Abstract
The dynamics of dissolved inorganic nitrogen and phosphorus in seawater after a dust event were followed to better understand the impact of dust deposition in low nutrient waters of the Mediterranean Sea. Three independent abiotic experiments were performed over three seasons (winter, spring, end of summer) characterized by contrasted biogeochemical conditions. Experiments consisted of seeding evapocondensed Saharan dust at the surface of a polyethylene tank filled with filtered surface seawater. Phosphate (PO43-), nitrate (NO3-), size and number of particles and transparent exopolymeric particles production (TEP) were measured over the course of one week following seeding. Dust deposition was followed by a transient increase in [PO43-] during the first three hours with a maximum input of 33, 9 and 39 nM respectively in May, October and February. The removal of almost all the PO43- initially released suggests a scavenging process of PO43- back onto ferric oxide-rich particles leading to concentrations at the end of the experiment close to the initial values (7 nM in May and October, and 6 nM in February). NO3- released from dust was high especially in May and October (maximum input of 23 and 11 µM respectively) and was attributed to nitrogen dissolution from the large amount of small particles (< 1µm) rich in nitrogen in the evapocondensed dust. [NO3-] remained high until the end of the experiment (16 µM in May and 11 µM in October), indicating that NO3- from dust is likely to be bioavailable for a longer period compared to PO43- from dust. The release of PO43- and NO3- was intrinsically linked to particle dynamics, governed by the quality/quantity of dissolved organic matter.
Highlights
Studying the interactions between atmosphere and ocean is essential for better understanding biogeochemical cycles in the ocean, a critical step toward accurate modeling of ocean dynamics under climate and anthropogenic changes (e.g., Law et al, 2013; Liss and Johnson, 2014)
To better understand the relationship between the dynamics of the nutrients and the particles, we took the average values of the 3-depths for each parameter
In May (Table 1), the seawater was typical of the post-bloom conditions with [Chla] = 0.28 μg L−1, a nutrient depletion ([NO−3 ] = 28 NO−3 (μM) and PO34− (nM); [PO34−] = 3 nM) and a high value of [transparent exopolymeric particles production (TEP)-C] (27.1 μmol C L−1)
Summary
Studying the interactions between atmosphere and ocean is essential for better understanding biogeochemical cycles in the ocean, a critical step toward accurate modeling of ocean dynamics under climate and anthropogenic changes (e.g., Law et al, 2013; Liss and Johnson, 2014). With 500 Mt per year of dust deposited to the surface ocean (Law et al, 2013), the atmosphere is Nutrients in seawater following dust deposition a significant pathway for the transport of material from natural and anthropogenic sources to the coastal and open ocean. A number of studies have investigated post-depositional processes (dissolution, adsorption) of atmospheric nutrients in seawater and the impact of atmospheric deposition on biological activity (i.e., Guieu et al, 2014b). As exchanges between dissolved and particulate phases occur while the atmospheric particles are sinking in the ocean, results from such “batch” approaches, that do not take into account the vertical dimension, could lead to incorrect quantifications of dissolution/scavenging processes involving atmospheric particles (de Leeuw et al, 2014). Most studies do not take into consideration the biogeochemical characteristics of the water used in experiments, such as the amount of dissolved organic matter
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
