Interhemispheric space–time attributes of the Dansgaard–Oeschger oscillations between 100 and 0 ka

Abstract

The persistence, stability and interhemispheric phasing of the Dansgaard–Oeschger (DO) climate oscillation over the last glacial period (0–100 ka) has been evaluated in oxygen isotope records of three polar ice cores (GRIP, GISP2, and Byrd Station) and a midlatitude deep-sea core from the North Atlantic Ocean (MD95-2042). The results show that DO oscillations in atmospheric conditions occurred in both northern and southern polar ice records, although in the southern records the oscillations had at most only ca. one-tenth the power of those in the north. The DO oscillations first appeared during Marine Isotope Stage (MIS) 4, and the average spectral power of the northern hemisphere DO oscillations increased markedly during MIS 3 (30–38 ka). The DO mode in the GISP2 record is confined to the frequency band 1/(1.59 kyr) to 1/(1.37 kyr), but in the GRIP record, the mode exhibits strong frequency splitting over a band that is wider by ca. 50%. Time-frequency analysis shows that in GRIP the DO mode undergoes a frequency modulation that is phase-locked with the Earth's obliquity cycle; this modulation does not appear in nearby GISP2. In the North Atlantic marine record, DO oscillations behaved somewhat differently, appearing sporadically during MIS 5 and 4. The planktonic DO oscillations increased in spectral power during MIS 3, leading peak power in the GISP2 record by ca. 3 kyr. DO oscillations were relatively stable in all five records during MIS 3; they could not be detected unequivocally in any of the records during the Holocene (0–11 ka). At other times, the DO mode in all of the records was amplitude-modulated by Earth's orbital parameters. Finally, interhemispheric phasing of DO oscillations over 10–90 ka was assessed between the Byrd Station and GISP2 records, and between the benthic and planktonic records of Core MD95-2042. Coherency studies reveal an apparent time lead of Byrd DO oscillations over GISP2 by 384±70 yr (2 σ level), and of the North Atlantic benthic over planktonic DO oscillations by 208±33 yr. This apparent time lead of the southern over the northern temperature proxies is likely the consequence of the distinctive harmonic shapes affecting the northern (rectangular) vs. southern (triangular) DO oscillations; the actual northern–southern relationship, as suggested by modelling and other recent data studies, is most probably in simple antiphase (cross phase of 180°).