Preprints
https://doi.org/10.5194/egusphere-2023-2915
https://doi.org/10.5194/egusphere-2023-2915
14 Dec 2023
 | 14 Dec 2023

Loss of nitrogen via anaerobic ammonium oxidation (anammox) in the California current system during the Quaternary

Zoë Rebecca van Kemenade, Zeynep Erdem, Ellen C. Hopmans, Jaap S. Sinninghe Damsté, and Darci Rush

Abstract. The California current system (CCS) hosts one of the largest oxygen minimum zones (OMZs) in the world: the Eastern North Pacific (ENP) OMZ, which is dissociated into a subtropical and tropical region (i.e., the ESTNP and ETNP). In the modern ENP OMZ, bioavailable nitrogen (N) is lost via denitrification and anaerobic ammonium oxidation (anammox). Even so, paleo-reconstructions of N-loss have focused solely on denitrification. Fluctuations in bulk sedimentary δ15N over glacial-interglacial cycles have been interpreted to reflect variations in denitrification rates in response to ETNP OMZ intensity changes. This δ15N signal is thought to be transported northwards to the ESTNP OMZ. Here, we present the first CCS sedimentary record of ladderane lipids, biomarkers for anammox, located within the ESTNP OMZ (32° N; 118° W). Over the last two glacial terminations (~160 cal ka BP), ladderane concentrations were analysed in combination with the index of ladderanes with five cyclobutane moieties (NL5), short-chain (SC) ladderane degradation products, and productivity proxies. This shows that: 1) ladderanes derived from anammox bacteria living within the ESTNP OMZ water column; 2) ladderanes were continuously present, with relatively high concentrations during both glacial- and interglacial-periods, showcasing the ESTNP OMZ must have retained an anoxic core in which N-loss occurred; and 3) anammox abundance appears to have been driven both by OM-remineralization and advection changes, which regulated nutrient and oxygen levels. Our study shows that anammox was an important feature in the CCS and provides a more holistic picture of N-loss dynamics and the development of the ESTNP OMZ over glacial-interglacial cycles. Lastly, ladderanes were also detected in 160–500 cal ka BP sediments (15.7–37.5 mbsf; analysed at a low temporal resolution), highlighting their potential as anammox biomarkers in relatively deeper buried sediments for future studies.

Zoë Rebecca van Kemenade, Zeynep Erdem, Ellen C. Hopmans, Jaap S. Sinninghe Damsté, and Darci Rush

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2915', Anonymous Referee #1, 10 Jan 2024
    • AC1: 'Reply on RC1', Zoe van Kemenade, 01 Feb 2024
  • RC2: 'Comment on egusphere-2023-2915', Anonymous Referee #2, 14 Jan 2024
    • AC2: 'Reply on RC2', Zoe van Kemenade, 01 Feb 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2915', Anonymous Referee #1, 10 Jan 2024
    • AC1: 'Reply on RC1', Zoe van Kemenade, 01 Feb 2024
  • RC2: 'Comment on egusphere-2023-2915', Anonymous Referee #2, 14 Jan 2024
    • AC2: 'Reply on RC2', Zoe van Kemenade, 01 Feb 2024
Zoë Rebecca van Kemenade, Zeynep Erdem, Ellen C. Hopmans, Jaap S. Sinninghe Damsté, and Darci Rush

Data sets

supplementary material 1 Z. R. van Kemenade, Z. Erdem, E. C. Hopmans, J. S. Sinninge Damsté, and D. Rush https://doi.org/10.25850/nioz/7b.b.sg

Zoë Rebecca van Kemenade, Zeynep Erdem, Ellen C. Hopmans, Jaap S. Sinninghe Damsté, and Darci Rush

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Short summary
The California current system (CCS) hosts one of the largest oxygen minimum zones (OMZ) in the world. Here, anaerobic bacteria cause a loss of bioavailable nitrogen (N). This study shows N-loss occurred in the CCS throughout the Quaternary during both glacial and interglacial periods, and was driven by the supply of organic matter and changes in ocean currents. These findings may have important consequences for biogeochemical models of the CCS.