NALPS19: Sub-orbital scale climate variability recorded in Northern Alpine speleothems during the last glacial period

• Main Authors: Moseley, Gina E., Spötl, Christoph, Brandstätter, Susanne, Erhardt, Tobias, Luetscher, Marc, Edwards, R. Lawrence
• Format: Text
• Language: English
• Published: 2019
• Subjects: Greenland; Greenland ice cores; ice core; NGRIP
• Online Access: https://doi.org/10.5194/cp-2019-44; https://www.clim-past-discuss.net/cp-2019-44/

Sub-orbital-scale climate variability of the last glacial period provides important insights into the rates that the climate can change state, the mechanisms that drive that change, and the leads, lags and synchronicity occurring across different climate zones. Such short-term climate variability has previously been investigated using speleothems from the northern rim of the Alps (NALPS), enabling direct chronological comparisons with highly similar shifts in Greenland ice cores. In this study, we present NALPS19, which includes a revision of the last glacial NALPS δ 18 O chronology over the interval 118.3 to 63.7 ka using eleven,newly-available, clean, precisely-dated stalagmites from five caves. Using only the most reliable and precisely dated records, this period is now 90 % complete and is comprised of 15 stalagmites from seven caves. Where speleothems grew synchronously, major transitional events between stadials and interstadials (and vice versa) are all in agreement within uncertainty. Ramp-fitting analysis further reveals good agreement between the NALPS19 speleothem δ 18 O record, the GICC05modelext NGRIP ice-core δ 18 O record, and the Asian Monsoon composite speleothem δ 18 O record. In contrast, NGRIP ice-core δ 18 O on AICC2012 appears to be considerably too young. We also propose a longer duration for the interval covering Greenland Stadial (GS) 22 to GS-21.2 in line with the Asian monsoon and NGRIP-EDML. Given the near-complete record of δ 18 O variability during the last glacial period in the northern Alps, we offer preliminary considerations regarding the controls on mean δ 18 O. We find that as expected, δ 18 O values became increasingly more depleted with distance from the oceanic source regions, and increasingly depleted with increasing altitude. Exceptions were found for some high-elevation sites that locally display δ 18 O values that are too high in comparison to lower-elevation sites, thus indicating a summer bias in the recorded signal. Finally, we propose a new mechanism for the centennial-scale stadial-level depletions in δ 18 O such as "pre-cursor" events GS-16.2, GS-17.2, GS-21.2, and GS-23.2, as well as the "within-interstadial" GS-24.2 event. Our new high-precision chronology shows that each of these δ 18 O depletions occurred shortly following rapid rises in sea level associated with increased ice-rafted debris and southward shifts in the Intertropical Convergence Zone, suggesting that influxes of meltwater from moderately-sized ice sheets may have been responsible for the cold reversals causing the AMOC to slow down similar to the Preboreal Oscillation and Older Dryas deglacial events.