Opening the carbon isotope "vital effect" black box, 2, Quantitative model for interpreting foraminiferal carbon isotope data

Abstract

Interpretation of carbon isotope records from late Quaternary planktonic foraminifers are confounded due to the presence of a significant physiological component in the carbon isotopic signal. A quantitative carbon isotope (QC) model is presented which relates the carbon isotopic composition of a foraminiferal shell to the physiological processes of respiration and symbiont photosynthesis and to the /5•3C value of seawater ZCO2. The QC model is calibrated with phySiological and stable isotopic data from laboratory experiments with living planktonic foraminifers. Model simulations of chamber and shell •5•3C values with the symbiont-bearing foraminifers, Orbulina universa and Globigerinoides sacculifer, suggest (1) variations in symbiont density and photosynthetic rate (light level or habitat depth) are the primary physiological parameters controlling intraspecific carbon isotopic variability in these species, (•) respiration has little effect on the /5•C of . universa, and (3) each chamber in a multichambered foraminiferal test will have a distinct value depending on its position in the test whorl. Size:•5•C value relationships reported for G. sacculifer from fossil assemblages can be explained as a function of increasing symbiont density during ontogenetic development. Experimental ecology of the temperate scleractinian coral Astrangia danae, II, Effect of temperature, light intensity, and symbiosis with zooxanthellae, Mar. Biol., 76, 136-148, 1983. JCrgensen, B.B., J. Erez, N.P. Revsbech, and Y.P. Cohen, Symbiotic photosynthesis in the planktonic foraminifera, Globigerinoides sacculifer (Brady), studies with microelectrodes, Limnol. Oxygen and carbon isotopes of individual shells of planktonic foraminifera from Ontong-Java Plateau, equatorial Pacific, Palaeogeogr. Palaeoclimatol. Palaeoecol., 33, 193-204, 1981. Kuile, B., and J. Erez, Uptake of inorganic carbon and internal cycling in symbiont-bearing benthonic foraminifera, Mar. Biol., 94, 499-509, 1987. McConnaughey, T., 13C and 180 isotopic disequilibrium in biological carbonates, II, In vitro simulation of kinetic isotope effects, Geochim. Resource partitioning by reef corals as determined 'from stable isotope composition I. •13C of zooxanthellae and animal tissue vs depth, Mar. Biol., 100, 185-193, 1989. Muthiga, N.A., and A.M. Szmant, The effects of salinity stress on the rates of aerobic respkation and photosynthesis in the hermatypic coral Siderastrea siderea, Biol. Bull., Woods Hole Mass., 173, 539-551. 1987. Nier, A.O., A redetermination of the relative abundances of the isotopes of carbon, nitrogen, oxygen, argon and potassium, Phys. Rev., 77, 789-793, 1950.

Ecological controls on the shell geochemistry of pink and white Globigerinoides ruber in the northern Gulf of Mexico: Implications for paleoceanographic reconstruction

“…Several studies support the idea that increased symbiont photosynthesis leads to enrichment of foraminiferal δ 13 C (Spero and DeNiro, 1987;Spero et al, 1991;Bijma et al, 1998). Symbionts preferentially utilize 12 C during photosynthesis, leaving the carbon pool in the calcification microenvironment enriched with respect to 13 C (Spero and Williams, 1988).…”

A diffusion-reaction model of carbon isotope fractionation in foraminifera

“…there is evidence that photosynthesis is decreasing with increasing pH. Spero et al 1991 w 2y x dark becomes the dominant process. Thus, at high pH the slope of shell d C vs. CO is determined to a 3 large degree by the results of the dark simulation.…”

Warm ocean processes and carbon cycling in the Eocene

“…Many species of near-surface-dwelling planktonic foraminifera have a symbiotic relationship with photosynthesizing algae, mainly dinoflagellates. These algae preferentially remove 12 C during photosynthesis, leaving the remaining seawater isotopically heavy with respect to ambient DIC; such locally elevated δ 13 C values may then be recorded by the foraminifera [26,[67][68][69][70][71][72]. As foraminifera grow to larger sizes, so the cloud of algae surrounding the foraminifer test increases, and the photosynthetic effect is increasingly pronounced in successive size fractions.…”

“…This is reflected in a general decrease in δ 13 C DIC values with depth in the upper part of the water column (figure 1). Potentially, depth-stratified planktonic foraminifera can also record this process of organic matter remineralization as a decrease in the δ 13 C of their test calcite with increased water depth habitat [26]. The actual shape of δ 13 C DIC -depth profiles is highly variable worldwide, but among the main controls on the shape of the profile are the depth and efficiency of remineralization processes in the water column.…”