FeCycle: Attempting an iron biogeochemical budget from a mesoscale SF6 tracer experiment in unperturbed low iron waters

An improved knowledge of iron biogeochemistry is needed to better understand key controls on the functioning of high‐nitrate low‐chlorophyll (HNLC) oceanic regions. Iron budgets for HNLC waters have been constructed using data from disparate sources ranging from laboratory algal cultures to ocean physics. In summer 2003 we conducted FeCycle, a 10‐day mesoscale tracer release in HNLC waters SE of New Zealand, and measured concurrently all sources (with the exception of aerosol deposition) to, sinks of iron from, and rates of iron recycling within, the surface mixed layer. A pelagic iron budget (timescale of days) indicated that oceanic supply terms (lateral advection and vertical diffusion) were relatively small compared to the main sink (downward particulate export). Remote sensing and terrestrial monitoring reveal 13 dust or wildfire events in Australia, prior to and during FeCycle, one of which may have deposited iron at the study location. However, iron deposition rates cannot be derived from such observations, illustrating the difficulties in closing iron budgets without quantification of episodic atmospheric supply. Despite the threefold uncertainties reported for rates of aerosol deposition (Duce et al., 1991), published atmospheric iron supply for the New Zealand region is ∼50‐fold (i.e., 7‐ to 150‐fold) greater than the oceanic iron supply measured in our budget, and thus was comparable (i.e., a third to threefold) to our estimates of downward export of particulate iron. During FeCycle, the fluxes due to short term (hours) biological iron uptake and regeneration were indicative of rapid recycling and were tenfold greater than for new iron (i.e. estimated atmospheric and measured oceanic supply), giving an “fe” ratio (uptake of new iron/uptake of new + regenerated iron) of 0.17 (i.e., a range of 0.06 to 0.51 due to uncertainties on aerosol iron supply), and an “Fe” ratio (biogenic Fe export/uptake of new + regenerated iron) of 0.09 (i.e., 0.03 to 0.24).

[1]  P. Boyd,et al.  Particulate iron dynamics during FeCycle in subantarctic waters southeast of New Zealand , 2006 .

[2]  P. Boyd,et al.  Spinning the “Ferrous Wheel”: The importance of the microbial community in an iron budget during the FeCycle experiment , 2005 .

[3]  M. Pinkerton,et al.  Temporal coupling between surface and deep ocean biogeochemical processes in contrasting subtropical and subantarctic water masses, southwest Pacific Ocean , 2005 .

[4]  S. Sander,et al.  Acquisition of iron bound to strong organic complexes, with different Fe binding groups and photochemical reactivities, by plankton communities in Fe‐limited subantarctic waters , 2005 .

[5]  P. Boyd,et al.  Impact of phytoplankton on the biogeochemical cycling of iron in subantarctic waters southeast of New Zealand during FeCycle , 2005 .

[6]  Sara M. Handy,et al.  Tracking changes in bioavailable Fe within high‐nitrate low‐chlorophyll oceanic waters: A first estimate using a heterotrophic bacterial bioreporter , 2005 .

[7]  N. Mahowald,et al.  Global Iron Connections Between Desert Dust, Ocean Biogeochemistry, and Climate , 2005, Science.

[8]  B. Sulzberger,et al.  Effect of siderophores on the light-induced dissolution of colloidal iron(III) (hydr)oxides , 2005 .

[9]  A. Baker,et al.  Short residence time for iron in surface seawater impacted by atmospheric dry deposition from Saharan dust events , 2004 .

[10]  Yoon-Seok Chang,et al.  Determination of diapycnal diffusion rates in the upper thermocline in the North Atlantic Ocean using sulfur hexafluoride , 2004 .

[11]  S. Baines,et al.  Cellular iron contents of plankton during the Southern Ocean Iron Experiment (SOFeX) , 2004 .

[12]  S. Baines,et al.  Element stoichiometries of individual plankton cells collected during the Southern Ocean Iron Experiment (SOFeX) , 2004 .

[13]  J. Hein,et al.  The global variation in the iron isotope composition of marine hydrogenetic ferromanganese deposits: implications for seawater chemistry? , 2004 .

[14]  P. Liss,et al.  Iron‐induced changes in oceanic sulfur biogeochemistry , 2004 .

[15]  M. Ellwood.  Zinc and cadmium speciation in subantarctic waters east of New Zealand , 2004 .

[16]  William Miller,et al.  The decline and fate of an iron-induced subarctic phytoplankton bloom , 2004, Nature.

[17]  P. Boyd,et al.  Episodic enhancement of phytoplankton stocks in New Zealand subantarctic waters: Contribution of atmospheric and oceanic iron supply , 2004 .

[18]  E. Boyle,et al.  Modeling the global ocean iron cycle , 2004 .

[19]  M. Pinkerton,et al.  Validation of SeaWiFS data from around New Zealand , 2004 .

[20]  M. Franka,et al.  The global variation in the iron isotope composition of marine hydrogenetic ferromanganese deposits : implications for seawater chemistry ? , 2004 .

[21]  B. Applegate,et al.  Characterization and field trials of a bioluminescent bacterial reporter of iron bioavailability , 2003 .

[22]  A. Watson,et al.  Vertical eddy diffusion and nutrient supply to the surface mixed layer of the Antarctic Circumpolar Current , 2003 .

[23]  D. Hutchins,et al.  A trace metal clean reagent to remove surface-bound iron from marine phytoplankton , 2003 .

[24]  F. Morel,et al.  The Biogeochemical Cycles of Trace Metals in the Oceans , 2003, Science.

[25]  D. M. Nelson,et al.  Ratios of Si, C and N uptake by microplankton in the Southern Ocean , 2003 .

[26]  S. Doney,et al.  The Impact of Climate Change and Feedback Processes on the Ocean Carbon Cycle , 2003 .

[27]  P. Harrison,et al.  Temporal Studies of Biogeochemical Processes Determined from Ocean Time-Series Observations During the JGOFS Era , 2003 .

[28]  M. Fasham,et al.  Ocean biogeochemistry: the role of the ocean carbon cycle in global change , 2003 .

[29]  E. Boyle,et al.  Iron in the Sargasso Sea: Implications for the processes controlling dissolved Fe distribution in the ocean , 2002 .

[30]  P. Boyd,et al.  ENVIRONMENTAL FACTORS CONTROLLING PHYTOPLANKTON PROCESSES IN THE SOUTHERN OCEAN1 , 2002 .

[31]  H. Ohmoto,et al.  Dissolution of iron hydroxides by marine bacterial siderophore , 2002 .

[32]  P. Boyd.  The role of iron in the biogeochemistry of the Southern Ocean and equatorial Pacific: a comparison of in situ iron enrichments , 2002 .

[33]  D. Turner,et al.  The Biogeochemistry of Iron in Seawater , 2001 .

[34]  Kenneth W. Bruland,et al.  Iron and macronutrients in California coastal upwelling regimes: Implications for diatom blooms , 2001 .

[35]  P. Boyd,et al.  Retention of dissolved iron and Fe II in an iron induced Southern Ocean phytoplankton bloom , 2001 .

[36]  T. Jickells,et al.  Atmospheric iron inputs to the oceans , 2001 .

[37]  P. Boyd,et al.  Iron-mediated changes in phytoplankton photosynthetic competence during SOIREE , 2001 .

[38]  P. Worsfold,et al.  The fate of added iron during a mesoscale fertilisation experiment in the Southern Ocean , 2001 .

[39]  Adrian P. Martin,et al.  A Lagrangian SF6 tracer study of an anticyclonic eddy in the North Atlantic: patch evolution, vertical mixing and nutrient supply to the mixed layer , 2001 .

[40]  A. Bowie,et al.  Macronutrient and trace-metal geochemistry of an in situ iron-induced Southern Ocean bloom , 2001 .

[41]  J. Moffett,et al.  Laboratory and field studies of colloidal iron oxide dissolution as mediated by phagotrophy and photolysis , 2000 .

[42]  S. Doney,et al.  Iron supply and demand in the upper ocean , 2000 .

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

[44]  Charles B. Miller,et al.  What sets lower limits to phytoplankton stocks in high-nitrate, low-chlorophyll regions of the open ocean? , 2000 .

[45]  T. Jickells.  The inputs of dust derived elements to the Sargasso Sea; a synthesis , 1999 .

[46]  P. Harrison,et al.  Seasonal variability in nitrogenous nutrition of phytoplankton assemblages in the northeastern subarctic Pacific Ocean , 1999 .

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

[48]  P. Stegmann,et al.  Global distribution of aerosols over the open ocean as derived from the Coastal Zone Color Scanner , 1999 .

[49]  S. Nodder,et al.  The effects of multiple trap spacing, baffles and brine volume on sediment trap collection efficiency , 1999 .

[50]  N. M. Price,et al.  Marine bacteria and biogeochemical cycling of iron in the oceans , 1999 .

[51]  S. Chiswell,et al.  Pelagic ecosystem structure and functioning in the Subtropical Front region east of New Zealand in austral winter and spring 1993 , 1999 .

[52]  Henk A. Dijkstra,et al.  Imperfections of the North-Atlantic wind-driven ocean circulation: continental geometry and windstress shape , 1999 .

[53]  F. Morel,et al.  BIOLOGICAL CYCLING OF IRON IN THE OCEAN , 1998 .

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

[55]  D. Hutchins,et al.  Iron-limited diatom growth and Si:N uptake ratios in a coastal upwelling regime , 1998, Nature.

[56]  A. Watson,et al.  Sulphur hexafluoride as a tracer of biogeochemical and physical processes in an open-ocean iron fertilisation experiment , 1998 .

[57]  M. Weinbauer,et al.  The role of sunlight in the removal and repair of viruses in the sea , 1998 .

[58]  F. Wilkerson,et al.  Silicate regulation of new production in the equatorial Pacific upwelling , 1998, Nature.

[59]  F. Morel,et al.  Biological cycling of iron in the ocean. In: Iron Transport and Storage in Microorganisms, Plants, and Animals , 1998 .

[60]  N. M. Price,et al.  Metabolic consequences of iron deficiency in heterotrophic marine protozoa , 1997 .

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

[62]  Edward A. Boyle,et al.  What controls dissolved iron concentrations in the world ocean? — a comment , 1997 .

[63]  K. Bruland,et al.  The role of organic complexation on ambient iron chemistry in the equatorial Pacific Ocean and the response of a mesoscale iron addition experiment , 1997 .

[64]  P. Tortell,et al.  The role of heterotrophic bacteria in iron-limited ocean ecosystems , 1996, Nature.

[65]  D. Kirchman.  Microbial ferrous wheel , 1996, Nature.

[66]  D. Hutchins,et al.  Copepod grazing and the biogeochemical fate of diatom iron , 1995 .

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

[68]  D. Farmer,et al.  Observations of the influence of diurnal convection on upper ocean dissolved gas measurements , 1995 .

[69]  P. Hesse.  The record of continental dust from Australia in Tasman Sea Sediments , 1994 .

[70]  D. Hutchins,et al.  Grazer-mediated regeneration and assimilation of Fe, Zn and Mn from planktonic prey , 1994 .

[71]  D. Hutchins,et al.  Iron and regenerated production: Evidence for biological iron recycling in two marine environments , 1993 .

[72]  E. Boyle,et al.  The trace metal composition of suspended particles in the oceanic water column near Bermuda , 1992 .

[73]  Jeff Gipson,et al.  Cycles , 1992, The Americas.

[74]  B. Hicks,et al.  The atmospheric input of trace species to the world ocean , 1991 .

[75]  R. Duce,et al.  Concentrations, sources, and fluxes of trace elements in the remote marine atmosphere of New Zealand , 1990 .

[76]  H. Jannasch,et al.  Nutrient assimilation, export production and 234Th scavenging in the eastern equatorial Pacific , 1989 .

[77]  W. Broenkow,et al.  Vertex: phytoplankton/iron studies in the Gulf of Alaska , 1989 .

[78]  J. Fuhrman,et al.  Diel variations in bacterioplankton, phytoplankton, and related parameters in the Southern California Bight. , 1985 .

[79]  N. Middleton,et al.  Dust storms in Australia: frequency, distribution and seasonality , 1984 .

[80]  Victor Smetacek,et al.  Pelagic ecosystem structure: Heterotrophic compartments of the plankton and their relationship to plankton size fractions 1 , 1978 .