Global ocean carbon uptake: magnitude, variability and trends

Abstract

Abstract. The globally integrated sea–air anthropogenic carbon dioxide (CO2) flux from 1990 to 2009 is determined from models and data-based approaches as part of the Regional Carbon Cycle Assessment and Processes (RECCAP) project. Numerical methods include ocean inverse models, atmospheric inverse models, and ocean general circulation models with parameterized biogeochemistry (OBGCMs). The median value of different approaches shows good agreement in average uptake. The best estimate of anthropogenic CO2 uptake for the time period based on a compilation of approaches is −2.0 Pg C yr−1. The interannual variability in the sea–air flux is largely driven by large-scale climate re-organizations and is estimated at 0.2 Pg C yr−1 for the two decades with some systematic differences between approaches. The largest differences between approaches are seen in the decadal trends. The trends range from −0.13 (Pg C yr−1) decade−1 to −0.50 (Pg C yr−1) decade−1 for the two decades under investigation. The OBGCMs and the data-based sea–air CO2 flux estimates show appreciably smaller decadal trends than estimates based on changes in carbon inventory suggesting that methods capable of resolving shorter timescales are showing a slowing of the rate of ocean CO2 uptake. RECCAP model outputs for five decades show similar differences in trends between approaches.

The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1) – Part 2: Historical simulations

“…Therefore, any comparison over a 20-year period between models has the potential to be biased by the number of El Niño or La Niña events. Figure 15 shows that, in the period 1986-2005, ACCESS-ESM1 is in good agreement with the spatial pattern and the magnitude of sea-air CO 2 fluxes of Wanninkhof et al (2013), hereafter referred to as W13. In the Southern Ocean (44-90 • S), which is an important net sink of carbon, ACCESS-ESM1 (−0.77 PgC yr −1 ) captures a larger annual-mean uptake than the sea-air CO 2 flux of W13, which only estimated an uptake of −0.18 PgC yr −1 .…”

“…Sea-air CO 2 fluxes: seasonal climatology of Wanninkhof et al (2013) based on the 1 • × 1 • global measurements of oceanic pCO 2 of Takahashi et al (2009).…”

A high-frequency atmospheric and seawater <i>p</i>CO<sub>2</sub> data set from 14 open-ocean sites using a moored autonomous system

“…While underway pCO 2 observations have greatly enhanced our understanding of the spatial variability in seaair CO 2 fluxes (Takahashi et al, 2009;Wanninkhof et al, 2013), they have not solved the problem of quantifying temporal variability at a given point in space. In highly variable regions such as the equatorial Pacific and coastal systems, fixed, high-frequency observations can improve our understanding of how short-term variability impacts CO 2 flux.…”

Characterization of a Time-Domain Dual Lifetime Referencing pCO2 Optode and Deployment as a High-Resolution Underway Sensor across the High Latitude North Atlantic Ocean

“…Data at higher temporal resolution is required to allow a more robust statistical evaluations of CO 2 fluxes over shorter time scales (Wanninkhof et al, 2013;Landschützer et al, 2014) and better constrain the mechanisms that drive the air sea fluxes (Schuster et al, 2013). This is of particular relevance to the North Atlantic sub-polar gyre, which forms an important CO 2 sink with sparse measurements (Corbière et al, 2007).…”