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 Diatoms Coccolithophores Biomarkers (organic components)

Marine sediments record the oceans through time Use of “proxies”: indirect measures of key climate variables e.g. Coccolithophores Biomarkers (organic components) 60°S – 60°N Müller et al. (1998)

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)

Temperature change (relative to the maximum recorded; °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

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