Reply to the discussion paper by R. Martin on Kroeck et al. "A review of Paleozoic phytoplankton biodiversity: Driver for major evolutionary events?".

In our recent publication on the biodiversity of Paleozoic phytoplankton (Kroeck et al., 2022) we cited several works of Martin (Martin, 1996; Martin and Quigg, 2012; Martin and Servais, 2020) to present the hypothesis that during the late Paleozoic nutrient availability in the oceans increased significantly from a rather (super-) oligotrophic early to middle Paleozoic. We put this view in contrast to the notion, based on data on terrestrial sediment input, that nutrient availability generally decreased over the course of the Paleozoic. In his discussion paper, Martin (2022) expands on this hypothesis and the role of nutrients for biodiversification, and clarifies the use of the term "superoligotrophy" (Martin, 1996) for the early to middle Paleozoic interval. Martin (2022) highlights factors we neglected in our review of marine phytoplankton diversity in the Paleozoic. We largely agree with the arguments presented, and therefore consider this discussion as an excellent addition to our review. [ABSTRACT FROM AUTHOR]