Relationships between mineral surfaces and organic carbon concentrations in soils and sediments

Relationships between mineral specific surface area and organic carbon ( OC ) concentration are examined forsediments and soil A-horizons from throughout the world. I found (published elsewhere) that continental shelfsediments from many different regions exhibit downcore loss of OC to a refractory background level which showsa consistent relationship with mineral surface area ( slope = 0.86 mg m-2 OC). This trend is equivalent to a mono-layer of organic matter over all surfaces, and is termed the monolayer-equivalent ( ME ) level. Sediments and soilsfrom other environments are compared to this empirically derived relationship. Several continental slope areasshow extension of this relationship to considerable depth. Marked excesses of OC above this trend, which persistdowncore, were found in sediments with high carbonate mineral content or slope sediments with low dissolvedoxygen concentrations in the overlying water column. About half of the soils examined also adhered to this rela-tionship, while soils with high carbonate content, low pH, or poor drainage showed OC concentrations higher thanthe ME level. OC concentrations below the ME level are found in deltaic regions and areas with low organic matterdelivery such as the deep sea or arid soils. The nature of mineral surfaces was examined using N2 adsorption-desorption isotherms, and most surface area was found to be present as pores with