Aquatic Sciences Meeting, Albuquerque 2001

SS16 Iron Bioavailability and Limitation to Primary Production (Disciplinary Connections)

Date: Monday, February 12, 2001, Time: 3:00:00 PM

Location: Mesilla

Firme, G, F, University of Delaware, Lewes, USA, gifirme@udel.edu

Hutchins, D, A, University of Delaware, Lewes, USA, dahutch@udel.edu

Bruland, K, W, University of California, Santa Cruz, Santa Cruz, USA, bruland@cats.ucsc.edu

Rue, E, L, University of California, Santa Cruz, Santa Cruz, USA, elrue@cats.ucsc.edu

THE SPATIAL EXTENT OF IRON LIMITATION IN THE HUMBOLDT CURRENT AND PERU UPWELLING AND EFFECTS ON NUTRIENT DRAWDOWN RATIOS

Phytoplankton iron limitation was investigated for the first time in the Peruvian coastal upwelling and Humboldt Current. Thirty small (1L) iron addition experiments were performed to assess the spatial extent of Fe limitation, using measurements of chlorophyll a, dissolved and particulate nutrients. Dissolved iron values ranged from severely depleted to abundant. Iron limitation was widespread in areas lacking shelf sources of Fe, as in earlier work in the California upwelling. Molar ratios of silicate to nitrate uptake off Peru were however generally much lower, ranging from 0.1 to 1.2. Si:N drawdown ratios decreased significantly in +Fe bottles, consistent with previous observations. Nitrate to phosphate uptake ratios ranged from 5 to 16, and increased significantly at iron limited stations after Fe addition. This effect was due to large increases in nitrate uptake relative to phosphate uptake, suggesting that iron limitation can be responsible for large deviations from Redfieldian N:P uptake ratios in this region.

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Aquatic Sciences Meeting, Albuquerque 2001

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