Sediment geochemistry PASOM research cruise (2009) - Murray Ridge region, northern Arabian Sea
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2012
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| _version_ | 1867170043866906624 |
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| author | Kraal, Peter Slomp, Caroline P Reed, Dan C Reichart, Gert-Jan Poulton, Simon W |
| author_facet | Kraal, Peter Slomp, Caroline P Reed, Dan C Reichart, Gert-Jan Poulton, Simon W |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | 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). 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. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_830824 |
| institution | PANGAEA |
| language | en |
| publishDate | 2012 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | Sediment geochemistry PASOM research cruise (2009) - Murray Ridge region, northern Arabian Sea Kraal, Peter Slomp, Caroline P Reed, Dan C Reichart, Gert-Jan Poulton, Simon W 64PE301; Ammonium; Arabian Sea; Calcium-Phosphate, authigenic; Carbon, organic, total; Carbon, organic, total, standard deviation; DEPTH, sediment/rock; Elevation of event; Event label; Fluorine; Iron, highly reactive; Iron 2+; Iron in pyrite; Iron oxides; Latitude of event; Longitude of event; MUC; MultiCorer; Oxygen; PASOM; PASOM_01B; PASOM_02; PASOM_04; PASOM_06B; PASOM_10; Pelagia; Phosphate; Phosphorus, inorganic; Phosphorus, iron-bound; Phosphorus, organic; Phosphorus, reactive; Temperature, water 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). 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. |
| title | Sediment geochemistry PASOM research cruise (2009) - Murray Ridge region, northern Arabian Sea |
| topic | 64PE301; Ammonium; Arabian Sea; Calcium-Phosphate, authigenic; Carbon, organic, total; Carbon, organic, total, standard deviation; DEPTH, sediment/rock; Elevation of event; Event label; Fluorine; Iron, highly reactive; Iron 2+; Iron in pyrite; Iron oxides; Latitude of event; Longitude of event; MUC; MultiCorer; Oxygen; PASOM; PASOM_01B; PASOM_02; PASOM_04; PASOM_06B; PASOM_10; Pelagia; Phosphate; Phosphorus, inorganic; Phosphorus, iron-bound; Phosphorus, organic; Phosphorus, reactive; Temperature, water |
| url | https://doi.org/10.1594/PANGAEA.830824 |