Eastern Mediterranean sea surfacetemperatures and δ18O (in the late Quaternary)

Kay-Christian Emeis1, Uwe Mikolajewicz2

1IfBM, University of Hamburg, Bundesstr. 55, 210146 Hamburg, FRG

2MPI for Meteorology, Bundesstr. 53, 20146 Hamburg, FRG

The modern Mediterranean Sea

anti-estuarine circulation (E>>P), nutrient poor, little biological productivity. Climate setting/hydrology influenced by southern hemisphere/tropical and subtropical/monsoonal processes, and North Atlantic.

87SL

71SL67SL78SL

KL71

KS8230

RL11

ODP 967

I. Sapropel periods and conditions

Climate-driven changes in biogeochemical character of and material fluxes in a now extremelyoligotrophic ocean.

•Paced by insolation since the (Miocene)/Pliocene

•Caused by anoxic conditions in deep water

•Lasting several 1000 years

Lourens et al., 1998

The astronomical pacemaker

Sakamoto et al., 1998

Insolation/climate forcing

Sapropels occur whennorthern hemispheresummer insolation is high and contrasts betweenseasons are large.

In the late Quaternary theymark the transition glacialto interglacial conditions

Age (k.y.before present)

Insola

tion a

t 65°

N in

summ

er(W

/m2 )

400

440

480

520

2000 2400 2800 3200 3600 4000

400

440

480

520

0 400 800 1200 1600 2000

Onset NH glaciation

Strong ice-volume effect

Precession dominant

Obliquity pronounced

freshwater input(+warming)

BiologyC:N:P,

Export PP

ChemistryRedox,C:N:P

C-flux to Sediments

Stratification

The schematic chain of events

The schematic chain of events

freshwater input(+warming)

BiologyC:N:P,

Export PP

ChemistryRedox,C:N:P

C-flux to Sediments

Stratification

Climatic trigger: Low/high latitude?

Biogeochemical consequences:Which processes are responsible for anoxia andincreased C-burial?

Variations of δ18O in surface waters

-3

-2

-1

0

1

2

3

40 500 1000 1500 2000

Age (k.y.)

δ18O

plank

tonic

foram

inifer

sEquatorial Pacific (Site 677; N. Shackleton)

Ionian Sea (KC01; M. Paterne)Levantine Sea (Site 967; D. Kroon)

Exaggerated basin effect: Combination of freshwaterinput, warming of surface layer, enhancedstratification, and pooling at surface

The late Quaternary

Mediterranean sea surface temperatures

0.4

0.5

0.6

0.7

0.8

0.9

0 1 2 3 4 5 6 7depth in core M40/4-71

Uk´

37 v

alue

26

23

20

17

14

11

SST

(°C

)

S9S8S7S5S4S3S1 S6

∆SST=12°C

δ18O patterns in sapropels: late Quaternary

-3

-2

-1

0

1

2

3

0 1 2 3 4 5 6 7depth in core M40/4-71

18

O G

. rub

erδδ δδ

∆δ18O=4.3‰

δ18O seawater reconstruction

Global ice effect = -0.12‰, Salinity = -3.4 psu

² 18 O=1.9‰ δ

-2.0

-1.0

0.0

1.0

16

17

18

19

20

21

22

23

24

117 120 123 126 129

δ18

O G

. rub

er

SS

T (°

C)

age (kyr)

Sapropel S-5/Levantine Basin

²SST=1.8°C=0.36‰

7°C = -1.47‰ 18 Oδ

∆δ18Oseawater and ∆ SST associated with transition to sapropels/E.Med.

2.0-0.6S105.12.23.5-2.16.72.90.76.6

-0.6S9-0.5S8-2.2S7-4.7S6-2.2S5-2.6S4-2.7S3-2.3S1

12

14

16

18

20

22

24

-30-20-100102030

SST

(°C

)

cm from sapropel base

M40-71

base S5

-2

-1

0

1

2

3

18 O

G. r

uber

δ

967

969

δ

Variations in SST of surface waters: Pliocene

1214161820222426

420

440

460

480

500

520

540

2220 2230 2240 2250 2260

SS

T(°C

) Insolation

Age (k.y.)

3 k.y.

Insolation cycle 218Insolation cycle 216

Base of Sapropel Base of Sapropel

Variations in δ18O of foram calcite: Pliocene

-1

0

1

2

400

420

440

460

480

500

520

540

2220 2230 2240 2250 2260

Sum

mer insolation 65°N

(W/m

2)

Insolation cycle 218Insolation cycle 216

Base of sapropelBase of sapropel

Age (k.y.)

δ18O

plank

tonic

foram

inifer

s

Not so much the absolute temperature…. A

vera

geS

ST

in s

apro

pels

(°C

)

δ18O

benth

icfor

amini

fersim

Easte

rn

Equa

torial

Pacif

ic (S

ite 84

6, Mi

x et a

l., 19

95)

12

14

16

18

20

22

24

262.5

3

3.5

4

4.5

5

0 500 1000 1500 2000 2500 3000 3500

Age (k.y.)

-3

-2

-1

0

1

2

3

4

-3

-2

-1

0

1

2

3

0 500 1000 1500 2000 2500 3000 3500

…nor an absolute value of seawater δ18O…Av

erag

eδ18

O sea

water

in sa

prop

els

Age (k.y.)

δ18O

benth

icfor

amini

fersim

Easte

rn

Equa

torial

Pacif

ic (S

ite 84

6, Mi

x et a

l., 19

95)

…but the change from cold&dry to warm&wet

Stratification, anoxia and enhanced C-flux...........

Fresh water influx and warming of surface watersenhance stratification.

Winter convection ceases to supply deep water, anoxiaresults.

Production increases due to changed internal cycling of phosphorus.

-2-10123

2.5

3

3.5

4

4.5

18O G. ruberδ

10 15 20 25

SST (°C)

0 50 100150 200 250

primary production(g C m-2 yr-1)

from Babio

>10°C>4 permil

S6

S5

S7

S4

Em

eis

et a

l., 2

003,

Wel

deab

et a

l., 2

003

Monsun-signal

∆S=-9 psu

Time: 200 – 100 ka

S6

S5

Meteor 40-4, 71SL,220-480 cm

S7

0 200 400 600

2.5

3

3.5

4

4.5

C:P molar ratio

-2 0 2 4 6 815N/14N

0 50 100150200250

primary production (g C m-2 yr-1)from Babio flux rates

......from natural eutrophication

Phosphorus is lost fromsediments.

Winter convectionentrains P-rich waters intosurface.

N:P ratios favor N-fixation.

Classical moisture sources

Ryan, 1972 (and many others later)Picture from Mangerud et al.,2001

Rossignol-Strick, 1983Picture from Ruddiman, 2001

Northern hemisphere Southern hemisphere/tropicalprocesses

Less classical moisture sources

Béthoux and Pierre, 1999 Rohling et al., 2004

∆ North Atlantic/Mediterranean ITCZ relocationsea water density differences

Gibraltar

Argentarolacave

Soreq/Pequiincaves

CoreM40-71SL

Linking terrestrial and marine records

-2

0

2

4

δ18O

G. r

uber

4 cores eastern Mediterranean

δ 18O

10

15

20

25

SS

T (°C)

SST

2 cores eastern Mediterranean

-8

-6

-4

-2

0 50 100 150 200 250

S1 S3 S4 S5 S6 S7 S8 S9

δ18O

spe

leot

hem

cal

cite

age (kyr)

Pequin+Soreq caves

δ 18O

δ18O in speleothems and marine forams(Bar-Matthews et al., 2003; Emeis et al., 2003)

-2

0

2

4

δ18O

G. r

uber

4 cores eastern Mediterranean

δ 18O

10

15

20

25

SS

T (°C)

SST

2 cores eastern Mediterranean

-8

-6

-4

-2

0 50 100 150 200 250

S1 S3 S4 S5 S6 S7 S8 S9

δ18O

spe

leot

hem

cal

cite

age (kyr)

Pequin+Soreq caves

δ 18O

δ18O in speleothems/marine forams & SST(Bar-Matthews et al., 2003; Emeis et al., 2003)

⇓

⇓

⇓

Bard et al., 2002

Western Mediterranean/ Tyrrhenian Sea speleothems

= S6

None quite fits the evidence…..

....because the trigger is also felt on land.....

Paleoclimate modelling: Questions

Which part of the climate system is responsible for the dramatic changes seen in the Mediterranean Sea?

Does the moisture originate from the tropical Atlantic or the Indian Ocean, or is the surplus moisture a consequence of enhanced evaporation within the Mediterranean catchment area?

What oceanographic and biogeochemical controls govern the switchfrom oligotrophic to eutrophic conditions in a progressively suboxicand finally anoxic ocean basin?

What are the time constants associated with this switch and do themodel data agree with available records on productivity levels and nutrient regimes?

Individual sapropels - multi-speciesreconstruction of conditions during S5

Preferred depth habitat/water mass preference/seasonal preference of foraminifers is reflected in the amplitude of the oxygenisotope ratios of shellcalcite.

Once established, thisknowledge can be used to reconstruct water massproperties by fitting modelsto observations......

Sapropel S5 (Eeemian)/Box model of isotopic change in different water masses

Paleoclimate modelling: Experiments withvariable orbital forcing (Tuenter, 2004)

Change in SSS in February due to precession-inducedchanges in P-E and river discharge (but look at sss change!

Paleoclimate modelling: Model system

Holocene/S1: Atmospheric moisture transport 8 ka – modern

(kg m-1 s-1)

Holocene/S1: Rain 8 ka – modern

(mm month-1)

Moisture transport 126-115 ka (S5)

(kg m-1 s-1)

Eemian/S5: Rain 126-115 ka

(mm month-1)

Conclusions

The “Big Picture” on forcing and and internal processes during sapropel formation is clear: SST changes (>10°C) and salinity changes (>3 psu) in surface waters are evident from records.

Moisture sources feeding both sea and land need to be atmospheric, but we are neither quite sure where that moisture originated, nor can we exclude multiple sources acting in concert.

Long-time transient simulations of the global and regional developments from glacial to interglacial conditions are yet lacking – but will be available within 2-3 years.