As part of an ongoing effort to facilitate synthesis of the many and diverse data sets obtained through the JGOFS program, the Synthesis and Modeling Program (SMP) has supported small workshops designed to bring together investigators with common research interests.  One such workshop was held 4 and 5 November at the Center for Coastal Physical Oceanography, which is part of Old Dominion University in Norfolk, VA.  The goal of this workshop was to discuss current understanding of the physical and biological interactions that contribute to the structuring of the lower trophic levels of the equatorial Pacific Ocean and to make recommendations for future studies of this system.  The workshop was attended by 23 participants who ranged from senior researchers to graduate students (see list below).

The initial portion of the workshop was devoted to overview presentations of current SMP studies of the equatorial Pacific Ocean. The first group of presentations focused on new production studies (Murray, Turk), carbon cycling (Peng), silicate dynamics (Dugdale), bacterial (Ducklow) and zooplankton dynamics (Roman), optical studies (Lewis), remote sensing of Trichodesmium(Clayton), and large-scale patterns in phytoplankton distributions in the equatorial Pacific as determined from SeaWiFS (McClain and Signorini).  These presentations were followed by talks on current efforts to model specific aspects of the equatorial Pacific.  The projects included simulation of La Nina dynamics (Murtugudde), three-dimensional basin-scale ecosystem simulations (Chai, Christian), and biological data assimilation (Friedrichs).  Other presentations focused on parameterization of iron limitation (Armstrong) and an assessment of the feasibility of seasonal and interannual prediction of El Nino-Southern Oscillation events (Busalacchi).  The latter presentations showed the considerable progress that has been made in modeling the physics and biology of the equatorial Pacific since the JGOFS EqPac field effort. Clearly, exciting studies are being done, and more are on the horizon.

As with most workshops, the initial intent was to break into working groups with suggested potential topics of: producing common data sets, especially rate measurements, from the JGOFS EqPac program and other field programs; identifying the benefits and limitations of using 1D models; and coordinating potential comparisons of 3D model structures and results, both physical and biological.  However, once the participants began the plenary discussion of the workshop topics, it was soon apparent that remaining as a single group was the preferred structure for arriving at workshop conclusions and recommendations.

The initial, and lively, discussions focused on defining a basic background state for the lower trophic levels of the equatorial Pacific Ocean.  The consensus was that the background state consists of a balanced system (gains = losses) that is dominated by microzooplankton and picoplankton.  The description of this system via sampling and empirical methods, and the accurate simulation of this state with mathematical models, were considered to be high priorities because only with this comprehensive approach can perturbations to this state be described and understood.  In particular, it was recognized that we need to understand the biological and physcial mechanisms and interactions that support and sustain the background state.  However, it was also pointed out that the background state of the circulation of the equatorial Pacific is not known (or perhaps does not exist); therefore we do not know how biological-physical interactions sustain the background ecosystem.  This is clearly an area of needed research.

To move forward in our understanding of the basic background state, the workshop participants listed several key biological processes and mechanisms that require further study: grazing behavior of micro- and mesozooplankton, sinking rate of phytoplankton as a function of nutritional state, iron and silicate interactions, switching in feeding behavior by the grazer community, and memory or time lag in the zooplankton response to changes in food supply.

All workshop participants recognized, and were impressed by, the advances that have been made in modeling the circulation of the equatorial Pacific Ocean.  The circulation models show considerable skill in hindcasting ENSO events and are now being used in a forecast mode.  While the circulation models are adequate for these applications, improvements are still needed for the circulation models is to be coupled with biological models.

Many of the initial ecosystem modeling efforts for the equatorial Pacific Ocean use one-dimensional models that are forced by the output of circulation models.  Circulation model results that are especially needed are simulated time series of vertical velocity, convective adjustment, vertical mixing, and vertical diffusion coefficients.  However, the physical dynamics that produce these motions are not always well represented in the circulation models.  Areas in which the circulation models need improvement are: simulation of the vertical velocity structure, entrainment velocity, heat content of the surface layer, mixed layer dynamics, the diel cycle of mixing, sea surface temperature, and the resolution of tropical instability waves and higher frequency motions.

The role of modeling and the many advances made in coupling circulation and biological models for the equatorial Pacific Ocean were recognized by the participants.  However, continued advances in this area require the input of data sets, especially as data assimilation becomes a routine component of biological modeling.  The acquisition of long-term monitoring data sets for biological variables are desired, much in the same way as physical observations are available via the Tropical Atmosphere Ocean array, for example.  Measurements that would be particularly useful and feasible to collect in a routine mode from moorings are pCO₂, optical properties, and nutrient concentration.  It was also recognized that the data analysis and modeling studies that have taken place since the JGOFS EqPac field program have highlighted the need for other types of data that were not part of the original study.  These additional measurements are iron profiles, size- and taxa-dependent rate measurements, and measurements to elucidate silicate cycling.  The workshop participants felt that these measurements should be a part of any future multidisciplinary field programs planned for the equatorial Pacific Ocean.

The workshop participants also identified topics that need attention now in order for the maximum use to be made of the existing EqPac data sets.  The topics of synthesis of existing zooplankton grazing parameters and biomass estimates, Beam C-particulate organic carbon (POC) calibration, calcification rates, and dissolved organic matter (DOM) production and consumption rates, were thought to be ones that can be addressed, perhaps through small SMP-sponsored workshops.  The availability of these results would greatly enhance the modeling and analyses efforts currently underway.

The final workshop discussions focused on defining group efforts that could facilitate synthesis of the ongoing equatorial Pacific modeling efforts.  As a starting point, the workshop participants who have coupled physical-biological models agreed to compare the output of their models at 140 W and 165 E for the periods of March 1992 and October 1992.  The comparisons will be made using simulations from the models currently being run by the University of Maine (Chai), Old Dominion University (Friedrichs), University of Washington (Murray), and the Goddard Space Flight Center (Christian) groups.  The comparisons will be made in terms of state variables, e.g. nutrients and chlorophyll, as well as derived quantities such as f-ratio, export flux (carbon, nitrogen, silicate) from the euphotic zone (taken to be 120 m), and primary and secondary production. Jim Christian, from Goddard Space Flight Center, agreed to lead this effort.  The results of this comparison exercise will help highlight differences and similarities among the models, help make recommendations for model improvements and modifications, and indicate areas where additional data are needed.

Robert Armstrong
AOS Program
Princeton University
P.O. Box CN 710
Princeton, NJ 08544-0710
Tel 609-258-5260
Fax 609-258-2850
raa@splash.princeton.edu

Richard Barber
Duke University Marine Lab
135 Duke Marine Lab Road
Beaufort, NC 28516-9751
Tel 919-504-7578
Fax 919-504-7648
rbarber@acpub.duke.edu

Tony Busalacchi
NASA/Goddard Space Flight Center
Mailstop 970.0
Greenbelt, MD 20771
Tel 301-614-5671
Fax 301-614-5666
tonyb@neptune.gsfc.nasa.gov

Fei Chai
School of Marine Sciences
5741 Libby Hall
University of Maine
Orono, ME 04469-5741
Tel 207-581-4317
Fax 207-581-4388
fchai@maine.edu

Jim Christian
Universities Space Research Association
NASA/Goddard Space Flight Center
Mailstop 970.2
Greenbelt, MD 20771
Tel 301-286-9911
Fax 301-286-1775
jrc@bluefin.gsfc.nasa.gov

Tonya Clayton
Center for Coastal Physical Oceanography
Crittenton Hall, 768 52nd Street
Old Dominion University
Norfolk, VA 23529
Tel 757-683-5557
Fax 757-683-5550
clayton@ccpo.odu.edu

Hugh Ducklow
Virginia Institute of Marine Sciences
College of William & Mary
Box 1346
Gloucester Point, VA 23062-1346
Tel 804-684-7180
Fax 804-684-7293
duck@vims.edu

Dick Dugdale
Romberg Tiburon Center for Environmental Studies
San Francisco State University
P.O. Box 855
3150 Paradise Drive
Tiburon, CA 94920-0855
Tel 415-338-3518
Fax 415-435-7120
rdugdale@sfsu.edu

Marjy Friedrichs
Center for Coastal Physical Oceanography
Crittenton Hall, 768 52nd Street
Old Dominion University
Norfolk, VA 23529
Tel 757-683-3234
Fax 757-683-5550
marjy@ccpo.odu.edu

Bruce Frost
School of Oceanography
Campus Box 357940
University of Washington
Seattle, WA 98195-7940
Tel 206-543-7186
Fax 206-543-0275
frost@ocean.washington.edu

Eileen Hofmann
Center for Coastal Physical Oceanography
Crittenton Hall, 768 52nd Street
Old Dominion University
Norfolk, VA 23529
Tel 757-683-5334
Fax 757-683-5550
hofmann@ccpo.odu.edu

Robert Le Borgne
Station Marine d'Endoume
Chemin de la batterie des lions
F-13007 Marseille
France
Tel 33 4 91 04 16 57
Fax 33 4 91 04 16 35
leborgne@com.univ-mrs.fr

Corinne Le Quere
Laboratoire des Sciences du Climat et de l'Environmente
UMR CEA-CNRS 1572
CE Saclay, Orme des Merisiers
91191 Gif sur Yvette
France
Tel 33 1 69 08 77 24
Fax 33 1 69 08 77 16
lequere@lsce.saclay.cea.fr

Marlon Lewis
Department of Oceanography
Dalhousie University
Halifax, Nova Scotia
Canada B3H 3J5
Tel 902-494-3513
Fax 902-494-3513
marlon@raptor.ocean.dal.ca

Harilaos Loukos
Laboratoire d'Oceanographie Dynamique et de Climatologie
Institut Pierre Simon Laplace
CNRS/UPMC/IRD
Universite Pierre et Marie Curie
Boite 100
4 Place Jussieu
75252 Paris cedex 05
France
loukos@ipsl.jussieu.fr

Chuck McClain
NASA/Goddard Space Flight Center
Code 971/Oceans and Ice Branch
Greenbelt, MD 20771
Tel 301-286-5377
Fax 301-286-0240
chuck@seawifs.gsfc.nasa.gov

Mike McPhadden
NOAA/PMEL R/E/PM
7600 Sand Point Way N.E.
Seattle, WA 98115-0070
Tel 206-526-6783
Fax 206-526-6815
mcphaden@pmel.noaa.gov

Christophe Menkes
LODYC-UPMC
Tour 15, 2eme etage
4, place Jussieu
75252 Paris cedex 05
France
Tel 44 27 34 81
Fax 44 27 38 05
menkes@thetis.lodyc.jussieu.fr

Jim Murray
School of Oceanography
Campus Box 357940
University of Washington
Seattle, WA 98195-7940
Tel 206-543-4730
Fax 206-685-3351
jmurray@ocean.washington.edu

Ragu Murtugudde
NASA/Goddard Space Flight Center
Code 970/Bldg. 22
Greenbelt, MD 20771
Tel 301-286-2071
Fax 301-286-1761
ragu@seetha.gsfc.nasa.gov

Tsung-Hung Peng
NOAA/AOML
Ocean Chemistry Division
4301 Rickenbacker Causeway
Miami, FL 33149-1026
Tel 305-361-4399
Fax 305-361-4392
peng@aoml.noaa.gov

Joel Picaut
NASA/Goddard Space Flight Center
Code 970
Greenbelt, MD 20771
Tel 301-614-5668
Fax 301-614-5666
jpicaut@neptune.gsfc.nasa.gov

Marie-Helene Radenac
University of Paris VI case 100
LODYC/ORSTOM
Tour 15, 2eme etage
4, place Jussieu
75252 Paris cedex 05
France
Tel 44 27 34 81
Fax 44 27 38 05
mhr@lodyc.jussieu.fr

Mike Roman
Horn Point Environmental Lab
University of Maryland
P.O. Box 775
Cambridge, MD 21613
Tel 410-228-8200 x8425
Fax 410-476-5490
roman@hpl.umces.edu

Baris Salihoglu
Center for Coastal Physical Oceanography
Crittenton Hall, 768 52nd Street
Old Dominion University
Norfolk, VA 23529
Tel 757-683-3234
Fax 757-683-5550
baris@ccpo.odu.edu

Sergio Signorini
NASA/Goddard Space Flight Center
Code 970.2, Bldg. 28
Greenbelt, MD 20771
Tel 301-286-9891
Fax 301-286-0268
sergio@bluefin.gsfc.nasa.gov

Robbie Toggweiler
NOAA/Geophysical Fluid Dynamics Laboratory
P.O. Box 308
Princeton University
Princeton, NJ 08542
Tel 609-452-6659
Fax 609-987-5063
jrt@gfdl.gov

Daniela Turk
Department of Oceanography
Dalhousie University
Halifax, Nova Scotia
Canada B3H 3J5
Tel 902-494-3557
Fax 902-494-3877
neli@raptor.ocean.dal.ca

Mark Verschell
NASA/Goddard Space Flight Center
Code 970
Lab. for Hydrospheric Proc.
Greenbelt, MD 20771
Tel 301-614-5669
Fax 301-614-5666
verschell@neptune.gsfc.nasa.gov

Jerry Wiggert
Earth System Science Interdisciplinary Center
University of Maryland
2207 Computer & Space Sciences Building
College Park, MD 20742
Tel 301-405-4971
Fax 301-405-8468
jwiggert@essic.umd.edu
NASA/Goddard Space Flight Center
Code 970.2, Bldg. 28
Greenbelt, MD 20771
Tel 301-286-0946
Fax 301-286-0268
jwiggert@neptune.gsfc.nasa.gov