Changes in dissolved iron deposition to the oceans driven by human activity: a 3-D global modelling study

[摘要] The global atmospheric iron (Fe) cycle is parameterized in the global 3-Dchemical transport model TM4-ECPL to simulate the proton- and the organicligand-promoted mineral-Fe dissolution as well as the aqueous-phasephotochemical reactions between the oxidative states of Fe (III/II). Primaryemissions of total (TFe) and dissolved (DFe) Fe associated with dust andcombustion processes are also taken into account, with TFe mineral emissionscalculated to amount to ~ 35 Tg-Fe yr⁻¹ and TFe emissions fromcombustion sources of ~ 2 Tg-Fe yr⁻¹. The model reasonablysimulates the available Fe observations, supporting the reliability of theresults of this study. Proton- and organic ligand-promoted Fe dissolution inpresent-day TM4-ECPL simulations is calculated to be~ 0.175 Tg-Fe yr⁻¹, approximately half of the calculated totalprimary DFe emissions from mineral and combustion sources in the model(~ 0.322 Tg-Fe yr⁻¹). The atmospheric burden of DFe iscalculated to be ~ 0.024 Tg-Fe. DFe deposition presents strong spatialand temporal variability with an annual flux of~ 0.496 Tg-Fe yr⁻¹, from which about 40 %(~ 0.191 Tg-Fe yr⁻¹) is deposited over the ocean. The impact ofair quality on Fe deposition is studied by performing sensitivity simulationsusing preindustrial (year 1850), present (year 2008) and future (year 2100)emission scenarios. These simulations indicate that about a 3 times increasein Fe dissolution may have occurred in the past 150 years due to increasinganthropogenic emissions and thus atmospheric acidity. Air-quality regulationsof anthropogenic emissions are projected to decrease atmospheric acidity inthe near future, reducing to about half the dust-Fe dissolution relative tothe present day. The organic ligand contribution to Fe dissolution shows aninverse relationship to the atmospheric acidity, thus its importance hasdecreased since the preindustrial period but is projected to increase in thefuture. The calculated changes also show that the atmospheric DFe supply tothe globe has more than doubled since the preindustrial period due to 8-foldincreases in the primary non-dust emissions and about a 3-fold increase in thedust-Fe dissolution flux. However, in the future the DFe deposition flux isexpected to decrease (by about 25 %) due to reductions in the primarynon-dust emissions (about 15 %) and in the dust-Fe dissolution flux(about 55 %). The present level of atmospheric deposition ofDFe over the global ocean is calculated to be about 3 times higher than for 1850 emissions, andabout a 30 % decrease is projected for 2100 emissions. These changes areexpected to impact most on the high-nutrient–low-chlorophyll oceanic regions.

[学科分类] 地球化学与岩石