Post-glacial climatic change and variability - The Global Climate System: Patterns, Processes, and Teleconnections - page 187

is also trapped with glacial ice formation, thus providing a multi-parameter
record of overall atmospheric characteristics through the Holocene. Thus,
Greenland's high elevation and position in NH circulation patterns enable the
GISP2 and GRIP records (American Geophysical Union 1998 ) to reflect
hemispheric and global climatic conditions.
Individual parameters measured in ice cores provide a tremendous wealth
of information about different aspects of changing environmental conditions
including climatic conditions and climatically influenced environmental
conditions. For example, physical characteristics of the ice (e.g. Alley et al.
1997a ) including the presence of melt layers (e.g. Koerner and Fisher 1990 )
and yearly accumulation time series (e.g. Meese et al. 1997 ) provide critical
information on changing summer temperature and precipitation conditions,
respectively. Oxygen isotopes measured in the melted ice are well known as
paleothermometers. In the GISP2 and GRIP ice cores the amount of tem-
perature depression in the NH is on the order of 8 8C or more during the last
glacial maximum (Figure 6.1 ). In addition to these parameters, various
chemical species provide proxy records of changing environmental condi-
tions (e.g. Mayewski et al. 1997 ).
The most versatile records from the GISP2 ice core that provide a multi-
parameter record of NH climatic and environmental conditions are the
various glaciochemical time series. As shown on Figure 6.3 , the time series
of these many species show that there is a cyclical nature to post-glacial
climatic conditions in the NH. For instance, concentrations of Na þ and Cl
in the ice are related to the concentration of sea salt species in the atmosphere
over the ice at the time of deposition. Atmospheric sea salt concentrations are
directly related to parameters such as wind speed, with greater overall wind
speeds leading to a greater amount of sea salt species over the Greenland Ice
Sheet. Sea salt species also may be inversely related to sea ice extent as the
less sea ice, the greater the amount of open water, the greater the amount of
sea salt that may be transported to Greenland. However, in the case of the
GISP2 record, the effect of greater sea ice extent during glacial conditions is
overwhelmed by more vigorous wind speeds resulting in high Na þ and Cl
concentrations during colder climates (Figure 6.3 ). Greater concentrations of
continental-derived dust species, such as Ca 2 þ ,Mg 2 þ ,K þ , also reflect
increased wind speeds in the NH as well as greater aridity in these source
areas. Furthermore, both marine and continental-derived species can be used
to postulate changes in NH pressure systems, and thus overall circulation
patterns. Thus, greater concentrations of these species also reflect the greater
wind speed and aridity associated with cooler climatic conditions in the NH
(Figure 6.3 ) . There are many other ice-core parameters that provide detailed
information on past environmental conditions (American Geophysical Union
1998 ), but those are not discussed in detail in this essay.