Fig. 7: Variation of δ34S and Δ33S values for chromium reducible sulphur (CRS) in pyrite- and greigite-dominated depths from core RKB 5260.

The yellow oval (labelled ‘OSR-pyrite’) represents typical sulphur isotope compositions of pyrite derived from organoclastic sulphate reduction (OSR) in shallow sediments of modern marine seep environments45,49. All data for pyrite-dominated (orange squares; 43.0–47.2 m) and greigite-dominated samples (green circles; 41.0–42.8 m) align along the mixing zone between OSR-pyrite and modern seawater sulphate end members. Error bars are from standard deviation (SD) for Δ33S values.