Comment on bg-2022-228

Abstract

Organic matter (OM) degradation in marine sediments is largely controlled by its reactivity and profoundly affects the global carbon cycle. Yet, there is currently no general framework that can constrain OM reactivity on a global scale. In this study, we propose a reactive continuum model based on a lognormal distribution (l-RCM) that is fully described by the mean μ and standard deviation σ of the sedimentary OM reactivity distribution. We use the l-RCM to inversely determine μ and σ at 123 sites across the global ocean. The results find that the apparent OM reactivity (<k>=μ·exp(σ2/2)) decreases with decreasing sedimentation rate (ω) and show that OM reactivity is more than three orders of magnitude higher in shelf than that in abyssal regions. Despite the general global trends, higher than expected OM reactivity is observed in certain deeper ocean regions, such as the Eastern-Western Coastal Equatorial Pacific and the Arabian Sea, emphasizing the complex control of the depositional environment (e.g., OM flux, oxygen content in the water column) on benthic OM reactivity. Notably, the l-RCM can also highlight the variability of OM reactivity in these regions. Based on inverse modeling results in our database, we establish the significant statistical relationships between <k> and ω, and further map the global OM reactivity distribution.