Evidence of Stable Foraminifera Biomineralization during the Last Two Climate Cycles in the Tropical Atlantic Ocean

Abstract

Planktonic foraminiferal biomineralization intensity, reflected by the weight of their shell calcite mass, affects global carbonate deposition and is known to follow climatic cycles by being increased during glacial stages and decreased during interglacial stages. Here, we measure the dissolution state and the mass of the shells of the planktonic foraminifera species Globigerina bulloides from a Tropical Eastern North Atlantic site over the last two glacial–interglacial climatic transitions, and we report no major changes in plankton calcite production with the atmospheric pCO2 variations. We attribute this consistency in foraminifera calcification to the climatic and hydrological stability of the tropical regions. However, we recorded increased shell masses midway through the penultimate deglaciation (Termination II). In order to elucidate the cause of the increased shell weights, we performed δ18O, Mg/Ca, and μCT measurements on the same shells from a number of samples surrounding this event. Compared with the lighter ones, we find that the foraminifera of increased weight are internally contaminated by sediment infilling and that their shell masses respond to local surface seawater density changes.

An Improved Cleaning Protocol for Foraminiferal Calcite from Unconsolidated Core Sediments: HyPerCal—A New Practice for Micropaleontological and Paleoclimatic Proxies

“…Furthermore, it paves the way for its use in modern analytical techniques that require some degree of automatization, such as image recognition software that are unable to recognize a lot of foraminifera images, whose umbilical aperture is not fully cleaned and is infilled with remaining nannofossil ooze [28]. On the other hand, it has proved beneficial for the upcoming practice of microfossil X-ray tomography, since CT image analysis software cannot easily discriminate between contaminated areas and areas referring to the foraminifera tests unless (subjective) manual labor intensive segmentation is employed [24].…”

“…Links to the raw tomographic data are given the Appendix A below. The images were subsequently analyzed in Avizo software, where the test and sedimentary infilled areas were segmented and discriminated as described in Section 3.3 of [24]. Table 1.…”

“…Studies that focus on foraminifera shell weight measurements are particularly vulnerable to the degree of test contamination, due to their foraminous nature, these specimens have the potential to include contaminants (i.e., sedimentary residuals), which can alter or skew the record toward heavier values [24]. Residual clays or nano-ooze in poral spaces and shell surface obstruct the study of test ultrastructure that yield information about the degree of carbonate dissolution [25] or test porosity [26].…”

Climate Change and Marine Geological Dynamics

“…Zarkogiannis et al (2020) [3] report no major changes in plankton calcite production with the atmospheric pCO 2 variations of the Late Quaternary in the tropical Atlantic Ocean. This consistency in foraminifera calcification is attributed to the climatic and hydrological stability of the tropical regions over the geologic time.…”

“…The book Climate Change and Marine Geological Dynamics includes nine contributions [1][2][3][4][5][6][7][8][9] to this Special Issue published during 2020-2021. Overall, the aim of this Special Issue is to collect studies that provide new views on marginal and open marine geological phenomena and processes by using different methodologies and approaches.…”