title: A Sedimentological and Micropaleontological Study of Quaternary Sections of Cores from the New Zealand Sector of the Southern Ocean

authors: Mackie, Jon

abstract: The Southern Ocean lies between the Subtropical Front (STF) at about 45⁰S latitude and the continental landmass of Antarctica. It plays an important role in global climatic and oceanic circulation patterns, and is responsible for production of most water characteristics below the thermocline. The New Zealand sector of the Southern Ocean (NZSSO) is situated in a unique position to study past changes in oceanic circulation and climate from the record preserved in deep-sea sediment cores. Using piston cores collected from water depths of 461-5100 m by USNS Eltanin during 1968-1972, a sedimentological, micropaleontological, and stable oxygen and carbon isotope study, including some radiocarbon dating, has been conducted on the upper 1 m of sediment in 12 cores spanning a latitudinal transect from 52°S to 61°S south of New Zealand. The transect crosses the modem position of the Subantarctic Front (SAF) at ∼56°S and extends as far as the Antarctic Polar Front (AAPF) at ∼63°S.
The study has shown the NZSSO cores must be viewed as two subgroups. The cores are divided at the SAF into a northern subgroup (north of the SAF) and a southern subgroup (south of the SAF) on the basis of sedimentary lithologies, textures, composition and depositional histories. The northern cores are located in the vicinity of the southern margin of Campbell Plateau and are all highly calcareous ( ∼95% ), being composed of planktic and benthic foraminifera and nannofossils with minimal terrigenous material content. The northern cores include two textural facies controlled by the dominant biogenic sediment. Facies A, a muddy sand, is dominated by the Subantarctic foraminiferal assemblage of Globigerina bulloides, Neogloboquadrina pachyderma (sinstral and dextral), Globigerinita spp., Globorotalia injlata and Globorotalia truncatulinoides. Facies B, a sandy mud, is dominated by calcareous nannofossils, especially Emiliania huxley, Coccolithus spp., and Calcidiscus spp.
The southern subgroup of cores lies in the Southwest Pacific Basin and are dominated by biogenic siliceous material and common (11-27%) terrigenous material. They belong to Facies C, a sandy silt, composed mainly of silt-sized frustules of diatomsand nassellaria radiolaria and terrigenous material (quartz, plagioclase feldspars, biotite and muscovite). Where calcareous material exists south of the SAF it is composed of an Antarctic foraminiferal assemblage involving Neogloboquadrina pachyderma (sinstral),Globigerina bulloides and Globorotalia injlata. All foraminifera of the Antarctic assemblage show evidence of dissolution. The northern subgroup of cores lies in an average water depth of 1200 m, while south of the SAF the average water depth of the cores is 4700 m. The lysocline for the NZSSO is determined at ∼3200-4100 m, with a carbonate compensation depth (CCD) of 4800 m. Any calcareous material south of the SAF is actively being affected by dissolution which biases the sedimentary record of the southern subgroup of cores to dissolution resistant organisms (diatoms and radiolaria) and terrigenous material.
The stable isotope records for the northern NZSSO cores show only a 0.8% shift between inferred glacial and interglacial conditions. Smoothing of the record may be due to bioturbation and/or to extensive sediment reworking by bottom currents, forming rather condensed sedimentary records, especially during glacial periods. Oxygen isotope stages back to stage 5 have been suggested in one core (36-42); this places the Last Glacial-Holocene transition at ∼7 cm, stage 2/3 boundary at ∼21 cm, stage 3/4 boundary at ∼65cm, and a possible stage 4/5 boundary at ∼95 cm downcore. The position of the Last Glacial and stage 2/3 boundary are confirmed by radiometric dates obtained from the same northern core: 19,120 +/- 110 yrs BP at 10 cm downcore and 23,900 yrs +/- 200 yrs BP at 20 cm downcore. Faunal changes in the benthic foraminifera occur near the glacialinterglacial transitions from Globocassidulina subglobosa-dominated during glacial periods to common Epistominella exigua during interglacials. Textural facies also show changes near these transitions, with Facies A characterising glacial periods and Facies B during interglacial periods. Associated with changes in texture are colour changes which allow the correlation of the glacial-interglacial transitions across many of the northern cores. The Last Glacial situation cannot be determined uniquely for the southern subgroup of cores as they have, to varying degrees, experienced extensive erosion and reworking during the Late Quaternary or earlier.
Collectively, the data suggest there has not been significant change in oceanic paleoenvironmental conditions north of the SAF, immediately south of New Zealand, between glacial and interglacial periods. This could be because the topographic high marking the southern edge of the Campbell Plateau has essentially fixed the SAF, irrespective of oceanic climatic conditions. The topographic lock would be further enhanced by sea level drops of ∼120 m during glacial periods. In contrast, east and west of New Zealand in open water conditions evidence from other studies indicates major northward shifts in the position of both the SAF and the AAPF. The limited variation downcore in the abundances of sinistrally coiled Neogloboquadrina pachydenna, the small shifts in the stable oxygen isotope record, and the lack of change in faunal assemblages together suggest that ranges in the sea surface temperature change between glacial and interglacial periods at higher latitudes were probably not so severe as at intermediate latitudes. Due to the relatively small temperature changes between glacial and interglacial conditions at higher latitudes the faunal and isotopic indicators may only record extreme events.

text: A Sedimentological and Micropaleontological Study of Quaternary Sections of Cores from the New Zealand Sector of the Southern Ocean The Southern Ocean lies between the Subtropical Front (STF) at about 45⁰S latitude and the continental landmass of Antarctica. It plays an important role in global climatic and oceanic circulation patterns, and is responsible for production of most water characteristics below the thermocline. The New Zealand sector of the Southern Ocean (NZSSO) is situated in a unique position to study past changes in oceanic circulation and climate from the record preserved in deep-sea sediment cores. Using piston cores collected from water depths of 461-5100 m by USNS Eltanin during 1968-1972, a sedimentological, micropaleontological, and stable oxygen and carbon isotope study, including some radiocarbon dating, has been conducted on the upper 1 m of sediment in 12 cores spanning a latitudinal transect from 52°S to 61°S south of New Zealand. The transect crosses the modem position of the Subantarctic Front (SAF) at ∼56°S and extends as far as the Antarctic Polar Front (AAPF) at ∼63°S.
The study has shown the NZSSO cores must be viewed as two subgroups. The cores are divided at the SAF into a northern subgroup (north of the SAF) and a southern subgroup (south of the SAF) on the basis of sedimentary lithologies, textures, composition and depositional histories. The northern cores are located in the vicinity of the southern margin of Campbell Plateau and are all highly calcareous ( ∼95% ), being composed of planktic and benthic foraminifera and nannofossils with minimal terrigenous material content. The northern cores include two textural facies controlled by the dominant biogenic sediment. Facies A, a muddy sand, is dominated by the Subantarctic foraminiferal assemblage of Globigerina bulloides, Neogloboquadrina pachyderma (sinstral and dextral), Globigerinita spp., Globorotalia injlata and Globorotalia truncatulinoides. Facies B, a sandy mud, is dominated by calcareous nannofossils, especially Emiliania huxley, Coccolithus spp., and Calcidiscus spp.
The southern subgroup of cores lies in the Southwest Pacific Basin and are dominated by biogenic siliceous material and common (11-27%) terrigenous material. They belong to Facies C, a sandy silt, composed mainly of silt-sized frustules of diatomsand nassellaria radiolaria and terrigenous material (quartz, plagioclase feldspars, biotite and muscovite). Where calcareous material exists south of the SAF it is composed of an Antarctic foraminiferal assemblage involving Neogloboquadrina pachyderma (sinstral),Globigerina bulloides and Globorotalia injlata. All foraminifera of the Antarctic assemblage show evidence of dissolution. The northern subgroup of cores lies in an average water depth of 1200 m, while south of the SAF the average water depth of the cores is 4700 m. The lysocline for the NZSSO is determined at ∼3200-4100 m, with a carbonate compensation depth (CCD) of 4800 m. Any calcareous material south of the SAF is actively being affected by dissolution which biases the sedimentary record of the southern subgroup of cores to dissolution resistant organisms (diatoms and radiolaria) and terrigenous material.
The stable isotope records for the northern NZSSO cores show only a 0.8% shift between inferred glacial and interglacial conditions. Smoothing of the record may be due to bioturbation and/or to extensive sediment reworking by bottom currents, forming rather condensed sedimentary records, especially during glacial periods. Oxygen isotope stages back to stage 5 have been suggested in one core (36-42); this places the Last Glacial-Holocene transition at ∼7 cm, stage 2/3 boundary at ∼21 cm, stage 3/4 boundary at ∼65cm, and a possible stage 4/5 boundary at ∼95 cm downcore. The position of the Last Glacial and stage 2/3 boundary are confirmed by radiometric dates obtained from the same northern core: 19,120 +/- 110 yrs BP at 10 cm downcore and 23,900 yrs +/- 200 yrs BP at 20 cm downcore. Faunal changes in the benthic foraminifera occur near the glacialinterglacial transitions from Globocassidulina subglobosa-dominated during glacial periods to common Epistominella exigua during interglacials. Textural facies also show changes near these transitions, with Facies A characterising glacial periods and Facies B during interglacial periods. Associated with changes in texture are colour changes which allow the correlation of the glacial-interglacial transitions across many of the northern cores. The Last Glacial situation cannot be determined uniquely for the southern subgroup of cores as they have, to varying degrees, experienced extensive erosion and reworking during the Late Quaternary or earlier.
Collectively, the data suggest there has not been significant change in oceanic paleoenvironmental conditions north of the SAF, immediately south of New Zealand, between glacial and interglacial periods. This could be because the topographic high marking the southern edge of the Campbell Plateau has essentially fixed the SAF, irrespective of oceanic climatic conditions. The topographic lock would be further enhanced by sea level drops of ∼120 m during glacial periods. In contrast, east and west of New Zealand in open water conditions evidence from other studies indicates major northward shifts in the position of both the SAF and the AAPF. The limited variation downcore in the abundances of sinistrally coiled Neogloboquadrina pachydenna, the small shifts in the stable oxygen isotope record, and the lack of change in faunal assemblages together suggest that ranges in the sea surface temperature change between glacial and interglacial periods at higher latitudes were probably not so severe as at intermediate latitudes. Due to the relatively small temperature changes between glacial and interglacial conditions at higher latitudes the faunal and isotopic indicators may only record extreme events.

year: 1998

title: Physical volcanology of Red Crater, Tongariro

authors: Bardsley, Candice Joy

subjects: Volcanoes, New Zealand

abstract: The Tongariro Volcanic Centre (TVC) is New Zealand's most recently active volcanic centre and comprises two large active andesitic cones, Ruapehu and Tongariro. Tongariro is a dominantly andesitic cone complex, yet located at its centre is Red Crater, a basaltic andesite vent with an eruptive nature in striking contrast to the rest of Tongariro. The main aim of this research was to reconstruct the eruption history of this vent and provide the basis to model the impact of a range of future eruption scenarios from Tongariro.

The Red Crater basaltic andesite vent occupies a small scoria cone (~ 0.3 km³) which has also erupted eleven lava flows including the single largest preserved lava flow on Tongariro, with a length of ~ 7 km and a volume of ~ 0.3 km³. This flow was erupted between 9.7 ka and 3.4 ka, providing a maximum age for the vent. A distinctive feature of this vent is the exposed drained dike in the eastern wall.

Clast density (vesicularity), SEM, grain size, and petrographic analysis were undertaken on the deposits erupted from Red Crater, and used to constrain the timing of the lava flows in relation to the construction of the scoria cone. Average vesicularities for the Red Crater scoria deposits, exposed in the eastern and southern crater walls in particular, range from 51.5% to 76.8%, while the range of individual clasts is from 30.5% to 82.1 %. These values classify Red Crater scoria as highly vesicular. This scoria section is ~ 60 metres thick and possibly erupted within a 48 hour period. The five lava flows erupted prior to this scoria cone construction (pre 1.85ka Taupo eruption) are andesitic blocky flows, with lengths up to ~ 7 km and thicknesses up to ~ 50 metres. Five basaltic andesite aa flows were erupted post 1.85ka and coincided with the construction of the scoria cone. Maximum thicknesses are ~ 5 metres with lengths up to 0.98 km. The change in composition of the lava flows at this time is reflected by a change in the eruptive processes. Effusive activity dominated pre 1.85 ka while strombolian style eruptions producing discrete gas bursts dominated during the scoria cone construction post 1.85 ka. Two dikes are intruded into the scoria cone; one is the eastern wall and the other in the western wall.

The eruptive history of Red Crater can be divided into three phases. Phase one was probably initiated with a violent phreatic eruption caused by the interaction of an intruding dike with groundwater. The loss of volatiles during this phreatic eruption and through the permeable country rock lead to sustained effusive activity which produced the five andesite flows into Oturere Valley. Phase two began when more basaltic magma was injected into the system, with strombolian eruptions rapidly building the scoria cone and erupting the remaining six basaltic andesite lava flows. The basaltic andesite flow (flow 9) into Central Crater has the most mafic composition of any lava flow from the entire Tongariro cone complex. Phase three began when the withdrawal of magma from the dike caused a series of phreatic explosions originating from the deeper section of the NE-SW orientated dike, which violently excavated the NE trending Emerald Lakes explosion pits, the northern section of the scoria cone and the explosion pit on the south face of the cone. Minor ash and steam eruptions have been observed at the end of the last century, but it is the active fumaroles surrounding the vent which reveal Red Crater's currently active state, and potential for future eruptions.

text: Physical volcanology of Red Crater, Tongariro The Tongariro Volcanic Centre (TVC) is New Zealand's most recently active volcanic centre and comprises two large active andesitic cones, Ruapehu and Tongariro. Tongariro is a dominantly andesitic cone complex, yet located at its centre is Red Crater, a basaltic andesite vent with an eruptive nature in striking contrast to the rest of Tongariro. The main aim of this research was to reconstruct the eruption history of this vent and provide the basis to model the impact of a range of future eruption scenarios from Tongariro.

The Red Crater basaltic andesite vent occupies a small scoria cone (~ 0.3 km³) which has also erupted eleven lava flows including the single largest preserved lava flow on Tongariro, with a length of ~ 7 km and a volume of ~ 0.3 km³. This flow was erupted between 9.7 ka and 3.4 ka, providing a maximum age for the vent. A distinctive feature of this vent is the exposed drained dike in the eastern wall.

Clast density (vesicularity), SEM, grain size, and petrographic analysis were undertaken on the deposits erupted from Red Crater, and used to constrain the timing of the lava flows in relation to the construction of the scoria cone. Average vesicularities for the Red Crater scoria deposits, exposed in the eastern and southern crater walls in particular, range from 51.5% to 76.8%, while the range of individual clasts is from 30.5% to 82.1 %. These values classify Red Crater scoria as highly vesicular. This scoria section is ~ 60 metres thick and possibly erupted within a 48 hour period. The five lava flows erupted prior to this scoria cone construction (pre 1.85ka Taupo eruption) are andesitic blocky flows, with lengths up to ~ 7 km and thicknesses up to ~ 50 metres. Five basaltic andesite aa flows were erupted post 1.85ka and coincided with the construction of the scoria cone. Maximum thicknesses are ~ 5 metres with lengths up to 0.98 km. The change in composition of the lava flows at this time is reflected by a change in the eruptive processes. Effusive activity dominated pre 1.85 ka while strombolian style eruptions producing discrete gas bursts dominated during the scoria cone construction post 1.85 ka. Two dikes are intruded into the scoria cone; one is the eastern wall and the other in the western wall.

The eruptive history of Red Crater can be divided into three phases. Phase one was probably initiated with a violent phreatic eruption caused by the interaction of an intruding dike with groundwater. The loss of volatiles during this phreatic eruption and through the permeable country rock lead to sustained effusive activity which produced the five andesite flows into Oturere Valley. Phase two began when more basaltic magma was injected into the system, with strombolian eruptions rapidly building the scoria cone and erupting the remaining six basaltic andesite lava flows. The basaltic andesite flow (flow 9) into Central Crater has the most mafic composition of any lava flow from the entire Tongariro cone complex. Phase three began when the withdrawal of magma from the dike caused a series of phreatic explosions originating from the deeper section of the NE-SW orientated dike, which violently excavated the NE trending Emerald Lakes explosion pits, the northern section of the scoria cone and the explosion pit on the south face of the cone. Minor ash and steam eruptions have been observed at the end of the last century, but it is the active fumaroles surrounding the vent which reveal Red Crater's currently active state, and potential for future eruptions.

year: 2004

title: An analysis of typical errors of young learners of te reo Maori

authors: Houia, Waldo

subjects: te reo Maori

abstract: In 1999, the New Zealand Ministry of Education commissioned the development of a draft proficiency test for learners of Māori in bilingual and immersion settings in Year 5 of schooling (aged 8 - 10). That test was, along with a range of survey materials, produced and piloted in a very short time - 13 weeks. Although it provided a starting point for further development of a proficiency battery, it did not prove sufficiently robust in itself to retain. What it did do, however, was provide a range of useful samples of the speaking and writing of Year 5 students (70 samples were collected from five different schools). These samples revealed a number of common errors, errors which were analysed and are discussed here.

text: An analysis of typical errors of young learners of te reo Maori In 1999, the New Zealand Ministry of Education commissioned the development of a draft proficiency test for learners of Māori in bilingual and immersion settings in Year 5 of schooling (aged 8 - 10). That test was, along with a range of survey materials, produced and piloted in a very short time - 13 weeks. Although it provided a starting point for further development of a proficiency battery, it did not prove sufficiently robust in itself to retain. What it did do, however, was provide a range of useful samples of the speaking and writing of Year 5 students (70 samples were collected from five different schools). These samples revealed a number of common errors, errors which were analysed and are discussed here.

year: 2002-02