Pyrite and reactive iron fluxes in deep (> 966 m) sediments of the Gulf of Mexico

Abstract

The Fe concentrations associated with operationally defined microbially reducible (FeMR), pyrite (Fepyr) and reactive (Fereac = FeMR + Fepyr) geochemical fractions were analyzed in 40 sedimentary cores collected from deep sediments (> 1000 m water depth) in the Gulf of Mexico (GoM) and in 27 surface sediment samples from the Yucatan continental shelf (YCS). The average concentrations of these three fractions for 34 of the 40 GoM cores were 79 ± 43 μmol g−1, 1.54 ± 0.65 μmol g−1, and 81 ± 43 μmol g−1, respectively, while for the YCS, these values were 20 ± 33 μmol g−1, 0.33 ± 0.50 μmol g−1, and 21 ± 33 μmol g−1, respectively. The remaining six cores were influenced by turbidite events from the Campeche Escarpment, which showed very low FeMR concentrations (0.63 ± 2.03 μmol g−1) and slightly higher Fepyr values (2.6 ± 1.1 μmol g−1). The average degrees of pyritization (DOP) values in the zone under the influence of turbidite events were very high (68 ± 36% to 94.0 ± 1.6%), whereas those in the rest of the GoM (3.1 ± 2.8%) and YCS (4.3 ± 5.2%) were small and showed limited spatial variability. The estimated FeMR, Fepyr, and Fereac fluxes for the GoM were (6.1 ± 4.7) x 102 μmol cm−2 ky−1, 11.3 ± 7.5 μmol cm−2 ky−1, and (6.2 ± 4.8) x 102 μmol cm−2 ky−1, respectively. Based on these values, we estimated that 0.0047 ± 0.0031 Tg of Fepyr, 0.25 ± 0.20 Tg of FeMR, and 0.26 ± 0.20 Tg of Fereac are buried annually in the ∼750,000 km2 total deep-sediment region of the GoM. On a global scale, these fluxes represent between 0.14 and 3.4% of the pyrite burial in deep ocean sediments. In addition, a GoM turbidite was estimated of being capable of transporting between 0.0351 and 0.141 Tg of Fepyr and 0.0404–0.161 Tg of S pyrite (Spyr) while producing an oxidized Fe deficit of 0.815–3.26 Tg.