Signatures and significance of aeolian, fluvial, bacterial and diagenetic magnetic mineral fractions in Late Quaternary marine sediments off Gambia, NW Africa

Just, J.; Dekkers, Mark J.; Dobeneck, Tilo von; Hoesel, Annelies van; Bickert, Torsten

doi:10.1029/2012gc004146

Cited by 52 publications

(60 citation statements)

References 151 publications

(190 reference statements)

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“…Although different terrigenous sediment sources dominate at specific latitudes, they are often mixed in the diffuse boundaries between such regions. Mixing of eolian dust and fluvially derived terrigenous material has been reported from low‐latitude marine sedimentary records in the northeast Atlantic (Figure 10) [ Bloemendal et al , 1988; Itambi et al , 2009, 2010b; Just et al , 2012] and the South China Sea [ Kissel et al , 2003]. Overall, these studies have consistently indicated an antiphase relationship between dust and riverine supply.…”

Section: Recent Developments In Environmental Magnetismmentioning

confidence: 67%

“… Heslop and Dillon [2007]also used the expectation that components within a mixed magnetic mineral assemblage have linearly additive magnetizations to develop end‐member modeling of IRM acquisition curves for a collection of samples. Quantitative unmixing of IRM acquisition curves is being increasingly used to unlock details of environmental processes to shed light on eolian, fluvial and biogenic components in marine environments [e.g., Köhler et al , 2008; Roberts et al , 2011b; Just et al , 2012].…”

Section: Fundamentals Of Rock and Environmental Magnetismmentioning

confidence: 99%

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Environmental magnetism: Principles and applications

Liu

Roberts

Larrasoaña

et al. 2012

Reviews of Geophysics

576

405

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

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Section: Recent Developments In Environmental Magnetismmentioning

confidence: 67%

Section: Fundamentals Of Rock and Environmental Magnetismmentioning

confidence: 99%

Environmental magnetism: Principles and applications

Liu

Roberts

Larrasoaña

et al. 2012

Reviews of Geophysics

576

405

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“…Isothermal remanent magnetization (IRM) acquisition curves are indicative for the magnetic mineral assemblage and the concentration of the different minerals. Just et al [2012] measured IRM acquisition curves using an automated 2‐G Enterprises 755R DC superconducting magnetometer for fields up to 700 mT and by using an “external” pulse magnetizer (2‐G Enterprises) for fields up 2700 mT. For further detail see Just et al [2012].…”

Section: Methodsmentioning

confidence: 99%

“…A further component, which may contribute to the fluvial load, is material advected from farther south (e.g., Geba River in Guinea‐Bissau). However, since the current velocities are moderate [ Just et al , 2012, Figure 1b], it is reasonable to assume that such advected material makes only a minor contribution to the sediment reaching the study site.…”

Section: Introductionmentioning

confidence: 99%

Multiproxy characterization and budgeting of terrigenous end‐members at the NW African continental margin

Just¹,

Heslop²,

Dobeneck³

et al. 2012

Geochem Geophys Geosyst

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[1] Grain-size, terrigenous element and rock magnetic remanence data of Quaternary marine sediments retrieved at the NW African continental margin off Gambia (gravity core GeoB 13602-1, 13 32.71′N, 17 50.96′W) were jointly analyzed by end-member (EM) unmixing methods to distinguish and budget past terrigenous fluxes. We compare and cross-validate the identified single-parameter EM systems and develop a numerical strategy to calculate associated multiparameter EM properties. One aeolian and two fluvial EMs were found. The aeolian EM is much coarser than the fluvial EMs and is associated with a lower goethite/ hematite ratio, a higher relative concentration of magnetite and lower Al/Si and Fe/K ratios. Accumulation rates and grain sizes of the fluvial sediment appear to be primarily constrained by shore distance (i.e., sea level fluctuations) and to a lesser extent by changes in hinterland precipitation. High dust fluxes occurred during the Last Glacial Maximum (LGM) and during Heinrich Stadials (HS) while the fluvial input remained unchanged. Our approach reveals that the LGM dust fluxes were $7 times higher than today's.©2012. American Geophysical Union. All Rights Reserved.1 of 18However, by far the highest dust accumulation occurred during HS 1 ($300 g m À2 yr À1 ), when dust fluxes were $80 fold higher than today. Such numbers have not yet been reported for NW Africa, and emphasize strikingly different environmental conditions during HSs. They suggest that deflation rate and areal extent of HSs dust sources were much larger due to retreating vegetation covers. Beyond its regional and temporal scope, this study develops new, in principle, generally applicable strategies for multimethod end-member interpretation, validation and flux budgeting calibration.

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“…Magnetization versus temperature curves for three samples A1, A2, and A3 located above, within, and below the M1 peak, respectively (Figures a–c), reveal a dramatic loss of magnetization between 20 and 300 K for samples A1 and A3, whereas there is a noticeable increase for the A2 sample. The low temperature experiments for A1 and A3 (Figures b and f) are characterized by converging ZFC and FC heating curves, which are consistent with the presence of goethite [ Liu et al ., ; Franke et al ., ; Just et al ., ]. There is also a clear Verwey transition in the heating curve for sample A2 and its derivative (Figure d), which is indicative of stoichiometric magnetite.…”

Section: Magnetic Mineralogy Variationsmentioning

confidence: 93%

Diagenetic modulation of the magnetic properties in sediments from the Northern Indian Ocean

Bouilloux

Valet

Bassinot

et al. 2013

Geochem Geophys Geosyst

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[1] Large changes in magnetic mineral concentration dependent parameters by more than 1 order of magnitude occur over 50-150 cm intervals in two marine sediment cores from the oxygen minimum zone in the Gulf of Aden. High-resolution sedimentological and chemical analyses indicate that these intervals are not associated with turbiditic events or sediment reworking, they do not result from changes in carbonate dilution or differences in sediment properties, and they do not correspond to volcanic layers. Magnetic mineralogical analyses reveal a change in magnetic mineral concentration from a magnetite-goethite assemblage to pure magnetite within the peak. The peaks almost disappear when the abundance of magnetic minerals is calculated after correcting for the magnetic moments of each magnetic mineral. Therefore, under the assumption that the variability of the magnetic parameters results from postdepositional mineralogical transformations, a relatively constant amount of magnetite was present at the surface of the sediment. Changes in redox conditions and nonsteady state diagenesis transformations have effectively been observed along both cores. Large values of total organic carbon coincide with poor preservation of biogenic and detrital magnetite, which reflects reductive dissolution of the finer magnetite grains. At the same levels, Fe 2þ release from reductively dissolved magnetite favored precipitation of goethite. The susceptibility peaks coincide with episodes of magnetite preservation caused by reduced surface

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Signatures and significance of aeolian, fluvial, bacterial and diagenetic magnetic mineral fractions in Late Quaternary marine sediments off Gambia, NW Africa

Cited by 52 publications

References 151 publications

Environmental magnetism: Principles and applications

Environmental magnetism: Principles and applications

Multiproxy characterization and budgeting of terrigenous end‐members at the NW African continental margin

Diagenetic modulation of the magnetic properties in sediments from the Northern Indian Ocean

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