A coupled ocean‐ecosystem model of the Ross Sea: 2. Iron regulation of phytoplankton taxonomic variability and primary production

[1] A model of the Ross Sea pelagic ecosystem has been developed by incorporating biological and nutrient dynamics into an ocean general circulation model. Surface heat and salt fluxes are calculated in the model using sea ice concentrations that are specified daily using the 20 year climatology derived from passive microwave satellite data. Surface spectral irradiance is calculated and propagated through both the water column and the sea ice. The biological state variables include two phytoplankton groups (diatoms and Phaeocystis antarctica), two nutrients (NO3 and Fe), detritus, and zooplankton. Nutrients are supplied to the sea surface from upwelling of nutrient-rich deep waters, and in the case of Fe, from melting sea ice and snow which have accumulated aeolian-derived Fe during the preceding autumn and winter. Phytoplankton growth rate is computed as a function of light or nutrient limitation. The model is able to accurately simulate the temporal evolution of the two well-described phytoplankton blooms that dominate the southwestern Ross Sea: the diatom bloom in the shallow mixed layer of the western continental shelf (including Terra Nova Bay) and the P. antarctica bloom in the more deeply mixed Ross Sea polynya region. The simulated temporal progression of both phytoplankton blooms as well as their magnitude of primary production are in good agreement with time series estimates made using satellite ocean color data as validated by in situ observations. Model results suggest that Fe availability controls annual primary production in the Ross Sea, with only about two thirds of the available macronutrients in surface waters being consumed during the course of the bloom, but that Fe has little role in determining phytoplankton community composition. Rather, the taxonomic composition of the phytoplankton blooms is determined by the differential responses of shade-adapted P. antarctica and high light-adapted diatoms to the different mixing (and hence light) regimes within the Ross Sea. The model also predicts the development of a previously undescribed phytoplankton bloom along the eastern continental shelf, just north of the Ross Ice Shelf. The physical environment of this third phytoplankton bloom differs from that of the western shelf and the Ross Sea polynya region in that it receives a larger input of sea ice-derived Fe and experiences complete exhaustion of surface NO3. Consequently, annual production on the eastern continental shelf is higher than anywhere else in the Ross Sea and supports an unusually large grazer population.

[1]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[2]  K. Timmermans,et al.  Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean , 1999 .

[3]  G. Kattner,et al.  Dissolved iron at subnanomolar levels in the Southern Ocean as determined by ship-board analysis , 1998 .

[4]  K. Arrigo,et al.  � 2003, by the American Society of Limnology and Oceanography, Inc. Anomalously low zooplankton abundance in the Ross Sea: An alternative explanation , 2022 .

[5]  W. Smith,et al.  Photosynthesis/irradiance relationships in the Ross Sea, Antarctica, and their control by phytoplankton assemblage composition and environmental factors , 2002 .

[6]  K. Carder,et al.  A simple spectral solar irradiance model for cloudless maritime atmospheres , 1990 .

[7]  D. H. Robinson,et al.  Bio‐optical properties of the southwestern Ross Sea , 1998 .

[8]  R. Dunbar,et al.  Water column sediment fluxes in the Ross Sea, Antarctica: Atmospheric and sea ice forcing , 1998 .

[9]  W. Cochlan,et al.  Trace metals and nitrogenous nutrition of Antarctic phytoplankton: experimental observations in the Ross Sea , 2002 .

[10]  M. Lipizer,et al.  Nutrient depletions in the Ross Sea and their relation with pigment stocks , 2000 .

[11]  D. Bromwich,et al.  Satellite Observations of Katabatic-Wind Propagation for Great Distances across the Ross Ice Shelf , 1992 .

[12]  B. Mitchell,et al.  Spatial and temporal distribution of phytoplankton and primary production in the western Bransfield Strait region , 1991 .

[13]  D. H. Robinson,et al.  Phytoplankton taxonomic variability in nutrient utilization and primary production in the Ross Sea , 2000 .

[14]  T. Markus.  Results from an ECMWF-SSM/I forced mixed layer model of the Southern Ocean , 1999 .

[15]  Donald J. Cavalieri,et al.  Reduction of weather effects in the calculation of sea ice concentration from microwave radiances , 1986 .

[16]  D. Biggs.  Zooplankton excretion and NH4+ cycling in near-surface waters of the Southern Ocean. I. Ross sea, austral summer 1977–1978 , 1982, Polar Biology.

[17]  Kevin R. Arrigo,et al.  Primary production in Southern Ocean waters , 1998 .

[18]  Dennis A. Hansell,et al.  ESTIMATION OF BACTERIAL RESPIRATION AND GROWTH EFFICIENCY IN THE ROSS SEA,ANTARCTICA , 1999 .

[19]  B. Quéguiner,et al.  Limitation of algal growth by iron deficiency in the Australian Subantarctic Region , 1999 .

[20]  S. Wright,et al.  Phytoplankton community structure and stocks in the East Antarctic marginal ice zone (BROKE survey, January-March 1996) determined by CHEMTAX analysis of HPLC pigment signatures , 2000 .

[21]  C. Jeandel,et al.  Dissolved inorganic carbon, alkalinity, nutrient and oxygen seasonal and interannual variations at the Antarctic Ocean JGOFS-KERFIX site , 2001 .

[22]  H. Ducklow,et al.  Constraining bacterial production, conversion efficiency and respiration in the Ross Sea, Antarctica, January–February, 1997 , 2000 .

[23]  S. Levitus,et al.  World ocean atlas 1994. Volume 1, Nutrients , 1994 .

[24]  D. M. Nelson,et al.  sedimentary fluxes on the Ross Sea continental shelf , 1996 .

[25]  A. Artegiani,et al.  Copepod Communities in the Pacific Sector of the Southern Ocean in Early Summer , 2000 .

[26]  K. Johnson,et al.  Trace metal concentrations in the Ross Sea and their relationship with nutrients and phytoplankton growth , 2000 .

[27]  C. S. Holling.  The components of prédation as revealed by a study of small-mammal prédation of the European pine sawfly. , 1959 .

[28]  Koji Suzuki,et al.  The distribution of Fe in the Australian sector of the Southern Ocean , 2000 .

[29]  D. H. Robinson,et al.  Phytoplankton community structure and the drawdown of nutrients and CO2 in the southern ocean , 1999, Science.

[30]  S. Fitzwater,et al.  Iron in Antarctic waters , 1990, Nature.

[31]  K. Arrigo,et al.  Spring Phytoplankton Production in the Western Ross Sea , 1994, Science.

[32]  D. Bromwich,et al.  Katabatic wind forcing of the Terra Nova Bay polynya , 1984 .

[33]  G. Jacques,et al.  Some ecophysiological aspects of the Antarctic phytoplankton , 1983, Polar Biology.

[34]  K. Johnson,et al.  A model of the iron cycle in the ocean , 2000 .

[35]  G. Mellor,et al.  Development of a turbulence closure model for geophysical fluid problems , 1982 .

[36]  J. C. Goldman.  Potential role of large oceanic diatoms in new primary production , 1993 .

[37]  G. Mellor,et al.  A Hierarchy of Turbulence Closure Models for Planetary Boundary Layers. , 1974 .

[38]  B. Mitchell,et al.  Bio-optical properties of Antarctic Peninsula waters: differentiation from temperate ocean models , 1991 .

[39]  P. Sedwick,et al.  Iron and manganese in surface waters of the Australian subantarctic region , 1997 .

[40]  M. C. Newman,et al.  The practice of structure activity relationships (SAR) in toxicology. , 2000, Toxicological sciences : an official journal of the Society of Toxicology.

[41]  P. Sedwick,et al.  Iron and Manganese in the Ross Sea, Antarctica: Seasonal Iron Limitation in Antarctic Shelf Waters , 2000 .

[42]  D. M. Nelson,et al.  Phytoplankton Bloom Produced by a Receding Ice Edge in the Ross Sea: Spatial Coherence with the Density Field , 1985, Science.

[43]  David H. Bromwich,et al.  Satellite analyses of Antarctic katabatic wind behavior , 1989 .

[44]  W. Campbell,et al.  Determination of sea ice parameters with the NIMBUS 7 SMMR , 1984 .

[45]  D. Hutchins,et al.  An iron limitation mosaic in the California upwelling regime , 1998 .

[46]  W. Smith,et al.  Hyperproductivity of the Ross Sea (Antarctica) polynya during austral spring , 1997 .

[47]  H. Ducklow,et al.  BACTERIAL GROWTH IN EXPERIMENTAL PLANKTON ASSEMBLAGES AND SEAWATER CULTURES FROM THE PHAEOCYSTIS ANTARCTICA BLOOM IN THE ROSS SEA, ANTARCTICA , 1999 .

[48]  K. Arrigo,et al.  Distributions of Phytoplankton Blooms in the Southern Ocean , 1993, Science.

[49]  B. Mitchell,et al.  Light limitation of phytoplankton biomass and macronutrient utilization in the Southern Ocean , 1991 .

[50]  P. Boyd,et al.  Role of iron, light, and silicate in controlling algal biomass in subantarctic waters SE of New Zealand , 1999 .

[51]  F. Dehairs,et al.  The distribution of Fe in the antarctic circumpolar current , 1997 .

[52]  V. Smetácek,et al.  Importance of iron for plankton blooms and carbon dioxide drawdown in the Southern Ocean , 1995, Nature.

[53]  W. Cochlan,et al.  Nitrogen uptake kinetics in the Ross Sea, Antarctica , 2001 .

[54]  W. Broecker,et al.  Factors limiting the reduction of atmospheric CO2 by iron fertilization , 1991 .

[55]  D. Caron,et al.  Microzooplankton herbivory in the Ross Sea, Antarctica , 2000 .

[56]  V. Asper,et al.  The influence of phytoplankton assemblage composition on biogeochemical characteristics and cycles in the southern Ross Sea, Antarctica , 2001 .

[57]  C. L. Leonard,et al.  Coastal zone color scanner pigment concentrations in the Southern Ocean and relationships to geophysical surface features , 1993 .

[58]  R. Goericke,et al.  Phytoplankton growth and herbivory in the subarctic Pacific: A chemotaxonomic analysis , 1991 .

[59]  Ulrich Sommer,et al.  Nitrate- and silicate-competition among antarctic phytoplankton , 1986 .

[60]  J. Sarmiento,et al.  Three‐dimensional simulations of the impact of Southern Ocean nutrient depletion on atmospheric CO2 and ocean chemistry , 1991 .

[61]  E. Wood,et al.  Microbiology of Antarctic Sea-ice: Microalgae and Antarctic Sea-ice , 1963, Nature.

[62]  André Morel,et al.  Available, usable, and stored radiant energy in relation to marine photosynthesis , 1978 .

[63]  P. Sedwick,et al.  Regulation of algal blooms in Antarctic Shelf Waters by the release of iron from melting sea ice , 1997 .

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

[65]  K. Banse.  Rates of phytoplankton cell division in the field and in iron enrichment experiments , 1991 .

[66]  B. Greg Mitchell,et al.  Xanthophyll cycling in Phaeocystis antarctica:changes in cellular fluorescence , 1998 .

[67]  A. H. Taylor,et al.  Seasonal succession in the pelagic ecosystem of the North Atlantic and the utilization of nitrogen , 1993 .

[68]  Dennis A. Hansell,et al.  Organic carbon partitioning during spring phytoplankton blooms in the Ross Sea polynya and the Sargasso Sea , 1998 .

[69]  A. Goffart,et al.  Factors controlling the distribution of diatoms and Phaeocystis in the Ross Sea , 2000 .

[70]  B. Mitchell,et al.  Photophysiological acclimation of Phaeocystis antarctica Karsten under light limitation , 1999 .

[71]  W. Richard,et al.  TEMPERATURE AND PHYTOPLANKTON GROWTH IN THE SEA , 1972 .

[72]  Andrew J. Watson,et al.  A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization , 2000, Nature.

[73]  D. Caron,et al.  Abundance and distribution of phototrophic and heterotrophic nano- and microplankton in the southern Ross Sea , 2001 .

[74]  P. Sedwick,et al.  Iron in East Antarctic snow: Implications for atmospheric iron deposition and algal production in Antarctic waters , 2001 .

[75]  B. Prézelin,et al.  The linkage between Upper Circumpolar Deep Water (UCDW) and phytoplankton assemblages on the west Antarctic Peninsula continental shelf , 2000 .

[76]  R. Chervin,et al.  Physical forcing of phytoplankton dynamics in the southwestern Ross Sea (Paper 97JC02326) , 1998 .

[77]  D. M. Nelson,et al.  Importance of Ice Edge Phytoplankton Production in the Southern Ocean , 1986 .

[78]  Dennis A. Hansell,et al.  Nutrient and carbon removal ratios and fluxes in the Ross Sea , 2000 .