{"id":480860,"date":"2026-10-20T12:17:07","date_gmt":"2026-10-20T19:17:07","guid":{"rendered":"https:\/\/climatescience.press\/?p=480860"},"modified":"2026-10-20T12:17:10","modified_gmt":"2026-10-20T19:17:10","slug":"bomb-carbon-from-1960s-tree-rings-reveals-biochar-stays-locked-in-soil-for-centuries","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=480860","title":{"rendered":"\u201cBomb Carbon\u201d from 1960s Tree Rings Reveals Biochar Stays Locked in Soil for Centuries"},"content":{"rendered":"\n
\"Close-up
AI generated by Grok<\/figcaption><\/figure>\n\n\n\n

Researchers at the Swedish University of Agricultural Sciences (SLU) developed a method using \u201cbomb carbon\u201d (elevated radiocarbon- 14 from 1960s atmospheric nuclear tests, preserved in tree rings) in wood shavings to track how stable biochar is when added to soil.<\/strong><\/p>\n\n\n\n

Biochar is a charcoal- like material produced by heating biomass (here, wood) in low- oxygen conditions (pyrolysis). It is of interest for improving soil properties and as a potential long-t erm carbon sink to help mitigate climate change, with global estimates suggesting it could sequester carbon equivalent to roughly 6- 16% of annual anthropogenic CO\u2082 emissions. A key uncertainty has been how quickly biochar mineralizes (breaks down into CO\u2082) in soil versus remaining stable for decades or centuries, and how to distinguish its contribution from native soil organic matter.<\/p>\n\n\n\n

The method<\/strong><\/h3>\n\n\n\n

Atmospheric nuclear testing in the 1950s- 1960s roughly doubled atmospheric \u00b9\u2074C levels, peaking around the mid-1960s. Tree rings from 1964-1967 therefore contain elevated \u201cbomb\u201d \u00b9\u2074C. SLU researchers selected mature Norway spruce and Scots pine trunks from a Swedish clear- cut, identified the relevant rings, and used a professional woodturner to carefully remove outer wood and collect the thin, high-\u00b9\u2074C layers as shavings. These were pyrolyzed into biochar (tested at highest treatment temperatures of ~400\u00b0C and 650\u00b0C).<\/p>\n\n\n\n

The resulting biochar had enough \u00b9\u2074C enrichment (on average ~61.7 percent modern carbon higher than bulk soil organic matter in one report) to serve as a natural tracer. In a one-year laboratory incubation, they mixed it into soil (at 2% by dry mass), trapped emitted CO\u2082, and measured its \u00b9\u2074C signature via accelerator mass spectrometry. This allowed them to quantify the share of CO\u2082 coming from the biochar versus the soil.<\/p>\n\n\n\n

Key findings<\/h3>\n\n\n\n