Dissolved and particulate phosphorus distributions and elemental stoichiometry throughout the Chukchi Sea

Abstract

As a major gateway from the Pacific to the open Arctic Ocean, biogeochemical transformations of nutrients in the Chukchi Sea are important for understanding the Arctic ecosystem as a whole. This study examines the biogeochemical cycling of the macronutrient phosphorus (P) relative to carbon (C) and nitrogen (N) in the eastern Chukchi Sea during the ICESCAPE mission. Sea ice and water column dissolved and particulate P samples were collected during summer expeditions in 2010 (n=543) and 2011 (n=553). Nearly all forms of P were higher in Pacific Winter Waters (PWW), indicating the potential importance of PWW to Chukchi Sea nutrient pools. Annual means of P concentrations in all its forms in the offshore waters throughout the Chukchi Sea were also consistently higher (TP2010=1.56±0.61µM, TP2011=1.67±0.68µM) relative to waters inshore and within the Alaska Coastal Current (ACC), suggesting coastal inputs were relatively minor during our sampling. Rather, biological modification of P pools dominated, with 30–40% of the total dissolved P pool (TDP) and nearly 50% of the total particulate P pool (TPP) comprised of organic P. Nutrient analyses of first year sea ice suggest that sea ice melt contains highly variable P concentrations that span an order of magnitude depending on particulate matter content. As such, sea ice melt may contribute significant nutrients to summer waters on a transient basis. Low N:P ratios (<2) within the mixed layer are consistent with summertime N limitation of biological production and demonstrate that the Chukchi Sea is a major source of excess P to other regions of the Arctic Ocean. Deeper water column dissolved N:P ratios of 7–9.1, while lower than the canonical Redfield ratio, are consistent with particulate N:P ratios of a diatom-dominated biological community. Combined, results suggest that the eastern Chukchi Sea plays an important role in the composition and magnitude of P that ultimately reaches other Arctic Ocean waters.