I/Ca ratios in benthic foraminifera from the Peruvian oxygen minimum zone: analytical methodology and evaluation as a proxy for redox conditions

N Glock,V Liebetrau,A Eisenhauer

doi:10.5194/bg-11-7077-2014

Abstract

Abstract. In this study, we explore the correlation of I/Ca ratios in three calcitic and one aragonitic foraminiferal species. I/Ca ratios are evaluated as possible proxies for changes in ambient redox conditions across the Peruvian oxygen minimum zone to the ambient oxygen concentrations in the habitat of the foraminiferal species studied. Cleaning and measurement methods for the determination of I/Ca ratios are tested. All species show a positive trend in their I/Ca ratios as a function of higher oxygen concentrations. The most promising species appears to be Uvigerina striata, which shows a highly statistically significant correlation between I/Ca ratios and bottom water (BW) oxygenation (I/Ca = 0.032(±0.004) × [O2]BW + 0.29(±0.03), R2 = 0.61, F = 75, P < 0.0001). Only for the aragonitic species Hoeglundina elegans is this relationship not significant. The iodine volatility in acidic solutions, the species dependency of I/Ca–[O2]BW correlations, and the individual variability of single tests, need to be accounted for when applying the I/Ca ratio as a proxy for redox conditions.

Highlights

Tropical oxygen minimum zones (OMZs) are the most important regions of low oxygen in the recent ocean, and the nutrient cycling in these regions influences the global ocean
I / Ca ratios are evaluated as possible proxies for changes in ambient redox conditions across the Peruvian oxygen minimum zone to the ambient oxygen concentrations in the habitat of the foraminiferal species studied
Coastal upwelling cells cover only about 0.14 % of the global ocean (Baturin, 1983; Wolf, 2002), in 2007, 15.5 million tons of fish were caught by commercial fisheries in eastern boundary upwelling ecosystems (Fréon et al, 2009), corresponding to ∼ 17 % of the global catches (91.2 million tons; source: FAO FishStat, 2013)

Summary

Introduction

Tropical oxygen minimum zones (OMZs) are the most important regions of low oxygen in the recent ocean, and the nutrient cycling in these regions influences the global ocean. This is important, because model calculations predict that the ocean will progressively lose oxygen over the 200 years (Bopp et al, 2002; Matear and Hirst, 2003; Joos et al, 2003), with adverse consequences for marine life and fisheries. The Peruvian upwelling cell alone contributed about 8 % of global fish catches (7.2 million tons; source: FAO FishStat, 2013). If the oxygen depletion in this area were to expand, habitats currently rich in pelagic fish would be endangered in the future

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