1. SEASONAL CHANGES IN BENTHIC FLUXES AND NET ECOSYSTEM METABOLISM IN THE RIA DE VIGO (NW SPAIN) F. Alonso-Pérez, Carmen G. Castro, Zuñiga, D., B. Arbones y F.G. Figueiras Instituto de Investigaciones Marinas (CSIC, Vigo)

2. Rías Baixas at the northern boundary of the Canary Current upwelling system Seasonal variation: Upwelling: April to September Downwelling: October to March MONTH Upwelling index (1987-2004) Courtesy of RMS from PML AVHRR Sea Surface Temperature August 1998 UPWELLING BACKGROUND

3. Fate of this high primary production? NCP 0.84 Respiration 0.56 Respiration ? Carbon flux 0.18 aphotic zone photic zone sediment Respiration ? 2-D non stationary box model for the Ria based on temporal variability of nutrient distributions Units: gC m -2 d -1 (Rosón et al. 1999) BACKGROUND

4. To study the fate of fixed carbon on a seasonal scale based on direct measurements of gross primary production, pelagic and benthic respiration and vertical export of organic matter in the Ria de Vigo. OBJECTIVE

5. RIA DE VIGO: SAMPLING STATION Reference Site 20 m depth main ria channel 2 weeks campaign in April-04, July-04, October-04 and January-05.  METHODS

6.    Seawater samples for nutrients and size-fractionated chlorophyll (0.2, 2 & 20  m) (5 depths) Net Community Production (NCP) and Dark Community Respiration (DCR) by in situ 24 h light-dark bottle oxygen incubations (5 depths). NCP = O 2 (24h) light – O 2 (t 0 ) DCR = O 2 (t 0 ) - O 2 (24h) dark Gross Primary Production: GPP = NCP + DCR Biogenic particle vertical fluxes by in situ 24 h deployment of a sediment trap METHODS Photos: Manuel E. Garci

7. Home made benthic chamber Measuring oxygen and nutrient benthic fluxes Cylindrical chape and incubating volume ~ 140 L Stirring by 3 centrifugal pumps Water samples at prefixed times by syringe sampler (50 mL) Continuous recording of T, pH, turbidity and oxygen METHODS Ferrón et al, 2008

8. Upwelling Index (m 3 /(s km) Temperature (ºC) Nitrate (µM) Chla (mg/m 3 ) APRILJULYJANUARYOCTOBER HYDROGRAPHIC CONDITIONS

9. WATER COLUMN INTEGRATED SIZE-FRACTIONED CHLOROPHYLL-a Units: mg Chl a m -2 Arbones et al, 2008

10. SEASONAL AVERAGES VERTICAL CARBON FLUXES

11. SEASONAL AVERAGES OF BENTHIC FLUXES

12. Using carbonic and boric dissociation constants (Luecker, 2000) TCO 2 benthic fluxes = MaxCox TCO 2 – ½ Alk corr MinCox

13. Annual benthic carbon flux : 0.26 g C m-2 d-1 ~ 13 % GPP

14. NCP 1.00 Respiration 1.25 Respiration 0.11 Carbon flux 0.96 APRIL-04 aphotic zone photic zone sediment Respiration 0.30 NCP 4.06 Respiration 1.07 Respiration 0.32 Carbon flux 1.12 JULY-04 sediment Respiration 0.26 NCP 0.46 Respiration 0.60 Respiration 0.02 Carbon flux 1.05 OCTOBER-04 aphotic zone photic zone sediment Respiration 0.28 NCP 0.22 Respiration 0.36 Respiration 0.01 Carbon flux 1.32 JANUARY-05 sediment Respiration 0.19 44%79% 43%38% 56%21% 56%62% 5%6% 2%1% 27%14% 23%31% Summary & Conclusions: 1 D SEASONAL BUDGETS Units: g C m -2 d -1