1. 1 The role of Anthropogenic and Climatic Forcing in the Long-term Changes of the Black Sea Ecosystem Temel Oguz oguz@ims.metu.edu.tr http://www.ims.metu.edu.tr/cv/oguz/main.html Varna, June 2005 Oguz (2005), Oceanography, 18(2), 112-121 Oguz (2005), Oceanography, 18(2), 122-133 IMS METU

2. 2 Some objectives of the workshop: 1) Mitigation of negative impacts of pollution 2) Sustainable use of the resources 3) Priority ecological problems and their impacts on the ecosystem Objective of the present talk: To provide a unified description of the ecosystem functioning from nutrients – to - plankton –to- higher predators under Anthropogenic and Climatic effects, and then To assess what we can expect in the future.

3. 3 The Black Sea: Great Ecological Concern The Black Sea: Great Ecological Concern The Black Sea has suffered from severe ecological changes since the 1970s due to concurent effects of intense eutrophication associated with excessive anthropogenic nutrient load and pollutants (bottom-up control) intense eutrophication associated with excessive anthropogenic nutrient load and pollutants (bottom-up control) trophic cascades as a result of overfishing and outburst of gelatinous carnivores (top-down control) trophic cascades as a result of overfishing and outburst of gelatinous carnivores (top-down control) natural climatic variations natural climatic variations They have been particularly effective because of very limited water exchange through the Bosphorus Strait and across the permanent pycnocline.

4. 4 Anthropogenic Forcing Yearly nutrient variations within the NW Shelf Pre-eutrophication phase (prior to 1970s) Early-eutrophication phase (1970s) Intense eutrophication phase (1980s) Post-eutrophication phase (after 1995)

5. 5 Climatic Variations Features: 1)Long-term warming trend ~0.25 o C / 100 years 2)Variations at multi-decadal time scales (4 phases in ~130 years) 3) sequence of cold-warm cycles with ~5 years duration Basin-averaged winter (December-March) SST variations

6. 6 Climatic Variations CIL

7. 7 Increase in surface nutrient concentration (DIN and DON) More enhanced phytoplankton and Bacterioplankton production Effects on the Biogeochemical Pump Effects on the Biogeochemical Pump

8. 8 Increase in surface nutrient concentration (DIN and DON) More enhanced phytoplankton and Bacterioplankton production Increase in particulate and dissolved organic nitrogen More efficient OM decomposition Increase in Subsurface DIN 1 Effects on the Biogeochemical Pump Effects on the Biogeochemical Pump

9. 9 Increase in surface nutrient concentration (DIN and DON) More enhanced phytoplankton and Bacterioplankton production Increase in particulate and dissolved organic nitrogen More efficient OM decomposition Increase in Subsurface DIN More pronounced oxygen consumption Broadening of SOL 1 2 Effects on the Biogeochemical Pump Effects on the Biogeochemical Pump

10. 10 Increase in surface nutrient concentration (DIN and DON) More enhanced phytoplankton and Bacterioplankton production Increase in particulate and dissolved organic nitrogen More efficient OM decomposition Increase in Subsurface DIN More pronounced denitrification Steeper gradients in subsurface DIN More pronounced oxygen consumption Broadening of SOL 1 3 2 Effects on the Biogeochemical Pump Effects on the Biogeochemical Pump

11. 11 Increase in surface nutrient concentration (DIN and DON) More enhanced phytoplankton and Bacterioplankton production Increase in particulate and dissolved organic nitrogen More efficient OM decomposition Increase in Subsurface DIN More pronounced denitrification Steeper gradients in subsurface DIN More pronounced oxygen consumption Broadening of SOL More pronounced Sulfur cycle Increase in H 2 S (more intense hypoxia and anoxia) 1 2 3 4 Effects on the Biogeochemical Pump Effects on the Biogeochemical Pump

12. 12 Overfishing Large pelagics Small pelagics Depletion of large pelagics; Small pelagics become main predator. More favorable phytoplankton growth. Increase in phytoplankton growth Supports higher small pelagic stock

13. 13 Beroe Interannual variations of the pelagic food web structure

14. 14 Climatic Oscillations

15. 15 Climatic Oscillations

16. 16 Climatic Teleconnections

17. 17 Conclusions: Present and future state of the ecosystem ? fish catch oscillating at the level of mid-1970s fish stocks dominated by small pelagics nutrient content in the water column decreasing and the system is shifting towards the oligotrophy warming persistent over a decade resource limitation associated with warming Beroe ovato controlling the Mnemiopsis Thus, it is reasonable to expect that the oligotrophy and warming will be two major controls of the ecosystem, and it will shift towards the low biomass system. Too soon to talk about ecosystem recovery