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Helena Filipsson, foto Erik Thor

Helena Filipsson

Professor

Helena Filipsson, foto Erik Thor

Foraminiferal Mn/Ca as Bottom-Water Hypoxia Proxy: An Assessment of Nonionella stella in the Santa Barbara Basin, USA

Author

  • I. Brinkmann
  • S. Ni
  • M. Schweizer
  • V. E. Oldham
  • N. B. Quintana Krupinski
  • K. Medjoubi
  • A. Somogyi
  • M. J. Whitehouse
  • C. M. Hansel
  • C. Barras
  • J. M. Bernhard
  • H. L. Filipsson
Show all

Summary, in English

Hypoxia is of increasing concern in marine areas, calling for a better understanding of mechanisms leading to decreasing dissolved oxygen concentrations ([O2]). Much can be learned about the processes and implications of deoxygenation for marine ecosystems using proxy records from low-oxygen sites, provided proxies, such as the manganese (Mn) to calcium (Ca) ratio in benthic foraminiferal calcite, are available and well calibrated. Here we report a modern geochemical data set from three hypoxic sites within the Santa Barbara Basin (SBB), USA, where we study the response of Mn/Caforam in the benthic foraminifer Nonionella stella to variations in sedimentary redox conditions (Mn, Fe) and bottom-water dissolved [O2]. We combine molecular species identification by small subunit rDNA sequencing with morphological characterization and assign the SBB N. stella used here to a new phylotype (T6). Synchrotron-based scanning X-ray fluorescence (XRF) imaging and Secondary Ion Mass Spectrometry (SIMS) show low Mn incorporation (partition coefficient DMn < 0.05) and limited proxy sensitivity of N. stella, at least within the range of dissolved [O2] (2.7–9.6 μmol/l) and Mnpore-water gradients (2.12–21.59 μmol/l). Notably, even though intra- and interspecimen Mn/Ca variability (33% and 58%, respectively) was only partially controlled by the environment, Mn/Caforam significantly correlated with both pore-water Mn and bottom-water [O2]. However, the prevalent suboxic bottom-water conditions and limited dissolved [O2] range complicate the interpretation of trace-elemental trends. Additional work involving other oxygenation proxies and samples from a wider oxygen gradient should be pursued to further develop foraminiferal Mn/Ca as an indicator for hypoxic conditions.

Department/s

  • Quaternary Sciences
  • Centre for Environmental and Climate Science (CEC)

Publishing year

2021-11

Language

English

Publication/Series

Paleoceanography and Paleoclimatology

Volume

36

Issue

11

Document type

Journal article

Publisher

Wiley-Blackwell

Topic

  • Geology

Keywords

  • benthic foraminifera
  • Deoxygenation
  • micro-analytical techniques
  • Mn
  • Ca
  • proxy calibration

Status

Published

Project

  • Tracing past bottom water oxygenation in the sea: a microanalytical approach to improve calcium carbonate based proxies (TOPICaL)
  • Tracing coastal bottom-water oxygenation: a microanalytical approach to improve calcium carbonate based proxies

ISBN/ISSN/Other

  • ISSN: 2572-4517