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First, they doubt that nannofossil paleofluxes trace carbonate productivity, due to modifications by dissolution during transport and burial, sediment dilution, and diagenesis.

Our nannofossil assemblages do have “less than half the diversity of global estimates of this age,” but we emphasize that dissolution is not “a major control” and that our assemblages are oceanic, normally characterized by low species richness.

First, multiple environmental and preservation factors influence the composition of nannofossil assemblages and must be given due consideration before concluding a surface ocean acidification effect.

Any primary ecological or geochemical signals have likely been modified by diagenesis, and we question the use of nannofossil accumulation rates as a proxy for primary carbonate production in these sediments.

Carbon-rich sediments have CO2-rich, acidic pore waters that lead to postdepositional dissolution and mobilization of carbonate that affect both nannofossil and geochemical records.