Erin L. McClymont

Department of Geography, Durham University

Aurora Elmore (Durham University), Benjamin Petrick (Newcastle University),

Sev Kender (British Geological Survey), Harry Elderfield (Cambridge University),

Antoni Rosell-Mele (Autonomous University of Barcelona), Sindia Sosdian (Cardiff University),

Yair Rosenthal (Rutgers University)

Palaeo-ocean proxies: reconstructing 4 million years of ocean temperature fluctuations.

Palaeo-ocean proxies and their application

• Motivation: why is it important to understand climate evolution

over the last 4 million years?

• How can we use marine sediments?– Climate “proxies”

• What role does the ocean play in climates of the past?– Ocean / ice-sheet interaction

– Global or regional climate changes

• New developments and future research directions

• What drives climate transitions?

• Which parts of the climate system are sensitive to change?

• How can climate change impacts be amplified?

Why did the Earth shift from global warmth in the Pliocene to the “ice

ages” in the Quaternary?

Climate change during the last 4 million years is important:

Why did the Earth shift from global warmth in the Pliocene to the “ice ages” in the Quaternary?

• “Onset of northern hemisphere glaciation” (ONHG) ~2.7 Ma

• The “mid-Pleistocene transition” (MPT) ~1 Ma: development of

larger ice-sheets which also survived for longer

Homo erectus(Am.Mus.Nat.Hist.)

Australopithecus boisei(Univ.Minnesota Duluth)

Marine sediments record the oceans through time

Marine sediments record the oceans through time

• Use of “proxies”: indirect measures of key climate variables e.g.

Foraminifera

DiatomsCoccolithophores

O

O

O

8

15

22

29

37:2

37:3

37:4

Biomarkers(organic components)

Marine sediments record the oceans through time

• Use of “proxies”: indirect measures of key climate variables e.g.

Coccolithophores

O

O

O

8

15

22

29

37:2

37:3

37:4

Biomarkers(organic components)

60°S – 60°N

Müller et al. (1998)

983

1087

806 849

882

1090

Q1: did surface ocean temperatures change during the expansion of the ice-sheets from 1 million years ago?

Mean annual SSTs (Levitus, 1994)

McClymont & Rosell-Mele (2005) Geology; McClymont et al. (2005) QSR; McClymont et al. (2008) Paleoceanography; Martínez-Garcia et al. (2010) Science; McClymont et al. (under review).

McClymont et al. (under review) Earth Science Reviews

• Sea-surface temperature records produced at high temporal resolution

• Long-term mean calculated by removing the high frequency variability

Was there a long-term cooling over the last 2 million years?

Approach

SST (°C)

Age (ka)

Tem

per

atu

re c

han

ge

(rel

ativ

e to

th

e m

axim

um

rec

ord

ed

; °C

)

McClymont et al. (under review) Earth Science Reviews

• Our data identify cooling in

the surface ocean ~1.2 million

years ago

• But the ice-sheets expanded

at ~ 1 million years ago

We suggest that cooler global

climate and evolving ocean

circulation were conducive to

the later ice-sheet growth

Results: all sites

983

1087

806 849

882

1090

Q2: did the ocean below the sea surface cool over the last 4 million years?

Mean annual SSTs (Levitus, 1994)

593

McClymont & Petrick (unpublished); Rosell-Mele et al. (under review, EPSL); McClymont, Elmore, Kender & Elderfield

(unpublished)

• Temperatures at and below the ocean surface

Q2: did the ocean below the sea surface cool over the last 4 million years?

McClymont & Petrick (unpublished); Rosell-Mele et al. (under review, EPSL); McClymont, Elmore, Kender & Elderfield

(unpublished)

• Temperatures at and below the ocean surface

Approach: below the surface

• A new technique exploits

the temperature-sensitive

incorporation of Mg into

foraminifera shells

• Foraminifera living on the

sea floor record

temperature at that depth

Uvigerina peregrina

Elderfield et al. (2010)

Results: below the surface

• Our preliminary data

show that at ~ 1000 m

below the sea surface, it

was ~2 °C warmer ~3 Ma

• On-going work will detail

the structure and

amplitude of the cooling

Uvigerina peregrina

McClymont, Elmore, Kender & Elderfield, Unpublished

SST

IWT

~3 MaLast ~130 kyr

Summary

• Marine sediments and their constituents allow us to:– Reconstruct past ocean properties (temperature, salinity…)

– Quantify rates and amplitudes of change

– Understanding the processes driving those changes

• Since the warmth of the Pliocene, the oceans have cooled:– Before the shift towards larger ice-sheets ~ 1 million years ago

– With varying regional expressions

– With outstanding questions about the drivers and feedbacks