John S. Killingley

Growth histories of strombid snails from Bermuda recorded in their O-18 and C-13 profiles

The isotopic ratios 18O/16O and 13C/12C show an annal periodicity in the strombid snails Strombus gigas and S. costatus from Bermuda. S. gigas appears to have a constant displacement of 0.5‰ from oxygen isotopic equilibrium, whereas S. costatus fractionates the oxygen istopes in accordance with established fractionation relationships. With this tool, the growth in strombid snails during different stage can readily be determined on one and the same snail. A 24.8 cm long S. gigas showed an age of 7, a 19.3 cm long S. costatus of 5, and a 7.8 cm long S. costatus of 2 years. From the annual range in oxygen isotopes, growth restricted to warmer periods of the year is assumed. The abundances of 18O and 13C tend to be positively correlated in adult S. gigas and S. costatus speciments, but were inversely related in a juvenile S. costatus.

Carbon isotopes in organic matter from a benthic alga Halimeda incrassata (Bermuda): Effects of light intensity

Abstract Carbon isotope composition of organic matter from the calcareous benthic alga Halimeda incrassata grown under controlled in situ conditions in Harrington Sound, Bermuda, suggests that isotope fractionation is not necessarily dependent upon temperature but appears to be related to light intensity. Light-related fractionation of carbon isotopes should be taken into account when making paleoclimatic interpretations from δ13C-values of marine organic matter.

Stable isotopes in benthic foraminifera from ontong-java plateau, box cores ERDC 112 and 123

Abstract Detailed oxygen and carbon isotope stratigraphies for two species of benthic foraminifera (Planulina wuellerstorfi; Oridorsalis umbonatus) are compared between two box cores, spanning the period of deglaciation and Holocene. Within-core stratigraphies are quite well correlated, between-core signals less so. Vertical mixing and (possibly) horizontal redeposition processes disturb the signals. Nevertheless, there is a strong suggestion of fluctuations in the ambient bottom-water conditions, fo the entire time span considered.

Stable isotopes in recent larger foraminifera

Abstract Oxygen and carbon isotope analyses have been made on large benthic foraminifera from Bermuda, the Persian Gulf, and the Philippines. The foraminifera belong to the two suborders Rotallina and Miliolina. Life spans range between one season to more than two years. Shells contain information about seasonal temperature ranges and life-history stages, recorded as fluctuations of oxygen and carbon isotopic values within the shell material. Almost all specimens studied showed the expected variations in δ 18O with respect to ambient conditions (water isotopic composition and seasonal temperature fluctuations). The specimens from Bermuda seemed enriched in 18O, whereas all specimens from the Philippines, independent of their taxonomic position, seemed to the depleted in 18O with respect to calcita equilibrium. Specimens from the same species showed about the same level and range of δ 18O values. The miliolid species Marginopora vertebralis, Cyclorbiculina compressa, Archaias angulatus, Peneroplis proteus, and Praesorites orbitolitoides cf. monensis commonly show carbon isotope values up to 2.5‰ lighter than expected equilibrium values independent of sample locality. The rotaliid species Heterostegina depressa, Operculina sp., and Calcarina spengleri show carbon isotope values more than 2‰ lighter than expected equilibrium values, also independent of sample locality. All analyzed miliolid species show a tendency, with age, towards lighter-than-equilibrium δ 13C values. The analyzed rotaliid species showed the reverse, that is, shells tend toward increased δ 13 values with age.

Loggerhead turtle movements reconstructed from 18O and 13C profiles from commensal barnacle shells

Abstract Commensal barnacles, Chelonibia testudinaria, from logger-head turtles have 18O and 13C variations in their calcitic shells that record the environments in which the turtles live. Isotopic profiles from the barnacle shells can thus be interpreted to reconstruct movements of the host turtle between open ocean and brackish-water regimes.

Mode of larval development in some deep-sea gastropods indicated by oxygen-18 values of their carbonate shells

Many prosobranch gastropods in the deep sea have been presumed to have planktotrophic development based on their larval shell morphologies. However, evidence for the pattern of dispersal in the water column for the planktotrophic larvae is scant and controversial. In this paper we analyze stable oxygen isotope composition of larval and adult shells for five planktotrophic and four lecithotrophic deep-sea prosobranchs. Larval and adult shells of the lecithotrophic species have the same δ18O composition, reflecting larval development in an egg capsule on the bottom with little or no dispersal. The planktotrophic species show significant differences in δ18O between larval and adult shells, indicating that larvae migrate vertically to warmer surface waters. Adult-larval differences in two planktotrophic species from several deep-sea basins in the North, Equatorial, and South Atlantic suggest that ontogenic vertical migration is a species-wide phenomenon. Results establish that planktotrophic larvae of some deep-sea prosobranch species undergo development and dispersal in surface waters, and confirm that larval shell morphology correlates with mode of development.