The dry Nile of Sirte

A couple years back I started Dartnell's Origins, only finishing it on LOCKDOWN. I was annoyed it didn't break out the Sahara into one such chunk.

Luckily Ineffable Island points to Cécile L. Blanchet: river activity between Tunis and Cyrene, over 160000 years. Through most of this span the shoreline was further north and that's whence they've got their sediment-core. It also encompasses my favourite era, that Almost-Holocene called Eemian. That should be 126-120 kBC here. The notion is, as with dust in the Canaries, that river effluvia at Sirte tells what was going on in the interior.

The article is Blanchet et al., "Drivers of river reactivation in North Africa during the last glacial cycle" doi 10.1038/s41561-020-00671-3:

We show that river runoff occurred during warm interglacial phases of Marine Isotope Stages 1 and 5 due to precession-forced enhancements in the summer and autumn rainfall over the entire watershed, which fed presently dry river systems and intermittent coastal streams. In contrast, shorter-lasting and less-intense humid events during glacial Marine Isotope Stages 3 and 4 were related to autumn and winter precipitation over the Libyan coastal regions driven by Mediterranean storms.

Usually when they talk MIS they're hitting upon Stage 1 at the top. As with their own "BP" system (and "BC") magnitude grows with age. So MIS 1 is us: post- Younger Dryas. Stage 5e begins peak Eemian 121 kBC, although 5a lingers to 69 kBC. If Blanchet started 158 kBC her team should have got quite a bit of MIS 6 in there as well; they seem to be taking 6a+5e for their "5".

The glacial periods illustrate the Greek Underworld, where "Winter" in Crete and points south is the nice time of year. Summer is hell. Over 69-27 kBC, Libya had some seasonal runoff, from storms, but was generally arid. The abstract doesn't tell of MIS 2 but I'll call it: utter desert.

It seems when it was globally warmest, in stages 1 and 5, it rained in the Sahara in the summer. That would have led to Nile-like floods downstream. That incorporates peak Lake Chad over the Mesolithic and the Eemian.

I do wonder, given global-warming attention, why the northern Sahara is not greening today. Are humans irrigating the moisture faster than it can build up?