What was done
The authors measured and analyzed a number of biological and geochemical parameters in four sediment cores obtained from a tundra lake (Arolik Lake: 59°28'N, 161°07'W) in southwestern Alaska that covered the period of time from 12 to 2.3 thousand years ago.  Due to the unconsolidated nature of the uppermost portions of the cores, no data could be obtained for the most recent 2.3 millennia.

What was learned
Hu et al. report finding clear evidence of "cyclic variations in climate and ecosystems during the Holocene," which "occurred with periodicities similar to those of solar activity and appear to be coherent with time series of the cosmogenic nuclides ¹⁴C and ¹⁰Be as well as North Atlantic drift ice."  These several changes were quite substantial.  Both aquatic and terrestrial productivity, for example, were found to have experienced what they describe as pronounced synchronous fluctuations.

What it means
In the words of the authors, "the general correspondence of prominent environmental changes in southwestern Alaska to variations in solar energy output and North Atlantic drift ice implies a solar influence on hemispheric-scale climatic oscillations during the Holocene," which occurred "at frequencies longer than those detectable by instrumental records."  They further state that this "cyclicity implies predictability," which clearly should be considered when attempting to determine causes of climate changes that are evident in instrumental records or when attempting to chart future climate trajectories.

With respect to the likely cause(s) of these climatic oscillations, Hu et al. suggest the possibility of a sun-climate linkage of the type described by Shindell et al. (2003) and Tourpali et al. (2003), as well as a sun-ocean-climate linkage of the type described by Bond et al. (2001), which we discus in our Editorial of 28 November 2001.

In view of these several observations, of which we have certainly not seen the last, the climate-alarmist argument that variations in solar activity are too weak to be responsible for climate variability throughout the 20th century are becoming less and less tenable, as a growing body of evidence is pointing ever more convincingly toward the behavior of the sun as being the primary determinant of both ancient and modern climate change.

References

Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G.  2001.  Persistent solar influence on North Atlantic climate during the Holocene.  Science 294: 2130-2136.

Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D. and Waple, A.  2001.  Solar forcing of regional climate change during the Maunder Minimum.  Science 294: 2149-2152.

Tourpali, K., Schuurmans, C.J.E., van Dorland, R., Steil, B. and Bruhl, C.  2003.  Stratospheric and tropospheric response to enhanced solar UV radiation: A model study.  Geophysical Research Letters 30: 10.1029/2002GL016650.