Distinguishing climate and time in the soil record: Mass-balance trends in Vertisols from the Texas coastal prairie

摘要

Mass-balance relationships of 10 major elements in a Vertisol climosequence and chronosequence formed on alluvial terraces on the Texas Gulf Coastal Plain indicate that the soils develop characteristic element translocation patterns in response to climatic forcing and reach mass-flux equilibrium within a relatively short period of time. Vertisols within the climosequence (age 35 ka, 800–1500 mm mean annual precipitation [MAP]) approach a net mass flux of –16% (±3%) of parent element contents, corresponding to a weathering flux of –1.0 x 10–3 to –1.3 x 10–3 g cm–2 yr–1, when MAP exceeds 900 mm. Net mass-flux assessments in a Vertisol chronosequence (0.4–35 ka, 1000 mm MAP) show that this equilibrium is achieved within 5–6 k.y. Below 900 mm MAP, positive net mass fluxes indicate that Vertisol profiles are gaining material (at a rate of 0.2 x 10–3 g cm–2 yr–1). Vertisols forming in drier MAP areas approach equilibrium with climate by different mechanisms and at different rates, compared to their wetter counterparts, and may not be as sensitive to millennial-scale climate shifts.