Eubuliminella tenuata as a new proxy for quantifying past bottom water oxygenation

Abstract

In response to modern global warming and climate emergency, large oxygen-depleted oceanic areas, known as Oxygen Minimum Zones (OMZs) have been expanding for the past decades, with negative ecological and economic consequences on food chains, marine ecosystems and resources, biodiversity, and fisheries. The future evolution of these areas and their expansion for the next decades and centuries remain uncertain, and information on their past behaviour during intervals of abrupt climate change (e.g. the last Glacial / Interglacial cycles) is needed to understand the biological and physical mechanisms involved.In this study, a new approach to quantitatively reconstruct past bottom water oxygenation (BWO) was developed, based on the relative abundance of a single benthic foraminiferal species: Eubuliminella exilis (Cushman 1927). A taxonomic review as well as a systematic revision of this taxa, previously assigned to the genus Buliminella Cushman 1911, and synonymised with Eubuliminella exilis (Brady 1884), was also carried out.The method was calibrated using 25 core tops recovered from the Western North Pacific (WNP), the Eastern North Pacific (ENP), the Eastern Equatorial Pacific (EEP), Eastern South Pacific (ESP) and the Arabian Sea (AS) OMZs. It was then applied to five cores from the WNP, and ENP OMZs. Data show a similar and consistent relationship with past [O2] values estimated by using the assemblages method developed in previous studies. We thus propose that the relative abundance of Eubuliminella tenuata (Cushman 1927) could be used as a global proxy for estimating past dissolved oxygenation.