Decadal-scale progression of Dansgaard-Oeschger warming events

Abstract

Abstract. During the last glacial period, proxy records throughout the Northern Hemisphere document a succession of rapid millennial-scale warming events, called Dansgaard-Oeschger (DO) events. A range of different mechanisms have been proposed that can produce similar warming in model experiments, however the progression and ultimate trigger of the events is still unknown. Because of their fast nature, the progression is challenging to reconstruct from paleoclimate data due to the limited temporal resolution achievable in many archives and cross-dating uncertainties between records. Here we use new high-resolution multi-proxy records of sea-salt (derived from sea spray and sea ice over the North Atlantic) and terrestrial (derived from the Central Asian deserts) aerosol concentrations over the period 10–60 ka from the Greenland NGRIP and NEEM ice cores in conjunction with local precipitation and temperature proxies from one of the cores to investigate the progression of environmental changes at the onset of the warming events at annual to multi-annual resolution. Our results show on average a small lead of the changes in both local precipitation and terrestrial dust aerosol concentrations over the change in sea-salt aerosol concentrations and local temperature of approximately one decade. This suggests that, connected to the reinvigoration of the Atlantic Meridional Overturning Circulation and the warming in the North Atlantic, both synoptic and hemispheric atmospheric circulation change at the onset of the DO warming, affecting both the moisture transport to Greenland and the Asian monsoon systems. Taken at face value, this suggests that a collapse of the sea-ice cover was not the initial trigger for the DO events.

Connecting the Greenland ice-core and U∕Th timescales via cosmogenic radionuclides: testing the synchroneity of Dansgaard–Oeschger events

“…For each record, only events that are well expressed and measured in high resolution have been fitted. The approach and inference procedure are described in more detail in Erhardt et al (2018).…”

“…For the ice-core record, t1 and t2 typically encompass 500 years prior to and after the nominal transition ages by Rasmussen et al (2014a). The exact values have been adjusted to exclude overlap with other transitions where necessary (Erhardt et al, 2018 14 C records that are suitable for synchronization because the resolution of the individual records decreases back in time, while their differences to each other grow steadily (see Fig. 1i).…”

Imprint of Arctic sea ice cover in North-Greenland ice cores

“…Details on the methodology are given in Sommer (1996) and Schwager (2000) and are summarized in the supplementary information. The 100.8 m B17 ice core was analysed at the University of Bern in 2017 by Continuous Flow 165 Analysis (for details on the method see: Kaufmann et al, 2018;Erhardt et al, 2019;Burgay et al, 2019 and references therein), coupled with a custumized fraction collector (BESTA-Technik GmbH, Germany) sampling the melt-water every 40-60 s. Details on the methodology are reported in the supplementary information.…”