Ocean-sediment

Biogeochemical processes in marine sediments are essential for understanding the global carbon cycle. Benthic biogeochemical dynamics can be traced back directly or indirectly to the degradation of organic matter. This process controls, among others, the recycling of inorganic carbon and nutrients, the dissolution of carbonates, the flux of organic carbon to the deep biosphere and, ultimately, the burial of organic carbon in the sedimentary record. As a result, organic matter degradation determines the net CO₂ removal from, and oxygen input to, the atmosphere.

We develop and use both local and global diagenetic models to quantitatively assess the fate of carbon and its feedbacks on global biogeochemical cycles and climate.

Relevant project(s): Nunataryuk, FIESTA, ChAOS

People involved: Sandra Arndt, Steeve Bonneville

Key publications:

• Arndt, S., Jørgensen, B.B., LaRowe, D.E., Middelburg, J.J., and Regnier, P. 2013, Quantification of organic matter degradation in marine sediments: A synthesis and model review. Earth-Science Reviews, 123, 53-86.

Marine surface sediments are key components in the Earth system. They host not only the largest carbon reservoir within the surficial Earth system, but also provide the primary long-term sink for atmospheric CO₂ and recycle nutrients. Physical and chemical processes in sediments depend on the water column and vice versa.

Diagenesis is controlled by the external supply of organic matter, calcium carbonate, opal from the overlying water column and is affected by overlying bottom water concentrations of solutes. At the same time, the short- and long-term storage of matter in marine sediments, the consumption of terminal electron acceptors or the recycling of nutrients in marine sediments exerts an important impact on oceanic biogeochemical cycling. This so-called benthic–pelagic coupling is thus essential understanding global biogeochemical cycles and climate.

We develop and use local, as well as global diagenetic models to assess the fluxes and transformations of elements in marine sediments and its impact on global biogeochemical cycling and climate.

Relevant project(s): Nunataryuk, FIESTA, ChAOS

People involved: Sandra Arndt

Key publications:

• Hülse D., Arndt S., Daines S., Regnier P. and Ridgwell A. (2018) OMEN-SED 1.0: a novel, numerically efficient organic matter sediment diagenesis module for coupling to Earth system models. Geosci. Model Dev., 11, 2649-2689, doi: 10.5194/gmd-11-2649-2018.

Paleo-environmental conditions are commonly reconstructed from sediment cores using micropaleontological, inorganic and isotope geochemical, and paleomagnetic techniques. However, the use of this data is often compromised by post-depositional microbially driven alterations that result in an early diagenetic overprint of the sediment’s primary physical and chemical properties and thus make a direct interpretation of the obtained proxy record difficult or sometimes even impossible.

However, secondary, diagenetic signals represent themselves excellent records of changing paleoenvironmental conditions. Organic carbon remineralization and associated diagenetic processes are coupled to oceanographic and atmospheric conditions. As a consequence, changes in environmental conditions often trigger transient shifts of benthic redox fronts and porewater profiles. These dynamics are generally recorded by diagenetic features, such as isotopic signatures, authigenic minerals or unusual shapes of porewater profiles.

We develop and use inverse diagenetic model to unlock the paleo-record of secondary, diagenetic features.

People involved: Sandra Arndt

Key publications:

Arndt, S., Jørgensen, B.B., LaRowe, D.E., Middelburg, J.J., and Regnier, P. 2013, Quantification of organic matter degradation in marine sediments: A synthesis and model review. Earth-Science Reviews, 123, 53-86.