oa Biofossils Versus Mircrofossils – Complements or Contradictions

Atmospheric CO2 concentration, sea water temperatures and nutrient supply constitute prime factors for spatiotemporal distribution of primary producers in the world ocean (e.g., Hallengraeff, 2010 ). Changes in the phytoplankton community structure in turn affect the marine food web, the biological pump and thereby the entire marine ecosystem and carbon cycling (e.g., Michaels and Silver, 1988 ). In the geological past, response of the entire association of marine phytoplankton towards climate change events is not well constrained as most our knowledge is mainly based on shell-forming (CaCO3, SiO2) phytoplankton groups, such as coccolithophorids, diatoms, radiolaria, and on organic-walled phytoplankton remains (e.g., dinoflagellate cysts) that can be optically identified. optically identifiable phytoplankton groups, however, represent only a small part of the marine primary producer community, which dominantly lacks preservable hard parts. Moreover, sediment diagenesis can impact mircofossil preservation and can thereby alter the micropaleontological record (Slater et al., 2019). A holistic assessment of phytoplankton community dynamics in the geological past can be based on the investigation of taxon-specific molecular fossils (biomarkers) that can be linked to different phytoplankton groups (e.g., ( Huang and Meinschein, 1979 ; Briggs and Summons, 2014 ).