THE UNSATURATED COAST (CARBON OBSERVATIONS ALONG SHORELINE TERRACES)

Soils are Earth's primary surface reservoir for mobile carbon, vastly exceeding the readily exchangeable carbon reservoirs of the oceans and atmosphere. Atmospheric CO2 has acted as a chief planetary climate regulator over short (sub-orbital wobble) to long (glacial-interglacial to hothouse-icehouse) time frames. Since the post-Proterozoic rise of large soil-mantled continents that support abundant life, changes in soil carbon have accompanied and mediated changes in the global carbon cycle, as evidenced by multiple proxies. The chief controls on soil carbon are biohydrological. Water availability is the first-order regulator of terrestrial biologic productivity, which in turn determines inputs of carbon to soil. Soil hydraulic properties strongly modulate water availability to roots. Hydraulic conductivity and storativity exhibit profound changes along predictable trajectories as soils develop through time. Coastal chronosequence studies show that mineral weathering, nutrient extraction, and nutrient retention are coupled through water movement, producing correlated changes in soil hydrologic properties and carbon stores. This paper will summarize initial findings from the "Carbon Observations along Shoreline Terraces" (COAST) research effort.