Table_1_On the dissolution of sponge silica: Assessing variability and biogeochemical implications.xlsx

The dissolution of the biogenic silica that constitutes the skeletons of silicifying organisms is an important mechanism for regenerating dissolved silicon in the ocean. The silica skeletons deposited to the seafloor after the organisms die keep dissolving until becoming definitively buried. The low dissolution rate of sponge skeletons compared to that of diatom skeletons favors their burial and makes sponges (Phylum Porifera) to function as important silicon sinks in the oceans. However, it remains poorly understood whether the large variety of siliceous skeletons existing in the Porifera involves similar variability in their dissolution rates, which would affect the general conceptualization of these organisms as silicon sinks. Herein we investigated kinetics of silica dissolution for major types of skeletons in the three siliceous lineages of Porifera, following standardized digestion conditions in 1% sodium carbonate with orbital agitation at 85°C. The results are compared with those of a previous study conducted under identical conditions, which considered diatom silica, sponge silica, and lithogenic silica. Unexpectedly, the silica of homoscleromorph sponges dissolved only a bit slower than that of freshly cultured diatoms and as fast as diatom earth. However, the rest of sponge skeletons were far more resistant, although with some differences: the isolated spicules of hexactinellid sponges dissolved slightly faster than when forming frameworks of fused spicules, being hexactinellid frameworks as resistant to dissolution as the silica of demosponges, irrespective of occurring in the form of isolated spicules or frameworks. The experiments also indicated that the complexation of sponge silica with aluminum and with chitin does not increase its resistance to dissolution. Because the rapidly-dissolving homoscleromorph sponges represent less than 1% of extant sponges, the sponge skeletons are still conceptualized as important silicon sinks due to their comparative resistance to dissolution. Yet, the turnover of silica into dissolved silicon will always be faster in environments dominated by hexactinellids with isolated spicules than in environments dominated by other hexactinellids and/or demosponges. We discuss whether the time required for a given silica type to completely dissolve in 1% sodium carbonate could be a predictor of its preservation ratio in marine sediments.</p

Video_1_On the dissolution of sponge silica: Assessing variability and biogeochemical implications.mp4

The dissolution of the biogenic silica that constitutes the skeletons of silicifying organisms is an important mechanism for regenerating dissolved silicon in the ocean. The silica skeletons deposited to the seafloor after the organisms die keep dissolving until becoming definitively buried. The low dissolution rate of sponge skeletons compared to that of diatom skeletons favors their burial and makes sponges (Phylum Porifera) to function as important silicon sinks in the oceans. However, it remains poorly understood whether the large variety of siliceous skeletons existing in the Porifera involves similar variability in their dissolution rates, which would affect the general conceptualization of these organisms as silicon sinks. Herein we investigated kinetics of silica dissolution for major types of skeletons in the three siliceous lineages of Porifera, following standardized digestion conditions in 1% sodium carbonate with orbital agitation at 85°C. The results are compared with those of a previous study conducted under identical conditions, which considered diatom silica, sponge silica, and lithogenic silica. Unexpectedly, the silica of homoscleromorph sponges dissolved only a bit slower than that of freshly cultured diatoms and as fast as diatom earth. However, the rest of sponge skeletons were far more resistant, although with some differences: the isolated spicules of hexactinellid sponges dissolved slightly faster than when forming frameworks of fused spicules, being hexactinellid frameworks as resistant to dissolution as the silica of demosponges, irrespective of occurring in the form of isolated spicules or frameworks. The experiments also indicated that the complexation of sponge silica with aluminum and with chitin does not increase its resistance to dissolution. Because the rapidly-dissolving homoscleromorph sponges represent less than 1% of extant sponges, the sponge skeletons are still conceptualized as important silicon sinks due to their comparative resistance to dissolution. Yet, the turnover of silica into dissolved silicon will always be faster in environments dominated by hexactinellids with isolated spicules than in environments dominated by other hexactinellids and/or demosponges. We discuss whether the time required for a given silica type to completely dissolve in 1% sodium carbonate could be a predictor of its preservation ratio in marine sediments.</p

Table_2_On the dissolution of sponge silica: Assessing variability and biogeochemical implications.xlsx

The dissolution of the biogenic silica that constitutes the skeletons of silicifying organisms is an important mechanism for regenerating dissolved silicon in the ocean. The silica skeletons deposited to the seafloor after the organisms die keep dissolving until becoming definitively buried. The low dissolution rate of sponge skeletons compared to that of diatom skeletons favors their burial and makes sponges (Phylum Porifera) to function as important silicon sinks in the oceans. However, it remains poorly understood whether the large variety of siliceous skeletons existing in the Porifera involves similar variability in their dissolution rates, which would affect the general conceptualization of these organisms as silicon sinks. Herein we investigated kinetics of silica dissolution for major types of skeletons in the three siliceous lineages of Porifera, following standardized digestion conditions in 1% sodium carbonate with orbital agitation at 85°C. The results are compared with those of a previous study conducted under identical conditions, which considered diatom silica, sponge silica, and lithogenic silica. Unexpectedly, the silica of homoscleromorph sponges dissolved only a bit slower than that of freshly cultured diatoms and as fast as diatom earth. However, the rest of sponge skeletons were far more resistant, although with some differences: the isolated spicules of hexactinellid sponges dissolved slightly faster than when forming frameworks of fused spicules, being hexactinellid frameworks as resistant to dissolution as the silica of demosponges, irrespective of occurring in the form of isolated spicules or frameworks. The experiments also indicated that the complexation of sponge silica with aluminum and with chitin does not increase its resistance to dissolution. Because the rapidly-dissolving homoscleromorph sponges represent less than 1% of extant sponges, the sponge skeletons are still conceptualized as important silicon sinks due to their comparative resistance to dissolution. Yet, the turnover of silica into dissolved silicon will always be faster in environments dominated by hexactinellids with isolated spicules than in environments dominated by other hexactinellids and/or demosponges. We discuss whether the time required for a given silica type to completely dissolve in 1% sodium carbonate could be a predictor of its preservation ratio in marine sediments.</p

DataSheet_1_On the dissolution of sponge silica: Assessing variability and biogeochemical implications.docx

The dissolution of the biogenic silica that constitutes the skeletons of silicifying organisms is an important mechanism for regenerating dissolved silicon in the ocean. The silica skeletons deposited to the seafloor after the organisms die keep dissolving until becoming definitively buried. The low dissolution rate of sponge skeletons compared to that of diatom skeletons favors their burial and makes sponges (Phylum Porifera) to function as important silicon sinks in the oceans. However, it remains poorly understood whether the large variety of siliceous skeletons existing in the Porifera involves similar variability in their dissolution rates, which would affect the general conceptualization of these organisms as silicon sinks. Herein we investigated kinetics of silica dissolution for major types of skeletons in the three siliceous lineages of Porifera, following standardized digestion conditions in 1% sodium carbonate with orbital agitation at 85°C. The results are compared with those of a previous study conducted under identical conditions, which considered diatom silica, sponge silica, and lithogenic silica. Unexpectedly, the silica of homoscleromorph sponges dissolved only a bit slower than that of freshly cultured diatoms and as fast as diatom earth. However, the rest of sponge skeletons were far more resistant, although with some differences: the isolated spicules of hexactinellid sponges dissolved slightly faster than when forming frameworks of fused spicules, being hexactinellid frameworks as resistant to dissolution as the silica of demosponges, irrespective of occurring in the form of isolated spicules or frameworks. The experiments also indicated that the complexation of sponge silica with aluminum and with chitin does not increase its resistance to dissolution. Because the rapidly-dissolving homoscleromorph sponges represent less than 1% of extant sponges, the sponge skeletons are still conceptualized as important silicon sinks due to their comparative resistance to dissolution. Yet, the turnover of silica into dissolved silicon will always be faster in environments dominated by hexactinellids with isolated spicules than in environments dominated by other hexactinellids and/or demosponges. We discuss whether the time required for a given silica type to completely dissolve in 1% sodium carbonate could be a predictor of its preservation ratio in marine sediments.</p

DataSheet_1_Revisiting the biogenic silica burial flux determinations: A case study for the East China seas.docx

The Coastal and Continental Margin Zones (CCMZs) contribute to 40% of the total burial flux of biogenic silica (bSi) of the world ocean. However, the accurate determination of the bSi content (bSiO2%) in marine sediments remains a challenge. The alkaline methods commonly used to quantitatively determine bSiO2% can completely digest the amorphous silica of diatoms but are less effective at digesting radiolarians and sponge spicules. In addition, the lithogenic silica (lSi) found in sediments is partly digested during these alkaline extractions, which can bias the accuracy of the determined bSiO2%. This is of importance in CCMZs where the lSi:bSi ratio is high. In this study, we examined sediments collected in the CCMZs of East China seas, an environment of peculiar interest given the large amount of lSi deposited by the Yellow River and the Yangtze River. The results show that alkaline digestions using stronger solutions and pretreatment steps resulted in an overestimate of the bSiO2% due to increased leaching of silica mainly from authigenic silicates and clays, whereas weak digestions underestimated the bSiO2% owing to incomplete digestion of sponge spicules. We found that the use of the Si/Al method accurately corrects for the lSi fraction in marine sediments, and thereby improves the determinations of bSiO2% in the sediments of East China seas CCMZs. Ensuring full digestion of all bSi remains challenging, in particular for sponge spicules, motivating both verifications via microscopy and longer extraction times. To emphasize the influence of these methodological differences, we revised the bSi burial flux in the East China seas and provide a new estimate of 253 (± 286) Gmol-SiO2 yr-1, which is one third of the previous estimates. We discuss the potential contribution from radiolarian and sponges and we propose a new general protocol for the determination of bSi in sediments that minimizes the methodological bias in bSi determination.</p

Table_1_Data quality control considerations in multivariate environmental monitoring: experience of the French coastal network SOMLIT.xls

IntroductionWhile crucial to ensuring the production of accurate and high-quality data—and to avoid erroneous conclusions—data quality control (QC) in environmental monitoring datasets is still poorly documented.MethodsWith a focus on annual inter-laboratory comparison (ILC) exercises performed in the context of the French coastal monitoring SOMLIT network, we share here a pragmatic approach to QC, which allows the calculation of systematic and random errors, measurement uncertainty, and individual performance. After an overview of the different QC actions applied to fulfill requirements for quality and competence, we report equipment, accommodation, design of the ILC exercises, and statistical methodology specially adapted to small environmental networks (Results, Discussion, ConclusionThe examination of the temporal variations (2001–2021) in the repeatability, reproducibility, and trueness of the SOMLIT network over time confirms the essential role of ILC exercises as a tool for the continuous improvement of data quality in environmental monitoring datasets.</p

DataSheet_1_Data quality control considerations in multivariate environmental monitoring: experience of the French coastal network SOMLIT.docx

IntroductionWhile crucial to ensuring the production of accurate and high-quality data—and to avoid erroneous conclusions—data quality control (QC) in environmental monitoring datasets is still poorly documented.MethodsWith a focus on annual inter-laboratory comparison (ILC) exercises performed in the context of the French coastal monitoring SOMLIT network, we share here a pragmatic approach to QC, which allows the calculation of systematic and random errors, measurement uncertainty, and individual performance. After an overview of the different QC actions applied to fulfill requirements for quality and competence, we report equipment, accommodation, design of the ILC exercises, and statistical methodology specially adapted to small environmental networks (Results, Discussion, ConclusionThe examination of the temporal variations (2001–2021) in the repeatability, reproducibility, and trueness of the SOMLIT network over time confirms the essential role of ILC exercises as a tool for the continuous improvement of data quality in environmental monitoring datasets.</p