Jürgen Matzka

Comparison of magnetic parameters of urban atmospheric particulate matter with pollution and meteorological data

Abstract Magnetic hysteresis parameters were measured for three sample sets of respirable atmospheric particulate matter collected in Munich, Germany, and were compared with pollution data and meteorological data using principal component analysis. The sample sets were collected at two urban locations by the filter method during August 1998–July 1999. The samples were measured in weekly batches, with the longest data set being 40 weeks. It was found that the magnetic hysteresis parameters generally had a stronger correlation with the meteorological data than with the pollution data. Correlations with the pollution data were found to be highly site dependent, that is, at one location there was a strong relationship between the magnetic parameters and vehicular derived combustion pollutants, but not at the other. The primary magnetic mineral was identified to be magnetite, in the grain size range 0.2– 5 μm , which is small enough to be particularly dangerous to humans as the particles can be inhaled deeply into the lung. The grain size-dependent magnetic hysteresis parameters were strongly dependent on relative humidity. The concentration of magnetic particulate matter was in the range of 0.3–0.6% by mass. As the amount of magnetic particulate matter did not always correlate significantly with the total particulate mass, the use of magnetic susceptibility as a rapid method of assessing the bulk magnetic content of atmospheric particulate matter could be misleading.

Magnetic state of 10–40 Ma old ocean basalts and its implications for natural remanent magnetization

Abstract The natural remanent magnetization (NRM) of ocean basalts, giving rise to the pattern of marine magnetic anomalies, is known to be of comparatively low intensity for about 20 Ma old oceanic crust. The aim of this study is to detect possible peculiarities in the rock magnetic properties of ocean basalts of this age, and to establish a link between magnetomineralogy, rock magnetic parameters, and the low NRM intensity. Ocean basalts covering ages from 0.7 to 135 Ma were selected for rock magnetic experiments and their room temperature hysteresis parameters, Curie temperature and temperature dependence of saturation magnetization MS(T) was determined and complemented by reflected light microscopy. The majority of samples is magnetically dominated by titanomagnetite and titanomaghemite with increasing oxidation state with age. For these, a strong dependence of hysteresis parameters on the age of the samples is found. The samples have a minimum in saturation magnetization and a maximum in magnetic stability in the age interval ranging from approximately 10 to 40 Ma, coinciding with the age interval of low NRM intensity. The observed change in saturation magnetization is in the same order as that for the NRM intensity. A further peculiarity of the titanomaghemites from this age interval is the shape of their MS(T) curves, which display a maximum above room temperature (Neel P-type) and, sometimes, a self-reversal of magnetization below room temperature (Neel N-type). These special rock magnetic properties can be explained by titanomagnetite low-temperature oxidation and highly oxidized titanomaghemites in the age interval 10–40 Ma. A corresponding measurement of the NRM at elevated temperature allows to identify a maximum in NRM intensity above room temperature for the samples in that age interval. This provides evidence that the NRM is equally carried by titanomaghemites and that the low NRM intensities for about 20 Ma old ocean basalts are caused consequently by the low saturation magnetization of these titanomaghemites.

A new type of a three-component spinner magnetometer to measure the remanence of rocks at elevated temperature

A new instrument to continuously determine the remanent magnetisation of standard paleomagnetic (inchsized) rock samples during heating and cooling (continuous thermal demagnetisation) was developed. The design as an off-axis spinner magnetometer (i.e. the samples rotate on a circular path in a radial distance to the spinning axis) allows the simultaneous measurement of several samples and offers a way to determine the full vector of magnetisation. Six fluxgate sensors are used to record three gradients of the magnetic fields caused by the samples and the vector of remanence is determined by regression analysis of the gradient signals. The sensitivity of the instrument is 2·10−7 Am2. Hot air is circulating through copper pipes which heat the samples by thermal radiation to avoid magnetic fields which would arise from direct electrical heating. Currently, the measurements are restricted to a maximum of 350°C. The instrument was tested with oceanic basalt samples that were given an artificial remanence. Some continuous thermal demagnetisation experiments of this artificial remanence and of the natural remanent magnetisations are shown for oceanic basalts.

Probing Earth’s conductivity structure beneath oceans by scalar geomagnetic data: autonomous surface vehicle solution

The electric conductivity distribution of the Earth’s crust and upper mantle provides a key to unraveling its structure. Information can be obtained from vector data time series of the natural variations of the magnetic and electric field in a directional stable reference frame. Applying this method, known as magnetotellurics, to oceanic regions is challenging since only vector instruments placed at the sea bottom can provide such data. Here, we discuss a concept of marine induction surveying which is based on sea-surface scalar magnetic field measurements from a modern position-keeping platform. The concept exploits scalar magnetic responses that relate variations of the scalar magnetic field at the survey sites with variations of the horizontal magnetic field at a reference site. A 3-D model study offshore Oahu Island (Hawaii) demonstrates that these responses are sensitive to the conductivity structure beneath the ocean. We conclude that the sensitivity, depending on the bathymetry gradient, is typically largest near the coast offshore. We show that such sea-surface marine induction surveys can be performed with the Wave Glider, an easy-to-deploy, autonomous, energy-harvesting floating platform with position-keeping capability.Graphical abstract.