Marine Phosphate Oxygen Isotopes and Organic Matter Remineralization in the Oceans

We show that the isotopic composition of oxygen (δ18O) in dissolved inorganic phosphate ( Pi) reveals the balance between Pitransport and biological turnover rates in marine ecosystems. Our δ18Op of Pi(δ18Op) measurements herein indicate the importance of cell lysis in the regeneration of Piin the euphotic zone. Depth profiles of the δ18Op in the Atlantic and Pacific Oceans are near a temperature-dependent isotopic equilibrium with water. Small deviations from equilibrium below the thermocline suggest that P remineralization in the deep ocean is a byproduct of microbial carbon and energy requirements. However, isotope effects associated with phosphohydrolase enzymes involved in P remineralization are quite large and could potentially lead to significant disequilibration of Pioxygen. The observed near equilibration of deep water Pilikely calls for continued slow rates of microbial uptake and release of Piand/or extracellular pyrophosphatase-mediated oxygen exchange between water and Pialong the deep water flow path.