title: Light limitation and water velocity modify the impacts of simulated marine heatwaves on juvenile giant kelp.

authors: Bunting, Imogen

subjects: coastal darkening

abstract: Coastal regions are complex habitats, where multiple natural and anthropogenic drivers can interact to affect the survival and growth of marine organisms. The giant kelp Macrocystis pyrifera is sensitive to increasing seawater temperatures and susceptible to marine heatwaves. Light availability and hydrodynamics can also affect the growth, morphology, and resilience of this species. In this experiment, juvenile sporophytes of M. pyrifera from Scorching Bay, Wellington, Aotearoa, New Zealand, a were exposed to a combination of simulated marine heatwaves at one of four different temperatures (20, 22, and 24°C compared to a 16°C control), one of two irradiance levels (shaded: 0.9 mol photons · m−2 · d−1 or ambient: 1.4 mol photons · m−2 · d−1), and one of two flow speeds (5.3 cm · s−1 or 6.1 cm · s−1) in a fully factorial design. Simulated heatwaves lasted for 21 days, with temperatures ramped by 2°C · d−1, followed by a 21-day recovery phase. The heatwave treatments represented severe heatwaves in present day or hypothetical future conditions, whereas the control represented historical average summer sea temperatures in Wellington, and 21 days represented a realistic duration for heatwaves in this region. Temperature was the main driver of negative physiological impacts, with 100% of sporophytes dying within 42 days of exposure to a 24°C heatwave. Sporophytes experienced 44% mortality at 20°C and 81% mortality at 22°C, and growth rates declined significantly with increasing temperature. However, survival rates were modified by light and water velocity, with 56% of sporophytes surviving under a combination of ambient light and fast water velocity, compared with less than 50% under each of the other light-velocity combinations. Light limitation also reduced sporophyte survival, growth rates, and effective quantum yield. Water velocity alone did not significantly affect sporophytes, but flow speeds had interactive effects with temperature and light. The findings of this experiment suggest that M. pyrifera at sites with optimal environmental conditions, including low sediment loads and fast tidal flows, could be more resilient to marine heatwaves, as long as temperatures do not exceed critical thresholds for survival.

text: Light limitation and water velocity modify the impacts of simulated marine heatwaves on juvenile giant kelp. Coastal regions are complex habitats, where multiple natural and anthropogenic drivers can interact to affect the survival and growth of marine organisms. The giant kelp Macrocystis pyrifera is sensitive to increasing seawater temperatures and susceptible to marine heatwaves. Light availability and hydrodynamics can also affect the growth, morphology, and resilience of this species. In this experiment, juvenile sporophytes of M. pyrifera from Scorching Bay, Wellington, Aotearoa, New Zealand, a were exposed to a combination of simulated marine heatwaves at one of four different temperatures (20, 22, and 24°C compared to a 16°C control), one of two irradiance levels (shaded: 0.9 mol photons · m−2 · d−1 or ambient: 1.4 mol photons · m−2 · d−1), and one of two flow speeds (5.3 cm · s−1 or 6.1 cm · s−1) in a fully factorial design. Simulated heatwaves lasted for 21 days, with temperatures ramped by 2°C · d−1, followed by a 21-day recovery phase. The heatwave treatments represented severe heatwaves in present day or hypothetical future conditions, whereas the control represented historical average summer sea temperatures in Wellington, and 21 days represented a realistic duration for heatwaves in this region. Temperature was the main driver of negative physiological impacts, with 100% of sporophytes dying within 42 days of exposure to a 24°C heatwave. Sporophytes experienced 44% mortality at 20°C and 81% mortality at 22°C, and growth rates declined significantly with increasing temperature. However, survival rates were modified by light and water velocity, with 56% of sporophytes surviving under a combination of ambient light and fast water velocity, compared with less than 50% under each of the other light-velocity combinations. Light limitation also reduced sporophyte survival, growth rates, and effective quantum yield. Water velocity alone did not significantly affect sporophytes, but flow speeds had interactive effects with temperature and light. The findings of this experiment suggest that M. pyrifera at sites with optimal environmental conditions, including low sediment loads and fast tidal flows, could be more resilient to marine heatwaves, as long as temperatures do not exceed critical thresholds for survival.

year: 2025

title: Comparison of wave and turbulence evolution in magnetohydrodynamics

authors: McAlley, Hamish

abstract: Magnetohydrodynamics (MHD) is the area of physics dedicated to the study of electrically conducting fluids. These fluids can support linear waves and non-linear turbulence dynamics. This thesis presents results and analysis of the evolution of the linearised MHD equations and the full non-linear MHD equations, starting from the same initial state. A systematic parameter study is conducted, varying the mean magnetic field strength, cross helicity, and Alfvén ratio. The focus is on incompressible MHD, though compressible systems also exist, and indeed are more prevalent as incompressible MHD is largely idealised.

text: Comparison of wave and turbulence evolution in magnetohydrodynamics Magnetohydrodynamics (MHD) is the area of physics dedicated to the study of electrically conducting fluids. These fluids can support linear waves and non-linear turbulence dynamics. This thesis presents results and analysis of the evolution of the linearised MHD equations and the full non-linear MHD equations, starting from the same initial state. A systematic parameter study is conducted, varying the mean magnetic field strength, cross helicity, and Alfvén ratio. The focus is on incompressible MHD, though compressible systems also exist, and indeed are more prevalent as incompressible MHD is largely idealised.

year: 2023

title: The Waikato invasion 1863-1864: A counter-insurgency approach

authors: Swears, Calum Robert

subjects: Counterinsurgency

abstract: Counter-insurgency as a strategy has only been explicitly espoused in American and British military tactical manuals in recent decades. It is anachronistic to military terminology before the last half century, but as this thesis illustrates counter-insurgency can be seen in embryonic form in the conflicts of the 1860s between Indigenous Māori and invading British forces in Aotearoa New Zealand. This thesis examines how early counter-insurgency strategy was evident in the tactical and strategic approaches used by Crown forces during the invasion of the Waikato in 1863-64. It asks: what evidence of counter-insurgency strategy can be seen in both British and Māori tactics at the time, and were they planned and intentional? 
Using two recent counter-insurgency tactical manuals - one American and the other British - this study compares present-day counter-insurgency principles, philosophies, and approaches to examples of Māori and British strategies during the 1860’s wars in Waikato, New Zealand. It illustrates how the Crown’s “suppression of rebellion” served as the contemporary political wording for its counter-insurgency campaign, which effectively repositioned Indigenous peoples as insurgents and “rebels” in their own territories and legitimated British colonial authority. Thus, this study argues that counter-insurgency in British military history arose from the various colonial invasions and occupations it undertook over several centuries. In Aotearoa, as this thesis argues, counter-insurgency tactics were used to establish legitimacy through civil-military operations such as land seizure, public proclamations and reports that vilified Māori and asserted British governing authority. The history of counter-insurgency as it is understood in British and American military thinking today, then, as this study contends is deeply connected to, and informed by, powerful colonial discourses, strategies, and experiences similar to those explored in this study of the Waikato invasion.

text: The Waikato invasion 1863-1864: A counter-insurgency approach Counter-insurgency as a strategy has only been explicitly espoused in American and British military tactical manuals in recent decades. It is anachronistic to military terminology before the last half century, but as this thesis illustrates counter-insurgency can be seen in embryonic form in the conflicts of the 1860s between Indigenous Māori and invading British forces in Aotearoa New Zealand. This thesis examines how early counter-insurgency strategy was evident in the tactical and strategic approaches used by Crown forces during the invasion of the Waikato in 1863-64. It asks: what evidence of counter-insurgency strategy can be seen in both British and Māori tactics at the time, and were they planned and intentional? 
Using two recent counter-insurgency tactical manuals - one American and the other British - this study compares present-day counter-insurgency principles, philosophies, and approaches to examples of Māori and British strategies during the 1860’s wars in Waikato, New Zealand. It illustrates how the Crown’s “suppression of rebellion” served as the contemporary political wording for its counter-insurgency campaign, which effectively repositioned Indigenous peoples as insurgents and “rebels” in their own territories and legitimated British colonial authority. Thus, this study argues that counter-insurgency in British military history arose from the various colonial invasions and occupations it undertook over several centuries. In Aotearoa, as this thesis argues, counter-insurgency tactics were used to establish legitimacy through civil-military operations such as land seizure, public proclamations and reports that vilified Māori and asserted British governing authority. The history of counter-insurgency as it is understood in British and American military thinking today, then, as this study contends is deeply connected to, and informed by, powerful colonial discourses, strategies, and experiences similar to those explored in this study of the Waikato invasion.

year: 2022