Environmentally controlled sedimentary microcosms were used to experim
entally determine temperature, salinity, and depth-horizon effects on
delta(13)C(DIC) profiles of dissolved inorganic carbon (DIG) in sedime
nt pore water (PW) and near-bottom water (BW). Simultaneously, benthic
foraminiferal populations of Ammonia beccarii were cultured and assay
ed for calcite delta(13)C to establish how accurately foraminiferal sh
ells recorded BW-PW delta(13)C(DIC). One treatment population was rest
ricted to the 0-1-cm sediment depth; in another treatment, the populat
ion could freely ''roam'' up and down in the sediment microcosm. Pore-
water DIC between the uppermost 0-0.5-cm sediment layer and the overly
ing BW (i.e. 3 cm above the sediment-water interface) showed steep gra
dients of core-top Delta delta(13)C(PW) averaging -3.6+/-1.6 parts per
thousand at 25 degrees C and -2.6+/-0.5 parts per thousand at 20 degr
ees C. Correspondingly, shell calcite delta(13)C for A. beccarii colle
cted from sediment microhabitats recorded a strong PW influence; delta
(13)C shell values averaged 1.1+/-0.8 parts per thousand lighter than
BW delta(13)C(DIC) but 1.6+/-0.6 parts per thousand enriched relative
to average 0-5-mm PW delta(13)C(DIC). Foraminifera restricted to the u
ppermost 1-cm sediment depth throughout their lives exhibited shell ca
lcite Delta delta(13)C values not significantly different from foramin
ifera allowed to free-roam through the sediment column.