Anoxic microniches in marine sediments induced by aggregate settlement: iogeochemical dynamics and implications

Niklas Lehto, Ronnie N. Glud, Gunnvør á Nordi, Hao Zhang, William Davison

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

Resumé

Spherical (*2 mm diameter) diatom (Skeletonema sp.) aggregates, representing analogues of ‘‘marine snow’’, were placed at the sediment–water interface of an experimental sediment system. Optode measurements showed that, after an initial lag period, oxygen concentrations within the aggregates decreased and then were gradually replenished, resulting in a temporary anoxic microniche. A multispecies, 3-dimensional, reactive transport model was used to simulate the oxygen dynamics and the associated biogeochemical consequences. Temporal
and spatial changes in oxygen were replicated assuming an exponential increase in the mineralisation rate constant and a gradual exhaustion of reactive organic
material. The peak value of the time-dependent reaction rate constant of organic matter mineralisation (kOMM) was seven to sixty times greater than analogous
values measured previously in water column experiments. The validated model was used to investigate how the size and reactivity of parcels of organic matter influence the formation of anoxic microniches at the sediment–water interface of typical deep-sea environments. As well as kOMM, the concentration of reactive organic matter in the aggregate, its size and porosity were also critical in determining the likelihood of anoxic microniche formation. For the optimum fitted parameters describing kOMM and the concentration of reactive organic atter, the minimum diameter of the parcel to induce anoxia was 1.8 mm, hereas it was 2.8 mm to make a significant contribution to the denitrification occurring in a typical deep-sea sediment. This work suggests that anoxic microniches resulting from the settlement of marine aggregates may play an overlooked role for denitrification activities in deep-sea sediments.
OriginalsprogEngelsk
TidsskriftBiogeochemistry
Vol/bind119
Sider (fra-til)307-327
ISSN0168-2563
DOI
StatusUdgivet - jun. 2014

Citer dette

Lehto, Niklas ; Glud, Ronnie N. ; Nordi, Gunnvør á ; Zhang, Hao ; Davison, William. / Anoxic microniches in marine sediments induced by aggregate settlement : iogeochemical dynamics and implications. I: Biogeochemistry. 2014 ; Bind 119. s. 307-327.
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Anoxic microniches in marine sediments induced by aggregate settlement : iogeochemical dynamics and implications. / Lehto, Niklas; Glud, Ronnie N.; Nordi, Gunnvør á; Zhang, Hao; Davison, William.

I: Biogeochemistry, Bind 119, 06.2014, s. 307-327.

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

TY - JOUR

T1 - Anoxic microniches in marine sediments induced by aggregate settlement

T2 - iogeochemical dynamics and implications

AU - Lehto, Niklas

AU - Glud, Ronnie N.

AU - Nordi, Gunnvør á

AU - Zhang, Hao

AU - Davison, William

PY - 2014/6

Y1 - 2014/6

N2 - Spherical (*2 mm diameter) diatom (Skeletonema sp.) aggregates, representing analogues of ‘‘marine snow’’, were placed at the sediment–water interface of an experimental sediment system. Optode measurements showed that, after an initial lag period, oxygen concentrations within the aggregates decreased and then were gradually replenished, resulting in a temporary anoxic microniche. A multispecies, 3-dimensional, reactive transport model was used to simulate the oxygen dynamics and the associated biogeochemical consequences. Temporaland spatial changes in oxygen were replicated assuming an exponential increase in the mineralisation rate constant and a gradual exhaustion of reactive organicmaterial. The peak value of the time-dependent reaction rate constant of organic matter mineralisation (kOMM) was seven to sixty times greater than analogousvalues measured previously in water column experiments. The validated model was used to investigate how the size and reactivity of parcels of organic matter influence the formation of anoxic microniches at the sediment–water interface of typical deep-sea environments. As well as kOMM, the concentration of reactive organic matter in the aggregate, its size and porosity were also critical in determining the likelihood of anoxic microniche formation. For the optimum fitted parameters describing kOMM and the concentration of reactive organic atter, the minimum diameter of the parcel to induce anoxia was 1.8 mm, hereas it was 2.8 mm to make a significant contribution to the denitrification occurring in a typical deep-sea sediment. This work suggests that anoxic microniches resulting from the settlement of marine aggregates may play an overlooked role for denitrification activities in deep-sea sediments.

AB - Spherical (*2 mm diameter) diatom (Skeletonema sp.) aggregates, representing analogues of ‘‘marine snow’’, were placed at the sediment–water interface of an experimental sediment system. Optode measurements showed that, after an initial lag period, oxygen concentrations within the aggregates decreased and then were gradually replenished, resulting in a temporary anoxic microniche. A multispecies, 3-dimensional, reactive transport model was used to simulate the oxygen dynamics and the associated biogeochemical consequences. Temporaland spatial changes in oxygen were replicated assuming an exponential increase in the mineralisation rate constant and a gradual exhaustion of reactive organicmaterial. The peak value of the time-dependent reaction rate constant of organic matter mineralisation (kOMM) was seven to sixty times greater than analogousvalues measured previously in water column experiments. The validated model was used to investigate how the size and reactivity of parcels of organic matter influence the formation of anoxic microniches at the sediment–water interface of typical deep-sea environments. As well as kOMM, the concentration of reactive organic matter in the aggregate, its size and porosity were also critical in determining the likelihood of anoxic microniche formation. For the optimum fitted parameters describing kOMM and the concentration of reactive organic atter, the minimum diameter of the parcel to induce anoxia was 1.8 mm, hereas it was 2.8 mm to make a significant contribution to the denitrification occurring in a typical deep-sea sediment. This work suggests that anoxic microniches resulting from the settlement of marine aggregates may play an overlooked role for denitrification activities in deep-sea sediments.

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JO - Biogeochemistry

JF - Biogeochemistry

SN - 0168-2563

ER -