Tools, methods and facilities

Palaeoclimate archives and proxy data extracted from historical and geological records is essential for understanding interconnected Earth System processes and for narrowing the knowledge gaps on the causes, tipping points and consequences of climate change.

Paleoclimate research is largely based on archives - physical records of past climate and environmental conditions. As a Geological Survey, research at GEUS focuses heavily on identifying, selecting, and sampling sediments and rock outcrops, as well as preserving them in optimal conditions until further processing.

1) A regional understanding of the geological and tectonic context. Beginning with the key scientific questions, it is necessary to ensure that the region of interest is best suited and contains a record of the processes and time periods under investigation. Essential methods include onshore geological mapping, onshore and offshore geophysical surveying, development of basin models to understand sources and sinks, paleographic models, and for longer time periods, plate reconstructions.

2) With the regional understanding in mind, specific locations must be identified to determine where the best records are likely to exist. This stage requires collection of new data specific to the sampling targets to optimize the sampling strategy. Essential methods include onshore geological mapping combined with geophysical surveys (esp. EM, gravity, magnetic), deep and high-resolution shallow seismic combined with sequence stratigraphic interpretation, and multibeam seabed mapping. In some cases, this local surveying can be done in conjunction with dedicated sampling, whereas in other cases, a high level of interpretation is required prior to selecting targets.

3) Choosing and carrying out the best sampling strategy. For shorter, more recent time periods, this could include gravity, box, or piston coring, whereas longer records and deeper time would require drilling, or for records onshore, may include outcrop sampling.

4) Having obtained the archive, it is finally necessary to preserve and store the archive for the next steps, which includes dating via biostratigraphic, radiocarbon and other dating methods to establish the timeline recorded by the various proxies. Some records, such as Holocene soft sediments, require temperature-controlled storage, to ensure the preservation of fine sedimentary structures, and sensitive proxies.


The grain size variability of sediments is a key parameter to reconstruct various types of changes in the physical system. For instance, ice rafted debris (IRD) is an important proxy for assessing ice sheet dynamics over many geological time scales and provides valuable input for studies of the Greenland ice sheet evolution and stability under different climate forcing scenarios.

Mean sortable silt variability can be used to assess past changes in the hydrodynamic energy level at the sea bed whereas aeolian sediment informs on past changes to wind regimes. A visual description of the sediment core material is routinely carried out at GEUS. This provides information on sedimentary facies, structures, grain size variations, disturbances and the general quality of the archive, which can be entered into a sedimentary log.

Core scanning is crucial for obtaining background information on sediment composition and properties. Scanning is ideally carried out prior to discrete sampling and analyses as it can inform about sedimentary cycles, vaguely defined structures (e.g. muddy turbidites) or compositional changes (e.g.carbonate content). A next step is usually to obtain discrete information on sediment texture and grain size distribution from where specific grain size related proxies can be extracted.

These analyses are carried out by the sedimentology lab that houses a Malvern mastersizer (laser particle size analyzer) and is also equipped to undertake hydrometer analysis and loss on ignition, amongst others.
On a micro-scale, sediments can be investigated using light microscopy and scanning electron microscopy (SEM) to provide information on the fine-grained fabric and the textural expression of grain surfaces. This can provide insights into the transportation history and diagenetic imprint of the sediment.

Inorganic geochemistry

Quantitative knowledge of the geochemical and mineralogical composition of the sedimentary archive is often essential for environmental interpretation and process-based understanding. Main and trace element composition of discrete samples is usually carried out by XRF or microprobe-SEM analyses. Information on sediment provenance and transportation history may be gained by single-grain radiogenic dating using laser-ICP-MS. At GEUS this technique has been applied to multiple mineral phases in order to constrain bedrock sediment source, sediment entry points in depositional basins, and paleo-ice flow.

Fossil records

Our knowledge of the past is to a large extent based on the interpretation of the marine and terrestrial fossil record across different timescales.
Fossil groups of particular interest are the microfossils (foraminifera, diatoms, dinoflagellate cysts, and calcareous nannofossils) and macrofossils (ammonites, bivalves, plants, etc.).
GEUS researchers have a broad expertise in several groups of fossils and their applications:

Tracing changes in past environments and climate
The premise for interpreting past fossil records is a solid understanding of the ecology and habitat of the organisms producing them, so that changes in the fossil assemblages are interpreted to reflect relative changes in specific parameters such as water depth or temperature, sea-surface temperature and salinity, sea-ice cover, freshwater runoff, and precipitation, among others. GEUS currently has facilities for preparing samples for analyses of foraminifera, diatoms, calcareous nannofossils, and macrofossils.

Biostratigraphy is one of the most commonly applied methods of stratigraphic correlation of sedimentary records and the basic tool for constructing the geological time scale.
Biostratigraphy uses fossils (their spatial and temporal distribution) to establish relative ages of sedimentary rocks and help to determine the stratigraphic position of sedimentary successions within or between depositional basins. Depending on the geological setting and the geological time-period, the key fossil group can vary. For example the key fossil group for the Upper Cretaceous in the North Sea basin are calcareous nannofossils, whereas the age of the Triassic-Jurassic transition in the North Sea Basin is best revealed by palynology (a combination of spores, pollen and dinocysts). GEUS has excellent expertise in deep-time biostratigraphy as well as Holocene to recent.

Organic geochemistry (Biomarkers)

Organic geochemical compounds (biomarkers, known as molecular fossils) which derive from living organisms can be preserved in the geological record and used for reconstructing various aspects of the paleoclimate and paleoenvironment, such as precipitation (e.g. leaf waxes), sea-surface temperatures (alkenones, glycerol dialkyl glycerol tetraether lipids (GDGTs)), primary productivity (sterols), and sea-ice conditions (highly branched isoprenoids- HBIs), among other parameters. Biomarkers generally have a good preservation potential and can be successfully applied on deep-time as well as to more recent sedimentary archives, as long as they are adequately calibrated.

Sedimentary ancient DNA

Sedimentary records are an under-explored reservoir of DNA, also from organisms who do not leave a fossil or biomarker record, and thus have the potential to revolutionize our understanding of past environments and climate. Sedimentary ancient DNA (by definition fragmented DNA from once-living organisms that is adsorbed to sediments) can be used to reconstruct entire ecosystems and food web composition changes. The field of sedimentary DNA is rapidly emerging as a front-runner in paleoclimate research, and GEUS researchers are engaged in several projects on sedaDNA both as leaders and partners. Laboratory facilities for downstream analyses of sedaDNA have been established as part of GEUS’s Clean Lab and PCR labs (including a ddPCR system for quantification of specific genetic markers) and dedicated facilities for routine sub-sampling and extraction of sedaDNA from sediment records are underway.

GEUS leads a glaciological monitoring programme (PROMICE) funded by the Danish Government and has developed great expertise over the years in numerical modeling of ice sheet evolution. This has spawned a new research field at GEUS integrating geological data with numerical models. Specifically, a large part of the paleoclimate research at GEUS focuses on reconstructing the Greenland ice sheet evolution and stability under past warm climates. Several GEUS projects draw on the model expertise in cross-collaborations: the ice sheet models help to answer geological questions, and the geological data, in turn, can be used to validate the ice sheet model by providing longer time series and exploring a larger range of ice sheet variability. Current ice sheet models used for prediction of future sea level change are only validated against 35 years of satellite data and the recent IPCC report points to this shortcoming and highlights the need for longer time series that only the eological record can provide.