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Spatio-temporal variability of size fractionated phytoplankton on the shelf adjacent to the Ebro river (NW Mediterranean)

AutorArin, Laura ; Estrada, Marta ; Salat, Jordi ; Cruzado, Antonio
Palabras claveEbro river shelf
Northwestern Mediterranean
Spatio-temporal variation
Chlorophyll a fractionation
Fecha de publicaciónjun-2005
CitaciónContinental Shelf Research 25(9): 1081-1095 (2005)
ResumenThe mesoscale distribution and seasonal variation of the size structure of phytoplankton biomass, as measured by chlorophyll a (chl a), was studied in the Ebro shelf area (NW Mediterranean) during three different seasons: autumn, winter andsummer. In autumn andsummer, when the water column was, respectively, slightly or strongly stratifiedand nutrient concentrations were low at surface, average total chl a values were 0.31 and0.29 mgm 3, respectively. In winter, the intrusion of nutrients into the photic zone by intense vertical mixing andstrong riverine inputs, producedan increase of the total autotrophic biomass (0.76 mgm 3). In the three seasons, the main contributor to total chl a was the picoplanktonic (o2 mm) size fraction (42% in winter andaround60% in autumn and summer). The nanophytoplankton (2–20 mm) contribution to total chl a showedthe lowest variability amongst seasons (between 29% and39%). The microplanktonic (420 mm) chl a size fraction was higher in winter (27%) than in the other seasons (less than 13%). The maximum total chl a concentrations were foundat surface in winter, at depths of 40m in autumn andbetween 50 and80 m in summer. The relative contribution of the o2 mm size fraction at these levels of the water column tendedto be higher than at other depths in autumn andwinter andlower in summer. In autumn andwinter, nutrient inputs from Ebro river discharge and mixing processes resulted in an increase on the 42 mm contribution to total chl a in the coastal zone near the Ebro Delta area. In summer, the contribution of the o2 and 42 mm chl a size fractions was homogeneously distributed through the sampling area. In autumn and summer, when deep chl a maxima were observed, the total amount of the autotrophic biomass in the superficial waters (down to 10 m) of most offshore stations was less than 10% of the whole integratedchl a (down to 100m or to the bottom). In winter, this percentage increaseduntil 20% or 40%. The 42 mm chl a increasedlinearly with total chl a values. However, the o2 mm chl a showeda similar linear relationship only at total chl a values lower than 1mgm 3 (in autumn andsummer) or 2mgm 3 (winter). At higher values of total chl a, the contribution of the o2 mm size fraction remainedbelow an upper limit of roughly 0.5 mgm 3. Our results indicate that the picoplankton fraction of phytoplankton may show higher seasonal and mesoscale variability than is usually acknowledged.
Descripción15 páginas, 8 figuras, 3 tablas.
Versión del editorhttps://dx.doi.org/10.1016/j.csr.2004.12.011
ISSN 0278-4343
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