The Younger Dryas, also referred to as the Big Freeze, was an abrupt and unexplained relapse into a glacial cold climate when the earth was emerging out of the last ice age. The dip is clearly seen in the traces below at about 11-12,000 years before present.
The shutdown of the North Atlantic thermohaline circulation is usually blamed, but this paper from 2000 suggests solar mediated cosmic ray flux could be responsible.
The concentration of radiocarbon, 14C, in the atmosphere depends on its production rate by cosmic rays, and on the intensity of carbon exchange between the atmosphere and other reservoirs, for example the deep oceans. For the Holocene (the past approx11,500 years), it has been shown that fluctuations in atmospheric radiocarbon concentrations have been caused mostly by variations in the solar magnetic field. Recent progress in extending the radiocarbon record backwards in time has indicated especially high atmospheric radiocarbon concentrations in the Younger Dryas cold period, between 12,700 and 11,500 years before the present. These high concentrations have been interpreted as a result of a reduced exchange with the deep-ocean reservoir, caused by a drastic weakening of the deep-ocean ventilation. Here we present a high-resolution reconstruction of atmospheric radiocarbon concentrations, derived from annually laminated sediments of two Polish lakes, Lake Gociacedilzdot and Lake Perespilno. These records indicate that the maximum in atmospheric radiocarbon concentrations in the early Younger Dryas was smaller than previously believed, and might have been caused by variations in solar activity. If so, there is no indication that the deep-ocean ventilation in the Younger Dryas was significantly different from today’s.
The difficulties that the climate science liberals have in explaining the Younger Dryas have been raised at ClimateAudit. Largely the long timescale for accumulation and absorption of CO2 in the atmosphere is not consistent with abrupt climate change. Changes must be on the same time scale as the forcings, and rapid changes must be explained either by high intrinsic variability in the system, or by sudden changes in system states. RealClimate in a recent post at least entertained a comet strike theory, perhaps an indication of the waning support for the shutdown of the North Atlantic thermohaline circulation as an explanation.
We have been looking at the Cosmic Ray Flux (CRF) theory of Nir Shaviv in the last few posts. CRF can vary relatively rapidly, when the sun shuts down its sunspot activity, or from cosmic sources. The scale is consistent with abrupt climate change. I don’t want to make the same mistake as climate liberals, and start blaming everything on the latest convenient explanation. But given the high concentration of atmospheric 14C during the Younger Dryas cold episode appears widely supported, does this not suggest an increase in CRF as the cause?
Variations of Younger Dryas atmospheric radiocarbon explicable without ocean circulation changes Nature 403, 877-880 (24 February 2000) | doi:10.1038/35002547; Received 23 April 1999; Accepted 21 December 1999
Tomasz Goslar, Maurice Arnold, Nadine Tisnerat-Laborde, Justyna Czernik & Kazimierz Wie cedilckowski