SMR/1884-8

Conference on Milankovitch cycles over the past 5 million years

Sindia SOSDIAN

22 - 24 March 2007

Instit. of Marine & Coastal SciencesRutgers University

71 Dudley Road

The Deep Ocean

Deep Ocean Temperature Changes across the Last 5 Ma

Sindia SosdianRutgers University

GENERAL RULE:

Benthic oxygen isotopic record:

function (ice volume, )Temperature

Cenozoic climate and deep sea temperature variation

-Long-term cooling trend across Cenozoic

Figure from Lear et al., 2001

Cooler/ increase ice volume

-Superimposed are transitions in climate characterized by an increase in continental ice sheet growth

associated with drifting of continents

Milankovitch cycles over the past ~5 million years

2

2.5

3

3.5

4

4.5

5

5.50 1000 2000 3000 4000 5000

0 1250 2500 3750 5000δ18

O (‰

)

Age (kyr)

ODP 846 Benthic Oxygen Isotope Record

Age (ka)

100-kyr world 41-kyr world

Warm interval

Northern Hemisphere Glaciation

mid-Pleistocene transition

Incr

ease

ice

volu

me,

coo

ler

-Long term trend of climatic cooling and increasing glacial cycle amplitude during the Plio-Pleistocene are suggestive of significant changes in the dynamics of the climate system.-the response to the Milankovitch forcing has changed over the past five million years.

(MPT)

(PPT)

What fraction of the isotopic variaton is related to temperature?Was their cooling associated with these transitions?

Climate TransitionsMid-Pleistocene transition (MPT) Pliocene-Pleistocene transition (PPT)

-deep ocean cooling-shoaling of the thermocline

-tectonic closure of the Isthmusof Panama

-Tibetan uplift-restriction of the Indonesian seaway-obliquity modulation

-global cooling (threshold response)

-change in ice sheet dynamics

-changes in sea ice formation-a gradual increase in the insolation threshhold for ice-sheet ablation

Each represent -a change in the dynamics of glacial cycles

-imply a climate response to a gradual deep ocean cooling trend

Causes are still poorly understood

Research Questions

• How much of the increase in amplitude of the δ18Ob cycles represents an increase in the ice volume relative to additional deep ocean cooling of deepwater?

• What is the relationship between climate and the cryosphere development?

• Did climate reach a threshold at the MPT and PPT?

Toolbox of a Paleoceanographer•Oxygen isotopic composition of benthic foraminifera

•Live in deep ocean and insulated from large seasonal, latitudinal, and geographical variations in temperature

•Recorder of high latitude climate change (global)

T(ºC)

Ice volume salinity

δδ1818O seawaterO seawater

••Reflect the Reflect the water temperatureswater temperaturesunder which the shells were under which the shells were deposited and the deposited and the oxygen isotope oxygen isotope composition of the seawatercomposition of the seawater

••Difficult to interpret oxygen Difficult to interpret oxygen isotope dataisotope data

δ18O and marine carbonates Benthic foraminifera

Oxygen isotopic composition of seawater (δ18Osw)

Source: University of Maine Stable Isotope Laboratory

Reconstruction of temperature from δ18O is complicated by:

(a) Correlation between local salinity and δ18Osw

(b) Whole ocean shifts in δ18O reflecting storage in isotopically light continental ice sheets

16O 16O 16O

18O

Foraminiferal isotope record• C. Emiliani (1955)-”discovered cyclicity of glaciation by isotopic analysis of

deep sea cores and in the process exhumed milankovitch from terminal oblivion”

6ºC surface temperature amplitude and δ18Osw=0.5‰

70%Temperature:30%ICE

Foraminiferal isotope record • N. Shackleton (1967) used oxygen isotope variations from

benthics to reinterpret/negate Emiliani’s result

-mainly changing δ18Osw (ice volume). Any reduction in T is hard to fathom since deep ocean is already near freezing point

“Universally and uncritically adopted”

-C. Emiliani

Independent deep ocean temperature estimates• Controlled by high-latitude

surface temperatures • Global temperature trends• Separating ice volume effect in

the δ18O record.• Orbital scale variability vs. long

term trend in temperature• Test the hypotheses to explain

climate transitionsδ18OswIce coresδ18OswPorewaterδ18OswUplifted coral reefsδ18Oswoxygen isotopes temperature

Mg/Ca-benthic forams/ostracod

ParameterTechnique

δ18O benthicTemperature δ18Osw

Ice

volumeSalinity

Mg/Ca-Benthic foraminiferal paleothermometryCaCO3 + Mg2+ --Keq MgCO3 + Ca2+

Lear et al., 2002

~10% Mg/Ca /ºC

-Quaternary and Cenozoic climate studies

-used to trace δ18Osw and deep sea temperature

-δ18O and Mg/Ca on same phase, evaluate phase

relationship

Oridorsalisumbonatus

Planulinawuellerstorfi

Uvigerinaperegrina Cibicidoides

mundulus

9% per ºC

Mg/Ca-Ostracode Shell Paleothermometry

Genus Krithe

bivalved crustaceans

9% per ºC

•-Separate bottom water temperature and δ18Osw influences in both the Quaternary and Pliocene.•Open, chamber free shells and thus less susceptible to contamination by intrashell accumulation of detrital material•Specimens are large

Cronin et al., 2005

Results

0 65Myrs

Lear et al., 2001 low resolution (1 My), general cooling trend

PaleoceneEocene5533.7

Oligocene245

MiocenePlioP

Billups et al., 2003, low resolution, general cooling trend

Lear et al., 2003 low resolution (0.2 My), Cooling across Plio-Pleistocene

0 5.31.8

PliocenePleistoceneH

Martin et al., 2002 G-I amplitude 2-4ºC (Atlantic and Pacific)

Dwyer et al., 1995 G-I amplitude increases from 2 to 4ºC (Atlantic)

Sosdian et al., 2006 Pleistocene cooling and G-I amplitude increase from 2 to 4ºC (Atlantic)

**G-I=glacial-interglacial

•Striking resemblance to benthic δ18O record (timing and magnitude)

•Glacial-interglacial temperature amplitude 2-4ºC

•100-kyr and 41-kyr spectral peaks

Last 250 kyrs (benthic foram.)…

Martin et al., 2002

Martin et al., 2002Atlantic

Pacific

•Both reflect significant cooling at high latitudes surface waters during glacial intervals

•BWT changes precede δ18O by 4 kyr in the orbital bands

•∆δ18Osw=1.0‰

Pacific-cooling tracks with the intensity of continental glaciations

Isotope record from Norwegian seas

Porewater

Atlantic-Combination of changes in deep water circulation and temperatures of water masses

-Compares well with other estimate of temperature from Labeyrie and Schrag

Study Site

AABW (T=0.5ºC)

NADW (T=2-4ºC)

607

DSDP site 607 Depth=3427 m 41ºN, 32ºW

-related to changes in NH ice sheets and ocean circulation

-High sedimentation rate (3kyr resolution)

-Note during LGM, influence of AABW was greater at 607 than holocene.

Late Pleistocene and Late Pliocene (Ostracodes)

Late Pleistocene (ka)

Late Pliocene (Ma) Dwyer et al., 1995

•Suggests a cooling trend associated with increased ice volume across the PPT and MPT

•BWT lead δ18O by 3.5 kyr

∆T=1.5ºC∆T=2.3ºC∆T=4ºC

Late Pleistocene (ka)

Late Pliocene (Ma)

δ18Osw- ice volume/sea level

60-70m sea level120-150 m sea levelIc

e vo

lum

e

Caution: Site is sensitive to ocean circulation changes

Pliocene warm interval (Ostracodes) Deep Atlantic Ocean

Cronin et al., 2005

•Short-term BWT oscillations

•G-I cycles characterized the interval, of smaller amplitude than the Quaternary

•Greater proportion of the δ18Obsignal was probably due to reduced ice volume than from increased BWTs

123456789

500 625 750 875 1000 1125 1250 1375 15001

2

3

4

5

6

7

8

9M

g/Ca-T

emperature (ºC

)Age (ka)

2.5

3

3.5

4

4.5

5

5.5500 625 750 875 1000 1125 1250 1375 1500

δ18O

Age (ka)

41 kyr100 kyr

∆δ18O=1.6 ∆δ18O=1.0

Preliminary Data

~1ºC cooling

Sosdian et al., 2006

∆T=4ºC ∆T=2ºC~100 41 kyr

1)General coherency between records

Abrupt

Spectral Analysis

0

1

2

3

4

5

6

7

8

0 0.02 0.04 0.06 0.08 0.1

800-1750 kyr

δ18O

Pow

er

Frequency (kyr-1)

41 k

yr

23 k

yr

100

kyr

0

2

4

6

8

10

12

0 0.02 0.04 0.06 0.08 0.1

800-1750 kyr BWT

Pow

er

Frequency (kyr-1)

100

kyr

41 k

yr

23 k

yr

***BWT leads δ18Ob by ~10kyr

a

b

Note the strong presence of the 41-kyr peak in both records.

Post-MPT periodicity is ~100 kyr.

Using cross-spectral analysis (not shown here), BWT leads δ18O by ~10kyr in the obliquity band.

800-1500 kyr

800-1500 kyr

Observations• Across the mid-Pleistocene, the deep Atlantic ocean cooled by 1ºC and

glacial periods became progressively colder.• The change in frequency (high->low) and amplitude (small->large) of

BWT, on orbital time scales, is coherent with the δ18Ob record. • BWT leads δ18O by ~10kyr in the obliquity band.

60:401.64100-kyr

50:501241-kyr

%T:%ICE∆δ18O (‰)

∆T (ºC)Time period

Using the relationship of 4ºC change per 1‰.

Summary of results

Late Pleistocene Pleistocene Pliocene

NH glaciation, glacial and interglacial periods cooler

Intensification of NH glaciation, glacial periods become cooler

100kyr

41 kyr ?

?

?

Summary of results• On average, the deep ocean became progressively colder throughout the

last 5 Ma.

•On orbital timescales, the changes in frequency and amplitude of BWT are coherent with the δ18Ob record. BWT leads ice volume.

•Temperature variation is a significant component of the benthic isotope record.

•Potentially across the PPT, both glacial and interglacial intervals cooled along with northern hemisphere glaciation. Whereas across the MPT, only glacial periods cooled with intensification of glaciation. • This suggests that the PPT is a fundamental change in the mean climate state while the MPT is a change in the dynamics of glaciation.

•BWT records and SST records from the eastern equatorial Pacific and upwelling regimes show a long term cooling throughout the last 5 Ma and transition in frequency and amplitude of signal. This suggests that the high latitudes and tropical ocean are linked on orbital time scales.

Future work

• Fundamental understanding of orbital scale deep ocean temperature variability across the last 5 Ma.

• Further investigation and application of Mg/Ca benthic foraminiferal and ostracodpaleothermometry at deep sea sites representative of a global temperature signal.

Foraminifera isotope record • N. Shackleton (1967) used oxygen isotope variations from benthics to reinterpret/negate

Emiliani’s result

-mainly changing δ18Osw. Any reduction in T is hard to fathom since deep ocean is already near freezing point

“Universally and uncritically adopted”

-C. EmilianiOO=calculated oxygen isotope composition of b. foram living today assuming a T of 4ºC and δ18Osw=-0.2‰

0.5‰

1.0‰

1.5‰

No change in T∆δ18Osw from G-I‰