title: The amplitude and origin of sea-level variability during the Pliocene epoch

authors: Grant, G.R.

subjects: Science & Technology

abstract: Earth is heading towards a climate that last existed more than three million years ago (Ma) during the ‘mid-Pliocene warm period’¹, when atmospheric carbon dioxide concentrations were about 400 parts per million, global sea level oscillated in response to orbital forcing²,³ and peak global-mean sea level (GMSL) may have reached about 20 metres above the present-day value⁴,⁵. For sea-level rise of this magnitude, extensive retreat or collapse of the Greenland, West Antarctic and marine-based sectors of the East Antarctic ice sheets is required. Yet the relative amplitude of sea-level variations within glacial–interglacial cycles remains poorly constrained. To address this, we calibrate a theoretical relationship between modern sediment transport by waves and water depth, and then apply the technique to grain size in a continuous 800-metre-thick Pliocene sequence of shallow-marine sediments from Whanganui Basin, New Zealand. Water-depth variations obtained in this way, after corrections for tectonic subsidence, yield cyclic relative sea-level (RSL) variations. Here we show that sea level varied on average by 13 ± 5 metres over glacial–interglacial cycles during the middle-to-late Pliocene (about 3.3–2.5 Ma). The resulting record is independent of the global ice volume proxy³ (as derived from the deep-ocean oxygen isotope record) and sea-level cycles are in phase with 20-thousand-year (kyr) periodic changes in insolation over Antarctica, paced by eccentricity-modulated orbital precession⁶ between 3.3 and 2.7 Ma. Thereafter, sea-level fluctuations are paced by the 41-kyr period of cycles in Earth’s axial tilt as ice sheets stabilize on Antarctica and intensify in the Northern Hemisphere³, ⁶. Strictly, we provide the amplitude of RSL change, rather than absolute GMSL change. However, simulations of RSL change based on glacio-isostatic adjustment show that our record approximates eustatic sea level, defined here as GMSL unregistered to the centre of the Earth. Nonetheless, under conservative assumptions, our estimates limit maximum Pliocene sea-level rise to less than 25 metres and provide new constraints on polar ice-volume variability under the climate conditions predicted for this century.

text: The amplitude and origin of sea-level variability during the Pliocene epoch Earth is heading towards a climate that last existed more than three million years ago (Ma) during the ‘mid-Pliocene warm period’¹, when atmospheric carbon dioxide concentrations were about 400 parts per million, global sea level oscillated in response to orbital forcing²,³ and peak global-mean sea level (GMSL) may have reached about 20 metres above the present-day value⁴,⁵. For sea-level rise of this magnitude, extensive retreat or collapse of the Greenland, West Antarctic and marine-based sectors of the East Antarctic ice sheets is required. Yet the relative amplitude of sea-level variations within glacial–interglacial cycles remains poorly constrained. To address this, we calibrate a theoretical relationship between modern sediment transport by waves and water depth, and then apply the technique to grain size in a continuous 800-metre-thick Pliocene sequence of shallow-marine sediments from Whanganui Basin, New Zealand. Water-depth variations obtained in this way, after corrections for tectonic subsidence, yield cyclic relative sea-level (RSL) variations. Here we show that sea level varied on average by 13 ± 5 metres over glacial–interglacial cycles during the middle-to-late Pliocene (about 3.3–2.5 Ma). The resulting record is independent of the global ice volume proxy³ (as derived from the deep-ocean oxygen isotope record) and sea-level cycles are in phase with 20-thousand-year (kyr) periodic changes in insolation over Antarctica, paced by eccentricity-modulated orbital precession⁶ between 3.3 and 2.7 Ma. Thereafter, sea-level fluctuations are paced by the 41-kyr period of cycles in Earth’s axial tilt as ice sheets stabilize on Antarctica and intensify in the Northern Hemisphere³, ⁶. Strictly, we provide the amplitude of RSL change, rather than absolute GMSL change. However, simulations of RSL change based on glacio-isostatic adjustment show that our record approximates eustatic sea level, defined here as GMSL unregistered to the centre of the Earth. Nonetheless, under conservative assumptions, our estimates limit maximum Pliocene sea-level rise to less than 25 metres and provide new constraints on polar ice-volume variability under the climate conditions predicted for this century.

year: 2019

title: Researching amid the heat and noise of political debate

authors: Thrupp, Martin

abstract: This article discusses the everyday politics surrounding research on a controversial government policy. The research in question is the Research, Analysis and Insight into National Standards (RAINS) project on National Standards in New Zealand primary schools being undertaken by the author. This three-year study was funded by the New Zealand primary teachers' union, the NZEI, an organisation opposed to the National Standards policy. The project was quickly attacked by a cabinet minister and the media but there have also been significant accomplishments in carrying out and reporting the research and in relevant activism. As the article discusses the political setbacks and successes while undertaking the research, it reflects on issues such as research funding, research 'independence', the reporting of findings from controversial research projects, the tensions between being a researcher and an activist and the importance of supportive networks. The article provides a case study of how challenges to the legitimacy of research and academic involvement in public debate may need to be anticipated and addressed by researchers much like other aspects of their work.

text: Researching amid the heat and noise of political debate This article discusses the everyday politics surrounding research on a controversial government policy. The research in question is the Research, Analysis and Insight into National Standards (RAINS) project on National Standards in New Zealand primary schools being undertaken by the author. This three-year study was funded by the New Zealand primary teachers' union, the NZEI, an organisation opposed to the National Standards policy. The project was quickly attacked by a cabinet minister and the media but there have also been significant accomplishments in carrying out and reporting the research and in relevant activism. As the article discusses the political setbacks and successes while undertaking the research, it reflects on issues such as research funding, research 'independence', the reporting of findings from controversial research projects, the tensions between being a researcher and an activist and the importance of supportive networks. The article provides a case study of how challenges to the legitimacy of research and academic involvement in public debate may need to be anticipated and addressed by researchers much like other aspects of their work.

year: 2013

title: Audiences, referees, and landscapes: Understanding the use of Māori and English in New Zealand dual language picturebooks through a sociolinguistic lens

authors: Daly, Nicola

abstract: When non-dominant perspectives are represented in children's literature, it is labelled multicultural, and this form of literature has much potential for altering existing power structures in society. Bishop (1990) first introduced the metaphor of multicultural children's literature offering the possibility of windows - an opportunity to see into others' worlds; mirrors - an opportunity to see your own world being reflected back; and glass sliding doors - an opportunity to step into a world through a book. However, to date, any exploration of the extent to which language diversity contributes to the representation of non-dominant perspectives in multicultural children's literature has been limited, and the use of sociolinguistic theories to frame and theorise such explorations almost non-existent.

text: Audiences, referees, and landscapes: Understanding the use of Māori and English in New Zealand dual language picturebooks through a sociolinguistic lens When non-dominant perspectives are represented in children's literature, it is labelled multicultural, and this form of literature has much potential for altering existing power structures in society. Bishop (1990) first introduced the metaphor of multicultural children's literature offering the possibility of windows - an opportunity to see into others' worlds; mirrors - an opportunity to see your own world being reflected back; and glass sliding doors - an opportunity to step into a world through a book. However, to date, any exploration of the extent to which language diversity contributes to the representation of non-dominant perspectives in multicultural children's literature has been limited, and the use of sociolinguistic theories to frame and theorise such explorations almost non-existent.

year: 2017