SIBER SPIS sept 2011.pdf - IMBER

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SIBER Science Plan and Implementation Strategy 4. Sub-decadal physical fluctuations are crucial for determining interannual to decadal dynamics of biogeochemical and ecological systems and provide an important and tractable scale for examining biogeochemical and ecosystem responses to physical variation. Models are therefore, required that include large-scale physical interactions (atmosphereocean and inter-basin) and their connections with global climate-related processes (e.g. the IOD, ENSO and the Antarctic Oscillation). Clarifying the interactive nature of these physical processes is required to determine the drivers of biogeochemical and ecological change. 5. Models predicting future climate-driven change in the global ocean have suggested that atmospheric warming will increase monsoon wind and precipitation variability. Increased variability in current speeds may result from increased wind speeds, and changes in freshwater budgets associated with precipitation changes will affect water column stability. However, a high degree of uncertainty is involved. This needs to be accounted for in simulating future change scenarios in relation to biogeochemical and ecological systems. 6. A wider network of physical and biological monitoring of oceanic systems is required to provide data for the robust development and testing of large-scale models. This could be achieved in conjunction with the IndOOS/RAMA mooring and observational network and by expanding and linking with IOGOOS measurements networks. 7. Circulation models at global and basin scales (such as the OFAM/BLUElink Project) and regional scales are valuable as stand-alone systems for examining circulation effects on biogeochemical and ecological systems. However, large-scale models may not capture key aspects of regional variation, which will be crucial in determining biogeochemical and ecosystem responses. For example, dynamic biogeochemical models that provide realistic simulations at regional scales are needed to better understand boundary current dynamics and oxygen minimum zone development in the AS and the BoB and responses to climate change. 8. High-resolution models that include adaptive vertical mixing schemes, the ability to handle steep topography, tidal effects, and processes over shelves are needed. Objective 2: To understand how ecosystem structure and dynamics affect biogeochemical cycles in the IO Development of biogeochemical models for the IO is advancing and models that simulate basinwide biogeochemical distributions are just becoming available. Acquisition of datasets that can provide evaluation of such model results will be an important focus for the next generation of IO research programs. Biogeochemical-based models have been developed for selected regions of, and across, the IO, for example, the AS (e.g. Hood et al., 2003; McCreary et al., 2001; McCreary et al., 1996), and the BoB (Vinayachandran et al., 2005). Wiggert et al. (2006) used a coupled physical-biochemical model to simulate nutrient limitation dynamics across the entire IO basin. These models provide very important insights as a basis for SIBER modeling studies. Model development should involve consideration of the following issues: 1. A focus for SIBER is to foster the development of regional coupled circulation-biogeochemical models, especially for areas identified as priority regions for field studies. 2. Understanding the influence of seasonally reversing boundary and open ocean currents on regional biogeochemical processes is crucial and presents methodological modeling challenges. Nested model structures can provide the space and time resolution for local scales as well as maintaining the larger scale connections between regions. A basinwide view could be developed by embedding high-resolution regional biogeochemical models into larger-scale circulation models. 86
SIBER Science Plan and Implementation Strategy 3. Development of basinwide and regional watershed models, especially for land areas surrounding the BoB, needs to be promoted. The importance of river-derived inputs of nutrients to material cycling in the IO has not been examined in models. Inclusion of sediment transport into circulation models, especially for coastal and continental shelf regions, also needs to be considered. 4. Development of generic models to determine how ecosystem structure influences biogeochemistry will be useful because potential feedbacks and control processes need to be specifically explored before attempts are made to construct complex simulations. 5. The importance of iron in regulating primary production should be incorporated into models of IO primary production (Wiggert et al., 2006) to begin to address questions regarding links between biogeochemical cycles and food web structure. 6. Impacts of ocean acidification and warming will require a specific focus on impacts at different levels of the ecosystem: stress on organisms through pH and temperature changes, alterations in calcification rates of autotrophic species (hence impacts on production and phytoplankton community composition) and changes in calcification rates and bleaching of coral species. Models are required that quantitatively assess these impacts and examine potential food web effects. 7. The next generation of biogeochemical models should include explicit food web dynamics. Validation and testing of such models will require appropriate data (that are not often collected simultaneously) at the required scales. This presents a challenge for the development of field programs. 8. Most biogeochemical models developed for the IO focus on the euphotic zone. Depthrelated vertical links in food webs, for example links to the mesopelagic layer and its role in controlling biogeochemical cycles and benthic production are largely unexplored in model studies. The biogeochemistry and ecosystem dynamics of this large and important environmental regime known as the mesopelagic zone, where organic material is remineralized, are poorly understood. 9. Coupling of pelagic-based biogeochemical models to benthic models will be important for some IO coastal regions to develop a more complete picture of pelagic-benthic coupling processes. Objective 3: To determine how ecosystem structure and dynamics should be incorporated into management approaches to sustainable exploitation of living resources in the Indian Ocean Model development should involve consideration of the following issues: 1. Much of the management-related modeling has tended to focus on single species harvestingbased models. In recent years there has been an increasing emphasis on the ecosystembased approach, incorporating food web interactions and environment links. 2. SIBER will complement and contribute to the work of IO island and rim nation fisheries management efforts in developing modeling approaches for sustainable management of IO resources, providing a broad ecological perspective. A range of models have been developed to examine upper trophic level food web interactions with a particular focus on the effects of harvesting (see for example Hill et al., 2006). 3. SIBER will investigate how the structure and dynamics of IO ecosystems should be represented in ecosystem models used in resource management. The complexity of these 87
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