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A Negative feedback mechanism for the long-term stabilization of Earths surface-temperature

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Abstract

It is suggested that the partial pressure of carbon dioxide in the atmosphere is buffered, over geological time scales, by a negative feedback mechanism, in which the rate of weathering of silicate minerals (followed by deposition of carbonate minerals) depends on surface temperature, which in turn depends on the carbon dioxide partial pressure through the greenhouse effect. Although the quantitative details of this mechanism are speculative, it appears able to partially stabilize the earth's surface temperature against the steady increase of solar luminosity, believed to have occurred since the origin of the solar system.
... The carbonate-silicate cycle is a geochemical cycle that is thought to have enabled temperate climates during the history of Earth by recycling CO 2 through planetary carbon reservoirs (Walker et al. 1981;Berner et al. 1983;Krissansen-Totton et al. 2018). The regulation of atmospheric CO 2 ensures that the greenhouse warming effect of CO 2 is sufficient to maintain a clement surface temperature T and a liquid water reservoir on the surface, which are vital for long-term habitability Catling & Zahnle (2020). ...
... During the Archean, when the sun was only 70% as bright as today (Sagan & Mullen 1972), a warmer climate was ensured by a higher CO 2 partial pressure P CO2 and a lower intensity of silicate weathering (Kasting et al. 1993). Walker et al. (1981) discovered that the weathering of continental silicate rocks provides negative feedback to create a thermostat-like effect. If outgassing increases, P CO2 rises and consequently weathering intensifies to increase the CO 2 drawdown. ...
... With the application of a multi-regime silicate weathering model (W = f (P CO2 , T )) of (Maher & Chamberlain 2014), Hakim et al. (2021) find that weathering exhibits negative feedback at low temperatures (W ∝ T ), but positive feedback at high temperatures (W ∝ 1/T , Fig. 1a). There is a transition from the classic kinetic limit (Walker et al. 1981) to the thermodynamic limit. The transition temperature is sensitive to rock composition 124 H. Kaustubh (e.g., kinetic and thermodynamic properties of granite, basalt or peridotite) and soil transport properties (e.g., flowpath length, soil age) (Hakim et al. 2021). ...
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Continental silicate weathering and seafloor carbonate precipitation are key steps in the carbonate-silicate cycle to draw down CO 2 . Contrary to the classic understanding of negative feedback, silicate weathering can exhibit positive feedback at high temperatures. Taking into account this positive feedback, the compensation depth (CCD) in exoplanet oceans becomes shallower, implying a potential instability in the carbonate-silicate cycle at high temperatures.
... 12) (Fig. 1). These observations have motivated a hypothesis that the silicate weathering feedback-thought to be the fundamental thermostat regulating our planet's climate 13 -breaks down or is weakened during these events 10,14 . However, the contribution of intrusive LIP carbon emissions, independent of surface lava extrusion, to variations in atmospheric CO 2 and global surface temperatures on long (10 6 year) timescales has not been studied in detail. ...
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Large igneous provinces erupt highly reactive, predominantly basaltic lavas onto Earth’s surface, which should boost the weathering flux leading to long-term CO2 drawdown and cooling following cessation of volcanism. However, throughout Earth’s geological history, the aftermaths of multiple Phanerozoic large igneous provinces are marked by unexpectedly protracted climatic warming and delayed biotic recovery lasting millions of years beyond the most voluminous phases of extrusive volcanism. Here we conduct geodynamic modelling of mantle melting and thermomechanical modelling of magma transport to show that rheologic feedbacks in the crust can throttle eruption rates despite continued melt generation and CO2 supply. Our results demonstrate how the mantle-derived flux of CO2 to the atmosphere during large igneous provinces can decouple from rates of surface volcanism, representing an important flux driving long-term climate. Climate–biogeochemical modelling spanning intervals with temporally calibrated palaeoclimate data further shows how accounting for this non-eruptive cryptic CO2 can help reconcile the life cycle of large igneous provinces with climate disruption and recovery during the Permian–Triassic, Mid-Miocene and other critical moments in Earth’s climate history. These findings underscore the key role that outgassing from intrusive magmas plays in modulating our planet’s surface environment.
... Earth's long-term climate state is regulated by the weathering of crustal rocks. Silicate weathering has the capacity to remove atmospheric CO 2 over timescales of 10 3 6 years and is recognized as the primary negative feedback on mantle CO 2 emissions in long-term climate simulations (Archer, 2005;Lenton et al., 2018;Walker et al., 1981). However, oxidative weathering of organic carbon (OC) in sedimentary rocks-variously referred to as either kerogen or petrogenic carbon-has been shown to account for CO 2 emissions to the atmosphere that are similar or greater in magnitude to global silicate weathering fluxes (Hilton & West, 2020;Zondervan et al., 2023). ...
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Oxidative weathering of organic carbon in sedimentary rocks is a major source of CO2 to the atmosphere over geological timescales, but the size of this emission pathway in Earth's past has not been directly quantified due to a lack of available proxy approaches. We have measured the rhenium isotope composition of organic‐rich rocks sampled from unweathered drill cores and weathered outcrops in south Texas, whose stratigraphic successions can be tightly correlated. Oxidative weathering of more than 90% of the organic carbon and ∼85% of the rhenium is accompanied by a shift to lower rhenium isotope compositions in the weathered outcrops. The calculated isotope composition of rhenium weathered from the initial bedrock for individual samples varies systematically by ∼0.7‰ with different fractions of rhenium loss. This variation can be empirically modeled with isotope fractionation factors of α = 1.0002–1.0008. Our results indicate that the isotope composition of rhenium delivered to the oceans can be altered by weathering intensity of rock organic matter and that the rhenium isotope composition of seawater is sensitive to past oxidative weathering and associated CO2 emissions.
... When silicates react with water and CO2, carbon (C) is locked up in carbonates, possibly for centuries and longer (Moosdorf et al., 2014). While the naturally occurring silicate rock weathering 25 process has been important for stabilizing climate at geological timescales, its pace is insufficient to substantially reduce the current rise in atmospheric CO2 (Berner, 2004;Walker et al., 1981). Enhanced silicate weathering (EW) aims to accelerate this natural process through the mechanical grinding of the rocks into a fine powder. ...
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Terrestrial enhanced silicate weathering is a CO2 removal technology involving the application of ground silicate materials to agricultural soils. Next to CO2 sequestration, it can improve soil fertility and crop growth, but silicate materials can also contain toxic trace elements. In a mesocosm experiment, we investigated the effect of basalt, concrete fines and steel slags on biomass, nutrients, and heavy metal concentration of Zea Mays, using a dose-response approach. Plant biomass increased with basalt, but not with concrete fines and steel slags. Generally, plant Ca, Mg, and corn Si concentrations increased with increasing silicate application amount as a result of increased plant availability. In contrast, plant N, P, and K concentrations were hardly affected by silicate application. Besides increased leaf Pb concentrations with steel slag application, which did not exceed the maximum limit set by the WHO and FAO (0.05 mg Pb kg-1 ww), heavy metal concentrations in aerial plant tissues mostly decreased with increasing silicate application amount, presumably because of an increased soil pH, and accumulation in plant roots. Our study thus indicates mixed effects of silicate application on maize while suggesting that the risk of heavy metal contamination after a one-time application of the tested silicates is limited.
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