sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

theoretical model of acoustic backscatter from a smooth seabed currently available mathematical models of acoustic scattering from the ocean bottom generally fail to predict backscatter levels of sufficient magnitude for two limiting cases as the bottom becomes increasingly smooth and as the grazing angle becomes small in this paper a mathematical model of acoustic backscattering that attempts to address these shortcomings for the case of a sediment bottom is derived in the model scattering is caused by fluctuations in sediment porosity the model allows for penetration of the incident wave into the bottom at subcritical grazing and retransmission of scattered spherical waves through the planar interface the frequency and grazing angle dependence of the acoustic backscatter are determined primarily by the correlation function of the porosity fluctuations while the magnitude of the backscatter is controlled by the mean square value of these fluctuations numerical results obtained from the model are tested against backscatter data available in the literature for several sediment bottoms over a wide range of frequencies 30 500 khz agreement between the model and literature data is good

inconsistent magnetic polarities between greigite and pyrrhotite magnetite bearing marine sediments from the tsailiao chi section southwestern taiwan abstract to establish a magnetobiostratigraphy for a 620 m thick middle to late pleistocene mudstone sequence in the lower gutingkeng formation of the tsailiao chi tlc section in southwestern taiwan we conducted paleomagnetic and mineral magnetic measurements together with sediment granulometry and calcareous nannofossil identification paleomagnetic samples from 65 sites revealed two types of thermal demagnetization 25 400 c behavior 1 single component stable characteristic remanence in magnetite and pyrrhotite dominated samples type s and 2 abrupt changes in polarity when samples with significant greigite concentrations were heated above 320 340 c type c the characteristic polarities derived from type s samples and from magnetite dominated type c samples obtained above 340 c are consistent with those determined from nannofossil biostratigraphy this implies that the nrm carried by magnetite and pyrrhotite is reliable the essentially antiparallel remanence components in type c samples below 340 c are attributed to greigite the almost antiparallel direction could have resulted from delayed formation of greigite but in this case the different direction of this component must have resulted from variable remanence lock in times alternatively the opposite polarities may result from self reversal which warrants further investigation pyrrhotite and greigite may have both formed authigenically but there is no clear explanation for the observed differences in direction

magnetic properties of sedimentary greigite fe3s4 an update greigite fe3s4 is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction it can also grow at any time when dissolved iron and sulfide are available during diagenesis greigite is important in paleomagnetic environmental biological biogeochemical tectonic and industrial processes much recent progress has been made in understanding its magnetic properties greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites the crystallographic c axis is the easy axis of magnetization with magnetic properties dominated by magnetocrystalline anisotropy robust empirical estimates of the saturation magnetization anisotropy constant and exchange constant for greigite have been obtained recently for the first time and the first robust estimate of the low field magnetic susceptibility is reported here the curie temperature of greigite remains unknown but must exceed 350 c greigite lacks a low temperature magnetic transition on the basis of preliminary micromagnetic modeling the size range for stable single domain behavior is 17 200 nm for cubic crystals and 17 500 nm for octahedral crystals gradual variation in magnetic properties is observed through the pseudo single domain size range we systematically document the known magnetic properties of greigite at high ambient and low temperatures and with alternating and direct fields and illustrate how grain size variations affect magnetic properties recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records including widespread remagnetizations

interannual and decadal modulations recently observed in the pacific storm track activity and east asian winter monsoon abstract interannual variability of the north pacific storm track observed over 17 recent winters is documented the local storm track activity is measured by a meridional flux of sensible heat associated with the lower tropospheric subweekly fluctuations the interannual variability in the heat flux over the northwestern nw pacific is found to be strongest in midwinter the first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the nw pacific in association with the decadal weakening of the east asian winter monsoon siberian high and the aleutian low that occurred in the late 1980s the most marked signature of this enhancement is that the midwinter minimum in the storm track activity which had been apparent in the early to mid 1980s almost disappeared afterward as opposed to linear theory of baroclinic instability the enhanced activity occurred despite the weakening of the pacific j

atmospheric response to zonal variations in midlatitude sst transient and stationary eddies and their feedback midwinter storm track response to zonal variations in midlatitude sea surface temperatures ssts has been investigated using an atmospheric general circulation model under aquaplanet and perpetual january conditions zonal wavenumber 1 sst variations with a meridionally confined structure are placed at various latitudes having these sst variations centered at 308n leads to a zonally localized storm track while the storm track becomes nearly zonally uniform when the same sst forcing is moved farther north at 408 and 508n large small baroclinic energy conversion north of the warm cold sst anomaly near the axis of the storm track near 408n is responsible for the large small storm growth the equatorward transfer of eddy kinetic energy by the ageostrophic motion and the mechanical damping are important to diminish the storm track activity in the zonal direction significant stationary eddies form in the upper troposphere with a ridge trough northeast of the warm cold sst anomaly at 308n heat and vorticity budget analyses indicate that zonally localized condensational heating in the storm track is the major cause for these stationary eddies which in turn exert a positive feedback to maintain the localized storm track by strengthening the vertical shear near the surface these results indicate an active role of synoptic eddies in inducing deep tropospheric scale response to midlatitude sst variations finally the application of the model results to the real atmosphere is discussed

characterization of hematite α fe2o3 goethite α feooh greigite fe3s4 and pyrrhotite fe7s8 using first order reversal curve diagrams 1 first order reversal curve forc diagrams have become a standard tool in rock magnetism yet magnetite is the only magnetic mineral that is well characterized using forc diagrams we present forc diagrams for predominantly single domain sd synthetic aluminous hematite a fe2 xalxo3 and goethite a feal ooh and natural greigite fe3s4 and pyrrhotite fe7s8 to constrain interpretation of forc diagrams from natural samples hematite and goethite have low spontaneous magnetizations and negligible magnetic interactions while greigite and pyrrhotite have higher spontaneous magnetizations and can have strong magnetic interactions the coercivity of hematite systematically increases with al content only for samples produced using the same synthesis method but it is variable for samples produced with different methods even for similar al content this precludes use of magnetic coercivity alone to quantify the al content of natural hematites goethite has much higher coercivity than hematite for all measured samples sd and superparamagnetic sp behavior is common in natural greigite samples with peak coercivities ranging from

reconciling astrochronological and 40ar 39ar ages for the matuyama brunhes boundary and late matuyama chron when five matuyama brunhes m b boundary records from the north atlantic are placed on isotope age models produced by correlation of the 18o record directly or indirectly to an ice volume model the m b boundary lies consistently at the young end of marine isotope stage 19 with a mean age for the midpoint of the reversal of 773 1 ka standard deviation 0 4 kyr 7 kyr younger than the presently accepted astrochronological age for this polarity reversal 780 781 ka two recently proposed revisions of the age of the 40ar 39ar fish canyon sanidine fcs standard to 28 201 0 046 ma and 28 305 0 036 ma would adjust 40ar 39ar ages applicable to the m b boundary and other reversals and excursions back to 1 2 ma to ages older than the new astrochronological ages by 8 24 kyr the variables used to construct the ice volume models cannot account for the discrepancy the fcs standard age that best fits the astrochronological ages is 27 93 ma which is within the uncertainty associated with the commonly used value of 28 02 0 16 ma but younger than the recently proposed fcs ages the edc2 and edc3 age models in the dome c antarctic ice core yield ages of 771 7 ka and 766 4 ka respectively for the 10be flux peak that denotes the paleointensity minimum at the reversal boundary implying that the edc2 rather than edc3 age model is consistent with the observations from marine sediments at least close to the m b boundary

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

environmental magnetic implications of greigite fe3s4 formation in a 3 m y lake sediment record from butte valley northern california authigenic greigite fe 3 s 4 has been identified in several horizons of lake beds in a 102 m core from butte valley northern california using mineral magnetic methods and x ray diffraction analysis the presence of greigite has several implications for the paleoenvironmental record from butte valley first its occurrence in 2 5 3 0 ma strata confirms that greigite can persist in the geological record for long periods of time second the detrital mineral magnetic record may be partially obscured by the presence of authigenic greigite and care must be taken in interpreting magnetic variations in the greigite bearing zones as paleoclimate proxies third differences in the timing of remanence acquisition for authigenic and detrital phases may compromise studies of high frequency geomagnetic field variations fourth greigite may also be significant as a paleoenvironmental indicator of lake and sediment chemistry the magnetic detection of greigite may therefore provide important information about paleolimnological conditions

intensification of ocean fronts by down front winds abstract many ocean fronts experience strong local atmospheric forcing by down front winds that is winds blowing in the direction of the frontal jet an analytic theory and nonhydrostatic numerical simulations are used to demonstrate the mechanism by which down front winds lead to frontogenesis when a wind blows down a front cross front advection of density by ekman flow results in a destabilizing wind driven buoyancy flux wdbf equal to the product of the ekman transport with the surface lateral buoyancy gradient destabilization of the water column results in convection that is localized to the front and that has a buoyancy flux that is scaled by the wdbf mixing of buoyancy by convection and ekman pumping suction resulting from the cross front contrast in vertical vorticity of the frontal jet drive frontogenetic ageostrophic secondary circulations ascs for mixed layers with negative potential vorticity the most frontogenetic ascs select a preferred cross front width and do not translate with

intratest porosity in foraminifera abstract studies of the physical properties and diagenesis of biogenous ooze are complicated by the hollow nature of the tests making up the sediment established relationships between porosity and other physical properties can be misleading when significant amounts of intratest water are present if the internal void volumes of biogenous particles are known total sediment porosity can be corrected for the excess water previously only a few estimates of the fraction of total sediment porosity attributable to hollow tests were available this paper documents direct and indirect measurements which indicate that average intratest void volume in foraminifera decreases from 73 percent to 61 percent as test diameter decreases from 0 to 4 un ts these internal voids can increase total sediment porosity by 44 percentage points at test diameters of 0 phi and by 35 percentage points at diameters of 4

using csem techniques to map the shallow section of seafloor from the coastline to the edges of the continental slope many important processes occur within the shallow section of the seafloor on the continental shelf and slope yet conventional geophysical constraints on the physical properties within this critical boundary layer are limited some of the key constraints involve quantification of fluids within the seafloor which can be provided by electrical methods this paper reviews the application of a towed em system to map the uppermost 20 m of seafloor in a variety of settings ranging from nearshore regions in water depths of approximately 10 m on the continental shelf out to water depths of 1300 m the system is a mapping tool that provides areal maps of seafloor resistivity and has been used for a variety of purposes including sedimentary characterization and facies mapping evaluation of groundwater discharge and mapping seafloor mounds in the gulf of mexico thought to contain massive deposits of gas hydrate

geomagnetic excursions knowns and unknowns geomagnetic excursions are short lived episodes when earth s magnetic field deviates into an intermediate polarity state understanding the origin frequency amplitude duration and field behavior associated with excursions is a forefront research area within solid earth geophysics recent advances in excursion research are summarized here and key further research is suggested to resolve major unanswered questions improving the global distribution of excursion records particularly from the southern hemisphere obtaining high resolution sedimentary excursion records with good age control from sites with sedimentation rates 10 cm kyr obtaining volcanic excursion records coupled with high precision geochronology and estimating excursion duration with high chronological precision will all facilitate hypothesis testing concerning the deep earth dynamics that generate geomagnetic excursions

significance of a midlatitude sst frontal zone in the formation of a storm track and an eddy driven westerly jet abstract in a set of idealized aquaplanet experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature sst is prescribed globally as the lower boundary condition an assessment is made of the potential influence of the frontal sst gradient upon the formation of a storm track and an eddy driven midlatitude polar front jet pfj and on its robustness against changes in the intensity of a subtropical jet stj in experiments with the frontal midlatitude sst gradient as that observed in the southwestern indian ocean transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the sst front with an enhanced low level baroclinic growth of eddies in the winter hemisphere another storm track forms just below the intense stj core but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath the near surface westerlies are strongest near the midlatitude sst front as observe

rock magnetism and palaeomagnetism of the montalbano jonico section italy evidence for late diagenetic growth of greigite and implications for magnetostratigraphy summary the montalbano jonico mj section cropping out in southern italy represents a potential candidate to define the lower middle pleistocene boundary and it has been proposed as a suitable global stratotype section and point gssp of the ionian stage middle pleistocene the mj section is the only continuous benthic and planktonic 18o on land reference in the mediterranean area for the mid pleistocene transition spanning an interval between about 1240 and 645 ka combined biostratigraphy and sapropel chronology tephra stratigraphy and complete high resolution benthic and planktonic foraminiferal stable oxygen isotope records already provide a firm chronostratigraphic framework for the mj section however magnetostratigraphy was still required to precisely locate the brunhes matuyama transition and to mark the gssp for the ionian stage we carried out a palaeomagnetic study of a subsection ideale section of the mj composite section sampling 61 oriented cores from 56 stratigraphic levels spread over a ca 80 m thick stratigraphic interval that correlates to the oxygen isotopic stage 19 and should therefore include the brunhes matuyama reversal the palaeomagnetic data indicate a stable and almost single component natural remanent magnetization nrm a characteristic remanent magnetization chrm was clearly identified by stepwise demagnetization of the nrm the chrm declination values vary around 0 and the chrm inclination around the expected value 59 for a geocentric axial dipole field at the sampling locality this result indicates that the section has been remagnetized during the brunhes chron a preliminary study of 27 additional not azimuthally oriented hand samples collected at various levels from other parts of the mj composite section indicates that all the samples are of normal polarity and demonstrates that the remagnetization is widespread across the whole exposed stratigraphic sequence a series of specific rock magnetic techniques were then applied to investigate the nature of the main magnetic carrier in the study sediments and they suggest that the main magnetic mineral in the mj section is the iron sulphide greigite fe3s4 scanning electron microscope observations and elemental microanalysis reveal that greigite occurs both as individual euhedral crystals and in iron sulphides aggregates filling voids in the clay matrix therefore we infer that the remagnetization of the section is due to the late diagenetic growth of greigite under reducing conditions most likely resulting in the almost complete dissolution of the original magnetic minerals iron sulphide formation in the mj section can be linked to migration of mineralized fluids our inferred timing of the remagnetization associated with greigite growth represents the longest remanence acquisition delay documented in greigite bearing clays of the italian peninsula so far

diagenetic magnetic enhancement of sapropels from the eastern mediterranean sea diagenetic dissolution of magnetic minerals has been widely observed in organic rich sediments from many environments organic rich sediments from the eastern mediterranean sea sapropels recovered during leg 160 of the ocean drilling program reveal a surprising catalogue of magnetic properties sapropels from all sites studied across the eastern mediterranean sea are strongly magnetic and the magnetization is directly proportional to the organic carbon content the magnetization of the sapropels is dominated by a low coercivity probably single domain magnetic mineral with an inverse magnetic fabric that exhibits a clear decay in magnetic properties when exposed to air during heating the magnetic particles irreversibly break down between 360 and 400 c the contrast between the magnetic properties of sapropels and surrounding sediments is marked with remanence intensities of sapropels often being more than three orders of magnitude higher than those of underlying sediments the contrast between the magnetic properties of sapropels and the surrounding sediments is apparently controlled by non steady state diagenesis sulphate reducing conditions dominated during sapropel deposition while overlying sediments were deposited under oxic conditions the mineral responsible for the magnetic properties of sapropels is most likely to have formed under sulphate reducing conditions that existed during times of sapropel formation attempts to identify this mineral have been unsuccessful but several lines of evidence point toward an unknown ferrimagnetic iron sulphide phase the influence of diagenesis on the magnetic properties of cyclically deposited eastern mediterranean sedimentary sequences suggests that magnetic parameters may be a useful proxy for diagenesis in these sediments

magnetostratigraphic and environmental implications of greigite fe3s4 formation from hole u1433a of the iodp expedition 349 south china sea abstract a detailed magnetic analysis has been done on sedimentary core of the international ocean discovery program iodp site u1433a during leg 349 in the south china sea scs results show that dominant carriers of the natural remanent magnetization are greigite and titano magnetite the major shift in both declination and inclination at 185 mbsf is assigned to the matuyama brunhes reversal boundary 0 773 ma constrained by biostratigraphic ages variations in magnetic parameters of the core can be well correlated to the marine oxygen isotope record at glacial interglacial cycles low values of concentration dependent magnetic parameters correspond to the interglacials and vice versa during the interglacial periods the dominant magnetic minerals are detrital titano magnetite and have relatively coarser grain sizes while fine grained greigites dominate the glacial periods this indicates that during the glacials greigite prevails at the anoxic condition with amount of terrigenous iron oxide caused by the disconnection between the scs and the indian ocean and the exposure of shelf but digenesis is suppressed at the opposite environment by the high sea level interglacials thus the preservation sulfide process of titano magnetite is intimately related to the transformation of sea level changes with the monsoon related rainfall caused by the glacial interglacial variation

influence of wintertime large scale circulation on the explosively developing cyclones over the western north pacific and their downstream effects 1 the relationships between large scale wintertime circulation and extratropical cyclones that develop explosively the so called bomb cyclones over the western north pacific are investigated using japanese long term reanalysis project data on a monthly basis the east asian winter monsoon variability strongly modulates the bomb cyclone activity in terms of its geographical distribution when the monsoon is strong the bomb cyclone activity tends to concentrate in the vicinity of the kuroshio current and the kuroshio extension near japan while when the monsoon is weak it disperses over the broader areas the enhancement of the monsoon increases the heat and moisture supply from warm currents facilitating unstable conditions within the atmospheric boundary layer and intensifying baroclinicity in the lower troposphere these factors are believed to play a role in inducing bomb cyclones particularly along the warm currents on submonthly timescales the stationary rossby wave propagation along the south asian waveguide serves as a prominent trigger for the rapid reinforcement of synoptic scale disturbances around japan when a pronounced bomb cyclone comes to its mature stage northeast of japan it is capable of exciting stationary rossby waves downstream from the asian jet exit region as vorticity forcing the stationary wave packets developing southeastward across the north pacific ocean basin induce surface cyclogenesis in the vicinity of the hawaiian islands by leading to the equatorward advection of higher potential vorticity from the midlatitudes bringing about the occurrence of kona storms which cause weather hazards in hawaii

deep electrical resistivity tomography along the tectonically active middle aterno valley 2009 l aquila earthquake area central italy three 2 d deep electrical resistivity tomography ert transects up to 6 36 km long were obtained across the paganica san demetrio basin bounded by the 2009 l aquila mw 6 1 normal faulting earthquake causative fault central italy the investigations allowed defining for the first time the shallow subsurface basin structure the resistivity images and their geological interpretation show a dissected mesozoic tertiary substratum buried under continental infill of mainly quaternary age due to the long term activity of the paganica san demetrio normal faults system psdfs ruling the most recent deformational phase our results indicate that the basin bottom deepens up to 600 m moving to the south with the continental infill largely exceeding the known thickness of the quaternary sequence the causes of this increasing thickness can be 1 the onset of the continental deposition in the southern sector took place before the quaternary 2 there was an early stage of the basin development driven by different fault systems that produced a depocentre in the southern sector not related to the present day basin shape or 3 the fault system slip rate in the southern sector was faster than in the northern sector we were able to gain sights into the long term psdfs behaviour and evolution by comparing throw rates at different timescales and discriminating the splays that lead deformation some fault splays exhibit large cumulative throws 300 m in coincidence with large displacement of the continental deposits sequence 100 m thus testifying a general persistence in time of their activity as leading splays of the fault system we evaluate the long term 3 2 5 myr cumulative and quaternary throw rates of most of the leading splays to be 0 08 0 17 mm yr 1 indicating a substantial stability of the faults activity among them an individual leading fault splay extends from paganica to san demetrio ne vestini as a result of a post early pleistocene linkage of two smaller splays this 15 km long fault splay can explain the holocene surface ruptures observed to be larger than those occurred during the 2009 l aquila earthquake such as revealed by palaeoseismological investigations finally the architecture of the basin at depth suggests that the psdfs can also rupture a longer structure at the surface allowing earthquakes larger than m 6 5 besides rupturing only small sections as it occurred in 2009

sediment chemistry and magnetic properties in an anomalously reducing core from the eastern mediterranean sea abstract in core kc19c 19 6 m long recovered in the abyssal plain between crete and cyprus in the eastern mediterranean a large number of organic rich layers sapropels occur which correlate to maxima in the insolation curve in contrast to other sites in the eastern mediterranean porewaters contain sulfide below a few meters below seafloor mbsf geochemical analyses were performed on the porewaters ammonium alkalinity sulfate manganese iron bisulfide chloride eh ph and sediments organic carbon barium total sulfur total iron manganese pyrite dithionite extractable iron in addition a series of magnetic parameters and ratios nrm arm irm in arm irm s ratio arm 20mt arm in were determined in the top of the sediments fe and mn hydr oxides occur at the oxic suboxic boundary just above the youngest sapropel si2 these hydr oxides appear to be more easily demagnetized by means of alternating fields than deeper hydr oxides which presumably are of detrital origin the transition from suboxic to anoxic sediments is located at 2 mbsf sulfide is produced possibly during sulfate reduction through anoxic methane oxidation at 17 5 mbsf from 17 5 mbsf sulfide migrates upward titrating reactive fe resulting in pyrite formation in the entire sediment column up to 2 mbsf at this depth the upward sulfide flux has been totally consumed by reaction with solid phase fe and dissolved fe ii diffusing downward from the suboxic zone above from 2 mbsf downward magnetic intensities are significantly reduced indicating reductive dissolution of fe oxide minerals and pyrite formation as a consequence no reliable nrm data can be obtained in the lower half of the core

high resolution analysis of early diagenetic effects on magnetic minerals in post middle holocene continental shelf sediments from the korea strait 1 two studied sediment cores from the korea strait contain mud sequences 14 m and 32 62 m in thickness that were deposited during the last 6 000 years the sediments have uniform lithology and geochemical properties however marked down core changes in magnetic properties suggest that diagenesis has significantly impacted the magnetic properties an expanded view of early diagenetic reactions that affect magnetic mineral assemblages is evident in these rapidly deposited continental shelf sediments compared to deep sea sediments the studied sediments are divided into four descending intervals based on magnetic property variations interval 1 is least affected by diagenesis and has the highest concentrations of detrital magnetite and hematite and the lowest solid phase sulfur contents interval 2 is characterized by the presence of paramagnetic pyrite and sharply decreasing magnetite and hematite concentrations which suggest active reductive dissolution of detrital magnetic minerals interval 3 is marked by a progressive loss of hematite with depth and coincides with the minimum magnetite concentration interval 4 has an increasing down core enhancement of authigenic greigite which apparently formed at depths of 3 30 m below the sediment water interface due to arrested pyritization reactions these results indicate delays of thousands of years for acquisition of magnetizations carried by greigite which suggests that studies of geomagnetic field behavior from greigite bearing continental shelf sediments should be conducted with care also virtually complete destruction of detrital magnetic minerals at depth suggests that magnetic studies of rapidly deposited shelf sediments are unlikely to provide a meaningful signature associated with syn depositional environmental processes

high resolution record of the upper olduvai transition from po valley italy sediments support for dipolar transition geometry abstract a detailed record of the upper olduvai polarity transition composed of 100 transitional directions has been obtained from the crostolo section in northern italy a careful examination of the rock magnetic properties of the sediments using standard paleomagnetic techniques thermomagnetic scanning electron microscopy microprobe x ray diffraction and mossbauer analysis shows that greigite is the main magnetic carrier of the remanence the correlation of a shift in the magnetic record to a small scale sedimentary feature observed in the section indicates that the magnetization was acquired at deposition or very shortly after the virtual geomagnetic pole vgp path is largely confined along a great circle over north and south america 90 west of the site and consists of three stages first the vgp moves to southern mid latitudes then after a period of standstill it comes back to almost true north and finally the south pole is reached in a third step although different from a record from the southern indian ocean this path is virtually identical to those obtained for the same transition from north pacific deep sea cores and partly coincides with a north atlantic record which suggests that a dipolar component may be present in the transitional field during the upper olduvai reversal a review of the recently obtained records of various transitions shows that in more than two thirds of the cases the vgp paths are similarly confined along a meridian over the americas or antipodal to them irrespective of the sampling site and of the sense of the transition although not deterministic this tendency suggests that a similar dipolar component might be present in the transitional fields of other reversals of different ages

effects of a semienclosed ocean on extratropical cyclogenesis the dynamical processes around the japan sea on 23 25 january 2008 1 based on a case study of an extratropical cyclone that developed rapidly near japan on 23 25 january 2008 this paper proposes a new type of atmospheric response to a surface warming cooling anomaly in the semienclosed japan sea which is approximately half a synoptic scale baroclinic wavelength in size the thermal effects of the japan sea during early cyclogenesis spread to the upper levels via an upward wind when the trough of the baroclinic wave is located west of the japan sea in the case of a relatively cold japan sea the lower level air temperature decreases over the sea and the baroclinic wave becomes weak around japan in the early stage as the cyclone progressively develops and travels east the positive and negative geopotential height anomalies induced by the sea surface cooling increase over time in the lower level trough and the upper level ridge outside the japan sea respectively the temperature anomaly spreads to upper levels through the development of a warm conveyer belt as the cyclone becomes fully developed a geopotential height anomaly pattern similar to the west pacific teleconnection forms as a result of the s shaped trough ridge structure in the middle and upper troposphere the cooling warming effect of the sea influences surface heat fluxes and precipitation in the pacific region outside the japan sea via a synoptic scale atmospheric bridge caused by the traveling and developing cyclone and cold air outbreak

fine scale sedimentary structure implications for acoustic remote sensing abstract detailed measurements of sediment properties and acoustic scattering were made at a carbonate sand silt clay site off dry tortugas in the florida keys the sediment is characterized by varying scales of biologically controlled random roughness and heterogeneity as well as surficial stratification on centimeter scales the interface roughness was determined from stereo photogrammetric digitization and parameterized by a power spectrum whereas sediment volume heterogeneity was determined from core measurements and parameterized by first order autoregressive models for sound speed and density fluctuations in contrast to previous investigations fine scale sediment bulk density fluctuations were examined in sediment cores with computerized tomography in addition to the standard gravimetric technique furthermore the strongly delineated sediment density and sound velocity transition layer was parameterized by piecewise linear fits these characterizations of the random and deterministic properties were used in acoustic scattering models in an effort to determine the feasibility of remotely measuring fine scale features of the seafloor the result was negative older low resolution models gave moderately good fits to the acoustic data but the fit did not improve for newer higher resolution models it is suggested that scattering due to shell fragments must be included to account for all features observed in the scattering data at this site

high resolution hematite and goethite records from odp 1143 south china sea co evolution of monsoonal precipitation and el nino over the past 600 000 years abstract precipitation has a larger variability than temperature in tropical monsoon regions thus it is an important climate variable however reconstructions of long term rainfall histories are scarce because of the lack of reliable proxies here we document that iron oxide minerals specifically the ratio of hematite to goethite hm gt is a reasonable precipitation proxy using diffuse reflectance spectrophotometry we measured samples from ocean drilling program odp 1143 drilling site 9 21 72 n 113 17 11 e 2777 m water depth for hematite and goethite whose formation processes are favored by opposing climate conditions in order to determine the content of hematite and goethite we produced a set of calibration samples by removing the iron oxides to generate the natural matrix to which hematite and goethite in known percentages were added from these calibration samples we developed a transfer function for determining hematite and goethite concentration from a sample s spectral reflectance applying this method to odp 1143 sediments top 34 m of a 510 m core with sampling interval of 10 cm we were able to reconstruct a continuous precipitation history for se asia of the past 600 kyr using the hm gt ratio as a proxy of the precipitation variability of asian monsoon the reliability of this hm gt proxy is corroborated by its consistency with the stalagmite 18o data from south china comparing long term hm gt records with the surface temperature gradient of equatorial pacific ocean we found that monsoon precipitation and el nino are correlated for the last 600 kyr the development of el nino like conditions decreased se asia precipitation whereas precipitation increases in response to la nina intensification

geoelectrical signals of geologic and hydrologic processes in a fringing reef lagoon setting summary coastal groundwater may discharge into nearshore and offshore waters forced by terrestrial fluxes controlled by local geology and modulated by the hydrodynamics of littoral water we investigated the electrical signature of these features with a dense multiscale network of electrical resistivity tomography ert surveys in the muri lagoon of rarotonga cook islands the ert surveys spanned from onshore to 400 m into the lagoon and used standard electrodes on land and across the foreshore submerged electrodes in the shallow subtidal zone and floating electrodes towed throughout the reef lagoon by a boat ert surveys on land mapped a typical freshwater lens underlain by a saltwater wedge but with possible deviations from the classical model due to an adjacent tidal creek further inland ert surveys imaged a layer of lava flow deposits that is potentially a confining hydrogeologic unit this unit was used to constrain the expected electrical resistivity of these deposits below the lagoon ert surveys across the intertidal zone and into the lagoon indicated fresh groundwater and porewater salinity patterns consistent with previous small scale studies including the seaward extension of fresh groundwater pathways to the lagoon electrical resistivity er variations in the lagoon subsurface highlighted heterogeneities in the lagoon structure that may focus submarine groundwater discharge sgd through previously unknown buried lava flow deposits in the lagoon a transition to higher er values near the reef crest is consistent with the er signature of porosity reduction due to ongoing differential cementation of reef deposits across the lagoon the imaged coastal hydrostratigraphic heterogeneity may thus control terrestrial and marine porewater mixing support sgd and provide the pathways for groundwater and the materials it transports into the lagoon this hydrogeophysical investigation highlighted the spatial heterogeneity of submarine coastal geology and its hydrogeologic control in a reef lagoon setting but is likely to occur in many similar coastal settings ignoring geologic complexity can result in mischaracterization of sgd and other coastal groundwater processes at many spatial scales

seabed characterization on the new jersey middle and outer shelf correlatability and spatial variability of seafloor sediment properties abstract nearly 100 collocated grab samples and in situ 65 khz acoustic measurements were collected on the new jersey middle and outer shelf within an area that had previously been mapped with multibeam backscatter and bathymetry data and more recently with chirp seismic reflection profiling eighteen short cores were also collected and probed for resistivity based porosity measurements the combined data set provides a basis for empirically exploring the relationship among the remotely sensed data such as backscatter and reflection coefficients and directly measured seabed properties such as grain size distribution velocity attenuation and porosity we also investigate the spatial variability of these properties through semi variogram analysis to facilitate acoustic modeling of natural environmental variability grain size distributions on the new jersey shelf are commonly multi modal leading us to separately characterize coarse 4 mm fine

magnetic signature of environmental changes in the last 1 2 myr at odp site 1146 south china sea abstract a detailed magnetic analysis has been done on the upper 145 m of the splice of odp site 1146 drilled during leg 184 in the south china sea first a magnetostratigraphic record was obtained the bruhnes matuyama reversal preceded by a precursor and the two jaramillo reversals were identified at 115 133 and 137 5 mcd meter composite depth respectively several known excursions during the brunhes period as well as the kamikatsura event during the matuyama chron were also identified coupled with the oxygen isotope record obtained from benthic foraminifera this allows us to establish a precise age model showing that the studied interval extends to 1 18 myr long term and short term variations have been documented in the magnetic parameters which appear at least in part related to changes in monsoon activity on the long term trend three main intervals with different magnetic trends were identified 1 2 0 7 0 7 0 2 and the most recent 0 2 myr during the oldest period the magnetic content decreases while the grain size of the magnetic mineral increases with large fluctuations the coercivity of the magnetic minerals also increases consistently with data obtained by other authors from pacific cores during the following 500 kyr all the magnetic properties are rather uniform with rather low abundance and relatively large grain sizes and low s ratio this probably illustrates a period of enhanced winter monsoon then in the most recent period the magnetic grain size decreases again with pronounced fluctuations on the short term scale a 23 kyr component is identified by power spectrum analysis in all magnetic parameters in the bottom part of the studied interval this component is correlated with the oxygen isotope record as shown by coherence analysis except for the most recent 200 kyr where the pattern changes cold warm periods coincide with low high magnetic content and magnetic grains are coarser during cold stages and finer during warm periods this is consistent with the clay mineral analysis and illustrates changes in the balance between arid humid periods corresponding to dominant winter summer monsoon and giving rise to physical erosion and wind blowing chemical weathering in the main fluvial plains and transport by oceanic current

magnetite dissolution diachronous greigite formation and secondary magnetizations from pyrite oxidation unravelling complex magnetizations in neogene marine sediments from new zealand detailed rock magnetic and electron microscope analyses indicate that the magnetic signature of neogene marine sediments from the east coast of new zealand is dominated by the authigenic iron sulphide greigite the greigite is present as a mixed population of stable single domain and superparamagnetic grains which is consistent with authigenic growth from solution this growth can result from pyritization reactions soon after deposition which also leads to dissolution of most detrital magnetite however where constrained by field tests our data suggest that remanence acquisition can occur 1 myr after deposition and can vary in timing at the outcrop scale strong viscous overprints result from oxidation of the iron sulphides probably during percolation of oxic ground water this process can sometimes destroy any ancient remanent magnetization this complex magnetic behaviour particularly the presence of late forming magnetizations carried by greigite means that the remanence in new zealand cenozoic sediments and in similar sediments elsewhere cannot be assumed to be primary without confirmation by field tests the reversals test should be employed with caution in such sediments as patchy remagnetizations can lead to false polarity stratigraphies

rock magnetism and palaeomagnetism of greigite bearing mudstones in the italian peninsula magnetic measurements were carried out on a collection of samples from different geological settings throughout the italian peninsula the samples display magnetic properties that indicate the presence of ferrimagnetic iron sulphide minerals paired samples were also investigated to compare the palaeomagnetic behaviour with respect to different demagnetization treatments thermal static and tumbling alternating field af demagnetization greigite fe3s4 was positively identified in most samples in agreement with previous studies of greigite the sediments display thermal decomposition of the magnetic carriers at temperatures above ca 230 c resulting in decreased magnetic susceptibility values and maximum unblocking temperatures tub mostly in the range 320 350 c high saturation isothermal remanent magnetization sirm to low field magnetic susceptibility k ratios sirm k 10 ka m hysteresis ratios that are typical for single domain sd grains mrs ms 0 5 and b0 cr b0 c 1 5 where mrs is the saturation remanence ms is the saturation magnetization b0 c is the coercive force and b0 cr is the coercivity of remanence moderate coercivity with b0 cr values that range between 52 and 81 mt and a tendency to acquire a significant rotational remanent magnetization rrm we also found that greigite bearing sediments are particularly sensitive to field impressed anisotropy we propose a new magnetic parameter that can be used as a rapid mean to screen a rock sample for the presence of greigite which relies on its sd behaviour in field impressed anisotropy experiments in greigite bearing sediments the magnetic susceptibility measured in a given direction is increased by the application of a relatively high magnetic field 0 9 t in our experiments at right angles to this direction the susceptibility increase is directly correlated to the concentration of greigite in the sediment the comparative palaeomagnetic analysis of standard demagnetization techniques indicates that thermal demagnetization in close steps up to 350 380 c is clearly the most effective treatment for the isolation of the remanent magnetization carried by greigite whereas af demagnetization treatments display significant acquisition of unwanted magnetic remanences gyroremanent remanent magnetization grm and rrm at fields above ca 40 mt

the subpolar front of the japan east sea part iii competing roles of frontal dynamics and atmospheric forcing in driving ageostrophic vertical circulation and subduction abstractthe effects of wind stress and surface cooling on ageostrophic vertical circulation and subduction at the subpolar front of the japan east sea are investigated using a nonhydrostatic numerical model in experiments forced by wind and or cooling ageostrophic vertical circulation is enhanced relative to the unforced case both surface cooling and wind stress intensify the circulation by enhancing frontogenesis associated with frontal meandering winds further strengthen vertical motions by generating internal gravity waves downfront winds i e oriented along the frontal jet transport surface water from the denser to lighter side of the front causing it to migrate toward the region of higher stratification and enhancing the vertical mixing at the front this induces outcropping of isopycnals from the middle of the pycnocline along which surface water is subducted hence downfront winds enhance subduction down to the middle of the pycnocline but not beneath on the other hand cooling uplifts i

western boundary currents and frontal air sea interaction gulf stream and kuroshio extension abstract in the northern hemisphere midlatitude western boundary current wbc systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean their potential contribution to the climate system motivated major parallel field programs in both the north pacific kuroshio extension system study kess and the north atlantic climate variability and predictability clivar mode water dynamics experiment climode and preliminary observations and analyses from these programs highlight that complexity the gulf stream gs in the north atlantic and the kuroshio extension ke in the north pacific have broad similarities as subtropical gyre wbcs but they also have significant differences which affect the regional air sea exchange processes and their larger scale interactions the 15 yr satellite altimeter data record which provides a rich source of information is combined here with the longer historical record from in situ data to describe and compare the curr

magnetic properties of marine magnetotactic bacteria in a seasonally stratified coastal pond salt pond ma usa summary magnetic properties of suspended material in the water columns of freshwater and marine environments provide snapshots of magnetic biomineralization that have yet to be affected by the eventual time integration and early diagenetic effects that occur after sediment deposition here we report on the magnetism geochemistry and geobiology of uncultured magnetite and greigite producing magnetotactic bacteria mb and magnetically responsive protists mrp in salt pond falmouth ma usa a small coastal marine basin 5 m deep that becomes chemically stratified during the summer months at this time strong inverse o2 and h2s concentration gradients form in the water column and a well defined oxic anoxic interface oai is established at a water depth of about 3 5 m at least four morphological types of mb both magnetite and greigite producers and several species of magnetically responsive protists are found associated with the oai and the lower sulphidic hypolimnion magnetic properties of filtered water were determined through the water column across the oai and were consistent with the occurrence of magnetite and greigite producing mb at different depths sharp peaks in anhysteretic remanent magnetization arm and saturation isothermal remanent magnetization sirm and single domain sd values of arm sirm occur within the oai corresponding to high concentrations of mb and mrp with magnetically derived cell densities of 10 4 10 6 ml 1 low temperature 1 per cent is present within magnetite magnetosomes produced either

environmental rock magnetism of pelagic clay implications for asian eolian input to the north pacific since the pliocene we conducted a rock magnetic study of pelagic sediments in order to document variations of asian eolian input to the north pacific since the pliocene the materials studied consist of five pelagic clay red clay cores of several meters long taken from the central north pacific and surface sediments of box cores obtained at 40 sites along two lines a n s line along 175 e and an e w line along 20 n the magnetic susceptibility concentration of magnetic minerals and s ratio relative abundance of low coercivity magnetic minerals of the five pelagic clay cores have decreased synchronously since about 2 5 ma this age coincides with the onset of the northern hemisphere glaciation and chinese loess deposition geographical distribution of s ratios measured on the surface sediments revealed that they are remarkably low in the central north pacific these facts suggest that s ratio can be used as a proxy for asian eolian dust mossbauer spectroscopy showed that hematite dominates the high coercivity minerals observation with a transmission electron microscope suggests two sources of magnetic minerals in the pelagic clay biogenic magnetite produced in situ and detrital magnetite and hematite the variations of s ratio and magnetic susceptibility with time and region can be explained by a model that asian eolian dust has higher lower hematite magnetite concentration than other sources of magnetic minerals and that its input to the central north pacific has increased since 2 5 ma we recognized subtle s ratio fluctuations of about 400 kyr in recurring intervals superimposed on the decreasing trend since 2 5 ma rock magnetic parameters diagnostic of magnetic grain size on the other hand showed small or no variations with age although eolian grain size is generally thought to have increased significantly since the pliocene based on sedimentological studies

variability and frontogenesis in the large scale oceanic frontal zones sea surface temperature sst from weekly global advanced very high resolution radiometer data for the period of 1982 1992 and estimates of the surface forcing due to wind stress and net heat flux are used to investigate a global monthly climatology of large scale oceanic frontal zones ofzs the variability of sst gradient in several frontal zones and the meridional frontogenesis in the north pacific subpolar frontal zones are identifiable in the sst gradient field throughout the whole year while subtropical frontal zones appear as seasonal phenomena in the northern hemisphere the magnitude and position of subtropical fronts were found to vary synchronously in both hemispheres with maximum intensity in november to march during this period subtropical fronts in the northern hemisphere become clearly identifiable separate features while in the southern hemisphere their southern boundaries tend to merge with the subpolar front in the northern hemisphere the northward shift of the subtropical frontal zones during late boreal spring results in a merger of the subpolar and subtropical zones by august in the southern hemisphere subtropical fronts separate from the subpolar front during this period and become clearly distinguishable though less intense singular spectrum analysis of the 11 year time series of sst gradient in several ofzs revealed a seasonal signal as well as interannual variations that in the equatorial zone are related to el nino events the amplitude of the annual cycle is comparable in the subtropical and subpolar north pacific but the subtropics leads the subpolar zone by about 4 months combined forcing due to wind stress and net surface heat flux was found to be sufficient to describe most of the observed frontogenesis variability in north pacific midlatitudes on seasonal timescales but not on shorter timescales in the subtropical zone the ekman convergence alone was not sufficient to provide the observed frontogenesis frontolysis on seasonal time scales in fact when the maximum frontogenesis associated with ekman convergence occurs in late spring early summer this is counteracted by the frontolytic effect of ekman pumping and the dominating frontolytic effect of surface heat forcing in summer ekman convergence is more important in the subpolar area where it is enhanced by the smaller frontogenetic effect of both ekman pumping and surface heat forcing surface forcing due to wind stress and heat flux considered in this study does not explain the high amplitude intraseasonal frontogenesis variations especially in the subpolar region

fracture mapping with electrical core images naturally fractured reservoirs often contain a range of different fracture types and networks fractures that are relatively permeable and relatively impermeable unconnected and connected to the part of the fracture network that carries fluid flow and naturally occurring or drilling induced consequently in terms of their fluid connectivity fractures may be open or closed while individual fractures may be isolated or well connected we have adapted our approach to imaging sedimentary fabric in the laboratory where we related electrical core images to properties such as porosity permeability grain size and cementation to enable electrical imaging of fractures in core our approach uses similar principles to those employed in down hole electrical imaging the results demonstrate an ability to image conductive fractures in fully saturated low porosity water bearing core these fractures being electrically connected from the flat measurement surface through to the outer surface of the core published results for numerical modelling of down hole electrical imaging tools show the electrical response is related to fracture depth and fracture aperture our experimental results on fractured core in the laboratory support these numerical observations increased current flowing into the fracture as the aperture increases the finite size of the electrode however means that this technique cannot distinguish between a single fracture and smaller groups of fractures intersecting the electrode

a stable chemical remanence in holocene sediments the ferrimagnetic iron sulphide greigite has been extracted from freshwater sediments from loch lomond and llyn geirionydd and identified by x ray diffraction and thermomagnetic analyses the authigenic greigite is probably the dominant carrier of a stable natural remanent magnetization in the freshwater sediments underlying marine sediments in loch lomond and in the lateglacial interstadial sediments from llyn geirionydd mineral magnetic analysis shows that greigite tends to have a higher sirm x ratio approximately 70 kam 1 than many natural magnetite assemblages this magnetic characteristic coupled with greigite s ability to oxidize easily and to change to a less magnetic mineral upon exposure to air may be used to indicate its presence in downcore magnetic profiles alternating field demagnetization cannot be used to distinguish chemical from detrital remanences in loch lomond or llyn geirionydd on account of the similar magnetic stabilities of greigite and magnetite the time lag between the acquisition of the primary detrital remanence and the secondary chemical remanence remains unknown and creates difficulties in understanding the record of paleomagnetic secular variation contained in these lake sediments

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

air sea heat exchanges characteristic of a prominent midlatitude oceanic front in the south indian ocean as simulated in a high resolution coupled gcm abstract an integration of a high resolution coupled general circulation model whose ocean component is eddy permitting and thus able to reproduce a sharp gradient in sea surface temperature sst is analyzed to investigate air sea heat exchanges characteristic of the midlatitude oceanic frontal zone the focus of this paper is placed on a prominent sst front in the south indian ocean which is collocated with the core of the southern hemisphere storm track time mean distribution of sensible heat flux is characterized by a distinct cross frontal contrast it is upward and downward on the warmer and cooler flanks respectively of the sst front acting to maintain the sharp gradient of surface air temperature sat that is important for preconditioning the environment for the recurrent development of storms and thereby anchoring the storm track induced by cross frontal advection of cold warm air associated with migratory atmospheric disturbances the surface flux is highly variable with intermittent en

possible modification of atmospheric circulation over the northwestern pacific induced by a small semi enclosed ocean 1 the surface conditions of a small semi enclosed ocean the japan sea largely controlled by the volume transport of the warm current influence the monthly mean atmospheric circulation over the northwestern pacific via active cyclogenesis the new dynamical processes induced by the japan sea are proposed in this letter when the surface temperature in the japan sea is lowered in a regional atmospheric model the monthly mean potential vorticity is increased over the japanese islands and the monthly mean okhotsk low is intensified at the 500 hpa level in the case of an amplified okhotsk low the mean cyclonic flow transports a cold air over the japan sea toward the pacific and transports relatively warm air over the bering sea toward siberia such westerly easterly air mass advections over the northwestern pacific area could produce the japan siberia temperature anomaly in the lower level troposphere via enhancement of the okhotsk low which contributes to the weakness of the synoptic scale north south temperature gradient at 120 180 e this newly found westerly cold easterly warm ocean air mass advection enhanced by the amplified quasi stationary eddy that acts to reduce the temperature gradient is distinct from poleward heat transport by well known transient baroclinic waves or annual mean ferrel circulation

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

two and three dimensional heterogeneity in carbonate sediments using resistivity imaging abstract volume heterogeneity was investigated in carbonate sediments using fine scale electrical resistivity data which are sensitive to porosity and to sediment macrostructure and microstructure variability in sediment density and porosity was assessed by x radiographic and two dimensional 2d electrical resistivity measurements in 3 cm thick slabs collected from the dry tortugas in the lower florida keys a comparison of the 2d correlation lengths calculated from each assessment indicates that using methods that differ in resolution these two methods measure quite different horizontal and vertical fluctuations in sediment density and porosity other electrical resistivity experiments were conducted using a 2d network of resistivity electrodes on the surface of freshly collected box cores the resulting three dimensional 3d resistivity data provide a unique insight into the spatial variability of sediment porosity and structure at the cm scale complementary x radiograph cores provide 2d datasets of resistivity and porosity at higher resolution these data are used to establish the porosity resistivity microstructure relationships for these carbonate sediments with microstructure being described in terms of tortuosity these relationships are used to extend our interpretation in terms of porosity and tortuosity to the corresponding 3d box core resistivity datasets sediment tortuosity is investigated by numerically modeling the flow of electrical currents through a range of pore morphologies in three dimensions the results show particular sensitivity to the intra particle porosity particle shape and the relative sizes of pores and throats the 3d methodology shows promise as a non invasive measurement of buried inhomogeneities that could lead to improving models for predicting acoustic backscattering from the sediment volume

development of the east asian summer monsoon evidence from the sediment record in the south china sea since 8 5 ma 128 samples from ocean drilling program odp site 1143 in the southern south china sea were analyzed for grain size clay minerals biogenic opal content and quartz in order to reconstruct changes in east asian monsoon climate since 8 5 ma an abrupt change of terrigenous mass accumulation rate mar clay mineral assemblage median grain size and biogenic opal mar about 5 2 ma suggests that between 8 5 5 2 ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern vietnam a simple model of east asian summer monsoon evolution was based on the clay feldspar ratio kaolinite chlorite ratio and biogenic opal mar the summer monsoon has two periods of maximum strength at 8 5 7 6 ma and 7 1 6 2 ma subsequently there was a relatively stable period at 6 2 3 5 ma continued intensification about 3 5 2 5 ma and gradually weakening after 2 5 ma since i ma the monsoon has intensified with remarkable high frequency and amplitude variability simultaneous increase in sedimentation rates at odp sites 1143 1146 and 1148 as well as in mar of terrigenous materials quartz feldspar and clay minerals at odp site 1143 at 3 5 2 5 ma may be the erosional response to both global climatic deterioration and the strengthening of the east asian summer monsoon after about 3 4 ma c 2006 elsevier b v all rights reserved

carbon sulfur iron relationships in sedimentary rocks from southwestern taiwan influence of geochemical environment on greigite and pyrrhotite formation the importance of the magnetic iron sulfide minerals greigite fe3s4 and pyrrhotite fe7s8 is often underappreciated in geochemical studies because they are metastable with respect to pyrite fes2 based on magnetic properties and x ray diffraction analysis previous studies have reported widespread occurrences of these magnetic minerals along with magnetite fe3o4 in two thick plio pleistocene marine sedimentary sequences from southwestern taiwan different stratigraphic zones were classified according to the dominant magnetic mineral assemblages greigite pyrrhotite and magnetite dominated zones greigite and pyrrhotite are intimately associated with fine grained sediments whereas magnetite is more abundant in coarse grained sediments we measured total organic carbon toc total sulfur ts total iron fet 1n hcl extractable iron fea and bulk sediment grain size for different stratigraphic zones in order to understand the factors governing the formation and preservation of the two magnetic iron sulfide minerals the studied sediments have low ts fea weight ratios 0 03 0 2 far below that of pyrite 1 15 which indicates that an excess of reactive iron was available for pyritization observed low ts 0 05 0 27 is attributed to the low organic carbon contents toc 0 25 0 55 which resulted from dilution by rapid terrigenous sedimentation the fine grained sediments also have the highest fet and fea values we suggest that under conditions of low organic carbon provision the high iron activity in the fine grained sediments may have removed reduced sulfur so effectively that pyritization was arrested or retarded which in turn favored preservation of the intermediate magnetic iron sulfides the relative abundances of reactive iron and labile organic carbon appear to have controlled the transformation pathway of amorphous fes into greigite or into pyrrhotite compared to pyrrhotite dominated sediments greigite dominated sediments are finer grained and have higher fea but lower ts we suggest that diagenetic environments with higher supply of reactive iron lower supply of labile organic matter and consequently lower sulfide concentration result in relatively high eh conditions which favor formation of greigite relative to pyrrhotite

palaeomagnetism and rock magnetism in the upper pliocene valle ricca rome italy section summary a revision of the magnetostratigraphy in the valle ricca monterotondo rome pliopleistocene section was carried out this section consisting mainly of blue grey marly clays was previously investigated for palaeomagnetic effects by arias et al 1980 1990 who detected a normal polarity interval close to a volcanic ash layer which was correlated to the reunion subchron this interpretation conflicts however with new biostratigraphic data and palaeomagnetic observations in order to investigate the possible origin of these discrepancies we performed a detailed sampling for palaeomagnetic and rock magnetic analyses in the controversial interval around the volcanic ash layer the present results show strong variations in the rock magnetic parameters and suggest significant changes in the magnetic mineralogy two levels with a high intensity low temperature normal component of magnetization were distinguished at these two levels the rock magnetic parameters are typical of greigite and a widespread occurrence of framboids of micron sized iron sulphide grains was found by mineralogical analyses a high temperature reversed component of magnetization carried by magnetite was isolated for the whole interval investigated we demonstrate that the previously recognized normal polarity interval is the effect of changes in the magnetic mineralogy and it does not represent a true reversal of the earth s magnetic field the origin of the low temperature normal component of magnetization is discussed in light of the present knowledge about greigite formation and remanence acquisition

intensification of the subpolar front in the sea of japan during winter cyclones the response of the subpolar front in the sea of japan also known as the east sea to winter cyclones is investigated based on quantitative analyses of gridded and satellite data sets cyclone passages affecting the sea are detected using time series of spatially averaged surface turbulent heat fluxes as the cyclones develop there are strong cold air outbreaks that produce twice the normal heat loss over the sea after removal of sea surface temperature sst seasonal trends we found that cyclone passage hence cooling mainly occurred over 3 days with maximum sst reduction of 0 4 c the greatest reduction was found along the subpolar front where frontal sharpness i e sst gradient increased by 0 1 c 100 km 1 results of a mixed layer model were consistent with both temperature and frontal sharpness and localized surface cooling along the subpolar front resulted from both horizontal heat advection and turbulent heat fluxes at the sea surface further analyses show that this localized cooling from horizontal heat advection is caused by the cross frontal ekman flow vertically averaged over the mixed layer and strong northwesterly winds associated with the cold air outbreak during cyclone passage

linking regional sources and pathways for submarine groundwater discharge at a reef by electrical resistivity tomography 222rn and salinity measurements 1 submarine groundwater discharge sgd is an important component of the hydrologic cycle connecting terrestrial to marine environments sgd in fringing reefs and its consequences on biogeochemistry and ecology remain mostly unexplored the 222rn activity and salinity of seawater indicate a substantial groundwater contribution throughout most of the 20 km2 studied tropical reef in pangasinan philippines over 30 km of electrical resistivity profiles with a penetration depth of 12 5 m shows widespread zones within the reef that are much more resistive than porous reef rocks or sediment saturated with typical seawater some discrete resistive areas are located close to where seawater has 222rn peaks and where geologic lineaments are likely located suggesting that these are preferential pathways for fresher groundwater discharging to the reef sgd at the site could be a major ecological factor connecting the reef to the subsurface environment which in turn may lead to connections to land

utilizing multichannel electrical resistivity methods to examine the dynamics of the fresh water seawater interface in two hawaiian groundwater systems 1 multichannel electrical resistivity er measurements were conducted at two contrasting coastal sites in hawaii to obtain new information on the spatial scales and dynamics of the fresh water seawater interface and rates of coastal groundwater exchange at kiholo bay located on the dry kona side of the big island and at a site in maunalua bay oahu there is an evidence for abundant submarine groundwater discharge sgd however the hydrologic and geologic controls on coastal groundwater discharge are likely to be different at these two sites while at kiholo bay sgd is predominantly through lava tubes at the maunalua bay site exchange occurs mostly through nearshore submarine springs in order to calculate sgd fluxes it is important to understand the spatial and temporal scales of coastal groundwater exchange from er time series data subsurface salinity distributions were calculated using site specific formation factors a salinity mass balance box model was then used to calculate rates of point source i e spatially discreet and total fresh water discharge from these data mean sgd rates were calculated for kiholo bay 9 200 m3 d and for the maunalua bay site 5 900 m3 d while such results are on the same order of magnitude to geochemical tracer derived sgd rates the er sgd rates provide enhanced details of coastal groundwater exchange that can enable a more cohesive whole watershed perspective

practical techniques for 3d resistivity surveys and data inversion1 techniques to reduce the time needed to carry out 3d resistivity surveys with a moderate number 25 to 100 of electrodes and the computing time required to interpret the data have been developed the electrodes in a 3d survey are normally arranged in a square grid and the pole pole array is used to make the potential measurements the number of measurements required can be reduced to about one third of the maximum possible number without seriously degrading the resolution of the resulting inversion model by making measurements along the horizontal vertical and 45 diagonal rows of electrodes passing through the current electrode the smoothness constrained least squares inversion method is used for the data interpretation the computing time required by this technique can be greatly reduced by using a homogeneous half space as the starting model so that the jacobian matrix of partial derivatives can be calculated analytically a quasi newton updating method is then used to estimate the partial derivatives for subsequent iterations this inversion technique has been tested on synthetic and field data where a satisfactory model is obtained using a modest amount of computer time on an 80486dx2 66 microcomputer it takes about 20 minutes to invert the data from a 7 by 7 electrode survey grid using the techniques described below 3d resistivity surveys and data inversion can be carried out using commercially available field equipment and an inexpensive microcomputer

climatology of explosive cyclones off the east asian coast abstract the climatology of explosive cyclogenesis off the east asian coast was studied based on 30 years 1958 87 of surface analyses there were two favorable areas for explosive deepening one over the eastern sea of japan and the other over the northwestern pacific east and southeast of japan the latter was located close to the warm kuroshio current the frequency of explosive cyclogenesis reached a local minimum over japan the geographic distribution of explosive cyclone frequency suggests that the explosive cyclogenesis is influenced by the japanese islands in addition a positive correlation is found between explosive cyclogenesis frequency and the el nino episodes during 1958 87 the physical relationship between these two phenomena however is not well understood

chronostratigraphic framework for the iodp expedition 318 cores from the wilkes land margin constraints for paleoceanographic reconstruction the integrated ocean drilling program expedition 318 to the wilkes land margin of antarctica recovered a sedimentary succession ranging in age from lower eocene to the holocene excellent stratigraphic control is key to understanding the timing of paleoceanographic events through critical climate intervals drill sites recovered the lower and middle eocene nearly the entire oligocene the miocene from about 17 ma the entire pliocene and much of the pleistocene the paleomagnetic properties are generally suitable for magnetostratigraphic interpretation with well behaved demagnetization diagrams uniform distribution of declinations and a clear separation into two inclination modes although the sequences were discontinuously recovered with many gaps due to coring and there are hiatuses from sedimentary and tectonic processes the magnetostratigraphic patterns are in general readily interpretable our interpretations are integrated with the diatom radiolarian calcareous nannofossils and dinoflagellate cyst dinocyst biostratigraphy the magnetostratigraphy significantly improves the resolution of the chronostratigraphy particularly in intervals with poor biostratigraphic control however southern ocean records with reliable magnetostratigraphies are notably scarce and the data reported here provide an opportunity for improved calibration of the biostratigraphic records in particular we provide a rare magnetostratigraphic calibration for dinocyst biostratigraphy in the paleogene and a substantially improved diatom calibration for the pliocene this paper presents the stratigraphic framework for future paleoceanographic proxy records which are being developed for the wilkes land margin cores it further provides tight constraints on the duration of regional hiatuses inferred from seismic surveys of the region

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

the occurrence of greigite in sediments from loch lomond greigite has been identified in the sediments of loch lomond using x ray diffraction greigite is the dominant magnetic mineral in the oldest sediments recovered while magnetite predominates in the younger sediments which had previously been used for palaeomagnetic secular variation studies a layer of sediment in between these two magnetic mineral regimes has very low magnetic concentrations probably as a consequence of magnetite dissolution associated with sulphide rich pore waters produced at the time of a marine incursion the greigite largely oxidises once the sediment is exposed to air but if freeze dried the greigite becomes surprisingly stable following freeze drying the greigite can be heated to 280 c in air before it alters and loses its strong ferrimagnetic properties

late quaternary paleoceanography of the south china sea glacial interglacial contrasts in an enclosed basin the sea surface paleotemperature of the south china sea scs is estimated quantitatively based on the quantitative analysis of planktonic foraminiferal faunas recovered from piston cores v36 06 3 v36 06 5 and so49 kl8 on the northern continental slope the results lead to a reconstruction of the history of paleocirculation patterns during the last 200 000 years the postglacial and interglacial transbasinal circulation pattern was replaced by a semienclosed basin flow pattern during glacial episodes lowered sea level transformed the scs into a semienclosed basin with the only passageway to the open ocean in its northeastern corner the east asian monsoon which governs circulation patterns in the scs both today and during the late quaternary created both clockwise summer and counterclockwise winter surface gyres during glacials the inflow of tropical surface water masses from both the pacific and indian oceans decreased or was completely cut off from this marginal sea causing a greater decrease in glacial sea surface temperature than in the open ocean of the same latitude inferred increased influence of pacific temperate waters and decreased influence of tropical subtropical waters are confirmed by changes in the planktonic foraminiferal assemblages glacial interglacial fluctuation in sea surface temperature sst 6 8 9 3 c for winter and 2 3 c for summer as well as the seasonality 4 6 c for postglacial and interglacials and 9 10 c for glacials are much greater than the adjacent open western pacific reflecting the amplification of the climatic signal in the marginal sea

post depositional remanent magnetization lock in and the location of the matuyama brunhes geomagnetic reversal boundary in marine and chinese loess sequences article i nfo pdrm lock in loess paleosol bioturbation disturbs detrital magnetic particles after deposition so accurate recording of the ancient geomagnetic field in bioturbated sediments is widely attributed to acquisition of a post depositional remanent magnetization pdrm whereby the geomagnetic field exerts a torque on a magnetic particle and aligns it with the field after the final mixing event experienced by the particle the relationship between the matuyama brunhes boundary mbb and oxygen isotope age tie points in marine sediments has been widely used to determine the depth at which the paleomagnetic signal is locked in however such analyses can be badly affected by age discrepancies among different paleoclimatic proxies and by varying isotopic compositions of seawater in different locations and from the presence of different water masses at different depths at the same location it is therefore necessary to separately compare paleomagnetic data with respect to either benthic or planktonic foraminiferal oxygen isotope records for sites from the same water mass to avoid inadvertently introducing age differences to the analysis when the global data set is subjected to such a rigorous analysis few reliable data remain for the mbb using two complementary approaches we estimate that the mbb is on average shifted 20 cm below its true position in marine sediments this offset is the sum of the thickness of the bioturbated surface mixed layer which is possibly dominant and the pdrm lock in depth there is also controversy concerning observed differences in the position of the mbb relative to paleoclimatic proxies in marine sediments and chinese loess deposits for the chinese loess quartz grain size is insensitive to pedogenic alteration and is a useful parameter for determining the true position of the mbb with respect to paleoclimatic boundaries we conclude that the mbb occurs late in marine oxygen isotope stage 19 and in the upper part of chinese paleosol unit s8 rather than at the mid or lower part of loess unit l8 our results require adjustment of the generally accepted positions for the mbb and resolve a longstanding chronological conundrum for marine and chinese loess sequences

spatial and temporal characterization of sea surface temperature response to tropical cyclones abstractthe spatial structure and temporal evolution of the sea surface temperature sst anomaly ssta associated with the passage of tropical cyclones tcs as well as their sensitivity to tc characteristics including tc intensity and translation speed and oceanic climatological conditions represented here by latitude are thoroughly examined by means of composite analysis using satellite derived sst data the magnitude of the tc generated ssta is larger for more intense slower moving and higher latitude tcs and it occurs earlier in time for faster moving and higher latitude storms the location of maximum ssta is farther off the tc track for faster moving storms and it moves toward the track with time after the tc passage the spatial extension of the cold wake is greater for more intense and for slower moving storms but its shape is quite independent of tc characteristics consistent with previous studies the calculations show that the mean ssta over a tc centered box nearly linearly corre

magnetic susceptibility variations and provenance of surface sediments in the south china sea magnetic susceptibility ms and grain sizes of surface sediments are measured to characterize sediment sources and their distribution in the south china sea scs distribution characteristics of ms of bulk samples msb fine grained fraction msf and coarse grained fraction msc are examined to explore the factors affecting ms values in sediment transport and deposition processes affected by dilution of quartz and carbonate abundance msc is not suitable for tracing sediment sources in the region instead msf provides a good parameter for tracking transport and deposition of complex and coarse grained sediments such as those from luzon island volcanics and from the pearl and mekong rivers which often have high msf values showing a decreasing trend with water depth on the continental shelf water depth 200 m to the west of luzon island kuroshio intrusion into the scs is the predominant factor for sediment transport after high msf volcanic materials from the luzon island are discharged into the sea sediments from the pearl river are transported southwestward under the china coastal current and then deposited between the pearl river mouth and hainan island to the southwest of taiwan island in the northeastern scs where sediments are mainly derived from taiwan island and or the yangtze river both the kuroshio intrusion and the china coastal current are significant in determining sediment transport and deposition in the south most of high msf sediments from the mekong river are transported eastward under the influence of northeastward currents in summer after entering the sea and then deposited on the northern sunda shelf c 2010 elsevier b v all rights reserved

variability in geoacoustic and related properties of surface sediments from the venezuela basin caribbean sea abstract the spatial variability of sediment geoacoustic and related properties was determined from replicate 0 25 m 2 usnel box core samples collected from three sedimentary provinces in the venezuela basin the maximum variation in sediment physical chemical and geoacoustic properties occurred among distant sites representing pelagic turbidite or hemipelagic sedimentary regimes rather than within sites or within core depth gradients variability among sites was a function of differences in calcium carbonate dissolution among a water depth gradient of 1550 m 3500 5050 m and differences in the relative contribution of particles from pelagic and terrigenous sources the least amount of variation was evident among subcores obtained from the same box core or site suggesting that a single subcore was adequate to describe sediment physical and geoacoustic properties over large areas of the sea floor the considerable amount of downcore variability in sediment properties was a function of gradients in biological activity biologically mediated chemical changes and the presence of ponded terrigenous sediments deposited by intermittent turbidite flows interspersed between sediments of pelagic origin for sediments with greater than 35 calcium carbonate porosity is a good predictor of compressional wave velocity whereas mean grain size is a good predictor of compressional wave attenuation porosity mean grain size relationships had little predictive value in carbonate sediments the differences among these and previously published empirical relationships show that particle size distribution of larger carbonate material and composition of the sediment matrix must be considered when predicting sediment geoacoustic properties sediment shear strength did not show any correlation with other sediment physical or acoustic properties and is primarily controlled by biological and chemical processes

diagenetic formation of ferrimagnetic iron sulphide minerals in rapidly deposited marine sediments south island new zealand abstract detailed magnetostratigraphic studies of late neogene siliciclastic sediments of the awatere group south island new zealand 41 45 s 174 05 e have revealed a wide range of palaeomagnetic behaviour examination of rock magnetic properties was undertaken using conventional palaeomagnetic techniques and thermomagnetic x ray diffraction and electron microprobe analyses these analyses indicate that the ferrimagnetic iron sulphide minerals greigite and pyrrhotite are responsible for a stable and intense magnetic remanence in fine grained sediments whereas titanomagnetite is the only remanence bearing mineral identified in coarser grained sediments which are less strongly and less stably magnetised than the fine grained sediments detrital titanomagnetite grains are likely to have undergone dissolution during early diagenesis as a result of iron sulphide formation which occurs commonly in rapidly deposited anoxic sediments that support active sulphate reduction and h 2 s formation preservation of greigite and pyrrhotite is inferred to result from the arrest of the pyritisation process probably due to the low permeability of the fine grained sediments and consumption of available h 2 s before full reaction to pyrite occurred relative palaeomagnetic instability and weak remanence intensities in coarser grained sediments is likely to be due to low titanomagnetite concentrations resulting from titanomagnetite dissolution

magnetostratigraphy of a greigite bearing core from the south yellow sea implications for remagnetization and sedimentation sediments from the continental shelf are sensitive to sea level climatic changes and local tectonic history in this study we carried out a high resolution magnetostratigraphic investigation on the longest core nhh01 125 64 m recovered from the south yellow sea sys an abnormal interval dominated by negative inclinations was discovered by applying alternating field demagnetization afd on samples from a greigite bearing layer 44 90 51 80 m in contrast the inclinations of most greigite bearing samples changed from negative to positive when heated to 360 c this strongly indicates that this inclination anomaly revealed by the afd alone is not a true negative subchron after neglecting the effects of greigite bearing layers the straightforward correlation of the interpreted magnetostratigraphy defines the matuyama brunhes boundary 781 ka and the jaramillo top 990 ka at 68 64 m and 101 54 m respectively the linearly extrapolated basal age of the core is 1 10 ma in addition several short lived inclination anomalies can be tentatively assigned to magnetic excursions which indicates that the sedimentation could be continuous even at the millennial time scale at depth intervals bracketing these fast geomagnetic events moreover the excellent correspondence between clay content variations of the core and the marine oxygen isotope record indicates the potential of clay content as a paleoclimatic proxy in the studied region in the past 1 ma in brief our study provides not only a robust age model in the sys but also a methodological guide for paleomagnetic studies in continental shelf region

sea level change and remagnetization of continental shelf sediments off new jersey odp leg 174a magnetite and greigite diagenesis summary palaeomagnetic and rock magnetic studies were performed on a seaward transect of continental shelf sediments from sites 1071 and 1072 of ocean drilling programme leg 174a on the new jersey margin the sediments recorded a polarity change from reversed to normal which was tentatively interpreted as the matuyama brunhes boundary the polarity boundary is closely correlated with the sequence boundary pp3 s which is considered to have formed as an erosional unconformity during regression and subsequent transgression related to global eustacy rock magnetic analyses indicate that the sediment contains comparable amounts of magnetite and greigite fe3s4 with possible trace amounts of haematite a marked change in rock magnetic properties is recorded at site 1072 with an increase in greigite concentration at the polarity boundary 62 4 metres below seafloor where the grain size does not change at site 1071 greigite is dominant from 2 m below pp3 s to 0 8 m above it these intervals are characterized by higher peak coercivities of remanence and subdued remanence in both the magnetite and greigite components palaeomagnetic analysis indicates that the intervals just below pp3 s have dual component magnetizations of reversed polarity and are considered to have been deposited during the matuyama chron c1r 1r and were possibly remagnetized during the brunhes chron through the formation of the pp3 s surface detrital magnetite and early diagenetic greigite might have carried the reversed polarity magnetization during the formation of pp3 s in the brunhes chron greigite might have formed at the oxidation front with ongoing downward formation due to oxidation of pyrite by percolating fresh water which might be a cause of the remagnetization our study indicates that careful rock magnetic investigation is necessary for magnetostratigraphic studies of continental shelf deposits in order to recognize remagnetizations induced by sea level changes

a role of the yellow and east china seas in the development of extratropical cyclones in winter abstractto investigate whether the relatively warm yellow and east china seas play an active role in the deepening of extratropical cyclones over east asia during winter surface wind vectors downloaded from the quick scatterometer quikscat website are used to compute the standard deviation of surface vorticity at resolution in addition a regional numerical atmospheric model is adopted to find atmospheric and or oceanic conditions favorable for development of extratropical cyclones over the study area these satellite derived and modeled vorticity fields demonstrate that on average extratropical cyclone activity is moderate over the warm yellow and east china seas this is because enhanced lower level baroclinicity over these ocean areas is transferred as far as the shelf break of the east china sea by strong northwesterly surface winds based on the numerical model results the weak northwesterly surface wind condition is required for enhancing lower level baroclinicity over the yellow and east

magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the eastern mediterranean sea summary magnetic properties irm arm xin s ratio at 0 3 t room temperature rt hysteresis and thermomagnetic curves and geochemical data fe s mn al ti organic c were studied in two eastern mediterranean boxcores abc26 and bc19 at a resolution of 3 5 mm the boxcores contain sapropel s1 9 6 kyr bp at a few decimetres below seafloor the magnetic fraction consists predominantly of single domain sd to pseudo singledomain psd magnetite in the entire cores the original input of magnetic grains comes from two sources aeolian dust both cores and volcanic ash from the minoan eruption of santorini core bc19 only non steady state diagenesis has changed the magnetic mineralogy considerably in these alternating organic rich organic poor sediments during deposition of sapropel s1 reductive diagenesis and pyritization in and just below the sapropel caused lower magnetic intensities coarser magnetic grain sizes and partial maghemitization in thermomagnetic curves two types of pyrite can be identified one oxidizes below 450 uc and the other above 450 uc the higher oxidation temperature is predominantly found below the sapropel this may be related to the microtexture of pyrite which is euhedral below sapropels and mainly framboidal within sapropels since the end of sapropel deposition a downward moving oxidation front has oxidized the upper half c 5 cm of the sapropel the oxidized part of the sapropel is enriched in diagenetically formed fe oxides with relatively high coercivity and arm the maximum coercivity is found in a distinct layer between the present day mn and fe redox boundaries at the top of the unoxidized sapropel the freshly precipitated fe oxides in this centimetre thick layer contain a mixture of superparamagnetic sp grains and high coercivity sd magnetite higher in the oxidized zone the freshly precipitated fe oxides have aged into generally slightly lower coercivity sd grains with relatively high arm in addition to the diagenetic formation of fe oxides at the top of the sapropel formation of a ferrimagnetic fe monosulphide may have occurred within the sapropel during later stages of diagenesis which may have enhanced the arm signal in the organic rich interval in particular

rock magnetic detection of distal ice rafted debries clue for the identification of heinrich layers on the portuguese margin abstract high resolution measurements of concentration and grain size dependent magnetic parameters along a sedimentary sequence deposited on the portuguese margin 38 n during the last 120 ka allowed the detection of multiple thin layers slightly enriched by a coarse lithogenic fraction sizes mineralogy shapes and mode of deposition identify the material as ice rafted detritus ird the four most recent events dated by calibrated radiocarbon ages are contemporaneous with heinrich events he1 he4 older events can be identified as he5 he6 or with minor ird that occurred during stage 5 the resolution and sensitivity obtained with rock magnetic methods enable the detection of multiple secondary events showing that iceberg delivery was a frequent phenomenon directly linked to temperature variations over ice caps heinrich events representing the extreme cases

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

geomagnetic field behavior during the iceland basin and laschamp geomagnetic excursions a simple transitional field geometry we present four new records of the iceland basin excursion ibe and five new records of the laschamp excursion le obtained from rapidly deposited marine sediments in the north atlantic ocean the nordic seas the gulf of mexico the south china sea and the southern indian ocean marked minima in relative paleointensity correspond with the paleomagnetic directional changes associated with all of the excursion records the virtual geomagnetic pole vgp paths of the four ibe records are all similar the vgps move southward over europe and africa reaching the southern hemisphere three reach antarctica and then move to more eastern longitudes before returning northward over australia and east asia describing a large counterclockwise loop the same vgp pattern is observed in other published records the vgp paths observed for the le are similar to those of the ibe however they loop clockwise instead of counterclockwise despite the different sense of looping the marked similarity among the paths for the two excursions suggests that a similar relatively simple geometry dominated the transitional field during both the ibe and the le similar dynamo mechanisms must therefore have been active in the earth s core for both excursions the duration of the excursions is estimated at 2 000 years which supports the suggestion that a difference exists between the mechanisms for excursions and reversals however the coincidence of the longitudinal bands for vgps associated with excursions compared to some reversal paths could also indicate an inherent link between the mechanisms for reversals and excursions

late quaternary paleoceanography of the south china sea surface circulation and carbonate cycles paleoceanographic information from 34 sediment cores is summarized to investigate the glacial interglacial variations in sea surface circulation and late quaternary carbonate cycles in the south china sea judging from the distribution pattern of deposition rates the enormous terrigenous supply by rivers is responsible for the high rate of hemipelagic sedimentation which was even higher during glacial periods paleotemperature maps based on transfer function temperature estimates have revealed a e w gradient of sst for glacial summer and a s n gradient for glacial winter and this agrees well with the clockwise surface circulation in summer and counterclockwise in winter during glacials as shown by a preliminary computer modelling the high resolution paleotemperature curves of core v36 3 from the northern slope show an abrupt cooling event which may belong to the younger dryas carbonate percentage in sediments and preservation of foraminifers and pteropods are used to study the carbonate cycles in the marginal sea it turns out that two mechanisms are functioning there being a basin with large drainage areas vast amount of river borne terrigenous input dilutes carbonate and its intensification during glacial decreases the glacial cac03 being a basin connected with the pacific the fluctuations of lysocline ccd and acd in the scs are related to those in the pacific ocean and dissolution is strengthened at interglacial thus above the present ccd the dilution factor predominates and the atlantic cycles are produced below the present ccd the dissolution factor prevails resulting in the pacific pattern of carbonate cycles

a 23 myr magnetostratigraphic time framework for site 1148 odp leg 184 in south china sea and its geological implications abstract the ocean drilling program odp leg 184 recovered a continuous sedimentary sequence since miocene at site 1148 in the northern south china sea scs which provided a unique record for better understanding the tectonic environmental and climatic evolution of the scs in this study we report a detailed paleomagnetic study on 881 discrete samples from the upper 460 m cores of hole 1148a through stepwise alternating field demagnetization af or thermal demagnetization td rock magnetic results from isothermal remanent magnetization irm acquisition temperature dependence magnetic susceptibility t and hysteresis loop parameters of representative samples indicate that the main magnetic mineral is low coercivity pseudo single domain magnetite the characteristic remanent magnetization chrm with moderate downward or upward inclinations was identified after removing a low stability drilling induced remanence with steep downward inclinations a new 23 myr magnetostratigraphic time framework was established by correlating the magnetic polarity sequence to the geomagnetic polarity time scale 2012 gpts 2012 ogg 2012 in combination with biostratigraphic data the mean sediment accumulation rates for lithostratigraphic units v and iv unit iii and lower unit ii upper unit ii unit ib and unit ia are calculated as 20 8 m myr 15 17 m myr 24 18 m myr 17 07 m myr and 49 01 m myr respectively

dependence of the climatological axial latitudes of the tropospheric westerlies and storm tracks on the latitude of an extratropical oceanic front 1 major storm tracks where migratory cyclones and anticyclones recurrently develop are observed around midlatitude oceanic frontal zones with strong meridional gradient of sea surface temperature sst a set of atmospheric general circulation model experiments is performed with zonally uniform sst prescribed at the model lower boundary the latitudinal sst profile for each hemisphere is characterized by a single front the frontal latitude is varied systematically from one experiment to another while the intensity of the frontal gradient is kept unchanged though idealized the experiments reveal a climatological tendency for a low level storm track to be organized along or slightly poleward of the sst front if located in the subtropics or midlatitudes as a surface manifestation of an eddy driven polar front jet pfj surface westerly axis tends to form on the poleward flank of the front this anchoring effect of the sst front is also hinted at upper levels but the climatological positions of the storm track and pfj are less sensitive to the frontal latitude for the sst front at subpolar latitude the joint primary axes of the upper level storm track and pfj form in midlatitudes away from the sst front their positions correspond to their counterpart simulated with a particular sst profile from which frontal gradient has been removed suggesting that the anchoring effect of a subpolar sst front on the storm track and pfj is overshadowed by atmospheric internal dynamics namely the self maintenance mechanism of a midlatitude storm track and pfj through their interactions

acoustic scattering from the seafloor modeling and data comparison an existing model of seafloor backscattering d r jackson d p winebrenner and a ishimaru j acoust soc am 79 1410 1422 1986 was implemented with the additions of volume scattering from a random inhomogeneous continuum and scattering from subbottom interfaces results of computer simulations with the extended model were compared with values of scattering strength obtained from processed gloria data from the monterey fan off the coast of california regions of well delineated high and low backscatter are seen in the gloria imagery the geoacoustic input parameters for the simulation runs were either taken directly from or estimated from core data obtained by ground truth sampling in the image area from the model simulation results it appears that the main factor causing the observed dichotomous character of the strength of returns in the fingers area is the presence or absence of a topmost inhomogeneous silt clay layer with a thickness of around 1 1 5 m in the high backscatter areas inh

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

paleomagnetic overprints in ocean sediment cores and their relationship to shear deformation caused by piston coring 1 we use paleomagnetic data from cores collected at ocean drilling program site 1062 on the bahama outer ridge as well as observations from prior cruises to quantify the nature and to assess the causes of drilling overprints the largest overprint arises from an isothermal remanent magnetization that is imparted to the core during coring or core retrieval a second type of overprint is apparent only in soft sediments collected with a piston corer and has coercivities and unblocking temperatures that completely overlap those of the primary remanent magnetization which means it cannot be removed by standard demagnetization methods this demagnetization resistant overprint can produce significant biases in paleomagnetic observations particularly those from split core sections we hypothesize that shearing which occurs as a result of friction on the inside wall of the piston corer as it rips through sediments and cuts a core deflects the ancient magnetization we develop and test a model that predicts how shear deformation can rotate remanence carrying grains and deflect the paleomagnetic remanence of a split core section using the shear model predictions and directions measured on split core sections and u channel samples from the undeformed core center we estimate the average deformation sustained and then correct the split core data for biases caused by shear deformation the reduction in the deviations between corrected split core data and u channel data is statistically significant indicating that the shear model is capable of accounting for a significant portion of the systematic biases observed in paleomagnetic observations obtained from piston cores

the magnetic fabric of surficial deep sea sediments in the hebble area nova scotian continental rise flood r d kent d v shot a n and hall f r 1985 the magnetic fabric of surficial deep sea sediments in the hebble area nova scotian continental rise in a r m nowell and c d hollister editors deep ocean sediment transport preliminary results of the high energy benthic boundary layer experiment mar geol 66 149 167 the anisotropy of magnetic susceptibility ams of surficial sediments in the hebble area depth 4820 m nova scotian continental rise has been measured to study the fabric of these sediments and to relate the sediment fabric to depositional conditions previous investigators have established that strong but variable bottom currents are important agents in redistributing bottom sediments in the area we observe that the upper 1 5 cm of the sediments has a primary fabric dominantly foliar with horizontal bedding created by bottom current activity while sediments deeper than 2 5 cm have a predominantly secondary fabric due to bioturbation the magnitude of the ams signal in these sediments is generally low making it difficult to measure some of the fabric elements especially the direction of the lineated fabric in the upper 1 5 cm magnetic grains are predominantly oriented parallel to the regional bathymetric contours but there is also a significant grouping of alignments perpendicular to the contours primary fabrics are observed in a few of the samples from the bioturbated sediments with the magnetic grains oriented parallel to the contours some of the variability observed between box cores in the magnetic fabric may reflect the variability of depositional conditions within the region an analysis of the magnitude of the ams fabric suggests that the parameter fs often used to denote bottom current fabrics is strongly dependent on the total anisotropy and only weakly dependent on the lineated nature of the fabric both primary and secondary fabrics can have relatively large f s values thus f s does not appear sufficient for delineating bottom current activity in the deep sea

gravity probability tomography a new tool for buried mass distribution imaging following the probability tomography principles previously introduced to image the sources of electric and electromagnetic anomalies we demonstrate that a similar approach can be used to analyse gravity data first we give a coherent derivation of the bouguer anomaly concept as a newtonian type integral for an arbitrary mass distribution buried below a non flat topography a discretized solution of this integral is then derived as a sum of elementary contributions which are cross correlated with the gravity data function in the expression for the total power associated with the bouguer anomaly to image the mass distribution underground we introduce a mass contrast occurrence probability function using the cross correlation product of the observed bouguer anomaly and the synthetic field due to an elementary mass contrast source the tomographic procedure consists of scanning the subsurface with the elementary source and calculating the occurrence probability function at the nodes of a regular grid the complete set of grid values is used to highlight the zones of highest probability of mass contrast concentrations some synthetic and field examples demonstrate the reliability and resolution of the new gravity tomographic approach