Calibration of the carbon isotope composition (δ13C) of benthic foraminifera
Résumé
The carbon isotope composition (δ 13 C) of seawater provides valuable insight on ocean circulation, air-sea exchange, the biological pump, and the global carbon cycle and is reflected by the δ 13 C of foraminifera tests. Here more than 1700 δ 13 C observations of the benthic foraminifera genus Cibicides from late Holocene sediments (δ 13 C Cibnat) are compiled and compared with newly updated estimates of the natural (preindustrial) water column δ 13 C of dissolved inorganic carbon (δ 13 C DICnat) 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 δ 13 C Cibnat and δ 13 C DICnat , confirming earlier work. Regression analyses indicate significant carbonate ion (À2.6 ± 0.4) × 10 À3 ‰/(μmol kg À1) [CO 3 2À ] and pressure (À4.9 ± 1.7) × 10 À5 ‰ m À1 (depth) effects, which we use to propose a new global calibration for predicting δ 13 C DICnat from δ 13 C Cibnat. This calibration is shown to remove some systematic regional biases and decrease errors compared with the one-to-one relationship (δ 13 C DICnat = δ 13 C Cibnat). 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 σ ≅ 0.25‰, with larger values found in the southeast Atlantic and Antarctic (σ ≅ 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 δ 13 C record.
Origine | Fichiers éditeurs autorisés sur une archive ouverte |
---|
Loading...