Abstract
We examine the importance of the rock weathering feedback mechanism during the last deglacial period (∼16 000–4000 BCE) using an Earth system model of intermediate complexity (the University of Victoria Earth System Climate Model (UVic ESCM)) with four box-model parameterizations of terrestrial weathering. The deglacial climate change is driven by changes in orbital parameters, ice core reconstructions of atmospheric CO2 variability, and prescribed removal of continental ice sheets. Over the course of the 12 000 year simulation period, increases in weathering provide a mechanism that slowly removes CO2 from the atmosphere, in opposition to the observed atmospheric CO2 increase during this period. These processes transfer both carbon and alkalinity to the ocean, the combination of which results in as much as a 1000 Pg C increase in total ocean carbon, relative to a control simulation with constant weathering. However, the rapid expansion of northern hemisphere vegetation introduces a significant uncertainty among the weathering parameterizations. Further experiments to test the individual impacts of weathering dissolved inorganic carbon and alkalinity fluxes on ocean biogeochemistry suggest that the worldwide distribution of rock types and the ratio of carbonate to silicate weathering may be crucially important in obtaining an accurate estimate of changes in global weathering rates.
Highlights
The weathering of carbonate and silicate rocks on land is a key process in the global carbon cycle and, through its coupling with calcium carbonate deposition in the ocean, is the primary sink of carbon on geological timescales (Urey 1952; Walker et al 1981)
Temperature was factored into the GEOCARB parameterization, but it makes little difference here as globally averaged surface air temperature (SAT) change in the UVic ESCM is mostly driven by changes in the CO2 content of the atmosphere
It is noteworthy that the GEOCARB and UZ parameterizations produce similar results despite being derived from entirely independent empirical methods, both yielding a 15 000 year increase in dissolved inorganic carbon (DIC) flux of about 0.03–0.04 Pg C/year compared with the last glacial maximum (LGM) control run
Summary
The weathering of carbonate and silicate rocks on land is a key process in the global carbon cycle and, through its coupling with calcium carbonate deposition in the ocean, is the primary sink of carbon on geological timescales (Urey 1952; Walker et al 1981). The rate at which these processes remove carbon from the Earth system is sensitive to changes in the environment, notably temperature (Berner 1991), biological production (Lenton and Britton 2006), and perhaps more indirectly, river runoff (Walker and Kasting 1992). This gives rise to a negative feedback mechanism that regulates the global climate on multimillennial timescales. This study allows us to make an estimate of the variations in weathering rates within glacial–interglacial timescales and their impact on the carbon cycle
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