The "solid earth", a term popular amongst climatologists, is a deceptive misnomer as the aesthenosphere is a deeply convecting fluid upon which flexible sheets of crust (i.e. This deeply convecting fluid tears these delicate plates apart at rift zones and crushes them together like the bonnet of a wrecked car at convergence zones.
Mountains rise out of fold belts resulting from the crumpling of plates, and where differences in plate buoyancy allow, one plate rides over another, forcing the other plate to follow the convection current into the aesthenosphere.
What this seen an increase in levels like this, but it’s only recently that our sophistication in measuring the carbon-14 levels in old tree rings like this has allowed us to test this. Looks like we’re going to have to unearth more old trees that can be radiocarbon-dated back to these years, and see whether they have elevated levels of carbon-14 in them.
If not, then it’s conceivable that these trees are just flukes, or that there was a mistake done in the analysis.
Furthermore, the discovery of a surprising number of submarine volcanoes highlights the underestimation of global volcanism and provides a loose basis for an estimate that may partly explain ocean acidification and rising atmospheric carbon dioxide levels observed last century, as well as shedding much needed light on intensified polar spring melts.
The only major fluctuation we know of occurred when we began detonating nuclear weapons in the open air, back in the mid-20th Century.
Well, if carbon-14 can decay into nitrogen-14 and other stuff, then we can create carbon-14 by combining nitrogen-14 with the proper stuff.