Dust Impacts on Ocean Productivity

The oceanic primary production and CO2 uptake is, among others, influenced by the supply of aeolian dust [1], because it can act as a nutrient for marine life. Nutrients transported within atmospheric dust particles are iron, phosphorus, nitrogen and silica minerals. They act as fertilizer and stimulate the production of plankton/algae blooms. These microscopic marine plants are containing chlorophyll pigments, with which they are able to convert inorganic compounds (water, nitrogen and carbon) into complex organic materials. They are the basic food for the whole marine life. In addition to that they are binding atmospheric CO2.

Iron is the essential nutrient for marine microorganisms [1], limiting the biological activity in many parts of the world ocean [2]. Its (globally) dominant external input into the ocean is aeolian desert dust transport [1].

Planktonic populations may respond very quickly to variabilities in the ocean such as changes in surface iron deposited with dust [3]. By changing the phytoplankton, dust has also an impact on the source of DMS, a trace gas which influences the climate [1].

The mechanisms of marine response to dust input of the atmosphere are still being faced with numerous uncertainties and a subject of scientific discussion. However, there are some examples indicating possible correlation between dust input and ocean productivity. Several of such events are listed below:

  • exceptionally warm weather and/or massive dust storms from the Sahara Desert are observed in the North East Atlantic in August 2004 together with algae bloom [4]
  • an increase in chlorophyll over a 2-week period is observed after passage of Gobi desert dust cloud [5]
  • dust storms in Australia (2002-2003) lead to advection of large dust plumes over the Southern Ocean, which resulted in large-scale natural dust fertilization (unusually strong south of 50°S) with a strong CO2 drawdown; observed coherence between optical characteristics of the Southern Ocean atmosphere and dust loading by satellite and field data on surface chlorophyll [6]
  • spring bloom in the northern East/Japan Sea, which is normally initiated as the surface mixed layer becomes shallower than critical depth, was observed (TOMS and SeaWiFS) to be initiated one month earlier than usual correlated with an Asian dust event in association with precipitation, which lead to wet deposition of bioavailable iron inducing deepening of the critical depth, which results in an early initiation of the bloom [7]
  • regions between 40°S and 60°S show correlations from 0.6 to 0.95 (significant at the 0.05 level) between chlorophyll concentrations and iron flux, particularly the Patagonian region; chlorophyll and iron flux follow similar patterns [2]
  • in the Gulf of Oman chlorophyll blooming was observed after dust deposition within a period of 1-2 up to 3-4 days during June–July–August and October–November–December months of 1997–2004 [8]

algae bloom in the Atlantic

Saharan dust blown west across the Atlantic Ocean, Atlantic plankton bloom; ESA

The composition and origin of the mineral dust has a general impact on acting as an efficient nutrient. Since iron is the most important nutrient, its content in aeolian dust is essential, but beyond that the nature of the iron content in the dust aerosol plays a major role. Only part of the iron content is freely available to the ocean. This free-iron is not directly proportional to the total iron content and depends on the origin and transport time of the dust particles [9]. To act as a micronutrient some fraction of the iron content has to be transformed (mobilized) into a form soluble in ocean water.

 

Iron solubility

The iron solubility of dust particles (the free-iron content) is extremely variable and ranges from 0.01-80% [10]. It could be controlled by different factors: scavenging (wet and dry deposition [11]) [12], lability related to the origin of the dust aerosols [12] relation of iron content to particle size [12], surface area to volume ratio [13], (chemical) composition of dust particles [14] and the pH factor of the ocean water [12].

dust processing

Dust processing during transport;

On their path through the atmosphere dust particles can be effected by different factors, so that the composition and the nature of the iron in the dust particles are changing.

The soluble iron fraction of dust particles increase with transport time from the source region due to several effects:

  • mixing with polluted air [15]
  • processing in clouds (acidification [16]) [17]
  • photochemistry due to radiation [18]
  • changing of the size distribution (decrease in dust concentration [19], changing of the surface area to volume ratio [13]).

The fine mode particles have generally a longer life time in the atmosphere and are consequently transported longer, so that their solubility is bigger than the coarse mode solubility [20]. Some studies report that fine mode desert dust particles have twice the solubility of coarse mode desert dust particles [21, 22].

The better understanding and assessing of the role of iron and other nutrients embedded in dust on marine biochemistry when it deposits into the ocean is one of the challenging research areas coordinated by WMO together with GESAMP.

 

Publications

[1] T.D. Jickels, Z.S. An, K.K. Andersen, A.R. Baker, G. Bergametti, N. Brooks, J.J. Cao, P.W. Boyd, R.A. Duce, K.A. Hunter, H. Kawahata, N. Kubilay, J. laRoche, P.S. Liss, N. Mahowald, J.M. Prospero, A.J. Ridgwell, I. Tegen, R. Torres; Global Iron Connections Between Desert Dust, Ocean Biogeochemistry, and Climate; Science 308; 2005

[2] D.J. Erickson III, J.L. Hernandez, P. Ginoux, W.W. Gregg, C. McClain, J. Christian; Atmospheric iron delivery and surface ocean biological activity in the Southern Ocean and Patagonian region; Geophysical Research Letters 30; 2003

[3] A.J. Gabric, R. Simó, R.A. Cropp, A.C. Hirst, J. Dachs; Modeling estimates of the global emission of dimethylsulfide under enhanced greenhouse conditions; Global Biogeochemical Cycles 18; 2004

[4] A.G. Ramos, A. Martel, G.A. Codd, E. Soler, J. Coca, A. Redondo, L.F. Morrison, J.S. Metcalf, A. Ojeda, S. Suárez, M. Petit; Bloom of the marine diazotrophic cyanobacterium Trichodesmium erythraeum in the Northwest African Upwelling; Marine Ecology Progress Series 301, p. 303–305; 2005

[5] J.K.B. Bishop, R.E. Davis, J.T. Sherman; Robotic Observations of Dust Storm Enhancement of Carbon Biomass in the North Pacific; Science 25, Vol. 298, No. 5594, p. 817-821; 2002

[6] A.J. Gabric, R.A. Cropp, G.H. McTainsh, B.M. Johnston, H. Butler, B. Tilbrook, M. Keywood; Australian dust storms in 2002–2003 and their impact on Southern Ocean biogeochemistry; Global Biogeochemical Cycles 24; 2010

[7] C.O. Jo, J.-Y. Lee, K.-A. Park, Y.H. Kim, K.-R. Kim; Asian dust initiated early spring bloom in the northern East/ Japan Sea; Geophysical Research Letters 34; 2007

[8] R.P. Singh, A.K. Prasad, V.K. Kayetha, M. Kafatos; Enhancement of oceanic parameters associated with dust storms using satellite data; Journal of Geophysical Research 113; 2008

[9] S. Lafon, J. Rajot, S.C. Alfaro, A. Gaudichet; Quantification of iron oxides in desert aerosol; Atmospheric Environment 38, p.1211–1218; 2004

[10] N.M. Mahowald, A.R. Baker, G. Bergametti, N. Brooks, R.A. Duce, T.D. Jickells, N. Kubilay, J.M. Prospero, I. Tegen; Atmospheric global dust cycle and iron inputs to the ocean; Global Biogeochemical Cycles 19; 2005

[11] W.J. Moxim, S. Fan, H. Levy II; The meteorological nature of variable soluble iron transport and deposition within the North Atlantic Ocean basin; Journal of Geophysical Research 116; 2011

[12] L. Patara, N. Pinardi, C. Corselli, E. Malinverno, M. Tonani, R. Santoleri, S. Masina; Particle fluxes in the deep Eastern Mediterranean basins: the role of ocean vertical velocities; Biogeosciences 6, p. 333–348; 2009

[13] A.R. Baker, T.D. Jickels; Mineral particle size as a control on aerosol iron solubility; Geophysical Research Letters 33; 2006

[14] R. Young, K. Carder, P. Betzer, D. Costello, R. Duce, J. Ditullio, N. Tindale, E. Laws, M. Uematsu, J. Merrill, R. Feely; Atmospheric iron inputs and primary productivity: phytoplankton responses in the North Pacific; Global Biogeochemical Cycles 5, p. 119-134; 1991

[15] R. Arimoto, Y.J. Kim, Y.P. Kim, P.K. Quinn, T.S. Bates, T.L. Anderson, S. Gong, I. Uno, M. Chin, B.J. Huebert, A.D. Clarke, Y. Shinozuka, R.J. Weber, J.R. Anderson, S.A. Guazzotti, R.C. Sullivan, D.A. Sodeman, K.A. Prather, I.N. Sokolik; Characterization of Asian Dust during ACE-Asia; Global and Planetary Change 52, p. 23–56; 2006

[16] N. Meskhidze, A. Nenes, W.L. Chameides, C. Luo, N. Mahowald; Atlantic Southern Ocean productivity: Fertilization from above or below?; Global Biogeochemical Cycles 21; 2007

[17] N.M. Mahowald, S. Engelstaedter, C. Luo, A. Sealy, P. Artaxo, C. Benitez-Nelson, S. Bonnet, Y. Chen, P.Y. Chuang, D.D. Cohen, F. Dulac, B. Herut, A.M. Johansen, N. Kubilay, R. Losno, W. Maenhaut, A. Paytan, J.M. Prospero, L.M. Shank, R.L. Siefert; Atmospheric Iron Deposition: Global Distribution, Variability, and Human Perturbations; Annual Review of Marine Science 2009, p. 245–278; 2009

[18] A.R. Baker, M. French, K.L. Linge; Trends in aerosol nutrient solubility along a west–east transect of the Saharan dust plume; Geophysical Research Letters 33; 2006

[19] S. Fan, W.J. Moxim, H. Levy II; Aeolian input of bioavailable iron to the ocean; Geophysical Research Letters 33; 2006

[20] J.L. Hand, N.M. Mahowald, Y. Chen, R.L. Siefert, C. Luo, A. Subramaniam, I. Fung; Estimates of atmospheric-processed soluble iron from observations and a global mineral aerosol model: Biogeochemical implications; Journal of Geophysical Research 109; 2004

[21] C. Luo, N.M. Mahowald, N. Meskhidze, Y. Chen, L. Siefert, A.R. Baker, A.M. Johansen; Estimation of iron solubility from observations and a global aerosol model; Journal of Geophysical Research 110; 2005

[22] Z.B. Shi, M.T. Woodhouse, K.S. Carslaw, M.D. Krom, G.W. Mann, A.R. Baker, I. Savov, G. Fones, B. Brooks, T.D. Jickells, L.G. Benning; Minor effect of physical size sorting on iron solubility of transported mineral dust; Atmospheric Chemistry and Physics Discussions 11, p. 14309–14338; 2011

 

Publication list in alphabetical order (including publications from above):

bibliography-impact-on-ocean [pdf, 199 kB]

 

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