Holliday et al.'s (2023) Gish Gallop: timing of the Younger-Dryas onset and Greenland platinum spike

Should the YD onset be defined according to changes in weather patterns or changes in temperature? Or how about ice layer thickness? The advantage of using d to define the onset of the YD is that is is very precisely defined – the abrupt change in d in the NGRIP ice core appears to occur in only a few years.

Why define the YD onset from a single ice core? And why should that ice core be the NGRIP ice core? We could have much more confidence in their definition for the onset of the YD if they could show this abrupt change in d just after 10,900 BCE was replicated in the other ice cores.

Another crucial issue is the way the different ice cores are linked or aligned which determines how the GISP2 platinum signal is aligned versus the NGRIP d anomaly at ~10,900 BCE. This alignment is described in Seierstad et al.

In fact we find the NGRIP and GISP2 ice cores are linked at two neighbouring chemo-stratigraphic points near the YD onset; 1) 1525.862 m = 1712.406 m, and 2) 1526.497 m = 1713.027 m. This latter point is close to the onset of the YD period according to Steffensen et al.

The platinum signal in the GISP2 ice core occurs at 1712.56 m and at 1712.19 m. That is, the platinum signal is around 0.5 – 0.8 meters higher in the GISP2 ice core than expected given Seierstad's definition of the YD onset, corresponding to about 15-25 years.

If any of these link points are wrong, the alignment of the ice cores and the position of the platinum signal vs the NGRIP definition of the YD onset will also be wrong.

Relative to the GISP2 platinum spike we need to see i) how the deuterium excess, d, compares between the different ice cores, and ii) how the different ice cores have been linked chemo-stratigraphically near the YD onset.

Until this platinum signal is located in all the Greenland ice cores, there is at least some doubt in the YD onset defined by Steffensen et al.

They use the Seso speleothem, from a cave in Spain, along with the Greenland NGRIP ice core to define the onset of the YD. Looking at the above plot from Cheng et al.

As we already know, NGRIP and several other Greenland ice cores are inconsistent at this point, which makes precise definition of the YD onset quite uncertain, as already discussed (see the plot above from Svensson et al.

The only evidence they provide that potentially contradicts the YDIH is the timing of the platinum spike in the GISP2 ice core versus the timing of the YD onset defined by Steffensen et al.

Platinum might be a better marker for linking the chronologies of the different ice cores near the YD. And finally, apparently simultaneous flooding near the YD onset from several distant ice sheet margins points towards a catastrophic event.