Modelling nitrogen fluxes in oligotrophic environments: NW Mediterranean and NE Atlantic

Stocks and fluxes of nitrogen in two oligotrophic ecosystems are evaluated using a vertically resolved turbulence-driven ecological model. The model simulates the intra-annual variability of the ecological processes in the upper 300 m of the water column in the Catalan Sea (CS), northwestern Mediterranean, and in the subtropical northeast Atlantic (NEA). Higher irradiance and daylight length making the euphotic layer thicker, together with a higher mixing layer depth explained that the phytoplankton maximum was deeper in NEA than in CS during summertime. In general, the amount of irradiance appears to control the chlorophyll maximum depth while the amount of nitrate transported from the bottom boundary is mainly constraining the phytoplankton stocks. The summer chlorophyll maximum was found at depths below the thermocline and close to the nitracline. In both locations, zooplankton grazing controlled the late winter phytoplankton bloom but reduced more than expected the subsurface phytoplankton concentration in summer. The nitrite maximum was successfully simulated to be close to the chlorophyll maximum, explained by the phytoplankton reduction of nitrate in the dark. The yearly estimates of upward fluxes of nitrate to the euphotic zone were variable depending on the horizon at which fluxes were computed. Just below the euphotic zone, the upward fluxes of nitrate were 0.64 and 0.22 mol N m −2 in the CS and NEA, respectively, more closely connected to the variation of the nitrogen gradient than to the density field. © 2003 Elsevier Science B.V. All rights reserved.

[1]  A. Herbland,et al.  Hydrological structure analysis for estimating the primary production in the tropical Atlantic Ocean , 1979 .

[2]  J. Tintoré,et al.  Modelling the deep-chlorophyll maximum : a coupled physical-biological approach , 1992 .

[3]  L. Prieur,et al.  A numerical study of primary production related to vertical turbulent diffusion with special reference to vertical motions of the phytoplankton cells in nutrient and light fields , 1994 .

[4]  T. Platt,et al.  Basin-scale estimates of oceanic primary production by remote sensing - The North Atlantic , 1991 .

[5]  J. Ryther,et al.  The annual cycle of primary production in the Sargasso Sea off Bermuda , 1959 .

[6]  J. Annan,et al.  The influence of different turbulence schemes on modelling primary production in a 1D coupled physical–biological model , 2000 .

[7]  L. Prieur,et al.  Biological and chemical signs of upward motions in permanent geostrophic fronts of the western Mediterranean , 1998 .

[8]  G. Hurtt,et al.  A pelagic ecosystem model calibrated with BATS data , 1996 .

[9]  W. Jenkins,et al.  Nitrate flux into the euphotic zone near Bermuda , 1988, Nature.

[10]  A. Longhurst.  Analysis of Marine Ecosystems , 1981 .

[11]  R. Goericke,et al.  Response of Sargasso Sea phytoplankton biomass, growth rates and primary production to seasonally varying physical forcing , 1998 .

[12]  D. Antoine,et al.  Algal pigment distribution and primary production in the eastern Mediterranean as derived from coastal zone color scanner observations , 1995 .

[13]  T. Platt,et al.  Vertical Nitrate Fluxes in the Oligotrophic Ocean , 1986, Science.

[14]  Andrew M. Edwards,et al.  The role of higher predation in plankton population models , 2000 .

[15]  G. Evans,et al.  The role of local models and data sets in the Joint Global Ocean Flux Study , 1999 .

[16]  J. Ryther,et al.  Annual variations in primary production of the Sargasso sea off Bermuda , 1961 .

[17]  M. Alcaraz.  Summer zooplankton metabolism and its relation to primary production in the western Mediterranean , 1988 .

[18]  David M. Glover,et al.  A new coupled, one-dimensional biological-physical model for the upper ocean: Applications to the JGOFS Bermuda Atlantic Time-series Study (BATS) site , 1996 .

[19]  N. Guixa-Boixereu,et al.  Bacterioplankton and phytoplankton biomass and production during summer stratification in the northwestern Mediterranean Sea , 1999 .

[20]  Frank J. Millero,et al.  International one-atmosphere equation of state of seawater , 1981 .

[21]  R. Bidigare,et al.  Nutrients and mixing, chlorophyll and phytoplankton growth , 1990 .

[22]  Patrick M. Holligan,et al.  Phytoplankton distribution and survival in the thermocline , 2001 .

[23]  S. Doney.  Major challenges confronting marine biogeochemical modeling , 1999 .

[24]  T. Osborn,et al.  Estimates of the Local Rate of Vertical Diffusion from Dissipation Measurements , 1980 .

[25]  Edward B. Rastetter,et al.  Validating models of ecosystem response to global change , 1996 .

[26]  J. Salat.  The interaction between the Catalan and Balearic currents in the southern Catalan Sea , 1995 .

[27]  J. Kremer,et al.  Origins of vertical patterns of phytoplankton and nutrients in the temperate, open ocean: a stratigraphic hypothesis , 1981 .

[28]  K. Baker,et al.  Relation between photosynthetically available radiation and total insolation at the ocean surface under clear skies1 , 1987 .

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

[30]  M. Follows,et al.  The Ekman transfer of nutrients and maintenance of new production over the North Atlantic , 1998 .

[31]  A. Carril,et al.  Climate change scenarios over the South American region: an intercomparison of coupled general atmosphere‐ocean circulation models , 1997 .

[32]  Thomas D. Brock,et al.  Calculating solar radiation for ecological studies , 1981 .

[33]  A. Morel,et al.  Pigment distribution and primary production in the western Mediterranean as derived and modeled from coastal zone color scanner observations , 1991 .

[34]  P. Raimbault.  Effect of temperature on nitrite excretion by three marine diatoms during nitrate uptake , 1986 .

[35]  Dag L. Aksnes,et al.  Modelling the primary production in the North Sea using a coupled three-dimensional physical-chemical-biological ocean model , 1995 .

[36]  Nicolas Gruber,et al.  Global patterns of marine nitrogen fixation and denitrification , 1997 .

[37]  J. Toggweiler,et al.  A seasonal three‐dimensional ecosystem model of nitrogen cycling in the North Atlantic Euphotic Zone , 1993 .

[38]  J. Tintoré,et al.  A simulation analysis of various biological and physical factors influencing the deep-chlorophyll maximum structure in oligotrophic areas , 1994 .

[39]  T. Platt,et al.  An estimate of global primary production in the ocean from satellite radiometer data , 1995 .

[40]  M. Lévy,et al.  Simulation of primary production and export è uxes in the Northwestern Mediterranean Sea , 1998 .

[41]  B. Tassin,et al.  1-D coupled physical-biological model of the northwestern Mediterranean Sea , 1997 .

[42]  T. Platt,et al.  Biogenic fluxes of carbon and oxygen in the ocean , 1985, Nature.

[43]  P. Malanotte‐Rizzoli,et al.  Simulations of phytoplankton seasonal cycle with multi-level and multi-layer physical-ecosystem models: the Black Sea example , 2001 .

[44]  Ann E. Gargett,et al.  Time and space scales of vertical mixing and advection of phytoplankton in the upper ocean , 1983 .

[45]  J. Sarmiento,et al.  Oceanic vertical exchange and new production: a comparison between models and observations , 2001 .

[46]  Temel Oguz,et al.  Simulation of annual plankton productivity cycle in the Black Sea by a one‐dimensional physical‐biological model , 1996 .

[47]  J. Goering,et al.  UPTAKE OF NEW AND REGENERATED FORMS OF NITROGEN IN PRIMARY PRODUCTIVITY1 , 1967 .

[48]  H. Ducklow,et al.  A nitrogen-based model of plankton dynamics in the oceanic mixed layer , 1990 .

[49]  H. Claustre,et al.  Prochlorococcus and Synechococcus: A comparative study of their optical properties in relation to their size and pigmentation , 1993 .

[50]  Trevor Platt,et al.  Regionally and seasonally differentiated primary production in the North Atlantic , 1995 .

[51]  E. Kraus.  Modelling and prediction of the upper layers of the ocean , 1977 .

[52]  J. Ryther,et al.  Marine Phytoplankton and the Distribution of Nitrite in the Sea , 1960 .

[53]  M. Estrada,et al.  Spatio-temporal variability of the winter phytoplankton distribution across the Catalan and North Balearic fronts (NW Mediterranean) , 1999 .

[54]  A. Robinson,et al.  Eddy-induced nutrient supply and new production in the Sargasso Sea , 1997 .

[55]  E. Hartwig,et al.  Biological production of nitrite in seawater , 1970 .

[56]  K. Johnson,et al.  Interrelationships among primary production, chlorophyll, and environmental conditions in frontal regions of the western Mediterranean Sea , 1988 .

[57]  Jonathan Sharples,et al.  Investigating the seasonal vertical structure of phytoplankton in shelf seas , 1999 .

[58]  S. Agustí,et al.  Nitrate uptake and diffusive nitrate supply in the Central Atlantic , 1999 .

[59]  Zoila Rosa Velasquez Forero.  Fitoplancton en el Mediterráneo noroccidental , 1998 .

[60]  C. Lancelot,et al.  Ecology of Phaeocystis-dominated ecosystems , 1994 .

[61]  P. Falkowski,et al.  Physiological stress and cell death in marine phytoplankton: Induction of proteases in response to nitrogen or light limitation , 1998 .

[62]  Patrick M. Holligan,et al.  Basin-scale variability of phytoplankton biomass, production and growth in the Atlantic Ocean , 2000 .

[63]  J. Dunne,et al.  Biogeochemical controls on new production in the tropical Pacific , 2002 .

[64]  W. Perry,et al.  Bacterioplankton and Phytoplankton Populations in a Rapidly-Flushed Eutrophic Reservoir , 1990 .

[65]  B. Peterson,et al.  Particulate organic matter flux and planktonic new production in the deep ocean , 1979, Nature.