Depth‐Resolved Net Primary Production in the Northeast Pacific Ocean: A Comparison of Satellite and Profiling Float Estimates in the Context of Two Marine Heatwaves

Abstract

Methods commonly used to estimate net primary production (NPP) from satellite observations are now being applied to biogeochemical (BGC) profiling float observations. Insights can be gained from regional differences in float and satellite NPP estimates that reveal gaps in our understanding and guide future NPP model development. We use 7 years of BGC profiling float data from the Northeast Pacific Ocean to quantify discrepancies between float and satellite NPP estimates and decompose them into contributions associated with the platform sensing method and depth resolution of observations. We find small, systematic seasonal discrepancies in the depth‐integrated NPP (iNPP) but much larger (>±100%) discrepancies in depth‐resolved NPP. Annual iNPP estimates from the two platforms are significantly, positively correlated, suggesting that they similarly track interannual variability in the study region. Using the long‐term satellite iNPP record, we identify elevated annual iNPP during two recent marine heatwaves and gain insights about ecosystem functionality.

The Use of VGPM to Estimate Oceanic Primary Production: A “Tango” Difficult to Dance

“…Nevertheless, by no means do we suggest that the above schemes have resolved all the issues and challenges associated with the remote sensing of PP, especially the vertical variations associated with biological and physiological properties [32][33][34]. Rather, it only indicates that it is not a requirement to include Chl (and then the involvement of a * ph ) in the algorithms or models.…”

Partitioning the Export of Distinct Biogenic Carbon Pools in the Northeast Pacific Ocean Using a Biogeochemical Profiling Float

“…Estimates of in situ NPP were computed by applying the Carbon‐based Productivity Model (CbPM; Westberry et al., 2008; Behrenfeld et al., 2005) to simultaneous satellite observations (PAR) and depth‐resolved float observations (b bp , Chl‐ a ) that have been rigorously calibrated against Canadian Line P Cruise observations (Long et al., 2021). Briefly, NPP is a product of phytoplankton carbon biomass (C phytoplankon ) and growth rate ( μ ), the former corresponding to POC concentration computed from the float b bp observations and the latter being an empirical function of b bp , Chl‐ a (from float observations), and PAR (from satellite observations, Equation 15): $$$\text{NPP}={{\mathrm{C}}_{\text{phytoplankton}}}_{}({\mathrm{b}}_{\text{bp}})\times \mu ({\mathrm{b}}_{\text{bp}},\,\text{Chl}a,\,\text{PAR})$$$ …”

“…To obtain the best possible Chl‐ a estimate, fluorescence‐to‐chlorophyll‐concentration relationships derived from Line P cruise discrete Chl‐ a samples and CTD fluorescence data were applied to the BGC float observations as described in Long et al. (2021).…”

“…Raw float fluorescence data were corrected for non-photochemical quenching before a background signal (minimum Chl-a between 100 and 300 m) was removed. To obtain the best possible Chl-a estimate, fluorescence-to-chlorophyll-concentration relationships derived from Line P cruise discrete Chl-a samples and CTD fluorescence data were applied to the BGC float observations as described in Long et al (2021).…”

Ocean Biogeochemical Signatures of the North Pacific Blob

“…While the temperature features of the marine heatwave have been well studied, only a few studies have discussed the associated ocean biogeochemical properties. At the basin scale, the marine heatwave has been connected to decreases in net community production and subarctic and subpolar transition zone productivity (Bif et al., 2019; Whitney, 2015), increases in particulate organic carbon concentration and net primary productivity (Long et al., 2021; Yu et al., 2019), and changes to northeast Pacific fish stocks (Cheung & Frölicher, 2020). Coastal biogeochemical impacts of the marine heatwave include anomalously low chlorophyll concentrations off the coast of Southern California (Jacox et al., 2016; Kahru et al., 2018), anomalously high surface ocean partial pressure of CO 2 (pCO 2 ) off the coast of Washington state (Siedlecki et al., 2016), and anomalously high aragonite saturation states (Ω arag ) off the coast of Alaska (Siedlecki et al., 2016).…”