the role of anthropogenic and climatic forcing on the long-term
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The role of Anthropogenic and The role of Anthropogenic and Climatic Forcing on the Long-Climatic Forcing on the Long-
term term Changes of the Black Sea Changes of the Black Sea
EcosystemEcosystem
Temel OguzMiddle East Technical University,
Institute of Marine Sciences, Erdemli, Turkey
oguz@ims.metu.edu.trhttp://www.ims.metu.edu.tr/cv/oguz/main.html
METU, Biology Department, 12 October 2005
IMSIMSMETUMETU
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The objective of the talk is to provide The objective of the talk is to provide an overviewan overview of the ecosystem functioning during of the ecosystem functioning during
the last 30 years under combined effects of the last 30 years under combined effects of Anthropogenic and Climatic forcingAnthropogenic and Climatic forcing
and thenand thentto assess what is the present situation and o assess what is the present situation and
what we can expect in the future. what we can expect in the future.
Outline of the talk:1) Background information on general characteristics of the
BS,2) Concurrent effects of overfishing, climatic and
anthropogenic forcing,3) Impacts and cascade effects of these forcing on the
ecosystem and the vertical biogeochemical structure,4) Present and possible future status of the ecosystem,5) Modelling complex structure of the BS vertical
biogeochemical pump (??)6) Model simulations from the BS circulation system (??)
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Morphological CharacteristicsMorphological Characteristics
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Stratification CharacteristicsStratification Characteristics The system possesses a The system possesses a two layer density stratificationtwo layer density stratification with relatively less saline surface waters within the with relatively less saline surface waters within the approximately upper 100m, overlying more dense salty approximately upper 100m, overlying more dense salty water from the Mediterranean origin.water from the Mediterranean origin.
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cyclonic gyres
rim current
meanders
coastalanticyclonic eddy
offshore filament
The building blocks
of the circulation
are:(i) the Rim Current
system around the periphery,
(ii)an interior cell involving different types of structural organizations of several interconnected cyclonic gyres, and
(iii) a series of anticyclonic eddies on the coastal side of the Rim Current
This system of circulation is further accompanied by meanders, filaments, offshore jets as well as cyclonically propogating, highly transient features of the Rim Current.
Circulation CharacteristicsCirculation Characteristics
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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
Observing the BS from space by ocean color satellite sensorsObserving the BS from space by ocean color satellite sensors
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Euphotic Zone (40-50m)
Oxycline (20-30m)
Suboxic Zone (20-40m)
Anoxic Layer
(2000m)
HH22SS
NHNH44
NONO33
DODO
MMain features ain features ooff the Black Sea Biogeochemical the Black Sea Biogeochemical PumpPump
PhytoplanktonBacteria
ZooplanktonNutrient
Radiation
Organic m
atter
Rec
yclin
g
Sinking
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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 into its NWS into its NWS ((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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Ecosystem structure Ecosystem structure during the 1980sduring the 1980s
Ecosystem structure Ecosystem structure during the 1990sduring the 1990s
Complex nComplex nonlinear coupling onlinear coupling exists between exists between these these three concurrently operating mechanismsthree concurrently operating mechanisms
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Climatic Climatic ForcingForcing
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
Temperature is the most important property to show the climate signature Temperature is the most important property to show the climate signature in marine and aquatic ecosystems.in marine and aquatic ecosystems.
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PCIPCIATIATI
ECOIECOI
Decadal scale oscillations are clearly evident at hydro-meterological
and ecological properties of the BS
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Collapse of small pelagic stocks
Decadal fluctuations helpDecadal fluctuations help us to assess us to assess possible future possible future
variations of the fish stocks variations of the fish stocks
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Climatic TeleconnectionsClimatic Teleconnections
??
??
The North Atlantic Oscillation is the most The North Atlantic Oscillation is the most dominant mode of natural climatic variability in dominant mode of natural climatic variability in
the Northern Hemisphere. It is driven by the the Northern Hemisphere. It is driven by the quasi-persistent low pressure system over the quasi-persistent low pressure system over the
Iceland and high pressure system over the Iceland and high pressure system over the Azores.Azores.
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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)
IG1 IG2IG1 IG2
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The excessive anthropogenic nutrient supply from the river The excessive anthropogenic nutrient supply from the river Danube has gone through the biological cycle, and finally Danube has gone through the biological cycle, and finally
accumulated within the subsurface layers.accumulated within the subsurface layers.
The system recently tends to transform back to its The system recently tends to transform back to its oligotrophic (background) state !oligotrophic (background) state !
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OverfishingOverfishing and collapse of and collapse of fisheryfishery
Large pelagicsLarge pelagics
Small pelagicsSmall pelagics
Depletion of large pelagics:Depletion of large pelagics:Small pelagics become main Small pelagics become main predator.predator.
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Increase in surface nutrient concentration (DIN and DON)
More enhanced phytoplankton andBacterioplankton production
Cascade eCascade effects on the Biogeochemical ffects on the Biogeochemical PumpPump
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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
Cascade eCascade effects on the ffects on the Biogeochemical PumpBiogeochemical 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
Cascade eCascade effects on the ffects on the Biogeochemical PumpBiogeochemical Pump
Konovalov and Murray, JMS (2001) Konovalov and Murray, JMS (2001)
2020
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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Cascade eCascade effects on the ffects on the Biogeochemical PumpBiogeochemical 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
Cascade eCascade effects on the ffects on the Biogeochemical PumpBiogeochemical Pump
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VVariations of the pelagic food web structureariations of the pelagic food web structure in in thethe 1980s1980s
AureliaAurelia
MnemiopsisMnemiopsis
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Beroe
VVariations of the pelagic food web structureariations of the pelagic food web structure in in thethe 1990s1990s
T (T (ooC)C)
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Present and future states of the ecosystem ?
AAnthropogenic perturbations are nthropogenic perturbations are in in decaying decaying phase, phase, and the ecosystem is now more strongly and the ecosystem is now more strongly regulated by natural climatic variations. regulated by natural climatic variations. But, high But, high technology fishing still continues to be a problem.technology fishing still continues to be a problem.
Some robust features of the Some robust features of the present present ecosystem ecosystem conditions conditions arearenutrient content in the water column is nutrient content in the water column is decreasing, decreasing,
and the system is shifting towards the and the system is shifting towards the oligotrophyoligotrophywarming is persistent over a decade, and warming is persistent over a decade, and
limiting biological productionlimiting biological productionfish catch is oscillating at the level of mid-1970s, fish catch is oscillating at the level of mid-1970s, andand
dominated by small pelagicsdominated by small pelagicsBeroe ovatoBeroe ovato continues to continues to supress supress Mnemiopsis Mnemiopsis populationpopulation
However, tHowever, too soon to talk about ecosystem oo soon to talk about ecosystem recovery.recovery. Note that anchovoy is still to small with respect Note that anchovoy is still to small with respect to its size during to its size during the early 1970s.the early 1970s.
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P. ProductionP. Production
Org. Matter Gen.Org. Matter Gen.
RemineralizationRemineralization
Sinking
Upta
keUp
take
NONO33
NHNH44
NitrogenCycle
DetritusDetritus
CCAA
CCMM
Bacteria
DON
Microbial loopMicrobial loop
N2
Mn+2 MnO2
NH4 H2S S0
Redox CycleRedox Cycle
DenitrificationDenitrification
Euphotic Zone
Oxycline
Suboxic Zone
Anoxic Layer
H2SNH4
NO3
DO
Mn+2
O2
Air-SeaAir-Seaexchangeexchange
DiatomsDiatomsDinoflagel.Dinoflagel.Small phytoSmall phytoE. huxleyiE. huxleyi
Opportun.Opportun.speciesspecies
Microzooplank.Microzooplank.Mesozooplank.Mesozooplank.
Gelatinous Gelatinous carnivorescarnivores
Coupled Physical-Biogeochemical
Model
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Chlorophyll distribution; Vedernikov and Demidov (1997)
Model Simulation (Oguz et al., 2004)
DiatoDiato
mmDinoflagellate Small phytoplankton
E. huxleyi
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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)
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H2S
NH4
NO3
DO
NHNH44
NitrogenCycle
The model reproduced the major features of the suboxic-anoxic interface zone structure similar to observations.
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The model reproduced the major features of the vertical nitrogen cycle fairly well, consistent with observations.
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