Solid-phase samples were collected onboard (RV Heincke expedition HE443) using cut-off syringes. The MUC was sliced and sampled. For sampling the GC, small windows were drilled into the liner through which the syringes were introduced. All samples were stored anoxically and frozen at -20°C until processing. The processing involved freeze-drying and grinding before splitting the samples for the different kinds of analyses.

The data have been partially published in PANGAEA before (Aromokeye, D A et al., 2018), but with core depth, not sediment depths.Methods:Bulk elemental composition: Dissolution of dry sediment in a mixture of 65% HNO3 (3 ml), 30% HCl (2 ml), and 40% suprapur® HF (0.5 ml) in a CEM Mars Xpress microwave system. Elemental contents determined by ICP-OES (Inductively coupled plasma – optical emission spectroscopy; Iris Intrepid II).Sequential Fe extraction after Poulton and Canfield (2005) and Henkel et al. (2016). Fe aca (1 M Na-acetate, 24 h, pH 4.5); Fe hyam (1 M hydroxylamine-HCl in 25% v/v acetic acid, 48 h); Fe di-ct (Na-dithionite (50 g L-1)/0.02 M Na-citrate, 2 h, pH 4.8); Fe oxa (0.2 M ammonium oxalate/0.17 M oxalic acid, 6 h). Iron contents determined by ICP-OES (Inductively coupled plasma – optical emission spectroscopy; Iris Intrepid II ICP-OES)