1 The role of Anthropogenic and Climatic Forcing in the Long-term Changes of the Black Sea Ecosystem Temel Oguz [email protected]

11

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

22

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.

33

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. .

44

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)

55

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

66

Climatic VariationsClimatic Variations

CIL

77

Increase in surface nutrient concentration (DIN and DON)

More enhanced phytoplankton andBacterioplankton production

Effects on the Biogeochemical PumpEffects on the Biogeochemical Pump

88



Increase in particulate and dissolved

organic nitrogenMore efficient OM decomposition

Increase in Subsurface DIN

1


99






More pronounced oxygen consumption

Broadening of SOL

1

2


1010






More pronounced denitrification

Steeper gradients

in subsurface DIN


Broadening of SOL

1

32


1111





Increase in Subsurface DINMore pronounced

denitrification

Steeper gradients

in subsurface DIN


Broadening of SOL

More pronounced Sulfur cycle

Increase in H2S (more intense hypoxia and anoxia)

1

23

4


1212

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

1313

Beroe

Interannual variations of the pelagic food web Interannual variations of the pelagic food web structurestructure

1414

Climatic OscillationsClimatic Oscillations

1515

Climatic OscillationsClimatic Oscillations

1616

Climatic TeleconnectionsClimatic Teleconnections

1717

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

Documents

1 The role of Anthropogenic and Climatic Forcing in the Long-term Changes of the Black Sea Ecosystem Temel Oguz [email protected]