A global compilation of dissolved iron measurements: focus on distributions and processes in the Southern Ocean

Abstract. Due to its importance as a limiting nutrient for phytoplankton growth in large regions of the world's oceans, ocean water column observations of concentration of the trace-metal iron (Fe) have increased markedly over recent decades. Here we compile >13 000 global measurements of dissolved Fe (dFe) and make this available to the community. We then conduct a synthesis study focussed on the Southern Ocean, where dFe plays a fundamental role in governing the carbon cycle, using four regions, six basins and five depth intervals as a framework. Our analysis highlights depth-dependent trends in the properties of dFe between different regions and basins. In general, surface dFe is highest in the Atlantic basin and the Antarctic region. While attributing drivers to these patterns is uncertain, inter-basin patterns in surface dFe might be linked to differing degrees of dFe inputs, while variability in biological consumption between regions covaries with the associated surface dFe differences. Opposite to the surface, dFe concentrations at depth are typically higher in the Indian basin and the Subantarctic region. The inter-region trends can be reconciled with similar ligand variability (although only from one cruise), and the inter-basin difference might be explained by differences in hydrothermal inputs suggested by modelling studies (Tagliabue et al., 2010) that await observational confirmation. We find that even in regions where many dFe measurements exist, the processes governing the seasonal evolution of dFe remain enigmatic, suggesting that, aside from broad Subantarctic – Antarctic trends, biological consumption might not be the major driver of dFe variability. This highlights the apparent importance of other processes such as exogenous inputs, physical transport/mixing or dFe recycling processes. Nevertheless, missing measurements during key seasonal transitions make it difficult to better quantify and understand surface water replenishment processes and the seasonal Fe cycle. Finally, we detail the degree of seasonal coverage by region, basin and depth. By synthesising prior measurements, we suggest a role for different processes and highlight key gaps in understanding, which we hope can help structure future research efforts in the Southern Ocean.

[1]  L. Gerringa,et al.  Observation of consistent trends in the organic complexation of dissolved iron in the Atlantic sector of the Southern Ocean , 2011 .

[2]  P. Laan,et al.  Dissolved iron in the Southern Ocean (Atlantic sector) , 2011 .

[3]  K. Arrigo,et al.  Early season depletion of dissolved iron in the Ross Sea polynya : Implications for iron dynamics on the Antarctic continental shelf , 2011 .

[4]  S. Sander,et al.  Vertical distributions of iron-(III) complexing ligands in the Southern Ocean , 2011 .

[5]  A. Bowie,et al.  Iron fractionation in pack and fast ice in East Antarctica: Temporal decoupling between the release of dissolved and particulate iron during spring melt , 2011 .

[6]  O. Aumont,et al.  A global compilation of over 13 000 dissolved iron measurements : focus on distributions and processes in the Southern Ocean , 2011 .

[7]  P. Boyd,et al.  The biogeochemical cycle of iron in the ocean , 2010 .

[8]  J. Nishioka,et al.  Significant portion of dissolved organic Fe complexes in fact is Fe colloids , 2010 .

[9]  Pierrick Penven,et al.  Physical speciation of iron in the Atlantic sector of the Southern Ocean along a transect from the subtropical domain to the Weddell Sea Gyre , 2010 .

[10]  J. Tison,et al.  Distribution of dissolved iron in Antarctic sea ice: Spatial, seasonal, and inter-annual variability , 2010 .

[11]  A. Bowie,et al.  Southern Ocean iron fertilization by baleen whales and Antarctic krill , 2010 .

[12]  B. Tilbrook,et al.  The Australian Integrated Marine Observing System Southern Ocean Time Series facility , 2010, OCEANS'10 IEEE SYDNEY.

[13]  M. Gehlen,et al.  Hydrothermal contribution to the oceanic dissolved iron inventory , 2010 .

[14]  S. Speich,et al.  An altimetry‐based gravest empirical mode south of Africa: 2. Dynamic nature of the Antarctic Circumpolar Current fronts , 2010 .

[15]  P. Boyd,et al.  Biogeochemical iron budgets of the Southern Ocean south of Australia: Decoupling of iron and nutrient cycles in the subantarctic zone by the summertime supply , 2009 .

[16]  L. Bopp,et al.  Evaluating the importance of atmospheric and sedimentary iron sources to Southern Ocean biogeochemistry , 2009 .

[17]  Patrice Klein,et al.  The oceanic vertical pump induced by mesoscale and submesoscale turbulence. , 2009, Annual review of marine science.

[18]  Richard S. Lampitt,et al.  Southern Ocean deep-water carbon export enhanced by natural iron fertilization , 2009, Nature.

[19]  K. Bruland.  SCOR-IUPAC WORKING GROUP ON IRON IN THE OCEANS CHAPTER 6 : IRON : ANALYTICAL METHODS FOR THE DETERMINATION OF CONCENTRATIONS AND SPECIATION , 2009 .

[20]  A. Bowie,et al.  Spatial and temporal distribution of Fe, Ni, Cu and Pb along 140°E in the Southern Ocean during austral summer 2001/02 , 2008 .

[21]  W. Landing,et al.  A commercially available rosette system for trace metal—clean sampling , 2008 .

[22]  K. Arrigo,et al.  Primary production in the Southern Ocean, 1997–2006 , 2008 .

[23]  P. Sedwick,et al.  Dissolved iron in the Australian sector of the Southern Ocean (CLIVAR SR3 section): Meridional and seasonal trends , 2008 .

[24]  P. Boyd,et al.  Winter‐time dissolved iron and nutrient distributions in the Subantarctic Zone from 40–52S; 155–160E , 2008 .

[25]  J. Tison,et al.  Iron study during a time series in the western Weddell pack ice , 2008 .

[26]  S. Sokolov,et al.  On the relationship between fronts of the Antarctic Circumpolar Current and surface chlorophyll concentrations in the Southern Ocean , 2007 .

[27]  C. Duarte,et al.  Krill as a central node for iron cycling in the Southern Ocean , 2007 .

[28]  B. Quéguiner,et al.  Effect of natural iron fertilization on carbon sequestration in the Southern Ocean , 2007, Nature.

[29]  J. K. Moore,et al.  Sedimentary and mineral dust sources of dissolved iron to the World Ocean , 2007 .

[30]  S. J. Tanner,et al.  Developing standards for dissolved iron in seawater , 2007 .

[31]  E. Boyle,et al.  Mesoscale Iron Enrichment Experiments 1993-2005: Synthesis and Future Directions , 2007, Science.

[32]  K. Arrigo,et al.  Processes governing the supply of iron to phytoplankton in stratified seas , 2006 .

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

[34]  P. Worsfold,et al.  A community-wide intercomparison exercise for the determination of dissolved iron in seawater , 2006 .

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

[36]  Ulf Riebesell,et al.  Synthesis of iron fertilization experiments: From the iron age in the age of enlightenment , 2005 .

[37]  Edward A. Boyle,et al.  Decoupling of iron and phosphate in the global ocean , 2005 .

[38]  Xiujun Wang,et al.  The distribution and behavior of dissolved and particulate iron and zinc in the Ross Sea and Antarctic circumpolar current along 170°W , 2005 .

[39]  F. Hernandez,et al.  A mean dynamic topography computed over the world ocean from altimetry, in situ measurements, and a geoid model , 2004 .

[40]  Daniele Iudicone,et al.  Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology , 2004 .

[41]  M. Öztürk,et al.  The distribution and speciation of iron along 6°E in the Southern Ocean , 2004 .

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

[43]  P. Sedwick,et al.  Analytical intercomparison between flow injection‐chemiluminescence and flow injection‐spectrophotometry for the determination of picomolar concentrations of iron in seawater , 2004 .

[44]  K. Arrigo,et al.  Annual changes in sea-ice, chlorophyll a, and primary production in the Ross Sea, Antarctica , 2004 .

[45]  J. Probst,et al.  Iron and other transition metals in Patagonian riverborne and windborne materials: geochemical control and transport to the southern South Atlantic Ocean , 2003 .

[46]  K. Arrigo,et al.  Impact of iceberg C‐19 on Ross Sea primary production , 2003 .

[47]  R. Hudson,et al.  Modeling complexometric titrations of natural water samples. , 2003, Environmental science & technology.

[48]  Mario Hoppema,et al.  Substantial advective iron loss diminishes phytoplankton production in the Antarctic Zone , 2003 .

[49]  Thorsten Markus,et al.  Ecological impact of a large Antarctic iceberg , 2002 .

[50]  F. Millero,et al.  The solubility of iron in seawater , 2002 .

[51]  M. Grotti,et al.  Temporal distribution of trace metals in Antarctic coastal waters , 2001 .

[52]  P. Worsfold,et al.  Determination of iron in seawater , 2001 .

[53]  E. Boyle,et al.  Soluble and Colloidal Iron in the Oligotrophic North Atlantic and North Pacific , 2001, Science.

[54]  Patrice Klein,et al.  Impact of sub-mesoscale physics on production and subduction of phytoplankton in an oligotrophic regime , 2001 .

[55]  S. Vink,et al.  Dissolved Fe in the upper waters of the Pacific sector of the Southern Ocean , 2001 .

[56]  Gurvan Madec,et al.  Impacts of sub-mesoscale physics on phytoplankton production and, subduction , 2001 .

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

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

[59]  K. Caldeira,et al.  The role of the southern ocean in uptake and storage of anthropogenic carbon dioxide , 2000, Science.

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

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

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

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

[64]  C. Provost,et al.  Transports of the Brazil and Malvinas currents at their confluence , 1998 .

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

[66]  Kenneth S. Johnson,et al.  Marine Chemistry Discussion Paper What controls dissolved iron concentrations in the world ocean , 1997 .

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

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

[69]  L. Stramma,et al.  Upper-level circulation in the South Atlantic Ocean , 1991 .

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

[71]  John H. Martin.  glacial-interglacial Co2 change : the iron hypothesis , 1990 .

[72]  K. Bruland,et al.  Sampling and analytical methods for the determination of copper, cadmium, zinc, and nickel at the nanogram per liter level in sea water , 1979 .

[73]  A. Gordon.  Circulation of the Caribbean Sea , 1967 .