The 1998 Thin Layers Experiments were designed to build upon what was learned in 1996. Although there was substantial interest in conducting a Thin Layers Experiment at some location in the coastal ocean, we chose to return to East Sound for several reasons:

East Sound is a location where:

• we have evidence that Thin Layers are often present (at least in summer), maximizing the likelihood that they would be present during the experiment.
• circulation is sufficiently constrained that layers can be synoptically sampled over a few days.
• gear does not have to be modified to work from ships that are moving vertically on meter scales (e.g. on the open coastal shelf).

Major Questions:

1. What are the temporal and spatial scales, as well as the composition of Thin Layers?

Note: it should be recognized that Thin Layers of temperature and/or salinity may not have the same time and space scales as Thin Layers of phytoplankton. Furthermore, Thin Layers of phytoplankton will not necessarily have the same patterns as layers of marine snow. Zooplankton may aggregate in, or avoid physical layers and phytoplankton layers. It is necessary to resolve the patterns of distribution for each component, and then use the full suite of data to determine interrelationships.

2. What processes, or mechanisms, influence the composition, formation, maintenance and dissipation of Thin Layers?

Note: Shear, mixing, wind stress, insolation, species composition, grazing, sinking, current structures, internal waves, predation and a variety of additional processes have all been implicated as potentially important mechanisms in the formation, maintenance, dynamics and dissolution of Thin Layers.

3. Do zooplankton aggregate in, or avoid some phytoplankton layers?

Note: This question is part of a larger one, namely, "Do zooplankton use Thin Layers?" Determination of use and the kind(s) of uses that zooplankton may have implies a much wider range of questions, including some related to behavior. We restricted the present objectives to address issues of spatial and temporal coherence of Thin Layers of physical structures (temperature, density, salinity, shear), zooplankton, phytoplankton and marine snow. We will add, if observed, acoustically and optically detected layers of particles other than living material.