MARUM
Scientist from MTU were involved in several research areas and sub-projects within MARUM during the funding periods until 2017, namely GB3 and SD2 in the period of Project GB3: Contribution of cold seeps to geological processes, carbon fluxes, and ecosystem
diversity
A. Boetius, G. Bohrmann, H. Sahling, F. Wenzhöfer; D. de Beer, N. Dubilier, M. Elvert, T. Feseker,
T. Goldhammer, K.-U. Hinrichs, S. Kasten, J. Notholt, T. Pape, V. Spieß, G. Wegener
Spatial and temporal variations in geophysical, geological, biogeochemical and biological processes
associated with hydrate formation and hydrocarbon gas emission from the seafloor will be
identified and quantified.
Cold seeps are sources of gases and reduced fluids to the hydrosphere, and with respect to gases,
potentially to the atmosphere (Jørgensen and Boetius 2007). The main objective of GB3 is to
gain a holistic, quantitative understanding of spatial and temporal variations of the geological, geochemical
and microbial processes controlling fluid flow and hydrocarbon emission at cold seeps
(Fig. GB4), and to improve the knowledge of the distribution and activity of cold seeps on continental
margins, in order to assess their contribution to global hydrocarbon budgets.
Recent investigations suggest that the number of active submarine mud volcanoes, gas chimneys,
pockmarks and shallow-hydrate reservoirs is much higher than anticipated, and that hydrocarbons
emitted from deep-sea seeps can reach the upper ocean (Sahling et al. 2008). However,
the spatial and temporal dynamics of gas emission from active submarine seeps remain poorly
quantified. Hydrocarbons and their products of anaerobic degradation are rich in chemical energy,
which is utilized efficiently by assemblages of microorganisms and chemosynthetic symbioses
(Boetius et al. 2000, Dubilier et al. 2008). However, in some systems considerable quantities
of hydrocarbons can escape the biological filter (Niemann et al. 2006). Quantifications of fluidflow
patterns linked to consumption of methane, sulfide, oxygen and other reactants are needed
for assessing the role of cold seeps in regional and global element budgets (Felden et al. 2010).
By using satellite imaging, geospatial statistics and long-term observations we will be able to esMARUM
2012-2017 54 Geosphere-Biosphere Interactions
timate the distribution of hydrocarbon flux to the ocean surface (Solomon et al. 2009) and the
temporal dynamics. This knowledge is key to evaluating the effects of both natural and anthropogenic
oil and gas leakages on deep-sea communities. We will focus on seeps of polar and temperate
margins as natural laboratories to study the timescales and ecosystem impact of petroleum
degradation, especially in the light of seafloor warming in response to climate change (Westbrook
et al. 2009). Geomicrobiological laboratory experiments and high-resolution molecular
studies will contribute to assessing the impact of hydrocarbon transformation on deep-sea ecosystems
(Schubotz et al. 2011a, b, Holler et al. 2011). Past variability of fluid flow will also be assessed,
e.g. by the analysis of authigenic minerals that typically precipitate in relation to AOM
(Nöthen and Kasten in press.). This project closely interacts with GB2 to assess the production
and migration of hydrocarbons, and with GB4 to compare the role of vents and seeps in carbon,
sulfur, nitrogen, and energy cycling.
Key hypotheses:
● Sedimentary, oceanic and tectonic conditions have a major impact on gas hydrates, free
gas formation and migration.
● The distribution of shallow gas hydrates and strength of hydrocarbon leakage determines
the distribution and composition of chemosynthetic communities and mineral precipitates.
● Local, regional and global methane emission rates from the ocean have been underestimated
due to incomplete knowledge of their lateral extent, their control mechanisms and
transport pathways to the ocean surface.
Project SD2: Climatic control on large-scale sedimentary structures
T. Schwenk, T. Hanebuth, T. Mörz, D. Hebbeln, R. Henrich; A. Bartholomä, M. Elvert,
A. Freiwald, S. Kasten, H. Keil, H. Lantzsch, H. Müller, M. Strasser, V. Spieß, T. v. Dobeneck
Depositional structures on continental shelves and slopes will be investigated in the field and assessed
by numerical modeling to quantify the climatic control (sea level, material availability,
ocean circulation) on shelf and slope sediment dynamics on centennial-to-millennial timescales.
The sedimentary systems of continental shelves and slopes host various large-scale depositional
and erosional features whose formation processes are controlled by sediment flux, hydrodynamic
conditions, sea level, and local topography (Nittrouer et al. 2007). All of these parameters commonly
interact with each other in a complex way and react strongly to climatic conditions. The
effect of climatic forcing on locally confined depocenters (shelf mud belts, shelf sand fields,
lowstand deltas, slope contourites), elongated depressions (paleo-valleys, slope canyons), and
characteristic erosional features (furrows, scars) will be studied by interdisciplinary approaches.
Major advances supporting such studies are provided through the MeBo system, which has already
been successfully applied for SD studies at the Uruguay margin, and by the newly developed
GOST system providing in-situ geotechnical data.
Key hypotheses:
Major transgressions cause significant reorganization of the entire shelf system that is best
recorded in shelf-crossing paleo-valleys.
Our understanding of paleo- and modern sediment dynamics related to transgressive scenarios
is limited due to the often discontinuous nature of open-shelf sedimentary records. Paleo-valleys
formed during sea-level lowstands offer a great preservation potential for early transgressional
sedimentary sequences (Green, 2009). Using seismic, sedimentological, geotechnical and numerical
modeling approaches, transgressional sedimentary sequences will be investigated following
in the wake of the last deglacial sea-level rise (Vink et al. 2007). Understanding the development
of shelf (re-)organization during transgressions is also of societal relevance. Regions of interest
are the Elbe/Weser paleo-valley and its tributaries in the central North Sea, and the continental
shelf off Uruguay.
Deciphering the formation history of shelf depositional and erosional elements is essential to
properly interpreting their sensitive records of environmental variability.
Locally confined sediment depocenters and erosional features in shelf systems reflect the variability
of hydrodynamic and climatic conditions (Hanebuth et al. 2011). Evolution of these elements
will be assessed by high-resolution seismo-acoustic mapping and ground-truthing (sedimentology,
geochemistry) combined with numerical sediment-transport modeling. Dislocation of such
depocenters (by sediment supply, current-topography interaction, relocation of transport pathways,
sea level) leads to a reorganization of the entire shelf system including sedimentary links
MARUM 2012-2017 70 Sediment Dynamics
from shelf to slope. We will calculate volumes and masses of sediment depocenter successions
and integrate them into a shelf-wide, LGM-to-present numerical sediment-distribution model to
unravel the dominant environmental forces and to extract responses within the shelf-slope system
in a prognostic way. Regions of interest are the shelves off SE South America, NW Spain
and the SE North Sea.
Climate change controls the complex build-up of contouritic depositional systems by the interaction
of different forces (e.g. sea level, ocean circulation, sediment input from land, etc.).
Contouritic depositional systems are generated by long-lasting contour-parallel currents whose
strengths and boundaries are forced by variations in climate and sea level. Their architecture is
also controlled by the interaction of ocean currents with local factors such as sediment supply
and bottom topography, and by events such as abyssal storms (Rebesco and Camerlenghi,
2008). The relative impacts of these forces on depositional geometries will be assessed. Additionally,
processes triggering the sediment instability frequently observed within contouritic deposits
will be investigated. Focusing on the current-dominated slope off Argentina/Uruguay,
seismo-acoustic, sedimentological, geochemical, geotechnical and transport/depositional modeling
approaches will be used to decipher the relevant long- and short-term processes.
Sediment dynamics within submarine canyons are governed by climate-controlled down-slope
transport processes and the interaction of along-slope transport and seafloor morphology.
Canyon systems operate either as primary conduits for sediments from the continental margin to
the deep sea or as major sediment sinks. Sea-level changes control the sediment delivery by
changing the shelf configuration and by influencing the dynamics of bottom currents, and therefore
their interaction with the canyon topography (Henrich et al. 2009). The type and volume of
material available and the sediment transport mode are linked to the climatic regime. In particular,
variations in the frequency and volume of turbidite successions will be explored in the context of
regional paleoceanographic (contour-currents) and paleoclimatic changes. We will apply geophysical,
geotechnical, sedimentological (MeBo drilling) and geochemical methods to the study of
canyon systems off SE South America and NW Africa.