Alkenone-Based Paleoclimate Proxies in Aquatic Systems

Alkenones are long-chain ketones produced by select haptophyte algae and have served as robust molecular proxies for reconstructing past temperatures in marine and lacustrine environments. The unsaturation state of C37 alkenones varies systematically with water temperature, enabling quantitative estimates of sea- or lake-surface temperatures through the U37K′ index. Discovery of a tetra-unsaturated variant (C37:4) in polar and ice-influenced settings has extended proxy applications to sea-ice and cold-season reconstructions. Advances in molecular ecology have revealed distinct genetic lineages within the order Isochrysidales, each with characteristic alkenone distributions, improving species-specific calibrations for diverse aquatic systems. Ongoing improvements in chromatographic and chemical clean-up techniques have reduced analytical biases, while sediment and environmental DNA records now provide high-resolution archives of abrupt climate events, seasonal biases and cryosphere dynamics. Taken together, these developments underscore the global significance of alkenone proxies for understanding past hydroclimatic variability and informing projections of future change.

Research from Nature Portfolio

High-resolution records from the Iberian Margin have clarified that elevated C37:4 percentages reflect rapid surface cooling rather than changes in salinity, refining interpretations of abrupt glacial events. Reconstructions of cold-season temperatures on the northeastern Tibetan Plateau, based on alkenone unsaturation, reveal unexpected winter warming during the Little Ice Age, emphasising the need to address seasonal biases in proxy data. Environmental DNA surveys have mapped the distribution of Group 2i Isochrysidales across ice-covered marine and lacustrine environments, establishing their characteristic alkenone signatures as a quantitative proxy for past sea-ice concentration.

Alkenone-Based Paleoclimate Proxies in Aquatic Systems publication trend

The graph below shows the total number of articles in alkenone-based paleoclimate proxies in aquatic systems across all publications each year (not limited to Nature Index journals).

Technical terms

Alkenones: Very long-chain methyl and ethyl ketones produced by certain Isochrysidales algae, used as molecular indicators of past water temperatures.

Alkenone unsaturation index (U37K′): Ratio of di- to tri-unsaturated C37 alkenones, calibrated empirically to reconstruct surface temperatures.

C37:4 percentage (C37:4%): Proportion of tetra-unsaturated C37 alkenones, commonly associated with sea-ice presence or cold-water conditions.

Group 2i Isochrysidales: Clade of psychrophilic haptophytes inhabiting ice-influenced marine and freshwater systems, characterised by distinctive tetra-unsaturated alkenone production.

References

1. Iberian Margin surface ocean cooling led freshening during Marine Isotope Stage 6 abrupt cooling events. Nature Communications (2023).
2. Unexpected cold season warming during the Little Ice Age on the northeastern Tibetan Plateau. Communications Earth & Environment (2023).
3. Group 2i Isochrysidales thrive in marine and lacustrine systems with ice cover. Scientific Reports (2024).
4. Impact of saponification and silver-nitrate purification on lacustrine alkenone distributions and alkenone-based indices. Journal of Chromatography A (2023).
5. Phylogenetic diversity in freshwater‐dwelling Isochrysidales haptophytes with implications for alkenone production. Geobiology (2019).
6. Successional blooms of alkenone‐producing haptophytes in Lake George, North Dakota: Implications for continental paleoclimate reconstructions. Limnology and Oceanography (2019).
7. Group 2i Isochrysidales produce characteristic alkenones reflecting sea ice distribution. Nature Communications (2021).