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Nutrient mineralization patterns in shelf waters of the Western Iberian upwelling

AuthorsÁlvarez-Salgado, Xosé Antón ; Castro, Carmen G. ; Pérez, Fiz F. ; Fraga, Fernando
Issue Date1997
PublisherPergamon Press
CitationContinental Shelf Research 17(10): 1247-1270 (1997)
AbstractA set of hydrographicdata collectedduring severalcruisesto theNWIberian upwelling systemhas been used to assess the patterns of nutrient mineralizationover the shelf. Mineralized nutrient ratios (N/P and N/Si)in the lowerwatercohrmnare clearlybelowthe ratios characteristicof freshly upwelled oceanic waters. Nitrogen mineralization, in comparison to phosphorus mineralization, is incomplete,in agreementwith phosphate’sfaster regenerationrate and the low residence time of water, which precludes complete mineralization. Silicate shows the highest enrichmentas a consequenceof the selectiveconcentrationof particulate biogenicsilica in the near bottom waters. Diffusionof nutrients mineralizedin the sedimentsseemsto representan important contribution.TheIowestmineralizationof the surveyedarea is foundto the north of CapeFinisterre, especiallywith regard to silicate.To the South, the Rias Baixas(four large embayments)return as reducingparticulate organicmatter (POM)a smallfraction of the upwellednutrientsimportedfrom the shelf. However,the out-flowingfreshwatercontributesto stratificationof coastal waters, which favoursPOMproduction,accumulationand sedimentation.In addition,highlevelsofnewdissolved organic matter (DOM) in the outflowcan also enhanceprimary productionin shelfsurface waters. Finally, highest mineralization was found to the south of the River Miiio, where there are no embayments and the shelf is wider. Mineralization tends to: (1) increase the potential primary productionof thisecosystembyupto 50%,(nitrogenIimitation)orup to 80%(siliconlimitation);(2) favour the developmentof phytoplanktonassemblagesdominatedbydiatoms(Sienrichmentdouble that ofN and P); and (3)bufferthe largespatial and temporaldifferencesintroducedbythe advected nutrients
Description24 páginas, 10 figuras, 2 tablas
Publisher version (URL)http://dx.doi.org/10.1016/S0278-4343(97)00014-9
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