The full programme book (PDF) - Royal Geographical Society

T7
Pleistocene sea-surface and intermediate water temperature evolution: early
cooling, delayed glacial intensification, and implications for the mid-Pleistocene
climate transition
E.L. McClymont 1 *, A.C. Elmore 1 , S.M. Sosdian 2 , H. Elderfield 3 , S. Kender 4 , A. Rosell-
Melé 5 , Y. Rosenthal 6
1 Department of Geography, Durham University, Durham, DH1 3LE
2 School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3AT
3 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ
4 British Geological Survey, Keyworth, Nottingham, NG12 5GG
5 Institut de Ciència i Tecnologia Ambientals, Universitat Autònoma de Barcelona, 08193 Bellaterra,
Spain
6 Institute of Marine and Coastal Sciences, and Department of Geology, Rutgers, The State University,
NJ 08901-8521 USA
The mechanisms driving the evolution of the global climate system through the Quaternary
continue to be debated, as does the nature of the feedbacks that translated such forcing
into global climate change. The mid-Pleistocene climate transition (MPT) is defined by the
emergence of high amplitude, quasi-100 kyr glacial-interglacial cycles from a prior regime
of more subtle 41 kyr cycles. This change in periodicity and amplitude cannot be explained
by a change in ‘external’ astronomical forcing.
Here, we first review the expression of sea surface temperature (SST) change associated
with the MPT using previously published records from both the alkenone (UK37’) and
foraminifera Mg/Ca proxies. We show that glacial-interglacial variability in SSTs is
superimposed upon longer-term cooling trends in oceanographic systems spanning the
low to high latitudes. Importantly, the SST cooling trends intensify from 1.2 Ma, pre-dating
the step-like increase in benthic δ18O at 0.9 Ma which is argued to reflect expansion of
continental ice-sheets. We also show that the long term decline in mean SSTs is driven by
cooling during glacial stages, potentially indicating development of feedbacks conducive to
later continental ice sheet growth.
To investigate these ideas further, we present new data examining the signature of
Pleistocene temperature change from within the intermediate waters of the ocean (~500-
1500 m water depth). Using Mg/Ca in benthic foraminifera species, we demonstrate that
Antarctic Intermediate Water temperatures also experienced a gradual glacial-stage
cooling the Pleistocene. However, interglacial periods only show a cooling trend after the
MPT. In comparison with other records from the Southern Ocean, these new results
demonstrate a more diverse pattern of ocean temperature change through the
Pleistocene. In turn, the timing and pattern of cooling raises questions about the role
played by northern hemisphere ice sheets in driving Pliocene-Pleistocene climate
transitions.
Keywords: Mid Pleistocene Transition; 100 ka cycles; sea surface temperatures;
alkenones; foraminifera