Punctuated Shutdown of Atlantic Meridional Overturning Circulation during Greenland Stadial 1

Abstract

The Greenland Stadial 1 (GS-1; ~12.9 to 11.65 kyr cal BP) was a period of North Atlantic cooling, thought to have been initiated by North America fresh water runoff that caused a sustained reduction of North Atlantic Meridional Overturning Circulation (AMOC), resulting in an antiphase temperature response between the hemispheres (the ‘bipolar seesaw’). Here we exploit sub-fossil New Zealand kauri trees to report the first securely dated, decadally-resolved atmospheric radiocarbon (14C) record spanning GS-1. By precisely aligning Southern and Northern Hemisphere tree-ring 14C records with marine 14C sequences we document two relatively short periods of AMOC collapse during the stadial, at ~12,920-12,640 cal BP and 12,050-11,900 cal BP. In addition, our data show that the interhemispheric atmospheric 14C offset was close to zero prior to GS-1, before reaching ‘near-modern’ values at ~12,660 cal BP, consistent with synchronous recovery of overturning in both hemispheres and increased Southern Ocean ventilation. Hence, sustained North Atlantic cooling across GS-1 was not driven by a prolonged AMOC reduction but probably due to an equatorward migration of the Polar Front, reducing the advection of southwesterly air masses to high latitudes. Our findings suggest opposing hemispheric temperature trends were driven by atmospheric teleconnections, rather than AMOC changes.

Evaluating the link between the sulfur-rich Laacher See volcanic eruption and the Younger Dryas climate anomaly

“…Sea ice tracked the southward-shifted polar front, resulting in more NH cooling, a weakened AMOC, and a further southward shift in global atmospheric circulation cells (Baldini et al, 2015a). Such a scenario is consistent with recent results based on tree ring radiocarbon measurements suggesting that GS-1 was not caused exclusively by long-term AMOC weakening but instead was forced by NH polar cell expansion and southward NH polar front migration (Hogg et al, 2016).…”

Decadally Resolved Lateglacial Radiocarbon Evidence from New Zealand Kauri

“…Individual analyses are given as XLS files (Radiocarbondating results.xls) in the Appendix, Supplementary data (sheets named 'Towai accepted', 'FIN11 accepted' and 'TOWAI_FIN11 rejected'). The χ2 agreement indices indicate a high level of reproducibility within each decade for both data sets -see Hogg et al (2016) for details. We also present the NH data with reassigned calendar ages (Radiocarbondating results.xls/NH).…”

“…Radiocarbon decadal means, rejection criteria and statistical analysis methods for both datasets are given in Hogg et al (2016). From a total of 1035 results, 11 were rejected from the Towai chronology and 2 from the tree FIN11.…”

“…If the reduction in offset noted in this research is confirmed by analysis of contemporaneous SH/NH sample pairs, it could be associated with increased ventilation of the Southern Ocean following the termination of the Antarctic Cold Reversal. This possibility is discussed fully in Hogg et al (2016). Comparisons with other 14 C time series…”

“…Decadal 14 C measurements were published by Hogg et al (2016). Here, we present individual kauri measurements from ~13,130 -11,370 cal BP, with additional details relating to the reconstruction of the LGIT/early Holocene NH 14 C record.…”