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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
• 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