SOLAR HISTORY AND PALEOHYDROLOGY DURING THE LAST 2 MILLENNIA

Fluvial paleohydrology provides a link between solar variability and t errestrial climate during the last two millennia by revealing progress ive changes in the degree of seasonality which reflect latitudinal shi fts in climatic belts. A latitudinally diachronous phase of channel de position which prevailed in AD 300-1850 in Eurasia between 45 degrees and 25 degrees N indicates more equable stream discharges prompted by a temporary southward displacement of the Atlantic depression zone. A similar effect in central Mexico, between 18 degrees and 28 degrees N, points to changes in the contribution of winter and autumn rains to t he annual total which may stem from latitudinal shifts in the high-pre ssure cells. The radiocarbon evidence suggests that the displacements coincided with an increase in solar activity that reached a maximum in about AD 600. The proposed association is consistent with evidence fr om 1948-1966 for increased frontal activity in the North Atlantic duri ng sunspot maxima, although it is not yet clear whether the process wa s mediated by UV absorption in the lower stratosphere or by the flux o f MeV-GeV particles.