Relationship between the GISP2 dust concentration profile and the Wolf sunspot number, 1752--1988 AD: Influence of solar variability and interference by explosive volcanism

There is evidence that solar variability has modulated the GISP2 dust concentration profile at radiocarbon periods of 11, 22, 90, and 200 years. The observed dust modulations were reported in pre-Holocene ice, and it was not possible to compare their timings with recorded changes in solar activity, which are only known for recent times.; Here, we report high resolution measurements of a new dust concentration profile along the top 120 m of the GISP2 ice core, which spans the period from 1597 to 1988 AD, and compare them with the Wolf sunspot number, a proxy for solar variability with monthly resolution from 1700 AD to the present. The two data sets are positively correlated during the periods 1860 to 1882 and 1944 to 1965, are negatively correlated from 1905 to 1915, and have a long period of low correlation from 1799 to 1835.; It is hypothesized that the observed solar-type dust modulations are due to the influence of the solar wind on the cosmic ray flux, which affects global cloud cover. Two competing cloud nucleation processes may be involved, both of which are enhanced by the cosmic ray flux. Electroscavenging of ice-forming nuclei increases precipitation, thereby decreasing atmospheric dust concentrations, and is expected to be dominant when the sun/dust correlation is positive. In contrast, ion-induced nucleation of sulfate aerosol particles decreases precipitation, thereby increasing atmospheric dust concentrations, and is expected to be dominant when the sun/dust correlation is negative.; Ion-induced nucleation is also enhanced by the addition of sulfate aerosol to the atmosphere, for example, as a result of volcanism. This is supported by our observation that periods of high sun/dust correlation coincide with periods of low volcanism, and periods of low or negative correlation coincide with periods of frequent volcanism. We show that large, low-latitude explosive eruptions cause a significant decrease in the sun/dust correlation.; Similar correlation reversals have already been noted for many other climatic indicators. Our work suggests that a large fraction of the correlation reversals may be attributed to explosive volcanic activity.