Alkenone producers during late Oligocene–early Miocene revisited

<jats:p>This study investigates ancient alkenone producers among the late Oligocene–early Miocene coccolithophores recorded at Deep Sea Drilling Project (DSDP) Site 516. Contrary to common assumptions, <jats:italic>Reticulofenestra</jats:italic> was not the most important alkenone producer throughout the studied time interval. The comparison between coccolith species‐specific absolute abundances and alkenone contents in the same sedimentary samples shows that <jats:italic>Cyclicargolithus</jats:italic> abundances explain 40% of the total variance of alkenone concentration and that the species <jats:italic>Cyclicargolithus floridanus</jats:italic> was a major alkenone producer, although other related taxa may have also contributed to the alkenone production at DSDP Site 516. The distribution of the different alkenone isomers (MeC<jats:sub>37:2</jats:sub>, EtC<jats:sub>38:2</jats:sub>, and MeC<jats:sub>38:2</jats:sub>) remained unchanged across distinct changes in species composition, suggesting similar diunsaturated alkenone compositions within the Noelaerhabdaceae family during the late Oligocene–early Miocene. However, the overall larger cell size of <jats:italic>Cyclicargolithus</jats:italic> may have implications for the alkenone‐based reconstruction of past partial pressure of CO<jats:sub>2.</jats:sub> Our results underscore the importance of a careful evaluation of the most likely alkenone producers for periods (>1.85 Ma) predating the first occurrence of contemporary alkenone producers (i.e., <jats:italic>Emiliania huxleyi</jats:italic> and <jats:italic>Gephyrocapsa oceanica</jats:italic>).</jats:p>