A total of 125 large fluence solar proton events identified from the nitrat
e deposition in ice core from Greenland for the period 1561-1950 are examin
ed in an exploratory study of the geophysical information that will be avai
lable from such data in the future. These data have been augmented with ion
ospheric and satellite data for the period 1950-1994. There were five perio
ds in the vicinity of 1610, 1710, 1790, 1870, and 1950, when large > 30 MeV
proton events with fluence greater than 2 X 10(9) cm(-2) were up to 8 time
s more frequent than in the era of satellite observation. There is a well-d
efined Gleissberg (approximately 80 year) periodicity in the large fluence
proton events, with six well-defined minima, two in close association with
the Maunder and Dalton minima in sunspot number. The present "satellite" er
a is recognized as a recurrence of this series of minima. Comparison of the
total solar proton production for the five Gleissberg cycles since 1580 sh
ows that the cycle 1820-1910 was the most active followed by the cycle 1580
-1660. The present Gleissberg cycle is one of the least effective in the pr
oduction of solar proton events at Earth. It is shown that the solar and so
lar proton event data both indicate that the Maunder Minimum ended about 17
00, 16 years before the commonly accepted date of 1716. It is proposed that
the delayed "switch on" of aurorae after the Maunder Minimum is due to the
changing nature of the solar corona from "Maunder Minimum" conditions to t
he more active conditions of the Gleissberg cycle, and a physical mechanism
is proposed in which variations in the coronal densities modulate the effi
ciency of solar proton event production throughout the Gleissberg cycle. Th
e "streaming limited fluence" for > 30 MeV protons is estimated to be 6-8 X
10(9) cm(-2), and the rapid decrease in the probability of occurrence of s
olar proton events observed in the vicinity of this fluence is proposed to
be due to this effect.