 |
| Titel |
Chemical fate and settling of mineral dust in surface seawater after atmospheric deposition observed from dust seeding experiments in large mesocosms |
| VerfasserIn |
K. Desboeufs, N. Leblond, T. Wagener, E. Bon Nguyen, C. Guieu |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 19 ; Nr. 11, no. 19 (2014-10-13), S.5581-5594 |
| Datensatznummer |
250117636
|
| Publikation (Nr.) |
 copernicus.org/bg-11-5581-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
| We report here the elemental composition of sinking particles in sediment
traps and in the water column following four artificial dust seeding experiments
(each representing a flux of 10 g m−2). Dry or wet dust deposition
were simulated during two large mesocosms field campaigns that took place in
the coastal water of Corsica (NW Mediterranean Sea) representative of
oligotrophic conditions. The dust additions were carried out with fresh or
artificially aged dust (i.e., enriched in nitrate and sulfate by mimicking
cloud processing) for various biogeochemical conditions, enabling us to test
the effect of these parameters on the chemical composition and settling of
dust after deposition. The rates and mechanisms of total mass, particulate
organic carbon (POC) and chemical elements (Al, Ba, Ca, Co, Cu, Fe, K, Li,
Mg, Mn, Mo, N, Nd, P, S, Sr and Ti) transfer from the mesocosm surface to the
sediment traps installed at the base of the mesocosms after dust deposition
show that (1) 15% of the initial dust mass was dissolved in the water
column in the first 24 h after seeding. Except for Ca, S and N, the
elemental composition of dust particles was constant during their settling,
showing the relevance of using interelemental ratios, such as Ti/Al as
proxy of lithogenic fluxes. (2) Whatever the type of seeding (using fresh
dust to simulate dry deposition or artificially aged dust to simulate wet
deposition), the particulate phase both in the water column and in the
sediment traps was dominated by dust particles. (3) Due to the high Ba
content in dust, Ba/Al cannot be used as productivity proxy in the case
of high dust input in the sediment traps. Instead, our data suggests that the
ratio Co/Al could be a good productivity proxy in this case. (4) After
7 days, between 30 and 68% of added dust was still in suspension in the
mesocosms. This difference in the dust settling was directly associated with a
difference in POC export, since POC fluxes were highly correlated to dust
lithogenic fluxes signifying a ballast effect of dust. The highest fraction
of remaining dust in suspension in the mesocosm at the end of the experiment
was found inversely correlated to Chl a increase. This suggests that the
fertilizing effect of dust on autotrophs organisms, the ballast effect, and
POC fluxes are strongly correlated. (5) Our data emphasize a typical mass
ratio Lithogenic/POC fluxes around 30 which could be used as reference
to estimate the POC export triggered by wet dust deposition event. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|