『Abstract
The geological record bears evidence of various periods of wide-scale
oceanic anoxia that are associated with perturbations of the marine
carbon and phosphorus (P) cycles. In this study, we examine the
impact of changes in bottom water oxygen and organic matter (OM)
input on burial of P in deep-sea sediments using a reactive-transport
model. Results show that the burial of key reactive P phases,
namely authigenic calcium associated P minerals (Ca-P), organic
P (org P) and iron-bound P (Fe-P), responds non-linearly to both
water column forcings, namely water column oxygeneration and OM
loading. High organic matter (OM) flux with either very low or
high oxygen (〜180μM) favor the formation of authigenic Ca-P, while
low oxygen and intermediate to high OM fluxes promote org P burial.
Iron-bound P is only preserved in the sediment when oxygen levels
are high and OM fluxes low. The conditions for maximum P recycling
(or minimum P burial) are low bottom water oxygen concentrations
and low OM fluxes to the sediment-water interface (hypoxic, oligotrophic
deep-sea settings). The bivariate dependence of P burial on oxygen
and OM flux was implemented in an existing box model of the global
marine P, oxygen and organic carbon cycles, replacing simple empirical
redox functions for P burial. The response of the original and
new box model to decreased ocean mixing was then assessed, in
the context of a long-term response. In the new model, org P instead
of authigenic Ca-P is the dominant burial phase of P in deep-sea
environments during periods of oceanic anoxia. Nevertheless, reduced
ocean mixing leads to a similar response in total P burial and,
as a consequence, to a similar increase in deep water anoxia and
decrease in open ocean productivity whether an empirical or mechanistic
description of phosphorus diagenesis is considered.
Keywords: Phosphorus; Seep sea; Anoxia; Sediment; Primary productivity;
Reactive transport model』
1. Introduction
2. Model and numerical experiment description
2.1. Reactive-transport model (RTM)
2.1.1. Numerical solution procedure
2.1.2. RTM parameterization
2.2. Numerical experiment
2.3. Box model
3. Results and discussion
3.1. Deep-sea environments
3.2. Sensitivity to forcings
3.3. Link to the global marine P cycle
4. Conclusions
Acknowledgments
Appendix A. Supplementary data
References