A MODEL ECOSYSTEM

Creating computer models of ocean physics isn't exactly a breeze.

At Scripps Institution of Oceanography and other research institutions, physical oceanographers like Art Miller spend years trying to design accurate simulations of the internal motion of the ocean. Armed with a long-term oceanic time series of temperature, salinity, current speed, and wind speed, as well as some serious memory in their computer hard drives, they set out to model past ocean activity and predict how the ocean might behave in the future.

Now Miller and former Scripps graduate student Emanuele Di Lorenzo are embarking on a new quest to create even more sophisticated models for the California Current portion of the Long-Term Ecological Research (LTER) project led by Scripps. In addition to the myriad variables that need to be taken into account to model major currents, eddies, and upwellings of cold water from the deep ocean to the surface, the new models will also include biological variables such as phytoplankton aggregations, grazing rates, and infusions of nutrients into given areas.

"No one's ever tried this before, so understanding complexity and trying to model it is the key issue," Miller said.

Computer modelers have tended to represent biological activity as simply as possible in their simulations, content to let a condition like phytoplankton abundance in a given parcel of ocean be represented by highly generalized characteristics. LTER biologists hope to provide Miller and Di Lorenzo with much more specific parameters describing biological processes to plug into their models.

One aspect of Miller's LTER work will be to develop models that fabricate a physical and climatic context in which to understand measurements made over the last six decades as part of the California Cooperative Oceanic Fisheries Investigations. As a first step, plans are under way to have Di Lorenzo, now at the Georgia Institute of Technology, take data from this year's initial LTER cruises and create models from them, fine-tuning the models until they match actual ocean conditions observed during the current cruises.

Far from previous representations of organisms in physical ocean models, which acknowledged their presence and little more, Miller said the new models will account for processes such as the grazing rates of micro-zooplankton on phytoplankton and develop competition scenarios when two or more plankton species inhabit the same parcel of ocean. Sound complex? It is, said Miller, who acknowledges the challenge.

"By constructing these models, we'll be able to determine the level of complexity needed to explain these observations," he said, "or know whether it is even possible to build a model that can explain them—or is the biology way too complicated?"