Collaborative Research: Silica Cycling in the Central North Pacific Gyre: Roles of Rhizosolenia Mats and Suspended Diatoms

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9401990 Brzezinski Global mass-balance consideration, vertical nutrient profiles, and seasonal nutrient cycle data all indicate that the large subtropical mid-ocean gyres may account for the majority of the global oceanic production of biogenic silica. Although diatoms can become abundant during spring blooms in these regions, the available evidence suggests that most of the annual silica production in summer and autumn. This may be especially true in the oligotrophic North Central Pacific which does not have a strong seasonal cycle of phytoplankton production due to Persistent stratification. The surface waters of the Central North Pacific contain the highest concentrations of silicic acid of any oligotrophic gyre. It is unknown whether this greater availability of silicic acid results in higher rates of silica production in this region compared to other mid ocean systems. Siliceous biomass in this region has been reported to be overwhelmingly dominated (90%) by centimeter- sized mats are not effectively sampled by traditional water bottle samplers and are typically collected by divers. This give rise to a unique situation where silica cycling in this region, which is likely to be significant in global terms, may be dominated by large rare sells that would be essentially invisible to investigations which employ traditional sampling methods. This project will be the first study of the production and dissolution of biogenic silica in the oligotrophic Central North Pacific Ocean. Our study will combine traditional water column sampling using water-bottle samplers with collections of mats made by divers to compare the relative roles of these large mats and suspended diatioms in the cycling of biogenic silica in the surface waters of this region. This study will have two major objectives: (1) to evaluate of the magnitude of silica production in the North Central Pacific Gyre, and (2) to assess the relative contribution mats of Rhizosoleni a sp. and unaaggregated diatoms in the cycling of Si. This work will be conducted during two cruises out of Hawaii.