Nutrient trapping in the equatorial Pacific: The ocean circulation solution

Nutrient trapping is a chronic problem found in global carbon cycle models with particle‐only remineralization schemes. It is defined as the excess of subsurface nutrient concentrations relative to observations and occurs principally in the eastern equatorial Pacific. Previous studies reduced excess simulated nutrients by increasing the complexity of modeled biogeochemistry, i.e., by adding pools for nutrients (and carbon) either in dissolved organic form or as plankton. Conversely, our study suggests that deficiencies in modeled circulation fields from global coarse‐resolution ocean models are mostly responsible. This new interpretation stems from our use of an ocean general circulation model with higher resolution, which offers a more realistic equatorial circulation. We used the same biogeochemical model Hamburg ocean carbon cycle model, version 3, as in some of the previous studies. Our model‐predicted distribution of PO43− in the equatorial Pacific agrees reasonably well with the observations both at the surface and in the subsurface. Subsurface PO43− concentrations in our model's eastern equatorial Pacific exceed observations by, at most, 15%, unlike coarser‐resolution models. Improvement is due to enhanced meridional resolution (0.5°) near the equator, which allows the model to simulate a vigorous equatorial undercurrent that brings in low‐nutrient water from the western basin. Furthermore, the model upwells no nutrient‐rich abyssal water into the surface equatorial Pacific. Our results suggest that dissolved organic carbon plays a minor role in the carbon budget of the equatorial Pacific.

[1]  G. Madec,et al.  A degradation approach to accelerate simulations to steady-state in a 3-D tracer transport model of the global ocean , 1998 .

[2]  Yasuhiro Yamanaka,et al.  Role of dissolved organic matter in the marine biogeochemical cycle: Studies using an ocean biogeochemical general circulation model , 1997 .

[3]  E. Peltzer,et al.  A timescale for dissolved organic carbon production in equatorial Pacific surface waters , 1997 .

[4]  J. Boutin,et al.  Long‐term variability of the air‐sea CO2 exchange coefficient: Consequences for the CO2 fluxes in the equatorial Pacific Ocean , 1997 .

[5]  O. Marti,et al.  Adjustment and feedbacks in a global coupled ocean-atmosphere model , 1997 .

[6]  R. Weisberg,et al.  The Zonal Momentum Balance of the Equatorial Undercurrent in the Central Pacific , 1997 .

[7]  Bruno Blanke,et al.  Kinematics of the Pacific Equatorial Undercurrent: An Eulerian and Lagrangian Approach from GCM Results , 1997 .

[8]  P. Delecluse,et al.  Sensitivity of an Equatorial Pacific OGCM to the Lateral Diffusion , 1997 .

[9]  Dennis A. Hansell,et al.  Predominance of vertical loss of carbon from surface waters of the equatorial Pacific Ocean , 1997, Nature.

[10]  E. Guilyardi,et al.  Performance of the OPA/ARPEGE-T21 global ocean-atmosphere coupled model , 1997 .

[11]  Katharina D. Six,et al.  Effects of plankton dynamics on seasonal carbon fluxes in an ocean general circulation model , 1996 .

[12]  Raphael Kudela,et al.  A massive phytoplankton bloom induced by an ecosystem-scale iron fertilization experiment in the equatorial Pacific Ocean , 1996, Nature.

[13]  Y. Yamanaka,et al.  The role of the vertical fluxes of particulate organic matter and calcite in the oceanic carbon cycle: Studies using an ocean biogeochemical general circulation model , 1996 .

[14]  Gurvan Madec,et al.  A global ocean mesh to overcome the North Pole singularity , 1996 .

[15]  L. A. Anderson,et al.  Global ocean phosphate and oxygen simulations , 1995 .

[16]  Richard J. Matear,et al.  Modeling the inorganic phosphorus cycle of the North Pacific using an adjoint data assimilation model to assess the role of dissolved organic phosphorus , 1995 .

[17]  M. Mcphaden,et al.  Seasonal variability in the surface currents of the equatorial Pacific , 1994 .

[18]  R. Feely,et al.  Physical and Biological Controls on Carbon Cycling in the Equatorial Pacific , 1994, Science.

[19]  E. Maier‐Reimer,et al.  El Niño‐Southern Oscillation related fluctuations of the marine carbon cycle , 1994 .

[20]  E. Maier‐Reimer,et al.  Geochemical cycles in an Ocean General Circulation Model , 1993 .

[21]  Bruno Blanke,et al.  Variability of the Tropical Atlantic Ocean Simulated by a General Circulation Model with Two Different Mixed-Layer Physics , 1993 .

[22]  P. Poulain.  Estimates of Horizontal Divergence and Vertical Velocity in the Equatorial Pacific , 1993 .

[23]  Klaus Hasselmann,et al.  Mean Circulation of the Hamburg LSG OGCM and Its Sensitivity to the Thermohaline Surface Forcing , 1993 .

[24]  C. S. Wong,et al.  Changes in equatorial CO2 flux and new production estimated from CO2 and nutrient levels in Pacific surface waters during the 1986/87 El Niño , 1993 .

[25]  J. Bauer,et al.  Cycling of dissolved and particulate organic matter in the open ocean , 1992 .

[26]  Frank Wentz,et al.  Measurement of oceanic wind vector using satellite microwave radiometers , 1992, IEEE Trans. Geosci. Remote. Sens..

[27]  P. Delecluse,et al.  Comment [on “Net diffusivity in ocean general circulation models with nonuniform grids” by F. L. Yin and I. Y. Fung] , 1992 .

[28]  K. Buesseler,et al.  Carbon and nitrogen export during the JGOFS North Atlantic Bloom experiment estimated from 234Th: 238U disequilibria , 1992 .

[29]  R. Wanninkhof.  Relationship between wind speed and gas exchange over the ocean , 1992 .

[30]  J. Toggweiler,et al.  Downward transport and fate of organic matter in the ocean: Simulations with a general circulation model , 1992 .

[31]  W. Broecker,et al.  The Peru Upwelling and the Ventilation of the South Pacific Thermocline , 1991 .

[32]  E. Maier‐Reimer,et al.  Dissolved organic carbon in modeling oceanic new production , 1991 .

[33]  N. Imasato,et al.  Diagnostic calculation for circulation and water mass movement in the deep Pacific , 1991 .

[34]  Philippe Gaspar,et al.  A simple eddy kinetic energy model for simulations of the oceanic vertical mixing: Tests at Station Papa and long-term upper ocean study site , 1990 .

[35]  E. Maier‐Reimer,et al.  Ocean-circulation model of the carbon cycle , 1990 .

[36]  Keith W. Dixon,et al.  Simulations of radiocarbon in a coarse-resolution world ocean model: 1. Steady state prebomb distributions , 1989 .

[37]  Yoshimi Suzuki,et al.  A high-temperature catalytic oxidation method for the determination of non-volatile dissolved organic carbon in seawater by direct injection of a liquid sample , 1988 .

[38]  E. Druffel,et al.  Radiocarbon in dissolved organic matter in the central North Pacific Ocean , 1987, Nature.

[39]  F. Chavez,et al.  An estimate of new production in the equatorial Pacific , 1987 .

[40]  P. Smolarkiewicz,et al.  The multidimensional positive definite advection transport algorithm: further development and applications , 1986 .

[41]  W. Broecker,et al.  The distribution of bomb radiocarbon in the ocean , 1985 .

[42]  Yoshimi Suzuki,et al.  A catalytic oxidation method for the determination of total nitrogen dissolved in seawater , 1985 .

[43]  Bernard Kilonsky,et al.  Mean Water and Current Structure during the Hawaii-to-Tahiti Shuttle Experiment , 1984 .

[44]  Sol Hellerman,et al.  Normal Monthly Wind Stress Over the World Ocean with Error Estimates , 1983 .

[45]  P. Smolarkiewicz.  A Simple Positive Definite Advection Scheme with Small Implicit Diffusion , 1983 .

[46]  P. Smolarkiewicz.  The Multi-Dimensional Crowley Advection Scheme , 1982 .

[47]  S. Levitus.  Climatological Atlas of the World Ocean , 1982 .

[48]  K. Wyrtki.  An Estimate of Equatorial Upwelling in the Pacific , 1981 .

[49]  M. Tsuchiya.  The Origin of the Pacific Equatorial 13°C Water , 1981 .

[50]  Richard C. Dugdale,et al.  NUTRIENT LIMITATION IN THE SEA: DYNAMICS, IDENTIFICATION, AND SIGNIFICANCE1 , 1967 .

[51]  P. Delecluse,et al.  OPA 8.1 Ocean General Circulation Model reference manual , 1998 .

[52]  J. Newton,et al.  Export flux of particulate organic carbon from the central equatorial Pacific determined using a combined drifting trap-234Th approach , 1996 .

[53]  H. Ducklow,et al.  Dissolved organic carbon in the upper ocean of the central equatorial Pacific Ocean, 1992: Daily and finescale vertical variations , 1995 .

[54]  Yoshimi Suzuki.  On the measurement of DOC and DON in seawater , 1993 .

[55]  J. Toggweiler,et al.  New Radiocarbon Constraints on the Upwelling of Abyssal Water to the Ocean’s Surface , 1993 .

[56]  Olivier Marti.  Etude de l'ocean mondial : modelisation de la circulation et du transport des traceurs anthropogeniques , 1992 .

[57]  L. Merlivat,et al.  Air-Sea Gas Exchange Rates: Introduction and Synthesis , 1986 .

[58]  R. Lukas.  The termination of the Equatorial Undercurrent in the eastern Pacific , 1986 .

[59]  Akio Arakawa,et al.  Computational Design of the Basic Dynamical Processes of the UCLA General Circulation Model , 1977 .

[60]  K. Wyrtki.  The horizontal and vertical field of motion in the Peru Current , 1963 .