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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-274
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-274
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Jul 2019

Submitted as: research article | 25 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Small-scale heterogeneity of trace metals including REY in deep-sea sediments and pore waters of the Peru Basin, SE equatorial Pacific

Sophie A. L. Paul1, Matthias Haeckel2, Michael Bau1, Rajina Bajracharya2, and Andrea Koschinsky1 Sophie A. L. Paul et al.
  • 1Department of Physics and Earth Sciences, Jacobs University Bremen, Bremen, 28759, Germany
  • 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, 24148, Germany

Abstract. Due to its remoteness, the deep-sea floor remains an understudied ecosystem of our planet. The patchiness of existing data sets makes it difficult to draw conclusions about processes that apply to a wider area. In our study we show how different settings and processes determine sediment heterogeneity on small spatial scales. We sampled solid phase and pore water from the upper 10 m of an approximately 7.4 × 13 km2 large area in the Peru Basin, south-east equatorial Pacific Ocean, at 4100 m water depth. Samples were analyzed for trace metals including rare earth elements and yttrium (REY) as well as for particulate organic carbon (POC), CaCO3, and nitrate. The analyses revealed a surprisingly high small-scale heterogeneity of the deep-sea sediment composition. While some cores have the typical green layer from Fe(II) in the clay minerals, this layer is missing in other cores, i.e. showing a tan color associated with Fe(III) in the clay minerals. This is due to varying organic carbon contents: nitrate is depleted at 2–3 m depth in cores with higher total organic carbon contents, but is present throughout cores with lower POC contents, thus inhibiting the Fe(III)-to-Fe(II) reduction pathway in organic matter degradation. REY show shale-normalized (SN) patterns similar to seawater with a relative enrichment of heavy REY over light REY, positive LaSN anomaly, negative CeSN anomaly, as well as positive YSN anomaly and correlate with the Fe-rich clay layer and in some cores also with P. We, therefore, propose that Fe-rich clay minerals, such as nontronite, as well as phosphates are the REY-controlling phases in these sediments. Variability is also seen in dissolved Mn and Co concentrations, which might be due to dissolving nodules in the suboxic sediment, as well as in concentration peaks of U, Mo, As, V, and Cu in two cores, which might be related to deposition of different material at lower lying areas.

Sophie A. L. Paul et al.
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Sophie A. L. Paul et al.
Data sets

Trace metal geochemistry from gravity corers of SONNE cruise SO242/1 at the DISCOL area, Peru Basin. S. A. L. Paul and A. Koschinsky https://doi.org/10.1594/PANGAEA.903019

Porewater geochemistry of sediment core SO242/1_38-1_GC 1 M. Haeckel https://doi.org/10.1594/PANGAEA.884953

Porewater geochemistry of sediment core SO242/1_51-1_GC 2 M. Haeckel https://doi.org/10.1594/PANGAEA.884954

Porewater geochemistry of sediment core SO242/1_84-1_GC 3 M. Haeckel https://doi.org/10.1594/PANGAEA.884960

Porewater geochemistry of sediment core SO242/1_89-1_GC 4 M. Haeckel https://doi.org/10.1594/PANGAEA.884961

Porewater geochemistry of sediment core SO242/1_100-1_GC 5 M. Haeckel https://doi.org/10.1594/PANGAEA.884946

Porewater geochemistry of sediment core SO242/1_123-1_GC 6 M. Haeckel https://doi.org/10.1594/PANGAEA.884949

Porewater geochemistry of sediment core SO242/1_132-1_GC 7 M. Haeckel https://doi.org/10.1594/PANGAEA.884951

Particulate geochemistry of sediment core SO242/1_38-1_GC 1 M. Haeckel https://doi.org/10.1594/PANGAEA.884981

Particulate geochemistry of sediment core SO242/1_51-1_GC 2 M. Haeckel https://doi.org/10.1594/PANGAEA.884982

Particulate geochemistry of sediment core SO242/1_84-1_GC 3 M. Haeckel https://doi.org/10.1594/PANGAEA.884988

Particulate geochemistry of sediment core SO242/1_89-1_GC 4 M. Haeckel https://doi.org/10.1594/PANGAEA.884989

Particulate geochemistry of sediment core SO242/1_100-1_GC 5 M. Haeckel https://doi.org/10.1594/PANGAEA.884974

Particulate geochemistry of sediment core SO242/1_123-1_GC 6 M. Haeckel https://doi.org/10.1594/PANGAEA.884977

Particulate geochemistry of sediment core SO242/1_132-1_GC 7 M. Haeckel https://doi.org/10.1594/PANGAEA.884979

Sophie A. L. Paul et al.
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Short summary
We studied the upper 10 m of deep-sea sediments including pore water in the Peru Basin to understand small-scale variability of trace metals. Our results show high spatial variability related to topographical variations which in turn impact organic matter contents, degradation processes, and trace metal cycling. Another interesting finding was the influence of dissolving buried nodules on the surrounding sediment and trace metal cycling.
We studied the upper 10 m of deep-sea sediments including pore water in the Peru Basin to...
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