bacterial magnetite produced in water column dominates lake sediment mineral magnetism lake ely usa summary environmental magnetic studies of annually laminated sediments from lake ely northeastern pennsylvania usa indicate that bacterial magnetite is the dominant magnetic mineral in the lake sediment in previous studies of lake ely sediment the dark organic rich layers in the annual laminae were interpreted to have high intensity saturation isothermal remanent magnetizations sirms while the light coloured silt rich layers have low intensity sirms to test the hypothesis that the magnetic grains in the sediments were an authigenic product of magnetotactic bacteria rather than detrital magnetic grains eroded from the watershed we analysed samples from the water column the lake sediment and a sediment trap installed near the lake bottom direct microscopic observation of the water column samples showed the presence of magnetotactic bacteria in and below the oxic anoxic transition zone oatz to characterize the magnetic minerals rock magnetic parameters were measured for material from the water column the sediment trap and the dark and light coloured lake sediments low temperature magnetic measurements tested for the presence of magnetosomes in separated dark and light coloured layer samples numeric unmixing of the low temperature results showed that biogenic magnetites were present in the lake sediment and contributed more significantly to the sirm in the dark organic rich layers than in the light coloured inorganic silt rich layers observations under the transmission electron microscope tem of magnetic extracts also show the abundance of magnetosomes in the lake sediment the presence of live magnetotactic bacteria in the water column and the predominance of bacterial magnetites in filtered particulate matter sediment traps and recent lake sediment all suggest that bacterial magnetites are the main magnetic minerals in lake ely sediment this finding suggests that changes in environmental factors that control the productivity of magnetic bacteria in the lake likely contribute to the variability of magnetic mineral concentrations observed in the lake sediments

mineral magnetic record of late quaternary climatic changes in a high alpine lake the magnetic properties of a sediment core from a high altitude lake in the swiss alps were compared with palynological and geochemical data to link climatic and mineral magnetic variations according to pollen data the sediments extend from the present to the younger dryas i e they cover more than 10 000 years of environmental change in the alps the major change in magnetic properties corresponds to the climatic warming of the early holocene high coercivity magnetic minerals that characterize the late glacial period almost disappeared during the holocene and the concentration of ferrimagnetic minerals increased sharply the contribution of superparamagnetic grains also decreased in the holocene sediments similar variations in sp content and coercivity of smaller magnitude are found in the holocene and are interpreted to represent minor climatic variations comparison with the historical record of the last 1000 years confirms this interpretation the magnetic mineralogy the superparamagnetic contents and the irm intensity in the coarse grained late glacial sediments are similar to those measured in the catchment bedrock this indicates a detrital origin the different properties and the higher concentration of magnetic minerals in the holocene sediments are due to authigenic phases magnetic properties provide a high resolution record of climatic change they are sensitive even to small variations that are not recorded in the pollen or loi data magnetic parameters show fine scale variation and constitute a valuable supplement to conventional climatic indicators 1999 elsevier science b v all rights reserved

magnetic records of climate change sediments deposited on the sea floor on lake bottoms as well as on land as accumulations of windblown silt loess and as ancient soils paleosols formed in the loess possess many different properties that record past changes in climate geologically recoverable information on paleoclimate includes changes in global temperature as it may affect global ice volume and thus temperature of sea water net precipitation storm intensity wind speed and frequency as well as wind direction such information further contributes to interpretations about changes in oceanic and atmospheric circulation patterns as such the understanding of past climatic changes can provide baselines of natural climatic fluctuations as related to those that may be induced or influenced by human activities

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

quantitative extraction and analysis of carriers of magnetization in sediments we have applied an integrated procedure for quantitative magnetic mineral extraction based on the separation method of petersen von dobeneck vali 1986 to a range of sediment types to examine the efficiency and representative nature of the extraction process carriers of magnetization have been identified by rock magnetic measurements microscopy and x ray diffraction quantification of the extraction efficiencies is achieved by before and after extraction rock magnetic measurements susceptibility anhysteretic and isothermal remanences these magnetic measurements show that our modified extraction method extracts large proportions of the magnetization carriers in a range of sediment types e g over 75 per cent for magnetite dominated sediments the extraction efficiency is dependent on the sample magnetic mineralogy and whether the magnetic grains occur as discrete grains or as inclusions within host grains susceptibility extraction efficiencies are strongly dependent on whether the susceptibility is of paramagnetic or ferrimagnetic origin the amount of material recovered in the extract shows some inverse correlation with the density of the sediment suspension used during extraction in terms of the mineralogies extracted we identify a diverse and complex range of mineral assemblages all sizes of discrete grains of magnetite are extracted including single domain and superparamagnetic grains and chains of bacterial magnetite other commonly extracted iron and titanium oxides are haematite and ilmenite ferrimagnetic chromites and sulphides were also obtained from some samples considerable amounts of quartz and feldspar are extracted due to the presence of magnetic inclusions within these diamagnetic host grains in the deep sea sediments we examined feldspars constitute a large proportion of the extracts but are significantly less abundant in other sediments where quartz is dominant a wide variety of paramagnetic minerals was identified in the extracts including pyroxenes amphiboles chlorites micas mg cr spinels garnets ti oxides apatites tourmaline and zircon many of which contain ferrimagnetic inclusions possibly less than 0 1 m in grain size dissolution of ultrafine grains of magnetite during pre extraction carbonate dissolution as suggested by sun jackson 1994 does not occur in our samples

characterization and quantification of magnetofossils within abyssal manganese nodules from the western pacific ocean and implications for nodule formation this work was supported financially by southern university of science and technology sustech grant y01316111 to y m c the national key r d program of china 2016yfa0601903 to q s l the national natural science foundation of china 41430962 to q s l the australian research council dp160100805 and dp200100765 to a p r and the 13th five year plan project of international maritime resources investigation and development dy135 c1 1 06 and dy135 r2 1 01 to x m s and the guangdong provincial key laboratory of marine resources and coastal engineering we thank the guangzhou marine geological survey for supplying the samples

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

pbsl dating of garnet and staurolite constraints on the paleoproterozoic crustal evolution of the eastern block north china craton abstract it is well accepted that the north china craton formed by assembly of the eastern and western blocks along the trans north china orogen with cratonization in the paleoproterozoic 1 85 ma however there is controversy about the formation of the eastern and western blocks themselves especially the timing of cratonization of the eastern block the jiao liao ji orogenic belt is the most important paleoproterozoic orogenic belt in the eastern block and consists mainly of the north and south liaohe groups and the liaoji granitoids the timing of metamorphism of the liaohe group is the key to understanding the evolution of the eastern block of the north china craton because the isotope systematics of metamorphic minerals can be used to date parts of the prograde thermal histories of metamorphic belts dating of minerals such as garnet and staurolite has the distinct advantage that time information can be related directly to the pressure temperature deformation history recorded by the same mineral in this paper we present results of precise 207pb 206pb stepwise leaching pbsl dating of garnet and staurolite from the metasedimentary rocks of the south liaohe group the primitive pb and radiogenic pb are selectively extracted from garnet and straurolite by leach steps and determined by multiple collector mc icp ms the garnet and staurolite record two groups of 207pb 206pb ages at 1 93 1 91 ga and 1 86 ga respectively these constrain the time of peak metamorphism of the liaohe group during collision between the longgang block in the north and the liaonan nangrim block in the south and a subsequent post collisional event respectively our data for the south liaohe group and previously published data for the liaoji granite combined with key lithological structural and metamorphic information indicate that the cratonization of the eastern block of the north china craton occurred at 1 93 1 91 ga

the mineral magnetic properties of an annually laminated holocene lake sediment sequence in northern sweden detailed mineral magnetic measurements were conducted on a 9000 year varved lake sediment sequence in northern sweden lake sarsjon the results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments which is controlled to a large extent by the intensity of the spring snow melt in contrast the concentration of ferrimagnetic magnetite reflected by initial magnetic susceptibility and magnetic hysteresis parameters is positively correlated to the concentration of organic carbon which is most likely of an autochthonous origin this magnetite has magnetic properties that are characteristic of stable single domain magnetite grains produced by magnetotactic bacteria the paramagnetic susceptibility record clearly points to a climatic excursion in the early holocene between 6100 174 bc and 5700 167 bc which can be correlated to an d18o excursion a cold event in the greenland ice cores and lake sediments in southern germany an

glacial interglacial climatic variations at the schirmacher oasis east antarctica the first report from environmental magnetism article i nfo we discuss in this paper the first detailed environmental magnetic record of glacial interglacial climatic varia tions in the schirmacher oasis east antarctica we determined environmental magnetic properties and inter parametric ratios lf fd arm s irm arm sirm arm lf arm fd s irm lf s ratio and hirm for sediment samples of a core from the sandy lake accelerator mass spectrometer ams 14 c dates were obtained on the organic matter from bulk sediment samples the sediment core spans the past 42 5 cal ka b p the magnetic minerals are mainly detrital and catchment derived as there is no evidence for the presence of authigenic greigite bacterialmagnetite ordiageneticdissolution the lastglacialperiodischaracterizedbya high concentra tion of ferrimagnetic minerals such as titanomagnetite high values of lf sirm etc and coarse magnetic grain size low arm sirm and arm lf values and high s ratio values deglaciation in the schirmacher oasis began around 21 cal kab p as suggested by the low magnetic mineral concentration the holocene period ischaracter ized by relatively warm climatic events as seen in the low values of magnetic susceptibility which is primarily contributed by fine grained titanomagnetite resulting from pedogenesis high fd v alues several of the rela

mineral magnetic proxies of erosion oxidation cycles in tropical maar lake sediments lake tritrivakely madagascar paleoenvironmental implications abstract mineral magnetic measurements were performed on the upper 16 m of five piston cored sedimentary sequences from lake tritrivakely madagascar ams 14 c dating and correlation of the five magnetic susceptibility records allowed establishment of a composite sedimentary record of the last 46 kyr our data suggest that mineral magnetic changes result from changes in concentration of strongly ferrimagnetic terrigenous minerals and from preservation dissolution cycles of detrital iron oxides primarily high coercivity fe iii phases such as hematite in alternately oxic and anoxic depositional environments high coercivity iron oxide phases are restricted to stratigraphic intervals that are interpreted to represent dry periods with oxic conditions comparison with other paleoenvironmental proxies pollen total organic carbon lithology suggests that the sediments record relatively humid conditions before 22 kyr bp and relatively dry conditions during the last glacial maximum lgm and the early holocene such results contrast with the previous observations of relatively dry glacial conditions and humid mid holocene conditions in the summer rainfall area of east and se africa

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

the magnetic susceptibility of sedimenting material trapped in lough neagh northern ireland and its erosional significance1 the magnetic susceptibility of sedimenting material trapped at two sites in lough neagh has been measured over 1 year the magnitude of susceptibility in one of the traps correlates with rainfall in the catchment suggesting a link between channel erosion and the magnetic properties of eroded sediment

the late holocene history of gormire lake ne england and its catchment a multiproxy reconstruction of past human impact sedimentary evidence spanning the last 3500 years from cores taken from the centre of gormire lake cleveland northeast england points to two periods of deforestation and catchment erosion the first mainly late iron age romano british phase began c 200 bc and ended c ad 600 the second began c ad 1200 the time of early monastic activity and continued into the nineteenth century the chronology for the core rests on 137cs 210pb and 14c measurements and on the history of lead accumulation in the sediments the majority of the ams 14c dates are shown to be too old to varying degrees depending on the source of the organic matter in the sediments the record of vegetation change is derived from pollen analysis evidence for changes in sediment composition and source and for catchment erosion comes from magnetic measurements element analyses using xrf and organic biogeochemical analyses there is a high degree of coherence between all these lines of evidence interpretation of the magnetic record

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

unraveling the record of successive high grade events in the central zone of the limpopo belt using pb single phase dating of metamorphic minerals abstract dating of relic metamorphic assemblages can provide important information about the timing and character metamorphic grade and or pt evolution of early high grade episodes in polymetamorphic provinces using pb stepwise leaching of metamorphic silicates we have dated multiple granulite facies metamorphic episodes in the central zone cz of the limpopo belt ages of 2 52 ga were obtained from sillimanite and cogenetic garnet and ages of about 2 01 ga from titanite garnet and clinopyroxene together with new and published conventional age data from accessory phases and in the context of combined petrological and structural data these results lead us to a reinterpretation of the tectono metamorphic history of the cz three distinct high grade events at about 3 2 3 1 ga 2 65 2 52 ga and 2 0 0 05 ga are recognized each of these is suggested to correspond to a tectonic episode of distinct character a for the 3 2 ga event magmatic activity can mainly be identified best represented for example by the sand river gneisses or the messina layered intrusion the field relationships concerning the tectonometamorphic history of this early archean event are largely erased by at least two high grade metamorphic overprints b late archean 2 6 2 52 ga low pressure granulite facies metamorphism was associated with voluminous granitic and charnockitic plutonism the anticlockwise p t evolution of these granulites probably reflects deep crustal processes associated with magmatic underplating or in plating contemporaneous with vertical crustal growth of the zimbabwe craton around 2 6 ga c during the proterozoic event 2 05 1 95 ga tectonic thickening was caused by the collision of the kaapvaal and zimbabwe cratons the cz was squeezed between these two cratons and as a consequence underwent high pressure granulite facies metamorphism with a clockwise p t evolution the structural metamorphic and geochronological data can be best explained with a tectonic model that describes this final event as a dextral transpressive orogeny

possible evidence for dissimilatory bacterial magnetite dominating the magnetic properties of recent lake sediments rock magnetic measurements including low temperature susceptibility and curie temperature experiments show that the most recent sediments from the bay of vidy close to lausanne on the north shore of lake geneva switzerland are rich in superparamagnetic magnetite the 137cs dated increase in magnetite concentration coincides with the beginning of sewage de phosphatization by the addition of iron chloride extracts of fine grained magnetite imaged by transmission electron microscopy form amorphous masses visually comparable to those detected as the product of extracellular magnetite production by bacteria this is the first indication that extracellular dissimilatory magnetite may survive and make a dominant contribution to the magnetic properties of sediments final confirmation of the bacterial origin of the magnetite will depend on rrna sequencing

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

bacterial magnetite and the magnetic properties of sediments in a swedish lake a comparison of the magnetic properties of lake sediments and catchment materials from pajep njakajaure north sweden demonstrates that high concentrations of single domain sd magnetite in the upper 70 cm of gyttja in the deepest part of the basin are not of detrital origin tem and light microscope examination revealed the existence of bacterial cells and magnetosomes in the upper sediments which are responsible for the presence of the sd magnetite most of the fossil magnetosomes appear to have been dissolved through reductive processes at lower depths although some are preserved in the lower sediments and carry a post depositional remanent magnetization pdrm the results highlight the complex effects of post depositional processes on mineral magnetic assemblages and natural remanent magnetization aquisition and demonstrate how mineral magnetic measurements may be used to identify magnetic grain size changes brought about by sediment diagenesis

magnetism of the huguangyan maar lake sediments southeast china and its paleoenvironmental implications abstract the huguangyan hgy lake a typical maar lake in the southeast of china is sensitive to the evolution of the asian monsoon system including the east asian summer monsoon easm and the indian summer monsoon ism so far the mechanism of how magnetic properties of the hgy lake sediments respond to climate changes has not been well determined in this study we performed a detailed mineral magnetic analysis on the high resolution hgy sediments results revealed that finer grained magnetite superparamagnetic and single domain magnetite mixed with a small amount of goethite and hematite is the dominant magnetic mineral which is consistent with the magnetic properties of the red weathered soils collected from the catchments but differs greatly from that of the aeolian inputs therefore magnetic minerals of the hgy sediments were originated mainly from the lake catchment rather than the wind blown dust inputs considering the high tephra wall relative elevation of 10 20 m and great precipitation surface runoff by rainfall is interpreted as the main process to transport red soils into the lake the magnetic records of hgy sediments revealed that the summer monsoon was enhanced at the early holocene and then declined abruptly at the mid late holocene 5 5 kyr cal bp this pattern strongly mimics the evolution pattern of ism but is inconsistent with the easm thus we suggest that the magnetic records from hgy have the great potential to investigate the evolution of ism

a rock magnetic record from lake baikal siberia evidence for late quaternary climate change rock magnetic measurements of sediment cores from the academician ridge region of lake baikal siberia show variations related to late quaternary climate change based upon the well dated last glacial interglacial transition variations in magnetic concentration and mineralogy are related to glacial interglacial cycles using a conceptual model interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals the variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods we also infer an increased contribution of eolian sediment during the colder windier and more arid glacial conditions when extensive loess deposits were formed throughout europe and asia eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals variations in magnetic concentration and mineralogy of lake baikal sediment correlate to the specmap marine oxygen isotope record the high degree of correlation between baikal magnetic concentration mineralogy and the specmap oxygen isotope record indicates that lake baikal sediment preserves a history of climate change in central asia for the last 250 ka this correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method future work must include providing better age control and additional climate proxy data thereby strengthening the correlation of continental and marine climate records

bacterial magnetite in swedish varved lake sediments a potential bio marker of environmental change abstract detailed mineral magnetic measurements were carried out on three varved lake sediment sequences in sweden which extend to ca 7000 bc the comparison of the magnetic properties of the organic rich varved lake sediments with their respective catchment materials indicates that the magnetic properties of the sediments are dominated by relatively high concentrations of single domain magnetite magnetosomes produced by magnetotactic bacteria the dimictic nature of the lakes which help form and preserve the varves due to the weakly oxic or suboxic environment also appear to be suitable for a high degree of magnetosome preservation the concentration of the magnetosomes in two of the sequences as determined by mass specific magnetic measurements exhibits a positive linear relationship with the total organic carbon content and suggests that magnetic remanence measurements reflect lake productivity via processes of organic matter accumulation and decomposition further research should focus on the potential to use the fossil magnetosomes as proxy climate environmental change indicators and as recorders of geomagnetic field variations and behaviour

climate controlled variability of iron deposition in the central arctic ocean southern mendeleev ridge over the last 130 000 years abstract distinct brown coloured mn rich layers are common features in quaternary sediments of the central arctic ocean but their paleoenvironmental significance is disputed glacial interglacial changes in bottom water ventilation variable riverine input and diagenetic processes have all been suggested to cause the cyclicity in optical and geochemical parameters in these deposits to better assess the nature and origin of these sediment intervals and their implications for nutrient cycles we applied bulk geochemical analyses and a sequential fe extraction scheme to a sediment record covering the last 130 ka on the southern mendeleev ridge all brown layers in this core are enriched in mn but also in fe oxyhydr oxides e g ferrihydrite lepidocrocite goethite that contribute to the characteristic sediment colour phosphorus and several trace metals as co cu mo ni are also enriched indicating that both mn and fe oxyhydr oxides adsorbed p and trace metals from the water column the metal enrichments are most probably caused by a combination of enhanced mn and fe input from arctic rivers and or the erosion of shelf deposits coupled with early diagenetic processes leading to precipitation of authigenic mn and fe oxyhydr oxides close to the sediment water interface both primary supply and diagenetic recycling of metals should have been enhanced by a more intense hydrological cycle under warmer climate conditions combined with seasonal increases in productivity and reactive organic matter export during ice free conditions in the central arctic ocean consequently the studied metal oxyhydr oxide rich layers were formed under interglacial interstadial climatic conditions in contrast sheet silicate bound fe e g chlorite a second major fe pool in these sediments 15 35 of total fe is enriched between the oxide rich layers thus the delivery of fe rich sheet silicates from the east siberian hinterland or the bering sea and subsequent deposition on the mendeleev ridge was enhanced by more intense physical weathering during glacial stadial periods these contrasts in fe speciation between the brown layers and the adjacent sediments document the direct response of biogeochemical element cycles to glacial interglacial variations in river input weathering regime and sea level in the arctic ocean

mineral magnetic properties of holocene lake sediments and soils from the karsa valley lappland sweden and their relevance to palaeoenvironmental reconstruction a mineral magnetic study of lacustrine sediments and soils from the karsa valley in lappland sweden was undertaken to estimate the potential of mineral magnetic techniques in elucidating the variability of climate recorded by glacier fluctuations and soil development sediment cores from two lake basins receiving sediment input from a glacial outflow stream and their respective catchments show a mineral magnetic record that can be interpreted in terms of glacial activity and soil development dissolution of magnetite is indicated during periods of climatic amelioration and causes a high s ratio during periods of glacial advance and colder wetter climate the minerogenic sediment supply is increased and magnetite is preserved in the sediment resulting in a low s ratio variations in the s ratio can then be used as a proxy climate indicator

shrimp u pb zircon geochronology of the liaoji granitoids constraints on the evolution of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton abstract the paleoproterozoic jiao liao ji belt lies at the eastern margin of the eastern block of the north china craton and is composed mainly of the liaohe group and the liaoji granitoids the liaoji granitoids are divisible into pre tectonic magnetite and hornblende biotite monzogranitic gneisses and post tectonic or anorogenic porphyritic monzogranites and alkaline syenites shrimp u pb zircon geochronology combined with cathodoluminescence cl imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the history of the paleoproterozoic jiao liao ji belt shrimp u pb zircon analyses reveal that the pre tectonic magnetite monzogranitic gneisses were emplaced in the period 2176 2166 ma and metamorphosed at 1914 ma and the pre tectonic hornblende biotite monzogranitic gneisses were emplaced at 2150 2143 ma these data demonstrate that the pre tectonic monzogranitic gneisses of the liaoji granitoids were not younger than the deposition of the liaohe group as previously considered since the latter contains a large amount of 2100 2000 ma detrital zircons in contrast the pre tectonic monzogranitic gneisses of the liaoji granitoids or similar aged granitoids may have been an important component of the provenance for the liaohe group shrimp u pb zircon analyses also reveal that the post tectonic porphyritic monzogranites and granites in the jiao liao ji belt were emplaced at 1875 10 and 1856 31 ma respectively simultaneously with the emplacement of the alkaline syenites that was dated at 1857 20 and 1843 23 ma similar post tecotnic or anorogenic granites are not only limited to the jiao liao ji belt but are also found in the north and south korea suggesting that the 1 85 ga post tectonic or anorogenic granitic magmatic event may have occurred in both the korean peninsula and the eastern block of the north china craton the shrimp zircon ages of this study combined with lithological structural metamorphic and geochemical data is consistent with a rift closure model which suggests that the archean complexes on the northern and southern sides of the jiao liao ji belt were originally situated on a single continental block that underwent paleoproterozoic rifting associated with the formation of the liaohe group and liaoji granitoids and closed upon itself at 1 9 ga

a high resolution sediment record of east asian summer monsoon from the northern south china sea spanning the past 7500 years high resolution holocene marine sediment records are limited which hampers our understanding of paleomonsoon evolution continental shelf sediment records are derived mainly from terrestrial weath

52 000 years of environmental history in zacapu basin michoacan mexico the magnetic record abstract mineral magnetic and total organic carbon toc measurements were performed on a 10 9 m long core from zacapu basin central mexico the sequence dated by ams 14 c spans the last ca 52 kyr curie temperature measurements low temperature susceptibility and low temperature remanence indicate that the magnetic fraction is characterized by oxidized titanomagnetites with variable ti content low s 300 ratios reflect the existence of high coercivity iron oxide phases these characteristics are considered to reflect the presence of goethite rather than hematite formed in relatively wet organic conditions where soil forming processes were intense comparison between magnetic and toc results suggests that the sediments record relatively humid conditions before 35 kyr bp and a later trend towards drier conditions a probable hiatus is recorded before 25 kyr and relatively dry conditions after this time that persisted throughout the late glacial maximum and mid holocene at 4 8 kyr these results contrast with previous observations of deep lake phases in the neighboring lake patzcuaro considered to be result of increased precipitation between 34 and 21 kyr bp

combined use of magnetometry and spectroscopy for identifying magnetofossils in sediments identification of the mineral remains of magnetotactic bacteria mtb known as magnetofossils is of particular interest because their occurrence can be used for environmental and climatic reconstructions single domain magnetite particles which are biomineralized in the cell body of mtb have characteristic properties that can be used to detect their fossil remains acquisition of anhysteretic and isothermal remanent magnetization arm and irm first order reversal curve forc diagrams and ferromagnetic resonance fmr spectra were used to detect the magnetic mineral inventory in holocene lake sediments a comparative analysis in terms of the discriminatory power of these methods is presented the forc diagrams contain two distinct features a sharp horizontal ridge centered on the horizontal axis bc and a feature with symmetric spread along the vertical bb axis the coercivity spectra derived from the central ridge coincides with that derived from arm and irm acquisition curves and is compatible with the presence of noninteracting linear chains of single domain magnetite the second feature on forc diagrams is indicative of interacting particles in clusters in the fmr spectra from bulk sediment two populations are separated empirically based on the forc information an asymmetric signal is taken to describe the population which contains single domain particles in clusters empirical spectral separation of this contribution results in fmr spectra that are similar to those of intact mtb which strongly suggests that a fraction of linear magnetosome chains is present combination of fmr and forc results demonstrates the strong potential of these methods for identifying magnetofossils based on alignment and interaction patterns of magnetic particles

mineral magnetic record of environment in late pleistocene and holocene sediments lake manas xinjiang china a study of magnetic parameters was carried out on a late pleistocene and holocene sedimentary sequence 5 m from lake manas northern xinjiang china that has already been ana lysed for bulk sediment mineralogy stables isotopes from carbon ates and biogenic material magnetic minerals confirm major changes in palaeoenvironmental and palaeohydrological conditions that were deduced from other methods they also provide complementary information on changes in the lake system during the early and middle holocene the most important mineral mag netic change results from the authigenic formation of ferrimagnetic greigite fe3s 4 during the lacustrine episodes dated from 8 7 kyr b p to 5 5 kyr b p 380 335 cm and from 4 5 kyr b p to 3 5 kyr b p 320 285 cm respectively our data also indicate an abrupt break in sedimentary conditions which coincides with a short term retmxtowards dry climatic conditions around 3 5 kyr b p which was only suggested from other proxy data

a biogenic origin for anomalous fine grained magnetic material at the paleocene eocene boundary at wilson lake new jersey 1 the paleocene eocene thermal maximum which occurred 55 5 ma was caused by a massive release of carbon as indicated by an 3 negative carbon isotope excursion recorded in the marine atmospheric and terrestrial reservoirs one suggested source for the carbon a cometary impactor is based on the sudden appearance and high concentration of single domain sd magnetite in paleocene eocene p e boundary cores from the north atlantic continental margin we evaluate the potential sources of sd magnetite at the p e boundary by presenting new magnetic hysteresis low temperature magnetic remanence and transmission electron microscopy data from the north atlantic coastal ocean our results show a similar increase in sd material but demonstrate that the magnetic material has a biogenic origin these findings indicate that the high concentrations of sd magnetite immediately above the p e boundary are the result of unusual accumulations and or preservation of magnetotactic bacteria such bacteria typically occupy the oxic anoxic transition zone near the sediment water interface or in the water column the high abundances of sd magnetite in sediments from across the shelf may be an artifact of nonsteady state redox conditions and exceptional preservation of sd magnetite it may also indicate that the oxic anoxic redox boundary shifted into the water column the latter explanation implies transient eutrophy of the coastal ocean in this region most likely due to seasonally enhanced runoff and increased stratification and nutrient loading

mangrove ecosystem changes during the holocene at spanish lookout cay belize abstract mangroves are halophytic plants living at the land sea interface and are therefore natural trackers of sea level multiple proxies of a continuous 8 m mangrove peat core bt 79 from spanish lookout cay belize illustrate mangrove ecosystem changes during the holocene radiocarbon measurements show this site was colonized by mangroves 8000 cal yrs bp with a significant decrease in the peat accumulation rate from 6000 to 1000 cal yrs bp stratigraphic characteristics of this peat core such as bulk density magnetic susceptibility and loss on ignition show relative uniformity inferring an uninterrupted mangrove ecosystem during a majority of the holocene this is supported by pollen data from bt 79 that show that the site has been consistently dominated by rhizophora mangle red mangrove with avicennia germinans black mangrove and laguncularia racemosa white mangrove present as well subfossil r mangle leaves are used for stable nitrogen carbon and oxygen isotope 15n 13c and 18o analyses 15n and 13c values provide a proxy of this plant s past physiology and stand structure showing that dwarf 15n

mineral magnetic analyses of sediment cores recording recent soil erosion history in central tanzania abstract sediment cores covering the period from ca 1835 to 1988 ad were retrieved from lake haubi located in a severely eroded area in the kondoa district central tanzania the results of mineral magnetic analyses undertaken on the sediment cores reflect two distinctly different depositional environments before ca 1902 ad the basin formed a seasonally inundated swamp which subsequently turned into a lake the swamp sediment is black uniform and extremely clay rich it contains antiferromagnetic minerals e g haematite but lacks ferrimagnetic minerals e g magnetite due to post depositional dissolution the lake sediment is also very clay rich but laminated here ferrimagnetic minerals magnetite dominate the magnetic assemblage the soil erosion history of the catchment has been reconstructed using results based on the mineral magnetic analyses and on the sedimentation rates obtained from 210 pb datings whereby variations in magnetic concentrations and ratios attributed to variations in sediment influx are assumed to reflect soil erosion within the catchment the results from the magnetic analyses are in general agreement with the sedimentation rates high sediment accumulation occurred around the turn of the century and increased generally since 1935 with particularly high rates between ca 1945 and 1950 and from ca 1955 to the present the reconstructed soil erosion history has been compared to both historical records of anthropogenic activity in the kondoa district and to rainfall data from this comparison we infer that effects on soil erosion from variations in rainfall are subordinate to those induced by man

characterizing magnetism of individual magnetosomes by x ray magnetic circular dichroism in a scanning transmission x ray microscope article i nfo soft x ray scanning transmission x ray microscopy stxm was used to measure the fe l2 3 x ray magnetic circular dichroism xmcd signal from individual 30 nm diameter magnetosomes in a magnetotactic bacterium specifically the marine vibrio strain mv 1 the fe l2 3 spectra recorded with circularly polarized x rays from an elliptically polarizing undulator were very similar in shape and magnitude to those of fully saturated magnetite fe3o4 as previously determined by other techniques our results show that the magnetic moments of individual magnetosomes arranged in linear chains in intact cells of strain mv 1 are all oriented in the same direction the magnitude of the xmcd signal averaged over a chain of 9 magnetosomes in one cell is similar to that of single crystal magnetite the spectral shape is slightly different and indicates that magnetosomes have excess fe ii

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

environmental influence on relative palaeointensity estimates from holocene varved lake sediments in finland abstract relative palaeointensity records were reconstructed from two sediment cores obtained from two small lakes lake lehmilampi and lake kortejarvi in eastern finland the sediments are annually laminated and they cover the last 5100 and 3700 years in lake lehmilampi and lake kortejarvi respectively mineral magnetic investigations indicate uniform magnetic properties with magnetic mineralogy dominated by single and pseudo single domain magnetite and only small variations in the concentration of magnetic minerals which makes them interesting targets for reconstructing relative palaeointensity three estimates of relative palaeointensity were obtained by normalising the natural remanent magnetisation after 30 mt alternating field af demagnetisation nrm 30mt by 1 low field magnetic susceptibility 2 anhysteretic remanent magnetisation after 30 mt af demagnetisation and 3 saturation isothermal remanent magnetisation imprinted at 1000 mt sirm 1000mt comparison of the palaeointensity estimates with relative mean x ray density reflecting variations in sediment composition suggested the normalised records were carrying an environmental imprint which contaminated especially the centennial features this interpretation was confirmed by coherence analyses which also indicated that nrm 30mt sirm 1000mt from lake lehmilampi was the most efficiently normalised despite the inevitable environmental imprint relative palaeointensity record nrm 30mt sirm 1000mt from lake lehmilampi shows similar millennial features in comparison with relative palaeointensity reconstructions from other lakes in the area archaeomagnetic records and cals7k 2 geomagnetic field model

misinterpreting proxy data for paleoclimate signals a comment on shukla et al 2020 shukla et al explored paleoclimatic signals from a 8 m thick profile of a moraine dammed lake in the central himalaya exposed due to lake burst from a flash flood in 2013 the main objective of t

magnetotaxis and acquisition of detrital remanent magnetization by magnetotactic bacteria in natural sediment first experimental results and theory 1 the widespread occurrence of magnetotactic bacteria mtb in several types of marine and freshwater sediment and the role of fossil magnetosomes magnetofossils as main remanent magnetization carriers therein has important paleomagnetic and paleoenvironmental implications despite numerous studies on mtb biology and on magnetofossil preservation in geological records no detailed information is yet available on how magnetotaxis i e the ability to navigate along magnetic field lines is performed in sedimentary environments and on how magnetofossils possibly record the earth magnetic field we provide for the first time experimental evidence for these processes mtb living in sediment are poorly aligned with the geomagnetic field contrary to what is observed in water this can explain the seemingly excessive magnetic moment of most mtb the observed alignment is sufficient for supporting magnetotaxis across the typical thickness of chemical gradients experiments with magnetofossil rich sediment suggest that a natural remanent magnetization nrm is acquired by magnetofossils in the so called benthic mixed layer where natural mtb populations usually occur the acquired nrm is proportional to the applied field at least up to 160 t and its intensity is compatible with values observed in nature for same sediment types therefore if fossil magnetosome chains are not subjected to further alteration by early diagenetic processes they can provide useful relative paleointensities we propose a preliminary model to explain early stages of magnetofossil nrm acquisition as the result of a dynamic equilibrium between magnetic torques and randomizing forces due to sediment mixing

single magnetic domains in magnetotactic bacteria magnetotactic bacteria construct an internal permanent magnetic dipole based on single magnetic domain particles of magnetite or greigite the organisms exert a high degree of control over the size and morphology of the particles this may be relevant in distinguishing biogenic from nonbiogenic iron mineral particles

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

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

bacterial magnetite in lake sediments late glacial to holocene climate and sedimentary changes in northern norway magnetic properties of sediments retrieved from a small lake in northern norway spanning the last f14500 cal years have been analyzed in detail the high resolution core with its ability to detect sub centurial variability records the rapid retreat of the fennoscandian ice sheet fis in northern lyngen and subsequently the establishment of a stable allerod to younger dryas watershed from early holocene and to the present magnetotactic bacteria mb producing stable single domain ssb magnetite become the dominating magnetic carrier the small low relief catchment area with its quartzite bedrock scattered till and vegetated surface generates a negligible contribution of detrital magnetic minerals this allows for the opportunity to follow the presence and changes of the magnetosomes during the last 10000 years a strong positive statistical relationship r 2 0 83 between the anhysteretic remanent magnetisation susceptibility varm and loss on ignition loi suggests an environmental control over the bacteria magnitude quart int 88 2002 13 that most likely is related to summer climate a comparison between the magnetic mineralogy as evident from the s ratio jirm100mt jsirm3t and the reconstructed summer temperatures from a nearby lake shows a close covariation between cooler summers and harder s ratios for a series of climatic events intervariability of loi data and other proxies such as august sea surface temperatures sst from the nordic sea suggests land ocean connections during converging phases of cooler climate where the most prominent in phase periods are approximately 1 6500 5000 2 3500 2400 and 3 1700 1000 cal years bp the most significant change in the holocene magnetic signal is initiated at f3700 cal years bp which we refer to here as the holocene turnover d 2004 elsevier b v all rights reserved

discovery prospects for a supernova signature of biogenic origin abstract approximately 2 8 myr before the present our planet was subjected to the debris of a supernova explosion the terrestrial proxy for this event was the discovery of live atoms of 60fe in a deep sea ferromanganese crust the signature for this supernova event should also reside in magnetite fe3o4 microfossils produced by magnetotactic bacteria extant at the time of the earth supernova interaction provided the bacteria preferentially uptake iron from fine grained iron oxides and ferric hydroxides using estimates for the terrestrial supernova 60fe flux combined with our empirically derived microfossil concentrations in a deep sea drill core we deduce a conservative estimate of the 60fe fraction as 60fe fe 3 6 10 15 this value sits comfortably within the sensitivity limit of present accelerator mass spectrometry capabilities the implication is that a biogenic signature of this cosmic event is detectable in the earth s fossil record

lake sediment records of atmospheric pollution in the romanian carpathians abstract short lake sediment cores from ten lakes in the romanian carpathians have been characterised both mineral magnetically and geochemically providing an assessment of the potential of these mountain lakes sediment records as a retrospective indicator of atmospheric pollution mineral magnetic characteristics suggests that recent sediments have been affected by atmospheric particulate pollution associated with fossil fuel combustion and vehicle emissions although the properties may also reflect within lake processes metal enrichment factors for contemporary sediments reveal that remote mountain lakes in this region appear to have been impacted by the long range atmospheric transport of metallic pollutants the results suggest that sites in the southern mountains are most impacted although trace metal levels are relatively modest initial findings suggest that some sites have the potential to provide lake sediment based pollution histories that will thereby contribute to a fuller europe wide understanding of the impact of atmospheric pollutants in upland regions

low temperature magnetic properties of pelagic carbonates oxidation of biogenic magnetite and identification of magnetosome chains 1 pelagic marine carbonates provide important records of past environmental change we carried out detailed low temperature magnetic measurements on biogenic magnetite bearing sediments from the southern ocean ocean drilling program odp holes 738b 738c 689d and 690c and on samples containing whole magnetotactic bacteria cells we document a range of low temperature magnetic properties including reversible humped low temperature cycling ltc curves different degrees of magnetite oxidation are considered to be responsible for the observed variable shapes of ltc curves a dipole spring mechanism in magnetosome chains is introduced to explain reversible ltc curves this dipole spring mechanism is proposed to result from the uniaxial anisotropy that originates from the chain arrangement of biogenic magnetite similar to published results for uniaxial stable single domain sd particles the dipole spring mechanism reversibly restores the remanence during warming in ltc measurements this supports a previous idea that remanence of magnetosome chains is completely reversible during ltc experiments we suggest that this magnetic fingerprint is a diagnostic indicator for intact magnetosome chains although the presence of isolated uniaxial stable sd particles and magnetically interacting particles can complicate this test magnetic measurements through the eocene section of odp hole 738b reveal an interval with distinct magnetic properties that we interpret to originate from less oxidized biogenic magnetite and enrichment of a biogenic hard component co occurrence of these two magnetic fingerprints during the late eocene in the southern ocean indicates less oxic conditions probably due to increased oceanic primary productivity and organic carbon burial

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

quantifying the concentration of ferrimagnetic particles in sediments using rock magnetic methods 1 we have developed a quantification method that uses mainly room temperature rock magnetic measurements to calculate concentrations of ferrimagnetic particles in sediments our method uses saturation magnetization ms as a total ferrimagnetic concentration proxy the saturation remanence ratio mrs ms as a magnetic grain size proxy the anhysteretic remanence ratio a mrs to estimate inter particle magnetostatic interactions and the normalized susceptibility of the ferrimagnetic fraction f ms to calculate the proportion of ultrafine superparamagnetic particles this approach eliminates the effect of dilution of the magnetic properties by weakly magnetic matter and allows the calculation of direct concentrations or fluxes for dated sedimentary profiles of constituent ferrimagnetic components we test our method on a short sediment core from an urban minnesota lake for which we calculate ferrimagnetic fluxes of four magnetic components and compare their pre and post european settlement values our quantification technique can be applied for reconstructing past environmental changes in a range of sedimentary environments and is particularly useful for large sets of samples where detailed magnetic unmixing methods are unfeasible due to time or instrument constraints

iron sulfides from magnetotactic bacteria structure composition and phase transitions using transmission electron microscopy we studied the structures and compositions of fe sulfides within cells of magnetotactic bacteria that were collected from natural habitats ferrimagnetic greigite fe3s4 occurred in all types of sulfide producing magnetotactic bacteria examined mackinawite tetragonal fes and tentatively sphalerite type cubic fes were also identified in contrast to earlier reports we did not find pyrite fes 2 or pyrrhotite fe12xs mackinawite converted to greigite over time within the bacteria that were deposited on electron microscope grids and stored in air orientation relationships between the two minerals indicate that the cubic close packed s substructure remains unchanged during the transformation only the fe atoms rearrange neither mackinawite nor cubic fes are magnetic and yet they are aligned in chains such that when converted to magnetic greigite the probable easy axis of magnetization 100 is parallel to the chain direction the resulting chains of greigite are ultimately responsible for the magnetic dipole moment of the cell both greigite and mackinawite magnetosomes can contain cu depending on the sampling locality because bacterial mackinawite and cubic fes are unstable over time only greigite crystals are potentially useful as geological biomarkers