Dr. Hendrik Müller

Electromagnetic surveying of seafloor magnetic susceptibility and electric resistivity in combination with deep-towed magnetometry and sediment acoustics

The magnetic susceptibility of marine sediments is a reliable proxy to study transport processes and the diagenetic alteration of marine sediments. While common measurements were applied to samples in the laboratory, only magnetometers measure the susceptibility of the ocean floor 'in-situ'. Their sensitivity to small scale variations of surface sediments is generally poor and often masked by stronger subsurface structures. Electromagnetic (EM) sounding with controlled sources allow to map the magnetic susceptibility as well as the electric resistivity (e.g. porosity / lithology) in one measurement (up to 25 samples per second) with high lateral resolution.
We started operations with scientific divers, our light Research Boat Neridis and a newly developed electromagnetic seafloor towed measuring device (NERIDIS II) at a test site in the Eckernförde Bay in summer 2007. In September/October 2007 the system was applied in a joint research project with the University of Vigo, Spain, as a tool for coastal environmental management. In June 2008, the system was deployed during Poseidon cruise P366/3 and performed 250 km of electromagnetic imaging of recent sediment transport and depositional processes on the NW-Iberian shelf. In 2009 the system was used off Uruguay and redesigned and rebuild by Marum funds in 2010/2011. The new NERIDIS III was tested with RV Alkor in February 2011 and used in May 2011 to continue work on the Galician shelf.

MARUM Project SD2

Dissertation (11/2009)

EM Profiler Technology

Data examples

Magnetic mapping and modeling of incised valley structures

Magnetic subsurface signatures in northern Germany and in the adjacent seas provide insight into the cutting structure of incised valleys and their infill by weakly or strongly magnetic material. In several student projects, marine and terrestrial magnetometer data were processed and modeled to highlight and analyze buried valley structures, anthropogenic contamination and deeper crust with State of the Art processing software and methods.

Heavy mineral placer deposits in the Bay of Plenty (New Zealand)

This project has the objective to quantify magnetic trace minerals in marine sediments by magnetic in-situ methods and mineral and grain-size specific bulk measurements. As hard and heavy relict minerals, iron oxides travel far and settle, sort and enrich in high-energy environments. They often have source-specific rock magnetic and elemental signatures. Originating mainly from igneous continental rocks, titanium rich magnetite is common along Northern New Zealand’s coasts and can form ‘black sand’ placer deposits that are of high scientific and even commercial interest.

In-situ and Laboratory experiments on the mechanisms of geomagnetic field recording in aquatic sediments

Sedimentary paleomagnetic records attain superior temporal resolution, but their paleofield information is not unambiguous. Numerous geological factors and especially the micro-environment control the mobility, alignment and fixation of magnetic particles.
Because the various natural conditions couldn’t be adequately simulated in our laboratory. I shifted my investigations from the laboratory into the natural sedimentation regime. Therefore I installed - with the help of scientific divers from Kiel - in November 2005 seven permanent-magnetic platforms in three maar lakes of the western Eifel, Germany. Each platform simulates a magnetic pole reversal in an investigation area of about 1 m³ that will be sampled in 6 month intervals. The aim is to characterise the change of the magnetic signal with time and depth when the sediment is exposed to a reversed field condition. This will allow us to deconvolve the modulated information in deep sedimentary records, to acquire a much better temporal resolution. (DFG-Priority-Program: Earth Magnetic Variations)

- Exploration geophysics - magnetic exploration: field work, data processing and interpretation techniques

- Data management with Geosoft “Oasis Montaj”

- Multi-Sensor Core-Logging

Seafloor characterization by electromagnetic benthic profiling

Given the environmental and economic relevance of ocean margins and their geophysical exploration, there is growing need to characterize surficial sediments in coastal and continental shelf systems by more than just their acoustic properties. A newly conceptualized benthic profiling and data processing approach based on controlled source electromagnetic (CSEM) imaging permits to coevally quantify the electric conductivity (~ salinity, porosity and grain-size variations) and the magnetic susceptibility (~ terrigenous or iron mineral content, redox state and contamination level) of shallow marine deposits. This approach has been successfully applied in a number of estuarine and shelf surveys with the first and second generation of the Neritic Discoverer (NERIDIS II & III). The narrow footprint of the concentric, coaxial CSEM sensor together with a relatively high sampling rate (25 Hz) and tow speed (up to 3-4 knots) enable to cover and resolve sediment patterns of very different lateral extent from sub-meter (e.g., iron sulfide nodules, UXO) to kilometer scales (e.g., drift bodies, placer deposits) within the same survey operation.
We will present the concept and development state of our benthic profiling project as well as new results from past and recent shelf expeditions. These exemplary results identify sedimentation patterns and cold seeps by their magnetic and conductive properties in sub-decimetre resolution. All presently available data indicate an eminent potential of EM profiling for assessing the complex distribution, accumulation and diagenesis of surficial sediments in coastal and continental shelf systems dedicated to numerous scientific and commercial aspects.

GEM-Shark: ELECTROMAGNETIC SEAFLOOR PROFILER FOR ENVIRONMENTAL MAGNETIC RESEARCH IN COASTAL AND SHELF SEAS

Conferences: MARELEC 7.-9.7.09 (Stockholm) and IAGA 23.-30.8.09 (Sopron)

A marine electromagnetic profiler was developed to survey the magnetic and electric signatures of marine near-surface sediments (0-50 cm). The system is devised for coastal and shelf operations of 5 to 500 m water depth, to resolve subtle and gradual variations in silt and clay content, porosity and diagenesis state at sub-meter resolution. A commercial electromagnetic induction (EMI) sensor was modified for submarine operations and mounted into a bottom-towed sledge enabling synchronous in-situ mapping of magnetic susceptibility and electrical conductivity. Magnetic susceptibility is used as a proxy for fine-grained terrigenous clay/silt content, diagenetically forced magnetite depletion, anthropogenic metallic contaminants as well as proneness to trace metal accumulation. Electric conductivity is primarily considered as a measure of porosity and grain-size distribution. The sensor is used to investigate patterns of sediment transport and deposition and to detect fluid seepage and pollution effects. The 3.2 m long non-magnetic and non-conductive sledge, named GEM-SHARK, is towed by small to large size research vessels at a typical speed of 2 to 4 knots. Onboard control and co-registration of seafloor measurements is provided via an up to 10 km long armored coax cable, supported by an autonomous registration, navigation and control system in the bottom-towed sledge. A complementary CTD tracks bathymetry and identifies bottom water characteristics.

Müller, H. (2011). Seafloor characterization by electromagnetic benthic profiling. MARELEC (San Diego) Conference Proceedings.

Müller, H., T. von Dobeneck, W. San Felipo, C. Hilgenfeldt, D. Rey und B. Rubio (in press). Mapping the magnetic susceptibility and electric conductivity of marine surficial sediments by benthic EM profiling. Geophysics.

Müller, H., T. von Dobeneck, W. Nehmiz, K. Hamer (2011) Near-surface electromagnetic, rock magnetic, and geochemical fingerprinting of submarine freshwater seepage at Eckernförde Bay (SW Baltic Sea). Geo-Marine Letters , 31 (2), 123-140. doi:10.1007/s00367-010-0220-0.

Müller, H. (2010). Characterization of marine near-surface sediments by electromagnetic profiling, Dissertation, Fachbereich Geowissenschaften, Universität Bremen, 152 S.

Rey, D., H. Müller, B. Rubio, T. von Dobeneck et al. (2008). Using electromagnetic sensors to estimate physical properties and environmental quality of surface sediments in the marine environment: Preliminary results, Geotemas, 10, 651-654.

Müller, H. (2008). EMSEAC – Electromagnetic seafloor profiler for environmental magnetic research in coastal and shelf seas. IAGA (Soppron) Conference Abstract.

Müller, H. (2008). GEM-Shark - Electromagnetic subsurface profiler for coastal and shelf research, MARELEC (Stockholm) Conference Proceedings.

Müller, H., T. von Dobeneck (2006). Magnetit im Kräfteregime uniaxial komprimierter Tiefseesedimente, 66. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, Bremen.

Müller, H., T. von Dobeneck (2004). Laborexperiment zum Einfluss der Kompaktion auf den Remanenzerwerb von marinen Sedimenten, 64. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, Berlin.

Müller, H. (2003). Der Beitrag der Kompaktion zum Remanenzerwerb von Tiefsee-Sedimenten; Entwicklung und Auswertung eines Laborexperiments, Diplomarbeit, Fachbereich Geowissenschaften, Universität Bremen, 128 S.