The full programme book (PDF) - Royal Geographical Society

THEME 7: THE OCEANS
Future Challenges for Quaternary Palaeoceanography: from Protists, to Proxies, to
Physics
Luke Skinner
Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of
Cambridge
Power-density spectra of Quaternary climate variability reveal peaks in variance that are
centred on diurnal, annual, millennial and ‘orbital’ timescales. The diurnal and annual
cycles are by far the strongest (on the 2 Ma timeframe), and have a well-known external
forcing: solar radiation, modulated by the regular spin and heliocentric orbit of the earth.
In contrast, the millennial variability of the Quaternary has no known external forcing, and
although the ‘orbital’ variability is clearly paralleled by similarly paced changes in the
distribution of incoming solar radiation with respect to latitude and the annual cycle, the
link between this forcing and the global climate response continues to defy complete
mechanistic explanation. Indeed, if explaining these dominant modes of climate variability
remains the central challenge of Quaternary palaeoclimatology, unravelling the ocean’s
role in their underlying physical mechanisms must be the central challenge of Quaternary
palaeoceanography.
The ocean’s role in the climate system stems primarily from its effect on the transport and
sequestration of heat and carbon. Classically, the ocean’s large scale overturning
circulation (OLSOC), especially in the field of palaeoceanography, has been understood in
terms of the metaphor of a ‘global ocean conveyor belt’ driven by buoyancy loss and deep
water export in the North Atlantic. However, this view of the OLSOC has been largely
superseded by a view that places greater emphasis on the energy budget of the ocean,
small scale mixing processes in the ocean interior and wind- and buoyancy forcing in the
Southern Ocean. The conveyor belt ‘heat engine’ has been replaced by a diffusive
‘energy sink’ that is both pushed and pulled. This revised understanding of the OLSOC
provides a new conceptual framework both to be developed further through future
palaeoceanographic research, and on which to base future revolutions in our
understanding of the ocean’s role in Quaternary climate change.
In this respect, three research questions stand out as being of central importance: 1) what
are the stability properties of the OLSOC – (how) can it become multi-stable and subject to
bifurcation- or noise induced abrupt transitions; 2) what was the state of the OLSOC at the
Last Glacial Maximum (LGM), and what was its impact on the carbon cycle; and 3) how
has the ocean contributed to the transfer of climatic variance from higher frequencies and
lower amplitudes (e.g. modulation of the seasonal cycle) to lower frequencies and higher
amplitudes (e.g. glacial-interglacial cycles)? Success in addressing these major research
questions will rely on future efforts to obtain new material (e.g. long high accumulation rate
sediment cores), to develop new methods (e.g. novel proxies and analytical techniques),
but especially to adopt new approaches. Central to the latter will be the careful design of
sampling arrays that are well suited to the analysis of basin-scale processes, as well as
the deployment of novel (e.g. inverse) modelling approaches and data-model comparisons
that take advantage of emerging data arrays. Examples of exciting new developments in
all of these areas can already be identified, and suggest that a robust description of the
LGM circulation, and more importantly the physical processes that have determined it,
may be obtainable within the decade.