Christopher C. Jenkins EAR-1118297 University of Colorado, Boulder PI: Potts, Donald C. EAR-1118306 University of California-Santa Cruz
Carbonate sediments are deposited extensively in the oceans and are a significant factor in global carbon budgets. But they are challenging to understand because they are created biologically, then modified geologically. Prior to this project, they had been modeled with rather simple rules-based methods which go under the name ?carbonate factory?. This project takes the next step and directly applies biological principles using advanced numerical modeling on the actual processes ? ?carbonate farm?. The population and community ecology of carbonate-skeleton organisms such as corals, bryozoans and algae is used to build realistic, detailed 3D time-geologic architectures. This opens productive new research paths into the carbon cycle, ocean acidification, rock properties, oil-gas resources, and environmental responses to global change. Perceptions that process modeling is not achievable are wrong ? the key is to employ good math tactics on the correct set of processes, for the key organisms, at appropriate time-space scales. In prototype this project has already produced emergent model features such as high-production ?bone yard? ecologies, and correct statistics for the variability of the accumulated sediments. The outputs can be compared even at the core-description level with Integrated Ocean Drilling Program (IODP) core logs and oil-industry reservoir variability statistics, promising cross-discipline results.
Carbonate rocks include limestones, and coral reefs and other large biological frameworks in the ocean and on land. They are special for several reasons: they have usually been formed biologically, they have a great amount of void space (porosity), and they are economically important for cement, groundwaters and oil/gas. Because they are biologically formed then physically/chemically altered, they are quite difficult to understand and manage. For instance, they can slowly be dissolved, and they form large caves and sinkholes. Math models of rocks are important to us because they hold (and computer-code) our present knowledge, and then they make predictions for the future or for where we cannot see. Math models of carbonate rocks till now have been quite primitive. They assumed one growth rate for all organisms, scaled to light, temperature and depth. But we know that corals grow beyond light, and that they cannot grow where young spawndo not settle, or where they are wiped out by competitors. So the next generation of models - like this one - takes account of biological factors that govern the organisms which build the carbonate rocks and sediments. This is "population ecology". We have used several math methods for population ecology, involving the organisms' growth, survival and death rates, and the amount of skeleton they leave after death. Then the model takes this and generates the sediment and finally rock mass. There are many good features of this approach, especially that it can model carbonates from many different types of organisms including the now-extinct forms that occur with the Middle Eastern oil reseroirs, for instance. The new model is operating and produces realistic results, even for unpredictable events such as mass coral bleaching (high temperatures), hurricanes, and freshwater floods. The populations recover from events over times that fit with real observations. The model is producing "virtual rock" that matches what we observe in boreholes and rock outcrops. The model is being published and will be released for general use by students and the public. Scientists will also use it to help make decisions on water resources, or reef conservation. Some will also take it and make the next steps for improvement.