Preserved particulate organic carbon is likely derived from the subsurface sulfidic photic zone of the Proterozoic Ocean: evidence from a modern, oxygen‐deficient lake

Biological processes in the Proterozoic Ocean are often inferred from modern oxygen‐deficient environments (MODEs) or from stable isotopes in preserved sediment. To date, few MODE studies have simultaneously quantified carbon fixation genes and attendant stable isotopic signatures. Consequently, how carbon isotope patterns reflect these pathways has not been thoroughly vetted. Addressing this, we profiled planktonic productivity and quantified carbon fixation pathway genes and associated organic carbon isotope values (δ13CPOC) of size‐fractionated (0.2–2.7 and >2.7 μm) particulate matter from meromictic Fayetteville Green Lake, NY, USA. The high‐O2 Calvin‐Benson‐Bassham (CBB) gene (cbbL) was most abundant in the