RAPID ENVIRONMENTAL CHANGES IN THE BLACK SEA OVER THE LAST 3 KYRS

M. Namık Çağatay1 and Emin Güngör2

1 İstanbul Technical University, Geology Department, Ayazağa 80626 İstanbul2 Çekmece Nuclear Research and Training Centre, K. Çekmece İstanbul

Main topics

1) Change in phytoplankton population at ~2700 yrs BP 2) Climate cooling at ~ 1700 AD 3) Increase in mass accumulation and land erosion rates in last few

hundred years4) Increased eutrophication and metal pollution in the last 50 yrs

Large, enclosed unoxic basin, covering 432,000 km2; max.depth: 2250 m.Anoxia below 100-150 m for the last 7-8 kyrs due to sharp density stratification, weak vertical circulation and organic matter degradation.Severe environmental degradation in the last 50 yrs, mainly because of riverine input of contaminants and nutrients.

Four undisturbed cores recovered by a multi-corer during 1998 and 2000 IAEA cruises

Total organic carbon (TOC) analysis by CHN elemental analysis

Total carbonate analysis by gasometric-volumetric method

Metals analysis by ICP-MS after a total digestion

210Pb dating by alpha counting of 210Po, followed by using a constant 210Pb flux (FPb-210 in Bq cm-2 yr-1) - constant MAR (g cm-2 yr-1) model

A compaction correction applied for 210Pb age modelling

Methodology

Stratigrafic level

Cal. Age (yr)

Method Source

Base Sapropel Unit (Unit II/III boundary)

7090±18066007540±13078005083

14C14C14C14CVarve counting

Ross ve Degens, 1974Calvert, 1987Jones ve Gagnon, 1994Arthur ve Dean, 1997Degens ve diğ., 1980

First Coccolith band

3450±1202720±16020001633

14C14C14CVarve counting

Ross & Degens, 1974Jones &Gagnon, 1994Arthur ve Dean, 1997Hay et al., 1991

Last coccolith invasion and base of Coccolith unit (Unit I)

3200±1401635±609981256

14C14CVarve countingVarve counting

Ross & Degens, 1974Jones & Gagnon, 1994Degens et al., 1980Hay et al., 1991

Chronostratigraphy

Çağatay & Güngör

2700 yrs BP

7540 yrs BP

Emiliania huxleyi

West Black Sea Basin East Black Sea Basin

Carbonate and Organic Carbon Distributions

The first E. Huxleyi invasion at ~2700 yrs BP; a mojor event in the oceanogrphic history

First Coccolith

Sedimentation & Mass accumm. Rates (MAR)

West Black Sea Basin East Black Sea Basin

According to 210Pb chronology, the carbonate peak corresponds to ~1700 AD and the blue shaded area to a time interval of 100 yrs

Late Maunder Minimum (1645-1715; Eddy, 1978; Pfister, 1994; Lutherbacher et al., 2001)

Oxygen and carbon isotope distributions

Carbonate

Temperature decrease during LMM (?)

Core MAR (g m-2 yr-1) LSR (cm yr-1)

BS98-9 171.5 0.72

BS98-15 71.25 0.34

BS2K-9 155.7 0.45

BS2K-23 87.31 0.26

Mass accumulation and Linear sedimentation rates for the last 125 yrs

The average total MAR values for the last 125 yr are 2 to 4 times higher than those for the last 2700 years, computed from published 14C ages, suggesting that the sedimentation rate has considerably increased in recent times, due to human impact.

Eutrophication and Metal Pollution

Core BS-15

Element Enrich.factor over backgr.

Ba 5.5

Zn 5

Pb 9

Cu 2

Core BS-9

Element Enrich.factor over backgr.

Ba 5

Zn 3.6

Pb 2

Cu 2.4

Conclusions

Core evidence shows four important rapid environmental changes in Black Sea:

1) Coccolitophore invasion at about 2700 yrs as result of salinity increase to 11 ppt. This event increased the CaCO3 burial by at least 3 times over the

previous period.

2) Cold climate: Late Maunder Minimum during 1645-1715 AD.

3) Increase in sedimentation and land erosion rates in the last few centuries.

4) Increase in eutrophication and metal pollutin in the last 50 yrs.

5) This study is onother demonstration of the usefulness of core studies in obtaining long records of environmental changes in marine basins. This is important for modelling and future predictions.