11

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

22

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 (??)

33

Morphological CharacteristicsMorphological Characteristics

44

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.

55

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

66

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

77

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

88

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. .

99

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

1010

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.

1111

PCIPCIATIATI

ECOIECOI

Decadal scale oscillations are clearly evident at hydro-meterological

and ecological properties of the BS

1212

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

1313

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.

1414

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

1515

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 !

1616

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.

1717

Increase in surface nutrient concentration (DIN and DON)

More enhanced phytoplankton andBacterioplankton production

Cascade eCascade effects on the Biogeochemical ffects on the Biogeochemical PumpPump

1818

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

1919

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

32

Cascade eCascade effects on the ffects on the Biogeochemical PumpBiogeochemical Pump

2121

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

23

4

Cascade eCascade effects on the ffects on the Biogeochemical PumpBiogeochemical Pump

2222

VVariations of the pelagic food web structureariations of the pelagic food web structure in in thethe 1980s1980s

AureliaAurelia

MnemiopsisMnemiopsis

2323

Beroe

VVariations of the pelagic food web structureariations of the pelagic food web structure in in thethe 1990s1990s

T (T (ooC)C)

2424

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.

2525

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

2626

Chlorophyll distribution; Vedernikov and Demidov (1997)

Model Simulation (Oguz et al., 2004)

DiatoDiato

mmDinoflagellate Small phytoplankton

E. huxleyi

2727

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)

2828

H2S

NH4

NO3

DO

NHNH44

NitrogenCycle

The model reproduced the major features of the suboxic-anoxic interface zone structure similar to observations.

2929

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