Roger Allan Cropp

End-To-End Models for the Analysis of Marine Ecosystems: Challenges, Issues, and Next Steps

Abstract 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.

Australian dust storms in 2002–2003 and their impact on Southern Ocean biogeochemistry

During late 2002 and early 2003 southern Australia was in the grip of drought and experienced one of its most active dust storm seasons in the last 40 years with large dust plumes frequently advected over the adjacent Southern Ocean. We use meteorological records of dust activity, satellite ocean colour and aerosol optical depth data, and dust transport modeling to investigate the transport and deposition of mineral dust from Australia over adjacent ocean regions and to correlate it with biological response in phytoplankton standing stock as measured by chlorophyll-a concentration in five-degree latitude bands from 40-60°S. Seasonal maxima in mean surface chlorophyll-a of ~0.5 mg m-3 were not achieved until late Jan 2003 or during February in the more southerly bands, which when compared with a 9-year satellite mean climatology suggests the phenology of the bloom in 2002-03 was atypical. Contemporaneous field data on CO2 fugacity collected on transects between Tasmania and Antarctica show that significant atmospheric CO2 drawdown occurred as far south as 60°S during February 2003. Our results provide strong evidence for a large-scale natural dust fertilization event in the Australian sector of the Southern Ocean, and highlight the importance of dust-derived nutrients in the marine carbon cycle of the Southern Ocean.

A first appraisal of prognostic ocean DMS models and prospects for their use in climate models

Ocean dimethylsulfide (DMS) produced by marine biota is the largest natural source of atmospheric sulfur, playing a major role in the formation and evolution of aerosols, and consequently affecting climate. Several dynamic process-based DMS models have been developed over the last decade, and work is progressing integrating them into climate models. Here we report on the first international comparison exercise of both 1D and 3D prognostic ocean DMS models. Four global 3D models were compared to global sea surface chlorophyll and DMS concentrations. Three local 1D models were compared to three different oceanic stations (BATS, DYFAMED, OSP) where available time series data offer seasonal coverage of chlorophyll and DMS variability. Two other 1D models were run at one site only. The major point of divergence among models, both within 3D and 1D models, relates to their ability to reproduce the summer peak in surface DMS concentrations usually observed at low to mid- latitudes. This significantly affects estimates of global DMS emissions predicted by the models. The inability of most models to capture this summer DMS maximum appears to be constrained by the basic structure of prognostic DMS models: dynamics of DMS and dimethylsulfoniopropionate (DMSP), the precursor of DMS, are slaved to the parent ecosystem models. Only the models which include environmental effects on DMS fluxes independently of ecological dynamics can reproduce this summer mismatch between chlorophyll and DMS. A major conclusion of this exercise is that prognostic DMS models need to give more weight to the direct impact of environmental forcing (e.g., irradiance) on DMS dynamics to decouple them from ecological processes.

Dimethylsulphide production in the subantarctic southern ocean under enhanced greenhouse conditions

Dimethylsulphide (DMS) is an important sulphur-containing trace gas produced by enzymatic cleavage of its precursor compound, dimethylsulphoniopropionate (DMSP), which is released by marine phytoplankton in the upper ocean. After ventilation to the atmosphere, DMS is oxidised to form sulphate aerosols which in the unpolluted marine atmosphere are a major source of cloud condensation nuclei (CCN). Because the micro-physical properties of clouds relevant to climate change are sensitive to CCN concentration in air, it has been postulated that marine sulphur emissions may play a rôle in climate regulation. The Subantarctic Southern Ocean (41–53°S) is relatively free of anthropogenic sulphur emissions, thus sulphate aerosols will be mainly derived from the biogenic source of DMS, making it an ideal region in which to evaluate the DMS-climate regulation hypothesis. We have extended a previous modelling analysis of the DMS cycle in this region by employing a coupled general circulation model (CGCM) which has been run in transient mode to provide a more realistic climate scenario. The CGCM output provided meteorological data under the IPCC/IS92a radiative forcing scenario. A DMS production model has been forced with the CGCM climate data to simulate the trend in the sea-to-air DMS flux for the period 1960 to 2080, corresponding to equivalent CO2 tripling relative to pre-industrial levels. The results confirm a minor but non-negligible increase in DMS flux in this region, in the range +1% to +6% predicted over the period simulated. Uncertainty analysis of the DMS model predictions have confirmed the positive sign for the change in DMS flux, that is a negative DMS feedback on warming.

The New Morris Method; an efficient second order screening method

The New Morris Method was proposed by Campolongo and Braddock [Reliab. Engng Syst. Saf. 64 (1999) 1] as an extension of the Morris Method [Technometrics 33 (1991) 161] 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.

Coupling between ocean biota and atmospheric aerosols: Dust, dimethylsulphide, or artifact?

[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.

An Antarctic Research Station as a Source of Brominated and Perfluorinated Persistent Organic Pollutants to the Local Environment

This study investigated the role of a permanently manned Australian Antarctic research station (Casey Station) as a source of contemporary persistent organic pollutants (POPs) to the local environment. Polybrominated diphenyl ethers (PBDEs) and poly- and perfluoroalkylated substances (PFASs) were found in indoor dust and treated wastewater effluent of the station. PBDE (e.g., BDE-209 26-820 ng g(-1) dry weight (dw)) and PFAS levels (e.g., PFOS 3.8-2400 ng g(-1) (dw)) in dust were consistent with those previously reported in homes and offices from Australia, reflecting consumer products and materials of the host nation. The levels of PBDEs and PFASs in wastewater (e.g., BDE-209 71-400 ng L(-1)) were in the upper range of concentrations reported for secondary treatment plants in other parts of the world. The chemical profiles of some PFAS samples were, however, different from domestic profiles. Dispersal of chemicals into the immediate marine and terrestrial environments was investigated by analysis of abiotic and biotic matrices. Analytes showed decreasing concentrations with increasing distance from the station. This study provides the first evidence of PFAS input to Polar regions via local research stations and demonstrates the introduction of POPs recently listed under the Stockholm Convention into the Antarctic environment through local human activities.

Modeling dimethylsulphide production in the upper ocean

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.

Uptake of zwitterionic antibiotics by rice (Oryza sativa L.) in contaminated soil

Antibiotics, including members of the tetracycline and fluoroquinolone families, are emerging organic environmental contaminants. Uptake from soil by plants is a means for antibiotics to enter terrestrial food chains. Chemical exchange between plant and the soil/water matrix occurs simultaneously with degradation in the soil/water matrix. In this study, the comparative temporal behaviour of rice (Oryza sativa L.) towards the zwitterionic antibiotics oxytetracycline, chlortetracycline and norfloxacin at initial soil/water concentrations of 10, 20 and 30 μg g(-1) (dry weight) is investigated. This is accomplished within the framework of an activity-based mass-conserving dynamic model. Plant antibiotic concentrations are observed to increase to a maximum then decline. Maximum concentrations in rice are compound-dependent linear functions of initial soil/water concentrations, but the relationships are not related to the compound octan-1-ol/water distribution ratio (DOW). The times required to attain maximal concentrations are independent of initial soil/water levels for a given antibiotic, but again vary between antibiotics and are not related to DOW values. Translocation from root to other tissues is not observed. The magnitudes of Root Concentration Factors (RCFs), the ratio of root and soil/water concentrations, are consistent with significant sorption to soil and consequent relatively low concentrations in interstitial water.

The Mechanisms of Coexistence and Competitive Exclusion in Complex Plankton Ecosystem Models

The biodiversity of plankton ecosystems may no longer be a paradox, but the mechanisms that determine coexistence of explicit competitors in ecosystems remain a mystery. This is particularly so in ecosystem models, where competitive exclusion remains the dominant process. Climate and fisheries models require plankton ecosystem sub-models that maintain competing plankton functional types extant, but coexistence can be reproduced in only a few ‘just so’ theoretical models. This limits our ability to predict the impacts of climate change and fisheries on ocean biota. We consider ecosystems of Kolmogorov form that conserve mass (CK systems). These systems describe a general class of ecosystem models that includes many theoretical and applied models. We develop heuristics that illuminate the key mechanisms that allow the coexistence of explicit competitors in these systems. These heuristics facilitate the identification of a large class of models with the structural property that all species coexist for all time. Our approach unifies many theoretical and applied models in a common biogeochemical framework, providing a powerful tool with the potential to generate new insights into the properties of complex ecosystems.