Successional blooms of alkenone‐producing haptophytes in Lake George, North Dakota: Implications for continental paleoclimate reconstructions

Alkenone-derived paleotemperature reconstruction holds great promise in lake environments. However, theoccurrence of multiple species of alkenone-producing haptophyte algae in a single lake can complicate thetranslation of alkenone unsaturation to temperature if each species requires an individual temperature calibra-tion. Here, we present thefirst systematic monitoring of two alkenone-producing haptophytes throughout thecourse of a seasonal cycle in Lake George, North Dakota, using a combined approach of DNA sequencing andalkenone lipid characterization. Field sampling revealed a nonoverlapping haptophyte succession, with both anearly and late season haptophyte bloom event. Culturing experiments demonstrated that the two haptophytespecies responsible for these blooms had statistically similar alkenone-temperature responses, although theculture-based calibrations were distinct from the in situ calibration. Bloom timing of each haptophyte speciescorresponded to surface-water temperatures that differed by more than 10?C, revealing that changes in bloomintensities for each species will skew the sediment-inferred temperatures to a different stage of the growth sea-son. These results highlight the importance of accounting for bloom timing when interpreting alkenone-derivedtemperatures in sediment cores, especially in lakes that experience large seasonalfluctuations in water columntemperature and salinity.