Vivianite formation in ferruginous sediments from Lake Towuti, Indonesia

Abstract. Ferruginous lacustrine systems, such as Lake Towuti, Indonesia, are characterized by a specific type of phosphorus cycling in which hydrous ferric iron (oxyhydr)oxides trap and precipitate phosphorus to the sediment, which reduces its bioavailability in the water column and thereby restricts primary production. The oceans were also ferruginous during the Archean, thus understanding the dynamics of phosphorus in modern-day ferruginous analogues may shed light on the marine biogeochemical cycling that dominated much of Earth's history. Here we report the presence of large crystals (>5 mm) and nodules (>5 cm) of vivianite – a ferrous iron phosphate – in sediment cores from Lake Towuti and address the processes of vivianite formation, phosphorus retention by iron and the related mineral transformations during early diagenesis in ferruginous sediments. Core scan imaging, together with analyses of bulk sediment and pore water geochemistry, document a 30 m long interval consisting of sideritic and non-sideritic clayey beds and diatomaceous oozes containing vivianites. High-resolution imaging of vivianite revealed continuous growth of crystals from tabular to rosette habits that eventually form large (up to 7 cm) vivianite nodules in the sediment. Mineral inclusions like millerite and siderite reflect diagenetic mineral formation antecedent to the one of vivianite that is related to microbial reduction of iron and sulfate. Together with the pore water profiles, these data suggest that the precipitation of millerite, siderite and vivianite in soft ferruginous sediments stems from the progressive consumption of dissolved terminal electron acceptors and the typical evolution of pore water geochemistry during diagenesis. Based on solute concentrations and modeled mineral saturation indices, we inferred vivianite formation to initiate around 20 m depth in the sediment. Negative δ56Fe values of vivianite indicated incorporation of kinetically fractionated light Fe2+ into the crystals, likely derived from active reduction and dissolution of ferric oxides and transient ferrous phases during early diagenesis. The size and growth history of the nodules indicate that, after formation, continued growth of vivianite crystals constitutes a sink for P during burial, resulting in long-term P sequestration in ferruginous sediment.

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Vivianite formation in ferruginous sediments from Lake Towuti, Indonesia

10.5194/bg-2019-426 ◽

2019 ◽

Author(s):

Aurèle Vuillemin ◽

André Friese ◽

Richard Wirth ◽

Jan A. Schuessler ◽

Anja M. Schleicher ◽

...

Keyword(s):

Sediment Cores ◽

Iron Phosphate ◽

Microbial Reduction ◽

Water Geochemistry ◽

Continuous Growth ◽

Iron Mineral ◽

Reducing Conditions ◽

Pore Water Geochemistry ◽

Mineral Transformations ◽

Lake Towuti

Abstract. Ferruginous lacustrine systems, such as Lake Towuti, Indonesia, can experience restricted primary production due to phosphorus trapping by hydrous ferric iron (oxyhydr)oxides that reduce P concentrations in the water column. The oceans were also ferruginous during the Archean, so understanding the dynamics of phosphorus in modern-day ferruginous analogues may shed light on the marine biogeochemical cycling that dominated much of Earth's history. Here we report the presence of large crystals (> 5 mm) and nodules (> 5 cm) of vivianite – a ferrous iron phosphate – in sediment cores from Lake Towuti, and address the processes of phosphorus retention and iron mineral transformations during diagenesis in ferruginous sediments. Core scans together with analyses of bulk sediment and pore water geochemistry document a 30 m long interval consisting of beds of sideritic and non-sideritic clays and diatomaceous oozes containing diagenetic vivianites. High-resolution imaging of vivianite revealed continuous growth of crystals from tabular to rosette habits that eventually form large (up to 7 cm) vivianite nodules in the sediment. Mineral inclusions like millerite and siderite reflect antecedent diagenetic mineral formation that is related to microbial reduction of iron and sulfate. This implies the formation and growth of vivianite crystals under reducing conditions during diagenesis. Negative ð56Fe values of vivianite indicated reductive dissolution of ferric oxides as the source of Fe in the vivianites with incorporation of microbially fractionated light Fe2+ into the crystals. The size and growth history of the nodules indicate that, after formation, continued growth of vivianite may constitute a significant sink for P in these sediments.

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Hydraulic control of pore water geochemistry within the oxic-suboxic zone of a permeable sediment

Limnology and Oceanography ◽

10.4319/lo.2000.45.3.0550 ◽

2000 ◽

Vol 45 (3) ◽

pp. 550-557 ◽

Cited By ~ 34

Author(s):

James L. Falter ◽

Francis J. Sansone

Keyword(s):

Pore Water ◽

Hydraulic Control ◽

Water Geochemistry ◽

Permeable Sediment ◽

Pore Water Geochemistry ◽

Suboxic Zone

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Constraining the Age and Evolution of the Tuaheni Landslide Complex, Hikurangi Margin, New Zealand, Using Pore‐Water Geochemistry and Numerical Modeling

Geophysical Research Letters ◽

10.1029/2020gl087243 ◽

2020 ◽

Vol 47 (11) ◽

Author(s):

Min Luo ◽

Marta E. Torres ◽

Sabine Kasten ◽

Joshu J. Mountjoy

Keyword(s):

Numerical Modeling ◽

New Zealand ◽

Pore Water ◽

Water Geochemistry ◽

Pore Water Geochemistry

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Recent Foraminifers and Stable Isotopes Records on a Bathymetric Transect off Portugal (Cruise JC089) and implications for the Palaeoxygenation proxy

10.5194/egusphere-egu2020-7567 ◽

2020 ◽

Author(s):

Maryline Mleneck-Vautravers ◽

David Hodell

Keyword(s):

Stable Isotopes ◽

Pore Water ◽

Bottom Water ◽

Habitat Preferences ◽

Sediment Cores ◽

Geochemical Data ◽

Major Influence ◽

The One ◽

Productive Systems ◽

Iberian Margin

The oceanographic cruise 89 (RRS James Cook) sailed in 2013 off the Iberian margin in support of an IODP proposal centred on IODP Site 1385. JC089 collected a range of hydrographic data and recovered a set of short sediment cores. We focus on 11 of the later, sampling the hydrography of the last c.400 years along a bathymetric gradient (600-4600 m). The stable isotopes (&#948;18O & &#948;13C) for: 8 common benthic foraminifer species with varied habitat preferences, the sediment pore-water and the bottom water above the sites were measured. The geochemical data is compared to various sedimentary and micropalaeontological data. The later comprises abundances of the main benthic foraminifera species >212&#956;m, checking for living position of the endo-fauna in Rose-Bengal stained samples and for the abundances of phytodetritus-loving species E.exigua in the >90&#956;m for all the 0-1cm samples. The study of the planktonic foraminifer assemblages along a gradient stretching 170 km offshore confirms the major influence of the upwelling to the East. Except for the epi-benthic species C.wuellestorfi, which records the bottom water &#948;13C at equilibrium, all other species failed to record the &#948;13C of the (pore) water at the depth of their living-position. We find that G.affinis could record the &#948;13CDIC near equilibrium with the pore-water at a depth of c.-1cm; therefore above its living population peak. This could be explained by vertical migrations through the sediment column at sites where the supply of organic matter is pulsed. The later assumption seems supported by a reverse correlation between high relative abundances of E.exigua and that of the planktonic upwelling indicator species G.bulloides under productivity pulses corresponding to higher &#916;&#948;13C(epi-G.affinis).The &#916;&#948;13C varies from 1.7 to 4.9&#8240; (n=6) across a decreasing but increasingly pulsed surface productivity gradient further away from the coast. Across this range, G.affinis is observed living at increasing depths in the sediment but always peaks in oxic sediments. The absence of G.affinis from water deeper than 3100 meters prevents &#916;&#948;13C estimates at deeper water depths. For 6 of the 11 sites where G.affinis was present C.wuellestorfi occurred only twice. The &#948;13C for H.elegans and C.mundulus adjusted by -1.08 and +0.25&#8240; respectively (this study) were used instead for the shallower sites. Off the Iberian Margin the style of seasonally fluctuating food supply could be the main factor on &#916;&#948;13C. The implication on future and long-ranging IODP-based palaeoclimatic studies is that the &#916;&#948;13C could be used to estimate the type of productivity regime back in time. In the one hand the sites mostly influenced by the main upwelling cell exhibit &#916;&#948;13C < 3&#8240; & correspond to less than 10% of the time spent in an oligotrophic setting below 0.2mg (chla)/m3. In the other hand &#916;&#948;13C >3&#8240; trace offshore rare productive surface filaments in an environment otherwise corresponding to c.90% of the time under oligotrophic surface water. The absence G.affinis (for the range of depths studied) could indicate a record sitting outside either of these productive systems' influence.

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