Dissolved Organic Phosphorus In Shelf Sediment Pore-waters

Marine sediments are a major reservoir for the macronutrient phosphorus (P). The cycling, fate and form of P in pore-waters has focussed almost exclusively on the easy to measure soluble reactive (SRP) forms. There are, however, very few data available for the “dissolved organic” forms of P, i.e. the difference between the total dissolved P and SRP. Preliminary data on “DOP” and SRP forms of P in shelf sediments around the UK show that the organic fraction can be important (up to 30% of the size of the SRP pool), and the magnitude of this “organic“ signal varies with season and delivery of post bloom organic matter to the sediment. A limited number of oceanic samples show a sequence of decreasing DOP concentrations in pore-waters on moving off shelf that decrease to undetectable levels in deep-water oxic sediments. Present budgets and diagenetic models ignore this “organic“ pool that represents an important intermediary in the benthic cycling of P.