Soils as generators and sinks of inorganic carbon in geologic time

TitleSoils as generators and sinks of inorganic carbon in geologic time
Publication TypeBook Chapter
Year of Publication2014
AuthorsH. Monger C
Book TitleSoil Carbon. Progress in Soil Science, 27
PublisherSpringer International Publishing Switzerland
Accession NumberJRN00630
Keywordscarbon sequestration, deserts, paleosols, pedogenic carbonate

Soil is a continuum in geologic time. Like today, pedogenesis in the geologic past altered soils by transformations, translocations, additions, and losses as continents drifted and collided across global climatic zones. One of the major biogeochemical systems operating in soils across geologic time is the carbonic acid system, which includes gaseous CO2(g), dissolved CO2(aq), carbonic acid H2CO3(aq), bicarbonate HCO3- (aq), carbonate CO3 2- (aq), and solid-phase calcium carbonate (mainly calcite). These chemical species, collectively referred to as inorganic carbon, increased in the Silurian when vascular plants colonized the continents and began pumping atmospheric CO2 into soils via photosynthesis and root respiration, which accelerated mineral weathering and made soils “generators” of bicarbonate. In humid regions soils are “flushing” and bicarbonate enters groundwater, streams, and is transported to the oceans. In arid regions soils are “non-flushing” and bicarbonate is not linked to the hydrological system, but precipitates in soil as pedogenic carbonate, making arid soils sinks of inorganic carbon. Pedogenic carbonate is documented in paleosols throughout the Cenozoic, Mesozoic, and back into the Silurian of mid-Paleozoic time. Paleogeographic maps from Present to Precambrian are useful for revealing where arid regions were located in geologic time and how they expanded and contracted; thus, propounding the question of how (and if) a currently expanding “Aridosphere” will impact the global carbon cycle.