wAbstract
@Widespread black shale depositional intervals termed oceanic
anoxic events (OAEs) occurred repeatedly during the Phanerozoic
Eon. Here we developed a new vertical one-dimensional ocean biogeochemical
cycle model that involves several chemical reactions in an oxic-anoxic-sulfidic
water column. To explore the theoretical constraints for global
oceanic anoxia/euxinia quantitatively and systematically, we conducted
sensitivity analyses of the proposed causal mechanisms, including
elevated rates of riverine phosphorus (P) input, ocean stagnation,
and lowered oxygen solubility due to climate warming. We gave
special attention to the vertical chemical structure of the ocean
and also to the characteristic behaviors of the marine P cycle
under anoxic conditions, because the relationship between the
depth of anoxia and the benthic phosphorus flux could be important
for the occurrence of oceanic anoxia/euxinia. Steady-state simulations
indicated that (1) a decrease in ocean stagnation or oxygen solubility
is not enough by itself to achieve widespread anoxia with the
present reactive P river input rate, and (2) shallow water anoxia
followed by massive P liberation from surface sediments can lead
to widespread eutrophication and anoxia/euxinia. We conclude that
elevated riverine flux of reactive P is the most important factor
for triggering global anoxic events via a positive feedback loop
among ocean anoxia, phosphorus regeneration, and surface biological
productivity.
Keywords: anoxia; euxinia; oceanic anoxic events; biogeochemical
cycles; phosphorus cyclex
1. Introduction
2. Model description
@2.1. Model ocean configuration and basic equation
@2.2. Biological pump
@2.3. Redox reactions and kinetics
@2.4. Burial of organic carbon and phosphorus
3. Results and discussion
@3.1. Standard case
@3.2. Sensitivity to reactive P riverine input flux and ocean
circulation rate
@3.3. Conditions for occurrence of oceanic anoxia/euxinia
@3.4. Effect of oxygen solubility
@3.5. Role of anoxia-productivity feedback
4. Conclusions and implications
Acknowledgements
References