Fig. 2.

Quadruple S-isotope data from core GKF01 (A) with a schematic mixing scenario (B). Δ³⁶S vs. Δ³³S trends for the new data (black and blue) superimposed on previously published data (gray circles; ref. 9). Regressions are given through the whole dataset (red) as well as through the C-S anomaly (blue) and background (black). Uncertainties are plotted conservatively, using the larger of the internal or external uncertainty (1σ), and are consistently smaller than a single data point. The insert (B) schematically illustrates the range of Δ³³S and Δ³⁶S values that can be expressed in pyrite (shaded gray area) formed via mixing of sulfide derived from MSR (open circles 3–4) with atmospherically derived S-MIF carried by sulfate (filled circle 1) and elemental sulfur (filled circle 2). The horizontal blue bar illustrates the Δ³⁶S-Δ³³S systematics of TSR derived sulfide. Note, biological activity has the potential to exert greater influence on Δ³⁶S/Δ³³S when pyrite carries a negative Δ³³S (i.e., derived from sulfate) rather than a positive Δ³³S (29) as observed in the C-S anomaly (Fig. 1). Additionally, mixing with TSR-derived sulfide moves the Δ³⁶S/Δ³³S to less negative values.