Sedimentary processes in various systems, ranging from tropical- and cold-water coral reefs to canyons, hydrocarbon seep sites, shelf systems, and deserts are studied in order to determine the environmental conditions under which they were formed. This modern-analogue approach allows us to determine the environmental conditions that lead to sediment deposition and offers the opportunity to better quantify environmental conditions from fossil sedimentary records.

The continental slope of passive continental margins provides ideal conditions for sediments to pile up, which can form a sediment archive of environmental change. In GEO we study these archives which have been retrieved from a range of environments (from tropical surface-water corals to deep cold-water corals, from submarine canyons to intertidal flats) using a score of drilling- and coring techniques. Coral and sediment cores are analysed at GEO using a wide range of methodologies to determine sedimentation rates, sediment origins, climate variability, etc…. Among those, X-ray Fluorescence (XRF) Core Scanning is developed at Geo for analyzing the sediment composition in a fast and non-destructive way.

For environmental reconstructions of past climate changes where instrumental records of e.g., Temperature, Salinity, wind- and current speed are not available, we rely on so-called proxies for these properties (e.g., inorganic paleothermometers like Mg/Ca, Sr/Ca, and organic paleothermometers like U^k’₃₇, TEX₈₆, d¹⁸O for past temperatures and salinity, grain size of dust for wind intensity). These proxies rely on experimental studies for quantification and application.

Knowledge of present and past environmental systems is applied to establish conceptual and numerical models to describe scenarios of future climate change, in relation to the ongoing global climate change.

Meso-scale eddies are a principal feature of ocean boundary currents with a potentially significant impact on continental margin sedimentation. Sediment-trap and ADCP equipped moorings across the Mozambique Channel show periodic off-shelf sedimentation of lithogenic and biogenic organic matter by fast-rotating, meso-scale eddies feeding the Agulhas Current. These eddies modulate seasonal fluxes of temperature-specific pelagic foraminifera and organic compounds. This has to be considered in paleo SST calibrations and organic-compound based proxies of past seasonal ocean-climate and land-sea interaction from sediment cores.

Submarine canyons are an important conduit for sediment dispersal on continental margins. Off central Portugal, canyons act as depocenters for metals like Pb, Zn, and Cr from industrialised metropolitan areas. Year-long lander deployments revealed that internal tides force sediment re-suspension and transport in the upper-middle canyon, while sediment gravity flows predominate at greater depth. Turbidity-current transport occurs on centennial or longer timescales, apparently restricted to earthquake-tsunami events.

The Saharan desert is the largest producer of wind-blown dust: 700-900 * 10⁶ Tons sediments are blown out of Northwestern Africa each year. Most of this dust ends up in the Atlantic Ocean where it potentially stimulates plankton growth, which consequently can influence climate through CO₂ sequestration. In addition, the dust piles up on the ocean floor and builds an archive of environmental change in the source area(s) of the dust. Using sediment traps and moored buoy with dust collector, we collect Saharan dust across the Atlantic Ocean in order to monitor spatial and temporal changes in dust dispersal and deposition as well as its marine environmental effects.

CWC-content

Fluvial and wind-blown sediments end up as complex mixtures in marine deposits. These can be un-mixed by end-member modelling of grain-size distributions to reveal changing environmental conditions on land. Sedimentary records with varying temporal resolutions off NW Africa and SE America show a linear relationship between desert-dust fluxes and the Atlantic Meridional Overturning Circulation, abrupt and persistent droughts in the Sahel throughout the past 57kyrs, and the disruption of this natural variability since the start of colonial land use. (Stuut et al., 2007; Mulitza et al., 2010)

Giant corals fill the data gap in Indian-Ocean climate history on human time scales. Coral carbonates record seasonal variability in sea surface temperature, hinterland erosion, and sediment discharge over centuries. Ultra Violet Spectral Luminescence discriminates between soil-derived humic acids and detritic sediments delivered by monsoonal river discharge. Regional responses in precipitation appear linked to accelerated Indian Ocean warming and natural multi-decadal variability. (Grove et al., 2010)

The marine sediment stack off large deserts records changes in environmental conditions in the source areas. Sediments delivered to the ocean by rivers can be easily distinguished from those brought to sea by winds or ice bergs on the basis of their grain-size signature, their bulk chemistry and mineralogy. A long sediment core collected off NW Australia contains a stratigraphy of about 2 million years, a time period that was characterised by strong changes in (monsoonal) precipitation and dust production and dispersal. These environmental parameters are being unravelled from this sediment core using the aforementioned techniques.

Methane is a strong greenhouse gas that escapes from seabed sediments in unknown quantities into the atmosphere. Ship-based hydroacoustic systems are used to improve spatial coverage and to determine free-gas fluxes remotely. Integrated approaches of direct observations, geophysical mapping, geochemical analysis, and bubble-dissolution modelling in the Black Sea enabled the first complete budget of methane fluxes from the seafloor into the atmosphere. The results show that only small amounts of methane reach the atmosphere under present day conditions. (Greinert et al., 2010; Greinert & Mc Ginnis, 2009).

Aeolian dust is a large source of metals and nutrients to the ocean, and is thought to play a pivotal role in climate change on geological timescales through the potential CO₂ sequestration that results from dust deposition. However, very little is known about the macro- and micro nutrients that are taken up by the dust particles under varying environmental conditions. Through abrasion studies under varying moisture conditions we study dust composition in terms of nutrient content. Mesocosm experiments with this “home-made dust” will answer questions regarding bio-availability of these nutrients to surface-ocean plankton.