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

**Stergios D. Zarkogiannis 1,\* , Assimina Antonarakou <sup>1</sup> , Vincent Fernandez <sup>2</sup> , P. Graham Mortyn 3,4 , George Kontakiotis <sup>1</sup> , Hara Drinia <sup>1</sup> and Mervyn Greaves <sup>5</sup>**


Received: 13 August 2020; Accepted: 21 September 2020; Published: 24 September 2020

**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 *p*CO<sup>2</sup> 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 δ <sup>18</sup>O, 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.

**Keywords:** planktonic foraminifera; shell weight; climate variability; sea surface density; carbonate production; X-ray microscopy (µCT); δ <sup>18</sup>O and Mg/Ca analyses
