Global assessment of ocean carbon export by combining satellite observations and food‐web models

Abstract

The export of organic carbon from the surface ocean by sinking particles is an important, yet highly uncertain, component of the global carbon cycle. Here we introduce a mechanistic assessment of the global ocean carbon export using satellite observations, including determinations of net primary production and the slope of the particle size spectrum, to drive a food-web model that estimates the production of sinking zooplankton feces and algal aggregates comprising the sinking particle flux at the base of the euphotic zone. The synthesis of observations and models reveals fundamentally different and ecologically consistent regional-scale patterns in export and export efficiency not found in previous global carbon export assessments. The model reproduces regional-scale particle export field observations and predicts a climatological mean global carbon export from the euphotic zone of~6 Pg C yr À1. Global export estimates show small variation (typically < 10%) to factor of 2 changes in model parameter values. The model is also robust to the choices of the satellite data products used and enables interannual changes to be quantified. The present synthesis of observations and models provides a path for quantifying the ocean's biological pump.

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

“…The global carbon export summaries are also robust to large changes in food-web model parameters or choice of satellite data algorithms. Further the modeled spatial patterns in export and export efficiency have a realism not found in previous global summaries of export efficiency (see Siegel et al, 2014 for more details).…”

“…The recent food-web model/satellite data synthesis by Siegel et al (2014) is a useful example for how the overall hypothesis could be tested. These authors use available satellite observations of NPP, particle size and phytoplankton carbon to diagnose size-fractionated phytoplankton carbon budgets and to model sinking export using a simple food web model ( Figure 3A).…”

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

“…Given the observed regional differences in physical and ecological characteristics within the North Atlantic (Longhurst 1995(Longhurst , 2010 and the impact that distinct biome-specific scaling has on global organic carbon export predictions (Britten and Primeau, 2016), high spatial and temporal resolution has become essential for providing robust estimates of carbon export and to assess links and sensitivity to large scale ecosystem variability and global change (Galbraith et al, 2015;Honjo et al, 2014;Siegel et al, 2014). Here, we discuss estimates of 234 Th and C export fluxes considering the biogeochemical characteristics of the sampled areas and present C export efficiencies along the entire transect.…”

“…In addition, these models have a predictive power that can be used to forecast impacts on the global carbon cycle from possible changes in environmental conditions (e.g., changes in temperature, stratification, etc.). Satellite-based models, however, also have a myriad of assumptions and limitations and recent studies have highlighted the necessity to develop sub-ecosystem-scale parameterization in order to provide more accurate results (Galbraith et al, 2015;Siegel et al, 2014).…”

“…Yet the understanding of the magnitude and variability of this flux over temporal and spatial scales remains limited (Britten and Primeau, 2016;Burd et al, 2010). As a consequence, global-scale models of ocean carbon export vary widely, ranging from ~ 5 to 13 Gt C y -1 (Henson et al, 2011;Laws et al, 2011;Siegel et al, 2014). This uncertainty highlights the need for continuing in situ carbon export field sampling over large geographical provinces and across seasonal timescales (Britten and Primeau, 2016;Siegel et al, 2016).…”