Phosphorus cycling in Lake Cadagno, Switzerland: A low sulfate euxinic ocean analogue

Xiong, Yijun; Guilbaud, Romain; Peacock, Caroline L.; Cox, Raymond P.; Canfield, Donald E.; Krom, Michael D.; Poulton, Simon W.

doi:10.1016/j.gca.2019.02.011

Cited by 65 publications

(50 citation statements)

References 126 publications

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“…Anaerobic organic matter remineralisation results in the preferential release of P, giving high C org /P org ratios relative to the Redfield ratio 45 , while reductive dissolution of Fe (oxyhydr)oxide minerals also releases P to solution 46 . The P released by these processes may undergo 'sink switching' to authigenic phases such as carbonate fluorapatite 43 or vivianite 47 , or may be re-adsorbed to Fe (oxyhydr)oxide minerals where they persist 48 . However, dissolved P may also be recycled back to the water column, particularly under anoxic conditions, potentially promoting a positive productivity feedback 41 .…”

Section: Discussionmentioning

confidence: 99%

“…Our redox data suggest limited sulfide production during diagenesis under both oxic and ferruginous conditions (giving very low Fe py /Fe HR ratios; see Supplementary Information). Such conditions would be expected to limit P recycling from the sediment, particularly under oxic conditions (where anaerobic organic matter degradation and the reductive dissolution of Fe (oxyhydr)oxide minerals are restricted), and this can be tested by considering C org /P org and C org /P reac ratios relative to the Redfield ratio 47 . In oxic samples of the Nama Group, C org / P org ratios (Fig.…”

Section: Discussionmentioning

confidence: 99%

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Regional nutrient decrease drove redox stabilisation and metazoan diversification in the late Ediacaran Nama Group, Namibia

Bowyer

Shore

Wood

et al. 2020

Sci Rep

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The late Ediacaran witnessed an increase in metazoan diversity and ecological complexity, marking the inception of the Cambrian Explosion. To constrain the drivers of this diversification, we combine redox and nutrient data for two shelf transects, with an inventory of biotic diversity and distribution from the Nama Group, Namibia (~550 to ~538 Million years ago; Ma). Unstable marine redox conditions characterised all water depths in inner to outer ramp settings from ~550 to 547 Ma, when the first skeletal metazoans appeared. However, a marked deepening of the redoxcline and a reduced frequency of anoxic incursions onto the inner to mid-ramp is recorded from ~547 Ma onwards, with full ventilation of the outer ramp by ~542 Ma. Phosphorus speciation data show that, whilst anoxic ferruginous conditions were initially conducive to the drawdown of bioavailable phosphorus, they also permitted a limited degree of phosphorus recycling back to the water column. A long-term decrease in nutrient delivery from continental weathering, coupled with a possible decrease in upwelling, led to the gradual ventilation of the Nama Group basins. This, in turn, further decreased anoxic recycling of bioavailable phosphorus to the water column, promoting the development of stable oxic conditions and the radiation of new mobile taxa.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Regional nutrient decrease drove redox stabilisation and metazoan diversification in the late Ediacaran Nama Group, Namibia

Bowyer

Shore

Wood

et al. 2020

Sci Rep

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“…may have exerted a strong control on the amount of phosphorus available for organic matter production and burial even in the low sulfate and euxinic paleo-ocean, thus ultimately influencing atmospheric oxygen levels 27 . The mechanism of vivianite formation has recently regained interest due to the importance of iron for the long-term retention of phosphorus under anoxic conditions, especially in modern eutrophized environments [28][29][30] .…”

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confidence: 99%

Rapid pyritization in the presence of a sulfur/sulfate-reducing bacterial consortium

Berg

Duverger

Cordier

et al. 2020

Sci Rep

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Sedimentary pyrite (feS 2) is commonly thought to be a product of microbial sulfate reduction and hence may preserve biosignatures. However, proof that microorganisms are involved in pyrite formation is still lacking as only metastable iron sulfides are usually obtained in laboratory cultures. Here we show the rapid formation of large pyrite spherules through the sulfidation of Fe(III)-phosphate (FP) in the presence of a consortium of sulfur-and sulfate-reducing bacteria (SRB), Desulfovibrio and Sulfurospirillum, enriched from ferruginous and phosphate-rich Lake Pavin water. In biomineralization experiments inoculated with this consortium, pyrite formation occurred within only 3 weeks, likely enhanced by the local enrichment of polysulfides around SRB cells. During this same time frame, abiotic reaction of FP with sulfide led to the formation of vivianite (Fe 3 (po 4) 2 •8H 2 o) and mackinawite (feS) only. our results suggest that rates of pyritization vs. vivianite formation are regulated by SRB activity at the cellular scale, which enhances phosphate release into the aqueous phase by increased efficiency of iron sulfide precipitation, and thus that these microorganisms strongly influence biological productivity and Fe, S and P cycles in the environment. Pyrite (FeS 2) is the main sedimentary sink for sulfur over geological time scales. Because the burial of (di) sulfides leaves behind oxidized products, pyrite burial exerts a major control on the oxidation state of the ocean-atmosphere system 1-3. The ubiquitous occurrence of pyrite in marine and freshwater sediments 4-7 makes it a keystone for the reconstruction of past biogeochemical conditions at the Earth's surface. There are two generally accepted pathways for pyrite formation, both starting from an FeS (e.g. mackinawite) precursor: the polysulfide 8,9 pathway via which zero-valent sulfur acts as an oxidant for FeS producing FeS 2 via the non-obligate intermediate greigite (Fe 3 S 4) 10 , and the H 2 S pathway resulting in the formation of H 2 8,9,11. While sulfur-and sulfate-reducing bacteria (SRB) are the main source of sulfide (H 2 S or HS −) for FeS formation in sediments, their role in the formation of pyrite is still widely debated. Based on isotopic signatures (∂ 56 Fe and ∂ 34 S) in sedimentary pyrites, it has been suggested that pyritization can be driven by a combination of abiotic processes (diagenesis) and microbial Fe and S reduction 12,13. However, pyrite has rarely been obtained in mixed bacterial cultures 14,15 and even more rarely in pure cultures of SRB 16 , which instead promote the formation of metastable Fe sulfides such as amorphous FeS, mackinawite, pyrrhotite or greigite 17-20. These minerals are usually associated with cell walls or extracellular polymeric substances (EPS) produced by bacteria 18,19. A single study of pure cultures of D. desulfuricans 16 reported the formation of pyrite and marcasite from the sulfidation of Fe(III)-oxyhydroxide (goethite) after 3 to 6 months. This suggests that the presence of Fe(III) promotes the ...

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“…However, under ferruginous conditions, bacterial P accumulation 16 and P uptake by iron minerals such as ferrihydrite 17 and green rust 18,19 in the water column may be particularly significant sinks for P. Upon settling, P may be released to pore waters and the water column during anaerobic diagenesis, via partial decomposition of organic matter and the reduction of Fe (oxyhydr)oxides [20][21][22][23] . This process may be compensated by re-adsorption onto Fe minerals at the sediment-water interface 24 , enhancing sedimentary P fixation in association with crystalline Fe oxides 25 or Fe phosphates 19,[26][27][28] . By contrast, phosphorus recycling back to the water column may be particularly intense under euxinic conditions 23,29 , due to the rapid reduction of P-bearing Fe (oxyhydr)oxides by hydrogen sulphide 30,31 , and the preferential release of P from decaying organic matter during sulphate reduction 21,23,29 .…”

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confidence: 99%

“…As a result, C:P ratios commonly surpass the canonical Redfield ratio of 106:1 by several orders of magnitude 21 . However, under all redox scenarios, some, or all, of the recycled phosphorus may be fixed in the sediment via the formation of authigenic phases during 'sink-switching', which involves the transfer of P from its carrier phase to a stable mineral form, such as authigenic apatite 29,32 or Fe phosphates (e.g., vivianite) 19,[26][27][28] .…”

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confidence: 99%

Phosphorus-limited conditions in the early Neoproterozoic ocean maintained low levels of atmospheric oxygen

et al. 2020

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Phosphorus cycling in Lake Cadagno, Switzerland: A low sulfate euxinic ocean analogue

Cited by 65 publications

References 126 publications

Regional nutrient decrease drove redox stabilisation and metazoan diversification in the late Ediacaran Nama Group, Namibia

Regional nutrient decrease drove redox stabilisation and metazoan diversification in the late Ediacaran Nama Group, Namibia

Rapid pyritization in the presence of a sulfur/sulfate-reducing bacterial consortium

Phosphorus-limited conditions in the early Neoproterozoic ocean maintained low levels of atmospheric oxygen

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