Paleomagnetism
Magneto- and cyclostratigraphy of marine sediments
Scientists: Grasiane Luz Mathias, Lucia Korff, Thomas Frederichs, Tilo von Dobeneck
Methods: Magnetostratigraphy, Relative Paleointensities, Cyclostratigraphy
Projects: INOPEX, DFG PP 1097, IODP

Topics: Geomagnetic pole positions, field intensities and polarities vary at time scales between 100 and 1.000.000 years. These changes form the base of three paleomagnetic methods - paleosecular variation, relative paleointensity and magnetostratigraphy - which enable us to date sediment sequences of continental margins as well as deep sea basins.

Geomagnetic field reversals in the history of human evolution

Lithology impact on Relative Paleointensity records
Scientists: Daniela Hofmann, Christine Franke, Karl Fabian, Tilo von Dobeneck
Projects: DFG SPP 1097 projects Do 705/1-1 and Fa 408/1

Summary: "Relative paleointensity" (RPI) is a relatively new high-resolution magnetostratigraphic technique tying calibrated sedimentary NRM intensity records to past fluctuations of geomagnetic dipole strength. The method assumes that the intensity of post depositional remanent magnetization (PDRM) depends exclusively on the geomagnetic field strength and the concentration of the magnetic carriers. Sedimentary remanence is regarded as an equilibrium state between aligning geomagnetic and randomizing interparticle forces. Just how strong these mechanical and electrostatic forces are, depends on many petrophysical factors related to mineralogy, particle size and shape of the matrix constituents.We have therefore systematically tested the reliability of the RPI method in different sediment facies and environments, finding that grain-size, matrix and diagenesis bias effects on RPI are sufficiently significant to warrant their consideration in the calibration procedure.
Selected Publications:
Hofmann D., Fabian K. (2009)
Correcting relative paleointensity records for variations in sediment composition: Results from a South Atlantic stratigraphic network
Earth and Planetary Science Letters, 284, 34 - 43
doi: 10.1016/j.epsl.2009.03.043

Franke C., Hofmann D., von Dobeneck T. (2004)
Does lithology influence relative paleointensity records? A statistical analysis on South Atlantic pelagic sediments
Physics of the Earth and Planetary Interiors, 147, 285 - 296
doi: 10.1016/j.pepi.2004.07.004

Magnetostratigraphy in the Arctic and Southern Ocean
Scientists: Thomas Frederichs, Norbert Nowaczyk, Ulrich Bleil
Projects: in preparation (Thomas)

Summary: High geographic latitudes are highly interesting areas of paleomagnetic research under several aspects.
One of these is dating being an essential prerequisite of almost all paleoeceanographic or paleoclimatic research on marine sediments. Conventional dating tools that are usally applied to long sediment sequences like isotope stratigraphy are often unfeasable due to the lack of calcareous nannofossils or foraminifera in these areas. Thus there is large demand for alternative methods for age determination. Temporal variations of the geomagnetic field as a global signal may serve as an alternative or complementary tool.
Another aspect refers to the proximity of high latitude regions to the magnetic poles. It is still under debate whether the observation that geomagnetic excursions are apparently more frequently recorded in sediments deposited at high latitudes than in those from low latitudes is an artifact due to depositional conditions or a true feature of the Earth's magnetic field.
Selected Publication:
Hillenbrand C., Kuhn G., Frederichs T. (2009)
Record of a Mid-Pleistocene depositional anomaly in West Antarctic continental margin sediments: an indicator for ice-sheet collapse?
Quaternary Science Reviews, 28, 1147 - 1159
doi: 10.1016/j.quascirev.2008.12.010

Knies J., Matthiessen J., Mackensen A., Stein R., Vogt C., Frederichs T., Nam S. (2007)
Effects of Arctic freshwater forcing on thermohaline circulation during the Pleistocene
Geology, 35, 1075 - 1078
doi: 10.1130/G23966A.1

Magnetostratigraphy in the Atlantic and its marginal seas
Scientists: Christine Franke, Frank Schmieder, Tilo von Dobeneck, Ulrich Bleil
Projects: IODP Leg 308, DFG project Do 705/2-1, RCOM C1

Summary: in preparation (Tilo)
Selected Publication:
Franke C., Fu Y., Heslop D., von Dobeneck T. (2009)
Data report: Natural remanent magnetization of IODP Holes U1319A, U1320A, U1322B, and U1324B and magnetic carrier identification by scanning electron microscopy
Proceedings of the IODP, 308, 0
doi: 10.2204/iodp.proc.308.209.2009

Magnetostratigraphy in the Pacific Ocean
Scientists: Lucia Korff, Thomas Frederichs
Projects: BMBF INOPEX

Summary: Topics (ongoing work):
How did the virtual axial dipole moment and the non-dipole part of the Earth's magnetic field vary in the North Pacific region during the Pleistocene? How are these variations related to available high-resolution geomagnetic records from the North amd South Atlantic.
High-reolution data sets from the North and South Atlantic are already available and may be used for a global reconstruction of the dipole and non-dipole parts of the Earth's magnetic field. But data sets of similar quality are still missing for the Pacific Ocean. Thus one goal of the paleomagnetic studies will be the high-resolution reconstruction of the variations of the Earth's magnetic field for the North Pacific area.
The combination of rock magnetic and physical property (in particular color) data will allow for the development of an independent stratigraphic correlation of the recovered sediment cores. This will allow to eliminate uncertainties of the magnetostratigraphic results on one hand and will provide information about the terrestrial dust input on the other hand. Rock magnetic proxy parameter measured on bulk sediment samples may quantify variations of the mineralogical and granulometric composition of the dust component.

Marum

Intercoast

Intercoast

Intercoast

IODP

MarTech

AWI

British Antarctic

British Antarctic

British Antarctic

British Antarctic

British Antarctic

British Antarctic

Stud.IP

University of Bremen Research group Marine Geophysics
Faculty of Geosciences | FB5