The distribution and chemical speciation of dissolved and particulate phosphorus in the Bering Sea and the Chukchi–Beaufort Seas

Water samples were collected from the Bering Sea and the Chukchi–Beaufort Seas during the 4th Chinese Arctic Research Expedition in summer 2010 to examine the abundance, spatial distribution and phase partitioning of phosphorus (P) between dissolved and particulate, inorganic and organic phases. Measurements of P species included dissolved inorganic P (DIP), dissolved organic P (DOP) and five particulate P species operationally defined by sequential extraction techniques. Inorganic P was generally the predominant form of both dissolved and particulate P, comprising on average up to 91±13% of the dissolved phase and 72±23% of the particulate phase in the study area. Concentrations of DIP in the water column of the Chukchi Sea and Bering Sea were considerably higher than those in the Beaufort Sea (>3 μM vs. ∼1 μM), showing a strong influence of North Pacific inflow waters. The percentage of DOP in the dissolved P pool was generally higher in surface waters than deeper waters, and higher in the Chukchi Sea than in the Bering Sea, consistent with their difference in primary productivity and reflecting sources of DOP from the surface waters. Within the particulate P pool, the labile P and ferric bound P were the two predominant species, especially in the upper water column (<1000 m), while authigenic or CaCO3 bound P and detrital P were the two least abundant particulate P species. A positive correlation between labile particulate P and particulate organic carbon (POC) or particulate nitrogen (PN) was observed, where labile P concentrations decreased with increasing DIP concentrations and decreasing biological activity in the upper water column, indicating the contribution of labile particulate P from biological production. Labile P was an active component in regeneration of particulate P in the water column. The authigenic P was relatively abundant in deeper waters, especially in the Bering Sea, suggesting an active transformation between labile-P and authigenic P and a possible sink for P as authigenic particulate P in the deeper water column. In contrast to labile P, authigenic P, and organic P, the distributions of ferric-bound P and detrital P were mostly regulated by physicochemical processes, such as lateral transport and sediment resuspension. Therefore, different particulate P species could play a distinct role in biogeochemical cycling of P in the water column and understanding the detailed chemical and phase speciation of P should provide a better understanding of the dynamic cycling of P in the marine environment.