Preprints
https://doi.org/10.5194/bg-2020-482
https://doi.org/10.5194/bg-2020-482

  03 Feb 2021

03 Feb 2021

Review status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

Toward a global calibration for quantifying past oxygenation in oxygen minimum zones using benthic Foraminifera

Martin Tetard1, Laetitia Licari1, Kazuyo Tachikawa1, Ekaterina Ovsepyan2, and Luc Beaufort1 Martin Tetard et al.
  • 1Aix Marseille Univ, CNRS, IRD, Coll France, INRAE, CEREGE, Aix-en-Provence, France
  • 2Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia

Abstract. Oxygen Minimum Zones (OMZs) are oceanic areas largely depleted in dissolved oxygen, nowadays considered in expansion in the face of global warming. Their ecological and economic consequences are being debated. The investigation of past OMZ conditions allows us to better understand biological and physical mechanisms responsible for their variability with regards to climate change, carbon pump and carbonate system. To investigate the relationship between OMZ expansion and global climate changes during the late Quaternary, quantitative oxygen reconstructions are needed, but are still in their early development. Here, past bottom water oxygenation (BWO) was quantitatively assessed through a new, fast, semi-automated, and taxonfree morphometric analysis of benthic foraminiferal tests, developed and calibrated using Eastern North Pacific (ENP) and the Eastern South Pacific (ESP) OMZs samples. This new approach is based on an average size and circularity index for each sample. This method, as well as two already published micropalaeontological approaches based on benthic foraminiferal assemblages variability and porosity investigation of a single species, were here calibrated based on availability of new data from 23 core tops recovered along an oxygen gradient (from 0.03 to 1.79 mL.L−1) from the ENP, ESP, AS (Arabian Sea) and WNP (Western North Pacific, including its marginal seas) OMZs. Global calibrated transfer functions are thus herein proposed for each of these methods.

These micropalaeontological reconstruction approaches were then applied on a paleorecord from the ENP OMZ to examine the consistency and limits of these methods, as well as the relative influence of bottom and pore waters on these micropalaeontological tools. Both the assemblages and morphometric approaches (that is also ultimately based on the ecological response of the complete assemblage and faunal succession according to BWO) gave similar and consistent past BWO reconstructions, while the porosity approach (based on a single species and its unique response to a mixed signal of bottom and pore waters) shown ambiguous estimations.

Martin Tetard et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2020-482', Anonymous Referee #2, 16 Feb 2021
    • AC1: 'Reply on RC1', Martin Tetard, 17 Mar 2021
  • RC2: 'Comment on bg-2020-482', Anonymous Referee #1, 18 Feb 2021
    • AC2: 'Reply on RC2', Martin Tetard, 17 Mar 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2020-482', Anonymous Referee #2, 16 Feb 2021
    • AC1: 'Reply on RC1', Martin Tetard, 17 Mar 2021
  • RC2: 'Comment on bg-2020-482', Anonymous Referee #1, 18 Feb 2021
    • AC2: 'Reply on RC2', Martin Tetard, 17 Mar 2021

Martin Tetard et al.

Martin Tetard et al.

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Short summary
Oxygen minimum zones are oceanic regions almost devoid of dissolved oxygen, that are currently expanding due to global warming. Investigation of their past behaviour will allow a better understanding of these areas and a better prediction of their future evolution. A new method to estimate past [O2] was developed based on morphometric measurements of benthic foraminifera. This method and two other approaches based on their assemblages and porosity were calibrated using 23 core tops worldwide.
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