itcz and enso pacing on east asian winter monsoon variation during the holocene sedimentological evidence from the okinawa trough deep sea fan sediments provide an excellent geological archive for paleoenvironment reconstruction grain size clay mineral and elemental ti fe ca compositions were measured for a core retrieved from a submarine fan in the okinawa trough varimax rotated principal component analysis v pca on time evolution of grain size spectrum reveals that since the holocene sediment was transported mainly by the benthic nepheloid layer 33 and upper layers 33 which is driven by the east asian winter monsoon eawm the intensification of the kuroshio current during the holocene masks the fluvial signal of the summer monsoon and obstructs clay minerals derived from the yellow river a major contributor prior to 12 ka bp a new grain size index gsi which represents the eawm well exhibits a negative correlation with the delta o 18 record in dongge cave china during the holocene when sea level was relatively steady this anti correlation suggests the southward migration of the intertropical convergence zone itcz the consistency among our records and rainfall records in peru ti counts in the cariaco basin monsoon records in oman and the averaged summer insolation pattern at 30 degrees n further support the itcz s impact on monsoon systems globally cross correlation analyses for gsi and log ti ca against delta o 18 record in dongge cave reveal a decoupling between the east asian winter and summer monsoon during 5500 2500 cal yr bp with greater complexity in the last 2500 years this can be attributed to exacerbated enso mode fluctuations and possibly anthropogenic interference superimposed on insolation and itcz forcing

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

quantitative estimates of pedogenic ferromagnetic mineral formation in chinese loess and palaeoclimatic implications abstract the quasi continuously deposited loess sediments of the central chinese loess plateau constitute one of the most complete and long lasting records of quaternary palaeoclimate on land much of this record has been uncovered by measurement and interpretation of the magnetic properties of the loess the polarity of natural remanent magnetization has provided absolute age dates by correlation with the geomagnetic polarity time scale magnetic low field susceptibility has been used to reconstruct the cyclic changes of pleistocene palaeoclimates although the origin of the signal is still poorly understood from comparison with the 10 be concentration throughout the sequence we are able to determine the contributions to susceptibility from inherited and authigenic sources for the last 130 ky since the production of authigenic magnetite is directly related to regional precipitation annual palaeoprecipitation rates can be calculated palaeoprecipitation rates similar to present day rates are derived for oxygen isotope stage 5 including the last interglacial in contrast cold periods corresponding to oxygen isotope stages 2 and 4 experienced negligible precipitation the beginning and end of the time interval represented by oxygen isotope stage 3 however was characterized by short episodes when precipitation exceeded the holocene average

detrital sediment supply in the southern okinawa trough and its relation to sea level and kuroshio dynamics during the late quaternary abstract during leg 195 of the ocean drilling program site 1202 was drilled in the subtropical northwestern pacific ocean beneath the kuroshio black current between northern taiwan and the ryukyu island arc on the northern flank of the i lan ridge at 1274 m water depth the upper 110 m of the site 1202 section composed of dark grey calcareous silty clay provide an expanded record of environmental changes during the last 28 kyr the sediments were deposited at high sedimentation rates between 3 0 and 5 0 m kyr and peak values of 9 0 m kyr between 15 1 and 11 2 ka bp variations in the modes and sources of detrital sediment input as inferred from sediment granulometry mineralogy and elemental xrf scanner data reflect changes in environmental boundary conditions related to sea level changes kuroshio variability and the climate driven modes of fluvial runoff the provenance data point to increased sediment supply from northwestern taiwan between 28 and 19 5 ka bp and from east china sources between 19 5 and 11 2 ka bp the change in provenance at 19 5 ka bp reflects increased fluvial runoff from the yangtze river and strong sediment reworking from the east china sea shelf in the course of increased humidity and postglacial sea level rise particularly after 15 1 ka bp the holocene was dominated by sediments that originated from rivers in northeastern taiwan for the pre holocene period prior to 11 2 ka bp low portions of sortable silt 63 10 m show that the kuroshio did not enter the okinawa trough because of low sea level in turn high proportions of sortable silt and sediment provenance from northeastern taiwan point to strong ocean circulation under the direct and persistent influence of the kuroshio during the holocene the reentrance of the kuroshio to the okinawa trough was heralded by two pulses in relative current strengthening at 11 2 and 9 5 ka bp as documented by stepwise increases in sortable silt in the lower holocene section from a global perspective environmental changes in the southern okinawa trough show affinities to climate change in the western pacific warm pool with little influence of climate teleconnections from the north atlantic realm otherwise seen in many other marine and terrestrial palaeoclimate records from southeastern asia

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

astronomical forcing of the east asian monsoon mirrored by the composition of pliocene south china sea sediments abstract high precision major and minor element records of pliocene core intervals from ocean drilling program odp site 1145 located in the northern part of the south china sea were generated at a 5 cm approximately 2 kyr resolution from the geochemical data distinct proxies those indicating changes in detrital matter provenance as well as those indicating productivity variations could be derived both the terrigenous input to the northern south china sea k si and variations in productivity ba al show a response to insolation forced monsoon variability while the fluvial input k si responds to changes in the summer monsoon productivity increases as documented by ba enrichments seem to reflect variations in winter monsoon intensity a stronger winter monsoon may have increased nutrient availability via dust input and or upwelling phenomena according to our geochemical proxy records summer and winter monsoons are approximately 180 out of phase this may imply forcing of the winter monsoon through southern hemisphere summer insolation maxima the k si ratio shows a linear correlation with the la90 1 0 5 northern hemisphere summer insolation record and has therefore been used to create an astronomical timescale for the investigated sediments of odp site 1145 carbonate contents and corresponding color reflectances display 41 and 100 kyr cycles we propose that these do not reflect glacial cycles but are rather the result of an interference signal of dilution by fluvial and eolian terrigenous material and carbonate production burial flux a sudden onset of gradual changes in sediment composition occurs after 3 0 ma this is also documented by an increase in sedimentation rates and may be caused by enhanced fluvial input from the pearl river due to intensified weathering rates on the asian continent this may be linked to tectonic processes around the himalayan tibetan complex and its consequences regarding land sea heating and atmospheric circulation

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

a new perspective for the sediment provenance evolution of the middle okinawa trough since the last deglaciation based on integrated methods abstract the sediment in the okinawa trough ot preserves considerable information regarding land ocean interactions and palaeoenvironmental evolution in the east asian marginal seas more specifically the sediment provenance in the ot must be studied to recover this information however arguments about this remain especially regarding the contribution of yellow river yr derived materials to middle ot depositions to resolve this problem we systematically investigated a gravity core m063 05 3 87 m in length since the last deglaciation collected from the middle ot by integrating environmental magnetism diffuse reflectance spectroscopy and transmission electron microscopy as well as analyses of sediment grain size clay mineralogy and major elements our results indicated that sediment from the yr has contributed dominantly to this core since the last deglaciation limited contributions were also made from the yangtze river and taiwan rivers during the holocene terrigenous inputs derived from the yr could be well characterized by the ratio of hematite hematite goethite additionally the kuroshio current kc activity since the last deglaciation which is an important influencing factor for sediment provenance changes was well deciphered using a new proxy reldm relative contribution of detrital ferrimagnetic minerals to bulk magnetic properties based on comprehensive analyses of our results and previously published studies we hypothesised that during the last deglaciation abundant resuspended sediment from the palaeo yr mouth was transported to the east china sea ecs continental shelf edge and the northern ot through seaward bottom flow and further spread into the middle ot since the middle to late holocene the central mud area of the south yellow sea and the mud area southwest off cheju island may have become the main sources to provide yr derived materials to the middle ot however the mud area derived sediment could only be restricted to a small range owing to the hindrance of the strengthened kc this study provides a new perspective for sediment provenance evolution of the middle ot since the last deglaciation and proposes new methods and parameters for future research on palaeoenvironmental evolution in the ecs

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals

experimental study on the gas phase permeability of montmorillonite sediments in the presence of hydrates abstract permeability is a key parameter influencing fluids flow capacity and the gas production rate of the marine hydrate bearing sediments in this study a series of experiments were carried out to find out the dependence of the gas phase permeability of montmorillonite on different hydrate saturations at effective axial stresses of 1 mpa 3 mpa and an experimental study of the decomposition of methane hydrate mh by depressurization was carried out it is found that with the increase of gas hydrate saturation the gas phase permeability of montmorillonite shows a trend of decreasing first and then increasing due to the effect of blockage of hydrate particles and the increase of pores in inter aggregate zones during methane hydrate formation furthermore the gas phase permeability of clay clearly decreases gradually with the increasing decomposition time under different hydrate saturations due to the formation of the bound water and the swelling of clay the magnitude of ch4 coefficient of permeability k a and that of transmission d reache 10 7and 10 8 respectively k a is also known as hydraulic conductivity in the darcy law it is defined as the unit flow rate under the unit hydraulic gradient indicating the difficulty of the fluid passing through the pore skeleton and d is the coefficient of transmission based on a modified form of fick s law which is a function of the volume mass properties of the soil and the gas density after the complete decomposition of the hydrate the permeability coefficient k a decreases with the increase of initial hydrate saturation when 4 02 s h 15 15 however 15 15 s h 27 26 the values of k a increase with the increase of initial hydrate saturation these experiments helped us understand some important aspects of mh behavior such as saturation of hydrate formation effective stress and permeability change during decomposition this work could be useful to research on the production efficiency of marine gas hydrate reservoir

magnetic properties as tracers for source to sink dispersal of sediments a case study in the taiwan strait abstract different lithologies between taiwan and southeastern china lead to diverse mineralogical composition for weathering products derived from the two shores of the taiwan strait pyrrhotite and magnetite are respectively the dominant magnetic minerals associated with fluvial sediments from western taiwan and southeastern china while magnetite commonly co exists with pyrrhotite in sediments sourced from taiwan pyrrhotite has not been found in sediments sourced from mainland china associated with such a distinction are vast differences in magnetic properties including magnetic susceptibility sirm hirm and the s ratio which can be used to study the provenances of sediments in the taiwan strait and adjoining marginal seas based on any two of these parameters the magnetic characteristics of much of the taiwan strait sediment can be explained using a two endmember mixing model source to sink dispersal of sediments in the taiwan strait can then be traced from the distribution of these parameters the results not only corroborate an earlier study based on radionuclides and particle size distribution huh et al 2011 but reveal more diagnostic details besides spatial distribution based on a large number 216 of surface sediments we also analyzed temporal variation of magnetic properties in six well dated cores collected at key sites along the sediment source to sink pathways from profiles of these parameters in cores from the middle of the northern taiwan strait it is calculated that sediment supply from taiwan has increased substantially in the past five decades which may very well be related to accelerated land use and increased frequency of intense rainfalls in taiwan during the same period the approach described in this work may be extended to other source to sink systems around the world and through time especially the mountainous islands fringing the pacific and indian oceans in southeastern asia as with taiwan these islands have high denudation rates and pyrrhotite is in all likelihood a mineral characteristic of their metamorphic terrains

surface water evolution of the eastern east china sea during the last 36 000 years abstract planktic foraminifera have been studied in two high resolution cores raised from the continental slope of the eastern east china sea ecs to reconstruct the surface water history ams 14c dating on fifteen horizons revealed that the two cores kh82 4 14 and rn80 pc3 contain continuous records of the last 36 and 17 thousand cal years respectively thirty one planktic foraminiferal species which are commonly found in the present western north pacific and the ecs are recognized in down core samples three faunal phases iii ii and i distinguished by characteristic planktic foraminiferal assemblages suggest three major paleoenvironmental stages of the surface water of the eastern ecs since 36 000 yr b p 1 a stage influenced by coastal water from 36 000 to 19 500 yr b p 2 a stage also influenced by coastal water and extremely low salinity from 19 500 to 10 500 yr b p and 3 a stage controlled by the modern open sea water related to the kuroshio with both higher temperature and higher salinity since 10 5 8 5 thousand years b p oxygen isotope records of the planktic foraminiferal species g bulloides show that the three planktic foraminiferal faunal phases correspond to the last glacial deglacial and postglacial stages respectively the planktic foraminiferal assemblage during the deglacial stage which is represented by high percentages of g quinqueloba is quite different from those during the glacial and postglacial stages linked to a large amount of river discharge from the chinese continent a negative oxygen isotope excursion in g bulloides during the same period is highly correlated to the g quinqueloba anomaly also indicating a decrease in surface water salinity furthermore the sedimentation rate of core kh82 4 14 during 19 15 thousand years b p is much higher than the rates during the glacial and postglacial stages suggesting a great increase in the supply of terrigenous material related to an increased river and sediment discharge during the early deglaciation the coastal water influenced stage of the eastern ecs terminated gradually at 10 5 8 5 thousand years b p since the warm kuroshio current and its branches flowed in the eastern ecs as today the formation of the postglacial surface water circulation pattern in the eastern ecs was closely related to the flow patterns of the kuroshio current

contrasting behavior of hematite and goethite within paleosol s5 of the luochuan profile chinese loess plateau 1 the chinese loess paleosol sequence provides an excellent record of long term variations in the east asian paleomonsoon for representative loess profiles paleosol units have enhanced magnetic properties compared to loess units however at some depth intervals with special paleoenvironmental conditions selective depletion of antiferromagnetic afm minerals hematite and goethite could occur resulting in complexities in accurately linking variations in magnetic properties to long term fluctuations in paleoclimate to resolve this problem we directly measured the mass concentrations of these afm minerals using second order diffuse reflectance spectroscopy drs and then correlated the drs results to high field isothermal remanent magnetization hirm from paleosol unit s5 at the luochuan profile central chinese loess plateau our results suggest that a low hirm anomaly just below the sub paleosol unit s5s1 is caused by fluctuations specifically in goethite content while the hematite concentration exhibits a maximum over the same depth interval this appears to rule out significant loss of hematite to reductive dissolution and further indicates that hematite and goethite may respond differently to changes in the paleoclimate conditions

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

clay mineral and grain size studies of sediment provenances and paleoenvironment evolution in the middle okinawa trough since 17 ka okinawa trough receives a large amount of fluvial sediment transported by complex oceanographic circulations and is an ideal location for the study of paleoceanography and paleoenvironment changes however our knowledge of the sediment provenance and paleoenvironment evolution in the trough during the past 17 ka is still limited based on high resolution grain size clay minerals and ams c 14 data of the core oki04 we present new evidences of the provenances and paleoenvironment evolution in the middle okinawa trough during the last 17 ka our results indicate that clay sized terrigenous sediment deposited in the middle okinawa trough is mainly from those rivers flowing into east china sea and yellow sea e g yangtze and yellow rivers and taiwanese rivers their contributions varied greatly in space and time during the past 17 ka from 16 5 to 13 8 ka sediment was mainly derived from the yangtze and yellow rivers with little contribution from taiwan from 13 8 to 5 4 ka the contributions from the yangtze and yellow rivers oscillated multiple times low in 13 8 11 6 ka high in 11 6 7 6 ka and back to low in 7 6 5 4 ka whereas the pattern of taiwanese contribution was opposite after 5 4 ka when the sea level was high and shoreline was far away from the okinawa trough the yangtze river and eastern taiwanese rivers became the main provenances the contribution from the yellow river decreased which is probably because yellow river mouth was far away from the middle trough sediment grain size data show that two environmentally sensitive populations are 71 7 mu m and 7 0 5 mu m the variation of the populations mean grain size and content shows that the strength of kuroshio current was weak during 16 5 11 6 ka and became strong in 11 6 5 4 ka in which tsushima warm current and yellow sea warm current formed around 8 5 and 6 5 ka respectively the strength of kuroshio current decreased in 5 4 ka and increased since 3 2 ka based on clay mineralogical analysis we find that the kaolinite chlorite could be used as a new effective indicator for the east asian winter monsoon s evolution in the trough since 17 ka c 2015 elsevier b v all rights reserved

processes controlling the geochemical composition of the south china sea sediments during the last climatic cycle abstract sediments of the upper 28 2 m of ocean drilling program odp site 1145 from the northern south china sea scs were analyzed for their geochemical composition most of the major and trace elements exhibit significant fluctuations at glacial interglacial scales implying a close relation with regional and global climate change al normalized elemental ratios can be subdivided into three principal components pc pc1 e g ca al ba al sr al displays significant glacial interglacial variation and is related to paleoproductivity in the northern scs pc2 e g k al mg al rb al is associated with the degree of chemical weathering in the source regions and shows little glacial interglacial variation pc3 e g ti al zr al reflects the relative contribution of coarse and fine grained materials in the terrigenous components of the scs sediments likely associated with changes in sea level and monsoon induced fluvial input spectral analyses indicate that paleoproductivity i e ba al in the south china sea lags hulu sanbao speleothem 18o record an indicator of annual average meteoric precipitation by 102 and indian summer monsoon multi proxy stack by 23 at the precession band indicating a close relationship with the indian summer monsoon however the chemical weathering degree in the source area pc2 is not sensitive to monsoon related changes at the precession band during the last climatic cycle

climatic interpretation of the luochuan and lingtai loess sections china based on changing iron oxide mineralogy and magnetic susceptibility abstract hematite and goethite estimated from diffuse reflectance spectra and magnetic susceptibility ms have been determined from both the luochuan and lingtai loess sections of the loess plateau of central china changing concentrations of these iron oxides and ms were used to determine paleoclimatic change based on a model that relates pedogenic production of hematite and magnetite to precipitation we propose two precipitation phases on the loess plateau during the last 2 6 ma from the wucheng red clay boundary up to paleosol s5 mis 13 precipitation on the loess plateau was moderate probably not frequently exceeding 450 mm yr and highly seasonal from s5 to the present precipitation during interglacial times has gradually increased to the present levels of 600 650 mm yr for the localities examined throughout the pleistocene spanning both glacial and interglacial conditions hematite to goethite ratios display a consistent decrease this decrease suggests that precipitation on the loess plateau has been getting less seasonal and or has been occurring during times when temperature was lower in addition to these long term changes it also appears that iron oxide records from the loess plateau exhibit 400 500 ka cycles from the wucheng red clay boundary to s5 these 400 500 ka cycles may be analogous to similar length cycles recorded in 13 c marine records in the south china sea and may be linked through weathering and silica production as a result of the asian monsoon

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

what do the hirm and s ratio really measure in environmental magnetism the hard isothermal remanent magnetization hirm and the s ratio are widely used in environmental magnetism to quantify the absolute and relative concentrations respectively of antiferromagnetic minerals hematite and goethite in mineral mixtures we demonstrate that synthetic al substituted hematite and goethite exhibit a wide range of coercivities which significantly influences the hirm and s ratio these parameters are therefore not necessarily straightforward indicators of the absolute and relative concentrations of hematite goethite to circumvent this problem we propose a new parameter the l ratio which is the ratio of two remanences after alternating field af demagnetization of an irm imparted in a 1 t field with a peak af of 100 mt and 300 mt irmaf 300mt irmaf 100mt these parameters are easily measured using modern vibrating sample or alternating gradient magnetometers changes in hirm only reflect changes in the absolute concentration of hematite and or goethite if the l ratio is relatively constant conversely l ratio fluctuations indicate variable coercivities that possibly reflect changes in the source of hematite goethite corresponding hirm and s ratio variations should be interpreted with caution in such cases the l ratio can be determined using equivalent terms depending on available instrumentation and measurement protocols for example the hirm is equivalent to irmaf 300mt likewise 0 5 sirm irm 100mt where irm 100mt represents the remanent magnetization obtained by first saturating the sample in a high field and then applying a back field of 100 mt is equivalent to irmaf 100mt the hirm 0 5 sirm irm 100mt ratio is therefore a suitable substitute for the l ratio when measurements are made with a long core magnetometer the newly proposed l ratio is straightforward to measure on a wide range of instruments and can provide significant new insights and reduce ambiguities associated with interpretation of two widely used parameters in environmental magnetism the hirm and s ratio

constraining atmospheric oxygen and seawater sulfate concentrations during paleoproterozoic glaciation in situ sulfur three isotope microanalysis of pyrite from the turee creek group western australia abstract previous efforts to constrain the timing of paleoproterozoic atmospheric oxygenation have documented the disappearance of large mass independent sulfur isotope fractionation and an increase in mass dependent sulfur isotope fractionation associated with multiple glaciations at least one of these glacial events is preserved in diamictites of the 2 4 ga meteorite bore member of the kungarra formation turee creek group western australia outcrop exposures of this unit show the transition from the boolgeeda iron formation of the upper hamersley group into clastic glaciomarine sedimentary rocks of the turee creek group here we report in situ multiple sulfur isotope and elemental abundance measurements of sedimentary pyrite at high spatial resolution as well as the occurrence of detrital pyrite in the meteorite bore member the 15 3 range of 33 s in one sample containing detrital pyrite 3 6 to 11 7 is larger than previously reported worldwide and there is evidence for mass independent sulfur isotope fractionation in authigenic pyrite throughout the section 33 s from 0 8 to 1 0 the 90 range in 34 s observed 45 5 to 46 4 strongly suggests microbial sulfate reduction under non sulfate limiting conditions indicating significant oxidative weathering of sulfides on the continents multiple generations of pyrite are preserved typically represented by primary cores with low 34 s 34 s 4 7 and enrichments in as ni and co the preservation of extremely sharp sulfur isotope gradients 30 p o 2 first became sufficiently high to permit pervasive oxidative weathering of continental sulfides yet remained low enough to permit the production and preservation of mass independent sulfur isotope fractionation

seasonality and composition of downward particulate fluxes at the continental shelf and okinawa trough in the east china sea abstract as part of the marginal sea flux experiment in the west pacific masflex program conventional sediment traps were deployed at three mooring sites on the east china sea shelf for 1 2 days during 4 seasonal cruises time series sediment traps also were deployed in the east china sea one at the northern part of the okinawa trough stn sst 1 and the other to the north west of the okinawa island sst 2 for 1 year from march 1993 to february 1994 the settling particles were analyzed for total mass flux and the abundance of major biogenic constituents organic carbon nitrogen inorganic carbon and opal on the inner shelf particulate fluxes were large and rapidly increased near the bottom throughout the year probably due to resuspended bottom sediment and suspended particles from the changjiang forming a bottom turbid layer btl on the central shelf particulate fluxes in the btl were extremely high in summer when changjiang discharge peaks possibly indicating a seasonal supply of the changjiang particles to the central shelf at the shelf edge the fluxes in the btl were significantly higher in autumn and winter than in spring and summer at the okinawa trough stations ca 1100 m particulate fluxes at 600 m depth were extremely low but increased noticeably with depth 800 and 50 m above the bottom the flux generally peaked from late autumn to early spring and was lowest during summer with an unusually large peak in september at sst1 considering that there is no strong seasonality of the primary productivity and phytoplankton biomass in the surface layers at the okinawa trough we hypothesize that the seasonality of particle fluxes at the deep waters of the trough is linked to seasonal events in shelf waters downwelling and seaward bottom flow induced by the northeast monsoon in winter favor the offshore transport of particles in the btl while in summer a transverse circulation pattern may inhibit it hu 1994 yanagi et al 1996 near bottom transport may be a key process for shelf to deep sea export of biogenic lithogenic particles as a result the continental slope and the okinawa trough may play an important role as a carbon sink for the east china sea

sediment magnetic signature of the mid holocene paleoenvironmental change in the central okinawa trough abstract the kuroshio current kc has strong effects on local paleoclimate fluctuations and the paleoenvironmental evolution of the east china sea ecs in the okinawa trough the changes in the spatial position of its long axis and or current strength since the last glacial stage have been a controversial topic a multi proxy study including both magnetic and non magnetic grain size measurements and ams 14 c dating approaches has been carried out on samples from core y179 2 53 m long recovered from the central okinawa trough to investigate the possible kc related holocene paleoenvironmental changes in the trough the core spans about the last 12 000 years and comprises dominantly clayey silt and silt magnetic measurements indicate that pseudo single domain psd magnetite of terrigenous origin is the main magnetic carriers with no apparent alteration due to early diagenesis based on physical properties the core can be divided into three zones i 0 1 05 m 7 2 cal kyr bp compared with zone iii zone i contains less abundant but coarser magnetite particles and shows notable differences in magnetic and non magnetic mineral components zone ii shows transitional features between zones i and iii in terms of magnetic properties constrained by 14 c ages zone ii coincides with the middle holocene paleoenvironmental event in the okinawa trough 7 3 7 0 cal kyr bp which was either previously identified to be associated with the re entering of the kc into the trough after its shifting away during the last glacial maximum lgm or interpreted as the kc strengthening at the same time the down core variations of magnetic properties in core y179 agree well with the environmental changes caused by the middle holocene kc related event in the okinawa trough therefore our new results provide environmental magnetic evidence for the middle holocene event in the trough