BGC-Argo NPP
Template:BreadcrumbsPrimaryProduction
| Float-derived NPP (BGC-Argo) |
|---|
| Approach: fluorescence and backscatter from profiling floats |
| Context: in situ, autonomous |
| Spatial scale: mesoscale, basin |
| Temporal scale: days to years |
| Units: mg C m-2 d-1 |
| Community captured: bulk |
| Co-measurements: fluorescence (proxy for Chl), optical backscatter (proxy for Cphyto), temperature, PAR |
Method Overview
BGC-Argo profiling floats are equipped with fluorometers and optical backscatter sensors that measure proxies for chlorophyll-a and phytoplankton carbon (Cphyto) throughout the water column during each ascent profile. NPP is estimated by applying a carbon-based productivity model (CbPM): Cphyto (derived from backscatter) is multiplied by a modelled specific growth rate (µ, d-1), which is estimated as a function of irradiance, temperature, and the Chl:Cphyto ratio. Depth integration over the euphotic zone yields daily NPP[1].
Alternatively, diel cycles in backscatter-derived Cphyto can be used to estimate division rates directly, independent of a growth model.
Scale of measurement
Floats profile from surface to ~2000 m every 5–10 days as they ascend; horizontal coverage is Lagrangian and limited by float drift. Regional to basin-scale coverage requires arrays of floats. The approach provides year-round observations in remote and seasonally ice-covered regions not accessible by ship.
Data generated
Depth-resolved and depth-integrated NPP in mg C m-2 d-1; time series from individual floats characterize seasonal and interannual variability at the float's location.
Units & currency
Units are mg C m-2 d-1. The currency is carbon.
Sample size
In situ sensor measurement; no discrete sample collection required.
Repositories & databases
BGC-Argo data are available at: argodatamgt.org.
Limitations
Backscatter-to-Cphyto and fluorescence-to-chlorophyll conversions are uncertain and vary with community composition and physiological state. Float trajectories cross water masses with different histories, complicating Lagrangian interpretation of temporal changes. NPP estimates have not been broadly validated against direct 14C measurements. Model-based growth rate estimates introduce structural uncertainty.
Example Applications & Protocols
Classic examples
- Arteaga et al. (2022) Vertical structure in phytoplankton growth and productivity inferred from biogeochemical-Argo floats and the carbon-based productivity model [1]
Recent applications
- Estapa et al. (2019) Direct observations of biological carbon export from profiling floats in the subtropical North Atlantic [2]
- Long et al. (2021) Depth-resolved net primary production in the Northeast Pacific Ocean: a comparison of satellite and profiling float estimates [3]
Common calculations/conversions
- NPP (mg C m-2 d-1) = ∫ Cphyto(z) × µ(z) dz; µ estimated from CbPM using irradiance, temperature, and Chl:Cphyto.
References
- ↑ 1.0 1.1 Arteaga, L. A., Behrenfeld, M. J., Boss, E., & Westberry, T. K. (2022). Vertical structure in phytoplankton growth and productivity inferred from biogeochemical-Argo floats and the carbon-based productivity model. Global Biogeochemical Cycles, 36, e2022GB007389. https://doi.org/10.1029/2022GB007389
- ↑ Estapa, M. L., Feen, M. L., & Breves, E. (2019). Direct observations of biological carbon export from profiling floats in the subtropical North Atlantic. Global Biogeochemical Cycles, 33, 282–300. https://doi.org/10.1029/2018GB006098
- ↑ Long, M. C., Stephens, B. B., McKain, K., Sweeney, C., Keeling, R. F., Kort, E. A., Brenninkmeijer, C. A. M., Bourgeois, T., Quay, P., Donets, V., Bent, J. D., & Ryerson, T. B. (2021). Depth-resolved net primary production in the Northeast Pacific Ocean. Geophysical Research Letters, 48, e2021GL093462. https://doi.org/10.1029/2021GL093462