Cycling of dissolved and particulate carbohydrates in a coastal upwelling system (NW Iberian Peninsula)

Abstract

The contribution of carbohydrates to the dissolved (DOC) and suspended (POC) organic carbon pools in NW Iberian shelf waters was assessed from May 2001 to April 2002. Particulate car- bohydrates (p-CHO) represented 26 ± 1 and 12 ± 1% of the POC changes in the middle of the Ria de Vigo (50 m water) and the middle of the adjacent continental shelf (150 m water), respectively. The contribution of dissolved carbohydrates (d-CHO) to the DOC changes was larger than p-CHO: 29 ± 4% in the ria and 31 ± 4% in the shelf. The correlations between p-CHO and POC (r = +0.88, n = 298, p < 0.001) and between d-CHO and DOC (r = +0.82, n = 298, p < 0.001) indicate that carbohydrate changes are linked to bulk organic carbon changes within the time scale of the sampling frequency (2 wk). Maximum carbohydrate accumulation occurred during the upwelling season at the 'spin down' phase of upwelling events; estimated rates of d-CHO production in the middle of the ria were ~1.5 µmol C l -1 d -1 , an order of magnitude larger than during the winter period. Although mono- saccharides represented 30 to 40% of the bulk d-CHO, they were responsible for less than 20% of the d-CHO changes, indicating that most of the freshly produced d-CHO is semi-labile sugar polymers.