Project Summary

Karen Wishner

U.S. GLOBEC: Cross-frontal Distributions and Exchange of Zooplankton on Georges Bank

This proposal, on the cross-frontal distributions and exchange of zooplankton on Georges Bank, is one of 3 linked proposals submitted for GLOBEC Phase III and recommended for funding. The other 2 proposals in the group are (1) Hebert / Barth and (2) Gifford / Sieracki / Belkin. Hebert / Barth is a physical oceanography proposal while the Gifford et al. and Wishner proposals combine biology and physics.

The major scientific questions addressed by the three proposals as a whole are:

• What is the 3-dimensional circulation associated with the target fronts over a fortnightly time-scale? (Hebert and Barth; Belkin)

• What is the effect of tidal current variability over semi-diurnal and fortnightly time-scales? (Hebert and Barth; Belkin)

• What are the dynamics and rates of cross-frontal exchange of water, including the cross-frontal fluxes and turbulent mixing rates? (Hebert and Barth; Belkin)

• What water masses are present? (Hebert and Barth; Belkin)

• What are the distributions of target zooplankton species across the fronts? (Wishner)

• What is the potential prey field (nanoplankton and microplankton) of target copepods and and larval fish in the frontal regions? (Gifford and Sieracki)

• What are the rates of feeding and growth of Calanus nauplii and copepodids at different cross-frontal locations? (Gifford and Sieracki)

• What are the cross-frontal exchange rates of zooplankton (Wishner), nano- and microplankton? (Gifford and Sieracki)

• How do biological and physical processes interact to control cross-frontal exchange of target organisms? (Wishner; Gifford, Sieracki and Belkin). For example, how do vertical distributions and migration of zooplankton interact with cross-frontal exchange processes at different depths and frontal locations? (Wishner)

• How does the spatial variability of frontal movement influence the distribution and exchange of organisms at different locations and depths? (Wishner; Gifford, Sieracki and Belkin)

• How do temporal variations of the front (e.g., spring/neap, tidal, and diel scales) interact with populations of target organisms? (Wishner; Gifford, Sieracki and Belkin)

• What are the potential consequences of these processes for recruitment of target organisms? (Wishner; Gifford, Sieracki and Belkin)

The work will be done as a coordinated two-ship operation, using one ship (Oceanus) for the SEASOAR work of Hebert and Barth and one ship (Endeavor) for the biological/physical work of Wishner and Gifford, Sieracki, and Belkin. Cross-frontal processes and exchange will be studied at two sites and times important to the biology of GLOBEC-targetted species and known to have strong thermal fronts at those times: the Northeast Peak Front in March (coincident with expected inflow of the copepod Calanus finmarchicus and the presence of cod larvae and high predator abundance) and the Southern Flank Tidal Mixing Front in June (coincident with high concentrations of Calanus and predators). Two 18-day cruises have been requested on the Endeavor by Wishner and Gifford et al., and a 16 and 18 day cruise have been requested on the Oceanus by Hebert / Barth.

Specific cruise activities, which would be done in each area, include:

• High resolution SEASOAR surveys to map the frontal region (radiator pattern) and shorter surveys (butterfly pattern) around an isopycnal float deployed, tracked, and recovered several times in the frontal areas (Hebert and Barth)

• High resolution SCANFISH surveys in the frontal areas (Belkin)

• Cross-frontal transects of zooplankton (Wishner, MOC-1, vertically-stratified tows), microplankton, and nanoplankton (Gifford, Sieracki, CTD, GO-FLO rosette), and hydrography (Belkin, CTD, SCANFISH)

• Time series stations (same instruments as above) (Wishner; Gifford, Sieracki and Belkin)

• Zooplankton vital rates (Gifford and Sieracki)

Sensors mounted on the SEASOAR include dual temperature and conductivity sensors, a fluorometer, transmissometer, and a Microsoar. Sensors mounted on the SCANFISH include temperature and conductivity sensors, a fluorometer, and oxygen sensor. MOCNESS sensors include temperature, salinity, a fluorometer, and transmissometer. The SEASOAR (Hebert and Barth) and SCANFISH (Belkin in conjunction with biologists) will be doing near real-time mapping of cross-frontal distributions of a wide variety of physical, biological, and chemical parameters, which will be used to determine cross-frontal exchanges and mixing of water. These data will be used in conjunction with the species distributional data from the MOCNESS and CTD-Go-FLO rosette to determine cross-frontal exchanges of nanophytoplankton, nanozooplankton, microphytoplankton, microzooplankton, and mesozooplankton. Thus, zooplankton distributions and variability will be analyzed within the context of a sophisticated physical understanding of cross-frontal exchange and dynamics. Our sampling scheme takes account of the semi-weekly and diurnal tidal cycle, day/night cycle, front location, and Bank topography.

Other direct collaborators, who will participate in these cruises, include Barbara Sullivan (cross-frontal distribution and exchange of small predators in MOC-1 samples), Larry Madin (predator distributions and feeding rates), and Ann Bucklin (Pseudocalanus cross-frontal distributions and genetics from MOC-1 samples). We will also coordinate closely with the mooring work (Bob Beardsley: Northeast Peak moorings, Jim Irish: Southern Flank moorings), remote sensing (Jim Bisagni: front detection), and shipboard ADCP analyses (Charlie Flagg), as well as other biologists, physicists, and modelers.