title: Effects of organic matter complexation on partitioning of  first-row transition metals into calcite: cave-analogue crystal growth studies

authors: Lindeman, Ingrid

subjects: Speleothem

abstract: Speleothems are important archives of terrestrial paleoclimate due to their wide geographical coverage and the ability to date their growth layers using U-Th and U-Pb radiometric dating. Extensive research into various speleothem-based geochemical proxies has been undertaken in the last half century, and a significant number of proxies are now used routinely for reconstructions of paleoclimate including stable oxygen and carbon isotopes (known to respond to variations in rainfall and temperature), fluorescence (indicative of the quality and quantity of organic matter present in cave dripwaters) and speleothem minerology (e.g. fabric defects and nano-crystal aggregation). Trace element proxies in speleothems have also garnered attention, but the suite of trace elements used to date has primarily been limited to the alkali earth metals as they exhibit simple partitioning and are characterised by partition coefficients (Kd values) less than 1. Their role in karst systems is thus comparatively well constrained.

In contrast, the first-row transition metals have been the focus of only a few speleothem-based studies, despite recent evidence suggesting some of these metals (namely Co, Ni and Cu) may be useful additions to the current suite of trace element proxies already utilised. Thus, although theoretical distribution coefficient data are available for these metals, their partitioning behaviour into speleothem calcite is not well understood. Theoretical distribution coefficients are useful in understanding partitioning behaviour under certain conditions, but the non-thermodynamic nature of partition coefficients during calcite precipitation in most natural contexts requires partitioning behaviour under speleothem-specific conditions to be established. For instance, despite theoretical distribution coefficients being greater than 1 for Co, Ni and Cu, apparent partition coefficients (Kd app) calculated for these metals in actual speleothem samples are frequently less than 1 due to the dependence of Kd app on a number of factors including calcite precipitation rate, crystal morphology, and complexation reactions between natural organic matter (NOM) and trace ions. Indeed, complexation of first-row transition metals in speleothem-forming dripwaters has been shown to significantly alter the availability of these metals for incorporation into speleothem calcite. This study therefore aimed to investigate the partitioning behaviour of Co, Ni and Cu into calcite precipitated under karst-analogue conditions and in the presence of organic ligands to help establish these metals as viable speleothem-based paleoclimate proxies.

In order to do this, a suitable method for growing calcite under karst-analogue conditions was first established. All experiments were undertaken inside a purpose-built chamber that ensured precise control of temperature, humidity and pCO2, and calcite was grown in a manner analogous to that observed for natural speleothems, with calcite precipitation occurring as a result of CO2 degassing from a thin solution film. Observed growth rates and structural characterisation of the precipitated CaCO3 indicated the method developed was suitable for the desired purpose, and the partitioning data obtained subsequently was considered to be applicable to ‘real-world’ speleothem and cave dripwater samples.

The partitioning behaviour of Co, Ni and Cu into calcite grown under speleothem-like conditions was assessed, and speleothem-specific Kd values of ~ 4, 1 and 44, respectively, were determined. The relatively high inorganic Kd values determined for Co and Cu illustrate the reason why these divalent metals have frequently been overlooked as paleoclimate proxies in speleothems: metals with high partition coefficients are thought to exhibit complex partitioning behaviour and are significantly affected by PCP. However, further experiments carried out with organic ligands present in solution illustrated that the complexation of Co, Ni and Cu by nitrilotriacetic acid (NTA) and Suwanee River fulvic acid (SRFA) significantly altered their partitioning behaviour, with apparent partition coefficients reduced below 1 for all three metals. It was shown that partitioning of Co, Ni and Cu into calcite was controlled not only by their affinity for the calcite lattice (i.e. inorganic Kd values) but also by the dissociation of the metal-ligand complexes, and that the amount of ‘free’ metal available for incorporation into calcite was dependent on residence time and the dissociation constants of the complexes.

The results found in this study highlight the fact that the incorporation of the divalent first-row transition metals into speleothem calcite cannot be considered in terms of simple inorganic partitioning, as the widespread presence of NOM in karst systems will alter their partitioning behaviour significantly. Thus, although the use of these metals as speleothem-based proxies has previously been overlooked in favour of elements such as the alkali earth metals which exhibit simple partitioning (i.e. Kd << 1), in reality the NOM present in karst systems will reduce the effects of PCP on these divalent first-row metals, and they should in fact be considered as useful additions to the current range of paleo-proxies used.

text: Effects of organic matter complexation on partitioning of  first-row transition metals into calcite: cave-analogue crystal growth studies Speleothems are important archives of terrestrial paleoclimate due to their wide geographical coverage and the ability to date their growth layers using U-Th and U-Pb radiometric dating. Extensive research into various speleothem-based geochemical proxies has been undertaken in the last half century, and a significant number of proxies are now used routinely for reconstructions of paleoclimate including stable oxygen and carbon isotopes (known to respond to variations in rainfall and temperature), fluorescence (indicative of the quality and quantity of organic matter present in cave dripwaters) and speleothem minerology (e.g. fabric defects and nano-crystal aggregation). Trace element proxies in speleothems have also garnered attention, but the suite of trace elements used to date has primarily been limited to the alkali earth metals as they exhibit simple partitioning and are characterised by partition coefficients (Kd values) less than 1. Their role in karst systems is thus comparatively well constrained.

In contrast, the first-row transition metals have been the focus of only a few speleothem-based studies, despite recent evidence suggesting some of these metals (namely Co, Ni and Cu) may be useful additions to the current suite of trace element proxies already utilised. Thus, although theoretical distribution coefficient data are available for these metals, their partitioning behaviour into speleothem calcite is not well understood. Theoretical distribution coefficients are useful in understanding partitioning behaviour under certain conditions, but the non-thermodynamic nature of partition coefficients during calcite precipitation in most natural contexts requires partitioning behaviour under speleothem-specific conditions to be established. For instance, despite theoretical distribution coefficients being greater than 1 for Co, Ni and Cu, apparent partition coefficients (Kd app) calculated for these metals in actual speleothem samples are frequently less than 1 due to the dependence of Kd app on a number of factors including calcite precipitation rate, crystal morphology, and complexation reactions between natural organic matter (NOM) and trace ions. Indeed, complexation of first-row transition metals in speleothem-forming dripwaters has been shown to significantly alter the availability of these metals for incorporation into speleothem calcite. This study therefore aimed to investigate the partitioning behaviour of Co, Ni and Cu into calcite precipitated under karst-analogue conditions and in the presence of organic ligands to help establish these metals as viable speleothem-based paleoclimate proxies.

In order to do this, a suitable method for growing calcite under karst-analogue conditions was first established. All experiments were undertaken inside a purpose-built chamber that ensured precise control of temperature, humidity and pCO2, and calcite was grown in a manner analogous to that observed for natural speleothems, with calcite precipitation occurring as a result of CO2 degassing from a thin solution film. Observed growth rates and structural characterisation of the precipitated CaCO3 indicated the method developed was suitable for the desired purpose, and the partitioning data obtained subsequently was considered to be applicable to ‘real-world’ speleothem and cave dripwater samples.

The partitioning behaviour of Co, Ni and Cu into calcite grown under speleothem-like conditions was assessed, and speleothem-specific Kd values of ~ 4, 1 and 44, respectively, were determined. The relatively high inorganic Kd values determined for Co and Cu illustrate the reason why these divalent metals have frequently been overlooked as paleoclimate proxies in speleothems: metals with high partition coefficients are thought to exhibit complex partitioning behaviour and are significantly affected by PCP. However, further experiments carried out with organic ligands present in solution illustrated that the complexation of Co, Ni and Cu by nitrilotriacetic acid (NTA) and Suwanee River fulvic acid (SRFA) significantly altered their partitioning behaviour, with apparent partition coefficients reduced below 1 for all three metals. It was shown that partitioning of Co, Ni and Cu into calcite was controlled not only by their affinity for the calcite lattice (i.e. inorganic Kd values) but also by the dissociation of the metal-ligand complexes, and that the amount of ‘free’ metal available for incorporation into calcite was dependent on residence time and the dissociation constants of the complexes.

The results found in this study highlight the fact that the incorporation of the divalent first-row transition metals into speleothem calcite cannot be considered in terms of simple inorganic partitioning, as the widespread presence of NOM in karst systems will alter their partitioning behaviour significantly. Thus, although the use of these metals as speleothem-based proxies has previously been overlooked in favour of elements such as the alkali earth metals which exhibit simple partitioning (i.e. Kd << 1), in reality the NOM present in karst systems will reduce the effects of PCP on these divalent first-row metals, and they should in fact be considered as useful additions to the current range of paleo-proxies used.

year: 2020

title: A discursive approach to relationship practices in classrooms: An exploratory study

authors: Kecskemeti, Maria

subjects: behaviour management

abstract: In today’s increasingly diverse classrooms it is well accepted that the relationship practices employed by teachers have consequences for the quality of the learning environment. Well chosen relationship practices are thought not only to help teachers to manage their classes but they can contribute to achieving desired educational outcomes. The principles and processes of restorative practice (RP) are seen by many to offer a significant contribution to relationship practices in schools. One of the challenges of realising this potential is to adapt RP for daily classroom use. However, increasing heterogeneity in the student population makes the classroom a complex environment where teachers and students are likely to operate from a range of paradigms of relationship. This study proposes that a discursive conceptualisation of relational identity supports the development of more equitable relationships. It is argued that this then manifests in greater individual and communal well-being. The research involved the development of specific conversational moves adapted from narrative therapy, which were taught to 39 teachers in two schools through a series of four workshops. Following the workshops, a series of seven focus group meetings were held in which teachers engaged in a process of guided deconstructive reflection. The study set out to investigate the contributions of both the conversational moves and the reflective group practices to teachers’ capacity for relationship management (with both students and adults), teaching, and maintaining their own well-being. The focus groups had a triple function of skill practice, reflection and sharing concerns. The group discussions were audio-taped. Examples given by participants of the effects of using the conversational moves were documented. The teachers’ concern narratives were analysed using Foucauldian Discourse Analysis. The study suggests that the use of both discursive conversation practices and deconstructive reflection increased the participants’ capacity for dialogue and tolerating differences. Deconstructive readings of the teachers’ concern narratives identified teacher-student conflicts as a product of multiple positionings and confusion about their respective roles. Deconstructive analysis exposed a range of discourses of care, professionalism, pedagogy and gender as problematic, often placing teachers and students in opposition, and undermining teaching and learning. These findings suggest that systematic deconstructive reflection can usefully inform teachers’ relational strategies in the classroom. It can provide the opportunity for individual teachers to develop an understanding of themselves as teachers, and at the same time it offers useful appreciation of the discursive influences operating in the wider school culture. Some of these discourses deserve critical attention as they are central to the development of teachers’ professional identities. This thesis argues that a discursive approach to relationship practice can support the development of teachers’ capacity to manage the complexities of their work, and as such it is also restorative practice. This critical theoretical approach offers significant potential for explaining how a collaborative relationship paradigm can be understood, practised, and studied.

text: A discursive approach to relationship practices in classrooms: An exploratory study In today’s increasingly diverse classrooms it is well accepted that the relationship practices employed by teachers have consequences for the quality of the learning environment. Well chosen relationship practices are thought not only to help teachers to manage their classes but they can contribute to achieving desired educational outcomes. The principles and processes of restorative practice (RP) are seen by many to offer a significant contribution to relationship practices in schools. One of the challenges of realising this potential is to adapt RP for daily classroom use. However, increasing heterogeneity in the student population makes the classroom a complex environment where teachers and students are likely to operate from a range of paradigms of relationship. This study proposes that a discursive conceptualisation of relational identity supports the development of more equitable relationships. It is argued that this then manifests in greater individual and communal well-being. The research involved the development of specific conversational moves adapted from narrative therapy, which were taught to 39 teachers in two schools through a series of four workshops. Following the workshops, a series of seven focus group meetings were held in which teachers engaged in a process of guided deconstructive reflection. The study set out to investigate the contributions of both the conversational moves and the reflective group practices to teachers’ capacity for relationship management (with both students and adults), teaching, and maintaining their own well-being. The focus groups had a triple function of skill practice, reflection and sharing concerns. The group discussions were audio-taped. Examples given by participants of the effects of using the conversational moves were documented. The teachers’ concern narratives were analysed using Foucauldian Discourse Analysis. The study suggests that the use of both discursive conversation practices and deconstructive reflection increased the participants’ capacity for dialogue and tolerating differences. Deconstructive readings of the teachers’ concern narratives identified teacher-student conflicts as a product of multiple positionings and confusion about their respective roles. Deconstructive analysis exposed a range of discourses of care, professionalism, pedagogy and gender as problematic, often placing teachers and students in opposition, and undermining teaching and learning. These findings suggest that systematic deconstructive reflection can usefully inform teachers’ relational strategies in the classroom. It can provide the opportunity for individual teachers to develop an understanding of themselves as teachers, and at the same time it offers useful appreciation of the discursive influences operating in the wider school culture. Some of these discourses deserve critical attention as they are central to the development of teachers’ professional identities. This thesis argues that a discursive approach to relationship practice can support the development of teachers’ capacity to manage the complexities of their work, and as such it is also restorative practice. This critical theoretical approach offers significant potential for explaining how a collaborative relationship paradigm can be understood, practised, and studied.

year: 2011

title: Outdoor education: Opportunities provided by a place based approach

authors: Brown, Mike

subjects: place-based

abstract: This paper calls for educators to consider the role that ‘place’ has in outdoor education experiences. It is suggested that greater emphasis and acknowledgment be given to ‘place(s)’ and how they may help students make sense of both their personal and communal identity. The paper is interwoven with a narrative from the author’s experiences of working with Pākehā and Māori students on a course that consciously utilised a ‘place-based’ approach to teaching and learning. The paper challenges the conception that outdoor education requires ‘high-impact’ adventurous activities, instead suggesting that we seek to develop a modest pedagogy which acknowledges our relationships with place(s) as a way to understand who we are , how we connect to others and how we both give and take meanings from the places in which we live and learn. These issues have potential implications for educators and programme designers.

text: Outdoor education: Opportunities provided by a place based approach This paper calls for educators to consider the role that ‘place’ has in outdoor education experiences. It is suggested that greater emphasis and acknowledgment be given to ‘place(s)’ and how they may help students make sense of both their personal and communal identity. The paper is interwoven with a narrative from the author’s experiences of working with Pākehā and Māori students on a course that consciously utilised a ‘place-based’ approach to teaching and learning. The paper challenges the conception that outdoor education requires ‘high-impact’ adventurous activities, instead suggesting that we seek to develop a modest pedagogy which acknowledges our relationships with place(s) as a way to understand who we are , how we connect to others and how we both give and take meanings from the places in which we live and learn. These issues have potential implications for educators and programme designers.

year: 2008