title: Lichen and moss communities of Botany Bay, Granite Harbour, Ross Sea, Antarctica

authors: Seppelt, Rodney D.

subjects: biodiversity

abstract: Antarctic soils are extremely cold, dry, and oligotrophic, yet harbour surprisingly high bacterial diversity. The severity of environmental conditions has constrained the development of multi-trophic communities, and species richness and distribution is thought to be driven primarily by abiotic factors. Sites in northern and southern Victoria Land were sampled for bacterial community structure and soil physicochemical properties in conjunction with the US and New Zealand Latitudinal Gradient Project. Bacterial community structure was determined using a high-resolution molecular fingerprinting method for 80 soil samples from Taylor Valley and Cape Hallett sites which are separated by five degrees of latitude and have distinct soil chemistry. Taylor Valley is part of the McMurdo Dry Valleys, while Cape Hallett is the site of a penguin rookery and contains ornithogenic soils. The influence of soil moisture, pH, conductivity, ammonia, nitrate, total nitrogen and organic carbon on community structure was revealed using Spearman rank correlation, Mantel test, and principal components analysis. High spatial variability was detected in bacterial communities and community structure was correlated with soil moisture and pH. Both unique and shared bacterial community members were detected at Taylor Valley and Cape Hallett despite the considerable distance between the sites.

text: Lichen and moss communities of Botany Bay, Granite Harbour, Ross Sea, Antarctica Antarctic soils are extremely cold, dry, and oligotrophic, yet harbour surprisingly high bacterial diversity. The severity of environmental conditions has constrained the development of multi-trophic communities, and species richness and distribution is thought to be driven primarily by abiotic factors. Sites in northern and southern Victoria Land were sampled for bacterial community structure and soil physicochemical properties in conjunction with the US and New Zealand Latitudinal Gradient Project. Bacterial community structure was determined using a high-resolution molecular fingerprinting method for 80 soil samples from Taylor Valley and Cape Hallett sites which are separated by five degrees of latitude and have distinct soil chemistry. Taylor Valley is part of the McMurdo Dry Valleys, while Cape Hallett is the site of a penguin rookery and contains ornithogenic soils. The influence of soil moisture, pH, conductivity, ammonia, nitrate, total nitrogen and organic carbon on community structure was revealed using Spearman rank correlation, Mantel test, and principal components analysis. High spatial variability was detected in bacterial communities and community structure was correlated with soil moisture and pH. Both unique and shared bacterial community members were detected at Taylor Valley and Cape Hallett despite the considerable distance between the sites.

year: 2010

title: Controlling speculative execution through a virtually ordered memory system

authors: McWha, David J. A.

abstract: Processors which extract parallelism through speculative execution must be able to identify when mis-speculation has occurred. The three places where mis-speculation can occur are register accesses, control flow prediction and memory accesses. Controlling register and control flow speculation has been well studied, but no scalable techniques for identifying memory dependence violations have been identified. Since speculative execution occurs out of order this requires tracking the causal order, as well as the addresses of memory accesses. 

This thesis uses simulations to investigate tracking the causal order of memory accesses using explicit tags known as virtual timestamps, a distributed and scalable method. Realizable virtual timestamps are necessarily restricted in length and it is demonstrated that naive allocation schemes seriously constrain execution by inefficiently allocating virtual timestamps. Efficiently allocating virtual timestamps requires analysis of the number required by each section of code. Basic statically and dynamically evaluated analysis methods are established to avoid virtual timestamp allocation becoming a resource bottleneck.

The same analysis is also used to efficiently allocate state saving resources in a fixed hardware order. The hardware order provides an alternative way of maintaining the causal order using a simple hardware organization. The ability to predict the resources required by regions of code is used as a way of selecting instructions to execute speculatively. This enables resources to be allocated efficiently and is shown to allow large amounts of parallelism to be extracted. It also promotes the effectiveness of speculative execution by issuing less instructions that will ultimately be rolled back. 

Using a hierarchy of hardware ordering modules, themselves ordered by explicit virtual timestamps, a scalable ordering system is proposed. This hierarchy forms the basis of a twisted memory system, a multiple version memory system capable of identifying speculative memory dependence violations. The preliminary investigations presented here show that twisted memory has the potential to support aggressive speculative parallel execution. Particular attention is paid to memory bandwidth requirements.

text: Controlling speculative execution through a virtually ordered memory system Processors which extract parallelism through speculative execution must be able to identify when mis-speculation has occurred. The three places where mis-speculation can occur are register accesses, control flow prediction and memory accesses. Controlling register and control flow speculation has been well studied, but no scalable techniques for identifying memory dependence violations have been identified. Since speculative execution occurs out of order this requires tracking the causal order, as well as the addresses of memory accesses. 

This thesis uses simulations to investigate tracking the causal order of memory accesses using explicit tags known as virtual timestamps, a distributed and scalable method. Realizable virtual timestamps are necessarily restricted in length and it is demonstrated that naive allocation schemes seriously constrain execution by inefficiently allocating virtual timestamps. Efficiently allocating virtual timestamps requires analysis of the number required by each section of code. Basic statically and dynamically evaluated analysis methods are established to avoid virtual timestamp allocation becoming a resource bottleneck.

The same analysis is also used to efficiently allocate state saving resources in a fixed hardware order. The hardware order provides an alternative way of maintaining the causal order using a simple hardware organization. The ability to predict the resources required by regions of code is used as a way of selecting instructions to execute speculatively. This enables resources to be allocated efficiently and is shown to allow large amounts of parallelism to be extracted. It also promotes the effectiveness of speculative execution by issuing less instructions that will ultimately be rolled back. 

Using a hierarchy of hardware ordering modules, themselves ordered by explicit virtual timestamps, a scalable ordering system is proposed. This hierarchy forms the basis of a twisted memory system, a multiple version memory system capable of identifying speculative memory dependence violations. The preliminary investigations presented here show that twisted memory has the potential to support aggressive speculative parallel execution. Particular attention is paid to memory bandwidth requirements.

year: 2003

title: Carbon dioxide and methane emissions from the Te Arawa lakes of Rotorua, New Zealand

authors: Santoso, Arianto Budi

subjects: global carbon cycle

abstract: One of the biggest issues confronting humankind today is global warming due to the rapidly increasing greenhouse gas (GHG) emissions, namely CO₂, CH₄ and N₂O. The Intergovernmental Panel for Climate Change (IPCC) has prepared an emission reduction strategy. So far, inland waters, including lakes and reservoirs, have not been included in the global carbon cycle. However, the contribution of inland waters to global CO₂ and CH₄ emissions has been identified to be important. Inland waters are also known to be a major sink for GHG emissions by attenuating carbon that would otherwise be transported from the terrestrial landscape to the ocean. Lakes are also very sensitive to climate change as well as to human impacts generally, and these effects will need to be considered in understanding the future role of lakes in the global carbon cycle.
This study aimed to improve understanding of CO₂ and CH₄ emissions from lakes, and to quantify these emissions under changing climate and nutrient loading regimes in a regionally discrete group of lakes of volcanic origin in North Island of New Zealand. It included a comprehensive field study of one lake, application of process-based numerical modelling to the lake, and collation and critical analysis of existing datasets for the group of lakes. The primary study site was Okaro, a monomictic eutrophic lake where a major restoration program has been in place for more than one decade. The study also extended to 10 other lakes in order to give insights into effects of different nutrient and mixing regimes on carbon sources and sinks
Based on observations over a one-period (September 2013 – October 2014), Lake Okaro accumulated CO₂ and CH₄ in the hypolimnion during summer stratification. These gases were entrained into surface waters as lake started to turnover just prior to complete mixing in winter. As recorded in many other eutrophic lakes, the net CO₂ flux was mostly from the atmosphere to the lake. However, CO₂, together with CH₄, escaped from the lake as a pulsed emission in winter.  Using a simple annual mass balance model it was calculated that, ~31% of CH₄ sourced from the sediment escaped to the atmosphere through diffusive flux. The remainder was likely to be oxidized in the water column. The model also showed that on an annual basis the net CO₂ emission is out of the lake. These findings suggest that eutrophic lakes may actually be net emitters of greenhouse gases and that pulsed emissions may be an important contributor to the direction of the flux. This study did not account for CH₄ ebullition, however, and therefore the magnitude of GHG emissions from this lake is likely to be lower than predicted. 
The effects on CO₂ and CH₄ emissions from Lake Okaro of a warming climate and changes in nutrient loads was simulated using a coupled hydrodynamic-ecological model (GLM-AED2). Future possible changes were simulated by altering model forcing data, increasing air temperature by 2.5 °C. Internal and external nutrient (nitrogen and phosphorus) loads were also either halved or increased by one half. Model simulations showed that annual CO₂ uptake by the lake was enhanced under a warmer climate, but emissions of CH₄ increased during lake overturn as a result of greater diffusive fluxes. Total GHG emissions, as CO₂ equivalent (kg CO₂-eq m⁻² y⁻¹), from the lake were predicted with model simulations to increase by 27% under a warming climate, relative to present conditions. This increase would be reduced to 19% if nutrient loading was halved.
A first-order diagenesis model was used to estimate the carbon deposition in the 11 Te Arawa lakes. The most productive lakes, using chlorophyll a as a proxy, had higher rates of carbon deposition in the bottom sediments than the less productive lakes. However, burial efficiency (buried carbon: deposited carbon) was lower in productive lakes meaning that most of the deposited carbon in these lakes is remineralized back into the water column. This remineralization process can be associated with CO₂ and CH₄ emissions from the lake.
The results of this study highlight that eutrophic lakes may contribute emit higher levels of GHGs to the atmosphere than has previously been estimated, primarily as a result of pulsed emissions associated with the onset of seasonal mixing, at least in monomictic lakes.  Eutrophication and climate warming are likely to enhance GHG emissions from lakes. The findings from this study have important implications for global GHG fluxes and indicate that fluxes into or from lakes need to be included in inventories. Reducing nutrient loads to lakes could offset some of the predicted increases in emissions of GHGs that are likely to occur with climate warming.

text: Carbon dioxide and methane emissions from the Te Arawa lakes of Rotorua, New Zealand One of the biggest issues confronting humankind today is global warming due to the rapidly increasing greenhouse gas (GHG) emissions, namely CO₂, CH₄ and N₂O. The Intergovernmental Panel for Climate Change (IPCC) has prepared an emission reduction strategy. So far, inland waters, including lakes and reservoirs, have not been included in the global carbon cycle. However, the contribution of inland waters to global CO₂ and CH₄ emissions has been identified to be important. Inland waters are also known to be a major sink for GHG emissions by attenuating carbon that would otherwise be transported from the terrestrial landscape to the ocean. Lakes are also very sensitive to climate change as well as to human impacts generally, and these effects will need to be considered in understanding the future role of lakes in the global carbon cycle.
This study aimed to improve understanding of CO₂ and CH₄ emissions from lakes, and to quantify these emissions under changing climate and nutrient loading regimes in a regionally discrete group of lakes of volcanic origin in North Island of New Zealand. It included a comprehensive field study of one lake, application of process-based numerical modelling to the lake, and collation and critical analysis of existing datasets for the group of lakes. The primary study site was Okaro, a monomictic eutrophic lake where a major restoration program has been in place for more than one decade. The study also extended to 10 other lakes in order to give insights into effects of different nutrient and mixing regimes on carbon sources and sinks
Based on observations over a one-period (September 2013 – October 2014), Lake Okaro accumulated CO₂ and CH₄ in the hypolimnion during summer stratification. These gases were entrained into surface waters as lake started to turnover just prior to complete mixing in winter. As recorded in many other eutrophic lakes, the net CO₂ flux was mostly from the atmosphere to the lake. However, CO₂, together with CH₄, escaped from the lake as a pulsed emission in winter.  Using a simple annual mass balance model it was calculated that, ~31% of CH₄ sourced from the sediment escaped to the atmosphere through diffusive flux. The remainder was likely to be oxidized in the water column. The model also showed that on an annual basis the net CO₂ emission is out of the lake. These findings suggest that eutrophic lakes may actually be net emitters of greenhouse gases and that pulsed emissions may be an important contributor to the direction of the flux. This study did not account for CH₄ ebullition, however, and therefore the magnitude of GHG emissions from this lake is likely to be lower than predicted. 
The effects on CO₂ and CH₄ emissions from Lake Okaro of a warming climate and changes in nutrient loads was simulated using a coupled hydrodynamic-ecological model (GLM-AED2). Future possible changes were simulated by altering model forcing data, increasing air temperature by 2.5 °C. Internal and external nutrient (nitrogen and phosphorus) loads were also either halved or increased by one half. Model simulations showed that annual CO₂ uptake by the lake was enhanced under a warmer climate, but emissions of CH₄ increased during lake overturn as a result of greater diffusive fluxes. Total GHG emissions, as CO₂ equivalent (kg CO₂-eq m⁻² y⁻¹), from the lake were predicted with model simulations to increase by 27% under a warming climate, relative to present conditions. This increase would be reduced to 19% if nutrient loading was halved.
A first-order diagenesis model was used to estimate the carbon deposition in the 11 Te Arawa lakes. The most productive lakes, using chlorophyll a as a proxy, had higher rates of carbon deposition in the bottom sediments than the less productive lakes. However, burial efficiency (buried carbon: deposited carbon) was lower in productive lakes meaning that most of the deposited carbon in these lakes is remineralized back into the water column. This remineralization process can be associated with CO₂ and CH₄ emissions from the lake.
The results of this study highlight that eutrophic lakes may contribute emit higher levels of GHGs to the atmosphere than has previously been estimated, primarily as a result of pulsed emissions associated with the onset of seasonal mixing, at least in monomictic lakes.  Eutrophication and climate warming are likely to enhance GHG emissions from lakes. The findings from this study have important implications for global GHG fluxes and indicate that fluxes into or from lakes need to be included in inventories. Reducing nutrient loads to lakes could offset some of the predicted increases in emissions of GHGs that are likely to occur with climate warming.

year: 2016