Processes controlling abundance of dominant copepod species on Georges Bank:

Local dynamics and large-scale forcing


PIs:  Cabell Davis (WHOI), Robert Beardsley (WHOI), Changsheng Chen (UMassD),

Rubao Ji (WHOI), Edward Durbin (URI), David Townsend (UMaine),

Jeffrey Runge (UNH), Charles Flagg (SUNY), Richard Limeburner (WHOI)


Project Summary

A fundamental goal of Biological Oceanography is to understand how underlying biological-physical interactions determine abundance of marine organisms.  For animal populations, it is well known that factors controlling survival during early life stages (i.e., recruitment) are strong determinants of adult population size, but understanding these processes has been difficult due to model and data limitations.   Recent advances in numerical modeling, together with new 3D data sets, provide a unique opportunity to study in detail biological-physical processes controlling zooplankton population size.  We propose to use an existing state-of-the-art biological/physical numerical model (FVCOM) together with the recently-processed large 3D data set from the Georges Bank GLOBEC program to conduct idealized and realistic numerical experiments that explore the detailed mechanisms controlling seasonal evolution of spatial patterns in dominant zooplankton species on Georges Bank.  We will examine a series of hypotheses that address how dominant copepod species populations are maintained on the bank, including local dynamics and large-scale forcing.  Specifically we will determine whether the observed characteristic seasonal-spatial pattern of each species (long-term and inter-annual) is predictable from the interaction between its characteristic life-history traits and physical transport.  The extent to which the copepod populations are controlled by food-availability (bottom-up) or predation (top-down) processes will be examined, including the influence of Warm Slope Water versus Labrador Slope Water (NAO-dependent) on nutrient influx through the Northeast Channel and subsequent upwelling and biological enhancement on the bank.  Self-sustainability of each species population on the bank itself and in the Gulf of Maine will be studied by controlling immigration from specific source regions.  Large-scale forcing including NAO and catastrophic global warming (e.g. complete polar ice melt) will be examined explicitly by forcing the model at the boundaries, using scenarios based on basin-scale data and from concurrent basin-scale modeling efforts.  Intellectual Merits:  The proposed modeling study will provide new insights into the role of local and large-scale processes controlling zooplankton abundance in the ocean.  The dominant copepod species to be studied include small species that are the dominant prey for larval cod and haddock in this region, thus providing critical information for concurrent larval fish modeling studies.  This detailed, process-oriented, regional-scale modeling with boundary forcing will lay the groundwork for integration with models of the entire ocean basin.  The resulting model will be a legacy of the GLOBEC Georges Bank program by providing a powerful new tool for understanding how local and large-scale forcing interact to control plankton production in the sea.  Broader Impacts:  Results of the proposed work will be broadly disseminated to the general oceanographic community, the fishing industry, K-12 institutions, and to the population at large, through web-based servers using existing infrastructure at the proposers’ institutions.  Web-based users will be able to access model results and run the model using chosen parameter settings to obtain predictions of currents, hydrography, and plankton abundance patterns given selected climate forcing scenarios.  Collaboration with the WHOI/UMASS COSEE program will foster communication with K12 students and the public both nationally and internationally.


1.      Background

The GLOBEC approach — Understanding complex marine ecosystems requires use of simplifying assumptions, which historically has involved trophodynamic analysis of energy or mass flow by measurement and modeling (Lindeman, 1942; Teal, 1962; Odum, 1957; Steele, 1974).  In regions of high diversity such as the oligotrophic ocean this approach remains the only feasible method of analysis (e.g., Sarmiento et al., 1993).  As an alternative in low diversity regions, it is possible to model the population dynamics of a few dominant species to understand processes controlling their abundance and to obtain information about system level functioning (e.g., Davis, 1987a).   The trophodynamic concept has been used to relate primary and secondary production to fish production (e.g., Clarke, 1946; Cushing, 1975; Sissenwine et al., 1984; Cohen and Grosslein, 1987; Nixon, 1988), but this method is of limited utility in predicting abundance of particular fish species.  It is well known that adult fish populations are dominated by a few strong year classes that are set by recruitment from early life stages (Hjort, 1914; Grosslein and Hennemuth, 1973).  The GLOBEC program recognizes recruitment as the dominant factor controlling population abundance in marine animal species (GLOBEC, 1991a).  The regional GLOBEC programs focus on target species and their dominant prey, with emphasis on individual organisms, population dynamics, and interactions with the physical environment, especially as it relates to global climate change (GLOBEC, 1991b, 1992, 1996, 1997, 2000).

Georges Bank GLOBEC: dominant zooplankton species — Georges Bank was chosen as the first GLOBEC study site due to its sensitivity to climate change, definable populations, importance as a fishing ground, and significant historical database (GLOBEC, 1992).  The goal of this program is to understand the biological and physical processes controlling abundance of cod and haddock larvae and their dominant prey species.  In the program implementation plan we emphasized the copepods Calanus finmarchicus and Pseudocalanus spp. as target species, since these are dominant prey items for larval cod and haddock.  Subsequent studies have found that small copepods (Pseudocalanus spp., Oithona similis, Centropages spp., Temora longicornis) are dominant prey items for cod and haddock larvae on Georges and Western Banks (Lough and Mountain, 1996; Lough et al, 1996; McLaren and Avendano. 1995; McLaren et al., 1997).  This contrasts sharply with the situation in the eastern Atlantic (North Sea and Norwegian Sea) where cod larvae feed almost solely on Calanus finmarchicus (Sundby, 1999), and decadal shifts in C. finmarchicus abundance affect larval cod survival (Beaugrand et al., 2003).  This difference in larval fish prey preference appears due to prey availability since the larval fish diets reflect ambient copepod species composition, and the shallow banks have high concentrations of small copepod species (Davis, 1987; Sherman et al., 1987; Meise, and O’Reilly, 1996., McLaren et al. 2001; Reiss et al, 2003).  In the shallow Baltic Sea, cod larvae also feed on small copepod species (Hinrichsen et al, 2002).  In general, small copepods are an important component of marine ecosystems (e.g., Davis, 1987b; Turner, 2004). The present proposal focuses on understanding the biological-physical processes controlling the abundance of dominant copepod species in the Georges Bank/ Gulf of Maine region, including Calanus finmarchicus and the smaller species, Pseudocalanus spp. (moultoni and newmani),  Oithona similis, Temora longicornis, Centropages spp. (typicus and hamatus).

1.1.   The Georges Bank Physical Environment

Local dynamics — Georges Bank (GB), the Gulf of Maine (GOM), and Scotian Shelf (SS) are part of a single regional coastal current system, driven in large part by upstream mass and buoyancy forcing (Fig. 1). The bank itself is a quasi-flow-through system, with water from offshore and upstream sources arriving on the bank, being modified locally by surface forcing and tidal mixing before moving off-bank to the Mid-Atlantic Bight or re-circulated northward along the Great South Channel.

The strongest currents over the bank are of tidal origin, and turbulent mixing associated with the tidal bottom boundary layer is most intense over the shallow cap of the bank, effectively eliminating local vertical temperature and salinity stratification throughout the year.  As seasonal stratification increases on the flanks of the bank, the tidal mixing front forms with associated secondary flow. The clockwise around-bank residual flow increases with seasonal stratification, becoming partially closed from June through

Figure 1. Circulation: 1 flow across GSC into the north flank jet, 2 tidal-pumping of deep water onto GB, 3 wind-driven near-surface flow, 4  small-scale cross-frontal processes, 5 SS cross-over

Figure 2. Schematic of the western North Atlantic shelf-break current system in summer,

 (Fratantoni and Pickart, 2005)

September until fall storms and surface cooling destroy the local stratification.  Surface heating drives the development of the seasonal thermocline.  Salinity on the bank is controlled by advective and mixing processes along the northern and southern flanks.  On the southern flank salinity is influenced by on-bank intrusions of saline shelf-break frontal water and very saline warm-core ring water (Fig. 1).  Along the northern flank salinity is controlled by advection from the western Gulf across the northern Great South Channel (Fig. 1, 1), tidally-driven near-bottom residual flow (the “tidal pump”, Fig. 1, 2), wind-driven near-surface flow (Fig. 1, 3), small-scale cross-frontal processes (Fig. 1, 4), and intermittent cross-over of low salinity SS surface water (Fig. 1, 5).  The tidal pump in particular provides a strong mechanism for bringing deep water from Georges Basin up onto the bank (Chen and Beardsley, 1998; Chen et al., 2003).

Figure 3. Schematic showing the strong westward penetration of LSW and northward position of the Gulf Stream following low winter North Atlantic Oscillation (NAO) index (left) and weak penetration of LSW and more southward position of Gulf Stream following high winter NAO index.  (Drinkwater et al, 2003)

Large-scale forcing — Water enters the GOM via two primary paths:  (1) the flow of relatively fresh water above 100m from the SS and (2) warmer, more saline Slope Water (SW) at depths greater than 100m through the Northeast Channel (NEC). The primary source of SS water is the West Greenland/Labrador Current system, with additional input from the St. Lawrence system (Fig. 2). As the Labrador Current flows around the Grand Banks, the large shoaling in shelf-break depth from ~300m in the north to ~100m to the southwest helps force the deeper Labrador Current water to flow along the upper slope, thus forming Labrador Slope Water (LSW), which flows west into the Laurentian Channel and along the Scotian upper slope. The westward extent of LSW depends on its source strength, thought to depend on basin-scale forcing (NAO) (Fig 3), and degree of mixing with ambient Warm Slope Water (WSW) of Gulf Stream origin. Since WSW is warmer, more saline, and nutrient rich than LSW, the relative mix of these two end members entering the NEC, and its transport relative to the inflow of SS water, strongly influences circulation, water property distributions, and nutrient content in the GOM/GB system.

Fig. 4.  GB salinity anomaly (Mountain, 2005)

Fig. 5.  Percent LSW in bottom water (150-

200 m) in 1998.  (Drinkwater et al, 2003)

Data from the 1995-1999 GB GLOBEC field study provide an excellent example of the flow-through nature of the GB/GOM system and its linkage to larger basin-scale forcing. The salinity on GB exhibited two significant freshening events between early 1996 to early 1997 and between late 1997 through 1998, with a net drop of ~1 psu (Fig. 4). These two events also were observed in surface (0-30m) GOM waters, suggesting significant increases in freshwater influx from the SS (Smith et al., 2001).  In the NEC, WSW was replaced by cooler, fresher LSW in January 1998 as the leading edge of LSW flow extended west due to an increase in the Labrador Current associated with a low NAO. As LSW entered the GOM during early 1998, it mixed with resident GOM water (Fig 5).  By early 1999, WSW was again flowing into the GOM through the NEC.  Since the tidal pump mechanism can carry deep water up on the northern flank of GB, advection of LSW in Georges Basin onto the bank can occur on relative short time scales (>=1 month), suggesting that part of the freshening on GB observed during 1998 was due  to the influx of LSW into the GOM.  Clearly, variations in the primary upstream sources (the SS Water, the mix of WSW versus LSW) linked to basin-scale forcing strongly control the water properties (including heat, salt and nutrients) through the GOM and onto GB.

Fig. 5a.  Scenario of nutrient input onto GB from the NEC (Townsend et al., 2004).

1.2.   Connection between NAO and plankton productivity on GB

NAO-dependent intrusions of LSW and WSW through the NEC greatly influence the nutrient (N, Si) input into the GOM.  It is believed that the tidal pumping mechanism along the northern edge of the bank can quickly transport nutrients from Georges Basin up onto the NE peak of GB, impacting the productivity of the bank very rapidly (Fig. 5a).  The ratio of N and Si in the inflow water can influence the duration of the diatom bloom.  In general, the NEC inflow can affect the total salt and nutrient budget of the GB/GOM, determining the thermohaline circulation and influencing upwelling along the western GOM and subsequent nutrient transport to western GB.  The potential impact of this inflow will be modeled in the proposed study.

1.3.   Characteristics of GB zooplankton

GB zooplankton is dominated by Calanus finmarchicus, Pseudocalanus spp., Oithona similis, Centropages spp., and Temora longicornis, and Paracalanus parvus (Bigelow, 1926; Davis, 1984, 1987b; Sherman et al, 1987; Durbin et al., 2003; Durbin and Casas, submitted).  Each species exhibits a characteristic life cycle and seasonal/spatial pattern in the GB/GOM region.  Calanus finmarchicus and Pseudocalanus spp. are cold-water species that avoid the warm surface layer (>10-12oC) during summer and fall and produce large spring populations.  Centropages spp, Temora, and Paracalanus are warm water species and are most abundant during late summer and fall.  Oithona is plentiful throughout the GB/GOM region year round.

Fig. 6. Calanus finmarchicus abundance (log10(#/10m2) in the GB/GOM, mean 1977-1987, (MARMAP data redrawn from Meise and OReilly, 1998).

Calanus finmarchicus This species spends the warmer months in a state of diapause as stage CV in cooler waters (5-7 oC) at depth in the GOM (Fig. 6). During late December, it emerges from diapause (mechanism unknown), swims to the surface and molts to adult.  Subsequent egg production depends on availability of phytoplankton (Durbin et al., 2003), with the first generation born in late December-early January (Durbin et al., 1997).  Generation time is ~2 months at the cold winter/spring temperatures (~5 oC), so G1 adults appear in March, and there is time for a total of 3 generations by the end of its growing season in July.  Overwintering females produce eggs for a prolonged period, smearing out cohorts (Durbin and Casas, submitted).   This annual cycle in the GB/GOM appears stable, having persisted for many decades (Bigelow, 1926; Clarke et al, 1946; Meise-Munns et al., 1991), but the extent to which this population is self-sustaining is unknown.

Fig. 7. Calanus finmarchicus abundance in the N Atlantic from CPR data (Spears 2005) and nets/OPC (Heath et al. 2004).  Note high densities in the Labrador and Norwegian Seas.

Calanus  finmarchicus is an open ocean species, occurring throughout the northern North Atlantic from the eastern US to the Barents Sea, with centers of population abundance in the Norwegian and Labrador seas (Fig. 7).  Immigration into the GB/GOM population from upstream sources may contribute to the apparent stability of the population.  C. finmarchicus enters the GOM from the SS and possibly from the SW through the NEC.  C. finmarchicus in the SW originate from the Labrador Sea and to an unknown extent from spill-over of the productive shelf populations.  Scotian Shelf C. finmarchicus originate from Labrador Sea via the SW (Head et al., 1999) and to some degree from the productive Gulf of St. Lawrence population (Zakardjian et al. 2003).  It is unlikely that immigration directly determines the large spring abundance peak in C. finmarchicus in the GB/GOM, since the water mass turnover time is long relative to the generation time, but a seeding type of immigration during the “off-season” could be important in determining the size of the startup population of CVs in December (Saumweber and Durbin, submitted).  Since the diapausing SW population resides at a depth of 500m (below the NEC sill depth), and high concentrations are not observed in the upper water column until April (Miller et al., 1991), well-after initiation of the GB/GOM population growth, it is unlikely that a SW population entering through the NEC contributes significantly to the GB/GOM C. finmarchicus population.

It may well be that the resident diapausing GOM population is sufficient to produce the large spring GOM/GB population.  At the end of the growing season, downward migrating diapausing CVs cannot reach their normal open ocean depths of 500-2000m, and they become trapped in the GOM basins.  A similar effect has been observed on the SS basins (Sameoto and Herman, 1990) and for C. pacificus in the Santa Barbara basin (Osgood and Checkley, 1997).  Lagrangian modeling studies have found retention of diapausing CVs in the GOM to be high, especially if the animals stay below 150 m (Johnson et al., submitted).  Thus it appears possible that the GB/GOM population could be self-sustaining, but further 3D modeling work is needed, using a concentration-based approach to quantify population dynamics and transport continuously throughout this region during the year.  This self-sustainability is in sharp contrast with the situation in the North Sea, which has no deep basins and is dependent on annual input from offshore waters (e.g. Heath et al., 1999).

Fig. 8. GLOBEC monthly mean Calanus abundance

           on GB, showing abundance “hole”

Fig. 9.  Pseudocalanus abundance in the GB/GOM. MARMAP bi-monthly means 1977-1987 (from McGillicuddy et al., 1998).

Although C. finmarchicus may be able to sustain itself in the GB/GOM system, it does not maintain itself on GB, since the bulk of the population disappears from the bank during the off-season (Fig. 6) and even during the growing season its abundance appears to be driven by GOM concentrations, with a well-defined “hole” in abundance in the center of the bank (Fig. 8, Durbin and Casas, submitted).  This hole results from a combination of advection around the bank of the large GOM population and possibly high predation over the crest.  A huge literature exists for C. finmarchicus egg production, development and growth as a function of food and temperature including several studies done as part of the GLOBEC GB process work (Campbell and Head, 2000; Campbell et al., 2001a,b; Runge et al. submitted).  Such data can be incorporated into the population model for this species and used together with the large field data base to conduct targeted forward modeling to examine biological/physical processes controlling observed patterns.

Pseudocalanus spp.— Like Calanus, the growth season for Pseudocalanus is winter/spring (Fig. 9, 10).  Its abundance is higher in shallower areas (<100m) and is highest in the crest region of the bank in June.  Pseudocalanus does not overwinter in the GOM as does Calanus and is not normally present in the central Gulf during winter.  This genus is an egg carrier and consequently has lower egg production and egg mortality rates (Corkett and McLaren, 1978; Ohman et al., 2002).  Pseudocalanus in the GB/GOM

Fig. 10. GLOBEC data for Pseudocalanus

Fig. 11.  A) Temora, B) Centropages hamatus C) Centropages typicus, D) Oithona similis.  Mean monthly GLOBEC data for 1995-1999, A,B,D May; C January; log10(#/m3+1)

region comprises two species: P. newmani and P. moultoni (Frost, 1989; McLaren et al., 1989a; Bucklin et al., 1998, 2001; McGillicuddy and Bucklin, 2002).   P. moultoni appears to be a colder water species and more abundant during winter/spring, while P. newmani is more plentiful during spring/summer (McLaren et al., 1989a,b).  P. moultoni is a coastal species and P. newmani an offshore one (Frost, 1989).  Thus P. moultoni may be carried onto the bank from western GOM coastal waters (e.g., Cape Cod Bay), while P. newmani may have a source from SS water, either crossing over the NEC, or indirectly through the central GOM (McGillicuddy and Bucklin, 2002).  Inverse modeling, representing the biology by a single source/sink term, revealed that the two species are likely to have different source locations on the bank but intermingle by June (McGillicuddy and Bucklin, 2002). The use of a simple cost function instead of a population model, however, meant that the independent species-specific life history information could not be included in the model.  Substantial information on development, growth and egg production as a function of food and temperature is available for Pseudocalanus (e.g. Corkett and McLaren, 1978; Vidal, 1980; Davis, 1983, 1984a,b; McLaren et al., 1989b; Ban et al., 2000; Lee et al., 2003; Dzierzbicka-Glowacka, 2004).  Use of these laboratory and shipboard derived rates together with field data on distributional patterns of the combined species (plus a subset of species-specific data, Bucklin et al., 2001) can be used in numerical models to explore the biological/physical processes controlling seasonal development of the spatial distribution patterns.  Targeted forward modeling experiments are required to determine the potential source locations and interactions controlling subsequent spatial patterns of each population, given their distinctive temperature-food dependent growth and reproductive rates.

Other Dominant Copepod Species — Each dominant copepod species on GB has its own characteristic temporal-spatial patterns and life histories (e.g., Davis, 1987a).  Copepods that lay bottom resting eggs, including Centropages hamatus and Temora longicornis, have well defined populations on the crest of the bank (Fig. 11A, B) (Davis, 1987; Sherman et al., 1987).  It has been suggested that these species use resting eggs as a strategy for “gluing” their populations to regions that are favorable for growth (Davis, 1987; Lindley and Hunt, 1989; Lindley, 1990; Marcus, 1996; Marcus and Lutz, 1998), but the necessary biological/physical dynamics have yet to be verified via modeling. Centropages typicus abundance is highest during late summer and fall and decreases markedly during winter and spring.  It is most abundant in the warm surface layer above the thermocline and not restricted to the crest of GB like C. hamatus.  Oithona similis is abundant year round and is not restricted to GB but has a pattern similar to C. finmarchicus, with a large off-bank population.   A substantial literature on life history information is available for these species, including egg production, development and growth rates as functions of food and temperature (e.g., Davis and Alatalo, 1992; Klein Breteler and Gonzalez, 1986; Klein Breteler et al., 1982, 1996; Sabatini and Kiørboe, 1994; Maps et al. 2005).

Fig. 12.  Abundance trends in GB copepod, GLOBEC 1995-1999.

Abundance trends during the GLOBEC years — Abundance of the dominant copepod species, except Calanus, increased significantly during the five-year GLOBEC GB field program (Fig. 12.).  While this trend may reflect a change toward smaller species, indicative of a warming trend, no concomitant increase in temperature was observed.  These changes were negatively correlated with salinity (Durbin and Casas, submitted.). High abundances in 1999 appear to be related to a phytoplankton bloom that took place during winter in the central GOM, leading to high reproductive rates and abundances (Durbin et al 2003). The elevated abundances may have been advected onto GB.  It is possible that low surface salinity during winter increased stability of the water column and led to the bloom. A negative correlation between salinity and chlorophyll on GB also was found at this time (Durbin and Casas, submitted), the reason for which is unknown.  The proposed modeling work will examine the potential causes of the zooplankton increase and its relationship to large-scale forcing and climate change.

1.4.   Available Data Sets

GLOBEC GB — The GLOBEC GB field program was conducted from 1995-1999 and included a combination of monthly broadscale and process-oriented cruises (GLOBEC, 1992; Wiebe et al, 2002).   Broadscale cruises provided 3D maps of the plankton species based on net tows (1-m2 MOCNESS, Wiebe et al., 1985) at a set of 41 standard stations covering the bank and adjacent waters, and plankton pump sampling (Durbin et al 1997, 2000) at ~18 of the standard stations. CTD bottle casts were made at all stations.  MOCNESS (0.15 mm mesh nets) zooplankton samples were collected from 0-15, 15-40 m, and 40-100 m or the bottom (if shallower than 100 m) and 100 m to the bottom or 450 m (if >100 m).  Pump (0.035-mm nets) samples were collected over the same depth ranges as the MOCNESS in the upper water column but the maximum depth it was deployed to was 70-100 m depending on wind and tides, or to the bottom on shallower parts of the bank.  For complete description of collection and processing methods see (Durbin et al. 1997; 2000).  Samples were sorted, and processed data now are available for all life stages of Calanus finmarchicus and Pseudocalanus spp. (N1-N6, C1-Adult).  For other copepod species life stages were sorted as adult males and females, copepodids, and nauplii. These data are stored in an Oracle database together with all of the CTD and chlorophyll data (  The complete GLOBEC GB data set for broadscale zooplankton includes >3500 net samples (41 stations, 3 depths, 30 cruises), plus >1500 pump samples (18 stations, 3 depths, 30 cruises).  In addition, vertically stratified data from several other cruises have been collected in deeper regions of the GOM.

Other Data Sets   Data from the bimonthly cruises of the MARMAP program 1977-87 and its follow-on program, ECOMON (1992-present), include shelf-wide distributions of hydrography and zooplankton (0.333mm bongos).  The complete data set is available to us via an NMFS Oracle database (D. Mountain, pers. comm.)  Although the zooplankton data are from integrated hauls, these data cover a broader area than the GLOBEC GB data, and, together with GLOBEC vertical data from deeper GOM, will allow us to approximate 3D spatial patterns of each species throughout the GOM region.  Further data from the GOM CPR transect, transatlantic CPR, UNH Coastal Observing Center, the 1939-41 GB study, and Canadian AZMP (see Head letter), allows the 1995-1999 GLOBEC data to be viewed in a larger context.

1.5.   Previous modeling

Several previous biological/physical models of the GB/GOM region have been developed.  Davis (1984) showed that the interaction between around-bank advection/diffusion and temperature-dependent development of the copepod Pseudocalanus could explain observed spatial patterns in population structure.  Subsequent studies have shown that this scenario is most likely for P. moultoni, with an admixture of P. newmani later in the season (McGillicuddy and Bucklin, 2002).  McGillicuddy et al. (1998) had used the same inverse approach to locate source/sink areas for the Pseudocalanus population.   Klein (1987) modeled the 2D NPZD-advection-diffusion on the bank and found that phytoplankton production was removed from the bank via detritus rather than grazing.  Lewis et al., (1994, 1991) used 3D modeling to show that strong wind forcing can cause a partial washout of plankton from the bank, increasing the phytoplankton/zooplankton ratio (NPZ model), and causing spatially-temporally sensitive larval populations (particle-based) to be lost from the bank, affecting recruitment.  The Calanus finmarchicus population in the GB/GOM has been modeled using the Dartmouth model to show that the deep basins and SS can contribute to the bank population; these models used 2D transport of concentration-based (Lynch et al. 1998), individual-based (Miller et al., 1998), and particle trajectories (Hannah et al 1998).  The C. finmarchicus population throughout the Gulf of  St. Lawrence/SS/GOM region was modeled to examine local dynamics and exchange between regions within the model interior (Zakardjian et al., 2003).  The latter model was a 3D concentration-based 13-stage population model with temperature-dependent development and was run for a full-annual cycle.  The results indicated that horizontal transport was dominant on the SS, but that the population is self-sustaining in the Gulf of St. Lawrence.  Food-dependence effects on population dynamics during the active season were not examined, however. 

1.6.   Combining existing models and data

Over the past decade, the GLOBEC GB program has acquired and processed an exceptional 5-year 3D data set of plankton and physical variables, while at the same time developing a high-resolution state-of-the-art prognostic 3D biological/physical model of this region (FVCOM).  Data processing and model development recently have reached the point where they can be effectively combined.  By the start of the proposed study, the FVCOM model will have been ported to a massively-parallel supercomputer. We now have the unique opportunity to use the data and model together to study the detailed mechanisms controlling zooplankton abundance patterns on GB, explicitly including boundary forcing determined by basin-scale dynamics.

We have assembled a team of PIs who are leading experts on the plankton and physical dynamics of this area.  Beardsley and Flagg are physical oceanographers with a long background in this region. Chen is a physical oceanographer and developer of the FVCOM model. Durbin is the scientist in charge of the broadscale data acquisition and processing.  Runge is an expert in copepod biology specializing in Calanus fertility and population dynamics.  Townsend is the lead scientist studying nutrient-plankton production in the GB/GOM region.  Davis is a zooplankton biologist who has done field, laboratory, and biological-physical modeling studies of copepod population dynamics in the GB/GOM region.  Davis and Beardsley helped formulate the theoretical underpinnings and approach for the GLOBEC GB program (GLOBEC, 1992).

2.      Proposed Research

2.1.   Hypotheses

Working  Hypothesis – The seasonal evolution of characteristic mean spatial abundance patterns of each dominant copepod species on GB is predictable from the interaction between its characteristic life-history traits and physical transport.  These life-history traits include egg production, development, and growth rates (temperature/food dependent) as well as other traits such as vertical migration and diapause.  Both the long-term, multi-year, mean and year-to-year variations in seasonal-spatial patterns are predictable by these interactions.  Within this working hypothesis, we will address three specific null hypotheses:

H10:  The abundance of copepod species on the bank is controlled by food availability (bottom-up control).  Here we will examine the scenario that GB productivity, and thus food availability for the dominant copepod species, is controlled by nutrient input into the GOM through the NEC, which is determined by the intrusions of Labrador Slope Water versus Warm Slope Water.  Alternative hypotheses include:  1) predatory control of copepod seasonal cycles (top-down control), 2) a combination of food-limitation and predation (time-space dependent), and 3) purely physical control by direct effects of temperature on vital rates or advection.  In 3), we will examine causes of the observed increase in warm-water copepod species during the GLOBEC years (1995-1999).

H20:   Copepod populations on GB and/or the GOM region are not self-sustaining.  We will examine the need for immigration from different sources to maintain the copepod populations over multiple years.  Key source regions will be examined including the SS and SW.  For self-sustainability on GB itself, we will examine potential sources from the coastal regions (e.g., Cape Cod Bay, Penobscot Bay), the GOM, and from bottom resting eggs.

H30:   Catastrophic global warming (e.g., total polar ice melt), parameterized as a lack of Labrador Sea water at the NEC, causes a regime shift on GB from cold-water copepod species to warm-water ones.

2.2.   Objectives

The overall goal of the proposed study is to understand the underlying biological-physical mechanisms controlling the seasonal development of spatial patterns of dominant copepod species on GB.  Our specific objectives are: 1) to examine how local-dynamics and external forcing control the abundance of these species on GB, 2) to determine the degree to which top-down versus bottom up processes control the dominant copepod species on GB, and 3) to use existing state-of-the-art 3D physical/biological numerical models together with existing high-quality 3D data sets from the GLOBEC GB field program (and other historical data sets), to conduct targeted numerical experiments that explore the likelihood of the hypotheses listed above.  

2.3.   Methods

2.3.1.      The Integrated Model System

The UMASSD-WHOI research team has developed an integrated model system for the GOM/GB region (Fig. 13). The major components of this system include: (1) the modified fifth-generation community mesoscale atmospheric model (MM5), (2) the unstructured grid Finite-Volume Coastal Ocean circulation Model (FVCOM), (3) a generalized lower trophic level food web model, and (4) multi-stage zooplankton models. The 4-D optimal interpolation (OI) and nudging data assimilation methods are used with FVCOM to incorporate satellite-derived sea-surface height (altimeter), insolation, SST, and remote sensing reflectance (RSR) as well as in-situ oceanographic data (moored and shipboard hydrographic and current data) in model simulations conducted with realistic forcing and boundary conditions and observed ocean response for specific periods of time. The integrated model system can be run with idealized forcing and boundary conditions to investigate specific processes.  A brief description of the integrated model system is given below.

MM5The current version of the meteorological model utilizes the fifth-generation mesoscale regional weather model (MM5) developed by NCAR/Penn State (Dudhia et al., 2003; Grell et al., 1994) for community use. MM5 uses NCAR/NCEP or ETA weather model fields as initial and boundary conditions with two-way nesting capability, and can provide continuous hindcasts and three-day forecasts. We have used MM5 to construct the surface weather hindcast and forecast system for fishery studies in the GOM/GB (Chen et al., 2004). This model (called GOM-MM5) is configured with a regional domain (covering the Northeast U.S.) and a local domain (covering the SS, GOM, and New England Shelf) with horizontal grid spacing of 30 and 10 km, respectively, and 31 sigma levels in the vertical with finer resolution in the PBL. To improve the model-based surface wind field, wind stress and heat flux estimates over the ocean, GOM-MM5 uses the COARE 2.6 bulk algorithm (Fairall et al, 2003) for the air-sea fluxes, satellite-based insolation, cloud cover, and SST data (International Satellite Cloud Climatology Project) for the radiative fluxes, and all coastal NDBC and C-MAN surface weather data available in the local domain are incorporated through 4D data assimilation.

GOM-MM5 is presently in operational use, with 3-day forecasts of the surface conditions, (including wind stress, heat flux, P-E) over the GOM/GB region posted on the SMAST website ( for research, education, and public use.  By this summer, we will complete the hindcast of the surface forcing fields with mesoscale (10-km) resolution covering the FVCOM domain for the 1995-1999 GLOBEC field period. This is the first calibrated mesoscale meteorological database built in the GLOBEC GB Phase 4 program.

FVCOM FVCOM is a prognostic, unstructured grid, finite-volume, free-surface, 3D primitive equation coastal ocean circulation model (Chen et al., 2003; Chen et al. 2004a). In common with other coastal models, FVCOM uses the modified Mellor and Yamada level 2.5 (MY-2.5) and Smagorinsky turbulent closure schemes for vertical and horizontal mixing, respectively (Mellor and Yamada, 1982; Galperin et al., 1988; Smagorinsky, 1963), and a sigma coordinate to follow bottom topography. The General Ocean Turbulent Model (GOTM) developed by Burchard’s research group in Germany (Burchard, 2002) has been added to FVCOM to provide optional vertical turbulent closure schemes. Unlike existing coastal finite-difference and finite-element models, FVCOM is solved numerically by flux calculation in the integral form of the governing equations over an unstructured triangular grid. This approach combines the best features of finite-element methods (grid flexibility) and finite-difference methods (numerical efficiency and code simplicity) and provides a better numerical representation of momentum, mass, salt, heat, and tracer conservation.  The ability of FVCOM to accurately solve scalar conservation equations in addition to the geometrical flexibility provided by unstructured meshes (Fig. 14) and the simplicity of the coding structure makes FVCOM ideally suited for interdisciplinary applications (Chen et al., 2005b-c; Ji 2003; Ji et al., 2005). Examples can be viewed on Chen’s research group website at

FVCOM has been validated through direct comparison with analytical solutions for idealized cases (Chen et al., 2005b; Huang et al., 2005a-c) and other models for application in estuaries (Chen et al., 2005d-e; Huang et al., 2005d), inter-bays (Zhao et al., 2005) and the GOM/GB region (Chen et al, 2003b; Chen et al., 2005c).  These studies show that different physical processes controlling currents and stratification in the coastal ocean have inherent time and space scales that must be carefully considered when determining model grid resolution for accurate simulation. This is particularly important with freshwater discharge, buoyancy-driven coastal plumes and currents, tidally-forced flows and upwelling, and fronts in the GOM/GB region (Chen et al 2005a).  For example, model dye experiments made to simulate Houghton’s May/June 1999 dye dispersion observations on GB suggest that the horizontal resolution needed to resolve the diffusive flux is 500 m (Chen et al., 2005c).  This resolution is also required to have a convergence solution of the tidal-induced residual current and buoyancy-induced current at the shelfbreak on GB (Chen et al., 2005b).  These requirements will be used to refine the final FVCOM grid used in the proposed work. FVCOM has been used to hindcast currents and hydrography in the GOM/GB region for 1995 and 1999 using GOM-MM5 surface forcing, 4D data assimilation of 5-day averaged satellite SST and available moored current data, and open boundary conditions (Chen et al., 2003b).  The model tidal currents compare very well with available surface elevation and current data, with overall uncertainties for the dominant M2 component of less than 3 cm in amplitude, 5° in phase, and 3 cm/s in the tidal current major axis (Chen et al., 2005c).  The model subtidal currents and stratification also compare well with existing in-situ measurements, capturing the seasonal cycle in vertical stratification and increased around-bank circulation during June-September.  These two hindcasts clearly illustrate significant short-term (daily to weekly) and long-term (seasonal and interannual) variability in the subtidal currents on GB.  For example, surface winds in March 1999 were stronger and more variable than in 1995, resulting in stronger monthly-mean offbank near-surface flow in 1999 than in 1995 (Fig 15). 

FVCOM Biological Module Various ecosystem models have been implemented in FVCOM, including NPZ, NPZD, NPZDB, and water quality models. To make FVCOM more flexible for ecosystem studies, we have built a generalized biological module into FVCOM to allow users to select either a pre-built biological model (such as NPZ, NPZD, etc) or construct their own biological model using the pre-defined pool of biological variables and parameterization functions, including zooplankton life-stage models.  This module acts like a platform that allows us to examine the relative importance of different physical and biological processes under well-calibrated physical fields.

Upstream Boundary Conditions  For this study, we plan to move the “upstream” boundary of the GOM/GB FVCOM domain eastward to cut across the SS and upper slope through Banquereau Bank. This choice simplifies the cross-shelf bathymetry and separation of along-shelf flow into inner-shelf and shelfbreak components (Han et al, 1997), and was used in the Hannah et al (2001) model simulations of the seasonal circulation on the western and central SS.  They used the Dartmouth circulation model (QUODDY4) to produce dynamically-consistent seasonal-mean solutions based on historical hydrographic, wind stress, and M2 tidal elevation data.  The model solutions show generally good agreement with moored current data and capture the strong seasonality of the major currents, indicating that the seasonal-mean barotropic and baroclinic pressure gradients specified along the upstream boundary were realistic.  We plan to use the Hannah et al (2001) seasonal-mean boundary conditions, a statistical method to compute the along-shelf wind-driven time-dependent transport over the inner-shelf (Schwing, 1992), recent hydrographic and moored data, and the new shelfbreak current system climatology (Fratantoni and Pickart, 2005a,b) to construct the best set of upstream boundary conditions for both process and long-term hindcast simulations.  In addition to the extensive hydrographic data set collected in GLOBEC GB, additional data have been collected in the GB/GOM by the ongoing NMFS ECOMON program and on the SS by the Canadian Atlantic Zone Monitoring Program (AZMP) (see letter from Dr. Erica Head).  Starting in 1997, a comprehensive suite of hydrographic, nutrient, and biological data is being collected 3-4 times a year along transects through Browns Bank, off Halifax, through Banquereau Bank (the “Louisbourg Line”), across Cabot Strait, and others further upstream.  The overlap of AZMP with GLOBEC GB field effort begins in 1997, the collocation of our upstream boundary with the AZMP Louisbourg Line will allow us to compute a climatology of physical and biological properties (1997-2005) which will help determine realistic boundary conditions and their interannual variability.  In formulating boundary conditions we will collaborate with Haidvogel (Rutgers) who is modeling basin-scale dynamics and with McGillicuddy et al. who have proposed a concurrent basin-scale adjoint modeling study of Calanus.[1]

We will not include the potential influence of warm core rings (eg., Flierl and Wroblewski, 1985) and other eddy features originating in the Gulf Stream (Fig. 1), because the larger regional and basin-scale models do not yet produce these features accurately enough in this region for us to use them to construct the boundary conditions along the open ocean part of FVCOM.  The influence of rings may be minor (e.g., Churchill et al., 2003), however, and we will be able to infer their potential importance by their omission.  As the larger-scale models mature in this respect, follow-on studies of these processes can be developed.

FVCOM Computational Aspects With GLOBEC GB Phase 4 support, FVCOM has been converted into a FORTRAN 95/2K parallelized program to take advantage of multi-processor computing (Cowles et al., 2003).  This implementation uses a SPMD (Single Program Multiple Data) approach with a message-passing model to perform the necessary inter-processor communication and synchronization. The physical domain is decomposed into sub-domains using the METIS graph partitioning libraries.  Each sub-domain is assigned to a processor for integration of the model equations. The exchange subroutines utilize non-blocking sends and receive from the MPI (Message Passing Interface) 2.0 library.  The efficiency of the code can be measured in terms of its speedup and/or scalability on a multiprocessor computer. Chen’s modeling lab will install a new high-performance 256-processor super-cluster computer this summer. With this computer, 1-yr model run with data assimilation and the existing GOM/GB FVCOM grid should take less than 1-day clocktime. We plan to use this computer with attached mass storage for the proposed Phase 4B model experiments (1995-1999 hindcasts and process studies), model/data comparisons, model result analysis and visualization, and archiving model output and results.

2.3.2.            Biological Models

We will incorporate a copepod population model and a simple food web model (NPZ) into the plug-in modules of FVCOM.  We will draw from our previous modeling work involving Calanus, Pseudocalanus, and other copepod species (Davis, 1984a,c, 1987; Lynch et al., 1998; McGillicuddy et al., 1998; Zakardjian et al., 2003), as well as our food web modeling (Davis, 1987b; Flierl and Davis, 1993; Lewis et al., 1994; Davis and Steele, 1994; Zeldis et al., 1995; Dadou et al. 1996; Ji, 2003, submitted a,b,c).

Population model — Copepod dynamics will be modeled using a stage-structured population model containing 15 life stages (egg, N1-6, C1-3, C4M-F, C5M-F, Adult) plus additional diapause stages (e.g. eggs or CV) as needed.  A standard formulation for the stage-based model will be used (e.g., Zakardjian et al., 2003).   A potential problem with using only 15 life stages is artificial diffusion of individuals through the life stages, and, to prevent this, age-within-stage models have been developed (Davis 1984c).  If necessary we will use a 150-age-stage class model (e.g., Davis 1984c) which will still run efficiently given the supercomputing power available.  Egg production, molting, and growth rate parameters as functions of temperature and food will be taken from the vital rate measurements made during the GLOBEC process cruises and from the large body of available literature (see citations in Background section). The model will be initialized and validated using observed patterns of copepod abundance according to the numerical experiments described below.  The copepod population then will grow based on ambient temperature and food levels.  Mortality rates will be inferred by adjusting them to match model and field abundances (Hall, 1964; Davis, 1984a).  Mortality is stage-specific and typically higher for younger stages (e.g., Davis, 1984a).  Mortality rates as a function of life-stage have been found for Calanus and Pseudocalanus as part of the GLOBEC GB studies (Ohman et al., 2002).  We will use relative stage-dependent mortality curves, from this and other studies, when inferring mortality rates.  We also will explore the possibility of conducting targeted inverse modeling to obtain the stage-dependent mortality rates (e.g. Li et al, in prep).  Vertical migration behavior observed from the GLOBEC data sets during process and broadscale cruises will be incorporated into the model using a simple biological advection term.  The temperature fields are given by the physical model.  For the food-fields we will use two approaches as described in the next section:  1) empirically-forced 3D static phytoplankton fields derived from 3D chlorophyll measurements and ocean color data, and 2) a dynamic 3D prey field based on a simple NPZ-type of food web model.  In the former case the copepods will be transported through static prey fields, and in the latter case the copepods and prey field will be transported together.

Lower trophic level food web model We will explore the possibility of generating temporally evolving 3D phytoplankton fields from a lower trophic level food web model (e.g. NPZ or NPZD) to provide food for the copepod population model.  We will use one-way coupling whereby the copepods depend on the food field but do not affect it (e.g. Carlotti, 1998; Batchelder et al., 2002).  In this case, the Z will represent microzooplankton grazers used solely as a closure term.  We can generate realistic 3D phytoplankton fields using a simple NPZ model (Ji, 2003).  It may also be possible to allow the copepods to graze the P and Z (e.g., Carlotti, 1996), but this approach may not be necessary or feasible in 3D.  The NPZ model will be adjusted so that the resulting fields approximate the 3D chlorophyll and satellite data.  The concept of using an NPZ model to generate spatially explicit prey fields has been used with an IBM of larval pollock in the Gulf of Alaska (Hermann et al., 2001), where the Z represented copepod prey.  Here we propose to use the NPZ to generate the P fields for spatially explicit population models of dominant copepod species.  The resulting copepod distributions will be used in a concurrent modeling study of Werner et al. who are proposing to develop an IBM of larval cod (see Werner letter).

Plankton food web models are variously complex, ranging from simple NPZ to models with multiple subcomponents. In the GOM/GB a simple NPZ (Klein, 1987; Lewis et al., 1994; Franks and Chen, 1996; Franks and Chen, 2001) and a nine-compartment model (Ji, 2003) have been used.  The NPZ model coupled with a 3-D nonlinear, primitive equation, finite-difference ocean circulation model (ECOM-si, Blumberg and Mellor, 1987) can successfully approximate 3D phytoplankton fields observed on GB from summer cruises and satellite data.  Robust features, such as the subsurface maximum and mixing-front induced productivity were produced with this model (Franks and Chen, 2001). More recently, a nine-compartment model (Ji, 2003), coupled to ECOM_si and FVCOM, captured the basic seasonal and spatial patterns of nutrients and phytoplankton on GB.  This model includes 3-N (nitrate, ammonia and silicate), 2-P (large and small), 2-Z (large and small), and two detrital pools (N and Si). Silicate can limit the spring diatom bloom on GB (Townsend and Thomas, 2001; Townsend and Thomas, 2002, Ji, 2003).

In the proposed study, the simple NPZ model will be used due to its capability and robustness, as well as the availability of observation data for the initial and boundary conditions. We also will explore the use of separate pools in the model for Si and N and for P (diatom, non-diatom).  The model will run continuously for 3 years from January 1997 to December 1999, a period when we have both nutrient and phytoplankton data from the GLOBEC GB program.  Initial horizontal distributions of nitrogen, phytoplankton and zooplankton during winter will be derived from climatological data (e.g. Petrie and Yeats, 2003), satellite imagery and MARMAP data, respectively.  An initial homogenous vertical distribution also will be specified (as observed in winter).  While the NPZ model is being tested against the observed data, these same data will be used to generate spatially and temporally interpolated 3D static prey fields for the copepod population model.  This empirical approach is complementary to the model-based approach.

Upstream dataBiological data for the SS and SW ­will be obtained from our Canadian colleagues, who have been actively involved in the GB and Canadian GLOBEC programs as well as in other studies of the SS and Labrador Sea including the AZMP (see Head letter).  To the extent available we will use interpolated data from 1995-1999 in the SS and SW.  We also will use idealized boundary scenarios based on observed data from other years and larger scales (eg. CPR data).

Biological transport — We will use concentration-based (Eulerian) rather than individual-based (Lagrangian) transport for the copepod and food web models. While we have used both types of models in the past, the use of concentration-based models allow us to compute fluxes and mass balances directly and more accurately.  This approach is necessary for quantifying such factors as sustainability of populations in particular areas.  The concentration-based approach lends itself easily to stage-structured population models.  This straightforward method avoids the necessity of using super-individual particles or spawning and removing particles at each time step. 

2.3.3.      Numerical experiments

We will conduct a series of targeted numerical experiments using prognostic forward model runs (rather than inverse methods) to address each of the above hypotheses.  Data and model will be compared using a maximum-likelihood method (Stock, 2005; Stock et al., submitted). These process studies will help interpret the basic behavior and inter-annual variability shown in the 1995-99 hindcast.  Detailed tasks and time table for this work are given in the required supplement on project management and data exchange.

Working hypothesis— We will initialize the model with the mean winter concentrations of each copepod species (in separate model runs).  The same model structure will be used for all species, changing only the parameter values (temperature/food/life-stage dependent egg production rate, development rate, growth rate, and normalized stage-dependent mortality) and behaviors, and thus expediting the model runs.  The inputs of characteristic life history traits of each species together with its initial abundance patterns should generate its observed characteristic seasonal/spatial patterns. The model will be run for a complete annual cycle and compared with the 5-year monthly mean abundance patterns.  To examine inter-annual variation we will model each copepod species during the complete 5-year GLOBEC period 1995-1999, first year by year, then continuously over the 5 years.  The result will be a complete 5-year biological/physical hindcast.

Food versus PredationWe will examine the degree of food-dependence and mortality with regard to inter-annual variability for each species.  First we will confirm that the NPZ model can be used to approximate the 3D distribution of phytoplankton for the multi-year monthly mean and year-to-year changes.  In parallel, we will use fixed 3D phytoplankton fields approximated from monthly averaged satellite and in situ data.  We will interpolate the phytoplankton fields between monthly values to avoid discontinuities.  We will use the NPZ model together with scenarios of salinity and nutrient (N, Si) input through the NEC, to determine the extent to which phytoplankton biomass/production on GB is determined by this forcing and the extent to which the copepod species are affected by it.  We will examine possible effects of temperature and transport during 1995-1999 on the trends in mean abundances of each species.

Self-sustainabilty— We will initialize the model with the observed distribution of each species and exclude input from other regions, to determine whether the local population is self-sustaining.  In particular we will examine the importance of Calanus input from SW and/or SS to the GOM/GB population, the input of Pseudocalanus from western GOM to the GB population, the key source regions for Oithona similis, and whether Centropages typicus depends on immigration to sustain its population on GB.  We will further examine whether resting eggs can explain high abundance of Centropages hamatus and Temora longicornis on the crest of GB.  We will initialize the population as resting eggs on the crest and determine whether the resulting plume of nauplii and subsequent copepodids matches the observed distributions.  We will examine the formation of the Calanus “hole” on GB by initializing with CVs in the GOM during December and determining the extent to which the hole forms as a result of gradient advection versus high crest mortality.

Catastrophic global warming— Finally we will use boundary forcing that represents a scenario of catastrophic warming (see FVCOM section).  We will run the model for single and multiple years to determine the impact on the NPZ fields and on each dominant copepod species.

2.3.4.      Work schedule— The schedule for the proposed modeling work together with a description of individual tasks, project management, dissemination, and timeline are described in the required supplemental documents.

3.      Significance of Proposed Research– Intellectual Merit

The proposed work will provide new insights into the role of local dynamics and large-scale forcing in controlling population dynamics of marine copepods.  We believe that the physical/biological model resulting from the proposed work will be a legacy of the Georges Bank GLOBEC program by providing a valuable tool that subsequent researchers can use to study the dynamics of this system in hindcast, nowcast, and forecast modes. The results of the targeted experiments will provide insights into the degree of bottom-up and top-down control and the degree of sustainability of copepod populations under different conditions of external forcing.  The work will provide a new understanding of the impact of basin-scale forcing, including catastrophic change, on local-scale plankton dynamics.  The resulting spatially explicit model of small and large copepod species will provide dynamic prey fields for concurrent and subsequent larval fish modeling studies, leading to a better understanding of recruitment in fish populations.

4.      Broader Impacts

The New England Regional Center for Ocean Science Education Excellence (NER-COSEE) at WHOI will work with us to facilitate development of the education and outreach component of this project. COSEE is a national program, with regional centers, designed to facilitate K-12, college, and public education and outreach.  The proposed work will provide a state-of-the art coupled biological/physical model of an important marine area.  We envision a broad user-base for this final product, which will be served via the web to our scientific colleagues as well as to fishermen, K-12 educators, and the general public.  The main web-page will be located at WHOI with links to the other institutions.  Chen’s group at UMD will create a website specifically for this work, expanding their existing FVCOM site, which now has user-friendly point-and-click modeling capacity.  Users will be able to examine 4D model data from the hindcast for the GLOBEC years as well as from pre-run nowcasts and forecasts.  Users will be able to change model parameters and create new model runs, with the level of sophistication depending on skill level. Further discussion of these broader impacts is given in the required supplementary section on this topic.



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[1] We note that several groups of other investigators (e.g., J. Wilkens and D. Haidvogel at Rutgers and D. Wright, C. Hannah, and others at BIO) are examining how well existing North Atlantic large regional (the Rutgers Northeast North Atlantic ROMs) and basin-scale (e.g., HYCOM, MERCATOR, OPA, POP3) models can hindcast observed physical conditions over the Northeast America continental margin between Cape Hatteras and the Grand Banks.  In particular, Loder and co-workers at BIO have just completed a long-term moored array study over the Scotian slope and the ongoing physical/biological transect data being collected in AZMP both provide an extensive data set for detailed comparison with large-scale model hindcasts.  We will follow their work closely during Phase 4B to help determine to what extent these larger-scale models can provide accurate boundary conditions along the North American Atlantic margin, including the shelfbreak/slope current system and the influence of Gulf Stream eddies and warm-core rings as they move along the margin, with the idea of using this capability when proven to drive our regional FVCOM integrated model system in future studies.