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2002 The orN theast Pacific GLOBEC Program: Coastal Gulf of Alaska Thomas J. Weingartner

Kenneth Coyle

Bruce Finney

Russell Hopcroft

Terry Whitledge

See next page for additional authors

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Repository Citation Weingartner, Thomas J.; Coyle, Kenneth; Finney, Bruce; Hopcroft, Russell; Whitledge, Terry; Brodeur, Richard; Dagg, Michael; Farley, Edward; Haidvogel, Dale; and Royer, Thomas, "The orN theast Pacific GLOBEC Program: Coastal Gulf of Alaska" (2002). CCPO Publications. 308. https://digitalcommons.odu.edu/ccpo_pubs/308 Original Publication Citation Weingartner, T. J., Coyle, K. O., Finney, B., Hopcroft, R., Whitledge, T., Brodeur, R., . . . Strom, S. (2002). The orN theast Pacific GLOBEC program: Coastal Gulf of Alaska. Oceanography, 15(2), 48-63. doi:10.5670/oceanog.2002.21

This Article is brought to you for free and open access by the Center for Coastal Physical Oceanography at ODU Digital Commons. It has been accepted for inclusion in CCPO Publications by an authorized administrator of ODU Digital Commons. For more information, please contact [email protected]. Authors Thomas J. Weingartner, Kenneth Coyle, Bruce Finney, Russell Hopcroft, Terry Whitledge, Richard Brodeur, Michael Dagg, Edward Farley, Dale Haidvogel, and Thomas Royer

This article is available at ODU Digital Commons: https://digitalcommons.odu.edu/ccpo_pubs/308 >-~' J.:.J,j,..;__":~• .._. ;,(_ ,~ • • ,_ • • ~ ~ ;; ~ :( r : 'z:• ~'~-<~~•~ SPECIAL ISSUE - U.S. GLOBEC The Northeast Pacific GLOBEC Program: Coastal Gulf of Alaska

Thomas J. Weingartner, Kenneth Coyle, Bruce Finney, Russell Hopcroft, Terry Whitledge University of Alaska. Fairbanks, Alaska USA

Richard Brodeur NOAA/Northwest Fisheries Science Center. Newport, Oregon USA

Michael Dagg Louisiana Universities Marine Consortium. Chauvin, Louisiana USA

Edward Farley NOAA/Auke Bay Laboratory. Juneau, Alaska USA

Dale Haidvogel Rutgers University. New Brunswick, New Jersey USA

Lew Haldorson, Un iversity of Alaska. Juneau, Alaska USA

Al Hermann, Sarah Hinckley, Jeffrey Napp, Phyllis Stabeno NOAA/Pacific Marine Environmental Laboratory. Seattle, Washington USA

Thomas Kline Prince William Sound Science Center. Cordova, Alaska USA

Craig Lee, Evelyn Lessard University of Washington. Seattle, Washington USA

Thomas Royer Old Dominion University. Norfolk, Virginia USA

Suzanne Strom Western Washington University.Anacortes, Washington USA

Introduction The Gulf of Alaska (GOA) continental shelf siderable variability on both interannual and longer encompasses approximately 370,000 km2, or about 13% time scales in harvest and recruitment success to this of the U.S. continental shelf, and supports a rich and and other GOA fisheries. Of recent interest are com­ diverse marine ecosystem including some of the pelling indications that abundances of salmon, other largest commercial fisheries in the U.S. Exclusive fish species, and zooplankton vary on decadal scales in Economic Zone. Of particular economic importance is association with North Pacific basin-scale climate tJ1e salmon fishery, which was worth on the order of changes (Beamish, 1995; Mantua et al., 1997; Roemmich $170 million (landed value) in 2000 accrued from a and McGowan, 1995; Brodeur et al., 1996; Francis et al., catch of over 100 million fish. However, there is con- 1998; Anderson and Piatt, 1999; Hollowed et al., 2001).

------Oceanography • Vo l. 15 • No. 2/2002 ------48 Salmon recruitment success appears to be predom­ both a freshwater reservoir and a sediment source for inantly established during the first year of life after the the shelf. juvenile salmon leave nearshore nursery areas and Climate variability in the GOA might be expressed move onto the shelf (Francis and Hare, 1994; Pearcy, in a number of ways. Atmospheric-induced variations 1992). For pink salmon (Oncorhynchus gorbuscha), could alter the wind and thermal regime both over the migration onto the shelf begins in July, peaks in August shelf and the basin and/ or perturb the hydrologic cycle and diminishes through fall (Boldt, through changes in precipitation rates 2001), although juveniles may remain or patterns or by altering the mass bal­ on the shelf through December (Welch ance of the glaciers and the seasonal et al., 1998). Individual growth and Of recent interest are snowpack. Alternatively, ocean cur­ mortality are high during this phase of compelling indications rents might efficiently carry remote cli­ the life history (Parker, 1968; Pearcy mate perturbation signals into this 1992; Boldt, 2001; Beamish and that abundances of region. In developing an understand­ Mahnken, 2001) and depend on the salmon, other fish species, ing of how climate variability affects complex interplay of a number of fac­ the CGOA ecosystem, a key challenge tors such as the composition, abun­ and zooplankton vary is to explain the physical basis of bio­ dance, density, and condition of plank­ on decadal scales in logical production on this shelf. The tonic prey, predator types and association with North CGOA is paradoxical because the high abundances, disease, turbulence, and biological productivity (as indicated by water temperature. Climate perturba­ Pacific basin-scale the magnitude of commercial fish land­ tions could influence any of these vari­ climate changes. ings) occurs in the face of both strong ables both directly and indirectly. Direct downwelling and a massive, nitrate- effects, such as control of predator poor coastal freshwater discharge. abundance or juvenile salmon growth Solving this intriguing problem and rates by water temperature are relatively easy to study. understanding how production processes might be Indirect effects, such as "bottom up" processes, are altered by climate change is a key focus of GLOBEC more difficult to determine. For example, climate vari­ studies in the CGOA. ability might affect the timing and/ or magnitude of the spring bloom, the effects of which then propagate Physical Setting through the food web to influence the timing, compo­ The dominant circulation features over the GOA sition, and biomass of summer-fall zooplankton, with shelf and slope are the Alaska Coastal Current (ACC) consequences for juvenile salmon feeding success and on the inner shelf and, along the continental slope, the growth rate (Denman et al. 1989; Gargett, 1997). The Alaska Current in the eastern gulf and its transforma­ target zooplankton species in GLOBEC-CGOA tion into the Alaskan Stream in the northwestern gulf (Coastal Gulf of Alaska) studies, Calanoid copepods (Figure 1). These currents are extensive, cyclonic, and and euphausiids (see Table 1 in Fogarty and Powell persist year-round. They flow over complicated bottom this issue; Strub et al., this issue), were selected as crit­ topography, so that mesoscale flow variations generat­ ically important elements in the food web dynamics of ed by flow-topography interactions are likely. The ACC this region. spans an alongshore distance of -2500 km from its ori­ In the NEP-GLOBEC program we are investigating gin on the British Columbian shelf (or perhaps even how large-scale climate signals are manifested at the further south in winter) (Royer, 1998) to its termination scale of the continental shelf ecosystem. Basin-or glob­ in the western gulf where it enters the Bering Sea al-scale climatic signals are likely modified by regional (Schumacher et al., 1982). It is a wind- and buoyancy­ processes, and it is this modified, local, signature that forced coastal current generally confined to within 40 presumably affects the regional biological response to a km of the coast and bounded offshore by a salinity given climate perturbation. The regional responses to front whose strength and structure varies seasonally in climate perturbations in the GOA are strongly depend­ response to variations in winds and freshwater dis­ ent on its high-latitude location and its geomorpholo­ charge. The Alaska Current and Alaskan Stream are, gy. Together these profoundly influence the meteorolo­ respectively, the eastern and western boundary cur­ gy, hydrology, and the response of this shelf ecosystem rents of the GOA and respond primarily to the cyclonic to climate variability. wind stress curl over this basin. The geomorphology of the GOA shelf reflects past These currents comprise the poleward limb of the (and present) glacial and tectonic processes. These North Pacific Subarctic Gyre and provide the oceanic have carved a convoluted coastline and punctuated link between the GOA shelf and the North Pacific this relatively deep (>150 m) shelf with numerous Ocean. In so doing, the boundary currents advect warm, troughs, canyons, and banks. Tectonic uplift has lower latitude waters into the northern gulf and there­ formed an extensive ring of coastal mountains around fore play an important role in the regional heat budget. the gulf. The mountains are covered by the Earth's The Alaska Current is a broad (-300 km), sluggish (5-10 1 third largest glacial field (Meier, 1984), with these being cm s- ) flow with weak horizontal and vertical velocity

------Oceanography • Vol. 15 • No. 2/2002 ------49 Annual Forcing Cycles / ~ ~

UrnH~lling .~ lnde, _.,

(6/i''' · /~'I",,., _-5,

-100

I = 2 mlyr precipitation

Figure 1. Regional map of the Gulf of Alaska showing the principal currents and mean annual precipitation rates (b lack verti­ cal bars) from coastal stations and, from Baumgartner and Reichel (1975), for the central gulf The red box delineates the region 3 of the CGOA GLOB EC field study. The inset shows the mean monthly upwelling index in red from 1946-2000 (units are m - s·1per 100 m of coastline) in the northern gulf and the mean monthly freshwater discharge in blue for the Gulf of Alaska (Royer, 1982 and pers. comm.) for the period 1930-2000. Negative values of the upwelling index imply onshore Ekman transport and coastal downwelling.

shears while the Alaskan Stream is narrow (-100 km) erately low (mean annual sea surface temperature = 1 and swift (-100 cm s· ) with large velocity shears (Reed 7°C) and temperature gradients generally weak. and Schumacher, 1986). The transformation of the Because of this, the large, but seasonally varying, Alaska Current into the Alaskan Stream entails con­ coastal freshwater discharge results in salinity being comitant changes in the velocity and thermohaline gra­ the primary variable controlling horizontal and vertical dients along the shelfbreak. Insofar as these gradients density gradients throughout much of the year, but influence fluxes between the shelf and slope especially from fall through spring. Climate perturba­ (Gawarkiewicz, 1991), this transformation, along with tions that affect the rates and timing of coastal dis­ the varying slope topography, suggests that shelfbreak charge might play an important role in the seasonal exchange mechanisms are probably not uniform evolution of density gradients and the shelf circulation. around the gulf. Moreover, the effects of these Energetic storms associated with the Aleutian Low exchanges on the shelf will also be influenced by the predominantly influence the regional meteorology. shelf width, which is ~ 25 km in the eastern gulf but Storms develop in the western and central North broadens to more than 200 km in the northwestern gulf. Pacific Ocean and, as they propagate eastward, they Gulf of Alaska shelf water temperatures are mod- intensify by absorbing heat and moisture from the

------Oceanography • Vol. 15 • No. 2/ 2002 ------50 ocean surface. The strength, trajectory, and frequency gram began with an opportunistic cruise in October of these lows are also influenced by both the Siberian 1997 in response to the developing El Nino and then on and East Pacific High pressure systems (Wilson and a systemic basis in March 1998. Overland, 1986). The position and strength of these Sampling is mainly focused along the Seward Line, three climatological systems varies seasonally and which extends -250 km from the coast across the conti­ interannually, leading to variations in wind velocity, nental slope (see Figure 2). Additional sampling is con­ cloud cover, precipitation, and runoff on equivalent ducted within Prince William Sound and at high spatial time scales. The coastal mountains bordering the gulf resolution within the ACC on a short transect along a inhibit the inland migration of storms so that lows relatively straight stretch of the coast between the often dissipate here. Consequently, the mean winds are sound and the Seward Line. The sampling activities in cyclonic and impel an onshore surface Ekman trans­ the LTOP and process components are timed to the port over the slope and shelf, generating coastal con­ principal biological and physical seasonal transitions vergence or downwelling. Downwelling favorable occurring on this shelf (Table 1). The mooring array, winds occur from September through May and are deployed in spring 2001, spans the shelf and shelfbreak maximal in January, whereas winds are weakly measuring temperature, salinity and currents. Several upwelling in summer on average (Figure 1 inset). moorings include nitrate analyzers and fluorometers Although maximum cyclonic wind stress occurs in the and one includes a bio-acoustic sensor to measure zoo­ northeastern gulf, the alongshore wind stress fluctua­ plankton biomass. Drifters, drogued at 40 m , are tions are largely coherent around the gulf (Livingstone released periodically along the Seward Line to track and Royer, 1980). The mountains force air masses broader-scale water movements and to provide infor­ upward, resulting in cooling, condensation and mation on mesoscale variability. enhanced coastal precipitation (Figure 1) . In most The 2002 field program will be augmented by months this precipitation feeds the many small water­ Seaglider surveys (autonomous, telemetering under­ sheds draining into the Gulf, but in winter, much of the water vehicles) that will make continuous high-resolu­ precipitation is stored in snowfields and glaciers where tion measurements at a horizontal resolution of it can remain for one or more seasons. Freshwater dis­ approximately 1.2 km and profile between the surface charge is a minimum in winter when precipitation is and 10 m of the seabed. Sea glider sampling will contin­ stored as snow, increases rapidly through summer ue throughout the year conducting 20-day repeat sur- through melting, and attains its maximum in fall when precipitation rates are greatest (Royer, 1982; Figure 1 inset). Slightly more than half of the discharge enters in southeast Alaska (Royer, 1982) with the remainder entering along the south central coast. Although the freshwater is a significant buoyancy source for the shelf, the runoff is nitrate poor owing to its glacial and mountainous origin (Reeburgh and Kipphut, 1986). Both the spatial structure of the winds and the distrib­ uted nature of the coastal runoff suggest spatially coherent patterns of wind and buoyancy forcing over much of this shelf. The CGOA Sampling Program The principal GLOBEC field effort in the CGOA entails two inter-related components: observational • and process-oriented studies. The Long Term • Observation Program (LTOP) is designed to provide a broader temporal and spatial context for interpretation • of process studies and to measure key variables required in physical and biological models of this sys­ tem. The process studies are designed to provide a mechanistic understanding of physical and biological rates and processes critical to ecosystem dynamics. Figure 2. Map showing location of moorings (green), The Long Term Observation Program (LTOP) LTOP stations (red, yellow, and blue). Stations colored In the LTOP study we are quantifying the temporal yellow are also the zooplankton process stations occupied (interannual and seasonal) and spatial variability of the in 2001. The blue circle indicates station GAK l where physical environment, nutrient concentrations, phyto­ nominally monthly CTD casts have been made since 1970. plankton production and abundance, and zooplankton and fish abundance and distribution. The LTOP pro-

------Oceanography • Vol. 15 • No . 2/2002 ------51 veys through the ACC between Prince William Sound surface salinity and temperature, chlorophyll, and and the Seward Line. Sampling will include tempera­ zooplankton. ture, conductivity, pressure, chlorophyll fluorescence, dissolved oxygen, optical backscatter, surface drift, and Process Studies vertically averaged currents. Seaglider data will be The process studies focus on measuring feeding periodically transmitted to the laboratory via the and growth rates of key organisms comprising the Iridium system. planktonic ecosystems (e.g. phytoplankton, het­ Fish sampling is conducted as part of the LTOP erotrophic protists, copepods, euphausiids,) as well as surveys in Prince William Sound and along the Seward juvenile salmon. A variety of analytical approaches Line and as part of an annual Gulf-wide survey con­ (microscopy, imaging-in-flow techniques, pigment bio­ ducted from mid-July through early August, under the markers, chlorophyll size fractionation) are being auspices of NOAA's Ocean Carrying Capacity (OCC) employed in conjunction with feeding and growth program. The latter effort involves trawling along experiments to elucidate trophic interactions among eleven cross-shelf transects between Southeast Alaska these groups. These process measurements are critical and the western Gulf. Data from all fish surveys are in order to make comparisons with the California con­ used to determine salmon condition, distribution, size, tinental shelf (CCS) ecosystem and for developing and age, diet, growth rate and genetic stock identification. evaluating regional ecosystem models having a prog­ Other fish species are counted and juvenile rockfish nostic capability. The process studies also include data (Sebastes species) and sablefish (Anoplopoma fimbria) are obtained from drifters and moored instruments. Both frozen for additional laboratory analyses. The fish sur­ techniques will provide high-resolution time series on veys also include the collection of oceanographic data the cross- and along-shore variations in the circulation. including CTD casts, currents (VM-ADCP), continuous Most of the process studies began in the spring of 2001

Table 1. Sampling schedule and rationale for CGOA LTOP and process sampling. Italicized months indicate time of process study cruises in 2001.

Month Physical Rationale Biological Rationale

March Strong downwelling and vertical mixing, Zooplankton migrate from depth low discharge, weak stratification (at shelfbreak) & transported inshore

April Moderate downwelling, discharge Phytoplankton bloom increasing, weak and spatially variable stratification

May Moderate-weak downwelling, Phytoplankton bloom and moderate discharge, stratification maximum oceanic copepod increasing biomass

July Weak up- and downwelling, Maximum zooplankton abundance discharge increasing, strong Juvenile salmon enter shelf stratification

August Weak up- and downwelling, Maximum juvenile salmon moderate-strong discharge, strong abundance on shelf stratification, deep onshore movement of nutrient-rich offshore waters

October Strong downwelling, maximal Juvenile salmon on shelf, possible discharge, strong stratification fall phytoplankton bloom

December Strong downwelling, decreasing Fall-winter deep mixing, assess discharge, weakening stratification small zooplankton condition.

------Oceanography • Val. 15 • No. 2/2002 ------52 with the results from the first process field season still being synthesized. 4 Scientific Highlights • • Accumulating field data and model results suggest 3 that the CGOA shelf is roughly organized into three • distinct physical regimes delineated by salinity fronts QJ whose strength and position varies seasonally. The u C 2 • QJ • • inner shelf is dominated by the low-salinity ACC; u Ill .-.. while the outer shelf, including the shelfbreak and QJ Ill ... +-' inner slope, is influenced by saltier and (generally) o- • • ::, 0 1 • more nutrient-rich oceanic waters advected within the ->u. ._, • • • boundary currents. The mid-shelf regime contains • waters of intermediate salinity and a highly variable • 0 flow field that is weakly westward on average. These - - observations, along with the low cross-shelf correlation l 2 3 4 5 6 7 8 9 10 l l 12 13 in along-shelf flow variability, suggests that distinctly Seward Line Stations different dynamics might apply to each regime. These physical regimes roughly delineate different biological habitats, as there are often distinct species assemblages found within each regime. Cross-shelf gradients in species assemblages are also evident; phytoplankton, microzooplankton and fish assemblages show a very heterogeneous cross-shelf distribution. Shipboard measurements, current meter data, drifter trajectories, and Sea WiFS satellite imagery all suggest that considerable mesoscale variability is embedded within these various shelf regimes. In springtime, the cross-shelf de-correlation scale is 5-20 km as derived from zooplankton biomass distributions obtained from continuously recording, towed acoustic sensors. Similarly, cyanobacteria, picoeukaryotes, het­ erotrophic dinoflagellates and ciliates are all abundant - - - (Figure 3) but show highly variable numbers and bio­ Figure 3. Upper panel: Chlorophyll fluorescence (volts, mass over short ( <10 km) distances. Process measure­ circles) at the fluorescence maximum and phytoplankton ments made in spring and summer 2001 indicate that assemblages at stations along the Seward Line during the phytoplankton and zooplankton productivity rates can 28 June-8 July 2001 LTOP cruise. Colored bars represent also vary widely over short spatial scales, even in mid­ different plankton assemblages. Red: large diatom-domi­ summer when low nitrate concentrations occur in the nated, Guinardia and Chaetoceros spp.; Orange: pico­ mixed layer. and nanoplankton dominated, cyanobacteria, crypto­ Satellite altimeter data indicates that mesoscale phytes, nano-diatoms; Blu e: small diatom-dominated, spatial variability over the shelfbreak and slope is Nitzschia spp.; Green: cyanobacteria, small Nitzschia, linked to meanders in the boundary flows or the large with increasing domination seaward by the large diatom, (>100 km diameter) anticyclonic eddies propagating Corethron. Bottom panels: epifluorescent micrographs along the continental slope (Okkonen et al., submit­ of the different assemblages. Photosynthetic organisms are ted). As these anticyclones propagate along the slope red-orange in color due to fluorescing chlorophyll pig­ they induce upwelling at the leading and trailing edges ment; heterotrophic flagellates and dinoflagellates fluo­ of the eddy and downwelling over the eddy center resce green. Smallest red dots are picoeukaryotes and with these effects reflected in chlorophyll biomass, smallest yellow dots are cyanobacteria. rates of primary productivity, and zooplankton biomass. Nutrient Dynamics The CGOA-GLOBEC program is concerned with mer. The summertime inflow of saline water onto the identifying and quantifying the mechanisms by which inner shelf is one means by which the slope and basin nutrients are transferred onto the inner shelf and sup­ communicate directly with the inner shelf; this water is plied to the euphotic zone. On an annual basis, salty, drawn from within the permanent halocline of the nutrient-rich water flows onshore when downwelling GOA. Although this is a potential source of nutrients winds relax and weak upwelling begins in early sum- for the phytoplankton, the bulk of this onshore flow

------Oceanography • Vol. 15 • No. 2/2002 ------53 occurs at depths greater than 100 m and beneath the Moreover, because fall-winter air temperatures were euphotic zone. Thus, upwelling in the CGOA differs also above normal over the GOA, the winter hydrolog­ from upwelling in the CCS in which nutrient-rich ic regime was altered with more of the precipitation waters are brought into the euphotic zone. This differ­ delivered as rainfall rather than snow. Therefore, in the ence is due to the weak upwelling winds and the dis­ months prior to spring 1998, the anomalously strong tributed nature of the coastal runoff into the CGOA. winds and runoff resulted in a freshening of the inner Modeling studies are showing that shelf. In contrast, the higher salinities buoyant plumes associated with a point observed in April 1999, were associated discharge (such as a single river) with anomalously weak freshwater dis­ respond differently to upwelling winds The summertime inflow charge and cyclonic winds throughout from those formed by a distributed dis­ of saline water onto the the GOA during the preceding fall and charge. Plumes formed by the latter, winter. which characterize the ACC, do not inner shelf is one means The differences in forcing by the detach from the coast during weak by which the slope and winds and runoff between these two upwelling as readily as plumes generat­ years was also reflected in differences ed by a point discharge (Williams, pers, basin communicate directly in the alongshore baroclinic transport comm.). Thus, other mechanisms are with the inner shelf within the ACC, as the transport in required to bring nutrients into the sur­ April 1998 was nearly twice that of face layers in the CGOA. This could be April 1999. The stronger ACC transport accomplished in the following winter in 1998 was also consistent with Strub by deep mixing although some of the nutrients at and James' (in press) findings of anomalously strong depth are also transported offshore by return flows cyclonic flow over the continental slope in 1998. associated with downwelling. Other potential mecha­ Conceivably, the anomalously large alongshore trans­ nisms include surface onshore Ekman transport in fall ports in the ACC and the slope currents also con­ and winter, onshore flows up canyons that intersect the tributed to the observed warming in 1998 through shelfbreak, topographically-induced upwelling, and enhanced advection of warm waters from farther exchanges fostered by eddies and meanders along the south. slope. However, the relative importance of these mech­ The low nitrate concentrations observed in late anisms has not been established. winter 1998 are consistent with the anomalously high nutrient poor coastal discharge, although other mecha­ lnterannual Variability and ENSO Effects nisms might also have contributed. For example, The LTOP program was fortunate enough to have anomalously low winter nitrate concentrations were captured both the 1997-98 El Nino and 1998-99 La prevalent throughout the euphotic zone of the North Nina events. Comparisons of temperature, salinity, and Pacific in winter 1998 (Goes et al., 2001) and these low nutrient concentrations along the Seward Line for nitrate waters could have been advected into the Gulf April of both years provide examples of the interannu­ by the slope currents and onshore by the cyclonic al variability (Figure 4). Temperatures were substan­ winds. tially higher and salinity and nitrate concentrations lower in 1998 compared to 1999. Averaged over the Stratification upper 100 m and within 100 km of the coast tempera­ Internannual differences in the onset of stratifica­ tures were approximately l.5°C higher, salinities 0.4 tion provide some insight into the complexities associ­ psu lower, and nitrate concentrations about 25% lower ated with the development of stratification on the in April 1998 compared to April 1999. GOA. While the shelf was unstratified in early May These anomalies are a consequence of both atmos­ 1999, it was strongly stratified by early May 1998, with pheric and oceanic forcing occurring over the previous the stratification due solely to the vertical salinity gra­ summer and fall (Weingartner et al., in prep.). dients. In general, early spring water temperatures are Unusually calm and cloud free conditions prevailed fairly uniform throughout the water column and across over the northern gulf in summer and early fall of 1997, the shelf. Density variations therefore depend on salin­ resulting in above-normal near-surface water tempera­ ity differences. Stratification begins adjacent to the tures. Cyclonic winds were anomalously strong coast (where the runoff first enters the ocean) and then throughout the Northeast Pacific (including the CCS gradually spreads offshore. The offshore dispersal of region), but particularly so in the northeastern gulf low salinity water is dependent on both vertical mixing (and east of the CGOA study area). Through fall and and the cross-shelf circulation field. Thus, initiation of winter the winds forced warm, low salinity surface spring blooms on the GOA shelf might not be as tight­ waters shoreward, which then downwelled along the ly in-phase with the annual solar cycle as on shelves coast. The fresher conditions in April 1998 were also where solar heating and vertical wind mixing exert the associated with greater precipitation and anomalously dominant control over upper ocean stratification. large freshwater discharge into the northeast Pacific Second, mixed layer development in the CGOA during summer-fall 1997 and early winter 1998. depends upon processes operating over a range of time

------Oceanography • Vol. 15 • No. 2/2002 ------54 April 1998 April 1999 • • • • • • • • • • ••••• • • • • • • • • • • • • • ••••• • 0 ~ 3 100 -0 CD-, 200 Ol C --, ~ 300 CD Cll co 0 ~ (/) Q) 100 Ol L,.. :::J :::J CJ) CJ) 200 Q) -<" L,.. a.. 300 0 100 200

3000 60 120 180 0 60 120 180 Distance from Shore (km)

3 •···························· Temperature (°C) ·························•• ► 7 31 •····························· Salinity (PSU) ··························• 34 0 •································· Nitrate [NOJ ··························•• ► 45

Figure 4. Temperature (top), salinity (middle) and nitrate (b ottom) along the Seward Line in April 1998 (left) and 1999 (right). The coast is on the left and the continental slope on the right in each panel.

scales and involves several variables affecting both tion might impact the zooplankton. Due to the short vertical mixing and the offshore flux of freshwater. growing season in the Gulf of Alaska zooplankton such These variables include the fractions of winter precipi­ as Neocalanus species that hibernate over winter at great tation delivered to the coastal watershed as snow and depth must awaken and spawn in anticipation of the rain, the timing and rate of spring snowmelt, and the spring bloom. Properly timed, younger stages in sur­ wind velocity. The relevant time scales range from a face waters may increase their weight by up to 10% per few days (storm events) to the seasonal or longer day, although this rate declines with development. If where the longer time scales reflect the advective feeding early stage Neocalanus arrive at the surface potential of the ACC to transport freshwater from the prior to the bloom, growth will be slow and mortality eastern GOA. We note that the development of stratifi­ will be high. Just such an impact was observed in cation is not exclusively dependent on the addition of March 2001 when zooplankton on the mid-shelf freshwater. We are finding, for example, that in the arrived prior to stratification and were growing poorly, absence of any significant freshwater additions, the while animals in Prince William Sound (which stratifies middle and outer shelf will stratify as solar radiation earlier than the shelf) were growing at healthy rates. increases and wind speeds decrease through May. Thus recruitment success of zooplankton, and by Differences in the timing of springtime stratifica- ex tension salmon, might depend upon physical

------Oceanography • Vol. 15 • No. 2/2002 ------55 processes within the ACC that occur over one or more seasons and which ultimately affect nutrient supply, May 1998 the onset of stratification in spring, and the timing of 1.8 the spring bloom. • M 1.2 Zooplankton Community Structure =Q • Interannual variability might also be reflected in ·;;; 0.6 =GI • • different community structures. For example, the zoo­ e • . • plankton community structure differed between May Q 0.0 • 1998 and 1999 according to groupings defined by mul­ • • • -0.6 tidimensional scaling based on the taxonomic compo­ • • • sition and developmental stage of the most abundant • -l.2 taxa collected (Figure 5). Distinct station groupings -1.8 -1.2 -0.6 0.0 0.6 1.2 1.8 were absent in May 1998, suggesting a fairly homoge­ Dimension 1 neous zooplankton community structure on the GOA May 1999 shelf. In May 1999 distinct zooplankton communities 1.6 r---.---,--,--"---,-,--:,,--.,,,----,------, were observed in Prince William Sound, the inner por­ tion of the shelf, and over the outer shelf and slope. A 1. .2 t----t----i---,---, similar pattern emerged in 2000 (not shown). M 0,8 r----~----i----i---; Enhanced ACC transport in 1998 might have increased .52= 0.4 the flushing rate of near-surface waters in Prince ="' William Sound, thereby washing out endemic species eo.o and replacing them with zooplankton from the shelf. Q -0.4 Phytoplankton Dynamics -0.6 Sampling during April, May and July 2001 illus­ -0.8 trated the tremendous range in phytoplankton bio­ -1.2 ~-~-~--~-~-~"=-...... _~-~ mass that characterizes the CGOA. In 2001, chlorophyll -1.6 -1.2 -0.8 -0.4 0.0 0.4 0.8 1.2 biomass varied by more than a factor of 20 over spatial Dimension 1 scales of 5 to 10 km. As has been observed for other planktonic ecosystems, increases in phytoplankton biomass (blooms) are typically associated with the Figure 5. Multi-dimensional scaling plots based on data build-up of large phytoplankton cells (Figure 6a). collected in MOCNESS tows in the northern Gulf of However, over the mid- and outer shelf episodic Alaska in May 1998 (top) and May 1999 (bottom). blooms of primariJy small ( <5 µm) phytoplankton cells Green circles correspond to stations on the inner shelf, occur episodically (lower left-hand comer of Figure red from the outer shelf, and blue from Prince William 6a). These contrasting bloom modes lend further sup­ Sound. The large circles are station groups from May port to the idea that this shelf hosts broadly contrasting 1999 with purple for the inner shelf, gray for the outer biological regimes with the boundary being the mid­ shelf, and yellow for Prince William Sound. shelf region. The reason(s) for the differences in bloom patterns is not clear but one possibility is that iron availability decreases seaward from the coast. Small phytoplankters are less susceptible to iron imitation than the large phytoplankton (Martin et al., 1989; Miller et al., 1991). We expect relatively high iron con­ Understanding the source of this variability-food centrations in the freshwater runoff and therefore on quality, temperature effects, top-down control of protist the inner shelf and the ACC, but relatively low concen­ grazers-will be key to understanding how the transfer trations in GOA basin waters flowing along the conti­ of primary production to larger animals is regulated. nental slope. This transfer is also being examined through studies of egg production and hatching success in dominate cope­ Zooplankton Grazing pod taxa (Pseudocalanus, Metridia, Calanus, Eucalanus) as Seawater dilution assays confirmed that microzoo­ a function of diet. It is now appreciated that microzoo­ plankton grazing consumed nearly all production by plankton are likely the dominant consumers of phyto­ phytoplankton cells <20 µm (see also Strom et al., plankton while planktonic copepods prey extensively 2001). Microzooplankton consumption of large phyto­ on these forms. In tum, juvenile salmon prey on larger plankton was highly variable, and preliminary obser­ zooplankton and other species (including forage fish­ vations show corresponding variation in the abun­ es), as they grow. Understanding these linkages is dance of large heterotrophic dinoflagellates and ciliates essential to determining how bottom-up effects might that might be capable of consuming diatoms. be mediated in this system.

------Oceanography • Vol. 15 • Na. 2/2002 ------56 Close coupling between copepods and microzoo­ lake/stream system to spawn and die (Burgner, 1991). plankton, with consequent effects on planktonic food The nutrients derived from spawned carcasses can be web structure, was also demonstrated in grazing significant relative to other sources, and may be recon­ experiments conducted and analyzed at sea in 2001 structed from palaeolimnological records of 81'N with the FlowCAM (Flow Cytometer and Microscope). (Finney et al., 2000). Salmon are enriched in 815N rela­ This instrument detects particles in a flow chamber tive to terrestrial nitrogen sources in Alaska. Periods of based on laser-induced fluorescence or light scattering. greater input of salmon-derived nutrients, and hence Particles in the 11-200 mm size range are counted, their greater sockeye abundance, correspond to higher sedi­ fluorescence and scattering intensity measured, and mentary 8"N. their image captured with a CCD camera, frame grab­ Reconstructions of salmon abundance over the past ber and image processor system (Sieracki et al., 1998). 300 years reveal similar patterns for three lakes on The ability to generate particle size spectra (Figure 6b) Kodiak Island (GOA) (Finney et al., 2000), consistent and "picture galleries" (Figure 6c) in near real-time was with the hypothesis of common forcing as a result of a great help in planning experiments. When coupled climatic change. Regimes of anomalous abundance with copepod grazing experiments, (815N anomalies) over this period occur FlowCAM analysis revealed the target- in an irregular pattern on timescales of ing by Neocalanus and Pseudocalanus of 30-100 years. A comparison of the particles in specific size ranges (Figures GOA sockeye records to Northeast 6d and e). Apparent negative clearance Catch data for GOA Pacific sea surface temperature as rates on small particles, observed fre­ salmon during the 2a1i derived from analysis of coastal tree quently during these experiments, sug­ Century suggest strong rings reveals changes at similar times gest that removal of larger microzoo­ (D' Arrigo et al., 1999). During certain plankton by copepods relieved grazing relationships between time periods, the pattern observed dur­ pressure on smaller cells, allowing them salmon abundance ing the 20'h Century of higher salmon to increase more in the presence of and climate change abundance during warm periods and copepods than in control bottles with­ lower salmon abundance during cooler out copepods. Such "trophic cascades", periods is maintained. However, dur­ although hypothesized to be important ing the period from approximately in aquatic ecosystems, have proven dif- 1840-1900, apparently high salmon ficult to demonstrate in the marine plankton. If wide­ abundance occurred during a period of cool sea surface spread in the CGOA, these cascades indicate that top­ temperature. Analysis of tree rings from sites along the down effects could have a large influence on food web Northeast Pacific coast reveals two substantial periods structure and function, and a full understanding of cli­ over the past 400 years where spatial temperature pat­ mate effects on shelf production will require considera­ terns are not consistent with that of the PDO (Gedalov tion of such effects. and Smith, 2000). One such period occurred between 1840 and 1920. This suggests that other modes of cli­ Retrospective Analysis mate and ecosystem variability exist than revealed by Retrospective studies provide important insights 20th Century data. Although the reconstruction of long into variability over longer space and time scales than term abundance is only possible for salmon species those covered by GLOBEC field programs. Catch data such as sockeye that utilize freshwater lake habitats, for GOA salmon during the 20th Century suggest strong historical records suggest that Kodiak sockeye abun­ relationships between salmon abundance and climate dance patterns are similar to those of GOA pink salmon change as measured by the Pacific Decadal Oscillation and other salmon species. (PDO) Index, an integrated measure of sea surface tem­ In other retrospective analyses, Doyle et al. (in perature in the North Pacific (Mantua et al., 1997). press) analyzed a 20-year time series of springtime However, these records are too short to define the per­ oceanographic and ichthyoplankton data collected by sistence and frequency of such relations. Moreover, the Alaska Fisheries Science Center in the northern human activities such as hatchery production, fishing GOA. The observed shallow to deep-water gradient in and habitat alteration complicate the identification of species occurrence and abundance reflects the habitat climatic effects. To gain a long-term perspective on rela­ preference and spawning location of adult fish. At finer tionships between GOA salmon abundance and climat­ scales variations in this primary assemblage structure ic change, retrospective studies were conducted to seems related to the local bathymetry and the prevail­ reconstruct salmon abundance prior to the onset of ing current patterns. They also show that interannual commercial fishing (ca.1880s). Long-term relationships variations in GOA larval fish densities exhibit long­ between sockeye salmon (Oncorhyncus nerka) popula­ term trends in species abundances similar to those tions and climatic change can be evaluated by analyz­ reported by Anderson and Piatt (1999) for older age ing sediment cores from their nursery lakes (Finney et classes. In another study Bailey and Picquelle (in press) al., 2000). Following 2 to 3 years of feeding in the North found that enhanced onshore larval transport might Pacific, sockeye salmon return to their natal contribute to strong year-classes of Pacific halibut. Both

______Oceanography • Vol. 15 • No. 2/2002 ------57 (a) 1. 0 100 ... • • • (b) 0.8 • T •• ..... E 75 ::1. • ' 0 • E N 0.6 • I\ • • T ~ 50 i:: ~ • (.) 0 ·-0 0.4 • outer t u • Ctl 25 Cl:I.... T mid a.. L!., 0.2 mne r \ . • • PWS 0 0.0 ...... N N w w ~ ~ 01 01 ... m m ... m ... m ... m 0 I 2 3 4 5 6 ...I rli rli l:, l:, !. !. 0, 0, 0) 1 01 0 01 0 01 0 01 0 01 0 Tota l chl orophyll ( ~1g liter" ) Particle ESD (µm)

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Figure 6. a) Total chlorophyll versus the fra ction of total in cells >20 µm for the CGOA during April, May and July 2001, b) size spectrum (as equivalent spherical diameter, £SD) of particles in the phytoplankton bloom (total chlorophyll= 5.3 7-tg/liter, 92 % >20 µ111 ), c) Representative FlowCAM images from the bloom. The dominant diatom was Thalassiosira sp.; central image is Gyrodiniwn sp., a large heterotrophic dinoflagellates, d) and e) Size spectra of clearance rates (mean ±1 sd) for copepod grazers Pseudocalanus d) and Neocalanus e). Note the increase in clearance rates for larger-bodied stages and taxa, as well as the generally elevated clearance rates on 36 to 55 µm particles. Negative clearance rates on smaller particles are interpreted as evidence for a trophic cascade involving top-down control of large microzooplankton grazers by copepods (see text).

Models tudies suggest that interan.nual changes in plankton Coupled biophysical models are being developed transport processes in the GOA might have a signifi­ in order to understand and to predict how the CCS and cant effect on the distributions and survival of fish lar­ CGOA ecosystems respond to clim ate variability. vae, some of which serve as prey for juvenile salmon. Results from the field and retrospective studies have

------Oceanography • Vol. 15 • No. 2/2002 ______58 Figure 7. The nested model domains that are currently in development for NEP­ GLOBEC. The grid sizes are 20-40 km for the global grid (red), 10 km for the regional grid (green) and 3 km (light blue) and 1-2 km for the local grids (dark blue). The inset is the NEP-model temperature fields at 10 m depth for September 18, 2001.

guided model development, and will be used to evalu­ al winds. The regional physical model of the CGOA ate model performance using hindcasting sh1dies and, and adjacent basin (GOA-1) was configured with eventually, data assimilative simulations. In addition, approximately 22 km resolution and 20 vertical levels the models serve as useful interpretive tools in several on a telescoped grid and forced by monthly fields of ways with respect to the observations, which are limit­ runoff, daily heat fluxes, and daily wind stresses appro­ ed both in space and time. The models are being used priate to specific years. We are now developing a new to examine nested system at higher spatial resolution so that the 1) Interannual-to-decadal scale changes in the cir­ new basin-scale model (NEPt extending from Baja culation, hydrography, and lower trophic level California through the Bering Sea, will have 10 km res­ dynamics in the CGOA; olution, and the regional CGOA model (GOA-2) will 2) Differences in along- and cross-shelf transport as have a spatial resolution of 3 km. a function of location; The velocity and thermohaline fields of both the 3) Spatial variation in tidal effects on mesoscale boundary currents and the ACC are easily identified in physical and biological properties; and both the GOA-1 and NEP regional models (Figure 8). 4) Effects of remote ocean forcing on CGOA The models also indicate a summer weakening/rever­ ecosystem variability. sal of the coastal current in the eastern CGOA, consis­ With these aims in mind we are developing a suite tent with inferences based on altimeter data (Strub and of nested physical and biological models (see article by James, in press). Interannual differences were evident Mantua et al., this issue). among the years simulated with GOA-1; for instance, spring 1997 exhibited significantly higher sea surface Numerical Hydrodynamic Models temperature than spring 1995. Preliminary compar­ The initial regional physical model of the CGOA isons of a NEP hindcast with current meter data for and adjacent basin (henceforth referred to as GOA-1) 2001 along the Seward Line suggest a stronger corre­ was based on the S-Coordinate Rutgers University spondence between model and data in the fall (when Model (SCRUM; Song and Haidvoget 1994. More the ACC is strongestt than in the summer (when the recently, we have reconfigured the modeling system so ACC is weak). The models are also capturing the sub­ that each of the nested physical models is based on the stantial gradients in tidal energy, consistent with pure­ Regional Ocean Modeling System (ROMS; Haidvogel ly tidal models for this region (Foreman et al., 2000) et al., 2000; Hermann et al., in press). across the northwestern shelf. These gradients might The initial set of nested physical models included establish important biological gradients insofar as the globat basin-scale, and regional grids (Figure n with NPZ model suggests that enhanced tidal mixing can the larger-scale models providing barotropic tidal and substantially increase biological production. subtidal velocity information to the regional scale Both the GOA-1 and NEP models also capture the model. The global circulation model is driven by glob- large 200 km scale variability observed in the Gulf by

------Oceanography • Vol. 15 • No. 2/ 2002 ------59 AVHRR imagery (Thomson and Gower, 1998) and diets. By seeding the model with "numerical floats" altimeter data (Crawford and Whitney, 1999; Crawford throughout the CGOA, we find that zooplankton over et al., 2000), especially in Southeast Alaska where the the slope and in the upper 5 m can indeed be transferred isobaths veer northwestward. The models indicate that into the ACC (Stabeno et al., submitted). However, at this eddy activity migrates slowly offshore from spring greater depths (>40 m) the onshore transport is much through winter. weaker because the flow is steered alongshore by topo­ graphic influences. The model results further suggest Coupled Biophysical Models that nutrients in the upper layer can also be supplied The physical modeling activity is also shedding from offshore to the inner shelf by wind-driven cross­ light on biologically important aspects of the CGOA. shelf transport, especially in fall and winter when the Critical issues here include the source of zooplankton winds are strong and phytoplankton consumption of and nutrients for the shelf. Cooney (1986) suggested near-surface nutrients is negligible. The float studies that, upon emergence from diapause, deep ocean zoo­ also indicate the important role that alongshore advec­ plankton could be transferred by onshore surface tion plays in the CGOA. We find that the onshore flow Ekman transport onto the inner shelf, where they preferentially occurs in the northeastern gulf (east of the become an important component in juvenile salmon CGOA study region) before the Alaska Current trans-

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32

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Figure 8. Detail from NEP model hindcast for September 18, 2001, showing salinity and velocity at 40 m depth in the vicini­ ty of the GAK line. The Seward Line is the thick blue line. Measured velocities from current meter moorings and interpolated to 40 m depth are shown as blue vectors.

------Oceanography • Vol. 15 • No. 2/ 2002 ------60 forms into the Alaskan Stream. Once onshore, the floats the 1998-99 La Nina events. The strong seasonality and move alongshore within the ACC. These results suggest distinct phasing of wind and runoff in this region, with that variations in the velocity and density structure of their apparent effects on the oceanographic environ­ the boundary currents (in conjunction with regional ment and biota, indicate a system highly susceptible to variations in the winds) are important in controlling climate variability. We have also begun to recognize shelf-basin exchange processes. and better define what appear to be distinct bio-physi­ The CGOA NPZ model is being used to explore the cal regimes on the CGOA shelf. While these different biological sensitivity of this ecosystem to physical forc­ shelf domains must be linked to one another, we do not ing. The results will be of particular value in under­ yet understand the nature of these connections, how standing how environmental or biological variations they are brought about, and how they vary in time. The affect the trophic structure and food availability for field, retrospective, and modeling components all indi­ fish. The NPZ model was initially constructed to run as cate that there is considerable mesoscale variability a one-dimensional model but recently was expanded within each regime that might exert important influ­ to utilize the three dimensional circulation and ther­ ences on species distribution and production. A further mohaline fields produced by the physical models. The challenge is to understand how the time scales that CGOA NPZ model consists of twelve compartments. govern physical forcing are linked to the apparently Nitrogen is modeled as both nitrate and ammonium to disparate time scales that govern biological production. determine the proportion of new versus recycled pro­ Among the key questions and results thus far in the duction and the effects of nitrogen source on the zoo­ CGOA-GLOBEC program are: plankton community. The phytoplankton community 1) What are the mechanisms by which nutrients are consists of two size fractions that differ in their use of supplied to the inner shelf? Are they advected across nitrate vs. ammonium, and which can support differ­ the shelf within the surface layers by the wind-driven ent herbivore species complexes. The microzooplank­ Ekman transport, supplied at depth in summer and ton community includes small heterotrophic nanofla­ then mixed into the surface layers in winter, or are they gellates, ciliates, medium sized dinoflagellates, and preferentially channeled inshore and vertically through large heterotrophic dinoflagellates, because these interactions between the bottom topography and the groups are important components of the GOA coastal alongshore flow? Observations and modeling indicate and oceanic ecosystems. Small copepods are represent­ that there might be preferred sites for onshelf transport ed by Pseudocalanus species and larger zooplankton are of nutrients and zooplankton, some occurring represented by Neocalanus species and euphausiids upstream (east) of the GLOBEC CGOA study area. If (Euphausia pacifica). A detrital component completes this proves to be the case, it suggests that alongshore the model. advection is important in influencing "downstream" A typical run of the one-dimensional model illus­ productivity at all trophic levels on this shelf. Modeling trates the seasonal evolution of the lower trophic lev­ exercises also indicate that gradients in tidal energy els. The large-phytoplankton bloom occurs first in dissipation might also strongly influence spatial pat­ spring followed by the small-phytoplankton bloom. terns shelf productivity. The temporal difference between these blooms occurs 2) How does the timing of juvenile salmon outmi­ because the larger phytoplankton grow at lower tem­ gration and their distribution on the shelf contribute to peratures, but are sensitive to nutrient depletion, recruitment success in the CGOA? Juvenile pink whereas the small phytoplankton grow better under salmon are generally most abundant within the ACC warmer temperatures and are less sensitive to low although it is not yet clear if this current is simply serv­ nutrient concentrations. Following the small-phyto­ ing as a migratory corridor for these fish or if it pro­ plankton bloom, surface nutrients are depleted as vides a critical habitat in terms of both prey type and observed (Childress, 2001; Napp et al., 1996). The evo­ abundance. Further, the timing of juvenile pink salmon lution of these phytoplankton blooms affects seasonal entry onto the shelf (August and September) is offset transitions in the zooplankton community. Initially, by several months from the spring phytoplankton heterotrophic dinoflagellates have higher densities bloom and zooplankton biomass peak (April and May). than ciliates because the dinoflagellates consume both Is spring production retained within the system in large and small phytoplankton. Neocalanus species some form that fuels late summer salmon growth or increase through early summer but then decrease as does this growth depend upon late summer primary they enter diapause. Euphausiid concentrations and secondary production? If the latter proves to be the increase gradually from spring through late summer. case then what are the physical and biological mecha­ nisms that support biological production in summer? Preliminary Conclusions and 3) How do the magnitude, timing and modes of the Future Directions spring bloom(s) vary from year to year, and what The CGOA-GLOBEC field program has occurred impact do variations in rates and timing of these during a period of strong contrasts in physical and bio­ blooms have on zooplankton and salmon success? We logical conditions related to the 1997-98 El Nino and have been struck by the complexity inherent in the

------Oceanography • Vol. 15 • No. 2/2002 ------61 development of stratification in the spring and the dif­ J. Fish. Aquat. Sci., 50, 2270-2291. ferent ways that freshwater and solar heating might Beamish, R.J. and C. Mahnken, 2001: A critical size and bring about stratification. In this regard, springtime period hypothesis to explain natural regulation of stratification develops as a consequence of three­ salmon abundance and the linkage to climate and cli­ dimensional circulation processes and probably does mate change. Progr. Oceanogr., 49, 423-137. not develop uniformly in time and space over the GOA Boldt, J.L., 2001: Ecology of juvenile pink salmon in the shelf. Such complexity is likely to directly influence north Gulf of Alaska and Prince William Sound. Ph.D. planktonic community size structure, species composi­ Thesis, University of Alaska, 217 pp. tion, and function. Brodeur, R.D., Frost, B., Hare, S.R., Francis, R.C. and W.J. 4) Retrospective studies are showing that the 20 th Ingraham, Jr., 1996: Interannual variations in zoo­ Century pattern of higher salmon abundance during plankton biomass in the Gulf of Alaska and covaria­ warm periods in the North Pacific Ocean and lower tions with California Current zooplankton biomass. salmon abundance during cooler periods does not CalCOFI Rcpt., 37, 81-99. appear to have consistently held prior to 1900. This Burgner, R.L., 1991: Life history of sockeye salmon suggests that other modes of climate and ecosystem (Oncorhyncus nerka). In: Pacific Salmon Life Histories. variability exist than revealed by 20th Century data. C. Groot and L. Margolis, eds., UBC Press, Vancouver, B.C., Canada, 1-117. How do these modes of variability arise, and what is Childress, A., 2001: Major nutrimt distribution in relation their effect on the CGOA ecosystem? to the physical structure of the Gulf of Alaska shelf These are among the many critical issues that are M.Sc. Thesis, University of Alaska, 102 pp. being addressed by the CGOA-GLOBEC program. The Cooney, R.T., 1986: The seasonal occurrence of Neocalanus answers will enable us to compare the CGOA and the cristatus, Neocalanus plumchrus, and Eucalanus bzmgii CCS ecosystems, to identify efficient strategies by over the shelf of the northern Gulf of Alaska. Cont. which to monitor long-term variability in these ecosys­ Shelf Res., 5, 541-553. tems, and to develop ecosystem models with a prog­ Crawford, W.R. and F.A. Whitney, 1999: Mesoscale eddy nostic capability. aswirl with data in Gulf of Alaska. EOS Trans. Am. This is U.S. GLOBEC contribution Number 233. ~ Geophys. Union, 80, 365-370. Crawford, W.R., J.Y. Cherniawsky and M.G.G. Foreman, Websites 2000: Multi-year meanders and eddies in the Alaskan Several websites are available that provide additional Stream as observed by TOPEX/Poseidon altimeter. information on the NEP and CGOA-GLOBEC program. Geophys. Res. Letts., 27, 1025-1028. These serve to communicate the activities and results of D'Arrigo, R.D, G. Wiles, G. Jacoby and R. Villalba, 1999: this program to the scientific community and to the public North Pacific sea surface temperatures: Past variations at large. An overview of the NEP-GLOBEC program is at inferred from tree rings. Geophys. Res. Letts., 26, http://globec.oce.orst.edu/ groups/ nep / index.html. 2757-2760. Material pertaining to modeling is at: Denman, K.L, H.J. Freeland and D.L. Mackas, 1989: http://www.pmel.noaa.gov/-dobbins/nep.html; Comparison of time scales for biomass transfer up the http://www.pmel.noaa.gov/-hermann/ globec- marine food web and coastal transport processes. Can. 2001 / ms.pdf. Further information on the LTOP program is Spec. Publ. Fish. Aquat. Sci., 108, 255-264. Doyle, M.D., K.L. Mier, R.D. Brodeur and M.S. Busby, at:http://murphydome.ims.uaf.edu:8000 / globec/intro/ 2002: Regional variations in ichthyoplankton assem­ and information related to the long-term time series at blages in the northeast Pacific Ocean. Progr. station GAK 1 on the Seward Line is at: Oceanogr., in press. http:/ /www.ims.uaf.edu/gakl/. Additional websites are Finney, B.P., I. Gregory-Eaves, J. Sweetman, M.S.V. under construction and can be found in the future through Douglas and J.P. Smol, 2000: Impacts of climatic links with those listed. change and fishing on Pacific salmon abundance over the past 300 years. Science, 290, 795-799. References Foreman, M.G.G., W.R. Crawford, J.Y. Cherniawsky, R.F. Anderson, P.J. and J.F. Piatt, 1999: Community reorgani­ Henry and M.R. Tarbotton, 2000: A high-resolution zation in the Gulf of Alaska following ocean climate assimilating tidal model for the Northeast Pacific regime shift. Mar. Ecol. Prag. Ser., 189, 117-123. Ocean. J. Geophys. Res., 105, 28629-28651. Bailey, K.M. and S.J. Picquelle, 2002: Larval distribution Francis, R.C. and S. R. Hare, 1994: Decadal-scale regime patterns of offshore spawning flatfish in the Gulf of shifts in the large marine ecosystems of the North-east Alaska: potential transport pathways and enhanced Pacific: a case for historical science. Fish. Ocemzogr., 3, onshore transport during ENSO events. Mar. Ecol. 279-291. Prag. Ser., in press. Francis, R.C., Hare, S.R., Hollowed, A.B. and W.S. Baumgartner, A and E. Reichel, 1975: The World Water Wooster, 1998; Effects of interdecadal climate variabil­ Balance. Elsevier, New York, 179 pp. ity on the oceanic systems of the NE Pacific. Fish. Beamish, R.J., 1995: Climate change and exceptional fish Oceanogr., 7, 1-21. production off the West Coast of North America. Can. Gargett, A.E., 1997: The optimal stability "window": a mechanism underlying decadal fluctuations in North

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