China's forest carbon, Labrador oxygen and soil NO2 were re-weighed against the models
Nature Geoscience re-attributed most of China's forest carbon sink to regrowth on already-forested land; the Labrador Sea carries most deep North Atlantic oxygen; Nature Communications showed soil microbes make NO2 through superoxide chemistry.
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Most of China's forest carbon sink returned on land that was already forest
A peer-reviewed study in Nature Geoscience rebuilt China's forest carbon balance from 1986 to 2019 at 30-metre resolution, using locally derived biomass accumulation curves for each one-degree grid cell and a spatially explicit bookkeeping model. Biomass carbon sinks averaged 0.139 plus or minus 0.052 petagrams of carbon a year, rising from 0.1 plus or minus 0.015 over 1990 to 1999 to 0.2 plus or minus 0.012 over 2010 to 2019. Most of that uptake came from regrowth after disturbance rather than from new planting on land that had not carried forest. Afforested tree cover expanded faster, at 1.31 million hectares a year, than reforestation after disturbance at 1.06 million hectares a year, but carbon moved the other way. Post-disturbance regrowth accumulated 1.47 plus or minus 0.42 tonnes of carbon per hectare a year against 0.96 plus or minus 0.28 tonnes for afforestation. The authors argue forest carbon accounting on the road to carbon neutrality should protect regrowing stands alongside targeted new planting.[1]
The Labrador Sea carries most oxygen reaching the deep North Atlantic
A Nature Geoscience team applied new calibration protocols to multi-year oxygen sensors on a mooring array spanning the Labrador Sea to quantify oxygen transport into the lower limb of the Atlantic Meridional Overturning Circulation. Local air-sea exchange adds about 4.1 teramoles of oxygen a year to dense Labrador Sea water, while deep convection moves about 23.5 teramoles a year from lighter water formed upstream into those same dense layers. The transport is enough to balance biological respiration across much of the deep North Atlantic, which puts the Labrador Sea at the centre of that ocean's oxygen supply even though it contributes little to the densification of the overturning's lower limb. The authors draw the consequence directly: future risk of deep North Atlantic deoxygenation depends on deep convection there as well as on whatever drives the overturning itself. The estimate rests on two years of mooring data.[2]
Soil microbes make nitrogen dioxide through superoxide chemistry
Current models treat the soil flux of nitrogen dioxide as purely depositional. Controlled factorial slurry experiments reported in Nature Communications show that native microbial communities produced roughly 10 times more nitrogen dioxide than sterile controls after exposure to nitric oxide, with superoxide concentration explaining 60 per cent of the variation in production rates. Stimulating superoxide production with NADH raised nitrogen dioxide formation 15- to 26-fold, while inhibiting NADH oxidase pushed it back towards baseline and superoxide dismutase cut it by 46 per cent to 71 per cent. Adding peroxynitrite to soil raised headspace nitrogen dioxide, which the authors treat as confirmation of the intermediate step. They suggest the pathway may help explain gaps between satellite observations and modelled soil nitrogen oxide emissions.[3]
