5:15 PM - 6:45 PM
[MIS12-P11] System analysis of biogeochemical processes and microbial ecosystems in anoxic marine and lacustrine environments with a vertical one-dimensional model
Keywords:biogeochemical cycle model, marine microbial ecosystem, Fe-P cycles, the Black Sea, Lake Matano
Most parts of the present-day oceans are oxic aerobic environments from the surface to the deep water. However, in some marine and lacustrine environments, the deep part of euphotic zone and deep waters are permanently anoxic, anaerobic, and enriched in dissolved hydrogen sulfide (H2S) or ferrous iron (Fe2+), called euxinic and ferruginous environments, respectively. In such environments, the redox states of chemical species and microbiota in the waters vary vertically. Understanding biogeochemical processes in such partly aerobic and partly anaerobic water environments is important for studying ocean anoxic events that occurred repeatedly throughout the Phanerozoic, as well as studying Precambrian marine environments under low pO2. Here we developed a vertical one-dimensional biogeochemical cycle model of surface 500 m of oceans with high resolution that incorporates microbial ecosystems and redox chemical reactions. We applied the model to modern marine and lacustrine environments which have redox boundary within the euphotic zone. We report the results and the implications obtained by comparing the numerical results with observations in the modern euxinic and ferruginous water environments.
First, we applied the model to the Black Seawhich is known as the largest modern basin with euxinic deep water. In the numerical results, green sulfur bacteria are active at the redox boundary, and they are vertically separated from cyanobacteria in the shallower surface water. The results also suggest that primary production is limited by nitrogen. These characteristic features are consistent with observations (Becker et al., 2018; Yayla et al., 2001).
We also applied our model to Lake Matano, Indonesia, which is a lake with ferruginous deep water. In such a ferruginous water environment, phosphate is adsorbed onto iron (oxyhydr-)oxides, resulting in depletion of phosphorous for primary producers. To investigate the coupling between the iron and phosphorus cycles (Fe-P cycles), we conducted a parameter study on the Fe/P ratio of settling iron oxide particles in the water column ([Fe/P]sorption). When [Fe/P]sorption =~20, the simulated vertical distributions of the chemical species agreed well with observations (Crowe et al., 2008), and anaerobic anoxygenic phototrophs (green sulfur bacteria and photoferrotrophs) coexisted with aerobic oxygenic cyanobacteria in a vertically segregated manner. In addition, we found that cyanobacterial activity is strongly limited when [Fe/P]sorption<~20 . This implies that phosphorus adsorption onto iron oxides has a strong influence on microbial ecosystem structures in ferruginous lacustrine environments including Lake Matano. It is therefore suggested that primary productivity and oxygen production may have been largely regulated by Fe-P cycles in the late Archean and early Proterozoic oceans.
References
Becker, et al. (2018) Appl. Environ. Microbiol. 84, e02736-17.
Crowe et al. (2008) Proc. Natl. Acad. Sci. U.S.A. 105, 15938–15943.
Yayla et al. (2001) Aquatic Ecosystem Health & Management 4, 33–49.
First, we applied the model to the Black Seawhich is known as the largest modern basin with euxinic deep water. In the numerical results, green sulfur bacteria are active at the redox boundary, and they are vertically separated from cyanobacteria in the shallower surface water. The results also suggest that primary production is limited by nitrogen. These characteristic features are consistent with observations (Becker et al., 2018; Yayla et al., 2001).
We also applied our model to Lake Matano, Indonesia, which is a lake with ferruginous deep water. In such a ferruginous water environment, phosphate is adsorbed onto iron (oxyhydr-)oxides, resulting in depletion of phosphorous for primary producers. To investigate the coupling between the iron and phosphorus cycles (Fe-P cycles), we conducted a parameter study on the Fe/P ratio of settling iron oxide particles in the water column ([Fe/P]sorption). When [Fe/P]sorption =~20, the simulated vertical distributions of the chemical species agreed well with observations (Crowe et al., 2008), and anaerobic anoxygenic phototrophs (green sulfur bacteria and photoferrotrophs) coexisted with aerobic oxygenic cyanobacteria in a vertically segregated manner. In addition, we found that cyanobacterial activity is strongly limited when [Fe/P]sorption<~20 . This implies that phosphorus adsorption onto iron oxides has a strong influence on microbial ecosystem structures in ferruginous lacustrine environments including Lake Matano. It is therefore suggested that primary productivity and oxygen production may have been largely regulated by Fe-P cycles in the late Archean and early Proterozoic oceans.
References
Becker, et al. (2018) Appl. Environ. Microbiol. 84, e02736-17.
Crowe et al. (2008) Proc. Natl. Acad. Sci. U.S.A. 105, 15938–15943.
Yayla et al. (2001) Aquatic Ecosystem Health & Management 4, 33–49.