CALCIFICATION GENERATES PROTONS FOR NUTRIENT AND BICARBONATE UPTAKE

The biosphere's great carbonate deposits, from caliche soils to deep-s ea carbonate oozes, precipitate largely as by-products of autotrophic nutrient acquisition physiologies. Protons constitute the critical lin k: Calcification generates protons, which plants and photosynthetic sy mbioses use to assimilate bicarbonate and nutrients. A calcium ATPase- based ''trans'' mechanism underlies most biological calcification. Thi s permits high calcium carbonate supersaturations and rapid carbonate precipitation. The competitive advantages of calcification become espe cially apparent in light and nutrient-deficient alkaline environments. Calcareous plants often dominate the lower euphotic zone in both the benthos and the plankton. Geographically and seasonally, massive calci fication concentrates in nutrient-deficient environments including alk aline soils, coral reefs, cyanobacterial mats and coccolithophorid blo oms. Structural and defensive uses for calcareous skeletons are someti mes overrated.