title: Stable isotopes of nitrate, sulfate, and carbonate in soils from the Transantarctic Mountains, Antarctica: A record of atmospheric deposition and chemical weathering

authors: Diaz, Melia A.

abstract: Soils in ice-free areas in Antarctica are recognized for their high salt concentrations and persistent arid conditions. While previous studies have investigated the distribution of salts and potential sources in the McMurdo Dry Valleys, logistical constraints have limited our investigation and understanding of salt dynamics within the Transantarctic Mountains. We focused on the Shackleton Glacier (85° S, 176° W), a major outlet glacier of the East Antarctic Ice Sheet located in the Central Transantarctic Mountains (CTAM), and collected surface soil samples from 10 ice-free areas. Concentrations of water-soluble nitrate (NO₃⁻) and sulfate (SO₄²⁻) ranged from <0.2 to ∼150 μmol g⁻¹ and <0.02 to ∼450 μmol g⁻¹, respectively. In general, salt concentrations increased with distance inland and with elevation. However, concentrations also increased with distance from current glacial ice position. To understand the source and formation of these salts, we measured the stable isotopes of dissolved water-soluble NO₃⁻ and SO₄²⁻, and soil carbonate (HCO₃ + CO₃). δ¹⁵N-NO₃ values ranged from −47.8 to 20.4‰ and, while all Δ¹⁷O-NO₃ values are positive, they ranged from 15.7 to 45.9‰. δ³⁴S-SO₄ and δ¹⁸O-SO₄ values ranged from 12.5 and 17.9‰ and −14.5 to −7.1‰, respectively. Total inorganic carbon isotopes in bulk soil samples ranged from 0.2 to 8.5‰ for δ¹³C and −38.8 to −9.6‰ for δ¹⁸O. A simple mixing model indicates that NO3⁻ is primarily derived from the troposphere (0–70%) and stratosphere (30–100%). SO₄²⁻ is primarily derived from secondary atmospheric sulfate (SAS) by the oxidation of reduced sulfur gases and compounds in the atmosphere by H₂O₂, carbonyl sulfide (COS), and ozone. Calcite and perhaps nahcolite (NaHCO₃) are formed through both slow and rapid freezing and/or the evaporation/sublimation of HCO₃ + CO₃-rich fluids. Our results indicate that the origins of salts from ice-free areas within the CTAM represent a complex interplay of atmospheric deposition, chemical weathering, and post-depositional processes related to glacial history and persistent arid conditions. These findings have important implications for the use of these salts in deciphering past climate and atmospheric conditions, biological habitat suitability, glacial history, and can possibly aid in our future collective understanding of salt dynamics on Mars.

text: Stable isotopes of nitrate, sulfate, and carbonate in soils from the Transantarctic Mountains, Antarctica: A record of atmospheric deposition and chemical weathering Soils in ice-free areas in Antarctica are recognized for their high salt concentrations and persistent arid conditions. While previous studies have investigated the distribution of salts and potential sources in the McMurdo Dry Valleys, logistical constraints have limited our investigation and understanding of salt dynamics within the Transantarctic Mountains. We focused on the Shackleton Glacier (85° S, 176° W), a major outlet glacier of the East Antarctic Ice Sheet located in the Central Transantarctic Mountains (CTAM), and collected surface soil samples from 10 ice-free areas. Concentrations of water-soluble nitrate (NO₃⁻) and sulfate (SO₄²⁻) ranged from <0.2 to ∼150 μmol g⁻¹ and <0.02 to ∼450 μmol g⁻¹, respectively. In general, salt concentrations increased with distance inland and with elevation. However, concentrations also increased with distance from current glacial ice position. To understand the source and formation of these salts, we measured the stable isotopes of dissolved water-soluble NO₃⁻ and SO₄²⁻, and soil carbonate (HCO₃ + CO₃). δ¹⁵N-NO₃ values ranged from −47.8 to 20.4‰ and, while all Δ¹⁷O-NO₃ values are positive, they ranged from 15.7 to 45.9‰. δ³⁴S-SO₄ and δ¹⁸O-SO₄ values ranged from 12.5 and 17.9‰ and −14.5 to −7.1‰, respectively. Total inorganic carbon isotopes in bulk soil samples ranged from 0.2 to 8.5‰ for δ¹³C and −38.8 to −9.6‰ for δ¹⁸O. A simple mixing model indicates that NO3⁻ is primarily derived from the troposphere (0–70%) and stratosphere (30–100%). SO₄²⁻ is primarily derived from secondary atmospheric sulfate (SAS) by the oxidation of reduced sulfur gases and compounds in the atmosphere by H₂O₂, carbonyl sulfide (COS), and ozone. Calcite and perhaps nahcolite (NaHCO₃) are formed through both slow and rapid freezing and/or the evaporation/sublimation of HCO₃ + CO₃-rich fluids. Our results indicate that the origins of salts from ice-free areas within the CTAM represent a complex interplay of atmospheric deposition, chemical weathering, and post-depositional processes related to glacial history and persistent arid conditions. These findings have important implications for the use of these salts in deciphering past climate and atmospheric conditions, biological habitat suitability, glacial history, and can possibly aid in our future collective understanding of salt dynamics on Mars.

year: 2020

title: Effects of infaunal bivalve density and flow speed on clearance rates and near-bed hydrodynamics

authors: Jones, Hannah Frances Emily

subjects: annular flume

abstract: The influence of bed density (from 0 to 1000 ind. M⁻²) and flow speed (2, 5, and 15 cm s⁻¹, i.e. “low”, “medium” and “high”, respectively) on clearance rates (CR) of an infaunal suspension-feeding bivalve (Austrovenus stutchburyi) and boundary layer dynamics were investigated in annular flumes. Near-bed flow speeds decreased and bed shear stresses increased with bivalve density due to the bed roughness generated by the shallow burrowers. At low densities (< 500 ind. m⁻²) there was no detectable effect of feeding currents on bed shear stress, but at high densities (1000 ind. m⁻²) and at the low flow speed bed shear stress was almost 80% higher when Austrovenus were feeding (0.0016 N m⁻²), compared to when they were not feeding (0.0009 N m⁻²). These results suggest that bed roughness generated by Austrovenus and their feeding currents are capable of influencing food supply to the bed. Individual CR were significantly (p < 0.01) greater at the high flow speed (0.88 L h⁻¹ ind. ⁻¹), compared to the medium and low flow speeds (0.34 to 0.54 L h− 1 ind.− 1). With increasing bed density, individual CR was significantly (p < 0.001) reduced; at low densities CR ranged from 0.6 to 1.4 L h⁻¹ ind. ⁻¹, but at high densities they were 0.1 to 0.8 L h⁻¹ ind. ⁻¹. Bed CR (L h⁻¹ m− 2) did not scale proportionally with density, initially increasing up to 500 ind. m− 2 but remaining relatively constant thereafter. This was in part due to the negative effect of density on individual CR but also because the proportion of bivalves feeding decreased with increasing density. Our results demonstrate that recording the number of bivalves feeding is necessary to interpret the effect of density on bed CR. Moreover, if the effects of both bivalve density and flow speed are not considered, then scaling up individual CR obtained using animals at low densities will over estimate population filtration capacity. As high (but equivalent to in situ) densities reduced both the number of animals feeding and individual CR other factors may offset this negative interaction, such as protection from wave disturbance or enhanced resuspension of benthic microalgae.

text: Effects of infaunal bivalve density and flow speed on clearance rates and near-bed hydrodynamics The influence of bed density (from 0 to 1000 ind. M⁻²) and flow speed (2, 5, and 15 cm s⁻¹, i.e. “low”, “medium” and “high”, respectively) on clearance rates (CR) of an infaunal suspension-feeding bivalve (Austrovenus stutchburyi) and boundary layer dynamics were investigated in annular flumes. Near-bed flow speeds decreased and bed shear stresses increased with bivalve density due to the bed roughness generated by the shallow burrowers. At low densities (< 500 ind. m⁻²) there was no detectable effect of feeding currents on bed shear stress, but at high densities (1000 ind. m⁻²) and at the low flow speed bed shear stress was almost 80% higher when Austrovenus were feeding (0.0016 N m⁻²), compared to when they were not feeding (0.0009 N m⁻²). These results suggest that bed roughness generated by Austrovenus and their feeding currents are capable of influencing food supply to the bed. Individual CR were significantly (p < 0.01) greater at the high flow speed (0.88 L h⁻¹ ind. ⁻¹), compared to the medium and low flow speeds (0.34 to 0.54 L h− 1 ind.− 1). With increasing bed density, individual CR was significantly (p < 0.001) reduced; at low densities CR ranged from 0.6 to 1.4 L h⁻¹ ind. ⁻¹, but at high densities they were 0.1 to 0.8 L h⁻¹ ind. ⁻¹. Bed CR (L h⁻¹ m− 2) did not scale proportionally with density, initially increasing up to 500 ind. m− 2 but remaining relatively constant thereafter. This was in part due to the negative effect of density on individual CR but also because the proportion of bivalves feeding decreased with increasing density. Our results demonstrate that recording the number of bivalves feeding is necessary to interpret the effect of density on bed CR. Moreover, if the effects of both bivalve density and flow speed are not considered, then scaling up individual CR obtained using animals at low densities will over estimate population filtration capacity. As high (but equivalent to in situ) densities reduced both the number of animals feeding and individual CR other factors may offset this negative interaction, such as protection from wave disturbance or enhanced resuspension of benthic microalgae.

year: 2011

title: Adopting a Maori property rights approach to fisheries

authors: Toki, Valmaine

abstract: For Maori, tikanga Maori or custom law not only underpinned the recognition of property rights to their fishery but also their environmental ethics and the sustainable management of that fishery. In comparison, the property right of non-indigenous peoples was sourced from a rights system determined by the State. The nature of these property rights, for Maori, has been acknowledged by legislation. The challenge for Maori is to effectively maintain, develop and manage this allocated resource in a way that will not only sustain the resource but also ensure its longevity both socially and economically for future generations. Among the issues Maori will face are how to balance effective governance and efficient management, together with the requirement to address global issues of over-fishing and property rights, all the while preserving and respecting tradition. Irrespective of these challenges, it is the tikanga, or philosophy, intrinsic to the traditional Maori worldview which will guide Maori through these challenges, and provide a way forward for global issues such as climate change.

text: Adopting a Maori property rights approach to fisheries For Maori, tikanga Maori or custom law not only underpinned the recognition of property rights to their fishery but also their environmental ethics and the sustainable management of that fishery. In comparison, the property right of non-indigenous peoples was sourced from a rights system determined by the State. The nature of these property rights, for Maori, has been acknowledged by legislation. The challenge for Maori is to effectively maintain, develop and manage this allocated resource in a way that will not only sustain the resource but also ensure its longevity both socially and economically for future generations. Among the issues Maori will face are how to balance effective governance and efficient management, together with the requirement to address global issues of over-fishing and property rights, all the while preserving and respecting tradition. Irrespective of these challenges, it is the tikanga, or philosophy, intrinsic to the traditional Maori worldview which will guide Maori through these challenges, and provide a way forward for global issues such as climate change.

year: 2010