scholarly journals A novel device for trace metal‐clean sampling of bottom water and suspended particles at the ocean's lower boundary: The Benthic Trace Profiler

2021 ◽  
Author(s):  
Anna Plass ◽  
Anna‐Kathrin Retschko ◽  
Matthias Türk ◽  
Tim Fischer ◽  
Florian Scholz
Keyword(s):  
Trace Metal ◽  
Bottom Water ◽  
Lower Boundary ◽  
Suspended Particles ◽  
Novel Device

scholarly journals Interaction between hydrocarbon seepage, chemosynthetic communities and bottom water redox at cold seeps of the Makran accretionary prism: insights from habitat-specific pore water sampling and modeling

2011 ◽  
Vol 8 (5) ◽  
pp. 9763-9811 ◽  
Author(s):  
D. Fischer ◽  
H. Sahling ◽  
K. Nöthen ◽  
G. Bohrmann ◽  
M. Zabel ◽  
...  
Keyword(s):  
Hydrogen Sulfide ◽  
Pore Water ◽  
Bottom Water ◽  
Microbial Mats ◽  
Lower Boundary ◽  
Accretionary Prism ◽  
Anaerobic Oxidation Of Methane ◽  
Cold Seeps ◽  
Remotely Operated Vehicle ◽  
Geochemical Environment

Abstract. The interaction between fluid seepage, bottom water redox, and chemosynthetic communities was studied at cold seeps across one of the world's largest oxygen minimum zones (OMZ) located at the Makran convergent continental margin. Push cores were obtained from seeps within and at the lower boundary of the core-OMZ with a remotely operated vehicle. Extracted pore water was analyzed for sulfide and sulfate contents. Depending on oxygen availability, seeps were either colonized by microbial mats or by mats and macrofauna. The latter, including ampharetid polychaetes and vesicomyid clams, occurred in distinct benthic habitats which were arranged in a concentric fashion around gas orifices. At most sites colonized by microbial mats, hydrogen sulfide was exported into the bottom water. Where macrofauna was widely abundant, hydrogen sulfide was consumed within the sediment. Numerical modeling of pore water profiles was performed in order to assess rates of fluid advection and bioirrigation. While the magnitude of upward fluid flow decreased from 11 cm yr−1 to <1 cm yr−1 and the sulfate/methane transition zone (SMTZ) deepened with increasing distance from the central gas orifice, the fluxes of sulfate into the SMTZ did not significantly differ (6.6–9.3 mol m−2 yr−1). Depth-integrated rates of bioirrigation increased from 162 cm yr−1 in central habitats characterized by microbial mats and sparse macrofauna to 348 cm yr−1 in habitats of large and small vesicomyid clams. These results reveal that chemosynthetic macrofauna inhabiting the outer seep habitats at the lower boundary of the OMZ efficiently bioirrigate and thus transport sulfate into the upper 10 to 15 cm of the sediment. In this way bioirrigation compensates for the lower upward flux of methane in outer habitats and stimulates rates of anaerobic oxidation of methane (AOM) with sulfate high enough to provide sulfide for chemosynthesis. Through bioirrigation macrofauna engineer their geochemical environment and fuel upward sulfide flux via AOM. Due to the introduction of oxygenated bottom water into the sediment via bioirrigation the depth of the sulfide sink gradually deepens towards outer habitats. We therefore suggest that – in addition to the oxygen levels in the water column which determine whether macrofaunal communities can develop or not – it is rather the depth of the SMTZ and thus of sulfide production that determines which chemosynthetic communities are able to exploit the sulfide at depth. Moreover, large vesicomyid clams most efficiently expand the sulfate zone in the sediment and cut off smaller or immobile organisms from the sulfide source.

Trace Metal Concentrations in the Anoxic Bottom Water of Framvaren

1984 ◽  
pp. 239-245 ◽  
Author(s):  
David Dyrssen ◽  
Per Hall ◽  
Conny Haraldsson ◽  
Åke Iverfeldt ◽  
Stig Westerlund
Keyword(s):  
Trace Metal ◽  
Bottom Water ◽  
Metal Concentrations

scholarly journals Mg/Ca and Mn/Ca ratios in benthic foraminifera: the potential to reconstruct past variations in temperature and hypoxia in shelf regions

2013 ◽  
Vol 10 (7) ◽  
pp. 5125-5138 ◽  
Author(s):  
J. Groeneveld ◽  
H. L. Filipsson
Keyword(s):  
Dissolved Oxygen ◽  
Trace Metal ◽  
Benthic Foraminifera ◽  
Bottom Water ◽  
Oxygen Depletion ◽  
Open Ocean ◽  
Low Oxygen ◽  
Saturation State ◽  
Bottom Water Temperature ◽  
Fish And Shellfish

Abstract. Shelf and coastal regions are exceptionally important for many countries as they provide the main habitat for many economically important fish and shellfish species. With ongoing climate change and human-induced eutrophication the shelf regions are especially affected, resulting in increased temperatures and stratification as well as oxygen depletion of the bottom waters. In order to be able to predict the magnitude of these changes in the future, it is necessary to study how they varied in the past. Commonly used foraminiferal climate and environmental proxies, e.g., stable isotopes and trace metal/Ca ratios, that are applied in open-ocean settings are not necessarily applicable in shelf regions, either as faunas are significantly different or as conditions can change much faster compared to the open ocean. In this study we explore the use of Mg/Ca as paleothermometer and Mn/Ca as a potential proxy for changing dissolved oxygen conditions in bottom water on the benthic foraminifera Bulimina marginata and Globobulimina turgida. Living specimens were collected from the Skagerrak and the Gullmar Fjord (SW Sweden); the latter is hypoxic for several months a year. As the specimens were alive when collected, we assume it unlikely that any diagenetic coatings have already significantly affected the trace metal/Ca ratios. The Mg/Ca ratios are similar to previously published values but display much larger variation than would be expected from the annual temperature change of less than 2 °C. An additional impact of the difference in the calcite saturation state between the Skagerrak and the Gullmar Fjord could explain the results. Mn/Ca ratios from G. turgida can potentially be related to variations in dissolved oxygen of the habitat where the foraminifera calcify. Samples from the Skagerrak display increased Mn/Ca in specimens that lived deeper in the sediment than those that lived near the surface. G. turgida samples from the low-oxygen Gullmar Fjord showed significantly increased Mn/Ca, being highest when bottom water dissolved oxygen was at a minimum. Our study suggests that trace metal/Ca ratios in benthic foraminifera from shelf regions have the potential to record past variations in bottom water temperature and dissolved oxygen concentrations, but an additional impact of the inorganic carbonate chemistry cannot be excluded.

scholarly journals Sedimentary phosphorus and iron cycling in and below the oxygen minimum zone of the northern Arabian Sea

2012 ◽  
Vol 9 (7) ◽  
pp. 2603-2624 ◽  
Author(s):  
P. Kraal ◽  
C. P. Slomp ◽  
D. C. Reed ◽  
G.-J. Reichart ◽  
S. W. Poulton
Keyword(s):  
Arabian Sea ◽  
Bottom Water ◽  
Surface Sediments ◽  
Lower Boundary ◽  
Oxygen Minimum Zone ◽  
Apatite Formation ◽  
Northern Arabian Sea ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
Burial Efficiency

Abstract. In this study, we investigate phosphorus (P) and iron (Fe) cycling in sediments along a depth transect from within to well below the oxygen minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water and solid-phase analyses show that authigenic formation of calcium phosphate minerals (Ca-P) is largely restricted to where the OMZ intersects the seafloor topography, likely due to higher depositional fluxes of reactive P. Nonetheless, increased ratios of organic carbon to organic P (Corg/Porg) and to total reactive P (Corg/Preactive) in surface sediments indicate that the overall burial efficiency of P relative to Corg decreases under the low bottom water oxygen concentrations (BWO) in the OMZ. The relatively constant Fe/Al ratio in surface sediments along the depth transect suggest that corresponding changes in Fe burial are limited. Sedimentary pyrite contents are low throughout the ~25 cm sediment cores at most stations, as commonly observed in the Arabian Sea OMZ. However, pyrite is an important sink for reactive Fe at one station in the OMZ. A reactive transport model (RTM) was applied to quantitatively investigate P and Fe diagenesis at an intermediate station at the lower boundary of the OMZ (bottom water O2: ~14 μmol L−1). The RTM results contrast with earlier findings in showing that Fe redox cycling can control authigenic apatite formation and P burial in Arabian Sea sediment. In addition, results suggest that a large fraction of the sedimentary Ca-P is not authigenic, but is instead deposited from the water column and buried. Dust is likely a major source of this Ca-P. Inclusion of the unreactive Ca-P pool in the Corg/P ratio leads to an overestimation of the burial efficiency of reactive P relative to Corg along the depth transect. Moreover, the unreactive Ca-P accounts for ~85% of total Ca-P burial. In general, our results reveal large differences in P and Fe chemistry between stations in the OMZ, indicating dynamic sedimentary conditions under these oxygen-depleted waters.

scholarly journals Bottom-water deoxygenation at the Peruvian margin during the last deglaciation recorded by benthic foraminifera

2020 ◽  
Vol 17 (12) ◽  
pp. 3165-3182
Author(s):  
Zeynep Erdem ◽  
Joachim Schönfeld ◽  
Anthony E. Rathburn ◽  
Maria-Elena Pérez ◽  
Jorge Cardich ◽  
...  
Keyword(s):  
Bottom Water ◽  
Sediment Cores ◽  
Lower Boundary ◽  
Climatic Conditions ◽  
Last Deglaciation ◽  
Oxygen Minimum Zones ◽  
Proxy Records ◽  
Water Deoxygenation ◽  
The Last Deglaciation ◽  
Oxygen Minimum

Abstract. Deciphering the dynamics of dissolved oxygen in the mid-depth ocean during the last deglaciation is essential to understand the influence of climate change on modern oxygen minimum zones (OMZs). Many paleo-proxy records from the eastern Pacific Ocean indicate an extension of oxygen-depleted conditions during the deglaciation, but the degree of deoxygenation has not been quantified to date. The Peruvian OMZ, one of the largest OMZs in the world, is a key area to monitor such changes in near-bottom-water oxygenation in relation to changing climatic conditions. Here, we analysed the potential to use the composition of foraminiferal assemblages from the Peruvian OMZ as a quantitative redox proxy. A multiple regression analysis was applied to a joint dataset of living (rose-bengal-stained, fossilizable calcareous species) benthic foraminiferal distributions from the Peruvian continental margin. Bottom-water oxygen concentrations ([O2]BW) during sampling were used as the dependant variable. The correlation was significant (R2=0.82; p<0.05), indicating that the foraminiferal assemblages are rather governed by oxygen availability than by the deposition of particulate organic matter (R2=0.53; p=0.31). We applied the regression formula to three sediment cores from the northern part of the Peruvian OMZ between 3 and 8∘ S and 997 and 1250 m water depth, thereby recording oxygenation changes at the lower boundary of the Peruvian OMZ. Each core displayed a similar trend of decreasing oxygen levels since the Last Glacial Maximum (LGM). The overall [O2]BW change from the LGM and the Holocene was constrained to 30 µmol kg−1 at the lower boundary of the OMZ.

scholarly journals Sedimentary phosphorus and iron cycling in and below the oxygen minimum zone of the northern Arabian Sea

2012 ◽  
Vol 9 (3) ◽  
pp. 3829-3880 ◽  
Author(s):  
P. Kraal ◽  
C. P. Slomp ◽  
D. C. Reed ◽  
G.-J. Reichart ◽  
S. W. Poulton
Keyword(s):  
Arabian Sea ◽  
Bottom Water ◽  
Surface Sediments ◽  
Lower Boundary ◽  
Oxygen Minimum Zone ◽  
Apatite Formation ◽  
Northern Arabian Sea ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
Burial Efficiency

Abstract. In this study, we investigate phosphorus (P) and iron (Fe) cycling in sediments along a depth transect from within to well below the oxygen minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water and solid-phase analyses show that authigenic formation of calcium phosphate minerals (Ca-P) is largely restricted to where the OMZ intersects the seafloor topography, likely due to higher depositional fluxes of reactive P. Nonetheless, increased ratios of organic carbon to organic P (Corg/Porg) and to total reactive P (Corg/Preactive) in surface sediments indicate that the overall burial efficiency of P relative to Corg decreases under the low bottom water oxygen concentrations (BWO) in the OMZ. The relatively constant Fe/Al ratio in surface sediments along the depth transect suggest that corresponding changes in Fe burial are limited. Sedimentary pyrite contents are low throughout the ~25-cm sediment cores at most stations, as commonly observed in the Arabian Sea OMZ. However, pyrite is an important sink for reactive Fe at one station in the OMZ. A reactive transport model (RTM) was applied to quantitatively investigate P and Fe diagenesis at an intermediate station at the lower boundary of the OMZ (bottom water O2: ~14 μ mol l−1). The RTM results contrast with earlier findings in showing that Fe redox cycling can control authigenic apatite formation and P burial in Arabian Sea sediment. In addition, results suggest that a large fraction of the sedimentary Ca-P is not authigenic, but is instead deposited from the water column and buried. Dust is likely a major source of this Ca-P. Inclusion of the unreactive Ca-P pool in the Corg/P ratio leads to an overestimation of the burial efficiency of reactive P relative to Corg along the depth transect. Moreover, the unreactive Ca-P accounts for ~85% of total Ca-P burial. In general, our results reveal large differences in P and Fe chemistry between stations in the OMZ, indicating dynamic sedimentary conditions under these oxygen-depleted waters.

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