Particle age distributions and O₂ exposure times: Timescales in bioturbated sediments

Abstract

[1] A stochastic particle tracking approach is used to compute particulate age distributions and oxygen exposure times (OETs) in bioturbated marine sediments. Simulations representative of abyssal plain, continental slope, and continental shelf sediments indicate that within the mixed zone, the variability in particle age is of the same order of magnitude as the average age itself. This spreading of particle age by bioturbation complicates the interpretation of sedimentary archives. The results further show that average and median ages of particle-bound constituents undergoing decay during early diagenesis deviate from those of inert tracers. Similarly, OETs depend on the biological mixing and biogeochemical reactivity of particulate constituents. Hence ratios of the O 2 penetration depth (L O2 ) and the linear sedimentation rate (w) may not offer reliable measures of actual OETs. Taking into account biodiffusional particle mixing and preferential degradation of organic matter under oxygenated conditions, the stochastic model predicts a global inverse relationship between the burial efficiency and the OET of organic carbon in ocean sediments. The relationship, however, differs significantly from that proposed by Hartnett et al. (1998), who used O 2 penetration depths divided by linear sedimentation rates (L O2 /w) to estimate OETs.Citation: Meile, C., and P. Van Cappellen (2005), Particle age distributions and O 2 exposure times: Timescales in bioturbated sediments, Global Biogeochem. Cycles, 19, GB3013,

The global marine phosphorus cycle: sensitivity to oceanic circulation

“…The threshold concentration [RS] 0 that must be exceeded for precipitation to take place is set at 0.03 mM, which is in accordance with the lower end of the range of dissolved sulfide concentrations observed in the Black Sea (Neretin et al, 2003). The model results for oxygen are insensitive to the actual value imposed for the sulfide threshold concentration, within the range 0.03-0.30 mM.…”

“…Previous global-scale modeling studies of the response of the coupled marine cycles of carbon (C) and phosphorus to changes in oceanic circulation and water column ventilation do not explicitly account for the role of the continental margins (Van Cappellen and Ingall, 1994;Wallmann, 2003;Nederbragt et al, 2004). Yet, in the modern ocean, up to 70-90% of burial of organic matter and reactive phosphorus takes place in nearshore environments and on the continental shelves (Berner, 1982;Ruttenberg, 1993;Howarth et al, global marine productivity (Walsh, 1991;Mackenzie et al, 1993;Ver et al, 1999).…”

“…The increased concentrations of soluble P may offset the drop in vertical mixing rates, possibly even causing phosphoruslimited ocean primary production to increase during periods of ocean stagnation (Van Cappellen and Ingall, 1994;Wallmann, 2003). Hence, redox-sensitive burial of reactive P in marine sediments has been proposed as a feedback mechanism involved in the occurrence of oceanic anoxic events, or OAEs (Kuypers, 2001;Nederbragt et al, 2004).…”

“…Consequently, insight into the various forcings and functioning of the marine P cycle is needed to underCorrespondence to: C. P. Slomp (slomp@geo.uu.nl) stand long-term variations in marine biological activity, atmospheric composition and climate (Holland, 1984;Van Cappellen and Ingall, 1996;Petsch and Berner, 1998;Bjerrum and Canfield, 2002). Important forcings include the supply of reactive P from the continents, oceanic circulation and sea level fluctuations (Föllmi, 1996;Compton et al, 2000;Handoh and Lenton, 2003;Wallmann, 2003;Bjerrum et al, 2006).…”

Modelling Marine Sediment Biogeochemistry: Current Knowledge Gaps, Challenges, and Some Methodological Advice for Advancement

“…They require less parameterisation than discrete models, but are difficult to apply to bioturbated sediments where age and reactivity of organic matter depend on the burial velocity and bioturbation rate (Meile and Van Cappellen, 2005). Parameterisation of the continuum model to bioturbated sediments better captures the degradation of labile material within the top few millimetres of sediment, and more accurately predicts the drawdown of oxygen and nitrate from the water column (Stolpovsky et al, 2015).…”