Arctic freshwater forcing of the Younger Dryas cold reversal

Abstract

The last deglaciation was abruptly interrupted by a millennial-scale reversal to glacial conditions, the Younger Dryas cold event. This cold interval has been connected to a decrease in the rate of North Atlantic Deep Water formation and to a resulting weakening of the meridional overturning circulation owing to surface water freshening. In contrast, an earlier input of fresh water (meltwater pulse 1a), whose origin is disputed, apparently did not lead to a reduction of the meridional overturning circulation. Here we analyse an ensemble of simulations of the drainage chronology of the North American ice sheet in order to identify the geographical release points of freshwater forcing during deglaciation. According to the simulations with our calibrated glacial systems model, the North American ice sheet contributed about half the fresh water of meltwater pulse 1a. During the onset of the Younger Dryas, we find that the largest combined meltwater/iceberg discharge was directed into the Arctic Ocean. Given that the only drainage outlet from the Arctic Ocean was via the Fram Strait into the Greenland-Iceland-Norwegian seas, where North Atlantic Deep Water is formed today, we hypothesize that it was this Arctic freshwater flux that triggered the Younger Dryas cold reversal.

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…As noted above (Section 2.5), GLA drainage through the Mackenzie River at the onset of the Younger Dryas has been proposed as an alternative route to the St. Lawrence on the basis of modelling (Tarasov and Peltier 2005) and dating of Mackenzie delta sands and upstream 23 gravels and erosional channels (Murton et al 2010). Here too, there is a contrast between the temporal resolution of central Arctic marine sediment records and those along Arctic continental margins.…”

“…Opinions differ about precise timing and routing of GLA overflow during the YD, because different approaches often yield different interpretations (e.g. deVernal et al, 1996;Tarasov and Peltier, 2005;Carlson et al, 2007;Murton et al, 2010;Not and Hillaire-Marcel, 2012;Cronin et al, 2012;Carlson and Clark, 2012). In a recent review, Carlson and Clark (2012) favoured an easterly route, but numerical modelling suggests a large influx of freshwater into the Arctic Ocean was more likely (although not necessarily from GLA: Tarasov and Peltier, 2005), and would have had a more significant impact on ocean circulation (Condron and Winsor, 2012).…”

“…Drainage events have been associated with cooling events during deglaciation (Section 2.5) and it is important to analyse the modelled climatic response, not only to different volumes and rates of meltwater release, but also to the location of the freshwater input in the oceans. In the context of analysing the likely causes of the YD cold period, analysed the effect of routing a large freshwater input into the Arctic Ocean as proposed by Tarasov and Peltier (2005). found that the effect of an Arctic Ocean input for the freshwater flux is very similar to the same input in the North Atlantic, albeit with a small delay of a decade, and some slight differences in the time evolution of the strength of the AMOC.…”

“…deVernal et al, 1996;Tarasov and Peltier, 2005;Carlson et al, 2007;Murton et al, 2010;Not and Hillaire-Marcel, 2012;Cronin et al, 2012;Carlson and Clark, 2012). In a recent review, Carlson and Clark (2012) favoured an easterly route, but numerical modelling suggests a large influx of freshwater into the Arctic Ocean was more likely (although not necessarily from GLA: Tarasov and Peltier, 2005), and would have had a more significant impact on ocean circulation (Condron and Winsor, 2012). Several studies of deep-sea Arctic oxygen isotopes , faunal assemblages , Taldenkova et al, 2013, and other proxies (reviewed in Carlson and Clark, 2012) provide evidence for significant meltwater discharge through the Mackenzie River at the onset of the YD (see also Section 2.6), as does an OSL-dated sequence at the mouth of the Mackenzie River (Murton et al, 2010).…”

Sensitivity of climate response to variations in freshwater hosing location

“…Perturbations in the MOC have been investigated as causes for Younger Dryas cooling, e.g. Manabe and Stouffer (1997), Tarasov and Peltier (2005) and Peltier et al (2006), and the 8.2-kiloyear event (Renssen et al 2001;. Furthermore, the response of the MOC to future warming due to the anthropogenic greenhouse effect has been investigated, e.g.…”