Constraining the Variability of the Atlantic Meridional Overturning Circulation During the Holocene

Abstract

There is a converging body of evidence supporting a measurable slowdown of the Atlantic Meridional Overturning Circulation (AMOC) as climate warms and Northern Hemisphere ice sheets inexorably shrink. Within this context, we assess the variability of the AMOC during the Holocene based on a marine sediment core retrieved from the deep northwest Atlantic, which sensitively recorded large-scale deglacial transitions in deep water circulation. While there is a diffuse notion of Holocene variability in Labrador and Nordic Seas overturning, we report a largely invariable deep water circulation for the last 11,000 years, even during the meltwater pulse associated with the 8.2-ka event. Sensitivity tests along with high-resolution 231 Pa/ 230 Th data constrain the duration and the magnitude of possible Holocene AMOC variations. The generally constant baseline during the Holocene suggests attenuated natural variability of the large-scale AMOC on submillennial timescales and calls for compensating effects involving the upstream components of North Atlantic Deep Water.

Latest Pliocene Northern Hemisphere glaciation amplified by intensified Atlantic meridional overturning circulation

“…However, although the upstream tributaries of NADW were dominated by decadal-scale, centennial-scale, and millennialscale fluctuations with different mechanisms 37 , antiphase variability was found only in the millennial-scale ones [35][36][37][38] . Rather, ISOW and DSOW showed in-phase variability on decadal-tocentennial scales (see Fig.…”

“…As we have discussed, the increased ISOW formation after the MIS G4/G3 deglaciation indicates the intensification of the Nordic Seas overturning circulation (northern sector of the AMOC). During the Holocene, however, activity of the lower limb of the AMOC remained relatively stable, as upstream tributaries of NADW (ISOW, DSOW, and Labrador Sea Water) fluctuated to compensate for each other on a millennial time scale [35][36][37][38] . This is because inflow and freshening of Arctic sea ice reduced convection in the Nordic Seas, whereas in the more southerly Labrador Sea, surface cooling, more important than sea ice during the interglacial, increased convection 38 .…”

Persistent Link Between Caribbean Precipitation and Atlantic Ocean Circulation During the Last Glacial Revealed by a Speleothem Record From Puerto Rico

“…PR‐LA‐1 δ 18 O values in comparison with (from top to bottom) (a) δ 18 O values from the NGRIP ice core using the GICC05 timescale (Svensson et al, 2008). Numbers indicate GIs after Rasmussen et al (2014); (b) speleothem δ 18 O values from Terciopelo Cave, Costa Rica (Lachniet et al, 2009); (c) speleothem δ 18 O values from Santo Tomas Cave, Cuba (Warken et al, 2019); (d) δ 18 O values from Abaco island, Bahamas (Arienzo et al, 2017); (e) SST reconstructed from G. ruber Mg/Ca values from core JPC26, Florida Strait (Them Il et al, 2015); (f) G. ruber Mg/Ca values from Caribbean core VM12‐107 (Parker et al, 2015); (g) reflectance record from the Cariaco Basin off Venezuela reflecting the mean meridional position of the ITCZ (Deplazes et al, 2013); (h) 231 Pa/ 230 Th compilation from the Bermuda Rise reflecting the strength of the AMOC (Böhm et al, 2015; Henry et al, 2016; Lippold et al, 2009, 2019; McManus et al, 2004). Vertical blue bars indicate intervals of high PR‐LA‐1 δ 18 O values indicative of cool/dry periods in Puerto Rico coinciding with a weak AMOC, such as Heinrich stadials (HS) 1–5.…”

Large-scale features and evaluation of the PMIP4-CMIP6 <i>midHolocene</i> simulations

“…McManus et al, 2004), although geochemical observations show that several additional factors influence Pa and Th distribution (Hayes et al 2013). The available Pa/Th records indicate no significant change in the AMOC between the mid-Holocene and the pre-industrial period (McManus et al, 2004;Ng et al, 2018;Lippold et al, 2019).…”