In:
Biogeosciences, Copernicus GmbH, Vol. 15, No. 21 ( 2018-11-09), p. 6659-6684
Abstract:
Abstract. This work reports on the current status of the global modeling of iron (Fe)
deposition fluxes and atmospheric concentrations and the analyses of the
differences between models, as well as between models and observations. A
total of four global 3-D chemistry transport (CTMs) and general circulation
(GCMs) models participated in this intercomparison, in the framework of
the United Nations Joint Group of Experts on the Scientific Aspects of Marine
Environmental Protection (GESAMP) Working Group 38, “The Atmospheric Input
of Chemicals to the Ocean”. The global total Fe (TFe) emission strength in
the models is equal to ∼72 Tg Fe yr−1 (38–134 Tg Fe yr−1)
from mineral dust sources and around 2.1 Tg Fe yr−1 (1.8–2.7 Tg Fe yr−1)
from combustion processes (the sum of anthropogenic
combustion/biomass burning and wildfires). The mean global labile Fe (LFe)
source strength in the models, considering both the primary emissions and the
atmospheric processing, is calculated to be 0.7 (±0.3) Tg Fe yr−1,
accounting for both mineral dust and combustion aerosols. The
mean global deposition fluxes into the global ocean are estimated to be in the range
of 10–30 and 0.2–0.4 Tg Fe yr−1 for TFe and LFe, respectively,
which roughly corresponds to a respective 15 and 0.3 Tg Fe yr−1 for the multi-model ensemble model mean. The model intercomparison analysis indicates that the representation of the
atmospheric Fe cycle varies among models, in terms of both the magnitude of
natural and combustion Fe emissions as well as the complexity of atmospheric
processing parameterizations of Fe-containing aerosols. The model comparison
with aerosol Fe observations over oceanic regions indicates that most models
overestimate surface level TFe mass concentrations near dust source
regions and tend to underestimate the low concentrations observed in remote
ocean regions. All models are able to simulate the tendency of higher Fe
concentrations near and downwind from the dust source regions, with the mean
normalized bias for the Northern Hemisphere (∼14), larger
than that of the Southern Hemisphere (∼2.4) for the ensemble model
mean. This model intercomparison and model–observation comparison study
reveals two critical issues in LFe simulations that require further
exploration: (1) the Fe-containing aerosol size distribution and (2) the
relative contribution of dust and combustion sources of Fe to labile Fe in
atmospheric aerosols over the remote oceanic regions.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-15-6659-2018
DOI:
10.5194/bg-15-6659-2018-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2158181-2
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