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

Abstract

We have developed a proxy measurement for the determination of organic carbon (Corg) oxidation rates (Cox) on the seafloor utilizing the δ13C values of two benthic foraminifera: Bolivina argentea, a near‐surface dwelling species, and Buliminella tenuata, an infaunal species. The δ13C isotopic composition of these tests preserve a record of the Σ13CO2 pore water gradient, which is directly related to Cox. On the seafloor of Santa Monica Basin, Cox 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, Cox increased from 1 to 2 mmolC m−2 d−1 and then decreased into the 1980s. By adding Cox to a high‐resolution record of Corg burial rate, we have derived the pattern of Corg 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 Corg 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 Corg raining to the seafloor; however, there is a trend toward lower burial efficiency with higher productivity and rain rate.