US GLOBEC Newsletter 13: NWA Process Studies

| Northwest Atlantic Phase III Process Studies: Final Season Now Underway by Elizabeth Turner US GLOBEC Northwest Atlantic enters into its final season of process field studies in Phase III. The objectives of the process cruises in this phase are centered on cross-frontal processes, and the program has an integrated approach to study frontal dynamics at fronts on both the Northern and Southern flanks. A total of 22 projects are involved in Phase III, involving 19 academic institutions, the NOAA / NMFS Northeast Fishery Science Center, 57 PIs, 44 technicians, four post-docs, and 26 students. The field cruises require over 350 days at sea, and GLOBEC is the major user of both R/V Oceanus and R/V Endeavor time in 1999. The coordination of proposals, activities, and ship time was accomplished with the input of the Phase III PIs, and their successful efforts are greatly appreciated. Energetically leading these activities has been Peter Wiebe, who will remain as the program coordinator and chair of the executive committee. The broadscale cruises will continue to give a wider context for the process studies, with Mountain, Berrien, and Green heading up the hydrography and ichthyoplankton effort, Townsend the nutrient measurements, and Durbin macrozooplankton and nauplii work, along with an army of co-PIs, students, technicians and sorters. Longer-term, more continuous measurements will be provided by moorings and drifters deployed by Brink, Irish, and Limeburner; and in a separate project by Schlitz. Brink et al. will also provide analysis of historical hydrographic data to understand the physical characteristics of Georges Bank during the field studies, and fit them within a longer-term context. Bisagni will interpret and analyze remotely-sensed data, providing real-time SST frontal positions to help guide the process studies, and quantifying aspects of cross-frontal mixing from both current SST data and analysis of longer-term data. Data and samples from the broad-scale cruises will be used by Miller to model the interaction of life history events in Calanus finmarchicus with advection and mixing in the Gulf of Maine and on Georges Bank. Miller will also characterize and quantify developmental stages, sexual maturation, and onset of diapause in copepodites, and relate developmental delays in copepodites to starvation events. Ohman and Durbin will measure the egg-laying rate of dominant cope-pods, the growth rate of Calanus and Pseudocalanus, and estimate the egg and naupliar mortality of Calanus and Pseudocalanus. One new addition to the program this year is the tracing of cross-frontal transport through the use of Rhodamine and Fluorescein dyes. Ledwell and Churchill will use Rhodamine WT to trace water parcels within the pycnocline and in the upper mixed layer at both the Northern flank and the Southern flank fronts. Davis will pro-vide a view and analysis of the associated plankton populations with the Video Plankton Recorder. Houghton will use Fluorescein to track the near-bottom flow in the same areas within the same time frame. Hebert and Barth will use a Coastal Ocean Lagrangian (COOL) float, in conjunction with a SeaSoar survey, to measure cross-frontal exchange pathways at the two fronts in two separate cruises. Their project will be co-located and coordinated with the vertically-stratified zooplankton sampling of Wishner, and the microzooplankton feeding and vital rate studies of Giffford. Certain projects focus primarily on the Northern flank, and influences of Scotian Shelf water on Georges Bank. Beardsley, Flagg and Limeburner, along with Canadian colleagues Smith, Loder, and Hannah, will examine the crossover of Scotian Shelf water onto Georges Bank, and investigate the mechanisms for transport of water, nutrients, and biota from the Gulf of Maine and the Scotian Shelf to the Northeast Peak and Southern flank of Georges Bank. Townsend and Radtke will use otolith elemental analysis and DNA micro-satellite techniques to identify the origin of larvae, with the goal of determining to what extent cod on Georges Bank are advected from Canadian waters in early developmental stages. Fairbanks and Houghton will use Oxygen-18 to assess the influence of local and far-field water sources on the Georges Bank environment. Several process studies will work primarily on the Southern flank tidal mixing front. Bucklin and McGillicuddy will investigate the distributions of Pseudocalanus spp. in relation to physical transport overall on Georges Bank, but especially on the Southern flank tidal mixing front. Madin, Sullivan, and Bollens will also focus on the southern tidal mixing front to determine the distribution and abundance of prey and predators along and across the front, the effect of frontal dynamics on aggregation and interaction, and the exchange of organisms from one side to the other. They will also continue their work to measure predation rates and analyze predator gut contents. Lough, Townsend, Buckley, and Incze will use the physical data and understanding provided by the Schlitz and Chen project to interpret their studies of the interaction between water stratification, tidal front processes and the transport, retention, and growth of cod and haddock larvae and their prey. Modeling studies include Franks and Chen, who will continue to explore the influence of tidally-mixed fronts on biological production systems for Georges Bank using their primitive equation / turbulence-closure ecosystem model developed in Phase I and II. Chen will also be involved with Schlitz and Lough in the real-time simulation of observational data, initializing the model with data from their first cruise in the spring, and comparing model output to direct ADCP data from the moorings and shipboard. Ultimately, their goal is to explore the physical processes that control the temporal and spatial variation of the tidally mixed front; stratification; and along frontal and cross-frontal circulation. Werner and Runge will use a biophysical IBM to investigate the growth and survival of cod and haddock larvae on Georges Bank. They will compare the importance of variation in copepod prey field production relative to other factors influencing larval fish, including circulation, temperature, turbulence, and light. Lynch, Werner, McGillicuddy, and Lough, along with their co-workers, have an ambitious project to use real-time data assimilation during field studies, using data from Bisagni, the broad-scale cruises, and shipboard measurements to produce a circulation forecast and guide directed sampling on some process cruises. The suite of studies in Phase III on Georges Bank are thoughtfully designed, well-coordinated, and offer tremendous potential for furthering our understanding of this vital and important ecosystem. Last updated: 21 February, 1999 Please address any comments, suggestions or questions to: GLOBEC Webmaster