The Importance of Terrestrial Weathering for Climate System Modelling on Extended Timescales: A Study with the UVic ESCM

English Abstract:

The chemical erosion of carbonate and silicate rocks 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 geologic timescales. The dynamic interdependence of terrestrial weathering rates with atmospheric temperature and carbon dioxide concentrations is crucial to the regulation of Earth’s climate over multi-millennial timescales. However any attempts to develop a modeling context for terrestrial weathering as part of a dynamic climate system are limited, mostly because of the difficulty in adapting the long timescales of the implied negative feedback mechanism with those of the atmosphere and ocean, the latter typically operating on timescales several orders of magnitude lower than the former. As a result we still have but a rudimentary understanding of the chemical weathering feedback mechanism and its effects on ocean biogeochemistry.

Much of the earlier work on this topic is based on box-model approaches, abandoning spatial variability for the sake of computational efficiency and the possibility to investigate the impact of weathering on climate change over time frames much longer than those allowed by traditional climate system models. Only one such attempt [Meissner et al., 2012, Global Biogeochemical Cycles 26] has been made with the University of Victoria Earth System Climate Model (UVic model), to investigate the role of weathering as a dynamic component of the global carbon cycle. Using a land map which takes into account a number of different rock lithologies as well as changes in sea level, and an empirical model of the temperature and NPP dependency of weathering rates for the different rock types, we introduce a two-dimensional representation of weathering processes into the carbon cycle component of the UVic model. Taking the last deglacial period (c. 21000BP to 13000BP) as a contextual timeframe, we compare results between our 2-D version of the weathering feedback mechanism and a simulation using only the box-model parameterizations of Meissner et al. [2012]. In doing so we hope to assess the importance of two dimensional factors (i.e., changes in sea level and rock type distribution) within the weathering negative feedback mechanism.