Norwegian Sea warm pulses during Dansgaard-Oeschger stadials: Zooming in on these anomalies over the 35–41 ka cal BP interval and their impacts on proximal European ice-sheet dynamics

Regional seesaw between the North Atlantic and Nordic Seas during the last glacial abrupt climate events

“…Recent monitoring data have revealed that (i) deuterium excess is low for subtropical Atlantic vapour and high for vapour formed at the Arctic sea-ice margin, where high kinetic fractionation occurs due to low relative humidity, and (ii) this vapour deuterium excess is preserved during transportation towards Greenland (Jouzel et al, 2013;Bonne et al, 2015). Higher deuterium excess recorded during GS (Masson-Delmotte et al, 2005) may reflect enhanced contribution of moisture from the Nordic Seas towards Greenland (as also previously suggested for Heinrich stadial 4 interval; Wary et al, 2016), when the Norwegian Sea appears relatively warm and surrounded by sea-ice-covered areas (providing low humidity air masses), while the North Atlantic surface is cold and marked by large sea-ice expansion (Hillaire-Marcel and de Vernal, 2008).…”

“…S6 for further details). We provide here new sea-surface reconstructions for cores MD95-2009, MD95-2010and MD99-2281 based on previously published dinocyst counts (Eynaud et al, 2002;Eynaud, 2003a, b;Zumaque et al, 2011) and extend the previously published reconstructions for core MD99-2285 (Wary et al, 2016; see also Wary et al, 2017 for the complete raw dinocyst counts of core MD99-2285). Our statistical approach provides direct and quantitative reconstructions for mean summer and mean winter SST (with, in the present case, root mean square errors of prediction -RMSEP -of 1.5 and 1.05 • C, respectively), mean summer and mean winter sea-surface salinities (SSS; respective RMSEP of 2.4 and 2.3 psu), and mean annual sea-ice cover (SIC) duration (RM-SEP of 1.2 months year −1 ).…”

“…A few earlier palaeoclimate studies have indeed suggested enhanced advection of warm Atlantic waters through the Continental Slope Current (flowing poleward along the eastern North Atlantic boundary) during stadial intervals (Peck et al, 2008, based on a core from the Porcupine Seabight) in response to a meltwater release detected at GI-GS transitions (see Wary et al, 2016). Compared to the modern climate system, the potentially reduced northward baroclinic volume transport of Atlantic waters associated with a weaker stadial deep-convection in the Nordic Seas could have been counteracted by (i) an increased northward barotropic transport (with compensation through a larger export at the Denmark Strait for instance), (ii) a larger heat transport due to higher temperature anomalies in the source area, and/or (iii) a greater impact of this northward heat transport on Nordic Seas SST thanks to a larger insolation forcing during MIS3 (Berger and Loutre, 1991).…”

“…Such warming might have enhanced iceberg releases from the bordering ice sheets, and might have therefore constituted a positive feedback for freshwater release. The origin of the freshwater-forcing input is still enigmatic, and may be related to, or precede (Barker et al, 2015;Wary et al, 2016), massive iceberg calving episodes. Our findings thus highlight an original case study for climate-ice-sheet interactions, and calls for additional numerical simulations focused on oceansea-ice-atmosphere interactions during MIS 3 millennial climatic events.…”

“…S1, Fig. S1, and Table S2 in the Supplement; Martinson et al, 1987;Manthé, 1998;Laj et al, 2004;Rasmussen et al, 2006;Zumaque et al, 2012;Caulle et al, 2013;Reimer et al, 2013;Wolff et al, 2010;Wary et al, 2016).…”