Geoscience Reference
In-Depth Information
Abrupt Climate Change Revisited
Harunur Rashid and Leonid Polyak
Byrd Polar Research Center, Ohio State University, Columbus, Ohio, USA
Ellen Mosley-Thompson
Byrd Polar Research Center, Ohio State University, Columbus, Ohio, USA
Department of Geography, Ohio State University, Columbus, Ohio, USA
This geophysical monograph volume contains a collection of papers presented at the
2009 AGU Chapman Conference on Abrupt Climate Change. Paleoclimate records
derived from ice cores, lakes, and marine sedimentary archives illustrate rapid changes
in the atmosphere-cryosphere-ocean system. Several proxy records and two data-
model comparison studies simulate Atlantic meridional overturning circulation during
the last deglaciation and millennial-scale temperature oscillations during the last
glacial cycle and thereby provide new perspectives on the mechanisms controlling
abrupt climate changes. Two hypotheses are presented to explain deep Southern
Ocean carbon storage, the rapid increase of the atmospheric carbon dioxide, and
retreat of sea ice in the Antarctic Ocean during the last deglaciation. A synthesis of two
Holocene climate events at approximately 5.2 ka and 4.2 ka highlights the potential of
a rapid response to climate forcing in tropical systems through the hydrological cycle.
Both events appear contemporaneous with the collapse of ancient civilizations in low-
latitude regions where roughly half of Earth
'
s population lives today.
of the D-O cycles in ice cores and their counterparts in
marine sediments of the North Atlantic, the search for
abrupt, millennial- or finer-scale events has intensified
across the globe (see Voelker et al. [2002] and Clement and
Peterson [2008] for an overview). In recent years, an in-
creasing number of paleoclimatic records, mostly in the
Northern Hemisphere show teleconnections with the D-O
cycles recorded in Greenland. The most commonly inferred
link between these rapid climate events is related to the
release of cold fresh water by iceberg melting. The introduc-
tion of this fresh water is assumed to slow or shut down the
formation of the North Atlantic Deep Water (NADW), thus
preventing the penetration of the North Atlantic Drift (the
northern branch of the Gulf Stream) into high latitudes. The
climatic importance of the Gulf Stream stems from the enor-
mous quantity of heat it transports to northwestern Europe
and its facilitation of the exchange of moisture between the
ocean and atmosphere.
1. INTRODUCTION
Remarkable, well-dated evidence of high-magnitude,
abrupt climate changes occurring during the last glacial
period between ~80 and 10 ka have been documented in
Greenland ice cores and marine and terrestrial records in the
Northern Hemisphere. These climate perturbations are
known as the Dansgaard-Oeschger (D-O) warming and
cooling cycles of 2
-
3 kyr duration. These are bundled into
Bond cycles of 5
-
10 kyr and are terminated by Heinrich
events consisting of massive iceberg rafting from the late
Pleistocene Laurentide Ice Sheet (LIS). Since the discovery
