Table 1: Mass balance for sedimentary Cr .
Potential sources of Cr in marine sediments are compared to evaluate the origin of the benthic Cr flux. Sediment phase percentages (organic matter, CaCO3, lithogenic material) are averages from the upper 4 cm (Table S6). Cr per phase is the concentration expected in each individual phase (surface phytoplankton: Martin & Knauer, 1973; CaCO3: Remmelzwaal et al., 2019; upper continental crust: Rudnick & Gao, 2003). Cr contributed to bulk sediment is the Cr that each phase would contribute to the bulk sediment concentration, based on sediment phases and Cr per phase. Cr needed is the required [Cr] in the sediments (i.e. the [Cr] of particles that must be delivered to sediments) to explain the calculated diffusive Cr flux from sediments (3.2 nmol cm-2 yr-1, Table S6), assuming a sedimentation rate in the region of 2 cm ka-1 (e.g. Cochran & Osmond, 1976). A sedimentation rate on the higher side of regional observations was chosen to give a minimum estimate of the Cr needed. The assumed sediment density is 1.7 g cm-3.