Croot, Peter

Dietze, Heiner

Duggen, Svend

Olgun, Nazli

English

OceanRep

Geophysical Research Abstracts,Vol. 11, EGU2009-5565, 2009EGU General Assembly 2009© Author(s) 2009Surface ocean iron fertilization: The role of airborne volcanic ash andiron-flux into the Pacific OceanN. Olgun (1,2), S. Duggen (1), P. Croot (2), and H. Dietze (2)(1) IFM-GEOMAR, Dynamics of the Ocean Floor, Kiel, Germany , (2) IFM-GEOMAR, Marine Biogeochemistry, Kiel,GermanyIron is a limiting micro-nutrient for marine primary production (MPP) in vast areas in the surface ocean. Hence,atmospheric supply of iron to the surface ocean can affect marine biogeochemical cycles, associated ocean-atmosphere exchange of CO2 and eventually climate development. Airborne volcanic ash from volcanic eruptionscan be an important atmospheric iron-source in the surface ocean by releasing bio-available iron while settlingthrough in the surface ocean. Here we present new data from time-dependent geochemical experiments withpristine (unhydrated) volcanic ash samples and natural seawater by means of Cathodic Stripping Voltammetry.Our results demonstrate that volcanic ash mobilizes significant amounts of soluble Fe within 60 minutes ofcontact with natural seawater. Depending on the amount of volcanic ash deposited offshore during major volcaniceruptions and the amount of iron that ash can release on contact with seawater, the calculated increase in thesurface ocean Fe levels range from several nanomolar up to several hundred nanomolar (nM). Only 2 nM increasein iron concentrations can stimulate massive diatom blooms in the oceanic regions in which MPP is limited bythe availability of iron (the iron-limited oceanic areas) (Wells, 2003). Therefore volcanic ash should be able tosignificantly affect marine phytoplankton growth in an ash fall area, acting as an iron fertilizer. Based on our newiron-release data and marine sediment core data we provide the first estimate of the flux of Fe from volcanic ashinto the Pacific Ocean that covers more than 60 percent of the iron-limited oceanic regions. Our calculations showthat the flux of Fe from volcanic ash is comparable to the order of magnitude of the flux of Fe from aeolian dust.Our study shows that volcanic ash is a major and so far underestimated atmospheric iron-source for the oceansand therefore an important component in marine biogeochemical iron cycles.Wells, M.L.: The level of iron enrichment required to initiate diatom blooms in HNLC waters, MarineChemistry, 82, 101-114, 2003.

Surface ocean iron fertilization: the role of airborne volcanic ash and iron-flux into the Pacific Ocean

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