CoOP's Great Lakes Science Plan
The interface between the land and the ocean is highly dynamic. Coastal waters throughout the world are sites of intense biological, chemical and geological processing of materials arriving from both the terrestrial and offshore zones. The character of these waters, from their capacity to assimilate anthropogenic inputs, to their ability to sustain viable and healthy fisheries, or their influence on regional climate, is dictated by a complex set of oceanographic processes and forcing functions which are often unique to coastal environments. The flux of materials through this region and the transformations they undergo have not been well studied, and consequently, the ability to forecast the impact of both natural and anthropogenically-induced phenomena remains poor.
The Laurentian Great Lakes represent systems dominated by their coastal nature. While oceanographic in scale (the lakes are large enough to be significantly influenced by the earth's rotation), the lakes are, at the same time, closed basins in which the influence of coastal processes are magnified beyond that of most coastal marine systems. Nowhere is an understanding of how complex physical, chemical, biological, and geological processes interact in a coastal system more important to a body of water than in the Great Lakes. As a site for studying these processes in a generic sense, the Great Lakes offer some distinct advantages. One is size. Another is a closed basin morphology. Both make for comprehensive studies in which basin scale, mesoscale, and microscale coverage is tractable, mass balances are possible, and hydrologic budgets, flushing and water residence times are well known. Similarly, the biology is simplified. Species diversity is low and food chains are short. Variability, on the other hand, as is typical of coastal regions, is high and ecologically non-steady state conditions prevail.
Historically, the lakes have been sites for some leading research in coastal hydrodynamics. In recent years, however, the Great Lakes have suffered from a lack of comprehensive studies designed to address fundamental questions concerning the biological, chemical and geological impact of coastal ocean processes. Physical limnology has fewer practitioners today than 30 years ago, despite vast improvements in the research technologies which offer the opportunity to achieve the needed understanding of such processes as coastal plumes, spill trajectories, coastal erosion and storm surges, weather effects, ice dynamics, and land-margin interactions. The CoOP Steering Committee decided that a major CoOP process study should be developed with substantial input from the combined Great Lakes and oceanographic community. The basic motivation for this effort arose not only from a series of compelling science questions but also from the realization that without such an effort, important gaps in our understanding of these lakes would remain unfilled, and our responsibility to maintain and preserve these systems into the future would be compromised.
The CoOP workshop "Great Lakes Coastal Ocean Processes Workshop" was held October 6-8, 1994, in Milwaukee, Wisconsin. The goal of the workshop was to create a document that defines a CoOP process study that would obtain a new level of quantitative understanding of the processes that dominate the transport, transformations and fates of biologically, chemically, and geologically important matter in the Great Lakes. The workshop was structured around eight working groups: Coastal Currents and Coastal Jets; Thermal Fronts: Vernal Dynamics and Structure; Upwelling and Stratified Conditions; Physical Dynamics of Coastal Systems and Their Relationship Among Biological, Chemical and Geological Components; Benthic-Pelagic Coupling in the Great Lakes: Implications for Hydrological, Solute, Sediment and Biotic Interactions; Air-Sea Interactions; Land-Margin Effects; and, Transformation of Solutes, Particles and Organisms. The workshop organizing committee drafted the CoOP Great Lakes Science Plan by synthesizing the recommendations of the eight working group reports.
Conducting a thorough suite of measurements and model formulation for every coastal region, or even every U.S. coast, is beyond the scope of the CoOP program. As described in Coastal Ocean Processes: A Science Prospectus (Brink et al., 1992), we assume that there is a set of dominant processes that can be found in different mixtures in different locations. Thus the CoOP approach is to quantify key processes in a few areas well enough to model them effectively in a variety of regions.
One of the most distinctive hydrodynamic features of the Great Lakes is the pronounced seasonality in thermal stratification which results in an annually recurring sequence of physical transport regimes that dominates the movement of materials between inshore and offshore, and fundamentally impacts the biology, chemistry and geology. These different regimes, and the transition from one to the other, dictate to a large degree the nature, timing and duration of cross-margin exchange processes which, in turn, exert a major influence on biological, geological and chemical interactions at a number of important boundaries and interfaces. During isothermal periods vertical mixing is extensive, often reaching the bottom and maintaining particles and organisms (e.g., algae) in suspension, and under exposure to incident light. During vertically stratified periods, waters in contact with the bottom are largely segregated from the photic zone by a stable and persistent thermocline, through which particles are lost by settling. The presence of partial to complete ice cover, a particular feature of the Great Lakes in the winter, reduces wind stress with a concomitant reduction in mixing and light penetration, but with increased wind stress curl at the ice edge. The timing and duration of the annual transition between unstratified and stratified conditions can have a fundamental impact on the biology, chemistry and sedimentology/geology of the system in the subsequent year. Interdisciplinary, quantitative studies conducted during this period, however, are lacking.
The major basins of the Great Lakes offer diversity as well as similarity. Both cross-lake and inter-lake comparisons in proposed CoOP process studies are possible. While Lakes Erie, Michigan and Ontario have been the most extensively studied, and have the most background to aid in planning a CoOP study (e.g. the International Field Year for the Great Lakes study [IFYGL], 1972), the workshop did not arrive at a consensus with respect to a specific location or locations for study. International scientific interest from Canada through the Canada Centre for Inland Waters (CCIW), and the addition of expertise and resources of CCIW would greatly enhance any U.S. CoOP Great Lakes research program.
The central focus of a CoOP Great Lakes process study is to address the following general question:
What is the influence of vertical stratification on cross-margin transport of biological, chemical and geological materials in the coastal margins of the Great Lakes?
Within this context, a number of important, process-directed issues evolved from the workshop deliberations. Interdisciplinary projects, part of a CoOP Great Lakes study, should address one or more of these specific processes.
While studies in other parts of the coastal ocean significantly enhance our understanding of Great Lakes processes, not all saltwater results will apply. Some features of the Great Lakes are unique to these freshwater systems. By the same token, however, Great Lakes processes are not entirely unique and studies launched within these lakes will have broad applicability in furthering fundamental advances in coastal science in general. The cross-fertilization of marine and freshwater perspectives is deemed as a positive outcome of a Great Lakes process study. A broad based research effort, a minimum of five years in duration, with a strong emphasis on process and interdisciplinary models, and a coordinated, technologically advanced observational program is recommended.