Coast and Shelf
Sediment dynamics in coastal and shelf areas
Scientists: Firoz Badesab, Tobias Kulgemeyer, Benjamin Baasch, Hendrik M├╝ller, Tilo v. Dobeneck
Methods: Enviromagnetics, Electromagnetics, Hydroacoustics, Sedimentology
Projects: MARUM Sediment Dynamics projects SD1, SD2, INTERCOAST projects IC8 IIC8 II

Topics: Large spatial variations in magnetic and heavy mineral content are typical for sublittoral sediment facies. These patterns reflect modern sediment dynamics driven by waves, tides and currents as well as relict structures of past sea-level change, tectonics or human impact. With electro- and enviromagnetics we can map these structures to reveal sediment facies, transport pathways and fractionation mechanisms.

Magnetite layers and ripples at Orokawa Beach, NZ

Magnetic minerals as markers of coastal zone evolution in the Bay of Plenty, NZ
Scientists: Firoz Badesab, Tobias Kulgemeyer, Hendik M├╝ller, Karin Bryan, Tilo von Dobeneck
Projects: International Research Training Group INTERCOAST Projects IC8 I, IC8 II

Summary: Magnetic iron minerals are widespread and indicative sediment constituents in estuarine, coastal and shelf systems. A combination of geophysical (in particular environmental magnetic and electromagnetic), sedimentological and numerical methods is used to identify magnetite-enriched placer-like zones in a complex coastal system and delineate their formation mechanisms.
Selected Publication:
Badesab F., von Dobeneck T., Bryan K., M├╝ller H., Briggs R., Frederichs T., Kwoll E. (2012)
Formation of magnetite-enriched zones in and offshore of a mesotidal estuarine lagoon: An environmental magnetic study of Tauranga Harbour and Bay of Plenty, New Zealand
Geochemistry Geophysics Geosystems, 13, Q06012
doi: 10.1029/2012GC004125

Sediment distribution on the NW Iberian Shelf
Scientists: Benjamin Baasch, Vera Bender, Hendrik M├╝ller, Thomas Frederichs, Tilo von Dobeneck
Projects: MARUM Sediment Dynamics SD1, SD2, EUROPROX Project 12b

Summary: The NW Iberian continental shelf is a high energy, low accumulation nonglaciated shelf of narrow width (25 to 50 km) and large variety of sediment types and patterns. Extensive EM cross-shelf profiling in this area on a 2008 RV Poseidon and 2010 RV Meteor cruise had the objective to classify the facies and textures of the four major surficial sediment types of the entire Galician shelf and to map their distribution at meter-scale spatial resolution with a special focus on transitions: (1) mud facies of fine-grained, mostly muddy Holocene high-stand sediments from the Duero and Mi├▒o rivers deposited in two successive coast-parallel mud belts, (2) mixed sand facies consisting of relict and reworked siliciclastic and carbonatic sands deposited at moderate regimes, (3) glaucony facies of mostly relict late Miocene sands indicative of slow to arrested sediment accumulation on the outer shelf, and (4) gravel facies dominated by bioclasts and siliciclasts representing low-stand shoreface and storm deposits. All facies could be easily discriminated by EM-based crossplots of sediment and matrix susceptibility against porosity, demonstrating the potential of EM-based sediment classification. Transitional environments between the sediment units cover several hundreds of meters within the profiles linking facies end-members in the crossplots. Large bedforms and seabed undulations clearly correlate with porosity and susceptibility profiles, indicating mud deposition in troughs and glauconite or magnetite enrichment on bottom-current exposed ridge crests. Ongoing work is devoted to a stratigraphic 1D inversion of multifrequency EM conductivity data and integration with hydroacoustic and laboratory results.
Selected Publication:

M├╝ller H., von Dobeneck T., Hilgenfeldt C., SanFilipo B., Rey D., Rubio B. (2012)
Mapping the magnetic susceptibility and electric conductivity of marine surficial sediments by benthic EM profiling
Geophysics, 77, E43 - E56
doi: 10.1190/GEO2010-0129.1

Bender V., Hanebuth T., Mena A., Baumann K., Franc├ęs G., von Dobeneck T. (2012)
Control of sediment supply, palaeoceanography and morphology on late Quaternary sediment dynamics at the Galician continental slope.
Geo-Marine Letters, 32(2), 313 - 335
doi: 10.1007/s00367-012-0282-2

Electromagnetic mapping of submarine freshwater seepage at Eckernf├Ârde Bay
Scientists: Hendrik M├╝ller, Kai Hamer, Wiebke Nehmiz, Tilo von Dobeneck
Project: RCOM/MARUM Sedimentation Processes Project C1

Summary: Submarine groundwater discharge in coastal settings can massively modify the hydraulic and geochemical conditions of the seafloor. Controlled source electromagnetic imaging offers an innovative dual approach to seep characterization by its ability to detect pore-water electrical conductivity, hence salinity, as well as sediment magnetic susceptibility, hence preservation or diagenetic alteration of iron oxides. The newly developed electromagnetic (EM) profiler Neridis II successfully realized this concept for the first time with a high-resolution survey of freshwater seeps in Eckernf├Ârde Bay (SW Baltic Sea). EM profiling creates a crisp and revealing fingerprint image of freshwater seepage and related reductive alteration of near-surface sediments. Our findings imply that (1) freshwater penetrates the pore space of Holocene mud sediments by both diffuse and focused advection, (2) pockmarks are marked by focused freshwater seepage, underlying sand highs, reduced mud thickness, higher porosity, fining of grain size, and anoxic conditions, (3) depletion of Fe oxides, especially magnetite, is more pervasive within pockmarks due to higher concentrations of organic and sulfidic reaction partners, and (4) freshwater advection reduces sediment magnetic susceptibility by a combination of pore-water injection (dilution) and magnetite reduction (depletion). The conductivity vs. susceptibility biplot resolves subtle lateral litho- and hydrofacies variations.

Processes at submarine freshwater seeps

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

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