U.S. GLOBEC Georges Bank Program
Phase II - Prologue

The primary objective of the U.S. GLOBEC Program is an extended understanding of the physical and biological processes controlling the abundance of marine animals in time and space. Studies under the GLOBEC banner focus on early life stages and recruitment as keys to population dynamical explanation of variation in fish and zooplankton stocks. GLOBEC seeks to demonstrate the links among climatic variation, physical processes active in the sea on shorter time scales, and recruitment rates (U.S. GLOBEC Report No. 6, 1992).

The U.S. GLOBEC program selected the Georges Bank area of the Northwest Atlantic as the first region for intensive study. The reasons were:

  1. Georges Bank is in a boundary region in respect to climate, ocean currents and faunal patterns. Therefore, ecosystems in and around Georges Bank can be expected to be highly sensitive to climatic variability.

  2. Secondary production on Georges Bank supports a large, commercially valuable fishery.

  3. Advective transport through the region is predicted to change more with climatic variation than that in other areas of the North Atlantic.

  4. Georges Bank causes a distinctive, regionally closed circulation. It is of sufficient size that this pattern of flow enables distinct, trackable populations to develop and persist for periods long enough to permit meaningful study by time-series sampling.

In Phase I, we have established that the physical regime over and around Georges Bank interacts with the timing of copepod and fish biological events to produce the long observed distributional patterns of copepods, common planktonic predators and larval fish. The most important example is that newly reproductive copepods, particularly Calanus finmarchicus, emerging in January from rest in the depths of the Gulf of Maine and beginning to reproduce are drawn into a current jet along the north edge of the bank and thus concentrated. When this jet of high stock turns and slows out over the Northeast Peak very high levels of naupliar abundance are established there, then spread all along the southern flank at the east end of the bank. Since this must recur (yet to be shown), it selects cod and haddock that spawn in the peak subregion. Currents moving from the jet at the north edge also carry copepods from the Gulf onto the top of the bank where they prosper for a time. In May flow over the top of the bank becomes divergent, and the fauna in shallow waters completely changes in character.

In Phase II, research will again focus on target species that are key elements in the planktonic assemblages of the Georges Bank region: pelagic larval stages of codfish (Gadus morhua), haddock (Melanogrammus aeglefinus) and the copepods Calanus finmarchicus, Pseudocalanus moultoni, and Pseudocalanus newmani. Hypotheses concerning these species for Phase II involve retention and loss of water and animals from over and around Georges Bank. Tests of those hypotheses involve four main activities:

  1. quantification of target species abundance patterns across Georges Bank and through their growing season;

  2. measurement of the population dynamical vital rates of target species;

  3. quantification of physical exchanges of water and biota across the boundaries of the bank;

  4. determination of the interaction of vertical migration and vertical position maintenance behavior on retention and loss of planktonic animals on the bank.

The U.S. GLOBEC Northwest Atlantic/Georges Bank study has four major components: a Broad-scale field survey, process-oriented observational and experimental studies, modeling investigations, and retrospective analyses.

Broad-scale field survey: This includes monthly shipboard surveys covering the bank with plankton and hydrographic stations in a clockwise grid, multi-disciplinary moorings and analysis of satellite data. Shipboard sampling will continue to determine the distribution and abundance of the target organisms in relation to their physical environment and to flow during the larval phase of cod and haddock (January through June). Long-term moorings will continue to monitor variations in flow and the response of flow to the wind. Satellite pictures will continue to provide the synoptic view of regional events needed for full interpretation of other data types necessarily less comprehensive. The broad-scale survey will provide the basis for inter-annual comparisons from which we expect to construct a scenario for the impact of climate change.

Process Studies: Process studies are nested within the broad-scale observations to investigate specific biological and physical processes. The focus in 1995 was on the influence of water column stratification on vital rates of the target species. The approach used was to identify and follow a patch of organisms while investigating the physical-biological interactions. The focus in 1997 will be on processes associated with source, retention, and loss of water and organisms as they impact the population dynamics of target-species on the Bank (See Report #6, pgs 36-39 for more detail). Close cooperation and interaction between the broad-scale and process components of the program is essential.

Modeling: Modeling studies are essential to the formulation and testing of hypotheses, to the interpretation of the data from the field studies, and to the integration of the results. Modeling studies to date have focussed on the development of 3-D models of the flow field of the Georges Bank and the surrounding regions, and linkages to the population dynamics of target species. In addition to site-specific modeling, modeling with a more regional scope is planned. Further, these efforts will incorporate more realistic biological/physical interaction and to allow for data assimilation.

Retrospective Analyses: Retrospective studies of existing data sets provide a means of investigating the biological and physical consequences of climatic variation. Previous studies have included processing of archived samples and interpretation of existing data sets. These studies will continue to look at past data sets and sample collections that allow integration, coordination, and comparison of Georges Bank data sets with those from other North Atlantic regions.