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.