Abstract
Environmentally controlled sedimentary microcosms were used to experimentally determine temperature, salinity, and depth‐horizon effects on δ13CDIC profiles of dissolved inorganic carbon (DIC) in sediment pore water (PW) and near‐bottom water (BW). Simultaneously, benthic foraminiferal populations of Ammonia beccarii were cultured and assayed for calcite δ13C to establish how accurately foraminiferal shells recorded BW‐PW δ13CDIC. One treatment population was restricted to the 0–1‐cm sediment depth; in another treatment, the population could freely “roam” up and down in the sediment microcosm. Pore‐water DIC between the uppermost 0–0.5‐cm sediment layer and the overlying BW (i.e. 3 cm above the sediment‐water interface) showed steep gradients of core‐top Δδ13CPW averaging −3.6±1.6‰ at 25°C and −2.6±0.5‰ at 20°C. Correspondingly, shell calcite δ13C for A. beccarii collected from sediment microhabitats recorded a strong PW influence; δ13C shell values averaged 1.1±0.8‰ lighter than BW δ13CDIC but 1.6±0.6% enriched relative to average 0–5‐mm PW δ13CDIC. Foraminifera restricted to the uppermost 1‐cm sediment depth throughout their lives exhibited shell calcite Δδ13C values not significantly different from foraminifera allowed to free‐roam through the sediment column.
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