Daily and seasonal variations of the partial pressure of CO2 in surface seawater along Belgian and southern Dutch coastal areas

The variations of the partial pressure of CO2 (pCO(2)) and related paramete rs were determined in surface seawater along the Belgian coast, from Januar y 1995 to June 1996, at both daily and seasonal time scales. The distributi on of pCO(2) in this area is regulated by river input from the Scheldt, bio logical activity and hydrodynamics. The contribution of each of these proce sses varies as a function of the considered time scale: (i) the daily varia tion of pCO(2) depends on the tide although modulated by the biological die l cycle; (ii) the seasonal variation of pCO(2) depends on the input from th e Scheldt and the seasonal variations of phytoplanktonic biomass. During wi nter, the plume of the river Scheldt is oversaturated in pCO(2) with respec t to the atmosphere. During spring and summer, phytoplankton blooms occur b oth in the lower Scheldt estuary and in the river plume and may lead to und ersaturation of pCO(2) in the easternmost area of the river plume. However, the degradation of phytoplankton induces oversaturation of pCO(2), in the westernmost area of the plume. Furthermore, the inter-annual variation of p CO(2) depends partly on the fluctuations of the discharge of the Scheldt. O ur preliminary results strongly suggest that, on an annual basis, the Schel dt plume behaves as a net source of CO2 to the atmosphere. (C) 1999 Elsevie r Science B.V. All rights reserved.