Benthic nitrogen cycling traversing the Peruvian oxygen minimum zone

Bohlen, Lisa; Dale, Andy W.; Sommer, Stefan; Mosch, Thomas; Hensen, Christian; Noffke, Anna; Scholz, Florian; Wallmann, Klaus

doi:10.1016/j.gca.2011.08.010

Cited by 94 publications

(124 citation statements)

References 84 publications

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“…The ammonium produced leaks out of the sediment and fuels water column N loss by anammox . Biological oxidation of sulfide is a major sink for sulfide in Peruvian shelf sediments (Bohlen et al, 2011;Dale et al, 2016). Bacterial biomass can be diminished if electron acceptors in the bottom water are depleted or if large amounts of organic matter are deposited on the sea bed (Gutiérrez et al, 2008).…”

Section: Site Descriptionmentioning

confidence: 99%

“…We used previous steady state models of the benthic N cycle on the Peruvian shelf to parameterize the model (Bohlen et al, 2011;Dale et al, 2016). There is uncertainty in applying the same parameterization to a non-steady state scenario since, as will become clear later, sediment geochemistry shows considerable temporal variability.…”

Section: Modelmentioning

confidence: 99%

“…There is uncertainty in applying the same parameterization to a non-steady state scenario since, as will become clear later, sediment geochemistry shows considerable temporal variability. Benthic fluxes and porewater concentration data are available at 11 • S and 12 • S from summer 2008 and 2013, respectively, and permit some constraint on the rates of modeled processes (Bohlen et al, 2011;Sommer et al, 2016). Importantly, however, the reactivity of organic matter in the sediment is not arbitrarily assigned based on literature values, but is carefully tailored to the Peruvian shelf, as described below.…”

Section: Modelmentioning

confidence: 99%

“…In the steady state version of our model, the reactivity of bulk POC pool is constrained directly from the ammonium (NH + 4 ) profile and decreases smoothly with depth in the sediment, that is, as a reactive continuum (Bohlen et al, 2011;Dale et al, 2016). However, this approach is not suitable for non-steady state applications because of complications in defining the boundary conditions for a single POC pool whose reactivity decreases with sediment depth (i.e., over time).…”

Section: Poc Degradationmentioning

confidence: 99%

“…Mass balances, model calculations and biogeochemical observations suggest that sulfide (H 2 S) oxidation to sulfate (SO 2− 4 ) coupled to nitrate (NO − 3 ) reduction by vacuolated Thioploca spp. is a major process in Peruvian shelf sediments (Henrichs and Farrington, 1984;Fossing et al, 1995;Huettel et al, 1996;Otte et al, 1999;Bohlen et al, 2011). This process, DNRA, can be described as (Zopfi et al, 2001):…”

Section: Benthic N Cyclementioning

confidence: 99%

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Strong and Dynamic Benthic-Pelagic Coupling and Feedbacks in a Coastal Upwelling System (Peruvian Shelf)

2017

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Monthly time-series data (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)) of bottom water oxygen, nitrate and nitrite concentrations from the outer shelf (150 m water depth) in the oxygen minimum zone offshore Peru were coupled to a layered biogeochemical sediment model to investigate benthic-pelagic coupling over multi-annual time scales. The model includes the mineralization of four reactive pools of particulate organic carbon (POC) with lifetimes of 0.13, 1.3, 20, and 1700 year that were constrained using empirical data. Total POC rain rates to the seafloor were derived from satellite based estimates of primary production. Solute fluxes and concentrations in sediment porewater showed highly dynamic behavior over the course of a typical year. Conversion of fixed N to N 2 by denitrification varied from 1.1 mmol m −2 d −1 of N in winter to 1.8 mmol m −2 d −1 of N in summer with a long term mean N loss for the shelf of 1.5 mmol m −2 d −1 of N. Fixed N loss across the whole time-series agreed very well with a previously-published vertically-integrated sediment model for coupling the benthic and pelagic N cycle in regional and global models. Dissimilatory nitrate reduction to ammonium (DNRA) emerges as a major process in the benthic N cycle, producing on average 1.9 mmol m −2 d −1 of ammonium: more than twice the rate of ammonification of organic nitrogen. The model predicts sulfide emissions from the sediment of up to 1 mmol m −2 d −1 when POC rain rate exceeds 20 mmol m −2 d −1 , in agreement with past observations of benthic sulfide fluxes and sulfide plume distributions in the water column. This study demonstrates that sediments on the Peruvian shelf are not static repositories that are independent of changes taking place in the water column. Our results strongly suggest the shelf sediments must exert an important feedback on biogeochemical processes in the overlying waters, and should be considered in regional model studies.

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Section: Site Descriptionmentioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

Section: Poc Degradationmentioning

confidence: 99%

Section: Benthic N Cyclementioning

confidence: 99%

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Strong and Dynamic Benthic-Pelagic Coupling and Feedbacks in a Coastal Upwelling System (Peruvian Shelf)

2017

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A revised global estimate of dissolved iron fluxes from marine sediments

Dale

Nickelsen

Scholz

et al. 2015

Global Biogeochemical Cycles

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158

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Literature data on benthic dissolved iron (DFe) fluxes (μmol m À2 d À1 ), bottom water oxygen concentrations (O 2BW , μM), and sedimentary carbon oxidation rates (C OX , mmol m À2 d À1 ) from water depths ranging from 80 to 3700 m were assembled. The data were analyzed with a diagenetic iron model to derive an empirical function for predicting benthic DFe fluxes: DFe flux ¼ γ Á tanh COX O2BW where γ (= 170 μmol m À2 d À1 ) is the maximum flux for sediments at steady state located away from river mouths. This simple function unifies previous observations that C OX and O 2BW are important controls on DFe fluxes. Upscaling predicts a global DFe flux from continental margin sediments of 109 ± 55 Gmol yr À1 , of which 72 Gmol yr À1 is contributed by the shelf (<200 m) and 37 Gmol yr À1 by slope sediments (200-2000 m). The predicted deep-sea flux (>2000 m) of 41 ± 21 Gmol yr À1 is unsupported by empirical data. Previous estimates of benthic DFe fluxes derived using global iron models are far lower (approximately 10-30 Gmol yr À1 ). This can be attributed to (i) inadequate treatment of the role of oxygen on benthic DFe fluxes and (ii) improper consideration of continental shelf processes due to coarse spatial resolution. Globally averaged DFe concentrations in surface waters simulated with the intermediate-complexity University of Victoria Earth System Climate Model were a factor of 2 higher with the new function. We conclude that (i) the DFe flux from marginal sediments has been underestimated in the marine iron cycle and (ii) iron scavenging in the water column is more intense than currently presumed.

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Toward a parameterization of global‐scale organic carbon mineralization kinetics in surface marine sediments

Stolpovsky

Dale

Wallmann

2015

Global Biogeochemical Cycles

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An empirical function is derived for predicting the rate-depth profile of particulate organic carbon (POC) degradation in surface marine sediments including the bioturbated layer. The rate takes the form of a power law analogous to the Middelburg function. The functional parameters were optimized by simulating measured benthic O 2 and NO 3 À fluxes at 185 stations worldwide using a diagenetic model. The novelty of this work rests with the finding that the vertically resolved POC degradation rate in the bioturbated zone can be determined using a simple function where the POC rain rate is the governing variable. Although imperfect, the model is able to fit 71% of paired O 2 and NO 3 À fluxes to within 50% of measured values. It further provides realistic geochemical concentration-depth profiles, NO 3 À penetration depths, and apparent first-order POC mineralization rate constants. The model performs less well on the continental shelf due to the high sediment heterogeneity there. When applied to globally resolved maps of rain rate, the model predicts a global denitrification rate of 182 ± 88 Tg yr À1 of N and a POC burial rate of 107 ± 52 Tg yr À1 of C with a mean carbon burial efficiency of 6.1%. These results are in very good agreement with published values. Our proposed function is conceptually simple, requires less parameterization than multi-G-type models, and is suitable for nonsteady state applications. It provides a basis for more accurately simulating benthic nutrient fluxes and carbonate dissolution rates in Earth system models.

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Benthic nitrogen cycling traversing the Peruvian oxygen minimum zone

Abstract: ABSTRACT

Cited by 94 publications

References 84 publications

Strong and Dynamic Benthic-Pelagic Coupling and Feedbacks in a Coastal Upwelling System (Peruvian Shelf)

Strong and Dynamic Benthic-Pelagic Coupling and Feedbacks in a Coastal Upwelling System (Peruvian Shelf)

A revised global estimate of dissolved iron fluxes from marine sediments

Toward a parameterization of global‐scale organic carbon mineralization kinetics in surface marine sediments

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