Fig. 3: Proportion of microbial groups and hgcA gene abundance profiles obtained from the metagenomes from the water column and the sedimentary archives of the Black Sea.

Oxygen zones (oxic, suboxic and anoxic) and chronozones (Sub-Atlantic, Sub-boreal, Atlantic, Preboreal–Boreal and Younger Dryas), according to Huang et al.24 and associated environmental conditions16, are displayed for metagenomes corresponding to the water column and sedimentary archives, respectively. Oxygen concentrations are grouped based on three categories: oxic, ≥2 mgO2 l−1; suboxic water, >0–2 mgO2 l−1; euxinic water, 0 mgO2 l−1.