Post-depositional processes: What really happens to new atmospheric iron in the ocean's surface?

Matthieu Bressac, Cécile Guieu

Research output: Contribution to journalArticle

Abstract

Abiotic iron removal processes such as scavenging can significantly and rapidly modify iron distribution in the dissolved-colloidal-particulate continuum. Therefore, these processes could be considered, in addition to ligand complexation, as a major control on atmospheric iron dissolution in seawater. In this work, we investigated the seasonal abiotic processes occurring once dust deposited on surface seawater using a series of artificial seeding experiments (allowing us to take into consideration the settling of particles on a 1 m depth layer). Here, we demonstrate that atmospheric dissolved iron concentration ([DFe]) is driven by the processes governed by the dissolved organic matter (DOM) pool. Following artificial dust seeding, an order magnitude range increase in the [DFe] (12 - 181 nmol L-1) was observed depending on the season. Under high and fresh DOM conditions (spring and summer), the rapid formation of aggregates induced a negative feedback on the [DFe] through scavenging, while a fraction of the DFe was likely organically complexed. In contrast, in low-DOM surface waters (winter), aggregation was not observed, allowing a very large transient increase in [DFe] (181 nmol L-1) before being removed by adsorption onto settling particles. A key result of the findings is that depending on the age and quantity of DOM, the "lithogenic carbon pump" is likely a major pathway for organic carbon export. Modeling studies should therefore relate both atmospheric iron dissolution in seawater and the intensity of the subsequent biological response, to the age and quantity of DOM. Key Points Atmospheric iron dissolution is driven by the dissolved organic matter poolSeawater biogeochemical conditions are a key determinant of iron solubilityLithogenic carbon pump is likely a major pathway for organic carbon export.

Original languageEnglish (US)
Pages (from-to)859-870
Number of pages12
JournalGlobal Biogeochemical Cycles
Volume27
Issue number3
DOIs
StatePublished - Sep 4 2013

Keywords

  • adsorption
  • aggregation
  • atmospheric dissolved iron
  • dissolved organic matter
  • scavenging

ASJC Scopus subject areas

  • Global and Planetary Change
  • Environmental Chemistry
  • Environmental Science(all)
  • Atmospheric Science

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