Processes controlling plankton abundance on Georges Bank:

Proc= esses 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), Richa= rd Limeburner (WHOI)

Proj= ect 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., recruitme= nt) 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 s= tudy in detail biological-physical processes controlling zooplankton population size. We propose to use an ex= isting 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 deta= iled mechanisms controlling seasonal evolution of spatial patterns in dominant zooplankton species on G= eorges Bank. We will examine a series of hypoth= eses that address how dominant copepod species populations are maintained on the bank, including local dynamics and large-scale forcing. Specifically we will determine whe= ther the observed characteristic sea= sonal-spatial pattern of each species (long-term and inter-annual) is predictable from the interaction between its characteris= tic 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 concurre= nt basin-scale modeling efforts. Intellectual Merits: The proposed modeling study will pr= ovide 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 provi= ding 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 lega= cy 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 t= he 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 ac= cess 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. Back= ground

The GLOBEC approach — Und= erstanding 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 analys= is (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., <= /span>Davis, 1987a). = The trophodynamic concept has been used to relate primary and second= ary production to fish production (e.g., Clarke, 1946; Cushing, 1975; Sissenwin= e 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, 1= 973). The GLOBEC program recognizes recruitment as the dominant factor controlling population abundance in mari= ne animal species (GLOBEC, 1991a). The = regional GLOBEC programs focus on target species and their dominant prey, with empha= sis on individual organisms, population dynamics, and interactions with the physical environment, especially as it relates to global climate change (GL= OBEC, 1991b, 1992, 1996, 1997, 2000).

Georges Bank GLOBEC: dominant zooplankton species — Georges Bank was chosen as the first GLOBEC study site due to its sensitivi= ty to climate change, definable populations, importance as a fishing ground, a= nd significant historical database (GLOBEC, 1992). The goal of this program is to understand the biological and physical processes controlling abundance of c= od 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 h= ave found that small copepods (Pseudoca= lanus spp., Oit= hona similis, C= entropages spp., = Temora longicornis) are dominant prey ite= ms for cod and haddock larvae on Georges and Western Banks (Lough and Mountain, 19= 96; 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 S= ea) 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 ref= lect 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 <= span style=3D'font-size:11.0pt'>Baltic Sea, cod larvae also feed on small copepod species (Hinrichsen et al, 2002).<= span style=3D'mso-spacerun:yes'> 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/<= /span> Gulf= of Maine region, including Calanus finmarchicus and the small= er species, Pseudocalanus spp. (moulton= i and newmani), Oithona similis, T= emora longicornis, Centropages spp. (typicus and hamatus).

1.1.=    The <= /span>Georges Bank Physical Environment =

Local dynamics — Geo= rges Bank (GB), the Gulf of Maine (GOM), and Scotian Shelf (SS) are part of a si= ngle 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. <= /span>

The strongest currents o= ver 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 stratificat= ion throughout the year. As seaso= nal stratification increases on the flanks of the bank, the tidal mixing front forms with associated secondary flow. The clockwise around-bank residual fl= ow increases with seasonal stratification, becoming partially closed from June through

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

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

= (Fratantoni and Pickart,= 2005)

September until fall sto= rms and surface cooling destroy the local stratification. Surface heating drives the develop= ment of the seasonal thermocline. = Salinity on the bank is controlled by advective and mixing processes along the north= ern 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 Sou= th Channel (Fig. 1, 1), tidally-driven near-bottom residual flow (the “ti= dal pump”, Fig. 1, 2), wind-driven near-surface flow (Fig. 1, 3), small-scale cross-frontal processes (Fig. 1, <= span style=3D'color:red'>4), and intermittent cross-over of low salin= ity SS surface water (Fig. 1, 5). The tidal pump in particular provides a strong mechanism for bringing deep water from Georges Basin up onto th= e 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 Oscillati= on (NAO) index (left) and weak penetration of LSW and more southward positio= n 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 relati= vely 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 Cur= rent 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 Wa= ter (LSW), which flows west into the Laurentian Cha= nnel 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 <= span lang=3DEN-GB style=3D'font-size:11.0pt;mso-ansi-language:EN-GB'>Gulf Strea= m origin. Si= nce WSW is warmer, more saline, and nutrient rich than LSW, the relative mix of the= se two end members entering the NEC, and its transport relative to the inflow = of SS water, strongly influences circulation, water property distributions, and n= utrient 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)<= span lang=3DDE style=3D'font-size:11.0pt;mso-ansi-language:DE'>

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 salini= ty on GB exhibited two significant freshening events between early 1996 to ear= ly 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 coo= ler, fresher LSW in January 1998 as the leading edge of LSW flow extended west d= ue 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 ag= ain flowing into the GOM through the NEC. Since the tidal pump mechanism can carry deep water up on the northe= rn flank of GB, advection of LSW in Georges Basin onto the bank can occur on relative short time scales (>=3D1 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, t= he mix of WSW versus LSW) linked to basin-scale forcing strongly control the w= ater 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.=    Conne= ction 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 ba= nk can quickly transport nutrients from Georges Basin up onto the NE peak of GB, impacting the productivity of the bank very ra= pidly (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 inflo= w 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<= /span>). Each species exhibits a characteristic life cycle and seasonal/spatial pattern in the GB/GOM region. Calanus finmarchicus and Pseudocalanus<= /i> spp. are cold-water species that avoid the warm surfa= ce layer (>10-12^oC) during summer and fall and produce large spr= ing populations. Centropages spp, Temora, and Paracalanus are warm water spec= ies 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 cool= er waters (5-7^oC) at depth in the GOM (Fig. 6). During late Decemb= er, it emerges from diapause (mechanism unknown), swims to the surface and molt= s to adult. Subsequent egg product= ion 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 th= e 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 se= ason 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 th= is population is self-sustaining is unknown.

Fig. 7. Calanus finmarchicus abundance i= n the N Atlantic from CPR data (Spears 2005) and nets/OPC (Hea= th et al. 2004). Note high densit= ies in the Labrador and Norwegian Seas.

Calan= us finmarchicus is an open ocean species, occurring throughout = the northern North Atlantic<= /span> from the eastern US to the Barents Sea, with centers of population abundance in the Norwegian and = Labrador seas (Fig. 7). Immig= ration into the GB/GOM population from upstream sources may contribute to the appa= rent stability of the population. = C. finmarchicus enters the GOM fro= m the SS and possibly from the SW through the NEC.&= nbsp; C. finmarchicus in the SW originate from the Labra= dor 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 degr= ee from the productive Gulf of S= t. Lawrence population (Zakardjian et al. 2003). It is unlikely tha= t immigration directly determines the large spring abundance peak in C. finmarchicus in the GB/GOM, since the water mass turnover ti= me is long relative to the generation time, but a seeding type of immigration during the “off-season” could be important in determining the s= ize of the startup population of CVs in December (<= span style=3D'font-size:11.0pt;mso-bidi-font-size:12.0pt'>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 dept= hs 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 fo= r C. pacificus in the Santa B= arbara basin (Osgood and Checkley= , 1997). Lagrangian modeling st= udies have found retention of diapausing CVs in the GOM to be high, especially if= the animals stay below 150 m (Johnson et al., submit= ted). 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 sha= rp contrast with the situation in the North Sea, whi= ch 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

       &nbs= p;   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, sin= ce 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.&nb= sp; A huge literature exists for C. finmarchicus egg production, development and growth as a function of fo= od and temperature including several studies done as part of the GLOBEC GB pro= cess work (Campbell and Head, 2000; Campbell et al., 2001a,b; Runge et al. submi= tted). Such data can be incorporated into= the population model for this species and used together with the large field da= ta 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 (Fi= g. 9, 10). Its abundance is higher = in shallower areas (<100m) and is highest in the crest region of the bank in June. Pseudocalanus do= es not overwinter in the GOM as does Calanus an= d 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 typicu= s, 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 a= l., 1989a,b). = P. moultoni is a coastal species a= nd P. newmani an offshore one (Frost, 1989). Thus P. moultoni may be carried onto the bank from western GOM coast= al 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 model= ing, 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, m= eant that the independent species-specific life history information could not be included in the model. Substa= ntial information on development, growth and egg production as a function of food= and temperature is available for Pseudo= calanus (e.g. Corkett and McLaren, 1978; Vidal, 1980; D= avis, 1983, 1984a,b; McLaren et al., 1989b; Ban et al., 2000; Lee et al., 2003; Dzierzbicka-Glowacka, 2004). Use of these laboratory and shipbo= ard 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 contr= olling seasonal development of the spatial distribution patterns. Targeted forward modeling experime= nts 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.<= /o:p>

Other Dominant Copepod Species &#= 8212; Each dominant copepod species on GB has its own characteristic temporal-spatial patterns and life histories (e.g., <= st1:City>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 sugge= sted that these species use resting eggs as a strategy for “gluing” their populations to regions that are favorable for growth (Davis, 1987; Li= ndley 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 dur= ing 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 pa= ttern similar to C. finmarchicus, wit= h 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.). Whi= le this trend may reflect a change toward smaller species, indicative of a war= ming trend, no concomitant increase in temperature was observed. These changes were negatively correlated with salinity (Durbin and Casas<= /span>, 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 sa= linity 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 re= ason for which is unknown. The pro= posed modeling work will examine the potential causes of the zooplankton increase and its relationship to large-scale forcing and= climate change.

1.4.=    Avail= able Data Sets

GLOBEC GB — The GLOBEC GB field program was conducted from 1995-1999 and includ= ed a combination of monthly broadscale and process-oriented cruises (GLOBEC, 199= 2; 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 ne= ts) samples were collected over the same depth ranges as the MOCNESS in the upp= er water column but the maximum depth it was deployed to was 70-100 m dependin= g on wind and tides, or to the bottom on shallower parts of the bank. For complete description of collec= tion 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 (http://globec.gso.uri.edu). 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 se= t is available to us via an NMFS Oracle database (D. Mountain, pers. comm.) Although the zooplankt= on data are from integrated hauls, these data cover a broader area than the GL= OBEC GB data, and, together with GLOBEC vertical data from deeper GOM, will allo= w 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 H= ead 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. <= st1:place>Davis (1984) showed that the interaction between arou= nd-bank advection/diffusion and temperature-dependent development of the copepod Pseudocalanus could explain observ= ed spatial patterns in population structure.&= nbsp; 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<= /span> 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 washo= ut 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 c= ontribute to the bank population; these models used 2D transport of concentration-bas= ed (Lynch et al. 1998), individual-based (Miller et al., 1998), and particle trajectories (Hannah et al 1998). The C. finmarchicus population thro= ughout the Gulf of St. Lawrence/SS/G= OM 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 horizon= tal transport was dominant on the SS, but that the population is self-sustainin= g 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 biolo= gical/physical model of this region (FVCOM). Data processing and model development recently have reached the point where they= can be effectively combined. By t= he 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 zoopla= nkton 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 backgrou= nd 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 exper= t in copepod biology specializing in Cal= anus 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 a= nd approach for the GLOBEC GB program (GLOBEC, 1992).

2.      Prop= osed Research

2.1.   Hypotheses

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

H1₀: Th= e abundance of copepod species on the bank is controlled by food availability (bottom-up control). Here we will examin= e the scenario that GB productivity, and thus food availability for the dominant copepod species, is controlled by nutrient input into the GOM through the N= EC, 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-limita= tion and predation (time-space dependent), and 3) purely physical control by dir= ect effects of temperature on vital rates or advection. In 3), we will examine causes of t= he 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-sustain= ing. We will examine the need for immig= ration from different sources to maintain the copepod populations over multiple ye= ars. Key source regions will be ex= amined 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), parameteri= zed as a lack of Labrador Sea water at the NEC, causes a regime shift on GB fro= m 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 spat= ial patterns of dominant copepod species on GB. Our specific objectives are: 1) to examine how local-dynamics and external forcing control the abundance of th= ese species on GB, 2) to determine the degree to which top-down versus bottom up proces= ses control the dominant copepod species on GB, and 3) to use existing state-of-the-art 3D physical/biological numerical models together with exis= ting high-quality 3D data sets from the GLOBEC GB field program (and other historical data sets), to conduct targeted numerical experiments that explo= re the likelihood of the hypotheses listed above.

2.3.   Methods


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


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


Fig. 7. Calanus finmarchicus abundance i= n the N Atlantic from CPR data (Spears 2005) and nets/OPC (Hea= th et al. 2004). Note high densit= ies in the Labrador and Norwegian Seas.