Using Integrated Approaches of In-situ Observations, Laboratory Experiments and Modeling to Study Atmospheric Iron and Its Input to the Ocean: A New Lesson Learned from the Southern Ocean and Coastal Antarctica

Atmospheric input of dust is an important source of iron (Fe) to phytoplankton growth in the surface waters of several large oceanic regions. However, the efficiency of Fe uptake by phytoplankton may depend on Fe properties in dust, such as Fe solubility and speciation. Many processes occurring in the atmosphere may alter dust properties and then its bioavailability in the ocean. During long range transport, dust particles may undergo heterogeneous reactions at gas-solid-liquid interfaces. Photochemical reduction in more acidic cloud waters and precipitation may promote dissolution of Fe in dust, leading to the production of soluble Fe (II) which is believed to be more readily used by phytoplankton. Relative contributions of atmospheric Fe input to the ocean by wet and dry deposition vary between coastal and remote oceans, and currently the estimates of the air-to-sea deposition of soluble Fe involves substantial uncertainties, in particular in the large high-nutrient-low-chlorophyll (HNLC) oceanic regions.

The Southern Ocean, surrounding Antarctica, plays an important role in regulating the global nitrogen and carbon cycles. The vast Southern Ocean is a HNLC region where phytoplankton growth is partially limited by micronutrient Fe. This region is extremely under-sampled due to its vast area and rough atmospheric and oceanic conditions for in situ observations, hindering the accurate estimate of the atmospheric dissolved Fe input. In this presentation, we will discuss our results of atmospheric Fe from recent shipboard aerosol measurements in the Southern Ocean and coastal East Antarctica. We will explore the interactions of different aerosol components and possible processes affecting atmospheric Fe solubility, and our thoughts on existing questions and future studies in the regions will also be shared.