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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Chemoautotrophic C fixation (mass balance) |- | '''Approach:''' mass balance synthesis from ocean carbon and respiration inventories |- | '''Context:''' ''in situ'', data synthesis |- | '''Spa..."

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{{BreadcrumbsPrimaryProduction}}

* [[Page authors|Page authors]]: [[PRIMO]]
* [[Responsible curator|Responsible curator]]: [[User:Hagi BucknWise|Hagen Buck-Wiese]]
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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
! Chemoautotrophic C fixation (mass balance)
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| '''Approach:''' mass balance synthesis from ocean carbon and respiration inventories
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| '''Context:''' ''in situ'', data synthesis
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| '''Spatial scale:''' ocean-wide to basin
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| '''Temporal scale:''' > years
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| '''Units:''' Pg C yr<sup>-1</sup>
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| '''Community captured:''' bulk
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| '''Co-measurements:''' ocean respiration rates; nitrification rates; C:N ratios
|}
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== Method Overview ==

Chemoautotrophic carbon fixation in the dark ocean is estimated by combining two constraints: (1) dark ocean community respiration rates (from AOU, <sup>14</sup>C-bicarbonate fixation, or ETS measurements), which set the total organic carbon demand; and (2) the stoichiometric relationship between oxidation of reduced nitrogen compounds (ammonium, nitrite) and CO<sub>2</sub> fixation. The classic formulation calculates dark ocean chemoautotrophic production by dividing dark respiration by the Redfield C:N ratio and applying the theoretical yield of one mole of CO<sub>2</sub> fixed per ~10 moles of ammonium oxidized<ref name="Middelburg2011">Middelburg, J. J. (2011). Chemoautotrophy in the ocean. ''Geophysical Research Letters'', 38, L24604. https://doi.org/10.1029/2011GL049725</ref>.

The approach synthesizes existing rate measurements and biogeochemical inventories to constrain the global magnitude of dark chemoautotrophic production, and is complementary to direct measurements (dark <sup>14</sup>C fixation, nanoSIMS).

=== Scale of measurement ===

Ocean-wide to basin-scale synthesis; the method does not provide spatial or temporal resolution within the dark ocean, but constrains the global budget.

=== Data generated ===

Estimated chemoautotrophic carbon production in Pg C yr<sup>-1</sup>, disaggregated by process (nitrification, sulphur oxidation, etc.) where sufficient data exist.

=== Units & currency ===

Units are Pg C yr<sup>-1</sup>. The currency is carbon.

=== Sample size ===

Not applicable; synthesis approach using existing datasets.

=== Repositories & databases ===

== Limitations ==

Relies on multiple assumptions: steady-state ocean, constant Redfield ratios, fixed stoichiometry of CO<sub>2</sub> fixation per mole of substrate oxidized. Uncertainty in both the respiration rate estimates and the stoichiometric constants propagates strongly into the chemoautotrophic production estimate. Emerging evidence suggests that nitrification may not dominate dark ocean chemoautotrophy in all regions or seasons, and that other pathways (sulphur oxidation, hydrogen oxidation) may contribute substantially.

== Example Applications & Protocols ==

=== Classic examples ===
* Middelburg (2011) ''Chemoautotrophy in the ocean'' <ref name="Middelburg2011" />

=== Recent applications ===
*

=== Common calculations/conversions ===
* Chemoautotrophic C fixation = dark respiration (Pg C yr<sup>-1</sup>) × (1 / Redfield C:N) × (1 / 10) for nitrification-based fixation.

== References ==

[[Category:Main Pages|Model types]]

Mass balance approach - Revision history