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The role of Anthropogenic and The role of Anthropogenic and Climatic Forcing in the Long-term Climatic Forcing in the Long-term
Changes of the Black Sea EcosystemChanges of the Black Sea Ecosystem
Temel Oguz
[email protected]://www.ims.metu.edu.tr/cv/oguz/main.html
Varna, June 2005
Oguz (2005), Oceanography, 18(2), 112-121Oguz (2005), Oceanography, 18(2), 122-133
IMSIMSMETUMETU
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Some objectives of the workshop:1) Mitigation of negative impacts of pollution2) Sustainable use of the resources3) 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.
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The Black Sea: Great Ecological The Black Sea: Great Ecological ConcernConcern
The Black SeaThe Black Sea has suffered fromhas suffered from severesevere ecological changesecological changes since the 1970s due to since the 1970s due to concurent effects of concurent effects of
• intense eutrophicationintense eutrophication associated with associated with excessive anthropogenic nutrient load and excessive anthropogenic nutrient load and pollutants pollutants ((bottom-up control)bottom-up control)
• trophic cascadestrophic cascades as a result of as a result of overfishingoverfishing and outburst ofand outburst of gelatinous carnivores gelatinous carnivores (top-(top-down controldown control))
• natural climatic variationsnatural climatic variations
They have been particularly effective because They have been particularly effective because of veryof very limited water exchangelimited water exchange through thethrough the Bosphorus StraitBosphorus Strait and across theand across the permanent permanent pycnoclinepycnocline. .
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Anthropogenic ForcingAnthropogenic Forcing
Yearly nutrient variations within the NW Shelf
Pre-eutrophication phase (prior to Pre-eutrophication phase (prior to 1970s)1970s)Early-eutrophication phase (1970s)Early-eutrophication phase (1970s)Intense eutrophication phase (1980s)Intense eutrophication phase (1980s)Post-eutrophication phase (after Post-eutrophication phase (after 1995)1995)
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Climatic VariationsClimatic Variations
Features:Features:1)1) Long-term warming trend ~0.25Long-term warming trend ~0.25ooC / 100 yearsC / 100 years2)2) Variations at multi-decadal time scales (4 phases in ~130 years) Variations at multi-decadal time scales (4 phases in ~130 years) 3)3) sequence of cold-warm cycles with ~5 years durationsequence of cold-warm cycles with ~5 years duration
Basin-averaged winter (December-March) SST variationsBasin-averaged winter (December-March) SST variations
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Climatic VariationsClimatic Variations
CIL
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Increase in surface nutrient concentration (DIN and DON)
More enhanced phytoplankton andBacterioplankton production
Effects on the Biogeochemical PumpEffects on the Biogeochemical Pump
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Increase in surface nutrient concentration (DIN and DON)
More enhanced phytoplankton andBacterioplankton production
Increase in particulate and dissolved
organic nitrogenMore efficient OM decomposition
Increase in Subsurface DIN
1
Effects on the Biogeochemical PumpEffects on the Biogeochemical Pump
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Increase in surface nutrient concentration (DIN and DON)
More enhanced phytoplankton andBacterioplankton production
Increase in particulate and dissolved
organic nitrogenMore efficient OM decomposition
Increase in Subsurface DIN
More pronounced oxygen consumption
Broadening of SOL
1
2
Effects on the Biogeochemical PumpEffects on the Biogeochemical Pump
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Increase in surface nutrient concentration (DIN and DON)
More enhanced phytoplankton andBacterioplankton production
Increase in particulate and dissolved
organic nitrogenMore efficient OM decomposition
Increase in Subsurface DIN
More pronounced denitrification
Steeper gradients
in subsurface DIN
More pronounced oxygen consumption
Broadening of SOL
1
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Effects on the Biogeochemical PumpEffects on the Biogeochemical Pump
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Increase in surface nutrient concentration (DIN and DON)
More enhanced phytoplankton andBacterioplankton production
Increase in particulate and dissolved
organic nitrogenMore efficient OM decomposition
Increase in Subsurface DINMore pronounced
denitrification
Steeper gradients
in subsurface DIN
More pronounced oxygen consumption
Broadening of SOL
More pronounced Sulfur cycle
Increase in H2S (more intense hypoxia and anoxia)
1
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4
Effects on the Biogeochemical PumpEffects on the Biogeochemical Pump
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OverfishingOverfishing
Large pelagics
Small pelagics
Depletion of large pelagics;Small pelagics become main predator.More favorable phytoplankton growth.
Increase in phytoplankton growthSupports higher small pelagic stock
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Beroe
Interannual variations of the pelagic food web Interannual variations of the pelagic food web structurestructure
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Climatic OscillationsClimatic Oscillations
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Climatic OscillationsClimatic Oscillations
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Climatic TeleconnectionsClimatic Teleconnections
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Conclusions:Present and future state of the ecosystemPresent and future state of the ecosystem ? ?
fish catch oscillating at the level of fish catch oscillating at the level of mid-1970smid-1970s
fish stocks dominated by small fish stocks dominated by small pelagicspelagics
nutrient content in the water column nutrient content in the water column decreasing and decreasing and
the system is shifting towards the the system is shifting towards the oligotrophyoligotrophy
warming persistent over a decadewarming persistent over a decaderesource limitation associated with resource limitation associated with
warmingwarmingBeroe ovatoBeroe ovato controlling the controlling the
MnemiopsisMnemiopsis
Thus, it is reasonable to expect that the Thus, it is reasonable to expect that the oligotrophyoligotrophy and and warming warming will be two major will be two major controls of the ecosystem, and it will shift controls of the ecosystem, and it will shift towards the low biomass system. towards the low biomass system. Too soon to talk about ecosystem Too soon to talk about ecosystem recoveryrecovery