absence of relationship between the inclination and the bulk density indicates that the directional changes do not depend on lithology a weak 100 ka cycle is present in the china sea inclination variations but this period is not in phase with the orbital eccentricity and thus not relevant all normalization parameters yielded similar estimates of relative paleointensity rpi but we have noticed the persistence of climatic components in the signal principal component analysis pca applied to different parameters related to climate lithology and paleointensity has allowed to extract a clean magnetic signal that we refer as principal component of paleointensity pcp which is in better agreement with the sint 2000 composite curve and provides a reliable record of relative paleointensity the presence of climatic frequencies in rpis most likely reflects the influence of lithology on the response of magnetization to field intensity we suggest that pca analysis can be very useful to approach these problems not only can the calculation separate overlapping climatic and magnetic signals but it indicates what confidence should be given to the data incidentally the present results emphasize the importance of carrying out detailed paleoclimatic analyses along with paleointensity studies

forced waves in the martian atmosphere from mgs tes nadir data abstract we have analyzed the temperature retrievals from mars global surveyor mgs thermal emission spectrometer tes nadir spectra to yield latitude height resolved maps of various atmospheric forced wave modes as a function of season for a full mars year among the isolated wave modes is the zonal mean time mean temperature which we used to derive zonal mean zonal winds and stationary wave quasi geostrophic indices of refraction diagnostic of their propagation the diurnal kelvin wave was isolated in the data with results roughly consistent with models wilson and hamilton 1996 j atmos sci 33 1290 1326 the s 1 and s 2 stationary waves were found to have significant amplitude in ducts extending up the winter polar jets while the s 3 stationary wave was found to be confined to near the surface the s 1 stationary wave was found to have little phase tilt with height during northern winter but significant westward phase tilt with height in the southern winter this indicates that the wave carries heat poleward slightly more than that found in barnes et al 1996 j geophys res 101 12 753 12 776 the s 1 stationary wave is likely the dominant mechanism for eddy meridional heat transport for the southern winter we noted that the phase of the s 2 stationary wave is nearly constant with time but that the s 1 stationary wave moved 90 of longitude from fall to winter and back in spring in the north while interannual variability is not yet addressed overall these results provide the first comprehensive benchmark for forced waves in mars s atmosphere against which future atmospheric models of mars can be compared

abundant bacterial magnetite occurrence in oxic red clay magnetotactic bacteria mtb produce chains of intracellular magnetite and or greigite crystals and respond to an ambient magnetic field mtb are considered to be microaerophilic to anaerobic organisms that live at and below the oxic anoxic transition zone of aquatic environments on the basis of rock magnetic analyses including first order reversal curve diagrams and isothermal remanent magnetization component analyses along with transmission electron microscopy we demonstrate that bacterial magnetites magnetofossils dominate magnetic mineral assemblages throughout a 76 m thickness of red clay at integrated ocean drilling program site u1365 in the south pacific gyre as well as in subsurface red clay of the north pacific gyre where the sediment column contains abundant dissolved oxygen and no oxic anoxic transition zone exists this implies that mtb inhabit red clay this conflicts with widespread interpretations of mtb ecology namely that they are microaerophilic requiring low levels of oxygen to grow and produce magnetite and that magnetotaxis is used to help them find optimal positions in a strong vertical chemical gradient most magnetofossils in the red clay have cubo octahedral morphology this supports the notion that magnetofossil morphology can be a paleoenvironmental indicator the proportion of elongated magnetofossils increases in less oxic environments our results also have implications for red clay paleomagnetism in that magnetofossils may cause much delayed remanence acquisition if mtb can live at decimeter depths within red clay

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

reflections on soft subglacial beds as a mosaic of deforming and stable spots abstract much discussion regarding subglacial processes is centred around the question of how soft beds respond to ice overriding in particular how widespread and penetrative is their deformation how does it affect the ice stability and what are the consequences for large scale sediment redistribution patterns contrasting views have been proposed which are difficult to verify and reconcile in the light of scarcity of agreed criteria to identify deforming beds here we suggest that soft beds under warm based glaciers can be envisaged as a mosaic of deforming and stable spots transient in time and space according to changes in the control parameters at the ice bed interface the subglacial mosaic model is consistent with field data showing heavily deformed beds interspersed with largely undisturbed beds it is suggested that deformation found in tills is a cumulative effect of strain within a relatively thin ephemeral deforming spots under the ice sole affecting the till as it accretes during ice overriding in accord with the coulomb plastic rheology the role of clast ploughing in bed deformation is emphasised

moc observations of the 2001 mars planet encircling dust storm abstract from 15 september 1997 through 21 january 2006 only a single planet encircling martian dust storm was observed by mgs moc the onset of the storm occurred on 26 june 2001 l s 184 7 earliest recorded to date it was initiated in the southern mid to low latitudes by a series of local dust storm pulses that developed along the seasonal cap edge in malea and in hellas basin l s 176 2 184 4 the initial expansion of the storm though asymmetric was very rapid in all directions 3 32 m s 1 the main direction of propagation however was to the east with the storm becoming planet encircling in the southern hemisphere on l s 192 3 several distinct centers of active dust lifting were associated with the storm with the longest persisting for 86 sols syria claritas these regional storms helped generate and sustain a dust cloud haze which reached an altitude of about 60 km and a peak opacity of dust 5 0 by l s 197 0 the cloud had encircled the entire planet between 59 0 s and 60 0 n obscuring all but the largest volcanoes the decay phase began around l s 200 4 with atmospheric dust concentrations returning to nominal seasonal low levels at l s 304 0 exponential decay time constants ranged from 30 117 sols the storm caused substantial regional albedo changes darkening and brightening as a result of the redistribution removal and deposition of a thin veneer of surface dust at least 0 1 11 1 m thick it also caused changes in meteorological phenomena i e dust storms dust devils clouds recession of the polar caps and possibly surface temperatures that persisted for just a few weeks to more than a single mars year the redistribution of dust by large annual regional storms might help explain the long period 30 years between the largest planet encircling dust storms events

origin of orbital periods in the sedimentary relative paleointensity records abstract orbital cycles with 100 kyr and or 41 kyr periods detected in some sedimentary normalized remanence relative paleointensity records by power spectral analysis or wavelet analysis have been attributed either to orbital forcing of the geodynamo or to lithologic contamination in this study local wavelet power spectra lwps with significance tests have been calculated for seven relative paleointensity rpi records from different regions of the world the results indicate that orbital periods 100 kyr and or 41 kyr are significant in some rpi records during certain time intervals and are not significant in others time intervals where orbital periods are significant are not consistent among the rpi records implying that orbital periods in these rpi records may not have a common origin such as orbital forcing on the geodynamo cross wavelet power spectra xwt and squared wavelet coherence wtc between rpi records and orbital parameters further indicate that common power exists at orbital periods but is not significantly coherent and exhibits variable phase relationships implying that orbital periods in rpi records are not caused directly by orbital forcing similar analyses for rpi records and benthic oxygen isotope records from the same sites show significant coherence and constant in phase relationships during time intervals where orbital periods were significant in the rpi records indicating that orbital periods in the rpi records are most likely due to climatic contamination although common power exists at orbital periods for rpi records and their normalizers with significant coherence during certain time intervals phase relationships imply that contamination at orbital periods is not directly due to the normalizers orbital periods are also significant in the nrm intensity records and contamination in rpi records can be attributed to incomplete normalization of the nrm records further tests indicate that contamination is apparently not directly related to physical properties such as density or carbonate content or to the grain size proxy arm however wtc between rpi records and the grain size proxy arm irm implies that arm irm does reflect the contamination in some rpi records it appears that orbital periods were introduced into the nrm records and have not been normalized when calculating rpi records through magnetite grain size variations reflected in the arm irm grain size proxy the orbital power in arm irm for some north atlantic sites is probably derived from bottom current velocity variations that are orbitally modulated and are related to the vigor of thermohaline circulation and the production of north atlantic deep water nadw in the case of odp site 983 the orbital power in rpi appears to exhibit a shift from 41 kyr to 100 kyr period at the mid pleistocene climate transition 750 ka reinforcing the climatic origin of these orbital periods rpi records from the atlantic and pacific oceans and rpi records with orbital periods eliminated by band pass filters are highly comparable with each other in the time domain and are coherent and in phase in time frequency space especially at non orbital periods indicating that contamination although present at orbital periods is not debilitating to these rpi records as a global signal that is primarily of geomagnetic origin

radio occultation measurements of transient eddies in the northern hemisphere of mars 1 we have characterized the behavior of transient eddies in the northern hemisphere of mars through analysis of radio science rs occultation data from mars global surveyor mgs the weather in the lowest scale height above the surface at 55 n 80 n is dominated by shallow eastward moving baroclinic eddies distinguished by their intensity and coherence the vertical structure of these eddies is fully resolved by the rs measurements which also yield unique estimates of the near surface meridional winds implied by geostrophic balance we identified and characterized the most prominent eddies through space time analysis of rs measurements of geopotential height at 610 pa a few kilometers above the surface eddy activity appears as well defined modes with zonal wave numbers 1 3 and variations in the amplitudes of these modes tend to be anticorrelated so that a large amplitude in one mode is often accompanied by a small amplitude in the others the wave number and period of the dominant mode shift at intervals of 30 50 sols eddy winds near the surface vary distinctively with season in response to changes in eddy amplitude and zonal wave number the meridional winds peak sharply in two seasonal windows one in early to middle autumn and the other in middle to late winter separated by a lull around winter solstice comparisons with previous results reveal close connections with the transient eddies observed by the viking landers and with distinctive southward moving frontal dust storms observed by the mgs mars orbiter camera

oligocene miocene magnetic stratigraphy carried by biogenic magnetite at sites u1334 and u1335 equatorial pacific ocean 1 sediments from the equatorial pacific ocean at the integrated ocean drilling program sites u1334 and u1335 record reliable magnetic polarity stratigraphies back to 26 5 ma late oligocene at sedimentation rates usually in the 5 20 m myr range putative polarity subchrons that do not appear in current polarity timescales occur within chrons c5acr c5adn and c5bn 1r at site u1335 and within chrons c6aar 2r c6br c7ar and c8n 1n at site u1334 subchron c5dr 1n 17 5 ma is recorded at both sites supporting its apparent recording in the south atlantic ocean and has an estimated duration of 40 kyr the oligocene miocene calcareous oozes have magnetizations carried by submicron magnetite as indicated by thermal demagnetization of magnetic remanences the anhysteretic remanence to susceptibility ratio and magnetic hysteresis parameters transmission electron microscopy of magnetic separates indicates the presence of low titanium iron oxide magnetite grains with size 50 100 nm and shape similar to modern and fossil bacterial magnetite supporting other evidence that biogenic submicron magnetite is the principal remanence carrier in these sediments in the equatorial pacific ocean low organic carbon burial arrests microbial pore water sulfate reduction thereby aiding preservation of bacterial magnetite

geomagnetic paleointensity and environmental record from labrador sea core md95 2024 global marine sediment and ice core chronostratigraphy for the last 110 kyr piston core md95 2024 from the labrador rise provides a continuous record of rapidly deposited detrital layers denoting laurentide ice sheet lis instability the core also provides a high resolution record of geomagnetic paleointensity that is consistent with but at higher temporal resolution than previous labrador sea records correlation to the greenland summit ice cores grip gisp2 is achieved by assuming that labrador sea detrital layers correspond to cold stadials in the ice cores this allows a gisp2 official chronology to be placed on md95 2024 which is consistent with the inverse correlation between paleointensity and the flux of cosmogenic isotopes 10 be and 36 cl in greenland ice cores synchronous millennial scale variability observed from the md95 2024 paleointensity

north polar frontal clouds and dust storms on mars during spring and summer the complete archive of mars global surveyor mgs mars orbiter camera moc mars daily global maps mdgm are used to study north polar clouds and dust storms that exhibit frontal structures during the spring and summer ls 0 180 results show that frontal events generally follow the edge of the polar cap during spring and mid late summer with a gap in the distribution in early summer the exact duration and timing of the gap vary from year to year ten to twenty percent of spring and summer time frontal events exhibit complex morphologies distinct temperature signatures are associated with features observed in images in many but not all cases the general travel paths of the frontal events are eastward around the polar cap westward paths exist only at the edge of the polar cap in late spring early summer occasionally the paths curve toward or away from the polar cap in certain longitude sectors

geomagnetic paleointensity variation with a 100 kyr quasi period abstract we analyzed records of geomagnetic field intensity paleointensity during the last 700 kyr in five sediment cores from a wide region of the pacific ocean a global paleointensity variation with a 100 kyr quasi period was successfully extracted using the wavelet transform because the variation does not correlate with that of magnetic properties of the sediments it originated from a change in the geomagnetic field the 100 kyr quasi period of the geomagnetic field is close to the timescales of eccentricity one of the earth s orbital elements and of the glacial interglacial cycle of the late quaternary paleoclimate in particular there is a correlation between the variations of the geomagnetic field intensity and climate with an 18 kyr time lag while the geodynamo has widely been thought to be a self sustained system our results support the possibility of an external energy supply of the variation through orbital forcing or climate change

martian clouds observed by mars global surveyor mars orbiter camera we have made daily global maps that cover both polar and equatorial regions of mars for ls 135 360 and 0 111 using the mars global surveyor mgs mars orbiter camera moc red and blue wide angle swaths taken from may 1999 to january 2001 we study the seasonal distribution of condensate clouds and dust clouds during roughly 1 martian year using these daily global maps we present the development and decay of the tropical cloud belt and the polar hoods the spatial and temporal distributions of lee waves and spiral clouds and an unusual aster cloud above the volcanoes consisting of rays around a central disk like the flower the tropical cloud belt contains mostly fibrous clouds during northern spring early summer and convective clouds during middle late northern summer the detailed development and decay of the tropical cloud belt is nonuniform in longitude two distinct stormy periods in late summer precede the formation of the north and south circumpolar hoods the north polar storms in late summer resemble baroclinic frontal systems on earth but contain both dust and condensate clouds spiral clouds occur only in the northern high latitudes and only during northern spring and summer the north polar hood displays a stationary wave number two structure during the fall and winter the south polar hood has fewer streak clouds and lee wave clouds than the north polar hood during this particular year the lee wave cloud abundance in the south had two peaks in early fall and late winter and the lee wave cloud abundance in the north had one peak in early fall

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

paleoposition of the intertropical convergence zone in the eastern pacific inferred from glacial interglacial changes in terrigenous and biogenic magnetic mineral fractions magnetic properties are increasingly used for paleoclimatic and paleoceanographic studies utilizing recently developed proxies an environmental magnetic study was conducted on the uppermost 12 m sediments of integrated ocean drilling program site u1337 in the eastern equatorial pacific ocean this interval is above the fe redox boundary and covers the past 800 k y the site is located near the present southern boundary of the intertropical convergence zone itcz and is thus expected to be sensitive to variations of the itcz position the ratio of anhysteretic remanent magnetization susceptibility to saturation isothermal remanent magnetization k arm sirm first order reversal curve diagrams and irm acquisition curves indicate that the magnetic mineral assemblage consists of a dominant biogenic component and a minor terrigenous component two groups the biogenic soft bs and hard bh are identified for the biogenic component and probably correspond to different magnetofossil morphology the bh component probably carried by elongated magnetofossils increases in sediments of glacial periods which are probably in less oxic conditions due to increased ocean productivity this demonstrates that magnetofossil morphology which can be discriminated by the rock magnetic technique is a sensitive indicator of slight oxic suboxic environmental fluctuations in sediments temporal variations of the terrigenous component most likely transported as eolian dust were estimated from the k arm sirm ratio and s ratio ratio of a moderate field irm to sirm representing relative contribution of lower and higher coercivity magnetic minerals significant glacial interglacial variations occurred at marine isotope stage mis 10 and before but not after in addition coeval upcore increases in sedimentation rates and the bh component were observed suggesting increased productivity these observations may indicate that the position of the itcz was more southward than today ca 250 ka and before

relative paleointensity rpi and oxygen isotope stratigraphy at iodp site u1308 north atlantic rpi stack for 1 2 2 2 ma narpi 2200 and age of the olduvai subchron 2015 elsevier ltd integrated ocean drilling program iodp site u1308 49 53 n 24 14 w water depth 3871 m provides a record of relative paleointensity rpi and benthic stable isotope stratigraphy back to 3 2 ma the record since 1 5 ma was published previously and here we present the interval from 1 5 ma to 3 2 ma early pleistocene late pliocene the benthic oxygen isotope record in this interval is correlated to marine isotope stage mis 51 to km2 with an apparent hiatus that removed part of the interval spanning mis 104 g2 2 6 2 65 ma at the gauss matuyama boundary the mean sedimentation rate for the 1 5 3 2 ma period is 8 5 cm kyr the age model was built by correlation of the benthic oxygen isotope record to a global stack lr04 apart from the expected polarity reversals three magnetic excursions are recorded punaruu in mis 31 32 at 1092 ka gilsa in mis 54 55 at 1584 ka and a newly recognized excursion labeled porcupine after the nearby porcupine abyssal plain in mis g6 g7 at 2737 ka the ages of polarity reversals at site u1308 on the lr04 time scale are consistent with the current geomagnetic polarity timescale gpts with the exception of the base of the olduvai subchron that occurred in mis 73 corresponding to 1925 ka on the lr04 time scale 25 kyr younger than in the current gpts the rpi record at site u1308 is calibrated using the oxygen isotope age model and combined with four other north atlantic records to obtain a north atlantic rpi stack for 1 2 2 2 ma narpi 2200 that is compared with published rpi stacks epapis sint 2000 and padm2m for 2 2 3 2 ma the site u1308 rpi record is compared with a rpi record from north atlantic iodp site u1314 and with the pacific epapis stack the mean sedimentation rates of the north atlantic sites in narpi 2200 are greater by about an order of magnitude than most of the records incorporated in other stacks the comparison of epapis and narpi 2200 yields an apparent lag for narpi 2200 relative to epapis attributed the epapis age model constructed by correlation of magnetic concentration parameters a proxy for carbonate percentage to a calibrated oxygen isotope record the long rpi record from site u1308 yields a very similar mean value for the brunhes and matuyama virtual axial dipole moments 7 05 1022 am2 implying no polarity bias in the strength of the main geomagnetic dipole in contrast to interpretations from sint 2000 and padm2m the results strengthen the case that rpi can be used to improve global stratigraphic correlation for sites with mean sedimentation rates up to several decimeters kyr

variable remanence acquisition efficiency in sediments containing biogenic and detrital magnetites implications for relative paleointensity signal recording widespread geological preservation of biogenic magnetite makes it important to assess how such particles contribute to sedimentary paleomagnetic signals we studied a sediment core from the south china sea that passes the strict empirical criteria for magnetic uniformity used in relative paleointensity studies such assessments are based routinely on bulk magnetic parameters that often fail to enable identification of mixed magnetic mineral assemblages using techniques that enable component specific magnetic mineral identification we find that biogenic and detrital magnetites occur in approximately equal concentrations within the studied sediments we analyzed normalized remanence signals associated with the two magnetite components to assess whether co occurring biogenic and detrital magnetites record geomagnetic information in the same way and with the same efficiency paleomagnetic directions for the two components have no phase lag which suggests that the biogenic and detrital magnetites acquired their magnetizations at equivalent times however we find that the biogenic magnetite is generally 2 4 times more efficient as the detrital magnetite in contributing to the natural remanent magnetization nrm despite their approximately equal magnetic contributions variations in the concentration and efficiency of remanence acquisition of the two components suggest that a significant part of the nrm is controlled by nongeomagnetic factors that will affect relative paleointensity recording we recommend that methods suited to the detection of variable recording efficiency associated with biogenic and detrital magnetites should be used on a routine basis in relative paleointensity studies

the seasonal behavior of water ice clouds in the tharsis and valles marineris regions of mars mars orbiter camera observations abstract the mars global surveyor mars orbiter camera was used to obtain global maps of the martian surface with equatorial resolution of 7 5 km pixel in two wavelength ranges blue 400 450 nm and red 575 625 nm the maps used were acquired between march 15 1999 ls 110 and july 31 2001 ls 205 corresponding to approximately one and a quarter martian years using the global maps cloud area in km2 has been measured daily for water ice clouds topographically corresponding to olympus mons ascraeus mons pavonis mons arsia mons alba patera the western valles marineris canyon system and for other small surface features in the region seasonal trends in cloud activity have been established for the three tharsis volcanoes olympus mons and alba patera olympus ascraeus and pavonis mons show cloud activity from about ls 0 220 with a peak in cloud area near ls 100 one of our most interesting observational results is that alba patera shows a double peaked feature in the cloud area with peaks at ls 60 and 140 and a minimum near ls 100 arsia mons shows nearly continuous cloud activity the altitudes of several of these clouds have been determined from the locations of the visual cloud tops and optical depths were measured for a number of them using the disort code of stamnes et al 1988 appl opt 27 2502 2509 several aspects of the observations e g cloud heights effects of increased dust on cloud activity are similar to simulations in richardson et al 2002 j geophys res 107 5064 a search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours unambiguous evidence for other periodicities was not found

traveling waves in the northern hemisphere of mars 1 analysis of temperature retrievals from mars global surveyor thermal emission spectrometer data has revealed the presence of regular eastward propagating waves in the northern hemisphere a large amplitude zonal wave 1 with a long 20 sol period is particularly prominent during early winter ls 220 270 after ls 270 a weaker and more rapidly propagating 6 5 sol period zonal wave 1 is dominant these waves have a deep vertical structure 40 km correlated with the axis of the winter hemisphere westerly jet simulations with a mars general circulation model suggest that the fast wave is associated with baroclinic instability due to the strong meridional temperature gradient at the surface and is consistent with surface pressure oscillations seen in viking lander data by contrast the slow wave has the appearance of a large amplitude rossby wave that is coupled with an inertially unstable region in the subtropics

observations of the initiation and evolution of the 2001 mars global dust storm 1 a global dust storm occurred on mars between june and october 2001 the storm began near hellas just before southern spring equinox ls 177 local storms likely forced by a combination of slope flow and ice cap thermal contrasts were observed to propagate along the northwestern rim of hellas apparently triggering the global storm cap edge storm activity for much of late southern winter was similar in 2001 to one mars year earlier however a very large storm propagated into the basin just after ls 177 subsequently the total area of storm activity in 2001 was roughly double that of the previous year for about 10 days dust lifting was limited to the hellas region as additional storms propagated into hellas activity built and extended northward into syrtis and eastward into hesperia it is not clear whether transport or spreading of lifting were of greatest importance for expansion at ls 185 the storm began to spread rapidly to the east along a line from the southern pole to the northern tropics essentially no storm propagation to the west occurred yielding strong zonal asymmetry of expansion as the dust storm reached the western edge of tharsis secondary dust lifting centers developed in daedalia and solis southeastern tharsis subsequently the storm rapidly encompassed the planet by ls 193 once fully global the syria solis daedalia lifting center appeared to dominate on the basis of cloud top morphology with hellas quiescent by ls 212 lifting could no longer be discerned thereafter dust haze appeared uniform and diffuse and decay appeared to have set in

analysis of 11 myr of geomagnetic intensity variation we have conducted a detailed exploratory analysis of an 11 million year long almost continuous record of relative geomagnetic paleointensity from a sediment core acquired on deep sea drilling project leg 73 at site 522 in the south atlantic we assess the quality of the paleointensity record using spectral methods and conclude that the relative intensity record is minimally influenced by climate variations isothermal remanence is shown to be the most effective normalizer for these data although both susceptibility and anhysteretic remanence are also adequate statistical analysis shows that the paleointensity variations follow a gamma distribution and are compatible with predictions from modified paleosccular variation models and global absolute paleointensity data when subdivided by polarity interval the variability in paleointensity is proportional to the average and further the average is weakly correlated with interval length spectral estimates for times from 28 77 until 22 74 ma when the reversal rate is about 4 myr 1 are compatible with a poisson model in which the spectrum of intensity variations is dominated by the reversal process in the frequency range 1 50 myr 1 in contrast between 34 7 and 29 4 ma when the reversal rate is about 1 6 myr 1 the spectra indicate a different secular variation regime the magnetic field is stronger and more variable and a strong peak in the spectrum occurs at about 8 myr 1 this peak may be a reflection of the same signal as recorded by the small variations known as tiny wiggles seen in marine magnetic anomaly profiles

observations of martian ice clouds by the mars global surveyor thermal emission spectrometer the first martian year successful operation of the mars global surveyor spacecraft beginning in september 1997 ls 184 has permitted extensive observations over more than a martian year initially thin normal optical depth 0 06 at 825 cm 1 ice clouds and hazes were widespread showing a distinct latitudinal gradient with the onset of a regional dust storm at ls 224 ice clouds vanished in the southern hemisphere to reappear gradually after the decay of the storm the zonally averaged cloud opacities show little difference between the beginning and end of the first martian year a broad low latitude cloud belt with considerable longitudinal structure was present in early northern summer apparently characteristic of the northern summer season it vanished between ls 140 and 150 the latitudinal extent of this feature is apparently controlled by the ascending branch of the hadley circulation the most opaque clouds optical depth 0 6 were found above the summits of major volcanic features these showed spatial structure possibly associated with wave activity variety among low lying late morning clouds suggests localized differences in circulation and microclimates limb observations showed extensive optically thin optical depth 0 04 stratiform clouds at altitudes up to 55 km considerable latitude and altitude variations were evident in ice clouds in early northern spring ls 25 near 30 km thin clouds extended from just north of the equator to 45 n nearly to the north polar vortex a water ice haze was present in the north polar night ls 30 at altitudes up to 40 km because little dust was present this probably provided heterogeneous nucleation sites for the formation of co2 clouds and snowfall at altitudes below 20 km where atmospheric temperatures dropped to the co2 condensation point the relatively invariant spectral shape of the water ice cloud feature over space and time indicates that ice particle radii are generally between 1 and 4 m

the identification and biogeochemical interpretation of fossil magnetotactic bacteria magnetotactic bacteria which most commonly live within the oxic anoxic transition zone oatz of aquatic environments produce intracellular crystals of magnetic minerals specifically magnetite or greigite the crystals cause the bacteria to orient themselves passively with respect to the geomagnetic field and thereby facilitate the bacteria s search for optimal conditions within the sharp chemical gradients of the oatz the bacteria may also gain energy from the redox cycling of their crystals because magnetotactic bacteria benefit from their magnetic moments natural selection has promoted the development of traits that increase the efficiency with which the intracellular crystals impart magnetic moments to cells these traits also allow crystals produced by magnetotactic bacteria called magnetofossils when preserved in sediments to be distinguished from abiogenic particles and particles produced as extracellular byproducts of bacterial metabolism magnetofossils are recognizable based on their narrow size and shape distributions distinctive morphologies with blunt crystal edges chain arrangement chemical purity and crystallographic perfection this article presents a scheme for rating magnetofossil robustness based on these traits the magnetofossil record extends robustly to the cretaceous and with lesser certainty to the late archean because magnetotactic bacteria predominantly live in the oatz the abundance and character of their fossils can reflect environmental changes that alter the chemical stratification of sediments and the water column the magnetofossil record therefore provides an underutilized archive of paleoenvironmental information several studies have demonstrated a relationship between magnetofossil abundance and glacial interglacial cycles likely mediated by changes in pore water oxygen levels more speculatively a better developed magnetofossil record might provide constraints on the long term evolution of marine redox stratification more work in modern and ancient settings is necessary to explicate the mechanisms linking the abundance and character of magnetofossils to ancient biogeochemistry

magnetic paleointensity stratigraphy and high resolution quaternary geochronology successes and future challenges abstract magnetic paleointensity stratigraphy is used to detect variations in the strength of earth s ancient magnetic field paleointensity studies have demonstrated that a dominantly dipolar geomagnetic signal can be recorded in a globally coherent manner in different types of sediments and in non sedimentary archives including ice core records and marine magnetic anomaly profiles the dominantly dipolar nature of geomagnetic paleointensity variations provides a global geophysical signal that has come to be widely used to date quaternary sediments despite the many successful applications of paleointensity assisted chronology the mechanisms by which sediments become magnetized remain poorly understood and there is no satisfactory theoretical foundation for paleointensity estimation in this paper we outline past successes of sedimentary paleointensity analysis as well as remaining challenges that need to be addressed to place such work on a more secure theoretical and empirical foundation we illustrate how common concepts for explaining sedimentary remanence acquisition can give rise to centennial to millennial offsets between paleomagnetic and other signals which is a key limitation for using paleointensity signals for geochronology our approach is intended to help non specialists to better understand the legitimate uses and limitations of paleointensity stratigraphy while pointing to outstanding problems that require concerted specialist efforts to resolve

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

dust devils on earth and mars 1 dust devils particle loaded vertical convective vortices found on both earth and mars are characterized by high rotating wind speeds significant electrostatic fields and reduced pressure and enhanced temperature at their centers on earth they are subordinate to boundary layer winds in the dust cycle and except possibly in arid regions are only nuisance level phenomena on mars though they seem to support the persistent background atmospheric haze to influence the surface albedo through the formation of tracks on the surface and to possibly endanger future exploration because of their high dust load and large potential gradients high resolution numerical simulations and thermophysical scaling models successfully describe dust devil like vortices on mars but fitting dust devil action into the martian global dust cycle is still problematic reliable parameterizations of their erosional abilities and solid temporal and spatial distribution data are still required to build and test a complete model of dust devil action

traveling waves in the martian atmosphere from mgs tes nadir data abstract we have characterized the annual behavior of martian atmospheric traveling waves in the mgs tes data set from the first two martian years of mapping there is a high degree of repeatability between the two years they are dominated by strong low zonal wavenumber waves with high amplitudes near the polar jets strongest in late northern fall and early northern winter the m 1 waves have amplitudes up to about 20 k are vertically extended and occasionally extend even into the tropics periods for m 1 range from 2 5 to 30 sols much weaker waves were identified in the south with amplitudes less than about 3 5 k traveling waves with m 2 and m 3 are also seen but their amplitudes are typically limited to less than 4 k and are generally more confined near the surface in the north they are more evident in fall and spring rather than winter solstice which is clearly dominated by m 1 waves some evidence of storm tracks has been identified in the data with accentuated weather related temperature perturbations near longitudes 200 to 320 e for both the southern and northern hemispheres near latitude 65 at the surface some evidence was also found for a sharpening of longitudinal gradients into what may be frontal systems ep flux divergences show the waves extracting energy from the zonal mean winds when the m 1 waves were strongest decelerations of the zonal jet of order 30 m s sol were measured above 1 scale height the waves extract energy from the jet predominately through barotropic processes but their character is overall mixed barotropic baroclinic inertial instabilities may exist at altitude on the equatorward flanks of the polar jets and marginal stability extends through to the tropics this may explain the coordination of the tropical behavior of the waves with that centered along the polar jet consistent with the ideas expressed in wilson et al 2002 geophys res lett 29 1684 and similar to those in barnes et al 1993 j geophys res 98 3125 3148 throughout the year there exist large regions with the meridional gradient of pv less than zero but they are strongest near winter solstice poleward of the winter jet the regions of instability reach the surface equatorward they do not these regions satisfying a necessary criterion for instability likely explain the genesis of the waves and perhaps also their bimodal character between surface faster waves and altitude slow m 1 waves

remanence acquisition efficiency in biogenic and detrital magnetite and recording of geomagnetic paleointensity relative paleointensity rpi variations of earth s magnetic field are widely used to understand geomagnetic field behavior and to develop age models for sedimentary sequences rpi estimation is based on a series of assumptions one key assumption that is rarely considered is that all magnetic particles in the sediment acquired a magnetization in an identical manner in this paper we test this assumption for sediments from the eastern equatorial pacific ocean that record well documented global rpi variations over the last 780 kyr the magnetization is carried by two stable single domain magnetic components which we identify as magnetite magnetofossils and titanomagnetite nanoparticle inclusions within larger silicate particles by analyzing signals carried by the two components separately we determine for the first time that magnetic nanoparticle inclusions can cause their host particles to record reliable but inefficient sedimentary paleomagnetic signals the magnetization carried by biogenic magnetite is acquired more efficiently than that carried by the nanoparticle inclusions variations in the concentration of both components are modulated climatically so that they record nearly identical rpi signals in many sediment types there is no correlation between the concentrations of different magnetic components so that variable remanence acquisition efficiency will complicate rpi recording our work demonstrates that detailed assessment of paleomagnetic recording by each constituent magnetic component needs to become a routine part of sedimentary rpi analysis

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

a mesoscale model study of summertime atmospheric circulations in the north polar region of mars 1 the oregon state university mars mm5 was used in a comprehensive high resolution study of northern polar summertime circulations three simulations ls 120 ls 135 and ls 150 characterize the changing circulation the atmosphere is dry and model dynamics are hydrostatic a modified tes thermal inertia map provides a realistic simulation of the polar thermal environment the highest resolution nest 18 km resolves complex flows near the cap zonal mean easterlies 10 m s and zonal mean katabatic winds 5 m s near the surface are relatively steady during this study katabatic flows are shallow 300 m the easterlies are deeper 1 5 km transient eddies are very important within the first scale height they are excited by mechanisms and at locations that change dramatically during this short study period at ls 120 they form along the residual cap edge with a zonal wave number one structure producing strong excursion winds 10 15 m s that blow consistently across the cap by ls 135 strong eddies are seen to form on the northern slopes of alba patera and tharsis these eddies are quite suggestive of the large annular cloud structures seen in hubble space telescope and mars orbital camera imagery at this location and season and can traverse the high latitudes to reach the residual cap before dissipating eddies in the earlier two simulations appear to be primarily excited by energetic flows near the surface by ls 150 an early fall polar jet causes strong winter like baroclinic eddies to develop the transient eddies found in this study are probably important in the water cycle of the northern residual cap

relative paleointensity and inclination anomaly over the last 8 myr obtained from the integrated ocean drilling program site u1335 sediments in the eastern equatorial pacific

simulation of the atmospheric thermal circulation of a martian volcano using a mesoscale numerical model mesoscale 100 km atmospheric phenomena are ubiquitous on mars as revealed by mars orbiter camera images numerical models provide an important means of investigating martian atmospheric dynamics for which data availability is limited but the resolution of general circulation models which are traditionally used for such research is not sufficient to resolve mesoscale phenomena to provide better understanding of these relatively small scale phenomena mesoscale models have recently been introduced here we simulate the mesoscale spiral dust cloud observed over the caldera of the volcano arsia mons by using the mars regional atmospheric modelling system our simulation uses a hierarchy of nested models with grid sizes ranging from 240 km to 3 km and reveals that the dust cloud is an indicator of a greater but optically thin thermal circulation that reaches heights of up to 30 km and transports dust horizontally over thousands of kilometres

cloud tracked winds for the first mars global surveyor mapping year we have measured winds using cloud motion in consecutive mars global surveyor mgs mars orbiter camera moc wide angle global map swaths taken during the first mapping year l s 135 360 111 we present a total of 11 200 wind vectors collected in the north polar region during l s 135 195 late summer early fall and l s 20 55 mid spring and in the south polar region during l s 337 10 late summer early fall for cases with good coverage we also present the derived mean zonal and meridional winds and the associated eddies the speed of the zonal winds in 60 n 70 n increases at 0 6 m s l s in late northern summer and that in 60 s 70 s increases at a rate of 0 7 m s l s in late southern summer the latitudinal distribution of zonal wind within 50 n 75 n from mid northern summer to early northern fall indicates that winds at higher latitudes are generally weaker than those at lower latitudes but the rate of increase with time is faster at higher latitudes there is a cyclonic gyre in the 90 w 0 30 e sector in the north polar region there are large scale waves in the weekly mean meridional wind and in the biweekly mean eddy momentum flux and eddy kinetic energy fields in the north polar region from mid to late summer the cloud tracked winds in the north are generally consistent with winds calculated by general circulation model at the water condensation level derived from mgs thermal emission spectrometer tes observations but appear stronger than the gradient winds derived from tes assuming no flow at the surface

a geomagnetic paleointensity record of 0 6 to 3 2 ma from sediments in the western equatorial pacific and remanent magnetization lock in depth

magnetic anisotropy magnetostatic interactions and identification of magnetofossils 1 single domain magnetite particles produced by magnetotactic bacteria mtb and aligned in chains called magnetosomes are potentially important recorders of paleomagnetic paleoenvironmental and paleolife signals rock magnetic properties related to the anisotropy of magnetosome chains have been widely used to identify fossilized magnetosomes magnetofossils preserved in geological materials however ambiguities exist when linking magnetic properties to the chain structure because of the complexity of chain integrity and magnetostatic interactions among magnetofossils that results from chain collapse during post depositional diagenesis in this paper magnetic properties of three sets of samples containing extracted magnetosomes of the culturedmagnetospirillum magneticumstrain amb 1 were analyzed to determine how chain integrity and particle concentration influence magnetic properties intact mtb and well dispersed magnetosome chains are characterized by strong magnetic anisotropy and weak magnetostatic interactions but progressive chain breakup and particle clumping significantly increase the degree of magnetostatic interaction this results in a change of the magnetic signature toward properties typical of interacting single domain particles i e a decrease of the ratio of anhysteretic remanent magnetization to the saturation isothermal remanent magnetization decreasing in the crossing point of the wohlfarth cisowski test and in the delta ratio between losses of field and zero field cooled remanent magnetization across the verwey transition as well as vertical broadening of the first order reversal curve distribution we propose a new diagram that summarizes the verwey transition properties with diagnostic limits for intact and collapsed chains of magnetosomes this diagram can be used in conjunction with other parameters to identify unoxidized magnetofossils in sediments and rocks

mars observer camera the mars observer camera moc is a three component system one narrow angle and two wide angle cameras designed to take high spatial resolution pictures of the surface of mars and to obtain lower spatial resolution synoptic coverage of the planet s surface and atmosphere the cameras are based on the push broom technique that is they do not take frames but rather build pictures one line at a time as the spacecraft moves around the planet in its orbit moc is primarily a telescope for taking extremely high resolution pictures of selected locations on mars using the narrow angle camera areas ranging from 2 8 km 2 8 km to 2 8 km 25 2 km depending on available internal digital buffer memory can be photographed at about 1 4 m pixel additionally lower resolution pictures to a lowest resolution of about 11 m pixel can be acquired by pixel averaging these images can be much longer ranging up to 2 8 500 km at 11 m pixel high resolution data will be used to study sediments and sedimentary processes polar processes and deposits volcanism and other geologic geomorphic processes the moc wide angle cameras are capable of viewing mars from horizon to horizon and are designed for low resolution global and intermediate resolution regional studies low resolution observations can be made every orbit so that in a single 24 hour period a complete global picture of the planet can be assembled at a resolution of at least 7 5 km pixel regional areas covering hundreds of kilometers on a side may be photographed at a resolution of better than 250 m pixel at the nadir such images will be particularly useful in studying time variable features such as lee clouds the polar cap edge and wind streaks as well as acquiring stereoscopic coverage of areas of geological interest the limb can be imaged at a vertical and along track resolution of better than 1 5 km different color filters within the two wide angle cameras permit color images of the surface and atmosphere to be made to distinguish between clouds and the ground and between clouds of different composition

11 million years of oligocene geomagnetic field behaviour summary an 11 million year long record of the oligocene geomagnetic field has been obtained from pelagic sediments of dsdp hole 522 an average sample spacing of 4 cm yielded approximately one specimen per 4 to 8 kyr the rock magnetics are remarkably consistent across the entire interval previous work demonstrated a magnetic mineralogy dominated by magnetically stable magnetite the natural remanent magnetism nrm carries an oligocene polarity timescale that is in excellent agreement with the oligocene reversal record as determined from marine magnetic anomalies mmas including many of the so called crypto chrons normalized nrm intensities from the undisturbed portions of the record yield a time series of variations with features consistent with a number of other palaeointensity time series derived from both sedimentary and lava sequences these features include consistent major decreases in palaeointensity dips at reversal boundaries and occasional dips between reversal boundaries that could correspond to lineated tiny wiggles in the mma records the data set suggests that the overall field strength was 40 per cent higher in the first half of the oligocene when the average reversal frequency was 1 6 myr l than in the second half when the reversal frequency was 4myr there is also a weak dependence of average field strength on length of polarity interval finally in the three cores suited to spectral analysis of coherent polarity and relative intensity independent of lithological contamination there is a persistent ca 30 50 ka periodicity in the variations of the relative intensity suggesting that the geomagnetic field pulses at about this frequency not only during the brunhes as demonstrated by tauxe shackleton 1994 but in the oligocene as well

a detailed paleomagnetic record between 2 1 and 2 75 ma at iodp site u1314 in the north atlantic geomagnetic excursions and the gauss matuyama transition 1 this study investigated the detailed geomagnetic field variation between 2 1 and 2 75 ma from a sediment core iodp site u1314 with high sedimentation rate 10 cm kyr and good age control characteristic remanent magnetization directions were well resolved by stepwise alternating field demagnetization as a proxy of relative paleointensity natural remanent magnetization nrm normalized by anhysteretic remanent magnetization arm was used after testing that the influence of magnetic interaction in arm is negligible as a result the following features of the geomagnetic field in the studied period have been revealed during the transition of the gauss matuyama g m reversal and the reunion subchron the paleointensity decreased to the value lower than 20 of the average intensity in the whole studied interval in addition to these lows eight paleointensity lows were found associated with large directional changes that satisfy the definition of a geomagnetic excursion four of these have ages close to ages reported for geomagnetic excursions in prior studies whereas the other four excursions have not previously been observed in our results we confirm that the g m transition occurred in marine isotope stage 103 even if we consider the shift in depth due to the lock in process of magnetic particles the temporal variation in paleointensity showed asymmetric behavior associated with the g m transition with a gradual decrease prior to the transition and a rapid recovery after the transition

further observations of regional dust storms and baroclinic eddies in the northern hemisphere of mars abstract we have investigated the near surface meteorology in the northern hemisphere of mars through detailed analysis of data obtained with mars global surveyor in january august 2005 the season in the northern hemisphere ranged from midsummer through winter solstice of mars year my 27 we examined composite wide angle images from the mars orbiter camera and compiled a catalog of the dust storms that occurred in this interval as in previous martian years activity in the northern hemisphere was dominated by regional flushing dust storms that sweep southward through the major topographic basins most frequently in acidalia planitia we also used atmospheric profiles retrieved from radio occultation experiments to characterize eddy activity near the surface at high northern latitudes there are strong correlations between the two sets of observations which allowed us to identify three factors that influence the timing and location of the regional dust storms 1 transitions among baroclinic wave modes which strongly modulate the intensity of meridional winds near the surface 2 storms zones which impose strong zonal variations on the amplitude of some baroclinic eddies and 3 stationary waves which further modulate the wind field near the surface the flushing dust storms ceased abruptly in midautumn possibly in response to source depletion co 2 condensation a shift in the period of the baroclinic eddies and changes in the tidal wind field near the surface our results extend the meteorological record of the northern hemisphere substantiate the findings of previous investigations and further illuminate the climatic impact of baroclinic eddies