El Niño Workshop Abstracts
December 6-9, 1999
Monterey Bay Aquarium Research Institute
1845-1910 The 1997-99 El Niño/La Niña Cycle in the Tropical Pacific
Michael J. McPhaden
NOAA/Pacific Marine Environmental Laboratory
This presentation reviews the evolution of the 1997-98 El Niño and the development of the subsequent 1998-99 La Niña in the tropical Pacific. The 1997-98 El Niño was by some measures the strongest on record. It began with rapid growth of SST anomalies in early 1997, and peaked in December. It then abruptly ended with an unprecedented 8C SST drop during one 30 day period in May-June 1998 in the eastern equatorial Pacific. The subsequent La Niña was strong and long lived, persisting to the present. The physical processes giving rise to climate swings associated with the 1997-99 El Niño/La Niña cycle will be described. Also, how these climate variations are likely to have affected the coastal regions of North and South America will be discussed.
1915-1940 El Niño effects on winter and spring weather along the California coast
1945-2010 Evolution and biological effects of the 1997-98 El Niño off northern and central Chile
Programa Regional de Oceanografía Física y Clima (PROFC)
Universidad de Concepción
Cabina 7 - Barrio Universitario
Casilla 1987, Correo 3
Current and temperature measurements from two mooring sites over the slope off Chile, at 21°S and 30°S, are used together with observations of coastal sea level( CSL) and coastal sea surface temperature (CT) from several tide gauge stations along the Peru and Chile coasts, and of biological properties at a time-series coastal station, at 23°S, to study the evolution and some biological effects of the 1997-98 El Niño off northern and central Chile.
Alongshore flow variability at about 200 m depth, near the core of the Peru-Chile undercurrent, was dominated by large and coherent intraseasonal fluctuations. The flow reached a poleward maximum by the end of 1997, weakening rapidly during early 1998. Positive CSL and CT anomalies were present along the Peru and Chile coasts from the beginning of 1997 to the middle of 1998. Like during other strong El Niño events, they were dominated by the superposition of an interannual oscillation and large intraseasonal fluctuations. The intraseasonal and other observed higher frequency oscillations of the alongshore flow and sea level propagated along the coast with a speed of about 3 m s-1, consistent with the phase speed of coastal-trapped waves and of similar magnitude to observations obtained during previous El Niño events.
While the temperature and the oxygen concentration of the coastal waters off northern Chile were noticeably higher during the El Niño event, total phytoplankton and zooplankton biomasses were not dramatically altered. In contrast, the herbivorous copepod Calanus chilensis exhibited greater abundance, higher specific growth rates, and its adult body size was reduced significantly. These latter results suggest a positive effect of the increase in temperature due to El Niño on zooplankton growth and production, and provide evidence for lack of food limitation on secondary production during this period.
2015-2040 The effects of the 1997-98 El Niño off Baja California
R. Durazo1, T.R. Baumgartner2, B. Lavaniegos2, G. Gaxiola2, M.E. Hernández3
1UABC- Facultad de Ciencias Marinas, Ensenada, México
also at Naval Postgraduate School, Monterey, CA
2CICESE, Apdo. 2732, Ensenada, México
3CICIMAR, Apdo. 592, La Paz, B.C.S., México
Beginning September 1997, quarterly cruises have been conducted in the California Current System off Baja California, México. The cruises are part of the IMECOCAL program (Investigaciones MExicanas de la COrriente de CALifornia) and have been scheduled to be in close timing to CalCOFI cruises in US waters. Results from cruises 9709, 9801, 9807, 9809 and 9901 are presented here. During 9709 and 9801, temperature and salinity were observed to be up to 8 ° C and 0.8 above the climatological mean. Lower than the mean temperatures (2 ° C) and salinities (0.2) were observed during 9809 and 9901. Maximum anomalies were observed between 50 and 100 m depth over the shelf break, but also extending offshore as a thin subsurface layer. The biological response to the ENSO warming were low values ( < 0.4 mg m-3) of surface chlorophyll a during summer-fall 1998, with some indications of recovery (1.5 mg m-3) by early 1999. Bio-volume distribution was patchy and in almost all cruises was associated to the Vizcaino Bay area. Zooplankton volumes were higher than previous El Niño CalCOFI cruises conducted in the region (1950-1970), suggesting a different response during the 97-98 ENSO event. Species composition of fish larvae was predominantly of warm affinity with some transitional species. The most abundant larvae were Vinciguerria lucetia followed by Triphoturus mexicanus, Diogenichthys laternatus and Synodus lucioceps, which combined contributed to 73.6% of the total abundance.
0815-0830 The response of the coastal ocean off Oregon to El Niño 1997-8
Adriana Huyer, Jane Fleischbein and Robert L. Smith
College of Oceanic and Atmospheric Sciences, Oregon State University
A zonal hydrographic section along 44.6 N off Newport Oregon, running from the coast to more than 150 km offshore, was occupied regularly from 1961 to 1971. Monitoring of this section was restarted in July 1997 as part of the GLOBEC Long Term Observational Program; 14 cruises between July 1997 and December 1999 have occupied stations on the Newport Hydrographic line. The recent data provide observations in Oregon coastal waters of El Niño 1997-8 and the putative La Niña conditions that followed. The data from the earlier decade provide a basis for defining normal conditions and allow comparisons with the present in terms of T, S, and geostrophic velocity sections, T/S analysis, and steric height profiles. The ocean was already anomalously warm in July 1997 offshore of 50 km and above 100 m. By September 1997 the strongest anomalies were inshore of 50 km and had deepened over the slope; the steric height of the sea surface sloped up toward the coast indicating poleward flow over shelf and slope. The November 1997 and February 1998 sections were warm, with strong poleward flow inshore of 100 km and extending to depths greater than 200 m. The April 1998 section closely resembled that of April 1983 (another El Niño year) but by June the anomalies were mostly gone. November 1998 was normal and the sections from subsequent cruises resemble the mean sections from 1961-1971; if La Niña is present, she is subtler than El Niño.
0835-0850 An Equatorward Undercurrent and a Poleward Shelfbreak Jet during the 1997-98 El Niño
P. Michael Kosro
College of Oceanic and Atmospheric Sciences, Oregon State University
Since June 1997, shipbased sampling has been conducted at least seasonally on zonal transects at 44.6N, from the Oregon coast to about 150 km offshore; repeated transects at other latitudes off Oregon and northern California were also made. Shipborne ADCP profiles collected on these cruises provide direct current measurements which span the 1997-98 El Niño. During November 1997, a strong poleward upper-ocean current jet was found near the continental shelf break on all four transects between 44.6N and and 38.5N; maximum current speeds were typically 0.5 m/s. In addition, a weak but distinct equatorward undercurrent was present on each section, attached to the upper continental slope. These same features were still present in February 1998, when sampling was conducted along 44.6N and 43.2N. The poleward jet was somewhat weakened (0.4 m/s) in February. By April 1998, the poleward undercurrent had been re-established, and poleward flows at the shelf break were much more modest (0-0.2 m/s).
0855-0910 The Origins of SST Anomalies in the Northeast Pacific During 1997-1998
Frank Schwing 1, Tom Murphree 2, and Lynn deWitt 1
1 Pacific Fisheries Environmental Laboratory, Pacific Grove, CA
2 Naval Postgraduate School, Monterey, CA
During the 1997-1998 El Niño event, there were remarkable sea surface temperature anomalies (SSTAs) in the northeast Pacific (NEP), especially along the west coast of North America. Much of the basic SSTA pattern developed during 1995-1996, well before the start of the El Niño event. This pattern intensified and underwent other modifications during February-October 1997, as the El Niño event was developing. Surface wind stress anomalies in the NEP during these months produced anomalous Ekman processes in the upper ocean that made a large contribution to the evolution of the SSTA patterns. However, these wind stress anomalies were not directly linked to the El Niño anomalies in the equatorial Pacific. The first clear evidence of a direct El Niño influence on the NEP SSTAs occurred in November 1997 by way of atmospheric wave trains from the western and central tropical Pacific. This influence continued through April 1998 and led, through alterations of the NEP surface wind stress and Ekman processes, to large changes in the SSTAs.
0915-0930 Changes in the hydrography of central California waters associated with the 1997-98 El Niño
Curt Collins, Carmen Castro and Francisco Chavez
0935-0950 The forcing of sea level along the central California coast during the 1997-98 El Niño
H. F. Ryan and M. Noble
Beginning in the spring of 1997, we observed long period (> 30 day) fluctuations in daily sea level with amplitudes of over 10 cm at San Francisco, CA. Temperature sensors deployed on the shelf offshore of Davenport (south of San Francisco) showed a rise in temperature at depth and a deepening of the thermocline associated with times of higher sea level. The observed coherence of the local alongshore wind stress and sea level at intraseasonal periods (36-72 days) indicates that the local wind stress can account for at most only 50% of the sea level rise. We propose that the rises in sea level were, in part, forced by the passage of remotely-generated coastally-trapped waves that were generated along the equator and propagated to the north along the west coast of North America. The propagation of coastally-trapped waves began in the spring of 1997, months earlier than predicted if the impacts of the El Niño on the extratropics were strictly tied to the annual cycle.
0955-1010 El Niño in the coastal waters of Southern California: A timeline of events
Thomas L. Hayward
Marine Life Research Group
Scripps Institution of Oceanography, UCSD
9500 Gilman Drive
La Jolla CA 92093-0227
Timely observation of the onset of El Niño conditions allowed CalCOFI to implement monthly sampling of a subset of the sample grid in order to better resolve the temporal pattern of events during the 1997-98 El Niño event. These data enable us to examine the relation between the timing of changes in physical and ecosystem structure. We can test simple hypotheses about cause-and-effect relations based upon the assumption that effects should follow the presumed causes with an appropriate time lag. Different indices can also be evaluated. Changes in physical structure associated with El Niño were evident in a range of indices including: sea surface and thermocline temperature anomalies, circulation patterns, T/S structure, the upwelling index, sea level and the multivariate equatorial El Niño index. Each of these indices reflects a different aspect of the physical environment. The indices differ in the timing of events, particularly with respect to the onset of El Niño conditions. El Niño conditions were evident in the equatorial Pacific by April 1997. Some physical changes were also evident in the CalCOFI study region by late spring of 1997. However, the strong deepening of the thermocline and nutricline did not occur until November to December 1997. This leads to the questions of what physical measurements are the most useful indices of El Niño conditions in the California Current, and what aspects of a changing physical environment have the greatest impact upon ecosystem structure and populations within the region.
Ecosystem structure and the abundance of individual species fluctuate greatly on a range of space-time scales. Unless the signals are large, it is difficult to attribute an observed change over time to a causal physical forcing process on a particular space-time scale. However, a few observed ecosystem impacts in the spring and summer of 1997 have been attributed to El Niño forcing, particularly the lack of success of pinniped pups in the Channel Islands in the summer of 1997. The major impacts of El Niño conditions upon the ecosystem were evident from winter 1997 to summer of 1998. These impacts included declines in macrozooplankton biomass, squid catch, seabird abundance, pinniped abundance and breeding success, rockfish larvae, euphausiid abundance and distribution, and coastal kelp forests. The fall and winter of 1998 marked the transition to La Niña conditions in both physical and biological properties. The relation between various indices of physical structure and timing of changes in populations residing within the CalCOFI study region will be discussed.
1030-1045 Boundary Current Variability in the NE Pacific Subarctic and Subtropical Gyres During the 1997-1998 El Niño.
P. Ted Strub
College of Oceanic and Atmospheric Sciences, Oregon State University,
Corvallis, OR 97331-5503
Over 9 years of altimeter data are now available, with over 7 continuous years of TOPEX data. These are used to demonstrate the out-of-phase covariability of surface currents in the eastern Alaska and Subtropical Gyres on interannual time scales. The seasonal cycles of altimeter-derived surface transports are removed to form non-seasonal transport anomalies. During the 1993-1998 period, variability in the non-seasonal surface transports is concentrated around the boundaries and the first EOF of these transports is dominated by the 1997-1998 El Niño. A weak connection to the interior North Pacific Current develops as the strengthened Aleutian Low spins up the entire Alaska Gyre during the second half of 1997. Anomalous poleward transports and high coastal sea levels propagate poleward from the equator in two pulses during May-July and October-December 1997. The first of these equatorial signals slows at the mouth of the Gulf of California, opposed by equatorward winds and currents farther north. It spreads poleward during transient wind relaxations and reversals. The second equatorial pulse is enhanced by poleward winds in fall and winter 1997, spreading quickly around the Alaska Gyre. The impact of the equatorial oceanic signal is strongest between the Equator and southern California. The impact of the basin-scale wind forcing is strongest in the Pacific Northwest and around the Alaska Gyre. Thus, the El Niño signal in the ocean off the western U.S. is a mix of the two signals, as found in previous El Niño's. The timing of the contribution of the two forcing sources differs between El Niño's.
1050-1105 Seasonal and interannual variability of satellite-derived chlorophyll and CDOM concentration in the California Current
M. Kahru and B. G. Mitchell,
Time series of surface chlorophyll a concentration and colored dissolved organic matter (CDOM) derived from the Ocean Color and Temperature Sensor (OCTS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) were evaluated for the California Current area using regional algorithms. CDOM is estimated with both a simple band ratio algorithm and a semianalytic algorithm. The results of the Carder et al.  multi-wavelength semianalytic algorithm are sensitive to estimates of the water-leaving radiances that are biased low at shorter wavelengths in turbid or high chlorophyll waters. The variation in CDOM concentration was significantly smaller than that of chlorophyll, both spatially and temporally. While being subject to large inter-annual and short-term variations, offshore waters (100-1000 km from the shore) have an annual cycle with a winter-spring (December-March) maximum and late summer minimum in both chlorophyll and CDOM. For inshore waters the maximum is more likely in early summer (April-May). Significant increase was detected from 1996 to 1999 in both chlorophyll and CDOM. The increase, most evident off Central California, can probably be attributed to the El Niño cycle and is correlated with the lowest sea-surface temperatures since 1989. These changes are difficult to detect based on in situ observations alone.
1110-1125 Interannual Variability of Chlorophyll in the California Current System: Effects of the 1997-1998 El Niño
Paul M. DiGiacomo (1) and Mary-Elena Carr (2), Jet Propulsion Laboratory, MS 300-323, 4800 Oak Grove Drive, Pasadena, California 91109-8099 USA
The 1997-1998 El Niño was one of the strongest of the century. Chlorophyll-a data from the Ocean Color and Temperature Scanner (OCTS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) were complemented by a suite of additional satellite and in situ measurements to characterize the impact of this event on phytoplankton biomass in the California Current System (CCS). Large interannual reductions (upwards of 75%) in CCS chlorophyll-a concentrations from 1996-1997 to 1997-1998 were attributed to El Niño. The interannual differences were greatest between 31º N and 40º N, from the coast offshore to several hundred kilometers. Coincident patterns of anomalously warm sea surface temperatures (SST), a depressed thermocline and nutricline, anomalously high sea levels and a weakening of upwelling-favorable winds were also observed, consistent with previous CCS El Niño studies. Evidence is presented for atmospheric and oceanic teleconnections. The impact of anomalous conditions on higher trophic levels in the CCS is also discussed.
1130-1145 Modeling New Primary Production From Multi-Platform Remote Sensing for Monterey Bay, California during the 1997-1998 El Niño
Raphael Kudela and Francisco Chavez
University of California Santa Cruz
Monterey Bay Aquarium Research Institute
The introduction of the SeaWiFS ocean color instrument in the autumn of 1997 coincided with the onset of perhaps the largest El Niño event of the century, providing us with the opportunity to monitor the impact of such events on biological and bio-optical properties in central California. We have previously demonstrated a physiologically based model of new primary production which relies on remotely sensed temperature and ocean color. Here we examine the impact of the 1997 El Niño, and in particular the spatial extent of the reduction in new production. As previously predicted, this El Niño event resulted in a collapse inwards towards the coast of the normally highly productive coastally upwelled waters. We also noted periods in 1998 of extensive runoff along the west coast. This runoff signal can potentially result in overestimates of chlorophyll, and hence productivity, in bio-optical models due to contamination in the ocean color signal from colored dissolved organic matter.
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1300-1315 Impact of the 1997-8 El Niño on nutrient supply and productivity of Gulf of Alaska waters
Institute of Ocean Sciences
Fisheries and Oceans Canada
tel 250 363-6816 fax 250 363-6476
The recent strong El Niño gave impetus to an expanded sampling of nutrient distribution in surface waters of the Gulf of Alaska. In 1998, winter nitrate on the B.C. continental shelf was only half of what was typical in the 1970s, and spring depletion occurred a month earlier. Compared with 1999, the area of summer nitrate depletion was greatly expanded off the coasts of BC and southern Alaska. Nitrate depletion results in decreased chlorophyll levels and primary productivity in the ocean's mixed layer. In such circumstances, phytoplankton are concentrated in a deep chlorophyll maximum and PP declines by about 40%.
1320-1335 Nutrient distributions off the coast of Oregon during El Niño and normal upwelling conditions.
Patricia A. Wheeler and Holly L. Corwith
College of Oceanic and Atmospheric Sciences, Oregon State University,
Corvallis, OR 97331.
We sampled inorganic nutrient concentrations for nitrate, nitrite, phosphate, silicate and ammonium for depth profiles at 5-7 stations along transects off Newport (44o39.1' N, 157 km from shore), Coos Bay (43o13'N, 63 km from shore), Crescent City (41o54' N, 93 km from shore), and Eureka (40o52' N, 65 km from shore) from September 1997- September 1999. We will present the nutrient data as contour maps showing the distribution of surface and integrated nutrients. Integrated nutrients will be determined to the bottom for shelf stations and to the depth of the euphotic zone for slope and offshore stations. The data will be used to compare differences in nutrient availability during the winter and during the upwelling season for El Niño conditions (September 1997- April 1998) and normal upwelling conditions (August 1998- September 1999). In addition, we will present a summary of the potential impact of nutrient availability on the standing stock of phytoplankton.
1340-1355 The nutrient consequences of the 1997-98 El Niño off Central California
Carmen Castro, Curt Collins, Peter Walz, Gernot Friederich, Reiko Michisaki, J. Tim Pennington and Francisco Chavez
From March 97 to January 99 a series of 13 cruises were carried out off Monterey Bay, as part of the project "Studies of Ecological and Chemical Responses to Environmental Trend (SECRET)". The primary objective was to determine how the spatial extent of the coastal upwelling process varied seasonally and interannually. Soon after the start of the program the strong 1997-98 El Niño 97-98 began and was the major source of variations in the hydrographic and chemical fields. Comparison of mean vertical fields with those determined during 1988-91 shows that the water column was warmer, fresher and with lower nutrient levels in the first 200m and within 150Km from the coast during 97 and 98. Although the El Niño effect was stronger in the upper 200m, it also modified the deep waters. At ~ 600m a core of relatively low temperature (D T » 0.1° C) and high silicate (D SiO2 >1 m mol× l-1) was observed during the El Niño period. Temporal variability was also studied by subtracting the 1988-91 monthly average from each SECRET cruise. The warming began in June 1997 and persisted until June 1998. During 1997, the waters were warmer but the salinity signal was ambiguous. A dramatic freshening occurred in early 1998 persisting until May 98. Near-zero nitrate levels were most notable in the 100-200 km from shore band. Low nitrate levels reached the coast by September 1997 and persisted until February 1998. From then on there were small episodic nutrient injections driven by either upwelling or coastal runoff. At deeper levels, a core of low temperature and high silicate water, confined to the slope, was a recurrent feature from September-97 to August-98. It shifted offshore in November-98, after the end of the El Niño.
1400-1415 Inorganic Carbon in the Central California Upwelling System during the 1997-1998 ENSO Event
Gernot E. Friederich, Peter M. Walz, Mike Burczynski and Francisco P. Chavez (Monterey Bay Aquarium Research Institute, P.O. Box 628, Moss Landing, CA 95039; 408-775-1713; email@example.com)
Seasonal upwelling from March until October is responsible for much of the high primary production along the central California coast. ENSO events will therefore usually impact this upwelling region in the spring when the temperatures along the equator are slowly returning to normal. Due to the timing of the recent ENSO event, some effects may have been observed during the late summer and early autumn of 1997. Results from local cruises and quarterly regional cruises during 1997-1998 are being examined and compared with historical data and a local time series that started in 1989. In addition to the shipboard data, moorings have been providing a continuous record of physical and optical parameters. The sea surface partial pressure of carbon dioxide was also measured from these moorings during most of this event. Upwelling started exceptionally early in 1997. Elevated partial pressure of carbon dioxide and decreasing temperature were evident at one of the moorings in late February and a cruise in early March confirmed these indicators. As the year progressed, a warm anomaly developed and the partial pressure of carbon dioxide fell below atmospheric values and has remained there with very minor short-lived exceptions until mid 1998. River runoff from strong winter rains in this ordinarily dry region may be responsible for some of the carbon dioxide decreases in the late winter of 1998.
1420-1435 Chlorophyll distributions off the coast of Oregon during El Niño and normal upwelling conditions.
Holly L. Corwith and Patricia A. Wheeler
College of Oceanic and Atmospheric Sciences, Oregon State University,
Corvallis, OR 97331.
We sampled chlorophyll concentrations through the euphotic zone at 5-7 stations along transects off Newport (44o39.1' N, 157 km from shore), Coos Bay (43o13'N, 63 km from shore), Crescent City (41o54' N, 93 km from shore), and Eureka (40o52' N, 65 km from shore) from September 1997- September 1999. We will present the chlorophyll data as contour maps showing the distribution of surface chlorophyll, depth of the chlorophyll maximum, and as integrated chlorophyll to the bottom for shelf stations and to 70 m depth for slope and offshore stations. The data will be used to compare differences in chlorophyll during the winter and during the upwelling season for El Niño conditions (September 1997- April 1998) and normal upwelling conditions (August 1998- September 1999). We will attempt to compare the distribution maps of patterns of surface and integrated chlorophyll to 8-day mean satellite images covering the west coast from Vancouver to Mexico.
1435-1450 A comparison of January 1997, 1998 and 1999 hydrography, nutrients and chlorophyll in the Gulf of the Farallones, CA.
Wilkerson, F., R. Dugdale, A. Marchi and C. Collins
Cruises were made in January 1997, 1998 and 1999 to the Gulf of the Farallones with stations stretching from Point Reyes to Half Moon Bay, and from the Golden Gate to the Farallone Islands. All cruises were made in periods of high river flow, but in normal (1977), El Niño (1998) and La Niña (1999) conditions. Nearshore temperatures ranged from cold (9.5-10.5ºC) during La Niña 1999, to average (11-13ºC) during 1997 to warm (13.5-15ºC) during El Niño 1998. Typically in January river flow into the Bay results in low salinity, high silicate, high nitrate water that exits San Francisco Bay through the Golden Gate and is advected northward along the coast. This occurred in both 1997 and 1998. However during La Niña (1999) this San Francisco plume was reduced and the nearshore water was more characteristic of high salinity oceanic water. The oceanic water penetrated shoreward in all years; in El Niño 1998 it was warm and had low or undetectable nitrate whereas in La Niña (1999) it penetrated all the way to the coast and was cold (10ºC) and nutrient rich (16 µM NO3, 30 µM Si(OH)4. The higher nutrients resulted in higher chlorophyll in 1999 than 1998 or 1997. The influence of El Niño and La Niña climatic conditions on the relative supply of nutrients to the Gulf of Farallones from the Bay versus offshore will be discussed.
1455-1510 The SECRET of the 1997-98 El Niño off central California
Francisco Chavez, J. Tim Pennington, Reiko Michisaki, Amy McPhadyen and John Ryan
During the onset of the 1997-98 El Niño we proposed that the major impact of El Niño on the coastal ecosystem should be observed in the coastal transition zone, the area between the near-shore site of active coastal upwelling and the California Current. To test this hypothesis we enhanced a program of cruises that had just been initiated to determine the spatial extent of the coastal upwelling process. We also deployed additional moorings with bio-optical sensors, current meters and sediment traps. In this presentation we describe the biological consequences of the 1997-98 El Niño off central California from shipboard and satellite estimates of chlorophyll and primary production. The results show the maintenance of a narrow inshore band of enhanced production and support our conceptual model of the impact of El Niño on the coastal upwelling ecosystem.
1515-1530 El Niño 1997/98 in the Point Loma Forest near San Diego: Physical Impacts and Biological Responses
Mia Tegner and John Largier
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, California 92093-0201
Kelp forests, organized around the giant kelp (Macrocystis pyrifera), are the California benthic community most heavily affected by El Niño events. With its high nutrient requirement, kelp growth ceases and considerable tissue deterioration reduces the structure and productivity available to the rest of the community. Here we consider data from 1997 through 1999, encompassing a strong El Niño event and the transition into La Niña conditions. To assess sources of nitrate, the nutrient that limits kelp growth, we deployed a cross-shore array of thermistors to investigate the form and effect of internal waves. We monitored runoff during two sharply contrasting rainy seasons and assessed accumulation in sediments susceptible to wave dispersal as alternate nutrient sources during El Niño periods when the thermocline is depressed below kelp forest depths. The effects of these nitrogen sources were evaluated with regular surface and bottom nutrient measurements and CHN samples of kelp tissues on a cross-shore transect through the forest. Biological responses, which varied with the sources of the nitrogen and depth and position in the forest, will be discussed in the context of long-term observations of kelp and invertebrate population dynamics at these sites.
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Open discussion 1550-1730
Poster session and mixer 1730-1930
0815-0830 Zooplankton community composition along the inner portion of Line P during the 1997-98 El Niño event
David L. Mackas
Fisheries and Oceans Canada
Institute of Ocean Sciences
Sidney, BC, Canada V8L 4B2
1996-1998 zooplankton samples from oceanic waters off Vancouver Island provide time series descriptions of biomass and community composition before, during, and immediately after the 1997-98 El Niño event. Sampling extended to about 200 km seaward of the continental shelf, along and adjacent to the inner third of the long-term Line P/Station P section (48º30'-49ºN, 126º-130º40'W). At the nearshore portion of the line (P2-P6), differences from 1979-1991 seasonal averages included lower total biomass; lower concentrations of boreal shelf copepods such as Calanus marshallae, Pseudocalanus mimus, and Acartia longiremis; unusually high concentrations of southern neritic and oceanic copepods such as Paracalanus parvus, Ctenocalanus vanus and Clausocalanus spp.; and an early (April) and anomalously weak spring peak of the normal dominant species Neocalanus plumchrus. Although from a more oceanic environment, these differences are generally very similar to W. Peterson's (1998)observations of 1970s vs late 1990s differences in the zooplankton of the central Oregon coast continental shelf. Toward the seaward end of the section (P8-P12), deviations from seasonal climatology are less apparent. The 1998 spring peak of Neocalanus is both larger and later (May) than at P4-P6, and similar to 1996-97 levels reported by Goldblatt et al. (99).
0835-0850 The effects of the 1997-87 El Niño event on hydrography and zooplankton off the central Oregon coast.
William T. Peterson
National Marine Fisheries Service
Hatfield Marine Science Center
2030 S. Marine Science Drive
Newport, OR 97365
Julie Keister and Leah Feinberg
Cooperative Institute for Marine Ecosystem Research
Oregon State University
Hatfield Marine Science Center
Background. We measure hydrographic conditions and take zooplankton samples off the central Oregon coast along the Newport Hydrographic Line, at biweekly intervals, at stations 1, 3, 5, 10 and 15 miles from shore. This sampling program began in May 1996. We chose to sample these stations because they were visited repeatedly during the 1960s and 1970s by physical and biological oceanographers from Oregon State University. Biological oceanographers also sampled along this line during spring/summer 1981, 1983, 1984 and 1990-1992.
Since we have been monitoring zooplankton species composition since 1996, we had the good fortune of sampling the 1997-98 el Niño before, during and after its passage and determining the response of hydrography and zooplankton to this perturbation. In this paper, we discuss the impacts of the recent el Niño on biomass and species composition of the copepod and euphausiid components of the pelagic ecosystem.
The 1997-98 el Niño event.
Prelude. February 1997 was clear and calm, resulting in an early and large spring bloom. The dominant local copepod species (Calanus marshallae and Pseudocalanus mimus) began to increase in numbers at that time. By May the Pseudocalanus population averaged 4.5 individuals per liter, the highest ever observed for that month (averaged over 8 years of data). The spring transition in 1997 came early, with cold (8°C) salty (> 33 psu) appearing at the five-mile station in early April. The situation changed dramatically in early May when two large southwesterly storms passed through the area; winds remained unfavorable for upwelling through June and early July; a brief upwelling event occurred 14 July - 19 August 1997. The summertime upwelling season lasted five weeks, making 1997 the shortest upwelling season on record. The Bakun Upwelling index for 1997 was 73 (the sum of May-September monthly values), the lowest value ever recorded. Prior to 1997, the three lowest values were observed in 1993 (127), 1976 (131), and 1983 (135).
Summer and autumn of 1997. The copepod species captured along the Newport Hydrographic line during April/May and July/August were chiefly boreal species, expected during times of upwelling. However, during relaxation of upwelling in June and especially in late August/September, a large proportion of the species captured were those classified as "warm water" species (Table 1). These species are normally found offshore of Oregon in summer, and in shelf and slope waters off California year-around. This same group of "warm water" species dominates the Oregon shelf and slope zooplankton assemblage during winter as a result of transport into the Oregon region by the poleward Davidson Current. Presence of these "warm water" species on the shelf in late August and September resulted from the massive downwelling event in late August caused by a wind reversal. Persistence through November (and through the winter of 97-98) indicates that it was at the end of August that poleward currents began to dominate the shelf environment.
Winter 97-98. Poleward flows continued through the winter months. With regards to copepod species composition, the winter of 97-98 was no different from any other winter. The euphausiid community composition however was strikingly different and the species which occurred off the coast indicate that the northward transport during the winter of 97-98 was stronger than that observed during the strong el Niño of 1983. Three euphausiid species were encountered in 1998 that have never occurred off Oregon (Euphausia recurva, Euphausia mutica and Euphausia gibba). All three are known only for the central Pacific water mass and the offshore regions of the California Current (but only off central and southern California). A fourth species, Nyctiphanes simplex, appeared off Oregon during the winter of 1997-98. This is a coastal euphausiid species which is normally not found north of Point Concepcion but which did appear off Oregon during the 1983 upwelling even (Brodeur and Pearcy 1985).
Spring/Summer 1998. The spring transition did not occur until early May. Significant amounts of upwelling-favorable winds did not set up until June. Despite upwelling, subsurface waters off Oregon remained anomalously warm through September 1998 (Smith and Huyer, this symposium), suggesting that the el Niño persisted through most of the summer of 1998.
The zooplankton biomass and species composition also follow closely the scenario of an el Niño event that persisted through August 1998. The southern coastal euphausiid Nyctiphanes simplex occurred commonly in our samples from January through August 1998. Another coastal euphausiid species, Thysanoessa spinifera which is usually common in mid-shelf waters of Oregon and northward was rare in our samples in 1998. In addition, the boreal copepod species which normally dominate the coastal zooplankton assemblage (Pseudocalanus mimus and Calanus marshallae) never became abundant during the 1998 upwelling season. Both populations only began to show an increase in population size beginning in September 1998. During the [apparent] January-August 1998 el Niño period, copepod species diversity continued to be high and all of the warm water species listed in Table 1 were present. Fewer warm water species occurred in September and October due to stronger equatorward flows. Copepod species diversity once again increased in November, signaling the onset of the Davidson Current.
Conclusion. The zooplankton story is the same as the sea level and hydrographic story -- increases in sea level in May/June 1997 resulted from downwelling due to southwesterly winds. A brief period of upwelling in mid-July/mid-August was interrupted by another southwesterly storm in late August. Poleward flows were associated with the late-August 1977 storm and it was at that time that the shelf waters became flooded with "warm water" copepod species. The euphausiids did not show any anomalous patterns until January 1998 at which time the species Nytciphanes simplex first appeared in our samples. The ocean off Oregon remained anomalously warm through the spring and summer of 1998 and it was not until September 1998 that the pelagic ecosystem began to return to normal. Thus, the influence of the el Niño might be said to have lasted from May 1997 through August 1998, 16 months (assuming that the equatorial el Niño affected the North Pacific High in May/June 1997 and August 1997).
Post el Niño Conditions. The wintertime Davidson Current was well-established by mid-November 1998 and continued through March 1999. The spring transition occurred during the first week of April and populations of boreal copepods began to increase in numbers. By May 1999 the ecosystem had returned to "normal" -- no warm water copepod species were ever found throughout that summer; all copepods were boreal in origin, and the abundance of boreal copepod species had returned to their historical highs.
Table 1. Density (number per cubic meter) of zooplankton species collected at a station five miles off Newport OR (water depth 60 m) during the summer of 1997 from July through November. The "warm event" began on 20 August and reached a maximum in mid-September, bringing with it warm water copepod species and doliolids (Dolioletta gegenbauri) to the continental shelf waters off Oregon.
Date (July through November)
7/1 7/23 7/30 8/6 8/14 8/21 8/28 9/2 9/9 10/15 11/3
Cool Water Species
Calanus marshallae 49 125 31 46 553 559 61 5 2
Pseudocalanus mimus 1470 1719 678 207 796 987 173 184 42 2
Centropages abdominalis 1138 72 157 103 73 17 17 4
Acartia longiremis 54 104 65 225 204 113 25 18 9 24
Oithona similis 601 1737 574 245 474 493 113 709 558 567 502
Warm Water Species
Calanus pacificus 4 17 36 75 23 42
Calanus tenuicornis 10 4 9 5 6
Paracalanus parvus 219 1218 130 84 103 102 555 495 1065 500 232
Eucalanus californicus 4 52 15 18 311
Ctenocalanus vanus 17 9 15 15 46 21
Clausocalanus arcuicornis 2 4
C. pergens 9 4
Calocalanus styliremis 4 7
Acartia danae 15 6 12 14
Acartia tonsa 16 5
Corycaeus anglicus 26 76 97 289 170
Dolioletta gegenbaurii 130 71 42 2 0
0855-0910 Productivity Cycles in the Monterey Bay Pelagic Ecosystem and La Niña Boom or Bust?
Baldo Marinovic, Don Croll, Francisco Chavez, and Scott Benson
Within the past three years, Monterey Bay has experienced to two acute and distinctly different climactic events that have had far reaching impacts on patterns of seasonal productivity within the pelagic ecosystem. Though many of the observed responses within this ecosystem were predictable, several went counter to expectation, further highlighting both our limited understanding of ecological processes within pelagic ecosystems as well as the importance of conducting research during these unique an unpredictable events.
The 1997/98 El Niño event was the strongest recorded this century and caused profound declines in nutrient upwelling, phytoplankton growth, zooplankton productivity and marine mammal abundance and reproduction. Our research indicated that the impacts caused by this event were less dramatic in the nearshore environment that in offshore waters (see Ecosystems Observations 1998). These results highlighted the importance of coastal upwelling centers as critical habitat for a number of predators, especially during periods of environmental stress.
This year, the La Niña conditions have prevailed in the Northeast Pacific, with colder than normal ocean temperatures occurring along most of the West Coast of North America. This has provided us once again with a unique opportunity to gain insights into the ecology of the pelagic ecosystems during acute climactic events.
Upwelling and Phytoplankton Productivity
Strong northwest winds during the spring of 1999 resulted in extremely high levels of upwelling. Upwelling indices were up to two standard deviations above normal for the Central California region (NOAA-PFEG). AVHRR satellite imagery from this period revealed numerous, long filaments of cold nutrient rich water extending far offshore from headlands associated with coastal upwelling centers including Pt. Arena, Pt. Reyes, Pt. Ano Nuevo, Pt. Sur and Pt. Conception. Nutrient input associated with this intense upwelling resulted in broad band of high phytoplankton productivity that extended up to 100 km offshore of Monterey Bay. Upwelling favorable winds dramatically diminished in July and were largely absent throughout the late summer and fall. In response, phytoplankton levels in Monterey Bay decreased markedly, and by late summer values were around the long term mean for this time of year.
Patterns of primary productivity within the Central California region during 1998 were distinctly different to those described above. Upwelling and phytoplankton levels were anomalously low during the spring and early summer of 1998 when the pelagic ecosystem was still heavily under the influence of El Niño conditions. By July of 1998, upwelling favorable winds returned to Central California and upwelling indicies remained well above the long term mean late into the fall.
High levels of primary productivity in the spring of 1999 translated to high zooplankton abundance in the early and mid summer. This followed the typical seasonal pattern of summer peaks in zooplankton biomass following spring peaks in phytoplankton productivity. Zooplankton levels during the summer of 1999 were the highest recorded during the past three years, and they remained high throughout the fall (Fig 1). In comparison, zooplankton levels were distinctly lower in the summer of 1998 but increased following the resurgence of upwelling in the late summer and fall.
Krill Abundance and Species Composition
High primary productivity levels in the spring of 1999 resulted in high levels of larval production and recruitment to krill populations within the Central California region. In addition krill, particularly larvae and juveniles, were broadly distributed offshore, due in all likelihood to advection caused by strong levels of upwelling. Numerous surface swarms of large reproductive adults were observed within Monterey Bay on several occasions in April and May of 1999, indicating ongoing spawning activity. These swarms were targeted by a number of predators including fish, seabirds and even opportunistic gray whales en route to their feeding grounds in Alaska! This was in stark contrast to conditions in the spring of 1998 when krill abundance was conspicuously lower. Krill levels declined noticeably with the cessation of coastal upwelling in July of 1999, however it is unclear whether this was due to declines in total abundance, dispersal to deeper water, or a combination of both.
A major shift in the species composition of the krill community in Monterey Bay also occurred between 1998 and 1999. Euphausia pacifica typically dominates the krill community year round in Monterey Bay, however in the early part of 1998, the southern species Nyctiphanes simplex comprised a substantial portion of the community and the cool temperate Thysanoessa spinifera was virtually absent (Fig 2). By late 1998, with the onset of coastal upwelling, the species composition gradually shifted back to a more typical mix of E. pacifica and T. spinifera. This pattern continued into 1999 with high levels of recruitment for T. spinifera observed both in the spring and fall.
What have we learned?
Both the 1997/98 El Niño and the current La Niña events have provided us with unique insights into ecological processes within the Monterey Bay pelagic ecosystem. Productivity at multiple levels demonstrated predictable responses to both these events, declining dramatically in 1997/98 and reaching high levels in late 1998 and 1999. There were, however, unexpected patterns observed during both events as well. In 1998, the return of upwelling late in the season resulted in dense krill aggregations within Monterey Bay that attracted record numbers of whales. In contrast, the fall of 1999 was characterized by relatively low levels of coastal upwelling. As a result krill aggregations were more diffuse and foraging whales were more scarce. One implication of these findings is that it appears that episodic periods of upwelling that persist into the fall are necessary to maintain dense aggregations of krill within Monterey Bay, even during years when overall (and especially springtime) productivity is high. These findings highlight the value of acute climactic events in providing insights into ecological processes as well as the importance of maintaining ongoing ecosystem monitoring within the pelagic waters of the sanctuary.
0915-0930 Copepod Communities off Monterey Bay During the 1997 to 1999 El Niño/La Niña
Hopcroft, R.R. and Chavez, F.P.
We present, and contrast, the composition, abundance and biomass of the copepod community during these periods, based on collections from 64-, 200- and 500-µm meshed nets from 1997 to 1999. During the El Niño, the timing and extent of upwelling were altered, resulting in lower phytoplankton standing stock, primary production, and zooplankton biomass, than observed during the La Niña period. Within the zooplankton, the shift was most apparent in larger copepod species (i.e. Calanus, Eucalanus), while smaller species of copepods (i.e. Clausocalanus, Oithona, Oncaea) were unaffected.
0935-0950 Annual differences in zooplankton, sardine eggs, and SST; El Niño to La Niña
Between the first half and latter half of 1998 the west coast regional SST anomalies changed from highly positive to strongly negative; initially in the Pacific northwest and lastly off southern California. By early 1999 La Niña conditions were well established. The large contrast in conditions allows a perspective in recognizing links between oceanographic and biological variables. The acoustic backscatter from the ADCP provides a high resolution index of the distribution of zooplankton. The coastally confined distributional pattern found in April 1998 closely matches that of the sardine eggs as does the wide-spread pattern found in April 1999. It is concluded that food availability limits the offshore extent of sardine spawning. The inshore extent of sardine spawning is apparently determined by temperatures too low for larval survival.
Break until 1010
1010-1025 Temporal variability in the cetacean community of a coastal upwelling system spanning an El Niño event.
Benson, S.R.1, Croll, D. A.2, Marinovic2, B., Chavez, F3., and Harvey, J.T.1
1 Moss Landing Marine Laboratories, P.O. Box 450, Moss Landing, California.
2Institute of Marine Science, University of California at Santa Cruz, Santa Cruz, California
3Monterey Bay Aqurium Research Institute, P.O. Box 628, Moss Landing, Ca. 95039
The world's most productive fisheries and marine mammal foraging areas are located in coastal upwelling centers. Temporal variability in strength of upwelling can affect primary production, zooplankton productivity, and the distribution and abundance of fish and marine mammals. In this study, we report on ecosystem studies in Monterey Bay, California during the summer upwelling periods of 1996-98, including impacts of the 1997/98 El Niño. We combine monthly line-transect surveys for marine mammals along random-systematic lines, hydrographic stations, zooplankton net tows, and hydroacoustic surveys of zooplankton backscatter with data from the Monterey Bay Aquarium Research Institute biological oceanographic monitoring program to examine the impacts of the 1997/98 El Niño event on higher trophic levels in Monterey Bay.
The abundance of the most common California Current small cetaceans varied among years. Dall's porpoise (Phocoenoides dalli) and common dolphin (Delphinus sp.) abundance mirrored oceanographic patterns. During 1996, temperatures were low (mean=13.1oC, S.D.=0.43, maximum=13.5oC), zooplankton abundance was moderate, Dall's porpoise were abundant (Abundance, N=408, C.V.=0.30), and common dolphins were rare (N=6, C.V.=~1.0). As temperatures warmed in 1997/98 (mean=15.5oC, S.D.=1.52, maximum=17.0oC), zooplankton abundance decline dramatically, Dall's porpoise abundance decreased to N=46 (C.V.=0.51), while common dolphin abundance increased to a peak of N=6,018 (C.V.=0.49). These patterns are consistent with previous coastwide studies. Large whales also responded strongly to El Niño conditions. A sharp drop in large whale abundance occurred between 1996 (N=32, C.V.=0.27) and 1997 (N=6, C.V.=0.75) as zooplankton productivity decreased. By summer 1998, while zooplankton volume slowly increased, rorqual abundance sharply increased to the highest observed abundance (N=83, C.V.=0.26) during the study period. We hypothesize that a dramatic reduction in productivity offshore concentrated rorquals in the remaining productive coastal upwelling areas, including Monterey Bay. These patterns exemplify short-term responses of cetaceans to large-scale changes in oceanic conditions and demonstrate the importance of coastal upwelling systems to higher trophic level predators.
1030-1045 Why is fish recruitment so good when California Current temperature is high and plankton is low?"
We have reason to believe that mesoscale structure is more important than broad-scale average temperature and zooplankton when considering fish recruitment success. Under this presumption, small, coastal intermittent production areas and large persistent offshore features offer opportunities for high recruitment success. When the population is small, the coastal domain is their home and when the population is large recruitment still fails most of the time but occasionally a very large recruitment is possible. The conditions under which this happens performs like a lottery and by chance the large juvenile stocks of hake occur, or sardine, or anchovy with a frequency determined by their proximity to the offshore core/eddies of the California Current.
1050-1105 Modeling CalCOFI observations during El Niño: Fitting physics and biology
Arthur J. Miller, Emanuele Di Lorenzo, Bruce Cornuelle,
Scripps Institution of Oceanography,
and John Moisan, Long Island University.
Hydrographic and ADCP surveys of temperature, salinity and velocity from CalCOFI, altimetric measurements of sea level and drifter observations of temperature and velocity during the 1997-98 El Niño are now being fit with an eddy-resolving ocean model of the Southern California Bight region to obtain dynamically consistent estimates of eddy variability. These fields also are driving a 3-D NPZD-type model of the region to be fit to sub-surface chlorophyll and nitrate from CalCOFI surveys and surface chlorophyll from SeaWiFS. Skill evaluations are quantified by the model-data mismatch (rms error) during the fitting interval and in the forecasting interval of independent data. Modeling activities by other research groups during the 1997-98 El Niño will also be discussed.
1110-1200 Open discussion
1315-1700 Working groups (Physics, remote sensing, nutrients, primary production, zooplankton)
0815- 0830 The State of the California Current During 1998-1999: Transition to Cool-water Conditions
We present an overview of the state of the California Current during 1998-1999, based primarily on observations made on the quarterly surveys of the California Cooperative Oceanic Fisheries Investigations (CalCOFI) and cooperative research programs. This period saw a transition from the warm-water conditions associated with the 1997-98 El Niño event to the cool-water conditions which were still prevalent in coastal southern California as of October 1999. Changes in ecosystem structure accompanied the transition in physical conditions, including the highest integrated chlorophyll concentrations ever measured in the CalCOFI region in April 1999 and unusually high abundances of fish eggs and macrozooplankton biomass through 1999. We conclude with a cautionary note on the comparison of regional anomalies, and present a set of hydrographic and biological climatologies of the 50-year CalCOFI time series for several baseline periods.
0840-1000 Open discussion on La Niña
1000-1200 Working group presentations
EFFECT OF THE 1997-98 EL Niño ON CHLOROPHYLL AND PRIMARY PRODUCTION ACROSS THE CENTRAL CALIFORNIA UPWELLING ZONE: TEMPORAL EVOLUTION, SPATIAL PATTERN, AND COMPARISON TO CLIMATOLOGY
Reiko P. Michisaki, J. Timothy Pennington and Francisco P. Chavez
MBARI, 7700 Sandholdt Road, Moss Landing CA 95039 USA
Effects of the 1997-98 El Niño on chlorophyll and primary production levels across the central California upwelling zone were observed with quarterly cruises from 0-275 km of the coast over 1997-99, and with semi-monthly cruises from 0-50 km of the coast over the decade 1989-99. The 0-275 km cruises show (1) normal early upwelling (FMA) season phytoplankton biomass and growth in 1997, (2) progressive restriction of high chlorophyll and productivity waters inshore during the late upwelling (MJJ), oceanic (ASO) and Davidson (NDJ) seasons of 1997, (3) severe depression of biomass and growth during the 1998 early and late upwelling seasons, and (4) recovery to normal or above-normal values in late 1998 and 1999. In the 100-200 km offshore spatial domain, 1998 early and late upwelling season chlorophyll and productivity levels were as much as 80-90% below data obtained in non-El Niño years. Values in the 0-50 km and 50-100 km spatial domains were less strongly depressed.
Results of the 0-50 km cruises are in accord the above observations. At a Monterey Bay station (C1) typically downstream from a recurring upwelling plume, the 1997-98 El Niño had little effect on chlorophyll and primary production in 1997 but strongly depressed values during the early and late upwelling seasons in 1998. At an upwelling plume station (M1), chlorophyll and productivity values were only moderately depressed in both 1997 and 1998.
Results of both cruise series suggest that biomass and production are reduced and compressed into areas of normally active upwelling during El Niño years. Such spatial compression could have important consequences for distribution of higher trophic level organisms.
Observations of acoustic backscatter and particle flux during 1998-99.
Amy Little, Carmen Castro, Mary Silver, and Francisco Chavez
Towards the end of El Niño in March 1998, two midwater acoustic Doppler current profilers (ADCPs, S2 and S3), two deep water Honjo sediment traps (Honjo2 and Honjo3), and two midwater IRS sediment traps (IRS2 and IRS3) were deployed in central California waters. Surface moorings with ADCPs, thermistor strings, chemical and bio-optical instruments (M1, M2, and M3) are available from the same time period. The deployments will continue until mid-2000. Mesozooplankton biomass and horizontal currents estimated from the moored ADCPs will be presented together with mass flux from the sediment traps. Several complex and dynamic physical and biological forces influence vertical particulate transport, including phytoplankton primary production and community structure, advection by water masses, re-suspension of continental shelf material, community structure of consumers, introduction of flux feeders accelerating transport, and various feeding strategies employed by zooplanktoners. We are currently evaluating the impact of these processes on vertical flux during our period of observations.