Reduced solar activity as a trigger for the start of the Younger Dryas?

It is generally assumed that changes in ocean circulation forced the abrupt climate changes during the Late Pleistocene, including the Younger Dryas event. Recently, however, it was proposed that variations in solar irradiance could have played a much more prominent role in forcing Pleistocene climate changes. Furthermore, two physical mechanisms were recently published that explain how relatively small changes in solar irradiance could have had a strong impact on the climate system. We discuss the possibility that an abrupt reduction in solar irradiance triggered the start of the Younger Dryas and we argue that this is indeed supported by three observations: (1) the abrupt and strong increase in residual C-14 at the start of the Younger Dryas that seems to be too sharp to be caused by ocean circulation changes alone, (2) the Younger Dryas being part of an similar to 2500 year quasi-cycle-also found in the C-14 record-that is supposedly of solar origin, (3) the registration of the Younger Dryas in geological records in the tropics and the mid-latitudes of the Southern Hemisphere. Moreover, the proposed two physical mechanisms could possibly explain how the North Atlantic thermohaline circulation was perturbed through an increase in precipitation together with iceberg influxes. In addition, the full magnitude of the Younger Dryas cooling as evidenced by terrestrial records in Europe could be explained. We conclude that a solar triggering of the Younger Dryas is a valid option that should be studied in detail with climate models. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.