Abstract: As authors of Meiler et al. (2022), we welcome Zehr and Riemann's (2023) comment and discussion. We agree, of course, with the general statement that “quantification of gene copy numbers is valuable in marine microbial ecology” and wish to clarify that one of the purposes of Meiler et al. (2022) was to address the specific challenge of using a compilation of quantitative polymerase chain reaction (qPCR) nifH data to evaluate the skill of biogeochemical models. In that particular case, the data were most helpful in constraining the range of diazotrophs, but several sources of uncertainty limited more detailed quantitative evaluations. This was not intended to imply a lack of value or promise for such applications of qPCR data: we believe that testing and constraining biogeochemical and ecological models will be an important application of qPCR data, yet the quantitative interface between molecular data and biogeochemical models remains at its infancy.

In the following, we first provide a background perspective for the Meiler et al. (2022) study, pointing out why observations and simulations are rooted in different currencies. We then discuss in more detail some of the specific points raised by Zehr and Riemann (2023) and highlight why further efforts toward intercalibration of currencies used to measure and simulate marine microbial populations is particularly significant if we are to fully exploit the data in biogeochemical and climate modeling applications. We end by summarizing some potentially fruitful avenues for future effort stimulated by this dialog.