Modeling and Historical Data Analysis

Theory and Modeling

The development of appropriate theory and mathematical models for physical/biological interactions is an essential component of U.S. GLOBEC. This activity can provide a clear picture of the status and limitations of existing theoretical knowledge, identify areas needing additional research, provide guidance for field studies and help interpret field measurements, and hopefully lead to model verification and improved predictive capabilities. This latter step is critical since U.S. GLOBEC aims to make reliable predictions of population changes associated with future climate change. As noted earlier, much guidance will be needed in planning field studies. In particular, a sampling design needs to be developed which will give the statistical power to actually reject specific null hypotheses. Spatial sampling as well as sampling which produces a few point time series would be appropriate given the different time scales at which individuals of the target species develop.

In February 1990, U.S. GLOBEC began a program of theory and modeling research. The GLOBEC Working Group on Theory and Modeling issued a report (GLOBEC, 1991a) identifying three broad categories where theoretical work was critically needed: a) conceptual studies of simplification and predictability; b) prototype investigations of biological processes in idealized flow fields; and c) site-specific models. Based on this report, NSF issued a call for proposals; after review, a total of seven awards were made for six research projects. Four of these relate to the Georges Bank Study and will be briefly described next (see Taylor (1991) for complete descriptions of all seven modeling projects):

Conceptual Studies

Direct numerical simulation of homogeneous turbulence for planktonic organisms: H. Yamazaki -- Project focuses on how turbulence can influence the contact rate between predator and prey. Uses direct numerical simulation to create a turbulent flow field and then conducts Lagrangian experiments with a stochastic model of plankton behavior.

Prototype Studies

Recruitment dynamics in event-driven bank circulations: C. Davis, G. Gawarkiewicz, D. Chapman, D. Olson, and G. Flierl -- Project focuses on the effects of storms and rings on advective exchange rates of planktonic organisms from a bank like Georges Bank. Uses a numerical circulation model to study the Lagrangian response of simple flows over an isolated bank to wind and ring forcing.
Development of quantitative, hydrodynamic and biological models of settlement of planktonic larvae of benthic animals: J. Eckman, T. Gross, and F. Werner -- Project focuses on the influence of velocity shear and turbulent mixing in the bottom-boundary layer on the settlement of benthic planktonic larvae. Initial effort is to use idealized one- and two-dimensional models of the turbulent bottom-boundary layer to identify and quantify key physical processes controlling larval flux at the boundary.

Site-Specific Studies

Significance of circulation to egg and larval distributions on Georges Bank: D. Lynch, F. Werner, J. Loder, M. Sinclair, D. Greenberg, and I. Perry -- Project focuses on testing whether observed distributions of eggs and larvae can be simulated using a simple larval drift model driven by a numerical circulation model with realistic regional topography, internal density field and surface forcing.

Additional theory and modeling research in all three categories is clearly needed for the Georges Bank Study. While new conceptual studies regarding the simplification of and predictability in coupled physical/biological models will help the entire U.S. GLOBEC effort, additional site-specific modeling studies are required to understand how the different physical/biological processes described above influence the population dynamics of the target species on Georges Bank. These studies should include prototype investigations of biological processes in the following idealized flows: one-dimensional well-mixed and stratified tidal flow with a turbulent bottom-boundary layer, simplified bank gyre with and without recirculation, and simple tidal mixing and shelf/Slope Water fronts. Further development of realistic local and regional three-dimensional numerical circulation models is also needed. These models should incorporate turbulent boundary layer physics and be used to study the following problems: the formation of tidal mixing and other fronts around the Bank, the seasonal evolution of the general circulation over the Bank, the different roles of surface and lateral buoyancy forcing and tidal mixing to establish the Bank stratification, the influence of tidal and wind forcing on mixing over the Bank, and the response of Bank waters to storms and rings. Research also is needed to incorporate basic biological processes into these new site-specific circulation models, so that state-of-the-art coupled physical/biological models for Georges Bank can become available during the course of the Georges Bank Study. Because of the complex nature of physical/biological interactions on the Bank and the need to optimize the design of field work, it is important to emphasize this theoretical work early in the Georges Bank Study. The above list of theoretical problems and issues is not meant to be inclusive, but suggestive of the types of studies to be encouraged.

Lastly, and perhaps most importantly, research is needed on how to incorporate data, both physical and biological, into models. Whether present techniques of data assimilation that have been developed for physical ocean models (e.g., Haidvogel and Robinson, 1989) are applicable to coupled physical/biological models needs to be assessed. Where lacking, new techniques need to be developed. Also, it is hoped that this exercise will ensure a good match between theory and measurement, and help identify new ways in which physical and biological data can be used to initialize, constrain, and verify coupled models.

Historical Data Sets

There are significant historical data sets which should be examined to provide an expanded time-series context for the data acquired during the Georges Bank Study. Given the relatively limited resources available for this study, it is essential that the program take advantage of past research efforts in the area. Some of these data sets are well known because of the many publications arising from them, while others have not been summarized in the open literature and are not generally known by the scientific community. They exist in various degrees of processing and public availability. In most cases, they are a combination of both biological and physical data, but were not used initially to address the specific issues that are the focus of this program. A partial list of major data sets and field survey programs includes:

The 1939/1940/1941 Bumpus time-series plankton study of Georges Bank
The 1961-present Continuous Plankton Recorder Gulf of Maine data set
The 1965-1966 NMFS Gulf of Maine Study
The 1970-1987 MARMAP study of the Gulf Of Maine, Georges Bank, and the Mid-Atlantic Bight
The 1978 American/Canadian Patch Study
The 1978-1980 New England Outer Continental Shelf Physical Oceanography Program
The 1979-1980 Nantucket Shoals Flux Experiment
The 1981 Nantucket Shoals Experiment
The 1981-1982 Warm-Core Ring Study
The 1983-1985 Southwest Nova Scotia Fisheries Ecology Program
The 1985-1986 Great South Channel Recirculation Experiment
The 1986-1987 UNH Gulf of Maine Study
The 1988-1989 South Channel Ocean Productivity Experiment
The 1978-1986 CZCS color data set and 1980-present AVHRR data set
Moored and coastal weather station data

In addition, other monitoring programs have provided physical and biological data for the region (e.g., 7 years of mooring records off Cape Sable, Nova Scotia before and during the Fisheries Ecology Program). There is currently a NOAA Marine Ecosystems Response-funded analysis of historical ichtyoplankton and hydrographic data from the Northeastern U.S. continental shelf region. Additional background information on some of the regions historical data can be found in O'Reilly (1987).

Researchers are encouraged to contribute to the Georges Bank U.S. GLOBEC program through analysis of historical data, especially through 1) the application of new analytical and statistical techniques to historical data sets, 2) the integration of unconnected databases, and 3) the evaluation of historical data in the context of climate and inter-annual variability.