The Younger Dryas in the UK

The Younger Dryas in the UK



Younger Dryas in the UK

The Younger Dryas refers to the final phase of cold, glacial conditions preceding the abrupt climatic warming at the beginning of the Holocene. The existence of the Younger Dryas in Europe has been known for most of this century, although recent research suggests that the Younger Dryas cooling may have been global. Estimates of the timing of the event have also improved in recent years, showing that both the onset and termination of the Younger Dryas were abrupt, occurring within decades.

The Younger Dryas has been linked with a large-scale shift of the North Atlantic thermohaline circulation (THC) to a near glacial mode with a consequent reduction in northward heat transport. This shift in the THC may have been triggered by a discharge of Laurentide ice, combined with meltwater inputs from several locations around the North Atlantic. Further study of the events leading up to the Younger Dryas is necessary for improving theoretical understanding of abrupt climatic change, and for evaluating GCM models which seek to simulate the response of the THC to freshwater forcing(Nicholas 2009).

With predicted increases in freshwater input to the North Atlantic resulting from increases in atmospheric CO2, a future shift in the THC is a possibility. Predicting the magnitude and climatic consequences of such an event depends upon further study of the Younger Dryas and of other abrupt palaeoclimatic changes which involved the THC.

The timing of the Younger Dryas was first established using radiocarbon dating and assigned to the approximate interval 11?000 to 10?000 years before the present (BP).

The radiocarbon timescale is now known to be in error for the late-glacial period, owing to rapid changes in global carbon reservoirs at that time. The true date of the Younger Dryas has now been established using cores of ice drilled from the Greenland ice sheet. Careful study of annual ice layers that built up near the centre of the ice sheet has established that the onset of the Younger Dryas was about 12?800 calendar year ago, and its termination about many years ago. The Greenland ice cores provide such a clear and strong record of the Younger Dryas that they can be used as a yardstick against which other types of evidence can be compared(Lehman 1992).

Reconstructed temperatures, based on the isotopic composition of oxygen locked up in the ice, are ...