Major Impact of Dust Deposition on the Productivity of the Arabian Sea

Guieu, Cécile; Azhar, Muchamad Al; Aumont, Olivier; Mahowald, N. M.; Lévy, Marina; Éthé, Christian; Lachkar, Zouhair

doi:10.1029/2019gl082770

Cited by 63 publications

(44 citation statements)

References 64 publications

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“…Region 2 is controlled by the strong East African and Middle East dust iron source (Figure 3b), linked to the summer monsoon (Guieu et al, 2019; Wiggert et al, 2005). Modeled seasonality matches long‐term (26 years) aerosol index observations (Banerjee & Kumar, 2016) with maximal dust deposition occurring in July.…”

Section: Resultsmentioning

confidence: 99%

“…Modeled seasonality matches long‐term (26 years) aerosol index observations (Banerjee & Kumar, 2016) with maximal dust deposition occurring in July. This highly productive tropical marine region (Roxy et al, 2016; Wiggert et al, 2005) is dependent upon nutrient supply from both upwelling and atmospheric deposition, with dust iron suggested to support at least half the Arabian Sea's primary production (Guieu et al, 2019). Recent rapid ocean warming is enhancing stratification of the water column, diminishing nutrient upwelling, and thus has significantly decreased long‐term productivity in the region (Roxy et al, 2016).…”

Section: Resultsmentioning

confidence: 99%

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Recent (1980 to 2015) Trends and Variability in Daily‐to‐Interannual Soluble Iron Deposition from Dust, Fire, and Anthropogenic Sources

Hamilton

Scanza

Rathod

et al. 2020

Geophysical Research Letters

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The iron cycle is a key component of the Earth system. Yet how variable the atmospheric flux of soluble (bioaccessible) iron into oceans is, and how this variability is modulated by human activity and a changing climate, is not well known. For the first time, we characterize Satellite Era (1980 to 2015) daily‐to‐interannual modeled soluble iron emission and deposition variability from both pyrogenic (fires and anthropogenic combustion) and dust sources. Statistically significant emission trends exist: dust iron decreases, fire iron slightly increases, and anthropogenic iron increases. A strong temporal variability in deposition to ocean basins is found, and, for most regions, dust iron dominates the absolute deposition magnitude, fire iron is an important contributor to temporal variability, and anthropogenic iron imposes a significant increasing trend. Quantifying soluble iron daily‐to‐interannual deposition variability from all major iron sources, not only dust, will advance quantification of changes in marine biogeochemistry in response to the continuing human perturbation to the Earth System.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Recent (1980 to 2015) Trends and Variability in Daily‐to‐Interannual Soluble Iron Deposition from Dust, Fire, and Anthropogenic Sources

Hamilton

Scanza

Rathod

et al. 2020

Geophysical Research Letters

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“…Other major model-related limitations concern the lack of representation of important biogeochemical processes such as N 2 fixation and the crude representation of microbial respiration in the model. Yet, on the one hand recent studies suggest that N 2 fixation has a limited effect on the AS OMZ as it constitutes only a negligible proportion of new nitrogen there (Guieu et al, 2019). On the other hand, simple representations of microbial respiration that miss potentially important biogeochemical feedbacks are a common problem in most existing biogeochemical models (Oschlies et al, 2018;Robinson, 2019).…”

Section: Caveats and Limitationsmentioning

confidence: 99%

Fast local warming of sea-surface is the main factor of recent deoxygenation in the Arabian Sea

Lachkar¹,

Mehari²,

Azhar³

et al. 2020

Preprint

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Abstract. The Arabian Sea (AS) hosts one of the most intense oxygen minimum zones (OMZs) in the world. Observations show a decline of O2 in the northern AS over the recent decades accompanied by an intensification of the suboxic conditions there. Over the same period, the local sea-surface temperature has risen significantly, particularly over the Arabian Gulf (also known as Persian Gulf, hereafter the Gulf), while summer monsoon winds have intensified. Here, we reconstruct the evolution of dissolved oxygen in the AS from 1982 through 2010 and explore its controlling factors, with a focus on changing atmospheric conditions. To this end, we use a set of eddy-resolving hindcast simulations forced with observation-based winds and heat and freshwater fluxes. We find a significant deoxygenation in the northern AS with O2 inventories north of 20° N dropping by over 2 % decade-1 and 7 % decade-1 in the top 200 m and the 200–1000 m layer, respectively. These changes cause an increase in the volume of suboxia and the rate of denitrification by 10 % decade-1 and 13 % decade-1, respectively. Using a set of sensitivity simulations we demonstrate that deoxygenation in the northern AS is essentially caused by a reduced ventilation induced by the recent fast warming of the sea surface, in particular in the Gulf. Concomitant summer monsoon wind intensification contributes to deoxygenation at depth and in the upper ocean north of 20° N but enhances oxygenation of the upper ocean elsewhere. This is because surface warming enhances vertical stratification, thus limiting ventilation of the intermediate ocean, while summer monsoon wind intensification causes the thermocline depth to rise in the northern AS and deepen elsewhere, thus contributing to lowering O2 levels in the upper 200 m in the northern AS and increasing it in the rest of the AS. Our findings confirm that the AS OMZ is strongly sensitive to upper-ocean warming and concurrent changes in the Indian monsoon winds. Finally, our results also demonstrate that changes in the local climatic forcing play a key role in regional dissolved oxygen changes and hence need to be properly represented in global models to reduce uncertainties in future projections of deoxygenation.

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“…Besides seasonal upwelling, these systems are also subjected to intense atmospheric depositions (Jickells and Moore 2015). Dust deposition generally stimulates surface productivity in the upwelling regions, such as the Monterey Bay (Mackey et al 2010) and the Oman coast of the northwestern Arabian Sea (Guieu et al 2019), the Aegean Sea of the eastern Mediterranean (Herut et al 2016), and the Bermuda coast of the Sargasso Sea (Mackey et al 2012). Meanwhile, atmospheric deposition of anthropogenic aerosols from India showed negligible effects on the phytoplankton community in the upwelling zone of the eastern Arabian Sea (Guieu et al 2019).…”

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confidence: 99%

Coastal phytoplankton responses to atmospheric deposition during summer

Zhou

2020

Limnology & Oceanography

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The northern South China Sea is subject to an increasing influence of aerosol loading, particularly over the past decades owing to the fast economic growth of mainland China. To study the response of the coastal phytoplankton community to atmospheric deposition, we performed onboard microcosm experiments at various coastal regions of the northern South China Sea, including a river plume zone and the two major upwelling zones. We found that the addition of aerosol and rainwater significantly increased the micro‐phytoplankton size‐fraction by 2.3–5.4‐folds regardless of the type of preexisting nutrient limitation in the phytoplankton community. There were three types of distinct responses to the manipulation additions observed: positive, negligible, or even negative effects. A significant inhibition effect (27–74% decrease) in the Qiongdong upwelling zone could be attributed to elevated metal toxicity on the phytoplankton community seeding from the subsurface after it had been brought up to the surface due to an outcrop of the thermocline. While Prochlorococcus growth was uniformly inhibited by the additions, both positive and negative effects were observed for the remainder of the picoplankton community. P‐limited Synechococcus was stimulated by aerosol and rainwater additions (1.2–2.8‐folds increase), whereas N‐limited Synechococcus was inhibited (decreased by 9–28%). Our results suggest that coastal phytoplankton responses to atmospheric depositions are regulated by both the fertilizing effects of aerosol nutrients and the toxic effects of aerosol metals. Our findings highlight the critical role of atmospheric depositions on spatial change of phytoplankton biomass and community structure in the coastal ocean, which could greatly affect ecosystem dynamics and biogeochemical cycles of the shelf sea.

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Major Impact of Dust Deposition on the Productivity of the Arabian Sea

Cited by 63 publications

References 64 publications

Recent (1980 to 2015) Trends and Variability in Daily‐to‐Interannual Soluble Iron Deposition from Dust, Fire, and Anthropogenic Sources

Recent (1980 to 2015) Trends and Variability in Daily‐to‐Interannual Soluble Iron Deposition from Dust, Fire, and Anthropogenic Sources

Fast local warming of sea-surface is the main factor of recent deoxygenation in the Arabian Sea

Coastal phytoplankton responses to atmospheric deposition during summer

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