Marine phosphate oxygen isotopes and organic matter remineralization in the oceans

摘要

We show that the isotopic composition of oxygen (δ¹⁸O) in dissolved inorganic phosphate (Pi) reveals the balance between Pi transport and biological turnover rates in marine ecosystems. Our δ¹⁸Op of Pi (δ¹⁸Op) measurements herein indicate the importance of cell lysis in the regeneration of Pi in 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 Pi oxygen. The observed near equilibration of deep water Pi likely calls for continued slow rates of microbial uptake and release of Pi and/or extracellular pyrophosphatase-mediated oxygen exchange between water and Pi along the deep water flow path.