To quantify the anthropogenic and climatic controls on regolith formation and global weathering fluxes, it is critical to understand the evolution of weathering profiles and the consumption of CO2 associated with weathering. Using a cascade of global circulation, biota, and weathering models, Goddéris et al. (2010) hindcasted the evolution of weathering profiles over the last 10k years along a loess transect in the Mississippi Valley. After using the weathering code, WITCH, in this way to investigate the dissolution and precipitation of silicate and carbonate minerals in loess along the climosequence, Godderis et al. (2013) then used a similar cascade of models to project the response of weathering of the transect through 2100 – we call this forward projection an “earthcast”. The effect of projected climate change on the weathering profile was largely dictated by increasing temperature (which slows the rate of advance of the dolomite reaction front but increases silicate weathering) and changes in drainage (variable along the transect). To a lesser extent, changes in soil CO2 affected weathering. The response of the dolomite reaction front acts like a terrestrial lysocline as it responds to changing CO2 and climate.
Here, we embark on a similar study of shale weathering. Like the loess formations, shale has high surface area of silicates per unit volume, and can contain carbonate minerals. Shale also comprises 25% of the continental landmass. Specifically, to explore how climate evolution controls shale weathering we are beginning to compare soils along a shale climosequence transect that spans from Wales to Puerto Rico (Dere et al. in press)—i.e., like the loess north- south transect, a climosequence of pedons. For the shales, we will also explore the effects of climate variables by comparing soils on the north- and south-facing hillslopes of the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO).
The eventual goal is to utilize our understanding of the climatic controls on shale weathering profiles and solute chemistry from these explorations to “earthcast” the next hundred years. We report our initial efforts to link the meteorological forcing from the North American Land Data Assimilation System (NLDAS-2), the fully-coupled land- surface Penn State Integrated Hydrologic Model (Flux-PIHM), and the geochemical box model WITCH. Our preliminary efforts show that WITCH can elucidate the controls on water and Mg weathering fluxes derived from clay weathering.
Sullivan, P.L., Godderis, Y., Shi, Y., Schott, J., Duffy, C., Brantley, S.L. (2013): Developing approaches to hindcast and earthcast climate controls on solute fluxes during shale weathering in the Critical Zone . Abstract EP11A-04 presented at 2013 Fall Meeting, AGU, San Francisco, CA, 9-13 Dec..
This Paper/Book acknowledges NSF CZO grant support.