RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 9, ES3002, doi:10.2205/2007ES000250, 2007
3. Long-Term Solar Activity Variations in the Holocene and Their Connection With Abrupt
 Data with a high time resolution of the order of 10-20 years are available for the Holocene
for both climate change and solar activity variations. This allows a more precise comparison of
the development of climatic processes and solar activity variations than for the Pleistocene.
Information on solar activity variations in the Holocene is obtained from measurements of the
concentration of radiocarbon
14C ( Δ14C) in dated tree rings. At present a series
14C data has been built for the last 11,400 years
[Stuiver et al., 1998].
This series is shown in Figure 3. Variations in the
14C concentration in tree rings reflect
slow variations in the geomagnetic field magnitude and also, as indicated above, faster solar
activity variations. It can be seen from Figure 3 that the periodicity of occurrence of deep solar
minima (maxima in the
14C density) is 2300-2400 years. The first of these minima corresponding
to the Maunder minimum was accompanied by a sharp cooling in Europe and the start of development of
the so-called Little Ice Age
Shindell et al., 2001;
Soon and Yaskell, 2003].
During the next, Homeric, minimum around 2700-2800 years BP, cooling and increase in humidity
in Europe and climate change on other continents were also observed
[Dergachev et al., 2005;
Raspopov and Dergachev, 2003;
Raspopov et al., 1998,
van Geel et al., 1998].
The solar minimum around 5400-5200 years BP was also accompanied by abrupt climate change
[Thompson et al., 2006].
At present data on climate change during the next deep solar minimum ~7000 years BP
are available: advance of glaciers occurred in Alaska and Canada
[Koch and Clague, 2006].
However, it should be borne in mind that the development of this solar minimum took place
on the background of the climatic optimum of the Holocene, and cooling could be not so noticeable.
The next two deep solar minima also fall on the years of abrupt climate changes, i.e., near
the boundary of the Holocene and Younger Dryas. Thus, almost all deep solar minima that occurred
with a periodicity of 2300-2400 years were accompanied by large-scale climate changes.
Along with this, analysis of abrupt climate changes in the Holocene has shown that not only
deep solar minima. but also other processes caused coolings and abrupt climate changes.
This is evident from the data presented in Figure 4. The upper panel of Figure 4 shows
200-year averaged data on the content of potassium (K) and sodium (Na) aerosols in Greenland
ice for 11,400 years
[Mayewsky et al., 2004].
These data contain information on the character of atmospheric circulation in the North Atlantic
region. A 2300-2400-year periodicity in the atmospheric circulation is clearly seen in the figure.
The lower panel shows results of wavelet filtering (Morle basis) of variations in the
concentration shown in Figure 3 for the range of periods 2000-3000 years. It can be seen that
the solar minima repeating with a periodicity of 2300-2400 years coincide with increases in
the contents of aerosols in Greenland ice, which points to intensification of the atmospheric
circulation during these time intervals. Figure 4 also shows time intervals of glacier advance
in Central Asia, the Southern Hemisphere, North America, and Scandinavia
[Denton and Karlén, 1973;
Haug et al., 2001]
and also the time intervals of glacier retreat in Switzerland
[Hormes et al., 2001].
It is evident from Figure 4 that the 2300-2400-year solar activity variations in the years
of solar minima are accompanied by glacier advance. However, there are also the time intervals
of cooling (glacier advance) that occurred at a high solar activity level. These intervals
(around 1200-1400, 4000 years BP) are marked by arrows in Figure 4. Coolings during these
time intervals are evidenced by the data on displacement of the Northern timberline in Northern
Scandinavia and Canada
Helamma et al., 2004].
The timberline is a sensitive indicator of climatic conditions and ecological situation on the whole.
It corresponds to a mean July isotherm of +11.5oC. A number of authors reported on multiple
variations in the latitudinal and altitudinal timberline in Scandinavia and North European part of
Russia derived from palynological and dendrochronological data
[Bjune et al., 2004;
Kultti et al., 2006;
MacDonald et al., 2000].
The maximum northward extent of forest was observed in the interval 4300-4000 years BP.
Beginning from 4000 years BP, a southward retreat of the timberline associated with cooling
has been taking place everywhere.
 Figures 5a,c show variations in the altitudinal timberline in Northern Finland and
Northern Sweden, respectively, for the Holocene. Figure 5d presents time distribution of
the number of subfossil logs used for plotting Figure 5a. In essence, this distribution also
gives information on the timberline displacement in Northern Finland. The curves demonstrate
that the timberline displaced around 5400-5200, 4200-3800, 2700-2200, 1500-1400, and
800-600 years BP. The first, third, and fifth time intervals correspond to deep solar minima,
and the second and forth intervals correspond to advance of glaciers shown in Figure 4.
Figure 5e presents variations in the high-latitude timberline in Canada, and Figure 5f shows
reconstructed temperature variations in this region. Like in Scandinavia, coolings around
5000, 3800, 2500 and 800 years BP are observed. Note that the curves of average annual
temperature in Scandinavia plotted on the basis of palynological data by
Seppä and Poska 
and Heikkila and Seppä 
demonstrate temperature variations in the time intervals 5400-5100, 4300-3800, and
2800-2200 years BP. During these periods, a slight temperature increase was at first observed,
then the temperature sharply fell, and after this an abrupt warming occurred.
 Analysis of palaeoclimatic data has shown that climate changes around 4200-3800 and
1500-1300 years BP had a global character
[Mayewsky et al., 2004;
While in Northern regions, such as Scandinavia and Canada, they were accompanied by coolings,
in southern regions, such as, for example, Mesopotamia and Mexico, they were accompanied by
the droughts that led to collapse of civilizations, such as the Akkadian Empire and Maya
deMenocal et al., 2000;
Hodell et al., 1991].
It is likely that the reason for such abrupt climate changes, which are not associated with
deep solar minima of the Maunder type, is the development of internal processes in
the atmosphere-ocean system.
 Analysis of bottom sediments of the North Atlantic has shown that ice-rafting events
occurred in the North Atlantic during both the Holocene and Pleistocene. A vivid example of ice
rafting and a massive freshwater outburst is the outbreak of Lake Agassiz from the North
American continent around 8200 years BP, which is well fixed in different palaeodata
[Renssen et al., 2001;
Rohling and Palike, 2005].
This outbreak resulted in cooling on the global scale and was recorded in bottom sediments
in the North Atlantic by an increase in the density of haematite grains and Iceland spar
[Bond et al., 2001].
 Comparison of the IRE development and solar activity variations (Figure 6) indicates that
the IRE onsets coincide with or follow the time intervals of a high solar activity. This is logical
because, as simulation has shown, the IRE development results in an increase in the ocean
[Shaffer et al., 2004],
which must indeed occur in the case of a higher solar activity and, hence, a higher level
of solar irradiance. It becomes evident from comparison of the times of glacier advance
(Figure 4b) and time intervals of IRE (Figure 6) that the time intervals 1500-1400
and 4200-3800 years BP correspond to development of IRE (no. 1 and 3 in Figure 6) and,
hence, the IRE could be stimulaters of abrupt global climate changes during these time intervals.
Thus, abrupt climate changes in the past could be caused by not only a low but also a high level
of solar activity.
Citation: (2007), Long-term solar activity variations as a stimulator of abrupt climate change, Russ. J. Earth Sci., 9, ES3002, doi:10.2205/2007ES000250.
Copyright 2007 by the Russian Journal of Earth Sciences.
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