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

Stergios D Zarkogiannis,Hara Drinia,Assimina Antonarakou,P Graham Mortyn,George Kontakiotis,Mervyn Greaves,Vincent Fernandez

doi:10.3390/jmse8100737

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.

Highlights

Planktonic foraminifera are important marine calcifiers, and the ongoing change in the oceanic carbon system makes it essential to understand the influence of environmental factors on the biomineralization of their shells [1]
The record of G. bulloides shell mass attained from GeoB 8502-2 for the last 200 ky shows no distinct mode of variability (Figure 3a)
Superimposed on this pattern is a broad maximum in shell weight centred on the Marine Isotope Stage (MIS) 5/6 boundary of Termination II (T-II) with a duration of approximately 2300 yr, during which shell masses increase by 30% above average

Summary

Introduction

Planktonic foraminifera are important marine calcifiers, and the ongoing change in the oceanic carbon system makes it essential to understand the influence of environmental factors on the biomineralization of their shells [1]. Because planktonic organisms lack active floatation devices, their only inert way to counterbalance seawater buoyancy changes and remain at certain depths is to modify their shell mass [9]. After assessing the preservation of the foraminifera tests, we report consistent shell weights, and steady foraminiferal calcification, independent of atmospheric pCO2, in agreement with a Pliocene Caribbean record [11]. We attribute this consistency to the stability of the hydrological conditions over time at the tropics, because the tropical environment is strongly associated with the notion of physical and chemical stability [12,13]

Methods

Results

Discussion

Conclusion