Decadal trends of ocean and land carbon fluxes from a regional joint ocean‐atmosphere inversion

Abstract

From 1980 until 2010, the combined CO2 sink strengths of ocean and land increased by nearly 50% (−0.55 Pg C yr−1 decade−1), but the spatial distribution of this trend is not well known. We address this by performing a joint cyclostationary ocean‐atmosphere inversion for the three decades 1980–1989, 1990–1999, and 2000–2008, using only carbon data from the ocean and atmosphere as constraints, i.e., without applying any prior information about the land fluxes. We find that in the inversion, most of the 30 year sink trend stems from the ocean (−0.44 Pg C yr−1 decade−1). The contribution of the terrestrial biosphere is commensurably smaller but has more decadal variability. First, the land sink strength intensified in the 1990s by 0.4 (±0.3) Pg C yr−1 compared to the 1980s but then weakened slightly by 0.2 (±0.4) Pg C yr−1 in the 2000s. The different land regions contributed very variedly to these global trends. While the northern extratropical land acted as an increasing carbon sink throughout the examined period primarily driven by boreal regions, the tropical land is estimated to have acted as an increasing source of CO2, with source magnitude and trend dominated by enhanced release in tropical America during the Amazon mean wet season. This pattern is largely unchanged if the oceanic inversion constraint, which is based on a stationary ocean circulation, is replaced by an estimate based on simulation results from an ocean biogeochemical general circulation model that includes year‐to‐year variability in the air‐sea CO2 fluxes and also has a trend (−0.07 Pg C yr−1 decade−1) that is at the very low end of current estimates. However, the land/ocean partitioning of the trend contribution is adjusted accordingly. Oceanic carbon data has a major impact on carbon exchange for all tropical regions and southern Africa but also for observationally better constrained regions in North America and temperate Asia. The European trend exhibits a strong sensitivity to the choice of the atmospheric CO2 network.

Global trends in surface eddy mixing from satellite altimetry

“…When implementing eddy parameterization schemes, a steady eddy diffusivity coefficient is often used (Gent and Mcwilliams, 1990;Griffies, 1998;Abernathey et al, 2011;Sun et al, 2021). However, in the context of global warming, significant trends have been found in ocean temperature and salinity, sea level, upper-ocean stratification, eddy kinetic energy (EKE) and ocean circulation (Church et al, 2011;Du et al, 2015;Hogg et al, 2015;Nan et al, 2015;Steinkamp and Gruber, 2015;Beal and Elipot, 2016;Landschützer et al, 2016;Patara et al, 2016;Syst et al, 2018;Yamaguchi and Suga, 2019;Johnson and Lyman, 2020;Martıńez-Moreno et al, 2021;Beech et al, 2022;Lee et al, 2022;Peng et al, 2022;Risaro et al, 2022). It remains unclear whether a trend in oceanic mesoscale eddy mixing exists in the context of this climate change.…”

Fluvial CO2 and CH4 patterns across wildfire‐disturbed ecozones of subarctic Canada: Current status and implications for future change

“…The boreal biome is a contemporary net carbon sink (Steinkamp & Gruber, ), with organic carbon accumulation during the Holocene resulting in this region storing more carbon per unit area than any other biome on Earth (Loisel et al, ; Tifafi, Guenet, & Hatté, ). A significant fraction of this stored carbon is trapped in permafrost (Hugelius et al, ), and thus is largely inaccessible for biogeochemical processing.…”

“…In ecosystems affected by wildfire and permafrost thaw, in particular, aquatic offsets of terrestrial net productivity are largely unknown despite evidence pointing to organic matter in permafrost being rapidly mineralized by microbes (Abbott et al, 2014;Drake, Guillemette, et al, 2018;Drake, Wickland, Spencer, McKnight, & Striegl, 2015;Spencer et al, 2015) and thus fuelling CO 2 production in streams. Given the rapid changes occurring in these regions (Callaghan et al, 2010;Rouse et al., 1997;Schuur et al, 2015), and their relevance to global carbon cycles (Steinkamp & Gruber, 2015), a better understanding of their net ecosystem carbon budgets is clearly required. Only by integrating estimates of terrestrial and aquatic carbon fluxes can net landscape carbon budgets be resolved, and the implications for future change in a warming climate be understood.…”