High potential activity of extracellular alkaline phosphatase in deep waters of the central Pacific

We found high potential activities of alkaline phosphatase associated with particles (0.2 μm or greater size fraction) in deep waters (1000–4000 m) of the central Pacific Ocean. The potential enzyme activity at depth (0.03 – 0.3 nM h−1) was up to 50% of that at the surface (0–125 m). In contrast, activities of α- and β-d-glucosidase in the deep layer were low (generally less than 1 % of those in the upper layer), yielding up to two orders of magnitude difference in the ratio of alkaline phosphatase and α- and β-d-glucosidase activities with depth. It is unlikely that the phosphatase is actively produced by microorganisms inhabiting the deep-sea environment, where labile organic carbon supply is limited and phosphate concentration is high (2.4 – 3.0 AM). Instead, deep-water phosphatase is probably supplied by rapidly sinking particles and their subsequent fragmentation and dissolution. Different distributions of phosphatase and glucosidase indicate that sinking particles of phytoplankton origin are an important source of alkaline phosphatase enzymes in the deep sea.