Using Lagrangian‐based process studies to test satellite algorithms of vertical carbon flux in the eastern North Pacific Ocean

Abstract

The biological carbon pump is responsible for the transport of ∼5–20 Pg C yr−1 from the surface into the deep ocean but its variability is poorly understood due to an incomplete mechanistic understanding of the complex underlying planktonic processes. In fact, algorithms designed to estimate carbon export from satellite products incorporate fundamentally different assumptions about the relationships between plankton biomass, productivity, and export efficiency. To test the alternate formulations of export efficiency in remote‐sensing algorithms formulated by Dunne et al. (2005), Laws et al. (2011), Henson et al. (2011), and Siegel et al. (2014), we have compiled in situ measurements (temperature, chlorophyll, primary production, phytoplankton biomass and size structure, grazing rates, net chlorophyll change, and carbon export) made during Lagrangian process studies on seven cruises in the California Current Ecosystem and Costa Rica Dome. A food‐web based approach formulated by Siegel et al. (2014) performs as well or better than other empirical formulations, while simultaneously providing reasonable estimates of protozoan and mesozooplankton grazing rates. By tuning the Siegel et al. (2014) algorithm to match in situ grazing rates more accurately, we also obtain better in situ carbon export measurements. Adequate representations of food‐web relationships and grazing dynamics are therefore crucial to improving the accuracy of export predictions made from satellite–derived products. Nevertheless, considerable unexplained variance in export remains and must be explored before we can reliably use remote sensing products to assess the impact of climate change on biologically mediated carbon sequestration.

Latitudinal distributions of particulate carbon export across the North Western Atlantic Ocean

“…Maiti et al (2013) conducted a similar comparison between 234 Th-and satellite-derived C export in the Southern Ocean and observed a 2 to 4-fold overestimation of C export using the L11 and D05 models, with NPP obtained from the VGPM and the CbPM models. Stukel et al (2015) found similar results in the eastern North Pacific Ocean. In the North Western Atlantic Ocean, we observe that D05 tends to significantly overestimate C export relative to in situ estimates in the equatorial domain, whereas L11 appears to underestimate C export, mainly in the northern half of the oligotrophic domain and at several riverine stations.…”

Mesoscale ocean fronts enhance carbon export due to gravitational sinking and subduction

“…Both models and in situ data suggest that this production−export imbalance results, in part, from lateral transport of particles produced in the coastal area to the offshore region where net export is expected (20)(21)(22)(23). However, the expected high export ratio in offshore waters of the CCE is not supported by existing in situ measurements (19,24).…”

Prediction of the Export and Fate of Global Ocean Net Primary Production: The EXPORTS Science Plan

“…Knowing phytoplankton size distribution and functional type together are first steps toward characterizing pelagic food webs (e.g., Michaels and Silver, 1988). It has been shown recently that the performance of the Siegel et al (2014) export flux model improves substantially if the parameters are regionally tuned supporting the importance of food web structure (Stukel et al, 2015). Further, recent field data summaries show strong relationships between the vertical scales of sinking flux attenuation in the TZ and both phytoplankton community structure in the EZ (Guidi et al, 2015;Puigcorbé et al, 2015) and environmental conditions in the TZ (Marsay et al, 2015).…”