We talk to Sven Fuchs about the global terrestrial heat flow database and its relevance for Earth system research. The GFZ recently launched an international collaborative initiative to comprehensively revise this database.
Data on the temperature distribution in the Earth's deep subsurface are rare, relevant raw data and research results on this are therefore correspondingly valuable. Sven Fuchs, head of the new working group "Exploration of Thermal Geosystems", located in Section 4.8 - Geoenergy, works with his team on, among other things, terrestrial heat flow as a key parameter for understanding thermal geosystem models. Sven Fuchs is an elected member of the "International Heat Flow Commission" (IHFC). This is a commission of the International Association of Seismology and Physics of the Earth's Interior (IASPEI) within the International Union of Geodesy and Geophysics (IUGG). Recently, Fuchs was appointed by the commission as custodian of the global terrestrial heat flow database.
Fuchs and his team have responsibility for the scientific curation of a global data collection that has grown over 80 years and contains more than 74,000 heat flow records. To ensure the quality of the deposited data and to adapt the database to today's possibilities and needs, the international "Global Heat Flow Data Assessment Project" was launched in May under his leadership with a collaborative revision and assessment approach. For this purpose, 80 scientists from 23 countries have already come together to tackle this major task.
Dr. Fuchs, what exactly is the Earth's global heat flow?
The Earth's heat flow results from the temperature difference between the Earth's interior and its surface and quantifies the surface heat loss of our planet, which has been gradually cooling since its formation. The heat flow is calculated from the temperature gradient in the Earth's interior and the thermal conductivity of the rocks. It therefore varies with depth and locally, depending on the structural and geochemical or petrological composition of the lithosphere.
Heat flow is an important fundamental parameter for describing the Earth's thermal field and heat budget and it is an indispensable input parameter for many thermal modeling efforts. Knowledge of heat flow is important, for example, in characterizing geodynamic processes and regional geologic units such as sedimentary basin systems. We also depend on this parameter when it comes to modelling for sustainable subsurface management and the use of geothermal resources. For example, we need to understand how subsurface geosystems act thermally when used technologically. Where we want to use the heat of the Earth directly, we need the heat flow for process understanding, among other things.
What is the relevance of the knowledge of this global heat flow for the technological use of the subsurface?
For geothermal energy, for example, as an applied field, heat flow plays a role both in exploring and predicting resources, production potentials and target depths and in evaluating the thermal sustainability of various development concepts. This means that its precise knowledge enables us to make more reliable statements about the duration of sustainable thermal site management. With such solid planning bases, we thus also promote the transition towards geothermal-powered and emission-neutral district heating networks. We are currently cooperating on this, for example, with the local municipalities in Potsdam and Schwerin. In addition, the parameter is important for all temperature-sensitive processes and their modeling in the subsurface. It therefore also plays a role for the thermal aspects in the geological storage of warm water in so-called ATES systems or of gases, such as in geological hydrogen storage.
You and many of your colleagues around the world are now planning to secure a large collection of data for the future. What is the specific idea behind this?
Heat flow has been researched for more than 80 years and systematically collected by the International Heat Flow Commission for about 60 years. During this period, a lot of progress has been made, both on methodological and technological levels. Many data in particular from older publications are hardly available in a consistent form. Also, the meta-data and indicators necessary for an assessment of the data quality are mostly not collected at all. The Global Heat Flow Data Assessment Project aims to revise and update the content of the existing data. As far as possible from the original publications, newly defined data field entries will be added for quality assurance. With over 74,000 data sets compiled by almost 2000 authors in more than 1400 publications, this huge task can only be accomplished by many hands and heads and will certainly take the next few years. Without this effort, however, we will not arrive at a true quality-assured and authenticated database. In short, at the moment the users of the database would simply not be able to judge the quality of the stored values and whether they are in fact useful for model calculations and validation at all.
What kind of data does the global heat flow database actually contain?
In addition to the heat-flow value, the database naturally contains data on the locality, the associated temperature gradients, and the thermal rock properties. In addition, numerous metadata on the methods used, conditions and any corrections made are documented. This also makes it possible to perform a quality assessment for the data, which also provides non-experts with clear information on the uncertainties of the listed values. The revised database thus provides science and industry with basic data for thermal models of whatever objective and scale and is a substantial contribution to an improved understanding of the Earth system.
You said that the data collection is the research results of nearly 2,000 scientists from more than 1,400 publications. What will be the key challenges in systematizing this knowledge? What are the milestones of the project?
The challenge will certainly be to manage the collaborative revision in an efficient and targeted manner so that the many participants can process the large number of data in a uniform and transparent manner. We have jointly defined guidelines for this in the heat flow community and are now administering the data management via the Internet. In three years, we want to have revised at least two-thirds of the data and accompany this with annual updates of the database in order to make the ongoing improvement of the database accessible in a timely manner. In addition, we also see the need to make authors, reviewers and journal editors more aware of the criteria for reliable heat flow data in order to have a lasting increase in the quality of publications. As we can see from the recent publications, there is definitely room for improvement.
At the moment 80 colleagues from 23 countries are participating in this initiative. What can they contribute?
A lot! The colleagues basically bear the main burden of managing the revision. All volunteers have committed to a minimum number of publications that they will revise each year. Beyond that, however, they mainly contribute with their scientific expertise, for example, in the determination of the marine or terrestrial heat flow, for which different methods and techniques are used in each case.
How did you get so many colleagues to support you?
The need for a quality-assured global heat flow database has long been a topic of discussion in the heat flow community. So far, however, the great effort of a revision has been shied away from. Networked and digital work makes it possible for many colleagues to contribute with a manageable amount of work and to become part of the valuable product. This is motivating. The initiative presented here has also met with broad approval beyond the narrower specialist community. We have just been granted the status of a 'Task Force' at the International Lithosphere Program (ILP). Such 'Task Forces' address global challenges at the interface of geology (IUGS) and geophysics (IUGG), as is the case for the revision of the global heat flow database. We are pretty much sure that, after the official start of the project, even more scientists will get involved in this exciting project.
How will the GFZ be able to contribute to this project? What know-how do we have?
The GFZ is leading and coordinating this global effort. Over many years, we have accompanied and helped shape the discussions in the global community with our expert involvement. We know the procedure and pitfalls for determining terrestrial heat flow from numerous projects with different data on different scales. We are aware of the bottlenecks in the laboratory when it comes to, for example, thermal in-situ characterization of rocks, but also of the impact heat flow can have on crustal and lithospheric models as an input or validation parameter. The amount of necessary revisions is immense and so far always exceeded the capacities of single persons.
One last question: for many scientists the pandemic year was very difficult because the possibility to do field research in the field was extremely limited. How was the time for you?
The year was difficult for us as well. Our data business is usually thermophysical measurements in the laboratory and temperature measurements in boreholes For a long time, these were only possible to an extremely limited extent or not at all. We focused heavily on digital research aspects during that time. For example, we were able to develop a new structure for the research data around the "Global Heat Flow Database" with a global team of about 20 volunteering scientists, probably also because the pandemic affected almost everyone. We also published an update of the database and developed online tools that will serve as a basis and steering tool for the revision that is now underway. Incidentally, the Library and Information Services (LIS) research data team was a great help to us with the publications.
Dr. Sven Fuchs
Phone: +49 331 288-1713