GEOGRAPHY

The Asian dust “iron fertilizer effect” strengthens biological carbon sequestration in the North Pacific


Zan Jinbo and Fang Xiaomin, researchers of the Cenozoic Environment Team of the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, and their collaborators have reconstructed the history of chemical form and content changes of iron in Asian inland dust over the past 3.6 million years, and the research proposed that the divalent iron content of Asian dust is more critical for phytoplankton growth in the Pacific region, and the glacier erosion process of the Qinghai-Tibet Plateau may be a key factor in the chemical morphology of Asian dust.

The relevant research results, published in the journal Proceedings of the National Academy of Sciences (PNAS) on June 6, provide direct evidence for a deeper understanding of the positive feedback mechanism of the carbon cycle of “increased iron input from dust in Asia, enhanced carbon sequestration by marine organisms, decreased atmospheric carbon dioxide, and cooling of the global climate”.

Zan Jinbo, the first author and co-corresponding author of the paper, introduced that the nutrients of the earth’s ecosystem and ocean are supplemented by rivers and dust, and the iron carried by continental dust enters the ocean under the action of wind transport, causing plankton to increase, and consuming a large amount of carbon dioxide, alleviating the harm of the greenhouse effect, which is called the “iron fertilizer effect” of dust. Observations have shown that nutrients such as iron in atmospheric dust in inland Asia are transmitted to the northwest Pacific region through high-altitude westerly circulation, promoting phytoplankton flourishing. In geological history, can Asian inland dust also enhance biological carbon sequestration in the North Pacific through the “iron fertilizer” effect and have a significant impact on the global climate and environment?

To this end, since 2007, the research team has been looking for long-term scale records of dust in inland Asia. On the southern edge of the Tarim Basin and on the northern slope of the West Kunlun Mountains, the team found the largest accumulation of loess ancient dust in inland Asia to date—with a sedimentation thickness of 671 meters and an age of about 3.6 million years. Satellite observations and geochemical tracking of material sources confirm that Tarim dust is a major source of nutrients such as iron from marine sediments in the North Pacific.

The study reconstructed the history of changes in the chemical morphological composition and content of iron over 3.6 million years of Asian inland dust. By analyzing the loess ancient dust sequence samples and the types and contents of iron oxides with loess particle components less than 5 microns, the research team found that since the Middle Pleistocene about 800,000 years ago, with the global cooling and the sharp increase of mountain glaciers in the middle and high latitudes of the northern hemisphere, the glacial erosion of the Qinghai-Tibet Plateau has significantly increased, resulting in the sudden transformation of Tarim dust iron oxides from hematite to magnetite, and at the same time, the total iron content and the content of highly bioactive ferric iron increased sharply. The research team further calculated that after the Mesoministocene climate transition, the total iron content and divalent iron flux transported to the North Pacific Ocean in the arid region of the Asian interior increased by about 70% and about 120%, respectively, which greatly promoted the flourishing of biomass in the North Pacific and may have changed the phytoplankton population structure, depleting carbon dioxide in the atmosphere, and causing further cooling of the global climate. (Source: China Science News, Han Yangmei, Liu Xiaoqian)

Related paper information:https://doi.org/10.1073/pnas.2304773120

Fig. 1 The path of Tarim dust transport to the North Pacific Ocean (shadow area) and the location of the loess core in the West Kunlun Mountains (pentagram). (Photo courtesy of the Tibetan Plateau Institute, Chinese Academy of Sciences)

Fig. 2 Increased glacial erosion in northern plateau drives the chemical composition of Asian dust Fe and the transformation of Pacific ecosystems. (Photo courtesy of the Tibetan Plateau Institute, Chinese Academy of Sciences)



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