Supporting data for manuscript: Beyond Bulk

We used soil density fraction data from The International Soil Radiocarbon Database (ISRaD v. 1.1.2 Lawrence et al., 2020; www.soilradiocarbon.org). ISRaD is an online repository for environmental radiocarbon data with a specific emphasis on soils and soil fractions. We utilized a subset of ISRaD data comprising measurements of radiocarbon (persistence), organic C concentration (abundance), or the proportion of organic C in the mineral-associated fraction (distribution) made on soil density fractions for the current analysis. Radiocarbon data are reported in units of Δ14C (‰) normalized to account for the year of sampling (Shi et al., 2020) (see below). In studies that employed sequential density separation (isolation of multiple free light, occluded light, and heavy fractions for the same sample), the multiple fractions were combined by taking a mass-weighted average for C abundance and C-weighted average for Δ14C values. C distribution among density fractions was normalized to sum to 100%. Overall, our meta-analysis included data from 52 studies. In addition to C measurements, ISRaD compiles ancillary data regarding site and sample characteristics that were either provided directly in the associated published works or provided as supplementary information from manuscript authors. When variables of interest were not available directly through ISRaD, these variables were populated through utilization of geolocated databases (see supplemental materials in associated published manuscript).