Schönfeld, Joachim, Glock, Nicolaas and Kuhnt, T. (2013) Constraints on benthic foraminiferal proxies for bottom-water oxygenation. [Poster] In: 11. International Conference on Paleoceanography (ICP11) 2013. , 01.-06.09.2013, Sitges - Barcelona, Spain .

Abstract

The distribution of dissolved oxygen in the world oceans mirrors deep circulation commencing where oxygen is exchanged with the atmosphere. Consumption by bacterial decay of organic matter reduces oxygenation of intermediate and deep waters along their pathways. Supply and consumption of oxygen at depth depend on circulation vigour and surface ocean primary productivity, both are sensitive to climate change. Reconstructions of past ocean ventilation from geological archives relied ratios of redox-sensitive elements and biotic indicators. Dissolved oxygen is a predominant environmental factor controlling the abundance and distribution of benthic organisms. In particular benthic foraminifera are sensitive to oxygenation changes but show a mutual response to both, an increase in particulate organic matter flux or a decrease in dissolved oxygen in near-bottom and pore waters. Reconstructions of ancient deep-water oxygen concentrations by using the ratio of species with oxic vs. suboxic or dysoxic environmental preferences showed a sufficient accuracy only at oxygen levels <65 µmol kg-1. Multivariate analyses and transfer functions improved the accuracy and robustness of the benthic foraminiferal proxy against changes in organic matter flux but they are applicable only between 180 and 270 µmol kg-1 and mainly rely on oxyphylic species. Recent approaches focussed on the pore density (PD) in foraminiferal tests, which covaries with the oxygen availability in the ambient seawater ([O2]). Calibrations of PDs versus [O2] for shallow endobenthic Bolivina spissa, B. pacifica, and Fursenkoina mexicana are constrained between 1 to 37, 4 to 130, and 50 to 200 µmol kg-1 repectively. The epibenthic Planulina limbata depicted a higher accuracy though only between 2 and 13 µmol kg-1. For the deep endobenthic Globobulimina turgida exists a calibration between 50 and 200 µmol kg-1, while Chilostomella oolina shows no significant relationship between PD and [O2].

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