A New biological proxy for deep-sea paleo-oxygen: Pores of epifaunal benthic foraminifera

Abstract

The negative consequences of fossil fuel burning for the oceans will likely include warming, acidification and deoxygenation, yet predicting future deoxygenation is difficult. Sensitive proxies for oxygen concentrations in ancient deep-ocean bottom-waters are needed to learn from patterns of marine deoxygenation during global warming conditions in the geological past. Understanding of past oxygenation effects related to climate change will better inform us about future patterns of deoxygenation. Here we describe a new, quantitative biological proxy for determining ocean paleo-oxygen concentrations: the surface area of pores (used for gas exchange) in the tests of deep-sea benthic foraminifera collected alive from 22 locations (water depths: 400 to 4100 m) at oxygen levels ranging from ~ 2 to ~ 277 μmol/l. This new proxy is based on species that are widely distributed geographically, bathymetrically and chronologically, and therefore should have broad applications. Our calibration demonstrates a strong, negative logarithmic correlation between bottom-water oxygen concentrations and pore surface area, indicating that pore surface area of fossil epifaunal benthic foraminifera can be used to reconstruct past changes in deep ocean oxygen and redox levels.

Figure 1

Global map showing site locations. Red dots represent locations where living/recently living individuals of deep-sea benthic foraminifera were collected for this study. The map was produced using Ocean Data View (Schlitzer, R., Ocean Data View, odv.awi.de, 2017).

Figure 2

Images of 3 epifaunal foraminiferal specimens. Image A: SEM photo of Cibicidoides wuellerstorfi collected alive from a site with dissolved bottom water oxygen concentration (BWDO) of 27.7 μmol/L, Southern California Margin. Image B: SEM photo of C. wuellerstorfi collected alive at a BWDO of 200.1 μmol/L, Southeastern Australian Margin. Note the pronounced difference in pore abundance between specimens A and B. Image C: pores highlighted from an SEM image of C. wuellerstorfi (using Adobe Photoshop ©) collected alive at BWDO of 27.2 μmol/L, Southern California Margin. Scale bars are 200 micrometers.

Figure 3

Relation between pore surface area on the penultimate and antepenultimate chambers of eipfaunal foraminifera and dissolved oxygen concentration in of ambient bottom waters. Large dots represent average values of specimens collected alive at each location; smaller dots represent individual values of specimen chambers. Lines with bars represent standard deviations.