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  • 2015-2019  (91)
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  • 1
    Online Resource
    Online Resource
    Biogeochemical cycling of iron and phosphorus under low oxygen conditions (2017)
    Kiel
    Details Availability
    Keywords: Hochschulschrift
    Description / Table of Contents: Benthic release of the key nutrients iron (Fe) and phosphorus (P) is enhanced from sediments that are impinged by oxygen-deficient bottom waters due to its diminished retention capacity for such redox sensitive elements. Suboxic to anoxic and sometimes even euxinic conditions are recently found in open ocean oxygen minimum zones (OMZs, e.g. Eastern Boundary Upwelling Systems) and marginal seas (e.g. the Black Sea and the Baltic Sea). Recent studies showed that OMZs expanded in the last decades and will further spread in the future. Due to the additional release of bioavailable key nutrients from the sediments in such high productivity regions, several feedback mechanisms can evolve. The scenarios range from positive to neutral and negative consequences on the evolution of the ocean’s oxygen levels. This controversial issue makes it crucial to investigate the biogeochemical cycling of Fe and P in OMZs
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource
    URL: http://nbn-resolving.de/urn:nbn:de:gbv:8-diss-212773
    URL: http://d-nb.info/1137509813/34
    URL: http://macau.uni-kiel.de/receive/dissertation_diss_00021277
    URN: urn:nbn:de:gbv:8-diss-212773
    DDC: 550
    Language: English
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  • 2
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    Benthic Dinitrogen Fixation Traversing the Oxygen Minimum Zone Off Mauritania (NW Africa) (2017)
    Frontiers
    In:  Frontiers in Marine Science, 4 (390).
    Details
    Publication Date: 2020-02-06
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3389/fmars.2017.00390
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Benthic phosphorus cycling in the Peruvian oxygen minimum zone (2016)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 13 (5). pp. 1367-1386.
    Details
    Publication Date: 2019-09-23
    Description: Oxygen minimum zones (OMZs) that impinge on continental margins favor the release of phosphorus (P) from the sediments to the water column, enhancing primary productivity and the maintenance or expansion of low-oxygen waters. A comprehensive field program in the Peruvian OMZ was undertaken to identify the sources of benthic P at six stations, including the analysis of particles from the water column, surface sediments, and pore fluids, as well as in situ benthic flux measurements. A major fraction of solid-phase P was bound as particulate inorganic P (PIP) both in the water column and in sediments. Sedimentary PIP increased with depth in the sediment at the expense of particulate organic P (POP). The ratio of particulate organic carbon (POC) to POP exceeded the Redfield ratio both in the water column (202 ± 29) and in surface sediments (303 ± 77). However, the POC to total particulate P (TPP = POP + PIP) ratio was close to Redfield in the water column (103 ± 9) and in sediment samples (102 ± 15). This suggests that the relative burial efficiencies of POC and TPP are similar under low-oxygen conditions and that the sediments underlying the anoxic waters on the Peru margin are not depleted in P compared to Redfield. Benthic fluxes of dissolved P were extremely high (up to 1.04 ± 0.31 mmol m−2 d−1), however, showing that a lack of oxygen promotes the intensified release of dissolved P from sediments, whilst preserving the POC / TPP burial ratio. Benthic dissolved P fluxes were always higher than the TPP rain rate to the seabed, which is proposed to be caused by transient P release by bacterial mats that had stored P during previous periods when bottom waters were less reducing. At one station located at the lower rim of the OMZ, dissolved P was taken up by the sediments, indicating ongoing phosphorite formation. This is further supported by decreasing porewater phosphate concentrations with sediment depth, whereas solid-phase P concentrations were comparatively high.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/bg-13-1367-2016
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Nitrate-dependent iron oxidation limits iron transport in anoxic ocean regions (2016)
    Elsevier
    In:  Earth and Planetary Science Letters, 454 . pp. 272-281.
    Details
    Publication Date: 2019-02-01
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1016/j.epsl.2016.09.025
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    An experimental and modeling investigation of sediment nutrient cycling during further deoxygenation on the Peruvian margin (2018)
    In:  [Poster] In: Ocean Deoxygenation Conference, 03.09.-07.09.2018, Kiel, Germany .
    Details
    Publication Date: 2018-12-04
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 6
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    Organic carbon production, mineralization and preservation on the Peruvian margin (2015)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 12 . pp. 1537-1559.
    Details
    Publication Date: 2019-09-23
    Description: Carbon cycling in Peruvian margin sediments (11° S and 12° S) was examined at 16 stations from 74 m on the inner shelf down to 1024 m water depth by means of in situ flux measurements, sedimentary geochemistry and modeling. Bottom water oxygen was below detection limit down to ca. 400 m and increased to 53 μM at the deepest station. Sediment accumulation rates and benthic dissolved inorganic carbon fluxes decreased rapidly with water depth. Particulate organic carbon (POC) content was lowest on the inner shelf and at the deep oxygenated stations (〈 5%) and highest between 200 and 400 m in the oxygen minimum zone (OMZ, 15–20%). The organic carbon burial efficiency (CBE) was unexpectedly low on the inner shelf (〈 20%) when compared to a global database, for reasons which may be linked to the frequent ventilation of the shelf by oceanographic anomalies. CBE at the deeper oxygenated sites was much higher than expected (max. 81%). Elsewhere, CBEs were mostly above the range expected for sediments underlying normal oxic bottom waters, with an average of 51 and 58% for the 11° S and 12° S transects, respectively. Organic carbon rain rates calculated from the benthic fluxes alluded to a very efficient mineralization of organic matter in the water column, with a Martin curve exponent typical of normal oxic waters (0.88 ± 0.09). Yet, mean POC burial rates were 2–5 times higher than the global average for continental margins. The observations at the Peruvian margin suggest that a lack of oxygen does not affect the degradation of organic matter in the water column but promotes the preservation of organic matter in marine sediments.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/bg-12-1537-2015
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Biological nitrate transport in sediments on the Peruvian margin mitigates benthic sulfide emissions and drives pelagic N loss during stagnation events (2016)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 112 . pp. 123-136.
    Details
    Publication Date: 2019-09-23
    Description: Highlights • Very high rates of dissimilatory nitrate reduction to ammonium by Thioploca. • Non-steady state model predicts Thioploca survival on intracellular nitrate reservoir. • Ammonium release by Thioploca may be coupled to pelagic N loss by anammox. • Thioploca may contribute to anammox long after bottom water nitrate disappearance. • Model indicates that benthic foraminifera account for 90% of benthic N2 production. Abstract Benthic N cycling in the Peruvian oxygen minimum zone (OMZ) was investigated at ten stations along 12oS from the middle shelf (74 m) to the upper slope (1024 m) using in situ flux measurements, sediment biogeochemistry and modelling. Middle shelf sediments were covered by mats of the filamentous bacteria Thioploca spp. and contained a large ‘hidden’ pool of nitrate that was not detectable in the porewater. This was attributed to a biological nitrate reservoir stored within the bacteria to oxidize sulfide to sulfate during ‘dissimilatory nitrate reduction to ammonium’ (DNRA). The extremely high rates of DNRA on the shelf (15.6 mmol m-2 d-1 of N), determined using an empirical steady-state model, could easily supply all the ammonium requirements for anammox in the water column. The model further showed that denitrification by foraminifera may account for 90% of N2 production at the lower edge of the OMZ. At the time of sampling, dissolved oxygen was below detection limit down to 400 m and the water body overlying the shelf had stagnated, resulting in complete depletion of nitrate and nitrite. A decrease in the biological nitrate pool was observed on the shelf during fieldwork concomitant with a rise in porewater sulfide levels in surface sediments to 2 mM. Using a non-steady state model to simulate this natural anoxia experiment, these observations were shown to be consistent with Thioploca surviving on a dwindling intracellular nitrate reservoir to survive the stagnation period. The model shows that sediments hosting Thioploca are able to maintain high ammonium fluxes for many weeks following stagnation, potentially sustaining pelagic N loss by anammox. In contrast, sulfide emissions remain low, reducing the economic risk to the Peruvian fishery by toxic sulfide plume development.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: text
    DOI: 10.1016/j.dsr.2016.02.013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Depletion of oxygen, nitrate and nitrite in the Peruvian oxygen minimum zone cause an imbalance of benthic nitrogen fluxes (2016)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 112 . pp. 113-122.
    Details
    Publication Date: 2019-09-23
    Description: Highlights • Sulphidic event on the shelf resulted in a temporal imbalance of the benthic N cycle. • Bacterial NOx storage is a major source of oxidative power during euxinia. • Peruvian shelf and upper slope sediments are strong recycling sites of fixed N. Abstract Oxygen minimum zones (OMZ) are key regions for fixed nitrogen loss in both the sediments and the water column. During this study, the benthic contribution to N cycling was investigated at ten sites along a depth transect (74–989 m) across the Peruvian OMZ at 12 °S. O2 levels were below detection limit down to ~ 500 m. Benthic fluxes of N2, NO3–, NO2–, NH4+, H2S and O2 were measured using benthic landers. Flux measurements on the shelf were made under extreme geochemical conditions consisting of a lack of O2, NO3– and NO2– in the bottom water and elevated seafloor sulphide release. These particular conditions were associated with a large imbalance in the benthic nitrogen cycle. The sediments on the shelf were densely covered by filamentous sulphur bacteria Thioploca, and were identified as major recycling sites for DIN releasing high amounts of NH4+up to 21.2 mmol m−2 d−1 that were far in excess of NH4+release by ammonification. This difference was attributed to dissimilatory nitrate (or nitrite) reduction to ammonium (DNRA) that was partly being sustained by NO3– stored within the sulphur oxidizing bacteria. Sediments within the core of the OMZ (ca. 200 to 400 m) also displayed an excess flux of N of 3.5 mmol m−2 d−1 mainly as N2. Benthic nitrogen and sulphur cycling in the Peruvian OMZ appears to be particularly susceptible to bottom water fluctuations in O2, NO3−and NO2−, and may accelerate the onset of pelagic euxinia when NO3−and NO2−become depleted.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.dsr.2016.03.001
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Biogeochemical cycling of iron and phosphorus under low oxygen conditions (2017)
    In:  (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, 152 pp
    Details
    Publication Date: 2020-02-06
    Description: Benthic release of the key nutrients iron (Fe) and phosphorus (P) is enhanced from sediments that are impinged by oxygen-deficient bottom waters due to its diminished retention capacity for such redox sensitive elements. Suboxic to anoxic and sometimes even euxinic conditions are recently found in open ocean oxygen minimum zones (OMZs, e.g. Eastern Boundary Upwelling Systems) and marginal seas (e.g. the Black Sea and the Baltic Sea). Recent studies showed that OMZs expanded in the last decades and will further spread in the future. Due to the additional release of bioavailable key nutrients from the sediments in such high productivity regions, several feedback mechanisms can evolve. The scenarios range from positive to neutral and negative consequences on the evolution of the ocean’s oxygen levels. This controversial issue makes it crucial to investigate the biogeochemical cycling of Fe and P in OMZs.
    Type: Thesis , NonPeerReviewed
    Format: text
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    OceanRep: Thesis - not published by a publisher
  • 10
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    Dissolved benthic phosphate, iron and carbon fluxes in the Mauritanian upwelling system and implications for ongoing deoxygenation (2019)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 143 . pp. 70-84.
    Details
    Publication Date: 2022-01-31
    Description: Highlights • next to organic matter degradation, bioirrigation and bottom water percolation through permeable surface sediments enhances benthic TPO43- and Fe2+ release • changes in bottom water oxygenation induce slight changes benthic TPO43- and Fe2+ release rates measured in 2011 and 2014 • deoxygenation experiments imply enhanced TPO43- and Fe2+ release at ongoing deoxygenation in the Mauritanian OMZ Abstract Benthic fluxes of total dissolved phosphate (TPO43-), dissolved iron (Fe2+), and dissolved inorganic carbon (DIC) were determined in situ using benthic chambers at nine stations along a depth transect between 47 and 1108 m water depth at 18 °N off Mauritania (NW Africa) during the upwelling season in 2014 (RV Meteor cruise M107). Bottom water oxygen (O2) concentrations were always ≥ 25 µM, and all fluxes (TPO43-, Fe2+, DIC) were consistently directed from the sediments into the bottom water. The highest benthic TPO43- release of 0.2 ± 0.07 mmol m2 d-1 was found at 47 m water depth (50 µM O2). The highest diffusive Fe2+ flux of 0.03 mmol m2 d-1, determined from porewater Fe2+ concentrations, occurred at 67 m water depth (27 µM O2). This was much lower than the detrital Fe supply as indicated by constant Fe/Al ratios along the depth transect. TPO43- release rates decreased concurrently with DIC flux and water depth. A difference of up to one order of magnitude between benthic chamber and diffusive TPO43- fluxes indicated that the total TPO43- release was strongly enhanced by bioirrigation. The observed fluxes were similar to those measured during an earlier cruise in 2011, generally indicating comparable release rates during both upwelling seasons. Furthermore, ex situ oxygen manipulation experiments showed an increase of the nutrient release (e.g. TPO43-, Fe2+) after seven days of anoxic bottom water conditions. The fluxes were enhanced by a factor of 1.4 for P and 7.3 for Fe compared to the measured release under natural conditions and reached values as high as those measured in the anoxic oxygen minimum zone off Peru. Our observations support the hypothesis that increasing deoxygenation of the oceans will likely enhance sedimentary TPO43- and Fe2+ release and thus contribute to a positive feedback mechanism with increasing nutrient levels and increased ocean productivity.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.dsr.2018.11.008
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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