1. Physical effects on plankton and productivity on the Faroe Plateau E. Gaard, B. Hansen, S. K. Eliasen and K. M. H. Larsen Faroese Fisheries Laboratory Tórshavn, Faroe Islands

2. Content of the talk Plankton variability Cod growth & recruitment variability Possible environmental effects

3. Location of the Faroe shelf

4. The Faroe Shelf ecosystem The shelf water is well separated from the surrounding offshore. Retention of holo- and meroplankton The plankton is different in composition, timing and production from offshore An ecosystem. The primary production is the basis for production in the higher trophic levels.

5. Phytoplankton biomass Seasonal, 1997-2003

7. Chlorophyll a & nitrate 1997 2000

8. Nitrate, 40 m 23 June - 1 July 2000

9. Nitrate, Faroe shelf 1995-2003

10. Index of potential new primary production Spring – mid summer, 1990-2003

11. Zooplankton in spring Calanus Reproduction Neritic zooplankton

12. Zooplankton in late April

13. Cod variability

14. Primary production and cod

15. What causes the large fluctuations in potential new primary production ?

16. Solar radiation – PPnew

17. Zooplankton DW & nitrate Faroe shelf, late June

18. Overwintered Calanus (CV-CVI) April On the shelfOffshore – Shelf difference

19. Modelled chlorophyll concentrations with high exchange rate (k = 4000 m/day), with & without Calanus off shelf

20. Modelled chlorophyll concentrations (high and low exchange rates) compared with observations from different years

21. Air temperature in Tórshavn (January-April) and Primary Production Index Air temperature PP index

22. 200m Surface temperature 18. April 2003 (from P. Miller, Plymouth Marine Lab)

23. Seasonal variations in mean month temperature

24. Heat and freshwater exchanges affect the shelf temperature, salinity, and density Cooling in winter Rain Horizontal exchange

25. Salinity difference across the shelf front

26. Density difference across the shelf front

27. Potential new primary production and density difference across the shelf front in May

28. Hypothesis Horizontal exchange inhibits primary production A large density difference across the shelf front inhibits horizontal exchange (through baroclinic instability, e.g.) The air temperature in Jan-April determines the density difference across the shelf front Cold winters give good production