Simulation and assimilation of global ocean <i>p</i>CO₂ and air&#x2013;sea CO₂ fluxes using ship observations of surface ocean <i>p</i>CO₂ in a simplified biogeochemical offline model

Abstract

We used an offline tracer transport model, driven by reanalysis ocean currents and coupled to a simple biogeochemical model, to synthesize the surface ocean pCO2 and air–sea CO2 flux of the global ocean from 1996 to 2004, using a variational assimilation method. This oceanic CO2 flux analysis system was developed at the National Institute for Environmental Studies (NIES), Japan, as part of a project that provides prior fluxes for atmospheric inversions using CO2 measurements made from an on‐board instrument attached to the Greenhouse gas Observing SATellite (GOSAT). Nearly 250 000 pCO2 observations from the database of Takahashi et al. (2007) have been assimilated into the model with a strong constraint provide by ship‐track observations while maintaining a weak constraint of 20% on global averages of monthly mean pCO2 in regions where observations are limited. The synthesized global air–sea CO2 flux shows a net sink of 1.48 PgC yr−1. The Southern Ocean air–sea CO2 flux is a sink of 0.41 PgC yr−1. The interannual variability of synthesized CO2 flux from the El Niño region suggests a weaker source (by an amplitude of 0.4 PgC yr−1) during the El Niño events in 1997/1998 and 2003/2004. The assimilated air–sea CO2 flux shows remarkable correlations with the CO2 fluxes obtained from atmospheric inversions on interannual time‐scales.

Data-based estimates of the ocean carbon sink variability – first results of the Surface Ocean &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; Mapping intercomparison (SOCOM)

“…Possibly this area has larger spatial heterogeneity not adequately represented by (some of) the methods. NIES-OTTM shows a seasonal cycle opposite to the other methods, a behaviour present in many biogeochemical process models at high latitudes (Valsala and Maksyutov, 2010;Schuster et al, 2013). Methods agree on smaller seasonal amplitude in the tropics, though substantial differences in amplitude and phase exist.…”

“…At each iteration, the forward model corrects the initial and boundary condition of DIC (dissolved inorganic carbon) according to the weighted adjoints. The iterations are truncated when the mismatch falls below a minimum value of 10 % of its initial value (see Valsala and Maksyutov, 2010). Documentation: Valsala and Maksyutov (2010).…”

Biological production in the Indian Ocean upwelling zones –Part 1: refined estimation via the use of a variable compensation depth in ocean carbon models

“…Details of all parameters in the biogeochemical model and calculations of solubility and biological pump are listed in Appendix A. The design and validation of the physical model is reported by Valsala et al (2008), Valsala and Maksyutov (2010b) and the biogeochemical model by Najjar and Orr (1998).…”

The Effect of GOSAT Observations on Estimates of Net CO₂ Flux in Semi-Arid Regions of the Southern Hemisphere

“…However, CO 2 uptake in semi-arid regions, as given by the GV-only inversion (−2.20 Pg C yr −1 ), was nearly two times larger than that given by the GOSAT inversion (−1.11 Pg C yr −1 ), resulting in that the former constitutes 84% and the latter 44% of (VISIT) (Ito 2008); 2) monthly ocean-atmosphere CO 2 fluxes generated from observations of surface ocean CO 2 partial pressure (pCO 2 ) (Valsala and Maksyutov 2010); 3) monthly biomass burning emissions estimated from an empirical relationship between biomass burning emission (the Global Fire Emissions Database (GFED) version 3.1 (van der Werf et al 2010)) and burnt area (GFED burnt area version 4.0 (Giglio et al 2013)), and; 4) monthly fossil fuel CO 2 emissions obtained by merging the Open source Data Inventory of Anthropogenic CO 2 emissions (ODIAC) ) and the Carbon Dioxide Information Analysis Center datasets (Andres et al 2011).…”