ORCID Profile
0000-0001-8245-0555
Current Organisation
Australian National University
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Magnetism and Palaeomagnetism | Geophysics | Palaeoclimatology | Quaternary Environments | Marine Geoscience | Geochronology | Geology | Oceanography | Inorganic Geochemistry | Physical Oceanography | Glaciology | Numerical Computation | Climate Change Processes | Tectonics
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Earth Sciences | Climate Variability (excl. Social Impacts) | Marine Oceanic Processes (excl. climate related) | Effects of Climate Change and Variability on Antarctic and Sub-Antarctic Environments (excl. Social Impacts) | Effects of Climate Change and Variability on Australia (excl. Social Impacts) | Expanding Knowledge in the Environmental Sciences | Understanding Australia's Past | Mineral Exploration not elsewhere classified |
Related Links
Publications
Rock magnetic identification and geochemical process models of greigite formation in Quaternary marine sediments from the Gulf of Mexico (IODP Hole U1319A)
Publisher: Elsevier BV
Date: 11-2008
Correlation of Himalayan exhumation rates and Asian monsoon intensity
Publisher: Springer Science and Business Media LLC
Date: 09-11-2008
DOI: 10.1038/NGEO351
Magnetotactic bacterial abundance in pelagic marine environments is limited by organic carbon flux and availability of dissolved iron
Publisher: Elsevier BV
Date: 10-2011
The new hominid skeleton from Sterkfontein, South Africa: age and preliminary assessment
Publisher: Wiley
Date: 07-1999
DOI: 10.1002/(SICI)1099-1417(199907)14:4<293::AID-JQS471>3.0.CO;2-X
End-member modelling of isothermal remanent magnetization (IRM) acquisition curves: a novel approach to diagnose remagnetization
Publisher: Oxford University Press (OUP)
Date: 08-2009
A statistical simulation of magnetic particle alignment in sediments
Publisher: Oxford University Press (OUP)
Date: 24-02-2014
DOI: 10.1093/GJI/GGU038
Estimation and propagation of uncertainties associated with paleomagnetic directions
Publisher: American Geophysical Union (AGU)
Date: 04-2016
DOI: 10.1002/2015JB012544
Concurrent tectonic and climatic changes recorded in upper Tortonian sediments from the Eastern Mediterranean
Publisher: Wiley
Date: 02-2010
Assessing the ability of first-order reversal curve (FORC) diagrams to unravel complex magnetic signals
Publisher: American Geophysical Union (AGU)
Date: 2005
DOI: 10.1029/2004JB003195
Influence of magnetostatic interactions on first-order-reversal-curve (FORC) diagrams: a micromagnetic approach
Publisher: Oxford University Press (OUP)
Date: 15-07-2004
Using non-negative matrix factorization in the unmixing of diffuse reflectance spectra
Publisher: Elsevier BV
Date: 06-2007
A Monte Carlo investigation of the representation of thermally activated single-domain particles within the day plot
Publisher: Springer Science and Business Media LLC
Date: 04-2005
New methods for unmixing sediment grain size data
Publisher: American Geophysical Union (AGU)
Date: 12-2015
DOI: 10.1002/2015GC006070
Late Miocene-early Pleistocene paleoclimate history of the Chinese Loess Plateau revealed by remanence unmixing
Publisher: American Geophysical Union (AGU)
Date: 25-03-2014
DOI: 10.1002/2014GL059379
Thermal Resolution of Unblocking Temperatures (TROUT): A Method for “Unmixing” Multi‐Component Magnetizations
Publisher: American Geophysical Union (AGU)
Date: 06-2023
DOI: 10.1029/2023GC010920
Abstract: Some rocks contain multiple remanence “components,” each of which preserves a record of a different magnetic field. The temperature ranges over which these remanence components unblock can overlap, making it difficult to determine their directions. We present a data analysis tool called Thermal Resolution Of Unblocking Temperatures (TROUT) that treats the process of thermal demagnetization as a function of temperature (or alternating field demagnetization as a function of coercivity). TROUT models the unblocking temperature/coercivity distributions of components in a demagnetization experiment, allowing these distributions to overlap. TROUT can be used to find the temperatures/coercivities over which paleomagnetic directions change and when two directional components overlap resulting in curved demagnetization trajectories. When applied to specimens given multi‐component Thermoremanent Magnetizations (TRMs) in the laboratory, the TROUT method estimates the temperature at which the partial TRMs were acquired to within one temperature step, even for specimens with significant overlap. TROUT has numerous applications: knowing the temperature at which the direction changes is useful for experiments in which the thermal history of a specimen is of interest (e.g., emplacement temperature of pyroclastic deposits, re‐heating of archaeological artifacts, reconstruction of cooling rates of igneous bodies). The ability to determine whether a single component or multiple components are demagnetizing at a given temperature is useful for choosing appropriate ranges of temperatures to use in paleodirection/intensity experiments. Finally, the width of the range of temperature overlap may be useful for inferring the composition, grain size and domain state of magnetic mineral assemblages.
An Automatic Model Selection‐Based Machine Learning Framework to Estimate FORC Distributions
Publisher: American Geophysical Union (AGU)
Date: 10-2020
DOI: 10.1029/2020JB020418
Searching for single domain magnetite in the pseudo-single-domain sedimentary haystack: Implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations
Publisher: American Geophysical Union (AGU)
Date: 08-2012
DOI: 10.1029/2012JB009412
Calculating uncertainties on predictions of palaeoprecipitation from the magnetic properties of soils
Publisher: Elsevier BV
Date: 11-2013
Magnetic paleointensity stratigraphy and high-resolution Quaternary geochronology: successes and future challenges
Publisher: Elsevier BV
Date: 02-2013
A Preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements: 2. Experimental testing
Publisher: American Geophysical Union (AGU)
Date: 08-04-2011
DOI: 10.1029/2010JB007844
Estimating best fit binary mixing lines in the Day plot
Publisher: American Geophysical Union (AGU)
Date: 2012
DOI: 10.1029/2011JB008787
Timing and structure of the mid-Pleistocene transition: records from the loess deposits of northern China
Publisher: Elsevier BV
Date: 09-2002
Are hydrodynamic shape effects important when modelling the formation of depositional remanent magnetization ?
Publisher: Oxford University Press (OUP)
Date: 03-10-2007
Paleomagnetic Recording Efficiency of Sedimentary Magnetic Mineral Inclusions: Implications for Relative Paleointensity Determinations
Publisher: American Geophysical Union (AGU)
Date: 07-2019
DOI: 10.1029/2018JB016859
Abstract: Sedimentary relative paleointensity (RPI) records are often carried by complex magnetic mineral mixtures, including detrital and biogenic magnetic minerals. Recent studies have demonstrated that magnetic inclusions within larger detrital silicate particles can make significant contributions to sedimentary paleomagnetic records. However, little is known about the role such inclusions play in sedimentary paleomagnetic signal recording. We analyzed paleomagnetic and mineral magnetic data for marine sediment core MD01‐2421 from the North Pacific Ocean, offshore of central Japan, to assess how magnetic inclusions and other detrital magnetic minerals record sedimentary paleomagnetic signals. Stratigraphic intervals in which abundant magnetic inclusions dominate the magnetic signal are compared with other intervals to assess quantitatively their contribution to sedimentary RPI signals. The normalized remanence record from core MD01‐2421 does not correlate clearly with global RPI stacks, which we attribute to a demonstrated lower paleomagnetic recording efficiency of magnetic inclusions compared to other detrital magnetic minerals. We also carried out the first laboratory redeposition experiments under controlled Earth‐like magnetic fields for particles with magnetic inclusions using material from core MD01‐2421. Our results confirm that such particles can be aligned by ambient magnetic fields but with a lower magnetic recording efficiency compared to other detrital magnetic minerals, which is consistent with normalized remanence data from core MD01‐2421. Our demonstration of the role of sedimentary magnetic inclusions should have wide applicability for understanding sedimentary paleomagnetic recording.
Coupled microbial bloom and oxygenation decline recorded by magnetofossils during the Palaeocene–Eocene Thermal Maximum
Publisher: Springer Science and Business Media LLC
Date: 10-2018
DOI: 10.1038/S41467-018-06472-Y
Abstract: Understanding marine environmental change and associated biological turnover across the Palaeocene–Eocene Thermal Maximum (PETM ~56 Ma)—the most pronounced Cenozoic short-term global warming event—is important because of the potential role of the ocean in atmospheric CO 2 drawdown, yet proxies for tracing marine productivity and oxygenation across the PETM are limited and results remain controversial. Here we show that a high-resolution record of South Atlantic Ocean bottom water oxygenation can be extracted from exceptionally preserved magnetofossils—the bioinorganic magnetite nanocrystals produced by magnetotactic bacteria (MTB) using a new multiscale environmental magnetic approach. Our results suggest that a transient MTB bloom occurred due to increased nutrient supply. Bottom water oxygenation decreased gradually from the onset to the peak PETM. These observations provide a record of microbial response to the PETM and establish the value of magnetofossils as palaeoenvironmental indicators.
Low‐Temperature Magnetic Properties of Marine Sediments—Quantifying Magnetofossils, Superparamagnetism, and Maghemitization: Eastern Mediterranean Examples
Publisher: American Geophysical Union (AGU)
Date: 09-2021
DOI: 10.1029/2021JB021793
Abstract: Periodic and marked redox changes in eastern Mediterranean marine sediments drive environmental and diagenetic changes to which magnetic minerals are sensitive. Magnetic property changes, therefore, provide useful indications of paleoceanographic conditions during and after periods of organic‐rich sediment (sapropel) deposition. Magnetic properties of eastern Mediterranean sediments at room temperature have been studied for decades however, few studies have considered low‐temperature magnetic properties. Here, we investigate the low‐temperature (10–300 K) magnetic properties of different eastern Mediterranean sediment types combined with room temperature (∼300 K) magnetic properties, transmission electron microscopy, and calibrated X‐ray fluorescence elemental data to illustrate the valuable information that can be obtained from low‐temperature magnetic analysis of sediments. Our low‐temperature magnetic results suggest that magnetite magnetofossils and superparamagnetic (SP) particles occur widely in eastern Mediterranean sediments. SP particle contents are highest in diagenetically reduced intervals associated with sapropels. In contrast, magnetite magnetofossils are most abundant in oxidation fronts at the tops of sapropels, where strong redox gradients formed, but are also widespread throughout other sedimentary intervals that have not been subjected to extensive reductive diagenesis. Moreover, the surfaces of magnetite particles are maghemitized (i.e., partially oxidized) in oxidation fronts at the tops of sapropels, and in other oxic sediment intervals. Our results demonstrate the value of LT magnetic measurements for quantifying erse sedimentary magnetic signals of interest in environmental magnetism when studying paleoceanographic and paleoenvironmental processes.
A Preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements: 1. Theoretical framework
Publisher: American Geophysical Union (AGU)
Date: 08-04-2011
DOI: 10.1029/2010JB007843
Magnetic Domain State Diagnosis in Soils, Loess, and Marine Sediments From Multiple First-Order Reversal Curve-Type DiagramsTaxonomyNumbers
Publisher: American Geophysical Union (AGU)
Date: 02-2018
DOI: 10.1002/2017JB015195
A Holocene record of coastal landscape dynamics in the eastern Kimberley region, Australia
Publisher: Wiley
Date: 02-2014
DOI: 10.1002/JQS.2691
Thermal Resolution of Unblocking Temperatures (TROUT): A method for “unmixing” multi-component magnetizations
Publisher: Authorea, Inc.
Date: 03-2023
DOI: 10.22541/ESSOAR.167768129.90101937/V1
Abstract: Some rocks contain multiple remanence “components”, each of which preserves a record of a different magnetic field. The temperature ranges over which these remanence components demagnetize can overlap, making it difficult to determine their directions. We present a data analysis tool called Thermal Resolution Of Unblocking Temperatures (TROUT) that treats the process of thermal demagnetization as a function of temperature (or alternating field demagnetization as a function of coercivity). TROUT models the unblocking temperature distributions of components in a demagnetization experiment, allowing these distributions to overlap. TROUT can be used to find the temperatures over which paleomagnetic directions change and when two directional components overlap resulting in curved demagnetization trajectories. When applied to specimens given multi-component Thermoremanent Magnetizations (TRMs) in the laboratory, the TROUT method estimates the temperature at which the partial TRMs were acquired to within one temperature step, even for specimens with significant overlap. TROUT has numerous applications: knowing the temperature at which the direction changes is useful for experiments in which the thermal history of a specimen is of interest (e.g. emplacement temperature of pyroclastic deposits, re-heating of archaeological artifacts, reconstruction of cooling rates of igneous bodies). The ability to determine whether a single component or multiple components are demagnetizing at a given temperature is useful for choosing appropriate ranges of temperatures to use in paleointensity experiments. Finally, the width of the range of temperature overlap may be useful for inferring the domain state of magnetic mineral assemblages.
Abrupt shifts of the Sahara-Sahel boundary during Heinrich stadials
Publisher: Copernicus GmbH
Date: 29-05-2013
Abstract: Abstract. Relict dune fields that are found as far south as 14° N in the modern-day African Sahel are testament to equatorward expansions of the Sahara desert during the Late Pleistocene. However, the discontinuous nature of dune records means that abrupt millennial-timescale climate events are not always resolved. High-resolution marine core studies have identified Heinrich stadials as the dustiest periods of the last glacial in West Africa although the spatial evolution of dust export on millennial timescales has so far not been investigated. We use the major-element composition of four high-resolution marine sediment cores to reconstruct the spatial extent of Saharan-dust versus river-sediment input to the continental margin from West Africa over the last 60 ka. This allows us to map the position of the sediment composition corresponding to the Sahara–Sahel boundary. Our records indicate that the Sahara–Sahel boundary reached its most southerly position (13° N) during Heinrich stadials and hence suggest that these were the periods when the sand dunes formed at 14° N on the continent. Heinrich stadials are associated with cold North Atlantic sea surface temperatures which appear to have triggered abrupt increases of aridity and wind strength in the Sahel. Our study illustrates the influence of the Atlantic meridional overturning circulation on the position of the Sahara–Sahel boundary and on global atmospheric dust loading.
On the statistical analysis of the rock magnetic S-ratio
Publisher: Oxford University Press (OUP)
Date: 07-2009
Penultimate deglacial warming across the Mediterranean Sea revealed by clumped isotopes in foraminifera
Publisher: Springer Science and Business Media LLC
Date: 29-11-2017
DOI: 10.1038/S41598-017-16528-6
Abstract: The variability of seawater temperature through time is a critical measure of climate change, yet its reconstruction remains problematic in many regions. Mg/Ca and oxygen isotope ( δ 18 O C ) measurements in foraminiferal carbonate shells can be combined to reconstruct seawater temperature and δ 18 O ( δ 18 O SW ). The latter is a measure of changes in local hydrology (e.g., precipitation/evaporation, freshwater inputs) and global ice volume. But diagenetic processes may affect foraminiferal Mg/Ca. This restricts its potential in many places, including the Mediterranean Sea, a strategic region for deciphering global climate and sea-level changes. High alkalinity/salinity conditions especially bias Mg/Ca temperatures in the eastern Mediterranean (eMed). Here we advance the understanding of both western Mediterranean (wMed) and eMed hydrographic variability through the penultimate glacial termination (TII) and last interglacial, by applying the clumped isotope ( Δ 47 ) paleothermometer to planktic foraminifera with a novel data-processing approach. Results suggest that North Atlantic cooling during Heinrich stadial 11 (HS11) affected surface-water temperatures much more in the wMed (during winter/spring) than in the eMed (during summer). The method’s paired Δ 47 and δ 18 O C data also portray δ 18 O SW . These records reveal a clear HS11 freshwater signal, which attenuated toward the eMed, and also that last interglacial surface warming in the eMed was strongly lified by water-column stratification during the deposition of the organic-rich (sapropel) interval known as S5.
Post-depositional remanent magnetization lock-in for marine sediments deduced from 10Be and paleomagnetic records through the Matuyama–Brunhes boundary
Publisher: Elsevier BV
Date: 11-2011
Magnetism of Al‐substituted magnetite reduced from Al‐hematite
Publisher: American Geophysical Union (AGU)
Date: 06-2016
DOI: 10.1002/2016JB012863
Hematite (α-Fe2O3) quantification in sedimentary magnetism: limitations of existing proxies and ways forward
Publisher: Springer Science and Business Media LLC
Date: 15-06-2020
DOI: 10.1186/S40562-020-00157-5
Abstract: Determination of hematite contributions to sedimentary magnetizations is an important but difficult task in quantitative environmental studies. The poorly crystalline and fine-grained nature of hematite nanoparticles makes quantification of their concentrations in natural environments challenging using mineralogical and spectroscopic methods, while the weak magnetization of hematite and often significant superparamagnetic nanoparticle concentrations make quantification difficult using magnetic remanence measurements. We demonstrate here that much-used magnetic parameters, such as the S -ratio and ‘hard’ isothermal remanent magnetization (HIRM), tend to significantly underestimate relative and absolute hematite contents, respectively. Unmixing of isothermal remanent magnetization (IRM) acquisition curves is among the more suitable approaches for defining magnetic mineral contributions, although it has under-appreciated uncertainties that limit hematite quantification. Diffuse reflectance spectroscopy and other methods can enable relative hematite and goethite content quantification under some conditions. Combined use of magnetic, mineralogical, and spectroscopic approaches provides valuable cross-checks on estimated hematite contents such an integrated approach is recommended here. Further work is also needed to rise to the challenge of developing improved methods for hematite quantification.
Resolving the Origin of Pseudo‐Single Domain Magnetic Behavior
Publisher: American Geophysical Union (AGU)
Date: 12-2017
DOI: 10.1002/2017JB014860
Climatic control of magnetic granulometry in the Mircea Vodă loess/paleosol sequence (Dobrogea, Romania)
Publisher: Elsevier BV
Date: 04-2013
A 3 million year index for North African humidity/aridity and the implication of potential pan-African Humid periods
Publisher: Elsevier BV
Date: 09-2017
Magnetic detection and characterization of biogenic magnetic minerals: A comparison of ferromagnetic resonance and first-order reversal curve diagrams
Publisher: American Geophysical Union (AGU)
Date: 08-2014
DOI: 10.1002/2014JB011213
Discrimination of biogenic and detrital magnetite through a double Verwey transition temperature
Publisher: American Geophysical Union (AGU)
Date: 2016
DOI: 10.1002/2015JB012485
Analysis of isothermal remanent magnetization acquisition curves using the expectation-maximization algorithm
Publisher: Oxford University Press (OUP)
Date: 2002
Remanence acquisition efficiency in biogenic and detrital magnetite and recording of geomagnetic paleointensity
Publisher: American Geophysical Union (AGU)
Date: 04-2017
DOI: 10.1002/2016GC006753
Can oceanic paleothermometers reconstruct the Atlantic Multidecadal Oscillation?
Publisher: Copernicus GmbH
Date: 02-03-2011
Abstract: Abstract. Instrumental records of the North Atlantic sea surface temperature reveal a large-scale low frequency mode of variability that has become known as the Atlantic Multidecadal Oscillation (AMO). Proxy and modelling studies have demonstrated the important consequences of the AMO on other components of the climate system both within and outside the Atlantic region. Over longer time scales, the past behavior of the AMO is predominantly constrained by terrestrial proxies and only a limited number of records are available from the marine realm itself. Here we use an Earth System-Climate Model of intermediate complexity to simulate AMO-type behavior in the Atlantic with a specific focus placed on the ability of ocean paleothermometers to capture the associated surface and subsurface temperature variability. Given their lower prediction errors and annual resolution, coral-based proxies of sea surface temperature appear to be capable of reconstructing the temperature variations associated with the past AMO with an adequate signal-to-noise ratio. In contrast, the relatively high prediction error and low temporal resolution of sediment-based proxies, such as the composition of foraminiferal calcite, limits their ability to produce interpretable records of past temperature anomalies corresponding to AMO activity. Whilst the presented results will inevitably be model-dependent to some degree, the statistical framework is model-independent and can be applied to a wide variety of scenarios.
A method for unmixing magnetic hysteresis loops
Publisher: American Geophysical Union (AGU)
Date: 03-2012
DOI: 10.1029/2011JB008859
Estimating the concentration of aluminum‐substituted hematite and goethite using diffuse reflectance spectrometry and rock magnetism: Feasibility and limitations
Publisher: American Geophysical Union (AGU)
Date: 06-2016
DOI: 10.1002/2015JB012635
Sill-controlled salinity contrasts followed post-Messinian flooding of the Mediterranean
Publisher: Springer Science and Business Media LLC
Date: 11-08-2022
Paleomagnetism and cyclostratigraphy of the Middle Ordovician Krivolutsky suite, Krivaya Luka section, southern Siberian platform: Record of nonsynchronous NRM-components or a non-axial geomagnetic field?
Publisher: Springer Science and Business Media LLC
Date: 2003
Anthropogenic Forcings on the Surficial Osmium Cycle
Publisher: American Chemical Society (ACS)
Date: 09-12-2009
DOI: 10.1021/ES901887F
Abstract: Osmium is among the least abundant elements in the Earth's continental crust. Recent anthropogenic Os contamination of the environment from mining and smelting activities, automotive catalytic converter use, and hospital discharges has been documented. Here we present evidence for anthropogenic overprinting of the natural Os cycle using a ca. 7000-year record of atmospheric Os deposition and isotopic composition from an ombrotrophic peat bog in NW Spain. Preanthropogenic Os accumulation in this area is 0.10 +/- 0.04 ng m(-2) y(-1). The oldest strata showing human influence correspond to early metal mining and processing on the Iberian Peninsula (ca. 4700-2500 cal. BP). Elevated Os accumulation rates are found thereafter with a local maximum of 1.1 ng m(-2) y(-1) during the Roman occupation of the Iberian Peninsula (ca. 1930 cal. BP) and a further increase starting in 1750 AD with Os accumulation reaching 30 ng m(-2) y(-1) in the most recent s les. Osmium isotopic composition ((187)Os/(188)Os) indicates that recent elevated Os accumulation results from increased input of unradiogenic Os from industrial and automotive sources as well as from enhanced deposition of radiogenic Os through increased fossil fuel combustion and soil erosion. We posit that the rapid increase in catalyst-equipped vehicles, increased fossil fuel combustion, and changes in land-use make the changes observed in NW Spain globally relevant.
Low-temperature magnetic properties of pelagic carbonates: Oxidation of biogenic magnetite and identification of magnetosome chains
Publisher: American Geophysical Union (AGU)
Date: 12-2013
DOI: 10.1002/2013JB010381
Syntectonic emplacement of Late Cretaceous mafic dyke swarms in coastal southeastern China: Insights from magnetic fabrics, rock magnetism and field evidence
Publisher: Elsevier BV
Date: 12-2014
Correction: Corrigendum: Bipolar seesaw control on last interglacial sea level
Publisher: Springer Science and Business Media LLC
Date: 12-08-2015
DOI: 10.1038/NATURE14960
A Critical Appraisal of the Day Diagram
Publisher: American Geophysical Union (AGU)
Date: 04-2018
DOI: 10.1002/2017JB015247
Understanding fine magnetic particle systems through use of first-order reversal curve diagrams
Publisher: American Geophysical Union (AGU)
Date: 10-2014
DOI: 10.1002/2014RG000462
Diagnosing the uncertainty of taxa relative abundances derived from count data
Publisher: Elsevier BV
Date: 05-2011
Insights into magmatic processes and hydrothermal alteration of in situ superfast spreading ocean crust at ODP/IODP site 1256 from a cluster analysis of rock magnetic properties
Publisher: American Geophysical Union (AGU)
Date: 08-2014
DOI: 10.1002/2014GC005343
Incremental Graph Pattern Based Node Matching
Publisher: IEEE
Date: 04-2018
Analyzing paleomagnetic data: To anchor or not to anchor?
Publisher: American Geophysical Union (AGU)
Date: 11-2016
DOI: 10.1002/2016JB013387
Comparison and Synthesis of Sea‐Level and Deep‐Sea Temperature Variations Over the Past 40 Million Years
Publisher: American Geophysical Union (AGU)
Date: 18-11-2022
DOI: 10.1029/2022RG000775
Abstract: Global ice volume (sea level) and deep‐sea temperature are key measures of Earth's climatic state. We synthesize evidence for multi‐centennial to millennial ice‐volume and deep‐sea temperature variations over the past 40 million years, which encompass the early glaciation of Antarctica at ∼34 million years ago (Ma), the end of the Middle Miocene Climate Optimum, and the descent into bipolar glaciation from ∼3.4 Ma. We compare different sea‐level and deep‐water temperature reconstructions to build a resource for validating long‐term numerical model‐based approaches. We present: (a) a new template synthesis of ice‐volume and deep‐sea temperature variations for the past 5.3 million years (b) an extended template for the interval between 5.3 and 40 Ma and (c) a discussion of uncertainties and limitations. We highlight key issues associated with glacial state changes in the geological record from 40 Ma to present that require attention in further research. These include offsets between calibration‐sensitive versus thermodynamically guided deep‐sea paleothermometry proxy measurements a conundrum related to the magnitudes of sea‐level and deep‐sea temperature change at the Eocene‐Oligocene transition at 34 Ma a discrepancy in deep‐sea temperature levels during the Middle Miocene and a hitherto unquantified non‐linear reduction of glacial deep‐sea temperatures through the past 3.4 million years toward a near‐freezing deep‐sea temperature asymptote, while sea level stepped down in a more uniform manner. Uncertainties in proxy‐based reconstructions hinder further distinction of “reality” among reconstructions. It seems more promising to further narrow this using three‐dimensional ice‐sheet models with realistic ice‐climate‐ocean‐topography‐lithosphere coupling, as computational capacities improve.
Millennial-scale northwest African droughts related to Heinrich events and Dansgaard-Oeschger cycles: Evidence in marine sediments from offshore Senegal
Publisher: American Geophysical Union (AGU)
Date: 06-02-2009
DOI: 10.1029/2007PA001570
Prediction of Geochemical Composition from XRF Core Scanner Data: A New Multivariate Approach Including Automatic Selection of Calibration Samples and Quantification of Uncertainties
Publisher: Springer Netherlands
Date: 2015
Influence of Sea Level Change and Centennial East Asian Monsoon Variations on Northern South China Sea Sediments Over the Past 36 kyr
Publisher: American Geophysical Union (AGU)
Date: 05-2018
DOI: 10.1029/2017GC007321
Asian monsoon modulation of nonsteady state diagenesis in hemipelagic marine sediments offshore of J apan
Publisher: American Geophysical Union (AGU)
Date: 11-2016
DOI: 10.1002/2016GC006344
Abstract: We have identified millennial‐scale variations in magnetic mineral diagenesis from Pacific Ocean sediments offshore of Japan that we correlate with changes in organic carbon burial that were likely driven by Asian monsoon fluctuations. The correlation was determined by identifying offsets between the positions of fossil diagenetic fronts and climatically induced variations in organic carbon burial inferred from magnetic and geochemical analyses. Episodes of intense monsoon activity and attendant sediment magnetic mineral diagenesis also appear to correlate with Heinrich events, which supports the existence of climatic telecommunications between Asia and the North Atlantic region. Several lines of evidence support our conclusions: (1) fluctuations in down‐core magnetic properties and diagenetic pyrite precipitation are approximately coeval (2) localized stratigraphic intervals with relatively stronger magnetic mineral dissolution are linked to enhanced sedimentary organic carbon contents that gave rise to nonsteady state diagenesis (3) down‐core variations in elemental S content provide a proxy for nonsteady state diagenesis that correlate with key records of Asian monsoon variations and (4) relict titanomagnetite that is preserved as inclusions within silicate particles, rather than secondary authigenic phases (e.g., greigite), dominates the strongly diagenetically altered sediment intervals and are protected against sulfidic dissolution. We suggest that such millennial‐scale environmental modulation of nonsteady state diagenesis (that creates a temporal diagenetic filter and relict magnetic mineral signatures) is likely to be common in organic‐rich hemipelagic sedimentary settings with rapidly varying depositional conditions. Our work also demonstrates the usefulness of magnetic mineral inclusions for recording important environmental magnetic signals.
Boundary scavenging at the East Atlantic margin does not negate use of 231Pa/230Th to trace Atlantic overturning
Publisher: Elsevier BV
Date: 06-2012
A ∼12 Myr Miocene Record of East Asian Monsoon Variability From the South China Sea
Publisher: American Geophysical Union (AGU)
Date: 07-2021
DOI: 10.1029/2021PA004267
Abstract: The long‐term evolution of the East Asian Monsoon and the processes controlling its variability under changing climate boundary conditions remain enigmatic. Here, we integrate new and published high‐resolution planktic and benthic foraminiferal isotope data with proxy records for chemical weathering derived from diffuse reflectance spectroscopy at Ocean Drilling Program Site 1146 (South China Sea) to reconstruct the evolution of the summer monsoon between ∼17 and 5 Ma. Our records show that an overall warm and humid tropical climate prevailed over southeastern Asia during the Miocene Climatic Optimum, suggesting northward expansion of the tropical rain belt in response to greenhouse gas forcing. By contrast, monsoon seasonality increased during the middle Miocene Climatic Transition in tandem with Antarctic glacial expansion and global cooling. Substantial weakening of the summer monsoon between ∼12.7 and 10.9 Ma supports that decreased weathering and riverine input of nutrients and alkalinity contributed to carbonate depletion in the deep ocean during the Carbonate Crash. Intensification of monsoonal circulation and strengthening of the biological pump through the late Miocene promoted carbon burial, drawdown of atmospheric CO 2, and climate cooling during the Biogenic Bloom. These results underscore the dynamic evolution of the East Asian Monsoon throughout the middle to late Miocene. Variations in local insolation forcing and in Southern Hemisphere ice volume, influencing the latitudinal thermal gradient, evaporation‐moisture budgets, and the strength of the tropical convection, exerted major controls on the development of the monsoon.
Estimation of significance levels and confidence intervals for first-order reversal curve distributions
Publisher: American Geophysical Union (AGU)
Date: 18-05-2012
DOI: 10.1029/2012GC004115
Magnetic vortex effects on first-order reversal curve (FORC) diagrams for greigite dispersions
Publisher: Elsevier BV
Date: 11-2022
Deriving confidence in paleointensity estimates
Publisher: American Geophysical Union (AGU)
Date: 07-2010
DOI: 10.1029/2010GC003071
Characterizing magnetofossils from first-order reversal curve (FORC) central ridge signatures
Publisher: American Geophysical Union (AGU)
Date: 06-2014
DOI: 10.1002/2014GC005291
Aspects of calculating first-order reversal curve distributions
Publisher: Elsevier BV
Date: 03-2005
Soil moisture balance and magnetic enhancement in loess-paleosol sequences from the Tibetan Plateau and Chinese Loess Plateau
Publisher: Elsevier BV
Date: 2015
Domain State Diagnosis in Rock Magnetism: Evaluation of Potential Alternatives to the Day Diagram
Publisher: American Geophysical Union (AGU)
Date: 06-2019
DOI: 10.1029/2018JB017049
Author Correction: Organic carbon burial in Mediterranean sapropels intensified during Green Sahara Periods since 3.2 Myr ago
Publisher: Springer Science and Business Media LLC
Date: 09-02-2022
Terrigenous input off northern South America driven by changes in Amazonian climate and the North Brazil Current retroflection during the last 250 ka
Publisher: Copernicus GmbH
Date: 28-04-2014
Abstract: Abstract. We investigate changes in the delivery and oceanic transport of Amazon sediments related to terrestrial climate variations over the last 250 ka. We present high-resolution geochemical records from four marine sediment cores located between 5 and 12° N along the northern South American margin. The Amazon River is the sole source of terrigenous material for sites at 5 and 9° N, while the core at 12° N receives a mixture of Amazon and Orinoco detrital particles. Using an endmember unmixing model, we estimated the relative proportions of Amazon Andean material ("%-Andes", at 5 and 9° N) and of Amazon material ("%-Amazon", at 12° N) within the terrigenous fraction. The %-Andes and %-Amazon records exhibit significant precessional variations over the last 250 ka that are more pronounced during interglacials in comparison to glacial periods. High %-Andes values observed during periods of high austral summer insolation reflect the increased delivery of suspended sediments by Andean tributaries and enhanced Amazonian precipitation, in agreement with western Amazonian speleothem records. Increased Amazonian rainfall reflects the intensification of the South American monsoon in response to enhanced land–ocean thermal gradient and moisture convergence. However, low %-Amazon values obtained at 12° N during the same periods seem to contradict the increased delivery of Amazon sediments. We propose that reorganizations in surface ocean currents modulate the northwestward transport of Amazon material. In agreement with published records, the seasonal North Brazil Current retroflection is intensified (or prolonged in duration) during cold substages of the last 250 ka (which correspond to intervals of high DJF or low JJA insolation) and deflects eastward the Amazon sediment and freshwater plume.
Unmixing hysteresis loops of the late Miocene-early Pleistocene loess-red clay sequence
Publisher: Springer Science and Business Media LLC
Date: 08-07-2016
DOI: 10.1038/SREP29515
Abstract: Magnetic paleoclimatic records often represent mixed environmental signals. Unmixing these signals may improve our understanding of the paleoenvironmental information contained within these records, but such a task is challenging. Here we report an ex le of numerical unmixing of magnetic hysteresis data obtained from Chinese loess and red clay sequences. We find that the mixed magnetic assemblages of the loess and red clay sediments both contain a component characterized by a narrow hysteresis loop, the abundance of which is positively correlated with magnetic susceptibility. This component has grain sizes close to the superparamagnetic/stable single domain boundary and is attributed to pedogenic activity. Furthermore, a wasp-waisted component is found in both the loess and red clay, however, the wasp-waisted form is more constricted in the red clay. We attribute this component to a mixture of detrital ferrimagnetic grains with pedogenic hematite. The abundance of this component decreases from the base to the top of the red clay, a pattern we attribute to decreased hematite production over the Chinese Loess Plateau (CLP) due to long-term climate cooling. This work demonstrates the potential of hysteresis loop unmixing to recover quantitative paleoclimatic information carried by both low and high coercivity magnetic minerals.
Indian Ocean glacial deoxygenation and respired carbon accumulation during mid-late Quaternary ice ages
Publisher: Springer Science and Business Media LLC
Date: 10-08-2023
DOI: 10.1038/S41467-023-40452-1
Abstract: Reconstructions of ocean oxygenation are critical for understanding the role of respired carbon storage in regulating atmospheric CO 2 . Independent sediment redox proxies are essential to assess such reconstructions. Here, we present a long magnetofossil record from the eastern Indian Ocean in which we observe coeval magnetic hardening and enrichment of larger, more elongated, and less oxidized magnetofossils during glacials compared to interglacials over the last ~900 ka. Our multi-proxy records of redox-sensitive magnetofossils, trace element concentrations, and benthic foraminiferal Δδ 13 C consistently suggest a recurrence of lower O 2 in the glacial Indian Ocean over the last 21 marine isotope stages, as has been reported for the Atlantic and Pacific across the last glaciation. Consistent multi-proxy documentation of this repeated oxygen decline strongly supports the hypothesis that increased Indian Ocean glacial carbon storage played a significant role in atmospheric CO 2 cycling and climate change over recent glacial/interglacial timescales.
Assessment of Magnetic Techniques for Understanding Complex Mixtures of Magnetite and Hematite: The Inuyama Red Chert
Publisher: American Geophysical Union (AGU)
Date: 2021
DOI: 10.1029/2020JB019518
Abstract: Magnetite and hematite mixtures occur widely in nature. Magnetic unmixing of the signals recorded by these minerals can be important for assessing the origin of their respective paleomagnetic remanences and for extracting geological and paleoenvironmental information. However, unmixing magnetic signals from complex magnetite and hematite mixtures is difficult because of the weak magnetization and high coercivity of hematite. We assess here the relative effectiveness of first‐order reversal curve (FORC) and extended FORC‐type diagrams, FORC‐principal component analysis (PCA), isothermal remanent magnetization (IRM) curve decomposition, and PCA of remanent hysteretic curves for unmixing magnetic components in s les from the magnetically complex Inuyama red chert, Japan. We also further characterize the domain state and coercivity distributions of both magnetite and hematite with FORC‐PCA and IRM acquisition analysis in the red chert. We show that IRM curve decomposition can provide valuable component‐specific information linked to coercivity, while FORC‐PCA enables effective magnetic domain state identification. PCA of remanent hysteretic curves provides useful information about the most significant factors influencing remanence variations and subtle coercivity changes. To identify components in complex magnetite and hematite mixtures, we recommend PCA analysis of remanent hysteretic curves combined with FORC analysis of representative s les to identify domain states and coercivity distributions.
Magnetic properties of pelagic marine carbonates
Publisher: Elsevier BV
Date: 12-2013
Revisiting the Paleomagnetic Reversal Test: A Bayesian Hypothesis Testing Framework for a Common Mean Direction
Publisher: American Geophysical Union (AGU)
Date: 09-2018
DOI: 10.1029/2018JB016081
Signatures of Reductive Magnetic Mineral Diagenesis From Unmixing of First-Order Reversal Curves
Publisher: American Geophysical Union (AGU)
Date: 06-2018
DOI: 10.1029/2018JB015706
A protocol for variable-resolution first-order reversal curve measurements
Publisher: American Geophysical Union (AGU)
Date: 05-2015
DOI: 10.1002/2014GC005680
Measuring, Processing, and Analyzing Hysteresis Data
Publisher: American Geophysical Union (AGU)
Date: 07-2018
DOI: 10.1029/2018GC007620
Abstract: Magnetic hysteresis loops are important in theoretical and applied rock magnetism with applications to paleointensities, paleoenvironmental analysis, and tectonic studies, among many others. Information derived from these data is among the most ubiquitous rock magnetic data used by the Earth science community. Despite their prevalence, there are no general guidelines to aid scientists in obtaining the best possible data and no widely available software to allow the efficient analysis of hysteresis loop data using the most advanced and appropriate methods. Here we outline detrimental factors and simple approaches to measuring better hysteresis data and introduce a new software package called Hysteresis Loop analysis box (HystLab) for processing and analyzing loop data. Capable of reading a wide range of data formats, HystLab provides an easy‐to‐use interface allowing users to visualize their data and perform advanced processing, including loop centering, drift correction, high‐field slope corrections, and loop fitting to improve the results from noisy specimens. A large number of hysteresis loop properties and statistics are calculated by HystLab and can be exported to text files for further analysis. All plots generated by HystLab are customizable and user preferences can be saved for future use. In addition, all plots can be exported to encapsulated postscript files that are publication ready with little or no adjustment. HystLab is freely available for download at reigpaterson/HystLab and in combination with our simple measurement guide should help the paleomagnetic and rock magnetic communities get the most from their hysteresis data.
Southernmost evidence of large European Ice Sheet-derived freshwater discharges during the Heinrich Stadials of the Last Glacial Period (Galician Interior Basin, Northwest Iberian Continental Margin)
Publisher: Elsevier BV
Date: 2017
Assessment and Integration of Bulk and Component‐Specific Methods for Identifying Mineral Magnetic Assemblages in Environmental Magnetism
Publisher: American Geophysical Union (AGU)
Date: 08-2020
DOI: 10.1029/2019JB019024
Abstract: Magnetic parameters are used extensively to interpret magnetic mineral assemblage variations in environmental studies. Conventional room temperature measurements of bulk magnetic parameters, like the anhysteretic remanent magnetization (ARM) and the ratio of the susceptibility of ARM to magnetic susceptibility (χ), can reflect, respectively, magnetic mineral concentration and/or particle size variations in sediments, although they are not necessarily well suited for identifying magnetic components within in idual magnetic mineral assemblages. More advanced techniques, such as first‐order reversal curve (FORC) diagrams and low‐temperature (LT) magnetic measurements, can enable detailed discrimination of magnetic assemblages. Here, we integrate conventional bulk magnetic measurements alongside FORC diagrams, LT measurements, and X‐ray fluorescence core‐scan data, transmission electron microscope observations, and principal component analysis of FORC diagrams to identify and quantify magnetic mineral assemblages in eastern Mediterranean sediments. The studied sediments were selected because they contain complexly varying mixtures of detrital, biogenic, and diagenetically altered magnetic mineral assemblages that were deposited under varying oxic (organic‐poor marls) to anoxic (organic‐rich sapropels) conditions. Conventional bulk magnetic parameters provide continuous records of environmental magnetic variations, while more time‐consuming LT and FORC measurements on selected s les provide direct ground‐truthing of mineral magnetic assemblages that enables calculation of magnetization contributions of different end members. Thus, a combination of conventional bulk parameters and advanced magnetic techniques can provide detailed records from which the meaning of environmental magnetic signals can be unlocked.
Magnetic domain state diagnosis using hysteresis reversal curves
Publisher: American Geophysical Union (AGU)
Date: 07-2017
DOI: 10.1002/2016JB013683
Quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation
Publisher: Elsevier BV
Date: 07-2001
Unmixing magnetic remanence curves without a priori knowledge
Publisher: Oxford University Press (OUP)
Date: 08-2007
Reduced North Atlantic Central Water formation in response to early Holocene ice-sheet melting
Publisher: American Geophysical Union (AGU)
Date: 09-2010
DOI: 10.1029/2010GL043878
Quantifying magnetite magnetofossil contributions to sedimentary magnetizations
Publisher: Elsevier BV
Date: 11-2013
Environmental magnetic fingerprinting of anthropogenic and natural atmospheric deposition over southwestern Europe
Publisher: Elsevier BV
Date: 09-2021
Salt production in pre-Funan Vietnam: archaeomagnetic reorientation of briquetage fragments
Publisher: Elsevier BV
Date: 2009
A wavelet investigation of possible orbital influences on past geomagnetic field intensity
Publisher: American Geophysical Union (AGU)
Date: 03-2007
DOI: 10.1029/2006GC001498
The Senegal River mud belt: A high-resolution archive of paleoclimatic change and coastal evolution
Publisher: Elsevier BV
Date: 12-2010
Sea-level variability over five glacial cycles
Publisher: Springer Science and Business Media LLC
Date: 25-09-2014
DOI: 10.1038/NCOMMS6076
Abstract: Research on global ice-volume changes during Pleistocene glacial cycles is hindered by a lack of detailed sea-level records for time intervals older than the last interglacial. Here we present the first robustly dated, continuous and highly resolved records of Red Sea sea level and rates of sea-level change over the last 500,000 years, based on tight synchronization to an Asian monsoon record. We observe maximum 'natural' (pre-anthropogenic forcing) sea-level rise rates below 2 m per century following periods with up to twice present-day ice volumes, and substantially higher rise rates for greater ice volumes. We also find that maximum sea-level rise rates were attained within 2 kyr of the onset of deglaciations, for 85% of such events. Finally, multivariate regressions of orbital parameters, sea-level and monsoon records suggest that major meltwater pulses account for millennial-scale variability and insolation-lagged responses in Asian monsoon records.
Spectral analysis of unevenly spaced climatic time series using CLEAN: signal recovery and derivation of significance levels using a Monte Carlo simulation
Publisher: Elsevier BV
Date: 03-2002
Distribution of major elements in Atlantic surface sediments (36 degrees N-49 degrees S): Imprint of terrigenous input and continental weathering
Publisher: American Geophysical Union (AGU)
Date: 2012
DOI: 10.1029/2011GC003785
An Improved Algorithm for Unmixing First-Order Reversal Curve Diagrams Using Principal Component Analysis
Publisher: American Geophysical Union (AGU)
Date: 05-2018
DOI: 10.1029/2018GC007511
Late Miocene paleoenvironmental changes in North Africa and the Mediterranean recorded by geochemical proxies (Monte Gibliscemi section, Sicily)
Publisher: Elsevier BV
Date: 2010
Simulation of Remanent, Transient, and Induced FORC Diagrams for Interacting Particles With Uniaxial, Cubic, and Hexagonal Anisotropy
Publisher: American Geophysical Union (AGU)
Date: 12-2019
DOI: 10.1029/2019JB018050
Abstract: The diagnostic power of first‐order reversal curve (FORC) diagrams has recently been enhanced by an extended measurement protocol that yields three additional FORC‐like diagrams: the remanent (remFORC), induced (iFORC), and transient (tFORC) diagrams. Here, we present micromagnetic simulations using this extended protocol, including numerical predictions of remFORC, iFORC, and tFORC signatures for particle ensembles relevant to rock magnetism. Simulations are presented for randomly packed single‐domain (SD) particles with uniaxial, cubic, and hexagonal anisotropy, and for chains of uniaxial SD particles. Noninteracting particles have zero tFORC, but distinct remFORC and iFORC signals, that provide enhanced discrimination between uniaxial, cubic, and hexagonal anisotropy types. Increasing interactions lessen the ability to discriminate between uniaxial and cubic anisotropy but reproduces a change in the pattern of positive and negative iFORC signals observed for SD‐dominated versus vortex‐dominated s les. Interactions in SD particles lead to the emergence of a bi‐lobate tFORC distribution, which is related to formation of flux‐closure in super‐vortex states. A predicted iFORC signal associated with collapsed chains is observed in experimental data and may aid magnetofossil identification in sediments. Asymmetric FORC and FORC‐like distributions for hexagonal anisotropy are explained by the availability of multiple easy axes within the basal plane. A transition to uniaxial switching occurs below a critical value of the out‐of‐plane/in‐plane anisotropy ratio, which may allow FORC diagrams to provide insight into the stress state of hexagonal minerals, such as hematite.
Increase in African dust flux at the onset of commercial agriculture in the Sahel region
Publisher: Springer Science and Business Media LLC
Date: 07-2010
DOI: 10.1038/NATURE09213
Abstract: The Sahara Desert is the largest source of mineral dust in the world. Emissions of African dust increased sharply in the early 1970s (ref. 2), a change that has been attributed mainly to drought in the Sahara/Sahel region caused by changes in the global distribution of sea surface temperature. The human contribution to land degradation and dust mobilization in this region remains poorly understood, owing to the paucity of data that would allow the identification of long-term trends in desertification. Direct measurements of airborne African dust concentrations only became available in the mid-1960s from a station on Barbados and subsequently from satellite imagery since the late 1970s: they do not cover the onset of commercial agriculture in the Sahel region approximately 170 years ago. Here we construct a 3,200-year record of dust deposition off northwest Africa by investigating the chemistry and grain-size distribution of terrigenous sediments deposited at a marine site located directly under the West African dust plume. With the help of our dust record and a proxy record for West African precipitation we find that, on the century scale, dust deposition is related to precipitation in tropical West Africa until the seventeenth century. At the beginning of the nineteenth century, a sharp increase in dust deposition parallels the advent of commercial agriculture in the Sahel region. Our findings suggest that human-induced dust emissions from the Sahel region have contributed to the atmospheric dust load for about 200 years.
Early-Pleistocene orbital variability in Northwest Australian shelf sediments
Publisher: Authorea, Inc.
Date: 04-08-2023
DOI: 10.22541/ESSOAR.169111698.82474165/V1
Abstract: Paleoclimate proxy records from regions sensitive to humidity/aridity extremes provide valuable insights into natural forcing mechanisms underlying long-term climate variability in the wider region. One such area is Northwest Australia, where the Australian monsoon impacts its northernmost fringes, which are bordered by the Great Sandy Desert inland. Marine sediments from the Australian Northwest Shelf record fluvial run-off and aeolian dust inputs during the wet and dry seasons, respectively. The location is therefore ideal for investigating long-term variability in the Australian monsoon and Northwest Australian dust fluxes over orbital timescales. However, there are few continuous, high-resolution paleoclimate records from the Australian Northwest Shelf spanning the Early Pleistocene, and there is ambiguous orbital phasing even among Late Pleistocene paleoclimate records from the region. Here, we present geochemical and environmental magnetic proxy records of CaCO3 and dust-flux variability spanning 2.9 to 1.6 Myr ago from International Ocean Discovery Program Site U1464 on the Australian Northwest Shelf. We establish a new, orbitally-tuned chronology for Site U1464, and observe strong obliquity variability (41 kyr and 54 kyr periodicities) but almost no precession signal in our dust records. We propose that the 41 kyr cycle in Northwest Australian dust fluxes could be a linear response to the East Asian winter monsoon (EAWM) and/or summer inter-tropical insolation gradient (SITIG), whereas the 54 kyr cycle might be a non-linear response to obliquity litude modulation via the SITIG effect on cross-equatorial flows.
BEM+Born series modeling schemes for wave propagation and their convergence analysis
Publisher: Elsevier BV
Date: 04-2010
Magnetic Domain State and Anisotropy in Hematite (α‐Fe2O3) From First‐Order Reversal Curve Diagrams
Publisher: American Geophysical Union (AGU)
Date: 12-2021
DOI: 10.1029/2021JB023027
Abstract: Hematite carries magnetic signals of interest in tectonic, paleoclimatic, paleomagnetic, and planetary studies. First‐order reversal curve (FORC) diagrams have become an important tool for assessing the domain state of, and magnetostatic interactions among, magnetic particles in such studies. We present here FORC diagrams for erse hematite s les, which provide a catalog for comparison with other studies and explain key features observed for hematite. Ridge‐type signatures typical of uniaxial single‐domain particle assemblages and “kidney‐shaped” FORC signatures, and combinations of these responses, occur commonly in natural and synthetic hematite. Asymmetric features that arise from the triaxial basal plane anisotropy of hematite contribute to vertical spreading in kidney‐shaped FORC distributions and are intrinsic responses even for magnetostatically noninteracting particles. The dominant FORC distribution type in a s le (ridge, kidney‐shaped, or mixture) depends on the balance between uniaxial/triaxial switching. The identified signals explain magnetization switching and anisotropy features that are intrinsic to the magnetic properties of hematite and other materials with multiaxial magnetic anisotropy.
Climatically Modulated Dust Inputs from New Zealand to the Southwest Pacific Sector of the Southern Ocean Over the Last 410 kyr
Publisher: American Geophysical Union (AGU)
Date: 05-2021
DOI: 10.1029/2020PA003949
Abstract: Eolian mineral dust is an active agent in the global climate system. It affects planetary albedo and can influence marine biological productivity and ocean‐atmosphere carbon dynamics. This makes the understanding of the global dust cycle crucial for constraining the dust/climate relationship, which requires long‐term dust emission records for all major dust sources. Despite their importance, the sources of atmospheric dust deposited in the Southern Ocean remain poorly constrained. Eolian dust in the Pacific sector of the Southern Ocean is generally assumed to originate from Australia, with minor contributions from New Zealand. Here, we present a high‐resolution elemental record of terrestrial inputs for the past ∼410 kyr from marine sediment core PS75/100‐4 recovered from east of South Island, New Zealand. Sediment grain size is slightly finer than that of loess deposits from South Island, New Zealand, and is coarser than that of marine sediments in the Tasman Sea to the west of New Zealand, which indicates that the dust originated mainly from New Zealand and not only from Australia. Core PS75/100‐4 records lithogenic mass accumulation rates ranging from ∼0.01 to 0.69 g/cm 2 /kyr (∼0.20 g/cm 2 /kyr average), with variations over a factor of ∼3–4 over glacial versus interglacial timescales for the past 410 kyr. Our geochemical data correlate well with the Southern Ocean and Antarctic eolian dust records and suggest a westerly wind‐supplied dust signal from New Zealand. Our findings, therefore, suggest that New Zealand should be considered an important long‐term regional dust source in global dust cycle models.
Tracking provenance change during the late Miocene in the eastern Mediterranean using geochemical and environmental magnetic parameters
Publisher: American Geophysical Union (AGU)
Date: 12-2008
DOI: 10.1029/2008GC002127
A 17,000 yr paleomagnetic secular variation record from the southeast Alaskan margin: Regional and global correlations
Publisher: Elsevier BV
Date: 09-2017
Widespread occurrence of silicate-hosted magnetic mineral inclusions in marine sediments and their contribution to paleomagnetic recording
Publisher: American Geophysical Union (AGU)
Date: 12-2016
DOI: 10.1002/2016JB013109
Fingerprinting of the Atlantic meridional overturning circulation in climate models to aid in the design of proxy investigations
Publisher: Springer Science and Business Media LLC
Date: 17-03-2011
Volcanic records of the Laschamp geomagnetic excursion from Mt Ruapehu, New Zealand
Publisher: Elsevier BV
Date: 08-2017
A new astronomical timescale for the loess deposits of Northern China
Publisher: Elsevier BV
Date: 12-2000
Variable remanence acquisition efficiency in sediments containing biogenic and detrital magnetites: Implications for relative paleointensity signal recording
Publisher: American Geophysical Union (AGU)
Date: 07-2014
DOI: 10.1002/2014GC005301
Comparison and synthesis of sea-level and deep-sea temperature variations over the past 40 million years
Publisher: Wiley
Date: 24-03-2022
Comparison and synthesis of sea-level and deep-sea temperature variations over the past 40 million years
Publisher: Wiley
Date: 05-09-2022
Using time- and temperature-dependent Preisach models to investigate the limitations of modelling isothermal remanent magnetization acquisition curves with cumulative log Gaussian functions
Publisher: Oxford University Press (OUP)
Date: 04-2004
Interhemispheric symmetry of the tropical African rainbelt over the past 23,000 years
Publisher: Springer Science and Business Media LLC
Date: 12-12-2010
DOI: 10.1038/NGEO1039
Sea level and deep-sea temperature reconstructions suggest quasi-stable states and critical transitions over the past 40 million years
Publisher: American Association for the Advancement of Science (AAAS)
Date: 25-06-2021
Abstract: New reconstructions suggest quasi-stable states and critical transitions in climate over the past 40 million years.
Assessing quality of a worksite health promotion programme from participants’ views: findings from a qualitative study in Malaysia
Publisher: Wiley
Date: 03-11-2011
The pseudo-Thellier palaeointensity method: new calibration and uncertainty estimates
Publisher: Oxford University Press (OUP)
Date: 16-09-2016
DOI: 10.1093/GJI/GGW349
Multilayered Magnetic Nanobeads for the Delivery of Peptides Molecules Triggered by Intracellular Proteases
Publisher: American Chemical Society (ACS)
Date: 31-08-2017
Sub-millennial scale variations in East Asian monsoon systems recorded by dust deposits from the north-western Chinese Loess Plateau
Publisher: Elsevier BV
Date: 1999
The role of magnetostatic interactions in sediment suspensions
Publisher: Oxford University Press (OUP)
Date: 06-2006
Midlatitude Southern Hemisphere Temperature Change at the End of the Eocene Greenhouse Shortly Before Dawn of the Oligocene Icehouse
Publisher: American Geophysical Union (AGU)
Date: 12-2019
DOI: 10.1029/2019PA003679
Is there a link between geomagnetic reversal frequency and paleointensity? A Bayesian approach
Publisher: American Geophysical Union (AGU)
Date: 07-2014
DOI: 10.1002/2014JB010947
Numerical strategies for magnetic mineral unmixing
Publisher: Elsevier BV
Date: 11-2015
Directions Old and New: Palaeomagnetism and Fisher (1953) Meet Modern Statistics
Publisher: Wiley
Date: 17-11-2021
DOI: 10.1111/INSR.12481
Abstract: Most modern articles in the palaeomagnetism literature are based on statistics developed by Fisher's 1953 paper ‘Dispersion on a sphere’, which assumes independent and identically distributed (iid) spherical data. However, palaeomagnetic s le designs are usually hierarchical, where specimens are collected within sites and the data are then combined across sites to calculate an overall mean direction for a geological formation. The specimens within sites are typically more similar than specimens between different sites, and so the iid assumptions fail. This article has three principal goals. The first is to review, contrast and compare both the statistics and geophysics literature on the topic of analysis methods for clustered data on spheres. The second is to present a new hierarchical parametric model, which avoids the unrealistic assumption of rotational symmetry in Fisher's 1953 paper ‘Dispersion on a sphere’ and may be broadly useful in the analysis of many palaeomagnetic datasets. To help develop the model, we use publicly available data as a case study collected from the Golan Heights volcanic plateau. The third goal is to explore different methods for constructing confidence regions for the overall mean direction based on clustered data. Two bootstrap confidence regions that we propose perform well and will be especially useful to geophysics practitioners.
Organic carbon burial in Mediterranean sapropels intensified during Green Sahara Periods since 3.2 Myr ago
Publisher: Springer Science and Business Media LLC
Date: 13-01-2022
DOI: 10.1038/S43247-021-00339-9
Abstract: Dark organic-rich layers (sapropels) have accumulated in Mediterranean sediments since the Miocene due to deep-sea dysoxia and enhanced carbon burial at times of intensified North African run-off during Green Sahara Periods (GSPs). The existence of orbital precession-dominated Saharan aridity/humidity cycles is well known, but lack of long-term, high-resolution records hinders understanding of their relationship with environmental evolution. Here we present continuous, high-resolution geochemical and environmental magnetic records for the Eastern Mediterranean spanning the past 5.2 million years, which reveal that organic burial intensified 3.2 Myr ago. We deduce that fluvial terrigenous sediment inputs during GSPs doubled abruptly at this time, whereas monsoon run-off intensity remained relatively constant. We hypothesize that increased sediment mobilization resulted from an abrupt non-linear North African landscape response associated with a major increase in arid:humid contrasts between GSPs and intervening dry periods. The timing strongly suggests a link to the onset of intensified northern hemisphere glaciation.
Bipolar seesaw control on last interglacial sea level
Publisher: Springer Science and Business Media LLC
Date: 10-06-2015
DOI: 10.1038/NATURE14499
Abstract: Our current understanding of ocean-atmosphere-cryosphere interactions at ice-age terminations relies largely on assessments of the most recent (last) glacial-interglacial transition, Termination I (T-I). But the extent to which T-I is representative of previous terminations remains unclear. Testing the consistency of termination processes requires comparison of time series of critical climate parameters with detailed absolute and relative age control. However, such age control has been lacking for even the penultimate glacial termination (T-II), which culminated in a sea-level highstand during the last interglacial period that was several metres above present. Here we show that Heinrich Stadial 11 (HS11), a prominent North Atlantic cold episode, occurred between 135 ± 1 and 130 ± 2 thousand years ago and was linked with rapid sea-level rise during T-II. Our conclusions are based on new and existing data for T-II and the last interglacial that we collate onto a single, radiometrically constrained chronology. The HS11 cold episode punctuated T-II and coincided directly with a major deglacial meltwater pulse, which predominantly entered the North Atlantic Ocean and accounted for about 70 per cent of the glacial-interglacial sea-level rise. We conclude that, possibly in response to stronger insolation and CO2 forcing earlier in T-II, the relationship between climate and ice-volume changes differed fundamentally from that of T-I. In T-I, the major sea-level rise clearly post-dates Heinrich Stadial 1. We also find that HS11 coincided with sustained Antarctic warming, probably through a bipolar seesaw temperature response, and propose that this heat gain at high southern latitudes promoted Antarctic ice-sheet melting that fuelled the last interglacial sea-level peak.
Uncertainty Propagation in Hierarchical Paleomagnetic Reconstructions
Publisher: American Geophysical Union (AGU)
Date: 06-2020
DOI: 10.1029/2020JB019488
Estimating particle size and coercivity distributions of pigmentary hematite in red chert with thermal fluctuation tomography
Publisher: Authorea, Inc.
Date: 15-12-2022
DOI: 10.22541/ESSOAR.167108840.05677255/V1
Abstract: Pigmentary hematite carries important signals in paleomagnetic and paleoenvironmental studies. However, weak magnetism and the assumption that it has high magnetic coercivity prevents prevents routine identification of the size distribution of pigmentary hematite, especially for fine particle sizes. We present a strategy for estimating joint hematite particle volume and microcoercivity (f (V, Hk0)) distributions from low-temperature demagnetization curves and thermal fluctuation tomography (TFT) of pigmentary hematite in bulk s les of Triassic-Jurassic Inuyama red chert, Japan. The coercivity of the pigmentary hematite increases exponentially with decreasing temperature, following a modified Kneller’s law, where microcoercivity has a wide but approximately symmetric distribution in logarithmic space from ~1 tesla to tens of tesla. All of the red chert s les contain stable single domain (SSD) hematite with 35 - 160 nm diameter a significant superparamagnetic (SP) hematite population with sizes down to several nanometers also occurs in Jurassic s les. The SP/SSD threshold size is estimated to be 8 - 18 nm in these s les. The fine particle size of the pigmentary hematite is evident in its low median unblocking temperature (194 °C to 529 °C) and, thus, this hematite may contribute to all four paleomagnetic components identified in published thermal magnetization studies of the Inuyama red chert. In this work, uniaxial anisotropy and magnetization switching via coherent rotation are assumed. Uniaxial anisotropy is often dominant in fine-grained hematite, although the dominant anisotropy type should be evaluated before using TFT. This approach is applicable to studies that require knowledge of coercivity and size distributions of hematite pigments.
A Bootstrap Common Mean Direction Test
Publisher: American Geophysical Union (AGU)
Date: 08-2023
DOI: 10.1029/2023JB026983
Abstract: Paleomagnetic statistical inference is underpinned by a family of parametric null hypothesis tests. In many cases, however, paleomagnetic data do not meet the distributional assumptions of these tests, which can lead to spurious inferences. Earlier studies have proposed the bootstrap as a nonparametric alternative for paleomagnetic analysis, which can be applied even when the distributional form of the data is unknown. Key among these approaches is the bootstrap test for a common mean direction, which relies on assessment of the overlap of estimated confidence regions. In its current form, the bootstrap test for a common mean paleomagnetic direction does not consider a null hypothesis and can yield outcomes that cannot be interpreted in terms of a statistical significance level. To resolve these issues, we use recent advances to place such bootstrap tests within a null hypothesis significance testing framework, and unify them with the existing family of paleomagnetic statistical tests. Furthermore, using numerical experiments we demonstrate the applicability of such a nonparametric approach to moderately sized paleomagnetic data sets typical of modern and legacy studies. Finally, we demonstrate how a confidence region can be estimated for the common mean of two sets of directions and how known directions, such as the expected field produced by a geocentric axial dipole, can be compared to that mean.
A Bayesian Approach to the Paleomagnetic Conglomerate Test
Publisher: American Geophysical Union (AGU)
Date: 02-2018
DOI: 10.1002/2017JB014526
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