Humpback whales are iconic mammals at the top of the Antarctic food chain. Their large reserves o... more Humpback whales are iconic mammals at the top of the Antarctic food chain. Their large reserves of lipid-rich tissues such as blubber predispose them to accumulation of lipophilic contaminants throughout their lifetime. Changes in the volume and distribution of lipids in humpback whales, particularly during migration, could play an important role in the pharmacokinetics of lipophilic contaminants such as the organochlorine pesticide hexachlorobenzene (HCB). Previous models have examined constant feeding and nonmigratory scenarios. In the present study, the authors develop a novel heuristic model to investigate HCB dynamics in a humpback whale and its environment by coupling an ecosystem nutrient-phytoplankton-zooplankton-detritus (NPZD) model, a dynamic energy budget (DEB) model, and a physiologically based pharmacokinetic (PBPK) model. The model takes into account the seasonal feeding pattern of whales, their energy requirements, and fluctuating contaminant burdens in the supporting plankton food chain. It is applied to a male whale from weaning to maturity, spanning 20 migration and feeding cycles. The model is initialized with environmental HCB burdens similar to those measured in the Southern Ocean and predicts blubber HCB concentrations consistent with empirical concentrations observed in a southern hemisphere population of male, migrating humpback whales. Results show for the first time some important details of the relationship between energy budgets and organochlorine pharmacokinetics. Environ Toxicol Chem 2014;9999:1-12. # 2014 SETAC
Persistent organic pollutants (POPs) are toxic man-made chemicals that do not readily degrade in ... more Persistent organic pollutants (POPs) are toxic man-made chemicals that do not readily degrade in the natural environment, and may be subject to long-range environmental transport, potentially reaching remote regions far from the emission sources. Chlorinated POPs are hydrophobic and lipophilic chemicals with octanol-water partition coefficients (K OW ) typically of the order of 10 4 to 10 7 . This combination of properties means that POPs have a propensity to bioconcentrate and bioaccumulate in living organisms, representing a significant risk to human and environmental health . The movement of chemicals such as POPs in the environment can be described using the concept of fugacity . Fugacity (literally 'fleeing tendency', f ) is an equilibrium criterion related to chemical potential that determines how a chemical will partition between multiple phases . The rate of chemical movement between phases is proportional to the difference in fugacity. A chemical in diffusive equilibrium between two phases is unlikely to have the same concentration in the phases, but it will have the same fugacity.
Persistent organic pollutants (POPs) are toxic man-made chemicals that do not readily degrade in ... more Persistent organic pollutants (POPs) are toxic man-made chemicals that do not readily degrade in the natural environment, and may be subject to long-range environmental transport, potentially reaching remote regions far from the emission sources. Chlorinated POPs are hydrophobic and lipophilic chemicals with octanol-water partition coefficients (K OW ) typically of the order of 10 4 to 10 7 . This combination of properties means that POPs have a propensity to bioconcentrate and bioaccumulate in living organisms, representing a significant risk to human and environmental health . The movement of chemicals such as POPs in the environment can be described using the concept of fugacity . Fugacity (literally 'fleeing tendency', f ) is an equilibrium criterion related to chemical potential that determines how a chemical will partition between multiple phases . The rate of chemical movement between phases is proportional to the difference in fugacity. A chemical in diffusive equilibrium between two phases is unlikely to have the same concentration in the phases, but it will have the same fugacity.
This study contributes new data on the spatial variability of persistent organic pollutants in th... more This study contributes new data on the spatial variability of persistent organic pollutants in the Indian-Pacific sector of the Southern Ocean and represents the first empirical data obtained from this region in 25 years. Paired high-volume atmospheric and seawater samples were collected along a transect between Australia and Antarctica to investigate the latitudinal dependence of the occurrence and distribution of legacy organochlorine pesticides (OCPs) and the current use pesticide chlorpyrifos in the Southern Ocean. Dissolved ΣHCH and dieldrin concentrations decreased linearly with increasing latitude from 7.7 to 3.0 and from 1.0 to 0.6 pg·L(-1), respectively. There was no consistent trend observed in the latitudinal profile of atmospheric samples; however, some compounds (such as dieldrin) showed reduced concentrations from 7.5-3.4 to 2.7-0.65 pg·m(-3) at the highest latitudes south of the Polar Front. Chlorpyrifos was found in samples from this area for the first time. Estimate...
There is growing interest in models of marine ecosystems that deal with the effects of climate ch... more There is growing interest in models of marine ecosystems that deal with the effects of climate change through the higher trophic levels. Such end-to-end models combine physicochemical oceanographic descriptors and organisms ranging from microbes to higher-trophic-level (HTL) organisms, including humans, in a single modeling framework. The demand for such approaches arises from the need for quantitative tools for ecosystem-based management, particularly models that can deal with bottom-up and top-down controls that operate simultaneously and vary in time and space and that are capable of handling the multiple impacts expected under climate change. End-to-end models are now feasible because of improvements in the component submodels and the availability of sufficient computing power. We discuss nine issues related to the development of end-to-end models. These issues relate to formulation of the zooplankton submodel, melding of multiple temporal and spatial scales, acclimation and adaptation, behavioral movement, software and technology, model coupling, skill assessment, and interdisciplinary challenges. We urge restraint in using end-to-end models in a true forecasting mode until we know more about their performance. End-to-end models will challenge the available data and our ability to analyze and interpret complicated models that generate complex behavior. End-to-end modeling is in its early developmental stages and thus presents an opportunity to establish an open-access, community-based approach supported by a suite of true interdisciplinary efforts.
Journal of Colloid and Interface Science, Aug 15, 2006
Extensive experimental investigation of the wetting processes of fibre/liquid systems during air ... more Extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment or flow of drops from fibres as airflow velocity increases.
Excessive catalyst emissions from Fluidized Catalytic Cracking Units (FCCU) during start up situa... more Excessive catalyst emissions from Fluidized Catalytic Cracking Units (FCCU) during start up situations are common, and have been deemed 'normal' with little research conducted on determining their causes. A simplistic model found to predict trends in emission rates under normal conditions has been expanded to better represent the actual processes inside an FCCU. First and second order sensitivity analysis techniques are used to assess the interactions between various operational parameters, with a genetic algorithm used to optimize the operating conditions to minimise air emissions. These 'key' parameters may then be altered to help manage both normal and start up emissions through operational changes. It was also found that significant scale up issues arise with the use of the attrition models found in the literature.
Extensive experimental investigation of the wetting processes of fibre/liquid systems during air ... more Extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment or flow of drops from fibres as airflow velocity increases.
Cropp and Gabric [Ecosystem adaptation: do ecosystems maximise resilience? Ecology. In press] use... more Cropp and Gabric [Ecosystem adaptation: do ecosystems maximise resilience? Ecology. In press] used a simple phytoplanktonzooplankton-nutrient model and a genetic algorithm to determine the parameter values that would maximize the value of certain goal functions. These goal functions were to maximize biomass, maximize flux, maximize flux to biomass ratio, and maximize resilience. It was found that maximizing goal functions maximized resilience. The objective of this study was to investigate whether the Cropp and Gabric [Ecosystem adaptation: do ecosystems maximise resilience? Ecology. In press] result was indicative of a general ecosystem principle, or peculiar to the model and parameter ranges used. This study successfully replicated the Cropp and Gabric [Ecosystem adaptation: do ecosystems maximise resilience? Ecology. In press] experiment for a number of different model types, however, a different interpretation of the results is made. A new metric, concordance, was devised to describe the agreement between goal functions. It was found that resilience has the highest concordance of all goal functions trialled, for most model types. This implies that resilience offers a compromise between the established ecological goal functions. The parameter value range used is found to affect the parameter versus goal function relationships. Local maxima and minima affected the relationship between parameters and goal functions, and between goal functions.
1] Dimethylsulphide (DMS) is produced by upper ocean ecosystems and emitted to the atmosphere, wh... more 1] Dimethylsulphide (DMS) is produced by upper ocean ecosystems and emitted to the atmosphere, where it may have an important role in climate regulation. Several attempts to quantify the role of DMS in climate change have been undertaken in modeling studies. We examine a model of biogenic DMS production and describe its endogenous dynamics and sensitivities. We extend the model to develop a one-dimensional version that more accurately resolves the important processes of the mixed layer in determining the ecosystem dynamics. Comparisons of the results of the one-dimensional model with an empirical relationship that describes the global distribution of DMS, and also with vertical profiles of DMS in the upper ocean measured at the Bermuda Atlantic Time Series, suggest that the model represents the interaction between the biological and physical processes well on local and global scales. Our analysis of the model confirms its veracity and provides insights into the important processes determining DMS concentration in the oceans.
1] Two hypotheses that postulate interactions between ocean biota and aerosols in the atmosphere ... more 1] Two hypotheses that postulate interactions between ocean biota and aerosols in the atmosphere have generated substantial research into marine systems. The stimulation of phytoplankton photosynthesis by the provision of iron, a micronutrient contained in deposited aeolian dust (the Iron Hypothesis), and the contribution of dimethylsulphide (DMS) produced by marine ecosystems to the atmospheric burden of aerosols (the CLAW Hypothesis) have been the focus of much research. Satellite sensors, such as the Seaviewing Wide Field-of-view Sensor (SeaWiFS) now provide moderate-resolution time series of measurements of the optical properties of the oceans and atmosphere over most of the Earth's surface. These data provide an unprecedented opportunity to investigate the ubiquity of biotic linkages between the ocean and atmosphere at the global scale. We analyzed 5 years of SeaWiFS 8-day fields of two variables, chlorophyll concentration and aerosol optical depth, for the global oceans. This first global, multiyear approach does not yet allow unequivocal conclusions, as satellite measurements of chlorophyll can be influenced by aerosol properties of the atmosphere and several variables we do not yet examine are likely to play a role. We find correlation between optical properties of the ocean and atmosphere over much of the globe, in particular the midlatitudes. While some regional analyses indicate that SeaWiFS chlorophyll retrievals are biased by dust in the atmosphere, our results do not support the existence of widespread bias in the SeaWiFS products, but are consistent with global-scale couplings posited by the Iron and CLAW hypotheses.
1] The hypothesis that marine plankton ecosystems may effectively regulate climate by the product... more 1] The hypothesis that marine plankton ecosystems may effectively regulate climate by the production of dimethylsulphide (DMS) has attracted substantial research effort over recent years. This hypothesis suggests that DMS produced by marine ecosystems can affect cloud properties and hence the averaged irradiance experienced by the phytoplankton that produce DMS's precursor dimethylsulphoniopropionate (DMSP). This paper describes the use of a simple model to examine the effects of such a biogenic feedback on the ecosystem that initiates it. We compare the responses to perturbation of a simple marine nitrogen-phytoplankton-zooplankton (NPZ) ecosystem model with and without biogenic feedback. Our analysis of this heuristic model reveals that the addition of the feedback can increase the model's resilience to perturbation and hence stabilize the model ecosystem. This result suggests the hypothesis that DMS may play a role in stabilizing marine plankton ecosystem dynamics through its effect on the atmosphere.
The New Morris Method was proposed by Campolongo and Braddock [1] as an extension of the Morris M... more The New Morris Method was proposed by Campolongo and Braddock [1] as an extension of the Morris Method [2] to include estimation of two-factor interaction effects. An undetected programming error prevented Campolongo and Braddock from appreciating the efficacy of the method. Testing on an analytic function reveals that the method is more powerful and efficient than previously thought.
... References Andreae, MO, W. Elbert, Y. Cai, TW Andreae, and JL Gras, Non-sea-salt sulfate, met... more ... References Andreae, MO, W. Elbert, Y. Cai, TW Andreae, and JL Gras, Non-sea-salt sulfate, methanesulfonate, and nitrate aerosol concentrations and size distributions at Cape Grim, Tasmania, J. Geophys. Res., 104(D17), 21,69521,706, 1999. Ayers, GP, and JL Gras ...
The exchange of important greenhouse gases between the ocean and atmosphere is influenced by the ... more The exchange of important greenhouse gases between the ocean and atmosphere is influenced by the dynamics of near-surface plankton ecosystems. Marine plankton ecosystems are modified by climate change creating a feedback mechanism that could have significant implications for predicting future climates. The collapse or extinction of a plankton population may push the climate system across a tipping point. Dynamic green ocean models (DGOMs) are currently being developed for inclusion into climate models to predict the future state of the climate. The appropriate complexity of the DGOMs used to represent plankton processes is an ongoing issue, with models tending to become more complex, with more complicated dynamics, and an increasing propensity for chaos. We consider a relatively simple (four-population) DGOM of phytoplankton, zooplankton, bacteria and zooflagellates where the interacting plankton populations are connected by a single limiting nutrient. Chaotic solutions are possible in this 4-dimensional model for plankton population dynamics, as well as in a reduced 3-dimensional model, as we vary two of the key mortality parameters. Our results show that chaos is robust to the variation of parameters as well as to the presence of environmental noise, where the attractor of the more complex system is more robust than the attractor of its simplified equivalent. We find robust chaotic dynamics in low trophic order ecological models, suggesting that chaotic dynamics might be ubiquitous in the more complex models, but this is rarely observed in DGOM simulations. The physical equations of DGOMs are well understood and are constrained by conservation principles, but the ecological equations are not well understood, and generally have no explicitly conserved quantities. This work, in the context of the paucity of the empirical and theoretical bases upon which DGOMs are constructed, raises the interesting question of whether DGOMs better represent reality if they include or exclude chaotic dynamics, but also points to a need for a comprehensive approach to model development and testing. We contend that the DGOM community can learn important lessons from the analysis of simple models, and should consider a spectrum of methods from the analysis of simple(r) zero-dimensional models of population interactions through to numerical simulations of fully coupled biogeophysical models.
The prospect of human-induced climate change has stimulated research into several biological proc... more The prospect of human-induced climate change has stimulated research into several biological processes that might affect climate. One such process that has attracted a substantial research effort is the so-called CLAW hypothesis . This hypothesis suggests that marine plankton ecosystems may effectively regulate climate by a feedback associated with the production of dimethylsulphide (DMS). observed that some of the DMS produced by marine ecosystems is transferred from the ocean to the atmosphere where it is the major source of cloud condensing nuclei (CCN) over the remote oceans. The aerosols resulting from biogenic DMS emissions can have a direct effect on the solar radiative forcing experienced by the Earth through scattering, absorption and reflection and can also lead to increased cloud formation; the CLAW hypothesis proposes that these mechanisms could regulate climate. argued that an increase in global temperature would lead to increased biogenic DMS emissions from the ocean and result in an increase in scattering, cloud cover and cloud albedo that would increase the proportion of the incoming solar radiation reflected back into space (thus changing the global albedo), and thereby cooling the planet.
Humpback whales are iconic mammals at the top of the Antarctic food chain. Their large reserves o... more Humpback whales are iconic mammals at the top of the Antarctic food chain. Their large reserves of lipid-rich tissues such as blubber predispose them to accumulation of lipophilic contaminants throughout their lifetime. Changes in the volume and distribution of lipids in humpback whales, particularly during migration, could play an important role in the pharmacokinetics of lipophilic contaminants such as the organochlorine pesticide hexachlorobenzene (HCB). Previous models have examined constant feeding and nonmigratory scenarios. In the present study, the authors develop a novel heuristic model to investigate HCB dynamics in a humpback whale and its environment by coupling an ecosystem nutrient-phytoplankton-zooplankton-detritus (NPZD) model, a dynamic energy budget (DEB) model, and a physiologically based pharmacokinetic (PBPK) model. The model takes into account the seasonal feeding pattern of whales, their energy requirements, and fluctuating contaminant burdens in the supporting plankton food chain. It is applied to a male whale from weaning to maturity, spanning 20 migration and feeding cycles. The model is initialized with environmental HCB burdens similar to those measured in the Southern Ocean and predicts blubber HCB concentrations consistent with empirical concentrations observed in a southern hemisphere population of male, migrating humpback whales. Results show for the first time some important details of the relationship between energy budgets and organochlorine pharmacokinetics. Environ Toxicol Chem 2014;9999:1-12. # 2014 SETAC
Persistent organic pollutants (POPs) are toxic man-made chemicals that do not readily degrade in ... more Persistent organic pollutants (POPs) are toxic man-made chemicals that do not readily degrade in the natural environment, and may be subject to long-range environmental transport, potentially reaching remote regions far from the emission sources. Chlorinated POPs are hydrophobic and lipophilic chemicals with octanol-water partition coefficients (K OW ) typically of the order of 10 4 to 10 7 . This combination of properties means that POPs have a propensity to bioconcentrate and bioaccumulate in living organisms, representing a significant risk to human and environmental health . The movement of chemicals such as POPs in the environment can be described using the concept of fugacity . Fugacity (literally 'fleeing tendency', f ) is an equilibrium criterion related to chemical potential that determines how a chemical will partition between multiple phases . The rate of chemical movement between phases is proportional to the difference in fugacity. A chemical in diffusive equilibrium between two phases is unlikely to have the same concentration in the phases, but it will have the same fugacity.
Persistent organic pollutants (POPs) are toxic man-made chemicals that do not readily degrade in ... more Persistent organic pollutants (POPs) are toxic man-made chemicals that do not readily degrade in the natural environment, and may be subject to long-range environmental transport, potentially reaching remote regions far from the emission sources. Chlorinated POPs are hydrophobic and lipophilic chemicals with octanol-water partition coefficients (K OW ) typically of the order of 10 4 to 10 7 . This combination of properties means that POPs have a propensity to bioconcentrate and bioaccumulate in living organisms, representing a significant risk to human and environmental health . The movement of chemicals such as POPs in the environment can be described using the concept of fugacity . Fugacity (literally 'fleeing tendency', f ) is an equilibrium criterion related to chemical potential that determines how a chemical will partition between multiple phases . The rate of chemical movement between phases is proportional to the difference in fugacity. A chemical in diffusive equilibrium between two phases is unlikely to have the same concentration in the phases, but it will have the same fugacity.
This study contributes new data on the spatial variability of persistent organic pollutants in th... more This study contributes new data on the spatial variability of persistent organic pollutants in the Indian-Pacific sector of the Southern Ocean and represents the first empirical data obtained from this region in 25 years. Paired high-volume atmospheric and seawater samples were collected along a transect between Australia and Antarctica to investigate the latitudinal dependence of the occurrence and distribution of legacy organochlorine pesticides (OCPs) and the current use pesticide chlorpyrifos in the Southern Ocean. Dissolved ΣHCH and dieldrin concentrations decreased linearly with increasing latitude from 7.7 to 3.0 and from 1.0 to 0.6 pg·L(-1), respectively. There was no consistent trend observed in the latitudinal profile of atmospheric samples; however, some compounds (such as dieldrin) showed reduced concentrations from 7.5-3.4 to 2.7-0.65 pg·m(-3) at the highest latitudes south of the Polar Front. Chlorpyrifos was found in samples from this area for the first time. Estimate...
There is growing interest in models of marine ecosystems that deal with the effects of climate ch... more There is growing interest in models of marine ecosystems that deal with the effects of climate change through the higher trophic levels. Such end-to-end models combine physicochemical oceanographic descriptors and organisms ranging from microbes to higher-trophic-level (HTL) organisms, including humans, in a single modeling framework. The demand for such approaches arises from the need for quantitative tools for ecosystem-based management, particularly models that can deal with bottom-up and top-down controls that operate simultaneously and vary in time and space and that are capable of handling the multiple impacts expected under climate change. End-to-end models are now feasible because of improvements in the component submodels and the availability of sufficient computing power. We discuss nine issues related to the development of end-to-end models. These issues relate to formulation of the zooplankton submodel, melding of multiple temporal and spatial scales, acclimation and adaptation, behavioral movement, software and technology, model coupling, skill assessment, and interdisciplinary challenges. We urge restraint in using end-to-end models in a true forecasting mode until we know more about their performance. End-to-end models will challenge the available data and our ability to analyze and interpret complicated models that generate complex behavior. End-to-end modeling is in its early developmental stages and thus presents an opportunity to establish an open-access, community-based approach supported by a suite of true interdisciplinary efforts.
Journal of Colloid and Interface Science, Aug 15, 2006
Extensive experimental investigation of the wetting processes of fibre/liquid systems during air ... more Extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment or flow of drops from fibres as airflow velocity increases.
Excessive catalyst emissions from Fluidized Catalytic Cracking Units (FCCU) during start up situa... more Excessive catalyst emissions from Fluidized Catalytic Cracking Units (FCCU) during start up situations are common, and have been deemed 'normal' with little research conducted on determining their causes. A simplistic model found to predict trends in emission rates under normal conditions has been expanded to better represent the actual processes inside an FCCU. First and second order sensitivity analysis techniques are used to assess the interactions between various operational parameters, with a genetic algorithm used to optimize the operating conditions to minimise air emissions. These 'key' parameters may then be altered to help manage both normal and start up emissions through operational changes. It was also found that significant scale up issues arise with the use of the attrition models found in the literature.
Extensive experimental investigation of the wetting processes of fibre/liquid systems during air ... more Extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment or flow of drops from fibres as airflow velocity increases.
Cropp and Gabric [Ecosystem adaptation: do ecosystems maximise resilience? Ecology. In press] use... more Cropp and Gabric [Ecosystem adaptation: do ecosystems maximise resilience? Ecology. In press] used a simple phytoplanktonzooplankton-nutrient model and a genetic algorithm to determine the parameter values that would maximize the value of certain goal functions. These goal functions were to maximize biomass, maximize flux, maximize flux to biomass ratio, and maximize resilience. It was found that maximizing goal functions maximized resilience. The objective of this study was to investigate whether the Cropp and Gabric [Ecosystem adaptation: do ecosystems maximise resilience? Ecology. In press] result was indicative of a general ecosystem principle, or peculiar to the model and parameter ranges used. This study successfully replicated the Cropp and Gabric [Ecosystem adaptation: do ecosystems maximise resilience? Ecology. In press] experiment for a number of different model types, however, a different interpretation of the results is made. A new metric, concordance, was devised to describe the agreement between goal functions. It was found that resilience has the highest concordance of all goal functions trialled, for most model types. This implies that resilience offers a compromise between the established ecological goal functions. The parameter value range used is found to affect the parameter versus goal function relationships. Local maxima and minima affected the relationship between parameters and goal functions, and between goal functions.
1] Dimethylsulphide (DMS) is produced by upper ocean ecosystems and emitted to the atmosphere, wh... more 1] Dimethylsulphide (DMS) is produced by upper ocean ecosystems and emitted to the atmosphere, where it may have an important role in climate regulation. Several attempts to quantify the role of DMS in climate change have been undertaken in modeling studies. We examine a model of biogenic DMS production and describe its endogenous dynamics and sensitivities. We extend the model to develop a one-dimensional version that more accurately resolves the important processes of the mixed layer in determining the ecosystem dynamics. Comparisons of the results of the one-dimensional model with an empirical relationship that describes the global distribution of DMS, and also with vertical profiles of DMS in the upper ocean measured at the Bermuda Atlantic Time Series, suggest that the model represents the interaction between the biological and physical processes well on local and global scales. Our analysis of the model confirms its veracity and provides insights into the important processes determining DMS concentration in the oceans.
1] Two hypotheses that postulate interactions between ocean biota and aerosols in the atmosphere ... more 1] Two hypotheses that postulate interactions between ocean biota and aerosols in the atmosphere have generated substantial research into marine systems. The stimulation of phytoplankton photosynthesis by the provision of iron, a micronutrient contained in deposited aeolian dust (the Iron Hypothesis), and the contribution of dimethylsulphide (DMS) produced by marine ecosystems to the atmospheric burden of aerosols (the CLAW Hypothesis) have been the focus of much research. Satellite sensors, such as the Seaviewing Wide Field-of-view Sensor (SeaWiFS) now provide moderate-resolution time series of measurements of the optical properties of the oceans and atmosphere over most of the Earth's surface. These data provide an unprecedented opportunity to investigate the ubiquity of biotic linkages between the ocean and atmosphere at the global scale. We analyzed 5 years of SeaWiFS 8-day fields of two variables, chlorophyll concentration and aerosol optical depth, for the global oceans. This first global, multiyear approach does not yet allow unequivocal conclusions, as satellite measurements of chlorophyll can be influenced by aerosol properties of the atmosphere and several variables we do not yet examine are likely to play a role. We find correlation between optical properties of the ocean and atmosphere over much of the globe, in particular the midlatitudes. While some regional analyses indicate that SeaWiFS chlorophyll retrievals are biased by dust in the atmosphere, our results do not support the existence of widespread bias in the SeaWiFS products, but are consistent with global-scale couplings posited by the Iron and CLAW hypotheses.
1] The hypothesis that marine plankton ecosystems may effectively regulate climate by the product... more 1] The hypothesis that marine plankton ecosystems may effectively regulate climate by the production of dimethylsulphide (DMS) has attracted substantial research effort over recent years. This hypothesis suggests that DMS produced by marine ecosystems can affect cloud properties and hence the averaged irradiance experienced by the phytoplankton that produce DMS's precursor dimethylsulphoniopropionate (DMSP). This paper describes the use of a simple model to examine the effects of such a biogenic feedback on the ecosystem that initiates it. We compare the responses to perturbation of a simple marine nitrogen-phytoplankton-zooplankton (NPZ) ecosystem model with and without biogenic feedback. Our analysis of this heuristic model reveals that the addition of the feedback can increase the model's resilience to perturbation and hence stabilize the model ecosystem. This result suggests the hypothesis that DMS may play a role in stabilizing marine plankton ecosystem dynamics through its effect on the atmosphere.
The New Morris Method was proposed by Campolongo and Braddock [1] as an extension of the Morris M... more The New Morris Method was proposed by Campolongo and Braddock [1] as an extension of the Morris Method [2] to include estimation of two-factor interaction effects. An undetected programming error prevented Campolongo and Braddock from appreciating the efficacy of the method. Testing on an analytic function reveals that the method is more powerful and efficient than previously thought.
... References Andreae, MO, W. Elbert, Y. Cai, TW Andreae, and JL Gras, Non-sea-salt sulfate, met... more ... References Andreae, MO, W. Elbert, Y. Cai, TW Andreae, and JL Gras, Non-sea-salt sulfate, methanesulfonate, and nitrate aerosol concentrations and size distributions at Cape Grim, Tasmania, J. Geophys. Res., 104(D17), 21,69521,706, 1999. Ayers, GP, and JL Gras ...
The exchange of important greenhouse gases between the ocean and atmosphere is influenced by the ... more The exchange of important greenhouse gases between the ocean and atmosphere is influenced by the dynamics of near-surface plankton ecosystems. Marine plankton ecosystems are modified by climate change creating a feedback mechanism that could have significant implications for predicting future climates. The collapse or extinction of a plankton population may push the climate system across a tipping point. Dynamic green ocean models (DGOMs) are currently being developed for inclusion into climate models to predict the future state of the climate. The appropriate complexity of the DGOMs used to represent plankton processes is an ongoing issue, with models tending to become more complex, with more complicated dynamics, and an increasing propensity for chaos. We consider a relatively simple (four-population) DGOM of phytoplankton, zooplankton, bacteria and zooflagellates where the interacting plankton populations are connected by a single limiting nutrient. Chaotic solutions are possible in this 4-dimensional model for plankton population dynamics, as well as in a reduced 3-dimensional model, as we vary two of the key mortality parameters. Our results show that chaos is robust to the variation of parameters as well as to the presence of environmental noise, where the attractor of the more complex system is more robust than the attractor of its simplified equivalent. We find robust chaotic dynamics in low trophic order ecological models, suggesting that chaotic dynamics might be ubiquitous in the more complex models, but this is rarely observed in DGOM simulations. The physical equations of DGOMs are well understood and are constrained by conservation principles, but the ecological equations are not well understood, and generally have no explicitly conserved quantities. This work, in the context of the paucity of the empirical and theoretical bases upon which DGOMs are constructed, raises the interesting question of whether DGOMs better represent reality if they include or exclude chaotic dynamics, but also points to a need for a comprehensive approach to model development and testing. We contend that the DGOM community can learn important lessons from the analysis of simple models, and should consider a spectrum of methods from the analysis of simple(r) zero-dimensional models of population interactions through to numerical simulations of fully coupled biogeophysical models.
The prospect of human-induced climate change has stimulated research into several biological proc... more The prospect of human-induced climate change has stimulated research into several biological processes that might affect climate. One such process that has attracted a substantial research effort is the so-called CLAW hypothesis . This hypothesis suggests that marine plankton ecosystems may effectively regulate climate by a feedback associated with the production of dimethylsulphide (DMS). observed that some of the DMS produced by marine ecosystems is transferred from the ocean to the atmosphere where it is the major source of cloud condensing nuclei (CCN) over the remote oceans. The aerosols resulting from biogenic DMS emissions can have a direct effect on the solar radiative forcing experienced by the Earth through scattering, absorption and reflection and can also lead to increased cloud formation; the CLAW hypothesis proposes that these mechanisms could regulate climate. argued that an increase in global temperature would lead to increased biogenic DMS emissions from the ocean and result in an increase in scattering, cloud cover and cloud albedo that would increase the proportion of the incoming solar radiation reflected back into space (thus changing the global albedo), and thereby cooling the planet.
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Papers by Roger Cropp