Geochemical investigation of gametogenic calcite addition in the planktonic foraminifera Orbulina universa

Abstract

Several species of planktonic foraminifera precipitate a final layer of calcite onto the shell surface immediately prior to gamete release at the end of the foraminifera life cycle. Here, we present the results of carbon-13, oxygen-18 and thermal labeling experiments conducted under high (HL) and low light (LL) regimes that vary symbiont photosynthetic activity. Mean experimental group data show that gametogenic (gam) calcite contributes between 4-17% and 14-20% to final shell mass for high and low light experiments respectively. These data indicate that past studies of gam calcite addition have overestimated the amount of gam calcite on foraminifera shells by~30-55%. Calculations indicate that the mass of gam calcite added to the O. universa shell, 4.2 ± 2.0 μg and 4.0 ± 2.4 μg, is constant in the HL and LL groups respectively. We propose that the production of gam calcite may be the result of the discharge of a relatively constant-volume cytoplasmic pool of either Ca 2+ or alkalinity (carbon pool) that increases the calcite saturation state in the microenvironment adjacent to the foraminifera shell just prior to gamete formation and release. Results from these experiments indicate that the geochemistry of thin-walled O. universa from deep sea sediments is composed of N 80% ontogenetic calcite that was precipitated in the primary, near surface habitat of this species. Published by Elsevier B.V.

Constraining foraminiferal calcification depths in the western Pacific warm pool

“…However, it was also shown that the amount of gametogenic calcite was constant (ca. 4 μg) independent of size (Hamilton et al, 2008). The fact that the foraminifera we analysed often still had their spines or remains thereof indicate that gametonenetic calcite was not present.…”

Morphometric and stable isotopic differentiation of Orbulina universa morphotypes from the Cariaco Basin, Venezuela

“…The sphere is the final chamber addition phase of this species. During gametogenesis, O. universa sheds its spines and adds a thin veneer of calcite that contributes~4-20% to the final shell calcite prior to the release of its gametes (Hamilton et al, 2008). Small and large pores on the final chamber serve as pathways for gas exchange and food and symbiont movement into and out of the cell protoplasm, respectively (Bé et al, 1980;Spero, 1987Spero, , 1988.…”

“…Based on oxygen isotopic compositions of pooled sediment trap shells and depth-stratified plankton tow samples, Deuser et al (1981) concluded that the thinner of the two morphotypes calcified at depths between 25 and 50 m, while the thicker morphotype calcified in deeper water. The thickness variations between the two morphotypes were ultimately attributed to the presence or absence of gametogenic calcite, though later studies suggest that the O. universa morphotypes from these studies may represent different cryptic species (Hamilton et al, 2008). Deuser (1987) also report that the differences between the oxygen isotopic compositions of the thick and thin varieties of O. universa is minimal during periods when the mixed layer is deep and increases rapidly as a more stratified water column is established.…”

Interindividual variability and ontogenetic effects on Mg and Sr incorporation in the planktonic foraminifer Globigerinoides sacculifer

“…Therefore, there is evidence to reject the hypothesis of a daily pH change in the microenvironment being responsible for Mg-and Sr-banding within the chamber walls. Sadekov et al (2005) showed that the high-Mg/Ca bands are found in all but the last chamber; an observation that can be explained by gametogenesis, where a different calcification mechanism is responsible only for the formation of this chamber (Hamilton et al, 2008). This causes the high-Mg/low-Mg band ratio to vary between chambers resulting in slightly different Mg/Ca values among them: the final chamber has a relatively low Mg/Ca value, whereas previous chambers have higher Mg contents (Fig.…”

“…Recently, Hamilton et al (2008) showed that the planktonic foraminifer Orbulina universa, adds a constant amount of calcite, of about 4 lg, to their tests during gametogenesis. When foraminifera add this so-called GAM-calcite deeper in the water column we expect it to be relatively depleted in Mg, because of the lower temperatures.…”