Post on 10-Mar-2021
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.