Greenland - Antarctic phase relations and millennial time-scale climate fluctuations in the Greenland ice-cores

The Greenland (GRIP/GISP2) and Antarctic (Byrd) ice-cores are examined in the frequency domain, with the data synchronized using common methane variations. Using conventional time-series analysis, a simple picture emerges: there is low-frequency (periods longer than about 10 kyr) coherence between the two records, consistent with a simple time delay, Antarctica leading by 1-2 kyr. Two geographical data points are however, inadequate to infer causality from the south to north time lag. At higher frequencies, in the millennial band, there is no measurable average relationship between the records and they appear to represent different processes, with a regional character. A serious question concerns the extent to which the Greenland cores reflect tracer concentration change without corresponding abrupt climate change. The large, abrupt shifts in ice 6180 can be rationalized as owing to wind trajectory shifts, perhaps of rather modest size. Many different physical phenomena probably do, however, contribute to the record as a function of time, and time scale. (C) 2003 Elsevier Ltd. All rights reserved.