Local remineralization patterns in the mesopelagic zone of the Eastern North Atlantic, off the NW Iberian Peninsula

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2006.09.002 Byline: C.G. Castro, M. Nieto-Cid, X.A. Alvarez-Salgado, F.F. Perez Keywords: Water masses; Remineralization; Nutrients; Dissolved organic matter; Mesopelagic zone; Northeast Atlantic Ocean; European ocean margin Abstract: The short-time-scale variability of the remineralization patterns in the domain of Eastern North Atlantic Central Waters (ENACW) off the NW Iberian Peninsula is studied based on biogeochemical data (oxygen, nutrient salts, total alkalinity, pH, dissolved organic matter and fluorescence of dissolved humic substances) collected weekly between May 2001 and April 2002. The temporal variability of inorganic variables points to an intensification of remineralization during the summer and autumn, with an increase of nutrients, total inorganic carbon and fluorescence and a decrease of oxygen. During the subsequent winter mixing, there is a biogeochemical reset of the system, with lower nutrients, total inorganic carbon and fluorescence and higher oxygen. In contrast to inorganic variables, the levels of dissolved organic matter in the ENACW seem to respond to short-term events probably associated with fast sinking particles, where solubilisation of organic matter prevails over remineralization. Applying a previously published stoichiometric model, we observed a vertical fractionation of organic-matter remineralization. Although there is a preferential remineralization of proteins and P compounds in the entire domain of ENACW, the percentage was higher in the upper ENACW (I80% for the upper ENACW and 63% for the lower. Likewise, the redissolution of calcareous structures contributes about 6% and 13% to the carbon regenerated in the upper and lower layers of ENACW, respectively. Author Affiliation: CSIC, Instituto de Investigacions MariA[+ or -]as, Eduardo Cabello 6, 36208 Vigo, Spain Article History: Received 15 July 2005; Revised 29 August 2006; Accepted 5 September 2006