Biogeochemical Systems

Former Department 2004 - 2017

With the retirement of Professor Martin Heimann (March 2017) the department was integrated into the new department "Biogeochemical Signals" under the leadership of Sönke Zaehle (May 2020).

Biogeochemical cycles are represented in the atmosphere by several important greenhouse gases, such as carbon dioxide, methane and nitrous oxide. In the Department of Biogeochemical Systems we develop methods to measure these gases in situ and by remote sensing, we expand the measurement network to remote hot-spot regions such as Siberia and Amazonia, and we develop and apply numerical models to quantify the large-scale sources and sinks of the greenhouse gases.

Many of the global biogeochemical cycles are reflected in the atmosphere by one or several trace gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) or also aerosols. Spatio-temporal variations of these tracers (and other quantities linked to them such as their isotopic composition) contain important information on location, magnitude and temporal variability of the various source and sink processes of the species of interest. The atmosphere thereby is used as a natural “integrator” of the complex pattern of surface fluxes because of the rapid mixing of air. Atmospheric measurements may thus be used to observe surface processes on a range of spatial and temporal scales, from a small-scale regional ecosystem to entire continents and the globe. Thereby atmospheric transport by winds and mixing has to be taken into account by using three-dimensional numerical meteorological models in an inversion or data assimilation mode. In the Department of Biogeochemical Systems we develop and apply this “top-down approach” in four focus areas:

Focus 1:  Expansion of the atmospheric network of in situ measurements of high-accuracy biogeochemical trace species

The current global atmospheric network for biogeochemical trace gases contains many gaps in important areas. An effort therefore is directed at the establishment of new measuring stations in undersampled locations, which constitute “hot-spots” in the Earth system. Geographically we pursue this along three directions:

(1) A string of tall towers from Europe into the Eurasian taiga at 60°N including the new 300 m high measurement mast in central Siberia (ZOTTO).

(2) A line of stations along the eastern Atlantic Ocean on remote islands and coasts (e.g. Shetland, Cape Verde, Namibia) for monitoring oceanic processes and air leaving the African continent.

(3) Jointly with the MPI for Chemistry in Mainz and partners in Brazil we will build and operate a 300 m tall measurement mast in central Amazonia (ATTO). A critical new development are quasi-continuous, concurrent observations of a whole suite of biogeochemical trace species, which allow us to discriminate between different source/sink processes.

Focus 2: Development of new measuring techniques and observing systems

The small spatial and temporal variability of long-lived biogeochemical atmospheric trace gases necessitates measurements with extreme accuracy. Ensuring this in remote areas under harsh environmental conditions poses a serious technical challenge. We explore new techniques, such as miniaturization of measurement devices for the deployment on routine civilian aircraft, application of ground-based Fourier Transformation Near-Infra-Red Spectroscopy of the sunlight, and, in collaboration with other partners, the development of new systems for space-based remote sensing of atmospheric biogeochemical trace gas concentrations.

Focus 3: Linking atmospheric point measurements with regional model grid averages

A critical “Achilles heel” in present regional and global inversion systems is the representation of point measurements in grid based atmospheric models, especially if the measurements are taken over land covered by a heterogeneous mosaic of greenhouse gas sources and sinks. In order to bridge this gap we conduct small and regional scale process studies by means of campaigns with a high density of observations using in situ stations, aircraft and remote sensing, together with high resolution regional meteorological modeling systems for the analysis.

Focus 4: Development and application of atmospheric inverse modeling and data assimilation frameworks

The determination of surface fluxes from atmospheric observations requires the use of realistic numerical models for the simulation of the atmospheric transport. Since in most cases observations from only a limited number of atmospheric stations are available, the underlying mathematical inversion problem is highly underdetermined. We attack this problem with a range of mathematical methods and by incorporating additional measurements: e.g. other atmospheric trace gas observations, surface properties such as the “greenness” of the vegetation seen from space, vegetation distributions and other geographical data. The ultimate goal is the development of a data assimilation framework consisting of land and ocean surface biogeochemical modules coupled to an atmospheric meteorological model. This is then is being optimized in a consistent way by the wealth of available observations, similar to what is being done routinely in numerical weather forecasting. With these tools, we can quantify and monitor where and how biogeochemical trace gas budgets respond to climatic (e.g. heat, drought) and human (e.g. fossil fuel burning, fires, deforestation) impacts (Figure below). This provides important information for the improvement of modules of biogeochemical cycles in global comprehensive Earth system models.

More information can be found on the home page of the former department Biogeochemical Systems.

Research impressions from the field

More information can be found on the home page of the former department Biogeochemical Systems.

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