Inconsistencies in annual variations of flux and reactivity of sinking particles in the Pacific Arctic: evidence from a sediment trap

Introduction Rapid Arctic sea-ice loss is reshaping deep particle export by lengthening the open-water season, altering ice-associated export, and enhancing lateral shelf-to-basin transport. However, it remains unclear whether annual variations in the flux and biochemical lability of sinking particles are synchronized. Methods We present a one-year record of amino acid and amino sugar compositions in sinking particles collected by a moored sediment trap at 870 m depth at station DM on the southern Northwind Ridge from August 2008 to September 2009. We used amino acid- and amino sugar-based indicators to assess the reactivity of sinking particles. Results Particulate organic carbon (POC) flux ranged from 0.91 to 30.53 mg C m -2 d -1 , and total hydrolysable amino acid carbon (THAA-C) accounted for 10.5-38.5% of POC. During spring under heavy ice cover, sinking particles showed a moderate POC flux but the highest reactivity. In contrast, during the ice-free season, POC flux was highest whereas particle reactivity was only moderate. This indicates a seasonal decoupling between export magnitude and biochemical reactivity. Discussion This decoupling may reflect efficient transport of relatively fresh organic matter to the deep sea by ice-algal aggregates in spring, whereas summer export likely includes a larger contribution of laterally transported and more reworked material. These findings indicate that evaluation of the Arctic Ocean biological pump should consider not only carbon export fluxes but also the biochemical reactivity of sinking particles.