Organic Geochemistry

Organic geochemistry examines the distribution, composition and transformation of organic compounds in geological and environmental systems. By identifying molecular fossils and biomarkers preserved in sediments, soils and rocks, it elucidates past biological activity, palaeoenvironmental conditions and diagenetic pathways. Key approaches include extraction of organic fractions, chromatographic separation and mass‐spectrometric characterisation of classes such as hydrocarbons, lipids, sterols and pigments. These methods support reconstructions of ancient climates, assessments of petroleum source‐rock potential and monitoring of contemporary pollutant fluxes. Beyond descriptive analysis, modern organic geochemistry integrates compound‐specific stable isotope measurements and molecular proxy calibration to quantify variables such as temperature, hydrology and redox state over timescales from decades to millions of years.

Research from Nature Portfolio

New multiproxy calibrations have resolved a long‐standing bias in branched GDGT palaeothermometry at the Horn of Africa, demonstrating that the traditional methylation index underestimates Holocene monsoon weakening by up to 2.7 °C in haloalkaline lakes. By incorporating local bacterial community clustering, the revised approach restores agreement with instrumental records and enhances global proxy applicability.

In polar environments, paired Mg/Ca and δ¹⁸O_c measurements in planktonic foraminifera have been combined to isolate the influence of seawater carbonate chemistry on the Mg/Ca palaeotemperature proxy. Application to last glacial–interglacial sequences reveals that marine polar amplification has been underestimated by up to 3 ± 1 °C when carbon‐system effects are neglected, refining our view of past high‐latitude climate change.

Organic Geochemistry publication trend

The graph below shows the total number of articles in organic geochemistry across all publications each year (not limited to Nature Index journals).

Technical terms

Branched GDGTs (brGDGTs): Bacterial membrane lipids whose methylation and cyclisation patterns vary with soil and water temperature and pH.

MBT′_5ME (Methylation Index of Branched Tetraethers): A ratio of specific brGDGT homologues used to estimate mean annual air or surface water temperature.

CBT (Cyclisation Ratio of Branched Tetraethers): The ratio of ring‐containing to non‐ring‐containing brGDGTs, correlated primarily with soil pH and water acidity.

BIT Index (Branched and Isoprenoid Tetraether Index): The proportion of brGDGTs relative to archaeal isoprenoid GDGTs, used to distinguish terrestrial versus aquatic organic inputs.

Mg/Ca Thermometry: Measurement of magnesium-to-calcium ratios in biogenic calcite shells (e.g. foraminifera) as a proxy for ambient water temperature at the time of calcification.

References

1. Principal Analytical Procedures in Organic Geochemistry.
2. Reversed Holocene temperature–moisture relationship in the Horn of Africa. Nature (2023).
3. A solution for constraining past marine Polar Amplification. Nature Communications (2024).
4. Biomarker-based quantitative constraints on maximal soil-derived brGDGTs in modern lake sediments. Earth and Planetary Science Letters (2023).
5. Distributions of 5- and 6-methyl branched glycerol dialkyl glycerol tetraethers (brGDGTs) in East African lake sediment: Effects of temperature, pH, and new lacustrine paleotemperature calibrations. Organic Geochemistry (2018).