岩石風化と気候:低山脈は最大の炭素吸収源である(Rock weathering and climate: low-relief mountain ranges are largest carbon sinks)

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2024-03-07 ミュンヘン大学(LMU)

地球表面の温度が安定しているのは、大気中の二酸化炭素濃度を調節する「サーモスタット」があるためであり、岩石の侵食や風化がその一部を担っている。最近の研究では、岩石の風化が大気中の炭素に与える影響がモデル化され、侵食率が年間約0.1ミリメートルの地形で最も高いことが示された。これにより、侵食率が適切な地域では風化反応が最大限に働き、二酸化炭素が大気から除去される。

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風化によるCO2排出量は適度な侵食速度で最大化する CO2 drawdown from weathering is maximized at moderate erosion rates

AARON BUFE, JEREMY K. C. RUGENSTEIN, AND NIELS HOVIUS
Science  Published:7 Mar 2024
DOI:https://doi.org/10.1126/science.adk0957

Editor’s summary

The role of erosion in the modulation of atmospheric carbon dioxide has been challenging to untangle because increased weathering fluxes do not always result in the drawdown of this greenhouse gas. Bufe et al. found that carbon dioxide drawdown peaks at a range of erosion rates that are much lower than the most active mountain belts. Peak drawdown occurs in various places on the planet, but very actively eroding landscapes are likely contributing carbon dioxide to the atmosphere. This observation helps to reconcile conflicting data on the role of weathering and atmospheric carbon dioxide. —Brent Grocholski

Abstract

Uplift and erosion modulate the carbon cycle over geologic timescales by exposing minerals to chemical weathering. However, the erosion sensitivity of mineral weathering remains difficult to quantify. Solute-chemistry datasets from mountain streams in different orogens isolate the impact of erosion on silicate weathering—a carbon dioxide (CO2) sink—and coupled sulfide and carbonate weathering—a CO2 source. Contrasting erosion sensitivities of these reactions produce a CO2-drawdown maximum at erosion rates of ~0.07 millimeters per year. Thus, landscapes with moderate uplift rates bolster Earth’s inorganic CO2 sink, whereas more rapid uplift decreases or even reverses CO2 sequestration. This concept of an “erosion optimum” for CO2 drawdown reconciles conflicting views on the impact of mountain building on the carbon cycle and permits estimates of geologic CO2 fluxes dependent upon tectonic changes.

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1702地球物理及び地球化学
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