Modeling &lt;SUP&gt;210&lt;/SUP&gt;Pb-derived mixing activity in ocean margin sediments: Diffusive versus nonlocal mixing

Soetaert, Karline; Herman, Peter M. J.; Middelburg, Jack J.; Heip, C.H.R.; deStigter, H.S.; Weering, Tjeerd C.E. van; Epping, Eric; Helder, W.

doi:10.1357/0022240963213808

Cited by 115 publications

(76 citation statements)

References 30 publications

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“…Subsurface maxima in 210 Pb excess in the SML, as evident in cores SL9, KG17 and KG37, have also been noted elsewhere, and have been ascribed to local injection of surficial material at depth, for example as infill of large burrows (e.g. Smith et al, 1987;Soetaert et al, 1996;Thomson et al, 2000). This local or impulse bioturbation contrasts with the reworking by multiple small-scale events (termed non-local mixing) that approximate diffusive mixing Radakovitch et al (1999) is shaded.…”

Section: Discussionmentioning

confidence: 63%

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Indications of low macrobenthic activity in the deep sediments of the eastern Mediterranean Sea

Basso¹,

Thomson²,

Corselli³

2004

Sci. Mar.

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SUMMARY:The fluxes and budget of organic matter from the oligotrophic surface waters of the eastern Mediterranean to the deep waters are poorly known, and little information is available on past and present macrobenthic activity on the sea floor. Evidence of macrobenthic activity can be direct, through recovery of living organisms or their autochthonous skeletal remains, or indirect, through bioturbation and trace fossils. The evidence of biological activity in deep eastern Mediterranean sediments has been evaluated and compared through 210 Pb profiles from box-cores and study of dredge samples from sites on Medina Rise (1374 m water depth), the Messina Abyssal Plain (4135 m) and several sites along the Mediterranean Ridge, SW and S of Crete (1783 to 3655 m). All these sites are remote from the continental shelves, so the biological benthic activity is expected to depend primarily on primary production from surface waters. The results show that present-day macrobenthos and trace fossils are generally scarce, especially at depths >2500 m. This observation is supported by surface sediment 210 Pb excess distributions that show a surface mixed layer (SML) <6 cm deep in cores from water depths <2500 m and only 2-3 cm at greater depths, and estimated bioturbation intensities similarly fall off with water depth. These values are much lower than the average SML of ~10 cm in marine sediments elsewhere. It is unlikely that the present-day primary production in the eastern Mediterranean can sustain any structured macrobenthic activity at >2500 m. The historical layer of some box-cores and the Pleistocene hardgrounds collected in the Cleft area (Mediterranean Ridge) do, however, record a macrobenthic activity that is apparently more intense than at present, which may be related to higher primary production of the Pleistocene glacial intervals. In contrast with most areas of the present-day deep eastern Mediterranean which depend on surface primary production based on photosynthesis, a relatively dense and diversified macrobenthic community based on chemosynthesis has been recognised at depths >1100 m on the Napoli Dome mud volcano in the Olimpi area, and on the Kazan and other mud volcanoes in the Anaximander Mountains.Key words: deep macrobenthos, eastern Mediterranean, 210 Pb profiles, surface mixed layer, trace fossils, chemosynthesis, sapropels, Pleistocene. RESUMEN: INDICACIONES DE BAJA ACTIVIDAD EN EL MACROBENTOS DE SEDIMENTOS PROFUNDOS EN EL MEDITERRÁNEO ORIEN-TAL. -En el Mediterráneo oriental los flujos de materia orgánica desde las aguas superficiales oligotróficas hasta las aguas profundas son poco conocidos y en general hay poca información sobre la actividad del macrobentos en el fondo del mar. La evidencia de la actividad macrobentónica puede ser directa, a través de los organismos vivos o de los restos de esqueletos autóctonos, o indirecta, a través de la bioturbación y fósiles. La evidencia de la actividad biológica en los sedimentos profundos del Mediterráneo oriental se ha evaluado y comparado por medio de ...

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Section: Discussionmentioning

confidence: 63%

“…Soetaert et al, 1996). 210 Pb is supplied to the surface ocean from the atmosphere, following its production in the atmosphere from the decay of 222 Rn that has emanated from the continental landmasses (Turekian et al, 1977).…”

Section: Introductionmentioning

confidence: 99%

Indications of low macrobenthic activity in the deep sediments of the eastern Mediterranean Sea

Basso¹,

Thomson²,

Corselli³

2004

Sci. Mar.

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“…Nevertheless, it is debatable whether biodiffusion always constitutes a valid general reflection of bioturbation, since non-local mixing (such as conveyor-belt and reverse conveyor-belt feeding) appears to be a common bioturbation mechanism , Blair et al 1996, Soetaert et al 1996, Boudreau 1997, Levin et al 1997a. In this study, bioturbation potential has been inferred from feeding and particle-transport.…”

Section: Environmental Settingmentioning

confidence: 91%

Effects of dissolved oxygen and fresh organic matter on the bioturbation potential of macrofauna in sublittoral sediments off Central Chile during the 1997/1998 El Niño

Gutiérrez¹,

Gallardo²,

Mayor³

et al. 2000

Mar. Ecol. Prog. Ser.

112

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A study off Concepción, central Chile, during the 1997/1998 El Niño (EN) revealed that the concentration of dissolved oxygen and the organic content and quality of the sediment control the vertical distribution of macrofauna in the sediment and bioturbation potential. The study area, characterized by organic-rich, silty sediments, lies within the most intense upwelling center off the coast of Chile, and is subject to the seasonal influx of hypoxic subsurface waters. Five stations (28 to 120 m depth) were sampled seasonally. The vertical distribution and integrated biomass and abundance of macrofauna (> 0.5 mm) were determined, as well as the dissolved oxygen content of the bottom water (BWDO) and sediment parameters such as total organic carbon (TOC), the C/N ratio, sulphide content, chl a content, and the thickness of the oxidized zone. Chl a proved to be a good indicator of fresh (highquality) organic matter. Major components contributing to variation in the macrofauna feeding guilds, bioturbation categories, and their vertical position in the sediment were: (1) the relative bioturbation potential (contribution of bioturbating taxa to the assemblage) and (2) the vertical distribution and ratio of surface-to subsurface deposit-feeders. Higher levels of BWDO and a lower quality of organic matter at the sediment surface tended to provide better conditions for potentially strong bioturbators, while lower BWDO levels and higher-quality organic matter were accompanied by the dominance of tube-dwelling, surface-defecating (and hence weakly bioturbating) species. Higher TOC levels and lower-quality organic matter at the surface resulted in deeper vertical distributions of animals and a higher relative abundance of subsurface deposit-feeders. During the study period, BWDO levels increased, while the total organic carbon and the quality of organic matter decreased. These conditions encouraged the vertical penetration of macrofauna into the sediment column and the relatively larger contribution of stronger bioturbators to the assemblage. The most drastic changes in faunal lifestyles and vertical distribution during the 1997/1998 EN were observed within the Bay of Concepción, an area usually characterized by sulphidic sediments under the conditions of severe seasonal hypoxia or anoxia obtaining during 'normal' (i.e. non-EN) years; and in the deepest shelf site, which usually experiences permanent hypoxia because of the influence of the 'oxygen minimum zone'.

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“…[8] Estimates of the magnitude of the bioturbation coefficient, D b , in marine sediments have been derived from fitting calculated to measured tracer distributions, in particular 210 Pb depth profiles [Boudreau, 1994;Soetaert et al, 1996]. On the basis of the analysis of various tracer profiles, global correlations have been derived, relating D b , the sedimentation rate (w) and water depth (z) [Boudreau, 1994;Middelburg et al, 1997;Tromp et al, 1995].…”

Section: Governing Equationmentioning

confidence: 99%

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

Meile

Cappellen

2005

Global Biogeochemical Cycles

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[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,

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Modeling <SUP>210</SUP>Pb-derived mixing activity in ocean margin sediments: Diffusive versus nonlocal mixing

Cited by 115 publications

References 30 publications

Indications of low macrobenthic activity in the deep sediments of the eastern Mediterranean Sea

Indications of low macrobenthic activity in the deep sediments of the eastern Mediterranean Sea

Effects of dissolved oxygen and fresh organic matter on the bioturbation potential of macrofauna in sublittoral sediments off Central Chile during the 1997/1998 El Niño

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

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Modeling <SUP>210</SUP>Pb-derived mixing activity in ocean margin sediments: Diffusive versus nonlocal mixing

Cited by 115 publications

References 30 publications

Indications of low macrobenthic activity in the deep sediments of the eastern Mediterranean Sea

Indications of low macrobenthic activity in the deep sediments of the eastern Mediterranean Sea

Effects of dissolved oxygen and fresh organic matter on the bioturbation potential of macrofauna in sublittoral sediments off Central Chile during the 1997/1998 El Niño

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

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