Molybdenum dynamics in sediments of a seasonally-hypoxic coastal marine basin

Peer reviewe

Із зали засідань Президії НАН України (24 жовт­ня 2012 року)

На черговому засіданні Президії НАН України 24 жовтня 2012 року члени Президії НАН України та запрошені заслухали такі питання: про діяльність Державного агентства з питань науки, інновацій та інформатизації України з удосконалення нормативно-правової бази у сфері наукової, науково-технічної, інноваційної діяльності та інформатизації протягом 2011–2012 рр. (доповідач — голова Агентства академік НАН України В.П. Семиноженко); про наукову та науково-організаційну діяльність Інституту хімії високомолекулярних сполук НАН України (доповідач — академік НАН України Є.В. Лебедєв); сучасні уявлення про механізми тертя (доповідач — доктор фізико-математичних наук О.М. Браун); про нагородження відзнаками НАН України та Почесними грамотами НАН України і Центрального комітету профспілки працівників НАН України (доповідач — академік НАН України В.Ф. Мачулін); кадрові та поточні питання

Imaging element distributions within small marine calcifiers : a NanoSIMS perspective

Climate change is one of the major challenges of our time. Human induced increase in atmospheric carbon dioxide will, without the effort to decrease carbon emissions world-wide, likely lead to a global mean surface temperature rise exceeding 1.5 °C by the end of the 21st century compared to pre-industrial times. In order to mitigate climate change, we rely on model simulations of the Earth System, which are based on observations of past climate. Indirect observations can be made by making use of proxies: chemical or isotopic signatures of old materials we can measure today, of which a relationship with environmental parameters has been established. Many proxies are based on inorganic chemical signatures of fossil shells of marine calcifiers, such as foraminifera and coccolithophores. However, all estimates based on proxies are burdened with uncertainties, not in the least because interactions between multiple environmental factors and biological processes, the so-called vital effects, influence the proxy signal. Understanding of the fundamental controls of biomineralization and thereby the underlying mechanisms of proxies, thus the how and why proxies actually work, is presently of large interest in the scientific community. In this thesis, nano-scale secondary ion mass spectrometry (NanoSIMS) is the analytical technique of choice to investigate the submicron-scale distribution of minor and trace elements in small marine calcifiers. NanoSIMS provides several important advantages over bulk analytical techniques: (1) high spatial resolution, which is sufficient to resolve small samples, such as coccoliths, in considerable detail; (2) high mass resolution, which is sufficient to gain data largely free of isobaric interferences; and (3) the capability to collect data as images, which enables one to selectively choose uncontaminated sample areas for investigation. As this technique is expensive in both time and money, it is used in this thesis not to establish analytical routines to construct proxy records, but rather to investigate, with a sub-micrometer resolution, the distribution of minor and trace elements in marine carbonates to enhance our understanding of paleoceanographic proxies based on coccoliths and foraminiferal calcite. Overall, this thesis emphasizes the importance of micro-scale measurements for gaining insights into the mechanisms involved in marine calcification and the concomitant incorporation of minor and trace elements into marine carbonates. Getting a handle on the underlying mechanisms of calcification improves the reliability of paleoceanographic proxies and will thus potentially help to advance our understanding of the climate system as a whole. Not only were pilot studies conducted whether additional, not yet investigated elements such as Na in coccoliths, or Cl in foraminifera, may potentially serve as new paleo proxies, this thesis also highlights the necessity in scrutinizing analytical procedures with highly-sensitive instruments such as the NanoSIMS

Imaging element distributions within small marine calcifiers: a NanoSIMS perspective

Climate change is one of the major challenges of our time. Human induced increase in atmospheric carbon dioxide will, without the effort to decrease carbon emissions world-wide, likely lead to a global mean surface temperature rise exceeding 1.5 °C by the end of the 21st century compared to pre-industrial times. In order to mitigate climate change, we rely on model simulations of the Earth System, which are based on observations of past climate. Indirect observations can be made by making use of proxies: chemical or isotopic signatures of old materials we can measure today, of which a relationship with environmental parameters has been established. Many proxies are based on inorganic chemical signatures of fossil shells of marine calcifiers, such as foraminifera and coccolithophores. However, all estimates based on proxies are burdened with uncertainties, not in the least because interactions between multiple environmental factors and biological processes, the so-called vital effects, influence the proxy signal. Understanding of the fundamental controls of biomineralization and thereby the underlying mechanisms of proxies, thus the how and why proxies actually work, is presently of large interest in the scientific community. In this thesis, nano-scale secondary ion mass spectrometry (NanoSIMS) is the analytical technique of choice to investigate the submicron-scale distribution of minor and trace elements in small marine calcifiers. NanoSIMS provides several important advantages over bulk analytical techniques: (1) high spatial resolution, which is sufficient to resolve small samples, such as coccoliths, in considerable detail; (2) high mass resolution, which is sufficient to gain data largely free of isobaric interferences; and (3) the capability to collect data as images, which enables one to selectively choose uncontaminated sample areas for investigation. As this technique is expensive in both time and money, it is used in this thesis not to establish analytical routines to construct proxy records, but rather to investigate, with a sub-micrometer resolution, the distribution of minor and trace elements in marine carbonates to enhance our understanding of paleoceanographic proxies based on coccoliths and foraminiferal calcite. Overall, this thesis emphasizes the importance of micro-scale measurements for gaining insights into the mechanisms involved in marine calcification and the concomitant incorporation of minor and trace elements into marine carbonates. Getting a handle on the underlying mechanisms of calcification improves the reliability of paleoceanographic proxies and will thus potentially help to advance our understanding of the climate system as a whole. Not only were pilot studies conducted whether additional, not yet investigated elements such as Na in coccoliths, or Cl in foraminifera, may potentially serve as new paleo proxies, this thesis also highlights the necessity in scrutinizing analytical procedures with highly-sensitive instruments such as the NanoSIMS

Distribution of chlorine and fluorine in benthic foraminifera

Over the last few decades, a suite of inorganic proxies based on foraminiferal calcite have been developed, some of which are now widely used for palaeoenvironmental reconstructions. Studies of foraminiferal shell chemistry have largely focused on cations and oxyanions, while much less is known about the incorporation of anions. The halogens fluoride and chloride are conservative in the ocean, which makes them candidates for reconstructing palaeoceanographic parameters. However, their potential as a palaeoproxy has hardly been explored, and fundamental insight into their incorporation is required. Here we used nanoscale secondary ion mass spectrometry (NanoSIMS) to investigate, for the first time, the distribution of Cl and F within shell walls of four benthic species of foraminifera. In the rotaliid species Ammonia tepida and Amphistegina lessonii, Cl and F were distributed highly heterogeneously within the shell walls, forming bands that were co-located with the bands observed in the distribution of phosphorus (significant positive correlation of both Cl and F with P; <). In the miliolid species Sorites marginalis and Archaias angulatus, the distribution of Cl and F was much more homogeneous without discernible bands. In these species, Cl and P were spatially positively correlated (<), whereas no correlation was observed between Cl and F or between F and P. Additionally, their F content was about an order of magnitude higher than in the rotaliid species. The high variance in the Cl and F content in the studied foraminifera specimens could not be attributed to environmental parameters. Based on these findings, we suggest that Cl and F are predominately associated with organic linings in the rotaliid species. We further propose that Cl may be incorporated as a solid solution of chlorapatite or may be associated with organic molecules in the calcite in the miliolid species. The high F content and the lack of a correlation between Cl and F or P in the miliolid foraminifera suggest a fundamentally different incorporation mechanism. Overall, our data clearly show that the calcification pathway employed by the studied foraminifera governs the incorporation and distribution of Cl, F, P, and other elements in their calcite shells

Distribution of chlorine and fluorine in benthic foraminifera

Over the last few decades, a suite of inorganic proxies based on foraminiferal calcite have been developed, some of which are now widely used for palaeoenvironmental reconstructions. Studies of foraminiferal shell chemistry have largely focused on cations and oxyanions, while much less is known about the incorporation of anions. The halogens fluoride and chloride are conservative in the ocean, which makes them candidates for reconstructing palaeoceanographic parameters. However, their potential as a palaeoproxy has hardly been explored, and fundamental insight into their incorporation is required. Here we used nanoscale secondary ion mass spectrometry (NanoSIMS) to investigate, for the first time, the distribution of Cl and F within shell walls of four benthic species of foraminifera. In the rotaliid species Ammonia tepida and Amphistegina lessonii, Cl and F were distributed highly heterogeneously within the shell walls, forming bands that were co-located with the bands observed in the distribution of phosphorus (significant positive correlation of both Cl and F with P; <). In the miliolid species Sorites marginalis and Archaias angulatus, the distribution of Cl and F was much more homogeneous without discernible bands. In these species, Cl and P were spatially positively correlated (<), whereas no correlation was observed between Cl and F or between F and P. Additionally, their F content was about an order of magnitude higher than in the rotaliid species. The high variance in the Cl and F content in the studied foraminifera specimens could not be attributed to environmental parameters. Based on these findings, we suggest that Cl and F are predominately associated with organic linings in the rotaliid species. We further propose that Cl may be incorporated as a solid solution of chlorapatite or may be associated with organic molecules in the calcite in the miliolid species. The high F content and the lack of a correlation between Cl and F or P in the miliolid foraminifera suggest a fundamentally different incorporation mechanism. Overall, our data clearly show that the calcification pathway employed by the studied foraminifera governs the incorporation and distribution of Cl, F, P, and other elements in their calcite shells.</p

Hydrogen isotope fractionation response to salinity and alkalinity in a calcifying strain of Emiliania huxleyi

Hydrogen isotope ratios of long-chain alkenones (δ2HC37) correlate with water isotope ratios and salinity, albeit with varying degrees of biological fractionation between alkenones and water. These differences in fractionation are the result of environmental and species related effects, which in some cases have consequences for the magnitude of the δ2HC37 response per unit increase in salinity. Earlier culture experiments have focused on constraining hydrogen isotope fractionation factor α in non-calcifying strains of Emiliania huxleyi. Here we studied isotopic fractionation in a calcifying strain of E. huxleyi and show that although absolute fractionation is different, the response to changes in salinity and alkalinity is similar to those of non-calcifying species. This suggests that calcification does not alter the δ2HC37 response to salinity significantly

Distribution of chlorine and fluorine in benthic foraminifera

Over the last few decades, a suite of inorganic proxies based on foraminiferal calcite have been developed, some of which are now widely used for palaeoenvironmental reconstructions. Studies of foraminiferal shell chemistry have largely focused on cations and oxyanions, while much less is known about the incorporation of anions. The halogens fluoride and chloride are conservative in the ocean, which makes them candidates for reconstructing palaeoceanographic parameters. However, their potential as a palaeoproxy has hardly been explored, and fundamental insight into their incorporation is required. Here we used nanoscale secondary ion mass spectrometry (NanoSIMS) to investigate, for the first time, the distribution of Cl and F within shell walls of four benthic species of foraminifera. In the rotaliid species Ammonia tepida and Amphistegina lessonii, Cl and F were distributed highly heterogeneously within the shell walls, forming bands that were co-located with the bands observed in the distribution of phosphorus (significant positive correlation of both Cl and F with P; <). In the miliolid species Sorites marginalis and Archaias angulatus, the distribution of Cl and F was much more homogeneous without discernible bands. In these species, Cl and P were spatially positively correlated (<), whereas no correlation was observed between Cl and F or between F and P. Additionally, their F content was about an order of magnitude higher than in the rotaliid species. The high variance in the Cl and F content in the studied foraminifera specimens could not be attributed to environmental parameters. Based on these findings, we suggest that Cl and F are predominately associated with organic linings in the rotaliid species. We further propose that Cl may be incorporated as a solid solution of chlorapatite or may be associated with organic molecules in the calcite in the miliolid species. The high F content and the lack of a correlation between Cl and F or P in the miliolid foraminifera suggest a fundamentally different incorporation mechanism. Overall, our data clearly show that the calcification pathway employed by the studied foraminifera governs the incorporation and distribution of Cl, F, P, and other elements in their calcite shells