Désert de Gobi | EPFL Graph Search

Le désert de Gobi (en mongol bitchig : ᠭᠣᠪᠢ, cyrillique : Говь, trans. : goby, littéralement « désert », traduit phonétiquement en ou plus brièvement ) est une vaste région désertique comprise entre le nord de la Chine et le sud de la Mongolie. Il englobe environ un tiers de la surface de la Mongolie. Le bassin désertique est délimité par les montagnes de l'Altaï, la steppe de Mongolie, le plateau tibétain et la plaine du Nord de la Chine. Au sens propre, le mot « gobi » (prononcé gov) désigne en mongol un territoire semi-aride (le désert est appelé tsöl) en forme de grande cuvette ( *gob « creux, concave »). En chinois, 戈壁 renvoient à la notion d'une barrière dangereuse avec 壁 (mur) et 戈 (hallebarde). Un espace infranchissable si l'on n'est pas armé pour affronter les conditions climatiques, les contraintes physiques du paysage. Il faut ajouter d'autres contraintes humaines : la dangerosité des tribus périphériques ou des bandes armées sillonnant un pays dans un espace où la re

Iron mobilization in mineral dust: Can anthropogenic SO2 emissions affect ocean productivity?

Athanasios Nenes

For Fe contained in long-range transported acolian dust to act as a micronutrient for oceanic phytoplankton it must be first dissolved or mobilized. We propose that Femobilization can occur in mineral dust from East Asia by the incorporation of SO2 into the advecting dust plumes and subsequent acidification of the dust through heterogeneous SO2 oxidation. To test this hypothesis, we consider a dust plume that originated from the gobi-deserts and advected over the Pacific Ocean. Data collected over the Yellow Sea confirm that this plume contained high concentrations of dust and SO2. Significant gaseous HNO3 concentrations indicate that the dust particles were acidified (i.e., pH < 2). At these pH's, 1-2% of the Fe contained in a deliquescent mineral dust particle would be mobilized within 3-5 days. These results suggest a possible link between the rate of C-fixation in so-called High-Nitrate-Low-Chlorophyll regions of the Pacific Ocean and SO2 emissions from East Asia. Copyright 2003 by the American Geophysical Union.

2003

Dust and pollution: A recipe for enhanced ocean fertilization?

Athanasios Nenes

For Fe contained in aeolian dust to act as a micronutrient for oceanic phytoplankton, some fraction of it must first be transformed (mobilized) into a form soluble in ocean water. Fe solubilization in deliquesced mineral dust aerosols emanating from East Asia during the springtime outflow conditions is investigated here with a Lagrangian box model of the gas and aqueous-phase chemistry. The model simulates the scavenging of soluble and reactive gaseous species by mineral dust aerosols, chemical reactions of these species and mineral dust ions in deliquesced solution, and dissolution of Fe-III oxides that occurs as a result of the acid mobilization. The calculations indicate that mineral calcite (CaCO3) strongly buffers deliquesced dust aerosols with a pH that remains close to 8 until the amount of acid added to the aerosol solution exceeds CaCO3 alkalinity. SO2 pollutant emissions are a potential source of acidity to advecting dust from East Asia. The model is used to simulate the chemical evolution of dust plumes formed from two contrasting documented Gobi-desert storms that advected dust to Fe-limited regions of the North Pacific Ocean (NPO). These calculations indicate that only plumes with relatively high initial SO2-to-dust ratios are capable of delivering significant amounts of bioavailable Fe to the NPO. The estimated change in phytoplankton population inferred from the model-calculated inputs of bioavailable Fe for these two episodes is consistent with the satellite-measured chlorophyll a concentrations in the NPO. Model simulations indicate that (1) large dust advection episodes, that can export vast amounts of mineral dust to the open ocean, should have insignificant dissolved iron fraction (DIF) as the amount of SO2 required to acidify such dust plumes is about an order of magnitude higher than what can typically be entrained in the plume during its advection; (2) smaller dust plumes will generally have higher DIFs because they require lower amounts of SO2 and, even if such small plumes may not cause algae blooms, they could still be important sources of dissolved Fe to the NPO. The calculations suggest that future changes in SO2-pollutant emissions from East Asia, either up or down, may affect the productivity of the NPO. Copyright 2005 by the American Geophysical Union.

2005

Dust and pollution: A recipe for enhanced ocean fertilization?

Athanasios Nenes

2005