title: Interaction of polar and tropical influences in the mid-latitudes of the Southern Hemisphere during the Mi-1 deglaciation

authors: Fox, Beth R.S.

subjects: Science & Technology

abstract: It is well-known from geologic archives that Pleistocene and Holocene climate is characterised by cyclical variation on a wide range of timescales, and that these cycles of variation interact in complex ways. However, it is rarely possible to reconstruct sub-precessional (< 20 kyr) climate variations for periods predating the oldest ice-core records (c. 800 ka). Here we present an investigation of orbital to potentially sub-precessional cyclicity from an annually resolved lake sediment core dated to a 100-kyr period in the earliest Miocene (23.03–22.93 Ma) and spanning a period of major Antarctic deglaciation associated with the second half of the Mi-1 event. Principal component analysis (PCA) of sediment bulk density, magnetic susceptibility (MS), and CIELAB L* and b* with a resolution of ~10 years indicates two major environmental processes governing the physical properties records, which we interpret as changes in wind strength and changes in precipitation. Spectral analysis of the principal components indicates that both processes are strongly influenced by obliquity (41 kyr). We interpret this 41-kyr cycle in wind strength and precipitation as related to the changing position and strength of the Southern Hemisphere westerly winds. Precipitation is also influenced by an 11-kyr cycle. The 11-kyr periodicity is potentially related to orbital cyclicity, representing the equatorial semi-precessional maximum insolation cycle. This semi-precession cycle has been identified in a number of records from the Pleistocene and Holocene and has recently been suggested to indicate that insolation in low-latitude regions may be an important driver of millennial-scale climate response to orbital forcing (Feretti et al., 2015). This is the first time this cycle has been identified in a mid-latitude Southern Hemisphere climate archive, as well as the first identification in pre-Pleistocene records. The 11-kyr cycle appears at around 23.01 Ma, which coincides with the initiation of a major phase of Antarctic deglaciation, and strengthens during the subsequent period of rapid ice decay. This pattern suggests that the westerly winds may have expanded north of 50°S at the height of Mi-1, excluding tropical influence from the Foulden Maar site, and subsequently contracted polewards in tandem with warming deep-sea temperatures and Antarctic deglaciation, allowing the advection of tropical waters further south.

text: Interaction of polar and tropical influences in the mid-latitudes of the Southern Hemisphere during the Mi-1 deglaciation It is well-known from geologic archives that Pleistocene and Holocene climate is characterised by cyclical variation on a wide range of timescales, and that these cycles of variation interact in complex ways. However, it is rarely possible to reconstruct sub-precessional (< 20 kyr) climate variations for periods predating the oldest ice-core records (c. 800 ka). Here we present an investigation of orbital to potentially sub-precessional cyclicity from an annually resolved lake sediment core dated to a 100-kyr period in the earliest Miocene (23.03–22.93 Ma) and spanning a period of major Antarctic deglaciation associated with the second half of the Mi-1 event. Principal component analysis (PCA) of sediment bulk density, magnetic susceptibility (MS), and CIELAB L* and b* with a resolution of ~10 years indicates two major environmental processes governing the physical properties records, which we interpret as changes in wind strength and changes in precipitation. Spectral analysis of the principal components indicates that both processes are strongly influenced by obliquity (41 kyr). We interpret this 41-kyr cycle in wind strength and precipitation as related to the changing position and strength of the Southern Hemisphere westerly winds. Precipitation is also influenced by an 11-kyr cycle. The 11-kyr periodicity is potentially related to orbital cyclicity, representing the equatorial semi-precessional maximum insolation cycle. This semi-precession cycle has been identified in a number of records from the Pleistocene and Holocene and has recently been suggested to indicate that insolation in low-latitude regions may be an important driver of millennial-scale climate response to orbital forcing (Feretti et al., 2015). This is the first time this cycle has been identified in a mid-latitude Southern Hemisphere climate archive, as well as the first identification in pre-Pleistocene records. The 11-kyr cycle appears at around 23.01 Ma, which coincides with the initiation of a major phase of Antarctic deglaciation, and strengthens during the subsequent period of rapid ice decay. This pattern suggests that the westerly winds may have expanded north of 50°S at the height of Mi-1, excluding tropical influence from the Foulden Maar site, and subsequently contracted polewards in tandem with warming deep-sea temperatures and Antarctic deglaciation, allowing the advection of tropical waters further south.

year: 2017

title: Globalization of tephrochronology: new views from Australasia

authors: Lowe, David J.

subjects: tephrochronology

abstract: Tephra (or volcanic ash) studies, once confined largely to volcanic lands, have become increasingly practised in countries far removed from areas of active or recent volcanism – and Australia is no exception. At the International Union for Quaternary Research (INQUA) conference in Cairns in July/August 2007, Sarah E. Coulter (née Davies), now a postdoctoral ice-core tephrochronologist at Queen’s University Belfast, reportedthe first occurrence of an exotic tephra in Australia in a core from Lynch’s Crater, Atherton Tableland, Queensland (Figure 1). The distal tephra, manifest as a tiny concentration of glass shards, was probably derived from a Papua New Guinean eruption around 75,000–80,000 years ago (S.E. Davies et al., 2007). Its value lies in providing a precise chronostratigraphic marker that potentially allows correlation of other long palaeoenvironmental sequences over wide distances. Davies’ study is but one of a revolutionary development in tephrochronology now focused on detecting diminutive, distal tephras that are invisible in the field and referred to as cryptotephras. From the Greek word kryptein, meaning ‘to hide’ (Hunt, 1999a; Hunt and Hill, 2001; Lowe and Hunt, 2001), cryptotephras typically comprise fine-ashsized (< ~100 μm) glass shards sparsely preserved and ‘hidden’ in peats or in lake, marine or aeolian sediments, or in ice cores (Figure 2). The cryptotephra theme is continued in section III, but beforehand nomenclature associated with the term ‘tephra’, which can be confusing and which sometimes is used incorrectly, is outlined.

text: Globalization of tephrochronology: new views from Australasia Tephra (or volcanic ash) studies, once confined largely to volcanic lands, have become increasingly practised in countries far removed from areas of active or recent volcanism – and Australia is no exception. At the International Union for Quaternary Research (INQUA) conference in Cairns in July/August 2007, Sarah E. Coulter (née Davies), now a postdoctoral ice-core tephrochronologist at Queen’s University Belfast, reportedthe first occurrence of an exotic tephra in Australia in a core from Lynch’s Crater, Atherton Tableland, Queensland (Figure 1). The distal tephra, manifest as a tiny concentration of glass shards, was probably derived from a Papua New Guinean eruption around 75,000–80,000 years ago (S.E. Davies et al., 2007). Its value lies in providing a precise chronostratigraphic marker that potentially allows correlation of other long palaeoenvironmental sequences over wide distances. Davies’ study is but one of a revolutionary development in tephrochronology now focused on detecting diminutive, distal tephras that are invisible in the field and referred to as cryptotephras. From the Greek word kryptein, meaning ‘to hide’ (Hunt, 1999a; Hunt and Hill, 2001; Lowe and Hunt, 2001), cryptotephras typically comprise fine-ashsized (< ~100 μm) glass shards sparsely preserved and ‘hidden’ in peats or in lake, marine or aeolian sediments, or in ice cores (Figure 2). The cryptotephra theme is continued in section III, but beforehand nomenclature associated with the term ‘tephra’, which can be confusing and which sometimes is used incorrectly, is outlined.

year: 2008

title: Grounding the state of exception in New Zealand: A case study of racial segregation in Pukekohe, Whiteness and the Carceral State

authors: Martin, Jessica

subjects: State of exception

abstract: Indigenous scholars in settler-colonial contexts have highlighted the hyper-imprisonment of Indigenous people, locating it as an extension of the colonial project. Although research on this issue in New Zealand is emerging, there is a notable gap in understanding how the carceral state has developed within this particular context. This study aims to address the following research question: How does the historical context of racial segregation in Pukekohe contribute to our understanding of the mechanisms of the carceral state in New Zealand?
To thoroughly examine the hyper-imprisonment of Māori, it is essential to unpack the historical origins of state violence. Despite existing research establishing a link between Māori over-representation in prisons and the enduring effects of colonisation, there is a lack of studies exploring the complex interplay among the carceral state, whiteness, policy, policing, and law, which collectively shape the current landscape of incarceration. This study focuses on the racial segregation in Pukekohe between 1920 and 1960 and utilises reflexive thematic analysis within a case study framework, drawing on the insights offered by Robert Bartholomew's book, No Māori Allowed (2020). The analysis centres on the theoretical concept of the state of exception, shedding light on how power was wielded by the white racial polity. Thus, providing a unique perspective on the carceral state and state-sanctioned violence.
The findings highlight the interconnectedness of various systemic control mechanisms employed by the carceral state. Housing, policing, and whiteness emerge as crucial factors in the control and confinement of Māori in Pukekohe. By emphasising the role of whiteness in suppressing this history, this study underscores the need for critical examination and recognition of white cultural imperialism as a fundamental pillar of the carceral state. Overall, this research offers significant insights into the construction of a targeted population and the enduring consequences of state-sanctioned violence, emphasising the importance of a comprehensive examination of New Zealand's racialised history in discussions on the hyper-imprisonment of Māori.

text: Grounding the state of exception in New Zealand: A case study of racial segregation in Pukekohe, Whiteness and the Carceral State Indigenous scholars in settler-colonial contexts have highlighted the hyper-imprisonment of Indigenous people, locating it as an extension of the colonial project. Although research on this issue in New Zealand is emerging, there is a notable gap in understanding how the carceral state has developed within this particular context. This study aims to address the following research question: How does the historical context of racial segregation in Pukekohe contribute to our understanding of the mechanisms of the carceral state in New Zealand?
To thoroughly examine the hyper-imprisonment of Māori, it is essential to unpack the historical origins of state violence. Despite existing research establishing a link between Māori over-representation in prisons and the enduring effects of colonisation, there is a lack of studies exploring the complex interplay among the carceral state, whiteness, policy, policing, and law, which collectively shape the current landscape of incarceration. This study focuses on the racial segregation in Pukekohe between 1920 and 1960 and utilises reflexive thematic analysis within a case study framework, drawing on the insights offered by Robert Bartholomew's book, No Māori Allowed (2020). The analysis centres on the theoretical concept of the state of exception, shedding light on how power was wielded by the white racial polity. Thus, providing a unique perspective on the carceral state and state-sanctioned violence.
The findings highlight the interconnectedness of various systemic control mechanisms employed by the carceral state. Housing, policing, and whiteness emerge as crucial factors in the control and confinement of Māori in Pukekohe. By emphasising the role of whiteness in suppressing this history, this study underscores the need for critical examination and recognition of white cultural imperialism as a fundamental pillar of the carceral state. Overall, this research offers significant insights into the construction of a targeted population and the enduring consequences of state-sanctioned violence, emphasising the importance of a comprehensive examination of New Zealand's racialised history in discussions on the hyper-imprisonment of Māori.

year: 2024