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The role of Anthropogenic and Climatic Forcing on the Long-term

The role of Anthropogenic and Climatic Forcing on the Long-term Changes of the Black Sea Ecosystem Temel Oguz Middle East Technical University, Institute of Marine Sciences, Erdemli, Turkey oguz@ims.metu.edu.tr http://www.ims.metu.edu.tr/cv/oguz/main.html

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The role of Anthropogenic and Climatic Forcing on the Long-term

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  1. The role of Anthropogenic and Climatic Forcing on the Long-term Changes of the Black Sea Ecosystem Temel Oguz Middle East Technical University, Institute of Marine Sciences, Erdemli, Turkey oguz@ims.metu.edu.tr http://www.ims.metu.edu.tr/cv/oguz/main.html METU, Biology Department, 12 October 2005 METU IMS

  2. The objective of the talk is to provide • an overview of the ecosystem functioning during the last 30 years under combined effects of Anthropogenic and Climatic forcing • and then • to assess what is the present situation and • what we can expect in the future. • Outline of the talk: • Background information on general characteristics of the BS, • Concurrent effects of overfishing, climatic and anthropogenic forcing, • Impacts and cascade effects of these forcing on the ecosystem and the vertical biogeochemical structure, • Present and possible future status of the ecosystem, • Modelling complex structure of the BS vertical biogeochemical pump (??) • Model simulations from the BS circulation system (??)

  3. Morphological Characteristics

  4. Stratification Characteristics The system possesses a two layer density stratification with relatively less saline surface waters within the approximately upper 100m, overlying more dense salty water from the Mediterranean origin.

  5. Circulation Characteristics coastal anticyclonic eddy rim current • The building blocks • of the circulation • are: • the Rim Current system around the periphery, • an interior cell involving different types of structural organizations of several interconnected cyclonic gyres, and • a series of anticyclonic eddies on the coastal side of the Rim Current offshore filament meanders cyclonic gyres This system of circulation is further accompanied by meanders, filaments, offshore jets as well as cyclonically propogating, highly transient features of the Rim Current.

  6. Observing the BS from space by ocean color satellite sensors A distinguishing feature of the Black Sea is the high biological activity in the lower trophic food web structure as compared to neighboring Aegean and Eastern Mediterranean basins

  7. Main features of the Black Sea Biogeochemical Pump Radiation Euphotic Zone (40-50m) Zooplankton Nutrient Bacteria Phytoplankton Oxycline (20-30m) DO Organic matter NO3 Suboxic Zone (20-40m) Recycling Anoxic Layer (2000m) Sinking NH4 H2S

  8. The Black Sea: Great Ecological Concern • The Black Seahas suffered fromsevereecological changessince the 1970s due to concurent effects of • intense eutrophicationassociated with excessive anthropogenic nutrient load and pollutants into its NWS (bottom-up control) • trophic cascades as a result ofoverfishingand outburst of gelatinous carnivores(top-down control) • natural climatic variations • They have been particularly effective because of verylimited water exchangethrough theBosphorus Straitand across thepermanent pycnocline.

  9. Complex nonlinear coupling exists between these three concurrently operating mechanisms Ecosystem structure during the 1980s Ecosystem structure during the 1990s

  10. Climatic Forcing Temperature is the most important property to show the climate signature in marine and aquatic ecosystems. Basin-averaged winter (December-March) SST variations • Features: • Long-term warming trend ~0.25oC / 100 years • Variations at multi-decadal time scales (4 phases in ~130 years) • sequence of cold-warm cycles with ~5 years duration

  11. Decadal scale oscillations are clearly evident at hydro-meterological and ecological properties of the BS PCI ATI ECOI

  12. Decadal fluctuations helpus to assess possible future variations of the fish stocks Collapse of small pelagic stocks

  13. Climatic Teleconnections The North Atlantic Oscillation is the most dominant mode of natural climatic variability in the Northern Hemisphere. It is driven by the quasi-persistent low pressure system over the Iceland and high pressure system over the Azores. ? ?

  14. Anthropogenic Forcing Pre-eutrophication phase (prior to 1970s) Early-eutrophication phase (1970s) Intense eutrophication phase (1980s) Post-eutrophication phase (after 1995) Yearly nutrient variations within the NW Shelf IG1 IG2

  15. The excessive anthropogenic nutrient supply from the river Danube has gone through the biological cycle, and finally accumulated within the subsurface layers. The system recently tends to transform back to its oligotrophic (background) state !

  16. Overfishing and collapse of fishery Small pelagics Large pelagics Depletion of large pelagics: Small pelagics become main predator.

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

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

  19. Cascade effects on the Biogeochemical Pump Increase in surface nutrient concentration (DIN and DON) More enhanced phytoplankton and Bacterioplankton production 1 Increase in particulate and dissolved organic nitrogen More efficient OM decomposition 2 More pronounced oxygen consumption Increase in Subsurface DIN Broadening of SOL Konovalov and Murray, JMS (2001)

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

  21. Cascade effects on the Biogeochemical Pump Increase in surface nutrient concentration (DIN and DON) More enhanced phytoplankton and Bacterioplankton production 1 Increase in particulate and dissolved organic nitrogen More efficient OM decomposition 2 3 More pronounced oxygen consumption Increase in Subsurface DIN More pronounced denitrification 4 Broadening of SOL Steeper gradients in subsurface DIN More pronounced Sulfur cycle Increase in H2S (more intense hypoxia and anoxia)

  22. Variations of the pelagic food web structure in the1980s Mnemiopsis Aurelia

  23. Variations of the pelagic food web structure in the1990s Beroe T (oC)

  24. Present and future states of the ecosystem ? • Anthropogenic perturbations are in decaying phase, and the ecosystem is now more strongly regulated by natural climatic variations. But, high technology fishing still continues to be a problem. • Some robust features of the present ecosystem conditions are • nutrient content in the water column is decreasing, • and the system is shifting towards the oligotrophy • warming is persistent over a decade, and • limiting biological production • fish catch is oscillating at the level of mid-1970s, and • dominated by small pelagics • Beroe ovatocontinues to supress Mnemiopsis population • However, too soon to talk about ecosystem recovery. • Note that anchovoy is still to small with respect to its size during • the early 1970s.

  25. Opportun. species Coupled Physical- Biogeochemical Model CA CM Diatoms Dinoflagel. Small phyto E. huxleyi Air-Sea exchange Microzooplank. Mesozooplank. Euphotic Zone Gelatinous carnivores P. Production DO Org. Matter Gen. Uptake Oxycline Microbial loop Detritus O2 Bacteria Suboxic Zone NO3 Remineralization DON Nitrogen Cycle Anoxic Layer NH4 Sinking Redox Cycle Mn+2 NO3 Mn+2 MnO2 NH4 Denitrification NH4 H2S S0 H2S N2

  26. Chlorophyll distribution; Vedernikov and Demidov (1997) E. huxleyi Model Simulation (Oguz et al., 2004) Diatom Dinoflagellate Small phytoplankton

  27. The model succesfully described how the eutrophic ecosystem responded to increased anthropogenic nutrient load (bottom-up control), and population explosions of gelatinous and opportunistic species (top-down control)

  28. The model reproduced the major features of the suboxic-anoxic interface zone structure similar to observations. DO NO3 Nitrogen Cycle NH4 NH4 H2S

  29. The model reproduced the major features of the vertical nitrogen cycle fairly well, consistent with observations.

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