Productivity and organic carbon rain to the California margin seafloor: Modern and paleoceanographic perspectives

We have developed a proxy measurement for the determination of organic carbon (C org ) oxidation rates (C ox ) on the seafloor utilizing the δ 13 C values of two benthic foraminifera: Bolivina argentea , a near‐surface dwelling species, and Buliminella tenuata , an infaunal species. The δ 13 C isotopic composition of these tests preserve a record of the Σ 13 CO 2 pore water gradient, which is directly related to C ox . On the seafloor of Santa Monica Basin, C ox has fluctuated between 0.6 and 2.5 mmolC m −2 d −1 and generally increased from 1600 to 1980 AD. Between 1920 and 1970, C ox increased from 1 to 2 mmolC m −2 d −1 and then decreased into the 1980s. By adding C ox to a high‐resolution record of C org burial rate, we have derived the pattern of C org rain to the seafloor, which fluctuated between 2.9 and 3.8 mmolC m −2 d −1 over the last 80 years. The ratio of C org rain at 900 m to primary productivity is constant at 10 ± 1% over a 40% change in mean annual primary productivity. Sediments in Santa Monica Basin accumulate ∼50% of the C org raining to the seafloor; however, there is a trend toward lower burial efficiency with higher productivity and rain rate.