title: Sulphate partitioning into calcite: Experimental verification of pH control and application to seasonality in speleothems

authors: Wynn, Peter M.

subjects: Science & Technology

abstract: Carbonate-associated sulphate (CAS) is a useful carrier of palaeoenvironmental information throughout the geologic record, particularly through its stable isotope composition. However, a paucity of experimental data restricts quantitative understanding of sulphate incorporation into carbonates, and consequently CAS concentrations and their diagenetic modifications are rarely interpreted. However, in the case of calcite speleothems, the remarkably high-resolution CAS records which are obtainable via modern microanalytical techniques represent a potentially invaluable source of palaeoenvironmental information. Here, we describe the results of controlled experiments of sulphate co-precipitation with calcite in freshwater solutions where pH, saturation state, and sulphate concentration were varied independently of each other. Solution pH is confirmed as the principal control on sulphate incorporation into calcite. The relative efficiency of incorporation was calculated as a partition coefficient Dₛₒ₄=(mSO₄/mCO₃)solid/(mSO₄/mCO₃)solution. High crystal growth rates (driven by either pH or saturation state) encouraged higher values of Dₛₒ₄ because of an increasing concentration of defect sites on crystal surfaces. At low growth rates, Dₛₒ₄ was reduced due to an inferred competition between sulphate and bicarbonate at the calcite surface. These experimental results are applied to understand the incorporation of sulphate into speleothem calcite. The experimentally determined pH-dependence suggests that strong seasonal variations in cave air PCO₂ could account for annual cycles in sulphate concentration observed in stalagmites. Our new experimentally determined values of Dₛₒ₄ were compared with Dₛₒ₄ values calculated from speleothem-drip water monitoring from two caves within the Austrian and Italian Alps. At Obir cave, Austria, Dₛₒ₄ (×10⁵) varies between 11.1 (winter) and 9.0 (summer) and the corresponding figures for Ernesto cave, Italy, are 15.4 (winter) and 14.9 (summer). These values approximate predicted Dₛₒ₄ values based on our chamber experiments containing both low (2 ppm) and high (20 ppm) sulphate concentrations. Our experimental values of Dₛₒ₄ obtained at crystal growth rates typical of stalagmites, closely match those observed in other cave sites from around the world. This validates the universality of the controls behind Dₛₒ₄ and will enhance the use of speleothem CAS as a palaeoenvironmental proxy.

text: Sulphate partitioning into calcite: Experimental verification of pH control and application to seasonality in speleothems Carbonate-associated sulphate (CAS) is a useful carrier of palaeoenvironmental information throughout the geologic record, particularly through its stable isotope composition. However, a paucity of experimental data restricts quantitative understanding of sulphate incorporation into carbonates, and consequently CAS concentrations and their diagenetic modifications are rarely interpreted. However, in the case of calcite speleothems, the remarkably high-resolution CAS records which are obtainable via modern microanalytical techniques represent a potentially invaluable source of palaeoenvironmental information. Here, we describe the results of controlled experiments of sulphate co-precipitation with calcite in freshwater solutions where pH, saturation state, and sulphate concentration were varied independently of each other. Solution pH is confirmed as the principal control on sulphate incorporation into calcite. The relative efficiency of incorporation was calculated as a partition coefficient Dₛₒ₄=(mSO₄/mCO₃)solid/(mSO₄/mCO₃)solution. High crystal growth rates (driven by either pH or saturation state) encouraged higher values of Dₛₒ₄ because of an increasing concentration of defect sites on crystal surfaces. At low growth rates, Dₛₒ₄ was reduced due to an inferred competition between sulphate and bicarbonate at the calcite surface. These experimental results are applied to understand the incorporation of sulphate into speleothem calcite. The experimentally determined pH-dependence suggests that strong seasonal variations in cave air PCO₂ could account for annual cycles in sulphate concentration observed in stalagmites. Our new experimentally determined values of Dₛₒ₄ were compared with Dₛₒ₄ values calculated from speleothem-drip water monitoring from two caves within the Austrian and Italian Alps. At Obir cave, Austria, Dₛₒ₄ (×10⁵) varies between 11.1 (winter) and 9.0 (summer) and the corresponding figures for Ernesto cave, Italy, are 15.4 (winter) and 14.9 (summer). These values approximate predicted Dₛₒ₄ values based on our chamber experiments containing both low (2 ppm) and high (20 ppm) sulphate concentrations. Our experimental values of Dₛₒ₄ obtained at crystal growth rates typical of stalagmites, closely match those observed in other cave sites from around the world. This validates the universality of the controls behind Dₛₒ₄ and will enhance the use of speleothem CAS as a palaeoenvironmental proxy.

year: 2018

title: The effect of AC magnetic  fields on liquid-metal free surfaces in industrialMHD.

authors: Spragg, Kirk John

subjects: MHD

abstract: In this thesis we investigate free-surface instabilities which occur in various
industrial processes involving liquid metal. Specifically, we examine a number
of simple problems with a view to developing a plausible theoretical description
based on MHD. Of particular interest is the behaviour of the free surface of a
pool of liquid metal when it is submitted to an alternating magnetic field.
  The first problem we examine considers the effect of a low-frequency mag-
netic field on a pool of liquid metal. An initially circular pool is deformed into
radially oscillating  starfish  modes at certain critical magnetic field strengths.
We study these azimuthal modes theoretically by investigating the behaviour
of an isolated mode. We also consider the influence of geometry in our studies
of a related problem invloving a rectangular  strip  of liquid metal. At certain
critical magnetic field strengths, an elongated pool is deformed into transverse
modes. Aside from complicated mode coupling, the behaviour of these trans-
verse modes is similar to the  starfish . Both the  starfish  and transverse
modes are caused by a Mathieu-type subharmonic instability.
  We next consider the effect of a medium-frequency magnetic field on an
initially circular pool of liquid metal. Experimentally we study the effect of
a vertical alternating medium-frequency magnetic field on an initially circular
pool. We observe two types of behaviour: slow radial oscillation of the pool
perimeter and rotation of the pool about its centre. The physics of this problem
are significantly more complicated than the  starfish  and  strip  problems.
Accordingly a description in terms of the previous theory is not possible.
  The final problem we consider is the effect of a high-frequency magnetic
field the surface of a conductor. Using a phase-field approach we consider two
simple problems: the first is to calculate the rest shape of an infinite strip
of liquid resting on a substrate in a vertical gravitational field; the second is
to calculate the equilibrium shape of the cross-section of a column of a liquid
conductor submitted to a high-frequency magnetic field whose field lines are
parallel far from the conductor. Our numeric solutions compare well with
previously known analytic solutions.

text: The effect of AC magnetic  fields on liquid-metal free surfaces in industrialMHD. In this thesis we investigate free-surface instabilities which occur in various
industrial processes involving liquid metal. Specifically, we examine a number
of simple problems with a view to developing a plausible theoretical description
based on MHD. Of particular interest is the behaviour of the free surface of a
pool of liquid metal when it is submitted to an alternating magnetic field.
  The first problem we examine considers the effect of a low-frequency mag-
netic field on a pool of liquid metal. An initially circular pool is deformed into
radially oscillating  starfish  modes at certain critical magnetic field strengths.
We study these azimuthal modes theoretically by investigating the behaviour
of an isolated mode. We also consider the influence of geometry in our studies
of a related problem invloving a rectangular  strip  of liquid metal. At certain
critical magnetic field strengths, an elongated pool is deformed into transverse
modes. Aside from complicated mode coupling, the behaviour of these trans-
verse modes is similar to the  starfish . Both the  starfish  and transverse
modes are caused by a Mathieu-type subharmonic instability.
  We next consider the effect of a medium-frequency magnetic field on an
initially circular pool of liquid metal. Experimentally we study the effect of
a vertical alternating medium-frequency magnetic field on an initially circular
pool. We observe two types of behaviour: slow radial oscillation of the pool
perimeter and rotation of the pool about its centre. The physics of this problem
are significantly more complicated than the  starfish  and  strip  problems.
Accordingly a description in terms of the previous theory is not possible.
  The final problem we consider is the effect of a high-frequency magnetic
field the surface of a conductor. Using a phase-field approach we consider two
simple problems: the first is to calculate the rest shape of an infinite strip
of liquid resting on a substrate in a vertical gravitational field; the second is
to calculate the equilibrium shape of the cross-section of a column of a liquid
conductor submitted to a high-frequency magnetic field whose field lines are
parallel far from the conductor. Our numeric solutions compare well with
previously known analytic solutions.

year: 2009

title: An evaluation of Te Rau Puawai workforce 100: Evaluation overview

authors: Nikora, Linda Waimarie

subjects: Maori students

abstract: In July 2001, the Maori & Psychology Research Unit of the University of Waikato was asked to conduct an evaluation of the Te Rau Puawai programme, a joint venture between the former Health Funding Authority and Massey University. The overall goal of the programme is to contribute at least 100 Maori graduates to the Maori mental health workforce within a five year period. The overall aim of the evaluation was to provide the Ministry of Health with a clearer understanding of the programme including: the perceived critical success factors, the barriers if any regarding Te Rau Puawai, the impact of the programme, the extent to which the programme may be transferable, gaps in the programme, and suggested improvements. Through archival search, questionnaire surveys and interviews, evaluative data was collected from major stakeholders in the Te Rau Puawai programme.

text: An evaluation of Te Rau Puawai workforce 100: Evaluation overview In July 2001, the Maori & Psychology Research Unit of the University of Waikato was asked to conduct an evaluation of the Te Rau Puawai programme, a joint venture between the former Health Funding Authority and Massey University. The overall goal of the programme is to contribute at least 100 Maori graduates to the Maori mental health workforce within a five year period. The overall aim of the evaluation was to provide the Ministry of Health with a clearer understanding of the programme including: the perceived critical success factors, the barriers if any regarding Te Rau Puawai, the impact of the programme, the extent to which the programme may be transferable, gaps in the programme, and suggested improvements. Through archival search, questionnaire surveys and interviews, evaluative data was collected from major stakeholders in the Te Rau Puawai programme.

year: 2002-05-01