title: Southwest Pacific Absolute Plate Kinematic Reconstruction Reveals Major Cenozoic Tonga-Kermadec Slab Dragging

authors: van de Lagemaat, Suzanna H.A.

subjects: Science & Technology

abstract: Tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench‐parallel slab motion through the mantle, recently defined as a form of “slab dragging.” We investigate here long‐term slab‐dragging components of the Tonga‐Kermadec subduction system driven by absolute Pacific plate motion. To this end we develop a kinematic restoration of Tonga‐Kermadec Trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle. Estimating Tonga‐Kermadec subduction initiation is challenging because another (New Caledonia) subduction zone existed during the Paleogene between the Australia and Pacific plates. We test partitioning of plate convergence across the Paleogene New Caledonia and Tonga‐Kermadec subduction zones against resulting mantle structure and show that most, if not all, Tonga‐Kermadec subduction occurred after ca. 30 Ma. Since then, Tonga‐Kermadec subduction has accommodated 1,700 to 3,500 km of subduction along the southern and northern ends of the trench, respectively. When placed in a mantle reference frame, the predominantly westward directed subduction evolved while the Tonga‐Kermadec Trench underwent ~1,200 km of northward absolute motion. We infer that the entire Tonga‐Kermadec slab was laterally transported through the mantle over 1,200 km. Such slab dragging by the Pacific plate may explain observed deep‐slab deformation and may also have significant effects on surface tectonics, both resulting from the resistance to slab dragging by the viscous mantle.

Plain Language Summary
In studying subduction zones, where one plate dives below another back into the mantle, we tend to focus on the relative motion between the two plates, normally by assuming that the upper plate is fixed relative to the underlying mantle. Plate reconstructions in an “absolute” mantle frame of reference show, however, that trenches often migrate parallel to their trend relative to the mantle. In this paper, we study the southwestern Pacific Tonga‐Kermadec Trench and demonstrate (1) that it is likely much younger than often assumed, and accommodated most if not all of its subduction after ~30 million years ago and (2) that even in this short time period, it moved as much as 1,200 km northward relative to the mantle, parallel to its strike. By comparing this history with the subducted plate that is seismically imaged in the mantle, we show that the subducted Pacific lithosphere underwent major northward slab dragging through the mantle. This dragging explains enigmatic deep earthquakes and seismological observations of mantle structure. Realizing the role of slab dragging may provide novel constraints for deep‐time geological reconstructions as well as natural hazards assessment.

text: Southwest Pacific Absolute Plate Kinematic Reconstruction Reveals Major Cenozoic Tonga-Kermadec Slab Dragging Tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench‐parallel slab motion through the mantle, recently defined as a form of “slab dragging.” We investigate here long‐term slab‐dragging components of the Tonga‐Kermadec subduction system driven by absolute Pacific plate motion. To this end we develop a kinematic restoration of Tonga‐Kermadec Trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle. Estimating Tonga‐Kermadec subduction initiation is challenging because another (New Caledonia) subduction zone existed during the Paleogene between the Australia and Pacific plates. We test partitioning of plate convergence across the Paleogene New Caledonia and Tonga‐Kermadec subduction zones against resulting mantle structure and show that most, if not all, Tonga‐Kermadec subduction occurred after ca. 30 Ma. Since then, Tonga‐Kermadec subduction has accommodated 1,700 to 3,500 km of subduction along the southern and northern ends of the trench, respectively. When placed in a mantle reference frame, the predominantly westward directed subduction evolved while the Tonga‐Kermadec Trench underwent ~1,200 km of northward absolute motion. We infer that the entire Tonga‐Kermadec slab was laterally transported through the mantle over 1,200 km. Such slab dragging by the Pacific plate may explain observed deep‐slab deformation and may also have significant effects on surface tectonics, both resulting from the resistance to slab dragging by the viscous mantle.

Plain Language Summary
In studying subduction zones, where one plate dives below another back into the mantle, we tend to focus on the relative motion between the two plates, normally by assuming that the upper plate is fixed relative to the underlying mantle. Plate reconstructions in an “absolute” mantle frame of reference show, however, that trenches often migrate parallel to their trend relative to the mantle. In this paper, we study the southwestern Pacific Tonga‐Kermadec Trench and demonstrate (1) that it is likely much younger than often assumed, and accommodated most if not all of its subduction after ~30 million years ago and (2) that even in this short time period, it moved as much as 1,200 km northward relative to the mantle, parallel to its strike. By comparing this history with the subducted plate that is seismically imaged in the mantle, we show that the subducted Pacific lithosphere underwent major northward slab dragging through the mantle. This dragging explains enigmatic deep earthquakes and seismological observations of mantle structure. Realizing the role of slab dragging may provide novel constraints for deep‐time geological reconstructions as well as natural hazards assessment.

year: 2018

title: eDNA is a useful environmental monitoring tool for assessing stream ecological health

authors: Suren, Alastair

abstract: Environmental DNA (eDNA) is increasingly used in biodiversity assessments, but there remain uncertainties regarding its congruence with data based on traditional approaches involving habitat sampling and morphological‐based taxonomy. Using eDNA for biomonitoring has several advantages, including improved processing efficiencies and precision of taxonomic identification. In contrast, traditional biomonitoring is time‐consuming and expensive, often limiting the number of sites monitored. Establishing that eDNA‐derived metrics are congruent with their traditional equivalents on a national scale would support its wider use in biomonitoring. Our study compared ecosystem health assessments made by traditional biomonitoring techniques to those using eDNA from 53 sites throughout Aotearoa New Zealand. Because eDNA sampling was not done concurrently with benthic sampling at most sites, we used the average community composition at each site based on previous sampling occasions. We also allocated species identified by eDNA to the traditional level of identification to allow comparisons with eDNA data identified to broader taxonomic groups. We assessed similarities between the three datasets and found a high degree of correlation and convergence between biotic indices calculated from the different methods. eDNA did, however, appear to under‐represent some taxa, reflecting challenges in matching barcodes with an often‐incomplete sequence library. eDNA data did not always perform better in terms of showing the effects of land use on invertebrate community composition, but all datasets produced similar patterns. Multivariate analyses (redundancy analysis and variation partitioning) identified congruent relationships between environmental and spatial variables with the invertebrate community structure described by the three methods. eDNA data replicated the environmental responses and showed the same overall patterns in community composition as the traditionally collected data. We suggest that eDNA biomonitoring can complement traditional methods, and will perform at least as well as traditional data at detecting patterns in invertebrate community composition and ecosystem health at a national scale.

text: eDNA is a useful environmental monitoring tool for assessing stream ecological health Environmental DNA (eDNA) is increasingly used in biodiversity assessments, but there remain uncertainties regarding its congruence with data based on traditional approaches involving habitat sampling and morphological‐based taxonomy. Using eDNA for biomonitoring has several advantages, including improved processing efficiencies and precision of taxonomic identification. In contrast, traditional biomonitoring is time‐consuming and expensive, often limiting the number of sites monitored. Establishing that eDNA‐derived metrics are congruent with their traditional equivalents on a national scale would support its wider use in biomonitoring. Our study compared ecosystem health assessments made by traditional biomonitoring techniques to those using eDNA from 53 sites throughout Aotearoa New Zealand. Because eDNA sampling was not done concurrently with benthic sampling at most sites, we used the average community composition at each site based on previous sampling occasions. We also allocated species identified by eDNA to the traditional level of identification to allow comparisons with eDNA data identified to broader taxonomic groups. We assessed similarities between the three datasets and found a high degree of correlation and convergence between biotic indices calculated from the different methods. eDNA did, however, appear to under‐represent some taxa, reflecting challenges in matching barcodes with an often‐incomplete sequence library. eDNA data did not always perform better in terms of showing the effects of land use on invertebrate community composition, but all datasets produced similar patterns. Multivariate analyses (redundancy analysis and variation partitioning) identified congruent relationships between environmental and spatial variables with the invertebrate community structure described by the three methods. eDNA data replicated the environmental responses and showed the same overall patterns in community composition as the traditionally collected data. We suggest that eDNA biomonitoring can complement traditional methods, and will perform at least as well as traditional data at detecting patterns in invertebrate community composition and ecosystem health at a national scale.

year: 2024-07

title: An exploration of different outlooks on science: towards an understanding of the under-representation of girls, and of Maori and Pacific Island students, in science

authors: Stead, Keith Eric

abstract: The research reported here was undertaken as a supplementary study to the Learning in Science Project conducted at Waikato University (1979-1981) and sought to understand why girls, Maori and Pacific Island students, are under-represented in the sciences. Two distinctive, but complementary, perspectives were developed; one qualitative, the other quantitative, to provide data from which an understanding of the problem was sought.
The qualitative perspective was provided by using a Kelly Repertory Grid methodology and intensive individual interviews with 26 students (and many of their parents) carefully chosen to provide a reasonably heterogeneous sample of students from a variety of different schools, of both sexes, of the three major ethnic groups (European, Maori, and Pacific Island), and from each of the four middle-school form levels (Fl to F4, inclusively).
The quantitative perspective was provided by a series of empirical measures chosen, not only to identify the students for the qualitative sample but also, to investigate particular variables suggested by the literature search to have possible implications for the teaching and learning of science. 
The resultant analyses suggested the sex differences in the students’ outlooks on science could be accounted for by the existence of a broad based ‘gender-related inequality’ in the way science is presented to them by the communication media, home, and school.
Similarly, the ethnic differences in students’ outlooks on science could be accounted for by the ‘cultural inequality’ present in New Zealand society which was identified in the way many of the Polynesian students and their parents, perceived the products, processes, and practitioners of science. 
The simplification presented here masks the complexity of the issues involved but, series of educational within these two broad postulates, a series of educational recommendations was suggested for affecting current educational practices identified as maintaining (or even creating) the existing under-representation of girls, Maori and Pacific Island students in the sciences. 
These included:
(i) Student beliefs about science need to be explored, challenged, modified, and/or extended
(ii) Students’ perceptions of other people’s views need to be identified, explored, challenged and/or extended 
(iii) Teachers’ styles of teaching science need to be examined
(iv) Parents’ own outlooks on science need to be developed.
This research has emphasised the need to have all students, but particularly girls, Maori, and Pacific Island students, develop positive outlooks on science in order that the current imbalance of girls and Polynesians in the sciences be redressed.

text: An exploration of different outlooks on science: towards an understanding of the under-representation of girls, and of Maori and Pacific Island students, in science The research reported here was undertaken as a supplementary study to the Learning in Science Project conducted at Waikato University (1979-1981) and sought to understand why girls, Maori and Pacific Island students, are under-represented in the sciences. Two distinctive, but complementary, perspectives were developed; one qualitative, the other quantitative, to provide data from which an understanding of the problem was sought.
The qualitative perspective was provided by using a Kelly Repertory Grid methodology and intensive individual interviews with 26 students (and many of their parents) carefully chosen to provide a reasonably heterogeneous sample of students from a variety of different schools, of both sexes, of the three major ethnic groups (European, Maori, and Pacific Island), and from each of the four middle-school form levels (Fl to F4, inclusively).
The quantitative perspective was provided by a series of empirical measures chosen, not only to identify the students for the qualitative sample but also, to investigate particular variables suggested by the literature search to have possible implications for the teaching and learning of science. 
The resultant analyses suggested the sex differences in the students’ outlooks on science could be accounted for by the existence of a broad based ‘gender-related inequality’ in the way science is presented to them by the communication media, home, and school.
Similarly, the ethnic differences in students’ outlooks on science could be accounted for by the ‘cultural inequality’ present in New Zealand society which was identified in the way many of the Polynesian students and their parents, perceived the products, processes, and practitioners of science. 
The simplification presented here masks the complexity of the issues involved but, series of educational within these two broad postulates, a series of educational recommendations was suggested for affecting current educational practices identified as maintaining (or even creating) the existing under-representation of girls, Maori and Pacific Island students in the sciences. 
These included:
(i) Student beliefs about science need to be explored, challenged, modified, and/or extended
(ii) Students’ perceptions of other people’s views need to be identified, explored, challenged and/or extended 
(iii) Teachers’ styles of teaching science need to be examined
(iv) Parents’ own outlooks on science need to be developed.
This research has emphasised the need to have all students, but particularly girls, Maori, and Pacific Island students, develop positive outlooks on science in order that the current imbalance of girls and Polynesians in the sciences be redressed.

year: 1984