The Magnetic View on the Marine Paleoenvironment: Parameters, Techniques and Potentials of Rock Magnetic Studies as a Key to Paleoclimatic and Paleoceanographic Changes

Frederichs, Thomas; Bleil, Ulrich; Däumler, K.; Dobeneck, Tilo von; Schmidt, Andrea

doi:10.1007/978-3-642-58646-0_24

Cited by 34 publications

(32 citation statements)

References 64 publications

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“…M ar and M ir curves differ strongly by their signal character and relative amplitudes. This effect was predicted by Frederichs et al [1999] on basis of rock magnetic data of the western equatorial sediment core GeoB 1505-1.…”

Section: Magnetic Grain Size: Mixing Versus Sortingmentioning

confidence: 77%

“…Their natural remanent magnetization helps to reconstruct paleofield history, plate tectonics and sediment age [e.g., Channell et al, 2004]. Their mineralogy and granulometry enable to track sediment sources and transport pathways and to characterize depositional regimes and geochemical environments [e.g., Frederichs et al, 1999]. Magnetic proxies delineate past climates, ocean currents, and wind systems [e.g., Roberts and Turner, 1993;de Menocal and Rind, 1993;Kissel et al, 1997].…”

Section: Introductionmentioning

confidence: 99%

“…The Amazon and Saharan plumes, however, carry relatively similar magnetic signatures. In a second analysis focused exclusively on equatorial Atlantic sediments and other rock magnetic parameters [Frederichs et al, 1999], the Amazonian sediments differ from the Saharan by a higher concentration of paramagnetic minerals (e.g., clay) and a higher coercivity.…”

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confidence: 99%

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Magnetic petrology of equatorial Atlantic sediments: Electron microscopy results and their implications for environmental magnetic interpretation

et al. 2007

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[1] The magnetic microparticle and nanoparticle inventories of marine sediments from equatorial Atlantic sites were investigated by scanning and transmission electron microscopy to classify all present detrital and authigenic magnetic mineral species and to investigate their regional distribution, origin, transport, and preservation. This information is used to establish source-to-sink relations and to constrain environmental magnetic proxy interpretations for this area. . Sediments from two depths corresponding to marine isotope stages 4 and 5.5 were processed. This selection represents glacial and interglacial conditions of sedimentation for the western, central, and eastern equatorial Atlantic and avoids interferences from subsurface and anoxic processes. Crystallographic, elemental, morphological, and granulometric data of more than 2000 magnetic particles were collected by scanning and transmission electron microscopy. On basis of these properties, nine particle classes could be defined: detrital magnetite, titanomagnetite (fragmental and euhedral), titanomagnetite-hemoilmentite intergrowths, silicates with magnetic inclusions, microcrystalline hematite, magnetite spherules, bacterial magnetite, goethite needles, and nanoparticle clusters. Each class can be associated with fluvial, eolian, subaeric, and submarine volcanic, biogenic, or chemogenic sources. Large-scale sedimentation patterns are delineated as well: detrital magnetite is typical of Amazon discharge, fragmental titanomagnetite is a submarine weathering product of mid-ocean ridge basalts, and titanomagnetite-hemoilmenite intergrowths are common magnetic particles in West African dust. This clear regionalization underlines that magnetic petrology is an excellent indicator of source-to-sink relations. Hematite encrustations, magnetic spherules, and nanoparticle clusters were found at all investigated sites, while bacterial magnetite and authigenic hematite were only detected at the more oxic western site. At the eastern site, surface pits and crevices were seen on the crystal faces indicating subtle early diagenetic reductive dissolution. It was observed that paleoclimatic signatures of magnetogranulometric parameters such as the ratio of anhysteretic and isothermal remanent magnetizations can be formed either by mixing of multiple sources with separate, relatively narrow grain size ranges (western site) or by variable sorting of a single source with a broad grain size distribution (eastern site). Hematite, goethite, and possibly ferrihydrite nanoparticles occur in all sediment cores studied and have either high-coercive or superparamagnetic properties depending on their partly ultrafine grain sizes. These two magnetic fractions are generally discussed as separate fractions, but we suggest that they could actually be genetically linked.

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Section: Magnetic Grain Size: Mixing Versus Sortingmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

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Magnetic petrology of equatorial Atlantic sediments: Electron microscopy results and their implications for environmental magnetic interpretation

et al. 2007

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“…Environmental magnetic techniques identify the concentration, mineralogy and grain-size of the magnetic sediment fraction by means of fast, non-destructive and sensitive measurements that require little sample preparation (Evans and Heller, 2003;Frederichs et al, 1999). In combination with geochemical major element and pore-water analysis, the magnetic properties of marine sediments are often used as proxy for paleoclimate and paleoceanography, to trace pollutants and to indicate provenance, transport and reworking of sediments.…”

Section: Marine Environmental Magnetismmentioning

confidence: 99%

Characterization of marine near-surface sediments by electromagnetic profiling

Müller

2010

GEOPHYSICS

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II PrefaceThe research, development and implementation of an electromagnetic seafloor profiler GEM Shark has been made possible through the joint funding of the Center for Marine Environ- The main part of this cumulative thesis (Chapters 2-4) consists of three journal manuscripts (one published, two ready for submission), which are for the most part based on my own theoretical and technical developments, programming, field work and data interpretation. AbstractThis thesis investigates the theory, develops the technology and demonstrates the applicabilities for synchronous in-situ mapping of the magnetic and electric signatures of marine near-surface sediments. A marine electromagnetic profiler has been developed for coastal and shelf operations in 5 to 500 m water depths. The system was designed to resolve subtle and gradual variations in silt and clay content, porosity and diagenesis state of marine sediments at a sub-meter scale. An electromagnetic (EM) induction sensor (Geophex GEM-3)was modified for submarine operations and mounted into a special bottom-towed sled.Seafloor magnetic susceptibility and electric conductivity were calculated from the in-phase and quadrature component of the secondary electromagnetic field using a half-space inversion algorithm. Seawater conductivity was measured synchronously by an integrated conductivitytemperature-depth (CTD) probe. The electric conductivity depends on porosity, the grain-size distribution and conductivity of the pore fluid. Magnetic susceptibility was used in this study as a proxy for fine-grained terrigenous clay/silt content, diagenetically forced magnetite depletion, as well as anthropogenic contaminants.The three attached manuscripts address different applications of the modified EM profiler.The first manuscript develops the physical and technical principles of the method and presents first results regarding the facies, early diagenesis, transport, and deposition of near-surface sediments on the NW Iberian shelf. The second manuscript combines high-resolution acoustic, magnetometric, and electromagnetic profiling with sample-based rock magnetic and geochemical analyses related to submarine groundwater discharge in a Baltic Sea estuary. The third manuscript is an application of the EM profiler to study the contamination of coastal areas by ferrous objects, organic matter and heavy metal pollution for coastal zone management of the Ría de Vigo, a NW Iberian estuary. Chapter 1

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“…Amongst many others, studies by Bloemendal et al (1992), Verosub and Roberts (1995), Frederichs et al (1999) and Peters and Dekkers (2003) have demonstrated the potential of environmental magnetism to discriminate sediments by lithology, origin, depositional and post-depositional processes from their magnetic mineralogy and grain size. Vigliotti et al (1999) and Funk et al (2004) showed that a combined magnetic and geochemical analysis can identify diagenetic alterations.…”

Section: Introductionmentioning

confidence: 99%

Millennial‐scale precipitation changes over Central Africa during the late Quaternary and Holocene: evidence in sediments from the Gulf of Guinea

Itambi

Dobeneck

Adegbie

2009

J Quaternary Science

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We combine environmental magnetism, geochemical measurements and colour reflectance to study two late Quaternary sediment cores: GeoB 4905-4 at 28 30 0 N off Cameroon and GeoB 4906-3 at 08 44 0 N off Gabon. This area is suitable for investigating precipitation changes over Central and West Africa because of its potential to record input of aeolian and fluvial sediments. Three magnetozones representing low and high degree of alteration of the primary rock magnetic signals were identified. The magnetic signature is dominated by fine-grained magnetite, while residual haematite prevails in the reduced intervals, showing increase in concentration and fine grain size at wet intervals. Our records also show millennial-scale changes in climate during the last glacial and interglacial cycles. At the northern location, the past 5.5 ka are marked by high-frequency oscillations of Ti and colour reflectance, which suggests aeolian input and hence aridity. The southern location remains under the influence of the Intertropical Convergence Zone and thus did not register aeolian signals. The millennial-scale climatic signals indicate that drier and/or colder conditions persisted during the late Holocene and are synchronous with the 900 a climatic cycles observed in Northern Hemisphere ice core records.

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The Magnetic View on the Marine Paleoenvironment: Parameters, Techniques and Potentials of Rock Magnetic Studies as a Key to Paleoclimatic and Paleoceanographic Changes

Cited by 34 publications

References 64 publications

Magnetic petrology of equatorial Atlantic sediments: Electron microscopy results and their implications for environmental magnetic interpretation

Magnetic petrology of equatorial Atlantic sediments: Electron microscopy results and their implications for environmental magnetic interpretation

Characterization of marine near-surface sediments by electromagnetic profiling

Millennial‐scale precipitation changes over Central Africa during the late Quaternary and Holocene: evidence in sediments from the Gulf of Guinea

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