First U.S. GLOBEC Field Program Set to Begin on Georges Bank

by William Peterson

The U.S. GLOBEC Georges Bank program was initiated in 1991 with funding from the NSF (Biological Oceanography) for two modelling projects (described in U.S. GLOBEC News No. 1, Spring 1991) and with funding from NOAA Climate and Global Change, Marine Ecosystems Response program for a pilot field project and some retrospective data analysis (summarized in U.S.GLOBEC News No. 2, Fall 1991). An additional modelling project was added in late 1991 as were two biotechnology projects.

In January 1992, a team of academic and NOAA scientists began meeting regularly at Woods Hole to write a plan which would lead to the implementation of a full-scale study of the physical and biological dynamics of Georges Bank. As a result, the Northwest Atlantic Implementation Plan was published in June 1992 (U.S. GLOBEC Report 6, 1992). Subsequently, a request for proposals (RFP) was issued by the newly-established NOAA/NSF Interagency Program Coordination Office, with a September 1992 deadline. Two review panels were convened in December 1992--one to provide advice on the long-term research goals outlined in the Northwest Atlantic implementation plan, and the other to provide an evaluation of the Northwest Atlantic proposals and their peer reviews. A total of 37 proposals, with over 100 co-principal investigators requesting $13,000,000, were received and evaluated. Eighteen projects have been recommended for funding (approx. $5,000,000) to 72 scientists at 24 institutions in the U.S. and Canada. Accompanying tables list the projects by title and PI.

The goal of scientists working in the U.S. GLOBEC program is to predict the effects of changes in the global environment on the abundance, variation in abundance and production of marine animals (particularly zooplankton and fish populations), through a fundamental understanding of the mechanisms that control variations in abundance in time and space. Our approach is to determine which (and how) physical and biological oceanographic processes control populations, and how variations in abundance might be partitioned between natural and anthropogenic causes. This will require:

Thus the overall program goals for all U.S. GLOBEC studies are:

These goals will be accomplished through an interdisciplinary effort involving physical and biological oceanographers and fisheries biologists, carrying out modelling studies, field studies, retrospective data analysis and long-term observations.

Why Begin With A Study Of Georges Bank?

Georges Bank was selected for several reasons. First, it is situated just north of a faunal boundary which separates subtropical species from temperate species. Global warming could result in a northward shift of this boundary, which would completely change the species composition, and, consequently, the ecosystem dynamics of the Bank. Such a shift would be immediately detectable and would serve as an early indicator of climate change. The shift could occur because of general warming, changes in coastal circulation driven by increased buoyancy of coastal waters (due to warming and ice melting), or shifts in the location of the core of the Gulf Stream. Other processes that could impact the Bank are changes in the frequency of severe storms that cross the Bank and frequency of collisions of Gulf Stream rings on the Bank. Another result of a shift of the faunal boundary could be that large schools of filter-feeding mackerel (a southern species) would arrive earlier than usual on Georges Bank and severely impact larval fish and copepod populations through predation. All of these topics are being studied by U.S. GLOBEC investigators.

Secondly, the Bank supports an economically valuable fishery for cod. Recently, all cod stocks along the western Atlantic have fallen into a state of decline, which many scientists believe can be attributed partially to subtle changes in climate. Fishing pressure may be a factor contributing to the decline as well, so we need to sort out the effects of fishing vs. environmental influences on the observed declines in cod stocks. Third, the Bank is of sufficient size and has a physical circulation (an anticyclonic retention gyre) which enables distinct populations to develop and persist for long periods (time scale of months), making them amenable for time-series study. Thus, we know that we can make repeated cruises to the Bank and study the dynamics of the same populations. Fourth, a 10+ year data base exists for interannual variations in cod and copepod abundance, hydrography, circulation, and SST and ocean color from satellites. These records need to be reanalysed in a climate change context. Finally, the target species selected for study (the codfish, Gadus morhua; haddock, Melanogrammus aeglefinus; and the copepods Calanus finmarchicus and Pseudocalanus), are subjects of intense ecological study by many nations around the north Atlantic, including Canada, Iceland, Norway, the United Kingdom and Denmark. This gives all scientists the opportunity to mount collaborative comparative studies of these species in a basin-wide oceanographic context. Such activities are moving forward through the ICES Cod and Climate Change program and through a "Calanus and Climate Change" program recently proposed to ICES.

The Georges Bank Research Program (In A Large Nutshell)

The Georges Bank Study contains these components: retrospective data analysis, fine-scale process studies, broad-scale surveys, long-term monitoring/in situ instrumentation, and numerical modelling.

Projects concerned with retrospective data analysis are looking at a 1939-1941 zooplankton data set from Georges Bank, the 1977- 1988 MARMAP data set on winds, hydrography and plankton abundance, and at the entire SST and ocean color data sets from satellites for the Bank. These studies will provide both the climatology, and, importantly, the degree of interannual variations to be expected for winds, SST, salinity, phytoplankton and abundances of copepods and larval fish.

Broad-scale survey cruises and fine-scale process cruises will be conducted each month, from January through July 1995. Broad-scale cruises of 16-day duration are followed by 12-day process cruises. Thus, at least one ship will be on the Bank nearly continuously for seven months. The broad-scale surveys provide information on bank-wide variations in temperature, salinity, currents, phytoplankton, zooplankton and fish using CTD, ADCP, satellite imagery, fluorometry, plankton nets and towed acoustic sensors. The zooplankton sampling contributes to the description and modelling of population dynamics of copepods, larval cod and larval haddock, a key component of the overall program. A companion laboratory study of factors controlling diapause in Calanus finmarchicus will contribute to an understanding of the dynamics of overwintering populations. Sampling during the broad scale surveys will be sufficiently intense to allow comparison of dynamics of populations in the Gulf of Maine (GOM) with those on Georges Bank (GB). Genetic structure of GOM, GB and other Calanus populations living around the North Atlantic will be compared to determine degree of isolation of populations. In addition to the hydrography and zooplankton work described above, monthly surveys of the distribution of schools of predatory fish (mackerel and herring) and invertebrate predators will provide data on the zooplankton predator fields. This last project is a collaborative effort co-funded by the NOAA Coastal Ocean/Coastal Fisheries Ecosystem program.

An added value of the monthly surveys is that they provide "snapshots" of the hydrography and the distribution and abundance of plankton which will aid greatly in the planning of each of the fine-scale processes cruises. The fine-scale studies planned for 1995 will focus on the processes controlling stratification of the water column, seasonal evolution of stratification, and effects of stratification on food chain dynamics. Physical oceanographic work includes study of currents using current meters, shipboard ADCPs, and drifters, and measurement of turbulence and mixing both within the water column and in the benthic boundary layer. Much of the biological work will involve following drogued patches of water for a number of days, during which larval fish and zooplankton are sampled for study of birth, feeding, growth and mortality rates in relation to hydrographic features. Growth rates of copepods and larval fish will be estimated using molecular techniques, as well as by conventional techniques (moulting rates for copepods; otolith analysis for fish larvae). Detailed studies of vertical distribution of larval fish in relation to their prey field--copepod eggs and nauplii and other microzooplankton--are planned using plankton pumps, nets, acoustics and video plankton cameras.

Long-term monitoring of circulation, phytoplankton and zooplankton biomass will be accomplished with continuous in situ measurements at three mooring sites: in the center of the Bank, at the northeast corner and along the southern flank. Currents will be monitored with bottom-mounted, upward-looking ADCPs (operating at 300 kHz) with several VMCM current meters for calibration. There will be two bio-optical packages on each mooring as well. Zooplankton biomass will be obtained from the ADCP data, but will also be provided by several dual beam/dual frequency and eight-frequency acoustic sensors developed by Tracor, Inc.

Modelling studies focus primarily on numerical simulation of circulation patterns on the Bank, particularly on the dynamics controlling the observed anticyclonic gyre which persists on the Bank. Modelling studies include analysis of the effects of varying wind fields on circulation and the effects of storms on the distribution and abundance of zooplankton. Modelling projects include both finite-element and spectral-primitive equation approaches. These modelling studies are a prelude for the fine-scale process studies planned for 1997 which will focus on sources, sinks and retention mechanisms of water and planktonic animals on the Bank. Most of the circulation studies carried out at the long-term mooring sites, and during shipboard surveys, have the goal of producing dynamic descriptions of the mean and variance of the around-bank flow patterns. An understanding of the processes controlling circulation patterns must be gained before we can reliably predict the effects of climate change on dynamics of animals populations on the Bank, and provide accurate assessments of the impact of climate change on the Georges Bank and other Northwest Atlantic bank ecosystems.

Institutions involved in the Georges Bank study.

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