Characterization of marine near-surface sediments by electromagnetic profiling [Elektronische Ressource] / vorgelegt von Hendrik Müller

Hendrik Conscience

Informations

• Publié par: universitat_bremen
• Publié le: 01 janvier 2009
• Nombre de lectures: 17
• Langue: English
• Poids de l'ouvrage: 22 Mo

Extrait

CHARACTERIZATION OF MARINE NEAR-SURFACE SEDIMENTS
BY ELECTROMAGNETIC PROFILING
Dissertation
Eingereicht zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat.)
am Fachbereich Geowissenschaften der Universität Bremen, Deutschland
In fulfillment of the requirements for the doctoral degree in natural sciences (Dr. rer. nat.)
at the Department of Geosciences at Bremen University, Germany
vorgelegt von
presented by
Hendrik Müller
Bremen, Germany, November 2009 Preface
The 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-
mental Sciences (MARUM) at the University of Bremen (research grant: Electromagnetic
sensor for surveying seafloor magnetic susceptibility and electric resistivity for the investi-
gation of sedimentary and diagenetic processes in the Ría de Vigo Estuary, NW Spain) and
the Marine and Environmental Geology Group (MARGO) at the University of Vigo (research
grant: PGDIT06TAM31201PR (XUGA) and CTM 2007-61227/MAR (MICINN)).
Throughout the period of this thesis the author has been the beneficiary of a doctoral student
and University staff position. From November 2005 to November 2008 the doctoral student
position was on the MARUM project C1 (Sedimentary signatures and diagenetic processes of
ocean margin deposits) from November 2008 to November 2009 the author was employed as
a member of staff at the University of Bremen.
Four survey campaigns with the RB Polarfuchs in the Western Baltic Sea were granted by
IfM GEOMAR in Kiel. A survey campaign with the RB Arao in the Ría de Vigo was
organized by the University of Vigo. An EM survey of the NW Iberian Shelf with the RV
Poseidon was part of International Graduate School “Proxies in Earth Science”
(EUROPROX) expedition P 366/3.
The thesis project has been supervised and reviewed by Prof. Dr. Tilo von Dobeneck (Dept.
of Geosciences, University of Bremen). The second thesis reviewer is Prof. Dr. Tobias Mörz
(Dept. of Geosciences, University of Bremen). Prof. Dr. Daniel Rey and Prof. Dr. Belén
Rubio (University of Vigo) and Dr. Kay Hamer (University of Bremen) have been project
partners and manuscript coauthors. The development of the hard- and software of the EM
profiler was accomplished in close cooperation with Dipl.-Ing. Christian Hilgenfeldt, engineer
of MARUM project C1, and support by I.J. Won, Manager of Geophex Ltd. (USA).
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.
Laboratory data of a co-supervised diploma project by Wiebke Nehmiz (Umweltmagnetische
und geochemische Untersuchungen an Grundwasseraustritten in der Eckernförder Bucht,
April 2007) have been integrated into Chapter 3.
IIFür
Kerstin und Theo
III IVContent
Abstract ...................................................................................................................... ....................... 1
Zusammenfassung ............................................................................................................... ............. 2
1 Introduction .......................................................................................................................... 5
1.1 Marine environmental magnetism ...................................................................................... 5
1.2 Marine magnetics ................................................................................................................ 8
1.3 Marine electromagnetic sounding ....................................................................................... 9
1.4 Fundamentals of the CSEM method ................................................................................. 13
1.5 Project chronicle ............................................................................................................... 18
1.6 Technical realization and operation .................................................................................. 26
1.7 Synopsis of manuscripts ................................................................................................... 32
1.8 References ......................................................................................................................... 34
2 Mapping the magnetic and electric signatures of marine near-surface sediments by
bottom-towed Controlled Source Electromagnetics .......................................................... 40
3 Near-surface electromagnetic, rock magnetic and geochemical fingerprinting of
submarine freshwater seepage at Eckernförde Bay (SW Baltic Sea) ................................ 74
4 Using electromagnetic sensors to estimate physical properties and environmental
quality of surface sediments in the marine environment. Preliminary results ................. 112
5 Conclusions and perspectives .......................................................................................... 122
6 Appendix .......................................................................................................................... 125
6.1 Eckernförde Bay magnetometer survey .......................................................................... 125
6.2 Pilot study: seafloor EM mapping in the Ria de Vigo, NW Spain ................................. 129
6.3 EM survey on the Galician Shelf .................................................................................... 140
6.4 EM survey on the Uruguayan Shelf ................................................................................ 143
6.5 LabVIEW data acquisition environment ........................................................................ 144
6.6 Matlab functions ............................................................................................................. 145
Curriculum Vitae .......................................................................................................................... 149
Danksagung .................................................................................................................... .............. 151
V VI Abstract
Abstract
This 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 conductivity-
temperature-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.
1 Zusammenfassung
Diese Doktorarbeit erforscht die Theorie, entwickelt die Technologie und präsentiert
Anwendungen zur synchronen in-situ Kartierung der magnetischen Suszeptibilität und
elektrischen Leitfähigkeit mariner Sedimente. Die magnetische Suszeptibilität erfasst den Ton
und Silt-Gehalt, das Ausmaß diagenetisch bedingter Magnetitlösung sowie die anthropogene
Kontamination des Sediments. Die elektrische Leitfähigkeit ist ein Maß für Porosität,
Korngrößenverteilung und Porenwassersalinität.
Dieses Ziel wurde durch die Entwicklung eines elektromagnetischen (EM) Meeresboden
‚Profiler’ realisiert, der speziell für den Schelf und Küsteneinsatz in Wassertiefen von 5 bis
500 m konzipiert ist. Das System ermöglicht eine hochauflösende profilierende Erfassung
auch gradueller Änderungen der Lithologie und Porosität sowie der diagenetischen Alteration
der Oberflächensedimen