That graph is fascinating to someone who's studied a lot of ancient history.
The thing that strikes me most is how bad things were after the fall of the Western Roman Empire. Yes, the eastern half kept chugging along. But judging from this data, it didn't chug very hard.
Another striking thing is how bad things things seem to have been in the first century BC. Apparently the problems during that time were not merely political squabbles at the top of a society that otherwise kept operating as usual.
Well remember that this record is a proxy of silver refining activity in Spain. I haven't had a chance to read the actual paper, but I don't think this dataset would well capture information regarding the activity of the Eastern Empire's mining/production centers.
That is interesting: the Riotinto silver was mixed with lead to a degree that eastern sources weren't?
(If that's the explanation, another interesting thing about this graph is the uptick in the early 700s, presumably due to the Moorish invasion. By 750 they seem to have been mining on a greater scale than the Romans, which is not what I'd have expected.)
I don't know if the lead/silver mix was different.
The paper specifically calls out mining activity around the Rhine as having significant impact on the lead signal, with a 2-5 fold greater impact compared to Spanish sites. The authors suggest that the 700s spike in lead pollution was driven by increased activity in France and Britain (which once again has a many fold greater impact on this measurement than in Spain).
Also, doing a cursory look at sources suggests that the eastern empire relied far more on gold and bronze coinage than silver, suggesting another possible source for the lack of an Eastern Empire signature.
They think there was a lot of mining going on in England in 750?
Huh, interesting. The paper calls out activity around Derbyshire, and cites a book "Mining, metallurgy and minting in the Middle Ages". The book itself appears to focus on a later period.
Poking around, it looks like there is evidence for lead mining in the Derbyshire region possibly including Roman times, but there isn't any great data floating around.
The other source the authors suggested (Merovingian mining and coin production in France at Melle) seems to have far stronger evidence for large scale production in that time period.
I have no trouble believing there was extensive lead mining in England in Roman times, but it's harder to believe it was happening in 750. I can't think of anything the Anglo-Saxons would have been using lead for, and it's hard to imagine there was much of an export trade. I would also be surprised if the Franks were making silver coins on anything like the scale the Romans did.
On the other hand, the lead's there in the data; it must have come from somewhere; so that part of the graph seems to me the most intriguingly mysterious bit.
I read that weather patterns carried airborne lead from Spain to Greenland, where it fell in snow and was preserved in ice. However, the winds from mines in the Eastern Mediterranean don't reach Greenland.