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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Carbon fixation (¹³C stable isotope) |- | '''Approach:''' stable isotope tracer (¹³C) uptake |- | '''Context:''' incubation, ''in situ'' |- | '''Spatial scale:''' point s..."

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Created page with "{{BreadcrumbsPrimaryProduction}} * Page authors: PRIMO * Responsible curator: Hagen Buck-Wiese ---- __TOC__ <div class="model-box"> {| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Carbon fixation (13C stable isotope) |- | '''Approach:''' stable isotope tracer (13C) uptake |- | '''Context:''' incubation, ''in situ'' |- | '''Spatial scale:''' point s..."

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{{BreadcrumbsPrimaryProduction}}

* [[Page authors|Page authors]]: [[PRIMO]]
* [[Responsible curator|Responsible curator]]: [[User:Hagi BucknWise|Hagen Buck-Wiese]]
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<div class="model-box">
{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
! Carbon fixation (13C stable isotope)
|-
| '''Approach:''' stable isotope tracer (13C) uptake
|-
| '''Context:''' incubation, ''in situ''
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| '''Spatial scale:''' point sample; single cell
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| '''Temporal scale:''' hours
|-
| '''Units:''' µmol C L-1 d-1; fmol C cell-1 d-1 (single cell)
|-
| '''Community captured:''' all (bulk > 0.7 µm); single-cell resolution available
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| '''Co-measurements:''' background δ13C (POC), DIC concentration, DIC 13C:12C ratio before and after incubation; can couple with 15N uptake in the same assay
|}
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== Method Overview ==

NaH13CO3, a stable (non-radioactive) isotope of bicarbonate, is added to seawater samples at tracer or enrichment levels. After incubation, particulate organic carbon is collected by filtration (GF/F, GF/D, or polycarbonate filters) and the 13C:12C ratio is measured by isotope ratio mass spectrometry (IRMS) or elemental analyser–IRMS (EA-IRMS). Carbon fixation rates are calculated from the isotopic enrichment of the POC relative to the enrichment of the DIC pool<ref name="Hama1983">Hama, T., Miyazaki, T., Ogawa, Y., Iwakuma, T., Takahashi, M., Otsuki, A., & Ichimura, S. (1983). Measurement of photosynthetic production of a marine phytoplankton population using a stable 13C isotope. ''Marine Biology'', 73, 31–36. https://doi.org/10.1007/BF00396282</ref><ref name="Slawyk1977">Slawyk, G., Collos, Y., & Auclair, J.-C. (1977). The use of the 13C and 15N isotopes for the simultaneous measurement of carbon and nitrogen turnover rates in marine phytoplankton. ''Limnology and Oceanography'', 22(5), 925–932. https://doi.org/10.4319/lo.1977.22.5.0925</ref>.

The stable isotope approach eliminates radioactive waste and allows simultaneous coupling with 15N uptake measurements using the same incubation bottles. At single-cell resolution, nanoSIMS (nano-scale secondary ion mass spectrometry) can measure the 13C:12C ratio in individually identified cells, providing cell-specific carbon fixation rates.

=== Scale of measurement ===

Bulk filtration provides a community-level point measurement. Size fractionation (e.g., 0.7 µm and 2.7 µm) resolves production across size classes. At the single-cell level, nanoSIMS can provide taxon-specific rates with spatial resolution of tens of nanometers, but requires a separate cell identification step (FISH or cell sorting).

=== Data generated ===

The method yields carbon fixation rates in µmol C L-1 d-1 (bulk) or fmol C cell-1 d-1 (single cell). When coupled with 15N, simultaneous C and N assimilation rates are obtained.

=== Units & currency ===

Units are µmol C L-1 d-1 for bulk, or fmol C cell-1 d-1 for single-cell nanoSIMS.

=== Sample size ===

Typical samples range from 0.3 to 4 L for bulk measurements; nanoSIMS requires only a few mL but extensive instrument time for sufficient cell numbers.

=== Repositories & databases ===

== Limitations ==

The natural abundance of 13C in the DIC pool (background δ13C) must be measured accurately; isotopic changes in the DIC pool during incubation can bias rate estimates if not corrected. For single-cell estimates, the initial cellular carbon content is assumed to be proportional to cell volume, introducing uncertainty for cell types with variable carbon densities. Bottle effects apply as in the 14C method.

== Example Applications & Protocols ==

=== Classic examples ===
* Hama et al. (1983) ''Measurement of photosynthetic production of a marine phytoplankton population using a stable 13C isotope'' <ref name="Hama1983" />
* Slawyk et al. (1977) ''The use of the 13C and 15N isotopes for the simultaneous measurement of carbon and nitrogen turnover rates in marine phytoplankton'' <ref name="Slawyk1977" />

=== Recent applications ===
* Wu et al. (2022) ''Single-cell measurements and modelling reveal substantial organic carbon acquisition by Prochlorococcus'' <ref name="Wu2022">Wu, S., Huang, R., & Jiao, N. (2022). Single-cell measurements and modelling reveal substantial organic carbon acquisition by Prochlorococcus. ''Nature Microbiology'', 7, 2068–2077. https://doi.org/10.1038/s41564-022-01250-5</ref>
* Irion et al. (2021) ''Small phytoplankton contribute greatly to CO₂-fixation after the diatom bloom in the Southern Ocean'' <ref name="Irion2021">Irion, S., Jardillier, L., Sassenhagen, I., & Christaki, U. (2021). Small phytoplankton contribute greatly to CO₂-fixation after the diatom bloom in the Southern Ocean. ''The ISME Journal'', 15, 2509–2522. https://doi.org/10.1038/s41396-021-00915-z</ref>

=== Common calculations/conversions ===
* C fixation rate = [(δ13CPOC,final − δ13CPOC,initial) / (δ13CDIC − δ13CPOC,initial)] × [POC] / incubation time.

== References ==

[[Category:Main Pages|Model types]]

13-Carbon uptake - Revision history