Christian Hilgenfeldt

Automated paleomagnetic and rock magnetic data acquisition with an in‐line horizontal “2G” system

Todays paleomagnetic and magnetic proxy studies involve processing of large sample collections while simultaneously demanding high quality data and high reproducibility. Here we describe a fully automated interface based on a commercial horizontal pass-through “2G” DC-SQUID magnetometer. This system is operational at the universities of Bremen (Germany) and Utrecht (Netherlands) since 1998 and 2006, respectively, while a system is currently being built at NGU Trondheim (Norway). The magnetometers are equipped with “in-line” alternating field (AF) demagnetization, a direct-current bias field coil along the coaxial AF demagnetization coil for the acquisition of anhysteretic remanent magnetization (ARM) and a long pulse-field coil for the acquisition of isothermal remanent magnetization (IRM). Samples are contained in dedicated low magnetization perspex holders that are manipulated by a pneumatic pick-and-place-unit. Upon desire samples can be measured in several positions considerably enhancing data quality in particular for magnetically weak samples. In the Bremen system, the peak of the IRM pulse fields is actively measured which reduces the discrepancy between the set field and the field that is actually applied. Techniques for quantifying and removing gyroremanent overprints and for measuring the viscosity of IRM further extend the range of applications of the system. Typically c. 300 paleomagnetic samples can be AF demagnetized per week (15 levels) in the three-position protocol. The versatility of the system is illustrated by several examples of paleomagnetic and rock magnetic data processing.

Keynote Speech - Mapping Seafloor Massive Sulfides at the Central Indian Ridge with a Novel Central Loop Electromagnetic Profiler

A novel frequency domain electromagnetic (EM) sounding system has been developed for mapping active and relict hydrothermal vent sites in the deep ocean. We present the concept and development state of this deep-sea electromagnetic profiler GOLDEN EYE, and first results of an interdisciplinary survey from the Central Indian Ridge. High-resolution electromagnetic conductivity data of the horizontal in-loop system show clear evidence for the presence of seafloor massive sulfide deposits related to active and inactive vent sites. In addition several buried structures were recognized that were not observable by acoustic and optical methods. We show that EM seabed characterization provides clear insights into the structure and spatial distribution of submarine hydrothermal deposits.

Reconstruction of Magnetic Susceptibility and Electric Conductivity from Marine Small-loop EMI Data

Electric conductivity and magnetic susceptibility are standard physical parameters in environmental geophysics. Both can be obtained from electromagnetic induction (EMI) methods. In comparison to the extensive use on land, near surface applications of EMI methods in coastal and shelf regions are relatively novel. Recognizing the power of electromagnetic data to provide information, useful for many different fields in marine and coastal geoscience ranging from geotechnics to sediment dynamics, we developed the electromagnetic benthic profiler NERIDIS III at the MARUM – Center for Marine Environmental Sciences. This bottom-towed sled is equipped with a commercial, controlled-source EMI sensor modified for underwater applications. We use an inversion algorithm employing the in-phase and quadrature components of five operation frequencies to reconstruct the lateral distributions of electric conductivity and magnetic susceptibility of shallow marine deposits. Vertical distribution of conductivity is also recovered through 1-D inversion. Both parameter offers complementary information as electric conductivity is primarily considered as a measure of porosity (grain size, sorting), while magnetic susceptibility is used as a proxy for fine-grained terrigenous or iron mineral content and anthropogenic metallic contaminants.