## Physical/Biological Moorings (1994-1998)

The moored array component should provide a continuous time history of the variability of the physical and biological properties occurring at select locations on and about Georges Bank. These moored observations should complement the shipboard surveys described above and the satellite surveys described below, providing the continuous time record to put these spatial surveys into temporal context. The spatial surveys should describe the horizontal structure on a scale smaller than that resolved by the moorings and thus complement the time-series observations. The sum of these various observations is required to describe adequately the important physical and biological processes occurring in the region.

The broad-scale mooring program will provide the basic description of temporal variability and provide the context for the more specific small-scale process studies discussed below. Selected mooring sites should be maintained continuously for the full 5 years of the field program. These observations will monitor the seasonal changes as well as inter-annual variability. Additional moorings should be deployed for the December through August period of concentrated study and will act as focal points for some small-scale process studies.

Questions: The broad-scale moored component should address the following questions:

1. What is the atmospheric forcing in the Georges Bank region (momentum, heat, buoyancy fluxes as well as available light), and how does it vary spatially over short time-scale events, seasonally, and inter-annually?

2. What is the temporal variability of basic physical (e.g., temperature, salinity, velocity), chemical (e.g., inorganic nutrients, oxygen), and biological (e.g., phytoplankton and zooplankton biomass) properties as a function of depth at selected sites?

3. What tidal and internal tidal energy is present in the sea surface elevation (bottom pressure) and current, and how does the internal wave component change with season and stratification at selected sites?

4. What is the subtidal current at selected sites around the Bank?

5. What is the temporal and spatial variability of the surface wave field over the Bank?

6. What is the temporal variability in the abundance of target species and associated biological indicators (e.g., dissolved oxygen, nutrient concentrations, upwelling radiance and downwelling irradiance, Photosynthetically Available Radiation, stimulated fluorescence, in situ measurement of primary production, optical transparency (beam attenuation), acoustical backscatter for biomass and video imagery for size distribution and taxonomic identification) as a function of depth at selected sites?

7. How does the occurrence and timing of episodic events such as storms or warm-core rings affect the physical and biological properties at selected sites on the Bank and their exchange with adjacent areas?

Strategy: These temporal observations should provide descriptions of the upstream source of water and biological populations, surface and lateral forcing on Georges Bank and time history of episodic events. Sampling is required on time scales of hourly to multi-year, and on space scales of a few meters to ten's of meters in the vertical, and ten's of kilometers in the horizontal. Mooring sites should include the edge of Wilkinson Basin as a source region for water and organisms, possibly two locations along the southern flank of Georges Bank, and possibly on the crest of the Bank (Figure 12). Information on the temporal and spatial variability in the surface wave field will be useful in calculations of bottom stress, since surface waves can make a significant contribution to bottom stress. These observations will need to be combined with the broad-scale survey, satellite imagery and drifter results as well as with feedback from the modeling effort to gain the maximum description of the broad-scale physical and biological processes.

The moored program will benefit from advances that are being made in acoustics, which not only can be used to determine the vertical structure of the water velocity field, but also can be used to study the time variations of the vertical distributions of scatterers. With shipboard survey calibration, estimates of the time variability of biomass can be made. The moorings will need the latest in meteorological technology, measuring wind speed and direction, atmospheric pressure, precipitation, atmospheric temperature, relative humidity, long and short wave radiation, and sea surface temperature. Results from a U.S. GLOBEC meterology buoy on the Bank should be combined with coastal meteorology and data from the NOAA NDBC environmental buoys on Cashes Ledge, Georges Bank, and Nantucket Shoals to provide a comprehensive description of surface forcing over the Bank (Figure 12).

Bio-optics is the study of optical processes of the upper ocean that affect and are affected by biological processes. The time history of bio-optical and biological activity measurements listed below coupled with physical oceanographic observations are vital in studies linking primary production to upper ocean dynamics. These include the measurement of temperature, salinity, water velocity, dissolved oxygen, upwelling radiance and downwelling irradiance, PAR (photosynthetically available radiation), stimulated fluorescence, optical transparency (beam attenuation), acoustical backscatter sampling for biomass, and video imagery for species identification. New instrumental approaches to the high resolution time-series measurement of inorganic nutrients and phytoplankton production will reduce the temporal disparity that commonly exists between physical and bio-optical observations, and allow measurements of biological activities that are influenced by the physical environment.

The moored program should take advantage of real-time data telemetry to routinely transfer the data collected on the remote platform to the laboratory. These data should be processed to the first order and made available to the rest of the scientists in the program to: (1) aid in the development and verification of models; (2) ascertain that the equipment is functioning properly; (3) allow scientific analysis to start; (4) identify important and unusual conditions or events which will allow for a modification of the shipboard surveys; and (5) provide the broad-scale context for the smaller-scale process-oriented studies. Temperature from the moorings will also be used to correct AVHRR data (see below); these data may then be used in near real-time to adjust or correct sampling strategies during cruises.