Climate of the Past
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2008
10.5194/cp-4-345-2008
http://www.clim-past.net/4/345/2008/
http://www.clim-past.net/4/345/2008/cp-4-345-2008.html
http://www.clim-past.net/4/345/2008/cp-4-345-2008.pdf
345
356
2008-12-09
The Southern Hemisphere at glacial terminations: insights from the Dome C ice core
R. Röthlisberger
rro@bas.ac.uk
M. Mudelsee
M. Bigler
M. de Angelis
H. Fischer
M. Hansson
F. Lambert
V. Masson-Delmotte
L. Sime
R. Udisti
E. W. Wolff
British Antarctic Survey, Natural Environment Research Council, Cambridge, UK
Climate Risk Analysis, Hannover, Germany
Niels Bohr Institute, University of Copenhagen, Denmark
Laboratoire de Glaciologie et Géophysique de l'Environnement, Grenoble, France
Alfred Wegener Institut, Bremerhaven, Germany
Climate and Environmental Physics, University of Bern, Switzerland
Department of Physical Geography and Quaternary Geology, Stockholm University, Sweden
Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France
Department of Chemistry, University of Florence, Italy
The many different proxy records from the European Project for Ice Coring in
Antarctica (EPICA) Dome C ice core allow for the first time a comparison of
nine glacial terminations in great detail. Despite the fact that all
terminations cover the transition from a glacial maximum into an
interglacial, there are large differences between single terminations. For
some terminations, Antarctic temperature increased only moderately, while
for others, the amplitude of change at the termination was much larger. For
the different terminations, the rate of change in temperature is more
similar than the magnitude or duration of change. These temperature changes
were accompanied by vast changes in dust and sea salt deposition all over
Antarctica.
<br>
<br>
Here we investigate the phasing between a South American dust proxy
(non-sea-salt calcium flux, nssCa<sup>2+</sup>), a sea ice proxy (sea salt sodium
flux, ssNa<sup>+</sup>) and a proxy for Antarctic temperature (deuterium, δD).
In particular, we look into whether a similar sequence of events
applies to all terminations, despite their different characteristics. All
proxies are derived from the EPICA Dome C ice core, resulting in a relative
dating uncertainty between the proxies of less than 20 years.
<br><br>
At the start of the terminations, the temperature (δD) increase and
dust (nssCa<sup>2+</sup> flux) decrease start synchronously. The sea ice proxy
(ssNa<sup>+</sup> flux), however, only changes once the temperature has reached a
particular threshold, approximately 5°C below present day temperatures
(corresponding to a δD value of −420‰). This reflects to a large
extent the limited sensitivity of the sea ice proxy during very cold periods
with large sea ice extent. At terminations where this threshold is not
reached (TVI, TVIII), ssNa<sup>+</sup> flux shows no changes. Above this
threshold, the sea ice proxy is closely coupled to the Antarctic
temperature, and interglacial levels are reached at the same time for both
ssNa<sup>+</sup> and δD.
On the other hand, once another threshold at approximately 2°C below
present day temperature is passed (corresponding to a δD value of
−402‰), nssCa<sup>2+</sup> flux has reached interglacial levels and does not
change any more, despite further warming. This threshold behaviour most
likely results from a combination of changes to the threshold friction
velocity for dust entrainment and to the distribution of surface wind speeds
in the dust source region.
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