Calibration of the carbon isotope composition (?13 C) of benthic foraminifera Academic Article uri icon

abstract

  • The carbon isotope composition (?13C) of seawater provides valuable insight on ocean circulation, air-sea exchange, the biological pump, and the global carbon cycle and is reflected by the ?13C of foraminifera tests. Here more than 1700 ?13C observations of the benthic foraminifera genus Cibicides from late Holocene sediments (?13CCibnat) are compiled and compared with newly updated estimates of the natural (preindustrial) water column ?13C of dissolved inorganic carbon (?13CDICnat) as part of the international Ocean Circulation and Carbon Cycling (OC3) project. Using selection criteria based on the spatial distance between samples, we find high correlation between ?13CCibnat and ?13CDICnat, confirming earlier work. Regression analyses indicate significant carbonate ion (?2.6 ± 0.4) × 10?3‰/(?mol kg?1) [CO32?] and pressure (?4.9 ± 1.7) × 10?5‰ m?1 (depth) effects, which we use to propose a new global calibration for predicting ?13CDICnat from ?13CCibnat. This calibration is shown to remove some systematic regional biases and decrease errors compared with the one-to-one relationship (?13CDICnat = ?13CCibnat). However, these effects and the error reductions are relatively small, which suggests that most conclusions from previous studies using a one-to-one relationship remain robust. The remaining standard error of the regression is generally ? ? 0.25‰, with larger values found in the southeast Atlantic and Antarctic (? ? 0.4‰) and for species other than Cibicides wuellerstorfi. Discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic ?13C record.

publication date

  • June 2017